Final Report Summary - BIOFOULCONTROL (Development of innovative and sustainable technology for control of marine biofouling on heat exchangers of vessels with ozone technology)
Executive summary:
The BIOFOULCONTROL project has developed a new method for control of marine biofouling in cooling systems of vessels with application of ozone. The project has been running for 27 months starting on 1 September 2009. It has been initiated by Normex AS, Norway in cooperation with 4 other small and medium-sized enterprises (SMEs) from 3 member countries. The consortium consisted also of 3 research and technological development (RTD) performers and 1 large shipping company. BIOFOULCONTROL has been funded by the European Union (EU)'s 'Research for the benefit of SMEs' Theme of the Seventh Framework Programme (FP7).
In spite of huge expenditures used to clean fouled components of marine structures, there is currently no technology that meets the need of the shipping industry to control settlement and growth of marine organisms on cooling systems that causes either blockage of inlet pipes of cooling water or hamper heat exchange. This results in increased working temperature of engines and other heated appliances and possible shorter life, or compromising of the vessel's safety.
Within the BIOFOULCONTROL project, an innovative ozone feeding system has been developed in order to attain efficient gas mass transfer of ozone into seawater. This enables enhanced dispersion of ozone in the cooling water and attain cost-effective inactivation of marine organisms that potentially settle in the cooling system. By this, the ozonation system enables minimised generation of by products that are toxic to the marine environment. As part of the development work, the project has developed an intelligent process control unit for monitoring of process parameters and control of ozone dosage to attain optimum system operation.
The innovative components have been integrated into a pilot plant and subjected to four months of functionality tests in a real situation. The functionality trials demonstrated that ozonation is a promising technology that can efficiently mitigate marine bio-fouling cost effectively without generating hazardous products to health, safety and the environment.
Project description:
The BIOFOULCONTROL project has been initiated by the Norwegian company Normex AS. The project has received funding under the EU's 'Research for the benefit of SMEs' Theme of the FP7. It has official start date on the 1st of September and duration of 27 months. The consortium that consists of 5 SMEs, 3 RTDs and 1 large end user enterprise is as follows:
- Normex AS, SME and coordinator of the project (Norway)
- Statiflo International Ltd., SME (United Kingdom (UK))
- Edur EDUR-Pumpenfabrik Eduard Redlien GmbH & Co. KG, SME (Germany)
- Hydro Eco Invest sp Z.O.O SME (Poland)
- Stogda Ship Design and Engineering Sp z O.O SME (Poland)
- Farstad Shipping ASA, OTH (Norway)
- Teknologisk Institutt AS, RTD (Norway)
- Chalmers Tekniska Hogskola AB, RTD (Sweden)
- LABOR SRL, RTD (Italy)
The main outcome of the project is a cost effective, environmentally acceptable, user-friendly and reliable technology for control of marine bio-fouling on heat exchangers of vessels. The technology developed can also be applied in other sectors including aquaculture, ocean thermal power generators, offshore platforms and water supply systems.
Marine bio-fouling is common place on marine structures including pilings, offshore platforms, boat hulls, pipings and condensors. For steel polymer and concrete structures, bio-fouling can be a severe problem, resulting in unwanted excess drag on the structures and marine craft and causing blockages in pipe systems. Regular removal is required often by expensive mechanical means, such as by divers using high-pressure water on offshore platforms or costly, mostly ineffective, prevention methods be employed such as chlorination of pipework systems or anti-fouling coatings.
The development of the BIOFOULCONTROL technology has focused prevention of marine biofouling on cooling systems of with application of ozone. In the shipping industry, bio-fouling costs tens of billions of euros each year worldwide. The costs associated with failures related to bio-fouling in cooling systems worldwide are estimated to be EUR 1 500 - 1 800 million.
Biofouling is caused by the attachment of the larvae of marine organisms to surfaces in contact with seawater and then rapidly growing to adult fouling organisms. Subsequently, the surface will be colonised by seaweeds and the marine invertebrate. Efficient operation of seawater-based cooling systems on vessels is thus hampered by the settlement of plant and animal life and accumulation and excessive growth of organisms on the surface of heat exchangers and pipes.
Biofouling reduces the heat transfer in heat exchangers due to slime and biofilm formation, it reduces the water circulation in condenser tubes and accelerates the bio-corrosion of metallic surfaces in cooling systems as a result of extra-cellular polymeric substances and acids released by colonies of the accumulated organisms, and salt formation on the walls of the cooling systems. Fouling is most pronounced during ship operations in warm waters and at shallow depths, e.g. at harbours, although fouling occurs everywhere in the oceans at all depths. In many cases, heat exchanger tubing may become blocked and can only be rectified by extensive and costly cleaning operations. The principal solution for marine fouling has been overhaul and maintenance procedures during which the heat exchanger is disassembled and the tubes are physically cleaned, as by ramming cleaning rods through the tubes.
Heat exchangers placed in sea chests as a cooling system (box coolers) are in constant contact with seawater stream used for receiving heat from the cooling medium. As a result, they are exposed to biofouling and consequently to reduced heat transfer rate, increased working temperature of engine and other heated appliances and possible shorter life time or failure unless effective control measure is established. In addition, intake piping systems could be clogged with marine organisms propagating along with cooling seawater that reduce the capacity of the cooling system and compromising the safety of the vessel.
To mitigate the problem various techniques have been tried or proposed to prevent, or at least reduce marine biofouling, but all of them have had their technological, economic and / or environmental limitations.
Despite the recognised value of ozone as an effective agent for mitigating accumulation of organisms on surfaces such as cooling boxes and pipes, there are a number of challenges associated with application of the technology in seawater due to processes and reactions that are not fully understood. The main challenge is limiting the generation of ozonation by-products such as bromates and halocarbons that are potentially hazardous to the aquatic environment, or contribute to depletion of the ozone layer if released to the atmosphere, e.g. release of bromoform.
Formation of hazardous by-products can be minimised by enhancing the dispersion of the ozone into the seawater and attain inactivation of target organisms at lower ozone dosage than currently used with available ozone delivery devices. Thus, a main focus of the project has been development of a cost-effective ozone feeding and dispersion unit.
For optimisation of ozonation, delivery of ozone needs an intelligent control system for monitoring key parameters and regulating the ozone dosage for eliminating or minimising generated hazardous compounds to a secure level. In this connection, the project is developing a prototype of a process control unit that will be integrated with the ozone delivery unit.
Work accomplished:
A through literature study and database search has been carried out on kinetics of gas liquid dispersion as well as available methods used for feeding of ozone to water. Moreover, the literature review covered the marine chemistry involved in ozonation of seawater as well as performance of ozone as an oxidising agent against marine organisms, especially blue mussels.
A test setup was constructed at Kristineberg Marine Research Station (KMRS) on the South West coast of Sweden for trials involving feeding and dispersion of ozone into seawater, and testing of devices for microbubble generation and gas liquid mixing. The test setup was also used for ecotoxicological experiments, studying the effect of ozonation of seawater on settling, survival and growth of blue mussels (Mytilus edulis) and chemical analyses on formation of ozonation by-products. KMRS is the largest field station for marine research in Sweden and one of Europes most modern marine research laboratories with facilities for conducting experimental work and for keeping live organisms for prolonged periods. Seawater for the experiments was extracted from two depths (5 and 30 m depth).
The ozone feeding and dispersion unit has been developed by integrating a micro-bubble generating and a gas-liquid dispersion device that give maximised mass transfer. Analyses of generated bubble size and density has been analysed using imaging technique and computation with a programme developed under LabView. In the analysis, the bubble size has been found to be a determining factor for effective ozone mass transfer.
The ecotoxicological and chemical investigations were used for validating the performance of the ozone feeding and dispersion unit. For ecotoxicological studies, larvae of Mytilus edulis, considered to be highly resistant to ozone were collected from the sea and cultivated. One group of specimen was subjected to ozonated sea water at different total residual oxidant (TRO) levels and for different duration, in addition to batch tests. Impact of the ozonation has been compared continuously with a reference group of specimen. Parallel with this, ozonated seawater was analysed to measure the levels of generated bromates and halocarbons.
Development of the ozone feeding and dispersion system and the scientific investigation related to preventing growth of the blue larvae as well as generation of bromates and halocarbons under ozonation of seawater was completed at the end of the first reporting period. Development of the process control unit that has been running parallel with development of the ozone feeding unit, and involving prototyping of the hardware including the scientific instrumentation and signal processing and acquisition unit and validation of the software, was concluded at the 19th month of the project period.
Having successfully developed the prototypes of the innovative components of the BIOFOULCONTROL system, a pilot plant has been integrated and installed on board a commercial vessel operated by Farstad Shipping AS in the North Sea. The installation was completed at the beginning of May, 2011 and the system was commissioned for functionality tests and validation on 13 May 2011. Trials of the pilot plant were completed at the middle of October 2011.
During the trial period on board the vessel, regular visual inspection and photographing of the ozonated surfaces in the vessel have been undertaken to monitor settlement of blue mussels that are a common problem in the North Sea where the vessel Far Seeker is operating. Along with trials on board Far Seeker, conditions of the inlet strainers and cooling box in a sister vessel, Far Searcher, which uses the Bioguard biocide, have been inspected occasionally. Meticulous cleaning of the surfaces in the cooling system of both vessels to be subjected to ozonation by the BIOFOULCONTROL system was carried out prior to the start of the trials.
The trial period consisted of two main phases driven by the level of ozone dosage. Dosage of the ozone feeding was varied by regulating the capacity of the ozone generator. The capacity was set at 25 % (25 g O3 / hr) for the first trial phase. In the second trial phase, the ozone generator was set at 50 % capacity (50 g O3 / hr). Trials of shorter duration were also undertaken with 100 and 75 % capacity to investigate the level of bromates generated at higher levels of ozone dosage.
Ozonated and control water samples for bromate analysis were collected during the vessel journeys at constant geographical positions in the sea. The control samples are used to see whether there is background in the water due to other substances than bromate that may disturb the analytical method. The background may vary between different geographical positions and, therefore, it was important to take the control samples parallel with the samples from ozonated water.
Other accomplished work:
The SME participants of BIOFOULCONTROL have been pursuing demonstration and innovation related activities with the main work concentrated in the second reporting period of the project. As a result, the technology and its benefits have been demonstrated to selected end users while the BIOFOULCONTROL system was under development and during trials of the pilot plant on board the commercial vessel.
A patent application has been filed and submitted to the Norwegian Industrial Property Office on February 2011 to be pursued in other countries as of February 2012.
In the dissemination activity, the consortium has actively pursued contact with companies of potential interest for the BIOFOULCONTROL technology. Main venues of contact have been conferences and exhibitions, 17 in all, attended by the consortium. In addition, dissemination of information brochures by email and visits to ship owners and designers, ship buildering companies as well as fish aquaculture companies have been carried out for presentation of the project and its results. In this connection, about 110 companies have been contacted during the project period.
The RTDs have carried out provision of training to the SMEs with main focus on the results of the project, and the SMEs have trained representatives of end user core groups on installation, maintenance and operation of the main components of BIOFOULCONTROL and the integrated system primarily with live demonstrations.
Attained main results:
The developed ozone feeding and dispersion unit manages generating microbubbles with average diameter of < 50 µm as envisaged in the project objectives. This has contributed to effective gas mass transfer of ozone to the seawater resulting in effective dispersion of ozone. Trial results at KMRS have shown that all larvae of the blue mussels can be eliminated at TRO level stipulated in the objectives of the project with continuous ozonation. The level of bromates generated under ozonation is about 300 times less than the level set in the objectives of the project and what is considered to be hazardous to aquatic life. There are no references on the limit of halocarbons, but the generation of bromoform can be a concern with potential limits that may be set by the International Maritime Organisation (IMO) or individual governments.
Development of the process control unit with ultimate objective of optimising ozone dosage for cost effective operation of the system and minimisation of generated ozonation by-products was successfully concluded with delivery of a prototype and a PC-based acquisition and logging of data. The PC is connected to sensors for monitoring system operation parameters for monitoring and controlling of the ozonation process. Before installation on board the vessel, the process control unit was tested in the laboratory by integrating with main components of the BIOFOULCONTROL system including the ozone generator and the ozone feeding unit as well as sensors for calibration and functionality tests.
The validation of the pilot plant on board Far Seeker showed that no new settlement of blue mussels or other living organisms has taken place in sections of the sea chest that have been ozonated with the different ozone dosages. On the other hand, seawater treated with the Bioguard agent has resulted in marked settlements where certain sections of the inlets and strainers were partially blocked by the blue mussels.
In case of questions, please contact the Coordinator of the project:
Mr Stig Johansen
Normex AS
Email: stig@normex.no
Phone: +47-701-21103/91708023
Project context and objectives:
BIOFOULCONTROL is a FP7 project within Research for the Benefit of SMEs. It had an official start date on 1 September 2009 and has a duration of 27 months. The project is aimed at developing a biofouling prevention system for heat exchangers in maritime seawater coolers with application of ozone.
Biofouling costs tens of billions of euros each year worldwide. For example, the United State (US) Navy alone spends EUR 5 billion per year due to bio-fouling related failures, while in the UK the cost related to fouling of vessels has been estimated at 1 500 - 2 300 million euro, a figure that approximates to 0.5 % of the British gross national product (GNP). Costs associated with failures related to bio-fouling in cooling systems worldwide amounts to EUR 1 500 - 1 800 million.
Biofouling is caused by the attachment of the larvae of marine organisms to surfaces in contact with seawater and then rapidly growing to adult fouling organisms. Subsequently, the surface will be colonised by seaweeds and the marine invertebrate. Efficient operation of seawater-based cooling systems on vessels is thus hampered by the settlement of plant and animal life and accumulation and excessive growth of organisms on the surface of heat exchangers and pipes.
Biofouling reduces the heat transfer in heat exchangers due to slime and biofilm formation, it reduces the water circulation in condenser tubes and accelerates the bio-corrosion of metallic surfaces in cooling systems as a result of extra-cellular polymeric substances and acids released by colonies of the accumulated organisms, and salt formation on the walls of the cooling systems. Fouling is most pronounced during ship operations in warm waters and at shallow depths, e.g. at harbours, although fouling occurs everywhere in the oceans at all depths. In many cases, heat exchanger tubing may become blocked and can only be rectified by extensive and costly cleaning operations. The principal solution for marine fouling has been overhaul and maintenance procedures during which the heat exchanger is disassembled and the tubes are physically cleaned, as by ramming cleaning rods through the tubes.
Heat exchangers placed in sea chests as a cooling system (box coolers) are in constant contact with seawater stream used for receiving heat from the cooling medium. As a result, they are exposed to biofouling and consequently to reduced heat transfer rate, increased working temperature of engine and other heated appliances and possible shorter life time or failure unless effective control measure is established. In addition, intake piping systems could be clogged with marine organisms propagating along with cooling seawater that reduce the capacity of the cooling system and compromising the safety of the vessel. To mitigate the problem various techniques have been tried or proposed to prevent, or at least reduce marine bio-fouling, but all of them have had their technological, economic and/or environmental limitations.
The SME participants of BIOFOULCONTROL have therefore initiated this project to develop a cost effective, environmentally acceptable, user friendly and safe method based on ozonation technique.
Despite the recognised value of ozone as an effective agent for mitigating accumulation of organisms on surfaces such as cooling boxes and pipes, there are a number of challenges associated with application of the technology in seawater due to processes and reactions that are not fully understood. The main challenge is limiting the generation of ozonation by-products such as bromates and halocarbons that are potentially hazardous to the aquatic environment, or contribute to depletion of the ozone layer if released to the atmosphere, e.g. release of bromoform.
Formation of hazardous by-products can be minimised by enhancing the dispersion of the ozone into the seawater and attain inactivation of target organisms at lower ozone dosage than currently used with available ozone delivery devices. Thus, a main focus of the project has been development of a cost effective ozone feeding and dispersion unit.
For optimisation of ozonation, delivery of ozone needs an intelligent control system for monitoring key parameters and regulating the ozone dosage for eliminating or minimising generated hazardous compounds to a secured level. In this connection, the project had to develop a prototype of a process control unit that will be integrated with the ozone delivery unit.
The project has the following technological and scientific objectives:
Scientific objectives:
Acquire new scientific knowledge on:
(a) The elimination rates of marine organisms and the impact of seawater parameters such as salinity, temperature and pH on biokill by ozone.
(b) The formation of ozonation by products, especially bromates from varying levels of injected ozone, and the impact of seawater parameters on the generation of bromates. Acquired knowledge will be used for control of ozone dosage and limit the generation of hazardous ozonation by products.
(c) The dynamics of dispersion of gas/ozone in seawater and the impact of seawater parameters on generation of microbubbles required for dispersion of ozone in seawater; characterization of optimum bubble size for effective dispersion of ozone in seawater.
(d) Hydrodynamic behaviour of micro-bubbles in two-phase media.
Technological objectives:
(a) achieving mitigation of bio-fouling with ozone concentration of 0.5 ppm with our innovative ozone injection and dispersion unit;
(b) 35% reduction in energy consumption per m3 of water processed in relation to existing bio-fouling control methods;
(c) development of a cooling water treatment system that meets environmental requirements;
(d) level of bromate in discharged cooling seawater after ozonation < 30 ppm (level at which population growth of sea organisms can be affected);
(e) achieving an operation cost that is 30% less than current methods.
The innovative components were planned to be developed based on laboratory studies and tested both in the laboratory and field studies.
Project results:
Description of the scientific and technological results:
From the outset, the RTD work of BIOFOULCONTROL has focused on attaining the scientific and technological results formulated in annex 1 of the grant agreement. The main results include: New scientific knowledge, new ozone injection and dispersion unit, new process control unit and validated prototype of the BIOFOULCONTROL system.
1. New scientific knowledge:
The new scientific knowledge that emerged from the project are related to ozonation of seawater and parameters that impact on the process, kinetics in connection with formation of ozonation by products. Further, new scientific knowledge comprises inactivation of blue mussels with ozone and the concentration required to attain mitigation of marine biofouling. New knowledge involves also kinetics of ozone dispersion into water, parameters that impact on gas mass transfer in relation to efficient dispersion of ozone into seawater as well as design of devices for generation of microbubbles and dispersion of these into seawater. Finally, new knowledge is gained in relation to materials that withstand corrosion due to ozonated seawater.
1.1 Generation of ozonation byproducts:
New knowledge has been acquired based on comprehensive literature study and laboratory investigations as well as validation trials of the pilot plant on board a vessel. Available literature shows that ozone itself is not stable in seawater; it has a very short chemical half-life of about 5 seconds. In seawater, ozone quickly reacts with bromide ions (Br-) to form a secondary oxidant, and possibly other brominated by-products. The seawater composition, e.g. natural organic matter content, affects the efficiency of ozonation and also the formation of toxic by-products. These issues have been important in addressing when optimizing the dose of ozone required. The chemistry of ozone in seawater is dominated by its initial reaction with bromide ions (Br-). This is due to the relatively high concentration of bromide in seawater (about 67 mg L-1 of Br-), and it has high reactivity compared to other seawater components. Ozone quickly reacts with bromide (Br-) in seawater to form hypobromite (BrO-) that is in equilibrium with hypobromous acid (BrOH). Hypobromite, in turn, can react with ozone, and the net of the two first reactions, , is a catalytical breakdown of ozone,
Hypobromite (BrO-), formed when seawater is ozonated, is in equilibrium with hypobromous acid (BrOH), and in seawater of pH 8, BrOH is the dominating form.
Bromine (BrOH / BrO-) works as a secondary, more stable oxidant, which also has disinfecting properties. The bromine concentration in a water, expressed as TRO, is an indirect measure of the oxidation capacity of the water and normally given in mg / L. Depending on the salt content of a water TRO consists of bromine and / or chlorine. Another halogen species present in high concentration in seawater is chloride, but because of its slow reaction with ozone it only plays a minor role in the ozonation process. The reaction of ozone with bromide ion is preferred to reaction with chloride, because of a much faster reaction rate. The reaction of ozone with chloride ion is slow, with a rate constant, k, of only 0.003 M-1s-1 (Grguric et al. 1994 and references therein).
After the initial reaction step, when ozone reacts with bromide ions, hypobromite and hypobromous acid can react with ozone or with seawater components. This will result in the formation of bromide ion or formation of ozonation by-products. Hypobromite, formed when ozone reacts with bromide ions, can react with ozone either to be reduced back to bromide ion in a catalytical breakdown of ozone. It can also be oxidised by ozone to form the disinfection by-product bromate, BrO3- .
Bromate is not naturally present in seawater, but when it has been formed it is stable in seawater environment. It is classified as a carcinogenic by the International Agency for the Research on Cancer (IARC) and the maximum contaminant level (MCL) established for bromate in drinking water is10 µg L-1.
In the presence of ammonia (NH3), BrOH / BrO- will react to form monobromamine (NH2Br). This reaction is very fast and thermodynamically favourable. Bromate is not formed as long as there was ammonia present in the water. Inhibition of bromate production takes place when ammonia was added to chlorinated artificial seawater. Inhibition of bromate formation by ammonia takes place also under ozonation of fresh water.
Bromoform (CHBr3): BrOH / BrO- reacts with natural organic matter in the water to form bromoform, (CHBr3). Bromoform is a confirmed animal carcinogen. The LC50 values for bromoform show that it is toxic to marine organisms, and reported values range from 7.1 mg / L for sheepshead minnows to 26 mg / L for the brown shrimp. It is a very stable compound with a half-life of 686 years.
1.2 Ozonation of seawater and impact of water quality parameters:
The seawater composition influences the oxidation capacity, and also the formation of hazardous by-products. In present scientific literature however, more effort is put on describing the loss of oxidation capacity or enhanced TRO decay, rather than the correlation to formation on by-products.
Regarding the influence of seawater composition on formation of by-products it was found that the effect of:
(a) increased salinity > increased formation of bromine by-products;
(b) increased temperature > increased formation of bromine by-products;
(c) increased pH influences the relation between by-products (increased production of bromated and a decrease in bromoform production);
(d) organic matter > no consensus.
1.3: Concentration of ozone / level of TRO required to attain mitigation of marine biofouling
The amount of ozone needed to reach and maintain a certain TRO level over time depends on the chemistry of the ozonated water: Water with higher ammonia concentration and higher concentration of organic carbon will require a higher ozone dose. A possible explanation to this is that both ammonia and organic matter can have very fast reactions with both ozone and bromine (BrOH / BrO-) that consumes the oxidant.
The TRO level required to eliminate blue mussels by continuous ozonation is 0.5 - 0.9 ppm. Formation of bromate was dependent on the TRO concentration - the higher TRO concentration the larger bromate formation. During a long term test series the bromate concentration was fairly constant between 30 and 60 ppb. The formation of bromoform and most other halocarbons are strongly TRO dependent - the higher TRO concentration the larger halogen formation.
1.4 Kinetics of mass gas transfer and application for ozonation of seawater
A combination of multiphase pumping and static mixing has demonstrated to be a novel method of efficient gas dispersion into liquid. Both the literature study, the laboratory investigations and the trials of the pilot plant in the BIOFOULCONTROL project have shown that the ozone delivery unit developed in the project gives the best dispersion of ozone into seawater for mitigation of marine biofouling.
The main parameter that determines the efficiency of mass transfer and thus performance of the ozone delivery system is the bubble size in the gas liquid mixture. The process as a whole as well as operation of system elements are however influenced by several factors as an ozonation system works under changing conditions that can influence its operation and efficiency. The other factors that may have impact on the process are thus the following:
- Temperature and pressure:
(a) Temperature rise leads to the decrease of solubility of gases in water. On the other hand the mass transfer coefficient rises with temperature.
- Temperature decrease leads to the riise of liquid density and viscosity.
- Ionic strength and contaminations in water:
(a) Ionic strength, correlated with the amount of salts in water, influences solubility negatively. Furthermore, it enhances coalescence rate which leads to larger bubbles. Contaminations that are present in water make the surface of the bubble rigid and less permeable and thus reduces the mass transfer rate.
- Turbulence and shear force:
(a) Turbulence of a liquid is correlated to the value of mass transfer coefficient. The more turbulence, the better mass transfer. The level of turbulence can be assessed by the power dissipated per liquid volume.
(b) High-turbulence level and associated level of shear force improves the rate of bubble break up, leading to the creation of smaller bubbles.
-Parameters influencing multi-phase pump operation:
(a) Pump operation can be influenced by the fraction of gas that is present in water. Multiphase pumps are able to cope well with gas-liquid mixtures for up to 30% of gas fraction. Nevertheless, high gas contents change the characteristic curve of a pump, lowering attainable head and flow rates as well as power input.
(b) The increase in density of water (e.g. sea water) increases the power input of a pump and decreases available head.
(c) Higher density of water leads to the increase in power input as well.
(d) Higher pressure built in the pump and outlet pipe leads to smaller bubbles released after relieve valve.
- Parameters influencing static mixer operation:
(a) Pressure drop developed along the static mixer depends on the design of mixing elements. It is lower for helical-shaped elements and higher for blade grids. It also depends on the number of elements.
(b) The number of mixing elements relates to the mixing quality. The more elements the better mixing.
(c) High gas flow improve the dispersion levels leading to lower bubble sizes.
(d) Position of a static mixer can influence the uniformity of dispersion. Vertical position may lead to better uniformity and higher mass transfer. Fluid mixtures flowing in horizontal mixer may be influenced by gravitational forces, with bubbles gathering in the upper part of a mixer.
1.5 Corrosive properties of ozone in seawater:
As part of the development work, two groups of materials that can potentially be applied in ozone delivery unit that is exposed to high concentration of ozone have been studied in relation to their resistance to corrosion. These are:
(a) polymer materials;
(b) metallic materials.
The literature study revealed that there is very limited knowledge on the effect of dissolved ozone in seawater on the corrosion behaviour of materials, although ozone based oxidation has been used for a considerable length of time. It appears that the material selection to most ozonisation processes is done without major detailed corrosion investigations.
In BIOFOULCONTROL, the polymer materials have been subjected to 11 week laboratory investigation at TI using artificial seawater prepared in a test vessel to which ozone is dispersed from a laboratory scale ozone generator with help of a ceramic diffuser. Besides, reference specimen of the polymers were prepared for comparison with the ozonated specimen at the end of the trial period.
The polymer materials include:
- ethylene propylene diene monomer (EPDM),
- teflon,
- polyvinyl chloride (PVC),
- neoprene.
After subjecting the ozonated and reference specimen to tensile strength tests, the changes seen for the four ozonated polymers are generally small. Apart from EPDM that has shown low resistance to tensile strength tests after ozonation compared to the reference specimen, all the polymer materials have good ozone resistance and can be applied for joints, gadgets, o-rings and pipes.
Three metallic materials (S31600L, CuNi, Ti) were also subjected to ozonation applying the same test equipment used in the trials of the polymers. Of the three metals tested, titanium is the most corrosion resistant material in these environments. No corrosion attack was observed during the 11 weeks of testing, which indicates that there will be no problems using this material in conformation of the literature study. The CuNi metal is a recommended material in fresh and seawater solutions. After testing in ozonated seawater environment, however, the material has suffered from general corrosion. Visible green verdigris was formed. On the surface in general, also under the gasket, another oxide is visible. This oxide layer is porous and can easily be scratched off. No localised corrosion is seen. There are other CuNi-alloys with higher content of Ni than the one used in our trial that are much more resistant against ozone according to available literature.
The results after testing of the S31600 L metal show that the material is not recommended in these environments without additional measures such as cathodic protection. The material suffer from both pitting- and crevice corrosion after just two weeks exposure to ozone in seawater, whereas it withstands corrosion of ozonation in fresh water.
2. New ozone injection and dispersion unit:
For ozonation to be cost effective and sustainable, highly efficient means of gas mixing and dispersion device need to be applied. For effective ozone dispersion, microbubbles have to be generated and effectively dispersed into the liquid. Microbubbles are required for even and maximized ozone dispersion due to their special features: large interfacial area, very low rise velocity (long residual time in the liquid), low bubble coalescence, higher gas hold up and good mixture character.
In BIOFOULCONTROL, the ozone injection and dispersion system consists of static mixing and multiphase pumping technologies in which the multiphase pump generates microbubbles, while the static mixer provides high mass transfer rate. In addition to creating microbubbles, the multiphase pump works also as a dynamic mixer to enhance the dissolution of ozone in water and delivering the two phases to the static mixer by gas charging. In the static mixer, turbulent conditions ensure a high intensity radial mixing action as a result of rotational circulation of the water stream around the hydraulic centre of each of the channels in the mixer formed by the mixing element.
In addition to pump pressure and gas / liquid relation, it is the configuration of the pump impeller that determines the size of micro-bubbles generated by the multi-phase pump. For generation of micro-bubbles with diameters < 50 µ in BIOFOULCONTROL, different multi-phase pump impellers were tested both with fresh water and seawater streams to select the impeller configuration that produces the optimum bubble size for subsequent cost effective dispersion of ozone into seawater.
Selection of impeller design was based on 3 factors that have implications for the efficiency of the ozone mixing and dispersion unit:
(a) diameter of the generated microbubbles;
(b) working pressure;
(c) gas / liquid ratio (gas content).
Increasing the gas/liquid ratio beyond 30 % caused sharp fall of the working pressure of the pump, and consequently increase in the size of the bubble sizes and decreased mass transfer. However, it was the peripheral impeller that gave the smallest bubbles at gas-liquid ratio between 20 - 30 %. Thus, validation of the ozone delivery unit prototype has been carried out with the peripheral impeller.
Static or motionless mixers have been used for many years to disperse gases into liquids for mass transfer applications. The effectiveness of the mixers has been, to a large extent dependent on the dispersed gas bubble size, which is in turn dependent on the fluid velocity through the mixer. The requirements for the BIOFOULCONTROL project were to disperse ozone into seawater stream. However, to meet the overall process specification, it was necessary to produce micro-bubbles with bubble diameter smaller than normally associated with economically viable static mixer systems. This could be achieved with multiphase pump with impeller configuration designed in the project, and use the static mixer for maximised mass transfer.
The performance of the mixing element has been enhanced in BIOFOULCONTROL by changing the pitch ratio to attain a more shear and turbulence within the mixer. By increasing the mixing intensity, it was possible to produce smaller bubbles (bubble break up) and less bubble coalescence. The pitch ratio is the length of each individual mixing element compared with the mixer diameter and is usually 1.5 : 1 for most mixers. Normally, mixing elements have a pitch ratio of1:1. Further decrease of the pitch ratio would however have a down side of pressure drop through the mixer that will increase the energy consumption, although this will not be a big issue for the BIOFOULCONTROL application.
Development of the ozone feeding unit in BIOFOULCONTROL has demonstrated that applying two static mixers gives the best result. The main factor that has contributed to such result is that the first mixer is breaking the random size and distributed bubbles from the multiphase pump into a uniform size and even distribution giving an even feed to the second mixer. With constant feed conditions, the smaller mixer can operate at optimum conditions resulting in a small and uniform size bubble, evenly distributed across the pipe section. Moreover, the diameter of the mixers has been selected to give a more optimum bubble velocity through them. Bubble velocity is a function of velocity and geometry of the mixer. The developed ozone feeding system enables elimination of blue mussels with ozone dosage of 0.5 - 1 ppm without intelligent control of the ozonation process. Annex 1 of the project has set only the level of bromates as a measure of generated hazardous by-products under ozonation with a target level of < 30 ppm under laboratory investigation. However, the validation has gauged formation of bromates as well as halocarbons including bromoform, dibromochloromethane, dichlorobromomethane and chloroform using the prototype ozone delivery system. The concentration recorded at the TRO level needed for complete elimination of the mussels is about 300 times less than the target set by the technological objective of the project (< 30 ppm).
The dominant halocarbon formed is Broform followed by dibromochloromethane and dichlorobrommethane. The chlorofom content was low and rather stabile during all measurements, probably representing a natural biogenic background.
3. The process control unit:
The two main objectives of the BIOFOULCONTROL system is effective mitigation of marine biofouling of cooling systems and optimum dosage of ozone to attain cost effective ozonation and eliminating generation of toxic and environmentally hazardous by products that exceeds accepted limits. This can be attained with application of intelligent process control unit that is integrated into the BIOFOULCONTROL system.
In the project, a functioning process control unit has been developed and validated as a component of the pilot plant. This monitoring and control system of the ozonation process has been developed through the following phases, i.e. development of:
(a) scientific instrumentation;
(b) signal processing and acquisition;
(c) software interface for the visualisation and logging of measurement;
(d) software for automatic process control (with remote capabilities).
The scientific instrumentation connected to the monitoring system is basically composed of sensors that collect all the information from the sections described in the previous schema. Appropriate sensors were chosen to measure described quantities.
The sensors applied in the process control unit are all trasducers, and values have to be acquired by their electrical values. To perform this acquisition a low cost acquisition card made by National Instruments: the NI-6008, a 0 - 10 V is applied. However, the majority of the sensors give their measurement in a 4 - 20 mA range (current instead of voltage); therefore a 4- 20 mA to 0 - 10 V converters have been selected for each signal. Converted signals are then connected to two acquisition cards which communicate data to a standard PC by a simple standard USB connection.
The monitoring software that has been developed is used to gather data from the process. This software is designed to start automatically at system start-up and builds up a file every 12 hours with header and all the useful data. The interface is designed to fully work without the intervention of operators, but some utility functions have been implemented to ease the interaction with the system, since the target was a touch panel PC, like screen keyboard, minimise and quit button and so on.
An integrated open productivity and connectivity (OPC) server that allows useful and important remote capabilities can supply all required data by OPC protocol. Alternatively, a TeamViewer installation is provided to extend simple data catching to remote desktop features. In this way the user can monitor in real time software interface, take interface command, transfer files and other extra-functions that can add many opportunities to work with partners.
4. The BIOFOULCONTROL System:
The BIOFOULCONTROL system is aimed at controlling fouling of cooling systems on board vessels with the application of ozone. It is an integrated unit that consists of the innovative sub systems that have been developed in WP2 and WP3 and subjected to individual functionality tests in the laboratory. These include the ozone delivery unit (deliverable 2 (D2)) and the process control unit (D3).
The ozone delivery unit contains a multiphase pump with peripheral impellers (8 litres / min capacity) for generation of microbubbles and a static mixer with specially designed mixing elements for further break-up of the microbubbles generated in the multiphase pump, and for even and efficient dispersion of the bubbles into the sea water through maximised gas mass transfer. This ensures maximised contact between water and ozone, reduced ozone consumption and efficient inactivation of organisms that cause fouling of cooling systems.
The process control unit consists of scientific instrumentation for monitoring: ozone dosage (g / m3), oxygen concentration in gas flow (%), ORP, salinity, pH level, water temperature as well as control of gas flow. Monitoring of these operation parameters allows establishment the relationship between performance of the system and values of the parameters, and to control the process so as optimum function of the pilot plant is attained. The scientific instrumentation is supported by a touch panel PC for data logging and control of the instruments, and software for control of gas flow and Internet remote control with the help of OPC server and / or TeamViewer.
In addition to the innovative components developed in the project, the pilot plant consists also other vital components including:
- air compressor,
- O2 generator,
- PLC for control of ozone injection and the pump,
- O3 generator,
- O3 detector for ambient air quality monitoring,
- water cooler for maintaining operation temperature of the O3 generator,
- strainer for screening away coarse materials in the seawater,
- vacuum, pressure and, water flow meters.
The BIOFOULCONTROL system has been subjected to functionality tests both in the laboratory and on board a supply vessel that sails between Kristiansund in north-western coast of Norway and the offshore oil and gas installations in North Sea. The system has been tested for about 4 months on board the vessel during which the systems effect towards control of fouling by blue mussels and formation of bromates has been monitored. The system functionality has also been compared with performance of existing method used by a sister ship. The existing method is application of a biocide called bio-guard.
During the trials, two different ozone doses were applied: 25 % capacity of the ozone generator (25 g O3 / h) and 50 % capacity of the generator (50 g O3 / h). In both cases, no traces of surplus of ozone could be detected in the cooling water. The average bromate concentration at the 25 and 50 % generator capacity were found to be 9.25 µg / L and 18.8 µg / l respectively. These are concentrations that are far lower than levels considered to be toxic for marine environment.
The killing effect of the method is very high with negligible generation of bromates. The control trial on the sister ship parallel with the validation of the BIOFOULCONTROL system showed, however, high level of fouling due to settlement and growth of blue mussels.
In BIOFOULCONTROL, application of multiphase pump with innovative impeller and static mixers with special mixing element enables ozone gas to be efficiently dispersed into seawater utilising enhanced surface area of microbubbles so that enhanced contact between ozone and marine organisms in sea water is attained. This technique enables effective inactivation of the organisms locally in the inlet of cooling water and across the coolers. The problem can thus be mitigated continuously, in other words before it is created using low ozone concentrations and without application of environmentally damaging chemicals.
Application of static mixers enables efficient dispersion of the gas as micro bubbles with bubble size of less than 50 micro meter after further breakdown of the bubbles generated by the multiphase pump. This implies that the ozone is not only well dispersed in the water and surfaces to be treated, but also attains large contact area that ensures that all the injected ozone reaches and inactivates maximum amount of organisms within a short period of time. Thus, the process attains exceptionally good effect of the ozone fed into the seawater allowing low dosage / concentration of ozone without compromising the efficiency of the process.
I connection with inlet of the cooling water, it is common that vessels install so called sea chest box as a projection of the fuselage at the inlet. It is therefore in the surrounding of this box dosing of ozone takes place according to the invention. However, there is a typical grating that connects the box to the rest of the sea and prevents intrusion of small to large particles into the inlet itself that is placed in the sea chest box. This grating is also exposed to fouling by marine organisms.
With specially designed circulation loop, ozone containing gas also comes in contact with the grating, preferably with the ozone containing gas fed to the outer surface of the grating and as a result of the flow of water towards the inlet it passes through the grating on its way to the inlet. For practical purposes, this can be configured in different ways. As an example, it is possible to move the grating backwards into the sea chest box so that the outlet is positioned in the outer area of the sea chest box and the grating itself positioned inwards.
In most vessels, the cooling water inlet consists of a typical sea chest box that is connected to a grating and a so called cross over across the body. There are one or more pipes of cooling water connected to the cross over from where the cooling water is transported to the engines of the vessel. The circulation loop of the ozonation system comprises multiphase pump, the static mixer and the pipes that connect these units and spreads ozonated cooling water to exposed surfaces to marine biofouling. The multiphase pump sucks seawater from the cross over and mixes it with gas (air or oxygen) that contains a controlled concentration of ozone. The gas will be in the form of bubbles in water when transported from the multiphase pump to the static mixer where the bubbles will be further broken into smaller bubbles that are showered out in the outer surface of the sea chest box and is then circulated back to the cross over. Thus, the gas that contains ozone comes in contact with all components of the cooling water inlet that is in contact with seawater and hinders any fouling of the surfaces by the marine organisms. With appropriate positioning of the grating in relation to the static mixer, the grating will also be in constant contact with ozone so as to protect the grating from fouling. The circulation loop can be duplicated as required.
Application of static mixers as described above, and intelligent control of the process enables effective mitigation of fouling at specially low concentrations of ozone without compromising the effectiveness of the technology. The technique enables that all the ozone fed into the system will be consumed in the process.
Potential impact
The successful completion of the BIOFOULCONTROL project and its potential application for control of fouling both in fresh and sea water has brought about a number of positive impacts. The main impacts are related to protection of aquatic environment, contribution to improved working environment, new knowledge on safe and reliable application of ozone, cost reduction in connection with removing accumulated fouling and safe operation of cooling systems without compromising the safety of vessels and other structures with heat exchangers.
Within the scope of the project, it has been demonstrated that there is high potential of ozonation for mitigation of marine biofouling. This has been done by developing and introducing innovative ozone delivery system, and electronic processes control unit along with new efficient means of designing and operating ozonation systems. Thus, the potential of positive effects in the near future from results of this project is related to environmental aspects, community policies, and societal objectives including reduced use of resources on cleaning of surfaces invaded by marine organisms.
According to the IMO convention of 2001, there is a requirement for monitoring of harmful antifouling systems on ships. This includes the application, reapplication, installation or use of antifouling systems that have negative impact on the aquatic environment, health and safety as well as air quality. In this regard, BIOFOULCONTROL would positively substitute currently used methods that either directly pose adverse impact on the environment, human health or as a result of wastes generated from the application or from removal of antifouling systems.
Today, there is a number of methods for control of biofouling that can be substituted by BIOFOULCONTROL in order to achieve positive impacts. These include:
- Thermal methods with high-energy consumption and potential thermal stress damage on the heat exchangers.
- Non oxidising toxic agents that are by their nature highly toxic to aquatic organisms, often environmentally persistent and can potentially cause long-term ecological damage. Because of their mode of action, the effectiveness of these substances decreases with time, especially in seawater and renewal is necessary. Therefore, the time required to clean and dry the cooling system for repainting is too long to make antifouling paints of these substances economically and practically viable.
- Oxidising agents such as chlorine that require manual handling and storage on board with safety concerns and need of special skills. Uncontrolled dosage often creates public pollution unless additional equipment is included for waste treatment with unnecessary high cost.
- Almost all available methods are ineffective, and fouled parts have to be cleaned mechanically at very high cost, not least due to interrupted operation of the vessel.
Finally, the IMO convention requires that the parties shall take appropriate measures to promote and facilitate scientific and technical research on the effects of anti-fouling systems as well as monitoring of such effects. The BIOFOULCONTROL project has contributed to the attainment of this goal as a result of a safe, reliable and efficient ant-fouling system.
Regarding application of ozone beyond control of biofouling, there is a recognized value of ozone to improve the management of water quality in the aquaculture sector. However, there remains a significant lack of knowledge in the industry relating to its cost effective and safe use that can be solved with new knowledge gained from BIOFOULCONTROL. Lack of knowledge in the aquaculture industry has resulted in a number of negative impacts on production systems due to high residual ozone concentrations that cause gross tissue damage and stock mortalities, high concentration of bromates formed as a result of reaction between ozone and bromides and change in water chemistry exposing the stock to changed physiochemical conditions which may impact the availability of dietary ingredients. In this connection, substantial losses have been incurred in the industry around the world. The complex combination of benefits and risks of ozone use has deterred and slowed the uptake of ozone technology by the aquaculture sector causing a bottleneck in enabling the EU industry to improve the sustainability of seafood production through fully exploiting the potential of recirculated aquaculture systems and so maintain a competitive edge in the international markets and increase employment in the industry. The innovations of BIOFOULCONTROL will redress this limitation and contribute to implementation of the EU policy of increased and sustainable seafood production. Exploitation of results: The planning and execution of exploitation and dissemination plans have been based on a model framing the activities of the project.
The plans for exploitation and dissemination activities consist of three stages:
Stage 1 - Awareness: The initial BIOFOULCONTROL dissemination will target the shipping sector. Potential secondary targets will include aquaculture, power supply, offshore oil installations and water supply structures. The information will be rather generic and general, meant to reach as many potential adopters as possible. In other words, the communication of the novel technology will initially target a broad scope of companies, organisations and individuals, before tapering down to a smaller number of interested parties and implementers. After having agreed on the content of the communicated message, the priority should be to identify the activities to engage in and who to contact. This list proposes some activities and functions supporting mass communication in the awareness phase, which is also represented in the BIOFOULCONTROL dissemination. In the awareness phase, the dissemination activities are not likely to give immediate effects. The first adopters are the most difficult and will require the most attention and work. In disseminating the technology, one must be aware that the response time is detained and a slow start is the norm.
Stage 2 - Interest: The purpose of the interest phase for BIOFOULCONTROL is to provide focused information to companies and organisations convincing them that the technology will be worthwhile and effective to the company. Therefore, prior to the implementation phase, our potential adapters need to know the qualities and characteristics of the technology, and the communication will focus on the beneficiary aspects of the technology applied to the relevant company or organisation. Reflecting on the potentially large number of possible buyers of the BIOFOULCONTROL technology, and due to the fact that many will not reach the implementation stage, the communication is best organised when targeting selected adopters at the same time. The activities organised in this period will thus focus on arrangements such as:
(a) meetings, seminars, workshops, demonstrations;
(b) brochures and project reports;
(c) call and visit relevant companies;
(d) collective meetings at the research and development (R&D) institution;
(e) market analysis - the economic potential is communicated.
At the interest stage the company / organisation becomes interested in the new idea and seeks additional information about it, and mentally applies the innovation to the present and anticipated future situation, and then decides whether or not to try it. The content of the communication at this stage will be more advanced technically, and it will be necessary to involve technical experts in the communication. This is because the technical experts will better identify the potential of the application, and tacit aspects of the technology will possibly be codified and understood by the technology adopter.
Stage 3 - Implementation: The implementation phase for BIOFOULCONTROL includes the decision to adopt the new technology and the actual implementation. The role of the SMEs is to support the decision making process and potentially assist the adaptation process. The technology will in this phase be communicated to individual companies, and the focus will be idiosyncratic adjustments and the profitability for the company. In the implementation phase, activities like these will be relevant:
(a) personal meetings with the company - demonstrate verified technology;
(b) simulate results;
(c) visits to pilot sites/reference sites ;
(d) produce and publicise articles;
(e) conferences;
(f) seed capital, prior to market entry;
(g) consultancy and training;
(h) pilot used as reference in media - new knowledge / technology conveyed, displayed and communicated (awareness phase).
The following exploitable new knowledge have been taken forward for exploitation actions: New knowledge on application of ozone for prevention of marine biofouling; New knowledge on effective delivery of ozone to seawater; New knowledge on control of ozonation process; The BIOFOULCONTROL system; New knowledge on design of anti-fouling devices.
The exploitable products include the process control unit, the ozone feeding unit, and the BIOFOULCONTROL system.
More details are presented in D8 and Template B2.
A patent application has been submitted to the Norwegian Industrial Property Office on 7 February 2011. The patent is to be pursued in other countries as of 7 February 2012.
Dissemination activities:
There has been increasing interest based on the promising results of the BIOFOULCONTROL project. The SMEs have been active in dissemination activities in the 2nd reporting period. The consortium has disseminated information to over 100 companies via Email with information about the technology with highly promising results.
The SME participants have taken part in 16 exhibitions and conferences around the globe that include the shipping, aquaculture and environmental protection sectors. In addition, separate meetings have been arranged with 10 companies and these have been provided with presentations of the technology.
The BIOFOULCONTROL pilot plant has been demonstrated to the consortium and end users in the shipping and aquaculture sectors. Based on the final test results of BIOFOULCONTROL, Farstad are very interested in adopting the technology for treatment of potable water as a hygienic barrier and for disinfection of water storage tanks. Negotiation is also in progress with Statoil, one of the largest global operators of offshore oil rigs for similar application. Finally, a preliminary version of a new business plan is under development for presenting to several potential investors, like the Norwegian seed investment companies - Springfondet and Proventure Management in Norway, and this process will be followed in the post-project period. We have generally had contact with the Norwegian Venture Capital Association to identify the most appropriate investors to potentially include in the technology shareholders group. TI has provided assistance to the SMEs in this activity. Detailed presentation of the dissemination activities is presented in D8 and Template A2.
List of websites: http://www.biofoulcontrol.com
The BIOFOULCONTROL project has developed a new method for control of marine biofouling in cooling systems of vessels with application of ozone. The project has been running for 27 months starting on 1 September 2009. It has been initiated by Normex AS, Norway in cooperation with 4 other small and medium-sized enterprises (SMEs) from 3 member countries. The consortium consisted also of 3 research and technological development (RTD) performers and 1 large shipping company. BIOFOULCONTROL has been funded by the European Union (EU)'s 'Research for the benefit of SMEs' Theme of the Seventh Framework Programme (FP7).
In spite of huge expenditures used to clean fouled components of marine structures, there is currently no technology that meets the need of the shipping industry to control settlement and growth of marine organisms on cooling systems that causes either blockage of inlet pipes of cooling water or hamper heat exchange. This results in increased working temperature of engines and other heated appliances and possible shorter life, or compromising of the vessel's safety.
Within the BIOFOULCONTROL project, an innovative ozone feeding system has been developed in order to attain efficient gas mass transfer of ozone into seawater. This enables enhanced dispersion of ozone in the cooling water and attain cost-effective inactivation of marine organisms that potentially settle in the cooling system. By this, the ozonation system enables minimised generation of by products that are toxic to the marine environment. As part of the development work, the project has developed an intelligent process control unit for monitoring of process parameters and control of ozone dosage to attain optimum system operation.
The innovative components have been integrated into a pilot plant and subjected to four months of functionality tests in a real situation. The functionality trials demonstrated that ozonation is a promising technology that can efficiently mitigate marine bio-fouling cost effectively without generating hazardous products to health, safety and the environment.
Project description:
The BIOFOULCONTROL project has been initiated by the Norwegian company Normex AS. The project has received funding under the EU's 'Research for the benefit of SMEs' Theme of the FP7. It has official start date on the 1st of September and duration of 27 months. The consortium that consists of 5 SMEs, 3 RTDs and 1 large end user enterprise is as follows:
- Normex AS, SME and coordinator of the project (Norway)
- Statiflo International Ltd., SME (United Kingdom (UK))
- Edur EDUR-Pumpenfabrik Eduard Redlien GmbH & Co. KG, SME (Germany)
- Hydro Eco Invest sp Z.O.O SME (Poland)
- Stogda Ship Design and Engineering Sp z O.O SME (Poland)
- Farstad Shipping ASA, OTH (Norway)
- Teknologisk Institutt AS, RTD (Norway)
- Chalmers Tekniska Hogskola AB, RTD (Sweden)
- LABOR SRL, RTD (Italy)
The main outcome of the project is a cost effective, environmentally acceptable, user-friendly and reliable technology for control of marine bio-fouling on heat exchangers of vessels. The technology developed can also be applied in other sectors including aquaculture, ocean thermal power generators, offshore platforms and water supply systems.
Marine bio-fouling is common place on marine structures including pilings, offshore platforms, boat hulls, pipings and condensors. For steel polymer and concrete structures, bio-fouling can be a severe problem, resulting in unwanted excess drag on the structures and marine craft and causing blockages in pipe systems. Regular removal is required often by expensive mechanical means, such as by divers using high-pressure water on offshore platforms or costly, mostly ineffective, prevention methods be employed such as chlorination of pipework systems or anti-fouling coatings.
The development of the BIOFOULCONTROL technology has focused prevention of marine biofouling on cooling systems of with application of ozone. In the shipping industry, bio-fouling costs tens of billions of euros each year worldwide. The costs associated with failures related to bio-fouling in cooling systems worldwide are estimated to be EUR 1 500 - 1 800 million.
Biofouling is caused by the attachment of the larvae of marine organisms to surfaces in contact with seawater and then rapidly growing to adult fouling organisms. Subsequently, the surface will be colonised by seaweeds and the marine invertebrate. Efficient operation of seawater-based cooling systems on vessels is thus hampered by the settlement of plant and animal life and accumulation and excessive growth of organisms on the surface of heat exchangers and pipes.
Biofouling reduces the heat transfer in heat exchangers due to slime and biofilm formation, it reduces the water circulation in condenser tubes and accelerates the bio-corrosion of metallic surfaces in cooling systems as a result of extra-cellular polymeric substances and acids released by colonies of the accumulated organisms, and salt formation on the walls of the cooling systems. Fouling is most pronounced during ship operations in warm waters and at shallow depths, e.g. at harbours, although fouling occurs everywhere in the oceans at all depths. In many cases, heat exchanger tubing may become blocked and can only be rectified by extensive and costly cleaning operations. The principal solution for marine fouling has been overhaul and maintenance procedures during which the heat exchanger is disassembled and the tubes are physically cleaned, as by ramming cleaning rods through the tubes.
Heat exchangers placed in sea chests as a cooling system (box coolers) are in constant contact with seawater stream used for receiving heat from the cooling medium. As a result, they are exposed to biofouling and consequently to reduced heat transfer rate, increased working temperature of engine and other heated appliances and possible shorter life time or failure unless effective control measure is established. In addition, intake piping systems could be clogged with marine organisms propagating along with cooling seawater that reduce the capacity of the cooling system and compromising the safety of the vessel.
To mitigate the problem various techniques have been tried or proposed to prevent, or at least reduce marine biofouling, but all of them have had their technological, economic and / or environmental limitations.
Despite the recognised value of ozone as an effective agent for mitigating accumulation of organisms on surfaces such as cooling boxes and pipes, there are a number of challenges associated with application of the technology in seawater due to processes and reactions that are not fully understood. The main challenge is limiting the generation of ozonation by-products such as bromates and halocarbons that are potentially hazardous to the aquatic environment, or contribute to depletion of the ozone layer if released to the atmosphere, e.g. release of bromoform.
Formation of hazardous by-products can be minimised by enhancing the dispersion of the ozone into the seawater and attain inactivation of target organisms at lower ozone dosage than currently used with available ozone delivery devices. Thus, a main focus of the project has been development of a cost-effective ozone feeding and dispersion unit.
For optimisation of ozonation, delivery of ozone needs an intelligent control system for monitoring key parameters and regulating the ozone dosage for eliminating or minimising generated hazardous compounds to a secure level. In this connection, the project is developing a prototype of a process control unit that will be integrated with the ozone delivery unit.
Work accomplished:
A through literature study and database search has been carried out on kinetics of gas liquid dispersion as well as available methods used for feeding of ozone to water. Moreover, the literature review covered the marine chemistry involved in ozonation of seawater as well as performance of ozone as an oxidising agent against marine organisms, especially blue mussels.
A test setup was constructed at Kristineberg Marine Research Station (KMRS) on the South West coast of Sweden for trials involving feeding and dispersion of ozone into seawater, and testing of devices for microbubble generation and gas liquid mixing. The test setup was also used for ecotoxicological experiments, studying the effect of ozonation of seawater on settling, survival and growth of blue mussels (Mytilus edulis) and chemical analyses on formation of ozonation by-products. KMRS is the largest field station for marine research in Sweden and one of Europes most modern marine research laboratories with facilities for conducting experimental work and for keeping live organisms for prolonged periods. Seawater for the experiments was extracted from two depths (5 and 30 m depth).
The ozone feeding and dispersion unit has been developed by integrating a micro-bubble generating and a gas-liquid dispersion device that give maximised mass transfer. Analyses of generated bubble size and density has been analysed using imaging technique and computation with a programme developed under LabView. In the analysis, the bubble size has been found to be a determining factor for effective ozone mass transfer.
The ecotoxicological and chemical investigations were used for validating the performance of the ozone feeding and dispersion unit. For ecotoxicological studies, larvae of Mytilus edulis, considered to be highly resistant to ozone were collected from the sea and cultivated. One group of specimen was subjected to ozonated sea water at different total residual oxidant (TRO) levels and for different duration, in addition to batch tests. Impact of the ozonation has been compared continuously with a reference group of specimen. Parallel with this, ozonated seawater was analysed to measure the levels of generated bromates and halocarbons.
Development of the ozone feeding and dispersion system and the scientific investigation related to preventing growth of the blue larvae as well as generation of bromates and halocarbons under ozonation of seawater was completed at the end of the first reporting period. Development of the process control unit that has been running parallel with development of the ozone feeding unit, and involving prototyping of the hardware including the scientific instrumentation and signal processing and acquisition unit and validation of the software, was concluded at the 19th month of the project period.
Having successfully developed the prototypes of the innovative components of the BIOFOULCONTROL system, a pilot plant has been integrated and installed on board a commercial vessel operated by Farstad Shipping AS in the North Sea. The installation was completed at the beginning of May, 2011 and the system was commissioned for functionality tests and validation on 13 May 2011. Trials of the pilot plant were completed at the middle of October 2011.
During the trial period on board the vessel, regular visual inspection and photographing of the ozonated surfaces in the vessel have been undertaken to monitor settlement of blue mussels that are a common problem in the North Sea where the vessel Far Seeker is operating. Along with trials on board Far Seeker, conditions of the inlet strainers and cooling box in a sister vessel, Far Searcher, which uses the Bioguard biocide, have been inspected occasionally. Meticulous cleaning of the surfaces in the cooling system of both vessels to be subjected to ozonation by the BIOFOULCONTROL system was carried out prior to the start of the trials.
The trial period consisted of two main phases driven by the level of ozone dosage. Dosage of the ozone feeding was varied by regulating the capacity of the ozone generator. The capacity was set at 25 % (25 g O3 / hr) for the first trial phase. In the second trial phase, the ozone generator was set at 50 % capacity (50 g O3 / hr). Trials of shorter duration were also undertaken with 100 and 75 % capacity to investigate the level of bromates generated at higher levels of ozone dosage.
Ozonated and control water samples for bromate analysis were collected during the vessel journeys at constant geographical positions in the sea. The control samples are used to see whether there is background in the water due to other substances than bromate that may disturb the analytical method. The background may vary between different geographical positions and, therefore, it was important to take the control samples parallel with the samples from ozonated water.
Other accomplished work:
The SME participants of BIOFOULCONTROL have been pursuing demonstration and innovation related activities with the main work concentrated in the second reporting period of the project. As a result, the technology and its benefits have been demonstrated to selected end users while the BIOFOULCONTROL system was under development and during trials of the pilot plant on board the commercial vessel.
A patent application has been filed and submitted to the Norwegian Industrial Property Office on February 2011 to be pursued in other countries as of February 2012.
In the dissemination activity, the consortium has actively pursued contact with companies of potential interest for the BIOFOULCONTROL technology. Main venues of contact have been conferences and exhibitions, 17 in all, attended by the consortium. In addition, dissemination of information brochures by email and visits to ship owners and designers, ship buildering companies as well as fish aquaculture companies have been carried out for presentation of the project and its results. In this connection, about 110 companies have been contacted during the project period.
The RTDs have carried out provision of training to the SMEs with main focus on the results of the project, and the SMEs have trained representatives of end user core groups on installation, maintenance and operation of the main components of BIOFOULCONTROL and the integrated system primarily with live demonstrations.
Attained main results:
The developed ozone feeding and dispersion unit manages generating microbubbles with average diameter of < 50 µm as envisaged in the project objectives. This has contributed to effective gas mass transfer of ozone to the seawater resulting in effective dispersion of ozone. Trial results at KMRS have shown that all larvae of the blue mussels can be eliminated at TRO level stipulated in the objectives of the project with continuous ozonation. The level of bromates generated under ozonation is about 300 times less than the level set in the objectives of the project and what is considered to be hazardous to aquatic life. There are no references on the limit of halocarbons, but the generation of bromoform can be a concern with potential limits that may be set by the International Maritime Organisation (IMO) or individual governments.
Development of the process control unit with ultimate objective of optimising ozone dosage for cost effective operation of the system and minimisation of generated ozonation by-products was successfully concluded with delivery of a prototype and a PC-based acquisition and logging of data. The PC is connected to sensors for monitoring system operation parameters for monitoring and controlling of the ozonation process. Before installation on board the vessel, the process control unit was tested in the laboratory by integrating with main components of the BIOFOULCONTROL system including the ozone generator and the ozone feeding unit as well as sensors for calibration and functionality tests.
The validation of the pilot plant on board Far Seeker showed that no new settlement of blue mussels or other living organisms has taken place in sections of the sea chest that have been ozonated with the different ozone dosages. On the other hand, seawater treated with the Bioguard agent has resulted in marked settlements where certain sections of the inlets and strainers were partially blocked by the blue mussels.
In case of questions, please contact the Coordinator of the project:
Mr Stig Johansen
Normex AS
Email: stig@normex.no
Phone: +47-701-21103/91708023
Project context and objectives:
BIOFOULCONTROL is a FP7 project within Research for the Benefit of SMEs. It had an official start date on 1 September 2009 and has a duration of 27 months. The project is aimed at developing a biofouling prevention system for heat exchangers in maritime seawater coolers with application of ozone.
Biofouling costs tens of billions of euros each year worldwide. For example, the United State (US) Navy alone spends EUR 5 billion per year due to bio-fouling related failures, while in the UK the cost related to fouling of vessels has been estimated at 1 500 - 2 300 million euro, a figure that approximates to 0.5 % of the British gross national product (GNP). Costs associated with failures related to bio-fouling in cooling systems worldwide amounts to EUR 1 500 - 1 800 million.
Biofouling is caused by the attachment of the larvae of marine organisms to surfaces in contact with seawater and then rapidly growing to adult fouling organisms. Subsequently, the surface will be colonised by seaweeds and the marine invertebrate. Efficient operation of seawater-based cooling systems on vessels is thus hampered by the settlement of plant and animal life and accumulation and excessive growth of organisms on the surface of heat exchangers and pipes.
Biofouling reduces the heat transfer in heat exchangers due to slime and biofilm formation, it reduces the water circulation in condenser tubes and accelerates the bio-corrosion of metallic surfaces in cooling systems as a result of extra-cellular polymeric substances and acids released by colonies of the accumulated organisms, and salt formation on the walls of the cooling systems. Fouling is most pronounced during ship operations in warm waters and at shallow depths, e.g. at harbours, although fouling occurs everywhere in the oceans at all depths. In many cases, heat exchanger tubing may become blocked and can only be rectified by extensive and costly cleaning operations. The principal solution for marine fouling has been overhaul and maintenance procedures during which the heat exchanger is disassembled and the tubes are physically cleaned, as by ramming cleaning rods through the tubes.
Heat exchangers placed in sea chests as a cooling system (box coolers) are in constant contact with seawater stream used for receiving heat from the cooling medium. As a result, they are exposed to biofouling and consequently to reduced heat transfer rate, increased working temperature of engine and other heated appliances and possible shorter life time or failure unless effective control measure is established. In addition, intake piping systems could be clogged with marine organisms propagating along with cooling seawater that reduce the capacity of the cooling system and compromising the safety of the vessel. To mitigate the problem various techniques have been tried or proposed to prevent, or at least reduce marine bio-fouling, but all of them have had their technological, economic and/or environmental limitations.
The SME participants of BIOFOULCONTROL have therefore initiated this project to develop a cost effective, environmentally acceptable, user friendly and safe method based on ozonation technique.
Despite the recognised value of ozone as an effective agent for mitigating accumulation of organisms on surfaces such as cooling boxes and pipes, there are a number of challenges associated with application of the technology in seawater due to processes and reactions that are not fully understood. The main challenge is limiting the generation of ozonation by-products such as bromates and halocarbons that are potentially hazardous to the aquatic environment, or contribute to depletion of the ozone layer if released to the atmosphere, e.g. release of bromoform.
Formation of hazardous by-products can be minimised by enhancing the dispersion of the ozone into the seawater and attain inactivation of target organisms at lower ozone dosage than currently used with available ozone delivery devices. Thus, a main focus of the project has been development of a cost effective ozone feeding and dispersion unit.
For optimisation of ozonation, delivery of ozone needs an intelligent control system for monitoring key parameters and regulating the ozone dosage for eliminating or minimising generated hazardous compounds to a secured level. In this connection, the project had to develop a prototype of a process control unit that will be integrated with the ozone delivery unit.
The project has the following technological and scientific objectives:
Scientific objectives:
Acquire new scientific knowledge on:
(a) The elimination rates of marine organisms and the impact of seawater parameters such as salinity, temperature and pH on biokill by ozone.
(b) The formation of ozonation by products, especially bromates from varying levels of injected ozone, and the impact of seawater parameters on the generation of bromates. Acquired knowledge will be used for control of ozone dosage and limit the generation of hazardous ozonation by products.
(c) The dynamics of dispersion of gas/ozone in seawater and the impact of seawater parameters on generation of microbubbles required for dispersion of ozone in seawater; characterization of optimum bubble size for effective dispersion of ozone in seawater.
(d) Hydrodynamic behaviour of micro-bubbles in two-phase media.
Technological objectives:
(a) achieving mitigation of bio-fouling with ozone concentration of 0.5 ppm with our innovative ozone injection and dispersion unit;
(b) 35% reduction in energy consumption per m3 of water processed in relation to existing bio-fouling control methods;
(c) development of a cooling water treatment system that meets environmental requirements;
(d) level of bromate in discharged cooling seawater after ozonation < 30 ppm (level at which population growth of sea organisms can be affected);
(e) achieving an operation cost that is 30% less than current methods.
The innovative components were planned to be developed based on laboratory studies and tested both in the laboratory and field studies.
Project results:
Description of the scientific and technological results:
From the outset, the RTD work of BIOFOULCONTROL has focused on attaining the scientific and technological results formulated in annex 1 of the grant agreement. The main results include: New scientific knowledge, new ozone injection and dispersion unit, new process control unit and validated prototype of the BIOFOULCONTROL system.
1. New scientific knowledge:
The new scientific knowledge that emerged from the project are related to ozonation of seawater and parameters that impact on the process, kinetics in connection with formation of ozonation by products. Further, new scientific knowledge comprises inactivation of blue mussels with ozone and the concentration required to attain mitigation of marine biofouling. New knowledge involves also kinetics of ozone dispersion into water, parameters that impact on gas mass transfer in relation to efficient dispersion of ozone into seawater as well as design of devices for generation of microbubbles and dispersion of these into seawater. Finally, new knowledge is gained in relation to materials that withstand corrosion due to ozonated seawater.
1.1 Generation of ozonation byproducts:
New knowledge has been acquired based on comprehensive literature study and laboratory investigations as well as validation trials of the pilot plant on board a vessel. Available literature shows that ozone itself is not stable in seawater; it has a very short chemical half-life of about 5 seconds. In seawater, ozone quickly reacts with bromide ions (Br-) to form a secondary oxidant, and possibly other brominated by-products. The seawater composition, e.g. natural organic matter content, affects the efficiency of ozonation and also the formation of toxic by-products. These issues have been important in addressing when optimizing the dose of ozone required. The chemistry of ozone in seawater is dominated by its initial reaction with bromide ions (Br-). This is due to the relatively high concentration of bromide in seawater (about 67 mg L-1 of Br-), and it has high reactivity compared to other seawater components. Ozone quickly reacts with bromide (Br-) in seawater to form hypobromite (BrO-) that is in equilibrium with hypobromous acid (BrOH). Hypobromite, in turn, can react with ozone, and the net of the two first reactions, , is a catalytical breakdown of ozone,
Hypobromite (BrO-), formed when seawater is ozonated, is in equilibrium with hypobromous acid (BrOH), and in seawater of pH 8, BrOH is the dominating form.
Bromine (BrOH / BrO-) works as a secondary, more stable oxidant, which also has disinfecting properties. The bromine concentration in a water, expressed as TRO, is an indirect measure of the oxidation capacity of the water and normally given in mg / L. Depending on the salt content of a water TRO consists of bromine and / or chlorine. Another halogen species present in high concentration in seawater is chloride, but because of its slow reaction with ozone it only plays a minor role in the ozonation process. The reaction of ozone with bromide ion is preferred to reaction with chloride, because of a much faster reaction rate. The reaction of ozone with chloride ion is slow, with a rate constant, k, of only 0.003 M-1s-1 (Grguric et al. 1994 and references therein).
After the initial reaction step, when ozone reacts with bromide ions, hypobromite and hypobromous acid can react with ozone or with seawater components. This will result in the formation of bromide ion or formation of ozonation by-products. Hypobromite, formed when ozone reacts with bromide ions, can react with ozone either to be reduced back to bromide ion in a catalytical breakdown of ozone. It can also be oxidised by ozone to form the disinfection by-product bromate, BrO3- .
Bromate is not naturally present in seawater, but when it has been formed it is stable in seawater environment. It is classified as a carcinogenic by the International Agency for the Research on Cancer (IARC) and the maximum contaminant level (MCL) established for bromate in drinking water is10 µg L-1.
In the presence of ammonia (NH3), BrOH / BrO- will react to form monobromamine (NH2Br). This reaction is very fast and thermodynamically favourable. Bromate is not formed as long as there was ammonia present in the water. Inhibition of bromate production takes place when ammonia was added to chlorinated artificial seawater. Inhibition of bromate formation by ammonia takes place also under ozonation of fresh water.
Bromoform (CHBr3): BrOH / BrO- reacts with natural organic matter in the water to form bromoform, (CHBr3). Bromoform is a confirmed animal carcinogen. The LC50 values for bromoform show that it is toxic to marine organisms, and reported values range from 7.1 mg / L for sheepshead minnows to 26 mg / L for the brown shrimp. It is a very stable compound with a half-life of 686 years.
1.2 Ozonation of seawater and impact of water quality parameters:
The seawater composition influences the oxidation capacity, and also the formation of hazardous by-products. In present scientific literature however, more effort is put on describing the loss of oxidation capacity or enhanced TRO decay, rather than the correlation to formation on by-products.
Regarding the influence of seawater composition on formation of by-products it was found that the effect of:
(a) increased salinity > increased formation of bromine by-products;
(b) increased temperature > increased formation of bromine by-products;
(c) increased pH influences the relation between by-products (increased production of bromated and a decrease in bromoform production);
(d) organic matter > no consensus.
1.3: Concentration of ozone / level of TRO required to attain mitigation of marine biofouling
The amount of ozone needed to reach and maintain a certain TRO level over time depends on the chemistry of the ozonated water: Water with higher ammonia concentration and higher concentration of organic carbon will require a higher ozone dose. A possible explanation to this is that both ammonia and organic matter can have very fast reactions with both ozone and bromine (BrOH / BrO-) that consumes the oxidant.
The TRO level required to eliminate blue mussels by continuous ozonation is 0.5 - 0.9 ppm. Formation of bromate was dependent on the TRO concentration - the higher TRO concentration the larger bromate formation. During a long term test series the bromate concentration was fairly constant between 30 and 60 ppb. The formation of bromoform and most other halocarbons are strongly TRO dependent - the higher TRO concentration the larger halogen formation.
1.4 Kinetics of mass gas transfer and application for ozonation of seawater
A combination of multiphase pumping and static mixing has demonstrated to be a novel method of efficient gas dispersion into liquid. Both the literature study, the laboratory investigations and the trials of the pilot plant in the BIOFOULCONTROL project have shown that the ozone delivery unit developed in the project gives the best dispersion of ozone into seawater for mitigation of marine biofouling.
The main parameter that determines the efficiency of mass transfer and thus performance of the ozone delivery system is the bubble size in the gas liquid mixture. The process as a whole as well as operation of system elements are however influenced by several factors as an ozonation system works under changing conditions that can influence its operation and efficiency. The other factors that may have impact on the process are thus the following:
- Temperature and pressure:
(a) Temperature rise leads to the decrease of solubility of gases in water. On the other hand the mass transfer coefficient rises with temperature.
- Temperature decrease leads to the riise of liquid density and viscosity.
- Ionic strength and contaminations in water:
(a) Ionic strength, correlated with the amount of salts in water, influences solubility negatively. Furthermore, it enhances coalescence rate which leads to larger bubbles. Contaminations that are present in water make the surface of the bubble rigid and less permeable and thus reduces the mass transfer rate.
- Turbulence and shear force:
(a) Turbulence of a liquid is correlated to the value of mass transfer coefficient. The more turbulence, the better mass transfer. The level of turbulence can be assessed by the power dissipated per liquid volume.
(b) High-turbulence level and associated level of shear force improves the rate of bubble break up, leading to the creation of smaller bubbles.
-Parameters influencing multi-phase pump operation:
(a) Pump operation can be influenced by the fraction of gas that is present in water. Multiphase pumps are able to cope well with gas-liquid mixtures for up to 30% of gas fraction. Nevertheless, high gas contents change the characteristic curve of a pump, lowering attainable head and flow rates as well as power input.
(b) The increase in density of water (e.g. sea water) increases the power input of a pump and decreases available head.
(c) Higher density of water leads to the increase in power input as well.
(d) Higher pressure built in the pump and outlet pipe leads to smaller bubbles released after relieve valve.
- Parameters influencing static mixer operation:
(a) Pressure drop developed along the static mixer depends on the design of mixing elements. It is lower for helical-shaped elements and higher for blade grids. It also depends on the number of elements.
(b) The number of mixing elements relates to the mixing quality. The more elements the better mixing.
(c) High gas flow improve the dispersion levels leading to lower bubble sizes.
(d) Position of a static mixer can influence the uniformity of dispersion. Vertical position may lead to better uniformity and higher mass transfer. Fluid mixtures flowing in horizontal mixer may be influenced by gravitational forces, with bubbles gathering in the upper part of a mixer.
1.5 Corrosive properties of ozone in seawater:
As part of the development work, two groups of materials that can potentially be applied in ozone delivery unit that is exposed to high concentration of ozone have been studied in relation to their resistance to corrosion. These are:
(a) polymer materials;
(b) metallic materials.
The literature study revealed that there is very limited knowledge on the effect of dissolved ozone in seawater on the corrosion behaviour of materials, although ozone based oxidation has been used for a considerable length of time. It appears that the material selection to most ozonisation processes is done without major detailed corrosion investigations.
In BIOFOULCONTROL, the polymer materials have been subjected to 11 week laboratory investigation at TI using artificial seawater prepared in a test vessel to which ozone is dispersed from a laboratory scale ozone generator with help of a ceramic diffuser. Besides, reference specimen of the polymers were prepared for comparison with the ozonated specimen at the end of the trial period.
The polymer materials include:
- ethylene propylene diene monomer (EPDM),
- teflon,
- polyvinyl chloride (PVC),
- neoprene.
After subjecting the ozonated and reference specimen to tensile strength tests, the changes seen for the four ozonated polymers are generally small. Apart from EPDM that has shown low resistance to tensile strength tests after ozonation compared to the reference specimen, all the polymer materials have good ozone resistance and can be applied for joints, gadgets, o-rings and pipes.
Three metallic materials (S31600L, CuNi, Ti) were also subjected to ozonation applying the same test equipment used in the trials of the polymers. Of the three metals tested, titanium is the most corrosion resistant material in these environments. No corrosion attack was observed during the 11 weeks of testing, which indicates that there will be no problems using this material in conformation of the literature study. The CuNi metal is a recommended material in fresh and seawater solutions. After testing in ozonated seawater environment, however, the material has suffered from general corrosion. Visible green verdigris was formed. On the surface in general, also under the gasket, another oxide is visible. This oxide layer is porous and can easily be scratched off. No localised corrosion is seen. There are other CuNi-alloys with higher content of Ni than the one used in our trial that are much more resistant against ozone according to available literature.
The results after testing of the S31600 L metal show that the material is not recommended in these environments without additional measures such as cathodic protection. The material suffer from both pitting- and crevice corrosion after just two weeks exposure to ozone in seawater, whereas it withstands corrosion of ozonation in fresh water.
2. New ozone injection and dispersion unit:
For ozonation to be cost effective and sustainable, highly efficient means of gas mixing and dispersion device need to be applied. For effective ozone dispersion, microbubbles have to be generated and effectively dispersed into the liquid. Microbubbles are required for even and maximized ozone dispersion due to their special features: large interfacial area, very low rise velocity (long residual time in the liquid), low bubble coalescence, higher gas hold up and good mixture character.
In BIOFOULCONTROL, the ozone injection and dispersion system consists of static mixing and multiphase pumping technologies in which the multiphase pump generates microbubbles, while the static mixer provides high mass transfer rate. In addition to creating microbubbles, the multiphase pump works also as a dynamic mixer to enhance the dissolution of ozone in water and delivering the two phases to the static mixer by gas charging. In the static mixer, turbulent conditions ensure a high intensity radial mixing action as a result of rotational circulation of the water stream around the hydraulic centre of each of the channels in the mixer formed by the mixing element.
In addition to pump pressure and gas / liquid relation, it is the configuration of the pump impeller that determines the size of micro-bubbles generated by the multi-phase pump. For generation of micro-bubbles with diameters < 50 µ in BIOFOULCONTROL, different multi-phase pump impellers were tested both with fresh water and seawater streams to select the impeller configuration that produces the optimum bubble size for subsequent cost effective dispersion of ozone into seawater.
Selection of impeller design was based on 3 factors that have implications for the efficiency of the ozone mixing and dispersion unit:
(a) diameter of the generated microbubbles;
(b) working pressure;
(c) gas / liquid ratio (gas content).
Increasing the gas/liquid ratio beyond 30 % caused sharp fall of the working pressure of the pump, and consequently increase in the size of the bubble sizes and decreased mass transfer. However, it was the peripheral impeller that gave the smallest bubbles at gas-liquid ratio between 20 - 30 %. Thus, validation of the ozone delivery unit prototype has been carried out with the peripheral impeller.
Static or motionless mixers have been used for many years to disperse gases into liquids for mass transfer applications. The effectiveness of the mixers has been, to a large extent dependent on the dispersed gas bubble size, which is in turn dependent on the fluid velocity through the mixer. The requirements for the BIOFOULCONTROL project were to disperse ozone into seawater stream. However, to meet the overall process specification, it was necessary to produce micro-bubbles with bubble diameter smaller than normally associated with economically viable static mixer systems. This could be achieved with multiphase pump with impeller configuration designed in the project, and use the static mixer for maximised mass transfer.
The performance of the mixing element has been enhanced in BIOFOULCONTROL by changing the pitch ratio to attain a more shear and turbulence within the mixer. By increasing the mixing intensity, it was possible to produce smaller bubbles (bubble break up) and less bubble coalescence. The pitch ratio is the length of each individual mixing element compared with the mixer diameter and is usually 1.5 : 1 for most mixers. Normally, mixing elements have a pitch ratio of1:1. Further decrease of the pitch ratio would however have a down side of pressure drop through the mixer that will increase the energy consumption, although this will not be a big issue for the BIOFOULCONTROL application.
Development of the ozone feeding unit in BIOFOULCONTROL has demonstrated that applying two static mixers gives the best result. The main factor that has contributed to such result is that the first mixer is breaking the random size and distributed bubbles from the multiphase pump into a uniform size and even distribution giving an even feed to the second mixer. With constant feed conditions, the smaller mixer can operate at optimum conditions resulting in a small and uniform size bubble, evenly distributed across the pipe section. Moreover, the diameter of the mixers has been selected to give a more optimum bubble velocity through them. Bubble velocity is a function of velocity and geometry of the mixer. The developed ozone feeding system enables elimination of blue mussels with ozone dosage of 0.5 - 1 ppm without intelligent control of the ozonation process. Annex 1 of the project has set only the level of bromates as a measure of generated hazardous by-products under ozonation with a target level of < 30 ppm under laboratory investigation. However, the validation has gauged formation of bromates as well as halocarbons including bromoform, dibromochloromethane, dichlorobromomethane and chloroform using the prototype ozone delivery system. The concentration recorded at the TRO level needed for complete elimination of the mussels is about 300 times less than the target set by the technological objective of the project (< 30 ppm).
The dominant halocarbon formed is Broform followed by dibromochloromethane and dichlorobrommethane. The chlorofom content was low and rather stabile during all measurements, probably representing a natural biogenic background.
3. The process control unit:
The two main objectives of the BIOFOULCONTROL system is effective mitigation of marine biofouling of cooling systems and optimum dosage of ozone to attain cost effective ozonation and eliminating generation of toxic and environmentally hazardous by products that exceeds accepted limits. This can be attained with application of intelligent process control unit that is integrated into the BIOFOULCONTROL system.
In the project, a functioning process control unit has been developed and validated as a component of the pilot plant. This monitoring and control system of the ozonation process has been developed through the following phases, i.e. development of:
(a) scientific instrumentation;
(b) signal processing and acquisition;
(c) software interface for the visualisation and logging of measurement;
(d) software for automatic process control (with remote capabilities).
The scientific instrumentation connected to the monitoring system is basically composed of sensors that collect all the information from the sections described in the previous schema. Appropriate sensors were chosen to measure described quantities.
The sensors applied in the process control unit are all trasducers, and values have to be acquired by their electrical values. To perform this acquisition a low cost acquisition card made by National Instruments: the NI-6008, a 0 - 10 V is applied. However, the majority of the sensors give their measurement in a 4 - 20 mA range (current instead of voltage); therefore a 4- 20 mA to 0 - 10 V converters have been selected for each signal. Converted signals are then connected to two acquisition cards which communicate data to a standard PC by a simple standard USB connection.
The monitoring software that has been developed is used to gather data from the process. This software is designed to start automatically at system start-up and builds up a file every 12 hours with header and all the useful data. The interface is designed to fully work without the intervention of operators, but some utility functions have been implemented to ease the interaction with the system, since the target was a touch panel PC, like screen keyboard, minimise and quit button and so on.
An integrated open productivity and connectivity (OPC) server that allows useful and important remote capabilities can supply all required data by OPC protocol. Alternatively, a TeamViewer installation is provided to extend simple data catching to remote desktop features. In this way the user can monitor in real time software interface, take interface command, transfer files and other extra-functions that can add many opportunities to work with partners.
4. The BIOFOULCONTROL System:
The BIOFOULCONTROL system is aimed at controlling fouling of cooling systems on board vessels with the application of ozone. It is an integrated unit that consists of the innovative sub systems that have been developed in WP2 and WP3 and subjected to individual functionality tests in the laboratory. These include the ozone delivery unit (deliverable 2 (D2)) and the process control unit (D3).
The ozone delivery unit contains a multiphase pump with peripheral impellers (8 litres / min capacity) for generation of microbubbles and a static mixer with specially designed mixing elements for further break-up of the microbubbles generated in the multiphase pump, and for even and efficient dispersion of the bubbles into the sea water through maximised gas mass transfer. This ensures maximised contact between water and ozone, reduced ozone consumption and efficient inactivation of organisms that cause fouling of cooling systems.
The process control unit consists of scientific instrumentation for monitoring: ozone dosage (g / m3), oxygen concentration in gas flow (%), ORP, salinity, pH level, water temperature as well as control of gas flow. Monitoring of these operation parameters allows establishment the relationship between performance of the system and values of the parameters, and to control the process so as optimum function of the pilot plant is attained. The scientific instrumentation is supported by a touch panel PC for data logging and control of the instruments, and software for control of gas flow and Internet remote control with the help of OPC server and / or TeamViewer.
In addition to the innovative components developed in the project, the pilot plant consists also other vital components including:
- air compressor,
- O2 generator,
- PLC for control of ozone injection and the pump,
- O3 generator,
- O3 detector for ambient air quality monitoring,
- water cooler for maintaining operation temperature of the O3 generator,
- strainer for screening away coarse materials in the seawater,
- vacuum, pressure and, water flow meters.
The BIOFOULCONTROL system has been subjected to functionality tests both in the laboratory and on board a supply vessel that sails between Kristiansund in north-western coast of Norway and the offshore oil and gas installations in North Sea. The system has been tested for about 4 months on board the vessel during which the systems effect towards control of fouling by blue mussels and formation of bromates has been monitored. The system functionality has also been compared with performance of existing method used by a sister ship. The existing method is application of a biocide called bio-guard.
During the trials, two different ozone doses were applied: 25 % capacity of the ozone generator (25 g O3 / h) and 50 % capacity of the generator (50 g O3 / h). In both cases, no traces of surplus of ozone could be detected in the cooling water. The average bromate concentration at the 25 and 50 % generator capacity were found to be 9.25 µg / L and 18.8 µg / l respectively. These are concentrations that are far lower than levels considered to be toxic for marine environment.
The killing effect of the method is very high with negligible generation of bromates. The control trial on the sister ship parallel with the validation of the BIOFOULCONTROL system showed, however, high level of fouling due to settlement and growth of blue mussels.
In BIOFOULCONTROL, application of multiphase pump with innovative impeller and static mixers with special mixing element enables ozone gas to be efficiently dispersed into seawater utilising enhanced surface area of microbubbles so that enhanced contact between ozone and marine organisms in sea water is attained. This technique enables effective inactivation of the organisms locally in the inlet of cooling water and across the coolers. The problem can thus be mitigated continuously, in other words before it is created using low ozone concentrations and without application of environmentally damaging chemicals.
Application of static mixers enables efficient dispersion of the gas as micro bubbles with bubble size of less than 50 micro meter after further breakdown of the bubbles generated by the multiphase pump. This implies that the ozone is not only well dispersed in the water and surfaces to be treated, but also attains large contact area that ensures that all the injected ozone reaches and inactivates maximum amount of organisms within a short period of time. Thus, the process attains exceptionally good effect of the ozone fed into the seawater allowing low dosage / concentration of ozone without compromising the efficiency of the process.
I connection with inlet of the cooling water, it is common that vessels install so called sea chest box as a projection of the fuselage at the inlet. It is therefore in the surrounding of this box dosing of ozone takes place according to the invention. However, there is a typical grating that connects the box to the rest of the sea and prevents intrusion of small to large particles into the inlet itself that is placed in the sea chest box. This grating is also exposed to fouling by marine organisms.
With specially designed circulation loop, ozone containing gas also comes in contact with the grating, preferably with the ozone containing gas fed to the outer surface of the grating and as a result of the flow of water towards the inlet it passes through the grating on its way to the inlet. For practical purposes, this can be configured in different ways. As an example, it is possible to move the grating backwards into the sea chest box so that the outlet is positioned in the outer area of the sea chest box and the grating itself positioned inwards.
In most vessels, the cooling water inlet consists of a typical sea chest box that is connected to a grating and a so called cross over across the body. There are one or more pipes of cooling water connected to the cross over from where the cooling water is transported to the engines of the vessel. The circulation loop of the ozonation system comprises multiphase pump, the static mixer and the pipes that connect these units and spreads ozonated cooling water to exposed surfaces to marine biofouling. The multiphase pump sucks seawater from the cross over and mixes it with gas (air or oxygen) that contains a controlled concentration of ozone. The gas will be in the form of bubbles in water when transported from the multiphase pump to the static mixer where the bubbles will be further broken into smaller bubbles that are showered out in the outer surface of the sea chest box and is then circulated back to the cross over. Thus, the gas that contains ozone comes in contact with all components of the cooling water inlet that is in contact with seawater and hinders any fouling of the surfaces by the marine organisms. With appropriate positioning of the grating in relation to the static mixer, the grating will also be in constant contact with ozone so as to protect the grating from fouling. The circulation loop can be duplicated as required.
Application of static mixers as described above, and intelligent control of the process enables effective mitigation of fouling at specially low concentrations of ozone without compromising the effectiveness of the technology. The technique enables that all the ozone fed into the system will be consumed in the process.
Potential impact
The successful completion of the BIOFOULCONTROL project and its potential application for control of fouling both in fresh and sea water has brought about a number of positive impacts. The main impacts are related to protection of aquatic environment, contribution to improved working environment, new knowledge on safe and reliable application of ozone, cost reduction in connection with removing accumulated fouling and safe operation of cooling systems without compromising the safety of vessels and other structures with heat exchangers.
Within the scope of the project, it has been demonstrated that there is high potential of ozonation for mitigation of marine biofouling. This has been done by developing and introducing innovative ozone delivery system, and electronic processes control unit along with new efficient means of designing and operating ozonation systems. Thus, the potential of positive effects in the near future from results of this project is related to environmental aspects, community policies, and societal objectives including reduced use of resources on cleaning of surfaces invaded by marine organisms.
According to the IMO convention of 2001, there is a requirement for monitoring of harmful antifouling systems on ships. This includes the application, reapplication, installation or use of antifouling systems that have negative impact on the aquatic environment, health and safety as well as air quality. In this regard, BIOFOULCONTROL would positively substitute currently used methods that either directly pose adverse impact on the environment, human health or as a result of wastes generated from the application or from removal of antifouling systems.
Today, there is a number of methods for control of biofouling that can be substituted by BIOFOULCONTROL in order to achieve positive impacts. These include:
- Thermal methods with high-energy consumption and potential thermal stress damage on the heat exchangers.
- Non oxidising toxic agents that are by their nature highly toxic to aquatic organisms, often environmentally persistent and can potentially cause long-term ecological damage. Because of their mode of action, the effectiveness of these substances decreases with time, especially in seawater and renewal is necessary. Therefore, the time required to clean and dry the cooling system for repainting is too long to make antifouling paints of these substances economically and practically viable.
- Oxidising agents such as chlorine that require manual handling and storage on board with safety concerns and need of special skills. Uncontrolled dosage often creates public pollution unless additional equipment is included for waste treatment with unnecessary high cost.
- Almost all available methods are ineffective, and fouled parts have to be cleaned mechanically at very high cost, not least due to interrupted operation of the vessel.
Finally, the IMO convention requires that the parties shall take appropriate measures to promote and facilitate scientific and technical research on the effects of anti-fouling systems as well as monitoring of such effects. The BIOFOULCONTROL project has contributed to the attainment of this goal as a result of a safe, reliable and efficient ant-fouling system.
Regarding application of ozone beyond control of biofouling, there is a recognized value of ozone to improve the management of water quality in the aquaculture sector. However, there remains a significant lack of knowledge in the industry relating to its cost effective and safe use that can be solved with new knowledge gained from BIOFOULCONTROL. Lack of knowledge in the aquaculture industry has resulted in a number of negative impacts on production systems due to high residual ozone concentrations that cause gross tissue damage and stock mortalities, high concentration of bromates formed as a result of reaction between ozone and bromides and change in water chemistry exposing the stock to changed physiochemical conditions which may impact the availability of dietary ingredients. In this connection, substantial losses have been incurred in the industry around the world. The complex combination of benefits and risks of ozone use has deterred and slowed the uptake of ozone technology by the aquaculture sector causing a bottleneck in enabling the EU industry to improve the sustainability of seafood production through fully exploiting the potential of recirculated aquaculture systems and so maintain a competitive edge in the international markets and increase employment in the industry. The innovations of BIOFOULCONTROL will redress this limitation and contribute to implementation of the EU policy of increased and sustainable seafood production. Exploitation of results: The planning and execution of exploitation and dissemination plans have been based on a model framing the activities of the project.
The plans for exploitation and dissemination activities consist of three stages:
Stage 1 - Awareness: The initial BIOFOULCONTROL dissemination will target the shipping sector. Potential secondary targets will include aquaculture, power supply, offshore oil installations and water supply structures. The information will be rather generic and general, meant to reach as many potential adopters as possible. In other words, the communication of the novel technology will initially target a broad scope of companies, organisations and individuals, before tapering down to a smaller number of interested parties and implementers. After having agreed on the content of the communicated message, the priority should be to identify the activities to engage in and who to contact. This list proposes some activities and functions supporting mass communication in the awareness phase, which is also represented in the BIOFOULCONTROL dissemination. In the awareness phase, the dissemination activities are not likely to give immediate effects. The first adopters are the most difficult and will require the most attention and work. In disseminating the technology, one must be aware that the response time is detained and a slow start is the norm.
Stage 2 - Interest: The purpose of the interest phase for BIOFOULCONTROL is to provide focused information to companies and organisations convincing them that the technology will be worthwhile and effective to the company. Therefore, prior to the implementation phase, our potential adapters need to know the qualities and characteristics of the technology, and the communication will focus on the beneficiary aspects of the technology applied to the relevant company or organisation. Reflecting on the potentially large number of possible buyers of the BIOFOULCONTROL technology, and due to the fact that many will not reach the implementation stage, the communication is best organised when targeting selected adopters at the same time. The activities organised in this period will thus focus on arrangements such as:
(a) meetings, seminars, workshops, demonstrations;
(b) brochures and project reports;
(c) call and visit relevant companies;
(d) collective meetings at the research and development (R&D) institution;
(e) market analysis - the economic potential is communicated.
At the interest stage the company / organisation becomes interested in the new idea and seeks additional information about it, and mentally applies the innovation to the present and anticipated future situation, and then decides whether or not to try it. The content of the communication at this stage will be more advanced technically, and it will be necessary to involve technical experts in the communication. This is because the technical experts will better identify the potential of the application, and tacit aspects of the technology will possibly be codified and understood by the technology adopter.
Stage 3 - Implementation: The implementation phase for BIOFOULCONTROL includes the decision to adopt the new technology and the actual implementation. The role of the SMEs is to support the decision making process and potentially assist the adaptation process. The technology will in this phase be communicated to individual companies, and the focus will be idiosyncratic adjustments and the profitability for the company. In the implementation phase, activities like these will be relevant:
(a) personal meetings with the company - demonstrate verified technology;
(b) simulate results;
(c) visits to pilot sites/reference sites ;
(d) produce and publicise articles;
(e) conferences;
(f) seed capital, prior to market entry;
(g) consultancy and training;
(h) pilot used as reference in media - new knowledge / technology conveyed, displayed and communicated (awareness phase).
The following exploitable new knowledge have been taken forward for exploitation actions: New knowledge on application of ozone for prevention of marine biofouling; New knowledge on effective delivery of ozone to seawater; New knowledge on control of ozonation process; The BIOFOULCONTROL system; New knowledge on design of anti-fouling devices.
The exploitable products include the process control unit, the ozone feeding unit, and the BIOFOULCONTROL system.
More details are presented in D8 and Template B2.
A patent application has been submitted to the Norwegian Industrial Property Office on 7 February 2011. The patent is to be pursued in other countries as of 7 February 2012.
Dissemination activities:
There has been increasing interest based on the promising results of the BIOFOULCONTROL project. The SMEs have been active in dissemination activities in the 2nd reporting period. The consortium has disseminated information to over 100 companies via Email with information about the technology with highly promising results.
The SME participants have taken part in 16 exhibitions and conferences around the globe that include the shipping, aquaculture and environmental protection sectors. In addition, separate meetings have been arranged with 10 companies and these have been provided with presentations of the technology.
The BIOFOULCONTROL pilot plant has been demonstrated to the consortium and end users in the shipping and aquaculture sectors. Based on the final test results of BIOFOULCONTROL, Farstad are very interested in adopting the technology for treatment of potable water as a hygienic barrier and for disinfection of water storage tanks. Negotiation is also in progress with Statoil, one of the largest global operators of offshore oil rigs for similar application. Finally, a preliminary version of a new business plan is under development for presenting to several potential investors, like the Norwegian seed investment companies - Springfondet and Proventure Management in Norway, and this process will be followed in the post-project period. We have generally had contact with the Norwegian Venture Capital Association to identify the most appropriate investors to potentially include in the technology shareholders group. TI has provided assistance to the SMEs in this activity. Detailed presentation of the dissemination activities is presented in D8 and Template A2.
List of websites: http://www.biofoulcontrol.com