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A Method for On-Line Cleaning of Heat Exchangers to Significantly Increase Energy Efficiency in the Oil, Gas, Power & Chemical Process Sectors

Final Report Summary - CLEANEX (A Method for On-Line Cleaning of Heat Exchangers to Significantly Increase Energy Efficiency in the Oil, Gas, Power & Chemical Process Sectors.)

Executive Summary:
This report covers the work carried out during the whole period of the CLEAN-EX project. More details on deliverables can be found in individual deliverable reports.

The Need
Approximately 65% of the heat exchanger market is dominated by the shell and tube type heat exchanger. This is largely due to its long performance history, relative simplicity, its wide temperature and pressure design ranges. Fouling of heat exchangers in the petroleum, mineral and chemical processing industries have a major impact on energy recovery for these systems. Preventing the build-up of fouling is vitally important to prevent loss of heat transfer, under-deposit corrosion and pressure loss all leading to reduced heat exchanger performance. Although it is possible to mitigate fouling by changing heat exchanger design and operating conditions, this is often in conflict with required optimal process conditions. Figure 1 illustrates typical fouling resistance as a function of time for crude oil pre-heat train heat exchangers. In this particular instance, the severity and magnitude of fouling is such that the heat exchanger would be taken out of service after 140 days of operation. As a result, there is a critical need to develop on-line cleaning methodologies to overcome this problem. Estimates on costs associated specifically with worldwide crude oil fouling in the pre-heat trains of oil refineries have been calculated in the order of $4.5 billion per annum. Despite the enormous costs associated with fouling and the research conducted in this field, there is no on-line cleaning system capable of mitigating this problem for high temperature, low velocity and chemically reactive fluids. Millions of tonnes of carbon dioxide emissions are the result of these shortcomings. Data from refineries suggest that crude oil fouling accounts for around 10% of the total CO2 footprint.

The Solution
The overall focus of the CLEAN-EX project is to develop an on-line cleaning system for heat exchangers to significantly improve energy efficiency in the oil, gas, power and chemical process sectors. The CLEAN-EX project is therefore a means to effectively mitigate fouling.
To achieve this, the consortium intends to enhance the understanding of fouling in shell and tube type heat exchanger systems (Work Package 1). In this respect, the consortium’s approach is to develop a system that does not merely mitigate the formation of deposits, but also attempts to suppress the initial nucleation and formation of layers altogether.
The overall work plan was divided into three distinct phases. Phase 1 (Work Package 1, 2 and 3) focuses on gaining the scientific knowledge required to enable the development and validation of a proof-of-concept CLEAN-EX prototype. Phase 2 (Work Package 4, 5, 6 and 7) involved the development, integration, validation and testing of the individual enabling technologies as well as the integrated proof-of-concept, the CLEAN-EX prototype. Phase 3 (Work Package 8 and 9) covers the innovation-related activities and consortium management required to protect the developments, prepare further in-field and pre-production engineering, prepare the market, effectively manage project activities and liaison with the EC.

Project Context and Objectives:
The technical work whole 42-month period (1st September 2009 to the 28th February 2013 has been spread over the tasks in the following Work Packages:-
• Work Package 1: Fouling characterisation research for high & low velocity heat exchangers
• Work Package 2: Preparatory research - simulation & modelling
• Work Package 3: Experimental validation and preliminary project specifications
• Work Package 4: Projectile structure and material development
• Work Package 5: Fluid propulsion systems
• Work Package 6: Projectile alignment, tracking and control
• Work Package 7: Integration and testing

Project Results:
The Cleanex Solution

Heat exchangers are the workhorse of most chemical, petrochemical, food processing and power generating processes. Of many types of heat exchangers, approximately 60% of the market is still dominated by the shell and tube heat exchangers. One major problem of shell and tube heat exchangers is directly related to the deposition of unwanted materials on the heat transfer surfaces.
Fouling may cause one or more of several major operating problems
i) loss of heat transfer
ii) under-deposit corrosion
iii) increased pressure loss
v) flow mal-distribution

There are many different mitigation techniques available in the market to keep the surfaces of heat exchangers clean to some extent. Among them, projectiles of various shape and sizes have been used to mitigate deposit in tubular exchangers for decades. They circulate by a separate loop through the exchanger. The advantages of this method are that it is very effective for fouling mitigation which would otherwise be required for a stable operation. Having said that, nevertheless, there are many unanswered questions such as optimum injection frequency, minimum required shear force to dislodge the fouling layer, applicability of projectiles at elevated temperatures and minimum required velocity for propulsion of projectiles inside the tubes, the random distribution of cleaning balls in different densities of projectiles and flow, viscosity, location of inlet nozzle and effect of flow diverter that need addressing.

The Clean-Ex project, funded by EC, intended to develop the following technologies that will be part of a flexible retrofitable on-line heat exchanger cleaning system for high temperature and wide range of velocity applications:
• Development and demonstration of a corrosion and wear resistant cleaning projectile for use in aggressive fluids and elevated temperatures of up to 300°C
• Development of a projectile trajectory system to give an almost uniform distribution of projectiles over the area of the tubeface
• Development of a fluid injection system to selectively increase fluid velocity through tube arrays with the aim of propelling cleaning projectiles through individual tubes
• Development of a projectile detection and tracking system to monitor cleaning of individual tubes and identify potential blockages

Within the framework of the CleanEx project, various test facilities in lab and industrial scales have been designed and constructed. In particular, a fouling rig was designed and constructed to investigate various foulants as well as ability to change dominant operating conditions such as velocity, surface and bulk temperatures, and concentration. In addition, the rig allows rigorous investigation of various projectiles, in different injection intervals, either being recirculated or simply collected after each injection.

The Cleanex project

The overall work plan was divided into three distinct phases.
Phase 1 (Work Package 1, 2 and 3) focuses on gaining the scientific knowledge required to enable the development and validation of a proof-of-concept CLEAN-EX prototype
Phase 2 (Work Package 4, 5, 6 and 7) involved the development, integration, validation and testing of the individual enabling technologies as well as the integrated proof-of-concept, the CLEAN-EX prototype
Phase 3 (Work Package 8 and 9) covers the innovation-related activities and consortium management required to protect the developments, prepare further in-situ and pre-production engineering, prepare the market, effectively manage project activities and liaison with the EC.

Work Progress and achievements and progress during the final period
• Developed projectile collection and cleaning process to remove projectiles from the exchanger
• Test rig prepared to test the flow of multiple projectiles in various flow conditions
• Characterization of various projectiles in terms of hardness, texture and shapes for different foulants
• Optimal injection of multiple projectiles under harsh fouling operating conditions
• Optimum timing of projectile injection
• Parameterization of tribological contact stability of hard and soft cleaning projectiles
• Full scale prototype of fluid diverter delivered. Full scale prototype of Indexer delivered. First stage testing completed and all sub components integrated into a working model used to create an optimised programmes
• Signal conditioning, processing electronics and firmware designed
• Integrated control and HX diagnostic system designed
• Lab scale prototype built
• Systems tested using the test rig
• Optical exchanger is designed and assembled at ITW, Stuttgart
• All pipework for the inlet and outlet fabricated
• Assembly of the optical exchanger rig with the sensory array and ready for first stage testing
• Incorporation of the injector and collection system into the main laboratory
• The control system and sensors for the laboratory including all sub components were installed
• First stage filling and running of all equipment
• Flood safety housing was assembled underneath the laboratory in the event of a water spillage
• Baffle Plate patent filed 01.07.2011
• Rotary Drop patent filed 24.05.2011
• Indexer filed 25.05.2011

The project made good progress and we are confident that in future, our partners, will succeed in achieving the goal of developing the on-line cleaning system for heat exchangers

Technical finding concerning benign use of projectiles

It can be drawn from the performed experiments that:
1- Increasing injection rates of projectiles (time between two subsequent injections) would intensify the cleaning efficiency and decreases the final fouling resistance;
2- Faster approach toward an asymptotic fouling resistance is accelerated when double injection is attempted in comparison with single or no injection;
3- Double injection retards the fouling process profoundly compared to that of single injection;
4- High injection rates reduce the fouling resistance hence it is possible to reach to the same effect using low injection rates together with multiple injections;
5- Increasing the diameter of the projectiles relative to the size of the heat exchanger tube can improve the cleaning capability of the projectile, but increases the pumping power;
6- Increasing irregularities in the surface of the projectile, i.e. notches and cavities, improves the cleaning capability of the projectile;
7- Contact area of projectiles and the tube inner wall and their stiffness are the most important parameters that determine the extent of projectile cleaning. Stiffness produces shear force and projectile size contact with the tube. To have the best cleaning performance, there is an optimum value for projectile size and stiffness. The best size is 10% bigger than the pipe and the optimum stiffness is 1% deformation under a 0.6 N force. Using projectiles out of this range may be problematic. Bigger and softer projectiles cannot withstand long time injections thus their life-expectancy would be short. Simultaneously harder projectiles are more liable to get stuck. R**/R* (the ratio of fouling resistance with and without injection) give a better sense for cleaning the heat exchanger and could decrease by 80% if a suitable projectile of right size and stiffness is selected;
8- The cleaning action of projectiles is not only related to their stiffness but also the contact stability with the tube. To examine the latter two additional tests of measuring hydrodynamic and dynamic forces are recommended. The experimental results show that hard projectiles exert much higher dynamic shear force than the soft projectiles. Nonetheless, under the propulsion force of flow, they do not exert a remarkable shear due to unstable contact between projectiles and the tube. As a result, their cleaning performance is not appreciably better than the softer ones. A set of fouling experiments with hard and soft projectiles and various injection rates confirmed this phenomenon. A new technical term, the contact stability or “Z factor”, is also proposed which is less than 0.2 for hard projectiles and between 0.6 - 0.9 for soft projectiles;
9- the injected projectile is capable of removing parts of the fouling layer at the early stage of the fouling process, and this capability decreases as the fouling layer builds up such that the projectile is not effective anymore when the asymptotic region is approached;
10- injecting projectiles at the end of the induction period delays the fouling process, and injecting projectiles from the beginning of operation fastens the fouling process; and finally
11- The optimum injection period should start after the induction period to make use of the long fouling free period of operation in case of no injection, and to stop injection as the asymptotic behaviour is approached, since the projectiles become ineffective at the asymptotic stage.

Potential Impact:
The Clean - Ex consortium has developed, produced and intend to sell systems based on the principle of projectiles repeatedly passing through the hot (up to 3000C) heat exchanger tubes, thus keeping them clean at all times, this will be done separately now by each company. Clean - Ex unit solves the fundamental problem in Heat Exchangers – namely scale and sediments clogging the tubes. Thanks to Clean - Ex unit, the efficiency and output of the Heat Exchanger are kept at maximum levels throughout production.
Heat exchangers are found in virtually all sectors of industry and commerce.
One of the central problems confronting these systems is how to keep the insides of the tubes clean and free from the gradual build-up of minerals (such as scale) which coat the inside of the tubes. It is universally recognized that the build-up of scale significantly affects the efficiency of the heat exchange and causes:
- A dramatic reduction in the efficiency of the heat exchanger
- Reduction or increase of pressure (in air conditioning systems), which causes the deterioration and/or destruction of the compressor
- A reduction in the ability of the system to supply the designed output (for example air conditioning systems result in the inability to cool the facility).
- An increase in maintenance time needed to service the system (increasing the down time, and the labour costs of maintenance personnel and materials).
- Periodic chemical treatments (usually various acids, soaps or salt derivatives) which cause wear and tear of the tubes and may be harmful to the environment that do not remove inert hydrocarbon scale or blockages.

The consortium finally did develop and planned to patent a unique solution to the removal of hydrocarbon and inert scale build-up in high temperature heat exchangers. Instead of trying to clean the tubes after the build-up has occurred, Clean-Ex unit maintained the tubes in a clean condition through the use of projectiles which constantly circulate through the tubes, wiping them clean before any build-up can occur.
The projectiles are designed to be slightly larger than the inner diameter of the tubes unlike traditional ball cleaning systems where the projectiles are undersize which allow them to bounce down the tubes. The hot media or injector (crude) flow pushes the ball through the tubes, constantly wiping the insides, before any build-up can occur. The projectiles (like balls) are caught in a trap after exiting the tubes, and returned to the starting point for reinsertion into the system at the desired, predetermined duty cycle. By maintaining the tubes in a clean condition, no build-up occurs. Therefore, there is no need for acids, chemicals, soaps, etc or even periodic offline, manual, mechanical cleaning. The system is equipped with high speed injector + projectile navigator which allows the unit to work in high viscosity, low velocity medium allowing the projectile to travel down all heat exchanger tubes.
In addition to saving traditional substantial maintenance costs, the system produces substantial energy and CO2 emission savings by preventing virtually all scale build-up, and therefore the system can operate continually at maximum efficiency.
Sponge-ball based systems have been in use in large power plant systems for over twenty years. The costs savings and increase in efficiency when using these systems are so great that virtually every large power station in the world is equipped with a sponge-ball based system of some kind.

The Clean-Ex solution will be available for small as well as large exchangers providing a very quick return on investment

Market for industrial heat exchangers

Global refinery crude throughputs are revised up 425 kb/d for 2010 on strong European runs. At 73.9 mb/d, 2010 global runs are 1.8 mb/d higher year-on-year, with growth underpinned by expansions in China and a recovery in US refinery activity.

Although demand is stable in most market segments the Chemical and Fuel processing industries are still the largest consumers of industrial heat exchangers and accounted for 40% of the market. The shell and tube heat exchanger is still the most popular type of heat exchanger with 65% of the market.
Estimates have been made of fouling costs due primarily to wasted energy through excess fuel burn, but also for increase maintenance, over sizing of equipment and lost production that are as high as 0.25 per cent of the gross national product (GNP) of the industrialized countries. According to Pritchard and Thackery (Harwell Laboratories), about 15% of the maintenance costs of a process plant can be attributed to heat exchangers and boilers, and of this, half is probably caused by fouling.

Rights and Patents
The Clean-Ex consortium were to register patents in the United States and other countries. Registration of parts of the patents - projectiles by C.Q.M and the injection (system) for the projectiles into the tubes by Tube Tech International and ISRI.
Continuous Development Efforts - New developments in process
1. Automatic Tube Cleaning System for heat exchangers with more than one pass
2. Scouring projectiles for hot and aggressive liquids
3. Such research In addition to Company knows how and management attention, investment in experienced manpower and extensive financial resources for technical testing, substantiation, and regulation approval.

Return to end-user
Every barrel of oil processed in the world passes through crude preheats trains prior to undergoing the first major step of the refining process. The crude preheat train (CPT) is a series of heat exchangers that take heat from other process streams that require cooling and use the heat to raise the temperature of the crude oil from ambient conditions to 200-2800C.
The crude is heated further to 330-3700C in a furnace before entering the distillation column. Nearly 60-70% of the thermal energy required to heat the crude prior to distillation is recovered from produce streams.
As oil flows through the heat exchanger, the heavy organics flocculate and deposit on the heat exchanger walls, fouling the surface. The fouling acts as a thermal insulator, reducing the rate of heat transfer from the hot process stream side of the heat exchanger to the cooler crude oil side. When the fouling reaches a limit predetermined by the refinery operators, the heat exchanger is taken offline to be cleaned. In some cases, there are spare heat exchangers that can be rotated into the CPT line up when one is taken offline for cleaning so that the performance of the CPT is unaffected. However, if more heat exchangers must be taken offline for cleaning than there are replacements or the heat exchanger to be cleaned is in such a location that there are no spares, the performance of the train is diminished and the downstream furnace must bear a greater heat load.

It is generally accepted that heat exchanger fouling is one the biggest inefficiencies affecting refineries. According to Shell Global Solutions, refinery operators often lack the tools to determine optimal cleaning schedules. Actual maintenance schedules therefore mainly rely on previous experience or simple models, which are a function of the type of heat exchanger, crude oil properties, temperature and pressure drop. The optimum run-time for a single heat exchanger is also determined by balancing the efficiency and margin losses due to fouling against the cost of downtime for cleaning. As a result cleaning cycles vary significantly and generally range between 6 months and 4 years.

Clean-Ex unit gives refinery operators the option to schedule the shutdown with time extension between shutdowns for cleaning.
Although some plants operate parallel networks of heat exchanger batteries, it is not always possible to avoid significant efficiency losses.
Unplanned shutdowns are costly in terms of safety, lost production, and additional energy consumed during shutdown and start up.
Lost production time can be valued at $500,000 to $1 million per day.

It is worth noting this project finished in not the most collaborative or cooperative manner so the partners will be pursuing the above commercial directions independently.

Please understand due to the disruptive nature of a partner this project didn’t finish as was envisaged, that said all the partners have gained a massive amount of data and ideas to pursue going forward. Also, this project was written in 2008/9 and now in 2015 there has been developments in these arenas as well.

Tubetech will certainly be developing the cleaning ball idea and have already requested the test rig be returned to the UK for them to progress the start made from this project.

ITW and CQM will also be progressing developments commercially and independently thus comments cannot be comment upon in this report.

ITW have certainly been very proactive with publications which are mentioned in the tables in sections Template A1 and A2 following this section.

UK Intelligent Systems Research Institute
Innovation Park,
Nottingham Road
Melton Mowbray
Phone: _+44 1664 501 501
Fax: +44 1664 501 589
Attn: Mr Ian Claris, Director

Cooling Quality Management Ltd.
Tirat-Yehuda 51 d.n. Hamerkaz
73175, ISRAEL
Phone: +972-3-9732080
Fax: +972-3- 9732059
Attn: Omer Livni

Tube Tech International Ltd.
14 Rawreth Industrial Estate
Rawreth Lane, Rayleigh
Essex, SS6 9RL
United Kingdom
Phone: +44 (0) 1268 786999
Fax: +44 (0) 1268 786998
Attn: Mr. Mike Watson, Managing Director

Universitaet Stuttgart (USTUTT( ITW)), Universitätsbereich Stadtmitte
Postfach 10 60 37
70049 Stuttgart
Phone: +49-(0)711-685-0
Fax: +49-(0)711-685-82271
Attn: Prof. Reza Malayeri - Head of fouling and cleaning in process industries

BiPro Tech Sp. z.o.o
Kapelanka 17/2 Str.
30-347 Kraków
Phone: +48 12 260-37-40
Fax: +48 12 267-83-37
Attn: Mr. Krzysztof Moskala, Director