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Safe co-combustion and extended use of biomass and biowaste in chp fb plants with accepted emissions (FBCOBIOW)


Based on the theory of bed agglomeration a bed material was found coming from a manufacturing process, which resists bed agglomeration by far better compared with usually used bed sand, and which is even ceaper compared to natural sand. Consequently with this bed material the share of biomass to be burned in the combustion chamber can be enhanced to an extend which enables existing power plants to run the boiler more economically due to reduced bed exchange rates or enhanced share of problematic biomass. The bed material is readily available and tested in a pilot plant with good results, but needs additional tests in a industrial boiler.
Meat and bone meal, (MBM) is produced in the rendering plants where animal offal and bones are mixed, crushed and cooked. In response to the recent outbreaks of BSE the EU has issued a temporary ban on animal meal in feed for all animals intended to human consumption. Firing MBM in power plants is attractive because of the payment to the power companies for destroying this waste. Its land filling is expensive and may cause serious hygienic problems, and finally this waste is destroyed through chemical reactions producing for example methane and carbon dioxide. Combustion of MBM in power plants contains high operational risks because of its high chlorine content. Chlorine and alkali metals form alkali chlorides, which vaporise from the fuel during combustion. These compounds act as Cl carriers to the superheaters leading to serious and expensive boiler damages (corrosion, hard deposits) as observed in EVO AG:s 80MW CFB after co-firing MBM with German hvb coal. MBM is also rich with calcium and phosphor, which can strengthen the operational problems started by alkali chlorides. In this project Cl deposition was prevented by co-firing MBM with coals containing highly reactive aluminium silicate. The original coal co-fired with MBM contained aluminium silicate deactivated partly with potassium. Therefore its protecting power was low. This result can be applied to MBM and other similar waste planned to be combusted in EVO AG s CFB and elsewhere.
Greenhouse and particulate emissions from (combined) heating and power plants and other smaller units are of great concern from an environmental point of view. The project mainly involves pilot scale studies to investigate the exploration of different fuels which could be used for co-combustion in small bubbling fluidised bed boilers, prevention of harmful emissions, fouling and agglomeration (both leading to operational problems) and to find optimal ways to burn risky biomass and bio waste. Experiments were carried out using a modified (for research purposes) fluidised bed boiler manufactured by the Dutch Company Crone (project partner) of thermal input of 1MWth. In order to obtain an improved understanding of the combustion process regarding emissions of fine particulate matter, Particle size measurements were performed using an 11 stage Mark V Pilat Cascade Impactor. The process parameters investigated in these experiments were fluidisation velocity, bed temperature, air staging and co-combustion of biomass. Experiments carried out with B quality wood (demolition wood) clearly indicate that running the system at higher fluidisation velocity reduces gaseous emissions due to better mixing within the bed zone of the combustor. Bed temperatures lower than 850oC have a negative effect on the combustion behaviour. In the experiments performed, it was shown that palletised Demolition wood (BQW) combusted very well with acceptable gaseous emissions. Pepper plant reside (PPR) pellets from greenhouses combusts very badly, probably related to its higher ash and potassium content. 100 % PPR pellet combustion experiments using normal bed material (sand) were not possible due to very fast rate of agglomeration. Co-combustion experiments, even with smaller shares (25 %) of PPR show very high gaseous emissions. Air staging shows comparatively (with non-air staging experiments) higher emissions for BQW, while air staging with co-combustion show low but still unacceptable gaseous emissions (CO and NO). ¿Agglostop¿, an additive delivered by the company Kvaerner Power to prevent agglomeration, acted against agglomeration to a certain extent but is not immune to agglomeration. Particulate emissions from both fuels are a major source of concern. The system contained a cyclone only, which led for all fired fuels to unacceptably (exceeding current standards) high solid emissions. Not only are these total solid emissions well beyond acceptable emission levels but also BQW fly ash was shown to contain comparatively high concentrations of Lead.
The main target sector of this result is Power or Power-Heat generation sector equipped with CFB boilers. Fluidised bed properties enable to fire a wide range of fuels of different sizes, shapes, moisture content and heating values. The general aim is to evaluate system to co-fire selected biomass with Polish brown coal in a CFB 670 boiler installed at Turów PS. The selection of biomass was based on local availability. The most suitable biomass that appeared was wood wastes, willow and straw. These biomasses were analysed and then their physical-chemical properties were determined to evaluate optimal storage and transporting system. The important part in the problem of co-combustion biomass with coal is to evaluate optimal feeding system by taking into account combustion parameters of the blends, fire safety of possible installations, investment, operational costs, and the local conditions. The two feeding systems of biomass to the CFB boilers were considered as the most suitable for CFB670 boiler according with the estimation analysis of selected criteria. Both systems transport biomass via fuel gallery resulting in dosing of mixture of biomass and lignite to combustion chamber. These feeding systems differ the storing of biomass near the lignite gallery and consequently the cost of systems. The feasibility study of biomass co-firing systems in CFB670 carried out for two selected feeding system, exhibited that the project is economically effective in every variant, i.e., with 10% and 20% of biomass.