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Safe combustion of B-wood in small BFB s planned originally to coal

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.

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