Combustion studies of high moisture content waste in a fluidised bed

The combustion of three high moisture content waste materials in a fluidised bed combustor has been investigated and a comparison with co-firing of these materials with coal in the same combustor has been made. Waste materials burnt were olive oil waste, municipal solid waste and potato, which is representative of vegetable waste. Mixtures of up to 20% mass concentration water in the waste were fed to the combustor. Above that value the moisture content was too high to sustain combustion without addition of coal. Measurements of CO, NOx, SO2 temperatures were made and the carbon combustion efficiency evaluated. Co-firing with coal resulted in markedly higher combustion efficiencies with an increase of approximately 10-80% when burning the simulated MSW. However, this was much lower than the value of 93% when coal was burnt on its own. It was also much lower than the value obtained, average 90%, when co-firing potato and olive oil waste with coal and there was little difference in the combustion efficiency between the two types of waste and with increasing moisture content. It was concluded that the high ash content of the simulated MSW 26%, compared with 5% in the other two waste materials resulted in slower burning and consequently the char particles were elutriated from the bed without being fully burnt. In term of gaseous emissions during co-combustion, CO emission is relatively insensitive to change in waste fraction. While emission of SO2 can be reduced as the waste fraction increases as a result of fuel-S dilution. But in terms of percent fuel-S converted, it is actually increased by increasing waste fraction. Emissions of NO and N2O increase slightly with MSW fraction.