Gasification of wastes in a pilot fluidized bed gasifier

• Four wastes were gasified in a fluidized bed and the results compared with wood
• Orujillo generated a gas similar to wood but the ash promotes sintering of the bed
• MBM gasification generated a gas with low heating value and high tar content
• DSS and MSW were gasified with low efficiency, leading to bed agglomeration

A technical assessment of fluidized bed (FB) gasification of various wastes was carried out by conducting tests in a 100 kWth pilot plant. Four feed stocks were tested: orujillo, meat and bone meal (MBM), dried sewage sludge (DSS) and compost from municipal solid waste (MSW). The air ratio (the ratio between the actual and stoichiometric air flow rates) was varied for each fuel between 0.23 and 0.43 giving temperatures in the range of 770–870 °C. Characterization of the process was made in terms of gas composition, heating value, gasification efficiency, carbon conversion and tar content. Comparison of the results to those previously obtained with wood pellets was made. It was found that orujillo is a suitable fuel to be gasified in FB, providing that the temperature in the bed is enough to reach high carbon conversion (higher than 850 °C). In the present work, orujillo was gasified by continuous removal of material from the bed to keep potassium concentration low, resulting in relatively low carbon conversion. However, improvement could be made if additives slowing the sintering of the bed material were used. MBM was easily gasified, even at relatively low temperatures (≈ 800 °C), but it produced a gas with a low heating value and high tar concentration, leading to very low process efficiency. Gasification of DSS and MSW fuels in a FB is challenging due to the amount and nature of the ash in these fuels, making operation at a high rate of ash removal necessary to maintain smooth conditions in the bed. The efficiency of the process is low, generating ashes which are difficult to dispose of.