Poultry Litter Gasification in a Fluidized Bed Reactor: Effects of Equivalence Ratio, Temperature and Limestone Addition on Tar Yield and Composition

Air gasification of poultry litter was experimentally studied in a laboratory scale bubbling fluidized bed gasifier.Gasification tests were conducted at atmospheric pressure using silica sand as the bed material. This paper investigates the effect of equivalence ratio (ER) in the range of 0.18 -0.41, temperature between 700 and 800 ° as well as the addition of limestone blended with the poultry litter, on tar yield and composition. The optimum conditions with regards to the tar (minimum totaltar yield ≈ 3.2 total tar kg-1 poultry litter (d.a.f.)) as well as product gas properties w 800 ° R = 0.3 using 8 % w/w of limestone blended with poultry litter. By varying ER poultry litter blended with limestone showed a reduction in total tar yield whereas poultry litter not blended with limestone showed increasing yield over the tested ER range. Moreover, in the presence of limestone, polycyclic aromatic hydrocarbons (PAHs) showed a tendency to reduce over the ER range tested. Increasing the temperature was shown to be effective to reduce the total tar yield but the amounts of PAHs increased. Due to the (≈ 6.5 % w/w (d.a.f.)) the chemical composition of the tar is distinctive compared with conventional lignocellulosic fuels. Nitrogen-containing hydrocarbons such as pyridine, 2-methyl pyridine, 2-methyl-1H-pyrrole, and benzonitrile were identified in significant amounts. It was demonstrated that poultry litter can be gasified by blending it with limestone, yielding a product gas with low tar content as well as diminishing the risk of agglomeration caused by the mineral composition of poultry litter ash (high K and P content).