Influence Of Temperature On The Gasification Of Cattle Manure In Fluid Bed

Large amount of animal manure from concentrated animal feeding operations (CAFOs) has posed tremendous challenges to environment since there are limited technology choices for manure treatment. Anyway animal manure is not always deleterious, it would be valuable if the contained biomass is appropriately treated and used. Manure biomass gasification is a state-of-the-art technology for animal manure treatment and utilization, but there is a lacking knowledge in literatures, therefore this study was designed to look at the effects of temperature on the gasification of animal manure in fluidized bed via several experiments, firstly the gasification feasibility of animal manure (including swine manure, poultry manure and cattle manure) and corn stalk were investigated, and animal manure with the best gasification performance were selected for the subsequent trials, then selected animal manure was gasified in fluidized bed, and the effects of temperature on the gasification, ash characteristics, and carbon and nitrogen contents. The results shown that cattle manure has the best gasification performance and the detailed outcomes of effects of temperature on the gasification of cattle manure in fluid bed are as follows:The low calorific value and the elements contents of dried cattle manure are similar to corn stalk, so cattle manure was best in terms of gasification. Ash yield of corn stalk (less than 10%) was far less than that of both animal manure ash (pig manure>20%; poultry and cattle manure=30%). The amount of volatile nitrogen (about 25g/kg) and phosphorus (about 3g/kg) of animal manure were higher than the counterparts of corn stalks (nitrogen about 15g/kg, few phosphorus), but the amount of volatile potassium (about 10g/kg) and sodium (rarely) of manure were much less than the counterparts of corn stalks (potassium about 25g/kg, sodium about 65g/kg). Therefore, ash and nitrogen pollution problem in animal manure gasification and high K and Na alkali metal in corn stalks gasification should considered.Temperature was an important factor in animal manure gasification, gas yield increased from 3.5m3/kg to 4.4m3/kg with gasification temperature from 600℃to 900℃) and gas calorific value (GCV) peaked at around 750℃with the value of 3600 kJ/m3 . The carbon conversion shown the same pattern as GVC, with maximum of 42.1% at 750℃. The maximum value of gasification efficiency (46.1%) appeared at 800℃. Equivalence ratio (ER) of 0.4-0.5 in combination with temperature in between 750-800℃were optimized for cattle manure, under such condition the gas heat value about 3600kJ/m3, gas production rate of 3.8-4.0m3/kg, and gasification efficiency of 45-50% were obtained, and no nitrogen pollution was incurred.Temperature had effects on solid matter production and elements contents. the concentration of heavy metals in fly ash increased with gasification temperature in between 600℃to 900℃, the content of Cu was 274ug/g at 900℃, the content of Zn was 537ug/g at 750℃, the content of Cr was 269ug/g at 900℃, the content of Ni was 166ug/g at 800℃, exceeding the limit values of GB8173-87. The K2O+Na2O content in slag was 18.6%, the index of alkaline oxides (AI) was 0.91, which indicated that the contents of Cu and Zn in slag were higher than GB8173-87 limits. Both fly ash and bottom char should be further processed.Temperature had no evident effects on carbon contents of combustible gas produced from manure gasification, carbon contents in solid products were 52.1% and 14.3% at temperature of 600℃and 800℃, respectively, which indicated a declining trend with temperature increase. And carbon contents in the liquid products were 1.32% at 600℃and 0.39% at 900℃, it decreased with temperature. Nitrogen contents shown differents shapes, its contents in gas product decline from 10.9% to 2.7% when temperature increased from 600℃to 800℃, and nitrogen contents in solid product declined from 51.1% at 600℃to 13.1% at 800℃.