Enriched-air fluidized bed gasification using bench and pilot scale reactors of dairy manure with sand bedding based on response surface methods

Enriched-air gasification was performed in fluidized bed reactors using the processed dairy manure which was mixed with sand bedding. The effects of temperature, modified equivalence ratio (ER_m), and oxygen concentration on the gas products were investigated based on the statistical models using a bench-scale reactor in order to obtain empirical correlations. Then, the empirical equations were applied to compare the produced gases from a pilot-scale fluidized bed gasifier. The empirical and actual H₂ and CH₄ compositions were within a 10% error, while the sum of produced CO and CO₂ gases showed similar composition within 3% error. The most influential factors for the syngas heating value were temperature followed by the oxygen concentration and ER (equivalence ratio). The composition of H₂ (2.1-11.5%) and CO (5.9-20.3%) rose with an increase in temperature and oxygen concentration. The variation of CO₂ (16.8-31.6%) was mainly affected by the degree of oxygen concentration in the gasifying agent. The ranges of the LHV (lower heating value), carbon conversion efficiency and cold gas efficiency were discussed. An economic review showed favorable indications for on-site dairy manure gasification process for electric power based on the depreciable payback period and the power production costs.