Gasification of Coal and Dairy Manure With Air-Steam as Oxidizing Agent

The animal waste from feedlots (called feedlot biomass, FB) and dairy farms (called dairy biomass, DB) can contribute to surface or ground water contamination and air pollution problems with the release of greenhouse gases (CH₄). In the present study, the feasibility of onsite gasification of DB with an air-steam mixture for production of H₂ rich syngas (a mixture of H₂ and CO) is considered. The composition of gases produced by DB is predicted using a) mass conservation and b) chemical equilibrium for adiabatic systems where heat produced by partial oxidation is used to strip H₂ from steam. Coal is used as standard fuel for comparison of gasification performance of DB with coal. A model is developed to estimate the ideal production of CH₄, H₂, CO, CO₂, N₂ and H₂S, and other compounds are assumed to be in trace amounts. The parameters investigated are equivalence ratio (1 to 10), air-steam ratio (0.1 to 1), and reaction temperature (600–1500 K). With the predicted composition of gases, the HHV of gas mixtures and the energy conversion efficiency are estimated. The predicted results show that higher ERs yield to elevated concentrations of CO and CH₄, high HHV mixtures and energy conversion efficiency, and low percentages of H₂ and CO₂. On the other hand, lower air-steam ratios produce more H₂, CO₂, and CH₄ but less CO under equilibrium or mass conservation methods. The results suggest that it is possible to obtain concentrations of H₂ from 0 to 50%, CO from 0 to 45%, and CH₄ from 0 to 45% approximately. The current results provide operational parameters for a gasifier fired with DB and a mixture of air and steam as oxidizers. Experiments are currently in progress to determine the actual composition of gases released from gasifier.