Gasification of Pig Manure with Ultra-Superheated Mixture of Steam and Carbon Dioxide

Experimental studies of steam and CO2-assited allothermal gasification of the original wet (moisture α=70%) and partly dried pig manure (PM) with α=45% and 15% are conducted on a laboratory-scale flow-through gasifier equipped with cyclones to capture fly ash particles. The high-temperature (~2000 °C) gasifying agent (GA) is generated by a pulsed-detonation gun operating on the stoichiometric natural gas (NG) – oxygen mixture. The dry off-gas obtained from the original wet PM typically contains 33–41 vol.% CO2, 34–40 vol.% CO, 17–22 vol.% H2, 2.5–4.0 vol.% CH4, and 0–2.5 vol.% CxHy with propane being the highest registered (less than 0.1%) hydrocarbon in CxHy, i.e., there is no tar as a gasification by-product. The reduction of feedstock moisture allows for reducing the yield of CO2 to 25% and increasing the yields of CO, H2, and CH4 to 45%, 25% and 5%, respectively. The size of solid residue particles taken from the cyclones ranges from 0.5 to 12 μm. The mass of solid residue is somewhat larger than the ash content in the dry PM due to the premature escape of partly gasified PM particles from the flow reactor. The results of experiments in terms of the off-gas temperature and composition agree satisfactorily with the results of thermodynamic calculations if one takes heat losses into account. In the existing version of the laboratory-scale setup, only about 33% of the thermal energy of the high-temperature GA is utilized for PM gasification, while the rest 67% is transferred to the coolant and environment. At these conditions, gasification of 1 kg of dry PM with the use of 1 kg of stoichiometric NG-oxygen mixture results in the production of 1.91 kg of combustible off-gas diluted with 25 vol.% CO2. To improve the energy efficiency of the gasification process, it is recommended to apply proper thermal insulation and heat recovery. To increase the yield of combustible gas, it is recommended to use the continuous supply of feedstock from a feeder and to improve mixing of PM and GA. To increase the carbon conversion efficiency, special measures must be taken to prevent premature entrainment of PM particles.