Sustainable Swine Manure Valorization: Gasification with High-Temperature Steam and CO2 Blend

Abstract

Experimental studies of sustainable, steam/CO₂-assisted allothermal gasification were conducted on raw wet swine manure (SM, 70% moisture) and partially dried SM (45% and 15% moisture). Tests were performed using a laboratory-scale flow-through gasifier equipped with cyclones for fly ash recovery. A pulsed detonation gun (PDG) fueled by a stoichiometric natural gas (NG)–oxygen mixture generated the high-temperature (~2000 K) gasifying agent (GA). The dry off-gas from the raw SM typically comprised 33–41 vol.% CO₂, 34–40 vol.% CO, 17–22 vol.% H₂, 2.5–6.0 vol.% CH₄, and 0–2.5 vol.% C_xH_y (with propane as the peak hydrocarbon below 0.1 vol.%), confirming tar-free gasification. Reducing SM moisture lowered the CO₂ yield to 26 vol.% while increasing CO, H₂, and CH₄ yields to 45, 25, and 5 vol.%, respectively. Measured off-gas temperatures and compositions closely matched thermodynamic calculations when accounting for heat losses. In the current laboratory setup, only 33% of the GA thermal energy is utilized for SM gasification, with 67% lost to the coolant and ambient environment. Under these conditions, gasifying 1 kg of dry SM using 1 kg of the stoichiometric NG–oxygen mixture yields 1.91 kg of combustible off-gas diluted with 26 vol.% CO₂. To achieve a self-sustaining process, a portion of this combustible off-gas can replace NG in the PDG. This approach was experimentally validated through off-gas detonability tests, where the stoichiometric off-gas–oxygen mixture achieved a detonation velocity of approximately 1800 m/s.