Co-Gasification of Gypsum and Municipal Solid Waste Components in CO₂ Atmosphere

In the United States, only 12% of the 284 million tons of municipal solid waste (MSW) generated per annum is currently processed for energy recovery. The limitations to processing more MSW for energy recovery include concern of pollutants emission from the current facilities, high investment cost, low product and economic value and thus economic competition with landfilling. The landfilling is not sustainable so that a permanent solution is urgently required. In this paper, we examine the synergistic potential of incorporating gypsum wastes from construction and demolition sector into the CO₂ assisted gasification of municipal solid waste. The effect of varying proportions of gypsum during the co-gasification of gypsum with MSW mixture and individual components (wood and polyethylene terephthalate (PET)) using CO₂ as the gasification agent was investigated. The results showed that an increase in gypsum proportion in MSW affected the syngas yield. The yield was reduced by 35% when gypsum was added at equal mass proportions (1:1) to MSW. Adding gypsum to wood increased the cumulative yield of syngas by 7%, and the optimum syngas yield was achieved at a 5:1 ratio of wood to gypsum. The yield of syngas also reduced with an increase of gypsum addition to PET. However, the syngas quality was improved with gypsum addition as the yields of hydrocarbon were reduced. Gypsum increased the syngas yield by 25% more for wood than that of MSW and 60% more than PET. This suggests that the feedstock components with a charring tendency to have greater yields of syngas with gypsum addition. This is attributed to gypsum reaction with char intermediates in a solid-solid reaction along with the reaction of CO₂ + C = CO to produce CO that has a significant impact on the syngas yield compared to the oxidation of volatiles by gypsum.