Thermodynamic Equilibrium Analysis on Limitation of Moisture and Ash for Optimal Air Gasification of Municipal Solid Waste

"Two-step oxidation" technology is a trend of municipal solid waste (MSW) thermal disposal technology because of its low emissions and efficient energy recovery. Gasification is the most important step in the process. Raw waste pretreatment is necessary to achieve optimal gasification of MSW. Limitation of moisture and ash for optimal air gasification of Chinese MSW has been simulated using the carbon boundary gasification method. Waste properties should be: moisture 15.5-27.8 %, ash 10-30 %, lower heating value 10.1-17.3 MJ/kg. Corresponding operating parameters are: equivalence ratio 0.20-0.26, and gasification temperature 600-650 degrees C. Besides, moisture limitation in the waste is much stricter for optimal gasification than that of ash. Higher (C + H)/O combustible waste permits a higher moisture and ash content for optimal gasification. The effect of air preheating on controlling moisture and ash for optimal gasification is small. However, the gasification performance is greatly improved. The simulated results were in good agreement with the experimental ones. Additional heat for pretreatment of raw MSW was also estimated. The study results provide references parameters for developing the two-step oxidation technology of MSW in China.