Experimental Study on Fixed-Bed Pyrolysis of Municipal Solid Waste

To investigate the gas product evolution characteristics and heating value variation of typical municipal solid wastes during fixed-bed pyrolysis, this study selected waste tires and municipal sewage sludge as research objects. Pyrolysis experiments were conducted in an externally heated fixed-bed reactor under nitrogen atmosphere. The composition, distribution characteristics of gas products, and their heating value variations with pyrolysis temperature were systematically examined for both materials, followed by a comparative analysis of their pyrolysis product properties. The results showed that the pyrolysis gas from waste tires was mainly composed of CH 4 , H 2 , and CnHm, accounting for more than 70% of the total gas, with CH 4 reaching up to 47%, H 2 up to 22%, and CnHm up to 15%. Each gas component began to evolve noticeably at approximately 400°C, and the CnHm content reached its peak around 530°C before declining due to intensified secondary cracking reactions. The heating value of tire pyrolysis gas increased significantly with the rising final temperature, reaching approximately 6800 kcal/m 3 at 650°C, which is comparable to that of natural gas. For municipal sewage sludge, the pyrolysis gas was mainly composed of CO 2 , CH 4 , and H 2 . At final temperatures ≤500°C, CO 2 accounted for the highest proportion, while CH 4 became dominant above 500°C. The onset temperature for significant gas evolution was about 480°C, approximately 80°C higher than that of waste tires. The heating value of sludge pyrolysis gas approached 3000 kcal/m 3 at 600°C, which was only about 40%–50% of that from waste tires. The differences in pyrolysis gas characteristics between the two materials originated from their intrinsic compositional distinctions: waste tires are rich in carbon and hydrogen with low ash and oxygen contents, favoring the generation of high-quality fuel gas, while sludge possesses high ash and oxygen contents, resulting in higher CO 2 proportion and lower heating value in its pyrolysis gas. This study provides fundamental experimental data for the graded pyrolysis treatment and differentiated energy utilization of municipal solid wastes.