Pyrolysis and Gasification of Municipal Solid Waste

Pyrolysis and gasification of Municipal Solid Waste (MSW)

Sireesha Aluri¹, Pradeep K. Agrawal¹, John D. Muzzy¹, Carsten Sievers¹, Derrick W. Flick², and John P. Henley³

¹School of Chemical & Biomolecular Engineering, Georgia Institute of technology, Atlanta, Georgia 30332; ²The Dow Chemical Company, Freeport, Texas, 77541; ³The Dow Chemical Company, Midland, Michigan

The biggest challenge in processing Municipal Solid Waste (MSW) is its variability. A part of MSW is recycled and/or used in heat recovery, and the rest is either discarded in landfills or incinerated. The discarded portion further undergoes pre-processing techniques to form Refuse Derived Fuel (RDF). Our goal is to utilize this RDF to produce syngas via pyrolysis and gasification. Different individual components were analyzed to determine the differences and similarities between each. Paper (Tissue paper, paperboard), plastics (LDPE, PET), food waste (orange peels, dog food), wood (pine), textile (cotton, PET) and rubber (SBR) fractions were selected to mimic the actual RDF produced.

Experiments with each of the individual components and the model MSW were carried out in a Thermogravimetric Analyzer (TGA) separately to understand if the effect of mixing the components is additive, inhibitive or synergistic. Pyrolysis studies were carried out at temperatures between 30 – 1000 °C and at atmospheric pressure with a heating rate of 20 K/min. Gasification studies were conducted after the pyrolysis step, at 800 °C and with CO₂ as the gasifying medium.

Individual components had char content from 10 – 32% (except for LDPE ~0%). DSC studies showed endothermic behavior for all components except food waste and rubber. Model MSW pyrolysis showed an additive behavior which was verified by comparing the weight loss curve with the addition of individual curves, which had a reproducibility of 98% or more. Gas analysis showed that major gas components released were CO and CO₂ below 550 °C and H₂ and CH₄ between 550 and 900 °C. Gasification results showed that there is a synergistic effect observed in the gasification of MSW, which could be attributed to the inorganic content distribution during the process. ‘K' present in orange peel is mobile at higher temperatures and aids in the gasification of entire MSW sample rather than just the orange peel. This theory was verified by comparison with individual curve addition.