Supercritical Water Gasification Experiments on Sewage Sludge
Gasification in water above its critical point, namely supercritical water gasification (SCWG), was investigated experimentally by using primary sewage sludge as a feedstock. The study focused on the intrinsic SCWG reaction for analyzing its behaviors. To avoid the catalytic effect caused by the wall of metal reactors, the SCWG experiments were carried out in 1 mm internal diameter quartz batch reactors. They are chemically inert and capable of withstanding the extreme reaction conditions. This paper presents the experimental results obtained from various reaction conditions where reaction temperature and time were varied in the range of 600 – 800 ºC and 10 – 180 seconds, respectively. Gases produced from the gasification reaction mainly consisted of hydrogen, methane, carbon monoxide, carbon dioxide and ethane with acetylene and ethylene being minor products. Ammonia and hydrogen sulfide were below detectable levels in all gas samples obtained. At 600 ºC, the ethane yield was high, reaching approximately 30 – 40 vol% in the product gas. At higher temperature, hydrogen, carbon monoxide and carbon dioxide concentrations were found to increase whereas methane and ethane yields decreased. No acetylene and ethylene were detected at 800 ºC. The experimental results revealed that increasing reaction temperature makes higher hydrogen production in the product gas, reducing the yield of hydrocarbons.