Pyrolysis gasification of dried sewage sludge in a combined screw and rotary kiln gasifier

A pyrolysis gasifier, with carbonization and activation steps, was developed to convert dried sludge into activated char and gas fuel energy. To determine the optimal driving conditions, parametric investigations were conducted on the amount of steam input, pyrolysis gasifier temperature and moisture content in the dried sludge.The optimal conditions for the dried sludge were found to be a steam input of 10 mL/min, gasifier temperature of 820 °C and moisture content of 11% with a holding time in the pyrolysis gasifier of 1 h.The specific area of the activated char was 40.1 m2/g, with an average pore diameter and volume of 63.49 Å and 0.2354 cm3/g, respectively. The pyrolysis gases were H2 (34.1%), CO (18.6%), CH4 (8.5%) and CO2 (8%). The higher heating value for the pyrolysis gas was 10,107 kJ/N m3. To determine the tar adsorption characteristics, a benzene adsorption test was conducted using a fixed bed adsorption tower (H/D = 2, GHSV = 1175/h). The saturation point of the activated char was found after 45 min, and the amount of adsorption was 140 mg/g.Therefore, the pyrolysis gasification of sewage sludge can produce activated char which can be used to reduce tar, and gasification gas which can be utilized as a high enthalpy gas fuel.