Hydrogen production from sewage sludge via updraft gasification process in a bench - scale fixed bed reactor

Abstract

Sewage sludge, the solid waste produced from the municipal wastewater treatment plant has created environmental problem due to continuous increasing number o f sewage sludge production. Thus, finding solutions for sewage sludge treatment and discharge are essential, to address the issues. Nowadays, the utilization o f sewage sludge as solid fuel for energy recovery is one o f the convenient solutions to improve waste management system whilst the gasification is one o f the preferable thermochemical conversion process to convert the sewage sludge to higher yield o f combustible light gases due to its simple and efficient process. Therefore, this study focuses on the conversion o f sewage sludge into energy via updraft gasification process and to investigate the performance o f the fixed bed gasifier (L = 1.549 m, D = 0.114 m) for maximum production o f hydrogen and total syngas yield (H2, CH4, CO, CO2 and N2). The reactor temperature was ranged between 600 to 900°C with equivalence ratio (ER) o f 0.10 to 0.20, with different gasifying agents i.e. air and steam. The produced syngas at different operating conditions was collected using gas sample bag and analysed using residual gas analyzer to identify the syngas yield. Results showed that the maximum hydrogen yield o f 3.18 % was obtained at 800°C with ER o f 0.20 while optimum total syngas yield was obtained at 63.43 % for 800°C and ER o f 0.15. For comparison, the steam gasification was also was carried out and it was found that 4.40 % and 70.40 % was observed for maximum hydrogen yield and optimum total syngas yield, respectively. Further, the effect o f gasifying agent on total syngas yield was found to be higher for air gasification at reactor temperature o f 600 and 700°C while at 800 and 900°C, the total syngas yield was found to be higher for steam gasification. It can be said that steam gasification gives more H2 yield (> 2.4 %) than air gasification. In conclusion, energy recovery from sewage sludge can be utilized by using gasification process, and thus, minimizing the environmental pollution. In addition, the produced syngas from these processes has a potential to be used for heat and power generation application.