title: Ultra high temperature gasification of municipal wastewater primary biosolids in a rotary kiln reactor for the production of synthesis gas.
abstract: Primary Fine-Sieved Solids (PFSS) are produced from wastewater by the use of micro-sieves, in place of primary clarification. Biosolids is considered as a nuisance product, however, it contains significant amounts of energy, which can be utilized by biological (anaerobic digestion) or thermal (combustion or gasification) processes. In the present study, an semi-industrial scale UHT rotary kiln gasifier, operating with electric energy, was employed for the gasification of PFSS (at 17% moisture content), collected from a municipal wastewater treatment plant. Two gasification temperatures (950 and 1050 °C) had been tested, with minimal differences, with respect to syngas yield. The system appears to reach steady state after about 30-40 min from start up. The composition of the syngas at near steady state was measured approximately as 62.4% H2, 30.0% CO, 2.4% CH4and 3.4% CO2, plus 1.8% unidentified gases. The potential for electric energy production from the syngas produced is theoretically greater than the electric energy required for gasification. Theoretically, approximately 3.8 MJ/kg PFSS of net electric energy may be produced. However, based on the measured electric energy consumption, and assuming that all the syngas produced is used for electric energy production, addition of excess electric energy (about 0.43 MJ/kg PFSS) is required to break even. The latter is probably due to heat losses to the environment, during the heating process. With the improvement of energy efficiency, the process can be self sustained, form the energy point of view.
authors.affiliation: School of Environmental Engineering, Technical University of Crete, Chania 73100, Greece. Electronic address: petros.gikas@enveng.tuc.gr.
authors.forename: Petros
authors.initials: P
authors.lastname: Gikas
mesh_terms: D004560:Electricity; D005740:Gases; D006358:Hot Temperature; D013696:Temperature; D062065:Wastewater; D018508:Water Purification
chemical_list: D005740:Gases; D062065:Wastewater
keywords: Biosolids; Gasification; Municipal sludge; Primary fine-sieved solids; Syngas; Waste to energy