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    Gasification of sewage sludge using a throated downdraft gasifier and uncertainty analysis
    (2002) Dogru M.; Midilli A.; Howarth C.R.
    The most important objectives to gasify sewage sludge are to produce a clean gas of acceptable composition for synthesis or combustion, and to convert this solid resource into combustible-clean gas at high efficiency. The experiments of the gasification were conducted using a 5 kWe-throated downdraft gasifier. It was concluded that sewage sludge can be gasified to produce low-quality combustible gas, and would be an acceptable alternative source to fossil fuels for the production of the clean energy. It is suggested that the downdraft gasifier should be operated at 3.69-3.71 kg/h ± 1.43% of the feed rate, at 2.28-2.34 N m3/kg ± 1.84% of the air fuel ratio, around 497.74-514 N m3/m2 h ± 1.50% of specific gasification rate and around 93.64-94.15% ± 1.92% of turndown ratio in order to achieve good quality gas and to avoid clinker formation at the throat of the gasifier because of high ash content of sludge. The thermal efficiency was calculated as between 39% and 40% at the optimum operation levels given above. © 2002 Elsevier Science B.V. All rights reserved.
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    Hydrogen production from sewage sludge via a fixed bed gasifier product gas
    (2002) Midilli A.; Dogru M.; Akay G.; Howarth C.R.
    The main objective pursued in this work is to investigate the hydrogen production potential from sewage sludge by applying downdraft gasification technique. An experimental study was conducted using a pilot scale (5 kWe) throated downdraft gasifier. During the experiments, all data were recorded with an analog to digital (ATD) converter linked to a computer for every 15 s. The flow rates of the wet product gas, the mass flow rate and volumetric percentage of hydrogen were determined and illustrated. The effects of temperatures of oxidation zone on the production of hydrogen were discussed, and the conversion ratios of dried sewage sludge to hydrogen and ash were also designated. It was concluded that substantial amount of hydrogen gas could be produced utilizing a renewable biomass source such as dried and undigested sewage sludge pellets by applying air blown downdraft gasification technique. The product gas obtained mainly consists of H2, N2, CO, CO2 and CH4 with a maximum average gross calorific value of 4 MJ/m3. Around 10-11%(V/V) of this product gas is hydrogen which could be utilized for fuel cells. Moreover, sewage sludge can be assumed as an alternative renewable energy source to the fossil fuels, and the environmental pollution originating from the disposal of sewage sludge can be partially reduced. © 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.