Ž . Fuel Processing Technology 75 2002 55–82 www.elsevier.comrlocaterfuproc Gasification of sewage sludge using a throated downdraft gasifier and uncertainty analysis Murat Dogru c , Adnan Midilli a,b,c, ) , Colin R. Howarth c a Mechanical Engineering Department, UniÕersity of Nigde, Nigde, Turkey b Visiting Research Fellow, UniÕersity of Newcastle, Newcastle upon Tyne, UK c Department of Chemical and Process Engineering, UniÕersity of Newcastle, NE1 7RU, UK Accepted 6 September 2001 Abstract 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 kgrh "1.43% of the feed rate, at 2.28–2.34 N m 3 rkg "1.84% of the air fuel ratio, around 497.74–514 N m 3 rm 2 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. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Gasification; Sewage sludge; Downdraft gasifier; Air fuel ratio; Specific gasification rate; Turndown ratio; HrC 1. Introduction Sewage sludge is a waste product from sewage treatment plant, and also contains wx significant amounts of heavy metals, organic toxins and pathogenic microorganism 1 , ) Corresponding author. Mechanical Engineering Department, University of Nigde, 51000 Nigde, Turkey. Tel.: q 90-462-3772960; fax: q 90-462-3255526. Ž . E-mail addresses: midilli@gmx.co.uk, midilli@nigde.edu.tr A. Midilli . 0378-3820r02r$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. Ž . PII: S0378-3820 01 00234-X