Combustion characteristics and thermal utilization of sewage sludge and coal mixtures

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Engineering, Department of Environmental Engineering, Turkey

Approval Date: 2013

Student: ONUR ATAK



Management of sewage sludge is generally one of the greatest problems that municipalities face due to its large quantities and different characteristics. Since dry sludge has a heating value close to a lignite coal, this energy can be recovered and used. The aim of this thesis is to investigate the beneficial use of sewage sludge by exploring its energy content. In this context, six Wastewater Treatment Plants (WWTPs) are chosen with different characteristics. Proximate and ultimate analysis, calorific value determination and thermogravimetric analysis (TGA) are carried out on the samples to determine the characteristics of sludges of these WWTPs. Then, co-combustion of these sludges with coal is investigated in a laboratory scale batch combustor. Sludge samples are added to coal at 3, 5, 10, 20, and 30% by wt. and combusted to see the effect of sludge addition on combustion efficiency and emissions. Elemental composition of ashes is also determined by X-Ray Fluorescence (XRF). In ash analysis of sludges alkali content was found in the range of 0.5-1.5% by wt. showing high slagging and fouling tendencies in the combustor if burned alone. Results of the experiments have shown that thermal characteristics of sludges depend on types and operating conditions of wastewater and sludge treatment processes. In combustion experiments as the sludge addition to fuel mixtures increased, carbon monoxide formation also increased and the efficiency of combustion is reduced. Lastly, kinetic analysis with TGA experiments show that sewage sludge decomposes according to multiple reaction models, however, the most dominant models are based on nucleation processes.