Evaluation of Gasification Efficiency of Miscellaneous Industrial Sewage Sludges in a Down Draft Fluidized Bed Reactor

Limited information is available about energy efficiency evaluation of industrial sewage sludge gasification nowadays. The goal of this study is to determine the best proper feeding waste combination/combinations of miscellaneous industrial sewage sludges in a down draft fluidized bed pilot-scale gasification reactor to maximize energy recovery. Different industrial sewage sludge samples were taken from dewatering units of wastewater treatment plants of textile, dairy, vegetable and non-vegetable oil, glass and metal industries, located in Thrace Region of Turkey (Thrace Catchment of Area) and characterized in terms of three important indicator parameters (moisture, ash and heating value) for identifying the best feeding waste combination of the reactor which has high gasification efficiency. In addition, the same parameters were also analysed for the char and cyclone dust samples that occurred as a result of gasification process, and then, energy yields of all industrial sewage sludge combinations have been calculated. Results revealed that the majority of sludge samples, apart from metal and glass industries, were found suitable for gasification process in terms of both organic and inorganic contents either alone or in mixture form. The heating value and ash content of vegetable and non-vegetable oil industrial sewage sludge were measured approximately two times higher (average 11,622 kcal.kg −1 = 48 MJ.kg −1 for oil and average 5163 kcal.kg −1 = 21.6 MJ.kg −1 for dairy) and nearly in the same values (average 9.3% for oil and 9.5% for dairy) compared to dairy industrial sewage sludge, respectively. According to these results, four feeding sludge combinations were determined based on their ash content and heating values. It was found that Combination 1, which has high calorific value and low ash ratio, has the highest energy efficiency (97%), while the other combinations were found below this value. If the proper sludge combination can be identified for a draft fluidized bed gasification reactor, energy efficiency may be increased. Moreover, identifying the best feeding combination for sludge gasification reactor may be the best way to obtain both high energy recovery and low char/tar products and to also minimize industrial sewage sludge before being sent to landfill.