Effect of Thermal Conditioning on Combustion and Pollutant Emissions Characteristics of Sewage Sludge

Abstract

Thermal conditioning (TC) can improve sludge mechanical dewaterability and drying performance, and produce solid fuel from sewage sludge with low-cost and harmlessness. This study investigates the influence of the TC on sludge combustion with thermogravemetric analysis of sewage sludge with/without TC. The experiments were carried out at a 150 mL/min air ambient with a heating rate of 10, 20, 30, 40, 50 °C/min. Tow integration approximation methods (Coats-Redfern and Flynn,-Wall-Ozawa) and a differential method (Kissinger method) were applied to study the kinetics. The Coats-Redfern method requires assuming the reaction’s kinetic mechanism. The calculated activation energy was lower than that from the Flynn-Wall-Ozawa and Kissinger, which were very close to each other. Among these methods, the Flynn-Wall-Ozawa can predict the energy required at every combustion stage, which therefore would be the best one to explore the combustion mechanism. The results show that the organic matters within sewage sludge are much more homogeneous after TC. The combustion of the thermal conditioning sludge (TCS) is much more stable with a 10% reduction in burnout time and a 9.94% reduction in combustion temperature range. The ignition temperature of the raw sludge keeps increasing from 188 to 224 °C with the heating rate, while that of the TCS is almost constant at 222-240 °C. The TC can improve the activation energy, which is about 144.52 and123.00 kJ/mol for the raw sludge (RS) and TCS. Considering the gaseous pollutant emissions, the TC can dramatically reduce NO emissions, which is decreased from 14.22 to 6.59 mg/g by the TC, representing a reduction of 50.7%. Therefore, the TC can promote the hydrolysis of macromolecular organics, which would improve the sludge combustion performance, and reduce the gaseous pollutant emissions from combustion.

Clean solid biofuel production from high moisture content waste biomass employing hydrothermal treatment

“…The combustion rate was largely improved, representing about 2-3 times higher than the untreated one. For the T i and combustion rate, similar results was observed in our study concentrating on the combustion characteristics of the hydrothermally treated sewage sludge at 200 °C for 30 min [255]. However, the results for the T m presents a little different, which relates to the heating rate of TGA.…”