Co-combustion technology can be a gateway to sewage sludge valorization and net CO2 reduction. In this study, combustion characteristics of sewage sludge, Australian black coal, shiitake substrate, and their blends were analyzed via thermogravimetric analysis (TGA) coupled with Fourier transform infrared spectroscopy. The ignition temperature, burnout temperature, flammability index (C), and combustion characteristics index (S) of the fuels and their respective blends were estimated. Kinetic parameters were also estimated using the Coats-Redfern method. The results showed that the oxidation of the blends had two distinct stages. Synergistic effects existed for all the blends, with negative ones occurring at temperatures between 300 and 500 °C and positive ones during the char oxidation period. In the first oxidation stage, both C and S indexes increased with sludge addition to the coal. However, they decreased with sludge addition in the final oxidation stage. The catalytic effect of the sludge and the shiitake was pronounced in the final oxidation stage and it resulted in a decrease of activation energy. As for the pollutant emissions, the results showed that NOx and SO2 emissions decreased for 25 wt.% sludge addition to the coal. For the sludge-shiitake blends, NOx and SO2 emissions decreased with increasing shiitake addition. The single-pellet combustion results showed that ignition delay time reduced with increasing sludge/coal ratio but increased with increasing sludge/shiitake ratio. The volatile combustion duration decreased with the addition of sludge and total combustion time decreased sharply with increasing sludge ratio.

No abstract

No abstract

Sewage sludge is a common form of municipal solid waste, and can be utilized as a renewable energy source. This study examines the effects of different key operational parameters on sewage sludge pyrolysis process for pyrolytic oil production using the Taguchi method. The digested sewage sludge was provided by the urban wastewater treatment plant of Tainan, Taiwan. The experimental results indicate that the maximum pyrolytic oil yield, 10.19% (18.4% on dry ash free (daf) basis) by weight achieved, is obtained under the operation conditions of 450 °C pyrolytic temperature, residence time of 60 min, 10 °C/min heating rate, and 700 mL/min nitrogen flow rate. According to the experimental results, the order of sensitivity of the parameters that affect the yield of sludge pyrolytic oil is the nitrogen flow rate, pyrolytic temperature, heating rate and residence time. The pyrolysis and oxidation reactions of sludge pyrolytic oil are also investigated using thermogravimetric analysis. The combustion performance parameters, such as the ignition temperature, burnout temperature, flammability index and combustion characteristics index are calculated and compared with those of heavy fuel oil. For the blend of sludge pyrolytic oil with heavy fuel oil, a synergistic effect occurs and the results show that sludge pyrolytic oil significantly enhances the ignition and combustion of heavy fuel oil.

No abstract

No abstract

Summary In this study, the thermochemical conversion process of a single wood pellet under low temperature (350°C‐650°C) isothermal heating is investigated to identify the outstanding low‐temperature ignition and combustion characteristics for heat generation, particularly during the preheating stages in the furnace. The thermal behavior of wood powder was analyzed using thermogravimetric/Fourier transform infrared spectroscopy. The suspended single pellet combustion phenomenon under a convective hot air stream was also explored. The results showed that the wood primarily decomposed in a range from 240°C to 520°C, and low‐temperature ignition was found at 293°C due to heterogeneous oxidation. For pellet combustion, an outstanding heterogeneous‐induced homogeneous combustion phenomenon occurred when the stream temperature was higher than 350°C. In contrast, the ignition mechanism shifted to volatile auto‐ignite mode at 650°C due to the interplay of fuel devolatilization and oxygen diffusion. The pellet temperature evolution was measured, and the results revealed a maximum heating rate of 6.61‐16.95 K/s under a stream temperature ranging from 350°C to 650°C. The weight loss evolution showed three stages during the entire heating process, and the average activation energy (13.12 kJ/mol) was obtained. Char combustion was found favorable to CO production for gaseous emissions, but the burning of volatiles tended to convert fuel into CO2. Finally, a simplified reaction scheme based on different onset temperatures, including pyrolysis, heterogeneous/homogeneous oxidation, and heterogeneous gasification was proposed to illustrate a potential thermochemical conversion route for further utilization.