Abstract
The conversion of solid waste into energy through combustion is sustainable and economical. This study aims to comprehensively evaluate and quantify the co-combustion characteristics, synergistic catalysis, and gaseous pollutant emission patterns of sewage sludge (SS) and coal gasification fine slag residual carbon (RC) as well as their blends through thermogravimetry coupled with mass spectrometry (TG-MS). The results showed that the co-combustion of SS and RC can not only improve the ignition and burnout property but also maintain the combustion stability and comprehensive combustion performance at a better level. The kinetic analysis results showed that a first-order chemical reaction and three-dimensional diffusion are the reaction mechanisms during the co-combustion of SS and RC. The synergistic catalysis between SS and RC can well explain the changes in activation energy and reaction mechanism. Furthermore, the blending ratio of SS is recommended to be maintained at 40% because of the lowest activation energy (Ea = 81.6 kJ/mol) and the strongest synergistic effect (Xi = 0.36). The emission of gaseous pollutants is corresponding to the primary combustion stages of SS, RC, and their blends. In co-combustion, the NH3, HCN, NOx, and SO2 emissions gradually rise with the increase of SS proportion in the blends due to the high content of organic compounds in SS.
Highlights
Sewage sludge is the by-product of urban sewage treatment plants [1]
The blending ratio of sewage sludge (SS) is recommended to be maintained at 40% because of the lowest total activation energy (Ea = 81.6 kJ/mol) and the strongest synergistic catalysis (Xi = 10.36)
The first-order chemical reaction is the reaction mechanism for Stage 1 of the cocombustion of SS and residual carbon (RC), while the most effective mechanisms for Stage 2 are changed from first-order chemical reactions to three-dimensional diffusion with the increase of the SS proportion in blends
Summary
Sewage sludge is the by-product of urban sewage treatment plants [1]. In China, about 30 million tons of sewage sludge (80% moisture content) is produced every year, and this is still growing [2]. Sewage sludge is considered to be a kind of solid waste, which contains numerous pollutants, such as bacteria, viruses, dioxins, and heavy metals. The co-combustion of sludge and other solid fuels is a feasible solution that can effectively improve the combustion performance [8]. Zhao et al [9] investigated the co-combustion characteristics of low-rank coal semicoke and oil sludge by the TG-FTIR method. They found that the blending of oil sludge on low-rank coal semicoke could effectively improve the ignition, burnout, and comprehensive combustion performance of blends
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