Structure–Reactivity Correlations in Pyrolysis and Gasification of Sewage Sludge Derived Hydrochar: Effect of Hydrothermal Carbonization

Abstract

Hydrothermal carbonization (HTC) has emerged as a promising way to improve the fuel quality of low-grade energy resource such as sewage sludge (SS) with substantial merits. Thus, it is important to establish the correlations between HTC treatment and subsequent pyrolysis/gasification of SS-derived hydrochars prepared at various HTC temperatures and HTC durations. The results showed that HTC treatment upgraded the fuel quality of SS and led to the evolution of aromatic structures. Such upgrading made SS-derived hydrochars toward the region of lignite in the Van Krevelen diagram. Thermogravimetric analysis indicated that both pyrolysis and gasification reactivity had a generally negative correlation with HTC temperature. Regarding the role of HTC duration, the opposite trend was observed between pyrolysis and gasification reactivities. In general, not only the fuel properties but also the pyrolysis and gasification reactivity were dependent on HTC temperature more significantly than on HTC duration. These findings can provide an insight into thermochemical utilization of SS-derived hydrochars.

Pyrolysis of Municipal Sewage Sludge for Biofuel Production: A Review

“…3,11,24,54,57−59 In addition to reducing the toxic compounds, eliminating the pathogens contained in sewage sludge, and decreasing the carbonaceous residue volume, this process can also produce energy and chemicals. 5,58 This process has suitable economic and environmental benefits and provides a high yield and quality of the desired products when process conditions are optimized. 46 The main sewage sludge pyrolysis products are syngas (including CO, H 2 , CO 2 , CH 4 (and other hydrocarbons) and condensable compounds), bio-oil, and carbonaceous residue (char).…”

“…3,5−9 In China, a production of 5.0 million tons was reported in 2004, 8 and 8.0 million tons was produced in 2010 8 with 3.71 million tons of dry matter, 10 at an annual increase of 13% between 2007 and 2013 with 6.25 million tons of dry sludge produced in 2013, 9 while 35 million tons was generated in 2014; 11 moreover, more than 26 million tons on a dry basis was produced in 2015, 12 and 40.83 million tons was generated in 2016. 5 A recent study also pointed out that the production of municipal sewage sludge will reach approximately 80.0 million tons in 2020. 6 The water in the produced municipal sewage sludge in China was reported to total approximately 80% in 2014, 11 while Gong et al 6 mentioned that this value was higher than 90% in 2019.…”

“…It can convert approximately 30−60% of the sewage sludge organic compounds into biogas but requires a long residence time that can last from 10 to 30 days. 5 The obtained biogas can be used for many purposes, such as electricity and heat generation and natural gas and transportation fuel after upgrading. Even though this process is a sustainable technology for sewage sludge management, 25,26 the process performance is low, and the management of reaction parameters with the aim of reducing emissions and improving the quality and yield of biogas generally requires additional energy input.…”

“…Its examination is the aim of this review paper. Municipal sewage sludge is produced by wastewater treatment plants after specific biological or chemical processes. , Its annual production is experiencing a remarkable growth worldwide as well as in China because of population growth, rapid urbanization, and economic development. ,− …”

“…Although landfills, composting, and simple incineration are the common traditional methods used to dispose of sewage sludge, they are becoming very problematic and more costly considering current environmental regulations and the high moisture content and low heating value of the feedstock. ,, Anaerobic digestion has also attracted increasing attention in sewage sludge disposal. It can convert approximately 30–60% of the sewage sludge organic compounds into biogas but requires a long residence time that can last from 10 to 30 days . The obtained biogas can be used for many purposes, such as electricity and heat generation and natural gas and transportation fuel after upgrading.…”