Shuanghui Deng

Investigation on the fast co-pyrolysis of sewage sludge with biomass and the combustion reactivity of residual char

Gaining the valuable fuels from sewage sludge is a promising method. In this work, the fast pyrolysis characteristics of sewage sludge (SS), wheat straw (WS) and their mixtures in different proportions were carried out in a drop-tube reactor. The combustion reactivity of the residual char obtained was investigated in a thermogravimetric analyzer (TGA). Results indicate that SS and WS at different pyrolysis temperatures yielded different characteristic gas compositions and product distributions. The co-pyrolysis of SS with WS showed that there existed a synergistic effect in terms of higher gas and bio-oil yields and lower char yield, especially at the WS adding percentage of 80wt%. The addition of WS to SS increased the carbon content in the SS char and improved char porous structures, resulting in an improvement in the combustion reactivity of the SS char. The research results can be used to promote co-utilization of sewage sludge and biomass.

A Mechanism Study on the Decomposition of Sulfate in Zhundong Coal with High Sulfur Content in Coal Ash

Sulfate in Zhundong (ZD) coal combustion plays a significant role in fouling, slagging, and particle emissions. This study aimed to investigate the effect of SiO2 and kaolin addition on sulfate transformation in ZD coal ash by using thermogravimetric analysis (TGA) and other characterizing methods for ash with SiO2 and kaolin addition under different temperatures. Results showed that SiO2 and kaolin both enhanced the decomposition of sulfates in ZD coal ash under higher temperatures. The decomposition of sulfates in pure ZD coal ash started above 1050 °C, while the starting temperature was ahead by 50 and 100 °C, when SiO2 and kaolin were added, respectively. Kaolin addition was more efficient to improve the thermal decomposition of sulfates than SiO2 addition. However, the enhanced effect of SiO2 and kaolin was very weak below 815 °C. The thermal calculation results also gave the similar result on the enhancement effect on sulfate decomposition of SiO2 and kaolin addition.

A kinetic study on the catalysis of KCl, K2SO4, and K2CO3 during oxy-biomass combustion

Biomass combustion under the oxy-fuel conditions (Oxy-biomass combustion) is one of the approaches achieving negative CO2 emissions. KCl, K2CO3 and K2SO4, as the major potassium species in biomass ash, can catalytically affect biomass combustion. In this paper, the catalysis of the representative potassium salts on oxy-biomass combustion was studied using a thermogravimetric analyzer (TGA). Effects of potassium salt types (KCl, K2CO3 and K2SO4), loading concentrations (0, 1, 3, 5, 8 wt%), replacing N2 by CO2, and O2 concentrations (5, 20, 30 vol%) on the catalysis degree were discussed. The comparison between TG-DTG curves of biomass combustion before and after water washing in both the 20%O2/80%N2 and 20%O2/80%CO2 atmospheres indicates that the water-soluble minerals in biomass play a role in promoting the devolatilization and accelerating the char-oxidation; and the replacement of N2 by CO2 inhibits the devolatilization and char-oxidation processes during oxy-biomass combustion. In the devolatilization stage, the catalysis degree of potassium monotonously increases with the increase of potassium salt loaded concentration. The catalysis degree order of the studied potassium salts is K2CO3 > KCl > K2SO4. In the char-oxidation stage, with the increase of loading concentration the three kinds of potassium salts present inconsistent change tendencies of the catalysis degree. In the studied loading concentrations from 0 to 8 wt%, there is an optimal loading concentration for KCl and K2CO3, at 3 and 5 wt%, respectively; while for K2SO4, the catalysis degree on char-oxidation monotonically increases with the loading potassium concentration. For most studied conditions, regardless of the potassium salt types or the loading concentrations or the combustion stages, the catalysis degree in the O2/CO2 atmosphere is stronger than that in the O2/N2 atmosphere. The catalysis degree is also affected by the O2 concentrations, and the lowest catalysis degree is generally around 20 vol% O2 concentration. The kinetic parameters under the different studied conditions are finally obtained.