Effect of Experimental Conditions on Gas Quality and Solids Produced by Sewage Sludge Cogasification. 1. Sewage Sludge Mixed with Coal

Abstract

Cogasification of sewage sludge mixed with coal showed that the amount of sewage sludge supplied to the gasifier, depending on its availability, could vary without affecting the gasifier performance; however, it had an influence on the syngas composition. The use of sewage sludge during coal gasification gave rise to an increasing gas yield and energy conversion, mainly because the gas produced had a greater hydrocarbon content. H2S, HCl, and especially NH3 were also found to increase, due to higher contents of nitrogen in the sewage sludge compared with coal. The rise of both the temperature and the air flow rate resulted in the production of more gas and a lowering of hydrocarbon, char, and tar contents. A decrease in NH3 content was also observed, as the increase of these parameters promoted the destruction of this compound. The rise in the equivalent ratio also led to lower contents of H2S and HCl, probably due to the partial oxidation of these compounds; however, the total amount of these elements released to the gas phase was not considerably affected. On the other hand, H2S formation was favored by the rise in temperature up to 850 °C, while the HCl concentration was not significantly affected. Heavy metals supplied with the fuel were mostly retained in solid residues, with Pb and Hg being the most volatile at 850 °C. However, the leachability of these metals was found to be below the analytical detection levels, and only small quantities of SO4 2- and Cl- were released.

Co‐gasification of woody biomass and sewage sludge in a fixed‐bed downdraft gasifier

“…[15][16][17] This is because the sewage sludge usually has high moisture and ash contents, and low heating value, hence the gasification of pure sewage sludge results in the low energy production efficiency. Pinto et al 18 found that the addition of sewage sludge during coal gasification increases the calorific value of the producer gas and fuel conversion. Moreover, they also studied cogasification of sewage sludge with biomass and it was found that the addition of biomass not only increases the production of syngas, but also minimizes the formation of undesirable gases usually generated from sludge gasification.…”

The kinetics of gasification of char derived from sewage sludge

“…Gasification of sewage sludge as well as co-gasification with coal as integrated processes involving primary and secondary reactions have been widely investigated during recent years [11][12][13][14][15][16][17][18]. However, the literature on the reaction of sewage sludge char with an oxidizing agent, which is considered as the most important step in the overall processes process, is very scarce, in contrast to the literature concerning the coal and biomass chars gasification reactions.…”

Gasification as a new thermal processes of sewage sludge utilization

“…Pinto et al [16,17] showed that activated carbon showed a significant role in tar cracking and H 2 production. When activated carbon was applied, the H 2 concentration (including N 2 ) in the producer gas considerably increased to 22 vol%, which was much higher compared to the 5 vol% H 2 concentration obtained without activated carbon.…”