Carbon consumption of activated coke in the thermal regeneration process for flue gas desulfurization and denitrification

Abstract

In the process of flue gas purification with activated coke, sulfuric acid and sulfate are deposited on the activated coke surface; therefore, thermal regeneration is needed to recover the activated coke activity, which leads to carbon consumption. In this work, various regeneration parameters, including temperature, time and atmosphere, were investigated to optimize carbon consumption. The experimental results showed that the desulfurization capacity of the activated coke was clearly improved after thermal regeneration, while the denitrification capacity demonstrated no obvious or regular changes. Based on dozens of groups of regeneration experiments, it was found that the chemical carbon consumption per mol SO2 recovery ranged from 0.5 to 2.0 mol, which was higher than the theoretical value of 0.5 mol. The proportion of CO2 in chemical carbon consumption ranged from 60%–80% with an average value of 70%, and the rest was CO. According to the results from temperature-programmed desorption (TPD), CO and CO2 consumption was mainly derived from the decomposition of carboxyl and anhydride groups, with a small contribution from the reduction reaction of sulfuric acid with carbon. CO and CO2 consumption occupied only 10%–18% of the total carbon-containing functional groups, so the reaction activity was retained after thermal regeneration. The carbon consumption in an NH3/N2 atmosphere was smaller than that in a N2 atmosphere, which was about half of that in a H2O/N2 atmosphere due to the inhibition of carboxyl group decomposition, based on the results from TPD and in situ diffuse reflectance infrared Fourier transform (In situ DRIFT). Analysis of the thermal regeneration process in four iron and steel factories revealed that the chemical carbon consumption of activated coke accounted for approximately 20%–40% of the total carbon consumption, which was smaller than the contribution from physical carbon abrasion.