Nitrogen migration in sewage sludge chemical looping gasification using copper slag modified by NiO as an oxygen carrier

Abstract

In view of the high cost and failure of resource utilization of waste copper slag, the copper slag modified by NiO is used as an oxygen carrier in the chemical looping gasification, where the sewage sludge is converted into syngas through the oxidation of copper slag. Additionally, current studies on nitrogen migration in chemical looping are limited to the detection of nitrogen compounds in gas products, and there is little research on nitrogen migration from raw materials to solid-liquid-gas products. Therefore, under different oxygen equivalent coefficients (Ω), steam contents, reaction times, and cycle number, the nitrogen changes in gas (Gas-N), tar (Tar-N) and char (Char-N) were investigated in this paper. With increasing of Ω (0–0.78), the oxidation and catalytic cracking reactions of the NOx precursors, Char-N and Tar-N were promoted, and the yield of N2 increased from 52.49% to 91.98%. The addition of steam would lead to a significant increase in the yield of NOx precursors. The release of NH3 and HCN was mainly concentrated in the first 5 min. As the numbers of cycle increased, NH3-N and HCN-N both gradually decreased. Based on the above results, the distribution and migration mechanism of nitrogen species were also summarized.