Reduction of zinc and iron in dust removal ash by H₂ generated from lignite pyrolysis

The article describes a process based on the hydrogen recovery of dust removal ash from lignite pyrolysis. The high volatile components in lignite will produce a large amount of H₂ during the pyrolysis process, which can replace part of C to reduce zinc and iron oxides in dust removal ash, thereby achieving the goal of reducing carbon consumption. Two methods were used to study the different pyrolysis behaviors of lignite, and it was found that the peak of H₂ release was reached at 700 °C. After 1000 °C, the pyrolysis of lignite basically ended, and the final pyrolysis gases were mainly H₂, CO, CO₂, CH₄, and a small amount of C_xH_y. In addition, the proportion of H₂ generated by the full pyrolysis of lignite at 1000 °C in H₂-H₂O is 84.4 %, and the proportion of CO in the CO-CO₂ system is 74 %, which can meet the reduction of zinc and iron oxides in dust removal ash. Based on the principle of minimum free energy and laboratory experiments, zinc oxide is completely reduced to zinc vapor above 906 °C, while the Fe obtained from iron oxide reduction increases with the increase of H₂/CO in the system above 810 °C, further confirming the feasibility of this process. The effects of temperature, lignite added amount and holding time on iron reduction and zinc volatilization during the reduction process of dust removal ash was investigated. The results indicate that due to the fast diffusion rate of H₂, the reaction rate is greatly increased, which can quickly increase the metallization rate of dust removal ash to over 95 % and the dezincification rate also increases from 19.60 % to about 98.76 % with the increase of carbon content under low temperature (1000 °C) and low carbon content (10 wt %) conditions.