Simultaneous Removal Of Hg⁰ And H₂S From Simulated Coal Gas Over Iron-based Sorbents

Coal gasification is the main approach of clean and efficient utilization coal, which is widely used as the clean coal technology. Pollutants of H2S and Hg in raw gas must be removed, because these pollutants are harmful on the environment, human health, facility and catalyst in the process of coal gases uses. Therefore, it has been paid highly attention to find the excellent sorbents for removing simultaneously Hg and H2S.Iron-based sorbents have been known to exhibit rich sulfur capacity and produce elemental sulfur. Sulfided iron-based sorbents, which resemble the sorbents impregnated by sulfur, should have the potential removal Hg capacity. And the fresh iron oxide based sorbents should also have the potential capacity of simultaneous removal Hg and H2S. Therefore, TG-A and TG-B iron based sorbents were chosed as the experiment materials. The evaluation experiments of sulfided sorbents TG-A-H2S and TG-B-H2S for Hg removal and the fresh sorbents TG-A and TG-B for Hg and H2S simultaneous removal were carried out using a fixed packed bed reactor. Based on the experimental results and the characterization of XRD, XPS and BET techniques, the following conclusions can be drawn:1) In N2 atmosphere, both TG-A-H2S and TG-B-H2S sorbent show much higher Hg removal efficiency than TG-A and TG-B sorbent. The preferable temperature range of Hg removal for TG-A-H2S sorbent is 100-120℃.The temperature range of 120-160℃is preferable for the Hg removal with TG-B-H2S sorbent. CO and H2 in inlet gas have the negligible effect on the efficiency of Hg removal. H2S is favorable for the removal of mercury.2) In N2 atmosphere, TG-A-H2S sorbent has much higher Hg removal efficiency than TG-B-H2S sorbent. The possible reason is that the elemental sulfur contents of TG-A-H2S sorbent are much higher than that of TG-B-H2S sorbent. Sulfur can react with elemental mercury to form stable mercury sulfide and the elemental sulfur in sorbent plays important role in the removal of mercury. 3) In the simulated coal gas, the temperature range of 100-140℃is preferable for the Hg removal with TG-A sorbent. TG-A sorbent can remove 85% of Hg and nearly all of H2S and the maintenance time is at least 10 hours at 140℃. TG-A sorbent can be used to remove simultaneously H2S and Hg in the typical coal gas atmosphere. CO and H2 in inlet gas also have the negligible effect on the efficiency of Hg removal in this ambient gases.4) In the simulated coal gas, TG-A sorbent has much higher Hg and H2S removal efficiency than TG-B sorbent. The possible reason is that the high Fe2O3 content in TG-A sorbent and the much elemental sulfur produced during desulfurization present the dominant role.5) H2S can react with Fe2O3 in the iron-based sorbents to form Fe2S3 and H2O or FeS, S and H2O. The elemental sulfur produced can react with elemental mercury to form stable mercury sulfide. So, H2S in gases can promote the removal of mercury.