煤化学链燃烧技术可有效实现CO2的捕集封存，对我国实现双碳目标具有重要意义。煤化学燃烧过程中产生的汞污染因其对人体的剧毒性以及对铝制CO2压缩设备的腐蚀性而亟需有效解决。为了推动煤化学链燃烧汞污染的有效治理，总结了气化介质、气化产物、载氧体和反应温度对煤化学链燃烧过程中汞释放、转化及迁移的影响及机理，并针对存在的问题提出发展建议。CO2不能直接将Hg0均相氧化，但会抑制HCl对载氧体脱汞的促进作用。H2O(g)不仅会通过促进煤中挥发分的析出、抑制孔结构的熔融以及提高煤燃烧效率来增强Hg的释放，还会与Hg反应生成Hg(OH)2继而分解成HgO和Hg0，并抑制HCl向Cl的转化而抑制Hg0向Hg2+的氧化。CO、H2和NH3等强还原性气化产物会通过消耗载氧体表面氧而抑制Hg0的氧化。H2S会与载氧体表面活性氧反应生成表面活性硫而促进载氧体对Hg0的脱除，但H2S浓度过高则会在载氧体表面生成对Hg0氧化并不活跃的环状硫或链状硫而抑制H2S的促进作用。HCl会增强载氧体的脱汞效果，其在低温段（80～280 ℃）的促进作用归因于HCl预吸附的Eley-Rideal机理，在中温段（280～580 ℃）的促进作用归因于Langmuir-Hinshelwood机理，在高温段（＞580 ℃）的促进作用主要归因于HCl对Hg0的均相氧化。载氧体对Hg0氧化的促进作用主要归因于载氧体表面活性氧对Hg0的直接氧化、载氧体将H2S氧化成活性S以及将HCl氧化成活性Cl和Cl2。燃料反应器温度升高会增强煤中Hg的释放，但也可通过促进Cl的生成和抑制CO的生成促进Hg0氧化。空气反应器温度升高，不仅有利于空气反应器中Hg0的氧化，还会通过增强煤的充分燃烧以及减弱焦炭对Hg的吸附作用而抑制Hg0从空气反应器出口逸出。鉴于H2O(g)含量对气化速率、Hg释放及Hg0氧化的影响，提出确定合适的H2O(g)含量以实现增强气化速率、减少Hg释放以及促进Hg0氧化协同效应。鉴于载氧体在实现氧高效传递和增强燃料反应器内Hg0氧化的协同效应，提出确定合适的载氧体以实现载氧体在氧传递和Hg0氧化的一体两用。鉴于燃料反应器温度对煤中Hg释放和Hg0氧化的影响，提出确定合适的燃料反应器温度以尽可能减少煤中Hg在燃料反应器内的释放以及增强Hg0的氧化，从而利于CO2富集提纯。鉴于空气反应器温度对Hg0氧化的影响，提出确定合适的燃料反应器温度以尽可能增强空气反应器中Hg0的氧化，从而减少Hg从空气反应器出口逸出。

Chemical looping combustion (CLC) of coal can effectively realize the capture and storage of CO2, which is of great significance for China to achieve the goal of carbon peaking and carbon neutral. Mercury (Hg) pollution during CLC of coal needs to be effectively solved because of its high toxicity to human and corrosion to aluminum CO2 compression equipment. In order to promote the effective treatment on Hg pollution from CLC, the effects and mechanisms of gasification medium, gasification products, oxygen carrier (OC), and reaction temperature on Hg release, conversion and migration during the process of CLC were summarized, and the development suggestions were proposed aiming at the problems. CO2 cannot directly oxidize Hg0 homogeneously, but it can inhibit the promoting effect of HCl on Hg removal by the OC. H2O vapor can not only enhances the release of Hg by promoting the precipitation of volatiles in coal, inhibiting the melting of pore structure, and improving coal combustion efficiency, but also reacts with Hg to generate Hg(OH)2 which is then decomposed into HgO and Hg0, and inhibits the conversion of HCl to Cl thereby inhibiting the oxidation of Hg0 to Hg2+. Strong reductive gasification products such as CO, H2 and NH3 inhibit the oxidation of Hg0 by consuming the surface oxygen of the OC. H2S will react with the surface active oxygen of the OC to form surface active sulfur and then promote the removal of Hg0 by the OC. However, the too much high concentration of H2S will lead to the formation of cyclic sulfur or chains sulfur on the surface of the OC that are not active in the oxidation of Hg0. HCl can enhance the performance of the OC on Hg removal. The promotion effect of HCl at low temperature (80-280 ℃) is attributed to the Eley-Rideal mechanism of HCl pre-adsorption, and the promotion effect at medium temperature (280-580 ℃) is ascribed to the Langmuir-Hinshelwood mechanism, and its promotion effect at high temperature (above 580 ℃) is mainly attributed to the homogeneous oxidation of Hg0 by HCl. The promotion of OC on Hg0 oxidation is mainly attributed to the direct oxidation of Hg0 to HgO by reactive oxygen species in the OC, the oxidation of H2S to reactive S, and the oxidation of HCl to reactive Cl and Cl2. The increase of temperature in fuel reactor enhances the release of Hg from coal, but also promotes Hg0 oxidation by promoting the production of Cl and inhibiting the production of CO. The increase of temperature in air reactor not only benefits to the oxidation of Hg0 in the air reactor, but also inhibits the release of Hg0 from the outlet of the air reactor by enhancing the full combustion of coal and weakening the adsorption of Hg by coke. Considering the influence of H2O vapor content on gasification rate, Hg release and Hg0 oxidation, it is proposed to determine the appropriate H2O vapor content to achieve the synergistic effect on enhancing gasification rate, reducing the release of Hg, and promoting Hg0 oxidation. Aiming at the synergistic effect of OC in achieving efficient oxygen transfer and enhancing Hg0 oxidation in fuel reactors, it is proposed to determine an appropriate OC to realize the "one-body dual-purpose" of OC in oxygen transfer and Hg0 oxidation. In view of the influence of fuel reactor temperature on Hg release and Hg0 oxidation in coal, it is proposed to determine the appropriate fuel reactor temperature to minimize the release of Hg in coal in the fuel reactor and enhance the oxidation of Hg0 thereby promoting the enrichment and purification of CO2. In view of the influence of air reactor temperature on Hg0 oxidation, it is proposed to determine the appropriate fuel reactor temperature to enhance the oxidation of Hg in the air reactor as much as possible, thereby reducing the release of Hg from the outlet of air reactor.

0 引言

1 iG-CLC反应原理及优势

2 气化介质的影响及机理

3 气化产物的影响及机理

4 载氧体的影响及机理

5 反应温度的影响及机理

6 结论

7 展望