机械化学法改性飞灰烟气喷射脱汞及产物稳定化机理研究

Highly effective and low cost sorbents for coal-fired flue gas demercuration and stabilization of mercury compounds in adsorbed product have become the key research and development subject for mercury control technologies in coal-fired power plants. This project proposes a novel chemical-mechanical process for preparing mercury sorbent derived from the coal-fired fly ashes used in injecting demercurition technology and for stabilizing mercury avoiding its re-emission in adsorbed products by use of halide salts selected as the modifying agent and elemental sulfur or sulfide selected as the stabilizer respectively during the mechanochemical modification/stabilization process. The mechanisms of fabricating high effective mercury sorbent modified by halides and of stabilizing mercury in adsorbed fly ash in mechanochemical process will be thoroughly and systematically investigated. The interaction mechanism of unburned carbon, metal oxide Fe2O3 and halide salt crystal in response to mechanical force and their impacts on mercury adsorption oxidation and catalytic oxidation behavior of fly ash will be further studied. The mechanisms of chemical-mechanical halogenation, mercury adsorption, as well as the mechanisms of mechanochemical stabilization by sulfur contained stabilizer will be thoroughly explored also. The reaction models of mercury sulfide generated from halogenated mercury, oxide mercury as well as sulfate mercury with Fe2O3/Al2O3 functioned as catalyst in the mechanochemical process will be established. It is hopefully to develop an advanced and novel technique for high efficient mercury removal in flue gas and stabilization of mercury in mercury contained byproduct with independent intellectual property, which will be applied into coal-fired power plants.

廉价高效适应性强的燃煤烟气喷射脱汞吸附剂及脱汞产物中汞的稳定化已成为当前燃煤电站脱汞技术发展的重要研究课题。本项目以燃煤飞灰作为吸附剂，以卤化物为改性剂，以硫化物为稳定剂，提出机械化学法改性飞灰脱汞及脱汞产物的稳定化方法及技术路线。系统深入地研究机械化学法卤素改性飞灰制备高效燃煤烟气喷射脱汞吸附剂、机械化学法硫化物添加剂对脱汞产物中汞的稳定化的机理。揭示机械化学力作用下飞灰中未燃尽碳、金属氧化物Fe2O3与卤化盐晶体形成的亲汞官能团的微观结构原理和汞吸附氧化与催化氧化脱除的机理；阐明机械化学法对脱汞产物中卤化汞、氧化汞、硫酸汞等化合物在Fe2O3/Al2O3催化作用下与含硫稳定剂相互作用的原理并获得脱汞产物中汞稳定化的方法。发展和完善机械化学法卤素改性飞灰脱汞及脱汞产物稳定性和稳定化的理论体系。以期孵化出具有我国自主知识产权符合我国国情的燃煤电厂烟气喷射脱汞技术及脱汞产物中吸附态汞的稳定化。

本项目以燃煤飞灰为吸附剂、以卤化物为改性剂、以硫化物为稳定剂，提出机械化学法卤素改性飞灰脱汞及脱汞产物的稳定化方法及技术工艺。系统深入地研究了机械化学卤素改性飞灰脱汞吸附剂的制备方法和工艺，探讨了机械球磨、化学负载对脱汞剂表面特性的影响和脱汞机理，阐明了机械化学改性前后吸附剂表面汞活性位的化学迁移机理，探究了球磨参数、溴负载量、负载形式等对脱汞性能的影响。对模拟飞灰化合物脱汞吸附剂进行了溴改性和脱汞特性研究，结果表明机械化学溴改性可显著增强飞灰的脱汞能力，Fe2O3存在有限的促进作用，硅铝酸盐等无明显作用。NaBr晶体在机械化学作用下可生成反应活性更强的Br自由基，未燃尽碳的结构在机械化学作用下发生改变，其破碎断面上生成了大量的不饱和碳与含氧含溴官能团，强化了改性飞灰吸附剂对汞的键合作用和催化氧化能力。采用毒性浸出实验探究了机械化学稳定和硫稳定后飞灰中汞的稳定特性以及稳定工艺参数对汞稳定化的影响规律。研究结果表明机械化学法通过增加未燃尽碳表面缺陷与含氧官能团（尤其是C-O）实现汞的稳定化，随着球磨时间的增加存在汞再释放的风险。稳定剂硫的引入生成了稳定的HgS可有效可防止汞的二次释放，同时发现碳酸钙成分通过提供碱性环境，降低汞的浸出风险。