Abstract:

Mercury pollution has attracted increasing attention due to serious harm to the human beings and ecosystem. This study aims to analyze the effects of CeO₂ oxygen carriers on the conversion of mercury during coal chemical looping combustion. The combustion characteristics of "CeO₂+coal", "SiO₂+coal" and "coal" in the fluidized bed reactor were investigated experimentally. In gasification atmosphere, the reaction between oxygen carrier and coal was mainly converted to CO₂ and a small amount of compositions including CO, CH₄, and H₂ . "CeO₂+coal" system consumed the largest amount of O₂ and produced the largest amount of CO₂, indicating that the CeO₂ oxygen carriers contributed to the fully combustion of the coal. Mercury was mainly released as Hg⁰ in the gasification atmosphere, and the Hg⁰ release from "CeO₂ + coal" accounted for 49.75% of the total mercury, which was significantly lower than that of the system without oxygen carriers. In air atmosphere, mercury was released in the form of Hg²⁺ with a small amount. The Hg⁰ and Hg²⁺ release from "CeO₂ + coal" system were both lower than those of the "coal" system. By changing the different locations between CeO₂ oxygen carriers and coal in experiments, it was shown that under gasification atmosphere, CeO₂ oxygen carriers had weak adsorption capacity for Hg⁰, and their catalytic and oxygen release properties were the key factors in removing Hg⁰, and the catalytic activity played a major role. Under gasification atmosphere, CO₂ could replenish the lattice oxygen consumed in CeO₂, thus improving its catalytic and regenerative performances. XPS analysis of the CeO₂ oxygen carriers after reduction and oxidation showed the peak position for Ce³⁺ in Ce 3d disappeared and all of them were converted to Ce⁴⁺, which indicated that the CeO₂ oxygen carrier had good cyclic performance.

Key words: chemical looping combustion, cerium dioxide, oxygen carrier, coal, mercury

摘要：

汞污染因其对人类和生态系统的严重危害而日益受到人们的关注，本研究旨在分析CeO₂载氧体在煤化学链燃烧过程中对汞迁移的影响。通过实验比较了“CeO₂+煤”“SiO₂+煤”“煤”在流化床反应器中的燃烧状况，在气化氛围中，载氧体与煤反应主要转化为CO₂和少量CO、CH₄、H₂等成分，“CeO₂+煤”体系消耗了最多的O₂，产生了最多的CO₂，表明CeO₂载氧体促使煤燃烧更加充分。汞在气化氛围下主要以Hg⁰的形式释放，“CeO₂+煤”的Hg⁰释放量占总汞量的49.75%，明显低于无载氧体组。汞在空气氛围下主要以Hg²⁺的形式再次微量释放，“CeO₂+煤”的Hg⁰和Hg²⁺释放量均低于纯煤组。通过改变CeO₂载氧体和煤之间的不同位置，表明在气化氛围下CeO₂载氧体对Hg⁰的吸附作用很弱，其催化性和释氧作用是脱除Hg⁰的关键因素，且催化性占据主要地位。在气化氛围下，CO₂可以补充CeO₂中消耗掉的晶格氧使其具有更好的催化和再生性能。通过对还原/氧化后CeO₂载氧体进行XPS（X射线光电子能谱分析仪）分析，发现Ce 3d中的Ce³⁺峰值消失全部转化为Ce⁴⁺，表明CeO₂载氧体具有良好的再生性能。

关键词: 化学链燃烧, 二氧化铈, 载氧体, 煤, 汞