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Alternative TitleReduction of NOX from Combustion Flue Gas by Char
Thesis Advisor林伟刚 ; 李松庚
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword半焦   no还原   选择性   经济性
Abstract氮氧化物(NOX)是主要的大气污染物之一。由于环境问题日益加剧,氮氧化物的排放法规逐年严格,尤其是在中国。为了适应严格的排放规定,许多新的氮氧化物脱除技术正在开发之中。在这些技术中,半焦还原脱硝法获得了广泛的关注。该方法不仅具有较高的脱除效率,而且具有相对较低的建设成本和广泛的碳资源。本文通过两种操作模式——恒温实验和程序升温实验,在固定床上反应器上通过模拟燃烧烟气进行了半焦还原脱硝法的研究。为了优化脱硝过程,考察了不同因素,包括半焦种类、反应温度、烟气中NO和O2浓度,以及空速的影响。同时引入ICP、SEM以及BET等多种表征手段探索脱硝过程的反应机理。本文在上述实验结果的基础上进行了经济性分析,并与SCR技术进行了对比。主要结论如下: (1)基于程序升温实验,可将半焦脱硝反应可分为三个阶段:气体吸附阶段、NO还原和焦气化阶段、NO完全还原阶段。NO和O2在半焦表面发生化学吸附所形成的表面络合物对NO还原起着重要作用。 (2)恒温实验表明,褐煤半焦相对烟煤半焦具有更高的脱硝效率和C-NO选择性。生物质焦中,松木粉半焦因含有较丰富的金属元素而具有较好的脱硝效果。在本研究的实验条件下,提高温度和O2浓度均可提高脱硝效率,但O2含量的增加会使C-NO选择性下降;并且烟气中NO浓度越高,脱硝效率越低,但C-NO选择性越高。 (3)经济性分析表明,当考虑热量回收利用时,半焦还原脱硝法相比SCR技术具有显著的优势。计算结果显示,若不考虑热量的回收利用,该技术仅适用于烟气中O2浓度低于1.6%的情况。随着O2浓度升高,大量碳消耗将带来费用的急剧增加。
Other AbstractNitrogen oxides (NOX) is well known as one of air pollutants. Due to increasing environmental concerns, the regulation for NOX emission gradually becomes more stringent each year, especially in China. In order to comply with the strict emission regulation, many new NOX removal technologies are being developed. Among them, NOX reduction by char has gained wide attention due to its advantages such as high NO removal efficiency, relatively low capital cost and extensive carbon resources. In this work, NO reduction by char was studied in a fixed bed reactor with simulated combustion flue gas. The tests were performed in two different operation modes: the isothermal and the temperature programmed. The influencing factors including temperature, coal type, NO and oxygen concentrations in flue gas and space velocity were investigated to optimize the process. Various characterization techniques such as ICP, SEM and BET were employed in attempt to explore the reaction mechanism. On a basis of the experimental results, an economic analysis was made in comparison with the SCR technology. Major conclusions can be drawn as follows: (1) Based on the temperature programmed experiments, NO reduction by coal char can be divided into three stages within the temperature range of 293K~923K: gas adsorption stage, NO reduction & char gasification stage, and NO complete reduction stage. Surface complexes formed by chemisorption of NO and O2 on carbon active sites play a key role in the NO reduction. (2) The isothermal experiments indicated that the lignite char has relatively higher NO removal efficiency and higher C-NO selectivity than the bituminous char . Pine char shows the better results than the other biomass char because of its higher trace metal content. Under the experimental conditions in this work, an increase in temperature or oxygen concentration in flue gas enhanced NO reduction. However, C-NO selectivity decreased with the increasing oxygen concentration. Higher NO concentration in flue gas led to lower NO reduction but higher C-NO selectivity. (3) The economic analysis indicated that the NO reduction by char has a significant advantage over the SCR technology when considering utilization of the heat released in the process. Without utilization of the heat, the technology presented in this work is only suitable to be applied in the flue gas where the oxygen concentration is lower than 1.6%. With a further increase in oxygen concentration, the cost will sharply increase due to the significant increase of carbon consumption by oxygen.
Document Type学位论文
Recommended Citation
GB/T 7714
方晓晴. 半焦直接还原脱除烟气氮氧化物实验研究[D]. 中国科学院研究生院,2014.
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