石灰石对循环流化床燃烧NO_(x)排放影响及粒度优化研究  

Study on the effect of limestone on NO_(x) emission in circulating fluidized bed combustion and particle size optimization

作　　者：尚曼霞 李怡然 蒋苓 李东方 黄中 张缦[1] 吕俊复[1] 柯希玮 SHANG Manxia;LI Yiran;JIANG Ling;LI Dongfang;HUANG Zhong;ZHNAG Man;LU Junfu;KE Xiwei(Key Laboratory for Thermal Science and Power Engineering of Ministry of Education,Tsinghua University,Beijing100084,China;School of Metallurgy and Energy Engineering,Kunming University of Science and Technology,Kunming 650093,China)

机构地区：[1]清华大学热科学与动力工程教育部重点实验室,北京100084 [2]昆明理工大学冶金与能源工程学院,昆明650093

出　　处：《清华大学学报（自然科学版）》2023年第12期2033-2041,共9页Journal of Tsinghua University(Science and Technology)

基　　金：“十四五”国家重点研发计划项目(2022YFB4100301);中国博士后科学基金面上资助项目(2022M721780)。

摘　　要：污染物排放标准日趋严格的背景下,如何解耦循环流化床(circulating fluidized bed, CFB)燃烧炉内石灰石高效脱硫与低NO_(x)排放之间的矛盾,是研究热点之一。该文利用一维两相混合CFB燃烧整体数学模型,对某550 MWe超超临界CFB锅炉燃烧和污染物排放情况进行了预测,计算值与现场实测值吻合良好。模拟结果表明,由于CaO对各含氮反应的显著催化作用,投放石灰石脱硫会直接或间接影响NO_(x)的生成及还原过程,导致NOx原始排放升高。但在相同钙硫比下,采用脱硫反应活性更高的细颗粒石灰石,其表面快速包覆的惰性产物层可以降低炉内总CaO有效反应面积,进而直接影响相关催化反应总体速率,既能有效提高炉内脱硫效率,又能缓解石灰石对NOx减排的负面作用。[Objective] In the context of increasingly stringent pollutant emission standards, more and more circulating fluidized bed(CFB) boilers are pursuing low-NO_(x) combustion and high-efficiency desulfurization in the furnace. How to decouple the contradiction between the two is one of the research hotspots. Previous studies found that when the separator efficiency is suitable, a reasonable adjustment of the limestone particle size can significantly improve the desulfurization efficiency in the furnace while effectively inhibiting the negative effect of limestone on NO_(x) emission. However, this phenomenon is only at the experimental stage and lacks theoretical analysis. [Methods] In this paper, a commercial 550 MWe ultra-supercritical CFB boiler was calculated with the help of the established comprehensive one-dimensional two-phase hybrid mathematical model for CFB combustion to obtain the rules and the effect of limestone particle size on NO_(x) emission desulfurization in a furnace. The comprehensive mathematical model for CFB combustion consists of three parts, namely, material balance(including ash, limestone, raw coal, and coke), gas balance, and energy balance. Moreover, this model specifically considers the local gas/solid fluidization state and gas/heat transfer conditions in different regions of the CFB combustor. Some two-or three-dimensional problems, such as bubble breakage over dense bed surface, secondary air injection, core annular flow structure, and particle clusters in freeboard, are also considered in the modeling. For nitrogen-containing catalytic reactions on the limestone surface, CaO has significant catalytic activity for many nitrogen-containing reactions, which is one of the important reasons for the increase of NO_(x) emission caused by limestone desulfurization in the CFB furnace. This paper considers four types of nitrogen-containing catalytic reactions on the surface of CaO particles, including oxidation of NH_3, hydrolysis of HCN, oxidation of CO, and catalytic reduction of NO by CO. T

关 键 词：循环流化床燃烧 石灰石粒度 炉内脱硫 NO_(x)排放 数学模型 

分 类 号：TK111[动力工程及工程热物理—热能工程]