生物质是零碳可再生能源,对我国实现碳达峰、碳中和目标具有重要意义。虽然被视为清洁能源,但生物质燃烧过程仍会排放NOx(NO、N2O)和温室气体(CH4、N2O、CO2),有必要对生物质直燃的NOx和温室气体排放特性进行研究。测量某15MW生物质循环流化床的NOx和温室气体排放,并探究了改变床压、一二次风比、前后墙二次风比、废木料掺烧比例等因素对NOx和温室气体排放特性的影响。燃烧调整试验表明:升高床压有利于降低NO排放,但降幅很小,且会造成CO和CH4体积分数上升,CO2体积分数降低;随一二次风比增大,NO排放略降低,这意味着可适当降低二次风以降低NO排放量,CO和CH4体积分数降低,CO2体积分数升高;当前墙二次风开度/后墙二次风开度较小或较大时,均有利于降低NO,CO和CH4排放量也较低;高含氮废木料掺烧比例由20%增至50%时,NO和CO2排放量先升高后降低,CO和CH4排放量先降低后升高。研究表明当前生物质循环流化床锅炉采用低过量空气系数控制NOx排放时,CO和CH4排放浓度显著提高,一方面降低了燃烧效率,另一方面CH4作为温室气体排放也需引起关注;炉内燃烧调整手段对NOx降低有限,高含氮燃料在不完全燃烧的情况下还会生成NH3和HCN。

Biomass is a " zero carbon" renewable energy source and is of great importance to China in achieving the goal of " peak carbonemission and achieve carbon neutrality" . Although it is considered as a clean energy source, biomass combustion still emits NOx(NO,N2O) and greenhouse gases (CH4, N2O, CO2). Therefore, it is necessary to investigate the NOx and greenhouse gas emissions characteristics of direct biomass combustion. NOx and greenhouse gas emissions from a 15 MW biomass circulating fluidized bed were measured,and the effects of bed pressure, primary and secondary air ratio, front and back wall secondary air ratio, waste wood blending ratio on NOxand greenhouse gas emission characteristics were investigated. The combustion adjustment experiments show that the increase in bed pressure is beneficial to reduce NO and CO2 emissions, but the reduction is small and causes an increase in the volume fraction of CO andCH4, and a decrease in CO2 volume fraction. With an increase in the primary to secondary air ratio, NO emissions are slightly reducedwith a low CO and CH4 emission, which means that the secondary air can be reduced appropriately to reduce NO emissions. When the ratio of secondary air from front and back walls is small or large, it is beneficial to reduce NO with a low CO and CH4 emission. Whenthe mixing ratio of waste wood with high content of N is increased from 20% to 50%, NO and CO2 emissions first emissions increases andthen decreases, while the CO and CH4 show a reverse trend. This study shows that when low excess air co-efficient combustion method isemployed to control NOx emissions of the biomass circulating fluidized bed boiler, the concentration of CO and CH4 emission is significantly increased, which reduces combustion efficiency. In addition, as a greenhouse gas emission, CH4 must be considered. Combustion adjustments method is not sufficient enough to control NOx, while high amount of NH3 and HCN are emitted when some certain highnitrogen-containing fuels are burned with low oxygen combustion.

0 引言

1 试验

   1.1 锅炉简介

   1.2 燃料特性分析

   1.3 测试方法及工况

2 结果与讨论

   2.1 床压对锅炉烟气排放特性的影响

   2.2 一二次风配比对锅炉烟气排放特性的影响

   2.3 前后墙二次风比对锅炉烟气排放特性的影响

   2.4 废木料掺烧比例对锅炉烟气排放特性的影响

   2.5 常规污染物排放特性

3 结论