【作者】 袁海荣；

【导师】 李秀金；

【作者基本信息】 北京化工大学 ， 环境工程， 2010， 博士

【摘要】 我国是世界上最大的农业国家,年产各类作物秸秆总量达7.1亿吨。其中,约有40%-50%秸秆未被利用,常被露天焚烧,导致严重的大气污染和火灾,秸秆焚烧已经成为全国各地都面临的一大环境问题。通过固化成型技术把秸秆转化成生物质固化成型燃料(Densified biomass briquetting fuel, DBBF)是秸秆能源化利用的有效方法。但是,当DBBF用于小型炊事炉时,存在点不着火、点火时间长和烟气污染等问题,从而严重影响了DBBF的推广和使用。因此,研制经济、有效和环境友好的成型燃料专用引火助燃剂,对解决成型燃料点火难、污染问题及成型燃料炉具的改进具有重要的实际意义。本文针对玉米秸秆固化成型燃料(Densified corn stover briquetting fuel, DCBF)及其LLA-6型生物质半气化炉,研制了多种DCBF引火助燃剂,并对其点火性能和点火特性进行了试验研究与评价、实现了DCBF的快速点燃,并且烟气排放达到了环保要求；同时,还开展了DCBF燃烧特性及其数值模拟方面的研究,获得了一些重要的结论。1.引火助燃剂研制及其点火特性和烟气排放特性研究。(1)用废机油、废柴油和工业酒精以不同的体积比研制出25种液体助燃剂,通过反复点火试验,综合考虑成本及点火特性等各种因素,初步选定ED15和DA51两种助燃剂做为备选助燃剂,其最佳用量分别为9 mL和8 mL,比不用助燃剂点火速度快30-40倍。(2)对不同用量的助燃剂ED15和DA51引燃过程中的烟气排放情况(包括烟气中的O2、CO2、CO、烟气温度、NO、NO2、NOx、SO2和燃烧效率这9项指标)进行了试验研究,研究结果表明：两种助燃剂烟气排放指标均符合北京市地方排放标准,助燃剂ED15用量为9 mL时污染物排放较低,因此,助燃剂ED15被确定为待推广的助燃剂。2. DCBF燃烧特性试验研究与分析。(1)利用柴炉热性能试验方法对LLA-6型炉具的热性能进行了测试,结果显示其热效率只有20%,没能达到北京市地方标准(热效率≥35%)。(2)利用热电偶温度传感器和精密天平分别对炉具内各位置的温度和燃烧失重量进行测定。根据所测温度和失重量数据对燃烧过程进行动力学分析。利用“多变混合速率扫描法”得出DCBF在LLA-6型炊事炉中燃烧时的燃烧机理：在快速升温阶段和降温阶段DCBF燃烧符合的三维扩散机理,球形对称,3D,D4,减速形a-t曲线,其积分形式表达式为；在快速升温与温度恒定之间的拐点处和恒定温度阶段DCBF燃烧机理属于化学反应,F2,减速形a-t曲线,其积分形式表达式。(3)利用烟气分析仪对燃烧过程中烟气排放的各种污染物指标进行监测,发现在整个燃烧过程中污染物排放指标均符合北京市地方污染物排放标准。有风条件下的各种污染物排放指标略高于无风条件下的各种污染物排放指标。因此,在无风条件下助燃剂ED15用量为9mL时效果最佳。3. DCBF燃烧特性的数值模拟。利用Fluent软件和燃烧过程所遵循的基本定律,采用湍流和有限速率等燃烧模型对DCBF燃烧特笥进行数值模拟,结果发现：(1)燃烧炉内CO2浓度为18.4%,在炉口处的CO2浓度为9%左右,排烟管中CO2浓度为6.47%；在助燃器内几乎没有任何化学反应发生,助燃器并没有起到应有的助燃作用,而是起了降低热效率的作用。(2)通过对32种不同改进情况进行模拟,结果表明助燃器通风孔全部关闭时(即没有二次进风)效果最好。助燃器内部温度范围为990-1020K,炉口处最高温度为1020K。没有二次进风时炉口处温度分别比关闭0排、1排、2排、3排和4排通风孔时高19.86%、29.86%、37.67%、39.59%和39.73%。因此,推荐改造最佳方案为不用助燃器,不带二次进风。由助燃器散热及二次进风带走的热损失q2和q3之和为19.21%。将助燃器及二次进风除掉,将助燃器部分直接改为火焰通道,可将原炉具的热效率20%提高到39.21%,可以使热效率提高近1倍,并可使炉具达到北京市地方标准。综上所述,助燃剂ED15用量为9 mL时引燃DCBF效果最佳,在无风条件下,将LLA-6型炉具助燃器部分改为封闭式的火焰通道,DCBF燃烧效果最佳,热效率可达到39.21%。更多还原

【Abstract】 China is one of the largest agricultural countries in the world. Approximately,0.71 billion tons of various crop residues are generated annually.50%-60% crop residues are not used, which are ussally burnt in open field, leading to serious air pollution and fire disaster, Crop stalks can be used to make densified biomass briquetting fuel (DBBF), which is one of effective ways to use crop stalks and widely used in rural areas in China. However, DBBF is facing a bottle-neck problem with igniting. DBBF is a kind of densified biomass with high density (0.8-1.4g/cm3), which is very difficult to be ignited. Farmers normally need to take 20 to 30 minutes for successfully igniting cooking stoves. In addition, long-time ignition causes thick smoke and harmful gases emission, posing serious environmental pollution and threat to people’s health. And it seriously affected the further promotion of DBBF. Therefore, it is imperitive to develop efficiency, affordable, and environmentally friendly ignition-assisting agents. Densified corn stover briquetting fuel(DCBF) was used as the experimental material for type LLA-6 household cooking stove. The research was conducted to:develop ignition-assisting agents, study on ignition characteristics, DCBF combustion characteristics and numerical simulation.1. Development of ignition-assisting agents and study on igniting and emission characteristics.25 kinds of ignition-assisting agents were developed by mixing waste engine, waste diesel oil, and industrial alcohol at different volume ratios. ED15 and DA51 achieved better igniting results. ED 15 with 9mL dosage and DA51 with 8mL dosage took 40 and 53 seconds to successfully ignite the DCBF, which were 30-40 times shorter than those without using ignition-assisting agent. ED 15 and DA51 showed similar emission and combustion characteristics in terms of O2, CO, CO2, NOx, and SO2 emissions, and fume gases temperature and combustion efficiency. The average concentrations of CO, CO2, NOx, and SO2 for ED 15 and DA51 at all dosages met the requirements by Beijing local standard. Compared to other agent and other dosages, ED15 at the dosage of 9mL achieved similar combustion efficiency but emitted less pollutants, therefore, is recommended for practical application.2. Experimental study on analyses on the combustion characteristics of DCBF. The thermal performance, temperature, and combustion weight loss were measured and analyszed. The results showed that thermal efficiency of type LLA-6 stove was only 20% and could not reach to Beijing local standard(thermal efficiency≥35%). The reaction mechanism of combustion of DCBF was obtained by the "volatile mix rate scanning method". The results showed that the reaction mechanism belonged to three-dimensional,3D, sphericity symmetry, D4 Deceleratory a-t curves in the rapid heating stage and the cooling stage during the combustion of DCBF process. The mechanisms function expression of integral form was ; The reaction mechanism belonged to chemical reaction, F2, Deceleratory a-t curves in the rapid heating inflection point and constant temperature stage. The mechanisms function expression of integral form was . Combustion results without wind condition was obviously better than that of with wind condition through temperature monitoring of different positions in the stove. Pollution emission concentrations met the requirement of Beijing local standard "General Technical Requirements of Household Biomass Stoves" (DB11/T 540-2008) through monitoring various pollutants. Pollutants emission of DCBF with wind was slightly higher than that of no wind. Therefore, combustion results was optimal in no wind conditions with a dosage of 9 mL.3. Numerical simulation on DCBF combustion characteristic. Model Fluent, Turbulent, and Finite-Rate were used to simulate DCBF combustion characteristics. The numerical simulation results showed that CO2 concentrations in stove, stove mouth and exhaust pipe were 18.4%,9% and 15%, respectively. No any chemical reaction was found in the combustion device, meaning that the combustion device did not play any role in ignition assisting. (2) Closed vent of combustion-assisting device was favourable to be the improving on combustion. The temperature was 990-1020K in combustion-assisting device and 1020K at stove mouth. The temperatures of stove mouth without secondary inlet were 19.86%,29.86%,37.67%,39.59% and 39.73% higher than those with inlet at stove, respectively, when ventilation holes was closed 0 row,1 row,2 rows,3 rows and 4 rows. The type LLA-6 stove achieved the best combustion results without combustion-assisting device. The heat loss from the combustion device (q2) and the second inlet(q3) were 19.21%. The thermal efficiency could be increasing from 20% to 39.21% if the combustion-assisting device was taken away and the second inlet was closed.Therefore, it is recommended to use ignition-assisting agent ED15 with a dosage of 9 mL for the ignition of DCBF. The thermal efficiency could reach to 39.21% at no wind and no combustion-assisting device.更多还原