The Impact of Biomass Cofiring on Volatile Flame Length
The Impact of Biomass Cofiring on Volatile Flame Length
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DOI：
10.1021/ef4013505
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发表时间：
2013-12-01
期刊：
影响因子：
5.3
通讯作者：
Axelbaum, Richard L.
中科院分区：
文献类型：
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作者：
Holtmeyer, Melissa L.;Li, Gengda;Axelbaum, Richard L.
生物质的物理特性和组成可能因煤和一种燃料与另一种燃料而有很大差异，这些差异可能影响所得粉末状燃料火焰的结构，特别是挥发性火焰。挥发性火焰是挥发物燃烧主导的区域，其长度和位置不仅对火焰的稳定性和长度很重要，而且对NOx等污染物的形成也很重要。本文研究了生物质挥发分和颗粒大小对煤粉和废柴共烧火焰挥发焰长度的影响。在35kw的燃烧装置上，通过沿中心线轴向测量CO和CO2，实验测量了挥发性火焰的长度。采用数值模拟的方法来解释木材废料共烧对挥发性火焰的影响。挥发性火焰区长度对挥发分释放位置和挥发分释放量敏感。大的生物质颗粒，轴向动量大，加热时间长，突破富燃料挥发性火焰区，向下游释放挥发物，进入富氧环境。挥发物的延迟释放减少了富燃料区挥发性燃料的数量，导致挥发性火焰变短，从而增加了挥发物完全释放前颗粒的突破。在CO和CO2浓度测量的基础上，发现含有20%木材废料和80%煤的共燃烧火焰的挥发性火焰比只含煤的火焰短21%。数值模拟证实，挥发性反应发生在挥发性火焰结束后。为了减少在完全脱挥发之前通过挥发火焰的颗粒量，减小了木材废料的粒径。与纯煤的挥发性火焰相比，20%共燃情况下产生的挥发性火焰长27%。增加的挥发物含量，生物质燃料的特点，导致增加的挥发物火焰长度时，所有的挥发物被释放在近燃烧器区域。
The physical characteristics and composition of biomass can vary significantly from coal and from one fuel to another, and these differences can impact the structure of the resulting pulverized fuel flame, particularly the volatile flame. The length and location of the volatile flame, which is the zone dominated by the combustion of volatiles, is important not only to flame stability and length but also to the formation of pollutants such as NOx. In this work, the effects of biomass volatile fraction and particle size on the length of the volatile flame were investigated for cofired flames of pulverized coal and wood waste. The volatile flame length was measured experimentally in a 35 kW combustion facility via axial measurements of CO and CO2 made along the centerline. Numerical simulations were employed to aid the interpretation of the impacts of wood waste cofiring on the volatile flame. The length of the volatile flame zone was found to be sensitive to the location of volatile matter release and the amount of volatile matter released within the volatile flame zone. Large biomass particles, with high axial momentum and long heating times, break through the fuel-rich volatile flame zone, releasing volatiles downstream into an oxygen-rich environment. The delayed release of volatiles reduces the amount of volatile fuel in the fuel-rich region, leading to shorter volatile flames, which in turn augments breakthrough of particles before complete release of volatiles. On the basis of CO and CO2 concentration measurements, cofired flames with 20 wt % wood waste and 80 wt % coal were found to have 21% shorter volatile flames compared with coal-only flames. Numerical simulations verified that volatile reactions take place past the end of the volatile flame. To reduce the amount of particles that pass through the volatile flame before complete devolatilization, the wood waste particle size was reduced. The resulting volatile flame was 27% longer for the 20 wt % cofired case compared with coal-only volatile flames. Increased volatile matter content, characteristic of biomass fuels, leads to an increased volatile flame length when all of the volatiles are released in the near-burner region.