Abstract:

Generally, biomass with high nitrogen resource endowments needs to control NO_x emissions in the process of energy utilization. Decoupled combustion falls within low-NO_x combustion technologies, which is suitable for high-water, high-nitrogen fuels and has better effects on suppressing NO_x formation compared to other combustion technologies. In order to make clear the potential of pyrolysis volatile for in-situ nitrogen control in decoupled combustion and to develop the dual fluidized bed decoupled combustion technology, with furfural residue as the material, a fixed-bed reactor and a dual fluidized bed combustion apparatus were respectively employed for studying its pyrolysis characteristics and simulating its decoupled combustion in the dual fluidized bed at approximately actual working conditions in this paper. Concretely, the product distribution of furfural residue pyrolysis at different temperatures was first investigated in the fixed-bed reactor, and then the effects of the on-line pyrolysis products on in-situ control of NO_x emission from synchronous combustion of the resulting pyrolysis char of the raw material in the dual fluidized bed combustion apparatus were revealed. The results showed that: in the pyrolysis temperature range of 500—700℃, with the increase of temperature, the semi-coke yield gradually decreased, from 45.2% to 39.8%; the gas yield showed an obvious upward trend, rising from 12.4% to 22.5%, the yield of reducing components such as CO, CH₄, and H₂ increased significantly; the yield of tar decreased slightly, from 15.9% to 12.9%; the yield of water did not change much. During the decoupling combustion experiments using the double fluidized bed, it was found that the volatiles produced by pyrolysis from furfural residue exhibited a good effect on in-situ nitrogen control for the combustion flue gas from its resulting pyrolysis char. The NO_x control effect of the pyrolysis volatiles for the char combustion flue gas depended heavily on the pyrolysis temperature and the proportion of secondary air. When the total excess air factor ER was 1.3, the pyrolysis temperature 600℃ and the secondary excess air factor ER₂=0.5, the effect of the volatiles from furfural residue pyrolysis on the in-situ nitrogen control for the flue gas from combustion (at 900℃ with the first excess air factor ER₁=0.8) of the char produced by pyrolysis at the same conditions reached the best, and the NO_x emission reduction ratio was high as 54.80%. These indicated that the yields and oxidation degrees of pyrolysis volatile products can be regulated to bring their potential for NO_x reduction into full play, thus visibly improving the in-situ nitrogen control effect for decoupled combustion.

Key words: furfural residue, pyrolysis, decoupled combustion, NO_x emission, in-situ nitrogen control

摘要：

通常，具有高含氮资源禀赋生物质在能源化利用过程中需控制NO_x排放。解耦燃烧是可适用于高含水、高含氮燃料的低NO_x燃烧技术，其对NO_x生成的抑制效果优于其他燃烧技术。为揭示解耦燃烧中热解挥发产物的原位控氮潜力、发展双流化床解耦燃烧技术，以糠醛渣为原料，借助固定床装置和双流化床装置，分别开展其热解特性和双流化床解耦燃烧近实际工况模拟研究。具体地，首先在固定床反应器中考察糠醛渣在不同温度下的热解产物分布，继而借助双流化床反应器考察了热解在线挥发产物对热解半焦同步燃烧烟气中NO_x的还原效果。结果表明：在500~700℃热解温度区间内，随温度的升高，半焦产率逐渐减少，从45.2%下降到39.8%；气体产率呈明显上升趋势，从12.4%上升到22.5%，CO、CH₄、H₂等还原性组分产率增加显著；焦油产率略有降低，从15.9%降低到12.9%；水分产率变化不大。双流化床解耦燃烧实验中，糠醛渣热解挥发产物对热解半焦同步燃烧所产烟气控氮效果良好，热解挥发产物对半焦燃烧烟气NO_x减排效果主要受热解温度、二次风占比影响，总过量空气系数ER=1.3，热解温度600℃、二次风过量空气系数ER₂=0.5时，糠醛渣热解挥发产物对相同热解条件下生成的半焦燃烧（900℃，过量空气系数ER₁=0.8）所产烟气原位控氮效果达到最优，NO_x减排率为54.80%。这表明，可通过控制热解挥发分产物产率、氧化程度，充分发挥挥发分的NO_x还原能力，从而明显改善解耦燃烧原位控氮效果。

关键词: 糠醛渣, 热解, 解耦燃烧, NO_x排放, 原位控氮