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Journal of Thermal Science

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2024 , Vol. 33 >Issue 6: 2413 - 2425

DOI: https://doi.org/10.1007/s11630-024-2045-6

Effect of Limestone on NO Emission during the Co-Combustion of Semi-Coke and Bituminous Coal

  • LIU Yanquan ,
  • TAN Wenyi ,
  • LIANG Shaohua ,
  • BI Xiaolong
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  • 1. School of Energy & Engineering, Nanjing Institute of Technology, Nanjing 211167, China
    2. School of Environment Engineering, Nanjing Institute of Technology, Nanjing 211167, China

网络出版日期: 2024-11-05

基金资助

This work was financially supported by the Scientific Research Startup Foundation of High-level Introduction Talents of Nanjing Institute of Technology (No. YKJ201914) and National Natural Science Foundation of China (NSFC) (No. 51678291).

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Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2024
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Effect of Limestone on NO Emission during the Co-Combustion of Semi-Coke and Bituminous Coal

  • LIU Yanquan ,
  • TAN Wenyi ,
  • LIANG Shaohua ,
  • BI Xiaolong
Expand
  • 1. School of Energy & Engineering, Nanjing Institute of Technology, Nanjing 211167, China
    2. School of Environment Engineering, Nanjing Institute of Technology, Nanjing 211167, China

Online published: 2024-11-05

Supported by

This work was financially supported by the Scientific Research Startup Foundation of High-level Introduction Talents of Nanjing Institute of Technology (No. YKJ201914) and National Natural Science Foundation of China (NSFC) (No. 51678291).

Copyright

Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2024
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摘要

当半焦在循环流化床内与高硫烟煤进行混燃时，炉内脱硫的必要性会增加。在此期间，石灰石，作为一种广泛使用的脱硫剂，对NO的排放也会产生影响。为了探究它在混燃过程中对NO排放的影响机理，本研究在循环流化床实验台和固定床反应器中均开展了燃烧实验。研究结果显示半焦中掺混烟煤会改变燃料中氮的赋存形式，更多的燃料NO会在挥发份析出阶段释放。在脱硫过程中，石灰石的煅烧会生成CaO，其对NO的氧化和还原反应都具有催化作用，它们的催化强度共同决定了对NO排放的最终影响。当掺混比例为50%的半焦/烟煤混合燃料（SC50BC50）在900°C下燃烧时，NO排放量在Ca/S=0~4范围内呈现先增加后降低的趋势。与半焦单独燃时的情况相比，在相同的Ca/S摩尔比下，混合燃料中的半焦有更多的机会与CaO接触，从而使NO的异相还原反应得到强化。当燃烧温度从800°C增加到1000°C时，石灰石对NO排放的影响从促进转化为抑制作用，这是因为较高的燃烧温度不仅能强化循环流化床密相区中NO前驱物的催化还原，还可以加强稀相区中NO与未燃尽碳之间的反应。此外，对于半焦和SC50BC50，气氛中较低的O2浓度同样有利用强化CaO对NO-char还原反应的催化作用，因此相比没有石灰石的情况，燃料N向NO的转化会受到抑制。本研究取得的成果有利于实现半焦和烟煤混燃时NOx和SO2的协同控制。

关键词： semi-coke; co-combustion; limestone; NO emission

本文引用格式

LIU Yanquan , TAN Wenyi , LIANG Shaohua , BI Xiaolong . Effect of Limestone on NO Emission during the Co-Combustion of Semi-Coke and Bituminous Coal[J]. 热科学学报, 2024 , 33(6) : 2413 -2425 . DOI: 10.1007/s11630-024-2045-6

Abstract

When semi-coke is co-combusted with bituminous coal with higher sulfur content in a circulating fluidized bed (CFB) boiler, the necessity of desulfurization in furnace increases. Meanwhile, limestone, which is a widely used desulfurizing agent, also has an effect on NO emission. In order to explore its effect during co-combustion, the combustion experiments were conducted in both a CFB test rig and a fixed bed reactor. The results show that blending semi-coke with bituminous coal will change the occurrence forms of nitrogen in the fuel and more fuel NO is released during the devolatilization stage. During the desulfurization process, CaO will be generated through the calcination reaction. It has catalytic effects on both the oxidation and reduction reactions of NO, and the catalytic strength in these two types of reactions decides the final effect on NO emission. For the blended fuel with 50% semi-coke and 50% bituminous coal (SC50BC50), the NO emission initially increases and then decreases as the Ca/S molar ratio increases from 0 to 4 at 900°C. Compared to the situation of burning semi-coke alone, semi-coke in the blended fuel has more opportunities to contact with CaO under the same Ca/S molar ratio, leading to the heterogeneous reduction reaction of NO enhanced. As the combustion temperature increases from 800°C to 1000°C, the effect of limestone on NO emission will change from promotion to inhibition. This is because the higher combustion temperature can intensify not only the catalytic reduction of NO precursors in the dense-phase region, but also the reaction between NO and unburnt char in the dilute-phase region in the CFB. Besides, the lower O2 concentration in the atmosphere is also favorable for enhancing the catalytic effect of CaO on the NO-char reduction reaction for semi-coke and SC50BC50, so the conversion of fuel-N/NO will be inhibited compared with the cases without limestone. The achievements of this study are beneficial for the coordinated control of NOx and SO2 during the co-combustion of semi-coke and bituminous coal.

Key words： semi-coke; co-combustion; limestone; NO emission

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