Principle and technology of low-NO x decoupling combustion based on restructuring reactions

doi:10.11949/0438-1157.20220716

Abstract

Abstract:

Decoupling combustion principle was first introduced to achieve low-NO _x and smokeless combustion of bituminous coal in 1995. By separating fuel pyrolysis from char combustion to break the spatio-temporal coupling of these reactions in traditional combustion, the principle can achieve complete combustion of volatiles and high-efficient NO _x reduction simultaneously through purposely restructuring such reactions. This combustion technology originating essentially from restructuring its involved reactions was formally defined as “decoupling combustion” in 1997. Focusing on the principle of high-efficiency and low-NO _x combustion and general concerns for restructuring the combustion-involved reactions, this article summarizes the major progress made in the last thirty years in fundamental research and technical development of decoupling combustion of coal and biomass as well as the typical applications of the technology for civil and industrial utilizations with proven effectiveness in intensifying combustion and reducing NO _x emission. The decoupling combustion can be combined with other advanced combustion technologies, such as fuel- and air-staged combustion, reburning and combustion based on the theory of fluidization state specification, to further improve combustion efficiency and lower air emissions. The decoupling combustion technology is especially suitable for high water content fuels, and has strong scientific significance and application value for innovative new technologies of high-efficiency and low-NO _x combustion of low-rank coal and organic waste.

Key words: decoupling combustion, low-NO _x combustion, grate boiler, fluidized bed, coal combustion, biomass

摘要：

解耦燃烧原理最早于1995年被用于烟煤的低氮无烟燃烧，其通过分离燃料热解与半焦燃烧，打破两反应在传统燃烧方式中的耦合作用，并通过重构热解挥发分与半焦的燃烧反应，实现挥发分完全燃烧的同时有效还原燃烧生成的NO _x。基于此方法的燃烧技术在1997年被定义为“解耦燃烧”。本文围绕固体燃料解耦燃烧高效低氮化原理、燃烧过程反应重构原则和反应过程定向调控关键要素，综合总结近三十年在煤炭与生物质解耦燃烧基础研究、技术开发、民用及工业燃烧典型应用及其实现的燃烧强化效果等方面取得的主要进展。解耦燃烧耦合其他诸如燃料再燃、燃料或空气分级燃烧、流态重构燃烧等先进燃烧技术可以进一步提高燃烧效率，降低空气污染物排放。解耦燃烧技术特别适合高含水燃料，对创新低阶煤和有机废弃物等的高效低氮燃烧新技术具有重要的科学意义和应用价值。

关键词: 解耦燃烧, 低氮燃烧, 炉排炉, 流化床, 煤燃烧, 生物质

CLC Number:

TQ 534

Xinhua LIU, Zhennan HAN, Jian HAN, Bin LIANG, Nan ZHANG, Shanwei HU, Dingrong BAI, Guangwen XU. Principle and technology of low-NO _x decoupling combustion based on restructuring reactions[J]. CIESC Journal, 2022, 73(8): 3355-3368.

刘新华, 韩振南, 韩健, 梁斌, 张楠, 胡善伟, 白丁荣, 许光文. 基于热解与燃烧反应重构的低NO _x 解耦燃烧原理与技术[J]. 化工学报, 2022, 73(8): 3355-3368.

Figures/Tables 19

Fig.1 Reaction sequence and chain in fuel combustion process

Fig.2 Principles of traditional combustion and decoupling combustion

Fig.3 NO reduction capabilities of pyrolysis products (NO reduction efficiency represents NO reduction capability) [25]

Fig.4 Typical structures and principles of traditional and decoupling combustion stoves

Fig.5 Machine learning-aided prompt design and optimization of decoupling combustion stoves[36]

Fig.6 Comparison of pollutant emissions in different combustion modes

Fig.7 NMHCs emission factors of different combustion modes[33]

Fig.8 Emissions from co-firing bituminous briquettes and biomass pellets

Fig.9 Typical structures and principles of the traditional grate-firing boiler and the decoupling combustion grate-firing boiler

Fig.10 Effect of fuel bed depth on pollutant emission and combustion efficiency in the decoupling combustion grate-firing boiler

Fig.11 Effect of pyrolysis-combustion combination on pollutant emission and combustion efficiency in the decoupling combustion grate-firing boiler

Fig.12 Distributions of temperature and oxygen content in the decoupling combustion grate-firing boiler

Fig.13 Pollutant emissions from burning different fuels in the decoupling combustion grate-firing boiler

Table 1 Improvement of traditional grate-firing boilers by using decoupling combustion technology［44］

Mode of

combustion

NO _x emissions/

(mg/m³)

Outlet oxygen content/% (vol)

LOI of slag/

% (mass)

Fig.14 Principle diagram of fluidized bed decoupling combustion (FBDC) technology[46]

Fig.15 Process flow diagram of a FBDC pilot treating 1000 t/a distilled spirit lees

Fig.16 Flue gas emissions from burning distilled spirit lees in different combustion modes[47]

Fig.17 Demonstration plant of FBDC with a capability of 60000 t/a distilled spirit lees

Fig.18 Variation of typical temperatures and flue gas emissions in the demonstration plant of FBDC

References 54

1	Yang H R, Yue G X, Lv J F, et al. An update of circulating fluidized bed combustion (CFBC) technology in China [J]. VGB PowerTech, 2012, 12: 1-5.
2	许光文, 高士秋, 余剑, 等. 解耦热化学转化基础与技术[M]. 北京: 科学出版社, 2016.
	Xu G W, Gao S Q, Yu J, et al. Fundamentals and Technologies of Decoupling Thermochemical Conversion [M]. Beijing: Science Press, 2016.
3	李静海, 许光文, 杨励丹, 等. 一种抑制氮氧化物的无烟燃煤方法及燃煤炉: 95102081.1 [P]. 1995-10-25.
	Li J H, Xu G W, Yang L D, et al. A NO _x -suppressed smokeless coal-fired method as well as corresponding stove: 95102081.1 [P]. 1995-10-25.
4	Li J H, Bai Y R, Song W L. NO _x -suppressed smokeless coal combustion technique [C]//Proceedings of International Symposium on Clean Coal Technology. Xiamen, China, 1997: 344-349.
5	李静海, 郭慕孙, 白蕴茹, 等. 解耦循环流化床燃烧系统及其脱硫与脱硝方法: 97112562.7 [P]. 1997-06-25.
	Li J H, Kwauk M, Bai Y R, et al. Decoupling circulating fluidized bed combustion system as well as its DeSO _x and DeNO _x methods: 97112562.7 [P]. 1997-06-25.
6	He J D, Song W L, Gao S Q, et al. Experimental study of the reduction mechanisms of NO emission in decoupling combustion of coal[J]. Fuel Processing Technology, 2006, 87(9): 803-810.
7	郝江平, 高士秋, 孙广藩, 等. 燃煤工业锅炉的发展与解耦燃烧技术的开发[J]. 工业锅炉, 2014(4): 7-11.
	Hao J P, Gao S Q, Sun G F, et al. Status of coal-fired industrial boilers and development of decoupling combustion technique[J]. Industrial Boiler, 2014(4): 7-11.
8	郝江平, 孙广藩, 李静海, 等. 一种燃煤解耦燃烧装置及燃烧方法: 201310381626.7 [P]. 2016-06-29.
	Hao J P, Sun G F, Li J H, et al. A decoupling coal-fired appliance as well as its combustion method: 201310381626.7 [P]. 2016-06-29.
9	刘新华, 郝江平, 张楠, 等. 一种解耦燃烧装置及燃烧方法: 201710512563.2[P]. 2017-06-29
	Liu X H, Hao J P, Zhang N, et al. A decoupling combustion appliance as well as its combustion method: 2017105112563.2 [P]. 2017-06-29.
10	刘新华, 郝江平, 张楠. 一种生物质解耦燃烧装置及方法: 202010454344.5 [P]. 2021-12-06.
	Liu X H, Hao J P, Zhang N. A decoupling biomass-fired appliance as well as its combustion method: 202010454344.5 [P]. 2021-12-06.
11	郝江平, 高士秋, 李静海, 等. 一种预燃式机械炉排解耦燃烧炉及其燃烧方法: 201110322136.0 [P]. 2015-02-18.
	Hao J P, Gao S Q, Li J H, et al. A pre-burning decoupling grate-firing boiler as well as its combustion method: 201110322136.0 [P]. 2015-02-18.
12	郝江平, 刘新华, 李静海, 等. 一种空气分级解耦燃烧机械炉排燃烧炉及其燃烧方法: 201710102625.2 [P]. 2017-02-24.
	Hao J P, Liu X H, Li J H, et al. An air-staged decoupling grate-firing boiler as well as its combustion method: 201710102625.2 [P]. 2017-02-24.
13	郝江平, 刘新华, 高士秋, 等. 一种解耦燃烧机械炉排炉及其燃烧方法: 202010468258.X [P]. 2021-12-09.
	Hao J P, Liu X H, Gao S Q, et al. A decoupling grate-firing boiler as well as its combustion method: 202010468258.X [P]. 2021-12-09.
14	姚常斌, 董利, 李强, 等. 一种高含水固体废弃物的解耦燃烧方法和装置: 201010218118.3 [P]. 2010-06-24.
	Yao C B, Dong L, Li Q, et al. A decoupling combustion method of high-moisture content solid wastes as well as corresponding combustion appliance: 201010218118.3 [P]. 2010-06-24.
15	Klein F, Platt S M, Farren N J, et al. Characterization of gas-phase organics using proton transfer reaction time-of-flight mass spectrometry: cooking emissions[J]. Environmental Science & Technology, 2016, 50(3): 1243-1250.
16	Glarborg P, Miller J A, Ruscic B, et al. Modeling nitrogen chemistry in combustion[J]. Progress in Energy and Combustion Science, 2018, 67: 31-68.
17	Johnsson J E. Formation and reduction of nitrogen oxides in fluidized-bed combustion[J]. Fuel, 1994, 73(9): 1398-1415.
18	Miller J A, Bowman C T. Mechanism and modeling of nitrogen chemistry in combustion[J]. Progress in Energy and Combustion Science, 1989, 15(4): 287-338.
19	Visona S P, Stanmore B R. Modeling NO _x release from a single coal particle(Ⅱ): Formation of NO from char-nitrogen[J]. Combustion and Flame, 1996, 106(3): 207-218.
20	Liu S Y, Wang Y, Wu R C, et al. Fundamentals of catalytic tar removal over in situ and ex situ chars in two-stage gasification of coal[J]. Energy & Fuels, 2014, 28(1): 58-66.
21	Dong L, Gao S Q, Song W L, et al. Experimental study of NO reduction over biomass char[J]. Fuel Processing Technology, 2007, 88(7): 707-715.
22	Molina A, Eddings E G, Pershing D W, et al. Char nitrogen conversion: implications to emissions from coal-fired utility boilers[J]. Progress in Energy and Combustion Science, 2000, 26(4/5/6): 507-531.
23	Li H L, Han J, Zhang N, et al. Effects of high-temperature char layer and pyrolysis gas on NO _x reduction in a typical decoupling combustion coal-fired stove[J]. Journal of Thermal Science, 2019, 28(1): 40-50.
24	Vilas E, Skifter U, Jensen A D, et al. Experimental and modeling study of biomass reburning[J]. Energy & Fuels, 2004, 18(5): 1442-1450.
25	Ballester J, Ichaso R, Pina A, et al. Experimental evaluation and detailed characterisation of biomass reburning[J]. Biomass and Bioenergy, 2008, 32(10): 959-970.
26	Munir S, Nimmo W, Gibbs B M. The effect of air staged, co-combustion of pulverised coal and biomass blends on NO _x emissions and combustion efficiency[J]. Fuel, 2011, 90(1): 126-135.
27	Song Y, Wang Y, Yang W, et al. Reduction of NO over biomass tar in micro-fluidized bed[J]. Fuel Processing Technology, 2014, 118: 270-277.
28	Do H S, Bunman Y, Gao S Q, et al. Reduction of NO by biomass pyrolysis products in an experimental drop-tube[J]. Energy & Fuels, 2017, 31(4): 4499-4506.
29	Cai L G, Shang X, Gao S Q, et al. Low-NO _x coal combustion via combining decoupling combustion and gas reburning[J]. Fuel, 2013, 112: 695-703.
30	Duan J, Luo Y H, Yan N Q, et al. Effect of biomass gasification tar on NO reduction by biogas reburning[J]. Energy & Fuels, 2007, 21(3): 1511-1516.
31	Liu C Y, Luo Y H, Duan J, et al. Experimental study on the effect of NO reduction by tar model compounds[J]. Energy & Fuels, 2009, 23(8): 4099-4104.
32	Zhang R Z, Liu C Y, Yin R H, et al. Experimental and kinetic study of the NO-reduction by tar formed from biomass gasification, using benzene as a tar model component[J]. Fuel Processing Technology, 2011, 92(1): 132-138.
33	Liang B, Bai H L, Bai D R, et al. Emissions of non-methane hydrocarbons and typical volatile organic compounds from various grate-firing coal furnaces[J]. Atmospheric Pollution Research, 2022, 13(4): 101380.
34	韩健, 刘新华, 何京东, 等. 民用解耦燃煤炉中的NO _x 和CO同时减排[J]. 化工学报, 2019, 70(5): 1991-1998.
	Han J, Liu X H, He J D, et al. Simultaneous reduction of NO _x and CO emissions in domestic decoupling coal-fired stoves[J]. CIESC Journal, 2019, 70(5): 1991-1998.
35	韩健, 刘新华, 何京东. 典型煤炭燃料在民用解耦炉中的燃烧实验研究[J]. 过程工程学报, 2020, 20(6): 728-736.
	Han J, Liu X H, He J D. Experimental study on the combustion of typical coal fuels in domestic decoupling stoves[J]. The Chinese Journal of Process Engineering, 2020, 20(6): 728-736.
36	Jin N N, Guo L, Liu X H. Machine learning-aided optimization of coal decoupling combustion for lowering NO and CO emissions simultaneously[J]. Computers & Chemical Engineering, 2022, 162: 107822.
37	梁斌, 白浩隆, 冯强, 等. 民用燃煤颗粒物及多环芳烃排放特性[J]. 化工学报, 2019, 70(8): 2888-2897.
	Liang B, Bai H L, Feng Q, et al. Emissions of particulate matter and polycyclic aromatic hydrocarbons from household coal combustions[J]. CIESC Journal, 2019, 70(8): 2888-2897.
38	Dong L, Gao S Q, Song W L, et al. NO reduction in decoupling combustion of biomass and biomass-coal blend[J]. Energy & Fuels, 2009, 23(1): 224-228.
39	Li H J, Chi H Y, Han H D, et al. Comprehensive study on co-combustion behavior of pelletized coal-biomass mixtures in a concentrating photothermal reactor[J]. Fuel Processing Technology, 2021, 211: 106596.
40	Rajh B, Yin C G, Samec N, et al. Advanced CFD modelling of air and recycled flue gas staging in a waste wood-fired grate boiler for higher combustion efficiency and greater environmental benefits[J]. Journal of Environmental Management, 2018, 218: 200-208.
41	Xu L, Zhao G B, Gao J M, et al. Effect of flue gas recirculation on nitric oxide (NO) emissions during the coal grate-fired process[J]. Toxicological & Environmental Chemistry, 2017, 99(5/6): 783-794.
42	Du H L, Zhang M, Zhang Y L, et al. Characteristics of NO reduction by char layer in fixed-bed coal combustion[J]. Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2017, 39(10): 963-970.
43	Jiao L, Kuang M, Chen Y Y, et al. Detailed measurements of in-furnace gas temperature and species concentration distribution regarding the primary-air distribution mode in a spreader and reversal chain-grate furnace[J]. Energy, 2021, 235: 121384.
44	王海苗, 宋令坡, 杨晓辉, 等. 预燃低氮燃烧技术在燃煤工业链条排炉中的应用[J]. 煤炭加工与综合利用, 2019(6): 83-87.
	Wang H M, Song L P, Yang X H, et al. Application of low-nitrogen pre-combustion technology in coal-fired industrial chain boiler[J]. Coal Processing & Comprehensive Utilization, 2019(6): 83-87.
45	Yao C B, Dong L, Wang Y, et al. Fluidized bed pyrolysis of distilled spirits lees for adapting to its circulating fluidized bed decoupling combustion[J]. Fuel Processing Technology, 2011, 92(12): 2312-2319.
46	Han Z N, Geng S L, Zeng X, et al. Reaction decoupling in thermochemical fuel conversion and technical progress based on decoupling using fluidized bed[J]. Carbon Resources Conversion, 2018, 1(2): 109-125.
47	姚常斌. 白酒糟双流化床解耦燃烧研究[D]. 北京: 中国科学院研究生院, 2011.
	Yao C B. Dual fluidized bed decoupling combustion of distilled spirits lees [D]. Beijing: Graduate University of Chinese Academy of Sciences, 2011.
48	Han Z N, Zeng X, Yao C B, et al. Comparison of direct combustion in a circulating fluidized bed system and decoupling combustion in a dual fluidized bed system for distilled spirit lees[J]. Energy & Fuels, 2016, 30(3): 1693-1700.
49	Zhang J W, Wu R C, Zhang G Y, et al. Technical review on thermochemical conversion based on decoupling for solid carbonaceous fuels[J]. Energy & Fuels, 2013, 27(4): 1951-1966.
50	Zhang C, Wu R C, Xu G W. Coal pyrolysis for high-quality tar in a fixed-bed pyrolyzer enhanced with internals[J]. Energy & Fuels, 2014, 28(1): 236-244.
51	Lin L X, Zhang C, Li H J, et al. Pyrolysis in indirectly heated fixed bed with internals: the first application to oil shale[J]. Fuel Processing Technology, 2015, 138: 147-155.
52	Zeng X, Ueki Y, Yoshiie R, et al. Recent progress in tar removal by char and the applications: a comprehensive analysis[J]. Carbon Resources Conversion, 2020, 3: 1-18.
53	Zeng X, Wang F, Han Z N, et al. Assessment of char property on tar catalytic reforming in a fluidized bed reactor for adopting a two-stage gasification process[J]. Applied Energy, 2019, 248: 115-125.
54	Zeng X, Wang F, Han Z N, et al. Characterization and pilot scale test of a fluidized bed two-stage gasification process for the production of clean industrial fuel gas from low-rank coal[J]. Carbon Resources Conversion, 2018, 1(1): 73-80.

[1]	Jiali ZHENG, Zhihui LI, Xinqiang ZHAO, Yanji WANG. Kinetics of ionic liquid catalyzed synthesis of 2-cyanofuran [J]. CIESC Journal, 2023, 74(9): 3708-3715.
[2]	Jiaqi CHEN, Wanyu ZHAO, Ruichong YAO, Daolin HOU, Sheying DONG. Synthesis of pistachio shell-based carbon dots and their corrosion inhibition behavior on Q235 carbon steel [J]. CIESC Journal, 2023, 74(8): 3446-3456.
[3]	Wentao WU, Liangyong CHU, Lingjie ZHANG, Weimin TAN, Liming SHEN, Ningzhong BAO. High-efficient preparation of cardanol-based self-healing microcapsules [J]. CIESC Journal, 2023, 74(7): 3103-3115.
[4]	Zhenghao YANG, Zhen HE, Yulong CHANG, Ziheng JIN, Xia JIANG. Research progress in downer fluidized bed reactor for biomass fast pyrolysis [J]. CIESC Journal, 2023, 74(6): 2249-2263.
[5]	Juhui CHEN, Qian ZHANG, Lingfeng SHU, Dan LI, Xin XU, Xiaogang LIU, Chenxi ZHAO, Xifeng CAO. Study on flow characteristics of nanoparticles in a rotating fluidized bed based on DEM method [J]. CIESC Journal, 2023, 74(6): 2374-2381.
[6]	Maolin DONG, Lidong CHEN, Liulian HUANG, Weibing WU, Hongqi DAI, Huiyang BIAN. Research progress in preparation of lignonanocellulose by acid hydrotropes and their functional applications [J]. CIESC Journal, 2023, 74(6): 2281-2295.
[7]	Yuanyuan ZHANG, Jiangyuan QU, Xinxin SU, Jing YANG, Kai ZHANG. Gas-liquid mass transfer and reaction characteristics of SNCR denitration in CFB coal-fired unit [J]. CIESC Journal, 2023, 74(6): 2404-2415.
[8]	Zihan YUAN, Shuyan WANG, Baoli SHAO, Lei XIE, Xi CHEN, Yimei MA. Investigation on flow characteristics of wet particles with power-law liquid-solid drag models in fluidized bed [J]. CIESC Journal, 2023, 74(5): 2000-2012.
[9]	Zefeng GE, Yuqing WU, Mingxun ZENG, Zhenting ZHA, Yuna MA, Zenghui HOU, Huiyan ZHANG. Effect of ash chemical components on biomass gasification properties [J]. CIESC Journal, 2023, 74(5): 2136-2146.
[10]	Haiqin LIU, Bowen LI, Zhe LING, Liang LIU, Juan YU, Yimin FAN, Qiang YONG. Facile preparation and properties of chemically modified galactomannan films via mild hydroxy-alkyne click reaction [J]. CIESC Journal, 2023, 74(3): 1370-1378.
[11]	Lingxin ZU, Rongting HU, Xin LI, Yudao CHEN, Guanglin CHEN. Carbon release products and denitrification bioavailability from chemical components of woody biomass [J]. CIESC Journal, 2023, 74(3): 1332-1342.
[12]	Jieyuan ZHENG, Xianwei ZHANG, Jintao WAN, Hong FAN. Synthesis and curing kinetic analysis of eugenol-based siloxane epoxy resin [J]. CIESC Journal, 2023, 74(2): 924-932.
[13]	Jianxin CHEN, Ruijie ZHU, Nan SHENG, Chunyu ZHU, Zhonghao RAO. Preparation of cellulose-derived biomass porous carbon and its supercapacitor performance [J]. CIESC Journal, 2022, 73(9): 4194-4206.
[14]	Zeguang HAO, Qian ZHANG, Zenglin GAO, Hongwen ZHANG, Zeyu PENG, Kai YANG, Litong LIANG, Wei HUANG. Study on synergistic effect of biomass and FCC slurry co-pyrolysis [J]. CIESC Journal, 2022, 73(9): 4070-4078.
[15]	Dongwang ZHANG, Hairui YANG, Tuo ZHOU, Zhong HUANG, Shiyuan LI, Man ZHANG. Cold-state experimental study on ash deposition of convection heating surface of biomass boiler [J]. CIESC Journal, 2022, 73(8): 3731-3738.