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Frontiers in Energy

ISSN 2095-1701

ISSN 2095-1698(Online)

CN 11-6017/TK

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Front. Energy    2021, Vol. 15 Issue (1) : 4-13    https://doi.org/10.1007/s11708-020-0804-y
RESEARCH ARTICLE
NOx and H2S formation in the reductive zone of air-staged combustion of pulverized blended coals
Jinzhi CAI, Dan LI, Denggao CHEN, Zhenshan LI()
Key Laboratory for Thermal Sciece and Power Engineering of the Ministry of Education, Department of Energy and Power Engineering, Tsinghua University, Beijing 100084, China
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Abstract

Low NOx combustion of blended coals is widely used in coal-fired boilers in China to control NOx emission; thus, it is necessary to understand the formation mechanism of NOx and H2S during the combustion of blended coals. This paper focused on the investigation of reductive gases in the formation of NOx and H2S in the reductive zone of blended coals during combustion. Experiments with Zhundong (ZD) and Commercial (GE) coal and their blends with different mixing ratios were conducted in a drop tube furnace at 1200°C–1400°C with an excessive air ratio of 0.6–1.2. The coal conversion and formation characteristics of CO, H2S, and NOx in the fuel-rich zone were carefully studied under different experimental conditions for different blend ratios. Blending ZD into GE was found to increase not only the coal conversion but also the concentrations of CO and H2S as NO reduction accelerated. Both the CO and H2S concentrations inblended coal combustion increase with an increase in the combustion temperature and a decrease in the excessive air ratio. Based on accumulated experimental data, one interesting finding was that NO and H2S from blended coal combustion were almost directly dependent on the CO concentration, and the CO concentration of the blended coal combustion depended on the single char gasification conversion.Thus, CO, NOx, and H2S formation characteristics from blended coal combustion can be well predicted by single char gasification kinetics.
Keywords blended coal combustion      NOx formation      H2S formation      air staged combustion     
Corresponding Author(s): Zhenshan LI   
Online First Date: 02 April 2020    Issue Date: 19 March 2021
 Cite this article:   
Jinzhi CAI,Dan LI,Denggao CHEN, et al. NOx and H2S formation in the reductive zone of air-staged combustion of pulverized blended coals[J]. Front. Energy, 2021, 15(1): 4-13.
 URL:  
https://academic.hep.com.cn/fie/EN/10.1007/s11708-020-0804-y
https://academic.hep.com.cn/fie/EN/Y2021/V15/I1/4
Coal Proximate analysis Ultimate analysis
M V FC A C H O N S
ZD 0.27 31.02 61.54 7.17 68.49 4.16 18.62 0.68 0.61
GE 1.09 28.54 63.46 6.91 80.55 4.65 3.96 2.00 0.86
Tab.1  Proximate and ultimate analysis of coals (as fired, %)
Fig.1  Size distribution of coal samples prepared.
Fig.2  Schematic of DTF installed with OFA.
Coals Coal feeding/(g·min–1) Temperature/°C SR1 SR2 SRt Sampling Location
ZD (ZD100%) 2.503 1200
1300
1400		 0.6
0.8
1.2		 0.6
0.4
0		 1.2 0.35 m, 0.6 m,
ZD:GE= 3:1 (ZD75%) 2.351 0.85 m, 1.1 m:
ZD:GE= 2:2 (ZD50%) 2.217 Reductive
ZD:GE= 1:3 (ZD25%) 2.097 Zone
GE (ZD0%) 1.900
Tab.2  Detailed experiment conditions
Fig.3  Combustible conversion along reaction distance.
Fig.4  Combustible conversion at different temperatures.
Fig.5  Combustible conversion at different primary air ratios.
Fig.6  (a) CO and (b) H2 concentrations along reaction distance.
Fig.7  (a) CO and (b) H2 concentrations at different blending ratios.
Fig.8  (a) CO and (b) H2 concentrations at different excess air ratios.
Fig.9  NO concentration along reaction distance.
Fig.10  NO concentration along reaction distance at 1200°C and SR1 = 0.6.
Fig.11  H2S concentration along reaction distance.
Fig.12  Char gasification conversion versus CO.
Fig.13  Relation between CO and NO concentration at different conditions.
Fig.14  Relation between CO and H2S concentration at different temperatures.
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