The Influence of the Air-coal Ratio on Transient Characteristics of the Ultra-supercritical Power Unit during the Load Cycling Processes

doi:10.11930/j.issn.1004-9649.202302026

Abstract

Abstract:

In order to study the influence of the air-coal ratio on the peak regulating characteristics of a coal-fired unit during load cycling transients, a dynamic model of a double-reheat ultra-supercritical coal-fired power plant with 660MW was established. The influence of the air-coal ratio on the live and reheat steam temperatures, the flowrates of the desuperheating water and the transient energy consumption was studied. A control scheme of air - coal ratio considering the steam temperature control effect and operational efficiency under different load cycling rates was proposed. The results show that, during the load cycling transient processes, a larger air-coal ratio benefits the stabilization of the live and reheat steam temperatures, while the average coal consumption rate of power during the transient process is higher. When the load cycling rate is equal to or less than 1%/min, a smaller air-coal ratio is preferred to reduce the average coal consumption by 1.2 g/(kW·h) during the load cycling transient process. When the load cycling rate is between 2%/min and 3%/min, a higher air-coal ratio is preferred to ensure that the deviations of the live and reheat steam temperatures can be controlled within 10℃．

Key words: air-coal ratio, double reheat, load cycling, steam temperature regulation, transient energy consumption

Yong ZHANG, Chaoqiang YIN, Yugang LIU, Bin ZHANG, Chunhong MO, Chaoyang WANG. The Influence of the Air-coal Ratio on Transient Characteristics of the Ultra-supercritical Power Unit during the Load Cycling Processes[J]. Electric Power, 2024, 57(3): 224-232.

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URL: https://www.electricpower.com.cn/EN/10.11930/j.issn.1004-9649.202302026

https://www.electricpower.com.cn/EN/Y2024/V57/I3/224

Figures/Tables 13

Fig.1 The thermal system of the ultra-supercritical double reheat coal-fired power plant

Table 1 Thermal parameters of each heat surface in the boiler

工况	主汽温/ ℃	主汽压/ MPa	主汽流量/ (kg·s^–1)	给水温度/ ℃	给水压力/ MPa	一再汽温/ ℃	一再压力/ MPa	一再流量/ (kg·s^–1)	二再汽温/ ℃	二再压力/ MPa	二再流量/ (kg·s^–1)
BMCR	605	32.45	496.0	314	36.45	623	11.05	463.5	623	3.33	396.0
75%THA	605	23.45	341.0	303	25.52	623	7.46	307.7	623	2.29	269.4
50%THA	605	15.57	222.3	277	16.58	623	4.99	204.1	623	1.55	181.8

Table 2 Proximate and ultimate analyses of coal (as received)

工业分析/%				元素分析/%					Q_ar,net/(kJ·kg^–1)
M_ar	A_ar	V_ar	FC_ar	C_ar	H_ar	O_ar	N_ar	S_ar	Q_ar,net/(kJ·kg^–1)
8.25	24.30	38.64	28.81	54.80	3.88	7.16	0.91	0.70	21430

Fig.2 Model of the boiler system

Fig.3 Model of the turbine system

Table 3 Excess air coefficient at different work conditions

工况		α
BMCR		1.15
75%THA		1.20
50%THA		1.40

Fig.4 Excess air coefficient during load cycling transients with Ve = 1%/min

Fig.5 Trends of steam temperatures during the loading up process with different variation rates

Fig.6 Trends of spraying water during the loading up process with different variation rates

Fig.7 Average standard coal consumption of the power unit during loading up processes

Fig.8 Trends of steam temperatures during the loading down process with different variation rates

Fig.9 Trends of spraying water during the loading down process with different variation rates

Fig.10 Average standard coal consumption of the power unit during loading down processes

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