Safety Calculation and Analysis of Water Wall for a 700 MW Ultra-Supercritical Circulating Fluidized Bed Boiler Without External Bed After Power Failure

doi:10.12096/j.2096-4528.pgt.23134

Abstract

Abstract:

By analyzing the change laws of flue gas temperature, steam temperature and working fluid mass flow during a power failure accident in a 660 MW power plant, the change laws of heat load in dense phase zone, transition zone and dilute phase zone over time were obtained. On this basis, a 700 MW ultra-supercritical circulating fluidized bed (CFB) boiler was taken as the research object, the calculation model of flow and heat transfer in water wall after power failure accident was established, and a calculation program for the transient characteristics of the water wall was developed based on the Fortran language. The dense phase zone, transition zone and dilute phase zone were analyzed, respectively. Through calculation, the change laws of the thermal parameters such as water wall metal temperature and working fluid temperature after power failure accident were obtained. The calculation results show that, after the power failure accident, the maximum water wall metal temperature at the outlet of dense phase zone is 558.6 ℃, and the maximum water wall metal temperature at the outlet of dilute phase zone is 579.6 ℃. Therefore, there is no need to equip emergency water supply pump to ensure the safety of the water wall after power failure. The research results can provide guidance for power plants to deal with power failure accidents of ultra-supercritical CFB boilers.

Key words: ultra-supercritical, circulating fluidized bed (CFB) boiler, power failure, heat load, water wall

CLC Number:

TK 22

Qigang DENG, Zhuo LÜ, You SHI, Jiayi LU, Xu ZHOU, Aoyu WANG, Dong YANG. Safety Calculation and Analysis of Water Wall for a 700 MW Ultra-Supercritical Circulating Fluidized Bed Boiler Without External Bed After Power Failure[J]. Power Generation Technology, 2024, 45(2): 240-249.

Figures/Tables 15

Fig. 1 Calculation program block diagram of transient characteristics in heating surface

Fig. 2 Schematic diagram of heating zone division

Tab. 1 Main design parameters of boiler

参数	数值(100% BMCR负荷下)
水冷壁入口流量/(t∙h^-1)	1 832.64
水冷壁出口压力/MPa	31.756
水冷壁出口温度/℃	430
省煤器入口流量/(t∙h^-1)	1 925
给水压力/MPa	32.25
给水温度/℃	309.8

Tab. 2 Structural parameters of water wall tube

参数	数值
下炉膛水冷壁厚度/mm	31.8
下炉膛水冷壁外径/mm	6.5
上炉膛水冷壁厚度/mm	33.4
上炉膛水冷壁外径/mm	7
下炉膛耐磨材料厚度/mm	47.5
下炉膛耐磨材料导热系数/[W/(m⋅K)]	3
水冷壁导热系数/[W/(m⋅K)]	22.6
浇注料区高度/m	11.5

Fig. 3 Schematic diagram of heat transfer process of refractory materials in dense phase zone of boiler

Fig. 4 Temperature variation of flue gas in dilute phase zone

Fig. 5 Temperature variation of flue gas in dense phase zone

Fig. 6 Heat load variation in each zone of boiler

Tab. 3 Inlet parameter variation of working fluid for economizer after power failure

时间/s	省煤器进口工质流量/(t⋅h^-1)	省煤器进口焓值/(kJ⋅kg^-1)
0	1 925.00	1 377.82
30	1 925.00	1 377.82
40	1 478.57	1 377.82
50	973.50	1 377.82
60	448.45	1 377.82
70	0	0
3 000	0	0

Fig. 7 Outlet pressure variation of water wall

Fig. 8 Variation of outlet working fluid temperature and wall temperature in dense phase zone

Fig. 9 Variation of outlet working fluid temperature and wall temperature in transition zone

Fig. 10 Variation of outlet working fluid temperature and wall temperature in dilute phase zon

Fig. 11 Outlet mass flow variation of water wall

Fig. 12 Inlet pressure variation of economizer

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