Optimization Study of Power Plant Direct Flow Cold-end Subsystem Based on Negative Digging

doi:10.12096/j.2096-4528.pgt.21005

Abstract

Abstract:

In view of the unstable performance of the cold-end system of traditional power plants and the high annual operating cost, a mathematical model based on the heat, resistance, civil construction and annual operating cost calculation of the direct flow cold end system based on negative digging depth was established, and the cold end system configuration was obtained from different conditions outside the tower. The optimal configuration was used to analyze the effect of cooling water for intlet tower water temperature, coagulator area unit price and condenser negative digging depth on the performance of cold end system. The results show that reducing the cooling water for intlet tower water temperature and condenser area unit price can reduce the annual operating cost of cold end system. The performance parameters of the cold end system with a negative digging depth of 3 to 5 m reach the lager value. Therefore, selecting the cold end system configuration according to different weather parameters outside the tower can improve the operating efficiency of the power plant and reduce the annual operating cost of the cold end system.

Key words: power plant, direct flow cold-end subsystem, cold-end optimization, negative digging depth, annual operating cost

CLC Number:

TK 264.1

Yun CHEN, Sen LI, Yuanbin ZHAO. Optimization Study of Power Plant Direct Flow Cold-end Subsystem Based on Negative Digging[J]. Power Generation Technology, 2022, 43(4): 655-663.

Figures/Tables 17

Tab. 1 Calculation formula for cold-end optimization

公式名称	公式
热平衡方程	$Q = K × Δ T × A = W c w t w 2 - t w 1$
凝结水温度	$t n = t w 1 + Δ t + δ t$
HEI传热计算法	$K = K 0 F t F m F c$
别尔曼总传热系数法	$K = 4 070 ξ 1 Φ W Φ t Φ z Φ δ$
凝汽器水阻	$H c p = L T × R T × R 1 + ∑ R E$
沟道沿程阻力损失	$v = 1 n R 2 / 3 i 1 / 2$
渠道沿程阻力	$i 0 = n 2 v 2 R 2 y + 1$
管、沟、渠的局部阻力	$h j = ∑ ξ 2 v 2 2 g$
年费用计算	$C = P ⋅ R A F C + A p - A t$
循环水泵耗电费用	$A p = 10 - 4 N b H l G p$
年微增功率收益	$A t = 10 - 4 t l G e ∑ N i$

Tab. 1 Calculation formula for cold-end optimization

公式名称	公式
热平衡方程	$Q = K × Δ T × A = W c w t w 2 - t w 1$
凝结水温度	$t n = t w 1 + Δ t + δ t$
HEI传热计算法	$K = K 0 F t F m F c$
别尔曼总传热系数法	$K = 4 070 ξ 1 Φ W Φ t Φ z Φ δ$
凝汽器水阻	$H c p = L T × R T × R 1 + ∑ R E$
沟道沿程阻力损失	$v = 1 n R 2 / 3 i 1 / 2$
渠道沿程阻力	$i 0 = n 2 v 2 R 2 y + 1$
管、沟、渠的局部阻力	$h j = ∑ ξ 2 v 2 2 g$
年费用计算	$C = P ⋅ R A F C + A p - A t$
循环水泵耗电费用	$A p = 10 - 4 N b H l G p$
年微增功率收益	$A t = 10 - 4 t l G e ∑ N i$

Tab. 2 Calculation parameters of the cold end subsystem

参数	取值
热力计算方法	HEI传热计算法
循泵配置	一机两泵
虹吸井管沟类型	矩形管沟
溢流堰类型	斜交堰
负挖深度/m	0
溢流堰堰顶绝对标高/m	11.8
虹吸井底板绝对标高/m	6
成本电价/［元/(kW^·h)］	0.24
微增电价/［元/(kW^·h)］	0.42
循环水泵效率	0.95
年固定分摊率	0.126 5
年运行时间/h	7 000
汽轮机排气量/(m³/h)	1 728
冷却水进水温度/℃	20
凝汽器单价/(元/m²)	1 000
盐度/(g/kg)	50
冷却管管材	钛管
背压形式	单背压
流程数	2
冷却管外径/mm	25
冷却管壁厚/mm	1
清洁系数	0.85
冷却管长度/m	13.3
管内流速范围/(m/s)	1.0~3.5

Tab. 3 Monthly water temperature and circulating water volume ratio for cold-end optimization

月份	1	2	3	4	5	6	7	8	9	10	11	12
温度/℃	12.6	14.1	17.2	20.8	23.5	24.9	24.9	24.6	23.3	20.6	16.8	13.5
水流量比值	0.85	0.85	0.85	1.00	1.00	1.00	1.00	1.00	1.00	1.00	0.85	0.85

Fig. 1 Loop flowchart for cold-end optimization

Tab. 4 Best back pressure of each month for cold-end optimization

月份	1	2	3	4	5	6	7	8	9	10	11	12
温度/℃	12.6	14.1	17.2	20.8	23.5	24.9	24.9	24.6	23.3	20.6	16.8	13.5
最佳背压/kPa	3.26	3.54	4.17	5.30	6.10	6.55	6.55	6.45	6.03	5.24	4.09	3.42

Tab. 5 The top ten optimal configuration parameters before cold-end optimization

参数组号	背压/kPa	冷却面积/m²	冷却倍率	主径/m	年费用/万元	水流量/(m³/h)	扬程/m	管根数	管流速/(m/s)
1	5.16	62 000	55	3.7	3 050.005	95 040	23.43	32 258	2.0
2	5.21	59 000	55	4.0	3 050.396	95 040	23.40	30 697	2.1
3	5.21	59 000	55	3.9	3 051.587	95 040	23.55	30 697	2.1
4	5.21	59 000	55	3.8	3 054.168	95 040	23.72	30 697	2.1
5	5.28	58 000	54	3.6	3 054.207	93 312	23.96	30 176	2.1
6	5.19	61 000	55	3.8	3 054.595	95 040	23.38	31 737	2.0
7	5.16	62 000	55	3.6	3 056.241	95 040	23.67	32 258	2.0
8	5.10	63 000	56	4.1	3 056.930	96 768	22.96	32 778	2.0
9	5.10	63 000	56	4.0	3 057.287	96 768	23.09	32 778	2.0
10	5.21	59 000	55	3.7	3 058.411	95 040	23.93	30 697	2.1

Fig. 2 Influence of cooling water temperature on back pressure and cooling rate

Fig. 3 Influence of cooling water temperature on cooling area and main pipe diameter

Fig. 4 Influence of cooling water temperature on circulating pump lift and cooling water flow rate

Fig. 5 Influence of cooling water temperature on annual cost value

Fig. 6 Influence of condenser area price on back pressure and cooling rate

Fig. 7 Influence of condenser area price on cooling area and main pipe diameter

Fig. 8 Influence of condenser area price on circulating pump lift and cooling water velocity

Fig. 9 Influence of condenser area price on annual cost value

Fig. 10 Influence of negative digging depth on cooling area and cooling rate

Fig. 11 Influence of negative digging depth on main pipe diameter and circulating pump lift

Fig. 12 Influence of negative excavation depth on cooling water outlet temperature and flow rate

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