多效蒸发海水淡化系统可行域时变分析与全周期操作优化

doi:10.11949/0438-1157.20210787

摘要/Abstract

摘要：

能耗过高制约了多效蒸发（MED）海水淡化技术的大规模应用，稳态操作优化虽然能够有效减少MED系统的短期蒸汽消耗速率，但污垢累积导致该系统在长周期运行时蒸汽消耗量升高和装置减产。为此，首先针对带蒸汽压缩机（TVC）的MED系统（MED-TVC）提出可行域的概念，分析表明操作点在可行域中的位置决定了系统的运行效益。随后通过可行域的时变分析发现操作点超出可行域是稳态优化中系统性能逐渐衰减的原因。最后利用可行域的性质，提出了时变约束的全周期操作优化方法。该方法通过调整MED-TVC系统在运行周期内的操作条件，获得全周期最低的蒸汽消耗量，同时利用时变的可行域约束保证优化结果在全周期内均满足淡水产量要求。结果表明，时变约束的全周期操作优化在维持MED-TVC系统的设计淡水产量的同时，全周期蒸汽消耗量相比于设计值减少了19.6%，能够很好地解决MED-TVC系统的操作优化问题。

关键词: 过程系统工程, 海水淡化, 多效蒸发, 全周期优化, 慢时变, 可行域

Abstract:

Excessive energy consumption restricts the large-scale application of multi-effect distillation (MED) seawater desalination technology. Although steady-state operation optimization can effectively reduce the short-term steam consumption rate of the MED system, the accumulation of fouling caused the system to increase steam consumption and reduce plant production during long-term operation. For this reason, the feasible region model of operating conditions in the MED system with thermal vapor compressor (MED-TVC) is established, which relates the location of operating points to the operating benefits. The time-varying analysis of feasible region shows that the operating point crossing the feasible region is the reason for the system performance degradation. Finally a full-cycle operating optimization method with time-varying constraints is proposed, which adjusts the operating conditions of the MED-TVC system in the full cycle to obtain the lowest steam consumption in the full cycle and uses the time-varying feasible region constraints to ensure that the optimization results meet the fresh water production requirements. The results show that the full-cycle operating optimization with time-varying constraints can effectively reduce the total motive steam consumption of the MED-TVC system while maintaining the designed fresh water output.

Key words: process system engineering, seawater desalination, multi-effect distillation, full-cycle optimization, slow time-varying, feasible region

中图分类号:

TQ 021.8

陈春波, 罗雄麟, 孙琳. 多效蒸发海水淡化系统可行域时变分析与全周期操作优化[J]. 化工学报, 2021, 72(11): 5686-5695.

Chunbo CHEN, Xionglin LUO, Lin SUN. Time-varying analysis of feasible region and full-cycle operating optimization in multi-effect distillation seawater desalination system[J]. CIESC Journal, 2021, 72(11): 5686-5695.

图/表 9

图1 八效MED-TVC海水淡化系统示意图[25]

Fig.1 Schematic diagram of the MED-TVC system with eight effects[25]

表1 八效MED-TVC系统设计运行参数［25］

Table 1 Specifications of the MED-TVC system［25］

固定条件	值	设计参数	值
海水流动方式	平行-交叉	每效进料流量/(kg?s^-1)	31.59
海水温度/℃	30	效间温差/℃	3
海水含盐量/(g?kg^-1)	30	预热器温升/℃	4
冷凝器出口温度/℃	35	TVC引射流量/(kg?s^-1)	4.50
驱动蒸汽压力/kPa	500	加热蒸汽流量/(kg?s^-1)	7.38
驱动蒸汽温度/℃	151.8	淡水产量/(kg?s^-1)	75.81
		造水比	10.27

表2 MED-TVC系统的操作条件稳态优化结果与设计值对比

Table 2 Comparison of operating conditions between steady-state optimization and design

效数	F_f/(kg?s^-1)		P/kPa		ΔT_p/℃		F_ent/kg?s^-1		F_mot/(kg?s^-1)
效数	设计值	优化值	设计值	优化值	设计值	优化值	设计值	优化值	设计值	优化值
1	31.59	19.84	27.34	26.33	4	2.78	4.43	4.06	7.38	6.45
2	31.59	18.48	23.92	23.39	4	2.83
3	31.59	18.77	20.86	20.69	4	2.87
4	31.59	19.66	18.15	18.22	4	3.06
5	31.59	21.97	15.74	15.97	4	3.80
6	31.59	23.34	13.61	13.83	4	5.45
7	31.59	18.06	11.73	11.84	4	8.03
8	31.59	19.58	10.07	10.12	—	—

图2 两种操作条件下的全周期淡水产量和蒸汽流量变化

Fig.2 Full-cycle variations in steam consumption and fresh water production under two operating conditions

图3 操作条件对单效性能的影响

Fig.3 Effect of operating conditions on the single effect performance

图4 稳态优化和设计条件下的单效可行域全周期变化

Fig.4 Variations of single-effect feasible region in the full cycle under the steady-state optimization and design conditions

图5 MED-TVC系统的全周期操作优化结果

Fig.5 Full cycle operating optimization results of the MED-TVC system

图6 全周期优化的MED-TVC系统可行域及操作点变化

Fig.6 Variations of feasible region and operating points of the MED-TVC system after full cycle optimization

表3 设计条件、稳态优化和全周期优化运行结果对比

Table 3 Comparison of design condition， steady-state optimization and full cycle optimization for full cycle operating results

参数	设计条件	稳态优化	全周期优化
淡水产量/(kg?s^-1)	75.81	[75.81, 66.76]	75.81
驱动蒸汽流量/(kg?s^-1)	[7.38, 10.71]	[6.45, 20.00]	[6.59, 6.91]
GOR	[10.30, 7.08]	[11.75, 3.34]	[11.51, 10.98]
总蒸汽量/10⁸ kg	5.30	10.40	4.26

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