Optimization of Heat Exchanger Network Based on Relaxation Strategy of Small Heat Exchanger Protection

doi:10.19596/j.cnki.1001-246x.8392

Abstract

Abstract:

As RWCE algorithm is used to optimize heat exchanger networks, the existence of fixed investment cost makes it difficult to produce and retain heat exchanger units with small loads. It makes structures that have not yet fully evolved be eliminated too early. We established a relaxation method of fixed investment cost. The fixed investment cost and the heat exchange of heat exchange unit are processed according to their variation. With heat exchange of heat exchange unit, relaxation strength in optimization process is adjusted in real time to guide and promote the smooth generation and evolution of small load heat exchange unit, so as to enhance structural evolution ability of heat exchange network. The relaxation strategy is applied to 9SP and 15SP examples to verify that the relaxation strategy promotes structural evolution effectively and improves optimization quality. The optimal results (2 903 528 ＄ ·a^-1, 5 115 061 ＄ ·a^-1) are better than those in literatures.

Key words: heat exchanger network, fixed investment cost, slack, small load heat exchanger unit, heat load

Lu ZHANG, Guomin CUI, Weiwei LIU, Yuan XIAO, Yue XU, Guanhua ZHANG. Optimization of Heat Exchanger Network Based on Relaxation Strategy of Small Heat Exchanger Protection[J]. Chinese Journal of Computational Physics, 2022, 39(3): 352-360.

Figures/Tables 13

Fig.1 Schematic diagrams of node unstructured model (a) node setting; (b) heat exchange network structure

Table 1 Statistics of heat exchange unit generation in 15SP example

固定投资费用	有效换热单元数	换热单元生成总数	有效生成概率/%
C_F	37 068	3 003 670	1.2
0	70 159	2 765 376	2.5

Fig.2 A schematic of obstacles in small load heat exchange unit

Fig.3 Fixed investment cost relaxation curve

Fig.4 Variation of comprehensive cost in optimization process (a) with different ω, (b) with different Qm

Fig.5 Optimal structure of Example 1

Table 2 Optimal results in Example 1

	换热单元数	热公用工程/kW	冷公用工程/kW	年综合费用/(＄·a^-1)
Ref.[14]	13	25 310	33 030	2.960×10⁶
Ref.[15]	12	25 090	32 810	2.936×10⁶
Ref.[16]	10	25 610	33 330	2.945×10⁶
Ref.[17]	16	23 350	31 070	2.943×10⁶
Ref.[18]	11	23 880	31 600	2.936×10⁶
Ref.[10]	14	23 878	31 597	2 926 788
Ref.[19]	17	24 656	32 376	2 926 485
Ref.[20]	18	23 770	31 490	2 924 117
Ref.[21]	15	23 994	31 714	2 922 515
本文	21	23 957	31 677	2 903 528

Fig.6 Variation of (a) comprehensive cost and (b) number of heat exchange units in optimization process

Fig.7 TAC with two algorithms

Table 3 Optimal results of Example 2

	换热单元数目	热公用工程/kW	冷公用工程/kW	年综合费用/(＄·a^-1)
Ref.[13]	24	41 349	59 219	6 019 310
Ref.[22]	29	43 280	61 150	5 613 283
Ref.[23]	26	27 380	45 250	5 233 287
Ref.[24]	26	27 223	45 068	5 169 883
图 8	23	27 418	45 229	5 155 770
图 9	24	26 500	44 311	5 115 061

Fig.8 Optimal structure by the RWCE algorithm

Fig.9 Optimal structure by the RWCE-PR algorithm

Fig.10 Variation of (a) TAC and (b) number of heat exchange units (with split flow) in optimization process in Example 2

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