采用换热器负荷图指导换热网络改造的新方法

doi:10.11949/0438-1157.20190948

摘要/Abstract

摘要：

目前大部分图形工具仅适用于以节能为目标的换热网络（HEN）设计或者改造。能量回收量的增加往往伴随换热单元数的增多，而换热单元数对设备投资费有较大影响。采用换热器负荷图（HELD）提出一种系统化的换热网络改造新方法。新方法基于夹点分析，在改造区间中选择匹配目标，重新构建改造用HELD，从而简化问题；通过在水平方向上平移热流股曲线实现跨夹点负荷的重新分配，完成节能目标，并结合经验规则，尽可能减少改造后换热网络的换热器数目。以一个工业造纸厂为例，对其进行节能改造方案设计，相较于文献报道结果，得到两个节能目标值相近且换热器改动数目更少的新方案，验证了新方法的有效性。

关键词: 传热, 过程系统, 优化, 改造, 换热器负荷图

Abstract:

At present, most graphic tools are only suitable for the design or retrofit of heat exchange networks (HEN) with the goal of saving energy. The increase of energy recovery is often accompanied by the increase of the number of heat exchange units, and the number of heat exchange units obviously affects the total equipment costs. A new method for the retrofit of heat exchanger networks by using heat exchanger load diagram (HELD) is proposed. Based on pinch analysis, selecting targeted matches and reconstructing the HELD, the problem is simplified. By shifting the heat flow curve horizontally, those cross-pinch heat loads are re-matched to reduce utility consumption, and the number of heat exchangers in the retrofitted heat exchanger network can be reduced as much as possible with the help of some heuristics. An industrial case of paper mill is retrofitted to demonstrate the effectiveness of the proposed approach. Compared with reported solutions, two new retrofit networks with similar energy saving values and fewer heat exchangers are obtained.

Key words: heat transfer, process system, optimization, retrofit, heat exchanger load diagram

中图分类号:

TQ 021.8

李保红, 李继文. 采用换热器负荷图指导换热网络改造的新方法[J]. 化工学报, 2020, 71(3): 1288-1296.

Baohong LI, Jiwen LI. New method for heat exchanger network retrofit using heat exchanger load diagram[J]. CIESC Journal, 2020, 71(3): 1288-1296.

图/表 14

图4 造纸厂的HELD

Fig.4 HELD of the paper mill

图1 用HELD表示最大换热负荷准则

Fig.1 Maximum heat transfer load criterion represented by HELD

图2 用HELD来表示规则2

Fig.2 Rule 2 represented by HELD

表1 造纸厂的流股数据

Table 1 Stream data of the paper mill

流股名称	实际温度/℃		热负荷 Q/kW	热容流率 FC_p/(kW/℃)	虚拟温度/℃
流股名称	T_s	T_t	热负荷 Q/kW	热容流率 FC_p/(kW/℃)	T_s*	T_t*
WW高温段	58	39.9	7951	439.3	53	34.9
WW低温段	39.9	30	1283	129.6	34.9	25
RC	60	30	2254	75.1	55	25
EX1^①	80	40	10216	255.4	70	30
EX2^①	80	40	10216	255.4	70	30
PS	70	20	7523	150.5	65	15
BW	11	61	10745	214.9	16	66
HW	50	61	2032	184.7	55	66
OI	30	50	727	36.4	35	55
BB	20	80	3763	62.7	30	90
PV	20	125	4946	47.1	30	135
RP	11	60	6306	128.7	16	65

图3 造纸厂的原始网格图

Fig.3 Grid diagram representation of the existing HEN

图5 造纸厂简化后的HELD

Fig.5 Simplified HELD of the paper mill

图6 造纸厂改造方案1的简化HELD

Fig.6 Simplified HELD of retrofit 1 for the paper mill

图7 改造方案1的HEN网格图

Fig.7 Grid diagram of HEN retrofit 1

图8 造纸厂改造方案2的简化HELD

Fig.8 Simplified HELD of retrofit 2 for the paper mill

图9 改造方案2的HEN网格图

Fig.9 Grid diagram of HEN retrofit 2

图10 方案3简化后的HELD

Fig.10 Simplified HELD of retrofit 3 for the paper mill

图11 改造方案3的HEN网格图

Fig.11 Grid diagram of HEN retrofit 3

表2 不同方案换热器的换热面积变化率

Table 2 Variation rate of heat transfer area of heat exchangers under different retrofit scenarios

换热器编号	换热面积变化率/%
换热器编号	方案1	方案2	方案3
C3	-22.3	-22.3	-17.9
C4	-2.6	-12.4	-8.8
E1	12.5	12.5	0
E2	82.9	17.0	0
H1	—	-62.9	-73.0
H2	0	—	-45.7

表3 不同方案的换热器变更情况

Table 3 Changes of heat exchangers under different retrofit scenarios

方案编号	新增换热器/个	利用的旧换热器/个	改造换热器/个	换热器总数/个
1	1	3	1	14
2	2	4	1	15
3	2	2	2	16

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