Load-shift laws and bottleneck identification strategy of disturbed heat exchanger network

doi:10.11949/0438-1157.20230840

Abstract

Abstract:

For the heat exchanger network (HEN) with source/sink parameter variation, a systemic disturbance response/parameter adjustment method is proposed to maintain the heat balance of the system, identify the bottleneck restricting energy recovery and propose corresponding debottlenecking strategy. Based on topology analysis, feasible response objects and disturbance propagation paths of the system are enumerated, and the load-shift laws of heat exchangers are clarified. The relationship between heat exchanger thermal resistance requirement (R^req), area increment (∆A), total annual system cost (Ct) and heat capacity flow rate fluctuation coefficient (α) is derived. The thermal resistance demand change trend diagram and economic change diagram are constructed. With the optimal cost taken as the goal, the best response object is selected, and its heat load change value is determined. The system energy bottleneck caused by thermal resistance restriction during the adjustment of the response variable is located, and the area increment required to solve the bottleneck is determined. The proposed method can determine the change of the heating/cooling medium’s flow rate and that of each heat exchanger’s area demand under the disturbance state without complex simulation calculation, which is intuitive and efficient and can guide the design, optimization, or retrofit of chemical processes. A benzene alkylation process is analyzed to illustrate its application. When α locates in the interval [0.75, 0.88] and [0.88, 1.35], two heaters are the optimal response objects, saving the total annual cost up to 19400 USD∙a^-1 and 24024 USD∙a^-1, respectively.

Key words: heat exchanger network, disturbance, load-shift, bottleneck, debottleneck

摘要：

对于发生源/阱参数变化的换热网络（HEN），提出一种系统的干扰响应/参数调整方法，用于平衡系统盈余热量/冷量，辨识制约能量回收的瓶颈及对应的解瓶颈策略。在拓扑结构分析基础上，枚举可行的响应对象及扰动传播路径，明确换热器的负荷转移规律。推导了换热器热阻需求（R^req）、面积增量（∆A）、系统年度总成本（Ct）与热容流率波动系数（α）之间的关系。构建热阻需求变化趋势图和经济变化图，以成本最优为目标，选择最佳的响应对象并确定其热负荷变化值，定位响应变量调整过程中因热阻制约而产生系统用能瓶颈，确定解瓶颈所需的面积增量。该方法无须复杂模拟计算即可确定扰动状态下加热/冷却介质流量需求变化值及各换热设备面积需增量，可以有效指导生产工艺的设计、优化和改造。以苯烷基化生产过程为例展示该方法的应用，当α位于［0.75，0.88］和［0.88，1.35］时，两台加热器分别是最优的响应对象，最大节省年度总成本19400 USD∙a^-1和24024 USD∙a^-1。

关键词: 换热网络, 扰动, 负荷迁移, 瓶颈, 解瓶颈

CLC Number:

TQ 021.8

Liwen ZHAO, Guilian LIU. Load-shift laws and bottleneck identification strategy of disturbed heat exchanger network[J]. CIESC Journal, 2023, 74(11): 4611-4621.

赵丽文, 刘桂莲. 扰动换热网络负荷迁移规律及瓶颈辨识策略[J]. 化工学报, 2023, 74(11): 4611-4621.

Figures/Tables 10

Fig.1 The schematic diagram of the interaction among units and the generation and elimination of bottleneck

Fig.2 A five-stream heat exchanger network

Table 1 The load-shift when CPC1 fluctuates

路径	换热设备
路径	E1	E2	E3	E4	HE1	HE2	CE1	CE2
DPP_C1-C1	0^③	0^③	0^③	0^③	- $Δ$ Q_HEN^①	0	0	0
DPP_C1-C3	0^③	- $Δ$ Q_HEN^②	0^③	$Δ$ Q_HEN^②	0	- $Δ$ Q_HEN^①	0	0
DPP_C1-H1	0^③	- $Δ$ Q_HEN^②	0^③	0^③	0	0	$Δ$ Q_HEN^①	0
DPP_C1-H2	- $Δ$ Q_HEN^②	0^③	0^③	0^③	0	0	0	$Δ$ Q_HEN^①

Table 1 The load-shift when CPC1 fluctuates

路径	换热设备
路径	E1	E2	E3	E4	HE1	HE2	CE1	CE2
DPP_C1-C1	0^③	0^③	0^③	0^③	- $Δ$ Q_HEN^①	0	0	0
DPP_C1-C3	0^③	- $Δ$ Q_HEN^②	0^③	$Δ$ Q_HEN^②	0	- $Δ$ Q_HEN^①	0	0
DPP_C1-H1	0^③	- $Δ$ Q_HEN^②	0^③	0^③	0	0	$Δ$ Q_HEN^①	0
DPP_C1-H2	- $Δ$ Q_HEN^②	0^③	0^③	0^③	0	0	0	$Δ$ Q_HEN^①

Fig.3 Rreqversusα curves

Fig.4 The trend chart of the total annual cost of the system with disturbance under different disturbance-response schemes

Fig.5 Anti-disturbance strategy identification diagram

Fig.6 Simplified HEN of the alkylation process from benzene to ethylbenzene

Fig.7 Change trend of Rreq

Fig.8 Economic variation diagram

Table 2 System variations when α changes to 0.8 and 1.2

扰动值α	响应对象	瓶颈位置	调整参数		节省年度总成本/(USD∙a^-1)
扰动值α	响应对象	瓶颈位置	ΔQ_RO /kW	ΔA_E_x /m²	节省年度总成本/(USD∙a^-1)
0.8	HE2	E2、HE2	941	5.9、22.2	15683.5
1.2	HE1	E3	-941	32.7	7892.9

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