CN114547823B - Heat exchange network optimization design method comprising phase-change flow strands - Google Patents

Abstract

An optimization design method for a heat exchange network containing phase-change flow strands belongs to the field of industrial heat exchange network design. The steps are as follows: 1) Extracting technological parameters and physical property data of the flow; 2) Judging the type of the stream; 3) Dividing the phase flow into a plurality of sections according to characteristics of the phase flow Wen Hantu, and respectively determining the heat capacity flow rate of each section; 4) Establishing a mixed integer nonlinear programming model: the mixed integer nonlinear programming model comprises an objective function, a flow heat balance constraint, each stage heat balance constraint, a public engineering heat balance constraint, a heat exchange quantity boundary constraint, a temperature difference constraint and a temperature feasibility constraint; 5) Initializing model parameters; 6) And (3) solving the model of the optimization problem according to the mixed integer nonlinear programming model established in the step (4) and the model parameters initialized in the step (5) to obtain the heat exchange network after optimization design. The phase-change heat exchange network optimization design can be realized, so that the energy utilization rate of the industrial process is improved, the production cost of the industrial process is reduced, and the energy is saved and the consumption is reduced.

Description

Heat exchange network optimization design method comprising phase-change flow strands

Technical Field

The invention belongs to the field of industrial heat exchange network design, and particularly relates to a heat exchange network optimization design method comprising phase-change flow strands.

Background

Energy is the material basis upon which human society depends for survival and development. With the rapid development of world economy and the increase of population, energy shortage has become an important factor for restricting the economic development and the living standard of people. The optimal design of the industrial process heat exchange network is an important way for realizing energy conservation, the process realizes the recovery of the energy in the system to the greatest extent through reasonable matching between cold and hot streams, and then the public engineering system is utilized for ensuring the heat exchange requirements of all streams in the whole production process, so that the heat exchange network is finally formed. Therefore, the optimal design of the heat exchange network is beneficial to improving the energy utilization rate and reducing the production cost, and has important significance.

Phase change is a common heat transfer form in industrial processes, and can be divided into isothermal phase change and non-isothermal phase change, and the phenomenon of the phase change is widely applied to stream heat exchange in typical industrial processes such as petrochemical industry, chemical industry, gas processing, low temperature, cryogenic industry and the like. However, the phase change process of the stream is often accompanied by a change in its heat capacity, even abrupt, which results in an enthalpy change of the phase stream that is difficult to describe in the optimal design of the heat exchange network. In the prior art, the heat exchange network optimization design generally adopts the assumption that the heat capacity of a flow is constant to describe the enthalpy change of a phase flow, and the assumption easily leads to larger deviation between the optimization design result of the heat exchange network and the industrial reality, and even possibly leads to that the designed heat exchange network cannot meet the heat exchange requirement of the actual process. At present, no optimal design method for the heat exchange network comprising isothermal phase change and non-isothermal phase change flows is reported at home and abroad.

Disclosure of Invention

The invention aims to provide the heat exchange network optimization design method containing the phase-change flow strands, which can process isothermal phase flow strands and non-isothermal phase flow strands simultaneously, realize phase-change heat exchange network optimization, further improve energy utilization rate, reduce industrial process production cost, save energy and reduce consumption.

The invention comprises the following steps:

1) Extracting technological parameters and physical property data of the flow: the flow is divided into a process flow and a public engineering flow, and the process parameters and physical property data comprise inlet and outlet temperatures, heat transfer coefficients, mass flow rates, enthalpies and specific heat capacities of the flow;

2) Judging the flow strand type: the flow comprises two types of phase flow and non-phase flow, wherein the phase flow is divided into isothermal phase flow and non-isothermal phase flow;

3) Phase-change strand segmentation: dividing the phase flow into a plurality of sections according to characteristics of the phase flow Wen Hantu, and respectively determining the heat capacity flow rate of each section;

4) Establishing a mixed integer nonlinear programming model: the mixed integer nonlinear programming model comprises an objective function, a flow heat balance constraint, each stage heat balance constraint, a public engineering heat balance constraint, a heat exchange quantity boundary constraint, a temperature difference constraint and a temperature feasibility constraint;

5) Initializing model parameters: the initialization model parameters comprise minimum heat transfer temperature difference, heat exchange network progression, maximum allowable heat exchange quantity of the heat exchanger, and heat exchanger and public engineering cost parameters;

6) And (3) solving the model of the optimization problem according to the mixed integer nonlinear programming model established in the step (4) and the model parameters initialized in the step (5) to obtain the heat exchange network after optimization design.

In the step 3), the phase change flow is divided into a plurality of intervals corresponding to a gas phase area, a gas-liquid two-phase area and a liquid phase area respectively, and the heat capacity can be regarded as different constants in the intervals;

The equivalent heat capacity for the two-phase region of the isothermal phase stream is defined by the following equation:

Where C ^e represents the equivalent heat capacity of the two-phase region of the stream, Q _λ represents the phase change enthalpy of the stream, and M represents the mass flow rate of the stream.

In step 4), the objective function is:

Wherein TAC represents the annual total cost of the heat exchange network; q _CU,i represents the heat exchange capacity of the hot stream and the cold utility; q _HU,j represents the cold stream and heat utility heat exchange capacity; c _CU、C_HU represents cold and hot utility costs; CF _E、CF_CU、CF_HU represents the fixed cost of the heat exchanger, cooler, and heater, respectively; z _i,j,k、Z_CU,i、Z_HU,j represents a binary variable for judging whether the heat exchanger, the cooler and the heater exist, if the heat exchanger exists, the value is 1, otherwise, the value is 0; CA _E、CA_CU、CA_HU represents the area cost of the heat exchanger, cooler, heater; a _i,j,k、A_CU,i、A_HU,j represents the areas of the heat exchanger, the cooler and the heater; beta represents an area cost index.

In step 4), the flow heat balance constraints include flow heat balance constraints, cold flow heat balance constraints;

the heat balance constraint of the heat flow strand is as follows:

Wherein TIN _i represents the inlet temperature of the hot stream; TOUT _i represents the outlet temperature of the hot stream; t _i,f1、T_i,f2 represents the region division temperature of the heat flow strand respectively; f _i ^g、F_i ^p、F_i ^l represents the heat capacity flow rate of the heat flow strand in the gas phase region, the heat capacity flow rate of the heat flow strand in the two-phase region and the heat capacity flow rate of the heat flow strand in the liquid phase region respectively; q _i,j,k represents the heat exchange amount of the hot stream and the cold stream at each stage;

The cold flow stream heat balance constraint is:

Wherein TIN _j represents the inlet temperature of the cold stream; TOUT _j represents the outlet temperature of the cold stream; t _j,f1、T_j,f2 represents the region division temperature of the cold stream, respectively; representing the gas phase zone heat capacity rate, the two phase zone heat capacity rate and the liquid phase zone heat capacity rate of the cold stream, respectively.

In step 4), each of the stage heat balance constraints is:

Wherein t _i,k represents the kth stage temperature of the hot stream; y _1,i,k,…,Y_8,i,k is a binary variable, when t _i,k+1≥T_i,f1, Y _1,i,k =1 and Y _2,i,k =0, otherwise Y _1,i,k =0 and Y _2,i,k =1; y _3,i,k =1 and Y _4,i,k =0 when t _i,k+1≥T_i,f2, else Y _3,i,k =0 and Y _4,i,k =1; y _5,i,k =1 and Y _6,i,k =0 when t _i,k≥T_i,f2, else Y _5,i,k =0 and Y _6,i,k =1; y _7,i,k =1 and Y _8,i,k =0 when t _i,k≥T_i,f1, else Y _7,i,k =0 and Y _8,i,k =1;

each stage of heat balance constraint of the cold stream is:

Wherein t _j,k represents the kth stage temperature of the cold stream; y _1,j,k,…,Y_8,j,k is a binary variable, the principle of which is similar to Y _1,i,k,…,Y_8,i,k.

In step 4), the utility thermal balance constraint is:

The utility heat balance constraint principle is similar to the heat balance constraint of each stage of the stream.

The heat exchange quantity boundary constraint is as follows:

In the method, in the process of the invention, Representing the maximum allowable heat exchange amount;

the temperature difference constraint is as follows:

θ_i,j,k≤t_i,k-t_j,k+γ(1-Z_i,j,k)

θ_i,j,k+1≤t_i,k+1-t_j,k+1+γ(1-Z_i,j,k)

θ_CU,i≤t_i,nok+1-TOUT_CU+γ(1-Z_CU,i)

θ_HU,j≤TOUT_HU-t_j,1+γ(1-Z_HU,j)

θ_i,j,k≥ΔT_min

Wherein, theta _i,j,k、θ_CU,i、θ_HU,j represents a single-side heat transfer temperature difference; deltaT _min represents the minimum heat transfer temperature difference; gamma represents a sufficiently large positive number.

The temperature feasibility constraint is:

TIN_i＝t_i,1

TIN_j＝t_j,nok+1

t_i,k≥t_i,k+1

t_j,k≥t_j,k+1

TOUT_i≤t_i,nok+1

TOUT_j≥t_j,1。

Compared with the prior art, the invention has the following advantages: 1) Based on the sectional characteristics of the phase-change flow strand temperature enthalpy diagram, the heat capacity change and mutation are reasonably described by adopting a heat capacity sectional mode, so that the optimal design result which is more in line with the actual heat exchange network can be obtained. 2) In heat exchange network design optimization, both isothermal and non-isothermal phase streams can be processed. 3) The invention can realize the optimal design of the phase-change heat exchange network, so as to improve the energy utilization rate of the industrial process, reduce the production cost of the industrial process and achieve the aims of energy conservation and consumption reduction.

Drawings

Fig. 1 is a structural diagram of a heat exchange network according to embodiment 1 of the present invention.

Fig. 2 is a structural diagram of a heat exchange network according to embodiment 2 of the present invention.

Detailed Description

The invention is further described below with reference to the drawings and examples.

The embodiment of the invention comprises the following steps:

Step 1: extracting process parameters and physical property data of a flow, wherein the flow is divided into a process flow and a public engineering flow, and the process parameters and the physical property data comprise flow inlet and outlet temperature, heat transfer coefficient, mass flow rate, enthalpy and specific heat capacity;

Step 2: judging the types of the flow strands, wherein the flow strands comprise two types of phase-change flow strands and non-phase-change flow strands, and the phase-change flow strands can be further divided into isothermal phase-change flow strands and non-isothermal phase-change flow strands;

Step 3: segmenting the phase flow, dividing the phase flow into a plurality of intervals corresponding to a gas phase area, a gas-liquid two-phase area and a liquid phase area respectively according to characteristics of the phase flow Wen Hantu, and further determining heat capacity flow rate of each interval; wherein the heat capacity is considered as a different constant in these intervals; for isothermal phase current strands, the equivalent heat capacity of the two-phase region is defined by the following equation:

wherein C ^e represents the equivalent heat capacity of the two-phase region of the stream, Q _λ represents the phase change enthalpy of the stream, and M represents the mass flow rate of the stream;

step 4: establishing a mixed integer nonlinear programming model, wherein the mixed integer nonlinear programming model comprises an objective function, a flow heat balance constraint, each stage heat balance constraint, a public engineering heat balance constraint, a heat exchange quantity boundary constraint, a temperature difference constraint and a temperature feasibility constraint; wherein the objective function is:

Wherein TAC represents the annual total cost of the heat exchange network; q _CU,i represents the heat exchange capacity of the hot stream and the cold utility; q _HU,j represents the cold stream and heat utility heat exchange capacity; c _CU、C_HU represents cold and hot utility costs, respectively; CF _E、CF_CU、CF_HU represents the fixed cost of the heat exchanger, cooler, and heater, respectively; z _i,j,k、Z_CU,i、Z_HU,j represents binary variables for judging whether the heat exchanger, the cooler and the heater exist or not respectively, wherein the heat exchanger exists and has a value of 1, otherwise, the value of 0; CA _E、CA_CU、CA_HU represents the area cost of the heat exchanger, cooler and heater; a _i,j,k、A_CU,i、A_HU,j respectively represents the areas of the heat exchanger, the cooler and the heater; beta represents an area cost index.

The heat balance constraint of the heat flow strand is as follows:

Wherein TIN _i represents the inlet temperature of the hot stream; TOUT _i represents the outlet temperature of the hot stream, T _i,f1、T_i,f2 represents the region split temperature of the hot stream, respectively; f _i ^g、F_i ^p、F_i ^l represents the gas phase region heat capacity rate, the two phase region heat capacity rate and the liquid phase region heat capacity rate of the hot stream respectively; q _i,j,k represents the heat exchange amount of the hot stream and the cold stream at each stage;

The cold flow stream heat balance constraints are:

Wherein TIN _j represents the inlet temperature of the cold stream, TOUT _j represents the outlet temperature of the cold stream, T _j,f1、T_j,f2 represents the zone split temperature of the cold stream respectively, Representing the gas phase zone heat capacity rate, the two phase zone heat capacity rate and the liquid phase zone heat capacity rate of the cold stream, respectively;

The heat balance constraint of each stage of the heat flow strand is as follows:

Wherein t _i,k represents the kth stage temperature of the hot stream; y _1,i,k,…,Y_8,i,k is a binary variable, when t _i,k+1≥T_i,f1, Y _1,i,k =1 and Y _2,i,k =0, otherwise Y _1,i,k =0 and Y _2,i,k =1; y _3,i,k =1 and Y _4,i,k =0 when t _i,k+1≥T_i,f2, else Y _3,i,k =0 and Y _4,i,k =1; y _5,i,k =1 and Y _6,i,k =0 when t _i,k≥T_i,f2, else Y _5,i,k =0 and Y _6,i,k =1; y _7,i,k =1 and Y _8,i,k =0 when t _i,k≥T_i,f1, else Y _7,i,k =0 and Y _8,i,k =1;

The heat balance constraints for each stage of the cold stream are:

Wherein t _j,k represents the kth stage temperature of the cold stream; y _1,j,k,…,Y_8,j,k is a binary variable, the principle of which is similar to Y _1,i,k,…,Y_8,i,k.

The utility heat balance constraint principle is similar to the heat balance constraint of each stage of the stream, which is:

The boundary constraint of the heat exchange amount is as follows:

In the method, in the process of the invention, Representing the maximum allowable heat exchange amount;

The temperature approach method is constrained as follows:

θ_i,j,k≤t_i,k-t_j,k+γ(1-Z_i,j,k)

θ_i,j,k+1≤t_i,k+1-t_j,k+1+γ(1-Z_i,j,k)

θ_CU,i≤t_i,nok+1-TOUT_CU+γ(1-Z_CU,i)

θ_HU,j≤TOUT_HU-t_j,1+γ(1-Z_HU,j)

θ_i,j,k≥ΔT_min

Wherein, theta _i,j,k、θ_CU,i、θ_HU,j represents a single-side heat transfer temperature difference; deltaT _min represents the minimum heat transfer temperature difference; gamma represents a sufficiently large positive number.

The temperature feasibility constraints are:

TIN_i＝t_i,1

TIN_j＝t_j,nok+1

t_i,k≥t_i,k+1

t_j,k≥t_j,k+1

TOUT_i≤t_i,nok+1

TOUT_j≥t_j,1

Step 5: initializing model parameters: the initialization model parameters comprise minimum heat transfer temperature difference, heat exchange network progression, maximum allowable heat exchange quantity of the heat exchanger, and heat exchanger and public engineering cost parameters;

Step 6: according to the mathematical model established in the step (4) and the model parameters initialized in the step (5), solving the model to obtain an optimally designed heat exchange network;

Example 1

In this embodiment, the specific steps are as follows:

Step 1, extracting process parameters and physical property data of the stream, wherein the process parameters and physical property data in the embodiment are shown in table 1, and the stream heat capacity flow rate is the product of the stream heat capacity and the stream mass flow rate.

TABLE 1 Process parameters and physical Property data for streams

Step 2, judging the flow strand type, in this embodiment, the hot flow strands H1 and H3 and the cold flow strands C1, C2 and C4 belong to isothermal phase change flow strands, and the hot flow strands H2 and H4 and the cold flow strand C3 belong to non-phase change flow strands.

Step 3, the phase-change flow is segmented, in this embodiment, the hot flow H1 is divided into two sections (gas phase section and two phase section), the hot flow H1 and the cold flow C3, C4 are divided into one section (two phase section), the hot flow H3 is divided into three sections (gas phase section, two phase section, liquid phase section), and the heat capacity rates of the sections are shown in table 1.

And 4, establishing a mixed integer nonlinear programming model in the embodiment.

Step 5, initializing model parameters, in this embodiment, the minimum approach temperature is set to 5K, the number of heat exchange network stages is set to 4, the maximum allowable heat exchange capacity of the heat exchanger is set to 16000kW, the heat exchanger cost formula is 379.5 (A) ^0.65 dollars/year (A represents heat exchanger area), the hot utility cost is 100 dollars/kW, and the cold utility cost is 10 dollars/kW.

And 6, solving the model according to the mathematical model established in the step 4 and the model parameters initialized in the step 5 in the embodiment, wherein the heat exchange network after optimization design is shown in the figure 1, and the annual total cost of the heat exchange network is 114,291 dollars/year.

Example 2

In this embodiment, the specific steps are as follows:

step 1, extracting process parameters and physical property data of the stream, wherein the process parameters and physical property data in the embodiment are shown in table 2, and the stream heat capacity flow rate is the product of the stream heat capacity and the stream mass flow rate.

TABLE 2 Process parameters and physical Property data for streams

And 2, judging the flow type, wherein in the embodiment, the hot flow H4 is a non-isothermal phase flow, and other flows belong to non-phase flow.

Step 3, the phase-change flow is segmented, in this embodiment, the non-isothermal phase-change heat flow H4 is divided into two sections (gas phase region and two phase region), and the heat capacity rate of each section is shown in table 1.

And 4, establishing a mixed integer nonlinear programming model in the embodiment.

Step 5, initializing model parameters, in this embodiment, the minimum approach temperature is set to 12K, the number of heat exchange network stages is set to 6, the maximum allowable heat exchange capacity of the heat exchanger is set to 8000kW, the heat exchanger cost formula is 2,638+211 (A) ^0.8 U.S. dollars/year (A represents heat exchanger area), the heat utility HU1 cost is 134 U.S. dollars/kW, the heat utility HU2 cost is 90 U.S. dollars/kW, and the cold utility cost is 6.7 U.S. dollars/kW.

And 6, solving the model according to the mathematical model established in the step 4 and the model parameters initialized in the step 5 in the embodiment, wherein the annual total cost of the heat exchange network after optimization design is 2,296,873 dollars/year and is 1.9% compared with that of the conventional heat exchange network as shown in fig. 2.

The invention can process the types of the phase flow strands, including isothermal phase flow strands and non-isothermal phase flow strands, divide the phase flow strands into a plurality of intervals according to the characteristics of the phase flow strands Wen Hantu and respectively correspond to a gas phase area, a gas-liquid two-phase area and a liquid phase area of the phase flow strands, further establish a mixed integer nonlinear programming model, and obtain an optimized structure comprising the phase flow strand heat exchange network by solving the model by taking the minimum annual total cost of the heat exchange network as an objective function.

Claims (2)

1. The heat exchange network optimization design method containing the phase-change flow strand is characterized by comprising the following steps of:

1) Extracting technological parameters and physical property data of the flow: the flow is divided into a process flow and a public engineering flow, and the process parameters and physical property data comprise inlet and outlet temperatures, heat transfer coefficients, mass flow rates, enthalpies and specific heat capacities of the flow;

2) Judging the flow strand type: the flow comprises two types of phase flow and non-phase flow, wherein the phase flow is divided into isothermal phase flow and non-isothermal phase flow;

3) Phase-change strand segmentation: dividing the phase flow into a plurality of sections according to characteristics of the phase flow Wen Hantu, and respectively determining the heat capacity flow rate of each section;

4) Establishing a mixed integer nonlinear programming model: the mixed integer nonlinear programming model comprises an objective function, a flow heat balance constraint, each stage heat balance constraint, a public engineering heat balance constraint, a heat exchange quantity boundary constraint, a temperature difference constraint and a temperature feasibility constraint;

The objective function is:

Wherein TAC represents the annual total cost of the heat exchange network; q _CU,i represents the heat exchange capacity of the hot stream and the cold utility; q _HU,j represents the cold stream and heat utility heat exchange capacity; c _CU、C_HU represents cold and hot utility costs; CF _E、CF_CU、CF_HU represents the fixed cost of the heat exchanger, cooler, and heater, respectively; z _i,j,k、Z_CU,i、Z_HU,j represents a binary variable for judging whether the heat exchanger, the cooler and the heater exist, if the heat exchanger exists, the value is 1, otherwise, the value is 0; CA _E、CA_CU、CA_HU represents the area cost of the heat exchanger, cooler, heater; a _i,j,k、A_CU,i、A_HU,j represents the areas of the heat exchanger, the cooler and the heater; beta represents an area cost index;

the flow heat balance constraint, wherein the hot flow heat balance constraint is:

Wherein TIN _i represents the inlet temperature of the hot stream; TOUT _i represents the outlet temperature of the hot stream; t _i,f1、T_i,f2 represents the region division temperature of the heat flow strand respectively; f _i ^g、F_i ^p、F_i ^l represents the heat capacity flow rate of the heat flow strand in the gas phase region, the heat capacity flow rate of the heat flow strand in the two-phase region and the heat capacity flow rate of the heat flow strand in the liquid phase region respectively; q _i,j,k represents the heat exchange amount of the hot stream and the cold stream at each stage;

The cold flow stream heat balance constraints are:

Wherein TIN _j represents the inlet temperature of the cold stream; TOUT _j represents the outlet temperature of the cold stream; t _j,f1、T_j,f2 represents the region division temperature of the cold stream, respectively; representing the gas phase zone heat capacity rate, the two phase zone heat capacity rate and the liquid phase zone heat capacity rate of the cold stream, respectively;

each stage of heat balance constraint is that:

Wherein t _i,k represents the kth stage temperature of the hot stream; y _1,i,k,…,Y_8,i,k is a binary variable, when t _i,k+1≥T_i,f1, Y _1,i,k =1 and Y _2,i,k =0, otherwise Y _1,i,k =0 and Y _2,i,k =1; y _3,i,k =1 and Y _4,i,k =0 when t _i,k+1≥T_i,f2, else Y _3,i,k =0 and Y _4,i,k =1; y _5,i,k =1 and Y _6,i,k =0 when t _i,k≥T_i,f2, else Y _5,i,k =0 and Y _6,i,k =1; y _7,i,k =1 and Y _8,i,k =0 when t _i,k≥T_i,f1, else Y _7,i,k =0 and Y _8,i,k =1;

each stage of heat balance constraint of the cold stream is:

Wherein t _j,k represents the kth stage temperature of the cold stream; y _1,j,k,…,Y_8,j,k is a binary variable, the principle of which is similar to Y _1,i,k,…,Y_8,i,k;

the utility heat balance constraint is:

(T_i,f2-TOUT_i)[F_i ^g·Y_1,i,k+F_i ^p·Y_2,i,k·Y_3,i,k+F_i ^l·Y_4,i,k]+(T_i,f1-T_i,f2)[F_i ^g·Y_1,i,k+F_i ^p·Y_2,i,k·Y_5,i,k+F_i ^l·Y_6,i,k]+(t_j,NOK+1-T_i,f1)[F_i ^g·Y_7,i,k+F_i ^p·Y_8,i,k·Y_5,i,k+F_i ^l·Y_6,i,k]＝Q_CU,i

The utility heat balance constraint principle is similar to the heat balance constraint of each stage of the stream;

The heat exchange quantity boundary constraint is as follows:

In the method, in the process of the invention, Representing the maximum allowable heat exchange amount;

the temperature difference constraint is as follows:

θ_i,j,k≤t_i,k-t_j,k+γ(1-Z_i,j,k)

θ_i,j,k+1≤t_i,k+1-t_j,k+1+γ(1-Z_i,j,k)

θ_CU,i≤t_i,nok+1-TOUT_CU+γ(1-Z_CU,i)

θ_HU,j≤TOUT_HU-t_j,1+γ(1-Z_HU,j)

θ_i,j,k≥ΔT_min

wherein, theta _i,j,k、θ_CU,i、θ_HU,j represents a single-side heat transfer temperature difference; deltaT _min represents the minimum heat transfer temperature difference; gamma represents a sufficiently large positive number;

the temperature feasibility constraint is:

TIN_i＝t_i,1

TIN_j＝t_j,nok+1

t_i,k≥t_i,k+1

t_j,k≥t_j,k+1

TOUT_i≤t_i,nok+1

TOUT_j≥t_j,1

5) Initializing model parameters: the initialization model parameters comprise minimum heat transfer temperature difference, heat exchange network progression, maximum allowable heat exchange quantity of the heat exchanger, and heat exchanger and public engineering cost parameters;

6) And (3) solving the model of the optimization problem according to the mixed integer nonlinear programming model established in the step (4) and the model parameters initialized in the step (5) to obtain the heat exchange network after optimization design.

2. The method for optimizing design of heat exchange network including phase-change flow as claimed in claim 1, wherein in step 3), the phase-change flow is divided into a plurality of sections corresponding to gas-phase section, gas-liquid two-phase section and liquid-phase section, respectively, and the heat capacity is regarded as different constants in the sections;

The equivalent heat capacity for the two-phase region of the isothermal phase stream is defined by the following equation:

Where C ^e represents the equivalent heat capacity of the two-phase region of the stream, Q _λ represents the phase change enthalpy of the stream, and M represents the mass flow rate of the stream.