Heat exchange equipment design method considering high efficiency, flexibility and cost

Abstract

The invention discloses a heat exchange equipment design method considering high efficiency, flexibility and cost, which comprises the following steps: firstly, establishing a full-working-condition dynamic thermodynamic model of a coal-fired power plant in a 20-100% load interval, and obtaining parameters such as a load fluctuation interval, a typical working condition proportion, fluid physical property parameters, a heat transfer capacity range, installation space limitation and equipment cost; taking the heat exchange area as a design variable, constructing a multi-target collaborative optimization model taking heat exchange equipment full working condition weighted average efficiency maximization, working condition switching response time minimization and comprehensive cost minimization as targets, and introducing an area constraint, a structure constraint and a dynamic response constraint; solving the model by adopting an improved non-dominated sorting genetic algorithm to obtain a multi-objective optimization scheme set; and finally, through feasibility analysis and comprehensive evaluation index calculation, an optimal scheme is screened out to determine the final heat exchange area. According to the method, through multi-target collaborative optimization, the high efficiency, flexibility and cost of the heat exchange equipment under the wide-load operation condition are effectively considered, and key technical support is provided for flexible peak regulation and energy efficiency improvement of a power plant.

Description

Technical Field

[0001] This invention relates to a design method for heat exchange equipment applicable to wide-load operation conditions in coal-fired power plants. Specifically, it relates to a multi-objective collaborative optimization design method for heat exchange area of ​​heat exchange equipment that takes into account flexible operation, efficient heat exchange, and total life cycle cost, aiming to achieve optimal comprehensive performance of the equipment throughout its entire life cycle. Background Technology

[0002] Driven by the "dual carbon" goals, coal-fired power plants need to participate extensively in grid peak shaving, resulting in their key heat exchange equipment operating under wide load and variable conditions for extended periods, ranging from 20% to 100% load. Traditional heat exchange equipment designs are typically based on rated operating conditions, making it difficult to adapt to the wide load and variable operating conditions required by deep peak shaving in coal-fired power plants, and failing to balance conflicting objectives under different operating conditions. However, existing heat exchange equipment design methods still primarily focus on a single rated operating condition, exhibiting fundamental flaws: at the modeling level, there is a lack of description of the dynamic thermodynamic characteristics across all operating conditions, and the impact of heat transfer coefficient decay on heat transfer efficiency under low load is not considered; at the objective level, static performance is prioritized while neglecting multi-objective coordination, and the coupling relationship between heat transfer coefficient and variable load response time is not established to optimize operational flexibility. Furthermore, economic analysis primarily focuses on initial investment, failing to incorporate the overall operating and maintenance costs throughout the equipment's lifecycle. This directly leads to poor heat transfer efficiency at low loads, insufficient heat exchange capacity at high loads, slow response during load switching, and poor overall lifecycle economics. Therefore, there is an urgent need for a design method for heat exchange equipment that can synergistically optimize thermal performance, operational flexibility, and life-cycle cost across all operating conditions. Summary of the Invention

[0003] To address the problems existing in the prior art, the present invention aims to provide a heat exchanger design method that considers efficiency, flexibility, and cost. By establishing a multi-objective optimization model covering all operating conditions, it solves the problem that fixed-structure heat exchangers struggle to simultaneously achieve high efficiency, high flexibility, and low cost under wide-load operating conditions. The goal is to achieve optimal overall performance of the equipment throughout its entire lifecycle.

[0004] To achieve the above objectives, the present invention employs the following technical solution: A design method for heat exchange equipment that considers efficiency, flexibility, and cost is applicable to the design of heat exchange area in coal-fired power plant heat exchange equipment. The heat exchange area is fixed and the structure is unchangeable after design. The method includes the following steps: S1: Establish a dynamic thermodynamic model of a coal-fired power plant under all operating conditions, and collect the core parameters related to the heat exchange equipment of the coal-fired power plant in the 20%-100% load range. The core parameters include basic parameters, technical parameters and economic parameters. The basic parameters include the load fluctuation range of the coal-fired power plant, multiple typical load conditions and the duration of each condition, the temperature, pressure and flow rate of the hot and cold fluids under each typical load, and the fluid properties that change with temperature, including specific heat capacity, thermal conductivity and viscosity. The technical parameters include the minimum threshold of heat exchange equipment efficiency under each typical load, the dynamic range of the heat transfer coefficient of the heat exchange equipment, the maximum allowable heat exchange area limited by the installation space of the heat exchange equipment, the specifications of the heat exchange tubes, and the specific heat capacity and density of the heat exchange tube wall material.

[0005] The economic parameters include the initial cost of the heat exchange equipment and the annual maintenance cost; S2: Based on heat exchange area A To design variables, a multi-objective collaborative optimization model is established, the model including: The objective function for thermal performance, used to maximize the overall energy efficiency under full load, is expressed as follows: ,in m The number represents the typical load condition. oh i For the first i The duration of each load condition accounts for a certain percentage and meets the following conditions. , e i (A) In order to achieve a heat exchange area of A Time i Heat transfer efficiency of heat exchange equipment under various load conditions; The operational flexibility objective function, used to minimize the dynamic response time under load changes, is expressed as follows: ,in t resp (A) The variable load response time, its value varies with the heat exchange area. A Increases with the increase of; The economic objective function, used to minimize the total cost over the entire lifecycle of the equipment, is expressed as follows: ,in C 1 represents the unit area cost of the heat exchange equipment. C op (A,t) The heat exchange area is A Time t Annual operating and maintenance costs n Design life of heat exchange equipment; S3: Define the constraints of the multi-objective collaborative optimization model, including: Area constraints: A min ≤ A ≤ A max ;inA min The critical area required to meet the minimum heat exchange requirement at the minimum load. A max The maximum permissible heat exchange area defined by the installation space of the heat exchange equipment; Structural constraints: A =N L π d; where N is the number of heat exchange tube rows, L is the length of a single tube, and d is the inner diameter of the heat exchange tube; Dynamic response constraints: t resp (A) ≤ t resp,max ,in t resp,max This is the maximum permissible variable load response time; this constraint, together with the area constraint, limits the heat transfer area. A The upper limit is set to prevent dynamic response timeouts due to excessive thermal inertia of the equipment; S4: An improved non-dominated sorting genetic algorithm is used to solve the multi-objective collaborative optimization model to obtain a Pareto optimal solution set. Each solution in the solution set represents a feasible heat transfer area design scheme that satisfies the constraints. S5: A comprehensive evaluation is performed on all feasible heat transfer area design schemes in the Pareto optimal solution set to determine the final heat transfer area design value; a comprehensive evaluation index is constructed: the comprehensive evaluation index... S(A) The calculation formula is: ,in These are the objective functions of thermodynamic performance. F 1. Objective function for operational flexibility F 2. Economic objective function F The normalized value of 3, K 1. K 2. K 3 is the comprehensive evaluation weight coefficient, and it satisfies K1+ K 2+ K 3=1; Calculate the comprehensive evaluation index of all feasible heat exchange area design schemes. S(A) And select the comprehensive evaluation index. S(A) The heat exchange area A corresponding to the scheme with the largest value is taken as the final design area of ​​the heat exchange equipment.

[0006] Furthermore, in step S2, the variable load response time t resp (A) Based on the inertia of the heat exchanger, the formula is derived as follows: ,in, m wallThe total mass of the heat exchange equipment. m wall With the heat exchange area A Positive correlation; c p,wall It is the specific heat capacity of the heat exchanger tube wall material; Δ T rep This refers to the change in heat exchanger tube wall temperature within the 20%-100% load range. Q diff (A) Total heat exchange during load changes.

[0007] Furthermore, in step S2, the first i Heat transfer efficiency of heat exchange equipment under various load conditions e i (A) The formula for calculation is: ,in, K i (A) For the first i Heat transfer coefficient under various load conditions; Δ t m,i It is the first i Logarithmic mean temperature difference of heat exchange equipment under various load conditions; Q max,i For the first i The theoretical maximum heat exchange under various load conditions.

[0008] Furthermore, in step S3, the critical area that satisfies the minimum load and minimum heat exchange is... A min Determined by the following formula: ,in Q min,20% The minimum heat exchange capacity required by the heat exchange equipment at 20% of rated load; K min,20% The minimum heat transfer coefficient at 20% of rated load; Δ t m,20% The logarithmic mean temperature difference between the hot and cold fluids at 20% of the rated load.

[0009] Furthermore, in step S5, the normalization rule is as follows: For maximizing the goal F 1. The formula for normalized values ​​is: For minimization objectives F 2. The formula for normalized values ​​is: For minimization objectives F 3. The formula for normalized values ​​is: ;in F 1,min and F1,max Among all feasible heat exchange area design schemes F The minimum and maximum values ​​of 1, where F 2,min and F 2,max Among all feasible heat exchange area design schemes F The minimum and maximum values ​​of 2, F 3,min and F 3,max For each of the feasible design schemes for all heat exchange areas F The minimum and maximum values ​​of 3.

[0010] Furthermore, in step S5, the comprehensive evaluation weight coefficient K 1. K 2. K The value of 3 satisfies K 1+ K 2+ K 3=1, and its specific value can be adjusted and configured according to the different power plants' priorities regarding efficiency, operational flexibility, and cost.

[0011] Furthermore, in step S4, the parameter settings of the improved non-dominated sorting genetic algorithm are optimized for the multi-condition characteristics of the 20%-100% load range.

[0012] Furthermore, the heat exchange equipment is suitable for peak-shaving operation of coal-fired power plants, including economizers, air preheaters, condensers, low-temperature economizers, and high-pressure heaters.

[0013] Compared with the prior art, the present invention has the following advantages: 1. This invention expands the design scope from a single rated operating condition to a full load range of 20%-100%. By establishing a dynamic thermodynamic model of a coal-fired power plant under all operating conditions, it ensures that the heat exchange equipment can maintain high heat transfer efficiency under wide load peak shaving operation, fundamentally solving the contradiction between low load efficiency decay and high load capacity insufficiency.

[0014] 2. This invention is the first to incorporate three key and mutually restrictive objectives—high efficiency, operational flexibility, and total life cycle cost—into a unified optimization model. By establishing a quantitative correlation between heat exchange area and equipment thermal inertia, heat transfer efficiency, and cost, it theoretically reveals their inherent laws and achieves synergistic optimization of the three in heat exchanger design.

[0015] 3. By introducing configurable comprehensive evaluation weight coefficients, this invention can flexibly adapt to the specific operating strategies and objectives of different power plants, greatly improving the practicality and applicability of the design method.

[0016] 4. Universal applicability and peak shaving compatibility: The method involved in this invention is universally applicable to key heat exchange equipment in coal-fired power plants, including economizers, air preheaters, condensers, low-temperature economizers, and high-pressure heaters. Its design results can effectively meet the deep peak shaving needs of the power grid and have broad engineering application prospects. Attached Figure Description

[0017] Figure 1 The present invention relates to a method for designing the area of ​​heat exchange equipment. Detailed Implementation

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0019] like Figure 1 As shown, after setting a heat exchange equipment area A, a dynamic thermodynamic model of a coal-fired power plant under full operating conditions is established. The core medium parameters of the heat exchange equipment within the 20%-100% load range of the coal-fired power plant are collected. The parameters include basic parameters, technical parameters and economic parameters.

[0020] Basic parameters include the load fluctuation range of the coal-fired power plant, multiple typical load conditions and the duration of each condition, the temperature, pressure, and flow rate of the hot and cold fluids under each typical load, and the fluid properties as a function of temperature, including specific heat capacity, thermal conductivity, and viscosity. Technical parameters include the minimum efficiency threshold of the heat exchange equipment under each typical load, the dynamic range of the heat transfer coefficient of the heat exchange equipment, the maximum allowable heat exchange area limited by the installation space of the heat exchange equipment, the specifications of the heat exchange tubes, and the specific heat capacity and density of the heat exchange tube wall material. Economic parameters include the initial cost of the heat exchange equipment and the annual maintenance cost.

[0021] After inputting the basic parameters, the heat exchange area is used as the basis. A To design variables, a multi-objective collaborative optimization model is established, the model including: The objective function for thermal performance, used to maximize the overall energy efficiency under full load, is expressed as follows: .in m The number represents the typical load condition. oh i For the first i The duration of each load condition accounts for a certain percentage and meets the following conditions. , e i (A) In order to achieve a heat exchange area of A Time i The heat transfer efficiency of heat exchange equipment under various load conditions.

[0022] The operational flexibility objective function, used to minimize the dynamic response time under load changes, is expressed as follows: .in tresp (A) The variable load response time, its value varies with the heat exchange area. A It increases as the value increases.

[0023] The economic objective function, used to minimize the total cost over the entire lifecycle of the equipment, is expressed as follows: .in C 1 represents the unit area cost of the heat exchange equipment. C op (A,t) The heat exchange area is A Time t Annual operating and maintenance costs n The design life of the heat exchange equipment.

[0024] Define the constraints for the multi-objective collaborative optimization model: Area constraints: A min ≤ A ≤ A max ;in A min The critical area required to meet the minimum heat exchange requirement at the minimum load. A max The maximum permissible heat exchange area is defined by the installation space of the heat exchange equipment.

[0025] Structural constraints: A =N L π d; where N is the number of heat exchange tube rows, L is the length of a single tube, and d is the inner diameter of the heat exchange tube.

[0026] Dynamic response constraints: t resp (A) ≤ t resp,max ,in t resp,max This is the maximum allowable variable load response time for the system; this constraint, together with the area constraint, limits the heat transfer area. A The upper limit is set to prevent dynamic response timeouts caused by excessive thermal inertia of the equipment.

[0027] If the constraints are not met, the area of ​​the heat exchange equipment should be redesigned.

[0028] If the constraints are met, the improved non-dominated sorting genetic algorithm is used to solve the multi-objective collaborative optimization model to obtain a Pareto optimal solution set. Each solution in the solution set represents a feasible heat exchange area design scheme that satisfies the constraints.

[0029] Next, a comprehensive evaluation of all feasible heat transfer area design schemes in the Pareto optimal solution set is performed to determine the final heat transfer area design value. Comprehensive evaluation indicators. S(A) The calculation formula is: .in These are the objective functions of thermodynamic performance. F 1. Objective function for operational flexibility F 2. Economic objective function F The normalized value of 3, K 1. K 2. K 3 is the comprehensive evaluation weight coefficient, and it satisfies K1+ K 2+ K 3=1. Calculate the comprehensive evaluation index for all feasible solutions. S(A) And select the comprehensive evaluation index. S(A) The heat exchange area A corresponding to the scheme with the largest value is taken as the final design area of ​​the heat exchange equipment.

[0030] When establishing a multi-objective collaborative optimization model, some parameters need to be explained. Variable load response time. t resp (A) The derivation formula is as follows: .in, m wall The total mass of the heat exchange equipment. m wall With the heat exchange area A Positive correlation; c p,wall It is the specific heat capacity of the heat exchanger tube wall material; Δ T rep This refers to the change in heat exchanger tube wall temperature within the 20%-100% load range. Q diff (A) Total heat exchange during load changes.

[0031] No. i Heat transfer efficiency of heat exchange equipment under various load conditions e i (A) The formula for calculation is: .in, K i (A) Let Δ be the heat transfer coefficient under the i-th load condition; t m,i It is the first i Logarithmic mean temperature difference of heat exchange equipment under various load conditions; Q max,i For the first i The theoretical maximum heat exchange under various load conditions.

[0032] Critical area to meet minimum heat exchange requirements at minimum load A min Determined by the following formula: .in Q min,20% The minimum heat exchange capacity required by the heat exchange equipment at 20% of rated load; K min,20% The minimum heat transfer coefficient at 20% of rated load; Δ t m,20% The logarithmic mean temperature difference between the hot and cold fluids at 20% of the rated load.

[0033] For maximizing the goal F 1. The formula for normalized values ​​is: For minimization objectives F 2. The formula for normalized values ​​is: For minimization objectives F 3. The formula for normalized values ​​is: .in F 1,min and F 1,max Among all feasible heat exchange area design schemes F The minimum and maximum values ​​of 1, where F 2,min and F 2,max Among all feasible heat exchange area design schemes F The minimum and maximum values ​​of 2, F 3,min and F 3,max Among all feasible heat exchange area design schemes F The minimum and maximum values ​​of 3.

[0034] The comprehensive evaluation weight coefficient K 1. K 2. K The value of 3 satisfies K 1+ K 2+ K The value is 3=1, and its specific value can be adjusted and configured according to the multi-condition characteristics of the 20%-100% load range and the different power plants' priorities for efficiency, operational flexibility, and cost, thereby ensuring that the optimization scheme is accurately matched with the operational needs of different power plants. Furthermore, the heat exchange equipment is suitable for peak-shaving operation of coal-fired power plants, including economizers, air preheaters, condensers, low-temperature economizers, or high-pressure heaters.

Claims

1. A design method for heat exchange equipment considering efficiency, flexibility, and cost, characterized in that, The method for designing the heat exchange area of ​​heat exchange equipment in coal-fired power plants, where the heat exchange area is fixed and the structure cannot be changed after design, includes the following steps: S1: Establish a dynamic thermodynamic model of a coal-fired power plant under all operating conditions, and collect the core parameters related to the heat exchange equipment of the coal-fired power plant in the 20%-100% load range. The core parameters include basic parameters, technical parameters and economic parameters. The basic parameters include the load fluctuation range of the coal-fired power plant, multiple typical load conditions and the duration of each condition, the temperature, pressure and flow rate of the hot and cold fluids under each typical load, and the fluid properties that change with temperature, including specific heat capacity, thermal conductivity and viscosity. The technical parameters include the minimum threshold of heat exchange equipment efficiency under each typical load, the dynamic range of heat transfer coefficient of heat exchange equipment, the maximum allowable heat exchange area limited by the installation space of heat exchange equipment, heat exchange tube specifications, and the specific heat capacity and density of heat exchange tube wall material. The economic parameters include the initial cost of the heat exchange equipment and the annual maintenance cost; S2: Based on heat exchange area A To design variables, a multi-objective collaborative optimization model is established, the model including: The objective function for thermal performance, used to maximize the overall energy efficiency under full load, is expressed as follows: ,in m The number represents the typical load condition. ω i For the first i The duration of each load condition accounts for a certain percentage and meets the following conditions. , ε i (A) In order to achieve a heat exchange area of A Time i Heat transfer efficiency of heat exchange equipment under various load conditions; The operational flexibility objective function, used to minimize the dynamic response time under load changes, is expressed as follows: ,in t resp (A) The variable load response time, its value varies with the heat exchange area. A Increases with the increase of; The economic objective function, used to minimize the total cost over the entire lifecycle of the equipment, is expressed as follows: ,in C 1 represents the unit area cost of the heat exchange equipment. C op (A,t) The heat exchange area is A Time t Annual operating and maintenance costs n Design life of heat exchange equipment; S3: Define the constraints of the multi-objective collaborative optimization model, including: Area constraints: A min ≤ A ≤ A max ;in A min The critical area required to meet the minimum heat exchange requirement at the minimum load. A max The maximum permissible heat exchange area defined by the installation space of the heat exchange equipment; Structural constraints: A =N L π d; where N is the number of heat exchange tube rows, L is the length of a single tube, and d is the inner diameter of the heat exchange tube; Dynamic response constraints: t resp (A) ≤ t resp,max ,in t resp,max This is the maximum permissible variable load response time; this constraint, together with the area constraint, limits the heat transfer area. A The upper limit is set to prevent dynamic response timeouts due to excessive thermal inertia of the equipment; S4: An improved non-dominated sorting genetic algorithm is used to solve the multi-objective collaborative optimization model to obtain a Pareto optimal solution set. Each solution in the solution set represents a feasible heat transfer area design scheme that satisfies the constraints. S5: A comprehensive evaluation is performed on all feasible heat transfer area design schemes in the Pareto optimal solution set to determine the final heat transfer area design value; a comprehensive evaluation index is constructed: the comprehensive evaluation index... S(A) The calculation formula is: ,in These are the objective functions of thermodynamic performance. F 1. Objective function for operational flexibility F 2. Economic objective function F The normalized value of 3, K 1. K 2. K 3 is the comprehensive evaluation weight coefficient, and it satisfies K1+ K 2+ K 3=1; Calculate the comprehensive evaluation index of all feasible heat exchange area design schemes. S(A) And select the comprehensive evaluation index. S(A) The heat exchange area A corresponding to the scheme with the largest value is taken as the final design area of ​​the heat exchange equipment.

2. The design method according to claim 1, characterized in that, In step S2, the variable load response time t resp (A) Based on the inertia of the heat exchanger, the formula is derived as follows: ,in, m wall The total mass of the heat exchange equipment. m wall With the heat exchange area A Positive correlation; c p,wall It is the specific heat capacity of the heat exchanger tube wall material; Δ T rep This refers to the change in heat exchanger tube wall temperature within the 20%-100% load range. Q diff (A) Total heat exchange during load changes.

3. The design method according to claim 1, characterized in that, In step S2, the first i Heat transfer efficiency of heat exchange equipment under various load conditions ε i (A) The formula for calculation is: ,in, K i (A) For the first i Heat transfer coefficient under various load conditions; Δ t m,i It is the first i Logarithmic mean temperature difference of heat exchange equipment under various load conditions; Q max,i For the first i The theoretical maximum heat exchange under various load conditions.

4. The design method according to claim 1, characterized in that, In step S3, the critical area that satisfies the minimum load and minimum heat exchange is determined. A min Determined by the following formula: ,in Q min,20% The minimum heat exchange capacity required by the heat exchange equipment at 20% of rated load; K min,20% The minimum heat transfer coefficient at 20% of rated load; Δ t m,20% The logarithmic mean temperature difference between the hot and cold fluids at 20% of the rated load.

5. The design method according to claim 1, characterized in that, In step S5, the normalization rule is as follows: For maximizing the goal F 1. The formula for normalized values ​​is: For minimization objectives F 2. The formula for normalized values ​​is: For minimization objectives F 3. The formula for normalized values ​​is: ;in F 1,min and F 1,max Among all feasible heat exchange area design schemes F The minimum and maximum values ​​of 1, where F 2,min and F 2,max Among all feasible heat exchange area design schemes F The minimum and maximum values ​​of 2, F 3,min and F 3,max For each of the feasible design schemes for all heat exchange areas F The minimum and maximum values ​​of 3.

6. The design method according to claim 1, characterized in that, In step S5, the comprehensive evaluation weight coefficient K 1. K 2. K The value of 3 satisfies K 1+ K 2+ K 3=1, and its specific value can be adjusted and configured according to the different power plants' priorities regarding efficiency, operational flexibility, and cost.

7. The design method according to claim 1, characterized in that, In step S4, the parameter settings of the improved non-dominated sorting genetic algorithm are optimized for the multi-condition characteristics of the 20%-100% load range.

8. The design method according to claim 1, characterized in that, The heat exchange equipment is suitable for peak-shaving operation in coal-fired power plants, including economizers, air preheaters, condensers, low-temperature economizers, and high-pressure heaters.

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