Fuzzy comprehensive evaluation method for scheme comparison and selection of natural gas pressure energy utilization system

Abstract

The invention discloses a fuzzy comprehensive evaluation method for scheme comparison and selection of a natural gas pressure energy utilization system, and relates to the technical field of energy utilization. The method comprises the following specific steps: providing an evaluation index system from four aspects of system efficiency, operation management, economic benefit and environmental protection for a natural gas pressure energy utilization system, and respectively calculating data values of various evaluation indexes in a primary expansion scheme and a secondary expansion scheme based on monitoring data of a natural gas purification plant system scheme; then constructing a hierarchical structure model of the evaluation index system by using an analytic hierarchy process, and determining an initial weight of each index according to expert experience; correcting the initial weight based on the information entropy of each index data by using an entropy weight method to obtain a combined weight; and finally, establishing an evaluation grade set by utilizing a fuzzy evaluation method based on the combined weight, and calculating a comprehensive score of a system scheme to realize effect evaluation and scheme comparison and selection. According to the invention, comprehensive and scientific comprehensive evaluation of the natural gas pressure energy utilization system can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of energy utilization, and in particular to a fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions. Background Art

[0002] As the consumption level of countries around the world increases, the global energy consumption structure is gradually transforming towards low-carbon, environmentally friendly and sustainable development, while traditional fossil energy will bring about a large amount of greenhouse gas emissions. As an efficient and clean energy, natural gas has become an important strategic measure for many countries to seek to ensure energy supply security and reduce pollutant emissions due to its high calorific value, large reserves, easy transportation, and few combustion pollutants. With the increasing demand for energy in my country and the country's increasing attention to energy conservation and emission reduction, my country's natural gas consumption has increased year by year, prompting the country to accelerate the construction of natural gas pipelines. Using natural gas pressure energy for power generation and refrigeration can not only effectively recover energy and improve energy utilization, but also reduce the overall energy consumption of the system and achieve energy conservation and emission reduction goals.

[0003] At present, the technology of natural gas pressure energy recovery and utilization is mainly reflected in power generation and refrigeration. For power generation technology, the expansion machine is mainly used to replace the pressure regulating valve, and the natural gas is naturally expanded to drive the shaft to generate mechanical energy, and then the mechanical energy is converted into other required forms of energy, which is usually used to generate electricity. For refrigeration technology, the cold energy of low-temperature natural gas after pressure reduction can be used to cool the lubricating oil of the unit, the cooling water of the inverter, the cooling of the drive motor and the liquefaction of natural gas. Making full use of the cold energy of natural gas can reduce the risk of freezing and leakage of pipelines due to sudden drops in natural gas temperature.

[0004] At present, the research on the evaluation index system is mainly aimed at the integrated energy system, and there are few evaluation studies on the utilization of natural gas pressure energy. At present, the research on the evaluation of the benefits of natural gas pressure energy utilization still has the problems of one-sided evaluation indicators and single evaluation methods. Literature 1 (Yao Li, Luo Minhai, Xiao Jun, et al. Technical and economic evaluation system and index design of natural gas industry [J]. Natural Gas Technology and Economy, 2019, 13 (1): 71-74.) only focuses on the single link of economic benefits in the process of natural gas pressure energy utilization, and lacks an overall analysis of the equipment performance, operation benefits and other derivative benefits of the entire system. Reference 2 (MA XD, SUN Q, ZHANG JM, et al. Research on comprehensive evaluation system of urban energy data based on AHP method [C] / / IOP Conference Series: Materials Science and Engineering. IOP Publishing, 2018, 382 (5): 05-2009.) only uses the basic analytic hierarchy process to obtain the index weights. The evaluation method is single, the system operation characteristics are not considered, and it is highly subjective. The evaluation results cannot accurately reflect the actual operation status of the entire system. Therefore, it is of great significance to consider multiple aspects of the natural gas pressure energy utilization system and establish a complete evaluation index and comprehensive evaluation method. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a fuzzy comprehensive evaluation method for the selection of natural gas pressure energy utilization system schemes. The natural gas pressure energy utilization system uses natural gas pressure energy to generate electricity through a turbine expander, uses a heat exchanger, a circulating water network and a unit lubricating oil system to recover cold energy, improves energy utilization efficiency, and makes comprehensive use of pressure energy. Then, comprehensive evaluation indicators of the natural gas pressure energy utilization system are proposed from four aspects: system efficiency, operation management, economic benefits and environmental protection, and a hierarchical analysis method-entropy weight method-fuzzy evaluation method is used for comprehensive evaluation to provide a more comprehensive and scientific comprehensive evaluation result.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions specifically includes the following steps:

[0008] S1. Collect monitoring data of the pressure energy utilization system of the natural gas purification plant, and calculate the data values ​​of various evaluation indicators in the primary expansion and secondary expansion schemes of the natural gas pressure energy utilization system based on the monitoring data and the energy analysis model;

[0009] The natural gas pressure energy utilization system includes a pressure energy power generation system and a cold energy utilization system. The pressure energy power generation system includes a turbine expander, a gear box, a coupling and a generator; the cold energy utilization system includes a heat exchanger, a circulating water transmission pipeline network, a unit lubricating oil system and a water storage tank;

[0010] The first-stage expansion scheme includes a preheater and a turbine expander, and adopts a preheating followed by expansion process;

[0011] The two-stage expansion scheme includes a preheater, two turbine expanders, and an intermediate heating process.

[0012] S2. According to the analytic hierarchy process, the evaluation index system of the natural gas pressure energy utilization system is decomposed into three levels, namely, the target level, the criterion level and the index level; the target level is the evaluation index system of the natural gas pressure energy utilization system; the criterion level includes four evaluation criteria, namely, system efficiency, operation management, economic benefits and environmental protection; the index level includes all evaluation indicators under different evaluation criteria classifications;

[0013] The evaluation indexes of the system efficiency include power generation, expansion generator set Efficiency, heat exchanger efficiency, annual power generation and annual cooling energy saving; the evaluation indicators under the operation management include technical transformation difficulty and operation and maintenance difficulty; the evaluation indicators under the economic benefit include power generation benefit, cooling benefit, equipment investment, annual operation and maintenance cost and investment payback period; the evaluation indicators under the environmental protection include CO2 emission reduction, NO x Emission reduction, SO2 emission reduction and emission reduction benefits;

[0014] S3, according to the classification results, the initial weights of various evaluation indicators are calculated by using the analytic hierarchy process; the initial weights of various evaluation indicators calculated by the analytic hierarchy process are firstly based on expert experience to establish a judgment matrix between various indicators, criteria and objectives, then extract characteristic vectors from the judgment matrix, calculate the initial weights of various evaluation indicators by using the square root method, and finally perform a consistency test to ensure the rationality of the judgment matrix;

[0015] The analytic hierarchy process is used to calculate the initial weights of various evaluation indicators. The specific process is as follows:

[0016] Firstly, a hierarchical model of natural gas pressure energy utilization system is established, including target layer, criterion layer and indicator layer;

[0017] Then, a judgment matrix is ​​constructed between the criteria layers and between the evaluation indicators under different evaluation criteria. Based on the expert experience and the importance scale quantification table, the importance of each evaluation indicator is evaluated to obtain the judgment matrix.

[0018] Then extract the eigenvector from the judgment matrix and perform standard normalization, and use the square root method as the weight calculation method. The specific steps are as follows:

[0019] First calculate the product of all elements in each row of the judgment matrix:

[0020]

[0021] Among them, a ij In order to use the experience of experts to evaluate the importance of each evaluation index, a ij Usually 1, 2, 3, ..., 9 and 1, 1 / 2, 1 / 3, ..., 1 / 9 are used as scales;

[0022] Then find b i The nth root of:

[0023]

[0024] Then for the vector M i =(M1,M2,...M n ) T Standard normalization:

[0025]

[0026] The normalized W i =(W1,W2,...W n ) T As the initial weight vector;

[0027] Finally, the consistency check of the eigenvector is performed to ensure the rationality of the judgment matrix. The specific steps are as follows:

[0028] First calculate the maximum eigenvalue λ of the judgment matrix max , the calculation formula is as follows:

[0029]

[0030] Among them, AW is the product of the judgment matrix A and its eigenvector W;

[0031] Then the consistency check is performed, and the calculation formula is as follows:

[0032]

[0033] Where n is the order of the matrix, CR is the consistency ratio, and RI is the random consistency index, which is determined by the order n of the matrix. When CR is less than 0.1, the consistency of the judgment matrix is ​​acceptable, otherwise the judgment matrix needs to be modified.

[0034] S4. According to the initial weights of various evaluation indicators, the weights are modified based on the information entropy of the indicator data using the entropy weight method, and the modified indicator weights are used as the combined weights of various evaluation indicators;

[0035] The entropy weight method is used to correct the initial weights of various evaluation indicators. The specific process is as follows:

[0036] First, an initial evaluation matrix is ​​established according to the data values ​​of the evaluation indicators described in step S1;

[0037] Then the positive indicators and reverse indicators in the initial evaluation matrix are standardized to obtain a standardized matrix. The calculation formula for the standardized processing is as follows:

[0038]

[0039]

[0040] Among them, X ij represents the evaluation index data of the i-th index (i=1,2,3,...m) and the j-th scheme (j=1,2,3,...,n), min(X i ) and max(X i ) are the minimum and maximum values ​​within the i-th index respectively;

[0041] Then calculate the feature proportion of the standardized matrix, calculate the entropy value based on the feature proportion, and then calculate the entropy weight based on the entropy value. The specific calculation is as follows:

[0042]

[0043] Among them, P ij represents the characteristic weight, e i represents the entropy value, μ i represents entropy weight;

[0044] Finally, the combined weights of the indicators are calculated and the weights are corrected. The specific calculation is as follows:

[0045]

[0046] Among them, W i ′ represents the combined weight after the initial weight is obtained by modifying the analytic hierarchy process using the entropy weight method.

[0047] S5. According to the combined weights of various evaluation indicators, the fuzzy evaluation method is used to establish an evaluation level set and calculate the comprehensive score of the system solution;

[0048] The fuzzy evaluation method is used to establish an evaluation level set to calculate the comprehensive score of the system solution. The specific process is as follows:

[0049] First, define the evaluation level set V = {v1, v2, ..., v Z}, where v Z Indicates that there are z evaluation levels;

[0050] Then the final weights of the evaluation indicators in step S4 are used as weight vectors in the fuzzy evaluation method;

[0051] Through expert scoring, the scoring data of each indicator is collected, and the scoring of each indicator is matched to the corresponding evaluation level according to the grading standard. The evaluation level is divided into "excellent", "good", "average", "poor" and "bad", and the corresponding membership scores are 100 points, 80 points, 60 points, 40 points and 20 points respectively. The distribution ratio of each indicator in each evaluation level is counted to determine the membership, and the membership matrix R can be obtained:

[0052]

[0053] Among them, r iz It represents the membership degree of the ith indicator at the zth evaluation level;

[0054] The comprehensive evaluation result is calculated based on the weight vector W and the membership matrix R. The calculation formula is as follows:

[0055]

[0056] Among them, b z It represents the comprehensive membership of the evaluation object at the zth evaluation level;

[0057] Finally, according to the fuzzy comprehensive evaluation vector B = {b1, b2, ..., b Z}, the maximum membership principle is used to select the evaluation level with the largest membership in the comprehensive evaluation vector as the evaluation result, and the weighted average method is used to calculate each comprehensive evaluation score to obtain a quantitative evaluation result. The calculation formula is as follows:

[0058]

[0059] Among them, s z It represents the membership score corresponding to each evaluation level, S represents the comprehensive evaluation score, and the higher S is, the better the solution is.

[0060] S6. Evaluate the effects and compare the plans based on the comprehensive scores of the system's primary expansion plan and secondary expansion plan.

[0061] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0062] 1. The present invention proposes a fuzzy comprehensive evaluation method for the selection of natural gas pressure energy utilization system solutions. The method considers four evaluation criteria, namely, system efficiency, operation management, economic benefits and environmental protection, for the pressure energy utilization system, realizes a comprehensive evaluation of the system, solves the problem of the singleness of evaluation indicators in the current evaluation field of natural gas pressure energy utilization system, and provides theoretical support for the optimal design, operation management and decision-making of the natural gas pressure energy utilization system;

[0063] 2. The present invention proposes a fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions. This method is a comprehensive evaluation method that integrates subjective and objective weights, and can provide a more comprehensive and scientific comprehensive evaluation result while retaining expert experience and relying on objective analysis of data;

[0064] 3. The natural gas pressure energy utilization system used in the present invention. The system combines the pressure energy power generation system and the cold energy utilization system to achieve comprehensive utilization of energy, improve energy utilization efficiency, and provide a reference for factories to achieve cost reduction, increase efficiency and promote green development;

[0065] 4. The cold energy utilization system used in the present invention. The system uses a heat exchanger to use the cold energy of low-temperature natural gas to cool the circulating water, and the cooled cooling water is used to cool the lubricating oil system of the unit, reducing the use of electric energy while improving the safety of the pipeline network. The system provides an efficient solution for the planning and construction of the pressure energy utilization system of the new purification plant and the upgrading and transformation of the existing purification plant. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a flow chart of the fuzzy comprehensive evaluation method of the present invention;

[0067] Figure 2 This is a primary expansion flow chart of a natural gas pressure energy utilization system according to an embodiment of the present invention;

[0068] Figure 3 This is a two-stage expansion flow chart of a natural gas pressure energy utilization system according to an embodiment of the present invention;

[0069] Figure 4 This is a schematic diagram of the evaluation index system of an embodiment of the present invention;

[0070] Figure 5 Schematic diagram of evaluation index weights according to an embodiment of the present invention. DETAILED DESCRIPTION

[0071] In order to further describe the fuzzy comprehensive evaluation method for comparing and selecting a natural gas pressure energy utilization system solution proposed by the present invention, an embodiment of the present invention is described in conjunction with the accompanying drawings to enhance the understanding of the purpose, method structure and application effect of the present invention. The embodiment is only a further explanation of the present invention, and researchers in this field can make further non-fundamental technical improvements based on the present invention, which are also within the scope of protection of the present invention.

[0072] A fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions specifically includes the following steps:

[0073] S1. Collect monitoring data of the pressure energy utilization system of the natural gas purification plant, and calculate the data values ​​of various evaluation indicators in the primary expansion and secondary expansion schemes of the natural gas pressure energy utilization system based on the monitoring data and the energy analysis model;

[0074] The natural gas pressure energy utilization system includes a pressure energy power generation system and a cold energy utilization system. The pressure energy power generation system includes a turbine expander, a gear box, a coupling and a generator; the cold energy utilization system includes a heat exchanger, a circulating water transmission pipeline network, a unit lubricating oil system and a water storage tank;

[0075] The first-stage expansion scheme includes a preheater and a turbine expander, and adopts a preheating followed by expansion process;

[0076] The two-stage expansion scheme includes a preheater, two turbine expanders, and an intermediate heating process;

[0077] S2. According to the analytic hierarchy process, the evaluation index system of the natural gas pressure energy utilization system is decomposed into three levels, namely, the target level, the criterion level and the index level; the target level is the evaluation index system of the natural gas pressure energy utilization system; the criterion level includes four evaluation criteria, namely, system efficiency, operation management, economic benefits and environmental protection; the index level includes all evaluation indicators under different evaluation criteria classifications;

[0078] S3, according to the classification results, the initial weights of various evaluation indicators are calculated by using the analytic hierarchy process; the initial weights of various evaluation indicators calculated by the analytic hierarchy process are firstly based on expert experience to establish a judgment matrix between various indicators, criteria and objectives, then the eigenvectors are extracted from the judgment matrix, the initial weights of various evaluation indicators are calculated by the square root method, and finally a consistency test is performed to ensure the rationality of the judgment matrix;

[0079] S4. According to the initial weights of various evaluation indicators, the weights are modified based on the information entropy of the indicator data using the entropy weight method, and the modified indicator weights are used as the combined weights of various evaluation indicators;

[0080] S5. According to the combined weights of various evaluation indicators, the fuzzy evaluation method is used to establish an evaluation level set and calculate the comprehensive score of the system solution;

[0081] S6. Evaluate the effects and compare the plans based on the comprehensive scores of the system's primary expansion plan and secondary expansion plan.

[0082] Example

[0083] The natural gas pressure energy utilization system in one embodiment is specifically as follows:

[0084] The system uses the energy generated by the work of the expander-generator set to generate electricity, and at the same time uses the cold energy of the low-temperature natural gas after expansion to cool the unit's lubricating oil system. In the first-level expansion scheme of the natural gas pressure energy utilization system, the natural gas is first input into the turbine expander through the high-pressure natural gas pipeline network through the flow meter and preheater. The expander is connected to the gear box and the generator, and the electricity generated is connected to the factory electricity. The expanded low-temperature natural gas transmits the cold energy to the circulating water pipeline network through the heat exchanger. The cold water produced by heat exchange is used to cool the unit's lubricating oil system. After recovering the cold energy, the normal temperature natural gas enters the low-pressure natural gas pipeline network through the subsequent processing device; in the second-level expansion scheme, the natural gas is first input into the first turbine expander through the high-pressure natural gas pipeline network through the flow meter, and then connected to the second expander through the preheater. Both expanders are connected to the generator for power generation, and the subsequent process is the same as the first-level expansion; through this integrated design, the system not only realizes the recovery of pressure energy, but also can utilize the cold energy generated during the expansion process to reduce the energy consumption of the entire plant, reduce costs and increase efficiency, and achieve green and low-carbon development. The first-level expansion flow chart of the system is as follows Figure 2 As shown, the system secondary expansion flow chart is as follows Figure 3 shown.

[0085] Take a natural gas purification plant as an example. The purification plant adopts a pressure energy utilization system. The expander equipment adopts a turbine expander, and the generator equipment adopts a synchronous generator solution. The relevant technical parameters of the system are shown in Table 1:

[0086] Table 1 Main parameters of pressure energy utilization system in purification plant

[0087]

[0088] Pressure energy utilization system energy model: using The analytical method calculates the pressure energy generated by natural gas in the system and the efficiency of each unit equipment in the system. It refers to the available energy in a certain energy, that is, the maximum amount of energy that can be reversibly converted into work. Its components include physical and Chemistry Among them, physics Also includes temperature and pressure physics Related to the pressure and temperature of the surrounding environment, mainly considering mechanical energy and thermal energy, while chemical The main consideration is the concentration of substances when doing work, which is often ignored in the research on pressure energy power generation. It has become the main component of evaluating the benefits of pressure energy power generation. The natural gas pipeline network is regarded as an open system, and the physical for:

[0089] Δe x =h1-h2-T0(s1-s2)

[0090] Wherein, h1 and h2 are the specific enthalpy of natural gas at the inlet and outlet of the equipment, J / kg; T0 is the ambient temperature, K; s1 and s2 are the specific entropy of natural gas at the inlet and outlet of the equipment, J / (kg·K);

[0091] The second law of thermodynamics states that the entropy of an isolated system will not decrease, which indicates the irreversibility of natural processes and the tendency toward disorder. Through the entropy calculation formula proposed by Boltzmann, we can calculate the entropy change during the expansion of natural gas:

[0092] Δe x =h1-h2-T0C p ln(T1 / T2)-Rln(P1 / P2)

[0093] Among them, C p is the specific heat capacity of natural gas, J / (kg·K); T1 and T2 are the natural gas temperatures at the inlet and outlet of the equipment, respectively, K; P1 and P2 are the natural gas pressures at the inlet and outlet of the equipment, respectively, MPa; R is the molar gas constant of natural gas, J / (kg·K); Combining the two formulas, we can get:

[0094] Δe x =h1-h2-T0C p ln(T1 / T2)-Rln(P1 / P2)

[0095] physics Can be divided into specific pressure caused by pressure difference and the specific temperature caused by the temperature difference The expression is:

[0096] e x,h =e x,T +e x,p

[0097] e x,T =h1-h2-T0C p ln(T1 / T2)

[0098] e x,p =T0Rln(P1 / P2)

[0099] Where: e x,h For natural gas kJ / kg;e x,T is the specific temperature of natural gas kJ / kg;e x,p is the specific pressure of natural gas kJ / kg.

[0100] The evaluation index system described in step S2 includes:

[0101] The present invention proposes evaluation indicators from four aspects: system efficiency, operation management, economic benefits and environmental protection, such as Figure 4 As shown:

[0102] (1) System efficiency index

[0103] Power generation: Taking into account the efficiency of the expander and the generator in actual operation, the power generation per unit mass of natural gas is calculated as follows:

[0104]

[0105] Where: P is the power generation, kW; C p is the isobaric specific heat capacity of natural gas per unit mass, kJ / (kg·K); T1 is the natural gas inlet temperature, K; P1 is the natural gas inlet pressure, MPa; P2 is the natural gas inlet pressure, MPa; k is the natural gas adiabatic index; η t is the expander efficiency; η g is the generator efficiency;

[0106] Expansion generator set efficiency: Efficiency indicates the energy conversion efficiency of the system, that is, the level at which the pressure energy of natural gas can be converted into electrical energy. The calculation formula is as follows:

[0107]

[0108] Where: η e For expansion generator Efficiency; P is the power generation, kW; is the natural gas mass flow rate, kg / s; h1 is the natural gas specific enthalpy at the expander inlet, J / kg; h0 is the natural gas specific enthalpy under ambient conditions, J / kg; T0 is the ambient temperature, K; s2 is the natural gas specific entropy at the expander outlet, J / (kg·K); s0 is the natural gas specific entropy under ambient conditions, J / (kg·K);

[0109] Heat Exchanger Efficiency: Indicates the level of cold energy recovery of the heat exchanger from the low-temperature natural gas passing through the expander outlet. The calculation formula is as follows:

[0110]

[0111] Where: η E For heat exchanger Efficiency; E2′ is the natural gas at the heat exchanger outlet kJ / kg; E2 is the natural gas at the outlet of the expander kJ / kg; Inlet circulating water for heat exchanger kJ / kg; Circulating water for heat exchanger outlet kJ / kg;

[0112] Annual power generation: refers to the amount of electricity generated by the generator when the system is in operation for one year, with 345 days in operation per year, 24 hours per day, and a total of 8280 hours of operation. The calculation formula is as follows:

[0113] Q=P×T

[0114] In the formula: Q is the annual power generation, kW; P is the power generation, kW; T is the annual operating time, h;

[0115] Annual electricity saving due to cooling energy: refers to the amount of electricity saved by using the cooling energy utilization system to cool the unit's lubricating oil.

[0116] (2) Operational management indicators

[0117] Difficulty of technical transformation: When conducting a comprehensive system evaluation, the difficulty of technical transformation is a reverse indicator, that is, the value of the technical transformation difficulty indicator is negatively correlated with the quality of the energy-saving technology. The larger the corresponding indicator value, the worse the energy-saving technology. The difficulty of technical transformation is set to 10 levels, and integers in the range of 1 to 10 are taken as the indicator values;

[0118] Operation and maintenance difficulty: When conducting a comprehensive system evaluation, the operation and maintenance difficulty is a reverse indicator, that is, the operation and maintenance difficulty index value is negatively correlated with the quality of energy-saving technology. The larger the corresponding index value, the worse the energy-saving technology. The operation and maintenance difficulty is set to 10 levels, and integers in the range of 1 to 10 are taken as the index values.

[0119] (3) Economic benefit indicators

[0120] Power generation efficiency: The power generation efficiency index is an important indicator to measure the economic contribution of the pressure energy comprehensive utilization system, which refers to the electricity cost saved by the system using pressure energy to generate electricity. The calculation formula is as follows:

[0121] R g =E f ×Pe

[0122] Where: R g is the power generation efficiency, yuan; E f P is the power generated by pressure energy, kWh; e is the unit price of factory electricity, RMB / kWh;

[0123] Refrigeration efficiency: refers to the electricity cost saved by the cold energy utilization system using low-temperature natural gas to produce cooling water. The calculation formula is as follows:

[0124] R m =E l ×P e

[0125] Where: R m is the cooling efficiency, yuan; E l Power saving for cold energy utilization system, kWh; P e is the unit price of factory electricity, RMB / kWh;

[0126] Equipment investment: Equipment investment of the pressure energy utilization system mainly involves the initial purchase cost of various equipment in the system, including the purchase cost of turbine expanders and generator sets, the construction cost of pipeline facilities, and the labor cost of initial installation and commissioning. Equipment investment is an important indicator for evaluating the economic feasibility of a project, and its rationality directly affects the operating efficiency, service life and long-term return on investment of the system.

[0127] Annual operation and maintenance cost: The annual operation and maintenance cost of the pressure energy utilization system mainly involves the daily operation and maintenance management of the equipment, the necessary maintenance and repair of the pressure difference generator set, the training costs of technicians, the replacement costs of wearing parts in the system and the power consumption costs of auxiliary equipment.

[0128] Payback period: The time required for a system to recover all costs is calculated in years, and is often widely used as an indicator of the economic efficiency of energy-saving technology. The calculation formula is as follows:

[0129]

[0130] Where: P t is the investment payback period, years; C is the total system investment, yuan; C t is the average annual profit of the system, yuan.

[0131] (4) Environmental protection indicators

[0132] Pollutant emission reduction: Using the emission factor method, determine the emission factor of each emission source based on the emission inventory, and determine the pollutant emission by multiplying the power generation by the emission factor, where 1kW·h of electricity can emit 0.997kg of carbon dioxide, 0.015kg of nitrogen oxides and 0.03kg of sulfur dioxide. The calculation formula is as follows:

[0133] E=Q·EF

[0134] Where: E is the pollutant emission, t; Q is the power generation, kW·h; EF is the emission factor, kg / (kW·h);

[0135] Emission reduction benefits: As of the end of 2023, the average transaction price of all transactions in the national carbon market is 56.38 yuan / ton, and this is used as the standard for calculating carbon trading income.

[0136] The present invention establishes a comprehensive evaluation method based on three evaluation methods: hierarchical analysis method, entropy weight method and fuzzy evaluation method, and its contents are as follows:

[0137] (1) Analytical Hierarchy Process

[0138] In the analytic hierarchy process, the pressure energy comprehensive utilization system evaluation system is first decomposed into three levels, namely the target level (A), the criterion level (C) and the indicator level (P); the target level is the natural gas pressure energy utilization system evaluation indicator system; the four indicators of the criterion level are system efficiency C1, operation management C2, economic benefit C3 and environmental protection C4; the indicators under the criterion level constitute the indicator level;

[0139] The importance of each indicator in each criterion layer to the criterion is different, and the importance of different criterion layers to the target layer is also different. Based on this, the importance of each indicator can be judged, and the judgment matrix between each indicator, criterion, and target can be obtained through this importance scale description.

[0140] The target layer element is A, which corresponds to a criterion layer containing four elements, namely C1, C2, C3, and C4. Through the pairwise comparison of experts based on the target A factor under different evaluation criteria, the judgment matrix can be obtained as shown in Table 2:

[0141] Table 2 Judgment matrix

[0142]

[0143] Among them, a ij Indicates that based on the principle of goal A, C i For C j The importance value is reflected in the ij Usually 1, 2, 3, ..., 9 and 1, 1 / 2, 1 / 3, ..., 1 / 9 are used as scales;

[0144] The quantitative reference values ​​of the importance scale are shown in Table 3:

[0145] Table 3 Importance scale quantification table

[0146]

[0147] Among them, 2, 4, 6, 8 and 1 / 2, 1 / 4, 1 / 6, 1 / 8 represent quantitative values ​​whose importance is between the corresponding upper and lower importance respectively; the above elements must also meet the following requirements: a ij ·a ji =1,a ij =1(i=j);

[0148] In order to obtain the weight of each evaluation criterion, it is necessary to extract the eigenvector from the judgment matrix and use the square root method as the weight calculation method. The specific steps are as follows:

[0149] First, calculate the product of all elements in each row of the matrix, that is:

[0150]

[0151] Then find b i The nth root of:

[0152]

[0153] Finally, the vector M i =(M1,M2,...M n ) T Standard normalization:

[0154]

[0155] Among them, W i =(W1,W2,...W n ) T is the target weight vector, indicating that based on target A, each element C i The weights for A are W1, W2, ..., W n ;

[0156] Since the judgment matrix is ​​constructed based on subjective judgment, there may be inconsistencies. To ensure the rationality of the judgment matrix, a consistency test is required;

[0157] First, calculate the maximum eigenvalue λ of the judgment matrix max , the calculation formula is as follows:

[0158]

[0159] Among them, AW is the product of the judgment matrix A and its eigenvector W;

[0160] Then the consistency check is performed, and the calculation formula is as follows:

[0161]

[0162] Among them, n is the order of the matrix, CR is the consistency ratio, RI is the random consistency index, which is determined by the order n of the matrix; the expected random consistency index RI value is shown in Table 4:

[0163] Table 4 RI value table of AHP

[0164] n 1 2 3 4 5 6 7 8 9 RI 0.00 0.00 0.58 0.90 1.12 1.24 1.32 1.41 1.45

[0165] When CR < 0.1, the consistency of the judgment matrix is ​​acceptable; otherwise, the judgment matrix needs to be modified.

[0166] (2) Entropy Weight Method

[0167] The entropy weight method is an objective weighting method. Its calculation principle is to calculate the weight of each indicator by considering the amount of information contained in the evaluation indicator. It can effectively avoid the influence of subjective factors in the calculation process and make the calculation results closer to the actual situation.

[0168] First, construct the initial evaluation matrix, the expression is as follows:

[0169]

[0170] Where X is the evaluation index data matrix, i represents the index (i = 1, 2, 3, ..., m), j represents n schemes to be evaluated (j = 1, 2, 3, ..., n), X ij Represents the evaluation index data of the i-th indicator and the j-th solution;

[0171] Then the positive indicators and negative indicators in the initial evaluation matrix are standardized to obtain a standardized matrix;

[0172] Positive indicator normalization:

[0173]

[0174] Reverse indicator normalization:

[0175]

[0176] Among them, min(X i ) and max(X i ) are the minimum and maximum values ​​within the i-th index respectively;

[0177] Then calculate the feature proportion of the standardized matrix, calculate the entropy value based on the feature proportion, and then calculate the entropy weight based on the entropy value. The specific calculation is as follows:

[0178]

[0179] Among them, P ij represents the characteristic weight, e irepresents the entropy value, μ i represents entropy weight;

[0180] Finally, the combined weights of the indicators are calculated and the weights are corrected. The specific calculation is as follows:

[0181]

[0182] Among them, W i ′ represents the combined weight after the initial weight is obtained by modifying the analytic hierarchy process using the entropy weight method.

[0183] (3) Fuzzy evaluation method

[0184] Fuzzy evaluation method is an evaluation method used to deal with fuzzy and uncertain information in complex systems. In fuzzy evaluation, the fuzzy membership function maps the evaluation data to a value on the interval [0,1], which represents the membership of a certain evaluation object to a certain evaluation level. The ultimate goal of the fuzzy evaluation method is to sort the various evaluation levels of the evaluation object by calculating the comprehensive membership, so as to achieve comprehensive judgment. The specific calculation process is as follows:

[0185] First, define the evaluation level set V = {v1, v2, ..., v Z}, where v Z Indicates that there are z evaluation levels; the definition of the evaluation level set can quantify the evaluation standards of each indicator, which is conducive to standardizing the data of different evaluation indicators;

[0186] Then the importance of each indicator is determined based on the combined weights calculated by the analytic hierarchy process and the entropy weight method;

[0187] Then, through expert scoring, the scoring data of each indicator is collected. The scoring of each indicator is matched to the corresponding evaluation level according to the grading standard, and the evaluation level is divided into "excellent", "good", "average", "poor", and "bad". The corresponding membership scores are 100 points, 80 points, 60 points, 40 points, and 20 points respectively. The distribution ratio of each indicator in each evaluation level is counted to determine the membership, and a membership matrix R is obtained:

[0188]

[0189] Among them, r iz It represents the membership degree of the ith indicator at the zth evaluation level;

[0190] According to the fuzzy comprehensive evaluation model, using the weight vector W i ′ and the membership matrix R to calculate the comprehensive evaluation result. The calculation formula is as follows:

[0191] B=W i ′·R

[0192] The expanded calculation process is:

[0193]

[0194] Among them, b z Indicates the comprehensive membership of the evaluation object at the zth evaluation level:

[0195]

[0196] The calculated B={b1,b2,...,b Z} is the fuzzy vector of the comprehensive evaluation result, each b z Represents the evaluation object at the corresponding level v j The degree of membership on ;

[0197] Finally, according to the fuzzy comprehensive evaluation vector B, the maximum membership principle is used to select the evaluation level with the largest membership in the comprehensive evaluation vector as the evaluation result. The weighted average method is used to calculate each comprehensive evaluation score to obtain a quantitative evaluation result. The calculation formula is as follows:

[0198]

[0199] Among them, s z It represents the membership score corresponding to each evaluation level, S represents the comprehensive evaluation score, and the higher S is, the better the solution is.

[0200] The monitoring data of the pressure energy utilization system of the natural gas purification plant is collected, and according to the energy analysis model and the relevant technical parameters of the purification plant in the embodiment, combined with the data of the primary expansion and secondary expansion schemes of the system, the data values ​​of various evaluation indicators in the primary expansion and secondary expansion schemes of the natural gas pressure energy utilization system are calculated as shown in Table 5, and an initial evaluation matrix is ​​constructed;

[0201] Table 5 Evaluation index data value table

[0202]

[0203] The evaluation index system is divided into three levels: target level (A), criterion level (C) and indicator level (P). Figure 4 As shown, a judgment matrix is ​​constructed, and the relative importance of each indicator is compared pairwise using the importance scale quantification table in Table 3. Then, the eigenvector is extracted from the judgment matrix, and the initial weight of each evaluation indicator is calculated using the square root method.

[0204] The entropy weight method is used to determine the objective weight of each indicator, the initial evaluation matrix is ​​standardized, and then the standardized indicator proportion, indicator entropy value and entropy weight are calculated. Finally, the correction coefficient μ is used to i Modified analytic hierarchy process to find the initial weight Wi , find the corrected weights, and finally get the combined weights of the indicators, as shown in Table 6.

[0205] As can be seen from Table 6, the system efficiency index (0.4292) and environmental protection index (0.3342) of the system are the core elements of the evaluation, reflecting its dual goals of green and low-carbon development and energy efficiency. Efficiency (0.1013) indicates that improving power generation efficiency and system efficiency is the core goal. Environmental protection is the second largest area of ​​concern, especially CO2 emission reduction (0.1191) as the main indicator. Pressure energy recovery technology can significantly reduce carbon emissions and promote green and low-carbon development. Although the economic benefit index (0.1684) and operation management index (0.0681) account for a relatively low proportion in the comprehensive weight, they take into account both economic efficiency and operation performance to provide a more comprehensive and scientific reference for the natural gas utilization system.

[0206] Table 6 Final weight table of evaluation indicators

[0207]

[0208] After normalizing the initial evaluation matrix, the combined weight W is obtained according to the hierarchical analysis method-entropy weight method. i ′, the fuzzy comprehensive evaluation method is used to first establish the evaluation level set, and then establish the membership of each evaluation index data. The comprehensive membership of each evaluation data is calculated according to the combined weight, and the weighted average method is used to calculate the comprehensive score of each evaluation index. The comprehensive evaluation score of the system solution is shown in Table 7.

[0209] Table 7 System solution comprehensive evaluation score table

[0210] plan Comprehensive score Evaluation results First-level expansion 72.48 better Secondary expansion 89.64 excellent

[0211] Comprehensive analysis of the various indicators of the primary expansion and secondary expansion schemes in Table 5 shows that the secondary expansion scheme shows higher system integration efficiency and resource conversion rate. This scheme not only improves the power generation and efficiency, and also achieves larger-scale cold energy recovery and energy conservation, thereby significantly reducing the system's operating energy consumption; in comparison, the primary expansion solution has certain advantages in equipment complexity and operation and maintenance costs, but its pressure difference energy conversion effect and comprehensive energy utilization rate are not as good as the secondary solution, resulting in limited energy-saving potential; in addition, the secondary expansion solution has outstanding performance in emission reduction benefits, with higher CO2 and NO x The emission reduction shows that it has a better emission reduction effect in engineering practice, and the comprehensive analysis results show that the two-stage expansion scheme is better than the one-stage expansion scheme.

[0212] As can be seen from Table 7, the comprehensive scores of the primary expansion scheme and the secondary expansion scheme using the method of the present invention are 72.48 and 89.64 respectively, and the evaluation results are good and excellent respectively, indicating that the secondary expansion scheme is better than the primary expansion scheme. The comprehensive evaluation score and the evaluation result are consistent with the data in Table 5, indicating that the evaluation result obtained by the fuzzy comprehensive evaluation method of the present invention is reliable, which fully demonstrates the effectiveness of the method of the present invention.

[0213] The above is an explanation of the method and system of the present invention, and researchers in the field can reproduce the present invention through these explanations. Based on the content of the present invention, other embodiments and results obtained by researchers without creative work should fall within the scope of protection of the present invention.

Claims

1. A fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions, characterized in that: The following steps are involved: S1. Collect monitoring data of the pressure energy utilization system of the natural gas purification plant, and calculate the data values ​​of various evaluation indicators in the primary expansion and secondary expansion schemes of the natural gas pressure energy utilization system based on the monitoring data and the energy analysis model; The natural gas pressure energy utilization system includes a pressure energy power generation system and a cold energy utilization system. The pressure energy power generation system includes a turbine expander, a gear box, a coupling and a generator; the cold energy utilization system includes a heat exchanger, a circulating water transmission pipeline network, a unit lubricating oil system and a water storage tank; The first-stage expansion scheme includes a preheater and a turbine expander, and adopts a preheating followed by expansion process; The two-stage expansion scheme includes a preheater, two turbine expanders, and an intermediate heating process; S2. According to the analytic hierarchy process, the evaluation index system of the natural gas pressure energy utilization system is decomposed into three levels, namely, the target level, the criterion level and the index level; the target level is the evaluation index system of the natural gas pressure energy utilization system; the criterion level includes four evaluation criteria, namely, system efficiency, operation management, economic benefits and environmental protection; the index level includes all evaluation indicators under different evaluation criteria classifications; S3, according to the classification results, the initial weights of various evaluation indicators are calculated by using the analytic hierarchy process; the initial weights of various evaluation indicators calculated by the analytic hierarchy process are firstly based on expert experience to establish a judgment matrix between various indicators, criteria and objectives, then extract characteristic vectors from the judgment matrix, calculate the initial weights of various evaluation indicators by using the square root method, and finally perform a consistency test to ensure the rationality of the judgment matrix; S4. According to the initial weights of various evaluation indicators, the weights are modified based on the information entropy of the indicator data using the entropy weight method, and the modified indicator weights are used as the combined weights of various evaluation indicators; S5. According to the combined weights of various evaluation indicators, the fuzzy evaluation method is used to establish an evaluation level set and calculate the comprehensive score of the system solution; S6. Evaluate the effects and compare the plans based on the comprehensive scores of the system's primary expansion plan and secondary expansion plan.

2. A fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions according to claim 1, characterized in that: Step S2: The criterion layer includes four evaluation criteria: system efficiency, operation management, economic benefits and environmental protection; the evaluation indicators under the system efficiency evaluation criteria include power generation, expansion generator set Efficiency, heat exchanger efficiency, annual power generation and annual cooling energy saving; the evaluation indicators under the operation and management evaluation criteria include technical transformation difficulty and operation and maintenance difficulty; the evaluation indicators under the economic benefit evaluation criteria include power generation benefit, cooling benefit, equipment investment, annual operation and maintenance cost and investment payback period; the evaluation indicators under the environmental protection evaluation criteria include CO2 emission reduction, NO x Emission reduction, SO2 emission reduction and emission reduction benefits.

3. The fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions according to claim 1 is characterized in that: Step S5 uses the fuzzy evaluation method to establish an evaluation level set and calculate the comprehensive score of the system solution. The specific process is as follows: First, define the evaluation level set V = {v1, v2, ..., v Z }, where v Z Indicates that there are z evaluation levels; Then the combined weights of the evaluation indicators in step S4 are used as the weight vector in the fuzzy evaluation method; Through expert scoring, we collect the scoring data of each indicator, correspond the scoring of each indicator to the corresponding evaluation level according to the level classification standard, and count the distribution ratio of each indicator in each evaluation level to determine the membership degree. We can get the membership degree matrix R: Among them, r iz It represents the membership degree of the ith indicator at the zth evaluation level; The comprehensive evaluation result is calculated based on the weight vector W and the membership matrix R. The calculation formula is as follows: Among them, b z It represents the comprehensive membership of the evaluation object at the zth evaluation level; Finally, according to the fuzzy comprehensive evaluation vector B={b1,b2,...,b Z }, determine the final evaluation result, and use the weighted average method to calculate each comprehensive evaluation score to obtain a quantitative evaluation result. The calculation formula is as follows: Among them, s z It represents the membership score corresponding to each evaluation level, S represents the comprehensive evaluation score, and the higher S is, the better the solution is.

4. The fuzzy comprehensive evaluation method for comparing and selecting natural gas pressure energy utilization system solutions according to claim 1 is characterized in that: Step S5 establishes an evaluation grade set, which includes five grades, namely excellent, good, average, poor and bad, and the corresponding membership scores are 100 points, 80 points, 60 points, 40 points and 20 points respectively. According to the maximum membership principle, the evaluation grade with the largest membership in the comprehensive evaluation vector is selected as the evaluation result.

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