Comprehensive evaluation method for natural gas differential pressure power generation technology

Abstract

The invention discloses a comprehensive evaluation method for a natural gas differential pressure power generation technology, and relates to the technical field of energy recycling evaluation. Comprising the following steps: determining a natural gas differential pressure power generation technology comprehensive evaluation principle; a natural gas differential pressure power generation technology evaluation index system is defined, a second-level evaluation index system and a third-level evaluation index system of the system are established, and a corresponding calculation model is provided for supporting; determining a natural gas differential pressure power generation technology evaluation index combination weight, and finally establishing a natural gas differential pressure power generation technology comprehensive evaluation model; analyzing an evaluation result; the comprehensive evaluation method for the natural gas differential pressure power generation technology is scientific, reasonable and high in operability, evaluation can be carried out before and during development of a natural gas differential pressure power generation technology project, an enterprise can be effectively helped to clarify the technical process improvement direction, and the comprehensive evaluation method has a good popularization prospect.

Description

Technical Field

[0001] The invention relates to the technical field of energy recovery and utilization evaluation, in particular to a comprehensive evaluation method for natural gas pressure difference power generation technology. Background Art

[0002] Natural gas differential pressure power generation technology is an innovative low-carbon energy technology. It does not consume natural gas during the power generation process. There is no sewage, waste gas and solid waste emission during the production and operation process. It will not affect the environment and is a clean and efficient distributed energy source. However, the differential pressure power generation system currently in use has practical problems such as fuzzy operating efficiency and lack of application effect analysis. The above situation seriously affects the safe and stable operation of differential pressure power generation. This requires a complete set of evaluation methods. However, when evaluating the natural gas differential pressure power generation system, the existing evaluation methods are often established in the macro-economic and management aspects. However, for the energy efficiency part of the energy unit of the natural gas differential pressure power generation system, the evaluation of the internal energy efficiency of the system equipment during operation is ignored, and there is a lack of quantitative evaluation. Therefore, the evaluation indicators lack integrity. For the natural gas differential pressure power generation technology, there is a lack of a complete set of evaluation index systems. The calculation of the index value also tends to be based on the expert evaluation method, without a scientific calculation model as support, resulting in the excessive subjectivity of the index weight, the reliability of the evaluation result is not high enough, and it is difficult to reflect the actual operation effect of the system. In addition, the current evaluation method focuses on the macro-economic and management evaluation. There is no suitable calculation model for the system energy efficiency index at the micro level. Summary of the invention

[0003] In order to solve the above problems, the purpose of the present invention is to provide a comprehensive evaluation method for natural gas pressure difference power generation technology.

[0004] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0005] A comprehensive evaluation method for natural gas pressure difference power generation technology comprises the following steps:

[0006] (1) Clarify the comprehensive evaluation principles of natural gas differential pressure power generation technology;

[0007] (2) Using the EEAE comprehensive evaluation method, starting from the four indicators of system energy efficiency, technical economy, technical operation management, and environmental protection, the evaluation index system of natural gas differential pressure power generation technology was clarified, the secondary and tertiary evaluation index systems of the system were established, and the corresponding calculation model was proposed to support it;

[0008] (3) A combined weighting method combining the subjective weighting method AHP and the objective weighting method EWM is used to determine the combined weights of the evaluation indicators of natural gas pressure difference power generation technology, and finally a comprehensive evaluation model of natural gas pressure difference power generation technology is established;

[0009] (4) Analysis of evaluation results.

[0010] Preferably, the comprehensive evaluation principles of natural gas pressure difference power generation technology include system comprehensiveness principle, scientific principle, practical principle and flexibility principle.

[0011] Preferably, the system energy efficiency uses the system performance coefficient γ to evaluate the energy efficiency level of the system, specifically:

[0012]

[0013] Where ρ is the density of natural gas, kg / m 3 ; v is the actual flow through the expander, m 3 / h; T1 is the natural gas inlet temperature, ℃; T2 is the natural gas temperature after expansion, ℃; η s is the actual isentropic efficiency of the expander at the node; C p is the specific heat capacity of gas at constant pressure, J / (kg·K); Q x The amount of heat required to heat natural gas, kW.

[0014] Preferably, the technical economic efficiency is embodied by the internal rate of return (IRR), which is the discount rate that makes the project net present value (NPV) equal to zero.

[0015]

[0016] ΔCF = ES - ΔOC - ΔCIT;

[0017]

[0018] Where J0 is the investment cost of the pressure difference generator set; ΔCF is the annual cash flow change caused by the installation of the pressure difference generator set; i is the set discount rate; t is the time of cash inflow; ES is the electricity sales revenue; ΔOC is the change in operating costs; ΔCIT is the change in corporate income tax;

[0019] Preferably, the technical operation management includes a technical transformation difficulty index and an operation maintenance index.

[0020] Preferably, the environmental performance includes carbon dioxide emission reduction, nitrogen oxide emission reduction and generator set vibration speed.

[0021] Preferably, the calculation formula for the combined weight of the natural gas pressure difference power generation technology evaluation index is:

[0022]

[0023] Where α j is the combined weight value; W j is the subjective weight value; V j is the objective weight value.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] The comprehensive evaluation method of the natural gas pressure difference power generation technology of the present invention proposes a comprehensive evaluation index system, comprehensively evaluates the natural gas pressure difference power generation technology from four dimensions: system energy efficiency, technical economy, operation management, and environmental protection, and adopts a scientific combined weight method to determine the weight of each index, and finally conducts a quantitative comprehensive evaluation of the natural gas pressure difference power generation system, which is scientific, reasonable, and highly operable.

[0026] The comprehensive evaluation method of the natural gas pressure difference power generation technology of the present invention can be used to evaluate the natural gas pressure difference power generation technology project before and during implementation. Before implementation, multiple natural gas pressure difference power generation technical processes can be evaluated at the same time to help the project select the optimal technical process; during implementation, a comprehensive evaluation can be conducted on the technical processes actually operated on site, effectively helping enterprises to clarify the direction of technical process improvement, and has a good promotion prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the main energy-consuming unit of pressure difference power generation technology. Analytical model diagram;

[0028] Figure 2 This is the black box model diagram of the expander;

[0029] Figure 3 This is the black box model diagram of the generator;

[0030] Figure 4 It is a gray box model of natural gas pressure difference power generation system. DETAILED DESCRIPTION

[0031] The purpose of the present invention is to provide a comprehensive evaluation method for natural gas pressure difference power generation technology. The present invention is further described below in conjunction with specific embodiments.

[0032] Example 1

[0033] A comprehensive evaluation method for natural gas pressure difference power generation technology comprises the following steps:

[0034] (1) Clarify the comprehensive evaluation principles of natural gas differential pressure power generation technology;

[0035] (2) Using the EEAE comprehensive evaluation method, starting from the four indicators of system energy efficiency, technical economy, technical operation management, and environmental protection, the evaluation index system of natural gas differential pressure power generation technology was clarified, the secondary and tertiary evaluation index systems of the system were established, and the corresponding calculation model was proposed to support it;

[0036] (3) A combined weighting method combining the subjective weighting method AHP and the objective weighting method EWM is used to determine the combined weights of the evaluation indicators of natural gas pressure difference power generation technology, and finally a comprehensive evaluation model of natural gas pressure difference power generation technology is established;

[0037] (4) Analysis of evaluation results.

[0038] Step (1) Clarify the comprehensive evaluation principles of natural gas pressure difference power generation technology, including:

[0039] ①Follow the principle of system comprehensiveness

[0040] When establishing an evaluation system, the technology should be considered in an all-round way, so as to be targeted, comprehensive and clear. There should be a clear subordinate relationship between indicators at different levels, and indicators at the same level should not interfere with each other, which can show a certain feature of the technology to be evaluated;

[0041] ② Follow the scientific principle

[0042] When establishing the index system, we must follow the scientific principle, take the relevant theories of natural gas pressure energy utilization technology as the core, and establish the index system based on the research results;

[0043] ③ Follow the principle of reality

[0044] The established evaluation index system should meet the actual requirements of the site when it is implemented at the site, be feasible and operational, and the selected indicators should comply with international standards and be recognized within the industry.

[0045] ④ Follow the principle of flexibility

[0046] Comprehensive evaluation needs to have a certain degree of flexibility depending on the specific situation and evaluation purpose, and the focus and methods of evaluation can be adjusted as needed.

[0047] The specific contents of step (2) are as follows:

[0048] When comprehensively evaluating natural gas pressure difference power generation technology, multiple indicators need to be considered. When enterprises choose this energy-saving technology, they usually consider system energy efficiency, technical economy, operation and management difficulty, and safety. Since natural gas expansion pressure difference power generation technology has met relevant safety regulations during implementation, the primary indicators of comprehensive evaluation include system energy efficiency indicators, economic benefit indicators, operation and management indicators, and environmental protection indicators.

[0049] 2.1 System energy efficiency indicators

[0050] Energy has not only the attribute of "quantity", but also the attribute of "quality". The energy analysis method only analyzes the entire system from the attribute of "quantity" of energy. The analysis method can analyze the entire system more comprehensively from different angles. There is still little research on analysis, and only simple Analysis and calculation. The patent of this invention is based on the three-box basic The analytical model was proposed, and the black-gray double-box coupling of natural gas pressure difference power generation was proposed. The analysis model treats each natural gas pressure difference power generation process as a system and establishes a black box for each energy-consuming device in the system. The gray box analysis model is then combined with the black box model to establish the gray box analysis model of the entire system, and finally the overall system Efficiency and Loss. The implementation steps are as follows:

[0051] 1) Main energy-consuming units analyze

[0052] use The black box model is used to analyze the main energy-consuming units of direct expansion pressure difference power generation technology, such as Figure 1-4 shown.

[0053] like Figure 1 As shown, the main energy units of pressure difference power generation technology are Analytical Model

[0054] E x，in =E x，loss +E x，out +E x，ele (1);

[0055] In the formula, E x，in Energy unit entrance kJ / kg; E x，loss Export for energy-consuming units kJ / kg; E x，out The total energy consumption unit Loss, kJ / kg; E x，ele To generate electricity kJ / kg;

[0056] 2) Energy-using subunit analyze

[0057] a. The black box model of the expander is as follows Figure 2 As shown,

[0058] E x，in =E x，loss1 +E x，out +W A (2);

[0059] Where E x，inFor expander inlet kJ / kg; E x，loss1 For expander outlet kJ / kg; E x，out For expander Loss, kJ / kg; W A Mechanical output for expander kJ / kg;

[0060] b. The black box model of the generator is as follows Figure 3 As shown,

[0061] W A =E x,loss2 +E x，ele (3);

[0062] E x，loss2 For generator Loss, kJ / kg; E x，ele To generate electricity kJ / kg;

[0063] 3) Gray box model

[0064] Natural gas differential pressure power generation system gray box Analysis model such as Figure 4 shown.

[0065] 4) Efficiency Model

[0066] According to the gray box model, the system The efficiency is:

[0067]

[0068] 5) System Loss Model

[0069] E x，loss =E x，loss1 +E x，loss2 =E x，in -E x，out -E x，ele (5)

[0070] 6) System performance coefficient

[0071] In a complete natural gas pressure difference power generation system, the key energy-consuming units include the expander and the generator, and the heater. The function of the heater is to heat the natural gas pipeline. It is necessary to study it from the perspective of thermal power. The patent of this invention introduces a performance coefficient γ to evaluate the energy efficiency level of the system:

[0072]

[0073] Where ρ is the density of natural gas, kg / m 3 ; v is the actual flow through the expander, m 3 / h; T1 is the natural gas inlet temperature, ℃; T2 is the natural gas temperature after expansion, ℃; η s is the actual isentropic efficiency of the expander at the node; C p is the specific heat capacity of gas at constant pressure, J / (kg·K); Q x The amount of heat required to heat natural gas, kW.

[0074] 2.2 Technical and economic indicators

[0075] 1) Payback period

[0076] The payback period refers to the time required for an investment project to fully recover the initial investment from the start of operation. It is a simple financial indicator used to evaluate the payback speed of an investment project. Specifically, the payback period refers to the length of time from the start of the project to gradually make up for the initial investment of the project through the positive cash inflow generated by the project. Generally speaking, the shorter the payback period, the faster the project will pay back, and the lower the risk is considered. It is usually widely used by enterprises as an indicator of the economic feasibility of energy-saving technology. This indicator is a reverse indicator. The smaller the indicator value, the better the energy-saving technology. Its calculation formula is:

[0077]

[0078] Where: PP is the payback period, years; CI is the total investment (including value-added tax), ten thousand yuan; C t The average annual profit is 10,000 yuan.

[0079] 2) Average annual profit

[0080] A single payback period indicator cannot comprehensively consider the time value of money and the economic effect after investment recovery, and cannot fully reflect the economic benefits of the project after transformation. Therefore, another economic indicator - average annual profit - is introduced. This indicator is a positive indicator, that is, the larger the indicator value, the better the energy-saving technology.

[0081] C t =C te (1-T) (7)

[0082] Where: C te is the average annual total product revenue, ten thousand yuan; T is the tax rate, %.

[0083] 3) Internal Rate of Return

[0084] The internal rate of return (IRR) is a financial indicator used to evaluate the profitability of an investment project. It represents the average annual rate of return on a project that makes the net present value of the project equal to zero. IRR is a measure of the return on investment, usually expressed as a percentage.

[0085] The calculation of the internal rate of return is based on the cash flows of a project, which include the initial investment in the project and the future cash inflows. The IRR is the discount rate that makes the net present value (NPV) of the project equal to zero.

[0086]

[0087] ΔCF=ES-ΔOC-ΔCIT; (9)

[0088]

[0089] Where J0 is the investment cost of the pressure difference generator set; ΔCF is the annual cash flow change caused by the installation of the pressure difference generator set; i is the set discount rate; t is the time of cash inflow; ES is the electricity sales revenue; ΔOC is the change in operating costs; ΔCIT is the change in corporate income tax.

[0090] 2.3 Operational Management Indicators

[0091] When enterprises choose energy-saving technologies, whether the energy-saving technologies are easy to operate and maintain is usually a very important reference indicator. This indicator has the characteristics of combining subjectivity and objectivity. On the one hand, in the process of implementing energy-saving technologies, factors such as the complexity of operation and the difficulty of management and maintenance are highly subjective. On the other hand, indicators such as equipment maintenance costs are highly objective.

[0092] 1) Difficulty of technical transformation

[0093] When conducting a comprehensive system evaluation, the difficulty of technical transformation is a reverse indicator, that is, the technical transformation 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 technical transformation difficulty is set to 10 levels, and integers in the range of 1 to 10 are taken as index values.

[0094] 2) Operation and maintenance

[0095] When conducting a comprehensive system evaluation, the difficulty of operation and maintenance is a reverse indicator, that is, the value of the operation and maintenance difficulty index is negatively correlated with the quality of the energy-saving technology. The larger the corresponding index value, the worse the energy-saving technology. The difficulty of operation and maintenance is set to 10 levels, and integers in the range of 1 to 10 are taken as the index values.

[0096] 2.4 Environmental performance indicators

[0097] The environmental protection evaluation of engineering projects mainly focuses on the impact of the project on the environment and ecological balance, involving factors such as pollutant emissions and gas emissions. However, in the natural gas pressure difference power generation process, since there is no pollutant emission involved, this factor is not an important evaluation indicator. For natural gas pressure difference generator sets, there is a certain degree of unit vibration problem. Equipment vibration will be related to the service life, operation effect and environmental protection of the unit. It needs to be used as an evaluation indicator.

[0098] In the context of the country's advocacy of energy conservation and emission reduction, natural gas pressure difference power generation reduces natural gas waste by effectively utilizing natural gas pressure energy, thereby reducing the use of fossil fuels. Therefore, carbon dioxide emission reduction and nitrogen oxide emission reduction become more critical environmental evaluation indicators, reflecting the positive impact of the project on the environment.

[0099] The most widely used method to consider pollutant emissions is the emission factor method proposed by the IPCC. The basic idea of ​​this method is to determine the emission factor (the amount of greenhouse gases released per unit of use of a certain emission source) of each emission source based on the emission inventory, and determine the pollutant emissions by multiplying the activity data (here, power generation) by the emission factor. The emission factors are shown in Table 1, and the pollutant emissions calculation formula is as follows:

[0100] E=AD·EF(10)

[0101] Where: E is the pollutant emission, kg; AD is the power generation, kW·h; EF is the emission factor, kg / (kW·h).

[0102] Table 1 Pollutant emission factor conversion table

[0103]

[0104] 1) Carbon dioxide emission reduction

[0105] Based on the above formula and the emission factors of each pollutant converted from the unit electricity saved, the calculation formula for carbon dioxide emission reduction is defined as follows:

[0106]

[0107] 2) Nitrogen oxide emission reduction

[0108] Based on the above formula and the emission factors of each pollutant converted from the unit electricity saved, the calculation formula for nitrogen oxide emission reduction is defined as follows:

[0109]

[0110] 3) Vibration speed

[0111] For natural gas differential pressure generator sets, the vibration effect is mainly reflected by the vibration velocity (mm / s). During the on-site evaluation process, a vibration detector is needed to quantify its value. The reference standard for vibration velocity is shown in Table 2. Of course, before testing, it is necessary to determine the test plan based on the actual on-site operation conditions, including the selection of test equipment, point design, on-site testing, and data statistical analysis. Among them, point design is particularly important. The designed test points need to include the key points of the entire process of the natural gas differential pressure power generation process (expander inlet and outlet, large-angle elbows, generators, natural gas main pipeline inlet and outlet, etc.).

[0112] Table 2 Vibration standard comparison table

[0113]

[0114]

[0115] Note:

[0116] Category 1: small machinery (such as motors below 15Kw);

[0117] Category II: Medium-sized machinery (such as motors of 15 to 75 kW and machinery below 300 kW);

[0118] Category 3: Large machinery (rigid foundation);

[0119] Category 4: Large machinery (flexible foundation) speed: 600~12000rpm; vibration measurement range: 10~1000Hz.

[0120] 2.5 Determine the comprehensive evaluation index system for natural gas pressure difference power generation The comprehensive evaluation index system for natural gas pressure difference power generation is shown in Table 3.

[0121] Table 3 Index system

[0122]

[0123]

[0124] 2.6 Data processing:

[0125] Considering that the operation of the natural gas pressure difference generator set is a dynamic process and will be affected by many factors, the data needs to be processed in the process of determining the above index values. The patent of the present invention adopts the average value method, that is, the parameters collected within a certain range are evaluated after the average value is removed. In the process of processing the technical data, the selected parameters such as the expander rated efficiency, the expander isentropic efficiency, and the generator power generation are directly averaged. From this, a set of typical data can be preliminarily obtained and recorded as shown in Table 4.

[0126] Table 4 Data processing results

[0127]

[0128] Step (3): Comprehensive evaluation model of natural gas pressure difference power generation technology based on improved AHP-EWM method

[0129] The subjective weighting method and the objective weighting method each have their own advantages and disadvantages in the process of weight determination. In order to better play the advantages of the two methods, the present invention combines the characteristics of the two methods. The method adopted in the comprehensive evaluation of the natural gas pressure difference power generation system is the combined weighting method. The calculation of subjective and objective weights is carried out by the analytic hierarchy process (AHP) and the entropy weight method (EWM), respectively.

[0130] 3.1 Determining subjective weights using the AHP method

[0131] When analyzing complex problems, the hierarchical analysis method usually proceeds step by step in a progressive manner. Its basic principle is to decompose the complex problem into several indicators, compare these indicators two by two at different levels to determine the difference in importance between the indicators, and construct a basic judgment matrix based on this. Then, mathematical methods are used to calculate the maximum eigenvalue and eigenvector of the judgment matrix. At this time, the final weight value is the same as the result obtained by the eigenvector.

[0132] 1) Construct the judgment matrix T

[0133] When constructing the judgment matrix, the expert consultation method is used to determine the importance of each indicator. The judgment principle of the importance between two indicators is usually defined by nine scales. The nine-scale importance judgment principle is shown in Table 5.

[0134] Table 5 Weight importance judgment matrix

[0135] Scale Importance illustrate 1 Importance Factor A is as important as Factor B 3 A slight gap in importance Factor A is slightly more important than Factor B 5 There is a big gap in importance Factor A is significantly more important than Factor B 7 Significant differences in importance Factor A is more important than Factor B 9 There is a huge gap in importance Factor A compared to Factor B and its importance

[0136] After collecting and summarizing the expert opinions, the judgment matrices are shown in Tables 6 to 10.

[0137] Table 6 Secondary indicator layer importance judgment matrix T1

[0138] Secondary indicator name System energy efficiency index Technical and economic indicators Operational management indicators Environmental performance index System energy efficiency index <![CDATA[c 11 ]]> <![CDATA[c 12 ]]> <![CDATA[c 13 ]]> <![CDATA[c 14 ]]> Technical and economic indicators <![CDATA[c 21 ]]> <![CDATA[c 22 ]]> <![CDATA[c 23 ]]> <![CDATA[c 24 ]]> Operational management indicators <![CDATA[c 31 ]]> <![CDATA[c 32 ]]> <![CDATA[c 33 ]]> <![CDATA[c 34 <!-- 9 -->]]> Environmental performance index <![CDATA[c 41 ]]> <![CDATA[c 42 ]]> <![CDATA[c 43 ]]> <![CDATA[c 44 ]]>

[0139] Table 7 System energy efficiency index importance judgment matrix T2

[0140]

[0141] Table 8 Technical and economic indicators importance judgment matrix T3

[0142] Name of the third-level indicator Payback period Average annual profit Internal Rate of Return Payback period <![CDATA[c 11 ]]> <![CDATA[c 12 ]]> <![CDATA[c 13 ]]> Average annual profit <![CDATA[c 21 ]]> <![CDATA[c 22 ]]> <![CDATA[c 23 ]]> Internal Rate of Return <![CDATA[c 31 ]]> <![CDATA[c 32 ]]> <![CDATA[c 33 ]]>

[0143] Table 9 Operation management index importance judgment matrix T4

[0144] Name of the third-level indicator Difficulty of operation and management Difficulty of operation and maintenance Difficulty of operation and management <![CDATA[c 11 ]]> <![CDATA[c 12 ]]> Difficulty of operation and maintenance <![CDATA[c 21 ]]> <![CDATA[c 22 ]]>

[0145] Table 10 Environmental protection index importance judgment matrix T5

[0146]

[0147]

[0148] 2) Hierarchical single sorting

[0149] First, it is necessary to determine the maximum eigenvalue and eigenvector of the judgment matrix T. There are many methods for calculating the maximum eigenvalue and eigenvector. The patent of this invention adopts the more commonly used product square root method for calculation. The specific steps are as follows:

[0150] a. According to each row element in the judgment matrix T, construct the nth root a of the product i :

[0151]

[0152] b. Add the vector (a1, a2, a3...a n ) is normalized, as shown in formula (14), W i That is the feature vector, and the numerical value in the vector represents the weight of each indicator.

[0153]

[0154] c.Consistency check

[0155] Due to the ij Empirical judgment is made, and the resulting errors will also cause the eigenvector to be biased, so there is:

[0156]

[0157] λ max The maximum eigenvalue of the judgment matrix. If the judgment matrix is ​​compatible, then λ max =n; if incompatible, λ max >n.

[0158] The consistency criteria that the judgment matrix must comply with are as follows:

[0159] CR=(CI / RI)<0.10 (16)

[0160]

[0161] Where n is the matrix order; CI is the consistency index; RI is the average random consistency index; CR is the random consistency ratio.

[0162] The average random consistency index value can be obtained by looking up the table, and the specific details can be found in Table 11.

[0163] Table 11 Average random consistency index comparison table

[0164] n 1 2 3 4 5 6 7 8 9 RI 0 0 0.52 0.89 1.12 1.26 1.36 1.41 1.46

[0165] If the required index can satisfy formula (16), it means that the consistency of the judgment matrix is ​​acceptable.

[0166] After substituting the data, the hierarchical single ranking weights and consistency test results of the energy efficiency level evaluation index of the natural gas expansion pressure difference power generation system are shown in Table 12.

[0167] Table 12 Hierarchical single ranking weights and consistency test results

[0168] Judgment Matrix Eigenvector Maximum eigenvalue Consistency Check <![CDATA[T1]]> <![CDATA[W1]]> <![CDATA[λ max =x1]]> Pass the consistency check <![CDATA[T2]]> <![CDATA[W2]]> <h2 style=";text-align:left;direction:ltr"><![CDATA[λ <h2 style=";text-align:left;direction:ltr"> max <h2 style=";text-align:left;direction:ltr"> =x2]]><h2 style=";text-align:left;direction:ltr"> Pass the consistency check <![CDATA[T3]]> <![CDATA[W3]]> <![CDATA[λ max =x3]]> Pass the consistency check <![CDATA[T4]]> <![CDATA[W4]]> <![CDATA[λ max =x4]]> Pass the consistency check <![CDATA[T5]]> <![CDATA[W5]]> <h2 style=";text-align:left;direction:ltr"><![CDATA[λ <h2 style=";text-align:left;direction:ltr"> max <h2 style=";text-align:left;direction:ltr"> =x5]]><h2 style=";text-align:left;direction:ltr"> Pass the consistency check

[0169] 3) Total ranking of levels

[0170] In the hierarchical analysis method, the total hierarchical ranking refers to the process of calculating the weight of each indicator contained in a certain level to the highest level indicator to which it belongs. The number of indicators is limited and each lower-level indicator only belongs to one upper-level indicator. The multiplication method can be used to calculate the indicator weight. The calculation results of the total hierarchical ranking are shown in Table 13.

[0171] Table 13. Total ranking of levels

[0172]

[0173] 3.2 EWM method to determine objective weights

[0174] The reason why the entropy method can be used to determine objective weights is that the effective information expressed by the entropy value in the data can be used to distinguish the differences between the same indicators in different evaluation objects. When the values ​​of a certain indicator of all evaluation objects are not significantly different, continuing to use this indicator for horizontal comparison cannot clearly express the relationship between the evaluation objects, that is, the indicator cannot provide enough effective information, then the weight of the entropy value of this indicator in the comprehensive evaluation of the system will also be very small, which makes the data full of uncertainty. On the contrary, if there is a large difference between the values ​​of a certain indicator among all evaluation objects, then this indicator can provide sufficient effective information, then the weight of its entropy in the comprehensive evaluation is large.

[0175] 1) Index preprocessing

[0176] When using the entropy method for comprehensive evaluation, the index values ​​obtained based on the original data will vary greatly due to different units and orders of magnitude, and the way each index points to the optimal value is also different. Therefore, they cannot be compared directly and index preprocessing is required.

[0177] Indicator preprocessing is to make indicators consistent and dimensionless. As mentioned above, each indicator has different directions for the optimal value. According to their different directions, they can be divided into positive indicators and negative indicators. Indicator consistency is to unify them into positive indicators. Dimensionless is to abandon the interference of data units and orders of magnitude. The indicator value after dimensionless is called the indicator evaluation value.

[0178] The present invention adopts the extreme value method to perform index preprocessing. The forward index preprocessing can adopt formula (18).

[0179]

[0180] The reverse indicator preprocessing can be done using formula (19).

[0181]

[0182] Where: X ij is the dimensionless standardized value of each indicator; x ij is the actual value of the jth indicator in the i-th technology to be evaluated; max X ij is the maximum value of the jth indicator in the i-th technology to be evaluated; min X ij It is the minimum value of the jth indicator in the i-th technology to be evaluated.

[0183] The value range of the positive indicator after preprocessing is [0, 1]. The specific results are shown in Table 14.

[0184] Table 14 Standardized evaluation values ​​of the three-level indicators

[0185]

[0186] 2) Objective weight calculation

[0187] The selected k=11 types of data are used as evaluation indicators. Since the method proposed in the present invention is also applicable to the simultaneous evaluation of multiple differential pressure power generation technologies, X ij Represents the jth evaluation index of the i-th technology (i=1, 2, 3...n; j=1, 2, 3...10), and the entropy value method weight calculation process of natural gas pressure difference power generation technology is as follows:

[0188] a. Calculate feature weight

[0189] Find the proportion p of the jth indicator value in the i-th technology in the sum of the standard values ​​of the indicator ij:

[0190]

[0191] b. Calculate entropy

[0192] Calculate the entropy value e of the indicator j :

[0193]

[0194] Wherein, k = 1 / ln n.

[0195] c. Calculate the coefficient of variation

[0196] Calculate the difference coefficient of the jth indicator of the evaluation object

[0197] g j =1-e j (twenty two)

[0198] d. Determination of evaluation index weights

[0199] The weight of the jth indicator of the evaluation object is calculated using the entropy value obtained in b:

[0200]

[0201] After arranging the calculation results, we can obtain the index entropy value weight table shown in Table 15:

[0202] Table 15 Index entropy weight table

[0203]

[0204] 3.3 Determine the combination weight by AHP-EWM method

[0205] Compared with the single weighting method, the combined weighting method can more comprehensively consider the weights of various indicators by combining the subjective weighting of the hierarchical analysis method and the objective weighting of the entropy weight method. The calculation steps of this method are to first use these two methods to calculate the weights of each indicator, then analyze whether these weights meet the actual needs, determine the relative importance of the subjective and objective weights in the comprehensive weights, and finally obtain the final comprehensive weights. This method combines the objective information of the original indicator value with the subjective opinions of experts, making the evaluation more scientific and reasonable. The calculation formula of the combined weight is as follows:

[0206]

[0207] Where α j is the combined weight value; W j is the subjective weight value; V j is the objective weight value.

[0208] The combined weights are determined according to formula (24) and recorded in Table 16.

[0209] Table 16 Combination weight values

[0210]

[0211] Step (4): Analysis of technical evaluation results

[0212] The comprehensive score of the evaluation object is the characteristic proportion p obtained by the entropy method. ij The product of the weights determined by the combined weighting method is then compared to determine the most suitable energy-saving technology for the enterprise. The comprehensive score F can be calculated using Formula 25.

[0213]

[0214] Each indicator can be calculated by formula (25) to get a comprehensive score. Enterprises can improve relevant indicators based on the evaluation results and project requirements. This method can also be used in the early stage of project implementation to evaluate a variety of differential pressure power generation projects and select the best natural gas differential pressure power generation technology based on the evaluation results.

Claims

1. A comprehensive evaluation method for natural gas pressure difference power generation technology, characterized by: The following steps are involved: (1) Clarify the comprehensive evaluation principles of natural gas differential pressure power generation technology; (2) Using the EEAE comprehensive evaluation method, starting from the four indicators of system energy efficiency, technical economy, technical operation management, and environmental protection, the evaluation index system of natural gas differential pressure power generation technology was clarified, the secondary and tertiary evaluation index systems of the system were established, and the corresponding calculation model was proposed to support it; (3) A combined weighting method combining the subjective weighting method AHP and the objective weighting method EWM is used to determine the combined weights of the evaluation indicators of natural gas pressure difference power generation technology, and finally a comprehensive evaluation model of natural gas pressure difference power generation technology is established; (4) Analysis of evaluation results.

2. The comprehensive evaluation method of natural gas pressure difference power generation technology according to claim 1 is characterized by: The comprehensive evaluation principles of natural gas pressure difference power generation technology include system comprehensiveness principle, scientific principle, practical principle and flexibility principle.

3. The comprehensive evaluation method of natural gas pressure difference power generation technology according to claim 1 is characterized by: The system energy efficiency uses the system performance coefficient γ to evaluate the system energy efficiency level, specifically: Where ρ is the density of natural gas, kg / m 3 ; v is the actual flow through the expander, m 3 / h; T1 is the natural gas inlet temperature, ℃; T2 is the natural gas temperature after expansion, ℃; η s is the actual isentropic efficiency of the expander at the node; C p is the specific heat capacity of gas at constant pressure, J / (kg·K); Q x The amount of heat required to heat natural gas, kW.

4. The comprehensive evaluation method of natural gas pressure difference power generation technology according to claim 1 is characterized by: The technical economic efficiency is reflected by the internal rate of return (IRR), which is the discount rate that makes the project's net present value (NPV) equal to zero. ΔCF = ES - ΔOC - ΔCIT; Where J0 is the investment cost of the pressure difference generator set; ΔCF is the annual cash flow change caused by the installation of the pressure difference generator set; i is the set discount rate; t is the time of cash inflow; ES is the electricity sales revenue; ΔOC is the change in operating costs; ΔCIT is the change in corporate income tax.

5. The comprehensive evaluation method of natural gas pressure difference power generation technology according to claim 1 is characterized by: The technical operation management includes technical transformation difficulty indicators and operation maintenance degree indicators.

6. The comprehensive evaluation method of natural gas pressure difference power generation technology according to claim 1 is characterized by: The environmental performance includes carbon dioxide emission reduction, nitrogen oxide emission reduction and generator set vibration speed.

7. The comprehensive evaluation method of natural gas pressure difference power generation technology according to claim 1 is characterized by: The calculation formula for the combined weight of the evaluation index of natural gas pressure difference power generation technology is: Where α j is the combined weight value; W j is the subjective weight value; V j is the objective weight value.

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