A method for analyzing natural gas pressure energy output characteristics considering dual uncertainty

Abstract

The present invention discloses a method for analyzing the output characteristics of natural gas pressure energy considering dual uncertainty. The method comprises: determining the factors affecting the output of natural gas pressure energy and the constraints of each link in the natural gas transmission process according to the power generation system architecture of natural gas pressure energy; establishing a natural gas load demand model to calculate the natural gas load demand at different times and regions; establishing a dual uncertainty model considering both natural gas flow and pressure based on uncertainty theory, and calculating the uncertain natural gas flow and pressure respectively; establishing a mathematical model for analyzing the output of natural gas pressure energy based on the #imgabs0# analysis theory, and analyzing the spatiotemporal characteristics of the output of natural gas pressure energy; and proposing a volatility index to describe the power variation amplitude and power fluctuation rate of pressure energy power generation on different time scales. The method can effectively analyze the factors affecting the output of natural gas pressure energy and the output characteristics, thereby contributing to improving the utilization efficiency of natural gas pressure energy.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy power generation output characteristic analysis, and in particular to a natural gas pressure energy output characteristic analysis method considering dual uncertainty. Background Art

[0002] The rapid development of the global economy has led to an increasing demand for energy, and the use of traditional fossil energy has brought about a large amount of greenhouse gas emissions. my country has proposed the goal of "striving to peak carbon dioxide emissions before 2030 and achieving carbon neutrality before 2060."

[0003] As a clean energy, natural gas accounts for an increasing proportion of the world's energy demand. Vigorously developing and efficiently utilizing natural gas has become an important strategic measure for my country to ensure energy supply security and reduce carbon dioxide emissions.

[0004] As of 2021, my country has built 110,000 kilometers of natural gas pipelines, gradually forming a large-diameter, high-pressure and networked natural gas pipeline network. Natural gas is transmitted to the user end over long distances and at high pressure, and it needs to be reduced in pressure to meet user needs. Using traditional pressure regulating valves to reduce pressure will cause a lot of pressure energy resources to be wasted. For example, when natural gas is reduced from 10MPa in the high-pressure pipeline network to 0.4MPa at the user end, the pressure energy it contains is as high as 498.94kJ / kg. Relevant data show that in 2021, the West-East Gas Pipeline will supply 1000×10 8 m 3 , equivalent to the mass of methane is 713.2×10 8 kg, taking this as an example, the recoverable pressure energy is 355844×10 8 kJ, equivalent to the annual power generation of a power plant with an installed capacity of 1128.4MW. Therefore, efficient utilization of natural gas pressure energy is one of the important ways to achieve the "dual carbon" goals.

[0005] With global energy shortages and environmental pollution becoming increasingly prominent, the utilization of natural gas pressure energy has seen rapid development. In 2015, the National Development and Reform Commission proposed to "actively encourage enterprises to utilize waste heat, excess pressure, and excess gas for power generation projects."

[0006] The analysis of factors affecting the utilization of natural gas pressure energy and its output characteristics can quantitatively adjust the natural gas operating conditions and improve the efficiency of pressure differential power generation. Among them, the output characteristics analysis provides important support for the subsequent consumption of pressure energy. Therefore, the analysis of factors affecting the utilization of natural gas pressure energy and its output characteristics is the basis for the design and operation management of comprehensive pressure energy utilization schemes, and is also one of the key technologies restricting its promotion and application.

[0007] However, existing research on the utilization of natural gas pressure energy mostly focuses on the principles of natural gas pressure energy power generation, key equipment for pressure difference power generation, and forms of pressure energy utilization. There is a lack of analysis of the factors affecting the utilization of natural gas pressure energy and the output characteristics, and it is impossible to further effectively improve the utilization efficiency of natural gas pressure energy. Summary of the Invention

[0008] In view of the above technical problems, the present invention provides a natural gas pressure energy output characteristic analysis method taking into account dual uncertainty, which solves at least some of the above technical problems. Through this method, the factors affecting the natural gas pressure energy output and the output characteristics can be effectively analyzed, thereby helping to improve the utilization efficiency of natural gas pressure energy.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] The present invention provides a method for analyzing natural gas pressure energy output characteristics considering dual uncertainty, the method comprising the following steps:

[0011] S1. Determine the factors affecting the output of natural gas pressure energy based on the power generation system architecture of natural gas pressure energy;

[0012] S2. Determine the constraints of each link in the natural gas transmission process based on the natural gas pipeline network structure and factors affecting the output of the natural gas pressure energy;

[0013] S3. Based on the natural gas pressure energy power generation system architecture and natural gas pipeline network structure, a natural gas load demand model is established to calculate the natural gas load demand at different times and regions;

[0014] S4. Based on the natural gas load demand and uncertainty theory, a dual uncertainty model is established that considers both the natural gas flow rate and pressure, and the uncertain natural gas flow rate and pressure are calculated respectively;

[0015] S5, based on Analyze the theory and establish the output of natural gas pressure energy Analyze the mathematical model and substitute the uncertain natural gas flow and pressure into the output Analyze mathematical models, calculate the power generated by natural gas pressure energy, and analyze the temporal and spatial characteristics of natural gas pressure energy output;

[0016] S6. Establish a natural gas pressure energy power generation fluctuation analysis model, combine the temporal and spatial characteristics of the natural gas pressure energy output, and calculate and analyze the fluctuation of the natural gas pressure energy output on different time scales.

[0017] Furthermore, in step S1, the factors affecting the output of the natural gas pressure energy include:

[0018] d. The process flow of high-voltage transmission and step-down power generation;

[0019] e. Equipment parameters of compressor, expander and generator;

[0020] f. Parameters of natural gas quality, flow, pressure, temperature and density.

[0021] Furthermore, in step S2, the constraints of each link in the natural gas transmission process include:

[0022] ① Upper and lower limits on the amount of gas produced per unit time by the natural gas source;

[0023] ②Compressor inlet and outlet pressure and transmission capacity constraints;

[0024] ③ Constraints on pipeline natural gas flow and airflow direction;

[0025] ④ Flow and pressure constraints at pipeline network nodes.

[0026] Furthermore, in step S3, the natural gas load demand model includes:

[0027] The total load model of the pressure regulating station, the residential gas consumption model, the commercial gas consumption model, the gas power generation gas consumption model, the industrial production gas consumption model, the gas heating gas consumption model and the gas vehicle gas consumption model.

[0028] Furthermore, in step S4, the dual uncertainty model of natural gas flow and pressure includes:

[0029] Traffic uncertainty model:

[0030]

[0031]

[0032] Pressure uncertainty model:

[0033]

[0034]

[0035] Where: Q j,t 、P j,t are the uncertain natural gas flow and pressure at the pressure regulating station j at time t, are the planned natural gas flow and pressure at the pressure regulating station j at time t; ΔQ j,t , ΔP j,t is the error fluctuation of natural gas flow and pressure at time t; ΔZ jQ , ΔZ jP Represent the error rates of natural gas flow and pressure respectively.

[0036] Furthermore, the error rate ΔZ between the natural gas flow and pressure jQ , ΔZ jP It obeys the normal distribution, and its probability function is:

[0037]

[0038] Where: μ is the expectation, σ 2 is the variance;

[0039] Based on the fluctuation range of natural gas flow and pressure at the pressure regulating station, the probability function whose confidence interval meets the preset threshold is selected for analysis.

[0040] Furthermore, in step S5, the output of the natural gas pressure energy The analytical mathematical model is:

[0041]

[0042] Among them, e x Natural gas ratio ; C p is the isobaric specific heat capacity of natural gas; T0 is the ambient temperature; T1 is the natural gas temperature at the expander inlet; T2 is the natural gas temperature at the expander outlet; R is the molar gas constant; M is the molar mass of natural gas; P j,t is the uncertain natural gas pressure at pressure regulating station j at time t; P1 is the natural gas pressure at the expander outlet;

[0043] The calculation formula for R is:

[0044]

[0045] Where: ω i is the mass fraction of each component in natural gas, R gi is the gas constant of each component in natural gas;

[0046] pass According to the analytical method, the electric power converted from the pressure energy generated during the natural gas decompression process can be expressed as:

[0047]

[0048] Where: P t is the theoretical power generation during the natural gas decompression process; ρ is the natural gas density under standard conditions; Q sum,t is the natural gas flow rate of the pressure regulating station;

[0049] The actual power generation capacity of natural gas pressure energy is:

[0050] P r =η eP t

[0051] Where: P r is the actual power generation power of pressure energy; η e For the pressure energy generation process efficiency.

[0052] Furthermore, in step S6, the natural gas pressure energy power generation fluctuation analysis model is:

[0053] ΔP=P(t+T)-P(t)

[0054]

[0055] Where: ΔP is the change in natural gas pressure energy output, P(t+T) is the pressure energy output at time t+T; P(t) is the pressure energy output at time t; ξ is the rate of change of natural gas pressure energy output; P basc is the rated installed capacity; T is the time interval.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] 1. The present invention provides a natural gas pressure energy output characteristic analysis method that takes dual uncertainty into account. This method can effectively analyze the factors affecting the natural gas pressure energy output and the output characteristics, thereby helping to improve the utilization efficiency of natural gas pressure energy.

[0058] 2. The present invention analyzes the impact of different natural gas operating conditions on pressure energy power generation, and can improve the utilization efficiency of natural gas pressure energy by changing the natural gas operating conditions.

[0059] 3. This invention analyzes the spatiotemporal characteristics of natural gas pressure energy output, the change amount and change rate of pressure energy output at different time scales, and provides support for the design, promotion, application and operation management of comprehensive utilization schemes of natural gas pressure energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0061] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0062] Figure 1A flow chart of a method for analyzing natural gas pressure energy output characteristics considering dual uncertainty provided by an embodiment of the present invention.

[0063] Figure 2 This is an architecture diagram of the natural gas pressure energy power generation system provided by an embodiment of the present invention.

[0064] Figure 3 A diagram of the regional natural gas pipeline network structure provided by an embodiment of the present invention.

[0065] Figure 4 A natural gas network node flow diagram provided by an embodiment of the present invention.

[0066] Figure 5 A schematic diagram of the error rate probability density function provided by an embodiment of the present invention.

[0067] Figure 6 Schematic diagram of daily changes in natural gas flow at the No. 1 regional pressure regulating station provided in an embodiment of the present invention.

[0068] Figure 7 Schematic diagram of monthly flow rate changes at regional pressure regulating stations No. 1, 2, and 3 provided in an embodiment of the present invention.

[0069] Figure 8 This is a graph of uncertainty flow rate changes provided by an embodiment of the present invention.

[0070] Figure 9 This is a graph of uncertainty pressure change provided by an embodiment of the present invention.

[0071] Figure 10 Schematic diagram of daily power generation of pressure energy in areas 1, 2, and 3 provided in an embodiment of the present invention.

[0072] Figure 11 Schematic diagram of monthly power generation of pressure energy in areas 1, 2, and 3 provided in an embodiment of the present invention.

[0073] Figure 12 A schematic diagram of the rate of change of pressure energy power generation under different time scales provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0074] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0075] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0076] Reference Figure 1 As shown, an embodiment of the present invention provides a method for analyzing natural gas pressure energy output characteristics considering dual uncertainty, the method comprising the following steps:

[0077] S1. Determine the factors affecting the output of natural gas pressure energy based on the power generation system architecture of natural gas pressure energy;

[0078] S2. Determine the constraints of each link in the natural gas transmission process based on the natural gas pipeline network structure and factors affecting the output of the natural gas pressure energy;

[0079] S3. Based on the natural gas pressure energy power generation system architecture and natural gas pipeline network structure, a natural gas load demand model is established to calculate the natural gas load demand at different times and regions;

[0080] S4. Based on the natural gas load demand and uncertainty theory, a dual uncertainty model is established that considers both the natural gas flow rate and pressure, and the uncertain natural gas flow rate and pressure are calculated respectively;

[0081] S5, based on Analyze the theory and establish the output of natural gas pressure energy Analyze the mathematical model and substitute the uncertain natural gas flow and pressure into the output Analyze mathematical models, calculate the power generated by natural gas pressure energy, and analyze the temporal and spatial characteristics of natural gas pressure energy output;

[0082] S6. Establish a natural gas pressure energy power generation fluctuation analysis model, combine the temporal and spatial characteristics of the natural gas pressure energy output, and calculate and analyze the fluctuation of the natural gas pressure energy output on different time scales.

[0083] The following is a detailed description of each of the above steps:

[0084] In the above step S1, this embodiment proposes a method as follows Figure 2 The parallel natural gas pipeline pressure energy power generation system architecture shown is as follows:

[0085] Under normal operation of a natural gas pressure energy power generation system, high-pressure natural gas is preheated and then fed into an expander. The mechanical energy generated drives the generator set, thereby converting and utilizing pressure energy. Because natural gas pressure energy power generation involves an isentropic expansion process, the temperature of the natural gas drops sharply after pressure reduction, which can cause ice blockage. To ensure normal gas supply to downstream residential areas, businesses, gas-fired power generation, industrial production, gas-fired heating, and gas-fired vehicles, heat exchangers are required to effectively utilize pressure energy resources. Under abnormal operation, the high-pressure natural gas is gradually pressure-regulated using conventional branch lines that can be combined, thereby ensuring efficient supply of gas to downstream demand.

[0086] Natural gas pressure energy generation is influenced by numerous factors. These factors include the high-pressure transmission and step-down power generation processes, as well as the parameters of key equipment such as expanders and generators. Furthermore, they are influenced by the natural gas's inherent operating conditions, including its gas quality, flow rate, pressure, temperature, and density. Gas quality and density have relatively little impact on pressure energy generation. Therefore, in this embodiment, the effects of natural gas flow rate, pressure, and temperature are primarily considered. However, flow rate and pressure are related to the gas source and downstream load demand, which is subject to uncertainty due to diurnal and seasonal variations.

[0087] In the above step S2, the natural gas pipeline network structure can be found in the attached Figure 3 As shown in , this embodiment establishes models for each link in the natural gas transmission process based on the natural gas pipeline network structure, power generation system architecture, and the aforementioned factors affecting the output of natural gas pressure energy, and further determines the relevant constraints of the models for each link in the natural gas transmission process; the main aspects include:

[0088] (1) Natural gas source model

[0089] After natural gas is extracted, it undergoes a series of refining and purification steps before being transported over long distances. Limited by the capacity of related equipment, the gas volume produced per unit time by gas well b is subject to upper and lower limits, as shown in the following mathematical expression:

[0090]

[0091] Where: WS b min , WS b max are the upper and lower limits of the gas output of gas well b per unit time; WS is the set of all gas sources.

[0092] (2) Compressor model

[0093] Long-distance natural gas transportation is affected by pipeline friction, requiring pressurization to maintain normal transmission. Since this paper focuses on the pressure energy of natural gas, and the pressurization process consumes relatively little energy, the compressor model is simplified, considering only the relationship between the compressor's inlet and outlet pressures and the transmission capacity limit.

[0094] P i Z c ≥P j (2)

[0095] 0≤P j ≤P c max (3)

[0096] Where: P i 、P j is the natural gas pressure at the compressor inlet and outlet; Z c is the compression factor; P c max Transfer capacity upper limit for the compressor.

[0097] (3) Pipeline flow model

[0098] During the natural gas transmission process, the steady-state equation for flow in the pipeline is affected by factors such as gas pressure, pipeline node pressure, and friction coefficient. Its expression is as follows:

[0099]

[0100]

[0101] Where: Q m km is the natural gas flow rate of the pipeline km section; sng p Represents the airflow direction in the pipeline; T b is the reference temperature (K); P b is the reference pressure (Pa); D is the inner diameter of the pipe (cm); P k 、P m Represents the absolute pressure at nodes k and m respectively; H c km is the slope pipe correction from node k to m; L km is the length of the pipeline from node k to node m (km); is the gas specific gravity; T a km is the average temperature of the pipeline gas connecting nodes k and m; Z a is the compression factor; f is the pipeline friction coefficient; E p For pipeline efficiency.

[0102] (4) Pipeline network node flow model

[0103] The natural gas network can be compared to the power system network, and the pipeline network nodes can be compared to the power network nodes. Therefore, Kirchhoff's law is also applicable to it, and the node flow balance equation is established, that is, the algebraic sum of the natural gas flow at any node at any time is zero. The model is as follows Figure 4 As shown:

[0104] In a natural gas network, the natural gas flow rate flowing into node i must remain within the contractually specified range. The pressure at node i cannot exceed the specified maximum value, but must be above the minimum pressure for normal use by downstream users. The mathematical model is as follows:

[0105]

[0106] Where: f ie,t is the natural gas flow out of node i at time t; f mi,t is the natural gas flow into node i at time t; s i is the net natural gas supply of node i; A is the set of natural gas pipelines connected to node i; e|(i,e)∈A is the natural gas pipeline flowing into node i; m|(m,i)∈A is the natural gas pipeline flowing out of node i; p i,min is the lower limit of the pressure at node i; p i,max is the upper limit of the pressure at node i.

[0107] In the above step S3, a natural gas load demand model is established to calculate the natural gas load demand at different times and regions. In this embodiment, the above natural gas load demand includes:

[0108] (1) Total load of the pressure regulating station

[0109] Changes in natural gas load demand are diverse and complex, with different load demand characteristics at different times and in different regions. Considering the vigorous promotion of the "coal to gas" policy, which has led to a tight natural gas supply during the heating season, the total natural gas load demand at the pressure regulating station during the heating and non-heating seasons is different. The total load demand model for the heating season is:

[0110]

[0111] Where: Q sum,t is the total load demand of different downstream users, m 3 ;Q re,t , Q co,t , Q ge,t , Q in,t , Q he,t , Q CNG,t Gas consumption for residential life, commercial use, gas-fired power generation, industrial production, gas-fired heating, and gas-fired vehicles, m 3 .

[0112] The total load demand model during the non-heating period is:

[0113]

[0114] (2) Residential gas consumption

[0115] Residential gas consumption is affected by factors such as the number of indoor gas-using devices, the number of gas users, gas prices, gas consumption indicators, and natural gas conversion rates. The specific model is as follows:

[0116]

[0117] Where: N is the number of residents; k is the natural gas gasification rate, which is 95%; q i The residential gas consumption quota is MJ / (person·h); q gas The calorific value of natural gas is about 34.5MJ / m 3 .

[0118] (3) Commercial gas consumption

[0119] Commercial gas consumption is affected by factors such as the number and scale of planned businesses, the performance of gas-using equipment, thermal efficiency, the operating conditions of commercial units, and regional climate conditions. Its mathematical model can be expressed as follows:

[0120]

[0121] Where: N is the number of residents; M is the proportion of each type of gas user to the population; q g It is the gas quota for various commercial uses, MJ / (person·h).

[0122] (4) Gas consumption for gas-fired power generation

[0123] The use of gas-fired power generation helps alleviate the pressure of environmental protection and reduce carbon dioxide and nitrogen oxide emissions. Gas-fired power generation accounts for a large proportion of the total natural gas load demand. Its mathematical model is as follows:

[0124]

[0125]

[0126] Where: P ge is the electrical energy generated by the gas turbine, kW; η GT is the power generation efficiency of the gas turbine, %; R GT is the gas turbine load rate; a1, a2, a3, and a4 are constant coefficients.

[0127] (5) Gas consumption in industrial production

[0128] Industrial production gas mainly refers to the amount of natural gas consumed in industrial production using natural gas as fuel or raw material. When the natural gas supply is sufficient, its mathematical model can be expressed as:

[0129]

[0130] If the natural gas supply is insufficient, other fuels will be consumed for industrial production, which can be expressed as:

[0131]

[0132] Where: E i is the output of the i-th type of product; H i Q is the gas consumption index of type i products; y is the consumption of other fuels except natural gas; h i is the calorific value of other fuels, MJ / kg; η i is the thermal efficiency of other fuel combustion equipment, %; η e is the thermal efficiency of natural gas combustion equipment, %.

[0133] (6) Gas consumption for heating

[0134] As the application of natural gas continues to expand, it is gradually being used as a distributed energy source to solve heating and other problems. Its gas consumption mainly depends on the building area used for gas heating, heating heat consumption index, and the length of the annual heating period. The specific mathematical model is as follows:

[0135]

[0136]

[0137] Where: K is the gas heating building area; q h is the heat consumption index of heating buildings, MJ / (m 2 h); e is the maximum utilization hours of heating load; η is the thermal efficiency of the gas heating system, %; e1 is the heating time; t1 is the indoor temperature during the heating period; t2 is the average outdoor temperature during the heating period; t3 is the outdoor temperature during the heating period.

[0138] (7) Gas consumption of gas vehicles

[0139] As a clean and efficient energy source, natural gas can be used in the city gas supply industry and as a vehicle fuel. Gas vehicles are an ideal alternative to electric vehicles. The formula for calculating gas consumption is:

[0140] Q CNG,t =n2Q c +n3Q b +n i Q i(17)

[0141] Where: n2 is the number of CNG taxis; Q c is the gas consumption of a single taxi; n3 is the number of CNG buses; Q b is the gas consumption of a single CNG bus; n i is the number of other CNG vehicles; Q i The gas consumption of other CNG vehicles.

[0142] In the above step S4, based on uncertainty theory, a dual uncertainty model is established that considers both natural gas flow and pressure, and the uncertain natural gas flow and pressure are calculated respectively, specifically:

[0143] The inlet temperature of natural gas pressure-energy power generation fluctuates minimally. Therefore, the present invention primarily considers the uncertainty caused by fluctuations in natural gas flow and pressure. During peak gas demand periods for downstream users, the natural gas flow and pressure at the pressure regulating station are increased to ensure sufficient load and stable pressure. During low gas demand periods, the flow and pressure are reduced.

[0144] Its natural gas flow uncertainty model is as follows:

[0145]

[0146]

[0147] Its natural gas pressure uncertainty model is as follows:

[0148]

[0149]

[0150] Where: is the planned natural gas flow and pressure at pressure regulating station j at time t; ΔQ j,t , ΔP j,t is the error fluctuation of natural gas flow and pressure at time t; ΔZ jQ , ΔZ jP Represent the flow rate and pressure error rates respectively.

[0151] Assume error rate ΔZ jQ , ΔZ jP All obey the normal distribution, and their probability functions are:

[0152]

[0153] Where: μ is the expectation, σ 2 is the variance.

[0154] Based on the actual natural gas flow and pressure fluctuation range of the pressure regulating station, the probability function with a 95% confidence interval is preferably selected for analysis in this embodiment. The probability density diagram is shown as follows: Figure 5 As shown:

[0155] In the above step S5, based on Analyze the theory and establish the output of natural gas pressure energy The analytical mathematical model is as follows:

[0156] The maximum amount of a certain energy that can theoretically be reversibly converted into useful work is called the available energy of that energy. The essence of the analytical method is to combine the first and second laws of thermodynamics and reflect the transfer and conversion of energy. From the perspective of thermodynamics, in this embodiment, the natural gas pipeline network can be regarded as an open system. The analytical method can calculate the pressure energy generated during the natural gas decompression process. Its mathematical model is as follows:

[0157]

[0158] Where: e x Natural gas ratio , kJ / kg; C p is the isobaric specific heat capacity of natural gas, kJ / (kg·K), which is taken as 2.15; T1 is the natural gas temperature at the expander inlet; T2 is the natural gas temperature at the expander outlet; R is the molar gas constant, kJ / (kmol·K); G is the molar mass of natural gas, kg / kmol; P j,t is the uncertainty natural gas pressure of pressure regulating station j at time t (i.e., the natural gas pressure at the expander inlet), MPa (absolute); P1 is the natural gas pressure at the expander outlet, MPa (absolute).

[0159] R is the molar gas constant of natural gas, kJ / (kmol·K), and its calculation formula is:

[0160]

[0161] Where: ω i is the mass fraction of each component in natural gas, R gi is the gas constant of each component in natural gas.

[0162] pass According to the analytical method, the pressure energy generated during the natural gas decompression process can theoretically be converted into electrical power as follows:

[0163]

[0164] Where: P tis the theoretical power generation power of the natural gas decompression process, kW; ρ is the density of natural gas under standard conditions, kg / m 3 ;Q sum,t is the natural gas flow rate of the pressure regulating station (i.e. the total load demand of different downstream users), m 3 / h.

[0165] Due to the influence of equipment efficiency in the pressure difference power generation system, the actual power generation capacity of natural gas pressure energy is:

[0166] P r =η e P t (26)

[0167] Where: P r is the actual power generation power of pressure energy, kW; η e For the pressure energy generation process efficiency.

[0168] In the above step S6, a natural gas pressure energy power generation fluctuation analysis model is established, specifically as follows:

[0169] The natural gas pressure energy output fluctuation is used to describe the power variation characteristics of its power generation on different time scales. In this embodiment, the pressure energy output variation and output variation rate are selected as two core indicators to reflect the power fluctuation.

[0170] The pressure energy power generation output variation (fluctuation) refers to the difference in power generation between two time points within a certain period of time, which can be used to characterize the magnitude of power generation variation. The pressure energy power generation power change rate (fluctuation rate) refers to the percentage of power generation output variation to rated installed capacity, which can be used to quantitatively evaluate power fluctuation. Its mathematical model is as follows:

[0171] ΔP=P(t+T)-P(t) (27)

[0172]

[0173] Where: P(t+T) is the pressure energy power generation output at time t+T; P(t) is the pressure energy power generation output at time t; P basc is the rated installed capacity; for different time scales, T corresponds to different values.

[0174] The present invention is further described in detail using a specific embodiment. It is necessary to point out that the specific implementation case described here is only used to illustrate the present invention and cannot be understood as limiting the scope of the present invention. The specific steps are as follows:

[0175] (1) Take a city's natural gas pipeline network as an example to analyze the pressure output characteristics. The regional pipeline network structure is as follows: Figure 3As shown in Figure 1, the pipeline network consists of two gas sources, 34 nodes, 50 pipe sections, and 17 loops. The two gas sources are located at nodes 16 and 34, respectively. Three natural gas pressure regulating stations are located at nodes 6, 32, and 33, respectively. The gas supply ranges of these pressure regulating stations can be divided into three distinct regions. Downstream natural gas load types can be broadly categorized as residential, commercial, gas-fired power generation, industrial production, and gas-fired vehicles. By analyzing the changes in natural gas load demand over time and across regions, the pressure-energy-output characteristics can be analyzed.

[0176] (2) By using equations (7)-(17), the natural gas flow rate is calculated using various downstream natural gas load demand models, and then the changing patterns of the natural gas flow rate of each regional pressure regulating station within one day and one year are analyzed, respectively. Figure 6 、 Figure 7 As shown:

[0177] (3) Considering that the natural gas flow and pressure at the pressure regulating station are affected by the downstream load demand, there is a certain degree of volatility. By constructing the dual uncertainty model of formulas (18)-(22), by intercepting Figure 5 The error probability function with a confidence interval of 95% is analyzed, and the uncertainty curves of natural gas flow and pressure change are calculated using the random sampling method, as shown in Figure 2. Figure 8 、 Figure 9 As shown:

[0178] (4) Output of natural gas pressure energy through construction The mathematical model is analyzed. Given the expander outlet natural gas pressure and temperature of 1.6 MPa and 15°C respectively, the influence of different flow rates, inlet pressures and temperatures on the pressure energy output is analyzed by the control variable method.

[0179] (5) The uncertainty of natural gas flow and pressure is calculated by equations (18)-(22), and then the power output is based on the natural gas pressure. Analyze the mathematical model, use formula (23)-(26) and the typical parameter values ​​of the three regional pressure regulating stations (the relevant parameter values ​​of typical natural gas pressure regulating stations are shown in Table 1 below), calculate the pressure energy power generation, and analyze the spatiotemporal characteristics of natural gas pressure energy output. Figure 10 、 Figure 11 As shown:

[0180] Table 1 Values ​​of relevant parameters of typical natural gas pressure regulating stations

[0181] area Pressure after pressure regulation / MPa Temperature before pressure regulation / K Temperature after pressure regulation / K 1 3.1 313.15 275.65 2 2.8 313.15 281.65 3 3.1 313.15 281.65

[0182] (6) Based on the time characteristics of the natural gas pressure output, in this embodiment, area 1 is selected as an example, and the time intervals T = 15 min, 30 min, 1 h, and 3 h are taken. The volatility index of pressure energy on different time scales is calculated by using formulas (27) and (28). Figure 12 The results show that the smaller the time interval T is, the more concentrated the pressure energy output power change rate is within ±0.1pu, and the weaker the pressure energy power generation fluctuation is, and vice versa.

[0183] In view of the problem that existing research on natural gas pressure energy mainly focuses on the principles of pressure energy power generation, research on key equipment for pressure difference power generation, and forms of pressure energy utilization, but lacks research on the factors affecting natural gas pressure energy and output characteristics, an embodiment of the present invention provides a natural gas pressure energy output characteristic analysis method considering dual uncertainty. This method conducts a detailed analysis of the factors affecting pressure energy output and the spatiotemporal characteristics of output, and proposes a volatility index to measure the pressure energy output characteristics. It can effectively analyze the factors affecting natural gas pressure energy output and the output characteristics, help improve the utilization efficiency of natural gas pressure energy, and lay the foundation for the promotion and application of natural gas pressure energy, pressure energy power generation and consumption, and the design and operation management of comprehensive pressure energy utilization plans.

[0184] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A natural gas pressure energy output characteristic analysis method considering dual uncertainty, characterized in that: The method comprises the following steps: S1. Determine the factors affecting the output of natural gas pressure energy based on the power generation system architecture of natural gas pressure energy; S2. Determine the constraints of each link in the natural gas transmission process based on the natural gas pipeline network structure and factors affecting the output of the natural gas pressure energy; S3. Based on the natural gas pressure energy power generation system architecture and natural gas pipeline network structure, a natural gas load demand model is established to calculate the natural gas load demand at different times and regions; S4. Based on the natural gas load demand and uncertainty theory, a dual uncertainty model is established that considers both the natural gas flow rate and pressure, and the uncertain natural gas flow rate and pressure are calculated respectively; S5, based on Analyze the theory and establish the output of natural gas pressure energy Analyze the mathematical model and substitute the uncertain natural gas flow and pressure into the output Analyze mathematical models, calculate the power generated by natural gas pressure energy, and analyze the temporal and spatial characteristics of natural gas pressure energy output; S6. Establish a natural gas pressure energy power generation fluctuation analysis model, combine the temporal and spatial characteristics of the natural gas pressure energy output, and calculate and analyze the fluctuation of the natural gas pressure energy output on different time scales.

2. A natural gas pressure energy output characteristic analysis method considering dual uncertainty according to claim 1, characterized in that: In step S1, the factors affecting the output of the natural gas pressure energy include: a. The process of high-voltage transmission and step-down power generation; b. Equipment parameters of compressor, expander and generator; c. Parameters of natural gas quality, flow, pressure, temperature and density.

3. A natural gas pressure energy output characteristic analysis method considering dual uncertainty according to claim 2, characterized in that: In step S2, the constraints of each link in the natural gas transmission process include: ① Upper and lower limits on the amount of gas produced per unit time by the natural gas source; ②Compressor inlet and outlet pressure and transmission capacity constraints; ③ Constraints on pipeline natural gas flow and airflow direction; ④ Flow and pressure constraints at pipeline network nodes.

4. A natural gas pressure energy output characteristic analysis method considering dual uncertainty according to claim 3, characterized in that: In step S3, the natural gas load demand model includes: The total load model of the pressure regulating station, the residential gas consumption model, the commercial gas consumption model, the gas power generation gas consumption model, the industrial production gas consumption model, the gas heating gas consumption model and the gas vehicle gas consumption model.

5. The natural gas pressure energy output characteristic analysis method considering dual uncertainty according to claim 4 is characterized in that: In step S4, the dual uncertainty model of natural gas flow and pressure includes: Traffic uncertainty model: Pressure uncertainty model: Where: Q j,t 、P j,t are the uncertain natural gas flow and pressure at the pressure regulating station j at time t, are the planned natural gas flow and pressure at the pressure regulating station j at time t; ΔQ j,t , ΔP j,t are the natural gas flow rate and pressure error fluctuation at time t; ΔZ jQ , ΔZ jP Represent the error rates of natural gas flow and pressure respectively.

6. A natural gas pressure energy output characteristic analysis method considering dual uncertainty according to claim 5, characterized in that: The error rate ΔZ of the natural gas flow and pressure jQ , ΔZ jP It obeys the normal distribution, and its probability function is: Where: μ is the expectation, δ 2 is the variance; Based on the fluctuation range of natural gas flow and pressure at the pressure regulating station, the probability function whose confidence interval meets the preset threshold is selected for analysis.

7. The natural gas pressure energy output characteristic analysis method considering dual uncertainty according to claim 6, characterized in that: In step S5, the output of the natural gas pressure energy The analytical mathematical model is: Among them, e x Natural gas ratio C p is the isobaric specific heat capacity of natural gas; T0 is the ambient temperature; T1 is the natural gas temperature at the expander inlet; T2 is the natural gas temperature at the expander outlet; R is the molar gas constant; M is the molar mass of natural gas; P j,t is the uncertain natural gas pressure at pressure regulating station j at time t; P1 is the natural gas pressure at the expander outlet; The calculation formula for R is: Where: ω i is the mass fraction of each component in natural gas, R gi is the gas constant of each component in natural gas; pass According to the analytical method, the electric power converted from the pressure energy generated during the natural gas decompression process can be expressed as: Where: P t is the theoretical power generation during the natural gas decompression process; ρ is the natural gas density under standard conditions; Q sum,t is the natural gas flow rate of the pressure regulating station; The actual power generation capacity of natural gas pressure energy is: P.S r Hη e P.S t Where: P r is the actual power generation power of pressure energy; η e For the pressure energy generation process efficiency.

8. The natural gas pressure energy output characteristic analysis method considering dual uncertainty according to claim 7, characterized in that: In step S6, the natural gas pressure energy power generation fluctuation analysis model is: ΔP=P(t+T)-P(t) Where: ΔP is the change in natural gas pressure energy output, P(t+T) is the pressure energy output at time t+T; P(t) is the pressure energy output at time t; ξ is the rate of change of natural gas pressure energy output; P basc is the rated installed capacity; T is the time interval.

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