An operation optimization method for a gas-electricity integrated system considering hydrogen blending in natural gas pipelines

Abstract

An operation optimization method for a gas-electricity integrated system considering hydrogen blending in natural gas pipelines, the method comprising the following steps: S1, collecting the basic parameters of the gas-electricity integrated system and the prediction curves of the electricity load, natural gas load and renewable energy output in the gas-electricity integrated system; S2, establishing a calculation model for the mass flow rates of natural gas and hydrogen at the nodes of the natural gas network; S3, establishing a dynamic model of the natural gas system considering hydrogen blending in pipelines; S4, establishing an optimal operation model for the gas-electricity integrated system considering hydrogen blending in natural gas pipelines, and solving the model to obtain the daily startup mode. This design not only reduces the system operation cost, but also reduces the carbon emissions.

Description

Technical Field

[0001] The present invention relates to the field of electrical engineering, and particularly to an operation optimization method for a gas-electricity integrated system considering hydrogen blending in natural gas pipelines, which is mainly applicable to cost reduction and carbon emission reduction. Background Art

[0002] In order to address environmental problems such as the excessive consumption of fossil energy and global warming, renewable energy has been widely used worldwide. In the future energy supply system, electricity will be the main source, and it is an inevitable trend for non-renewable energy units such as thermal power to gradually withdraw and the proportion of renewable energy to continuously increase. However, the volatility of the output of renewable energy such as wind power and photovoltaic power poses higher requirements for the flexibility of power system operation to effectively ensure the security of system operation.

[0003] Gas turbines not only have good dynamic characteristics and can quickly respond to the fluctuations in the output of renewable energy, but also cause less environmental pollution compared with traditional coal-fired units. Therefore, they are increasingly widely used in power systems. At the same time, with the emergence and development of the power-to-gas (P2G) technology, the surplus renewable energy electricity in the power system can be further consumed by converting it into natural gas (mainly referring to CH4) and pumping it into the natural gas pipeline network. At the same time, the coupling between the power system and the natural gas system is further strengthened. By using gas turbines and P2G units to achieve bidirectional coupling between the two, the consumption of renewable energy can be promoted while improving the flexibility and security of system operation.

[0004] With the rapid development of hydrogen energy, higher requirements are also put forward for hydrogen energy storage and transportation technologies. By utilizing the gas storage capacity of pipelines, the transportation and storage of hydrogen can be achieved simultaneously. However, there is a problem of large upfront investment in building dedicated hydrogen transmission lines. In this regard, if the technology of hydrogen-blended natural gas can be developed, the existing natural gas pipelines can be utilized, and through limited transformation, the large-scale transportation of the mixed gas can be realized, so that the large-scale storage and transportation of hydrogen can be achieved with less investment, effectively promoting the transformation of the energy structure and the realization of the "dual carbon" goal. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects and problems of high cost and high carbon emissions in the prior art, and provide an operation optimization method for a gas-electricity integrated system considering hydrogen blending in natural gas pipelines with low cost and low carbon emissions.

[0006] To achieve the above purpose, the technical solution of the present invention is: an operation optimization method for a gas-electricity integrated system considering hydrogen blending in natural gas pipelines, the method comprising the following steps:

[0007] S1. Collect the basic parameters of the gas-electricity combined system and the prediction curves of the power load, natural gas load, and renewable energy output in the gas-electricity combined system;

[0008] S2. Establish a calculation model for the mass flow rates of natural gas and hydrogen at the nodes of the natural gas network;

[0009] S3. Establish a dynamic model of the natural gas system considering hydrogen blending in pipelines;

[0010] S4. Establish an optimal operation model of the gas-electricity combined system considering hydrogen blending in natural gas pipelines, and solve the model to obtain the daily startup pattern.

[0011] In step S2, the hydrogen blending ratio of natural gas in the pipeline is defined as:

[0012]

[0013] In the formula, R V is the volume ratio of hydrogen blending in natural gas, is the volume of hydrogen in the pipeline at time t, is the volume of natural gas in the pipeline at time t, Δt is the time step, is the density of hydrogen at the considered node at time t, is the density of natural gas at the considered node at time t, is the mass of hydrogen in the pipeline at time t, is the mass of natural gas in the pipeline at time t, is the mass flow rate of hydrogen at the considered node at time t, is the mass flow rate of natural gas at the considered node at time t;

[0014] The relationship between the mass flow rate of hydrogen and the mass flow rate of natural gas is:

[0015]

[0016] Let Then:

[0017]

[0018] Denote the mass flow rate of the mixed gas at time t as It can be obtained that:

[0019]

[0020]

[0021]

[0022] The gas state equation is:

[0023]

[0024]

[0025] In the formula, is the hydrogen pressure at the node considered at time t, is the natural gas pressure at the node considered at time t, and c is the speed of sound;

[0026] Then under standard conditions, there is:

[0027]

[0028]

[0029] By combining the equations, we can obtain:

[0030]

[0031] Furthermore, there is:

[0032]

[0033] Under the condition that P V is determined, K t is a constant, denoted as K.

[0034] In step S3, the movement process of the mixed gas is described by the following three equations:

[0035] Momentum equation of the mixed gas:

[0036]

[0037] In the formula, A ij is the cross-sectional area of pipeline ij, M Fij，t+1 is the mass flow rate of the mixed gas at the front end of pipeline ij at time t + 1, M Eij，t+1 is the mass flow rate of the mixed gas at the end of pipeline ij at time t + 1, M Fij，t is the mass flow rate of the mixed gas at the front end of pipeline ij at time t, ME ij，t is the mass flow rate of the mixed gas at the end of pipeline ij at time t, Δt is the time step, L ij is the length of the pipeline, p j，t+1 is the mixed gas pressure at the end node j of pipeline ij at time t + 1, p i，t+1 is the mixed gas pressure at the front node i of pipeline ij at time t + 1, p j，t is the mixed gas pressure at the end node j of pipeline ij at time t, p i，t is the mixed gas pressure at the front node i of pipeline ij at time t, and λ is the friction coefficient. is the average flow velocity of the mixed gas in pipeline ij, d ij is the diameter of pipeline ij;

[0038] Pipeline material balance equation:

[0039]

[0040] Gas state equation:

[0041] p = c 2 ρ

[0042] Wherein, c is the speed of sound, p is the pressure of the mixed gas, and ρ is the density of the mixed gas.

[0043] In step S3, the boundary condition constraints of each node in the natural gas system are:

[0044] (1) The mass flow rate of the mixed gas at the load node is:

[0045]

[0046]

[0047] Wherein, represents the gas load mass flow rate of load node i at time t without considering hydrogen blending, represents the mass flow rate of the mixed gas at load node i at time t after hydrogen blending, represents the calorific value of hydrogen, represents the calorific value of natural gas, K I is the set of load nodes, M Eki，t is the mass flow rate of the mixed gas at the end of pipeline ki at time t;

[0048] (2) The pressure and density constraints of the mixed gas at the gas source node are:

[0049]

[0050] Wherein, p sj is the pressure of the mixed gas at the gas source node, ρ si is the density of the mixed gas at the gas source node;

[0051] (3) The material balance constraint of each intermediate connection node in the natural gas network is:

[0052]

[0053] Wherein, (.)k represents the set of natural gas pipelines with the end node k, k(.) represents the set of natural gas pipelines with the front node k, K m is the set of connection nodes;

[0054] (4) Upper and lower limit constraints on pipeline mass flow and nodal air pressure:

[0055]

[0056]

[0057]

[0058] In step S4, the objective function of the gas - electric combined optimal operation model is:

[0059]

[0060] In the formula, N g is the number of traditional thermal power units, c coal is the real - time price of standard coal in the current month, N gas is the number of gas source nodes in the natural gas system, is the coal consumption of thermal power unit i at time t, is the unit start - stop cost of thermal power unit i; S udi，t is the change in the start - stop state of thermal power unit i at time t, which is a 0 - 1 variable. When the start - stop state at time t is different from the previous moment, S udi，t = 1, otherwise, S udi，t = 0; c M is the price of natural gas, c H is the price of hydrogen, is the mass flow of natural gas in the mixed gas injected into the gas source node of the natural gas network, is the mass flow of hydrogen in the mixed gas injected into the gas source node of the natural gas network, and Δt is the time step.

[0061] In step S4, the constraint conditions of the gas - electric combined optimal operation model are:

[0062] (1) Power balance constraint

[0063]

[0064] In the formula, is the wind power of wind farm i at time t, is the load power of load j at time t, is the output of thermal power unit i at time t, is the output of the gas - fired unit at time t, is the power consumption of the power - to - gas unit i at time t;

[0065] (2) Branch transmission capacity constraint

[0066] -f 1im ≤SP≤f1im

[0067] Wherein, f lim is the column vector of the maximum transmission power of the line, S is the sensitivity matrix for determining the line transmission power from the node injection power, and P is the column vector of injection power composed of the injection powers of each node;

[0068] (3) Constraints on the upper and lower limits of unit output

[0069]

[0070]

[0071]

[0072] Wherein, u i，t is the on - off state of thermal power unit i at time t, which is a 0 - 1 variable. When it is in the state of starting up at time t, u i，t = 1, otherwise, u i，t = 0; P i g，max is the minimum output limit of the thermal power unit, P i g，min is the maximum output limit of the thermal power unit, P i gas，max is the maximum output limit of the gas turbine unit, P i p2g，max is the maximum consumption power of the thermal power unit;

[0073] (4) Constraints on the start - stop state of thermal power units

[0074] S udi，1 = 0

[0075]

[0076]

[0077] (5) Constraints on the minimum start - stop time of thermal power units

[0078] u i，t-1 ≤u i，t ≤T i U

[0079] u i，j ≤u i，t-1 t≤T i D

[0080]

[0081]

[0082] Wherein, T i U is the minimum on - line time that unit i needs to maintain, and T i D is the minimum off - line time that unit i needs to maintain;

[0083] (6) Unit ramp - up and ramp - down constraints

[0084]

[0085]

[0086] Wherein, is the maximum up - ramp power of thermal power unit i, is the maximum down - ramp power of thermal power unit i, and M is a constant;

[0087] (7) Gas turbine unit operation constraints

[0088]

[0089] Wherein, is the gas - to - electricity conversion efficiency of gas turbine unit i for hydrogen - blended natural gas, is the gas mass flow rate consumed by gas turbine unit i;

[0090] (8) Power - to - gas unit operation constraints

[0091]

[0092]

[0093]

[0094] Wherein, is the power consumption of the power - to - methane unit at power - to - gas node i at time t, is the power consumption of the power - to - hydrogen unit at power - to - gas node i at time t, is the produced gas mass flow rate of power - to - gas at power - to - gas node i, is the gas production efficiency of the power - to - methane unit at power - to - gas node i, is the gas production efficiency of the power - to - hydrogen unit at power - to - gas node i.

[0095] Compared with the prior art, the beneficial effects of the present invention are:

[0096] In an operation optimization method of a gas-electricity integrated system considering hydrogen blending in natural gas pipelines of the present invention, a dynamic model of the natural gas system considering hydrogen blending in pipelines is established. In the model, a calculation model of the mass flow rates of natural gas and hydrogen at the nodes of the natural gas network is established according to the hydrogen blending ratio in the natural gas pipelines. And a natural gas system model considering dynamic energy flow is established based on the pipeline momentum equation and the material balance equation, which more accurately expresses the dynamic operation process of the natural gas system. On this basis, an operation optimization method of the gas-electricity integrated system considering hydrogen blending in natural gas pipelines is proposed, taking into account the dynamic characteristics of the natural gas system, and making full use of the characteristics of gas turbines, power-to-methane units, and electrolytic hydrogen production units to achieve two-way energy coupling between the power system and the natural gas system. While improving the flexibility of the system, it promotes the consumption of renewable energy, reduces carbon emissions, and provides a reference for the application of hydrogen-blended natural gas pipeline technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0097] Figure 1 is a flowchart of an operation optimization method of a gas-electricity integrated system considering hydrogen blending in natural gas pipelines of the present invention.

[0098] Figure 2 is a schematic diagram of the topology of a 39-node power system in an embodiment of the present invention.

[0099] Figure 3 is a schematic diagram of the topology of a 27-node natural gas system in an embodiment of the present invention.

[0100] Figure 4 is a curve graph of power load, wind power output, and natural gas load in an embodiment of the present invention.

[0101] Figure 5 is a schematic diagram of the start-up mode of a thermal power unit in an embodiment of the present invention.

[0102] Figure 6 is a schematic diagram of the output of each unit in the gas-electricity integrated system in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0103] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0104] See Figure 1 , an operation optimization method of a gas-electricity integrated system considering hydrogen blending in natural gas pipelines, the method includes the following steps:

[0105] S1. Collect the basic parameters of the gas-electricity integrated system and the predicted curves of power load, natural gas load, and renewable energy output in the gas-electricity integrated system;

[0106] Determine the topological structure of the gas-electricity integrated system (i.e., the studied power system and natural gas system) and the topological connection between the two, and determine the relevant parameters of each component, device, and equipment in the gas-electricity integrated system. The relevant components, devices, and equipment mainly include: power system lines, natural gas system pipelines, thermal power units, gas turbines, wind turbines, and power-to-gas units;

[0107] Collect the predicted curves of the power load, natural gas load, and wind power output in the studied gas-electricity integrated system as the known input data for the optimal operation of the gas-electricity integrated system;

[0108] S2. Establish a calculation model for the mass flow rates of natural gas and hydrogen at the nodes of the natural gas network;

[0109] For the hydrogen-blended natural gas pipeline, to ensure the safe and reliable operation of the pipeline, the method of equal-proportion hydrogen blending is adopted, and it is assumed that the natural gas (mainly methane CH 4 ) and hydrogen in the pipeline are mixed evenly. Define the hydrogen blending ratio of natural gas in the pipeline as:

[0110]

[0111] Perform the following transformation on the above formula:

[0112]

[0113] In the formula, R V is the volume ratio of hydrogen in natural gas, that is, the ratio of the volume of hydrogen incorporated into the pipeline to the volume of natural gas, with a dimension of 1; is the volume of hydrogen in the pipeline at time t, is the volume of natural gas in the pipeline at time t, Δt is the time step, is the density of hydrogen at the considered node at time t, is the density of natural gas at the considered node at time t, is the mass of hydrogen in the pipeline at time t, is the mass of natural gas in the pipeline at time t, is the mass flow rate of hydrogen at the considered node at time t, is the mass flow rate of natural gas at the considered node at time t;

[0114] The relationship between the mass flow rate of hydrogen and the mass flow rate of natural gas is:

[0115]

[0116] Let Then:

[0117]

[0118] The mass flow rate of the mixed gas at time t is We can get:

[0119]

[0120]

[0121]

[0122] The gas state equation is:

[0123]

[0124]

[0125] In the formula, is the pressure of hydrogen at the node considered at time t, is the pressure of natural gas at the node considered at time t, c is the speed of sound;

[0126] Under standard conditions, we have:

[0127]

[0128]

[0129] The joint column can be obtained:

[0130]

[0131] Further:

[0132]

[0133] In R V If it is determined, K t is a constant, denoted as K;

[0134] S3. Establish a dynamic model of the natural gas system considering pipeline hydrogen blending;

[0135] For natural gas in pipelines, its transmission process is driven by the pressure at both ends of the pipeline and is related to its own temperature, density and other factors. The flow process of natural gas in pipelines can be regarded as a one-dimensional fluid motion process with state variables of velocity, density and pressure. For hydrogen-blended natural gas pipelines, it is assumed that natural gas and hydrogen are evenly mixed and the hydrogen mixing volume ratio remains constant.

[0136] Considering the slow dynamic process of the mixed gas in the pipeline caused by the load change of the natural gas network node, the movement process of the mixed gas can be described by the following three equations: pipeline momentum equation, pipeline material balance equation and gas state equation.

[0137] The pipeline momentum equation, i.e., the Navier-Stokes equation, is used to describe the momentum transport of the mixed gas in the pipeline:

[0138]

[0139] where t and x represent time and spatial distance respectively; p is the gas pressure with the unit of Pa; ω is the gas flow velocity with the unit of m / s; ρ and ρ α represent the gas density parallel to the horizontal plane and the gas density at an angle α with the horizontal plane respectively, with the unit of kg / m 3 ; d is the pipeline diameter with the unit of m; g is the acceleration due to gravity with the unit of m / s 2 ; λ represents the friction coefficient; describes the acceleration effect of the mixed gas in the pipeline; describes the convection effect of the mixed gas; describes the hydrostatic effect of the mixed gas; g(ρ - ρ a )sinα describes the influence of the horizontal height on the momentum equation; represents the second-order partial stress tensor component;

[0140] The material balance equation in the natural gas pipeline describes the flow of the mixed gas in the pipeline:

[0141]

[0142] The gas state equation is constructed between the pipeline gas pressure and density through the sonic velocity c:

[0143] p = c 2 ρ

[0144] The gas material momentum transport equation in the pipeline based on fluid mechanics is very complex. The gas momentum transport equation and the pipeline material balance equation are complex partial differential equations. In this method, these two equations are simplified through certain assumptions.

[0145] Assume that the gas transmission in the pipeline is an isothermal process, that is, the influence of temperature change is ignored, then the sonic velocity remains unchanged; since the convection term only exists when the fluid velocity is close to the sonic velocity, for the flow process of the mixed gas in the pipeline, this term can be ignored; at the same time, it is considered that the pipeline height remains unchanged, then the term related to the height is also 0; under the above assumptions, the gas momentum transport equation can be simplified to:

[0146]

[0147] Since the partial stress tensor in the momentum equation is a non-linear term containing the product of the square of the gas flow velocity ω and the density ρ, in order to linearize the model, the average flow velocity of the mixed gas is used to approximately represent the quadratic term in the above formula:

[0148]

[0149] Meanwhile, the mass flow rate M of the mixed gas, with the unit of kg / s, is adopted to represent the flow condition of the mixed gas in the pipeline, and it has the following relationship with the density ρ of the mixed gas, the flow velocity ω, and the cross-sectional area A (m 2 ) as follows:

[0150] M = ρωA

[0151] By substituting the mass flow rate M for the flow velocity ω in the momentum equation and the pipeline material balance equation, and at the same time using the state equation to express the density ρ in the formula with the pressure p, it can be further simplified:

[0152]

[0153]

[0154] After a certain simplification, the natural gas momentum equation and the pipeline material balance equation are still partial differential equations and cannot be directly applied in the optimization field. Therefore, the Lax-Wendroff difference method is used to linearly difference the above partial differential equations. The general form of the Lax-Wendroff difference method is as follows:

[0155]

[0156]

[0157]

[0158] In the formula, Δt and Δx are the step sizes of time and spatial distance respectively;

[0159] For perform differential linearization, where for the spatial distance x, a variable step size form is adopted, that is, for the dynamic equation and the material balance equation of each pipeline ij, its Δx is equal to the pipeline length L ij , and at the same time the pipeline node subscript i + 1 also corresponds to the end node j of the pipeline; for any pipeline ij, there are linearized mixed gas momentum equations and pipeline material balance equations;

[0160] Mixed gas momentum equation:

[0161]

[0162] In the formula, A ij is the cross-sectional area of pipeline ij, M Fij，t+1 is the mass flow rate of the mixed gas at the front end of pipeline ij at time t + 1, M Eij，t+1is the mass flow rate of the mixed gas at the end of pipeline ij at time t+1, M Fij，t is the mass flow rate of the mixed gas at the front end of pipeline ij at time t, M Eij，t is the mass flow rate of the mixed gas at the end of pipeline ij at time t, Δt is the time step, L ij is the length of the pipeline, p j，t+1 is the mixed gas pressure at the end node j of pipeline ij at time t+1, p i，t+1 is the mixed gas pressure at the front node i of pipeline ij at time t+1, p j，t is the mixed gas pressure at the end node j of pipeline ij at time t, p i，t is the mixed gas pressure at the front node i of pipeline ij at time t, λ is the friction coefficient, is the average flow velocity of the mixed gas in pipeline ij, d ij is the diameter of pipeline ij;

[0163] Pipeline material balance equation:

[0164]

[0165] Gas state equation:

[0166] p = c 2 ρ

[0167] In the formula, c is the speed of sound, p is the mixed gas pressure, and ρ is the mixed gas density;

[0168] The boundary condition constraints of each node in the natural gas system are:

[0169] (1) Assuming that hydrogen and natural gas are mixed evenly into a gas with a unified mixed calorific value, the mass flow rate of the mixed gas at the load node is:

[0170]

[0171]

[0172] In the formula, represents the gas load mass flow rate of load node i at time t without considering hydrogen doping, represents the mass flow rate of the mixed gas at load node i at time t after hydrogen doping, represents the calorific value of hydrogen, represents the calorific value of natural gas, K I is the set of load nodes, M Eki，t is the mass flow rate of the mixed gas at the end of pipeline ki at time t;

[0173] (2) The mixed gas pressure and mixed gas density constraints of the gas source node are:

[0174]

[0175] where p s i is the mixed gas pressure of the gas source node, ρ si is the mixed gas density of the gas source node;

[0176] (3) The material balance constraint for each intermediate connection node in the natural gas network is:

[0177]

[0178] where (.)k represents the set of natural gas pipelines with the end node being k, k(.) represents the set of natural gas pipelines with the previous node being k, and K m is the set of connection nodes;

[0179] (4) Upper and lower limit constraints on pipeline mass flow and node air pressure:

[0180]

[0181]

[0182]

[0183] S4. Establish a gas - electric integrated optimal operation model considering hydrogen blending in natural gas pipelines, and solve the model to obtain the daily startup pattern;

[0184] Based on the dynamic model of the natural gas system considering pipeline hydrogen blending proposed in step S3, considering the energy bidirectional coupling effect of gas - fired units (GFU) and power - to - gas (P2G) units during the combined operation of the power system and the natural gas system, a gas - electric integrated optimal operation model considering hydrogen blending in natural gas pipelines is established;

[0185] The objective of the proposed gas - electric integrated optimal operation model is to minimize the operation cost of the combined system, that is, the sum of the operation costs of the power system and the natural gas system. The piece - wise linearization method is used to linearize the operation cost of thermal power units. The objective function of the gas - electric integrated optimal operation model is:

[0186]

[0187] where N g is the number of traditional thermal power units, c coal is the real - time price of standard coal in the current month, N gas is the number of gas source nodes in the natural gas system, is the coal consumption (t) of thermal power unit i at time t, is the unit start - stop cost (yuan / time) of thermal power unit i; S udi，tThe start-stop status change of thermal power unit i at time t, which is a 0-1 variable. When the start-stop status at time t is different from the previous time, S udi，t = 1; otherwise, S udi，t = 0; c M is the price of natural gas (yuan / kg), c H is the price of hydrogen (yuan / kg), is the mass flow rate of natural gas in the mixed gas injected at the gas source node of the natural gas network (kg / m 3 ), is the mass flow rate of hydrogen in the mixed gas injected at the gas source node of the natural gas network (kg / m 3 ), and Δt is the time step;

[0188] For the gas-electricity integrated system considering hydrogen blending in natural gas pipelines, in addition to meeting the constraints on the natural gas system in step S3, it also needs to meet the operation and safety constraints of the power system, as well as the energy coupling constraints between the natural gas system and the power system;

[0189] The constraint conditions of the gas-electricity integrated optimal operation model are as follows:

[0190] (1) Power balance constraint

[0191]

[0192] In the formula, is the wind power of wind farm i at time t (MW), is the load power of load j at time t (MW), is the output of thermal power unit i at time t (MW), is the output of the gas turbine unit at time t (MW), is the power consumption of the power-to-gas unit i at time t (MW);

[0193] (2) Branch transmission capacity constraint

[0194] -f lim ≤SP≤f lim

[0195] In the formula, f lim is the column vector of the maximum transmission power of the line, S is the sensitivity matrix for determining the line transmission power from the node injection power, and P is the injection power column vector composed of the injection powers of each node;

[0196] (3) Unit output upper and lower limit constraints

[0197]

[0198]

[0199]

[0200] where u i，t is the start-up and shut-down state of thermal power unit i at time t, which is a 0-1 variable. When it is in the start-up state at time t, u i，t = 1; otherwise, u i，t = 0; P i g，max is the minimum output limit of the thermal power unit, and P i g，min is the maximum output limit of the thermal power unit, and P i gas，max is the maximum output limit of the gas turbine unit, and P i p2g，max is the maximum power consumption of the thermal power unit;

[0201] (4) Start-up and shut-down state constraints of thermal power units

[0202] S udi，1 = 0

[0203]

[0204]

[0205] Without considering the change in the start-up and shut-down state of the unit at the initial moment, so let S udi，1 = 0;

[0206] (5) Minimum start-up and shut-down time constraints of thermal power units

[0207] u i，t-1 ≤ u i，t t ≤ T i U

[0208] u i，t ≤ u i，t-1 t ≤ T i D

[0209]

[0210]

[0211] where T i U is the minimum start-up time that unit i needs to maintain, and T i D is the minimum shut-down time that unit i needs to maintain;

[0212] (6) Unit ramp rate constraints

[0213]

[0214]

[0215] In the formula, is the maximum upward ramp power (MW / h) of thermal power unit i, is the maximum downward ramp power (MW / h) of thermal power unit i, and M is a constant;

[0216] (7) Gas turbine unit operation constraints

[0217]

[0218] In the formula, is the gas-electricity conversion efficiency (MW / (kg / s)) of gas turbine unit i for hydrogen-blended natural gas, is the gas mass flow rate (kg / s) consumed by gas turbine unit i;

[0219] (8) Power-to-gas unit operation constraints

[0220]

[0221]

[0222]

[0223] In the formula, is the power consumption (MW) of the power-to-methane (P2M) unit at power-to-gas node i at time t, is the power consumption of the power-to-hydrogen (P2H) unit at power-to-gas node i at time t, is the gas production mass flow rate (kg / s) of power-to-gas at power-to-gas node i, is the gas production efficiency of the power-to-methane (P2M) unit at power-to-gas node i, is the gas production efficiency ((kg / s) / MW) of the power-to-hydrogen (P2H) unit at power-to-gas node i.

[0224] This embodiment analyzes the integrated gas-electricity system composed of a 39-node power system and a 27-node natural gas system. As Figure 2 , Figure 3 shown, considering the equal-proportion hydrogen blending in the natural gas pipeline, the hydrogen blending volume ratio is set to 5%; this system has a total of 6 coal-fired units, 2 gas turbine units (GFU), 2 wind turbine units, and 2 P2G units; power system nodes 32 and 33 are connected to natural gas system nodes 13 and 22 through gas turbine units, and power system nodes 17 and 22 are connected to natural gas system nodes 27 and 8 through P2G units. The unit parameters are shown in Table 1. The power load, wind power pre-output, and natural gas load curves in the integrated gas-electricity system are as Figure 4As shown, the coal price is 500 yuan / t, the natural gas price is 2 yuan / kg, and the hydrogen price is 20 yuan / kg.

[0225] Based on the above parameters collected, a model of the gas-electricity combined system is established according to this method and solved. The operating costs of the system are shown in Table 2, and the start-up modes of the thermal power units obtained by solving are as Figure 5 shown, and the corresponding system operation strategies are as Figure 6 shown. The participation of gas turbines and power-to-gas units makes the system operation more flexible.

[0226] The standard coal conversion coefficient of natural gas is taken as 1.674 tons of standard coal / ton of natural gas, and the carbon emission coefficient of standard coal is taken as 2.66 tons of CO 2 / ton of standard coal. The carbon emissions of the gas-electricity combined system are calculated respectively considering the cases of hydrogen blending in the natural gas pipeline and no hydrogen blending in the natural gas pipeline. Through comparison, it can be found that the CO 2 emissions in the case of hydrogen blending in the natural gas pipeline are 2 18 tons less than the CO emissions in the case of no hydrogen blending in the natural gas pipeline, as shown in Table 3. The participation of clean energy hydrogen reduces the system carbon emissions. With the development and maturity of the hydrogen blending technology in the natural gas pipeline, the operation of hydrogen blending in the pipeline will be achievable, and the hydrogen blending ratio can be further increased, and the emission reduction benefit will also be further improved, which is conducive to the realization of the goal. Thus, compared with the traditional model, this design method can effectively reduce carbon emissions on the premise of ensuring the system operation.

[0227] Table 1 Unit parameters of the hydrogen-blended gas-electricity combined system

[0228]

[0229] Table 2 Operating costs of the gas-electricity combined system

[0230]

[0231] Table 3 Comparison of carbon dioxide emissions

[0232]

Claims

1. A method for optimizing the operation of a gas-electricity combined system considering hydrogen blending in natural gas pipelines. It is characterized in that The method comprises the following steps: S1. Collect basic parameters of the gas-electricity combined system and forecast curves of power load, natural gas load and renewable energy output in the gas-electricity combined system; S2. Establish a calculation model for the mass flow of natural gas and hydrogen at natural gas network nodes; The hydrogen blending ratio of natural gas in the pipeline is defined as: where R V is the volume ratio of hydrogen in natural gas, is the hydrogen volume in the pipeline at time t, is the natural gas volume in the pipeline at time t, and Δt is the time step, is the density of hydrogen at the node considered at time t, is the density of natural gas at the node considered at time t, is the mass of hydrogen in the pipeline at time t, is the mass of natural gas in the pipeline at time t, is the mass flow rate of hydrogen at the node considered at time t, is the mass flow rate of natural gas at the node considered at time t; The relationship between the mass flow rate of hydrogen and the mass flow rate of natural gas is: Let Then: Denote the mass flow rate of the mixed gas at time t as It can be obtained that: The gas state equation is: wherein, is the hydrogen pressure at the node under consideration at time t, is the natural gas pressure at the node under consideration at time t, and c is the speed of sound; Under standard conditions, we have: The joint column can be obtained: Further: When R V is determined, K t is a constant, denoted as K; S3. Establish a dynamic model of the natural gas system considering pipeline hydrogen blending; The movement of mixed gases is described by the following three equations: Momentum equation for mixed gas: Where A ij is the cross-sectional area of pipeline ij, M Fij，t+1 is the mass flow rate of the mixed gas at the front end of pipeline ij at time t+1, M Eij，t+1 is the mass flow rate of the mixed gas at the end of pipeline ij at time t+1, M Fij,t is the mass flow rate of the mixed gas at the front end of pipeline ij at time t, M Eij，t is the mass flow rate of the mixed gas at the end of pipeline ij at time t, Δt is the time step, L ij is the length of the pipeline, p j，t+1 is the mixed gas pressure at the end node j of pipeline ij at time t+1, p i，t+1 is the mixed gas pressure at the front node i of pipeline ij at time t+1, p j,t is the mixed gas pressure at the end node j of pipeline ij at time t, p i，t is the mixed gas pressure at the front node i of pipeline ij at time t, λ is the friction coefficient, is the average flow velocity of the mixed gas in pipeline ij, d ij is the diameter of pipeline ij; Pipeline material balance equation: Gas state equation: p = c 2 ρ In the formula, c is the speed of sound, p is the pressure of the mixed gas, and ρ is the density of the mixed gas; S4. Establish a gas-electricity joint optimization operation model considering hydrogen blending in natural gas pipelines, and solve the model to obtain the day-ahead startup mode; The objective function of the gas-electricity combined optimization operation model is: Where, N g is the number of traditional thermal power generation units, c coal is the real-time price of standard coal in the current month, N gas is the number of gas source nodes in the natural gas system, is the coal consumption of thermal power generation unit i at time t, is the unit start-stop cost of thermal power generation unit i; S udi，t is the change in the start-stop state of thermal power generation unit i at time t, which is a 0-1 variable. When the start-stop state at time t is different from the previous moment, S udi，t = 1, otherwise, S udi，t = 0; c M is the price of natural gas, c H is the price of hydrogen, is the mass flow rate of natural gas in the mixed gas injected into the gas source node of the natural gas network, is the mass flow rate of hydrogen in the mixed gas injected into the gas source node of the natural gas network, and Δt is the time step.

2. A method for optimizing the operation of a gas-electricity combined system considering hydrogen blending in natural gas pipelines according to claim 1, Features: In step S3, the boundary condition constraints of each node in the natural gas system are: (1) The mass flow rate of the mixed gas at the load node is: In the formula, represents the mass flow rate of the gas load at the load node i at time t without considering hydrogen doping, represents the mass flow rate of the mixed gas at the load node i at time t after hydrogen doping, represents the calorific value of hydrogen, represents the calorific value of natural gas, K l is the set of load nodes, M Eki，t is the mass flow rate of the mixed gas at the end of the pipeline ki at time t; (2) The mixed gas pressure and mixed gas density constraints at the gas source node are: where p si is the mixed gas pressure of the gas source node, and ρ si is the mixed gas density of the gas source node; (3) The material balance constraint of each intermediate connection node in the natural gas network is: Wherein, (.)k represents the set of natural gas pipelines with the end node being k, k(.) represents the set of natural gas pipelines with the previous node being k, and K m is the set of connection nodes; (4) Upper and lower limit constraints of pipeline mass flow and node pressure:

3. A method for optimizing the operation of a gas-electricity combined system considering hydrogen blending in natural gas pipelines according to claim 1, Features: In step S4, the constraints of the gas-electricity combined optimization operation model are: (1) Power balance constraints In the formula, is the wind power of wind farm i at time t, is the load power of load j at time t, is the output of thermal power unit i at time t, is the output of gas turbine unit at time t, is the consumption power of power-to-gas unit i at time t; (2) Branch transmission capacity constraints -f lim ≤SP≤f lim where f lim is the column vector of the maximum transmission power of the line, S is the sensitivity matrix for determining the line transmission power from the nodal injection power, and P is the column vector of injection power composed of the injection powers of each node; (3) Upper and lower limits of unit output where, u i，t is the start-up and shut-down state of thermal power unit i at time t, which is a 0-1 variable. When it is in the start-up state at time t, u i，t = 1; otherwise, u i，t = 0; P i g，max is the minimum output limit of the thermal power unit, P i g，min is the maximum output limit of the thermal power unit, P i gas，max is the maximum output limit of the gas turbine unit, P i p2g，max is the maximum consumption power of the thermal power unit; (4) Constraints on the start and stop status of thermal power units S udi，1 ＝0 (5) Minimum start and stop time constraints for thermal power units u i，t-1 ≤u i，t t ≤ T i U u i，t ≤u i，t-1 t ≤ T i D where, T i U is the minimum on - line time that unit i needs to maintain, and T i D is the minimum off - line time that unit i needs to maintain; (6) Unit climbing constraints In the formula, is the maximum upward ramp rate of thermal power unit i, is the maximum downward ramp rate of thermal power unit i, M is a constant, is the output of thermal power unit i at time t; (7) Gas unit operation constraints Wherein, is the gas-electricity conversion efficiency of gas turbine unit i for hydrogen-blended natural gas; is the mass flow rate of gas consumption of gas turbine unit i; (8) Power-to-gas unit operation constraints Wherein, is the power consumption of the power-to-methane unit at the power-to-gas node i at time t, is the power consumption of the power-to-hydrogen unit at the power-to-gas node i at time t, is the mass flow rate of the gas produced by the power-to-gas at the power-to-gas node i, is the gas production efficiency of the power-to-methane unit at the power-to-gas node i, is the gas production efficiency of the power-to-hydrogen unit at the power-to-gas node i, is the power consumption of the power-to-gas unit i at time t.

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