Thermal power plant peak regulation system based on heat storage device

Abstract

The invention discloses a thermal power plant peak shaving system based on a heat storage device. The thermal power plant peak shaving system comprises a medium-pressure steam turbine, a low-pressure steam turbine, a condenser, a generator, a steam compressor and the heat storage device. The heat storage device comprises a heat storage material storage tank and a working medium storage tank, the heat storage material storage tank is connected with a steam compressor, a steam turbine unit, the working medium storage tank and a heat supply pipe network through working medium pipelines, the heat storage material storage tank comprises two heat exchangers, and the steam compressor is connected with a low-pressure steam turbine through a steam extraction pipeline. The steam compressor can compress and convert low-pressure working medium steam into medium-pressure working medium steam, and the generator and the steam compressor are both connected with a power grid. The system provided by the invention is a thermal power plant peak regulation system with high # imgabs0 # efficiency, is beneficial to stabilizing unit load change, and improves the economical efficiency of a thermal power plant by controlling the steam quantity of a pipeline.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal power plant peak regulation, and in particular to a thermal power plant peak regulation system based on a heat storage device. Background Art

[0002] Currently, there are three mainstream approaches to improving the flexibility of coal-fired power plants: thermal-electric decoupling, adding energy storage equipment, and steam turbine retrofits. However, all three methods face the following challenges: first, there are few standard, demonstrable technologies; second, they are not economically viable and their feasibility still needs to be evaluated; and third, they are technically difficult. This invention aims to address these challenges by adding heat storage tanks to thermal power plants themselves. Summary of the Invention

[0003] In order to enable thermal power plants to smooth the load curve of units by means of heat storage, participate in the peak load regulation of the power grid, realize peak load shifting and valley load filling, achieve carbon reduction goals, and at the same time deliver excess steam to the heating network, the present invention provides a thermal power plant peak load regulation system based on a heat storage device. The system is easy to configure, It has high efficiency and can be coupled with existing thermal power plants to improve the operating economy of thermal power plants.

[0004] To achieve the above objectives, the present invention provides a thermal power plant peak-shaving system based on a heat storage device, comprising a medium-pressure steam turbine, a low-pressure steam turbine, a condenser, a generator, a steam compressor, and a heat storage device. The heat storage device comprises a heat storage material tank and a working fluid tank. The heat storage material tank is connected to the steam compressor, the medium-pressure steam turbine, the low-pressure steam turbine, the working fluid tank, and the heating network via working fluid pipelines. The steam compressor is connected to the low-pressure steam turbine via a steam extraction pipeline, compressing low-pressure steam into medium-pressure steam. The generator and steam compressor are both connected to the power grid.

[0005] Valves V1, V2, V3, V4, and V5 are installed on the steam extraction pipeline between the low-pressure steam turbine and the steam compressor, the working fluid pipeline between the steam compressor and the heat storage material tank, the working fluid pipeline between the heat storage material tank and the working fluid tank, the working fluid pipeline between the heat storage material tank and the medium-pressure steam turbine outlet, and the working fluid pipeline between the heat storage material tank and the heating network. The operation of the thermal power plant's peak-shaving system is controlled by adjusting the opening and closing of each valve and the amount of steam in the pipeline. The opening and closing of valves V1 and V2 correspond to the energy storage process and can be used to control the system's heat storage process. The opening and closing of valves V3, V4, and V5 correspond to the energy release process and can be used to control the system's power supply and heating processes. Specifically, valves V3 and V4 are used to regulate the power supply process, while valves V3 and V5 are used to regulate the heating process.

[0006] The working fluid tank is used to store saturated water at medium temperature and medium pressure. It is connected to the thermal storage material tank via a working fluid pipeline. The thermal storage material tank is filled with medium-temperature thermal storage materials such as mixed nitrates, hydrated inorganic salts, and polyethylene glycol.

[0007] The heat storage material storage tank contains two heat exchangers. When valves v1 and v2 are opened and the steam compressor is running, superheated steam flows through one of the heat exchangers in the heat storage material storage tank and transfers heat to the heat storage material filled in the heat storage material storage tank; when valve v3 is opened and saturated water in the working fluid storage tank flows out, the saturated water flows through the other heat exchanger in the heat storage material storage tank and absorbs heat from the heat storage material filled in the heat storage material storage tank.

[0008] Thermal storage tanks are connected to the steam turbine units (i.e., the intermediate-pressure and low-pressure turbines) and the heating network via working fluid pipelines. The intermediate-pressure steam discharged from the thermal storage tanks can be fed into the steam turbine units to perform work or transported to the heating network. The steam turbine units in coupled thermal power plants are typically condensing steam turbine units.

[0009] The steam extraction pipe of the low-pressure steam turbine is connected to the steam compressor. The low-pressure steam is converted into medium-pressure steam in the steam compressor, and then flows through the heat storage material tank, releases heat to the heat storage material through the heat exchanger, and is converted into medium-temperature water, which flows into the working fluid storage tank for storage.

[0010] The peak-shaving system of a thermal power plant based on a heat storage device described in the present invention can work in two steps. First, the objective function is solved to obtain a result of maximizing the benefit. Second, the energy storage or release process is carried out according to the solution result.

[0011] The thermal power plant of the present invention improves the economic efficiency of the thermal power plant by adjusting the opening and closing of each valve and the amount of steam in the pipeline. The specific steps are as follows:

[0012] Step S1: Based on the different benefits of power supply, heat supply and heat storage, establish the objective function of maximizing benefits:

[0013] MaxR=R h +R e

[0014] in:

[0015] R h =x1·η h ·P h

[0016]

[0017] Where R is the total revenue of thermal power plant, R h Heat supply income for thermal power plants, R eis the power generation income of the thermal power plant; x1 is the amount of steam provided by the thermal power plant to the heating network, x2 is the amount of steam used by the thermal power plant for power generation, and x3 is the amount of steam sent by the thermal power plant to the heat storage device; η h is the heating efficiency, P h is the heating price, η1 is the turbine efficiency, Δh1 is the steam enthalpy change after passing the intermediate pressure turbine, Δh2 is the steam enthalpy change after passing the steam compressor, η2 is the efficiency of the steam compressor, T is the power generation time, P e is the grid price;

[0018] Constraints:

[0019]

[0020] Where x is the total steam volume;

[0021] Step S2: By solving the objective function, the steam volume that can be dispatched by each valve for supplying different functions such as heat storage, power supply and heating is obtained;

[0022] Step S3: The thermal power plant controls the opening and closing of valves v1, v2, v3, v4, and v5 based on the solution, thereby adjusting the amount of steam supplied to different functions, achieving more heat release when electricity prices are high and more heat storage when electricity prices are low, thereby improving the economic efficiency of the thermal power plant.

[0023] When the power price of the power grid is low and the steam turbine unit needs to operate at reduced load, the peak-shaving system of the thermal power plant performs a heat storage process. The process is as follows: the superheated steam with temperature T1 and entropy S1 at the outlet of the medium-pressure steam turbine enters the low-pressure steam turbine to perform work, and part of the steam expands into outlet exhaust gas with temperature T3 and entropy S3, and is then cooled in the condenser to water with temperature T4 and entropy S4, and enters the thermal power plant for steam-water circulation. Start the steam compressor, open the valve v1 on the extraction pipe of the low-pressure steam turbine and the valve v2 on the working fluid pipe at the steam compressor outlet, and a part of the steam with a temperature of T2 and an entropy of S2 that has expanded in the low-pressure steam turbine is drawn out from the low-pressure steam turbine through the extraction pipe and enters the steam compressor, where it is compressed into superheated steam with a temperature of T5 and an entropy of S5, and then enters the heat storage material tank. Through the heat exchanger in the heat storage material tank, the superheated steam releases heat to the heat storage material in the heat storage material tank, and stores the heat in the heat storage material. The steam is then converted into saturated water with a temperature of T6 and an entropy of S6, and flows into the working fluid tank for storage. Close valves v2 and v1, shut down the steam compressor, and realize the heat storage process.

[0024] When the power price of the power grid is high and the steam turbine unit needs to increase its load or the heating network needs to supplement medium-pressure steam, the peak-shaving system of the thermal power plant performs a heat release process. The process is as follows: if the steam turbine unit needs to increase its load, open the valve v3 on the working fluid pipeline between the heat storage material tank and the working fluid tank and the valve v4 on the working fluid pipeline between the heat storage material tank and the medium-pressure turbine outlet. Saturated water with a temperature of T6 and an entropy of S6 in the working fluid tank flows into the heat storage material tank, passes through the heat exchanger in the heat storage material tank, absorbs the heat energy stored in the heat storage material, and is converted into superheated steam with a temperature of T1 and an entropy of S1. It then flows to the exhaust pipe of the medium-pressure turbine. The exhaust steam of the medium-pressure turbine flows to the low-pressure turbine to expand and perform work, driving the generator to generate electricity and transmit electricity to the power grid (i.e., the power supply function). If the heating network needs to be supplemented with medium-pressure steam, open the valve v3 on the working fluid pipeline between the heat storage material tank and the working fluid tank, and the valve v5 on the working fluid pipeline between the heat storage material tank and the heating network. The saturated water with a temperature of T6 and an entropy of S6 in the working fluid tank flows into the heat storage material tank, passes through the heat exchanger in the heat storage material tank, absorbs the heat energy stored in the heat storage material, and is converted into superheated steam with a temperature of T1 and an entropy of S1. The steam then flows to the heating network to supplement the medium-pressure steam, thereby achieving the purpose of supplying heat to the heating network (i.e., the heating function).

[0025] When this system recovers and compresses steam into medium pressure, The efficiency is:

[0026]

[0027] Where ε is Efficiency, m is the working fluid mass, e is the low-pressure steam ratio E in is the power consumption of the compressor, e′ is the medium pressure steam ratio

[0028] When this system recovers low-pressure steam and provides it all back to the power plant to perform work, the round-trip efficiency of the system is:

[0029]

[0030] Where η is the round trip efficiency of the system, E out The power generation generated by the expansion of the medium-pressure steam stored in the turbine during the power generation process, E in is the power consumption of the compressor during the heat storage process.

[0031] The beneficial effects of the present invention are:

[0032] By integrating thermal storage tanks within the medium- and low-pressure steam turbine units, this system eliminates the high-pressure, temperature-resistant structures required by traditional thermal storage systems, significantly reducing equipment procurement and installation costs. The thermal storage tanks utilize a modular design and can be deployed directly within existing turbine space, eliminating the need for civil engineering modifications.

[0033] By dynamically adjusting the steam supply in real-time optimization, the energy demand of different functional ends (such as heating, power generation, and heat storage) can be accurately matched to achieve low-peak heat storage and peak-peak energy release, thereby improving the operating economy of the overall system.

[0034] This system modification is easy, retaining the existing system's main structure and requiring only the installation of a heat storage device and control valves. The modification cycle is short and requires no unit shutdown, making it suitable for over 90% of operating medium and low-pressure units. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the peak-shaving system of a thermal power plant based on a heat storage device according to the present invention.

[0036] Figure 1 Medium: 1. Medium-pressure steam turbine; 2. Low-pressure steam turbine; 3. Condenser; 4. Generator; 5. Steam compressor; 6. Heat storage material tank; 7. Working fluid tank; 8. Heating pipeline network; 9. Power grid.

[0037] Figure 2 This is a temperature-entropy diagram of the working fluid during operation of a peak-shaving system of a thermal power plant based on a heat storage device according to the present invention. DETAILED DESCRIPTION

[0038] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0039] The present invention is described in detail by taking the process of recycling 1kg of low-pressure steam and storing it for heat or supplying it all back to the power plant for power generation as an example. The extraction temperature of the low-pressure steam turbine is 97℃ and the extraction pressure is 0.084MPa, and the exhaust temperature of the medium-pressure steam turbine is 297℃ and the exhaust pressure is 0.63MPa. When performing the heat storage process, Figure 1 As shown, start the steam compressor, open the valve v1 on the extraction pipe of the low-pressure steam turbine and the valve v2 on the outlet working medium pipe of the steam compressor, and a part of the steam expanded in the low-pressure steam turbine is drawn out from the low-pressure steam turbine through the extraction pipe and enters the steam compressor, where it is compressed into superheated steam. Figure 2 In the temperature-entropy diagram, the state point b goes to the state point e. Then it enters the heat storage material tank, passes through the heat exchanger in the heat storage material tank, and the superheated steam releases heat to the heat storage material in the heat storage material tank, storing the heat in the heat storage material. The steam then turns into saturated water and flows into the working fluid tank for storage, that is, from Figure 2In the temperature-entropy diagram, from state point e to state point f. Close valves v2 and v1, shut down the steam compressor, and realize the heat storage process. Open valve v3 on the working fluid pipeline between the heat storage material tank and the working fluid tank, and valve v4 on the working fluid pipeline between the heat storage material tank and the outlet of the medium-pressure steam turbine 1. The saturated water in the working fluid tank flows into the heat storage material tank, passes through the heat exchanger in the heat storage material tank, absorbs the heat energy stored in the heat storage material, and converts it into superheated steam, that is, Figure 2 In the temperature-entropy diagram, the flow goes from state f to state a. It then flows to the exhaust pipe of the intermediate-pressure steam turbine. The exhaust steam from the intermediate-pressure steam turbine expands and performs work in the low-pressure steam turbine, moving from state a to state c. The exhaust steam completes the condensation process in the condenser, moving from state c to state d, driving the generator to generate electricity and transmit electrical energy to the grid, completing the power generation process.

[0040] The present invention discloses a thermal power plant peak-shaving system based on a heat storage device, which can improve the economic efficiency of the thermal power plant by adjusting the steam volume. The steps are as follows:

[0041] Step S1: Based on the different benefits of power supply, heat supply and heat storage, establish the objective function of maximizing benefits:

[0042] MaxR=R h +R e

[0043] in:

[0044] R h =x1·η h ·P h

[0045]

[0046] Where R is the total revenue of thermal power plant, R h Heat supply income for thermal power plants, R e is the power generation income of the thermal power plant; where the total steam volume is x, x1 is the steam volume provided by the thermal power plant to the heating network, x2 is the steam volume used by the thermal power plant for power generation, x3 is the steam volume sent to the heat storage device by the thermal power plant, and η h is the heating efficiency, which can be taken as 0.9 here, P h is the heating price, η1 is the turbine efficiency, which is taken as the isentropic efficiency of 0.9 here, Δh1 is the enthalpy change of steam passing through the medium-pressure turbine, Δh2 is the enthalpy change of steam passing through the steam compressor, η2 is the efficiency of the steam compressor, which is 0.9 here, T is the power generation time, P e is the grid price;

[0047] Constraints:

[0048]

[0049] Step S2: By solving the objective function, the dispatchable steam quantity for different functions (heat storage, power supply and heating) is obtained;

[0050] Step S3: The thermal power plant controls the opening and closing of valves v1, v2, v3, v4, and v5 based on the solution, thereby adjusting the amount of steam supplied to different functions, achieving more heat release when electricity prices are high and more heat storage when electricity prices are low, thereby improving the economic efficiency of the thermal power plant.

[0051] Take the turbine isentropic efficiency η1 = 0.9, the steam compressor adiabatic efficiency η2 = 0.9, the generator efficiency η3 = 0.98, and the mechanical efficiency η4 = 0.98. The low-pressure cylinder extraction parameters are t2 = 97 ° C, p2 = 0.084 MPa, h2 = 2671.8 kJ / kg, s2 = 7.4297 kJ / (kg·K), ex2 = 619.90 kJ / kg. The superheated steam parameters at the outlet of the isentropic process steam compressor are t 5i =322.21℃, p 5i =0.63MPa,h 5i =3107.5kJ / kg,s 5i =7.4297kJ / (kg·K),ex 5i =1055.6kJ / kg. The specific compression work of the steam compressor is The actual process parameters for the superheated steam at the steam compressor outlet are t5 = 344.96°C, p5 = 0.63 MPa, h5 = 3155.0 kJ / kg, s5 = 7.5079 kJ / (kg·K), and ex5 = 1079.8 kJ / kg. The parameters for the saturated water formed after the superheated steam releases heat to the thermal storage material are t6 = 160.74°C, p6 = 0.63 MPa, h6 = 678.69 kJ / kg, s5 = 1.9499 kJ / (kg·K), and ex5 = 260.57 kJ / kg. When steam is needed to supply the power plant, the saturated water flows through the thermal storage tank and becomes medium-pressure steam. Its parameters are t1 = 297°C, t1 = 0.63 MPa, h1 = 3055 kJ / kg, s1 = 7.3395 kJ / (kg·K), and ex1 = 1030.0 kJ / kg. The exhaust gas parameters at the outlet of the isentropic process turbine are t 3i =45.81℃, p 3i =0.01MPa,h 3i =2325.7kJ / kg,s 3i =7.3395kJ / (kg·K),ex 3i =300.71kJ / kg, the specific expansion work of the steam turbine is w turb =(h1-h 3i)·η1=656.37kJ / kg, the actual process parameters of superheated steam at the outlet of the steam compressor are t3=45.80℃, p3=0.01MPa, h5=2398.6kJ / kg, s5=7.5681kJ / (kg·K), ex5=305.46kJ / kg.

[0052] Systematic The efficiency is:

[0053]

[0054] Where ε is Efficiency, m is the working fluid mass, e is the low-pressure steam ratio E in is the power consumption of the compressor, e′ is the medium pressure steam ratio

[0055] The round-trip efficiency of the system is:

[0056]

[0057] Where η is the round trip efficiency of the system, E out The power generation generated by the expansion of the medium-pressure steam stored in the turbine during the power generation process, E in is the power consumption of the compressor during the heat storage process.

[0058] In summary, the peak load regulation system of thermal power plant based on heat storage device has 93.30% efficiency under this working condition. The round-trip efficiency is 130.21%, which is because the system directly couples the heat storage device through the medium and low pressure turbine bypass, avoiding the traditional heat storage system loss.

Claims

1. A peak-shaving system for a thermal power plant based on a heat storage device, characterized by: The invention comprises a medium-pressure steam turbine (1), a low-pressure steam turbine (2), a condenser (3), a generator (4), a steam compressor (5) and a heat storage device; the heat storage device comprises a heat storage material storage tank (6) and a working fluid storage tank (7); the heat storage material storage tank (6) is connected to the steam compressor (5), the medium-pressure steam turbine (1) and the low-pressure steam turbine (2), the working fluid storage tank (7) and the heat supply pipe network (8) through a working fluid pipeline; the steam compressor (5) is connected to the low-pressure steam turbine (2) through a steam extraction pipeline; the steam compressor (5) is connected to the power grid and can use electricity in the power grid (9); the low-pressure steam turbine (2) is connected to the condenser (3), the outlet exhaust gas output by the low-pressure steam turbine (2) enters the condenser (3) for cooling, and the low-pressure steam turbine (2) is also connected to the generator (4) When the low-pressure steam turbine (2) rotates, it drives the generator (4) to generate electricity and supply power to the power grid (9); the steam extraction pipeline between the low-pressure steam turbine (2) and the steam compressor (5), the working fluid pipeline between the heat storage material storage tank (6) and the steam compressor (5), the working fluid pipeline between the heat storage material storage tank (6) and the working fluid storage tank (7), the working fluid pipeline between the heat storage material storage tank (6) and the outlet of the medium-pressure steam turbine (1), and the working fluid pipeline between the heat storage material storage tank (6) and the heat supply network (8) are respectively provided with valves v1, v2, v3, v4, and v5. By adjusting the opening and closing of each valve, the operation of the peak regulation system of the thermal power plant is controlled. Valves v1 and v2 are used to control the heat storage process of the system, valves v3 and v4 are used to regulate the power supply process, and valves v3 and v5 are used to regulate the heating process.

2. A thermal power plant peak-shaving system based on a heat storage device according to claim 1, characterized in that the control method of the valves v1, v2, v3, v4, and v5 comprises the following steps: Step S1: Based on the different benefits of power supply, heat supply and heat storage, establish the objective function of maximizing benefits: MaxR=R h +R e in: R h =x1·η h ·P h Where R is the total revenue of thermal power plant, R h Heat supply income for thermal power plants, R e is the power generation income of the thermal power plant; x1 is the amount of steam provided by the thermal power plant to the heating network, x2 is the amount of steam used by the thermal power plant for power generation, and x3 is the amount of steam sent by the thermal power plant to the heat storage device; η h is the heating efficiency, P h is the heating price, η1 is the turbine efficiency, Δh1 is the steam enthalpy change after passing the intermediate pressure turbine, Δh2 is the steam enthalpy change after passing the steam compressor, η2 is the efficiency of the steam compressor, T is the power generation time, P e is the grid price; constraints: Where x is the total steam volume; Step S2: By solving the objective function, the steam volume that can be dispatched by each valve for supplying different functions such as heat storage, power supply and heating is obtained; Step S3: The thermal power plant controls the opening and closing of valves v1, v2, v3, v4, and v5 based on the solution, thereby adjusting the amount of steam supplied to different functions.

3. The peak-shaving system for a thermal power plant based on a heat storage device according to claim 2, characterized in that: The heat storage material storage tank (6) contains two heat exchangers. When valves v1 and v2 are opened and the steam compressor (5) is running, superheated steam flows through one of the heat exchangers in the heat storage material storage tank (6) and transfers heat to the heat storage material filled in the heat storage material storage tank (6); when valve v3 is opened and saturated water in the working fluid storage tank (7) flows out, the saturated water flows through the other heat exchanger in the heat storage material storage tank (6) and absorbs heat from the heat storage material filled in the heat storage material storage tank (6).

4. The peak-shaving system for a thermal power plant based on a heat storage device according to claim 1, characterized in that: The medium-pressure steam turbine (1) and the low-pressure steam turbine (2) are steam turbine units in a thermal power plant.

5. The peak-shaving system for a thermal power plant based on a heat storage device according to claim 4, characterized in that: The system can realize heat storage process and heat release process, wherein the heat release process is divided into two uses: supplying steam to the steam turbine unit and supplying steam to the heating pipe network.

6. The peak-shaving system for a thermal power plant based on a heat storage device according to claim 5, characterized in that: The outlet steam of the medium-pressure steam turbine (1) enters the low-pressure steam turbine (2), the steam compressor (5) is started, the valve v1 on the extraction pipe of the low-pressure steam turbine (2) and the valve v2 on the outlet working medium pipe of the steam compressor (5) are opened, the steam in the low-pressure steam turbine (2) enters the steam compressor (5) through the extraction pipe, is compressed into superheated steam, and then enters the heat storage material storage tank (6), the superheated steam releases heat to the heat storage material in the heat storage material storage tank (6), the heat is stored in the heat storage material, the steam is converted into saturated water, and flows into the working medium storage tank (7) for storage, the valves v2 and v1 are closed, the steam compressor (5) is shut down, and the heat storage process is realized.

7. The peak-shaving system for a thermal power plant based on a heat storage device according to claim 5, characterized in that: The valve v3 on the working fluid pipeline between the heat storage material storage tank (6) and the working fluid storage tank (7) and the valve v4 on the working fluid pipeline between the heat storage material storage tank (6) and the outlet of the medium-pressure steam turbine (1) are opened, and the saturated water in the working fluid storage tank (7) flows into the heat storage material storage tank (6), absorbs the heat energy stored in the heat storage material through the heat exchanger in the heat storage material storage tank (6), and is converted into superheated steam. The steam then flows to the exhaust pipe of the medium-pressure steam turbine (1), and the exhaust steam of the medium-pressure steam turbine (1) flows to the low-pressure steam turbine (2), thereby supplying steam to the steam turbine unit and driving the generator (4) to generate electricity, thereby transmitting electric energy to the power grid.

8. The peak-shaving system for a thermal power plant based on a heat storage device according to claim 5, characterized in that: The valve v3 on the working fluid pipeline between the heat storage material storage tank (6) and the working fluid storage tank (7) and the valve v5 on the working fluid pipeline between the heat storage material storage tank (6) and the heating pipe network (8) are opened, and the saturated water in the working fluid storage tank (7) flows into the heat storage material storage tank (6), passes through the heat exchanger in the heat storage material storage tank (6), absorbs the heat energy stored in the heat storage material, and is converted into superheated steam. The steam then flows to the heating pipe network (8) to supplement the steam, thereby achieving the purpose of supplying heat to the heating pipe network (8).

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