Gas-steam combined cycle energy-saving and consumption-reducing method and system

Abstract

The invention provides a gas-steam combined cycle energy-saving and consumption-reducing method and system, and belongs to the field of gas unit power generation. A gas-steam combined cycle energy-saving and consumption-reducing method is applied to a gas-steam combined cycle unit, and the gas-steam combined cycle unit comprises a gas turbine, a steam turbine, a waste heat boiler, a fused salt heat storage device, a flue gas heat exchange pipeline and a steam-water heat exchange pipeline. The first end of the flue gas heat exchange pipeline is connected with a flue of the waste heat boiler and a flue gas outlet of the gas turbine, and the second end of the flue gas heat exchange pipeline is used for inputting air; the first end of the steam-water heat exchange pipeline is used for inputting water generated after the steam turbine does work, and the second end of the steam-water heat exchange pipeline is used for conveying steam to the steam turbine; the method comprises the steps that in the starting stage of the gas-steam combined cycle unit, heat stored by the fused salt heat storage device is used for heating water generated after the steam turbine does work through the fused salt heat storage device, and obtained steam is conveyed to the steam turbine so as to preheat the steam turbine in advance.

Description

Technical Field

[0001] The invention relates to the field of gas-fired unit power generation, and in particular to a gas-steam combined cycle energy-saving and consumption-reducing method and a gas-steam combined cycle energy-saving and consumption-reducing system. Background Art

[0002] Gas-steam combined cycle units have the characteristics of high efficiency, clean and environmental protection, fast start-up, and easy operation. They can bear different types of power supply loads and heat supply loads, and are currently a form of power generation that is being vigorously developed. However, since combined cycle units have the tasks of frequent start-up and shutdown and deep peak regulation, they need to meet the needs of power supply and heat supply at the same time under variable operating conditions, which greatly affects their power generation efficiency and operating economy.

[0003] As an emerging energy storage device, molten salt heat storage devices have received a lot of attention in recent years, but they are rarely mentioned and applied in the field of gas-steam combined cycle. In the current relevant papers and patents, molten salt heat storage devices are mainly used in coal-fired power generation units, and the molten salt heat storage devices are independent of the units for steam-water heat exchange. The stored heat is only considered for stable external heating or peak load regulation. The molten salt heat storage device is not fully coupled into the gas-steam combined cycle, and the dual mode of flue gas heat exchange and steam-water heat exchange of the molten salt heat storage device is not considered. Summary of the invention

[0004] In order to solve the above-mentioned technical defects, the present invention provides a gas-steam combined cycle energy-saving and consumption-reducing method and system. The gas-steam combined cycle energy-saving and consumption-reducing method uses a molten salt heat storage device to provide heat for a steam turbine and a steam-water cycle during the startup phase of the gas-steam combined cycle unit, preheats the steam turbine in advance, and enables the steam turbine to reach the steam parameters and quality requirements required for the start-up as soon as possible, thereby shortening the startup time of the gas-steam combined cycle unit, reducing the operating time of the gas turbine under low-load and low-efficiency conditions during the startup phase, and saving the amount of fuel consumed by the gas turbine.

[0005] A first aspect of the present invention provides a gas-steam combined cycle energy-saving and consumption-reducing method, which is applied to a gas-steam combined cycle unit, wherein the gas-steam combined cycle unit comprises: a gas turbine, a steam turbine, a waste heat boiler, a molten salt heat storage device, a flue gas heat exchange pipeline, and a steam-water heat exchange pipeline, wherein a first end of the flue gas heat exchange pipeline is respectively connected to a flue of the waste heat boiler and a flue gas outlet of the gas turbine, and a second end of the flue gas heat exchange pipeline is used to input air; a first end of the steam-water heat exchange pipeline is used to input water generated after the steam turbine does work, and a second end of the steam-water heat exchange pipeline is used to transport steam to the steam turbine;

[0006] The method comprises:

[0007] During the startup phase of the gas-steam combined cycle unit, the heat stored in the molten salt heat storage device is used to heat the water generated by the steam turbine after work, and the steam is transported to the steam turbine to preheat the steam turbine in advance.

[0008] In an embodiment of the present invention, the method further includes:

[0009] During the startup phase of the gas-steam combined cycle unit, by increasing the load of the gas turbine and reducing the load of the steam turbine, the excess outlet flue gas generated by the gas turbine enters the molten salt heat storage device, and the molten salt heat storage device uses the molten salt heat exchange medium to exchange and store the heat of the excess outlet flue gas generated by the gas turbine.

[0010] In an embodiment of the present invention, the method further includes:

[0011] During the peak operation phase of the gas-steam combined cycle unit, the molten salt heat storage device uses the stored heat to heat the water generated by the steam turbine after it does work, and the steam is transported to the steam turbine to improve the work capacity of the steam turbine.

[0012] During the peak operation stage of the gas-steam combined cycle unit, the molten salt heat storage device uses the stored heat to heat the air input into the flue gas heat exchange pipe. The hot air is then transported to the waste heat boiler. The waste heat boiler uses the input hot air to generate steam and transports it to the steam turbine to improve the working capacity of the steam turbine.

[0013] In an embodiment of the present invention, the method further includes:

[0014] During the shutdown phase of the gas-steam combined cycle unit, the molten salt heat storage device uses the stored heat to heat the air input into the flue gas heat exchange pipe, and the hot air is then transported to the waste heat boiler to achieve heat preservation of the waste heat boiler.

[0015] In an embodiment of the present invention, the method further includes:

[0016] When the gas-steam combined cycle unit is provided with two gas turbines and one steam turbine, the water generated by the steam turbine is heated by the stored heat through the molten salt heat storage device, and the steam is transported to the steam turbine to improve the working capacity of the steam turbine.

[0017] A second aspect of the present invention provides a gas-steam combined cycle energy-saving and consumption-reducing system, comprising: a gas-steam combined cycle unit and a molten salt heat storage system;

[0018] The gas-steam combined cycle unit comprises: a gas turbine, a steam turbine and a waste heat boiler;

[0019] The molten salt heat storage system comprises: a molten salt heat storage device, a flue gas heat exchange pipeline and a steam-water heat exchange pipeline;

[0020] The first end of the flue gas heat exchange pipeline is connected to the flue of the waste heat boiler and the flue gas outlet of the gas turbine respectively, and is used to transport hot air to the waste heat boiler and receive the outlet flue gas generated by the gas turbine; the second end of the flue gas heat exchange pipeline is used to input air;

[0021] The first end of the steam-water heat exchange pipe is used to input water generated after the steam turbine does work, and the second end of the steam-water heat exchange pipe is used to transport steam to the steam turbine;

[0022] The molten salt heat storage device is provided with a molten salt heat exchange medium, which is used to exchange and store the heat of the outlet flue gas generated by the gas turbine, and the stored heat is used to heat the air input into the flue gas heat exchange pipe to obtain hot air, which is transported to the waste heat boiler through the flue gas heat exchange pipe, and the stored heat is used to heat the water generated by the steam turbine to obtain steam, which is transported to the steam turbine through the steam-water heat exchange pipe.

[0023] In the embodiment of the present invention, the connection point between the first end of the flue gas heat exchange pipe and the waste heat boiler is determined according to the temperature, pressure and flow rate in the flue of the waste heat boiler under rated conditions.

[0024] In an embodiment of the present invention, the first end of the flue gas heat exchange pipeline is connected to the flue of the high-pressure evaporator of the waste heat boiler.

[0025] In an embodiment of the present invention, the molten salt heat storage device includes a plurality of heat exchange modules, each of which is provided with a molten salt heat exchange medium with a different temperature gradient.

[0026] In an embodiment of the present invention, the system further comprises: a deaerator and a steam-water separator;

[0027] The input end of the deaerator is used to input water generated after the steam turbine does work, and the output end of the deaerator is connected to the first end of the steam-water heat exchange pipe. The deaerator is used to thermally deoxygenate the water generated after the steam turbine does work;

[0028] The input end of the steam-water separator is connected to the second end of the steam-water heat exchange pipe, and the output end of the steam-water separator is used to connect to the steam input end of the steam turbine.

[0029] The gas-steam combined cycle energy-saving and consumption-reducing method uses a molten salt heat storage device to provide the required steam for the steam turbine during the startup phase of the gas-steam combined cycle unit, preheats the steam turbine in advance, and enables the steam turbine to reach the steam parameters and quality requirements required for the start-up as soon as possible, thereby shortening the startup time of the gas-steam combined cycle unit, reducing the operating time of the gas turbine under low-load and low-efficiency conditions during the startup phase, and saving the amount of fuel consumed by the gas turbine.

[0030] Other features and advantages of the technical solution of the present invention will be described in detail in the specific implementation section below. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0032] Figure 1 It is a structural schematic diagram of a gas-steam combined cycle energy-saving and consumption-reducing system provided in an embodiment of the present invention.

[0033] Description of Reference Numerals

[0034] 1- molten salt heat storage device, 2- gas turbine, 3- steam turbine, 4- waste heat boiler, 41- high-pressure evaporator, 5- flue gas heat exchange pipeline, 6- steam-water heat exchange pipeline, 7- deaerator, 8- steam-water separator. DETAILED DESCRIPTION

[0035] In order to make the technical solutions and advantages of the embodiments of the present invention more clearly understood, the exemplary embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than an exhaustive list of all the embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0037] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0038] In the present invention, unless otherwise clearly specified and limited, the terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] In the process of realizing the present invention, the inventors found that the gas-steam combined cycle unit has the characteristics of high efficiency, clean and environmental protection, fast startup, and convenient operation. It can bear different types of power supply loads and heating loads, and is currently a form of power generation that is being vigorously developed. However, since the combined cycle unit has the tasks of frequent start-stop and deep peak regulation, it needs to meet the needs of power supply and heating at the same time under the variable operating mode, and its power generation efficiency and operating economy are greatly affected.

[0040] As an emerging energy storage device, molten salt heat storage devices have received a lot of attention in recent years, but they are rarely mentioned and applied in the field of gas-steam combined cycle. In the current relevant papers and patents, molten salt heat storage devices are mainly used in coal-fired power generation units, and the molten salt heat storage devices are independent of the units for steam-water heat exchange. The stored heat is only considered for stable external heating or peak load regulation. The molten salt heat storage device is not fully coupled into the gas-steam combined cycle, and the dual mode of flue gas heat exchange and steam-water heat exchange of the molten salt heat storage device is not considered.

[0041] In response to the above problems, an embodiment of the present invention provides a gas-steam combined cycle energy-saving and consumption-reducing method, which is applied to a gas-steam combined cycle unit, wherein the gas-steam combined cycle unit comprises: a gas turbine, a steam turbine, a waste heat boiler, a molten salt heat storage device, a flue gas heat exchange pipe and a steam-water heat exchange pipe, wherein a first end of the flue gas heat exchange pipe is respectively connected to the flue of the waste heat boiler and the flue gas outlet of the gas turbine, and a second end of the flue gas heat exchange pipe is used to input air; a first end of the steam-water heat exchange pipe is used to input water generated after the steam turbine does work, and a second end of the steam-water heat exchange pipe is used to transport steam to the steam turbine; the method comprises: in the startup stage of the gas-steam combined cycle unit, heating the water generated after the steam turbine does work by using the heat stored in the molten salt heat storage device, obtaining steam and transporting it to the steam turbine, so as to preheat the steam turbine in advance. The gas-steam combined cycle energy-saving and consumption-reducing method uses a molten salt heat storage device to provide the required steam for the steam turbine during the startup phase of the gas-steam combined cycle unit, preheats the steam turbine in advance, and enables the steam turbine to reach the steam parameters and quality requirements required for the start-up as soon as possible, thereby shortening the startup time of the gas-steam combined cycle unit, reducing the operating time of the gas turbine under low-load and low-efficiency conditions during the startup phase, and saving the amount of fuel consumed by the gas turbine.

[0042] Figure 1 Schematic diagram of a gas-steam combined cycle energy-saving and consumption-reducing system provided by an embodiment of the present invention. Figure 1 As shown, the gas-steam combined cycle energy-saving and consumption-reducing system provided in this embodiment includes: a gas-steam combined cycle unit and a molten salt heat storage system;

[0043] The gas-steam combined cycle unit comprises: a gas turbine 2, a steam turbine 3 and a waste heat boiler 4;

[0044] The molten salt heat storage system comprises: a molten salt heat storage device 1, a flue gas heat exchange pipeline 5 and a steam-water heat exchange pipeline 6;

[0045] The first end of the flue gas heat exchange pipe 5 is connected to the flue of the waste heat boiler 4 and the flue gas outlet of the gas turbine 2, respectively, for conveying hot air to the waste heat boiler 4 and receiving the outlet flue gas generated by the gas turbine 2; the second end of the flue gas heat exchange pipe 5 is used for inputting air;

[0046] The first end of the steam-water heat exchange pipe 6 is used to input water generated after the steam turbine 3 does work, and the second end of the steam-water heat exchange pipe 6 is used to transport steam to the steam turbine 3;

[0047] The molten salt heat storage device 1 is provided with a molten salt heat exchange medium, and the molten salt heat exchange medium is used to heat and store the heat of the outlet flue gas generated by the gas turbine 2. The stored heat is used to heat the air input into the flue gas heat exchange pipe 5 to obtain hot air, and the hot air is transported to the waste heat boiler 4 through the flue gas heat exchange pipe 5. The stored heat is used to heat the water generated after the steam turbine 3 works to obtain steam, and the steam is transported to the steam turbine 3 through the steam-water heat exchange pipe 6.

[0048] In this embodiment, the connection point between the first end of the flue gas heat exchange pipe 5 and the waste heat boiler 4 is determined according to the temperature, pressure and flow rate in the flue of the waste heat boiler 4 under rated conditions.

[0049] In this embodiment, the first end of the flue gas heat exchange pipeline 5 is connected to the flue of the high-pressure evaporator of the waste heat boiler 4 .

[0050] In this embodiment, the molten salt heat storage device 1 includes a plurality of heat exchange modules, each of which is provided with a molten salt heat exchange medium with a different temperature gradient.

[0051] In this embodiment, the system further comprises: a deaerator 7 and a steam-water separator 8;

[0052] The input end of the deaerator 7 is used to input water generated after the steam turbine 3 does work, and the output end of the deaerator 7 is connected to the first end of the steam-water heat exchange pipe 6. The deaerator 7 is used to perform thermal deoxygenation on the water generated after the steam turbine 3 does work; further, the water generated after the steam turbine 3 does work is specifically: the exhaust steam after the steam turbine does work and is cooled is input into the condenser, and after being condensed into water by the condenser, the deaerator extracts the condensed water in the condenser hot well through the condenser pump. The deaerator performs thermal deoxygenation on the water generated after the steam turbine 3 does work, so that the gas dissolved in the water is precipitated, thereby achieving the purpose of removing oxygen and protecting thermal equipment and pipelines.

[0053] The input end of the steam-water separator 8 is connected to the second end of the steam-water heat exchange pipe 6 , and the output end of the steam-water separator 8 is used to connect to the steam input end of the steam turbine 3 .

[0054] In this embodiment, one side of the flue gas heat exchange system of the molten salt heat storage device 1 is connected to the atmosphere, and the other side is connected to the flue of the waste heat boiler 4, and has a two-way heat exchange capability. When the molten salt heat storage device 1 stores heat, the high-temperature flue gas generated by the gas turbine 2 provides heat to the heat storage device; when the molten salt heat storage device 1 releases heat, the heat storage device provides hot air to the flue of the waste heat boiler 4.

[0055] In this embodiment, the connection position between the molten salt heat storage device 1 and the flue of the waste heat boiler 4 is selected according to the temperature, pressure and flow rate of the flue gas in the flue of the waste heat boiler 4 under rated conditions, and the high-pressure evaporator position is generally considered as the connection point.

[0056] The molten salt heat storage device 1 is connected to the high-pressure evaporator position of the waste heat boiler flue. The main consideration is that the molten salt in the molten salt heat storage device 1 is used as a heat storage and release medium, and good flow characteristics need to be ensured. The molten salt temperature needs to be guaranteed to be above 260°C (taking binary salt as an example), which requires that the temperature of the flue gas section cannot be lower than 260°C; in order to ensure the stability of the chemical properties of the molten salt, the molten salt temperature needs to be lower than the decomposition point temperature of 590°C (taking binary salt as an example), so the temperature of the flue gas section is required not to exceed 590°C. Within the range of above 260°C and below 590°C, higher temperatures can provide the quality of molten salt storage energy as much as possible, thereby improving the efficiency of the molten salt heat storage device 1. And because the flue gas temperature of the high-pressure evaporator position of the mainstream E-class, F-class, and H-class gas turbines 2 in service does not exceed 590°C, the high-pressure evaporator position is preferably selected as the connection point.

[0057] In this embodiment, one side of the steam-water heat exchange system of the molten salt heat storage device 1 is connected to the deaerator 7, and the other side is connected to the low-pressure cylinder of the steam turbine 3 and the heat user after passing through the steam-water separator 8. When the molten salt heat storage device 1 stores heat, the high-temperature flue gas generated by the gas turbine 2 provides heat to the heat storage device; when the molten salt heat storage device 1 releases heat, the water generated by the deaerator 7 is heated by the heat storage device to form steam, which provides energy to the low-pressure cylinder of the steam turbine 3 or the heat user.

[0058] The molten salt heat storage device 1 has the ability to absorb heat and release heat. When the molten salt heat storage device 1 absorbs heat, the molten salt heat storage device 1 inputs high-temperature flue gas generated by the gas turbine 2 through the flue gas heat exchange pipe 5, and the heat of the high-temperature flue gas is exchanged and stored through the molten salt heat exchange medium. When the molten salt heat storage device 1 releases heat, the molten salt heat storage device 1 inputs air from the outside through the flue gas heat exchange pipe 5. The input outside air uses the heat stored in the molten salt device during the heat absorption process to obtain hot air. The flue gas heat exchange pipe 5 inputs the hot air to the waste heat boiler 4. The waste heat boiler 4 generates high-temperature steam according to the input hot air, and the high-temperature steam is input to the steam turbine 3. When the molten salt heat storage device 1 releases heat, the molten salt heat storage device 1 inputs water treated by the deaerator 7 through the steam-water heat exchange pipe 6. The molten salt heat storage device 1 heats the water to steam. The steam enters the steam-water separator 8 through the steam-water heat exchange pipe 6. The steam-water separator 8 separates the steam and water to obtain pure steam. The pure steam enters the steam turbine 3, increasing the work done by the steam turbine 3.

[0059] The gas-steam combined cycle energy-saving and consumption-reducing method provided in this embodiment is applied to a gas-steam combined cycle unit, wherein the gas-steam combined cycle unit comprises: a gas turbine 2, a steam turbine 3, a waste heat boiler 4, a molten salt heat storage device 1, a flue gas heat exchange pipeline 5 and a steam-water heat exchange pipeline 6, wherein the first end of the flue gas heat exchange pipeline 5 is respectively connected to the flue of the waste heat boiler 4 and the flue gas outlet of the gas turbine 2, and the second end of the flue gas heat exchange pipeline 5 is used to input air; the first end of the steam-water heat exchange pipeline 6 is used to input water generated after the steam turbine 3 does work, and the second end of the steam-water heat exchange pipeline 6 is used to transport steam to the steam turbine 3;

[0060] The method comprises:

[0061] During the startup phase of the gas-steam combined cycle unit, the molten salt heat storage device 1 uses the heat stored in the molten salt heat storage device 1 to heat the water generated after the steam turbine 3 does work, and the obtained steam is transported to the steam turbine 3 to preheat the steam turbine 3 in advance.

[0062] In this embodiment, the first end of the steam-water heat exchange pipe is connected to the deaerator 7, and the water generated after the steam turbine 3 performs work is obtained through the deaerator 7.

[0063] Specifically, the method can improve the startup flexibility of the gas-steam combined cycle unit and shorten the startup time of the gas-steam combined cycle unit. During the startup phase of the gas-steam combined cycle unit, when the steam turbine 3 needs to use steam to preheat the system, heat can be transferred through the steam-water heat exchange pipe 6 of the molten salt heat storage device 1 to preheat the pipeline valve of the steam turbine 3, and the pipeline can be flushed to remove impurities such as rust so that the steam-water quality can meet the start-up requirements of the steam turbine 3 as soon as possible.

[0064] Furthermore, during the startup phase of the gas-steam combined cycle unit, the molten salt heat storage device 1 uses the heat stored in the molten salt heat storage device 1 to heat the water generated by the steam turbine 3 after work, and the steam is transported to the steam turbine 3 to preheat the steam turbine 3 and the steam-water system associated with the steam turbine and the waste heat boiler in advance. Steam preheats the pipes and valves in the steam-water system.

[0065] In this embodiment, the method further includes:

[0066] During the startup phase of the gas-steam combined cycle unit, by increasing the load of the gas turbine 2 and reducing the load of the steam turbine 3, the excess outlet flue gas generated by the gas turbine 2 enters the molten salt heat storage device 1, and the molten salt heat storage device 1 uses the molten salt heat exchange medium to exchange and store the heat of the excess outlet flue gas generated by the gas turbine 2.

[0067] Specifically, the method can improve the power generation efficiency of the gas turbine 2 and reduce pollutant emissions during the startup phase of the gas-steam combined cycle unit. During the startup phase of the gas-steam combined cycle unit, by increasing the load of the gas turbine 2, the excess heat generated by the increased load of the gas turbine 2 before the steam turbine 3 is started is stored in the molten salt heat storage device 1 and released in other phases to improve the power generation efficiency of the gas turbine 2 and increase the overall energy utilization rate. In addition, since the NOx and CO emissions of the gas turbine 2 are lower in the high-load phase than in the partial-load phase, the pollutant emissions of the gas turbine 2 can be reduced by allowing the gas turbine 2 to operate at high load or full load and the steam turbine 3 to operate at low load or zero load in this partial-load condition of the gas-steam combined cycle unit.

[0068] In this embodiment, the method further includes:

[0069] During the peak operation phase of the gas-steam combined cycle unit, the molten salt heat storage device 1 uses the stored heat to heat the water generated by the steam turbine 3 after the steam turbine 3 does work, and the steam is transported to the steam turbine 3 to improve the work capacity of the steam turbine 3 and the overall efficiency of the gas-steam combined cycle unit;

[0070] During the peak operation stage of the gas-steam combined cycle unit, the molten salt heat storage device 1 uses the stored heat to heat the air input into the flue gas heat exchange pipe 5, and the hot air is then transported to the waste heat boiler 4. The waste heat boiler 4 uses the input hot air to generate steam and then transports it to the steam turbine 3, so as to improve the working capacity of the steam turbine 3, thereby improving the overall efficiency of the gas-steam combined cycle unit.

[0071] Furthermore, the waste heat boiler 4 uses the input hot air to perform heat exchange with the steam-water system, obtains steam and then transmits it to the steam turbine 3. The steam-water system is a connection system between the waste heat boiler and the steam turbine.

[0072] In this embodiment, the method further includes:

[0073] During the shutdown phase of the gas-steam combined cycle unit, the molten salt heat storage device 1 uses the stored heat to heat the air input into the flue gas heat exchange pipe 5, and the hot air is transported to the waste heat boiler 4 to keep the waste heat boiler 4 warm.

[0074] Specifically, the method also has a heat release function during the shutdown phase of the gas turbine 2, and the tail flue of the gas turbine 2 and the flue of the waste heat boiler 4 are kept warm. After the gas-steam combined cycle unit is shut down, the temperature in the tail flue of the gas turbine 2 and the flue of the waste heat boiler 4 drops rapidly. The tail flue of the gas turbine 2 (i.e., the tail of the first end of the flue gas heat exchange flue) and the flue of the waste heat boiler 4 are heated by the molten salt heat storage device 1, which can prevent the temperature from dropping too fast and causing adverse effects on the high-temperature heating surface of the waste heat boiler 4. After the insulation, the next startup time of the unit can also be shortened.

[0075] In this embodiment, the method further includes:

[0076] When the gas-steam combined cycle unit is provided with two gas turbines 2 and one steam turbine 3, the molten salt heat storage device 1 utilizes the stored heat to heat the water from the deaerator 7, and the steam is obtained and transported to the steam turbine 3, so that the steam turbine 3 generates more electricity and improves the working capacity of the steam turbine 3.

[0077] Specifically, for a "two-to-one" type gas-steam combined cycle unit (i.e., a gas-steam combined cycle unit including two gas turbines 2 and one steam turbine 3), at this time, only one gas turbine 2 is started, and heat is output to the steam-water heat exchange pipeline 6 through the molten salt heat storage device 1, generating additional steam to drive the steam turbine 3 to generate more electricity. This can reduce the energy consumed by starting another gas turbine 2 during short-term peak operation, and improve the overall combined cycle efficiency.

[0078] In the case where the gas turbine 2 is fully loaded and the steam turbine 3 has a surplus load in the "one-to-one" operation mode (i.e., a gas-steam combined cycle unit including a gas turbine 2 and a steam turbine 3), the molten salt heat storage device 1 outputs heat to the steam-water heat exchange pipe 6 to generate additional steam to drive the steam turbine 3 to generate more electricity. This can increase the total load of the combined cycle unit and improve the peak operation capacity of the unit.

[0079] Preferably, in this embodiment, the molten salt heat storage device 1 can quickly expand heat users to meet the various heat needs of the gas-steam combined cycle unit, and plays an important role in the peak load regulation of the unit operation, shutdown insulation of the waste heat boiler 4, shutdown insulation of the turbine 3, preheating of the turbine 3, natural gas heating, and gas turbine inlet temperature heating.

[0080] The beneficial effects produced by the present invention are:

[0081] (1) During the startup phase of the gas-steam combined cycle unit, the steam required by the steam turbine 3 can be provided by the molten salt heat storage device 1, thereby preheating the steam turbine 3 in advance, improving the startup flexibility of the unit and shortening the startup time of the combined cycle.

[0082] (2) During the peak load stage of the gas-steam combined cycle unit, because the power generation efficiency of gas turbine 2 is higher than that of steam turbine 3, and the power generation efficiency of gas turbine 2 is higher during the high load stage than during the partial load stage, the NOx and CO emissions of gas turbine 2 are lower during the high load stage than during the partial load stage. By making gas turbine 2 operate at high load or full load and steam turbine 3 operate at low load or zero load in this partial load condition of the gas-steam combined cycle unit, the energy saving and consumption reduction effect of the unit can be achieved. The specific implementation method after matching with molten salt heat storage is: during the peak load process, the gas turbine 2 is not allowed to reduce the load or reduce the load slightly, and the large amount of flue gas generated is heat exchanged and stored in the molten salt heat storage device 1, and only a small amount of flue gas enters the waste heat boiler 4 for heat exchange to generate a small amount of steam that enters the steam turbine 3 for power generation.

[0083] (3) For the "two-to-one" gas-steam combined cycle units, or the "one-to-one" operation mode units with a large load margin of turbine 3, when the units need to operate at a higher load for peak power generation, the molten salt heat storage outputs heat to generate additional steam to drive turbine 3 to generate more electricity, which can reduce the energy consumed by starting the other unit of the "two-to-one" unit, gas turbine 2, in a short time, or increase the maximum load of turbine 3 of the "one-to-one" unit, thereby achieving an overall improvement in the overall combined cycle efficiency.

[0084] The molten salt heat storage system has many application scenarios and can be quickly expanded to include users. The system can be used to provide heat in the shutdown and insulation of waste heat boiler 4, shutdown and insulation of steam turbine 3, preheating of steam turbine 3, natural gas heating, and gas turbine inlet temperature heating.

[0085] This embodiment also provides the following specific examples:

[0086] Analysis of molten salt heat storage scheme and operation economics during the cold start-up phase of a 9H-class gas-steam combined cycle unit.

[0087] When the gas turbine 2 operates at partial load, the exhaust temperature is higher than that at full load, and the heat consumption is also higher than that at full load. The power generation efficiency of the gas turbine 2 is higher at full load, so the operation of the gas turbine 2 at partial load is bound to cause energy waste.

[0088] Gas turbine 2 has the characteristics of rapid start and stop, and must be started and stopped frequently according to the grid dispatching instructions when undertaking peak load regulation tasks.

[0089] According to the start-stop interval of the gas turbine 2, the start-up state can be divided into four states: cold state, warm state, hot state, and extremely hot state. In this embodiment, combined with the basic operating parameters of the unit under the cold start condition of the 9H unit, its basic operating conditions and the start-up plan after the molten salt heat storage device 1 is put into use are analyzed, and the operation economy is compared.

[0090] 1. Basic operating conditions - unit startup method and economic calculation without molten salt heat storage device 1

[0091] Without considering the situation of the molten salt heat storage device 1, under normal startup conditions, the gas turbine 2 increases the load to 20% in the 25th minute after startup, stays for about 140 minutes to wait for the water quality of the waste heat boiler 4 and the steam turbine 3 to be qualified before the steam turbine 3 is started. In the 170th minute, the gas turbine 2 quickly increases the load from 20% load (about 110MW) to 100% (i.e., Baseload condition). During this process, the gas turbine 2 stays for 140 minutes, and the natural gas flow rate is about 36t / h. Based on the natural gas price of 6000 yuan / t and the natural gas calorific value of 48000kJ / kg, the natural gas cost consumed in this stage is about 6000*36*140 / 60=490,000 yuan.

[0092] When the gas turbine 2 is running the steam turbine 3 stably for 140 minutes under the load condition of 20%, the heat of the natural gas entering the gas turbine 2 is about 48000*36*1000*140 / 60=4032000MJ. The thermal efficiency of the gas turbine 2 under this load condition is about 24%, and the heat in the flue gas is about 359MW.

[0093] If the molten salt heat storage device 1 is not added, the heat converted from this part of natural gas into flue gas is equivalent to being wasted. The natural gas consumption is large but the utilization efficiency is very low, resulting in a significant decrease in the economic efficiency of the unit operation, and it will also cause problems such as the gas turbine 2 being difficult to meet emission standards.

[0094] 2. Start-up method and economic efficiency of the unit of molten salt heat storage device 1

[0095] After installing the molten salt heat storage system, there are two energy utilization options during the startup phase.

[0096] (1) Option 1

[0097] The idea of ​​​​Scheme 1 is that the gas turbine 2 is not started before the steam turbine 3 meets the conditions for starting, and the molten salt heat storage device 1 directly provides the gas turbine 2 with the same heat as the tail flue gas under 20% load conditions. Under this idea, it is necessary to calculate the heat exchange efficiency, molten salt amount, temperature difference and other boundary parameters of the molten salt heat storage device 1 based on the heat of the gas turbine 2 under 20% load conditions. The advantage of this idea is that the start-up time of the gas-steam combined cycle is not affected by the time required for preheating of the waste heat boiler 4 and the steam turbine 3, and the combined cycle start-up curve is almost the same as the simple cycle start-up curve of the gas turbine 2. Under this idea, the heat exchange capacity of the molten salt heat storage device 1 is 359MW, and the designed heat storage capacity of the molten salt energy storage system is 359*140 / 60=837.66MW·h.

[0098] (2) Option 2

[0099] The idea of ​​the second scheme is to increase the load of the gas turbine 2 when the steam turbine 3 is started, establish a coupling relationship between the molten salt heat storage device 1 and the gas-steam combined cycle unit, and reduce energy loss. The starting point of this idea is that the thermal efficiency of the gas turbine 2 is higher when it is running at a higher load, so it is considered to increase the load of the gas turbine 2 before the steam turbine 3 is started. In addition, by reasonably setting the molten salt heat storage device 1, it can form a complementary relationship with the waste heat boiler 4 and the steam-water heat exchange system of the steam turbine 3 under various working conditions.

[0100] The following is a preliminary design of the heat storage system and an analysis of the operating benefits for Scheme 2. The operating benefits are reflected in the improvement of the comprehensive utilization efficiency of the gas-steam combined cycle unit during the 140 minutes when the steam turbine 3 is waiting for the start-up, that is: comprehensive utilization efficiency = total utilization energy / natural gas energy. Among them, total utilization energy = energy storage device storage energy * conversion efficiency + power generation. Here, the conversion efficiency of the molten salt heat storage system is considered to be 75%. Under the condition of 20% load of gas turbine 2, the heat storage device is not considered to be put into use. At this time, the comprehensive efficiency is the power generation efficiency of gas turbine 2, that is, the comprehensive utilization efficiency is 24%.

[0101] 1) When steam turbine 3 is running, the load of gas turbine 2 is increased from 20% to 30%

[0102] The load of gas turbine 2 increases from 20% to 30%, and the exhaust enthalpy increases by about 51MW. The designed heat storage capacity of the molten salt energy storage system is 51*140 / 60=119MW·h. After calculation, the comprehensive utilization efficiency is 38.9% at this time.

[0103] 2) When steam turbine 3 is running, the load of gas turbine 2 is increased from 20% to 50%

[0104] The load of gas turbine 2 increases from 20% to 50%, and the exhaust enthalpy increases by about 146MW. The designed heat storage capacity of the molten salt energy storage system is 146*140 / 60=340MW·h. After calculation, the comprehensive utilization efficiency is 41.5% at this time.

[0105] 3) When steam turbine 3 is running, the load of gas turbine 2 is increased from 20% to 70%

[0106] The load of gas turbine 2 increases from 20% to 70%, and the exhaust enthalpy increases by about 236MW. The designed heat storage capacity of the molten salt energy storage system is 236*140 / 60=551MW·h. After calculation, the comprehensive utilization efficiency is 44.1% at this time.

[0107] 4) When steam turbine 3 is running, the load of gas turbine 2 is increased from 20% to 100%

[0108] The load of gas turbine 2 increases from 20% to 100%, and the exhaust enthalpy increases by about 498MW. The designed heat storage capacity of the molten salt energy storage system is 498*140 / 60=1162MW·h. After calculation, the comprehensive utilization efficiency is 47.7% at this time.

[0109] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0110] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

[0111] The optional implementation modes of the present invention are described in detail above in conjunction with the accompanying drawings. However, the implementation modes of the present invention are not limited to the specific details in the above implementation modes. Within the technical concept of the implementation modes of the present invention, a variety of simple modifications can be made to the technical solutions of the implementation modes of the present invention, and these simple modifications all belong to the protection scope of the implementation modes of the present invention. It should also be noted that the various specific technical features described in the above specific implementation modes can be combined in any suitable manner without contradiction, and as long as the combination does not violate the concept of the implementation modes of the present invention, it should also be regarded as the content disclosed in the implementation modes of the present invention.

Claims

1. A gas-steam combined cycle energy-saving and consumption-reducing method, applied to a gas-steam combined cycle unit, It is characterized in that The gas-steam combined cycle unit comprises: a gas turbine, a steam turbine, a waste heat boiler, a molten salt heat storage device, a flue gas heat exchange pipeline and a steam-water heat exchange pipeline, wherein the first end of the flue gas heat exchange pipeline is respectively connected to the flue of the waste heat boiler and the flue gas outlet of the gas turbine, and the second end of the flue gas heat exchange pipeline is used to input air; the first end of the steam-water heat exchange pipeline is used to input water generated after the steam turbine does work, and the second end of the steam-water heat exchange pipeline is used to transport steam to the steam turbine; The method comprises: During the startup phase of the gas-steam combined cycle unit, the heat stored in the molten salt heat storage device is used to heat the water generated by the steam turbine after work, and the steam is transported to the steam turbine to preheat the steam turbine in advance.

2. The gas-steam combined cycle energy saving and consumption reduction method according to claim 1, It is characterized in that The method further comprises: During the startup phase of the gas-steam combined cycle unit, by increasing the load of the gas turbine and reducing the load of the steam turbine, the excess outlet flue gas generated by the gas turbine enters the molten salt heat storage device, and the molten salt heat storage device uses the molten salt heat exchange medium to exchange and store the heat of the excess outlet flue gas generated by the gas turbine.

3. The gas-steam combined cycle energy saving and consumption reduction method according to claim 2, It is characterized in that The method further comprises: During the peak operation phase of the gas-steam combined cycle unit, the molten salt heat storage device uses the stored heat to heat the water generated by the steam turbine after it does work, and the steam is transported to the steam turbine to improve the work capacity of the steam turbine. During the peak operation stage of the gas-steam combined cycle unit, the molten salt heat storage device uses the stored heat to heat the air input into the flue gas heat exchange pipe. The hot air is then transported to the waste heat boiler. The waste heat boiler uses the input hot air to generate steam and transports it to the steam turbine to improve the working capacity of the steam turbine.

4. The gas-steam combined cycle energy saving and consumption reduction method according to claim 1, It is characterized in that The method further comprises: During the shutdown phase of the gas-steam combined cycle unit, the molten salt heat storage device uses the stored heat to heat the air input into the flue gas heat exchange pipe, and the hot air is then transported to the waste heat boiler to achieve heat preservation of the waste heat boiler.

5. The gas-steam combined cycle energy saving and consumption reduction method according to claim 1, It is characterized in that The method further comprises: When the gas-steam combined cycle unit is provided with two gas turbines and one steam turbine, the water generated by the steam turbine is heated by the stored heat through the molten salt heat storage device, and the steam is transported to the steam turbine to improve the working capacity of the steam turbine.

6. A gas-steam combined cycle energy-saving and consumption-reducing system, It is characterized in that include: Gas-steam combined cycle unit and molten salt heat storage system; The gas-steam combined cycle unit comprises: a gas turbine, a steam turbine and a waste heat boiler; The molten salt heat storage system comprises: a molten salt heat storage device, a flue gas heat exchange pipeline and a steam-water heat exchange pipeline; The first end of the flue gas heat exchange pipeline is connected to the flue of the waste heat boiler and the flue gas outlet of the gas turbine respectively, and is used to transport hot air to the waste heat boiler and receive the outlet flue gas generated by the gas turbine; the second end of the flue gas heat exchange pipeline is used to input air; The first end of the steam-water heat exchange pipe is used to input water generated after the steam turbine does work, and the second end of the steam-water heat exchange pipe is used to transport steam to the steam turbine; The molten salt heat storage device is provided with a molten salt heat exchange medium, which is used to exchange and store the heat of the outlet flue gas generated by the gas turbine, and the stored heat is used to heat the air input into the flue gas heat exchange pipe to obtain hot air, which is transported to the waste heat boiler through the flue gas heat exchange pipe, and the stored heat is used to heat the water generated by the steam turbine to obtain steam, which is transported to the steam turbine through the steam-water heat exchange pipe.

7. The gas-steam combined cycle energy-saving and consumption-reducing system according to claim 6, It is characterized in that The position of the connection point between the first end of the flue gas heat exchange pipe and the waste heat boiler is determined according to the temperature, pressure and flow rate in the flue of the waste heat boiler under rated conditions.

8. The gas-steam combined cycle energy-saving and consumption-reducing system according to claim 6, It is characterized in that The first end of the flue gas heat exchange pipeline is connected to the flue of the high-pressure evaporator of the waste heat boiler.

9. The gas-steam combined cycle energy-saving and consumption-reducing system according to claim 6, It is characterized in that The molten salt heat storage device comprises a plurality of heat exchange modules, each of which is provided with a molten salt heat exchange medium with a different temperature gradient.

10. The gas-steam combined cycle energy-saving and consumption-reducing system according to claim 6, It is characterized in that The system also includes: a deaerator and a steam-water separator; The input end of the deaerator is used to input water generated after the steam turbine does work, and the output end of the deaerator is connected to the first end of the steam-water heat exchange pipe. The deaerator is used to thermally deoxygenate the water generated after the steam turbine does work; The input end of the steam-water separator is connected to the second end of the steam-water heat exchange pipe, and the output end of the steam-water separator is used to connect to the steam input end of the steam turbine.

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