System and method for improving combined cycle operation efficiency of gas turbine by using LNG (Liquefied Natural Gas) cold energy

Abstract

The invention belongs to the technical field of gas turbine combined cycle power generation, and discloses a system and method for improving the gas turbine combined cycle operation efficiency through LNG cold energy. Cold energy provided by an LNG evaporator is combined with an air-water heat exchanger and a gas compressor cooling system, the working temperature of a gas compressor can be effectively reduced, and the gas turbine combined cycle power generation efficiency is improved. Therefore, the efficiency of the compressor is improved. When the efficiency of the gas compressor is improved, the quality of air entering the gas turbine is better, energy waste is reduced, the efficiency of the combustion process in the gas turbine is directly improved due to reduction of the air temperature, and due to the fact that the density of cold air is large, the combustion efficiency can be improved, incomplete combustion is reduced, and then output is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas turbine combined cycle power generation, and particularly relates to a system and method for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy. Background Art

[0002] A gas turbine combined cycle (GTCC), also known as a gas-steam combined cycle, refers to a power generation method that combines a gas turbine and a steam turbine, mainly composed of three parts: a gas turbine (compressor, combustion chamber, turbine, control system, and auxiliary system), a heat recovery steam generator, and a steam turbine.

[0003] The main function of the compressor in the gas turbine is to compress air and increase the pressure of the working medium, which is an important process in the gas turbine thermodynamic cycle. The compressor does work on the air through high-speed rotating blades to increase its pressure, and this process is crucial for subsequent combustion and energy conversion. The inlet steam temperature of the compressor is one of the important factors affecting the performance and efficiency of the gas turbine. The level of the inlet air temperature directly affects the combustion efficiency, mechanical performance, and emissions of the gas turbine, has a great impact on the operating efficiency of the gas turbine unit, and thus affects the power generation capacity. The lower the inlet air temperature, the higher the efficiency of the gas turbine.

[0004] The lower the inlet air temperature of the gas turbine, the higher the power generation capacity of the gas turbine unit; the smaller the change in the inlet air temperature, the more stable the power generation capacity; the temperature of the gas turbine inlet air after cooling should not be too low, otherwise the inlet of the compressor will freeze and cause the gas turbine to malfunction. Reasonable design of the inlet air temperature of the gas turbine unit is very crucial for the performance of the gas turbine. A reasonable inlet air temperature can not only achieve the high-efficiency power generation ability of the gas turbine unit but also ensure the safe and stable operation of the compressor. The actual inlet air temperature of the compressor is generally the ambient temperature. With the change of weather, especially in summer, the actual inlet air temperature of the compressor is relatively high, the efficiency of the compressor decreases, and the combustion efficiency of the gas turbine decreases, resulting in insufficient output of the gas turbine.

[0005] LNG is the abbreviation of Liquefied Natural Gas, which is formed by liquefying natural gas under ultra-low temperature conditions. It is mainly obtained by purifying natural gas, compressing and heating it, cooling to remove heat, and then throttling and expanding. LNG has the physical characteristics of low temperature. It exists in liquid form at about -162°C, with methane as the main component, and its volume is 1 / 625 of that of natural gas with the same mass. LNG increases the flexibility of natural gas storage, transportation and utilization, expands the application range of natural gas, and as a clean energy source, it is an effective alternative to traditional energy sources. LNG contains a large amount of cold energy. It needs to be gasified into gaseous natural gas above 5°C and transported to the pipe network, and finally enters the combustion chamber of the gas turbine as fuel to generate high-temperature and high-pressure mixed gas, which enters the turbine to do work and generate electricity. The traditional gasification method directly releases the cold energy into the environment, resulting in great energy waste. Recycling and utilizing cold energy has become a research hotspot. Summary of the Invention

[0006] The purpose of the present invention is to overcome the problem of insufficient output of the gas turbine caused by the decline of the compressor efficiency and the combustion efficiency of the gas turbine, and to provide a system and method for improving the operating efficiency of the gas turbine combined cycle by utilizing the cold energy of LNG.

[0007] To achieve the above purpose, the present invention adopts the following technical solutions: In the first aspect, the present invention provides a system for improving the operating efficiency of a gas turbine combined cycle by utilizing the cold energy of LNG, including an LNG evaporator. The natural gas outlet of the LNG evaporator is connected to a burner, the cooling water outlet of the LNG evaporator is connected to the cooling water inlet of an air-water heat exchanger, the cooling water outlet of the air-water heat exchanger is connected to the cooling water inlet of the LNG evaporator, and the air outlet of the air-water heat exchanger is connected to a compressor.

[0008] A further improvement of the present invention is that the liquefied natural gas inlet of the LNG evaporator is connected to an LNG source.

[0009] A further improvement of the present invention is that the air inlet of the air-water heat exchanger is connected to an air source.

[0010] A further improvement of the present invention is that a cooling water circulation pump is provided on the pipeline between the cooling water outlet of the LNG evaporator and the cooling water inlet of the air-water heat exchanger.

[0011] A further improvement of the present invention is that the gas outlet of the compressor is connected to the gas inlet of the combustion chamber, and the gas outlet of the combustion chamber is connected to the turbine.

[0012] A further improvement of the present invention is that the compressor is connected to the generator and the turbine through a shaft.

[0013] A further improvement of the present invention is that the exhaust outlet of the turbine is connected to a waste heat boiler.

[0014] In a second aspect, the present invention provides a working method for a system that utilizes the cold energy of LNG to improve the operating efficiency of a gas turbine combined cycle, comprising the following steps: Liquefied natural gas is vaporized into natural gas in an LNG evaporator, and after purification, it is sent to a combustion chamber according to the required pressure to cool down the inside of the combustion chamber; The cold energy generated when liquefied natural gas is vaporized into natural gas in the LNG evaporator cools down the cooling water, and the cooled cooling water is sent into an air-water heat exchanger to exchange heat with normal-temperature air, so as to cool down the normal-temperature air; The cooled cooling water is sent back into the LNG evaporator for cooling again; The cooled air is sent into a compressor for cooling.

[0015] A further improvement of the present invention lies in that the temperature of the LNG source of the LNG evaporator is -162 °C, and the outlet temperature of natural gas from the LNG evaporator is 157 °C.

[0016] A further improvement of the present invention lies in that after the cooling water passes through the cooling water outlet of the LNG evaporator, it is pressurized by a cooling water circulation pump and then sent into the cooling water inlet of the air-water heat exchanger.

[0017] Compared with the prior art, the present invention has the following beneficial effects: Through the cold energy provided by the LNG evaporator, in combination with the air-water heat exchanger and the compressor cooling system, the present invention can effectively reduce the working temperature of the compressor, thereby improving the efficiency of the compressor. When the efficiency of the compressor is improved, the air quality entering the gas turbine is better, reducing energy waste, and the decrease in air temperature directly improves the efficiency of the combustion process in the gas turbine. Since cold air has a higher density, the combustion efficiency can be increased, incomplete combustion can be reduced, and thus the output can be improved. The combination of cooling air and improving the efficiency of the compressor in the present invention may also reduce the temperature of the exhaust gas of the gas turbine, making the thermal energy conversion efficiency of the system higher, thereby enhancing the thermal efficiency of the combined cycle. By integrating the LNG cold energy with the systems of the compressor and the gas turbine, the present invention can reduce the external cooling demand or the energy consumption brought by traditional cooling methods, achieving an energy-saving effect. The configuration of the air-water heat exchanger in the present invention reduces the demand for cooling water, or at least enables more efficient use of the existing cooling water, reducing the energy consumption and maintenance costs of the system. By reducing the temperature fluctuations of the gas turbine components through cooling and efficiency improvement means, the present invention can improve the stability and long-term operation reliability of the system, and extend the service life of the equipment. In summary, the present invention optimizes the working environment of the compressor and the gas turbine, improves the combustion efficiency and the overall thermal efficiency, thereby effectively enhancing the output power and economy of the gas turbine combined cycle, and overcoming the negative impact brought by the decline in the efficiency of the compressor. Description of the Drawings

[0018] Figure 1 is the system diagram of the present invention; Figure 2 is the working flow chart of the present invention; Among them, 1. LNG evaporator; 2. Combustion chamber; 3. Air-water heat exchanger; 4. Compressor; 5. Generator; 6. Turbine; 7. Waste heat boiler; 8. Cooling water circulation pump. Specific embodiments

[0019] In the following text, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the present invention. Therefore, the drawings and the description are considered to be exemplary in nature rather than restrictive.

[0020] See Figure 1 , a system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy, including an LNG evaporator 1. The natural gas outlet of the LNG evaporator 1 is connected to a burner 2. The cooling water outlet of the LNG evaporator 1 is connected to the cooling water inlet of an air-water heat exchanger 3. The cooling water outlet of the air-water heat exchanger 3 is connected to the cooling water inlet of the LNG evaporator 1. The air outlet of the air-water heat exchanger 3 is connected to a compressor 4.

[0021] See Figure 2 , a working method of a system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy, including the following steps: S1, Liquefied natural gas is vaporized into natural gas in the LNG evaporator 1. After purification, it is sent to the combustion chamber 2 according to the required pressure to cool down the inside of the combustion chamber 2.

[0022] S2, The cold energy generated when liquefied natural gas is vaporized into natural gas in the LNG evaporator 1 cools down the cooling water. The cooled cooling water is sent into the air-water heat exchanger 3 to exchange heat with normal-temperature air to cool down the normal-temperature air.

[0023] S3, The heat-exchanged cooling water is sent back into the LNG evaporator 1 for cooling down again.

[0024] S4, The cooled air is sent into the compressor 4 for cooling down.

[0025] In the present invention, air exchanges heat with cooling water in an air-water heat exchanger, and the normal-temperature air is cooled and then sent into a compressor. This cooling helps increase the density of the air inhaled by the compressor, reduces the power consumption of the compressor, and makes the compressor operate more efficiently. The cold air is conducive to the compressor compressing with lower energy consumption, thereby improving its efficiency. The present invention reduces the air temperature, which decreases the working pressure of the compressor when compressing air, thus reducing the energy consumption of the compressor and improving its performance, and avoiding the problem of efficiency decline caused by excessive temperature. During operation, after the cooled air enters the combustion chamber, it can provide a better combustion environment. The larger density of the cold air makes the mixture of fuel and air more uniform, which helps achieve more complete combustion. This not only improves the combustion efficiency but also reduces fuel waste and improves the working efficiency of the gas turbine. The stable input of low-temperature air helps control the temperature fluctuation in the combustion chamber and avoid the decrease in thermal loss and combustion efficiency caused by excessive temperature. This can optimize the operation of the gas turbine and maintain a high combustion efficiency. The cold energy generated by the LNG evaporator is used to cool the cooling water, and then the cold energy is transferred to the normal-temperature air through the air-water heat exchanger, thereby reducing the energy loss of the system. By this method, the system can utilize the cold energy of LNG more efficiently, reduce external energy consumption, and reduce the energy waste caused by traditional cooling means. The recycling of the cooling water in the system not only reduces the energy demand of external cooling equipment but also improves the overall cooling effect, enabling the gas turbine to maintain a high operating efficiency and stability. The cooled cooling water re-enters the LNG evaporator for cooling, enabling the cooling water to be recycled, thereby reducing the demand for cooling water. Through this closed-loop cooling system, the overall heat exchange efficiency is improved. Reducing the temperature of the cooling water helps improve the heat exchange efficiency of the system, thereby enhancing the overall thermal efficiency of the system and optimizing the utilization of energy. This method effectively improves the overall thermal efficiency of the combined cycle system because the high efficiency of the cooling system directly affects the working state of the gas turbine and improves the thermal efficiency by increasing energy recovery, ultimately enhancing the energy efficiency of the overall system. In summary, the present invention can make full use of the cold energy of LNG, optimize the working environments of the compressor and the combustion chamber, and improve the operating efficiency of the gas turbine and the overall thermal efficiency of the system. Specifically, the improvement of the compressor efficiency and the combustion efficiency can not only overcome the problem of insufficient output caused by the decline of the compressor efficiency and the combustion efficiency of the gas turbine but also reduce the operating cost of the system, improve the system stability, extend the equipment life, and reduce emissions, thereby improving the environmental protection performance.

[0026] Example 1: In this embodiment, the LNG source of the LNG evaporator is defined. Specifically, the liquefied natural gas inlet of the LNG evaporator 1 is connected to the LNG source. The LNG source is an LNG receiving terminal. The LNG from the LNG receiving terminal is about -162 °C, which is vaporized into natural gas through the LNG evaporator 1, and the temperature rises to above 5 °C. After being processed such as pressure stabilization and purification, it enters the combustion chamber.

[0027] In this embodiment, by directly connecting the LNG source, it can ensure a stable and sufficient supply of liquefied natural gas to the LNG evaporator, thereby maintaining the continuity and stability of the cooling effect. This avoids fluctuations in system performance caused by interrupted or insufficient LNG supply, and ensures the efficient operation of the system. The connection of the LNG source makes the system more flexible in energy supply. When more cold energy is needed, the flow rate of LNG can be adjusted to meet the demand and provide more cooling capacity; at the same time, if the cooling demand decreases, the supply volume can be adjusted, thereby saving resources and avoiding unnecessary waste. In short, the direct connection of the LNG source enhances the stability and flexibility of cold energy supply, while optimizing the energy utilization efficiency and system economy, improving the overall operation effect and environmental friendliness of the gas turbine combined cycle system.

[0028] Embodiment 2: In this embodiment, the air source of the air-water heat exchanger 3 is defined. Specifically, the air inlet of the air-water heat exchanger 3 is connected to the air source.

[0029] In this embodiment, by directly connecting the air source to the air-water heat exchanger, the air temperature entering the heat exchanger can be more precisely controlled. If the air source has a lower temperature, it can provide a cooling effect for the heat exchanger, further reducing the inlet air temperature of the compressor and the gas turbine, improving the compressor efficiency, and then enhancing the combustion efficiency of the gas turbine. The selection of the air source can ensure a lower air inlet temperature of the heat exchanger, enhancing the cooling effect of the air-water heat exchanger. The lower air temperature can effectively reduce the working temperature of the compressor, enable the compressor to operate at a lower temperature, reduce energy loss, and improve the compressor efficiency. Therefore, adding the connection of the air source to the air-water heat exchanger can not only improve the system cooling efficiency, enhance the working efficiency of the compressor and the gas turbine, but also reduce the system operation cost and enhance the system's adaptability and environmental protection performance by reducing energy consumption and cooling water use.

[0030] Embodiment 3: In this embodiment, the pressurization device between the LNG evaporator 1 and the air-water heat exchanger 3 is further defined. Specifically, a cooling water circulation pump 8 is provided on the pipeline between the cooling water outlet of the LNG evaporator 1 and the cooling water inlet of the air-water heat exchanger 3. After the cooling water passes through the cooling water outlet of the LNG evaporator 1, it is pressurized by the cooling water circulation pump 8 and then sent to the cooling water inlet of the air-water heat exchanger 3.

[0031] In this embodiment, by setting up a cooling water circulation pump, it can ensure that the flow of cooling water in the system is more stable and continuous. This continuous water flow can avoid uneven flow of cooling water caused by temperature changes or environmental factors, ensuring the high efficiency and stability of the cooling effect. The cooling water circulation pump can make the cooling water pass through the pipeline between the LNG evaporator and the air-water heat exchanger at an appropriate flow rate, improving the heat exchange efficiency between water and the heat exchanger. By increasing the flow rate of the cooling water, the cooling effect of the LNG evaporator can be effectively improved, and it can ensure that the air-water heat exchanger works at a higher efficiency, thus enhancing the thermal efficiency of the entire system. In this embodiment, by controlling the flow rate and flow volume of the cooling water, it can avoid poor heat exchange caused by too high temperature or uneven flow of the cooling water. This can ensure that the LNG evaporator and the air-water heat exchanger always maintain the best working state, making the overall cooling effect of the system more stable, and avoiding a decrease in system efficiency due to uneven temperature or insufficient cooling.

[0032] Example 4: In this embodiment, the gas turbine system is further defined. Specifically, the gas outlet of the compressor 4 is connected to the gas inlet of the combustion chamber 2, the gas outlet of the combustion chamber 2 is connected to the turbine 6, the compressor 4 is connected to the generator 5 and the turbine 6 through a shaft, and the exhaust outlet of the turbine 6 is connected to the waste heat boiler 7.

[0033] In the compressor stage, the compressor 4 of the gas turbine inhales air from the atmosphere and compresses it through the compressor 4 to increase the pressure and density of the air, preparing for combustion.

[0034] In the combustion chamber stage, the compressed air is sent into the combustion chamber 2, where the compressed air is mixed with fuel and ignited. The combustion process generates high-temperature and high-pressure gas, and these gases have high thermal energy.

[0035] In the turbine power generation stage, the high-temperature and high-pressure gas then enters the turbine 6, driving the blades of the turbine 6 to rotate. The turbine 6, the compressor 4 and the rotor of the generator 5 are coaxially connected. Therefore, the rotation of the turbine 6 can drive the normal operation of the compressor 4 and drive the generator 5 to generate electricity at the same time.

[0036] The high-temperature exhaust gas generated after the gas enters the turbine 6 for power generation enters the waste heat boiler 7.

[0037] In this embodiment, the compressor is connected to the turbine and the generator through a shaft, enabling efficient energy transfer. The compressed air provided by the compressor is combusted in the combustion chamber, driving the turbine to rotate. At the same time, the power of the turbine drives the generator to generate electricity through the shaft, thus achieving effective energy conversion and power output. This linkage enables the gas turbine combined cycle system to continuously and stably provide a higher power output. Due to the coordinated operation of each part, the system can avoid some equipment being in a high-load state for a long time during high-efficiency operation, thereby reducing wear and extending the service life of the equipment. At the same time, reducing unnecessary energy loss and temperature fluctuations also helps to protect the reliability of the key components in the system.

[0038] The foregoing has shown and described the basic principles, main features and advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above-described exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, it is intended to embrace all changes that fall within the meaning and scope of the equivalent elements of the claims in the present invention. Any reference signs in the claims should not be construed as limiting the claimed invention.

[0039] It should be understood that when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations. Although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art. The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention fall within the protection scope of the claims of the present invention.

Claims

1. A system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy, characterized in that: The invention comprises an LNG evaporator (1), wherein the natural gas outlet of the LNG evaporator (1) is connected to the burner (2), the cooling water outlet of the LNG evaporator (1) is connected to the cooling water inlet of the air-water heat exchanger (3), the cooling water outlet of the air-water heat exchanger (3) is connected to the cooling water inlet of the LNG evaporator (1), and the air outlet of the air-water heat exchanger (3) is connected to the compressor (4).

2. The system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 1 is characterized in that: The liquefied natural gas inlet of the LNG evaporator (1) is connected to an LNG source.

3. The system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 1, characterized in that: The air inlet of the air-water heat exchanger (3) is connected to an air source.

4. The system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 1, characterized in that: A cooling water circulation pump (8) is provided on a pipeline between the cooling water outlet of the LNG evaporator (1) and the cooling water inlet of the air-water heat exchanger (3).

5. The system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 1, characterized in that: The gas outlet of the compressor (4) is connected to the gas inlet of the combustion chamber (2), and the gas outlet of the combustion chamber (2) is connected to the turbine (6).

6. The system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 1, characterized in that: The compressor (4) is connected to the generator (5) and the turbine (6) via a shaft.

7. The system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 1, characterized in that: The exhaust gas outlet of the turbine (6) is connected to the waste heat boiler (7).

8. A method for using LNG cold energy to improve the efficiency of a gas turbine combined cycle, characterized in that: The following steps are involved: The liquefied natural gas is gasified into natural gas in the LNG evaporator (1), and after being purified, is sent into the combustion chamber (2) according to the required pressure to cool the combustion chamber (2); The cooling water is cooled by the cold energy generated when the liquefied natural gas is gasified into natural gas in the LNG evaporator (1). The cooled cooling water is sent to the air-water heat exchanger (3) to exchange heat with the normal temperature air, thereby cooling the normal temperature air. The cooling water after heat exchange is sent back to the LNG evaporator (1) for cooling; The cooled air is sent to the compressor (4) for cooling.

9. The working method of the system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 7, characterized in that: The LNG source temperature of the LNG evaporator (1) is minus 162°C, and the natural gas outlet temperature of the LNG evaporator (1) is 157°C.

10. The working method of the system for improving the operating efficiency of a gas turbine combined cycle by utilizing LNG cold energy according to claim 7, characterized in that: After passing through the cooling water outlet of the LNG evaporator (1), the cooling water is pressurized by a cooling water circulation pump (8) and then fed into the cooling water inlet of the air-water heat exchanger (3).

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