Working medium storage tank for improving safety of LNG cold energy power generation ORC system and use method thereof

Abstract

The application relates to the technical field of LNG cold energy power generation, and particularly discloses a working medium storage tank for improving the safety of an LNG cold energy power generation ORC system and a use method thereof, which is used for storing the circulating working medium of the LNG cold energy power generation ORC system and comprises a tank body, a heat exchange pipe is arranged in the tank body, and the heat exchange pipe is connected in parallel with an LNG side pipeline of an ORC system condenser. The use method of the working medium storage tank for improving the safety of the LNG cold energy power generation ORC system comprises the following steps: when the working medium of the LNG cold energy power generation ORC system is in a non-circulating state, LNG is introduced into the heat exchange pipe in the working medium storage tank, and the LNG flow in the heat exchange pipe is controlled by adjusting the opening degree of a valve; and when the working medium of the LNG cold energy power generation ORC system is in a circulating state, the LNG flow to the heat exchange pipe is cut off. The scheme is used to solve the problem that, after the LNG cold energy power generation ORC system fails, the working medium in the storage tank absorbs ambient heat, the pressure in the tank body increases, and the working medium is discharged.

Description

Technical Field

[0001] This invention relates to the field of liquefied natural gas (LNG) cold energy power generation technology, specifically to a working fluid storage tank and its usage method for improving the safety of LNG cold energy power generation ORC systems. Background Technology

[0002] The Organic Rankine Cycle (ORC) system is a commonly used method for generating electricity from LNG cold energy. In this system, the working fluid in the storage tank is pressurized by a working fluid pump and sent to the evaporator. The working fluid absorbs heat and vaporizes in the evaporator. The high-pressure vaporized working fluid drives the expander to do work and drives the generator to generate electricity. The working fluid that has done work flows to the condenser, where it is cooled and liquefied. The cooled and liquefied working fluid then flows back to the storage tank, completing one cycle.

[0003] Under normal operation, the working fluid in an LNG cold power generation ORC system is in a circulating state, and the working fluid conditions in each unit of the system remain stable. However, if the LNG cold power generation ORC system malfunctions, the working fluid needs to stop circulating and cannot obtain cooling in the condenser. At this time, the working fluid in the storage tank will inevitably absorb ambient heat, and the temperature and pressure will rise. When the pressure in the working fluid storage tank of the existing LNG cold power generation ORC system exceeds the standard, the working fluid is usually discharged and burned in the combustion tower to ensure the safety of the working fluid storage tank.

[0004] Currently, most LNG-fired cold-powered ORC systems used in domestic engineering applications employ a single-element circulating working fluid. In the event of a system failure, the small amount of working fluid discharged has minimal impact on system operation, and the system itself has a low probability of failure. Using a non-azeotropic mixture as the circulating working fluid in an ORC system can reduce heat exchange... While the ORC system suffers losses, the vaporization and discharge of a portion of the non-azeotropic working fluid alters the remaining working fluid composition, affecting the system's heat-to-work conversion efficiency. Furthermore, the refueling of the working fluid is labor-intensive and resource-intensive. Especially for LNG-fired cold-power ORC systems serving as technology verification platforms, frequent technical adjustments make them more prone to system shutdowns. Without countermeasures to prevent the discharge of the working fluid when circulation ceases, system operation will face significant challenges.

[0005] In addition, existing working fluid storage tanks require connection to multiple ports such as safety valve interface, pressure gauge interface, vent port, level gauge port, circulating working fluid inlet, and circulating working fluid outlet. Each opening has its own location and size requirements. When all these openings are made on the tank body, there are too many openings on the surface of the tank body, and too many openings have a significant impact on the overall strength of the tank body. Summary of the Invention

[0006] The present invention aims to provide a working fluid storage tank and its usage method to improve the safety of LNG cold energy power generation ORC system, so as to solve the problem that the working fluid in the working fluid storage tank will be discharged due to the increased pressure caused by absorbing ambient heat after the failure of LNG cold energy power generation ORC system.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A working fluid storage tank for improving the safety of an LNG-fired power generation ORC system is disclosed. The tank, comprising a tank body, contains heat exchange tubes connected in parallel to the LNG-side pipeline of the ORC system condenser. The inlet of the heat exchange tubes is connected to the LNG inlet section of the ORC system condenser LNG-side pipeline via an LNG inlet branch pipe. The outlet of the heat exchange tubes is connected to the LNG outlet section of the ORC system condenser LNG-side pipeline via an LNG outlet branch pipe. Valves are installed on both the LNG inlet and outlet branch pipes.

[0009] The principles and advantages of this scheme are:

[0010] This scheme studies the entire structure of an LNG-cooled power generation ORC system. By installing heat exchange tubes in parallel with the LNG side pipeline of the ORC system condenser in the working fluid storage tank, when the ORC system fails and the working fluid stops circulating, the valves on the LNG inflow and outflow branches open, allowing LNG to flow into the heat exchange tubes. This cools the working fluid in the storage tank, balances the heat entering the tank from the external environment, and keeps the working fluid in the tank stable, ensuring the safety of the storage tank and preventing working fluid vaporization and overpressure discharge. The heat exchange tube device has a very simple structure and is easy to apply.

[0011] In a clever and simple way, heat absorption of the working fluid in the storage tank is achieved without adding a refrigeration system. This solves the problem of heat absorption and pressure increase of the working fluid in the storage tank during non-circulation of the ORC system, which leads to discharge. It also avoids filling the storage tank with working fluid, greatly reduces the operating cost of the LNG cold energy power generation ORC system, and enhances the system's operational stability.

[0012] Preferably, as an improvement, the heat exchange tube is a coil, which includes an inlet section, an intermediate section and an outlet section connected in sequence. The inlet section, the intermediate section and the outlet section are all in the shape of [,] and the outlet section encloses the inlet section and the intermediate section encloses the outlet section.

[0013] Beneficial effects: This solution uses a multi-segment heat exchange coil in the shape of an "[" to make the contact between the heat exchange tube and the working fluid in the working fluid storage tank more uniform, preventing local vaporization of the working fluid in the tank due to uneven distribution of the cold source.

[0014] Preferably, as an improvement, the heat exchange tube is located at the bottom of the tank.

[0015] Beneficial effects: The heat exchange tubes are located at the bottom of the tank, allowing them to be immersed in the liquid working fluid, thus improving the heat exchange efficiency of the heat exchange tubes.

[0016] Preferably, as an improvement, the tank body is connected to an auxiliary pipe extending out of the tank body, and the auxiliary pipe is provided with multiple interfaces, which can be used as pressure gauge interfaces, safety valve interfaces or venting ports as needed.

[0017] Beneficial effects: The auxiliary pipe with multiple interfaces in this solution eliminates the need for these interfaces to be located on the tank body as in existing technologies, greatly ensuring the strength of the tank body and reducing the difficulty of processing the tank body.

[0018] Preferably, as an improvement, the tank body is connected to a thermometer sleeve, which extends into the tank body and is used to house the thermometer and isolate the inner cavity of the tank body from the thermometer.

[0019] Beneficial effects: The presence of the thermometer sleeve in this solution creates an isolation between the thermometer and the working fluid inside the tank, ensuring both accurate temperature monitoring and the safety of the thermometer.

[0020] Preferably, as an improvement, the tank is provided with a circulating working fluid inlet and a circulating working fluid outlet, with the circulating working fluid outlet connected to the bottom of the tank.

[0021] Beneficial effects: This solution connects the circulating working fluid outlet to the bottom of the tank, ensuring that the outflowing working fluid is liquid, thus avoiding the situation where the working fluid flowing to the working fluid pump contains gaseous working fluid during the working fluid circulation of the LNG cold energy power generation ORC system.

[0022] Preferably, as an improvement, the tank body is also provided with a pump return port, which is connected to the working fluid pump. When the LNG cold energy power generation ORC system is first started, the temperature of the working fluid pump is not very low. When the low-temperature working fluid flows to the working fluid pump, it will boil and vaporize. At this time, the vaporized working fluid gas flows back into the tank body through the pump return port.

[0023] This invention also provides a method for using a working fluid storage tank to improve the safety of an LNG cold power generation ORC system. The LNG cold power generation ORC system includes the aforementioned working fluid storage tank for improving the safety of the LNG cold power generation ORC system; it also includes the following operations:

[0024] When the working fluid in the LNG cold power generation ORC system is in a non-circulating state, LNG is introduced into the heat exchange tube in the working fluid storage tank, and the LNG flow rate in the heat exchange tube is controlled by adjusting the valve opening to control the heat exchange heat. When the working fluid in the LNG cold power generation ORC system is in a circulating state, the flow of LNG to the heat exchange tube is stopped. Attached Figure Description

[0025] Figure 1 This is a cross-sectional schematic diagram of the working fluid storage tank according to an embodiment of the present invention.

[0026] Figure 2 This is a top view of the heat exchange tube inside the working fluid storage tank according to an embodiment of the present invention.

[0027] Figure 3 This is a simplified structural diagram of the working fluid storage tank in an LNG cold energy power generation ORC system according to an embodiment of the present invention. Detailed Implementation

[0028] The following detailed description illustrates the specific implementation method:

[0029] The reference numerals in the accompanying drawings include: tank body 1, tank inner cavity 11, circulating working fluid inlet 12, circulating working fluid outlet 13, insulation layer 14, heat exchange tube 2, heat exchange tube inlet 21, heat exchange tube outlet 22, inlet section 23, intermediate section 24, outlet section 25, auxiliary pipe 3, pressure gauge interface 31, safety valve interface one 32, safety valve interface two 33, vent 34, thermometer sleeve 4, level gauge port 5, pump return gas port 6, drain port 7, base 8, LNG inflow branch pipe 911, LNG inflow pipe section 912, LNG outflow branch pipe 913, LNG outflow pipe section 914, regulating valve 915, on / off valve 916 / 917 / 918, working fluid storage tank 94, working fluid pump 95, evaporator 96, expander 97, generator 98, condenser 99.

[0030] Example

[0031] Combination Figures 1 to 3 A working fluid storage tank for improving the safety of an LNG cold energy power generation ORC system is disclosed. The inner cavity 11 of the tank is used to store the working fluid used in the LNG cold energy power generation ORC system circulation. The tank body 1 is equipped with a circulating working fluid inlet 12 and a circulating working fluid outlet 13. The material of the tank body 1 is selected, and the wall thickness of the tank body 1 is determined according to the working pressure and temperature of the working fluid inside the tank body 1.

[0032] A heat exchange tube 2 is installed in the inner cavity 11 of the tank body. The heat exchange tube 2 is located at the lower part of the tank body 1. LNG can be introduced into the heat exchange tube 2. The heat exchange tube inlet 21 and the heat exchange tube outlet 22 are welded to the tank body 1. The heat exchange tube 2 is a coil. The heat exchange tube 2 includes an inlet section 23, an intermediate section 24 and an outlet section 25 connected in sequence. The inlet section 23, the intermediate section 24 and the outlet section 25 are all in the shape of []. The outlet section 25 encloses the inlet section 23 and the intermediate section 24 encloses the outlet section 25.

[0033] The heat exchange tube 2 is connected in parallel with the LNG side pipeline of the condenser 99; the LNG side pipeline of the condenser is connected to the LNG inlet section 912 and the LNG outlet section 914; the heat exchange tube inlet 21 is connected to the LNG inlet section 912 via the LNG inlet branch pipe 911; the heat exchange tube outlet 22 is connected to the LNG outlet section 914 via the LNG outlet branch pipe 913; a regulating valve 915 is installed on the LNG inlet branch pipe 911; a switch valve 916 is installed on the LNG inlet section 912; a switch valve 917 is installed on the LNG outlet branch pipe 913; and a switch valve 918 is installed on the LNG outlet section 914.

[0034] Select the type, material, and diameter of heat exchanger tube 2, and determine the wall thickness of heat exchanger tube 2 based on the LNG pressure; set the LNG flow rate of heat exchanger tube 2, and calculate the heat exchange area and tube length of heat exchanger tube 2 based on the LNG temperature at the inlet 21 of heat exchanger tube, the heat exchange between tank 1 and the environment, the surface characteristics of heat exchanger tube, and the physical properties of the working fluid outside heat exchanger tube 2; check the pressure difference between the inlet 21 and outlet 22 of heat exchanger tube, which should be less than the design pressure difference between the LNG inflow branch pipe 911 and the LNG outflow branch pipe 913; the heat exchange area of ​​heat exchanger tube 2 should have a certain margin.

[0035] An auxiliary pipe 3 extends out of the tank body 1. The auxiliary pipe 3 has multiple interfaces: a pressure gauge interface 31, a safety valve interface 1 32, a safety valve interface 2 33, and a vent port 34. Pressure gauge interface 31 is used to install a pressure gauge; safety valve interfaces 1 and 2 are used to install safety valves; and vent port 34 connects to a pipe leading to the combustion tower. This pipe is equipped with a switch valve, which opens during tank body 1 purging. The wall thickness of the auxiliary pipe 3 is determined based on the working pressure and temperature of the working medium.

[0036] A thermometer sleeve 4 is connected to the tank body 1, extending into the tank body 1. The thermometer sleeve 4 is used to house the thermometer and isolate the inner cavity 11 of the tank from the thermometer. A level gauge port 5 is provided on the tank body 1 for inserting a level gauge. The wall thickness of the thermometer sleeve 4 is determined based on the working pressure and temperature of the working medium.

[0037] In addition, a pump return port 6 is installed on the tank body 1. The pump return port 6 is used to connect with the working fluid pump 95. When the LNG cold energy power generation ORC system is first started, the temperature of the working fluid pump 95 is not very low. When the low temperature working fluid flows to the working fluid pump 95, it will boil and vaporize. At this time, the vaporized working fluid gas is sent back to the tank body 1 through the pump return port 6.

[0038] A drain outlet 7 is also installed at the bottom of the tank body 1; in addition, a base 8 is fixed at the bottom of the tank body 1 to provide support for the tank body 1.

[0039] The LNG cold energy power generation ORC system includes the aforementioned working fluid storage tank 94, working fluid pump 95, evaporator 96, expander 97, generator 98, and condenser 99. The input end of the working fluid pump 95 is connected to the circulating working fluid outlet 13 of the working fluid storage tank 94. The evaporator 96 is connected between the working fluid pump 95 and the expander 97. The evaporator 96 is used to heat the working fluid pumped out by the working fluid pump 95. The working fluid gas expands in the expander 97, does work, and outputs mechanical energy. The output mechanical energy is converted into electrical energy through the generator 98. The expander 97 is connected to the working fluid side pipe section of the condenser 99. The condenser 99 is used to cool the circulating working fluid.

[0040] A method for using a working fluid storage tank to improve the safety of an LNG cold energy power generation ORC system involves closing switch valves 916 and 918 and opening regulating valves 915 and 917 when the working fluid in the LNG cold energy power generation ORC system is in a non-circulating state. This allows LNG to flow into heat exchange tube 2 through LNG inflow branch pipe 911 and then out through LNG outflow branch pipe 913. The regulating valve 915 controls the LNG flow rate and the heat exchange capacity of heat exchange tube 2, ensuring that the heat removed from the working fluid in tank 1 by heat exchange tube 2 is equal to the heat absorbed by the working fluid in tank 1 from the environment. This stabilizes the temperature, pressure, and gas phase mole fraction of the working fluid in tank 1, preventing the working fluid in tank 1 from being discharged due to excessive pressure.

[0041] When the working fluid in the LNG cold energy power generation ORC system is in circulation, by opening the switching valves 916 and 918 and closing the regulating valves 915 and 917, the heat exchange tube 2 no longer undertakes the heat exchange function.

[0042] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A working fluid storage tank for improving the safety of an LNG cold power generation ORC system, used to store the circulating working fluid of the LNG cold power generation ORC system, comprising a tank body, characterized in that: The tank is equipped with heat exchange tubes, which are connected in parallel with the LNG side pipeline of the ORC system condenser. The inlet of the heat exchange tube is connected to the LNG inlet section of the ORC system condenser LNG side pipeline through an LNG inlet branch pipe, and the outlet of the heat exchange tube is connected to the LNG outlet section of the ORC system condenser LNG side pipeline through an LNG outlet branch pipe. Valves are installed on both the LNG inlet branch pipe and the LNG outlet branch pipe. The heat exchange tube is located at the bottom of the tank. The heat exchange tube is a coil and includes an inlet section, an intermediate section and an outlet section connected in sequence. The inlet section, the intermediate section and the outlet section are all in the shape of []. The outlet section encloses the inlet section and the intermediate section encloses the outlet section. The tank body is connected to an auxiliary pipe extending out of the tank body, and the auxiliary pipe is provided with multiple interfaces; the tank body is provided with a circulating working fluid inlet and a circulating working fluid outlet, and the circulating working fluid outlet is connected to the bottom of the tank body.

2. The working fluid storage tank for improving the safety of an LNG cold energy power generation ORC system according to claim 1, characterized in that: The tank is connected to a thermometer sleeve that extends into the tank. The thermometer sleeve is used to house the thermometer and to isolate the inner cavity of the tank from the thermometer.

3. The working fluid storage tank for improving the safety of an LNG cold energy power generation ORC system according to claim 1, characterized in that: The tank is also equipped with a pump return port, which is connected to the working fluid pump.

4. A method for using a working fluid storage tank to improve the safety of an LNG cold energy power generation ORC system, characterized in that, The LNG cold power generation ORC system includes the working fluid storage tank as described in any one of claims 1-3 to improve the safety of the LNG cold power generation ORC system; it also includes the following operations: When the working fluid in the LNG cold power generation ORC system is in a non-circulating state, LNG is introduced into the heat exchange tube in the working fluid storage tank, and the LNG flow rate in the heat exchange tube is controlled by adjusting the valve opening to control the heat exchange heat. When the working fluid in the LNG cold power generation ORC system is in a circulating state, the flow of LNG to the heat exchange tube is stopped.

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