Plug-in double-tube condensing gasification heat exchanger, heat exchange system and control method thereof

Abstract

The application provides a plug-in double-pipe condensing gasification heat exchanger, which comprises a heat exchanger cylinder and a plurality of heat exchange pipes; a tube plate and a transition plate are arranged in the heat exchanger cylinder, so that the heat exchanger cylinder is divided into a heat exchange cavity, a pipe box and a steam cavity; the heat exchange pipe is a double-pipe structure, so that the condensed water after condensation of high-temperature steam is located between the inner pipe and the outer pipe and acts as an intermediate medium, which can effectively avoid problems caused by direct heat exchange between the high-temperature steam and LNG; a heat exchange system comprises a simulation module, a control module, a heat exchanger and the heat exchanger; and a control method is as follows: the simulation module is used to simulate the heat exchange process, so that the appropriate running LNG liquid level height can be determined; when the LNG liquid level height is at the appropriate running LNG liquid level height, the heat exchange effect is optimal; in cooperation with the LNG liquid level sensor arranged in the cylinder, the actual LNG liquid level height can be monitored; when the LNG liquid level height is increased, the control module adjusts the air inlet flow control valve to increase the steam flow, so that the heat exchange efficiency is ensured.

Description

Technical Field

[0001] This invention relates to the field of heat exchanger technology, and in particular to an insertion-type double-tube condenser-vaporizer heat exchanger, a heat exchange system, and a control method thereof. Background Technology

[0002] A heat exchanger is a device that transfers some of the heat from a hot fluid to a cold fluid. It can be used as a heater, cooler, condenser, evaporator, and reboiler.

[0003] Traditional shell-and-tube condenser-gasification heat exchangers consist of a tube side and a shell side. When used for LNG vaporization, water vapor flows through the tube side and LNG flows through the shell side. Because LNG has an extremely low temperature of -162°C, the high-temperature steam will condense into ice and block the pipes the moment it exchanges heat with LNG. This prevents the high-temperature steam from flowing and exchanging heat normally, making the heat exchange process extremely unstable and violent. More seriously, thermal expansion and contraction may cause the materials to break and damage the equipment.

[0004] Therefore, improvements to existing technologies are necessary. Summary of the Invention

[0005] This invention provides an insertion-type dual-tube condenser-vaporizer heat exchanger, a heat exchange system, and a control method thereof to solve the above-mentioned problems.

[0006] One technical solution adopted by the present invention is: to provide an insertion-type dual-tube condenser-gasification heat exchanger, comprising: a heat exchanger shell, a plurality of heat exchange tubes, a steam inlet pipe, a condensate outlet pipe, an LNG inlet pipe and an NG outlet pipe;

[0007] The heat exchanger shell is provided with a top cover, inside which a tube sheet and a transition plate are installed, dividing the heat exchanger shell into a heat exchange chamber, a tube box and a steam chamber.

[0008] The heat exchange tube has a double tube structure, including an outer tube and an inner tube. The outer tube is set inside the heat exchange chamber, its upper end is closed, and its lower end passes through the tube sheet and communicates with the tube box. The inner tube is set inside the outer tube, its upper end is open and communicates with the outer tube, and its lower end passes through the transition plate and communicates with the steam chamber.

[0009] The steam inlet pipe is located at the bottom of the heat exchanger shell and communicates with the steam chamber. It is equipped with an inlet flow control valve.

[0010] The condensate outlet pipe is located on the side of the heat exchanger shell and is connected to the tube box.

[0011] The LNG inlet pipe is located on the side of the heat exchanger shell and is connected to the bottom of the heat exchange chamber. It is equipped with an inlet flow control valve.

[0012] The NG outlet pipe is located on the upper cover and communicates with the top of the heat exchange chamber;

[0013] An LNG level sensor is also installed inside the cylinder.

[0014] During operation, high-temperature steam flows through the inner tube and LNG flows through the shell. The high-temperature steam rises along the inner tube and gradually and slowly condenses into condensate after entering the outer tube. This is equivalent to using condensate as an intermediate medium. The condensate level is below the end of the inner tube, allowing the continuously entering high-temperature steam to exchange heat with the LNG through the condensate, thus preventing the condensate from freezing and clogging the pipeline.

[0015] Furthermore, a positioning plate is provided between the inner tube and the outer tube to make the inner and outer tubes coaxial. There are three positioning plates, which are vertically set on the outer circumferential surface of the upper end of the inner tube. The upper end of each positioning plate has an inclined surface.

[0016] Furthermore, the heat exchange chamber is also equipped with several tie rods, the lower ends of which are fixed to the tube sheet, and baffles are spaced apart on them. The LNG entering the heat exchange chamber flows between the baffles and exchanges heat fully. The baffles are also reserved with through holes through which the heat exchange tubes pass.

[0017] Furthermore, a wire mesh demister is provided at the top of the heat exchange chamber to remove mist entrained in the NG gas, and an anti-impact plate is provided at the bottom of the steam chamber, located above the steam inlet pipe inlet.

[0018] Furthermore, the heat exchange chamber is connected to the tube box via a flange structure, and the tube sheet is clamped inside the flange structure. The tube sheet and heat exchange tube structure can be easily removed by disassembling the flange structure, which is convenient for maintenance and replacement. A drain pipe is also provided on one side of the tube sheet. The drain pipe passes through the tube sheet and communicates with the heat exchange chamber, which is used to drain the heat exchange chamber during shutdown maintenance.

[0019] Another technical solution adopted by the present invention is to provide a heat exchange system and its control method;

[0020] The heat exchange system includes a simulation module, a control module, and a heat exchanger;

[0021] The heat exchanger is the aforementioned insertion-type double-tube condensation vaporization heat exchanger.

[0022] The control module is electrically connected to the LNG level sensor, the air intake flow control valve, and the liquid intake flow control valve.

[0023] The control method for the heat exchange system includes the following steps:

[0024] S1. The simulation module simulates the heat exchange process according to preset conditions and obtains the simulated curve of LNG liquid level height and temperature in the heat exchange chamber.

[0025] S2. Determine the liquid critical value of LNG based on its pressure, and determine the simulated liquid level height of LNG in the heat exchange chamber from the simulation curve based on the liquid critical value;

[0026] S3. During the heat exchange process, the control module monitors the actual LNG level height through the LNG level sensor. When the actual level height is higher than the simulated level height, the inlet flow control valve is adjusted to gradually increase the steam flow.

[0027] Furthermore, the simulation module uses ASPEN EDR to simulate the heat exchange process, with preset conditions including LNG flow rate, steam flow rate, cylinder size, and heat exchange area under the usage scenario.

[0028] Furthermore, the liquid inlet flow control valve and the gas inlet flow control valve also have flow monitoring and alarm functions. During the heat exchange process, an alarm will be triggered when the LNG flow rate or steam flow rate is lower than the warning value.

[0029] Furthermore, when the actual liquid level is lower than half of the simulated liquid level, the air intake flow control valve is adjusted to gradually reduce the steam flow.

[0030] The beneficial effects of the insertion-type double-tube condenser-vaporization heat exchanger, heat exchange system and control method of the present invention are:

[0031] 1. By designing a double-tube heat exchange tube, the condensate after the high-temperature steam is condensed is placed between the inner and outer tubes, which acts as an intermediate medium to buffer the heat exchange between LNG and high-temperature steam. This can effectively avoid the freezing phenomenon caused by the direct heat exchange between high-temperature steam and LNG, avoid pipe blockage, and avoid material breakage and equipment damage caused by thermal expansion and contraction.

[0032] 2. When the pressure and temperature of the high-temperature steam main change suddenly, it only affects the pressure and temperature of the condensate in a short time, and has little impact on the temperature of the LNG being exchanged for heat, thus effectively weakening the influence of external steam factors.

[0033] 3. By simulating the heat exchange process through the simulation module, the appropriate LNG liquid level can be determined. At this liquid level, the heat exchange effect is optimal. In conjunction with the LNG liquid level sensor installed in the cylinder, the actual LNG liquid level can be monitored in real time. When the LNG liquid level rises, the steam flow can be increased by adjusting the air intake flow control valve to ensure heat exchange efficiency. Attached Figure Description

[0034] Figure 1 This is a front sectional view of the insertion-type double-tube condenser-vaporizer heat exchanger according to the first embodiment of the present invention;

[0035] Figure 2 This is a top sectional view of the heat exchange chamber area of ​​the insertion-type double-tube condenser-vaporizer heat exchanger according to the first embodiment of the present invention;

[0036] Figure 3 This is a simulated curve of LNG liquid level height versus temperature in the heat exchange chamber according to the first embodiment of the present invention;

[0037] The components in the attached diagram are labeled as follows: 1. Heat exchanger shell, 2. Heat exchange tube, 3. Steam inlet pipe, 4. Condensate outlet pipe, 5. LNG inlet pipe, 6. NG outlet pipe, 11. Top cover, 12. Tube sheet, 13. Transition plate, 14. Tie rod, 15. Baffle plate, 16. Wire mesh demister, 17. Flange structure, 21. Outer pipe, 22. Inner pipe, 121. Drain pipe. Detailed Implementation

[0038] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0039] In the description of this invention, it should be understood that the terms "upper", "lower", "left", "right", "front", "back", "horizontal", "vertical", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this invention, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0040] Please see Figure 1 and Figure 2 The first embodiment of the present invention provides an insertion-type dual-tube condensation vaporization heat exchanger, comprising: a heat exchanger body 1, a plurality of heat exchange tubes 2, a steam inlet pipe 3, a condensate outlet pipe 4, an LNG inlet pipe 5, and an NG outlet pipe 6;

[0041] The heat exchanger shell 1 is provided with a top cover 11, and a tube sheet 12 and a transition plate 13 are provided inside the heat exchanger shell 1, which divide the interior of the heat exchanger shell 1 into three spaces: heat exchange chamber, tube box and steam chamber.

[0042] The heat exchange tube 2 has a double tube structure, including an outer tube 21 and an inner tube 22. The outer tube 21 is installed in the heat exchange chamber, its upper end is closed, and its lower end passes through the tube sheet 12 and is connected to the tube box. The inner tube 22 is installed in the outer tube 21, its upper end is open and connected to the outer tube 21, and its lower end passes through the transition plate 13 and is connected to the steam chamber.

[0043] The steam inlet pipe 3 is located at the bottom of the heat exchanger shell 1 and communicates with the steam chamber of the heat exchanger shell 1. It has an inlet flow control valve.

[0044] The condensate outlet pipe 4 is located on the side of the heat exchanger shell 1 and is connected to the tube box of the heat exchanger shell 1. It has an inlet flow control valve.

[0045] The LNG inlet pipe 5 is located on the side of the heat exchanger shell 1 and is connected to the bottom of the heat exchange chamber of the heat exchanger shell 1.

[0046] An LNG level sensor is also installed inside the cylinder;

[0047] The NG outlet pipe 6 is installed on the upper cover 11 and is connected to the top of the heat exchange chamber of the heat exchanger body 1;

[0048] During operation, high-temperature steam flows through the tube side (inner tube 22) of the heat exchanger shell 1, and LNG flows through the shell side. The high-temperature steam flows upward along the inner tube 22 and gradually and slowly condenses into condensate after entering the outer tube 21 (between the inner and outer tubes 21). This is equivalent to using condensate as an intermediate medium. The liquid level of condensate is calculated and controlled to be below the end of the inner tube 22, so that the continuously entering high-temperature steam exchanges heat with LNG through the condensate and avoids the condensate freezing and blocking the pipeline.

[0049] Specifically, the top of the heat exchanger shell 1 has a top cover 11 flange, which is fastened to the top cover 11 flange by a stud and nut structure. The top cover 11 is also equipped with a safety valve and a lifting lug. The former is used to release the pressure inside the heat exchanger shell 1, and the latter is used to lift the top cover 11.

[0050] Specifically, a wire mesh demister 16 is also provided at the top of the heat exchange chamber. The wire mesh demister 16 is installed in the heat exchange chamber through a connecting frame and is used to remove mist entrained in the NG gas.

[0051] Specifically, an anti-impact plate is also installed at the bottom of the steam chamber, located above the inlet of steam inlet pipe 3.

[0052] To ensure that the LNG entering the heat exchange chamber can fully exchange heat with the condensate inside the heat exchange tube 2 (between the inner and outer tubes 21), staggered baffles 15 also need to be installed.

[0053] Inside the heat exchange chamber, near the inner wall of the cylinder, there are four tie rods 14. The lower end of the tie rods 14 is fixed to the tube sheet 12. Baffles 15 are spaced on the tie rods 14. A spacer tube is sleeved on the tie rods 14 between adjacent baffles 15 to control the position of the baffles 15. The LNG entering the heat exchange chamber flows between the baffles 15 and exchanges heat fully.

[0054] Specifically, the baffle plate 15 also has a through hole for the heat exchange tube 2 to pass through.

[0055] To ensure the stability of the position between the inner pipe 22 and the outer pipe 21 and to provide sufficient space for condensate flow, a positioning plate is also provided between the inner pipe 22 and the outer pipe 21 to make the inner and outer pipes 21 coaxial.

[0056] Specifically, the upper end of the inner tube 22 has three vertical positioning plates on its outer circumference. Each positioning plate has an inclined surface at its upper end, which facilitates pushing the inner tube 22 into the outer tube 21.

[0057] If the heat exchange tube 2 structure is installed from the top of the heat exchanger shell 1, the stroke is too long and it is difficult to position. Therefore, the heat exchanger shell 1 is split into two parts:

[0058] The heat exchange chamber and the tube box are connected by a flange structure 17. The tube sheet 12 is clamped in the flange structure 17. The heat exchange tube 2 structure is assembled on the tube sheet 12 and the transition plate 13 to form a single-sided double tube sheet 12 structure. The single-sided double tube sheet 12 structure can be easily removed by disassembling the flange structure 17. It is easy to separate and convenient for maintenance and replacement.

[0059] Specifically, a drain pipe 121 is also provided on one side of the tube sheet 12. The drain pipe 121 passes through the tube sheet 12 and communicates with the heat exchange chamber, and is used to drain the heat exchange chamber during shutdown maintenance.

[0060] Specifically, one side of flange structure 17 is connected by a shouldered double-ended stud and nut, and is also equipped with an anti-loosening lug; the other side is connected by a double-ended stud and nut, and is also equipped with a spiral wound gasket.

[0061] To ensure that the condensate acts as a buffer, it is necessary to control both the LNG level and the condensate level.

[0062] The condensate level is below the upper end of the inner tube 22 and between the inner and outer tubes 21. This height needs to be calculated to ensure that after the high-temperature steam rushes out of the top of the inner tube 22, it condenses into condensate.

[0063] The LNG level is lower than the condensate level;

[0064] A heat exchange structure of high-temperature steam → condensate → LNG is formed by liquid level control. After the double tube is used, the condensate between the inner and outer tubes 21 can act as an intermediate medium, and the steam in the inner tube 22 can effectively prevent the condensate from freezing and blocking, and stabilize the material damage caused by temperature changes.

[0065] The first embodiment of the present invention also provides a heat exchange system and a control method thereof;

[0066] The heat exchange system includes a simulation module, a control module, and a heat exchanger. The heat exchanger is the aforementioned insertion-type dual-tube condensation and vaporization heat exchanger. The control module is electrically connected to the LNG level sensor, the inlet gas flow control valve, and the inlet liquid flow control valve.

[0067] The control method for a heat exchange system includes the following steps:

[0068] S1. The simulation module simulates the heat exchange process according to preset conditions and obtains the simulated curve of LNG liquid level height and temperature in the heat exchange chamber.

[0069] S2. Determine the liquid critical value of LNG based on its pressure, and determine the simulated liquid level height of LNG in the heat exchange chamber from the simulation curve based on the liquid critical value;

[0070] S3. During the heat exchange process, the control module monitors the actual LNG level height through the LNG level sensor. When the actual level height is higher than the simulated level height, the inlet flow control valve is adjusted to gradually increase the steam flow. When the actual level height is lower than half of the simulated level height, the inlet flow control valve is adjusted to gradually decrease the steam flow.

[0071] Specifically, the simulation module uses ASPEN EDR to simulate the heat exchange process, with preset conditions including LNG flow rate, steam flow rate, cylinder size, and heat exchange area under the usage scenario.

[0072] Take the following use case as an example:

[0073] LNG flow rate: 1.0 MPa, -162℃;

[0074] Steam flow rate: 0.6 MPa, 200℃;

[0075] Cylinder dimensions: DN500;

[0076] Heat exchange area: 36 square meters.

[0077] The simulated curves of LNG liquid level height versus temperature in the heat exchange chamber are shown below. Figure 3 In the simulated state, the heat exchange effect is optimal when the water between the outer pipes is condensed within a 2-meter height range inside the heat exchange chamber, and the liquid LNG is present inside the cylinder within a 1-meter height range.

[0078] During the heat exchange process, when the actual LNG level is higher than 1 meter, the control module adjusts the inlet flow control valve to gradually increase the steam flow. When the actual LNG level is lower than 0.5 meters, the inlet flow control valve is adjusted to gradually decrease the steam flow.

[0079] Specifically, the liquid inlet flow control valve and the gas inlet flow control valve also have flow monitoring and alarm functions. During the heat exchange process, an alarm will be triggered when the LNG flow rate or steam flow rate is lower than the warning value.

[0080] In addition, the control module and simulation module can be integrated into the software and deployed on the server side. Customers can log in to the software via mobile phone, set the adjustment range of the steam flow limit through the mobile phone, receive alarm information, and promptly carry out maintenance on upstream equipment.

[0081] Reasons for insufficient steam flow: Usually related to the boiler. Insufficient boiler fuel supply will lead to incomplete combustion and failure to generate enough heat to heat water or steam. Boiler water level that is too low or too high will affect heat transfer efficiency, resulting in low steam temperature.

[0082] Reasons for insufficient LNG flow: Generally related to the submersible pump, the pressure after the pump does not reach the design pressure, or the pipe diameter after the submersible pump is too small and the flow rate is low.

[0083] The beneficial effects of the insertion-type double-tube condenser-vaporization heat exchanger, heat exchange system and control method of the present invention are:

[0084] 1. By designing a double-tube heat exchange tube, the condensate after the high-temperature steam is condensed is placed between the inner and outer tubes, which acts as an intermediate medium to buffer the heat exchange between LNG and high-temperature steam. This can effectively avoid the freezing phenomenon caused by the direct heat exchange between high-temperature steam and LNG, avoid pipe blockage, and avoid material breakage and equipment damage caused by thermal expansion and contraction.

[0085] 2. When the pressure and temperature of the high-temperature steam main change suddenly, it only affects the pressure and temperature of the condensate in a short time, and has little impact on the temperature of the LNG being exchanged for heat, thus effectively weakening the influence of external steam factors.

[0086] 3. By simulating the heat exchange process through the simulation module, the appropriate LNG liquid level can be determined. At this liquid level, the heat exchange effect is optimal. In conjunction with the LNG liquid level sensor installed in the cylinder, the actual LNG liquid level can be monitored in real time. When the LNG liquid level rises, the steam flow can be increased by adjusting the air intake flow control valve to ensure heat exchange efficiency.

[0087] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A control method of a heat exchange system, comprising the following steps: S1, simulating a heat exchange process according to preset conditions by a simulation module to obtain a simulated curve of a liquid level height and a temperature of LNG in a heat exchange cavity; S2, determining a liquid critical value of the LNG according to a pressure of the LNG, and determining a simulated liquid level height of the LNG in the heat exchange cavity from the simulated curve according to the liquid critical value; S3, during the heat exchange process, monitoring an actual liquid level height of the LNG by a LNG liquid level sensor, and adjusting an inlet gas flow control valve to gradually increase a steam flow when the actual liquid level height is higher than the simulated liquid level height. Wherein: The heat exchange system comprises a simulation module, a control module and an insert type double-pipe condensation and vaporization heat exchanger; The insert type double-pipe condensation and vaporization heat exchanger comprises a heat exchanger cylinder, a plurality of heat exchange pipes, a steam inlet pipe, a condensate outlet pipe, an LNG inlet pipe and an NG outlet pipe; The heat exchanger cylinder is provided with an upper cover at the top thereof, and a tube sheet and a transition plate are arranged in the upper cover to divide the heat exchanger cylinder into a heat exchange cavity, a pipe box and a steam cavity; The heat exchange pipe is a double-pipe structure comprising an outer pipe and an inner pipe, the outer pipe is arranged in the heat exchange cavity, the upper end of the outer pipe is closed, and the lower end of the outer pipe penetrates through the tube sheet to communicate with the pipe box, the inner pipe is arranged in the outer pipe, the upper end of the inner pipe is open to communicate with the outer pipe, and the lower end of the inner pipe penetrates through the transition plate to communicate with the steam cavity; The steam inlet pipe is arranged at the bottom of the heat exchanger cylinder and communicates with the steam cavity, and the steam inlet pipe is provided with an inlet flow control valve thereon; The condensate outlet pipe is arranged at the side of the heat exchanger cylinder and communicates with the pipe box; The LNG inlet pipe is arranged at the side of the heat exchanger cylinder and communicates with the bottom of the heat exchange cavity, and the LNG inlet pipe is provided with an inlet flow control valve thereon; The NG outlet pipe is arranged at the upper cover and communicates with the top of the heat exchange cavity; The cylinder is further provided with a LNG liquid level sensor; The control module is electrically connected with the LNG liquid level sensor, the inlet flow control valve and the inlet flow control valve.

2. The control method of a heat exchange system according to claim 1, characterized by, The simulation module uses ASPEN EDR to simulate the heat exchange process, and the preset conditions are LNG flow, steam flow, cylinder size and heat exchange area in a use scenario.

3. The control method of a heat exchange system according to claim 2, characterized by, The inlet flow control valve and the inlet flow control valve further have a flow monitoring and alarm function, and an alarm is given when the LNG flow or the steam flow is lower than an alarm value during the heat exchange process.

4. The control method of a heat exchange system according to any one of claims 1 to 3, characterized in that, When the actual liquid level height is lower than one half of the simulated liquid level height, the inlet flow control valve is adjusted to gradually reduce the steam flow.

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