A steady-state circulation control system for a natural gas flow calibration loop

Abstract

The application discloses a loop steady circulation control system for natural gas flow calibration, which comprises a loop unit, a temperature control unit, a flow control unit, a flow detection unit and a main control unit; natural gas circulates in the loop unit; the temperature control unit comprises a heat exchanger arranged on the loop unit and a cooling unit connected with the heat exchanger; the cooling unit comprises a hydraulic balance device, a refrigerating unit, a return water pipe group and an outlet water pipe group; an adjusting valve and a compensation heater are arranged on the outlet water pipe group, and a first return pipe group and a second return pipe group are arranged between the outlet water pipe group and the return water pipe group; the flow detection unit comprises a working standard flowmeter arranged on the loop unit and a detected flowmeter; the flow control unit comprises a circulating fan and a return regulator arranged on the loop unit; the system can quickly and accurately make the temperature, pressure and flow of the natural gas in the loop reach a preset range, has strong holding capacity, high calibration precision and simple operation.

Description

Technical Field

[0001] This invention relates to the field of natural gas testing equipment technology, and specifically to a loop steady-state circulation control system for natural gas flow testing. Background Technology

[0002] According to relevant requirements, all natural gas flow meters used in trade transactions need to be sent to a natural gas flow meter calibration institution for verification. Currently, calibration institutions often use a loop calibration system. The main working principle of the loop calibration system is as follows: according to the requirements of the calibration procedure for temperature, pressure, and flow stability during the calibration process, natural gas is injected into the circulating process system. When the required calibration pressure is reached, the gas injection process is closed to maintain pressure stability. The gas medium in the loop system will also remain stable. The loop power equipment (circulating fan) is then started, and the required calibration flow rate is set according to the requirements of the calibration procedure. However, in the existing loop calibration system, the temperature of the pressurized gas is relatively high. If the gas is not cooled in time, the uncertainty of the measurement result will increase, making the calibration results obtained by this loop calibration method inaccurate. Summary of the Invention

[0003] The purpose of this invention is to provide a loop steady-state circulation control system for natural gas flow calibration. This system can quickly and accurately bring the temperature, pressure and flow of natural gas in the loop to a preset range, has strong holding capability, high calibration accuracy, and is simple and convenient to operate.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A natural gas flow rate calibration loop steady-state circulation control system includes a loop unit, a temperature control unit, a flow control unit, a flow detection unit, and a main control unit; natural gas circulates within the loop unit.

[0006] The temperature control unit includes a heat exchanger installed on the loop unit and a cooling unit connected to the heat exchanger. The cooling unit is used to control the tube-side temperature of the heat exchanger, and the natural gas in the loop unit maintains a stable temperature after passing through the tube-side of the heat exchanger.

[0007] The cooling unit includes a hydraulic balancing device, a refrigeration unit installed on the primary side of the hydraulic balancing device, and a return water pipe assembly and an outlet water pipe assembly installed on the secondary side of the hydraulic balancing device. The return water pipe assembly injects cooling water from the heat exchanger into the hydraulic balancing device, which then enters the refrigeration unit for cooling via the primary side of the hydraulic balancing device. After cooling, the water flows through the hydraulic balancing device into the outlet water pipe assembly, which then injects the cooled water back into the heat exchanger for further cooling.

[0008] Multiple regulating valves are connected in parallel on the outlet pipe group. A first return pipe group and a second return pipe group are provided between the outlet pipe group and the return pipe group. The first return pipe group and the second return pipe group are located on both sides of the multiple regulating valves. A compensation heater is provided on the outlet pipe group. The compensation heater is used to heat the water in the outlet pipe group.

[0009] The flow detection unit includes a working-level standard flow meter and a flow meter under test, which are installed on the loop unit. The working-level standard flow meter is used to calibrate the flow meter under test.

[0010] The flow control unit includes a circulating fan and a return flow regulator installed on the loop unit. The circulating fan and the return flow regulator circulate the natural gas in the loop unit according to a preset flow range. The circulating fan includes a high-speed explosion-proof motor and a fan body connected by a magnetic coupler. The fan body is connected in series on the loop unit.

[0011] The temperature control unit, flow control unit, and flow detection unit are all electrically connected to the main control unit.

[0012] Preferably, the loop unit includes a main loop pipeline and a loop inlet and a loop outlet located on one side of the main loop pipeline. A first valve is installed in the loop inlet and a second valve is installed in the loop outlet. The loop inlet and loop outlet connect the main loop pipeline to an external natural gas pipeline.

[0013] Preferably, a pressure control unit is provided between the ring inlet and the external natural gas pipeline. The pressure control unit is used to inject natural gas from the external natural gas pipeline into the main ring pipeline through the ring inlet at a preset pressure.

[0014] Preferably, two circulating fans and two heat exchangers are provided, with one circulating fan and one heat exchanger connected in series to form a group, and the two groups are connected in parallel.

[0015] Preferably, a first temperature transmitter, a second temperature transmitter, and a third temperature transmitter are respectively installed at the upper, middle, and lower positions within the hydraulic balancing device; A1 and A2 water pipe joints are provided on the primary side of the hydraulic balancing device, and the water inlet of the refrigeration unit is connected to the A1 water pipe joint through the first water inlet pipe group; the water outlet of the refrigeration unit is connected to the A2 water pipe joint through the second water inlet pipe group; B1 and B2 water pipe joints are provided on the secondary side of the hydraulic balancing device, and the return water pipe group is connected to the B1 water pipe joint, and the outlet water pipe group is connected to the B2 water pipe joint.

[0016] Preferably, a constant pressure water supply unit is provided on the return water pipe assembly, which is used to ensure the water pressure in the cooling unit; the constant pressure water supply unit is connected to the tap water pipe through a softened water module.

[0017] Preferably, when the flow rate on the primary side of the hydraulic balancing device is the same as the flow rate on the secondary side of the hydraulic balancing device, the temperature at the A1 water pipe joint is the same as the temperature at the B1 water pipe joint, and the temperature at the A2 water pipe joint is the same as the temperature at the B2 water pipe joint. At this time, the medium inside the hydraulic balancing device is relatively static, and the temperature stratification between the upper and lower parts tends to be stable.

[0018] When the flow rate on the primary side of the hydraulic balancing device is less than the flow rate on the secondary side, the temperature at the A1 water pipe joint is the same as the temperature at the B1 water pipe joint, and the temperature at the A2 water pipe joint is greater than the temperature at the B2 water pipe joint. At this time, a portion of the return water at the B2 water pipe joint participates in the water supply at the B1 water pipe joint, and the internal temperature of the hydraulic balancing device gradually increases from top to bottom.

[0019] When the flow rate on the primary side of the hydraulic balancing device is greater than the flow rate on the secondary side, the temperature at the A2 water pipe joint is the same as the temperature at the B2 water pipe joint, and the temperature at the A1 water pipe joint is greater than the temperature at the B1 water pipe joint. At this time, a portion of the return water at the A2 water pipe joint participates in the return water at the A1 water pipe joint, and the internal temperature of the hydraulic balancing device gradually decreases from top to bottom.

[0020] Preferably, the cooling unit's refrigeration operation includes a pre-cooling stage and a temperature regulation stage;

[0021] The precooling stage includes:

[0022] M1, first start a set of refrigeration units on the primary side of the hydraulic balancing device, and inject water into the refrigeration unit through the first water inlet pipe group, so that the water circulates between the hydraulic balancing device, the first water inlet pipe group, the refrigeration unit and the second water inlet pipe group to reduce the water temperature;

[0023] M2 monitors the operating temperature of the hydraulic balancing device in real time through the first temperature transmitter, the second temperature transmitter and the third temperature transmitter. When the temperature at the top of the hydraulic balancing device reaches the preset value t1, the precooling stage is completed, and the precooling stage completion signal is fed back to the main control unit.

[0024] The temperature regulation stage includes: real-time monitoring of the natural gas temperature at the heat exchanger outlet, and adjusting the number of stages and opening ratio of the regulating valves in the return water pipe group by comparing the detected temperature with the set temperature to regulate the temperature.

[0025] When the temperature of the natural gas at the outlet of the heat exchanger exceeds the preset temperature, the regulating valve in the return water pipe group is gradually opened to increase the flow rate of cooling water entering the heat exchanger and cool it down.

[0026] When the temperature of the natural gas at the outlet of the heat exchanger reaches the preset temperature, the regulating valve maintains its current opening.

[0027] When the temperature of the natural gas at the outlet of the heat exchanger is lower than the preset temperature, the number of stages and the opening ratio of the regulating valve in the return water pipe group are adjusted in reverse to reduce the flow rate of cold water entering the heat exchanger, so as to ensure that the temperature of the natural gas at the outlet of the heat exchanger tends to the preset temperature and stabilizes.

[0028] When the natural gas at the heat exchanger outlet does not require cooling, the parallel regulating valves are all closed. At this time, the water in the return water pipe group is returned to the outlet water pipe group through the first return pipe group to achieve fluid circulation.

[0029] When all the parallel regulating valves are closed, and the natural gas temperature at the heat exchanger outlet is still lower than the set temperature, the compensation heater is started to raise the water temperature in the return water pipe group. When the natural gas temperature at the heat exchanger outlet reaches the set temperature, the compensation heater is automatically stopped.

[0030] Preferably, when the water pressure in the cooling unit is lower than 1.4 bar, the constant pressure water supply unit is activated to automatically supply water, and the water supply is automatically stopped when the pressure reaches 1.5 bar.

[0031] Preferably, when the temperature at the top of the hydraulic balancing device is higher than t2, the cooling capacity of the refrigeration unit is increased; when the temperature in the middle of the hydraulic balancing device is higher than t2, the second refrigeration unit is started; when the temperature at the bottom of the hydraulic balancing device is higher than t2, the main control unit issues an over-temperature alarm; when the temperature in the middle of the hydraulic balancing device returns to t1, the second refrigeration unit is shut down.

[0032] In this invention, the main control unit can control the entire system and display the working status of different components, as well as measured values ​​such as stability and pressure. It features strong human-machine interaction and is easy to operate. The circulating fan and reflux regulator can circulate the natural gas in the loop according to a set flow rate, enabling calibration of multiple flow points and precise flow control. The cooling unit reduces the heat generated by the circulating fan on the natural gas during operation, maintaining a stable temperature.

[0033] The circulating fan uses a high-speed explosion-proof motor connected to the fan body via a magnetic coupler. The explosion-proof motor and fan do not require mechanical connection, eliminating the risk of natural gas leakage, preventing high-order harmonic pollution to the power grid, and avoiding electromagnetic interference issues, ensuring high reliability. The magnetic coupling connection enables soft start and soft stop of the fan body. During startup, the high-speed explosion-proof motor first drives the conductor rotor of the magnetic coupler, and then drives the permanent magnet rotor to start at full load. This phased startup process is smooth, with minimal impact, reducing mechanical stress on the high-speed explosion-proof motor and the fan body. Since there is no mechanical connection, there are no sparks or hot surfaces. Furthermore, the magnetic coupling design ensures that power transmission can be quickly cut off in the event of a fault, further reducing safety risks.

[0034] The cooling unit continuously maintains the natural gas temperature at the heat exchanger outlet within the set range. By monitoring the temperature at the upper, middle, and lower positions of the hydraulic balancing device, the required cooling capacity at the heat exchanger outlet is determined, and the cooling capacity of the refrigeration unit is adjusted accordingly, avoiding over-adjustment and achieving rapid, precise, and stable control. When the natural gas temperature at the heat exchanger outlet is higher or lower than the preset temperature, the main control unit automatically adjusts the number of stages and opening ratio of the regulating valve or activates the compensating heater according to the built-in program, achieving automatic cooling or heating control without manual intervention and quickly reaching a stable temperature. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the system principle of the present invention;

[0036] Figure 2 This is a schematic diagram of the flow control unit and temperature control unit of the present invention;

[0037] Figure 3 This is a schematic diagram of the cooling unit principle of the present invention;

[0038] Figure 4 This is a schematic diagram illustrating the structural principle of the hydraulic balancing device of the present invention;

[0039] In the diagram: 1. Loop unit; 2. Temperature control unit; 3. Flow control unit; 4. Flow detection unit; 5. Main control unit; 6. External natural gas pipeline; 7. Pressure control unit; 8. Auxiliary heater; 10. Main loop pipeline; 11. Loop inlet; 12. Loop outlet; 20. Heat exchanger; 21. Cooling unit; 30. Circulating fan; 31. Reflux regulator; 40. Working-grade standard flow meter; 41. Flow meter under test; 81. First temperature transmitter; 82. Second temperature transmitter; 83. Third temperature transmitter; 84. A 1. Water pipe connector; 85. A2 water pipe connector; 86. B1 water pipe connector; 87. B2 water pipe connector; 88. First inlet water pipe assembly; 89. Second inlet water pipe assembly; 210. Hydraulic balancing device; 211. Refrigeration unit; 212. Return water pipe assembly; 213. Outlet water pipe assembly; 214. Regulating valve; 215. First return flow pipe assembly; 216. Second return flow pipe assembly; 217. Compensating heater; 218. Constant pressure water supply unit; 219. Softened water module; 300. Magnetic coupler; 301. High-speed explosion-proof motor; 302. Fan body. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings:

[0041] like Figure 1 , Figure 2 , Figure 3 and Figure 4 The diagram illustrates a loop steady-state circulation control system for natural gas flow rate calibration. This control system includes a loop unit 1, a temperature control unit 2, a flow control unit 3, a flow detection unit 4, and a main control unit 5. The temperature control unit 2, flow control unit 3, and flow detection unit 4 are all electrically connected to the main control unit 5. In this embodiment, the main control unit 5 is an industrial computer that communicates via an RS485 bus. It has a display, a memory, and is equipped with the Modbus communication protocol for data interaction with a host computer. The display shows the measured parameter values ​​of the system. The main control unit 5 contains a built-in program for the system's operation. This program is set by those skilled in the art according to operational requirements and is well-known in the field; therefore, it will not be described in detail here. Figure 1 The dashed line connecting to the main control unit 5 represents the signal line for electrical connection.

[0042] Natural gas circulates within loop unit 1. Loop unit 1 includes a main loop pipe 10 and a loop inlet 11 and a loop outlet 12, which are sealed and fixedly installed on one side of the main loop pipe 10. A first valve is installed in the loop inlet 11, and a second valve is installed in the loop outlet 12. Both the first and second valves are electrically controlled valves, and their opening and closing can be controlled by the main control unit 5. The loop inlet 11 and loop outlet 12 connect the main loop pipe 10 to the external natural gas pipeline 6. A pressure gauge is installed on the main loop pipe 10 to measure the pressure of the natural gas inside. The pressure value measured by the pressure gauge is transmitted to the main control unit 5 in real time and displayed on a display.

[0043] A pressure control unit 7 is installed between the loop inlet 11 and the external natural gas pipeline 6. The pressure control unit 7 is used to inject natural gas from the external natural gas pipeline 6 into the main loop pipeline 10 at a preset pressure through the loop inlet 11. In this embodiment, the pressure control unit 7 is a compressor, which injects natural gas at a specified pressure into the main loop pipeline 10 according to system requirements.

[0044] The temperature control unit 2 includes a heat exchanger 20 disposed on the loop unit 1 and a cooling unit 21 connected to the heat exchanger 20. The cooling unit 21 is used to control the tube temperature of the heat exchanger 20. The natural gas in the loop unit 1 undergoes temperature exchange after passing through the tube of the heat exchanger 20, so that it is kept within the set temperature range and stable.

[0045] The heat exchanger 20 is used to remove the heat generated by the natural gas in the main loop pipeline 10 due to the pressurization work of the flow control unit 3. During the calibration process, the temperature change of the calibration gas should not exceed ±0.5 ℃. In this embodiment, a tube bundle heat exchanger is selected, which consists of a set of parallel tubes placed inside a shell. One or more channels are formed between the shell and the tube bundle, allowing a second fluid to flow outside the tube bundle. Through heat exchange between the tube bundle and the shell, heat transfer between the two fluids can be achieved. During operation, natural gas flows inside the tubes, and cooling water flows outside the tubes. When the hot fluid passes through the tube bundle, heat is transferred to the cold fluid through the tube wall. If the temperature of the hot fluid is higher than that of the cold fluid, heat will be transferred from the hot fluid to the cold fluid, and vice versa. This heat exchanger 20 has a large heat transfer area, improving heat exchange efficiency. The tube bundle is detachable for easy cleaning and maintenance, and it is suitable for various fluids and a wide range of temperatures and pressures.

[0046] The cooling unit 21 includes a hydraulic balancing device 210, a chiller unit 211 installed on the primary side of the hydraulic balancing device 210, and a return water pipe assembly 212 and an outlet water pipe assembly 213 installed on the secondary side of the hydraulic balancing device 210. The return water pipe assembly 212 injects cooling water from the heat exchanger 20 into the hydraulic balancing device 210, which then flows through the primary side into the chiller unit 211 for cooling. After cooling, the water flows through the secondary side of the hydraulic balancing device 210 into the outlet water pipe assembly 213, which then injects the cooled water back into the heat exchanger 20 for further cooling. The hydraulic balancing device 210 is used to balance hydraulic interference caused by the simultaneous operation of constant flow and variable flow systems, effectively preventing the chiller unit 211 from shutting down due to reduced flow. It removes microbubbles as small as 10µm and particulate impurities as small as 5µm, and also functions as an energy storage buffer tank.

[0047] The flow control unit 3 includes a circulating fan 30 and a return flow regulator 31 installed on the loop unit 1. The circulating fan 30 and the return flow regulator 31 circulate the natural gas in the loop unit 1 according to a preset flow range. The circulating fan 30 includes a high-speed explosion-proof motor 301 and a fan body 302 connected by a magnetic coupler 300. The fan body 302 is connected in series on the loop unit 1 to provide power for the flow of natural gas. The return flow regulator 31 uses a bypass electric flow control valve, which can accurately control the opening and closing and flow control. Flow control uses a frequency converter equipped with the circulating fan 30 for large flow regulation. To further ensure stable operation at low flow rates, the return flow regulator 31 controls the flow at 20% of the maximum flow of a single circulating fan 30, achieving accurate regulation of the medium flow in the loop unit across the entire range.

[0048] The magnetic coupling connection transmits power without any mechanical contact, replacing traditional mechanical connections and offering superior reliability and safety. It also enables soft starting, ensuring a smooth start-up process with minimal impact and reducing mechanical stress on the motor and fan. The high-speed explosion-proof motor 301 features a compact and robust design, significantly reducing fan size and weight; it boasts high efficiency, directly driving the load and minimizing energy loss. Because the high-speed explosion-proof motor 301 is externally mounted, cooling does not require an external water cooling system, reducing the risk of leakage in the loop system. The low temperature rise at the fan inlet and outlet greatly reduces the power consumption of the associated heat exchange and refrigeration systems. Component replacement is convenient, making motor maintenance easier; and the flow rate adjustment range is wider, with a flow rate adjustment ratio of up to 1:20, allowing for more precise adjustment at low flow rates.

[0049] In this embodiment, two circulating fans 30 and two heat exchangers 20 are provided. One circulating fan 30 and one heat exchanger 20 are connected in series to form a group, and the two groups are set in parallel. During operation, one or both can be turned on simultaneously as needed.

[0050] The flow detection unit 4 includes a working standard flow meter 40 and a flow meter under test 41 installed on the loop unit 1. The working standard flow meter 41 is used to calibrate the flow meter under test 40. When the pressure, flow rate and temperature in the main loop pipe 10 reach the set requirements, the corresponding flow point of the flow meter under test 40 is calibrated.

[0051] Multiple regulating valves 214 are connected in parallel on the outlet pipe assembly 213. A first return pipe assembly 215 and a second return pipe assembly 216 are provided between the outlet pipe assembly 213 and the return pipe assembly 212. The first return pipe assembly 215 and the second return pipe assembly 216 are located on both sides of the multiple parallel regulating valves 214. A compensation heater 217 is provided on the outlet pipe assembly 213. The compensation heater 217 is used to heat the water in the outlet pipe assembly 213.

[0052] A first temperature transmitter 81, a second temperature transmitter 82, and a third temperature transmitter 83 are respectively installed at the upper, middle, and lower positions within the hydraulic balancing device 210. Water pipe connectors A1 and A2 are fixedly installed on the primary side of the hydraulic balancing device 210. The water inlet of the chiller unit 211 is connected to the A1 water pipe connector via the first water inlet pipe group 88. An auxiliary heater 8 is also installed on the first water inlet pipe group 88. When the top temperature of the hydraulic balancing device 210 is lower than 6℃ (the shutdown temperature of the chiller unit 211), the auxiliary heater 8 is activated to maintain the unit at its minimum load and ensure that the chiller unit 211 does not shut down. The auxiliary heater 8 is electrically heated and its opening and closing are controlled by the main control unit 5. A temperature transmitter for temperature detection, a pressure transmitter for pressure detection, a circulation pump for providing circulation power to the water, and an electrically controlled flow valve are installed on the first water inlet pipe group 88. The temperature transmitter, pressure transmitter, circulating pump, and electrically controlled flow valve are all electrically connected to the main control unit 5.

[0053] The outlet of the refrigeration unit 211 is connected to the A2 water pipe connector 85 via the second inlet pipe assembly 89. A temperature transmitter for temperature detection and an electrically controlled flow valve for opening and closing are installed on the second inlet pipe assembly 89. Both the temperature transmitter and the electrically controlled flow valve are electrically connected to the main control unit 5.

[0054] On the secondary side of the hydraulic balancing device 210, there are water pipe joints B1 86 and B2 87. One end of the return water pipe assembly 212 is connected to the B1 water pipe joint 86, and one end of the outlet water pipe assembly 213 is connected to the B2 water pipe joint 87. A pressure transmitter, a thermometer, a temperature transmitter, and an electrically controlled flow valve are installed on the return water pipe assembly 212. An electrically controlled flow valve, a circulating pump, a pressure transmitter, a flow meter, and a temperature transmitter are installed on the outlet water pipe assembly 213. All of these components are electrically connected to the main control unit 5.

[0055] In a preferred embodiment, a constant pressure water supply unit 218 is provided on the return water pipe assembly 212. The constant pressure water supply unit 218 is used to ensure the water pressure in the cooling unit 21. The constant pressure water supply unit 21 is connected to the tap water pipe through a softened water module 219. The softened water module 219 softens the water from the tap water pipe and then supplies the softened water to the constant pressure water supply unit 21. The softened water module 219 is a commercially available fully automatic water softening device, and the constant pressure water supply unit 218 is a commercially available constant pressure water supply device. When the water pressure in the cooling unit 21 is lower than 1.4 bar, the constant pressure water supply unit 218 is activated to automatically supply water, and automatically stops supplying water when the pressure reaches 1.5 bar.

[0056] When the flow rate on the primary side of the hydraulic balancing device 210 is the same as the flow rate on the secondary side, the temperature at water pipe joint 84 of A1 is the same as the temperature at water pipe joint 86 of B1, and the temperature at water pipe joint 85 of A2 is the same as the temperature at water pipe joint 87 of B2. At this time, the internal medium of the hydraulic balancing device 210 is relatively static, and the temperature stratification between the upper and lower parts tends to be stable; this state is the ideal state.

[0057] When the flow rate on the primary side of the hydraulic balancing device 210 is less than the flow rate on the secondary side, the temperature at water pipe joint 84 of A1 is the same as the temperature at water pipe joint 86 of B1, and the temperature at water pipe joint 85 of A2 is greater than the temperature at water pipe joint 87 of B2. At this time, a portion of the return water at water pipe joint 87 of B2 participates in the water supply at water pipe joint 86 of B1, and the internal temperature of the hydraulic balancing device 210 gradually increases from top to bottom. This state indicates that the cooling capacity cannot meet the energy requirements of the cooling operation.

[0058] When the flow rate on the primary side of the hydraulic balancing device 210 is greater than the flow rate on the secondary side, the temperature at water pipe joint 85 (A2) is the same as the temperature at water pipe joint 87 (B2), and the temperature at water pipe joint 84 (A1) is greater than the temperature at water pipe joint 86 (B1). At this time, a portion of the return water at water pipe joint 85 (A2) participates in the return water flow at water pipe joint 84 (A1), causing the internal temperature of the hydraulic balancing device 210 to gradually decrease from top to bottom. This state represents a situation where the cooling capacity exceeds the energy required for the cooling operation.

[0059] The cooling operation of the cooling unit 21 includes a pre-cooling stage and a temperature regulation stage;

[0060] The pre-cooling stage includes:

[0061] After receiving the cooling command from the main control unit 5, M1 first starts a set of refrigeration units 211 on the primary side of the hydraulic balancing device 210. Water is injected into the refrigeration unit 211 through the circulation pump in the first water inlet pipe group 88, so that the water circulates between the hydraulic balancing device 210, the first water inlet pipe group 88, the refrigeration unit 211 and the second water inlet pipe group 89 to reduce the water temperature.

[0062] M2 monitors the operating temperature of the hydraulic balancing device 210 in real time through the first temperature transmitter 81, the second temperature transmitter 82 and the third temperature transmitter 83. When the temperature at the top of the hydraulic balancing device 210 reaches the preset value t1, the precooling stage is completed, and the precooling stage completion signal is fed back to the main control unit 5. In this embodiment, t1 is 7°C.

[0063] When the first set of circulating fans 30 is running, the main control unit 5 interlocks and starts the secondary side circulating pump (i.e., the circulating pump in the outlet pipe group 213) of the hydraulic balancing device 210 in the corresponding cooling unit 21; when the second set of circulating fans 30 is running, the main control unit 5 interlocks and starts the secondary side circulating pump of the hydraulic balancing device 210 in the corresponding cooling unit 21; when both sets of circulating fans 30 are running simultaneously, the main control unit 5 interlocks and starts the secondary side circulating pump of the hydraulic balancing device 210 in the cooling unit 21, with one circulating pump operating at a variable frequency and the other operating at a fixed frequency.

[0064] The temperature regulation stage includes: real-time monitoring of the natural gas temperature at the outlet of the heat exchanger 20, and adjusting the number of stages and opening ratio of the regulating valve 214 in the return water pipe group 212 by comparing the detected temperature with the set temperature to regulate the temperature.

[0065] When the temperature of the natural gas at the outlet of the heat exchanger 20 exceeds the preset temperature (20℃+0.5℃), the regulating valve 214 in the return water pipe group 212 is gradually opened to increase the flow rate of cooling water entering the heat exchanger 20 and cool it down. In this embodiment, three regulating valves 214 are arranged in parallel, namely DN50, DN100 and DN150.

[0066] When the temperature of the natural gas at the outlet of the heat exchanger 20 reaches the preset temperature, the regulating valve 214 maintains the current opening; in this embodiment, the preset temperature is 20°C.

[0067] When the temperature of the natural gas at the outlet of the heat exchanger 20 is lower than the preset temperature (20℃-0.5℃), the number of stages and the opening ratio of the regulating valve 214 in the return water pipe group 212 are adjusted in the reverse direction to reduce the flow rate of cold water entering the heat exchanger 20, so as to ensure that the temperature of the natural gas at the outlet of the heat exchanger 20 tends to the preset temperature (20℃) and stabilizes.

[0068] When the natural gas at the outlet of the heat exchanger 20 does not need cooling, the parallel regulating valves 214 are all closed. At this time, the water in the return water pipe group 212 is returned to the outlet water pipe group 213 through the first return pipe group 88 to achieve fluid circulation and prevent pressure buildup.

[0069] When all the parallel regulating valves 214 are closed, and the natural gas temperature at the outlet of the heat exchanger 20 is still lower than the set temperature, the compensation heater 217 is started to increase the water temperature in the return water pipe group 212. When the natural gas temperature at the outlet of the heat exchanger 20 reaches the set temperature, the compensation heater 217 is automatically stopped.

[0070] When the top temperature of the hydraulic balancing device 210 is higher than t2, the cooling capacity of the refrigeration unit 211 is increased. In this embodiment, t2 is 12°C. Rapid cooling is achieved by increasing the operating frequency of the internal circulation pump of the first inlet pipe group 88 and increasing the cooling capacity of the refrigeration unit 211. When the middle temperature of the hydraulic balancing device 210 is higher than t2, the second refrigeration unit 211 is started. When the bottom temperature of the hydraulic balancing device 210 is higher than t2, the main control unit 5 issues an over-temperature alarm to remind the operator to check the system status. When the middle temperature of the hydraulic balancing device 210 returns to t1, the second refrigeration unit 211 is shut down.

[0071] When the circulating fan 30 controls the total flow of the working-grade standard flow meter 40 within 5% of the calibration flow point, the current flow point is deemed stable and effective. When the system determines that the total flow fluctuation of the working-grade standard flow meter 40 does not exceed a preset value of 5%, the temperature fluctuation of the working-grade standard flow meter 40 does not exceed 0.5℃, and the pressure fluctuation of the working-grade standard flow meter 40 does not exceed 0.5% within a certain timeframe, and these three conditions are met simultaneously, automatic calibration of that flow point begins.

[0072] The above embodiments are merely illustrative of the concept and implementation of the present invention and are not intended to limit it. Under the concept of the present invention, technical solutions without substantial changes are still within the scope of protection.

Claims

1. A loop steady-state circulation control system for natural gas flow rate calibration, characterized in that: The control system includes a loop unit, a temperature control unit, a flow control unit, a flow detection unit, and a main control unit; natural gas circulates within the loop unit. The temperature control unit includes a heat exchanger installed on the loop unit and a cooling unit connected to the heat exchanger. The cooling unit is used to control the internal temperature of the heat exchanger, and the natural gas in the loop unit maintains a stable temperature after passing through the internal cavity of the heat exchanger. The cooling unit includes a hydraulic balancing device, a refrigeration unit installed on the primary side of the hydraulic balancing device, and a return water pipe assembly and an outlet water pipe assembly installed on the secondary side of the hydraulic balancing device. The return water pipe assembly injects cooling water from the heat exchanger into the hydraulic balancing device, which then enters the refrigeration unit for cooling via the primary side of the hydraulic balancing device. After cooling, the water flows through the hydraulic balancing device into the outlet water pipe assembly, which then injects the cooled water back into the heat exchanger for further cooling. A first temperature transmitter, a second temperature transmitter, and a third temperature transmitter are respectively installed at the upper, middle, and lower positions within the hydraulic balancing device. Water pipe joints A1 and A2 are installed on the primary side of the hydraulic balancing device. The inlet of the refrigeration unit is connected to water pipe joint A1 via a first inlet pipe assembly. The outlet of the refrigeration unit is connected to water pipe joint A2 via a second inlet pipe assembly. Water pipe joints B1 and B2 are installed on the secondary side of the hydraulic balancing device. The return water pipe assembly is connected to water pipe joint B1, and the outlet water pipe assembly is connected to water pipe joint B2. An auxiliary heater is also installed on the first inlet pipe assembly. Multiple regulating valves are connected in parallel on the outlet pipe group. A first return pipe group and a second return pipe group are provided between the outlet pipe group and the return pipe group. The first return pipe group and the second return pipe group are located on both sides of the multiple regulating valves. A compensation heater is provided on the outlet pipe group. The compensation heater is used to heat the water in the outlet pipe group. The flow detection unit includes a working-level standard flow meter and a flow meter under test, which are installed on the loop unit. The working-level standard flow meter is used to calibrate the flow meter under test. The flow control unit includes a circulating fan and a return flow regulator installed on the loop unit. The circulating fan and the return flow regulator circulate the natural gas in the loop unit according to a preset flow range. The circulating fan includes a high-speed explosion-proof motor and a fan body connected by a magnetic coupler. The fan body is connected in series on the loop unit. The temperature control unit, flow control unit, and flow detection unit are all electrically connected to the main control unit; The cooling unit's refrigeration operation includes a pre-cooling stage and a temperature regulation stage; The precooling stage includes: M1, first start a set of refrigeration units on the primary side of the hydraulic balancing device, and inject water into the refrigeration unit through the first water inlet pipe group, so that the water circulates between the hydraulic balancing device, the first water inlet pipe group, the refrigeration unit and the second water inlet pipe group to reduce the water temperature; M2 monitors the operating temperature of the hydraulic balancing device in real time through the first temperature transmitter, the second temperature transmitter and the third temperature transmitter. When the temperature at the top of the hydraulic balancing device reaches the preset value t1, the precooling stage is completed, and the precooling stage completion signal is fed back to the main control unit. The temperature regulation stage includes: real-time monitoring of the natural gas temperature at the heat exchanger outlet, and adjusting the number of stages and opening ratio of the regulating valves in the return water pipe group by comparing the detected temperature with the set temperature to regulate the temperature. When the temperature of the natural gas at the outlet of the heat exchanger exceeds the preset temperature, the regulating valve in the return water pipe group is gradually opened to increase the flow rate of cooling water entering the heat exchanger and cool it down. When the temperature of the natural gas at the outlet of the heat exchanger reaches the preset temperature, the regulating valve maintains its current opening. When the temperature of the natural gas at the outlet of the heat exchanger is lower than the preset temperature, the number of stages and the opening ratio of the regulating valve in the return water pipe group are adjusted in reverse to reduce the flow rate of cold water entering the heat exchanger, so as to ensure that the temperature of the natural gas at the outlet of the heat exchanger tends to the preset temperature and stabilizes. When the natural gas at the heat exchanger outlet does not require cooling, the parallel regulating valves are all closed. At this time, the water in the return water pipe group is returned to the outlet water pipe group through the first return pipe group to achieve fluid circulation. When all the parallel regulating valves are closed, and the natural gas temperature at the heat exchanger outlet is still lower than the set temperature, the compensation heater is started to raise the water temperature in the return water pipe group. When the natural gas temperature at the heat exchanger outlet reaches the set temperature, the compensation heater is automatically stopped.

2. The natural gas flow rate calibration loop steady-state circulation control system according to claim 1, characterized in that: The loop unit includes a main loop pipeline and a loop inlet and a loop outlet located on one side of the main loop pipeline. A first valve is installed in the loop inlet and a second valve is installed in the loop outlet. The loop inlet and loop outlet connect the main loop pipeline to an external natural gas pipeline.

3. The natural gas flow rate calibration loop steady-state circulation control system according to claim 2, characterized in that: A pressure control unit is installed between the loop inlet and the external natural gas pipeline. The pressure control unit is used to inject natural gas from the external natural gas pipeline into the main loop pipeline through the loop inlet at a preset pressure.

4. The loop steady-state circulation control system for natural gas flow calibration according to claim 1 or 3, characterized in that: Two circulating fans and two heat exchangers are provided. One circulating fan and one heat exchanger are connected in series to form a group, and the two groups are connected in parallel.

5. The natural gas flow rate calibration loop steady-state circulation control system according to claim 4, characterized in that: A constant pressure water supply unit is installed on the return water pipe assembly. The constant pressure water supply unit is used to ensure the water pressure in the cooling unit. The constant pressure water supply unit is connected to the tap water pipe through a softened water module.

6. The natural gas flow rate calibration loop steady-state circulation control system according to claim 5, characterized in that: When the water pressure in the cooling unit is lower than 1.4 bar, the constant pressure water supply unit is activated to automatically supply water, and the water supply automatically stops when the pressure reaches 1.5 bar.

7. The natural gas flow rate calibration loop steady-state circulation control system according to claim 5, characterized in that: When the temperature at the top of the hydraulic balancing device is higher than t2, the cooling capacity of the refrigeration unit is increased; when the temperature in the middle of the hydraulic balancing device is higher than t2, the second refrigeration unit is started; when the temperature at the bottom of the hydraulic balancing device is higher than t2, the main control unit issues an over-temperature alarm; when the temperature in the middle of the hydraulic balancing device returns to t1, the second refrigeration unit is shut down.

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