Pressure and flow distribution system and method for a multi-column ethane recovery plant

Abstract

The application discloses a natural gas ethane recovery engineering multi-column device pressure and flow distribution system, which comprises multiple single-column natural gas ethane recovery devices, the multiple single-column natural gas ethane recovery devices are connected in parallel, the multiple single-column natural gas ethane recovery devices are all connected with a collecting pipe, raw material gas enters into each single-column natural gas ethane recovery device branch pipe through the collecting pipe, flow and pressure control is performed inside each single-column natural gas ethane recovery device, raw material gas inlet flow of the multiple-column natural gas ethane recovery device is consistent, frequent pressure fluctuation is avoided, and stable operation of the multiple-column natural gas ethane recovery device is ensured.

Description

Technical Field

[0001] This invention belongs to the field of light hydrocarbon recovery technology, and relates to a pressure and flow distribution system for multiple units in a natural gas ethane recovery project, as well as a method for pressure and flow distribution in multiple units in a natural gas ethane recovery project. Background Technology

[0002] my country's ethylene feedstock mainly comes from naphtha, which is entirely derived from petroleum. In recent years, persistently high petroleum prices have increased ethylene production costs. Furthermore, projects relying on imported ethane as a key feedstock for ethylene production are susceptible to supply constraints, weakening the competitiveness of my country's ethane-based ethylene industry and introducing uncertainty into the Chinese ethylene market. With increasing demand for ethane, and given that natural gas recovery currently focuses primarily on light hydrocarbons, ethane extraction from natural gas is emerging as a new trend in natural gas condensate recovery technology. Natural gas ethane recovery, as a project to improve efficiency within China's petroleum system, aims to achieve integrated and efficient development of the upstream and downstream natural gas industry.

[0003] Most existing natural gas dehydrogenation units in China have small processing capacities, generally below 2 million cubic meters per day. A typical natural gas dehydrogenation plant typically has only one or two units, and only recovers propane (C3) and higher-order components, not ethane (C2). For large-scale natural gas processing plants, multiple units need to operate simultaneously. For example, a processing capacity of 20 billion cubic meters per year would require four units, each with a capacity of 15 million cubic meters per day, for natural gas ethane recovery. The simultaneous operation of multiple units inevitably leads to unstable priming gas pressure and flow, as well as repeated pressure fluctuations, which are detrimental to the stable operation of the plant. Therefore, it is crucial to adopt reasonable technologies to regulate the flow and pressure of each unit. Summary of the Invention

[0004] One objective of this invention is to provide a pressure and flow distribution system for multiple units in a natural gas ethane recovery project, which solves the problem of frequent pressure and flow fluctuations and unstable operation in existing natural gas ethane recovery units.

[0005] Another objective of this invention is to provide a method for distributing pressure and flow rates in multiple units of a natural gas ethane recovery project.

[0006] The technical solution adopted in this invention is a pressure and flow distribution system for a multi-row natural gas ethane recovery project, comprising multiple single-row natural gas ethane recovery units connected in parallel, all of which are connected to a manifold. Raw gas enters the branch pipe of each single-row natural gas ethane recovery unit through the manifold, and the flow and pressure are controlled within each single-row natural gas ethane recovery unit.

[0007] The invention is further characterized in that,

[0008] Each single-row natural gas ethane recovery unit includes a cold box, which is connected to an expander and a cryogenic separator. The cryogenic separator is connected to a demethanizer, and the methane tower is connected to the cold box. The feed gas enters each row of branch pipes through the manifold, passes through the cold box, and goes to the cryogenic separator. The liquid separated by the cryogenic separator enters the bottom of the demethanizer, and part of the gas in the demethanizer returns to the cold box for subcooling.

[0009] The cryogenic separator is connected to a level controller and a JT valve. A flow regulating valve is installed on the pipeline connecting the cryogenic separator to the demethanizer. When the pressure does not exceed 4.1 MPa, the gas phase separated from the cryogenic separator enters the demethanizer through the JT valve. The liquid phase in the cryogenic separator is connected to the bottom of the demethanizer through the flow regulating valve. The liquid level is automatically adjusted by the flow regulating valve controlled by the level controller.

[0010] The expander includes an expander pressurization end, an expander expansion end, and an expander control module. When the pressure does not exceed 4.1 MPa, the cryogenic separator is connected to the expander expansion end inlet, and the expander expansion end is connected to the demethanizer inlet. Part of the gas in the cryogenic separator goes to the expander expansion end, and after expansion and refrigeration, it goes to the demethanizer inlet. The demethanizer output end is connected to the cold box inlet through the demethanizer output pipeline. The cold box output is connected to the expander pressurization end inlet through a pipeline, and the expander pressurization end output is connected to the centrifugal compressor through a pipeline. The output ports of each centrifugal compressor are connected to the external output manifold through pipelines.

[0011] A third pressure transmitter is connected to the output pipeline of the expander's expansion end, and the output pipeline of the expander's expansion end is connected to the inlet of the demethanizer. The gas is input to the expander's expansion end through the expansion end inlet pipeline. After being processed by the expander's expansion end, the gas is delivered to the demethanizer. The third pressure transmitter detects the pressure of the gas entering the tower.

[0012] A second pressure transmitter and a pressure regulating valve are connected sequentially to the output pipeline of the demethanizer; the second pressure transmitter detects the pressure of the gas exiting the tower.

[0013] The manifold is equipped with a first pressure transmitter and a first flow transmitter.

[0014] A guide vane valve is connected to the expansion end of the expander, and the guide vane valve controls the opening degree of the expander guide vanes.

[0015] The raw gas enters each branch pipe through the manifold. A second flow transmitter is installed on each branch pipe to monitor the inlet flow of each natural gas ethane recovery unit. The first pressure transmitter, the first flow transmitter, the second flow transmitter, the guide vane valve, the pressure regulating valve, the second pressure transmitter, the third pressure transmitter, the JT valve, the level controller, and the liquid flow regulating valve are all electrically connected to the expander control module.

[0016] Another technical solution adopted in this invention is a pressure and flow distribution method for multiple units in a natural gas ethane recovery project. Using the aforementioned pressure and flow distribution system for multiple units in a natural gas ethane recovery project, the specific steps are as follows: The flow and pressure signals of each unit in the natural gas ethane recovery project are controlled by the expander control module. When flow control is selected, the flow rate of each unit is set to Fi = F / m, where Fi is the flow control setpoint, F is the flow rate displayed by the first flow transmitter, and m is the number of units in the natural gas ethane recovery project. When pressure control is selected, the pressure is controlled in a segmented manner, with a segmented control setpoint of 4.1 MPa. When the feedback value PC1 from the third pressure transmitter is ≥ 4.1 MPa, the expander control module adjusts the output signal and simultaneously adjusts the opening of the JT valve, thereby controlling the natural gas pressure passing through this unit's expander to not exceed 4.1 MPa. The third pressure transmitter measures the inlet pressure PC1; if PC1 < 4.1 MPa, the pressure is controlled by adjusting the opening of the guide vane valve.

[0017] The second pressure transmitter detects the natural gas pressure in the demethanizer output pipeline and transmits it to the expander control module. The expander control module changes the natural gas pressure in each demethanizer output pipeline by controlling the speed of the expander booster end according to the PID algorithm.

[0018] When the second pressure regulator measures the demethanizer outlet pressure value PC2 > 3.2 MPa, it sends the value to the expander control module. The expander control module adjusts the output signal and simultaneously adjusts the guide vane valve opening.

[0019] The beneficial effects of this invention are as follows: The pressure and flow distribution system for multiple natural gas ethane recovery units in this invention includes multiple parallel single-row natural gas ethane recovery units. Each row of natural gas ethane recovery units includes a demethanation tower, an expander expansion end, an expander pressurization end, an expander control module, guide vanes, and JT valves. The expander control module provides linkage protection for the expander guide vane-JT valve control, offering multiple control methods including selective control, split-range control, and over-pool control. This ensures consistent feed gas flow rates across multiple rows of natural gas ethane recovery units, avoiding frequent pressure fluctuations and guaranteeing stable operation of the multiple rows of natural gas ethane recovery units. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the pressure and flow distribution system of the multi-stage unit in the natural gas ethane recovery project of the present invention.

[0021] In the diagram, 1. First pressure transmitter, 2. First flow transmitter, 3. Second flow transmitter, 4. Cold box, 5. Cryogenic separator, 6. Expander booster end, 7. Expander expansion end, 8. Guide vane valve, 9. Electric regulating valve, 10. Second pressure transmitter, 11. Third pressure transmitter, 12. JT valve, 13. Demethanizer, 14. Liquid flow regulating valve, 15. Liquid level controller, 16. Expander control module, 17. Centrifugal compressor. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] This invention relates to a pressure and flow distribution system for multiple units in a natural gas ethane recovery project, such as... Figure 1 As shown, it includes multiple single-row natural gas ethane recovery units, which are connected in parallel and all connected to a manifold. The raw gas enters the branch pipe of each single-row natural gas ethane recovery unit through the manifold. The flow and pressure are controlled inside each single-row natural gas ethane recovery unit to achieve stable pressure and flow and avoid repeated fluctuations in unit pressure.

[0024] Each single-row natural gas ethane recovery unit includes a cold box 4, which is connected to an expander and a cryogenic separator 5. The cryogenic separator 5 is connected to a demethanizer 13, and the methane tower 13 is connected to the cold box 4. The raw gas enters each row of branch pipes through the manifold, passes through the cold box 4, and goes to the cryogenic separator 5. The liquid separated by the cryogenic separator 5 enters the bottom of the demethanizer 13, and part of the gas in the demethanizer 13 returns to the cold box 4 for subcooling.

[0025] The cryogenic separator 5 is connected to the level controller 15 and the JT valve 12 respectively. A liquid flow regulating valve 14 is installed on the pipeline connecting the cryogenic separator 5 to the demethanizer 13. When the pressure does not exceed 4.1 MPa, the gas phase separated from the cryogenic separator 5 enters the demethanizer 13 through the JT valve 12. The liquid phase in the cryogenic separator 5 is connected to the bottom of the demethanizer 13 through the liquid flow regulating valve 14. The liquid level is automatically adjusted by the liquid flow regulating valve 14 controlled by the level controller 15.

[0026] The expander includes an expander booster end 6, an expander expansion end 7, and an expander control module 16. When the pressure does not exceed 4.1 MPa, the cryogenic separator 5 is connected to the inlet of the expander expansion end 7, which is connected to the inlet of the demethanizer 13. A portion of the gas in the cryogenic separator 5 goes to the expander expansion end 7, and after expansion and refrigeration, it reaches the inlet of the demethanizer 13. The output of the demethanizer 13 is connected to the inlet of the cold box 4 via a demethanizer output pipeline. The output of the cold box 4 is connected to the inlet of the expander booster end 6 via a pipeline, and the output of the expander booster end 6 is connected to the centrifugal compressor via a pipeline. The outputs of each centrifugal compressor are connected to the external output manifold via pipelines. The expander booster end 6 is used to recover the energy from the gas exchange pressure difference, driving the centrifugal compressors linked to it to work, further changing the pressure in the pipeline. When the system is working, the intake and exhaust occur simultaneously, forming a dynamic balance in each single-row natural gas ethane recovery unit.

[0027] A third pressure transmitter 11 is connected to the output line of the expander expansion end 7. The output line of the expander expansion end 7 is also connected to the inlet of the demethanizer 13. Gas is input to the expander expansion end 7 via the expansion end inlet line. After processing by the expander expansion end 7, the gas is delivered to the demethanizer 13. The third pressure transmitter 11 detects the pressure of the gas entering the tower. A second pressure transmitter 10 and a pressure regulating valve 9 are connected sequentially to the output line of the demethanizer 13. The second pressure transmitter 10 detects the pressure of the gas exiting the tower.

[0028] The manifold is equipped with a first pressure transmitter 1 and a first flow transmitter 2.

[0029] A guide vane valve 8 is connected to the expansion end 7 of the expander. The guide vane valve 8 controls the opening of the expander guide vanes, thereby controlling the flow rate in the pipeline. The guide vane opening is 0 to 100%.

[0030] The raw gas enters each branch pipe through the manifold. A second flow transmitter 3 is installed on each branch pipe to monitor the inlet flow of each natural gas ethane recovery unit. The first pressure transmitter 1, the first flow transmitter 2, the second flow transmitter 3, the guide vane valve 8, the pressure regulating valve 9, the second pressure transmitter 10, the third pressure transmitter 11, the JT valve 12, the liquid level controller 15, and the liquid flow regulating valve 14 are all electrically connected to the expander control module 16.

[0031] This invention discloses a method for pressure and flow distribution in a multi-stage natural gas ethane recovery project. The method utilizes the aforementioned pressure and flow distribution system for a multi-stage natural gas ethane recovery project. The specific steps are as follows: The expander control module 16 controls the flow and pressure signals of each stage of the natural gas ethane recovery unit. When flow control is selected, the flow rate of each stage is set to Fi = F / m, where Fi is the flow control setpoint, F is the flow rate displayed by the first flow transmitter, and m is the number of stages of the natural gas ethane recovery unit. When pressure control is selected, the pressure is controlled in a segmented manner. The segmented control setpoint is 4.1 MPa. When the feedback value PC1 from the third pressure transmitter 11 is ≥ 4.1 MPa, the expander control module 16 adjusts the output signal and simultaneously adjusts the opening of the JT valve 12, thereby controlling the natural gas pressure passing through this stage of the expander to not exceed 4.1 MPa. The third pressure transmitter 11 measures the inlet pressure PC1. If PC1 < 4.1 MPa, the pressure is controlled by adjusting the opening of the guide vane valve 8.

[0032] The second pressure transmitter 10 detects the natural gas pressure in the demethanizer output pipeline and transmits it to the expander control module 16. The expander control module 16 changes the natural gas pressure in each demethanizer output pipeline by controlling the speed of the expander booster end 6 according to the PID algorithm.

[0033] When the second pressure regulator 10 measures the demethanizer outlet pressure value PC2 > 3.2 MPa, it sends the value to the expander control module 16. The expander control module 16 adjusts the output signal and simultaneously adjusts the opening of the guide vane valve 8.

[0034] If the expander fails and stops, the expander control module 16 immediately outputs a valve position setpoint for the JT valve 12, setting a preset opening of 30%. Based on the normal value P0 or F0, the PID algorithm controls the opening of the JT valve 12 so that the value measured by the third pressure transmitter 10 is maintained at P0 or the flow rate of the second flow transmitter 3 is maintained at F0.

[0035] In each single-row natural gas ethane recovery unit, the expander control module 16 forms a PID control loop through the guide vane valve 8 and JT valve 12 to adjust the expander inlet guide vanes. When the guide vane valve 8 controls the guide vane opening to reach 100%, the operation considers a 1-minute average value as feedback, and the JT valve 12 takes over the adjustment. The processing capacity range is 1050~1500×10⁴ m³. 3 / d, the set value is determined based on the value of the first flow transmitter 2 in the manifold, the value of the first flow transmitter 2 is denoted as Fi, and the set value FC = Fi / m, where m is the number of device columns.

[0036] The expander control module 16 performs split-range control of the expander inlet pressure. The expander inlet pressure, the expander inlet guide vane, and the JT valve 12 form a PID control loop to adjust the expander inlet guide vane. When the guide vane opening reaches 100%, the JT valve 12 takes over and starts adjusting. The normal set value is 3.8 MPa.g.

[0037] The expander control module 16 provides overpressure protection for the expansion end outlet pressure. When the expander outlet pressure exceeds 3.2 MPa.g, the expansion end inlet guide vane and JT valve will preferentially adjust the PT-04A0406 value. The PT-04A0406 setting value is 3.2 MPa.g, and manual confirmation is required for reset.

[0038] The expander control module 16 controls the independent operation of the JT valve 12: When the expander is under maintenance, the JT valve 12 independently controls the inlet flow rate, inlet pressure and outlet pressure. The opening of the JT valve is automatically adjusted according to the gas collection area flow rate or the expander inlet pressure or the expander outlet pressure. The flow rate and pressure setpoint is 3.8MPa, and the outlet pressure protection is 3.2MPa.

[0039] Expander control module 16 automatically connects to the JT valve 12 for emergency shutdown in case of expander failure or high liquid level interlock in cryogenic separator, and performs PID adjustment based on expander inlet pressure or device flow rate.

[0040] The expander control module 16 monitors the expander booster unit: The booster unit is equipped with a PLC to independently complete normal loading, start-up, shutdown, anti-surge, protective shutdown, and emergency shutdown, and exchanges data with the DCS via redundant Ethernet. The unit features hard-wired remote monitoring: allowing start-up, stop, running status, and fault alarms. See the IO table and DCS monitoring table for details. Emergency stop status contact signal output (including fault and other emergency stop logic triggers, relative to normal stop output), and guide vane opening 4-20mA output.

[0041] Example 1

[0042] In this embodiment 1, the pressure and flow distribution system of the multi-unit natural gas ethane recovery project includes four single-unit natural gas ethane recovery units connected in parallel, totaling four units. Each unit includes a demethanation tower, an expander expansion end, an expander pressurization end, an expander control module, guide vanes, and a JT valve, enabling stable operation of the multi-unit natural gas ethane recovery system and avoiding frequent pressure fluctuations.

[0043] Example 2

[0044] In this embodiment 2, the pressure and flow distribution system of the multi-row natural gas ethane recovery project includes four single-row natural gas ethane recovery units connected in parallel. The raw gas enters the branch pipes of each row of units through the manifold, passes through the cold box 4 to the cryogenic separator 5, and the liquid separated by the cryogenic separator 5 enters the bottom of the demethanizer 13. Part of the gas returns to the cold box for subcooling, and the other part goes to the expansion end inlet 7 of the expander. After expansion and cooling, it reaches the inlet of the demethanizer 13. The manifold is equipped with a first pressure regulator 1 and a first flow transmitter 2, and the branch pipes of each row are equipped with a second flow transmitter 3, all of which are electrically connected to the expander control module. A third pressure transmitter 11 is also connected to the outlet pipeline of the expander expansion end 7. The third pressure transmitter 11 is connected to the expander control module 16. The output port of the expander expansion end 7 is connected to the input port of the demethanizer 13 through the expansion end output pipeline. The output port of the demethanizer 13 is connected to the input port of the cold box 16 through the demethanizer output pipeline. A second pressure transmitter 10 and a pressure regulating valve 9 are also connected to the output pipeline of the demethanizer 13. The output port of the cold box 4 is connected to the input port of the expander booster end 6 through a pipeline. The output port of the expander booster end 6 is connected to the centrifugal compressor through a pipeline. A guide vane valve 8 is also connected to the expander expansion end 7. The guide vane valve 8 is electrically connected to the expander control module. The inlet pipeline of each column of expander end is connected to its respective pretreatment device. The output ports of each column of centrifugal compressor are connected to the external output manifold through pipelines.

[0045] Example 3

[0046] This embodiment 3 describes a multi-row pressure and flow distribution system for a natural gas ethane recovery project. It includes multiple single-row natural gas ethane recovery units connected in parallel, all connected to a manifold. Raw gas enters each single-row natural gas ethane recovery unit's branch pipe through the manifold. Flow and pressure are controlled within each single-row natural gas ethane recovery unit. Each single-row natural gas ethane recovery unit includes a cold box 4, connected to an expander and a cryogenic separator 5. The cryogenic separator 5 is connected to a demethanizer 13, and the methane tower 13 is connected to the cold box 4. Raw gas enters each branch pipe through the manifold, passes through the cold box 4, and goes to the cryogenic separator 5. The liquid separated by the cryogenic separator 5 enters the bottom of the demethanizer 13, and a portion of the gas in the demethanizer 13 returns to the cold box 4 for subcooling. The cryogenic separator 5 is connected to the level controller 15 and the JT valve 12 respectively. A liquid flow regulating valve 14 is installed on the pipeline connecting the cryogenic separator 5 to the demethanizer 13. When the pressure does not exceed 4.1 MPa, the gas phase separated from the cryogenic separator 5 enters the demethanizer 13 through the JT valve 12. The liquid phase in the cryogenic separator 5 is connected to the bottom of the demethanizer 13 through the liquid flow regulating valve 14. The liquid level is automatically adjusted by the liquid flow regulating valve 14 controlled by the level controller 15.

[0047] The expander includes an expander booster end 6, an expander expansion end 7, and an expander control module 16. When the pressure does not exceed 4.1 MPa, the cryogenic separator 5 is connected to the inlet of the expander expansion end 7, and the expander expansion end 7 is connected to the inlet of the demethanizer 13. Part of the gas in the cryogenic separator 5 goes to the expander expansion end 7, and after expansion and refrigeration, it goes to the inlet of the demethanizer 13. The output end of the demethanizer 13 is connected to the inlet of the cold box 4 through the demethanizer output pipeline. The output port of the cold box 4 is connected to the inlet of the expander booster end 6 through a pipeline. The output port of the expander booster end 6 is connected to the centrifugal compressor through a pipeline. The output ports of each centrifugal compressor are connected to the external output manifold through pipelines. The cryogenic separator 5 is connected to the level controller 15 and the JT valve 12 respectively. A liquid flow regulating valve 14 is installed on the pipeline connecting the cryogenic separator 5 to the demethanizer 13. When the pressure does not exceed 4.1 MPa, the gas phase separated from the cryogenic separator 5 enters the demethanizer 13 through the JT valve 12. The liquid phase in the cryogenic separator 5 is connected to the bottom of the demethanizer 13 through the liquid flow regulating valve 14. The liquid level is automatically adjusted by the liquid flow regulating valve 14 controlled by the level controller 15.

[0048] Example 4

[0049] In Example 4, the pressure and flow distribution system of the multi-unit natural gas ethane recovery project is as follows: Figure 1 As shown, the system includes multiple single-row natural gas ethane recovery units connected in parallel. Each unit is connected to a manifold. The feed gas enters the branch pipe of each single-row natural gas ethane recovery unit through the manifold. Flow and pressure are controlled within each unit. Each unit includes a cold box 4, which is connected to an expander and a cryogenic separator 5. The cryogenic separator 5 is connected to a demethanizer 13, which is connected to the cold box 4. The feed gas enters each branch pipe through the manifold, passes through the cold box 4, and goes to the cryogenic separator 5. The liquid separated by the cryogenic separator 5 enters the bottom of the demethanizer 13, and a portion of the gas in the demethanizer 13 returns to the cold box 4 for subcooling.

[0050] The cryogenic separator 5 is connected to the level controller 15 and the JT valve 12 respectively. A liquid flow regulating valve 14 is installed on the pipeline connecting the cryogenic separator 5 to the demethanizer 13. When the pressure does not exceed 4.1 MPa, the gas phase separated from the cryogenic separator 5 enters the demethanizer 13 through the JT valve 12. The liquid phase in the cryogenic separator 5 is connected to the bottom of the demethanizer 13 through the liquid flow regulating valve 14. The liquid level is automatically adjusted by the liquid flow regulating valve 14 controlled by the level controller 15.

[0051] The expander includes an expander booster end 6, an expander expansion end 7, and an expander control module 16. When the pressure does not exceed 4.1 MPa, the cryogenic separator 5 is connected to the inlet of the expander expansion end 7, which is connected to the inlet of the demethanizer 13. A portion of the gas in the cryogenic separator 5 goes to the expander expansion end 7, undergoes expansion and cooling, and then reaches the inlet of the demethanizer 13. The output of the demethanizer 13 is connected to the inlet of the cold box 4 via a demethanizer output pipeline. The output of the cold box 4 is connected to the inlet of the expander booster end 6 via a pipeline, and the output of the expander booster end 6 is connected to the centrifugal compressor via a pipeline. The outputs of each centrifugal compressor are connected to the external manifold via pipelines. A third pressure transmitter 11 is connected to the output pipeline of the expander expansion end 7, which is connected to the inlet of the demethanizer 13. The gas is input to the expander expansion end 7 via the expansion end inlet pipeline, and after being processed by the expander expansion end 7, it is delivered to the demethanizer 13. The third pressure transmitter 11 detects the pressure of the gas entering the tower. A second pressure transmitter 10 and a pressure regulating valve 9 are connected sequentially to the output pipeline of the demethanizer 13; the second pressure transmitter 10 detects the pressure of the gas exiting the tower. A first pressure transmitter 1 and a first flow transmitter 2 are installed on the manifold. A guide vane valve 8 is connected to the expansion end 7 of the expander, which controls the opening of the expander guide vanes, thereby controlling the flow rate in the pipeline. The guide vane opening is 0-100%.

[0052] The raw gas enters each branch pipe through the manifold. A second flow transmitter 3 is installed on each branch pipe to monitor the inlet flow of each natural gas ethane recovery unit. The first pressure transmitter 1, the first flow transmitter 2, the second flow transmitter 3, the guide vane valve 8, the pressure regulating valve 9, the second pressure transmitter 10, the third pressure transmitter 11, the JT valve 12, the liquid level controller 15, and the liquid flow regulating valve 14 are all electrically connected to the expander control module 16.

Claims

1. A pressure and flow distribution system for multiple units in a natural gas ethane recovery project, characterized in that, It includes multiple single-row natural gas ethane recovery units, multiple single-row natural gas ethane recovery units connected in parallel, and multiple single-row natural gas ethane recovery units are all connected to a manifold. The raw gas enters the branch pipe of each single-row natural gas ethane recovery unit through the manifold, and the flow and pressure are controlled inside each single-row natural gas ethane recovery unit. Each single-row natural gas ethane recovery unit includes a cold box (4), which is connected to an expander and a cryogenic separator (5). The cryogenic separator (5) is connected to a demethanizer (13), and the demethanizer (13) is connected to the cold box (4). The raw gas enters each row of branch pipes through the manifold, passes through the cold box (4), and goes to the cryogenic separator (5). The liquid separated by the cryogenic separator (5) enters the bottom of the demethanizer (13), and part of the gas in the demethanizer (13) returns to the cold box (4) for subcooling. The cryogenic separator (5) is connected to the level controller (15) and the JT valve (12) respectively. A liquid flow regulating valve (14) is installed on the pipeline connecting the cryogenic separator (5) to the demethanizer (13). When the pressure does not exceed 4.1 MPa, the gas phase separated from the cryogenic separator (5) enters the demethanizer (13) through the JT valve (12). The liquid phase in the cryogenic separator (5) is connected to the bottom of the demethanizer (13) through the liquid flow regulating valve (14). The liquid level is automatically adjusted by the liquid flow regulating valve (14) controlled by the level controller (15). The expander includes an expander pressurization end (6), an expander expansion end (7), and an expander control module (16). When the pressure does not exceed 4.1 MPa, the cryogenic separator (5) is connected to the inlet of the expander expansion end (7), and the expander expansion end (7) is connected to the inlet of the demethanizer (13). A portion of the gas in the cryogenic separator (5) goes to the expander expansion end (7), and after expansion and refrigeration, it goes to the inlet of the demethanizer (13). The output end of the demethanizer (13) is connected to the inlet of the cold box (4) through the demethanizer output pipeline. The cold box (4) output port is connected to the expansion pressurization end (6) input port through a pipeline. The expansion pressurization end (6) output port is connected to the centrifugal compressor through a pipeline. The output ports of each centrifugal compressor are connected to the external output manifold through pipelines. The output pipeline of the expansion end (7) of the expander is connected to the third pressure transmitter (11), and the output pipeline of the expansion end (7) of the expander is connected to the inlet of the demethanizer (13). The gas is input to the expansion end (7) of the expander through the expansion end inlet pipeline. After being processed by the expansion end (7) of the expander, the gas is delivered to the demethanizer (13). The third pressure transmitter (11) detects the pressure of the gas entering the tower. The output pipeline of the demethanizer (13) is connected in sequence to a second pressure transmitter (10) and a pressure regulating valve (9); the second pressure transmitter (10) detects the pressure of the gas in the tower; A first pressure transmitter (1) and a first flow transmitter (2) are installed on the manifold. The expansion end (7) of the expander is connected to a guide vane valve (8), which controls the opening degree of the expander guide vane. The raw gas enters each branch pipe through the manifold. A second flow transmitter (3) is installed on each branch pipe. The second flow transmitter (3) is used to monitor the inlet flow of each natural gas ethane recovery unit. The first pressure transmitter (1), the first flow transmitter (2), the second flow transmitter (3), the guide vane valve (8), the pressure regulating valve (9), the second pressure transmitter (10), the third pressure transmitter (11), the JT valve (12), the liquid level controller (15), and the liquid volume regulating valve (14) are all electrically connected to the expander control module (16).

2. Pressure and flow distribution method for multiple units in natural gas ethane recovery project, using the pressure and flow distribution system for multiple units in natural gas ethane recovery project described in claim 1 above, the specific steps are as follows: the flow and pressure signals of each unit in natural gas ethane recovery project are controlled by the expander control module (16). When flow control is selected, the flow rate of each unit is set to Fi=F / m, where Fi is the flow control setting value, F is the flow value displayed by the first flow transmitter, and m is the number of units in natural gas ethane recovery project. When pressure control is selected, the pressure is controlled in a split range. The split range control setting value is 4.1MPa. When the feedback value PC1 of the third pressure transmitter (11) is ≥4.1 MPa, the expander control module (16) adjusts the output signal and simultaneously adjusts the opening of the JT valve (12) to control the pressure of natural gas passing through the expander of this unit. The pressure does not exceed 4.1MPa. The third pressure transmitter (11) measures the inlet pressure PC1. PC1<4.1 MPa. The pressure is controlled by adjusting the opening of the guide vane valve (8). The second pressure transmitter (10) detects the natural gas pressure in the demethanizer output pipeline and transmits it to the expander control module (16). The expander control module (16) changes the natural gas pressure in each demethanizer output pipeline by controlling the speed of the expander booster end (6) according to the PID algorithm. When the second pressure transmitter (10) measures the demethanizer outlet pressure value PC2 > 3.2MPa and sends it to the expander control module (16), the expander control module (16) adjusts the output signal and simultaneously adjusts the opening of the guide vane valve (8).

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