Two-phase flow recognition system and method based on key elevation difference map

Abstract

This invention discloses a two-phase flow identification system and method based on critical elevation maps, comprising the following steps: acquiring relative position data of all equipment, pipes, and valves in the pipeline system to be analyzed, from the starting equipment to the final equipment, as well as operating temperature, operating pressure, and medium composition data of each material flow point; drawing a critical elevation map based on the collected data; and analyzing the impact of pressure and temperature changes at each material flow point on the medium phase state using the critical elevation map, combined with the thermodynamic properties and flow characteristics of the medium, to identify locations prone to gas-liquid two-phase flow. This invention, by establishing critical elevation maps, can identify pipelines prone to two-phase flow in advance, preventing gas-liquid two-phase flow in process equipment pipelines, which can lead to long-term pipeline vibration, resulting in pipeline fatigue, support structure failure, weld cracking, and flange leakage. Furthermore, for pump inlet pipelines, it avoids the presence of two-phase flow that could cause pump cavitation and damage to the pump equipment.

Description

Technical Field

[0001] This invention relates to the field of two-phase flow identification technology, and more specifically to a two-phase flow identification system and method based on key elevation difference maps. Background Technology

[0002] In process plants, gas-liquid two-phase flow pipelines are common but also extremely complex. Due to the instability of their flow states, two-phase flow pipelines can cause serious hazards and challenges to the process plant. The periodic changes in two-phase flow pipelines lead to uneven mass and velocity distribution within the pipeline, generating periodic impact forces and causing problems such as pipeline fatigue and weld cracking. This problem is particularly prone to occur in pipelines with saturated liquid phases.

[0003] Identifying existing two-phase flow piping primarily relies on two aspects: 1. The process package documentation will specify the two-phase flow piping; 2. Case studies from previous process installations. However, considering that established process package providers generally rely on their past experience, less experienced providers, due to their prioritization of experience, may not effectively inform the design institute. For entirely new process installations, the lack of prior project references can also make it difficult to identify piping prone to two-phase flow. Summary of the Invention

[0004] The purpose of this invention is to provide a two-phase flow identification system and method based on critical elevation maps. By drawing critical elevation maps, points that are prone to two-phase flow can be identified in the early stages of design, and the occurrence of gas-liquid two-phase flow can be avoided through effective means.

[0005] The objective of this invention can be achieved through the following technical solutions: A two-phase flow identification system based on key elevation maps includes the following steps: Step 1: Obtain the relative position data of all equipment, pipelines, and valves in the pipeline system to be analyzed, from the starting equipment to the final equipment, as well as the operating temperature, operating pressure, and medium composition data of each material flow point; Step 2: Draw a key elevation difference map based on the collected data, and mark the elevation positions of each piece of equipment, pipeline, valve and process parameters of the material flow point on the map; Step 3: By using the key elevation difference map, combined with the thermodynamic properties and flow characteristics of the medium, analyze the influence of pressure and temperature changes at each flow point on the phase state of the medium, and identify the locations where gas-liquid two-phase flow is likely to occur. Step 4: Based on the identification results, make targeted adjustments to the equipment layout and pipeline routing to avoid the generation of gas-liquid two-phase flow.

[0006] As a further aspect of the present invention: the criteria for identifying locations prone to gas-liquid two-phase flow by using key elevation difference diagrams include: pressure reduction at the material flow point leading to flash evaporation of dissolved gas in the medium, low pressure in the saturated gas pipeline causing liquid condensation and accumulation, and failure of the saturated liquid pipeline to achieve step-by-step low pressure leading to gas phase flash evaporation.

[0007] As a further aspect of the present invention: for saturated gas-liquid two-phase flow pipelines, the pipeline is checked by using a key elevation difference diagram to see if it meets the requirement of no low-pressure bag, and the gas-liquid two-phase flow pipeline can flow by gravity to the downstream equipment, while requiring a liquid separator to be installed at the downstream equipment.

[0008] As a further aspect of the present invention: for saturated liquid gas-liquid two-phase flow pipelines, the pipeline is checked to see if it meets the step-by-step lowering arrangement requirements by using a key elevation difference diagram; for saturated liquid pipelines connected to regulating valves, the elevation of the regulating valve is checked to see if it is lower than the upstream liquid storage equipment by using a key elevation difference diagram, and when the operating pressure difference between the equipment before and after the regulating valve is small, the elevation of the upstream equipment is higher than that of the downstream equipment.

[0009] As a further aspect of the present invention: the adjustment of equipment layout in step four includes automatically or assistedly generating improved solutions for equipment layout adjustment, pipeline routing optimization, addition of liquid separators or adjustment of regulating valve positions based on the pressure analysis results of the key elevation difference diagram, so as to avoid gas-liquid two-phase flow caused by a sudden drop in medium pressure due to improper equipment elevation.

[0010] As a further aspect of the present invention: the critical elevation difference map uses color coding to distinguish different types of pipelines, and notes the layout requirements and risk prevention points of each type of pipeline in the map.

[0011] As a further aspect of the present invention: a two-phase flow identification method based on key elevation difference maps, comprising the following steps: Obtain the equipment elevation, operating pressure, and medium properties along the target pipeline system; The static pressure difference between adjacent devices is calculated based on the device elevation, and the pressure distribution curve along the pipeline direction is reconstructed by combining the friction loss along the pipeline. Calculate the saturated gas pressure curve of the medium at the current operating temperature based on the medium's physical properties. Compare the pressure distribution curve with the saturated gas pressure curve; If at a certain node, the pressure value of the pressure distribution curve is lower than the pressure value of the saturated gas pressure curve, then that node is determined to be a two-phase flow risk point; Further measures were taken, including adjusting equipment elevation, optimizing pipeline routing, and adding a separator.

[0012] The beneficial effects of this invention are: This invention, by establishing a critical elevation difference diagram, can identify pipelines prone to two-phase flow in advance, thereby preventing the generation of gas-liquid two-phase flow in pipelines in process units, which can lead to long-term pipeline vibration, resulting in pipeline fatigue, support structure failure, weld cracking, and flange leakage. Furthermore, for pump inlet pipelines, it can prevent the presence of two-phase flow from causing pump cavitation, which can damage the pump equipment.

[0013] This invention can clearly determine whether the relative arrangement of equipment on a gas-liquid two-phase pipeline is appropriate, thus effectively avoiding the need for modification after a two-phase flow pipeline has occurred during the factory start-up phase, which would lead to delays in the factory start-up schedule and economic losses. Attached Figure Description

[0014] The invention will now be further described with reference to the accompanying drawings.

[0015] Figure 1 This is a schematic diagram of the improved MDEA decarburization process; Figure 2 This is a schematic diagram of the existing MDEA decarburization process; Figure 3 This is a schematic diagram of the improved low-temperature methanol washing process. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] A two-phase flow identification system based on key elevation maps includes the following steps: Step 1: Obtain the relative position data of all equipment, pipelines, and valves in the pipeline system to be analyzed, from the starting equipment to the final equipment, as well as the operating temperature, operating pressure, and medium composition data of each material flow point; Step 2: Draw a key elevation difference map based on the collected data, and mark the elevation positions of each piece of equipment, pipeline, valve and process parameters of the material flow point on the map; Step 3: By using the key elevation difference map, combined with the thermodynamic properties and flow characteristics of the medium, analyze the influence of pressure and temperature changes at each flow point on the phase state of the medium, and identify the locations where gas-liquid two-phase flow is likely to occur. The criteria for judgment are: whether the pressure of the medium at a certain node is lower than its saturated vapor pressure at that temperature; whether there is a "low-pressure bag" or "air bag" structure in the pipeline, which may cause gas or liquid phase accumulation; whether the pressure difference before and after the regulating valve may cause the medium to flash; and whether the pump inlet meets the effective net positive suction head (NPSH) requirement to avoid cavitation caused by two-phase flow.

[0018] Step 4: Make targeted adjustments to the equipment layout and pipeline routing based on the identification results to avoid the generation of gas-liquid two-phase flow: The adjustment of the equipment layout includes automatically or assistedly generating improvement schemes such as equipment layout adjustment, pipeline routing optimization, addition of liquid separators or adjustment of regulating valve positions based on the pressure analysis results of the key elevation difference diagram; adjust the frame layout elevation of heat exchangers, pumps, and towers to avoid gas-liquid two-phase flow caused by a sudden drop in medium pressure due to improper equipment elevation.

[0019] Specifically, the criteria for identifying locations prone to gas-liquid two-phase flow through key elevation difference maps include: pressure reduction at the material flow point leading to flash evaporation of dissolved gases in the medium; low pressure in the saturated gas pipeline causing liquid condensation and accumulation; and failure of the saturated liquid pipeline to achieve step-by-step low pressure, resulting in gas phase flash evaporation.

[0020] For saturated gas-liquid two-phase flow pipelines, check whether the pipeline meets the requirement of no low-pressure bag by using the key elevation difference diagram, and whether the gas two-phase flow pipeline can flow by gravity to the downstream equipment. At the same time, it is required that a liquid separator be installed at the downstream equipment.

[0021] For saturated liquid gas-liquid two-phase flow pipelines, the critical elevation difference diagram is used to check whether the pipeline meets the step-by-step lowering layout requirements. For saturated liquid pipelines connected to regulating valves, the critical elevation difference diagram is used to check whether the elevation of the regulating valve is lower than that of the upstream liquid storage equipment. When the operating pressure difference between the equipment before and after the regulating valve is small, the elevation of the upstream equipment is higher than that of the downstream equipment.

[0022] The critical elevation difference map uses color coding to distinguish different types of pipelines, and notes the layout requirements and risk control points for each type of pipeline on the map.

[0023] A two-phase flow identification method based on key elevation difference maps includes the following steps: Obtain the equipment elevation, operating pressure, and medium properties along the target pipeline system; The static pressure difference between adjacent devices is calculated based on the device elevation, and the pressure distribution curve along the pipeline direction is reconstructed by combining the friction loss along the pipeline. Calculate the saturated gas pressure curve of the medium at the current operating temperature based on the medium's physical properties. Compare the pressure distribution curve with the saturated gas pressure curve; If at a certain node, the pressure value of the pressure distribution curve is lower than the pressure value of the saturated gas pressure curve, then that node is determined to be a two-phase flow risk point; Further measures were taken, including adjusting equipment elevation, optimizing pipeline routing, and adding a separator.

[0024] This embodiment takes two core processes in the coal chemical industry (MDEA decarbonization process and low-temperature methanol washing process) as specific application scenarios, and elaborates in detail the specific implementation steps, operation methods and application effects of the two-phase flow identification system based on the key elevation difference diagram. The technical solutions in this embodiment are all implemented in the first phase of the olefin, aromatic and deep processing engineering of the Shaanxi Coal Yulin Chemical 15 million tons / year coal quality-grade clean and efficient conversion demonstration project. All process parameters and equipment layouts are engineering design data. Example 1

[0025] Take the MDEA decarburization process as an example. Figure 1-2 As shown, the MDEA solution after process regeneration exits from the bottom of tower C-002, passes through heat exchangers E-001 and E-002, and then enters pump P-001. After pressurization, it goes to C-001. The initial design only drew a conventional PID flow diagram. During the design process, E-002 was placed on a 9.0-meter frame. It was not realized that this MDEA solution contains a small amount of CO2 gas. As the pressure decreases, dissolved CO2 will flash out, causing vibration of the E-002 outlet pipeline during plant operation and resulting in cavitation at the P-001 inlet.

[0026] I. Implementation of Key Elevation Map Drawing 1. Collect the relative position parameters of all equipment, pipelines, and valves in the decarbonization process path, as well as the process parameters of the three core material flow points (Material flow point 1: C-002 tower outlet; Material flow point 2: E-001 outlet / E-002 inlet; Material flow point 3: E-002 outlet / P-001 inlet). The specific parameters are shown in the table below: 2. Graphic drawing: such as Figure 1 As shown, using CAD as the drawing tool, a key elevation difference diagram is drawn, the elevation coordinates of all equipment are marked, the pipeline connection direction is drawn and marked with cyan lines, the above process parameters are marked next to each material flow point, and the calculated value of pressure loss along the pipeline is also marked.

[0027] II. Specific Implementation Measures for Two-Phase Flow Avoidance By integrating elevation information and process parameters from the key elevation difference map, it was calculated that when E-002 is located on a 9.0-meter plane, its actual operating pressure at the outlet drops to 0.03-0.04 MPaG due to the elevation difference, which is far lower than the design pressure of 0.10 MPaG at logistics point 3. Combined with the physical properties of the MDEA solution, at this pressure value, the CO2 dissolved in the solution will undergo violent flash evaporation, and the medium will change from a single-phase liquid phase to a gas-liquid two-phase phase, directly causing vibration of the E-002 outlet pipeline and cavitation at the P-001 inlet.

[0028] III. Specific Implementation Measures for Two-Phase Flow Avoidance Based on the identification results of the key elevation difference map, the two-phase flow is avoided by adjusting the equipment elevation. Specifically, the layout plane of E-002 is adjusted from the 9.0-meter frame to the 0.00-meter plane, maintaining the same elevation as E-001 and P-001. After adjustment, the actual operating pressure at the outlet of E-002 is restored to 0.09-0.10 MPaG, meeting the design requirements. There is no risk of CO2 flash evaporation, and the generation of gas-liquid two-phase flow is completely avoided. Example 2

[0029] Take the low-temperature methanol washing process as an example. Figure 3 As shown, the gas exiting C-001 is a saturated gas, and its components are easily liquefied, leading to the formation of a gas-liquid two-phase system. Therefore, this pipeline cannot have a low-lying bag. The saturated gas exiting V-001, after being cooled by E-001, inevitably forms a gas-liquid two-phase system. Therefore, the outlet of this equipment must flow by gravity to downstream equipment, and a separator tank is required to promptly separate the liquid phase. The gas exiting V-001 is also a saturated gas, and its outlet has two heat exchangers and one separator tank; therefore, the relative height of its arrangement is subject to requirements.

[0030] I. Implementation of Key Elevation Map Drawing 1. Collect the design elevation, operating pressure, and medium phase state at the inlet and outlet of all equipment, including C-001, C-002, V-001, V-002, E-001, E-002, V-002, and regulating valve LV. (C-001 outlet is saturated gas phase, V-001 outlet is gas-liquid two phase, and V-002 outlet is saturated liquid phase.)

[0031] 2. Create a key elevation difference diagram, mark the core elevation parameters of each piece of equipment, draw the pipeline connection route, and mark the medium phase of each pipe section.

[0032] 3. Mark the saturated gas pipeline from C-001 to V-001 in blue, with the note "Avoid low-level bags to prevent liquid condensation and accumulation"; mark the gas-liquid two-phase pipeline from V-001 to V-002 in yellow, with the note "Downstream equipment must be lower than upstream, and a separator tank should be added"; mark the saturated liquid pipeline from V-002 to the regulating valve LV in yellow, with the note "Pipeline gradually lower, valve position lower than upstream equipment".

[0033] II. Intuitive Analysis of Phase Change Risk By integrating elevation and process parameters from key elevation difference maps, risk analysis was conducted on each pipe section individually: Saturated gas pipelines from C-001 to V-001: If there is a low bag in the pipeline, the liquid condensed by the saturated gas will accumulate at the low bag, forming a gas-liquid two-phase flow, which will lead to pipeline erosion. Gas-liquid two-phase pipeline from V-001 to V-002: The outlet medium of V-001 is gas-liquid two-phase. If the elevation of the downstream equipment is higher than that of the upstream, the medium cannot flow by gravity, which will cause uneven phase separation and aggravate pipeline vibration. The saturated liquid pipeline from V-002 to the control valve LV: The outlet of V-002 is a saturated liquid phase. If the elevation of the control valve LV is higher than that of V-002, the pressure drop during the liquid flow will cause flashing, forming a gas-liquid two-phase flow, which will affect the control accuracy and operating performance of the control valve.

[0034] III. Specific Implementation Measures for Two-Phase Flow Avoidance Based on the identification results of the key elevation difference map, and combined with the approach of pipeline routing optimization, equipment elevation verification, and the addition of a distribution tank, targeted avoidance measures are implemented: For the blue saturated gas pipelines from C-001 to V-001: optimize the pipeline routing, eliminate all low-bag arrangements in the design, and adopt a "straight downward, no-recessed" pipeline routing to prevent condensate accumulation; For the yellow gas-liquid two-phase pipelines from V-001 to V-002: verify and confirm the equipment elevation, and ensure that the elevations of E-001, E-002, and V-002 are all lower than the upstream equipment to achieve gravity flow of the medium. At the same time, a separator is added at the outlet of V-001 to separate the liquid phase in the gas-liquid two-phase flow in a timely manner and reduce the risk of two-phase flow in the pipeline. For the yellow saturated liquid pipeline from V-002 to the regulating valve LV: optimize the pipeline route and adopt a "step-down" layout, with the pipeline elevation gradually decreasing from EL14.80m at V-002 to EL10.80m at the regulating valve LV, ensuring that the elevation of the regulating valve LV is lower than that of V-002, and avoiding liquid flash evaporation to form a gas-liquid two-phase flow.

[0035] By using the key elevation difference diagram, you can intuitively check: 1. Whether the height of the equipment containing two-phase flow medium meets the requirement of step-down; 2. Whether the gas phase two-phase flow pipeline can flow by gravity to the downstream equipment; 3. Whether the operating pressure difference between the equipment before and after the regulating valve is very small, whether the height of the upstream equipment is higher than that of the downstream equipment, and whether the liquid can smoothly go to C-002; 4. Whether the regulating valve is lower than the position of V-002.

[0036] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A two-phase flow identification system based on key elevation difference maps, characterized in that, Includes the following steps: Step 1: Obtain the relative position data of all equipment, pipelines, and valves in the pipeline system to be analyzed, from the starting equipment to the final equipment, as well as the operating temperature, operating pressure, and medium composition data of each material flow point; Step 2: Draw a key elevation difference map based on the collected data, and mark the elevation positions of each piece of equipment, pipeline, valve and process parameters of the material flow point on the map; Step 3: By using the key elevation difference map, combined with the thermodynamic properties and flow characteristics of the medium, analyze the influence of pressure and temperature changes at each flow point on the phase state of the medium, and identify the locations where gas-liquid two-phase flow is likely to occur. Step 4: Based on the identification results, make targeted adjustments to the equipment layout and pipeline routing to avoid the generation of gas-liquid two-phase flow.

2. The two-phase flow identification system based on key elevation difference maps according to claim 1, characterized in that, The criteria for identifying locations prone to gas-liquid two-phase flow using key elevation difference diagrams include: pressure reduction at the material flow point leading to flash evaporation of dissolved gases in the medium; low pressure in the saturated gas pipeline causing liquid condensation and accumulation; and failure of the saturated liquid pipeline to achieve step-by-step low pressure, resulting in gas phase flash evaporation.

3. The two-phase flow identification system based on key elevation difference maps according to claim 2, characterized in that, For saturated gas-liquid two-phase flow pipelines, check whether the pipeline meets the requirement of no low-pressure bag by using the key elevation difference diagram, and whether the gas two-phase flow pipeline can flow by gravity to the downstream equipment. At the same time, it is required that a liquid separator be installed at the downstream equipment.

4. The two-phase flow identification system based on key elevation difference maps according to claim 1, characterized in that, For saturated liquid gas-liquid two-phase flow pipelines, the critical elevation difference diagram is used to check whether the pipeline meets the step-by-step lowering layout requirements. For saturated liquid pipelines connected to regulating valves, the critical elevation difference diagram is used to check whether the elevation of the regulating valve is lower than that of the upstream liquid storage equipment. When the operating pressure difference between the equipment before and after the regulating valve is small, the elevation of the upstream equipment is higher than that of the downstream equipment.

5. The two-phase flow identification system based on key elevation difference map according to claim 1, characterized in that, Step four involves adjusting the equipment layout, which includes automatically or assistedly generating improved plans for equipment layout adjustment, pipeline routing optimization, and the addition of liquid separators or adjustment of regulating valve positions based on the pressure analysis results of the key elevation difference diagram. This is to avoid gas-liquid two-phase flow caused by a sudden drop in medium pressure due to improper equipment elevation.

6. The two-phase flow identification system based on key elevation difference maps according to claim 1, characterized in that, The critical elevation difference map uses color coding to distinguish different types of pipelines, and notes the layout requirements and risk control points for each type of pipeline on the map.

7. A two-phase flow identification method based on key elevation difference maps, characterized in that, Includes the following steps: Obtain the equipment elevation, operating pressure, and medium properties along the target pipeline system; The static pressure difference between adjacent devices is calculated based on the device elevation, and the pressure distribution curve along the pipeline direction is reconstructed by combining the friction loss. Calculate the saturated gas pressure curve of the medium at the current operating temperature based on the medium's physical properties. Compare the pressure distribution curve with the saturated gas pressure curve; If at a certain node, the pressure value of the pressure distribution curve is lower than the pressure value of the saturated gas pressure curve, then that node is determined to be a two-phase flow risk point; Further measures were taken, including adjusting equipment elevation, optimizing pipeline routing, and adding a separator.

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