Liquid ammonia pipeline discharge system and method based on pigging displacement

Abstract

The invention discloses a liquid ammonia pipeline discharge system and method based on pigging displacement, the system comprises a replaceable valve chamber system, an efficient recovery system, a trunk line displacement and replacement system and a gas treatment system, by replacing valve chamber pipe fittings, effective displacement and recovery are carried out on pipe storage media in a liquid ammonia pipeline to be overhauled, and the liquid ammonia pipeline discharge efficiency is improved. And residual media are safely treated and emptied, so that the media in the pipe are efficiently displaced to enter a downstream pipeline system to the greatest extent, the problems of arrangement of a recovery storage tank, secondary pressurization of liquid ammonia, phase change, low temperature and the like in the conventional pressure relief process are avoided, it is guaranteed that no toxic gas directly enters the atmosphere in the relief process, and the purposes of efficiently recovering and overhauling the liquid ammonia pipeline are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid ammonia pipeline drainage, and particularly relates to a liquid ammonia pipeline drainage system and method based on pigging displacement. Background Art

[0002] Liquid ammonia can be used as a hydrogen carrier for efficient storage, transportation, energy conversion or industrial applications. Pipeline transportation of liquid ammonia is an effective means to achieve planned long-distance transportation.

[0003] The critical pressure of liquid ammonia is about 11.40 MPa, and the critical temperature is about 132.5 °C. Gas-phase or liquid-phase transportation methods can be adopted in pipelines. In the pipeline transportation of conventional hydrocarbons, periodic in-pipeline detection is a key means to effectively diagnose the internal state of the pipeline, and external maintenance also needs to be carried out regularly; when abnormal conditions occur in the pipeline body, maintenance and replacement of the target pipe section are required, which requires shutting down the pipeline and emptying the medium in this section of the pipeline. Due to the phase change, toxicity, and flammability characteristics of liquid ammonia, issues such as efficiently emptying the internal medium of the pipeline, preventing low temperature inside the pipeline, and safely treating the drained medium need to be considered when draining the liquid ammonia pipeline; at the same time, shutting down the pipeline will have a greater impact on the medium transportation, which poses technical requirements for efficient drainage. An efficient, safe, and reasonable drainage strategy is the key to ensuring the operation quality of liquid ammonia pipelines.

[0004] However, there is little relevant introduction to the safety recovery and drainage system of liquid ammonia pipelines in the existing public literature. Therefore, it is necessary to carry out relevant research to achieve efficient recovery and drainage of liquid ammonia pipelines after shutdown. Summary of the Invention

[0005] The purpose of the present invention is to provide a liquid ammonia pipeline drainage system and method based on pigging displacement to overcome the defects of the prior art. Based on the basic physical properties of liquid ammonia and the characteristics of pipeline maintenance conditions, aiming at the characteristics of large pipe volume (at least 8 km pipe length) and high medium inventory between the cut-off valves of liquid ammonia pipelines, from the perspectives of controlling drainage time, safely treating the medium, suppressing phase change in the pipe, etc., a replaceable valve chamber system, an efficient recovery system, a main pipeline displacement and replacement system, a gas treatment system, a safety monitoring system, etc. are respectively set up to achieve safe and efficient discharge of the liquid ammonia medium in the pipeline under pipeline maintenance conditions.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A liquid ammonia pipeline drainage system based on pigging displacement, the liquid ammonia pipeline includes an upstream main pipeline, a midstream main pipeline, and a downstream main pipeline, and the system includes:

[0008] Replaceable valve chamber system, the replaceable valve chamber system includes several valve chambers with a cut-off function provided on each main line of the liquid ammonia pipeline, and the valve chamber includes an upstream bypass and a downstream bypass;

[0009] Main line displacement and replacement system, the main line displacement and replacement system is provided in the valve chamber of the upstream main line, and includes a pig launcher pipeline for displacing and replacing the internal pipeline of the valve chamber to be replaced, recovering the ammonia gas and natural gas discharged during the displacement process, and at the same time displacing the liquid ammonia stored in the middle main line and discharging it into the downstream main line;

[0010] Efficient recovery system, the efficient recovery system is provided in the valve chamber of the downstream main line, and includes a pig receiver pipeline for guiding the liquid ammonia pushed in from the upstream by supporting the main line displacement and replacement system into the downstream main line;

[0011] Gas treatment system, the gas treatment system is provided in the valve chamber of the downstream main line, and is used for safely burning the natural gas-ammonia mixed medium that may exist upstream of the pig after the main line displacement and the natural gas-ammonia mixed medium inside the pig receiver, and discharging the nitrogen gas used for subsequent replacement.

[0012] Furthermore, the relief system further includes a safety monitoring system, and the safety monitoring system includes a temperature monitoring device and a pressure monitoring device provided in the valve chamber, and a mixed medium sampling valve provided in the main line displacement and replacement system.

[0013] Furthermore, the valve chamber includes a first cut-off valve, a second cut-off valve and a third cut-off valve. The upstream bypass is provided between the first cut-off valve and the second cut-off valve, and the downstream bypass is provided between the second cut-off valve and the third cut-off valve. The upstream bypass further includes an upstream bypass cut-off valve, and the downstream bypass further includes a downstream bypass cut-off valve.

[0014] Furthermore, the main line displacement and replacement system includes a compressed natural gas storage tank, a nitrogen gas vaporization system and a pig launcher. The compressed natural gas storage tank is connected to a natural gas air-cooled heat exchanger through a natural gas pressure regulating valve. The natural gas air-cooled heat exchanger is connected to a natural gas cut-off valve. The nitrogen gas vaporization system is connected to a nitrogen gas cut-off valve. The natural gas cut-off valve and the nitrogen gas cut-off valve are connected through a valve chamber replacement first cut-off valve and the upstream bypass cut-off valve. The pig launcher is connected to the natural gas cut-off valve and the nitrogen gas cut-off valve through a pig launcher cut-off valve, and the pig launcher is also connected to the liquid ammonia pipeline between the second cut-off valve and the third cut-off valve through a supporting pipeline.

[0015] Further, the pig receiver pipeline includes a pig receiver, a pig receiver inlet pipeline, and a pig receiver outlet pipeline. The pig receiver is connected to the liquid ammonia pipeline between the second shut-off valve and the third shut-off valve through the pig receiver inlet pipeline. A third shut-off valve of the pig receiver is provided on the pig receiver outlet pipeline. The pig receiver is respectively connected to both ends of the third shut-off valve of the pig receiver through a first shut-off valve of the pig receiver and a second shut-off valve of the pig receiver.

[0016] Further, the gas treatment system includes a venting flare, and the venting flare is connected to the pipeline between the second shut-off valve and the third shut-off valve of the pig receiver through a relief regulating valve.

[0017] On the other hand, the present invention also provides a method for discharging liquid ammonia in a pipeline based on pigging displacement. The method is implemented based on any of the foregoing discharging systems, and the method includes:

[0018] Step A: During normal transportation, the operating pressure of the liquid ammonia pipeline is controlled above a preset pressure threshold. In the case of planned shutdown for maintenance, the upstream external transmission pump and the valve chamber shut-off valve are closed.

[0019] Step B: After the pipeline stops transporting, by replacing the pipeline and the electric shut-off valve in the valve chamber, using the replaced main line displacement and replacement system, high-efficiency recovery system, etc. to displace the liquid ammonia in the middle main line, discharging it into the downstream main line under pressure, displacing the medium in the downstream main line into the downstream storage tank, and using the pipeline volume of the downstream main line to receive the liquid ammonia in the middle main line.

[0020] Step C: Displace the liquid ammonia inside the middle main line using the pig launcher pipeline and the pig receiver pipeline.

[0021] Step D: Discharge and treat the residual medium in the middle main line through the gas treatment system.

[0022] Further, the specific steps of Step B include:

[0023] Install the main line displacement and replacement system in the valve chamber at the upstream of the main line and the valve chamber at the downstream of the main line in sequence, and displace and recover the liquid ammonia in the main line inside the valve chambers at the upstream and downstream of the main line.

[0024] Further, the specific steps of Step C include:

[0025] Use a pig to displace the liquid ammonia in the middle main line into the downstream main line, control the running speed of the pig within a preset speed range, and when the pig enters the downstream pig receiver, close the pig receiver pipeline and prepare for discharging and treating the residual medium in the middle main line.

[0026] Further, the method further includes:

[0027] Step E: Dismantle and remove the high-efficiency recovery system, trunk line displacement and replacement system, and gas treatment system installed in the upstream valve chamber and downstream valve chamber of the main line, and restore and install the pipe sections in the valve chamber.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) In view of the transportation medium and operation characteristics of the liquid ammonia pipeline, the present invention proposes a variety of safety recovery and discharge measures from the perspectives of avoiding external recovery of liquid ammonia during maintenance and improving the discharge efficiency of the maintenance main line.

[0030] (2) Based on the actual scenario of planned maintenance, the present invention sets up a mobile replaceable valve chamber system, high-efficiency recovery system, trunk line displacement and replacement system, and gas treatment system, which reflects the advantages of low cost and reusability in terms of engineering investment. In terms of the transfer of liquid ammonia medium, by setting up a high-efficiency recovery system and a trunk line displacement and replacement system, most of the liquid ammonia in the pipe section to be maintained can be pressured-displaced and recycled, on the one hand, avoiding the direct discharge of liquid ammonia, and on the other hand, avoiding the problem of liquefying and pressurizing the transfer of liquid ammonia from the pressurized liquid phase to the low-pressure gas phase. In addition, by adopting the pressured-displacement scheme, the discharge and recovery time of liquid ammonia is greatly reduced, the pipeline shutdown time occupied by the medium transfer process is optimized, and the utilization efficiency and utilization time of the pipeline are improved.

[0031] (3) The key process system configurations such as the high-efficiency recovery of the in-pipe medium and the safe discharge of the residual medium after shutdown proposed by the present invention contribute to improving the operation safety and operation efficiency of the liquid ammonia pipeline. Description of the Drawings

[0032] Figure 1 It is a schematic diagram of the liquid ammonia pipeline discharge system based on pigging displacement in the embodiment of the present invention.

[0033] Description of the Drawings: 1 - Upstream main line, 2 - Middle - stream main line, 3 - Downstream main line, 11 - First cut - off valve of the first valve chamber, 12 - Second cut - off valve of the first valve chamber, 13 - Third cut - off valve of the first valve chamber, 14 - Upstream bypass of the first valve chamber, 15 - Downstream bypass of the first valve chamber, 16 - First pressure transmitter of the first valve chamber, 17 - First temperature transmitter of the first valve chamber, 18 - Second pressure transmitter of the first valve chamber, 19 - Second temperature transmitter of the first valve chamber, 20 - Cut - off valve of the upstream bypass of the first valve chamber, 21 - Cut - off valve of the downstream bypass of the first valve chamber, 22 - First cut - off valve of the second valve chamber, 23 - Second cut - off valve of the second valve chamber, 24 - Third cut - off valve of the second valve chamber, 25 - Upstream bypass of the second valve chamber, 26 - Downstream bypass of the second valve chamber, 27 - First pressure transmitter of the second valve chamber, 28 - First temperature transmitter of the second valve chamber, 29 - Cut - off valve of the upstream bypass of the second valve chamber, 30 - Cut - off valve of the downstream bypass of the second valve chamber, 31 - Compressed natural gas storage tank, 32 - Natural gas pressure regulating valve, 33 - Natural gas air - bath heat exchanger, 34 - Natural gas cut - off valve, 35 - Nitrogen vaporization system, 36 - Nitrogen cut - off valve, 37 - Temperature transmitter, 38 - Cut - off valve of the pig launcher, 39 - First cut - off valve for valve chamber replacement, 40 - Pig launcher, 41 - Pipeline for pig - launching supporting, 42 - Second cut - off for valve chamber replacement, 43 - Gas storage tank for valve chamber replacement, 51 - Inlet pipeline of the pig receiver, 52 - Pig receiver, 53 - First cut - off valve of the pig receiver, 54 - Second cut - off valve of the pig receiver, 55 - Third cut - off valve of the pig receiver, 56 - Outlet pipeline of the pig receiver, 61 - Relief regulating valve, 62 - Flare stack, 71 - Sampling valve for mixed medium. Detailed Embodiments

[0034] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0035] All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0036] However, there is little relevant introduction to the safety recovery and relief system for liquid ammonia pipelines in the existing public literature. Therefore, it is necessary to carry out relevant research to achieve efficient recovery and relief of liquid ammonia pipelines after shutdown.

[0037] To solve the above - mentioned technical problems, the following various embodiments of a liquid ammonia pipeline relief system and method based on pigging displacement are proposed in the present invention.

[0038] Example 1

[0039] This embodiment provides a liquid ammonia pipeline drainage system based on pigging displacement. This system relies on a conventional pipeline system, that is, it includes an upstream main line 1, a midstream main line 2, and a downstream main line 3.

[0040] Refer to Figure 1 , as Figure 1 shown is a schematic diagram of the liquid ammonia pipeline drainage system based on pigging displacement provided in this embodiment. This system includes a replaceable valve chamber system, an efficient recovery system, a main line displacement and replacement system, a gas treatment system, and a safety monitoring system.

[0041] The first cut-off valve 11 of the first valve chamber, the second cut-off valve 12 of the first valve chamber, the third cut-off valve 13 of the first valve chamber, the upstream bypass 14 of the first valve chamber, the downstream bypass 15 of the first valve chamber, the first pressure transmitter 16 of the first valve chamber, the first temperature transmitter 17 of the first valve chamber, the second pressure transmitter 18 of the first valve chamber, the second temperature transmitter 19 of the first valve chamber, the upstream bypass cut-off valve 20 of the first valve chamber, the downstream bypass cut-off valve 21 of the first valve chamber, the first cut-off valve 22 of the second valve chamber, the second cut-off valve 23 of the second valve chamber, the third cut-off valve 24 of the second valve chamber, the upstream bypass 25 of the second valve chamber, the downstream bypass 26 of the second valve chamber, the first pressure transmitter 27 of the second valve chamber, the first temperature transmitter 28 of the second valve chamber, the second pressure transmitter of the second valve chamber, the second temperature transmitter of the second valve chamber, the upstream bypass cut-off valve 29 of the second valve chamber, and the downstream bypass cut-off valve 30 of the second valve chamber, etc. constitute a replaceable valve chamber system, which is used to provide the main line cut-off / connection function for the first valve chamber and the second valve chamber, and the bypass is used to provide functions such as replacement of the internal pipeline of the valve chamber, main line displacement and replacement, and auxiliary recovery of the medium in the main line for the planned maintenance of the midstream main line. There may be multiple main line valve chambers in actual engineering projects, and the function settings can refer to this example.

[0042] Specifically, in the shown system, the first shut-off valve 11, the second shut-off valve 12, and the third shut-off valve 13 in the first valve chamber are arranged on the main line of the first valve chamber and are used to connect / cut off the main line pipeline. When replacing the liquid ammonia in the downstream pipeline, the second shut-off valve 12 in the first valve chamber can be disassembled; the first shut-off valve 11 in the first valve chamber is a full-bore manual ball valve, with a welded connection on the upstream side and a flange connection on the downstream side; the second shut-off valve 12 in the first valve chamber is a full-bore electric ball valve with an emergency shut-off function, and both sides are welded; the third shut-off valve 13 in the first valve chamber is a full-bore manual ball valve, with a flange connection on the upstream side and a welded connection on the downstream side; the upstream bypass 14 of the first valve chamber is arranged between the first shut-off valve 11 and the second shut-off valve 12 in the first valve chamber, made of carbon steel, and is used to provide a replacement channel for the main line segment of the valve chamber and a displacement channel for the subsequent main line; the downstream bypass 15 of the first valve chamber is arranged between the second shut-off valve 12 and the third shut-off valve 13 in the first valve chamber, made of carbon steel, and is used to provide a replacement channel for the main line segment of the valve chamber and a displacement channel for the subsequent main line; the first pressure transmitter 16 and the first temperature transmitter 17 in the first valve chamber are arranged on the upstream bypass 14 of the first valve chamber and are used to provide real-time detection of the pressure and temperature at this point and in the nearby area; the second pressure transmitter 18 and the second temperature transmitter 19 in the first valve chamber are arranged on the downstream bypass 15 of the first valve chamber and are used to provide real-time detection of the pressure and temperature at this point and in the nearby area; the upstream bypass shut-off valve 20 and the downstream bypass shut-off valve 21 in the first valve chamber are both carbon steel manual ball valves, normally closed, and are respectively installed at the ends of the upstream bypass 14 and the downstream bypass 15 of the first valve chamber, with the other ends connected to the blind end, and are used to connect to the high-efficiency recovery system, the main line displacement and replacement system; the first shut-off valve 22, the second shut-off valve 23, and the third shut-off valve 24 in the second valve chamber are arranged on the main line of the second valve chamber and are used to connect / cut off the main line pipeline. When replacing the liquid ammonia in the downstream pipeline, the second shut-off valve 23 in the second valve chamber can be disassembled; the first shut-off valve 22 in the second valve chamber is a full-bore manual ball valve, with a welded connection on the upstream side and a flange connection on the downstream side; the second shut-off valve 23 in the second valve chamber is a full-bore electric ball valve with an emergency shut-off function, and both sides are welded; the third shut-off valve 24 in the second valve chamber is a full-bore manual ball valve, with a flange connection on the upstream side and a welded connection on the downstream side; the upstream bypass 25 of the second valve chamber is arranged between the first shut-off valve 22 and the second shut-off valve 23 in the second valve chamber, made of carbon steel, and is used to provide a replacement channel for the main line segment of the valve chamber and a displacement channel for the subsequent main line; the downstream bypass 26 of the second valve chamber is arranged between the second shut-off valve 23 and the third shut-off valve 24 in the second valve chamber, made of carbon steel, and is used to provide a replacement channel for the main line segment of the valve chamber and a displacement channel for the subsequent main line; the first pressure transmitter 27 and the first temperature transmitter 28 in the second valve chamber are arranged on the upstream bypass 25 of the second valve chamber and are used to provide real-time detection of the pressure and temperature at this point and in the nearby area;The second pressure transmitter and the second temperature transmitter in the No. 2 valve chamber are installed on the downstream bypass 26 of the No. 2 valve chamber, and are used to provide real-time detection of the pressure and temperature at this point and in the nearby area; the upstream bypass block valve and the downstream bypass block valve in the No. 2 valve chamber are both carbon steel manual ball valves, normally closed, and are respectively installed at the ends of the upstream bypass 25 and the downstream bypass 26 of the No. 2 valve chamber, and the other ends are connected to blind ends, and are used to connect the high-efficiency recovery system, the main line displacement and replacement system.

[0043] The compressed natural gas storage tank 31, the natural gas pressure regulating valve 32, the natural gas air bath heat exchanger 33, the natural gas block valve 34, the nitrogen gas vaporization system 35, the nitrogen gas block valve 36, the temperature transmitter 37, the pig launcher block valve 38, the first block valve for valve chamber replacement 39, the pig launcher 40, the pipeline for pig launching support 41, the second block valve for valve chamber replacement 42, the valve chamber replacement gas storage tank 43, etc. constitute the main line displacement and replacement system, which is used to displace and replace the internal pipeline of the valve chamber to be replaced, and recover the ammonia gas and natural gas discharged during the displacement process. At the same time, a movable pig launcher is provided to displace the liquid ammonia stored in the middle reaches of the main line into the downstream main line, avoiding the installation of a liquid ammonia recovery device in the downstream valve chamber. It should be noted that some of the equipment and pipelines for displacing the valve chamber pipelines in this system are assembled in skids and can also be used for pre-replacement of the No. 2 valve chamber.

[0044] Specifically, in the shown system, the compressed natural gas storage tank 31 is a complete set of compressed natural gas supply storage tank for providing compressed natural gas for displacement and purging; the natural gas pressure regulating valve 32 is an electric control regulating valve for regulating the flow rate and pressure of the compressed natural gas, preferably made of low-temperature carbon steel; the natural gas air-cooled heat exchanger 33 is arranged downstream of the natural gas pressure regulating valve 32 for regulating the temperature of the pressure-regulated natural gas, and preferably the outlet temperature after regulation is greater than -10 °C; the natural gas cut-off valve 34 is arranged downstream of the natural gas air-cooled heat exchanger 33, a manual ball valve for connecting / closing the natural gas supply channel; the nitrogen gas vaporization system 35 is a small-scale skid-mounted system including a nitrogen gas storage tank, a nitrogen gas regulating valve, a nitrogen gas small-scale boosting system, etc., for providing pressurized nitrogen gas for downstream system replacement and purging; the nitrogen gas cut-off valve 36 is arranged downstream of the nitrogen gas vaporization system 35, a manual ball valve for connecting / closing the nitrogen gas supply channel; the temperature transmitter 37 is arranged on the nitrogen gas / natural gas pipeline for detecting the medium temperature after pressure regulation and temperature regulation; the pig launcher cut-off valve 38 is arranged upstream of the pig launcher 40, a manual ball valve for connecting / closing the gas supply channel of the pig launcher; the valve chamber replacement first cut-off valve 39 is arranged on the bypass of the pig launcher cut-off valve 38, a manual ball valve for connecting / closing the gas supply channel for valve chamber internal pipeline replacement; the pig launcher 40 is a pig launching barrel made of carbon steel for launching the pig used when displacing liquid ammonia in the middle reaches main pipeline 2; the launching supporting pipeline 41 is used to connect the pig launcher 40 and the main pipeline cut-off valve; the valve chamber replacement second cut-off 42 is a manual ball valve for connecting / truncating the replacement / purging gas discharge channel of the valve chamber internal pipeline, arranged downstream of the unilateral valve chamber bypass cut-off valve inside the valve chamber; the valve chamber replacement gas storage tank 43 is a horizontal carbon steel storage tank, and the design pressure is preferably 2.5 MPa, for recovering media such as ammonia gas and natural gas discharged from the valve chamber replacement. Further, the compressed natural gas storage tank 31, the natural gas pressure regulating valve 32, the natural gas air-cooled heat exchanger 33, the natural gas cut-off valve 34, the nitrogen gas vaporization system 35, the nitrogen gas cut-off valve 36, and the temperature transmitter 37 are preferably skidded for providing the gas source for replacement and purging; the valve chamber replacement second cut-off 42 and the valve chamber replacement gas storage tank 43 are preferably skidded for recovering the internal media of the valve chamber.

[0045] The pig receiver inlet pipeline 51, the pig receiver 52, the pig receiver first cut-off valve 53, the pig receiver second cut-off valve 54, the pig receiver third cut-off valve 55, the pig receiver outlet pipeline 56, etc. form an efficient recovery system, which is arranged in the No. 2 valve chamber in this example, for supporting the main pipeline displacement and replacement system, guiding the liquid ammonia pushed in from the upstream into the downstream main pipeline, and immediately introducing some of the media after pigging and ball receiving into the gas treatment system; in addition, the pig receiver is used to perform the pig receiving operation on the pig pushed in from the upstream.

[0046] Specifically, in the shown system, the inlet pipeline 51 of the pig receiver is made of carbon steel and is used to connect the first shut-off valve in the second valve chamber and the pig receiver 52, providing a flow channel for the medium and the pig during the displacement of the middle reaches main line 2; the pig receiver 52 is a pig receiver for receiving pigs used during the displacement of liquid ammonia in the middle reaches main line 2, made of carbon steel; the first shut-off valve 53 of the pig receiver is a manual ball valve, made of carbon steel, installed on the branch pipe of the small cylinder of the pig receiver 52, and is only opened during pigging displacement; the second shut-off valve 54 of the pig receiver is a manual ball valve, made of carbon steel, installed on the branch pipe of the large cylinder of the pig receiver 52, and is opened after the pigging displacement is completed, used to introduce the natural gas (containing some leaked ammonia) used for pig displacement into the vent flare 62 for safety treatment.

[0047] The relief regulating valve 61, the vent flare 62, etc. constitute a gas treatment system, which is set in the second valve chamber in this example, used for the safe combustion treatment of the natural gas-ammonia mixed medium that may exist upstream of the pig and the natural gas-ammonia mixed medium inside the pig receiver after the main line displacement, and for the discharge treatment of the nitrogen used for subsequent replacement.

[0048] Specifically, in the shown system, the relief regulating valve 61 is a manually controlled regulating valve, made of carbon steel, used to adjust the flow rate of the power medium (natural gas, natural gas / ammonia mixed medium) in front of the pig isolation and send it into the vent flare 62 for combustion treatment; the vent flare 62 is a vertical elevated flare with an electronic ignition system, used for the safe combustion treatment of the medium to be vented. In addition, a sampling and detection port for the mixed medium is equipped upstream of the relief regulating valve 61.

[0049] In addition, multiple pressure transmitters and temperature transmitters set in this system, as well as the mixed medium sampling valve 71 set in the main line displacement and replacement system, constitute a safety monitoring system, used for detecting the pressure and temperature at key process points during the operation process, and for real-time monitoring of the component of the replacement medium through the sampling valve to guide the safe implementation of the replacement process.

[0050] The working principle of this embodiment is as follows:

[0051] (1) Under normal operating conditions, liquid ammonia is generally transported in a liquid phase state. After the pipeline needs to be truncated and repaired, the liquid ammonia in the pipe section to be repaired needs to be discharged. Since liquid ammonia is toxic and has high economic value, it is preferably received by recycling the liquid ammonia to be discharged. Further, in order to improve the liquid discharge efficiency and avoid the influence of the phase change and low temperature problems of liquid ammonia during the conventional pressure relief process on the discharge speed, the present invention proposes a scheme of injecting the liquid ammonia in the pipe section to be repaired into the downstream pipeline under pressure, on the one hand, avoiding the pressure drop of liquid ammonia during the emptying process, and on the other hand, avoiding the scheme of using a large-capacity storage tank to recover the liquid ammonia discharge medium and re-pressurize it into the liquid ammonia storage tank.

[0052] (2) To achieve the pressure-driven displacement of liquid ammonia medium, the present invention provides a replaceable valve chamber system and a main pipeline displacement and replacement system. The replaceable valve chamber system enables the flexible disassembly of the valve chambers at both ends of the main pipeline and their replacement with a movable liquid ammonia displacement system. Compressed natural gas and a pig are used as the power source and isolation object for liquid ammonia displacement. At the same time, an efficient recovery system is set up in the downstream valve chamber to directly introduce the displaced pressurized liquid ammonia into the downstream main pipeline, achieving no pressure loss and low-temperature phase change of liquid ammonia throughout the process.

[0053] (3) To avoid the environmental impact of the toxicity of vaporized liquid ammonia, the present invention, in combination with the actual engineering situation, preferably uses compressed natural gas as the medium for displacing liquid ammonia, so as to safely burn the natural gas-ammonia mixed medium through combustion, and a gas treatment system is set up to achieve this; in combination with the pipeline maintenance requirements, a nitrogen injection system is further set up as a solution for displacing the residual natural gas in the pipeline.

[0054] (4) For the problem of liquid ammonia disposal in the internal pipeline system of the valve chamber, the valve chamber bypass and the main pipeline displacement and replacement system are used to recover the liquid ammonia existing in the valve chamber main pipeline into a storage tank, and the residual medium is gradually replaced with natural gas and nitrogen. On the one hand, it facilitates the safe combustion disposal of the natural gas-ammonia mixed medium, and on the other hand, it facilitates the safe evacuation of the nitrogen-natural gas medium.

[0055] (5) For the efficient utilization of assets, the present invention sets the efficient recovery system, the main pipeline displacement and replacement system, and the gas treatment system as movable skid-mounted devices, which on the one hand meet the requirements of planned operation, and on the other hand enable the multi-station reuse of the devices.

[0056] Example 2

[0057] Based on the liquid ammonia pipeline drainage system based on pigging displacement provided in the foregoing embodiment, this embodiment further provides a liquid ammonia pipeline drainage method based on pigging displacement, including the following main contents:

[0058] Step 1: During normal transportation, the operating pressure of the liquid ammonia pipeline is controlled above 1.5 MPa.g, and the transportation temperature is close to the soil temperature. Under the planned shutdown and maintenance condition, the upstream external transmission pump, each main pipeline block valve (in this example, the first block valve 11, the second block valve 12, the third block valve 13 of the first valve chamber, the first block valve 22, the second block valve 23, the third block valve 24 of the second valve chamber, etc.) are closed in an orderly manner, and the main pipeline realizes safe shutdown.

[0059] Step 2: Taking the present invention as an example, after the pipeline is shut down, by replacing some pipelines and electric block valves in the first valve chamber and the second valve chamber, the liquid ammonia in the middle reaches main pipeline 2 is displaced by using the replaced main pipeline displacement and replacement system, high-efficiency recovery system, etc., and is discharged into the downstream main pipeline 3 under pressure, displacing the medium in the downstream main pipeline 3 into the downstream storage tank, and using the pipeline volume of the downstream main pipeline 3 to accommodate most of the liquid ammonia in the middle reaches main pipeline 2. Specifically, first, the main pipeline displacement and replacement system is successively installed in the No. 1 valve chamber and the No. 2 valve chamber to safely displace and recover the liquid ammonia in the main pipeline inside the valve chambers of the No. 1 valve chamber and the No. 2 valve chamber. In this example, keep the pig launcher block valve 38 closed, open the downstream bypass block valve 21 of the first valve chamber, the second block valve for valve chamber replacement 42, and the second block valve 12 of the first valve chamber, and self-discharge the liquid ammonia in the pipeline between the first block valve 11 and the third block valve 13 of the first valve chamber. The liquid ammonia enters the valve chamber replacement gas storage tank 43. When the pressure detected by the second pressure transmitter 18 in the first valve chamber is stable, it indicates the end of self-discharge. Subsequently, open the natural gas pressure regulating valve 32 and the natural gas block valve 34, and use the regulated high-pressure natural gas to displace the residual ammonia gas in the pipeline for no less than 10 minutes until the volume fraction of ammonia gas in the natural gas-ammonia gas mixed component obtained by the mixed medium sampling valve 71 is less than 0.1%; then close the natural gas pressure regulating valve 32 and the natural gas block valve 34, open the nitrogen gas vaporization system 35 and the nitrogen gas block valve 36, use the pressurized nitrogen gas to purge the residual natural gas in the pipeline, and discharge it into the atmosphere through the riser pipe extended from the mixed medium sampling valve 71 for no less than 5 minutes. When the volume fraction of natural gas in the natural gas-nitrogen gas mixed medium is less than 2%, the replacement ends. Similarly, the same operation is performed on the second valve chamber to complete the nitrogen replacement of the pipeline between the first block valve 11 and the third block valve 13 of the first valve chamber and the pipeline between the first block valve 22 and the third block valve 24 of the second valve chamber. Subsequently, remove the pipeline between the first block valve 11 and the third block valve 13 of the first valve chamber and the pipeline between the first block valve 22 and the third block valve 24 of the second valve chamber, connect the pig launcher supporting pipeline 41 to the third block valve 13 of the first valve chamber, connect the pig receiver inlet pipeline 51 to the first block valve 22 of the second valve chamber, connect the pig receiver outlet pipeline 56 to the third block valve 24 of the second valve chamber, put the pigging ball into the pig launcher 40 in advance, and perform natural gas replacement of air on the connected pipeline.

[0060] Step 3: Displace the liquid ammonia inside the middle reach main pipeline 2. Specifically, open the third isolation valve 13 of the first valve chamber, the first isolation valve 22 of the second valve chamber, the second isolation valve 54 of the pig receiver, and the third isolation valve 55 of the pig receiver to balance the pressures of the balancing pig launcher 40, the pig launching pipeline 41, the middle reach main pipeline 2, the pig receiver inlet pipeline 51, the pig receiver 52, and the pig receiver outlet pipeline 56; gradually open the natural gas pressure regulating valve 32 and the natural gas isolation valve 34, and then open the third isolation valve 24 of the second valve chamber to push the pig to displace the liquid ammonia in the middle reach main pipeline 2 into the downstream main pipeline 3; control the opening degree of the natural gas pressure regulating valve 32 to control the running speed of the pig at 2 - 2.5 m / s. When the pig enters the downstream pig receiver 52, immediately close the third isolation valve 55 of the pig receiver and prepare for the discharge treatment of the residual medium in the middle reach main pipeline 2.

[0061] Step 4: Conduct the discharge treatment of the residual medium in the middle reach main pipeline 2. Specifically, open the relief regulating valve 61, close the natural gas pressure regulating valve 32 and the natural gas isolation valve 34, relieve the pressure of the natural gas (which may contain a small amount of liquid ammonia escaping from the rear end of the pig to the front end) in the middle reach main pipeline 2, and burn it through the flare stack 62. During the discharge process, control the discharge rate and the medium temperature in the middle reach main pipeline 2 through the relief regulating valve 61. When the temperature displayed by the second temperature transmitter 19 of the first valve chamber or the first temperature transmitter 28 of the second valve chamber is lower than -20°C, temporarily stop the discharge. When the pressure in the middle reach main pipeline 2 is lower than 0.2 MPag, it indicates that the discharge of the natural gas - ammonia mixture in the pipeline is nearly complete. At this time, open the sampling device near the relief regulating valve 61 to sample the ammonia concentration of the discharge medium. When the ammonia concentration is less than 0.1%, it can directly enter the nitrogen purging; otherwise, it is necessary to open the natural gas pressure regulating valve 32 and the natural gas isolation valve 34 again, and continuously push the remaining natural gas - ammonia mixture in the pipeline into the flare stack for combustion treatment. When the ammonia concentration is less than 0.1% and meets the malodorous substance emission standard, open the nitrogen vaporization system 35 and the nitrogen isolation valve 36, and use the pressurized nitrogen to purge the remaining natural gas in the pipeline. When the volume fraction of natural gas in the natural gas - nitrogen mixture is less than 2%, the replacement is completed.

[0062] Step 5: Dismantle and remove the high - efficiency recovery system, the main pipeline displacement and replacement system, and the gas treatment system installed in the first valve chamber and the second valve chamber, reinstall the pipe segments in the valve chamber, and complete the recovery and discharge process of the liquid ammonia pipeline based on pig displacement.

[0063] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A liquid ammonia pipeline drainage system based on pigging displacement, the liquid ammonia pipeline including an upstream main line, a midstream main line, and a downstream main line, characterized in that, the system includes: A replaceable valve chamber system, which includes several valve chambers with cut-off functions provided on each main line of the liquid ammonia pipeline. The valve chamber includes an upstream bypass and a downstream bypass; A main line displacement and replacement system, which is arranged in the valve chamber of the upstream main line and includes a pig launcher pipeline for displacing and replacing the internal pipeline of the valve chamber to be replaced, recovering ammonia gas and natural gas discharged during the displacement process, and at the same time displacing the liquid ammonia stored in the midstream main line and discharging it into the downstream main line; An efficient recovery system, which is arranged in the valve chamber of the downstream main line and includes a pig receiver pipeline for guiding the liquid ammonia pushed in from the upstream by supporting the main line displacement and replacement system into the downstream main line; A gas treatment system, which is arranged in the valve chamber of the downstream main line and is used for safely burning the natural gas-ammonia mixed medium that may exist upstream of the pig after main line displacement and the natural gas-ammonia mixed medium inside the pig receiver, and discharging the nitrogen gas for subsequent replacement.

2. The liquid ammonia pipeline drainage system based on pigging displacement according to claim 1, characterized in that, the drainage system further includes a safety monitoring system, which includes a temperature monitoring device and a pressure monitoring device arranged in the valve chamber, and a mixed medium sampling valve arranged in the main line displacement and replacement system.

3. The liquid ammonia pipeline drainage system based on pigging displacement according to claim 1, characterized in that, the valve chamber includes a first cut-off valve, a second cut-off valve, and a third cut-off valve. The upstream bypass is arranged between the first cut-off valve and the second cut-off valve, and the downstream bypass is arranged between the second cut-off valve and the third cut-off valve. The upstream bypass further includes an upstream bypass cut-off valve, and the downstream bypass further includes a downstream bypass cut-off valve.

4. The liquid ammonia pipeline drainage system based on pigging displacement according to claim 3, characterized in that, the main line displacement and replacement system includes a compressed natural gas storage tank, a nitrogen gas vaporization system, and a pig launcher. The compressed natural gas storage tank is connected to a natural gas air-cooled heat exchanger through a natural gas pressure regulating valve. The natural gas air-cooled heat exchanger is connected to a natural gas cut-off valve. The nitrogen gas vaporization system is connected to a nitrogen gas cut-off valve. The natural gas cut-off valve and the nitrogen gas cut-off valve are connected through a first cut-off valve for valve chamber replacement and the upstream bypass cut-off valve. The pig launcher is connected to the natural gas cut-off valve and the nitrogen gas cut-off valve through a pig launcher cut-off valve, and the pig launcher is also connected to the liquid ammonia pipeline between the second cut-off valve and the third cut-off valve through a supporting pipeline.

5. The liquid ammonia pipeline drainage system based on pigging displacement according to claim 1, characterized in that, the pig receiver pipeline includes a pig receiver, a pig receiver inlet pipeline, and a pig receiver outlet pipeline. The pig receiver is connected to the liquid ammonia pipeline between the second cut-off valve and the third cut-off valve through the pig receiver inlet pipeline. A third cut-off valve for the pig receiver is provided on the pig receiver outlet pipeline. The pig receiver is respectively connected to both ends of the third cut-off valve for the pig receiver through a first cut-off valve for the pig receiver and a second cut-off valve for the pig receiver.

6. The ammonia pipeline drainage system based on pigging displacement according to claim 5, characterized in that, the gas treatment system includes a venting flare, and the venting flare is connected between the second shut-off valve and the third shut-off valve of the pig receiver through a drainage regulating valve.

7. A method for draining an ammonia pipeline based on pigging displacement, the method being implemented based on the drainage system according to any one of claims 1-6, characterized in that, the method includes: Step A: During normal transportation, the operating pressure of the ammonia pipeline is controlled above a preset pressure threshold. Under the condition of planned shutdown for maintenance, the upstream external transmission pump and the valve chamber shut-off valve are closed; Step B: After the pipeline stops transporting, by replacing the pipelines and electric shut-off valves in the valve chamber, using the replaced main pipeline displacement and replacement system, high-efficiency recovery system, etc. to displace the liquid ammonia in the middle main pipeline, and discharging it into the downstream main pipeline under pressure, displacing the medium in the downstream main pipeline into the downstream storage tank, and using the pipeline volume of the downstream main pipeline to receive the liquid ammonia in the middle main pipeline; Step C: Displace the liquid ammonia inside the middle main pipeline using the pig launcher pipeline and the pig receiver pipeline; Step D: Perform drainage treatment on the residual medium in the middle main pipeline through the gas treatment system.

8. The method for draining an ammonia pipeline based on pigging displacement according to claim 7, characterized in that, Step B specifically includes: Install the main pipeline displacement and replacement system in the valve chamber at the upstream of the main pipeline and the valve chamber at the downstream of the main pipeline in sequence, and displace and recover the liquid ammonia in the main pipeline inside the valve chambers at the upstream and downstream of the main pipeline.

9. The method for draining an ammonia pipeline based on pigging displacement according to claim 7, characterized in that, Step C specifically includes: Use a pig to displace the liquid ammonia in the middle main pipeline into the downstream main pipeline, control the running speed of the pig within a preset speed range, and close the pig receiver pipeline when the pig enters the downstream pig receiver and prepare for draining the residual medium in the middle main pipeline.

10. The method for draining an ammonia pipeline based on pigging displacement according to claim 7, characterized in that, the method further includes: Step E: Dismantle and remove the high-efficiency recovery system, main pipeline displacement and replacement system, and gas treatment system installed in the valve chamber at the upstream of the main pipeline and the valve chamber at the downstream of the main pipeline, and reinstall the pipe sections in the valve chamber.

Images