A pigging displacement based liquid ammonia pipeline relief system and method

Abstract

The application discloses a kind of liquid ammonia pipeline discharge system and method based on pigging displacement, including replaceable valve chamber system, efficient recovery system, trunk displacement and replacement system and gas treatment system, by replacing valve chamber pipe fitting, the medium in the liquid ammonia pipeline to be overhauled is effectively displaced and recovered, and residual medium is safely handled and emptied, maximum degree realizes that medium in pipe is efficiently displaced into downstream pipeline system, avoid setting recovery tank, liquid ammonia secondary pressurization, conventional pressure relief process phase change low temperature etc., guarantee that no toxic gas directly enters atmosphere in discharge process, reach the purpose of liquid ammonia pipeline efficient recovery and overhaul.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of liquid ammonia pipeline blowdown, and particularly relates to a liquid ammonia pipeline blowdown system and method based on pigging displacement. BACKGROUND

[0002] Liquid ammonia can be used as a hydrogen carrier for efficient storage and transportation, and can be used for energy conversion or industrial applications. Liquid ammonia transportation through pipelines 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 DEG C. In the pipeline, the gas phase or liquid phase transportation mode can be used. In the conventional pipeline transportation of hydrocarbons, periodic pipeline internal 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 the pipeline body has an abnormal condition, the target pipeline section needs to be maintained and replaced, which requires the pipeline to be shut down and the medium in the pipeline section to be emptied. Due to the phase change, toxicity and flammability of liquid ammonia, efficient emptying of the internal medium of the liquid ammonia pipeline, internal low-temperature prevention and control, safe treatment of the blowdown medium and other problems need to be considered during blowdown. At the same time, pipeline shutdown will have a great impact on medium transportation, which puts forward technical requirements for efficient blowdown. Efficient, safe and reasonable blowdown strategy is the key to ensuring the operation quality of the liquid ammonia pipeline.

[0004] However, there is little introduction of liquid ammonia pipeline safety recovery and blowdown system in the existing public literature, so it is necessary to carry out related research to realize efficient recovery and blowdown of the liquid ammonia pipeline after shutdown. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art, and to provide a liquid ammonia pipeline blowdown system and method based on pigging displacement. Based on the basic physical properties of liquid ammonia and the pipeline maintenance working condition characteristics, and in view of the characteristics of large pipe volume (at least 8 km of pipe length) and high medium storage between the liquid ammonia pipeline shut-off valves, the replaceable valve chamber system, the efficient recovery system, the dry line displacement and replacement system, the gas treatment system and the safety monitoring system are respectively set up from the aspects of controlling blowdown time, medium safety treatment and pipe phase change inhibition, so as to realize safe and efficient discharge of liquid ammonia medium in the pipeline under pipeline maintenance working condition.

[0006] The purpose of the present application is achieved by the following technical scheme:

[0007] A liquid ammonia pipeline blowdown system based on pigging displacement, the liquid ammonia pipeline comprising an upstream dry line, a middlestream dry line and a downstream dry line, the system comprising:

[0008] The replaceable valve chamber system comprises several valve chambers with cutting-off function arranged on each trunk of the liquid ammonia pipeline, and the valve chamber comprises an upstream bypass and a downstream bypass.

[0009] The trunk displacement and replacement system is arranged in the valve chamber of the upstream trunk, and comprises a ball launching cylinder pipeline for displacement and replacement of the internal pipeline of the valve chamber to be replaced, recovery of the ammonia gas and natural gas discharged during the displacement process, and displacement of the liquid ammonia in the middle trunk pipeline into the downstream trunk.

[0010] The high-efficiency recovery system is arranged in the valve chamber of the downstream trunk, and comprises a ball collecting cylinder pipeline for guiding the liquid ammonia pushed by the trunk displacement and replacement system into the downstream trunk.

[0011] The gas treatment system is arranged in the valve chamber of the downstream trunk, and is used for safe combustion treatment of the natural gas-ammonia mixed medium possibly existing upstream of the pig after the trunk displacement, the natural gas-ammonia mixed medium in the ball collecting cylinder, and discharge of the nitrogen gas for subsequent replacement.

[0012] Further, the relief system further comprises a safety monitoring system, and the safety monitoring system comprises a temperature monitoring device and a pressure monitoring device arranged in the valve chamber, and a mixed medium sampling valve arranged in the trunk displacement and replacement system.

[0013] Further, the valve chamber comprises a first cutting-off valve, a second cutting-off valve and a third cutting-off valve, the upstream bypass is arranged between the first cutting-off valve and the second cutting-off valve, and the downstream bypass is arranged between the second cutting-off valve and the third cutting-off valve, the upstream bypass further comprises an upstream bypass cutting-off valve, and the downstream bypass further comprises a downstream bypass cutting-off valve.

[0014] Further, the trunk displacement and replacement system comprises a compressed natural gas storage tank, a nitrogen gas vaporization system and a ball launching cylinder, the compressed natural gas storage tank is connected with a natural gas air bath type heat exchanger through a natural gas pressure regulating valve, the natural gas air bath type heat exchanger is connected with a natural gas cutting-off valve, the nitrogen gas vaporization system is connected with a nitrogen gas cutting-off valve, the natural gas cutting-off valve and the nitrogen gas cutting-off valve are connected with the first cutting-off valve and the upstream bypass cutting-off valve through the valve chamber, the ball launching cylinder is connected with the natural gas cutting-off valve and the nitrogen gas cutting-off valve through a ball launching cylinder cutting-off valve, and the ball launching cylinder is further connected to the liquid ammonia pipeline between the second cutting-off valve and the third cutting-off valve through a matching pipeline.

[0015] Further, the ball collecting cylinder pipeline comprises a ball collecting cylinder, a ball collecting cylinder inlet pipeline and a ball collecting cylinder outlet pipeline, the ball collecting cylinder is connected to the liquid ammonia pipeline between the second shut-off valve and the third shut-off valve through the ball collecting cylinder inlet pipeline, the ball collecting cylinder outlet pipeline is provided with a ball collecting cylinder third shut-off valve, and the ball collecting cylinder is connected to both ends of the ball collecting cylinder third shut-off valve through a ball collecting cylinder first shut-off valve and a ball collecting cylinder second shut-off valve respectively.

[0016] Further, the gas treatment system comprises a venting flare, and the venting flare is connected to the ball collecting cylinder second shut-off valve and the ball collecting cylinder third shut-off valve through a blowdown regulating valve.

[0017] In another aspect, the application also provides a liquid ammonia pipeline blowdown method based on pigging displacement, which is implemented based on any of the foregoing blowdown systems, and the method comprises the following steps:

[0018] Step A: During normal transportation, the operating pressure of the liquid ammonia pipeline is controlled to be above a preset pressure threshold, and in a planned shutdown and maintenance condition, the upstream delivery pump and the valve chamber shut-off valve are closed;

[0019] Step B: After the pipeline is shut down, the liquid ammonia in the middle stream trunk line is displaced by replacing the pipeline and the electric shut-off valve of the valve chamber, using a replacement trunk line displacement and replacement system, a high-efficiency recovery system and the like, and is discharged into the downstream trunk line under pressure, replaces the medium in the downstream trunk line and enters the downstream storage tank, and the pipeline volume of the downstream trunk line is used to receive the liquid ammonia in the middle stream trunk line;

[0020] Step C: The liquid ammonia in the middle stream trunk line is displaced by using the ball launching cylinder pipeline and the ball collecting cylinder pipeline;

[0021] Step D: The residual medium in the middle stream trunk line is discharged and treated by using the gas treatment system.

[0022] Further, the step B specifically comprises:

[0023] The trunk line displacement and replacement system is sequentially installed in the valve chamber upstream of the trunk line and the valve chamber downstream of the trunk line, and the liquid ammonia in the trunk line inside the valve chamber upstream of the trunk line and the valve chamber downstream of the trunk line is displaced and recovered.

[0024] Further, the step C specifically comprises:

[0025] The pigging ball replaces the liquid ammonia in the middle stream trunk line and enters the downstream trunk line, the running speed and degree of the pigging ball are controlled to be within a preset speed range, the ball collecting cylinder pipeline is closed after the pigging ball enters the downstream ball collecting cylinder, and the discharge and treatment of the residual medium in the middle stream trunk line is prepared.

[0026] Further, the method further comprises:

[0027] Step E: dismount, move away the high-efficiency recovery system, the trunk displacement and replacement system, the gas treatment system arranged in the valve chamber upstream of the trunk and the valve chamber downstream of the trunk, and restore and install the pipe section in the valve chamber.

[0028] The present application has the advantages that:

[0029] (1) The present application is directed to the medium and operation characteristics of liquid ammonia pipeline, and proposes various safe recovery and discharge measures from the perspective of avoiding external recovery of liquid ammonia during maintenance and improving the discharge efficiency of the trunk.

[0030] (2) The present application is based on the actual scene of planned maintenance, and sets up a movable and replaceable valve chamber system, a high-efficiency recovery system, a trunk displacement and replacement system, and a gas treatment system, which reflects the advantages of low cost and reusability in engineering investment. In terms of liquid ammonia medium transfer, by setting up a high-efficiency recovery system and a trunk displacement and replacement system, most of the liquid ammonia in the pipe section to be maintained can be displaced and recovered under pressure for reuse, which avoids direct discharge of liquid ammonia and also avoids the problem of liquefying and pressurizing the transfer of liquid ammonia from liquid phase under pressure to low-pressure gas phase. In addition, by using the displacement under pressure scheme, the discharge and recovery time of liquid ammonia is greatly reduced, the pipeline downtime 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 configuration of the present application, such as efficient recovery of the medium in the pipeline after shutdown and safe discharge of residual medium, helps to improve the operation safety and efficiency of the liquid ammonia pipeline. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic diagram of the liquid ammonia pipeline discharge system based on pigging displacement according to an embodiment of the present application.

[0033] BRIEF DESCRIPTION OF DRAWINGS: 1-upstream trunk line, 2-middle trunk line, 3-downstream trunk line, 11-first shut-off valve of No.1 valve chamber, 12-second shut-off valve of No.1 valve chamber, 13-third shut-off valve of No.1 valve chamber, 14-upstream bypass of No.1 valve chamber, 15-downstream bypass of No.1 valve chamber, 16-first pressure transmitter of No.1 valve chamber, 17-first temperature transmitter of No.1 valve chamber, 18-second pressure transmitter of No.1 valve chamber, 19-second temperature transmitter of No.1 valve chamber, 20-shut-off valve of upstream bypass of No.1 valve chamber, 21-shut-off valve of downstream bypass of No.1 valve chamber, 22-first shut-off valve of No.2 valve chamber, 23-second shut-off valve of No.2 valve chamber, 24-third shut-off valve of No.2 valve chamber, 25-upstream bypass of No.2 valve chamber, 26-downstream bypass of No.2 valve chamber, 27-first pressure transmitter of No.2 valve chamber, 28-first temperature transmitter of No.2 valve chamber, 29-shut-off valve of upstream bypass of No.2 valve chamber, 30-shut-off valve of downstream bypass of No.2 valve chamber, 31-compressed natural gas storage tank, 32-natural gas pressure regulating valve, 33-natural gas air bath heat exchanger, 34-natural gas shut-off valve, 35-nitrogen vaporization system, 36-nitrogen shut-off valve, 37-temperature transmitter, 38-shut-off valve of launching cylinder, 39-first shut-off valve of valve chamber replacement, 40-launching cylinder, 41-launching cylinder matching pipeline, 42-second shut-off valve of valve chamber replacement, 43-gas storage tank of valve chamber replacement, 51-inlet pipeline of collecting cylinder, 52-collecting cylinder, 53-first shut-off valve of collecting cylinder, 54-second shut-off valve of collecting cylinder, 55-third shut-off valve of collecting cylinder, 56-outlet pipeline of collecting cylinder, 61-drainage regulating valve, 62-flare stack, 71-mixed medium sampling valve. DETAILED DESCRIPTION

[0034] The advantages and effects of the present application can be easily understood by those skilled in the art from the above description. The present application can also be implemented or applied in other different specific embodiments, and the details in the description can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following examples and features in the examples can be combined with each other without conflict.

[0035] All other embodiments obtained by those skilled in the art without creative labor based on the examples in the present application belong to the scope of protection of the present application.

[0036] However, there are few relevant introductions to the safety recovery and drainage system of liquid ammonia pipelines in the existing public documents, so it is necessary to carry out relevant research to realize efficient recovery and drainage of liquid ammonia pipelines after shutdown.

[0037] In order to solve the above technical problems, the following embodiments of the liquid ammonia pipeline drainage system and method based on pigging displacement are proposed.

[0038] Example 1

[0039] The present example provides a pigging displacement-based liquid ammonia pipeline relief system, which relies on a conventional pipeline system, i.e., including an upstream trunk 1, a midstream trunk 2 and a downstream trunk 3.

[0040] Referring to Figure 1 As Figure 1 The pigging displacement-based liquid ammonia pipeline relief system provided by the present example is shown in the schematic diagram. The system includes a replaceable valve chamber system, an efficient recovery system, a trunk displacement and replacement system, a gas treatment system and a safety monitoring system.

[0041] The replaceable valve chamber system is composed of a first cutoff valve 11 of the first valve chamber, a second cutoff valve 12 of the first valve chamber, a third cutoff valve 13 of the first valve chamber, an upstream bypass 14 of the first valve chamber, a downstream bypass 15 of the first valve chamber, a first pressure transmitter 16 of the first valve chamber, a first temperature transmitter 17 of the first valve chamber, a second pressure transmitter 18 of the first valve chamber, a second temperature transmitter 19 of the first valve chamber, an upstream bypass cutoff valve 20 of the first valve chamber, a downstream bypass cutoff valve 21 of the first valve chamber, a first cutoff valve 22 of the second valve chamber, a second cutoff valve 23 of the second valve chamber, a third cutoff valve 24 of the second valve chamber, an upstream bypass 25 of the second valve chamber, a downstream bypass 26 of the second valve chamber, a first pressure transmitter 27 of the second valve chamber, a first temperature transmitter 28 of the second valve chamber, a second pressure transmitter of the second valve chamber, a second temperature transmitter of the second valve chamber, an upstream bypass cutoff valve 29 of the second valve chamber, a downstream bypass cutoff valve 30 of the second valve chamber, etc., which are used to provide trunk cutoff / communication functions for the first valve chamber and the second valve chamber, and the bypass is used to provide valve chamber internal pipeline replacement, trunk displacement and replacement, trunk medium recovery assistance, etc. functions for the planned maintenance of the midstream trunk. In actual engineering projects, there may be multiple trunk valve chambers, and the functional settings can be referred to the present example.

[0042] Specifically, in the system, the first, second and third cutting valves of the first valve chamber 11, 12 and 13 are arranged on the trunk line of the first valve chamber for connecting and cutting off the trunk line pipeline, and the second cutting valve 12 of the first valve chamber can be disassembled when replacing liquid ammonia in the downstream pipeline; the first cutting valve 11 of the first valve chamber is a full-bore manual ball valve, which is welded on the upstream side and flange-connected on the downstream side; the second cutting valve 12 of the first valve chamber is a full-bore electric ball valve with emergency cutting function, which is welded on both sides; the third cutting valve 13 of the first valve chamber is a full-bore manual ball valve, which is flange-connected on the upstream side and welded on the downstream side; the upstream bypass 14 of the first valve chamber is arranged between the first and second cutting valves 11 and 12 of the first valve chamber and is made of carbon steel, which is used to provide a replacement and displacement channel for the trunk line section of the valve chamber; the downstream bypass 15 of the first valve chamber is arranged between the second and third cutting valves 12 and 13 of the first valve chamber and is made of carbon steel, which is used to provide a replacement and displacement channel for the trunk line section of the valve chamber; the first pressure transmitter 16 and the first temperature transmitter 17 of the first valve chamber are arranged on the upstream bypass 14 of the first valve chamber, which are used to provide real-time detection of pressure and temperature at the point and the nearby area; the second pressure transmitter 18 and the second temperature transmitter 19 of the first valve chamber are arranged on the downstream bypass 15 of the first valve chamber, which are used to provide real-time detection of pressure and temperature at the point and the nearby area; the upstream bypass cutting valve 20 and the downstream bypass cutting valve 21 of the first valve chamber are both carbon steel manual ball valves, which are normally closed and are respectively installed at the ends of the upstream bypass 14 and the downstream bypass 15 of the first valve chamber, and the other ends are blind end connected, which are used to connect the high-efficiency recovery system, the trunk line displacement and replacement system; the first, second and third cutting valves 22, 23 and 24 of the second valve chamber are arranged on the trunk line of the second valve chamber for connecting and cutting off the trunk line pipeline, and the second cutting valve 23 of the second valve chamber can be disassembled when replacing liquid ammonia in the downstream pipeline; the first cutting valve 22 of the second valve chamber is a full-bore manual ball valve, which is welded on the upstream side and flange-connected on the downstream side; the second cutting valve 23 of the second valve chamber is a full-bore electric ball valve with emergency cutting function, which is welded on both sides; the third cutting valve 24 of the second valve chamber is a full-bore manual ball valve, which is flange-connected on the upstream side and welded on the downstream side; the upstream bypass 25 of the second valve chamber is arranged between the first and second cutting valves 22 and 23 of the second valve chamber and is made of carbon steel, which is used to provide a replacement and displacement channel for the trunk line section of the valve chamber; the downstream bypass 26 of the second valve chamber is arranged between the second and third cutting valves 23 and 24 of the second valve chamber and is made of carbon steel, which is used to provide a replacement and displacement channel for the trunk line section of the valve chamber; the first pressure transmitter 27 and the first temperature transmitter 28 of the second valve chamber are arranged on the upstream bypass 25 of the second valve chamber, which are used to provide real-time detection of pressure and temperature at the point and the nearby area;The second pressure transmitter of the second valve chamber and the second temperature transmitter of the second valve chamber are arranged on the bypass 26 downstream of the second valve chamber to provide real-time detection of the pressure and temperature of the point and the nearby area; the bypass upstream shutoff valve of the second valve chamber and the bypass downstream shutoff valve of the second valve chamber are carbon steel manual ball valves, are normally closed, are respectively installed at the end of the bypass 25 upstream of the second valve chamber and the bypass 26 downstream of the second valve chamber, and have a blind end connected at the other end, and are used for connecting the high-efficiency recovery system and the trunk displacement and replacement system.

[0043] The trunk displacement and replacement system is composed of a compressed natural gas storage tank 31, a natural gas pressure regulating valve 32, a natural gas air bath heat exchanger 33, a natural gas shutoff valve 34, a nitrogen gas vaporization system 35, a nitrogen gas shutoff valve 36, a temperature transmitter 37, a launching cylinder shutoff valve 38, a first shutoff valve 39 for valve chamber replacement, a launching cylinder 40, a launching cylinder pipeline 41, a second shutoff valve 42 for valve chamber replacement, a valve chamber replacement gas storage tank 43 and the like, is used for displacing and replacing the internal pipeline of the valve chamber to be replaced, recovering the ammonia and natural gas discharged in the displacement process, and providing a movable pig launching cylinder for displacing the liquid ammonia in the trunk pipeline in the middle stream, discharging into the downstream trunk pipeline, and avoiding the liquid ammonia recovery device arranged in the downstream valve chamber. It should be noted that part of the equipment and pipeline for displacing the valve chamber pipeline in the system is combined in a pry, and can also be used for the replacement of the second valve chamber.

[0044] Specifically, in the system shown, the compressed natural gas storage tank 31 is a complete compressed natural gas supply storage tank for providing compressed natural gas for displacement and purging; the natural gas pressure regulating valve 32 is an electrically controlled regulating valve for regulating the flow and pressure of the compressed natural gas, preferably made of low-temperature carbon steel; the natural gas air bath heat exchanger 33 is arranged downstream of the natural gas pressure regulating valve 32 and is used for temperature regulation of the regulated natural gas, preferably with an outlet temperature greater than -10℃; the natural gas shut-off valve 34 is arranged downstream of the natural gas air bath heat exchanger 33 and is a manual ball valve for connecting / closing the natural gas supply channel; the nitrogen vaporization system 35 is a small skid-mounted system including a nitrogen storage tank, a nitrogen regulating valve, a small nitrogen booster system, etc., for providing pressurized nitrogen for displacement and purging of the downstream system; the nitrogen shut-off valve 36 is arranged downstream of the nitrogen vaporization system 35 and is a manual ball valve for connecting / closing the nitrogen supply channel; the temperature transmitter 37 is arranged on the nitrogen / natural gas pipeline for detecting the temperature of the regulated and temperature-regulated medium; the ball launching cylinder shut-off valve 38 is arranged upstream of the ball launching cylinder 40 and is a manual ball valve for connecting / closing the gas supply channel of the ball launching cylinder; the valve chamber displacement first shut-off valve 39 is arranged in bypass of the ball launching cylinder shut-off valve 38 and is a manual ball valve for connecting / closing the gas supply channel for displacement of the internal pipeline of the valve chamber; the ball launching cylinder 40 is a pig launching cylinder made of carbon steel and is used to launch the pig ball used for displacement of liquid ammonia in the middle dry line 2; the ball launching cylinder auxiliary pipeline 41 is used to connect the ball launching cylinder 40 and the dry line shut-off valve; the valve chamber displacement second shut-off valve 42 is a manual ball valve for connecting / closing the displacement / purging gas discharge channel of the internal pipeline of the valve chamber and is arranged downstream of the single-sided valve chamber bypass shut-off valve arranged inside the valve chamber; the valve chamber displacement gas storage tank 43 is a carbon steel horizontal storage tank with a design pressure of preferably 2.5 MPa and is used to recover ammonia gas, natural gas, etc. displaced from the valve chamber. Further, 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 shut-off valve 34, the nitrogen vaporization system 35, the nitrogen shut-off valve 36, and the temperature transmitter 37 are preferably skid-mounted for providing the displacement and purging gas source; the valve chamber displacement second shut-off valve 42 and the valve chamber displacement gas storage tank 43 are preferably skid-mounted for recovering the medium inside the valve chamber.

[0045] The ball collecting cylinder inlet pipeline 51, the ball collecting cylinder 52, the ball collecting cylinder first shut-off valve 53, the ball collecting cylinder second shut-off valve 54, the ball collecting cylinder third shut-off valve 55, the ball collecting cylinder outlet pipeline 56, etc. constitute a high-efficiency recovery system arranged in the second valve chamber in this example and are used in conjunction with the dry line displacement and displacement system to guide the liquid ammonia pushed from the upstream into the downstream dry line and immediately introduce the medium after pig collection into the gas treatment system; in addition, the ball collecting cylinder is used for ball collection of the pig ball pushed from the upstream.

[0046] Specifically, in the system shown, the ball collecting cylinder inlet pipeline 51 is made of carbon steel, is used to connect the first cutoff valve of the second valve chamber and the ball collecting cylinder 52, and is used to provide a medium flow channel for the displacement of the middle trunk 2; the ball collecting cylinder 52 is a pig ball collecting cylinder made of carbon steel, and is used to receive the pig ball used when the middle trunk 2 is displaced by liquid ammonia; the ball collecting cylinder first cutoff valve 53 is a manual ball valve made of carbon steel, is arranged on the small cylinder branch of the ball collecting cylinder 52, and is opened only during pig displacement; and the ball collecting cylinder second cutoff valve 54 is a manual ball valve made of carbon steel, is arranged on the large cylinder branch of the ball collecting cylinder 52, is opened after pig displacement is completed, and is used to guide the natural gas (containing part of the leaked ammonia gas) used for pig displacement into the flare stack 62 for safe treatment.

[0047] The gas treatment system composed of the blowdown regulating valve 61 and the flare stack 62 is arranged in the second valve chamber in this example, is used to safely burn the natural gas-ammonia mixed medium possibly existing upstream of the pig and the natural gas-ammonia mixed medium in the ball collecting cylinder, and is used to discharge the nitrogen used for subsequent replacement.

[0048] Specifically, in the system shown, the blowdown regulating valve 61 is a manually controlled regulating valve made of carbon steel, is used to regulate the flow of the power medium (natural gas, natural gas / ammonia mixed medium) separated from the front end of the pig, and is used to send the medium into the flare stack 62 for burning treatment; and the flare stack 62 is a vertical high-altitude flare stack with an electronic ignition system, and is used to safely burn the medium to be discharged. In addition, the blowdown regulating valve 61 is also provided with a mixed medium sampling detection port.

[0049] In addition, the multiple pressure transmitters and temperature transmitters arranged in the system and the mixed medium sampling valve 71 arranged in the trunk displacement and replacement system constitute a safety monitoring system, which is used to detect the pressure and temperature of key process points during operation, and is used to monitor the composition of the replacement medium in real time through the sampling valve to guide the safe implementation of the replacement process.

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

[0051] (1) In the normal operating condition, the liquid phase state is generally used for liquid ammonia transportation. After the pipeline needs to be cut off and repaired, the liquid ammonia in the to-be-repaired pipeline section needs to be discharged. Since the liquid ammonia is toxic and has high economic value, it is preferred to receive the discharged liquid ammonia by recovery. Further, in order to improve the liquid discharge efficiency and avoid the phase change and low temperature problems of the liquid ammonia in the conventional pressure relief process affecting the discharge speed, the present application proposes a scheme of displacing the liquid ammonia in the to-be-repaired pipeline section into the downstream pipeline under pressure, which avoids the pressure drop of the liquid ammonia in the emptying process and avoids the scheme of using a large-capacity storage tank to recover and re-pressurize the liquid ammonia discharge medium and inject it into the liquid ammonia storage tank.

[0052] (2) In order to realize the liquid ammonia medium displacement under pressure, the application sets up the replaceable valve chamber system and the trunk displacement and replacement system, uses the replaceable valve chamber system to realize the trunk flexible disassembly at both ends of the trunk, and replaces the movable liquid ammonia displacement system, uses the pressurized natural gas and the pig ball as the power source and the insulator of the liquid ammonia displacement, and sets up the high-efficiency recovery system in the downstream valve chamber, directly introduces the replaced pressurized liquid ammonia into the downstream trunk, and realizes the liquid ammonia pressure loss and low-temperature phase change in the whole process.

[0053] (3) In order to avoid the toxic influence of the vaporized liquid ammonia on the environment, the application optimizes the pressurized natural gas as the liquid ammonia displacement medium according to the engineering actual situation, so as to realize the safe combustion treatment of the natural gas-ammonia gas mixed medium through combustion, and sets up the gas treatment system to realize it; and further sets up the nitrogen injection system as the residual natural gas displacement scheme in the pipeline according to the pipeline maintenance requirement.

[0054] (4) For the liquid ammonia disposal problem of the valve chamber internal pipeline system, the valve chamber bypass and the trunk displacement and replacement system are used to recover the liquid ammonia in the valve chamber trunk into the tank, and to gradually replace the residual medium with natural gas and nitrogen, which is convenient for the safe combustion disposal of the natural gas-ammonia gas mixed medium, and is convenient for the safe emptying of the nitrogen-natural gas medium.

[0055] (5) In order to efficiently utilize the assets, the high-efficiency recovery system, the trunk displacement and replacement system, and the gas treatment system are set up as the movable skid-mounted device, which meets the requirement of the planned operation, and realizes the device multi-station field reuse.

[0056] Embodiment 2

[0057] On the basis of the liquid ammonia pipeline blowdown system based on the pig displacement provided in the foregoing embodiment, the embodiment further provides a liquid ammonia pipeline blowdown method based on pig displacement, which includes the following main contents:

[0058] Step one: during normal transportation, the operating pressure of the liquid ammonia pipeline is controlled to be above 1.5 MPa.g, and the transportation temperature is close to the soil temperature. In the planned shutdown maintenance condition, orderly close the upstream delivery pump, the trunk cutoff valve (in this example, the first cutoff valve 11 of the first valve chamber, the second cutoff valve 12 of the first valve chamber, the third cutoff valve 13 of the first valve chamber, the first cutoff valve 22 of the second valve chamber, the second cutoff valve 23 of the second valve chamber, and the third cutoff valve 24 of the second valve chamber) and the like, and the trunk pipeline realizes safe shutdown.

[0059] Step two: in the example of the present application, after the pipeline stops, the liquid ammonia in the middle trunk 2 is displaced by replacing the trunk displacement and replacement system, high-efficiency recovery system, etc., and is discharged into the downstream trunk 3 under pressure, replacing the medium in the downstream trunk 3 into the downstream storage tank, and using the pipe volume of the downstream trunk 3 to receive most of the liquid ammonia in the middle trunk 2. Specifically, first, install the trunk displacement and replacement system in the No. 1 valve chamber and the No. 2 valve chamber in sequence, and safely displace and recover the liquid ammonia in the valve chamber internal trunk of the No. 1 valve chamber and the No. 2 valve chamber. In this example, keep the launching cylinder cutoff valve 38 closed, open the No. 1 valve chamber downstream bypass cutoff valve 21, the valve chamber replacement second cutoff 42, and the No. 1 valve chamber second cutoff valve 12, and self-flow discharge the liquid ammonia in the pipeline between the No. 1 valve chamber first cutoff valve 11 and the No. 1 valve chamber third cutoff valve 13, and the liquid ammonia enters the valve chamber replacement gas storage tank 43, until the No. 1 valve chamber second pressure transmitter 18 detects that the pressure is stable, indicating that the self-flow discharge is complete, then open the natural gas pressure regulating valve 32 and the natural gas cutoff valve 34, and use the regulated high-pressure natural gas to replace the residual ammonia gas in the pipeline, for a duration of not less than 10 min, 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 cutoff valve 34, open the nitrogen gas vaporization system 35 and the nitrogen gas cutoff valve 36, use the pressurized nitrogen gas to purge the residual natural gas in the pipeline, and discharge into the atmosphere through the extended standpipe of the mixed medium sampling valve 71, for a duration of not less than 5 min, when the volume fraction of natural gas in the natural gas-nitrogen gas mixed medium is less than 2%, the replacement is complete. Similarly, the same operation is performed on the No. 2 valve chamber, and the nitrogen gas replacement is completed for the pipeline between the No. 1 valve chamber first cutoff valve 11 and the No. 1 valve chamber third cutoff valve 13 and the pipeline between the No. 2 valve chamber first cutoff valve 22 and the No. 2 valve chamber third cutoff valve 24. Then, remove the pipeline between the No. 1 valve chamber first cutoff valve 11 and the No. 1 valve chamber third cutoff valve 13, remove the pipeline between the No. 2 valve chamber first cutoff valve 22 and the No. 2 valve chamber third cutoff valve 24, connect the launching cylinder auxiliary pipeline 41 to the No. 1 valve chamber third cutoff valve 13, connect the receiving cylinder inlet pipeline 51 to the No. 2 valve chamber first cutoff valve 22, connect the receiving cylinder outlet pipeline 56 to the No. 2 valve chamber third cutoff valve 24, put the cleaning ball into the launching cylinder 40 in advance, and perform natural gas replacement air on the connected pipeline.

[0060] Step three: Displacement of liquid ammonia in the middle trunk 2. Specifically, open the third shut-off valve 13 of the first valve chamber, the first shut-off valve 22 of the second valve chamber, the second shut-off valve 54 of the ball collecting cylinder, the third shut-off valve 55 of the ball collecting cylinder, balance the pressure of the ball launching cylinder 40, the ball launching auxiliary pipeline 41, the middle trunk 2, the ball collecting cylinder inlet pipeline 51, the ball collecting cylinder 52 and the ball collecting cylinder outlet pipeline 56; gradually open the natural gas pressure regulating valve 32 and the natural gas shut-off valve 34, then open the third shut-off valve 24 of the second valve chamber, push the pig to replace the liquid ammonia in the middle trunk 2 into the downstream trunk 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 ball collecting cylinder 52, immediately close the third shut-off valve 55 of the ball collecting cylinder, and prepare to carry out the discharge treatment of the residual medium in the middle trunk 2.

[0061] Step four: Discharge treatment of the residual medium in the middle trunk 2. Specifically, open the discharge regulating valve 61, close the natural gas pressure regulating valve 32 and the natural gas shut-off valve 34, discharge the natural gas (possibly containing a small amount of liquid ammonia escaping from the rear end of the pig to the front section) in the middle trunk 2, and burn through the flare 62. The discharge process controls the discharge rate and the medium temperature in the middle trunk 2 through the discharge regulating valve 61, and temporarily stops discharging when the temperature of the first temperature transmitter 19 of the first valve chamber or the first temperature transmitter 28 of the second valve chamber is lower than -20℃. When the pressure in the middle trunk 2 is lower than 0.2 MPag, it indicates that the discharge of the natural gas-ammonia mixed medium existing in the pipeline is close to completion, at which time the sampling device near the discharge regulating valve 61 is opened to sample the ammonia concentration of the discharge medium. When the ammonia concentration is less than 0.1%, nitrogen blowing can be directly carried out; otherwise, the natural gas pressure regulating valve 32 and the natural gas shut-off valve 34 need to be opened again to continuously push the residual natural gas-ammonia mixed medium in the pipeline into the flare for burning treatment. When the ammonia concentration is less than 0.1% and meets the odor emission standard, the nitrogen vaporization system 35 and the nitrogen shut-off valve 36 are opened, and the residual natural gas in the pipeline is blown by the pressurized nitrogen. When the volume fraction of natural gas in the natural gas-nitrogen mixed medium is less than 2%, the replacement is completed.

[0062] Step five: disassemble, remove the high-efficiency recovery system, the trunk displacement and replacement system and the gas treatment system arranged in the first valve chamber and the second valve chamber, restore and install the pipe sections in the valve chamber, and complete the liquid ammonia pipeline recovery and discharge process based on pig displacement.

[0063] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A liquid ammonia pipeline discharge system based on pigging and displacement, wherein the liquid ammonia pipeline comprises an upstream trunk line, a midstream trunk line and a downstream trunk line, characterized in that: The system comprises: A replaceable valve chamber system, comprising a plurality of valve chambers with a shutoff function provided on each trunk line of the liquid ammonia pipeline, each valve chamber including an upstream bypass and a downstream bypass; A trunk line displacement and replacement system, which is located in the valve chamber of the upstream trunk line and includes a ball-launching tube pipeline. It is used to displace and replace the internal pipes of the valve chamber to be replaced, and to recover ammonia and natural gas emitted during the displacement process. At the same time, it displaces the liquid ammonia stored in the midstream trunk line and discharges it into the downstream trunk line. An efficient recovery system, which is located in the valve chamber of the downstream trunk line and includes a ball collecting tube pipeline, and is used to cooperate with the trunk line displacement and replacement system to guide the liquid ammonia pushed in from the upstream into the downstream trunk line; A gas processing system, located in the valve chamber of the downstream trunk line, is used to safely burn any natural gas-ammonia mixture that may exist upstream of the pig and inside the pig collection tube after the trunk line is displaced, and to discharge the nitrogen used for subsequent displacement; The valve chamber includes a first shutoff valve, a second shutoff valve, and a third shutoff valve, an upstream bypass is provided between the first shutoff valve and the second shutoff valve, a downstream bypass is provided between the second shutoff valve and the third shutoff valve, the upstream bypass further includes an upstream bypass shutoff valve, and the downstream bypass further includes a downstream bypass shutoff valve; The trunk displacement and replacement system includes a compressed natural gas storage tank, a nitrogen vaporization system and a ball launcher. The compressed natural gas storage tank is connected to a natural gas air bath heat exchanger through a natural gas pressure regulating valve. The natural gas air bath heat exchanger is connected to a natural gas shut-off valve. The nitrogen vaporization system is connected to a nitrogen shut-off valve. The natural gas shut-off valve and the nitrogen shut-off valve are connected to the upstream bypass shut-off valve through a valve chamber replacement first shut-off valve. The ball launcher is connected to the natural gas shut-off valve and the nitrogen shut-off valve through the ball launcher shut-off valve. The ball launcher is also connected to the liquid ammonia pipeline between the second shut-off valve and the third shut-off valve through a matching pipeline.

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

3. The liquid ammonia pipeline discharge system based on pigging and displacement according to claim 1, characterized in that: The ball collecting cylinder pipeline includes a ball collecting cylinder, a ball collecting cylinder inlet pipeline and a ball collecting cylinder outlet pipeline. The ball collecting cylinder is connected to the liquid ammonia pipeline between the second shut-off valve and the third shut-off valve through the ball collecting cylinder inlet pipeline. The ball collecting cylinder outlet pipeline is provided with the third shut-off valve for ball collecting cylinder. The ball collecting cylinder is connected to both ends of the third shut-off valve for ball collecting cylinder through the first shut-off valve for ball collecting cylinder and the second shut-off valve for ball collecting cylinder respectively.

4. The liquid ammonia pipeline discharge system based on pigging and displacement according to claim 3, characterized in that: The gas processing system includes a venting flare, which is connected between the second shut-off valve of the ball collecting cylinder and the third shut-off valve of the ball collecting cylinder through a discharge regulating valve.

5. A method for discharging a liquid ammonia pipeline based on pigging and displacement, the method being implemented based on the discharge system according to any one of claims 1 to 4, characterized in that: The method comprises: Step A: During normal transportation, the operating pressure of the liquid ammonia pipeline is controlled above the preset pressure threshold. In the case of planned shutdown and maintenance, the upstream external transmission pump and valve chamber shut-off valve are closed; Step B: After the pipeline is shut down, the liquid ammonia in the midstream trunk line is displaced by replacing the pipeline and electric shut-off valve in the valve chamber using the replaced trunk line displacement and replacement system and the high-efficiency recovery system, and discharged under pressure into the downstream trunk line, displacing the medium in the downstream trunk line and entering the downstream storage tank. The liquid ammonia in the midstream trunk line is then received by the pipeline capacity of the downstream trunk line. Step C: Use the ball launching tube pipeline and the ball receiving tube pipeline to displace the liquid ammonia inside the midstream trunk line; Step D: Discharge the residual medium in the midstream trunk line through the gas treatment system.

6. The method for releasing liquid ammonia from a pipeline based on pigging and displacement according to claim 5, characterized in that: The step B specifically includes: The trunk line displacement and replacement system is sequentially installed in the valve chamber upstream of the trunk line and the valve chamber downstream of the trunk line to displace and recover the liquid ammonia in the trunk line inside the valve chambers of the valve chambers upstream of the trunk line and downstream of the trunk line.

7. The method for releasing liquid ammonia from a pipeline based on pigging and displacement according to claim 5, characterized in that: The step C specifically includes: The pig is used to displace the liquid ammonia in the midstream trunk line and enter the downstream trunk line. The speed of the pig is controlled within the preset speed range. When the pig enters the downstream ball collecting drum, the ball collecting drum pipeline is closed and preparations are made for the discharge of the residual medium in the midstream trunk line.

8. The method for releasing liquid ammonia from a pipeline based on pigging and displacement according to claim 5, characterized in that: The method further comprises: Step E: Dismantle and move away the high-efficiency recovery system, trunk displacement and replacement system, and gas treatment system installed in the upstream valve chamber and downstream valve chamber of the trunk line, and restore and install the pipe section in the valve chamber.

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