Safe recovery and discharge system and method for liquid ammonia pipeline

Abstract

The invention discloses a liquid ammonia pipeline safety recovery and discharge system and method.The system comprises a safety recovery system, a safety discharge system and an efficient replacement system.The liquid ammonia in a pipeline is recovered through the safety recovery system after transportation of the pipeline is stopped; and the residual ammonia gas is displaced and replaced by using an efficient replacement system and a safe recovery system. According to the invention, the liquid ammonia after the pipeline is stopped can be efficiently recovered, and the residual ammonia gas can be discharged.

Description

Technical Field

[0001] This invention belongs to the field of liquid ammonia transportation technology, and particularly relates to a liquid ammonia pipeline safe recovery and release system and method. Background Technology

[0002] Against the backdrop of ever-increasing demands for energy conservation, emission reduction, and environmental protection in the energy and chemical industry, the demand for efficient utilization of new energy sources is growing rapidly. Wind and solar power for hydrogen production and application is a recognized route for new energy utilization. To address the challenges of hydrogen storage and transportation, the need for liquid ammonia storage and transportation technology has emerged. Liquid ammonia can serve as a hydrogen carrier for efficient storage and transportation, enabling energy conversion or industrial applications. Pipeline transportation of liquid ammonia is an effective means of achieving planned, long-distance transport.

[0003] Liquid ammonia has a critical pressure of approximately 11.40 MPa and a critical temperature of approximately 132.5℃, and can be transported in pipelines using either gas or liquid phase methods. Furthermore, to improve transport efficiency, liquid phase transport is preferred. Liquid ammonia has a boiling point of approximately -33℃ at normal pressure, posing a certain low-temperature challenge under extreme discharge conditions. Simultaneously, liquid ammonia possesses a degree of toxicity and flammability. While relatively safe for closed-loop pipeline transport, reasonable and safe safeguards must be implemented during discharge and injection to avoid energy waste and air pollution, achieving environmentally friendly and economical treatment.

[0004] In conventional hydrocarbon pipeline transportation, periodic pipeline inspection is a key means of effectively diagnosing the internal condition of the pipeline, and external maintenance also needs to be carried out regularly. When an abnormality occurs in the pipeline body, the target pipeline section needs to be maintained and replaced, which requires shutting down the pipeline and emptying the medium in that section of the pipeline.

[0005] Due to the phase change, toxicity, and flammability of liquid ammonia, the release of liquid ammonia from pipelines requires consideration of issues such as efficient emptying of the internal medium, prevention of cryogenic conditions within the pipeline, and safe handling of the released medium. Furthermore, pipeline shutdown will significantly impact medium transport, posing technical requirements for efficient release. It should be noted that during the depressurization and discharge process of liquid ammonia, nitrogen is used for medium replacement. However, the boiling point of the nitrogen-liquid ammonia mixture is significantly lower than that of liquid ammonia, potentially leading to extremely low temperatures inside the pipeline and causing damage. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a safe recovery and release system and method for liquid ammonia pipelines. This method recovers liquid ammonia in the pipeline through a safe recovery system, and then uses a high-efficiency replacement system and a safe recovery system to displace and replace the residual ammonia gas, thereby achieving efficient recovery and release of ammonia gas.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A safe recovery and release system for liquid ammonia pipelines, the system comprising a main pipeline, the main pipeline being divided into an upstream pipeline, a midstream pipeline, and a downstream pipeline by a first main pipeline shut-off valve and a second main pipeline shut-off valve; an upstream branch pipe of the first main pipeline shut-off valve is located upstream of the first main pipeline shut-off valve, and a downstream branch pipe of the first main pipeline shut-off valve is located downstream of the first main pipeline shut-off valve; an upstream branch pipe of the second main pipeline shut-off valve is located upstream of the second main pipeline shut-off valve, and a downstream branch pipe of the second main pipeline shut-off valve is located downstream of the second main pipeline shut-off valve; the system further comprises:

[0009] A safe recovery system, which is connected to the upstream branch of the second main line shut-off valve, is used for flow regulation, pressure regulation, reliquefaction, pressurization, or storage of liquid ammonia in the midstream pipeline during the recovery process.

[0010] A safety relief system is connected to a branch pipe downstream of the second main line shut-off valve, used to release and burn residual ammonia that has not been recovered by the safety recovery system;

[0011] A high-efficiency replacement system is connected to the downstream branch of the first main line shut-off valve and is used to drive and replace the gas in the safely recovered midstream pipeline by injecting natural gas or nitrogen.

[0012] Furthermore, the safe recycling system includes a recycling branch pipe, a refrigeration module, and a recycling storage tank. The upstream branch pipe of the second main line shut-off valve is connected to the inlet end of the recycling branch pipe, the outlet end of the recycling branch pipe is connected to the inlet of the refrigeration module through a recycling regulating valve, and the outlet of the refrigeration module is connected to the recycling storage tank through a recycling first shut-off valve.

[0013] Furthermore, the safe recovery system also includes a second recovery shut-off valve and a liquid phase pump. The second recovery shut-off valve is connected in parallel across the two ends of the recovery regulating valve, and the liquid phase pump is connected in parallel across the two ends of the first recovery shut-off valve.

[0014] Furthermore, the safety relief system includes a relief branch pipe, a venting separator, and a venting torch. The downstream branch pipe of the second main line shut-off valve is connected to the inlet end of the relief branch pipe, the outlet end of the relief branch pipe is connected to the inlet of the venting separator through a relief regulating valve, and the outlet of the venting separator is connected to the venting torch.

[0015] Furthermore, the venting torch is also equipped with a combustion-supporting system, which is used to provide combustion-supporting gas to the torch nozzle of the venting torch.

[0016] Furthermore, the high-efficiency replacement system includes a liquid nitrogen storage tank, a natural gas storage tank, a liquid nitrogen booster pump, a vaporization heat exchanger, and a natural gas heat exchanger. The downstream branch pipe shut-off valve of the first main line shut-off valve is connected to the outlet end of the vaporization heat exchanger and the outlet end of the natural gas heat exchanger respectively through the replacement shut-off valve. The natural gas storage tank is connected to the inlet end of the natural gas heat exchanger through a natural gas regulating valve, and the liquid nitrogen storage tank is connected to the inlet end of the vaporization heat exchanger through a liquid nitrogen booster pump.

[0017] Furthermore, the safe recovery and release system also includes a sampling and detection shut-off valve located downstream of the release regulating valve.

[0018] Furthermore, the safe recovery system, safe release system, and efficient replacement system are prefabricated, mobile skid-mounted systems.

[0019] On the other hand, the present invention also provides a method for the safe recovery and release of liquid ammonia pipelines, the method being implemented based on any of the aforementioned safe recovery and release systems for liquid ammonia pipelines, the method comprising:

[0020] After the pipeline is shut down, the safety relief system and the efficient replacement system are kept closed, and the liquid ammonia in the midstream pipeline is recovered through the safety recovery system.

[0021] After the recovery is complete, the safety recovery system is shut down, and the high-efficiency replacement system and safety release system are activated to drive and replace the residual ammonia in the midstream pipeline, thus completing the release of the participating medium in the liquid ammonia pipeline.

[0022] Furthermore, the displacement and replacement of residual ammonia in the midstream pipeline specifically includes:

[0023] Compressed natural gas is injected to displace and mix with the residual ammonia in the midstream pipeline. The mixed gas then enters the safety relief system for combustion treatment until the ammonia volume fraction in the mixed gas entering the safety relief system is less than the preset ammonia threshold. Nitrogen is then injected to displace and replace the residual natural gas in the midstream pipeline until the natural gas volume fraction in the mixed gas entering the safety relief system is less than the preset natural gas threshold.

[0024] The beneficial effects of this invention are as follows:

[0025] Based on the basic physical properties of liquid ammonia and the characteristics of pipeline maintenance, this invention addresses the large pipe volume and high medium storage in liquid ammonia pipeline shut-off valves. From the perspectives of economic recovery of stored medium, emission reduction, and safe disposal, it proposes a safe recovery and release system and method for liquid ammonia pipelines. This system effectively recovers and reduces emissions of liquid ammonia in the target maintenance section after pipeline shutdown, and provides a reference for future liquid ammonia pipeline transportation projects. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a liquid ammonia pipeline safety recovery and release system according to an embodiment of the present invention. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. 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 other different specific embodiments, and 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, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0028] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0029] Due to the phase change, toxicity, and flammability of liquid ammonia, the release of liquid ammonia from pipelines requires consideration of issues such as efficient emptying of the internal medium, prevention of cryogenic conditions within the pipeline, and safe handling of the released medium. Furthermore, pipeline shutdown will significantly impact medium transport, posing technical requirements for efficient release. It should be noted that during the depressurization and discharge process of liquid ammonia, nitrogen is used for medium replacement. However, the boiling point of the nitrogen-liquid ammonia mixture is significantly lower than that of liquid ammonia, potentially leading to extremely low temperatures inside the pipeline and causing damage.

[0030] To address the aforementioned technical problems, the following embodiments of a liquid ammonia pipeline safe recovery and release system and method of the present invention are proposed.

[0031] Example 1

[0032] Reference Figure 1 ,like Figure 1 The diagram shown is a structural schematic of a liquid ammonia pipeline safety recovery and release system according to this embodiment. In this embodiment, the liquid ammonia pipeline safety recovery and release system specifically includes a valve chamber connection system, a safety recovery system, a safety release system, a high-efficiency replacement system, and a safety monitoring system. By setting up this system, the liquid ammonia pipeline medium stored during maintenance conditions can be effectively recovered and emptied, ensuring that no toxic gases directly enter the atmosphere during the recovery and release process, achieving the goal of efficient liquid ammonia recovery and safe discharge.

[0033] Specifically, the valve chamber connection system includes the existing upstream pipeline 1, the first main line shut-off valve 2, the midstream pipeline 3, the second main line shut-off valve 4, the downstream pipeline 5, the upstream pressure transmitter of the first main line shut-off valve 6, the upstream temperature transmitter of the first main line shut-off valve 7, the downstream pressure transmitter of the first main line shut-off valve 8, the downstream temperature transmitter of the first main line shut-off valve 9, the upstream branch pipe of the first main line shut-off valve 10, the downstream branch pipe of the first main line shut-off valve 11, the upstream branch pipe shut-off valve of the first main line shut-off valve 12, the downstream branch pipe shut-off valve of the first main line shut-off valve 13, and the upstream... Pressure transmitter 14, upstream temperature transmitter 15 of the second main line shut-off valve, downstream pressure transmitter 16 of the second main line shut-off valve, downstream temperature transmitter 17 of the second main line shut-off valve, upstream branch pipe 18 of the second main line shut-off valve, downstream branch pipe 19 of the second main line shut-off valve, upstream branch pipe shut-off valve 20 of the second main line shut-off valve, and downstream branch pipe shut-off valve 21 of the second main line shut-off valve, etc., are used to provide channels and main line shut-off functions for the main line transportation of liquid ammonia pipelines. At the same time, by setting up upstream and downstream branch pipes of the shut-off valves, the basic functions of recovery and discharge of intermediate pipelines between adjacent shut-off valves are guaranteed.

[0034] It should be noted that this example only illustrates the basic configuration of adjacent shut-off valves. Actual engineering projects may involve multiple shut-off valves; this example can be used as a reference for functional settings. Furthermore, the valve chamber connection system is a basic configuration for pipeline transportation projects and is not an innovative feature of this embodiment.

[0035] In the system shown, upstream pipeline 1, first main line shut-off valve 2, midstream pipeline 3, second main line shut-off valve 4, and downstream pipeline 5 are fixed configurations of the liquid ammonia transportation pipeline, used to provide main line transportation channels and shut-off functions. All are made of carbon steel, with a preferred impact toughness test temperature of -35℃. In actual engineering, there are multiple main line shut-off valves and multiple sections of main line pipelines. Upstream pressure transmitter 6 and upstream temperature transmitter 7 of the first main line shut-off valve are installed on upstream branch pipe 10 of the first main line shut-off valve, both made of carbon steel, used to provide pressure and temperature parameters for a portion of the area upstream of the first main line shut-off valve 2. Downstream pressure transmitter 8 and downstream temperature transmitter 5 of the first main line shut-off valve... A downstream temperature transmitter 9 is installed on the downstream branch pipe 11 of the first main line shut-off valve 2 to provide pressure and temperature parameters for a portion of the area downstream of the first main line shut-off valve 2. An upstream branch pipe 10 of the first main line shut-off valve 2, made of carbon steel, is installed upstream of the first main line shut-off valve 2 to provide a channel for recovery, venting, or replacement of the upstream pipe section of the first main line shut-off valve 2. A downstream branch pipe 11 of the first main line shut-off valve 2, also made of carbon steel, is installed downstream of the first main line shut-off valve 2 to provide a channel for recovery, venting, or replacement of the downstream pipe section of the first main line shut-off valve 2. Upstream branch pipe shut-off valve 12 and downstream branch pipe shut-off valve 13 are respectively installed on the upstream branch pipe 10 and downstream branch pipe 13 of the first main line shut-off valve. At the end of the downstream branch pipe 11 of the main line shut-off valve, there is a manually operated ball valve, made of carbon steel, normally closed, used to connect to a portable high-efficiency replacement system, safety recovery system, or safety relief system; the upstream pressure transmitter 14 and the upstream temperature transmitter 15 of the second main line shut-off valve are installed on the upstream branch pipe 18 of the second main line shut-off valve, both made of carbon steel, used to provide pressure and temperature parameters for a portion of the upstream area of ​​the second main line shut-off valve 4; the downstream pressure transmitter 16 and the downstream temperature transmitter 17 of the second main line shut-off valve are installed on the downstream branch pipe 19 of the second main line shut-off valve, used to provide pressure and temperature parameters for a portion of the downstream area of ​​the second main line shut-off valve 4; the second main line shut-off valve... The upstream branch pipe 18 of the shut-off valve is located upstream of the second main line shut-off valve 4, and is made of carbon steel. It is used to provide a channel for recovery, discharge, or replacement of the upstream pipe section of the second main line shut-off valve 4. The downstream branch pipe 19 of the second main line shut-off valve is located downstream of the second main line shut-off valve 4, and is made of carbon steel. It is used to provide a channel for recovery, discharge, or replacement of the downstream pipe section of the second main line shut-off valve 4. The upstream branch shut-off valve 20 and the downstream branch shut-off valve 21 of the second main line shut-off valve are respectively located at the ends of the upstream branch pipe 18 and the downstream branch pipe 19 of the second main line shut-off valve. They are manual ball valves, made of carbon steel, normally closed, and are used to connect to a portable high-efficiency replacement system, a safe recovery system, or a safe discharge system.

[0036] The safe recovery system includes a recovery branch pipe 31, a recovery regulating valve 32, a refrigeration module 33, a recovery first shut-off valve 34, a recovery storage tank 35, a recovery second shut-off valve 36, a liquid phase pump 37, a recovery branch pipe temperature transmitter 38, and a recovery branch pipe pressure transmitter 39, etc., and is used for flow regulation, pressure regulation, reliquefaction, pressurization, and storage of liquid ammonia in the midstream pipeline 3 during the recovery process, and to recover liquid ammonia (or ammonia gas) within the pressure value range.

[0037] The safe recovery system consists of a recovery branch pipe 31, a recovery regulating valve 32, a refrigeration module 33, a recovery first shut-off valve 34, a recovery storage tank 35, a recovery second shut-off valve 36, a liquid phase pump 37, a recovery branch pipe temperature transmitter 38, and a recovery branch pipe pressure transmitter 39. It is used for flow regulation, pressure regulation, reliquefaction, pressurization, and storage of liquid ammonia in the midstream pipeline 3 during the recovery process, and for recovering liquid ammonia (or ammonia gas) with pressure value.

[0038] Specifically, in the system shown, the recovery branch pipe 31 is located downstream of the valve chamber bypass branch pipe, preferably made of carbon steel, and provides a flow channel between the main line and the recovery storage tank 35; the recovery regulating valve 32 is located on the recovery branch pipe 31, preferably an electrically controlled valve, and is used to regulate the recovery flow rate of liquid ammonia in the midstream pipeline 3, and is made of carbon steel; the refrigeration module 33 is a small refrigeration skid used for the liquefaction of liquid ammonia after pressure regulation, including refrigerant, circulating compressor, heat exchanger, throttle valve, etc., the refrigerant is preferably propane, and the temperature of liquid ammonia after heat exchange is controlled at -35℃; the recovery first shut-off valve 34 is located downstream of the refrigeration module 33, an electrically driven ball valve, which opens in conjunction with the recovery regulating valve 32 when it is opened, and closes when the liquid phase pump 37 is started; the recovery storage tank 35 is a horizontal storage tank with an overpressure safety valve, and is made of carbon steel. The system is used to receive liquid ammonia after secondary cooling, with a maximum operating pressure of 1.4 MPa. The tank is replaced when the internal pressure exceeds 1.2 MPa. A second shut-off valve 36, an electric ball valve made of carbon steel, is located in the bypass of the recovery regulating valve 32. It closes when the recovery regulating valve 32 is open and opens when the medium pressure in the midstream pipeline 3 is lower than the pressure in the recovery storage tank 35. A liquid phase pump 37, preferably a canned pump, is located in the bypass of the first shut-off valve 34. It opens when the medium pressure in the midstream pipeline 3 is lower than the pressure in the recovery storage tank 35 to provide secondary pressurization to the subcooled ammonia liquid at the outlet of the refrigeration module 33 before sending it into the recovery storage tank 35. A recovery branch pressure transmitter 39 is located at the inlet of the recovery storage tank 35 to monitor the internal pressure of the recovery storage tank 35 in real time. Furthermore, this system is a mobile skid-mounted unit, which can be moved to the vicinity of the valve chamber and connected when medium recovery is required.

[0039] The safety relief system, consisting of a relief branch pipe 41, a relief regulating valve 42, a venting separator 43, a venting flare 44, a combustion-supporting system 45, and a relief branch temperature transmitter 46, is used to release and burn residual low-pressure ammonia gas from the main pipeline that does not have pressure value. This system requires a high-efficiency replacement system to work in conjunction with it.

[0040] Specifically, in the system shown, the vent branch pipe 41 is located downstream of the valve chamber bypass branch pipe, preferably made of carbon steel, and is used to provide a flow channel between the main line and the vent flare 44; the vent regulating valve 42 is located at the beginning of the vent branch pipe 41, is a manual regulating valve, is made of carbon steel, and is used to control the flow rate of the medium discharged into the vent flare 44; the vent separator 43 is located downstream of the vent branch pipe 41, is made of carbon steel, is a horizontal tank, and is used to temporarily separate the vented medium into gas and liquid phases, provide conditions for the liquid phase medium to evaporate, and prevent the gas-liquid two-phase ammonia from entering the vent flare 44; the vent flare 44 is located downstream of the vent separator 43 and is used to ignite and burn the vented ammonia, ammonia-natural gas mixture, and natural gas; the combustion-supporting system 45 is located near the vent flare 44 and is used to provide combustion-supporting gas to the flare outlet of the vent flare 44 and preferentially ignite it, thereby improving the combustion effect of the ammonia discharged from the vent flare 44. This system is a mobile skid-mounted unit that can be moved to the vicinity of the valve chamber and connected when media venting is required.

[0041] The liquid nitrogen storage tank 51, liquid nitrogen booster pump 52, vaporization heat exchanger 53, nitrogen regulating valve 54, CNG storage tank 55, CNG regulating valve 56, CNG heat exchanger 57, replacement shut-off valve 58, and replacement temperature transmitter 59 constitute a high-efficiency replacement system, which is used to replace the gas in the midstream pipeline 3 that is about to be emptied. First, CNG (natural gas) replaces ammonia, and both enter the safety release system for combustion treatment. Then, nitrogen replaces natural gas, and the gas enters the safety release system for venting treatment.

[0042] Specifically, in the system shown, the liquid nitrogen storage tank 51 is a commercial liquid nitrogen storage tank used to store nitrogen to be injected into the midstream pipeline 3; the liquid nitrogen booster pump 52 is preferably a shielded pump, located downstream of the liquid nitrogen storage tank 51, used to pressurize the liquid nitrogen injected into the midstream pipeline 3, with a discharge pressure preferably of 0.2 MPa, and is made of stainless steel; the vaporization heat exchanger 53 is located downstream of the liquid nitrogen booster pump 52, used to vaporize the pressurized liquid nitrogen, with a vaporization temperature preferably above -20℃; the nitrogen regulating valve 54 is a manual control valve, located downstream of the vaporization heat exchanger 53, used to control the nitrogen injection flow rate; the liquid nitrogen storage tank 51, liquid nitrogen booster pump 52, vaporization heat exchanger 53, and nitrogen regulating valve 54 are combined to form a nitrogen replacement unit, used to replace and displace the natural gas in the midstream pipeline 3; C NG storage tank 55 is a commercial CNG storage tank used to store compressed natural gas and provide a medium for replacing residual ammonia in midstream pipeline 3. CNG regulating valve 56 is a manual regulating valve made of carbon steel, used to regulate the natural gas discharge from CNG storage tank 55. CNG heat exchanger 57 is an air-bath heat exchanger used to regulate the temperature of the natural gas after pressure regulation, preferably above -20℃. CNG storage tank 55, CNG regulating valve 56, and CNG heat exchanger 57 together form a natural gas replacement unit used to replace and displace residual ammonia in midstream pipeline 3. Replacement shut-off valve 58 is a manual shut-off valve used to connect or close the high-efficiency replacement system. Replacement temperature transmitter 59 is located upstream of replacement shut-off valve 58 and used to monitor the temperature of nitrogen or natural gas after pressure regulation in real time. This system is a mobile skid-mounted unit, which is moved to the vicinity of the valve chamber and connected when medium replacement is required.

[0043] The safety monitoring system consists of a pressure transmitter, a temperature transmitter, and a sampling and detection shut-off valve 61 installed in the pipeline valve chamber. It is used to detect the pipeline temperature, pipeline pressure, and displacement effect during the liquid ammonia pipeline discharge process.

[0044] The working principle of the liquid ammonia pipeline safety recovery and release system in this embodiment is as follows:

[0045] (1) Under normal operating conditions, liquid ammonia is generally transported in the liquid phase. After the pipeline needs to be cut off and repaired, the liquid ammonia in the section to be repaired needs to be discharged. Furthermore, in order to reduce the mass of the medium stored in the pipeline, considering that liquid ammonia has a certain compressibility, it is preferable to reduce the overall pipeline operating pressure before stopping the transport, so as to reduce the mass of the medium stored in the pipeline.

[0046] (2) Since liquid ammonia is toxic and is a good chemical raw material, from the perspective of environmental protection and economy, it is preferable to recycle liquid ammonia. At the same time, since liquid ammonia vaporizes after depressurization, the liquid ammonia in the main line will experience pressure reduction and vaporization simultaneously during the release process. Therefore, this invention, in combination with the economic considerations of liquid ammonia recycling, proposes the division of valuable pressure range and non-value pressure range. Liquid ammonia in the valuable pressure range is recycled and treated, while ammonia in the non-value pressure range is treated before being discharged.

[0047] (3) In order to reduce the investment in valve chamber equipment, the present invention adopts a skid-mounted configuration for the safety recovery system, safety release system and high-efficiency replacement system. That is, the valve chamber only has a bypass interface reserved, and the skid-mounted system is connected in advance when relevant operations are required.

[0048] (4) Liquid ammonia is recovered using a recovery storage tank. The recovery process is considered in two modes: Mode 1: When the pressure of the medium in the main pipeline is greater than the pressure of the recovery storage tank, a non-pressurized liquefaction mode is used for injection. The temperature of the liquefied medium is -35℃ to ensure that the liquid ammonia is completely liquefied before entering the recovery storage tank. Mode 2: When the pressure of the medium in the main pipeline is less than the pressure of the recovery storage tank, a liquefied and then pressurized mode is used for injection. The temperature of the liquefied medium is -35℃ to ensure that the liquid ammonia is completely liquefied before entering the recovery storage tank. A small refrigeration system is used for liquefaction, with propane being the preferred refrigerant to provide subcooling and ensure that the cooled liquid ammonia is completely liquefied. A safety valve is installed on the recovery storage tank. When the pressure inside the tank exceeds the set pressure of the safety valve, the released ammonia gas is stored in a scattered gas recovery tank. Thus, most of the liquid ammonia in the main pipeline is recovered.

[0049] (5) Residual ammonia in the main pipeline is treated by safe combustion followed by venting to prevent direct release of ammonia into the atmosphere. The key issue is the displacement of residual ammonia. This invention adopts a two-stage displacement mode. First, compressed natural gas is introduced into the pipeline after adjustment. The purpose is to displace and replace the ammonia. Since natural gas and ammonia can be ignited by the flare at any mixing ratio, the combustibility of the natural gas-ammonia mixture is guaranteed, which makes up for the problem that the flare cannot be ignited when nitrogen directly replaces nitrogen. After the ammonia in the pipeline is displaced, nitrogen is used to displace and replace the natural gas, ultimately achieving gas replacement in the main pipeline. A combustion-supporting unit is set up near the flare to achieve the effect of a "constant light" at the flare outlet by actively supplying fuel, ensuring efficient combustion of ammonia.

[0050] (6) In addition, during the release of liquid ammonia in the midstream trunk line, the medium inside the pipeline will undergo continuous pressure reduction, temperature reduction and phase change. Therefore, based on the atmospheric boiling point of liquid ammonia of -33℃, the low temperature impact requirement of carbon steel for pipelines is proposed to be -35℃, which avoids the requirement of conventional carbon steel pipelines to control the release temperature at -20℃ and can greatly improve the release speed.

[0051] Example 2

[0052] Based on the working principle of the liquid ammonia pipeline safe recovery and release system in the aforementioned embodiments, this embodiment proposes a method for the safe recovery and release of liquid ammonia pipelines, including the following main contents:

[0053] Step 1: During normal transport, the operating pressure of the liquid ammonia pipeline is controlled above 1.5 MPa.g, and the transport temperature is close to the soil temperature. Under planned shutdown and maintenance conditions, the upstream export pumps, intermediate booster pumps, and all main line shut-off valves are shut down in an orderly manner, achieving a safe shutdown of the main pipeline. Furthermore, to improve the operational efficiency of subsequent steps, before the planned shutdown, it is preferable to reduce the pipeline operating pressure to approximately 1.2 MPa.g to reduce the quality of the medium within the pipeline section under maintenance.

[0054] Step Two: Taking this invention as an example, after the pipeline is shut down, since the pipeline medium between at least two shut-off valves needs to be emptied during upstream trunk line maintenance, and the emptying volume is relatively large, and considering the economic efficiency of ammonia and the environmental pollution caused by direct emissions, it is considered to recover most of the remaining medium in the pipeline. Therefore, a high-efficiency replacement system is connected to the downstream branch shut-off valve 13 (keeping closed) of the first trunk line shut-off valve in the upstream valve chamber; a safety recovery system and a safety relief system are connected to the downstream branch shut-off valve 20 (keeping closed) of the second trunk line shut-off valve in the downstream valve chamber. Further, the safety recovery system is replaced, preferably with nitrogen or ethane as the replacement medium, maintaining a slight positive pressure.

[0055] Step 3: Prioritize the recovery of liquid ammonia from the midstream pipeline 3. Specifically, open the upstream branch shut-off valve 20 of the second main line shut-off valve, the refrigeration module 33, and the recovery first shut-off valve 34, while keeping the recovery second shut-off valve 36 and the liquid phase pump 37 closed, and keeping the safety relief system closed. Slowly open the recovery regulating valve 32. The throttled and vaporized ammonia gas is liquefied after being regulated by the refrigeration module 33, and then discharged into the recovery storage tank 35. The outlet temperature of the refrigeration module 33 is controlled at -34℃. When the pressure in the recovery storage tank 35 exceeds 1.2MPa, it is replaced, and a spare recovery storage tank is installed and connected. When the downstream pressure of the recovery regulating valve 32 is higher than the medium pressure in the midstream main line (the detection value of the pressure transmitter 14 upstream of the second main line shut-off valve), close the recovery regulating valve 32, open the recovery second shut-off valve 36 and the liquid phase pump 37, and pressurize the liquefied liquid ammonia through the liquid phase pump 37 and send it into the recovery storage tank 35. In addition, during the recovery and injection process, the overpressure safety valve of the recovery storage tank 35 can discharge the liquid ammonia that has been volatilized due to environmental factors, and temporarily store it in the matching scattered gas recovery tank to avoid direct discharge into the atmosphere.

[0056] Step 4: When the medium pressure in the downstream pipeline 3 is lower than 0.15 MPa.g, stop the liquid ammonia recovery operation in the main pipeline, and preferably treat the residual ammonia gas with safe combustion. At this time, shut down the safety recovery system.

[0057] Step 5: Safely combust the residual ammonia. Specifically, first, activate the high-efficiency replacement system, i.e., open the CNG regulating valve 56, CNG heat exchanger 57, and replacement shut-off valve 58, while keeping the liquid nitrogen booster pump 52, vaporization heat exchanger 53, and nitrogen regulating valve 54 closed. Use regulated natural gas to displace and replace the residual ammonia in the midstream pipeline 3. The displaced gas then enters the safety relief system for combustion. Subsequently, activate the safety relief system, i.e., open the relief regulating valve 42 and the combustion-supporting system 45, controlling the maximum relief flow rate through the relief regulating valve 42. During the venting process, the volume of the vented medium is measured. When the measured vented volume reaches 120% of the actual gas (ammonia) volume stored in the midstream main pipeline, the sampling and detection shut-off valve 61 is used to sample the mixed medium until the ammonia volume fraction in the mixed medium (natural gas and ammonia mixture) is less than 0.5%, at which point the natural gas displacement operation is stopped. Subsequently, the CNG regulating valve 56 and CNG heat exchanger 57 are closed, and the liquid nitrogen booster pump 52, vaporization heat exchanger 53, and nitrogen regulating valve 54 are turned on to use nitrogen to displace and replace the residual natural gas in the midstream pipeline 3. The sampling and detection shut-off valve 61 is used to sample the mixed medium until the natural gas volume fraction in the mixed medium (natural gas and nitrogen mixture) is less than 0.5%, at which point the nitrogen displacement operation is stopped. Thus, the efficient recovery of liquid ammonia and the safe discharge of residual medium inside the midstream pipeline 3 are achieved.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A safe recovery and release system for liquid ammonia pipelines, the system comprising a main pipeline, the main pipeline being divided into an upstream pipeline, a midstream pipeline, and a downstream pipeline by a first main pipeline shut-off valve and a second main pipeline shut-off valve, characterized in that, The system includes: an upstream branch pipe for the first main line shut-off valve and a downstream branch pipe for the first main line shut-off valve; an upstream branch pipe for the second main line shut-off valve and a downstream branch pipe for the second main line shut-off valve; and the system further includes: A safe recovery system, which is connected to the upstream branch of the second main line shut-off valve, is used for flow regulation, pressure regulation, reliquefaction, pressurization, or storage of liquid ammonia in the midstream pipeline during the recovery process. A safety relief system is connected to a branch pipe downstream of the second main line shut-off valve, used to release and burn residual ammonia that has not been recovered by the safety recovery system; A high-efficiency replacement system is connected to the downstream branch of the first main line shut-off valve and is used to drive and replace the gas in the safely recovered midstream pipeline by injecting natural gas or nitrogen.

2. The liquid ammonia pipeline safety recovery and release system as described in claim 1, characterized in that, The safe recycling system includes a recycling branch pipe, a refrigeration module, and a recycling storage tank. The upstream branch pipe of the second main line shut-off valve is connected to the inlet end of the recycling branch pipe, the outlet end of the recycling branch pipe is connected to the inlet of the refrigeration module through a recycling regulating valve, and the outlet of the refrigeration module is connected to the recycling storage tank through a recycling first shut-off valve.

3. The liquid ammonia pipeline safe recovery and release system as described in claim 2, characterized in that, The safe recovery system also includes a second recovery shut-off valve and a liquid phase pump. The second recovery shut-off valve is connected in parallel across the two ends of the recovery regulating valve, and the liquid phase pump is connected in parallel across the two ends of the first recovery shut-off valve.

4. The liquid ammonia pipeline safety recovery and release system as described in claim 1, characterized in that, The safety relief system includes a relief branch pipe, a venting separator, and a venting flare. The downstream branch pipe of the second main line shut-off valve is connected to the inlet end of the relief branch pipe, the outlet end of the relief branch pipe is connected to the inlet of the venting separator through a relief regulating valve, and the outlet of the venting separator is connected to the venting flare.

5. The liquid ammonia pipeline safety recovery and release system as described in claim 4, characterized in that, The flare torch is also equipped with a combustion-supporting system, which is used to provide combustion-supporting gas to the torch nozzle.

6. The liquid ammonia pipeline safety recovery and release system as described in claim 1, characterized in that, The high-efficiency replacement system includes a liquid nitrogen storage tank, a natural gas storage tank, a liquid nitrogen booster pump, a vaporization heat exchanger, and a natural gas heat exchanger. The downstream branch pipe shut-off valve of the first main line shut-off valve is connected to the outlet end of the vaporization heat exchanger and the outlet end of the natural gas heat exchanger respectively through the replacement shut-off valve. The natural gas storage tank is connected to the inlet end of the natural gas heat exchanger through a natural gas regulating valve. The liquid nitrogen storage tank is connected to the inlet end of the vaporization heat exchanger through a liquid nitrogen booster pump.

7. The liquid ammonia pipeline safety recovery and release system as described in claim 4, characterized in that, The safe recovery and release system also includes a sampling and detection shut-off valve located downstream of the release regulating valve.

8. The liquid ammonia pipeline safety recovery and release system as described in claim 1, characterized in that, The safe recovery system, safe release system, and efficient replacement system are prefabricated, mobile skid-mounted systems.

9. A method for the safe recovery and release of liquid ammonia from a pipeline, characterized in that, The method is implemented based on the liquid ammonia pipeline safety recovery and release system according to any one of claims 1-8, and the method includes: After the pipeline is shut down, the safety relief system and the efficient replacement system are kept closed, and the liquid ammonia in the midstream pipeline is recovered through the safety recovery system. After the recovery is complete, the safety recovery system is shut down, and the high-efficiency replacement system and safety release system are activated to drive and replace the residual ammonia in the midstream pipeline, thus completing the release of the participating medium in the liquid ammonia pipeline.

10. The method for safe recovery and release of liquid ammonia in a pipeline as described in claim 9, characterized in that, The displacement and replacement of residual ammonia in the midstream pipeline specifically includes: Compressed natural gas is injected to displace and mix with the residual ammonia in the midstream pipeline. The mixed gas then enters the safety relief system for combustion treatment until the ammonia volume fraction in the mixed gas entering the safety relief system is less than the preset ammonia threshold. Nitrogen is then injected to displace and replace the residual natural gas in the midstream pipeline until the natural gas volume fraction in the mixed gas entering the safety relief system is less than the preset natural gas threshold.

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