CN110671605A

CN110671605A - System and method for safely emptying valve chamber of hydrogen-mixed natural gas pipeline

Info

Publication number: CN110671605A
Application number: CN201910931725.5A
Authority: CN
Inventors: 陈俊文; 汤晓勇; 郭成华; 谌贵宇; 郭艳林; 李天雷; 杨帆; 施岱艳; 陈静; 李科
Original assignee: China Petroleum Engineering and Construction Corp
Current assignee: China National Petroleum Corp; China Petroleum Engineering and Construction Corp; China Petroleum Engineering Co Ltd
Priority date: 2019-09-29
Filing date: 2019-09-29
Publication date: 2020-01-10

Abstract

The invention discloses a system and a method for safely emptying a hydrogen-mixed natural gas pipeline valve chamber. According to the invention, the temporary air replacement system is arranged to exhaust air in the emptying pipeline during initial emptying, so that the safe operation of the initial emptying stage is guaranteed essentially; the emptying rate compensation system is adopted to prevent the problem that the pressure of the emptying pipe is reduced due to the fact that the medium flow velocity is too small because the pressure in the pipe is reduced in the middle and later periods of emptying; meanwhile, the flame arrester is arranged to further improve the anti-backfire performance of the system. By the aid of the method, the valve chamber of the hydrogen-mixed natural gas pipeline is safely emptied. On one hand, the invention omits a facility for isolating air from the emptying system during the operation period, and on the other hand, the safety problem of the mixed hydrogen natural gas in the valve chamber discharge is avoided by setting strict replacement and compensation emptying functions.

Description

System and method for safely emptying valve chamber of hydrogen-mixed natural gas pipeline

Technical Field

The invention relates to a system and a method for safely emptying a hydrogen-mixed natural gas pipeline valve chamber.

Background

Hydrogen is one of the important development directions of new energy, compared with the traditional fossil fuel, the hydrogen has the remarkable advantages of high heat value, no environmental pollution of combustion products, wide sources and reproducibility, is called as future clean energy, and becomes a new way for solving increasingly severe energy and environmental problems in the future for human beings. The transportation of hydrogen is an important link for hydrogen energy utilization, and the adoption of a reliable pipeline transportation mode for connecting a hydrogen gas source with a target user is a key for optimizing energy consumption and promoting hydrogen energy utilization. Compared with a high-purity hydrogen pipeline (the hydrogen content is higher than 99%) which is directly paved on a natural gas main pipeline (used for long-distance output of a natural gas main pipeline after mixing) or a user, the hydrogen-mixed natural gas pipeline has the characteristics of flexible resource allocation and high pipeline utilization rate, an upstream hydrogen product can be mixed into an adjacent natural gas branch pipeline to reach the user or a natural gas main pipeline mixing station, remote transmission in the same pipe is realized, or methane hydrogen generated by ethane cracking is transmitted to the user or the natural gas main pipeline mixing station, and the long-distance relay transportation and utilization path of the hydrogen resource which is hot in the future becomes. However, hydrogen is prone to leakage and the explosion limit is wide (4% to 75%); meanwhile, spontaneous combustion (combustion) is likely to occur after the hydrogen is discharged, and the combustion mechanism mainly comprises diffusion spontaneous combustion, friction spontaneous combustion and ignition combustion, and the hydrogen is extremely easy to develop into the internal detonation or explosion of the pipeline. Further, the characteristics of the hydrogen-natural gas system are more complicated after blending natural gas in different proportions.

The emptying system of the mixed hydrogen natural gas conveying pipeline system is one of the cores of the safety guarantee system and is used for discharging media in the pipeline under the working conditions of overpressure, maintenance and the like. Compared with stations which can depend on large-scale relief facilities, such as the first station and the last station of the pipeline, the safety configuration problem of the emptying system of the valve chambers along the pipeline needs to comprehensively consider the problems of feasibility, safety, economy and the like. For a hydrogen-mixed natural gas system, in the initial discharge stage, diffusion spontaneous combustion without an ignition source caused by the fact that a large amount of media enter an emptying pipeline can occur, friction spontaneous combustion caused by severe friction between the media and the pipeline can also occur, and the media can be ignited by the outside to cause combustion near a pipe orifice when leaving an emptying vertical pipe; when the closed pipeline is burnt, deflagration or explosion is easily induced. At the same time, due to the combustion characteristics of the hydrogen, a flashback may occur in the vent line which is stronger than the natural gas bleed. Therefore, for a large station with better emptying depending conditions, the mixed hydrogen natural gas can be safely discharged through a torch system, but for the emptying system of the mixed hydrogen natural gas pipeline valve chamber, due to the relatively poorer depending conditions, safety and economic configuration research of the emptying system should be carried out, emptying safety is guaranteed, so that the blank reported in the prior art is made up, and the technical progress in the field is promoted.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a system and a method for safely emptying a valve chamber of a mixed hydrogen natural gas pipeline, wherein a temporary air replacement system is arranged to exhaust air in an emptying pipeline during initial emptying, so that the safe operation in an initial emptying stage is guaranteed essentially; the emptying rate compensation system is adopted to prevent the problem that the pressure of the emptying pipe is reduced due to the fact that the medium flow velocity is too small because the pressure in the pipe is reduced in the middle and later periods of emptying; meanwhile, the flame arrester is arranged to further improve the anti-backfire performance of the system. By the aid of the method, the valve chamber of the hydrogen-mixed natural gas pipeline is safely emptied.

The technical scheme adopted by the invention is as follows: the utility model provides a mix hydrogen natural gas line valve room safety unloading system, includes that the trunk cuts off system, unloading and unloading compensating system and air replacement system, wherein:

the main line cut-off system comprises a main line pipeline and a cut-off ball valve arranged on the main line pipeline, a main line bypass is arranged at the upstream and downstream of the cut-off ball valve, bypass cut-off valves and pressure transmitters are arranged at the positions, close to the main line, of the two ends of the main line bypass, and the pressure transmitter is arranged on the main line bypass between the two bypass cut-off valves;

the emptying and emptying compensation system comprises a bypass external pipeline, a high-pressure branch pipe, an emptying junction, an emptying header pipe and an emptying torch which are sequentially connected with a main line bypass, wherein emptying block valves and flow-limiting pore plates or regulating valves are arranged on two branch pipelines of the high-pressure branch pipe;

the air replacement system comprises two replacement air injection branch pipes arranged on a main line bypass near the downstream of two bypass block valves, three replacement exhaust branch pipes arranged at the starting end and the tail end of a bypass external pipeline and an emptying header pipe, block valves arranged on the two replacement air injection branch pipes, and block valves and check valves arranged on the three replacement exhaust branch pipes.

The invention also provides a safe emptying method for the hydrogen-mixed natural gas pipeline valve chamber, which comprises the following steps:

step one, when a main line of a hydrogen-mixed natural gas pipeline needs to be overhauled, remotely closing main line cut-off ball valves adjacent to valve chambers at the upstream and downstream of the main line; or when the main line of the hydrogen-mixed natural gas pipeline leaks, the system automatically closes the main line cut-off ball valves close to the valve chamber at the upstream and the downstream of the main line where the leakage position is located; meanwhile, keeping both the two bypass block valves closed;

when the mixed hydrogen natural gas in an upstream trunk or a downstream trunk needs to be discharged through the valve chamber, a No. 1 movable nitrogen supply device is connected with a joint of a bypass gas injection branch pipe close to one side of the downstream or the upstream, the emptying cut-off valves on two branch pipelines of the emptying and emptying compensation system are opened, the four full cut-off valves arranged on a displacement exhaust branch pipe and a flare cushion gas injection branch pipe are kept closed, nitrogen is continuously injected for at least 10 minutes, and the air in the emptying pipeline is pushed to an emptying flare; simultaneously, three cut-off valves on the displacement exhaust branch pipe are respectively opened at intervals, and each cut-off valve is kept opened for at least 0.5 minute to ensure that air in the emptying pipeline is exhausted nearby; then closing three cut-off valves on the replacement exhaust branch pipe, continuously keeping nitrogen injection, simultaneously connecting an interface of the flare cushion gas injection branch pipe by using a No. 2 movable nitrogen supply device, opening the cut-off valves on the flare cushion gas injection branch pipe, introducing nitrogen, and pushing the air in the flare cushion region out of a flare outlet; finally, closing the emptying block valve on one branch pipeline;

step three, opening a bypass block valve at one side of a pipeline to be discharged, closing the No. 1 movable nitrogen supply device, feeding the mixed hydrogen natural gas into a venting system, limiting and reducing the pressure through a flow-limiting orifice plate or a regulating valve on one branch pipeline, and feeding the mixed hydrogen natural gas into a venting pipeline; closing the No. 2 movable nitrogen supply device; continuously igniting the torch head until the hydrogen-mixed natural gas at the outlet of the torch is discharged and continuously burning;

and step four, after the pressure of the upstream pipeline is reduced to 50%, opening a stop valve on the other branch pipeline until the discharge is finished.

Compared with the prior art, the invention has the following positive effects:

the invention provides a set of reasonable safe emptying system for the hydrogen-mixed natural gas valve chamber according to the combustion characteristics of hydrogen in the hydrogen-mixed natural gas and based on the combustion mechanism of the hydrogen. According to the system, on one hand, a facility for setting air to enter in the operation period isolation emptying system is omitted, and on the other hand, the safety problem in the discharge of the mixed hydrogen natural gas is avoided by setting strict replacement and compensation emptying functions. The system is characterized in that:

(1) science of setup

The invention adopts careful relief safety measures for relief of the hydrogen-mixed natural gas pipeline valve chamber based on the basic principle of hydrogen gas emptying and spontaneous combustion. Air in the emptying system is thoroughly isolated by arranging emptying pipeline replacement and torch cushion gas replacement; by arranging 2 emptying branch pipes, the instantaneous discharge rate in the emptying process is further ensured, and the positive pressure effect of the emptying system is kept; by providing a flare ignition system, bleed diffusion and air ingestion are prevented by the combustion of the medium. The effect of safe emptying of the hydrogen-mixed natural gas pipeline valve chamber is achieved by combining measures in various aspects.

(2) Good economical efficiency

The invention avoids the method of setting a power seal for long-term operation to isolate the air in the emptying system, and selects a more economic replacement mode before discharge by combining the objective conditions of the valve chamber.

(3) Advanced in concept

At present, a hydrogen-mixed natural gas pipeline is not built in a large range in China, related safety experience is few, and in view of the fact that the medium contains hydrogen and the hydrogen proportion is high, a relief result based on the combustion characteristic of the hydrogen needs to be focused on in the relief process, and the thought and the method provided by the invention provide reference and reference for the safe relief of the hydrogen-mixed natural gas pipeline valve chamber.

Drawings

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a hydrogen-mixed natural gas pipeline valve chamber safety venting system of the invention.

Detailed Description

A mixed hydrogen natural gas pipeline valve room safety system of unloading mainly includes: the device comprises a main pipeline 1, a cut-off ball valve 2, a main pipeline bypass 3, a pressure transmitter 4/5/6, a bypass cut-off valve 7/8, a bypass external pipeline 9, a high-pressure branch pipe 10, a vent cut-off valve 11/13, a flow-limiting orifice plate 12/14, a vent header pipe 15, a vent header pipe 16, a vent torch 17, a displacement gas injection branch pipe 31/32, a displacement gas exhaust branch pipe 33/34/35, a torch cushion gas injection branch pipe 36, a cut-off valve 18/19/20/22/24/26, a check valve 21/23/25, a flow transmitter 27 and a flame arrester 28.

The main line cut-off system such as the main line pipeline 1, the cut-off ball valve 2, the main line bypass 3, the bypass cut-off valve 7/8 and the pressure transmitter 4/5/6 is responsible for instructing the cut-off ball valve to close when a fault occurs at the upstream or downstream of the pipeline or the maintenance is needed, isolating the upstream and the downstream so as to perform partition emptying, and reducing the pressure difference between the upstream and the downstream by using the bypass when the pipeline is restarted. The bypass external pipeline 9, the high-pressure branch pipe 10, the emptying shutoff valve 11/13, the flow-limiting orifice plate 12/14, the emptying manifold 15, the emptying header pipe 16, the emptying torch 17, the flow transmitter 27 and the flame arrester 28 form an emptying and emptying compensation system which is responsible for the safe discharge of the hydrogen-mixed natural gas stored in the trunk line, ensures the discharge speed and maintains the positive pressure of the emptying pipeline; the replacement gas injection branch 31/32, the replacement gas exhaust branch 33/34/35, the torch cushion gas injection branch 36, the shut-off valve 18/19/20/22/24/26, the check valve 21/23/25 and the like form an air replacement system and are responsible for emptying air in the emptying pipeline before discharging.

Through this system, carry out technical guarantee to the safe emptying of mixing hydrogen natural gas line block valve room. Before the valve chamber is emptied, the emptying pipeline is deeply replaced, so that air residue is avoided to the maximum extent, and the emptying safety is guaranteed, so as to replace the scheme of arranging continuous torch sealing; in the emptying process, in view of the problem of emptying tempering caused by the influence of hydrogen in the hydrogen-mixed natural gas, 2 emptying branch pipes are arranged, and the discharge capacity compensation is carried out in the middle and later periods of emptying, so that the problem of insufficient positive pressure in the emptying pipeline caused by low flow velocity in the emptying pipeline due to the reduction of upstream pressure in the middle and later periods of emptying is avoided; the torch with the field ignition function is arranged at the tail end of the emptying pipe, so that the discharged gas is fully combusted, and the hidden danger of diffusion explosion after the discharged gas is discharged is effectively avoided. Through the system, the hydrogen-mixed natural gas pipeline valve chamber can be safely and economically emptied, and the development of related technologies in the field is promoted.

Specifically, in the illustrated system, the main pipeline 1 is a hydrogen-mixed natural gas pipeline, made of carbon steel, connecting an upstream pipeline and a downstream pipeline, in this case represented by a block valve upstream main pipeline and a block valve downstream main pipeline; the cut-off ball valve 2 is arranged on the main pipeline 1, is an electric ball valve or a gas-liquid linkage ball valve and is responsible for executing closing action when an upstream pipeline or a downstream pipeline leaks or needs to be overhauled; the trunk line bypass 3 is made of carbon steel, and two ends of the trunk line bypass are respectively connected with an upstream pipeline and a downstream pipeline of the cutoff ball valve 2 to play a role in communication; the bypass cut-off valve 7/8 is a manual control ball valve, is respectively arranged on the trunk bypass 3 and respectively close to the upstream trunk and the downstream trunk, and plays a role in selectively controlling the trunk emptying pipe section; a pressure transmitter 4 is arranged on the trunk bypass 3 between the bypass block valve 7 and the upstream trunk; a pressure transmitter 6 is arranged on the trunk bypass 3 between the bypass block valve 8 and the upstream trunk; a pressure transmitter 5 is mounted on the main line bypass 3 between the bypass block valve 7 and the bypass block valve 8.

Specifically, in the system, a bypass external pipeline 9 is connected with a main line bypass 3 and enters an inlet channel of a downstream emptying system as a discharge medium during emptying; one end of the high-pressure branch pipe 10 is connected with the bypass external pipeline 9, and the other two ends are symmetrically distributed to form a constant-diameter branch pipe which plays the roles of using 1 branch channel at the initial stage of discharge and using 2 branch channels at the middle and later stages of discharge; the emptying block valve 11 and the flow limiting pore plate 12 are arranged on a single-side branch pipeline, and the emptying block valve 13 and the flow limiting pore plate 14 are arranged on an opposite-side branch pipeline to play roles in controlling a discharge channel and limiting the maximum discharge amount; the branch pipelines are collected in an emptying manifold 15, the emptying manifold 15 is made of stainless steel materials and is connected with a downstream emptying header pipe 16; the emptying header pipe 16 is made of stainless steel and is buried in the ground and laid to the emptying torch 17; the two ends of the emptying main pipe 16 are respectively provided with a pi-shaped bend, so that the effect of relieving medium impact load in the emptying process is achieved; a flame arrester 28 is arranged at the tail end of the emptying header pipe 16 close to the emptying torch 17 and plays a role in preventing backfire; and a flow transmitter 27 is arranged on the emptying header pipe 16 and used for monitoring the medium flow and early warning the blockage of the emptying pipeline in the process of replacing air by nitrogen. Furthermore, the discharge flow control can also be selectively provided with a regulating valve instead of the flow-limiting orifice plate.

Specifically, in the illustrated system, the replacement

gas injection manifolds

31 and 32 are connected to the trunk bypass 3 adjacent downstream of the

bypass block valves

7 and 8, respectively, and

block valves

18 and 19 are installed for connecting to the movable nitrogen supply means during replacement, preferably double block valves are installed to prevent the replacement gas injection manifolds from leaking the venting medium during venting; the replacement

gas injection manifolds

31 and 32 do not operate simultaneously; the displacement

exhaust branch pipes

33, 34 and 35 are respectively arranged at the starting end of the bypass external pipeline 9, the emptying header pipe 16 and the tail end of the emptying header pipe 16 and are used for being opened at intervals in the nitrogen displacement process so as to provide a nearby exhaust channel of potential convoluted air in the pipeline and improve the displacement efficiency; the displacement exhaust branch pipe is respectively provided with a cut-off valve 20/22/24 and a check valve 21/23/25 which play a role in preventing outside air from entering in the evacuation process, and preferably adopts a double cut-off valve to prevent the exhaust branch pipe from leaking emptying media in the discharge process; a flare blanket gas injection branch pipe 36 is connected to the bottom of the flare 17, and a shut-off valve 26 is installed to effect the injection of nitrogen gas therein to discharge the flare bottom blanket air, preferably using a double shut-off valve.

The working principle of the invention is as follows:

when the main line of the hydrogen-mixed natural gas pipeline needs to be overhauled or when the main line of the hydrogen-mixed natural gas pipeline leaks, the cut-off ball valve 2 is controlled to be closed. Before the mixed hydrogen natural gas in an upstream main line or a downstream main line is discharged through the valve chamber, in order to exhaust the air in a discharge pipeline and avoid the diffusion spontaneous combustion in the discharge of the mixed hydrogen natural gas, a movable nitrogen supply device is connected through a replacement gas injection branch pipe, a continuous nitrogen injection discharge system is provided, the air accumulated in the discharge system is replaced, and the air is discharged through an outlet of a discharge torch; in order to prevent residual air in the emptying pipeline, a plurality of displacement exhaust branch pipes are arranged, and are opened at intervals in the nitrogen displacement process, so that residual air nearby is further discharged; in the emptying process, the upstream pressure is gradually reduced along with the emptying, so that a standby emptying branch is arranged to supplement the emptying rate in time in order to avoid that the inside of the emptying pipe is in a low flow rate for a long time during the emptying and the positive pressure in the emptying pipe is insufficient; in order to prevent the emptying system from being exposed to air to form rust inside and further cause friction spontaneous combustion during emptying, the material of the emptying pipeline is selected to be stainless steel; the pi-shaped bend is arranged on the emptying pipeline to improve the flexibility of the emptying pipeline and avoid the problems of overhigh stress level and overlarge deformation of the pipeline caused by medium impact at the initial moment of discharge. Through the means, the hydrogen-mixed natural gas medium is safely discharged in the valve chamber.

The invention also discloses a safe emptying method of the hydrogen-mixed natural gas pipeline valve chamber, which comprises the following main contents:

the method comprises the following steps: when the mixed hydrogen natural gas pipeline trunk line 1 needs to be repaired, remotely closing trunk line cut-off ball valves (ball valves 2) adjacent to the valve chambers upstream and downstream of the section of the trunk line; or when the main line of the hydrogen-mixed natural gas pipeline leaks, the system automatically closes the main line cut-off ball valves (ball valves 2) adjacent to the valve chambers at the upstream and downstream of the main line where the leakage position is located, and keeps the bypass cut-off

valves

7 and 8 closed.

Step two: when the mixed hydrogen natural gas in the upstream trunk line or the downstream trunk line is required to be discharged through the valve chamber, a No. 1 movable nitrogen supply device is connected with a joint of a bypass gas injection branch pipe (if the upstream trunk line is required to be discharged, the joint of the bypass gas injection branch pipe 32 close to the downstream side is connected, if the downstream trunk line is required to be discharged, the joint of the bypass gas injection branch pipe 31 close to the upstream side is connected), the blow-down system cut-off

valves

11 and 13 are opened, the cut-off valve 20/22/24/26 of the bypass gas exhaust branch pipe is kept closed, nitrogen is continuously injected for at least 10 minutes, and the air in the blow-down pipeline is pushed to a blow-down torch; simultaneously, the cut-off valves 20/22/24 of the exhaust branch pipes are respectively opened at intervals and kept open for at least 0.5 minute to ensure that the air in the emptying pipeline is exhausted nearby; closing the stop valve 20/22/24 of the exhaust branch pipe, keeping nitrogen injection, simultaneously connecting the interface of the flare cushion gas injection branch pipe 36 by using a No. 2 movable nitrogen supply device, opening the stop valve 26, introducing nitrogen, and pushing the air in the flare cushion area out of the flare outlet; the 1-way blow down manifold shut-off valve 13 is closed. If the flow transmitter 27 indicates that the flow rate is too low during the nitrogen injection process, it is verified that the vent pipe is blocked and should be overhauled.

Step three: opening a main line

bypass block valve

7 or 8 at one side of a pipeline to be discharged, closing a No. 1 movable nitrogen supply device, enabling the mixed hydrogen natural gas to enter a vent system, limiting and reducing the pressure through a flow-limiting orifice plate 12 of a 1-way vent branch pipe, and then entering a vent pipeline; closing the No. 2 movable nitrogen supply device; and continuously igniting the torch head until the hydrogen-mixed natural gas at the outlet of the torch is discharged for continuous combustion.

Step four: when the pressure of the upstream pipeline is reduced to 50%, the cut-off valve 13 of the other 1 way of emptying branch pipe is opened to increase the discharge amount of the hydrogen-mixed natural gas until the discharge is finished.

Claims

1. The utility model provides a mix hydrogen natural gas line valve room safety unloading system which characterized in that: including trunk cut-off system, unloading and unloading compensating system and air replacement system, wherein:

2. The mixed hydrogen natural gas pipeline valve chamber safety venting system of claim 1, wherein: the main pipeline and the main bypass are made of carbon steel, the cut-off ball valve is an electric ball valve or a gas-liquid linkage ball valve, and the bypass cut-off valve is a manual control ball valve.

3. The mixed hydrogen natural gas pipeline valve chamber safety venting system of claim 1, wherein: the emptying manifold and the emptying header pipe are both made of stainless steel materials, and the emptying header pipe is buried underground and laid to an emptying torch.

4. The mixed hydrogen natural gas pipeline valve chamber safety venting system of claim 1, wherein: and the two ends of the emptying header pipe are respectively provided with a pi-shaped bend.

5. The mixed hydrogen natural gas pipeline valve chamber safety venting system of claim 1, wherein: and a flame arrester is arranged at the tail end of the emptying main pipe close to the emptying torch.

6. The mixed hydrogen natural gas pipeline valve chamber safety venting system of claim 1, wherein: and a flow transmitter is arranged on the emptying header pipe.

7. The mixed hydrogen natural gas pipeline valve chamber safety venting system of claim 1, wherein: the bottom of the emptying torch is connected with a torch cushion gas injection branch pipe, and a cut-off valve is arranged on the torch cushion gas injection branch pipe.

8. The mixed hydrogen natural gas pipeline valve chamber safety venting system of claim 7, wherein: the shut-off valve of the air displacement system is a double shut-off valve.

9. A safe emptying method for a hydrogen-mixed natural gas pipeline valve chamber is characterized by comprising the following steps: the method comprises the following steps:

and step four, after the pressure of the upstream pipeline is reduced to 50%, opening a stop valve on the other branch pipeline, and increasing the discharge rate until the discharge is finished.

10. The method for safely venting a hydrogen-mixed natural gas pipeline valve chamber according to claim 9, wherein: in the nitrogen injection process, when the flow transmitter arranged on the emptying header pipe displays that the flow is too low, the emptying pipeline is overhauled to remove blockage.