Natural gas dehydration tail gas methane recovery system and method

Abstract

The invention relates to the technical field of tail gas treatment, and discloses a natural gas dehydration tail gas methane recovery method which comprises the following steps: firstly introducing tail gas into a heat exchanger in a sealing manner for cooling, condensing water vapor into liquid water, then entering a gas-liquid separator for gas-liquid separation, and introducing separated gas into a buffer tank; gas in a buffer tank is compressed, after the pressure of the buffer tank reaches 30-60 kPa, the pressurized gas is fed into a fuel gas system to be used in a plant / station, and the methane gas in the dehydrated tail gas of the natural gas is recycled in combination with a recycling system.

Description

Technical Field

[0001] The invention relates to the technical field of tail gas treatment, and in particular to a system and method for recovering methane from tail gas of natural gas dehydration. Background Art

[0002] The natural gas collected from the gas field contains various harmful impurities such as hydrogen sulfide, carbon dioxide, organic sulfur, water vapor, etc. In order to make the purified natural gas meet the first and second category natural gas standards in the national standard GB17820-2018, the domestic alcohol amine method and sulfone amine method are often used for desulfurization and decarbonization, and triethylene glycol is used for dehydration.

[0003] The process flow of TEG dehydration is as follows: first, wet natural gas is separated from free water through a separator, and then enters the tower from the bottom of the absorption tower. The gas phase moves to the top of the tower and contacts the TEG solution entering from the top of the tower in countercurrent. Since TEG has strong hygroscopicity, the water in the natural gas is absorbed, and the dry natural gas flows out from the top of the absorption tower. The possible entrained glycol is separated by the dry gas coalescing filter and then transported out. The TEG that has absorbed water is called rich liquid. After the rich liquid is heated by the distillation column, it enters the flash tank and flashes out part of the natural gas. After mechanical and activated carbon filtration, the rich liquid enters the reboiler through the bottom of the distillation column. In the reboiler, the rich liquid is heated and the water vapor inside is resolved, and TEG is regenerated. After cooling, cooling, and collection, it is pumped back to the absorption tower by the TEG pump to participate in the absorption again to complete the cycle.

[0004] During the regeneration of triethylene glycol, the gas generated during the heating process of the rich liquid is directly discharged into the atmosphere. In this process, the gas evaporated from the rich liquid contains not only water vapor, but also a large amount of methane and other hydrocarbon combustible gases, and there may also be a small amount of organic sulfide. Methane, alkanes, and sulfides will diffuse into the air along with water vapor, causing environmental pollution and waste of resources. Summary of the invention

[0005] The present invention aims to provide a method for recovering methane from tail gas of natural gas dehydration, so as to realize the recovery of methane from exhaust gas in the process of dehydrating natural gas by triethylene glycol.

[0006] To achieve the above object, the present invention adopts the following technical solution: a method for recovering methane from natural gas dehydration tail gas, comprising the following steps: Step 1: collecting the tail gas generated at the distillation column through a closed pipeline; Step 2: passing the tail gas into a heat exchanger for cooling, so that the water vapor in the tail gas condenses into free water; Step 3: passing the cooled tail gas into a gas-liquid separator to separate free water; Step 4: The gas separated by the gas-liquid separator is introduced into a buffer tank; Step 5: compress the gas in the buffer tank and introduce the compressed gas into the fuel gas system for use, wherein the gas is pressurized at a pressure of 30-60 kPa.

[0007] The principles and advantages of this application are: The temperature of the tail gas of natural gas dehydration is greater than 100°C. Hydrocarbons such as water and methane are collected in gaseous form and sent to the tail gas heat exchanger. After heat exchange, the temperature is reduced, and the water vapor condenses into liquid water, which enters the gas-liquid separator for gas-liquid separation. The separated gas enters the buffer tank, and the gas in the buffer tank is compressed. After the pressure of the buffer tank reaches 30-60kPa, the pressurized gas is sent to the gas system for use in the plant / station, thereby realizing the recovery and utilization of methane in the tail gas of natural gas dehydration. A small amount of sulfide is sealed and sent to the gas system, and is no longer directly discharged into the atmosphere.

[0008] Furthermore, in step 2, a water-cooled heat exchanger is used to cool the exhaust gas, the water-cooled heat exchanger has a water circulation loop and an exhaust gas heat exchange passage, the water circulation loop is connected to a vent pipe, and the vent pipe is provided with a vent valve for venting the water-cooled heat exchanger.

[0009] Furthermore, in step 2, the exhaust gas is connected to the water-cooled heat exchanger through an exhaust gas pipeline. A pressure gauge for measuring the pressure in the exhaust gas pipeline and a pressure transmitter matching the pressure gauge are installed on the exhaust gas pipeline. A thermometer and a temperature transmitter for measuring the exhaust gas temperature are also installed. The pressure gauge is used to measure the pressure value on the exhaust gas pipeline, and the thermometer is used to measure the temperature value on the exhaust gas pipeline.

[0010] Furthermore, in step three, the gas-liquid separator structure includes a tank body, a separation liner is installed inside the tank body, a gas pipeline spiraling upward is provided on the separation liner, a hollow fiber tube is provided on the gas pipeline, the fiber tube is inclined downward, the end is open, and the separation, the bottom of the separation tank body is a drain pipe, and the top is an exhaust pipe. Through the separate design of the internal structure of the gas-liquid separator, the cooled exhaust gas is allowed to enter the tank body, and when the gas passes through the gas pipeline, the liquid is retained from the hollow fiber tube, and the gas rises to the exhaust pipe and is discharged. The hollow fiber tube further cools the gas, cools the water vapor that is not completely liquefied, and further removes the water vapor in the gas.

[0011] Furthermore, an automatic drain valve is connected to the drain pipe of the gas-liquid separator, and a liquid level gauge is installed on the tank body. When the liquid level gauge reaches a set value, the automatic drain valve automatically opens to send the liquid in the tank body into the production wastewater system, thereby realizing automatic discharge of the waste liquid.

[0012] Finally, in step five, the buffer tank is pressurized by the compressor. A pressure transmitter is provided between the buffer tank and the compressor. When the pressure in the buffer tank is less than 30 kPa, it is fed back to the compressor through the pressure transmitter to start the compressor. When the pressure in the buffer tank is greater than 60 kPa, the compressor is shut down to keep the gas in the buffer tank at 30-60 kPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of a process for recovering methane from tail gas from natural gas dehydration according to an embodiment of the present invention; Figure 2 It is a methane recovery system for natural gas dehydration tail gas.

[0014] The reference numerals in the drawings of the specification include: a water-cooled heat exchanger 1, a gas-liquid separator 2, a buffer tank 3, a compressor 4, a vent valve 5, a liquid level gauge 6, an automatic drain valve 7, and a pressure transmitter 8. DETAILED DESCRIPTION

[0015] The following is further described in detail through specific implementation methods: As attached Figure 1 A method for recovering methane from natural gas dehydration tail gas is shown, comprising the following steps: Step 1 S01, collecting tail gas generated at the distillation column through a closed pipeline; Step 2 S02, passing the tail gas into a heat exchanger for cooling, so that the water vapor in the tail gas condenses into free water; Step 3 S03, passing the cooled tail gas into a gas-liquid separator to separate free water; Step 4 S04: The gas separated by the gas-liquid separator is introduced into a buffer tank; Step 5 S05: compress the gas in the buffer tank and introduce the compressed gas into the fuel gas system for use, wherein the gas is pressurized at a pressure of 30-60 kPa.

[0016] The temperature of the tail gas of natural gas dehydration is greater than 100°C. Hydrocarbons such as water and methane are collected in gaseous form and sent to the tail gas heat exchanger. After heat exchange, the temperature is reduced, and the water vapor condenses into liquid water, which enters the gas-liquid separator for gas-liquid separation. The separated gas enters the buffer tank, and the gas in the buffer tank is compressed. After the pressure of the buffer tank reaches 30-60kPa, the pressurized gas is sent to the gas system for use in the plant / station, thereby realizing the recovery and utilization of methane in the tail gas of natural gas dehydration. A small amount of sulfide is sealed and sent to the gas system, and is no longer directly discharged into the atmosphere.

[0017] like Figure 2As shown, the system for realizing methane recovery includes a water-cooled heat exchanger 1, which includes a water circulation loop and an exhaust gas heat exchange passage. The water circulation loop is connected to a vent pipe, and a vent valve 5 is provided on the vent pipe for venting the water-cooled heat exchanger 1.

[0018] The exhaust gas is connected to the water-cooled heat exchanger through the exhaust gas pipeline. A pressure gauge for measuring the pressure in the exhaust gas pipeline and a pressure transmitter matching the pressure gauge are installed on the exhaust gas pipeline. A thermometer and a temperature transmitter for measuring the exhaust gas temperature are also installed. The pressure gauge is used to measure the pressure value on the exhaust gas pipeline, and the thermometer is used to measure the temperature value on the exhaust gas pipeline.

[0019] The water-cooled heat exchanger 1 connects the cooled tail gas to the gas-liquid separator 2. The structure of the gas-liquid separator 2 includes a tank body, a separation liner is installed inside the tank body, and a spiral gas pipeline is provided on the separation liner. The gas pipeline is provided with a hollow fiber tube, which is inclined downward and has an open end. The bottom of the separation tank body is a drain pipe and the top is an exhaust pipe. Through the separate design of the internal structure of the gas-liquid separator, the cooled tail gas enters the tank body. When the gas passes through the gas pipeline, the liquid is retained from the hollow fiber tube, and the gas rises to the exhaust pipe and is discharged. The hollow fiber tube further cools the gas, cools the water vapor that is not completely liquefied, and further removes the water vapor in the gas.

[0020] An automatic drain valve 7 is connected to the drain pipe of the gas-liquid separator 2, and a liquid level meter 6 is installed on the tank body 1. When the liquid level meter 6 reaches the set value, the automatic drain valve 7 automatically opens to send the liquid in the tank body into the production wastewater system, thereby realizing automatic discharge of the waste liquid.

[0021] The gas discharged from the gas-liquid separator 2 is connected to the buffer tank 3, and the buffer tank 3 is connected to the compressor 4. The compressor 4 pressurizes the buffer tank 3, and a pressure transmitter 8 is provided between the buffer tank 3 and the compressor 4. When the pressure in the buffer tank 3 is less than 30kPa, it is fed back to the compressor 4 through the pressure transmitter 8 to start the compressor 4. When the pressure in the buffer tank 3 is greater than 60kPa, the compressor 4 is turned off, so that the gas in the buffer tank 3 is maintained at 30-60kPa.

[0022] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. Natural gas dehydration tail gas methane recovery system, characterized in that: It includes a heat exchanger connected to the distillation column, the heat exchanger includes a cooling circuit and an exhaust gas heat exchange passage, the exhaust gas heat exchange passage is connected to a gas-liquid separator, the gas outlet of the gas-liquid separator is connected to a buffer tank, a gas compressor is connected to the buffer tank, the outlet of the buffer tank is connected to a pressure gauge, and after the pressure value reaches 30kPa, the gas in the buffer tank is connected to the gas system.

2. A method for recovering methane from natural gas dehydration tail gas, characterized in that: The steps include: Step 1: collecting the tail gas generated at the distillation column through a closed pipeline; Step 2: passing the tail gas into a heat exchanger for cooling, so that the water vapor in the tail gas condenses into free water; Step 3: passing the cooled tail gas into a gas-liquid separator to separate free water; Step 4: The gas separated by the gas-liquid separator is introduced into a buffer tank; Step 5: compress the gas in the buffer tank and introduce the compressed gas into the fuel gas system for use, wherein the gas is pressurized at a pressure of 30-60 kPa.

3. The method for recovering methane from natural gas dehydration tail gas according to claim 2, characterized in that: In step 2, a water-cooled heat exchanger is used to cool the exhaust gas. The water-cooled heat exchanger has a water circulation loop and an exhaust gas heat exchange passage. The water circulation loop is connected to a vent pipe, and a vent valve is provided on the vent pipe for venting the water-cooled heat exchanger.

4. The method for recovering methane from natural gas dehydration tail gas according to claim 3, characterized in that: In step 2, the exhaust gas is connected to the water-cooled heat exchanger through the exhaust gas pipeline. The exhaust gas pipeline is installed with a pressure gauge for measuring the pressure in the exhaust gas pipeline and a pressure transmitter matching the pressure gauge. A thermometer and a temperature transmitter for measuring the exhaust gas temperature are also installed. The pressure gauge is used to measure the pressure value on the exhaust gas pipeline, and the thermometer is used to measure the temperature value on the exhaust gas pipeline.

5. The method for recovering methane from natural gas dehydration tail gas according to claim 4, characterized in that: In step three, the gas-liquid separator structure includes a tank body, a separation liner is installed inside the tank body, a gas pipeline spiraling upward is provided on the separation liner, a hollow fiber tube is provided on the gas pipeline, the fiber tube is tilted downward, the end is open, and the separation, the bottom of the separation tank body is a drain pipe, and the top is an exhaust pipe. Through the separate design of the internal structure of the gas-liquid separator, the cooled exhaust gas enters the tank body, and when the gas passes through the gas pipeline, the liquid is retained from the hollow fiber tube, and the gas rises to the exhaust pipe for discharge.

6. The method for recovering methane from natural gas dehydration tail gas according to claim 4, characterized in that: The drainage pipe of the gas-liquid separator is connected with an automatic drain valve, and the tank body is equipped with a liquid level meter. When the liquid level meter reaches a set value, the automatic drain valve automatically opens to send the liquid in the tank body into the production wastewater system.

7. The method for recovering methane from natural gas dehydration tail gas according to claim 5, characterized in that: In step five, the buffer tank is pressurized by the compressor. A pressure transmitter is provided between the buffer tank and the compressor. When the pressure in the buffer tank is less than 30 kPa, it is fed back to the compressor through the pressure transmitter to start the compressor. When the pressure in the buffer tank is greater than 60 kPa, the compressor is shut down.

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