Method for recovering tail gas of isopentane tower

Abstract

The invention relates to the technical field of tail gas recovery, in particular to an isopentane tower tail gas recovery method, which comprises the following steps: exhaust gas from the top of an isopentane tower is discharged into an air cooler, and a part of air-cooled n-butane enters a top space position of a reflux tank through an air-cooled high-point non-condensable gas pipeline; the other part of the n-butane after air cooling is dissolved into the isopentane in the air cooling process, and is released through pressure reduction after entering the reflux tank, a part of the n-butane gas escapes from the isopentane, and a part of the isopentane gas is taken away while escaping and is mixed and polymerized with a non-condensable gaseous component at the top of the reflux tank; components at the top of the reflux tank enter the oil-gas separator, and are treated by the multi-stage demister and the multi-stage temperature change coil in the oil-gas separator, so that the n-butane in the tail gas of the isopentane tower can be effectively removed, and the separation and recovery of isopentane and n-butane oil gas can be quickly completed.

Description

Technical Field

[0001] The present invention relates to the technical field of tail gas recovery, and specifically relates to a method for recovering the tail gas of an isopentane tower. Background Art

[0002] After normal butane enters the isopentane tower, it is controlled by the temperature in the tower and always exists in the gas phase in the reflux drum at the top of the isopentane tower. At the same time, a part of normal butane is dissolved in isopentane after being cooled by the air cooler, resulting in a continuous decrease in the purity of isopentane. The general adjustment method is to discharge the non-condensable gas of normal butane in the reflux drum at the top of the tower. Since the temperature of the reflux drum is about 50°C, a large amount of uncondensed isopentane gas will be carried in the discharged normal butane gas. These gas phases will be cooled into the liquid phase in the low-pressure flare drum before leaving the device, and then discharged to the underground waste oil tank and finally returned to the raw material tank area for secondary processing and separation. The non-condensable gas of normal butane not only brings unstable factors to the normal operation of the isopentane tower, but also causes certain economic losses. Therefore, it is necessary to design a method for recovering the tail gas of an isopentane tower to remove the existence of normal butane in the isopentane product. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the existing technology and propose a method for recovering the tail gas of an isopentane tower, which can effectively remove normal butane in the tail gas of the isopentane tower.

[0004] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0005] A method for recovering the tail gas of an isopentane tower, comprising:

[0006] Discharging the exhaust gas outside the top of the isopentane tower into an air cooler. A part of the normal butane after air cooling will enter the top space of the reflux drum through the non-condensable gas pipeline at the high point of the air cooler, and form a non-condensable gas component with the isopentane gas here. Another part of the normal butane after air cooling will be dissolved in isopentane during the air cooling process. After entering the reflux drum and undergoing pressure reduction and release, a part of the normal butane gas will escape from isopentane, and a part of the isopentane gas will be carried away during the escape and mixed with the non-condensable gas component at the top of the reflux drum;

[0007] The components at the top of the reflux drum enter an oil-gas separator and are treated by a primary demister in the oil-gas separator to quickly recover nearly liquid isopentane;

[0008] After being treated by the primary demister, it is heated by a primary temperature change coil to reduce the solubility of normal butane and at the same time increase the escape speed of non-condensable normal butane gas;

[0009] After being treated by the primary temperature change coil, it is treated by a secondary demister to quickly recover gas-liquid isopentane;

[0010] After being processed by the secondary demister, it is cooled by the secondary temperature-changing coil to completely condense and recover the isopentane gas;

[0011] After being processed by the secondary temperature-changing coil, it is processed by the tertiary demister to prevent fluctuations in the external exhaust gas flow rate.

[0012] Furthermore, the temperature at the top of the isopentane tower is 62 °C, the pressure before air cooling is 180 kPa, the pressure after air cooling is 127 kPa, the temperature after cooling is 50 °C, and the temperature of the non-condensable gas at the high point of air cooling is 60 °C.

[0013] Furthermore, the demister uses a wire mesh for demisting, which can quickly reduce the temperature of isopentane, contribute to the liquefaction of isopentane. At the same time, the support plate of the demister has a liquid collection and drainage function, sending the liquefied isopentane to the position of the vessel wall and allowing it to fall along the vessel wall for recovery.

[0014] Furthermore, the temperature-changing coil uses a metal coil structure, mainly completing gas-liquid contact heat transfer to meet the heat transfer requirements for the temperature rise and fall of non-condensable gas.

[0015] Furthermore, an oil collection tray is arranged inside the oil-gas separator, which is located below the secondary demister and is used for oil collection and recovery.

[0016] Furthermore, the oil collection tray uses a bubble cap-type metal oil collection tray, mainly completing the oil collection and recovery of liquefied isopentane after the temperature rise of the isopentane vessel. The liquefied isopentane rising and the liquefied isopentane falling from the demister are collected into the oil collection tray and sent to the bottom of the oil-gas separator through the provided overflow port for recovery.

[0017] The present invention also provides another technical solution:

[0018] An isopentane tower tail gas recovery device includes an isopentane tower, an air cooler, a reflux drum, and an oil-gas separator. The top of the isopentane tower is connected to the inlet of the air cooler through a pipeline, and the outlet of the air cooler is connected to the reflux drum; one side of the oil-gas separator is connected to the top of the air cooler through a non-condensable gas pipeline at the high point of air cooling, and the other side is connected to the reflux drum. A tail gas inlet is arranged at the bottom of the oil-gas separator and is connected to the reflux drum, and a tail gas outlet is arranged at the top.

[0019] Furthermore, a primary demister, a primary temperature-changing coil, a secondary demister, a secondary temperature-changing coil, and a tertiary demister are sequentially arranged inside the oil-gas separator from bottom to top.

[0020] Furthermore, one end of the primary temperature-changing coil is communicated with the non-condensable gas pipeline at the high point of air cooling, and the other end is communicated with the reflux drum; the secondary temperature-changing coil is connected to an external water pipe and is filled with circulating water inside.

[0021] The technical effects of the present invention:

[0022] Compared with the prior art, a method for recovering the tail gas of an isopentane tower according to the present invention utilizes the heat of non-condensable gases, which can reduce the temperature of non-condensable gases and reduce the accumulation of non-condensable gases in the reflux drum. The separated isopentane oil can settle and reflux by itself, achieving effective oil-gas separation. The present invention rationally designs an oil-gas separator to quickly complete the separation and recovery of isopentane and n-butane oil-gas. The demisting tray is used to remove most of the critical-state isopentane in the rising gas. The first-stage temperature-changing coil uses the temperature of non-condensable gases at the high point of air cooling to heat up the demisted non-condensable gases, reducing the solubility of n-butane in isopentane. The oil collection tray of the present invention mainly targets the heated oil-gas, changes the form of isopentane through the temperature of the tray made of metal, collects the liquid isopentane, and sends it to the bottom of the separator for recovery through the provided overflow port. The second-stage temperature-changing coil of the present invention mainly removes isopentane in non-condensable gases, and liquefies and recovers isopentane in the tail gas by cooling down. Description of the Drawings

[0023] Figure 1 It is a schematic structural diagram of the device for recovering the tail gas of an isopentane tower according to the present invention;

[0024] Figure 2 It is a schematic structural diagram of the oil-gas separator according to the present invention.

[0025] In the figure, 1, isopentane tower; 2, air cooler; 3, reflux drum; 4, oil-gas separator; 5, non-condensable gas pipeline at the high point of air cooling; 6, water inlet; 7, water return port; 8, first-stage demister; 9, first-stage temperature-changing coil; 10, second-stage demister; 11, second-stage temperature-changing coil; 12, third-stage demister; 13, oil collection tray; 14, tail gas inlet; 15, tail gas outlet. Detailed Embodiments

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the specification.

[0027] Embodiment 1:

[0028] As Figure 1 shown, a method for recovering the tail gas of an isopentane tower involved in this embodiment is realized based on a device for recovering the tail gas of an isopentane tower.

[0029] The isopentane tower tail gas recovery device includes an isopentane tower 1, an air cooler 2, a reflux drum 3, and an oil and gas separator 4. The top of the isopentane tower 1 is connected to the inlet of the air cooler 2 through a pipeline, and the outlet of the air cooler 2 is connected to the reflux drum 3. One side of the oil and gas separator 4 is connected to the top of the air cooler 2 through an air-cooled high-point non-condensable gas pipeline 5, and the other side is connected to the reflux drum 3. The bottom of the oil and gas separator 4 is provided with a tail gas inlet 14 and is connected to the reflux drum 3, and the top is provided with a tail gas outlet 15. Inside the oil and gas separator 4, a primary demister 8, a primary temperature-changing coil 9, a secondary demister 10, a secondary temperature-changing coil 11, and a tertiary demister 12 are sequentially arranged from bottom to top. One end of the primary temperature-changing coil 9 is communicated with the air-cooled high-point non-condensable gas pipeline 5, and the other end is communicated with the reflux drum 3 through an outlet. The secondary temperature-changing coil 11 is connected to an external water pipe, one end is a water inlet 6, and the other end is a water return port 7. The inside of the secondary temperature-changing coil 11 is filled with circulating water. An oil collection tray 13 is also arranged inside the oil and gas separator 4. The oil collection tray 13 is located below the secondary demister 10 and above the primary temperature-changing coil 9 for collecting and recovering oil.

[0030] The isopentane tower tail gas recovery method includes:

[0031] Discharge the external exhaust gas at the top of the isopentane tower 1 into the air cooler 2. A part of the n-butane after air cooling will enter the top space position of the reflux drum 3 through the air-cooled high-point non-condensable gas pipeline 5, and form a non-condensable gaseous component with the isopentane gas here. Another part of the n-butane after air cooling will dissolve into the isopentane during the air-cooling process of temperature reduction. After entering the reflux drum 3 and undergoing pressure reduction and release, a part of the n-butane gas will escape from the isopentane, and a part of the isopentane gas will be carried away during the escape and mixed with the non-condensable gaseous component at the top of the reflux drum 3;

[0032] The components at the top of the reflux drum 3 enter the oil and gas separator 4 and are treated by the primary demister 8 inside the oil and gas separator 4 to quickly recover the nearly liquid isopentane;

[0033] After being treated by the primary demister 8, it is heated by the primary temperature-changing coil 9 to reduce the solubility of n-butane and at the same time increase the escape speed of the non-condensable n-butane gas;

[0034] After being treated by the primary temperature-changing coil 9, it is treated by the secondary demister 10 to quickly recover the gas-liquid isopentane;

[0035] After being treated by the secondary demister 10, it is cooled by the secondary temperature-changing coil 11 to completely condense and recover the isopentane gas;

[0036] After being treated by the secondary temperature-changing coil 11, it is treated by the tertiary demister 12 to prevent fluctuations in the external exhaust gas flow rate.

[0037] The top temperature of the isopentane column 1 is 62 °C, the pressure before air cooling is 180 kPa, the pressure after air cooling is 127 kPa, the temperature after cooling is 50 °C, and the temperature of the non-condensable gas at the high point of air cooling is 60 °C. The demister uses a wire mesh for demisting, which can quickly reduce the temperature of isopentane, contribute to the liquefaction of isopentane. At the same time, the support plate of the demister has a liquid collection and drainage function, sending the liquefied isopentane to the position of the wall of the device and flowing down along the wall for recovery. The temperature-changing coil uses a metal coil structure, mainly to complete the gas-liquid contact heat exchange and meet the heat exchange requirements for the temperature rise and fall of non-condensable gas. The oil collection tray 13 uses a bubble cap-type metal oil collection tray 13, mainly to complete the collection and recovery of the liquid isopentane after the temperature rise of the isopentane device, collecting the rising liquid isopentane and the liquid isopentane falling from the demister into the oil collection tray 13 and sending it to the bottom of the oil-gas separator 4 through the overflow port provided for recovery.

[0038] The primary demister 8 of the present invention conducts demisting: The isopentane reflux liquid enters the reflux tank 3. The dissolved n-butane will escape from the isopentane due to the release in the space of the reflux tank 3, the pressure drop, etc., and accumulate in the upper space of the reflux tank 3. At the same time, the gas velocity during the escape of n-butane is relatively fast, and it will carry away a part of the isopentane gas-liquid mixture on the liquid level surface. Therefore, n-butane gas state and isopentane gas-liquid mixed state are accumulated in the upper part of the reflux tank 3. Under the environment of the absolute pressure of 228 kPa and temperature of 50 °C in the reflux tank 3, at the critical state of the gas-liquid two phases of isopentane, as the time of entering the reflux tank 3 extends, a part of the isopentane completely liquefies and falls, while the gas-liquid state in the feed rises. Therefore, in the remaining space of the reflux tank 3, a simple gas-liquid exchange state will be formed. When the reflux tank 3 is depressurized, this balance will be broken, and a part of the gas-liquid two-phase isopentane will be carried away. Therefore, the nearly liquid isopentane can be quickly recovered through the primary demister 8.

[0039] The primary temperature-changing coil 9 of the present invention conducts temperature rise: The exhaust gas discharged externally passes through the primary demister 8 to recover most of the isopentane, leaving a mixture of n-butane and isopentane gases. In order to reduce the solubility of n-butane and isopentane gases, the temperature of the mixed gas can be increased through the primary temperature-changing coil 9 to reduce the solubility, and at the same time, the escape speed of the non-condensable n-butane gas is increased.

[0040] The secondary demister 10 of the present invention conducts demisting: After the temperature of the two gas mixtures rises, the gas velocity changes, and the rising speed of n-butane gas increases, which will carry some isopentane upward. In order to remove the upward gas-liquid isopentane, secondary demisting is selected, which can reduce the gas velocity of isopentane, extend the liquefaction time of isopentane gas, and reduce the solubility of n-butane.

[0041] The secondary temperature-changing coil 11 of the present invention conducts temperature drop: The temperature drop condenses all the isopentane gas. After secondary demisting, the content of isopentane in the rising n-butane gas decreases a lot. After another condensation, all the isopentane gas in it is recovered.

[0042] The three - stage demister 12 of the present invention performs demisting: It can prevent special situations such as fluctuations in the external exhaust gas flow rate and sudden increase in the flow rate, and provide early prevention and increased guarantee for controlling the components of the external exhaust gas.

[0043] The present invention recovers all the isopentane in the external exhaust gas of the isopentane tower 1 by performing heat exchange on the external exhaust gas at the top of the isopentane tower 1 and the non - condensable gas at the high point of the isopentane air cooler. This can not only reduce the economic losses brought to the device by the external discharge of product oil, but also improve the product purity of the isopentane tower 1. At the same time, it reduces unnecessary operating procedures of the device, ensures the stable operation of the isopentane tower 1, and can be widely applied to the field of tail gas recovery of the isopentane tower 1.

[0044] The above - mentioned specific implementation manners are only specific cases of the present invention. The patent protection scope of the present invention includes but is not limited to the above - mentioned specific implementation manners. Any appropriate changes or modifications made by any person skilled in the art who meets the claims of the present invention shall fall within the patent protection scope of the present invention.

Claims

1. A method for recovering the tail gas of an isopentane tower, characterized in that, Including: The off-gas discharged from the top of the isopentane tower is sent to an air cooler. A part of the n-butane after air cooling will enter the top space of the reflux drum through the non-condensable gas pipeline at the high point of the air cooler, and form a non-condensable gaseous component with the isopentane gas here. Another part of the n-butane after air cooling will dissolve into the isopentane during the air cooling process. After entering the reflux drum and undergoing pressure reduction and release, a part of the n-butane gas will escape from the isopentane, and at the same time, it will carry away a part of the isopentane gas and mix with the non-condensable gaseous component at the top of the reflux drum; The components at the top of the reflux drum enter an oil-gas separator and are treated by a primary demister inside the oil-gas separator; After being treated by the primary demister, it is heated by a primary temperature-changing coil to reduce the solubility of n-butane and at the same time increase the escape speed of non-condensable n-butane gas; After being treated by the primary temperature-changing coil, it is treated by a secondary demister to quickly recover gaseous and liquid isopentane; After being treated by the secondary demister, it is cooled by a secondary temperature-changing coil to completely condense and recover the isopentane gas; After being treated by the secondary temperature-changing coil, it is treated by a tertiary demister to prevent fluctuations in the off-gas flow rate.

2. The method for recovering the tail gas of the isopentane tower according to claim 1, wherein The temperature at the top of the isopentane tower is 62 °C, the pressure before air cooling is 180 kPa, the pressure after air cooling is 127 kPa, the temperature after cooling is 50 °C, and the temperature of the non-condensable gas at the high point of the air cooler is 60 °C.

3. The isopentane tower tail gas recovery method according to claim 1, wherein The demister uses a wire mesh.

4. The method for recovering the tail gas of the isopentane tower according to claim 1, wherein The temperature-changing coil uses a metal coil structure.

5. The method for recovering the tail gas of the isopentane tower according to claim 1, wherein, An oil collecting tray is arranged inside the oil-gas separator, below the secondary demister.

6. The method for recovering off-gas from an isopentane column according to claim 5, wherein The oil collecting tray uses a bubble cap type metal oil collecting tray.

7. An isopentane tower tail gas recovery device for implementing the isopentane tower tail gas recovery method according to any one of claims 1-6, characterized in that, Including an isopentane tower, an air cooler, a reflux drum and an oil-gas separator. The top of the isopentane tower is connected to the inlet of the air cooler through a pipeline, and the outlet of the air cooler is connected to the reflux drum; One side of the oil-gas separator is connected to the top of the air cooler through the non-condensable gas pipeline at the high point of the air cooler, and the other side is connected to the reflux drum. A tail gas inlet is arranged at the bottom of the oil-gas separator and is connected to the reflux drum, and a tail gas outlet is arranged at the top.

8. The isopentane column tail gas recovery device according to claim 7, characterized in that, Inside the oil-gas separator, a primary demister, a primary temperature-changing coil, a secondary demister, a secondary temperature-changing coil and a tertiary demister are arranged in sequence from bottom to top.

9. The isopentane column tail gas recovery device according to claim 8, wherein, One end of the primary temperature-changing coil is communicated with the non-condensable gas pipeline at the high point of the air cooler, and the other end is communicated with the reflux drum; The secondary temperature-changing coil is connected to an external water pipe and is filled with circulating water inside.

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