Method for reducing supporting liquid of methanol washing tower

Abstract

The invention relates to the technical field of gas purification, in particular to a method for reducing supporting liquid of a methanol washing tower, which comprises the following steps: washing unconverted raw material gas: sequentially carrying out desulfurization and decarbonization treatment on the unconverted raw material gas, and enabling semi-lean methanol led out from a section C1 to enter the top of a section A3 of a flash tower through an exhaust pipeline on a coiled tube heat exchanger I; washing the converted raw material gas: sequentially carrying out desulfurization and decarbonization treatment on the unconverted raw material gas, and converging the semi-lean methanol led out from the section C2 with an exhaust pipeline on the coiled tube heat exchanger I through an exhaust pipeline on the coiled tube heat exchanger II; and flash recovery. The coiled tube heat exchanger I and the coiled tube heat exchanger II have a gas resistance phenomenon at a high point, and gas accumulation can be reduced and the gas resistance phenomenon at the high point can be eliminated by additionally arranging the exhaust pipeline to the flash tower, so that methanol flows smoothly, the liquid level height of the liquid collecting tray is reduced, and the methanol recovery efficiency is improved. The conditions that the purified gas exceeds the index due to methanol circulation interruption and the methanol directly drops from the gas rising cap are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of gas purification, in particular to a method for reducing methanol washing tower liquid. Background Art

[0002] Low-temperature methanol scrubbing technology is a physical absorption process widely used in gas purification, primarily for removing acidic gases (such as H2S, CO2, and COS) from industrial gases such as synthesis gas and natural gas. Its core principle is to utilize the high solubility selectivity of methanol at low temperatures to achieve efficient and low-energy gas purification.

[0003] Shifted or non-shifted gas enters the scrubber from the bottom, passing through it from bottom to top. Purified gas exits from the top and enters the downstream process. Low-temperature methanol is sprayed in from the top and passes through each layer of the tower tray and liquid collection tray from top to bottom to reach the bottom of the tower. Because low-temperature methanol scrubbing is a physical method, the solubility of acidic gases such as H2S, COS, and CO2 in methanol decreases with increasing temperature. To ensure absorption, methanol is drawn from the liquid collection tray, cooled in a heat exchanger, and then returned to the scrubber. However, air resistance in the heat exchanger reduces the flow rate of methanol, leading to liquid support on the tray. This is a phenomenon where the liquid level continues to rise and flows from the gas lift cap to the next tower section, reducing the cooling effect between methanol sections and causing the temperature inside the tower to rise, affecting the performance of the purified gas leaving the tower. In addition, large fluctuations in the liquid level affect system stability and are detrimental to the operation of the device. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a method for reducing the support liquid of the methanol washing tower. By adding an exhaust pipeline to the flash tower, the high-point gas resistance phenomenon is eliminated, thereby making the methanol flow smooth, reducing the liquid level height of the liquid collecting tray, avoiding the situation where the methanol circulation is interrupted and the purified gas exceeds the index, and avoiding the situation where the methanol is directly dropped from the gas lifting cap.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for reducing the methanol washing tower liquid, using a methanol washing device, comprising:

[0006] The unconverted gas scrubber is divided into sections A1, B1 and C1 from bottom to top;

[0007] The shift gas scrubber is divided into sections A2, B2, C2, and D from bottom to top;

[0008] The flash tower is divided into sections A3 and B3 from bottom to top;

[0009] A coil-wound heat exchanger 1 is provided in the C1 section of the unconverted gas scrubber;

[0010] The same set of coil heat exchangers 2 are installed in the C2 and D sections of the shift gas scrubber, and the same set of coil heat exchangers 3 connected to the flash tower are installed in the A2 and B2 sections;

[0011] An exhaust pipeline is connected to the top of the tubes of the coiled heat exchanger 1 and the coiled heat exchanger 2, and the other end of the exhaust pipeline is connected to the flash tower.

[0012] Preferably, a propylene cryogenic cooler 1 is installed on the pipeline between the shift gas scrubber C2 section and the coil-wound heat exchanger 2.

[0013] Preferably, a second propylene cryogenic cooler and a third propylene cryogenic cooler are respectively installed on the two groups of pipelines between the third coil heat exchanger and the flash tower.

[0014] A method for reducing methanol washing tower liquid, comprising the following steps:

[0015] (1) Unconverted feed gas washing: Unconverted feed gas enters the bottom of the unconverted gas washing tower and moves upward along the tower top. At the same time, low-temperature lean methanol injected from the tower top moves downward along the tower bottom. The two gas streams come into contact in reverse order, achieving desulfurization and decarbonization treatment in turn. The semi-lean methanol drawn from the C1 section enters the top of the flash tower A3 section through the exhaust line on the coiled heat exchanger 1.

[0016] (2) Shift feed gas scrubbing: Shift feed gas enters the shift gas scrubber from the bottom and moves upwards along the top of the tower. Simultaneously, low-temperature lean methanol injected from the top of the tower moves downwards along the bottom of the tower. The two gases come into contact in reverse order, achieving desulfurization and decarbonization treatments in sequence. The semi-lean methanol drawn out from the C2 section is combined with the exhaust pipeline on the coil heat exchanger 2 through the exhaust pipeline on the coil heat exchanger 1.

[0017] (3) Flash recovery: The sulfur-rich methanol flowing out from the bottom of the conversion gas scrubber is cooled and depressurized by the coil heat exchanger 3 and the propylene cryogenic cooler 3, and then enters the flash tower A3 section for flash treatment; the sulfur-free methanol flowing out from the conversion gas scrubber B2 section is cooled and depressurized by the coil heat exchanger 3 and the propylene cryogenic cooler 2, and then enters the flash tower B3 section for flash treatment.

[0018] Preferably, in step (1), the temperature of the unconverted raw gas is -29.6°C and the pressure is 3.16 MPaG; the temperature of the low-temperature lean methanol is -57°C and the pressure is 3.93 MPaG; and the liquid level of the C1 section of the unconverted gas scrubber is 30-35%.

[0019] Preferably, in step (2), the temperature of the conversion feed gas is -25.9°C and the pressure is 3.11 MPaG; the temperature of the low-temperature lean methanol is -57°C and the pressure is 3.93 MPaG; the liquid level of the C2 section of the conversion gas scrubber is 25-30%, and the liquid level of the D section is 0-5%.

[0020] Preferably, in step (3), the temperature of the sulfur-rich methanol is -16.3°C and the pressure is 3.11 MPaG, and the temperature after cooling and reducing pressure is -40.4°C and the pressure is 1.0 MPaG.

[0021] Preferably, in step (3), the temperature of the sulfur-free methanol is -20.3°C and the pressure is 3.07 MPaG, and the temperature after cooling and reducing the pressure is -40.3°C and the pressure is 1.1 MPaG.

[0022] The present invention provides a method for reducing methanol washing tower liquid, which has the following beneficial effects compared with the prior art:

[0023] In the present invention, the first and second coil heat exchangers have gas blockage at high points. By adding an exhaust pipeline to the flash tower, gas accumulation can be reduced and the gas blockage at high points can be eliminated, thereby ensuring smooth methanol circulation and reducing the liquid level of the liquid collecting tray. This avoids the situation where the methanol circulation is interrupted and the purified gas exceeds the index, and the situation where methanol is directly dropped from the gas lift cap.

[0024] In the present invention, the low-temperature semi-lean methanol flowing to the flash tower through the exhaust pipeline can also wash the dissolved CO2 and H2S gases flashed out in sections A3 and B3 of the flash tower due to its low saturation, thereby purifying the effective H2 and CO gases and concentrating the CO2 and H2S gases. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1 This is a flow chart of low-temperature methanol washing of the present invention;

[0027] Figure 2 For the present invention Figure 1 Enlarged schematic diagram of part a. DETAILED DESCRIPTION

[0028] The following examples illustrate the implementation methods of the present application in detail, so that the implementation process of how the present application applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0029] Example 1

[0030] A methanol washing device, comprising:

[0031] Unconverted gas scrubber T04208 is divided into sections A1, B1, and C1 from bottom to top;

[0032] The shift gas scrubber T04201 is divided into sections A2, B2, C2, and D from bottom to top;

[0033] Flash tower T04202 is divided into sections A3 and B3 from bottom to top;

[0034] The C1 section of the unconverted gas scrubber T04208 is equipped with a coiled heat exchanger (E04225). An exhaust line is connected to the top of the coiled heat exchanger's tubes, with the other end of the exhaust line connected to the flash tower T04202. Semi-lean methanol drawn from the C1 section's liquid collection tray flows through the outflow line into the coiled heat exchanger (E04225) for cooling. After cooling, it returns to the unconverted gas scrubber T04208 through the reflux line. Some of this semi-lean methanol flows through the exhaust line to the A3 section of the flash tower T04202.

[0035] The same set of coiled-tube heat exchangers E04206 are installed in the C2 section and D section of the conversion gas scrubber T04201. An exhaust pipeline is connected to the top of the tube side of the coiled-tube heat exchanger E04206. The other end of the exhaust pipeline is connected to the flash tower T04202. A propylene cryogenic cooler E04205 is installed on the pipeline between the C2 section of the conversion gas scrubber T04201 and the coiled-tube heat exchanger E04206. The semi-lean methanol drawn from the D section liquid collection tray enters the second coil heat exchanger E04206 through the outflow pipeline for cooling, and then returns to the shift gas scrubber T04201 through the reflux pipeline. The semi-lean methanol drawn from the C2 section liquid collection tray enters the first propylene cryogenic cooler E04205 through the outflow pipeline, and then enters the second coil heat exchanger E04206 for cooling, and then returns to the shift gas scrubber T04201 through the reflux pipeline. Part of the semi-lean methanol flows to the A3 section of the flash tower T04202 through the exhaust pipeline.

[0036] The A2 and B2 sections of the shift gas scrubber T04201 are equipped with a single set of coiled heat exchangers (E04207), connected to the flash tower T04202. Propylene cryocooler (E04203) and propylene cryocooler (E04204) are installed on the two sets of pipes between coiled heat exchanger (E04207) and flash tower T04202, respectively. The sulfur-free methanol flowing out of section B2 flows sequentially through coiled heat exchanger (E04207) and propylene cryocooler (E04204) before reaching section B3 of flash tower T04202. The sulfur-containing methanol flowing out of section A2 flows sequentially through coiled heat exchanger (E04207) and propylene cryocooler (E04203) before reaching section A3 of flash tower T04202.

[0037] Example 2

[0038] A method for reducing methanol washing tower liquid, using the methanol washing device in Example 1, comprising the following steps:

[0039] (1) Unconverted feed gas washing: Unconverted feed gas enters the bottom of the unconverted gas washing tower and moves upward along the tower top. At the same time, low-temperature lean methanol injected from the tower top moves downward along the tower bottom. The two gas streams come into contact in reverse order, achieving desulfurization and decarbonization treatment in turn. The semi-lean methanol drawn from the C1 section enters the top of the flash tower A3 section through the exhaust line on the coiled heat exchanger 1.

[0040] Specifically, unshifted feed gas at a temperature of -29.6°C and a pressure of 3.16 MPaG enters the A1 section of the unshifted gas scrubber for desulfurization. The unshifted gas scrubber is divided into three sections: the bottom section (A1) is the desulfurization section, and the two upper sections (B1 and C1) are the decarburization sections. In the desulfurization section, the feed unshifted gas is scrubbed with a partially CO2-rich methanol solution from the decarburization section at a temperature of -28.2°C and a pressure of 3.12 MPaG. After removing components such as H2S, COS, and some CO2, it enters the decarburization section, leaving the gas sulfur-free upon entering the decarburization section. A coiled heat exchanger (BHE) 1 is installed between the decarburization sections of the unshifted gas scrubber to lower the absorption temperature of the rich methanol and improve absorption capacity. A vent line from the liquid phase outlet of section C1 to the top of the coiled heat exchanger 1 tube leg draws a stream of semi-lean methanol to the top of the lower flash tower (A3 section) for use as a scrubbing agent. The liquid level of the C1 section of the unconverted gas washing tower is controlled at 30-35%. The top of the tower is washed with lean methanol liquid with a temperature of -57°C and a pressure of 3.93 MPaG to remove CO2 in the raw unconverted gas to ≤20 ppm to meet the purification requirements.

[0041] (2) Shift feed gas scrubbing: Shift feed gas enters the shift gas scrubber from the bottom and moves upwards along the top of the tower. Simultaneously, low-temperature lean methanol injected from the top of the tower moves downwards along the bottom of the tower. The two gases come into contact in reverse order, achieving desulfurization and decarbonization treatments in sequence. The semi-lean methanol drawn out from the C2 section is combined with the exhaust pipeline on the coil heat exchanger 2 through the exhaust pipeline on the coil heat exchanger 1.

[0042] Specifically, the shift feed gas at a temperature of -25.9°C and a pressure of 3.11 MPaG enters the desulfurization section of the lower tower of the shift gas scrubber. The shift gas scrubber is divided into four sections: the bottom section (Section A2) is the desulfurization section, and the top three sections (Sections B2, C2, and D) are the decarbonization sections. In the desulfurization section, the shift feed gas is scrubbed with a partially CO2-rich methanol solution at a temperature of -28.1°C and a pressure of 3.06 MPaG from the decarbonization section. This removes components such as H2S, COS, and some CO2 before entering the decarbonization section. The gas entering the decarbonization section is sulfur-free. A second coil heat exchanger and a first propylene cryocooler are installed between the decarbonization sections of the shift gas scrubber to reduce the absorption temperature of the rich methanol and improve absorption capacity. A stream of semi-lean methanol is drawn from the top exhaust line of the tube from the liquid phase outlet of section C2 to the second coil heat exchanger to the top of the flash tower (section A3) for use as a scrubbing agent. The liquid level in section D of the shift gas scrubber is controlled at 0-5%, and in section C2 at 25-30%. Lean methanol at a temperature of -57°C and a pressure of 3.93 MPaG is used at the top of the shift gas scrubber to remove CO2 from the raw shift gas to ≤20 ppm, meeting purification requirements.

[0043] (3) Flash recovery: The sulfur-rich methanol flowing out from the bottom of the conversion gas scrubber is cooled and depressurized by the coil heat exchanger 3 and the propylene cryogenic cooler 3, and then enters the flash tower A3 section for flash treatment; the sulfur-free methanol flowing out from the conversion gas scrubber B2 section is cooled and depressurized by the coil heat exchanger 3 and the propylene cryogenic cooler 2, and then enters the flash tower B3 section for flash treatment.

[0044] Specifically, after absorbing H2S and CO2, the sulfur-rich methanol exiting the desulfurization section of the shift gas scrubber has a temperature of -16.3°C and a pressure of 3.11 MPaG. After heat exchange, cooling, and decompression in coil-wrap heat exchanger 3 and propylene cryogenic freezer 3, the temperature drops to -40.4°C and the pressure drops to 1.0 MPaG. Dissolved H2, CO, and small amounts of CO2, H2S, and other gases are flashed off in flash tower section A3. Similarly, the sulfur-free methanol exiting the decarbonization section of the shift gas scrubber has a temperature of -20.3°C and a pressure of 3.07 MPaG. After heat exchange, cooling, and decompression in coil-wrap heat exchanger 3 and propylene cryogenic freezer 2, the temperature drops to -40.3°C and the pressure drops to 1.1 MPaG. Dissolved H2, CO, and other gases are flashed off in flash tower section B3. The semi-lean methanol flowing out of the tube-side exhaust line of coiled heat exchanger 2 in the shifted gas scrubber C2 and the semi-lean methanol flowing out of the tube-side exhaust line of coiled heat exchanger 1 in the unshifted gas scrubber C1 are combined and delivered to the top of flash tower A3. This is used to wash the dissolved H2S gas flashed out of flash tower A3 and the small amount of dissolved CO2 flashed out of flash tower B3. The flash gas exiting the top of the flash tower is recycled.

[0045] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for reducing methanol washing tower liquid, characterized in that, A methanol washing device is used, comprising: The unconverted gas scrubber is divided into sections A1, B1, and C1 from bottom to top; The shift gas scrubber is divided into sections A2, B2, C2, and D from bottom to top; The flash tower is divided into sections A3 and B3 from bottom to top; A coil-wound heat exchanger 1 is provided in the C1 section of the unconverted gas scrubber; The same set of coil heat exchangers 2 are installed in the C2 and D sections of the shift gas scrubber, and the same set of coil heat exchangers 3 connected to the flash tower are installed in the A2 and B2 sections; An exhaust pipeline is connected to the top of the tubes of the coiled heat exchanger 1 and the coiled heat exchanger 2, and the other end of the exhaust pipeline is connected to the flash tower.

2. The method for reducing methanol washing tower liquid according to claim 1, wherein A propylene cryogenic cooler 1 is installed on the pipeline between the C2 section of the conversion gas scrubber and the second coil heat exchanger.

3. The method for reducing methanol washing tower liquid according to claim 2, wherein: Propylene cryogenic cooler 2 and propylene cryogenic cooler 3 are respectively installed on the two groups of pipelines between the coiled tube heat exchanger 3 and the flash tower.

4. The method for reducing methanol washing tower liquid according to claim 3, wherein: The following steps are involved: (1) Unconverted feed gas washing: Unconverted feed gas enters the bottom of the unconverted gas washing tower and moves upward along the tower top. At the same time, low-temperature lean methanol injected from the tower top moves downward along the tower bottom. The two gas streams come into contact in reverse order, achieving desulfurization and decarbonization treatment in turn. The semi-lean methanol drawn from the C1 section enters the top of the flash tower A3 section through the exhaust line on the coiled heat exchanger 1. (2) Shift feed gas scrubbing: Shift feed gas enters the shift gas scrubber from the bottom and moves upwards along the top of the tower. Simultaneously, low-temperature lean methanol injected from the top of the tower moves downwards along the bottom of the tower. The two gases come into contact in reverse order, achieving desulfurization and decarbonization treatments in sequence. The semi-lean methanol drawn out from the C2 section is combined with the exhaust pipeline on the coil heat exchanger 2 through the exhaust pipeline on the coil heat exchanger 1. (3) Flash recovery: The sulfur-rich methanol flowing out from the bottom of the conversion gas scrubber is cooled and depressurized by the coil heat exchanger 3 and the propylene cryogenic cooler 3, and then enters the flash tower A3 section for flash treatment; the sulfur-free methanol flowing out from the conversion gas scrubber B2 section is cooled and depressurized by the coil heat exchanger 3 and the propylene cryogenic cooler 2, and then enters the flash tower B3 section for flash treatment.

5. The method for reducing methanol washing tower liquid according to claim 4, characterized in that, In step (1), the temperature of the unconverted raw gas is -29.6°C and the pressure is 3.16 MPaG; the temperature of the low-temperature lean methanol is -57°C and the pressure is 3.93 MPaG; and the liquid level of the C1 section of the unconverted gas scrubber is 30-35%.

6. The method for reducing methanol washing tower liquid according to claim 4, characterized in that: In step (2), the temperature of the conversion feed gas is -25.9°C and the pressure is 3.11 MPaG; the temperature of the low-temperature lean methanol is -57°C and the pressure is 3.93 MPaG; the liquid level of the C2 section of the conversion gas scrubber is 25-30%, and the liquid level of the D section is 0-5%.

7. The method for reducing methanol washing tower liquid according to claim 4, characterized in that: In step (3), the temperature of the sulfur-rich methanol is -16.3°C and the pressure is 3.11 MPaG. After cooling and reducing the pressure, the temperature is -40.4°C and the pressure is 1.0 MPaG.

8. The method for reducing methanol washing tower liquid according to claim 4, characterized in that: In step (3), the temperature of the sulfur-free methanol is -20.3°C and the pressure is 3.07 MPaG. After cooling and reducing the pressure, the temperature is -40.3°C and the pressure is 1.1 MPaG.

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