An improved process for methanol wash gas stripping

Abstract

The application discloses an improved methanol gas washing and stripping process, characterized in that two or more gas stripping towers are arranged, or two or more gas inlets are designed in the same gas stripping tower; one of the first stage gas inlets of the gas stripping tower is the outlet gas of a first stage adsorption separation device for liquefied non-condensable gas, the carbon dioxide concentration of which is 3-10%; the other is the stripping gas of the second stage of the gas stripping tower, the carbon dioxide concentration of which is more than 10%; the gas inlet of the last stage of the gas stripping tower adopts the outlet gas of the adsorption separation device, the carbon dioxide concentration of which is less than 10 ppm; the carbon dioxide concentration of the outlet gas of the gas stripping tower is 70-83%, and the carbon dioxide is compressed and adsorbed and separated to 3-10% to become a first stage decarburization gas, a part of which is used as the first stage gas inlet of the gas stripping tower, and a part of which is sent to the last stage adsorption separation system to obtain the outlet gas with the carbon dioxide concentration of less than 10 ppm, which is called a last stage decarburization gas and is sent to the last stage gas inlet of the gas stripping tower. Therefore, high-concentration carbon dioxide can be obtained, and the amount of traditional process pure nitrogen gas used for stripping can be reduced or stopped.

Description

Technical Field

[0001] This invention relates to the fields of chemical engineering, environmental protection, and energy conservation, and is an improved method for methanol washing and stripping process. Background Technology

[0002] The methanol washing process utilizes methanol at low temperatures to physically absorb acidic gases such as CO2, selectively removing these gases from the feed gas to obtain purified gas products. The methanol-rich liquid after CO2 absorption is often regenerated via nitrogen stripping, which consumes a large amount of pure nitrogen. The CO2-containing tail gas after stripping is then difficult to utilize and is directly emitted.

[0003] CN202110882632.5 discloses a high-efficiency composite low-temperature methanol washing CO2 recovery tower. This tower addresses the separation of CO2 and H2S from methanol-rich liquid in a low-temperature methanol washing process for acidic gases, eliminating the need for nitrogen stripping. The invention offers two solutions: for new installations, it efficiently integrates the original H2S concentration tower and nitrogen stripping tower used for CO2 separation from methanol-rich liquid, along with most of the cold and heat exchange recovery processes, into a single tower; for retrofitting existing installations, it efficiently integrates the original nitrogen stripping tower used for CO2 separation from methanol-rich liquid, along with a portion of the cold and heat exchange recovery processes, into a single tower.

[0004] CN202221269266.2 discloses a device for reducing effective gas emissions in a low-temperature methanol washing and purification process. A methanol-rich pipeline is connected to a methanol-rich stripping tower; the top of the methanol-rich stripping tower is connected to a condenser heat exchanger; the bottom of the methanol-rich stripping tower is connected to an evaporator heat exchanger; the condenser heat exchanger is connected to a separation tank; the bottom of the separation tank is connected to the evaporator heat exchanger; and the evaporator heat exchanger is connected to the methanol-rich pipeline. A methanol-rich pressure-reducing control valve is installed on the connecting pipeline between the methanol-rich pipeline and the methanol-rich stripping tower. The top of the separation tank is connected to a circulating gas pipeline via a pressure control valve. The flash vapor of the methanol-rich gas is condensed to obtain liquid carbon dioxide, which is then heated and vaporized as the stripping gas source for the methanol-rich gas. The condensed flash vapor is recycled, significantly reducing the content of effective gases in the methanol-rich gas, reducing the loss of effective gases during the gas purification process, saving energy and reducing environmental pollution from gas emissions.

[0005] CN202220222012.9 discloses a device for staged gas stripping to recover energy from low-temperature methanol washing tail gas, comprising a sulfur-free flash evaporator, a sulfur-containing flash evaporator, and a stripping tower. The top of the upper column of the sulfur-free flash evaporator is connected in sequence to a first pressure reducing valve and a pipeline from the medium-pressure flash evaporator for sulfur-free methanol via pipelines. The bottom of the upper column is connected in sequence to a second pressure reducing valve, the top of the lower column of the sulfur-free flash evaporator, a fifth pressure reducing valve, and the top of the upper column of the hydrogen sulfide concentration tower via pipelines. The top of the upper column of the sulfur-containing flash evaporator is connected in sequence to a third pressure reducing valve and a pipeline from the medium-pressure flash evaporator for sulfur-containing methanol via pipelines. The bottom of the upper column is connected in sequence to a fourth pressure reducing valve, the top of the lower column of the sulfur-containing flash evaporator, a sixth pressure reducing valve, and the feed inlet in the middle section of the middle column of the hydrogen sulfide concentration tower via pipelines.

[0006] Although the above-mentioned methanol washing gas process increases the recovery of effective gas, CO2, or cold energy, the recovery methods often require a large amount of separation energy consumption, which is not economical. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides an improved method for a methanol washing and stripping process. The method is characterized by: setting up two or more stripping towers, or designing two or more gas inlets for the same stripping tower; one of the first-stage inlet gases of the stripping tower is the outlet gas from the first-stage adsorption separation unit of liquefied non-condensable gas, with a carbon dioxide concentration of 3-10%; the other is the stripping gas from the second stage of the stripping tower, with a carbon dioxide concentration of 10% or higher; the final-stage inlet gas of the stripping tower uses the outlet gas from the final-stage adsorption separation unit, with a carbon dioxide concentration below 10 ppm; the carbon dioxide concentration in the outlet gas of the stripping tower is 70-83%. Compression and adsorption separation of carbon dioxide to 3-10% is called the first-stage decarbonization gas. Part of this gas is used as the first-stage inlet gas of the stripping tower, and part is sent to the final-stage adsorption separation system to obtain gas with an outlet carbon dioxide concentration below 10 ppm, which is called the final-stage decarbonization gas and sent to the final-stage inlet gas of the stripping tower. This method can obtain high-concentration carbon dioxide or liquid carbon dioxide while reducing or eliminating the energy waste of using pure nitrogen as the stripping inlet gas in traditional processes.

[0008] Preferably, there are two or more stripping towers and two or more gas inlets.

[0009] When a stripping tower is designed with three gas inlets, the process is as follows: One of the inlet gases for the first stage of the stripping tower is the outlet gas from the first-stage adsorption-separation unit of liquefied non-condensable gas, with a carbon dioxide concentration of 3-10%; the other is the stripping gas from the second stage of the stripping tower, with a carbon dioxide concentration of over 10%. One of the inlet gases for the second stage of the stripping tower is the outlet gas from the second-stage adsorption-separation unit, with a carbon dioxide concentration of 1-3%; the other is the stripping gas from the third stage of the stripping tower, with a carbon dioxide concentration of over 3%. The inlet gas for the third stage of the stripping tower is the outlet gas from the third-stage adsorption-separation unit, with a carbon dioxide concentration below 10 ppm. The carbon dioxide concentration in the outlet gas is 70-83%. After compression and adsorption separation of carbon dioxide to 3-10%, it is called primary decarbonization gas. Part of it is used as the first-stage inlet gas of the stripping tower, and part of it is sent to the second-stage adsorption separation to 1-3% to become secondary decarbonization gas. Part of the secondary decarbonization gas is used as the second-stage inlet gas of the stripping tower, and part of it is sent to the third-stage adsorption separation system to obtain gas with an outlet carbon dioxide concentration of less than 10 ppm, which is called tertiary decarbonization gas. It is used as the third-stage inlet gas of the stripping tower. In this way, high-concentration carbon dioxide or liquid carbon dioxide can be obtained while reducing or eliminating the energy waste of using pure nitrogen as the stripping inlet gas in traditional process stripping towers.

[0010] Advantages of this invention: 1. When starting up, nitrogen is used as the inlet gas for the stripping tower. Once the cycle begins, nitrogen is no longer used, or only a small amount of nitrogen needs to be added, thereby saving nitrogen. 2. Multi-stage staged gas stripping can use some low-concentration carbon dioxide gas as the stripping inlet gas, which can reduce the operating costs of the first or earlier stages of carbon dioxide purification and save on purification investment. Attached Figure Description

[0011] Figure 1 This invention relates to a process flow with two gas inlets in the same stripping tower.

[0012] Figure 2 The present invention relates to a three-stage gas stripping tower series process flow. Implementation

[0013] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0014] Example 1: As Figure 1The stripping tower shown has two gas inlets. One of the first-stage inlet gases is the outlet gas from the first-stage adsorption separation unit of liquefied non-condensable gas, with a carbon dioxide concentration of 4%. The other is the stripping gas from the second stage of the stripping tower, with a carbon dioxide concentration of 12%. The second-stage inlet gas is the outlet gas from the second-stage adsorption separation unit, with a carbon dioxide concentration of 8 ppm. The carbon dioxide concentration in the outlet gas of the stripping tower is 80%. After compression and adsorption separation of carbon dioxide to 4%, it is called the first-stage decarbonization gas. Part of it is used as the first-stage inlet gas of the stripping tower, and part of it is sent to the second-stage adsorption separation system to obtain the outlet gas with 8 ppm carbon dioxide, which is called the second-stage decarbonization gas and sent to the second-stage inlet gas of the stripping tower. In this way, high-concentration carbon dioxide or liquid carbon dioxide can be obtained while reducing or eliminating the energy waste of using pure nitrogen as the stripping inlet gas in traditional process stripping towers.

[0015] Example 2: A single stripping tower is designed with three gas inlets. One of the inlet gases for the first stage of the stripping tower is the outlet gas from the first-stage adsorption separation unit of liquefied non-condensable gas, with a carbon dioxide concentration of 5%. The other is the stripping gas from the second stage of the stripping tower, with a carbon dioxide concentration of 18%. One of the inlet gases for the second stage of the stripping tower is the outlet gas from the second-stage adsorption separation unit, with a carbon dioxide concentration of 1%. The other is the stripping gas from the third stage of the stripping tower, with a carbon dioxide concentration of 3% or higher. The inlet gas for the third stage of the stripping tower is the outlet gas from the third-stage adsorption separation unit, with a carbon dioxide concentration of 5 ppm. The gas exiting the stripping tower... The carbon dioxide concentration in the gas is 83%. After compression and adsorption separation of carbon dioxide to 5%, it is called primary decarbonization gas. Part of it is used as the first-stage inlet gas of the stripping tower, and the rest is sent to the second-stage adsorption separation to 1% carbon dioxide, which is called secondary decarbonization gas. Part of the secondary decarbonization gas is used as the second-stage inlet gas of the stripping tower, and the rest is sent to the third-stage adsorption separation system to obtain gas with 5ppm carbon dioxide at the outlet, which is called tertiary decarbonization gas. It is used as the third-stage inlet gas of the stripping tower. In this way, high-concentration carbon dioxide or liquid carbon dioxide can be obtained while reducing or eliminating the energy waste of using pure nitrogen as the stripping inlet gas in traditional process stripping towers.

[0016] Example 3: As Figure 2The diagram shows a three-stage stripping tower connected in series. One inlet gas of the first-stage stripping tower is the outlet gas from the first-stage adsorption-separation unit of liquefied non-condensable gas (LNG), with a carbon dioxide concentration of 8%. The other inlet gas is the stripped gas from the second-stage stripping tower, with a carbon dioxide concentration of 15%. One inlet gas of the second-stage stripping tower is the outlet gas from the second-stage adsorption-separation unit, with a carbon dioxide concentration of 1.5%. The other inlet gas is the stripped gas from the third-stage stripping tower, with a carbon dioxide concentration of 4%. The inlet gas of the third-stage stripping tower is the outlet gas from the third-stage adsorption-separation unit, with a carbon dioxide concentration of 6 ppm. The outlet gas of the stripping tower contains… With a carbon dioxide concentration of 82%, the carbon dioxide is compressed and separated by adsorption to 8%, which is called primary decarbonization gas. Part of it is used as the inlet gas of the first-stage stripping tower, and the rest is sent to the second-stage adsorption separation to 1.5%, which is called secondary decarbonization gas. Part of the secondary decarbonization gas is used as the inlet gas of the second-stage stripping tower, and the rest is sent to the third-stage adsorption separation system to obtain gas with 6ppm carbon dioxide at the outlet, which is called tertiary decarbonization gas. This gas is used as the inlet gas of the third-stage stripping tower. In this way, high-concentration carbon dioxide or liquid carbon dioxide can be obtained while reducing or eliminating the energy waste of using pure nitrogen as the stripping inlet gas in traditional process stripping towers.

Claims

1. A methanol wash gas stripping method characterized by The same stripping tower has two or more gas inlets. One of the first-stage inlet gases is liquefied non-condensable gas from the outlet of the first-stage adsorption separation unit, with a carbon dioxide concentration of 3-10%. The other is stripping gas from the second stage of the stripping tower below, with a carbon dioxide concentration of more than 10%. The last-stage inlet gas at the bottom of the stripping tower is the outlet gas from the last-stage adsorption separation unit, with a carbon dioxide concentration of less than 10 ppm. The carbon dioxide concentration in the outlet gas of the stripping tower is 70-83%. After compression and adsorption separation of carbon dioxide by the first-stage adsorption separation unit to 3-10%, it is called the first-stage decarbonization gas. Part of it is used as the first-stage inlet gas of the stripping tower, and part of it is sent to the next-stage adsorption separation unit. The gas with an outlet carbon dioxide concentration of less than 10 ppm obtained by the last-stage adsorption separation unit is called the last-stage decarbonization gas, which is sent to the last-stage gas inlet of the stripping tower. In this way, high-concentration carbon dioxide can be obtained while reducing or eliminating the energy waste of using pure nitrogen as the stripping inlet gas in traditional process stripping towers.

2. The methanol washing and stripping method according to claim 1, characterized in that... Two or more gas inlets constitute two.

3. A methanol washing and stripping method, characterized in that... The system consists of two or more stripping towers. One of the inlet gases for the first-stage stripping tower is liquefied non-condensable gas from the outlet of the first-stage adsorption separation unit, with a carbon dioxide concentration of 3-10%. The other is stripped gas from the second-stage stripping tower, with a carbon dioxide concentration of over 10%. The inlet gas for the final-stage stripping tower is the outlet gas from the final-stage adsorption separation unit, with a carbon dioxide concentration of less than 10 ppm. The carbon dioxide concentration in the outlet gas of the first-stage stripping tower is 70-83%. After compression and adsorption separation by the first-stage adsorption separation unit to remove carbon dioxide to 3-10%, this is called the first-stage decarbonization gas. Part of this gas is used as the inlet gas for the first-stage stripping tower, and the other part is sent to the next-stage adsorption separation unit. The gas with a carbon dioxide concentration of less than 10 ppm obtained from the outlet of the final-stage adsorption separation unit is called the final-stage decarbonization gas and is sent to the inlet of the final-stage stripping tower. This allows for the production of high-concentration carbon dioxide while reducing or eliminating the energy waste of using pure nitrogen as the inlet gas for stripping in traditional processes.

4. The methanol washing and stripping method according to claim 3, characterized in that... The term "two or more stripping towers" refers to two towers.

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