Method for hydrogen recovery and cascade refrigeration carbon dioxide capture in methanol cracking hydrogen production tail gas

Abstract

The invention discloses a method for hydrogen recovery and cascade refrigeration carbon dioxide capture in methanol cracking hydrogen production tail gas, and relates to the field of capture and recovery of carbon dioxide in industrial tail gas. The method comprises the following steps: (1) dehydrating and separating; (2) separating and purifying industrial-grade carbon dioxide; (3) separating and purifying food-grade carbon dioxide; and (4) separating and purifying high-purity hydrogen. According to the method, high-content carbon dioxide in the desorbed gas discharged in the methanol cracking hydrogen production process is firstly purified, then low-content hydrogen is purified, the occupied area of equipment is greatly reduced, the equipment investment is low, internal energy of the system is comprehensively utilized, the operation energy consumption of the system is low, the industrial safety is improved, and the method is suitable for industrial production. And meanwhile, industrial-grade and food-grade carbon dioxide and high-purity hydrogen are co-produced, the generated solid waste is less, and the pollution to the environment is greatly reduced.

Description

Technical Field

[0001] The invention relates to the field of carbon dioxide capture and recovery in industrial tail gas, and in particular to a method for recovering hydrogen and capturing carbon dioxide by cascade refrigeration in tail gas produced by hydrogen production through methanol cracking. Background Art

[0002] At present, domestic industrial production of carbon dioxide mainly uses industrial carbon-containing waste gas (CO2 content> 80%) as raw material for separation and purification. In addition to CO2, industrial carbon-containing waste gas also contains impurities such as H2, CO, H2S, COS, H2O, C2H4, C2H6, C3H6, C6H6, and CH3OH. CO2 products can be obtained through high pressure method, low pressure cryogenic method, pressure swing adsorption method, shallow low temperature adsorption distillation method, washing adsorption and low temperature distillation combination method, catalytic oxidation and distillation combination method and other methods. The quality of carbon dioxide products obtained by different methods is different, and their uses are also different. The carbon dioxide products produced by high pressure method, low pressure cryogenic method, pressure swing adsorption method and shallow low temperature adsorption distillation method are all industrial grade carbon dioxide and can only be used for general industrial purposes. The washing adsorption and low temperature distillation combination method is more suitable for the production of industrial grade liquid carbon dioxide from fermentation gas in alcohol plants. The catalytic oxidation and distillation combination method can produce food grade carbon dioxide, but catalytic oxidation dehydrogenation will produce a large amount of solid waste, which will pollute the environment. In addition, the production equipment used in this method occupies a large area, has high investment cost, high operating energy consumption and low profit. Summary of the invention

[0003] The present invention aims to solve the problems existing in the prior art in the above-mentioned background technology, and aims to provide a method for recovering hydrogen from tail gas of methanol cracking hydrogen production and capturing carbon dioxide by cascade refrigeration. The method uses the analytical gas discharged in the process of methanol cracking hydrogen production as raw material, can produce industrial-grade carbon dioxide and food-grade carbon dioxide, does not generate solid waste in the production process, has good process safety, improves the utilization rate of raw materials, reduces the emission of CO2 in the production process, and simultaneously utilizes pressure swing adsorption (PSA) purification technology to produce high-purity hydrogen, realizes comprehensive utilization of resources, and turns waste into treasure.

[0004] In order to achieve the above object, the present invention adopts the following technical solution:

[0005] The present invention provides a method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration, comprising:

[0006] (1) Dehydration and separation

[0007] The decomposed gas discharged from the methanol cracking hydrogen production process with a CO2 content of 65-71% is sent to the raw material compressor for pressurization treatment as a raw material, and then sent to the drying tower, cooled by the dry precooler, dehydrated by the dry separator, and then sent to the carbon dioxide deweighting tower;

[0008] (2) Industrial-grade carbon dioxide separation and purification

[0009] The low-temperature raw materials after dehydration and separation are heated by the dehydration tower reboiler at the bottom of the carbon dioxide dehydration tower, and the light component gas coming out of the top of the carbon dioxide dehydration tower is condensed by the dehydration tower condenser and separated by the dehydration tower separator. The liquid material separated at the bottom of the dehydration tower separator is divided into two paths, the first path refluxes into the carbon dioxide dehydration tower, and the second path enters the carbon dioxide light removal tower. The industrial-grade carbon dioxide extracted from the kettle of the carbon dioxide dehydration tower enters the product supercooler for cooling and is sent to the industrial-grade carbon dioxide storage tank;

[0010] (3) Food-grade carbon dioxide separation and purification

[0011] The light component impurities coming out from the top of the carbon dioxide light removal tower and the light component gas coming out from the top of the carbon dioxide heavy removal tower are connected and then enter the heavy removal tower condenser. The liquid food-grade carbon dioxide is extracted from the kettle of the carbon dioxide light removal tower and then cooled in the product supercooler and sent to the food-grade carbon dioxide storage tank.

[0012] (4) Separation and purification of high-purity hydrogen

[0013] The non-condensable gas separated from the top of the de-heavy tower separator is sent to the de-light tower condenser for condensation and separation. The liquid material separated from the bottom of the de-light tower separator is refluxed and sent to the carbon dioxide de-light tower. The low-temperature hydrogen-rich component separated from the top of the de-light tower separator flows through the dry pre-cooler as a cold source, and then is separated into high-purity hydrogen through the pressure swing adsorption system for filling.

[0014] Furthermore, the heat source of the deweighting tower reboiler comes from the gaseous ammonia pressurized by the ammonia compressor. The gaseous ammonia enters the ammonia-liquid separator after heat exchange in the deweighting tower reboiler. The low-temperature liquid ammonia coming out of the bottom of the ammonia-liquid separator is used as a cold source and is divided into two paths to enter the deweighting tower condenser and the product supercooler for heat exchange. After heat exchange, both flow back into the ammonia-liquid separator to continue circulation. The gaseous ammonia coming out of the top of the ammonia-liquid separator enters the ammonia compressor to continue circulation.

[0015] Furthermore, the liquid material entering the carbon dioxide removal tower enters the gas-liquid separator after heat exchange in the lightness removal tower regenerator at the bottom of the tower. The liquid carbon dioxide separated by the gas-liquid separator enters the lightness removal tower condenser as a cold source, refluxes into the gas-liquid separator for circulation after heat exchange, and the gaseous carbon dioxide separated by the gas-liquid separator enters the lightness removal tower regenerator as a heat source, enters the carbon dioxide compressor for pressurization after heat exchange, and is then sent to the carbon dioxide removal tower.

[0016] Further, the raw material compressor pressurizes the raw material to 3.5 MPa.

[0017] Further, the dry precooler cools the raw material to -25°C.

[0018] Furthermore, the operating pressure of the carbon dioxide deheavy tower is 2.5 MPa, and the operating pressure of the carbon dioxide delight tower is 2.0 MPa.

[0019] Furthermore, the pressure of the hydrogen-rich gas before entering the pressure swing adsorption system is 1.8 MPa.

[0020] Furthermore, the pressure swing adsorption system includes a buffer tank and multiple adsorbers. The buffer tank is connected to the multiple adsorbers arranged in parallel. Each adsorber is filled with an adsorption filler for adsorbing impurity components in the hydrogen-rich gas. Each adsorber is switched at a regular time to alternately adsorb and regenerate, so that the hydrogen-rich gas is continuously input and the high-purity hydrogen is continuously output.

[0021] The technical advantages and progress of the present invention are:

[0022] 1. The method of the present invention realizes the capture and recovery of CO2 from industrial tail gas containing medium-concentration CO2 (CO2 content of 65-71%), and first purifies the carbon dioxide with a large content in the analytical gas discharged in the process of hydrogen production by methanol cracking, and then purifies the hydrogen with a small content, the equipment footprint is greatly reduced, especially the adsorber volume and footprint in the pressure swing adsorption system are significantly reduced, the equipment investment is low, the internal energy of the system is comprehensively utilized, the system operation energy consumption is low, the solid waste generated is less, the pollution to the environment is greatly reduced, the industrial safety is improved, and industrial-grade and food-grade carbon dioxide and high-purity hydrogen are co-produced at the same time, the purity of industrial-grade carbon dioxide can reach 99.98%, the purity of food-grade carbon dioxide can reach 99.995%, and the purity of high-purity hydrogen can reach 99.999%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a process flow chart of the method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration in the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the present invention is further described below through specific embodiments in combination with the accompanying drawings, but the implementation mode of the present invention is not limited thereto.

[0025] This embodiment uses the desorption gas discharged from the methanol cracking hydrogen production process of a certain company as a raw material to purify high-purity carbon dioxide and high-purity hydrogen.

[0026] Table 1 Analysis of the desorption gas emitted from a company's methanol cracking hydrogen production process

[0027] project Total molar flow temperature pressure index 580kmol / h 40℃ 0.01MPa project <![CDATA[H2]]> <![CDATA[CO2]]> CO index 24.00％ 70.00％ 0.32％ project Total hydrocarbons <![CDATA[CH4]]> benzene index 1545.792ppm 1171.136ppm 50ppm project Methanol Total Sulfur benzene index 0.784ppm 0.127ppm 169.271ppm project Vinyl chloride Acetaldehyde index 252.352ppm 0.624ppm

[0028] like Figure 1 As shown, the method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration in this embodiment comprises:

[0029] (1) Dehydration and separation

[0030] The desorption gas discharged from the methanol cracking hydrogen production process is sent to the raw material compressor as a raw material, pressurized to 3.5MPa, and then sent to the drying tower, cooled to -25℃ by the drying precooler, dehydrated by the drying separator, and then sent to the carbon dioxide deweighting tower. The operating pressure of the carbon dioxide deweighting tower is 2.5MPa.

[0031] (2) Industrial-grade carbon dioxide separation and purification

[0032] The low-temperature raw materials after dehydration and separation are heated by the dehydration tower reboiler at the bottom of the carbon dioxide dehydration tower, and the light component gas coming out of the top of the carbon dioxide dehydration tower is condensed by the dehydration tower condenser and separated by the dehydration tower separator. The liquid material separated at the bottom of the dehydration tower separator is divided into two paths, the first path refluxes into the carbon dioxide dehydration tower, and the second path enters the carbon dioxide lightness removal tower. The operating pressure of the carbon dioxide lightness removal tower is 2.0MPa. The industrial-grade carbon dioxide extracted from the kettle of the carbon dioxide dehydration tower enters the product supercooler for cooling and is sent to the industrial-grade carbon dioxide storage tank;

[0033] (3) Food-grade carbon dioxide separation and purification

[0034] The light component impurities coming out from the top of the carbon dioxide light removal tower and the light component gas coming out from the top of the carbon dioxide heavy removal tower are connected and then enter the heavy removal tower condenser. The liquid food-grade carbon dioxide is extracted from the kettle of the carbon dioxide light removal tower and then cooled in the product supercooler and sent to the food-grade carbon dioxide storage tank.

[0035] (4) Separation and purification of high-purity hydrogen

[0036] The non-condensable gas separated from the top of the de-heavy tower separator is sent to the de-light tower condenser for condensation and separation. The liquid material separated from the bottom of the de-light tower separator is refluxed and sent to the carbon dioxide de-light tower. The low-temperature hydrogen-rich component separated from the top of the de-light tower separator flows through the dry pre-cooler as a cold source, and then is separated into high-purity hydrogen by the pressure swing adsorption system for filling. The pressure of the hydrogen-rich gas before entering the pressure swing adsorption system is 1.8MPa.

[0037] Specifically, the heat source of the deweighting tower reboiler comes from the gaseous ammonia pressurized by the ammonia compressor. The gaseous ammonia enters the ammonia-liquid separator after heat exchange in the deweighting tower reboiler. The low-temperature liquid ammonia coming out of the bottom of the ammonia-liquid separator is used as a cold source and is divided into two paths to enter the deweighting tower condenser and the product supercooler for heat exchange. After heat exchange, both are refluxed into the ammonia-liquid separator to continue circulation. The gaseous ammonia coming out of the top of the ammonia-liquid separator enters the ammonia compressor to continue circulation.

[0038] Specifically, the liquid material entering the carbon dioxide removal tower enters the gas-liquid separator after heat exchange in the lightness removal tower regenerator at the bottom of the tower. The liquid carbon dioxide separated by the gas-liquid separator enters the lightness removal tower condenser as a cold source, refluxes into the gas-liquid separator for circulation after heat exchange, and the gaseous carbon dioxide separated by the gas-liquid separator enters the lightness removal tower regenerator as a heat source, enters the carbon dioxide compressor for pressurization after heat exchange, and is then sent to the carbon dioxide removal tower.

[0039] Specifically, the pressure swing adsorption system includes a buffer tank and 6 adsorbers. The buffer tank is connected to the 6 adsorbers arranged in parallel. Each adsorber is filled with an adsorption filler for adsorbing impurity components in the hydrogen-rich gas. Each adsorber is switched at a regular time to alternately adsorb and regenerate, so that the hydrogen-rich gas is continuously input and high-purity hydrogen is continuously output.

[0040] The composition of the industrial grade carbon dioxide product obtained in this example is as follows:

[0041] project Total hydrocarbons Methane Total Sulfur benzene index 153.909ppm Not detected 0.123ppm 2.651ppb project Vinyl chloride Acetaldehyde Methanol purity index 136.499ppm 0.045ppm 0.028ppm 99.98％

[0042] The purity of the food-grade carbon dioxide obtained in this embodiment is 99.995%, and the purity of the high-purity hydrogen is 99.999%.

[0043] This example uses the desorption gas discharged from a company's methanol cracking hydrogen production process as raw material, with an hourly consumption of 13000Nm 3 The hourly output of liquid carbon dioxide is 17.5 tons, and the annual output is 150,000 tons / year. The hourly output of hydrogen is 0.2 tons, and the annual output is 1,600 tons.

[0044] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration, characterized in that: include: (1) Dehydration and separation The decomposed gas discharged from the methanol cracking hydrogen production process with a CO2 content of 65-71% is sent to the raw material compressor for pressurization treatment as a raw material, and then sent to the drying tower, cooled by the dry precooler, dehydrated by the dry separator, and then sent to the carbon dioxide deweighting tower; (2) Industrial-grade carbon dioxide separation and purification The low-temperature raw materials after dehydration and separation are heated by the dehydration tower reboiler at the bottom of the carbon dioxide dehydration tower, and the light component gas coming out of the top of the carbon dioxide dehydration tower is condensed by the dehydration tower condenser and separated by the dehydration tower separator. The liquid material separated at the bottom of the dehydration tower separator is divided into two paths, the first path refluxes into the carbon dioxide dehydration tower, and the second path enters the carbon dioxide light removal tower. The industrial-grade carbon dioxide extracted from the kettle of the carbon dioxide dehydration tower enters the product supercooler for cooling and is sent to the industrial-grade carbon dioxide storage tank; (3) Food-grade carbon dioxide separation and purification The light component impurities coming out from the top of the carbon dioxide light removal tower and the light component gas coming out from the top of the carbon dioxide heavy removal tower are connected and then enter the heavy removal tower condenser. The liquid food-grade carbon dioxide is extracted from the kettle of the carbon dioxide light removal tower and then cooled in the product supercooler and sent to the food-grade carbon dioxide storage tank. (4) Separation and purification of high-purity hydrogen The non-condensable gas separated from the top of the de-heavy tower separator is sent to the de-light tower condenser for condensation and separation. The liquid material separated from the bottom of the de-light tower separator is refluxed and sent to the carbon dioxide de-light tower. The low-temperature hydrogen-rich component separated from the top of the de-light tower separator flows through the dry pre-cooler as a cold source, and then is separated into high-purity hydrogen through the pressure swing adsorption system for filling.

2. The method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration according to claim 1, characterized in that: The heat source of the deweighting tower reboiler comes from the gaseous ammonia pressurized by the ammonia compressor. The gaseous ammonia enters the ammonia-liquid separator after heat exchange in the deweighting tower reboiler. The low-temperature liquid ammonia coming out of the bottom of the ammonia-liquid separator is used as a cold source and is divided into two paths to enter the deweighting tower condenser and the product supercooler for heat exchange. After heat exchange, both flow back into the ammonia-liquid separator to continue circulation. The gaseous ammonia coming out of the top of the ammonia-liquid separator enters the ammonia compressor to continue circulation.

3. The method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration according to claim 2, characterized in that: The liquid material entering the carbon dioxide removal tower enters the gas-liquid separator after heat exchange in the lightness removal tower regenerator at the bottom of the tower. The liquid carbon dioxide separated by the gas-liquid separator enters the lightness removal tower condenser as a cold source, refluxes into the gas-liquid separator for circulation after heat exchange, and the gaseous carbon dioxide separated by the gas-liquid separator enters the lightness removal tower regenerator as a heat source, enters the carbon dioxide compressor for pressurization after heat exchange, and then is sent to the carbon dioxide removal tower.

4. The method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration according to claim 1, characterized in that: The raw material compressor pressurizes the raw material to 3.5 MPa.

5. The method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration according to claim 1, characterized in that: The dry precooler cools the raw material to -25℃.

6. The method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration according to claim 1, characterized in that: The operating pressure of the carbon dioxide deheavy tower is 2.5MPa, and the operating pressure of the carbon dioxide delight tower is 2.0MPa.

7. The method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration according to claim 1, characterized in that: The pressure of the hydrogen-rich gas before entering the pressure swing adsorption system is 1.8 MPa.

8. The method for recovering hydrogen from tail gas of hydrogen production by methanol cracking and capturing carbon dioxide by cascade refrigeration according to claim 1, characterized in that: The pressure swing adsorption system includes a buffer tank and multiple adsorbers. The buffer tank is connected to the multiple adsorbers arranged in parallel. Each adsorber is filled with an adsorbent filler for adsorbing impurity components in the hydrogen-rich gas. Each adsorber is switched at a regular time to alternately adsorb and regenerate, so that the hydrogen-rich gas is continuously input and the high-purity hydrogen is continuously output.

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