Recovery and purification process and device of hydrogen and carbon monoxide in tail gas of ethanol plant

Abstract

The invention provides a process and device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device. The process comprises: after the pressure of hydrogen-rich gas is adjusted, ethanol after pre-cooling or ethanol-rich liquid after pre-cooling is used as an absorbent to absorb macromolecular impurities contained therein, so as to obtain purified hydrogen-rich gas and ethanol-rich solution or ethanol-rich solution; after the pressure of carbon monoxide-rich gas is adjusted, ethanol after pre-cooling or ethanol-rich liquid after pre-cooling is used as an absorbent to absorb macromolecular impurities contained therein, so as to obtain purified carbon monoxide-rich gas and ethanol-rich solution or ethanol-rich solution; or, the process comprises: after the pressure of a mixture of hydrogen-rich gas and carbon monoxide-rich gas is adjusted, ethanol after pre-cooling or ethanol-rich liquid after pre-cooling is used as an absorbent to absorb macromolecular impurities contained therein, so as to obtain a purified hydrogen-rich gas and carbon monoxide-rich gas mixture and ethanol-rich solution or ethanol-rich solution.

Description

Technical Field

[0001] The invention relates to a process and a device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device, belonging to the technical fields of natural gas chemical industry, coal chemical industry and petrochemical industry. Background Art

[0002] Conventional ethanol plant tail gas, whether hydrogen-rich tail gas or carbon monoxide-rich tail gas, contains a large number of macromolecular impurities, such as methanol, ethanol, dimethyl ether, methyl acetate, ethyl acetate, etc. These macromolecular impurities need to be removed before the above hydrogen-rich gas and carbon monoxide-rich gas can be recovered. The boiling points and freezing points of the main macromolecular impurities in the ethanol plant are shown in Table 1 below.

[0003] Table 1 Boiling point and freezing point of main macromolecular impurities in tail gas of ethanol plant

[0004] Components Chemical formula Molecular weight Boiling point / ℃ Freezing point / ℃ Methanol <![CDATA[CH4O]]> 32 64.7 -97 Ethanol <![CDATA[C2H6O]]> 46 78 -114 dimethyl ether <![CDATA[C2H6O]]> 46 -23 -138.5 Methyl acetate <![CDATA[C3H6O2]]> 74 57.8 -98.7 Ethyl acetate <![CDATA[C4H8O2]]> 88 77 -84

[0005] At present, the main methods for recovering and purifying tail gas from ethanol plants are: condensation method and temperature swing adsorption method. The condensation method uses the high boiling point of impurity components. After cooling step by step, the macromolecular impurities are condensed and separated into gas phase and liquid phase, where the gas phase is purified hydrogen-rich gas or carbon monoxide-rich gas or a mixture of hydrogen and carbon monoxide. Temperature swing adsorption uses the strength of the interaction between molecules and adsorbents to separate components. It is a physical adsorption phenomenon. The unadsorbed components are discharged from the adsorber as hydrogen-rich or carbon monoxide-rich or hydrogen-rich and carbon monoxide mixture products, while the adsorbed medium needs to be heated for desorption. The heat required for regeneration is supplied by an external heat source. After desorption, it can be discharged to the flare or fuel gas pipeline network.

[0006] Whether using the "condensation method" or the "temperature swing adsorption method", both forms of ethanol tail gas recovery and purification processes have certain limitations.

[0007] Firstly, the condensation method requires cooling the exhaust gas of the entire ethanol plant to a very low temperature in order to remove large molecular impurities with higher boiling points such as methanol, ethanol, dimethyl ether, methyl acetate, ethyl acetate, etc., and the condensation method has a poor separation effect on dimethyl ether. Even if the carbon monoxide-rich exhaust gas of the ethanol plant is cooled to -50°C, the gas phase still contains 1.144v% dimethyl ether. If it is directly sent to the downstream synthesis unit without other treatment, it may cause process problems such as catalyst carbon deposition in the downstream gas-using unit (such as the methanol synthesis unit).

[0008] Secondly, the traditional pressure swing adsorption method cannot achieve the decompression of large molecular impurities in the tail gas of the ethanol unit at room temperature, and temperature swing adsorption must be used. Temperature swing adsorption is usually more reasonable for treating impurity contents of tens to hundreds of ppmv, but when the content of large molecular impurities is too high, not only the filling amount of the adsorbent is greatly increased, but also the energy consumption of the regeneration heating desorption process is greatly increased. The above purification methods are too large and not very economical.

[0009] Based on the above factors, providing a new tail gas recovery and purification process and device for ethanol plants has become a technical problem that urgently needs to be solved in this field. Summary of the invention

[0010] In order to solve the above-mentioned shortcomings and deficiencies, an object of the present invention is to provide a process for recovering and purifying hydrogen and carbon monoxide in the tail gas of an ethanol plant.

[0011] Another object of the present invention is to provide a device for recovering and purifying hydrogen and carbon monoxide in tail gas from an ethanol plant.

[0012] In order to achieve the above objectives, on the one hand, the present invention provides a process for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol plant, wherein when the tail gas of the ethanol plant is hydrogen-rich gas and carbon monoxide-rich gas and the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified respectively, the process comprises:

[0013] After the pressure of the hydrogen-rich gas is adjusted, the pre-cooled ethanol or the pre-cooled ethanol-rich liquid is used as an absorbent to absorb the macromolecular impurities contained therein, thereby obtaining the purified hydrogen-rich gas and the ethanol-rich solution or the ethanol-rich solution;

[0014] After the pressure of the carbon monoxide-rich gas is adjusted, the pre-cooled ethanol or the pre-cooled ethanol-rich liquid is used as an absorbent to absorb the macromolecular impurities contained therein, thereby obtaining the purified carbon monoxide-rich gas and the ethanol-rich solution or the ethanol-rich solution;

[0015] When the tail gas of the ethanol plant is hydrogen-rich gas and carbon monoxide-rich gas and the mixture of hydrogen-rich gas and carbon monoxide-rich gas is recovered and purified, the process includes:

[0016] After the pressure of the hydrogen-rich gas and carbon monoxide-rich gas mixture is adjusted, the pre-cooled ethanol or the pre-cooled ethanol-rich liquid is used as an absorbent to absorb the macromolecular impurities contained therein, thereby obtaining a purified hydrogen-rich gas and carbon monoxide-rich gas mixture and an ethanol-rich solution or an ethanol-rich solution.

[0017] In the process described above, under normal circumstances, the temperature of the tail gas discharged from the ethanol unit is usually less than 50°C (such as room temperature), but the pressure is relatively high, up to 5.0 MPaG. Therefore, the tail gas needs to be pressure-regulated before it is recovered and purified. However, the present application does not make specific requirements on the degree of pressure regulation, and technical personnel in this field can reasonably determine the degree of pressure regulation based on actual needs on site. Under normal circumstances, the pressure of the tail gas discharged from the ethanol unit to be treated in this process and the gas obtained after treatment are not higher than 5.0 MPaG, and the pressure drop of the gas before and after the process is very small, and the obtained gas can be directly sent downstream after being reheated to room temperature.

[0018] Preferably, the above process further comprises performing pressure swing adsorption on the purified hydrogen-rich gas to obtain high-purity hydrogen.

[0019] Preferably, the above process further comprises performing membrane separation on the purified carbon monoxide-rich gas to obtain high-purity carbon monoxide.

[0020] Preferably, the above process further comprises performing heat and cold exchange between the hydrogen-rich gas and carbon monoxide-rich gas mixture and the purified hydrogen-rich gas and carbon monoxide-rich gas mixture.

[0021] Preferably, the above process also includes performing heat exchange between the hydrogen-rich gas and the purified hydrogen-rich gas and / or the purified carbon monoxide-rich gas; performing heat exchange between the carbon monoxide-rich gas and the purified carbon monoxide-rich gas and / or the purified hydrogen-rich gas.

[0022] In the process described above, the pre-cooling needs to be appropriately adjusted according to the freezing point of the component with the highest freezing point among the macromolecular impurity components, and the temperature of the absorbent after pre-cooling cannot be lower than the freezing point of the component with the highest freezing point; preferably, the pre-cooling is to reduce the temperature of the absorbent from room temperature to 0 to -80°C, more preferably to reduce the temperature of the absorbent from room temperature to -30°C.

[0023] The pre-cooling can be achieved by utilizing a circulation process such as an ice machine or propylene refrigeration.

[0024] In the above-mentioned process, the ethanol-rich liquid used as the absorbent can be, for example, the ethanol-rich liquid produced by the ethanol plant and a mixture of ethanol and methanol, which are mixtures whose main component is ethanol, and it is necessary to ensure that the impurities therein do not cause an increase in the partial pressure of macromolecular impurities. Among them, when the absorbent used is ethanol, the product obtained after absorption corresponds to an ethanol-rich solution; when the absorbent is an ethanol-rich solution, the product obtained after absorption corresponds to an ethanol-rich solution.

[0025] In the above-mentioned process, preferably, the operating pressure of the absorption process is 3.0-8.0 MPaG. For example, in one specific embodiment of the present invention, the operating pressure of the absorption process is 3.7 MPaG. The present application is operated at a pressure of 3.7 MPaG, and the recovered and purified tail gas of the ethanol unit can be directly sent to the downstream methanol synthesis unit as raw gas without pressurization.

[0026] Preferably, the above process further comprises: separating the macromolecular impurities from the rich ethanol solution or the rich-rich ethanol solution obtained after absorbing the macromolecular impurities after reheating, and then recycling the poor ethanol solution or the poor-rich ethanol solution obtained after separation as an absorbent. In a specific embodiment of the present invention, the operation can be carried out according to the following specific steps:

[0027] The ethanol-rich solution or the rich-rich ethanol solution discharged from the bottom of the absorption tower after absorbing the macromolecular impurities is returned to the ethanol device for ethanol separation after reheating, and then other macromolecular components are separated (the conventional methods in the art can be used for separation), and the regenerated lean ethanol solution or lean-rich ethanol solution is pressurized by a pump and circulated as an absorbent.

[0028] In the above-mentioned process, preferably, the absorption process is carried out in an absorption tower; more preferably, the absorption tower comprises a packed tower or a plate tower.

[0029] The process provided by the present invention is a process for recovering and purifying hydrogen and carbon monoxide in the tail gas of an ethanol plant. By using the process, an ethanol plant can realize the recovery and purification of H2-rich and CO-rich tail gas of an ethanol plant. The process can also be applied to existing plants that use ethanol to produce olefins or use ethanol processes to produce other chemical products. The process can solve the risk problem that the recovery and purification of the tail gas of the ethanol plant requires the use of temperature swing adsorption separation technology, which is easy to cause high-temperature desorption and carbon deposition, causing adsorbent failure, etc., thereby reducing the energy consumption of the tail gas recovery process of the ethanol plant, and at the same time, can maximize the purity of the product carbonyl synthesis gas.

[0030] On the other hand, the present invention also provides a device for recovering and purifying hydrogen and carbon monoxide in the tail gas of an ethanol device for realizing the above-mentioned process for recovering and purifying hydrogen and carbon monoxide in the tail gas of an ethanol device, wherein:

[0031] When the hydrogen-rich gas and carbon monoxide-rich gas mixture is recovered and purified, the device comprises: a gas mixer, a refrigerator and an absorption tower, the hydrogen-rich gas and the carbon monoxide-rich gas are mixed in the gas mixer to obtain the hydrogen-rich gas and carbon monoxide-rich gas mixture; the absorbent is sent to the absorption tower after being cooled by the refrigerator to absorb the macromolecular impurities contained in the hydrogen-rich gas and carbon monoxide-rich gas mixture to obtain the purified hydrogen-rich gas and carbon monoxide-rich gas mixture and ethanol-rich solution or ethanol-rich solution;

[0032] When the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified respectively, the device comprises: a refrigerator, a first absorption tower and a second absorption tower, or the device comprises: a refrigerator and a segmented absorption tower; the absorbent is cooled by the refrigerator and sent to the first absorption tower and the second absorption tower respectively, or the absorbent is cooled by the refrigerator and sent to the segmented absorption tower for absorbing the macromolecular impurities contained in the hydrogen-rich gas and the carbon monoxide-rich gas, and obtaining the purified hydrogen-rich gas and ethanol-rich solution or ethanol-rich solution; the purified carbon monoxide-rich gas and ethanol-rich solution or ethanol-rich solution.

[0033] In the device described above, when the device includes: a refrigerator and a segmented absorption tower, the absorbent is cooled by the refrigerator and then sent to the segmented absorption tower to absorb the macromolecular impurities contained in the hydrogen-rich gas and the carbon monoxide-rich gas in the upper and lower sections of the segmented absorption tower respectively. After absorption, the upper section obtains purified hydrogen-rich gas and ethanol-rich solution or ethanol-rich solution; the lower section obtains purified carbon monoxide-rich gas and ethanol-rich solution or ethanol-rich solution.

[0034] Preferably, when the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified respectively, the device further comprises a pressure swing adsorption device for performing a pressure swing adsorption treatment on the purified hydrogen-rich gas to obtain high-purity hydrogen.

[0035] Preferably, when the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified respectively, the device further comprises a membrane separation device for performing membrane separation on the purified carbon monoxide-rich gas to obtain high-purity carbon monoxide.

[0036] Preferably, when the hydrogen-rich gas and carbon monoxide-rich gas mixture is recovered and purified, the device further comprises a heat exchanger for performing heat and cold exchange between the hydrogen-rich gas and carbon monoxide-rich gas mixture and the purified hydrogen-rich gas and carbon monoxide-rich gas mixture.

[0037] Preferably, when the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified, the device further includes a heat exchanger, and the device further includes a first heat exchanger and a second heat exchanger, the first heat exchanger is used for performing cold and heat exchange between the hydrogen-rich gas and the purified hydrogen-rich gas and / or the purified carbon monoxide-rich gas; the second heat exchanger is used for performing cold and heat exchange between the carbon monoxide-rich gas and the purified carbon monoxide-rich gas and / or the purified hydrogen-rich gas.

[0038] The process and device for recovering and purifying hydrogen and carbon monoxide in the tail gas of an ethanol device provided by the present invention adopts pre-cooled ethanol or ethanol-rich liquid produced by the pre-cooled ethanol device as an absorbent to absorb hydrogen-rich gas and carbon monoxide-rich gas in the tail gas of the ethanol device, and then recovers and purifies hydrogen and carbon monoxide components. It can not only avoid many disadvantages brought about by the conventional condensation method and temperature swing adsorption method in the art, but also effectively reduce the energy consumption of the device, and can improve the recovery rate of hydrogen and carbon monoxide components in the tail gas of the ethanol device, and at the same time, it can also improve the product purity of hydrogen and carbon monoxide components in the tail gas of the ethanol device to meet the requirements of raw material impurity components of downstream devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 This is a schematic diagram of the structure of the device provided in Example 1 of the present invention.

[0041] Figure 2 This is a schematic diagram of the structure of the device provided in Example 2 of the present invention.

[0042] Figure 3 This is a schematic diagram of the structure of the device provided in Example 4 of the present invention.

[0043] Figure 4 This is a schematic diagram of the structure of the device provided in Example 5 of the present invention.

[0044] Description of main figures:

[0045] H2R, hydrogen-rich gas;

[0046] COR, carbon monoxide-rich gas;

[0047] HAC, a mixture of hydrogen-rich gas and carbon monoxide-rich gas;

[0048] EtOH, ethanol absorbent;

[0049] OXO, carbonyl gas;

[0050] REtOH, ethanol-rich solution;

[0051] Ex1C, cold logistics;

[0052] Ex1H, thermal logistics;

[0053] Ex1H1, first hot stream;

[0054] Ex1H2, second hot stream;

[0055] 1. Absorption tower;

[0056] 11. The first absorption tower;

[0057] 12. The second absorption tower;

[0058] 2. Refrigerator;

[0059] 3. Gas mixer;

[0060] 4. Heat exchanger;

[0061] 41. A first heat exchanger;

[0062] 42. Second heat exchanger. DETAILED DESCRIPTION

[0063] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical scheme of the present invention is now described in detail in conjunction with the following specific embodiments, but it should not be understood as limiting the applicable scope of the present invention.

[0064] Example 1

[0065] This embodiment provides a device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device. The structural schematic diagram of the device is shown in FIG. Figure 1 As shown, from Figure 1 It can be seen that the device includes: a gas mixer 3, a refrigerator 2 and an absorption tower 1. The hydrogen-rich gas H2R and the carbon monoxide-rich gas COR are mixed in the gas mixer 3 to obtain a hydrogen-rich gas and a carbon monoxide-rich gas mixture HAC; the absorbent (such as ethanol absorbent EtOH) is sent to the absorption tower 1 after being cooled by the refrigerator 2 to absorb the macromolecular impurities contained in the hydrogen-rich gas and the carbon monoxide-rich gas mixture HAC to obtain a purified hydrogen-rich gas and a carbon monoxide-rich gas mixture (carbonyl synthesis gas OXO) and an ethanol-rich solution REtOH.

[0066] Example 2

[0067] This embodiment provides a device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device. The structural schematic diagram of the device is shown in FIG. Figure 2 As shown, from Figure 2It can be seen that the device includes: a refrigerator 2, a first absorption tower 11 and a second absorption tower 12; the absorbent (such as ethanol absorbent EtOH) is sent to the first absorption tower 11 and the second absorption tower 12 respectively after being cooled by the refrigerator 2, and is used to absorb the macromolecular impurities contained in the hydrogen-rich gas H2R and the carbon monoxide-rich gas COR, and obtain the purified hydrogen-rich gas and ethanol-rich solution REtOH; the purified carbon monoxide-rich gas and ethanol-rich solution REtOH are obtained respectively.

[0068] Example 3

[0069] This embodiment provides a device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device, wherein the device comprises: a refrigerator, a first absorption tower and a second absorption tower; the absorbent is cooled by the refrigerator and sent to the first absorption tower and the second absorption tower respectively, for absorbing macromolecular impurities contained in hydrogen-rich gas and carbon monoxide-rich gas, and obtaining purified hydrogen-rich gas and ethanol-rich solution respectively; purified carbon monoxide-rich gas and ethanol-rich solution;

[0070] In this embodiment, the device further includes a pressure swing adsorption device (not shown in the figure) for performing pressure swing adsorption treatment on the purified hydrogen-rich gas to obtain high-purity hydrogen;

[0071] In this embodiment, the device further comprises a membrane separation device (not shown in the figure) for performing membrane separation on the purified carbon monoxide-rich gas to obtain high-purity carbon monoxide.

[0072] Example 4

[0073] This embodiment provides a device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device. The structural schematic diagram of the device is shown in FIG. Figure 3 As shown, from Figure 3 As can be seen in the figure, the device comprises: a gas mixer 3, a refrigerator 2 and an absorption tower 1. The hydrogen-rich gas H2R and the carbon monoxide-rich gas COR are mixed in the gas mixer 3 to obtain a hydrogen-rich gas and a carbon monoxide-rich gas mixture HAC; the absorbent (such as ethanol absorbent EtOH) is sent to the absorption tower 1 after being cooled by the refrigerator 2 to absorb the macromolecular impurities contained in the hydrogen-rich gas and the carbon monoxide-rich gas mixture HAC to obtain a purified hydrogen-rich gas and a carbon monoxide-rich gas mixture (carbonyl synthesis gas OXO) and an ethanol-rich solution REtOH;

[0074] In this embodiment, the device also includes a heat exchanger 4, which is arranged on the pipeline between the gas mixer 3 and the absorption tower 1, and is used for performing heat and cold exchange on the cold logistics Ex1C and the hot logistics Ex1H to maximize heat recovery and reduce utility consumption; wherein, the cold logistics Ex1C is a purified hydrogen-rich gas and carbon monoxide-rich gas mixture (carbonyl synthesis gas OXO), and the hot logistics Ex1H is a hydrogen-rich gas and carbon monoxide-rich gas mixture HAC.

[0075] Example 5

[0076] This embodiment provides a device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device. The structural schematic diagram of the device is shown in FIG. Figure 4 As shown, from Figure 4 It can be seen that the device includes: a refrigerator 2, a first absorption tower 11 and a second absorption tower 12; the absorbent (such as ethanol absorbent EtOH) is sent to the first absorption tower 11 and the second absorption tower 12 respectively after being cooled by the refrigerator 2, and is used to absorb the macromolecular impurities contained in the hydrogen-rich gas H2R and the carbon monoxide-rich gas COR, and obtain the purified hydrogen-rich gas and the ethanol-rich solution REtOH; the purified carbon monoxide-rich gas and the ethanol-rich solution REtOH;

[0077] In this embodiment, the device further includes a first heat exchanger 41 and a second heat exchanger 42, which are respectively located in the pipeline between the hydrogen-rich gas H2R and the first absorption tower 11, and the carbon monoxide-rich gas COR and the second absorption tower 12;

[0078] The first heat exchanger 41 is used to perform heat exchange between the cold stream Ex1C and the second hot stream Ex1H2 to maximize heat recovery and reduce utility consumption; the second hot stream Ex1H2 is hydrogen-rich gas, and the cold stream Ex1C is purified hydrogen-rich gas;

[0079] The second heat exchanger 42 is used for performing heat exchange between the cold logistics Ex1C and the first hot logistics Ex1H1 to maximize heat recovery and reduce utility consumption; the first hot logistics Ex1H1 is carbon monoxide-rich gas, and the cold logistics Ex1C is purified carbon monoxide-rich gas.

[0080] Example 6

[0081] This embodiment provides a process for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device, wherein the process is implemented using the device provided in Example 1, and the process includes:

[0082] With the large-scale industrialization of syngas-to-ethanol plants, the amount of tail gas emitted by ethanol plants has gradually increased. Taking a 500,000-ton / year ethanol plant as an example, the standard gas flow rates of hydrogen-rich gas and carbon monoxide-rich gas emitted during the normal process are 1865 Nm 3 / h and 5280Nm 3 / h, the above two gases are mixed in a gas mixer and then sent to an absorption tower from the bottom of the tower for recovery and purification. The absorbent is an ethanol liquid or an ethanol-rich liquid (such as the ethanol-rich liquid produced by an ethanol device) at about -30°C and enters the absorption tower from the top of the absorption tower. The hydrogen-rich gas and the carbon monoxide-rich gas mixture and the absorbent are subjected to countercurrent mass transfer and heat transfer in the tower;

[0083] Afterwards, light components not absorbed by the absorbent, such as hydrogen, carbon monoxide, methane, ethane, ethylene, propylene, nitrogen, argon and other components, are discharged from the top of the absorber to obtain a purified hydrogen-rich gas and carbon monoxide-rich gas mixture (carbonyl synthesis gas). After the carbonyl synthesis gas is reheated to room temperature, it can be directly sent as raw gas to the downstream methanol synthesis unit supporting the ethanol synthesis process or the device requiring carbonyl synthesis gas as a raw material. The trace amount of absorbent ethanol component present in the carbonyl synthesis gas is within the acceptable range of the downstream methanol device or other device users; while the macromolecular components absorbed by the absorbent, such as methanol, dimethyl ether, methyl acetate, ethyl acetate, etc. are enriched in the ethanol liquid or the ethanol-rich liquid, that is, they correspond to the ethanol-rich liquid or the ethanol-rich liquid, respectively, and are discharged from the bottom of the absorber. After reheating, they can be returned to the ethanol device for ethanol separation, and then other components are separated. The regenerated lean ethanol liquid or the lean-rich ethanol liquid is pressurized by a pump and circulated as an absorbent.

[0084] The material balance corresponding to the process provided in this embodiment is shown in Table 2 below.

[0085] Table 2

[0086]

[0087]

[0088] Note: Mole Frac in Table 2 is mole fraction.

[0089] The logistics in the above Table 2 are calculated without heat recovery and are only used for illustration. The specific heat recovery can be matched by utilizing the temperature difference between the inlet and outlet logistics of the absorption tower, mainly for the heat exchange between the purified gas and the raw gas entering the tower.

[0090] Example 7

[0091] This embodiment provides a process for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol device, wherein the process is implemented using the device provided in Example 2, and the process includes:

[0092] This example still takes a 500,000 ton / year ethanol plant as an example. The standard gas flow rates of hydrogen-rich gas and carbon monoxide-rich gas discharged during the normal process are 1865 Nm 3 / h and 5280Nm 3 / h,

[0093] After the pressure is adjusted, the hydrogen-rich gas is sent from the bottom of the second absorption tower to the second absorption tower for recovery and purification. The absorbent is an ethanol liquid or an ethanol-rich liquid (such as the ethanol-rich liquid produced by the ethanol device) at about -30°C and enters the second absorption tower from the top of the second absorption tower. The hydrogen-rich gas and the absorbent are subjected to countercurrent mass transfer and heat transfer in the second absorption tower.

[0094] Afterwards, light components that are not absorbed by the absorbent, such as hydrogen, carbon monoxide, methane, ethane, ethylene, propylene, nitrogen, argon and other components, are discharged from the top of the second absorption tower to obtain a purified hydrogen-rich gas, which can be directly sent to a downstream device after being reheated to room temperature. The trace amount of absorbent ethanol components present in the purified hydrogen-rich gas is within the acceptable range of the downstream device; while the large molecular components absorbed by the absorbent, such as methanol, dimethyl ether, methyl acetate, ethyl acetate and the like, are enriched in the ethanol liquid or the ethanol-rich liquid, that is, they correspond to the ethanol-rich liquid or the ethanol-rich liquid, respectively, and are discharged from the bottom of the second absorption tower. After being reheated, they can be returned to the ethanol device for ethanol separation, and then other components are separated. The regenerated lean ethanol liquid or lean-rich ethanol liquid is pressurized by a pump and circulated as an absorbent.

[0095] The material balance corresponding to the process provided in this embodiment is shown in Table 3 below.

[0096] Table 3

[0097]

[0098] Note: Mole Frac in Table 3 is mole fraction.

[0099] The carbon monoxide-rich gas is sent from the bottom of the first absorption tower to the first absorption tower for recovery and purification after pressure adjustment. The absorbent is an ethanol liquid or an ethanol-rich liquid (such as the ethanol-rich liquid produced by the ethanol device) at about -30°C and enters the first absorption tower from the top of the first absorption tower. The carbon monoxide-rich gas and the absorbent are subjected to countercurrent mass transfer and heat transfer in the first absorption tower.

[0100] Afterwards, light components that are not absorbed by the absorbent, such as hydrogen, carbon monoxide, methane, ethane, ethylene, propylene, nitrogen, argon and other components, are discharged from the top of the first absorption tower to obtain a purified carbon monoxide-rich gas, which can be directly sent to a downstream device after being reheated to room temperature. The trace amount of absorbent ethanol components present in the purified carbon monoxide-rich gas is within the acceptable range of the downstream device; while the large molecular components absorbed by the absorbent, such as methanol, dimethyl ether, methyl acetate, ethyl acetate and the like are enriched in the ethanol liquid or the ethanol-rich liquid, that is, they correspond to the ethanol-rich liquid or the ethanol-rich liquid, respectively, and are discharged from the bottom of the first absorption tower. After being reheated, they can be returned to the ethanol device for ethanol separation, and then other components are separated. The regenerated lean ethanol liquid or the lean-rich ethanol liquid is pressurized by a pump and circulated as an absorbent. In this embodiment, the ethanol-rich liquid or ethanol-rich liquid obtained after the recovery and purification of the hydrogen-rich gas and the ethanol-rich liquid or ethanol-rich liquid obtained after the recovery and purification of the carbon monoxide-rich gas can be mixed after the absorption is completed and sent out of this unit together to the downstream ethanol device for recovery and regeneration and then recycled.

[0101] The material balance corresponding to the process provided in this embodiment is shown in Table 4 below.

[0102] Table 4

[0103]

[0104]

[0105] Note: Mole Frac in Table 4 is mole fraction.

[0106] In summary, the device provided by the present invention has no rotating parts inside, and only the heat exchange equipment is set in the device, which is not prone to failure; compared with the condensation method and the temperature swing adsorption method, it not only has low energy consumption, simple equipment and low investment, but also does not require low temperature operation;

[0107] The process provided by the present invention can directly remove large molecular hydrocarbon impurities such as methanol, ethanol, dimethyl ether, methyl acetate, ethyl acetate and other components in the tail gas of the ethanol plant to the greatest extent possible. After the absorbent is regenerated, the above impurities can be discharged to the flare or the fuel gas pipeline network to prevent such large molecular gases from causing problems such as catalyst carbon deposition in the downstream devices, thereby improving the online rate of the downstream devices; at the same time, the recovery rate of hydrogen and carbon monoxide components in the hydrogen-rich gas and carbon monoxide-rich gas of the ethanol plant can be as high as 99v% or more, and the purity can fully meet the requirements of various devices in the ethanol plant factory for impurity components in the raw gas; while the conventional temperature swing adsorption method in the field must be subjected to gas heating backblowing regeneration, and part of the product will be lost in the process, which cannot achieve such a high recovery rate as the process used in the present application.

[0108] The above is only a specific embodiment of the present invention, and cannot be used to limit the scope of the invention. Therefore, the replacement of equivalent components, or equivalent changes and modifications made according to the protection scope of the patent of the present invention, should still fall within the scope of this patent. In addition, the technical features of the present invention can be freely combined with each other, with each other and with each other, and with each other.

Claims

1. A process for recovering and purifying hydrogen and carbon monoxide in tail gas from an ethanol plant, characterized in that: When the tail gas of the ethanol device is hydrogen-rich gas and carbon monoxide-rich gas and the hydrogen-rich gas and carbon monoxide-rich gas are recovered and purified respectively, the process includes: After the pressure of the hydrogen-rich gas is adjusted, the pre-cooled ethanol or the pre-cooled ethanol-rich liquid is used as an absorbent to absorb the macromolecular impurities contained therein, thereby obtaining the purified hydrogen-rich gas and the ethanol-rich solution or the ethanol-rich solution; After the pressure of the carbon monoxide-rich gas is adjusted, the pre-cooled ethanol or the pre-cooled ethanol-rich liquid is used as an absorbent to absorb the macromolecular impurities contained therein, thereby obtaining the purified carbon monoxide-rich gas and the ethanol-rich solution or the ethanol-rich solution; When the tail gas of the ethanol plant is hydrogen-rich gas and carbon monoxide-rich gas and the mixture of hydrogen-rich gas and carbon monoxide-rich gas is recovered and purified, the process includes: After the pressure of the hydrogen-rich gas and carbon monoxide-rich gas mixture is adjusted, the pre-cooled ethanol or the pre-cooled ethanol-rich liquid is used as an absorbent to absorb the macromolecular impurities contained therein, thereby obtaining a purified hydrogen-rich gas and carbon monoxide-rich gas mixture and an ethanol-rich solution or an ethanol-rich solution.

2. The process according to claim 1, characterized in that The process also includes performing pressure swing adsorption on the purified hydrogen-rich gas to obtain high-purity hydrogen.

3. The process according to claim 1 or 2, characterized in that The process also includes performing membrane separation on the purified carbon monoxide-rich gas to obtain high-purity carbon monoxide.

4. The process according to claim 1 or 2, characterized in that The process also includes exchanging heat and cold between the hydrogen-rich gas and carbon monoxide-rich gas mixture and the purified hydrogen-rich gas and carbon monoxide-rich gas mixture.

5. The process according to claim 1 or 2, characterized in that: The process also includes performing heat and cold exchange between the hydrogen-rich gas and the purified hydrogen-rich gas and / or the purified carbon monoxide-rich gas; performing heat and cold exchange between the carbon monoxide-rich gas and the purified carbon monoxide-rich gas and / or the purified hydrogen-rich gas.

6. The process according to claim 1, characterized in that The pre-cooling is to reduce the temperature of the absorbent from room temperature to 0 to -80°C.

7. The process according to claim 6, characterized in that The pre-cooling is to reduce the temperature of the absorbent from room temperature to -30°C.

8. The process according to any one of claims 1, 6-7, characterized in that: The operating pressure of the absorption process is 3.0-8.0MPaG.

9. The process according to claim 1, characterized in that The absorption process is carried out in the absorption tower.

10. The process according to claim 9, characterized in that The absorption tower includes a packed tower or a plate tower.

11. The process according to any one of claims 1-2, 6-7, 9-10, characterized in that: The process also includes: reheating the ethanol-rich solution or the ethanol-rich solution obtained after absorbing the macromolecular impurities to separate the macromolecular impurities, and then recycling the ethanol-poor solution or the ethanol-poor-rich solution obtained after the separation as an absorbent.

12. A device for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol plant for realizing the process for recovering and purifying hydrogen and carbon monoxide in tail gas of an ethanol plant as claimed in any one of claims 1 to 11, characterized in that: When the hydrogen-rich gas and carbon monoxide-rich gas mixture is recovered and purified, the device comprises: a gas mixer, a refrigerator and an absorption tower, the hydrogen-rich gas and the carbon monoxide-rich gas are mixed in the gas mixer to obtain the hydrogen-rich gas and carbon monoxide-rich gas mixture; the absorbent is sent to the absorption tower after being cooled by the refrigerator to absorb the macromolecular impurities contained in the hydrogen-rich gas and carbon monoxide-rich gas mixture to obtain the purified hydrogen-rich gas and carbon monoxide-rich gas mixture and ethanol-rich solution or ethanol-rich solution; When the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified respectively, the device comprises: a refrigerator, a first absorption tower and a second absorption tower, or the device comprises: a refrigerator and a segmented absorption tower; the absorbent is cooled by the refrigerator and sent to the first absorption tower and the second absorption tower respectively, or the absorbent is cooled by the refrigerator and sent to the segmented absorption tower for absorbing the macromolecular impurities contained in the hydrogen-rich gas and the carbon monoxide-rich gas, and obtaining the purified hydrogen-rich gas and ethanol-rich solution or ethanol-rich solution; the purified carbon monoxide-rich gas and ethanol-rich solution or ethanol-rich solution.

13. The device according to claim 12, characterized in that When the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified respectively, the device further comprises a pressure swing adsorption device for performing a pressure swing adsorption treatment on the purified hydrogen-rich gas to obtain high-purity hydrogen.

14. The device according to claim 12 or 13, characterized in that When the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified respectively, the device further comprises a membrane separation device for performing membrane separation on the purified carbon monoxide-rich gas to obtain high-purity carbon monoxide.

15. The device according to claim 12, characterized in that When the hydrogen-rich gas and carbon monoxide-rich gas mixture is recovered and purified, the device further comprises a heat exchanger for performing heat and cold exchange between the hydrogen-rich gas and carbon monoxide-rich gas mixture and the purified hydrogen-rich gas and carbon monoxide-rich gas mixture.

16. The device according to claim 12, characterized in that When the hydrogen-rich gas and the carbon monoxide-rich gas are recovered and purified, the device further includes a heat exchanger, and the device further includes a first heat exchanger and a second heat exchanger, wherein the first heat exchanger is used for performing cold and heat exchange between the hydrogen-rich gas and the purified hydrogen-rich gas and / or the purified carbon monoxide-rich gas; and the second heat exchanger is used for performing cold and heat exchange between the carbon monoxide-rich gas and the purified carbon monoxide-rich gas and / or the purified hydrogen-rich gas.

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