Vapor recovery system with counterflow and parallel flow absorbent streams

Abstract

A method of absorbing a solvent from a gas stream can involve flowing a gas stream comprising air and a hydrocarbon through an absorption tower in a counter-current direction with a first lean absorbent liquid to absorb a solvent from the gas stream and produce a first conditioned gas stream and a first rich absorbent liquid. The method can subsequently involve flowing the first conditioned gas stream through the absorption tower in a co-current direction with a second lean absorbent liquid to absorb a solvent from the first conditioned gas stream and produce a second conditioned gas stream and a second rich absorbent liquid, the second conditioned gas stream having a reduced concentration of the hydrocarbon compared to the first conditioned gas stream.

Description

[0001] Related Applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 487,467, filed February 28, 2023, the entirety of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to gas absorption systems, and more particularly, to gas absorption systems for removing solvent vapor from non-condensable exhaust gas during a liquid extraction process. BACKGROUND

[0004] Many different industries use extractors to extract and recover a substance entrained within a solid. For example, producers of products from renewable organic sources use extractors to extract carbohydrates and / or oils from solid substances such as soybeans, rapeseed, sunflower seeds, peanuts, cotton seeds, palm kernels, and corn germ. The substance is contacted with a solvent within the extractor, resulting in the extraction of the desired product from the surrounding cellular structure into the solvent. This can form a miscella stream containing the solvent, which carries the material extracted from the cellular structure of the solid into the solvent, and the extracted residual solvent-wetted solid material.

[0005] After the substance is processed through the extractor, the miscella stream and the residual solvent-wetted solid material can each be further processed to remove residual solvent from the two streams. The miscella stream can be evaporated, for example, in a flash evaporator and / or a distillation column, to separate the extracted material (e.g., oil) from the solvent. The solvent-wetted solid material can also be desolventized to separate the solvent and the residual extracted solid material. For example, the solvent-wetted solid material can be processed in a desolventizer for evaporating the solvent from the extracted solid material.

[0006] Non-condensable exhaust gas, such as air, can enter the extraction system with the solid and mix with other gas streams. For example, the gas stream produced by evaporating the miscella stream and / or desolventizing the solvent-wetted solid material can carry vaporized solvent. Each gas stream can pass through a condenser to cool and condense the vaporized solvent for recovery and reuse. However, the gas passing through the condenser can still carry a residual amount of solvent that needs to be removed before the exhaust gas can be discharged into the atmospheric environment. The non-condensable exhaust gas can be processed in an absorption column to absorb one or more non-condensable constituent components from the gas before the gas is discharged into the atmospheric environment. Improving the efficiency of the absorption system can reduce the operating cost of the system and / or increase the amount of solvent removed from the exhaust gas before atmospheric discharge. SUMMARY

[0007] Generally, the present disclosure relates to systems and techniques for absorbing solvent from a gas stream, such as absorbing organic solvent from a gas stream produced by one or more unit operations in a solvent extraction process. In some examples, an extraction system includes an extractor that contacts an oleaginous feedstock with an organic solvent to produce a miscella stream composed of the solvent containing extracted oil and a residual solids stream composed of solids wetted with solvent having a reduced oil concentration. The miscella stream can be processed to separate the extracted oil from the solvent, such as by passing the stream through one or more distillation columns and / or stripping vessels. The solvent-wetted solids can also be processed to dry the solids and remove residual solvent. These and other processes within the solvent extraction system can produce exhaust gas containing residual organic solvent. For example, steam used to vaporize solvent in a distillation column, stripping vessel, and / or solids desolventizer can be passed through a condenser (e.g., evaporator condenser, exhaust gas condenser) to recover condensable liquids. Residual non-condensable gas containing any entrained organic solvent can form exhaust gas that requires further processing.

[0008] In some configurations according to the present disclosure, an absorption system is provided for processing a gas stream, such as exhaust gas from a solvent extraction system, to remove entrained organic solvent from the gas stream. The absorption system can process the exhaust gas by passing the exhaust gas in a counter-current direction with an absorbent liquid and further passing the exhaust gas in a co-current direction with the absorbent liquid. For example, the exhaust gas can be passed in a counter-current direction with a first lean absorbent liquid to absorb solvent from the gas stream to produce a first conditioned gas stream. Subsequently, the resulting first conditioned gas stream can be passed in a co-current direction with a second lean absorbent liquid to absorb solvent from the first conditioned gas stream and produce a second conditioned gas stream. The absorption system can be implemented using a single absorption column that includes both counter-current and co-current flow zones or by using two different vessels, with one vessel providing a counter-current flow direction and the other vessel providing a co-current flow direction.

[0009] By configuring the absorption system with a counter-current absorbent flow followed by a co-current absorbent flow, the absorption system can provide different stages of contact of the gas being processed with the absorbent to absorb solvent from the gas. In each of the two stages, the relative flow rates of the gas and absorbent can be independently controlled. For example, in the first counter-current flow stage, the ratio of absorbent to exhaust gas can be relatively low. This can enable the gas to be properly contacted and mixed with the absorbent without flooding within the absorption column. In the second co-current flow stage, the ratio of absorbent to exhaust gas can be increased relative to the first counter-current flow stage. For example, in the second stage, the flow rate of absorbent can be significantly increased relative to the first counter-current stage while passing substantially the same flow rate of gas through both stages.

[0010] The absorption system is configured with a first counter-current flow stage that effectively absorbs most of the residual solvent from the exhaust gas entering the system, while a second co-current flow stage, providing an increased absorbent flow rate, removes an additional amount of solvent from the exhaust gas before discharge. Therefore, the additional second co-current flow stage effectively "fine-treats" the exhaust gas, further reducing the amount of residual solvent in it. This better purifies the exhaust gas for further treatment and / or environmental emissions.

[0011] In one example, a method for absorbing solvent from a gas stream is described. The method includes flowing a gas stream containing air and hydrocarbons countercurrently through an absorption tower with a first lean absorbent liquid to absorb solvent from the gas stream and produce a first conditioning gas stream and a first rich absorbent liquid. The method further includes flowing the first conditioning gas stream and a second lean absorbent liquid cocurrently through the absorption tower to absorb solvent from the first conditioning gas stream and produce a second conditioning gas stream and a second rich absorbent liquid, the second conditioning gas stream having a reduced concentration of hydrocarbons compared to the first conditioning gas stream. This exemplary method may also include discharging the second conditioning gas stream from the absorption tower.

[0012] In another example, an absorption system is described, comprising a vertical tower divided into a countercurrent flow zone and a cocurrent flow zone. The vertical tower includes a gas inlet, a first absorbent inlet, a transition zone, a second absorbent inlet, and a gas outlet. According to this example, the gas inlet is configured to receive a gas stream containing air and hydrocarbons and supply the gas stream to the countercurrent flow zone. The first absorbent inlet is configured to receive a first lean absorbent liquid and supply the first lean absorbent liquid countercurrently from the gas stream to the countercurrent flow zone, the first lean absorbent liquid absorbing solvent from the gas stream to produce a first conditioning gas stream and a first rich absorbent liquid. The transition zone connects the countercurrent flow zone and the cocurrent flow zone. According to this example, the transition zone is configured to receive the first conditioning gas stream exiting the countercurrent flow zone and supply the first conditioning gas stream to the cocurrent flow zone. The second absorbent inlet is configured to receive a second lean absorbent liquid and supply the second lean absorbent liquid and the first conditioning gas stream in a parallel flow direction to the parallel flow zone. The second lean absorbent liquid absorbs solvent from the first conditioning gas stream to generate a second conditioning gas stream and a second rich absorbent liquid. The gas outlet is configured to discharge the second conditioning gas stream from the vertical column.

[0013] Details of one or more examples are set forth in the accompanying drawings and the following description. Other features, objects, and advantages will be apparent from the specification, the drawings, and the claims. Attached Figure Description

[0014] Figure 1This is a block diagram illustrating an exemplary extraction system according to the present disclosure.

[0015] Figure 2 This is an example that can be used with Figure 1 A block diagram of an exemplary absorption system used in conjunction with an exemplary extraction system.

[0016] Figure 3 It is a cross-sectional view of an exemplary construction of an absorption system, wherein the absorption system is implemented as a single tower or container divided into different flow zones. Detailed Implementation

[0017] Generally, this disclosure relates to liquid-solid extractor systems and processes, including solvent recovery systems and processes. In some examples, oily materials are processed in a continuous flow extractor that delivers a continuous stream of material from its inlet to its outlet while an organic solvent is delivered countercurrently from the solvent inlet to the solvent outlet. As the solvent is delivered from its inlet to its outlet, the concentration of the extracted oil relative to the solvent increases from a relatively low extract-to-solvent ratio to a relatively high extract-to-solvent ratio. Similarly, when the solid material is delivered in the opposite direction, the concentration of the extract in the solid feedstock decreases from a relatively high concentration at the inlet to a relatively low concentration at the outlet.

[0018] The organic solvent discharged from the extractor (which may be referred to as the mixed oil) contains the oil extracted from the oily feedstock. The residual solids discharged from the extractor contain solvent-wetted solids with a reduced oil concentration compared to the original oily feedstock. The mixed oil can be treated in a solvent recovery unit to evaporate the organic solvent from the extracted oil. The residual solids can be treated in a desolventizer unit to evaporate the organic solvent from the solids. The vapor stream from the solvent recovery unit and / or desolventizer unit can be condensed to remove condensate and / or organic solvent, resulting in an exhaust stream containing air and residual organic solvent.

[0019] In some examples of this disclosure, the waste gas stream can be treated in an absorption system to help remove residual organic solvents from the gas stream (e.g., before discharging the gas stream into the atmosphere). The waste gas stream containing air and residual organic solvents can pass through two absorption stages: a counter-current stage and a co-current stage. In the counter-current stage, the gas stream can flow in the opposite direction to the absorbent stream contacting the gas stream. In the co-current stage, the gas stream can flow in the same direction as the absorbent stream contacting the gas stream. The organic solvents in the waste gas stream can be absorbed into the absorbent in both the counter-current and co-current stages, for example, thereby producing a substantially solvent-free waste gas stream. The amount of organic solvents present in the waste gas stream can be initially reduced in the counter-current stage, thereby producing a first conditioning gas stream with a reduced organic solvent concentration compared to the incoming gas stream supplied to the counter-current stage. Subsequently, this first conditioning gas stream can be supplied to the co-current stage to further reduce the amount of organic solvents present in the gas stream, thereby producing a second conditioning gas stream with a reduced organic solvent concentration compared to the incoming first conditioning gas stream.

[0020] Using a combination of countercurrent and cocurrent flow to treat gas streams can benefit the absorption efficiency of the absorption system and reduce the amount of residual organic solvents in the process gas stream. The flow rates in the countercurrent and cocurrent phases can be controlled independently, for example, by providing different absorbent flow rates and / or different gas flow rates in each phase, to help maximize treatment efficiency. For example, the absorbent flow rate in the countercurrent phase can be controlled to provide good liquid-gas mixing without causing overflow of the absorber tower in that phase. The absorbent flow rate in the cocurrent phase can be increased, for example, to increase the amount of absorbent relative to the amount of gas used for final scrubbing before the gas stream is discharged into the atmosphere.

[0021] Reference Figure 2 and Figure 3 The exemplary absorption system and techniques will be described in more detail. However, reference will first be made to... Figure 1 An exemplary extraction system is described that can generate an exhaust gas containing organic solvents to be removed via an absorption system.

[0022] Figure 1 This is a block diagram illustrating an exemplary extraction system 10 according to the present disclosure. System 10 includes an extractor 12, a solvent recovery unit 14, and a desolventizer unit 16. In operation, a feedstock 18 containing the material to be extracted is introduced into the feed inlet of the extractor 12, and a solvent 20 is introduced into the solvent inlet of the extractor. The feedstock 18 contacts the solvent 20 within the extractor 12 to extract oil from the feedstock into the solvent. The extractor may generate a mixed oil stream 22 containing the extracted oil in an organic solvent. The extractor may also generate a solvent-wetted residual solids stream 24 containing residual solid material from the feedstock from which the oil has been extracted.

[0023] In an exemplary configuration of system 10, a mixed oil stream 22 is fed to a solvent recovery unit 14. The mixed oil stream 22 can be processed within the solvent recovery unit to separate the extracted oil from the organic solvent. For example, the solvent recovery unit 14 may receive steam that evaporates the solvent from the mixed oil stream 22. The solvent recovery unit 14 may produce an extracted oil stream 26 that is substantially or completely free of organic solvents and a first recovered solvent stream 28. The organic solvent in the first recovered solvent stream 28 may be a vaporized solvent mixed with air and / or steam (e.g., providing a gas phase stream). In some examples, the first recovered solvent stream 28 is passed through a condenser 30 to remove condensable liquid 32, including the recovered solvent, thereby producing a residual stream of non-condensable exhaust gas 34. This first exhaust gas 34 may contain residual and / or entrained organic solvents that have not been condensed within the condenser.

[0024] exist Figure 1 In an exemplary configuration, a solvent-wetted solids stream 24 is conveyed to a solvent remover unit 16. The solvent remover unit 16 can dry the solvent-wet solids discharged from the extractor 12. For example, the solvent remover unit 16 can directly or indirectly apply heat to the solvent-wet solids, such as using forced air and / or steam, to evaporate the solvent from the surface of the solids. The solvent remover unit 16 can produce a dried residual solids stream 36 and a second recovered solvent stream 38. The organic solvent in the second recovered solvent stream 38 can be a vaporized solvent mixed with air and / or steam (e.g., providing a gas phase stream). The second recovered solvent stream 38 can pass through a condenser 40 to remove condensable liquid 42, including solvent recovered from the solvent-wet solids, thereby producing a residual stream of non-condensable waste gas 44. The second waste gas 44 may contain residual and / or entrained organic solvents that have not been condensed in the condenser.

[0025] Extractor 12 can be implemented using any suitable type of extractor construction. In various examples, extractor 12 may be an immersion extractor, a percolation extractor, or other type of extractor design. Independent of the specific construction of extractor 12, the extractor may be configured to operate such that the feed stream 18 and the solvent stream 20 flow countercurrently through the extractor housing. For example, fresh oily feed 18 may flow through one inlet of the extractor housing, while fresh solvent containing substantially or no extractable oil flows through a second inlet of the extractor. As the solvent flows from the solvent inlet through the extractor housing to the mixed oil outlet, the solvent may flow countercurrently to the solid material stream from the feed inlet to the residual solids outlet. The solvent may mix with the oily material within the extractor, thereby extracting oil and / or other extractable components from the solid feed into the solvent. The concentration of the extract (e.g., oil) relative to the solvent increases from a relatively small extract-to-solvent ratio to a relatively large extract-to-solvent ratio. Similarly, as the solid feed is conveyed in the opposite direction, the concentration of the extract in the solid feed decreases from a relatively high concentration at the inlet to a relatively low concentration at the outlet.

[0026] Extractor 12 can use any suitable extraction fluid to process any desired oily feedstock. Exemplary types of oily materials that can be processed by extractor 12 include, but are not limited to, soybean (and / or soybean protein concentrate), rapeseed, hemp, sunflower seeds, peanuts, cottonseed, palm kernels, corn germ, and combinations thereof, as well as other oil-bearing seeds and fruits. Solvents that can be used to extract the oil contained within the oily material being processed are typically organic solvents, such as acetone, hexane, toluene, and / or alcohol-based solvents (e.g., ethanol). Typical oily materials processed using extractor 12 are plant-based materials, producing triglyceride vegetable oil as the extracted oil product.

[0027] The solvent recovery unit 14, which processes the mixed oil stream 22 to separate the extracted oil from the solvent, can be implemented using one or more separation units. For example, the solvent recovery unit 14 can be implemented using one or more distillation columns, stripping columns, and / or evaporator units. Regardless of the specific construction of the solvent recovery unit 14, the solvent recovery unit can effectively remove substantially all organic solvents from the extracted oil in the mixed oil stream 22. For example, the solvent recovery unit 14 can produce an extracted oil stream 26 having less than 5% by weight of organic solvent (such as less than 3% by weight, less than 1% by weight, or less than 0.5% by weight).

[0028] The desolventizer unit 16 for processing the residual solids stream 24 can also be implemented using one or more separation units. For example, the desolventizer unit 16 can be configured as a desolventizer baker or other desolventizing device that increases the temperature of the solids stream 24. The temperature of the stream can be raised to a temperature higher than the boiling point of the solvent introduced into the extractor 12, thereby causing the residual solvent to evaporate. In some configurations, steam is injected into the desolventizer unit 16 in addition to, or in lieu of, any other direct or indirect heating.

[0029] The waste gas generated by the extraction system 10 may contain residual solvents that did not condense under the operating conditions of the condensers 30 and 40. For example, the extraction system 10 may generate a first waste gas 34 from the solvent recovery unit 14, which contains residual organic solvents that did not condense in the condenser 30. Similarly, the extraction system 10 may generate a second waste gas 44 from the desolventizing unit 16, which contains residual organic solvents that did not condense in the condenser 40. The waste gas generated by the extraction system 10 may be treated in an absorption system to remove the residual solvents carried by the waste gas, thereby preparing waste gas for subsequent emission. For example, the first waste gas 34 and / or the second waste gas 44 generated by the extraction system 10 may be sent to one or more absorption units to remove the organic solvents carried by the waste gas. In some embodiments, the waste gas generated by the extraction system 10 (including the first waste gas 34 and the second waste gas 44) may be combined to generate a composite waste gas stream, which is fed into the inlet of the absorption system for combined treatment. In either case, the organic solvents carried by the exhaust gas can be absorbed by the absorbent liquid in the absorption system, for example, reducing the concentration of residual organic solvents in the exhaust gas to a level (e.g., in accordance with local environmental regulations) suitable for allowing the exhaust gas to be discharged into the atmosphere.

[0030] Figure 2 This is an example that can be used with Figure 1 A block diagram of an exemplary absorption system 50 used in conjunction with the extraction system 10. In the illustrated example, the absorption system 50 includes a first absorption tower 52, a second absorption tower 54, and a stripping tower 70. The first absorption tower 52 may operate as a countercurrent stage, wherein the absorbent liquid flows in a direction countercurrent to the gas stream being processed. The second absorption tower 54 may operate as a cocurrent stage, wherein the absorbent liquid flows in a cocurrent direction with the gas stream being processed. The stripping tower 70 may strip the absorbed organic solvent from the absorbent liquid used in the first absorption tower 52 and / or the second absorption tower 54 to regenerate the absorbent liquid for reuse in the absorption system 50. Although the exemplary configuration shows two absorption towers and a single stripping tower, it should be understood that actual specific implementations of such systems may include one or more absorption towers 52 and / or one or more stripping towers 70. For example, as will be referred to Figure 3 As described, the absorption system 50 can be implemented using a single absorption tower that includes a counter-current phase and a parallel-current phase, instead of utilizing, for example... Figure 2 The different absorption towers shown.

[0031] exist Figure 2In the example, the first absorption tower 52 may receive waste gas 56 containing residual organic solvents from one or more processing units of the extraction system 10. For example, the first absorption tower 52 may receive first waste gas 34 from solvent recovery unit 14, second waste gas 44 from solvent remover unit 16, and / or gas from any other processing unit within the extraction system that generates the waste gas. Waste gas streams from different processing units may be combined and treated as a single stream by the first absorption tower 52, or separate waste gas streams from individual processing units may be treated in different absorption towers. Typically, the waste gas delivered to the first absorption tower 52 will first pass through condensers 30, 40 to remove condensable gases and / or liquids from the gas stream. Therefore, the waste gas treated by this absorption tower may be a cooled, non-condensable gas.

[0032] To remove residual organic solvents from the waste gas stream 56, the waste gas stream can be introduced into the first absorption tower 52 together with the first lean absorbent liquid 58. For example, the waste gas 56 can be introduced into one end of the vertical first absorption tower 52, which is substantially opposite to the end of the tower into which the first lean absorbent liquid 58 is introduced. The waste gas 56 and the first lean absorbent liquid 58 can flow countercurrently along the length of the first absorption tower 52. For example, the first lean absorbent liquid 58 can be pressurized by one or more pumps and delivered to an elevated position in the first absorption tower 52, thereby allowing the first lean absorbent liquid to flow downward relative to gravity. The waste gas 56 can be pressurized and can flow upward relative to gravity in a countercurrent direction relative to the flow direction of the first lean absorbent liquid 58.

[0033] Within the first absorption tower 52, the organic solvents contained in the waste gas 56 can be transferred from the gas phase to the liquid phase. The organic solvents in the waste gas 56 can be absorbed by the first lean absorbent liquid 58, thereby increasing the concentration of organic solvents in the first lean absorbent liquid as it flows from the inlet to the outlet of the absorption tower. The resulting absorbent liquid with the increased organic solvent concentration can be referred to as the first rich absorbent liquid 60, and can be discharged from the first absorption tower 52 through the first rich absorbent liquid outlet. When the waste gas 56 passes through the first absorption tower 52, the concentration of organic solvents in the gas decreases as the solvent is absorbed by the liquid absorbent. The resulting waste gas stream with the reduced organic solvent concentration can be referred to as the first conditioning gas stream 62, and can be discharged from the first absorption tower 52 through the first conditioning gas stream outlet.

[0034] exist Figure 2In the example, the absorption system 50 includes a second absorption tower 54 located downstream of the first absorption tower 52 and connected to the first absorption tower via a pipe. The second absorption tower 54 can receive the waste gas stream after it has been treated in the first absorption tower 52, and can contact the waste gas stream with a second lean absorbent liquid 64 to absorb additional residual solvent from the gas stream. The second absorption tower 54 can be configured to convey the waste gas stream discharged from the first absorption tower 52 along with the second lean absorbent liquid in a parallel flow direction through the tower.

[0035] For example, to remove residual organic solvents, a first conditioning gas stream 62 discharged from the first absorber tower 52 can be introduced into the second absorber tower 54. When the second absorber tower 54 is configured such that the first conditioning gas stream 62 and the second lean absorbent liquid 64 flow in a parallel flow direction, these two streams can be introduced at the same end of the vertical second absorber tower 54. For example, the first conditioning gas stream 62 and the second lean absorbent liquid 64 can be introduced under pressure at the upper end of the second absorber tower 54, causing them to flow downwards along the length of the tower in a parallel flow direction. For example, the second lean absorbent liquid 64 can be pressurized by one or more pumps and delivered to an elevated position of the second absorber tower 54, thereby enabling the second lean absorbent liquid to flow downwards relative to gravity. The first conditioning gas stream 62 can also be pressurized and introduced into an elevated position of the second absorber tower 54, causing it to flow downwards relative to gravity in a parallel flow direction relative to the flow direction of the second lean absorbent liquid 64.

[0036] Within the second absorber tower 54, residual organic solvents contained in the first conditioning gas stream 62 can be transferred from the gas phase to the liquid phase. The organic solvents in the first conditioning gas stream 62 can be absorbed by the second lean absorbent liquid 64, thereby increasing the concentration of organic solvents in the second lean absorbent liquid as it flows from the inlet to the outlet of the absorber tower. The resulting absorbent liquid with the increased organic solvent concentration can be referred to as the second rich absorbent liquid 66 and can be discharged from the second absorber tower 54 through the second rich absorbent liquid outlet. As the first conditioning gas stream 62 passes through the second absorber tower 54, the concentration of organic solvents in the gas decreases as the solvent is absorbed by the liquid absorbent. The resulting gas stream with the decreased organic solvent concentration can be referred to as the second conditioning gas stream 68 and can be discharged from the second absorber tower 54 through the second conditioning gas stream outlet. One or more separation devices (such as baffles, cyclone separators, and / or demister pads) can be used to reduce the liquid that may be carried in the gas stream. In either case, the second conditioning gas stream 68 can be discharged into the atmosphere and / or otherwise treated.

[0037] In the first absorption tower 52 and the second absorption tower 54, the absorption of organic solvents from the gas phase to the liquid phase effectively removes a sufficient amount of organic solvent to allow the second conditioning gas stream 68 to be further processed and / or discharged into the atmosphere. In some examples, the exhaust gas 56 entering the absorption tower 52 may contain 30% to 70% organic solvent. In contrast, after contact with the first absorbent liquid in the first absorption tower 52 and the second absorbent liquid in the second absorption tower 54, the second conditioning gas stream 68 may contain less than 15% organic solvent, such as less than 10% organic solvent, less than 5% organic solvent, less than 3% organic solvent, less than 1% organic solvent, less than 0.5% organic solvent, less than 0.25% organic solvent, or less than 0.1% organic solvent.

[0038] In practice, most of the weight of solvent removed from the gas stream processed by absorption system 50 can be removed in the first absorption tower 52, while a relatively small amount of solvent is removed by the second absorption tower 54. For example, the ratio of the amount of solvent removed from the gas stream by the first absorption tower 52 (e.g., the amount of solvent in exhaust gas 56 minus the amount of solvent in the first conditioning gas stream 62) to the amount of solvent removed from the gas stream by the second absorption tower 54 (e.g., the amount of solvent in the first conditioning gas stream 62 minus the amount of solvent in the second conditioning gas stream 68) can be greater than 1.0, such as greater than 2.0, greater than 3.0, greater than 4.0, or greater than 5.0.

[0039] The amount of solvent removed from the gas stream by the first absorption tower 52 and the second absorption tower 54 can be controlled, for example, based on the size and construction of the two towers and / or by the flow rates of the two towers. The gas flow rates and / or absorbent liquid flow rates through the first absorption tower 52 and the second absorption tower 54 can be independently controllable to adjust the relative flow rates of the gas and absorbent liquid to the two different towers. For example, in some embodiments, the ratio of the absorbent flow rate to the gas flow rate in the first absorption tower 52 can be relatively low when flowing counter-currently, but the ratio of the absorbent flow rate to the gas flow rate in the second absorption tower 54 can be increased when flowing co-currently. In some examples, the second absorption tower 54 can be operated at an absorbent flow rate that would cause an overflow in the first absorption tower 52 (if the first absorption tower were operated at that rate, it would cause an overflow), but this flow rate is permissible due to the co-current flow direction in the second absorption tower.

[0040] Increasing the ratio of absorbent flow rate to gas flow rate in the second absorption tower 54, compared to the first absorption tower 52, can increase the amount of organic solvent absorbed from the gas stream (e.g., to prepare the gas stream for final emission). In some examples, such as when the gas flow rates through the first absorption tower 52 and the second absorption tower 54 are substantially the same, the flow rate of the second lean absorbent liquid 64 can be greater than the flow rate of the first lean absorbent liquid 58.

[0041] For example, the ratio of the flow rate of the first lean absorbent liquid to the flow rate of the second lean absorbent liquid may be less than 1.0, such as less than 0.8, or 0.3 to 0.6. When the gas flow through the first absorption tower 52 is substantially the same as the gas flow through the second absorption tower 54 (the flow rate of gas flow 56 is substantially the same as the flow rate of the first conditioning gas flow 62), the flow rate of the second lean absorbent liquid may be at least 25% greater than the flow rate of the first lean absorbent liquid, such as at least 50%, at least 75%, at least 100%, or at least 150%. For example, the flow rate of the second lean absorbent liquid may be in the range of 1.25 to 3.5 times the flow rate of the first lean absorbent liquid, such as in the range of 1.5 to 2.5 times the flow rate of the first lean absorbent liquid, or in the range of 1.5 to 2.0 times the flow rate of the first lean absorbent liquid.

[0042] Various liquids can be used as absorbent liquids for the first absorption tower 52 and the second absorption tower 54. In one example, mineral oil is used as the absorbent liquid for both absorption towers. In another example, it is extracted by extractor 12 ( Figure 1 The extracted oil, generated and recovered as extract oil stream 26, can be used as the absorbent liquid for both absorption towers. Other exemplary absorbent liquids may include aqueous absorbent liquids, such as water (e.g., the absorbent liquid may consist of water or be substantially composed of water), when the solvent used in the extraction process is an alcohol-based solvent (e.g., anhydrous ethanol; a mixture of ethanol and water). In a typical implementation, the first absorption tower 52 and the second absorption tower 54 may use the same type of absorbent liquid (e.g., mineral oil), although in other applications, different absorbent liquids with different chemical compositions may be used for each absorption tower.

[0043] In some implementations, the absorbent liquid (e.g., the first lean absorbent liquid 58 and / or the second lean absorbent liquid 64) is temperature-conditioned before contact with the corresponding gas flow. For example, the absorbent liquid may be heated to a temperature higher than the temperature of the gas flow to which the absorbent liquid will contact, such as at least 5 degrees, at least 10 degrees, at least 20 degrees, at least 30 degrees, or at least 50 degrees higher than the gas flow temperature. The first lean absorbent liquid 58 may be heated to the same temperature as the second lean absorbent liquid 64, or may be heated to a different temperature (e.g., a hotter temperature) than the second lean absorbent liquid 64.

[0044] The first absorber 52 and the second absorber 54 can each have a variety of different configurations. In some examples, one or both absorber towers include one or more packed beds and corresponding support plates and liquid distribution hardware to mix the exhaust gas and the extracted absorbent liquid. Additionally or alternatively, one or both absorber towers can be configured as plate towers, which may or may not have one or more packed bed sections. In a plate tower configuration, the absorber tower may include multiple trays vertically spaced apart from each other. Each tray may have an opening allowing gas to flow from one tray to an adjacent tray and a downcomer guiding liquid flow from one tray to an adjacent tray. For example, each tray may be configured as a valve tray with either a movable valve or a fixed valve. A fixed valve tray configuration can be used to provide good contact between the rising exhaust gas and the descending oil used as the absorbent medium, while helping to minimize performance degradation due to scaling and other service life issues.

[0045] After the treated gas stream has passed through the second absorber 54, the resulting second conditioning gas stream 68 can be discharged into the atmosphere or directed to other suitable downstream treatment. The absorbent liquid containing organic solvents absorbed from the gas (e.g., a first rich absorbent liquid 60 and / or a second rich absorbent liquid 66) can be treated in the stripper 70 to remove the absorbed organic solvents. In some configurations, stripping gas (such as steam 72) is introduced into the stripper 70 to strip organic solvents from the oil absorption medium. Thus, the stripper 70 can produce a recovered absorbent liquid 74 that is substantially or completely free of organic solvents absorbed from the waste gas stream. The stripper 70 can also produce a recovered solvent stream 76 containing solvent vapors mixed with the stripping gas, which can then be sent to a condenser for condensation and further treatment. Although not illustrated, an oil heater and / or other treatment equipment can treat the rich absorbent liquid before it enters the stripper 70.

[0046] In some embodiments, the first rich absorbent liquid 60 and the second rich absorbent liquid 66 are each sent to one or more stripping columns 70 to strip the organic solvent, thereby regenerating the lean first absorbent liquid 58 and the lean second absorbent liquid 64, respectively. In some examples, at least a portion of the second rich absorbent liquid 66 is recycled for use as the first lean absorbent liquid 58. Because the concentration of solvent absorbed into the second rich absorbent liquid 66 is generally less than the concentration of solvent absorbed into the first lean absorbent liquid 60, the second rich absorbent liquid 66 can be recycled for use as the first lean absorbent liquid 58 before stripping in the stripping column 70.

[0047] For example, in Figure 2In an exemplary configuration, the second rich absorbent liquid 66 produced by the second absorber tower 54 is recycled to be used as the first lean absorbent liquid 58 of the first absorber tower 52. The absorption system 50 may include an absorbent reservoir 78 into which the second rich absorbent liquid 66 is discharged, and from which the first lean absorbent stream is drawn and supplied to the first absorber tower 52. When the second absorber tower 54 operates at a higher absorbent flow rate than the first absorber tower 52, an amount of the second rich absorbent liquid 66 exceeding the supply requirements of the first lean absorbent 58 can be processed independently. For example, excess second rich absorbent liquid 66 may be delivered (e.g., via line 79) to the second absorbent reservoir and / or stripping tower 70 for stripping.

[0048] As briefly discussed above, the absorption system 50, which includes a countercurrent absorption stage and a cocurrent absorption stage, can be implemented in a variety of different ways, in which the gas stream being treated flows countercurrently and cocurrently with one or more absorbent liquids, respectively. Figure 2 An absorption system 50 is illustrated using two distinct absorption towers, which are physically separate containers fluidly connected to each other. In other examples, the treatment principle discussed herein can be achieved using a single absorption tower divided into different zones, including counter-current and parallel-current zones. Constructing the absorption system 50 as a single absorption tower internally divided into different flow zones can help reduce the footprint and space required to deploy the absorption system.

[0049] Figure 3 This is a cross-sectional view of an exemplary configuration of an absorption system 50, wherein the absorption system is implemented as a single tower or container divided into different flow zones. Specifically, in the illustrated example, the absorption system 50 is illustrated as a single tower 100, which is divided into a counter-current flow zone 102 and a co-current flow zone 104. The tower 100 may be oriented vertically relative to gravity, for example, such that the gas being treated flows upward against the downward flow of the absorbent liquid in the counter-current flow zone, and both the gas being treated and the absorbent liquid flow downward in the counter-current flow zone. Figure 3 The countercurrent flow zone 102 and the cocurrent flow zone 104 of the absorption system 50 can utilize the feed (e.g., gas and absorbent liquid composition and flow rate), processing characteristics (e.g., absorbent flow rate, gas flow rate), absorption tower internals, and exhibit the performance characteristics (e.g., solvent removal characteristics) discussed above with respect to the first absorption tower 52 and the second absorption tower 54, respectively.

[0050] exist Figure 3 In the example, tower 100 is illustrated as having a gas inlet 106, which is configured to supply gas from extractor system 10 ( Figure 1The gas stream 56 is received. The gas stream 56 may include air and hydrocarbons (e.g., organic solvents), as discussed above. The gas stream inlet 106 may supply the gas stream to the countercurrent flow zone 102 of the column for countercurrent flow and contact with the first lean absorbent liquid.

[0051] To supply a first lean absorbent liquid to the countercurrent flow zone 102, the tower 100 may include a first absorbent inlet 108. The first absorbent inlet 108 may receive a first lean absorbent liquid 58 and supply it, along with a gas stream 56, to the countercurrent flow zone 102 in a countercurrent direction. Within the countercurrent flow zone 102, the first lean absorbent liquid 58 may absorb solvent from the gas stream to generate a first conditioning gas stream 62 and a first rich absorbent liquid 60.

[0052] To connect the countercurrent flow zone 102 and the cocurrent flow zone 104, the tower 100 may include a transition zone 110 connecting the two flow zones. The transition zone 110 may receive a first conditioning gas flow 62 exiting the countercurrent flow zone 102 and supply the first conditioning gas flow to the cocurrent flow zone 104. The transition zone 110 may be a space within the tower 100 in which the countercurrent flow zone 102 and the cocurrent flow zone 104 are fluidly connected, and fluid (e.g., gas) from the countercurrent flow zone transitions into the cocurrent flow zone.

[0053] Further reference Figure 3 In an exemplary configuration, tower 100 may include a second absorbent inlet 112 configured to receive a second lean absorbent liquid 64. The second absorbent inlet 112 may supply the second lean absorbent liquid 64 and the first conditioning gas stream 62 in a co-current direction to a co-current flow zone 104. In some specific embodiments, the second lean absorbent liquid 64 for absorbing additional organic solvents from the first conditioning gas stream 62 comprises some or all of a first rich absorbent liquid 60 supplemented with an additional amount of absorbent liquid carried from the counter-current flow zone 102. This provides an increased amount (e.g., rate) of the second lean absorbent liquid 64 relative to the amount (e.g., rate) of the first lean absorbent liquid 58 supplied to the counter-current flow zone 102. Within the co-current flow zone 104, the second lean absorbent liquid 64 may absorb solvent from the first conditioning gas stream 62 to produce a second conditioning gas stream 68 and a second rich absorbent liquid 66. Tower 100 may include a gas outlet 114 to discharge the second conditioning gas stream 68 from the tower.

[0054] As mentioned, tower 100 may be oriented vertically relative to gravity, for example, such that the gas being treated flows upward against the downward flow of the absorbent liquid in a countercurrent flow zone, and both the gas being treated and the absorbent liquid flow downward in the countercurrent flow zone. For example, tower 100 may have a gas inlet near the bottom of the tower, a first absorbent inlet 108 may be positioned near the top of the tower, and a second absorbent inlet 112 may be positioned near the top of the tower.

[0055] To supply absorbent liquid to the countercurrent flow zone 102 and the cocurrent flow zone 104 of the tower 100, the absorption system 50 may include a first absorbent liquid reservoir 116 and a second absorbent liquid reservoir 118. The first absorbent liquid reservoir 116 is fluidly connected to the countercurrent flow zone 102 and is positioned to receive a first absorbent-rich liquid 60 discharged from the countercurrent flow zone. The second absorbent liquid reservoir 118 is fluidly connected to the cocurrent flow zone 104 and is configured to receive a second absorbent-rich liquid 66 discharged from the cocurrent flow zone. The first absorbent liquid reservoir 116 and the second absorbent liquid reservoir 118, or both, are illustrated as being vertically positioned below the countercurrent flow zone 102 and the cocurrent flow zone 104 of the tower 100. Specifically, the second absorbent liquid reservoir 118 is illustrated as being vertically stacked relative to the first absorbent liquid reservoir 116 (wherein the second absorbent liquid reservoir is positioned at a vertically elevated position above the first absorbent liquid reservoir). Other storage arrangements may be implemented without departing from the scope of this disclosure.

[0056] In some examples, the second absorbent reservoir 118 includes a fresh absorbent inlet 120 that receives a supply of fresh absorbent liquid (e.g., from stripper 70) to the second absorbent reservoir. This provides a mixture of fresh absorbent liquid and second rich absorbent liquid 66. A pump 122 can extract the mixture of fresh and rich absorbent liquids from the second absorbent reservoir 118 and supply this mixture as first lean absorbent liquid 58 to first absorbent inlet 108 and as second lean absorbent liquid 64 to second absorbent inlet 112. A heater 123 (e.g., a jacketed line) can heat the absorbent liquid to a target temperature. The first absorbent reservoir 116 may have an outlet 124 in fluid communication with stripper 70.

[0057] In the illustrated arrangement, the countercurrent flow zone 102 is illustrated as extending parallel to the cocurrent flow zone 104 along the length of the vertical tower. For example, the tower 100 may define an annular portion having an inner cylinder and an outer ring. The countercurrent flow zone 102 may be constructed as the inner cylinder, and the cocurrent flow zone 104 may be constructed as the outer ring (or vice versa). In an alternative embodiment, the tower 100 may be divided along its length (e.g., without defining an annular space), and the countercurrent flow zone 102 and the cocurrent flow zone 104 may be defined by different partitions of the container.

[0058] Various examples have been described. These and other examples are within the scope of the appended claims.

Claims

1. A method for absorbing solvent from a gas stream, the method comprising: A gas stream containing air and hydrocarbons is passed through the absorption tower in a countercurrent direction with a first lean absorbent liquid to absorb solvent from the gas stream and generate a first conditioning gas stream and a first rich absorbent liquid. The first conditioning gas stream and the second lean absorbent liquid flow through the absorption tower in a parallel flow direction to absorb solvent from the first conditioning gas stream and generate a second conditioning gas stream and a second rich absorbent liquid, the second conditioning gas stream having a lower concentration of hydrocarbons compared to the first conditioning gas stream; and The second conditioning gas stream is discharged from the absorption tower.

2. The method according to claim 1, wherein the first lean absorbent liquid and the second lean absorbent liquid are the same absorbent.

3. The method according to claim 1 or 2, wherein the absorption tower is fluidly connected to the first absorbent liquid reservoir and the second absorbent liquid reservoir, and the method further comprises: The first absorbent liquid is discharged into the first reservoir; as well as The second absorbent liquid is discharged into the second reservoir.

4. The method of claim 3, further comprising introducing a fresh absorbent liquid into the second reservoir to provide a mixture of the fresh absorbent liquid and the second enriched absorbent liquid, wherein: The process of allowing the gas stream and the first lean absorbent liquid to flow through the absorption tower in the countercurrent direction includes: extracting the mixture of the fresh absorbent liquid and the second rich absorbent liquid from the second reservoir and providing the mixture as the first lean absorbent; and The process of allowing the first conditioning gas stream and the second lean absorbent liquid to flow through the absorption tower in the co-current direction includes: extracting the mixture of the fresh absorbent liquid and the second rich absorbent liquid from the second reservoir and providing the mixture as the second lean absorbent.

5. The method according to any one of claims 1 to 4, the method further comprising stripping the first absorbent-rich liquid to remove the hydrocarbon.

6. The method according to any one of claims 1 to 5, wherein the absorption tower comprises: The first absorption tower, wherein the first lean absorbent liquid and the gas flow are conveyed through the first absorption tower in a countercurrent direction; The second absorbent liquid and the first conditioning gas flow are conveyed through the second absorbent tower in a parallel flow direction.

7. The method according to any one of claims 1 to 5, wherein the absorption tower comprises a single tower divided into a countercurrent flow zone and a cocurrent flow zone.

8. The method according to any one of claims 1 to 7, wherein the ratio of the flow rate of the first lean absorbent liquid to the flow rate of the second lean absorbent liquid is in the range of 0.2 to 1.5, such as 0.3 to 1.2, or 0.6 to 1.

2.

9. The method according to any one of claims 1 to 7, wherein the ratio of the flow rate of the first lean absorbent liquid to the flow rate of the second lean absorbent liquid is less than 1.0, such as 0.3 to 0.

6.

10. The method according to any one of claims 1 to 5 and 7 to 9, wherein: The absorption tower includes a vertically oriented tower, which is divided into a counter-current flow zone and a parallel flow zone; The process of causing the gas stream and the first lean absorbent liquid to flow through the absorption tower in the countercurrent direction includes: causing the gas stream to flow upward through the countercurrent flow zone and causing the first lean absorbent liquid to flow downward through the countercurrent flow zone; and The process of causing the first conditioning gas stream and the second lean absorbent liquid to flow through the absorption tower in the parallel flow direction includes: causing the first conditioning gas stream and the second lean absorbent liquid to flow downward through the parallel flow zone.

11. The method of claim 10, wherein the countercurrent flow region extends parallel to the parallel flow region along the length of the vertical orientation tower.

12. The method according to claim 10 or 11, wherein the vertical orientation tower includes an annular portion having an inner cylinder and an outer ring, the countercurrent flow zone being the inner cylinder, and the cocurrent flow zone being the outer ring.

13. The method according to any one of claims 10 to 12, wherein the vertical orientation tower further comprises a top space connecting the countercurrent flow zone and the parallel flow zone, wherein the first conditioning gas flow exits the countercurrent flow zone and enters the parallel flow zone in the top space.

14. The method according to any one of claims 1 to 14, wherein passing the gas stream through the absorber and passing the first conditioning gas stream through the absorber comprises: A vacuum is applied to the outlet of the absorption tower, thereby drawing the second conditioning gas stream out of the absorption tower.

15. The method according to any one of claims 1 to 14, wherein the hydrocarbon comprises hexane.

16. The method according to any one of claims 1 to 15, further comprising: The material to be treated is extracted in an extractor with a solvent containing the hydrocarbon to produce a solvent-wetted stream of extracted material and a mixed oil stream; In a desolventizer, the solvent-wetted extract stream is desolventized to generate a vapor stream and a desolventized extract stream; and The vapor stream is passed through a condenser to produce a condensed liquid and an uncondensed gas stream, the uncondensed gas stream forming at least a portion of the gas stream flowing through the absorption tower.

17. An absorption system, the absorption system comprising: A vertical tower, divided into a counter-current flow zone and a parallel flow zone, comprising: A gas inlet, configured to receive a gas stream containing air and hydrocarbons and supply the gas stream to the countercurrent flow zone; A first absorbent inlet is configured to receive a first lean absorbent liquid and supply the first lean absorbent liquid from the gas flow to the countercurrent flow zone in a countercurrent direction, the first lean absorbent liquid absorbing solvent from the gas flow to generate a first conditioning gas flow and a first rich absorbent liquid. A transition zone connecting the countercurrent flow zone and the parallel flow zone, the transition zone being configured to receive the first conditioning gas flow leaving the countercurrent flow zone and supply the first conditioning gas flow to the parallel flow zone; A second absorbent inlet, configured to receive a second lean absorbent liquid and supply the second lean absorbent liquid and the first conditioning gas stream in a parallel flow direction to the parallel flow region, wherein the second lean absorbent liquid absorbs solvent from the first conditioning gas stream to produce a second conditioning gas stream and a second rich absorbent liquid; and A gas outlet, configured to discharge the second conditioning gas stream from the vertical tower.

18. The system of claim 17, further comprising a first absorbent liquid reservoir and a second absorbent liquid reservoir, wherein the countercurrent flow region is fluidly connected to the first absorbent liquid reservoir and configured to discharge the first absorbent-rich liquid into the first absorbent liquid reservoir, and the cocurrent flow region is fluidly connected to the second absorbent liquid reservoir and configured to discharge the second absorbent-rich liquid into the second absorbent liquid reservoir.

19. The system of claim 18, wherein the second absorbent liquid reservoir includes a fresh absorbent inlet configured to supply fresh absorbent liquid to the second absorbent liquid reservoir to provide a mixture of the fresh absorbent liquid and the second rich absorbent liquid, and the system further includes a pump configured to extract the mixture of the fresh absorbent liquid and the second rich absorbent liquid from the second absorbent liquid reservoir and supply the mixture as a first lean absorbent liquid to the first absorbent inlet and as a second lean absorbent liquid to the second absorbent inlet.

20. The system of claim 18 or 19, wherein the first absorbent liquid reservoir includes an outlet in fluid communication with the stripper.

21. The system according to any one of claims 17 to 20, wherein the vertical tower is a filled tower containing filling material.

22. The system according to any one of claims 17 to 21, wherein: The gas inlet is located near the bottom of the vertical tower; The first absorbent inlet is adjacent to the top of the vertical tower; and The second absorbent inlet is located adjacent to the top of the vertical tower.

23. The system according to any one of claims 17 to 22, wherein the countercurrent flow zone extends parallel to the parallel flow zone along the length of the vertical tower.

24. The system according to any one of claims 17 to 23, wherein the vertical orientation tower includes an annular portion having an inner cylinder and an outer ring, the countercurrent flow zone being the inner cylinder, and the cocurrent flow zone being the outer ring.

25. The system according to any one of claims 17 to 24, further comprising: An extractor configured to extract the material to be treated with a solvent containing the hydrocarbon to produce a solvent-wetted stream of extracted material and a mixed oil stream; A desolventizer is configured to receive a solvent-wetted stream of extractant from the extractor and desolvent the solvent-wetted stream of extractant to produce a vapor stream and a desolventized stream of extractant. and A condenser configured to receive the vapor stream from the desolvation process and condense the vapor stream to produce a condensed liquid and an uncondensed gas stream, the uncondensed gas stream being supplied to the gas inlet of the vertical column.

26. An absorption system: A first absorption tower, the first absorption tower comprising: A gas inlet, configured to receive a gas stream containing air and hydrocarbons; and a first absorbent inlet, the first absorbent inlet being configured to receive a first lean absorbent liquid, wherein the gas flow inlet is positioned relative to the first absorbent inlet to partition the gas flow and the first lean absorbent liquid in a countercurrent direction, and the first lean absorbent liquid is configured to absorb solvent from the gas flow to produce a first conditioning gas flow and a first rich absorbent liquid; and A second absorption tower, the second absorption tower comprising: a first conditioning gas inlet, the first conditioning gas inlet being configured to receive the first conditioning gas flow from the first absorption tower; The second absorbent inlet is configured to receive a second lean absorbent liquid, wherein the first conditioning gas flow inlet is positioned relative to the second absorbent inlet such that the first conditioning gas flow and the second lean absorbent liquid flow in a parallel flow direction, and the second lean absorbent liquid is configured to absorb solvent from the first conditioning gas flow to produce a second conditioning gas flow and a second rich absorbent liquid, wherein the second absorber tower further includes a gas outlet configured to discharge the second conditioning gas flow.

27. The absorption system of claim 26, further comprising a stripping tower configured to receive one or both of the first absorbent-rich liquid and the second absorbent-rich liquid.

28. The absorption system according to claim 26 or 27, further comprising: An extractor configured to extract the material to be treated with a solvent containing the hydrocarbon to produce a solvent-wetted stream of extracted material and a mixed oil stream; A desolventizer is configured to receive a solvent-wetted stream of extractant from the extractor and desolvent the solvent-wetted stream of extractant to produce a vapor stream and a desolventized stream of extractant. and A condenser configured to receive the vapor stream from the desolvation process and condense the vapor stream to produce a condensed liquid and an uncondensed gas stream, the uncondensed gas stream being supplied to the gas inlet of the first absorption tower.

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