NL2028191B1

NL2028191B1 - Method and system for CO2 capture

Info

Publication number: NL2028191B1
Application number: NL2028191A
Authority: NL
Inventors: Di Domênico Pinto Diego
Original assignee: Hovyu Holding B V
Priority date: 2021-05-11
Filing date: 2021-05-11
Publication date: 2022-11-29
Also published as: WO2022240290A1

Abstract

Title: Method and system for CO2 capture Abstract The invention is in the field of CO2 capture. The invention is in particular directed to a method to recover CO2 from a feed gas and a system for the method. The method comprises providing a feed gas stream in an absorber comprising a basic liquid to absorb CO2 to obtain a COz-rich liquid stream. The CO2-rich liquid stream is led to a desorption vessel comprising an acidic stripping agent to obtain a CO2-rich gas stream and a salt solution stream. The method further comprises leading the salt solution stream to an electrical separator to regenerate the basic liquid and acidic stripping agent.

Description

P129851NL00 Title: Method and system for CO: capture The invention is in the field of CO: capture. The invention is in particular directed to a method to recover CO: from a feed gas and a system for the method.

Carbon dioxide (COs) is a naturally occurring compound. The amount of CO: emission has significantly increased in the past decades due to z.a. industrial processes that burn fossil fuels. The increasing amount is considered to be one of the major causes for climate change.

It is accordingly widely acknowledged that it is desirable to minimize carbon dioxide emission, and move towards a more sustainable and circular economy (i.e. a system of closed loops in which renewable sources are used and in which the used materials lose their value as little as possible). Several methods to achieve this goal have been presented, such as carbon taxes (e.g. taxes for each ton CO: emitted) and alternative energy sources such as solar, wind and hydro-powered sources. However, increased taxes may lead to resistance of i.a. the industry and the alternative energy sources generally depend on the amount of available sunlight, wind, water etc.

Another method to minimize the carbon dioxide emission is to capture and optionally regenerate the CO: from e.g. the flue gasses from industry. Captured and/or regenerated carbon dioxide may z.a. be stored underground or may be sold for further use such as for enhanced oil recovery.

Conventional CO»: capture and regeneration include processes as described in US1783901 and typically comprise feeding a carbon dioxide containing gas to an absorber wherein an alkaline solvent, often an amine- based solvent, is provided. The CO: may react with the solvent leaving a CO»-lean gas that can leave the absorber. The CO:-rich stream may be fed to the top of a regeneration column (e.g. a stripper) passing through e.g. a cross heat exchanger to recover part of the available thermal energy. Typically, a reboiler is present at the bottom of the regeneration column which can provide the required energy to reverse the reaction between the carbon dioxide and the solvent, thereby releasing (i.e. regenerating) carbon dioxide and vaporizing at least part of the solvent. The reboiler however requires additional energy. The gas produced in the reboiler may flow upwards in the regeneration column and may accordingly promote solvent regeneration. The vapor that may leave the top of the regeneration column (1.a. water, volatile components) can be condensed and recycled back to the process. The regenerated solvent can also be recycled.

An additional drawback of these systems is that they require additional steps to further process the CO: gas, such as compression before it can be e.g. stored and/or transported.

A further drawback of the above-described conventional CO: capture processes is that they are generally not be suitable for gases that comprise molecular oxygen due to degradation of the solvent. Degradation of the solvent may pose problems such as emissions, corrosion and/or safety issues.

A particular example of a CO»: capture and regeneration process that aims to provide a more energy efficient method to capture carbon dioxide and regenerate the solvent is for instance disclosed in EP2163294. Herein carbon dioxide is separated from the solvent by bipolar membrane electrodialysis. However, the bipolar membrane electrodialysis based separation of carbon dioxide from the solvent is typically energy-intensive and expensive.

US2020/0038803 discloses a system and a method to regenerate a carbon-rich amine solution produced in a carbon dioxide capture from a mixed gas. The system comprises a bipolar membrane electrodialysis apparatus and a carbon dioxide removal apparatus.

Another example is presented in EP2329875, that discloses a method comprising providing water and processing the water using electrochemical steps to generate an acidic and an alkaline solution.

The acidic solution is neutralized, and the alkaline solution is used for capturing carbon dioxide.

However disadvantageously, the reaction product formed by the reaction of carbon dioxide with the alkaline solution is disposed and neither the CO: nor the alkaline solution is regenerated, leading to substantial waste streams.

It is an object of the present invention to provide an improved method for recovering carbon dioxide from a feed gas that overcomes at least part of the above-mentioned drawbacks.

The present inventor surprisingly found that a such a method can be obtained using a basic liquid and an acidic stripping agent that can be regenerated using electrical separation.

Figure 1 illustrates a schematic overview of the method according to the present invention.

Figure 2 illustrates a schematic overview of a preferred embodiment of the method according to the present invention.

Figure 3 illustrates a schematic overview of a preferred embodiment of the method according to the present invention.

Figure 4 illustrates a schematic overview of a system according to the present invention.

Figure 5 illustrates a schematic overview of a preferred embodiment of a system according to the present invention.

Figure 6 illustrates a schematic overview of a suitable electrical separator comprising electrodialysis.

Thus, in a first aspect the present invention is directed to a method for at least partially recovering CO: from a feed gas stream (1). The method is schematically illustrated in Figure 1 and comprises:

- providing the feed gas stream (1) in an absorber (2) that comprises a basic liquid to absorb CO: in the basic liquid to obtain a CO»- rich liquid stream (3) and a COgz-lean gas stream (4); - leading the COg-rich liquid stream (3) to a desorption vessel (5) that comprises an acidic stripping agent to obtain a COz-rich gas stream (6) and a salt solution stream (7); - recovering the CO:-rich gas stream from the desorption vessel to obtain a recovered CO:-gas stream; - leading the salt solution stream to an electrical separator (8) to subject the salt solution stream to electrical separation to obtain a regenerated acidic stripping agent stream (9) and a regenerated basic Liquid stream (10). Advantageously, each of the steps has a minimal complexity and highly specialized apparatuses may not be needed. Additionally, the individual steps typically present more possibilities for individually and separately choosing the conditions such as the pressure and temperature. Any gas may suffice as feed gas as long as carbon dioxide is present in the gas. Suitable feed gasses may for instance further comprise molecular oxygen (e.g. up to 21 vol%) and/or molecular nitrogen. Examples of suitable feed gasses include flue gasses from industrial processes, air (e.g. for direct air capture, also referred to as DAC), exhaust gases from engines, natural gas and/or biogas. The method may accordingly be used for any process that desires the capture of carbon dioxide, these processes may include, but are not limited to, natural gas sweetening, biogas upgrading and/or hydrogen production.

The feed gas is provided in an absorber that comprises a basic liquid. The basic liquid is chosen such that it is capable of absorbing carbon dioxide. Preferably, the basic liquid selectively absorbs carbon dioxide. This may be beneficial to limit any contamination of the basic liquid that may complicate the regeneration thereof. Absorption of the CO: may for instance be achieved by a reaction between CO: and the basic liquid. Such a reaction is typically exothermic (i.e. energy is released), which may result in an increased temperature in the absorption vessel. It may be preferred that the feed gas is provided in the absorber at a temperature between 20 and 80 °C, 5 such as approximately 40 °C. In the absorber, the temperature may be between 20 and 80 °C, such as between 30 and 50 °C, such as approximately 40 °C.

The basic liquid preferably comprises an organic and/or inorganic liquid, preferably an inorganic liquid. In contrast to organic liquids such as monoethanolamine (MEA), methyldiethanolamine (MDEA) and piperazine (PZ), inorganic liquids generally allow for no degradation of the basic liquid if molecular oxygen is present in the feed gas. Degradation is typically associated with lower process efficiency and issues such as emission, corrosion, foaming, equipment fouling and safety hazards. It is particularly preferred that the basic liquid comprises ammonia (NH) and/or a metal hydroxide, for example alkali hydroxide such as NaOH and/or KOH or alkaline hydroxide. The concentration of ammonia and/or the metal hydroxide in the basic liquid is preferably at least 1 mol/liter. The metal hydroxide may typically be present in approximately 10 wt% and the ammonia may typically be present in around 5 wt%.

Absorption of CO: in the basic liquid results in a CO»-rich liquid stream and a CO:-lean gas stream. The CO»-lean gas stream may be recovered from the absorber. The CO: removal rate is typically more than 90%, preferably more than 95%, more preferably more than 99% based on the total CO: content in the feed gas stream.

The CO»-rich liquid stream 1s led to a desorption vessel. In the desorption vessel, CO: is desorbed from the CO:»-rich liquid stream. The pressure in the desorption vessel may be ambient pressure (i.e. approximately 1 bar). However. it may be preferred that the pressure in the desorption vessel is at least 2 bar, preferably at least 4 bar, more preferably at least 5 bar, even more preferably at least 6 bar, most preferably at least 7 bar. An elevated pressure (i.e. above ambient pressure) may be beneficial as the recovered CO»-gas stream may accordingly be under pressure and the CO: can be directly liquefied or at least further processing steps may be minimized for the CO: to be suitable for e.g. storage and/or transport. The pressure typically dictates the pressure at which the CO»-rich liquid stream is lead to the desorption vessel. For instance, the COgz-rich liquid stream may be pressurized before leading it to the desorption vessel to reach a similar pressure. Alternatively, if the pressure in the desorption vessel is at ambient pressure, the recovered CO:-gas stream may be further processed, by for instance leading it to a compressor which may be followed by Liquifying. Accordingly, the method may further comprise liquefying and/or compressing the recovered CO:2-gas stream.

The temperature of the CO»-rich Liquid stream generally depends on the temperature at which it is obtained from the absorption vessel. Accordingly, the temperature is typically between 20 and 80 °C, preferably between 30 and 50 °C, more preferably the temperature is around 40 °C. Similarly, the temperature in the desorption vessel is typically dictated by the temperature of the incoming COg-rich liquid stream. Advantageously, there is little to no need for input of thermal energy to the desorption vessel.

The desorption vessel comprises an acidic stripping agent. The stripping agent may advantageously be used to obtain a CO:-rich gas stream and a salt solution stream. The stripping agent promotes the release of CO: from the COg-rich liquid stream. Additionally, the acidic stripping agent typically reacts with basic liquid present in the CO:-rich liquid stream to form a salt.

The acidic stripping agent preferably comprises an organic and/or inorganic acid solution, preferably said acid solution comprises an organic acid. Organic acids are typically preferred over inorganic acids such as H2SO,; and HCI as the regeneration of organic acids may be energetically more favorable. Particularly, it is preferred that the organic acid 1s selected from the group consisting of lactic acid, citric acid, acetic acid, formic acid, fumaric acid, picolinie acid, propionic acid, pyruvic acid, succinic acid, tartaric acid, butyric acid, glyceric acid, malic acid, salicylic acid and combinations thereof.

Leading the COg-rich liquid stream to the desorption vessel comprising an acidic stripping agent may thus result in a COz-rich gas stream and a salt solution stream. For example, if NaOH is used as basic liquid and lactic acid as acidic stripping agent the salt solution stream may contain sodium lactate.

The salt solution stream may be led to an electrical separator to subject the salt solution stream to electrical separation to obtain a regenerated acidic stripping agent stream and a regenerated basic liquid stream. Electrical separation is particularly beneficial as it generally only requires electrical energy and no thermal energy. For instance, the electrical input for regeneration of the acidic stripping agent and the basic liquid may be between 3-4 Md kg CO». The electrical separation preferably comprises an electro-membrane process as for instance detailed in the review article by Handojo et al. (RSC Adv., 2019, 9, 7854-7869). Preferably the electro- membrane process comprises electrodialysis (ED), electrometathesis (EMT), electro-10n substitution (EIS), electro-electrodialysis (EED), electrodialysis with bipolar membranes (EDBM), and electrodeionization (EDI) and/or a combination thereof. Electro-membrane processes may be beneficially used to limit z.q. concentration steps, use of hazardous solvents and high energy consumption.

Electro-membrane processes are typically performed in cells comprising one or more anionic exchange membranes and cation exchange membranes arranged between an anode and a cathode. The anionic exchange membranes are typically permeable to anionic species while substantially blocking the passage of cationic species and vice versa.

Applying an electrical field results in the migration of ionic species and due to the membranes selective passage of ions may be possible. Accordingly, electro-membrane processes are generally based on the selective permeability of the ion-exchange membranes. For instance, a suitable electrical separator (8) may comprise electrodialysis wherein the separator typically comprises a cationic exchange membrane (203) is located between two anionic exchange membranes (202, 204) which are arranged between a anode (201) and an cathode (205) as illustrated in Figure 6. The salt solution stream (7) may be fed to the separator at the indicated locations. When an electric field is applied, ionic species tend to move and selectively pass through the ionic exchange membranes. Accordingly, after some time a regenerated basic liquid stream (10) and a regenerated acidic stripping agent stream (9) may be obtained at the indicated locations.

As illustrated in Figure 2, the regenerated acidic stripping agent stream (9) may advantageously be recycled to the desorption vessel (5). The regenerated acidic stripping agent stream may be concentrated before it is recycled back to the absorber. Additionally or alternatively, the regenerated basic liquid stream (10) can be recycled to the absorber (2). The water balance is typically crucial as it is often not desirable to dilute the basic liqud.

Preferably, the method is a continuous method.

It may also be preferred that the method further comprises leading the salt solution stream (7) to a flash tank (11) before leading the salt solution into the separator (8) as illustrated in Figure 3. For instance, if the desorption vessel is at an elevated pressure, there may be some CO: dissolved in the salt solution stream. By leading this stream to a flash tank, the dissolved CO: may be released to obtain a released CO:-gas stream (6b), which may be rejoined with the obtained CO»-gas stream.

The invention is further directed to a system (100) suitable for the method according to the present invention. The system is schematically illustrated in Figure 4. The system comprises an absorber (2) adapted to during use comprise a basic liquid. The absorber comprises a feed gas inlet (21), a basic liquid inlet (22), a CO»-lean gas outlet (23), and a CO:-rich liquid outlet (24). The system further comprises a desorption vessel (5) adapted to during use comprise an acidic stripping agent. The desorption vessel comprises a COz-rich liquid inlet (51), a salt solution outlet (52), a CO:-rich gas outlet (53) and a stripping agent inlet (54). The system further comprises an electrical separator (8) comprising a salt solution inlet (81), a basic liquid outlet (82) and a stripping agent outlet (83). In the system the COg-rich liquid outlet (24) is in fluid connection with the CO:-rich liquid inlet (51), the salt solution outlet (52) is in fluid connection with the salt solution inlet (81), the stripping agent outlet (83) is in fluid connection with the stripping agent inlet (54) and the basic liquid outlet (82) is in fluid connection with the basic liquid inlet (22).

It may be appreciated that when the system is not installed and/or not operational, it may not contain the basic liquid and/or the acidic stripping agent as this allows for z.a. easier transportation and/or installation. If it is operational, the system thus comprises the basic liquid in the absorber and the acidic stripping agent in the desorption vessel.

It may be preferred that the feed gas inlet (21) is located below the basic liquid inlet (22). Additionally or alternatively, in order for the system to be able to perform under a preferred pressure (vide infra), the desorption vessel may be adapted to be under ambient pressure (i.e. approximately 1 bar), but may also be adapted to be under a pressure of at least 2 bar, preferably at least 4 bar, more preferably at least 5 bar, even more preferably at least 6 bar, most preferably at least 7 bar.

A particularly preferred embodiment is illustrated in Figure 5. In this preferred embodiment a fan (17) may be present to lead the feed gas to the absorber (2). The system may further comprise pumps, such as centrifugal pumps (14, 16) and/or heat exchangers (13, 15). For instance,

pump (14) for pumping the COg-rich liquid stream may be located between the absorber (2) and the desorption vessel (5). A heat exchanger (15) may further be present between the pump and the desorption vessel. Similarly, a pump (16) may be present between the electrical separator (8) and the absorber (2) to pump the regenerated basic liquid. Further, a heat exchanger (13) may be located between the pump (16) and the absorber (2). Additionally, it may be preferred to have a stirring device (12), such as a mechanical stirring in the desorption vessel. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. The invention may further be illustrated by the following, non- limiting examples.

Example 1 Flue gas from a gas-fired turbine, after pre-treatment, comprising 4% COa:, 10% O2, 86% N32 (on molar dry basis) and water saturated enters the bottom of a packed absorber at 1.05 bar and 40 °C. In the absorber, the gas is contacted with the basic liquid comprising 10% NaOH in water (mass basis) entering at the top of the absorber. The CO: 1s removed from the gas and reacts with the sodium hydroxide according to the following reaction: NaOH + CO, > NaHCO, The gas leaving the top of the absorber is lean in CO: containing less than 10% of the amount of CO: that entered the absorber. The COg-rich liquid stream leaving at the bottom of the absorber is pumped to a desorption vessel operating at 7 bar where a solution of acetic acid (HAc) 1s added.

In the desorption vessel the CO: is released according to the following reaction: NaHCO; + HAc — NaAc + H,0 + CO,

The CO: released leaves at the top of the desorption vessel while the salt solution stream of sodium acetate is sent to the electrical separator.

In the electrical separator, the sodium acetate is converted and separated in two regenerated streams of sodium hydroxide and acetic acid.

The sodium hydroxide solution is sent back to the absorber while the acetic acid is returned to the desorption vessel.

The high-pressure CO: produced at the desorption vessel is sent to a cooler for liquefaction.

The process is schematically illustrated in Fig. 5.

Claims

Conclusions

A method for at least partially recovering CO: from a feed gas stream (1), said method comprising: - providing said feed gas stream (1) in an absorber (2) comprising a basic liquid to absorb CO: in said basic liquid to obtain a CO2-rich liquid stream (3) and a CO2-lean liquid stream (4); - directing said CO2 -rich liquid stream to a desorption vessel (5) containing an acidic stripping agent to obtain a CO2 -rich gas stream (6) and a brine stream (7); - recovering said CO2 -rich gas stream from said desorption vessel to obtain a recovered CO2 -rich gas stream; - passing said brine stream to an electrical separator (8) to electrically separate said brine stream to obtain a regenerated acid stripping agent stream (9) and a regenerated base stream (10).

A method according to the preceding claim, wherein said method further comprises directing said regenerated acid stripping agent stream (9) to the desorption vessel (5) and/or directing said regenerated basic stream (10) to the absorber (2 ) includes.

A method according to any of the preceding claims, wherein the electrical separation comprises an electromembrane process, preferably an electromembrane process comprising electrodialysis, electrometathesis, electroion substitution, electroelectrodialysis, bipolar membrane electrodialysis, electrodeionization, and/or a combination thereof.

A method according to any one of the preceding claims, wherein said basic liquid comprises an inorganic liquid, preferably wherein said basic liquid comprises ammonia (NH 3 ) and/or a metal hydroxide, preferably wherein said metal hydroxide is selected from the group consisting from NaOH and/or KOH.

A method according to any one of the preceding claims, wherein said acid stripping agent comprises an organic and/or inorganic acid solution, preferably wherein said acid solution comprises an organic acid, preferably wherein said organic acid is selected from the group consisting of lactic acid , citric acid, formic acid, fumaric acid, picolinic acid, propionic acid, pyruvic acid, succinic acid, tartaric acid, butyric acid, glyceric acid, malonic acid, salicylic acid, and combinations thereof.

A method according to any one of the preceding claims, further comprising passing said brine stream (7) to a flash tank (11) before passing said brine stream into the separator (8).

A method according to any one of the preceding claims, further comprising concentrating said regenerated acid stripping agent stream (9) before passing said regenerated acid stripping agent stream to said desorption vessel (5).

A method according to any one of the preceding claims, wherein the temperature in said desorption vessel is between 20 and 80°C, preferably between 30 and 50°C, more preferably around 40°C.

A method according to any one of the preceding claims, wherein said feed gas has a temperature between 20 and 80°C, preferably around 40°C.

A method according to any one of the preceding claims, further comprising liquefying and/or compressing said recovered CO2 -rich gas stream (6).

A method according to any one of the preceding claims, wherein the pressure in the desorption vessel is at least 2 bar, preferably at least 4 bar, more preferably at least 5 bar, even more preferably at least 6 bar, most preferably at least least 7 bar.

A method according to any one of the preceding claims, wherein said method is continuous.

A system (100) for the method according to any one of the preceding claims, wherein said system comprises: - an absorber (2) adapted to contain a basic liquid during use, said absorber comprising a feed gas inlet (21), a basic

liquid inlet (22), a CO 2 lean gas outlet (23), and a CO 2 rich liquid outlet (24); - a desorption vessel (5) adapted to contain an acidic stripping agent during use; said vessel comprising a CO2 rich liquid inlet (51), a saline outlet (52), a CO2 rich gas outlet (53) and a dot agent inlet (54); - an electrical separator (8) comprising a saline inlet (81), a basic liquid outlet (82) and a stripping agent outlet (83); wherein said CO 2 rich fluid outlet (24) is in fluid communication with said CO 2 rich fluid inlet (51), said saline outlet (52) is in fluid communication with said saline inlet (81), said stripping agent outlet (83) is in fluid communication with said stripping agent inlet (54 ) and wherein said basic liquid outlet (82) is in fluid communication with said basic liquid inlet (22).

A system according to the preceding claim, wherein said feed gas inlet (21) is located below the basic liquid inlet (22).

A system according to any one of the preceding claims 13 to 14, wherein said desorption vessel is adapted to be under pressure of at least 2 bar, preferably at least 4 bar, more preferably at least 5 bar, even more preferably at least 6 bar, most preferably at least 7 bar.