An apparatus and method for carbon capture

Abstract

An apparatus for carbon capture comprises one or more adsorption canisters (C1, C2) containing an adsorbent material selected from one or more zeolite and xerogel materials, wherein each canister has an inlet for receiving an exhaust gas stream from an internal combustion engine and an exhaust gas outlet. Also discloses is a method for the removal of CO2 from internal combustion engine exhaust gas streams, which method comprises adsorbing CO2 in the exhaust gas stream onto an adsorbent material, and removing the CO2 using a pressure swing adsorption apparatus or a temperature swing adsorption apparatus.

Description

AN APPARATUS AND METHOD FOR CARBON CAPTURE

[0001] The present invention relates to an apparatus and method for carbon capture, and in particular an apparatus comprising an adsorbent material, and method for carbon capture using the same, preferably the capture of carbon dioxide (CO2) in internal combustion engine (ICE) exhaust gas streams.

[0002] It is well documented that climate change (global warming) caused by CO2emissions from the burning of fossil fuels is having an increasing impact on the environment. Various measures have been proposed to combat increasing CO2emissions, including the promotion of renewable energies, improvements to energy efficiency, and carbon capture and storage (CCS).

[0003] CCS is a process in which CO2from an industrial source is separated, captured and transported to a storage location. Technologies which are used for CO2capture from power plants and process industries include amine absorption, membrane separation, and cryogenic separation and adsorption. However, proposals for reducing CO2emissions through CCS in the transportation sector have been more limited, due for example to the mobile nature of the source of CO2, the relatively small production rate of CO2, the discontinuous nature of the CO2emissions, and limited space for the CCS system, including on-board CO2storage.

[0004] The present invention seeks to provide an apparatus and method for carbon capture which is an improvement on prior art materials and methods.

[0005] Thus, according to the present invention in a first aspect there is provided an apparatus for carbon capturecomprising one or more adsorption canisters containing an adsorbent material selected from one or more zeolite materials and xerogel materials, each canister having an inlet for receiving an exhaust gas stream from an ICE and at least one gas outlet.

[0006] The apparatus of the present invention preferably comprises a plurality of canisters, more preferably linked in a parallel array through which the ICE exhaust gases pass. In preferred embodiments, the apparatus comprises at least two canisters, to allow for substantially continuous ICE exhaust gas processing. During this through-flow, CO2 is stripped from the ICE exhaust gases and is retained by the adsorbent material. The containers may be formed from any suitable material, for example steel.

[0007] Each canister preferably comprises an entry connection at the inlet and an exit connection at the outlet. The canisters are preferably connected in a parallel array, and preferably have a valving arrangement to allow inlet flow and outlet flow to be changed between each canister autonomously. The apparatus may comprise a plurality of canister arrays, the plurality of arrays preferably themselves arranged in parallel. Each canister and / or array may be plumbed directly into the exhaust pipework of an ICE. The valving preferably allows each canister to be individually isolated, and may additionally comprise further valved pipework leading to a vacuum pump to allow gaseous CO2to be stripped from the material. The stripped CO2may for example be piped to a compression and refrigeration unit to liquify the gas. The liquid CO2may then be transferred, for example by a cryogenic pump, to a storage tank, for example a cryogenic tank, for ongoing storage.

[0008] The one or more adsorption canisters used in theapparatus of the present invention contains an adsorbent material selected from one or more zeolite and xerogel materials. For the avoidance of doubt, the apparatus of the present invention may comprise one or more zeolite materials, one or more xerogel materials, or a mixture of one or more zeolite materials and one or more xerogel materials.

[0009] Zeolites are microporous, crystalline aluminosilicate materials, which are used as adsorbents and catalysts, mainly comprising silicon, aluminium, and oxygen. Zeolites have a typical pore diameter of 0.1-1nm within a framework formed by a 3D-network of Si-O-Al, Si-O-Si, and Al-O-Al linkages. Zeolites have high physical and chemical stability, and are used for the adsorption of hydrophobic molecules, and as catalysts, with their well-defined pore structure making them highly active in a large variety of reactions.

[0010] Various natural zeolites have been identified, including analcime, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite, and phillipsite. In addition, many zeolites have been synthesized, including zeolites A, X, and Y.

[0011] Four well known generic forms of zeolite are designated 3A, 4A, 5A and 13X, according to pore size, all of which are known in the art and commercially available. Each form has its own specific properties and applications. Zeolite 13X is the sodium form of zeolite X and has pores (pore size approximately 10Å) which are larger than those of zeolite type A, to adsorb molecules of a size between approximately 3.64Å and 10Å.

[0012] Whilst any of the above identified zeolites are suitable for use in the apparatus of the present invention, a preferred zeolite is zeolite 13X. Zeolite 13X iscommercially available as a molecular sieve and is a highly porous sodium form of zeolite X that is widely used in the purification of air before liquefaction, natural gas purification, separation of substances, and drying. It is also used for the adsorption of large molecules such as aromatics, branched-chain hydrocarbons, and organosulphur compounds.

[0013] Xerogels are solid materials derived from gels which comprise interconnected particles or polymers dispersed in a liquid. The gel structure is subjected to a drying process (e.g. slow evaporation or freeze-drying) to remove the liquid phase and leave behind a solid material. During the drying process the liquid is extracted from the gel while attempting to preserve its original shape and structure as much as possible. Xerogels exhibit unique properties such as high porosity and a large surface area due to the interconnected network of pores formed during drying.

[0014] A preferred xerogel for use in the apparatus of the present invention is a resorcinol-formaldehyde xerogel. Resorcinol-formaldehyde xerogels may be synthesized via a polymerization reaction between resorcinol and formaldehyde in a solvent to form a three-dimensional porous organic network in the liquid medium. The polymeric structure which forms depends upon the concentration of the reagents, and can be tailored accordingly. The solvent is then removed to obtain a dry polymer with pores which are free of solvent. For xerogel synthesis the solvent is typically removed by direct evaporation, for example through subcritical drying.

[0015] The xerogel may then be subjected to a “carbonization” process. Thus, the organic polymeric xerogel structure may be thermally treated, preferably in an inert atmosphere, torelease volatile materials from the xerogel leaving micropores, and to allow reorganization and condensation reactions to occur to produce a thermally stable material. Additionally, the microporosity of the xerogel may be modified by “activating” the xerogel, either during or after carbonization. The xerogel may be chemically activated (for example with KOH or phosphoric acid), or physically activated (for example with CO2or steam). The microporosity of the xerogel can be tailored to requirements by suitable activation. Thus, in the case of the present invention, the xerogel is preferably selected to preferentially absorb CO2.

[0016] The adsorbent material for use in the one or more canisters may comprise or consist of zeolite material formed into particles (e.g. spheres), for example zeolite particles having an average particle diameter of 1-3mm, for example Zeolite 13X. The adsorbent material for use in the one or more canisters may comprise or consist of carbon xerogel material, for example sintered carbon xerogel material, formed into particles (e.g. spheres), for example carbon xerogel particles having an average particle diameter of 1- 3mm.

[0017] The apparatus of the present invention should have a size which is appropriate for the particular application of use. For example, apparatus for use with an ICE road vehicle needs to be small enough to be fitted to the vehicle. In a preferred embodiment for use on a ship, the apparatus may conveniently fit within a “20 foot” shipping container, the typical dimensions of which are 20 feet (6.06m) long x 8 feet (2.44m) wide x 8 feet 6 inches (2.59m) tall. Such an apparatus for use on a ship may comprise one or more adsorption canisters which are, for example, substantially cylindrical, and which may have a height / length of 1 to 1.5m, and a diameter of 0.25 to 1.0m. The size of the apparatus, e.g. thenumber and size of canisters and number of arrays of canisters, will also depend upon the particular application of use. For example, again in a preferred embodiment for use on a ship, a typical 2000bhp industrial ship’s diesel engine may have the following exhaust characteristics (CO2content of exhaust gases as a mole fraction, and exhaust gas flow rate, at a given engine load, see Table 1):

[0018] Table 1 Engine load % 25 50 75 94 CO2mol fraction 0.043 0.067 0.075 0.079 Exhaust flow rate (m3 / min) 41.67 71.67 110.0 123.33

[0019] In use, once adsorbent material within the canisters(s) becomes saturated with CO2, exhaust gas flow is preferably diverted by means of an autonomous valving array to other canisters(s) within the apparatus, which then repeat the adsorption process so that CO2is constantly stripped from the ICE exhaust gas stream. Thus, if two canisters are working in parallel with an appropriate valving arrangement, one canister may be adsorbing while the other is desorbing. The CO2adsorbed onto the adsorbent material may be desorbed using a pressure swing adsorption (PSA) apparatus or a temperature swing adsorption (TSA) apparatus. The apparatus of the present invention may thus further comprise a PSA or TSA apparatus.

[0020] Thus, according to the present invention in a second aspect there is provided a method for the removal of CO2 from ICE exhaust gas streams, which method comprises adsorbing CO2in the exhaust gas stream onto an adsorbent material, and removing the CO2 using a pressure swing adsorption apparatus or a temperature swing adsorption apparatus.

[0021] The method of the present invention is preferably performed using an apparatus according to the present invention.

[0022] Temperature swing adsorption (TSA) and pressure swing adsorption (PSA) are techniques known in the art which are used to separate individual gas species from mixtures of gases, through adsorption onto an adsorbent material, based upon the principle that different gases have different affinities for an adsorbent material. Thus, in TSA adsorbent materials are used to preferentially adsorb a target gas from the mixture of gases at low temperature, and desorb the target gas by raising the temperature. In PSA, adsorbent materials are used to preferentially adsorb a target gas from the mixture of gases at high pressure, and the gas is then desorbed from the adsorbent at low pressure. According to the method of the present invention, adsorbed CO2may be removed from the adsorbent material under vacuum.

[0023] A preferred PSA apparatus for use in the method of the present invention is a four-step pressure vacuum swing adsorption apparatus (PVSA). The PVSA apparatus preferably operates to remove CO2from an ICE exhaust gas feed through a four-step process: 1) adsorption, 2) blowdown, 3) evacuation, and 4) pressurization:

[0024] 1) Adsorption – an ICE exhaust gas stream is introduced into an adsorption canister containing an adsorbent material which has an affinity for CO2over the other gases in the stream (adsorption pressure = pHand adsorption step time = tads). At the end of the adsorption step, a certain amount of CO2has been adsorbed onto the surface of the adsorbent material.

[0025] 2) Blowdown – the pressure in the canister is reduced (from pHto blowdown pressure pI) to release other gases which are present, over a period of time tbd.

[0026] 3) Evacuation – the pressure in the canister is further reduced (from pIto evacuation pressure pL) to release CO2from the canister, over a period of time tevac. The gas stream obtained from the evacuation step is CO2-rich.

[0027] 4) Pressurisation – the pressure in the canister is increased back up to pH,over a pressurization period tpresby allowing the compressed exhaust gas stream to re-enter the canister.

[0028] An example of a multi-canister apparatus and method is illustrated by Figures 1a to 1c.

[0029] Thus, Figure 1a shows a two canister (C1 and C2) parallel array connected via an arrangement of valves V1 to V8. Figure 1b illustrates a suitable PVSA cycle using the Figure 1a arrangement. By using two canisters in this way, substantially continuous ICE exhaust gas processing can be achieved, with a few seconds of idle time between steps 4) and 1) as indicated. Thus, whilst C1 is in step 1), C2 passes through steps 2) to 4) and a few seconds of idle time, following which C1 passes through steps 2) to 4) and a few seconds of idle time whilst C2 is in step 1). The cycle then repeats.

[0030] Figure 1c shows how multiple arrays of canisters may be arranged.

[0031] The removed / desorbed CO2may then be cooled and compressed as liquid CO2, which can be stored. Methods of liquifying CO2are known in the art. For example, in a typicalCO2purification and liquefaction process, desorbed CO2is purified to remove water and other additional components by scrubbing and the use of different adsorbers and filters, compressed to the desired liquification pressure (liquid CO2can only exist at a pressure above 5.1 atm and a temperature between −56.6 and 31.1°C), cooled and transferred, for example by means of a cryogenic pump, to a cryogenic tank for ongoing storage.

[0032] Preferred performance indicators for the method of the present invention are the CO2purity (e.g. the mole percentage of CO2in the step 3) exhaust gas stream), and the CO2recovery levels (e.g. the moles of CO2recovered from the exhaust gas stream as a percentage of the total moles of CO2in the ICE exhaust gas stream).

[0033] Embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

[0034] Figure 1a to 1c illustrate embodiments of an apparatus and method according to the present invention;

[0035] Figure 2 illustrates an embodiment of an apparatus and method of the present invention;

[0036] Figures 3 to 6 show the results of CO2capture testing performed using embodiments of the apparatus and method of the present invention, as described in more detail in the following Examples.

[0037] Examples

[0038] Canister design

[0039] An adsorbent canister for use in an embodiment of theapparatus of the present invention was designed with the properties shown in Table 2 below: Table 2 Property Value Canister radius (m) 0.5 Canister length (m) 1.5 Adsorbent Zeolite 13X Particle radius (m) 0.001 Adsorbent density (kg / m3) 1130 Bed porosity 0.37 Bed density (kg / m3) 712

[0040] The performance of the canister was tested using a test feed comprising 8mol% CO2and 92mol% N2(the same feed composition is used in all testing described herein) at a feed temperature of 298.15K and pressure of 1 bar, as is described further below.

[0041] Definitions and calculations

[0042] Unconstrained optimization of adsorption canisters was performed by simultaneously maximizing the purity of the CO2recovered and the mole percentage amount of CO2recovered. Optimization was performed at a fixed evacuation pressure (pL) of 0.025 bar whilst varying the following parameters within the upper and lower limits (bounds):

[0043] vf= feed velocity

[0044] Optimization – results

[0045] Two different canister sizes were tested: a first larger canister as described above with reference to Table 2, and a second smaller canister having a canister length of 1m and a canister diameter of 0.29m (otherwise as described in Table 2). The larger canister was tested using four arrays of two canisters per array, and the second canister was tested using 36 arrays of three canisters per array (all canisters within each array, and arrays arranged in parallel). The operating details are given in Table 3 below:

[0046] Table 3 Operating Smaller canister Larger canister conditions (L=1m, D=0.29m) (L=1.5m, D=1m) Exhaust flow rate, 7.336 7.336 mol CO2s-1Flow rate (one 0.205 2.011 array), mol CO2s-1No. canisters per 3 2 array No. arrays 36 4 No. canisters 108 8 Mass of adsorbent, 5044 6710 kg Total volume of 7.1 9.42 canisters, m3Cycle time, s 340 340 Adsorption1.99 1.90pressure, ^^H [bar]Blowdown pressure, 0.45 0.40^^I [bar]Evacuation 0.025 0.025pressure, ^^L[bar] Adsorption step114 153time, ^^ads [s]Blowdown step73 63time, ^^bd [s]Evacuation step65 58time, ^^evac [s]Pressurisation20 20step time, ^^pres [s]Feed velocity vf1.31 1.13 [m / s]

[0047] The results of the optimization testing are shown graphically in Figure 3. The pareto front values for CO2purity and recovery were 95.4 mol% and 68.6 mol% respectively for the arrays of smaller canisters, and were 93.3 mol% and 64 mol% respectively for the arrays of larger canisters.

[0048] The performance of the larger canister under different operating conditions was tested further, per the details given in Table 4 below (all canisters and arrays in parallel): Table 4 Operating (1) (2) (3) conditions Exhaust flow rate, 7.336 7.336 7.336 mol CO2s-1Flow rate (one 2.011 2.300 1.595 array), mol CO2s-1No. canisters per 2 3 3 array No. arrays 4 4 5 No. canisters 8 12 15 Mass of adsorbent, 6710 10064 12580kg Total volume of 9.42 14.4 17.7 canisters, m3Cycle time, s 304 315 283

[0049] The results of the testing are shown graphically in Figure 4. The pareto front values for CO2 purity and recovery were 93.3 mol% and 64.0 mol% respectively for the arrays of operating condition (1), 90.1 mol% and 73.5 mol% respectively for the arrays of operating condition (2), and 80.9 mol% and 81.7 mol% respectively for the arrays of operating condition (3).

[0050] Effect of feed pressure Different arrangements of the larger canister were tested at different feed pressures (adsorption pressure, ^^H). The operating details are given in Table 5 below (all canisters and arrays in parallel): Table 5 Operating conditions Exhaust flow rate, 7.336 7.336 mol CO2s-1Flow rate (one 5.026 2.011 array), mol CO2s-1No. canisters per 3 2 array No. arrays 2 4 No. canisters 6 8 Mass of adsorbent, 5032 6710 kg Total volume of 7.1 9.42canisters, m3Cycle time, s 360 304 Adsorption3.4 1.90pressure, ^^H [bar]Blowdown pressure, 0.42 0.40^^I [bar]Evacuation0.025 0.025pressure, ^^L [bar]Adsorption step120 153time, ^^ads [s]Blowdown step107 63time, ^^bd [s]Evacuation step97 58time, ^^evac [s]Pressurisation20 20step time, ^^pres [s]Feed velocity vf1.56 1.13 [m / s]

[0051] The results of the optimization testing are shown graphically in Figure 5. The pareto front values for CO2purity and recovery were 98.6 mol% and 65.4 mol% respectively for the higher feed pressure, and were 93.3 mol% and 64 mol% respectively for the lower feed pressure.

[0052] The performance of the larger canister under different operating conditions at the higher feed pressure was tested further, per the details given in Table 6 below (all canisters and arrays in parallel): Table 6 Operating (4) (5) conditions Exhaust flow rate, 5.026 7.336mol CO2s-1Flow rate (one 2.011 2.300 array), mol CO2s-1No. canisters per 3 4 array No. arrays 2 2 No. canisters 6 8 Mass of adsorbent, 5032 6710 kg Total volume of 7.1 9.4 canisters, m3Cycle time, s 360 324

[0053] The results of the testing are shown graphically in Figure 6. The pareto front values for CO2purity and recovery were 98.6 mol% and 65.4 mol% respectively for the arrays of operating condition (4), and 95.4 mol% and 83.3 mol% respectively for the arrays of operating condition (5).

[0054] It will be appreciated that the specific embodiments described herein are for illustrative purposes only, and that further modifications and variations of the embodiments are possible without departing from the scope of the present invention as defined by the appended claims.

Claims

CLAIMS 1. An apparatus for carbon capture comprising one or more adsorption canisters containing an adsorbent material selected from one or more zeolite and xerogel materials, wherein each canister has an inlet for receiving an exhaust gas stream from an internal combustion engine and an exhaust gas outlet.

2. An apparatus according to claim 1 which comprises a plurality of canisters linked in a parallel array.

3. Apparatus according to claim 1 or 2 which comprises a plurality of canisters in an array and a valving arrangement to allow inlet flow and outlet flow to be changed between each canister autonomously.

4. An apparatus according to any one of claims 1 to 3 which comprises a plurality of arrays of canisters, wherein the arrays are arranged in parallel.

5. An apparatus according to any preceding claim wherein a valving arrangement allows each canister to be individually isolated.

6. An apparatus according to any preceding claim which is configured for use on board a road vehicle or a ship.

7. An apparatus according to claim 6 which is configured to fit within a container having dimensions 20 feet (6.06m) long by 8 feet (2.44m) wide by 8 feet 6 inches (2.59m) tall.

8. An apparatus according to any preceding claim wherein each canister has a length of 1 to 1.5m, and a diameter of 0.25 to 1.0m.

9. An apparatus according to any preceding claim wherein the adsorbent material comprises or consists of zeolite material.

10. An apparatus according to claim 9 wherein the zeolite material comprises zeolite particles.

11. An apparatus according to claim 10 wherein the zeolite particles have an average particle size of 1-3mm.

12. An apparatus according to any one of claims 9 to 11 wherein the zeolite material comprises one or more zeolite materials selected from analcime, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite, phillipsite, zeolite A, zeolite X, and zeolite Y.

13. An apparatus according to any one of claims 9 to 12 wherein the zeolite material comprises one or more zeolite materials selected from zeolite 3A, 4A, 5A and 13X.

14. An apparatus according to claim 13 wherein the zeolite material comprises zeolite 13X.

15. An apparatus according to any preceding wherein the adsorbent material comprises or consists of a xerogel material.

16. An apparatus according to claim 15 wherein the xerogel material comprises xerogel particles.

17. An apparatus according to claim 16 wherein the xerogel particles have an average particle size of 1-3mm.

18. An apparatus according to any one of claims 15 to 17 wherein the xerogel material comprises a resorcinol-formaldehyde xerogel.

19. An apparatus according to any one of claims 15 to 18 wherein the xerogel has been carbonized and / or activated.

20. An apparatus according to any previous claim which further comprises a pressure swing adsorption apparatus or a temperature swing adsorption apparatus.

21. A method for the removal of CO2from internal combustion engine exhaust gas streams, which method comprises adsorbing CO2in the exhaust gas stream onto an adsorbent material, and removing the CO2using a pressure swing adsorption apparatus or a temperature swing adsorption apparatus.

22. A method according to claim 21 which is performed using an apparatus according to any one of claims 1 to 20.

23. A method according to claim 21 or 22 which comprises the further steps of cooling and compressing the removed CO2as liquid CO2for storage.

24. A method according to any one of claims 21 to 23 comprising a pressure swing adsorption apparatus, wherein the pressure swing adsorption apparatus comprises a four-step pressure vacuum swing adsorption apparatus.

25. A method according to claim 24 wherein the four-step pressure vacuum swing adsorption apparatus operates to remove CO2from an internal combustion engine exhaust gas feed through a four-step process comprising the steps of 1) adsorption, 2) blowdown, 3) evacuation, and 4) pressurization.

26. A method according to claim 25 wherein the adsorptionstep comprises introducing an internal combustion engine exhaust gas stream into an adsorption canister containing an adsorbent material which has an affinity for CO2 over the other gases in the stream to adsorb CO2onto the surface of the adsorbent material.

27. A method according to claim 25 or 26 wherein the blowdown step comprises reducing the pressure in the canister to release other gases which are present.

28. A method according to any one of claims 25 to 27 wherein the evacuation step comprises further reducing the pressure in the canister to release CO2from the canister.

29. A method according to any one of claims 25 to 28 wherein the pressurization step comprises increasing the pressure back to the pressure of the adsorption step by allowing theexhaust gas stream to re-enter the canister.

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