A PROCESS FOR CAPTURING CARBON DIOXIDE

Abstract

The present invention provides a process for capturing CO.sub.2 from a gas stream, the process at least comprising the steps of: (a) providing a CO.sub.2-containing gas stream; (b) contacting the gas stream as provided in step (a) in an adsorption zone with solid adsorbent particles thereby obtaining CO.sub.2-enriched solid adsorbent particles (c) passing CO.sub.2-enriched solid adsorbent particles as obtained in step (b) from the bottom of the adsorption zone to the bottom of a first desorption zone; (d) removing a part of the CO.sub.2 from the CO.sub.2-enriched solid adsorbent particles in the first desorption zone, thereby obtaining partly CO.sub.2-depleted solid adsorbent particles and a first CO.sub.2-enriched gas stream; (e) passing the partly CO.sub.2-depleted solid adsorbent particles as obtained in step (d) via a riser to a second desorption zone; (f) removing a further part of the CO.sub.2 from the partly CO.sub.2-depleted solid adsorbent particles in the second desorption zone thereby obtaining regenerated solid adsorbent particles and a second CO.sub.2-enriched gas stream; and (g) recycling regenerated solid adsorbent particles as obtained in step (f) to the adsorption zone of step (b); wherein the second desorption zone is located above the adsorption zone.

Claims

1. A process for capturing carbon dioxide (CO.sub.2) from a gas stream, the process at least comprising the steps of: (a) providing a CO.sub.2-containing gas stream; (b) contacting the gas stream as provided in step (a) in an adsorption zone with solid adsorbent particles thereby obtaining CO.sub.2-enriched solid adsorbent particles, wherein the adsorption zone has at least two beds of fluidized solid adsorbent particles and wherein the solid adsorbent particles are flowing downwards from bed to bed and wherein the gas stream is flowing upwards; (c) passing CO.sub.2-enriched solid adsorbent particles as obtained in step (b) from the bottom of the adsorption zone to the bottom of a first desorption zone; (d) removing a part of the CO.sub.2 from the CO.sub.2-enriched solid adsorbent particles in the first desorption zone, thereby obtaining partly CO.sub.2-depleted solid adsorbent particles and a first CO.sub.2-enriched gas stream; (e) passing the partly CO.sub.2-depleted solid adsorbent particles as obtained in step (d) via a riser to a second desorption zone; (f) removing a further part of the CO.sub.2 from the partly CO.sub.2-depleted solid adsorbent particles in the second desorption zone thereby obtaining regenerated solid adsorbent particles and a second CO.sub.2-enriched gas stream, wherein the second desorption zone has at least two beds of fluidized solid adsorbent particles and wherein the solid adsorbent particles are flowing downwards from bed to bed and a stripping gas is flowing upwards; and (g) recycling regenerated solid adsorbent particles as obtained in step (f) to the adsorption zone of step (b); wherein the second desorption zone is located above the adsorption zone.

2. The process according to claim 1, wherein the adsorption zone comprises two or more adsorption vessels, each adsorption vessel containing at least two beds of fluidized solid adsorbent particles and each adsorption vessel defining a separate flow path for a part of the solid adsorbent particles and a part of the gas stream.

3. The process according to claim 1, wherein the first desorption zone is located below the adsorption zone.

4. The process according to claim 1, wherein the solid adsorbent particles near the top of the first desorption zone are heated.

5. The process according to claim 1, wherein the first desorption zone contains internal heating means, and wherein preferably the second desorption zone does not contain internal heating means.

6. The process according to claim 1, wherein the partly CO.sub.2-depleted solid adsorbent particles as passed via a riser in step (e) are separated in a gas/solids separator before entering the second desorption zone, thereby obtaining a solids-enriched and a gas-enriched stream, wherein the solids-enriched stream is passed to the second desorption zone, and wherein preferably at least part of the gas-enriched stream obtained in the gas/solids separator is used as a riser gas in the riser of step (e).

7. The process according to claim 1, wherein at least a part of the partly CO.sub.2-depleted solid adsorbent particles as passed via the riser in step (e) and fed into the second desorption zone are separated in the top of the second desorption zone, thereby obtaining a solids-enriched and a gas-enriched stream, wherein the solids-enriched stream is passed on in the second desorption zone and wherein at least a part of the gas-enriched stream is used as a riser gas in the riser of step (e).

8. The process according to claim 1, wherein the regenerated solid adsorbent particles as obtained in step (f) are cooled before entering the adsorption zone.

9. The process according to claim 1, wherein water is added to the regenerated solid adsorbent particles that are being recycled in step (g) to the adsorption zone of step (b), before the regenerated solid adsorbent particles enter the adsorption zone.

10. An apparatus suitable for performing the process for capturing carbon dioxide (CO.sub.2) from a gas stream according to claim 1, the apparatus at least comprising: an adsorption zone for contacting a CO.sub.2-containing gas stream with solid adsorbent particles thereby obtaining CO.sub.2-enriched solid adsorbent particles, wherein the adsorption zone has at least two beds of fluidized solid adsorbent particles and wherein during use the solid adsorbent particles can flow downwards from bed to bed and wherein the CO.sub.2-containing gas stream can flow upwards; a first desorption zone for receiving the CO.sub.2-enriched solid adsorbent particles as obtained in the adsorption zone and removing a part of the CO.sub.2 from the CO.sub.2-enriched solid adsorbent particles, thereby obtaining partly CO.sub.2-depleted solid adsorbent particles and a first CO.sub.2-enriched gas stream; a riser for passing the partly CO.sub.2-depleted solid adsorbent particles as obtained in the first desorption zone to a second desorption zone; the second desorption zone for removing a further part of the CO.sub.2 from the partly CO.sub.2-depleted solid adsorbent particles in the second desorption zone thereby obtaining regenerated solid adsorbent particles and a second CO.sub.2-enriched gas stream, wherein the second desorption zone has at least two beds of fluidized solid adsorbent particles and wherein the solid adsorbent particles can flow downwards from bed to bed and a stripping gas can flow upwards; and a recycle line for recycling regenerated solid adsorbent particles as obtained in the second desorption zone to the adsorption zone; wherein the second desorption zone is located above the adsorption zone.

Description

[0071] Hereinafter the present invention will be further illustrated by the following non-limiting drawings. Herein shows:

[0072] FIG. 1 schematically a flow scheme of the process for capturing CO.sub.2 from a gas stream according to the present invention.

[0073] For the purpose of this description, same reference numbers refer to same or similar components.

[0074] The flow scheme of FIG. 1 generally referred to with reference number 1, shows a quench cooler 2, an adsorption zone 3, a first desorption zone 4, a riser 5, a second desorption zone 6, an overhead condenser 7 and a g/l-separator 8. Furthermore, FIG. 1 shows a heat exchange cycle 9, containing heat exchangers 10 (a cooler) and 11 (a heater).

[0075] During use, a CO.sub.2-containing flue gas stream is provided as stream F3. As shown in the embodiment of FIG. 1, the stream F3 was pressurized (as stream F1) in a booster and pre-treated (as stream F2) in a water quench in quench cooler 2 (for water knock-out and temperature adjustment). Before entering the adsorption zone 3 near the bottom thereof, the stream F3 may be split in several streams which are treated in parallel in two or more separate adsorption vessels, wherein each adsorption vessel defines a flow path for a part of the solid adsorbent particles and a part of the gas stream.

[0076] Although not clearly reflected in the (schematic) FIG. 1, the second desorption zone 6 is located above the adsorption zone 3, thereby allowing for gravity flow for the solid adsorbent particles between the second adsorption zone 6 and the adsorption zone 3.

[0077] The gas streams F3 is contacted with solid adsorbent particles in the adsorption zone 3 thereby obtaining CO.sub.2-enriched solid adsorbent particles and a CO.sub.2-depleted stream. The CO.sub.2-depleted stream leaves the adsorption zone 3 as stream F4 and is for example sent to a flue gas stack (in case the feed stream F1 would be a flue gas).

[0078] In the embodiment of FIG. 1, the adsorption zone 3 has five beds of fluidized solid adsorbent particles. The solid adsorbent particles are flowing downwards from bed to bed whilst the gas stream is flowing upwards, hence counter-currently. As shown in the embodiment of FIG. 1, each of the beds in the adsorption zone 3 is provided with cooling means (in the form of cooling coils). However, and as preferred according to the present invention, at least the two lowest beds in the adsorption zone 3 can do without such cooling coils to save on CAPEX costs.

[0079] The CO.sub.2-enriched solid adsorbent particles as obtained in the adsorption zone 3 are passed via gravity flow (not fully reflected in FIG. 1) as stream M10 from the bottom of the adsorption zone 3 to the bottom of the first desorption zone (the ‘pre-regenerator’) 4, in which the solid adsorbent particles are partly regenerated. In the embodiment of FIG. 1, stream M10 is heated in heat exchanger 11 and enters the first desorption zone 4 as stream M12.

[0080] In the first desorption zone 4 (in the embodiment of FIG. 1 located below the adsorption zone 3 to allow gravity flow for the streams M10 and M12), a part of the CO.sub.2 is removed from the CO.sub.2-enriched solid adsorbent particles, thereby obtaining partly CO.sub.2-depleted solid adsorbent particles (stream M13) and a first CO.sub.2-enriched gas stream (F13). As shown, the first desorption 4 zone contains a heating coil that uses a heating fluid (e.g. low-pressure steam) to heat up the solid adsorbent particles.

[0081] To help the solid adsorbent particles stream fed as M12 pass through the first desorption zone 4 (and subsequently through the riser 5), stream F12 (as discussed below) is used as a riser gas.

[0082] The partly CO.sub.2-depleted solid adsorbent particles M13 and the first CO.sub.2-enriched gas stream F13 are passed together via the riser 5 to the second desorption zone (the ‘regenerator’) 6.

[0083] As shown in the embodiment of FIG. 1, the combined stream M13+F13 is fed into the second desorption zone 6 (at the top thereof) and separated in the top thereof, thereby obtaining a solids-enriched stream and a gas enriched stream. The solids-enriched stream flows downwards (by gravity flow) from bed to bed in the second desorption zone 6. The gas-enriched stream leaves the second desorption zone 6 near the top thereof as stream F7. In the embodiment of FIG. 1, stream F7 is the combination of (steam) stream F5 after having passed upwards through the second desorption zone 6 whilst picking up some CO.sub.2 and the gas stream F13 as passed through the riser 5 and fed into the top of the second desorption zone 6.

[0084] As shown in the embodiment of FIG. 1, the gas-enriched stream F7 is split in two streams F14 and F18. Stream F14 is pressurized in a booster and fed to the bottom of the first desorption zone 4 to help the solid adsorbent particles pass therethrough and through the riser 5 in the upwards direction.

[0085] Stream F18 is sent to the overhead condenser 7 and separated in g/l-separator 8. CO.sub.2-rich overhead stream F8 may be sent to a compression train for subsequent compression and storage (not shown); condensate stream F9 may be sent to e.g. a wastewater treatment plant.

[0086] As shown in FIG. 1, the second desorption zone 6 comprises in this embodiment seven beds, whilst heating is provided (via steam-heated coils) in only the upper part of the second desorption zone 6 and in only three of the seven beds (i.e. less than half). Further, steam is added near the bottom of the second desorption zone 6 via stream F5. In a preferred embodiment of the present invention, the second desorption zone 6 does not contain any heating coils (or other indirect heating means) at all.

[0087] In the second desorption zone 6 a further part of the CO.sub.2 from the partly CO.sub.2-depleted solid adsorbent particles is removed thereby obtaining regenerated solid adsorbent particles and a second CO.sub.2-enriched gas stream. The second CO.sub.2-enriched gas stream (also containing steam) moves upwards through the second desorption zone 6 and leaves the second desorption zone 6 as stream F7, whilst the regenerated solid adsorbent particles are recycled as stream M11 (via gravity flow) to the adsorption zone 3. As shown in the embodiment of FIG. 1 the regenerated solid adsorbent particles in stream M11 are cooled in heat exchanger 10 and enter the top of the adsorption zone 3 as stream M14.

EXAMPLE

[0088] The flow scheme of FIG. 1 was used for illustrating the capture of CO.sub.2 from a gas stream. The compositions and conditions of the fluid (i.e. gas and liquid) streams in the various flow lines are provided in Table 1 below and for the solid streams they are indicated in Table 2.

[0089] As solid adsorbent particles, spherically-shaped Lewatit VP OC 1065 particles (a weak base anionic exchange resin, commercially available from Lanxess (Cologne, Germany)) were used, having a particle size of from 315 to 1250 micrometer, an average total surface area of 50 m.sup.2/g and a pore volume of 0.3 ml/g.

TABLE-US-00001 TABLE 1 Fluid stream F1 F2 F3 F4 F5 F6 F7 F8 F9 Phase V V V V V V V V L T [° C.] 92 100 30 57 120 119 118 30 30 p [bara] 1.00 1.07 1.07 1.00 1.70 1.00 1.00 1.00 1.00 CO.sub.2 [kg/s] 41.45 41.45 41.45 4.15 — 15.61 43.59 37.30 — H.sub.2O [kg/s] 35.53 35.53 16.22 23.52 23.42 8.84 18.85 0.67 15.44 N.sub.2 [kg/s] 466.01 466.01 466.01 466.01 — — — — — O.sub.2 [kg/s] 86.13 86.13 86.13 86.13 — — — — — Ar [kg/s] 7.18 7.18 7.18 7.18 — — — — — CO.sub.2 [mol. %] 4.2 4.2 4.4 0.5 — 41.9 48.6 95.8 — H.sub.2O [mol. %] 8.8 8.8 4.2 6.2 100 58.1 51.4 4.2 100 N.sub.2 [mol. %] 74.2 74.2 77.9 79.6 — — — — — O.sub.2 [mol. %] 12.0 12.0 12.6 12.9 — — — — — Ar [mol. %] 0.8 0.8 0.8 0.9 — — — — — Fluid stream F10 F11 F12 F13 F14 F17 F18 Phase L L V V V L V T [° C.] 104  75 137 118 118 30 118 p [bara]  3  8 1.20 1.00 1.00 1.00 1.00 CO.sub.2 [kg/s] — — 6.29 27.98 6.29 — 37.30 H.sub.2O [kg/s]   172.04   172.04 2.73 10.00 2.73 19.31 16.12 N.sub.2 [kg/s] — — — — — — — O.sub.2 [kg/s] — — — — — — — Ar [kg/s] — — — — — — — CO.sub.2 [mol. %] — — 48.6 53.4 48.6 — 48.6 H.sub.2O [mol. %] 100 100 51.4 46.6 51.4 100 51.4 N.sub.2 [mol. %] — — — — — — — O.sub.2 [mol. %] — — — — — — — Ar [mol. %] — — — — — — —

TABLE-US-00002 TABLE 2 Solid stream M10 M11 M12 M13 M14 T [° C.] 50 120 88 118 100
As can be seen from Table 1, the process according to the present invention allows for an effective way of capturing carbon dioxide from a CO.sub.2-containing stream: by passing through the adsorption zone 3, the CO.sub.2-containing flue gas stream F3 (4.4 mol. % CO.sub.2) was for 90% reduced in CO.sub.2 content after leaving the adsorption zone as stream F4 (0.5 mol. % CO.sub.2).

[0090] Further, the CO.sub.2-containing gas stream F8 leaving the gas/liquid-separator 8 has a high purity (and contains apart from CO.sub.2 mainly moisture). This stream F8 is suitable to be compressed in standard compressors and suitable to be used in various industrial processes to produce various products, for CO.sub.2 storage, in greenhouses to accelerate plant growth, etc.

[0091] Also, the process according to the present invention is suitable for large gas flows (to be fed as stream F3 to the adsorption zone), containing low or high CO.sub.2 concentrations.

[0092] The person skilled in the art will readily understand that many modifications may be made without departing from the scope of the invention. Further, the person skilled in the art will readily understand that, while the present invention in some instances may have been illustrated making reference to a specific combination of features and measures, many of those features and measures are functionally independent from other features and measures given in the respective embodiment(s) such that they can be equally or similarly applied independently in other embodiments.