Method For Recovery of Chemically Absorbed CO2 With Low Energy Consumption

Abstract

A method for removing carbon dioxide (CO.sub.2) from a gas is described. The method provides a sorbent liquid for the CO.sub.2 in countercurrent flow with a gas stream comprising the CO.sub.2 and absorbs the CO.sub.2 in the sorbent liquid to obtain a gas with a reduced concentration of CO.sub.2, and a sorbent liquid enriched with the absorbed CO.sub.2. The absorbed CO.sub.2 is stripped from the enriched sorbent liquid to obtain a regenerated sorbent liquid and CO.sub.2-containing gas. The absorbing step a) is performed at a first facility provided in a first location and the sorbent liquid enriched with the absorbed CO.sub.2 is then transported from the first facility to a second facility provided in a second location and at a distance of minimum 3 kilometers from the first location. The stripping step b) is performed at the second facility and at least 24 hours later than the absorbing step a). The second facility is a greenhouse.

Claims

1. Method for removing carbon dioxide (CO.sub.2) from a gas, for instance a flue gas, the method comprising: a) providing a sorbent liquid for the CO.sub.2, such as an amine solvent, in countercurrent flow with a gas stream comprising the CO.sub.2 and absorbing the CO.sub.2 in the sorbent liquid so as to obtain a gas with a reduced concentration of CO.sub.2, and a sorbent liquid enriched with the absorbed CO.sub.2; b) stripping the absorbed CO.sub.2 from the enriched sorbent liquid so as to obtain a regenerated sorbent liquid and CO.sub.2-containing gas, wherein the absorbing step a) is performed at a first facility provided in a first location; the sorbent liquid enriched with the absorbed CO.sub.2 is transported from the first facility to a second facility distinct from the first facility and provided in a second location at a distance of at least 3 km from the first location; the stripping step b) is performed at the second facility and at least 24 hours later than the absorbing step a); there is no pipeline connection between the first facility and the second facility; and the second facility comprises a greenhouse.

2. Method as claimed in claim 1, wherein the sorbent liquid enriched with the absorbed CO.sub.2 is stored at the first facility before transporting it to the second facility.

3. Method as claimed in claim 1, wherein the sorbent liquid enriched with the absorbed CO.sub.2 is stored at an intermediate location in between the first and second facilities.

4. Method as claimed in claim 2, wherein the total time of transporting and storing the sorbent liquid enriched with the absorbed CO.sub.2 is at least 24 hours.

5. Method as claimed in any one of the preceding claims claim 1, wherein the sorbent liquid enriched with the absorbed CO.sub.2 is transported at ambient pressure and/or ambient temperature, for instance by a road transport vehicle.

6. Method as claimed in claim 1, wherein direct pipe connections between the first facility and the second facility are lacking.

7. Method as claimed in claim 1, wherein a shortest distance between the first and the second facilities is at least 3 km, more preferably at least 5 km, and most preferably at least 10 km.

8. Method as claimed in claim 1, wherein the first facility comprises a sailing or harbored vessel and the second facility comprises an onshore facility.

9. Method as claimed in claim 1, wherein the stripping step b) is performed at a temperature below 100 C., more preferably below 70 C., even more preferably below 40 C., and most preferably at ambient temperature.

10. Method as claimed in claim 1, wherein the stripping step b) is performed at ambient pressure.

11. Method as claimed in claim 1, wherein the second facility comprises a greenhouse and the stripping step b) uses greenhouse air and/or ambient air as stripping gas and/or as transport medium of the CO.sub.2-containing gas back to the greenhouse.

12. Method as claimed in claim 11, wherein the CO.sub.2-containing gas as obtained after the stripping step b) is carried back to the greenhouse to enhance crop growth.

13. Method as claimed in claim 1, wherein the stripping step b) is carried out with a stripper unit, preferably without a reboiler and/or condenser unit.

14. Method as claimed in claim 1, wherein the CO.sub.2-containing gas obtained from the stripping step b) contains from 100 to 10000 ppm (1 vol. %), more preferably from 200 to 5000 ppm, and most preferably from 400 ppm to 1500 ppm CO.sub.2.

15. Method as claimed in claim 1, wherein at least 5 wt. % of the CO.sub.2 that is present in the gas stream comprising the CO.sub.2 is absorbed in the sorbent liquid during the absorbing step a), more preferably at least 10 wt. % CO.sub.2, even more preferably at least 30 wt. % CO.sub.2, and most preferably at least 50 wt. % CO.sub.2.

16. Method as claimed in claim 1, wherein at most 90 wt. % of the CO.sub.2 that is present in the gas stream comprising the CO.sub.2 is absorbed in the sorbent liquid during the absorbing step a), more preferably at most 70 wt. % CO.sub.2, and most preferably at most 50 wt. % CO.sub.2.

17. Method as claimed in claim 1, wherein the second facility comprises a greenhouse with a fired heater, and wherein the second facility is used to absorb CO.sub.2 from the flue gas of the fired heater during night time so as to obtain a flue gas with a reduced concentration of CO.sub.2 and enrichment of the sorbent liquid with CO.sub.2.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0049] The above brief description, as well as other objects, features and advantages of the present invention will be more fully appreciated by reference to the following detailed description of a presently preferred, but nonetheless illustrative embodiment, when taken in conjunction with the accompanying drawing wherein:

[0050] FIG. 1 is a schematic representation of CO.sub.2 absorption from a gas stream comprising CO.sub.2. In the example shown CO.sub.2 is absorbed from flue gas, released by the propulsion system of a vessel, into a sorbent liquid. The sorbent liquid is contained in an exchangeable container;

[0051] FIG. 2 is a schematic representation of CO.sub.2 absorption from a gas stream comprising CO.sub.2. In the example shown CO.sub.2 is absorbed from the flue gas of a vessel into a sorbent liquid. The sorbent liquid is contained in a permanently installed tank on board of the vessel;

[0052] FIG. 3 is a schematic representation of unloading/reloading of an exchangeable tank containing sorbent liquid at a harbor;

[0053] FIG. 4 is a schematic representation of unloading/reloading sorbent liquid with a hose from a tank which is permanently installed aboard a vessel;

[0054] FIG. 5 is a schematic representation of transport of a tank containing sorbent liquid with absorbed CO.sub.2 to an onshore facility, a greenhouse. Intermediate storage of the tank containers is an option. The sorbent liquid is transported and stored at ambient conditions;

[0055] FIG. 6 is a schematic representation of transport of a tank containing sorbent liquid with absorbed CO.sub.2 to an onshore facility for recovery of pure CO.sub.2. Intermediate storage of tank containers with sorbent liquid, with or without absorbed CO.sub.2, is an option;

[0056] FIG. 7 is a schematic representation of stripping absorbed CO.sub.2 from the sorbent liquid at an onshore facility. In this example it is a greenhouse. The stripping is done at ambient pressure and at ambient temperature, optional at elevated temperature. Ambient air is used as the stripping agent, is enriched with CO.sub.2 and carried into the greenhouse to enhance crop growth;

[0057] FIG. 8 is s schematic representation of the stripping conditions of the enriched sorbent liquid. It shows the equilibrium relation between CO.sub.2 partial pressure and CO.sub.2 content of a sorbent liquid (approx. 30 m.-% MEA in water) at low and high temperature. The graph compares conventional stripping to stripping at low CO.sub.2 partial pressure & low temperature;

[0058] FIG. 9 is a schematic representation of absorption of CO.sub.2 from flue gas of a fired greenhouse heater during night time; and

[0059] FIG. 10 is a representation of CO.sub.2 concentrations in stripping air leaving the stripper operating at ambient temperature and ambient pressure, as measured during operation at a greenhouse.

DETAILED DISCLOSURE OF THE INVENTION

[0060] A scheme of the absorption system at a first offshore facility, a vessel, is shown in FIG. 1. The components of the absorption system comprise a CO.sub.2 absorber or scrubber 2, a sorbent liquid container 3, a pump 4 and an optional solvent cooler 5. Part or all of the flue gas from the ship propulsion system (stream S1) is carried through the CO.sub.2 scrubber 2. Part or most of the CO.sub.2 present in the stream SI is absorbed by the sorbent liquid in the scrubber 2. The sorbent liquid is pumped from the exchangeable container 3 into the scrubber 2 by the pump 4, optionally cooled by the cooler 5. The flue gas from which CO.sub.2 has been at least partly stripped is discharged as stream S2, for instance into the air. The sorbent liquid, enriched with CO.sub.2 absorbed from the flue gas (S1), is drained back to the container 3.

[0061] As known in the art, the scrubber 2 may be fitted with a liquid distributor and packing material for improvement of flue gas-sorbent liquid contact and CO.sub.2 transfer, at the same time keeping pressure drop as low as possible. The scrubber 2 is preferably operated with counter-current flow of flue gas and sorbent liquid. The optional sorbent liquid cooler 5 removes absorption heat from the sorbent liquid and keeps sorbent liquid temperature low to maximize the CO.sub.2 absorption capacity of the sorbent.

[0062] Operation of the absorption system is straightforward: the sorbent liquid is circulated through the scrubber 2 until saturation of the sorbent at operating conditions is achieved. Maximum CO.sub.2 absorption capacity depends on type and concentration of the sorbent liquid chemical, and temperature and CO.sub.2 content of the flue gas stream (S1), as well as temperatures of the flue gas and the sorbent liquid.

[0063] As shown in FIG. 1, the first offshore facility, a vessel 1, is provided with an exchangeable tank container 3 for the sorbent liquid. FIG. 2 shows an alternative first offshore facility, a vessel 1, provided with a permanently installed container or tank 6 to contain the sorbent liquid. The sorbent liquid can be loaded via line 62, and can be unloaded via line 61, and transported by lorry or barge to onshore storage or to an end-user.

[0064] Referring to FIG. 3, handling of a sorbent liquid tank container 3 at a harbour is shown. One or more containers 3 with fresh sorbent liquid with relatively low CO.sub.2-content can be loaded from a lorry 8 by hoist 7 onto a vessel 1 or other off-shore facility in a harbour. One or several containers 3, with sorbent liquid enriched with CO.sub.2, can be off-loaded in a harbour by hoist 7 and transported by lorry 8 or barge to onshore storage or to an end-user.

[0065] With reference to FIG. 4, pumping of sorbent liquid to (or from) a tank 6 permanently installed on a vessel 1 via hose 63 is schematically shown. Unloading occurs via a line 61, while filling the tank 3 may be carried out via line 62. In this embodiment, loading is to (or from) a lorry 8 with tank.

[0066] FIG. 5 shows a lorry 8 transporting a tank container 3 with sorbent liquid, rich in CO.sub.2, to an end-user, which, in this embodiment comprises a greenhouse 9 on shore. Intermediate storage of sorbent liquid containers 16 is an option, as shown. Transport and storage is preferably done at ambient temperature and ambient pressure.

[0067] FIG. 6 shows another embodiment in which tank containers 3 with sorbent liquid, rich in CO.sub.2, are provided to a (second) stripping facility 10 for recovery of pure CO.sub.2 (stream S7). The pure CO.sub.2 may be pressurized and/or liquefied according to the requirements of the end-user. The containers 3 with sorbent liquid (rich in CO.sub.2 or stripped from CO.sub.2) may be stored at the stripping facility 10 or elsewhere onshore 16.

[0068] FIG. 7 shows yet another embodiment in which stripping of CO.sub.2 from a sorbent liquid in container 3 is performed at an end-user, in particular a greenhouse 9, using a stripper 10. The stripper operates at near ambient pressure and temperature. Pump 11 circulates sorbent liquid (stream S3) from the sorbent liquid tank container 3 through the stripper 10. Heater 13 enables stripping at higher temperatures and is optional. Sorbent liquid leaving the stripper (S4) is drained back by gravity to the tank container 3. Air, external or from the greenhouse (stream S5), is carried through the stripper by an air fan 12 and is enriched with CO.sub.2. The air provides heat required for the CO.sub.2-sorbent liquid (amine) dissociation reaction, it acts as the stripping medium, and it acts as transport medium for the CO.sub.2. Air enriched with CO.sub.2 (stream S6) is supplied to the greenhouse 9 to enhance crop growth. CO.sub.2 analysers may be provided in the air stream entering the stripper 15 and leaving the stripper 14 and enable monitoring of the CO.sub.2 content of the air in the greenhouse.

[0069] The stripper 10 may be fitted with a liquid distributor and packing material for improvement of flue gas-sorbent liquid contact and CO.sub.2 transfer, at the same time keeping pressure drop as low as possible. The stripper 10 is preferably operated with counter-current flow of air and sorbent liquid. The optional sorbent liquid heater 13 increases the temperature of the sorbent liquid, to improve stripping of CO.sub.2 from the sorbent liquid.

[0070] Operation of the stripper system is straightforward: the sorbent liquid (S3) is supplied to the stripper 10, air (S5) is passed through the stripper. CO.sub.2 analysers (14, 15) provide information on the CO.sub.2 content of the air in the greenhouse. Control is by switching on or off, or throttling sorbent liquid flow and/or air flow through the stripper. Analysers (14, 15) also indicate when the sorbent liquid is stripped from CO.sub.2.

[0071] FIG. 8 schematically shows the relation between a gas phase containing CO.sub.2 at a certain partial pressure (y-axis) and the CO.sub.2 content of a sorbent liquid containing about 30 wt. % MEA in water, in chemical equilibrium with each other at temperatures of 40 C. and 120 C. (x-axis). The condition of the sorbent liquid in equilibrium with flue gas containing about 8.5 vol. % flue gas at about 40 C. is represented by point P1.

[0072] As is known to a person skilled in the art of conventional sorbent stripping, recovery of pure CO.sub.2 at 1-3 bar pressure from a CO.sub.2-containing MEA solvent requires high temperatures. Stripping at about 120 C. to release pure CO.sub.2 at about 3 bar is indicated by point P2. At this condition, about 0.4-0.45 kmole CO.sub.2 /kmole MEA remains in the sorbent liquid. Only about 30% of the CO.sub.2 contained in the sorbent liquid is recovered. Stripping with ambient air, which has low CO.sub.2 partial pressure (currently about 420 ppm CO.sub.2, about 0.00042 bar), results in far higher recovery of CO.sub.2 from the sorbent liquid. The stripper can be operated at low temperature, ambient or mildly elevated. Energy consumption is minimized. The achievable condition of the sorbent liquid is indicated by point P3. At about 40 C. only about 0.2 kmole CO.sub.2 /kmole MEA remains in the sorbent liquid, more than 60% of the CO.sub.2 contained in the sorbent liquid can be recovered.

[0073] An option is to increase the temperature of the sorbent liquid supplied to the stripper to 80-100 C., if cheap heat at this temperature level is available. The sorbent liquid can then be stripped to the condition indicated by point P4, increasing CO.sub.2 recovery to about 90%.

[0074] FIG. 9 schematically shows absorption of CO.sub.2 from flue gas of a fired greenhouse heater. The stripper (10) in this embodiment is operated in reverse mode as an absorber. The CO.sub.2 in the flue gas from the fired heater, after cooling down, is absorbed by the sorbent. The CO.sub.2 can be stripped and utilized to enhance crop growth during daytime. This method of operation can be applied during night time, and when no assimilation light is used in the greenhouse. Under such conditions there is no consumption of CO.sub.2 by the crop. The stripper (10) in FIG. 7 is used as an absorber (10) in FIG. 9. Flue gas from the fired heater (stream S5) is carried through the absorber (10). The

[0075] CO.sub.2 in the flue gas enriches the sorbent, and can be stripped and utilized for crop growth during daytime. Pump (11) circulates sorbent liquid (stream S3) from the sorbent liquid tank container (3) through the absorber (10). The absorption is performed at near ambient pressure and-temperature. Sorbent liquid leaving the absorber (S4) is returned the sorbent container (3). Flue gas discharged by the absorber (10) is discharged to ambient (stream S6). The heat produced by the fired heater (16) is transferred to the greenhouse. Optional, cooler (17) removes absorption heat from the sorbent, which can be used to supply additional heat to the greenhouse by a heat transfer fluid circulated by pump (19) through a greenhouse heater (21). Pump (18) circulates heat transfer fluid through the fired heater (16) and through a heater (20) in the greenhouse. The CO.sub.2 analysers in the flue gas stream S5 entering the absorber (15) and in the flue gas stream S6 leaving the absorber (14) enable monitoring of the absorption process.

[0076] The absorber (10) may be fitted with a liquid distributor and packing material for improvement of flue gas-sorbent liquid contact and CO.sub.2 transfer, at the same time keeping pressure drop as low as possible. Further, the absorber (10) is preferably operated with counter-current flow of air and sorbent liquid, and the optional sorbent liquid cooler (17) may reduce the temperature of the sorbent liquid, to improve the absorption of CO.sub.2 by the sorbent liquid.

[0077] The absorption system operates such that the sorbent liquid (stream S3) is supplied to the absorber (10) by pump (11). The enriched sorbent liquid (stream S4) returns to the sorbent storage container after (optional) cool down by cooler (17).

[0078] FIG. 10 finally represents CO.sub.2 concentrations in stripping air leaving the stripper operating at ambient temperature and ambient pressure. The amine solvent had been enriched in an absorber installed on sailing vessel. Enrichment of air up to an end concentration of 1000 ppm CO.sub.2, resulting in near maximum enhancement of crop growth in a greenhouse, is already achieved at a stripper temperature of approx. 15 C.