Method For Chemical Absorption And Recovery Of CO2 With Low Energy Consumption At Low Temperatures

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 at a distance from the first location. The stripping step b) is performed at the second facility and at least 4 hours later than the absorbing step a). The stripping step b) is performed by a membrane separation system.

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 counter-current 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 from the first location; the stripping step b) is performed at the second facility with a membrane separation system and at least 4 hours later than the absorbing step a). 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 or barge.

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 4 hours.

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

6. 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.

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

8. Method as claimed in claim 1, wherein the stripping step b) is performed with the membrane separation system at a temperature below 100 C., more preferably below 70 C., even more preferably below 40 C.

9. 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.

10. 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.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0027] 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:

[0028] FIG. 1 is a schematic representation of a method for CO.sub.2 absorption from a gas stream comprising CO.sub.2 in accordance with an embodiment of the invention;

[0029] FIG. 2 is a schematic representation of a method for CO.sub.2 absorption from a gas stream comprising CO.sub.2 in accordance with another embodiment of the invention;

[0030] FIG. 3 is a schematic representation of unloading/reloading sorbent liquid with a hose from a tank which is permanently installed aboard a vessel according to another embodiment of the invention;

[0031] FIG. 4 is a schematic representation of unloading/reloading of an exchangeable tank containing sorbent liquid at a harbor according to an embodiment of the invention; [0032] and

[0033] FIG. 5 is a schematic representation of stripping absorbed CO.sub.2 from the sorbent liquid with a gas-liquid membrane separation system according to an embodiment of the invention.

DETAILED DISCLOSURE OF THE INVENTION

[0034] A scheme of the absorption system at a first off-shore facility, a vessel, is shown in FIG. 1. In the example shown CO2 is absorbed from flue gas, released by the propulsion system of a vessel 1, into a sorbent liquid. The sorbent liquid is contained in an exchangeable container; 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 S1 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. Container 3 may consist of multiple containers.

[0035] As known in the art, the scrubber 2 may be fitted with 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.

[0036] 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, on CO.sub.2 content of the flue gas stream (S1), as well as on temperatures of the flue gas and the sorbent liquid.

[0037] As shown in FIG. 1, the first off-shore facility, a vessel 1, is provided with an exchangeable tank container 3 for the sorbent liquid. FIG. 2 shows an alternative first off-shore 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 can be transported by lorry or barge to on-shore storage or to an end-user.

[0038] Referring to FIG. 4, handling of a sorbent liquid tank container 3 at a harbour is shown. One or multiple 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 multiple 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 on-shore storage or to an end-user.

[0039] With reference to FIG. 3, 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.

[0040] FIG. 5 shows an embodiment of a membrane separation system for recovery of CO.sub.2 from chemical solvents. The system in particular comprises an exchangeable liquid container 31 provided with enriched sorbent liquid, an exchangeable liquid container 32 provided with regenerated or lean sorbent liquid, a solvent pump 10, an optional solvent heater 9, an optional filter 11, a membrane separation unit 12 and a vacuum pump 13. The enriched solvent (stream S4) is carried by pump 10 through the optional heater 9, the optional filter 11 and made to flow through the membrane separation unit 12. The conditions in the membrane separation unit 12 with regard to temperature, and pressures at liquid and gas side, are such that most of the CO.sub.2 present in the enriched solvent (stream S4) is released to the gas side. The regenerated or lean solvent (stream S5) is discharged to the container with lean solvent 32. Pure recovered CO.sub.2 is extracted from the membrane separation unit 12 by the vacuum pump 13 and discharged (stream S6) to the subsequent user. The low temperature heat supplied to solvent heater 9 can be provided from sustainable resources, for example solar or geothermal sources. The power input to pump 10 and vacuum pump 13 can also be provided from sustainable sources, for example wind or solar.

[0041] The stripping is preferably performed at mildly elevated temperature and at sub-ambient pressure at the gas-side. The method allows producing and discharging substantially pure CO.sub.2.