SEPARATION OF CO2 FROM GAS MIXTURES
Processes for separating carbon dioxide from a gas mixture that comprises CO 2 and N 2 that are based upon formation of gas hydrates, and systems useful for implementing such processes, are disclosed.
1 . A system for separation of CO 2 from combustion product or other gas comprising a hydrate formation reactor (HFR) that comprises an outer vessel configured:
with a plurality of stages arranged with a first stage proximal a first end of the vessel and second and any subsequent stages successively more proximal a second end of the vessel;
one or more gas feed inlets placed at a distance from the first end of the vessel the same as said distance of a stage that is a second or subsequent stage and configured to feed a gas stream into the vessel;
one or more aqueous phase inlets configured to feed an aqueous solution into the first end of the vessel or proximate thereto;
one or more hydrate slurry outlets configured to draw off a hydrate slurry stream from the first end of the vessel or proximate thereto;
one or more gas product outlets configured to draw off a gas product stream from the second end of the vessel or proximate thereto; and
a temperature control system effective to establish a temperature gradient or a series of temperature steps from a first temperature T 1 in a region proximate to the first end of the vessel to a second temperature T 2 in a region proximate to the second end of the vessel, and controlling the temperature at each of the stages, wherein T 1> T 2 ;
wherein the gas stream and the aqueous phase flow in a countercurrent manner through the vessel.
2 . The system of claim 1 that further comprises a solid-liquid separator configured to receive an aqueous hydrate slurry from the hydrate slurry outlet for separation into an aqueous phase product and a solid hydrate.
3 . The system of claim 2 in which the solid-liquid separator comprises an aqueous phase recirculating line that feeds the aqueous phase product of the solid-liquid separator into the vessel.
4 . The system of claim 3 in which the recirculating line includes a cooling plant for cooling the aqueous phase liquid product.
5 . The system of claim 1 that further comprises a hydrate decomposition facility including a hydrate decomposition plant for decomposing a hydrate and a vapor-liquid separator for separating a vapor product from an aqueous phase and that is operably connected to the hydrate formation reactor so as to receive a hydrate slurry from the hydrate slurry outlet of the hydrate formation reactor.
6 . The system of claim 5 , in which the hydrate decomposition plant comprises a heater for raising the temperature of the hydrate.
7 . The system of system of claim 5 , in which the hydrate decomposition plant is one that lowers the pressure of a hydrate slurry.
8 . The system of claim 5 , that further comprises an aqueous phase recirculating line that feeds the aqueous phase product of the vapor-liquid separator into the vessel.
9 . The system of claim 8 , in which the aqueous phase recirculating line includes a cooling plant for cooling the aqueous phase liquid product.
10 . The system of claim 1 that further comprises an inlet for adding a hydrate promoter to the gas feed stream.
11 . The system of claim 2 that further comprises an inlet for adding a hydrate promoter to the gas feed stream.
12 . The system of claim 8 that further comprises an inlet for adding a hydrate promoter to the gas feed stream.
13 . The system of claim 3 , wherein the aqueous phase recirculating line includes an input for adding a hydrate promoter to the aqueous phase.
14 . The system of claim 8 , wherein the aqueous phase recirculating line includes an input for adding a hydrate promoter to the aqueous phase.
15 . The system of claim 12 , wherein the aqueous phase recirculating line includes an input for adding a hydrate promoter to the aqueous phase.
16 . The system of claim 13 that further comprises an inlet for adding a hydrate promoter to the gas feed stream.
17 . The system of claim 1 , in which the product gas outlet(s) are configured to transport the product gas to a storage facility for storing the product gas at a pressure above atmospheric pressure.
18 . The system of claim 1 , in which the product gas outlet(s) are configured to transport the product gas to a turbine for generating electricity.
19 . A process for purifying CO 2 from a gas comprising N 2 , the process comprising intimately contacting a feed gas stream comprising CO 2 and N 2 gases and an aqueous phase stream in a countercurrent flow to form a CO 2 -rich hydrate in the aqueous phase, a temperature T f being maintained at a gas feed stage f in the countercurrent flow, a temperature T 2 such that T 2 <T f being maintained at a stage n>f, and a temperature T 1 being maintained at a stage m≤f such that T 1 ≥T f ;
wherein:
T 2 is in the range from the incipient vapor temperature for CO 2 to the incipient hydrate temperature for CO 2 at the operating pressure of the process, and
T 1 is a temperature at or below a temperature of convergence of the incipient CO 2 hydrate formation and incipient CO 2 vapor formation curves at the operating pressure of the process.
20 . The process of claim 19 , further comprising separating the gas phase from the aqueous phase and collecting a hydrate slurry formed in the aqueous phase and comprising hydrate particles enriched in CO 2 .
21 . The process of claim 20 , further comprising concentrating the hydrate from the hydrate slurry and sequestering the hydrate.
22 . The process of claim 21 , in which the hydrate is sequestered on the deep ocean floor or buried in the sea floor, or in which the hydrate is encapsulated.
23 . The process of claim 19 , further comprising collecting a N 2 -rich gas from the gas stream after contact with the aqueous phase.
24 . The process of claim 20 , further comprising collecting a N 2 -rich gas from the separated gas.
25 . The process of claim 24 that is conducted at 2200 psia, T 2 is from 31 to 34° F. (−0.5 to 1.1° C.) and T 1 is about 54° F. (12.2° C.).
26 . The process of claim 24 , in which there are 3 stages and T f is about 33° F. (0.5° C.), T 1 is about 35° F. (1.6° C.) and T 2 is about 31° F. (−0.5° C.).
27 . The process of claim 19 , in which the feed gas stream comprises a hydrate promoter.
28 . The process of claim 19 , in which the aqueous phase stream comprises a hydrate promoter.
29 . The process of claim 27 , in which the aqueous solution stream comprises a hydrate promoter.