These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
A carbon dioxide separation system 10 comprises a heat exchanger 12, a separator 14 and a condenser 16, as shown in
While not to be limited by a particular theory, mechanisms for CO2 selectivity in microporous materials include molecular sieving, surface diffusion and capillary condensation. CO2 can be removed selectively from a stream containing other gas molecules with a larger kinetic diameter, such as N2, through a membrane with sufficiently small pores. A material that has an affinity for CO2 relative to other gases in a stream will show a preferred adsorption and surface diffusion of CO2. Furthermore, the presence of the adsorbed CO2 molecules, through capillary condensation, will effectively block the pore from the more weakly adsorbing gases, thereby hindering their transport. The performance properties of such inorganic membranes at a given operating condition can be improved by a person skilled in the art by modifying the surface, altering the pore size or changing the composition of the membrane.
Hybrid membranes that incorporate polymer and ceramic materials integrated at the molecular level can show enhanced CO2 selectivity properties at elevated operating conditions. The invention is not restricted to any particular membrane material or type and encompasses any membrane comprising any material that is capable of providing suitable levels of permeance and selectivity. That includes, for example, mixed matrix membranes, facilitated transport membranes, ionic liquid membranes, and polymerized ionic liquid membranes. In practice, separator 14 often comprises a separation layer that is disposed upon a support layer. For asymmetric inorganic membranes, the porous support can comprise a material that is different from the separation layer. Support materials for asymmetric inorganic membranes include porous alumina, titania, cordierite, carbon, Vycor and metals. Porous metal support layers include stainless steel, iron-based alloys, nickel, and nickel-based alloys.
Separator 14 physically separates first flow path 18 and second flow path 22 and promotes thermal transfer and carbon dioxide transport therebetween. Condenser 16 is in flow communication with second flow path 22 and receives and condenses the heat transfer fluid 24 to isolate carbon dioxide 26 contained therein.
In one embodiment, fluid comprising carbon dioxide 20 is an exhaust gas, for example, an exhaust gas having a temperature in the range between about 200C to about 700C. The high temperature exhaust gas 20 is directed into heat exchanger 12 along first flow path 18. At least a portion of second flow path 22 is defined by separator 14. For example, in one embodiment second flow path 22 is defined by piping or tubing and a portion of that piping or tubing is exposed to the high temperature exhaust gas 20 (i.e. separator 14) and is made of a material with selective permeability of carbon dioxide. Separator 14 is integrated within the carbon dioxide separation system 10 to be in thermal transfer and carbon dioxide transport relationship with the first flow path 18. As separator 14 is exposed to the high temperature exhaust gas 20, at least a portion of the carbon dioxide contained within the exhaust gas 20 is transported through separator 14 to the heat transfer fluid 24 contained within the second flow path 22. Additionally, the heat transfer fluid 24 extracts heat from the exhaust gas and, in turn, undergoes a phase change to a gaseous phase.
The gaseous phase heat transfer fluid 24 containing carbon dioxide is directed to condenser 16, where the heat transfer fluid 24 is condensed back to a liquid phase and the carbon dioxide 26 is isolated in a gaseous form within the condenser 16. While this invention has been discussed in relation to higher temperature exhaust gas containing carbon dioxide 20, this invention can be utilized with fluids containing carbon dioxide 20 over a wide range of temperatures. This system can be utilized over a wide range of systems for any exhaust gas, for example, furnace exhaust, thermal oxidizers, metal processing or any other industrial process. In fact, fluids containing carbon dioxide 20 can be at ambient temperature with a suitable phase change heat transfer fluid 24 being selected, for example, refrigerant, alcohols like butane, silicon oils or the like. In addition, while this invention is discussed in relation to CO2 capture systems, a material selective to other constituents within the exhaust gas steam, for example, CO, NOx or other pollutants or species, may be utilized to capture the other constituents in a similar fashion.
A combined cycle CO2 capture system 100 of the instant invention is shown in
At least a portion of at least one cooling circuit 108 is a carbon dioxide extraction circuit 120. Carbon dioxide extraction circuit 120 is made of a material with selective permeability of carbon dioxide. As the high temperature exhaust gas 104 travels through the HRSG 106 and contacts the carbon dioxide extraction circuit 120, carbon dioxide 122 is transported through the carbon dioxide extraction circuit 120 into the water 110 or steam 112 that is circulating through the cooling circuit and is directed to the steam turbine system 114 along with the steam 112. The mixed flow of steam 112 and CO2 122 is directed to steam turbine system 114 to generate electricity. The content of the CO2 122 within the steam turbine system 114 may lead to an improvement in the overall work extracted from the system. The flow exiting steam turbine system 114 is directed to a condenser 124 where the steam 112 is condensed back to water 110, which water 110 is then typically directed back to the HRSG 106. The CO2 122, is isolated in the condenser 124 and is drawn off along path 126 to be captured, stored, or otherwise utilized.
In one embodiment, a portion 128 of reduced temperature exhaust gas 118 is recycled back to the electricity generation system 102 to increase the overall CO2 content in the exhaust gas 104 to improve the extraction efficiency of the system 100. Ideally, the CO2 content of exhaust gas 104 should be in the range between about 10% by volume to about 15% by volume for improved extraction efficiency through carbon dioxide extraction circuit 120. In order to achieve these levels of CO2 such technologies as exhaust gas recirculation can be employed.
A retrofitable carbon capture system 200 of the instant invention is shown in
Retrofitable carbon capture system 200 further comprises a carbon dioxide extraction system 202. Carbon dioxide extraction system 202 includes an extraction circuit 220 that is made of a material with selective permeability of carbon dioxide and a condenser 221. A heat transfer fluid 224 is directed through the carbon extraction circuit 220 and upon exposure to a predetermined temperature of exhaust gas, undergoes a phase change from a liquid to gaseous phase. As the high temperature exhaust gas 104 travels through the HRSG 106 and contacts the carbon dioxide extraction circuit 220, carbon dioxide 222 is transported through the carbon dioxide extraction circuit 220 into the heat transfer fluid 224 that is circulating through the extraction circuit 220. The mixed flow of heat transfer fluid 224 and CO2 222 is directed to condenser 221 where the heat transfer fluid 224 is condensed back to a liquid phase. The CO2 222, is isolated in the condenser 221 and is drawn off along path 226 to be captured, stored, or otherwise utilized.
Retrofitable carbon capture system 200 offers the significant benefit that it can be retrofitted into any installed system for immediate utilization and carbon capture. The heat transfer fluid 224 is selected based on the temperatures that the extraction circuit 220 is exposed to.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.