Carbon dioxide capture from power or process plant gases
The present invention are methods for removing preselected substances from a mixed flue gas stream characterized by cooling said mixed flue gas by direct contact with a quench liquid to condense at least one preselected substance and form a cooled flue gas without substantial ice formation on a heat exchanger. After cooling additional process methods utilizing a cryogenic approach and physical concentration and separation or pressurization and sorbent capture may be utilized to selectively remove these materials from the mixed flue gas resulting in a clean flue gas.
1. A method for removing a preselected substance from a flue gas stream comprising:
cooling the flue gas stream by direct contact with a cool liquid to remove water from the flue gas stream;
compressing the flue gas stream to approximately 120 psia to remove additional water;
dehydrating the compressed flue gas stream with either a first absorbent or a first adsorbent;
cooling the compressed, dehydrated flue gas stream by indirect heat exchange with cold expanded flue gas components;
contacting the compressed, dehydrated flue gas stream with a second absorbent or a second adsorbent to physically absorb or adsorb the preselected substance;
regenerating the second absorbent or the second adsorbent, thereby releasing the preselected substance from the second absorbent or the second adsorbent into a separate stream; and
expanding the compressed, dehydrated, treated flue gas stream through a gas expander, thus producing electric power, and cooling the expanded stream which is reheated by indirect heat exchange with the compressed, dehydrated flue gas stream.
2. The method of claim 1 wherein at least one of said preselected substances contains a material selected from the group consisting of CO 2 , SO 2 , NO2, HCL, H 2 SO 4 , SO 3 , Hg, As, Se.
3. The method of claim 1 wherein heat exchange is performed between cooling water and the cool liquid in order to cool and condense water from the flue gas stream.
4. The method of claim 1 wherein contact between the flue gas stream and the cool liquid is performed in a quench tower, a spray tower, or a venturi scrubber.
5. The method of claim 1 wherein the compressing the flue gas stream comprises using a multistage compressor with intercoolers and an aftercooler to condense additional water from the compressed flue gas stream.
6. The method of claim 1 wherein the first adsorbent is triethylene glycol, the first absorbent is a small pore molecular sieve, and wherein the second absorbent is at least one of the following: propylene carbonate, methanol, a mixture of polyethyleneglycol dimethyl ethers, and normal methyl pyrrolidone (NMP), and wherein the second adsorbent is at least one of the following: metal organic frameworks, CO 2 selective natural zeolites, and CO2 selective man-made microporous materials.
7. The method of claim 1 wherein the compressing the flue gas stream comprises using an axial flow compressor and an aftercooler to condense water from the compressed flue gas stream.