Systems and methods for removing materials from flue gas via regenerative selective catalytic reduction
Regenerative selective catalytic reduction (RSCR) systems and process are provided whereby NO x levels in gases are reduced by mixing the gas with a reactant and then introducing the gas into an RSCR apparatus for treatment that entails heating the gas, causing the gas to undergo one or more catalytic reactions, and then directing the gas through a heat transfer area, to which the gas provides heat for use in connection with successive cycles of the RSCR process.
1. A regenerative selective catalytic process, comprising the steps of:
(a) causing a predetermined concentration of at least one reactant to be mixed with a predetermined quantity of a contaminant-containing gas to form a mixed gas;
(b) introducing the mixed gas into a treatment apparatus; and
(c) treating the mixed gas within the treatment apparatus to reduce the concentration of contaminant in the mixed gas, wherein the treatment apparatus includes a plurality of heat transfer areas and a plurality of catalyst areas, and wherein such treatment entails:
(i) causing the mixed gas to accept heat from at least a first of the plurality of heat transfer areas and to provide heat to at least a second of the plurality of heat transfer areas;
(ii) causing the mixed gas to encounter at least a first of the plurality of catalyst areas and a second of the plurality of catalyst areas, and wherein the mixed gas undergoes catalytic reduction at each of the at least first of the plurality of catalyst areas and the second of the plurality of catalyst areas; and
(iii) causing the mixed gas to flow in at least a first direction and a second direction within the apparatus during such treatment, the first direction being different than the second direction;
(d) causing the mixed gas to be expelled from the apparatus by activating a first gas movement influencing device that is in communication with at least one of the plurality of heat transfer areas of the apparatus; and
(e) purging reactant from the apparatus during treatment step (c) by activating a second gas movement influencing device that is in communication with at least a third of the plurality of heat transfer areas of the apparatus not being used in said treatment step (c).
2. The process of claim 1 , wherein the mixed gas flows in the first direction from the first of the plurality of heat transfer areas to the first of the plurality of catalyst areas and in the second direction from the second of the plurality of heat transfer areas to the second of the plurality of catalyst areas.
3. The process of claim 1 , wherein the apparatus includes a plurality of chambers, and wherein both the first of the plurality of heat transfer areas and the first of the plurality of catalyst areas are located in a first of the plurality of chambers, and wherein both the second of the plurality of heat transfer areas and the second of the plurality of catalyst areas are located in a second of the plurality of chambers.
4. The process of claim 1 , wherein the first of the plurality of heat transfer areas provides heat to the mixed gas and the second of the plurality of heat transfer areas accepts heat from the mixed gas.
5. The process of claim 1 , further comprising the step of:
prior to step (b), pre-heating the first of the plurality of heat transfer areas to a predetermined temperature.
6. The process of claim 5 , wherein the predetermined temperature is in the range of about 600° F. to about 800° F.
7. The process of claim 1 , wherein the first and second gas movement influencing devices are each a fan.
8. The process of claim 1 , wherein the first gas movement influencing device is in communication with the at least one chamber via a conduit.
9. The process of claim 8 , wherein the conduit includes a damper, and wherein the damper is open when the gas movement influencing device is activated.
10. The process of claim 1 , wherein the treatment apparatus includes at least one heat producing device.
11. The process of claim 10 , wherein the at least one heat producing device has a predetermined location whereby it can provide heat to the mixed gas prior to the mixed gas encountering one of the plurality of catalyst areas.
12. The process of claim 10 , wherein the at least one heat producing device is a burner.
13. The process of claim 10 , wherein the temperature of the at least one heat producing device is in the range of about 900° F. to about 1600° F. upon being encountered by the mixed gas.
14. The process of claim 1 , wherein the at least one reactant is ammonia.
15. The process of claim 1 , wherein the temperature of the mixed gas is in the range of about 200° F. to about 400° F. following step (a).
16. The process of claim 15 , wherein the temperature of the mixed gas is in the range of about 300° F. to about 350° F. following step (a).
17. The process of claim 16 , wherein the temperature of the mixed gas is about 325° F. following step (a).
18. The process of claim 1 , wherein the contaminant-containing gas contains nitrogen oxide (NO x ).