Selective catalytic reduction via electrolysis of urea
A method and apparatus for producing ammonia suitable for use as a reductant in a selective catalytic reduction (SCR), a selective non-catalytic reduction (SNCR), or a flue gas conditioning system is provided. A method for treating combustion exhaust gas with ammonia is provided that includes the electrolytic hydrolysis of urea under mild conditions. The electrolysis apparatus includes an electrolytic cell, which may be operatively coupled to an exhaust gas treatment system to provide an apparatus for reducing nitrogen oxides (NO x ) and/or particulate in exhaust gases.
1. A method for supplying NH 3 to an exhaust gas treatment system comprising:
producing ammonia by an electrolytic hydrolysis of urea effected by applying a voltage difference to an electrolytic cell comprising:
a cathode having a first conducting component,
an anode having a second conducting component,
urea, and
an alkaline electrolyte composition in electrical communication with the anode and the cathode, where the alkaline electrolyte composition has a hydroxide concentration of at least 0.01 M or a pH of at least 8,
wherein the voltage difference is applied across the cathode and the anode, wherein the voltage difference is sufficient to effect the electrolytic hydrolysis of urea to produce at least NH 3 ;
recovering at least a portion of the NH 3 ; and
transferring the at least a portion of the NH 3 to the exhaust gas treatment system.
2. The method of claim 1 , wherein the first conducting component comprises carbon, cobalt, copper, iridium, iron, nickel, palladium, platinum, rhodium, ruthenium, or mixtures or alloys thereof.
3. The method of claim 1 , wherein the second conducting component comprises cobalt, copper, iridium, iron, platinum, nickel, rhodium, ruthenium, or mixtures or alloys thereof.
4. The method of claim 1 , wherein the second conducting component comprises an oxidized form of cobalt, copper, iridium, iron, platinum, nickel, rhodium, ruthenium, or mixtures or alloys thereof.
5. The method of claim 1 , wherein the voltage difference is within the range from about 0.85 volts to about 1.7 volts.
6. The method of claim 1 , wherein the voltage difference is applied as a constant voltage.
7. The method of claim 1 , wherein the exhaust gas treatment system includes at least one of a selective catalytic reduction system, a selective non-catalytic reduction system, or a flue gas conditioning system.
8. The method of claim 1 , further comprising:
affecting a rate of NH 3 production by
varying at least one of
a temperature of the electrolytic cell,
a pressure of the electrolytic cell,
an electrical current applied to the electrolytic cell, or
a voltage applied to the electrolytic cell;
varying a voltage applied to a portion of the anode, wherein the anode comprises an anodic catalyst bed; or
varying an area percentage of a total area of the anodic catalyst bed contacting a urea solution.
9. The method of claim 1 , wherein the alkaline electrolyte composition comprises an alkali metal or alkaline earth metal salt of a hydroxide, a carbonate, a bicarbonate, or combinations thereof.
10. The method of claim 1 , wherein the electrolytic cell further comprises
a heater apparatus operatively coupled to electrolytic cell, and
a recirculation system operatively coupled to the electrolytic cell, wherein the recirculation system contains at least a portion of the alkaline electrolyte composition.
11. A method for reducing nitrogen oxide (NO x ) emissions and/or particulate matter in a combustion exhaust gas during ongoing operation, comprising:
injecting ammonia into the combustion exhaust gas upstream of at least one of a selective catalytic reduction (SCR) device, a selective non-catalytic reduction (SNCR) device, or an electrostatic precipitator device, wherein said ammonia is supplied by:
applying a voltage difference to an electrolytic cell comprised of:
a cathode having a first conducting component,
an anode having a second conducting component,
urea, and
an alkaline electrolyte composition in electrical communication with the anode and the cathode, where the alkaline electrolyte composition has a hydroxide concentration of at least 0.01 M or a pH of at least 8,
wherein the voltage difference is applied across the cathode and the anode, and wherein the voltage difference is sufficient to effect the electrolytic hydrolysis of urea to produce at least NH 3 .
12. The method of claim 11 , wherein the first conducting component comprises carbon, cobalt, copper, iridium, iron, nickel, palladium, platinum, rhodium, ruthenium, or mixtures or alloys thereof.
13. The method of claim 11 , wherein the second conducting component comprises cobalt, copper, iridium, iron, platinum, nickel, rhodium, ruthenium, or mixtures or alloys thereof.
14. The method of claim 11 , wherein the voltage difference is within the range from about 0.85 volts to about 1.7 volts.
15. The method of claim 11 , wherein the voltage difference is between about 1.2 volts and about 1.6 volts.
16. The method of claim 11 , wherein applying the voltage difference to the electrolytic cell further comprises varying the voltage difference to control the production of NH 3 .
17. The method of claim 11 , wherein the electrolytic cell further comprises a temperature control system including a heat source.
18. The method of claim 11 further comprising increasing a fuel combustion efficiency of a combustion system, the method comprising:
supplying H 2 to a combustion chamber of the combustion system, wherein the hydrogen is supplied by:
applying the voltage difference to the electrolytic cell, wherein the voltage difference applied across the cathode and the anode is sufficient to produce NH 3 and H 2 .
19. An exhaust gas treatment system comprising:
at least one of a selective catalytic reduction system, a selective non-catalytic reduction system, or a flue gas conditioning system; and
an ammonia generator comprising an electrolytic cell comprised of:
a cathode having a first conducting component,
an anode having a second conducting component,
urea,
a voltage source,
an alkaline electrolyte composition in electrical communication with the anode and the cathode, where the alkaline electrolyte composition has a hydroxide concentration of at least 0.01 M or a pH of at least 8; and
an ammonia outlet from the ammonia generator in communication with the at least one of the selective catalytic reduction system, the selective non-catalytic reduction system, or the flue gas conditioning system.
20. The system of claim 19 , wherein the first conducting component comprises carbon, cobalt, copper, iridium, iron, nickel, palladium, platinum, rhodium, ruthenium, or mixtures or alloys thereof.
21. The system of claim 19 , wherein the second conducting component comprises cobalt, copper, iridium, iron, platinum, nickel, rhodium, ruthenium, or mixtures or alloys thereof.
22. The system of claim 19 , wherein the voltage difference is within the range from about 0.85 volts to about 1.7 volts.