NOx reduction methods and apparatuses

Details NOx reduction methods and apparatuses NOx reduction methods and apparatuses

2001-09-21

2004-10-26

Bos, Steven (Department: 1754)

Chemistry of inorganic compounds

Modifying or removing component of normally gaseous mixture

Mixture is exhaust from internal-combustion engine

C423S213200

Reexamination Certificate

active

06808694

ABSTRACT:

TECHNICAL FIELD
The invention pertains to methods of reducing NO
x
and apparatuses for reducing NO
x
.
BACKGROUND OF THE INVENTION
A wide variety of technology exists that is aimed at reducing NO
x
, wherein x is greater than zero, in emission sources. As emission limits decrease and cost reductions are desired, new NO
x
emission control methods are being evaluated. One emission source identified for improved NO
x
reduction includes lean burn spark and compression ignition engine exhaust. One example of such an emission source includes diesel engines.
A desire exists to improve NO
x
reduction for emission sources including, but not limited to, diesel engines.
SUMMARY OF THE INVENTION
In one aspect of the invention, a NO
x
reduction method includes treating a first gas containing NO
x
, wherein x is greater than zero, and producing a second gas containing NO
2
. A portion of the NO
2
in the second gas can be reduced to N
2
and a third gas produced containing less NO
x
than the first gas, substantially all of the third gas NO
x
being NO. The third gas can be treated and a fourth gas produced containing NO
2
. A portion of the NO
2
in the fourth gas can be reduced to N
2
and a fifth gas produced containing less NO
x
than the third gas, substantially all of the fifth gas NO
x
being NO. As one example, a fraction of the first gas NO
x
treated to second gas NO
2
can approximately equal a fraction of the third gas NO
x
treated to fourth gas NO
2
. Also, the portion of the second gas NO
2
reduced can be less than about 70 volume percent (vol %).
In another aspect of the invention, a NO
x
reduction method includes treating a first gas containing NO
x
, wherein x is greater than zero, with a first plasma and producing a second gas containing NO
2
. The method includes reducing a portion of the NO
2
in the second gas to N
2
with a first catalyst and producing a third gas containing less NO
x
than the first gas, substantially all of the third gas NO
x
being NO. The third gas containing NO
x
can be treated with a second plasma and a fourth gas produced containing NO
2
. A portion of the NO
2
in the fourth gas can be reduced to N
2
with a second catalyst and a fifth gas produced containing less NO
x
than the third gas. As an example, the first and third gases can further contain hydrocarbon. Treating the first gas and reducing a portion of the NO
2
in the second gas can provide oxidation of less than 50 vol % of the hydrocarbon in the first gas. Treating the third gas and reducing a portion of the NO
2
in the fourth gas can provide oxidation of less than 50 vol % of the hydrocarbon in the third gas. The method can further include controlling energy consumption of the first and second plasmas independent of each other. A combined energy consumption of the first and second plasmas can be substantially minimized.
In yet another aspect of the invention, a NO
x
reduction method can include performing a step at least three times in series. The step includes converting NO
x
, wherein x is greater than zero, comprised by an inlet gas to NO
2
with a plasma and catalytically reducing NO
2
at least to N
2
and NO comprised by an outlet gas. The at least three performances of the step can be operated to plasma convert approximately equal fractions of the inlet gas NO
x
to NO
2
. As an example, the outlet gas of at least two of the three performances of the step can comprise the inlet gas for a subsequent performance of the step.
In a further aspect of the invention, a NO
x
reduction apparatus includes a plurality of reactor units in series. Individual reactor units include a plasma device and a reducing catalyst. The plasma device exhibits the property of converting NO
x
, wherein x is greater than zero, to NO
2
. The reducing catalyst exhibits the property of reducing NO
2
to a reaction product consisting essentially of N
2
and NO. The apparatus can further include a plurality of separate power control devices for respective plasma devices of individual reactor units. The plasma devices can include dual dielectric barrier discharge devices. The reducing catalysts can include at least one of barium zeolite Y type (Ba—Y) and sodium zeolite Y type (Na—Y).


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Tonkyn, et al, “Lean NOxReduction in Two Stages: Non-thermal Plasma Followed by Hetergeneous Catalysis”, SAE International Fall Fuels and Lubricants Meeting and Exposition, Oct. 16-19, 2000, SAE Technical Paper 2000-01-2896.
M. Lou Balmer, et al, “NOxDestruction Behavior of Select Materials When Combined with a Non-Thermal Plasma”, SAE International Fall Fuels and Lubricants Meeting and Exposition, Oct. 25-28, 1999, SAE Technical Paper 1999-01-3640.

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