U.S. patent application number 14/767003 was filed with the patent office on 2015-12-31 for method and catalyst for the simultaneous removal of carbon monoxide and nitrogen oxides from flue or exhaust gas.
This patent application is currently assigned to Haldor Topsoe A/S. The applicant listed for this patent is HALDOR TOPSOE A/S. Invention is credited to Francesco Castellino, Viggo Lucassen Hansen.
Application Number | 20150375207 14/767003 |
Document ID | / |
Family ID | 50031348 |
Filed Date | 2015-12-31 |
![](/patent/app/20150375207/US20150375207A1-20151231-D00001.png)
United States Patent
Application |
20150375207 |
Kind Code |
A1 |
Castellino; Francesco ; et
al. |
December 31, 2015 |
METHOD AND CATALYST FOR THE SIMULTANEOUS REMOVAL OF CARBON MONOXIDE
AND NITROGEN OXIDES FROM FLUE OR EXHAUST GAS
Abstract
A method and a catalyst, where flue gas or exhaust gas
containing harmful carbon monoxide, organic compounds (VOC) and
NO.sub.x is contacted with a layered catalyst in which a first
layer comprises an oxidation catalyst and in an underlying layer a
NH3-SCR catalyst for the simultaneous removal of the carbon
monoxide and NO.sub.x.
Inventors: |
Castellino; Francesco;
(Frederiksberg C, DK) ; Lucassen Hansen; Viggo;
(Bronshoj, DK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HALDOR TOPSOE A/S |
Kgs. Lyngby |
|
DK |
|
|
Assignee: |
Haldor Topsoe A/S
Kgs. Lyngby
DK
|
Family ID: |
50031348 |
Appl. No.: |
14/767003 |
Filed: |
February 3, 2014 |
PCT Filed: |
February 3, 2014 |
PCT NO: |
PCT/EP2014/052043 |
371 Date: |
August 11, 2015 |
Current U.S.
Class: |
423/239.1 ;
502/339 |
Current CPC
Class: |
B01J 23/22 20130101;
B01D 53/9468 20130101; B01D 2255/20707 20130101; B01J 23/6482
20130101; B01D 2255/20723 20130101; B01D 2255/9022 20130101; B01J
35/023 20130101; B01J 35/0006 20130101; B01D 2255/1023 20130101;
B01J 21/063 20130101 |
International
Class: |
B01J 23/648 20060101
B01J023/648; B01D 53/94 20060101 B01D053/94; B01J 35/02 20060101
B01J035/02; B01J 23/22 20060101 B01J023/22; B01J 35/00 20060101
B01J035/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2013 |
DK |
PA 2013 00091 |
Claims
1. Method for the reduction of amounts carbon monoxide, volatile
organic compounds and nitrogen oxides in flue or exhaust gas
comprising the steps of: introducing ammonia and/or a precursor
thereof into the flue or exhaust gas; converting the precursor if
any into ammonia; contacting the gas and the ammonia at a
temperature of up to 350.degree. C. with a layered catalyst
comprising an upper first catalyst layer with an oxidation catalyst
and an underlying second catalyst layer with an NH3-SCR catalyst
supporting completely the first layer and oxidizing at least part
of the amounts of carbon monoxide and the volatile organic
compounds in the upper first layer without affecting the ammonia
further contained in the gas and reducing the amounts of nitrogen
oxides in the underlying second catalyst layer by reaction with the
ammonia.
2. The method of claim 1, wherein the oxidation catalyst in the
first layer consists of palladium, vanadium oxide and titanium
oxide.
3. The method of claim 2, wherein the oxidation catalyst consists
of 0.45 wt % palladium, 4.5 wt % vanadium pentoxide and supported
on titanium oxide.
4. The method of claim 1, wherein the first catalyst layer has a
layer thickness of between 10 and 200 micron.
5. The method of claim 1, wherein the first catalyst layer has a
layer thickness of between 10 and 50 micron.
6. The method of claim 1, wherein the NH-3-SCR catalyst in the
second catalyst layer comprises oxides of tungsten, molybdenum,
vanadium and titanium.
7. The method of claim 1, wherein the flue or exhaust gas is
additionally treated with a conventional not layered SCR catalyst
either upstream or downstream the layered catalyst.
8. A catalyst for simultaneous oxidation of carbon monoxide and
volatile organic compounds and selective reduction of nitrogen
oxides by reaction with ammonia, the catalyst comprises a first
layer of an oxidation catalyst and a second layer of an NH3-SCR
catalyst completely supporting the first layer.
9. The catalyst of claim 8, wherein the oxidation catalyst consists
of palladium, oxides of vanadium and oxides of titanium.
10. The catalyst of claim 9, wherein the oxidation catalyst
consists of 0.45 wt % palladium, 4.5 wt % vanadium pent-oxide and
supported on titanium oxide.
11. The catalyst of claim 8, wherein the first catalyst layer has a
layer thickness of between 10 and 200 micron.
12. The catalyst of claim 8, wherein the first catalyst layer has a
layer thickness of between 10 and 50 micron.
13. The catalyst of claim 8, wherein the NH3-SCR catalyst in the
second catalyst layer comprises oxides of tungsten, molybdenum,
vanadium and titanium.
Description
[0001] The present invention relates to a method and catalyst for
the simultaneous removal of carbon monoxide and nitrogen oxides
(NOx) contained in flue or exhaust gas.
[0002] More particularly, the invention provides a method, where
flue gas or exhaust gas containing harmful carbon monoxide, organic
compounds (VOC) and NOx is contacted with a layered catalyst in
which a first layer comprises an oxidation catalyst and in an
underlying layer a NH3-SCR catalyst for the simultaneous removal of
the carbon monoxide and NOx.
[0003] Removal of NOx, VOC and CO from flue or exhaust gas is
conventionally exercised by use of two different catalyst
compositions, wherein an oxidation catalyst is arranged upstream of
an SCR catalyst with injection of a reductant between the
catalysts. NOx removal is typically performed by selective
catalytic reduction (SCR) with NH3 on vanadium oxide or
zeolite-based catalysts in monolithic form. Ammonia is injected
upstream the SCR catalyst and reacts with the NOx on the catalyst
surface. An optimal temperature window for the vanadium oxide-based
catalysts is 200-400.degree. C., while zeolite based catalysts are
more active at temperatures >400.degree. C.
[0004] In the case of CO and VOC removal by catalytic oxidation,
the platinum metals are the most common choice due to their high
reactivity already at temperatures >200.degree. C.
[0005] As an example of a flue gas containing both CO, VOCs and NOx
is the flue gas from a turbine operating on natural gas.
Traditionally, in the HRSG design the CO oxidation catalyst, often
based on Pt, is located upstream the SCR catalyst and the ammonia
injection grid ("AIG"). This location has been chosen mainly due to
the fact that the oxidation catalyst is very active in the
oxidation of NH3 to NOx, which is highly undesired. Having the CO
oxidation catalyst located upstream the AIG makes sure that no NH3
is wasted, but all amounts of injected ammonia reach the SCR
catalyst limiting the operation costs of the utility.
[0006] In an alternative configuration, the oxidation catalyst is
arranged downstream the SCR catalyst. When positioned this way the
oxidation catalyst is operated at lower temperatures than the
conventional layout. The problem with this configuration is that if
not designed correctly, the oxidation catalyst may oxidize the NH3
slip to NOx, thus reducing the overall NOx removal of the plant.
Possibly, the oxidation catalyst may be designed in a way that NH3
is converted to N2 instead, but such a catalyst is typically more
expensive than a conventional oxidation catalyst due to both the
kind and quantity of the noble metals used for its production.
[0007] In the above configurations, the resulting reactor consists
of two separate catalyst units, i.e. one SCR catalyst unit and one
oxidation catalyst unit. More precisely, the total volume of
catalyst installed will be determined by the size of the SCR
catalyst unit, plus the size of the oxidation catalyst unit.
[0008] In order to reduce the size of the reactor, a combination of
the two catalysts partly on the same support has been attempted and
in some cases accomplished.
[0009] U.S. Pat. No. 7,390,471 discloses an exhaust gas treatment
apparatus for reducing the concentration of NO.sub.x, HC and CO in
an exhaust gas stream. The treatment apparatus includes a
multifunction catalytic element having an upstream reducing-only
portion and a downstream reducing-plus-oxidizing portion that is
located downstream of an ammonia injection apparatus. The selective
catalytic reduction (SCR) of NO.sub.x is promoted in the upstream
portion of the catalytic element by the injection of ammonia in
excess of the stoichiometric concentration with the resulting
ammonia slip being oxidized in the downstream portion of the
catalytic element. Any additional NO.sub.x generated by the
oxidation of the ammonia is further reduced in the downstream
portion before being passed to the atmosphere. The reduction-only
catalyst may be vanadium/TiO 2 and the reduction-plus-oxidizing
catalyst includes a reduction catalyst having 1.7 wt percent of
vanadium/TiO2 impregnated with 2.8 g/ft 3 each of platinum and
palladium.
[0010] However, the SCR activity of the oxidation catalyst is
considerably lower than the SCR activity of an SCR-only catalyst
meaning that the total volume of catalyst installed will be equal
to the volume of the oxidation catalyst plus the volume of the SCR
catalyst needed to compensate for the low SCR activity of the
oxidation catalyst.
[0011] In the cleaning of gas turbine flue gas as an example,
number one priority from a utility point of view is to reduce the
total catalyst volume as much as possible. Large volumes in fact
mean high pressure drop across the catalyst bed and overall lower
efficiency of the HRSG. The pressure drop has a direct impact on
the net power achievable from the turbine and an indirect effect on
the heat flux, i.e. the calories that can be extracted from the
flue gas by the HRSG.
[0012] In order to reduce the catalyst volume to a minimum, the SCR
activity of the oxidation catalyst has to be increased to the same
high levels of an SCR-only catalyst. One essential condition for
obtaining this is the use of an oxidation catalyst very active in
the oxidation of CO and VOC, but not reacting with NH3. Another
important condition is that the oxidation catalyst must still have
the same oxidation activity as an oxidation-only catalyst.
[0013] By the present invention these two conditions are achieved,
the total volume of the resulting catalyst for the combined removal
of both CO, VOC and NOx is equal to the volume of the largest
catalyst between a dedicated oxidation and a dedicated SCR
catalyst, which dependents on the required removal of CO, VOCs and
NOx for a particular installation.
[0014] Thus, this invention provides a method for the reduction of
amounts of carbon monoxide, volatile organic compounds and nitrogen
oxides in flue or exhaust gas, said method comprising the steps of
[0015] introducing ammonia and/or a precursor thereof into the flue
or exhaust gas; [0016] converting the precursor if any into
ammonia; [0017] contacting the gas and the ammonia at a temperature
of up to 350.degree. C. with a layered catalyst comprising in flow
direction of the gas an upper first catalyst layer with an
oxidation catalyst and an underlying second catalyst layer with an
NH3-SCR catalyst supporting completely the first layer and
oxidising at least part of the amounts of carbon monoxide and the
volatile organic compounds in the upper first layer without
affecting the ammonia further contained in the gas and reducing the
amounts of nitrogen oxides in the underlying second catalyst layer
by reaction with the ammonia.
[0018] A CO, VOC oxidation catalyst not active in the oxidation of
NH3 at temperatures up to 350.degree. C. for use in the method
according to the invention has been developed.
[0019] Thus, in an embodiment of the invention, the oxidation
catalyst in the first layer consists of palladium, vanadium oxide
and titanium oxide.
[0020] By coating this catalyst on a commercial NH3-SCR catalyst
e.g. a NH3-SCR catalyst in comprising oxides of tungsten,
molybdenum, vanadium and titanium according to a further embodiment
of the invention, the resulting catalyst consists of a first
catalyst layer oxidizing CO and VOC but not ammonia and a second
layer of NH3-SCR-only catalyst.
[0021] Referring to FIG. 1 in the drawings at gas temperatures up
to 350.degree. C., CO and VOC will be oxidized to CO2 in the first
oxidation layer 2 of layered catalyst 1, while all injected NH3 for
the NOx abatement will simultaneously diffuse through oxidation
layer 2 and react instead on the underlying SCR catalyst layer
3.
[0022] By enhancing the pore structure and thickness of the first
catalyst layer, both NOx and NH3 will easily access the underlying
SCR catalyst and very limited SCR activity will be lost due to the
diffusion rate of reagents across the oxidation catalyst layer.
[0023] Thus, in a further embodiment of the invention the first
catalyst layer has a layer thickness of between 10 and 200 micron,
preferably of between 10 and 50 micron.
[0024] In the method according to invention as described above, the
flue or exhaust gas can additionally be treated with a conventional
not layered SCR catalyst either up or downstream the layered
catalyst.
[0025] The invention provides additionally a catalyst for
simultaneous oxidation of carbon monoxide and volatile organic
compounds and selective reduction of nitrogen oxides by reaction
with ammonia, the catalyst comprises a first layer of an oxidation
catalyst and a second layer of an NH3-SCR catalyst supporting
completely the first layer.
[0026] Preferably, the oxidation catalyst consists of palladium,
oxides of vanadium and oxides of titanium.
[0027] The preferred oxidation catalyst according to en embodiment
of the invention also has some SCR activity due to the presence of
both TiO2 and vanadium oxides. Full SCR activity is thus preserved
without the need of increasing the addition of ammonia. In this
way, the desired removal of both CO and NOx can be accomplished
with a significantly reduced catalyst volume.
[0028] In an embodiment of the invention the first catalyst layer
has a layer thickness of between 10 and 200 micron, preferably of
between 10 and 50 micron.
[0029] When structuring the layered catalyst in monolithic form,
the resulting monolith catalyst will have a uniform catalyst
composition across the monolith length. CO, VOC and NOx removal
proceeds simultaneously along the whole length of the monolith.
EXAMPLE
[0030] A V/Ti based commercial SCR catalyst has been coated with a
catalyst consisting of 0.45 wt % Pd, 4.5 wt % V2O5 on TiI2. The NOx
removal efficiency has been measured and compared to the NOx
removal efficiency of the same SCR catalyst not coated with the
oxidation catalyst. The results and conditions of the test are
shown in Table 1 below:
TABLE-US-00001 TABLE 1 DeNOx, % DeCO, % NH3 slip, ppmv SCR 93.5 0
5.7 OXIDATION + SCR 92.9 97.8 4.4
[0031] Test conditions. Gas inlet composition: 50 ppmv NOx, 55 ppmv
NH3, 100 ppmv CO, 15% vol O2, 10% vol H2O, N2 balance. Gas space
velocity, NHSV=27 000 h-1. Temperature: 350.degree. C.
[0032] As apparent from Table 1, the same (within experimental
uncertainty) NOx removal efficiency has been obtained in both
tests.
* * * * *