U.S. patent application number 11/761018 was filed with the patent office on 2007-09-27 for method of cleaning and/or regenerating wholly or partially de-activated catalysts for stack-gas nitrogen scrubbing.
This patent application is currently assigned to ENBW Energy Solutions GMBH, a German corporation. Invention is credited to Jochen Benz, Peter Buck, Gunter Schneider.
Application Number | 20070221250 11/761018 |
Document ID | / |
Family ID | 7799704 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070221250 |
Kind Code |
A1 |
Schneider; Gunter ; et
al. |
September 27, 2007 |
METHOD OF CLEANING AND/OR REGENERATING WHOLLY OR PARTIALLY
DE-ACTIVATED CATALYSTS FOR STACK-GAS NITROGEN SCRUBBING
Abstract
The invention concerns a method of cleaning and/or regenerating
wholly or partially de-activated catalysts for stack-gas nitrogen
scrubbing, in which the catalysts are treated with a washing and/or
regenerating liquid, characterized by the washing or regenerating
liquid consisting wholly or in part of demineralized water.
Inventors: |
Schneider; Gunter;
(Buchholz, DE) ; Benz; Jochen; (Ludwigsburg,
DE) ; Buck; Peter; (Neckarsulm, DE) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
ENBW Energy Solutions GMBH, a
German corporation
|
Family ID: |
7799704 |
Appl. No.: |
11/761018 |
Filed: |
June 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10654450 |
Sep 4, 2003 |
|
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|
11761018 |
Jun 11, 2007 |
|
|
|
09842621 |
Apr 27, 2001 |
6631727 |
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10654450 |
Sep 4, 2003 |
|
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|
09147477 |
Jan 7, 1999 |
6232254 |
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PCT/EP97/03650 |
Jul 10, 1997 |
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09842621 |
Apr 27, 2001 |
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Current U.S.
Class: |
134/6 |
Current CPC
Class: |
B01J 38/48 20130101;
Y02P 20/584 20151101; F22B 1/1846 20130101; B01J 38/485 20130101;
B01J 23/92 20130101; B01J 38/60 20130101; Y02P 20/52 20151101; B01D
53/88 20130101; C10J 3/86 20130101; B01D 53/8625 20130101 |
Class at
Publication: |
134/006 |
International
Class: |
B08B 7/00 20060101
B08B007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 1996 |
DE |
196 28 212.8 |
Claims
1. A method for scrubbing and/or regenerating of wholly or
partially deactivated catalytic devices for nitrogen removal from
stack gases, wherein the catalytic devices are treated with a
scrubbing, or respectively regenerating fluid, characterized in
that the scrubbing, or respectively regenerating fluid is partially
or wholly desalinated water.
2. The method in accordance with claim 1, characterized in that the
scrubbing, or respectively regenerating fluid is moved in
circulation, wherein a partial flow is removed downstream of the
catalytic device and replaced by fresh scrubbing, or respectively
regenerating fluid.
3. The method in accordance with one of the preceding claims,
characterized in that a scrubbing, or respectively regenerating
fluid with a pH value of .ltoreq.7 is used.
4. The method in accordance with one of the preceding claims,
characterized in that the surface of the catalytic device is
additionally treated with an abrasive.
5. The method in accordance with one of the preceding claims,
characterized in that at least one catalytically active component
is added to the scrubbing, or respectively regenerating fluid.
6. The method in accordance with one of the preceding claims,
characterized in that prior to treatment coarse dust deposits are
removed manually or by means of suitable cleaning devices, for
example steam blowers.
7. The method in accordance with one of the preceding claims,
characterized in that following treatment the catalytic devices are
cleaned by air or stack gas.
8. The method in accordance with claim 7, characterized in that
drying of the catalytic devices is performed immediately following
the treatment of a partial section.
9. The method in accordance with one of claims 7 or 8,
characterized in that the treatment and drying of the catalytic
devices is performed by means of a unit.
10. The method in accordance with one of the preceding claims,
characterized in that existing steam or air blowing devices used
for removing flying dust are employed for introducing the
scrubbing, or respectively regenerating fluid.
11. The method in accordance with one of the preceding claims,
characterized in that the catalytic devices are subjected to a bath
in the scrubbing, or respectively regenerating fluid.
12. The method in accordance with claim 11, characterized in that
the honeycombs of the catalytic device or respectively the nitrogen
removal reactor are closed at their bottom, and the catalytic
devices are filled with the scrubbing, or respectively regenerating
fluid.
13. The method in accordance with one of the preceding claims,
characterized in that tap water is used as the scrubbing, or
respectively regenerating fluid.
Description
[0001] The invention relates to a method for scrubbing and/or
regenerating of wholly or partially deactivated catalytic devices
for nitrogen removal from stack gases; wherein the catalytic
devices are treated with a scrubbing, or respectively regeneration
fluid.
[0002] Such catalytic devices are also called SCR (selective
catalytic reduction) catalytic devices. The deactivation of such
catalytic devices has several different causes, mainly: [0003]
Clogging of the honeycomb structure, or respectively the free
spaces in the catalytic device. Because of this, the stack gas does
not reach the catalytic device and the clogged conduit of the
catalytic device is not used for the catalytic reaction. In order
to use the installed catalytic material as efficiently as possible,
attempts are made to decrease the clogging of honeycomb channels or
plate channels by cleaning measures, such as steam blowers in the
DENOX installation or manual cleaning actions. In spite of this,
some of these honeycombs, or respectively free spaces in the
catalytic device, become clogged over time. With some installations
the catalyst modules are removed and placed on an appropriate
shaking device. The clogs are loosened by the shaking movements. In
this way the stack gas again gains access to the catalytic
material. The increase in activity does not constitute a
regeneration, it only provides access to the clogged catalytic
material. The surface layer being formed during operation remains
untouched by this cleaning step. [0004] Worsening of the gas
diffusion at the surface of the wall of the catalytic device
because of the growth of a thin surface layer of approximately 1 to
100 .mu.m and clogging of pores. Because of this, the stack gas can
only reach the pores of the catalytic material poorly or not at
all. The formation of a thin surface layer worsens the chemical
transformation of NO.sub.X and NH.sub.3 into. N.sub.2 and H.sub.2O,
because the gas diffusion into the catalytic material is greatly
hampered. [0005] Clogging of the active catalytic centers on the
surface of the catalytic devices by means of the accumulation of
the so-called catalytic poisons, for example As, K, Na. The
settling of catalytic poisons, such as arsenic, for example, on the
active centers of the catalytic device makes the reaction at these
centers impossible and in this way also aids in a reduction of the
activities of the catalytic material. [0006] Abrasion of catalytic
material by solids, such as fly ash, contained in the stack gas.
The catalytic material is reduced because of the loss of catalytic
material and therefore of the surface available for the reaction.
The abrasion of catalytic material is an irreversible process which
results in a permanent loss of activity. The following actions can
also simultaneously occur in the course of abrasion by fly ash:
[0007] Removal of catalytic material and of an existing surface
layer, [0008] Retention of components of the fly ash and therefore
formation of a fresh gas diffusion-hindering surface layer.
[0009] A method is described in DE 38 16 600 C2 in which the
regeneration of catalytic devices contaminated by arsenic is
described. This method does not take into consideration the portion
of the deactivation by a gas diffusion-hindering surface layer.
Aqueous solutions of nitric acid, hydrochloric acid, sulfuric acid
or acetic acid are employed as the scrubbing suspension in the
method according to DE 38 16 600 C2. These scrubbing suspensions
have the disadvantage that for one they are too expensive and also
that the disposal of the acids contaminated by arsenic is
elaborate.
[0010] A method is described in EP 0 136 966 B1, in which initially
the dust adhering to the surface is removed with dry steam. The
catalytic poisons are then intended to be dissolved and rinsed out
in a second step by wet steam with a moisture content of
.ltoreq.=0.4. Drying is performed with dry steam again. In the
method in accordance with EP 0 136 966 B1, the thin, gas
diffusion-hindering layer is not removed in a first step, instead
clogged conduits are merely opened again. This has already been
done on a large-scale basis for a long time in the form of
so-called dust or soot blowers. The second step of this method can
have an activity-increasing effect only with catalytic devices
wherein the gas diffusion-hindering layer does not exist over the
entire surface or not at all. Also, the generation of large amounts
of dry and wet steam is very energy-intensive.
[0011] A method for the reactivation of catalytic devices is
described in DE 30 20 698 C2, which removes the deactivating
substances by means of a defined pressure and a defined
temperature. Various gases, for example methane, propane, carbon
dioxide or argon can be added in the process for optimizing the
method. This method also does not consider the gas
diffusion-hindering surface layer.
[0012] A great disadvantage of most of the mentioned methods is the
fact that they can only be performed in a separate installation. To
this end the removal of the catalytic devices and therefore an
outage of the installation is required.
[0013] Accordingly, it is the object of the invention to further
develop a method of the type mentioned above in such a way that gas
diffusion on the surface of the catalytic devices is again made
possible, wherein additionally the clogging of the active centers
by catalytic poisons is reversed to the greatest extent possible,
and which can be performed inside the nitrogen removal installation
without the removal of the catalytic devices.
[0014] This object is attained in that the scrubbing, or
respectively regenerating fluid is fully desalinated water.
[0015] The function of the invention is based on the dissolution
and removal of the surface layer for restoring the gas diffusion
and exposing of active centers for the nitrogen-removing reaction
of the surface of the catalytic device. In this case the
composition of the fluid must be selected in such a way that, along
with a small consumption of regenerating suspension, the fastest
possible dissolution of the surface layer is achieved. In
connection with the regeneration of SCR catalytic devices it has
surprisingly been shown to be useful to employ fully desalinated
water, for example demineralized water, for dissolving the surface
layer. The use of demineralized water as the scrubbing fluid
prevents the introduction of catalytic poisons with the scrubbing
fluid. In comparison with other possible fluids, demineralized
water has the advantage that it is relatively inexpensive and that
in most cases it can be produced at the location of the power plant
itself. The cleaning and regeneration of the catalytic devices is
performed at ambient temperatures, so that no energy is required
for heating the fluid. By means of this method it is possible to
drastically reduce the number of deactivated catalytic devices to
be disposed. Above all, in large installations for the reduction of
nitric oxides; so-called DENOX installations, this method is
suitable for regenerating the used and deactivated catalytic
devices, i.e. to again increase the reduced catalytic activities,
without having to remove them.
[0016] An advantageous further development of this method provides,
that the catalytic devices are first mechanically cleaned by
vacuuming or blowing the deposits out, which is then followed by a
scrubbing cycle, which removes the surface layer by means of a
regenerating suspension and dissolves the clogs of the active
centers to a great extent. It has been shown to be advantageous for
the consumption of regenerating suspension if only a small portion
of the regenerating suspension is continuously removed and
regenerated, i.e. the larger part can be employed in a
recirculating operation.
[0017] An additional opportunity for reducing the scrubbing water
is the use of a suitable abrasive which only removes the surface
layer. This method can also be practiced inside the nitrogen
removal installation. The abrasive (for example small glass
spheres), together with the parts of the gas diffusion-hindering
surface layer, can then be disposed of together with the fly ash
from the electronic filter.
[0018] Further advantageous developments of the invention are
defined in the dependent claims.
[0019] An exemplary embodiment for the use of a suitable
regeneration device will be described in greater detail in what
follows, making reference to the attached drawings. Represented are
in:
[0020] FIG. 1, a schematic structure of a catalytic device strip
with surface layers,
[0021] FIG. 2, the enlargement of a portion of FIG. 1,
[0022] FIG. 3, a method flow graph for the cleaning of catalytic
devices inside a DENOX installation,
[0023] FIG. 4, a schematic view of the cleaning of the catalytic
device by means of an abrasive.
[0024] FIGS. 1 and 2 show an enlarged sectional view through a
catalytic device strip 60 of a catalytic device 6. A catalytic
device strip 60 of a honeycomb catalytic device with pores 61 is
represented. A surface layer 62 of a thickness of approximately 1
to 100 .mu.m grows with increasing length of operation which, with
increasing thickness, more and more hinders the diffusion of the
stack gas to be cleaned into the catalytic material, in particular
the pores 61.
[0025] An exemplary embodiment of the present invention becomes
clear by means of the flow graph of the method represented in FIG.
3.
[0026] A container 11 is filled with desalted water, for example
demineralized water, from the complete desalination installation of
a power plant, via a line 1. Additives can be supplied to the
scrubbing fluid via lines 2 and 3, for example hydrochloric acid
for lowering the pH value, or regenerating substances, such as
vanadium, molybdenum or tungsten, for example. The pump 4 conveys
the regenerating suspension through the line 5 into the DENOX
installation 17, where the catalytic devices 6 are scrubbed. The
scrubbing fluid with the materials contained in the surface layer
and the catalytic poisons are conducted via a suitable catching
device, for example a funnel, and a pump 7 to a separating device
8. There, the materials contained are separated in a suitable
manner from the scrubbing fluid. A hydrocyclone, for example, is
suitable for this. However, filters or the like are also
conceivable. The underflow from the separating device 8, which is
heavily loaded with solids, is conveyed via the pump 16 to a
settling tank 9. The solid components are further concentrated in
this settling tank 9, are drawn off in a partial flow via a line
10, and conveyed to a suitable waste water treatment, not
represented here. The overflow of the settling tank 9 and the upper
flow of the separating device 8 are conveyed to the container 11
via the lines 12 and 13 and pumps 14 and 15.
[0027] This structure can be expanded by suitable precipitation
stages, in which dissolved noxious matter, such as the catalytic
poison arsenic, for example, is precipitated, so that it can be
separated by means of the separating device 8 and removed from the
scrubbing fluid. The scrubbing, or respectively regenerating fluid
is conveyed in circulation in this way, from which only a defined
volume of fluid with the concentrated noxious matter, is removed
per circuit. This volume is replenished through the lines 1, 2 and
3.
[0028] A further possibility for execution is closing the
honeycombs of the catalytic device, or respectively of the reactor,
below the catalytic device 6. The catalytic devices are thereafter
filled with the scrubbing, or respectively regenerating fluid.
During this bath in the regenerating fluid, first the gas
diffusion-hindering surface layer is loosened. The catalytic
poisons inside the pores of the catalytic device are then loosened
from the active centers on the surface of the catalytic device and
are transferred into the regenerating fluid. Because of the
concentration drop between the regenerating fluid inside the pores
of the catalytic device and the regenerating fluid in the honeycomb
channels, the dissolved catalytic poisons move to the honeycomb
channels. After a defined period of time the regenerating fluid
with the components of the gas diffusion-hindering surface layer
and the catalytic poisons is drained. The catalytic devices are
thereafter dried by means of stack gas or hot air. The advantage of
this embodiment lies in the low consumption of regenerating
fluid.
[0029] Complementing the mentioned exemplary embodiments it is also
possible to connect the regeneration of catalytic devices directly
with drying. In large nitrogen-removing installations it can occur
that some tons of regenerating fluid still remain in the catalytic
devices 6. The structural steel for receiving the catalytic modules
must be designed for this additional weight. This is not the case
in some installations. It is then necessary to dry a partial
section immediately after the regeneration of this section. In the
course of this, the catalytic devices 6 are first regenerated as
described. Following regeneration, the regenerated section is dried
by means of hot air or hot gas. By means of this the regenerating
suspension remaining in the catalytic devices 6 is evaporated and
removed.
[0030] FIG. 4 shows in a schematic representation a complementing
option for removing the surface layer 62 from the catalytic devices
6. An abrasive 63, for example sand or glass, is used for
mechanically removing the surface layer 62. The abrasive 63 is
blasted through a tube 64 or the like on the surface 65 of the
catalytic device 6. The abrasive material 66, which has been
contaminated with portions of the surface layer, is blown out of
the catalytic device 6, or rinsed out during cleaning with the
scrubbing fluid, for example.
Example:
[0031] The invention was tested on used and deactivated catalytic
devices. To this end, a deactivated catalytic element of a total
length of 84.0 mm and edges of the length of 150.times.150 mm was
removed from a DENOX installation and treated in accordance with
the regenerating method. Prior to regeneration with demineralized
water, the catalytic element was examined in a test stand. The
catalytic element was thereafter rinsed for 5 minutes with
demineralized water and subsequently dried with hot air. A
subsequent examination showed that the NOX precipitation rate was
increased by approximately 5% to 6% over the entire mol ratio range
of NH.sub.2/NOX of 0.8 to 1.2, as shown in the following table.
TABLE-US-00001 Mol ratio NH.sub.2/NOX 0.8 0.9 1.0 1.1 1.2 NOX
precipitation rate 64.8 70.6 73.7 75.2 76.4 before regeneration NOX
precipitation rate 70.4 75.8 78.9 80.6 81.8 after regeneration
* * * * *