U.S. patent application number 14/235915 was filed with the patent office on 2014-06-19 for pollution control system for kiln exhaust.
The applicant listed for this patent is FLSMIDTH A/S. Invention is credited to Peter T. Paone, III, Jorn Moller Rasmussen, John S. Salmento, Iver Schmidt.
Application Number | 20140170046 14/235915 |
Document ID | / |
Family ID | 47629586 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140170046 |
Kind Code |
A1 |
Schmidt; Iver ; et
al. |
June 19, 2014 |
POLLUTION CONTROL SYSTEM FOR KILN EXHAUST
Abstract
Disclosed is a method and apparatus for the reduction of organic
compounds and other emissions from an industrial plant utilizing a
cement or minerals kiln that has a high level of organic compound
emissions. The invention consists of a filter for the control of
particulate emissions which has been treated with a catalyst to
provide catalytic destruction of gaseous emissions as process gases
are passed through the porous medium of the filter.
Inventors: |
Schmidt; Iver; (Skorping,
DK) ; Rasmussen; Jorn Moller; (Virum, DK) ;
Paone, III; Peter T.; (North Catasaqua, PA) ;
Salmento; John S.; (Nazareth, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FLSMIDTH A/S |
Valby |
|
DK |
|
|
Family ID: |
47629586 |
Appl. No.: |
14/235915 |
Filed: |
July 16, 2012 |
PCT Filed: |
July 16, 2012 |
PCT NO: |
PCT/US2012/046848 |
371 Date: |
January 29, 2014 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61574273 |
Jul 29, 2011 |
|
|
|
Current U.S.
Class: |
423/239.1 ;
423/240R; 423/242.1; 423/245.1; 423/247 |
Current CPC
Class: |
B01D 2251/404 20130101;
F23J 2217/104 20130101; B01D 2251/10 20130101; F27B 7/2033
20130101; F23J 15/025 20130101; B01D 53/46 20130101; B01D 2257/502
20130101; F23J 15/04 20130101; B01D 2259/12 20130101; B01D 2257/602
20130101; C04B 7/364 20130101; B01D 2258/0233 20130101; B01D
2257/708 20130101; F23J 2217/101 20130101; B01D 53/8631 20130101;
F23J 15/006 20130101; B01D 2253/102 20130101; B01D 53/8653
20130101; B01D 53/86 20130101; F23J 2219/10 20130101; B01D 2251/304
20130101; B01D 2257/404 20130101 |
Class at
Publication: |
423/239.1 ;
423/245.1; 423/247; 423/242.1; 423/240.R |
International
Class: |
F23J 15/02 20060101
F23J015/02; F23J 15/04 20060101 F23J015/04 |
Claims
1. A method for the reduction of contaminant emissions including
organic compounds present in vapor form from the process gases of
an industrial plant utilizing a kiln and/or calciner to heat treat
a raw material, said method comprising (i) directing plant process
gas containing entrained particulate matter and contaminant
emissions from the plant to a pollution control device comprising a
process gas inlet and process gas outlet and an interior portion
located intermediate the inlet and outlet, said interior portion
containing at least one filtering element for removing the
particulate matter from the gas, said at least one filtering
element containing at least one catalyst for removing some of the
contaminant emissions; (ii) directing the process gas through the
inlet and thereafter through the filtering element, wherein
entrained particulate matter is separated from the process gas and
the process gas comes in contact with the at least one catalyst to
thereby reduce the contaminant emissions contained in the gas ; and
(iii) directing cleaned process gas through the outlet of the
pollution control device.
2. The method of claim 1 further comprising: removing the separated
particulate matter from the pollution control device.
3. The method of claim 1 wherein the process gas is comprised of at
least one of kiln off gas, preheater off gas, precalciner off gas,
raw material milling system off gas, solid fuel milling system off
gas product cooler vent gases and kiln process product milling off
gases.
4. The method of claim 3 wherein the process gases comprise product
cooler vent gases.
5. The method of claim 1 wherein the process gases within the
pollution control device are maintained at a temperature between
80.degree. C. and 450.degree. C.
6. The method of claim 1 wherein the at least one catalyst is
selected from the group comprising vanadium, platinum, palladium,
ruthenium, titanium, lanthanum, cerium, yttrium, zirconium,
tungsten, manganese, niobium, molybdenum, nickel, iron and
copper.
7. The method of claim 1 wherein the filtering element is a
fiberglass bag.
8. The method of claim 1 wherein the filtering element is treated
with a membrane.
9. The method of claim 1 wherein the filtering element is a porous
ceramic structure.
10. The method of claim 1 wherein at least one reactive agent is
contacted with the at least one catalyst agents to increase the
reduction of hydrocarbons present in the filtering elements.
11. The method of claim 10 in which the at least one reactive agent
is selected from the group comprising ozone, peroxide, potassium
permanganate, calcium chloride, sodium hydroxide, sodium bromide,
bromine and chlorine.
12. The method of claim 2 wherein removal of the separated
particulate matter from the pollution control device is achieved by
pulsing gas through the filtering elements.
13. The method of claim 2 wherein removal of the separated
particulate matter from the surface of the filtering elements is
achieved through sonic or ultrasonic vibration.
14. The method of claim 2 wherein removal of the separated
particulate matter from the surface of the filtering elements is
achieved through mechanical removal of particulate matter with a
solid object.
15. The method of claim 2 further comprising: returning the removed
particulate matter to the industrial plant process.
16. The method of claim 1 in which the organic compounds comprise
Total Hydrocarbons.
17. The method of claim 1 wherein the organic compounds comprise at
least one of formaldehyde, acetaldehyde, xylene, benzene, styrene,
and naphthalene.
18. The method of claim 1 wherein the organic compound comprise
Volatile Organic Compounds.
19. The method of claim 1 in which mercury compounds within the
process gas are oxidized by the at least one catalyst.
20. The method of claim 1 wherein at one of nitrogen oxides,
dioxin/furan emissions and carbon monoxide are reduced by the at
least one catalyst.
21. The method of claim 1 further comprising injection of a sorbent
upstream of the pollution control device for the adsorption of at
least one of sulfur dioxide, sulfur trioxide, arsenic, thallium,
mercury, hydrogen chloride, hydrogen fluoride, or hydrogen
bromide.
22. The method of claim 21 wherein the sorbent includes at least
one of calcium oxide, calcium hydroxide, trona, sodium bicarbonate,
cement kiln dust, calcined material, and activated carbon.
23. The method of claim 19 wherein a nitrogenated agent is
introduced to increase the reduction of nitrogen oxides.
24. The method of claim 23 wherein the nitrogenated agent includes
at least one of ammonia, urea, ammonium bisulfate, or flyash.
25. The method of claim 1 further comprising injection of a sorbent
downstream of the pollution control device for the adsorption of at
least one of sulfur dioxide, sulfur trioxide, arsenic, thallium,
mercury, hydrogen chloride, hydrogen fluoride, or hydrogen
bromide.
26. The method of claim 25 wherein the sorbent includes at least
one of calcium oxide, calcium hydroxide, trona, sodium bicarbonate,
cement kiln dust, calcined material, and activated carbon.
Description
BACKGROUND OF THE INVENTION
[0001] There is an increasing level of awareness concerning the
emission of certain volatile organic compounds (VOCs), combustion
byproducts such as carbon monoxide and NO.sub.X, and dioxin/furans
from industrial plants such as cement manufacturing facilities.
With this heightened level of awareness, more stringent
environmental regulations are being adopted to ensure low emissions
from these industrial plants. In some cases, the level of emissions
currently experienced may not be adequately reduced using existing
technologies in order to meet new environmental regulations. In
other cases, existing technologies for emissions controls in other
applications are prohibitively costly in industrial applications.
Consequently, there is an interest in developing new systems for
controlling these high levels of emissions to meet newly proposed
regulations, and that is an object of the present invention.
[0002] Very few cement and lime kilns have installed specialized
controls for emissions of organic compounds. Cement kilns in the
United States have attempted the use of Regenerative Thermal
Oxidizers (RTOs), such as those devices described in U.S. Pat. No.
5,352,115 and U.S. Pat. No. 5,562,442. These devices subject the
process gases to intense oxidizing conditions produced by applying
a direct heat source and introducing air to the system in order to
incinerate the organic compounds in the gas stream. The exhaust
gases are heated to a temperature in excess of 800.degree. C., and
much of this heat is recovered through the system and used for
preheating the gas stream prior to the combustion region. The
devices require a clean fuel for heating, as soot and ash
introduced from the fuel can reduce the thermal efficiency of the
unit. These devices are of limited applicability in use with cement
and minerals processing systems for several reasons--they are small
in size relative to the process gas stream that must usually be
treated (requiring multiple, parallel units), the intense oxidizing
conditions produced in the unit can oxidize SO.sub.2 present in the
gas stream to SO.sub.3 (which necessitates the use of a wet
limestone scrubber or other SO.sub.2 control device prior to the
RTO), and the use of additional fuel firing for operation will
increase emissions of carbon monoxide and carbon dioxide. Combined,
these disadvantages make RTOs very difficult to install in
industrial plants such as cement kilns because of the large space
required for the RTO and supporting equipment, the high cost of
installation, and the high cost of operation.
[0003] An alternative approach that may be attempted is the use of
catalytic means of the destruction of organic compounds and carbon
monoxide. Catalyst applications in cement kiln systems have
generally been targeted towards the removal of nitrogen oxides
through "Selective Catalytic Reduction", but the art of using
catalysts in similar applications for the removal of organic
constituents may also be practiced, as in U.S. Pat. No. 6,156,277.
In this method, the exhaust gas from a cement kiln is directly
passed through a reduction catalyst for the destruction of the
emissions from the kiln system. The temperatures required for the
chemical reactions for the destruction of NOx and other emissions
products is generally between 250.degree. C. and 450.degree. C. in
practice, although wider temperature ranges are available with
specific designed catalysts. In a typical cement kiln process, the
exhaust gas from a preheater/precalciner system is typically in
such a range. While this temperature range is conducive to a high
activity for the catalyst, these systems often see issues
associated with the loading of particulate matter in the exhaust
gas stream. Typical dust loadings in these gas streams may be in
the range of 20 to 50 grams of particulate per cubic meter of
exhaust gas, although dust contents exceeding 150 grams of
particulate per cubic meter of exhaust gas can be seen. The
particulate matter is typically comprised of the fine dust fraction
of feed material introduced to the kiln system which is not
completely captured within the kiln or preheater system. This fine
dust is comprised of varying amounts of and compositions containing
calcium, aluminum, silica, and iron, as well as sodium, potassium,
chlorides, sulfur and minor constituents such as phosphorous,
arsenic, thallium, and zinc. Depending on the catalyst structure in
use, any of these compounds can cause degradation of the catalytic
effect of the system through de-activation of the surface,
poisoning of the catalyst, erosion of the catalytic surface, or the
blocking of the catalyst surface from contact with the gaseous
constituents. In addition, the dust content of the gas stream
requires larger openings in the catalytic structures in use in
these systems, requiring larger catalyst structures to obtain the
same catalytic surface as is found in other industrial
applications. In systems where SCR is practiced, soot blowers for
dedusting and periodic cleaning of the catalyst surface are
required. The loss in efficiency associated with dust loading
therefore leads to higher costs for these systems for design and
operation than in comparable industries with low dust loads.
[0004] As an improvement over these "high dust SCR" applications,
systems have been proposed which include a step for removal of the
dust present in these industrial applications prior to the catalyst
structure. These systems comprise an additional cleaning step
utilizing a dust filter or a precipitator prior to the catalytic
structure, such as is described in US Application 2010/0307388. In
this arrangement, the gases coming from a cement kiln system are
first passed through a dust precipitation system to remove
particulate matter. The gases are then passed through the reduction
catalyst for destruction of the targeted pollutants. After
treatment in the reduction catalyst, the hot gases may then be used
in other devices found in the industrial facility, such as grinding
mills, and vented through a stack. This "low dust SCR" arrangement
offers several advantages over the "high dust SCR" arrangement,
including a longer lifetime for catalyst structures before
replacement, the usage of smaller openings between catalyst plates
or honeycombs which allows for a smaller and less costly catalytic
structure, and lower operating costs associated with less
replacement of catalyst. This arrangement does come with several
disadvantages. The requirement for a dust collection device such as
a filter or precipitator is an added piece of process equipment
that comes with installation and long term operating and
maintenance expenses. The additional pressure drop through the
precipitator or filter, in addition to the catalyst structure, will
increase the power requirements on any fans utilized for drafting
gas through the overall system. In addition, the layout
requirements of the cement kiln or minerals processing facility
will often make it difficult or impossible to fit both the filter
or precipitator and a catalytic structure within the confines of
available areas for installation.
[0005] In view of the prior art issues, the objects of the present
invention include improving the control of various undesirable
emissions from cement and minerals, and obtaining a high efficiency
of catalytic activity such as is found in a "low dust SCR"
applications while having a high inlet dust loading similar to that
encountered in "high dust SCR" applications, while utilizing fewer
pieces of equipment and a lower pressure drop than a "low dust SCR"
system.
BRIEF DESCRIPTION OF THE INVENTION
[0006] The above and other objects are achieved by utilizing a
device fitted with a filter element or filter elements which are
pretreated with the catalyst or composed of the catalytic materials
dispersed through the filter elements.
[0007] According to the invention, there is a method for the
reduction of organic compounds and other emissions from an
industrial plant having a cement or mineral kiln or calciner system
that has a high level of emissions. The invention treats the
exhaust gas stream from the cement or minerals processing plant on
a filter medium in order to remove entrained particulate, and
destroys the targeted pollutant within the structure of the filter
medium. Particulate captured on the surface of the filter medium is
periodically removed from the surface of the medium to prevent
blockage of the porous filter medium and to avoid undesireable
increases in energy consumption at the processing plant. Such
removal can be achieved by a number of methods, including
subjecting the filter medium to sonic or ultrasonic vibration or
the mechanical removal of particulate matter with a solid object.
Pre-treatment of the exhaust gas stream can be used to enhance the
pollutant destruction capabilities of the filtration device, or to
prevent oxidation of entrained pollutants to less desirable
compounds. This invention is not limited to cement or lime plants.
It can be used in any industrial processing plant where the
emission of organic compounds, total organic carbons or volatile
organic carbons, carbon monoxide, nitrogen oxides, or dioxin/furans
require a very high degree of treatment for attainment of
regulatory requirements, such as, for example, in plants that use
long dry cement kilns, short cement kilns with precalciners, and
lime kilns.
DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagram of a plant for the production of cement
clinker adapted to the cleaning of hydrocarbons and other
contaminants according to the invention.
[0009] FIG. 2A is a diagram of one embodiment of the invention in a
cement or minerals kiln system.
[0010] FIG. 2B is a more detailed view of a filter element utilized
in the invention.
[0011] FIG. 3 is a diagram of another embodiment of the invention
utilizing a different method for holding and supporting the
catalytic filter elements.
[0012] FIG. 4A is a diagram of another embodiment of the invention
utilizing another method for holding and supporting the catalytic
filter elements and for removal of the collected particulate
matter.
[0013] FIG. 4B is an isometric view of the embodiment of the
invention depicted in FIG. 4A.
[0014] FIG. 5 is another general diagram of a plant for the
production of cement clinker adapted to the cleaning of
hydrocarbons and other contaminants according to the invention.
[0015] FIG. 6 is an example of organic compound reduction curves
comparing removal efficiencies of the invention at varying
temperatures and for various organic compounds.
DESCRIPTION OF THE INVENTION
[0016] Although the invention is particularly directed to the
reduction in emissions of organic compound emissions, the present
invention also applies to the removal of other products of
incomplete or partial combustion such as carbon monoxide,
condensable VOC's, nitrogen oxides, and dioxin/furans that
contaminate manufacturing processes. Many of the organic compounds
that this invention is directed towards fall under numerous
overlapping categories of compounds, such as Total Organic Carbon
(TOC), Total Hydrocarbons (THC), and Volatile Organic Compounds
(VOC), and this invention is broadly aimed to the various compounds
which are classified under these general categories. Also, while
emphasis is placed on a cement manufacturing process, the present
invention is applicable to other minerals and kiln manufacturing
processes, such as lime manufacturing processes and other
industrial processes where very high starting emission levels of
these contaminate compounds can not be sufficiently controlled
using existing methods, or where existing methods of control are
cost prohibitive.
[0017] Emissions of organic compounds from industrial process may
originate from a variety of different sources within a system. In
minerals processing systems such as cement kilns, these sources may
include incomplete combustion of fuels fired within the system,
decomposition or partial combustion of organic species within feed
components, contamination of gas streams with organic materials
such as from oiled-compressors, introduction of organic components
in process water used for cooling, and from introduction of ambient
air which may contain organic components in small quantities. Also,
the oxygen concentrations at the exhaust of many industrial
processes such as cement kilns are kept low in order to improve
efficiencies within the systems, but such low oxygen concentrations
inhibit full combustion of these various organic compounds prior to
release from the system. These minor components may contribute to
localized conditions such as smog, and are therefore seeing
increased levels of regulation.
[0018] The invention in part comprises the use, in conjunction with
a kiln exhaust, of a device fitted with a filter element or filter
elements which are pretreated with the catalyst or composed of the
catalytic materials dispersed through the filter elements. The
catalyst utilized in the pretreatment or the construction of the
filter element is chosen prior to installation of the filter
elements within the device in order to treat those gaseous
emissions within the exhaust stream from the industrial process
which must be controlled in order to achieve regulatory compliance.
While the catalysts are designed for the control of organic
compound emissions such as Volatile Organic Compounds (VOC), Total
Hydrocarbons (THC), Total Organic Carbon (TOC), and similar
classifications of emissions, the catalyst for the pretreatment of
the filter elements or the dispersal through the filter elements
may also be chosen for the reaction or destruction of other
compounds including dioxins, furans, carbon monoxide, or oxides of
nitrogen (NO.sub.X), or can be used for the oxidation of mercury
for further treatment and capture after the device. The catalytic
elements used in the treatment or manufacture of the filter
elements can contain a mixture of any of vanadium, platinum,
palladium, ruthenium, titanium, lanthanum, cerium, yttrium,
zirconium, tungsten, manganese, niobium, molybdenum, nickel, iron
and copper in compositions designed to remove those emissions which
must be reduced in the gas stream.
[0019] The filter elements are porous membranes which allow for the
passing of exhaust gases through the elements, but of sufficiently
small pore size to capture a significant quantity of the dust on
the surface of the elements which is exposed to the process exhaust
gas containing entrained dust. The surface of the filter element
exposed to the process exhaust gas containing entrained dust is
referred to as the "dirty side" of the filter element, while the
surface of the filter opposite the "dirty side" and through which
the dedusted process gases pass to the outlet of the filter is
referred to as the "clean side" of the filter elements. The filter
element is comprised of the porous substrate as well as the
catalytic component of the filter element during the manufacturing
process. The filter elements are treated with the catalysts either
in whole or in part, with catalysts deposited on both the "clean
side" surface and the "dirty side" of the filter element
penetrating through a depth to the inside of the filter element,
with the maximum penetration of the catalysts being through the
entire thickness of the filter element, i.e. from the "clean side"
to the "dirty side" of the filter element. In all cases, it is
preferred not to have the catalysts applied only to the "dirty
side" of the filter element, as this exposes the catalyst to the
dust particles which may erode or "poison" the catalyst and reduce
its lifetime. The non-catalytic portion of the filter element,
which serves as a substrate to the catalyst and as the porous
filter for entrained dust in the gas stream, is composed of a
material which is designed to retain sufficient filtering
properties through the design range at which the filter elements
will be exposed for filtration of dust and for catalytic reduction
of gaseous pollutants. The non-catalytic composition of the filter
element may be comprised of any of porous ceramic, glass fibers,
ground quartz, alumino-silicate ceramic fiber, rutile, calcite,
corundum, kaolinite, and diatomaceous earth, among others.
[0020] The surface of the filter elements which is exposed to the
process exhaust gas entering the device is periodically cleaned to
prevent excessive accumulations of dust, which would otherwise
increase the pressure drop of the device, and thus increase the
power consumption of the system in operation. Cleaning of the
device may be performed through mechanical cleaning, such as
scraping or "rapping" of the filter elements, but is preferentially
performed through periodic "pulsing" of gas counter to the flow of
the industrial process exhaust gas entering the filter element.
Dust which is released from the filter element may be returned to
the cement or mineral processing facility, or may be withdrawn and
stored for use elsewhere.
[0021] The filter element is placed such that the exhaust gases
from the cement or minerals industrial process, which contain
entrained particulate matter, are passed through its porous filter.
The majority of the entrained particulate matter is captured on the
surface of the filter element and will not come into contact with
the interior of the filter element. Gases passing through the pores
of the filter element come in direct contact with the catalytic
compounds with which the element has been treated, ensuring contact
time between the gas and the catalyst. This reduces the required
residence time with the catalyst and allows for the possibility of
a smaller installation. By using the filter elements as the
catalyst substrate, the steps of separation (of the dust from the
gases) and catalytic contact may occur within the same device, also
reducing the size and cost of an installation.
[0022] By suitable pretreatment or post treatment of the gases
around the filter device, additional pollutant controls may be
achieved. In one variant of the invention, a sorbent for sulfur
emissions may be injected before the device to capture sulfur
dioxide emissions prior to the filter elements and the catalyst. In
this manner, the sulfur dioxide may be captured prior to the gases
contacting the catalyst, preventing the potential formation of
sulfur trioxide within the filter elements through catalytic
oxidation.
[0023] In one variation of the invention, a sorbent for capture of
mercury emissions is injected after the filter device in order to
capture mercury emissions which have been oxidized in contact with
the catalyst.
[0024] In one variation of the invention, a nitrogenated agent such
as ammonia, urea, ammonium bisulfate, or flyash may be injected
prior to the filter device in order to reduce NO.sub.X emissions.
For example, injection of ammonia may be placed immediately prior
to the inlet of the filter device, or may be injected in excess
within the industrial process producing the exhaust gas with the
resulting ammonia slip further reacting within the filter
device.
[0025] Placement of the catalytic filter device into the industrial
process is dependent upon the pollutants in the exhaust gas stream
that are to be destroyed. The activity of the catalyst and the
selectivity of the catalyst for destruction of gaseous emissions
are dependent upon the temperature of the gas stream. Organic
compounds such as methanol can be destroyed in large percentages
even at temperatures as low as 120.degree. C., while organic
compounds such as propane may require temperatures as high as
300.degree. C. It is preferential for the destruction or reaction
of shorter-chain (less than 7 carbon atoms) hydrocarbons, of
single-bonded (i.e. saturated) hydrocarbons, and NO.sub.X emissions
to place the device as close to the exhaust of the cement or
minerals processing system as is possible in order to obtain a gas
temperature in the range of 250 to 400.degree. C., and more
preferentially 300 to 350.degree. C. If the destruction or reaction
of longer-chain hydrocarbons (7 or more carbon atoms), double- or
triple-bonded (i.e. unsaturated) hydrocarbons, and/or cyclic or
aromatic hydrocarbon compounds are desired, without need for higher
temperatures for the treatment of other emissions through catalytic
means, then the device may preferentially be used in the
temperature range of 80.degree. C. to 250.degree. C., and more
preferentially between 150.degree. C. and 200.degree. C.
[0026] The catalytic activity of the filter elements may also be
enhanced through the treatment of the gas stream with other means.
These means would include the use of ozone, peroxide, potassium
permanganate, calcium chloride, sodium hydroxide, or other
oxidizing species injected upstream of the filter element or within
the filter device.
[0027] The invention is explained in greater detail below with the
aid of drawings.
[0028] In the system of the present invention illustrated in FIG.
1, material is treated in a kiln 1, which heats the material to
undergo chemical changes. In cement kiln systems, the feed entering
kiln 1 through conduit 2 may first be preheated in a preheater
system 50 comprising a number of counter current heat exchangers 51
in the form of cyclones. The material may also pass through a
calciner or pre-calciner 52 for removal of carbon dioxide prior to
entering kiln 1. Product from kiln 1 is discharged into a material
cooler 3 which serves the purpose of cooling the kiln product
before discharge 4, and of recuperating heat from the product to be
returned to the kiln 1 or to the calciner 52. Cooling air is passed
over the material and is heated before passing through the kiln
hood 5 to enter kiln 1 or to enter the calciner 52 through conduit
6. The air flowing to kiln 1 and calciner 52 is utilized in
combustion process. Excess air that enters cooler 3 for product
cooling is directed to an exhaust vent 7. In typical arrangements,
the air exiting cooler 3 through exhaust vent 7 are cooled in a
heat exchanger 8, and entrained particulate matter is removed in a
dust collector 9 and removed as a product stream 10. The cooler
excess air may then be vented to atmosphere at 11, or used in other
means within the process. Gases exiting from kiln 1 are directed
through calciner 52 and into preheater system 50. Feed material 20
to the system is directed to the preheater system 50 for thermal
treatment, and may be split between various counter current heat
exchangers 51 for the control of temperature from the exhaust gas
21 or for the high temperature treatment of the feed material. In
the typical configuration, the feed material is directed to the
uppermost cyclone heat exchanger as depicted. Emissions of organic
compounds, mercury, and carbon monoxide from the thermal treatment
of feed material 20 within preheater system 50, and emissions of
organic compounds, carbon monoxide, and other products of
incomplete combustion from the calciner 52 or kiln 1, will leave
the system in the exhaust gas stream 21. Nitrogen oxides created
and mercury released from combustion processes in calciner 52 and
kiln 1 will also leave the system in the exhaust gas stream 21. The
exhaust gas from the kiln system is then directed through the
catalytic filter system 100 for the destruction or reaction of
gaseous emissions in exhaust gas stream 21. After passing through
the catalytic filter system 100, treated exhaust gas stream 22 may
be directed to a gas conditioning tower 23 which utilizes cooling
water 24 for the cooling of the gas stream for further processing.
Conditioned gas 25 from the gas conditioning tower 23 may be
directed to a raw mill system 60 or multiple mill systems, or to a
main dust collector 70 for final particulate control. Raw feed
materials 61 are introduced to the raw mill system 60 which grinds
the feed materials to a size suitable for the production of cement
clinker. The product material from the mill exits the mill 60 with
an exhaust gas stream 65 and is separated in a collection device
such as a cyclone 62 or cyclones. The material 63 captured in the
cyclone 62 is transported to a blending and/or storage silo 90 for
use in the kiln system. The gases 64 from cyclone 62 are then
directed to a main dust collector 70 for collection of fine
particulate matter not captured in the cyclone. The gases from the
main dust collector may then be vented from the system 80. Material
71 captured in the main dust collector is then transported to the
blending and/or storage silo 90, or to some other storage area for
further treatment or disposal. Material blended and/or stored in
silo 90 is used as kiln feed 20 for the kiln system. If the kiln
system utilizes a solid fuel for heating of material, hot gases may
be removed from the system 31 for use in a milling system for the
solid fuel or for other heating processes within the plant
facility. The hot gases may alternatively be removed from the
system after the catalytic filter system and before the gas
conditioning tower, or after the gas conditioning tower and before
the main dust collector. Exhaust gases from the solid fuel grinding
system may be returned to the system in a gas stream 41 prior to
the catalytic filter system, may be directly vented to atmosphere,
or may be combined with the exhaust gases 80 from the main dust
collector 70 before being vented to the atmosphere.
[0029] The catalytic filter system 100 is depicted as being
positioned between the preheater/precalciner system and the gas
conditioning tower, but depending on the configuration of the kiln
system and the requirements for gas flows for processing within the
system, the catalytic filter system may alternatively be placed at
a number of other locations within the system. For example, the
catalytic filter system may be placed at location A (between the
exit of the preheater system 50 and the hot gas stream 31 removed
from the preheater exhaust gas stream 21), at location B (between
the hot gas stream 31 removed from preheater exhaust gas stream and
the returned gas stream 41 from the solid fuel grinding system), or
at location C (after the exhaust of the gas conditioning tower
23).
[0030] It may be preferred to utilize sorbents in the process prior
to the position of the catalytic filter system in order to capture
items that otherwise may oxidize to less preferable components in
the catalytic filter systems. Sorbents such as calcium oxide,
calcium hydroxide or hydrated lime, trona, activated carbon, or
proprietary sorbents such as Minsorb.TM. or Sorbacal.TM., may be
utilized in this capacity in one or all of locations S1, S2, and
S3. The injection of additional reactive agents such as ozone,
peroxide, potassium permanganate, calcium chloride, sodium
hydroxide, or other oxidizing species, or ammonia, urea, or other
nitrogenous compounds for conversion of emission components to
those more readily destroyed within the catalytic filter system or
to directly improve the destruction of compounds in the catalytic
filter system may be utilized in one or all of locations S1, S2,
S3, S4 and S5.
[0031] FIG. 2A shows one embodiment of the present invention, with
emphasis on area 100 of FIG. 1. Process gases 101 from the exit of
the kiln installation, such as the exit of a cement kiln,
preheater, or precalciner system or a lime kiln or preheater system
are directed via a conduit 102 to the catalytic filter unit 103.
Filter unit 103 comprises housing XXX, which encloses an interior
portion of the unit which is partitioned by a sheet 105 through
which filter elements 104 are inserted. The filter elements are a
porous material, such as a fiberglass bag or a porous ceramic
structure, which will allow the process gases to pass through, but
which will trap a large portion of particulate matter on the
surface of the filter element. It is preferred that the porous
filter will reduce the dust load of the gas passing through the
filter element to 5 grams per cubic meter of process gas or less,
preferentially less than 30 milligrams per cubic meter of process
gas, and most preferentially less than 5 milligrams of particulate
per cubic meter of process gas. Particulate matter collected on the
surface of the filter elements is removed from the surface of the
filter and collected in the bottom of the device at 106 and removed
through a withdrawal system 107. Cleaning of the material on the
surface may be conducted on a routine basis at set time intervals,
or may be controlled by monitoring the accumulation of material on
the filter element surface by means of a pressure monitoring device
108 to monitor the difference in pressures attained across the
partition between the clean and dirty sides of the filter. Gases
passing through the filter elements come into contact with the
catalytic material with which the filter elements have been treated
or produced. Contaminants such as organic compounds react upon the
catalytic elements of the filter elements and are destroyed. The
reaction activity of the catalyst to increase the reduction of
hydrocarbons present in the filtering element may be improved by
contacting the catalytic agents with a reactive agent, such as by
injecting one or more reactive agents at a point located prior to
the catalytic filter as described previously. The temperature of
the gas stream is monitored at position 109 to ensure that the
interior of the filter device is maintained at a temperature that
facilitates sufficient activity of the catalyst, and if the
temperature within the filter device is not suitable for the
destruction of the targeted pollutant(s), process changes can be
made prior to the catalytic filter to ensure sufficient temperature
for efficient destruction of the entrained pollutants. The
temperature within the filter device can also be controlled through
the introduction of a gas stream 120 prior to the catalytic filter
system. Examples of gas streams for temperature control include
ambient air introduced by a fan or damper to reduce inlet
temperature, hot gas streams from heat sources such as stand-by
heaters, or waste heat from other areas of the cement or minerals
processing kiln system such as from a cooler vent exhaust stream.
While depicted as being located on the clean side of the filter
elements at 109, the temperature monitor can be placed on the dirty
side of the filter, or in the duct work prior to or after the
catalytic filter.
[0032] The cleaned gases 110 exit the catalytic filter via a duct
111, and can be used elsewhere in the process or vented to
atmosphere.
[0033] FIG. 2B shows a more detailed view of a filter element 104.
The gas stream with entrained particulate matter 152 impacts on the
surface of the filter element adjacent to the filter elements 156.
The gas stream follows the direction of flow as shown by dotted
line 151 and is forced through the porous portion 150 of the filter
element to come into contact with catalytic agents container
therein. The clean gas stream from which particulate matter has
been removed passes to the "clean side" 155 of the filter. The
particulate matter 154 entrained in the gas stream is collected on
the surface of the dirty side of filter elements 104 and is removed
periodically.
[0034] While the filter elements are depicted in FIG. 2A as being
supported by the partition within the catalytic filter, and the
inlet gas enters below the partition and exits above the partition,
multiple arrangements of partition, filter elements, and gas inlets
and outlets may be utilized depending on the possible layouts
within the system and the materials of construction used for the
catalytic filter and the filter elements. By example, a porous
ceramic filter element may be limited in length by the strength of
the filter element at the support point, which may necessitate a
large number of filter elements to achieve sufficient particulate
matter control or catalytic activity. In this example, it may be
necessary to utilize a filter element which is supported from
beneath by the partition to allow for a greater strength in
compression than is available in tension.
[0035] FIG. 3 depicts another embodiment of the system and method
of the present invention in the context of a cement or minerals
processing kiln installation. Process gases 201 from the exit of
the kiln installation, such as the exit of a cement kiln,
preheater, or precalciner system or a lime kiln or preheater system
are directed via a conduit 202 to the catalytic filter unit 203.
The filter unit is partitioned by sheet 215 and sheet 216 through
which filter elements 204 are inserted. The support provided to
filter element 204 by sheet 215 is in tension, while the support
provided to filter element 204 by sheet 216 is in compression.
With, for example, a ceramic filter, as element 204 gets longer its
weight becomes a concern at the support point. If such an element
is supported only from above a large shear stress can be created on
the element and it can crack at the support. It it's also supported
from below, the stress is in compression, which is easier for the
ceramic to accommodate without cracking. By distributing the
support for the element in this manner, a longer filter element may
be used in the filter device. By using a longer filter element,
fewer elements may be used in the filter device. The longer
elements will increase the height of the filter device, but this
can save on the length and width of the filter device, which may be
of critical importance when installing the filter device in areas
with other existing equipment.
[0036] Particulate matter collected on the surface of the filter
elements is removed from the surface of the filter and collected in
the device 206 and removed through a withdrawal system 207.
Pressure monitoring device 208 is used to monitor the difference in
pressures attained across the partition between the clean and dirty
sides of the filter. The temperature of the gas stream is monitored
at 209 The cleaned gases 210 exit the catalytic filter via a duct
211.
[0037] FIG. 4A depicts another embodiment of the system and method
of the present invention. Process gases 301 from the exit of the
kiln installation are directed via a conduit 302 to the catalytic
filter unit 303. The filter unit features a number of filter
elements 304 supported on a series of chambers or plenums 317
through which air passes from the interior of the filter elements
to the exterior of the filter device via exit 311. Each plenum 317
supports a plurality of filter elements, an arrangement shown more
clearly in FIG. 4B, and plenums 317 are closed from the inlet
stream with a partition 316. The filter elements are supported from
lateral movement with a support structure 315. The support provided
to the element by partition 316 is in compression. Particulate
matter collected on the surface of the filter elements is removed
from the surface of the filter, falls between the clean air plenums
at 319, and is collected in the device 306 and removed at 307. The
arrangement allows for a flow of gas to exit at 311 from the bottom
of the filter, that is, below the elements. This allows for the
installation of this filter in line with the existing gas flow from
the exhaust duct of some types of kiln systems using cyclone
preheaters, and is an advantage in retrofit applications. By
employing the arrangement of FIGS. 4A and 4B, the ID fan can be
closer to the tower, and the support of the elements is such that a
longer element could be used. Overall, this would allow for the
tallest and skinniest installation, allowing for the easiest
retrofit in many installations. Pressure monitoring device 308
monitors the difference in pressures attained across the partition
between the clean and dirty sides of the filter. The temperature of
the gas stream is monitored at 309 The cleaned gases 311 in the
chambers or plenums are removed from the catalytic filter via a
duct 310.
[0038] FIG. 4B depicts an isometric view of the embodiment depicted
in FIG. 4A, with similar numbers depicting similar elements.
Process gases 301 from the exit of the kiln installation, such as
the exit of a cement kiln, preheater, or precalciner system or a
lime kiln or preheater system are directed via a conduit 302 to the
catalytic filter unit 303. The filter unit features a number of
filter elements 304 supported on a series of chambers or plenums
closed from the inlet stream with a partition 316. The filter
elements are supported from lateral movement with a support
structure 315. Particulate matter collected on the surface of the
filter elements is removed at 307. The cleaned gases 311 in the
chambers or plenums are removed from the catalytic filter via a
duct 310.
[0039] FIG. 5 shows a similar system as depicted in FIG. 1, but
utilizes the catalytic filter system 100 in place of the main dust
collector 80 shown in FIG. 1. In FIG. 5, similar numbers to those
of FIG. 1 depict similar elements. This arrangement offers the
advantage that the use of pollution control equipment is minimized,
as the catalytic filter system is used as the main dust collector,
which in turn reduces the installation and operational costs as
well as power consumption. The use of this arrangement is more
difficult to implement in that the operating temperatures of the
incoming gas stream are typically lower than the operating
temperatures found nearer to the exit of the kiln or preheater
system. This arrangement is preferred when the primary emissions
that the catalytic filter system is intended to destroy can be
effectively reduced in the temperature range found in this
location. As an alternative, a hot gas source 95, such as a portion
or all of the gas stream leaving the cooler vent and removed from
gas stream 7, between heat exchanger 8 and dust collector 9, or
from the stack gas 11, may be used to return the gas temperature to
a higher range which will improve the activity of the catalytic
filter system. The use of waste heat from the cooler vent system is
preferred in that dust collector 9 may also be eliminated in whole
or reduced in size if sufficient gas flow is continuously removed
from this location, further reducing installation and operational
costs as well as system power consumption.
[0040] FIG. 6 shows an example set of organic compound reduction
curves comparing the removal efficiency of a catalytic filter
system operated at varying temperatures for different examples of
organic compounds for a catalytic filter system of the invention.
The catalyst in use exhibits greater than 90% destruction of
methanol at temperatures ranging between 100 and 225.degree. C.,
increasing rates of toluene removal from less than 30% at
approximately 120.degree. C. to greater than 90% destruction above
approximately 200.degree. C., increasing rates of heptanes
destruction ranging from less than 50% at approximately 160.degree.
C. to greater than 90% above approximately 240 .degree. C., and
increasing propane removal from 20% at 300.degree. C. to greater
than 60% at approximately 370.degree. C. In laboratory testing,
generation of these hydrocarbon reduction curves is achieved
through the passage of a carrier gas of similar composition to the
gas stream exiting a cement or minerals processing system
containing carbon dioxide, water vapor, nitrogen, and oxygen, as
well as typical particulate matter in set concentrations, and
introducing known quantities of hydrocarbons into the gas stream.
Measurements taken before and after the catalytic filter system are
used to determine the percentage of incoming organic compound that
is destroyed within the catalytic filter system. Varying the
temperature of the gas stream in the catalytic filter system
provides data for the generation of the reduction curve with regard
to temperature. Organic compound reduction curves such as that
depicted in FIG. 6 will vary with the selection of the catalytic
elements used in the production of the filter elements utilized in
the catalytic filter system, as well as any reactive agents
utilized in conjunction with the catalytic filter elements.
Knowledge of the constituent organic compounds in the cement or
minerals kiln or calciner exhaust gas, through direct measurement
or previously established predictive means, in comparison to
organic compound reduction curve with regard to operating
temperature, can be utilized to select the location and specific
design configuration of the catalytic filter system as depicted in
FIGS. 1 through 5, or in similar variations. As an example, the
control of a process gas stream containing high levels of methanol
and toluene may more efficiently utilize the catalytic filter
system as depicted in FIG. 5 and FIG. 6, while the control of a
process gas stream containing high levels of propane may more
efficiently utilize the catalytic filter system as depicted in FIG.
1 and FIG. 6.
[0041] Using this invention, the exhaust gases from an industrial
plant such as a cement or mineral kiln can be treated to reduce or
destroy organic compounds and other pollutants from the exhaust
until the total content of organic compounds and other pollutants
in the gas stream is below levels that may be considered safe for
release to the atmosphere. Treatment of the gas stream may also
allow for removal of other pollutants, or additional treatment
downstream.
[0042] The invention having been thus described it will be obvious
that the same may be varied in many ways without departing from the
spirit and scope thereof. All such modifications are intended to be
included within the scope of the invention which is defined by the
following claims.
* * * * *