US20080081010A1 - Modular system and method for the catalytic treatment of a gas stream - Google Patents
Modular system and method for the catalytic treatment of a gas stream Download PDFInfo
- Publication number
- US20080081010A1 US20080081010A1 US11/981,391 US98139107A US2008081010A1 US 20080081010 A1 US20080081010 A1 US 20080081010A1 US 98139107 A US98139107 A US 98139107A US 2008081010 A1 US2008081010 A1 US 2008081010A1
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- US
- United States
- Prior art keywords
- gas
- gas stream
- catalyst
- axial fan
- impeller
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
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- 239000003638 chemical reducing agent Substances 0.000 claims description 13
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- 229910001930 tungsten oxide Inorganic materials 0.000 claims 2
- 229910001935 vanadium oxide Inorganic materials 0.000 claims 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 26
- 229910021529 ammonia Inorganic materials 0.000 description 12
- 238000006722 reduction reaction Methods 0.000 description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
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- 238000004227 thermal cracking Methods 0.000 description 5
- 238000006243 chemical reaction Methods 0.000 description 4
- 238000002485 combustion reaction Methods 0.000 description 4
- 229910052815 sulfur oxide Inorganic materials 0.000 description 4
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 3
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- XTQHKBHJIVJGKJ-UHFFFAOYSA-N sulfur monoxide Chemical class S=O XTQHKBHJIVJGKJ-UHFFFAOYSA-N 0.000 description 2
- 239000004408 titanium dioxide Substances 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- OTMSDBZUPAUEDD-UHFFFAOYSA-N Ethane Chemical compound CC OTMSDBZUPAUEDD-UHFFFAOYSA-N 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- GQPLMRYTRLFLPF-UHFFFAOYSA-N Nitrous Oxide Chemical compound [O-][N+]#N GQPLMRYTRLFLPF-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 150000001336 alkenes Chemical class 0.000 description 1
- 150000003973 alkyl amines Chemical class 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 238000010531 catalytic reduction reaction Methods 0.000 description 1
- SQWDWSANCUIJGW-UHFFFAOYSA-N cobalt silver Chemical compound [Co].[Ag] SQWDWSANCUIJGW-UHFFFAOYSA-N 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
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- 229910052802 copper Inorganic materials 0.000 description 1
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- 238000013461 design Methods 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- TXKMVPPZCYKFAC-UHFFFAOYSA-N disulfur monoxide Inorganic materials O=S=S TXKMVPPZCYKFAC-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
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- 239000000446 fuel Substances 0.000 description 1
- 239000007792 gaseous phase Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 1
- 231100000719 pollutant Toxicity 0.000 description 1
- 239000001294 propane Substances 0.000 description 1
- 238000009877 rendering Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 229930195734 saturated hydrocarbon Natural products 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910052719 titanium Inorganic materials 0.000 description 1
- WFKWXMTUELFFGS-UHFFFAOYSA-N tungsten Chemical compound [W] WFKWXMTUELFFGS-UHFFFAOYSA-N 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 239000010937 tungsten Substances 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- GPPXJZIENCGNKB-UHFFFAOYSA-N vanadium Chemical compound [V]#[V] GPPXJZIENCGNKB-UHFFFAOYSA-N 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8621—Removing nitrogen compounds
- B01D53/8625—Nitrogen oxides
- B01D53/8631—Processes characterised by a specific device
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/88—Handling or mounting catalysts
- B01D53/885—Devices in general for catalytic purification of waste gases
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9431—Processes characterised by a specific device
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/011—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more purifying devices arranged in parallel
- F01N13/017—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more purifying devices arranged in parallel the purifying devices are arranged in a single housing
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
- F01N3/28—Construction of catalytic reactors
- F01N3/2892—Exhaust flow directors or the like, e.g. upstream of catalytic device
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/30—Sulfur compounds
- B01D2257/302—Sulfur oxides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2257/00—Components to be removed
- B01D2257/40—Nitrogen compounds
- B01D2257/404—Nitrogen oxides other than dinitrogen oxide
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2290/00—Movable parts or members in exhaust systems for other than for control purposes
- F01N2290/02—Movable parts or members in exhaust systems for other than for control purposes with continuous rotary movement
- F01N2290/06—Movable parts or members in exhaust systems for other than for control purposes with continuous rotary movement driven by auxiliary drive
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2330/00—Structure of catalyst support or particle filter
- F01N2330/06—Ceramic, e.g. monoliths
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2330/00—Structure of catalyst support or particle filter
- F01N2330/30—Honeycomb supports characterised by their structural details
- F01N2330/34—Honeycomb supports characterised by their structural details with flow channels of polygonal cross section
Definitions
- FIG. 5 illustrates a honeycomb catalyst structure useful in the gas phase reactor of the present invention.
- the present invention advantageously provides a great deal of flexibility in choosing suitable methods for controlling the system 10 .
- one method of controlling flue gas velocity and throughput is in-flight variable pitch control of the angle of the blade units 135 while the fan is operating.
- Systems for in-flight variable pitch control are known. See e.g., U.S. Pat. Nos. 4,090,812, 4,778,344 and 4,844,697, all of which are incorporated by reference.
- a second option for in-flight control is to vary the speed of impeller rotation, faster speed producing high gas velocity and throughput.
- Another alternative is to use individually adjustable blade units which can be manually adjusted when the fan is stopped to provide a desirable blade pitch.
- Yet another means of controlling gas flow through the catalyst beds is by means of spill back control, i.e., control of the recycle flow of flue gas. Spill back control is discussed in more detail below with reference to the recycle manifold 330 .
- the treated and cooled flue gas thereafter enters a duct 60 with a side surface 61 which is tapered so as to maintain a constant static pressure at the outlet of the heat recovery section 500 .
- the flue gas is thereafter diverted to upward flow through stack 70 into the atmosphere.
Abstract
A system for catalytically treating a gas stream includes a gas phase reactor containing a catalyst for the treatment of the gas stream in at least one catalyst bed having an upstream end and a downstream end, an axial fan positioned upstream of the at least one catalyst bed and having an impeller for moving the gas stream through the gas phase reactor. The gas flow is modified between the impeller and the gas phase reactor to decrease gas stream velocity and increase gas flow uniformity.
Description
- The present application is a Continuation of co-pending U.S. application Ser. No. 09/973,401 filed Oct. 9, 2001, to which priority is claimed and which is herein incorporated by reference.
- 1. Field of the Invention
- The invention herein relates to a system and method for catalytically treating a gas stream, and particularly to a system and method for catalytically reducing the content of undesirable compounds in a flue gas resulting from the combustion of fuel.
- 2. Description of the Related Art
- Catalytic treatment for modifying the composition of gas streams is well known in the art. Various types of catalyst beds have been used such as fixed beds and fluid beds. Among fixed beds there are axial flow reactors, radial flow reactors and parallel flow reactors.
- Environmental concerns and new regulations are motivating further research and development in the treatment of gas streams to reduce the content of pollutants such as nitrogen oxides (NOx) and sulfur oxides (SOx) from the exhaust gases resulting from combustion processes such as engine or turbine exhaust gases, or furnace stack gas. Such gases can result from the operation of power plants, thermal cracking furnaces, incinerators, internal combustion engines, metallurgical plants, fertilizer plants, chemical plants, and other industrial operations.
- For example, processes for selectively reducing the NOx content of flue gas are known. Generally such processes employ the reaction of NOx with a reducing agent, such as ammonia or urea, optionally in the presence of a catalyst. The reduction of NOx with ammonia can be performed catalytically at a temperature generally ranging from about 500° F. to about 950° F. in a process known as selective catalytic reduction (“SCR”).
- One problem associated with the catalytic treatment of large volumes of gas is providing an even distribution of the gas across the face of the catalyst, and an even mixing of the flue gas with the reducing agent. As can be readily appreciated, uneven distribution reduces the efficiency of the system. Reduced efficiency, in turn, requires the use of larger catalyst beds.
- The weight and bulk of the equipment necessary to achieve satisfactory removal of NOx is yet another important factor. Many industrial plants need to be retrofitted with NOx removal (“deNOx”) or SOx removal (“deSOx”) equipment in order to meet the requirements of more stringent government regulations. However, because of the physical bulk of the deNOx/deSOx systems, the flue gas must be diverted to ground level for treatment and then sent back to the stack for subsequent exhaust to the atmosphere. It would be advantageous to provide a relatively lightweight deNOx and/or deSOx unit which can be incorporated directly into the stack. It can readily be appreciated that better system efficiency, and the consequent reduced bulk of the deNOx and/or deSOx system, is advantageous in providing a stack reactor system suitable for mounting to a stack.
- In accordance with the present invention a system is provided herein for catalytically treating a gas stream, the system comprising:
- a) a gas phase reactor containing a catalyst for the treatment of the gas stream in at least one catalyst bed having an upstream end and a downstream end, and;
- b) an axial fan positioned upstream of the at least one catalyst bed and having a rotatable impeller for moving the gas stream through the gas phase reactor; and,
- c) gas flow modification means positioned between the impeller and the gas phase reactor for decreasing gas stream velocity and increasing gas flow uniformity.
- The system advantageously provides increased efficiency by rendering the velocity profile of the gas stream more uniform before it enters the reactor and preventing uneven flow through the catalyst bed. Furthermore, the uniformity of the composition of the gas stream is also increased.
- Various embodiments are described below with reference to the drawings wherein:
-
FIG. 1 is a diagrammatic perspective view of the system of the present invention; -
FIG. 2 is a cutaway perspective view of the fan system of the present invention; -
FIG. 3 is a cut away side view of an impeller assembly employed in the fan system of the present invention; -
FIG. 4 is a perspective view of a twin blade unit for use in the impeller assembly; -
FIG. 5 illustrates a honeycomb catalyst structure useful in the gas phase reactor of the present invention; and, -
FIG. 6 is a diagrammatic view of a catalyst bed for use in the reactor system of the present invention. - As used herein the terms “stack” and “flue” are used synonymously. The term “nitrogen oxide” as used herein refers to any oxide of nitrogen such as, for example, NO, NO2, N2O4 or N2O, and is alternatively designated as NOx The term “sulfur oxide” refers to any oxide of sulfur such as, for example, SO2 or SO3, and is alternatively designated as SOx.
- While the present invention is particularly exemplified by its embodiment in a stack gas treatment system, any catalytic treatment of any gas stream is contemplated as being within the scope of the invention.
- The present invention is advantageously used in conjunction with the treatment of exhaust gas resulting from a high temperature combustion process, for example, turbine exhaust or fired heater stack gas. The increased efficiency achieved by the present invention is particularly advantageous with respect to deNOx and/or deSOx systems.
- Referring now to
FIG. 1 , a system 10 for the catalytic treatment of a gas stream is shown. The system 10 is illustrated in conjunction with the SCR deNOx treatment of a flue gas from theconvection section 20 of a fired heater such as a thermal cracking unit. Such thermal cracking units are well known in the art and, for example, are typically used to produce olefins from saturated hydrocarbon feedstocks such as ethane, propane, naphtha, and the like. - SCR is often employed to reduce the NOx content of a flue gas by reacting the NOx component with a reducing agent such as ammonia, urea, or alkyl amines and the like, in the presence of a catalyst to produce nitrogen and water as shown in the following chemical equation (not stoichiometrically balanced):
NOx+NH3→N2+H2O - The flue gas generated by a thermal cracker furnace typically includes the following components:
Nitrogen 60-80 vol. % Oxygen 1-4 vol. % Water vapor 10-25 vol. % Carbon dioxide 2-20 vol. % Nitrogen oxide 50-300 ppm. - The reducing agent, preferably ammonia, is injected into a flue gas recycle stream (discussed below) and introduced into the
convection section 20. The flue gas with reducing agent exits theconvection section 20 throughduct 40 at a temperature ranging from about 400° F. to about 700° F., and is moved by means of anaxial fan system 100. A high temperature axial fan suitable for use in the present system is available from ABB Fan Group Inc., of Niles, Mich. under the model designation PFS-14-095-21 TG. While the system 10 is configured for generally horizontal flow of the flue gas through the system, other orientations such as vertical or inclined can alternatively be employed if desired. - Referring now to
FIGS. 1, 2 and 3, apreferred fan system 100 is mounted to aplatform 30 above theconvection section 20 of a thermal cracking furnace or other similarly configured heater.Fan system 100 includes adrive unit 120,fan housing 110 for enclosing animpeller assembly 130 andtail cone 140, and acontrol unit 150. - More particular,
drive unit 120 includes a drive motor 121 (FIG. 1 ) enclosed within a motor housing 122 (FIG. 2 ), and a rotatableaxial shaft 125 for transmitting rotary motion to animpeller assembly 130. Themotor 121 is sized for adequate movement of the flue gas. In apreferred embodiment motor 121 has a rated output of 250 HP at 1800 rpm, and operates at 316 amps/480 volts and on a 60 cycle current. Thepresent fan system 100 is adapted to handle flue gas throughput of up to about 300,000 lbs/hr efficiently. - Other size motors can be used in accordance with desired flue gas loads. Selecting an appropriately sized motor and fan is within the purview of those with skill in the art.
- Referring to
FIG. 3 , theimpeller assembly 130 is attached toshaft 125 and includes arotor 131, and a plurality ofblade units 135 removably and adjustably fixed to the circumferential periphery of therotor 131. The blade units can possess single or, preferably, twin blades. - Referring to
FIG. 4 , a preferredtwin blade unit 135A includes a disc shapedbase 138 from which substantiallyparallel blades base 138 includesapertures 139 through which bolts or screws may be disposed for attachment to thecircumferential periphery 131A ofrotor 131. Theblade units - The present invention advantageously provides a great deal of flexibility in choosing suitable methods for controlling the system 10. For example, one method of controlling flue gas velocity and throughput is in-flight variable pitch control of the angle of the
blade units 135 while the fan is operating. Systems for in-flight variable pitch control are known. See e.g., U.S. Pat. Nos. 4,090,812, 4,778,344 and 4,844,697, all of which are incorporated by reference. A second option for in-flight control is to vary the speed of impeller rotation, faster speed producing high gas velocity and throughput. Another alternative is to use individually adjustable blade units which can be manually adjusted when the fan is stopped to provide a desirable blade pitch. Yet another means of controlling gas flow through the catalyst beds is by means of spill back control, i.e., control of the recycle flow of flue gas. Spill back control is discussed in more detail below with reference to therecycle manifold 330. - A significant feature of the present invention is the uniformity of the gas flow entering the catalyst beds. Conventional fan systems such as radial fans and unmodified axial fans produce a high velocity exhaust which has an uneven velocity profile. This results in uneven and inefficient use of catalyst, and therefore requires a greater bed volume to achieve the desired conversion of NOx If the kinetic energy of the flue gas in the duct feeding the catalyst modules is high relative to the module pressure drop (for example, a kinetic energy greater than approximately 20% of the bed pressure drop) maldistribution will occur and the required deNOx efficiency will not be achieved. The ratio of the catalyst module pressure drop to inlet kinetic energy should be as high as possible. This will minimize dynamic effects and assure proper flow distribution if the flow characteristics of the catalyst modules themselves and downstream heat economizer tubes are uniform. With low pressure drop catalyst beds the associated kinetic energy of the catalyst bed inlet stream must be very low. This means that the exhaust from the fan must be decelerated and the kinetic energy of the exhaust must be reduced. Conventional design methods prescribe the use of long sections of duct with gradually increasing cross sectional area (also known as evase ducting) to decelerate the flow and convert the kinetic energy of the fan exit stream to static pressure. Also, the exhaust gas acquires a “swirl”, or spinning component of velocity from the rotary motion of the impeller. The swirl must be converted to axial flow.
- A characteristic of the present system is the evenness of the flue gas velocity profile. The flue gas stream entering the catalyst beds should have variations in gas velocity of no more than about 10% deviation from the average velocity, and preferably no more than about 5% deviation from average velocity. The average or mean velocity is defined as the total volumetric flow divided by the cross sectional flow area of the approach duct. Likewise, the content of the reducing agent should be as uniform as possible, which can be achieved by more effective mixing, as discussed below.
- In order to achieve more even flow of flue gas the
fan system 100 includes a gasflow modification section 200 for decreasing the flue gas velocity and flattening the velocity profile of the gas. The gasflow modification section 200 includes a generally cylindrical, longitudinally extendingtail cone 140 having a distally pointingtapered end portion 141 with a generally conical shape. Thetail cone 140 is supported by longitudinally orientedplanar struts 145 positioned in the annular space between thetail cone 140 and the interior surface of thehousing 110. The planar struts 145 not only help support thetail cone 140 but also act as baffles to reduce the gas flow swirl and redirect the spinning component of the gas velocity towards axial flow of the flue gas through the system. - The
housing 110 has adistal end section 111 which flares outward in diameter such that the exit diameter of thehousing 110 is greater than the diameter at the impeller. As can be seen, the cross-sectional area of the annular space between thetail cone 140 and thehousing 110 is the area available for gas flow. The combined reduction of the diameter of thetail cone 140 attapered end 141 and the increasing diameter of the housing at flaredsection 111 forms an annular diffuser which increases the cross sectional area available for gas flow and thereby reduces the velocity of the gas and tends to flatten the velocity profile of the gas. - Referring now to
FIG. 1 , thetransition section 300 is positioned between the gasflow modification section 200 of the fan system and thegas phase reactor 400, and is adapted to redirect and distribute the flow of the flue gas evenly across the face of thecatalyst bed 410. Transition section includes ahousing 301 defining an interior chamber for enclosing aguide vane unit 310, andtransition duct 320.Guide vane unit 310 is positioned at or near theinlet 302 of the transition section and includes louvers for redirecting the flow of flue gas. Guide vane units suitable for use in thetransition section 300 are commercially available and those skilled in the art can readily select an appropriate guide vane unit for a particular application. Theguide vane unit 310 further decelerates the flue gas flow and redirects the flue gas outward from the axial centerline of the flow so as to spread the flue gas flow evenly over the proximal face of thecatalyst bed 410. Thetransition duct 320 includeswalls 321 which are perforated in the direction of the longest flow paths. The perforations serve to permit boundary layer suction to be applied to the panels, thereby preventing flow separation and increasing diffuser efficiency and improving flow uniformity. The boundary layer fluid is withdrawn through the perforations in thewalls 321 into aproximal portion 303 of the chamber defined byhousing 301 and is drawn intorecycle manifold 330. - The gas
flow modification section 200 andtransition section 300 both provide means for modifying the gas flow through system 10 in order to accomplish one or more of: decelerating the gas, reducing swirl, flattening the velocity profile, and directing the gas evenly across the face of the catalyst bed. These gas flow modifications are achieved by expanding the cross-sectional area available to gas flow, and the use of guide vanes, baffles, and other such surfaces for orienting the flow direction of the gas. -
Recycle manifold 330 includes one ormore pipe branches 331 extending from theside wall 304 ofhousing 301 for drawing flue gas from theproximal portion 303 of the chamber. Thepipe branches 331 connect to a pipe main 332. Ammonia, or other reducing agent, is injected into the pipe main 332 atinlet 338. The recycled flue gas is directed throughhorizontal distributor pipe 334 and returnpipes 335. Thereturn pipes 335 are laterally spaced apart and provide a return flow of recycled flue gas into multiple regions of theconvection section 20. Avalve 333 is a means for controlling the recycling of flue gas and thereby provides spill back control for the system 10. The recycling of the flue gas helps to reduce fluctuations in the ammonia content of the flue gas entering the catalyst bed by more thoroughly distributing the ammonia. The fluctuation of the ammonia content of the gas is no more than about 10% deviation from the average ammonia content, preferably no more than 5% deviation, and more preferably no more than 3% deviation from the average value of the ammonia content. - Referring now to
FIGS. 1 and 6 the advantageous features of the present invention are particularly suited to the axial flow reactor system described below. The preferred gasphase reactor system 400 includes twocatalyst beds - Catalysts for the selective reduction of nitrogen oxides in the presence of a reducing agent are known in the art. Representative examples of such catalysts include, but are not limited to, oxides of vanadium, aluminum, titanium, tungsten and molybdenum. Zeolites can also be used. Examples of the latter include ZSM-5 modified with protons, or with copper, cobalt silver, zinc, or platinum cations or their combination. It is to be understood that the scope of the present invention is not limited to a specific SCR catalyst or catalyst composition.
- A preferred catalyst for NOx removal for use in the present system is vanadium pentoxide (V2O5) on a titanium dioxide (TiO2) support. The catalyst is optionally provided as a honeycomb catalyst. Honeycomb catalysts are known in the art. Referring to
FIG. 5 ,honeycomb catalyst 450 includes amonolithic catalyst body 452 containing a plurality ofparallel passageways 451, which are preferably hexagonal in cross-sectional shape. The gas stream to be catalytically treated is moved through thepassageways 451. Alternatively, the passageways can possess a circular cross-section or other shape such as square, rectangular and the like. - Another catalyst suitable for use in the present system is a microengineered catalyst (“MEC”) supported on a mesh-like support having at least about 85% void space. The mesh-like support of the MEC catalyst can include wires, metal felt, metal gauge, metal fiber filter or the like, and can include one or more layers. The catalyst (e.g., V2O5, with or without TiO2 or other support) can be coated onto the mesh by a variety of techniques such as dipping, spraying, etc. in an amount sufficient to achieve the desired conversion of NOx. A MEC catalyst suitable for use in the present invention is described in copending U.S. Patent application Ser. No. 60/222,261 filed Jul. 31, 2000, entitled “Conversion of Nitrogen Oxides in the Presence of a Catalyst Supported on a Mesh-Like Structure” the contents of which are incorporated by reference herein in their entirety.
- In the system 10 herein, the catalyst beds are oriented for horizontal flow of the flue gas therethrough.
FIG. 6 illustrates the structure ofcatalyst bed 410,catalyst bed 420 being of the same structure.Catalyst bed 410 includes six stackable, separableindividual modules catalyst elements 417, preferably arranged in an 8×10 configuration. In a preferred embodiment each catalyst element has dimensions of 160 mm×160 mm×1205 mm. Theentire bed 410 has dimensions of 4.80 meters×2.56 meters×1.205 meters. The modular construction of thereactor system 400 facilitates the removal and/or replacement of thecatalyst beds - The catalyst beds are preferably operated at a temperature of from about 400° F. to about 700° F., more preferably from about 500° F. to 600° F., and most preferably from about 550° F. to about 570° F. The pressure drop through each catalyst bed preferably can range from about 1 inch to about 5 inches, more preferably from about 2 inches to about 4 inches, and most preferably from about 3 inches to 3.5 inches.
- The gas exiting the
reactor section 400 has a reduced content of NOx. At least a 90% reduction of NOx content is achieved, preferably at least a 93% reduction of NOx content is achieved, and more preferably at least a 95% reduction of NOx content is achieved. - The treated flue gas enters the
heat recovery section 500 and flows through an array oftubes 501. The cracker feedstock can be used as the heat recovery fluid, thereby maintaining the overall temperature and duty profile of the furnace while cooling the flue gas from the range of 400° F.-700° F. to the range of 300° F.-400° F. Other streams, such as Boiler Feed Water to steam generation equipment can alternatively be used to cool the treated flue gas and improve the thermal efficiency of the operation. Thetubes 501 can alternatively be positioned in a horizontal orientation or a vertical orientation depending upon whether the cooling fluid flowing throughtube 501 is vaporized by passage therethrough, or is already in a gaseous phase. - The treated and cooled flue gas thereafter enters a
duct 60 with aside surface 61 which is tapered so as to maintain a constant static pressure at the outlet of theheat recovery section 500. The flue gas is thereafter diverted to upward flow throughstack 70 into the atmosphere. - The system 10 for the catalytic treatment of flue gas is exemplified by the Example set forth below.
- A system for the catalytic treatment of flue gas as illustrated in
FIG. 1 is provided. - A flue gas is generated by a thermal cracking furnace at the rate of 272,370 lb/hr, the flue gas containing the following components:
O2 6.00 vol. % N2 72.82 vol. % H2O 14.88 vol. % CO2 6.30 vol. % NOx 30.00 lb/hr - Anhydrous ammonia is added to the flue gas via the recycle grid. The ammonia flow rate to the reactor is 10.8 lb/hr.
- The flue gas is moved horizontally by means of the fan system described above and passes through the diffuser and transition duct into the reactor containing two modular catalyst beds in series. The catalyst for the reactor section is vanadium pentoxide on titanium dioxide honeycomb catalyst positioned for horizontal flow. The catalyst bed is operated at a temperature of 560° F. The flue gas experiences a pressure drop of 3.0″ H2O across the reactor. At the reactor exit the treated flue gas has a NOx concentration of only 2.5 lb/hr. This represents a NOx reduction efficiency of about 91.7% based on the inlet NOx concentration of 30 lb/hr. An ammonia slip of 5 ppm is observed.
- While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the invention, but merely as exemplifications of preferred embodiments thereof. Those skilled in the art will envision many other possibilities within the scope and spirit of the invention as defined by the claims appended hereto.
Claims (57)
1. A system for catalytically treating a gas stream, which comprises:
a) a gas phase reactor containing a catalyst for the treatment of the gas stream in at least one catalyst bed having an upstream end and a downstream end;
b) an axial fan positioned upstream of the at least one catalyst bed and having a rotatable impeller for moving the gas stream through the gas phase reactor; and,
c) gas flow modification means positioned between the impeller and the gas phase reactor for decreasing gas stream velocity and increasing gas flow uniformity.
2. The system of claim 1 wherein the gas flow uniformity is increased by the gas flow modification means such that the gas stream entering the gas phase reactor has a velocity profile exhibiting not more than about 10% velocity deviation from an average gas stream velocity at the upstream end of the at least one catalyst bed.
3. The system of claim 2 wherein the velocity profile of the gas stream exhibits no more than about a 5% velocity deviation from an average gas stream velocity at the upstream end of the at least one catalyst bed.
4. The system of claim 1 wherein the axial fan includes a housing and a tail cone, and the gas flow modification means includes a distally pointing tapered end portion of the tail cone and a flared portion of the housing having a gradually increasing diameter.
5. The system of claim 4 wherein the gas flow modification means further includes a transition duct having perforated walls which flare outward so as to gradually increase cross-sectional area available to gas stream flow.
6. The system of claim 1 wherein the gas flow modification means includes a transition duct having perforated walls which flare outward so as to gradually increase cross-sectional area available to gas stream flow.
7. The system of claim 1 further including means for recycling a portion of the gas stream from downstream of the axial fan to a position upstream of the axial fan.
8. The system of claim 1 wherein the gas stream contains nitrogen oxide.
9. The system of claim 1 wherein the catalyst bed includes a plurality of stackable, individually separable modules containing one or more materials selected from the group consisting of vanadium oxide, aluminum oxide, titanium oxide, tungsten oxide, molybdenum oxide and zeolite.
10. The system of claim 9 wherein the modules each comprise a plurality of stacked catalyst elements having a honeycomb type structure.
11. The system of claim 1 wherein the catalyst bed comprises a catalyst supported on a mesh-like structure having a void space of at least about 85%.
12. The system of claim 1 wherein the catalyst bed includes a vanadium pentoxide catalyst on titanium oxide support.
13. The system of claim 1 wherein the gas phase reactor comprises at least two catalyst beds arranged in series.
14. The system of claim 1 wherein the fan impeller includes a plurality of blade units attached to and extending radially outward from a circumferential periphery of the impeller.
15. The system of claim 14 wherein the blade units each comprise two blades.
16. The system of claim 14 wherein the blade units have a variable pitch which is controllable while the impeller is rotating.
17. The system of claim 14 wherein the impeller has a variable speed of rotation which is adjustable while the impeller is rotating.
18. The system of claim 1 further including a heat recovery section positioned downstream of the gas phase reactor for cooling the gas stream.
19. The system of claim 1 further including means for introducing reducing agent into the gas stream.
20. The system of claim 19 further including a gas stream recycle manifold for communicating a portion of the gas stream downstream of the axial fan to a convection section of a furnace positioned upstream of the axial fan, wherein the means for introducing reducing agent comprises an inlet for introducing the reducing agent into the gas stream recycle manifold.
21. A system for catalytically treating a furnace flue gas, which comprises:
a) a gas phase reactor containing a catalyst for the treatment of the flue gas in at least one catalyst bed having an upstream end and a downstream end;
b) an axial fan positioned upstream of the at least one catalyst bed and downstream of a furnace and having a rotatable impeller for moving the flue gas from the furnace through the gas phase reactor; and,
c) means for recycling a portion of the flue gas from downstream of the axial fan to a convection section of the furnace located upstream of the axial fan.
22. The system of claim 21 wherein the means for recycling a portion of the flue gas comprises a gas stream recycle manifold.
23. The system of claim 22 wherein the gas stream recycle manifold includes an inlet for introducing reducing agent into recycle manifold.
24. The system of claim 22 wherein the gas stream recycle manifold includes a control valve.
25. The system of claim 22 further comprising a transition duct having perforated walls which flare outward so as to gradually increase cross-sectional area available to flue gas flow.
26. The system of claim 25 wherein the gas stream recycle manifold has at least one inlet connected to the transition duct, and at least one outlet connected to the convection section of the furnace.
27. The system of claim 21 wherein the axial fan includes a housing and a tail cone, the housing having a flared distal portion and the tail cone having a distally pointing tapered end portion.
28. The system of claim 21 wherein the catalyst bed includes a plurality of stackable, individually separable modules containing one or more materials selected from the group consisting of vanadium oxide, aluminum oxide, titanium oxide, tungsten oxide, molybdenum oxide and zeolite.
29. The system of claim 28 wherein the modules each comprise a plurality of stacked catalyst elements having a honeycomb type structure.
30. The system of claim 21 wherein the catalyst bed comprises a catalyst supported on a mesh-like structure having a void space of at least about 85%.
31. The system of claim 21 wherein the flue gas contains nitrogen oxide.
32. The system of claim 31 wherein the at least one catalyst bed includes a vanadium pentoxide catalyst on titanium oxide support.
33. The system of claim 21 wherein the gas phase reactor comprises at least two catalyst beds arranged in series.
34. The system of claim 21 wherein the fan impeller includes a plurality of blade units attached to and extending radially outward from a circumferential periphery of the impeller.
35. The system of claim 34 wherein the blade units each comprise two blades.
36. The system of claim 34 wherein the blade units have a variable pitch which is controllable while the impeller is rotating.
37. The system of claim 34 wherein the impeller has a variable speed of rotation which is adjustable while the impeller is rotating.
38. The system of claim 21 further including a heat recovery section positioned downstream of the gas phase reactor for cooling the flue gas.
39. A method for catalytically treating a gas stream comprising:
a) moving the gas stream through an axial fan from an upstream position to a downstream position;
b) modifying the gas stream flow from the axial fan to decrease gas flow velocity and increase gas flow uniformity;
c) recycling a portion of the gas stream from downstream of the axial fan to a position upstream of the axial fan; and,
d) passing the gas stream through a gas phase reactor having at least one catalyst bed.
40. The method of claim 39 wherein the gas flow uniformity is increased by the step of modifying the gas stream flow such that the gas stream entering the gas phase reactor has a velocity profile exhibiting not more than about 10% velocity deviation from an average gas stream velocity at the upstream end of the at least one catalyst bed.
41. The method of claim 40 wherein the velocity profile of the gas stream exhibits no more than about a 5% velocity deviation from an average gas stream velocity at the upstream end of the at least one catalyst bed.
42. The method of claim 39 further including the step of introducing a reducing agent into the recycled portion of the gas stream.
43. The method of claim 39 further including the step of cooling the gas stream after the gas stream has been passed through the gas phase reactor.
44. The method of claim 39 wherein the axial fan includes a variable speed impeller, and wherein the step of moving the gas stream through the axial fan is controlled at least in part by varying the speed of the impeller.
45. The method of claim 39 wherein the axial fan includes a plurality of variable pitch blades movably attached to a circumferential periphery of the rotatable impeller, and the step of moving the gas stream is controlled at least in part by varying the pitch of the blades.
46. The method of claim 39 wherein the step of recycling a portion of the gas stream includes withdrawing the portion of the gas stream as boundary layer suction and returning the portion of the gas stream through a recycle manifold having one or more exits into a convection section of a flue gas furnace.
47. The method of claim 46 wherein the recycle manifold includes a control valve.
48. The method of claim 39 wherein the catalyst bed comprises a catalyst supported on a mesh-like structure having a void space of at least about 85%.
49. The method of claim 39 wherein the catalyst bed includes a vanadium pentoxide catalyst on titanium oxide support.
50. The system of claim 1 , wherein the gas flow modification means comprises:
a housing including a tail cone, wherein the housing surrounds the axial fan, and wherein the tail cone is positioned downstream from the axial fan; and,
a transitional duct having perforated walls that are flared outward disposed downstream from the housing.
51. The system of claim 50 , wherein the tail cone has a substantially conical shape and comprises a distally pointing tapered end portion.
52. The system of claim 51 , wherein the tail cone is supported within the housing by longitudinally oriented planar struts positioned in an annular space between the tail cone and an interior surface of the housing, wherein the struts act as baffles to reduce swirl and direct gas flow towards an axial flow of the flue gas through the system.
53. The system of claim 50 , wherein the housing further comprises:
an outlet, wherein a diameter of the outlet is greater than a diameter of an impeller of the axial fan, and wherein the circumference of the housing gradually increases from a position of the housing at the axial fan to the outlet of the housing.
54. The system of claim 50 , wherein the gas flow modification means further comprises a guide vane unit disposed at an inlet of the transition duct, wherein the guide vane unit includes louvers for redirecting the flow of the flue gas.
55. The system of claim 4 , wherein the gas flow modification means further comprises:
a transition duct having perforated walls that flare outward positioned downstream from the housing; and,
a guide vane unit disposed at an inlet of the transition duct, wherein the guide vane unit includes louvers for redirecting the flow of the flue gas.
56. The system of claim 6 , wherein the gas flow modification means further comprises:
a transition duct having perforated walls that flare outward positioned downstream from the housing; and,
a guide vane unit disposed at an inlet of the transition duct, wherein the guide vane unit includes louvers for redirecting the flow of the flue gas.
57. The system of claim 27 , wherein the gas flow modification means further comprises:
a transition duct having perforated walls that flare outward positioned downstream from the housing; and,
a guide vane unit disposed at an inlet of the transition duct, wherein the guide vane unit includes louvers for redirecting the flow of the flue gas.
Priority Applications (1)
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US11/981,391 US20080081010A1 (en) | 2001-10-09 | 2007-10-31 | Modular system and method for the catalytic treatment of a gas stream |
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US11/981,391 US20080081010A1 (en) | 2001-10-09 | 2007-10-31 | Modular system and method for the catalytic treatment of a gas stream |
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US11/981,391 Abandoned US20080081010A1 (en) | 2001-10-09 | 2007-10-31 | Modular system and method for the catalytic treatment of a gas stream |
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RU2729422C1 (en) | 2019-10-24 | 2020-08-06 | ФЕДЕРАЛЬНОЕ ГОСУДАРСТВЕННОЕ БЮДЖЕТНОЕ УЧРЕЖДЕНИЕ НАУКИ ИНСТИТУТ ОРГАНИЧЕСКОЙ ХИМИИ им. Н.Д. ЗЕЛИНСКОГО РОССИЙСКОЙ АКАДЕМИИ НАУК (ИОХ РАН) | Catalyst for removal of sulphur oxides from flue gases of power plants |
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WO2013133798A2 (en) * | 2012-03-06 | 2013-09-12 | International Engine Intellectual Property Company, Llc | Heating jacket having pitch and drain hole |
WO2013133798A3 (en) * | 2012-03-06 | 2014-04-24 | International Engine Intellectual Property Company, Llc | Heating jacket having pitch and drain hole |
Also Published As
Publication number | Publication date |
---|---|
WO2003031783A1 (en) | 2003-04-17 |
US20030072693A1 (en) | 2003-04-17 |
US7572414B2 (en) | 2009-08-11 |
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