TITlE;
A process for fabrication of metallic wire-mesh supported by SCR catalyst.
FIELD OF INVENTION:
The present invention relates to a process for fabrication of metallic wire-mesh supported by SCR catalyst.
BACKGROUND OF THE INVENTION:
Emission regulations for unburned hydrocarbons, nitrogen oxides (NO, N02 and N20, combinedly called NOx) and particulates are becoming more stringent throughout the world.
The major sources of NOx from stationary sources are power generation, stationary engines, industrial boilers, process heaters and gas turbines. Post combustion NOx control technologies that are currently being applied to coal-fired utility boilers include selective non catalytic reduction (SNCR), selective catalytic reduction (SCR), and combined SNCR/SCR systems (hybrid SNCR/SCR) respectively. SCR can be applied as a stand-alone NOx control or with other technologies, including selective non-catalytic reduction (SNCR) and combustion controls such as low NOx burner (LNB) and flue gas recirculation (FGR).
SCR is typically implemented on stationary source combustion unit/s requiring a higher level of NOx reduction than achievable by selective non-catalytic reduction (SNCR) or combustion controls. SCR systems can be designed for NOx removal efficiencies upto 100%, though in practice, commercial coal, oil, and natural gas-fired SCR systems are often designed to meet over 90% efficiency. However, the reduction may be less than 90% when SCR follows other NOx controls such as LNB or FGR that achieve relatively low emissions on their own.

Either ammonia or urea may be used as the NOx reduction reagent in SCR systems. Urea is generally converted to ammonia before injection. Majority electric utilities that operate SCR systems use (-80%) use ammonia (anhydrous and aqueous), and -20% use urea.
Catalytic combustion is the most accepted procedure to convert toxic exhaust gases into less toxic or benign gases [1]. A typical reactor type for catalytic combustion of volatile organic carbons (VOCs) is a monolithic support that is characterized by very low pressure drop, even at high flow rate. Monoliths are normally shaped as honeycombs or layered plates, and commonly composed of ceramic or metal materials [2]. The main drawbacks of ceramic monoliths are their susceptibility to thermal and mechanical shock and high manufacturing cost. Therefore, application of metal substrates as catalyst supports has gained significant interest recently. The primary advantages of metal substrates are high thermal conductivity, high surface to volume ratio, low pressure drop and low manufacturing cost.
Use of metal wire mesh as catalysts support is well documented in this field. Wire-mesh catalysts have excellent mass and heat transfer performance of pellet-type catalysts, with merits of low pressure drop and high effectiveness factor in the monolith, therefore exhibiting a higher efficiency over honeycomb modules [5]. Various techniques have also been reported. Applying thin catalytically active zeolite coatings to fibrous substrates by several novel approaches have also been suggested [6,7]. Typical preparation procedures consist of immersing the support structure in an aqueous solution containing the reactant for the in situ hydrothermal synthesis of zeolite, after which the system is heated and the zeolite crystals grow on the surface of the support. Zeolite coated metal wire mesh supports have been used in SCR system for de-NOx with NH3 dosing. The electrophoretic deposition (EPD) method has been considered as another technique since it requires a short deposition time and simple apparatus. It is based on the deposition of particles or colloid suspensions on the surface of an electrode driven by an electric field [8]. Vorob'eva et al. have tried to prepare wire mesh coated with active alumina using electrophoretic deposition (EPD) of alumina sol [9].

US20050085383 A1 dated April 21, 2005 by Jakob Hoj &Claus Jorgensen [10] reported a catalyst support material and catalysts made therefrom having improved resistance towards erosion showing improved resistance towards erosion are used in flue gas containing a large amount of particulate matter and for selective catalytic reduction of nitrous oxides. The catalyst support contains at least 20% by weight of Ti02 being present mainly in the anatase form. Furthermore, the catalyst support contains diatomaceous earth in an amount of at least 2% and less than 80% by weight of the catalyst support. In one embodiment catalysts made from said catalyst support contain oxides or sulfates of base metals from the group of V, W, Mn, Nb, Mo, Ni, Fe or Cu. Another option is a catalyst prepared from said catalyst support containing Pt or Pd. Said catalysts are used for treatment of a flue gas. Similar reports are also available in patent numbers, e.g., CN1628906A [11], DE602004025657D1 [12], EP1524024A1 [13], EP1524024B1 [14], US7431904 [15] respectively.
Patent number KR101659818(B1) by Nano Co. Ltd., Korea [16] described a manufacturing method of plate type selective catalytic reduction catalyst for DeNOx and plate type selective catalysts reduction catalysts capable of removing a nitrogen oxide included in exhaust gas. The method includes, a catalyst manufacturing step of manufacturing a hill for a catalyst; a catalyst application step of dropping the hill onto a mesh and then inserting the hill into a gap between an upper roll and a lower roll, rotating near each other, to pressurize and apply the hill; a dry step of drying the mesh to which the hill is applied in the catalyst application step; a forming step of curving and forming the mesh, dried in the dry step, into a predetermined shape; a cutting step of cutting the mesh, curved in the forming step, in a predetermined standard; a stacking step of stacking the mesh, cut in the cutting step, in a block of which both sides are opened; and a thermal treatment step of thermally treating the block in which the mesh is stacked.
Another patent number CN103349981 (A) by Jiangsu Wonder Environmental Prot Technology Co. Ltd. [17] describes the manufacturing of plate-type SCR de-nitration catalyst, and preparation method and application thereof. The method comprises the

steps of kneading, aging, stretching production of a steel mesh, coating and baking, wherein in the kneading step, mixing step by step is adopted, that is Ti02-W-1, Ti02-D-2, deionized water, ammonia water, ammonium heptamoiybdate, clay, an ammonium metavanadate solution, hydroxyethyl cellulose and polyethylene oxide are added into a mixer for kneading; the coating step is that the ageing material is uniformly coated on the stainless steel wire mesh.
Usage of metal wire mesh for de-NOX catalyst is also reported by Jie Yao [18]. Both flat and corrugated wire mesh sheets were coated with aluminium powder by using electrophoretic deposition (EPD) method. Controlled thermal sintering of coated samples yielded uniform porous aluminium layer with a thickness of 100 urn that was attached firmly on the wire meshes. Subsequent controlled calcination formed a finite thickness of AI203 layer on the outer surface of each deposited aluminium particles, which resulted in the formation of AI203/AI double-layered composite particles that were attached firmly on the wire surface to form a certain thickness of porous layer. A rectangular-shaped wire-mesh honeycomb (WMH) module with triangular-shaped channels was manufactured by packing alternately the flat sheet and corrugated sheet of the AI203/AI-coated wire meshes. This WMH was further coated with V205-Mo03-W03 catalyst by wash-coating method to be applied for the selective catalytic reduction (SCR) of NO with NH3. With an optimized catalyst loading of 16 wt%, WMH catalyst module shows more than 90% NO conversion at 240°C and almost complete NO conversion at temperatures higher than 300°C at GHSV 5,000 If1.
Fabrication of SCR catalyst modules using metal wire mesh supported structures by numerous technologies involving various conceptual fabrication methods and processes is a continued interest. In this context, this invention describes a fabrication process in a continuous mode by utilizing specific support structure, catalyst material, binder system along with the processing conditions for the fabrication process for manufacturing metallic wire-mesh supported SCR (selective catalytic reduction for de-NOx) plate-type catalyst structures by using a so-called 'Roller-assisted Casting Machine', in which SCR catalyst plate structures could be

fabricated with NOx to elemental nitrogen conversion efficiency in the range of 85 -90% with space velocity in ihe range of 1500 - 2000 per hour having erosion rate of the plates in the range of 0.01 - 0.05 g/min, by following the steps as explained in the following.
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a process for fabricating metallic wire mesh supported SCR catalyst plate-type structures in a continuous mode.
Another objective is to propose the said fabrication process by defining specified metallic support structure, SCR catalyst material, binder system to be used in the process.
Further object of the present invention is to propose the processing parameters of the fabrication process by defining drying & firing conditions of the derived SCR catalyst green structures thereof
Still further object of the present invention is to propose a process wherein the specific properties of the final product, is defined i.e., metallic wire mesh supported SCR catalyst plate type structures in terms of conversion efficiency for de-NOx applications including coal-fired power plants and erosion properties of the product.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a process for fabrication of metallic wire-mesh supported by SCR catalyst comprising:
preparing a binder formulation having 9 to 12% inorganic binder, 1 to 3% of organic binder and 1 to 5% of polymeric binder,
mixing the binders with SCR catalyst to form either a dough, paste or noodles, applying the SCR catalyst noodles on the surface of the selected metallic wire-mesh structure,

subjecting the SCR catalyst structures to the step of profilation into various shapes in
green form,
drying of the green SCR catalyst structures,
firing of the dried SCR catalyst structure to remove organic and polymeric binders,
subjecting the fired SCR catalyst plates to the step of testing.
DETAILED DESCRIPTION OF THE INVENTION:
As per the invention, the following steps are to be followed in order to fabricate metal wire mesh supported SCR (selective catalytic reduction) catalyst plate-type structure for the purpose of de-NOx applications by using specified i) Metallic wire mesh support material, ii) standard SCR catalyst material, iii) Binder formulation for the SCR catalyst, iv) Preparation of SCR catalyst dough/paste/noodles, v) Forming method & fabrication parameters, vi) Specific profiling of SCR catalyst structure, vii) Drying of the green SCR catalyst structures, viii) Firing of the dried SCR catalysts structures so as to yield the final product, i.e., SCR plate-type catalyst structures at the end of the fabrication process and finally ix) Testing of the SCR catalyst plates to confirm specified levels of conversion efficiency of NOx gas, erosion resistance of the catalyst structure, bond strength etc. respectively.
The following sections describe each step of the fabrication process sequentially:
i) Metallic Wire Mesh Support Material:
The support material in the described fabrication process is metallic wire mesh type structure in which stainless steel wire mesh could preferably be used. Stainless steel wire mesh with grades of SS304, SS316, SS430 etc. respectively or similar metallic wire mesh structural materials with counter properties, i.e., a) number of opening per inch in the range of 20-26, b) standard wire thickness gauge in the range of 20-26, c) overall thickness in the range of 0.4-1.0 mm, d) aperture of the mesh in the range of 0.4-1.0 mm etc. could be used for fabricating the stainless steel wire-mesh supported SCR (selective catalytic reduction for de-NOx) catalyst plate-type structures.

In order to toughen the support structure and wherever toughened base structure is a necessity for applications, the wire mesh structure could be heat treated in an electric or gas firing furnace at any set temperature in the temperature range of 600-750°C in air for a period of 1-2 hours prior use. Alternatively, such wire mesh structures without any heat treatment could be used. As described previously in another of our patent application, the heat treatment process toughens the stainless steel wire mesh structure, which produces stiffer SCR plate structure at the end and heat treatment of the metal mesh could be used depending on the criteria of toughness of the structure.
ii) SCR Catalyst Material:
The SCR catalyst material is a standard vanadia-based material that is dispersed in titania (anatase crystallographic form) and other constituents having specific surface area in the range of 90 -120 m2/g.
iii) Binder Formulation of the SCR Catalyst:
SCR catalyst material which is to be applied on the surface of the metallic wire mesh structure in the forming process, cannot be applied without the aid of a binder. The binder formulation in this invention is described as a combination of: a) inorganic binder in the weight range of 9.0 - 12 %, b) organic binder in the weight range of 1-3 % and c) polymeric binder in the weight range of 1-5 % respectively. The specific combination of the above three types of binders comprise the "Binder Formulation" of the SCR catalyst.
The inorganic binder comprise a mixture of a) clay (3-5 w%), b) bentonite (3-5 w%), c) glass fiber (1-3 w% and d) colloidal silica (0.5 - 1.0 w%) respectively. While the organic binder comprise carbomethoxy cellulose (CMC) in the range of 0.5 - 2.0 w%, which could be used either as 'solid powder' or in the form of an aqueous solution. While the polymeric binder is a combination of a) poly-ethelene glycol (PEG) having molecular weight in the range of 400-1200, preferably around 600 (2-4 w%) and b) polyvinyl alcohol (PVA) having molecular weight in the range of

50,000-200,000, preferably around 125,000 (1-5 w%) respectively. PVA is to be used in the form of an aqueous solution only having concentration in the range of 1-5 w%.
The constituents of the binder is added in specific step/s in the course of fabrication of SCR plate-type catalyst structure in desired proportion as per the above weight range in the binder formulation, which is discussed in the subsequent section.
iv) Preparation off SCR catalyst Douqh/Paste/Noodles:
In order to prepare SCR catalyst in the form of 'dough' or 'paste', the SCR catalyst powder is first mixed with inorganic binder in desired proportions and then homogenised/mixed by using a bail mill machine for a period of 6-10 hours. The resultant milled powder is further mixed with organic binder followed by polymeric binder in desired proportions by using a 'Sigma Blade Mixer1 or 'Sigma Kneader Machine' for a period of another 1-2 hours after which SCR catalyst paste or a dough resulted. The moisture level of the SCR dough is maintained in the range of 20-30 w% by adding de-ionized water either separately or by adding de-ionized water with the polymeric binder, PVA.
After the SCR catalyst paste is formed and paste is extruded in the form of noodles having the diameter in the range of 1-10 mm. The noodle form of the SCR catalyst paste facilitates the distribution of catalyst material uniformly in the plate structure in the course of fabrication, though formation of noodle is not a mandatory condition.
V) Forming Method & Fabrication Parameters:
In this step, the resultant SCR catalyst noodles are to be applied on the surface of the selected metallic wire mesh structure by maintaining uniform thickness throughout the plate structure by using the so-called in-house designed "Roller-assisted Casting Machine". In order to do this, the selected metallic wire mesh structure profile with defined properties, i.e., aperture size, overall thickness, number of opening/per unit inch, standard wire thickness gauge etc. is allowed to pass in between the two rollers in the said "Roller-assisted Casting Machine" and further

through a set of rollers with a gradient of decreasing gap in the between the rollers in sequential manner in a manner that the SCR catalyst noodles are coated on the surface of the metallic wire mesh support structures with a desired thickness uniformly throughout the plate structure in a continuous mode thereby resulting green structures of the SCR catalyst plates, which are subsequently to be profiled depending on the application requirement and other ease of assembly in the SCR catalyst modules. Furthermore, as mentioned previously, if required and depending on the application area, metallic wire mesh structure could also be heat treated in the temperature range of 600-750°C for a period of 1 -2 hours in order to harden the wire mesh prior applying SCR catalyst noodles on the wire mesh surface in which more hardened SCR catalyst plate green structures are obtained at the end of the process.
vi) Specific Profiling of SCR Catalyst Structures:
In this step in the fabrication process, the derived SCR catalyst plate green structures are profiled into numerous shapes like, "V", or "Z" or "S" etc. in the green form itself by using the same "Roller-assisted Casting Machine" having one set of roller with the impression of specific profile desired. Accordingly, the green structures could be profiled into various shapes as mentioned, like V, or "Z° or "S" etc. in the green form itself. These profiles help to maintain desired pitch level of the plates in the module assembly, besides ease of convenience in maintaining physical array of assembled SCR catalyst plates in modules with predetermined design for actual De-NOx application/s.
vii) Drying of the Green SCR catalyst structures:
As the derived SCR catalyst plate structure is green, which is to be dried in order to obtain dried plates within the moisture level 2 + 1 w%. The green SCR catalyst plates are dried in an oven (electrical or gas fired) at any set temperature in the temperature range of 60°-100°C for a period of 6-12 hours, which gives dried plates with a moisture level 2 + 1 w%.

viii) Firing of the Dried SCR Catalyst Structures:
The dried SCR catalyst plates are fired in order to remove the organic and polymeric binders from the structures. The dried plates are to be fired at any set temperature in the temperature range of 500° - 650°C in a kiln (electrically heated or gas-fired or similar kilns) for a period of 3 - 6 hours holding at the set temperature by maintaining a rate of heating of 1-2°/minute and by maintaining a rate of cooling of 1-27minute. The fired plates are the final product which is called metal supported SCR catalyst plate-type structures for De-NOx applications.
ix) Testing of the SCR Catalyst Plate Structures:
In order to confirm the efficiency of NOx conversion and specific erosion profiles, the fired SCR catalyst plates undergo NOx conversion test, air jet erosion test (erosion profile) and counter tests etc.
In NOx conversion test, the fired SCR catalyst plates of specific dimensions are inserted in a test rig in a manner that uniformity in the pitch between the plates plays are maintained. As per the testing protocol, around 11 number of SCR catalyst plates with a Z, S, V or any other profile having dimensions of 65mmx120mm are stacked in the test rig that confirmed a De-NOx efficiency in the range of 85 - 90% with a space velocity in the range of 1500 - 2000 per hour.
In case of air jet erosion test, the SCR catalyst plates with the dimension of 30mmx30mm is placed against the flow stream of air and abrasive sands with a velocity of 35m/s was allowed to hit by varying the angle between the flow stream and the position of the plate with multiple angles namely 15°, 30°, 45°, 60°, 75° & 90° respectively. The erosion rate of the SCR catalyst plates were in the range of 0.01 -0.05g/min comprising angles of impingement at specific levels of 15°, 30°, 45°, 60°, 75° & 90° respectively, in which the erosion increases with the increase in angle of impact until 900, angle at which the erosion was found to be maximum.
The process could be better understood in terms of examples as given in the below.

EXAMPLE 1:
In this example, the following steps are to be followed in order to fabricate metal wire mesh supported SCR (selective catalytic reduction) catalyst plate-type structure for the purpose of de-NOx applications. The following are the specific steps , i.e., i) specifying metallic wire mesh support structure material, ii) specifying the formulation of SCR catalyst material, iii) specifying the binder formulation for the SCR catalyst, iv) specifying the procedure for the preparation of SCR catalyst dough/paste/noodles, v) specifying the forming method & fabrication parameters, vi) specifying specific the profiling of SCR catalyst structure, vii) specifying the drying of the green SCR catalyst structures, viii) specifying the firing of the dried SCR catalysts structures so as to yield the final product, i.e., SCR catalyst plate-type structures, ix) Conducting the testing of the SCR catalyst plates to confirm specified levels of conversion efficiency of NOx gas, erosion resistance of the catalyst structure etc.

EXAMPLE 2:
In this example, most of the parameters remain the same except in few exceptions as described in the following:
I. Metal mesh support structure is altered
II. Binder formulation is altered
III. Casting speed is altered
IV. Profile of the plates is altered
V. Firing temperature is altered

EXAMPLE 3:
In this examples, most of the parameters remain the same as example 1 except in
few exceptions as described in the following: i) Metat mesh support structure is altered ii) Binder formulation is altered iii) Casting speed is altered iv) Profile of the plates is altered v) Firing temperature is altered

Viii) Testing of the final Product SCR Catalyst Plate Structure:
De-NOx Efficiency
Testing temperature SLPM (Standard liters per minute) De-NOx Efficiency
350° C 5 93-95
10 91-93
15 89-91
325° C 5 9T9I
10 89-91
~ ~ ~15 87-90
300°C 5 88-90
10 86-88
15~ " ~~ 84-86
Air jet erosion test
Test conditions Angle of impact Erosion rate (grams/minute)
Air and sand mixture flow 15° 0.015
stream velocity = 38 LPM 30° ~™~ 0.025
sand flow rate = 45° 0.039
2grams/min 605 0.045
7S5 0.058
905 0.066

WE CLAIM:
1. A process for fabrication of metallic wire-mesh supported by SCR catalyst
comprising:
preparing a binder formulation having 9 to 12% inorganic binder, 1 to 3% of organic
binder and 1 to 5% of polymeric binder,
mixing the binders with SCR catalyst to form either a dough, paste or noodles,
applying the SCR catalyst noodles on the surface of the selected metallic wire-mesh
structure,
subjecting the SCR catalyst structures to the step of profilation into various shapes in
green form,
drying of the green SCR catalyst structures,
firing of the dried SCR catalyst structure to remove organic and polymeric binders,
subjecting the fired SCR catalyst plates to the step of testing.
2. The process as claimed in claim 1, wherein the said metallic support material is stainless steel wire mEsh.
3. The process as claimed in claim 1, wherein the said SCR catalyst material is vanadia-based material that disperses in titania and other constituents such as oxide of tungstate and molybdenum having specific surface area in the range of 90-120 m2/g.
4. The process as claimed in claim 3, the binder system is a combination of: a) inorganic binder in the weight range of 9.0 - 12 %, b) organic binder in the weight range of 1-3 % and c) polymeric binder in the weight range of 1-5 % respectively, further, the inorganic binder comprise a mixture of a) clay (3-5 w%), b) bentonite {3-5 w%), c) glass fiber (1-3 w% and d) colloidal silica (0.5 - 1.0 w%) respectively. While the organic binder comprise carbomethoxy cellulose (CMC) in the range of 0.5 - 2.0 w%, which could be used either as 'solid powder' or in the form of an aqueous

solution, While the polymeric binder is a combination of a) poly-ethylene glycol (PEG) having molecular weight in the range of 400-1200, preferably around 600 ( 2-4 w%) and b) polyvinyl alcohol (PVA) having molecular weight in the range of 50,000-200,000, preferably around 125,000 (1-5 w%) respectively. PVA is to be used in the form of an aqueous solution only having concentration in the range of 1-5 w%.
5. A process as claimed in claim 1, wherein to prepare SCR catalyst in the form of 'dough' or 'paste', the SCR catalyst powder is first mixed with inorganic binder in desired proportions and then homogenised/mixed by using a ball mill machine for a period of 6-10 hours, resulting milled powder, which is further mixed with organic binder followed by polymeric binder in desired proportions by using a 'Sigma Blade Mixer' or 'Sigma Kneader Machine' for a period of another 1-2 hours thereafter resulting SCR catalyst paste or dough having moisture level in the range of 20-30 w% that is maintained by adding de-ionized water either separately or by adding de-ionized water with the polymeric binder, PVA, the SCR catalyst paste or dough is formed, the same is extruded in the form of noodles having the diameter in the range of 1-10 mm.
6. The process as claimed in claim 1, wherein the said SCR catalyst noodles are applied on the surface of the selected metallic wire mesh structure by using the so-called "Roller-assisted Casting Machine" by passing the selected wire mesh structure in between the two rollers in the said "Roller-assisted Casting Machine" and further through a set of rollers with a gradient of decreasing gap in the between the rollers in sequential manner in a manner that the SCR catalyst noodles are coated on the surface of the metallic wire mesh support structures with a desired thickness uniformly throughout the plate structure in a continuous mode thereby resulting green structures of the SCR catalyst plates.
7. The process as claimed in claim 1, wherein the derived SCR catalyst plate-type structure are profiled into numerous shapes like, "V", or "Z" or "S" etc. in the green form with the assistance of "Roller-assisted Casting Machine" having one set of roller

with the impression of specific profile, the profiles of which help to maintain desired pitch level of the plates in the module assembly, besides ease of convenience in maintaining physical array of assembled SCR catalyst plates in modules with predetermined design for actual De-NOx application/s.
8. The process as claimed in claim 7, wherein the said green SCR catalyst plate structure is dried in an oven (electrical or gas fired) at any set temperature in the temperature range of 60o-100°C for a period of 6-12 hours, which gives dried plates with a moisture level 2+1 w%.
9. The process as claimed in claim 8, wherein the dried SCR catalyst plates are fired at any set temperature in the temperature range of 550° - 650°C in a kiln (electrically heated or gas-fired or similar kilns) for a period of 3 - 6 hours holding at the set temperature by maintaining a rate of heating of 1-2°/minute and by maintaining a rate of cooling of 1-2°/minute, the fired plates are the final product which is called metal supported SCR catalyst plate-type structures for De-NOx applications including NOx control in coal-fired power plants.
10. The process as claimed in claim 9, wherein the said SCR catalyst plates has a conversion efficiency in the range of 85 - 95% having space velocity in the range of 1500 - 2000 per hour and with erosion rate in the range of 0.01 - 0.05g/min comprising angles of impingement at specific levels of 15°, 30°, 45°, 60°, 75° & 90° respectively.