Claims:WE CLAIM:

1. A corrosion resistant polymer coating comprises Resin mixed with hardner in a ratio of 2:1 to 4:1, wherein the Resin is selected from Novolac epoxy filled with ceramic and Novolac vinyl ester epoxy filled with glass flakes, and the Hardener includes Cycloaliphatic amines.

2. A method of preventing corrosion in FGD duct and chimney liner by applying polymer coating comprises the steps of:
- Surface preparation of the surface to be coated,
-Mixing of resin and hardner in a ratio of 2:1 to 4:1 for a time period of 10-15 minutes that a homogeneous mixture of resin and hardener is obtained,
- Applying prepared mixture over the surface and
- Curing the applied coating for about 7 days,
wherein the Resin is selected from Novolac epoxy filled with ceramic and Novolac vinyl ester epoxy filled with glass flakes, and the Hardener includes Cycloaliphatic amines.

3. The polymer coating and method for applying thereof as claimed in claims 1-2, wherein the hardner acts as curing agent.

4. The polymer coating and method for applying thereof as claimed in claims 1-3, wherein
the polymers are 100% solid by weight.

5. The method as claimed in claim 2, wherein the mixture of resin and hardner is applied over sand blasted surface by airless spray or hand roller or brush.

6. The method as claimed in claim 2, wherein the Curing of the applied coating is done for about 7 days.

7. The method as claimed in claims 2-6, wherein the polymer mixture having thickness of 1.5 mm to 2 mm is coated over the surface.

8. The polymer coating and method for applying thereof as claimed in claims 1-7, wherein the coating does not fail in the immersion atmosphere of 30% sulfuric acid at 700C for more than 1000 hours.

9. The polymer coating and method for applying thereof as claimed in claims 1-8, wherein the coating has the pull-off bond strength of ~3000 PSI.

10. The polymer coating and method for applying thereof as claimed in claims 1-9, wherein the coating looses ~60mg in taber wear test done for 3000 cycles and 1000kg load.
, Description:This application is modification/improvement of the main application number 1340/KOL/2015 of 28.04.2015

Title: Corrosion resistant polymer coating and method for applying thereof for preventing corrosion in FGD duct and Chimney liner

FIELD OF THE INVENTION:
[001] This present invention relates to the field of corrosion resistant polymer coating and method for applying thereof for preventing corrosion in FGD duct and Chimney liner. The main objective of this invention is to develop a corrosion resistant polymer coating for FGD duct and chimney liner which can replace comparatively expensive solution in the form of Titanium cladding.

BACKGROUND OF INVENTION/PRIOR ART:
[002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[003] Wet lime/limestone flue gas desulfurization technology has become one of the leading flue gas desulfurization techniques in many power plants around the world, owing to its advantages of high desulfurization efficiency, wide adaptation and long-run stability etc. However, it also brings about serious corrosion problems to the outlet duct and inner wall of stacks. In this way, it is indispensable to protect outlet duct and stacks from corrosion after the wet flue gas desulfurization (WFGD) system. Reference may be made to Figure 1 showing FGD in thermal power plant, which indicates the following features:
Economizer – 101
Bottom ash/slag collection – 102
Air heater – 103
Particulate collector – 104
Fly ash collection – 105
FGD absorber – 106
FGD gypsum collection – 107
Stack - 108

[004] Primary reason behind corrosion in FGD components is presence of SO2 in flue gas coming out of scrubber/absorber. Flue gas entering the FGD scrubber has a temperature in the range of 150-1700C, which is quenched to a lower temperature of around 60-700C before it enters to scrubber. To remove SO2 from the flue gas, lime stone slurry is sprayed, which comes in contact with flue gas and reacts with SO2. Gypsum is produced as a byproduct and processed flue gas leaves the scrubber. However, there is a residual SO2 present in flue gas leaving scrubber and temperature of flue gas is in the range of 700C. All these reasons contribute to severe corrosion of FGD duct stack liners due to formation of H2SO4.

[005] To avoid corrosion in FGD duct and chimney liners, Titanium cladded plates have been predominantly used in these areas. Titanium cladding is the process of joining Titanium plate and carbon steel plates by explosion bonding. Titanium cladded plates are generally imported to India. Hence complex process of manufacturing Titanium cladded plates and its import result in excessively higher price of these plates.

[006] On the other hand, polymer coatings possess excellent corrosion and chemical resistivity at comparatively lower cost. Hence as a cost reduction step, development of corrosion resistant polymer coating for FGD duct and chimney liner was taken up.

PRIOR ART OF THE INVENTION:
[007] Corrosion plays a predominant role in all the major industries that use corrosive materials mainly of chemical industries. Generally, corrosion may be controlled by adopting corrosion control methods. There are various types of corrosion control methods, among those polymer coatings over the medium mainly generates corrosion resistance to the base material, which contains toxic and hazardous materials that damage the environment, to an extent. These major commitments have led the researchers for the development of innovative polymer coating materials and methods which adopts carbon-based materials and nanocomposites. Recent developments indicate that mainly the polymer coatings have increased the attention of the industrial and research community due to its economic viability and improved applications. Generally, polymers hold a long carbon linkage chain which therefore is capable to block wider area of the metal surfaces over corrosion which is due to the adsorption property. The deposition of thin coating over the corrosive surface behaves as a barrier between both the metal surface and the environment for protecting such surfaces. These types of coatings can include urethane, epoxy, acrylic, silicone, natural or synthetic rubber, polyvinyl chloride, nitrocellulose, and phenolic resins.

[008] These coatings have been predominantly used in Marine applications and chemical industries. However, in recent years, Power plant industries have also immerged as a potent area for use of these coatings. One such component in power plants is condenser, which encounters severe sea water corrosion. To combat this corrosion, Titanium condenser tube sheet has been used mainly. But by realizing the potential of polymer coatings, BHEL R&D has worked in the direction of replacing titanium tube sheets with polymer coated tube sheets in condensers. A patent has been filed in this regard. Project was successfully completed and implement at one unit of Tuticorin Thermal Power Station, Tuticorin, Tamilnadu.

[009] Flue gases coming out of coal based power plant stacks contain many hazardous gases such as SOx and NOx, which are the main reason behind acid rains. Government earlier focused mainly on controlling particulate matters before releasing flue gas to the atmosphere, but it has become mandatory for a coal based power plant to have FGD system these days considering the environmental and health hazards associated with SOx. And as discussed earlier, due to its working principal and environment, FGD components experience severe corrosion issue.

[0010] As FGD system is new to Indian market, there has not been much of research or development works and the established developments were adopted conveniently. One of such adoption is in the form of Titanium cladding for prevention of corrosion in FGD outlet duct and chimney liner. Titanium cladded plates are produced by explosion bonding of Titanium plate and carbon steel plates and these are imported to India mainly for vendors. These factors result in higher price of Titanium cladded plates and in turn, overall higher cost of FGD.

[0011] In view of the above, the present invention has been introduced which can address the aforesaid shortcomings and serve the purpose efficiently.

OBJECTS OF THE INVENTION:
[0012] An objective of this invention is to provide an advanced polymer coating for preventing corrosion in FGD duct and chimney liner by replacing expensive Titanium cladding.

[0013] Another object of the invention is to provide corrosion resistant polymer coating and method for applying thereof for preventing corrosion in FGD duct and Chimney liner, which obviates shortcomings of the prior art(s).

[0014] Still another object of the invention is to provide corrosion resistant polymer coating and method for applying thereof for preventing corrosion in FGD duct and Chimney liner, which is cost effective.

[0015] Yet another object of the invention is to provide corrosion resistant polymer coating and method for applying thereof for preventing corrosion in FGD duct and Chimney liner, which is simple and serves the purpose effectively.

[0016] These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.

SUMMARY OF THE INVENTION:

[0017] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus/composition and a method as claimed in the present disclosure. Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.

[0018] According to the invention, there is provided a corrosion resistant polymer coating comprises Resin mixed with hardener in a ratio of 2:1 to 4:1, wherein the Resin is selected from Novolac epoxy filled with ceramic and Novolac vinyl ester epoxy filled with glass flakes, and the Hardener includes Cycloaliphatic amines.

[0019] Further, according to the invention, there is provided a method of preventing corrosion in FGD duct and chimney liner by applying polymer coating comprises the steps of:
- Surface preparation by sand blasting of the surface to be coated,
- Proper mixing of polymer resin and hardness in a ratio of 2:1 to 4:1,
- Applying prepared mixture over sand blasted surface and
- Curing the applied coating for about 7 days,
wherein the Resin is selected from Novolac epoxy filled with ceramic and Novolac vinyl ester epoxy filled with glass flakes, and the Hardener includes Cycloaliphatic amines.

[0020] The hardner acts as curing agent.
[0021] The polymers are 100% solid by weight.
[0022] The mixture of resin and hardner is applied over sand blasted surface by airless spray or hand roller or brush.
[0023] The Curing of the applied coating is done for about 7 days.
[0024] The coating does not fail in the immersion atmosphere of 30% sulfuric acid at 700C for more than 1000 hours.
[0025] The coating has the pull-off bond strength of ~3000 PSI.
[0026] The coating looses ~60mg in taber wear test done for 3000 cycles and 1000kg load.

[0027] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

[0028] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure.

[0029] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMAPANYING DRAWINGS:
[0030] The illustrated embodiments of the subject matter will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and processes that are consistent with the subject matter as claimed herein, wherein:-
Figure 1 shows: FGD in thermal power plant.
Figure 2 shows: A bar chart which depicts the weight loss of samples after completion of 1000 hrs of immersion testing.
Figure 3A shows: Samples before start of test.
Figure 3B shows: Samples after completion of test.
Figure 4A shows: Pull off adhesion tester.
Figure 4B shows: Pull off adhesion test sample.
Figure 5 shows: Shore hardness testing.
Figure 6A shows: Taber wear test equipment.
Figure 6B shows: Taber wear titanium sample.
Figure 6C shows: Taber wear Polymer coated sample.

[0031] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAIL DESCRIPTION OF THE INVENTION OF THE PREFERRED EMBODIMENT(S) WITH REFERENCE TO THE ACCOMPANYING DRAWING(S):

[0032] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure.

[0033] The proposed application relates to an invention pertaining to a technology regarding corrosion resistant polymer coatings.

[0034] Various resins were taken for experiments and development including Novolac, Novolac epoxy and Novolac vinyl ester epoxy. However, the resin Novolac failed at high temperature. Therefore, finally Novolac epoxy and Novolac vinyl ester epoxy were selected to prepare the polymer coating of invention.

[0035] These polymers are either without fillers or loaded with glass flakes/ceramics. These polymers have two parts i.e. Base/Resin and hardener. Both these components i.e. Base/Resin and hardener are mixed in a certain ratio either by weight or by volume for coating. Higher amount of hardener than the prescribed ratio could reduce the pot life and lower amount of hardener could result in unreacted resin molecules. Both the cases were avoided to get the best result.

[0036] Samples were prepared for Accelerated immersion testing, Taber wear testing, Pull-off bond strength testing and shore hardness testing. Acid spray testing and accelerated immersion testing of these polymers were done along with Titanium samples to study the comparative corrosion resistance. Evaluation of the samples was done post completion of these testings. It was observed that Novolac epoxy filled with ceramic and Novolac vinyl ester epoxy filled with glass flake sustained sever acidic corrosion and shown satisfactory result in all the experiments. Hence, developed coating with Novolac epoxy filled with ceramic and Novolac vinyl ester epoxy filled with glass flake can replace existing Titanium cladding from FGD duct and chimney liner and serve the purpose effectively.

Coating methodology:

[0037] Resins and hardeners are mixed in a certain ratio to get a homogeneous mixture.
[0038] Resin can be selected from Novolac epoxy filled with ceramic and Novolac vinyl ester epoxy filled with glass flake. The Hardener includes Cycloaliphatic amines, which acts as curing agent.

[0039] Resin is mixed with hardener in a ratio of 2:1 to 4:1 for a time period of 10-15 minutes.

[0040] The mixing is carried out under atmospheric condition.

[0041] This mixture was flowy at start and slowly starts setting hard as soon as resin and hardener starts reacting with each other. Time taken for a polymer from mixing resin and hardener to getting set is known as Pot life. Each polymer has Pot life of approximately 30-40 Minutes.

[0042] Thus, the method of preventing corrosion in FGD duct and chimney liner by applying polymer coating comprises the following steps:
- Surface preparation by sand blasting of the surface to be coated,
- Proper mixing of polymer resin and hardner,
- Applying prepared mixture over sand blasted surface by airless spray or hand roller or brush, and
- Curing the applied coating for about 7 days.

Coating application:

[0043] Prepared polymer mixture having thickness of 1.5 mm to 2 mm is coated on the base material to make the test samples ready. Carbon steel rods and plates were used as the base material. Round rod samples were used to make the test samples for accelerated immersion testing, whereas flat samples were used to make the test samples for bond test, shore hardness test and taber abrasion test.

[0044] Coating could be applied either by airless spray, hand roller or bush. Here, coating was applied on the test samples by brush to a thickness of ~2mm. All the edges of the samples were also carefully coated as polymer coating tends to form lower thickness at the sharp corners. Eventually applied coating was cured for around 7 days.

WORKING EXAMPLE:

[0045] The method of preventing corrosion by applying polymer coating comprises the following steps:
- Surface preparation by sand blasting of the surface to be coated,
- Proper mixing of Novolac epoxy filled with ceramic and curing agent i.e. Cycloaliphatic amines in a ratio of 3:1,
- Applying prepared mixture over sand blasted surface by brush, and
- Curing the applied coating for 7 days.

TESTING:

I-Accelerated Immersion corrosion test (ASTM D543):
[0046] As the polymers were to be tested for their chemical and corrosion resistance, Immersion testing as per the ASTM D543 was carried out on test samples of size 16mm dia and 180mm length. This testing was carried out in 30% sulfuric acid solution with pH value of approximately 0.5 at 700C for 1000 hours. All the samples were measured for their weight before start of test with a weighing scale of 0.01gm accuracy. A Titanium sample was also tested along with 4 number of polymer samples to study the comparative results.

[0047] Solution of 30% sulfuric acid was replaced after every 200hrs and stir to the solution was given on daily basis. Samples were taken out after completion of every 200 Hrs of testing for weight measurement and inspection was done to check for corrosion traces. A bar chart can be seen in figure 2, which depicts the weight loss of samples after completion of 1000 hrs of immersion testing.
[0048] It was observed that Titanium lost its weight of approximately 48gms from initial weight of 208gms in 1000hrs. Small pits were also formed on its surface due to severe corrosion resulting in very rough surface. However, samples coated with Novolac vinyl ester with glass filler and Novolac epoxy with Ceramic filler showed no traces of corrosion and weight loss. Sample coated with Novolac epoxy without any filler developed blisters and crack. This coating failed and shown a weight loss of approximately 4gms.

[0049] Reference may be made to Figure 3A and 3B for Samples before start of test and Samples after completion of test respectively.

II-Pull off adhesion test (ASTM D4541):

[0050] One of the critical property of a polymer coating is pull-off adhesion strength or known as bond strength. To conduct this test, a dolly of 15mm dia was used which was glued to a flat carbon steel plate and later on pulled by a hydraulic puller in order to obtain the pull off adhesion strength. To prepare the samples, carbon steel flat plates of 50x50x5mm were first sand blasted according to surface preparation standard SSPC-SP 5. Dolly also was sand blasted along with the carbon steel plates. Now polymer was applied on the sand blasted surfaces of dolly and carbon steel plate and both the faces were glued together. Once the polymer was cured and dolly was set, pull off adhesion testing was carried out on all the samples. A table below shows the different pull off adhesion strength readings. Reference may be made to Figure 4A and 4B indicating Pull off adhesion tester and Pull off adhesion test sample respectively.

Material Bond strength (PSI)
Novolac epoxy 3076
Novolac epoxy with Ceramic filler 2874
Novolac vinyl ester with glass filler 2981

III-Shore hardness - Scale D test (ASTM D2240):
[0051] Shore hardness of the polymer samples were tested on scale D though digital shore hardness tester as illustrated in Figure 5. Observed shore hardness is in the range of 80-85 which is satisfactory.

IV-Taber wear test (ASTM D4060):
[0052] Taber wear test is done to check the wear resistivity of the plastics and polymers. Samples were prepared by applying polymer coating on a 100x100x3mm carbon steel plates. Taber wear test was done for 3000 cycles on a load of 1000kg. Now, reference may be made to Figure 6A, 6B and 6C indicating Taber wear test equipment, Taber wear titanium sample and Taber wear Polymer coated sample respectively.

Observed loss of different polymers and titanium is given below.
Material Loss(gm)
Titanium 32
Novolac epoxy 40
Novolac epoxy with Ceramic filler 55
Novolac vinyl ester with glass filler 58

[0053] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.

[0054] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all groups used in the appended claims.

[0055] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogue to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances, where a convention analogous to “at least one of A, B, or C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.

[0056] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.

[0057] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and functions, or alternatives thereof, may be combined into other systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims.

[0058] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.

[0059] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.