White Papers & Presentations Improving the Performance of Coal-Fired Power Plants with Advanced Wear Protection Technologies Download PDF Here. (900 KB)  The Challenge Power production facilities are under ever-increasing pressure to reduce production costs to compete in a market environment that is more complex today than it’s ever been in the past. Failure to effectively reduce production costs to a competitive level means reduced profits for each MW-hr sold, and may result in reduced dispatch load—a double jeopardy in a market plagued by over capacity. The situation is further complicated by the need for production facilities to balance costs against compliance with a growing number of stringent air quality restrictions for NOx, SOx, Mercury, and particulates. These challenges often manifest themselves in a conflicting effort to reduce day-to-day operating costs while managing offsetting capital investment and maintenance costs. The Conflict Before the days of the Clean Air Act Amendment and deregulation, power producers were relatively unconstrained in the fuels, technologies, and production strategies they employed to meet the market demand for power. Their primary objective was to provide a reliable source of quality power. Whatever equipment was in place per original design could be used without a great deal of concern for the quality or type of fuel being burned. Original equipment design took into account the planned fuel formulation, and auxiliary equipment was selected primarily based upon these original specifications. Equipment deterioration was accepted as a normal cost of operation, and was dealt with through frequent and relatively long maintenance outages. In recent years, however, competitive market conditions combined with tough emissions standards have created entirely new challenges that generate potential conflicts between fuel procurement, asset managers, and maintenance teams. Fuel procurement teams are rewarded for saving a nickel per ton even if the cheaper fuel has higher than originally specified Sulphur or other undesirable constituents that may cause increased rates of equipment deterioration and emissions. Asset managers are confronted with the need to invest in SCRs, scrubbers, and other high-cost assets in order to comply with tougher emissions restrictions. Meanwhile, maintenance teams that have experienced significant reductions in staff are striving to increase operating runs between maintenance windows. Because fuel and emissions management assets represent such a large percentage of operating costs, maintenance teams are often left with the conflicting challenge of keeping equipment online for longer periods when changes in fuel and equipment might otherwise increase equipment wear rates. The Consequences The result is that maintenance teams are expected to do more with less. Equipment that was wearing out every 12 to 18 months, is now being asked to run for 24 – 36 months or more. When combined with new fuel specifications and the addition of emissions management systems, some of the critical components are tending towards a shorter life rather than a longer one. This conflicting challenge manifests itself in highly undesirable consequences, including emergency calls to the Maintenance Superintendent at 2:00 AM, as well as forced and otherwise unplanned outages that negatively impact overall profitability. While it might seem obvious that the solution involves a holistic approach to regulatory, operations, and maintenance objectives, the reality is that maintenance – typically managed at the plant level -- often takes a back seat to fuel and emissions management due to their relative magnitudes and visibility at the corporate offices. Maintenance teams are, therefore, frequently asked to manage many of the old problems as well as the new ones created by changes in fuel specifications and additions to or changes in emissions management systems. Many maintenance teams have addressed these conflicting challenges – and others are beginning to do so – by exploring innovative value-added ways to invest their maintenance budgets in technologies designed to squeeze longer life from mission critical equipment subject to the wear mechanisms present in a typical power plant. While many maintenance teams have embraced this approach on an ad hoc basis, it will be more and more important for the successful thought leaders in the industry to take a more holistic approach to increasing equipment longevity. Those who have embraced these innovative life-extension technologies at the plant level, could impact the overall success of their companies by communicating their own successes to other plants in their system as well as to management at headquarters. Further, the employment of innovative life-extension technologies as a part of new systems design will further improve the competitive position of these thought-leaders. The Problem Areas Equipment wear is generally caused by one or a combination of five primary mechanisms: Erosion Corrosion Abrasion Impact Adhesion (galling and fretting) In a coal-fired power plant, these mechanisms can cause unnecessary maintenance activities/expenditures and system downtime or derates in some or all of the following areas: Fans (ID, FD, Hot-Primary Air, Gas recirc, Mechanical Collectors, Booster/Scrubbers, Pulverizer exhaust, etc.) Burners, Burner Tubes, and Burner tips Boiler and Steam Generator Tubes Pulverizers Ash and Coal Conveyance Systems (tubes, pipes, elbows) Fans Fans, depending upon their function and location in the system, are subject to a combination of the previously listed wear mechanisms. This situation represents a scenario referred to as “Complex Wear”. An ID fan, for example, will frequently experience erosion due to typical ash loading, as well as impact from clinkers. Under certain operating conditions, the same fan will experience corrosive attack from caustics entrained in the ash stream. Erosion and other wear mechanisms can cause significant reduction in life-expectancy, leading to excessive maintenance expenditures, frequent unit derates and downtime, as well as increased risk of unplanned or forced outage.   Figure 1. Radial flow fan blade showing wear after 3 months service. Traditional attempts to reduce erosion of fan components includes the application of large amounts of Chrome carbide weld overlay or in some cases of simple blade geometry, the application of silica or alumina (ceramic) or even Tungsten carbide tiles. Chrome carbide weld overlay is limited in its ability to protect against erosion, and has the added challenge of being extremely heavy for a given amount of erosion protection. Ceramic and Tungsten carbide tiles are also relatively heavy, and have the added challenge of limited bond strength which can add to the risk of catastrophic damage resulting from tile loss. The weight issue related to CrC weld overlay and tiles can be of great concern considering the stress and balance implications of a large rotating fan. Burners Burner tubes and tips may be subject to erosion depending upon the type of coal being used and the velocities and volume of the coal passing through the burner. Depending upon the flow characteristics of the coal, burners are frequently subjected to a wear mechanism called “roping”. Burner wear can result in the need to replace burners at regular intervals in order to maintain even flow distribution across burner groups. LoNOx burners are particularly sensitive to erosion since optimum burn temperatures and distribution is highly dependent upon burner component geometry. Even the slightest amount of erosion can cause a loss of optimum geometry resulting in an undesirable increase in NOx emissions.   Figure 2. Typical Burner Tube and Burner Tip Attempts to protect burners have included the application of ceramic tiles. Ceramic tiles, however, are limited to areas that are not subject to large thermal shock and thermal variations. Such thermal shock stresses the bonding limits of tile, and increases the risk of failure. The relatively large thickness of ceramic tiles also causes a restriction of flow area, which limits their use when flow cross-section is critical to optimum burner operation.     Figure 3. Sensitive Geometry of LoNOx Burners   Figure 4. Typical Superheater Tube Leg with a Direct Application of Conforma Clad Tungsten Carbide Cladding Boiler and Steam Generator Tubes   Boiler tubes in certain areas are subject to impingement of hot burning coal and ash particles. Depending upon the location of the tubes and the flow characteristics throughout, erosion may result in the need for regular replacement of boiler tubes. Highly susceptible areas are typically either replaced frequently or are protected with sacrificial tube protectors. Direct application of protective devices to boiler tubes are not generally successful due to thermal shock issues, geometry, and Dissimilar Metal Weld (DMW) issues. In some steam generator applications, the use of costly Hammertek elbows has been employed. Pulverizers Pulverizers come in all shapes, sizes, designs, and methods of pulverization. Housings, liners, ledge covers, deflectors, clips and pegs, nuts, and other pulverizer components are subject to some of the most continuous erosion and abrasion wear of any system in the plant. Typical solutions include the use of hard alloys in sacrificial applications. These sacrificial components are replaced on a regular basis.   Figure 5. Vertical Spindle Mill and Bowl Mill Pulverizer Housings and Deflectors Ash and Coal Conveyance Systems Pipes, tubes, and especially elbows are often subject to severe erosion wear. Depending upon the size, shape, and critical nature of the flow area, application of ceramic tiles is sometimes very successful. However, tile will not provide a reliable solution in many cases where geometry is complex, radii are tight, and/or thermal shock is present.   Figure 6. Material Conveyance Systems   The Solution Extending the usable life of critical system components such as fans, burners, pulverizers, and boiler tubes will enable operators to increase unit availability, productivity, profitability, and competitiveness of equipment owners. Conventional coatings such as plasma spray, HVOF, DGun, and Chrome carbide have been unable to effectively protect equipment against many of the wear issues facing power equipment maintenance teams. In both laboratory and field application testing, Conforma Clad’s proprietary thin layer infiltration brazed Tungsten carbide cladding technology has proven to outperform virtually all other wear protection solutions in applications where weight, balance, resistance to thermal shock, thickness, thickness consistency, and/or applicability to complex geometries is a factor. All of the five equipment categories referred to above typically fall into this category. What Makes it Different? Conforma Clad WC-200 combines the hardness of Tungsten carbide with the toughness of a proprietary metal matrix into a flexible cloth that is applied to the component to be protected then infiltration brazed to create a true metallurgical bond with a strength of approximately 70,000 PSI. The result is a tough yet hard protective cladding that will not spall from impact or from differential component thermal expansion, is relatively lightweight, very thin, and extremely consistent in thickness. The following is a high-level description of how Conforma Clad WC cladding is applied. Mix proprietary combination of materials to create the desired wear characteristics to create a sort of “pasta dough” The dough is rolled into a cloth with specified weight and density depending upon the application and desired cladding characteristics The cloth is applied to the component with application-specific brazing compound The component is then fixtured and placed into an inert vacuum brazing furnace for specified period   Figure 7. Conforma Clad WC Application Process What Does it Look Like? The result is a component with a consistent thickness of tough/hard cladding. The following micrograph shows the even layer (0.060”) of cladding, the bond line between the cladding, and the substrate. Because there is minimal dilution of the cladding from the substrate, this cladding will have a linear wear rate as it wears away. That is, the last .005” will wear at the same rate as the first .005”.     Figure 8. Photomicrograph of Conforma Clad WC cladding Features Wear Resistance > 70%+ Tungsten Carbide Loading > 72+ Rockwell Hardness Durability > 70,000+ psi Metallurgical Bond > High Inter-Particle Bond Strength Predictable Life Consistent Thickness and Density Minimal Dilution No Interconnected Porosity or Check-Cracking How Does it Perform in the Lab? 1/16 inch thickness Conforma Clad WC has the equivalent wear resistance of 1 inch of Chrome carbide weld overlay at 1/10th the weight. In other words, pound for pound, WC outperforms Chrome carbide by 10X. This is a critical factor on rotating equipment such as fans, and equipment where flow area is critical, such as burner tubes. 1/16 inch of Conforma Clad WC has the equivalent wear resistance of 3 inches Carbon Steel at 1/80th the weight. Laboratory Results – Abrasion Resistance Standard testing for abrasion resistance was performed in accordance with ASTM G65. This test method is used to determine abrasion rates. The following chart summarizes the abrasion performance of Conforma Clad WC200 and WC210 as compared against several alternative abrasion resistant applications. ASTM G65 Results Sand Abrasion Measures Volume loss (mm3), DV Abrasion Resistance Factor (ARF) = 1/DV     Figure 9. Comparative Abrasion Resistance (G65) Laboratory Results – Erosion Resistance In November 1988, EPRI (in conjunction with the Westinghouse Research and Development Center--WRDC) performed a field-based “rainbow” ID fan comparison of Conforma Clad WC 200 against ten other erosion resistant coatings, including D-Gun, Plasma spray, weld overlay, and Chrome plating. The results of this EPRI analysis are summarized below. Details of this study (Report CS-6068, Project 1649-4 Nov. 1988) are available upon request. Upon completion of the field testing program, the WRDC concluded that, “Conforma Clad’s Tungsten carbide material displays superior erosion resistance.” The EPRI test team concluded the following: “Furnace brazed Conforma Clad Tungsten carbide offers erosion protection equivalent to about three inches of steel at 1/50th the weight.” “Based on the many advantages, we have used Conforma Clad as part of the EPRI field replaceable armoring system.” “The best performing material was Conforma Clad’s Tungsten carbide. The cladding stayed on the four test blades better than the other materials.” “Conforma Clad has the highest resistance to attack from fly ash.” The following chart summarizes the results of the data collected during the 1988 EPRI/WRDC field study.     Figure 10. Comparative Erosion Resistance (G76) Laboratory Results – Corrosion Resistance Laboratory analysis of three different formulations of WC cladding shows that Conforma Clad cladding performs better than 17-4PH and 316L in both Sulfuric and Hydrochloric acid environments. Details of this analysis, performed in accordance with ASTM G31 procedures, are available upon request.      Figure 11. Comparative Corrosion Resistance (ASTM G31) Laboratory Results – Cladding Bond Strength Laboratory of three different formulations of WC cladding shows that Conforma Clad’s metallurgically bonded WC cladding consistently exceeds a bond strength of 70,000 PSI. This exceeds the bond strength of most flame spray applications by a factor of 10.     Figure 12. Comparative Bond Strength How Does it Perform In Real Life? TVA Kingston Rainbow Test TVA Kingston Station has several Induced Draft (ID) fans which are located upstream of their precipitators. Prior to 1999, this condition resulted in severe ash loading on the fans precipitating the need for complete fan overhaul about every 12 – 14 months. In 1999, new soot blowers were installed, driving the fan overhaul cycle down to 9 months. After running for this period, fan blades, center hub, and supporting hardware had been eroded so badly that the unit reliability was at risk. This frequent overhaul requirement was very costly, as it required several man-days of labor, plus parts, and required that an otherwise (24/7) base loaded system would require a derate. In order to identify potential solutions to this challenge, TVA’s Energy Research and Technology Applications (ER&TA) Group teamed up with EPRI to perform additional field testing of various protective coating solutions. Approximately one dozen suppliers were asked to propose their solution, nearly half of whom declined due to the severity of the wear environment defined in the test specifications. The remaining six suppliers offered test solutions including Carbon Steel, Tungsten carbide composites, Tungsten carbide thermal sprays, and Chrome carbide weld overlay. Conforma Clad offered its flexible cloth infiltration brazed Tungsten carbide application. Six different solutions were applied to the blades of a double-inlet single-exhaust 400KCFM Westinghouse model 16MVID Induced Draft fan, which was then placed into severe wear service. After 60 days of operation, only the four blades clad with Conforma Clad WC infiltration brazed Tungsten carbide showed no visible signs of wear. All other test specimens showed complete wear-through of the protective coating, and were immediately removed from the fan. The results of this test predict a fan blade life of 24 – 36 months with Conforma Clad versus the previous runtime of approximately nine months. The figure below shows photographs of the blades after 60 days of operation comparing their relative wear.     Figure 13. TVA/EPRI Rainbow Test Results Other Field Studies in Process After performing their own independent laboratory analyses similar to those presented above, a major manufacturer of LoNOx burners has determined that the performance characteristics of Conforma Clad WC infiltration brazed cladding exceed that of all other alternatives tested. This OEM has consequently contracted with Conforma Clad for wear protection on several of their burner components, including flame spreaders, flame stabilizers, support tubes, and venturis. Several of these burner components have been in service for more than a year, and show minimal wear. Conclusion Plant maintenance teams are experiencing greater and greater pressures to reduce the cost of maintaining mission critical equipment, and are expected to use innovative methods to extend the operating period between unit shutdowns. There are technologies available that have proven their ability, in both the laboratory and in the field, to provide substantial protection against some of the most common causes of aggressive equipment wear present in a coal-fired power plant. Conforma Clad, because of its proven ability to extend equipment life cycles, can enable asset managers to capitalize equipment expenditures through upgrade programs that would otherwise be categorized as maintenance expense. While such an approach may not create immediate cash flow improvement, it does have the benefit of enhancing reported income streams while offering owners the ability to project higher cash flows for future years. This added benefit of Conforma Clad life extension upgrade solutions can play a critical role in the evaluation process when you or another manager are negotiating extended or new longer term debt instruments in support of business growth. The additional benefit of added market confidence results from the ability of Conforma Clad wear solutions to reduce the risk of unscheduled or otherwise forced outages driven by uncontrollable and unpredictable equipment wear. Such technologies as Conforma Clad’s WC infiltration brazed Tungsten carbide cladding have undergone and passed the rigorous scrutiny of leading industry innovators such as TVA and EPRI in order to prove their effectiveness in the industry. Others before you have played “the Guinea Pig” over more than a decade so that you can benefit from this advanced wear resistance technology without the risk associated with being a technology pioneer.