Materials technology is key to efficient wear protcetion & longer life of power generation plant
- 04 June 2012
- Product News
Wear protection is one of the key technologies in helping operators meet the requirements for reliable, efficient operation of equipment in the power generation industry. However, the process involves much more than the application of hard metal deposits onto process equipment using traditional welding methods. In coal fired power stations, with their conveyor systems, transfer chutes, pulverising mills, bunkers, tanks and pipework- et al, there is no universal 'one- size- fits- all solution', due to the differing levels of impact, friction and sliding induced abrasion experienced at various points in the coal processing and feeding system.
Every installation or equipment type in the power generation sector that requires wear protection has its own specific requirements in terms of lining material. These materials are constantly being uprated or replaced with newer, more efficient types that more effectively combat the abrasive effects of coal, biomass, secondary refuse or waste derived fuels and the residual ash created, leading to continually increasing warranty periods – some of the order of 10-12 years.
In this article, John Connolly, MD of wear protection specialist, Kingfisher Industrial discusses the specification and use of new lining materials on equipment used in power generation, and outlines an actual case study in the power generation sector resulting from their successful application.
"With ever increasing targets for plant availability and efficiency of operations, ensuring that plant and equipment is protected against the cyclical effects of conveyance of materials is vital. Nowhere is the process more important than in coal fired power stations, where all operations from coal reception to boiler, and onward from the boiler with ash discharge are affected.
At the start of the process, Reception Hoppers need to be protected, not only against the effects of the coal itself, but also against foreign particles in the fuel: metallic, wood, and other debris.
To counter the effects of this harsh combination, we have developed a two-stage process of lining the coal reception hoppers with a combination of K-FLOW ferritic stainless steel and also our K-PLAS polyethylene lining systems. These materials are used in various grades and various thicknesses to successfully protect against the impact and friction induced abrasive wear associated with discharging coal from rail wagons, trucks and bulk cargo ships.
Applied using traditional welding and mechanical fixing, providing a totally seamless lining inside the hoppers, K-FLOW delivers a high degree of wear protection, due to its true hardness of approximately 240 Brinell. It also has a very low coefficient of friction, as the stainless steel surface polishes in service. In addition, the fact that the lining is fully welded prevents any internal corrosion taking place on the internal steel substrate.
K-PLAS, the complementary lining to K-FLOW in the hoppers, is a high performance thermoplastic with a crystallite molecular structure that has a greater density than many other plastics produced. With its main characteristics of abrasion resistance, high impact strength and an extremely low coefficient of friction, K-PLAS is ideally suited to counter the problems incurred when handling abrasive and 'sticky' substances in gravity fed applications in bulk handling industries.
From the reception hoppers coal is fed via a conveyor belt through a series of transfer chutes to the station bunkers. As the transfer chutes are subject to impact, friction and sliding induced abrasion, we have lined these units with our ceramic range of lining materials. This combination of K-ALOX, K-BAS and K-ZAS materials takes into account the differing levels of wear at various points in the transfer chutes. The linings are supplied in various thicknesses, guaranteeing long term protection (10-12 years-plus) against perforation of the fabrication, and against any discharge within the surrounding areas, thus avoiding potential accidents and reducing clean up costs.
K-ALOX is a high alumina ceramic lining system that offers excellent resistance against all forms of abrasion, and also superior resistance to corrosion and chemicals. By applying this protection system, we know that we can extend the life of transfer chutes by several factors, compared with conventional methods of wear protection using stainless or hardened steel liner plates.
Complementing K-ALOX is the K-BAS cast basalt lining system. K-BAS is an extremely hard and smooth material that is resistant to most acids and alkalis. K-ZAS, the third Kingfisher lining used on the transfer chutes, is a fused corundum system rated nine on the MOHS hardness scale. Ideally suited to the protection of plant and equipment encountering severe abrasion and erosion, K-ZAS offers the added benefit of excellent thermal shock resistance.
The station coal bunkers, which are fed from a series of transfer and tripper chutes, are another area that can be optimised using wear protection; not only in terms of achieving longer life, but also increased mass flow to provide higher discharge into the feeders to the coal mill. In this area we have once again employed our K-FLOW ferritic stainless steel, applied using traditional welding and mechanical fixing. In conjunction with this lining we have also, in a number of projects, redesigned some of the internal geometry of the bunkers using radius sections as well re-profiling the bunker outlet to achieve customer objectives of improving mass flow. This is all part of a process to guarantee that the correct amount of tonnage is fed through to the coal mill, to ensure an efficient milling process, and correct distribution of coal feed up to the burners.
When the coal reaches the mill, it is ground down to a micron sized powder, which is then dried and finally exits the mill via pulverised fuel outlets. This process of grinding or pulverising coal causes severe abrasion to virtually all internals areas of the mill, and the classification system used to separate the finely ground fuel, and also fuel that needs to be reprocessed due to its non-compliant particle size. Be it mill feed chutes, grinding wheels, tables, rings, classifier blades (static & dynamic) reject cones and outlet ports, they all suffer from both impact and friction induced abrasion. Using a combination of both ceramic and metallic liners this equipment can be protected to eliminate the risk of continual downtime.
Typically, operators require continual mill operating performance in excess of 8,000hrs, between re-builds, which gives them the flexibility to maintain the bank of mills they have within the station fleet. In supplying parts and liners such as K-HARD castings, K-CLAD chromium carbide deposit plate and weld overlay systems, along with our K-ALOX ceramic liners, we have achieved significant improvements on the required operating cycles.
K-HARD is a white cast iron complemented with either an added nickel or chrome alloy content. As the name implies, K-HARD has extreme hardness characteristics (HB500) to counter impact, sliding and friction- induced abrasion in pneumatic, mechanical or hydraulic states. The material offers the added advantages that it can be easily fixed or replaced, and that castings can cater for complex forms.
K-CLAD is a chromium carbide deposit that can be used to extend plant and equipment life in virtually every area of industrial processes where bulk solids materials are being conveyed or processed. With a hardness rating of between 550 and 650 BHN, K-CLAD is the ideal liner to protect both light and heavy industrial processes against impact and sliding induced abrasion.
The wear protected pipework eventually conveys the pulverised coal to a splitter: bifurcator, trifurcator, or rifle box assembly. These are mass flow devices that divide the coal flow equally between two or three legs. Because of the amount of wear that takes place in these legs, and in the associated pipework itself, all are lined with Kingfisher's range of K-ALOX, K-BAS, K-CAST, K-SIL ceramic and K-HARD metallic materials. These liners offer the key benefit of countering the different amounts of wear that occur in bend sections, trifurcators, non- return valves (NRV's) and within the burners, where abrasion is at its greatest.
K-CAST is a monolithic ceramic lining material that offers the benefit that it can be applied by trowel or by casting to provide a flexible solution to a wide variety of abrasion induced problems.
At the last interface, prior to combustion, fuel is fed into the boiler via strategically positioned burners, which encounter extreme wear and heat radiation. Kingfisher plays an important role in ensuring that these components are protected against the constant effect of conveying fuels at velocities up to 35 mps, and the radiant heat associated with the combustion process itself. The use of bespoke ceramic systems has been recognised as the most suitable solution to this problem. This is achieved by designing parts that match the contours of the assemblies, whilst ensuring the correct internal geometries are maintained to compliment the need for OEM's unique operating processes.
Problems of abrasion and wear do not cease after the combustion cycle, due to the requirement to handle hot clinker and coarse ash. Recently Kingfisher has provided a wear protection solution for a UK power station solution where two other competitive lining systems failed. The Kingfisher solution, the company's K-ZAS Ceramic Liner system is effectively handling the severe abrasion and corrosion resulting from conveying hot coarse clinker to an ash reception hopper.
Kingfisher was called in by the plant engineer at the power station following unsuccessful trials of both cast basalt and hi-chrome castings as lining materials for handling the hot clinker. The problem was that, although the course clinker was suspended and conveyed hydraulically, the internal surface of the pipeline was subjected to severe abrasion and erosion.
Having had previous experience with this type of application, Kingfisher recommended its 25mm thick K-ZAS ceramic lining system. The system was supplied in cylinder form, to ensure that internal concentricity was maintained, and that the excellent impact and sliding wear resistant characteristics of the K-ZAS liners were employed to the full. Subsequent operation of the system has shown that the K-ZAS liners considerably outperform the previously used wear resistant system."