Robert Howard describes how silicon carbide burner components are a proven technology for coal fired power plants.
Coal fired power plants now have the answer for burner system components failing due to heat deformation or coal particle erosion. Burner nozzles, tips, inserts and protection tubes made from Ceraforte experience extended life times of up to 2-3 times in operation and are backwards compatible with all burner systems. Ceraforte is suited to replace steel components that fail in the first four years of operation due to heat deformation and wear.
Elkem Silicon Materials has developed the Ceraforte family of materials through extensive testing, both in their laboratories and in industrial applications. Focusing on properties such as strength, wear and chemical resistance and high temperatures operations up to 1500°C, Ceraforte is designed to be a 'drop in' replacement for steel in burner systems.
Enhancing aggregate properties
Components are monolithically cast from a proprietary mortar with a microsilica binder that locks in place the Silicon Carbide aggregate. The binder is specially designed to enhance the aggregate properties and ensure the extreme density of the structure while allowing enough free flow to cast complex shapes. Once cast, the parts are pre-fired for up to seven days and ready for installation at the customer site.
Originally installed in Elkem's own foundries in Norway, the company soon branched out in the early 1990s to supply the Aluminum, Ferro, Cement and Incineration industries with specialty high temperature wear products marketed under the Ceramite brand. These products set the standards for crucibles, charging pipes, high temperature ducts, cement kilns, burner tubes, TAD Dampers etc, and are found in all major markets including China, India, North America, Europe, Africa and the Middle East.
Elkem began working with the power industry in the late 1990s, focusing mostly on coal and ash handling systems, but recognised the need for more complex shapes to fit in the burner system. This required further development to meet the environment found in the burner: High temperature variation from front to back, temperature spikes, multiple cold and hot starts and the mechanical strength needed to survive as a 'moving' part. After several years of development, Elkem started casting its first burner components from Ceraforte in 2002 in South Africa.
"The silicon carbide based material is formulated to be resistant to thermal shock and heat damage and to have high abrasion resistance," says Alan Newall, who was the first to design Ceraforte burners in 2002. "Unique among all high temperature materials tested, Elkem Ceraforte actually increases in strength up to 1500°C and can be cast in any shape I need."
He now heads both the global design and manufacturing group responsible for Ceraforte. The team converts customer steel drawings to Ceraforte and assists customers in designing Ceraforte products.
"Ceraforte has some rules that you have to obey," says Alan. "Minimum wall thicknesses begin at 25mm, which is thicker than steel, but we can then eliminate most of the structural elements in steel components used to maintain its shape against heat deformation. This results in a simpler, streamlined part and ensures cross sectional areas which are equivalent to steels, important in burners where air flow speed is critical."
Over the years, the product design team has settled on a few simple design technologies which customers can then build upon incorporating their own IP. For burner nozzles, for example, Elkem Ceraforte has two basic designs: burner nozzle inserts and complete nozzles. The inserts consist of the splitter plates and a locking pin mount which connects it to the outershell and is the mostly used in retrofits for tilting burners. Complete nozzles are best suited for static systems or new designs. For all components, the customer has final engineering authority and owns their own IP. Elkem Ceraforte casts to the customers design and provides engineering input on an 'as needed basis', but is able to provide full design services for those customers who want the additional support.
Elkem Ceraforte has been installed in 700+ burner systems in Africa, Europe and North America since 2002, and to date, not one burner nozzle, tip or insert has failed in operation.
"Problems sometimes occur such as erosion due to a partially blocked nozzle," says Alan. "This effectively reduces the cross sectional area of the nozzle with a commensurate increase in air velocity which can cause abnormal wear."
Additionally, cracks have been observed in some nozzles where the wall thickness was thinner than recommended. The structural integrity of the nozzles was not impacted and are still in operation.
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Robert Howard is with Elkem Silicon Materials, Kristiansand, Norway. www.elkem.no
