Burner wear components for coal fired power plants

Paul Boughton

Robert Howard describes the negative impact of eroded and deformed burner nozzles and core air tubes.

Coal-fired power plants now have the answer for burner system components failing due to heat deformation or coal particle erosion. Corner fired burner nozzles and core air protection tubes for wall fired burners made from Ceraforte experience extended life times of up to 6 times in operation and are compatible with all burner systems. Ceraforte is a drop in replacement for steel components that fail in operation due to heat deformation and wear.

Since the early 1980s, 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.

All PFC fired units suffer wear, heat damage and slag in their burner systems due to the quality of the coal, choice of wear parts and the operating regime of the plant. Switching from stainless and mild steels to Ceraforte for burner system wear parts will significantly help maintain the original PFC distributions and the design efficiencies of the boiler thus minimising coal usage and downtimes.

Ceraforte maintains it shape throughout its entire lifetime. It is resistant to coal particle erosion due to the Silicon Carbide aggregates and is virtually impervious to thermal shock and heat damage.[Page Break]

Burner Nozzles and Core Air Tubes

Corner fired boilers create a thoroughly mixed fire ball fed tangentially from the corners of the boiler through PFC burner nozzles. This fireball must be kept in a turbulent and free mixing state to ensure optimum combustion. Through the tilting mechanism on the burner nozzle, the fireball is moved up and down inside the boiler furnace cavity to control the temperature of the steam leaving the boiler.

As the original stainless steel nozzles wear out and deform during their 18 to 24 months life, the original PFC distribution and the ability to control the shape and location of the fireball is lost. This immediately and negatively impacts the boiler efficiency.

Replacing stainless steel nozzles with Ceraforte will ensure that the boiler will not operate with efficiency losses due to nozzle deterioration. Further benefits are gained due to the long operating life of Ceraforte in relation to Stainless Steel, effectively 3-4 times longer under the same operating conditions. This means that the burner nozzles only have to be replaced once in every six to eight years, instead of every two years.

With front and opposed wall fired boilers, PFC and primary air is fed into the boiler furnace through circular PFC burners. The point at which PFC and primary air come into contact with the steel components of the burner is the point of change in direction of flow and the point at which most erosion takes place. This erosion is generally severe and causes a considerable amount of down time and repair work.

The replacement of the current steels with a Ceraforte tube over the core air pipe will greatly extend the life of these components. When wear takes place, the tube is rotated to move a new Ceraforte surface into the path of the PFC stream resulting in a lifetime extension of 4-6 times or current solutions.[Page Break]

Ash deposits adhering on the furnace walls in and around the burner zone can cause pressure part wastage, leading ultimately to tube failure and un-anticipated shutdowns. The non-wetting qualities and characteristics of Ceraforte minimises slag in and around the burner zone allowing for a clear and uniform flow path for the pulverised fuel to exit the burner nozzle.

The silicon carbide based material is formulated to be resistant to thermal shock and heat damage and to have high abrasion resistance. Unique among all high temperature materials tested, Elkem Ceraforte actually increases in strength up to 1500°C and can be cast in any shape required. Minimum wall thicknesses begin at 15mm for core air tubes and 25mm for burner nozzles. Trowellable versions can be put directly on the inside surfaces of the burner system and other hard to get areas that are susceptible to slagging. Expected life times are 2-3 times stainless steel in the same operating conditions.

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Robert Howard is with Elkem Silicon Materials, Kristiansand, Norway. www.elkem.com/silicon-materials

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