Engineers from Integrated Global Services, Richmond, Va., and Uniper Technologies, England, evaluated advanced weld overlay, thermal spray, and laser-clad coatings as surface protection of a waste-wood-fired fluidized boiler, in a presentation at the ASM International ITSC 2019 conference in Japan.
Different surface protection technologies were investigated in a full scale commercial waste wood-fired, bubbling-bed, fluidized boiler. This biomass fuel environment is more aggressive than those firing virgin wood, due to the elevated presence of sodium, potassium, lead, and zinc, leading to the deposit of alkali and heavy metal chlorides in conjunction with ash on boiler tube surfaces.
As laboratory tests are seldom representative of the complex firing, chemistry, temperature, and local heat flux in true operating conditions, five different commercial, near-commercial, and development coatings were applied to a one-meter length of PG235GH plain carbon steel tubing used in the furnace walls.
The coatings were fully characterised and measured prior to installation and after exposure. Advanced iron and nickel based weld overlays, two high-velocity thermal spray coatings, and a laser clad nanosteel-type coating were tested. After exposure, the tube was extracted from the boiler with the structure and circumferential distribution of the corrosion scales and material loss rates evaluated in comparison to the unprotected tube material. The technologies considered here could be employed to reduce current wastage rates in existing units and provide protection against uncertain future fuel mixes.
Evaluation of advanced weld overlay, thermal spray and laser clad coatings in an operating waste wood fired biomass boiler
Iain Stuart Hall, Integrated Global Services, Richmond, Virginia
Colin Davis, Uniper Technologies, Ratcliffe on Soar, United Kingdom
