Power boilers experience slagging as the molten ash adheres to the surrounding substrates. This is also commonly referred to as slag. The amount of slag is primarily dependent on temperature and the types of coal being used and whether it is anthracite, bituminous coal, subbituminous coal, or lignite. Boilers will often slag in the upper sections of the furnace where the temperatures are higher near the superheat pendants, but slagging may also occur on the waterwalls. Many utilities have installed soot blowers to control the amount of slag, as it has a negative effect on boiler operation. The slag acts as an insulation to the tube substrate and this loss of heat transfer is not optimal. When the slag builds up on the tubes, the heat transfer decreases lowering the temperature of the steam going to the superheated portion of the system, therefore decreasing the overall efficiency of the system. Finding a solution to excessive slagging can have tremendous benefits for a boiler operators bottom line.
IGS anti-slagging technology bonds tightly to the boiler tube’s surface, creating a non-porous, non-wetting, non-reactive surface. The coating will significantly limit molten slags from bonding to the surface, reducing slag and fouling agglomerations. Waterwall furnace tubes and Superheater tubes can benefit from being protected with the IGS coatings. IGS has developed a series of ceramic coating formulations which are modified to match a specific tubes properties and excel in a specific boiler environment.
IGS ceramic coatings can help increase heat absorption into boiler tubes by reducing the amount of slag or fouling on the OD surface of the tube, and by eliminating the formation of corrosion scales on the tubes surface.
The coating itself exhibits high thermal conductivity and high emissivity, which means the coating layer will not insulate the tubes. A coated tube will have higher heat absorption compared to an un-coated scaled tube. It is possible to rebalance a boiler that is suffering from severe slagging or fouling. The lower FGET is possible by absorbing more heat into the waterwalls while achieving the same final steam temp (reduced fuel input, same final steam temp, reduced waste heat) is even possible to help address boilers that have de-rated their MW output capacity due to superheater fouling.
By significantly reducing the amount of slag or fouling on a tubes surface, it is possible to greatly reduce the frequency at which sootblowers or water cannons are activated. Because there will be less slag attached on the tubes, lowering heat absorption, there’s no need to continuously run the slag control equipment. When sootblowers or retractable lances remove slag and fouling, the tube itself will be thermally shocked due to the removal of the dirty insulating material, creating the potential for circumferential cracking or corrosion assisted fatigue (CAF) of the tube. Reducing sootblower usage inhibits this, and slows the wasting of the tubes surfaces.
IGS offers solutions for the most challenging environments and always works with our customers to address their unique needs. For example, when facilities burn sub-bituminous coal, such as coal mined from the Powder River Basin in the northwest region of the US, it can create a thick layer of alumina known as white reflective fly ash. This ash is sticky and poses many problems to boiler operators, especially in units that have been converted to handle this type of coal from another type of coal. The ash fusion temperature is lower compared to other coals, and the slag is incredibly sticky, leading to significant superheater fouling and possible boiler derating. By re-engineering the surface with an advanced coating technology, we can reduce these maintenance challenges.