Problems with leakages and fly ash
Across the world, the design and operation of power plants face the challenge of sealing the roof on Pulverized Fuel (PF) fired boilers, against ingress of fly ash into the so called dead space on top of the boiler.
In all steps of the operation of the boiler, the pipe work in the boiler - carrying water and steam under high pressure - will move slightly due to the thermal expansion of the metal. This movement causes the concrete wall of the boiler to crack in the areas around the pipe lead-in. Locating a durable metallic sealing to prevent fly ash from entering the leaks created has been difficult.
As the pressure outside the boiler is lower than that of the boiler house environment, flue gas, carrying the fly ash from the incineration of the pulverised coal, will pass through the leaks in the boiler wall. Once outside the incineration chamber, the fly ash will precipitate in the dead space or be carried further towards the top of the boiler (convection pass, penthouse etc.)
Emission of fly ash is not the sole problem of leaks in the boiler.
Leaks around the front cross, nose arch, ash hopper and the expansion joints, result in ingress of cold air from the atmosphere. This greatly reduces the efficiency of the incineration process.
Consequences of boiler leaks
The following consequences of the leakage have been experienced:
Risk of boiler roof collapse
The build up of fly ash may grow to several meters in height, with a combined stress of several hundred tons on the boiler roof. Over time, this strain on the building structure may result in metallurgical fatigue, and in rare cases, entire boilers have collapsed under the weight of the fly ash. Ingress of steam or water in the fly ash layer will further increase the risk of damage, as the weight will increase accordingly.
Reduced lifetime of steel structures
The hot fly ash constitutes good insulation conditions, and un-cooled construction parts such as rods and hangers may reduce in strength and lifetime, due to overheating.
Until the thick layer of fly ash has cooled down and is removed, a process that normally takes one week, repairs to pipe works is impossible. With the ISOMEMBRANE® in place, the cool down process is shorter, and repairs possible immediately, as there is no ash layer to remove first.
Reduced combustion efficiency in boiler
The bypass of flue gas and fly ash into the upper dead spaces of the boiler environment will reduce the combustion efficiency. Tight pipe lead-in’s with an ISOMEMBRANE® seal will ensure the best incineration environment, as flue gases and fly ash is kept in the incineration chamber and routed through filters to the chimney.
Increased power consumption
Loss of energy because of heating up ingress air and extra load on the induced draught fan