Corrosing and Fouling

With over 70 years experience of supplying rotary regenerative heat exchangers Howden offers unrivalled advice on optimizing element life in arduous operating environments.

All air preheaters on coal and oil fired plants are subject to some degree of corrosion and fouling caused by the approach to either the sulphuric acid or water dewpoint.

Acid enhanced fouling is dependent on the sulphur content of the fuel and the amount of SO2 to SO3 conversion in the boiler and SCR plant. On coal fired units such fouling and corrosion may be mitigated by the presence of flyash particles. On oil fired units  higher conversion of SO2 to SO3 can occur with effectively no mitigation due to the minimal amount of inherent ash in the fuel.

Corrosion
Corrosion can be minimized by the use of a cold end layer of higher grade steel or enamel coating. We have our own software to calculate the cold end temperature for each case, thus ensuring the most economic choice and depth of this more expensive material.

Hot End Fouling
Hot end elements are prone to fouling as a result of large particles of fused ash becoming lodged in the element passages and smaller particles compacting behind them. These large particles generally arise as a result of less than optimum combustion conditions in the furnace. This can be overcome by the use of an element profile that is less prone to fouling and easier to clean and/or by the installation of hot end sootblowers.

Cold End Fouling
Cold end fouling is generally a result of there being insufficient ash in the flue gas to absorb the condensing acid formed from the sulphur in the fuel. The use of a "closed" profile element increases the effectiveness of the sootblowers. Cold end fouling can also be caused by the high sulphur content in fuel oil in combination with very low combined cold end temperatures.

---