All fuels (gaseous fuel, liquid fuel, and solid fuel) has comprise some sulphur if it is burned will generate compounds which can cause corrosion. Corrosion must be prevented because it would damage the pressure part in the steam boiler.
may be separated from the fuels but it would require an expensive process. When in burning process of sulphur, two products of sulphur such as sulphur dioxide (SO2) and sulphur dioxide (SO3) will be generated. Water that be produced from combustion of hydrogen will combine with these compounds (SO2 and SO3) to generate acids. Sulphur
At acid dew point, these acids will be condensed between temperature 120o C and 175o C depending on the number of sulphur content in the fuels. These acids will be absorbed by some soot deposits contained in stack, economizer, air heater, and other pressure part also in flue gas will be fused and formed acid smut. The water dew point will be achieved when the temperature down to reach 55o C. and these acids will melt. It is the process which will cause corrosion.
The corrosion can be prevented if the metal temperature in the steam boiler is maintained in high temperature. The flue gas temperature exit of steam boiler is usually maintained at minimum 200o C to avoid the formation of acid in air heater, economizer, stack and other pressure part also flue gas. For best design, the stack must be insulated to avoid cooling and corrosion. If the steam boiler is shut down, all parts should be cleaned to remove all acids in the steam boiler.