Boiler Refractory dry out is to ensure proper drying, curing of refractory applied on furnace and other components. The refractory usually undergoes considerable chemical changes, during initial heating. Controlled heating, through these reactions ensures maximum strength. While heating, there must be free air flow over the system to ensure removal of moisture.
In order to commence refractory dry out, the following pre-requisites and inputs have to be ensured.
Prior to carrying out this test, all the pre-commissioning checks should have been completed.
Ensure tlie availability of adequate feed water as per recommendation of the boiler supplier, adequate wooden logs to the required sizes, Draft system and instruments required for the Boiler firing.
Ensure the availability of adequate qualified boiler operating staff and operators.
Keep open all the vent lines ( 100% open) on the boiler drum, top super heater header throughout the refractory dry out period.
Procedure for Boiler Refractory Dry out
Refractory baking and dry out cycle requires very slow and controlled heating of refractory as recommended by the refractory manufacturers. Thermal stresses will be produced if heating rate is too rapid. Longer period of low temperature drying causes more even heat distribution resulting better refractory dry out.
Fill the drum with the specified quality feed water 50mm below the normal water level since the water level in gauge will raise as heat is absorbed. Maintain normal water level in the drum throughout the period. Place the dry fire wood (2inch diameter and 2 feet length), free from nails and packing metal strips, on the grate. Start ID and FD fan at minimum load to light up the boiler. Ensure that rate of heating is maintained at the rate of 25°C per hour. Raise the temperature of flue gas at boiler outlet to 100°C and hold the temperature to up to 10 hours at 100°C for soaking refractory castables. If the temperature falls, increase the firing rate and maintain the required temperature. Then raise the flue gas temperature at boiler outlet to 250°C and hold it 6 hours for soaking the refractory castables. Again raise flue gas temperature at boiler outlet to 350°C and hold it for 10 hours for soaking the refractory castables. Once the above heating schedule is over, the fire is extinguished and the boiler may be allowed to cool down naturally keeping FD, ID & SA fans off. Fan auxiliary dampers should be in fully closed condition. A thorough examination is to be made to check refractory condition after boiler is cooled down. Minor cracks (up to 3mm) are to be filled with castable refractory.
Refractory dry out should be carried out as per the curve given by Refractory manufacturer.