Boiler Refractory Dryout (Courtesy of Rentech Boiler Systems)
The refractory material was not normally thermally cured at the factory. It is not uncommon for moisture to be absorbed by the refractory during final stages of in-shop fabrication, transit to the job site, and before the upstream combustion products are first passed through the unit. Therefore, residual moisture and any absorbed moisture must be removed after installation but prior to commencement of start-up operations. Otherwise, trapped moisture will steam, causing cracking, and in many cases, the refractory will separate from the metal in large pieces. As a minimum, follow these steps to protect the refractory from damage.
1. Ideally, the refractory lining should be air-set in dry air, preferably not less than 70°F for at least 24 hours.
2. Using treated water (normal boiler feedwater) fill the unit to approximately the midpoint of the gauge glass, which is normal water level.
3. Verify that the feedwater system is operational.
4. Warm the furnace and gas chamber of the unit to 200°F and maintain that temperature for six hours.
5. Raise the inlet gas temperature at 100°F per hour to 500°F, while venting the generated steam to atmosphere. The valve positions are similar to the boil-out
condition given in the "Summary of Valve Positions".
6. Hold the furnace at this temperature for a minimum of two hours.
7. Continue to raise the inlet gas temperature at 100°F per hour to 1,000°F.
8. Hold the furnace at this temperature to the anticipated operating level at a rate not exceeding 50°F per hour.
9. Elevate the furnace at this temperature to the anticipated operating level at a rate not exceeding 50°F per hour.
10. Hold the furnace at this temperature for a minimum of two hours.
11 Remove the heat source and allow the refractory to cool by natural radiation. Do not introduce cold air with a fan.