Why do you carryout refractory dry out for Boilers?
It is done to ensure proper drying & curing of refractory in furnace & other areas where refractory is applied. The refractory under goes chemical changes during initial heating. While heating there must be free air flow over the refractory to ensure complete removal of moisture.
What are the Prechecks carried out before refractory dry out?
- Ensure Boiler erection work is completed with all respect
- Ensure Boiler official Hydraulic test is done
- Ensure insulation work is completed
- Ensure abundant quantity feed water is available
- Ensure required quantity wood logs are available
- Ensure sufficient & qualified operation staff is available
- Ensure thermal expansion pointers are fitted at all required locations
- Ensure steam drum & super heater vents are opened
Write down the standard procedure for refractory dry out
Refractory dry out is done as per OEM recommendation, too rapid heating of refractory may collapse the refractory material due to development thermal stresses. So it is recommended to heat the refractory for longer time at low temperature.
- Cover all air & coal nozzles with bed materials, this will avoid the damage to the nozzles (This is not applicable for Travelling grate & dumping grate Boilers) while throwing wood logs into furnace
- Select the required size wood logs generally 2 to 3” diameter & 2 to 3 feet length wood sizes are preferred. Ensure wood logs do not have nails, packing strip
- Ensure wood logs have optimum moisture. Too dry or too wet woods are not good for dry out
- Ensure refractory dry out is done on natural daft, no fans are necessary. Ensure all the suction & discharge dampers of fans are kept open
- Put the woods on bed materials, spray the small amount of diesel & then fire the woods
- Initially temperature raising should be slow at the rate of 25 deg c per hour for 3 to 4 hours
- Then raise the boiler outlet flue gas temperature up to 100 deg C & hold for 8 to 10 hours (as recommended by OEM) for soaking the refractory inside the Boiler
- Then raise the boiler outlet flue gas temperature up to 250 deg C & hold for 6 to 8 hours (as recommended by OEM) for soaking the refractory inside the Boiler
- Finally raise the boiler outlet flue gas temperature up to 350 deg C & hold for 8 to 10 hours (as recommended by OEM) for soaking the refractory inside the Boiler
- After completing the above process, firing is stopped & Boiler is allowed to cool naturally
- After cooling down, Boiler must inspected for refractory damage/crack etc
- Minor cracks formed during dry out procedure should be rectified with same quality refractory material