1.5 BOILER REFRACTORY DRY OUT PROCEDURE

PROCEDURE FOR SLOW FIRING (FBC BOILERS)

REFRACTORY DRY OUT:

                 After the refractory works are completed, the refractory work must be subjected to proper curing                 and initial heating. These two procedures must be strictly carried out. Otherwise, cracks may occur                 on the refractory surface. The procedure is given below.

 

CURING FOR CASTABLE REFRACTORY:

                 All the castable are hydraulic setting type and need the presence of moisture for setting process,                     so it is necessary to ensure that the castable does not dry out to exposure or due to heat                     produced within the mass. It should not be allowed to dry during first 24 hours after it has been                  placed.

Moist condition has to be maintained by covering the castable with wet gunny sacks or by frequent sprinkling of fine mist of cold water on all exposed surfaces. Sprinkling should be started after the castable has set partially. It is generally advisable to spray water on dense castables every 45 minutes for 24 hours.

 

INITIAL HEATING FOR REFRACTORY:

                 Proper attention should be given during initial heat up of castables, as they have considerable                         lower permeability when compared to brick. It is more difficult for the water to pass through the                  castable and escape as the refractory is heated more rapidly.

Rapid heating also causes the hot face to dry up and heat up while the rest of castables is still comparatively cool.

This will lead to expansion of hot face and hence develops a crack on cold face.

 

SLOW FIRING PROCEDURE:

                 Following are to be done before slow firing is started:

        a)    All the coal nozzles and air nozzles must be fully covered with bed material.

b)                            No fans should be operated for the heating purpose. Firing should be done only by                     natural draught. For this all dampers should be kept open.

        c)    Sufficient sized fire wood required has to be stocked for the dry out.

d)                            Slow firing can be done by burning sized wood in the furnace. The sized wood can be              fed in the furnace through the manhole. The fuel required shall be computed as if the                 boiler would be operated to generate 20% MCR load.

                The following heat and curing schedule is recommended:

            1.            Heat gradually up to 110°C and hold at this temperature for six hours.

              2.            Then raise the temperature at rate of 10°C per hour up to 550°C (or) to the                                 maximum possible temperature between 350°C to 550°C and hold at this                                     temperature for six hours.

             3.            After this the furnace can be cooled naturally.

                    Note:

                The above chart is a general guideline only.