Refractory bricks when wet

refractory materials like bricks is porious material, the water the brick absorbed and when heated, the water would turn into vapour and explode the bricks.

If water can saturate them steam can get out.

Having rebuilt combustion chambers, it was common practice not to reuse the bricks,

For one of the reasons I posted earlier. (replaced with ceramic wool)

If water can saturate them steam can get out.

As long as the steam can escape fast enough. when temperature gets to a flash point of the water, proceed with caution......... i.e. run

are there some kind of rating on the brick?

Dear Deron,

If I recall correctly from my early days in engineering, moisture in refractory brick that has not been installed yet can leach out into the mortar used to set the brick in the furnace. This can affect the ability of the mortar to hold the brick in place, especially if this is a round kiln, and you may find bricks falling out shortly after start-up. As for moisture exploding bricks, assuming you start up the furnace and bring the heat up slowly, you should be okay. Keep in mind that refractory works because of its very poor heat conductivity. Therefore, it will take a longer time to heat the base of the brick than the surface. If the brick is brought up to full temperature too quickly trapped water can turn to steam but the porous nature of the brick should help relieve the pressure increase. I believe your best bet is to install the brick and bring it to moderate temperature (250 to 300 degrees F) slowly and hold this temperature until all moisture is baked out of the brick (roughly 24 hours) before bringing to full temperature. Check with your refractory vendor for specific instructions.

I agree completely. From experience with coke oven battery rebuilds, in cases where refractories haven't been chemically decrepitated by the moisture saturating the brick it has been standard practice to heat them very slowly until the entire brick (not just the surface) exceeds 100-110 C and hold them at temperature for period of a few hours. This can be done by controlled heating in a dutch oven arrangement. The temperature can then generally be increased without further harm to the brick from moisture.

You just reminded me of an early experience on a Boy Scout campout when one of the boys used rocks from the creek bed to line his campfire. We thought we were under attack! Fortunately the damage was only holes in the tents, no boys got hurt.

If it is porous fire brick then hold the kiln temperature to 120'C for 1 hour, then run up to 225'C for 1 hour. This will drive off the physosorbed and the chemisorbed water. The bricks will work fine after that. If hard brick, then just extend the time to 2 hours.

Right. My post was supposed to say 250 to 300 F for approx 2-4 hrs, not 24 hours.

Guys,

How helpful you have been imparting me. You enlighten me with your engineering sense. Thank you very much.

Regards,

deron