Keep it Hot
Improve Refractory Life During Cyclical Business Conditions
“I’m not operating as much, so shouldn’t the refractory last as long, or longer, then when we’re running full out?” The answer is usually no because thermal cycling is refractory’s enemy.
For the sake of today’s discussion, I am not focusing on naturally thermal cycle-resistant materials like fused silica linings. Let’s talk about traditional castable utilized more for maintenance and rebuilds.
The following basics can begin to improve refractory life until production levels increase allowing you to “keep it hot.” If you cannot keep it hot, cool it down slow and controlled. Remember, cycling damage can occur in both rapid heat-up and rapid cool-down scenarios.
Keep it hot! Anything you can do to keep a temporarily idled refractory lined unit hot will be your best approach. Yes, the fuel to keep the unit warm is a cost but reducing the thermal cycling will save refractory life. Give it a try.
Cannot keep it hot? If your facility is not running a full 24/7 schedule, you may not be able to monitor the equipment. In this case, the slowest possible controlled cool down is recommended. Cover the refractory lined equipment with a ceramic fiber blanket. Or consider custom fabricated lids with stacked bonded ceramic fiber or high-temperature cloth covers. Both are mechanically sound and provide heat retention. You may even find that enough residual heat is maintained to give you a head start on the Monday morning start-up.
Clean units before heat-up. Cold clean units because residual slag, large bottom heals, and metal fins are all potential troublemakers. The preheaters and burners can rapidly heat up refractory lined equipment melting any residual metal before the lining has “soaked” with temperature and before the refractory has had a chance to expand and seal any of the open joints from molten metal. This phenomenon provides potential joint penetration, breakouts, and reduced refractory life. So, take heat-up slow!
Soak, Soak, Soak!: Bring the equipment up slowly in temperature with one or two holds in the schedule. A slow heat-up allows heat to “soak” into the lining. A general rule of thumb is to hold for 1 hour per inch of refractory thickness. At operating temperature, use an optical pyrometer to establish the baseline shell temperature. A baseline can be a good way to predict failures and future maintenance needs.
How can Onex help? We can provide proper cold clean and patching services, fabricated cooling covers, preheater upgrades, service to outdated preheater systems and controls, thermal calculations to predict maintenance requirements, and technical assistance to get you through any issues you may have.
