Suspension preheaters are a series of cyclones and duct vessels to preheat the raw meal. Temperatures progressively increase as the kiln feed moves towards the lower stages. Almost all suspension preheaters include a calciner vessel where additional fuel is burned to support the calcination process. The upper stages of the preheater utilize refractories based on fireclay and have approximately 40% alumina content.
This type of refractory offers good abrasion resistance and insulating value. In the lower preheater, medium alumina content refractories are used in response to the higher temperatures. Alkali resistance is important, and 50% to 60% alumina refractories are more appropriate.
Most linings within the preheater are two components, a dense working lining and an insulating layer. RescoCast 3, RescoCast 3-35, and QuikLite 3 are commonly selected for the insulating layer. Gunite refractories are commonly used for maintenance in the upper preheater including RescoCast 15GM, Progun 26LI and Progun 28LI.
In the lower preheater, Shotcrete is the preferred installation method. EZ Cubed 3000 and Vibrocast 60Z PC are conventional low cement castables selected for the working lining within the lower preheater. Vibrocast 60Z PC contains zircon which provides a moderate amount of build-up resistance. QuikTurn castables are very popular selections for the lower preheater including QuikTurn 60 PC and QuikTurn 60Z PC. QuikLite 3 is the companion insulation gunite for a QuikTurn lining. For severe build-up applications, EZ Cubed AZS and QuikTurn AZS PC are standards in the industry. QuikTurn AZS G provides a gunite selection in a severe build-up location.