In the production of cement, there is commonly a waste product collected from the hot gas discharge of the kiln. This waste material is commonly called Cement Kiln Dust or CKD. There are some limited markets for this product, so it is common practice to dispose of the CKD in surface impoundments or landfills. This extremely fine, dry, dusty powder is typically “conditioned” by adding water to the solids before loading into trucks for disposal. CKD can be difficult to get a consistent moisture content to ensure that all the dry solids are wetted to a dustless mixture.
A common method to “condition” the CKD is the use of a continuous mixer like a pug mill. Some common problems with a pug mill for this application is either over saturation or dry pockets of dust. This inconsistent mixing process can lead to problems.
If too much water is added, it can cause solids to harden as soon as the mixer is stopped, causing a headache for the maintenance personnel to break out the hardened dust from around the mixer shaft.
Another common problem with over saturation is additional water weight reduces the amount of solids transported in each load. This can be costly if shipping a long distance. (Another issue is if the mixture is too wet, it can drain on the roadway in certain types of trucks)
If the solids are under conditioned and still dry, this can cause dust escaping around the plant site or even as the trucks transport the solids down a public road. This is the main reason why the mixer was installed.
By using a high speed, high intensity mixer in a batch process, this can guarantee a dustless mixture discharged into the trucks. Typically a Turbin, or pan style mixer, with paddles rotating at speeds up to 600 feet per minute can condition a batch of CKD in 30 seconds. This works because we control each batch by adding the same weight of solids, the same volume of water, and mixing this for the same amount of time. This process can be done at rates as high as 200 tons per hour @ 50 pounds per cubic foot.
A truck driver can start the mixing process from a simple control station mounted next to the truck station. Additional options like rubber lined pan and automatic wash down system, reduce the time operations or maintenance personnel need to clean and maintain the mixer.