Rotary Kiln Temperature Control

Rotary kilns (or rotary dryers) are used extensively in industry for drying solids. They consist basically of a large metal tube which is rotated while hot air and wet solids are fed into it. Both co-current and counter-current configurations are used. Below is a schematic of a typical dryer used to dry polymer powders:

Often final product quality and profitablilty is heavily dependent on the drying operation. On one hand, if the dryer is run too cool, residual liquid may be left in the product and ultimately effect the polymer's performance when it is extruded (melted). On the other hand, running the kiln too hot may cause the polymer to burn or melt prematurely, changing the polymer's properties and again effecting its performance when it is molded. Finally, lest we forget we are ultimately trying to make money, suppose our customer allows a certain amount or moisture in your product. Why spend the extra energy (i.e. $$) over-drying your product?

Rotary kilns are also used extensively in the paper industry to convert lime "mud" (slurry) into powdered lime. Typically the air flow for this application is counter current and there are two manipulated variables and two measured outputs:

For those of you that travel the Massachusetts Turnpike and would like to view a lime kiln firsthand, there is a lime manufacturer called the Lee Lime Company, in (where else) Lee Massachusetts, just over the border from New York. Their kiln is easily visible from the interstate on the East side of their plant. There are also a few so-so pictures at, the web site for Phillips Kiln.

For this case study problem we will be modeling, simulating, and finally controlling a lime kiln. You will be given a "black box" in Simulink format which you are to regard as the actual plant. You will perform step tests to develop a model, then using that model, develop controllers to run the process. Since this is a MIMO system, you will also be asked to suggest the controller "pairing" that is best for this system. Finally, you will present and discuss your results.