After I visited the plant, I saw what he meant. The kiln was running and firing products, but several things just weren't right. The kiln's stability was marginal, and several zones did not achieve set point temperature. Uniformity was not good; in fact, many of the excellent controls built into the kiln's firing system were under-utilized or used incorrectly.
For example, we all know that tunnel kilns can be operated in various ways, and their operation has to do with the volume of air that is exchanged between the cooling and heating zone. Normally, it is a great advantage to exchange as much cooling air as possible to the main firing zone, because a lot of BTUs are available in the hot air. Further, the high volume of flow improves convection within the tunnel. When O2 is important, the cooling air transport provides plenty of oxygen that can be used in part for combustion, and further downstream, a plentiful amount of oxygen helps oxidize hydrocarbons present in clays and binders. Last, those extra BTUs are very effective in heating the incoming load, reducing the total input in the preheating zone and saving fuel. Effectively operating these complex systems requires a considerable amount of training and experience. Many tunnel kilns consume more than $500,000 in fuel each year, and an informed operator can easily save his annual salary in fuel reduction through skilled operation.
But it isn't just the subtle things. I once saw a roller hearth kiln turned into a high-temperature dough mixer because operators continued to charge products into the kiln despite the fact that nothing was coming out of the other end! In this case, tiles being fired began to wrap around the rollers of the kiln, creating a unique dough mixer scenario resembling the appearance of molten lava.
I once read about a plant that managed to push a tunnel kiln car nearly through the sidewall of a kiln, and I have also seen pusher plate kilns where the individual plates climbed one upon the other until they pushed up through the roof of the kiln. People compensate for their lack of understanding by making adjustments-often incorrect ones-that can have dire consequences later on.
Maybe one of these days I will finish a book that provides comprehensive kiln operating information. In the meantime, get your people some help-your kiln will do a better job and your people will be more satisfied to be making a positive contribution. Plus, you'll surely see improved quality, reduced energy consumption and greater productivity.
Ralph Ruark is a registered professional engineer with degrees in ceramic engineering and business, and 28 years of experience in the ceramic industry. He formed Ruark Engineering Inc. several years ago and serves as a technical consultant to a number of ceramic manufacturers and kiln companies. He is dedicated to assisting ceramic companies with a variety of kiln and firing needs, leading kiln analysis efforts, providing training expertise, and improving operations. Ruark can be reached at (941) 360-3111, fax (941) 360-3211, e-mail firstname.lastname@example.org or online at http://www.ruarkengineering.com .