Energy Economics of a Modern Suspension Preheater Plant Compared to a Modern Plant Incorporating Cogeneration

The rising cost of fuel experienced over the past several years has caused the cement industry to look for more energy efficient systems for producing cement. Probably the most popular system has been the suspension preheater, frequently coupled with a roller mill, a flash calciner, or both. While these systems have yielded greatly improved fuel efficiencies, they have also contributed to higher consumption of electrical energy. This, coupled with the rapid rise in cost of electrical energy, has led to a renewed interest in cogeneration, wherein the heat contained in the kiln off-gases is used to produce steam to run turbine generators, thereby increasing the use of lower cost fuel energy while decreasing the use of higher cost purchased electric power energy. The production cost of a suspension preheater is different than for a plant utilizing cogeneration, so the production cost per ton of the two systems is compared, and the differences are used to determine the feasibility of cogeneration for a specific set of conditions. Two cogeneration cases will be examined. One is a plant utilizing generated power from waste heat only, all of which is consumed by the plant. The other is a plant which not only utilizes waste heat power but also produces for sale back to the utility company.