Burning hazardous waste in cement kilns

The cement manufacturing process is one of the oldest in the world, having been in practice for over 2000 years. It is also one of the most energy intensive, with up to 65 percent of the cost of the product attributable to energy consumption. In addition to high energy demand, the process conditions include extremely high temperatures. Cement clinker forms when the correct mixture of raw materials is heated to 2650/sup 0/ F. This requires combustion temperatures exceeding 3000/sup 0/ F. under oxidizing conditions. To accomplish this, gas temperatures above 2000/sup 0/ F. occur for several seconds (typically five seconds), which is much longer than residence times in permitted hazardous waste incinerators. These conditions are extremely favorable to the destruction of organic compounds and have led to extensive investigation into the potential for burning hazardous waste in cement kilns. Cement kilns consuming hazardous wastes have been tested for air emissions under various operating conditions. The substantial body of information on the emissions and handling of hazardous wastes from these studies has demonstrated that effective destruction of wastes can be accomplished with the added benefits of energy conservation and no significant change in air emissions.