Preventing the Self-Destruction of the Indirect Coal Firing System

The most widely used fuel in the cement industry is pulverized coal. The current trend is to burn coal through the use of an indirect firing system, as opposed to direct firing which was formerly standard for cement kilns. Indirect firing is favored for precalciners and to improve thermal efficiency, but the benefits are sometimes overshadowed by increased hazard potential. Thoughtful design and careful operating practices are essential for safe operation. The hazards are primarily a result of the explosive mixture of coal and air which can be formed in various parts of the system and the tendency for coal to self-heat and undergo spontaneous combustion. The systems for indirect coal firing are reviewed, with emphasis on the potential fire and explosion hazards. The effectiveness of various methods to extinguish a fire or suppress an explosion is discussed, together with their applicability and related operating problems. The available alarm systems are evaluated according to their ability to signal impending danger in time for corrective action. Some parameters of safe design and operating practices are outlined as a guide to avoiding the types of problems that have been experienced at some existing installations.