The Hazardous Waste Incinerator Figure 5 provides a very generalized schematic flow diagram of a rotary kiln incinerator. Features of this process, which are critically different form cement kilns and can impact emissions, are noted below. Therefore, gases exiting the incinerator directly reflect what is happening in the combustion zone of the kiln. In an incinerator, the gases are moving the same direction as solids and liquids. This tends to drive any phase equilibrium to the gaseous side of the equation thus increasing emissions such as metals.
Vapor pressure becomes the critical factor.
The thermal capacity and therefore thermal stability of an incinerator is relatively low. Process upsets can occur within a matter of minutes or even seconds that can allow uncombusted organics to escape from the process. The use of an afterburner is largely prompted by this potential. In a cement kiln, the dehydration and calcination steps produce large quantities of gases that largely mask gaseous emissions from the combustion zone of the cement kiln. Nearly half the mass of raw materials that enter a wet process cement kiln leave the kiln as gases, primarily water vapor and carbon dioxide, yet they are not combustion by-products.