On the Occurrence of Transient Puffs in a Rotary Kiln Incinerator Simulator
I. Prototype Solid Plastic Wastes

Abstract

In the operation of practical rotary kiln incinerators, the hazardous waste charge is often introduced in drums or containers in a batch mode. The ensuing transient condition, caused by the rapid devolatilization of waste materials, can momentarily deplete or displace local levels of excess oxygen in the kiln, resulting in heavy transient loadings of unburned gaseous and particulate hydrocarbons (here denoted as "puffs") leaving the kUn. This system upset must then be handled by an afterburner and subsequent air pollution control devices downstream. Such an overcharging or transient condition may even result in unacceptably low destruction of principal organic hazardous constituents (POHC) and the formation of products of incomplete combustion (PIC).

A 73-kW (250,000-Btu/h) rotary kiln simulator was designed and constructed to provide engineering insight into the chemical and physical parameters associated with failure mode conditions. To this end, a statistically designed parametric investigation was undertaken to determine which waste and kiln variables (charge mass, charge surface area, charge composition, and kiln temperature) significantly affect both instantaneous intensity and total magnitude of the pollutant puffs leaving the kiln. Emphasis was on the incineration of simple prototype plastic wastes, ranging from polyethylene to polyvinyl chloride.

Results demonstrate the relative ease with which failure conditions are experienced, even at high excess air values and high ktin temperatures. Transient puffs leaving the kiln contain a number of hazardous compounds. Increasing kiln temperature does not necessarily decrease the puff intensity and may in fact cause an increase. However, the total mass emitted decreases with increasing temperature. In addition, the mass, surface area, and composition of the charge are all important.