Application of Pulse Combustion to Solid and Hazardous Waste Incineration

A bench-scale Rotary Kiln Incinerator Simulator was retrofitted with a frequency-tunable pulse combustor in order to enhance the efficiency of combustion. The pulse combustor excites pulsations in the kiln and increases the completeness of combustion by promoting better mixing within the system. One phenomenon that is unique to batch-fed incineration systems, and rotary kilns in particular, is the formation of transient "puffs," or plugs of unburned material that are formed when the instantaneous bed waste release rate is greater than the available local stoichiometric oxygen supplied from the primary burner. It is hypothesized that the additional mixing induced by the pulse combustor can reduce gas-phase stratification and enhance transport of available oxygen into the local fuel-rich zones of the puff. Tests were performed using toluene (C 7 H 8 ) sorted onto a ground corn cob sorbent and placed in cardboard containers. The burner was operated in a non-pulse mode as a baseline condition, and then in a pulse mode in which the frequency of the pulse combustor was adjusted to the natural frequency of the combustion chamber, creating resonant pulsations of large magnitude. The test was also performed using polyethylene tube bundles to simulate a solid waste and to investigate a surrogate which produces different puff characteristics. Products of incomplete combustion (PICs), measured as carbon monoxide (CO), total hydrocarbon (THC), and soot, were monitored from a sample extracted immediately downstream of the kiln, in addition to other exhaust gas species (oxygen, carbon dioxide, nitrogen oxides). The addition of turbulence in the rotary kiln due to high amplitude acoustic pulsations has a strong tendency to reduce the amount of soot and/or semi-volatile and non-volatile THC that is measured. Mass emissions of soot were consistently reduced in all tests. CO increased during acoustic pulsations in the toluene tests. Toluene is a fast burning surrogate hazardous waste which preferentially forms soot during transient puffs. The decrease in soot and apparent corresponding increase in CO indicate that the pulsations had a beneficial effect on the combustion process. This phenomenon could be the result of two effects: 1) either the formation of soot is being inhibited due to disruption of the coagulation process that occurs during soot formation; or 2) the high amplitude acoustic waves could be breaking down the boundary layer in the local environment of the soot