This project adapts high volumetric heat release rate aerospace combustion technology to hazardous waste incineration. The incinerator is derived from an aerospace dump combustor. A pre-mixed flame is stabilized within a rectangular duct by a sudden expansion in cross section at the dump plane. Waste is injected into hot, oxidative recirculation regions downstream of the dump plane, where it experiences relatively long residence times in comparison to incinerators of comparable size but of more conventional design.
Heat release in the pre-mixed region frequently couples with hydrodynamic and acoustic phenomena to produce strong combustion instabilities in this device. Certain of these instabilities can be used to promote higher rates of heat release and mixing, and thus better waste destruction. A significant part of this study focuses on identification of instability modes favorable and unfavorable for waste destruction, and on how favorable modes can be excited and controlled.
Surrogate waste destruction is monitored by probe sampling and gas chromatographic analysis. Combustion driven acoustic instabilities are examined using a combination of OH chemiluminsecence, OH and NO planar laser-induced fluorescence, and pressure transducer measurements. Recirculation zone stability is examined by particle image velocimetry. Numerical simulation of the incineration process has also been completed.
As waste minimizatiion efforts lead to smaller, geographically dispersed waste streams, compact incineration technology is expected to become increasingly attractive from both economic and political perspectives.
National Science Foundation, Office of Naval Research
Most risk assessment studies performed in conjunction with siting hazardous or municipal waste incinerators identify emissions of such heavy metals as cadmium, lead, and mercury as having relatively high potential for harming the surrounding population. These elements are usually emitted in the form of oxide aerosols, which are formed in the flame. Further, a significant fraction of the aerosol is in the sub-micron size range, which is both very difficult to handle with conventional particulate control devices and easily respirated into the lungs. Once in the lungs, these metal oxides can lead to cancer and other health problems.
This project is includes both experimental measurements and modeling of the evolution of metal oxide aerosol size distribution above flat methane-air flames. Heavy metals are introduced into fuel-air mixture as dry aerosols of acetate or nitrate salts. We measure extinction and both polarization components of the scattered laser light at 45 degrees. Mie theory gives the moments of an assumed lognormal distribution along with the particle number density. Experiments have been completed for zinc oxide, which is not toxic and are in progress for cadmium oxide.
The results of this study are expected to provide input to incineration risk assessment models.
Environmental Protection Agency
osmith@seas.ucla.edu ark@seas.ucla.edu