Project at a Glance
Title: Engineering evaluation and control of toxic airborne effluents
Principal Investigator / Author(s): Chang, Daniel P. Y.
Contractor: Department of Civil Engineering and Department of Mechanical Engineering, UC Davis, and Combustion Research Facility, Sandia National Laboratory
Contract Number: A6-051-32
Research Program Area: Emissions Monitoring & Control
Topic Areas: Stationary Sources, Toxic Air Contaminants
Implementation of federal and state regulations controlling the treatment and disposal of hazardous wastes has stimulated interest in hazardous waste incineration. Many hazardous wastes are chlorinated hydrocarbon liquids and are candidates for incineration in spray-fired combustors. Proper design of incinerators to handle these materials depends on an under-standing of their vaporization and combustion characteristics. Because of the complexities inherent in hazardous waste incinerators (HWIs), a thorough understanding of the destruction of chlorinated hydrocarbons (CHCs) in full-scale HWIs has not been possible. This realization has motivated the need to conduct laboratory and pilot-scale studies of portions of the HWI problem.
Pilot-scale HWIs have been used to study the destruction efficiency (DE) of chlorinated hydrocarbons (CHC) as a function of combustor operating conditions (Kramlich et al., 1984; La Fond et al., 1985; Waterland, 1984; Wolbach, 1984; Chang, 1988). While insights have been gained regarding factors influencing DE, quantitative predictions of DE in full-scale HWIs have not been possible because of the uncertainty in the scaling of turbulent mixing effects. Numerous premixed CHC flame and non-flame studies (Bose and Senkan, 1983; Chang, et al., 1986; Gupta and Valeiras, 1984; Frenklach et al., 1986; Dellinger et al., 1984; Graham et al., 1986; Senser et al., 1987) have been conducted, but we are aware of only one group that has studied CHC diffusion flames (VanDell and Shadoff, 1984). These studies have been used to determine the structure, kinetic mechanisms, sooting behavior and speed of CHC flames as well as to determine mechanisms of CHC thermal decomposition in hot, non-flame environments. This report describes an experimental study involving the gasification (burning and vaporization) of single droplets of various CHCs, a diffusion flame phenomenon.
Despite the development of newer technologies, spray combustion is still the preferred method of HWI (Oppelt, 1987). Because sprays are made up of individual droplets it is not unreasonable to expect some correlation between the burning of individual droplets and the burning of sprays. In the field of spray combustion, there has been considerable discussion on the role of group burning vs. individual droplet burning. The ratio of inter-drop distance to drop diameter, C, has been found to be an important parameter which governs whether a spray burns as a group or as individual droplets. For droplets far apart (C > 10) individual droplet behavior is expected. For very dense sprays (1 c c < 51, there are intense interaction effects between droplets. However for most sprays (C = 10) single droplet vaporization theory still applies (Correa and Sichel, 1982). Thus single droplet burning can be used to describe spray combustion when droplets are far apart, and droplet vaporization effects can be used to describe vaporization which occurs in the spray interior.
Single droplet burning can also be used to describe the combustion of large oversized droplets which can be produced as a result of an atomizer failure. Calculations show that if a small number of these large "rogue droplets", escape the core of the spray region and fail to burn completely outside of the flame envelope, reduced incinerator DE may result (Mulholland et al., 1986). Experimental results have also shown that the production of large droplets results in a decreased DE (Kramlich et al., 1984; Chang et al., 1988). Single droplet burning characteristics can therefore be used to describe burning of these "rogue droplets". Finally, because droplet gasification has been well studied for many conventional fuels and mixtures (Law, 1982), the physical insight gained from these studies can be applied to the additional chemical complexities associated with CHC combustion.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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