Influence of atomization quality on the destruction of hazardous waste compounds

The correlation between atomization quality and the destruction efficiency of hazardous organic compounds was studied in a turbulent spray flame. The atomization quality was varied by both changing spray nozzle parameters and by inducing disruptive droplet combustion (secondary atomization) within the flame. The primary atomization quality was characterized by laser diagnotic size distribution measurements. The secondary atomization quality was determined from observations of disruptive atomization intensity on a train of monodisperse droplets within a high-temperature laminar reactor. For the primary atomization work, No. 2 fuel oil was doped with four target hazardous organic compounds (acrylonitrile, chloroform, benzene, and monochlorobenzene). The destruction efficiency of these compounds was measured under correct atomizer operating parameters and under off-design conditions in which the spray quality was degraded. The degraded spray quality conditions resulted in decreased destruction efficiency of the waste, and increased combustion intermediate emissions (carbon monoxide and total hydrocarbons). Comparison of measured droplet size distributions with performance showed that destruction efficiency was more closely correlated with the large droplet wing of the dropsize distribution than with the mean droplet size. A droplet evaporation/ trajectory model showed that the appearance of the target compounds in the exhaust corresponded with the fraction of the droplets that passed through the primary reaction zone unevaporated. The distruptive droplet combustion results showed that hazardous waste compounds are capable of inducing secondary atomization. Testing of benzal chloride (which did not cause the turbulent flame reactor showed that the occurrence of disruptive combustion correlated with increased target compound destruction efficiency and reduced combustion intermediate emissions. Thus, the results suggest that the presence of certain compounds or additives in waste streams may assist in obtaining improved performance when primary atomization is poor, as it is for slurry or sludge waste streams. © 1988 Combustion Institute

Flame-mode destruction of hazardous waste compounds

Incineration is a promising technique for the disposal of organic hazardous wastes. However, the waste destruction characteristics of turbulent spray flames have not been characterized. In the present research two reactors are used to simulate various aspects of liquid injection incinerator flame zones. The following questions are addressed: (1) Under what conditions do flames quantitatively destroy waste compounds, and (2) how must the flame be perturbed to cause it to fail to quantitatively destroy wastes. The two reactors operated on a simulated waste stream consisting of acrylonitrile, benzene, chlorobenzene, and chloroform. A microspray reactor was used to investigate destruction processes associated with individual droplets of waste compounds. A turbulent flame reactor used a heptane-fueled waste-doped turbulent spray flame to simulate incinerator flame-zone processes. The flames were found to be capable of quantitative waste destruction without the necessity of using common post-flame processes such as afterburners. Furthermore, the high waste destruction efficiency conditions corresponded to high combustion efficiency conditions (i.e., minimum CO and hydrocarbon emissions). Failure to achieve high destruction efficiency resulted from the perturbation of flame parameters. Failure conditions were identified with high and low theoretical air, low temperature, poor atomization quality, and flame impingement on a cold surface. Each failure condition also resulted in elevated CO and hydrocarbon emissions. Thus, the results suggest that CO and hydrocarbon measurements can be used as an indirect, continuous means of monitoring incinerator flame-zone performance. © 1985 Combustion Institute

Flame-mode destruction of hazardous waste compounds

Incineration is a promising technique for the disposal of organic hazardous wastes. However, the waste destruction characteristics of turbulent spray flames have not been characterized. In the present research two reactors are used to simulate various aspects of liquid injection incinerator flame zones. The following questions are addressed: (1) Under what conditions do flames quantitatively destroy waste compounds, and (2) how must the flame be perturbed to cause it to fail to quantitatively destroy wastes. The two reactors operated on a simulated waste stream consisting of acrylonitrile, benzene, chlorobenzene, and chloroform. A microspray reactor was used to investigate destruction processes associated with individual droplets of waste compounds. A turbulent flame reactor used a heptane-fueled waste-doped turbulent spray flame to simulate incinerator flame-zone processes. The flames were found to be capable of quantitative waste destruction without the necessity of using common post-flame processes such as afterburners. Furthermore, the high waste destruction efficiency conditions corresponded to high combustion efficiency conditions (i.e., minimum CO and hydrocarbon emissions). Failure to achieve high destruction efficiency resulted from the perturbation of flame parameters. Failure conditions were identified with high and low theoretical air, low temperature, poor atomization quality, and flame impingement on a cold surface. Each failure condition also resulted in elevated CO and hydrocarbon emissions. Thus, the results suggest that CO and hydrocarbon measurements can be used as an indirect, continuous means of monitoring incinerator flame-zone performance. © 1985 Combustion Institute

Formation and measurement of N2O in combustion systems

Direct N2O emissions from fossil fuel combustion have previously been reported to be equivalent to 25-40% of the NOx levels. At these levels, fossil fuels have been suggested to be a major anthropogenic source of N2O. Recent tests have shown these measurements to be in error, most of the N2O having been formed by reaction between NOx, SO2, and H2O in the sample containers. Time resolved measurements of gas samples stored in Tedlar bags, supported by chemical kinetic calculations, indicate that the majority of N2O forms over a time period of 6 hours. The conversion of NOx to N2O in the sample containers is shown to depend on the amount of SO2 present. This sampling artifact raises questions about the validity of the existing data base, collected by grab sampling methods. As a result, a continuous infrared analyzer, developed primarily for characterization of N2O emissions from full scale combustion sources, was used to perform on line N2O measurements at several full scale utility combustion systems. A variety of conventional and advanced utility combustion systems (firing pulverized coal, oil, and gas) were tested. The measurements from conventional systems (natural gas, oil, and pulverized coalfired) indicate that the direct N2O emission levels are generally less than 5 ppm and are not related to the NOx levels in the flue gas. However circulating fluidized bed units produced elevated N2O emissions. At one circulating fluidized bed combustor firing a bituminous coal, N2O levels ranged from 84 to 126 ppm as the load was varied from 100% to 55%, respectively. The N2O emissions from the circulating fluidized bed appeared to be inversely related to the bed temperature. However, temperature is not the only parameter affecting N2O emissions from fluidized beds; all three of the units studied operated at similar temperatures during full load operation, but the N2O emissions ranged between 25 and 84 ppm. N2O emissions were also elevated at a full-scale boiler using selective non-catalytic NOx reduction with urea; 11-13% of the reduced NOx was converted to N2O. © 1991 Combustion Institute

Kinetics and Mechanisms of the Oxidation of Gaseous Sulfur Compounds

The problems associated with global climate change in general, and acid rain in particular, have led to a great deal of research on the atmospheric and combustion chemistry of sulfur. Developments over the last decade have led to significant progress in our understanding of the kinetics and mechanisms of the atmospheric oxidation chemistry of natural and anthropogenic sulfur. Rather less effort, however, has been placed on developing an understanding of sulfur combustion kinetics; the emphasis of mitigation research has instead been placed on removal of sulfur from fuels or development of scrubbing techniques to remove SO2 from stack gases