Vic A. Cundy

Characterization of thermal desorption phenomena for the cleanup of contaminated soil

Abstract The overall goal of this research is to develop an understanding of the fundamental transport phenomena associated with the evolution of hazardous constituents from several types of solid materials, in particular, soils. At the present time, incineration is a relatively costly alternative for the cleanup of contaminated soils. An understanding of the mass transfer and heat transfer limitations might lead to a more economical option, where the contaminants and other constituents are desorbed from the soil at lower temperatures in a primary combustor and then a secondary,high temperature combustor (afterburner) decomposes the potentially hazardous off-gases. This work is aimed at providing fundamental rate information which will be used to model thermal desorption of chemical constituents from soils under a Variety of thermal conditions, soil properties, and contaminants. The experimental approach is threefold. First, a bench-scale particle-characterization reactor (PCR) has been developed and is being used to characterize intraparticle transport under conditions where the bulk concentration and temperature at the particle surface are known. Following these studies, a packed-bed reactor will be used to examine interparticle transport within a well-characterized bed of particles. In the third portion of the work a 73 kW pilot-scale rotary kiln will be used to obtain time resolved measurements of trace species evolution. This paper reports recent PCR results which indicate that soil properties, type of contaminant, and temperature are important in the desorption of contaminants from soil particles.

Chemical Species and Temperature Profiles of Laminar Dichloromethane-Methane-Air Flames.I. Variation of Chlorine/ Hydrogen Loading

Abstract Gas samples have been extracted from laminar atmospheric pressure CH2 CI2-CH4 -air flat flames using uncooled quartz probes with 0.05 to 0.10 mm orifices. The samples ( 50torr total pressure) were analyzed by gas chromatography for a number of major C1 and C2 hydrocarbons, chlorinated hydrocarbons and CO, CO2, O2 CH4 N2and H2 Temperatures were obtained throughout the reaction zone and into the postflame region using Pt-Pt (13 percent Rh) uncoated thermocouples with typical bead diameters of 0.15 mm. Measurements of species concentrations (major and minor stable products) along with temperatures are provided as a function of vertical distance above the burner for three separate flames with Cl/ H ratios of 0.060, 0.33 and 0.72 for φ 0.80. All intermediate species (with the exception of CHC13) are observed to fall below detectable limits when the CH2 CI2 concentration is less than 1 percent of its initial value. Peak values of major intermediates are presented as a function of Cl/ H ratio. In additi...

Construction and novel application of a flat flame burner facility to study hazardous waste combustion

The construction and application of a flat flame facility specifically used in hazardous waste combustion studies are reported. The corrosive nature of the products formed during combustion of organic hazardous wastes requires special consideration in not only the design and selection of materials, but also in maintenance procedures. Sustained operational reliability, accurate measurement capabilities, and minimal human hazards were targeted as principal design considerations. Details are provided regarding the configuration of the laboratory scale burner chamber, the reactant feed systems, and the exhaust handling equipment, along with the probe arrangements used to collect experimental species and temperature data. A unique pumpless feed system capable of both metering and vaporizing liquid hazardous feed stocks is detailed. Special experimental constraints and the procedures followed to overcome these complexities are described. Test data for a dichloromethane/methane/air flame are provided.

Thermal analysis of rotary kiln incineration : comparison of theory and experiment

Abstract A comprehensive heat-transfer model and associated simplified scaling laws are developed and verified using a pilot-scale, directly fired rotary kiln with a slumping bed of dry or wet, 6-mm clay sorbent particles. The kiln operating conditions examined include: rotation rate (0.1–0.9 rpm), percent fill fraction (3–8), feed moisture content (0–20 wt. %), and inner-wall temperature (190°–790°C). The model is used to determine the relative importance of several heat-transfer mechanisms, including radiation, gas-to-solid convection, and wall-to-solid convection. Simple scaling laws are also developed for water vaporization. Generally good agreement is obtained between theory and experiment without adjusting any model parameters. Further, the simplified scaling laws provide a reasonable estimate of the pilot scale performance. The key conclusions of this study for kilns at the conditions examined are (1) water exerts a profound effect on the solids thermal profile, (2) simple geometrical scaling is not sufficient, (3) the assumption of a well mixed (radially isothermal) solids bed for the heat transfer analysis is appropriate, (4) a dimensionless group, which is a function of temperature, can be defined giving the relative importance of radiative and convective modes of heat transfer, and (5) moisture vaporization rates can be roughly approximately by assuming that the water vaporizes at the boiling point at a rate controlled by the rate of heat transfer to the bed. The implications of the scaling laws for scale-up and kiln design are also examined.

Constant-tension thermocouple rake suitable for use in flame mode combustion studies

An improved design for a thermocouple rake configuration to be used in fundamental combustion studies is presented. Experience with the constant‐tension thermocouple rake has nearly eliminated thermocouple sensing wire sag which is common using conventional rake configurations.

Heat transfer between a rotating cylinder and a moist granular bed

Abstract A model is developed which describes the heat transfer process between the rotating wall of a desorber and an adjacent bed of wet, granular solids. A heat-balance integral method is used. This solution includes the effects of water evaporation near the wall and a thermal contact resistance between the wall and the first layer of particles. The model allows for water evaporation before the bulk bed temperature reaches the saturation temperature of the water. Experimentally measured evaporation rates compare favorably to those predicted by the model. In particular, the water evaporation that occurs before the bulk bed temperature reaches the water saturation temperature is predicted.

Rotary kiln incineration ― combustion chamber dynamics

Abstract A multifaceted experimental and theoretical program aimed at understanding rotary kiln performance is underway. The overall program involves university, industry, and government participation and is broken into distinct sub-programs. This paper discusses in some detail the research effort performed to date in two of the sub-programs: full-scale in situ sampling and kiln-simulator experimentation. Full-scale in situ measurements are obtained from the Louisiana Division rotary kiln facility of Dow Chemical USA, located in Plaquemine, Louisiana. Summary results obtained from controlled experiments that were performed during continuous processing of carbon tetrachloride and preliminary results obtained during batch mode processing of toluene-laden sorbent packs are presented. Kiln-simulator data are obtained by using the facilities of the Chemical Engineering Department at the University of Utah. Recent kiln-simulator work, conducted in support of the full-scale measurements sub-program, has aided in providing an understanding of the results that have been obtained at the full-scale. Modeling efforts, conducted at Louisiana State University and the University of Utah, have concentrated on the development of realistic, fluid-flow and heat-transfer models, near-term chlorinated kinetic models and bed mass-transfer models to be incorporated into a global three-dimensional kiln-simulator model. The paper concludes with an overview of these modeling efforts.

THE COMBUSTION CHARACTERISTICS OF SELECTED CHLORINATED METHANES IN A FLAT FLAME ENVIRONMENT

Incineration in a properly designed and operated facility has been recommended as a preferred control technology for combustible organic hazardous wastes. In principle, a completely efficient incinerator converts organic hazardous material via high temperature thermal oxidation to carbon dioxide, water and low volume inert ash material. During the incineration of halogenated hazardous waste streams, significant quantities of halogen acids are also formed. In order to optimally design incinerators and to ensure that incinerators perform according to current United States Environmental Protection Agency regulations, it is critical to better understand the thermal destruction behavior of organic hazardous wastes. This paper reports initial results, principally empirical in nature, concerning a kinetically based study into the combustion of selected chlorinated methanes. A complete description of the experimental facility, operational procedures and operational experiences is provided. Results obtained with a...

Combustion of bagasse: Use of an agricultural-derived waste

Abstract The recent escalation in price of conventional fossil fuels and their uncertain availability has precipitated an intense effort world-wide to develop so called ‘unconventional’ or ‘alternative’ fuels. The waste product from the sugar cane grinding process, termed bagasse, represents an agricultural energy resource which is increasingly used in the sugar industry as a fuel. Currently, the pile burning configuration involving high excess air levels and low combustion efficiencies constitutes the major method of bagasse combustion. This Paper reports on a novel burner which has been developed to burn bagasse efficiently in full-suspension at low excess air levels (down to 5%) thereby generating high combustion efficiencies. To accomplish this excess air level the bagasse was dried to a maximum of 16% moisture and pulverized so that 60–65% passed a 30 US Standard Sieve mesh. A discussion is included concerning optimum methods of bagasse preparation for this system.

DYNAMICS OF ROTARY KILN INCINERATION OF TOLUENE/SORBENT PACKS

Abstract The dynamic response of an industrial incinerator to the batch loading of single plastic packs loaded with a toluene/sorbent mixture is reported. Specifically, stable species concentrations and temperature are reported as a function of time for the upper half of the exit region of a rotary kiln, and the exit of the afterburner. Volatile organic sampling train (VOST) samples and continuous measurements of O2, and CO at the stack are also reported. Inconjuction with video tape recordings of the phenomena occurring in the kiln during the processing of each pack, the data provide a much clearer picture than heretofore possible of the conditions that exist in an industrial incinerator. A number of observations are notable. The existence of intermittent releases of hydrocarbon from the processing of each pack has been confirmed. Attendant to these excursions is the production of large quantities of soot in the bottom half of the kiln and the formation of significant vertical gradients in temperature an...