Christopher B. Leger

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.

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.

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...

Rotary Kiln Incineration III. An Indepth Study—Kiln Exit/Afterburner/Stack Train and Kiln Exit Pattern Factor Measurements During Liquid CCl4 Processing

Temperature and stable species concentration data are presented from various locations within a full-scale rotary kiln incinerator firing natural gas/carbon tetrachloride/air. The data are being collected as part of a cooperative program involving university, industry and government participation. The overall goal of the program is to develop a more sophisticated understanding of and a predictive capability for rotary kiln and afterburner performance as influenced by basic design and operational parameters. Non-uniformities in stable species and temperature exist for this particular kiln, at the kiln exit, under certain operating conditions. Flow perturbations from within the kiln were found to persist into the afterburner, but not into the stack. High destruction and removal efficiencies (DRE’s) were achieved under the operating conditions of these tests through adequate secondary combustion processing.

The desorption of toluene from a montmorillonite clay adsorbent in a rotary kiln environment

The vaporization of toluene from pre-dried, 3 mm montmorillonite clay particles was studied in a 130 kW pilot-scale rotary kiln with inside dimensions of 0.61 by 0.61 meters. Vaporization rates were obtained with a toluene weight fraction of 0.25 percent as a function of kiln fill fractions from 3 to 8 percent, rotation rates from 0.1 to 0.9 rpm, and kiln wall temperatures from 189 to 793 C. Toluene desorption rates were obtained from gas-phase measurements and interpreted using a desorption model that incorporates the slumping frequency of the solids, the fill fraction of the kiln, the diffusion of toluene in the bed, and the rate of particle desorption using an Arrhenius-type expression that is a function of bed temperature and average bed concentration. The model included three adjustable desorption parameters which were obtained by fitting the experimental data at one set of conditions with a least squares technique. Solid and kiln-wall temperatures were continuously recorded and used in the model at predicting the effects of fill fraction and rotation rate over a range of temperatures. A methodology for predicting full-scale performance was developed. Full-scale toluene desorption predictions were completed for different operating temperatures.

Rotary Kiln Incineration of Dichloromethane and Xylene: A Comparison of Incinerability Characteristics Under Various Operating Conditions

Comparisons are made, for the first time, between the combustion characteristics of dichloromethane and xylene in an industrial rotary kiln incinerator. The comparisons are made under different operating conditions, including variable kiln rotation rate and operation both with and without turbulence air. Continuous gas composition and temperature measurements and batch gas composition measurements were obtained from two vertical locations hear the exit region of the rotary kiln. The measurements show that there is significant vertical stratification at the exit of the kiln. Addition of turbulence air enhanced combustion conditions throughout the kiln during xylene processing. During dichloromethane processing, however, the addition of turbulence air had minimal effect and only promoted greater bulk mixing; chlorinated compounds transported from the lower kiln during operation with turbulence air were not efficiently processed in the upper kiln. Evolution of test liquids from the bed was not constant but r...

Field-scale rotary kiln incineration of batch loaded toluene/sorbent. I: Data analysis and bed motion considerations

Abstract In this study, a field-scale rotary kiln incinerator was used for experiments on the processing of toluene contaminated sorbent contained in plastic pa

Field-scale rotary kiln incineration of batch loaded toluene/sorbent. II. Mass balances evolution rates and bed motion comparisons

Abstract A field-scale rotary kiln incinerator is used to obtain data on the processing of toluene contaminated sorbent contained in plastic packs. The solids b

Rotary Kiln Incineration IV. An Indepth Study— Kiln Exit, Transition and Afterburner Sampling During Liquid CCl4 Processing

Detailed temperature and stable species concentration data are presented from the kiln exit, transition section and afterburner of a full-scale incinerator facility firing natural gas/carbon tetrachloride/air. The data are collected as part of a cooperative program involving university, industry and government participation. The overall goal of the program is to develop an understanding and predictive capability for rotary kiln and afterburner performance as influenced by basic design and operational parameters. The data demonstrate that nonuniformities in stable species and temperature exist, under certain operating conditions, at the kiln exit in the vertical direction only. Measurements from the transition section indicate that non-uniformities may exist within this region under certain operating conditions. Flow perturbations from within the kiln can persist into the afterburner, although the degree of nonuniformity is substantially reduced compared to either the kiln or transition sections. High dest...

Estimating dichloromethane evolution rates from a sorbent bed in a field-scale rotary kiln incinerator

Estimates of dichloromethane evolution rates from the bed of a field-scale rotary kiln are provided during several modes of operation. The calculations of evolution rates are based on stoichiometry and combustion measurements; assumptions that are necessary due to practical limitations imposed on the experiments are discusscd in detail in the paper. A sensitivity analysis of the calculation procedure is also discussed. Mass closures have been shown to range from 65 to 110% depending on the operating condition. Given the uncertainties associated with field-scale testing, these closures are quite remarkable