Thomas H. Fletcher

• Bachelor of Science, Master of Science, PhD
• Professor (Full) at Brigham Young University

Background Fire models have used pyrolysis data from oxidising and non-oxidising environments for flaming combustion. In wildland fires pyrolysis, flaming and smouldering combustion typically occur in an oxidising environment (the atmosphere). Aims Using compositional data analysis methods, determine if the composition of pyrolysis gases measured...

The aim of this study was to investigate the pyrolysis of selected California foliage and estimate the energy content of the released volatiles to show the significance of the pyrolysis of foliage and its role during wildland fires. While the majority of the volatiles released during the pyrolysis of foliage later combust and promote fire propagati...

Biomass char particles produced by pyrolysis may have different morphologies, which has important implications on burning mode, conversion rate and boiler efficiency. These features are difficult to address due to the complexity of biomass structure and pyrolysis reaction models. The present work reports preliminary results on the morphological cha...

Simulations of pulverized coal boilers and gasifiers have become easier and more complex as computational resources become more available. The improvements in simulations have generally focused on the fluid dynamics and grid resolution, with marginal improvements in treatments of the fundamental coal reactions. In this work, suggestions are made in...

The purpose of this study was to investigate the merging behavior of small-scale buoyant flames that might be representative of flames from a leaf in a shrub. Zirconia felt pads soaked in n-heptane were suspended on thin rods and spaced both horizontally and vertically. Time-dependent video images from flames from two-pad and three-pad configuratio...

Slow-heating pyrolysis experiments of 14 plant species native to forests in the southern United States were conducted in a TGA to find the kinetic parameters for slow pyrolysis of all live and air-dried plant samples. Kinetic coefficients were determined from the data using model-fitting methods, resulting in single kinetic parameters for the entir...

Pyrolysate gas mixtures are multivariate and relative in nature. Statistical techniques applied to these data generally ignore their relative nature. Published data for permanent gases (CO, CO2, H2, CH4) and tars produced by pyrolysing 15 wildland fuels were reanalysed using compositional data analysis techniques. Mass and mole fractions were compo...

Accurately measuring a fuel’s heating value is one of the first steps in the classification of a new fuel. Heating values are widely used in coal combustion research and are becoming more useful in other fuel types as well. Many different empirical correlations to predict heating values based on primary organic (CHONS) elemental composition are fou...

This comprehensive critical review combines, for the first time, recent advances in nanoscale surface chemistry, surface science, DFT, adsorption calorimetry, and in situ XRD and TEM to provide new insights into catalyst sintering. This work provides qualitative and quantitative estimates of the extent and rate of sintering as functions of nanocrys...

The Grate-Kiln process is employed for sintering and oxidation of iron ore pellets. In this process, a fuel (typically coal) is combusted with a large amount of excess air in a rotary kiln and the high air-to-fuel ratio leads to significant NOx formation. The current paper is an assessment of NOx reduction measures that have been tested in pilot-sc...

During wildland fires, which include both planned (prescribed fire) and unplanned (wildfire) fires, live and dead plants may be subject to both radiative and convective heat transfer mechanisms. In this study, the pyrolysis of 14 live plant species native to the forests of the southern United States was investigated using a flat-flame burner (FFB)...

The Chemical Percolation Devolatilization (CPD) model for coal pyrolysis was first published in 1989 and a completed version that included the vapor-liquid equilibrium model and crosslinking model was published in 1992. The CPD model was one of three pyrolysis models developed using a lattice model to account for the chemical structure of the coal,...

Coal is, and will remain, a critical energy production resource for the foreseeable future. Advanced models of coal conversion behavior in air and oxy-coal environments enhance boiler operational efficiency and design optimization. Though coal conversion models have continuously improved over decades of research, not all aspects of coal particle he...

The influence of changes in aliphatic structure on char surface area during coal pyrolysis was modeled, and the effect was introduced to a previous char surface area model for lignite pyrolysis established based on the chemical percolation devolatilization (CPD) model. The modified model can predict not only the N2 and CO2 char surface area during...

Simulations of large-scale coal combustors rely on accurate submodels to describe the chemical and physical changes in coal during reaction. Typically, researchers use simplified empirical submodels tuned to experimental data to reduce the computational complexity. When data are not readily available, researchers use simplifying assumptions, which...

The fundamental combustion behavior of live wildland vegetation is not fully understood. Since the combustion process during wildland fire starts with pyrolysis, there is a need for better understanding of pyrolysis to develop improved wildland fire models. The kinetics of pyrolysis of live and dead wildland vegetation has not been explored in deta...

Wildland fire, which includes both planned (prescribed fire) and unplanned (wildfire) fires, is an important component of many ecosystems. During wildland fires, low heating rate pyrolysis (slow pyrolysis) occurs during preheating and/or smoldering of plant material. High heating rate pyrolysis (fast pyrolysis) exists in the flame region. Pyrolysis...

To study coal pyrolysis behavior at underground coal thermal treatment (UCTT) conditions, a modified CPD (M-CPD) model was developed and evaluated using two scales of experiments, as well as two different coals, Utah Sufco and Illinois #6. Compared with the original CPD model, three major aspects were changed, including: 1) rewriting the algorithm...

Prescribed burning (controlled burning) is used to decrease accumulation of combustible materials and reduce impact of uncontrolled wildland fires. Prescribed fires are often used to burn undergrowth in Southern forests of the United States. In order to improve prescribed fire application, accomplish desired fire effects, and limit potential runawa...

Some industrial gas turbines are currently being fired using heavy fuel oil, which contains a small percentage of inorganic material that can lead to fouling and corrosion of turbine components. Deposits of heavy fuel oil ash were created in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University under gas turbine-related con...

A series of silver-promoted, 20 wt% cobalt Fischer-Tropsch synthesis (FTS) catalysts supported on an alumina modified with 5 wt% silica were prepared using two methods: traditional incipient wetness impregnation (IWI) and a new solvent deficient precipitation (SDP) technique. Catalysts containing silver promoter concentrations of 0.3, 0.6, 1.2, and...

Flame and mass loss data for chaparral, a mixture of shrub plants from the Mediterranean climate zone of southwestern North America, from five previously reported experiments were used to evaluate several published models relating flame characteristics to mass loss and heat release rates. These data are unique with fuel moisture content ranging fro...

The Coanda effect is the phenomenon in which a jet entering quiescent fluid attaches to a nearby solid object due to inhibited entrainment of ambient fluid near the solid. Little is known about the influence of the Coanda effect on wildland fire behavior. Specifically, there is a lack of knowledge regarding how the flame attachment on slopes influe...

Oxy-fired coal combustion is a promising potential carbon capture technology. Predictive CFD simulations are valuable tools in evaluating and deploying oxy-fuel and other carbon capture technologies either as retrofit technologies or for new construction. However, accurate predictive combustor simulations require physically realistic submodels with...

This paper presents a statistical method for model calibration using data collected from literature. The method is used to calibrate parameters for global models of soot consumption in combustion systems. This consumption is broken into two different submodels: first for oxidation where soot particles are attacked by certain oxidizing agents; secon...

A model for the evolution of pore structure in a lignite particle during pyrolysis was established previously based on the chemical percolation devolatilization (CPD) model, using coal polymer network parameters to calculate surface area and porosity of the particle. In this paper, to get accurate surface area of coal particle at high pyrolysis tem...

Some industrial gas turbines are currently being fired directly using heavy fuel oil, which contains a small percentage of inorganic material that can lead to fouling and corrosion of turbine components. Deposits of heavy fuel oil ash were created in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University under gas turbine-re...

Oxy-fired coal combustion is a promising potential carbon capture technology. Predictive CFD simulations are valuable tools in evaluating and deploying oxy-fuel and other carbon capture technologies either as retrofit technologies or for new construction. However, accurate predictive simulations require physically realistic submodels with low compu...

A semi-empirical model was developed which forms shrub geometries from distinct fuel elements (e.g. leaves) and describes flame spread from element to element. Ignition, flame growth and flame decay patterns were based on combustion data of single leaves. Extension of the model to various heating conditions was achieved by scaling the flame growth...

This chapter presents fundamentals of gasification, with a focus on solid fuel gasification, although there are some industrial applications of liquid and gaseous fuel gasification. Fundamental concepts, mechanisms, and rate laws pertaining to gasification of solid fuels are presented. Fuel characterization techniques and classification of fuels ba...

Petroleum products which are used in a wide variety of industries as energy sources and raw materials have become a major concern in pollution of terrestrial and marine environments. The purpose of this study was to assess the potential of indigenous microbial isolates for degradation of diesel fuel. Two most proficient bacterial strains among five...

Simulations of coal combustors and gasifiers generally cannot incorporate the complexities of advanced pyrolysis models, and hence there is interest in evaluating simpler models over ranges of temperature and heating rate that are applicable to the furnace of interest. In this paper, six different simple model forms are compared to predictions made...

Oxy-fired coal combustion is a promising potential carbon capture technology. Predictive CFD simulations are valuable tools in evaluating and deploying oxy-fuel and other carbon capture technologies either as retrofit technologies or for new construction. However, accurate predictive simulations require physically realistic submodels with low compu...

When performing large-scale, high-performance computations of multi-physics applications, it is common to limit the complexity of physics sub-models comprising the simulation. For a hierarchical system of coal boiler simulations a scale-bridging model is constructed to capture characteristics appropriate for the application-scale from a detailed co...

Deposition of coal flyash in gas turbines has been studied to support the concept of integrated gasification combined cycle (IGCC). Although particle filters are used in IGCC, small amounts of ash particles less than 5 μm diameter enter the gas turbine. Previous deposition experiments in the literature have been conducted at temperatures up to abou...

In this paper, on the basis of the chemical percolation devolatilization (CPD) model and using the coal polymer network parameters to calculate the surface area and porosity of the particle, a model for the evolution of pore structure in a lignite particle during pyrolysis is established. The model connects the polymer network structure and the por...

Recent detailed chemical structure analyses of three demineralized kerogens from Green River oil shale samples were used to generate input parameters for the chemical percolation devolatilization (CPD) model. This model uses a lattice network to describe pyrolysis of solid hydrocarbons, such as coal and biomass. It was necessary to modify the formu...

A model was established previously to predict the swelling ratio of high volatile bituminous coal during pyrolysis based on the assumption that the structure of bubble distribution in the particle at the beginning of the plastic stage is a central bubble surrounded by many surrounding bubbles. The initial number and size of the bubbles when the par...

The role and distribution of moisture during thermal degradation and gas phase combustion of a vertically oriented solid fuel subjected to convective and radiative heating is investigated experimentally and numerically. Manzanita (Arctostaphylos glandulosa) leaves were exposed to convective (flat flame burner at 1000 o C) and radiative (50 kW/m^2)...

Current field models for wildfire prediction are mostly based on dry or low-moisture fuel combustion research. To better study the live fuel combustion behavior, a laminar flow flat-flame burner was used to provide a convection heating source to ignite an individual live fuel sample. In this research project, four Utah species were studied: Gambel...

Three bituminous coal chars (Illinois #6, Utah Skyline, & Pittsburgh #8) were gasified separately at total pressures of 10 and 15 atm in an entrained-flow reactor using gas temperatures up to 1830 K and particle residence times < 240 ms. Most of the experiments were performed at conditions where the majority of particle mass release was due to H2O...

Burning behaviors of individual live and dead leaves were measured in a well-instrumented, well-controlled flat-flame burner. Manzanita (Arctostaphylos glandulosa) branches were harvested from the Chaparral near Riverside, California. Leaves were conditioned to several moisture contents. Two “live” (i.e., not fully dried) groups remained above the...

In this paper, a model is established to predict the swelling ratio of high-volatile bituminous coal during pyrolysis, based on the assumption that the structure of bubble distribution in the particle at the beginning of the plastic stage is a central bubble surrounded by many surrounding bubbles. The initial number and size of the bubbles when the...

In this paper, a model is established to predict the swelling ratio of high-volatile bituminous coal during pyrolysis, based on the assumption that the structure of bubble distribution in the particle at the beginning of the plastic stage is a central bubble surrounded by many surrounding bubbles. The initial number and size of the bubbles when the...

An entrained-flow flat-flame burner reactor was used to measure apparent CO2 gasification rates of near-spherical biomass chars of poplar sawdust, switchgrass, and corn stover using particle residence times <270 ms at total pressures of 10 and 15 atm. The gas temperature and bulk CO2 partial pressure ranges in these gasification experiments were 12...

Two petcoke samples were gasified by CO2 at total pressures of 10 and 15 atm in a high-pressure flat-flame burner reactor at conditions where the bulk phase consisted of either 40 or 90 mol % CO2 with gas temperatures up to 1909 K. Particle diameters of 45-75 μm were used in the experiments. The morphology of the two petroleum coke chars was drasti...

The evolution of pressure in a lignite particle during pyrolysis was simulated on the basis of the gas motion equation in porous media and considering the Klinkenberg effect. The chemical percolation devolatilization (CPD) model was used to describe pyrolysis. The pore diameter in the particle is close to the average free path of volatile gas molec...

This paper is Part II of a study of the chemical structural components of the organic matter of oil shale in the Green River formation. Three sections of a well-characterized oil shale core from the Utah Green River formation were demineralized, and the resulting kerogen was pyrolyzed at 10 °C/min in nitrogen at atmospheric pressure at temperatures...

Improved models of fire spread and fire characteristics are desired for live shrub fuels, since the majority of existing research efforts focus on either dead fuel beds or crown fires in trees. Efforts have been made to improve live fuel modeling, including detailed studies of individual leaf combustion, with results incorporated into a shrub combu...

The effect of season and heating mode on ignition and burning behavior of living vegetation were studied in a flat-flame burner system with a radiant panel. The goal is to identify what plant characteristics have the greatest influence on burning behavior and to summarize the effects of heating mode on ignition and burning. Experiments were perform...

An entrained-flow flat-flame burner reactor was used to measure apparent CO2gasification rates of near-spherical biomass chars of poplar sawdust, switchgrass, and corn stover using particle residence times < 270 ms at total pressures of 10 and 15 atm. The gas temperature and bulk CO2partial pressure ranges in these gasification experiments were 127...

Steam gasification kinetics of 3 bituminous coal chars (Illinois #6, Utah Skyline, & Pittsburgh #8) were determined from experiments at entrained-flow conditions in a pressurized flat-flame burner facility at high temperature and elevated pressure. The experimental conditions utilized gas temperatures up to 1830 K and total pressures of 10 and 15 a...

Volatile products from an oil shale from the Colorado Green River formation were studied by several methods. The oil shale was demineralized, and the resulting kerogen was also chemically analyzed. Both the oil shale and the demineralized kerogen were pyrolyzed at 10 K/min, and the pyrolysis products (light gas, tar, and char) were analyzed using 1...

A pressurized flat-flame burner (PFFB) was used to conduct coal gasification studies. The PFFB was designed to provide an environment with laminar, dispersed entrained flow, with particle heating rates of 105 K/s, pressures of up to 15 atm, and gas temperatures of up to 2000 K. Residence times were varied from 30 to 700 ms in this study. Char gasif...

High heating rate pyrolysis experiments were performed on a softwood sawdust in a flat-flame burner reactor at temperatures from 1163 to 1433 K with particle residence times ranging from 23 to 102 ms at atmospheric pressure. Volatile yields of the 45–75 μm sawdust were measured and are believed to be similar to those that would occur in an industri...

The pyrolysis and CO2 gasification of two petroleum coke samples from industry was studied in a pressurized flat-flame burner at particle heating rates of 105 K/s at pressures up to 15 atm. The ASTM volatiles value of petroleum coke appeared to be a good approximation of the mass release experienced during pyrolysis at conditions of high initial pa...

The pyrolysis and CO2 gasification of four biomass feed stocks (Poplar sawdust, straw, switchgrass, and corn stover) were studied at conditions of high initial particle heating rates (∼105 K/s) using two flatflame burner reactors. The chosen feed stocks include energy crops as well as both woody and agricultural residues. Pyrolysis experiments were...

The behavior of live fuels is clearly different from that of dead fuels in wildfire conditions. Fire spread is sustainable at higher fuel moisture contents in live fuels than in dead fuels, but the fundamental reasons for this difference are not understood. Studies have examined the ignition times, rates of fire spread, moistures of extinction, and...

Wildfire models serve many purposes, from highly empirical operational models that provide decision support for fighting active fires to physical models which provide insights about fire behavior. The fuel structure of live fuels is usually complex and while leaf-scale fuel placement and behavior can significantly impact bulk fire behavior, a model...

A generalized model for describing the pyrolysis behavior of low-grade fuels is being developed for incorporation into larger combustion simulation models. Light gas and tar yields from black liquor or biomass pyrolysis can be predicted using the chemical percolation devolatilization (CPD) model originally developed for coal. The initial approach i...

A model was previously developed to describe the decrease in swelling during coal pyrolysis at atmospheric pressure when maximum particle heating rates increase from 104 K/s to 105 K/s. That model included effects of coal type using chemical structure properties. This paper presents results of new experiments to study the effects of elevated pressu...

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the nature of flyash deposits near film cooling holes. Deposition on both bare metal and thermal barrier coating (TBC) coupons was studied, with hole spacing (s/d) of 2.25, 3.375, and 4.5. Sub-bituminous coal ash particles (mass mean diameter o...

Iron-based catalysts have been shown to enhance coal pyrolysis and char oxidation at low to moderate temperatures and heating rates (< 1250 K and 1–1000 K/s). Such catalytic activity has not been demonstrated at high heating rates and temperatures approaching pulverized coal combustion applications. The effect of an iron-based additive on coal pyro...

Individual cuttings from five shrub species were burned over a flat-flame burner under wind conditions of 0.75–2.80 m s–1. Both live and dead cuttings were used. These included single leaves from broadleaf species as well as 3 to 5 cm-long branches from coniferous and small broadleaf species. Flame angles and flame lengths were determined by semi-a...

Thermal swelling of coal during pyrolysis strongly influences combustion and gasification rates. Coal swelling is known to vary strongly with coal rank, heating rate, and total pressure. New experiments confirm and clarify previous observations that maximum swelling occurs for high-rank bituminous coals at heating rates slightly below 10(4) K/s. Ad...

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the effects of flyash particle size and trench configuration on deposits near film cooling holes. Deposition on two bare metal Inconel coupons was studied, with hole spacings (s/d) of 3.4 and 4.5. Two sizes of sub-bituminous coal ash particles...

Time-dependent deposition characteristics of fine coal flyash were measured in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University. Two samples of subbituminous coal fly ash, with mass mean diameters of 3 and 13 μm, were entrained in a hot gas flow with a gas temperature of 1250°C and Mach number of 0.25. A nickel base su...

Crushed samples of Green River Oil Shale and its kerogen extract were pyrolyzed at heating rates from 1 to 10 K/min at pressures of 1 and 40 bar and temperatures up to 1000 °C. Two to four mass release peaks were observed with the major two corresponding to kerogen pyrolysis and carbonate decomposition. The transient pyrolysis data were fit with a...

Three coals were studied in a flat flame burner (FFB) to determine nitrogen release during pyrolysis as a function of the temperature from 1600 to 1900 K in an oxy-fuel environment. The oxy-fuel environment was created by replacing the background N2 with CO2 in the FFB experiments. Both types of experiments were conducted under fuel-rich conditions...

CO2 gasification kinetics of petroleum coke were studied in a high pressure flat-flame burner from 1 to 15 atm and particle heating rate of 105 K/s. The rapid pyrolysis of sawdust was also studied using an atmospheric flat-flame burner. The high initial particle heating rates of the pressurized flat-flame burner more closely match industrial heatin...

Although remarkable progress has been made in developing technologies for the clean and efficient utilization of coal, the biggest challenge in the utilization of coal is still the protection of the environment. Specifically, electric utilities face increasingly stringent restriction on the emissions of NO and SO, new mercury emission standards, an...

Thermogravimetric analysis (TGA) at a constant heating rate is a popular technique for characterizing reaction behavior. Determination of kinetic coefficients from such TGA data has given rise to a large range of reported activation energies for similar samples. In general, rate coefficients are determined using either a linearized integral method...

The chemical processes of gas phase combustion in wildland fires are complex and occur at length-scales that are not resolved in computational fluid dynamics (CFD) models of landscape-scale wildland fire. A new approach for modelling fire chemistry in HIGRAD/FIRETEC (a landscape-scale CFD wildfire model) applies a mixture–fraction model relying on...

Individual samples of high moisture fuels from the western and southern United States and humidified aspen excelsior were burned over a flat-flame burner at 987° ± 12°C and 10 ± 0.5 mol% O2. Time-dependent mass and temperature profiles of these samples were obtained and analysed. It was observed that significant amounts of moisture remained in the...

In a slagging entrained-flow coal gasifier, a large portion of the inorganic matter will form liquid slag that may have strong physical and chemical interactions with char. Understanding the char−slag interaction is important for improving the modeling and design of gasifiers. This paper reports the characteristics of residual carbon in both coarse...

Coal is the energy resource which is important with the new remarking energy resource. Coal combustion produces more NOx per unit of energy than any other major combustion technology. Pollutant emission associated with coal combustion will have a huge impact on the environment. Coal conversion has three processes which are drying, coal devolatiliza...

The chemical percolation devolatilization (CPD) model describes the devolatilization behavior of rapidly heated coal based on the chemical structure of the coal. It predicts the overall char, tar, and light gas yields. This paper presents an improved CPD model with improved capability for predicting light gas composition. This is achieved by incorp...

Combustion experiments were performed over a flat-flame burner that provided the heat source for multiple leaf samples. Interactions of the combustion behavior between two leaf samples were studied. Two leaves were placed in the path of the flat-flame burner, with the top leaf 2.5 cm above the bottom leaf. Local gas and particle temperatures, as we...

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the nature of flyash deposits near film cooling holes. Deposition on both bare metal and TBC coupons was studied, with hole spacings (s/d) of 2.25, 3.375, and 4.5. Sub-bituminous coal ash particles (mass mean diameter of 13 microns) were accele...

Experiments were conducted to determine the impact of synfuel deposits on film cooling effectiveness and heat transfer. Scaled up models were made of synfuel deposits formed on film-cooled turbine blade coupons exposed to accelerated deposition. Three distinct deposition patterns were modeled: a large deposition pattern (max deposit peak ≅ 2 hole d...

Numerical computations were conducted to simulate flyash deposition experiments on gas turbine disk samples with internal impingement and film cooling using a CFD code (FLUENT). The standard k-ω turbulence model and RANS were employed to compute the flow field and heat transfer. The boundary conditions were specified to be in agreement with the con...

Particulate deposition experiments were performed in a turbine accelerated deposition facility to examine the effects of flyash particle size and trench configuration on deposits near film cooling holes. Deposition on two bare metal Inconel coupons was studied, with hole spacings (s/d) of 3.375 and 4.5. Two sizes of sub-bituminous coal ash particle...

Soot produced from coal during gasification plays a significant role in radiative heat transfer inside a gasifier, changing the predicted flame temperature by hundreds of degrees. The radiation from the soot can also increase the wear on the coal injector. Coal tar and soot act as carriers for fuel nitrogen. Additionally, soot may be more difficult...

A flat-flame burner system has been developed to pyrolyze and gasify coal at ~105 K/s, temperatures of 1200-1800 K, and total pressures of 2.5-15 atm. The burner is fueled by methane, hydrogen, and air. The flame stoichiometry was adjusted to provide a fuelrich environment for gasification. This system was used to pyrolyze and gasify a sub-bitumino...

A premixed, staged, down-fired, pulverized coal reactor and a flat flame burner were used to study the evolution of nitrogen in coal contrasting differences in air and oxy-combustion. In the premixed reactor, the oxidizer was staged to produce a fuel rich zone followed by a burnout zone. The initial nominal fuel rich zone stoichiometric ratio (S.R....