Development of a Drop Tube Furnace for Visualization of 
Combustion of Fuel Particles 
 
by 
 
Fengming Huang 
 
 
 
 
 
A thesis submitted to the Graduate Faculty of 
Auburn University 
in partial fulfillment of the 
requirements for the Degree of 
Master of Science 
 
Auburn, Alabama 
May 14, 2010 
 
 
 
 
Keywords:  drop tube furnace, alternative fuels, combustion, 
visualization 
 
 
Copyright 2010 by Fengming Huang 
 
 
Approved by 
 
Steve R. Duke, Chair, Associate Professor of Chemical Engineering 
Gopal A. Krishnagopalan, Professor of Chemical Engineering 
Mario R. Eden, Associate Professor of Chemical Engineering  
Anton K. Schindler, Associate Professor of Civil Engineering  
 
ii 
 
 
 
 
 
 
Abstract 
 
 
This thesis describes the development of a laboratory-scale burn simulator 
designed to maximize visualization capability in a combustion furnace with a high degree 
of control of temperature and particle presence. A specific research goal is to provide an 
understanding of combustion phenomena under conditions that simulate energy 
generation processing in cement production, such that alternative fuels can be evaluated 
as possible replacements for coal and other fossil fuels.  
The solid fuels used for this study were coal, wood chips and switch grass. The 
fuel particles used in the experiments were approximately 100 microns in size. 
Microscope and scanning electron microscope (SEM) devices were used to obtain images 
of the fuel particles to display their sizes and shapes. 
The thesis presents a description of a drop tube furnace and experiments that were 
conducted in it to observe and evaluate combustion characteristics and phenomena 
related to a high-temperature conversion of solid fuels. The design and operating 
conditions of the furnace were selected to evaluate the effectiveness of alternative fuels 
wood and switch grass in comparison to coal for application in cement production. A 
facility was designed and constructed for visualization of solid particles in a drop tube at 
laboratory room temperature and high temperatures (900 oC). Three visualization systems 
with different functions were applied to obtain images of particles in the furnace. The 
magnifications of different imaging systems were determined. The magnification for the 
 iii 
images of combustion of particles in the furnace drop tube was 2.31 ?m/pixel while the 
magnification of microscope images was 0.30 ?m/pixel. The resolution of the 
combustion images in the vertical direction was 0.031 mm/cycle and 0.050 mm/cycle in 
the horizontal direction.  
A fuel particle injection system is described and shown to be effective at 
providing a controlled delivery of solid particles to the furnace drop tube. Particles were 
introduced via a vibrating syringe and flat-tip needle into a water-cooled injection nozzle 
to drop particles into the heated retort in the furnace. Dropping conditions were different 
for coal, wood and switch grass particles, and experiments determined that No. 21 gauge 
needles were best for coal particles while No. 20 gauge needles were best for wood 
particles and switch grass particles. 
            Clear and highly resolved images of coal, wood, and switch grass particles 
undergoing combustion at 900 oC in air were obtained. SEM and microscope images 
were obtained of the fuel particles before and after combustion.  Images of the burning 
particles revealed clarity and intensity contrast sufficient to estimate particle and flame 
size and shape. Particles were infrequently in the camera field of view at the highest 
magnifications because they meandered as they fell. Nevertheless, the capability of the 
furnace and imaging system was demonstrated, validating the potential of the system to 
provide color images for surface temperature measurement of solid particles undergoing 
combustion. 
 
 
 
 
 iv 
 
 
 
 
 
Acknowledgements 
 
 
The author would like to thank Dr. Steve Duke for his help and support in this 
research. He has been an excellent research advisor and motivator. I would like to express 
my gratitude towards my committee members, Drs. Mario Eden, Gopal Krishnagopalan, 
and Anton Schindler for their time and assistance in helping me complete this task. I 
would like to show my deep appreciation to Brian Schwieker for mounting the furnace 
system and useful technical suggestions to improve the system. I also would like to thank 
Dr. Oladiran Fasina for providing fuel samples and use of his equipment for particle 
preparation. 
The author would like to thank the U.S. Department of Energy for financial 
support. 
The author would also like to thank all of the undergraduate and graduate students 
that assisted with the development of the methods and equipment used in this research: 
Joshua Thompson for developing the imaging system, Jager Livingston for installing the 
water cooling system, and Rajeshwar Chinnawar, Jingran Duan, Brock Wilson and 
Brandon Norris for their assistance with the research. 
Finally, the author would like to thank his parents for their support through this 
research. This success would not have been accomplished without them. 
 
 
 
 
v 
 
 
 
 
 
Table of Contents 
 
 
Abstract................................................................................................................................ii 
Acknowledgements.............................................................................................................iv 
List of Tables......................................................................................................................................vii 
List of Figures...................................................................................................................viii 
Chapter 1: Introduction........................................................................................................1 
Chapter 2: Background ........................................................................................................4 
2.1 Coal as a Fossil Fuel ...............................................................................................6 
2.2 Wood as an Alternative Fuel ...................................................................................7 
2.3 Switch Grass as an Alternative Fuel .......................................................................8 
2.4 Multi-stage Combustion Process for Solid Fuels..................................................10 
2.5 Laboratory Burning Simulators ............................................................................11 
Chapter 3: Equipment and Experiment Procedures...........................................................20 
3.1 Coal, Wood and Switch Grass as Fuel Samples....................................................20 
3.1.1 Coal.............................................................................................................20 
3.1.2 Wood ...........................................................................................................22 
3.1.3 Switch Grass ...............................................................................................23 
3.2 Particle Preparation...............................................................................................24 
3.3 Microscope and SEM Imaging of Particles...........................................................25 
3.3.1 Microscope Imaging ...................................................................................25 
3.3.2 SEM Imaging..............................................................................................31 
3.4 Furnace and Particle Injection Systems ................................................................34 
 
 vi 
3.4.1 Description of Furnace................................................................................34 
3.4.2 Cooling Water System ................................................................................38 
3.4.3 Particle Injection System ............................................................................39 
3.5 Imaging System ....................................................................................................44 
3.6 Movie Building .....................................................................................................50 
3.7 Calculation of Imaging Resolution and Magnification.........................................51 
3.8 Furnace Operation.................................................................................................54 
Chapter 4: Results..............................................................................................................57 
4.1 Furnace Operation Results....................................................................................58 
4.2 Particle Dropping Rate at Lab -Room Temperature Results.................................60 
4.3 Particle Combustion at High-Temperature Results...............................................65 
Chapter 5: Conclusions......................................................................................................70 
Chapter 6: Recommendation for Future Work...................................................................72 
Bibliography ......................................................................................................................73 
Appendix A: Needle Gauge Comparison Chart.................................................................78 
Appendix B: Key Specifications of Furnace .....................................................................79 
Appendix C: Kodak SR-500 Motion Corder Analyzer Specifications ..............................80 
Appendix D: Nikon D40X DSRL Camera Specifications.................................................81 
Appendix E: COHU 2122 Monochrome Video Camera Specifications............................82 
Appendix F: File Batch......................................................................................................83 
Appendix G: Movie Speed Setting ....................................................................................84 
Appendix H: Movie Building Procedure ...........................................................................85 
Appendix I: Furnace Bake Out Procedure.........................................................................86 
Appendix J: Resolution and Magnification Results...........................................................87 
Appendix K: Coal Sample Results from ROBERTA Plant................................................89 
 
 vii 
Appendix L: Particle Dropping at Lab-room Temperature................................................90 
 
 
 
 
 
 viii 
 
 
 
 
 
List of Tables 
 
 
Table 4-1: Controller temperature and temperatures in retort??????............59 
Table 4-2: Optimum needle delivery system???????????????...61 
Table 4-3: Coal particle dropping test with No. 21 gauge needle??.?????...62 
Table 4-4: Wood particle dropping test with No. 20 gauge needle...????....?...63 
Table 4-5: Switch grass particle dropping test with No. 20 gauge needle?.....?......64 
Table J-1: USAF 1951 resolution test chart (from Edmund)...................??.???..88 
Table K-1: Cement plant results of coal samples?.........................................?........89 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ix 
 
 
 
 
 
List of Figures 
 
 
Figure 2-1: Schematic of furnace designed by Levendis et al.(1992)????.?.?12 
Figure 2-2: Schematic of furnace designed by Levendis et al.(1993)????..??14 
Figure 2-3: Schematic of furnace designed by Baxter et al.(1992).?????.??16 
Figure 2-4: Schematic of furnace designed by Rush et al.(1998)??????..?..18 
Figure 3-1: Sample of ground coal from the Roberta plant???????..??...21 
Figure 3-2: Sample of wood chips from the Rock-Tenn Company???.????22 
Figure 3-3: Sample of hammer-milled switch grass????????????....23 
Figure 3-4: Microscope image of pulverized coal particles (40X)?.??..??...?26 
Figure 3-5: Microscope image of wood particles (100X)...????.?....................27 
Figure 3-6: Microscope image of switch grass particles (400X)????............?.27 
Figure 3-7: Microscope image of chars of pulverized coal (720X)...???..?...?.29 
Figure 3-8: Microscope image of chars of wood chips (720X)...????.?...........29 
Figure 3-9: Microscope image of chars of switch grass (720X).????.??....?30 
Figure 3-10: SEM image of coal at magnification of 1000X?.??????..?...32 
Figure 3-11: SEM image of wood at magnification of 1000X????????....32 
Figure 3-12: SEM image of switch grass at magnification of 1100X....?.????.32 
Figure 3-13: Furnace and controller system..........................???.?.??.?...?.36 
Figure 3-14: Schematic diagram of laboratory furnace????...........???........36 
Figure 3-15: Ace quartz retort (left) and ATS quartz retort (right) ?????.........37 
Figure 3-16: Vibration system?????..???????????.??.?......41 
Figure 3-17: Quartz nozzle???????..??????...???..?..?.??.42 
 
 x 
Figure 3-18: Quartz injection nozzle with running water?????........????42 
Figure 3-19: Stainless steel nozzle???????????..??????.??43 
Figure 3-20: Stainless steel injection nozzle with cooling water lines?.....????43 
Figure 3-21: High-speed camera and view window????????????.?45 
Figure 3-22: Kodak SR-500 Motion Corder Analyzer????????.??.?...46 
Figure 3-23: Cohu camera with Questar lens????????????.???..49 
Figure 3-24: Ruler..............................????????...??????.???..52 
Figure 3-25: Scale on a microscope slide....................???????.?.??.?..53 
Figure 3-26: Operating furnace at controller temperature of 900oC............................55 
Figure 3-27: Heating zone during operation via view window.?????.???..56 
Figure 4-1: Schematic diagram of temperature measurement?................????..59 
Figure 4-2: Burning coal particles at 856oC ?.......................................??.?..?..67 
Figure 4-3: Burning switch grass particle at 856oC.......................???????..68 
Figure 4-4: Burning wood particles at 856oC ..............................?.?.............??..69 
Figure J-1: USAF 1951 resolution test pattern (from Edmund).....................???..87 
Figure L-1: Dropping particles at laboratory-room temperature?.............???.....91 
Figure L-2: Dropping coal particles with needle by the angle of 35o........?.??.....92 
Figure L-3: Dropping wood particles with vertical needle ...............??????..93 
 
 
 
1 
 
 
 
 
 
Chapter 1  
Introduction 
This thesis describes the development of an apparatus and a technique for the 
visualization of combustion of particles of solid fuels, including coal, wood and 
switch grass, in a laboratory scale furnace. The hypothesis is that by observing and 
evaluating high-resolution and high-magnification images of particles undergoing 
combustion, burn properties and phenomena can be obtained. The thesis introduces a 
visualization system used to provide digital images and videos of the burning process 
for individual fuel particles, as they undergo combustion in a furnace quartz retort 
through a quartz viewing window. The technique provides a means to compare 
alternative fuels with coal under controlled combustion conditions. A specific 
research goal is to provide an understanding of combustion phenomena under 
conditions that simulate energy generation processing in cement production, such that 
alternative fuels can be evaluated as possible replacements for coal and other fossil 
fuels for this industry.  
The cement industry is a significant component of the economy of the United 
States with 39 companies operating 118 cement plants and annual shipments valued at 
approximately $8.6 billion in 2002 [Portland Cement Association, 2009]. Global 
cement production is much larger, with U.S. production ranked behind China and 
 
 
2 
India. The production of cement is energy intensive. It is estimated that energy 
required to produce one metric ton of clinker can be as much as 4.02 million KJ for 
pre-heater and pre-calciner dry-process kilns and 6.17 million BTU for wet process 
kilns [Oss, 2002]. In 2001, 88 million metric tons of cement was produced in the U.S., 
an increase of 20.45% over the period from 1993 to 2001, while the total U.S. energy 
consumption for cement production increased 20.52% in 2001 [Jacott et al., 2003]. 
Because of the high energy consumption of the cement industry, there is a strong 
motivation to substitute alternative fuels for expensive and non-renewable fossil fuels.  
In 2005 researchers at Auburn University and Lafarge North America began a 
joint study of the impact of using alternative fuels in the cement manufacture process 
with financial support from U.S. Department of Energy. The research in this thesis 
contributes to this study. 
The important contribution of this research study is the integration of a 
laboratory-scale furnace and a visualization system. An aspect is placing a camera 
near the heated zone of interest to allow appropriate focusing for high-resolution 
imaging of small combusting particles. Another research contribution is the 
development of methods to control the rate of single-particle falling through an 
injection nozzle at the top of the furnace. 
Visualizations were performed at laboratory room temperature to obtain 
qualitative information about physical properties of fuel particles. Experiments were 
performed at high controlled temperature (900 ?C) to obtain qualitative information 
about burning characteristics of solid fuels. Target size of selected solid fuel particles 
 
 
3 
was 100 microns; this size was chosen to match typical coal particle sizes used for 
cement manufacturing. 
Chapter Two provides a brief background of worldwide energy consumption 
and the environmental impacts of fossil fuels and biomass alternative fuels, with 
emphasis on cement production. The physical properties and other characteristics of 
coal, wood, and switch grass as industrial fuels are discussed. Drop tube and 
furnace-based visualization studies from other research groups are presented.  
Chapter Three provides a description of experimental apparatuses and 
procedures, and the specifications of the fuel samples used in the research. The 
imaging acquisition and analysis systems used, the particle feeding systems, and the 
specialized furnace system are described in detail. Microscope images of raw fuel 
samples and fuel chars after the combustion, as well as SEM images of raw fuel 
samples are presented and described.  
Chapter Four provides results obtained from furnace and particle injection 
operation in the form of images and calculation results. Key results include particle 
injection rates, camera resolution and magnification, and images of combustion of 
solid fuels.  
Chapter Five offers the several conclusions made from the discussion of the 
experimental results. 
Chapter Six gives suggestions for future work in the area of visualization of 
combustion of solid fuels. 
 
 
 
 
4 
 
 
 
 
 
Chapter 2 
Background 
In cement production, the mixture of raw materials is fed to the pre-heater, in 
which it is calcinated before entering the kiln. In the kiln, the raw materials are fixed 
together with the ash of all the feeds used. At the end of the kiln, the flux is rapidly 
added to form clinker. The clinker is cooled and ground with an appropriate 
proportion of sulfate to form cement [Taylor, 1997]. In order to increase 
energy-efficiency and economical aspects, the exact manufacturing process varies 
from one plant to another [Jackson, 1998]. Some plants run a wet process, in which 
the raw materials are suspended in water in the process; these plants are very 
energy-efficient and tend to only be used in plants. Most plants run the dry process 
where grinding and blending are completed on the dry raw materials before they enter 
the pre-heater [Kosmatka, 2002]. 
In cement manufacturing, it is essential in the clinker burning process to keep 
the kiln temperature between 1400 to 1500 oC, and the kiln gas temperature is at 
about 2000 oC. The solid fuel fed via the burner produces the main flame with the 
flame temperature at approximately 2000 oC. Hot kiln gases are piped in to combust 
the fuel [Keefe, 2003]. Hot gases from the combustion process are then used in the 
 
 
5 
pre-heater, and the ash, residue and unburned samples are swept into the kiln.  
In a modern indirectly fired burner, the combustion flame is shaped and 
adjusted by the primary air, which is about 10-15% of total combustion air 
[Karstensen, 2004]. The pulverized fuel is blown into the kiln with the mill sweeping 
air which acts as a carrier and a primary air. 
Alternative fuels include waste wood, used tires, and switch grass, etc. Waste 
wood and used tires have been applied to replace coal or oil as sources of thermal 
energy in cement manufacturing process [PCA, 2009]. 
Fossil fuel usage is a huge contributor to the production of green house gas 
(GHG) emissions. Hanson [Hanson, 2004] estimated that in 2002, 98% or 5,682 
million metric tons of total U.S. carbon dioxide emissions resulted from fossil fuel 
combustion with approximately 50% from coal fired electrical production and 
petroleum products usage. Overall, total U.S. GHG emissions had risen by 13% from 
1990 to 2002 [Hockstad, 2004]. About 3.4% of global CO2 emission is from fossil 
fuel combustion and cement production. U.S. is the world?s third largest cement 
producer, with production occurring in 37 states [EPA, 2004]. In the U.S. 
combustion-related emissions from cement production were estimated at 
approximately 36 million ton CO2, which was about 3.7% of combustion-related 
emissions in the U.S. industrial sector [United State Geological Survey, 2002]. 
Expectations are that emissions will continue to rise in the near term.  
 
 
6 
2.1 Coal as a Fossil Fuel 
Coal is a combustible black or brownish-black sedimentary rock, which 
consists of carbon along with variable quantities of other elements. Coal is the 
largest source of fuel and is primarily used as a fuel for the generation of electricity 
worldwide. Coal?s combustion is the largest source of CO2 emission worldwide. CO2 
is the major contributor to increase global warming and other climate changes. The 
energy density of coal is about 24 MJ/kg [Deutch, 2007].  
In general, the traditional process of burning coal in boilers or reactors to 
drive steam turbines is relatively inefficient with a maximum overall efficiency of 
approximately 38% [Schilling, 2005]. Coal can be crushed into fine particles, then 
blown into the boiler, and ignited to form a long flame. It also tends to produce many 
emissions of nitrogen oxides (NOX) and sulfur dioxide (SO2), which is a major 
source of the formation of destroying ozone and acid rain. In some types of boilers, 
the burning coal would rest on grates. The typical useful energy output of coal is 
about 30% [Fisher, 2003]. 
However, there are several special boilers around the world with 
high-efficiency. A new technique, called a fluidized bed boiler, made a major 
improvement in the basic system. Coal in a fluidized bed boiler produced a high 
pressure stream of combustion gases that spin a gas turbine to generate electricity, 
and then boil water for a steam turbine - two sources of electricity from the same 
fuel [Beach, 2009]. 
 
 
7 
 2.2 Wood as an Alternative Fuel 
Wood is one of the important renewable energy sources produced as 
manufacturing waste products. The material is generally called fuel wood. 
Hardwood has less resin and burns slower. Softwood burns quickly [Hoadley, 2000]. 
It can be made from brush, saplings, waste wood, tree slash as well as from roadside 
maintenance operations [Redmond, 2006]. Wood has been used as fuel in 
manufacturing plants and power plants [Maker, 2004], but there are few reports and 
literature about usage of wood as a thermal energy in cement manufacturing. 
The heat content of wood is variable, and mainly depends on its moisture 
contents. The average energy value of the bone-dry wood chips is approximately 
19.8 kJ/kg. However, the actual energy value of any wood sample depends on the 
mixture of species in the sample and can be measured by laboratory methods [Maker, 
2004]. Teislev [2002] reported that wood fuel contains 42% of moisture, typically, 
and has the following chemical composition: Carbon 50.1%, Oxygen 42.7%, 
Hydrogen 6.2%, Ash 1.0% and Nitrogen 0.2%. Wood does not have the element of 
sulfur, so does not produce sulfur oxide gases in combustion, which is different to 
fossil fuels, but wood combustion will also produce carbon monoxide, nitrogen 
oxide and volatile organic compound emissions. 
Seventy percent of Alabama are covered by forests, and Alabama?s forests 
produce 2.5 times more timber volume now than 50 years ago. From 2001 to 2008, 
hard wood in Alabama grew by 18.7 million tons annually and soft wood grew by 
37.9 million tons annually, for a combined 5.3% increase annually [AFC, 2009]. 
 
 
8 
2.3 Switch Grass as an Alternative Fuel 
Switch grass is a warm season grass native to North America, and it is used as 
a biomass crop and recently as an alternative fuel. It can be found in remnant prairies, 
pastures and as an ornamental plant in gardens [Sami, 2001].  
In some warm humid southern zones such as Alabama, it has the ability to 
produce up to 25 Oven Dried Ton (ODT)/ha. A summary of switch grass yields across 
13 research trial sites in the United States found the top two cultivars in each trial to 
yield 9.4 to 22.9 ton/ha, with an average yield of 14.6 ODT/ha. Switch grass contains 
approximately 18.8 billion J/ODT of biomass [McLaughlin, 2005; Samson, 2008].  
Now, switch grass is being used as a substitute for coal in power generation 
and other industrial applications. For example, in Eastern Canada, some plants use 
switch grass on a pilot scale as a boiler fuel for commercial heating application, and 
develop switch grass as a pellet fuel because of lack of wood residues [Samson, 2009]. 
Switch grass has been identified by the U.S. Department of Energy as a possible 
energy source primarily to be used in existing energy utilities as a feedstock to be 
co-fired with coal. Dry switch grass?s heating value is about 3900 kJ/kg, a fact which 
results in switch grass having a low energy density when compared to conventional 
energy sources, but average when compared to other energy crops such as willow 
[Miura, 2001]. Switch grass can also be directly combusted or co-fired with coal to 
lower emissions associated with the burning of that fuel. However, for switch grass to 
become practical as a direct-combusted fuel in coal plants, retrofitting current boilers 
from coal to co-fired applications is required. The main products from switch grass 
 
 
9 
combustion are gases and an ash residue. 
Though switch grass has been burnt successfully with coal in power plants, it 
has not been used in a cement plant before. In power plants, some problems will 
appear during the combustion from elements in switch grass (such as sodium, silica, 
etc.) due to erosion, fouling and slagging, so decreasing efficiency while increasing 
maintenance cost [Sami, 2001]. However, in a cement kiln, these problems will not 
exist because ash can be mixed into the clinker. Hence, switch grass burning is a 
decent option in cement kilns, if it does not change the properties of the clinker. 
Another variable affecting the economics of burning switch grass is from the extent of 
preparation process for switch grass before it is fed into the kiln [Boylan, 2000]. 
Inherent in the combustion of switch grass is the production of a solid phase 
residue [Boylan, 2000]. The mass varies from 2-4% of the original sample weight and 
is primarily composed of metal oxides and ash. If combustion proceeds to completion 
then the only by-products are CO2 and water; however, if incomplete combustion 
occurs, then by-products such as CO, hydrocarbons, NOX or some other less desirable 
products are possible. Ash is primarily comprised of silicates and metal oxides and 
will not undergo combustion at these temperatures but will undergo volatilizations at 
much higher temperatures associated with the melting points of these components 
[Yang, 2008]. 
 
 
10
2.4 Multi-staged Combustion Process for Solid Fuels  
Combustion is a multi-staged process, and there is a variation in the 
combustion of different solid fuels. In general, there are five reaction zones existing 
in the combustion of solid fuels: 1) the non-reacting solid zone, and solid fuel heats 
up to approximately 100oC evaporating the moisture in it; 2) the condensed phase 
reaction zone; 3) the gas phase reaction (pyrolysis) zone, and solid fuel starts to 
break down converting the fuel into gas at about 300 oC; 4) the primary (gas phase) 
combustion zone, and the major energy in the solid fuel is released from 300 oC to 
600 oC when fuels vaporize containing approximately 40% to 60% of the energy 
burn; and 5) the post-flame reaction zone. Four basic stages are defined by the 
concept of solid fuel combustion reaction mechanisms: 1) heating and drying; 2) 
solid particle pyrolysis; 3) gas phase pyrolysis and oxidation; and 4) char oxidation. 
Heating and drying occur in the non-reacting solid zone [Tillman, 1981].  
Combustion is also a complex process of exothermic chemical reactions 
between a fuel and an oxidant accompanied by the production of heat or both heat 
and light in the form of flames or a glow, with an appearance of light flickering. 
Direct combustion in atmospheric oxygen is a reaction mediated by radical 
intermediates [Tillman, 1981]. The conditions for radical production are naturally 
produced by thermal runaway, where the heat generated by combustion is necessary 
to maintain the high temperature for radical production. Incomplete combustion 
occurs when there is not enough oxygen to allow solid fuel to react completely 
during burning to produce CO2, or when the burning is quenched by a heat sink. 
 
 
11 
2.5 Laboratory Burning Simulators 
Many researchers focus on combustion of solid fuels (such as coal, wood, 
etc.) and develop laboratory-scale combustion facilities designed to study burn 
mechanics and chemical analysis. Optical apparatuses are used in this study to 
visualize the combustion process in the laboratory-scale burn simulator. The drop 
tube furnaces designed to burn solid fuels and their accessory visualization 
apparatuses are introduced herein. 
Levendis et al. [Levendis, 1992] designed a laboratory-scale furnace to burn 
particles with a three-color ratio pyrometer to obtain surface temperatures of particles 
and high-temperature combustion rates of burning carbonaceous particles. They then 
compared the features and performances of this instrument with those of a two-color 
ratio pyrometer. They monitored the combustion of particle flow coaxially, from 
observation windows located at top of the furnace injectors, but not the side view 
windows as our furnace. Coaxial monitoring is hard to obtain dropping condition and 
the velocity of the particle, but has the advantage that the whole combustion process 
can be monitored. A schematic of this furnace is shown in Figure 2-1. 
 
 
12
 
Figure 2-1: Schematic of furnace designed by Levendis et al. (1992). 
 
 
 
 
 
 
13
The temperature-time history of burning particles was recorded by a 
pyrometer in Levendis? experiment. Narrow (or medium) bandwidth interference 
filters guide monochromatic radiation to solid-state silicon photo-detectors. The 
associated amplification is linear and/or logarithmic. 
Levendis et al. [Levendis, 1993] designed another type of furnace system to 
study the combustion emissions from pulverized solid fuels: NO, SOX and CO. A 
schematic of this furnace can be seen in Figure 2-2. The particles were burnt in an 
electrically heated drop tube furnace at high particle heating rates (104-105 K/s) and 
elevated gas temperatures (1300-1600 K). A small amount of particles were 
introduced into a test tube from a syringe pump [Wheatley, 1993; Levendis, 1993; 
Courtemanche, 1998]. 
 
 
14
 
Figure 2-2: Schematic of furnace designed by Levendis et al. (1993). 
 
 
 
15
The particles were dropped via a water-cooled injector. A Type S thermocouple 
was used to measure the wall temperature and a suction thermometer was used to 
measure the gas temperature (aspirated shielded thermocouple) in the furnace. The 
flow rate of the gas was adjusted to provide a calculated gas residence time under 
different temperatures in the heating zone of the furnace. The furnace gas in their 
experiment was below 100 oC at the exit of the furnace.   
Baxter et al. [Baxter, 1992] designed a type of furnace to co-fire coal and 
biomass to valuate the use of the alternative fuels in industrial application. It was a 
pilot scale, down-fired, turbulent flow simulator as shown in Figure 2-3. 
Composition histories and gas temperature were tested in the combustion system. 
The simulator was an electric heating system to control the wall temperature with an 
inner diameter of 15 cm [Baxter, 1992; Robinson, 2002]. Solid fuel introduction rate 
was 3.5 kg/h through a water-cooled lance inserted at the side of the furnace, which 
equaled a heat input of 30 kW of bituminous coal. A natural gas-preheated burner 
was applied to create an air stream.  
 
 
16
          
Figure 2-3: Schematic of furnace designed by Baxter et al. (1992). 
 
 
 
 
 
 
 
 
 
 
 
17
Ruth et al. [Clean Coal Technology Demonstration Program, 1996; Ruth, 1998] 
developed a burn simulator in their experiment to study the combustion of coal and 
municipal solid waste (MSW) in terms of fuel characteristics, combustion 
technologies, emissions, and ash utilization/disposal showed in Figure 2-4.  
However, most of the previous studies focused on measurement of the 
relationship between combustion temperature and time as well as the measurement of 
chars and emissions after the combustion, while few studies focused on the 
visualization of combustion characteristics. In this thesis, particle injection, 
temperature distribution and particle combustion phenomena were evaluated.  
 
 
 
18
   
Figure 2-4: Schematic of furnace designed by Ruth et al (1998). 
 
 
19
For the coal particle injection and combustion, immediately after its 
introduction into the furnace, the fuel was rapidly heated by radiation from the 
combustion process and by convection from the hot furnace gases. Any moisture in 
the fuel was driven off, followed by a process in which volatile material evolved from 
the fuel, ignites, and burns. Finally, the fixed carbon in the devolatilized fuel particles 
was ignited. The composition of coal provided to the burners of a combustion system 
might vary from hour to hour, or even minute to minute, in the content of volatiles, 
total carbon, sulfur, moisture, etc [Clean Coal Technology Demonstration Program, 
1996].  
Fuel particle feeding is a major step in combustion process, and the method to 
introduce the particle into the burner controls the particle dropping rate. While gas 
flow is used as a force to drop the particle into the burner, vibrating system can be 
discussed in later chapters in this thesis. 
The visualization (capturing still images and videos) of particle combustion is 
a method to estimate the characteristics of particle combustion, such as the outer 
shape of burning particles, temperature distribution during combustion and the 
characteristics of chars and unburned samples. Meanwhile, the magnification, the 
resolution, and other specifications of the camera system will affect the quality of the 
visualization process. It is necessary to adjust these settings to a proper value to obtain 
better experimental data during the operation. 
 
 
 
 
20
 
 
 
 
 
Chapter 3 
Equipment and Experiment Procedures 
3.1 Coal, Wood and Switch Grass as Fuel Samples 
Pulverized coal, wood chips and switch grass are the materials of interest for 
the combustion studies performed in this study. Wood chips and switch grass are the 
alternative fuels, while coal is the standard fossil fuel burned as a comparison. 
3.1.1 Coal 
The pulverized coal samples were supplied by the Lafarge North America, Inc. 
Roberta cement plant in Alabama. A picture of the ground coal used in this study is 
shown in Figure 3-1. Analytical results from cement plant materials testing showed 
that, on a dry-coal basis, the values (wt.%) of ash, fixed carbon and volatile matter 
were 18.78, 53.85, and 27.37, respectively. The heat value is 6,761 kcal/kg. The 
detailed analytical reports are shown in Appendix K. 
 
 
21
     
Figure 3-1: Sample of ground coal from the Roberta plant 
 
 
 
22
3.1.2 Wood  
The wood chip samples were southern sweet gum trees, supplied by 
Rock-Tenn Company in Georgia. A picture of the wood chips used in this study is 
shown in Figure 3-2. The samples were field dried to be ground into pulverized 
particles by a grinder machine (Model: OII 350S) from GRAEGER company. 
 
Figure 3-2: Sample of wood chips from the Rock-Tenn Company 
 
 
 
23
3.1.3 Switch grass 
The switch grass samples were from the E.V. Smith Research Center of 
Auburn University, and consisted of the whole plant material, or the entire leaf and 
stem. The plants were from a lowland variety called "Alamo". The shape of switch 
grass was very inregular and tangled. The samples were ground with a hammer mill 
making the size of most particles between 0.5-1 mm. A picture of the switch grass 
used in this study is shown in Figure 3-3. 
  
Figure 3-3: Sample of hammer-milled switch grass 
 
 
 
 
 
 
 
24
3.2 Particle Preparation 
The ground coal, as received from the Reberta plant, was screened for about 
15 minutes using sieves with a shaker (Retsch AS 200). The sieves were Fischer sieve 
trays No. 40, No. 60, No. 100, No. 140, No. 170, and No. 200. The size fractions were 
approximately: larger than 400 ?m, from 400 ?m to 250 ?m, from 250 ?m to 150 ?m, 
from 150 ?m to 106 ?m, from 106 ?m to 90 ?m, from 90 ?m to 75 ?m, and smaller 
than 75 ?m. The samples were stored in a desiccator to ensure they remained dry.  
The wood chips were screened by the same series of sieves used for the coal. 
The pulverized particles were dried in an oven at 100 oC for 10 hours and were then 
stored in sealed Ziplock bags to ensure they remained dry. The hammer-milled switch 
grass particles were further ground by a coffee grinder to obtain smaller particles. 
These particles were then screened by sieves to select different sizes of particles (used 
the same method that applies to coal). The selected switch grass particles were dried 
in an oven at 100 oC for 10 hours and stored in Ziplock bags for dryness.  
The size of most ground coal burned in the cement plant (full scale test burns) 
was between 70-100 ?m, and coal particles were used as a basis in the experiment. 
Hence, the visualization system was designed for a particle at 100?m. The size 
fraction of the particles (including coal, wood and switch grass particles) used in the 
experiments was between 90-106 ?m for better comparison of combustion 
performance, although waste wood and switch grass were used in larger forms in the 
cement plant. The other size fractions of particle were stored for possible future use.  
 
 
25
3.3 Microscope and SEM Imaging of Particles 
Microscope and SEM analyses were performed to observe the outer structure 
of the different fuel particles. 
3.3.1 Microscope Imaging  
Pulverized coal, wood chips and switch grass samples were placed on 
microscope slides. The sizes of the particles selected were between 90-106 ?m, and 
the particles were analyzed using a microscope manufactured by National Optical. 
Slides were mounted on the microscope and imaged with a Canon digital camera. The 
camera was connected to a computer, so that it could be controlled by the software to 
adjust, focus and capture the photographs.  
Each slide had many particles, and was viewed at 40 times (40X) 
magnification (low magnification), 100 times magnification (100X), 400 times 
magnification (400X), and 1000 times high magnification (1000X). Five images at 40 
times (40X) as well as five at 400 times (400X) were taken of each microscope slide 
sample. Frames of a ruler were captured on the microscope slides to establish scale. 
The focus was kept in the same position while imaging the particle samples in order 
to maintain the same scale.  
Figures 3-4, 3-5 and 3-6 show microscope images of solid fuel particles. The 
corresponding scales are shown on the images. 
      Figure 3-4 is an image of pulverized coal particles at 40X magnification. The 
image clearly shows that dry coal particles tend to agglomerate, instead of separate.  
 
 
26
Figure 3-5 is an image of wood particles with the magnification of 100X. This 
image shows that the wood particles have consistent structures. 
Figure 3-6 is an image of switch grass particles with the magnification of 
400X. This image shows that most of the particles are quadrate, instead of rounded.                                                   
 
Figure 3-4: Microscope image of pulverized coal particles (40X) 
 
 
27
 
Figure 3-5: Microscope image of wood particles (100X) 
 
Figure 3-6: Microscope image of switch grass particles (400X) 
 
 
28
During combustion experiments, unburned particles and chars dropped onto 
the cap at the bottom of the retort and deposited there. Char samples of different fuels 
were selected and placed on microscope slides. Five images at 72 times (72X) as well 
as five at 720 times (720X) were taken of each microscope slide sample. The focus 
was kept in the same position while imaging the particle samples to maintain the same 
scale. Figures 3-7, 3-8 and 3-9 show images of chars of solid fuels under high 
magnification (720X) on the microscope. The corresponding scales are shown on the 
images. 
Figure 3-7 is an image of chars of pulverized coal. The image shows that coal 
chars look like big agglomerates. Their color is black, and is same as uncombusted 
coal particles. Visual observation of many coal chars under the microscope showed 
that the size of most chars was about 50 ?m, when the assumed size of pulverized 
coal particles was 100 ?m.  
Figure 3-8 is an image of chars of wood particles. The image shows that 
different sizes of chars occurred due to different extents of combustion or different 
initial sizes of particles. 
Figure 3-9 is an image of chars of switch grass. The image shows that, after 
burning, most of the chars look like agglomerates, but are not quadrate in shape. 
 
 
 
 
 
 
29
 
Figure 3-7: Microscope image of chars of pulverized coal (720X)  
 
Figure 3-8: Microscope image of chars of wood chips (720X)   
 
 
30
 
Figure 3-9: Microscope image of chars of switch grass (720X) 
 
 
 
 
 
 
 
 
 
31
3.3.2 SEM Imaging  
SEM images were captured using a ZEISS SEM manufactured by Carl Zeiss 
SMT, Inc. SEM is a useful technique widely applied in visualization of combustion 
[Atal, 1995]. The SEM machine is located in the Advanced Microscopy and Imaging 
Laboratory of Auburn University. 
      The SEM images provided valuable qualitative data to help analyze the 
prepared solid fuel samples. Figures 3-10, 3-11 and 3-12 are SEM images of 
pulverized coal, wood chips and switch grass particles, respectively.  
 
 
32
 
Figure 3-10: SEM image of coal at magnification of 1000X 
 
Figure 3-11: SEM image of wood at magnification of 1000X 
 
Figure 3-12: SEM image of switch grass at magnification of 1100X 
 
 
33
      Figure 3-10 is a SEM image of pulverized coal particles at a magnification of 
1000X. The image shows that the shapes are variable with a large amount of small 
dust. Figure 3-11 is a SEM image of wood particles at a magnification of 1000X. The 
image shows that most of the particles are rectangular with a size of approximately 
100 ?m. Figure 3-12 is a SEM image of switch grass particles at a magnification of 
1100X. The image shows that some particles are irregular in shape. 
 
 
 
 
 
34
3.4 Furnace and Particle Injection Systems 
The drop tube furnace and particle injection method that was developed for 
this thesis are two main components in the combustion system. Drop tube furnace 
systems are relatively inexpensive to operate and can generate multiple data sets in a 
short time. Of utmost importance is the ability of these systems to simulate key 
full-scale combustion conditions. Visualization devices include cameras (high speed 
camera, high resolution camera and regular camera), lenses, computers and imaging 
processing software. 
3.4.1 Description of Furnace 
The drop tube furnace was manufactured by Applied Test Systems, Inc. It is 
an ATS Series 3420 split- tube furnace mounted vertically. The dimensions of furnace 
are 32.5 cm wide, 35 cm across, and 75 cm high. Figures 3-13 and 3-14 show 
photographs and a diagram of the furnace system. Appendix B displays the Series 
3420 product description provided by ATS. The maximum furnace temperature rating 
is 1450 oC. There are three heating zones with a total power capacity of 8000 Watts. 
There are three quartz view windows located on two sides of the furnace with one 
window centered on one of the side split lines and two windows located near the top 
and bottom of the split line on the other side. Each view window is 22.5 cm long and 
2.5 cm wide. This window arrangement allows visualization of along the full length 
of the drop tube. A quartz glass retort is mounted in the center of the furnace, 
supported by flanges at both ends of the retort tube. The flanges are made of stainless 
 
 
35
steel and are water-cooled. The flanges are parts of a retort end-cap assembly that 
includes inconel radiation shields that extend into the retort. The whole furnace 
weights 90 kg, and it is mounted with carriage bolts to a bracket. The bracket was 
mounted to a steel roller cart for some experiments and to a fixed structure aluminum 
frame for other studies. Levendis [1992] used a similar furnace to burn carbonaceous 
particles. 
      The furnace has four heating elements located inside the refractory box and 
adjacent to the retort. The quartz retort is 6.25 cm in outer diameter and 90 cm long. 
The quartz retorts provided by ATS were manufactured such that the outer surface of 
the tube had slight undulations; the refraction due to these undulations resulted in 
blurred images. A retort was obtained from Ace Glass that had smooth inner and outer 
surfaces to allow for better imaging. ATS quartz retort and Ace quartz retort are 
shown in Figure 3-15, the left retort was Ace quartz retort while the right one was 
ATS quartz retort. The undulations of the ATS retort are clearly evident. 
The temperature-control system has three Series 2404 Barber Colman 
Programmable controllers manufactured by Eurotherm. This system allows 
temperature control in three different heating zones. The heating rate in each zone can 
be controlled independently. The blue electronics cabinet shown in Figure 3-13 
contains the controls system. 
 
 
 
 
36
 
Figure 3-13: Furnace and controller system 
 
 
                         
Figure 3-14: Schematic diagram of laboratory furnace 
 
 
37
 
Figure 3-15: Ace quartz retort (left) and ATS quartz retort (right) 
 
 
38
3.4.2 Cooling Water System 
In order to keep the injection nozzle and flanges cool and to prevent particle 
burning in the nozzle, a cooling water system was required. The cooling water system 
was designed by Jager Livingston [Livingston, 2010] to supply water to the flanges of 
the retort and to the particle injection nozzle. The water cooling system is shown in 
Figure 3-14. The water supply goes through a filter to remove impurities to keep the 
fouling in the flanges and nozzle to a minimum. Water enters a manifold that splits it 
into five lines. One line goes to the injection nozzle, two lines go to the flange at the 
top of the retort, and two lines go to the flange at the bottom of the retort. Valves 
allow independent adjustment of the supply to the whole system as well as the flow 
rate to each individual line. 
 
 
39
3.4.3 Particle Injection System 
The particle injection system has two main components: a vibrating needle 
apparatus to control the rate at which particles are dropped, and a water-cooled nozzle 
to keep particles cool and to prevent them from combusting as they fall through the 
top of the furnace. The radiation shields and the top of the uppermost visualization 
window are approximately 20 cm below the top of the furnace. A quartz nozzle and a 
stainless steel nozzle were designed and tested, and both are described in this section. 
The vibration system that was developed to deliver particles from an injection 
needle is shown in Figure 3-16. The vibrator and controller were manufactured by 
FMC Technologies (Model: V-2-B). The vibrator was fixed to a metal stand base 
approximately 2 cm from the stand rod. Approximately 0.2 gram of fuel particles 
were placed in a 15-mL luer-tip glass syringe. Different gauges of stainless steel 
flat-tip needles were used depending on the types and sizes of particles. The syringe 
and needle were from Fisher Scientific. The syringe was clamped to the rod of the 
vibration stand and the angle of the syringe could be changed at the clamp. As will be 
discussed later, a specific needle size, angle, and vibration intensity were selected for 
each fuel type to achieve a suitable delivery rate. The needle tip dropped particles into 
the top of a furnace injection nozzle. 
A quartz nozzle was designed and constructed in the Auburn University Glass 
Shop. A 6-mm quartz tube was jacketed with a 16-mm quartz tube and the ends of 
these tubes were sealed together. A second 6-mm tube was located in the cooling 
 
 
40
jacket space and provided a connection for water to be able to flow down to the 
bottom of the cooling jacket. A 7-mm water outlet connection was located at the top 
of the jacket. The centered small tube served as the particle dropping tube and was 
open at the top and bottom. The nozzle is shown in Figures 3-17 and 3-18. The quartz 
nozzle was mounted to the furnace end cap assembly such that it extended slightly 
beyond the radiation disks, with the top of the nozzle 6.25 cm above the cap and the 
bottom of the nozzle at 20 cm below the cap. Holes were cut into the radiation disks 
to allow the nozzle to be inserted. The inner diameter of the dropping tube was 4 mm 
and the inner diameter of the inlet of water was 5 mm while the outer diameter of 
whole nozzle was 2 cm. Because of the different heating characteristics of the quartz 
and stainless steel radiation disks, insulation paper was used to prevent direct contact 
between the quartz nozzle and the radiation disks. The quartz nozzle proved to be too 
fragile and broke on several occasions, but it served as a first test of feasibility for the 
water-cooled injection nozzle concept. 
A stainless steel nozzle was designed and constructed in the Chemical 
Engineering Machine Shop. Based on a similar design rationale used for the quartz 
nozzle, two small steel tubes were mounted in a large tube and welded together. One 
was the drop tube for the particles to fall through and the other was the inlet for 
cooling water. This nozzle was mounted directly to the flange at the top of the retort, 
with the top at 6.25 cm above the cap and the bottom at 20 cm below the cap. The 
inner diameter of the dropping tube was 3 mm and the inner diameter of the water 
inlet was 5 mm. The outer diameter of the whole nozzle was 4.5 cm. No insulation 
 
 
41
paper was required with this nozzle, because the radiation disks were welded directly 
to the jacket of the nozzle, and since all of the material was metal, expansion 
differences were negligible. The stainless steel nozzle is shown in Figures 3-19 and 
3-20.  
 As discussed previously, the cooling water was supplied and controlled by a 
valve on the manifold of the water system supplying the jacket and the retort flanges.  
 
Figure 3-16: Vibration system 
 
 
42
 
Figure 3-17: Quartz nozzle 
 
Figure 3-18: Quartz injection nozzle with running water 
 
 
 
43
 
Figure 3-19: Stainless steel nozzle 
 
Figure 3-20: Stainless steel injection nozzle with cooling water lines 
 
 
44
3.5 Imaging system 
Three imaging systems were used for the visualization of the combustion of 
particles studies. One is a standard digital SLR system that employs a NIKON D40X 
camera (10 Megapixel) with four different lenses, including a Nikon 60 mm F/2.8D 
AF micro-Nikkor lens, a Nikon 17-55 mm F/3.5-5.6G AF-S lens, a Nikon 50 mm 
F/1.8D lens, and a Nikon 24 mm F/1.8D lens all with different sets of filters.  
In general, the Nikon camera was operated in Manual mode to capture images. 
The shutter speed was set to 1-10 per second for targets in weak background light and 
50-100 per second for targets in strong background light. The size of the image was 
3872 x 2592 pixels (10.0 Megapixel).  
Some of the images were acquired with a high speed imaging Kodak SR-500 
Motion Corder Analyzer with two halogen light sources. The camera worked with a 
professional SONY video monitor and a computer. The system is shown in Figures 
3-21 and 3-22. A 100-Watt incandescent lamp was used with the Kodak camera for 
back lighting to create a strong white background so that the particles could be better 
seen and brought into focus. The distance from the lens to the target was 20-37.5 cm. 
 
 
 
45
        Figure 3-21: High-speed camera and view window  
 
 
 
46
    
Figure 3-22: Kodak SR-500 Motion Corder Analyzer 
 
 
47
The Kodak camera had a maximum resolution of 512x512 pixels 
non-interlaced with a rate of 250 frames per second. Focus lenses consisted of several 
Nikon Nikkor lenses, which could supply detailed shots with a field of view of 9.4 
cm2 and wide shots with a field of view of 25 cm2. The camera had memory to record 
1365 frames, which equaled to about 5.5 seconds of video. Then the onboard frames 
were transferred to the computer through a SCSI connection. Jasc Animation Shop 3 
was used for building the movies from individual frames. The camera system had 
been used for other studies in Prof. Duke?s research group [Davies, 2000; Emerson, 
2006; Tuin, 2008]. 
The Kodak camera was mounted to a tripod and camera rail, which allowed 
vertical and horizontal camera and lens positioning relative to the retort. The tripod 
could be raised and lowered to position the camera at each of the different heights of 
the three view windows of the furnace.  
A USAF 1951 resolution test pattern was used to determine image resolution 
and a scientific ruler was used to determine magnification; these were also used for 
other visualization systems [Roy, 2001; Emerson, 2006]. 
The last device is a high resolution monochrome video system: a Cohu 2122 
CCD camera and a Questar QM 100 MK III long distance microscope lens. The Cohu 
camera had 768 x 494 pixels with a pixel size of 8.4 x 9.8 microns. The rate was set 
for 30 frames per second. The Questar QM 100 had a working distance ranging from 
8-35 cm. An available adapter allowed attachment to any F-Mount camera. The 
camera system was modified from a similar one designed by Amendi Stephens, a 
 
 
48
former MS student in Prof. Duke?s research group. Stephens [2003] set up the system 
to visualize the particle formation processes in supercritical fluids.  
This system had been applied to view particle dropping and combustion in the 
furnace. The Cohu camera is shown in Figure 3-23 with the Questar lens attached. 
The Questar was equipped with both manual and motorized focus. Manual focusing 
can be done by the focus knob located on the front and rear corners of the lens. The 
motorized focusing consisted of a hand control, motor and power supply. A top port 
on the lens allowed open viewing of the field and targets in the microscope.  
 
 
 
49
 
Figure 3-23: Cohu camera with Questar lens 
 
 
50
3.6 Movie Building 
      The Kodak camera system captures and stores still images. It is necessary to 
build a movie from still images obtained in the experiments. The detailed procedures 
are shown in Appendix F, G and H. The built movie is stored as a video clip while 
the still images are stored as JPEG files. 
 
 
51
3.7 Calculation of Imaging Resolution and Magnification 
Resolution and magnification are two main characteristics of a camera 
system. After an image is taken, it is necessary to find the resolution and 
magnification in the horizontal and the vertical directions.  
An Edmund Scientific USAF 1951 resolution test pattern and a scientific 
ruler were used to determined resolution and magnification. A test chart (Table J-1) 
was used to calculate the resolution of the camera and analyze the images of the 
dropping particles. Images of the USAF 1951 resolution target were captured with 
the target place in the plane where the patterns were in focus. On the USAF 
resolution test target, the pattern consists of numerous groups of three-bars with 
dimensions from large to small. The smallest visual three-bar that the image can 
discern is the limitation of the resolving power in the experiment. 
The target format consists of six "groups" in three layers of patterns. The 
largest groups, forming the first layer, are located on the outer sides of the pattern. 
The smaller layers repeat the same pattern but are progressively smaller toward the 
center. Each group consists of six elements, numbered from 1 to 6. Within the same 
layer, the odd-numbered groups appear contiguously from 1 through 6 from the 
upper right corner. The first element of the even-numbered groups is at the lower 
right of the layer, with the remaining 2 through 6, at the left.  
As the resolution test usage rule, images were obtained of the target; these 
were analyzed to determine the three-bar set in a certain direction on the chart that is 
smallest and resolved, which in this case means showing all three bars separately, 
 
 
52
not a solid square shape. Group and Element bar set is chosen on the image, and 
"cycles/mm" chart (Figure J-2) can be used to calculate the resolution of the camera 
[Edmund Scientific, 2009]. Hence, the resolution of the image in the vertical was 
31?m. In horizontal, the resolution of the image was 50?m.  
The ruler was vertically inserted into the retort in the furnace, and part of the 
rule was located in the field of view of the camera while the camera was set up in 
front of the view window with the distance of 13 inches to the ruler. The value of 
line length measured by ImageJ was the value of pixels, but not the actual length. 
The unit on the rule is 0.416 mm, and the pixels of the image were 640 x 480. The 
actual length of one unit on the image (shown in Figure 3-24, captured by COHU 
camera and Questar lens) was 180 in vertical while the actual length of image in 
vertical was 480, so it could be calculated that the magnification of the image is 
2.31?m/pixel.  
 
Figure 3-24: Ruler 
 
 
53
The unit on the rule is 10 ?m, and the pixels of the image were 2274 x 1704. 
The actual length of one unit on the image (shown in Figure 3-25, captured by the 
Canon camera under microscope) was 13 while the actual length of image in vertical 
was 668, so it was calculated that the magnification of the image was 0.30 ?m/pixel.  
 
Figure 3-25: Scale on a microscope slide 
 
 
 
54
3.8 Furnace Operation 
The controller temperature was set at 900 oC for all the experiments in this 
thesis. 
After the manufacturer?s suggested bake out process was completed (see the 
details in Appendix I), the furnace was operated for experiments. It took about 2 
hours to heat the furnace from laboratory room temperature to 900 oC. The heating 
rate could be adjusted by the ?OUTPUT PERCENT? switch on the temperature 
controller. The heating rates were 12 oC/min through the range of laboratory room 
temperature to 500 oC and 5 oC/min through the range of 500 oC to 900 oC. Figures 
3-26 and 3-27 show the operating furnace in the laboratory. 
The furnce cooled slowly after shut down. There was no additional cooling 
system to increase the cooling rate of the furnace. It took between 8-9 hours to drop 
the temperature from 900 oC to room temperature.  
 
 
 
55
 
Figure 3-26: Operating furnace at controller temperature of 900 oC 
 
 
56
 
Figure 3-27: Heating zone during operation via view window 
 
 
 
 
 
 
 
 
 
 
57
 
 
 
 
 
Chapter 4 
Results 
A study was performed to observe characteristics of fuel particles undergoing 
combustion in the furnace. Pulverized coal, wood, and switch grass were chosen to 
study a fossil fuel and two alternative fuels. In order to determine characteristics of 
different fuels, a standard microscope and a scanning electron microscope were used. 
The target size of particles used in the experiments was 90-106 ?m. 
      Experiments were performed to determine the resolution and magnification in 
the field of view of the visualization system. Experiments were performed to evaluate 
the dropping rate of particles of the solid fuels. Temperatures in the retort during 
operation were also measured. 
      Pulverized coal, wood, and switch grass particles were stored in the injection 
needle, and dropped through the nozzle and into the furnace tube when vibration was 
applied. The camera system was located in front of the viewing window of the 
furnace to visualize the combustion of the fuel particles. 
 
 
 
58
4.1 Furnace Operation Results  
Temperature measurements were obtained using an OMEGA long-handle 
thermocouple to determine temperatures in the furnace retort tube. Figure 4-1 shows 
placement of the thermocouple tip at positions 4 and 10 cm below the water-cooled 
nozzle tip. Table 4-1 shows temperature measurement obtained at several temperature 
controller settings. For each of these measurements, the controller was set to the 
temperature shown and the furnace was allowed to remain at the set temperature for 
20 minutes. The cooling water was supplied to the flanges and injection nozzle. 
Temperature T1 was measured by placing the thermocouple 4 cm below the nozzle tip 
and T2 was measured by 10 cm below the nozzle tip. It can be seen that on average, T1 
was 40 oC colder than controller temperature and T2 was 20 oC colder. The delta 
values on the table is the difference between the controller temperatures and the 
measured temperatures. Temperature measured in the tube of the injection nozzle was 
on the average 30 oC. The bottom of the retort was capped during these 
measurements. 
 
 
 
 
59
 
Figure 4-1: Schematic diagram of temperature measurement 
 
         Table 4-1: Controller temperature and temperatures in retort 
 
Controller 
Temperature 
(oC) 
 T1 in retort 
(oC) 
Delta T1 
(oC) 
T2 in retort 
(oC) 
Delta T2 
(oC) 
600 559 41 577 23 
650 613 37 630 20 
700 659 41 682 18 
750 706 44 730 20 
800 756 44 783 17 
850 806 44 836 14 
900 856 44 885 15 
 
 
 
 
60
4.2 Particle Dropping Rate at Lab-Room Temperature Results 
Experiments were performed to determine the particle dropping rates for the 
needle vibration delivery system at laboratory room temperature. The goal of these 
tests was to select needle sizes, vibration settings, and syringe placement for each 
fuel type such that individual particles would drop from the needle at rate of about 
one particle per second. No. 19, 20, 21, and 22 gauge needles were tested to drop 
particles of each fuel type. Large gauge needles were showed to let groups of 
particles fall through the needle, while small needle prevented particles dropping 
into the injection nozzle. Table 4-2 shows the optimum needle sizes and vibration 
settings for-each fuel type. Tables 4-3, 4-4 and 4-5 show test results for coal, wood, 
and switch grass particle dropping tests with the optimal gauge needles under 
different vibration setting and syringe placements. The vibrator speed range is 1 to 6. 
If the vibrator speed is too high, the needle tip would touch the inner wall of the 
injection nozzle tube during vibration. If the vibrator speed was too low, no particle 
would drop through the needle into the injection nozzle, but remain in the syringe. 
For each test, about 30 second of video was taken to record the fuel particle dropping 
using the Kodak camera and Nikon 60mm micro lens with the frame rate of 250 fps 
and the shutter speed of 1/10000 s.  
 
 
 
61
Table 4-2: Optimum needle delivery system 
 
 
No. 
needle 
gauge 
Inner 
diameter 
of needle 
Vibrator 
setting 
Needle 
angle 
Needle 
height 
Pulverized 
coal 21 0.495mm 5 90
o 50cm 
Wood  20 0.584mm 5 90o 37.5cm 
Switch grass 20 0.584mm 5 60o 50cm 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
62
 
 
 
 
63
 
 
 
 
64
 
 
65 
4.3 Particle Combustion at High-Temperature Results 
Figures 4-2, 4-3, and 4-4 show images of fuel particles undergoing 
combustion in the furnace retort. These images are still frames taken from video 
obtained with the Cohu CCD camera with a frame rate of 30 fps and shutter speed of 
1/4000 seconds. The Questar lens was used. The field of view of the camera was 
centered approximately 4 cm below the injection nozzle tip. The magnification of the 
images of combustion was 2.31 ?m/pixel. The resolutions of the images were 31 
?m/cycle in the vertical direction and 50 ?m/cycle in the horizontal direction. The 
magnification value was used to provide the scale bar on each image. The controller 
temperature was set at 900 oC, and thus the temperature in the field of view is 
approximately 856 oC as was determined by thermocouple measurements (position 
T1). The combustion gas was air at atmospheric pressure. 
Figure 4-2 shows images of burning coal particles. Image (a) shows a burning 
particle falling in the furnace tube, and the size of the particle and its flame was 
approximately 60 ?m. Image (b) shows one coal particle burning with a weak 
intensity, indicating that the particle is out of focus and not in the depth of field or that 
its flame is of low intensity. Images (c) and (d) show several particles burning with 
intense flames. The particles in images (e) and (f) show that the resolution of these 
images allows distinction between particle surface features and flames, and capability 
to measure the size and intensity of each feature.  
Figure 4-3 shows images of burning switch grass particles. Images (a), (c), and 
(e) show multiple falling particles within the field of view, each particle can be 
 
 
66
distinguished and the size and intensity of the flames can be determined. Images (b), 
(d) and (f) show single high-magnification burning switch grass particles, again, each 
showing the clarity and resolution that allows estimation of particle shape and flame 
intensity.  
Figure 4-4 shows images of burning wood particles. Images (a) and (b) show 
very faint particles with the size of approximately 140 ?m: these were either in the 
foreground or background (out of the depth of field) or they were particles that had 
not reached a temperature to begin burning of volatiles with high intensity flames. 
Images (c) and (d) shows wood particles with intense flames. 
It was shown from the images that the burning particles had flames with 
different brightness (intensity) and different sizes, and the reasons could be that the 
burning particles were at different combustion stages, or some of them were in the 
focus of view and some of them were out of focus. Particles were infrequently in the 
field of view camera system, numerous particles combusted to the right and to the left 
of the field of view because they meandered as they fell due to thermal convection of 
the gas in the retort and due to forces resulting from the vibration of the nozzle tip. 
But in general it was typical to be able to obtain at least five clear images of particles 
during three or four minutes of video. 
 
 
67
 
 
 
Figure 4-2: Burning coal particles at 856 oC 
 
 
 
68
 
 
 
Figure 4-3: Burning switch grass particles at 856 oC 
 
 
69
 
 
Figure 4-4: Burning wood particles at 856 oC 
 
 
70
 
 
 
 
 
Chapter 5 
Conclusions 
A laboratory-scale burn simulator (a drop tube furnace) was designed and 
developed to study the combustion of solid fuel particles. Unique features of the 
system are three clear quartz windows on the sides of the furnace and a clear retort 
tube making it possible to obtain visualizations of falling particles undergoing 
combustion processes. A water system was designed and installed and it kept the 
flanges and nozzle cool, preventing the falling particles from burning in the nozzle, 
allowing all combustion to occur in the clear drop tube. An injection nozzle was 
designed and achieved delivery of individual fuel particles into the furnace. A number 
of camera systems and lenses were used, and the Questar lens was found to provide 
the needed image clarity and resolution for 100 ?m particles undergoing combustion 
at 900 oC. A quartz glass retort from Ace Glass was determined to be needed to 
replace the original ATS quartz glass retort, because the ACE glass tube had a 
smoother finish, and resulted in less image distortion due to refraction. 
We measured the temperature distribution in the retort during furnace 
operation with no imposed air flow, and the temperature in the center of the furnace 
retort was less than 40 oC lower than the temperatures readings on the furnace 
controller. We were able to achieve retort temperatures of approximately 900 oC ( and 
 
 
71
visualization at these temperatures) and thus achieved our goal of temperature in the 
retort that was similar to the temperature in the industrial cement production process 
where alternative fuels and coal are fed.  
The syringe vibration system was successful at delivering fuel particles at a 
slow rate to the injection nozzle. Appropriate particle dropping rates required different 
vibration intensities and needle sizes for coal, wood and switch grass particles. 
Experiments determined that No. 21 gauge needles were selected for coal particle 
dropping while No. 20 needles were selected for wood and switch grass particles. 
Clear and highly resolved images of coal, wood, and switch grass particles 
undergoing combustion at 900 oC in air were obtained. The magnification of these 
images was 2.31 ?m/pixel and the resolution in the vertical direction was 0.031 
mm/cycle and 0.050 mm/cycle in the horizontal direction. SEM and microscope 
images were obtained of the fuel particles before and after combustion. 
Images of the burning particles revealed clarity and intensity contract 
sufficient to estimate particle size and shape, and flame properties. Particles 
meandered and moved from side-to-side as they fall through the tube because of the 
convective flows in the furnace; with the small field of view resulting from the high 
magnification this proved troublesome because particles were infrequently in the 
camera field of view. Nevertheless, the capability of the furnace and imaging system 
was demonstrated and found to be appropriate and validated the potential of the 
system to provide color images for surface temperature measurement.  
 
 
72
 
 
 
 
 
Chapter 6 
Recommendation for Future Work 
Further studies may include additional modification to the visualization 
procedures and using new color camera systems to measure spatially and temporally 
temperature distributions on surfaces of fuel particles. 
Observation and measurement of fuel particle temperatures and flame 
distributions in controlled combustion gas atmospheres will allow evaluation of 
combustion efficiency and effectiveness. Studies can be conducted to determine 
effects of fuel type, particle size, gas composition, gas temperature, and other process 
factors.  
       
                                    
 
 
 
 
 
 
 
 
73
 
 
 
 
 
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Appendix A 
Needle Gauge Comparison Chart 
Needle Nominal Outer Diameter Nominal Inner Diameter 
Gauge mm inches tol. (in.) mm inches tol. (in.) 
15 1.829 0.0720 ?0.0005 1.372 0.0540 ?0.0015 
16 1.651 0.0650 " 1.194 0.0470 " 
17 1.473 0.0580 " 1.067 0.0420 " 
18 1.270 0.0500 " 0.838 0.0330 " 
19 1.067 0.0420 " 0.686 0.0270 " 
20 0.902 0.0355 +0.0005 
-0.0000 
0.584 0.0230 +0.0015 
-0.0000 
21 0.813 0.0320 " 0.495 0.0195 " 
22 0.711 0.0280 " 0.394 0.0155 " 
22s 0.711 0.0280 " 0.140 0.0055 " 
23 0.635 0.0250 " 0.318 0.0125 " 
24 0.559 0.0220 " 0.292 0.0115 " 
25 0.508 0.0200 " 0.241 0.0095 " 
25s 0.508 0.0200 " 0.140 0.0055 " 
26 0.457 0.0180 " 0.241 0.0095 " 
26s 0.467 0.0184 " 0.114 0.0045 " 
27 0.406 0.0160 " 0.191 0.0075 " 
28 0.356 0.0140 " 0.165 0.0065 " 
29 0.330 0.0130 " 0.165 0.0065 " 
30 0.305 0.0120 " 0.140 0.0055 " 
(Source: Sigma-Aldrich Company) 
 
 
 
 
79
 
 
 
 
 
Appendix B  
Key Specifications of Furnace 
Dimensions of furnace: 32.5cm W x 35cm H. x 75cm Long  
Dimensions of retort: 6.25 cm I.D. x 97.5 cm Long 
Heating Elements: Silicon carbide (SiC) "rammed rod" 
Zones: Three zone 2600 watts per zone 55 amps/8000 watts total 
Quartz View Port: 2.5 cm W x 22.5 cm Long. x 3 
Flange Material: 304 Stainless Steel 
Flanges: Integral type with water cooling, flange seals and flange 
 
 
 
 
 
 
 
 
 
 
 
 
80
 
 
 
 
 
Appendix C  
Kodak SR-500 Motion Corder Analyzer 
Specifications 
Input power: 110 or 220 volts 
Shutter speed: 1/30 ? 1/20000 sec 
Max resolution: 512 x 480 pixels 
Frame rate: 30 - 1000 fps 
Gray scale: 256 levels 
Lens mount: C-Mount 
Sensor: 658 x 496 pixels 
Frame storage: 546 full frames with standard memory 
 
 
 
 
 
81
 
 
 
 
 
 
 
 
Appendix D 
Nikon D40X DSRL Camera Specifications 
Sensor Size: 15.6 x 23.7 mm2 
Image Sensor Type: CCD 
Effective Pixels: 10.2 million 
Shutter Speed: 30?1/4,000 sec 
LCD Monitor Resolution: 230,000 dots 
Weight: 495 g 
Highest Expanded ISO Sensitivity: Hi1 (ISO 3200 equivalent) 
Lens Mount: Nikon F mount with AF coupling and AF contacts 
Picture Angle: Equivalent in 35 mm format is approx. 1.5X lens focal length 
Dimension: 126 x 94 x 64 mm3  
LCD Monitor Type: TFT-LCD 
 
 
 
 
 
82
 
 
 
 
 
 
 
Appendix E 
COHU 2122 Monochrome Video Camera  
Specifications 
Pixels: 768 x 494 
Pixel Size: 8.4 x 9.8 microns2 
Lens Mount: C/CS-mount 
Operating Temperature: -10 to 500 oC 
Weight: 200 g 
S/N Ratio: >55dB 
Shutter Speed: 1/60-1/10,000 s 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
83
 
 
 
 
 
 
Appendix F 
File Batch 
1) Download imaging from Kodak camera to computer. 
2) Build a file with certain file name. 
3) Save the group of imaging in the file. 
4) Go to the folder the images are in, let the images shown in 5 rows. Click on 
the first file (f_000001.bmp) in the directory and then scroll down the 1st to the 
606th file (f_000606.bmp) and click it holding the SHIFT key. Then do the 
operation to 3rd and 5th row according to select 60% of entire images. Make 
sure (save as new file) is highlighted. 
5) Set the save folder to the folder you are taking images from, which makes the 
job easier in seeing the files already converted. 
6) Click CTRL + A to select all the images, and then click right button to run 
rotate clockwise. 
7) Once all the images are all rotated, close the file. 
 
 
 
 
84
 
 
 
 
 
 
 
Appendix G 
Movie Speed Setting 
1) Once the batch change is done and all the images are converted, open Jasc 
Animation Shop to adjust the movie speed with the frame rate in the 
experiment. 
2) Click on File > Animation Wizard. 
3) Choose same size as the first image frame, click NEXT. 
4) Choose transparent as the background canvas color, click NEXT.  
5) Choose default setting, click NEXT.  
6)   Choose play 1 time and 1/100th of a second to display each frame (fastest      
frame rate is 100 frame per second), click NEXT to complete the setting. 
 
 
 
 
 
 
 
85
 
 
 
 
 
 
Appendix H 
Movie Building Procedure 
1) Once the movie setting is done, add images from the batch to the Animation 
Shop. 
2) Click Add Image, find the batch saving the files, and then click on the first file 
(f_000500.bmp) in the directory and then scroll to the 500th file 
(f_000001.bmp). 
3) Once the images are selected, click NEXT to complete the file selection.   
4) Click View Animation on the top bar to preview the movie. 
5) Once the quality of the movie and speed are good, click File > Save As. 
6) Name the save file. 
7) Save as: AVI.   
8) The movie building takes about 3-5 minutes to complete depending on 
memory load and number of frames. 
9) Make sure save the movie in the right batch. 
10) When the building is done it shows the movie in the saved batch.  To open 
the movie, go to the directory and double click it. Windows Media Player 
opens it up and plays the 100 frames per second movie. 
 
 
86
 
 
 
 
 
 
 
Appendix I 
Furnace Bake Out Procedure 
1) Mount retort into furnace. Vent retort during bake. 
2) The first time the furnace is fired, heat up to 900 oC. The heating up rate can be 
rapid from room temperature to 500 oC (about 5 oC/min), and 3 oC/min from 
500 oC to 900 oC. Let the furnace sit at the temperature for about two hours. 
3) Increase the furnace temperature to 1200 oC at a rate of 80 oC/hr. Let furnace sit 
for about one hour at this temperature. 
4) After temperature is reached, let the furnace sit. To shut down the furnace, shut 
off power and with door or end caps closed, allow the furnace to slowly cool 
8?10 hours or overnight before opening. 
 
 
 
 
 
 
 
 
 
 
 
 
87
 
 
 
 
 
 
 
Appendix J 
Resolution and Magnification Results 
 
Figure J-1: USAF 1951 resolution test pattern (from Edmund) 
The USAF 1951 resolution test pattern was vertically inserted into the retort in 
the furnace. The target was located in the field of view of the camera; the camera was 
set up in front of the view window with the distance of 13 inches to the target. Images 
were obtained at laboratory room temperature. Cohu camera and Questar lens were 
used. The smallest resolved bars in the vertical direction was Group Five, Element 
 
 
88
One, with the resolution values - mmcycle32 , so the resolution of the image in vertical 
was calculated: cyclemm32 = 31?m. In horizontal, the smallest resolved bars was Group 
Four, Element Three with a resolution value mmcycle16.20 , so the resolution of the 
image: cyclemm16.20  = 50 ?m.  
Table J-1: USAF 1951 resolution test chart (from Edmund)  
 
 
 
 
 
 
 
 
 
 
 
 
 
89
 
 
 
 
 
 
 
Appendix K 
Coal Sample Results from ROBERTA Plant 
Table K-1: Cement plant results for coal samples 
 
Test Parameter Value (wt. %) 
Ash 18.78 
Fixed Carbon 53.85 
Pro
xim
ate
 
An
aly
sis
 
Volatile Matter 27.37 
Carbon 70.28 
Hydrogen 4.29 
Nitrogen 1.38 
Oxygen 3.61 
Ul
tim
ate
 A
na
lys
is 
Sulfur 2.6 
Al2O3 24.03 
CaO 6.30 
Fe2O3 9.86 
K2O 2.33 
MgO 1.10 
Na2O 0.17 
SiO2 48.1 S
tan
da
rd 
Pa
ram
ete
rs 
SO3 6.51 
Heat Value 1 12169 
Notes: 1 Value is reported as BTU/lb. 
 
 
 
90
 
 
 
 
 
 
 
Appendix L 
Particle Dropping at Lab-room  
Temperature 
The high-speed video allowed estimation of the particle dropping velocity. 
With the given conditions: average particle size of 100 ?m, high speed camera 
frame rate of 250 fps, shutter speed of 1/10000 s, No. 20 gauge needle nominal 
outside diameter of 900 ?m. 
Then software-ImageJ was used to estimate the dropping particle rate at 
different vibration speeds and Window Paint was used to draw the captured images. 
Here, three heights were chosen to hold the needle. The first height was 25cm higher 
than the vibrator at the bottom of the metal stand that fixed the injection needle; the 
second height was 37.5 cm higher than the vibrator while the third height was 50cm 
higher as shown in Figure 3-16. Different heights on the clamp obtained different 
vibrating intensity. The vibrator had a vibration speed range from 1 to 6, 1 being the 
lowest and 6 being the highest vibration intensity. One sample was analyzed to 
estimate the particle dropping rate (wood particles, No. 20 gauge needle): height at 25 
cm, vibration speed of 4. In Figure L-1, A, B and C were different spots (different 
distances to the bottom of the needle) of particles after dropping via the nozzle. The 
 
 
91
scale on the particle showed the real size of each particle on the image. 
 
 
Figure L-1: Dropping particles at laboratory-room temperature  
Figure L-1 shows sample image to calculate the resolution of wood particles. 
These images were captured in the retort by the KODAK camera with NIKON 60mm 
micro lens. The details about resolution of particles were shown in Appendix J. Hence, 
the resolution of KODAK camera with NIKON 60mm micro lens was 62.5 ?m/cycle. 
On Figure L-2, the needle was set at an angle of 35?, vibration speed at 5 and 
the needle height of 50 cm. The camera was set with the frames rate of 250 fps, and 
the video was built up at 100 fps. 
 
 
92
 
Figure L-2: Dropping coal particles with needle at the angle of 35? 
 
 
 
 
 
 
 
 
 
 
 
93
In Figure L-3, the needle was set vertically, the vibration speed at 5 at the 
height of 37.5 cm. The camera was set with the frame rate of 250 fps. After observing 
and comparing the two set ups, more particles were dropping based on qualitative 
observation in same time at the height of 37.5 cm. 
 
Figure L-3: Dropping wood particles with vertical needle