Gao, DC
1994
Effect of Pressure on Oxidation Rates of MM-Sized Char
Bateman, K.J.; Smoot, L.D.; Germane, G.J.; Blackham, A.U. and Eatough, C.N.
Fuel, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
Mass loss and burnout ties of large (five and eight millimeter diameter) char particles at pressures between 101 to 760 kPa have been measured in a newly designed and constructed high-pressure reactor. A cantilever balance attachment was fitted to the reactor to measure instantaneous particle mass while an optical pyrometer measured particle temperature continuously. The process was also videotaped at 1/30 s frame speed. Sixty-two combustion experiments produced burning and oxidation times for two sizes of Utah bituminous (HVBB) coal and North Dakota Lignite (L) at 101, 507, 760 kPa total pressure. The reactor air temperatures were about 900 or 1200 K while the airflow Reynolds Number was varied by a factor of two. Coal particles were placed in a platinum-wire basket inside the reactor at the end of the balance beam. The oxidation process was recorded by computer and on videotape, while continuous char oxidation rates were measured to burnout. An ash layer accumulated around the particles, and receded as the char was consumed. In all of the tests, including the elevated pressure tests, a linear decrease in the cube root of char mass with time was observed during char oxidation until near the end of burnout. Changes in air velocity had little effect on oxidation times while either increasing gas temperature or increasing pressure from 101 kPa to 507 kPa reduced oxidation times by about one-quarter. Further increase in pressure caused no further reduction in burn time. Pairs of nearly equally sized particles of coal had oxidation times similar to single particles that had a mass equal to the sum of the pairs.
A Facility for High-Pressure Measurement of Reaction Rates of MM-Sized Coal
Bateman, K.J.; Germane, G.J.; Smoot, L.D. and Eatough, C.N.
Energy & Fuels, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
A study was undertaken to design, construct, characterize, and demonstrate a new facility for determination of reaction rates of large coal particles at elevated pressures. A cantilever balance attachment (CBA) was designed, fabricated, and utilized in conjunction with the existing High Pressure Controlled Profile (HPCP) reactor. Large particle (8mm diameter) combustion experiments of Utah HVBB coal at both atmospheric and elevated pressures were performed to demonstrate the facility's capabilities. Measurements were obtained of particle mass loss rate and surface temperature coupled with a video record for visual observation.
Improved Diameter, Velocity, and Temperature Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Monson, C.R.; Germane, G.J. and Hecker, W.C.
Energy & Fuels, 8(4):925-931, 1994. Funded by ACERC, Advanced Fuel Research and US Department of Energy.
Coal combustion researchers have typically used the average temperature and residence time of a burning particle cloud to determine the high-temperature reactivity of coals and chars. These average values, however, cannot account for particle-to-particle variations or their possible causes. Researchers at Sandia National Laboratories developed a pyrometry technique to simultaneously measure the temperature, velocity, and diameter of individual char particles burning in a transparent-wall flat-flame facility. This work reports two significant advances relative to the optical pyrometry technique. First, pyrometer modifications together with a new analysis technique now permit the particle properties to be measured for smaller/cooler particles. Second, the modified pyrometer has been implemented in two heated-wall drop-tube reactors, rather than transparent-wall, flat-flame burners. This is significant because drop-tube reactors allow greater flexibility/control of gas environments and operating pressures during char oxidation. Glowing reactor walls, however, present some unique challenges for these optical measurements. Means of overcoming these challenges are discussed, and reliable in situ measurement of particle temperatures, velocities, and diameters is verified. The results of measurements made in these drop-tube reactors, both for calibration tests and actual oxidation tests with Spherocarb and a Utah bituminous coal char, are also presented.
1993
Comparison of Measurements and Predictions of Flame Structure and Thermal NOx, in a Swirling, Natural Gas Diffusion Flame
Boardman, R.D.; Eatough, C.N.; Germane, G.J. and Smoot, L.D.
Combustion Science and Technology, 20: 1-18, 1993. (Previously presented at the First International Conference on Combustion Technologies For a Clean Environment, Vilamoura, Portugal, September 1991). Funded by Morgantown Energy Technology Center.
A combined thermal and fuel nitric oxide submodel has recently been added to a generalized, 2-dimensional pulverized coal gasification and combustion model (PCGC-2). This model is applicable to reacting and non-reacting gaseous and particle-laden flows. The thermal NO model is based on the extended Zel'dovich mechanism. To perform an evaluation of the NOx submodel, combustion measurements of gas velocities, temperatures, and species concentrations were made in a laboratory-scale, experimental reactor with a 150 kW natural gas flame at an equivalence ratio of 1.05 and a secondary-air swirl number of 1.5. Combustion measurements of velocities and major species concentrations show generally good agreement with predicted values. Gas temperature measurements closely match predictions in the recovery region but fail to show predicted high temperature in the annular region. This study provides an evaluation of a comprehensive combustion model and the NOx submodel that can be useful as a design tool to provide pollutant formation trends in applied systems as combustion parameters are varied.
Process Data and Strategies
Germane, G.J.; Eatough, C.N. and Cannon, J.N.
Chapter 2, Fundamentals of Coal Combustion: For Clean and Efficient Use, (L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded by ACERC.
This chapter documents the measurement methods and multidimensional data for evaluation of combustion models. Data are reported for several scales from laboratory to full-scale furnaces. The design of advanced combustion systems and processes for gas, liquid and solid fossil fuels can be greatly enhanced by the utilization of verified predictive and interpretive combustion models. Development of an accurate three-dimensional model applicable to non-reacting and reacting flow systems, and specifically coal combustion and entrained flow gasification, is a primary research initiative of ACERC, and is also being pursued in several other countries. Once the code, with appropriate submodels, has been completed, it is necessary to make comparisons of code predictions to data from turbulent flames in reactors that embody various aspects of turbulent combustion of coal, oil, gas or slurry fuels. Consequently, data from a range of different-sized facilities are necessary in order to adequately demonstrate the adequacy of the code predictions, and to establish the degree of precision that the code can give in making predictions for industrial furnaces. Such detailed data gives new insights into combustion processes and strategies. The detailed measurements possible in the laboratory-scale facilities complement the coarser or sparser measurements of three-dimensional flow patterns and flame heat transfer characteristics obtained in industrial and utility furnaces.
Thrust Area 6. Model Evaluation Data and Process Strategies
Germane, G.J.
Energy & Fuels, 7, (6):906-909, 1993. Funded by ACERC.
The mission of ACERC is to conduct advanced experimental and theoretical combustion engineering research and produce useful products that have the promise of improving the technical competitiveness of U.S. industry. The strategic plane of this Thrust Area includes developing advanced instrumentation for combustion measurements and obtaining detailed combustion data to properly evaluate the predictive and interpretive computational models being developed in ACERC. A cylindrical, down-fired reactor (CPR) has been built which allows detailed control of wall temperature, inlet air velocities, and swirl, fuel type, inlet conditions, and complete radial and axial optical and intrusive probe access to the flame. Researchers in the Thrust Area have been involved in obtaining appropriate validation data using advanced instruments such as CARS in natural gas and coal flames in the CPR, where the near field is accessible and inlet conditions are well-characterized, and in full-scale industrial coal-fired boilers where far-field data obtained with advanced particle in situ counting and sizing instrumentation and radiometers provide valuable information concerning the heat-transfer and combustion products composition essential to model evaluation. Comparison of ACERC comprehensive codes with other coal-quantified models, such as CQIM, is also a research initiative in Thrust Area 6.
A High-Pressure Drop-Tube Facility for Coal Combustion Studies
Monson, C.R. and Germane, G.J.
Energy & Fuels, 7 (6):928-936, 1993. Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
A number of processes, including coal gasification, combined cycles and heat engines, are being used or developed that combust coal at elevated pressures. While practical research is being conducted on the use of coal in these applications, little is known about the basic nature of high-pressure coal combustion. The few studies that have examined the effect of pressure on these reactions during the past 25 years have been limited by experimental apparatus (shock tubes) and have produced conflicting results. A need clearly exists for well-characterized facilities that can be used for high-pressure coal combustion research. This paper describes the design and characterization of an elevated pressure drop-tube facility. This unique facility consists of a high-pressure drop-tube reactor, a tar/char/gas separation and collection system, an optical pyrometer and support equipment. The electrically heated, computer controlled reactor was shown to provide the following capabilities: pressure from 1 to 5 atm, wall and gas temperatures from 1000 to 1700 K, controllable temperature profile along the reaction tube length, particle residence times from 30 to 1000 ms, variable gas compositions of inert and oxidizing gases, and optical access ports for in situ diagnostics. Characterization of the reactor over the range of design operating conditions verified the suitability of the reactor for coal combustion experiments. Results from a series of char oxidation tests are also presented, demonstrating the wide range of possible experimental conditions; these oxidation experiments spanned a broader range of conditions than other known work.
1992
Comparison of Measurements and Predictions of Flame Structure and Thermal NOx, in a Swirling, Natural Gas Diffusion Flame
Boardman, R.D.; Eatough, C.N.; Germane, G.J. and Smoot, L.D.
Combustion Science and Technology, 1992 (in press). (Previously presented at the First International Conference on Combustion Technologies For a Clean Environment, Vilamoura, Portugal, September 1991.) Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research and ACERC.
A combined thermal and fuel nitric oxide submodel has recently been added to a generalized, 2-dimensional pulverized coal gasification and combustion model (PCGC-2). This model is applicable to reacting and non-reacting gaseous and particle-laden flows. The thermal NO model is based on the extended Zel'dovich mechanism. To perform an evaluation of the NOx submodel, combustion measurements of gas velocities, temperatures, and species concentrations were made in a laboratory-scale, experimental reactor with a 150 kW natural gas flame at an equivalence ratio of 1.05 and a secondary-air swirl number of 1.5. Combustion measurements of velocities and major species concentrations show generally good agreement with predicted values. Gas temperature measurements closely match predictions in the recovery region but fail to show predicted high temperature in the annular region. This study provides an evaluation of a comprehensive combustion model and the NOx submodel that can be useful as a design tool to provide pollutant formation trends in applied systems as combustion parameters are varied.
Char Oxidation at Elevated Pressures
Monson, C.R.; Germane, G.J.; Blackham, A.U. and Smoot, L.D.
Fall Meeting of Western States Section/The Combustion Institute, Berkely, CA, October 1992. Funded by US Department of Energy/Morgantown Energy Technology Center through Advanced Fuel Research and ACERC.
Most of the coal currently being consumed is combusted at atmospheric pressure in utility furnaces, but several other processes are also being used and developed for either the direct combustion of coal or its conversion into other products. Many of these other processes, including coal gasification, operate at elevated pressure. While a great deal of research has been conducted on coal and char combustion at atmospheric pressure, elevated pressure char oxidation has largely been ignored. This paper describes the results obtained from char oxidation experiments at atmospheric and elevated pressures.
The experiments were carried out in a high-pressure, electrically heated drop tube reactor. A particle imaging system provided in situ, simultaneous measurement of individual particle temperature, size and velocity. Approximately 100 oxidation experiments were performed with two sizes (70 and 40 µm) of Utah and Pittsburgh bituminous coal chars at 1, 5, 10, and 15 atm total pressure. Reactor temperatures were varied between 1000 and 1500K with 5 to 21% oxygen in the bulk gas, resulting in average particle temperatures ranging from 1400 to 2100K and burnouts from 15 to 96%. Independently determined particle temperature and overall reaction rate allowed an internal check of the data consistency and provided insight into the products of combustion. Results from atmospheric pressure tests were shown to be consistent with results obtained by other researchers using the same coal. The chars burned in a reducing density and diameter mode in an intermediate regime between the kinetic and pore diffusion zones, irrespective to total pressure. Significant CO2 formation occurred at the particle surface at particle temperatures below about 1800K over the entire pressure range. Particle temperatures were strongly dependent on the oxygen and total pressures; increasing oxygen pressure at constant total pressure resulted in substantial increases in particle temperature, while increasing the total pressure at constant oxygen pressure led to substantial decreases in particle temperature. Increasing total pressure from 1 to 5 atm in an environment of constant gas composition led to modest increases in the reaction rate coefficients (based on the nth order rate equation) showed a large pressure dependence; both the activation energy and frequency factor decreased with increasing pressure. The results suggested that the empirical nth order rate equation is not valid at elevated pressures.
CARS Temperature Measurements in the Brigham Young University Controlled Profile Reactor in Natural Gas and Natural Gas-Assisted Coal Flames
Pyper, D.K.; Blackham, S.; Warren, D.; Hansen, L.; Christensen, J.; Haslam, J.; Germane, G.J. and Hedman, P.O.
Fall Meeting of the Western States Section/Combustion Institute, Berkeley, CA, October 1992. Funded by ACERC.
Coherent anti-Stokes Raman spectroscopy (CARS) is a laser diagnostic technique that can be used to determine temperature and major species concentrations in harsh combustion environments without the disturbing influence of a sample probe. CARS can be applied to dirty, luminous systems because it has a large signal to interference ratio due to high signal conversion efficiency and the coherent nature of the CARS spectral emission. CARS has been shown to be an effective means of determining the temperature and species concentrations in clean gas flames (Boyack, 1990). CARS measurements are more difficult to make in particle-laden flames due to the increased luminosity and enhanced background caused by particle and gas breakdown. The increased luminosity and breakdown alter the shape and intensity of the CARS signal, thus making analysis with unmodified versions of standard CARS fitting codes more complex.
The objectives of this study were to extend the capability at Brigham Young University (BYU) of making temperature measurements in the BYU-ACERC Controlled Profile Reactor (CPR) with gaseous and pulverized coal fuels, to demonstrate the ability of making reliable CARS temperature measurements in both clean and dirty flame, and to collect representative sets of data in a natural gas and in natural gas assisted coal flames. CARS temperatures were produced with a natural gas flame and with a mixture of natural gas and Utah Blind Canyon bituminous coal. The CARS signal in the natural gas-assisted coal flame showed the same resonant spectra from particle-induced gas breakdown as has been seen previously (Hancock, 1991 and 1992). The techniques of Hancock were used to account for the background spectra in analyzing the data from the coal flame. The coal concentration in the flame was limited by the CARS signal strength and the particle-induced gas breakdown signal strength at the detector.
CARS measurements were obtained at 4 cm intervals from -20 to +40 cm across the diameter of the 80 cm combustor. These radial data sets were collected at 10 different axial locations along the 2.5 m height of the reactor, giving a total of 160 separate locations. Two hundred single laser pulses were used at each location within the reactor to collect "single shot" temperature data, which allowed the calculation of local mean temperatures as well as probability density functions. These 200 single shots were repeated at least twice during the same test and several tests were duplicated. It was found that the temperature measurements were in good agreement during a single test, but the accuracy was in the order of ±100 K from test to test.
1991
Improved Temperature, Velocity and Diameter Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Hecker, W.C.; Monson, C.R. and Germane, G.J.
Western States Section/The Combustion Institute, Los Angeles, CA, October 1991. Funded by Advanced Fuel Research, Morgantown Energy Research Center and ACERC.
Early attempts to determine the high-temperature reactivity of coals and chars were hampered by the inability to measure a burning particle's temperature and residence time. Researchers have typically approximated these values with the average temperature and residence time of a cloud of burning particles. Average values, however, do not account for particle-to-particle variations or their possible causes. In 1984 researchers at Sandia National Laboratories developed an optical technique to simultaneously measure the temperature, velocity and diameter of individual particles burning in a flat flame facility. This work reports modifications to the Sandia technique that allow measurement of smaller particles (ca. 30-200 µm) and its application to particles burning in atmospheric and elevated pressure drop-tube reactors.
The modified pyrometer is applied to drop-tube reactors, rather than flat flame burners, to allow a broad range of well-controlled gas environments and operating pressures for char oxidation experiments. Electrical wall heating allows good control of particle temperature histories, however glowing reactor walls present some unique challenges. Diffuse radiation emitted from the reactor walls enters the pyrometer's optical path, producing excess noise in the particle signal. This noise has been minimized by optimizing the design of the reactors' optical ports and the alignment of the pyrometer. The possibility of temperature measurement error caused by wall emissions reflecting off of the particle is shown to be minimal by Maxwell's electromagnetic equations.
Particle properties are obtained by focusing the burning particle's image onto a coded aperture that, as re-designed at Brigham Young University, contains a series of carefully sized blackouts and windows. Temperature is measured by conventional 2-color pyrometry, while velocity is obtained from the particle's transit time. Particle size is extracted from the signal by means of a unique geometric/statistical fitting technique developed during this work. Proper operation of the modified pyrometer has been verified during oxidation of both Spherocarb and coal char in the drop-tube reactors.
Comparison of Measurements and Predictions of Flame Structure and Thermal NOx, in a Swirling, Natural Gas Diffusion Flame
Boardman, R.D.; Eatough, C.N.; Germane, G.J. and Smoot, L.D.
First International Conference on Combustion Technologies For a Clean Environment, Vilamoura, Portugal, September 1991. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
A combined thermal and fuel nitric oxide submodel has recently been added to a generalized, 2-dimensional pulverized coal gasification and combustion model (PCGC-2). This model is applicable to reacting and non-reacting gaseous and particle-laden flows. The thermal NO model is based on the extended Zel'dovich mechanism. To perform an evaluation of the NOx submodel, combustion measurements of gas velocities, temperatures, and species concentrations were made in a laboratory-scale, experimental reactor with a 150 kW natural gas flame at an equivalence ratio of 1.05 and a secondary-air swirl number of 1.5. Combustion measurements of velocities and major species concentrations show generally good agreement with predicted values. Gas temperature measurements closely match predictions in the recovery region but fail to show predicted high temperature in the annular region. This study provides an evaluation of a comprehensive combustion model and the NOx submodel that can be useful as a design tool to provide pollutant formation trends in applied systems as combustion parameters are varied.
1988-1986
Lignite Slurry Spray Characterization and Combustion Studies
Eatough, C.N.; Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Western States Section, The Combustion Institute, Dana Point, California, 1988. Funded by US Department of Energy (Morgantown Energy Technology Center) and ACERC (National Science Foundation Associates and Affiliates).
Lignite slurry atomization and combustion characteristics were studied using two atomizers, one developed at Brigham Young University (laboratory nozzle) and the other a Parker-Hannifin Model 6840610 M3 atomizer (commercial nozzle). These nozzles were used because of the significantly different spray patterns produced by each. In these cold-flow studies, it was found that the laboratory nozzle produced a solid cone type spray pattern with the highest mass flux near the spray center line. The commercial nozzle has a hollow cone spray pattern with a larger spray angle. Atomization studies were performed with these nozzles to determine the effect of atomizing air to slurry mass flow ratio (A/S) on particle/droplet size and velocity, and slurry spray mass distribution. These measurements were then used to study the effect of particle/droplet size and velocity, and spray mass distribution on carbon burnout in a laboratory scale reactor using hot-water dried lignite slurry as a fuel. Both the laboratory and commercial nozzles follow the same trends for mean droplet size and droplet velocity with variation in A/S. As expected, mean droplet size decreased with A/S and velocity increased with A/S. Spray angle decreased for the laboratory nozzle but increased for the commercial nozzle with increase in A/S.
Analysis of combustion data indicates an expected strong dependence of burnout on particle/droplet size. Burnout increased markedly as particle/droplet size decreased. Burnout was also affected by the mass distribution of the slurry spray. Large spray angles directed slurry to the relatively cool reactor walls resulting in lower burnout values. Burnout values from both nozzles followed the same trends with regard to droplet size. Burnout increased with decreasing mean droplet size to about 50 mm, which corresponded closely with the coal particle size in the slurry which has a mean diameter of about 40 mm. A mean droplet diameter larger than about 80 mm with a 300 mm top size could not sustain combustion in the laboratory reactor.
A combustion map of burnout values was made using the laboratory nozzle at an A/S of 0.7, swirl number of 1.5 and SR of 1.1.
Laboratory-Scale Combustion of Coal-Water Mixtures
Rawlins, D.C.; Germane, G.J.; Hedman, P.O. and Smoot, L.D.
Combustion and Flame, 63, 59-72, 1986. 14 pgs. Funded by Pittsburgh Energy Technology Center.
A detailed study of the combustion of coal-water mixtures (70-73% coal, 27-30% water) and formation of nitrogen-containing pollutants has been performed in a vertical, laboratory-scale combustor. Space-resolved, local measurements of solid and gaseous combustion products were made with a stainless steel, water quenched probe to determine the percentage of coal burnout and local gaseous composition at various locations within the reactor. Rapid mixing of the gas and particle streams eliminated fuel-rich regions within the reactor. Carbon monoxide was found only near the inlet region of the reactor with the highest concentration being 0.8%. Particle residence time in the reactor was estimated to be about 100 ms, with coal burnout (daf) ranging from 82 to 98% as secondary air swirl number and stoichiometric ratio were varied. The only nitrogen-containing pollutant found was nitrogen oxide, with the exit concentrations ranging from 180 to 750 ppm.
Low Rank Coal-Water Fuel Combustion in a Laboratory Scale Furnace
Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Accepted for publication in Combustion and Flame, 1988. Funded by US Department of Energy.
A detailed study of hot-water dried lignite slurry combustion and the formation of nitrogen-containing pollutants was performed in a vertical, laboratory-scale combustor. Space-resolved local measurements of solid and gaseous combustion products were obtained from throughout the combustion zone using a stainless steel, water-quenched sample probe. Coal burnout (daf) of greater than 99% was achieved without supplementary fuel support, in an estimated residence time of 1.4s. Flame stability was strongly affected by the atomized droplet size, which is controlled by the atomizing air to slurry mass ration (A/S). For A/S greater than 0.7, coal burnout was relatively insensitive to further increases in A/S, yet burnout decreased rapidly as A/S was decreased. Nitric oxide (NO) emissions were not affected greatly by changes in A/S. Decreasing stoichiometric ration (SR) to about 0.8, caused coal burnout to decrease from about 98% to 94% and NO emissions to decrease from around 600 PPM to less than 100 PPM Changes in secondary air swirl number from 0 to 4.25 had little or no effect on coal burnout or NO emissions for a SR of 1.1 and an A/S of 0.75. At low A/S (0.24), high secondary air swirl was required in order to stabilize the slurry flame. Reactor mapping tests showed rapid mixing between the slurry and the combustion air. CO was found only near the slurry inlet at a maximum concentration of 0.3%. No other fuel-rich species were detected in measurable quantities.
A Technical Review of Automotive Racing Fuels
Germane, G.J.
SAE Fuels and Lubricants Transactions, 1, 876-878, 1986. 2 pgs. Funded by Angus Chemical Company.
Automobile racing engine performance has historically progressed with and aided the development of automotive technology. Racing engine performance has been improved in various applications with specialized liquid fuels, such as nitroparaffins, alcohol (methanol) and certain hydrocarbons used in racing gasolines.
This paper presents physical and thermodynamic properties of commonly used racing fuels and selected additives, including nitrous oxide and hydrazine. Improving the antiknock properties of gasoline for racing purposes is also discussed. Engine operating characteristics and power output for each fuel are discussed in terms of appropriate fuel properties and engine parameters such as air/fuel ratio and compression ratio. Combustion of various fuels is discussed along with the effect of dissociation and heat loss of performance. Some experimental performance data are presented, and theoretical and practical considerations that affect fuel utilization are also discussed.
Lignite Slurry Atomizer Spray Distribution and Characterization Studies
Eatough, C.N.; Germane, G.J. and Smoot, L.D.
8th International Symposium on Coal Slurry Fuels Preparation and Utilization, 1986, Orlando, FL. 12 pgs. Funded by Morgantown Energy Technology Center.
The Brigham Young University (BYU) Combustion Laboratory has been investigating the combustion characteristics of dried, low-rank coal-water slurries under contract to the US Department of Energy's Grand Forks Project Office. This paper contains results of atomization studies of low-rank, coal-water slurry provided by the Grand Forks Project Office for a laboratory nozzle and a commercial atomizer.
Photographic techniques were used to characterize 58 wt% coal-water slurry sprays produced by a laboratory air-blast nozzle, used for coal slurry combustion tests in the Combustion Laboratory, and a Parker-Hannifin Model 6480610 M3 atomizer. Studies in non-reacting slurry sprays to determine spray droplet size and droplet velocities, and separate slurry spray mass distribution tests were conducted. The variables for all spray tests were the mass ratio of atomizing air to slurry fuel flow, and nozzle type. Swirl number was varied only for spray mass distribution tests.
Results of the spray droplet measurements show that the mean droplet diameter of the slurry spray is strongly dependent on the air to CWM mass ratio and essentially independent of the mass flow rate of slurry for the range in flow rates tested. The laboratory nozzle produced mean spray droplet diameters about 20% smaller than the commercial atomizer for the same atomizing air to slurry mass flow ratio and slurry mass flow. This indicates that better mixing can occur in a combustor with the laboratory nozzle, though the commercial nozzle was operated well below its design capacity. The laboratory nozzle also produced higher axial velocities than the commercial atomizer, which may result in a shorter particle residence time in the combustor for the laboratory nozzle.
Radial spray mass distribution was measured using a patternator located in two orthogonal positions in a plane perpendicular to the nozzle centerline a short distance form the nozzle tip. The spray mass distribution was characterized by the radius of gyration of the mass of collected slurry on any side of the nozzle centerline. This calculated distance defined a characteristic spray angle. The laboratory nozzle spray pattern is that of a solid cone with higher spray flux near the spray centerline. The commercial atomizer produces a heavy spray flux in an annular cone around the spray centerline. Results show that the both nozzles, spray mass distribution was influenced by atomizing air to slurry mass flow ratio but not by combustion air swirl. The spray flux produced by the laboratory atomizer becomes less evenly distributed and more concentrated along the centerline of the nozzle as the atomizing air to slurry mass flow ratio is increased, while the opposite effect is evident with the commercial nozzle. The effects of the observed difference in spray characteristics for both nozzles on carbon burnout during combustion tests are also reported in the paper.
Lignite Coal Water Slurry Combustion Characteristics in a Laboratory-Scale Furnace
Rawlins, D.C.; Jones, R.G.; Germane, G.J. and Smoot, L.D.
8th International Symposium on Coal Slurry Fuels Preparation and Utilization, 1986, Orlando, FL. 14 pgs. Funded by Morgantown Energy Technology Center.
The Brigham Young University (BYU) Combustion Laboratory is currently conducting a low-rank coal-water slurry characterization and combustion research program for the US Department of Energy through the Grand Forks, North Dakota Project Office. The lignite slurry used in this study was prepared at the University of North Dakota Energy Research Center (UNDERC) by a hot water drying process. The slurry contains 58% by weight solids and 42% water. No additives have been included to increase slurry stability. Slurry characterization studies, which have been conducted at both BYU and UNDERC, include slurry rheology, particle size distribution and slurry stability.
Combustion tests are being conducted in a vertically oriented, cylindrical combustor, 3.0 m high and 35 cm in interior diameter, with CWM and air injection at the top. Access ports are located along the entire length of the reactor for visual observation of the flame and for insertion of a stainless steel water-quenched sample probe. Solid and gaseous products of combustion are removed form the combustion zone and analyzed for coal burnout and local gaseous compositions. The combustion tests show that a strong, stable flame can be achieved without secondary fuel support. Flame stability appears to be strongly affected by the ratio of the spray nozzle atomizing air to the slurry feed rate. Stoichiometric ratio and secondary air swirl number affect flame stability to a lesser exten. Coal burnout of greater than 99% has been achieved with a reactor residence time estimated to be slightly greater than one second. NO emissions have been measured in the range of 200 to 600 PPM No attempt has been made to control or reduce these emissions.
A Comparison of Combustion Characteristics Between Lignite-Water Slurry and Pulverized Lignite
Rawlins, D.C.; Smoot, L.D. and Germane, G.J.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 27 pgs. Funded by the Morgantown Energy Technology Center.
Experiments of the combustion of hot-water dried lignite slurry and its parent, pulverized coal have been performed in a laboratory-scale combustor. The operating parameter that had the greatest effect on flame location for lignite slurry combustion was the slurry mean droplet diameter. A stable flame could not be maintained with large droplet sizes. The air blast of the slurry-atomizing nozzle caused the mixing of the primary and secondary streams to be much more rapid for slurry combustion than for pulverized coal. Due to this rapid mixing, fuel-rich products of combustion were only observed in trace quantities near the top of the combustion zone during slurry combustion; however, with pulverized coal combustion, significant concentrations persisted throughout the combustor. Secondary air swirl number had the greatest effect on the pulverized lignite flame location. A minimum in nitrogen oxide (NO) concentration was observed during the pulverized coal combustion as swirl was increased. Secondary air swirl, however, had only a negligible effect on coal burnout and NO emissions for slurry combustion. A five-fold increase in the primary air velocity more than doubled NO concentrations at the exit plane. Changing the primary air velocity through the slurry atomizer (by changing the air mass flow rate) did not affect NO emissions during slurry combustion. Changes in the water concentration within the combustion system did not affect combustion performance with pulverized coal. Thus, NO emissions are more strongly controlled by the mixing of the fuel with the secondary air than by flame temperature reduction caused by water added to the combustion system.
Gao, DC
1994
Effect of Pressure on Oxidation Rates of MM-Sized Char
Bateman, K.J.; Smoot, L.D.; Germane, G.J.; Blackham, A.U. and Eatough, C.N.
Fuel, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
Mass loss and burnout ties of large (five and eight millimeter diameter) char particles at pressures between 101 to 760 kPa have been measured in a newly designed and constructed high-pressure reactor. A cantilever balance attachment was fitted to the reactor to measure instantaneous particle mass while an optical pyrometer measured particle temperature continuously. The process was also videotaped at 1/30 s frame speed. Sixty-two combustion experiments produced burning and oxidation times for two sizes of Utah bituminous (HVBB) coal and North Dakota Lignite (L) at 101, 507, 760 kPa total pressure. The reactor air temperatures were about 900 or 1200 K while the airflow Reynolds Number was varied by a factor of two. Coal particles were placed in a platinum-wire basket inside the reactor at the end of the balance beam. The oxidation process was recorded by computer and on videotape, while continuous char oxidation rates were measured to burnout. An ash layer accumulated around the particles, and receded as the char was consumed. In all of the tests, including the elevated pressure tests, a linear decrease in the cube root of char mass with time was observed during char oxidation until near the end of burnout. Changes in air velocity had little effect on oxidation times while either increasing gas temperature or increasing pressure from 101 kPa to 507 kPa reduced oxidation times by about one-quarter. Further increase in pressure caused no further reduction in burn time. Pairs of nearly equally sized particles of coal had oxidation times similar to single particles that had a mass equal to the sum of the pairs.
A Facility for High-Pressure Measurement of Reaction Rates of MM-Sized Coal
Bateman, K.J.; Germane, G.J.; Smoot, L.D. and Eatough, C.N.
Energy & Fuels, 1994 (in press). Funded by US Department of Energy/Morgantown Energy Technology Center and ACERC.
A study was undertaken to design, construct, characterize, and demonstrate a new facility for determination of reaction rates of large coal particles at elevated pressures. A cantilever balance attachment (CBA) was designed, fabricated, and utilized in conjunction with the existing High Pressure Controlled Profile (HPCP) reactor. Large particle (8mm diameter) combustion experiments of Utah HVBB coal at both atmospheric and elevated pressures were performed to demonstrate the facility's capabilities. Measurements were obtained of particle mass loss rate and surface temperature coupled with a video record for visual observation.
Improved Diameter, Velocity, and Temperature Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Monson, C.R.; Germane, G.J. and Hecker, W.C.
Energy & Fuels, 8(4):925-931, 1994. Funded by ACERC, Advanced Fuel Research and US Department of Energy.
Coal combustion researchers have typically used the average temperature and residence time of a burning particle cloud to determine the high-temperature reactivity of coals and chars. These average values, however, cannot account for particle-to-particle variations or their possible causes. Researchers at Sandia National Laboratories developed a pyrometry technique to simultaneously measure the temperature, velocity, and diameter of individual char particles burning in a transparent-wall flat-flame facility. This work reports two significant advances relative to the optical pyrometry technique. First, pyrometer modifications together with a new analysis technique now permit the particle properties to be measured for smaller/cooler particles. Second, the modified pyrometer has been implemented in two heated-wall drop-tube reactors, rather than transparent-wall, flat-flame burners. This is significant because drop-tube reactors allow greater flexibility/control of gas environments and operating pressures during char oxidation. Glowing reactor walls, however, present some unique challenges for these optical measurements. Means of overcoming these challenges are discussed, and reliable in situ measurement of particle temperatures, velocities, and diameters is verified. The results of measurements made in these drop-tube reactors, both for calibration tests and actual oxidation tests with Spherocarb and a Utah bituminous coal char, are also presented.
1993
Comparison of Measurements and Predictions of Flame Structure and Thermal NOx, in a Swirling, Natural Gas Diffusion Flame
Boardman, R.D.; Eatough, C.N.; Germane, G.J. and Smoot, L.D.
Combustion Science and Technology, 20: 1-18, 1993. (Previously presented at the First International Conference on Combustion Technologies For a Clean Environment, Vilamoura, Portugal, September 1991). Funded by Morgantown Energy Technology Center.
A combined thermal and fuel nitric oxide submodel has recently been added to a generalized, 2-dimensional pulverized coal gasification and combustion model (PCGC-2). This model is applicable to reacting and non-reacting gaseous and particle-laden flows. The thermal NO model is based on the extended Zel'dovich mechanism. To perform an evaluation of the NOx submodel, combustion measurements of gas velocities, temperatures, and species concentrations were made in a laboratory-scale, experimental reactor with a 150 kW natural gas flame at an equivalence ratio of 1.05 and a secondary-air swirl number of 1.5. Combustion measurements of velocities and major species concentrations show generally good agreement with predicted values. Gas temperature measurements closely match predictions in the recovery region but fail to show predicted high temperature in the annular region. This study provides an evaluation of a comprehensive combustion model and the NOx submodel that can be useful as a design tool to provide pollutant formation trends in applied systems as combustion parameters are varied.
Process Data and Strategies
Germane, G.J.; Eatough, C.N. and Cannon, J.N.
Chapter 2, Fundamentals of Coal Combustion: For Clean and Efficient Use, (L.D. Smoot, ed.), Elsevier Science Publishers, The Netherlands, 1993. Funded by ACERC.
This chapter documents the measurement methods and multidimensional data for evaluation of combustion models. Data are reported for several scales from laboratory to full-scale furnaces. The design of advanced combustion systems and processes for gas, liquid and solid fossil fuels can be greatly enhanced by the utilization of verified predictive and interpretive combustion models. Development of an accurate three-dimensional model applicable to non-reacting and reacting flow systems, and specifically coal combustion and entrained flow gasification, is a primary research initiative of ACERC, and is also being pursued in several other countries. Once the code, with appropriate submodels, has been completed, it is necessary to make comparisons of code predictions to data from turbulent flames in reactors that embody various aspects of turbulent combustion of coal, oil, gas or slurry fuels. Consequently, data from a range of different-sized facilities are necessary in order to adequately demonstrate the adequacy of the code predictions, and to establish the degree of precision that the code can give in making predictions for industrial furnaces. Such detailed data gives new insights into combustion processes and strategies. The detailed measurements possible in the laboratory-scale facilities complement the coarser or sparser measurements of three-dimensional flow patterns and flame heat transfer characteristics obtained in industrial and utility furnaces.
Thrust Area 6. Model Evaluation Data and Process Strategies
Germane, G.J.
Energy & Fuels, 7, (6):906-909, 1993. Funded by ACERC.
The mission of ACERC is to conduct advanced experimental and theoretical combustion engineering research and produce useful products that have the promise of improving the technical competitiveness of U.S. industry. The strategic plane of this Thrust Area includes developing advanced instrumentation for combustion measurements and obtaining detailed combustion data to properly evaluate the predictive and interpretive computational models being developed in ACERC. A cylindrical, down-fired reactor (CPR) has been built which allows detailed control of wall temperature, inlet air velocities, and swirl, fuel type, inlet conditions, and complete radial and axial optical and intrusive probe access to the flame. Researchers in the Thrust Area have been involved in obtaining appropriate validation data using advanced instruments such as CARS in natural gas and coal flames in the CPR, where the near field is accessible and inlet conditions are well-characterized, and in full-scale industrial coal-fired boilers where far-field data obtained with advanced particle in situ counting and sizing instrumentation and radiometers provide valuable information concerning the heat-transfer and combustion products composition essential to model evaluation. Comparison of ACERC comprehensive codes with other coal-quantified models, such as CQIM, is also a research initiative in Thrust Area 6.
A High-Pressure Drop-Tube Facility for Coal Combustion Studies
Monson, C.R. and Germane, G.J.
Energy & Fuels, 7 (6):928-936, 1993. Funded by US Department of Energy, Morgantown Energy Technology Center and ACERC.
A number of processes, including coal gasification, combined cycles and heat engines, are being used or developed that combust coal at elevated pressures. While practical research is being conducted on the use of coal in these applications, little is known about the basic nature of high-pressure coal combustion. The few studies that have examined the effect of pressure on these reactions during the past 25 years have been limited by experimental apparatus (shock tubes) and have produced conflicting results. A need clearly exists for well-characterized facilities that can be used for high-pressure coal combustion research. This paper describes the design and characterization of an elevated pressure drop-tube facility. This unique facility consists of a high-pressure drop-tube reactor, a tar/char/gas separation and collection system, an optical pyrometer and support equipment. The electrically heated, computer controlled reactor was shown to provide the following capabilities: pressure from 1 to 5 atm, wall and gas temperatures from 1000 to 1700 K, controllable temperature profile along the reaction tube length, particle residence times from 30 to 1000 ms, variable gas compositions of inert and oxidizing gases, and optical access ports for in situ diagnostics. Characterization of the reactor over the range of design operating conditions verified the suitability of the reactor for coal combustion experiments. Results from a series of char oxidation tests are also presented, demonstrating the wide range of possible experimental conditions; these oxidation experiments spanned a broader range of conditions than other known work.
1992
Comparison of Measurements and Predictions of Flame Structure and Thermal NOx, in a Swirling, Natural Gas Diffusion Flame
Boardman, R.D.; Eatough, C.N.; Germane, G.J. and Smoot, L.D.
Combustion Science and Technology, 1992 (in press). (Previously presented at the First International Conference on Combustion Technologies For a Clean Environment, Vilamoura, Portugal, September 1991.) Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research and ACERC.
A combined thermal and fuel nitric oxide submodel has recently been added to a generalized, 2-dimensional pulverized coal gasification and combustion model (PCGC-2). This model is applicable to reacting and non-reacting gaseous and particle-laden flows. The thermal NO model is based on the extended Zel'dovich mechanism. To perform an evaluation of the NOx submodel, combustion measurements of gas velocities, temperatures, and species concentrations were made in a laboratory-scale, experimental reactor with a 150 kW natural gas flame at an equivalence ratio of 1.05 and a secondary-air swirl number of 1.5. Combustion measurements of velocities and major species concentrations show generally good agreement with predicted values. Gas temperature measurements closely match predictions in the recovery region but fail to show predicted high temperature in the annular region. This study provides an evaluation of a comprehensive combustion model and the NOx submodel that can be useful as a design tool to provide pollutant formation trends in applied systems as combustion parameters are varied.
Char Oxidation at Elevated Pressures
Monson, C.R.; Germane, G.J.; Blackham, A.U. and Smoot, L.D.
Fall Meeting of Western States Section/The Combustion Institute, Berkely, CA, October 1992. Funded by US Department of Energy/Morgantown Energy Technology Center through Advanced Fuel Research and ACERC.
Most of the coal currently being consumed is combusted at atmospheric pressure in utility furnaces, but several other processes are also being used and developed for either the direct combustion of coal or its conversion into other products. Many of these other processes, including coal gasification, operate at elevated pressure. While a great deal of research has been conducted on coal and char combustion at atmospheric pressure, elevated pressure char oxidation has largely been ignored. This paper describes the results obtained from char oxidation experiments at atmospheric and elevated pressures.
The experiments were carried out in a high-pressure, electrically heated drop tube reactor. A particle imaging system provided in situ, simultaneous measurement of individual particle temperature, size and velocity. Approximately 100 oxidation experiments were performed with two sizes (70 and 40 µm) of Utah and Pittsburgh bituminous coal chars at 1, 5, 10, and 15 atm total pressure. Reactor temperatures were varied between 1000 and 1500K with 5 to 21% oxygen in the bulk gas, resulting in average particle temperatures ranging from 1400 to 2100K and burnouts from 15 to 96%. Independently determined particle temperature and overall reaction rate allowed an internal check of the data consistency and provided insight into the products of combustion. Results from atmospheric pressure tests were shown to be consistent with results obtained by other researchers using the same coal. The chars burned in a reducing density and diameter mode in an intermediate regime between the kinetic and pore diffusion zones, irrespective to total pressure. Significant CO2 formation occurred at the particle surface at particle temperatures below about 1800K over the entire pressure range. Particle temperatures were strongly dependent on the oxygen and total pressures; increasing oxygen pressure at constant total pressure resulted in substantial increases in particle temperature, while increasing the total pressure at constant oxygen pressure led to substantial decreases in particle temperature. Increasing total pressure from 1 to 5 atm in an environment of constant gas composition led to modest increases in the reaction rate coefficients (based on the nth order rate equation) showed a large pressure dependence; both the activation energy and frequency factor decreased with increasing pressure. The results suggested that the empirical nth order rate equation is not valid at elevated pressures.
CARS Temperature Measurements in the Brigham Young University Controlled Profile Reactor in Natural Gas and Natural Gas-Assisted Coal Flames
Pyper, D.K.; Blackham, S.; Warren, D.; Hansen, L.; Christensen, J.; Haslam, J.; Germane, G.J. and Hedman, P.O.
Fall Meeting of the Western States Section/Combustion Institute, Berkeley, CA, October 1992. Funded by ACERC.
Coherent anti-Stokes Raman spectroscopy (CARS) is a laser diagnostic technique that can be used to determine temperature and major species concentrations in harsh combustion environments without the disturbing influence of a sample probe. CARS can be applied to dirty, luminous systems because it has a large signal to interference ratio due to high signal conversion efficiency and the coherent nature of the CARS spectral emission. CARS has been shown to be an effective means of determining the temperature and species concentrations in clean gas flames (Boyack, 1990). CARS measurements are more difficult to make in particle-laden flames due to the increased luminosity and enhanced background caused by particle and gas breakdown. The increased luminosity and breakdown alter the shape and intensity of the CARS signal, thus making analysis with unmodified versions of standard CARS fitting codes more complex.
The objectives of this study were to extend the capability at Brigham Young University (BYU) of making temperature measurements in the BYU-ACERC Controlled Profile Reactor (CPR) with gaseous and pulverized coal fuels, to demonstrate the ability of making reliable CARS temperature measurements in both clean and dirty flame, and to collect representative sets of data in a natural gas and in natural gas assisted coal flames. CARS temperatures were produced with a natural gas flame and with a mixture of natural gas and Utah Blind Canyon bituminous coal. The CARS signal in the natural gas-assisted coal flame showed the same resonant spectra from particle-induced gas breakdown as has been seen previously (Hancock, 1991 and 1992). The techniques of Hancock were used to account for the background spectra in analyzing the data from the coal flame. The coal concentration in the flame was limited by the CARS signal strength and the particle-induced gas breakdown signal strength at the detector.
CARS measurements were obtained at 4 cm intervals from -20 to +40 cm across the diameter of the 80 cm combustor. These radial data sets were collected at 10 different axial locations along the 2.5 m height of the reactor, giving a total of 160 separate locations. Two hundred single laser pulses were used at each location within the reactor to collect "single shot" temperature data, which allowed the calculation of local mean temperatures as well as probability density functions. These 200 single shots were repeated at least twice during the same test and several tests were duplicated. It was found that the temperature measurements were in good agreement during a single test, but the accuracy was in the order of ±100 K from test to test.
1991
Improved Temperature, Velocity and Diameter Measurements for Char Particles in Drop-Tube Reactors
Cope, R.F.; Hecker, W.C.; Monson, C.R. and Germane, G.J.
Western States Section/The Combustion Institute, Los Angeles, CA, October 1991. Funded by Advanced Fuel Research, Morgantown Energy Research Center and ACERC.
Early attempts to determine the high-temperature reactivity of coals and chars were hampered by the inability to measure a burning particle's temperature and residence time. Researchers have typically approximated these values with the average temperature and residence time of a cloud of burning particles. Average values, however, do not account for particle-to-particle variations or their possible causes. In 1984 researchers at Sandia National Laboratories developed an optical technique to simultaneously measure the temperature, velocity and diameter of individual particles burning in a flat flame facility. This work reports modifications to the Sandia technique that allow measurement of smaller particles (ca. 30-200 µm) and its application to particles burning in atmospheric and elevated pressure drop-tube reactors.
The modified pyrometer is applied to drop-tube reactors, rather than flat flame burners, to allow a broad range of well-controlled gas environments and operating pressures for char oxidation experiments. Electrical wall heating allows good control of particle temperature histories, however glowing reactor walls present some unique challenges. Diffuse radiation emitted from the reactor walls enters the pyrometer's optical path, producing excess noise in the particle signal. This noise has been minimized by optimizing the design of the reactors' optical ports and the alignment of the pyrometer. The possibility of temperature measurement error caused by wall emissions reflecting off of the particle is shown to be minimal by Maxwell's electromagnetic equations.
Particle properties are obtained by focusing the burning particle's image onto a coded aperture that, as re-designed at Brigham Young University, contains a series of carefully sized blackouts and windows. Temperature is measured by conventional 2-color pyrometry, while velocity is obtained from the particle's transit time. Particle size is extracted from the signal by means of a unique geometric/statistical fitting technique developed during this work. Proper operation of the modified pyrometer has been verified during oxidation of both Spherocarb and coal char in the drop-tube reactors.
Comparison of Measurements and Predictions of Flame Structure and Thermal NOx, in a Swirling, Natural Gas Diffusion Flame
Boardman, R.D.; Eatough, C.N.; Germane, G.J. and Smoot, L.D.
First International Conference on Combustion Technologies For a Clean Environment, Vilamoura, Portugal, September 1991. Funded by Morgantown Energy Technology Center through subcontract from Advanced Fuel Research Co.
A combined thermal and fuel nitric oxide submodel has recently been added to a generalized, 2-dimensional pulverized coal gasification and combustion model (PCGC-2). This model is applicable to reacting and non-reacting gaseous and particle-laden flows. The thermal NO model is based on the extended Zel'dovich mechanism. To perform an evaluation of the NOx submodel, combustion measurements of gas velocities, temperatures, and species concentrations were made in a laboratory-scale, experimental reactor with a 150 kW natural gas flame at an equivalence ratio of 1.05 and a secondary-air swirl number of 1.5. Combustion measurements of velocities and major species concentrations show generally good agreement with predicted values. Gas temperature measurements closely match predictions in the recovery region but fail to show predicted high temperature in the annular region. This study provides an evaluation of a comprehensive combustion model and the NOx submodel that can be useful as a design tool to provide pollutant formation trends in applied systems as combustion parameters are varied.
1988-1986
Lignite Slurry Spray Characterization and Combustion Studies
Eatough, C.N.; Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Western States Section, The Combustion Institute, Dana Point, California, 1988. Funded by US Department of Energy (Morgantown Energy Technology Center) and ACERC (National Science Foundation Associates and Affiliates).
Lignite slurry atomization and combustion characteristics were studied using two atomizers, one developed at Brigham Young University (laboratory nozzle) and the other a Parker-Hannifin Model 6840610 M3 atomizer (commercial nozzle). These nozzles were used because of the significantly different spray patterns produced by each. In these cold-flow studies, it was found that the laboratory nozzle produced a solid cone type spray pattern with the highest mass flux near the spray center line. The commercial nozzle has a hollow cone spray pattern with a larger spray angle. Atomization studies were performed with these nozzles to determine the effect of atomizing air to slurry mass flow ratio (A/S) on particle/droplet size and velocity, and slurry spray mass distribution. These measurements were then used to study the effect of particle/droplet size and velocity, and spray mass distribution on carbon burnout in a laboratory scale reactor using hot-water dried lignite slurry as a fuel. Both the laboratory and commercial nozzles follow the same trends for mean droplet size and droplet velocity with variation in A/S. As expected, mean droplet size decreased with A/S and velocity increased with A/S. Spray angle decreased for the laboratory nozzle but increased for the commercial nozzle with increase in A/S.
Analysis of combustion data indicates an expected strong dependence of burnout on particle/droplet size. Burnout increased markedly as particle/droplet size decreased. Burnout was also affected by the mass distribution of the slurry spray. Large spray angles directed slurry to the relatively cool reactor walls resulting in lower burnout values. Burnout values from both nozzles followed the same trends with regard to droplet size. Burnout increased with decreasing mean droplet size to about 50 mm, which corresponded closely with the coal particle size in the slurry which has a mean diameter of about 40 mm. A mean droplet diameter larger than about 80 mm with a 300 mm top size could not sustain combustion in the laboratory reactor.
A combustion map of burnout values was made using the laboratory nozzle at an A/S of 0.7, swirl number of 1.5 and SR of 1.1.
Laboratory-Scale Combustion of Coal-Water Mixtures
Rawlins, D.C.; Germane, G.J.; Hedman, P.O. and Smoot, L.D.
Combustion and Flame, 63, 59-72, 1986. 14 pgs. Funded by Pittsburgh Energy Technology Center.
A detailed study of the combustion of coal-water mixtures (70-73% coal, 27-30% water) and formation of nitrogen-containing pollutants has been performed in a vertical, laboratory-scale combustor. Space-resolved, local measurements of solid and gaseous combustion products were made with a stainless steel, water quenched probe to determine the percentage of coal burnout and local gaseous composition at various locations within the reactor. Rapid mixing of the gas and particle streams eliminated fuel-rich regions within the reactor. Carbon monoxide was found only near the inlet region of the reactor with the highest concentration being 0.8%. Particle residence time in the reactor was estimated to be about 100 ms, with coal burnout (daf) ranging from 82 to 98% as secondary air swirl number and stoichiometric ratio were varied. The only nitrogen-containing pollutant found was nitrogen oxide, with the exit concentrations ranging from 180 to 750 ppm.
Low Rank Coal-Water Fuel Combustion in a Laboratory Scale Furnace
Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Accepted for publication in Combustion and Flame, 1988. Funded by US Department of Energy.
A detailed study of hot-water dried lignite slurry combustion and the formation of nitrogen-containing pollutants was performed in a vertical, laboratory-scale combustor. Space-resolved local measurements of solid and gaseous combustion products were obtained from throughout the combustion zone using a stainless steel, water-quenched sample probe. Coal burnout (daf) of greater than 99% was achieved without supplementary fuel support, in an estimated residence time of 1.4s. Flame stability was strongly affected by the atomized droplet size, which is controlled by the atomizing air to slurry mass ration (A/S). For A/S greater than 0.7, coal burnout was relatively insensitive to further increases in A/S, yet burnout decreased rapidly as A/S was decreased. Nitric oxide (NO) emissions were not affected greatly by changes in A/S. Decreasing stoichiometric ration (SR) to about 0.8, caused coal burnout to decrease from about 98% to 94% and NO emissions to decrease from around 600 PPM to less than 100 PPM Changes in secondary air swirl number from 0 to 4.25 had little or no effect on coal burnout or NO emissions for a SR of 1.1 and an A/S of 0.75. At low A/S (0.24), high secondary air swirl was required in order to stabilize the slurry flame. Reactor mapping tests showed rapid mixing between the slurry and the combustion air. CO was found only near the slurry inlet at a maximum concentration of 0.3%. No other fuel-rich species were detected in measurable quantities.
A Technical Review of Automotive Racing Fuels
Germane, G.J.
SAE Fuels and Lubricants Transactions, 1, 876-878, 1986. 2 pgs. Funded by Angus Chemical Company.
Automobile racing engine performance has historically progressed with and aided the development of automotive technology. Racing engine performance has been improved in various applications with specialized liquid fuels, such as nitroparaffins, alcohol (methanol) and certain hydrocarbons used in racing gasolines.
This paper presents physical and thermodynamic properties of commonly used racing fuels and selected additives, including nitrous oxide and hydrazine. Improving the antiknock properties of gasoline for racing purposes is also discussed. Engine operating characteristics and power output for each fuel are discussed in terms of appropriate fuel properties and engine parameters such as air/fuel ratio and compression ratio. Combustion of various fuels is discussed along with the effect of dissociation and heat loss of performance. Some experimental performance data are presented, and theoretical and practical considerations that affect fuel utilization are also discussed.
Lignite Slurry Atomizer Spray Distribution and Characterization Studies
Eatough, C.N.; Germane, G.J. and Smoot, L.D.
8th International Symposium on Coal Slurry Fuels Preparation and Utilization, 1986, Orlando, FL. 12 pgs. Funded by Morgantown Energy Technology Center.
The Brigham Young University (BYU) Combustion Laboratory has been investigating the combustion characteristics of dried, low-rank coal-water slurries under contract to the US Department of Energy's Grand Forks Project Office. This paper contains results of atomization studies of low-rank, coal-water slurry provided by the Grand Forks Project Office for a laboratory nozzle and a commercial atomizer.
Photographic techniques were used to characterize 58 wt% coal-water slurry sprays produced by a laboratory air-blast nozzle, used for coal slurry combustion tests in the Combustion Laboratory, and a Parker-Hannifin Model 6480610 M3 atomizer. Studies in non-reacting slurry sprays to determine spray droplet size and droplet velocities, and separate slurry spray mass distribution tests were conducted. The variables for all spray tests were the mass ratio of atomizing air to slurry fuel flow, and nozzle type. Swirl number was varied only for spray mass distribution tests.
Results of the spray droplet measurements show that the mean droplet diameter of the slurry spray is strongly dependent on the air to CWM mass ratio and essentially independent of the mass flow rate of slurry for the range in flow rates tested. The laboratory nozzle produced mean spray droplet diameters about 20% smaller than the commercial atomizer for the same atomizing air to slurry mass flow ratio and slurry mass flow. This indicates that better mixing can occur in a combustor with the laboratory nozzle, though the commercial nozzle was operated well below its design capacity. The laboratory nozzle also produced higher axial velocities than the commercial atomizer, which may result in a shorter particle residence time in the combustor for the laboratory nozzle.
Radial spray mass distribution was measured using a patternator located in two orthogonal positions in a plane perpendicular to the nozzle centerline a short distance form the nozzle tip. The spray mass distribution was characterized by the radius of gyration of the mass of collected slurry on any side of the nozzle centerline. This calculated distance defined a characteristic spray angle. The laboratory nozzle spray pattern is that of a solid cone with higher spray flux near the spray centerline. The commercial atomizer produces a heavy spray flux in an annular cone around the spray centerline. Results show that the both nozzles, spray mass distribution was influenced by atomizing air to slurry mass flow ratio but not by combustion air swirl. The spray flux produced by the laboratory atomizer becomes less evenly distributed and more concentrated along the centerline of the nozzle as the atomizing air to slurry mass flow ratio is increased, while the opposite effect is evident with the commercial nozzle. The effects of the observed difference in spray characteristics for both nozzles on carbon burnout during combustion tests are also reported in the paper.
Lignite Coal Water Slurry Combustion Characteristics in a Laboratory-Scale Furnace
Rawlins, D.C.; Jones, R.G.; Germane, G.J. and Smoot, L.D.
8th International Symposium on Coal Slurry Fuels Preparation and Utilization, 1986, Orlando, FL. 14 pgs. Funded by Morgantown Energy Technology Center.
The Brigham Young University (BYU) Combustion Laboratory is currently conducting a low-rank coal-water slurry characterization and combustion research program for the US Department of Energy through the Grand Forks, North Dakota Project Office. The lignite slurry used in this study was prepared at the University of North Dakota Energy Research Center (UNDERC) by a hot water drying process. The slurry contains 58% by weight solids and 42% water. No additives have been included to increase slurry stability. Slurry characterization studies, which have been conducted at both BYU and UNDERC, include slurry rheology, particle size distribution and slurry stability.
Combustion tests are being conducted in a vertically oriented, cylindrical combustor, 3.0 m high and 35 cm in interior diameter, with CWM and air injection at the top. Access ports are located along the entire length of the reactor for visual observation of the flame and for insertion of a stainless steel water-quenched sample probe. Solid and gaseous products of combustion are removed form the combustion zone and analyzed for coal burnout and local gaseous compositions. The combustion tests show that a strong, stable flame can be achieved without secondary fuel support. Flame stability appears to be strongly affected by the ratio of the spray nozzle atomizing air to the slurry feed rate. Stoichiometric ratio and secondary air swirl number affect flame stability to a lesser exten. Coal burnout of greater than 99% has been achieved with a reactor residence time estimated to be slightly greater than one second. NO emissions have been measured in the range of 200 to 600 PPM No attempt has been made to control or reduce these emissions.
A Comparison of Combustion Characteristics Between Lignite-Water Slurry and Pulverized Lignite
Rawlins, D.C.; Smoot, L.D. and Germane, G.J.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 27 pgs. Funded by the Morgantown Energy Technology Center.
Experiments of the combustion of hot-water dried lignite slurry and its parent, pulverized coal have been performed in a laboratory-scale combustor. The operating parameter that had the greatest effect on flame location for lignite slurry combustion was the slurry mean droplet diameter. A stable flame could not be maintained with large droplet sizes. The air blast of the slurry-atomizing nozzle caused the mixing of the primary and secondary streams to be much more rapid for slurry combustion than for pulverized coal. Due to this rapid mixing, fuel-rich products of combustion were only observed in trace quantities near the top of the combustion zone during slurry combustion; however, with pulverized coal combustion, significant concentrations persisted throughout the combustor. Secondary air swirl number had the greatest effect on the pulverized lignite flame location. A minimum in nitrogen oxide (NO) concentration was observed during the pulverized coal combustion as swirl was increased. Secondary air swirl, however, had only a negligible effect on coal burnout and NO emissions for slurry combustion. A five-fold increase in the primary air velocity more than doubled NO concentrations at the exit plane. Changing the primary air velocity through the slurry atomizer (by changing the air mass flow rate) did not affect NO emissions during slurry combustion. Changes in the water concentration within the combustion system did not affect combustion performance with pulverized coal. Thus, NO emissions are more strongly controlled by the mixing of the fuel with the secondary air than by flame temperature reduction caused by water added to the combustion system.