Hedman, PO

1997

Comprehensive Model for Lean Premixed Combustion in Industrial Gas Turbines - Part I. Validation

Cannon, S.M.; Brewster, B.S.; Smoot, L.D.; Murray, R. and Hedman, P.O.
Presented at the Spring Meeting of the Western States Section/The Combustion Institute, Sandia National Laboratories, Livermore, California, April 14-15, 1997. Funded by US Department of Energy.

The velocity composition pdf model coupled with a mean flow CFD model was used to describe the turbulent fluid flow, heat transfer, chemistry, and their interactions in a swirling, lean premixed, methane-air combustor for which laser-based measurements of mean velocity and temperature were made. A flame was stabilized in this axi-symmetric, lab-scale, gas-turbine combustor (LSGTC. A reduced, 5-step chemical mechanism, for describing fuel oxidation and NO chemistry, was used in this LSGTC model. NO emissions from thermal, N2)-intermediate, and prompt pathways were described with this 5-step mechanism. The chemistry calculations were performed efficiently with and in-situ look-up table. An axi-symmetric, unstructured grid consisting of 2283 vertices and 4302 triangular elements was used for solving the Eulerian, mean flow equations and the vertices were used to store mean statistics for solving the Lagrangian, fluid particle (~310,000 fluid particles) equations. Predicted velocity and composition statistics were compared to measurements in the LSGTC for lean equivalence ratios of 0.8 and 0.65. The comparisons of predicted mean velocity and temperature were reasonable good throughout the combustor. The location and magnitude of peak axial velocity was well represented by the model at near inlet regions, through the negative mean axial velocity in the internal recirculation zone was over-predicted. The predicted maximum mean temperature and the penetration zone of the cold unburned fluid were in reasonable agreement with the experimental data. Correct trends in CO and NO with equivalence ration were predicted with the model. The in situ tabulation method was used to represent the chemical kinetics in this axi-symmetric combustor without requiring significant CPU time and memory. The model is currently being applied to simulate 3-dimensional, gas-turbine combustor geometries and is described in a companion paper.

Differential Mass and Energy Balances in the Flame Zone from a Practical Fuel Injector in a Technology Combustor

Warren, D.L. and Hedman, P.O.
Journal of Engineering for Gas Turbines and Power, 119:352-61(1997). Funded in part by ACERC.

This paper presents further analysis of experimental results from and Air Force program conducted by researchers at Brigham Young University (BYU), Wright-Patterson Air Force Base (WFAFB), and Pratt and Whitney Aircraft Co. (P&W) (Hedman et al. 1994a, 1995). These earlier investigations of the combustion of propane in a practical burner installed in a technology combustor used: (1) digitized images from video and still film photographs to document observed flame behavior as fuel equivalence ratio was varied; (2) sets of LDA data to quantify the velocity flow fields existing in the burner; (3) CARS measurements of gas temperature to determine the temperature field in the combustion zone, and to evaluate the magnitude of peak temperature; and (4) two-dimensional PLIF images of OH radical concentrations to document the instantaneous location of the flame reaction zones. This study has used the in situ velocity and temperature measurements from the earlier study, suitably interpolated, to determine local mass and energy balances on differential volume elements throughout the flame zone. The differential mass balance was generally within about ±10 percent with some notable exceptions near regions of very high shear and mixing. The local differential energy balance has qualitatively identified the regions of the flame where the major heat release is occurring, and has provided quantitative values on the rate of energy release (up to -400 kJ/m³s). The velocity field data have also been used to determine Lagrangian pathlines through the flame zone. The local velocity and temperature along selected pathlines have allowed temperature timelines to be determined. The temperature generally achieves its peak value, often near the adiabatic flame temperature, within about 10 ms. These temperature timelines, along with the quantitative heat release data, may provide a bases for evaluating kinetic combustion models.

1996

The Use of Two Pyromethane Dyes in a Single Strokes Dye Laser to Make CARS Temperature and Multiple Species (CO, CO2, O2, N2) Concentration Measurements

Haslam, J.K. and Hedman, P.O.
Proceedings at the Fall Meeting of the Western States Section/Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC and Morgantown Energy Technology Center (ATS).

New laser dyes allow improvement in existing coherent ant-Strokes Raman spectroscopy (CARS) instruments. In the past, single Strokes, beam CARS instruments have been used to probe one species for temperature and concentration (e.g. N2). In order to probe multiple species simultaneously (CO, CO2, O2, N2), two Strokes beams are often used in what is known as a dual-Strokes CARS instrument. However. The dual-Strokes beam instruments are relatively inefficient, difficult to align and optics intensive. With new Pyromethene dyes, a single Strokes beam can be used to probe the same species as the dual Strokes with enhanced performance. In this experiment, two new CARS system dyes were compared and evaluated for enhanced multi-species detection. The improved CARS instrument uses a mixture of Pyromethene 597 and Pyromethene 650 for a single Strokes laser beam. These two mixed dyes have sufficient spectral band width and improved intensity to replace the traditional Rhodamine 575/601 dye and Rhodamine 640 dyes of an earlier dual-Strokes CARS instrument. The improved Pyromethene single Strokes CARS system has been used to obtain CARS spectra (CO, CO2, O2, N2) that allowed CARS temperature and species concentration measurements in a swirling, turbulent, premixed natural gas/air burner to be obtained.

A Technique for Determining Instantaneous N2, CO2, O2, CO, and H2O Species Concentrations Using Multiplex CARS in Premixed Gaseous Flames

Dawson, R.W. and Hedman, P.O.
Proceedings at the Fall Meeting of the Western States Section/ Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC and Morgantown Energy Technology Center (ATS).

An approach for analyzing instantaneous CO, O2, CO2, and H2O species concentrations using multiplex coherent anti-Strokes Raman spectroscopy (CARS) in premixed combustion systems in introduced and demonstrated. A dual-dye, single broadband Strakes dye laser was used to produce CARS spectral signals from N2, CO, O2, and CO2. A computer code obtained Sandia National Laboratories was used to determine the temperature as well as the value Chinr/Xi where Xi is the specie mole fraction and Chinr is the signal contribution form non-resonant gases. Temperatures as well as the non-resonant signal contribution (Chinr) for each laser shot were obtained from the nitrogen spectra. Initial estimate of Chinr were made by assuming that nitrogen concentrations were known and remained constant throughout premixed combustion. Equilibrium predictions, based upon the instantaneous nitrogen temperature, were used in conjunction with the estimated value of Chinr as initial estimates needed to resolve the instantaneous CO, O2, and CO2 spectra into concentration measurements. This technique reduced the computational demand of determining the best fit between theoretical and experimental spectra.

The H2O mole fraction was determined from an oxygen elemental mass balance and the assumption that any oxygen not accounted for in the measured concentrations of CO, O2, and CO2 was in H2O. The partially reacted natural gas will bee in the form of various hydrocarbon fragments that are difficult to quantify. The hydrogen that is not reacted to water is assumed to be unaccounted for by the measurements and is lumped into a H* mole fraction, and the carbon that is not measured as CO2 or CO is unaccounted for carbon, which is lumped into a C* mole fraction. The magnitude of H* and C* gives an indication of the extent of the combustion reaction and the ratio H* to C* gives an indication of the effective composition of the partially reacted hydrocarbon gases (CXHY). The results show that this technique is effective in determining concentrations of the major combustion species in a premixed gaseous-fueled flame. The paper describes the detail of the technique and presents example results for a swirling, turbulent, premixed natural gas/air flame.

Simultaneous Measurements of the Temperature and Species Concentration of Premixed Natural Gas Flames Using a Dual Dye, Single Strokes CARS System

Flores, D.V. and Hedman, P.O.
Proceedings at the Fall Meeting of the Western States Section/Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC and Morgantown Energy Technology Center (ATS).

The objective of this study was to obtain temperature and species (CO, CO2, O2, N2 and H2O) concentration measurements using coherent anti-Stokes Raman spectroscopy (CARS) from and atmospheric pressure, swirling, turbulent, premixed natural gas/air flame in a model combustor that simulates the characteristics of a utility gas turbine engine. The Brigham Young University (BYU)/ACERC laboratory-scale, gas-turbine combustor (LSGTC) simulates many of the key combustion characteristics of commercial gas turbines, while providing optical access for the CARS laser beams. In situ data (temperature and species concentrations) have been collected as a function of radial and axial position at several locations over the combustion zone.

This paper demonstrates the applicability of two new developments made at the BYU/ACERC optics laboratory: (1) a new CARS systems that uses a dual dye, single Stokes laser with sufficient spectral band-width to simultaneously excite the Strokes frequencies of N2, CO, O2, CO2 and (2) a newly proposed method that allows the calculation of additional species concentrations from reduced CARS data from local elemental mass balances. The species concentrations calculated include H2O, and unaccounted-for hydrogen (H*) and carbon (C*).

Iso-coutour maps of temperature and species concentrations from instantaneous CARS measurements on premixed natural gas flames are presented. The combustor was operated at a medium swirl number of 0.74 and a fuel equivalence ratio of 0.65. Early results indicate that the measurements of species concentrations are self-consistent. Nevertheless CO measurements are above expected levels based on both kinetic and equilibrium predictions. Investigation on the source of this discrepancy is underway. In addition, estimated concentrations of H2O and unaccounted-for carbon (C*) and hydrogen (H*), deduced from oxygen, carbon, and hydrogen mass balances (from known premixed composition) are presented. Observations on flame behavior from these measurements are made. These data provide considerable insight into the flame behavior as well as a database for model evaluation.

Development of a Turbulent Toroidal Flow Stabilized Premixed Natural Gas/Air Burner

Kinghorn, K.B. and Hedman, P.O.
Proceedings at the Fall Meeting of the Western States Section/Combustion Institute, The University of Southern California, Los Angeles, California, October 28-29, 1996. Funded by ACERC and Morgantown Energy Technology Center (ATS).

A new burner design that may have application in gas turbine engines was designed and fabricated and preliminary operational characteristics were determined in a laboratory-scale gas turbine combustor. The adjustable burner uses a ring-shaped cylindrical cavity wherein the combustion zone is stabilized by a toroidal body of hot rotating gases. With this design, the toroidal flow of the burner maintained a stable flame over a range of fuel equivalence ratios (Phi = 0.50 to 1.2). Quantitative experiments were conducted to evaluate operation over a range of fuel equivalence ratios (Phi =0.6, 0.7, 0.8, 0.9,1.0, 1.1, and 1.2) and inlet velocities (7.5, 10, 30, 50, 70, 90, and 100 m/sec). The flame appeared to be more stable at lower inlet velocities. The magnitudes of the inlet velocity controls the rotational speed of the toroidal flow, which seems to affect the flame stability.

In order to better understand the mechanisms involved in the toroidal flow stabilization, a two-dimensional slice of the full-scale burner was designed and fabricated. This 2-D section of the full burner allows for optical access and laser diagnostics. The design and testing of both burners is presented and the operational characteristics are discussed. Future research possibilities are also presented.

1994

Observations of Flame Behavior from a Practical Fuel Injector Using Gaseous Fuel in a Technolgoy Combustor

Hedman, P.O.; Sturgess, G.J.; Warren, D.L.; Goss, L.P. and Shouse, D.T.
Transactions of the ASME, 1994 (in press). (Also presented at the ASME International Gas Turbine and Aeroengine Congress and Exposition, The Hague, Netherlands, June 1994. Funded by ACERC, Wright Patterson Air Force Base and Air Force Office of Scientific Research.

This paper presents results from an Air Force program being conducted by researchers at Brigham Young University (BYU), Wright-Patterson Air Force Base (WPAFB), and Pratt and Whitney Aircraft Co. (P&W). This study is part of a comprehensive effort being supported by the Aero Propulsion and Power Laboratory at Wright-Patterson Air Force Base, and Pratt and Whitney, Inc. in which simple and complex diffusion flames are being studied to better understand the fundamentals of gas turbine combustion near lean blowout. The program's long-term goal is to improve the design methodology of gas turbine combustors.

This paper focuses on four areas of investigation: 1) digitized images from still film photographs to document the observed flame structures as fuel equivalence ratio was varied, 2) sets of LDA data to quantify the velocity flow fields existing in the burner, 3) CARS measurements of gas temperature to determine the temperature field in the combustion zone, and to evaluate the magnitude of peak temperature, and 4) two-dimensional images of OH radical concentrations using PLIF to document the instantaneous location of the flame reaction zones.

Aspects of Flame Stability in a Research Dump Combustor

Sturgess, G.J.; Hedman, P.O.; Sloan, D.G. and Shouse, D.T.
Transactions of the ASME, 1994 (in press). (Also presented at the ASME International Gas Turbine and Aeroengine Congress and Exposition, The Hague, Netherlands, June 1994. Funded by ACERC, Wright Patterson Air Force Base and Air Force Office of Scientific Research.

The lean blowout process is studied in a simplified, nominally diffusion flame, research combustor that incorporates the essential features of the combustor primary zone for an aircraft gas turbine engine. The research combustor is provided with extensive optical access. To investigate the blowout, a variety of diagnostic techniques are employed, including direct flame observation, laser-Doppler anemometry, spontaneous OH-imaging, thin-filament pyrometry, laser-induced fluorescence OH imaging, coherent anti-Stokes Raman spectroscopy, and computational fluid dynamics. Lean blowouts in the research combustor are related to well-stirred reactor blowout. A blowout sequence is found to be initiated by the loss of a key flame structure in the form of an attached pilot flame. The behavior of this attached flame is investigated. It is concluded that a major contribution to the existence of the attached flame is near-field, non-stationary radial transport of reactants directly into the recirculation zone, rather than by mean flow recirculation of hot products. "Lift" of the attached flame is the reason that lean blowout in the research combustor is related to well-stirred reactor blowout since it allows at least partial premixing of reactants to take place.

Turbulent Velocity and Temperature Measurements from a Gas-Fueled Technology Combustor with a Practical Fuel Injector

Hedman, P.O. and Warren, D.L.
Combustion and Flame, 1994 (in press). (Presented at the 25th Symposium [International] on Combustion, University of California at Irvine, Irvine, California. Funded by ACERC, Wright Patterson Air Force Base and Air Force Office of Scientific Research.

Combustion characteristics of a propane-fueled, practical injector operating in a burner that closely reproduce the flow patterns of a gas turbine combustor have been investigated. The practical injector converges co-swirling airsheets on either side of a coannular fuel sheet into the central air passage. Instantaneous planar laser induced fluorescence (PLIF) images of OH radical, laser Doppler anemometer (LDA) measurements of mean and rms velocity, and coherent anti-Stokes Raman spectroscopic (CARS) measurements of mean and rms temperatures in the same burner at the same operating conditions have provided improved understanding of the complicated processes in a gas turbine combustor. The PLIF images of the OH radical have confirmed the vortex characteristics of the swirling flames and the highly variable nature of the flame shape as ø must lie between the lean and rich flammability limits for a flame to be locally present. Three recirculation zones were identified from LDA measurements. The highest axial velocity region is about 75 mm downstream for the fuel lean case, but is near the injector for the fuel rich case. The highest tangential velocities are located near the injector for both lean and rich cases. The effects of the injector on velocity were dissipated by one combustor diameter downstream. Large rms velocities occurred in areas where significant velocity gradients exist. The high temperatures changed location as the fuel equivilence ratio was varied from fuel lean (over the injector) to fuel rich (near the outer recirculation zone). The high temperature regions are consistent with the PLIF images of OH radical, and become relative uniform by about one combustor diameter downstream. Measured temperatures never exceeded the peak theoretical adiabatic flame temperature.

1992

Coherent Anti-Stokes Raman Spectroscopy (CARS) in Pulverized Coal Flames

Hancock, R.D.; Boyack, K.W. and Hedman, P.O.
Chapter 15, Advances in Coal Spectroscopy, (H.L.C. Meuzelaar, ed.), Plenum Publishing Corp., New York, 1992. Funded by Pittsburgh Energy Technology Center/Consortium for Fossil Fuel Liquefaction, US Department of Energy and ACERC.

Coherent anti-Stokes Raman spectroscopy (CARS) is a diagnostic technique involving the use of high powered lasers to determine the temperature and concentration of the various major species found in combustion processes. This laser diagnostic technique allows in situ temperature and species concentration measurements to be obtained without disturbing the flame, as would most traditional thermocouples and sampling devices. Furthermore, there is no temperature limit associated with CARS because it is purely an optical technique.

CARS was first introduced by Taran and his co-workers at ONERA in France and was quickly recognized by other researchers throughout the world as a valuable diagnostic technique. Soon, numerous theoretical discussions, innovations, and practical applications of the CARS technique were introduced to the scientific community. CARS research has been implemented by various laboratories in the United States, Canada, England, France, Germany, Japan, and the Soviet Union.

Initially, CARS was applied to clean gas flames. However, as the instrument evolved, its diagnostic strengths were used to probe increasingly complex combustion environments. One such complex environment is that created by the introduction of particles into gas flames. Several researchers have studied such particle-laden flames and found them more difficult to probe, with the resulting CARS spectra more complex to analyze. These researchers have demonstrated that CARS measurements are possible in particle-laden flames.

Particle-laden flames are more difficult to probe because the particles attenuate the laser beams and can induce breakdown. Attenuation of the laser beams results in a loss of beam and signal strength. Breakdown alters the shape and intensity of the experimental spectra. The focus of this study was to develop methods by which consistent CARS measurements could be made on a regular basis in laboratory-scale particle-laden flames with coal loadings similar to those encountered in industrial burners.

This study extended the existing CARS instrument capability at Brigham Young University to a new laminar flame reactor that was designed to study flame speeds in pulverized coal flames. The facility modifications required the CARS laser beams to be transmitted over a 23-meter path length from the optical table to the reactor. The CARS signal was returned from the test chamber to the spectrometer with a fiber optic cable. The CARS signals were analyzed employing a modified version of the fitting code FTCARS from Sandia National Laboratories, using temperature and concentration libraries calculated with the CARS spectra code developed at Mississippi State University.

The Sensitivity of Entrained-Flow Coal Gasification Diffusion Burners to Changes in Geometry

Sowa, W.A.; Hedman, P.O.; Smoot, L.D. and Richards, D.O.
Fuel, 71(5):593-604, 1992. Funded by US Department of Energy, Morgantown Energy Technology Center.

Three axisymmetric diffusion flame burners were designed and installed on a laboratory-scale, downfired, entrained-flow, coal gasifier operated at pressures up to 560 kPa. Each burner was studied by varying reactor pressure, oxygen/coal ratio and steam/coal ratio. The gasifier performance was assessed by collecting space-resolved gas and char samples in the reaction chamber and analyzing them for carbon conversion, gas composition (CO, CO2, H2, H20 and CH4) and cold gas efficiency. Burner geometry affected carbon conversion, gas composition and cold gas efficiency. Each burner had unique flame structural characteristics that resulted in burner-unique trends with reactor pressure, oxygen/coal ratio and steam/coal ratio. At 560 kPa, diffusion flame burner performance approached premixed flame performance. The results from this study suggest that it might be possible to design a diffusion burner that outperforms a fuel-oxidant premixing burner for some operating conditions due to its flame structure and its characteristic energy transfer to the chamber. Performance characteristics of diffusion burners correlated with system pressure, oxygen/coal ratio or steam/coal ratio cannot be generalized into trends representative of all diffusion flame burners.

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.

Investigation of the Combustion Characteristics of a Swirled Injector in a Confined Coannular System with a Sudden Expansion

Warren, D.; Pyper, D.K.; Blackham, S.; Christensen, J.; Hedman, P.O.; Goss, L.P.; Trump, D.; Sarka, B.; Hsu, K.Y. and Roquemore, W.M.
Fall Meeting of the Western States Section/The Combustion Institute, Berkeley, CA, October 1992. Funded by Wright-Patterson Air Force Base and Air Force Office of Scientific Research.

This paper presents preliminary results of an Air Force Office of Scientific Research (AFOSR) program being conducted at Brigham Young University (BYU), Provo, Utah and at Wright-Patterson Air Force Base (WPAFB) under Summer Faculty and Research Initiation Programs. This study is part of an extensive research effort being carried out by the Fuels Combustion Group of the Aero Propulsion and Power Laboratory at Wright Patterson Air Force Base (APPL, WPAFB), Dayton, Ohio, in which simple and complex diffusion flames are being studied to better understand the fundamentals of gas turbine combustion. The program's long-term goal is to improve the design methodology of gas turbine combustors.

The work at BYU is being accomplished by the systematic study of a geometrically simple burner "designed and developed to specifically reproduce recirculation patterns and lean blow out (LBO) processes that occur in a real gas turbine combustor" (Sturgess, et al., 1990). There are two configurations used in the burner. The Task 100 burner uses a central fuel tube surrounded by a concentric air jet with a step expansion at the plane of discharge. The Task 150 burner has replaced the central fuel and air tubes with a double swirler injector from an actual Pratt-Whitney jet engine. Both configurations have been designed to be nearly axisymmetric and incorporate quartz windows to allow laser diagnostics. The burner is currently fueled by propane.

This paper contains a brief summary of work done at BYU and at Wright-Patterson Air Force base during the AFOSR summer faculty research programs. Intriguing flame structures have been visually characterized and captured in both still and video images with both the Task 100 and Task 150 configurations. Additional images of the flame and flow structures have been taken with laser sheet lighting, including Mie scattering and OH- florescence. These two-dimensional laser images have frozen structures missed with the visual observations due to the integrating nature of the eye and camera. LDA velocity maps have been collected over a variety of conditions, ranging from the relatively simple flow of the Task 150. This information not only yields velocity and turbulence data but will be used to obtain streamline functions as well. Both isothermal flow and combusting hot flow data have been collected. Limited CARS temperature data is compared in the paper LDA velocity maps and LIF image of OH-. Additional CARS temperature data are currently being collected at the test conditions of the LDA measurements and OH- images.

1991

Coherent Anti-Stokes Raman Spectroscopy (CARS) Measurements in Coal-Seeded Flames

Hancock, R.D.; Hedman, P.O. and Kramer, S.K.
Combustion and Flame, 87:77-88, 1991. 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. CARS has been successfully applied to clean gas flames, but much less attention has been given to particle-laden flames like those encountered in industrial coal burners. Typically, experimental CARS spectra are obtained from a flame and then compared with theoretical CARS spectra to determine temperature and species concentration information. This information is more difficult to acquire in coal flames due to background and nonresonant interferences. These interferences alter the shape and intensity of the CARS signal, thus making analysis with unmodified version of standard CARS fitting codes impractical. Nitrogen temperature measurements were obtained in heavily coal-seeded natural gas/air flames. Two different coals and several coal feed rates and stoichiometries were investigated in order to determine possible limits associated with making CARS measurements in coal flames. Carbon monoxide signals were observed in some of the fuel-rich coal-seed flames but the signals were weak and of poor quality, therefore, quantitative results are not reported. Temperature measurements were obtained with nonresonant background levels caused by particle-induced breakdown as high as 100% of the peak N2 resonant signal. CARS N2 temperatures generally agreed with equilibrium code calculations.

Flame Stability and Lean Blowout

Sturgess, G.J.; Sloan, D.G.; Roquemore, W.M.; Reddy, V.K.; Schouse, D.; Lesmerises, A.L.; Ballal, D.R.; Heneghan, S.P.; Vangsness, M.D. and Hedman, P.O.
10th International Society of Air Breathing Engines, Nottingham, England, September 1991. Funded by US Air Force.

A progress report is presented on a comprehensive research program aimed at improving the design and analysis capabilities for flame stability and lean blowout in the combustors of aircraft gas turbine engines. The motivation and aims of the program are reviewed, and the unusual approach adopted to address the research issues is outlined. The supporting experimental program and the test vehicles involved are described, together with some major results obtained to date. The modeling techniques that are being explored are summarized. Their potential and limitations are highlighted. Although much work remains yet to be done, the progress made thus far gives rise to reasonable optimism for achieving the program objectives.

Experimental and Theoretical Studies in a Gas-Fueled Research Combustor

Roquemore, W.M.; Reddy, V.K.; Hedman, P.O.; Post, M.E.; Chen, T.H.; Goss, L.P.; Trump, D.; Vilimpoc, V. and Sturgess, G.J.
AIAA 29th Aerospace Sciences Meeting, Reno, NV, January 1991. Funded by US Air Force.

This paper reports the results of an investigation to determine the flow and flame characteristics of a burner which has been carefully designed to "specifically reproduce recirculation patterns and lean-blow-out (LBO) processes that occur in a real gas turbine combustor." When operated in a fuel rich mode, the flame is very stable and is anchored in the jet shear layer by a pilot flame attached to the step, near the outer edge of the air supply tube. As the equilivalence ratio is reduced, the flame becomes less stable, and eventually reaches a point where the pilot flame becomes detached (lifts) from the base region, and the entire flame structure becomes stabilized downstream. Thus, there are two distinct operating modes for the combustor: a fully attached flame and a lifted flame. As the fuel equivalence ratio is further reduced, the flame becomes progressively less stable in its lifted condition, and eventually blows out. Photographs of the flame clearly illustrate the attached and lifted flame operational regimes of the combustor. However, visual observation and conventional photographic techniques are unable to quantify the precise details of the flame transition from an attached to a lifted condition. A Computational Fluid Dynamics (CFD) model with one step chemistry was used to investigate the time-averaged features of the reacting and non-reacting flow fields. The difficulties of predicting the characteristics of the attached flame with a time averaged CFD type model are discussed. Measurements, using OH emissions and gray body radiation from 14 µm diameter filaments located near the base of the flame, clearly indicate the dynamic or intermittent nature of both the attached and lifted flames. It is theorized that unburned hydrocarbon combustion products are transported into the recirculation zone by the intermittent process; and it is these products that provide the fuel needed for the flame to attach to the outer edge of the step.

1990

Furnace Design Using Comprehensive Combustion Models

Smith, P.J.; Sowa, W.A. and Hedman, P.O.
Combustion and Flame, 79 (2), 111-121, 1990. Funded by Brigham Young Unviersity.

A new design methodology is presented that allows for the use of comprehensive coal combustion codes in design applications and provides a priori information on the cost of the optimization. A statistical response surface methodology is used to determine appropriate sample points from the design space at which the computation for the comprehensive code is performed. Statistical regression analysis is used to provide interpolation functions for the optimization process. The optimum design point is then checked with a final comprehensive code calculation. The technique is demonstrated with simple examples for the design of two injectors for an entrained coal gasifier and a burner for a pulverized coal combustor. The three designs demonstrate the method as well as showing significantly different optima for different configurations. The importance of specifying operating conditions independently for different injectors or burners is demonstrated.

Reduction of Fuel-NO by Increased Operating Pressure in a Laboratory-Scale Coal Gasifier

Nichols, K.M.; Hedman, P.O. and Blackham, A.U.
Fuel, 69, 1339-1344, 1990. Funded by US Department of Energy and Morgantown Energy Technology Center.

Measurements of NO during laboratory-scale gasification of a Utah bituminous coal verified that small increases in pressure (from 1 to 2 atm) at constant residence time resulted in dramatic decreases in effluent NO levels. Tests were conducted at 3 target levels of pressure (1, 2 and 4 atm) and 2 target levels of residence time (450 and 900 ms). Oxygen-to-coal ratio for all tests was 0.90 (stoichiometric ration SR=0.45). The dominant factor in causing lower effluent NO levels was the increased kinetic rate of NO decay. Increased residence time in the fuel-rich gasifier contributed to lower effluent NO levels, but was of minor importance when compared to the effect of pressure on the decay rate. Concentrations of N2 appeared to be slightly increased and concentrations of total fuel nitrogen (TFN) decreased as pressure was increased. Also, concentrations of N2 increased and concentrations TFN decreased as residence time was increased at 1 atm pressure. For all tests, nitrogen conversion exceeded carbon conversion by about 10%. Neither nitrogen conversion nor carbon conversion was found to increase with increasing pressure. Both increased slightly (4-5%) with increasing residence time, evidence that most of the coal nitrogen and carbon was released during devolatilization.

Dual-Stokes CARS System for Simultaneous Measurement of Temperature and Multiple Species in Turbulent Flames

Boyack, K.W. and Hedman, P.O.
Twenty-third Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, 1990. Funded by ACERC.

A dual-Stokes coherent anti-Stokes Raman scattering (CARS) instrument has been used to make simultaneous time- and space-resolved measurements of temperature and the mass fractions of N2, CO, O2, and CO2. Calculation of the mixture fraction, a conserved scalar, is possible for each data point, making the technique useful in turbulent combustion environments. The viability of this instrumental approach has been demonstrated by calibrations in laminar CO/N2 flat flames of many different stoichiometries. Maximum single-shot rms values due to instrument fluctuations are attained in near stoichiometric mixtures and are ±45 K for temperature, ±0.042 for YN2 and YCO2, ±0.015 for YO2 and YCO, and ±0.036 for mixture fraction.

Measurements have been made using this instrument in turbulent nonpremixed jet flames of CO/N2 with small amounts of H2. These measurements demonstrated that for turbulent systems, limitations are imposed on the CARS technique due to insufficient dynamic range and image persistence problems with the intensified photodiode array (IPDA) detector. These limitations are minimized with proper experimental parameters and data correction methods.

1989

Furnace Design Using Comprehensive Combustion Models

Smith, P.J.; Sowa, W.A. and Hedman, P.O.
Accepted for publication in Combustion and Flame, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates) and Brigham Young University.

A new design methodology is presented which allows for the use of comprehensive coal combustion codes in design applications and provides a priori information on the cost of the optimization. A statistical response surface methodology is used to determine appropriate sample points from the design space at which the computation for the comprehensive code are performed. Statistical regression analysis is used to provide interpolating functions for the optimization process. The optimum design point is then checked with a final comprehensive code calculation. The technique is demonstrated with simple examples for design of two injectors for an entrained coal gasifier and of a burner for a pulverized coal combustor. The three designs demonstrate the method as well as showing significantly different optima for different configurations. The importance of specifying operating conditions independently for different injectors or burners is demonstrated.

An Analysis of Coal Particle Temperature Measurements with Two-Color Optical Pyrometers

LaFollette, R.M.; Hedman, P.O. and Smith, P.J.
Combust. Sci. and Tech., 66, 93-105, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).

Two-color optical pyrometers have been used to measure the temperature of reacting pulverized-coal particles. An analysis of such measurements was performed to determine the effect of several possible conditions on the measured temperature. The conditions investigated were the use of a single photo-multiplier to alternately measure the radiant emission at the two selected wavelengths, the presence of soot, light extinction, the choice of wavelengths used to compute the two-color temperature, and non-uniform particle clouds. A computer model of a one-dimensional coal particle cloud was written for this analysis. Results of calculations showed that artificially high temperatures can result if a pyrometer with a single photo detector is used to measure temperatures in a rapidly fluctuating flame. Emission by soot in the coal particle cloud caused unrealistically high temperature measurements. Light absorption by soot lowered the two-color temperature, but not enough to compensate for the rise in observed temperature caused by soot emission. When the wavelengths used are in the visible spectrum, the hotter particles are weighted much more heavily than when the wavelengths are in the infrared region. The use of Wein's Law, a valid approximation to Planck's Law in the visible spectrum, causes substantial error for longer wavelengths. Finally, the two-color temperature of a non-isothermal cloud was weighted most heavily by the hotter particles, depending upon the wavelengths used for the measurement. From this analysis important questions have been raised as to the validity of such measurements under transient conditions and during devolatilization.

Effects of Pressure and Coal Rank on Carbon Conversion in an Entrained-Coal Gasifier

Cope, R.F.; Smoot, L.D. and Hedman, P.O.
Fuel, 68, 806-808, 1989. Funded by US Department of Energy (Morgantown Energy Technology Center).

Elevated-pressure gasification tests were completed with North Dakota lignite, Wyoming subbituminous and Illinois No. 6 bituminous coals. Carbon conversion values obtained in theses tests were compared with those obtained with the same three coals at atmospheric pressure. Increased pressure produced greater increases in carbon conversion as coal rank decreased.

Coherent Anti-Stokes Raman Spectroscopy (CARS) Temperature and Species Concentration Measurements in Coal-Seeded Flames

Hancock, R.D.; Hedman, P.O. and Kramer, S.K.
AIChE Annual Meeting, San Francisco, California, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).

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. CARS has been applied to clean gas flames with great success, but very little research has been conducted in particle-laden flames like those encountered in industrial coal burners. Typically, experimental CARS spectra are obtained from a flame and then compared to theoretical CARS spectra to determine temperature and species concentration information. This information is more difficult to acquire in coal 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.

CARS temperature and CO concentration measurements were obtained in heavily coal-seeded natural gas/air flames. Two different coals and several coal feed rates and stoichiometries were investigated in order to determine possible limits associated with making CARS measurements in coal flames. Temperature measurements were obtained with nonresonant background levels caused by particle-induced breakdown as high as 100% of the peak N2 resonant signal. CO concentration measurements deduced from the CO CARS spectra were less precise due to the difficulties of interpreting the CO CARS spectra in the presence of the enhanced background. Results generally agreed with thermochemical equilibrium combustion code calculations.

Measurements of Instantaneous Flame Properties in Turbulent Non-Premixed Jet Flames of CO/N2 Using Coherent Anti-Stokes Raman Spectroscopy (CARS)

Boyack, K.W. and Hedman, P.O.
Western States Section, The Combustion Institute, Livermore, California, 1989. (Also presented as a poster at the 1989 Gordon Conference on the Physics and Chemistry of Laser Diagnostics in Combustion, Plymouth, New Hampshire). Funded by ACERC (National Science Foundation and Associates and Affiliates).

The Coherent anti-Stokes Raman Scattering (CARS) technique has been used to make simultaneous time- and space-resolved measurements of temperature and the mass fractions of N2, CO, O2, and CO2. Calculation of the mixture fraction, x, conserved scalar, is possible for each data point, making the technique useful in turbulent combustion environments. The viability of this instrumental approach was demonstrated by calibrations in CO/N2 flat flames of many different stoichiometries. Maximum single-shot rms of fluctuations are attained in near stoichiometric mixtures and are estimated to be ±45 K for temperature, ±0.042 for YN2 and YCO2, ±0.015 for YO2 and YCO, and ±0.036 for mixture fraction.

Measurements have been made using this instrument in turbulent nonpremixed jet flames of ~70% CO / 30% N2 with various amounts of H2 ranging from zero to 2.8%. Local extinction has been seen to occur as the H2 content is reduced, until the entire flame is extinguished. This extinction is thought to be due to insufficient radical concentrations, thus inhibiting chain-branching steps in the wet CO oxidation mechanism.

Reduction of Fuel NO by Increased Operating Pressure in a Laboratory-Scale Coal Gasifier

Nichols, K.M.; Hedman, P.O. and Blackham, A.U.
1989 Joint Environmental Protection Agency/Electric Power Research Institute Symposium on Stationary Combustion NOx Control, San Francisco, California, 1989. Funded by ACERC (National Science Foundation and Associates and Affiliates).

Measurements of NO during laboratory-scale gasification of a Utah bituminous coal verified that small increases in pressure (from 1 to 2 atm) at constant residence time resulted in dramatic decreases in effluent NO levels. Tests were conducted at 3 target levels of pressure (1, 2, and 4 atm) and 2 target levels of residence time (450 and 900 ms). Oxygen-to-coal ratio for all tests was 0.90 (SR = 0.45). The dominant factor in causing lower effluent NO levels was the increased kinetic rate of NO decay. Increased residence time in the fuel-rich gasifier contributed to lower effluent NO levels, but was of minor importance when compared to the effect of pressure on the decay rate. Concentrations of N2 appeared to be slightly increased and concentrations of TFN decreased as pressure was increased. Neither TFN or N2 concentrations were affected by increasing residence time. For all tests, nitrogen conversion exceeded carbon conversion by about 10%. Neither nitrogen conversion nor carbon conversion was found to increase with increasing pressure. Both increased slightly (4-5%) with increasing residence time, evidence that most of the coal nitrogen and carbon was released during devolatilization.

1988-1986

Sulfur Pollutant Formation During Coal Combustion

Zaugg, S.D.; Blackham, A.U.; Hedman, P.O. and Smoot, L.D.
Submitted to Fuel, 1988. Funded by Electric Power Research Institute.

A laboratory-scale pulverized coal combustor was used to determine the effects of secondary air swirl, stoichiometric ratio (O2/fuel), and coal type on the formation and reaction of sulfur pollutants (SO2, H2S, COs and CS2). Detailed local measurements within the reactor were obtained by analyzing solid-liquid-gas samples collected with a water-quenched probe. Increasing the stoichiometric ratio increased sulfur conversion and SO2 levels, and decreased H2S, COs, and CS2 levels. Swirl of secondary combustion air had a pronounced effect on the distribution of sulfur species formed at an O2-coal stoichiometric ratio of 0.87, but had very little effect at stoichiometric ratios of 0.57 and 1.17. Combustion of a bituminous coal produced more SO2 and less H2S, COs, and CS2 compared to a subbituminous coal.

Measurement and Prediction of Entrained-Flow Gasification Processes

Brown, B.W.; Smoot, L.D.; Smith, P.J. and Hedman, P.O.
AIChE Journal, 34, 3, 435-446, 1988. 12 pgs. Funding source by Morgantown Energy Technology Center.

A detailed mathematical model is used to predict local and effluent properties within an axisymmetric, entrained-flow gasifier. Laboratory experiments were conducted to provide local properties for four coal types from a gasifier operating at near-atmospheric pressure. Effects of selected model parameters and test variables were examined and compared with measurements in most cases. The comparison of predictions and measurements provides the first evaluation of capabilities and limitations of a comprehensive model for entrained-flow gasifiers.

The Impact of Diffusion Flame Injectors on Entrained Coal Gasification

Sowa, W.A.; Hedman, P.O. and Smoot, L.D.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. Funded by Morgantown Energy Technology Center.

The impact of diffusion flame burner geometry on entrained flow coal gasification was studied. Three diffusion flame burners were designed and installed on a laboratory-scale, downfired, entrained-flow, coal gasifier operated at pressures up to 560 kPa. Each burner was studied by varying reactor pressure, oxygen/coal ratio and steam/coal ratio. Gasifier performance was assessed by collecting space resolved gas and char samples in the reaction chamber and analyzing them for carbon conversion, gas compositions (CO, CO2, H2, H2O, and CH4), and cold gas efficiency. Burner geometry was found to significantly affect carbon conversion, gas compositions, and cold gas efficiency. Each burner had unique flame structure characteristics that resulted in burner-unique trends with reactor pressure, oxygen/coal ratio and steam/coal ratio.

Effective Sorbent Mixing in a Simulated Entrained-Flow Reactor: A Cold Flow Study

Braithwaite, D.J. and Hedman, P.O.
AIChE Annual National Meeting, Washington, DC, 1988. Funded by ACERC (National Science Foundation and Associates and Affiliates).

The injection of sorbent particles into an entrained-flow coal reactor was simulated by the injection of a jet normal to a fully developed airflow. Effects investigated were the free stream Reynolds number, jet size and velocity, and number of jets. Test techniques included smoke injection for flow visualization, tracer gas extraction, and laser-Doppler velocity measurements. The results showed that the trajectory of a jet in cross flow is dependent on the jet to main flow momentum ratio, as well as the size of the jet. Buoyancy played an important role in jet behavior at low free stream Reynolds numbers. Greater turbulence intensity and enhanced mixing occurred when the jet momentum was sufficient to cause the jet to impinge on the opposing wall or another jet.

The Sensitivity of Entrained-Flow Coal Gasification Diffusion Burners to Changes in Geometry

Sowa, W.A.; Hedman, P.O. and Smoot, L.D.
Western States Conference, 1987. 25 pgs. Funded by Morgantown Energy Technology Center.

The impact of diffusion flame burner geometry on entrained flow coal gasification was studied. Three diffusion flame burners were designed and installed on a laboratory-scale, downfield, entrained-flow, coal gasifier operated at pressures up to 560 kPa. Each burner was studied by varying reactor pressure, oxygen/coal ratio and steam/coal ratio. Gasifier performance was assessed by collecting space resolved gas and char samples in the reaction chamber and analyzing them for carbon conversion, gas compositions (CO, CO2, H2, H2O, and CH4), and cold gas efficiency. Burner geometry was found to significantly affect carbon conversion, gas compositions, and cold gas efficiency. Each burner had unique flame structure characteristics which resulted in burner-unique trends with reactor pressure, oxygen/coal ratio and steam/coal ratio.

Effects of Flame Type and Pressure on Entrained Coal Gasification

Azuhata, S.; Hedman, P.O.; Smoot, L.D. and Sowa, W.A.
Fuel, 65, 1511-1515, 1986. 5 pgs. Funded by Morgantown Energy Technology Center.

An experimental study of pulverized coal gasification was performed to evaluate the effects of flame type and gasifier pressure. O2/coal ratio (0.53-1.09 kg/kg), coal feed rate (22.9-34.5 kg/h), and pressure (100, 500 and 1050 K Pa) were varied for premixed and diffusion flames in the gasifier. Premixing of coal and oxygen markedly increased carbon conversion, compared with that for diffusion flames at constant pressure. Above an O2/coal ratio of 0.8, carbon conversion increased with increasing pressure for diffusion flames, but no such increase was observed for premixed flames. At higher pressures in premixed flames, all reactions were completed near the burner with little change in gas concentrations elsewhere in the gasifier.

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.

Effect of Coal Type of Entrained Gasification

Brown, B.W.; Smoot, L.D. and Hedman, P.O.
Fuel, 65, 673-678, 1986. 6 pgs. Funded by Morgantown Energy Technology Center.

The effect of coal type for four coals of varying rank was studied in an entrained flow gasifier at atmospheric pressure. The reactor was modified to increase residence time and gas temperature and to provide for direct measurement of the exit gas flow rate. Space-resolved samples were collected from within the gasifier with a water-quenched probe. Correlation of results shows that the most important factors on carbon conversion are O2/coal ratio, coal particle size, coal heating value, missing of reactant feed streams, and coal char reactivity. Premixing of stream with coal and oxygen produced higher levels of hydrogen, but a lower CO/CO2 ratio. Elimination of stream increased the reaction temperature and raised the carbon conversion.

Carbon Conversion in an Atmospheric-Pressure Entrained Coal Gasifier

Azuhata, S.; Hedman, P.O. and Smoot, L.D.
Fuel, 65, 212-217, 1986. 6 pgs. Funded by Morgantown Energy Technology Center.

Entrained gasification tests with a Utah high-volatile bituminous coal were performed at atmospheric pressure to assess the influence of particle size, coal feed rate, steam-coal ratio and oxygen-coal ratio. Independent argon-carbon balance and ash balance methods were used to evaluate carbon conversion, with good agreement observed between the methods. A higher O2-coal ratio and finer particles increased the carbon conversion. Carbon conversion and hydrogen formation showed little dependence on the amount of steam injected in the secondary stream, indicating minimal steam-coal reaction. When the coal feed rate was varied from 23 to 27 kg/h, a small increase in carbon conversion was observed with no significant change in the gas composition.

LDV Measurements in Simulated Entrained Gasifier Flows

Lindsay, J.D.; Hedman, P.O. and Smith, P.J.
Submitted to AlChE Journal, 1988. 15 pgs. Funded by Morgantown Energy Technology Center.

Entrained-flow gasification of pulverized-coal has the potential to become a competitive source of energy. One near-commercial application of entrained-flow coal gasification that has been receiving considerable attention is the use of an entrained-flow gasifier in an Integrated Gasification Combined Cycle (IGCC) (e.g., 1, 2). In order to better understand and to improve pulverized-coal gasification processes, a large body of gasification data from within a laboratory-scale entrained-flow gasifier has been collected at this laboratory (e.g., 3-7) and applied toward the development of a comprehensive computer model for pulverized-coal reactors (8-10). This paper summarizes a companion study of the flow processes in an isothermal flow facility that simulates the flow characteristics of the entrained-flow coal gasifier.

A laser Doppler-velocimeter (LDV) was used to make measurements of mean and turbulent velocities both at the inlet, and from within the flow chamber. Isothermal air flows were used to isolate the basic flow properties from such complications as density gradients and chemistry-turbulence interactions. This study emphasized the effects of inlet conditions on flow properties within the simulated reactor (e.g., axial velocity decay, location of recirculation zones, turbulence levels). A knowledge of the effect of inlet conditions on flow properties can lead to improved gasifier operating conditions, can assist in the interpretation of in situ chemical species data from the gasifier, and can guide modeling efforts.

Comparison of experimental measurements with predictions made by a specific computer model was a second objective of this study. The model, PCGC-2 (Pulverized-Coal Gasification and Combustion: 2-Dimensional), is a comprehensive code for pulverized-coal and coal-water slurry processes that has been developed at this laboratory (8-10). The code employs the k-e model for turbulent fluid mechanics. Much of the earlier experimental flow data was collected with intrusive probes, which in some cases seriously distorted the flow being measured. Furthermore, most of the earlier studies did no include measurements at the inlet. Documentation of the inlet boundary condition is needed if experimental data are to be properly applied to model development.

The Sensitivity of Entrained-Flow Coal Gasification Burners to Changers in Inlet Boundary Conditions

Sowa, W.A.; Hedman, P.O. and Smoot, L.D.
Submitted to Fuel, 1988. 25 pgs. Funded by Morgantown Energy Technology Center.

The impact of diffusion flame burner geometry on entrained flow coal gasification was studied. Three diffusion flame burners were designed and installed on a laboratory-scale, downfired, entrained-flow, coal gasifier operated at pressures up to 560 kPa. Each burner was studied by varying reactor pressure, oxygen/coal ratio, and steam/coal ratio. Gasifier performance was assessed by collecting space-resolved gas and char samples in the reaction chamber and analyzing them for carbon conversion, gas composition (CO, CO2, H2, H2O, and CH4), and cold gas efficiency. Burner geometry affected carbon conversion, gas composition, and cold gas efficiency. Each burner had unique flame structural characteristics that resulted in burner-unique trends with reactor pressure, oxygen/coal ratio, and steam/coal ratio.

Effects of Pressure and Coal Rank on Carbon Conversion in an Entrained-Coal Gasifier

Cope, R.F.; Smoot, L.D. and Hedman, P.O.
Accepted for publication Fuel, 1988. 9 pgs. Funded by Morgantown Energy Technology Center.

Between 1946 and 1962, the U.S. Bureau of Mines developed and operated five different atmospheric pressure and elevated pressure entrained-coal gasifiers. From 1963 to 1982, Bituminous Coal Research, Inc. and others developed and operated the Bi-Gas pressurized two-stage entrained-coal gasifier. These programs demonstrated the feasibility of gasifying US coals in entrained gasifiers, and investigated the effects of such operating variables as pressure and coal rank. A number of other entrained coal gasification processes have demonstrated the ability to operate at elevated pressure with several coals of different rank (e.g. Texaco, Shell and Mountain Fuel Resources), but little research has been performed with these processes to determine how carbon conversion is affected by coal rank at elevated pressures.

Sebastion, Strimbeck et al., and Brown et al. reported that carbon conversion increased as coal rank decreased in atmospheric pressure entrained-coal gasification. Preliminary tests in the BI-Gas study show a similar coal rank effect at elevated pressures, but simultaneous changes in other operating variables (i.e. coal, oxygen and steam feed rates) obscure the combined effects of pressure and coal rank on carbon conversion. In a limited investigation of pressure effects in a laboratory gasifier (using bituminous coal only), McIntosh and Coates observed a 10 to 20 percent increase in exit carbon conversion as operating pressure was increased from 1050 to 2320 kPa. Studies conducted by Azuhata et al., showed that for a diffusion flame and an O2/coal ratio greater than 0.8, increasing the operating pressure form 100 to 500 kPa produced a 10-15 percent increase in the carbon conversion of Utah bituminous coal. A similar pressure effect was not observed in the Azuhata et al. premixed flame data. The objective of this study was to determine the combined effects of coal rank and elevated operating pressure on carbon conversion, in entrained-coal gasification.

The Sensitivity of Entrained-Flow Coal Gasification Diffusion Burners to Changes in Geometry

Sowa, W.A.; Hedman, P.O. and Smoot, L.D.
Western States Conference, 1987. 25 pgs. Funded by Morgantown Energy Technology Center.

The impact of diffusion flame burner geometry on entrained flow coal gasification was studied. Three diffusion flame burners were designed and installed on a laboratory-scale, downfield, entrained-flow, coal gasifier operated at pressures up to 560 kPa. Each burner was studied by varying reactor pressure, oxygen/coal ratio and steam/coal ratio. Gasifier performance was assessed by collecting space resolved gas and char samples in the reaction chamber and analyzing them for carbon conversion, gas compositions (CO, CO2, H2, H2O, and CH4), and cold gas efficiency. Burner geometry was found to significantly affect carbon conversion, gas compositions, and cold gas efficiency. Each burner had unique flame structure characteristics which resulted in burner-unique trends with reactor pressure, oxygen/coal ratio and steam/coal ratio.

The Impact of Diffusion Flame Injectors on Entrained Coal Gasification

Sowa, W.A.; Hedman, P.O. and Smoot, L.D.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. Funded by Morgantown Energy Technology Center.

The impact of diffusion flame burner geometry on entrained flow coal gasification was studied. Three diffusion flame burners were designed and installed on a laboratory-scale, downfired, entrained-flow, coal gasifier operated at pressures up to 560 kPa. Each burner was studied by varying reactor pressure, oxygen/coal ratio and steam/coal ratio. Gasifier performance was assessed by collecting space resolved gas and char samples in the reaction chamber and analyzing them for carbon conversion, gas compositions (CO, CO2, H2, H2O, and CH4), and cold gas efficiency. Burner geometry was found to significantly affect carbon conversion, gas compositions, and cold gas efficiency. Each burner had unique flame structure characteristics that resulted in burner-unique trends with reactor pressure, oxygen/coal ratio and steam/coal ratio.

Effective Sorbent Mixing in a Simulated Entrained-Flow Reactor: A Cold Flow Study

Braithwaite, D.J. and Hedman, P.O.
AIChE Annual National Meeting, Washington, DC, 1988. Funded by ACERC (National Science Foundation and Associates and Affiliates).

The injection of sorbent particles into an entrained-flow coal reactor was simulated by the injection of a jet normal to a fully developed airflow. Effects investigated were the free stream Reynolds number, jet size and velocity, and number of jets. Test techniques included smoke injection for flow visualization, tracer gas extraction, and laser-Doppler velocity measurements. The results showed that the trajectory of a jet in cross flow is dependent on the jet to main flow momentum ratio, as well as the size of the jet. Buoyancy played an important role in jet behavior at low free stream Reynolds numbers. Greater turbulence intensity and enhanced mixing occurred when the jet momentum was sufficient to cause the jet to impinge on the opposing wall or another jet.

LDA Measurements in Simulated Gasifier Flows with Swirl

Lindsay, J.D.; Hedman, P.O. and Smith, P.J.
International Symposium on Laser-Doppler Velocimetry, 1986, Lisbon, Portugal. 6 pgs. Funded by Morgantown Energy Technology Center and US Department of Energy.

A laser-Doppler system was used in a cold-flow study of a simulated pulverized-coal gasifier. The study was designed to provide fundamental information about the behavior of flow in such a gasifier and to provide data for the validation of a computer model. Measurements in 21 flow cases with and without swirl were made. Results are compared with predictions from a comprehensive model that uses a k-e turbulence submodel. Several levels of replication were used in the testing in order to examine reproducibility and to permit statistical analysis of results.

Release and Reaction of Fuel-Nitrogen in a High-Pressure Entrained-Coal Gasifier

Nichols, K.M.; Hedman, P.O. and Smoot, L.D.
Fuel, 66, 1257-1263, 1987. 7 pgs. Funded by Morgantown Energy Technology Center.

Effects of pressure, flame type and coal feed rate on fuel-nitrogen release and nitrogen pollutant formation were examined in a laboratory scale, entrained-coal gasifier. A Utah, high-volatile bituminous coal was used. With a water-quenched probe, gas-particulate samples were collected for oxygen-coal mass ratios from 0.6 to 1.1, pressures of 1, 4.9 and 10.4 atm and coal feed rates of 25 and 35 kg·h-1. Two injector types were utilized; one produced a diffusion flame, the other a premixed flame. Fuel-nitrogen release from the coal showed little dependence on oxygen-coal ratio, pressure or coal feed rate. Values at the gasifier exit averaged 83% for the diffusion flame and 92% for the premixed flame.

Fuel-nitrogen release, mostly during devolatilization, exceeded fuel-carbon release by . 10% for the premixed flame and . 30% for the diffusion flame, depending on oxygen-coal mass ratio. Over 50% of the released fuel-nitrogen formed N2, with significant amounts of NH3 and HCN, and smaller amounts of NO. Increased pressure at constant mass feed rates caused sharp decreases in effluent NO concentrations (to near zero) for both flame types which was explained by a combination of increased residence time and increased homogeneous NO decay rate. Elevated pressure also increased the effluent NH3 and decreased HCN concentrations for the diffusion flame whereas the more complete mixing of the premixed flame resulted in lower NH3 and HCN levels, and higher N2 levels. In general, nitrogen species concentrations were not largely affected by coal feed rate, though increased coal feed rate decreased NH3 levels somewhat. From these observations, together with observations from other investigators; possible explanations are postulated.

Sulfur Species Formation in a High-pressure Entrained-Coal Gasifier

Nichols, K.M.; Hedman, P.O.; Smoot, L.D. and Blackham, A.U.
Western States Section, 1987, The Combustion Institute, Provo, UT. 16 pgs. Funded by Morgantown Energy Technology Center.

This work summarizes several observations concerning the effects of pressure and oxygen-to-coal mass ratio on the fate of coal-sulfur during entrained gasification. A high-volatile bituminous coal was pulverized to a mass mean of near 50 mm. The coal was gasified with oxygen in a laboratory-scale entrained-flow gasifier. Test pressures were atmospheric (1.0 ATM, 101 kPa), 4.9 ATM (500 kPa), and 10.4 ATM (1050 kPa). Oxygen-to-coal mass ratios between 0.6 and 1.1 were investigated. Gas-particulate samples were collected with a water-quenched probe from the gasifier chamber effluent stream. Measurements were made of the sulfur retained in the char particles and of the concentrations of H2S, SO2, COS and CS2 in the product gas. Conversion of sulfur to the gas phase was observed to decrease with increasing pressure, possibly through sulfur captured by char. Changing pressure caused a change in the distribution of gas phase sulfur species. At higher pressure, the proportions of SO2 and CS2 decreased, and the proportion of H2S increased. This redistribution with increasing pressure is not predicted by equilibrium calculations, nor was it observed in learner (less particle laden) combustion environments. This suggests the importance of char in determining the fate of the coal-sulfur during gasification. Increasing oxygen-to-coal mass ratio increased sulfur conversion, SO2 concentration, and COs concentration, while it decreased H2S and CS2 concentrations.