ACERC
Abstracts - 1986-1988 |
ACERC
Abstracts - 1986-1988 |
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Thrust Area 6: Model Evaluation Data and Process Strategies |
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.
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.
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.
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.
Smoot, L.D. and Brown, B.W.
Fuel, 66, 1249-1256, 1987. 8 pgs. Funded by Morgantown Energy Technology
Center.
Controlling mechanisms in the fuel-rich reaction of pulverized coal with oxygen at atmospheric pressure were investigated through analysis of experimental data and by comparison with predictions of a comprehensive model. Gasification data were obtained for four coal types at various oxygen-steam-coal ratios and effects of coal feed rate, particle size and flame type (premixed, diffusion) were also determined. The results show that coal particle heat-up and devolatilization occur very rapidly (<60-80 ms) near the coal inlet with up to 70% of the coal consumed. Coal volatiles and oxygen are rapidly consumed through gas-phase reaction, producing high gas temperature and high CO2 concentrations. Addition of steam plays little role in the coal reaction process, while residual char (typically containing 20-30% of the carbon) is consumed less rapidly (>200 ms) through surface reaction with CO2 and H2O, and possibly O2 at the onset. This general reaction process varies little among the coal types examined. The surface reactions are controlled in high-temperature regions through oxidizer diffusion to the char surface; however, as the gasifier temperature declines through heat loss and endothermic reaction, heterogeneous char-oxidizer reaction near the particle external surface become more important, giving rise to some dependence on coal type.
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.
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.
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.
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.
Sowa, W.A.; Free, J.C.;
Smith, P.J. and Hurst, T.N.
ASME Annual Meeting, 1986. 5 pages. Funded by US Department of Energy.
Concepts from statistical response surface methodology (RSM) and nonlinear optimization theory have been combined in a method for efficiently searching a "design space" when using large-scale analysis. The method is applied to a theoretical study of entrained-flow coal gasification, using PCGC-2, a two-dimensional, axisymmetric model developed at Brigham Young University, that predicts local properties in a reaction chamber. RSM was used to sample the design space and to construct a regression model, which was then linked to OPTDES, BYU, a program containing several nonlinear programming algorithms.
Two test plans were used to verify the performance of the RSM optimization algorithm in solving a gasification example problem. The method is shown to provide accurate results, while de-coupling the search and analysis phases of optimization. The importance of a proper test plan for conducting an un-biased exploration of design space is also demonstrated by comparing the results of the two test plans.
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.
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.
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.
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.
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.
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.
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.
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