Rawlins, DC
1988-1986
Lignite Slurry Spray Characterization and Combustion Studies
Eatough, C.N.; Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Western States Section, The Combustion Institute, Dana Point, California, 1988. Funded by US Department of Energy (Morgantown Energy Technology Center) and ACERC (National Science Foundation Associates and Affiliates).
Lignite slurry atomization and combustion characteristics were studied using two atomizers, one developed at Brigham Young University (laboratory nozzle) and the other a Parker-Hannifin Model 6840610 M3 atomizer (commercial nozzle). These nozzles were used because of the significantly different spray patterns produced by each. In these cold-flow studies, it was found that the laboratory nozzle produced a solid cone type spray pattern with the highest mass flux near the spray center line. The commercial nozzle has a hollow cone spray pattern with a larger spray angle. Atomization studies were performed with these nozzles to determine the effect of atomizing air to slurry mass flow ratio (A/S) on particle/droplet size and velocity, and slurry spray mass distribution. These measurements were then used to study the effect of particle/droplet size and velocity, and spray mass distribution on carbon burnout in a laboratory scale reactor using hot-water dried lignite slurry as a fuel. Both the laboratory and commercial nozzles follow the same trends for mean droplet size and droplet velocity with variation in A/S. As expected, mean droplet size decreased with A/S and velocity increased with A/S. Spray angle decreased for the laboratory nozzle but increased for the commercial nozzle with increase in A/S.
Analysis of combustion data indicates an expected strong dependence of burnout on particle/droplet size. Burnout increased markedly as particle/droplet size decreased. Burnout was also affected by the mass distribution of the slurry spray. Large spray angles directed slurry to the relatively cool reactor walls resulting in lower burnout values. Burnout values from both nozzles followed the same trends with regard to droplet size. Burnout increased with decreasing mean droplet size to about 50 mm, which corresponded closely with the coal particle size in the slurry which has a mean diameter of about 40 mm. A mean droplet diameter larger than about 80 mm with a 300 mm top size could not sustain combustion in the laboratory reactor.
A combustion map of burnout values was made using the laboratory nozzle at an A/S of 0.7, swirl number of 1.5 and SR of 1.1.
Low Rank Coal-Water Fuel Combustion in a Laboratory Scale Furnace
Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Accepted for publication in Combustion and Flame, 1988. Funded by US Department of Energy.
A detailed study of hot-water dried lignite slurry combustion and the formation of nitrogen-containing pollutants was performed in a vertical, laboratory-scale combustor. Space-resolved local measurements of solid and gaseous combustion products were obtained from throughout the combustion zone using a stainless steel, water-quenched sample probe. Coal burnout (daf) of greater than 99% was achieved without supplementary fuel support, in an estimated residence time of 1.4s. Flame stability was strongly affected by the atomized droplet size, which is controlled by the atomizing air to slurry mass ration (A/S). For A/S greater than 0.7, coal burnout was relatively insensitive to further increases in A/S, yet burnout decreased rapidly as A/S was decreased. Nitric oxide (NO) emissions were not affected greatly by changes in A/S. Decreasing stoichiometric ration (SR) to about 0.8, caused coal burnout to decrease from about 98% to 94% and NO emissions to decrease from around 600 PPM to less than 100 PPM Changes in secondary air swirl number from 0 to 4.25 had little or no effect on coal burnout or NO emissions for a SR of 1.1 and an A/S of 0.75. At low A/S (0.24), high secondary air swirl was required in order to stabilize the slurry flame. Reactor mapping tests showed rapid mixing between the slurry and the combustion air. CO was found only near the slurry inlet at a maximum concentration of 0.3%. No other fuel-rich species were detected in measurable quantities.
A Comparison of Combustion Characteristics Between Lignite-Water Slurry and Pulverized Lignite
Rawlins, D.C.; Smoot, L.D. and Germane, G.J.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 27 pgs. Funded by the Morgantown Energy Technology Center.
Experiments of the combustion of hot-water dried lignite slurry and its parent, pulverized coal have been performed in a laboratory-scale combustor. The operating parameter that had the greatest effect on flame location for lignite slurry combustion was the slurry mean droplet diameter. A stable flame could not be maintained with large droplet sizes. The air blast of the slurry-atomizing nozzle caused the mixing of the primary and secondary streams to be much more rapid for slurry combustion than for pulverized coal. Due to this rapid mixing, fuel-rich products of combustion were only observed in trace quantities near the top of the combustion zone during slurry combustion; however, with pulverized coal combustion, significant concentrations persisted throughout the combustor. Secondary air swirl number had the greatest effect on the pulverized lignite flame location. A minimum in nitrogen oxide (NO) concentration was observed during the pulverized coal combustion as swirl was increased. Secondary air swirl, however, had only a negligible effect on coal burnout and NO emissions for slurry combustion. A five-fold increase in the primary air velocity more than doubled NO concentrations at the exit plane. Changing the primary air velocity through the slurry atomizer (by changing the air mass flow rate) did not affect NO emissions during slurry combustion. Changes in the water concentration within the combustion system did not affect combustion performance with pulverized coal. Thus, NO emissions are more strongly controlled by the mixing of the fuel with the secondary air than by flame temperature reduction caused by water added to the combustion system.
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.
Lignite Coal Water Slurry Combustion Characteristics in a Laboratory-Scale Furnace
Rawlins, D.C.; Jones, R.G.; Germane, G.J. and Smoot, L.D.
8th International Symposium on Coal Slurry Fuels Preparation and Utilization, 1986, Orlando, FL. 14 pgs. Funded by Morgantown Energy Technology Center.
The Brigham Young University (BYU) Combustion Laboratory is currently conducting a low-rank coal-water slurry characterization and combustion research program for the US Department of Energy through the Grand Forks, North Dakota Project Office. The lignite slurry used in this study was prepared at the University of North Dakota Energy Research Center (UNDERC) by a hot water drying process. The slurry contains 58% by weight solids and 42% water. No additives have been included to increase slurry stability. Slurry characterization studies, which have been conducted at both BYU and UNDERC, include slurry rheology, particle size distribution and slurry stability.
Combustion tests are being conducted in a vertically oriented, cylindrical combustor, 3.0 m high and 35 cm in interior diameter, with CWM and air injection at the top. Access ports are located along the entire length of the reactor for visual observation of the flame and for insertion of a stainless steel water-quenched sample probe. Solid and gaseous products of combustion are removed form the combustion zone and analyzed for coal burnout and local gaseous compositions. The combustion tests show that a strong, stable flame can be achieved without secondary fuel support. Flame stability appears to be strongly affected by the ratio of the spray nozzle atomizing air to the slurry feed rate. Stoichiometric ratio and secondary air swirl number affect flame stability to a lesser exten. Coal burnout of greater than 99% has been achieved with a reactor residence time estimated to be slightly greater than one second. NO emissions have been measured in the range of 200 to 600 PPM No attempt has been made to control or reduce these emissions.
Rawlins, DC
1988-1986
Lignite Slurry Spray Characterization and Combustion Studies
Eatough, C.N.; Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Western States Section, The Combustion Institute, Dana Point, California, 1988. Funded by US Department of Energy (Morgantown Energy Technology Center) and ACERC (National Science Foundation Associates and Affiliates).
Lignite slurry atomization and combustion characteristics were studied using two atomizers, one developed at Brigham Young University (laboratory nozzle) and the other a Parker-Hannifin Model 6840610 M3 atomizer (commercial nozzle). These nozzles were used because of the significantly different spray patterns produced by each. In these cold-flow studies, it was found that the laboratory nozzle produced a solid cone type spray pattern with the highest mass flux near the spray center line. The commercial nozzle has a hollow cone spray pattern with a larger spray angle. Atomization studies were performed with these nozzles to determine the effect of atomizing air to slurry mass flow ratio (A/S) on particle/droplet size and velocity, and slurry spray mass distribution. These measurements were then used to study the effect of particle/droplet size and velocity, and spray mass distribution on carbon burnout in a laboratory scale reactor using hot-water dried lignite slurry as a fuel. Both the laboratory and commercial nozzles follow the same trends for mean droplet size and droplet velocity with variation in A/S. As expected, mean droplet size decreased with A/S and velocity increased with A/S. Spray angle decreased for the laboratory nozzle but increased for the commercial nozzle with increase in A/S.
Analysis of combustion data indicates an expected strong dependence of burnout on particle/droplet size. Burnout increased markedly as particle/droplet size decreased. Burnout was also affected by the mass distribution of the slurry spray. Large spray angles directed slurry to the relatively cool reactor walls resulting in lower burnout values. Burnout values from both nozzles followed the same trends with regard to droplet size. Burnout increased with decreasing mean droplet size to about 50 mm, which corresponded closely with the coal particle size in the slurry which has a mean diameter of about 40 mm. A mean droplet diameter larger than about 80 mm with a 300 mm top size could not sustain combustion in the laboratory reactor.
A combustion map of burnout values was made using the laboratory nozzle at an A/S of 0.7, swirl number of 1.5 and SR of 1.1.
Low Rank Coal-Water Fuel Combustion in a Laboratory Scale Furnace
Rawlins, D.C.; Germane, G.J. and Smoot, L.D.
Accepted for publication in Combustion and Flame, 1988. Funded by US Department of Energy.
A detailed study of hot-water dried lignite slurry combustion and the formation of nitrogen-containing pollutants was performed in a vertical, laboratory-scale combustor. Space-resolved local measurements of solid and gaseous combustion products were obtained from throughout the combustion zone using a stainless steel, water-quenched sample probe. Coal burnout (daf) of greater than 99% was achieved without supplementary fuel support, in an estimated residence time of 1.4s. Flame stability was strongly affected by the atomized droplet size, which is controlled by the atomizing air to slurry mass ration (A/S). For A/S greater than 0.7, coal burnout was relatively insensitive to further increases in A/S, yet burnout decreased rapidly as A/S was decreased. Nitric oxide (NO) emissions were not affected greatly by changes in A/S. Decreasing stoichiometric ration (SR) to about 0.8, caused coal burnout to decrease from about 98% to 94% and NO emissions to decrease from around 600 PPM to less than 100 PPM Changes in secondary air swirl number from 0 to 4.25 had little or no effect on coal burnout or NO emissions for a SR of 1.1 and an A/S of 0.75. At low A/S (0.24), high secondary air swirl was required in order to stabilize the slurry flame. Reactor mapping tests showed rapid mixing between the slurry and the combustion air. CO was found only near the slurry inlet at a maximum concentration of 0.3%. No other fuel-rich species were detected in measurable quantities.
A Comparison of Combustion Characteristics Between Lignite-Water Slurry and Pulverized Lignite
Rawlins, D.C.; Smoot, L.D. and Germane, G.J.
Western States Section, 1988, The Combustion Institute, Salt Lake City, UT. 27 pgs. Funded by the Morgantown Energy Technology Center.
Experiments of the combustion of hot-water dried lignite slurry and its parent, pulverized coal have been performed in a laboratory-scale combustor. The operating parameter that had the greatest effect on flame location for lignite slurry combustion was the slurry mean droplet diameter. A stable flame could not be maintained with large droplet sizes. The air blast of the slurry-atomizing nozzle caused the mixing of the primary and secondary streams to be much more rapid for slurry combustion than for pulverized coal. Due to this rapid mixing, fuel-rich products of combustion were only observed in trace quantities near the top of the combustion zone during slurry combustion; however, with pulverized coal combustion, significant concentrations persisted throughout the combustor. Secondary air swirl number had the greatest effect on the pulverized lignite flame location. A minimum in nitrogen oxide (NO) concentration was observed during the pulverized coal combustion as swirl was increased. Secondary air swirl, however, had only a negligible effect on coal burnout and NO emissions for slurry combustion. A five-fold increase in the primary air velocity more than doubled NO concentrations at the exit plane. Changing the primary air velocity through the slurry atomizer (by changing the air mass flow rate) did not affect NO emissions during slurry combustion. Changes in the water concentration within the combustion system did not affect combustion performance with pulverized coal. Thus, NO emissions are more strongly controlled by the mixing of the fuel with the secondary air than by flame temperature reduction caused by water added to the combustion system.
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.
Lignite Coal Water Slurry Combustion Characteristics in a Laboratory-Scale Furnace
Rawlins, D.C.; Jones, R.G.; Germane, G.J. and Smoot, L.D.
8th International Symposium on Coal Slurry Fuels Preparation and Utilization, 1986, Orlando, FL. 14 pgs. Funded by Morgantown Energy Technology Center.
The Brigham Young University (BYU) Combustion Laboratory is currently conducting a low-rank coal-water slurry characterization and combustion research program for the US Department of Energy through the Grand Forks, North Dakota Project Office. The lignite slurry used in this study was prepared at the University of North Dakota Energy Research Center (UNDERC) by a hot water drying process. The slurry contains 58% by weight solids and 42% water. No additives have been included to increase slurry stability. Slurry characterization studies, which have been conducted at both BYU and UNDERC, include slurry rheology, particle size distribution and slurry stability.
Combustion tests are being conducted in a vertically oriented, cylindrical combustor, 3.0 m high and 35 cm in interior diameter, with CWM and air injection at the top. Access ports are located along the entire length of the reactor for visual observation of the flame and for insertion of a stainless steel water-quenched sample probe. Solid and gaseous products of combustion are removed form the combustion zone and analyzed for coal burnout and local gaseous compositions. The combustion tests show that a strong, stable flame can be achieved without secondary fuel support. Flame stability appears to be strongly affected by the ratio of the spray nozzle atomizing air to the slurry feed rate. Stoichiometric ratio and secondary air swirl number affect flame stability to a lesser exten. Coal burnout of greater than 99% has been achieved with a reactor residence time estimated to be slightly greater than one second. NO emissions have been measured in the range of 200 to 600 PPM No attempt has been made to control or reduce these emissions.