Energy Fuels 2009, 23, 4893–4899 Published on Web 09/10/2009
: DOI:10.1021/ef900363q
Effect of the Fuel Bias Distribution in the Primary Air Nozzle on the Slagging near a Swirl Coal Burner Throat Lingyan Zeng, Zhengqi Li,* Hong Cui, Fucheng Zhang, Zhichao Chen, and Guangbo Zhao School of Energy Science and Engineering, Harbin Institute of Technology, 92, West Dazhi Street, Harbin 150001, People’s Republic of China Received December 13, 2008. Revised Manuscript Received August 26, 2009
Three-dimensional numerical simulations of slagging characteristics near the burner throat region were carried out for swirl coal combustion burners used in a 1025 tons/h boiler. The gas/particle two-phase numerical simulation results and the data measured by a particle-dynamics anemometer (PDA) show that the numeration model was reasonable. For the centrally fuel-rich swirl coal combustion burner, the coal particles move in the following way. The particles first flow into furnace with the primary air from the burner throat. After traversing a certain distance, they move back to the burner throat and then toward the furnace again. Thus, particle trajectories are extended. For the case with equal air mass fluxes in the inner and outer primary air/coal mixtures, as the ratio of the coal mass flux in the inner primary air/coal mixture to the total coal mass flux increased from 40 (the reference condition) to 50%, 50 to 70%, and 70 to 100%, the maximum number density declined by 22, 11, and 4%, respectively, relative to the reference condition. In addition, the sticking particle ratio declined by 13, 14, and 8%, respectively, compared to the reference condition.
the primary air. Under the influence of the cone separators, pulverized coal carried by the primary air is concentrated in the central zone of the primary air, resulting in a coal-rich flow in the central zone and a coal-lean flow in the peripheral zone. The objective is to minimize the tendency for slagging to occur on the water-cooled tube wall. Slagging characteristics of the burner were investigated by three-dimensional numerical simulations. Using the numerical simulation method, we can use the slagging model to predict the slagging situation in the region of the burner and then obtain the optimized burner structure and running parameters with the least slagging. Also, the model can provide a theoretical basis for burner design.
1. Introduction Coal is used globally as the energy resource for thermal power plants, mostly as pulverized coal. Emissions and ash problems are the main concern in the design and operation of pulverized coal-fired boilers. Slagging refers to molten deposits within the furnace in areas directly exposed to flame radiation, such as the furnace walls and widely spaced pendant superheaters. Slagging can cause four problems in boiler operation.1 (1) The slag that cannot be removed by soot blowing can build up on and insulate the water-cooled tube walls, reduce the ability to raise steam, and require a superheater spray. (2) The slag on the wall can lead to increased corrosion. (3) The slag can drop to the bottom of the furnace, causing damage to the tubes, and may lead to hopper blockage or difficulty in grinding the bottom ash. (4) Slagging in the burner vent area may partially plug the throat, causing a series of combustion problems, such as affecting flame organization and damaging the bottom of the furnace by fallen slag. Li and co-workers2,3 proposed a new burner, the centrally fuel-rich swirl coal combustion burner (Figure 1), in 2003. Both the inner and outer secondary air are swirling, which is produced by 16 axial and 12 tangential vanes, respectively. The centrally fuel-rich burner has cone separators in the primary air tube to effect distribution of pulverized coal in
2. Mathematical Model and Calculation Method 2.1. Mathematical Model of the Burner Flow Field. The flow field of the burner was calculated using FLUENT6.3.26 software, with a series of wisely used numerical models. The gas turbulent flow was taken into account by a realizable k-ε model.4 The Lagrangian stochastic tracking model was applied to analyze the gas/particle flow field,5 while the coupling calculation of the gas-particle two phase used the particle source in cell (PSIC) method.6 Radiation was described using the P-1 model,7 and the devolatilization process was modeled by a two competing rate Kobayashi model.8 The combustion of volatiles (4) Shih, T. H.; Liou, W. W.; Shabbir, A.; Yang, Z.; Zhu, J. A new k-ε eddy viscosity model for high Reynolds number turbulent flows-model development and validation. Comput. Fluids 1995, 24 (3), 227–238. (5) Gosman, A. D.; Loannides, E. Aspects of computer simulation of liquid-fuelled combustors. AIAA 19th Aerospace Science Meeting, 1981; pp 81-323. (6) Crowe, C. T.; Sharma, M. P.; Stock, D. E. The particle-sourcein-cell (PSIC) method for gas-droplet flows. J. Fluid Eng. 1977, 99 (2), 325–332. (7) Cheng, P. Two-dimensional radiation gas flow by a moment Method [J]. AIAA J. 1964, 2, 1662–1664. (8) Smoot, L. D.; Smith, P. J. Coal Combustion and Gasification; Plenum Press: New York, 1985.
*To whom correspondence should be addressed. Telephone: þ86451-86418854. Fax: þ86-451-86412528. E-mail:
[email protected]. (1) Su, S.; Pohl, J. H.; Holcombe, D.; Hart, J. A. Slagging propensities of blended coals. Fuel 2001, 80, 1351–1360. (2) Li, Z. Q. Radial-bias-combustion and central-fuel rich swirl pulverized coal burners for wall-fired boilers. In Leading-Edge Electric Power Research; Nova Science Publishers, Inc.: New York, 2008; pp 5-125. (3) Chen, Z. C.; Li, Z. Q.; W, F. Q.; Jing, J. P.; Chen, L. Z.; Wu, S. H. Gas/particle flow characteristics of a centrally fuel rich swirl coal combustion burner. Fuel 2008, 87, 2102–2110. r 2009 American Chemical Society
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Energy Fuels 2009, 23, 4893–4899
: DOI:10.1021/ef900363q
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ratio of the critical and particle viscosities. The relationships are given by eq 1.16 Pi ðTps Þ ¼ μref =μ μ > μref Pi ðTps Þ ¼ 1 μeμref
ð1Þ
Pi is the sticking probability of the particle group i with average viscosity μ. Tps is the temperature of particle group i, and μref is the critical viscosity. Generally, when slag changes from the liquid to the plastic state, there is a mutational point in the viscosity curve. At this temperature, a large number of crystals vanish and the viscosity at the mutational point is usually taken as the critical viscosity. The outstanding advantage of this model is that it is simple and appropriate for engineering applications. All current studies use this model to simulate the slagging process and obtain the sticking particle number. Generally, the critical viscosity is treated as a constant during the slagging process, and the value commonly selected is 105 Pa s.10,11 In the present study, a temperature sub-area method17 has been used to compute particle viscosity. The formulas for the high- and low-temperature viscosities are different, and the maximum of these two viscosities is selected. This model is sufficiently precise if the particle critical viscosity is in the range of 104-109 Pa s, which includes the commonly selected critical viscosity. Consequently, this model can give credible results and has wide application. The particle viscosity can be calculated by the following procedure.17-20 Determine the mole fractions of all components based on the oxide composition of fly ash.
Figure 1. Centrally fuel-rich swirl coal combustion burner: 1, primary air duct; 2, monitoring pipe; 3, cone separators; 4, inner secondary air vanes; 5, inner secondary air duct; 6, outer secondary air vanes; 7, outer secondary air duct.
was modeled using the probability density function theory,8 and char combustion was modeled using the diffusion/kinetics model.9 2.2. Slagging Model of the Water-Cooled Tube Wall. To calculate slagging information for the water-cooled tube wall, we used FLUENT6.3.26 software to compute the reacting-flow field of the single burner and then added a slagging subroutine to Fluent based on the result of the hot-state flow field. The subroutine was written in C language, with user-defined functions. When particles struck the water-cooled tube wall, the program called this subroutine. Figure 2 shows the flowchart of the slagging calculation. Considerable advances have been made in developing models to predict ash deposition behavior.10-15 Wang10 carried out ash deposition in large-scale coal combustion facilities. Detailed analyses of coal ash deposits were performed using scanning electron microscopy (SEM), X-ray diffraction, and image analysis, to characterize local deposit properties as a function of the position. Fan et al.11 developed a model to simulate deposition growth under slagging conditions and simulated the coal combustion and slagging process in the whole furnace. The predictions indicated that the numerical model can be used to optimize the design and operation of pulverized coal-fired boilers. On the basis of a review of the slagging models, it was concluded that many factors influence the slagging process, for example, particle or water-cooled wall surface temperature, particle incident angle and velocity, and particle components. The particle viscosity is considered primarily and is the most important factor. Currently, most investigations use critical viscosity to study the effect of particle viscosity on the slagging process, by defining a sticking particle number. If the particle viscosity is smaller than the critical viscosity, it can be considered that this particle can completely stick on the water-cooled tube wall, and the sticking probability is taken as 1. If the particle viscosity is larger than the critical viscosity, the sticking probability is the
NBO=T ¼ ðCaO þ MgO þ FeO þ Na2 O þ K2 O -Al2 O3 Þ= ððSiO2 þ TiO2 Þ=2 þ Al2 O3 Þ
ð2Þ
R ¼ CaO þ MgO þ FeO þ Na2 O þ K2 O þ 2TiO2 = ðCaO þ MgO þ FeO þ Na2 O þ K2 O þ 2TiO2 þ Al2 O3 Þ ð3Þ Calculate the high-temperature BH using Senior and Srinivasachar’s coefficients, where BH ¼ BH0 þ BH1R þ BH2R2 þ SiO2 ðBH3 þ BH4R þ BH5R2 Þ þ ðSiO2 Þ2 ðBH6 þ BH7R þ BH8R2 Þ þ ðSiO2 Þ3 ðBH9 þ BH10R þ BH11R2 Þ
ð4Þ
If BH < 0 or BH > 50.0, use Kalmanovitch and Frank’s coefficients to calculate BH, where BH ¼ BK0 þ BK1R þ BK2R2 þ SiO2 ðBK3 þ BK4R þ BK5R2 Þ þ ðSiO2 Þ2 ðBK6 þ BK7R þ BK8R2 Þ
(9) Zhou, L. X. Theory and Numerical Modeling of Turbulent GasParticle Flows and Combustion; CRC Press, Inc.: Boca Raton, FL, 1993. (10) Wang, H. F. Modeling of ash formation and deposition in PC fired utility boilers. Ph.D. Thesis, Brigham Young University, Provo, UT, 1998. (11) Fan, J. R.; Zha, X. D.; Sun, P. Simulation of ash deposit in a pulverized coal-fired boiler. Fuel 2001, 80, 645–654. (12) Lee, F. C. C.; Lockwood, F. C. Modeling ash deposition in pulverized coal-fired applications. Prog. Energy Combust. Sci. 1999, 25, 117–132. (13) Costen, P. G.; Lockwood, F. C.; Siddique, M. M. Mathematical modeling of ash depostion in pulverized fuel-fired combustors. In Proceedings of the Combustion Institute, Combustion Institute, Pittsburgh, PA, 2000; pp 2243-2250. (14) Wang, H. F.; Harb, J. N. Modeling of ash deposition in largescale combustion facilities burning pulverized coal. Prog. Energy Combust. Sci. 1997, 23, 267–282. (15) You, C. F.; Zhou, Y. Effect of operation parameters on the slagging near swirl coal burner throat. Energy Fuels 2006, 20 (5), 1855– 1861.
þ ðSiO2 Þ3 ðBK9 þ BK10R þ BK11R2 Þ
ð5Þ
(16) Walsh, P. M.; Sayre, A. N.; Loehden, D. O.; Monroe, L. S.; Beer, J. M.; Sarofim, A. F. Deposition of bituminous coal ash on an isolated heat exchanger tube: effects of coal properties on deposit growth. Prog. Energy Combust. Sci. 1990, 16, 327–346. (17) Senior, C. L.; Srinivasachar, S. Viscosity of ash particles in combustion systems for prediction of particle sticking. Energy Fuels 1995, 9, 277–283. (18) Machin, J. S; Yee, T. B. Viscosity studies of the system CaO-MgO-Al2O3-SiO2: II, CaO-Al2O3-SiO2. J. Am. Ceram. Soc. 1948, 31, 200–204. (19) Mills, K. C.; Rhine, J. M. The measurement and estimation of the physical properties of slags formed during coal gasification. Fuel 1989, 68, 193–200. (20) Machin, J. S.; Yee, T. B.; Hanna, D. L. Viscosity studies of the system CaO-MgO-Al2O3-SiO2: III, 35, 45, and 50% SiO2. J. Am. Ceram. Soc. 1952, 35, 322–325.
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: DOI:10.1021/ef900363q
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Figure 2. Flowchart of the slagging calculation.
Calculate the low-temperature Srinivasachar’s coefficients, where
BL
using
Senior
The larger viscosity is selected as the particle viscosity between the high- and low-temperature viscosities.
and
μ ¼ maximum of ðμH, μLÞ
BL ¼ BL0 þ BL1R þ BL2R2 þ SiO2 ðBL3 þ BL4R þ BL5R2 Þ þ ðSiO2 Þ2 ðBL6 þ BL7R þ BL8R2 Þ 3
þ ðSiO2 Þ ðBL9 þ BL10R þ BL11R2 Þ
The particle temperature T is determined by the temperature field, which is calculated by the combustion model and read by the macro function P(T). Senior and Srinivasachar’s coefficients BH0-BH11 and BK1-BK11 and Kalmanovitch and Frank’s coefficients BL0-BL11 and BW0-BW11 can be found in ref 10. On the basis of the computed temperature field, a stochastic trajectory model was used to compute particle trajectory and count the sticking particle number. The total particle trajectory number was 960 000.
ð6Þ
If BL < 10.0 or BL > 60.0, use modified coefficients to calculate BL, where BL ¼ BW0 þ BW1R þ BW2R2 þ SiO2 ðBW3 þ BW4R þ BW5R2 Þ þ ðSiO2 Þ2 ðBW6 þ BW7R þ BW8R2 Þ þ ðSiO2 Þ3 ðBW9 þ BW10R þ BW11R2 Þ
3. Three-Dimensional Numerical Simulations for the Burner Model
ð7Þ
Calculate the high-temperature AH, where AH ¼ -2:81629 -0:46341BH -0:35342NBO=T
3.1. Verification of Two-Phase Flow Simulations. To verify the validity and feasibility of grid divisions, the calculation model and methods, and the correctness of boundary conditions, simulation results and data from experiments were compared. The full industrial size burner was a burner on a 1025 tons/h (tph) lean coal-fired boiler. The ratio of the burner model to the full-scale burner was 1:7. In an airparticle test facility, a three-dimensional particle dynamics anemometer (PDA) was used to measure air-particle flows in the near-burner region of the burner model.21 The simulation geometric model was set up to closely mimic the experimental rig. Cold-state gas/particle simulation was carried out with the experimental parameters shown in Table 1. Figures 4-6 show the simulation results and data acquired from experiments,21 where x and d represent the distance
ð8Þ
Calculate the low-temperature AL, where AL ¼ -0:982 -0:902473BL if NBO=Tg1:3 AL ¼ 2:478718 -0:902473BL -2:662091NBO=T if 0:2eNBO=T < 1:3 AL ¼ 9:223 -0:902473BL -36:3835NBO=T < 0:2
if 0:0eNBO=T
AL ¼ 9:223 -0:902473BL if NBO=T < 0:0
ð9Þ
Calculate the high-temperature viscosity μH (Pa s) at a given temperature T (K), where μH ¼ T10AH þ 1000BH=T
(21) Chen, Z. C.; Li, Z. Q.; Jing, J. p.; Wang, F.; Chen, L.; Wu, S. The influence of fuel bias in the primary air duct on the gas/particle flow characteristics near the swirl burner region. Fuel Process. Technol. 2008, 89, 958–965. (22) Li, Z. Q.; Jing, J. P.; Chen, Z. C.; Ren, F.; Xu, B.; Wei, H.; Ge, Z. Combustion characteristics and NOx emissions of two kinds of swirl burners in a 300-MWe wall-fired pulverized-coal utility boiler. Combust. Sci. Technol. 2008, 180, 1370–1394.
ð10Þ
Calculate the low-temperature viscosity μL (Pa s) at a given temperature T (K), where μL ¼ T10AL þ 1000BL=T
ð12Þ
ð11Þ 4895
Energy Fuels 2009, 23, 4893–4899
: DOI:10.1021/ef900363q
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Figure 3. Burner model for gas/particle flow simulation (dimensions in millimeters): 1, fuel-rich primary air duct; 2, fuel-lean primary air duct; 3, inner secondary air duct; and 4, outer secondary air duct.
Figure 5. Comparison of calculated gas radial velocities with measured data.
Figure 4. Comparison of calculated gas axial velocities with measured data. Table 1. Experimental Parameters of the Burner Modela fuel-rich primary air exit area (m2) air velocity (m s-1) air temperature (°C) mass flow rate of glass beads (kg s-1) swirl number total swirl number
fuel-lean primary air
0.000375 10.00 25 0.0155
0.001125 10.00 25 0
0
0
inner outer secondary secondary air air 0.0046 10.58 25 0
2.534 0.494
Figure 6. Comparison of calculated gas tangential velocities with measured data.
0.0075 16.07 25 0
With jet development, the gas mean radial velocities gradually decreased. From x/d = 0.1 to 0.3, some gas radial velocities took negative values in the central recirculation zone, indicating that primary air-coal mixture diffused into the central recirculation zone. Consequently, the particle concentration became larger in this zone. Both gas temperature and particle concentration were high in the central zone of the burner, which was advantageous for heating pulverized coal, release of coal volatiles, and char combustion, and flame stability was enhanced. Figure 6 shows profiles of gas mean tangential velocities. At the x/d = 0.1 cross-section, gas mean tangential velocities were small, with a radius 1773
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: DOI:10.1021/ef900363q
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Figure 10. Distribution of the sticking number density along the water-cooled wall for the case in which the ratio of the coal flux in the inner primary air/coal mixture to the total coal flux was 50%.
The water-cooled tube wall above the burner throat was divided into 10 parts to obtain slagging information for different zones. The height of each part was 70 mm (0.058D, D = 1211 mm; D is the diameter of the outermost cone of the burner; see Figure 7). The sticking number density was defined as the ratio of the number of sticking particles to the wall area. Figure 10 shows the sticking number density in the case for which the coal mass flux and air mass flux in the inner and outer primary air/coal mixture were equal. We tracked equal particles in the inner and outer primary air/coal mixture and obtained the corresponding sticking number densities. The total sticking number density is the sum of the sticking number density from the inner primary air/coal mixture and that from the outer one. The sticking number density from the inner primary air/coal mixture had a similar distribution to that from the outer one. As Y - D/2 increased from 0 to 490 mm, the sticking number density increased and then decreased and had a maximum value at Y - D/2 = 105 mm. As Y - D/2 increased from 490 to 700 mm, the sticking number density increased slowly. The sticking number density from the outer primary air/coal mixture was 1.09 times larger than that from the inner primary air/coal mixture. Because the inner primary air/coal mixture was in the center zone of the primary air/coal mixture, the particles in it had lower radial and tangential velocities and a smaller probability of sticking on the wall, in contrast with the particles in the outer primary air/coal mixture. The total sticking number density had a similar profile to the sticking number densities from the inner or outer primary air/coal mixture. Figure 11 shows that the distributions of the total sticking number densities for different ratios of the coal flux in the inner primary air/coal mixture to the total coal flux. As the ratio of the coal flux in the inner primary air/coal mixture to the total coal flux increased, the maximum total sticking number density decreased from 19 273 to 12 153 m-2 (37% decrease). The number density maxima were all at Y - D/2 = 105 mm. As the ratio of the coal flux in the inner primary air/coal mixture to the total coal flux increased from 40 to 50%, 50 to 70%, and 70 to 100%, the maximum values declined by 22, 11, and 4%, respectively, compared to the value for the 40% ratio. Thus, the maximum total sticking number density declined most rapidly as the ratio increased from 40 to 70% and least rapidly as the ratio increased from 70 to 100%. The sticking particle ratio is the ratio of the total number of sticking particles to the number of tracked particles. Figure 12 shows the effect on the sticking particle ratio of
Figure 9. Particle trajectories in the furnace.
collided with the water-cooled tube wall would have a finite probability of sticking to the wall, and others did not collide with the water-cooled tube wall. Coal particles show such movement: particles first flow into the furnace with the primary air from the burner throat. After traversing a certain distance, they move back to the burner throat and then toward the furnace again. Thus, particle trajectories are extended. 3.3.2. Slagging Characteristics near the Burner Throat. According to the fuel distribution in the primary air/coal mixture, swirl coal combustion burners can be divided into three categories: (1) General swirl burner, for which the primary air duct radius is R, the zone with radius from 0 to √ ( 2)/2R is the inner primary air/coal mixture zone, and the √ zone with radius from ( 2)/2R to R is the outer primary air/ coal mixture zone. These two zones have equal areas. The characteristic of this type of burner is that the primary air and coal mass fluxes of the inner and outer primary air/coal mixture zones are equal, occupying 50% the mass flux of the primary air and coal mass flux, respectively. (2) The burner with the inner fuel-rich primary air/coal mixture. The inner primary air/coal mixture has 50% mass flux of primary air and more than half of the coal mass flux and can be called the inner fuel-rich primary air/coal mixture. The outer primary air/coal mixture has the rest of the primary air and coal. The centrally fuel-rich swirl coal combustion burner belongs to this type. (3) The burner with the outer fuel-rich primary air/ coal mixture. Opposite to the secondary type of burner, the outer primary air/coal mixture has 50% mass flux of the primary air and more than half of the coal mass flux and is the fuel-rich primary air/coal mixture. The volute swirl coal burner and enhanced ignition dual-register burner3 belong to this type. In this paper, the mass flux of the primary air of both inner and outer primary air/coal mixtures have 50% of the mass flux of the primary air. However, they had different coal. Taking into account this difference, we obtained slagging characteristics of different types of burner. Figure 8 shows that the gas temperature distribution at the x-z section with y = 0 was a little different from that at the x-y section with z = 0. With the same ash, the particle viscosity was a function only of the particle temperature. Consequently, the slagging characteristics on the watercooled tube wall near the burner throat were similar in the horizontal and vertical directions. The slagging characteristics were investigated on the water-cooled tube wall above the burner throat. 4898
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: DOI:10.1021/ef900363q
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combustion burner used in a 1025 tph lean coal-fired boiler. The following conclusions can be obtained: (1) The results of measured and calculated particle/gas flows were in good agreement. (2) The gas temperature near the central recirculation zone of the centrally fuel-rich swirl coal combustion burner was about 1480 K, imparting good flame stability to the burner. The coal particles move in the following way. The particles first flow into the furnace with the primary air from the burner throat. After traversing a certain distance they move back to the burner throat and then toward the furnace again. (3) In the case with equal coal mass flux and air mass flux in the inner and outer primary air/coal mixtures, tracking equal numbers of particles, the sticking number density of the inner primary air/coal mixture is less than that of the outer one. (4) In the case with equal air mass flux in the inner and outer primary air/coal mixtures, as the ratio of the coal mass flux in the inner primary air/coal mixture to the total coal mass flux increased from 40 to 50%, 50 to 70%, and 70 to 100%, the maximum number density declined by 22, 11, and 4%, respectively, and the sticking particle ratio declined by 13, 14, and 8%, respectively, compared to the case for which the ratio of the coal mass flux in the inner primary air/coal mixture to the total coal mass flux was 40%.
Figure 11. Variation of the sticking number density with the ratio of the coal flux in the inner primary air/coal mixture to the total coal flux increasing from 40 to 100%.
Acknowledgment. This work was supported by the Hi-Tech Research and Development Program of China (Contract 2007AA05Z301), Postdoctoral Foundation of Heilongjiang Province (LRB07-216), the Ministry of Education of China via the 2004 New Century Excellent Talents in University (Contract NECT-04-0328), Heilongjiang Province via 2005 Key Projects (Contract GC05A314), Key Project of the National Eleventh Five-Year Research Program of China (Contract 2006BAA01B01), and the National Basic Research Program of China (Contract 2006CB200303).
Figure 12. Effect of the ratio of the coal flux in the inner primary air/ coal mixture to the total coal flux on the sticking particle ratio.
the ratio of coal flux in the inner primary air/coal mixture to the total coal flux. As the ratio of the coal flux in the inner primary air/coal mixture to the total coal flux increased from 40 to 100%, the sticking particle ratio declined from 3.97 to 2.57% (35.12% relative decrease). As the ratio of coal flux in the inner primary air/coal mixture to total coal flux increased from 40 to 50%, 50 to 70%, and 70 to 100%, the maximum sticking particle ratios declined by 13, 14, and 8%, respectively, compared to the maximum sticking particle ratio for the 40% coal flux ratio. Thus, the burner with the outer fuelrich primary air/coal mixture has the highest sticking particle ratio and then the general swirl burner, and the burner with the smallest ratio has the inner fuel-rich primary air/coal mixture. Although this study was focused on a specific burner, we summarized the distributions of the pulverized coal in the primary air duct of different types of burner and obtained slagging characteristics affected by these distributions. When the burner structure changes, the degree of slagging may change but the slagging trend will not.
Nomenclature μ = particle viscosity (Pa s) Pi = sticking probability of the particle group i with average viscosity μ μref = critical viscosity (Pa s) Tps = temperature of the particle (K) NBO/T = ratio of nonbridging oxygens to tetrahedral oxygens (see eq 2) R = ratio of mole fraction network modifiers to the sum of network modifiers and amphoteric (see eq 3) μH = high-temperature viscosity (Pa s) μL = low-temperature viscosity (Pa s) BH = high-temperature viscosity parameter that adopts Senior and Srinivasachar’s coefficient for calculation (see eqs 4 and 5) BL = low-temperature viscosity parameter that adopts Kalmanovitch and Frank’s coefficient for calculation (see eqs 6 and 7) AH = high-temperature viscosity parameter that adopts the parameter BH for calculation (see eq 8) AL = low-temperature viscosity parameter that adopts the parameter BL for calculation (see eq 9)
Conclusions Numerical simulations were carried out for particle/ gas flows, combustion, and slagging on a single swirl coal
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