Flame coal

A.B. Hedley and E.W. Jackson. A Simplified Mathematical Model of a Pulverized Coal Flame Showing the Effect of Recirculation on Combustion Rate. J. Inst. Fuel, 39 208,1966. 

L.S. Pedersen, P. Glarborg, K. Dam-Johansen, P.W. Hepburn, and G. Hesselmann. A Chemical Engineering Model for Predicting NO Emissions from Pulverised Coal Flames. Combust. Sci. Techn., 132 251-314,1998. 

Measure radiant furnace heat profile This will enable the comparison of the heat absorption profiles of SRC and coal flame and will also provide the necessary information to make judgements on the adequacy of furnace cooling surfaces. 

In this work the mode of occurrence of coal silicate minerals, and the flame induced vitrification and sodium initiated sintering mechanisms have been studied. The pulverized coal flame temperature is sufficiently high to vitrify the quartz particles. 

Table II shows that the small irregularly shaped particles transform to spheres in coal flame when the viscosity of the material is several orders higher than that required for bulk flow under gravity, which is about 25 N s m". A laboratory technique was used to determine the minimum temperature at which coal mineral species are transformed to spherical shapes (17). Particles of 10 to 200 pm in diameter were introduced into a gas stream and then passed through a vertical furnace. The temperature of the furnace was varied from 1175 to 2025 K and was measured by a radiation pyrometer and by thermocouples placed in the furnace. The residence time of particles in the furnace was between 0.2 and 0.5 sec. depending on the particle size.

The coal sodium originally present as chloride and organo-metallic compounds is rapidly volatilized in the pulverized coal flame <23). Subsequently the volatile species are partly dissolved in the surface layer of flame heated silicate particles and partly sulphated in the flue gas (8). The formation of sodium sulphate can proceed via two routes ... 

Some potassium sulphate can also be formed via the two routes. Potassium is present in coal chiefly in the form of potassium alumino-silicates (Table I) and a large part of the alkali-metal will remain involatile in the flame heated silicate particles. Some 5 to 20 per cent of the potassium is released for sulphation (24) which takes place partly at the surface of the parent particles (25) and partly via the volatilization routes as described above. However, sodium sulphate content of fly ash heated in pulverized coal flame, and chimney solids is always higher than that of potassium sulphate. 

The mineral matter in coal consists chiefly of silicate, sulphide, carbonate species, and chlorides and organo-metallic compounds associated with the fuel substance (1,2). The silicate mineral particles vitrify partially or completely, in the pulverized coal flame ( 3), and thus the silicate ash fraction of the initial deposit consists of particles of variable amounts of a glassy phase and crystalline species ( ). 

The effective emissivity and transmissivity of coal flames were measured in situ, although the scattering effects were not accounted for in detail [232-236], These data are best suited for use in zonal method calculations and cannot be employed readily in differential models of the radiative transfer equation. Therefore, they cannot be considered very useful for the present or next-generation modeling attempts. However, it is possible to use this information to vali-... 

A. Lowe, 1. M. Stewart, and T. F. Wall, The Measurement and Interpretation of Radiation from Fly Ash Particles in Large Pulverized Coal Flames, Seventeenth Symposium (International) on Combustion, Combustion Institute, Pittsburgh, pp. 105-112,1979. 

Lockwood, F. C., and Mahmud, T. "The Prediction of Swirl Burner Pulverized Coal Flames." 22nd Symposium (International) on Combustion. The Combustion Institute, Pittsburgh, PA, 165-73,1988. 

Lockwood, F. C., Mahmud, T., and Yehia, M. A. "Mathematical Modelling of Some Semi-Industrial Pulverized Coal Flames." The Eighth Annual International Pittsburgh Coal Conference, 41-46, 1991. 

Sample comparison of measured and theoretical CARS spectral profile for a coal flame. 

Images of air only and oxygen-enhanced coal flames on one of 16 burners in a 125 MW coal fired utility boiler. (From Bradley, J. L., Bool, L. E., and Kobayashi, H., 29th International Technical Conference on Coal Utilization and Fuel Systems, Clearwater, FL, 2004. With permission.)... 

PHYSICAL PROPERTIES dark-brown to black solid dispersed in air physical properties vary depending upon the specific coal type lignite is distinguished as a soft brown coal bituminous coals can be classified according to their degree of carbonification into flame coal, flame-gas coal, gas coal, fat coal, steam coal, lean coal and anthracite the carbonaceous content rises from 50 to 91.5%, the oxygen content falls from 44 to less than 2.5%, and the moisture content from 6 to less than 3.8% in the sequence wood, peat, brown coal, bituminous coal, anthracite soft brown coal contains 30-65% moisture, bituminous coals may contain up to 7% moisture and up to 30% ash spectroscopy and chemical analyses show that bituminous coal is predominantly of aromatic character material is insoluble in water. 

PHYSICAL PROPERTIES dark-brown to black solid dispersed in air physical properties vary depending upon the specific coal type lignite is distinguished as a soft brown coal bituminous coals can be classified according to their degree of carbonification into flame coal, flame-gas coal, gas coal, fat coal, steam coal, lean coal and anthracite the carbonaceous content... 

Raask, E., 1984. Creation, capture and coalescence of mineral species in coal flames. J. Inst. Energy 57 231-239. 

Fuel NO typically accounts for 75-95% of the total NOx accumulation in coal flames. Nitrogen in coal is predominantly found as a heteroatom in aromatic rings. Nitrogen primarily evolves from tars as HCN, with much... 

In a typical coal flame, char retains a significant fiaction (30-60%) of the initial nitrogen. NO formation during char reactions often accoimts for 20-30% or more of the total NO formed. 

Coarser alite (average = 50 to 60 pm) with a few large inclusions Longer coal flame (Kramer, 1960)... 

Most models assume that the fuel-bound nitrogen that is released by the devolatilization of coal is in the form of HCN, or some instantaneous transforms of HCN, which in turn form the base species of NO formation. It is believed that the HCN not only contributes to fuel NOx formation but also to some destruction of NOx and that the net formation might depend on the chemical as well as the thermal state of the mixture. The global chemical reactions involved for coal flames might therefore be expressed as... 

Reactions (6.57) and (6.58) are important and reaction (6.59) is significant only under highly fuel rich conditions. The reaction step (6.59) is usually neglected for coal combustion because coal flames are normally very lean in fuel. 

B. M. Visser. Mathematical Modeling of Swirling Pulverized Coal Flames. PhD Dissertation, IFRF, 1991. 

Testing showed no appreciable impact on flame temperature, upper furnace temperature, or flame intensity when firing petroleum coke with high sulfur coal. Flame intensity decreased when firing petroleum coke briefly with low sulfur coal. Similarly, there were no operability issues main steam and reheat steam temperatures did not decrease, and maintaining load was not at issue [34]. 

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