Kinetics, coal combustion

The presented brief survey of basic mechanisms of NO formation during coal combustion allows the MEIS construction with their simultaneous inclusion in the kinetic constraints. Kinetic constraints can be formulated according to the third way among those considered in Section 3.4. 

The studies on NO formation by the traditional MEIS have been performed at Melentiev Energy Systems Institute for a long time. In parallel with MEIS the use was made of kinetic models and full-scale experiments that assisted in turn to gain information for variant calculations on MEIS. The results of these calculations allowed the conditions for nitrogen oxides formation by different mechanisms to be determined and the ways for improvement of coal combustion technology to increase environmental safety of boiler units to be outlined. 

At the same time calculations on the modified MEIS are possible without additional kinetic models and do not require extra experimental data for calculations, which makes it possible to use less initial information and obviously reduces the time and labor spent for computing experiment. Furthermore, there arise principally new possibilities for the analysis of methods to mitigate emissions from pulverized-coal boilers, since at separate modeling of different mechanisms of NO formation the measures taken can result in different consequences for each in terms of efficiency. Consideration of kinetic constraints in MEIS will substantially expand the sphere of their application to study other methods of coal combustion (fluidized bed, fixed bed, etc.) and to model processes of forming other pollutants such as polyaromatic hydrocarbons, CO, soot, etc. 

The advantage of thermodynam ic models of such complex processes as coal combustion over kinetic ones can be clearly understood, if we briefly deal with the current problems of kinetic description of this process... 

From the above said, it may be concluded that a detailed kinetic model of coal combustion process that combines all three basic processes can not virtually be constructed, as it is impossible to do for each process separately. Therefore, the empirical models based on separation and experimental study of the limiting stages are extensively used. Such models separately do not reveal general regularities and do not allow the generalized conclusions to be drawn. The thermodynamic model makes it possible to study the whole attainability region and hence to consider states of the considered system as a whole and to keep track of the variation in the amounts of any component as a function of some or other kinetic constraints. The latter are written, as was shown above, easily enough even for such complex processes as coal combustion. 

Solomon, P. R., and Serio, M. A., Evaluation of Coal Pyrolysis Kinetics, in Fundamentals of Physical Chemistry of Pulverized Coal Combustion, J. Lahaye and G. Prado (Eds ), Martinus Nijhoff Publishers, 1987. 

Intelligent design of circulating fluidized bed boilers depends on sufficient understanding of the physico-chemical hydrodynamics occurring in the combustors, such as chemical kinetics of coal combustion and pollutant formation, hydrodynamics of gas-solid two phase flow, mixing of gas and solids, distribution of heat released, and heat transfer between immersed... 

Luo, G. A kinetic model of coal combustion in fast fluidized bed, M. S. thesis (in Chinese), Institute of Chemical Metallurgy, Academia Sinica (1990). 

Slovak Technical University, Laboratory of Air Protection Technology (CHTF, 2004), studies on air pollution transport and kinetics of coal combustion in the atmosphere of carbon dioxide are performed. 

Future studies will evaluate the kinetics of combustion and the relative contribution of these oxidized entities in the global analyses related to relevant parameters (1) coal rank, (2) particle size, (3) gas phase transport, (4) catalytic adducts, (5) coal porosity, (6) temperature, (7) pressure, etc. 

Reaction kinetics of coal combustion in oxygen-enriched environment is investigated by non-iso-thermal method in this work. The reaction kinetic equation of coal combustion can be expressed as (Liu et al. 2005, Li 2007, Shan et al. 2005, QI et al. 2010) ... 

Hamor, R Smith, I., and Tyler, R. (1973) Kinetics of combustion of a pulverized brown coal char between 630 and 2200K. Combustion and Flame, 21 (2), 153-162. 

Volatiles produced on pyrolysis burn with oxygen in coal combustion processes either immediately as the volatiles leave the particles or after the volatile Jets break thro a a distance from the particle. The rate of the volatile combustion is controlled in the immediate combustion by rate of pyrolysis while in the delayed combiistion by the rate of mixing with oxygen. Information on the kinetics volatile combiastion is very limited. 

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