Coal pyrolysis in a rotary kiln: Part II. Overall model of the furnace

Abstract

In order to simulate coal pyrolysis in a rotary kiln in the steady-state regime, a mathematical model has been developed which calculates the temperature profiles in the charge, the gas, and the furnace walls, together with the gas composition and the degree of removal of volatile species. The model takes into account the principal physicochemical and thermal phenomena involved, including the complex movements of the charge; the gas flow; heat transfer between the charge, the gas phase, and the furnace walls; drying and pyrolysis of the coal; the cracking of tars; the combustion of volatile species; and the combustion and extinction of the coke. The data necessary for the model were obtained by specific experiments or from the literature. The model has been validated by comparing its predictions to measurements performed on an industrial rotary kiln. The model has been used to study the influence of operating parameters such as the furnace rotation speed, in order to optimize the process. It is shown how a modification to the extinction zone leads to an increase in coke yield of 0.75 pct.

Coal pyrolysis in a rotary kiln: Part I. Model of the pyrolysis of a single grain

“…Nevertheless, this article. [22] it will be seen in Part II of this article that ⌬ r H pyro influences the temperatures in the overall model of the rotary kiln.…”

“…The (3) and a grain inside the charge, which does not exchange calculations concern a grain 20 mm in diameter, heated at heat with its neighbors, assumed to be at the same either 8.7 or 27.7 K min Ϫ1 . Over the range of values tested, temperature, the enthalpy of pyrolysis and the thermal emissivity of the grain have practically no influence, either on the maximum N q R ϭ 0 [22] temperature difference between the center and surface (⌬T max ) or on the time taken to attain an overall conversion The way these different heat exchanges and the correspondof 0.99 (t X pyro ϭ 0.99 ). A more-precise determination of ⌬ r H pyro ing coefficients are calculated is described in Part II of and gr does not, therefore, seem necessary.…”

The rotary kiln: An investigation of bed heat transfer in the transverse plane

“…(1) The average particle diameter: [1] (2) The normalized standard deviation : [2] As given in Table I, the ranges for and were, respectively, 1.2 mm to 3.0 mm and 0.09 to 0.29. Based on qualitative visual observation after each trial, segregation occurred with all mixes, but was most evident for mixes 1 and 2, which had the largest values.…”

“…Heat transfer to the exposed and covered bed surfaces has been the subject of numerous studies, [1,2,3] and it is generally accepted that regeneration by the refractory wall is significant only when heat-transfer conditions to the exposed bed surface are relatively weak; i.e., at low to moderate freeboard gas temperatures where convection is the primary mechanism for heat transfer. Radiation to the exposed bed surface increases rapidly as the gas temperature exceeds ϳ1000 °C and is the dominant mechanism over the majority of the kiln length.…”

Process simulation of activated carbon production using a rotary kiln

“…Coal pyrolysis in a rotary kiln has been modeled to examine the role of operating parameters, such as the kiln rotation speed for the process optimization [2,3]. A review of charcoal production technology was published to explain the production technique and its relation to the charcoal properties [4].…”