Tomasz Radko

Isokinetic effect in coal pyrolysis

A method is developed for evaluation of the temperature range to calculate the kinetic parameters of coal pyrolysis. The accuracy of evaluation is estimated. For 12 coal samples of different rank it is shown that pyrolysis in the temperature range 553–853 K is a first-order process with an activation energy of 78–151 kJ mol−1. An isokinetic effect is also observed for the coal samples investigated.

Evaluation of the solutions of a standard kinetic equation for non-isothermal conditions

Abstract It is shown that the method of solving the temperature integral in a standard kinetic equation for non-isothermal conditions affects the value of the estimated activation energy E and the frequency factor A for the known mechanism of conversion. A compensation dependence is suggested as a control test, as well as a kinetic equation solution derived from Coats-Redfern considerations.

The possibility of identification of activation energy by means of the temperature criterion

Abstract The influence of the selection of the f (α) function, which represents the reaction/process mechanism, on the values of the resulting kinetic parameters is discussed. It has been found that the solutions, in the form of the Arrhenius equation constants, show an isokinetic effect over a wide range of temperature. A special relationship between α (degree of conversion), E and T holds for low values of degree of conversion.

Estimation of kinetic parameters based on finite time of reaction/process: thermogravimetric studies at isothermal and dynamic conditions

A method for the comparison of kinetic parameters of reaction/process for thermogravimetric measurements at isothermal and dynamic conditions and processes on a larger scale were considered. It is based on the concept of finite time and corresponding total conversion of the solid phase. The method allows for the determination of Arrhenius parameters without the selection of process mechanism. The results obtained for isothermal and dynamic conditions (comparison between dehydration process and thermal decomposition of calcite) indicate that the values of parameter E in both cases are similar, but values of ln A (the entropic factor) differ from each other. It also has been shown that the method of coke and char preparation notably influences the activation energy values of the CO2 gasification reaction, which is associated with varying degrees of devolatilization and corresponding development of the sample pore surface area.

Influence of initial assumptions on the kinetic models of CO2 gasification of chars and cokes in solid phase

Kinetic studies of CO2 gasification of different materials were carried out using the Geneva method in an apparatus for determining the reactivity of cokes. The main purpose of these studies was parallel analysis of the Boudouard–Bell (B–B) reaction progress on the basis of both solid-phase and gaseous products combined with the mass balance of the process. The kinetic equations involve the conversion degree of the solid (x) or gaseous phase (α) with the kinetic reaction rate constant. It was proved that the mathematical form of the mass balance is similar to the simplest kinetic equation, in which the kinetic constant k is replaced by the known process constant C. Complete kinetic description of the B–B reaction is determined by adopting initial conditions and taking into account the chemical reaction that occurs in a short time interval.

The influence of mineral material upon the coking characteristics of coal

Modelling coal pyrolysis using conventional kinetic methods demonstrates that at temperatures below 1073K the conversion of coal into coke can be treated as two competitive processes which take place in two apparent areas of the kinetic and diffusion range. The relative arrangement of these areas reflects the coking ability of individual coals. It has been shown that the effect of the ash content upon the coking characteristics of the coals investigated can be evaluated using this kinetic-diffusion model.

Estimation of the Parameters Describing the Changes of Conversion Degree Under Polyisothermal Conditions

The possibility of estimation of a slope of the independent variable 1/T, for the observed conversion degree in the form of a [time*temperature] matrix, has been analyzed. It has been shown that for such a case the covariance of time and temperature does not amount of zero; the procedure of estimation of the slope can be simplified by making one of the variables (time) latent.