EFFECT OF BERTINATION ON THE KINETICS OF THERMAL DESTRUCTION OF ITAT BROWN COAL

Ya. A. Belikhmaer, K. K. Stramkovskaya

(Presented by the scientific-methodological seminar of the CTF)

The process of thermal destruction of coals is distinguished by a special specificity, determined by the unknown chemical composition of the coal substance and by the complexity of the combination of various phenomena. The specificity of the process of thermal destruction of the coal substance makes it necessary, in its experimental study, to regard the obtained characteristics of the process as effective, averaged ones [1].

Very often the kinetics of thermal destruction is judged by the evolution of volatile products during coal heating. The effective rate of the process of evolution of volatile substances from coal under conditions of a linear temperature rise can be represented mathematically as the sum of the rates of individual reactions:

\[ \left(\frac{dx}{dt}\right)_{\mathrm{eff}} = \frac{dx}{dt}\,(E_1 x_1 K_{0_1}) + \frac{dx}{dt}\,(E_2 x_2 K_{0_2}) +\ldots+ \frac{dx}{dt}\,(E_n x_n K_{0_n}), \]

where \(E\) is the activation energy of an individual reaction;
\(x\) is the concentration of reaction groups;
\(K_0\) is the pre-exponential factor.

Since in the process of thermal destruction of coal the weakest bonds are broken and the strongest chemical bonds accumulate, the kinetics of the process is characterized by a continuous increase in the activation energy: [2].

\[ E_n > E_{n-1} > E_{n-2} > \ldots > E_1. \]

If the group of reactions proceeding at low temperatures is excluded from the process of thermal destruction, i.e., if preliminary bertination of the coal is carried out, then the effective activation energy of the process should increase. It is clear that this statement will be valid if the process of evolution of volatile products from bertinated coal is described by a formal reaction equation of the same order. This conclusion is very clearly illustrated graphically (Fig. 1).

Fig. 1. Change in the rate of evolution of volatile products during a linear temperature rise. \(a\) — initial coal, \(b\) — bertinated coal.

A more intense increase in the rate with increasing temperature for bertinated coal indicates a higher value of the effective activation energy.

The kinetics of the release of volatile products during the thermal destruction of Itat brown coal was studied by the derivatographic method. The experimental procedure and the method for calculating kinetic parameters from the derivatogram were described by us earlier [3, 4]. Preliminary thermal treatment of the coal was carried out at 200, 250, and 300°C for 30 min. The experimental results are presented in Fig. 2.

Fig. 2. Dependence of \( \lg K_{\mathrm{eff}} \) on \(1/T\) for the process of release of volatile products.
1. Coal bertinated at 200°C. 2. Coal bertinated at 250°C. 3. Coal bertinated at 300°C.

In one of our papers [4] it was shown that, up to a temperature of 470°C, the rate of the process of release of volatile substances during the thermal destruction of Itat brown coal is described by the equation of a first-order reaction:

\[ \frac{dx}{d\tau}=K_0 \cdot e^{-\frac{E_{\mathrm{eff}}}{RT}}\cdot (x_0-x_\tau), \]

where \(x_0\) is the initial coal charge;
\(\quad x_\tau\) is the coal charge at time \(\tau\);
\(\quad E_{\mathrm{eff}}\) is the effective activation energy of the process;
\(\quad K_0\) is the preexponential factor.

As can be seen from Fig. 2, the rate of the process of release of volatile substances during the thermal destruction of bertinated coal is also described, up to a temperature of 470°C, by the equation of a first-order reaction. It is also evident from this that, with an increase in the bertination temperature from 200 to 300°C, the effective activation energy increases from 8.7 to 15.8 kcal/mole. Thus, the experimental studies confirm the theoretical conclusion that bertination increases the values of the effective activation energy of the process of thermal destruction of brown coal.

Conclusion

It has been shown that preliminary heat treatment changes the kinetic parameters of the process of thermal destruction of coal.

References

1. D. M. Lisin, K. A. Matasova. Diffusion-kinetic studies of the thermal destruction of coal substance in a layer. Izv. SO AN SSSR, No. 7, 1962.

2. Z. I. Syunyaev, I. D. Voloshin. On the kinetics of thermal decomposition of solid carbonaceous substances. Izv. vuzov, “Neft i gaz,” 4, 1967.

3. K. K. Stramkovskaya, Ya. A. Belikhmaer. Vertinization of brown coals of the Itatskoye deposit. Izv. TPI, vol. 148, 1967.

4. Ya. A. Belikhmaer, K. K. Stramkovskaya. On the question of the kinetics of thermal decomposition of solid fuels. Izv. TPI (in press).