Bertination of Brown Coals from the Itatskoye Deposit

K. K. Stramkovskaya, Ya. A. Belikhmaer

(Presented by the Scientific-Methodological Seminar of the Chemical-Technological Faculty)

The initial stage has a significant influence on the entire subsequent course of the process of thermal decomposition of solid fuel. In this connection, the study of the initial stage of decomposition is of special theoretical interest for understanding the primary processes of the thermal destruction of fuel, as well as the processes of formation of the products obtained in the subsequent stages of pyrolysis. At the same time, consideration of this process is also of great practical importance. Thus, the literature contains many works in which the positive effect of thermal preparation (bertination) of coal charges on the yield and quality of coke has been shown [1, 2, 3]. Preliminary heat treatment at 200°C makes it possible to increase the productivity of coke ovens by 40% and to shorten the coking period by 4 hours [4]. The organization of the process of thermal processing of fuel in power-engineering schemes by stages may serve as one of the ways of controlling it [5].

However, the initial stage of thermal decomposition of fuel has been studied far from completely. The process of bertination of peat under conditions of rapid heating has been investigated most thoroughly [6, 7]. There are several works on the thermal preparation of brown coals [8, 9]. In this direction, little study has been made of the brown coals of the Itatskoye deposit, which, in their comprehensive utilization, may serve as a source of valuable chemical raw material.

The aim of the present work was to study the process of bertination of Itatskoye brown coal, the characteristics of which are given in Tables 1 and 2. We have also given a derivatographic evaluation of these coals, since this method makes it possible to study the dynamics of the process of thermal destruction of fuel. The principle of derivatography consists in the simultaneous recording, during heating, of the integral curve of change in the weight of the sample, TG, the rate of change in weight, DTG, and the thermophysical properties (thermal effects), DTA.

The experiments were carried out on a derivatograph of the F. Paulik, J. Paulik, and L. Erdey system [10]. The heating rate of the sample was 5 deg/min; aluminum oxide was used as the inert sample. To create an inert medium, nitrogen purified over copper turnings at 500°C was continuously supplied to the electric furnace.

Figure 1 shows the derivatogram of the original coal. From the course of the DTG curve it is evident that Itatskoye brown coal is characterized by two pronounced maxima at temperatures of 180 and 470°C. The maximum on the DTG curve and the negative thermal effect on the DTA curve at 180°C signify

Table 1

Table 2

Yields of semicoking products
(in % of the dry coal substance)

the removal of hygroscopic and colloid-bound moisture. From the DTG curve it is evident that volatile products of thermal decomposition begin to be released from this coal at a temperature of 300°C, while the maximum

Fig. 1. Derivatogram of the original coal.

Fig. 2. Derivatogram of coal bertinated at 200°C.

rate of their release is observed at 470°C. Then the rate of release of volatile products decreases and, beginning at a temperature of 650°C, remains practically constant.

The endothermic effect of the maximum rate of release of volatile products on the DTA curve is shifted in time relative to the maximum on the DTG curve and appears at a temperature of 500°C. An exothermic effect is observed at 340°C. Beginning at 550°C, the process of coal decomposition proceeds with the release of heat, having a small negative thermal effect at 600°C. The data obtained from the derivatographic study of the initial coal showed that bertination should be carried out at temperatures not higher than 300°C.

Table 3

Yields of bertination products (in % of the dry coal substance)

The method of coal bertination was as follows. A quartz reactor with a 15 g coal charge was placed in a tubular furnace. The rate of temperature rise was maintained strictly at 5°/min by means of a program regulator. Upon reaching the specified temperature, the charge was held under isothermal conditions for 30 minutes. The water released during the decomposition process was trapped by a condenser, and the gaseous products were collected in a gasometer. Gas analysis was carried out on a VTI-2 and an KhT-2M chromatograph. Bertination was carried out at temperatures of 200, 250, and 300°C.

The results of the experiments are presented in Table 3, from which it is clear that, with increasing temperature, the yield of solid residue decreases and the yield of pyrogenetic water and gas increases. The bertination gas at 200°C consists of 92.5% CO₂ and 7.2% CO. With an increase in the process temperature, the content of combustible components in the gas increases and the CO₂ content decreases. At 300°C, 7.43% of the dry mass of the fuel passes into volatile products, of which 3.9% is CO₂ and 0.8% is CO.

The solid residue after thermal treatment at the indicated temperatures was subjected to derivatographic analysis. The derivatograms of the bertinated coal show that on the DTA curves (Figs. 2, 3, 4) the endothermic effect disappears, which in turn indicates complete removal of moisture upon heating to 200°C.

In both the initial and the thermally treated coal, the maximum rate of release of volatile products is found at a temperature of 470°C. The solid residue evidently has a highly developed surface. This is indicated by the appearance on the DTG curve (Figs. 3, 4) of a small maximum (increase in weight), which is associated with the sorption of nitrogen from the system. Bertinated coal is very reactive. Thus, upon brief contact with air it sorbs oxygen, which during secondary heating leads to the presence of processes with a positive thermal effect. In experiments with loading of the sample in a stream of nitrogen, such thermal effects are absent (Fig. 4, DTA-a curve). These

data show that the further course of pyrolysis will be influenced not only by the temperature of thermal treatment, but also by the conditions under which it is carried out. Contact of the bertinated residue

Fig. 3. Derivatogram of coal bertinated at 250°C.

Fig. 4. Derivatogram of coal bertinated at 300°C. a) with loading of the sample in a stream of nitrogen.

with air will apparently have a substantial effect on the quality of the subsequent pyrolysis products.

Table 4

Composition of the bertination gas

Conclusions

1. Bertination of Itatskoye brown coal was carried out under slow heating in the temperature range 200—300°C; the yields of the products were determined and the gas was analyzed.

2. Derivatographic analysis was performed for the initial coal and the solid residues.

References

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2. G. N. Makarov, A. M. Zagorets, V. N. Kudryashov et al. Coking in a ring furnace of a preliminarily heated coal charge. Coke and Chemistry, No. 4, 30, 1965.

3. E. P. Starke, D. M. Lisin. On the causes of the positive effect of thermal preparation of coals on coke quality. Proceedings of KhMI SO AS USSR, issue 16, 53, 1961.

4. N. S. Gryaznov, I. M. Lazovsky, M. G. Feldbrin. Preparation of coals for coking by preliminary heating and rational crushing. Coke and Chemistry, No. 11, 10, 1962.

5. E. A. Shapatina, V. V. Kalozhny, Z. F. Chukhanov. Rate of the process of release of volatile substances during thermal decomposition of the organic mass of fuel. Doklady of the USSR Academy of Sciences, 22, No. 5, 869, 1950.

6. L. P. Malashenko, E. A. Shapatina, N. D. Edemskaya, M. A. Orlova. On the bertination of peat under conditions of high-speed heating. Proceedings of IGI, vol. 17, 21, 1962.

7. M. Ya. Dalbin, V. Ya. Bayars. Experiments on studying the process of high-speed bertination of peat with a gaseous heat carrier. Proceedings of the Institute of Chemistry, Academy of Sciences of the Latvian SSR, vol. 2, 122, 1958.

8. V. V. Kalozhny. High-speed bertination of solid fuels. In: Energy-Technological Utilization of Fuel, issue 1, 68, 1960.

9. E. I. Kazakov, A. A. Tyazhelova, L. P. Malashenko. Chemical processing of fuels. Publishing House of the Academy of Sciences of the USSR, 98, 1957.

10. F. Paulik, J. Paulik, L. Erdey. A new complex thermoanalytical method—derivatography. PRESTO Publishing House, Budapest, 1956.