STUDY OF THE FEATURES OF PRODUCING PEAT THERMAL BRIQUETTES ON A PILOT-SCALE UNIT

S. G. MASLOV, S. I. SMOLYANINOV, A. V. SHKURIN

(Presented by the Scientific-Methodological Seminar of the Organic Departments of the Faculty of Chemical Technology)

Thermal briquetting is currently regarded as a promising method for producing metallurgical and household fuel based on milled peat. Earlier work carried out under laboratory conditions revealed the main technological factors of thermal briquetting and the principal aspects of the mechanism of this process [1—7].

The purpose of this work was to study the features of producing peat thermal briquettes on a pilot-scale unit. The experiments were carried out with air-dry peat from the Tagan deposit of Tomsk Oblast, which had the following characteristics: degree of decomposition—35%; \(W^a\)—11.11%; \(A^c = 8.72\%\); \(V^r\)—68.42%; \(S^c\)—0.10%; \(C^r\)—59.27%; \(H^r\)—6.10; \(N^r\)—2.74%; \(O^r\)—31.89%.

The peat was heated to the thermal-briquetting temperature in a rocking retort furnace of the system of the Kuznetsk Branch of VUKhIN at a rate of 200—300° per minute. Briquetting was carried out in a heated die 60 mm in diameter on a P474A hydraulic press. The briquettes obtained were tested for resistance to crushing and abrasion. For each point, 5—10 tests were performed. The values found were processed by methods of mathematical statistics. The root-mean-square error ranged from 2 to 10%, and the probable error of the arithmetic mean at a confidence level of 0.05 lay within the range from 6 to 11 kg/cm².

The influence on the strength properties of thermal briquettes of the following factors was studied: the temperature of peat heating before the application of pressure, the holding time of the heated peat before the application of pressure and under pressure, and the magnitude of the briquetting pressure. The results obtained are presented in Fig. 1.

It follows from them that, with an increase in the peat heating temperature, the strength of the thermal briquettes increases, reaches a maximum at 290°C, and then begins to decrease (curve 1), i.e., as was to be expected, the character of the dependence of the strength of thermal briquettes on temperature remained the same as according to data obtained on laboratory units [1,2].

However, it is interesting to note that the optimum temperature of thermal briquetting in the second case is lower (270°C), even under conditions of high-speed heating (Table 1), although the rate of peat heating on the pilot-scale unit is significantly lower than on the laboratory unit and, proceeding from the theory of high-speed heating of fuels and the theory

Fig. 1. Dependence of the strength of thermal briquettes on a number of technological factors:
1 — peat heating temperature; 2 — briquetting pressure; 3 — holding time under pressure; 4 — holding time before the application of pressure.

In thermal briquetting, the optimum temperature should be the higher, the greater the heating rate [7, 8].

This apparent contradiction, in our view, can be explained by the increase in the size and mass of the thermal briquettes. The greater the mass of the peat being pressed, the greater the difficulties in removing the gaseous products of the thermal decomposition of peat. The briquette delaminates and even “explodes.” For this reason, pressure has to be applied not during the period when the optimum level of the thermal-decomposition reactions of peat is reached, which ensures the production of briquettes of maximum strength, but somewhat later, when gas formation becomes less significant.

The dependence of the strength of thermal briquettes on the holding time of the heated peat before the application of pressure has the previously established character [1], i.e., as the holding time increases it rises, reaches a maximum, and then falls (curve 4). It follows from Table 1 that the optimum holding time in both cases is 120 sec, although, on the basis of the theory of high-speed heating and the theory of thermal briquetting [7, 8], in the case of the enlarged unit it should be considerably shorter.

Table 1

Optimum conditions for obtaining peat thermal briquettes

This fact can also be explained if one takes into account the difficulty of gas release in producing briquettes on the enlarged unit, owing to the considerably greater volume of the mass being pressed.

Figure 1 (curves 2, 3) presents the results obtained in studying the dependence of the strength of thermal briquettes on the briquetting pressure and the holding time under pressure. As was to be expected, the character of the dependence and the optimum values of the indicated factors (Table 1) remained similar to those obtained earlier on laboratory units [1, 2].

From all of the foregoing it may be concluded that increasing the size and mass of the thermal briquettes obtained has a noticeable effect on the optimum values of a number of technological factors, such as the temperature of preliminary heating of the peat and the holding time before pressure is applied; by contrast, the optimum values of the briquetting pressure and of the holding time under pressure, obtained on enlarged units, can be transferred to larger aggregates.

REFERENCES

1. S. I. Smolyaninov, V. E. Voronin, Peat Industry, 426, 1962.

2. S. I. Smolyaninov, A. M. Denisov, Izv. TPI, 112, 82, 1963.

3. S. I. Smolyaninov, S. G. Maslov, G. G. Krinitsyn, Izv. TPI, 196, 143, 1969.

4. S. G. Maslov, S. I. Smolyaninov, Proceedings of the 1st Conference of Young Scientist-Chemists of Tomsk, 1970, p. 214.

5. S. I. Smolyaninov, S. G. Maslov, G. G. Krinitsyn, Izv. TPI, 163, 1970.

6. S. G. Maslov, S. I. Smolyaninov, N. M. Smolyaninova, I. A. Oshchepkov, Izv. TPI, 175, 102, 1971.

7. S. I. Smolyaninov, S. G. Maslov, Chemistry of Solid Fuel, 4, 76, 1971.

8. A. P. Kashurichev, Z. F. Chukhanov, Report of the Academy of Sciences of the USSR, vol. 101, No. 1, 115, 1955.