Dynamics of Nitrogen Conversion into Volatile Products of Peat Thermal Decomposition
Abstract Generated abstract
This study examines the redistribution of nitrogen during thermal decomposition of raised-bog and lowland peat, a problem relevant to peat processing and interpretations of coal formation. One-gram samples were heated in quartz tubes at 5 degrees per minute to temperatures between 200 and 550°C, and nitrogen contents in the resulting solid residues were determined, with derivatographic data used to characterize nitrogen transfer into volatile products. The results show that nitrogen in solid residues generally decreases up to about 450°C, rises near 500°C, and then declines again, indicating relative nitrogen enrichment of residues at a carbonization stage approaching weakly metamorphosed hard coal. The study also finds that peat type affects nitrogen release, with raised-bog peat transferring a larger fraction of nitrogen to volatile products at 500°C and showing a distinct release-rate maximum near 300°C, while lowland peat exhibits a more complex pattern.
Full Text
DYNAMICS OF NITROGEN TRANSFER INTO VOLATILE PRODUCTS OF THERMAL DESTRUCTION OF PEAT
S. I. SMOLYANINOV, L. N. EREMENKO, V. M. IKRIN, Ya. A. BELIKHMAER
(Presented by the Scientific-Methodological Seminar of the Organic Departments of the Chemical-Technological Faculty)
The question of peat nitrogen and the regularities of its redistribution among the products of thermal decomposition is of very great importance both for the practice of industrial peat processing and for understanding the coal-forming process.
The study of the dynamics of nitrogen release with the volatile products of peat was carried out with two samples, whose characteristics are given in Table 1.
Table 1
Characteristics of peats, %
| Sample No. | Type of peat | Degree of decomposition, % | $W^a$ | $A^c$ | $V^r$ | $C^r$ | $H^r$ | $N^r$ | $O^r$ | $S^r$ |
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | High-moor | — | 11.79 | 4.92 | 75.61 | 56.00 | 4.93 | 1.3 | 37.7 | 0.08 |
| 2 | Lowland | 35 | 9.27 | 16.90 | 68.42 | 53.80 | 5.21 | 2.3 | 38.7 | — |
Thermal treatment of the samples was carried out by the following method. An analytical peat sample weighing 1 gram was heated in a quartz test tube to the specified temperature at a rate of 5 deg/min. Upon reaching the required temperature, the test tube was removed from the furnace and rapidly cooled. The nitrogen content was determined according to GOST 2408-49. The results of the determinations are summarized in Table 2.
Table 2
Change in nitrogen content in solid residues as a function of heat-treatment temperature
| Indicator, nitrogen content in the solid residue, % | 200 | 250 | 300 | 350 | 400 | 450 | 500 | 550 |
|---|---|---|---|---|---|---|---|---|
| High-moor peat | 1.18 | 1.10 | 0.99 | 0.81 | 0.72 | 0.75 | 0.80 | 0.74 |
| Lowland peat | 2.44 | 2.19 | 2.18 | 2.02 | 1.91 | 1.94 | 2.19 | 2.14 |
As can be seen from this table, the nitrogen content in the solid residues decreases with increasing temperature from 200 to 450°C. With further—
With a further increase in temperature, the nitrogen content begins to rise and then falls again. At a temperature of \(500^\circ\mathrm{C}\), a relative enrichment of the solid residues with nitrogen occurs. It is interesting to note that at this temperature the solid residues of the thermal decomposition of peats, in terms of their degree of carbonization, approach weakly metamorphosed hard coals. It follows from this that in coals of the brown-coal stage of metamorphism the nitrogen content should be lower than in coals of the early hard-coal stage. In [1], A. G. Titov indicates that hard coals contain more nitrogen than brown coals.
On the basis of the regularities found, the different nitrogen contents in the hard coals of the Kuzbass and Donbass deposits can apparently also be explained by the fact that the Kuzbass coals were formed predominantly from lowland peats. The Donbass coals, by their origin, are due to the metamorphism mainly of raised-bog peats.
Since the absolute nitrogen content in raised-bog and lowland peats differs noticeably [2], a lower nitrogen content may be observed in weakly metamorphosed hard coals of “raised-bog origin” than in brown coals of “lowland origin.”
Fig. 1. Change in the rate of nitrogen transfer into volatile products as a function of temperature: 1—raised-bog peat; 2—lowland peat
The dynamics of nitrogen transfer into volatile products depends to a significant degree on the nature of the peat. Thus, at \(500^\circ\mathrm{C}\), 59.0% passed into volatile products from lowland peat, and 68.2% from raised-bog peat.
The difference in the behavior of peats is clearly manifested in Fig. 1. The curve of the rate of nitrogen removal, constructed using data from derivatographic analysis, has one well-defined maximum at \(300^\circ\mathrm{C}\) for raised-bog peat, whereas the rate curve for lowland peat has a more complex appearance.
REFERENCES
- N. G. Titov, A. V. Zharkova, L. A. Borozdina. Izvestiya AN SSSR, Otd. tekhn. nauk, vol. 3, p. 359, 1948.
- N. M. Karavaev. Khimiya tverdogo topliva, no. 6, p. 6, 1972.