Experimental data on the composition of burning coal primary products

Transcription

1 Experimental data on the composition of burning coal primary products B P Aduev, D R Nurmukhametov, R Y Yakovlev, Y V Kraft, Z R Ismagilov and A N Zaostrovsky Federal Research Center of Coal and Coal Chemistry SB RAS, Kemerovo, Russia lesinko-iuxm@yandex.ru Abstract. Development of preparation technologies and coal burning is not possible without understanding the coal structure. Investigation of the coal structure, and coal substance behavior under heating will improve the existing technology, furthermore will form deep coal processing technology. The paper expound literature experimental data on the composition volatile products of thermal coal decomposition. Coal products thermal decomposition identification was carried out by gas chromatography-mass spectrometry. A large number of studies on the thermal coal decomposition produced through various pyrolysis reactors. The literature also notes that one of the most promising tools for coal thermal decomposition purposes may be a laser. 1. Introduction For a long time there is a tendency to deterioration in the solid fuels quality burned in power. Proven reserves of solid combustible fuels, particularly coal, enough for the longest period of consumption [1]. There is a need to improve the technology preparation and burning coals. It requires an understanding of the processes taking place under the influence of external factors. The organic part of coal is not thermodynamically stable formation. This part of the coal is undergoing profound change at heating. Weiser's formula has become very popular to reflect the structure of the organic part for bituminous coal (figure 1) [1]. Bond strength atoms unequally in various parts of the basic structural units of the coal organic portion. Coal combustion characteristics depend strongly on the coal rank. Accordingly, the thermal decomposition conditions, the yield and products composition of the thermal coal decomposition of different rank, differ. The coal thermal decomposition begins at temperatures of about 200 C. Gassing begins at temperatures over 200 C. At 300 C begins the resin vapors allocation, formed pyrogenic water. Resin stops formed at about 550 C. At higher temperatures, gas evolution ends from nonvolatile product [3]. In this paper will be discussed, in greater detail, the experimental data on the volatile products composition of coal thermal decomposition. 2. Experimental data Coal products thermal decomposition identification is carried out by mass spectrometry or by gas chromatography-mass spectrometry. The methods are based on determining the mass to charge ratio of the ion.

2 Figure 1. Hypothetical formula bituminous coal [1]. In [4] have been examined a wide range of China's coal, corresponding to all coal ranks. According to the authors, coal thermal conversion can be divided into three stages: below 300 C, 300 to 600 C and from 600 to 900 C. Physically associated moisture and a small amount of adsorbed gases (CO и CO 2 ) released at temperatures below 300 С. Organic part decomposition of coal is not observed up to 300 C. In the temperature range from 300 to 600 C starts organic part decomposition of coal. Coal macromolecules are broken down to form the short-lived free radicals. Free radicals undergo recombination. For low rank coal, the maximum intensity of the unstable products formation is in a lower temperatures zone. As the coal rank increases, this maximum shifts to higher temperatures. In addition to H 2 O, CO и CO 2, are allocated aliphatic and aromatic hydrocarbons. In the third step, at temperatures ranging from 600 to 900 C, only CH 4, H 2 O, CO and CO 2 were detected. Figure 2. Relation between the relative intensity of formation CO + or C 2 H 4 + and the temperature [4].

3 For all coal marks, except anthracite, in the temperature range from 360 to 560 C, formation of benzene, toluene and xylene observed. For fat, gas fat coals, in the temperature range from 360 to 500 C, the naphthalene formation was observed. For gas coal in the same temperature range, revealed the formation of methylnaphthalene, acenaphthylene and naphthalene. Methane is formed in all coal marks in a wide temperature range from 360 to 800 C. In high sulfur coal marks, in the temperature range from 400 to 600 C, revealed the formation of S +, HS +, H 2 S +, SO 2 +. In [4], the authors are not focused on the stable products detection. Physically bound moisture is released in all coal marks by heating to 300 C. At temperatures above 300 C, some pyrogenetic water released due to decomposition of various oxygen-containing groups, mainly -OH groups. There is a rise in temperature at which water stands out, with an increase in coal rank. As mentioned above, the mass spectrometry do not study molecular mass. Mass spectrometry techniques study the ratio of the mass to ion charge. Some of the ions having the same ratio of M/Q is not distinguishable. The relation between the relative intensity of formation CO + or C 2 H 4 + (M/Q = 28) and the temperature is shown in figure 2. Particular attention should be paid to polycyclic aromatic hydrocarbons (PAHs). Many of these are especially toxic and carcinogenic. In [5] performed an analysis of a wide range PAHs in various coal mark from eleven coal basins worldwide. Analysis of the components was carried out using gas chromatography-mass spectrometry. 52 PAHs was identified (figure 3). Figure 3. List of identified PAHs [5] Concentrations of extractable PAHs ranged between 14 and 2090 mg kg -1. The concentrations of high molecular (HMW) PAHs weight ranged from 1 to 94 mg kg -1. The highest concentrations of HMW-PAHs were recorded in the inertinite-rich coal marks. Relationship between vitrinite reflectance (R 0 ) and the concentrations of extractable PAHs in coals from different basins is shown in figure 4. It should be noted that the concentration of aromatics in the coals increased with increasing coal ranks, while the concentration of aliphatic and oxygen-containing fractions decreased. Figure 5 is a ternary plot showing the composition of coal pyrolyzates.

4 Figure 4. Relationship between vitrinite reflectance (R0) and the concentrations of extractable PAHs in coals from different basins [5] Aromatic fraction includes PAHs, biphenyl, and their alkylated derivatives. Aliphatic fraction contains alkanes and alkenes. Oxygen containing fraction consists of phenol, dibenzofuran, and their alkylated derivatives. It has been shown that aliphatic compounds were dominant in the liptinite-enriched samples. Aromatic compounds were more abundant in the inertinite-rich samples. Research has shown that dominant components are low molecular weight (LMW) PAHs, containing 2-3 rings, irrespective of the coal origin. Only in the anthracites the higher molecular weight (4-6 ring) PAHs dominated. Figure 5. Ternary plot showing the composition of coal pyrolyzates [5]. It is necessary to highlight the work [6]. This study was conducted PAH determination in different coal ranks of the Kuznetsk coal basin. Revealed conical relationship between vitrinite reflectance (R 0

5 = %) and the total PAH composition. The maximum of the curve corresponds to R 0 = %. As in the previous study, noted an increase in HMW-PAHs with increasing coal rank. A large number of studies on the thermal coal decomposition produced through various pyrolysis reactors. The literature also notes that one of the most promising tools for coal thermal decomposition purposes may be a laser. It was shown in several experiments [7-9]. Large energy density ( W/mm 2 ) when exposed to a coal particles (up to 0.2 mm) leads to intensive thermal destruction and active allocation of volatile products with high speed (up to 0.1 seconds). The laser beam can create on the surface of coal particle temperature about C. Laser ignition of coal produced in recent studies [10, 11]. Lignite of Kaychaksky deposits were used as samples. Samples were used as in the form of compressed tablets and in powder form. Size fraction of pulverized coal was less than 100 microns. Authors have found non-elementary nature of the spectral-kinetic curve, which indicates about evaporation and ignition of volatile matter when exposed to radiation. It also indicates the chemical reactions after exposure pulse. The study [12] analyzed the coal based on gas chromatography and mass spectrometry of laser pyrolysis products. It is noted that the products composition differs from the products of benzoic extraction and thermal desorption. According to the results, in the laser pyrolysis products predominate condensed aromatic compounds. There are also smaller unsaturated compounds (styrene, propylene, acetylene, etc.). 3. Conclusion It should be noted that the coal is not only energy fuel, but also a valuable raw material for chemical industry. Hydrocarbons contained in the coal at pyrolysis is not combusted and released from the coal as a gas or liquid fractions. Due to modern technology it is possible to produce more than 130 kinds of chemical intermediates from coal. Chemical intermediates can be used to produce more than 5 thousand kinds of products [13]. According to [14] the chemical industry dependence in 2013 on imports of raw materials amounted to 17.3%. Coal deep processing can significantly reduce imports of raw materials for the chemical industry. The development of coal technology deep processing is impossible without the concepts of composition and coal organic structure. Accordingly, it is necessary to make a research of the thermal decomposition products composition (including laser pyrometer) of the Kuznetsk Basin coals. References [1] Energy Strategy of Russia for the period till 2030 Available at: (Accessed 11 April 2016) [2] Lipovich V G 1988 Himija i Pererabotka Uglja [Chemistry and Coal Processing] (Moscow: Chemistry Publ.) 336p [3] Agroskin A A 1969 Himija i Tehnologija Uglja [Chemistry and Coal Technology] (Moscow: Subsoil Publ.) 240p [4] Li X 2003 Investigation of pyrolysis of Chinese coals using thermal analysis/mass-spectrometry Journal of Thermal Analysis and Calorimetry [5] Laumann S 2011 Variations in concentrations and compositions of polycyclic aromatic hydrocarbons (PAHs) in coals related to the coal rank and origin Environmental Pollution [6] Habibulina E R 2015 PAHs determination in the coals of different metamorphic grade by HPLC IV Konferencija molodyh uchenyh «Aktual'nye voprosy uglehimii i himicheskogo materialovedenija [Proc. 4th Conf. Topical issues of Coal Chemistry and Chemical Materials ] 2015 Kemerovo p 20 [7] Chen John C 1995 Observation of laser ignition and combustion of pulverized coals Fuel [8] Mingchang Q 1996 Ignition and combustion of laser-heated pulverized coal Fuel [9] Taniguchi M 1996 Laser ignition and flame propagation of pulverized coal dust clouds Twenty-

6 Sixth Symposium (International) on Combustion pp [10] Aduev B P 2015 Brown coal ignition by laser pulses from a neodymium laser in the freerunning mode Uglehimija i jekologija Kuzbassa: Mezhdunarodnyj Rossijsko-Kazahstanskij simpozium [Int. Russian-Kazakh Symp.: Coal chemistry and Kuzbass ecology] 2015 Kemerovo p 9 [11] Aduev B P 2015 Spectral and kinetic features of brown coal ignition by nanosecond laser pulses Uglehimija i jekologija Kuzbassa: Mezhdunarodnyj Rossijsko-Kazahstanskij simpozium [Int. Russian-Kazakh Symp.: Coal chemistry and Kuzbass ecology] 2015 Kemerovo p 10 [12] Janitschke W 2000 Investigations of coals by on-line coupled laser desorption: gas chromatography: mass spectrometry (LD:GC:MS) Journal of Analytical and Applied Pyrolysis [13] Development program of innovative territorial cluster "coal complex processing and industrial waste" in Kemerovo region Available at: (Accessed 18 April 2016) [14] Berezinskaja O 2015 Production dependence on imports of Russian industry and the mechanism of strategic import substitution Voprosy Jekonomiki [Economics Questions] (1)