Comprehensive Scheme of the Lignite Waste Recycling Using Electromagnetic Microwave Radiation

COMPREHENSIVE SCHEME OF THE LIGNITE WASTE RECYCLING USING ELECTROMAGNETIC MICROWAVE RADIATION

O. DANILOV*, A. TASKIN*, I. GREBENYUK* AND A. BELOV*

* Far Eastern Federal University (FEFU), 10 Ajax Bay, Russky Island, 690922, Russia

SUMMARY: A new method of complex utilization of the most common waste of coal industry (coal dust), which allows to use the potential of both organic and mineral constituents of solid fuel, is proposed in this work.

1. INTRODUCTION

The reserves of brown coal are very significant in a global scale. In Russia, more than half of the balance reserves of fossil coals (194.6 billion tons) consist of brown coal. As in any other industry, in coal mining there are both commodity product used as fuel in the energy sector and waste represented by substandard carbon-containing fossil fuels. Brown coal are characterized by a tendency to oxidation, rapid loss of strength and destruction after mining in environmental conditions (by the formation of coal dust). Wastes are strongly oxidized coals, comprising up to 6% of all stocks of solid fuel. They, as a rule, accumulate in dumps together with empty rocks, or are left in the seams. A simple calculation of the volume of lignite waste in the Russian Federation shows that they are very significant - more than 5.8 billion tons. Such volumes of coal should be used rationally, it is necessary to reveal their potential as a secondary raw material for practical use in technological redistribution and to solve the problem of utilization, through the development of integrated processing schemes. Technological and research work in this direction is conducted both in various foreign countries, for example, the USA, Australia, France, and in the Russian Federation. The solution of the problem of recycling and processing of lignite waste will solve an entire range of issues related to environmental protection, saving energy and natural resources, creating new jobs. At the same time, when developing technological solutions for waste processing, it is necessary to consider that their energy consumption should be less, or comparable with the processing of natural raw materials and have a positive technical and economic efficiency. Electromagnetic microwave radiation has international recognition and is widely used in various industries (chemical, mining, etc.) and allows to reduce energy consumption and dramatically improve the technical and economic efficiency of production. Therefore, based on the abovementioned material, we can conclude that the theme of the

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 research has the necessary degree of novelty and relevance.

2. COMPREHENSIVE SCHEME FOR THE UTILIZATION OF LIGNITE WASTE USING ELECTROMAGNETIC MICROWAVE RADIATION

2.1 Schematic diagram of the utilization of lignite waste using electromagnetic microwave radiation

For effective utilization and processing of brown coal dust, the authors offer the following complex technological scheme: waste → active coal → use of active coal in various technological processes → active coal (waste) → extraction of rare and noble metals → burning of the recieved waste in an underground gas generator during gasification of coal seams. Electromagnetic microwave radiation in the presented technological conversion will be used, firstly, for processing of initial lignite waste into active coal. The feasibility of the technical and technological solution is justified by author's developments in the field of brown fossil coals processing into active coals. Secondly, radiation will be used to intensify the extraction of rare and noble metals from the ash residue (ash and slag waste), after the utilization of active coal. The feasibility of this technical and technological solution is justified also by author's developments.

In general, the choice of a new energy source can be explained by the unique properties which electromagnetic microwave radiation has, which make it possible to significantly increase the competitiveness of the processes of processing lignite waste:

- non-contact exposure; - the possibility of concentrating energy in a limited area of space and, in practice, inertia-less controllability of power, which allows to localize radiation effect in a certain zone, to change rapidly the influencing factors when pyrolysis conditions change; - volumetric heating; - volumetric distribution of heat sources; - Because the absorption of microwave energy occurs in a complex manner depending on the size of the body and the wavelength, it allows the creation of various heating regimes; - multiple acceleration of various chemical reactions; - compactness of electromagnetic microwave radiation.

2.2. Studies of the processes of obtaining active coal from lignite waste using electromagnetic microwave radiation

At the first stage of the proposed scheme, the waste should be converted into a commercial product with added value - active coal. In the presented work, experimental studies were conducted to evaluate the effect of electromagnetic microwave radiation on the structure and properties of fossil coal. The brown coals of mark 2B of the Kangalasskiy coal deposit, which is part of the Lenskiy basin of the Republic of Sakha (Yakutia), were chosen as the object of the study. These coals have the following qualitative indicators(%):Ad = 19,7; Vdaf = 50,9. The working moisture of the coals was 9, 20 and 32% (3 series of experiments). Adsorption activity by iodine (%): I = 18.1. The experimental conditions were set as follows: 1) frequency of electromagnetic microwave Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 radiation - 2.45 GHz; 2) the power of electromagnetic microwave radiation is 900 W; 3) the operational humidity of the samples is 9%, 20%, 32%; 4) sample weight - 30 g; 5) the time of exposure to radiation - from 10 to 22.5 minutes, in increments of 2.5 minutes.

2.3 Research on the metal content in ash and slag wastes of the Far Eastern brown coal using energy enterprises

It is well-known that fossil coals, including brown coals, accumulate in their mineral skeleton a lot of valuable metals in the process of their formation. Consequently, the obtained active coal after use can be processed with the extraction of valuable elements which are demanded by the market. The object of the study was ash and slag waste from thermal power plants of Primorsky region of the Russian Federation: 1) CHP-2 (Vladivostok city); 2) CHP (Arseniev town); 3) Primorskaya GRES (Luchegorsk town); 4) CHP (Bolshoy Kamen); 5) CHP (Artem); 6) GRES (Partizansk town). 57 representative samples of ash and slag wastes were selected from the sites of power plants to conduct analytical studies on the presence of metals. For the analysis, the samples were preliminary prepared: they were quarted (homogenized), mechanical grinding was carried out to create particles size less than 0.1 mm. In analytical studies, inductively coupled plasma spectrometry (Agilent 7700 spectrometer) was used to determine the chemical composition of samples, and atomic absorption spectrophotometry (Shimadzu 6800 atomic absorption spectrophotometer) was used to determine silver and platinum group metals (Pt, Pd).

3. RESULTS AND DISCUSSION

Table 1 shows the results of studies on the effect of electromagnetic microwave radiation on the structure and properties of brown coal. During the experiments to study the effect of electromagnetic microwave radiation on the structure and properties of brown coal, the following indicators were recorded:

1) adsorption activity on iodine without drying (I,%); 2) mass of the residue of the coal sample, after exposure to radiation (A,%); 3) temperature of coal heating (T, °C); 4) Qualitative characteristics of the products obtained after exposure to radiation (Wr, Ad, Vdaf, %).

Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017

Table 1. Results of experiments on the effect of electromagnetic microwave radiation on brown coal Exposure time, min № experimental series Wr, % Citeria* 10 12,5 15 17,5 20 22,5

I 19,9 22,8 24,9 30,3 30,6 34,9 A 87,3 86,6 81 77 74,3 71,4 1 9 Т 160 194 227 256 289 315 Ad 19,4 19,7 20,0 20,1 21,7 24,4 Vdaf 50,2 49,9 48,6 46,8 44,3 36,6 I 19,8 24,1 24,5 24,6 31,5 33,2

A 77,3 75,8 73,3 71,6 64,2 62,6 2 20 Т 156 173 218 249 288 332 Ad 21,0 21,1 21,5 23,1 24,4 24,2 daf V 50,2 50,0 48,4 46,4 40,1 36,7 I 17,7 21,7 21,6 23,5 29,6 29,7 A 66,9 66,2 65,7 64,0 58,4 53,6 3 32 Т 155 200 225 290 298 320 Ad 20,0 20,1 20,3 20,8 22,0 23,6 Vdaf 50,3 49,2 48,7 47,8 45,2 39,5 Note: Wr – operational humidity, %; Ad – ash content on a dry basis, %; Vdaf- The yield of volatile substances on a dry, ashless mass,%.

As experiments have shown, that the brown coal:

1) absorbs electromagnetic microwave radiation, which is expressed in an increase in the temperature of its heating in all series of experiments with different moisture content of the raw material; 2) changes its structure (ash content increases, humidity and volatile matter decreases) and properties (iodine sorption activity increases) under the influence of electromagnetic microwave radiation with a frequency of 2.45 GHz in all series of experiments with different moisture content of the raw material. During the investigation of the metalliferous properties of ash and slag wastes formed as a result of burning of brown coals of the Pavlovskoye coal deposit of the Primorskiy Region of the Russian Federation, the following was established. Analysis of coal showed a high content of the following chemical elements (g / t): 1) vanadium - 54.83; 2) chrome - 139.65; 3) nickel - 60.28; 4) rubidium - 102.83; 5) zirconium - 204; 6) barium - 592.9; 7) cerium - 56.97.

4. CONCLUSIONS

As a result of the work, the following was researched and ascertained:

1) the possibility of changing the structure and properties of brown coal from the Russian Federation Far East under the influence of electromagnetic microwave radiation, with its transformation into active coal; 2) high contents of industrially important refractory and rare metals in ash and slag wastes of the Far East of the Russian Federation. Thus, it can be concluded that the proposed integrated scheme for the disposal of lignite Sardinia 2017 / Sixteenth International Waste Management and Landfill Symposium / 2 - 6 October 2017 waste has great prospects for practical use.

AKNOWLEDGEMENTS

The work was carried out with the financial support of the Ministry of Education and Science of the Russian Federation in the framework of the state task in the field of scientific activity № 10.3706.2017/4.6.

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