IGNITION OF COAL DUST FROM THE TOMSK REGION TALOVSKY DEPOSIT BY AIR FLOW

This paper focuses on the experimental studies of the ignition characteristics of brown coal dust particles from the Tomsk region Talovsky deposit under the conditions of convective heating. The boundary conditions of combustion initiation have been established. The approximation dependence of ignition delay time from the temperature of a heat source has been found.


INTRODUCTION
Coal is a one of major energy sources in a modern world fuel and energy complex [1][2][3][4]. Also, this fossil is a unique rock, which is a raw material for the production of different products, from electricity to nanomaterials.
The Talovsky brown coal deposit is a promising alternative source to imported solid fuels for thermal power plants in the Tomsk region of Russian Federation. Its main advantages are the low cost of extraction, processing and transportation. According to preliminary estimates, the volume of coal production can reach 10-15 million tons per year. Nowadays, the option of building a power plant on the outskirts of Tomsk is considered. The power plant will operate with a new type of fuel to generate heat and electricity. The development and implementation of design solutions require the full amount of information about the characteristics of physical and chemical processes occurring during coal ignition [5][6][7][8].
The aim of this paper is the experimental study of the ignition of coal dust from the Talovsky deposit during its moving in a stream of heated air. Fig. 1 shows a setup for studying coal particles ignition during convective heating.

EXPERIMENTAL SETUP AND PROCEDURE
The setup contains the basic equipment with the following characteristics:  The operation principle of the setup (Fig. 1) is as follows. A high-pressure blower 1 delivers air at the ambient temperature to the input of an air heater 2. The air pass through the tubular electric heaters. As a result, the air is heated to a predetermined temperature. The temperature is monitored by thermocuple K. Heated air is fed into the hollow glass cylinder 4 via channel 3 with thermal insulation. A high-speed video camera 5 records fast processes within the cylinder during the induction period. Video saving and processing is performed in a computer 8 with the help of specialized software. A ruler 6 with a sampling scale of 0.1 mm is used for determining the spatial position of experimental samples during experiments. An analytical balance 7 is used for measuring the mass of the experimental samples. An exhaust ventilation system 10 and 11 removes the gaseous products of carbon thermal decomposition and oxidation to the atmosphere.
Air temperature T p was monitored by a thermocouple measurements method. In preliminary experiments it was found that the dispersion of experimental data increases with decreasing T p . Therefore, the number of experiments at a fixed value T p was chosen in view of this feature.
The heater 2 heated air flow to a predetermined temperature (Fig. 1). After stabilizing the temperature in the channel, coal particles were put in a glass cylinder cavity. Video recording starts at the moment of introducing a particle into gas flow. Ignition delay time t d was determined from a video recording and counts until the flame.
The systematic measurement error of air temperature did not exceed 0.8-1.6%. The observational error of T p was ±0.4%. This deviation can be neglected in the analysis, as the temperature of the heat source was not less than 450 K in the experiments. The random measurement errors of t d were found from the results of the experiments. We conducted a series of experiments for each particle size at the fixed value of T p . After that, the average values for T p and t d , as well as standard deviations have been determined. The analysis of the values of t d established that variation coefficients ranged from ±3.8% to ±7.5% in a series of experiments.
We performed experimental studies for dust from the Talovsky lignite deposit. The average size of coal dust particles (Fig. 2) was 80 ȝm and corresponded to the particle size of solid fuel burnt in power boilers.

Results and discussion
As a result of data analysis we found the dependence (Fig. 3) of ignition delay time from the temperature of a heat source. The temperature T p =450 K is the limit value necessary and sufficient to initiate combustion under the conditions of interaction between coal dust with air flow (at a rate of 4 m/s). The experimental data curve (Fig. 3) is well described by an exponential dependence t d =f(T p ): t d =1.393·10 3 ·e (-0.013·Tp) , s at 723 K T p 873 K.
The dependence is well illustrated in the video recordings of the investigated process (Fig. 4).  It can be seen (Fig. 4) that if the temperature of an energy source decreases, dust particles pass greater distance until their ignition.

Conclusion
As a result of experimental studies we established the boundary conditions of the ignition of lignite dust particles from the Tomsk region Talovsky deposit (Russian Federation). We considered particles with the size of 80 ȝm during their motion in convective flow. The approximation dependence of ignition delay time from the temperature of an energy source has been found. No. 15-19-10003). The experimental setup was developed with the financial support of the program to improve the competitiveness of Tomsk Polytechnic University (project VIU_ENIN_2014).