A non-invasive technique for compositional analysis of coal

Abstract

India has some of the largest coal reserves in the world (approx. 267 billion tones). The increasing demand and use of energy internationally, especially in India is heavily dependent on coal. Indian coal industries mainly deals with bituminous and sub-bituminous coal in which the ash content varies from 25 to 75%. Quality of Coal (ash content in the coal) is one of the important factors which directly affects the power generation in the thermal power plant and the efficiency of blast furnace in steel plants. High ash content reduces the thermal efficiency of the coal. Moreover the ash content has to be controlled based on the plant’s capacity and ash handling systems. The proximate analysis methods which are being employed now are less accurate and time consuming. The present work describes an Infrared (IR) Thermography based fast and low cost technique for the compositional analysis of coal taking into account the change in average temperature due to the variation in thermal absorptivity of coal constituents. Different coal samples with ash content varying in the range of 25.0 to 85.0 wt.% and moisture content from 1.0 to 6.0 wt.% have been collected from Coal Characterization Centre in CSIR-NML. Fixed quantities of these samples were uniformly heated using a microwave oven, for a duration of 40s which is just sufficient to create a difference between the sample constituents in the extent of their respective infrared emissions. The thermal image of the heated samples is captured by IR Thermography and the average temperature of these samples is evaluated from the thermal image. This experiment has been done with samples obtained from two different mines; Sambaleswari and Talcher mines. The composition of the coal samples in terms of their ash and moisture content is obtained from proximate analysis results. Calibration curves relating average temperature and the ash and moisture content in coal samples is obtained. Finally, a software program has been developed in LabVIEW for estimating the ash and moisture content in a fixed quantity of coal sample from the calibration curves. This technique can be used for the determination of ash and moisture content in coal samples without carrying out proximate analysis and thereby would be useful in finding the suitability of specific coals for individual combustion systems.