Quantitative evaluation of the influence of coal particle size distribution on gas diffusion coefficient by image processing method

Abstract

Coal particles have been widely used to measure the gas diffusion coefficient which is a key parameter to characterize the gas diffusion behavior, and the average particle size is a necessary parameter for calculating the diffusion coefficient. At present, people often use the arithmetic mean of upper and lower sieve surface specifications to characterize the average diameter of coal particles, which has large errors. It is necessary to obtain the particle size distribution in advance to determine the average diameter scientifically and accurately. A laser particle analyzer is usually used to measure particle size distribution, but due to the limitation of its measurement principle, it has poor measurement accuracy for irregular and large particles. In this article, we offer an integrated approach for quantitative evaluation of the influence of coal particle size distribution on gas diffusion coefficient. Laser particle analyzer and image analysis were used to measure the particle size distribution of 6 coal samples with the size range of 1 ∼ 2 mm. Based on obtaining the size distribution, the average diameter was calculated. Then the diffusion coefficient was calculated by using the average diameter obtained by different methods. The results show that the particle size distribution measured by the laser method has a large deviation and poor repeatability, and the volume mean diameter calculated by it is far less than the arithmetic mean value of 1.5 mm. The imaging method can extract the morphological data of each particle, and so the obtained particle size distribution is more accurate and reliable. The equivalent area mean diameter calculated by the image method is close to 1.5 mm. The average diameter obtained by considering the particle size distribution can more truly reflect the particle size characteristics of coal samples, while the conventional method of using the arithmetic mean to calculate the diffusion coefficient will produce a non-negligible deviation. This also reveals the importance of obtaining particle size distribution when using the particle method to solve the diffusion coefficient.