126 / 2023-06-21 11:28:03

Study on the effect of coal particle size on the kinetics of gas hydrate generation

gas hydrates; gas consumption; growth rate; coal and gas outburst; porous media

Coal is the main energy source in China, and with the exhaustion of shallow coal resources in China and the increase of coal mining depth, coal and gas outburst disasters occur frequently. On the basis that hydrate has controllable generation conditions, Wu Qiang proposed hydration curing anti-outburst technology for coal and gas outburst prevention and control, which uses medium-high pressure waterflooding and adds surfactant to water to make most of the mine gas in coal seam exist in hydrate state and reduce the pressure and content of the mine gas, so as to reduce the occurrence of coal and gas outburst accidents. The use of hydration curing technology can theoretically effectively control the occurrence of coal and gas outburst accidents, but because of the growth process of hydrate is constantly mass and heat transfer, there are usually limitations in the process of hydrate generation with long induction time, slow generation rate, and high thermodynamic conditions of phase equilibrium. Nowadays, there have been much more research results have pointed out that porous media can promote hydrate generation due to its huge specific surface area. The reaction environment for coal and gas outburst disaster prevention and control which is based on gas hydration solidification method is in the protruding coal body, which has more complex multi-scale pore structure compared with other porous media, so it is particularly important to explore the analysis of factors which is influencing gas hydrate generation in coal particles in depth. However, at present, there are few reports on the kinetics of hydrate generation process in coal particles at home and abroad, and there is a lack of data on the kinetics of hydrate growth in coal particles. Accordingly, in this paper, hydrate growth kinetics experiments were conducted under four different coal particle sizes (C1: 0.425-0.850 mm, C2: 0.250-0.425 mm, C3: 0.180-0.250 mm, C4: 0-0.180 mm) to obtain kinetic parameters such as gas consumption and average growth rate during hydrate generation. The main conclusions are: (1) The hydrate growth kinetics experiments were carried out in four coal particle size systems with two types of gas samples, CO₂ and CH₄, under 278.15 K and 2 MPa pressure driving force in different coal particle sizes. The results show that there is a similar trend in the gas consumption curves of the four particle sizes, which is with the gas consumption increasing rapidly at first, and then its growth rate decreasing slowly and leveling off in the end. (2) The relationship between coal particle size and CO₂ hydrate gas consumption and average growth rate is positive, which is as the coal particle size decreases, the CO₂ hydrate gas consumption gradually decreases and the average growth rate of CO₂ hydrate gradually slows down. It means that the larger particle size of coal facilitates hydrate formation. (3) The relationship between coal particle size and CH₄ hydrate gas consumption and average growth rate is non-linear. That is, with the decrease of coal particle size, the gas consumption and average growth rate of CH₄ hydrate show a pattern of decreasing first and then slightly rebounding.