Gas hydrate formation in a gas-liquid mixture behind a shock wave

Abstract

621 In this work, a new shock-wave technique for intensifying the process of hydrate formation of gases in gas‐liquid mixtures is proposed. There exist different methods for increasing the rate of this process, namely, fine dispersion of a jet saturated by a gas in a gas atmosphere [1‐3], intense stirring of water saturated by a gas dissolved in it [2, 4], exposure of a gas-saturated liquid to vibration [5], and exposure of a medium to ultrasound [6]. The main disadvantage of these methods is the low rate of gas hydrate formation and, as a consequence, the low efficiency of setups based on these techniques. In the absence of pipelines, one of the promising methods for transportation of natural gas consists in converting it into the gas hydrate state and then transporting it in a solid state at atmospheric static pressure and a low temperature (‐10 ° C to ‐20 ° C). The estimates made by Japanese and Norwegian scientists show that the gas hydrate technique for transportation and storage of natural gas is most cost-effective for small gas fields and shelf natural gas fields. A possible way of using the method proposed is the crystal hydrate method for demineralization of mineralized water. Using freon hydrates for this purpose is simplest from the engineering standpoint and most cost-effective [7]. In [8‐10] and some other books, the properties of gas hydrates and the main conditions and features of their formation are described and the mechanisms of gas hydrate formation and the types of their crystallization are presented. Much attention is given to physical and chemical methods for studying both man-made and natural gas hydrates. In this study, we experimentally investigate the process of gas bubble fragmentation and dissolution with the formation of freon-12 hydrate behind a shock wave of a moderate amplitude in water with gas bubbles. We carry out a theoretical analysis of the process of hydrate formation behind a steplike shock front and compare the results to the experimental data. The experiments were conducted in a shock tube. The test section was a 1.5 m-long vertical thick-walled steel tube with an inner diameter of 53 mm, which was limited from below by a rigid wall. The test section was filled with water containing freon-12 bubbles and was thermostatically controlled. The bubble dimensions were determined by capturing them with a digital camera equipped with additional optics through optical windows made in the upper part of the test section with a required time lag behind the shock front. The steplike pressure waves were generated by the breakdown of a diaphragm separating a 2 m-long high-pressure chamber and the test section. The pressure wave profiles were recorded by pressure transducers located along the test section and mounted flush with its inner wall. The local profile of the variation of the gas content (by volume) behind the shock wave was measured by a conductivity transducer placed at the middle part of the test section. Signals from the transducers were applied to an analog-to-digital converter and were then com