Numerical study of microwave impact on gas hydrate plugs in a pipeline

Abstract

Purpose. Development of a technique for the numerical study on the decomposition of gas hydrate plugs in deep-water pipelines under microwave radiation using a coaxial source. Theoretical efficiency evaluation of using such an impact to unblock the pipelines. Methodology. Mathematical modeling and computational experiment. Findings. An original mathematical model is proposed to describe heat transfer processes during the decomposition of gas hydrates in a pipeline under the action of heat sources distributed over the volume. The non-stationary problem of heat transfer was considered in a one-dimensional formulation. An algorithm for numerical computation is proposed. A mathematical expression is obtained for distributed heat sources generated by the microwave radiation from a coaxially located SHF antenna. Parametric numerical studies on temperature fields and decomposition dynamics of a gas hydrate plug are performed for specified parameters of pipe and microwave radiation power. The boundaries of the decomposition area and the dynamics of change in this area are determined. The decomposition time of a gas hydrate plug with a diameter of 0.3 m was determined using a 300 W microwave source. The complete decomposition took approximately 40 hours. Originality. The task of thermal decomposition of a cylindrical gas hydrate plug in a pipeline due to microwave heating using a coaxial microwave power source has been considered for the first time. The process is viewed as a sequence of several stages: heating, heating and decomposition, decomposition after complete heating of the gas hydrate layer. To model the volumetric dissociation of gas hydrate, it was proposed to use special functions that characterize the amount of decomposed gas hydrate. The introduction of such functions makes it possible to construct an efficient computational algorithm taking into account the action of volumetric sources in the decomposition area. The known models mainly consider only surface thermal effect or microwave impact on gas hydrate in porous mediums. The presented model allows describing the decomposition during volumetric heating of a solid hydrate adequately. Practical value. Blocking plugs may occur due to hydrate formation when transporting gas through deep-water pipelines or through pipelines in cold environments. The elimination of such complications is a complex technical task. In particular, a special source of microwave radiation, which was proposed by the authors in previous works, can be used to unblock the pipeline. The device that makes the microwave radiation is located along the pipe axis. The results of this work allow us to evaluate the effectiveness of the microwave method for eliminating the gas hydrate plug. The mathematical model and computational method can be used in the development of appropriate technologies using a coaxial microwave heating source.