| Natural gas hydrate is currently a new type of clean energy which has great potential for exploitation and utilization.It is enough to meet the demand for more than one thousand years.Natural gas hydrate is mainly distributed in the deep seabed in the word,while natural gas hydrate on the seabed surface is more reasonable to use cutter suction mining method.Due to the vertical pipeline in the hydraulic transportation system is a very key part,and the research of deep-sea coarse-grained hydraulic conveying theory is relatively less,so the flow law of natural gas hydrate slurry in vertical pipeline is analyzed with the 4000m long vertical pipeline as the object.According to the theory of liquid-solid two-phase flow,the hydraulic conveying parameters,pressure distribution,head and effective power for lift pump of natural gas hydrate slurry vertical pipeline were analyzed,while the force of coarse particles of natural gas hydrate was discussed and its equation of motion was established.Then,based on FLUENT software and the two-phase flow model,the flow state of natural gas hydrate slurry fluid-solid two-phase was simulated and analyzed,summing up that the effect of particle density,particle diameter,pipe diameter,conveying speed and volume concentration on flow field,resistance loss,pressure loss and efficiency of the system.The energy consumption of the hydraulic conveying system was further optimized by using genetic calculation method.Considering that natural gas hydrate started to decompose and generate gas at the critical point,gas volume increased and exceeded 30%.That impact on the conveying system can not be neglected.Therefore,based on the relationship between decomposition kinetics and pressure distribution,the mathematical model of relationship of the critical point of natural gas hydrate decomposition,the quality of natural gas hydrate decomposition,the gas quality,gas volume and gas density produced by natural gas hydrate decomposition and the depth of sea were setted up.Besides,the influence of hydraulic conveying parameters on gas formation was analyzed.In addition,the mechanism of the gas produced by natural gas hydrate decomposition to reduce resistance was also discussed.Finally,selecting the RNG turbulence model and the population balance model to simulate and analyse gas-liquid-solid three-phase flow of natural gas hydrate slurry in vertical pipeline,so the three phase distribution,velocity distribution law and the optimal value of hydraulic conveying parameters were summarized.Also,the influence of gas phase on the row distance,head and effectibe power of the hydraulic lifting system were discussed.It was concluded that the existence of gas increased the pitch of 64m?491m and the required head and effective power of gas-liquid-solid three-phase flow on the basis of the liquid-solid two-phase flow were respectively reduced by about 1.8%?51.2%and 0.9%?26.4%.Because of the decomposition of natural gas hydrate,natural gas hydrate slurry in the vertical pipe were in two flow states of liquid-solid two-phase and gas-liquid-solid three-phase,which maked the flow field become very complex.Through the combination of theory and simulation,the law of flow field can be summed,which can provide theoretical support for the exploitation of natural gas hydrate in the deep seabed. |
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