Experimental Study on Plugging Caused by Methane Hydrate Formation in Pipes

This paper describes experiments to circulate a mixture of synthetic seawater and ice particles, in other words, an ice slurry, in a flow-loop apparatus consisted of double-tube heat exchangers with acrylic tubes placed along the loop to observe the inner flow. As a method to prepare ice slurry, the ice injection method and stepwise cooling method were tried. In the experiments by the ice injection method, ice in the slurry was gradually melted due to heat transfer from the outer fluid, which was circulated in the annulus of the heat exchangers, because the temperature of the slurry became lower than that of the outer fluid. On the other hand, in experiments by the stepwise cooling method, the seawater was gradually frozen to form ice slurry with flaky ice, and finally, ice layers were formed in the wall of the inner tube in the heat exchangers. The observation of the ice layers implied that iron rusts were contained in the flow to affect the formation of flaky ice. These results suggest that the formation of methane hydrate in a flow of seawater through pipes could be affected by muddiness or turbidity in seawater.