Effect of cyclopentane addition on increasing the energy storage density in a CO₂ hydrate power generation system

Abstract

In this study, we clarify the effect of cyclopentane (CP), which is a formation reaction promoter and shifts the phase equilibrium curve to high temperature and low pressure, on the energy storage density of the proposed CO2 hydrate power generation system. The phase change should be shifted to a higher temperature for expanding the operating conditions of the power generation systems. In addition, the formation of hydrates is facilitated by the repeated formation and dissociation of gas hydrates (the memory effect). Although the memory effect mechanism during hydrate formation has not yet been clarified, its occurrence has been reported in many studies, where the reformation of each gas hydrate began more quickly when compared with the initial case. Hydrate formation and dissociation were conducted at least once in a day in the proposed power generation system. Therefore, the power generation cycle can be repeatedly performed in a short time period if the memory effect is effectively applied. Hence, we conducted experiments in the presence or absence of CP and with respect to the time duration of the dissociation state in the formation and dissociation cycles. Furthermore, we calculated the hydrate amount and the time required for its formation under each condition. Subsequently, the energy storage density of the proposed power generation system can be estimated based on the calculation results. The conducted experiments and calculations reveal that a CO2 hydrate power generation system containing CP is more beneficial when compared with a pure CO2 hydrate power generation system in terms of the energy storage density and the time required for storing energy.