Study on a Carbon Dioxide Hydrate Power Generation System Employing an Unstirred Reactor with Cyclopentane
Study on a Carbon Dioxide Hydrate Power Generation System Employing an Unstirred Reactor with Cyclopentane
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DOI：
10.1016/j.energy.2021.120822
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发表时间：
2021-05
期刊：
影响因子：
9
通讯作者：
M. Kawai;Shuhei Obara
中科院分区：
文献类型：
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作者：
M. Kawai;Shuhei Obara
提出了一种适用于寒冷地区的CO2水合物发电系统。在该系统中，利用来自外部空气的冷热形成CO2水合物，并且利用低温废热通过分解水合物获得的高压气体驱动发电机。在这项研究中，我们澄清了环戊烷（CP）作为一个形成反应促进剂在拟议的系统中的效果。环戊烷使相平衡压力曲线向高温和低压移动，增加了驱动形成反应的过冷度。通常，作为促进水合物形成的手段，在反应器中进行搅拌以增加气液接触面积。有趣的是，据报道，在使用透明树脂反应器的实验中，加入CP的未搅拌的CO2水合物中吸收了更多的CO2，并且从水-CP界面开始形成。然而，当在实际的金属反应器中重复形成-解离循环时，例如在所提出的发电系统中使用的反应器，没有结果被报道。在这项研究中，实验进行了使用不锈钢非搅拌反应器，以澄清的影响CP上重复的CO2水合物的形成-分解循环。二氧化碳吸收，即，研究了水合物形成量和诱导时间作为上述效果的评价指标。根据反应器内的温度和压力，考虑CO2气体的压缩系数，利用气体状态方程计算CO2的吸收量。由于无法目视确认形成开始的时间，因此将热电偶安装在反应器中的四个不同深度处，并根据温度的时间变化计算诱导时间。其结果是，CP-添加的CO2水合物的诱导时间和CO2吸收相对于重复的形成-解离循环表现出再现性。多个深度的温度测量结果表明，形成始于水-CP界面，这与之前研究中的目视观察结果非常一致。此外，我们通过考虑三种不同的水/CP体积比（25 cm 3/25 cm 3、37.5 cm 3/12.5 cm 3和43.8 cm 3/6.2 cm 3）进行了实验，并观察到CO2的吸收在37.5 cm 3/12.5 cm 3时最大，这是最接近CP-CO2水合物的理论混合比的值。
A CO2hydrate power generation system for cold regions has been proposed. In this system, CO2hydrate is formed using cold heat from the outside air and a generator is driven by high-pressure gas obtained by dissociating the hydrate using low-temperature waste heat. In this study, we clarified the effect of cyclopentane (CP) as a formation reaction promoter in the proposed system. Cyclopentane shifts the phase equilibrium pressure curve to high temperature and low pressure, increasing the degree of supercooling that drives the formation reaction. Generally, as a means of promoting the formation of hydrate, stirring is performed in the reactor to increase the gas–liquid contact area. Interestingly, it has been reported that more CO2is taken up in unstirred CO2hydrates with CP added and formation starts from the water–CP interface in experiments that use a transparent resin reactor. However, no results have been reported when the formation–dissociation cycle is repeated in a practical metal reactor, such as that used in the proposed power generation system. In this study, experiments were conducted using a stainless steel unstirred reactor to clarify the effect of CP on the repetition of the CO2hydrate formation–dissociation cycle. Carbon dioxide uptake, i.e., the amount of hydrate formation and the induction time, was investigated as an evaluation index of the above effects. The CO2uptake was calculated from the temperature and pressure in the reactor, considering the compression coefficient of the CO2gas and using the gas state equation. Because the timing at which formation starts cannot be visually confirmed, thermocouples were installed at four different depths in the reactor and the induction time was calculated from the time change of temperature. As a result, CP-added CO2hydrate showed reproducibility in induction time and CO2uptake with respect to repeated formation–dissociation cycles. The results of temperature measurements at multiple depths showed that the formation started at the water–CP interface, which was in good agreement with the visual observation results in a previous study. Furthermore, we conducted experiments by considering three different water/CP volume ratios (25 cm3/25 cm3, 37.5 cm3/12.5 cm3, and 43.8 cm3/6.2 cm3) and observed that the uptake of CO2was the greatest at 37.5 cm3/12.5 cm3, which is the closest value to the theoretical mixing ratio of CP–CO2hydrate.