深海掩埋液態CO2技術之最佳注入深度及液滴大小探討

Abstract

溫室效應為日漸嚴重之全球性環境問題，其中又以二氧化碳(CO2)氣體對溫室效應的影響最大。目前雖已具備相當成熟的煙道CO2氣體控制技術，但對於這些被分離吸收之CO2氣體卻缺乏適當之處置場地，而在大氣中二氧化碳濃度持續增加的情況下，若能利用海洋做為二氧化碳主要儲存槽，將可減緩地球的溫室效應。 本研究之主要目的在探討深海掩埋液態CO2之各項溶解行為與液滴之最佳注入大小。經由理論之分析與假設，並考量液滴表面之水合薄膜層，建立出一連續性液滴溶解模式，來模擬液滴於深海中之各項行為。由研究結果顯示，當液滴之注入深度為500 ~ 1500公尺時，，而其溶解速率在半徑在1cm ~ 0.1cm，其值約為4.56*10-7 ~ 1.27 ×10-6 (m/s)，而當液滴之粒徑愈小或是注入之深度愈淺時，其溶解速率將變得愈快。 而液滴粒徑(<0.3 cm)較小部份於各深度下，所需之溶解距離約為200公尺以內，溶解時間約在60分鐘內即可完全溶解於海中。而在同一液滴粒徑下，當注入之深度愈深，達完全溶解所需之溶解距離將變的較短，而其溶解時間會則因注入深度較深而需要較長。 當注入之深度愈深時，可容許之最大液滴粒徑將隨之增加，其中若是注入深度為1500公尺深，可容許之最大液滴之半徑值為0.72 cm，而在1000公尺之注入深度下，可容許之最大液滴半徑值則為0.48 cm。因此只要符合在各深度下最大粒徑之限制內，將可順利的完成CO2液滴掩埋於海水中之目的。

The greenhouse effect is a serious problem that leads worldwide concerns, and the carbon dioxide is the major source that causes the global warming. The carbon dioxide removal techniques from flue gas streams are mature so that they can be applied anytime upon requested. However, the removed carbon dioxide still required further disposal. The ocean is a major sink of carbon dioxide in the carbon balance cycle. The carbon dioxide in the deep ocean remains unsaturated therefore ocean could be a good disposal site for the collected carbon dioxide. The focus of this study is on the evaluation of possibility for releasing liquid carbon dioxide at intermediate ocean depth. In order to understand the phenomenon of dissolution in deeper ocean, mass transfer correlation approach is employed. The results show that shrinkage rate (-dr/dt) of CO2 droplets considering the effect of hydrate film is about 4.56 ×10-7 ~ 1.27 ×10-6 m/s, and it decreases with the increasing injection depth or with larger the droplet radii of liquid CO2 . The effects of initial drop radii and initial releasing position of liquid CO2 are evaluated. When a CO2 droplet is released to the deeper depth at a constant size, the dissolving distance of the CO2 droplet becomes shorter and its dissolving becomes longer. Additionally, the maximum initial droplet radii and the distance of dissolution of carbon dioxide are calculated. The maximum allowable injection radius of the CO2 droplet is 0.72 cm at the depth of 1500m, and 0.48cm at the depth of 1000m. The results of this study can provide the decision makers as a reference on marine disposal carbon dioxide