超低溫發電機組增壓系統噴射時間之最佳化

Abstract

為發展超低溫儲能技術，本研究建立一套將液態氮轉換為高壓氮氣的增壓系統，藉此產生高壓流體，用以作功發電。該系統以高壓氮氣將液氮射入裝水的封閉鍋爐內，使液氮與水快速地熱交換，並持續增壓直到達熱力學平衡。結果顯示水和氮在鍋爐中快速增壓，由於液氮的消耗，會於鍋爐產生比噴射液氮時更高的壓力。在噴射過程中，液氮一旦與水接觸，將以極快的速度汽化。如果未能及時結束噴射，汽化後的氮氣將會回流，導致最終鍋爐壓力下降。因此，液氮的噴射時間為系統運作的一個關鍵參數。本研究基於氣體動力學理論建立了一套噴射模型，透過實驗所得的熱傳功率，能夠準確模擬系統的噴射過程，並預測最佳的噴射時間，以及最佳噴射時所得的最終鍋爐壓力。實驗結果顯示，當噴射壓力較低時，容易出現噴射不完全的情況。而隨著噴射壓力的增加，熱傳功率也相應上升。然而，熱傳功率的提升同時限制了噴射時間的長度。因此，在適當的噴射壓力下，仍需搭配相應的噴射時間，才能獲得預期的最終鍋爐壓力。本研究的最終目的是使每單位液氮能輸出更多功，亦即在相同空間內射入更多的液氮，增加液氮吸熱量的同時也將增加輸出功。藉由本文中探討的噴射壓力、熱傳功率和噴射時間之間的關係，為進一步提升液氮增壓提供了有價值的指引。

To explore the feasibility and application value of liquid air energy storage (LAES), we developed an experimental device to convert liquid nitrogen into high-pressure nitrogen; and the converted high pressure can be used for power generation. In this device, liquid nitrogen is pressurized by high pressure nitrogen and injected into a closed boiler containing an aqueous solution; after the liquid nitrogen is mixed with the aqueous solution, there is a rapid heat exchange continuously pressurized until thermal equilibrium. The results show rapid pressurization of the vapourization process and downstream pressurization above the injection pressure due to liquid nitrogen consumption. During the injection process, once the liquid nitrogen comes into contact with water, it will vaporize very rapidly. If the injection is not completed in time, the vaporized nitrogen will flow back, and the final boiler pressure will decrease. Hence, the injection time of liquid nitrogen is a crucial parameter for system operation. In this study, an injection model based on gas dynamic theory was developed to accurately simulate the injection process. By utilizing experimentally obtained heat transfer power, the model can predict the optimal injection time and final boiler pressure at the optimal injection time. The experimental results indicate incomplete injection is more likely to occur when the injection pressure is low. As the injection pressure increases, the heat transfer power also increases. However, the increase in heat transfer power imposes limitations on the duration of the injection time. Therefore, achieving the desired final boiler pressure requires the appropriate combination of injection pressure and corresponding injection time. The ultimate goal of this study is to maximize the work output per unit of liquid nitrogen, i.e., injecting more liquid nitrogen into the same space, which will increase the heat absorption of the liquid nitrogen and the work output. The relationship between injection pressure, heat transfer power, and injection time explored in this paper provides a valuable guide to improving liquid nitrogen boost.