綠色甲醇作為永續燃料的純氧發電製程分析

Abstract

甲醇從長期儲存和運輸的角度來看是一種有效的氫能載體，因其在常溫常壓下為液態。當需要釋放能量時，一個方法是甲醇重組。然而，重組過程、後續的氫氣和二氧化碳分離及純化、以及二氧化碳液化均相當耗能，導致整體再生能源發電效率僅約30%，且碳捕捉率也僅約80%，表示仍有20%的二氧化碳釋放到大氣中。在這項研究中，提出了一種替代方法，即利用NET Power發電循環進行甲醇燃燒。NET Power發電循環有兩個特點：富氧燃燒和使用二氧化碳作為工作流體。富氧燃燒使得該製程的燃燒產物僅有水和二氧化碳，而這兩者的分離相對簡單，僅需經過冷凝就能移除水。加上該製程本身就需要壓縮二氧化碳使之成為液態以作為工作流體，因此不需要再為了碳捕捉耗費額外的能量進行液化。此外，該製程的碳捕捉率近乎100%。本研究分析了甲醇燃燒的NET Power發電循環，並進行敏感性分析和最佳化，以了解各項變數對發電循環的影響並實現效率最大化。結果顯示，發電循環本身效率最高可達56.95%，碳捕捉率為100%，捕捉到的二氧化碳純度為99.63%。而整個再生能源供應鏈的發電效率可達37.0%。證實了以NET Power發電循環進行甲醇燃燒的可行性及優越性。

Methanol is an effective hydrogen energy carrier from the perspective of long-term storage and transportation since its liquid phase at room temperature and pressure. For energy release, a novel method is methanol reforming. However, the process of reforming, followed by the separation (between H2 and CO2) and purification, and CO2 liquefication are very energy-intensive, resulting in an overall renewable energy cycle efficiency of only about 30%, and a carbon capture rate of only about 80%, meaning that still 20% of CO2 released to the atmosphere. In this study, an alternative method of energy release, methanol combustion with NET Power cycle, is proposed. NET Power cycle has two features: oxy-combustion and CO2 as the working fluid. With oxy-combustion, the resulting combustion products consist solely of water and CO2, and the separation of the two is relatively simple, primarily through condensation to remove water. Additionally, the process itself involves compressing CO2 to the liquid state to be the working fluid, eliminating the need for additional liquefaction for carbon capture. Furthermore, the carbon capture rate in this process is nearly 100%. In this research, the NET Power cycle with methanol as a fuel is studied to evaluate its performance. Sensitivity analysis and optimization are performed to examine the effects of various variables on the cycle and to achieve maximum efficiency. The results show that the maximum cycle efficiency is 56.95% with 100% carbon capture and 99.63% purity of CO2, and the electricity conversion rate can reach up to 37.0% for the overall renewable energy supply chain, confirming the outstanding performance of the NET Power cycle and methanol.