Oxygen extraction from air employing adsorption technology

• Main Author: Seah, Jaymus Min Yew
• Other Authors: Anutosh Chakraborty
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Mechanical engineering::Fluid mechanics
• Online Access: https://hdl.handle.net/10356/158707
• Institution: Nanyang Technological University

This research is aimed at improving oxygen purity extracted from air using a Pressure Swing Adsorption Device in the Energy Systems Laboratory by examining various parameters such as mass flow rate, pressure of feed gas, purge flow rate, adsorption, and pressurization Time. In the experimental setup, molecular sieves from silica gel, zeolite JLOX-101, and 13X are used to adsorb water vapor, nitrogen, and carbon dioxide, respectively. The experimental set-up is controlled by a series of valves connected to PLC-CPU: Siemens SIMATIC S7-200 via a PLC Ladder Program using timers with high precision. This helps to automate the whole process of oxygen production, capable of operating without additional external control once the timers are inputted. The findings revealed that the estimation for optimal settings derived from theoretical understanding turned out to be quite different. For mass and purge flow rate, a higher quantity did not necessarily produce a higher oxygen purity. A higher flow rate would cause rate of air flowing to be much faster than adsorption/desorption rates, resulting in insufficient time for optimal adsorption. From literature review, a higher pressure normally leads to higher adsorption uptake which leads to higher product purity for PSA generators. However, the experiments conducted in this project revealed that there exists an optimal pressure between the low and high end to maximize the oxygen purity. When the pressure of the feed gas is too high, the flow rate increases and hence a lower residence time is experienced in the adsorbent bed, resulting in lower uptake. The optimal pressure for the current set-up is found to be around 2 Bar. In the studying the effects of adsorption and pressurization time, it was found that there is significant importance in identifying the breakthrough time for maximum adsorption uptake. Since the experimental set-up is a laboratory-scaled one, the breakthrough time is short at 2 seconds and 0.2 seconds for adsorption and pressurization time respectively. A mathematical model was also developed to represent a two variable adsorption using a general mass balance equation, Langmuir isotherm and Linear Driving Force Model from literature review. The pressure swing adsorption device used in this experiment is proven to be prospective in the future research and application in the medical industry. To achieve higher purity, removal of argon gas and utilizing all four beds in the current set-up could be explored. Equation 33 from mathematical modelling can also be solved to further investigate the relationship between pressure and time for advance modelling.