466195 The Experimental and Simulated Investigation on Carbon Dioxide Absorption into Aqueous Alkanoamines Aqueous Solution in the Hollow Fiber Membrane Contactor
The experimental and simulated investigation on carbon dioxide absorption into aqueous alkanoamines aqueous solution in the hollow fiber membrane contactor
bClean Energy Technologies Research Institute (CETRI), Faculty of Engineering and Applied Science
University of Regina, Regina, Saskatchewan, S4S 0A2, Canada
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Key Words:CO2 absorption; Amine solution; Hollow fiber membrane contactor; wetting phenomenon; Membrane separation
Either nowadays or in the next decades, fossil fuels still play very important roles in energy consumption worldwide. Ahuge number of carbon dioxide (CO2) was discharged into atmosphere with combustion of fossil fuels, which was considered to be one of dominating greenhouse gas responsible for global warming. Accordingly, given that when confronted with increasingly severe situation of CO2 emission, it is extremely urgent for human to take effective measures to capture CO2 released from industrial processes, especially from coal fired power plant.
Current major research efforts for mitigating CO2 emission have been focusing on the development of novel CO2 separation techniques. Generally, the most common method for CO2 capture is applied by amine-based absorption in various gas-liquid contactors including packed, bubble, and spray columns. However, aforementioned conventional mass transfer equipments usually are exposed to their inherent drawbacks considerably weakening mass transfer performance in operation process such as entrainment, foaming, flooding and channeling. What¡¯s worse, an enormous capital and operation costs will also impose restrictions on a large-scale application. In order to overcome these problems, researchers have already proposed several alternatives. Amongst varieties of alternatives, the application of hollow fiber membrane contactors (HFMCs) employed for chemical absorption into aqueous alkanolamines has been proved to be a promising alternative on account of distinguished advantages over conventional gas-liquid contactor. HFMCs are a hybrid process combing chemical absorption with membrane contactors. Porous-structured property in HFMCs guarantees a higher gas-liquid contacting area so as to improve mass transfer performance remarkably compared with conventional contactors. In addition, it is flexible for HFMCs to scale-up and save space to meet actual requirements in terms of modularity and compactness respectively. Regardless of advantages above, It is generally known that the disadvantage of membrane contactors is membrane wetting phenomenon due to the intrusion of liquid absorbent into membrane pores, which causes a sharp decline in gas absorption process due to great contribution of resistance to mass transfer within membrane to resistance to total mass transfer. Hence, numerous researchers have been devoting themselves to wetting problem of hydrophobic membrane micropores in HFMCs[1-5].
This paper mainly investigates CO2 absorption performance into aqueous solutions of monoethanolamine (MEA), methyldiethanolamine (MDEA) Diethylaminoethanol (DEEA) and their blends using a commercial micro-porous poly(tetrafluoroethylene) (PTFE) hollow fiber membrane contactor. CO2 absorption performance with various operational parameters inclusive of liquid flow rate, gas flow rate, CO2 concentration, composition of solution, gas-liquid flow orientation as well as CO2 loading was performed under non-wetted and partially wetted mode. A 2D mathematical model on the basis of finite element method was established for the CO2 capture in the flue gas by employing COMSOL Multiphysics. The model can present concentration profiles and flux vectors of transferred species existing in the tube side, membrane, shell side respectively. When it comes to real operating conditions, the wetting phenomenon (partially wetted mode) was taken into consideration for ensuring the accuracy of the model. The experimental results revealed that the order of decarburization performance is DEEA>MDEA, the impact of the gas phase parameters on CO2 capture and mass transfer performance is more significant than that of liquid phase parameters. The simulated results indicated the membrane pores were partially wetted in the process of gas absorption. which makes the mass transfer performance of hollow fiber membrane contactor suffer from enormous losses. Even though a very small region of membrane pore is wetted, the CO2 absorption flux will drop significantly compared with non-wetted mode,
Fig.1 Scheme of Hollow Fiber
The financial supports from the National Natural Science Foundation of China (Nos. 21376067, U1362112 and 21476064), Innovative Research Team Development Plan-Ministry of Education of China(No. IRT1238), National Key Technology R&D Program (Nos. 2012BAC 26B01 and 2014BAC18B04), Specialized Research Fund for the Doctoral Program of Higher Education (No. 20130161110025), Key Project of International & Regional Scientific and Technological Cooperation of Hunan Provincial Science and Technology Plan (2014WK2037), and China¡¯s State ¡°Project 985¡± in Hunan University ¨C Novel Technology Research & Development for CO2 capture are all gratefully acknowledged.
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