Study On Fluid Flow And Mass Transfer In Multi-Sparger Multi-Stage Airlift Loop Reactor

Airlift loop reactor (ALR) was developed from the bubble column. ALR has a lot of advantages, such as simple structure, convenient operation, low power consumption, and more importantly, it does not need mechanical agitation. It has been widely applied in biochemical fermentation, chemical industry and wastewater treatment processes. However, the fluid mixing and mass transfer mainly focused on the gas-liquid separation zone in traditional ALRs, which led to long mixing time and low-efficiency mass transfer. A multi-stage airlift loop reactor (MSALR) is used in our experiment; the draft tube is divided into three sections, which can greatly improve the mixing and mass transfer performance of the reactor.The experimental part of this dissertation focuses on the hydrodynamic studies and flow patterns. The result shows that MSALR, compared with ALR, possesses lower mixing time and higher volumetric mass transfer coefficient. This paper presents a liquid driving force model to describe the flow pattern. In this model, the line slope is used to discern patterns. Compared with the drift flux model, this model has higher precision in flow pattern discrimination.However, there are perforated plates or other internals in MSALR, which can increas the fluid flow resistance, lead to the reduced circulating liquid velocity. Therefore, this paper proposes a multi-sparger multi-stage airlift loop reactor (MS-MSALR). Because of the gas ejection force, the flow pressure drop is reduced, and the bubble breaking is enhanced. This paper focuses on the air inlet ratio, which plays an important role in the changes of hydrodynamics. It is showed that, in MS-MSALR, the volumetric mass transfer coefficient increases significantly, and it forms a parabolic distribution, as well as liquid circulation velocity. Based on the modified double film theory, the correlations of volumetric mass transfer coefficient were obtained.In order to study the property of MSALRs used in gas-liquid-solid three-phase reactions, the oxidations of glucose to glucose are experimented. The experimental result shows that the reaction rate increases with increasing superficial gas velocity of MSALR. The reaction rates in MS-MSALR were higher than those in MSALR, and the reaction rate has a maximum value, so it will not change when it reaches a certain maximum value. In MS-MSALR, under lower gas flow rate, the influence of external diffusion can be eliminated, and the energy consumption and the reactor load are reduced.The gas-liquid two-phase flow in MSALR has been studied by the software Fluent6.3. The numerical model shows a good agreement with the measured data on gas holdup, gas velocity and liquid circulation velocity. The simulation method is also used to study the structure of MSALR. The draft tube and gas-liquid separation zone structures are discussed. In the third section, hydrodynamics is obviously influenced by the draft tube structure and the gas-liquid separator structure.