Numbering-up of mini-and microchannel contactors and reactors
Multiphase downstream units and chemical conversion units with internal structures containing a variety of parallel flow channels are a promising technology to intensify, to rapidly develop, and to operate more safely absorption, extraction, or reaction processes. The performance of these units depends strongly on the distribution of the phases at the entrance. Technologies should provide a uniform phase distribution which is directly linked with a narrow residence time distribution of the fluids and the complete utilization of the solid surface for heat transfer, mass transfer and conversion. Furthermore, the scale-up should be straight forward from small structures to large structures. This work presents a novel distributor design for feeding two immiscible fluids such as a gas phase and a liquid phase into structures that contain several flow channels (1). It can be used either to feed separate channel arrays in the form of monolithic blocks, or can be integrated into existing channel structures of micro process equipment. The investigation of air-water flows in a 10-channel array verified that this simple distributor concept creates highly uniform Taylor flows in terms of bubble velocities, as well as gas bubble and liquid slug lengths irrespective the flow orientation.
Gas-liquid multiphase reactors containing a large number of small parallel channels, also known as monolithic reactors, flow reactors with honeycomb packings, or microstructured reactors, were developed and improved significantly during the last decades due to their potentials a) to intensify processes in terms of enhanced heat and mass transfer, b) to control precisely contact times between the phases, and c) to improve operating safety (2-4). Besides the application as chemical or biocatalytic reactors (4-10), this concept may also be used as extractor (11-12) or absorber (13). The mentioned benefits arise from the high surface-to-volume ratios of the reactors as well as from a specific flow regime, the Taylor flow, occurring in small channels for certain flow conditions. This regime is also known as segmented or slug flow and is characterised by a flow of two immiscible fluids in separate compartments. The main features of Taylor flow are large interfacial areas, short diffusion distances, internal circulation vortices and nearly plug flow behaviour (14-15).
Scale-up is typically proposed as simple which help to minimize implement ...