The Use of Directional Momentum Devices on Fractionation Trays

INTRODUCTION Since almost all industrial scale columns are round, the side downcomers present unique challenges for liquid distribution both to and from the downcomers. Liquid leaving these downcomers needs to spread outwardly, away from the flow path centerline, in order to evenly feed the diverging tray active area. Also, one of the characteristics of side downcomers is that they naturally tend to focus emerging liquid towards the center of the tray, opposite of what is desired. Even though a standard downcomer clearance takes a pressure drop that should help to equalize the liquid flow distribution onto the tray, testing has shown that a typical tray will have a disproportionate amount of liquid flow along the flow path centerline while the outer portions of the tray deck tend to stagnate because they are fed with below average amounts of liquid. Various types of directional momentum devices have been used on fractionation trays over the years in an effort to better control fluid flows on the tray deck and subsequently enhance tray performance. Types of mechanical diverters can range from simple baffles to a combination of shaped downcomer clearances and outlet weirs. Vapor momentum can also be used to direct the liquid flows. Devices using this means can be individual directional vapor valves dispersed on the tray deck or groups of carefully organized directional push valves and froth promoters. This paper will review the fundamental aspects of these different devices, present new research data, and conclude with commercial operating results.