The moving valve tray is one of the most common tray types in distillation and absorption columns in the oil refining, petrochemical, and chemical industry. In addition to high capacity and good efficiency, it provides excellent turndown with good efficiency, typically down to 20-25% of the maximum operating loads. This is because at low vapor loads the valves close, preventing liquid weep that is detrimental to tray efficiency. This excellent turndown is a common reason for designers and operators to favor moving valve trays.
Recently, experiences were reported in which turndown of 2-pass moving valve trays fell short of the expected. This is of great concern, as most trays larger than 8 feet in diameter are two-pass or multi-pass. While comments were made that maldistribution could have played a role, the nature and mechanism of this maldistribution have remained a mystery. This paper explores this maldistribution mechanism.