(197b) Deep-Seal Sieve Trays for Improved Scrubbing Performance

In trayed columns, outlet weirs on the order of 2" high are commonly used to maintain liquid level on the deck. Shorter weirs, at least in froth regime operation, can reduce efficiency, and higher weirs are generally thought to increase pressure drop with little benefit in efficiency.

In some applications, however, pressure drop is actually advantageous. For example, packed towers are a common choice for scrubbing of acid gases because of their low pressure drop, but are less effective at scrubbing particulates. As particle diameter decreases, the pressure drop required to get good contact between the particulate and the scrubbing liquid, and therefore efficient removal, increases. For really small droplets, the pressure drop required can be substantial, well beyond what a typical packed column, or even a trayed column, can deliver.

This paper describes an application of deep-seal sieve trays, which have been successful in improving scrubbing performance of a formerly-packed column in an operating facility. It summarizes parameters necessary for successful design and operation of these trays, based on previously-published but not-widely-understood criteria. Because the weir depth, at 12", is outside the range over which typical tray correlations were developed, the fact that these operate well may have additional implications on how some well-established correlations extrapolate.