Stainless Steel Liquid Distributor

A trough-type liquid distributor is the metal internal that receives the feed entering a packed column and parcels it out evenly over the packing surface. In place of a solid tray it uses a series of parallel open channels, the troughs, carried across the tower a short way above the bed and usually supplied from a bigger feed channel, the parting box. The liquid travels along each trough and discharges at many points on the way: over V-notches or weirs cut in the walls, or through short drip pipes in the floor, so it lands on the packing as a fine, regular array of streams. The vapour rising in the column simply threads the open lanes between the troughs, adding almost no resistance. Troughs are chosen over a perforated tray to beat fouling, their outlets being large and self-clearing, so heavy, gritty or high-rate liquids that would gradually plug a fine-holed unit flow on undisturbed. The distribution has to be even because a packed bed only works its chemistry where liquid is actually wetting it; feed the bed unevenly and much of it sits idle.

There are three common distributor forms, each suited to a different duty. A tube type, a header feeding a set of perforated pipes, offers the lowest resistance to the gas and a very clean layout, but its holes are small and clog easily, so it is best kept to clean liquids at medium to low rates. A trough type, the open channels described here, has large, self-draining openings that resist fouling and handle high flows and viscous or dirty liquids well, which makes it the workhorse for demanding service. A disc type is a compact pan that combines the liquid distribution and gas passage in one shallow unit and holds a wide flow range, around ten to one, so it fits short or space-limited towers. As a rule: tube for clean, light duty; trough for high, viscous or fouling loads; disc where headroom is tight. Tell us the liquid and the flow and we will pick the type.

The material follows the temperature and the chemistry. Stainless steel in grade 304 or 316 is the default, strong, heat-tolerant and resistant to everyday corrosion, with 316 or 316L picked out for chlorides and stronger acids. Where the process runs very hot, to around 800 degrees, or is abrasive, ceramic is specified, brittle and heavy though it is. And for liquids so corrosive that even stainless would be eaten, concentrated acids or aggressive solvents, the distributor is made in PTFE, or lined with it. Metal is the usual pick because it bears heat and load beyond any plastic and can be welded up to any tower size. Give us the liquid and its temperature and we will settle the material.

Two design numbers set how well a distributor works. The first is the drip-point density, how many separate liquid streams reach each square metre of packing, and a good distributor delivers at least 100 points per square metre, so no part of the bed is starved. The second is the open gas-flow area, kept at 25 percent or more of the tower cross-section, so the gas passes without a pressure penalty. Within those rules the troughs and their notches are sized to the liquid rate and its viscosity. In a tower a stainless trough distributor sits over the packing, at the feed to the top bed and again at any redistribution point on a tall column where the liquid needs re-spreading, and it runs equally in atmospheric, pressurised or vacuum columns doing distillation, absorption or extraction. It is at its best on the awkward duties: thick, high-viscosity liquids, and rates that rise and fall, both of which the wide trough outlets take in their stride. By spreading the feed properly it also stops the liquid sliding down the wall and bypassing the bed, and being welded metal it can be built into the largest towers at reasonable cost. Give us the column, the liquid and its flow range and we will engineer the distributor.