Shed trays

Damaged shed-trays in the bottom section of the main cloumn can cause coke formation due to non-uniform contact between upflowing vapors and downflowing liquid. 

Hold the main column shed tray s liquid temperature under 700°F and minimize the level and residence time of the hot liquid. Ensure adequate wash to shed decks to minimize coking in the bottom of the main column. Some paraffinic feeds may require a lower temperature. 

Fractionation Section. A typical fractionation section includes the coker fractionator and attendant heat exchange equipment, the light gas oil side stream stripper and the overhead system. The coke drum overhead vapors enter the fractionator under shed trays which are located below conventional wash trays. Hot induced gas oil reflux is pumped to the wash trays to condense recycle and to wash the product vapors. The light and heavy gas oil products are condensed as sidestream products. The light gas oil product is usually steam stripped in a sidestream stripper. The overhead vapors from the fractionator are partially condensed and the gas and gasoline products are directed to the vapor recovery unit. 

The bottom section of the main column provides a heat transfer zone. Shed decks, disk/doughnut trays, and grid packing are among some of the contacting devices used to promote vapor/liquid contact. The overhead reactor vapor is desuperheated and cooled by a pumparound stream. The cooled pumparound also serves as a scrubbing medium to wash down catalyst fines entrained in the vapors. Pool quench can be used to maintain the fractionator bottoms temperature below coking temperature, usually at about 700°F (370°C). 

Baffle Trays Baffle trays ( shed decks, shower decks ) (Fig. 14-28 ) are solid half-circle plates, sloped slightly in the direction of outlet flow, with weirs at the end. Gas contacts the liquid as it showers from the plate. This contact is inefficient, typically giving 30 to 40 percent of the efficiency of conventional trays. This limits their application mainly to heat-transfer and scrubbing services. The capacity is high and pressure drop is low due to the high open area (typically 50 percent of the tower cross-sectional area). Since there is not much... 

Have exposures to existing buildings (including pipe racks and cable trays) been considered when siting new vessels, utilities, temporary/permanent buildings or sheds, and others ... 

In another somewhat similar design, a level of water several inches deep is maintained on each tray, and the bottom of each tray is perforated so that water jets flow downward to the tray below, entraining gas bubbles in the liquid on that tray. As in the previous design, the gas flows horizontally in the space between adjacent trays, then up through an opening at one end of the upper tray and back in the opposite direction in the next tray space. Plates of this type are sometimes referred to as shed or showor trays. 

Second, the optimization is carried out for a 40% decrease in the feed flowrate. The optimal feed trays become Npjs, = 12 and Nf,b = 15, and a 9% savings in the vapor rate is observed. As pointed out earlier, this has the same effect as that from reaction rate increases, and we should move the feed trays closer to each other. The results clearly indicate that we should change the feed tray locations as the production rate changes because 9% or 28% energy can be saved by simply moving the feed trays. The next question then becomes, how can we implement such a control strategy The coordinated control of Doukas and Luyben shed some light in this direction. ... 

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