Wash trays

Equipment The equipment selected for CCD circuits may consist of multiple-compartment washing-tray thickeners or a train of... 

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. 

Two or three trays just above the flash zone are wash trays to prevent entrainment of dark color bodies into the heavy gas oil. The internal reflux flow on these trays should be limited to a few percent of the molal vapor rate, for good energy conservation and minimum residue handling. These trays are often equipped with anti-blowing baffles. The wash rate is sometimes controlled by using a total draw for the heaviest gas oil, then metering the wash oil rate. 

Carbon dioxide removal in ammonia plants is usually accomplished by organic or inorganic solvents with suitable activators and corrosion inhibitors. In a few circumstances, C02 is removed by pressure swing adsorption (PSA) (see Chapter 3). The removed C02 is sometimes vented to the atmosphere, but in many instances it is recovered for the production of urea and dry ice. Urea is the primary use of carbon dioxide and, in case of a natural gas feed, all of the C02 is consumed by the urea plant. This practice is especially significant since C02 is a proven greenhouse gas. Typically, 1.3 tons of C02/ton of NH3 is produced in a natural gas-based ammonia plant. The C02 vented to the atmosphere usually contains water vapor, dissolved gases from the absorber (e.g., H2, N2, CH4, CO, Ar), traces of hydrocarbons, and traces of solvent. Water wash trays in the top of the stripper and double condensation of the overhead help to minimize the amount of entrained solvent. The solvent reclaimer contents are neutralized with caustic before disposal. Waste may be burned in an incinerator with an afterburner and a scrubber to control NOx emissions. 

In order to keep methanol losses down, the atmospheric offgases will either have to be treated with water over a few wash trays, or their methanol will have to be condensed by cooling them to very low temperatures. Normally,... 

To recover liquid in order of preference of settlers, Section 5.8, thickeners. Section 5.10 and sedimentation centrifuges. Section 5.12 clarifier, settler, washing tray thickener, reactortubular bowl centrifuge, batch automatic (horizontal or vertical bowl, disc with intermittent nozzle discharge) continuous disc bowl centrifuge with nozzle discharge. 

Reduce light gas oil in vacuum tower feed Reduce number of wash trays Replace PAR trays with packing... 

Any restriction to vapor flow above the flash zone must increase the flash-zone pressure. An increase in AP across the wash trays below the... 

Reduce the number of wash trays in the vacuum tower. In one installation, two bubble-cap trays replaced four tunnel-cap trays. The flash-zone pressure was therefore reduced. The net effect was beneficial in that the lower pressure drop was more useful than the loss in fractionation represented by the two trays removed. 

Liquid inld distributor installed properly (including spray direction) and with flow area dimensions as in drawing Liquid distributor tray(s) installed Wash trays installed, sealed and secured correctly — saiisfaeiory leakage rate test carried out... 

Dimensions and number of holes/bubbie-caps on wash tray(s) as on PDS Weir tray heights as in process data sheet Downcomers — width and clearance at bottom lip as in process data sheet... 

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