Steam stripper /stripping efficiency

Catalyst residence time in the stripper is determined by catalyst circulation rate and the amount of catalyst in the stripper. This amount usually corresponds to the quantity of the catalyst from the centerline of a normal bed level to the centerline of the lower steam distributor. A higher catalyst residence time, though it increases hydrothermal deactivation of the catalyst, will improve stripping efficiency. 

Disrupt uniform catalyst flow and catalyst to steam contacting in the spent catalyst stripper zone as reflected by rednced stripping efficiency. 

Cold flow tests indicate that a too high superhcial mass flux in the stripper causes a dramatic decrease in stripping efficiency. The normal stripping steam flow pattern is disrupted to the point where stripping steam becomes entrained downward [6]. 

Wet steam will also reduce stripping efficiency. The water in the steam will be turned into steam when it contacts the hot diesel oil in the stripper, shown in Fig. 10.1. The heat of vaporization for this water must come from the sensible heat of the diesel. This reduces the temperature of the diesel, which also reduces its vapor pressure, which then makes it more difficult to vaporize its lighter gasoline components. 

High liquid levels in the bottom of the stripper will also reduce stripping efficiency. A liquid level above the steam inlet will cause the stripping trays to flood. Flooding vastly decreases tray efficiency, and hence stripping efficiency. 

Slowly opening the steam inlet, I adjusted the steam flow until the AGO stripper bottoms temperature dropped to about 600°F, which is an indication of reasonable stripping efficiency. 

Zip informed me that adjusting the steam to the jet fuel stripper did not influence its flash point. That is, the steam was ineffective in removing lighter hydrocarbons (i.e. naphtha) from the stripper feed. This was odd, because the stripper draw temperature was 435°F and the stripper bottoms temperature was 395°F. Typically, a 40°F AT indicates good stripping efficiency. However, when 1 inspected the stripper column, I saw that both the feed line and the stripper shell were entirely without insulation. The 40°F temperature reduction was primarily due to the ambient heat loss. 

The problem was not the lack of stripping steam. The problem was also not the excessive pH of the stripper bottoms as my client in India suspected. It is quite normal for the stripper bottoms to have a higher pH than the feed, if the stripping efficiency is inadequate. That is, the acidic H S is stripped out of the sour water more easily than the basic ammonia. The problem of excessive NHj in the stripped water effluent was low tray efficiency. 

Process condensate from reforming operations is commonly treated by steam stripping. The stripper is operated at a sufficiently high pressure to allow the overhead stripping steam to be used as part of the reformer steam requirement (71). Contaminants removed from the process condensate are reformed to extinction, so disposal to the environment is thereby avoided. This system not only reduces atmospheric emissions, but contributes to the overall efficiency of the process by recovering condensate suitable for boiler feedwater make-up because the process is a net water consumer. 

Changing the vapor line from a 3-in pipe to a 4-in pipe reduced the line s pressure drop from 3 to 0.7 psi. This permitted the stripping steam flow to be increased to the stripper, without impeding the jet fuel flow from the fractionator. The higher stripping steam flow efficiently removed the contaminant naphtha from the jet fuel product. 

Description Urea is formed from CO (18) and NH3 (19) in the HP loop (1) in a reactor (2) fitted with Casale-Dente high-efficiency trays. The urea solution (3) from the reactor (2), which still contains unreacted NH3 and CO2, is first treated in a stripper (4), operating at the same pressure as the reactor, heated with steam and using CO (18) as stripping agents to recover most of the unreacted NH3 and CO. ... 

A yield improvement option was identified from the hydrocracking unit (HCU) as a part of the energy optimization project. It was found that a large amount of diesel was lost into the unconverted oil due to poor fractionation efficiency in the main fractionators. To recover this lost diesel with an estimated value of 12 MM/year, a new stripper column will be installed. The stripper column will require stripping LP steam of 150t/day costing 1.0 MM per year. The cost for related piping would be estimated as part of HCU revamp project... 

Unbaffled Strippers Not Recommended if Stripping Steam Efficiency a Concern... 

The rich benzolized wash oil is stripped of its light oil content by fractional distillation—most commonly in a tray column operated at substantially atmospheric pressure with direct-steam addition to the bottom. The number of theoretical trays required for the separation can be calculated by conventional techniques and the actual requirement estimated on the basis of an assumed tray-efficiency. Overall efficiencies of 45 to 70% have been reported as typical for light oil stripper stills (Silver and Hopton, 1942 Glawacki, 1945), and 10 to 15 actual trays are commonly employed below the feed. 

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