Monthly Archives for June 2013

Dirty Naphtha

Naphtha products may suddenly assume a yellowish cast and then return to a normal water-white condition. If this proves to be a recurring problem, the difficulty is probably water in the top reflux. First, obtain a sample of the reflux … Continue reading

27. June 2013 by Jack
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Light-Naphtha End Point

Operators may attempt to maximize heavy naphtha production at the expense of light naphtha by increasing the fractionator top reflux rate, which drops the tower top temperature. The water vapor in the overhead hydrocar­bon vapors begins condensing at its dew … Continue reading

27. June 2013 by Jack
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Raise Pumparound To Save Energy

Operators are usually more interested in making on-spec products than in saving energy. In the field one will often find pumparound rates cut back to 50% of their proper level. Try increasing pumparound circulation until the product separation is adversely … Continue reading

27. June 2013 by Jack
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Improper Heat Balance

Hot vapors, flowing up the fractionator from the flash zone, are partially condensed by contact with cooler pumparound liquid. The heat absorbed by the pumparound stream is used to preheat crude. As the pumparound circulation rate is increased, both heat … Continue reading

27. June 2013 by Jack
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Upset Tray Decks

Although trays can corrode through, a more common cause of damage is unit upsets. A high liquid level, above the flash zone, will cause the trays to be bumped by the up-flowing vapors. Slugs of water can dislodge tray decks … Continue reading

27. June 2013 by Jack
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Decreased Fractionation

Accounting for a loss in fractionation is a common troubleshooting assignment. For example, crude unit operators find that they can no longer meet furnace oil end-point specs unless they sacrifice furnace oil yield. On one unit, furnace oil production had … Continue reading

27. June 2013 by Jack
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Foamovers

A large carry-over of coke or partially coked resid from the coke drum is called a foamover. Preventing such foamovers is vital to continued opera­tion of a delayed coker. Depending on the volume of material carried over, the effect on … Continue reading

25. June 2013 by Jack
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Coking Cycle

While the continuous aspect of delayed coking is straightforward, prob­lems arise in the batchwise filling and emptying of coke drums. The table below summarizes a typical cycle. While one drum of the pair is filling, the other drum is either … Continue reading

25. June 2013 by Jack
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Delayed Coker Process

Coking is an old process but one that is becoming more important as the quality of the world’s crude supply deteriorates. As the sulfur, metals, and conradson carbon contents of crudes increase, coking the bottom of the barrel is looking … Continue reading

25. June 2013 by Jack
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Dead Time in Process Control

The time interval (Td) in which no response of the system is detected following a small (usually 0.25% – 5%) step input. It is measured from the time the step input is initiated to the first detectable response of the … Continue reading

21. June 2013 by Jack
Categories: Control Valve | Tags: | Leave a comment

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