In order to decrease storage costs and to get rid of some imposed restrictions for intermediate products as feed for downstream units, is it possible to connect output of upstream unit (e.g. distillation unit) to downstream unit (e.g. Hydrocracker) directly? Because of sequential changes in crude feed characteristics, we have encountered some surge and instability in straight run products of distillation unit.
Answers
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12/12/2014
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Jayaraj Jayam, Chennai Petroleum Corporation Limited, njayaraj@gmail.com
Upstream crude unit should keep the downstream unit's requirement in mind whenever making changes in crude type or changing their operating parameter. However, to maintain level in feed surge drum of the downstream unit, it is required to have a cold stream from storage. Likewise, when the downstream unit gets upset for some reason and needs to reduce the feed rate, upstream unit production has to be diverted to storage fully or partly.
So it is not possible to operate the units smoothly without having intermediate tanks.
Feed to downstream units can be taken as hot by bypassing the product cooler(s) and thereby you can save energy to a good value.
For hot feed case also, it is difficult to have smooth operation at upstream or downstream unit without having intermediate tanks.
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11/12/2014
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Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Yes. It is called “running hot.” Intermediate storage is usually provided for to use during downtimes or upsets. To operate directly from other units, a feed surge drum is essential. When new facilities are designed for running hot, standby coolers in both units are included for when the operation is not running hot. For existing units, such as your case, you need to check the exchanger services in both units to see if additional surface areas are needed.
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