You are currently viewing: Literature



Why produce diesel from the vacuum unit?

Look ahead five years. The economy is likely to keep tightening and the rush to control pollution will inevitably be accompanied by demands for greater energy conservation. Consequence? A growing market for diesel which yields more energy per unit volume. Yet many continue to believe that producing diesel from the vacuum unit is poor design—that it should be produced only from the atmospheric column. Hence many refiners feed 20-30% diesel boiling range material to their FCCs or hydrocrackers. But where most motor fuel is diesel, refiners have long known that producing vacuum unit diesel can increase production up to 5 volume percent on whole crude.

Maximum diesel production is simply not possible in the atmospheric column because flash zone temperature would need to be 760°F or higher. Moreover, the inherent reflux rate below the diesel draw results in molar L/V ratio less than 0.15. But in vacuum columns it can be 0.4 or higher. And distillation is driven by L/V!

Also: eliminating diesel from vacuum unit feed cuts vacuum gas oil (VGO) yield because it is more difficult to vaporize the feed in the vacuum column flash zone. If atmospheric diesel recovery is very high, VGO yield is low. As crudes get heavier it is essential to leave some diesel in the vacuum column feed to achieve reasonable VGO cutpoints.

Lastly, if you process Canadian oils sands Dilbit and Synbit, you can’t run the atmospheric heater hotter than 680°F resulting in very high diesel boiling range material in the vacuum feed. To obtain reasonable diesel recovery from the whole crude you must produce it in the vacuum unit.

Other Literature

Oil sands crude – profits and problems?

Canadian bitumen production currently runs about 1 MMbpd, with some being sold as Synbit and Dilbit. Over the next 10-12 years output is expected to increase to 3.5 MMbpd and more refiners will begin investing to process it and come to depend on the Synbit and Dilbit for a significant part of their supply. ...


Nasty stuff

Heavy crudes are here to stay. As longs as oil prices remain high, Canadian, Venezuelan, Deep Water Gulf of Mexico, Mexican and other low API gravity crude oils will play an ever more important role in supplying world refineries. And prices promise to remain high because gainsayers notwithstanding, Hubbert ...


Designing deepcut vacuum units that really work

Every barrel of vacuum gas oil (VGO) you can save from being reduced to coke in the delayed coker unit is a barrel more that can go to the FCCU. That’s a good reason to raise HVGO cutpoint. But how to do it? Some people think the job can be done just by running computer models in the engineering ...


A time for grass roots thinking ?

Within the past year or two spiking crude prices and surging refinery margins have led to overheated talk about increasing refinery capacity worldwide. Plans for construction of as many 60 grass roots refineries have been discussed. But stretched out lead times for major equipment and inflated prices, ...


A single integrated vacuum system

Failure to design the vacuum unit as an integrated system will invariably result in unsatisfactory yield and poor product quality (high vanadium, nickel, microcarbon, or asphaltenes), and ultimately, an unscheduled shutdown. To avoid these revamp problems the charge pump, fired heater, transfer line, ...


Is pinch enough?

Back in the late 1970’s and early 1980’s when fuel gas prices were high, energy utilization assumed major importance. A new method of calculating heat exchanger networks was developed. It was called Pinch Technology. Today pinch has been rediscovered by engineers who have access to fast computer ...


Opportunity knocks

A group of interesting articles* deals with opportunity crudes, a mixed breed that includes very heavy, sour and high total acid number types as well as those with unexceptional naphthenic acid content but which do have significant concentrations of aliphatic acids or possess the ability to generate ...


Processing heavy Canadian crude

Reducing crude oil cost is the major incentive driving crude and vacuum unit projects to handle heavy Canadian crudes. But such crudes–Albian Heavy, Christina Lake, MacKay River and others derived from oil sands–today present refiners with a unique set of problems not just because of extra-low ...


Why do many crude/vacuum units perform poorly?

In many cases it’s because the original design was based more on virtual than actual reality. There is no question: computer simulations have a key role to play but it’s equally true that process design needs to be based on what works in the field and not on the ideals of the process simulator. ...


Why produce diesel from the vacuum unit?

Look ahead five years. The economy is likely to keep tightening and the rush to control pollution will inevitably be accompanied by demands for greater energy conservation. Consequence? A growing market for diesel which yields more energy per unit volume. Yet many continue to believe that producing diesel ...