Back

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, column internals and ejector system must all be evaluated and designed as a unified whole so that critical variables – heater outlet temperature, coil steam injection rate, flash zone temperature and pressure – may be properly balanced. A thorough understanding of requisite theory is necessary and computer modeling is useful but theory and simulations are not enough. Process flow sheet models must be calibrated using actual field data, and appropriate allowances made for less-than-ideal equipment performance. One cannot rely alone on manufacturers’ specification sheets because only rarely will they reflect actual field-tested performance. Only by exercising such caution can under-utilized equipment be exploited and investment in new equipment minimized. An experienced revamp engineer will then be able to optimize critical temperatures and pressures to ensure satisfactory yields, product quality and length of run.

The critical link: heater-ejector system
Today many refiners have set 4-5 year run length and higher HVGO TBP cutpoints as goals. Increasing heater outlet temperature to achieve these goals requires all equipment to work together to keep cracked gas low, for if an ejector system is incapable of handling higher cracked gas production from a 10-15ºF increase in heater outlet temperature, column flash zone pressure will increase and gas oil yield can actually be reduced. Hence, not only must the ejector system be sized properly but the heater must be well designed to minimize both cracked gas and coke make – and the two must be balanced. Contrary to conventional wisdom this means designing upstream: from the ejector system back to the heater (and all the way back to the charge pump to ensure total unit performance.) For the designer to accomplish this, baseline and revamp process models must reflect existing equipment design including all shortcomings. This entails making a thorough test run. Following these guidelines can effect a significant increase in revenue – the bottom line goal of every revamp.

DOWNLOAD LITERATURE

Sponsor:

Process Consulting Services

Categories:

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 ...