Be smart about FCC olefin recovery

Whether the driver is propylene as a chemicals feedstock or propylene and butylene as alky feed, FCC units worldwide are being pushed to maximize olefin production. Increased hydrotreating to meet Tier 3 gasoline requirements is reducing gasoline pool octane at a time of high premium-to-regular gasoline price differentials. Maximizing FCC olefi ns to produce high octane alkylate barrels is attractive – if they can be recovered in the FCC gas plant LPG stream.

Higher reactor LPG yields increase wet gas compressor loading. So, in a unit that is already limited by wet gas compressor capacity, revamp modifications must be made to accommodate higher reactor LPG yields. Replacing the compressor entirely or installing a new parallel compressor are expensive options.

Instead, the keys to a practical off gas compressor revamp lie in the polytropic head equation (bottom right). Look to minimize main column inlet to wet gas compressor inlet pressure drop and overhead receiver temperature. Next, compressor speed and rotor modifications may afford additional capacity. On a mass basis, FCC wet gas rates have been increased by over 40% without installing a parallel compressor.

After compression to gas plant pressure of around 220 psig, the LPG must be condensed in the high pressure receiver or the absorber. Increasing reactor LPG yield stresses gas plant cooling systems and increases absorber and stripper column loads. Furthermore, high LPG yield often comes at the expense of naphtha yield, meaning that there is more vapor and less liquid in the absorber – this must be addressed to maintain high propylene recovery.

There is a strong incentive to maximize FCC olefin production with reactor temperature and catalyst formulation. Executing the correct revamp can economically address main column, wet gas compressor, and gas plant constraints so that theoretical reactor yields become actual barrels of valuable product.


View More

  • 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 ...

  • Responsive image Catalysts for optimal performance
  • Responsive image Shut-off valves
  • Responsive image The eco-friendly sulphur recovery solution
  • Responsive image Extensive tray portfolio
  • Responsive image Swagelok® Valves
  • Responsive image Oil and gas water treatment applications
  • Responsive image Valves and Pumps for the Energy Industry
  • Responsive image Atlas Copco Expander Compressors