The steady drop in heavy fuel oil demand has asked for further developments in Visbreaker Technology. Shell Global Solutions has developed the Vacuum Flasher Technology, for which ABB Lummus Global acts as the authorized licensor.
Vacuum Flasher Technology has two major advantages when added to a Shell Soaker Visbreaker:
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Additional distillate products are being produced which are suitable for thermal cracking, catalytic cracking or hydrocracking to improve the overall performance of the refinery. |
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It produces a heavier, more viscous residue, which is still suitable for fuel blending or which can be gasified to produce hydrogen and can be used as fuel for a power plant directly. |
The Shell proprietary design of the transfer line between the atmospheric Fractionator and the Vacuum Flasher and of the Vacuum Flasher internals minimizes coke formation and hence maximizes the runlength. This design also ensures a maximum yield of distillate products while entrainment of heavy residue is avoided.
A large number of Vacuum Flashers downstream of visbreakers and thermal gasoil units are in operation. Shell Soaker Visbreaker units have successfully been revamped with the addition of a Vacuum Flasher.
When a refinery has a Visbreaker unit in operation, it is worthwhile to investigate whether additional distillate processing capacity is available. If this is the case, revamping the Visbreaker unit using Vacuum Flasher technology will result in more distillate products, and thus improved margins.
With a limited amount of investment, Vacuum Flashing technology offers two advantages over Visbreaker units without a Vacuum Flasher:
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Additional distillate products are produced which are suitable for thermal cracking, catalytic cracking or hydrocracking. This results in improve economics of the refinery. |
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It produces a heavier, more viscous residue, which is still suitable for blending into fuel oil, and can be burned in the refinery fuel system. As an alternative, this residue stream can be gasified to produce hydrogen and is then used as fuel for a power plant directly. |
When a Vacuum Flasher is added to a Visbreaker unit, only minor modifications to the Fractionator system are required. The feed preheat train and product rundown will typically be checked for the new situation.
The Vacuum Flasher concept has evolved from the crude / vacuum column design. In a Vacuum Flasher the following products are produced:
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Heavy Gas Oil (HGO) |
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Vacuum Gas Oil (VGO) |
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Vacuum Flashed Visbreaker Residue |
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HGO |
1 - 2 % |
cut point 350 - 365 °C |
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VGO |
11 - 15 % |
cut point 365 - 520 °C |
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VF Residue |
65 – 70 % |
cut point 520 °C - plus |
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By-Products: |
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Vacuum Flasher Off-gas: |
0.1 wt % |
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Vacuum Flasher Sour Water |
2.0 wt % |
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Slops |
0.1 - 0.2 wt % |
A calculation has been done for a typical visbreaker unit with a capacity of 4000 t/sd, processing Middle East Vacuum residue with a viscosity of 3900 cSt at 100 °C. Below, the difference in blending of a visbreaker unit and a visbreaker unit with Vacuum Flasher has been indicated.
Figure 1: Blending example
The difference in gross margin between a Shell Soaker Visbreaker and a Shell Soaker Visbreaker with Vacuum Flasher is approximately $5 per ton of residue feed. For a 4000 T/SD Visbreaker, the advantage is $ 6.6 Million per year. The difference in investment cost for the addition of a Vacuum Flasher is approximately $ 6 Million. The pay out time for Shell Vacuum Flasher technology is thus less than 1 year.
ABB Lummus Global has a history of executing various visbreaker revamp projects. A typical revamp project would start with assessment of operating data of the existing visbreaker plant, followed by a feasibility study phase, where different revamp options are evaluated in more detail. Results from the feasibility study are discussed with the client and a plan will be made for the next phase of the project which is the preparation of the basic design package. The basic design phase will be followed by the detailed engineering.
The Vacuum Flasher section can be built in a modular way and added next to the visbreaker plot. Given below is an example of a 3-D model of a visbreaker unit which was originally built by Shell and for which a Vacuum Flasher was added later on. The Vacuum Flasher section has been highlighted.
3D model of visbreaker unit with Vacuum Flasher