Amoco
Valhall Platform
By Mohan Thiagarajah, Applications Consultant, Honeywell UK
Amoco Valhall is an oil field which is located on the maritime border
between Norway and UK. It was put into production in 1982, and is currently
producing around 100,000 barrels per day.
Introduction
In 1998, Honeywell in Norway received a $1 million
order to retrofit the turbomachinery control and condition monitoring
systems. The main objective of this retrofit is to maximise oil production,
which in turn requires gas production to be maximised. This can only be
achieved by running both parallel gas production streams at full load.
However, such operations are not possible with the existing turbomachinery
controls, mainly due to their dated and inflexible designs.
The platform has two 'strings of compression',
each with four compressors stages driven by two Rolls-Royce Avon gas turbines
and a fifth driven by a gas expander. Both strings are identical and arranged
for cascade gas compression. The diagram below shows a Rolls-Royce Avon
driving a two-stage compressor.
Honeywell also supplied a VisSim
model-based dynamic simulator to test the system thoroughly during the
factory acceptance test (FAT) and thus avoid unnecessary delays during
commissioning. This will be combined with Amoco's spares to construct
a realistic training aid
A Rolls-Royce Avon Driving A Two-Stage Compressor.
The Role of VisSim
VisSim Professional was used to simulate 2 electric motors, 4 Rolls-Royce
Avon gas turbines, 10 compressors, 10 re-cycle valves and 10 flow measurement
elements. All these models were linked to Computer Boards I/O cards via
VisSim/Real-Time Pro. This allowed us to test the all the controller
/ control modes simultaneously. Thus we were able to start-up any or all
of the turbo-compressors, run them in series / parallel load-sharing configurations,
and then shut them down at will. The result was that control system became
operational at the press of the button. Amoco was able to start and get
machines on-line in a manner that was unheard of previously.
The VisSim model building exercise took two months
of engineering. It was worth it because the Amoco Project Manager (Karl
Ole Stones) was convinced that the modelling exercise saved 21 days of
off-shore commissioning. In terms of financial gain, this equates to;
(21 days) x (100,000 barrels per day) x ($15
per barrels) = $millions
Conclusion So the moral of this
story is 'a stitch in time saves nine'.
"As a mechanical engineer, my main role at
Honeywell is to solve turbomahinery control problems - not learn complex
programming languages and simulation environments. So when I was tasked
with simulating turbomachinery to test control systems before they left
our factory, I chose VisSim. All you need is a logical brain and some
knowledge of engineering mathematics. VisSim makes the rest very simple.
I was able to use its intuitive programming environment to create very
complex gas turbine and compressor models. They were so good that the
control systems that we tested became 'plug-n-play' items in the field.
This is previously unheard of. Many other control system suppliers deliver
'plug-n-pray' items which are debugged through 'trial and horror' at the
customers expense."
-- Mohan Thiagarajah
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