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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