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Jul-2014

Revamping advanced process control

A programme to update a refiner’s APC systems employed a novel approach to the way new controllers are developed and existing controllers are maintained

STEFANO LODOLO, Aspen Technology
OLEG VEDERNIKOV, Isab

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Article Summary

Isab, an Italian refiner controlled by Lukoil, recently standardised Aspen Technology’s Advanced Process Control suite across two different sites in Priolo, Italy. In the two years Lukoil has been with Isab, old, low-performing controllers have been replaced or revamped and new controllers have been built. This rapid execution was possible thanks to a set of technologies implemented with close collaboration between Isab and AspenTech. These technologies have significantly impacted the methodology, development, benefits and sustainability of APC applications.

The new technologies, collectively called Adaptive Process Control, are unique and present a number of advantages that alter the way that new controllers are developed and existing controllers are maintained. The overall result is that a new controller can be deployed just a few weeks after a project begins, immediately accruing benefits while the model is simultaneously improved on-line. Existing controller benefits are consistently maintained at peak levels, transforming maintenance from a reactive process, which is often neglected, to an automated and proactive process.

An APC Benchmark comparison tool designed by AspenTech demonstrates the results achieved during the two-year programme.

Improved return of investment
The majority of refineries in Western Europe are struggling to improve their margins. Aside from current capital cost investments with a medium to long return on investment (ROI), they are looking for initiatives that could permit a quicker ROI and reduced cost investments.

APC permits a quick ROI based on small investments, providing a good opportunity to improve existing assets profitably.

Isab runs two integrated refineries in Italy with a combined processing capacity of 300 000 b/d. When Lukoil took control of Isab, it began a number of improvement initiatives with the overall objective of improving profitability and competitiveness within the stagnant market.

Isab has a long history of APC on its units, previously adopting three different technologies with varying results.

One of the main issues in sustaining the benefits of APC over time is the specialised skillset, through internal resources or external consultants, required to maintain applications. Sustaining the APC benefits over time is even more complicated and expensive when technology is outdated. Several technology suppliers offer maintenance solutions but they are manual activities.

Isab started an ambitious, multi-year APC programme in order to cover the main units of the refinery, standardise on one technology, and adopt innovative APC solutions. This initiative allowed it to:
• Reduce the skills required to develop and maintain APC applications
• Automate all possible tasks to relieve the limited workforce available
• Reduce the labour costs of APC controller maintenance
• Minimise erosion of benefits due to process, quality, market and other changes that should trigger some actions on the APC applications to restore performance
• Return controllers to service faster after turnarounds.

The APC programme at Isab
The APC programme at Isab was founded on a master services agreement with AspenTech which included a medium term plan with a detailed roadmap.

The plan was developed around the main refinery units, requiring old controller revamps or replacements (some with a change of APC technology supplier) and development of new applications.

The main controllers that have been revamped are related to:
• Crude distillation unit
• Vacuum distillation unit
• Light ends
• Fluid catalytic cracking unit.

Some of the new units that have been covered by APC controllers include:
• Diesel hydrotreater 1
• Diesel hydrotreater 2.

Other units are being covered by new APC applications:
• Gasoline reformer
• Hydrogen plant
• Hydrogen network optimisation.

More applications will be implemented in the future as per the Isab APC roadmap.
The first step in the APC programme was the replacement of two existing, outdated APC controllers on the CDU and VDU which were based on a different APC technology.  The revamp of these large, profitable units has been a success, creating a new overall momentum for the entire APC programme.

APC innovations
Isab determined AspenTech’s APC technology to be the best solution available, based on the new Adaptive Process Controller controller, recently made available and patented by AspenTech.

APC was designed around the idea that developing new applications and maintaining existing applications should not require the highest skilled resources, should be less labour intensive, and should empower end users.

APC enables customers to:
• Start a new APC application within two to four weeks from project kick-off meeting
• Optimise while step testing the plant to produce data suitable for model identification
• Perform all tasks required to update controller models without the need to turn off the controller
• Ensure that the controller can tolerate model mismatch during the periods between model updates
• Handle maintenance as a built-in and continuous part of the process and eliminate the need to wait for turnarounds to revamp controllers
• Incorporate control knowledge within the products and leave it to the users to leverage their in-depth knowledge of the production process.

APC has several advantages over traditional sustained value approaches:
• The controller model is continually analysed for accuracy
• Poorly performing areas of the model are identified
• Non-disruptive background testing collects new process data while the unit is being optimised
• New data are monitored in real time and bad data are automatically identified and removed
• New candidate models are automatically created and presented to the engineer for review and simulation before on-line deployment.


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