Control performance supervision enhances revamp

Borealis operates a facility in Porvoo, Finland, that produces ethylene, propylene, butadiene, acetone, phenol and polyethylene. The complex, which employs almost 900 people, is integrated with a refinery upstream. In the spring of 2007, Borealis upgraded an ethylene cracker there. To get a solid return on the millions of euros invested in the project, it was essential to meet the target production rates each week once the ethylene unit came online. The company realized that improved control performance was crucial to achieving that goal. With almost 1,000 control loops in the ethylene cracker and only a few control engineers, Borealis needed to focus efforts on the most important areas.

Project scope

 

The dashboard provides an overall view and, with drilling down, highlights major opportunities for improvement.

The revamp was designed to increase annual capacity from 330,000 tons to 380,000 tons. The project included equipment upgrades to a gas compressor, hydrogen purification unit and several distillation columns. Regulatory and Advanced Process Controls (APC ) were updated to handle the modified process. For the advanced controls to deliver the best results, all regulatory controls must properly function.

Without any dedicated tools or techniques for control loop monitoring, Borealis relied heavily on instrument maintenance and control engineers to detect problems. This reactive approach meant that only the most obvious and visible problems were addressed. Equipment repairs were based on age of service rather than objective measures of condition. Without the tools for continuous monitoring, problems often progressed to the point of failure before being reported and corrected.

To prepare the controls for successful startup, the company adopted three major strategies:

1. operator training with a simulator
2. revision of APC
3. improvement of regulatory controls.

Operator training — Ethylene crackers average five years between turnarounds, so operators don’t develop much experience with startup and shutdown situations. To fill that experience gap, Borealis installed an operator training simulator.

The simulator trains operators to handle:

• startup
• shutdown
• normal operation
• abnormal and emergency situations.

Advanced controls — With the changing process, Borealis needed to revise the APC. They were extended to include the new process equipment; models also were updated to reflect the performance of the new system.

To ensure that APC could deliver the most value, Borealis focused particularly on stabilizing and improving the underlying regulatory controls. Even small levels of cycling or instability may cause the APC to back away from optimal operation.

Regulatory control improvements — Borealis recognized that issues such as control valve mechanical problems, poor controller tuning and instrument failures were undermining regulatory control and directly affecting the performance of the plant.

To address these issues, we installed PlantTriage performance supervision software from ExperTune. This software connects to the control system via OPC and then identifies and prioritizes opportunities to improve regulatory control.

The software allowed us to see, for the first time, the performance of all the important control loops in our plant. Within a few days of software installation, we had uncovered a host of control system opportunities.

Dashboard insights

The Borealis team used plant performance dashboards (Figure 1) to determine the most important issues. Through these dashboards plant personnel could quickly identify the issues, drill down to root causes and then take appropriate actions.

 

Figure 2. Tuning and valve repair significantly enhanced furnace temperature control.

One of the most useful tools was the “Biggest Payback Loops” list, which singles out the 10 most important opportunities in the plant ranked by technical and economic criteria. Using this list, control engineers could allocate their time to deliver the greatest value. Drilling down on each loop in the Biggest Payback list shows specific details and the likely root cause of poor performance.

For instance loop FC-16026 was diagnosed as having extremely high valve travel — which causes high process variability, increased valve wear-and-tear and valve mechanical problems. Simply adding a small filter to the instrument signal can address the issue. Process stability improves almost immediately. “In most plants, valve travel may be reduced by a factor of 50% or more through the application of a filter and some appropriate tuning,” notes John Gerry, president and founder of ExperTune.

“When plants first start with performance monitoring, it is quite common to find some ‘low hanging fruit.’ These are problems that have been overlooked because most plants do not monitor some of the most important key performance indicators,” Gerry adds.