Control is the core in Billerud Korsnäs' steam net

When Billerud Korsna's factory in Gävle was to rebuild and renew its energy production, the development of new control strategies began early in collaboration with Optimation AB.

Getting involved from the start is a dream for all control system engineers, a profession group who often comes in too late at major industrial projects.

"It was a strategy by Billerud Korsnäs that Optimation should manage the control system of the existing steam grid from the beginning," says Andreas Krafft.

To succeed in implementing a simple and thoughtful control strategy, there is a huge advantage to be part of the project from the outset. With this approach, the challenge instead becomes that you can work on repeated installations over a long period of time as new installations are implemented.

Andreas Krafft appreciates the opportunity to participate throughout the project with new steam systems at Korsnäs.

"Optimations project model lets the control needs of the components show how to build a plant and control system."

By applying this approach to Korsnäs, Optimation has fully implemented its principle of having a control for each pressure level to be controlled, and having a clear priority order in the system.

"It has long been common for industry to have a controller per valve, and it often leads to them 'fighting' each other," says Andreas Krafft.

Many opportunities to control

The steam system at the Gävle plant, operated by the newly formed company Bomhus Energi AB, consists of a number of different pressure levels. A new boiler and a new turbine are also part of the project. The aim is to make as much steam as possible through the turbine and, to increase efficiency further, increases the utilization of the large steam accumulator with 300 cubic meters of water. The accumulator allows the system to maintain the pressure in the net during temporary disturbances in the steam usage. The system also manages to change the load in the boiler slowly, giving the boiler an opportunity to reset without disturbing the operation.

Opportunities such as dump capacitor and free blowing should only be used as last resort in the control strategy. The system is, of course, automatic, and designed to cope with all the different operating instances in the factory. Much work has also been done to make it easy to follow how the system works.

An important factor is, as often in major industrial projects, that old equipment is still left far into the project. In this project, for example, the old turbine and boiler can be in operation even after the new control strategy is fully connected.

Three years with Billerud Korsnäs

The project at Gävle plant has been in progress since spring 2010. Then a preliminary study was made, based on the current needs.

"It's important to get a good preliminary project," says Andreas Krafft. "This allows you to build a good simulator and thus create a good base for the continuation of the project."

In the fall of 2010, the main project began.

"Then we built the simulator. Together with a group, with different skills, we looked at different operating scenarios. Then we modified the simulator according to the needs we could identify."

When everyone was satisfied with the simulator, the programming was done by a subcontractor.

In March 2011 it was time for the first commissioning. Since then, Optimation has had intense working periods as various parts of the plant have been put into operation. The last parts of the control system came into operation in December 2012.

"Towards the end of the project, more and more suppliers have come in, including ÅF, Siemens and Metso. Together we have had many discussions about regulatory strategies and technical solutions. Although the work has been complicated, we have kept the timetable from start to finish, which has been a very good project," summarizes Andreas Krafft.