Aracruz Celulose is unusual in that the mill uses eucalyptus trees for making pulp, which is shipped around the world to paper producers who make tissue, fine printing, writing and specialty paper products. The advantage of eucalyptus trees is that they grow so quickly, reaching mature heights of about 35 metres within just seven years of growth. This means that they can be harvested much more frequently than the slow growing pine forests of North America.
In 1995, Aracruz management overhauled the production lines to modernise and eliminate bottlenecks, while expanding overall production capacity to 1,2 million tons per annum. At this time, the original pneumatic control systems were replaced with a Foxboro I/A Series DCS. This was configured in a five node local area network, combining multiple application processors and user workstations interfaced to PLCs. As many as 125 field enclosures provided the I/O interfacing to more than 1500 field instruments, using FoxCom communications. In addition, InTouch Human Machine Interface software from Wonderware was installed to create new process visualisation screens for operator control of wood yard operations.
This approach to production control worked so well that in 2000 Aracruz management undertook their largest project of all – the construction of Fiberline C and the upgrading of Line A and B controls. The goal was to allow each line to operate independently, but to provide a unified view into all operations for better management of overall plant productivity.
Following a year of planning, consultation and project definition, Aracruz management decided to continue their strong relationship with Invensys Operations Management and used the Foxboro I/A Series DCS to operate Fiberline C. The Fiberline A controls architecture was so effective that it was used as the basis for the Fiberline C plant expansion with significant savings generated from reusable engineering. Retrofitting controls on Fiberline B was simplified using Foxboro’s plug-in migration strategy. I/A Series I/O modules, manufactured to be one-for-one, form fit replacements for the original Provox I/O modules, plug-in to the legacy I/O racks. The physical switchover was accomplished without moving any field wiring with total process downtime to migrate this 1000 point system less than 3 hours and 15 minutes.
The complete Foxboro I/A Series DCS on Fiberline C consist of five network nodes with Windows NT workstation processors. A Trident triple modular redundant safety shutdown system from Triconex is used for protection of the oxygen reactor. All Foxboro field instruments – ranging from pressure and temperature devices to magnetic, mass, pH and conductivity devices – are interfaced with the system by means of the FoxCom protocol, using remote I/O racks that are physically close to the process. Motor controls are connected via intelligent MCCs to as many as 25 Micro I/A nodes via Profibus networks, without having to use PLCs. Foxboro I/A Advanced Controls packages were also installed in each production area to gather baseline measurements for evaluating performance improvements obtained from the advanced process controls. All engineering work for regulatory control is being managed by Invensys as well, through subcontracts with the nine primary equipment suppliers. Simulation packages for this effort, to emulate actual use of all control processors and Micro I/A units, were supplied by SimSci-Esscor.
Foxboro command centres with thin profile LCD displays have now been installed in all three control rooms. The processors and I/O cards have been swapped out for Foxboro I/A replacements that have the same form factor, but which incorporate today’s latest electronics circuitry technology. This helped bring the new line on-stream faster and provides a strong avenue for future growth in production capacity. In fact, with this facility upgrade, Aracruz was the first pulp mill to start up with all advanced controls in place and running. That is a good situation to be in because the so called ‘paperless revolution’ that has been talked about for years never really occurred. That means this world will always need fine papers for use in computer printout, copiers and old fashioned hand written letters.
For more information contact Jaco Markwat, Invensys Operations Management, +27 (0)11 607 8100, tech@invensys.co.za, www.iom.invensys.co.za
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