Unified control migration
Lush green forests sweep grandly from the mountains to the ocean in the coastal states of Espirito Santo and Bahia, Brazil, about 450 kilometers north of Rio de Janeiro. What's unusual about these forests is that they're part of nearly 611,000 acres of eucalyptus plantations owned and managed by Aracruz Celulose, one of the world's leading producers of market pulp, which is shipped around the w...
Lush green forests sweep grandly from the mountains to the ocean in the coastal states of Espirito Santo and Bahia, Brazil, about 450 kilometers north of Rio de Janeiro. What's unusual about these forests is that they're part of nearly 611,000 acres of eucalyptus plantations owned and managed by Aracruz Celulose, one of the world's leading producers of market 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 meters in seven years. Also, the eucalyptus fiber's short length is highly desirable because of its high opacity, softness and capacity to absorb ink well.
The Aracruz pulp mill has grown to be the world's largest producer of bleached eucalyptus pulp and operates the world's largest single pulp production facility, producing more than 2 million tons of pulp per year. To support and grow that level of product, Aracruz has taken measured steps to bring all of its operations under a consistent process control and optimization strategy. Recent commissioning of its new Fiberline C marks a significant milestone in the mill's transition to a fully integrated production enterprise, in which all production lines are controlled from functional control points, and advanced process control is used to optimize everything from digesting to drying.
Aracruz built Fiberline C using modern, integrated control technology that eventually will run all mill processes. Its first line, Fiberline A, has been upgraded with these controls, as have the boiler and evaporation units of Fiberline B. Fiberline C is believed to be the world's first pulp operation designed and built with advanced process control (APC) and optimization technology.
The mill's progress to this stage is part of an ongoing process of capacity expansion and system upgrades, which started with pulp production via Fiberline A in 1976. At that time, Fiberline A was producing 400,000 tons of bleached pulp per year, under control of Foxboro PCI 100 pneumatic instrumentation. In 1988, Aracruz built Fiberline B, which expanded annual production by 600,000 tons, using Provox DCS.
In 1995, Aracruz modernized lines A and B, eliminating production bottlenecks while expanding capacity to 1.2 million tons per year. At Fiberline A, the original pneumatic control systems were replaced with the Invensys' Foxboro I/A Series. This control system was configured in a six-node local area network (LAN) with multiple application processors, user workstations, and an interface to programmable logic controllers (PLCs). As many as 125 field enclosures provided the I/O interfacing to more than 1,500 field instruments, using FoxCom communications protocol. In addition, InTouch human-machine interface software from Invensys' Wonderware was installed to create new process visualization screens for operator control of wood yard operations.
Because Fiberline A controls architecture was deemed effective, in 2000 Aracruz management used it as the basis for construction of Fiberline C and upgrades on other lines. The goal was to allow each line to operate independently and provide a unified control strategy and view into operations for better management of overall plant productivity.
This graphic shows details of processes linked to a DCS on the three lines prior to Line B migration.
Basic production processes are similar in all three lines. Logs arrive daily by truck or barge from the plantations. As needed, the wood is loaded into debarkers and chippers that feed each line. Chips are conveyed into stainless steel pulp digesters, where they are cooked with caustic liquors to form the pulp. Brown pulp stock is washed and screened before being bleached white and fed into drying machines. At the end of each drying machine, the "pulp blankets" are cut into rectangular sheets and baled for shipping. Wrapped bales are then transported by truck to a nearby port for shipping.
Different vendors supplied equipment for each step (see DCS configuration graphic), but all processes are integrated into a common control strategy managed under the I/A Series control system.
Flexible I/O modules
I/A Series automation packages on Fiberline C consist of five network nodes with UNIX servers and Microsoft Windows NT workstation processors.
A Trident triple modular redundant safety shutdown system from Invensys' Triconex business unit protects the oxygen reactor. Foxboro field instruments—including pressure, temperature, magnetic flow, mass flow, pH, and conductivity devices—interface with the system by means of the FoxCom protocol, using remote I/O racks located close to the process. Motor controls are connected via intelligent MCCs to as many as 25 Micro I/A Series nodes via Profibus networks, without using PLCs.
"The final step in upgrading the plant was completely changing the layout of three control rooms for the Fiberlines, recovery line, and drying machines to consolidate Lines A, B, and C," says Renato Gueron, project manager. "This was necessary because Line A had Foxboro CRT consoles and monitors, while Line B had competitive CRT consoles and monitors, which meant that there would be no space to add Line C operating stations. They now all operate under one master control system."Workstations with thin-profile LCD screens have now been installed in all three control rooms.
Retrofitting controls on Fiberline B was simplified because of Invensys' plug-in migration strategy, by which other processors and I/O cards have been exchanged with Foxboro I/A Series replacements of the same form factor, incorporating updated electronics circuitry. These I/O modules are functionally identical to ordinary I/A Series modules, but are repackaged to plug into most legacy I/O racks, enabling the switchover without moving any field wiring, minimizing production downtime.
At Fiberline B, the "plug-in" method has been used to replace the Provox systems that controlled boiler and evaporation units.
This approach helped bring the new line on-stream faster—and under budget—and it provides a path for future growth in production capacity, making it easier for all three fiberlines to use the same regulatory controls to support the advanced process control and optimization already underway for Fiberline C.
Maria Eunice Casulli is account manager for pulp and paper industry, Invensys Process Systems;