Fraser Papers saves over $2 million annually with Emerson upgrade of bleach plant controls and instrumentation.
An automation upgrade project providing advanced controls for existing bleaching, washing, and screening areas of the Fraser Papers magnesium bisulphate pulp mill in Edmundston, New Brunswick, Canada, resulted in annualized savings of $2.2 million Canadian. Savings were realized through lower startup costs, reduced bleach chemicals consumption, and increased production capacity. Completed in late 2000, the project was a joint effort of the Emerson Process Management Pulp & Paper Industry Center, Atlanta; Laurentide Controls, Emerson's local area representative headquartered in Montreal; and mill personnel.
Fraser Papers Inc., a wholly owned company of Nexfor, Inc., produces 700+ tpd of fully bleached softwood pulp for use at its fine paper mill in Madawaska, Maine. Robert Duncan, process engineering supervisor at the Edmundston mill, summarized project impact following 14 months of operation, saying, "The $2.2 million savings and accompanying 1.9 percent mill efficiency increase have exceeded expectations of the project. Pulp production has been running at levels never before thought possible, ClO2 generator efficiency and stability is much improved, chemical bleaching costs are stabilized, and quality has improved slightly." Duncan estimated that 15 additional tons of pulp are produced per startup -- a bonus of almost 1000 tons of pulp in 14 months -- while off-quality pulp has been greatly reduced along with the environmental impact.
Finding a way to meet the pulp mill's goals of reducing bleaching costs, improving pulp quality, and increasing the efficiency of ClO2 generation dates back to 1999 when Emerson engineers audited the mill and made recommendations, including installation of pre-engineered, turnkey automation systems called CyberBLEACH™ and CyberWASH™. These solutions are based on the PlantWeb digital plant architecture including the DeltaV digital automation system for all process areas, replacing an existing distributed control system that controlled the bleaching process and chlorine dioxide generator.
Selected control valves, bleach plant sensors, and field instrumentation were also replaced. Newly installed intelligent Fisher valves with FIELDVUE digital valve controllers, Rosemount transmitters, Micro Motion Coriolis flowmeters, and Rosemount Analytical devices all perform online diagnostics. The bulk of the installation was completed as the mill continued to operate, and final conversion to the new technology was completed during a seven-day shutdown period in June 2000.
The new bleachery control room has three NT operator workstations, each with dual monitors. The control system includes an application station and engineering station. Two remote workstations -- one in the sulphite foreman's office and the other in the technical office -- are used for monitoring various operations and information gathering. The main control strategies involve automatic startup and shutdown sequences, production rate controls, pH and chemical residual controls, delignification degree and brightness development controls, "virtual" sensor calibration, and pulp tracking.
Automated startup and shutdown sequences for the three major processes -- washing and screening, bleaching, and chlorine dioxide generation -- were key factors. These processes, which were formerly started by pushing a series of buttons manually, are now safely started or shut down by depressing just one button. What once took longer than an hour to complete is now done in less than 30 minutes, enabling more pulp to be processed.
Duncan reported that a plant efficiency increase of 1.9 percent has been attributed to the advanced controls now in place. In-depth evaluations conducted more than a year after the control system was commissioned revealed a number of economic benefits, including:
Reduced chemical usage
Increased chlorine dioxide generator efficiency
Improved pulp quality
Substantial reductions in chemical dosages have been recorded in each of four stages through improved pH measurement and control using filtrate extractors. The kappa number of unbleached and extracted pulps is carefully monitored in line, allowing greater kappa factor control and thus application of a minimum amount of chemicals for efficient bleaching. The kappa factor actually decreased by 7.3 percent, and total equivalent chlorine demand has decreased by almost 3 percent. Duncan estimates that a 13 percent reduction of bleaching costs has been achieved.
The Solvay chlorine dioxide generator was running well beyond design capacity, and consequently its efficiency had dropped below the desired target. By automating the controls, installing improved flow measurement devices, and revamping the control strategy, the efficiency of this unit increased by 2.4 percent, Duncan said.
In addition, variations in pulp quality are improved, largely due to the new bleaching sensors and automated controls. Bleach control models were also developed for pulp delignification and brightness development. Duncan reports that the percentage of on-spec product for brightness and dirt count has improved slightly, while fine-tuning continues in this area.
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