E. TECHNICAL SESSION
An outline of the technical session is described below. PowerPoint presentations and/or overheads are attached where applicable.
Douglas C. Pryke ( Consultant ),Rob Laurendeau ( CANFOR )
( Presentation at end of minutes )
In October 1999, CANFOR LTD’s, Prince George, B.C. upgraded the control strategy from Compensated Brightness Control (CBC) to Compensated Kappa Factor Control (CKFC) in the Do stage of their market pulp mill. The pulp mill bleaches oxygen delignified softwood at 20 kappa no. using a DoEopDEpD sequence. The pulp mill produces approximately 290,000 ADt per year at 90% ISO brightness for the international market.
An assessment of the Compensated Kappa Factor Control (CKFC) strategy compared to the prior Compensated Brightness Control (CBC) strategy over both long and short term operating periods showed:
• The Do kappa factor, DoEop kappa factor and overall bleaching sequence kappa factor decreased significantly;
• Overall-bleaching costs decreased approximately 5% - 7%;
• Oxidising chemical consumption decreased 8-9%;
• Bleaching costs (based on oxidising chemicals) decreased 10%;
• Pulp quality was maintained; and
• Final brightness variability decreased.
The operators readily adopted the new control strategy and the control system has averaged 97% availability
.Laurier Morrisette – BTG
( Presentation at end of minutes )
This presentation outlined the benefits of good pH control with the focus on medium consistency applications and the impact on control strategy in the oxygen delignification, D0, and D1 stages. In the case of the oxygen delignification stage good pH control will have a stabilising effect on K number.
Good pH control in the D0 and D1 stages will result in more even kinetics of ClO2 and allows for excellent feed forward prediction on both the D0 and D1. Because soda carryover introduces variability a pre and a post ClO2 injection pH meter will yield the best results for optimum ClO2 usage.
In line pH meters are subject to extremes and can result a high degree of maintenance. Best pH control is achieved with the use of a filtrate extractor and an offline pH measurement. This improves ease of calibration and maintenance.
3. CARBON DIOXIDE USE AT THE CANFOR SPECIALTY PULP AND PAPER MILL
Jeff Bennett - CANFOR
( Presentation at end of minutes )
Production rates were restricted at the CANFOR Specialty Pulp and Paper Mill due to
unacceptable brownstock washer performance. Acidifying the brownstock washer
shower water with carbon dioxide was investigated as a means of enhancing the
washer operation.
A number of trials were performed between November 1997 and August 1998, investigating different aspects of the washer, screen room, and bleach plant performance. The trial results showed:
These results were achieved with a CO2 application between 2.0 and 4.0 kg CO2 / ADUt pulp.
The trials showed such a significant improvement in the operation that the CO2 system has been in continuous use since January 1998. The use has been justified based on increased screen room effluent cleanliness and improved digester rates during periods of typically high resin acids.
4. Bleach Plant Cost Monitoring at CANFOR’s Specialty Pulp and Paper Mill
Jeff Bennett - CANFOR
( Presentation at end of minutes )
The mill identified a need to have cost data available at least on a daily basis and accounting could not provide this service. The mill had the data indirectly through their DCS. The need for up to the minute cost data was also driven by the various configurations of the bleach plants as several grades are produced and grade changes are frequent.
Initial development started in 1994 and was expanded in 1997 to include all grades. The overall accuracy is not as exact as accounting but it is real time and can provide trends. Awareness has reduced bleaching costs since 1997 and quality has been maintained.
5. Bleach Plant Operating Strategies at Irving Pulp and Paper
Don McCabe – Irving Pulp and Paper
( Presentation at end of minutes )
This presentation focused on how the entire fiberline is involved in maintaining good bleaching control. The main focus was to minimise variation from one department to another. Good bleaching really starts with the wood handling area by trying to reduce chip variation. good mixing of chips results in a more uniform cook and lower K# variation. The O2 delignification system is equipped with a DCS based control program to further reduce variation resulting in a more uniform product to the bleach plant.
The bleach plant also employs a DCS control system that in addition to controlling chemical application also monitors the pulp throughout the bleach plant. Various tools including SPC are available to troubleshoot and monitor any upsets.
6. FRP Inspection
Craig Reid - CANSPEC
Craig Reid of gave an excellent presentation of FRP inspection. Three basics of inspection are observation, interpretation and reaction. Observation, visual and NDT inspection, as well as coupon removal and excavation is the preliminary data gathering.
Interpretation of the observation part must include the knowledge of the fabrication history of the FRP as well as its operating conditions (past and present), previous inspection degree, and rate of deterioration.
For the action part, experience plays a big role in knowing when to repair and when to replace. It is always a good idea to retain core samples for future comparison and if possible, retain the cores from flange or taps from when the pipe or tank was first put in service.
Several FRP samples were [presented showing various modes and degrees of failure. Differences between metal failure and FRP failure were highlighted.