16 PULP & PAPER CANADA November/December 2014 www.pulpandpapercanada.com
Its an ideal situation if a paper or board mill project aimed at reliability and improved machine operation can have a cascading, positive effect on the operat-ing costs in other mill departments. The ROI effect is thus amplified. That sort of scenario was realized earlier this year at Sonocos Trent Valley mill in the hamlet of Glen Miller, Ont. A board machine dryer-section project to solve chronic syphon reli-ability and dryer flooding problems did just that and, additionally, lowered the costs of generating steam. The cogeneration plant crew gives thanks, as well as the board mill production staff.
The dryer project targeted board machine 3 (BM3), which produces liner-board, coreboard, boxboard and specialty
grades from 39 to 100 lb./1000 sq.ft. (9 point to 28 point). It has a width of five metres and runs at machine speeds rang-ing from 110 to 193 m/min. The 6.7 MW natural gas-fired cogeneration power plant produces 115,000 lb./hr. of steam for the board machine and the turbine.
Previous syphons had short life spanMill staff realized that something had to be done to solve recurring and persistent problems with dryer section syphon fail-ures, condensate-flooded dryers and associ-ated dryer bearing failures. Jean Franois Dsilets, production superintendent, says that at most times before the project an average of 10 dryers were locked out, the
majority of which were for broken syph-ons. Some were shut for safety issues. We repaired 4 to 6 syphons on a main-tenance shut, but we never got ahead of the problem since the syphons had such as short lifetime; it was hit and miss. He also notes that, during machine operation, there could be a number of flooded dry-ers but the operating crew had no way of knowing since there were no sight glasses. The need to operate at slower speeds on heavy weight grades was another problem caused by lower drying capacity.
Wilbur Wilton, chief operating engi-neer, adds his description of the issues: We allocated two to three maintenance people every shutdown to repair syph-ons but the problem was getting worse. We could repair five syphons but not 10 since we didnt have enough manpower. We were also repairing a lot of leaks at the shutdown. These leaks caused some unsafe, slippery floors in the basement. Since the condensate return was unreli-able, the cogen plant across the road was spending too much money for treating and heating fresh makeup water from the Trent river.
Premature dryer bearing failures were another problem created by frequent dryer flooding since the extra condensate load added stress to the bearings. A dryer head failure last year convinced the mill staff to focus on the issue and make some decisive corrective action. Moreover, over the long run, the maintenance cost had to be cut since too much effort was being put into correcting chronic problems. To rectify these urgent problems the mill
Syphon retrofit has mill-wide benefitsA turnkey dryer project at Sonocos Trent Valley mill eliminated previous syphon failures and flooding, while reducing fresh water makeup costs in the cogen plant.
By Mark Williamson, journalist engineer
Board machine #3.
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contracted Kadant Canada to conduct a machine study in Novem-ber, 2012, that revealed an inherent weakness in 50 existing syph-ons. These were very old, thin-wall bent pipe stationary syphons. The remaining 10 dryers that form the dry-end high-pressure sec-tion were equipped with Kadant HDRS rotary syphons. Kadants proposal to replace the bent pipe stationary syphons with rotary scoop syphons was accepted in June, 2013, and the installation was completed in January, 2014, during a scheduled press rebuild
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shutdown. The project was more complex than usual since the dryers had different journals and manhole placements. The new products started up with no issues according to Dsilets.
Designed for lower speed machines, rotary scoop syphons efficiently remove condensate that pools at the bottom the dryer shell. At lower speeds, the condensate pools rather than rimming in an even layer around the circumference of the shell as con-densate does at higher speeds. The scope of the turnkey project
Left: Flooding has been eliminated as shown by condensate flow sight glasses on all dryers.
Middle: Jean-Franois Dsilets.
Right: Wilbur Wilton.Phot
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18 PULP & PAPER CANADA November/December 2014 www.pulpandpapercanada.com
also included installing dual flow rotary joints, steam and con-densate isolation ball valves, flex hoses and sight glasses that show condensate flows from each dryer, as well as replacing components in the thermocompressor to match its operating curve to the new syphons. As an extra benefit, the move to com-mon syphons and steam joints made the spare parts inventory consistent for all dryers.
Raised the bar for maintenanceSince the startup, the syphons have been completely reliable and the flooding problems have disappeared. The new sight glasses are in place just in case there is a future problem. The frequency of dryer bearing replacements has been reduced dra-matically, from an average of once per month. There have been no replacements since the installation of the scoop syphons. Regular bearing temperature measurements show that the bear-ings are running 15 to 20 F cooler than before. That should extend their lifetime.
On the boardmaking side, Dsilets sees that board quality has been improved as papermakers can predictably set the top and bottom dyers for effective board curl control. Before, the crew did not know the extent or locations of flooded dryers. Also, production speed can be maintained on heavy grades.
The reduction in maintenance burden has been a welcome relief to Wilton since he can now plan preventive maintenance more effectively rather than reacting to chronic problems. We have a more even distribution of time and manpower. Now, we can plan and focus on priorities. This project has set a precedent and raised the bar for our maintenance. By stabilizing the drying and condensate return the rest of the steam system can now be optimized, he says.
Wilton says the cogen steam generation is more economical since, with more condensate return, the fresh water makeup has been reduced from 35% to 14%. This means less consumption of pH-controlling amine and water softening chemicals for fresh water and less energy to heat the river water from its sometimes frigid level. Wilton estimates the consumption of expensive food grade amines has been reduced by almost 80%.
Financial returnsThe total numbers, as compiled by process engineer Cassandra Bailey, tell the financial story. The maintenance and machine downtime costs related to syphon failures, flooding and asso-ciated bearing replacements have been eliminated up to July, 2014. This results in a saving of more than $12,000 per month. The savings in amine for pH control is almost $11,000 year to date in July and the water softening chemical saving for the same period is $3,000. From May to July, 2014, the fresh water make-up has been reduced by about 1,190 cu.m. /month to 1,1360, amounting to a fuel cost saving of $4,000 to $5,500/month. The cost of the study and the project was partially subsidized by Union Gas, the local gas distributor. The mill has applied for a gas consumption rebate under the Ontario EnerSmart program.
Mill manager Jason Giffen gives his final assessment of the project results: This was a big win for our mill. It has been a game changer since we have been able to tackle and solve these repetitive problems. PPC
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