CPPA Bleaching Committee

Mill Problems and Solutions Session, October 22, 1996

 

 

 

Q:  Thurso - Getting high ClO2 consumption at D1 stage.  Could not explain increase .  Also getting higher pitch deposit.    Have cut back on chemical usage to reduce usage.   Any ideas?

A:  Any change in pH profile before the Bleach Plant?

A:  Now controlling pH with acid but this was started after the problem occurred.

A:  France - added talc for pitch control.     Maybe washing talc out with additional washing?

A:  Prince George - use to have lots of pitch, now using a hot Eo stage at pH 11.2, with no defoamer usage in the bleach plant.

A:  Thurso - No increase in defoamer consumption in the bleach plant   (1.8 kg/t)

A:  pH or temperature shocks?

A:  Thurso - Same temperature,    pH of brown stock is unknown.

A:  Eric Yee - suggest analysis by Paprican.  They have had Paprican in their mill.  Looked at age of chips.  Also have has some experience with calcium in the wood supply (90% hwd / 10% swd)

A:  Scan mills have recycled tall oil to digester for pitch control.

A:  Thurso - new sulphuric acid control in September

A:  Lots of discussion on this and suggestions,  but nothing concrete.

 

 

Q:  Alcell Forest:   What chemicals savings can be expected in converting Do Stage from  L/C to M/C?

A:  Harmac found a 13% reduction.  pH control is important,  also higher retention time.

A:  Eka -  no change on lab evaluation

A:  Thurso -  30% reduction due to longer retention time (16 min. increased to 40 min.)

 

 

Q:  E.B. Eddy -  Having problems with ClO2 absorption tower level indication when either generator vacuum is lost or quickly changed.  A safety incident has recently caused the S3 to overflow back to the generator and overflow generator liquor from the explosion hatch.  May have found cause (air leak where purge air lines connect to impulse tubing, but not sure yet.  Anyone else with this problem??  Would the leaks cause this type of problems.   Has anyone seen this?

A:  Dennis Owen - thinks that Crofton may also have had this problem.  Dennis will go back to them to ask them and get back to John Griffiths.

A:  System not holding pressure.   If pressure is up, will continuously lose pressure.

A:  Stone is also having problems.

 

 

Q:  Champion (Canton):   Has anyone had experience with barium sulphate deposit problems?

A:  Weyerhaeuser - Columbus mill has had experience.  Gary can not remember what they have done.   Does not do anything to eliminate.

Q:  Using sulphuric acid for pH control.

A:  Doug Reid -  Increasing D0 Stage temperature by 10 - 15 °C  would make the barium more soluble.   Perhaps that is too much saltcake carryover from the post-oxygen washing stages.

Q:  Marco Solinas -  heating up the stage should held increase BaSO4 solubility

 

 

Q:  Softwood with M/C O2 delignification.    Maximum % delignification?

A:  No answers

 

 

Q:  Does anyone have experience changing scrubber media from packed to turbotak?

A:  Howe Sound has done this.   Works well

A:  Carlos dal Monte has presented a paper on this.  Residual and spraying water is important.

Q:  Bleach plant scrubber operation.  Is anyone using on-line ClO2 stack analyser?

A:  Harmac looking at installing a unit.

A:  Multifibre Process has been developing a unit (Clotan Analyser) for low concentration for stack analysis

A:  Howe Sound has unit now and will be installing new electrochemical unit.

A:  Howe Sound uses analyser to adjust white liquor flow to scrubber (0.4L/sec).   Operator looks at white liquor flow to judge the ClO2 concentration from scrubber.  Spend white liquor is sewered to help control chloride concentration.  Problem is getting a good flow to analyser with no condensate in the line in order not to get a false low reading.

 

 

Q:  Howe Sound:   Experiencing trouble with D1 and D2 stage brightness controller since switching to ECF.   Meter would get coating on lens and stop reading.   We moved the meter from cone of upflow tube to pipe before ClO2 addition.  Meter no longer gets coating but is affected by the NaOH added at the washer for pH control of upflow.   How are other mills controlling?

A:  Mill Experiences:

            A:  Marcos -  same problems

            A:  Kamloops - did a lot of work with sensors

            A:  Repap - new sensor.   Kajaani sending research persons over because they can not

                        get them working because of filming over.

            A:  Marathon - same type of coating.  Moved the sensor to further along the stock line.

            A:  Crestbrooke - same type of problem

            A:  Prince Albert  - has change the lens to get away from the problem

            A:  Kajaani -  has developed a new lens with ultrasonic cleaning

A:  Suggestions:

            A:  Move further up the upflow where pH is lower

            A:  Switch to new style lens which to resistant to coating deposition.

            A:  Add microwave cleaning system.

            A:  Lower pH in upflow line.

 

 

Q:  Powell River:  Problems - drift and shift in Kajaani’s brightness signal in D1 Stage.

A:  It seem to be related to the position of the Kajaani probe.   Common Problem.

 

 

Q:  Learning to run 100% ClO2 substitution.  Have had very high chemical usage up to 4.5 kg/t in the Do stage.  Any answers?

Mixer:  Ahlmix                           Do - ClO2:  4.2-4.5 kg/t               Temperature:  60-64 °C

Retention time:  17 minutes        Kappa Number:    25                  Kappa Factor:  0.33

Inlet pH controlled at  3.3            nil or trace residual                     Vat pH  2.1 - 2.5

Do brightness yellowish              Eo brite  50-52

 

A:  If cut ClO2 back what happens?

A:  Eric Yee:  have decided to cut back by 40% last night at Prince Albert.  Now at 2.5% on pulp and have seen no change in brightness.

A:  Operate on Do Brightness

A:  Cut ClO2 back until it effects the brightness on Do stage.   Repap goes to ~35 Do brightness

A:  Do not worry about residual.  Marathon controls to zero residual and 50% brightness in the Eop stage.  Control is move on Kappa Factor.

A:  If cut back on ClO2 will also see higher pH which may result in the ClO2 working more efficiently.

A:  Summary:

            Lower Do temperature,  62 - 64 °C is too high.

            Control Do washer brightness,

            Target for Kappa Factor rather than ClO2 residual at the Do Stage

            Don’t worry, just cut back ClO2 in the Do Stage

Q:  Domtar (Senneville):   On recycled pulp, Cornwall using an acid stage to remove iron  (at 2.5 pH,  50% removal with  EDTA in acid stage)   Supplier has suggested low pH chelants, phosphoric acid etc.  Removal at pH > 4.5 is inefficient.   Are there any effective low-pH chelants?  Has anyone had any experience?

A:  Canton has tried acid, chelants with no success

A:  Some iron you just can not get out.

A:  Paprican - reduce pH to 1.1.   There is a portion of the iron that is very hard to remove.  If imbedded in the pulp, even higher to remove.  The more severe treatments would hurt pulp properties (e.g., pH = 1.8), did not think phosphoric and phosphorous acids would work either.

 

 

Q:  Domtar (Senneville):  (DZ) Technology - I need an update on IP’s patent claims?.  Is (ZD) unprotected by patents?

A:  Gord Homer said that Air Liquide lawyers OK’d DZ work.

 

 

Q:  Malette:   revisiting chemicals addition around O2 delignification.   What are additional points  locations for magnesium sulfate?

A:  Harmac, Howe Sound, Crestbrooke and Cariboo add to repulper of last stage of washing

A:  Pulp of last stage brown stock washer repulper steam heater standpipe prior to reactor.

 

 

Q:  Irving:  Getting brightness drop from D2 washer to dried pulp.   Experiences?

A:  E.B. Eddy -  get 1.5 points decrease,  1 point on pulp press

A:  Repap - 1.5 point drop

A:  Marathon -  get 1.0 drop on one machine and 1.5 point drop on the other pulp machine.  Higher drop on the machine producing the lowest air-dry.   Something different with that machine, probably air distribution.

A:  Howe Sound -  0.6 point at 60% subst.,  with ECF:  1.5 points decrease

A:  Crestbrooke -  get an increase of 1-1.5 points,  but using SO2

A:  Port Alberni -  increase in brightness due to bisulphide use.

Q:  changes HWD to SWD?

A:  Prince Albert -  0.5 increase with HWD.    D2 stage pH  5.7 - 6.0.

A:  Some species have different reversion rates

A:  SO2 gives less brightness drop and caustic the most.

 

 

Q:  Northwood -  No problems

Solution:  were experiencing an acid misting problem at acid unloading.   Moved unloaded pipe from into acid through dip tube to above the acid level.   Eliminate the misting.   Theory maybe from entrained air bubbles from unloading going from acid to surface exploding on surface.  Discharge in the air get a lot of bubbling, so no splashing and misting.

A:  Dennis Owen -  Design is free flowing acid addition to the tank.  CXY changed their tank design recently to free flowing, due to acid bubbling and misting.

A:  Must also control unloading pressure @ 25 psi

 

 

Q:  FMC:  Customer has had H2O2 in Eo stage off and on, but have been having problems with viscosity drop at the machines at 0.3% H2O2 on pulp.  Comments?

A:  Prince Albert -  removed peroxide from Eo due to viscosity drop.

A:  Harmac -  no problem 3 kg/t

A:  Thurso -  no problem

Q:  Possibility of carryover resulting in the problem?

A:  Howe Sound -  at 4 kg/t no problems.  Have not really seen anything at 6 kg/t

 

 

Q:  Powell River:  into J-tube 165-170 °F.     In tower probe 135 °F.   Any thought why lower temperature?     (uninsulated tower,   downflow tower)

A:  Channeling?  

A:  Remove probe to calibrate in boiling water and thermometer

A:  Move probe to bottom of well

 

 

Q:  Nuclear level on R8 level? who has?   Portage du Fort considering changing

A:  Standard with R8 and SVP

A:  Crofton, Prince Albert,  Marathon (since startup),  etc.

 

 

Q:  Condensate in Bleach Plant:  Who uses clean condensate or stripped MEE condensates?

A:  no answers

 

 

Q:  Marathon:  For mills using a Paprispec (with vibrating flat screen) for plastic analysis, what slot size is being used?   0.008”,  0.010”,  0.012”?  How you tried different slot sizes?.  What levels of plastic have been found for different slot sizes (# specks / 100 kg pulp)?  If you wish to share your experiences, please call Jim Collins.

A:  Cariboo did.    Now using flotation device.

A:  Kamloops -  flotation device

 

 

Q:  Repap:  installed Ahlmix at bottom of D1 stage.   Have seen no improvements in mixing  after replacing peg mixer.   Reasons?

A:  Prince Albert -  you have air in the pulp

A:  E.B. Eddy -  have unit after thick stock pulp,  a distance away with no problems.

A:  Need retention time after a mechanical pump.   Problem with pumping air.   You get pulse flow from cloverotor.  Also affect the ClO2 flow.

A:  Prince Albert -  Lower consistency  to 8-10% from 12%.  More water will smooth out the flow.

 

 

Q:  Harmac:    no problems

 

 

Q:  Celgar:   Acid addition to Do stage?   How?

A:  Harmac -  by pH control

A:  100% ClO2 substitution survey says 30% of mills add acid

A:  Howe Sound -  Two pH meter:   in brown HD and after ClO2 stage.   Cascade to control pH.

 

 

Q:  Thurso:    WL mixed with water,      how often washing and how?

A:  Northwood -  Scrubber after r8, first hot water wash,  then scale removal by HCl ejection.

 

 

Q:  Cariboo:   Who still operates  Matheson ClO2 Generators?

A:  Crestbroooke

 

 

Q:  Repap:  Chemical filter for ClO2 generator.   Problems with canister size and diameter.   Used pool filter.   Replacement housing will not fit the filter.   Suggestion?

A:  Hitrect filters at Prince Albert

A:  Dennis Owen will give Stuart a name of a new filter casing housing manufacture other than Sterling

 

Q:  Malette:   Run DED at end of bleach,  has anyone run with wash instead of adding caustic?

A:  E.B. Eddy -  have tried but loss brightness

A:  Howe Sound -  have done by error,   got lower brightness

A.  Norm Liebergott -  says you should always something  to extract

A:  Jack Histed -  in simplified bleaching,   if use DD instead of DnD, get higher bleaching costs

A:  Dennis Owen -  One mill runs DD for 30 yr.  They have just accepted higher bleaching costs.

A:  For DnD, losing ‘n’ caustic costs brightness.  If caustic there, its useful.  Taking off can also require more ClO2 in O2.

 

 

Q:  Anyone for CO2 for B/S on twin roll presses?

A:  Noone does

 

Q:  Who is working towards ISO 14000?

A:  Marathon,   Harmac,  Kamloops and several others   (8).

 

 

Q:  Don McCabe:   interested in any information of pulp properties variation with degree of ClO2 substitution.   ???

A:  Gordon Homer will send some information

A:  Marathon has some information that can be sent to Don McCabe.

 

 

Q:  Thurso:   Bleach Plant operator training,  having problems with practical training.   They went to use trainers with more experience.   Comments?

A:  Repap -  two week classroom training.    7 weeks total.

A:  Dennis Owen -  important to rotate trainee through all shifts.    Question is how do we know they are fully trained?   Sign-off by senior operator.    He will only learn 60% of one trainer’s knowledge.

A:  Mallette and Repap -  exams after theory and practical.   If do not pass back to training.

A:  Portage du Fort has simulator

A:  Thurso -   problem is training in the field.   Operators want more practice.

A:  Training at classroom and field trips.

A:  Practical training evaluation is important