modern kraft pulp mill 7th INTERNATIONAL COLLOQUIUM ON EUCALYPTUS - PowerPoint PPT Presentation

Management of chloride levels in a modern kraft pulp mill 7th INTERNATIONAL COLLOQUIUM ON EUCALYPTUS PULP May 26-29, 2015 Vitória, ES, Brazil

Introduction 50% 50%  Veracel is a joint venture of Stora Enso and Fibria.  Located in southern Bahia  Annual production: 1.1 million tons of pulp

Introduction  Project: Chloride reduction at Recovery Boiler ash  Area: Recovery Boiler  Objective: Reduce the Cl level in the RB ash and keep it below 3 % (guarantee to operate 12 months continuously).

Introduction  Cl and K: Non process elements.  Where they come from? Veracel, 2011  Where they come out?  84% Ash Leaching

Introduction  Problems regarding Cl/K:  Plugging: A sh melting points (first melting point and sticky temperature)  Corrosion Reference: Hong Tran, 2007

Introduction  Ash treatment technologies:  Crystallization  Ion exchange  Ash Leaching ASH LEACHING - VERACEL Cl/ Cl/K Na Na 2 SO SO 4

Materials and Methods Study case in Veracel mill (2013/2014)  The recovery boiler and the ash leaching are from Valmet.  The boiler capacity is 4900 tds/day and the regular load of the  ash leaching is 160 t/day .

Materials and Methods  Tools used in the study:  Data from Aspen (PIMS)  Six Sigma  Minitab  WinGEMS Time Series Plot of Cloreto (%) 5,5 5,0 4,5 Cloreto (%) 4,0 3,5 3,0 3 2,5 2,0 3/1/11 30/6/11 21/11/11 9/5/12 9/10/12 12/3/13 6/8/13 10/12/13 21/5/14 6/10/14

Results and Discussion  Chloride levels tendency (2011 – 2013) in the ash precipitator:

Results and Discussion The First step in this project was to increase the system availability.  Actions:   Study of shutdowns root causes  Preventive maintenance each 15 days  Training program with all operators and mechanics.

Results and Discussion Even with a good availability the chloride level was nevertheless  over 3% most of the time. The main actions on this second phase of the project were:   Purge control  Implementation of new feedback and feedforward level control in ash leaching tank.  Implementation of new torque control.  Simulations of the effect of process changes upon the chloride levels in the mill.

Results and Discussion Purge control  Increase the purge of ash leaching reject  (liquid phase) until the chloride level of the dust reached below 3%. This occurred just after the shutdown, when the Cl was around 4.5%. PURGE

Results and Discussion Purge control: results during 15 days 

Results and Discussion Automation improvements: a new feedback and feedforward  level control was implemented in the ash leaching tank and a new torque control was created .

Results and Discussion Automation improvements: Torque plot of the ash leaching  centrifuge before and after implementing a new torque control

Results and Discussion Once the ash leaching was running quite well and the chloride level  was under control, the next actions were related to strategy during system stops. Simulations were made using a WinGEMs model of the mill in order  to support the decisions related to the centrifuge shutdowns in a predictive way.

Results and Discussion  An ash leaching stop of 20 days was simulated. The Cl content in ash increased from 3 to 5.4 weight %. The increase in the model and mill was generally the same. Time Series Plot of Cl and K (WinGEMS x Aspen) 6 Variable Cl (WinGEMS) K (WinGEMS) K (Mill) 5 Cl (Mill) Cl, K (%) 4 3 2 0,000 2,958 5,958 8,958 11,958 14,958 17,958 20,958 23,958 26,958 29,958 Time (days)

Results and Discussion  A stop for 12 hours will increase the Cl content from 2.8 % to above 3 %. A total stop for more than 12 hours might require ash purge to prevent the risk of plugging. To keep the Cl levels lower than 3 % during a longer shutdown, the mill must purge around 45 kg ash/ADT to prevent it to rise

Results and Discussion  The result after all those actions have contributed the decrease of the chloride level and keep this parameter under control, i.e. less than 3%. I Chart of Chloride (%) by Step Before Step 1 Step 2 5,5 5,0 4,5 4,0 % 3,5 UCL=3,103 _ 3,0 X=2,839 LCL=2,575 2,5 2,0 8/2/13 7/5/13 18/7/13 20/9/13 25/11/13 10/2/14 8/5/14 21/7/14 26/9/14 4/12/14 3/3/15

Results and Discussion  The chloride level average has been around 2.84%. Interval Plot of Chloride (%) 95% CI for the Mean 4,5 4,19 4,0 Chloride (%) 3,5 3,25 3,0 2,84 Before Step 1 Step 2

Results and Discussion  The results out of specification were reduced by 88% . 85.4% Out of Specification 10.3 % Out of Specification

Conclusions  A preventive maintenance and training program with all operators were very important to run the system with a high availability.  The purge control and the automation improvements allowed the decreased of chloride.  Simulations were also important to predict the Cl and K levels to support strategies to keep the Cl in the ash under 3%.

Thank you! Work group: Carla Medeiros – Veracel Diego Monteiro – Veracel Flavia Silva – Veracel Kleverson Figueredo – Andritz Matheus Guimaraes – Fibria Per Andersson – Stora Enso Rickard Wadsborn – Stora Enso