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

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

Aug 12, 2023 94 likes •350 views

Management of chloride levels in a modern kraft pulp mill 7th INTERNATIONAL COLLOQUIUM ON EUCALYPTUS PULP May 26-29, 2015 Vitria, ES, Brazil Introduction 50% 50% Veracel is a joint venture of Stora Enso and Fibria. Located in

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Management of chloride levels in a modern kraft pulp mill

7th INTERNATIONAL COLLOQUIUM ON EUCALYPTUS PULP

May 26-29, 2015 Vitória, ES, Brazil

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

Introduction

50% 50%

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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).

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Introduction

  • Cl and K: Non process elements.
  • Where they come from?
  • Where they come out?  84% Ash Leaching

Veracel, 2011

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SLIDE 5

Introduction

  • Problems regarding Cl/K:

 Plugging: Ash melting points (first melting point and sticky temperature)  Corrosion

Reference: Hong Tran, 2007

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SLIDE 6

Introduction

  • Ash treatment technologies:

 Crystallization  Ion exchange  Ash Leaching ASH LEACHING - VERACEL

Cl/ Cl/K Na Na2SO SO4

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SLIDE 7

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.

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  • Tools used in the study:

 Data from Aspen (PIMS)  Six Sigma  Minitab  WinGEMS

Materials and Methods

6/10/14 21/5/14 10/12/13 6/8/13 12/3/13 9/10/12 9/5/12 21/11/11 30/6/11 3/1/11

5,5 5,0 4,5 4,0 3,5 3,0 2,5 2,0 Cloreto (%) 3

Time Series Plot of Cloreto (%)

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Results and Discussion

  • Chloride levels tendency (2011 – 2013) in the ash precipitator:
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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.

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Results and Discussion

  • Even with a good availability the chloride level was nevertheless
  • ver 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.

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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

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Results and Discussion

  • Purge control: results during 15 days
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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.

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SLIDE 15

Results and Discussion

  • Automation improvements: Torque plot of the ash leaching

centrifuge before and after implementing a new torque control

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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.

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SLIDE 17

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.

29,958 26,958 23,958 20,958 17,958 14,958 11,958 8,958 5,958 2,958 0,000 6 5 4 3 2 Time (days) Cl, K (%)

Cl (WinGEMS) K (WinGEMS) K (Mill) Cl (Mill) Variable

Time Series Plot of Cl and K (WinGEMS x Aspen)

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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

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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%.

3/3/15 4/12/14 26/9/14 21/7/14 8/5/14 10/2/14 25/11/13 20/9/13 18/7/13 7/5/13 8/2/13 5,5 5,0 4,5 4,0 3,5 3,0 2,5 2,0 % _ X=2,839 UCL=3,103 LCL=2,575 Before Step 1 Step 2

I Chart of Chloride (%) by Step

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Results and Discussion

  • The chloride level average has been around 2.84%.

Step 2 Step 1 Before 4,5 4,0 3,5 3,0 Chloride (%)

2,84 3,25 4,19 Interval Plot of Chloride (%)

95% CI for the Mean

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Results and Discussion

  • The results out of specification were reduced by 88%.

85.4%

Out of Specification

10.3 %

Out of Specification

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Conclusions

  • A preventive maintenance and training program with all
  • perators 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%.

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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