Recovery of Liquors & Bleaching II PPT 110

DE(OP)PD Bleaching D stage E(OP) stage P stage D stage

Why Bleaching Lignin Itself Chromophoric Groups Attached

Two Approaches Brightening True Bleaching Selective Destruction of groups Temporary Effect True Bleaching Delignify Attempt to preserve strength

Brightening GW, TMP, NSSC – high yield/lignin Destroys/reduces color groups Temporary eye appeal Will yellow and degrade

Bleaching Sequence Symbols Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

Bleaching Objectives Brightening by lignin removal decolourizing Cleaning by shive & dirt bleaching Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

Bleaching Objectives Optical Qualities High Brightness Brightness stability Cleanliness Opacity Strength Environmental Quality Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

Bleaching at Evergreen Was CEHEH Now ODE(o)D

Easier to Bleach? Softwood or Hardwood Why?

BLEACH PLANT Chemicals Vapour to Scrubber Water Steam Unbleached Pulp Bleached Pulp BLEACH PLANT Effluent to Recovery Effluent to Discharge Reeve, Douglas W., TAPPI Bleach Plant Operations Short Course, 1998.

Upflow and Downflow towers Multistage Bleaching Upflow and Downflow towers

Simplified Bleaching Reactions

Chlorine Make It or Rail Cars Safety Environmental 2-4% cons. – dissipate exothermic Time & Temperature Pulp consumption vs solubilize lignin Proper Mixing

Caustic Extraction 12-15% cons 60-80 deg C Good washing from previous stage Retention Time up to 2 hrs Opens up fiber Remove chlorinated and/or oxidized lignin

Reduces Environmental Issues Oxygen Reduces Environmental Issues Watch for pulp degradation

O2 Delignification

O2 Delignification Reduces Kappa number Reduced effluent loading BOD5 – 50% Color – 70% COD – 50% Reduces chemical costs – 30% Lowers pulp viscosity – but equal strength

Extended Cooking Leads to Lower Yield

Hypochlorite Mix Chlorine with NaOH or Ca(OH)2 Usage is declining 35-40 deg C for 1-2 hrs pH control to protect cellulose attack Watch pulp viscosity decreases Calcium(cheap) but scale vs sodium

Damaged Low Viscosity Pulp Fiber

ClO2 Plant

Chlorine Dioxide Generate from Sodium chlorate ClO2 gas is explosive but soluble in water First used in 1946 Highly selective destruction Preserves strength High and stable brightness

TCF or ECF?

Dioxin 1985 – 2,3,7,8, TCDD was found in fish downstream from a paper mill and subsequently found in mill effluent 1988 – National Council for Air and Stream Improvement (NCASI) reported on a five mill study that showed TCDD (Tetrochloro Dibenzo Dioxin) and TCDF (Tetrochloro Dibenzo Furan) were formed in bleaching operations March, 1988 – PAPRICAN (Pulp and Paper Research Institute of Canada) reported finding precursors DBF (Dibenzo Furan) and DBD (Dibenzo Dioxin) in defoamers and oil

World Chlorine Trends 1990-2001 Elemental Chlorine Free and Total Chlorine Free

Bleaching Trends Lower incoming Kappa number Improved washing – reduce black liquor carryover Oxygen delignification Lower Cl2 multiplier High ClO2 substitution Eo, Ep, Eop Short sequence bleaching Pretreatment with NO2 Ozone bleaching OZEoP Improved mixing technology Aerated lagoons

Final Bleach Plant Washer

Decker for Pulp Thickening

High Density (HD) Pulp Storage

Bleach water Recycling Less water treatment (in and out) Heat conservation Chemical savings Test for corrosivity Test for pH