Retention-Drainage-Formation By: Saurabh Mittal Ravi S Joshi

This presentation will cover RETENTION DRAINAGE FORMATION THEORY

POLYMER CHEMISTRY Polymer Chemistry - Polymer chemistry is important because knowing the terminology, the structures and functionality of the polymers will help in the understanding of how a polymer performs and reacts in various conditions.

CHARACTERISTICS THAT DEFINE A POLYMER: Monomers in the Polymer Charge of the Polymer Molecular Weight Configuration Natural or Synthetic Monomer - The number and type of monomers in the polymer (i.e., homopolymer, copolymer of AETAC and Acrylamide Charge - Includes the overall charge (i.e., cationic, anionic) and the charge density (i.e., mole %) Molecular Weight - What it is, how it is measured Configuration - Configuration of the polymer includes general shape (linear, branched), monomer distribution in the polymer and the shape in different conditions. Natural, Synthetic - Natural or synthetic in origin - starch (natural) vs. polyacrylamide (synthetic)

GENERAL CLASSIFICATIONS OF MOLECULAR WEIGHT Low Medium High Molecular Weight Range < 100,000 100,000 x <1,000,000 1,000,000 Classification - This is a classification that is commonly accepted in the industry. Most coagulants are low molecular weight. Most flocculant type products are high molecular weight. Polymers in the weight range of 100,000 to 1,000,000 are sometimes referred to as medium molecular weight. There can be large differences in molecular weights within each classification. For example, high molecular weight anionic flocculants have typically higher molecular weights than high molecular weight cationic polymers. Gen Reference 7, 2

RETENTION-DRAINAGE MECHANISMS Three steps of retention and drainage Coagulation Flocculation Filtration Coagulation - Coagulation is the reduction of the repellant forces between particles such that they no longer repel one another. Flocculation - Flocculation is combining or forming a “bridge” between the neutralized particles to produce discrete agglomerates. Filtration - Filtration is the trapping of the agglomerated particles in the forming sheet.

+ COAGULATION – – – – – – + – – – + + – + + + + – + – + – – – – – – – Coagulation reduces the repellant forces between fillers and fines by development of charged patches (charge neutralization) – – – – – – + – – – + + + + – + + + + – + – + – – – – – – – Coagulant Coagulation Coagulation is based on formation of cationic sites or “patches” with a high charge density on the fiber or particle surface by cationic poly-electrolytes. The polymer can be adsorbed in cationic patches on the negatively charged particle surface so that partial charge neutralization occurs. Coagulation will then occur through electrostatic attraction between oppositely charged parts of the particles.24 Fillers & Fines - It is important to keep the relative size of particles and polymer in perspective. The picture may be somewhat relative for small particles (fillers) and small fines, but not for large fibers. – Agglomerated Fillers And Fines Through Patching Discrete Fillers And Fines

Anionic Trash & Neutralization Anionic polymeric substances able to interact with cationic polymers Poorly washed pulps, coated broke or hydrogen peroxide bleaching are the main sources Highly closed systems accumulate anionic substances with time Two Types: Inorganic Alum PAC Synthetic - low molecular weight, high-charged cationic polymers Polyamines PolyDADMAC’s Generates small, compact floc structures Molecular Weight - The polymers used for coagulants are typically in the 10,000-600,000 molecular weight range. Polyamines - For more info on polyamines, see Polymer Chemistry. DADMAC’s - For more info on polyDADMAC’s, see Polymer Chemistry. PEI - For more info on PEI, see Polymer Chemistry. Microflocs - Microflocs are reversible; they will reform after disruption by mechanical shear forces.

Attachment of HMW Polymer FLOCCULATION Combining or forming a bridge between particles with a polymer to produce discrete agglomerates – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – Bridging - In bridging, one part of the polymer chain becomes attached to one or more adsorption sites, while its other part extends into the bulk solution. These extended loops and tails can be adsorbed onto other particles, thus forming polymer bridges.24 Particles - The particle polymer interaction can be the result of opposite charges (anionic particle - cat polymer) or patch charge - polymer interface (cationic patch, anionic polymer). Flocculation by Particle Bridging Attachment of HMW Polymer

FLOCCULATION DUE TO BRIDGING High level of hydrodynamic volume favors bridging - long loops and tails Bridging influenced strongly by molecular weight of the polymer Bridging also influenced (to lesser extent) by the amount of polymer charge Generates large diffuse floc structure (macro flocs) Shear sensitive; higher the charge, the stronger the bond Hydrodynamic Volume - Hydrodynamic volume is an indication of how much volume a polymer chain occupies under a set of conditions. This relates to how coiled or linear a polymer chain is. Shear Sensitive - Flocs due to bridging are unstable to shearing. Reflocculation is slow, not only because the flocs are broken but because the polymer chains can also be broken by shearing and their conformation on the particle surface changed. The macro flocs formed by bridging flocculation are therefore regarded as irreversible. 24

IMPACT OF SHEAR ON FLOC FORMATION Charged Patches Polymer Bridging Disruptive Force Redispersion Charged Patches - When flocs formed through the coagulation mechanism and charged patches are subjected to shear, they can reform. Polymer Bridging - When flocs formed through the bridging mechanism are subjected to shear, they do not reform readily and result in weaker, smaller flocs. Bonds Re-formed Reduced Bridging

RETENTION/DRAINAGE The papermaker’s goal is to produce: The most uniform product (formation) At the highest speed (drainage) At the lowest cost (retention) These factors are interrelated and must be balanced to meet the paper maker’s needs Factors - The following table shows the typical relative impact of each factor/variable on formation, drainage and retention. Factor/Variable Formation Drainage Retention Short Fiber Length + - - Fillers + - - Refining (hydration) - - + Refining (cutting) + - - Low HBX consistency + - - High HBX consistency - + + HBX Turbulence + + - Velocity Forming -/+ - + Pressure Forming + + - Table Shear/Turbulence + + -

FOUR STAGES OF WATER REMOVAL Gravity drainage Vacuum assisted water removal Mechanical pressure (table and press) Drying (heat energy) Stages - Drainage is divided into four stages because each stage can react differently to a system change. It is possible to improve drainage in the first two stages and hurt drainage in stages 3 & 4, resulting in a net overall loss in drainage as measured by machine speed and energy requirements. Gravity Drainage - Gravity drainage occurs as water drains from the stock through the forming fabric via filtration and fiber mat thickening. Gravity (head pressure) is the force that causes drainage. This is the portion of drainage that we can test in the lab.26 Vacuum-Assisted - Vacuum drainage is accomplished by the foil blades, vacuum boxes and couch roll. Mechanical - Water can be mechanically removed from the sheet on the table and in the press. On the table, the stock jet can be forced into the forming fabric or removal can be mechanically assisted with the use of table rolls or the dandy roll.

FACTORS AFFECTING DRAINAGE Large flocs - high retention of fines Stage 1: Fast gravity drainage due to large void areas between flocs. Stage 2: Slow drainage over vacuum units due to thin spots caused by heavy floccing. This increases the openness of the sheet and allows vacuum to be lost through the sheet. Stage 3: Large, high fines content flocs are dense, making it difficult to remove water by pressing and drying. Dispersed, unflocculated system, low retention of fines Stage 1: Slow gravity drainage due to high fines level of system; sheet two-sidedness. Stage 2: Good drainage over vacuum units due to uniform sheet providing high vacuum. Stage 3 & 4: Good drainage in the press and dryers unless a high level of fines causes severe two-sidedness

FACTORS AFFECTING DRAINAGE Uniform microflocs, good fines retention Stage 1: Small flocs provide for paths of water drainage. Fines controlled at low equilibrium level. Stage 2: Uniform flocs and sheet gives good vacuum drainage. Stage 3: Uniform floc size and well-distributed fines give good pressing and drying.

Benefits of RDF Program High FPR% & FPAR% High Chemical Retention Lowers Back-Water Turbidity Less Load on ETP Better Formation at High Retention Fast Drainage

Example: Volume of Water Removal Given: 25.00 ton/hr @ 7% reel moisture & Calculation - 23.25 ton/hr Bone-Dry Fiber @40% Press Section Solids @42% Press Section Solids 60% water 58% water Ratio 1.5:1 Ratio 1.38:1 34.9 ton/hr water 32.1 ton/hr water 2.7 m3/hr less water to be evaporated in the dryers Stages - Drainage is divided into four stages because each stage can react differently to a system change. It is possible to improve drainage in the first two stages and hurt drainage in stages 3 & 4, resulting in a net overall loss in drainage as measured by machine speed and energy requirements. Gravity Drainage - Gravity drainage occurs as water drains from the stock through the forming fabric via filtration and fiber mat thickening. Gravity (head pressure) is the force that causes drainage. This is the portion of drainage that we can test in the lab.26 Vacuum-Assisted - Vacuum drainage is accomplished by the foil blades, vacuum boxes and couch roll. Mechanical - Water can be mechanically removed from the sheet on the table and in the press. On the table, the stock jet can be forced into the forming fabric or removal can be mechanically assisted with the use of table rolls or the dandy roll.

Drainage – Rule of Thumb 1% increase in press solids correlates to: –11-13% increase in wet-web strength 4-5% machine speed increase (directly related to production increase) on drying-limited grades 4-5% reduction in steam consumption Stages - Drainage is divided into four stages because each stage can react differently to a system change. It is possible to improve drainage in the first two stages and hurt drainage in stages 3 & 4, resulting in a net overall loss in drainage as measured by machine speed and energy requirements. Gravity Drainage - Gravity drainage occurs as water drains from the stock through the forming fabric via filtration and fiber mat thickening. Gravity (head pressure) is the force that causes drainage. This is the portion of drainage that we can test in the lab.26 Vacuum-Assisted - Vacuum drainage is accomplished by the foil blades, vacuum boxes and couch roll. Mechanical - Water can be mechanically removed from the sheet on the table and in the press. On the table, the stock jet can be forced into the forming fabric or removal can be mechanically assisted with the use of table rolls or the dandy roll.

Application Technology Flocculants Feedpoint Selection - Based on desired results Post screen will achieve the most efficient and maximum retention Post screen will also typically provide the best gravity drainage Prescreen will result in less negative impact on formation Prescreen will result in less efficient retention but may not reduce drainage

Application Technology Flocculants Feed Scheme Feed ring Before or after screen Injection quill Often before screen Post dilution At least 10 to 1 More is better Fresh water if possible (can dilute at feed system) Clean white water only at feedpoint

Filler pre-treatment Treating filler stream with additive maximizing interactions with retention program Non – flocculative pre-treatment Reduction of zeta potential – coagulant additon Sensitizing filler particle for flocculant addition (Phenol formaldehyde resin additon) Flocculative pre-treatment Increasing filtration component of filler retention:

Wet-end Process Variables Effecting RDF Chemistry – water and additives – already discussed Headbox Set-up and Headbox Type Former Set-up and Former Type Furnish Components and Ratios Refining Forming Fabric Temperature, pH, consistency, mill closure Entrained air Basis Weight Distribution of fines and fillers Chemistry – already discussed Furnish Components and Ratios - Virgin pulp higher former dewatering rate, but higher steam demand Recycled pulp lower former dewatering rate, but lower steam demand Refining – increased refining leads to decreased drainage and fines generation – blocks pore area and reduces water flow Types of drainage Forming fabric – to be discussed Former design – to be discussed Former set up/Headbox set up –to be discussed Temperature – Hotter the stock the lower the viscosity and the greater the drainage – also easier to dry Entrained air – Typical is 1% or less. Old best practice was 0.5%, now the new standard is 0.1%. Dramatic impact on vacuum dewatering and sheet consolidation. Lower air allows increased water passage through consolidated sheet Basis Weight – Distribution of fine and fillers -

Case Study Mill Information:   Mill is having one machine of 200 TPD along with integrated pulp of 170 TPD. They are producing pulp of 70 kappa no. Mill is producing Kraft Liner Board of 120 – 250 GSM. Mill is using bagasse as basic raw material. Mill follows Cobb 120 in place of Cobb 60 and maintaining Cobb 120 @ 50 - 60. Mill is using solid rosin along with solid non ferric alum.

Case Study Lab Trial Report:    1.  Set 1:- Pulp + Alum (20 Kg) + Rosin (1.5 Kg) + Defoamer (0.8 Kg)   =   pH @ 4.1, Cobb 120 @ 131 & Drainage @ 340 ml/30 sec.   2.  Set 2:- Pulp + Alum (20Kg) + Rosin (1.5Kg) + WSR (10Kg) + Defoamer(0.8 Kg)    =   pH @ 4.2, Cobb 120 @ 160 & Drainage @ 345 ml/30 sec. 3.  Set 3:- Pulp + AKD (4Kg) + WSR (10Kg) + Defoamer (0.3 Kg)     =     pH @ 6.95, Cobb 120 @ 38 & Drainage @ 335 ml/30 sec. 4.  Set 3 A:- Pulp + AKD (4 Kg) + Defoamer (0.3 Kg)     =     pH @ 7.1, Cobb 120 @ 63 & Drainage @ 330 ml/30 sec. 5.  Set 3 B:- Pulp + WSR (10Kg) + AKD (4Kg) + DCPAM (0.15 Kg) + Defoamer (0.3Kg)    =    pH 7.4, Cobb 120 @ 41 & Drainage @ 398 ml/10 sec.      

Case Study 6. Set 4:- Pulp + WSR (10Kg) + AKD (4 Kg) + DCPAM (0.15 Kg) + LAPAM (0.15 Kg) + Defoamer (0.3 Kg)    =    pH @ 7.49, Cobb 120 @ 37 & Drainage @ 400 ml/30 sec.   Set 5:- Pulp + WSR (10 Kg) + AKD (4 Kg) + DCPAM (0.15 Kg) + LAPAM (0.15 Kg) + Bentonite (2 Kg) + AF 270 (0.3 Kg)    =    pH 7.35, Cobb 120 @ 30 & Drainage @ 445 ml/30 sec. 8.  Set 6:- Pulp + WSR (10 Kg) + AKD (4 Kg) + DCPAM (0.15 Kg) + Bentonite (2 Kg/T) + Defoamer (0.3 Kg/T)    =    pH @ 7.41, Cobb 120 @ 34 & Drainage @ 430 ml/30 sec. 9.  Set 7:- Pulp + WSR (10 Kg) + AKD (4 Kg) + DCPAM (0.3 Kg) + LPAM L (0.15 Kg) + Defoamer (0.3 Kg)      =      pH @ 7.5, Cobb 120 @ 28 & Drainage @ 472 ml/30 sec. 10.Set 8:- Pulp + WSR (10Kg) + AKD (4 Kg) + LCCP (0.3 Kg) + LCCP (1 Kg) + Defoamer (0.3 kg)      =       pH @ 7.5, Cobb 120 @ 38 & Drainage @ 560 ml/30 sec.

RDF Thanks