Tall Oil Recovery TAPPI Kraft Recovery Short Course C.D. Foran, Arizona Chemical Co., Savannah GA Slide 1 Tall oil soap is a mixture of the sodium salts of rosin acids, fatty acids and neutrals that separates from kraft black liquor. Composition of Crude Tall Oil Southern USA Northern USA & Canada Scandinavia New Zealand & Chile Acid Number 165 135 132 158 Resin Acids % 41 3 23 43 Fatty Acids % 51 55 57 4 Neutrals % 8 15 2 14 1
Slide 2 How Much Tall Oil Can Be Recovered? Region Tall Oil kg/1 kg OD Wood Tall Oil lb/ ODT Wood Piedmont 24 48 Coastal 26 52 Canada 11.5 23 Southwestern 31.5 63 West of Cascades 7.5 15 NZ & Chile 12 24 Finland 18.5 37 Sweden 25 5 Lb. CTO/ODT Pine Wood Tall Oil Loss 52 51 5 49 48 47 46 Recovery 25.5 24.5 23.5 45 22.5 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 1% 8% 6% 4% 2% % Average Impact of Storage Time on Tall Oil Loss 2 4 6 8 1 12 14 16 18 2 22 24 26 28 Storage Time (weeks) Outside Chips Roundwood Chips 26 25 24 23 kg CTO/ODt Pine Wood Slide 3 Why Should Tall Oil Be Recovered? To improve pulp and paper mill operations To reduce the toxicity of pulp mill effluents, To reduce accidents due to slips and falls. To increase mill revenue 2
Slide 4 Tall Oil Should Be Recovered To Improve Pulp and Paper Mill Operations : 1. Reduce evaporator fouling, 2. Increase evaporator uptime, 3. Increase recovery boiler solids burning capacity, reduction efficiency 4. Reduce paper machine foaming, 5. Reduce bleaching costs, Heat Transfer Coefficient (of Initial Maximum) Impact of Improved Removal on Evaporator Overall Heat Transfer 11% 1% 9% 8% 7% 6% 1 2 3 4 Hours Running No Recovery Poor Recovery Good Recovery Influence of Skimmer Outlet Residual on: Slide 65 Evaporator Time On-Line Evaporation Rate 1% 1% Availability 98% 96% 94% 92% 9% 88% 86% 84% 82% Fraction of Maximum Evaporation Rate 98% 96% 94% 92% 9% 8%.5.7.9 1.1 1.3 1.5 1.7 1.9 2.1 88%.5.7.9 1.1 1.3 1.5 1.7 1.9 2.1 Skimmer Outlet Residual (% CTO on a Solids Basis) Skimmer Outlet Residual (% CTO on a Solids Basis) 3
How Skimming Affects Evaporator Performance Overall Slide 6 Good Skimming Skimmer Residual (%).6 Downtime (hr./month) 45 Evaporation 323 Rate (Mkg/hr) Production (Tonnes) Unbleached 345 Bleached 247 Poor Skimming 1.1 75 315 321 23 Change.5 3-8 -24-17 Tall Oil Should Be Recovered To Reduce Pulp Mill Effluent Toxicity 1. Fatty Acids, Resin Acids and Phenols affect both the toxicity to fish and the taste and color of fish. 2. Sodium soaps of resin acids account for 8% of the effluent toxicity. 3. Sodium soaps of unsaturated fatty acids account for 2% of the effluent toxicity. 4. Toxicity is independent of oxygen demand. Slide 7 4
Slide 8 9 What causes soap to separate from black liquor? Increased liquor solids, Decreased liquor temperature, Residual effective alkali above 6 gpl, Increased fatty acid to resin acid ratio Decreased hardwood liquor content. Slide 9 Solubility Tall Oil % of Solids 3.5 3. 2.5 2. 1.5 1..5. PAST NOW 1 15 2 25 3 35 4 45 5 55 Black Total Solids (%) 16 F 71 C 12 F 49 C 8 F 27 C At washer filtrate temperatures, soap begins to come out of solution at about 8% solids. Minimum solubility occurs at 25 3% solids. 5
The Effect of Residual Effective Alkalinity and Composition on Solubility Slide 1 Solubility ( % -Solids basis).5.45.4.35.3.25.2.15.1.5 5 1 15 Residual Effective Alkali ( g/l) FA/RA = 5 FA/RA < 2 1. Minimum solubility occurs at 6-8 gpl REA, 2. Increasing the fatty acid : resin acid ratio will reduce soap solubility. 3. The fatty acid : resin acid ratio is determined by the wood species used. Influence of Hardwood Content on Tall Oil Solubility Slide 11 1.2 lb CTO/ 1 lb BLS 1.8.6.4.2 Mill A Mill B % 2% 4% 6% 8% 1% Hardwood in Furnish 6
Slide 12 Where does soap separate from black liquor? 1. Washer filtrate tanks 2. Weak liquor storage tanks 3. Evaporator soap skimmers 4. (Heavy liquor storage tanks) Why Should be Removed from Weak Storage Tanks acts as a surfactant that stabilizes foams and increases evaporator liquor carryover. At weak liquor solids levels greater than 14%, soap accumulates rapidly, reducing weak liquor storage significantly. Weak liquor skimming increases overall soap removal by reducing the load on the evaporator soap skimmers. Slide 14 13 7
Slide 14 Foam liquor carryover will occur if the height of a column of foam is taller than the height of the vapor space in the evaporator. Foam Height = Volumetric Evap. Rate* Bubble Life Foam Column Area The bubble life is increased by lower temperatures, smaller bubble diameter and increased soap content. Removal of the soap before evaporation will reduce the bubble life and reduce liquor carryover. Slide 15 Common Configurations for Manual Weak Skimming Slide 15 Advantage Simple and inexpensive to install Disadvantages Requires much operator attention Can result in significant liquor carryover. 8
Weak Floating Skimmers VENT TO NCG SYSTEM Slide 16 LIQUOR FEED 16% SOLIDS SOAP LEVEL LIQUOR LEVEL LIQUOR RETURN PUMP Advantages Reduces the risk of soap surges to the evaporators Increases the effective liquor storage capacity SOAP CONCENTRATOR (OPTIONAL) SOAP PUMP TO STORAGE Disadvantages Higher capital cost Skimmer Efficiency (Inlet - Outlet ) (3.% -.6%) = (Inlet - Solubility) (3.% -.45%) Slide 17 = 94% Good skimming greater than 85% efficiency Tall Oil Solubility @ 71 C (16 F) Tall Oil % of Solids 3.5 3 2.5 2 1.5 1.5 1 15 2 25 3 35 4 45 5 55 Black Solids (%) 9
Skimmer Baffling to Prevent ShortCircuiting Baffle Slide 18 Path Baffles Path To Storage Poor Baffling y to Skimmer Bed Good Baffling Skimmed Circular Skimmer Layout Baffle Scraper Rotation In Collection Trough Scraper Bed Out In Baffle Pump Collection Trough Out 1
Slide 19 How Skimmer Dimensions Affect Skimmer Efficiency will not separate if the soap particle rise rate is less than the liquor downdraft. (Superficial Velocity) Effect of Superficial Velocity on Skimmer Efficiency Skimmer Efficiency 1% 8% 6% 4% 2% % 1 2 3 4 5 6 Superficial velocity ( mph) Canadian Mills Southeast US Mills Slide 2 How Skimmer Dimensions Affect Skimmer Efficiency Efficiency 75% Efficiency 9% 4 Ft. 12 m Residence time 155 min Superficial Velocity 13 fph (4 mph) 33 Ft. 1 m 6 Ft. 18 m Residence time 158 min Superficial Velocity : 6 fph (2 mph) 15 Ft. 4.6 m Feed Rate 2 gpm (758 lpm) 11
Skimmer Level Control Slide 21 To Storage y to Skimmer Bed A X Overflow Standpipe Skimmed A= X *Dl/(Dl-Ds) Ds - Density of Dl - Density of A= 4 *1.13/(1.13-.94) = 24 Skimmer Efficiency Improvement Stabilize skimmer level control. bed depth < 2 ft. (.6 m) Remove solids buildup Ensure that the inlet is well isolated from the outlet Evaluate air injection to the suction of the skimmer feed pump. Evaluate chemical additives Dens. & Skim. Resid. 8 6 4 2 Effect of Air Injection 9 min. Residence Time Slide 22.5 1 1.5 2 2.5 SCFM/1 gpm Skimmer Feed Density (lb/gal) Residual lb/mlb BLS Content (%) 24 18 12 6 Content (%) 12
How Air Addition Affects and Bed Depth at a Fixed Skimmer Level Set-Point sp.gr. 1.14 sp.gr..12 sp.gr..54 sp.gr..96 Slide 23 2 Depth 15 1 5 High Air Addition Moderate Air Addition No Air Addition Depth (in.) Bed Depth Slide 24 Pumping, Piping Ensure that the pump suction is not restricted or reduced, Minimize the length of the pump suction Use positive closure ball valves Isolate spare soap pumps by ball valves, never use check valves Use positive displacement pumps Provide steam clean-out lines See also http://www.pumpschool.com 13
Positive displacement pump flow rate is relatively independent of viscosity 1 Flow vs. Viscosity 8 Flow (%) 6 4 2 25 5 Viscosity centi-poise Positive Displacement Centrifugal Positive Displacement Pumps Produce Essentially Constant Flow That Is Almost Independent Of Pressure Centrifugal Pump Curve Pressure (Head) Positive Displacement Pump Curve Flow Rate 14
Positive displacement pump flow rate is relatively independent of viscosity 1 8 Flow vs. Viscosity Flow (%) 6 4 2 25 5 Viscosity centi-poise Positive Displacement Centrifugal Positive Displacement Pumps Produce Essentially Constant Flow That Is Almost Independent Of Pressure Centrifugal Pump Curve Pressure (Head) Positive Displacement Pump Curve Flow Rate 15
Slide 25 Pumping Problems Ensure that the pump suction is not restricted or reduced, Check the pump rotation Positive displacement pumps: Set the internal pressure relief valve 5 1% above the Normal system pressure Check Gear pumps for wear Too much Lower the skimmer level ~ 1% Low Density ( <.23 sp. Gravity) Reduce air addition to soap skimmer Use soap Concentrators Slide 27 Fiber Content (ppm) Mill Fiber Content 16 14 12 1 8 6 4 2 1-Jan 1-Mar 3-Apr 29-Jun 28-Aug 27-Oct 26-Dec Actual Upper Control Limit 16
Summary Slide 26 Tall oil soap is a mixture of the sodium salts of rosin acids & fatty acids that separates from black liquor. Depending on wood species, good soap recovery is about 45 Kg soap / ODt wood. Good soap recovery reduces evaporator fouling, recovery boiler loading & effluent toxicity.. Summary Slide 27 solubility is minimized at 3% black liquor solids and 6-1 gpl residual effective alkali. separates in the washer filtrate tanks, weak liquor storage, evaporator soap skimmers. is best removed in tanks that have a downdraft less than 2 m/h, are well baffled & have stable level control. Improve soap skimming by isolating the inlet and outlet liquor, controlling the soap bed depth at.6 m, injecting 7.5 lpm air /m^3 feed liquor. 17