Tall Oil Soap 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

Northern New Southern USA & Zealand & USA Canada Scandinavia Chile

Acid Number 165 135 132 158 Resin Acids % 41 30 23 43 Fatty Acids % 51 55 57 40 Neutrals % 8 15 20 14

1 Slide 2 How Much Tall Oil Can Be Recovered ?

Soap Recovery Tall Oil Tall Oil 52 26 51 25.5 kg/1000 kg lb/ ODT Region 50 25 OD Wood Wood 49 24.5 Piedmont 24 48 48 24 47 23.5 kg CTO/ODt Pine Wood Pine CTO/ODt kg Coastal 26 52 Lb. CTO/ODT Pine Wood46 23 45 22.5 Canada 11.5 23 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average Southwestern 31.5 63 Impact of Storage Time on West of 7.5 15 Tall Oil Loss 100%

Cascades 80%

60%

NZ & Chile 12 24 40% Tall Oil Loss Tall Finland 18.5 37 20% 0% 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Sweden 25 50 Storage Time (weeks)

Outside Chips Roundwood Chips

Slide 3

Why Should Tall Oil Soap 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 Soap Should Be Recovered To Improve Pulp and Paper Mill Operations :

Impact of Improved Soap Removal on Evaporator Overall Heat Transfer

1. Reduce evaporator fouling, 110% 2. Increase evaporator uptime, 3. Increase recovery boiler 100%

solids burning capacity, 90% reduction efficiency 4. Reduce paper machine 80% (of Initial Maximum) (of foaming, 70% Heat Transfer Coefficient Coefficient Transfer Heat 5. Reduce bleaching costs, 60% 0 10203040 Hours Running

No Soap Recovery Poor Soap Recovery Good Soap Recovery

Slide 65 Influence of Skimmer Outlet Residual on:

Evaporator Time On-Line Evaporation Rate

100% 100%

98% 98% 96%

94% 96%

92%

90% 94%

Availability 88% 92% 86%

84% 90% Fraction of Maximum Evaporation Rate 82%

80% 88% 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 Skimmer Outlet Soap Residual Skimmer Outlet Soap Residual (% CTO on a Solids Basis) (% CTO on a Solids Basis)

3 Slide 6 How Soap Skimming Affects Evaporator Performance Overall

Good Poor Skimming Skimming Change Skimmer Residual (%) 0.6 1.1 0.5 Downtime (hr./month) 45 75 30 Evaporation 323 315 -8 Rate (Mkg/hr) Production (Tonnes) Unbleached 34500 32100 -2400 Bleached 24700 23000 -1700

Slide 7 Tall Oil Soap 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 80% of the effluent toxicity. 3. Sodium soaps of unsaturated fatty acids account for 20% of the effluent toxicity. 4. Toxicity is independent of oxygen demand.

4 SlideSlide 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

Soap Solubility

3.5 3.0 PAST 2.5 160 F 71 C 2.0 120 F 49 C 1.5 NOW 80 F 27 C 1.0 0.5

Tall Liquorof Solids Oil % 0.0 10 15 20 25 30 35 40 45 50 55 Black Liquor Total Solids (%)

At washer filtrate temperatures, soap begins to come out of solution at about 8% solids. Minimum solubility occurs at 25 – 30% solids.

5 Slide 10 The Effect of Residual Effective Alkalinity and Soap Composition on Soap Solubility

0.5

0.45 0.4 1. Minimum solubility 0.35 occurs at 6 - 8 gpl REA, 0.3 2. Increasing the fatty acid : 0.25 resin acid ratio will 0.2 reduce soap solubility. 0.15 3. The fatty acid : resin acid 0.1 ratio is determined by the 0.05 Soap Solubility% ( Soap-Solids basis) wood species used. 0 051015 Residual Effective Alkali ( g/l)

FA/RA = 5 FA/RA < 2

Slide 11 Influence of Hardwood Content on Tall Oil Soap Solubility

1.2

0.8 Mill A

0.6 Mill B 0.4 lb CTO/ 100 lb BLS lb 100 CTO/ lb 0.2

0 0% 20% 40% 60% 80% 100% 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)

Slide 1413 Why Soap Should be Removed from Weak Liquor Storage Tanks

• Soap 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.

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

Slide 15 Common Configurations for Manual Weak Liquor Soap Skimming

Soap

Liquor

Advantage Simple and inexpensive to install

Disadvantages Requires much operator attention

Can result in significant liquor carryover.

8 Slide 16 Weak Liquor Floating Soap Skimmers VENT TO NCG SYSTEM

SOAP CONCENTRATOR (OPTIONAL) SOAP LEVEL

LIQUOR LEVEL SOAP PUMP TO STORAGE

LIQUOR FEED 16% SOLIDS LIQUOR RETURN PUMP Advantages Disadvantages •Reduces the risk of soap Higher capital surges to the evaporators cost •Increases the effective liquor storage capacity

Slide 17 Soap Skimmer Efficiency (Inlet Soap - Outlet Soap) (3.0% - 0.6%) = (Inlet Soap - Soap Solubility) (3.0% - 0.45%)

=94% Good skimming greater than 85% efficiency

Tall Oil Solubility @ 71 C (160 F)

3.5 3 2.5 2 1.5 1 0.5 Tall Oil % Solids Liquor of Oil Tall 0 10 15 20 25 30 35 40 45 50 55 Black Liquor Solids (%)

9 Slide 18 Skimmer Baffling to Prevent Soap ShortCircuiting

Baffle Baffles Liquor Path Liquor Path

Poor Baffling Good Baffling Soap To Storage Soapy Liquor to Soap Bed Skimmer Skimmed Liquor

Circular Soap Skimmer Layout Soap Liquor Collection Soap Trough Scraper In Rotation Baffle

Liquor Out Soap Scraper Liquor In Soap Bed Baffle Soap Pump

Liquor Soap Out Collection Trough

10 Slide 19 How Skimmer Dimensions Affect Skimmer Efficiency

Soap will not separate if the soap particle rise rate is less than the liquor downdraft. (Superficial Liquor Velocity)

Effect of Superficial Liquor Velocity on Skimmer Efficiency

100% 80% 60% 40% 20%

Skimmer Efficiency Skimmer 0% 0123456 Superficial Liquor velocity ( mph)

Canadian Mills Southeast US Mills

Slide 20 How Skimmer Dimensions Affect Skimmer Efficiency

Efficiency 75% Efficiency 90%

40 Ft. 12 m

Residence time 155 min 60 Ft. 18 m 33 Ft. Superficial Liquor Residence time 158 min 10 m 15 Ft. Velocity 13 fph (4 Superficial Liquor Velocity : 4.6 m mph) 6 fph (2 mph)

Feed Rate 2000 gpm (7580 lpm)

11 Slide 21 Skimmer Level Control

Soap To Storage X Soap Bed A Soapy Liquor to Liquor Skimmer Overflow Standpipe

Skimmed Liquor A= X *Dl/(Dl-Ds) A= 4 *1.13/(1.13-0.94) Ds - Density of Soap = 24 Dl - Density of Liquor

Slide 22 Soap Skimmer Efficiency Improvement

Stabilize skimmer level control.

Soap bed depth < 2 ft. (0.6 m) Effect of Air Injection Remove solids buildup 90 min. Residence Time 8 24 Ensure that the inlet is well 6 18 isolated from the outlet 4 12

Evaluate air injection to the 2 6 Dens. & Skim. Resid. suction of the skimmer feed Soap Liquor Content (%) 0 0 pump. 00.511.522.5 SCFM/1000 gpm Skimmer Feed Density (lb/gal) Residual lb/Mlb BLS Liquor Content (%) Evaluate chemical additives

12 Slide 23 How Air Addition Affects Soap and Liquor Bed Depth at a Fixed Skimmer Level Set-Point Liquor Soap Soap Soap sp.gr. 1.14 sp.gr. 0.12 sp.gr. 0.54 sp.gr. 0.96

200

150

Depth 100

0 High Air Addition Moderate Air No Air Addition Addition

Liquor Depth (in.) Soap Bed Depth

Slide 24 Soap Pumping, Piping

Î Ensure that the pump suction is not restricted or reduced, Î Minimize the length of the pump suction Î Use positive closure ball valves Î Isolate spare soap pumps by ball valves, never use check valves Î Use positive displacement pumps Î Provide steam clean-out lines Î See also http://www.pumpschool.com

13 Positive displacement pump flow rate is relatively independent of viscosity

Flow vs. Viscosity 100

40 Flow (%)Flow 20

0 0 250 500 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

Flow vs. Viscosity 100

40 Flow (%)Flow 20

0 0 250 500

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 Soap Pumping Problems ÎEnsure that the pump suction is not restricted or reduced, ÎCheck the pump rotation ÎPositive displacement pumps: Set the internal pressure relief valve 50 – 100% above the Normal system pressure ÎCheck Gear pumps for wear ÎToo much Liquor – Lower the skimmer level ~ 1% ÎLow Soap Density ( < 0.23 sp. Gravity) Reduce air addition to soap skimmer Use soap Concentrators

Slide 27

Mill Soap Fiber Content 1600 1400 1200 1000 800 600 400 200

Soap Fiber Content (ppm) 0 01-Jan 01-Mar 30-Apr 29-Jun 28-Aug 27-Oct 26-Dec

Actual Upper Control Limit

16 Slide 26 Summary

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..

Slide 27 Summary

Soap solubility is minimized at 30% black liquor solids and 6 - 10 gpl residual effective alkali.

Soap separates in the washer filtrate tanks, weak liquor storage, evaporator soap skimmers.

Soap 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 0.6 m, injecting 7.5 lpm air /m^3 feed liquor.