Mechanisms for Flotation of Fine Oil Droplets

Friday, February 5, 16 The Produced Water Society Seminar 2016 1

MECHANISMS FOR FLOTATION OF FINE OIL DROPLETS

Hank Rawlins, Technical Director eProcess Technologies Friday, February 5, 16 The Produced Water Society Seminar 2016 2 Presenter - Hank Rawlins [email protected] • eProcess – Technical Director • Metallurgical Engineer (PhD, P.E.) • 25 years experience • Facilities Sand Management Systems • Compact Separation Technology • Produced Water Treatment Systems • Fifty Publications • (former) Chair of SPE Separations Technical Section • Adjunct at Montana Tech Friday, February 5, 16 The Produced Water Society Seminar 2016 3

Topside Focus Areas

WATER SOLIDS OIL GAS TREATMENT REMOVAL/HANDLING PRODUCTION PRODUCTION

Desander Systems Wellhead Desander Partial Processing Wellhead Gas Desander Deoiler Systems Dual Pot Filters Preseparation Dehydration Compact Degasser Systems IGF/DGF Systems Sand Washing Systems Compact Production Systems (CPS) Sump Caissons Collection | Transport | Store Extended Well Test Packages (EWT) Friday, February 5, 16 The Produced Water Society Seminar 2016 4

Outline

• Mineral and Oil Flotation • Bubble/Droplet Buoyancy • Bubble Generation & Sizes • Bubble-Droplet Attachment Profiles • Free Energy Minimization • Water-Oil-Gas Interfacial Tension Properties • Attachment Mechanism Model & Results • Production Factors Affecting IFT • Summary Friday, February 5, 16 The Produced Water Society Seminar 2016 5

Mineral Froth Flotation

Selective separation of hydrophobic minerals from hydrophilic • Desired mineral is chemically altered to make hydrophobic then floated The single more important unit operation in upgrading sulfide ores Developed in late 1880’s in UK and Australia Uses both mechanical and hydraulic flotation cells

Copper flotation at Asarco’s Mission mine (www.tucsoncitizen.com) PGM flotation in South Africa (www.flsmidth.com) Friday, February 5, 16 The Produced Water Society Seminar 2016 6 Particle-Bubble Attachment Collector chemical added to improve hydrophobicity -38 micron coal particles in single layer on air bubbles (SME Froth Flotation – A Century of Innovation)

175 micron coal particles on air bubbles forming clusters (SME Froth Flotation – A Century of Innovation)

Galena conditioned with xanthate showing point attachment on air bubbles (www.tecmin.wordpress.com) Friday, February 5, 16 The Produced Water Society Seminar 2016 7 Why Do We Use Flotation? In upstream oil & gas Primarily for water cleanup • Not selective separation for oil recovery Use mechanical and hydraulic cells Air bubble rise faster than oil droplets • Bubble flotation reduces residence time versus straight gravity separation • Reduces footprint and size of separation equipment Also less consumables - especially compared to filters

www.netl.doe.gov Friday, February 5, 16 The Produced Water Society Seminar 2016 8

Bubble/Droplet Buoyancy

Want largest bubble for rise rate but strong bubble-droplet bond to 300 prevent detachment 280 Gas Bubble Oil Droplet 260 P=0.5 bar Small gas bubbles and oil droplets 240 T=35° C 220 Water: 10% salinity OIl: 30 API nearly spherical (use Stokes Law) 200 Gas : 18 MW Stokes’ relationship valid for: 180 • Dilute suspensions and Re<0.1 160 • Re<1.0 (~10% error) 140 120 2 Velocity (cm/min) ρ u d gd p (ρl − ρ p ) 100 l ∞ p v = Re = ∞ 80 18µl µl 60 BubbleStokes Region 40 Example at right: DropletStokes Region • v = 5.8v 20 bubble droplet 0 • 100 µm bubble + 100 µm droplet = 0 50 100 150 200 250 126µm combined = 5.3X Drop or Bubble Diameter (µm) • 100 µm bubble + 10 µm droplet = 101µm combined = 576X

Friday, February 5, 16 The Produced Water Society Seminar 2016 9

Oil Naturally Floats on Water

There are constraints! • Limited footprint • Limited weight • Motion sensitivity • Oil shear sensitivity • Methane flotation gas • Hypersaline water

Friday, February 5, 16 The Produced Water Society Seminar 2016 10

Bubble Generation & Sizes

Myriad of ways to generate and introduce bubbles into flotation: • Shear pumps, eductors, shatter plates, nozzles, porous frits, cavitation tubes, dissolution/nucleation, fluidic oscillators, air sparged cyclone, etc. Variety of recommended bubble sizes: • Millibubble (10-3), microbubble (10-6), nanobubble (10-9), picobubble (10-12) • …opening in the market for femtobubble (10-15) technology!

What size is really needed? (Does size matter?) Friday, February 5, 16 The Produced Water Society Seminar 2016 11 Deep Thoughts …or I think too much while fly fishing Does bubble size matter, or is amount more important? • Probably population/flux/swarm-density What size bubble is really need to capture fine (10 µm) droplets? • If flotation is primary treatment, droplet size is probably 50 microns • If flotation is secondary, after deoilers, droplet size is probably 10-20 microns What is the strongest attachment for bubble-droplet? • We don’t want to lose (detach) captured droplet What is main difference between oil droplet and mineral particle flotation, from a micro point of view? • Oil naturally floats and is naturally hydrophobic (that’s a big help!) • Oil droplets shear and coalesce (rocks don’t) • More interestingly – an oil droplet is deformable and can flow to adapt to bubble surface • What is thermodynamic stable state once bubble-droplet attach? Friday, February 5, 16 The Produced Water Society Seminar 2016 12 Attachment Profiles Various possible mechanisms

l Oil e Initial contact v Droplet Oil droplets a r t

in streamline f

o Streamline

n o i

t Gas c Gas bubble Nucleate

e Bubble r i nucleation coalescence D Gas Bubble

Oil droplet in Oil droplets and Full or partial turbulent Gas bubble Gas bubble gas bubbles encapsulation, or Oil film (or) Oil lens (or) Point wake aggregate “mat” growth Attachment rising point contact (a) (b) (c) (d)

What drives oil to form film, lens, or point attachment? Friday, February 5, 16 The Produced Water Society Seminar 2016 13

Single Attachment Profiles

l Oil Forward Gas e Initial contact v Droplet Encapsulation Bubble a r t

o Streamline

n o i

t Gas Droplet c

e Bubble Reverse r i Encapsulation D

Internal Lens

Oil film (or) Oil lens (or) Point Attachment Mixed Lens Friday, February 5, 16 The Produced Water Society Seminar 2016 14 Free Energy Minimization Thermodynamic Stable State Bubble ΔV ⎛ ∂G ⎞ γ = ⎜ ⎟ Forward Gas 0 ⎝ ∂A ⎠P,T ,n Encapsulation Bubble

Gaggregate < (Gbubble + Gdroplet ) Droplet + Drop Full Reverse Encapsulation Volume

< + Internal +Drop Full Lens Volume

γ og Abubble +γ ow Aoilfilm − γ wg Abubble + γ ow Adrop < 0 + Drop Partial ( ) ( ) Mixed Lens Volume Friday, February 5, 16 The Produced Water Society Seminar 2016 15

Produced Water ρ & µ

1.20 1.8

1.6 1.15 1.4

1.2 1.10

1.0

1.05 0.8

0.6 1.00 0.4 Produced Water Viscosity (cP) at 14.7 psia Produced Water Specific Gravity at 14.7 psia

0.95 0.2 0 5 10 15 20 25 20 30 40 50 60 70 80 90 Total dissolved solids (wt. %) Temperature (°C) Friday, February 5, 16 The Produced Water Society Seminar 2016 16

Water-Hydrocarbon IFT

80 58

75 53

43 60 Interfacial Tension (dyne/cm) at 14.7 psia Interfacial Tension (dyne/cm) at 14.7 psia

55 38 20 30 40 50 60 70 80 90 20 30 40 50 60 70 80 90 Temperature (°C) Temperature (°C) Friday, February 5, 16 The Produced Water Society Seminar 2016 17

Hydrocarbon Gas-Liquid IFT

26 Interfacial Tension (dyne/cm) at 14.7 psia

25 20 30 40 50 60 70 80 90 Temperature (°C) Friday, February 5, 16 The Produced Water Society Seminar 2016 18 Spreading Coefficient Not really useful for this exercise

-6.0

Decreased Cn S -6.5 20% NaCl o = γ wg −γ ow −γ og

-7.0 10% NaCl γ wg > (γ ow +γ og ) 5% NaCl 0% NaCl -7.5 Indicates spreading of oil droplet along gas-water interface -8.0 n-dodecane does not wet the -8.5 methane-water interface, but Spreading Coeff. (dyne/cm) at 14.7 psia Dodecane-Methane-Water System forms a definite contact angle -9.0 20 30 40 50 60 70 80 90 Surfactant that lowers γow may be Temperature (°C) necessary

Friday, February 5, 16 The Produced Water Society Seminar 2016 19 Attachment Mechanism 0% Salinity, 25°C 6.0E-10 5.0E-10 Forward Encapsulation Reverse Encapsulation 4.0E-10 Internal Lens 3.0E-10 Mixed Lens 2.0E-10 1.0E-10 0.0E+00 -1.0E-10 -2.0E-10 -3.0E-10 Net Free Energy Change (J) -4.0E-10 Salinity: 0% -5.0E-10 Temp: 25°C -6.0E-10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

ddrop/dbubble Friday, February 5, 16 The Produced Water Society Seminar 2016 20 Attachment Mechanism 20% Salinity, 25°C 6.0E-10 5.0E-10 Forward Encapsulation Reverse Encapsulation 4.0E-10 Internal Lens 3.0E-10 Mixed Lens 2.0E-10 1.0E-10 0.0E+00 -1.0E-10 -2.0E-10 -3.0E-10 Net Free Energy Change (J) -4.0E-10 Salinity: 20% -5.0E-10 Temp: 25°C -6.0E-10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

ddrop/dbubble Friday, February 5, 16 The Produced Water Society Seminar 2016 21 Attachment Mechanism 0% Salinity, 60°C 6.0E-10 5.0E-10 Forward Encapsulation Reverse Encapsulation 4.0E-10 Internal Lens 3.0E-10 Mixed Lens 2.0E-10 1.0E-10 0.0E+00 -1.0E-10 -2.0E-10 -3.0E-10 Net Free Energy Change (J) -4.0E-10 Salinity: 0% -5.0E-10 Temp: 60°C -6.0E-10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

ddrop/dbubble Friday, February 5, 16 The Produced Water Society Seminar 2016 22 Attachment Mechanism 20% Salinity, 60°C 6.0E-10 5.0E-10 Forward Encapsulation Reverse Encapsulation 4.0E-10 Internal Lens 3.0E-10 Mixed Lens 2.0E-10 1.0E-10 0.0E+00 -1.0E-10 -2.0E-10 -3.0E-10 Net Free Energy Change (J) -4.0E-10 Salinity: 20% -5.0E-10 Temp: 60°C -6.0E-10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

ddrop/dbubble Friday, February 5, 16 The Produced Water Society Seminar 2016 23 Free Energy Model Observations Primary attachment mechanisms are internal lens and forward encapsulation • Transition point is droplet:bubble ratio of ~0.70 • Reverse encapsulation not favored at any condition

Temperature is stronger factor than salinity Methane-Water IFT is primary driving energy factor

Flotation favored by high gas-water IFT and low gas-crude IFT

A 10 µm droplet requires <14 µm bubble for forward encapsulation Most flotation cell bubbles are >100 microns, therefore attachment mechanism for fine droplets is primarily internal lens However, forward encapsulation favors droplet coalescence so microbubbles should improve overall capture efficiency

Friday, February 5, 16 The Produced Water Society Seminar 2016 24

Process Factors Affecting IFT Factor Example Gas-Water IFT Gas-Oil IFT Oil-Water IFT Temperature - Inverse Inverse Inverse Pressure - Inverse Inverse Direct

Cn/Molecular Weight - Direct Direct Direct Salinity (NaCl) - Direct N/A Direct pH - Inverse N/A Inverse Oil Acid # - Inverse Direct Inverse Antifoam (oil) Fatty Acid Ester/polymethysiloxane Inverse Inverse Inverse Demulsifier (oil) Nonionic Polymer Inverse N/A Inverse Reverse Demulsifier (water) Cationic Polymer Inverse N/A Inverse Scale Inhibitor (water) Phosphonic Acid Salts Inverse N/A N/A Corrosion Inhibitor (water) ADBAC Inverse N/A Inverse Biocide (water) Aldehyde Inverse N/A Inverse Hydrate Inhibitor (oil/gas) MeOH/MEG Inverse N/A Inverse Oxygen Scavenger (water) Ammonium Bisulfate N/A N/A N/A Drag Reducing Agent (oil) Polyalphaolefin Inverse Inverse Inverse Paraffin Inhibitor Ester Polymer Inverse Inverse Inverse Friday, February 5, 16 The Produced Water Society Seminar 2016 25 Flotation Cell Discharge Photos courtesy of Jorin Limited

dbubble=84 µm

Ratio=0.083 ddrop=7 µm

Large bubbles and small droplets Droplets staying as spheres on outside of bubbles Friday, February 5, 16 The Produced Water Society Seminar 2016 26

Summary

Oil droplets naturally hydrophobic, low density, spherical shape, and low energy of cohesion Produced water has increased viscosity, density, and IFT with hydrocarbons as dissolved solids increase IFT between methane-water-oil drives interaction Increased rise velocity decreases residence time for separation Free energy minimization does not favor point attachment between droplet and bubble Process factors unassociated with flotation can have impact on oil removal efficiency in produced water system

Friday, February 5, 16 The Produced Water Society Seminar 2016 27

Hank Rawlins, PhD, P.E., Technical Director [email protected] www.eprocess-tech.com