WEIR Froth Presentation

ExcellentEngineeringSolutions

Weir Minerals North America

Froth Pumping

Presentation to:Calgary Pump SymposiumNovember 9th, 2007



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Froth Pumping: Background

Air can be present in slurry due to:

local vortices on free surface of hopper

tank levels too low (“snoring”)

incoming stream free falling into tanks

purposefully adding air via flotation process

Aeration can:

affect pump performance reducing developed head and flow

can increase wear on pump parts

Air bubbles may be:

finely dispersed throughout the slurry as part of a froth

large “slugs” or bubbles which can be easily separated from liquid

or somewhere in between



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Froth Pumping: Effect of Air

Effect of air on pump performance:reduced head output at low and high volume flowcorresponding reduction in efficiencyand power drawflow instability



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Froth Pumping: System Improvements

Traditional system modifications to improve performance include:

Launders

Baffles

Feed wells and submerged inlets

Spray nozzles and misting

Vent Pipes

Casing rotation

Tangential inlet

All of the above are designed to minimize the entrainment of air in the slurry, and to maximize venting of air in the sump, suction and pump.



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Launders:

provide additional surface area and vent as much air as possible prior to the sump

provide a gentler flow into the sump to minimize additional air entrainment from a high velocity downward cascade



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Baffles:a shield for the downward flow of slurry from the pump suctionmore horizontal dispersion and larger surface area of the slurry to maximize release of aira “dead zone” under the baffle to allow for additional air release

Vent pipes:vent pipes assist with removal of air from the suction and impeller eye



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Submerged Inlets:to prevent additional entrainment of air from the downward cascading flow of slurry

Feed Wells:a shield between the downward flow of slurry and the pump suctionto allow time for venting of entrained air and prevent direct ingestion of air into the pump inlet



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Spray nozzles and misting:assist in breaking down the froth and releasing air bubbles from the slurry in the launders and sump

Mist spray on active side of baffleLack of mist spray on inactive side of baffle



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Vented Suction Pipe:

may consist of an inverted tee with vented stand pipe

or oversized inlet with eccentric venting back to suction tank/sump



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Tangential feed:

to minimize air entrainment

Oversized conical suction (eccentric):

to reduce velocity and allow venting back to the sump



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Rotated pump casing:

Top 45 degree discharge

Top horizontal discharge

to assist with venting of the air out of the casing (past the cutwater)



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All of the above are designed to minimize the entrainment of air in the slurry, and to maximize venting of air in the sump, suction and pump.

The degree of improvement brought about is dependent upon the quality of their implementation and the tenacity of the froth.



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Froth Pumping: Pump Types

Traditional Horizontal Slurry Pumps:typically use large frothfactors (multiples of design flow rate)oversized to handle largeair volumeoperates well to the left ofthe best efficiency pointoften utilizing open or recessed impellerscorresponding low efficiency



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Vertical Froth Pumps:tangential inletself ventinglimited tank volumehead limited by critical speed of overhung shafthigher cost than horizontal pump (*disregarding the fact that horizontal pump requires a suction tank/sump)



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Warman AHF, LF, and MF Flow Inducer Froth Pumps:

very large inletconfiguration

unique flow inducerimpeller design

inlet sized for aeratedvolume flow, dischargesized for design flow



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Warman AHF, LF, and MF Flow Inducer Froth Pumps

based on proven WarmanAH, L, and M seriesheavy duty slurry pumps

easily convertible to or fromenclosed impeller pump design



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Froth Pumping: Warman Pump Selection

Key Parameters:

Froth Type:

Mineral Froth

Bitumen Froth

Percent Air Volume

System Curve



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Froth Type:

Mineral Froth:

tenacious or brittle

charted corrections for head and efficiency

typically Turbulent Flow/Exponential System Curve

Bitumen Froth:

specific head and efficiency ratios

dependent upon bitumen content

dependent on temperature

laminar or turbulent flow depending upon above



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Calculation of Froth Volume Factor (FVF)



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Froth Volume Factor

Example: 20% air volumeFVF = 1/(1-.20)FVF = 1.25



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Flow Terminology:

Qs = Slurry flow rate = Design flow = Compressed flow = De-aerated Flow

Qf = Froth flow rate = Uncompressed (aerated) flow

Qf = FVF x Qs



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Calculation of Aerated Flow:

Example: Design flow: 2000 gpmDesign head: 60 ftSpecific gravity: 1.15% Air volume: 20%FVF (previous calc.): 1.25

Uncompressed (aerated) flow= 1.25 x 2000 gpm= 2500 gpm



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Froth Pump Selection:

Select pump with Qf to left of BEP

Select Pump withNPSHr @ Qfless than 12 ft

Design circuit withminimal friction,minimal static head,& minimal total head,to keep speed low



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Plot system curve with statichead

This example: 30 ft. static head

Determine system headat Qf, uncompressed (aerated) Flow

This example: 75 ft. system head @ 2500 gpm



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Mineral Froth Head and Efficiency Corrections:

HRf = Head on froth Head on water

ERf = Efficiency on froth Efficiency on water

Note: Only QU1 Flow Inducer Impellers are used now



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Mineral Froth Head and Efficiency Corrections:

Our example:

20% air volume,1.25 FVF:

HRf = 0.95

ERf = 0.95

Note: Only QU1 Flow Inducer Impellers are used now



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Apply Head Ratio:Required water head

= uncompressed head

head ratio

Our example:Required water head

= 75 ft/.95 HRf= 79 ft

Required water speed @ uncompressed flow and water head (2500 gpm @ 79 ft):

= 640 rpm



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Calculate Slurry Efficiency:

Water efficiency at 2500 gpm @ 79 ft: 68 %

ERf, efficiency ratio: 0.95

Slurry efficiency = water efficiency x efficiency ratio = 68 % x 0.95 = 64.6 %



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Calculate Required Horsepower:

HP = (Qf)(corresponding system head)(specific gravity/froth volume factor) (3960)(fractional slurry efficiency)

For our example:HP = (2500 gpm) (75 ft.)(1.15 s.g./1.25 FVF)

(3960)(.646)HP = 67 BHP

Select a motor with 20% margin to allow for fluctuations in duty due to variations in air content. That is, select 100 BHP for this application.



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Froth Pumping: Bitumen Froth

Saskatchewan Research Council Pipeline Technology Center:

An offshoot of theUniversity of Saskatchewan

Tests slurries and fluids forCanadian industry

Warman 8 inch Froth Pumpfeeding Warman 10/8 AHSlurry Pump in 20 inch loopfor Syncrude Bitumen FrothTest



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Saskatchewan Research Council Pipeline Technology Center:

Warman 3 inch Froth Pump feedingWarman 4/3 AH Slurry Pump

6 inch test loop

Testing on:

Bitumen Froth

Paste



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Bitumen Froth Characteristics:

viscous

viscosity dependent upon temperature and bitumen content

laminar, plug flow at high bitumen content and low temperature

turbulent, highly aerated at low bitumen content



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Bitumen Froth Corrections:

similar correction method to mineral froth

HRf and ERf dependent upon temperature and bitumen content

HRf varies from approximately 0.6 to 1.05

ERf varies from approximately 0.4 to 1.0



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Bitumen Froth Corrections:

Flow Inducer Froth Pump significantly outperforms conventional slurry pump with respect to:

head ratio

head/flow stability

efficiency ratio

final slurry efficiency



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Froth Pumping: Pump Installations

12 TAHF:bitumen flotation froth recyclereplaced horizontal pump with open impellerreplaced horizontal pump with recessed impeller and inducer



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350 FF LF:bitumen flotation froth recyclereplaced undersized Warman 8 MF horizontal froth pumpvery high air volume (25 to 40 percent)



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14 TUAHF:Based on Warman 16/14 TUAH1125 mm impellerFlows in 2000 to 3000 m3/hr range Heads to 40 m300 & 500 PSI designs



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Froth Pumping: Recommendations

Recommendations to maximize system performance:Minimize pump speed by designing system with low system headMinimize entrainment of air in sump by use of launders and tangential inletsMaximize release of air by use of baffles, spray mists, vent pipes, enlarged eccentric suctions, proper casing orientationMaximize NPSHaSelect appropriate pump for the dutyPreferably select pump with NPSHr less than 12 to 14 ft at aerated flow rateAvoid parallel pumpingDon’t over speed pumps: utilize VFD’s to maximize control of system

WEIR Froth Presentation

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