andres ortiz - paterson & cooke - the effect of porosity in the design of slurry pipelines

The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 1

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The Effect of Porosity in the Design of Slurry Pipelines Andres Ortiz, Paterson & Cooke Australia Dr. Angus Paterson and Bruno Salvoldi, Paterson & Cooke South Africa 4th Slurry Pipelines Conference 2014, Perth


Porosity?

Source: http://www.atl.semtechsolutions.com/sites/atl.semtechsolutions.com/files/imagecache/image_gallery_display/1coalash.png

Coal Ash


Not a new topic… … although some times it’s forgotten

§  Evans (1973) §  Woskoboenko (1985) §  Boger et al (1987)

§  Chander and Sharma (1980)

§  Dahlstrom (1985)

§  Chik and Msatef (1999)

Studies on raw coal porosity: Slurry flow behaviour is modified by the presence of pores

Studies on Nickel Ore High surface area due to external and internal structure of the ore

Measurement techniques of porosity on phosphate ores

Thickening, Filtering, Drying: “optimum shape is spherical particle of zero porosity”


Outline

§  Definitions §  Implications for slurry pipeline transport §  Measurement techniques §  Interpretation of data §  Case studies (slurry pipelines): phosphate, iron ore §  Conclusions


Definitions

High porosity mixture Low porosity mixture

§  Porosity is a “measure of the empty spaces in a material” volume of voids (spaces)

the total volume e.g. 20% porosity = 20% of the material is filled with voids

§  Mono-sized particle mixtures have a have a higher porosity than well

graded mixtures •  Interstitial voids: Void space between particles that are filled with smaller

particles


Definitions §  Solid particle porosity: particles have different pore types and sizes:

•  Open pore: A void that connects to the surface of the particle. •  Closed pore: Interior voids that are inaccessible from the surface of the

particle.

§  Pore sizes: •  Macropores: Pores with diameters larger than 50 nm. •  Mesopores: Pores with diameters between 50 nm & 2 nm. •  Micropores: Pores with diameters smaller than 2 nm. •  Note: 1 nm = 10 Å = 1/1 000 000 mm

Open pore

Closed pore


Definitions §  Particle solids density is usually determined by measuring the dry mass

of a sample of particles and the volume of the sample using a pycnometer.

§  For porous particles various density definitions exist, each one includes and excludes specific volumes and voids:

Density Definition Volumes Included in Definition

Solid Volume

Closed Pore

Open Pore

Interstitial Void

Bulk density: Mass of particles divided by the bulk volume they occupy (including interstices).

P P P P

Effective density: Mass of particles divided by the volume of the particles (excluding interstices).

P P P

Skeletal density: Mass of particles divided by the skeletal volume (solid volume and closed pores).

P P

True density: Mass of particles divided by the solid volume.

P


Implications for slurry transport §  Slurry pipelines are designed to transport “dry tonnes” of ore using

water as the transport medium. §  Typically long distance pipelines transport concentrate at mass

concentrations of between 50% to 70%m, where:

•  Solids concentration by mass = dry mass of solids/dry mass of solids + mass of water 

§  Viscosity and yield stress are closely related to solids concentration by volume, where: •  Solids concentration by volume = volume of solids/volume of solids +

volume of water 


Implications for slurry transport §  Particles that are porous have a lower effective solids density than

particles than are not porous •  For a constant volume, the particle mass decreases as voids increase •  For a constant mass, the particle volume increases

•  For air filled voids: effective solids density = (1−P). ρ↓s  + P.ρ↓air  •  For water filled voids: effective solids density = (1−P). ρ↓s  + P.ρ↓water  (where: P = porosity (%), ρ↓s = solids density, ρ↓air  = air density)

Volume = 1.00 Porosity = 0% Mass = 3.00 Effective Density = 3.00 Skeletal Density = 3.00




Implications for slurry transport §  A pipeline designed to transport a fixed dry tonnage of material at a

fixed mass concentration:




For a non-porous material - will operate at a constant volume concentration and flow rate

For a variable porosity material the number / volume of particles must increase to maintain tonnage


Implications for slurry transport §  Example: Effect of particle porosity on volume occupied by solids:

•  Skeletal Solid density = 3.0 t/m3 and 60% slurry mass concentration •  Diagrams below illustrate visual effect of porosity on volume occupied by

solids considering mixture at rest and voids filled with air.

30% Porosity: Solids volume concentration = 48%


Mass = constant Mass = constant Mass = constant


Mass = constant


Implications for slurry transport §  Now considering mixture in suspension (slurry flow):

•  Increased crowding of solids with increasing particle porosity •  Increased effective viscosity as volume fraction increases •  Results in increased pipeline head-loss gradient

Mass = constant Mass = constant Mass = constant

0% Porosity: Solids volume concentration = 33% e




Measurement Methods Method Advantage Disadvantage

Mercury intrusion

Pore size distribution, interstitial and particle pores can be differentiated

Repeatability not great. Skeletal density will be inaccurate if lots of micropores are present. Extensive experience required for data analysis.

Helium intrusion

Provides skeletal density and interstitial and particles pore volume

Can not differentiate between different pore volumes. Can not provide particle porosity.

Water intrusion

Provides skeletal density and interstitial and particles pore volume.

Agitation and deaerated water/heating is required to ensure all pores are intruded. Can not differentiate between different pore volumes. Can not provide particle porosity.

Evaporation Provides mass concentration of the slurry.

Can not differentiate between different pore volumes. Skeletal density needs to be measured separately. Can not provide particle porosity unless a single large particle is used.


Measurement of porosity §  Mercury intrusion method:

•  Mercury is a non-wetting liquid that has to be forced to enter a pore by application of pressure.

•  Measures the volumetric intrusion of the mercury as the pressure is increased. •  The pore diameter sizes intruded are estimated by the opposing forces of the

pressure required to intrude a pore and the mercury surface tension.

Pore Size (nm)

Pore Size (µm)

Mercury porosimetry rangeWater intrusion range

Helium gas intrusion range

Macropore Mesopore Micropore


Interpretation of results §  Critical points in the determination of volume and density for granular

samples: Point A is used to determine bulk volume, points A and B are used to determine interstitial void volumes and points B and C are used to determine skeletal volumes.


Interpretation of results §  There is an important difference between measuring porosity of single

particles and granular samples. §  For a single particle Coal Sample no interstitial voids are present.

Cum

ulat

ive

Intr

usio

n (m

L/g)

Diameter (Armstrong)


Interpretation of results §  For a granular iron ore sample the intrusion curve has to be interpreted

as interstitial void filling (points A to B) need to be accounted for.

B

A

C


Data §  Slurries that have variable porosities include:

http://skywalker.cochise.edu/wellerr/mineral/bauxite/6bauxite144a.jpg

http://www.atl.semtechsolutions.com/sites/atl.semtechsolutions.com/files/imagecache/image_gallery_display/images/coalash1.png

•  Bauxite •  Bottom ash •  Coal •  Iron ore

•  Kaolinite •  Nickel •  Phosphate •  Uranium tailings


Case Study 1 – Phosphate rock slurry pipeline Porosity 0% Porosity 20% Porosity 30%

Solids skeletal density 3.0 t/m3

Solids effective density 3.0 t/m3 2.6 t/m3 2.4 t/m3

Slurry mass concentration 60% (design)

Slurry density 1.7 t/m3

Slurry volume concentration 33%

Effective volume concentration 33% 41.2% 47.1%

§  Challenge: Particles with variable porosity: the solids concentration by volume increases and affects viscosity, and the discharge pressure increases


Case Study 1 – Phosphate rock slurry pipeline §  In terms of hydraulic gradient:

0.000

0.001

0.002

0.003

0.004

0.005

0.006

0.007

0.008

1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 2.60 2.80 3.00

Hyd

raul

ic g

radi

ent (

m/m

)

Velocity (m/s)

Water

Porosity value: 0%

Porosity value: 10%

Porosity value: 15%

Porosity value: 20%

Design velocity = 2.18 m/s

P 20%: 0.005 m/m

P 0%: 0.004 m/m


Case Study 1 – Phosphate rock slurry pipeline §  Pumping Requirements per 100 km of horizontal pipe:

Porosity 0% Porosity 20%

Total head loss 400 mslurry 500 mslurry

Required discharge pressure 6.7 MPa 8.3 MPa

Power requirement per 1,000 m3/h of slurry 2,300 kW 2,900 kW

What if porosity

reaches 30%?

May push the design

pressure rating to the next one up?

How about power

supply?

What if porosity wasn’t

considered?


Case Study 2 – Iron ore slurry pipeline

Porosity 0% Porosity 5% Porosity 15%

Solids skeletal density 3.8 t/m3

Solids effective density 3.8 t/m3 3.66 t/m3 3.38 t/m3

Slurry mass concentration 60% (design)

Slurry density 1.8 t/m3

Slurry volume concentration 28.2%

Effective volume concentration 28.2% 29.7% 33.2%

Note: Pipeline length: 20 km Product: Coarse iron ore


Case Study 2 – Iron ore slurry pipeline §  In terms of hydraulic gradients:

0.00

0.01

0.02

0.03

0.04

0.05

0.06

1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4

Hyd

raul

ic G

radi

ent (

m/m

)

Velocity (m/s)

water

Porosity value: 0%

Porosity value: 5%

Porosity value: 10%

Porosity value: 15%

Design velocity = 2.9 m/s

P 15%: 0.030 m/m

P 0%: 0.026 m/m


Case Study 2 – Iron ore slurry pipeline §  Pumping Requirements per 20 km of horizontal pipe:

Porosity 0% Porosity 15%

Total head loss 522 mslurry 592 mslurry

Required discharge pressure 9.2 MPa 10.4 MPa

Power requirement per 1,000 m3/h of slurry 3,200 kW 3,600 kW

May push the design pressure rating to the

next one up? (class 600 or class

900?)


Conclusions

1.  Particle porosity is an important parameter that influences the flow behaviour of slurries.

2.  The presence of porous particles increases the effective volumetric solids concentration substantially, resulting in a sharp increase in pipeline pressure loss due to the increased viscosity at the same mass concentration.


Conclusions

3.  To mitigate this increase in pressure loss: §  The solids concentration can be diluted to reduce the effective

volume concentration. §  The dry tonnage throughput can be reduced. The consequences on flow rate need to be considered when evaluating options to control the effects of particle porosity.

4.  The measurement of porosity requires a careful interpretation of results as the nature of the pores and pore sizes need to be evaluated in order to determine the effective increase in volumetric solids concentration.


THANK YOU

Contact us: §  Andres Ortiz

Director, P&C Australia [email protected] Tel + 61 8 9226 1407 / +61 4 3911 9031

andres ortiz - paterson & cooke - the effect of porosity in the design of slurry pipelines

Presentations & Public Speaking

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