The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 1 www.PatersonCooke.com 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 4 th Slurry Pipelines Conference 2014, Perth
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The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 1
www.PatersonCooke.com
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 2
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 3
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”
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 4
Outline
§ Definitions § Implications for slurry pipeline transport § Measurement techniques § Interpretation of data § Case studies (slurry pipelines): phosphate, iron ore § Conclusions
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 5
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 6
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 7
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 8
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 9
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
Volume = 1.25 Porosity = 20% Mass = 3.00 Effective Density = 2.40 Skeletal Density = 3.00
Volume = 1.00 Porosity = 20% Mass = 2.40 Effective Density = 2.40 Skeletal Density = 3.00
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 10
Implications for slurry transport § A pipeline designed to transport a fixed dry tonnage of material at a
fixed mass concentration:
Volume = 1.00 Porosity = 0% Mass = 3.00 Effective Density = 3.00 Skeletal Density = 3.00
Volume = 1.00 Porosity = 20% Mass = 2.40 Effective Density = 2.40 Skeletal Density = 3.00
Volume = 1.25 Porosity = 20% Mass = 3.00 Effective Density = 2.40 Skeletal Density = 3.00
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 11
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%
0% Porosity: Solids volume concentration = 33%
Mass = constant Mass = constant Mass = constant
20% Porosity: Solids volume concentration = 42%
Mass = constant
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 12
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
20% Porosity: Solids volume concentration = 42%
30% Porosity: Solids volume concentration = 48%
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 13
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.
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 14
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 15
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.
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 16
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)
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 17
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 18
Data § Slurries that have variable porosities include:
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 19
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
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 20
Case Study 1 – Phosphate rock slurry pipeline § In terms of hydraulic gradient:
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 24
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?)
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 25
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.
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 26
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.
The Effect of Porosity in the Design of Slurry Pipelines, November 2014, Slide 27
THANK YOU
Contact us: § Andres Ortiz
Director, P&C Australia [email protected] Tel + 61 8 9226 1407 / +61 4 3911 9031