Towards the development of a virtual bitumen froth settling process

Towards The Development of a Virtual

Bitumen Froth Settling Process

D.M. Kirpalani

Research Officer - Oil sands Program

August 25th ₂₀₀₉

Introduction

• Gravity separation of hydrocarbon

solvent treated bitumen froth is used for oil sands extraction.

• This reduces the bottom sediments

and water as a result of:

– (A) Partial precipitation of asphaltenes and – (B) Aggregate formation of water droplets,

mineral solids and asphaltenes.

• By stacking plates in a pack and on an

angle decreases the footprint required

and intensifies the separation process. • Froth is fed into the plate pack through a

manifold. As it flows upwards the

particles will settle due to gravity

Application of Inclined

Plate Settlers for

Research Goals

• Develop a Compression Settling Model and append the model to Hindered settling model developed previously

(Kirpalani and Matsuoka, Fuel J. , 2008) based on laboratory experiments.

• Incorporate the combined model into CFD

• Apply the developed model for examining the performance of an Inclined Plate Settler for settling of bitumen froth.

• Study the effect of angle of inclination on the pilot scale settler performance in the presence of instabilities

IPS Research History

• Research in IPS settling has concentrated on separation of bi-dispersed suspensions

• Whitmore,1955 – Effect of neutrally buoyant particles on heavier suspensions.

• Weiland and McPherson 1979, Fessas and Welland, 1981 – used positively buoyant light particles –local instabilities or fingers

• Fessas and Welland, 1984, modeled the initial settling in the presence of fingers

• Law et al, 1987, Selim et al 1983, Patwardhan and Tein 1985 • Nasr el-Din et al, 1988 studied continuous separation in IPS

system and

• Masliyah et al. 1989 examined continuous separation using bi-dispersed particles at low total solids concentrations

Hindered Settling- Long

et al., 2004

From the Richardson-Zaki approximation, the hindered settling rate can be approximated using;

alpha is the solids volume fraction,

As a result, we obtain Long et al. (Fuel J., 2004) equation:

n s

u

u

1

D

g

u

and

1

18

D

g

u

1

18

1

Fractal Approach for

Hindered Settling

1

d

d

d

g

v

18

Terminal velocity of a single particle

Difference in density between the particle P and the surrounding Liquid, L

Initial porosity of the aggregates A, can be defined as;

Combining the above equations,

Conservation Equations

R

g

P

v

v

t

v

0

v

t

dV

V

The volume fraction balance equation is (q = L, S)

Mass conservation equation

CFD Two Phase Euler

Solver- Compression

Settling

Granular flow theory equations applied: VISCOSITY MODEL (Gidaspow Model)

FRICTIONAL STRESS MODEL (Johnson and Jackson, 1987)

I2D – 2nd invariant of the deviatoric stress tensor

fr S kin S col S S , , , fr S kin S col S S S,col S,kin S,fr S , , , 2 1 , 0 , 1 5 4 _S SS SS S S S col S d g e 2 , 0 , 0 , 1 5 4 1 1 96 10 SS S SS SS SS S S S S k in S g e g e d D M cri S S f

I

A

2

sin

Two Phase Euler

Solver- Compression

Settling

GRANULAR PRESSURE MODEL (Kirpalani, WCCE 2009)

RADIAL MODEL (Gidaspow’s Model)

DRAG MODEL (Fractal Approach – Kirpalani and Matsuoka, 2008)

cri S S S SS S SS S S S S S e g p 2 1 2 _{0, ,} cri S S M cri S S S SS S SS S S S S S e g A p 2 1 2 _{0, , ,} 1 3 1 max , , 0 1 S S SS g S L LS drag K v v f 2 1 _S n T S L S LS v g K D A P L A L P T d d d g v 3 2 18

CFD Results Based on

Long et al.

CFD with Proposed

Combined Model

CFD Validation with

Laboratory Experiments

C5-C6 Solvent Treated Bitumen Froth at 30 C

Ref. Experimental Data Kirpalani et al. Long et al. 0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 U p p e r In te rf a c e L e v e l, c m Time, min

C5-C6 Solvent Treated Bitumen Froth at 75 C

Ref. Experimental Data Kirpalani et al. Long et al. 0.0 50.0 100.0 150.0 200.0 250.0 300.0 350.0 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 U p p e r In te rf a c e L e v e l, m m Time, min

C7 Solvent Treated Bitumen Froth at C

Ref. Experimental Data Kirpalani et al. Long et al. 0.0 50.0 100.0 150.0 200.0 250.0 300.0 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 U p p e r In te rf a c e L e v e l, m m Time, min

C7 Solvent Treated Bitumen Froth at 70 C

Ref. Experimental Data Kirpalani et al. Long et al.

C5-C6 Solvent Treated Bitumen Froth

Pilot Scale IPS - CETC

Single Inclined Plate

Geometry

Isometric Views of IPS

•Top view •Iso-view

•Front

view _{•Side view} (left)

Grid Refinements

Hexahedral Mesh - Overflow box,

IPS Geometry –Initial

Conditions

• Initially, the entire plate is filled with a solids volume fraction of 0.121 • The inlet, which is

located near the center of geometry on the side, forces the slurry (0.121 volume fraction) into the plate settler at a rate of 1 mm/s

C5-C6 Treated Froth at

30

°

C-Effect of Angle of

Effect of Angle of

Inclination on Settling

C5-C6 solvent treated bitumen froth settling curves on 45 and 55 inclined plates of 0.3m. X 1.65 m at 30°C

Results and Discussion

-

• Laboratory scale experiments by Long et al. that describe the use of C5 – C6 and C7 solvents for bitumen froth treatment at 30 °C and 70 °C were modeled.

• Fractal dimension for each test condition was obtained by calculating the settling velocity and are based on the solvent used.

• The fractal dimensions for the C7 solvent system are lower than those of C5-C6 solvent system, suggesting that the porosity of aggregates for C7 solvent system is higher than that of C5-C6 solvent system.

• The settling curves of these simulations show good

agreement with empirical data in hindered settling zone and the inclusion of fractal dimension in the model reduces the dependency on experimental variables.

Results and Discussion

- Model for Compression Settling in Laboratory Experiments

• For compression settling model development, the critical

volume fractions of solids were set equivalent to initial volume fractions.

• Values of Parameters A and M:

– The value of M was determined to be 1.695, while the value of

A are varied for each case.

– Larger values of A result in higher solids pressure. – The values of A are considered to be directly related to

particle and aggregate properties

The limitation in the original Richardson-Zaki approximation, due to its development on spherical non-porous solids, has been overcome by accounting for the porous and fractal nature of the aggregates.

Results and Discussion

- Pilot Inclined Plate Settler Study

• The settling behavior of bitumen froth was further evaluated in a pilot scale IPS geometry

• It was found that there is a significant amount of sloshing of the solid-liquid interface as the froth settles and that the

settling rate was higher with settler plate angles at 45° in comparison to 55° and hence higher throughputs.

• This work shows that CFD can be applied to complex bitumen froth settler geometries along with knowledge of the

underlying physics of froth settling for design and scale up for increased settling efficiency.

• This numerical approach outlines an alternate method for predicting settling rates and improving froth settling.