Pulp Suspension Rheology James A. Olson, P.Eng. Pulp and Paper Centre Mechanical Engineering Dept. 604.822-5705 [email protected]General Questions • What is pulp? • How do we characterize a pulp suspension? • What are the key consistency ranges? • What is the crowding factor? • What are the regimes of pipe flow? • How does pulp affect piping head losses?
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Pulp Suspension Rheology - University of British Columbia
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• Chemical flocculation (colloidal)• Mechanical flocculation
mechanical forceselastic fibre bending
Mechanical Forces
Elastic Fibre Bending
Elongational Flow
Flow Through Griddisruption by stretching (more than 5:1)
not shear
TU
RB
UL
EN
TF
LO
W
INT
ER
ME
DIA
TE
FL
OW
INC
IPIE
NT
PL
UG
FL
OW
Refloculation Times
CM (%)
0.15
0.45
1.0
2.0
3.0
4.0
Velocity (m/s)
0.8 - 1.0
Time (s)
2
1.2 - 2.0
7.6
10.2
0.6
0.01
0.04
0.01
0.001
Velocity gradient
She
ar s
tres
s
dV
dy
NEWTONIAN
dV
dy
BINGHAM PLASTIC
Modes of Flow
How does pulp affect piping losses?
WATER
Velocity, V
Frict
ion
loss
,dP
/dX
PULP
A
B
CD
H
A Yield stressA-B Plug flow with
wall contactB-C Plug flow with
water annulus C-D Annulus becomes
turbulentD-H True mixed flow
How do we design a pump and pipe systems for such a complex flow?
• Standardized method for pipe design – TAPPI TIS 0410-14
– “Generalized method for determining the pipe friction loss of a flowing pulp suspension”
Tappi TIS 0410-14
• Calc Vmax– Point where annulus starts (B)
• If V < Vmax calc head as …• If V > VMax
– Calc Vw (velocity at which it acts just like water
– If Vmax < V < Vw then use Vmax in above
– If V > Vw then calc friction loss as if it is just water.
• Beware!– D is in mm– C is in %– V in M– DH/L is head (m) per 100 m of length
maxV K CH
FKV C DL
1.441.22wV C
Example
10m
2m100 mm
Tank A1% SWK Pulp
Tank B
This example looks at how to ‘estimate’ the head loss in pulp pipe flow Remember the Energy Balance in one dimension (for example, MECH 280, White Ch. 3.6)
2 2
2 2 friction pump turbine
in out
P V P Vz z h h h
g g g g
h = head loss/gain (in units of meters)Tank A contains 1% (Cm) consistency softwood, kraft pulp at 725 CSF at 35 degrees C. The tank is full to a height of 10m. It is draining through a 100mm diameter smooth stainless steel pipe into a second tank B. The height of the pulp in Tank B is 2m and both are open to the atmosphere. If the mean velocity of the pulp in the pipe is 1 m/s and you neglect minor losses, how long is the pipe connecting the two tanks?