1. Sedimentation Text book, Chapter 3 Reading Materials:
Perry’s Handbook, Chapter 18
Coulson and Richardson’s Chemical Engineering, Volume 2, Chapter 5

2. What is Sedimentation?
Sedimentation is a process for the gravity separation of a dispersed phase from a fluid due to density difference
Hindered vs Free Settling
Factors to be considered:
Feed rate
Settling rate of the materials
Modes of operation
Batch settler
Continuous settler

3. For highly aggregates flocs

4. Sedimentation of Fine Particles

5. Settling velocity of a concentrated suspension
Viscosity of suspension:
OR:
For a more concentrated suspension

6. Height of suspension

7. Concentration of suspension

8. Rate of sedimentation H0 H0

9. Batch Settler Occur in vessel or ponds
Tap
Points
Solid
Removal
Occur in vessel or ponds
Are simply filled and then allowed to stand until the desired degree of separation is achieved
More tap points can be implemented

10. Continuous Settler
To treat a stream for clarification or slurry to be thickened
Feed and flow from thickener (or tap points) are continuous
Solids removal – continuous or intermittent
Horizontal, vertical, or inclined
Tap
Points
Feed
Solid
Removal

11. Horizontal Separators
Used for clarification operations
Feed enters on one end and the clarified liquid overflows at the other
Solid removal is done intermittently at the bottom of the vessel

12. Vertical Thickeners

13. Types of Settling Mechanism
“Most common”
“Rare”

14. Settling Mechanism

15. Settling Test
To determine the solids settling velocity
Type I

17. Type I I

19. If above correlation is given, How you can estimate C1 and C2
Particle volumetric
Flux
(1)
If above correlation is given, How you can estimate C1 and C2

20. Sedimentation Theory Net Flow:
Relative velocity between the fluid and solid:
Batch
So, we have:

21. Sharp Interfaces in Sedimentation
Consider the above Figure, the interface between a suspension of concentration c1 containing particles settling at a velocity v1 and a suspension of concentration c2 containing particles settling at a velocity v2. The interface is falling at a velocity vint. All velocities are measured relative to the vessel walls. The mass balance over the interface gives
Mass balance: 
Define a particle volumetric flux,  = vc. We have

22. Kynch Analysis
Batch Settling:

23. c = volume fraction (m3/m3)

25. Assume 1 kg total mass
Density of water =
1000kg/m3=1.0kg/l)

27. Height (cm)
Time (s)

38. Sizing of Gravity Settling Tank:

39. Sizing of Gravity Settling Tank:

40. Find the area of the gravity settling required the optimal condition

42. Sizing of industrial thickeners:

43. Sizing of industrial thickeners:

44. Sizing of thickeners:
At any point in the tank, the volumetric downward flow rate of solids, q, is given by:
is the interface settling velocity (from batch tests)
C is the concentration corresponding to the
is the relative velocity
Specifically, at underflow point at concentration and

45. EQUATION (1)=(2) = q(feed)

46. Eliminating In general, at bottom is small in comparison to Then
q ????
Note that feed solids volumetric flow rate q is equal where Q
is the feed volumetric flow rate and is the volumetric feed solids
Concentration.

47. If the mass flow rate is known, it can be simply be substituted:
The area required for a feed rate of solids is then given by:
We will require the maximum area since, for any smaller area the solids will not settle and will eventually overflow. This means, the calculation has to be repeated for each concentration and associated settling velocity to find maximum:

48. Formula one
Formula two
(max or min)

49. minimum

51. 1
minimum
(max or min)