This document discusses gas-solid separation techniques, emphasizing the importance of various phases in the gas cleaning process. It details different types of gas cleaning equipment, primarily cyclone separators, including their design, operational principles, advantages, disadvantages, and key parameters affecting performance. The efficiency of separation processes, the relationship between flow rate and pressure drop, and factors for selecting appropriate equipment are also explored.

1. SAJJAD KHUDHUR ABBAS
Ceo , Founder & Head of SHacademy
Chemical Engineering , Al-Muthanna University, Iraq
Oil & Gas Safety and Health Professional – OSHACADEMY
Trainer of Trainers (TOT) - Canadian Center of Human
Development
Episode 42 : Gas Solid
Separation

2. INTRODUCTION
The process may be interpreted to mean both degassing of solids and
dedusting of the solids.
3 phases may be distinguished in any gas cleaning process, i.e;
• transport of particles onto a surface (separation)
• collection of separated particles from the separation
surface into discharge hoppers (or particle fixation)
• disposal of the collected particles from the gas cleaning
equipment
All phases are equally important as the failure of any of the phases
will result in the failure of the separation process
.

3. In the 1st
. phase, forces are applied to the particles in order
to bring them to a collecting surfaces.
The principles of particles separation are usually classified
according to the nature of the force involved. These may
be:
1.External forces due to fields of acceleration which are
external to the gaseous suspension, such as gravity,
electrostatic or magnetic forces
2.Internal forces due to fields of effects which take place
within the suspension itself. E.g. intertial or centrifugal
forces, diffusion, coagulation, electrostatic effect
Gas cleaning equipment often combines 2 or more of the
above mentioned principles in one unit.

4. The most common classification of g-c equipment- is divided
into 4 groups, i.e.
1. aero-mechanical dry separators in which gravity and/or
inertial effects prevail. This group includes yclone, settling
chambers, inertials separators, dual vortex separators and
fan collectors (or mechanical cyclones)
2. aero-mechanical wet separators (scrubbers) which make use
of diffusional and inertial effect
3. electrostatic precipitators which depend on electrostatic and
gravity forces
4. filters which use inertial and diffusional effects

5. General characteristics of equipment
The factors affecting the choice of gas cleaning equipment. For any particular
application are;
1. flowrate-pressure drop relationship
2. efficiency
3. economic criteria
4. suitability for different conditions (the nature of both solids and ga)
5. solids concentration,
6. method of disposal
7. reliability

6. Flowrate-pressure drop relationship
Most gas-cleaning devices have fixed relationship between static pres. drop and gas
flowrate, depending on the configuration of the equipt.
Most frequently, the relationship is expressed is expressed as:
∆P =(1/2).Eu.v2
ρg (1)
where:
∆P is static pressure drop
Eu is the Euler number, and is a resistance coeff. (analogous to CD) which
may be function of Re, other operational variables such as the feed
concentration of solids, etc.
v is characteristic velocity = Q/A where A is characteristic area in the
separator ( e.g cross-section of the cylindrical body in cyclone)
ρg is gas density
One exception in the application of eq. 1 is in air filters, where pressure drop is
also a function of the amount of dust deposited on the filter.

7. Efficiency
It is an important criteria since it governs the degree of cleaning. It is best expressed
as gred efficiency. G(d) increases from zero for ultrafine particles to 100 for
coarse particles.
Figure 6.1 shows typical gred efficiency curves for dry sep (D), wet sep. (W),
electrostatic and filter

9. Economic criteria
It is consist of the capital and running costs.
Capital cost is normally expressed per
1000m3
of cleaned gas per hour. It may be
further split into the cost of the construction
material, cost of labour, erection, design, etc.
The running cost include cost of power,
maintenance, water, etc.

10. Suitability for different conditions
 Thera are a number of other factors such as gas temperature
and humidity, the cohesiveness and abrasiveness of th dust,
reliaility, limits in dust concentrations, etc, which may exert
an overiding influence on the final choice

11. Gas Solid Separation: Cyclone

12. Definition of cyclone separators
A cyclone separator is an equipment for the
removal from air streams of particles above 10
micrometer in diameter.
The equipment is a settling chamber in the form
of a vertical cylinder, so arranged that the particle
laden air spirals round the cylinder to create
centrifugal forces which throw the particles to the
outside walls (Learle, 1966 )

13. Advantages/disadvantages
The advantages of cyclone and all aero-mechanical dry
separators include:
 Simple design
 Low capital cost
 Suitability for higher temperatures
 Low energy consumption
 Product is dry
 Reliability
Disadvantages:
Their relatively low efficiency for very fine particles which
leads to their frequent role as a pre-cleaner

14. Cyclone types most commonly used
 Cyclone separators can be classified according to either their
geometrical configuration in (tangential inlet axial discharge,
tangential inlet peripheral discharge, axial inlet and discharge, and
axial inlet peripheral discharge, Figures a-d below, respectively)
 or their efficiency in (( high efficient (98-99%), moderate efficient
( 70- 80%),and low efficient ( 50%)) (Othmer,1978) and (Storch et
al.,1979).

15.  Figures (Othmer,
1978.) [112]
Figure a. Tangential
inlet, axial discharge.
Figure b. Tanential
inlet, peripheral
discharge
Figure c. Axial inlet,
axial discharge
Figure d. Axial inlet,
peripheral discharge

16. Operating principles of cyclone
separators
 Although there are four commonly used cyclone separators, their
operating principles based on that of the conventional cyclone, are
very similar
 In the conventional cyclone, the gas enters a cylinder tangentially,
where it spins in a vortex as it proceeds down the cylinder.
 A cone section causes the vortex diameter to decrease until the gas
reverses on itself and spins up the center to the outlet pipe or vortex
finder.

17.  A cone causes flow reversal to occur sooner and
makes the cyclone more compact.
 Dust particles are centrifuged toward the wall and
collected by inertial impingement.
 The collected dust flows down in the gas boundary
layer to the cone apex where it is discharged
through an air lock or into a dust hopper serving
one or more parallel cyclones (Othmer, 1978 ) .
 Although conventional cyclones can be built to
larger diameter, they are commonly 600 to 915 mm
in diameter.
Operating principles of cyclone
separators

19. Applications of cyclone separators
 Cyclones can be used for separating particles from
liquids as well as from gases and they can also be
used for separating liquid droplets from gases
(Learle,1966 ).
 The first cyclones used for dust separation probably
were built about 1885 by the Knickerboker
Company ( U.S.Pat.325,521) (Othmer, 1978 ).
 In industries such as food industries, cyclones are
used for removing the dry product from the air.

20.  In synthetic detergent production, fast reactor cyclones are used in
separating a cracking catalyst from vaporized reaction products
(Coker, 1993 ).
 Cyclones are used for classification as for example, in the degritting of
kaolin clay where sand is removed from the crude clay suspension
before finer classification in a conveyor discharge centrifuge and final
product recovery in a disk centrifuge.
Applications of cyclone separators

21. Key parameters of cyclone separators
 The most important parameters of a cyclone as for any separating
device are its collecting efficiency and the pressure drop across the
unit. (Storch ,et al.,1979).
 The collecting efficiency of a cyclone is defined as its ability toability to
capture and retain dust particlescapture and retain dust particles
 whereas the pressure drop is the amount of power that the unit needs
to do so.

22. Pressure Drop
 Factors that contribute to cyclone pressure drop (static pressure
differential across the cyclone):
1. Gas expansion as it enters the cyclone
2. Formation of vortex
3. Wall friction
4. regain of rotational kinetic energy as pressure energy

23. 





=∆ 2
2
1
vEuP fρ
Pressure Drop
EU is a resistance coeff., the Euler no.
ρf is the gas density
ν is the characteristic velocity
( )2
/4 DQv π=
Q is the gas flow rate
D is the cyclone inside diameter

24. Efficiency
 Is defined as the fraction of particles of acertain
size that are collected by the cyclone.
 It increases with:
1. Increasing particle diameter and density
2. ⇑ gas inlet velocity
3. ⇓ cyclone diameter
4. ⇑ cyclone length
5. Drawing some of the gas from the cyclome
through the dust exit
6. Wetting the cyclone walls

25. Typical cyclone fractional efficiency
curve
The particle size for
which the grade
efficiency is 50%, d50
is often used as a
single number
measurement of the
efficiency of the
ccyclone.
d50 –the cut size of the
cyclone (or other
separation device)

27. Scale up
 The scale up of cyclones is based on a dimensionless group,
the stokes number, which characterized the separation
performance of a family of geometrically similar cyclones.
D
x
Stk p
µ
νρ
18
2
50
50=
50
12
Stk
Eu =

29. Geometries , Euler and Stokes
numbers for 2 common cyclones
Cyclon
e type
A B C E J L K N
Eu Stk50
Stairma
nd, HE
4.
0
2.
5
1.
5
0.3
75
0.50 0.2 0.5 0.5 320 1.4 x 10-
4
Stairma
nd, HR
4.
0
2.
5
1.
5
0.5
75
0.875 0.375 0.7
5
0.7
5
46 6 x 10-3
Correctly designed n operated cyclone
should operate at pressure drop within a
recommended range ( at ambient
conditions), is between 50-150 mm of water
gauge (WG) (500-1500Pa)

30. Data necessary for cyclone design
 Particle size distribution
 Inlet dust loading (g/m3
)
 Particle density (kg/m3
)
 Gas flowrate (m3
/h)
 Gas temperature (o
C)
 Special condition of corrosivity, abrasiveness, fluctuation in
gas flowrate.etc.

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