The document provides a comprehensive overview of multi-cyclones, focusing on their design, working principles, and efficiency in removing dust particles from flue gases in coal-fired boilers. It discusses different types of cyclones, performance metrics like efficiency and pressure drop, as well as advantages and disadvantages of using multi-cyclones for gas treatment. Additionally, the document outlines design considerations and key parameters needed for effective cyclone operation.

1. Jignesh J. Raiyani
ME III (160280718015),
LDCE-AHMEDABAD.
1

2. 1. Introduction
2. Working Principle
3. Types of Cyclone
4. Need of Multi-Cyclone and it’s type
5. Factor Affecting Efficiency of Cyclone
6. Advantages and Disadvantage of Multi-Cyclone
7. Application
8. Costing
9. Design Consideration
2

3.  In coal fired boilers the flue gases have certain particles of solid matter in
suspension, this is called smoke or dust. In case of pulverized coal furnaces the fly
ash remains in suspension with flue gases. If the particle in suspension are of size
ranging from 1-100 𝜇m, it is called dust or smoke.
 Any dust particles leaving into chimney exhaust are objectionable and harmful for
the health of human being and for plant life.
 Now a days rules and regulations regarding emissions and pollution control are
getting strict. Therefore, it is always necessary to clean the gas from dust, smoke,
or cinder particles before it is to be discharged from the chimney. Therefore to
reduce the emission from steam producing industries we are willing to design and
manufacture different type dust collector.
3

4. Source : wark & warner 4

5.  Mechanical Separator :
 Gravity Separator – Gravity Chamber(above 50 micron)
 Centrifugal Separator(up to 10 micron)
 Cyclone Separator
 Cyclone in Parallel
 Multi-Cyclone
 Multi-Cyclone :
It is the device that utilize specific configuration of N number of cyclones
(diameter equal or greater than 300 mm) to treat higher volume of gas efficiently.
5

6.  Cyclones are one of the most
utilized devices for solid–gas
separation. It works by
forcing the gaseous
suspension to flow spirally
(thus the name cyclone)
within a confined space, so
that the particles are
expelled toward the walls of
the vessel by centrifugal
force. Once on the walls, the
particles move downward,
mainly by gravity, and are
removed from the cyclone,
whereas the gas spins out,
usually upward.
 Source : Enginnering360 6

7. 7

8. 1. Conventional Cyclone(medium
efficiency ; pressure drop 2 – 4
in. of WC)
2. High Efficiency Cyclone
(removes up 10 micron particle
with 90 % efficiency ; pressure
drop 4 -6 in. of WC)
3. High Throughput Cyclone
(removes efficiently only
particle>20 micron ; low
efficiency ; pressure drop 8-10
in. of WC)
 Source : Novatech Equipment 8
(3) (3) (2) (2)

9. Types and PM
size
PM greater than
10 micron
PM10 PM2.5
Conventional
Cyclone
70-90 30-90 0-40
High Efficiency
Cyclone
80-99 60-95 20-70
High Throughput
Cyclone
80-90 10-40 0-10
Multi-Cyclone - 80-99 80-95
 Source : USEPA 9

10. 10Source : wark & warner

11.  Above three types of cyclone have limitation of capacity to treat the largevolume
of flue gas (up to maximum 25000 m3/hour).
 However capacity of standard cyclone can be increased by increasing inlet
velocity but in practice velocity above certain value(12 - 22 m/s) cause pressure
drop and also induce excessive turbulence that cause efficiency to fall.
 To overcome above difficulties following to devices are used :
1. Cyclone in Parallel : high volume of gas (generally above 25000 m3/hour)
2. Cyclone in Series : high efficiency (up to 95 % for particle > 5 micron)
3. Multi-Cyclone : higher efficiency and high volume of gas simultaneously.
11

12.  Source : T,.K. Ray, Vol.
1.
12

13.  Types of Multi-Cyclone :
1. Tangential entry reverse flow multi-cyclone
2. Straight through multi-cyclone
3. Axial entry reverse flow multi-cyclone
 Small cyclone often called cell is arranged in arrays and mounted on plate which
can be vertical , horizontal, stepped depending on the design.
 Cell diameter varies from 150 mm to 250 mm.
 Material of construction is generally alloy cast iron having hardness of 430 – 450
brinell.
 The design limits the number of cells in the gas flow direction to 10 cells.
13

14. • Cells are mounted on stepped
plate called ‘cell tube sheet’.
• Position of cell is inclined for
easy flow of the collected dust.
• At the end , one common pipe is
provide to flow down collected
dust.
 Source : T,.K. Ray, Vol. 14

15. 15

16. • Horizontal cell are mounted on
vertical sheet
• This design essentially
incorporates the secondary
circuit provided with secondary
cyclone.
 Source : T,.K. Ray, Vol.
1.
16

17. • Cells are mounted on horizontal
plate
• Fixed spinner to give the
incoming gas a spinning effect
• Outlet recovery vanes are used
to recover the rotational energy
of the exit gas(Not recommended
in case of sticky dust)
 Source : T,.K. Ray, Vol.
1.
17

18. 18 Source : Asphalt plant dust collection system

19.  Source : Apzem instrument
19

20. 20

21.  Efficiency will increase with increase in :
 Dust particle size
 Particle density
 Gas inlet velocity(12-22 m/s)
 Cyclone body or cone length (provide more retention time)
 Efficiency will decrease with :
 Increase in gas viscosity or density (increase drag force)
 Cyclone diameter
 Inlet width or inlet area
21

22.  Advantages of cyclones are:
 Low capital cost
 Ability to operate at high temperatures (up to 350︒ C)
 Low maintenance requirements because there are no moving parts.
 Dry collection and Disposal
 Disadvantages of cyclones are:
 Unable to tackle sticky material
 High efficiency unit may experience high pressure drop(8 – 10 inch of WC)
 High operating costs (owing to power required to overcome pressure drop).
22

23.  Often multi-cyclone is suffer from problem called
‘hopper cross flow ’. This is mainly due to uneven
distribution of flue gas In some cells, gas does not flow
back to the clean gas tube, instead it enters into the
hopper only to flow through the other cells. This reduces
the efficiency of multi-cyclone.
 This problem can be overcome by drawn out small
amount of gas through hopper. This is called ‘hopper
evacuation’.
 For this hopper evacuation 15% gas withdrawn is
adequate.
 Experiments shows that efficiency of multi-cyclone can
ne increased from 89 to 95 percent with the help of
hopper evacuation.
 Source : T,.K. Ray, Vol. 23

24.  Since the multi-cyclone can remove efficiently the particle with diameter greater
than 5 micron , it is used as a pre-collector before fabric filter or ESP.
 It can be also used as Demister (source : aixprocess)
24

25. Parameter➡
Control Equipment⬇
Particle Size , μm Efficiency , % Pressure Drop △P ,
inch in Water Column
Settling Chamber 50 60 - 70 0.2 – 0.5
Conventional Cyclone > 20 50 1 – 3
High Efficiency Cyclone ≧ 10 80 3 - 5
Multi-Cyclone Up to 5 90 4.5
Scrubber 0.1 - 20 90 – 98 2 - 50
Fabric Filter > 0.001 95 - 99 4 – 6
Electrostatic Static
Precipitator
0.05 - 200 80 – 99 0.2 – 0.5
25Source : wark & warner

26.  Capital Cost : Rs. 2,18,500 - Rs. 8,55,000 per m3/s
 Maintenance Cost(Annually) : Rs. 18,500 - Rs. 75,000 per m3/s
 Here consider , Flow is between 0.5 – 50 m3/s
Dust Loading is between 2.3 – 23o g/m3
Efficiency is 90 %
26

27.  Data required for design :
 Gas Volume(m3/ hr )
 Type of gas : Boiler /Blast furnace/ Cement kiln etc. flue gas
 Type of dust :Hygroscopic/Abrasive/Sticky/Light and Fluffy/Explosive/Dust with build up
characteristics etc.
 Temperature of gas(‘C)
 Altitude(m)
 Particle Size Distribution :
 Particle Diameter in micron
 Particle Fraction in % by weight
 Particle Density(kg/m3)
27

28.  Design Step :
 Take density of individual gas component from table – 2 and calculate the overall density of flue
gas(this is at 0’C and 760mm Hg)
Correct the density with respect to Altitude and Temperature of flue gas by multiplying above
overall density with Altitude correction factor and Temperature correction factor :
1. Altitude Correction factor can be found with help of table-3
2. Temperature correction factor can be found by equation = 273/(T +273)
Density of our flue gas =(overall density *TEMP CF *ALT CF)
Find the Dynamic Viscosity of flue gas at given temperature by using table-1
Assume the Diameter of cell : Dc (between 150 mm- 250mm). Now dimension of the other part
are as follows (as per stairmand model),
Inlet width Wi = 0.2Dc , Inlet length Li =0.5Dc ,
Outlet Diameter Do = 0.5Dc , Bottom Diameter Db= 0.25 Dc ,
Length of Cylinder H1= 1.5Dc , Length of Cone H2= 2.5Dc ,
Length of Vortex finder H3 =0.5Dc
28

29.  Source : T,.K. Ray, Vol. 29

30.  Source : T,.K. Ray, Vol.
1.
30

31.  Source : T,.K. Ray, Vol. 31

32.  Assume the inlet velocity (Vi)through cell in m/s (12 – 22 m/s).
Calculate the flow through cell : Qc = (Wi*Li)*Vi
No of cell = Q/Qc
Now, provide the array of cell in such way that no of cell in the direction of gas
flow does not exceed 10 cell to ensure even distribution of air
 Design Casing with : Edge Distance of 0.6 Dc and C/C distance of 1.2 Dc
Calculate the total length and width of inlet section : (W*L)m
Height of the inlet section H = Q/(Vi*W)
Provide the outlet section with same dimension : (W*L*H)m
 Design the Hopper Bottom : It’s depend on casing size (W*L) ,dust discharge opening
(300 mm * 300mm in case of rotary air lock valve) and Valley angle (25’ – 30’)
Find the ‘a’ (shown in below figure ) by using Pythagoras theorem.
Find Height of hopper : Hh = a/ tan (valley angle)
32

33.  Source : T,.K. Ray, Vol.
1.
33

34.  Now , find the Efficiency of multi-cyclone :
Find natural length of cyclone : L = H1+(H2/2)
Find Distance between two consecutive helix : W= 0.5Dc
Turning Angle : θ= 2ΠL / W
Use the following equation to find the efficiency of multi-cyclone.
34

35.  Calculate the pressure drop :
Find the value of ‘n’ for the cyclone diameter Dc and given temperature by using graph-1(below)
Find the value of ‘k’ from graph-2 (below) by using ratio Dc/Do and value of ‘n’.
Now by using following equation find the pressure drop.
35
Where , K = factor (find from graph above)
Ui=Vi inlet velocity , m/s
De=Dc cyclone diameter ,m
a= Wi inlet width , m
b=Li inlet length , m
Pg=gas density @given temperature , kg/m3
△P = pressure drop ,kg/m/s2

36.  Source : T,.K. Ray, Vol.
1.
36

37.  Source : T,.K. Ray, Vol.
1.
37

38.  T.K. Ray , volume 1.
 USEPA
 Air Pollution Control Engineering by Lawrence Wang
 “Review of Multi-cyclone Dust Collector” , IJATES, Volume 4, Issue No 3.
 Google
38

39. 39