Multi cyclone dust collector

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.

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

2. Contents Introduction Working Principle Types of Cyclone Need of Multi-Cyclone and it’s type Factor Affecting Efficiency of Cyclone Advantages and Disadvantage of Multi-Cyclone Application Costing Design Consideration 2

3. introduction 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. Particle size distribution of flue gas 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. Working Principle 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. Different type of cyclone Conventional Cyclone(medium efficiency ; pressure drop 2 – 4 in. of WC) High Efficiency Cyclone (removes up 10 micron particle with 90 % efficiency ; pressure drop 4 -6 in . of WC) 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 of cyclone and it’s removal efficiency in % Types and PM size PM greater than 10 micron PM 10 PM 2.5 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. Fractional collection efficiency of Cyclone Efficiency vs particle diameter 10 Source : wark & warner

11. Need of multi-cyclone 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 : Cyclone in Parallel : high volume of gas (generally above 25000 m3/hour ) Cyclone in Series : high efficiency (up to 95 % for particle > 5 micron) Multi-Cyclone : higher efficiency and high volume of gas simultaneously. 11

12. Cyclone in parallel arrangement Source : T,.K. Ray, Vol. 1. 12

13. Types of Multi-cyclone Types of Multi-Cyclone : Tangential entry reverse flow multi-cyclone Straight through multi-cyclone 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. Tangential entry reverse flow multi-cyclone 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. 1. 14

15. 15

16. Straight through multi-cyclone 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. Axial entry reverse flow multi-cyclone Cells are mounted on horizontal plate Fixed spinner to give the incoming gas a spinning effect O utlet 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 Axial entry reverse flow multi-cyclone

19. Source : Apzem instrument 19

20. 20

21. Factor affecting efficiency 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 and disadvantages 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. Problem : Hopper cross flow 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. 1. 23

24. Application OF MULTICYCLONE 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. I t can be also used as Demister (source : aixprocess ) 24

25. Comparison with other Control Equipment Parameter ➡ Control Equipment ⬇ Particle Size , μ m 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 25 Source : wark & warner

26. costing Capital Cost : Rs . 2,18,500 - Rs . 8,55,000 per m3/s Maintenance Cost(Annually) : Rs . 18,500 - Rs . 7 5,000 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. Design of multi-cyclone Data required for design : Gas Volume(m 3 / 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 : Altitude Correction factor can be found with help of table-3 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. Table – 1 : Dynamic viscocity and Composition of gas Source : T,.K. Ray, Vol. 1. 29

30. Table – 2 : Density of individual gas Source : T,.K. Ray, Vol. 1. 30

31. Table – 3 : altitude and density correction factor Source : T,.K. Ray, Vol. 1. 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 = 2 Π L / 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. graph - 1 : n vs d c Source : T,.K. Ray, Vol. 1. 36

37. Graph – 2 : k vs d c / d o Source : T,.K. Ray, Vol. 1. 37

38. References 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. Thank you… 39