21053 2105382 82 21053 2105382 82 UNIT OPERATIONS I UNIT OPERATIONS I UNIT OPERATIONS I UNIT OPERATIONS I Separation of Particle from fluid: Cyclone Separation of Particle from fluid: Cyclone fluid: Cyclone fluid: Cyclone Apinan Soottitantawat Apinan Soottitantawat Apinan Soottitantawat Apinan Soottitantawat [email protected]
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
2105321053828221053210538282
UNIT OPERATIONS IUNIT OPERATIONS IUNIT OPERATIONS IUNIT OPERATIONS I
Separation of Particle from fluid: Cyclone
Separation of Particle from fluid: Cyclonefluid: Cyclonefluid: Cyclone
There are many cases during the processing and handling of particulatesolids when particles are required to be separated from suspension in asolids when particles are required to be separated from suspension in agas or a liquid. How to separate them ?
Classification of separation techniques according to phases involvedp q g p
2S.Apinan
Separation: CycloneSeparation: Cyclone
One of the widely used is Cyclone.
GasGas CycloneCyclone: Separate the particle solid (aerosol) from- GasGas CycloneCyclone: Separate the particle solid (aerosol) fromthe gas.
- HydrocycloneHydrocyclone: Separate the particle solid (aerosol) fromthe liquid.
Purpose of the separationPurpose of the separation1 Ai ll ti t l i fl h l f l t fl1. Air-pollution control, as in fly-ash removal from power-plant flue
gases2. Equipment-maintenance reduction, as in filtration of engine intake
air or pyrites furnace-gas treatment prior to its entry to a contactsulfuric acid plant
3. Safety- or health-hazard elimination, as in collection of siliceous andymetallic dusts around grinding and drilling equipment and in somemetallurgical operations and flour dusts from milling or baggingoperationsoperations
4. Product-quality improvement, as in air cleaning in the production ofpharmaceutical products and photographic film
5 Recovery of a valuable product as in collection of dusts from dryers5. Recovery of a valuable product, as in collection of dusts from dryersand smelters
6. Powdered-product collection, as in pneumatic conveying; the spraydrying of milk eggs and soap; and the manufacture of high purity
5S.Apinan
drying of milk, eggs, and soap; and the manufacture of high purityzinc oxide and carbon black
• In any application, the size of the particles to be removed from the gas determine the method to be used for their separationdetermine, the method to be used for their separation.
• Generally speaking, particles larger than about 100 mm can be separated easily by gravity settling.
• For particles less than 10 mm more energy intensive methods such as• For particles less than 10 mm more energy intensive methods such as filtration, wet scrubbing and electrostatic precipitation must be used.
Particles in the gas are subjected to centrifugal forces which move them radiallyoutwards, against the inward flow of gas and towards the inside surface of thecyclone on which the solids separate. The direction of flow of the vortex reversesnear the bottom of the cylindrical section and the gas leaves the cyclone via theoutlet in the top. The solids at the wall of the cyclone are pushed downwards byth t t d t f th lid itthe outer vortex and out of the solids exit.
9S.Apinan
CycloneCyclone
10S.Apinan
Cyclone: ComponentsCyclone: Components
(cylinder)
11S.Apinan
Cyclone: Type of inletCyclone: Type of inlet รปแบบทอทางเขาของไซโคลนรปแบบทอทางเขาของไซโคลน
• It is useful to represent the efficiency with which various sizes or grades ofparticles are distributed between the outputs of separation devicesparticles are distributed between the outputs of separation devices.
1. Grade or fractional efficiency2. Overall efficiency
22S.Apinan
Total Efficiency and Grade EfficiencyTotal Efficiency and Grade Efficiency
Materials Balance
cf MMM +=fMcf
f Component Balance
Mfmif ,
fccmiffmimi MfMfMf ,, +=M
Mmifcmif , FractionMassfmi =
cM
23S.Apinan
Total EfficiencyTotal Efficiency
Total efficiency
ME ct =fM
MEt
MM
McM
24S.Apinan
Grade Efficiency G(x)Grade Efficiency G(x)
Grade efficiency G(x)
fM
M MfMM
MMfMf
MM
xGmi
ccmi
fi
cii
,
,
,)( =
cM f
25S.Apinan
Know Grade Efficiency G(x) to calculate EtKnow Grade Efficiency G(x) to calculate Et
M MfMG ccmici)(
MME c
t = Mff
MxG
mi
ccmi
feedi
cii
,
,
,)( =
MxGMM )(∑∑feedmii
feediiicct fxG
MMxG
MM
MME ,
, )()(
∑∑∑ ====
fGE )(∑ feedmiit fxGE ,)(∑=26S.Apinan
Know Et to calculate Grade Efficiency G(x)Know Et to calculate Grade Efficiency G(x)
Mf MMf
MfxG
f di
ccmii
,)( =MME c
t =Mf feedmi, MGrade efficiency G(x)
f cmit f
fExG ,)( =
feedmif ,
27S.Apinan
Total & Grade Efficiency G(x)Total & Grade Efficiency G(x)
ME c MMM +=M
E ct = cf MMM +=
MfMfMf +=
ifccmiffmimi MfMfMf ,, +=
mi
cmit f
fExG ,)( =
mif
EfEff )1( +−= tcmitfmimi EfEff ,, )1( +−=
28S.Apinan
Example: Total & Grade EfficiencyExample: Total & Grade Efficiency
Tests on a reverse flow gas cyclone give the results shown in th t bl b lthe table below:
Lower Upper Mass in feed (g) Coase product size (g)
0 5 10.00 0.10
5 10 15.00 3.53
10 15 25 00 18 0010 15 25.00 18.00
15 20 30.00 27.30
20 25 15.00 14.63
25 30 5.00 5.00
From these results determine the total efficiency of the cyclone and grade efficiency of each particle range
29S.Apinan
Solution: Total efficiencySolution: Total efficiency
Example: Size distribution and cyclone efficiency Example: Size distribution and cyclone efficiency
Air in a foundry is dusty because of handling sand used to makemolds, shaking castings out of the sand molds, and so on. A, g g ,sample of the workplace air was draw through a cyclone at a rateof 0.15 L/min for a period of 100 s. The sampled air contained 240particles which were counted and size optically on the basis ofparticles, which were counted and size optically on the basis ofdiameter as shown in the table. (density of particle = 1.74 g/cm3)
33S.Apinan
Example: Size distribution and cyclone efficiency Example: Size distribution and cyclone efficiency
It has been proposed to remove particle from the air with acyclone whose fractional (grade) efficiency is given below.y (g ) y g
1 Pl t th i di t ib ti f th l i b th f l h1. Plot the size distribution of the sample in both of normal graphand lognormal graph for number and mass basis.
2. Will this cyclone be able to bring the workplace air intoy g pcompliance with the OSHA standard that specifies that themaximum allowable concentration for nonrespirable nusancedust is 15 mg/m3?
2. Will this cyclone be able to bring the workplace air intocompliance with the OSHA standard that specifies that thecompliance with the OSHA standard that specifies that themaximum allowable concentration for nonrespirable nusancedust is 15 mg/m3?g
Step 1: Determine the initial over all dust mass concentration
Determine the initial over all dust mass concentration
35 mparticles/1060.9ionconcentratNumber ×=
6ionConcentratNumberionconcentratMass
3mDρπ
×=
6)1034.38(kg/m17401060.9ionconcentratMass
3635
−××××=
π
335 mg/m3.49kg/m1093.4ionconcentratMass =×= −
39S.Apinan
Solution:Solution:
Step 2: The minimumum over all efficiency to pass the standard (concentration for nonrespirable nusance dust is 15 mg/m3)concentration for nonrespirable nusance dust is 15 mg/m3)
Mass Balance
3mg/m3.34152.49 =−=−= finefeedc MMM
334M 6957.03.493.34
minimum, ===MME c
t 3.49M
40S.Apinan
Solution:Solution:
Step 3: Determine the actual overall efficiency from gradeefficiencyefficiency
Cyclone Grade Efficiency in PracticeCyclone Grade Efficiency in Practice
• There are the another way to show the efficiency of collector/separator as cut diameter (critical size criticalcollector/separator as cut diameter (critical size, critical diameter, xcrit, dpcirt)
• For cyclone, the grade efficiency curve for gas cyclones is y , g y g yusually S-shaped.
• The particle size for which the grade efficiency is 50%, cut size, x50, is often used as a single number measurement of the efficiency of the cyclone.
• x is sometimes simply referred to as the cut size of the• x50 is sometimes simply referred to as the cut size of the cyclone (or other separation device).
• The concept of x50 cut size is useful where the efficiency p 50 yof a cyclone is to be expressed as a single number independent of the feed solid size distribution, such as in
53S.Apinan
scale-up calculation.
Cut size/ Cut diameter in cycloneCut size/ Cut diameter in cyclone
1.00
0.80 , G
(x)
0.60
ficiency ,
0 20
0.40
Grade
Eff
0.00
0.20 G
0 10 20 30Diameter (μm)
sizeCut xD ==54S.Apinan
5050sizeCut xDp ==
LOGO
Prediction of collection Prediction of collection efficiency efficiency efficiency efficiency
Prediction of collection efficiencyPrediction of collection efficiency
Number of turns of vortex (Ne)Number of turns of vortex (Ne)
vortexofturnsofNumberNe = ffe
)(1 cLLN +≅ )2
( cbe L
HN +≅
58S.Apinan
Prediction of collection efficiencyPrediction of collection efficiency
2. Cut diameter approach2. Cut diameter approach• A semiempirical approach developed by Lapple used larminar
flow treatment but introduced the concept of a cut size, dp50.p50• Therefore he could fine the cut diameter as
VdN ρπ 2
WVdN gppe
μρπ
η9
5.0 ==
Wμ9
μ
gpep VN
Wdρπμ
29
50 =
59S.Apinan
gpeρ
Prediction of collection efficiencyPrediction of collection efficiency
Lapple`graphLapple`graph
1( )250 /1
1)(pip
i dddpG
+=
pp
6060S.Apinan
Prediction of collection efficiencyPrediction of collection efficiency
3. 3. LeithLeith & & LichtLicht’ s ’ s modelTheoreticalmodelTheoretical approach approach (Laminar flow)(Laminar flow)
• The laminar flow model has limitations, as gas flow in a cyclone is not simply laminar (nor is it fully turbulent, because the boundary layer has a significant depth).
• Leith&Licht have derived the equation which was in the formq
• Connecting cyclones in series is often done in practice to iincrease recovery.
• Usually the primary cyclone would be of medium or low efficiency design and the secondary and subsequentefficiency design and the secondary and subsequent cyclones of progressively more efficient design or smaller diameter.
SS71S.Apinan
SeriesSeries
Cyclones in parallelCyclones in parallel
• The x50 cut size achievable for a given cyclone geometry d ti d d ith d iand operating pressure drop decreases with decreasing
cyclone size. • The size a single cyclone for treating a given volume flowThe size a single cyclone for treating a given volume flow
rate of gas is determined by that gas flow rate. • For large gas flow rates the resulting cyclone may be so g g g y y
large that the x50 cut size is unacceptably high.• The solution is to split the gas flow into several smaller
l ti i ll lcyclones operating in parallel. • In this way, both the operating pressure drop and x50 cut
size requirements can be achievedsize requirements can be achieved.
72S.Apinan
Cyclones in series and parallelCyclones in series and parallel