EPA-650/2-74-119-CI



OCTOBER 1974
Environmental  Protection  Technology Seri
                                                                  es










                 i::^!:::^

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                                EPA-650/2-74-119a
ENTRAINMENT SEPARATORS
       FOR SCRUBBERS  -
        INITIAL REPORT
                  by

       S. Calvert, I.L. Jashnani, S. Yung,
              and S. Stalberg

               A.P.T. , Inc.
               P.O. Box 71
         Riverside, California 92502

          Contract No. 68-02-0637
         Program Element No. 1AB013
            ROAPNo.  21ACX-086

         Project Officer:  L.E. Sparks

         Control Systems Laboratory
     National Environmental Research Center
   Research Triangle Park, North Carolina 27711

               Prepared for

    OFFICE OF RESEARCH AND DEVELOPMENT
     ENVIRONMENTAL PROTECTION AGENCY
         WASHINGTON, D.C. 20460

               October 1974

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This report has been reviewed by the Environmental Protection Agency
and approved for publication. Approval does not signify that the con-
tents necessarily reflect the views and policies of the Agency, nor does
mention of trade names or commercial products constitute endorsement
or recommendation for use.
                                   11

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                         PREFACE

     This report, "Entrainment Separators 'for Scrubbers",
is the interim report submitted to the Control System
Laboratory for E.P.A. Contract No. 68-02-0637.
     The scope of work of this experimental and theoretical
study was to
     1.  Evaluate present technology.
     2.  Conduct an experimental study of air water
         systems aimed at simulating the performance
         of various types of entrainment separators.
     3.  Develop improved engineering equations and
         methods for entrainment separator selection.
     4.  Develop and evaluate on a small pilot basis
         new entrainment separator designs.
     5.  Develop specific research and development
         recommendations.
     Dr. Leslie E.  Sparks, of the Control Systems Laboratory,
National Environmental Research Center, Environmental Pro-
tection Agency, was the Project Officer for this program.
     Dr. Seymour Calvert, of A.P.T., Inc., was the Project
Director,
                          iii

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                   ACKNOWLEDGEMENT
A.P.T., Inc. wishes to express its appreciation for
excellent technical coordination and for very helpful
assistance in support of our technical effort to
Dr. Leslie Sparks, E.P.A. Project Officer.
                         IV

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                      TABLE OF CONTENTS
                                                   Page
Acknowledgement	iv
List of Figures	ix
List of Tables	xvii
Nomenclature  	 xix
Abstract	xxv

Sections
Introduction  	 1-1
Summary and Conclusions 	 2-1
Literature Survey 	 3-1
     Collection Mechanisms	3-3
          Inertial Impaction  	 3-3
          Sedimentation 	 3-6
     Entrainment Drop Diameters  	 3-6
     Design Equations for Entrainment Separators.  • 3-9
          Cyclone	3-10
               Primary Efficiency 	 3-10
               Pressure Drop	3-13
          Packed Bed	3-14
               Primary Efficiency 	 3-15
               Pressure Drop	3-16
          Zigzag Baffles  	 3-16
               Primary Efficiency .... 	 3-16
               Pressure Drop  	3-21
          Tube Bank	3-21
               Primary Efficiency 	 3-21
               Pressure Drop	3-23
          Mesh  	3-23
               Primary Efficiency 	 3-24
               Pressure Drop  	3-25

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                                                       Page

           Sieve Plates	3-27
                Primary Efficiency  	  3-27
                Pressure Drop	3-27
      Reentrainment  	  3-31
           Transition from Separated to Separator -
           Entrained Flow	3-32
                Horizontal Flow in Circular Tube   •  •  •  3-33
                Vertically Upward  Flow  in  a
                Circular Tube	3-36
                Vertically Downward Flow in a
                Circular Tube	3-38
                Effect  of  Impingement of Gas Jet   .  .  .  3-38
                Interfacial Waves  	  3-38
                Entrained  Fraction  and  Rate  of Entrainment  3-47
                Drop  Diameter of Reentrainment	3-50
          Reentrainment Due  to Rupture  of Bubbles.  .  .  3-51
                Drop  Diameter of Reentrainment	3-52
                Formation  of  Jet After Bubble Burst  .  .  3-55
                Trajectory	3-57
          Creeping of  Fluids	3-60
          Shattering of Drops	3-62
     Manufacturers'  Survey 	  3-62
Theory	4-1
     Zigzag Baffles	4-1
          Primary Efficiency 	 4-1
          Pressure Drop	4-8
          Reentrainment	4-8
               Horizontal Baffles   	 4-11
               1.  Derivation of (X	4-11
               2. Additional Equations	4-15
               Vertical Baffles  	 4-16
               1. Liquid Flow  Due to Pressure  Gradient4-18
               2. Liquid Flow  Due to Gravity	4-19
               3. Additional Equations	4-20
                            VI

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                                                      Page
     Cyclone	4_20
          Primary Efficiency  	 4-20
          Reentrainment  	 4-26
               Onset of Reentrainment	4-26
               Drop Diameter of Reentrainment	4-27
               Rate of Reentrainment	4-27
               Reentrainment Calculation 	 4-28
Auxiliary Experiment 	 5-1
     Sampling for Droplet Size Distribution  	 5-2
     Discussion	5-6
     Results	5-8
     Conclusions	5-17
Experimental Pilot Plant 	 6-1
     Description of the Pilot Plant	6-1
          Air Prefilter	6-2
          Blower	6-2
          Air Heater	6-2
          Spray Section	6-2
          Observation Sections 	 6-6
          Drainage of Liquid in the Test  Section •  •  • 6-9
          Liquid Catch Tanks 	 6-10
          Liquid Supply Tanks  	 6-10
          Control Panel for  Equipment	6-10
          Electrical Supply  Panel   	 6-11
          Water Supply	6-11
     Test Section	6-11
          Mesh	6-12
          Packed Bed	6-13
          Zigzag Baffles  	 6-13
          Cyclone	  . 6-13
          Tube  Bank	6-17
     Calibration	6-17
     Experimental Procedure   	 6-20
     Sampling Procedure	6-21
     Problems and Possible Errors  in the  Experiments  •  6-28
                         vii

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                                                      Page
Experimental Results and Discussion	7-1
     Inlet Entrainment	7-1
     Experimental Results   	  7-9
          Packed Bed	7-10
               Overall Efficiency   	  7-10
               Pressure Drop	7-10
               Reentrainment  	  7-10
          Zigzag Baffles 	  7-16
               Overall Efficiency	7-16
               Pressure Drop	7-21
               Reentrainment  	  7-21
               Liquid Flow on the Baffles	7-29
          Mesh	7-33
               Overall Efficiency   	  7-33
               Pressure Drop	7-35
               Reentrainment	7-35
               Visual Observation of Reentrainment  .  .  7-42
          Tube Bank	7-44
               Overall Efficiency	7-44
               Pressure Drop	7-49
               Reentrainment  	  7-53
     General Observations   	  7-S3
          Pressure Drop	7-53
          Reentrainment	7-66
Future Research and Development Recommendation . .  .  .  8-1
Appendix
Glossary
References
                        Vlll

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                    LIST OF FIGURES

                                                       Page

 3-1      Entrainment Separator  	 3-2

 3-2      Theoretical Impaction Efficiency  as  a
         Function  of Inertial  Parameter  for
         Different Targets   	 3-2

 3-3      Terminal  Settling  Velocity and  Reynolds
         Number  for Water Drops  in  Air at  20°C
         and  760 mm Hg   	3-8

 3-4      Cyclone with Tangential  Gas  Inlet	3-11

 3-5      Generalized Flooding  and Pressure Drop
         Correlation for  Packed Beds   	3-17

 3-6      Theoretical and  Experimental Collection
         Efficiencies of  Rectangular Aerosol Jets  .  .  . 3-22

 3-7      Friction  Factor, "f", Versus Reynolds
         Number, "N  ", for Wire  Mesh Entrainment
         Separator   e  Without Entrainment Load  .... 3-26

 3-8      Pressure  Drop Due to Presence of Liquid in
         the Knitted Mesh Wire with the  Crimps in
         the Same  Direction	3-28

 3-9      Pressure Drop Due to Presence of Liquid in
         the Knitted Mesh with the Crimps in the
        Alternate Direction   	  3-29

 3-10    Baker Chart	3-34

 3-11    Flow Pattern Diagram for Horizontal Flow  •  •  .  3-35

3-12    Onset of Entrainment in Air-Water Flow .... 3-37

3-13    Comparison of Entrained Fraction in Upward
        and Downward Co-current Annular Flow in
        1.25 cm I.D. Tube	3-39

3-14    Extrapolation Method for Determination of
        Point of Onset  of Entrainment for Vertical
        Downflow in 2.2 cm I.D. Tube	3-40
                          IX

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 No.

 3-15    Region of Wave Flow in Air-Water Flow in
         a 3.2 cm Bore Tube	3-42

 3-16    Relationship Between Effective Roughness
         Height and Film Thickness	3.45

 3-17    Breakdown of Disturbance Wave by Undercutting. 3-46

 3-18    Breakdown of Disturbance Wave by Rolling .  .  . 3-46

 3-19    Correlation of Entrainment  Data by Hughmark.  . 3-49

 3-20    Histogram Showing Size Distribution of
         Large and Small Drops  Resulting from
         Bubble Burst	3-54

 3-21    Sauter Mean Diameter D  Against Bubble
         Diameter  at 25°C .  .  .s	3.54

 3-22    Time  Against Velocity  Curves  for Drops
         of Varying  Degree	3-59

 3-23    Height Against  Velocity  Curves  for  Drops
         of Varying  Diameter	3-59

 3-24    Calculated  Collection  Efficiency for
         Water Droplets  in Air  for ACS Mesh	3-64

 3-25    Pressure Drop Versus Air Velocity for
         10 cm Thick  ACS Style  4CA Mesh	3-65

 3-26     Pressure Drop Versus Steam Velocity at
         Various Pressures through 10 cm  Thick
         ACS Mesh	3.66

 3-27     Collection Efficiency Versus Particle
         Diameter for Air Purification Method
         Cyclone Separator with Inlet Velocity
         of 16-21 m/sec	3-68

3-28     Comparison of Pressure  Drop Characteristics
         of Beco Engineering Type E/N-1 Pad and
         Conventional Pad	 3-70

3-29    Efficiency Curves for Burgess Industries
        Centrifuge	3-72

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No.                                                   Page

3-30    Pressure Drop Characteristics of 10 cm
        Thick Nu-Standard and 15 cm Thick Hi-
        Thruput Mist Eliminators 	 3-73

3-31    Safe Operating Limits for Nu-Standard
        and Hi-Thruput Mist Eliminators  	 3-74

3-32    Flooding Correlation for Fibrous Bed
        Structure by Porter and Lucas	3-77

3-33    Performance of Koch Fleximesh Separator. .  .  . 3-80

3-34    Collection Efficiency of Particulate
        Collectors .	3-81

3-35    Efficiency Comparison of York Scrubber
        with Two Stage Wire Mesh Mist Eliminator .  .  .3-83

4-1     Continuous Zigzag Baffles  	 4-2

4-2     Drag Coefficient Versus Reynolds Number
        After Foust et al. (1959), with Sphericity
        IMF " as the Parameter	4-5

4-3     Penetration Versus Gas Velocity for
        Baffle Section 	 4-6

4-4     Comparison of Primary Efficiency Curves
        Based on Theoretical Model for Complete
        Mixing and For No Mixing Models	4-7

4-5     Drag Coefficients for Flow Past Inclined
        Flat Plates	4-9

4-6     Forces on An Element of Liquid Film on
        Baffle	4-12

4-7     Effects of Baffle Edges on Reentrainment .  .  . 4-12

4-8     Maximum Liquid Load, QT/Qr, Versus Gas
        Velocity in Horizontal   b Baffle Section.  .  . 4-17

4-9     Predicted Effect of Liquid Loading in
        Inlet on Reentrainment from Vertical Baffles  . 4-21

4-10    Predicted Effect of Liquid Loading in
        Inlet on Reentrainment from Vertical Baffles  . 4-22
                        xi

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    '                                                   Page

 4-11    Cross Section of a Cyclone  .......... 4-25

 4-12    Predicted Effect of Inlet Gas Velocity
         on Reentrainment in Cyclone with
a = 9.2 cm, b - 28 cm, d  = 127 cm,
h= 132 cm, and d  = 67 cm
                                                        4-29
 4-13    Predicted Effect of Liquid Loading in
         Inlet on Reentrainment in Cyclone with
         a = 9.2 cm, b = 28 cm, d  = 127 cm,
         hs = 132 cm and dg = 67 cm ..........  4-30

 4-14    Predicted Effect of Inlet Gas Velocity
         on Efficiency of Cyclone with a = 9.2 cm
         b = 28  cm,  d  = 127 cm, h  = 132 cm and
         de = 67 cm  ' ......  •  ..........  4-31

 4-15    Predicted Collection Efficiency With and
         Without Reentrainment for Cyclone with
         a =9.2 cm,  b = 28 cm,  d   =  127 cm,
         hg = 381 cm, and d  = 67ccm   .........  4-33

 5-1      Apparatus to Study Onset  of  Entrainment
         Velocities  ..................  5.3

 5-2      Predicted Effect of Drop  Diameter on
         Capture  Efficiency by 5 cm Diameter
         Filter  Paper held  Perpendicular to  the
         Air  Velocity .................  5.7

 5-3      Distribution  of  Droplet Size  in Air-Water
         Entrained-Separated  Flow  ...........  5-9

 5-4      Distribution  of  Droplet Size  in Entrained-
         Separated Flow on  Log-Probability Graph. . . .  5-10

 5-5      Comparison of Drop Size by Different
         Investigators  ................  S-ll

 5-6     Effect of Impingement Angle on Drop Size . . . 5-13

5-7     Effect of Liquid Flow Rate on Impingement
        Angle for Onset of Entrainment ........ 5-14

5-8     Comparison of Entrainment Onset Velocity
        by Different Investigators ..........  5-15
                         xii

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No.                                                    Page

6-1      Block Diagram of Experimental Apparatus. .  .  .  6-3

6-2      Top View of the Entrainment Separator
        Pilot Plant	6-4

6-3      Flow Diagram Showing Connection Between
        Various Tanks and Pumps	6-5

6-4      Nozzle Position in the 30.5 cm x 61 cm Duct.  .  6-8

6-5      Calculated Collection Efficiency for
        Water Droplets in Air	6-14

6-6      Pressure Drop Versus Air Velocity for
        10 cm Thick ACS Style 4CA Mesh	6-15

6-7      Baffle Section	6-16

6-8      Cyclone Assembly 	  6-18

6-9      Test Section with Bank of Tubes	6-19

6-10    Form for Recording Test Data	6-22

6-11    Calibration of Whatman No. 1 Filter Paper.  .  .  6-25

6-12    Liquid Load Sampling	6-26

6-13    Sampling Device Consisting of Impactor,
        Heated Inlet Probe, Dry and Wet Bulb
        Thermometer and Accessories	6-29

7-1      The Effect of Gas Velocity on the Mass
        Median Drop Diameter	7-3

7-2      Drop Diameter Versus Volume Percentage
        for Hollow Cone Nozzle Spraying Water at
        10.2 atm Gauge Pressure	7-6

7-3      Drop Diameter Versus Volume Percentage
        for Hollow Cone Nozzle Spraying Water at
        6.8 atm Gauge Pressure	7-7

7-4      Drop Diameter Versus Volume Percentage
        for Fulljet Nozzles Spraying Water at
        2.7 atm Gauge Pressure	7-8

7-5      Experimental Collection Efficiency of a
        Packed Bed as a Function of Gas Velocity
        with Horizontal Flow	7-11
                         Xlll

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No.                                                   Page

7-6     Dry Pressure Drop in Packed Bed Versus
        Gas Velocity	7-12

7-7     Wet Pressure Drop in Packed Bed Versus
        Gas Velocity	7-13

7-8     Maximum Drop Diameter in the Entrainment
        Versus Gas Velocity for 30 cm Packed Bed . .  . 7-14

7-9     Mass Median Drop Diameter Versus Geometric
        Standard Deviation Downstream of 30.5 cm
        Packed Bed	7-15

7-10    Collection Efficiency Versus Gas Velocity
        in the Zigzag Baffle Device with n = 6
        and 9 = 30°	7-17

7-11    Collection Efficiency Versus Gas Velocity
        in the Zigzag Baffle Device with n - 6
        and 6 = 30°, d   - 380 ym and a  = 1.52. . .  . 7-18
                      Pg               g
7-12    Collection Efficiency Versus Gas Velocity
        in Zigzag Baffle Device with n = 6,
        6 = 30°, d   = 1,225 ym and a  = 1.75.

        Theory Predicts 100% Efficiency	7-19

7-13    Experimental Collection Efficiency as a
        Function of Gas Velocity in the Vertical
        Baffles.  Solid Line Represents Theory  .... 7-20

7-14    Dry Pressure Drop in Baffles Versus Gas
        Velocity	7-23

7-15    Wet Pressure Drop in Baffles Versus Gas
        Velocity	7-24

7-16    Outlet Drop Diameter Versus Gas Velocity
        for Zigzag Baffles with Inlet Mass Median
        Diameter of 380 ym	7-25

7-17    Outlet Drop Diameter Versus Gas Velocity
        for Zigzag Baffle with 1,225 ym Inlet
        Mass Median Drop Diameter	7-26

7-18    Size Distribution of Drops Leaving Baffle
        Entrainment Separators 	 7-27

7-19    Maximum Outlet Drop Diameter in the
        Entrainment Versus Gas Velocity for
        Zigzag Baffles 	 7-28
                           xiv

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No.                                                   Page

7-20    Drop Diameter Versus Geometric Standard
        Deviation at Zigzag Baffle Outlet  	 7-30

7-21    Effect of Gas Velocity and Liquid Load
        on Performance of Baffle Type Separator. . .  . 7-31

7-22    Some Observed Phenomena in Entrainment
        Separator	7-32

7-23    Experimental Collection Efficiency of Wire
        Mesh as a Function of Gas Velocity	7-34

7-24    Pressure Drop in Wire Mesh Versus Gas
        Velocity with Liquid Load as Parameter  .... 7-36

7-25    Outlet Drop Diameter Versus Gas Velocity
        for Mesh with 82 ym Inlet Drop Diameter  . .  . 7-37

7-26    Outlet Drop Diameter Versus Gas Velocity
        for Mesh with 1,225 ym Inlet Drop Diameter .  . 7-38

7-27    Maximum Outlet Drop Diameter in the
        Entrainment Versus Gas Velocity for Mesh . .  . 7-39

7-28    Drop Diameter Versus Geometric Standard
        Deviation for Mesh	7-40

7-29    Effect of Gas Velocity and Liquid Load
        on Performance of Mesh	7-41

7-30    Onset of Reentrainment Velocity Curves
        for Mesh	7-43

7-31    Collection Efficiency Versus Gas Velocity
        in Tube Bank with n = 6, d   = 84 ym and
        a  = 1.32	Pf	7-45
         g
7-32    Collection Efficiency Versus Gas Velocity
        in Tube Bank with d   = 380 ym and a  = 1.52  . 7-46
                           Pg               g
7-33    Collection Efficiency Versus Gas Velocity
        in Tube Bank	7-47

7-34    Dry Pressure Drop in Tube Bank Versus
        Gas Velocity	7-50

7-35    Wet Pressure Drop in Tube Bank Versus
        Gas Velocity	7-51
                          xv

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No.                                                    Page

7-36    Friction Factor Versus Gas Velocity in the
        Bank of Tubes	7-52

7-37    Outlet Drop Diameter Versus Gas Velocity
        for Tube Bank with 380 ym Inlet Drop
        Diameter	7-54

7-38    Outlet Drop Diameter Versus Gas Velocity
        for Tube Bank with 1,230 ym Inlet Drop
        Diameter	7-55

7-39    Size Distribution of Drops Leaving
        Tube Bank Entrainment Separators 	 7-56

7-40    Outlet Mass Median Drop Diameter Versus
        Geometric Standard Deviation for Tube Bank . . 7-57

7-41    Maximum Drop Diameter in the Entrainment
        Versus Gas Velocity for Tube Bank	7-58

7-42    Experimental Results Showing the Effect of
        Gas Velocity and Liquid Load on Performance
        of Tube Bank	7-59

7-43    Pressure Drop in the Empty Section Versus
        Gas Velocity	7-60

7-44    Dry Pressure Drop Versus Gas Velocity in
        Different Separators Used in Pilot Plant .  . . 7-62

7-45    Pressure Drop Through Entrainment Separator
        As a Function of Superficial Gas Velocity  . . 7-63

7-46    Comparison of Pressure Drop Data of
        Houghton and Radford with Present Data .... 7-64

7-47    Minimum Outlet Drop Diameter Versus Gas
        Velocity	7-70
                          xvi

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                      LIST OF TABLES

No.                                                      Page

3-1      Summary of Available Information on
         Entrainment Separators 	 3-4

3-2      Summary of Conventional Entrainment
         Separators	3-5

3-3      Packing Factors, "F", for Dumped Pieces	3-18

3-4      Packing Factors, "F", for Grids and
         Stacked Pieces  	 3-20

3-5      Knitted Mesh Specifications  .	3-30

3-6      Mesh Parameters	3-67

6-1      Nozzles Used in Spray Section	 6-7

7-1      Nozzles Used in Spray Section	7-2

7-2      Drop Size Analysis	7-5

7-3      Comparison of Baffle Type Entrainment
         Separators	7-21

7-4      Comparison of Tube Banks	„  . 7-48

7-5      Comparison of Wire Mesh Demister	7-65

7-6      Effect of Liquid Load on Reentrainment in
         Different Entrainment Separators 	 7-67

7-7      Observed Minimum Drop Size in the
         Reentrainment   	 7-69

7-8      Reentrainment Observed by Kotov  	 7-71

A-l      Overall Performance of Entrainment
         Separator	A-l

A-2      Drop Diameters of the Entrainment Entering
         and Leaving the Test Section	A-8

A-3      Liquid Material Balance  	 A-16

A-4      Pressure Drop Data	A-23
                               xvii

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XV111

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                      NOMENCLATURE

Latin
A    = fractional area of the entrained drops projected
       onto a plane
A    = total flow area, cm2
A'   = measured value of the fractional area of a plane
       occupied by the drops
a    = acceleration due to centrifugal force, cm/sec2
a1   = cross-sectional area of all the tubes in one row, cm2
a^   = height of entrance to cyclone, cm
a~   = specific area of mesh; surface area of wires per unit
       volume of mesh pad, cm2/cm3
a,   = constant of Equation (3-22)
a4   = defined after Equation (3-52), constant
a5   = defined in Equation (3-57), constant
a,   = defined after Equation (3-59), constant
B    = empirical constant for Equation (3-41)
b    = spacing between two consecutive baffles in the
       same row, cm
b'   = perpendicular distance between two consecutive baffles
       in the same row, cm
b.,   = width of entrance to cyclone, cm
b    = diameter of bottom part of cone, cm
 6
C    = wave velocity
C    = parameter reflecting the shape of the cyclone
C1   = Cunningham correction factor
C,   = drag coefficient
c    = number concentration, #/cm3
c    = initial number concentration, #/cm3
c, , c9 = constants, defined by  Equation (7-1)
 -L   Lt
                           XIX

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 d     = bubble  diameter,  cm
 d     = duct diameter,  cm
 d,    = blot diameter,  cm
 d/    = measured blot diameter,  cm
 d     = cyclone diameter, cm
 d>
 d     = packing diameter, cm
 cl
 dg    = diameter of exit  pipe of cyclone, cm
 d__   = equivalent (hydraulic) diameter of liquid film, cm
 eq
 d,    » sieve plate hole  diameter, cm
 d.    = diameter of jet,  cm
 d.    - size parameter, cm
 d     = knitted mesh wire diameter, cm
 d     = mass median drop  diameter, cm
 dn^   = number of drops removed
 d     = drop diameter,  cm
 d_a   = aerodynamic drop  diameter, cm (g/cm3) V2
 (d £/dz).  = frictional pressure gradient for liquid
       flowing alone in  a tube, dyne/cm3
 (d .p/dz)p = frictional pressure gradient for gas flowing
       alone in a tube, dyne/cm3
d     = inlet mass median drop diameter, cm
 r o
d     = Sauter mean diameter, cm
 j
d     = diameter of large drops, cm
 s, n,
d     = diameter of small drops, cm
E     = fractional collection efficiency of an entrainment
       separator
                        xx

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F    = packing factor
F,    = foam density, ratio of clear liquid height
       to total foam height
F    = correction factor = 1,1
f    = friction factor
fD   = drag coefficient

fg   = friction factor in the absence of liquid phase
f^   = fraction of the perforated open area in the plate
G    = mass flow rate of gas, Kg/m2sec
G^   = mass flow rate of liquid, Kg/m2sec
Gg   = mass flow rate of gas, Kg/m2sec
g    = acceleration of gravity, cm/sec2
H^   = fractional liquid hold-up in the bed
h    = overall cyclone height, cm
h,    = height of a jet, cm
h^   = dry-plate head loss
h    = head over the weir
h    = residual pressure drop
h    = height of vertical cylinder of cyclone, cm
h    = weir height
 W
j    = ratio of channel width to packing diameter
K    = inertial parameter
K    = Kutateladze number
K,    = constant
L    = mass flow rate of liquid, Kg/m2sec
Si    = length of baffle, cm
                           xxi

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fl^   = natural height of vortex in cyclone, cm
&2   = length of mesh pad in the direction of flow, cm
&_   = unbroken length of jet, cm
&4   = broken length of jet, cm
N    = number of blots in a given area if the blots do
       not overlap
N    = number of stages in the tube bank
N1   = number of blots in a given area
NR  „ = drop Reynolds number
Nne G = gas  Reynolds number
^Re L = liquid Reynolds number

n    = number of rows of baffles or tubes
n    = vortex exponent
n,   = number of semicircular bends in packed bed
n.   = collection efficiency for a given particle diameter
 •^     in one stage of rectangular jet impingement
P    = dimensionless parameter defined by Equation (5-15)
P    = pressure,  dyne/cm2
P    = pressure outside bubble, dyne/cm
                                       2
 ,    = pressure due to gas velocity,  dyne/cm2
Pt   = penetration
AP   = pressure drop, cm W.C.
APj   = pressure drop in absence of liquid, cm W.C.
APT  = pressure drop due to presence of liquid, cm W.C,
  L*
APwet " APdry + iPL
                        XXI1

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Q    = volumetric flow rate, cm3/sec
QL   = liquid flow rate due to gravity, cm3/sec
R    = entrainment parameter defined by Equation (3-41)
r    = radius, cm
S    = distance traveled by drop, cm
S,   = height of exit pipe inside cyclone, cm
T    = temperature, °K
t    = time
t,   = blot thickness, cm
u^   = cyclone inlet velocity, cm/sec
UG   = superficial gas velocity, based on empty duct, cm/sec
u^   = actual gas velocity, cm/sec
UQ   = mean gas velocity, cm/sec
UGC  = reentrai-nment velocity, critical gas velocity for
       reentrainment, cm/sec
ut   = terminal deposition velocity, cm/sec
u    = tangential velocity, cm/sec
v,   = velocity of gas through hole in sieve plate, cm/sec
vi   = actual gas velocity near the tubes
v    = relative velocity, cm/sec
W    = mass flow rate, g/sec
WLE  = mass flow rate of entrained liquid, g/sec
w    = baffle width
w^   = weir length, m
X    = Martinelli parameter defined by Equation  (3-40)
Y    = distance from baffle to any point  in the  liquid film, cm
Z    = bed length, cm
                           xxi 11

-------
Greek
a    = volumetric flow ratio
a    = initial surface disturbance, cm
a    = amplitude of surface disturbance of a jet, cm


-------
                       ABSTRACT

     Entrained drops of liquid must be separated from the
gas leaving scrubbers.  This report gives results of an
evaluation of present technology, experimental studies of
entrainment separator characteristics, and theoretical
analysis.  A pilot plant with 85 m3/min (3,000 CFM) maximum
capacity was built and experiments performed on zigzag
baffle, knitted mesh, tube bank, packed bed, and cyclone
devices.  Horizontal gas flow was used in all cases, and
the cyclone axis was vertical.
     Drop size distribution measurements on the inlet and
outlet enable the determination of collection efficiency
and reentrainment as related to drop size.  Pressure drop
as a function of gas flow rate is also reported.  Mathe-
matical models for primary collection efficiency are satis-
factory but useful reentrainment models are not yet available.
     An auxiliary experiment was made to determine reentrain-
ment from liquid sheets under the influence of an air stream.
Work is still in progress on vertical gas flow systems,
solid deposition, mathematical modeling, and the development
of improved designs.
                        xxv

-------
XXVI

-------
                               T-T
high.   Liquid drainage from the  entrainment separator is a
    ST  B8JB aDBjj:ns ofjToaas alia  aja^M. ^s.ioq.B.iBaas tfsaui aai
related problem.   Poor "drainage  will  contribute to increased
PUB paq ps^DBd ui uouimoo ST StJTpooTj
effects  of reentfainment and flooding.
{3uTUTB,ip  uiojcj pinbit s:j.uaA9.m MOIJ SB
    ' .Separators0als6 suffer from plugging and caking due to
 si AiTDOraA SBS  uo q.i:iuTi; jcaaan  UB aoj  asnBO j.9\{T.o §UQ
particle deposition and 'solute precipitation.  Slugging; and
          •A5iDo-[9A t{3Tq q.B uoi^f jiaao^Jioj  A^iBuod B&SuT%oauiT
caking  increase pressure drop'and corrosion rate.  The re-
the separator  this w.      ,      ,
  pus KouaioTjIa uoTjodnoo XjBuiijd jo  s}D9jja psutquioo
1001 efficiency


seSKttSSoefi|ictf

SCOPE 9xqBioaj;ddv   'uiaq.sXs j:aqqnjos ajt^ua  at|q. jo uoiq.Bjado
 n
                         sq.uBjnTlod piios 10 pinbiT  'snoasBS


                         ^tRS

        available unpublished
                           8f mmmm '
  SB PSSJCOl^JBdas q.uauiutBjau8 Jaqqnjtos
                             1-2

-------
C.  Determine and evaluate the adequacy of existing
    theoretical models and design methods for pre-
    dicting the performance of entrainment separators.
D.  Review and evaluate performance of all major
    types of entrainment separators currently avail-
    able.  Assess the advantages, disadvantages and
    limitations of each type of equipment.
E.  Identify specific operating and maintenance prob-
    lems associated with entrainment separators.
    Particular attention will be paid to the problems
    encountered in S09 scrubbing systems under develop-
                     w
    ment in E.P.A. programs.
Experimental Study
Conduct an experimental study of gas-water systems
aimed at simulating the performance of various types
of entrainment separators in the presence of soluble
and insoluble particulate matter.  The experimental
study will investigate such variables as efficiency,
pressure drop, reentrainment, velocity, plugging and
related problems.
Selection and Design
Develop improved engineering equations and methods for
entrainment separator selection and design.
Pilot Test
Develop and evaluate on a small pilot basis new en-
trainment separator designs which offer improved
performance, e.g., efficiency, pressure drop, velocity,
freedom from reentrainment, and freedom from plugging
and related problems, when compared with available
entrainment separator designs.
Recommendations
Develop specific research and development recommenda-
tions for improving wet scrubber entrainment separators
                        1-3

-------
1-4

-------
                  SUMMARY AND CONCLUSIONS

     This program of investigating wet scrubber entrain-
ment separators has been partially completed at this time.
The study indicates that presently available entrainment
separators suffer from various shortcomings such as over-
designs which necessitate large equipment size, lower
operating velocities due to flooding or reentrainment,
lack of reliable operating data on industrial separators,
and plugging.
     The objectives of this study are to  (1)  Evaluate
present technology,  (2)  Conduct an experimental study of
air-water systems aimed at simulating the performance of
various types of entrainment separators,  (3)  Develop
improved engineering equations and methods for entrainment
separator selection,  (4)  Develop and evaluate on a small
pilot basis new entrainment separator design, and  (5)  De-
velop specific research and development recommendations.
EVALUATE PRESENT TECHNOLOGY
     A literature search was carried out to evaluate the
technology on wet scrubber entrainment separators.  Visits
were made to several libraries,and the literature available
in the A.P.T. library and identified by an APTIC computer
search was reviewed.  Manufacturers of entrainment separators
were contacted by mail and asked for information.  Visits
were made to E.P.A. and T.V.A. facilities to identify the
specific operating and maintenance problems associated with
entrainment separators.
     The existing theoretical and empirical models to predict
the performance of the entrainment separators were evaluated.
The criteria for this evaluation were soundness of derivation
and closeness of comparison with actual performance.
                            2-1

-------
Experimental Study
     A pilot plant to study wet scrubber entrainment sepa-
rators was built.  It has a gas flow capacity of 85 m3/min
(3,000 CFM) and it consists of prefilter, blower, heater,
spray section, observation sections, test section, various
supply and catch tanks, and auxiliary equipment.  Five
types of entrainment separators, namely, mesh,  tube bank,
packed bed, cyclone,and baffles were studied.  Up to now,
air-water systems with cross flow have been used in the
experiments.  Observations include collection efficiency,
pressure drop, reentrainment, flooding, drainage, drop
size distribution and other variables.
Selectj^on _and Design
     Attempts are made to develop mathematical models where
needed.  Models for determining the following were developed
in the present study:
     1.  Primary collection efficiency in zigzag baffle
         type entrainment separators.
     2.  Pressure drop in zigzag baffle type separators.
     3.  Primary collection based on either complete
         turbulent mixing or no mixing.
     4.  Reentrainment in vertical zigzag baffles.
     5.  Reentrainment in horizontal zigzag baffles.
     6.  Reentrainment in a cyclone.
Auxiliary Experiment
     Equipment was constructed and experiments were conducted
to determine  (1)  Onset of entrainment velocities in sepa-
rated flow,  (2)  Drop size distribution of entrainment,
(3)  Effect of duct dimension, and  (4)  Effect of air jets
impinging on liquid film at various angles.
                           2-2

-------
CONCLUSIONS
         The theoretical model developed to determine
         primary collection efficiency for zigzag baffle
         type separator agrees fairly well with experi-
         mental results.  Thus, the flow through the
         zigzag baffles can be described as a series of
         alternating bends with inertial mechanism
         responsible for separation.
         The pressure drop in zigzag baffles can be
         determined from drag coefficients for inclined
         plates held in the flow.
         The overall collection efficiency in zigzag
         baffles can be increased by staggering the
         baffles.  The pressure drop may be reduced by
         keeping 1-3 cm distance between rows.
         Models based on turbulent mixing reach 100%
         efficiency as an asymtote with increasing gas
         velocity.  On the other hand, models based on
         no mixing reach 1001 efficiency as a straight
         line on efficiency-versus-gas-velocity curve.
         The assumption of turbulent mixing gives better
         agreement with actual performance of entrainment
         separators .
         It is possible to predict the drop collection
         efficiency of entrainment separators at low gas
         velocities (under industrially used conditions),
         at least on pilot plant scale, from the available
         literature.
         At high gas velocities, reentrainment is a defi-
         nite problem.  Reentrainment may take place by
         various mechanisms such as:  a)  Transition from
         separated flow to separated-entrained flow,
                           2-3

-------
      b)   Rupture  of  bubbles,   c)   Creeping  of  liquid
      on  the  entrainment  separator  surface,  and
      d)   Shattering  of liquid  drops  resulting  from
      splashing.
  7.   Transition from separated flow  to  separated-
      entrained flow  depends upon gas velocity,  liquid
      Reynolds number and liquid properties.  The tran-
      sition  does  not depend upon the duct dimensions.
      The  drop size distribution is independent  of the
      duct dimensions.  The average drop diameter re-
      sulting from this transition  is about  250  urn.
      The  reentrainment velocity is considerably
      reduced if jets  of  air stream strike the  liquid
      film at an angle.   Therefore, sharp angles should
      be reduced to avoid  reentrainment.
  8.   The mechanism of reentrainment in zigzag baffles
      is tearing of the liquid  sheets caused by high gas
      velocities and  shattering  of liquid drops.  Reen-
      trainment in cross flow baffles with horizontal
      gas flow should  be less than in baffles with verti-
      cal gas flow.   Zigzag baffles inclined at 30° from
      gas flow direction should  have less reentrainment
      than baffles inclined at  45° from gas flow direc-
      tion.
 9.  The reentrainment mechanisms in packed bed and mesh
     pad are shattering of drops and rupture of bubbles.
     Reentrainment resulting from small drops  (less than
     40 ym)  due to rupture of bubbles is insignificant.
10.  The mass median drop diameter due to reentrainment
     was determined to vary between 80 ym and 750 ym.
     Large drops   (above 200 ym) are present due to
     shattering of drops.
                       2-4

-------
11.  Sampling of liquid drops and entrainment needs
     careful consideration,  Due to large drop size
     in the reentrainment,  a sedimentation effect is
     present.
12.  Drainage arrangements  should be designed with
     caution.  An underdesign will lead to liquid
     creeping in the separator and an overdesign may
     result in reentrainment, from drainage,  due to
     gas flow.
13.  The capital cost and the operating cost  of en-
     trainment separators in wet scrubbers represent
     a significant factor and therefore entrainment
     separators should be given more design attention.
14.  The experience with wet scrubbers in power plants
     indicates that performance of the entrainment
     separator is crucial to the whole operation of
     the scrubber.
                      2-5

-------
2-6

-------
                    LITERATURE SURVEY

     The literature survey and background information
discussed in this chapter are examples of the selected
material on entrainment separators.  For brevity, all
the literature in the field of separators is not men-
tioned.  The following material summarizes what can be
distilled from a survey of the background information
and is a concept of what was known at the onset of this
study.
     Figure 3-1 describes the entrainment separator.  To
determine the performance of the separator, one needs to
know inlet loading (concentration and drop diameter),
primary collection efficiency, reentrainment, secondary
collection, liquid drainage and pressure drop.  These
factors may be considered from a design point of view.
The inlet loading coupled with operating conditions will
determine reentrainment and drainage.  Also, different
entrainment separators are limited to certain drop dia-
meters, below which their efficiency falls off sharply.
It is necessary to have engineering equations to determine
primary collection efficiency and pressure drop.
     If the reentrainment rate and the size distribution of
the reentrained drops are known, secondary collection may
be determined.  At the time of this study, no work had been
reported on the rate of reentrainment.  All one can deter-
mine at this point is the range of gas velocities at which
onset of reentrainment takes place.  The size distribution
of the reentrained drops may be guessed by assuming the most
probable mechanism of reentrainment for a given separator.
     Knowledge of the pressure drop through a system is
important in calculating the energy loss incurred and in
selecting the proper pumps and other auxiliary equipment
to overcome that energy loss.
                           3-1

-------
              Inlet  Loading
              Concentration   —
              and  Drop  Diameter
Primary
Collection
Efficiency
to
Reentrain-
ment and
Secondary
Collection
   Outlet loading
•* Concentration
   and Drop Diameter
                                         Liquid Drainage
                                Figure 3-1.   Entrainment separator

-------
     Information which has been obtained from the litera-
ture survey is presented in Tables 3-1 and 3-2.  A summary
of the literature search, dealing with primary collection
efficiency, pressure drop, reentrainment, entrainment
separator problems and details of separators now in use,
follows.

COLLECTION MECHANISMS
     Knowledge of the basic mechanisms of drop collection
is fundamental to an understanding of entrainment separa-
tors.  Some of these mechanisms are inertial impaction,
interception, sedimentation, diffusion and electrostatic
precipitation.  Normal industrial operating conditions for
wet scrubbers are such that exiting drop diameters are
larger than 50 ym.  The design and operating conditions of
separators thus favor inertial impaction and sedimentation
as the principal mechanisms of collection.
Iner t i al Imp ac t ion
     This  is the major drop collection mechanism in wet
scrubber entrainment separators.  When fluid approaches
an obstacle the fluid streamlines spread around it.  At
the same time inertial forces carry drops across the stream-
lines so that the drops hit and stick to the obstacle.  It
is assumed that all drops colliding with the obstacle  adhere
to it.
     Two factors determine impaction collection efficiency.
The first  is the velocity distribution of the  gas flowing
by the  collector, which varies with the Reynolds number of
the gas with respect to the collector.  The second factor
is the  drop trajectory, which depends on the mass of the
drop, its  air resistance, the size and shape of the collec-
tor, and the rate of flow of  the  gas stream.
                             3-3

-------
    Table 3-1.  SUMMARY OF AVAILABLE INFORMATION ON ENTRAINMENT SEPARATORS

Cyclone
Mesh type
Separator
Tube
Bundle
Packed
Beds
Sieve
Plates
Baffles
Mechani-
cally
Aided
Impingement
Type
Typical Inlet Loading
Concen-
tration
<2£/m3
<2.7xlO-2
cm3/sec
cm2 of
liquid
"
*<'

— —


Drop
Diameter
>5ym
> y

>3ym

>20ym

>3ym
'•
Primary
Collection
Efficiency
/
/
/
/
/
X
X
/
Pressure
Drop
/
/
/
/
/
X
X
/
Approx.
Velocity
for Reen-
trainment
15-50m/sec
5-15m/sec
< 20m/sec
1-1 . Sm/sec
=3m/sec
•*• *^ Ani/cor*
•J • till/ o cC

30-45m/sec
Reen-
trainment
Drop
Diameter
70-400ym
100-500ym

100-500ym
small drops
^SOym
large drops
-0 . 1cm
100-500ym


  Design information available in literature
X Design information not avialable in literature

-------
                  Table 3-2. SUMMARY OF CONVENTIONAL ENTRAINMENT SEPARATORS
Entrainment
Separator
(Construction
Material)
Cyclone
(Steel, S.S.)
Mesh
(Any material
that can be
drawn into
wire)




Fiber Bed
(Needs fibers
l-10ym)
Packed Bed
(Packing of
any mat'l)

Baffles
(Any mat '!)
^
Max imum
Capacity
m3/sec
141






65


Minimum
Drop
Size
5ym (2ym
for small
cyclones
Sum (1-
5pm for
series
combina-
tion)




0.3ym
3pm

lOym
Gas
Velocities
m/sec
Maximum
15-20
0.3-5




0.025-0.15
0.75-2.5

2-3.5
».
Separation
Efficiency
for Minimum
Drop
95%
951




99%
85%

85-95%
Pressure
Drop
cm W.C.
5-15
0.5-3




10-15
5-10%
of bed
length

2-2.5
Liquid
Load
Maximum

2.5 x
io-3
g/sec-
cm2





From
gener-
alized
corre-
lation
5% of
gas flow
rate by
weight
Comments
Surfaces may
erode easily
Basically 3
different
mesh
1. Crimped in
alternate
direction.
2. Nested
double
layer.
3 . Wound .
(Can plug
easily)
Can plug
easily
Better
drainage in
cross flow

Vertical
baffles
give better
drainage
than horiz.
04
I
in

-------
     The equations of motion,  the size and shape of the
collector, the mass of the drop and operating conditions
may be used to determine target collection efficiency.
Figure 3-2, from Golovin and Putnam (1962), gives theo-
retical impaction efficiency as a function of the inertial
parameter for different targets.
Sedimentation
     The second collection mechanism important in entrain-
ment separators is sedimentation.  Figure 3-3, from Fuchs
(1964), is a plot of drop terminal settling velocity versus
drop radius.  Drop diameters encountered in wet scrubber
entrainment may vary from 50 to 500 ym, and the terminal
settling velocity for these drops will therefore range from
0.1 to 2.0 m/sec.  The gas velocities used in entrainment
separators vary from 1.0 to 12.0 m/sec; however, except for
cyclone-type separators, which operate at very high veloci-
ties, most operate below 4.0 to 5.0 m/sec.  Therefore, sedi-
mentation can be expected to affect the separation of drops.

ENTRAINMENT DROP DIAMETERS
     To determine primary collection efficiency, it is
necessary to know the inlet entrainment drop diameter, which
depends on the entrainment source.  The drop diameter may be
obtained by direct measurement or by the following method
if, as is often the case in wet scrubbers, entrainment is
cuased by pneumatic atomization.  A correlation presented by
Nukiyama (1938, 1940) gives Sauter mean diameter as:
                         o.s       „ *«
         A  - 58,600 /  a \      ,q? PL    /, nno ^
-------
 U
 U
 W
1.0


0.8


0.6


0.4



0.2
                   	Rtclangular half body
                   	(ribbon with waltt)
                                                   Cylinder
           -	I Ribbon normal
             	"" I to
                    . flow
                                                Ellipsoid of
                                               revolution 101
                                                  thick
                                                  Ellipiold
                                                   " revolu-
                                                   vi>,20»
                                                   ick.
N'ACA 65A004 at
lero ancle o{
attack A\ thick
                                              low-drag symmet-
                                              rical airfoil
                                         Joukowskl IS! thick sym-
                                         metrical airfoil a: terq
                                         angle of attack
          0.1         1            10
                 INERTIAL  PARAMETER,  K  =
                                          100
                                                          "
Figure  3-2  -  Theoretical  impaction  efficiency  as
                 a function  of  inertial  parameter
                 for  different  targets.
                 Golovin  § Putnam  (1962)
                                3-7

-------
   1,000
                                        T-T 100
U
<
                                     W
                                              ex,
                                              o
                                              tat
                                              o
                                1000    3000


                   DROP RADIUS, ym
 Figure 3-3 - Terminal  settling velocity and

            Reynolds  number for water drops

            in air at 20°C and 760 mm Hg.

            After Fuchs (1964)
                      3-8

-------
where   d    = Sauter mean diameter, cm
        v    = relative velocity, cm/sec
        a    = surface tension, dyne/cm
        p,   = liquid density, g/cm3
        UL   = liquid viscosity, poise
      QL/QG  = liquid to gas volumetric ratio

     In wet scrubbers the liquid load, QL/Qg» varies between
1.33x10-" m3/m3 and 4xlO'3 m3/m3 (1-30 gal/1,000 CFM).  Gas
velocities are on the order of 60-100 m/sec  (200-300 ft/sec).
The drop  diameters obtained under these operating conditions
are between 50 urn and 500 ym.
     If the liquid entrainment is formed in  any other manner,
the entrainment drop diameter may be obtained as explained
later in  this chapter in the section for the appropriate
reentrainment mechanism.

DESIGN EQUATIONS FOR ENTRAINMENT SEPARATORS
     Our  examination of collection mechanisms yielded the
basis upon which equations for primary collection effi-
ciency have been developed.  Methods for determining en-
trainment drop diameter, a key variable in the calculation
of primary efficiency, were also reviewed.
     Another important factor  in the design  of entrainment
separators is the pressure drop.  A knowledge of the pres-
sure drop through a separator  is useful for  the selection
of auxiliary equipment such as blowers and for calculating
the separator's operating costs.
     Six  different kinds of entrainment separators will be
discussed in this section:  cyclone, packed  bed, zigzag
baffles,  tube bank, mesh and  sieve plate.  A brief descrip-
tion of each is given, after  which, equations for primary
efficiency and pressure drop  are presented.  These equations
                           3-9

-------
were selected  as  the best  available  expressions, based  on
agreement with experimental  data  and soundness  of deriva-
tion.  Calvert et  al.  (1972) have  evaluated  some of  these
equations.
     The following  assumptions  are generally made in the
derivation of  the primary  collection efficiency equations:
     1.  A drop is  spherical in shape.
     2.  The motion of a drop is not influenced by the
         presence of neighboring drops.
     3.  All drops  striking  the collector surface adhere.
Cyclone
     Commercially available  cyclones  in standard designs
for entrainment separators have a maximum capacity of up
to 141 m3/sec  (300,000 CFM)  of  gas.   Efficiencies of about
951 are claimed for 5 ym diameter drops in a well-designed
cyclone.  Some manufacturers use a bundle of small cyclones
(multicyclones), which can efficiently collect  drops as
small as 2 ym  in diameter.  However,  this arrangement re-
duces the capacity  of the device.
Primary Efficiency  - Leith and  Licht  (1971)  derived an
equation to predict primary  collection efficiency in conical
bottom cyclones as  pictured  in  Figure 3-4.   With slight modi-
fication it can be  applied to cylindrical cyclones.   The
following assumptions were made:
     1.  The drag force in the  radial direction on the drop
         is given by Stokes law.
     2.  The tangential velocity component of the drop is
         related to the radial  position by a modified form
         of the equation for a  free vortex in an ideal fluid
                             ut rn = constant          (3-2)
                             3-10

-------
Figure 3-4.  - Cyclone with tangential gas inlet.
                     3-11

-------
     3.
where "r" is the distance  from  the  vertical  axis
of the cyclone and "n"  is  defined below in
equation (3-5).
Backmixing of  the drops takes place in  the gas  phase.
     The primary efficiency for  a  conical  bottom cyclone is
expressed as:
        E = 1 - exp
                              f"
                              2  (CV
                                         (3-3)
          TT  d
     C  =
2(1 -
                       1 +
                             h
                                      Sl - V
                                                 - s.
                                         (3-4)
                         0.3
                        (0.393  d  )
                           2.5
                                                         (3-5)
                      S! * *i - hs
                         h - h
                                                         (3-6)
 H,  =  2.3 d  ,
  1         e \an
                             1/
                    1/3
                                                         (3-7)
             = K
                  n+1
                              (n + 1)
                                         (3-8)
                              3-12

-------
where   E   = fractional collection efficiency of an
              entrainment separator
        C   = parameter reflecting the shape of the cyclone
        H!   = size or operating characteristic
        n   = vortex component
        d   = cyclone diameter, cm
        a-j^  = height of the entrance to the cyclone, cm
        b,  - width of the entrance to the cyclone, cm
        d   = gas exit pipe diameter in cyclone, cm
        S,  = height of the exit pipe inside the cyclone, cm
        £,  = natural height of vortex in cyclone, cm
        h   = height of vertical cylinder of cyclone, cm
         j
        d.  = size parameter, cm
        T   = temperature, °K
        b   = diameter of bottom part of cone, cm
         e                       f
        h   = overall cyclone height, cm
        K   = inertial parameter
        a   = drop density, g/cm3
        d   = drop diameter, cm
        u   = tangential velocity, cm/sec
        yfi  = gas viscosity, poise

Pressure Drop - Because cyclones are operated  at higher gas
velocities  than other entrainment separators,  the pressure
drop  in a cyclone is usually higher than in other devices.
Cyclones  are sometimes equipped with inlet vanes, which
serve  to  introduce the gas stream to the cyclone more
smoothly.   The pressure drop in a device with  an inlet
vane  is expected  to be lower than in one without.   Shepherd
and  Lapple  (1940) derived  an equation for  a cyclone with
inlet  vanes for pressure drop  as a function of inlet  gas
velocity  and the  cyclone inlet  and outlet  dimensions:
                            3-13

-------
            AP = 0.00513 pG

where   PG = gas density, g/cm3

     Equation (3-9) can be modified by writing it as a
function of the geometric average of the gas velocity at
the cyclone inlet and outlet:

            AP = 0.00513 x 5.89 p  v                 (3-10)
     Shepherd and Lapple also developed an equation for a
cyclone without inlet vanes:

                            / Q  \2/16 a,b \
            AP = 0.00513 p    
-------
Primary Efficiency - Jackson and Calvert (1966)  and Calvert
(1968) have developed a theoretical relationship between
particle collection efficiency and packed bed operating
parameters by considering the bed to be made of  a series
of semicircular channels.  Their formulation included  the
following assumptions:
     1.  The drag force on the drop is  given by  Stokes Law.
     2.  The number of semicircular bends, "n,", is related
         to the overall height, "Z", of the packed section
         of the bed, the packing diameter, "d ", and the
         channel width, "b,", when any  consistent units
         may be used, by:

                          ni • 3-ri-               CJ-12)
     These  assumptions led to the following equation for
 predicting  the primary efficiency for a packed bed
     E =  1  ' ""Hd + j*' (. . Hd)  ajY  KP1       <3-13'

     i *  7T-                                         (3-14)
    KP • r

where   j   = ratio of channel width to packing diameter
            = bed porosity
        Hd  = fractional liquid hold-up in the bed
        Z   = bed length, cm
        ^cl = Packi-ng diameter, cm
        UG  = superficial gas velocity, cm/sec
        dpa = aerodynamic drop diameter, cm(g/cm3)^2
                           3-15

-------
Pressure Drop - Perry  (1963) gives a generalized pressure
drop and flooding correlation plot which appears as Fig-
ure 3-5, where a dimensional group of function 	 ,
                                                pGpLg
(centipoise)02, is plotted against a dimensionless group

of function i- (-—•)   , where "G" and "L" refer to the gas

and liquid mass flow rates respectively.  Values for the
packing factor, "F", for dumped pieces, stacked pieces and
grids are given in Tables 3-3 and 3-4.  If "F" is not known,
— may be used instead.
e3
     The operation of packed beds is limited by flooding.
The flooding lines for dumped pieces, grids and stacked
rings are shown in Figure 3-5.  Pressure drop should be
obtained by using the largest gas and liquid streams.
Zigzag Baffles
     Baffles can efficiently separate drops greater than
10 ym in diameter, while some of the better designed
devices can separate drop diameters of 5-8 ym.  Common gas
velocities are 2.0-3.5 m/sec, and the pressure drop for a
6-pass separator is about 2-2.5 cm W.C,
     The most common baffle shape is zigzag with 3 or 6
passes.  These can be fabricated from a continuous wavy
plate or each pass is separated, in which case the separa-
tion distance is normally smaller than the width of the
baffles.  Cross-flow baffles are claimed to have higher
drainage capacity than countercurrent flow baffles.
Primary Efficiency - A theoretical equation to predict
primary collection efficiency in zigzag baffles is not
available.  However, Sarokin, Demidova and Kuzman (1968)
give the condition for minimum entrainment in the exit
stream:
                            3-16

-------
 Ci,
  •
 U
ft,
       0.5
       0.2
       0.1
      0.05
      0.02
      0.01
     0.005
     0.002
     0.001
         0.01
    FLOODING
      LINES
             Pressure cbrop
              meters ot
/Pressure  Drop,
[inches  H20  per]
xft.  of  packing/
              H20 per
              meter of
              packing
                               (dimensionless)
          Figure  3-5  -  Generalized flooding and pressure drop
                       correlation for packed beds (Perry, 1963)
                               3-17

-------
00
Raschig rings,
  ceramic
   .16 cm wall
   .32 cm wall
   .63 cm wall
   .95 cm wall

Raschig rings,
  carbon
   .16 cm wall
   .32 cm wall
   .63 cm wall
   .79 cm wall

Raschig rings,
  metal
   .08 cm wall
   .16 cm wall

Lessing rings,
  porcelain
   .32 cm wall
   .63 cm wall

Lessing rings,
  metal
   .08 cm wall
   .16 cm wall
                          Table 3-3.   PACKING  FACTORS,  "F",  FOR DUMPED PIECES (m2/m3)

                          	Nominal  size of packing, cm 	

                           [0.64]  [0.95]  [1.27]  [1.59]  [1.9]  .[2.5] [3.2] [3.8]  [5]   [8]  [10]
                           5,250   3,280
                                                              510
                                                                          430   210
                                                                                     121   98
                           5,250
1,340
                                                        920   525
                                                                          430   210
                                                                                     118
                           2,300   1,280     980    560     510   380
                                         1,340    950     720   450   360   272   187  105
                                                             (800)
                                                                               (360)
                                        (1,060)
              (630)
                                                             (472)  (387)  (295) (200)

-------
            Table 3-3.  PACKING FACTORS, "F", FOR DUMPED PIECES (m2/ni3) (continued)

                                Nominal size of packing , cm

                  [0.64] [0.95] [1.27] [1.59] [1.9] [2.5] [3.2] [3.8]  [5]  fs]  [10]
Partition  rings                                                             262  190

Pall  rings,                             318           171          105    82
  plastic

Pall  rings,                             230           158           92    66
  metal


Berl  saddles     2,950          790            560    360          213   148

Intalox saddles, 2,380  1,080   660            475    322          171   131   72
  ceramic

Intalox saddles,                                     108                 69   52
  plastic

Super-Intalox,                                       200                100
  ceramic

Pellerettes                                                            150
Parentheses denote a value of a/e3, rather than empirical F.

-------
  Table 3-4.  PACKING FACTORS,"?"  FOR  GRIDS AND  STACKED  PIECES
              (m2/m3)
                        Nominal  size  of packing,  cm

Wood grid
Metal grid
Grid tiles
2.5
20
8.2

3.8
11


5
8.2


8 10
5.9 4.9


13


118
14 15



Checker brick,
  e=0.55                                                  135
Raschig rings,
  ceramic
   .63 cm wall                95        16
   .95 cm wall                          36      12.8
Raschig rings,                          21
  metal
Partition rings,
  diameter
   7.6 cm length                     (1,200)    (725)
   10.2 cm length                              (705)             (410)
   15.2 cm length                                               (375)
Partition rings,
  square set
   7.6 cm length                      (690)    (460)
   10.2 cm length                              (450)             (275)
   15.2 cm length                            .                   (260)
Parentheses denote a value of a/e3, rather than empirical F.
                                 3-20

-------
          0.35 < k = 10 yr(	]  < 0.40      (3-16)
where   k = Kutateladze number

     This equation was confirmed with experimental data by
the authors.
Pressure Drop - No equation for the pressure drop in the
zigzag baffle type entrainment separator is available.
Mathematical models for predicting primary efficiency and
pressure drop in this device will be presented in the next
chapter.
Tube Bank
     Although tube banks have not been used in entrainment
separators, equations predicting primary efficiency and
pressure drop have been developed and are presented below.
Primary Efficiency - Calvert and Lundgren (1970) found
that the collection efficiency for closely packed rods is
given by the equation for rectangular jet impaction.  The
collection efficiency of each stage of impaction can be
found in Figure 3-6.  Each row of tubes except the first
represents one stage of impaction.  "B" is used as a para-
meter in Figure 3-6 and is defined by:

                       3 = 2 H/b                     (3-17)

where   b = jet orifice width
        H - distance between orifice and impingement plane
"K ", the inertia parameter, is defined with drop radius,
"r ", rather than diameter as in Figure 3-2.
     Efficiency for the bank of tubes is given by:

                   E = 1 - (1 - n.)N                  (3-18)
                           3-21

-------
1.0
                                                Chow
                                                Exp.  •
                                           s  Theory
 0
    Figure  3-6 - Theoretical and experimental
                collection efficiencies of
                rectangular aerosol jets.
                      3-22

-------
where   n. = collection efficiency for a given particle
             diameter in one stage of rectangular jet
             impingement
        N  = number of stages in the tube bank
     If the tubes are widely spaced, the target efficiency,
"n", can be calculated from Figure 3-2.  In this case the
efficiency for the entire tube bank is:

             B - i - (i - n ^-)n                    (3-19)

where   a1 = cross-sectional area of all the tubes in one
             row
        A  = total flow area
        n  = number of rows

Pressure Drop - a properly designed tube bank is claimed to
offer low pressure drop.  Radford and Houghton (1940) found
a lower pressure drop in tests using a bank of tubes than
in using zigzag baffles or knitted mesh.  Moyers (1960) ex-
pressed the pressure drop per row as:
             AP = 4.95 x 10"spGuG2'19                 (3-20)
Mesh
     Knitted mesh of varying density and voidage  is widely
used for entrainment separators.  There are basically  three
different kinds of mesh:   (1)  Layers with crimp  in the
same direction - each  layer is actually a nested  double
layer.   (2)  Layers with crimp in alternate directions -
this results in an increase in voidage, reduced sheltering,
a decrease  in pressure  drop per unit length and an  increase
in  target efficiency per layer   (3)  Spirally wound layers  -
the pressure drop  is lower by about  2/3 than  in layers with
crimp  in the same  direction, but  the creeping of  fluids,  which
contributes to reentrainment, is  expected to be higher.
                           3-23

-------
      Standard mesh  10-15  cm  thick having  a density of about
 0.15  g/cm3  is used  to  remove  drops  larger than  5 ym  in dia-
 meter.  Gas velocities  range  from 0.3 to  5 m/sec and liquid
 flow  rate is limited by the  drainage capacity of the mesh
 to  2.5 x 10"3 g/sec cm2 of mesh.  A lower density mesh made
 of  standard wires is used when 10-20% higher flow rates are
 desired.
      Often  two mesh type  separators in series are used to
 remove drops in the 1-5 ym diameter range.  The first mesh,
 normally made of fine wires,  coalesces the small drops, and
 the second mesh, made of  standard wires,  removes them.  The
 first mesh  is operated  beyond the flooding velocity and the
 second under flooding velocity.  A  major  disadvantage with
 this  arrangement is a pressure drop which may reach 25 cm
 W.C.
      Some manufacturers use two or  three  stages of mesh, the
 first being coarser and the final being finer, to remove
 large and small drops successively.
     A mesh type separator has the  advantage that it can be
 made  to fit vessels of  any shape.  Any material which can be
 drawn into the shape of a wire can be used for fabrication.
 However, mesh separators  are  limited in application because
 they plug easily.   This can be avoided by upstream washing,
which will decrease removal efficiency and increase pressure
 drop.
 Primary Efficiency  - Bradie and Dickson (1969) present the
 following expression for primary efficiency in mesh separa-
 tors :
                   E =  1  - exp (-| TT a2H2 n)           (3-21)

where   a^ = specific area of mesh; surface area of wires
             per unit volume  of mesh pad, cm2/cm3
        &2 = length of mesh pad in the direction of flow, cm
        r\  <= collection efficiency of cylinder wire
                           3-24

-------
     The collection efficiency of cylindrical wire "n" can
be obtained from Figure 3-2.  The factor of 2/3 in the ex-
ponential was introduced by Carpenter and Othmer (1955) to
correct for the fact that all the wires in the knitted mesh
are not perpendicular to the flow.  That factor is the ratio
of the projected area of wires perpendicular to the flow to
the cross-sectional area of wires along the wire length.
     The maximum allowable gas velocity in the knitted mesh
is calculated from the equation of Souders and Brown  (1934):

                               /Pi - PG\V2
              ur mav = 30.5 a^ ( Ji-	£)              (3-22)
               G,max         3 \   pg    /

where "a," varies with operating  conditions and mesh  design.
For most cases,  a_ = 0.35.
Pressure Drop - The additional pressure drop due to the
liquid load may exceed the pressure drop in a dry knitted
mesh.  York and Poppele  (1963) have suggested that the
total pressure drop in the knitted mesh is the sum of the
pressure drop in the dry knitted  mesh and the pressure drop
due to the presence of liquid:

                   AP =  APdry + APL                   (3-23)

where   AP,   = pressure drop in  absence of liquid, cm W.C.
        APr   = pressure drop due to presence of liquid,
                cm W.C.
    "AP,  " can be obtained from  an "f"  (friction factor)
versus "NR  p"  (gas Reynolds number) correlation presented
in Figure 3-7.  Carman  (1937) developed the correlation  to
determine the pressure drop in solid granular materials  as
a dotted line on the plot.  A similar curve  is presented
for wire mesh by Stasangee  (1948) and Shuring  (1946).  York
and Poppele  obtained the data for knitted mesh both with
                           3-25

-------
oS
ii
   5.0
   2.0
     .0
03  0.5
a.
   0.2 h

   0.1
       10
                	r-	1	
                 Satsangee  data  (1948)
                 and  Shuring  data  (1946)
                 •Carman correlation for
                 solid granular materials
                                Crimp directioa
                                 alternated
                Crimps in
                same direction
                                 _L
                   100
                N
                 Re,G
1,000
                           UG/a2
10,000
     Figure 3-7 - Friction factor, f, versus Reynolds
                  number, NRg, for wire mesh entrain-
                  ment separator without entrainment
                  load.
                       3-26

-------
the crimps alternated and in the same direction.  Their
curves are plotted in Figure 3-7 and should be used in
determining pressure drop.  If the specific area, "a2",
is not specified, it can be determined from the mesh
porosity, "e", and the knitted mesh wire diameter, "dm":
                      4 ,-,   _s j
                                 m
                                                    (3-24)
     Pressure drop data due to presence of liquid are not
available for all operating conditions or for mesh of dif-
ferent styles.  Values of "AP/1 obtained by York and Poppele
are presented in Figures 3-8 and 3-9, with liquid velocity
as the parameter.  The specifications of the knitted mesh
used in the two figures are shown in Table 3-5.
Sieve Plates
Primary Efficiency - Taheri and Calvert (1968) derived an
equation for sieve plate primary collection efficiency:
                    1 - exp (-40 F* K )
where   0.30 < F.^ < 0.65
                    P " 9
                                                    (3-25)

                                                    (3-26)

                                                    (3-27)
where
        F, -

        Vi =
        d, =
             foam density, ratio of clear  liquid height  to
             total foam height
             velocity of  gas through hole,  cm/sec
             hole diameter, cm
Pressure Drop  -  Perry  (1963) has  suggested  that  the  pressure
drop  in sieve  plates can  be  calculated  according to:
                 AP  =  hw  +  how  +  hdp  +  hr
                                                    (3-28)
                             3-27

-------
               10
              1.0
              0.1
            0.01
                           i—i   i
                              liquid
                                  velocity
                   I   i L  I   I  I
                 3  456  7  8  9 10 11 12 13

                    UG[PG/(PL"PG}]  >  cm/sec
Figure 3-8 -
Pressure drop due to presence  of
liquid in the knitted mesh  with
the crimps in the same direction
                        3-28

-------
          u
          6
          o
               10,
                 z r  i  i   i   i  I   I   i   i  E
              i.o.
              0.
             0.01
                   I  I   I  I   I
I   I
                              I
   34  5  67  8 9 10 11 12 13


                       '
                     ucf PG/(PL'PG}]  '  •  cm/sec
Figure 3-9 -
Pressure drop due to presence of     i
liquid in the knitted mesh with
the crimps in the alternate direction
                         3-29

-------
Table 3-5. KNITTED MESH  SPECIFICATIONS

Direction of
crimps
e
a, cm2 /cm3
wire diameter,
d , cm
c*
Figure 3-8
same
0.977
3.61
0.028
Figure 3-9
alternate
0.99
1.51
0.028
                 3-30

-------
where   h  = weir height = 4-9 cm, assume 5 cm,         (3-29)
             if unknown                     0
        hQW = head over the weir • 0.143 FW ~          (3-30)

                                     i  Pr vv,
        hdp = dry Plate head loss =       T^            (3-31)
                                    C   Jj  ^
        h_  = residual pressure drop = 0.013  water     (3-32)
         r                                     PL
        -~  = 1.14 [0.4 (1.25 - fh) + (1 - fh)2]        (3-33)
        w

where   FW  = column wall curvature correction factor = 1.1
        QL  = liquid flow rate, here in m3/hr
        w^  = weir length, m
        f^  = fraction of the perforated open area in the
              plate

REENTRAINMENT
     As a result of the design equations presented in the
previous section, one is able to determine the primary col-
lection efficiency for five types of entrainment separators.
However, the overall separator efficiency is found to be
less than the primary efficiency because of reentrainment.
Increasing overall efficiency means reducing reentrainment,
the achievement of which requires a knowledge of the para-
meters important in determining the extent of reentrainment.
Thus, engineering equations describing this process are
vital to improved efficiency.
     One mechanism of reentrainment results from high gas
velocity.  In order to avoid this hazard, entrainment
separators are operated at lower gas velocities, resulting
in the large size and high cost of this equipment.
                          3-31

-------
     Another source of difficulty is that the theory of two-
phase flow, which can serve as the basis for developing the
desired equations, is itself not well developed.
     Due to the complexity of the subject and the necessity
of starting from the basics of two-phase flow, the following
material provides a lengthy but useful base from which
equations predicting reentrainment might be developed.
     Reentrainment from an entrainment separator may  take
place by any one or more of the following mechanisms:
     1.  Transition from separated to separated-entrained
         flow caused by high gas velocity.
     2.  Rupture of bubbles at the gas liquid interface
         and subsequent drop formation.
     3.  Creeping of the liquid along the solid surface
         and movement into the gas exit in the entrainment
         separator.
     4.  Shattering of liquid drops due to impaction.
The last three mechanisms of reentrainment depend upon the
design of entrainment separators.  The first mechanism
represents the upper limit of the operation of entrainment
separators.
Transition from Separated to Separated-Entrained Flow
     Reentrainment may occur at high gas velocities due to
transition from separated to separated-entrained flow.  In
simple geometries such as straight tubes, the transition
takes place at much higher velocities than those at which
entrainment separators are operated.  Yet reentrainment is
observed in separators at the lower velocity.  This is
caused by such phenomena as the impingement of the gas
stream onto the liquid at an angle and the presence of gas
jets.  Also the flow pattern in the entrainment separator
is not so uniform as in circular tubes.   However, due to
                             3-32

-------
the limited information available, we must consider two-
phase flow in a simple geometry such as the circular tube.
     In the operation of entrainment separators, flows may
be horizontal, vertically upward or downward, or inclined.
The onset of reentrainment depends upon the flow direction,
flow geometry and the fluid properties.  We will examine
reentrainment in the simple geometries for which literature
is available.
Horizontal Flow in Circular Tube - The best known and most
widely used flow regime map for horizontal flow is that of
Baker (1954), which is shown in Figure 3-10.  The Baker
chart as modified by Scott (1963) is shown in Figure 3-11.
where "GL" and "G " stand for the mass flow rates of liquid
and gas, respectively, in kg/m2 sec.  The dimensionless
parameters "X" and " V," represent allowances for the fluid
physical properties in the system and are defined by the
following:
                v  - (°JL\
                 1   \aL/
                                                      (3-34)
0.5
                (3-35)
where   p. = density of air, g/cm3
        Pw = density of water, g/cm3
        aw = surface tension of water, dyne/cm
        CL = surface tension of liquid, dyne/cm
        yw = viscosity of water, poise

     The onset of  reentrainment may be considered  as  a
transition from  separated flow to  entrained  flow.   The
curve  separating the two regions is shown  in Figure 3-10
                           3-33

-------
  1,000
u

-------
1,000 LI  i Mi  i  I III  I  I III  I  I  HI I   I '+
             DISPERSED
             ANNULAR
                                BUBBLY
                                  OR
                                FROTH
            STRATIFIED
                          i u>  i  i m  T  ii
    0.1
      0.1    1.0
10
10'
    Figure  3-11  - Flow pattern diagram for
                 horizontal flow (After Baker,
                 1954, as modified by Scott,
                 1963).
                     3-35

-------
 From  that  figure,  it  can be  calculated that  for an air-water
 system,  entrained  flow  starts  at   GG = 125 Kg/m2 sec when
 GL/GG =  1  Kg/Kg.   If  GL/GG  =  100  Kg/Kg, entrained flow
 starts at   GG  = 37.5  Kg/m2 sec.  This corresponds to a re-
 entrainment velocity  of 100  m/sec  at a liquid loading of
 1.33  x 10"3 m3/m3.  The transition velocity  drops to 30 m/sec
 at a  liquid loading of  0.133 m3/m3.
 Vertically Upward  Flow  in a  Circular Tube -  Cousins et al.
 (1965) studied the transition  from separated to separated-
 entrained flow in  a 0.95 cm  bore vertical tube.  The flow
 was in the upward  direction.   Their general  conclusion is
 that  for thin liquid  films at  low  liquid Reynolds numbers,
 the gas velocity for  entrainment increases rapidly with de-
 creasing liquid rate, and a  limiting liquid  flow rate may
 be reached,below which  no entrainment occurs irrespective
 of further increases  of gas  rate.  At higher liquid flow
 rates, both gas and liquid flow rates are important in
 governing the onset of  entrainment.  Figure  3-12 from the
work of Cousins et al.  (1965)  illustrates this conclusion.
     For the asymptotic case of a limiting liquid flow rate,
 the onset of entrainment corresponds closely to the formation
of large disturbance waves in  the liquid film.  For lower gas
 flow rates the existence of large disturbance waves is not a
sufficient condition  for the onset of entrainment.   Thus,
 there is a region in which the gas velocity  is sufficient to
give rise to large waves on the surface but is insufficient
to break these waves  into droplets.  Zhivaikin (1962)  sug-
gested that the onset of droplet entrainment in upward flow
can be correlated by  the equation:

                                    .5
                                                       (3-36)
/     V
\>w)
                            3-36

-------
  800
  600
Hj400


-------
where   u~    =  critical  gas velocity for entrainment
        NR  L =  liquid Reynolds number

Vertically Downward Flow  in Circular Tube - For downward flow
the onset of entrainment  equations are presented by Chien and
Ibele  (1962), Steen and Wallis  (1964) and Zhivaikin (1962)
and appear in Chapter 4.  Each  investigator defined onset of
entrainment differently and thus their predictions for onset
of entrainment differ significantly.  Their data were ob-
tained in a 2.5  cm bore tube.
     Measurements of the  amount of liquid entrainment in
upward and downward co-current  two-phase annular flow are
presented in Figure 3-13.  It can be seen that for upward
flow the quantity entrained passes through a minimum with
increasing air flow rate, while for downward flow entrainment
increases with total liquid flow rate.
Effect of Impingement of  Gas Jets - As mentioned earlier, the
gas and liquid phases do  not flow parallel in the entrainment
separator.  Jets of gas are present, which may impinge on the
liquid film at various angles.  The presence of gas jets,
their impingement on the  liquid film at various angles, etc.
depend upon the entrainment separator design.
     Wallis (1962) studied entrainment in ducts with various
inlet designs.  The reentrainment velocity varies with inlet
design, from 1,800 cm/sec to 2,400 cm/sec.  The data are
shown in Figure 3-14.
Interfacial Waves - The study of interfacial wave behavior is
important in the determination of transition from separated
flow to separated-entrained flow.  Experimental and theoreti-
cal studies of wave behavior and its influence on other
phenomena are still at a  very early stage of development.
The most advanced theoretical studies have been concerned
                            3-38

-------
        40
    H
    2
    w
        30
    2   20
        10
Water Flow
Rate, cc/min
                                   I
          0       10       20      30

                AIR VELOCITY, m/sec
Figure 3-13 - Comparison of entrained fraction in
              upward and downward cocorrent annular
              flow in 1.25 cm I.D. tube.  Solid line
              represents upflow and dotted line
              represents downflow.
                        3-39

-------
 H
 S5
 W
 W
60


50


40


30


20


10
                20
                   40
60
           AIR VELOCITY, m/sec
Figure 3-14 - Extrapolation method for
              determination of point of
              onset of entrainment for
              vertical downflow in 2.2 cm
              I.D. tube.  Water flow rate =
              1,280 cm3/min.  The curves are
              shown for different inlet
              designs.  After Wallis (1962)
                   3-40

-------
with the problem of the initial formation of waves, rather
than their development and influence.  However, the in-
stability of the waves represents the physical phenomenon
responsible for transition from separated to separated-
entrained flow.  Thus, to understand the physical phenomena
responsible for reentrainment in entrainment separators, one
should look at the interfacial waves, breaking of the waves,
drag friction on the film due to gas flow, etc.
     A flow map showing different regions of interfacial
structure observed in air-water flow at atmospheric pres-
sure is illustrated in Figure 3-15 (Hall-Taylor et al.  1963).
As the air velocity is increased, ripple waves and distur-
bance waves take place.  These waves represent instability
of the interface.  One theory that explains interfacial in-
stability is the Kelvin-Helmholtz theory.
     Consider the case of the flow of two inviscid fluids
of different densities (say a gas and a liquid), separated
by a vertical interface on which a regular train of waves
is moving with a velocity, "C".  As the gas flows around
the curves of the streamlines, centrifugal forces are set
up and these must be balanced by a pressure gradient in the
direction normal to the streamline:

                    - If- >G? CSG - C)2            (3-37)
where   r  = radius of curvature, cm
        Ug = mean gas velocity, cm/sec
        n  = direction normal to the streamline
     The pressure at the interface can be found by inte-
grating this equation between the interface and infinity.
     It follows from Equation (3-37) that for surfaces of
positive curvature the pressure at the interface will be
less than the undisturbed pressure at infinity, whereas for
                           3-41

-------
o

-------
surfaces of negative curvature the pressure at the interface
will be greater than the value at infinity.  Thus, the gas
flowing past the wavy interface generates an increased pres-
sure over the troughs and suction over the crests.  A similar
line of argument obviously applies on the liquid side of the
interface, only the liquid exerts an outward pressure at the
crests and suction at the troughs.
     For vertical flow the only forces opposing these normal
stresses are those due to surface tension.  For a stable
interface condition, the surface tension stresses exactly
balance the effects of the normal stress.  On the other hand,
the wave will grow in amplitude when the sum of the local
liquid and gas normal stresses exceeds the surface tension
stress.  It can be further deduced that the thinner the
liquid film the greater the gas velocity needed to cause
an increase in amplitude of a given size wave.
     It may be expected that the effect of waves will be to
increase the friction factor.  To determine the liquid flow
rate, it is necessary to have interfacial  friction factor.
     Roberts and Hartley (1961) found, on plotting friction
factor as a function of liquid film thickness for a given
gas velocity, that the friction factor did not begin  to  in-
crease with film thickness until a certain value had  been
exceeded.  They were able to correlate the difference between
the interfacial friction factor and that for the same gas
flow rate in the absence of the liquid phase, by the  equation:
         fi  "  fG
                         eq
    5    /2\'-5l
" *^  l£GJ  J
6      a    " »  i             (3-38)
                             3-43

-------
 and,   £.  =  T.   T PG  UG                                (3-39)
where   f.^   =  interfacial  friction  factor
        fG   -  friction  factor  in  the  absence  of  liquid
              phase   i
        6    =  liquid  film  thickness,  cm
        d    =  equivalent (hydraulic)  diameter, cm
        T^   =  interfacial  shear stress, gm/cm sec2
     Thus,  for very  thin  liquid  films there  would be no sig-
nificant waves on the  interface  and  no effective roughness.
For thicker films there would be a minimum instantaneous film
thickness corresponding to the troughs of the waves on the
surface.
     Gill et  al. (1963) calculated the equivalent roughness
height  and plotted it  as  a function  of the film thickness
defined by Roberts and Hartley.  The correlation is shown
in Figure 3-16.
     Hanratty and Woodmansee  (1965)  suggested that the onset
of reentrainment may result from suction on  the wave by the
Kelvin-Helmholtz mechanism.  This suction will lead to a
tearing of the wave tips.
     A number of possible mechanisms have been suggested by
which transfer of droplets can be effected by the waves, but
at present there is no definite evidence to  favor any parti-
cular one.  Lane (1957) described the mechanism illustrated
in Figure 3-17.  The gas starts to "undercut" the wave and a
round, open ended bubble begins to form.  The bubble grows,
leaving a thick-ringed filament around its base and event-
ually breaks up into droplets.  Once the breakup occurs, the
excess  (dynamic)  pressure  inside the bubble  gives rise to a
rapid radial transport of  the droplets.
                          3-44

-------
U
              0.01    0.02    0.03

            FILM THICKNESS,  cm

  Figure 3-16 -Relationship between
               effective roughness
               height and film
               thickness.
            3-45

-------
       Gas
                       •Time
                 Figure 3-17  -
 Breakdown  of Disturbance Wave by Undercutting
                 Time-
               Figure 3-18 -
Breakdown of Disturbance  Wave by Rolling
                3-46

-------
     An alternative form of breakup is illustrated in
Figure 3-18.  A large amplitude wave on a shallow liquid
layer tends to steepen at the front and then to form a
breaking wave.  If the gas velocity is very high, it might
be expected that the tips of the waves would be drawn out
into thin liquid sheets with subsequent breakup.
Entrained Fraction and Rate of Reentrainment - If the gas
velocity is increased beyond the onset of reentrainment,
some of the liquid that is collected on the entrainment
separator elements will be reentrained*  To determine the
overall efficiency of a separator, one must know the
equilibrium entrainment fraction, rate of reentrainment,
and reentrainment drop diameter. . In this section we will
deal with entrained fraction and the rate of reentrainment.
     There are no reliable methods at present for estimating
the fraction of liquid flowing as entrained droplets out of
an entrainment separator.  Geometrical factors, inlet con-
ditions, physical and chemical properties and change of
conditions along the entrainment separator can all affect
the results obtained.  Therefore, any correlations that have
been developed for entrained fraction estimation should be
treated critically.
     Wickes and Dukler (1960) have attempted to correlate
the data for entrained droplet flow rate by means of the
Martinelli  (1949) parameter "X":
                     X  =
(dp./dz)
                                     1/2
where    (dpr/dz)L  =  frictional  pressure  gradient  for  liquid
                     flowing  alone  in  a tube,  dyne/cm3
         (dp^/dz),,  =  frictional  pressure  gradient  for  gas
                     flowing  alone  in  a tube,  dyne/cm3
                           3-47

-------
     A dimensional entrainment parameter "R" was obtained by
intuitive reasoning and was defined as:
               3.8x103 B W   u./ur
          R •             B      G
where  W.£ = the flow rate of entrained  liquid, g/sec
       B   = empirical constant,  22  for  smooth  injection
             and 13 for shock injection
     Collier § Hewitt's (1961) data  correlate fairly closely
about a line given by the following  equation
                     X = 0.069 R0-39                    (3-42)
     Hughmark (1973) correlated the  entrainment data of
Collier $ Hewitt, Alia, et al. (1965) and Wicks and Dukler.
The data are plotted in Figure 3-19.  Empirical correlating
equations are:
yj < 36       a = 0                                    (3-43)
36 < y* < 42, a = -0.000442 + 0.000013 y*              (3-44)
42 < y* < 60, a = -0.000625 + 0.0000172 y*             (3-45)
60 < y*     .  a • 5xlO-8 (y*)22                        (3-46)
      O                    \3
           WL PG
where  a = rr=	 = volumetric flow ratio
           WG PL
       and W,,  W_ are liquid and gas flow rates, g/sec
     Anderson,  Bellinger § Lamb (1964) obtained the rate of
interchange between entrainment and  separated flow in horizon-
tal pipes.  Their results show that  the rate of interchange
(% of the total liquid flow per 30.5 cm length of pipe) can
be correlated as follows:
                            3-48

-------
            10'
            I02
            l0"3
             I04
             I05
                               • COLLIER AND HEWITT (1961)
                               OALIA CT AL   (1965)
                               oCCUSINS ET AL (1965)
               10
                              100
                                             1000
Figure 3-19  - Correlation  of entrainment data
                by Hughmark  (1973).
                 3-49

-------
% interchange = 4 for NRe L > 2,570, NRe fi  > 3,000    (3-47)
% interchange =0.5 for NRe L = 1,150, NRe G  > 3,000  (3-48)
% interchange = 0 for NRg G  < 3,000                   (3-49)

Drop Diameter of Reentrainment - Another important factor,
besides the amount of reentrainment, is the drop diameter of
reentrainment.  If a secondary entrainment separator is used
to remove the reentrained drops, it is necessary to know the
drop diameter of reentrainment to design the secondary
separator.
     Few investigators have measured the drop size distri-
bution arising from separated flow.  Wicks and Dukler (1966)
obtained data for co-current downward flow in a 15 cm x
1.8 cm rectangular vertical channel.  The mass median drop
diameter varied between 150 and 450 ym.  The smallest drop
diameter found in the entrainment was 45 ym.
     Cousins and Hewitt (1968) obtained data during experi-
ments on the mass transfer of liquid droplets subsequent to
removal of liquid film.  Photographs of the droplets were
obtained for a zone immediately adjacent to the channel wall.
The mass median drop size was between 90 ym to 175 ym.  They
also found a minimum droplet size of 45 ym.  Both sets of
data show a decrease in the mass median diameter with in-
creasing gas velocity.
     Fraser et al. (1963) studied drop formation from liquid
sheets by an air blast at 90°.  They observed that the
liquid sheet does not break down upon immediate impact with
the air stream but is deflected away from it.   Waves are
initiated at the point of impact and the sheet breaks down
into drops through the formation of unstable ligaments.  The
air velocity was varied between 103cm/sec and 6xl03cm/sec
and the liquid flow rate between 12.5 and 125 g/sec.  The
                           3-50

-------
liquid drop size varied from 30 urn to 250 ym.  They ob-
served that the average drop size increases with increase
in liquid flow rate and decreases with increase in air
velocity.
Reentrainment Due to Rupture of Bubbles
     The second mechanism which leads to reentrainment is
rupture of bubbles.  Again the important questions are at
what velocity reentrainment begins, what is the drop dia-
meter of the reentrainment, what is the amount of liquid
in the reentrainment, etc.  The effect of operating
variables such as gas velocity, liquid flow rate, etc.
should also be determined.
     The following section deals with the mechanism of
bubble rupture, the drop size distribution created by
rupture of bubbles, and the trajectory of these re-
entrained drops.
     Rupture of bubbles is the main cause of the re-
entrainment of liquid drops into the gas phase in devices
such as sieve plate, bubble cap plate, packed bed, and
mesh type separators.  The collapse of a bubble when
exiting from the liquid phase is associated with thinning
of the liquid film starting at the top part of the bubble.
The upper surface thins to the extent of becoming weak
enough to rupture.  Rupture of the upper part of the bubble
film takes place when the  film thickness if of the order of
0.1 ym, provided there are no external disturbance forces
leading to the rupture of  films  (Kitchener,  1964; Jashnani,
1971).  The collapse of the bubble at the interface leads
to the release of surface  tension energy which is converted
into kinetic energy.  The  kinetic energy is  sufficient  to
impart high velocities to  liquid drops formed during  this
process.
                           3-51

-------
Drop Diameter of Reentrainment  - The liquid drops which are
formed during the rupture of bubbles are of two distince
diameter'ranges.  Small drops  (about 30 to 40 ym) are formed
from the top of the bubble surface, and large drops (about
1 mm) are formed due to the disturbances in the liquid phase
following the bubble rupture.   Formation of the small drops
was observed by Stumpner (1936), and he attributes drop
formation to the rupture of the projecting dome of the
bubble into fragments.
     Davis (1940) cites the work of Edgerton, Germeshausen
and Grier (1936) on the rupture of a soap bubble to estab-
lish that during collapse, the  dome opens and forms an
initial perforation near the apex without creating drops.
He suggests that large drops are subsequently formed by the
breakup of the liquid jet which forms when the surrounding
liquid moves inward to fill the depression caused by the
bubble.  The depth of the depression is a function of the
bubble size.  Drops are more likely to form from small,
rather than large, bubbles.  The work of Dombrowski and
Frazer (1954) shows that a thin liquid film on the top of
the bubble breaks up by the initial formation of a number
of perforations which subsequently expand to give a lace-
like structure.  The liquid ligaments so formed are unstable
and break into small drops of varying size.
     Drop formation due to bubble burst occurs in three
steps.   The first step, the lifetime of the bubble at the
interface, lasts on the order of l/100th sec.or longer; the
actual bubble burst, the second step, takes a few micro-
seconds;  and events subsequent to the bubble burst extend
over a few milliseconds.
     Newitt et al. (1954)  measured the drop size distribution
due to the rupture of a bubble, and a typical distribution is
                            3-52

-------
shown in Figure 3-20.  They also observed that in all cases the
Sauter mean diameter of large drops,"d   ", decreases nearly
                                      S ,Jt
linearly and the number of large drops, "No"» increases with
decreasing bubble diameter.  Furthermore, both "d  0" and
                                                 s, x>
"N " decrease with rising temperature, and the change in the
  At
number of drops produced by the bursting of large bubbles
decreases markedly as the temperature is raised.   Figure 3-21
shows the variation of the Sauter mean diameter "d  *" with
                                                  s, x,
the bubble diameter at 25°C, using distance from the inter-
face as parameter.
     Large drops are formed from jets of liquids which are
formed following bubble rupture.  As the liquid surrounding
the bubble moves inward to fill the depression caused by the
bubble, it usually forms a jet of liquid.  As the bubble
diameter is reduced, the internal pressure rises and the
energy available for jet formation increases.  This  gives
rise to jets of higher initial velocity and hence greater
unbroken length.  Stuhlman (1932), experimenting with bubbles
of 0.25 cm diameter or less, showed that the resulting jets
became progressively thinner with decreasing bubble diameter
and break down into two or more drops per jet.
     Garner, et al. (1954) found that 95% of the droplets
entrained in the evaporator were below 20 ym, but because of
their low mass they formed only a small fraction (about 2%)
of the total weight of the entrained liquid.
     Droplets from the rupture of bubbles larger than 0.5 cm
diameter were almost entirely produced from the bubble dome.
The entrainment resulting from bursting bubbles increased by
20 fold when the bubble diameters were reduced from 0.6 cm
to 0.2 cm.  Mass median drop diameters of 440 ym, 660 ym
and 820 ym were obtained from bubbles having 0.2 cm, 0.3 cm
and 0.4 cm diameter, respectively.
                            3-53

-------
         w
s  30
         C/3
         w
   25


   20


   15
G  10
w
&   5
w
pi
*   0
                      I
                    &
                        irar
±31
1
                        I
                          TTT
                  m
     II
                            Sfi
                             •tr1

                                  Jil!
mm
                                     il
               0
        Size range of small
        particles .micron
                 140 1 - 16
                      Size range of large
                      particles, cm
Figure 3-20 - Histogram showing size distribution of
              large and small drops resulting from
              bubble burst
         .101
                                       ••64 cm
                                        1.91 cm
                                        3.17
                                             cm
                                     -->i4.44  cm
                                        5.71  cm
             30   35   40   45   50   55

                 BUBBLE DIAMETER, cm

 Figure 3-21 - Sauter mean diameter, D  p, against
               bubble diameter at 25°C  '
                          3-54

-------
     Small drops travel outward from the point of burst at
angles of up to 80° from the vertical.  Thus, some of the
drops will be collected on the walls.
Formation of Jet After Bubble Burst - To determine re-
entrainment in the gas phase, it is necessary to study
the kinetics of the liquid jet formed after the bubble
burst.  The dimensions of the jet are important, as the
instability of jets produces drops which are reentrained
in the gas phase.  The velocity of rise of the liquid jet
will give the large drops their initial velocity.
     Davis (1940) gives the following equation for jet
velocity based on the pressure pulse following bubble
rupture:
                  u = 6 _£*                        (3-50)
                        °Ld
where   t = time during which the impulse force is applied
            (about 3 x 10'5 sec)
        d = bubble diameter, cm

     Equation  (3-50) predicts velocities which are very small,
about 0.1 cm/sec.  According to Newitt et al .  (1954), when
the rupture of a bubble takes place, a partial vacuum is
created due to the impulse force, and therefore the absolute
pressure rather than pressure excess should be used as an
impulse force:
                u =                                 (3-51)
                    2      aLd

where   P  = pressure outside the bubble, dyne/cm2
     Equation  (3-51) assumes no correction for  the  change  in
bubble diameter due to the contact with  air by  part of the
bubble surface.
                            3-55

-------
     Newitt  et  al.  give  the  following equation for the height
 of  the  jet:
                                                        (3-52)
     For air water  system,  a4  =  1  cm2,  a  =  73  dynes/cm,
g - 980 cm/sec2  and PL  =  1  g/cm3 give h^ 0.404  cm.   The
experimental jet height as  obtained  from  photographs  is
0.44 cm.
     Weber  (1931) has calculated the relationship  between
the unbroken length of  the  jet and its  velocity.   In  the
range of velocities  created by 0.2 to 0.5 cm bubble diameters,
the relationship between  velocity  and length is  linear.
Haenlein's  (1931) experimental values confirm  this.   The
distance, "A j", of the unbroken  jet  is given  by  the  expression:

*3 = t' u
where  t1 = rise           ___-._—_   £=!*$   —  - -          (3-53)
time of the unbroken                 _______
length of jet, sec         ^-r-r-JI^—l-^-Ir-jr^r

     The velocity obtained  from  Equation  (3-51)  should be
used in Equation  (3-53) to  calculate the  length  of the
unbroken jet.
     If the length  of the liquid jet is longer than the peri
meter of its cross-section, it becomes  unstable  and breaks
up.  The breakup occurs at  different lengths along the jet,
and it is this broken part  which forms  the  liquid  drop.
     For non-viscous liquids Weber (1931) gives  the most
favorable wave length for breakup  of a  jet  as:

                          djet  =  4'42 djet
                             3-56

-------
where   d.   = diameter of the jet, cm
         jet
     Equating a cylindrical length of jet, equal to 4.42 d.  ,
with the volume of a drop formed, results in:
                     dp = 1.89 d.et                 (3-55)
     Castleman (1931) gives the following expression, based on
the work of Rayleigh (1879, 1889) and Weber  (1931), for the
time of break-up of a liquid jet:

               t = iil log ^i                       (3-56)
                   a5      ao
                           (v 0-5
                     4d^—]                         (3-57)

where, d  = bubble diameter, cm
       a.^ = amplitude of surface disturbance of the
            jet - 0.5 d.Qt
       a  = initial surface disturbance = 10~5 cm
     The above equation gives times which are roughly 4 times
greater than actually observed.
     The total length of jet will be the sum of unbroken and
broken parts :
                 h, = £_ + St.. = t* u + 4.42 d. .     (3-58)
                  A    J    *f                j e L.

Trajectory - Reentrainment will depend upon  gas velocity,
flow direction, terminal and initial velocities of drops and
hydrodynamic properties.  Large drops which have a terminal
settling velocity greater than the upward gas velocity will
eventually fall down.  However, it is necessary to provide
enough height following the mist eliminator, for these drops
to reverse direction and start falling.
                          3-57

-------
     If the gas velocity  is  in  the  vertical  direction,  the
vertical height traveled  by  the large  drops  (with  diameter
"ds £M) is given by Equation 3-59,  from  Lapple  and Shepherd
(1940) :

          U)
                     Udu
                   a6u
                       1'*
                           g
                                             u  du
                                          a,ultlf - g
                                                        (3-59)
where
           = -r^ -  .  The equation  is based  on  drag  coeffi-
cient  Cd = 18.5 NR~°'6
              u-u
                         The time for vertical  travel  is:
                               u,.
               f     du     +  f 	du_
               I      1 U  .      I    1 U
               J   a,u •   + e    / a^u
               *    f\      &   •?»  A
                                                        (3-60)
     Figures 3-22 and 3-23 give a plot  of  time  and height
versus initial drop velocity with drop  diameter as parameter
(gas velocity ur = 0).
     The drop ballistics for small drops with drop diameter,
"d   ", differs from that of the large  ones because  the
  S y S
initial velocity of the small drops  is  not necessarily in
the vertical direction.
     Lapple and Shepherd give integrated forms  for this  case,
based on Stokes Law:
     PL dl.s
      18 u-
Sh " ~IF
               1  -  exp
                            dl,s
                                                        (3-61)
                                                        (3-62)
      18
      U
                     -  u
              In
                 ut  - u
               Ut
                        PL
                           d2
                                 1  -  exp
                                           'L us,s
                                                        (3-63)
(3-64)
                            3-58

-------
       u
       
-------
where    S   »  the  distance  traveled by  drop  and  subscripts  "h"
              and  "v"  refer to  the horizontal  and  the vertical
              direction,
         u   =  the  initial velocity in horizontal  (Equations
              3-61 and 3-62)  and  in vertical  (Equations 3-63
              and  3-64) direction
Creeping of Fluids
     The presence  of  drag  forces due to gas flow  leads to
creeping of liquid in  the  entrainment  separator.  Creeping
may be prevented  by providing  a  proper drainage system.  If
creeping is not prevented,  reentrainment may  occur.
     In  the entrainment separator gas usually flows vertically
upward or horizontally.  If  there is creeping of  liquid, it
flows as a  film or as  drops.   The liquid and  gas  flow in the
same direction.   Thus, to  determine the effect of creeping,
we need  equations to predict liquid flow rate due to drag
forces exerted by gas  in various directions and in various
geometries.  Again, we are limited to the theoretical devel-
opment to predict two phase  flow in simple geometries.
     Consider liquid and gas flowing in a vertical tube.  The
gas is flowing vertically upward and liquid is flowing as a
film and therefore forming an  annulus.  The liquid film is
subject to various forces:  drag  force due to gas flow in the
vertically upward direction, gravity force in the downward
direction and frictional force due to tube wall.
     For gas velocity lower than the critical velocity the
liquid near the wall flows downward due to gravity.  As the
gas velocity is increased  the  liquid at the interface reverses
its flow direction and moves with the gas; as a result the
liquid film begins to thicken.  At a critical gas flow rate
the liquid does not flow down  any more, and the liquid film
thickens rapidly.
                           3-60

-------
     Shearer and Nedderman  (1965) give the equation for shear
stress inside the liquid film:
       dp   _  _\ /D-2 6\ ,  /  dp           p
T =
  at - PG g
• itn ' PL
                                                    C3-65)
where  D = the diameter of the tube, cm
       T = shear stress measured at a distance  My" from the
           wall, dyne/cm2
     The velocity profile for the liquid can be obtained by
integrating Equation  (3-65) . The liquid is assumed to be
Newtonian and the boundary condition is given by u. =0
                                                  LI
at y = 0 for a laminar flow:
u,
                                                    (3-66)
QT -
Integration of Equation (3-66) gives Equation (3-67):

                         gpT63   gprD62
      \^IJ A/U  .  «LJ | U  1
    ' -& -5— + -tt I TT I '
 L
irD
v
                           (3-67)
     However, in the case of a liquid film flowing vertically
downward, terms containing "g" should be more  important than
terms containing"-^",
                 az m „
     The situation is significantly more complex  in the
general case when the flow is not steady and part of the
film is in turbulent motion.  In entrainment separators the
situation is further complicated due to entrance  effect.
     When the flow channel is not vertical, Equation (3-67)
should be modified by replacing "g" by "gCosB"; where  "6"  is
the angle between the channel direction and the vertical.
However, if the effect of gravity is larger than  the effect
of the pressure gradient, the thickness of the film across
the channel will be uneven and separated flow  rather than
annular flow may form.  Equations are not available for the
case of cross flow.
                          3-61

-------
Shattering of Drops
     Reentrainment may take place due to shattering of drops
in two ways.
     1.  Due to splashing of drops on the solid surface,
     2,  Due to high relative velocity between gas and
         liquid drops.
     Garner et al, (1954) observed splashing in a 10 cm
glass evaporator.  The size distribution of the shattered
drops showed a large variation.  The drops were larger
than 200 ym.  The splashing was observed in a gas-liquid
system where localized areas of high velocity were present.
     Shattering of the drops due to high relative velocity
between gas and liquid drops does not increase entrainment
in the gas phase.  However, small drops are more liable to
be carried away in the gas phase than large drops and
therefore shattering of drops should be avoided.
MANUFACTURERS' SURVEY
     The information received from the manufacturers of
entrainment separators was reviewed.  Cyclone, mesh, fiber
bed, packed bed and baffles are commonly used as entrain-
ment separators.  Sometimes two or more devices are combined
in the entrainment separation process.  The description of
the available entrainment separators is given in the
proceeding paragraphs.  The first paragraph gives the code
used in the description.
Manufacturer
     (Type)  Type of separator
     (L)     liquid load, cm3/cm3, and drop diameter, ym
     (G)     Gas volume, m3/sec
     (UG)     Gas velocity, cm/sec (maximum operating range)
     (E)     Overall separation efficiency, %
                          3-62

-------
     (AP)     Pressure drop, cm  W.C.
     (Lim.)   Limitations
     (App.)   Application
     (Mat.)   Materials of construction
     (Com.)   Comments
ACS Industries
     (Type)   Mesh
     (L)      up to 2.71 g/cm2 sec, d  > 5 ym

     (G)      UG = k  [(PL - PG)/PG] k = 0.35 for oil and gas,
                 = 0.25 for steam at 1 atm, =0.2 for pressure
                   500 cm Hg, =  0.15 - 0.2 for vacuum
     (E)      Figure  3-24
     (AP)     Figures.3-25 and 3-26,  Table 3-6
     (App.)   Mists of petroleum, H^SO., caustic, HC1,
              water soluble dusts
     (Mat.) .  Steel,  SS, MO, Ni, Haste alloy, PP, Teflon
Aerodyne Development  Corporation
     (Type)   Cyclones, integral part of wet scrubber
     (G)      14.1 (30,000 CFM)
     (Com.)   Uses secondary air to impart centrifugal action
AgetManufacturing Company
     (Type)   Fiber filter
     (G)      0,141 - 1.22 (300  - 2,600 CFM)
     (App.)   Mists from screw machine, thread grinders,
              centerless machines
     (Mat.)   Glass wool
Air Purification Methods
     (Type)   Cyclone with vanes
     (L)      2.66x10-* -l.lxlO'3
     (G)      0.19 -  15.5 (400-33,800 CFM)
     (UG)     1,130 - 1,480 cm/sec
     (E)      95% for 10 ym and  1001 for > 13 ym,
              See Figure 3-27
                          3-63

-------
   100
w
t—I
(_)
I—I
V*
O

U
20 SffigiS
     0
       0
                     2.5

             GAS VELOCITY,  m/sec
     Figure 3-24 - Calculated collection  efficiency
                   for water droplets  in  air  for ACS mesh
                        3-64

-------
    100
u
 E
 u
a,
o
w
CO

w
                    5    10


               AIR VELOCITY, m/sec
50  100
 Figure 3-25 - Pressure drop versus air velocity

               for 10 cm thick ACS style 4CA mesh.

               L/A = superficial liquid velocity,

                     cm/min.
                     3-65

-------
      30
u
 *

s
g
!=>

CO
     0.5 -,
     0.3
                        STEAM VELOCITY,   m/sec
     Figure  3-26  -
Pressure drop versus steam velocity at

various pressures through 10 cm thick

ACS mesh.
                            3-66

-------
                Table 3-6.  MESH PARAMETERS

Mesh     Density     Wire Diameter    Percent    Wire Surface
Style     g/cm3           cm	     Voids       cm2/cm3
 4BA      0.192         0.028           97.6         3.77
 4CA      0.144         0.028           98.2         2.79
 7CA      0.080 -        0.028           99.0         1.48
 3BF      0.115         0.015           98.6         3.93
                         3-67

-------
100
                I    i    r
                         i    i     i    i
           10   15   20    25   30   35

           PARTICLE  DIAMETER, ym
40
  Figure 3-27  - Collection  efficiency  versus
                particle  diameter  for  Air
                Purification Methods cyclone
                separator with  inlet velocity
                of  16-21  m/sec
                 3-68

-------
Air Purification Methods  (continued)
     (App.)   in venturi  scrubbers and mist removal
Arco Scrubbers (Envirotech)
     (Type)   Baffles, packed bed and cyclone
     (G)      65 (138,000  CFM)
     (Com.)   cross flow  in packed bed
B. B. Barefoot 5 Associates
     (Type)   Cyclone, integral part of scrubber
     (G)      2.4  - 47.2  (5,000 to 100,000  SCFM)
     (App.)   Foundry, furnaces, sinter plants
Balston, Inc.
     (Type)   Fiber filters
     (G)      0.38 (800 CFM)
     (E)      99.99
     (AP)     351
     (App.)   Sterilization of air, air to  instruments,
              laboratory  air clean up, breather filters
              in underground mines
     (Mat.)   Glass fiber 90% void
Beco Engineering Co.
     (Type)   Packed  beds of 1.9 cm x 1.9 cm hexagonal
              cylindrical pellets from three dimensional
              bonded  fibers
     (L)      No limit
     (G)      35.2 (75,000 CFM)
     (AP)     See  Figure  3-28
     (App.)   Distillation, fume scrubbers, packed towers
     (Mat.)   Nylon 6.6 for pH > 4, epoxy bonded  polyester
              for  acidic  medium
Beetle  Plastics
     (Type)   Packed  bed
     (G)      0.16 -  33.6 (350  - 50,000  SCFM)
     (UG)     220
     (App.)   Hcl, HF and NH3  fumes
                          3-69

-------
       50
  e
  o
  (X.
  o
  w
  OS
  D
  CO
  C/D
      10.
      5.0
     1.0
     0.5
                        I   r
                 /Conventional
                 'pad
 E-pack

Type E/N-1
            I   III   il i i i I
        1.0
         10
          AIR VELOCITY,  m/sec
Figure 3-28 - Comparison of pressure drop

         characteristics of Beco Engineering
         Type E/N-1 pad and conventional
         Pad length is 30 cm and air at room
         temperature and 1 atm pressure.
                      3-70

-------
Burgess Industries (Delta P Division)
     (Type)
     U)
     (E)
     CAP)
     (Lim.)
     (App . )
     (Mat.)
     (Com.)
     (Type)
     (L)
     (Mat.)
     (Type)
     (L)
     (E)
     (Mat.)
Cal-Metex
     (Type)
     (UG)
     (E)
     (AP)
      (Lim.)

      (Mat.)
      (Com.)
Centrifugal
>5 vim, liquid load less than 51 by weight
99+% See Figure 3-29
<1% of abs. line pressure
Maximum pressure 25 atm
Compressors, expanders, vacuum pumps
Carbon steel
Coalescer recommended for below 5 ym
Small cyclone tubes
Maximum 5% load
95% for 4 ym, 98% for 6 ym
Carbon steel, stainless steel and alloy steel
Zigzag baffles
liquid load < 5%, drops > 5 ym
99.991 for 8 ym
Carbon steel

Mesh
30-460, 10% higher for hi-thruput
99.9+%
= 0.034 pG u* (Figure 3-30) for 10 cm  thick
  standard mesh, - 0.02 PG u5, for 15 cm thick
  hi-thruput mesh
Sauder Brown constant, a = 0.25 for standard,
= 0.23 for hi-thruput and 0.22 for extra dense
S.S., carbon steel, Ni, Cu, PP
density = 0.145 g/cm3 for standard, =  0.08 g/cm3
for hi-thruput and = 0.195 g/cm3 for extradense.
See Figure  3-31 for onset of reentrainment
velocities.
                         3-71

-------
 I
55      -6
°    10
o
OH"*
n e
H  -

O O
  i—i
«H FH
  U
     10
       -7
     10
       -8
  Figure  3-29.-  Efficiency curve for Burgess
                Industries centrifuge.  Inlet
                drop diameter is greater than
                5  urn and maximum liquid in
                inlet is 5% of gas weight.
               3-72

-------
      10
u
OH
o
en
I
in
w
    0.01
     I    I     I

-Nu-Standard
             1.0  2   3    4    5


            GAS VELOCITY,  m/sec
Figure 3-30 - Pressure drop characteristic

              of 10 cm-thick Nu-standard

              and 15 cm thick Hi-thruput mist

              eliminators.
                    3-73

-------
      5.5

   u
   0)


  S   5.0
>:  4.5
H


I   4-°

>
    7 5
t/j   ** • **



    3.0
                    Hi-Thruput
          — Nu-Standard
                   I
         0        1        2       3



        ENTRAINMENT LOADING, g/cm2-min
Figure 3-31 - Safe operating limits for

              Nu-standard and Hirthruput

              mist eliminators.  Reentrainment

              will not occur when velocities

              do not exceed those shown.
                        3-74

-------
Cebeco Manufacturing Company
     (Type)
     CL)
     (G)
     (AP)
     (App . )

     (Mat.)
     (Com.)
Ceilcote
     (Type)
     (L)

     (G)
     (UG)
     (E)
     (AP)

     (Lim.)

     (Mat.)
     (Type)
     (L)
     (G)
     (UG)
     (E)
     (AP)
Fiber filter
0.5 urn
118 (250,000 CFM)
99.9% for > 0.5 ym
17.5-25
H2SO^ mists, organic plasticizers, oil mists,
carbon black
Glass wool - finer than used in laboratories
5 cm thick, wash may be'used for solids

Packed column - crossflow and counterflow
>3 vim, >8 ym for countercurrent with upstream
washing
0.15 - 23.6 (330-50,000 CFM)
215 (maximum 255 - for lower liquid loads)
Crossflow: 95+% for > 10 ym and 85-95% for
<10 ym.  Counterflow: 85-95% for > 10 ym and
50-85% for < 10 ym
0.008 cm/cm of packing at recommended velocity
in crossflow
If solids are present countercurrent flow is
recommended
Steel, steel lined with flakeline, rubber, etc
Wet cyclone
>5 ym
1,4-23.6 (3,000-50,000 ACFM)
1,650
95%
5-10
                         3-75

-------
 Centri  Spray Corporation
      (Type)    Zigzag  baffles
      (G)
      CUG)
14.1 (30,000 CFM)
195
Scrubbers in foundry cupolos
Galvanized steel, PP
      (App.)
      (Mat.)
Chemico  Industry
      (Type)    Cyclone
      (Com.)    Cyclone  is  integral  part  of  scrubber
Donaldson  Company
      (Type)    Multiple  cyclone
      (G)       26 (55,000  CFM)
      (E)       99.97 for >  0.3 ym
      (App.)    Air purification  in  mines
      (Com.)    Irrigation with 2,66xlO'5  -  0.67xlO-s
               L/G recommended
DuPont
      (Type)    Fibrous bed, 0.1-0.3 mm diameter  fiber
      (G)       14.1 (30,000 CFM)
      (App,)    Foundry cupolos,  mist of H2S04, mists from
               venturi scrubber
      (Com.)    Irrigation with water to avoid plugging,
               flooding correlation shown in Figure 32
Edwards Engineering Corp.
      (Type)   Mesh
      (L)      Drops formed by condensation
      (App.)   Vapor condensers
Fisher Klosterman,  Inc.
      (Type)   Cyclones
      (L)      Critical drop diameter 6-27 \im
      (G)      19.6  (42,000 CFM)
      (UG)     1,400
                        3-76

-------
O4
I
•vl
      P-
      id
     i
      O
        0
        0)
Q.
 O
Q.
                 Figure 3-32 - Flooding  correlation for fibrous bed structures by
                               Porter  and Lucas (1968)

-------
 Fisher Klosterman,  Inc.  (continued)
      (E)       1001  above critical diameter drops
      (AP)      15
      (Type)    Three stage  filter consisting of 14-18 mesh,
               fiberglass,  submicron diameter fiber filter
      (G)       15.1  (32,000 CFM)
      (AP)      0.25  -  7.5,  0.26  at rated capacity
      (Lim.)    Filters need replacement
      (App.)    Oil mist collection
 Industrial Plastic  Fabricators
      (Type)    Packed bed 15 cm  deep or  mesh 10  cm  deep
      (G)       0.23  - 11.8  (500-25,000 CFM)
      (E)       90-99% (efficiency  of total  scrubber)
      (Mat.)    Knitted mesh or PP
      (Com.)    Integral part of fume  scrubber
Koch  Engineering Company
      (Type)   Cyclone
      (G)      1.18-47.2 (2,500 - 100,000 CFM)
     (AP)      2.5-5
     (Com.)   Wall wash available if scaling is expected
     (Type)   Zigzag vane 3 or 6 passes
     (UG)      355
     (AP)      2.5  for 6  passes
     (Mat.)   PP
     (Type)   Spin vane
     (G)       47.2 (100,000 CFM)
     (AP)      10
     (Com.)    Less wear  on  shell,  effective for vessels  largef
              than 400 cm in diameter
     (Type)    Fleximesh
     (L)       2.7xlO"3 to  2.7xlO-2  g/sec cm2
     (UG)      150-450
                         3-78

-------
Koch  Engineering Company (continued)
     (E)      See Figure 3-33
     (AP)     1.25 - 7.5 depending upon liquid load
     (Lim.)   Not recommended for high liquid loads (5x10 "''L/G)
     (App.)   In wet scrubbers, removal of acid mist, oil drop-
              lets, in distillation columns
     (Mat.)   SS, Inconel, Monel, Ni, Ti, PP, Teflon, Hastelloy
Lau, Inc.
     (Type)   Centrifugal, mechanical aided and fiber filter
     (AP)     12,5 maximum
     (App.)   Oil mist created by coolent or cutting lubricant
     (Mat.)   Polyurethene-filter
Monsanto-Enviro Chem Systems, Inc.
     (Type)   Fiber filter, high volume and high efficiency
              filters
     (L)      No limitation on high efficiency, 3 pm on
              high volume
     (UG)     <30 for high volume, <15 for high efficiency
     (E)      See Figure 3-34
     (Lim.)   Cannot handle excessive solids, upstream washing
              recommended to avoid plugging
     (Mat.)   Fibers < 10 ym in diameter
     (Com.)   Above velocities represent onset of reentrainment
North American Rockwell
     (Type)   Mesh, panel filters, two stage on line mesh
              separators
     (G)      up to 4.7  (10,000 CFM) maximum actual volume
              = 0.47 (1,000'CFM) at  10 atm
     (E)      99.96 on 0.3 urn drops  - by DOP method
     (AP)     60-250 when clean, 350-500 at 10 atm
     (Lim.)   10 atm, 120°C
     (App.)   Removal of mist from compressed air
     (Com.)   All  the data is for two stage mesh
                          3-79

-------
u
2
U4
M
U4
H
CJ
U4
                  246


                 GAS VELOCITY, m/sec
      Figure 3-33  -  Performance  of Koch fleximesh

                     separator
                          3-80

-------
I
CO
          u
          2
C_J
I— I
U4
A
w

2
o
HH
H
u
W
100
 99

 95

 90


 85


 80


 75


 70
                      (7)Brink  H-E mist  eliminate
                                        0.3   0.5    1.0     2

                                         PARTICLE SIZE, ym
                                                                 10
                                                                     20
                  Figure 3-34  -  Collection efficiency of particulate collectors.

-------
Research Cottrell
     (Type)   Cyclone - integrated with flooded disc wet
              scrubber
     (L)      8-20
     (AP)     2.5
     (App,)   cupolas, electric arc furnace, gas.cooling
     (Mat.)   316 SS
Tailor § Company
     (Type)   Cyclone
     (G)      141 (300,000 ACFM)
     (E)      exit gas < 2.33xlO"6 L/G
     (Com.)   Cyclone connected to sicrubber
Wright Austin Company
     (Type)   Cyclone
     (G)      0.0025-47 (5-100,000 SCFM)
     (UG)     4,050 no reentrainment up to 7,800
     (E)      99* for > 10 ym
     (AP)     50
     (App.)   Removal of drops from wet steam, compressed
              air and gas
     (Com.)   Can be directly connected to steam lines
              0.6 cm to 120 cm in diameter
York Separators
     (Type)   Mesh single stage and two stage
     (L)      5 ym for single stage, 0.3 ym for two stage
     (G)      450-540 (950,000-1,040,000 CFM)                {
     (UG)     Sauder Brown constant for single stage, k, s 0'
              for 7.5 cm disengaging space and k = 0.43 for
              38 cm disengaging space
     (E)      99.9 for single stage, 100% up to 1 ym for
              2 stage - See Figure 3-35
                          3-82

-------
0\°
100
u
w
S 90
pt,
PH
W
z 80
o
H
• 1 «

York Type S

M_



—


U
W 7nL_
j 70h-
o 1 1 1 1
U 123
1 1

/Two Stage
Wire
Mesh



-


j 1
4 5
     PARTICLE SIZE, ym

Figure 3-35- Efficiency comparison of
             York scrubber with two stage
             wire mesh mist eliminator.
              3-83

-------
York Separators (continued)
     CAP)     <2.5 for single stage, 25 for two stage
     (App.)   Refinery vacuum towers, distillation equipment,
              evaporators, absorbers, scrubbers
     (Mat.)   SS, Mo, Ni, Inconel, Ti, Ta, Cu, Hastelloy, PE,
              PP, Teflon
Zurn Industry
     (Type)   Impingement separator
     (G)      0.57 to 34 (1,200 to 72,000 CFM)
     (type)   Cyclone - integral part of venturi scrubber
     (G)      56.3 (120,000 CFM)
                          3-84

-------
                          THEORY

      In the previous chapter equations predicting primary
 collection efficiency and pressure drop were presented
 for cyclone, packed bed,  tube bank, mesh and sieve plate
 entrainment separators.   Part of this  chapter is  devoted
 to the development of mathematical models for primary
 efficiency and pressure  drop in a zigzag baffle separator.
 In addition, models for  reentrainment  in both horizontal
 and vertical baffles and  in  cyclones are discussed.  At
 this point in the  study,  these are the only  separators
 for which  mathematical models of reentrainment have been
 formulated.
 ZIGZAG BAFFLES
 Primary Efficiency
      A zigzag baffle  section  is  shown  in  Figure 4-1,  The
 gas  flow pattern in a baffle  section is  too  intricate
 to be  described as  a  series of gentle bends.   The model
 used  to characterize  the flow must  include the effects
 of turbulent mixing.  One can assume either that mixing
 occurs after flow through each bend or that mixing occurs
 continuously throughout the flow path.   The latter assumption
 is made here.
     The presumption of turbulence may  be verified by
calculating the gas Reynolds  number as  follows:
   Hydraulic Diameter - 4*                     - ' "> -   C4-1)
           2b'uipr   2burp
                          4-1

-------
        n=4
 t
u.
Figure 4-1 - Continuous zigzag baffles
              4-2

-------
 where   b1  » perpendicular distance between two consecutive
              baffles in the same row, cm
         u,!,  = actual gas velocity between the baffles,  cm/sec
         b  = spacing between two consecutive baffles  in the
              same row,  cm
         ufi  = superficial gas velocity based on empty duct,
              cm/sec = uiCosS

      Under  typical conditions used in the  pilot plant,
 b  =  7.25 cm, pfi = 1.25  x 10'3 g/cm3,  yfi  =  1.8 x 10-* poise
 and  UG  «  300  cm/sec.   Therefore,  NRe  G  =  3  x  10"  and  the
 flow should be  turbulent.   The  presence of  corners  and  edges
 in the  baffle section  should enhance  the  turbulence.
      The  gas  is assumed to  flow as  in Figure  4-1.   The  flow
 path is a series of  alternate bends of  angle  26,  and  the
 total number  of bends  equals the  number of  rows of  baffles
 in the  entrainment separator.
      The  terminal settling  velocity of  a  drop, in cm/sec, is:

                             d 2a  a
                        ut -  -f-2-                    (4-3)
where   d  «= drop diameter, cm
        p  = drop density, g/cm3
        UG - gas viscosity, centipoise
        a  = acceleration due to centrifugal force, cm/sec2
     The acceleration due to centrifugal force was approxi-
mated on the basis of an average radius of curvature in the
baffles, as follows:
                                                      (4-4)
                         w cote
Equation (4-3) is based on Stokes law and applies only if
the drop Reynolds number NRe D < 0.1.  If NRg D > 0.1, an
appropriate friction factor should be included in the
                           4-3

-------
calculation.  Foust, et  al.  (1959) give a plot of drag co-
efficient  as a function  of Reynolds number  in Figure 4-2,
which can  be used to determine  "ut".  The effect of sur-
rounding drops on the motion of any individual drop is
neglected.
     A number balance on the drops entering and leaving an
element of fluid rd6 long, where r ~ cot 0 (see Figure 4-1),
                                    Lt
b1 thick and of unit width gives:
                  u^b'dc = cutrde                      (4-5)
where   c  » number concentration, #/cm3
For the boundary conditions c » c  (initial concentration)
at 6 *» 0 and c e c at 9  = 2n0 (where n B number of rows),
Equation (4-4)  can be integrated to yield:
       S- = Pt = exp  --J ±gji  - exp  -ji jSgjj    C4-6J
        Ob                b
where Pt = penetration
     Figure 4-3 shows penetration versus gas velocity for
n = 6 with "9" and "d " as parameters.  For a single baffle
angle penetration is predicted to increase as the drop dia-
meter is lowered.  Increasing the angle should result in
decreased penetration for a particular drop diameter.  In
all cases increasing gas velocity is expected to lower the
penetration.  The effect becomes more pronounced as "9" and
"d " are increased.
     If drop mixing is neglected, penetration can be
expressed as:            u
                Pt - 1 - —   nw9-                   (4-7)
                Ft   L   UG b tane                   ^ /J

A comparison of the theoretical primary efficiency curves
is presented in Figure 4-4.  The model based on mixing gives
                            4-4

-------
     10,00
 o
h
  w
  (D
 •H
  o
  (1)
  (U
  O
  o
  03

  FH

 P
       0.001
              0,01
                                                D  vp

                         Reynolds number (N,,  =-2—1
                                             <->n   y  J
                       Re
       Figure  4- 2  -
Drag coefficient versus Reynolds  number after

Foust et al  (1959), with sphericity

the parameter.
                                                             as
                                  4-5

-------
Z
O
h-1
H


H
w
PL,
                         = 30°   d, = 30 ym——i-
                  3.0       4.2       5.4

                     VELOCITY,  m/sec
    Figure 4-3  - Penetration versus  gas  velocity
                 for baffle section.
                        4-6

-------
u
Z
W
hH
U
2
O
I-H
s
1-J
O
§
Q
    100
     80
     60
     40
     20
                                               30 urn  ortri

                                               20 ym
                                     45°, dd = 10 urn
        1.8
2.4       3.0       3.6       4.2

       GAS VELOCITY,  m/sec
4.8:
  Figure  4-4  -  Comparison  of primary efficiency curves
               based  on theoretical  model for complete
               mixing (	)  and for  no mixing C	)  models
                       4-7

-------
an asymptotic increase to 100% efficiency as gas velocity
is increased, while the model based on no mixing predicts
a linear increase.  However, experimental values of primary
efficiency in entrainment separators do not show a linear
increase with increasing gas velocity.  Hence the model
based on mixing is considered more valid.
     This model was developed for a continuous baffle
system.  If the baffles are discontinuous and staggered,
the efficiency will be higher than that predicted from the
present model.
Pressure Drop
     Determination of the pressure drop is based on the
drag coefficient, "fD", for a single plate held at an
angle "6" to the flow as presented in Figure 4-5 (Page
and Johanson, 1927).  Neglecting the effect of neighboring
plates, pressure drop may be expressed as:
                      n       u'2
                 AP ^Z £D pG -|-                    (4-8)

where the summation is made over the number of rows of
baffles.
     The actual gas velocity,"uA", in the baffle section
should be used in Equation (4-8).  Note that the angle of
incidence for the second and subsequent rows of baffles
will be twice the angle of incidence for the baffles in
the first row.
Reentrainment
     The following sections are devoted to a theoretical
development of equations describing the conditions necessary
for the occurrence of reentrainment in baffle-type entrain-
ment separators.  The first section deals with reentrainment
                             4-8

-------
    1.2F
    0.8
M-l
U
i— i
IX,
PH
            Plate Inclined  to  Flow
            : : . r ::: I . : ri
     0
       0
20        40         60

  ANGLE OF INCIDENCE
80
    Figure 4-5 - Drag coefficients for flow past
                 inclined flat plates (data from
                 A. Page $ F. C. Johansen, (1927)
                    4-9

-------
 in  horizontal  baffles,  and  the  second with  the  same
 phenomenon  in  vertical  baffles.
      The  significant  difference between vertical and
 horizontal  baffles  is that  in horizontal baffles:
      1.   Prior to the onset  of  reentrainment  conditions,
          liquid flows on both sides of the  baffles.
      2.   The wetted perimeter for gravity flow  is in
          proportion to  the  length of the baffle.
      3.   Depending  upon baffle  angle to vertical, only
          the "g  cos 6"  component of "g" is  available for
          flow  due to the gravity.
      4.   All the liquid has  to flow through the bottom
          row of baffles.
      5.   The drag force due  to gas velocity and the
          force  due  to the gravity are acting  in opposite
          directions.
Whereas in  the vertical baffles:
      1.   Liquid flows on only one side of the baffle.
      2.   The wetted perimeter for gravity flow is pro-
          portional  to the width of the baffle.
      3.   Gravity is acting in the optimum direction for
          liquid collection.
      4.   Liquid can be  collected on each baffle.
      5.   The drag force due to gas velocity and the
          force due to gravity are acting at right angles.
      The  effects of corners, capillaries and film detach-
ment have not been accounted for.   Thus, it is possible
for reentrainment to occur before the conditions the model
predicts.   Nevertheless, the model can be used to determine
the upper limit of operating conditions.
                             4-10

-------
 Horizontal Baffles - The goal of this section is to derive
 a relationship which gives the theoretical maximum liquid
 load, "QT/QQ", at a given air velocity, "UG", with no re-
 entrainment.  The gas flow rate, "QG", can be expressed as:
                        A      cm3/sec               (4-9)

 where   a - baffle length, cm
 The liquid flow rate, "QL", cm3/sec, is made up of flow due
 to drag force between the gas and the liquid film and flow
 due to gravity.  The derivation of MQL" which follows,
 results in a system of six equations in nine variables.  At
 that point two additional equations will be  formulated in
 order to determine the desired relationship.   For certain
 selected values of "UG",  the maximum "QL/QG" cai* then be
 found.   A diagram of the  results  is presented.
 Derivation of Q.  - The following  assumptions  are made in
 considering liquid flow in horizontal  baffles:
      1.   Prior to liquid  reentrainment,  circulation  of
          the liquid on the baffles  takes  place,  i.e.,
          both sides of the baffle  are  wet.
      2.   Interfacial  stress  is  the  same  on both  sides  of
          the  baffle,  i.e.,  film thickness is  the same  on
          both sides  of the baffle.
      3.   Film flow takes  place  on the  baffle.
      The  derivation begins by considering the forces  acting
on a  liquid  film  of thickness, "6",  as  shown in Figure  4-6 54-7.
A force balance on  the  liquid film bounded by the planes
at a  distance, "6" and  "Y", frtfm the baffle surface gives:
           (6-Y) dzprgcos9 + (P +
                    L             az
                                    •*• P(6-Y)£      (4-10)
                         4-11

-------
Figure 4-6 -
Forces on an element of
liquid film on baffle
                                                    S
                                                  cosG
                          u,
Figure 4-7 -
Effect of baffle edges
on reentrainment
                 4-12

-------
                                  2
where    T  =  shear stress,  dyne/cm
         Y  =  distance  from  baffle  to  any point  in the
             liquid film, cm
                                       cm
         g  -  acceleration of  gravity,
                                      sec2
         P  = pressure,  dyne/cm2
       T.  = interfacial  shear stress,  dyne/cm2

Equation (4-10)  can be rearranged  to:
                                     dp
            T -  T. -  (6-Y)(pLgcose  + 2|.)            (4-11)

A force balance  on the gas core gives:

             2T-A - -(b'-2<5)£ ||                    (4-12)

For laminar flow in the  liquid layer:

                T = -U ~                           (4-13)

     Substitute the value of "TJ" from Equation  (4-12) and
the value of "T" from Equation (4-13) into Equation (4-11)
and rearrange to yield:
   du =                + (6.y)(p gcose +   ,  dY    (4
        V   L  2.   dz          L        dz J
     Integrate over the limits  0  to "u" and  0  to "Y"
(no slip flow) to obtain the velocity profile:
    u .
                         4-13

-------
      "QL"  can  now  be  determined by substitution into  its
defining equation:
                           6
                   QT  =  2y*u£dY                   (4-16)
which results  in:

                                 (pL,co,e*«)]   C4-17)
     Neglect  the  term  containing  "63-7=-"  as  compared to
                                     dz
"62__"  (to check:  effect  of  neglecting  = ,(,..   If
   dz                                     D / i
6 - 0.1 cm and b'  =  5  cm,  effect  =  °'1 x 2  <  2%)  to obtain:
                                     D X  «J
     Equation  (4-18) expresses  the  liquid  flow  rate  as  the
sum of its pressure gradient  and gravity components. How-
ever, it is valid only for laminar  flow.   Sherwood and
Pigford (1952) and Grimley (1948) give  the following
conditions for determining the  flow regime:
     Laminar flow without rippling,  NRg ^  <  4 to  25
     Laminar flow with rippling, 4  to 25 <  Np
-------
                                                      C4-19)
 Therefore,  the expression for total  liquid  flow rate with

 rippling is:
 Additional  Equations  -  Having  derived an equation for "QT",

 we  now have two  equations,  (4-9) and (4-20), in five un-

 knowns,  "QL",  "Q ", "UG", "6", and lldZ".  To narrow the
                                    CLZ

 gap, we  return to Equation  (4-12):
                   (b'-26) dP _   b'dP
            Ti  =  -— 2    ar- "2 ar
if 6 B o at the gas-liquid interface.  By Equation (4-39):
Substitute (4-22) into (4-21) and solve for — :
                                            dz
         d7 = " ST £i UG2 " "  b cos 6               C4-23)
where   b = b' cos 6 and UG • UQ cos 0.


     Equation (4-23) introduces a sixth  unknown,  "£.",' the

interfacial friction factor.   Equation (3-38)  states:
         fi  =  £G  +  1'5   hr-"fc"Tv/*7l           C4-24)
                          4-15

-------
     The two new quantities which appear in Equation (4-24) ,
"NR  p" and "f /-.", can be related by commonly available
graphs correlating them.  "NRe p" can be expressed as:
                      d   u' pr   2b ur pr
              NRe G =   q u     -- iT— -           (4'25)
               KC , ij       y ^         y G
     At this point we have six equations in eight unknowns,
and we need an expression for 6.  The pressure on the
liquid film due to gas velocity, assuming a drag coefficient
of 1 , is :
                       P  = !££                   (4.26)
where P,  = pressure due to gas velocity, dyne/cm2
      ur  = reentrainment velocity, cm/sec
     Since gas is flowing on both sides of the baffles, a
force balance on the liquid film yields:
or
                    U2  5 <* 2q cos e                 (4-28)
                     Gc        pp

     Now we have seven equations  (4-19, 4-20, 4-23, 4-24,
4-25, 4-28) and the correlation between "NRe G" and "£G" in
nine unknowns  (QL, QG, UG, 
-------
    10
Of
~*x
 J
Of
 •V

Q
D
C/

                           9=30°=Ba££le Angl
    10
6.0       7.2       8.4       9.6

        GAS VELOCITY,   m/sec
                                                10.8
   Figure 4-8   Maximum  liquid  load,  QL/QG versus

                gas velocity  in horizontal baffle

                section.
                  4-17

-------
liquid flow on the baffles,  "Qi11* will be derived.  Combined
with other equations, we will be able to construct a diagram
for theoretical reentrainment.
Liquid Flow Due to Pressure  Gradient - The following assump-
tions are made in the derivation of "Q, " :
     1.  Reentrainment takes place only on the edges of
         the baffles.
     2.  Film flow takes place on the baffle surface.
     3.  Liquid collected per unit area of the baffle
         surface is the same everywhere on a given baffle.
     4.  Laminar flow with rippling is present everywhere
         on the baffle.
     Consider Figures 4-6 and 4-7, which show a portion of
the baffle with liquid film  thickness, "6".  A force balance
on the film bounded by planes at a distance "<$" and "Y" from
the baffle surface gives:
                                      +  P(5-Y)£        (4-29)
which can be rearranged  to :
                    T =  T. -  (6-Y) jjZ                (4-30)

Assume laminar flow:
                        T " -Pay                      (4-31).
Substitute and rearrange:

               du - -  [>Ti  - ^-Y)ar]dY             (4-32)
A force balance on the gas core gives:
                2TiA£ «  - (b'-26)AAdT|                (4-33)
Substitute the value of TJ from Equation (4-21) into
Equation (4-32) :
           du .               +  (,-«     dV          (4-34)
                             4-18

-------
 Integrate over limits "u" from 0 to "u" and "Y" from 0 to
 "Y" (no slip flow) :

              1   b        dP
          u .            y    . (4Y .   j           C4.3S,

 The volumetric flow rate of liquid is:

                    QL "  i"6 u AA dY                 (4-36)

 where the integrand must be a small section of the baffle
 length,  "AA", rather than the entire length "A".  Inte-
 gration  yields:

                                                    (4-S7)

 If  the term containing  "63-— " is neglected compared to "6
                           dz                               dz

                      0   _ AA b'62  dP
                      QL  ' vT T— 37               04-38}

                          dP
 Substitute  the value  of  "-gg"  from  Equation (4-23)  to  obtain
 the liquid  flow rate  in  the horizontal  direction:

                                                    C4-39)
Liquid Flow Due to Gravity - As in horizontal flow  a section
of the baffle must be considered, rather than the entire
baffle.  Ripple flow on a vertical surface of width "Aw" is
of the same form as Equation (4-19):
                                                   <4-40>
                          4-19

-------
The differences  in Equation  (4-40) from Equation  (4-19) are
caused by flow on only one side of the baffle and 6=0 for
vertical flow, making cos 0-1.
     The total flow rate is  the sum of the individual flow
rates.
Additional Equations - Equations for "6" and "f." have been
detailed in the  derivation for horizontal baffles.  The
expressions to be used for this case are identical.
     In order to solve the system of equations for vertical
baffles, a stepwise calculation on a digital computer must
be carried out.  In this instance, intervals of Aw = w, w/2,
w/3 and w/4 were used with AA = A, A/2, A/3, A/4, respec-
tively.  In the present calculations reentrainment was
determined using Aw = w/4 and AA = A/4.
     Figures 4-9 and 4-10 show the results of these calcula-
tions, with gas velocity as  the parameter.  Both give re-
entrainment as a function of liquid loading.  Figure 4-9
utilizes a baffle angle of 30°, while for Figure 4-10, 9 - 45°
     A comparison of the two figures shows that reentrainment
is higher and starts at lower superficial gas velocities for
6 = 45°.  This is due to the fact that at the same super-
ficial velocity, the actual  velocity in the baffle section
with 9 = 45° is higher than  the actual velocity in the
baffle section with 9 = 30°.

CYCLONE
Primary Efficiency
     The following derivation gives primary efficiency of a
cyclone as a function of the average residence time of a
drop in the cyclone.  The derivation is based on the fol-
lowing assumptions:
     1.  Drop motion is not  influenced by neighboring drops.
     2.  There is no coalescence of liquid drops in the gas
         phase.
                            4-20

-------
    3x10
CX
 w
cx
E-
h-l
X


2:


H
H
2
W
W
oi
                                                                         :m/sec
    2x10
    1x10
                 Zigzag  bafEle

                    0  =  30°
                                                 j^ Jr My^l  :y^T	1
                                                 ?!>r:-w*«f-d>^ru:
        Figure 4-9  -
      IxlO'3               2xlO~3


       QL/QG COLLECTED  ON  BAFFLE, m3/m3



Predicted effect  of liquid loading in  inlet  on
reentrainment  from vertical baffles.   Gas
velocity is  the parameter.
                                                                     3x10-
                               4-21

-------
3x10-
            Zigzag Battle

               9 = 45°
                                                                    sec
                                                       iHTiilH^l^ 4.2
                        lxlQ-3             2xlO'3

                     QL/QG COLLECTED ON BAFFLE, m3/m:
3xlO'3
     Figure  4-10 -  Predicted effect of liquid loading in inlet on
                   reentrainment from vertical baffles.   Gas
                   velocity is the parameter.
                                  4-22

-------
      3.  The radial velocity of the gas is zero.
      4.  The tangential velocity component of the drop is
          the same as that of the gas stream, i.e., there
          is no slip in the tangential direction between
          the drops and the gas.
      5.  The tangential velocity component is related to
          the radial position by  a modified form of the
          equation for a free vortex in an ideal fluid.

                      u.   rn = constant               (4-41)

      where  u   =  tangential gas  velocity,  cm/sec
            r   -  radius,  cm
            n   =  vortex  exponent,  defined  by Equation (3-5).
      6.   The drag force,  turbulent mixing,  and  drop
          bouncing or reentrainment are sufficiently
          prevalent to  insure  that  a uniform concentration
          of uncollected  drops  is maintained in  the gas
          flowing  through  any  horizontal  cross-section of
          a  cyclone,  i.e.,  that back-mixing  is complete.
      7.   Reentrainment takes  place  only  in  the  cylindrical
          part of  the cyclone.
      8.   The  gas  velocity  near the  vortex wall  inside  the
          cyclone  is  equal  to  the gas velocity in the
          cyclone  inlet.
      9.   The  gas  enters the exit core  (below the cyclone
          exit) only  in the  conical  portion  of the cyclone.
A force balance on a drop  in the cyclone yields:

         dr^lSudr     9   ,n    1       .       'f A
                           4-23

-------
 From  Equation  (4-41) :
                                 d \n
                    Utg r  • ui Vr                  (4"43)
where   u, =  cyclone  inlet velocity,  cm/sec
        d  =  cyclone  diameter,  cm

     Neglecting the second order differential  from Equation
(4-42)  and combining  Equations  (4-42)  and  (4-43):

     If the drop just reaches the cyclone wall  in time "At",
then r = d /2 and from integration of Equation  (4-44):
                d
At = ,..??.  f,,.. "j  1  1 - /|I
                                          2n+2
                                                     (4-45)
     Consider a horizontal cross-section of a cyclone, as
shown in Figure 4-11.  In time "dt", all drops a distance
"dr" or less from the cyclone wall will move to the wall
and be collected.  Meanwhile the drops will travel a distance
"rde" tangentially and "dh" vertically.  The number of drops
removed, "dn.", will be:


                                                    C4-46)
where   c = number concentraion of drops, #/cm3
     The total number concentration of drops in the sector
from which drops are removed is:

                      ni = nr dc c dh               (4-47)
                            4-24

-------
Figure 4-11 - Cross section of a cyclone.
            4-25

-------
The  fraction of drops  removed  in  time  "dt"  is  therefore:
                 dn,
                  ni
              d  dr  - dr'
               c
                  4dr
(4-48)
neglecting the second order differential.
     In order to relate the fraction of  drops  collected  to
the average residence time, it  is necessary  to express
Equation  (4-48) in terms of time.  This  may  be done  through
Equation  (4-44) :
  dr
  ar
             2d
2 dc
  T"
                                      2x1+2)
                                                (4-49)
Combining Equations  (4-48) and  (4-49) :
     i+l
  /
                 At
  ni
dn,
 n.
                                        Can+!
                                 dt  (4-50)
Integrating up to the average residence time "t" we obtain
the equation for primary collection efficiency:
                      - 2
                             (n+l)At
                                                         (4-51)
Reentrainment
Onset of Reentrainment - There is great disagreement among
results for the onset of reentrainment obtained by different
investigators.  This is indicative of the problem of defining
                             4-26

-------
 the onset of reentrainment .   Zhivaikin's (1962) equations
 will be used here for the onset of reentrainment:
         r>   ooo\t""0«75    4 £  XT     ..0.085
         P = 29'2 NRe,L     lf  NRe,L * "T         (4-52)
         p . 10OV
                 L                        e>L
                                 VL               L
         P = 43.2 VT 1>25        ND  .  > 2JL1
                   L             Re,L  -  VL           (4-54)
 where  P = -2-                                       (4-55)
      It is assumed that reentrainment does not take place
 if  the onset  of reentrainment conditions  are  not met.   The
 liquid Reynolds number used to determine  onset of reentrain-
 ment  is based on the  liquid flowing  in the film.  It is
 assumed that  the diameter  of the  inner core of the vortex
 is  the same as  the diameter of the exit pipe,  d .   Thus,  the
 hydraulic diameter is (d -  d ).
                        G     &
 Drop Diameter of Reentrainment -  The  drop  diameter of  the
 reentrained liquid has  a size distribution which varies
with gas  flow rate, liquid  flow rate,  fluid properties  and
perhaps pipe  diameter.  The  average drop diameter  decreases
with increase in gas flow rate.   On the other  hand,  the
liquid  flow rate  has only a  weak  and  ambiguous  effect.
When the  gas  velocity exceeds  6,000 cm/sec, high liquid
flow rate has no  effect on  the drop size distribution.
Rate of Reentrainment - It  is believed  that reentrainment
takes place due  to penetration of liquid waves  into  the
turbulent zone of  the gas.    The amplitude  of the waves
increases exponentially with  liquid flow rate.   Therefore,
reentrainment is  assumed to  take place  in  proportion to
exp(Kn  NT,  T)  where "K, " is  a constant,
     J.  K6 , L          -L                                    .
                         4-27

-------
     The rate of reentrainment depends upon gas flow rate,
liquid flow rate and fluid properties.  According to Anderson
et al. (1964), the rate of reentrainment is approximately 41
for NR  , > 2,750 and is seen to increase slightly with
NT?O r (3.5% for NDo r = 3 x 10", 41 for N~  r - 1.6 x 105) .
 Re, G v          Re,G          f         Re,G            '
Below NR  L = 2,750, the only data available are for
NR  ,  = 1,150, at which point reentrainment is 0.5%.

Reentrainment Calculation - In order to determine reentrain-
ment in a cyclone, a stepwise calculation was carried out
with the aid of a digital computer.  Each step represented
30 cm of gas travel.  The primary collection efficiency,
reentrainment velocity, reentrainment and secondary col-
lection were calculated, and a material balance was carried
out at the end of each step.  Some of the results appear in
the following four figures.
     Figure 4-12 shows the predicted reentrainment from a
cyclone as a function of gas velocity with inlet drop dia-
meter as the parameter.  Reentrainment is seen to be insensi-
tive to drop diameter at velocities greater than about 37.5
m/sec.
     Figure 4-13 gives the theoretical reentrainment as a
function of liquid loading.  A gas velocity of 30 m/sec and
an inlet drop diameter of 50 ym was used to plot this curve.
As expected, increased liquid loading should increase the
reentrainment under the stated conditions.
     Figure 4-14 is a comparison of the primary and overall
efficiencies of a cyclone.  The effect of the drop size
distribution is seen to be small.  The overall efficiency
curves are obtained by subtracting reentrainment from the
primary efficiency curve.
                           4-28

-------
x
w
H
Z
W
    3x10-"
    2x10
    IxlO'"
                   y'lBi
            ~ : ^-t-j                             h - f - • , ^
            TI^Liquid load  concentration  in T
             Tinlet = QL/QG  -  1.33  l/

                                     '
               (10  gal/1,000  cu.ft.)

                                                      . L...
                            8^T  id,  (drop diameter of
                           *^T~      inlet entrainment)
        150 ym
        100 ym
         50 ym
                             LiZiE
" * J
n
n

n-


n
i


— -— '

^
t
i

j

.
;

i
. - . ' i
I/.: ._•::._
1
t


. ! .
,
— :

.



	 rrr-
•
• Ti




-•—

.- . „



' ' '
I







	



r—

            15   20
                    INLET GAS VELOCITY,   m/sec
       Figure 4-12 -
Predicted effect of inlet gas ^velocity
on reentrainment in cyclone with
a=9.2 cm, b=28 cm, dc=127 cm, hg=132 cm,
and d =67 cm.
     e
                         4-29

-------
    4x10"'
m
 s
ry
 W
cr
g   2x10-"
H
2:

S
                              T
              Drop diameter  in  the  inlet
              entrainment  =  50  ym
                 I
                                                  I
               IxlO'3

QT/Qr IN THE INLET,  m3/m3
 Ju  Li
                                                2xlO'3
            Figure 4- 13 - Predicted effect of liquid
                          loading in inlet on
                          reentrainment  in cyclone
                          with a=9.2 cm, b=28 cm, d =127  cm,
                          h =132 cm and  d =67cm.
                           3             ^
                               4-30

-------
   100
   50
1
    0
      15
             Primary efficiency (no reentrainment)
Overall efficiency (with reentrainment)
Reentrainment drop diameter = 200 ym
Reentrainment drop diameter - 125 ym, 250 jam'
       (50% each)
Drop diameter in inlet gas = 50 ym
Liquid load in inlet gas, QL/QG - 1.33x10~3
             30
45
60
                           INLET  GAS  VELOCITY,   m/sec
     Figure 4-14 -  Predicted effect  of inlet  gas velocity
                   on efficiency  of  cyclone with a=9.2  cm,
                   b=28 cm,  d =127 cm, h =132 cm and
                   de=67 cm. c          s
                               4-31

-------
     Figure 4-15 gives the predicted efficiency for an
efficient or long cyclone.  A height of 381 cm for the
cylindrical part of the cyclone is used instead of 127 cm
as in Figure 4-14.  Reentrainment is predicted to cause
a sharper drop in the overall efficiency for the longer
cyclone, despite the fact that overall efficiency is
higher.
                             4-32

-------
    100
w
CJ
                         Primary  efficiency  (no reentrainment)
         Overall  efficiency
         (with  reentrainment)
 Inlet liquid load =  Q /Q
                      L  G
                          30                   45

                  INLET GAS VELOCITY,  m/sec
Figure 4-15 -
                      Predicted collection efficiency with and
                      without reentrainment.for cyclone with
                      ?;2'3 C^      Cm' dc=127 cm» ^,,=381 cm,
                      and d =67 cm.       c          s
                           w

-------
4-34

-------
                  AUXILIARY EXPERIMENT

      As  discussed in Chapter 3,  the  first  mechanism  for
 reentrainment,  i.e.  transition from  separated  to  separated-
 entrained flow  caused by high gas  velocity,  represents
 the  theoretical upper limit of entrainment separator
 operation.   However,  in  actual practice  reentrainment
 takes  place  at  much  lower velocities  due to  the fact that
 gas  and  liquid  do not flow in a  simple geometry as in
 annular  flow.   For instance,  jets  of  the gas stream  may
 strike the water film at an angle, resulting in entrained
 droplets.
      In  view of our  need for  additional  information, a
 small  scale  experiment was  carried out to  make visual
 observations of the  transition from separated  flow to
 separated-entrained  flow,  including the  following:
     A.   Observe  the  effect of duct dimensions.
     B.   Study  entrainment velocities as a function  of the
          liquid flow  rate.
     C.   Study  drop  size  distribution created by the above
          transition.
     D.   Study  the effect of  impingement angle between
          air and water phase  on entrainment velocities.
     For  design purposes  it is necessary to know the effect
of duct dimensions and liquid  flow rate on the transition
from separated  to entrained flow.  The drop size created
by reentrainment will govern  the efficiency of separation
                             ff
of any later stages.   For example, a series of two entrain-
ment separators can be used so that the first stage acts as
a high-velocity coalescer, while the second is a low-velocity,
efficient separator.   Thus, the drop size of the reentrainment
in the first separator will play an important role in the
overall efficiency.
     Cousins and Hewitt  (1968) and Wicks  and Dukler (1966)

                         5-1

-------
studied the drop size distribution obtained  in the separated-
entrained flow.  Chien and  Ibele  (1962), Steen and Wallis
(1964) and Zhivaikin (1962) studied the onset of entrainment
in separated flow.  Most of this work was done on small
diameter tubes and there are some differences in the results,
Thus, it is necessary to check their results and obtain
further information for design of entrainment separators.
No work has been reported on the effect of impingement
angle.
     Figure 5-1 shows the apparatus used to study two-phase
flow.  It consisted of an open channel 6.5 cm wide and
inclined at 30° from the horizontal connected to an over-
flow tank at the top and a collection funnel at the bottom.
The channel was 77 cm long and made of aluminum.  Air was
blown through a nozzle 5.4 cm x 1.9 cm directly on the water
film in the channel at various angles from 0° (parallel to
water flow) to 40°.  A pitot tube connected to an inclined
manometer was used to measure air velocity.
     The liquid was introduced into the channel from the
overflow tank.  Air was introduced with the air inlet
nozzle positioned slightly above the liquid film so as
not to disturb it.  Visual observation and a technique
utilizing chemically treated filter paper were used to
determine the transition from separated to separated-
entrained flow.

SAMPLING FOR DROPLET SIZE DISTRIBUTION
     Due to its simplicity, the chemically treated filter
paper technique was used to obtain drop size distribution
of the entrainment.  The method is described by Chilton
(1952) and utilizes Whatman filter paper #1 treated with
alkali fast green for sampling.  The blot diameter is
                           5-2

-------
en
t
Pitot
Tube
      Blowe
                                                           Air Nozzle
                                                                  Open Channel
                         Figure  5-1  - Apparatus  to study  onset of entrainment velocities

-------
usually larger than  the drop  diameter  due  to  expansion,  and
the correlation between the diameters  is given by  Chilton.
It has been determined that there  is no effect of  using
different chemicals,except that chemicals  affecting  surface
tension will have a  different  correlation.
     Some errors in  the sampling of drop diameters by
filter paper are discussed below:
     (1)  If the concentration of  the  blots on the filter
paper is high, a few of the blots  will overlap.  A correct!0"
is necessary if the  area occupied  by the blots exceeds 10$
of the area of the filter paper.
     During the sampling,  drops  spread in  the filter paper.
It is assumed that the blots  in the filter paper all have
thickness "t^" which is independent of the blot size in  the
range of diameters measured on filter  paper.  Then, by
material balance:
                    7r^2i--7r^3                 re -n
                    T db tl " 6" dp                C5'1)
where, t,  = blot thickness, cm
       d,  = blot diameter, cm, if  blots do not overlap
                      :. d a db2/3                   (5-2)
     The 2/3 slope in the correlation between blot diameter
and drop diameter by Chilton  (1952) confirms Equation (5-2)-
Thus, even if the drops overlap, the area occupied by the
blots on the filter paper will be  the  same.
     Sauter (1952)  showed by statistical analysis that if
drops in air are projected onto a  plane, the measured
value of the fractional area occupied by the shadows, "A1",
is related to the actual value of  fractional area, "A", by:

                     A = -ln(l-A')                 (5-3)
                          5-4

-------
where   A =  the  fractional  area  of  the  shadows  if  the  drops
do  not  overlap.   Thus,  in  the present  case:
                        A a Nd£2                    (5-4)
          and            A'  a N'd£2                  (5-5)
where   N' = number  of blots in  a given area
        N = number  of blots in  a given area  if blots  do
            not  overlap.
        d/ = measured blot  diameter, cm
         b
                      - N  = N'jL                   (5-6)

                        N  - N' (rAnr)             (5-7)
Since, Ndb2 = N'd^2:                               (5-8)
                    db = diJ±-T-                C5-9)
     This is the average correction and should be  applied
to the mean diameter of the blots.
     The fractional area can be obtained by simply measuring
the blot diameters in a unit area and using the following
relationship:
                    A = I I N' d,;2                 (5-10)
     (2) While measuring the blot diameters, care should be
taken not to repeat or leave out some blots.  This error
possibility may be reduced by using the same technique used
to count blood cells.
     (3) The capture efficiency of the filter paper is
not 100%.  A correction is necessary to obtain the actual
size distribution.
                         5-5

-------
      To  determine  the  error  in  the  sampling,  Figure  5-2 was
constructed.  Drop  collection efficiency  of a  filter paper
is plotted against  drop diameter, with gas velocity  as
a parameter.  Drop  collection efficiency  was obtained from
the correlation between impaction efficiency and  inertial
parameter by Golovin and Putnam  (1962).   The adhesion of
the particle to the collector is assumed  to be 1001  in
this  case.  As seen in Figure 5-2,  the error  in measuring
drop  size distribution at the gas velocities and  drop
diameters used for  these experiments  is quite  small.
DISCUSSION
      The liquid film was about 1-3 mm thick and was
quite smooth, with no  pulsation except when the entrainmen*
velocity was approached.  The liquid  film thickness was
constant in the bottom of the channel in  the absence of the
air flow.  With air flowing, the liquid film thickness in
the corners of the channel was higher than in  the center of
the channel.  This  increase  in the flow rate of the liquid
in the corners increases with increase in the  total liquid
flow  rate.
      The liquid film thickness at the point of air impinge^6
was much smaller than  the thickness upstream from that p
(for  impingement angle >0°).  At a certain distance
downstream from the point of air impingement, the liquid
film  regained its former thickness.  Entrainment was
observed to take place near the downstream spot where the
liquid film rose.
      The air velocity measured is the actual air velocity
and should be distinguished from the superficial air
velocity used by other investigators.  If the liquid film
1-3 mm thick and the tube diameter 2.5 cm, the difference
between actual and superficial velocities may be 10 to 40$
                          5-6

-------
              100
           0\°
           v—'


           u

           w
           t-H
           U
           I—I


           w


           o
           U
           W
           O
           U
          O
          rt
          Q
                                          100
                      DROP WAMETER, urn
Figure 5-2 - Predicted effect of drop diameter on
             capture efficiency by 5 cm diameter
             filter paper held perpendicular to
             the air velocity.
                     5-7

-------
RESULTS
     Figure 5-3 shows the drop size distribution in the
separated-entrained flow.  The drop size distribution was
measured by increasing the air velocity to the point where
measurable entrainment was first observed on the coated
filter paper.  There is no significant effect of different
flow rates on the drop size distribution.  The average drop
diameter is about 250 ym.  The distribution of the drop
sizes is such that the majority of the drops are small, but
these contribute relatively little to the total volumetric
drop flow.
     Figure 5-4 represents, on a log-probability diagram,
the same size distribution as shown in Figure 5-3.  It is
log normal with mass median drop diameter of 250 urn and
geometric standard deviation of 1.5.
     A comparison of drop size distributions obtained by
various investigators with the present results is shown in
Figure 5-5.  The data of Cousins and Hewitt (1968) were
obtained during experiments on the mass transfer of liquid
droplets subsequent to the removal of the liquid film.
Photographs of the droplets were obtained for a zone imme-
diately adjacent to the channel wall, and the images on the
photographs were measured to produce drop size data.
     The Wicks and Dukler (1966) data were obtained by a
technique using variable spaced needles.  The liquid was
injected using a porous wall section.  These data should be
treated with some reservations, since the reliability of the
method of measurement is still uncertain.   Figure 5-5 shows
that all the distributions are similar in form with slight
variation from present results near the end of the curve.
     In the present runs the effect of gas velocity on the
drop size distribution was found to be negligible.  However,
the data of other investigators, as shown in Figure 5-5,
                              5-8

-------
       0
100
                       VOLUME PERCENT OVERSIZE
Figure 5-3 - Distribution of droplet size in air-water
             entrained-separated flow.
                          5-9

-------
en
i
                1,000
             Pi
             a,
             o
                                 10
20
 30  40  50   60  70   80


VOLUME PERCENT OVERSIZE
                                                                           90
                                          95
98
                    Figure 5-4  -
                                                                  entrained-separated

-------
   2,000
   1,000   -
Es
w
H
W

§
i—*
Q
a,
o
                                       Present Investigation
                                       Data of Cousins and
                                       Hewitt (1968)
                                       Data of Wicks  and
                                       Dukler (1966)
                              Liquid      Pipe
                              Flow        or
                              cm3/sec     Duct
            Air
            Flow
      Curve cm/sec
                                          6.5 cm wide
                                          open channel
                         107-191
                         Range ot |
4,900-8,500
                              flow rates
                                     0.95 cm tube
                                          15.2 Gmx
                                          1.9 cm
                                          vertical
                                          duct
               8,325
               2,345
               3,750
30  -
     20
                    VOLUME PERCENT OVERSIZE
                                                              100
Figure 5-5 - Comparison of drop size by different  investigators
                            5-11

-------
indicate that increasing gas velocity tends to reduce the
mass median diameter.  In the velocity range depicted in
Figure 5-5, the mass median diameter decreases by roughly
40% when the gas velocity is doubled.
     The effect of impingement angle between the gas and
the liquid stream is shown in Figure 5-6.  It shows the
drop diameter versus volume percent oversize in separated-
entrained flow.  Impingement angle is used as a parameter
and was varied for a given water flow rate until entrainment
was detected.  These data were obtained with air velocity
of 38 m/sec through the nozzle outlet, a velocity smaller
than the critical velocity needed for entrainment in
parallel flow.  Thus, the effect of impingement angle O0°)
is a reduction in entrainment velocity.  From Figure 5-6 a
slight effect of impingement angle on the drop size dis-
tribution is seen.
     The effect of liquid flow rate on the impingement angle
needed to produce entrainment is shown in Figure 5-7.  Air
velocity was 38.8 m/sec during these runs.  The effect of
increasing the impingement angle is to reduce the liquid
velocity required for entrainment.
     Figure 5-8 compares the results for entrainment velo-
cities obtained by various investigators.  Here UG<, = gas
velocity causing entrainment and the liquid Reynolds number,
"ND  T", is the superficial liquid Reynolds number based on
  K6 , L
the empty cross-section of the duct:
                      %a,L '

where   VL = kinematic viscosity of the liquid, cm2/sec
        d  = duct width, cm
                            5-12

-------
E-H
W
8
Q
    300
                                           dNP_  A
    200 —
    100
     70

     60


     50


     40



     30
    20
   Air  velocity 38.8 m/sec
     Impingement   Water
      Angle       Flow
     degrees     cm3/sec
o
A
D
40

30


17
107

145


191
                          i
                         1
      0
     20        40        60

          VOLUME PERCENT OVERSIZE
                           80
                         100
Figure  5-6  -  Effect of impingement  angle on drop size
                        5-13

-------
PJ
CJ
 20
       Air velocity 38.8 m/sec
 10
1 1 1 1 1 1 1 1
1
   100
               120        140        160

                 LIQUID FLOW RATE,  cm3/sec
180
200
Figure 5-7
                Effect of liquid flow rate on  impingement
                angle for onset of entrapment.
                     5-14

-------
   100
o

-------
The results differ significantly  due  to  the  problem  of
defining the onset of  entrainment.  Zhivaikin  (1962), who
defined the onset of entrainment  as occurring  when it is
first detectable, expressed his results  in terms  of  the
following empirical equations  for the  critical gas velo-
city "UQ " for the onset of entrainment:

     P = 29.2  N-°;[5          if  NRejL<_°i       (5.12)
                    4_l               »      A-.~ , .u    V T
                                   VL              L

     P = 43.2 vi"'.         if  NRe H^-         (S.14)


where   "P"  is defined by:

                        p = l!§c^L                     (5.15)


     Steen and Wallis (1964) defined the onset of entrain-
ment as that air velocity which represents the extrapolation
of the straight line portion of a graph of entrainment per-
centage versus air velocity.  Since the increase in en-
trainment with air velocity is similar to the exponential
function, their results lie considerably above those of
Zhivaikin.  Steen and Wallis also obtained an expression
for "P", when viscous forces in the liquid film can be
ignored, as:

             P = 2.46 x 10-* (yL/uG)(pL/pG)^        (5-16)

     Chien and Ibele (1962) defined the transition on the
basis of pressure drop versus gas flow rate curves.  A
change in the slope of the curve was taken to indicate
the onset of gross entrainment.  Their results apply to
                             5-16

-------
 conditions where a large fraction of the total liquid flow
 is entrained, so their prediction of "UQC" is even higher
 than that of Steen and Wallis.   Chien and Ibele correlated
 their data by the following equation:
where  NR  G   =  gas  phase  Reynolds  number with  UG  = uf

Equation (5-17)  can be  rearranged  as:
              1.2 x  10'
                          o
-0 . 3
             (5-18)
     The present results are comparable with those of Chien
and Ibele.  In this study we defined the onset of entrain-
ment as when the entrained drops made an impression on the
treated filter paper.  The present results may be slightly
higher due to the fact that actual air velocity in the
inlet nozzle rather than the superficial velocity in the
channel was measured.

CONCLUSIONS
     A.  Because our results were comparable with others
         in terms of entrained drop diameter despite
         differences in duct dimensions, it is  concluded
         that  duct  size does not affect the reentrained
         drop  size  distribution.
     B.  Entrainment velocity depends  upon  liquid Reynolds
         number  as  shown  in Figure  5-8.   The Chien and
         Ibele curve is recommended for determining the
         onset of reentrainment.
     C.   Increased  impingement  angles  result in  decreased
         entrainment velocities  as  shown in Figure 5-7.
         Thus, sharp angles  in  the  entrainment separators
         should be  avoided.

                         5-17

-------
5-18

-------
                EXPERIMENTAL PILOT PLANT

      An experimental pilot plant for the study of entrain-
 ment separators was designed and built.  The purpose of the
 pilot plant was to do the following:
      1.  To obtain reliable data over a wide range of
          operating variables to provide a basis for
          improved or new methods
      2.  To check presently available design equations
          for entrainment separators
          A.  Efficiency of separation
          B.  Pressure drop
      3.  To determine the effect of higher  gas  velocity
          on reentrainment, bouncing of  drops and
          impaction mechanism
      4.   To study liquid drainage  and flooding
      5.   To study problems associated with  entrainment
          separators
      6.   To study vertical and  horizontal sections
DESCRIPTION OF  THE PILOT PLANT
      The maximum  capacity of the wet  scrubber entrainment
separator is 85 m3/min  (3,000 CFM).   This capacity was
selected based  on  the following consideration.  The entrain-
ment  separator  cross-section was selected to be 30.5 cm x 61 cm
This  section is sufficiently large  to have minimal wall effects
for separators  and provides a fairly  long (61 cm) collection
element when cross-flow  effects are important.  Normally, the
maximum air velocity in  industrial  separators is around
3.0 m/sec.   If velocities 2,5 times higher are studied, the
maximum air velocity will be 7.5 m/sec.    This will give the
maximum capacity of 85 m3/min.
                          6-1

-------
     A block diagram of the pilot plant is shown in Figure 6-1.
The equipment consists of a filter, blower, heater, spray
sections, observation sections, entrainment separator test
sections, liquid tanks, pumps, etc.  The top view of the pilot
plant is shown in Figure 6-2.  Figure 6-3 shows the connections
between various tanks at the bottom of the platform.
     A description of the equipment in the pilot plant is
given below.
Air Prefilter
     Automotive air filters were used to clean the incoming
air.  The air supply was taken from outside the building and
was connected to a box containing prefilters with a 48 cm
diameter galvanized duct.  The prefilter consisted of 5 filters
in parallel, each having a capacity of 18.5 m3/min.  The
pressure drop at this capacity is 0.25 cm W.C.
Blower
     A Western Blower size 122 Bl and Class III was used.  It
has a capacity rating of 88 m3/min at 30.5 cm W.C.(static
pressure), a 7.5 KW (10 HP) motor, rotatable housing and an
opposed blade discharge damper.  The blower was supported on
a hard rubber base to prevent vibrations, and it had a flex-
ible duct connected at the outlet.  The blower was insulated
with accoustical fiberglass and concrete blocks to reduce
the noise level.
Air Heater
     A gas-fired air heater rated at 30 kcal/hr (120,000
Btu/hr) was used to heat the air.
Spray Section
     The spray section served to humidify the incoming air
stream and to generate entrainment for the test section.  It
                           6-2

-------
ON

OJ
          Air
                                 dry

                                 wet
                                                   i j
                                                    dry
                                                   [•
                                                   wet   -  AP  -    wet
                     B! Obi
                     8. Liquid Catch Tanks
                                                           8
                                                                          •Vent
                        Figure 6-1 - Block diagram  of
experimental apparatus.

-------
Figure 6-2 - Top view of the entrainment separator pilot plant.  All
             dimensions in cm.

-------
i
Ol
             Valves

             Unions

              Vent
              — Flow
FP1

FP2

  U

 P2


 Tl
ATI
AT 2

 T2
-T6
- 110 fc/min
  Pump
- 11 fc/min
  Pump
- Vacuum Pump

- Recycle Pump
           - Feed Tanks
           - Catch  Tanks
                        Figure  6-3  -  Flow diagram showing  connection  between
                                     various  tanks and  pumps.

-------
was equipped with various nozzles  from  Spraying  Systems  Co.
The nozzle  specifications are  given  in  Table  6-1.   In  any
section the nozzles were equispaced  as  shown  in  Figure 6-4
to generate uniform flow.
     The 1/4 M6 nozzle, a single fluid  hollow cone  nozzle
with a 0.105 cm orifice, was operated at  3.4  atm line pressui"6
and produced drops of about 250 ym in diameter,  in  agreement
with the manufacturer's claim.  If operated at 13.6  atm, it
is expected to produce drop diameters ranging from  40 to
100 ym.
     The 1/4 M6SS nozzles were connected  with 1.25  cm iron
pipe.  The remaining nozzles were  connected with 2.5 cm
p.v.c. pipe.  Two spray sections were used in the pilot plant-
The 1/4 M6 nozzles were installed  in the  first spray section,
which had inside dimensions of 30.5 cm  x  61 cm cross-section
and 46 cm length.
     The second spray section, 76  cm in length,  was equipped
with 1/4 M26 nozzles, and arrangement was made to accommodate
any of the remaining nozzles.  There was  considerable reducti0
in the cross-sectional area due to the presence  of 2.5 cm
p.v.c. pipes.  The reduction was compensated  by  enlarging the
cross-section to 46 cm x 61 cm.  Whenever 1/4 M6 nozzles were
used to generate spray,  the second spray  section was replaced
by a blank section having a cross-section 30.5 cm x 61 cm.
     The spray section was equipped with  a drain at the bottom
to catch the liquid collected on the walls of the spray secti°p
Observation Sections
     Two observation sections were used, one at  each end of
the entrainment separator test section.   They had dimensions
of 30.5 cm x 61 cm cross-section and 50 cm length.  Two plexi'
glass windows,  30 cm x 30 cm, were installed on  opposite sides
on each observation section.  A door was provided for sampling
of entrainment  and drop diameters.
                           6-6

-------
Table 6-1.  NOZZLES USED IN  SPRAY SECTION
Type of Nozzle
Hollow cone
Fogjet Nozzle
Full Cone
Hollow Cone
Model #
(Spray Systems)
1/4 M6SS
1-11 1/2 F18
1 1/2-11 1/2
F35
1/8 GG3
1/4 M26
Pressure
atm
13.6
2.7
2.7
2.7
2.7
# of
Nozzles
12
1
1
12
12
Flow rate
cm /sec
nozzle
14.2
1140
2200
63.0
27.2

-------






— c
fl


1
- 7.6 —

rs f
J A,

c





\ ' r
J
f
\.




V
5.3-*
V.
•\
J
f


\
j
•
5.1

fl - - im


f
k




k |
J

")


f]
!
—5.1





*\

— 7.6 —
to
*
CO


1
1
C1
0
a
3
r>
CO

c
a
c
a
c
•
1
r>
• cH
D VO
•^
3
f)
CO
4-
•
CO
1

Figure 6-4 - Nozzle positions in the 30.5cmx61cm
             duct.  All dimensions in cm.
                    6-8

-------
 Drainage of Liquid in the Test Section
      Liquid drainage is important in the design of entrain-
 ment separators.  The original drainage system in the test
 section consisted of 20 equispaced openings, 0.6 cm in
 diameter, per 30 cm length of the test section and a false
 bottom, giving a space of 1.8 cm height, which was filled
 with Raschig Rings.  It was observed that the drainage in
 the test section was  not 100% effective.  The bottom sur-
 face was coated with  hydrophobic resin, and the collected
 liquid had a tendency to flow around the holes and thus
 creep along the length of the test section.
      To solve  this problem the holes were enlarged to
 0.8 cm diameter,  and  the number of holes was increased
 from 20 to  40  per 30  cm length of the test section.   To
 avoid creeping of fluids at  the bottom of the test section,
 notches 0.6 cm wide and 28  cm long (perpendicular  to  the
 air flow direction) were made at  30  cm intervals in  the
 test section bottom.   The  number  of  Raschig  Rings  was
 reduced to  about  1/3 under the false  bottom.   This drainage
 system  was  quite  efficient for low liquid  loads.
      The  theoretical maximum  air  flow (without  Raschig  Rings
 in  the  false bottom) through  the  false  bottom is 21 of  the
 total flow.  The  presence of  liquid and Raschig Rings  in  the
 false bottom should lower this percentage significantly.
 No  reentrainment  from the false bottom  was observed.  At
 higher  liquid  flow rates (57  fc/min and  higher), the liquid
 built up to 3-4 mm in height  for  drainage.  The total
 drainage capacity of the test section was more than 150 Jl/min,
However, most of the liquid was collected in  the first two
 drainage sections of the test section.
     The notch dimensions were increased to 2.5 cm width
since it was observed that a notch is more effective than
a hole in drainage.  This change resulted in efficient
                          6-9

-------
drainage.  In a few runs a problem was observed.  When the
air flow rate is high and the liquid load is small, some
reentrainment is caused from the notch.
Liquid Catch Tanks
     Four 0.2 m3 (55 gal) drums were used as catch tanks.
These were connected to the test section to collect sepa-
rated liquid alont the length of the test section.  One
additional 0.2m3 drum was used to collect liquid from the
bottom of,the spray section.  Each tank was connected to a
water meter and a pump with liquid level controller for re-
circulation of the liquid.
Liquid Supply Tanks
     Three 0.2 m3 (55 gal) drums were used as supply tanks.
These tanks were connected to receive fresh water and re-
circulated water.  On the outlet side were located rotameters
for flow measurement and pumps.
Control Panel for Equipment
     The control panel was equipped with the following:
     1.  Electrical connections
        ,A.  Magnetic starter for 88 m3/min blower
         B.  Switches for pumps, heater, sampling pump,
             observation lights, etc.
         C.  Temperature recorder
     2.  Non-electrical connections
         A.  Rotameters and water meters
         B.  Dry gas meter
         C.  Pressure gauges
         D.  Needle valve, diaphragm valve, globe valves,
             and gate valves
         E.  Manometers to measure pressure drop.
                          6-10

-------
 Electrical Supply Panel
      A 110 V, 3 phase, 100 amp/phase electrical supply panel
 was installed near the equipment site,
 Water Supply
      The maximum fresh water supply was 50 Jt/min (13 gpm) .
      Water supply to fine spray nozzles:
          Piston pump - 1P741 (Grainger catalog)
          Maximum pressure - 34 atm (500 Psi)
          Flow rate at maximum pressure - 11.4 £/min (3 gpm)
          Motor rpm - 1,725
          Motor KW 1.1 (1.5 HP)
      A rotameter with +_ 21 accuracy was used  to measure flow
 rate.   A  needle  valve and auxiliary line near the pump were
 used to control  flow rate. A pressure  gauge  was used  to
 measure static pressure.
     Water  supply  to  coarse spray nozzles:
          Centrifugal  pump - Model 165U  (Barnes  Pump)
          Maximum pressure - 3.4  atm (50  Psi)
          Flow  rate at maximum pressure  -  120  A/min  (31  gpm)
          Motor rpm -  3,450
          Motor KW 1.1 (1.5 HP)
     A  rotameter with +_ 2% accuracy was used  to  measure flow
rate.  A  diaphragm valve  and  auxiliary line near the pump
were used to control  flow  rate,  A pressure gauge was used
to measure pressure.
TEST SECTION
     Five  different types  of entrainment separators  were
studied:
     1. Mesh
     2.  Packed bed
     3.  Zigzag baffles
     4.  Cyclone
     5.  Tube bank

                           6-11

-------
     Entrainment separators 1  through 4 were selected
because they  are the most common separators used in in-
dustry.  The  fifth separator,  the tube bank, was studied
to verify claims that it operates with a low pressure drop,
gives high efficiency, and has a high reentrainment
velocity.
     The design of the test section was kept flexible to
facilitate any changes which may be necessary.  The housings
used for the  mesh, packed bed, zigzag baffles and tube bank
had the same  dimensions, and thus it was a simple matter to
interchange the test sections.
     The test sections were provided with a SO cm x 90 cm
plexiglass window in front and a 25 cm x 90 cm plexiglass
window at the top for observation.  The dimensions of the
test section were 30.5 cm x 61 cm cross-section and 122 cm
in length.  A false bottom was provided along the length of
the test section.  The spacing of 1.9 cm height along the
length of the test section was loosely packed with Raschig
Rings and was divided into four parts to segregate for later
measurement,  the collected liquid along the length of the
test section.  A 5 cm diameter p.v.c. drainage pipe was pro-
vided in each section.  A 30 cm liquid seal was provided in
each catch tank.
     The five entrainment separators are described below.
Mesh
     Model-4CA (ACS Industries)
     Type - layered (with layers crimped in alternate
            directions)
     Density - 0.144 g/cm3
     Wire diameter - 0.028 cm
     Percent voids - 98.2
     Mesh surface area - 2.8 cm2/cm3
     Thickness - 10 cm
                           6-12

-------
       Material of construction -  AISI  304
       Separation efficiency -  Figure 6-5
       Pressure drop  data  -  Figure 6-6
       The  mesh was supported by a grid made from 0.16 cm
       wire with 1,25  cm width  and 2.5 cm height of spacing.
       The  mesh was located  in  the first 30 cm of the test
       section.
 Packed Bed
       Packing  -  2.5 cm pall rings
       Specific  surface - 1.9 cm2/cm3
      Density  -  0.088 g/cm3
      Material of construction - Polypropylene plastic
      Packing was supported by the same grid which  is used
      to support the  mesh.
      Some  experiments were conducted using a  90  cm long bed.
 Later the  bed length was  reduced  to 30  cm.   In both  cases
 the  support  grid at  the upstream  of the packing was  located
 at the beginning of  the test  section.
 Zigzag Baffles
      Baffle  dimension - 7.5 cm width and 61 cm height
                        thickness 0.16 cm
     No. of  rows  - 6
     Spacing between  rows - 2.5 cm
     Angle between baffle and  air flow direction -  30°
     Spacing between baffles in a row - 6.9 cm
     For details see Figure 6-7.
Cyclone
     Diameter - 61 cm
     Overall  height - 244  cm
     Inlet  height -  30.5  cm
     Inlet  width - 15 cm
     Maximum  inlet velocity -  30  cm/sec., higher using an
                              inlet vane
                          6-13

-------
   100
H
U
PH
w
w
H-l
1-5
o
       0
         2.5


GAS VELOCITY, m/sec
5.0
 Figure 6-5  -  Calculated collection efficiency for

               water  droplets  in air.   (ACS Industries)
                           6-14

-------
    100
 •
U
s
U
ex,

«
CO
CO
ex,

                    5     10           50

                  AIR VELOCITY, m/sec
100
 Figure  6-6  -  Pressure drop versus air velocity
              for 10 cm thick ACS style 4CA mesh
              L/A = superficial liquid velocity,
              cm/min (ACS Industries)
                     6-15

-------
               f i
in_L.

OM'i
    \\\
////
  v\ \ M
   i /  /  /
                CM
               i
               in
               o
               m
               t f
        30.5
         air flow
Figure 6-7. Baffle Section. All
   dimensions in cm. Aluminum baffles
   are 0.16 cm thick, 7.5 cm wide, and
   61 cm  long.
       6-16

-------
      For details see Figure 6-8 and Stearman and Williams
      (1971) .
 Tube Bank
      Number of rows - 6
      External diameter - 1.9 cm
      Length - 61 cm
      Number of tubes in a row - 8
      For details see Figure 6-9.
 CALIBRATION
      1.  Thermocouples:   All the thermocouples  were calibrated
 using thermometers.   Ice-water,  boiling water and room temp-
 erature were used.   It  was  found that  thermocouples give  some
 errors  in reading temperatures.
      2.  Liquid  level  in  the tank:   The liquid  level  as a
 function of liquid height in the 0.2m3 drums was  determined
 by measuring the  liquid level  and  the  weight  of the tank.
 The liquid  level  in  the catch  tanks  was controlled within
 5  cm during the  experiment.  Tanks Tj,  T3, T.,  T-,  T,
 contained 2.55 a/cm-of height, and tanks T2,  A^,  AT2
 contained 5.06 £/cm  of height  (see Figure 6-3).
      3.   Water Meters:  Water meter number 1  (on tank T ) was
 calibrated  using  a rotameter and a calibrated 0.2 m3 drum.
 Calibration was done at flow rate intervals of  3.79 £/min
 (1  gpm).
     Water meter Numbers 2 to 6 were connected  to the outlets
 of  catch tanks Numbers 2 to 6.  To calibrate any water meter
 e.g., number 3, the outlet from water meter Number 1 was con-
nected to the inlet of tank 3.  Tank 3 was filled with water
 so that  the liquid level was between an arbitrary upper and
 lower limit.  The pump was kept on to control the liquid level
in tank  3.  The calibration  was done  by comparing the readings
                          6-17

-------
                          I
Figure 6-8  - Cyclone assembly.  All
             dimensions are in cm.
            6-18

-------
                                         in
Ki:
1*3. 8»f3. 8**3. »j*3. 8*3. 8*K3. W«3. 8^
        Di O i Q.  O Q ;  O:OO i
        -
               8>f«3.8>f'3.8>r'3.8n*3.8»|-3.8*r0.8 *•
                                            0.95
                       air flow
Figure 6^-9  - Test  section with bank of tubes,
             All dimensions in cm.
                      6-19

-------
on water meter numbers 1 and 3.  Appropriate correction was
applied for the change in liquid level in tank number 3 and
for the calibration of water meter number 1.  To avoid the
dynamic error, the calibration was done at flow rates of
3.79 Jl/min (1 gpm) intervals,
EXPERIMENTAL PROCEDURE
     The major points of the experimental procedure are
described, below.  The procedure was modified as required for
individual runs.
     1.  All the tanks were emptied before starting the
         experiment in order to avoid rust in the water.
     2.  All the wet bulb thermometers were checked for
         water.
     3.  All the valves were checked so that the required
         valves were kept open and the rest closed.
     4.  All the recycle pumps were kept on to maintain the
         liquid level in the tanks between the upper and
         lower limits.
     5.  All the catch tanks were filled with liquid until
         the level was between the upper and lower controlled
         limits.
     6.  The feed supply tank was filled to the overflow
         line.  Fresh water was continuously added to the
         system during the experiment to supplement the
         water loss in the exit air and to introduce fresh
         water to the system.
     7.  The zero position of the inclined manometer was
         adjusted.
     8.  Readings were noted for all the water meters and
         the liquid levels in the catch tanks.
     9.  The desired air flow was started.
                        6-20

-------
      10.  Pressure drop across the test section was
           measured.
      11.  The desired water flow rate was started.
      12.  About 1-5 minutes were needed to reach steady
           state.  The experiment was continued for 2 hours.
      13.  Air flow rate, water flow rate, etc., were
           checked every few minutes.
      14.  Visual observations of penetration,  flooding,
           liquid drainage,  bouncing of drops,  liquid flow
           on elements of the entrainment separator,  etc.,
           were made for the duration of the  experiment.
      15.  Readings were taken of temperature (each hour),
           entrainment drop  size,  pressure  drop,  entrainment
           loading,  etc.  (once  during each  run).
      16.  At the end  of the experiment,  liquid  and air  flow
           were shut down.   Readings  were noted  for water
           levels in the  tanks  and water  meter readings.
      The blank forms  used for  the experiments are  shown in
Figure  6-10.
SAMPLING PROCEDURE
      Drop  size determination:  The drop  diameter in the
experiments varied between  40  to 2,000 ym.  Chemically  treated
filter papers were used to  determine the drop diameters.  The
grain size of the chemicals normally limits the lower diameter
by this method to 5-10 ym.  Filters coated with the following
chemicals were studied for  drop size measurement.
         Potassium permanganate
         Lissamine green
         Erio green
         1% potassium ferricyanide and ferrous
         ammonium sulfate.
                         6-21

-------
Entrainment Separation Project
Experiment #
Date
Test Section:
Air velocity
Water flow rate
Time on:

Types of nozzles
Water flow =


Thermocouples
Before
°F
After
°C

1









cm/sec
, Pitot tube -
ft/min
gal/min, Water pressure


, Time off:





psi
, Number of nozzles
SJ

\L
in
I 	
2





Total liquid level
After
Before
Net
cc
X

3





min

4



x 3.79xl03
5



i
i

2




6





3




cc
gal
7





4





8




cc
9^

^^
^^
^^^
	 **
5




—^


^^
„
^*t'
Water meter
After
Before
Net
x!03x
cc
Total
1






2






AP = Dry = +0.05 =
APxO.826 =
Abs . Pressure =
Dry

3






cm Wet =
cm,

Wet
4






+ 0.

OS «
5






o
,
^
	


	 „
cm
cm
cm Hg.
Drop diameter in inlet =
Geom. Standard deviation
Water overflowing
mass average
=


1-2


jjm

2-3




3
-4
           Figure 6-10  - Form  for recording test data.
                              6-22

-------
Reentrainment § Penetration


     Approximate drop size  of large  drops  	  mm

     Vertical distance 	cm Horizontal  distance         cm

     Height  of flooded section  	cm

     Reentrainment  present  in observation
     Section  	yes 	no

     Vertical  height  in which reentrainment

     Present  	cm

    No. of seconds sample taken 	
    No. of drops on the filter paper
    Isokinetic sample taken 	yes 	no

    Drop diameter	_ave.  (mass)

    Geometric Standard Deviation

    COMMENTS:
                     Figure 6-10 -  continued.
                           6-23

-------
     Individual drops were most easily seen when 1% potassium
ferricyanide and ferrous ammonium sulfate were used as the
coating.  A correlation given by Chilton (1952) Figure 6-11,
was used to convert blot diameter on filter paper to actual
drop diameter.
     In a few runs isokinetic sampling through a filter holder
containing a treated filter was used to measure entrainment
drop diameter.  This method gave good results when the entrain-
ment load was sufficiently small for individual drops to be
seen, or the gas velocity or drop diameter was such that the
collection efficiency of filter paper held in air is poor.
     Determination of entrainment load:
     1.  Initially, the arrangement shown in Figure 6-12,was
         used for liquid load measurement at the inlet and
         outlet ends.  Isokinetic sampling was used.  It
         was observed that all of the liquid was collected
         in the inlet nozzle and none in the gravity sepa-
         rator, cyclone or filter holder.  The results
         obtained were poor, which may be attributed to:
         A.  Entrainment may not be evenly distributed
             in the cross-section of the duct.
         B.  Some liquid may have collected or drained
             down from the sampling nozzle to the collection
             flask during sampling.
     2.  The second method used to obtain entrainment loadings
         was by material balance.  The entrainment in the in-
         let was obtained by subtracting liquid collected on
         the walls before the test section from the liquid
         feed and applying a correction for the humidity of
         the ambient air.  The entrainment in the outlet was
         obtained by subtracting the liquid collected in
         various parts of the test section from the inlet
         entrainment.
                            6-24

-------
DROP DIAMETER, microns
M ^
o ' en "o "c
0 S ° C
0 0 0 C
'«—







x







/









;








^ ^
/






^
/
1






/*






-r*
/^







•
^









•
^









;;



















       0.3 O.S   1          5

           BLOT DIAMETER, mm
10
Figure 6-11 - Calibration of Whatman No,  1
              filter paper.
                 6-25

-------
        Isokinetic  Sampling
      Air
      Flow
 gravity
separation
                1
      catch
  collection
                                Filter Holder
                                      	xrptameter
                          cyclone
 j| b  needle/
 /\valve   "
LA
               0


               IT
                                                 dry
                                                 gas
'^  manometer
                     catch         	
                   collection   vacuum pump
           Figure 6-12 - Liquid load sampling
                       6-26

-------
 This method was discarded due to errors in the
 liquid balance caused by a fluctuation in the
 inlet feed rate during the experiment.  The
 fluctuation may have been caused by the nozzles.
 These errors may have been 5 to 10%.   However,
 in some experiments they may have been magnified
 because liquid collected on the walls  before  the
 test section was as high as 80% of the feed.  Also,
 some errors were found in the humidity correction
 due to  erroneous functioning of the thermocouples.
 A  third method was  based on counting the  number of
 drops collected on  a filter paper.  The entrainment
 load could be  determined if the mass average  drop
 diameter and the sampling time were measured.  This
 method  has the following disadvantages:
 A.   As  shown in the  previous  chapter,  the  drop
     collection efficiency by  the  filter paper varies
     with the entrainment  drop  diameter  and  gas
     velocity and is  not  100%.
 B.   The  error  which  is introduced  in the measurement
     of  drop  diameter  is  magnified when  the  volume
     of  the drop  is calculated  to determine  the
     entrainment  load.
 C.  An  error is  introduced  in  inserting and removing
     the  filter paper  from the  duct because  of the
    short  sampling time.  When the entrainment load
     is high, the sampling time is one second or less.
D.   The  sample represents entrainment load at a single
    sampling point in the duct which may not represent
    the average entrainment load.
                 6-27

-------
         E,  Some error is also introduced due to overlapping
             of blots on the filter paper.
     4.  A method based on measuring the entrainment by con-
         verting it to vapor and measuring the humidity of
         the gas was selected for use in all experiments.  An
         isokinetic sample was drawn through a nozzle which
         was heated to evaporate the entrainment.  The air
         sample humidity was measured by dry and wet bulb
         thermometers following the nozzle.  A thermostat
         was used 
-------
          Transformer
Electrical
supply
Wet and dry
bulb thermometers
             Impactor
                                  •
                                         Rotameter
                                         Needle valve
                                         Vacuum pump
       Figure 6-13  -  Sampling device consisting of impactor,
                     heated inlet probe,  dry and wet  bulb
                     thermometer and accessories
                                6-29

-------
was 3.8 Jl (1 gal.) per experiment, a maximum error of about
one half of one percent.
     2.  Liquid level.  The maximum error in reading the
liquid level was about 2 mm, or one half of one percent.  This
corresponds to 500 cm3 of liquid in catch tanks numbers 3 to 6
and 1 £ of liquid in catch tank number 2.
     3.  Water meter reading.  All the water meters were
calibrated as a function of average flow rate (continuous
in water meter #1 and discrete flow in the rest of the water
meters).   However, reproducibility was poor and the maximum
error was 5%.
     4.  Rotameter reading.  The rotameter error was specified
as less than 2% of the maximum reading.  However, additional
errors may have resulted during the experiments due to
fluctuation and drift in the flow.  The two rotameters have
a maximum capacity of 8.4 £/min and 84 5,/min.
     5.  Temperature.  The maximum error in temperature
reading with a thermometer was 1°C.
     6.  Air flow rate.  Air flow rate was measured with a
pitot tube connected to an inclined manometer.  The inclined
arm of the manometer was scaled to give velocity.  Two types
of error were present:  a)  Error due to fluctuation in the
air flow rate, and  b)  Error due to change in fluid density
caused by a temperature change.  The maximum error due to
temperature change was 50 cm/sec or 3-41, corresponding to
change of air velocity of 20 cm/sec in the test section.
                         6-30

-------
        EXPERIMENTAL RESULTS AND DISCUSSION

     At the time of writing, experiments had been run
on the pilot plant with horizontal gas flow through
packed bed, zigzag baffle, tube bank and mesh entrainment
separators.  In each run air was used as the gas, water was
the liquid, and no solids were present.  Results on overall
collection efficiency, pressure drop, reentrainment and
liquid flow patterns are presented and discussed in this
chapter.  However, before the performance of various test
sections can be considered, the size distribution of the
inlet entrainment must be determined.
INLET ENTRAINMENT
     Various nozzles were used in the experiments, although
only one type of nozzle was used in any given experiment.
A description of the nozzles is given in Table 7-1. A complex
relationship among the characteristics of the individual
spray nozzles, the interaction of multiple nozzles, the con-
figuration of the experimental duct and the air velocity
determines the inlet entrainment size distribution.
     The spray generated from the M6 nozzles was analyzed
under experimental conditions by filter papers coated with
II potassium ferricyanide and ferrous ammonium sulfate, as
described in Chapter 5.  The drop diameter generated from the
other nozzles was greater than 100 ym.  For these, the manu-
facturer's data were used to determine drop diameters.
     The effect of gas velocity on mass median drop diameter
generated from M6 nozzles is shown in Figure 7-1. There is no
definite trend.  The mass median diameter varies from 76 to
102 ym and averages 84 ym, with an average geometric standard
                         7-1

-------
                             Table 7-1.  NOZZLES USED IN SPRAY  SECTION
Type of Nozzle
Hollow cone
Fogjet Nozzle

Full Cone
Hollow Cone
Model #
(Spray Systems)
1/4 M6SS
1-11 1/2 F18
1 1/2-11 1/2
F35
1/8 GG3
1/4 M26
i
Pressure,
atm gauge
13.6
2.7
2.7
2.7
2.7
# o£
Nozzles
12
1
1
12
12
&/m/nozzle
0.853
68
133
4
2
I
to

-------
   100
w
H
o
oS
Q
C/3
       0
10
                 GAS VELOCITY,  m/sec
    Figure 7-1  -  The effect of  gas  velocity  on
                  drop diameter  for M6 nozzles
                       7-3

-------
deviation of 1.32.  The minimum drop diameter found in the
inlet was 30 ym.
     Inlet entrainment measurements were made at a point
75 cm downstream of the spray nozzles and 30 cm upstream of
the test section.  The average water supply pressure was
13.6 atm. gauge (200 psig) .  The nozzles were oriented toward
the downstream side and gave the drops an initial velocity
of 51 m/sec,
     An analysis of the drop diameters created by each nozzle
is given in Table 7-2, and more detailed information concerning
the size distribution curves, as provided by the manufacturers,
is presented in Figures 7-2 through 7-4.  These distributions
were measured 30 cm from the nozzles.
     In these experiments the M26 nozzles were operated at
2,7 atm pressure, but the drop size data provided by the
manufacturer are for 6.8 atm and 10.2 atm.  The mass median
drop diameter produced by M26 nozzles was obtained from
fitting the following relation for the effect of operating
pressure on drop diameter:
where  d   = mass median drop diameter, cm
        mm
       AP  = pressure drop at nozzle, atm
     c. , c2= constant
     The mass median drop diameter for an operating pressure
of 2.7 atm was 380 ym.  The geometric standard deviation was
1.52 and did not significantly vary with operating pressure.
     The nozzles often plugged, due to formation of rust in
the water tanks.  This resulted in a decreased water flow
rate and also may have caused some variation in the drop
diameter and standard deviation.
                          7-4

-------
                         Table  7-2.  DROP SIZE ANALYSIS
I
en
Source of
Data
Manufacturer
Manufacturer
This Study
Manufacturer
Manufacture r
Predicted From
Equation (7-1)
Manufacturer
Type of
Nozzle
M6
M6
M6
M26
M26
M26
GG3
Operating
Pressure
atm gauge
6.8
10.2
13.6
6.8
10.2
2.7
2.7
Mass Median
Diameter,
ym
127
110
84
295
265
380
1,230
Minimum Drop
Diameter,
ym
45*
45*
30
110*
102*
-
450*
Geometric
Standard
Deviation
1.5
1.5
1.3
1.5
1.5
1.5
1.8
          !2%  of the drops are smaller than this diameter.

-------
w
H
O
erf
Q
1,000





  500




  300



  200





  100





   50



   30



   20





   10
                   T-I—i   i  i  i  i  i  i—rn—r
                    i  i    i  i   i  i  i  i  i   i  j	i
                2   5   10   20     50     80  90 95 98


                   ACCUMULATED VOLUME, %
       Figure 7-2  -  Drop diameter versus volume percentage for
                    hollow  cone nozzle spraying water at 10.2
                    gauge pressure.  (Manufacturer's data)
                           7-6

-------
E
a.
2
Q
a,
o
   1,000
     500
     300
     200
     100
      50


      30


      20




      10
                1   I   I    I  I  I  I  I  I  I    I   I   I
                    II    I  I  I  I  I   I J    I	II
                 2   5   10  20      50     80   90  95  98

                  ACCUMULATED VOLUME,  %
         Figure  7^3  - Drop diameter  versus  volume  percentage
                     for hollow  cone  nozzle  spraying water at
                     6.8 atm  gauge  pressure,  (Manufacturer's data)
                               7-7

-------
oo
<
)—I
Q

CU

§
                   3,000,
                   2,000
                   1,000
                     500
                     400
                     300
I     I
                 J	L
                                    10
T—i—r
                                         i—i—r
                                                                    T—r
                                                                GG3
                  1   I   i    I    »
                           J	L
                           20  30
                    50
                  70   80
90
                                       ACCUMULATED VOLUME,  %
95   98
                         Figure  7-4  -  Drop diameter versus volume percentage for
                                      fulljet  nozzles  spraying water at 2.7 atm gauge
                                      pressure.  (Manufacturer's data)

-------
      It was observed that  the entrainment flow rate reaching
the entrainment  separator  decreased with decreasing air
velocity.  This  is due  to  an increase  in collection by the
walls of the spray section.

EXPERIMENTAL RESULTS
      Experimental data  (see Appendix)  for 153 runs are given
in Tables A-l to A-4.   Table A-l gives the overall perfor-
mance of the entrainment separator.  Liquid to gas volumetric
ratio and the entrainment  mass median  drop diameter are
measured at the  inlet of the test section.  Collection
efficiency is the overall  efficiency and represents the
effect of primary efficiency, reentrainment and secondary
collection.  Similarly, pressure drop  is the overall pressure
drop  for the test section.
      Table A-2 gives the drop diameters of the entrainment
entering and leaving the test section.  Since the water
feed  rate, water pressure  and type and number of nozzles
affect drop diameter in the inlet, these variables are in-
cluded in this table.  The entry type  and number of nozzles
give  the nozzle model number followed  in brackets by the
number of nozzles.  The details of these nozzles are given
in Table 7-1.
     Table A-3 gives the liquid material balance in the sys-
tem.  As explained in the details of the equipment, the liquid
collected in the test section is divided into four parts
along the length of the test section.  Liquid collected on
the side of the spray section and the observation section
upstream of the test section is also measured.
     In some experiments liquid flowing as entrained drops
after the test section is determined by material balance,
i.e.,  [water in air after test section] = [total water
supplied] - [total water collected].  In the rest of the
experiments,  liquid flowing as entrained drops was measured
                          7-9

-------
directly by measuring the humidity of a heated outlet gas
sample.
     Table A-4 gives pressure drop data for the system.
"APd  "'-and "APwetfl represent the pressure drops in the
test section at the experimental condition without and
with liquid flowing.
Packed Bed
Overall Efficiency - Efficiency data for packed beds are
presented in Figure 7-5.  Runs at gas velocities (Note:
All gas velocities are superficial.) lower than 6.0 m/sec
did not show any penetration.  The theory for primary col-
lection efficiency, shown as a solid line, is based on
Equation (3-13) and predicts 1001 primary efficiency over
the range of gas velocities studied.  The data for overall
efficiency agrees well with the theory for primary efficiency,
which indicates that little or no reentrainment is taking
place.
Pressure Drop - Figures 7-6 and 7-7 show the pressure drop
in packed bed separators.  There is no effect of liquid
load on pressure drop.  The slope of the straight line on
the log-log graph is 1.94.
Reentrainment - According to Figure 7-8, there is no direct
dependence of the maximum outlet drop diameter on the gas
velocity in a packed bed.  Figure 7-9 shows that the geo-
metric standard deviation increases with increasing outlet
mass median drop diameter.  In both figures, the inlet mass
median drop diameter is used as a parameter, but no trends
can be detected as it is varied.
     The minimum and maximum outlet drop diameters are
important in consideration of design criteria for a second
                             7-10

-------
   100
 ss
 w
 o
 I— I

 E-
            Inlet Drop Diameter, ym


              V        84


              O


              D
     0
       0
8
10
                    GAS VELOCITY,   m/sec
Figure 7-5    Experimental collection efficiency of a

              packed bed as a function of gas velocity

              with horizontal flow.
                      7-11

-------
    10
e
u
      5  si
   0.5
   0.2
   0.1
      1.0                 5       10



            GAS VELOCITY, m/sec
Figure  7-6  - Dry pressure drop  in packed

             bed versus gas velocity
                 7-12

-------
   10.0
    5.0
 §
    0.2
    0.1
         1                 5      10

           GAS VELOCITY, m/sec
Figure 7-7 - Wet pressure drop in packed bed
             versus gas velocity
                   7-13

-------
1,OQO
  800
  600
  400
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    0

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GAS VELOCITY, m/sec
8
     Figure 7-8 - Maximum drop diameter in the
                  entrainment versus gas velocity
                  for 30 cm packed bed
                       7-14

-------
   1,000 m--±-j=jgJHg
Q
a,
CO
CO
w
     100
     10
                     Inlet  Drop Diameter, ym
                 1.4        1.8        2.2

              GEOMETRIC STANDARD  DEVIATION
2.6
  Figure 7-9 - Mass median drop diameter versus
               geometric standard deviation
               downstream of 30.5 cm packed bed
                        7-15

-------
stage entrainment separator.  For packed beds the minimum
outlet drop diameter ranged from 40 to 60 ym.
Zigzag Baffles
Overall Efficiency - The overall collection efficiency for
horizontal gas flow through vertical zigzag baffles was
determined as a function of gas velocity.  Figures 7-10
through 7-12 are plotted for different drop diameters in
the inlet entrainment.  The separator attains 100% efficiency
for gas velocities between 3.0 and 6.0 m/sec.  The efficiency
falls sharply for gas velocities below 3.0 m/sec for experi-
ments in which the inlet entrainment consisted of drops with
84 ym mass median diameter.  Figure 7-13 shows data for all
the runs with zigzag baffles.
     A theoretical curve for collection efficiency for
liquid droplets which have a median drop diameter of 90 ym
and geometric standard deviation of 1.35 is also shown in
Figure 7-10, where:
      n    = number of rows
      9    = angle between the superficial and actual
             air flow directions in the baffles
      d    = inlet mass median drop ciameter, cm
       Pg
      a    = geometric standard deviation of inlet
       o
             entrainment
     Experimental results reported by Bell and Strauss (1973)
for zigzag baffles are plotted in Figure 7-10 along with
points obtained in this study for d   - 380 ym and a line
representing the data of Houghton and Radford (1938).  The
inlet entrainment of the Bell and Strauss experiments was
comparable to this study, but their overall efficiency was
much lower.  This is probably due to the differences in
separator design as reported in Table 7-3 .
                            7-16

-------
           u
           §
           w
           CJ
           w
           8
                  100
                  20
                   0
                    0123456

                             GAS VELOCITY,  m/sec
Figure 7-10 - Collection efficiency versus gas velocity in the

              zigzag baffle device with n = 6 and 9 = 30°.

              The solid line represents theoretical curve for

              d  = 90 ym and a  =1.35.
               XT O             O
                             7-17

-------
       U
       z
       w
       §
       1-1
       H
       U
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       0
           100
            80
            60
            40
            20
             0
                  L£ Houghton  §  Radford

                    : Data,  n=6,  6=30°
                  -*-i-t-     f     f

                                  Strauss
                                        tData for 2 "V"
                                        ^Baffles  in

               01          3456

                       AIR VELOCITY,  ra/sec
                                          8
Figure 7-11 -
Collection efficiency versus  gas  velocity in

the zigzag baffle device with n = 6, 9 = 30°,
    =                =
              d   = 380 ym and a  = 1.52,

                                6
                             7-18

-------
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                 1          3456

                     GAS VELOCITY,   m/sec
                                            8
Figure 7-12 -  Collection efficiency versus gas velocity in
              zigzag baffle device  with n = 6t g = 30°,
              d   * 1,230 ym and  a   = 1.8.   Theory predicts

              1001 efficiency.
                          7-19

-------
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                       34567


                       GAS  VELOCITY,  m/sec
9   10
       Figure  7-13  -  Experimental  collection efficiency as a
                     function of gas  velocity in the vertical
                     baffles.   Solid  line represents theory.
                              7-20

-------
Table 7-3 .COMPARISON OF BAFFLE TYPE ENTRAINMENT SEPARATORS

Number of rows
9°
Lip to prevent
reentrainment
Staggering of rows
Distance between
rows

Spacing between
baffles in a row
Width of baffles
Present
Design
6
30
none
2 .5 cm
2.5 cm


6.9 cm
.7,5 cm
Bell $ Strauss
(1973)
4
45
1.9 cm on 1st
$ 3rd row only
none
3 .1 cm between
2nd § 3rd row
only
8.8 cm
6.2 cm
Houghton §
Radford (1938)
6
30
0.5 on 4th §
5th row only
none
0


2 cm
5 cm
                            7-21

-------
     Houghton and Radford's experiments were conducted
under two operating conditions:  (1)  Liquid flow rate
=38 cm3/min and spray drop diameter ranging from about
1 to 60 ym, the predominant size being 40 ym, and
(2)  Liquid flow rate = 12.3 fc/min and spray drop diameter
ranging from 2 to 800 ym, the predominant size being about
300 ym.  The results obtained under both conditions were
similar and were comparable with the present results due
to similarities in the design, as summarized in Table 7.3.
Pressure Drop - Experimental dry and wet pressure drop
versus gas velocity for baffles is plotted in Figures 7-14
and 7-15, respectively.  In both figures the solid lines
represent the theoretical prediction of pressure drop as
presented in Equation (4-8).  The liquid load does not
have a significant effect on the pressure drop in the
baffle section.  This should be expected as liquid hold-
up in the baffles is small because of the high drainage
rates.
Reentrainment - Figures 7-16 and 7-17 show the experi-
mentally determined dependence of the outlet mass median
drop diameter on the gas velocity.  For an inlet drop
diameter of 280 ym, the outlet drop diameter increases
with rising gas velocity, as pictured in Figure 7-16.
However, Figure 7-17 reveals that no pattern is in evi-
dence for an inlet drop diameter of 1,230 ym.
     The size distribution of drops leaving a zigzag baffl®
separator is depicted in Figure 7-18, with liquid flow rate
as the parameter.  The two curves have nearly identical
slope on the log-probability diagram, but the lower liquid
flow rate resulted in larger reentrained drops.
     The maximum drop diameter found in the outlet of a
baffle separator is graphed versus gas velocity for two
inlet drop diameters in Figure 7-19.  A correlation can
                            7-22

-------
  CJ
  PL,
  <
              ttFn' iJ'' MMiiin i''iiif iliiiiiiiii'
                 ttrtttn ;i' m nr'il1 H i MUM! ill
02
                              5        10

              GAS VELOCITY,  m/sec
Figure 7-14  -  Dry pressure  drop  in baffles
                versus  gas velocity
                  7-23

-------
    5.0
u
U
    2.0
    .02
              2345      10

         GAS VELOCITY, m/sec
 Figure  7-15  - Wet pressure drop  in
               baffles versus gas velocity
                     7-24

-------
       1,200
   w
   H
   §
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   H
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       1,000
         800
         600
         400
         200
           01          34

                   GAS VELOCITY,
  5    6

m/sec
Figure 7-16 - Outlet drop diameter versus gas velocity
             for zigzag baffles with inlet mass median
             diameter of 380 ym.
                    7-25

-------
     1,000
  w
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  Pi
  fi
  en
  W
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       800
       600
       400
       200

                             I

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                          4:::
                            1 n
               ._-t-_;
                             M
                           5th
Km
             IT;.

                123456

                   GAS VELOCITY,  m/sec
Figure 7-17  - Outlet drop diameter versus  gas velocity
              for  zigzag baffle with  1,230 ym inlet
              mass median drop diameter.
                     7-26

-------
 1,000
   500
6
.i
   100
    50
   10
                O  Air  velocity 6 m/sec, water flow rate 13.2 Jl/min



                    Air  velocity 6 m/sec, water flow rate 7.6
                                                   	i	










                                                    m
                                                    •!!'
                                    •
                                    U-4-
                                                         5
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                                    UJTuT
                                    i i • • i ;
10     20   30  40  50  60   70   80     90


          CUMULATIVE NUMBER, %
                            f
                                                                  95
                98
   Figure 7-18 .  size  distribution of drops leaving baffle entrainment

                 separators
                              7-27

-------
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                         Inlet Drop Diameter, ym
                      380
                                 1,230
                       I
                   -T-:-
                   ; 1 • -
                   I j •" -"•
0
                    2
                           6
8
                     GAS VELOCITY,   m/sec
Figure 7-19 -
 Maximum outlet drop  diameter in the
 entrainment versus gas velocity for
 zigzag baffles.
                    7-28

-------
be established  for  380 ym drops but not for the large
1,230 ym drops.  The minimum drop size in the reentrain-
ment was observed to range  from 50 to 80 ym.
     The geometric  standard deviation gets larger as the
outlet mass median  increases, as seen in Figure 7-20.
     Two very important parameters for determining re-
entrainment are gas velocity and the liquid to gas ratio.
The combination of  these two which results in reentrain-
ment as observed experimentally is shown in the shaded
region in Figure 7-21.  The reentrainment observed is
0.5 - 1% of the inlet entrainment.
Liquid Flow on the  Baffles  - Flow of liquid on the baffle
surface was observed in some of the runs.  As the flow
increases, the film thickness of the liquid near the down-
stream edge increases.  The gas stream forms a wake at the
back side of the baffle, which tears away some of the liquid
at the downstream edge.  The approximate shape of the wake
is shown in Figure  7-22.  The wake formation becomes more
pronounced with increasing  gas velocity.  The flow of liquid
film on the back side of the baffle is shown in the same
figure.
     If the liquid  flow on  the baffle surface is small, only
drop flow takes place on the back side of the baffle.  Some
of these drops reach the upstream edge of the baffle, where
they are reentrained.  The reentrained drops splash on the
adjacent baffle in  the same row and disintegrate.   Some of
these small drops are reentrained in the air.  The drops
normally splash on  the third quarter width of the baffles
as measured from the upstream.  The drops flowing on the
back side of the baffles are 3-4 mm in diameter.
     Reentrainment  from the downstream edge of the baffle
was more significant compared to reentrainment from the
                           7-29

-------
       10
   Q


   I
   Q
   Q
   W


   CO
   cn
   H
   W
   o
       10
        10
 . I . -1   . ;
H : -f . '"^- r •:-••
                    1.4       1,8       2.2


               GEOMETRIC STANDARD DEVIATION
             2.6
Figure 7-20 - Drop diameter versus geometric  standard
              deviation at zigzag baffle outlet.
                       7-30

-------
    10
      - 3
 6
\
CO
 6
   10
en
o
H
   10
     - 5
   A Some  reentrainment (<1%)
                                   i   . .
   XN Reentrainment in part of     I  . ;":
_J_. N/duct  only                       ;
      Primary  efficiency <100%
                                  T f i ' ~ j~
  : O No penetration
   : i  > l f' i ; t - ; r' I • •—-•••-- i ; . = : i- : : !  ; "TT
                      3456

                  GAS VELOCITY, m/sec
  Figure 7-21   Effect of gas velocity and liquid
                load on performance of baffle type
                separator.
                       7-31

-------
    Formation  of wake
                           Wall  acting as  collector
         .1
Pulsating
liquid flow
on the back
side of the
baffle
Figure 7-22 - Some observed phenomena in entrainment
              separator  (a)  formation of wake
              (b)  liquid flow on the back side of
              the baffle  (c)  wall effect
                     7-32

-------
 upstream edge.   If the  liquid flow on  the  baffle  surface
 was  drop flow,  some of  these  drops reached the  downstream
 edge and  (1) were reentrained,   (2) were  turned  to  the
 back side of  the baffle,   (3)  fell down  at the  edge  due to
 gravity, or   (4)  stayed at  the edge of the baffle  until
 they grew by  coalescing with  other drops.   Most of the
 drops were collected by the third  or fourth step.  If the
 liquid was flowing as a film  on  the baffle,  part  of  the
 film was torn and reentrained at the downstream end.  The
 drops reentrained from  the  downstream  edge of the  baffle
 were 3-5 mm in  diameter.  These drops  were normally  col-
 lected on the baffles of the  second row, i.e.,  drops re-
 entrained from  the second row  were  collected on the  baffles
 in the fourth row.
     Some  wall  effect was observed  in  the  baffle section.
 There were four baffles  in  a  row and the side walls  of the
 test section acted as collectors for the entrainment.  This
 effect is  shown  in Figure 7-22.
     The  liquid flow pulsated  whenever reentrainment took
 place and  occurred in film  flow and in drop flow.  It was
 difficult  to determine  the  amplitude of the pulsating film
which may  have been of  the  order of 0.05 cm.  The frequency
of the wave was not measured.
Mesh
Overall  Efficiency  - The overall collection efficiency data
for horizontal flow through wire mesh are plotted in
Figure 7-23.   No penetration was observed  in experiments
at low gas velocity, less than 3.0 m/sec.  At higher velo-
cities penetration due to reentrainment was observed.  The
dotted line,  predicting 1001 efficiency,  represents the
theoretical curve based on Equation (3-21).  In the range
of experimental data, the curve given by the manufacturer
                          7-33

-------
i nn


on
oU
vs
u
Jz;
M
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HH
£ 60
w
COLLECTION
•t*
o

20
0
(
1 | | II! ! | I
w-J V V-Jy VI "'Bjty \/ "i11 iy Ljj V ^pv 1aiHjytj'"\/
';• /' • • • I ;• • ; ; ^ i
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:':: •': -'•'•:: j ;: • \ : ;
; . . : • '
— • • ' 	 , 	 :• ...... .. ._
! ' ' ; ' ' j
Inlet Drop Diameter, urn
V 84
O 380
E 1,230 i
O > 1,230 ;
,11111111
J.I 23 4 56788 9 1C
                  GAS  VELOCITY,   m/sec
Figure 7-23
Experimental collection efficiency of
wire mesh as a function of gas velocity.
                        7-34

-------
 (ACS  Industries)  for  mesh  efficiency  corresponds  to  the
 theoretical  curve.
 Pressure  Drop  -  In  contrast  to  the  results  for  packed beds
 and zigzag baffles, the  pressure  drop in wire mesh sepa-
 rators  is affected  by liquid load,  as seen  in Figure 7-24.
 The slope of the  straight  lines on  the log-log  plot  is 1.65;
 thus, "AP" can be represented as  a  function of  "lu1'6511.   In
 Figure  7-24, L/A  =  0  represents the dry pressure  drop
 "APd  " through the mesh.  For  0 < L/A < 1  the  pressure
 drop  is 1.5  AP,   ,  and for 1 <  L/A <  5 the  pressure  drop
 is 2.3  APdry.
 Reentrainment  - The outlet mass median drop diameter is
 plotted as a function of gas velocity in both Figures 7-25
 and 7-26.  Each curve shows  a dependence in the range of
 gas velocities studied,  but  it  is more pronounced for
 inlet drop diameters  of  82 ym than for large drops of
 1,230 ym diameter.
     Figure  7-27  demonstrates that no  trend can be detected
 relating gas velocity with the maximum drop  diameter in the
 reentrainment.  However, the minimum  drop diameter was found
 to range from 40  to 80 ym.   As seen in Figure 7-28, there is
 a positive straight-line correlation between geometric
 standard deviation and the mass median drop  diameter in the
 outlet.
     Figure 7-29  shows the combination of gas velocity and
 liquid to gas ratio which will result  in reentrainment in
mesh separators.  The  shaded  area is  the region where
 onset of reentrainment was observed.
     Buerkholz (1970)   collected reentrainment data for
 sulfuric acid mist 150 cm  downstream of a mesh separator.
He found that reentrainment  increased  from  1.6 to 4.0$
 (0.3 to 1.3 mg/m3) as   the  gas velocity was  increased from
                         7-35

-------
       3.0
  u
  0
  U
                        1 < L/A <  5
                        lffliii!ill,!ilM:l'):;|;;:;ltJij£si:

                       0 <  L/A < 1
             GAS VELOCITY,  m/sec
Figure 7-24  -
Pressure  drop in wire mesh
versus gas  velocity with  liquid
load as parameter
L/A = Superficial liquid  velocity
      cm/min
                     7-36

-------
      1,000
   Pi
   W
   H
   P
   O

   g
   CO
   LO
   H
   w
   -J
   H

   §
        800
        600
        400
        200 -
         0
                12345

                 GAS VELOCITY,  m/sec
Figure 7-25 - Outlet drop diameter versus gas velocity
              for mesh with 82 pm inlet drop diameter.
                    7-37

-------
   500
w
H
3
§
n
Q
w
2

CO
3
H
O
   400
300
200 —
100 —-
                 2345     67

                   GAS VELOCITY, m/sec
Figure 7-26 - Outlet drop diameter versus gas velocity
              for mesh with 1,230 ym  inlet drop
              diameter
                         7-38

-------
     1,000
 OH
 O
 X
 ,-J
 H
       800
       600
       400
       200
        0
          0              3456

                     GAS VELOCITY,  m/sec
Figure 7-27 - Maximum outlet drop diameter in the
              entrainment versus gas velocity for
              mesh
                   7-39

-------
ym
ETER
DROP
Q
W
S

co
H
W
P
O
M
0
     10
                 1.4        1.8        2.2

             GEOMETRIC  STANDARD  DEVIATION
2.6
igure7-28 _ Drop diameter versus geometric standard
            deviation for mesh.
                   7-40

-------
       1x10
     - 3
 e

 CO
 6
 O
 M
 H
g
o
ex
HH
-J
1x10
    IxlO"5
                   Reentrainment
Figure  7-29  -
                 GAS VELOCITY,  m/sec



         Effect  of sas  velocity and  li
         load on performance  of mesh
                    7-41

-------
4.7 to 8.2 m/sec.  The outlet mass median drop diameter also
increased from 150 to 750 ym.  Buerkholz1 data, plotted in
Figure 7-30, were collected on a 15 cm x 15 cm mesh with
sedimentation present between the mesh and the sampling point.
The solid line in Figure 7-30 is the onset of reentrainment
curve obtained in the present study.  The data show good
agreement in determining the reentrainment velocity of 5 m/sec
at very small liquid loads.
     The reentrainment curve obtained from the manufacturer
also appears in Figure 7-30.  The manufacturer predicts
higher reentrainment velocity than the present results.  The
differences may be due to the fact that the manufacturer used
vertical gas flow.
Visual Observation of Reentrainment - Reentrainment in the
mesh section was observed to take place in the following ways:
     1.  At low liquid loads the mesh operated without
flooding.  Apparently, the drops that are collected on the
mesh wires grew to 3-5 mm diameter before they drained down.
If the air velocity is high, the path of the drop is not
vertically downward.  Some of these drops were airborne and
struck the wires of the grid supporting the mesh.  Normally,
the drop shattered into one large drop slightly smaller than
the original size and 2-4 satellite drops which were
     Some of the drops collected on the grid wire drained at
once, whereas the rest drained after growing to a larger size.
There were other drops which missed striking any wires and
emerged from the mesh.  These drops were collected at the
downstream side of the mesh.  The drops passing through the
mesh without striking any wires were carried farther down-
stream of the mesh than others.  All these reentrained drops
were 4-5 mm in diameter and upon reaching the bottom, they
shattered into a few (3-4) satellite drops.  The rest of the
liquid in the original drop was mixed with the liquid film
                             7-42

-------
    10
      - 3
6

 M

o
I—I

E-
    10
D
cc
    10

         0
                                  8
                      GAS VELOCITY,   m/sec
Figure  7-30
Onset of reentrainment velocity curves for

mesh.  (—) Experimental data, (--) manu-

facturer's catalog, (0) Reentrainment data
observed by Buerkholz (1970),
                      7-43

-------
at the bottom.  These satellite drops flew into the air due
to kinetic energy, and their initial trajectory formed a
cone along a vertical axis.  The angle of the cone was de-
pendent upon initial drop velocity and was observed to range
from 0° to 90°.  Some of these satellite drops were re-
entrained while others fell down.
     2.  Some drops were reentrained inside the mesh, and
the process of reentrainment could not be observed; it is
assumed to be the same as described in the earlier part of
the first method.
     3.  When the liquid load was high, partial flooding was
observed.  Reentrainment by methods 1 and 2 took place above
the flooded zone.  In the flooded section the air flow rate
was low.  The flooded section was partially covered by the
falling drops from above on the downstream side of the mesh.
The reentrainment mechanism was rupture of bubbles, but it
could not be observed properly.  Reentrainment by the above
mechanisms was observed in runs 43 and 46.
Tube Bank
Overall Efficiency - Collection efficiency versus gas velocity
data for horizontal flow through tube banks are plotted in
Figures 7-31 through 7-33 for various inlet drop diameters.
Penetration due to primary efficiency of less than 100% was
observed for velocities lower than 3.0 m/sec.
     Houghton and Radford's (1938) data for strut separators
are also plotted in Figure 7-32.  They found a constant col-
lection efficiency of 96.2% for gas velocities from 1.25 to
17.5 m/sec.  The inlet entrainment contained drops as small
as 1 ym.  However, no increase in penetration at lower velo-
cities or reentrainment at higher velocities was observed. A
comparison between the configuration used in the present
study and that of Houghton and Radford is given in Table 7-4'
                             7-44

-------
 o
 hH
 H
 U
 w
 o
 u
          0
8
                     GAS VELOCITY,  m/sec
Figure 7-31 - Collection efficiency versus gas velocity
              in tube bank with n = 6, d   = 84 urn and
              a  = 1.32.
                  7-45

-------
          100
                 Houghton  $ Radford Data  (1938)
               |: OWater loading 17.1 £/min
              M Awater loading  6.8 £/min

                         loading 11,4
                 OWater loading  3.8 £/min
            o
                  123456
                      GAS VELOCITY,  m/sec
Figure 7-32  - Collection  efficiency versus gas velocity in
              tube  bank with  d    =  380  ym  and  a   =1.5
                            7-46

-------
    100
w
 PU
 H
 U
 W
 O
 u
     80
     60
     40
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1- ! 1 1
                 234567

                  GAS  VELOCITY,   m/sec
Figure 7-33 - Collection efficiency versus gas
              velocity in tube bank.  Solid line
              represents theory.
                     7-47

-------
    Table  7-4.  COMPARISON OF TUBE BANKS
                      Present
                      Study
         Houghton §
         Radford  (1938)
Tube  (minor-major
axis) diameter, cm

Spacing between
tubes, center to
center, cm

Spacing between
rows, center to
center, cm

Number of rows

Material of
tubes
1.9


3.8



3.3



 6

Al
1.25x3.2
   2.5
                         7-48

-------
Pressure^ Drop  - Dry and wet pressure drop  through  the tube
bank is plotted in Figures 7-34 and 7-35.  There is no
effect of liquid load on the pressure drop; the slope of
both curves is 2.33.  Therefore the data may be correlated
by the following equation:

                AP = l.Z.xlO-5 n  pQ vG2'33           (7-2)

where   n  = number of rows (6 in present  experiments)
        v^ = actual gas velocity  near the  tubes
     The actual gas velocity "vV! is twice the superficial
gas velocity, which is shown on the horizontal axes of
Figures 7-34 and 7-35.  An average value of 1.17x10"3 g/cm3
is used for MPG"«
     Manufacturer's data (Union Carbide Corporation for
M.V. separator) for banks of streamlined struts of 2,2 cm
equivalent diameter gave the following empirical equation
for pressure drop:

                AP = 2.33x10-6 n  PG Vg2'19           (7-3)

A comparison of Equations (7-2) and (7-3) shows that the
former equation gives 5-8 times higher pressure drops for
cylindrical tubes with 1.8 cm equivalent diameter than for
streamlined struts with larger equivalent diameter.
     Grimison  (1937) has presented friction factor as a
function of tube bank configuration at various Reynolds
numbers.   For the configuration studied in the pilot plant,
friction factor versus superficial gas velocity is plotted
in Figure 7-36.  Substituting the value of friction factor
into the pressure drop relation results in:

                AP - 4.33x10-* n  PG Vg1'9            (7-4)

Equation (7-4) predicts pressure  drop twice as high as that
observed in the present study for VG = 6.0 m/sec.
                        7-49

-------
        2.0
     CJ
      *

     3=


     6



      A


     <
        .02
       .01
          1                 5       10

             GAS VELOCITY, m/sec
Figure 7-34 - Dry pressure drop  in  tube

              bank versus gas velocity
                     7-50

-------
          2.0
      u
      o
      PL,
      <\
         .02
         .01
               GAS VELOCITY, m/sec
Figure 7-35 -
Wet pressure drop in tube
bank versus gas velocity
                  7-51

-------
    0.15
M-i
             1.0     2345      10

                   GAS  VELOCITY,  m/sec
50
  Figure  7-36  -  Friction  factor versus gas velocity
                 in  the  bank of tubes
                          7-52

-------
Reentrainmeiit
     Figures 7-37 and 7-38 reveal no definite relationship
between gas velocity and outlet mass median drop diameter.
However, the size distribution curves shown in Figure 7-39
are similar to those obtained from zigzag baffles in
Figure 7-18.  For both types of separators, a higher liquid
flow rate caused smaller drops to be formed.
     Figure 7-40 gives a similar relationship between geo-
metric standard deviation and outlet mass median drop
diameter as seen for each of the other three types of  .
separators studied.  The maximum outlet drop diameter
rises with increasing gas velocity, according to Figure 7-41,
to a peak of about 350 ym at 7.0 m/sec gas velocity.  The
minimum drop diameter at the outlet, on the other hand,
ranged between 40 and 70 ym.
     Figure 7-42 depicts the values of gas velocity and
liquid load observed as being necessary for reentrainment.
As in the case of zigzag baffles (Figure 7-21), the re-
entrainment region has an upper and lower gas velocity
boundary for a given liquid load, whereas for the mesh
(Figure 7-29) there is only a lower boundary.

GENERAL OBSERVATIONS,
Pressure Drop
    The pressure drop in the empty test section housing as
a function of gas velocity is plotted in Figure 7-43.  The
housing for each separator studied thus far has the same
dimension.  When the pressure drop is less than 1 mm W.C.,
it is essentially negligible.  Therefore, there is no sig-
nificant pressure drop for a gas velocity less than about
5.0 m/sec.
                         7-53

-------
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            0
                             4567

                     GAS VELOCITY,   m/sec
Figure 7-37 -
           Outlet drop diameter versus gas velocity
           for tube bank with 380 ym inlet drop
           diameter.
                      7-54

-------
   OS
   w
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           Bip Nozzles Used ±g
                          ±ttt
123456


   GAS VELOCITY,   m/sec
'igure  7-38  -  Outlet drop diameter versus  gas  velocity
              for tube bank with  1,230  ym  inlet drop
              diameter.
                   7-55

-------
  1,000
    500
    100
on
w
H
Q



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     50
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  30  40  50  60  70


CUMULATIVE NUMBER, %
                                                      80
                             90
95
98
     Figure  7- 39 - Size distribution  of  drops  leaving tube bank

                   entrainment  separators.
                                  7-56

-------
       10
    w
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    OH
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UTLET
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                   1,230
           1        1.4       1.8       2,2

                 GEOMETRIC STANDARD DEVIATION
                                    2.6
Figure 7-40
-Outlet mass median drop diameter versus
 geometric standard deviation for tube
 bank.
                  7-57

-------
     1,000
   n
  w
  O
  (X,
  1
   s
   o
       800
      600
      400
      200
       0
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I.JH-Hli:
                  Inlet  Drop Diameter,  ym
                   A        84
          0
                         8
                   GAS VELOCITY,   m/sec
Figure 7-41 - Maximum drop diameter in the entrainment
              versus gas velocity for tube bank.
                    7-58

-------
     1x10
 6
•v.
€n
 6
 •k
O
i—i
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CO
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                          A ;Some reentrainment
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                 E£
             O  No penetration
             or  <$>  penetration
             due  to less than
             100% primary
             efficiency
                      GAS VELOCITY,  m/sec
     Figure  7-42    Experimental results showing the
                   effect of gas velocity and liquid
                   load on performance of tube bank.
                    7-59

-------
    u
        0.1
       0.05
               GAS VELOCITY,  m/sec
:igure  7,43  - Pressure drop in the empty
              section versus gas velocity
                    7-60

-------
     During the operation of the entrainment separator, the
velocity distribution changes due to the presence of the
separator.  Thus, the wall effects measured by the above
method may not represent the true wall effect.  However,
the presence of the separator does reduce the wall effect.
Also, the pressure drop in the empty test section is 10-20%
of the pressure drop with entrainment separator.  Hence,
the effect of the walls on the total pressure drop is small.
     The dry pressure drop versus gas velocity relationships
for different entrainment separators are shown in Figure 7-44
The packed bed is seen to have the greatest pressure drop.
It should be noted that the efficiencies of different sepa-
rators at a given velocity are not the same.
     Bell and Strauss' pressure drop data for baffles are
compared with present results for baffles and tubes in
Figure 7-45.  The high pressure drop found by Bell and
Strauss can be explained by the variations in design, dif-
ferences in "0" and the distance between rows and the use
of lips.
     The pressure drop data of Houghton and Radford are
compared with the present results in Figure 7-46.  The
results show good agreement.  The small differences in the
pressure drops may be explained as below.
     The differences in the design are given in Tables 7-3,
7-4, and 7-5.  The higher pressure drop in the baffle sec-
tion obtained by Houghton and Radford may be due to lips
on the fourth and fifth row of baffles and no spacing
between the rows.
     Houghton and Radford's pressure drop data in the tube
section give comparable results at velocities lower than
500 cm/sec.  At higher velocities the present study gives
higher pressure drops, which may be due to smaller spacing
between rows and to the use of tubes with circular cross-
section rather than struts with streamlined cross-section.
                           7-61

-------
       8



       5
  S
  u
0.5




0.3



0.2






0.
    0.05
    0.03
         1                 5      10

             GAS VELOCITY, m/sec
Figure 7-44 - Dry pressure drop versus gas

              velocity used in pilot plant
                   7-62

-------
     12
   w
   o
   H
   PH

   U4

   CO
    *

   CJ
   6
   u
     10
   w
   OS
   CO
8
      0
                   23456

                   GAS VELOCITY,  m/sec
Figure 7-45 - Pressure  drop  through entrainment

              separator as a function  of superficial
              gas velocity
                        7-63

-------
   u
    •
   12
    •V

   PH
            =Zigzag Baffles
                       Mesh
      0.1
                           5      10

                 GAS VELOCITY, m/sec
Figure 7-46 - Comparison of pressure drop data of
              Houghton § Radford (1938) with present
              results.  The dashed lines represent
              the present results.  The three curves
              for the mesh represent L/A = 0,
              0 <_ L/A <_ 1, 1 < L/A 1 5.  Here, "L/A"
              is superficial liquid velocity, cm/min.
                     7-64

-------
Table 7-5. COMPARISON OF WIRE  MESH DEMISTER

Mesh Density,
g/cm3
Void space
Wire diameter,
cm
Bed length,
cm
Material
Miscellaneous
Present
Results

98.2
0.028
10
SS

Bell § Strauss
(1973)
0.16

0.025
10
SS

Houghton §
Radford (1938)





Number 4 mesh
layers kept
5 cm apart
                       7-65

-------
Reentrainment
     Entrainment in the outlet is due to less than 100%
primary efficiency or reentrainment.  In some runs at low
gas velocity, 1.2-2.4 m/sec, entrainment occurred because
primary efficiency was less than 100%.  Increasing the gas
velocity caused the entrainment to disappear in the outlet.
Entrainment due to low primary efficiency occupied the
entire cross-section of the duct and was observed in runs
5, 146, 147, and 152.
     The mass median drop diameter of the reentrainment
varied between 70 and 1,000 ym with a geometric standard
deviation of 1.2 to 2.4.  Some drops settled by gravity
between the test section and the position downstream where
drop diameters were measured.  These measurements were
taken at the estimated middle of the cross-section in which
entrainment was present, resulting in a variation of the
sampling point elevation.  No correction for these two
effects has been made in the analysis of drop diameters.
     As noted earlier in this chapter, the mass median drop
diameter increases with increase in geometric standard
deviation.  Thus the drop diameter distribution becomes
broader as the median diameter increases.  Similar results
were obtained by Garner et al. (1954).  They attribute large
values of geometric standard deviation to reentrainment
caused by shattering of drops.  The resulting drops are
larger than 200 urn with mass median diameter between 250 and
1,000 ym.
     The effect of liquid feed rate on the typical outlet
mass median drop diameter and on the reentrainment velocity
for different separators is summarized in Table 7-6.  The
typical diameter and reentrainment velocity are both seen
to rise as the liquid feed rate is decreased.  Figures 7-38
and 7-39 confirm the data of Table 7-6 for baffles and tube
                             7-66

-------
Table 7-6. EFFECT OF LIQUID LOAD ON REENTRAINMENT IN DIFFERENT
           ENTRAINMENT SEPARATORS.
Test Section
Tube Bank
Tube Bank
Mesh
Mesh
Zigzag Baffles
Zigzag Baffles
Typical Outlet
Mass Median
Diameter
90 vim
350 ym
170 ym
260 ym
700 ym
700 ym
Average Liquid
Feed
cm3/sec
4xl02
2.7xl02
4xl02
l.SxlO2
4xl02
2.7xl02
Reentrain-
ment "Velo-
city m/sec
1.5
3.5
1.8
4.5
1.5
3.0
                         7-67

-------
banks, respectively.  In the case of mesh, experimental data
show that the mass median drop diameter increases with liquid
load.
     The minimum diameter of reentrainment for each type of
separator is given in Table 7-7, which is a distillation of
the data plotted in Figure 7-47.  In a few experiments with
baffles, the minimum size was as high as 190 ym.  As shown
in Figure 7-47, most data points lie between 40 and 80 ym.
     Kotov (1972) has summarized reentrainment from various
separators (Table 7-8) .   Reentrainment velocities in the
present study were much higher than those obtained by Kotov.
However, the experimental details of his work are not avail-
able, and it is difficult to make comparisons.
                              7-68

-------
Table 7-7.  OBSERVED MINIMUM DROP SIZE
            IN THE REENTRAINMENT
Separator
Baffles
Mesh
Packed Bed
Tube Bank
Minimum
50
40
40
40
Drop Diameter
urn
- 80
- 80
- 60
- 70
                 7-69

-------
    200
 *
rt

H
CM
O
OS
n
HH
2

S
L '
s
H->
en
0
M
O
0
en
0
      o
GAS
                            4567


                           VELOCITY, m/sec
    Figure  7-47  - Minimum outlet drop diameter versus
                  gas  velocity
                            7-70

-------
  Table  7-8.   REENTRAINMENT OBSERVED BY  KOTOV
 Device or
 Mechanism
Liquid Load
In Outlet
  m3/m3
Gas
Velocity
 m/sec
Screen or Mesh

Ceramic Rings

Bubble Break Up
0.4 - O.SxlO6

0.83 - l.lSxlO6

0.7 - 8xl06

14 - 19xl06
<2.8

 2.8 - 3.0
                  7-71

-------
7-72

-------
     FUTURE RESEARCH AND DEVELOPMENT RECOMMENDATION
     The primary objectives of the present research were to
evaluate the available technology on wet scrubber entrainment
separators, advance theoretical development and design
a pilot scale entrainment separator based on the above
information.  It is also important to define the areas
where additional work is needed.  At this time, the present
contract is in progress and the recommendations made in
the following paragraphs are subject to modification as
more is learned during the course of the research program.
REENTRAINMENT
     One of the problems which present day entrainment
separators suffer is their large size which is due to low
operating velocities.  The gas velocities are limited by
reentrainment velocities and flooding conditions.  Reentrain-
ment may take place due to various mechanisms, depending
on flow rates and geometry.
     While the present program will provide information on
the conditions under which reentrainment occurs in several
separator configurations, it would be helpful to have more
detailed knowledge of this phenomenon.   It is quite
possible that a fundamental study of the mechanisms of
reentrainment from different geometric arrangements would
enable one to develop more efficient separator designs.   At
least the results of such a study would delineate the limits
of performance possible and save effort which might otherwise
be expended in unprofitable directions.
     The study needed is onset of reentrainment conditions,
rate of reentrainment,  equilibrium constant between en-
trainment and liquid in film,  drop size distribution, smooth
and shock type contact  of gas  and liquid, effect of duct
                          8-1

-------
 dimensions, etc.  The  application to entrainment separator
 will  include  improving design methods to determine re-
 entrainment under operating conditions, effect of higher
 gas velocities and  improvements in design to reduce
 reentrainment,

 SOLID DEPOSITION
     Solids deposition and consequent plugging is a major
 operational problem in scrubber systems.  It would be very
 helpful to have insight into the mechanism(s) by which sus-
 pended and dissolved solids deposit and the effects of
 operating and design parameters.  Given a clearer picture
 of how solids deposit, it should be easier to conceive of
 and design for conditions which would minimize deposition.
     It is probably unavoidable that some deposition will
 take place in a high efficiency entrainment separator.
 Therefore, means for removing deposits are required.  Washing,
 either intermittently  or continuously, is the most common
method used and it has the undesirable feature of introducing
 liquid where it is not wanted.  Research on methods of
washing and flow rate  required would be worth doing, with
 the objective of finding the optimum way to use the least
 liquid.

FIELD TESTING OF INDUSTRIAL ENTRAINMENT SEPARATORS
     Performance data on industrial entrainment separators
are generally not available.  The industrial data are col-
lected to evaluate the overall performance of the scrubber
and it is assumed that the entrainment separators have 100%
efficiency.  Also, all the liquid introduced in the wet
scrubber is assumed to be removed by entrainment separator.
The effects of sedimentation,  bends in the duct carrying
entrainment, etc. are neglected.  The distance between
                            8-2

-------
sampling point and entrainment separator elements is
important.  Also, the effects of industrial operating
conditions on performance of entrainment separators should
be determined.
     The aim of development of entrainment separators is
to improve performance of separators under industrial
conditions.  Thus, it is necessary to collect data on
industrial separators.  The data, when compared with
theoretical models, will represent possible problems re-
sulting from industrial conditions and will help in de-
signing future entrainment separators,

DEMONSTRATION PLANT
     From the present contract work, it is felt that we
can determine the performance of an entrainment separator
with reasonable accuracy.  It is possible to obtain im-
provement in the performance due to better design.  We
would like to move from the present research and develop-
ment to a demonstration of an improved design in the field.
The capacity of the present pilot plant is 85 m3/min.
Therefore, the next size should be around 1,000 m3/min
(35,000 CFM).
     The demonstration plant operation will involve
selecting an organization which operates a suitable plant
having entrainment separation problems and which is willing
to participate in the demonstration plant program.  The
design effort will include obtaining the necessary data
concerning the source of entrainment, preparing overall
design and selecting a final design.  The fabrication and
start up will involve selection and negotiation with sub-
contractors, procurement of components and supervision of
subcontractor efforts.  The test program will be to deter-
mine performance, observe the effect of change in variables
and compare the performance with theoretical developments.
                          8-3

-------
TO STUDY COMBINATIONS OF ENTRAINMENT SEPARATORS
     It seems that if more than one entrainment separator
is used, the combined series unit will offer a synergistic
effect.  It is possible to combine two different entrain-
ment separators to include the best features of each.  Some
examples are as follows:
     1.  The maximum gas velocity in the entrainment
separator is limited to the onset of reentrainment velocity.
It is generally the case, however, that a separator which
has high primary drop collection efficiency will have a low
reentrainment velocity, while one with high reentrainment
velocity will have low primary collection efficiency.  If
a combined unit is used with the first unit being used for
primary collection and coalescence of drops and the second
one for collection of large drops while being below the
onset of reentrainment velocity, increased capacity will
result.  The combination of efficiency and capacity will
exceed what either unit can do alone.
     Because the size of the entrainment separator will be
smaller, the initial capital cost will be lower.  The mini-
mum drop size that can be separated in the entrainment
separator is limited by the operating velocity.  This prob-
lem can be solved by using a combination of entrainment  •
separators.
     2.  Sometimes the entrainment load is high and con-
stituted of particles in a wide size range.  A single
entrainment separator may be inefficient, flooded or may
present reentrainment in this situation.  A combined unit
may be used in this case.  The first separator is a pre-
cleaner with low pressure drop, which removes large particles
constituting a significant fraction of the entrainment.  The
second separator will be an efficient device.
                            8-4

-------
APPENDIX

-------
Table A-l.   OVERALL PERFORMANCE OF ENTRAINMENT SEPARATOR
Exp.
No.
1
2
3
4
5
6
8
9
11
12
13
14
15
17
18
19
20
21
22
23
Test
Section
Baffle
Baffle
Baffle
Baffle
Jaffle
'Baffle
Baffle
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Mesh
Mesh
Mesh
Mesh
Air
Velocity
m/sec
4.8
3.2
6.1
2.4
1.8
1.2
4.9
5.4
4.2
3.0
2.0
2.4
1.2
6.3
6.4
6.2
6.1
4.4
3.0
211
.4
Liquid to
Gas Ratio
m3/m3
3.4xlO-5
2.97xlO-5
5.65xlO-5
4.66xlO"s
4.95xlO"5
9.14xlO-'5
1.213xlOr"
1.133x10-"
N.A.
3.224xlO-5
N.A.
5.609xlO-5
1.122x10""
1. 676x10'"
N.A.
3.06x10-"
1.36x10-"
1.83x10-"
2.1x10'"
2.5x10-"
Median
Drop
Diameter
ym
97
94
97
102
93.6
87
79
76 /

84
83
82
78
1225
1225
1225
1225
1225
1225
1225
Collection
Efficiency
%
*100
*100
*100
*100
N.A.
69.2
=aoo
*100
*100
*100
N.A.
78.8
78.6
=aoo
*100
100
94
N.A.
>99.9
>99.9
Pressure
Drop
cm W.C»
1,7
0.41
3.3
0.41
.0.12
0.12
1.5
0.82
0.29
0.16
0.08
0.12
0
1.3
1.4
1.5
2.2 -
1.3
0.62
0.54
Reentrainment
Present in
Observation
Section

—
— '
fm
-

fm
^
mm
-

—
_
fm
-

_
_
^


-------
Table A-l.   OVERALL PERFORMANCE OF ENTRAPMENT SEPARATOR
            (continued)
•
Exp.
No.
24
25
26
27
28
29
30
31
32
33
34
35
36
Test J
Section 1
Mesh
Mesh
Mesh
Mesh
Mesh
Mesh
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
37 (Tubes
38 [Tubes

40 Mesh
41 Mesh
43 Mesh
45 Mesh
46
i
i
Mesh


Mr
Velocity
m/sec
1.8
2.4
. 2
1.2
2.4
3.2
6.0
6.3
6.5
4.5
3.0
1.5
2.2
3.0
6.9
4.5
1.5
7.1
3.0
6.9



Liquid to
Gas Ratio
2.72x10-"
2.37x10-"
3.87x10-"
7.46x10'"
4.55x10-"
3.57x10-"
2.53x10'"
3.78x10-"
2.936x10-"
4.026x10-"
5.224x10-"
1.733xlO-3
5.661x10'"
1.297x10""
6.636xlO"5

2.579xlO-5
1.403xlQ-5
9.48x10- 6
5.685xlO-5
2.577xlO-5


edian
rop
iameter
ym
1225
1225
1225
1225
1225
1225
1225
1225
1225
1225
1225
1225
1225
380
380

84
84
. 84
84
84


Collection
Efficiency
i
>99.9
N.A.
. 100
100
90.3
87.8
N.A.
91
87.8
90.0
94.4
98.2
99.8
100
98.7

94.3
100
97.7
50
91.8


Pressure
Drop
cm W.C.
0.21
0.45
0.21
.0.29
0.54
0.78
1.6
1.8
1.3
N.A.
0.37
0.12
0.12
0_ *
.54
1.03

0.620
0.084
1.36
0.29



Reentrainment
Present in
Observation
Section
-
*•
—
—

-
*~
~
Some
"
Yes
••
~
—
—

-
—
Yes
*™




-------
Table A-l
OVERALL PERFORMANCE OF ENTRAINMENT SEPARATOR
 (continued)
Bxp.
No.
47
48
49
50
51
52
53
54
55
56
58
59
60
61
63
64
65
66
67
69
Test
Section
Mesh
Mesh
Mesh
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Tubes
Mesh
Mesh
Mesh
Mesh
Mesh
Mesh
Air
Velocity
m/sec
4.8
6.0
5.0
6.0
5.4
4.8
4.0
7.0
4.2
5.2
6.8
4.2
5.4
7.1
7.4
6.0
7.8
6.0
4.5
6.0
Liquid to
Gas Ratio
m3/m3
4.21xlO-5
3.532X10'5
2.448xlO-5
1.317x10-*
N.A.
9.782xl(T5
1.0127x10-"
9.374xlO-5
8.445xlO-s
8.442xlO-5
4.859xlO-5
5.739xlO-s
4.552xlO"5
2,171xlO-5
8.38X10-11
8.23X10-11
2, 34x10- 5
3.442xlO-5
4.616xlO-5
8. 354x10 -5
Median
Drop
Diameter
yra
84
84
84
380
380
380
380
380
380
380
380
380
380
380
84
84
84
84
84
84
Collection
Efficiency
%
64.8
63.1
80.8
100
• N.A.
100
100
83.2
93.7
95.1
100
94.94
98.6
74.6
61.5
57.6
100
73.22

100
Pressure
Drop
cm w.C,
0.87
1.3
0.87
0.87
0.87
0.66
0.55
1.5
0. 5
0.79
1.3
0.54
0.91
W • mJ J_
1.36
1.6
1.1
 w <3
Yes
Some

Very little
Some


Some



Yes
* \* «j
Yes

Some
U V/1ILW
Yes
JL w O
Some

-------
Table A-l.   OVERALL PERFORMANCE OF ENTRAINMENT SEPARATOR
             (continued)
Exp.
No.
70
71
73
74
75
76
77
78
79
80
Test
Section
Mesh
36" Pall
36" Pall
36" Pall
36" Pall
36" Pall
Baffle
Baffle
Baffle
Baffle
81 Baffle
82 Baffle
83 Baffle
84 Baffle
85 Baffle
86 Baffle
88 baffle
89
90
91
Baffle
Baffle
Jaffle
Air
Velocity
m/sec
4.5
5.0
4.9
1.0
5.0
4.9
6.9
6.0
5.0
6.0
6.8
3.0
3.0
7.0
6.0
1.5
7.0
6.0
4.5
3.0
Liquid to
Gas Ratio
m3/m3
5.383xlO"s
6.607xlO-5
2.950x10-"
4.588x10-"
1.131xlO-3
1.553xlO-3
6.873xlO-5
4.733xlO"5
7.005xlO-5
5.849xlO-5
6.297xlO-5
7.850xlO-s
4.351x10-"
2.330x10-"
2.393x10-"
5.384x10""
1.602x10-"
1.718x10-"
2.784x10'"
3.501x10'"
Median
)rop
Diameter
ym
380
380
380
1,225
1,225
_
— »
380
380
380
380
380
380
1,225
1,225
1,225
1,225
1,225
1,225
1,225
Collection
Efficiency
%
100
100
100
100
90.8
100
80
97.7
100
100
77.9
100
100
100
100
100
100
100
100
100
Pressure
Drop
cm W.C,
0.54
8.9
9.3
0.37
4.2
9.5
3.2
2.5
1.8
2.4
2.9
0.5
0.5
3.0
2.2
0.45
2.9
2.0
1.2
0.45
Reentrainment
Present in
Observation
Section
Slight
No
No
No
No
No
Yes
Some
Very little
-
Yes
Little
Little
Some
Some
Little
Little
Little
Some


-------
Table A-l.   OVERALL PERFORMANCE OF ENTRAINMENT SEPARATOR
            (continued)
Exp.
No.


92
93
94
95
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
Test
Section


Baffle
Baffle
Baffle
12" Pall
12" Pall
12" Pall
L2" Pall
L2" Pall
I1 Pall
Rings
it
it
jt
i*
tt
it
it
tt
tt
tt
tt
Air
Velocity

m/sec
2.0
1.0
7.1
5.8
2.0
1.0
5.9
4.5
2.0
1.0
1.0
6.0
3.5
6.0
3.5
6.0
6.0
4.5
6.0
4.5
Liquid to
Gas Ratio

mVm3
4.281x10-*.
6.9i3xio-*
8. 008x10-*
9.672x10-*
2.038xlO'3
3.233xlO-3
1.310xlO-3
l,689xlO-3
2.48xlO-3
3. 86x10- 3
6.56x10- 5
2.28xlO-5
I. 33x10- 5
3.16x10- 5
1.37x10-"
2.76xlO-s
1.15x10"*
5.21xlO"5
2.88x10'*
3.53x10-*
Median
Drop
Diameter
ym
1,225
1,225
1,225

-
-
84
84
84
84
84
84
380
380
1,225
1,225
Collection
Efficiency

"1
100
100
100
100
100
100
100
100
100
100
100
88.7
100
100
100
100
93.7
100
N.A.
100
Pressure
Drop

cm W.C.
0 25
0 33
2.6
N.A.
0.54
0.12
7.6
% n
3 . U
0.45
0.17
0.21
6.5
2.2
6.5
2.3
6.6
6.5
3.7
6.6
4.2
Reentrainment
Present in
Observation
Section


Yes
Slight
No
No
No
No
No
Slight
No
No
No
No
Some
No
Some
No

-------
                               Table A-l.   OVERALL PERFORMANCE OF ENTRAINMENT SEPARATOR
                                           (continued)
o\
Exp. Test
No. Section '
113 1' Pall
Rings
m"
i
115 "
116
117
118 " •
119 "
i
120 "
•^ i
121
122
123 tesh
124
125
126
127
128
130
131
132
133
11
it
ii
H
it
rt
ti
it
it
kir
Velocity
m/sec
6.0
6.0
6.0
6.0
4.5
6.0
3.5
6.0
3.5
6.0
7.2
4.5
1.0
3.0
7.0
6.0
3.5
2.0
3.0
7.2
Liquid to 1
Gas Ratio
mVm3
2.85x10-"
2.20x10-*
2. 07x10-*
2.60x10'*
3.47x10"*
2. 5 8x10 -5
4.l2xlO"5
ll.67xlO-s
1.74x10-*
2.75xlO-5
8.03xlO-5
4.06xlO-5
4.67xlO"5
4.55xlO-5
2.48xlO'5
S.OOxlO"5
5.87xlO'5
8.81xlO-5
1.920x10-*
2.794x10'*
1
Median
Drop
Diameter
um
1,225
1,225
1,225
1,225
1,225
84
84
84
84
84
84
84
84
84
84
84
84
84
1,225
1,225
Collection
Efficiency
%
N.A.
N.A.
N.A.
N.A.
100
100
100
100
100
100
88.7
100
100
100
87.6
79.1
100
100
100
100
Pressure
Drop
cm W . C .
6.7
6.6
6.7
7.1
4.3
6.4
2.60
7*T
.3
2.5
6y-
.5
1.9
0. 87
0.04
0.29
1.9
1.4
0.45
0.12
0.54
1.9
Reentrainment
Present in
Observation
Section
Some
Some
Some


















-------
Table A-l. OVERALL PERFORMANCE  OF ENTRAINMENT  SEPARATOR
           (continued)
Exp.
No.
134
135
136
137
138
140
141
142
143
145
146
147
148
149
150
151
152
153

Test
Section
Mesh
it
11
"
it
it
it
it
it
11
Tubes
it
it
it
it
Baffle
it
Packed
Bed 12"
Air
Velocity
m/sec
5.0
6.6
6.8
6.8
6.8
2.4
3.2
6.0
5.0
7.0
1.2
2.4
7.0
6.4
4.5
6.8
1.2
6.0

Liquid to
Gas Ratio
mVm3
3.390x10-*
2.861x10"*
2.73x10-*
8.31x10-*
8.34xlO~*
5.62xlO~5
2.23x10'*
4.606xlO"5
5 .'836x10 ~5
4.96xlO-5
1.006x10'*
8.634xlO-5
1.099xlO"5
3.022x10-*
3.471xlO-5
6.&07xlO-5
6.627xlO-5
4.277xlO"5

Median
)rop
Diameter
ym
1,225
1,225
1,225
_
-
380
1,225
84
84
84
84
84
380
1,225
1,225
380
84
84

Collection
Efficiency
100
100
100
100
100
100
100
100
100
99
99.5
99.2
99.5
100
99.8
99.8
99.7
100

Pressure
Drop
cm W . C .
1.5
2.5
2.5
2.9
2.8
0.27
0.62
1.5
0.95
1.6
0.04
0.21
1.5
1.20
0.79
2.8
0.08
5.4

Reentrainment
Present in
Observation
Section




















-------
Table A-2.  DROP DIAMETERS OF THE ENTRAINMENT  ENTERING AND
           LEAVING THE TEST SECTION
Exp.
1
Water
Feed Rate
cm3/sec
9.48X101
2 J9, 48x10 J
3
4
5
6
8
9
11
12
13
14
15
"i *i
17
18
19
20
21
22
23
1.52x10*
1.52xl02
1.52xl02
1.52xl02
3.16xl02
1.77xl02
1.64xl02
1.48xl02
L.26xl02
L.33xl02
L.33xl02
1 ,21x10
2.21xl02
l.llxlO2
1.90xl02
L.90xl02
L;90xl02
L.90xl02
Water
Pressure
atm. ("gauge")
5.44.
5.78
13.61
14,29
14.29
14.97
3.40
N.A.
N.A,
N.A.
N.A."
N.A.
N,A,
3.33
1.95
3.27
3.27
3.33
3.33
3.33
Type § No .
of nozzles
M6SS(12)
M6SS(12)
M6SS(12)
M6SS(12)
M6SS(12)
M6SSC12)
M26C12)
M6SS(12)
M6SS(12)
M6SS(12)
M6SS(12)
M6SS(12)
M6SS(12)
GG3(6)
GG3(6)
GG3(12)
GG3(6)
GG3C6)
GG3C6)
GG3C6)
Inlet
Median.
Drop Dia-
meter
urn
97
94
97
102
.- 94
87
79
. 76
78
84
83
82
78
1225
1225
1225
1225
1225
1225'
1225
Geometric
Standard
Devi at ion
1.4
1.3
1.3
1.4
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.8
1.8
1.8
1.8
1.8
1.8
1.8
Outlet 1
Median Drop
Diameter




N.A.
N.A.


-
93
86
70

-


91
120
. 91
Geometric
Standard
P ej/ iation




N.A.
N.A.


_
1.3
1.3
1 7
JL . £•
..


1.3
1.2
1.3

-------
Table A-2.  DROP DIAMETERS OF THE ENTRAPMENT ENTERING AND
      . .  . LEAVING THE TEST SECTION (continued)
Ixp.
Jo.
t
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
40
41 .
43
45
46
Water
Feed Rate
cmVsec
1.90xl02
M
1. 90x10*
1.90xl02
3.16xl02
3.16xl02
3.16xl02
f*
3.16xl02
4.11xl02
3.45xl02
4.00xl02
4.01xl02
3.98xl02
4.01xl02
2.15xl02
1.94xl02
6.64xlOl
•
5.36X101 .
4. 75x10 l
M
l.OlOxlO2
1.072xl02
Water
Pressure
atm. ("gauge")
3.33
3,33
3.33
3,33
3.33
3.33
3.33
3.33
3.40
3.40
3.4
3.4 '
3,4
3.4
3.4
13.95
13.6
13.6
13.6
13.6
Type g No,
o£ nozzle;
GG3(6)
GG3(6)
GG3(6)
GG3(9)
GG3(9)
GG3(9)
GG3(9)
GG3(12)
GG3(12)
GG3(12)
GG3(12)
GG3(12)
GG3(12)
M26(12)
M26(12)
M6SS(6)
M6SS(6)
M6SS(6)
M6SS(12)
M6SS.(12)
Inlet
Median
Drop Dia-
meter
urn
1225
1225
1225
1225
1225
122*5
1225
1225
1225
1225
1225
1225
1225
380
380
84
..84
84
84
84
Geometric
Standard
Deviation
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.8
1.5
1.5
1.3
1.3
1.3
1.3
1.3
Outlet i
Median Drop
Diameter
}im
91

* ^
_
96
76
83
115
94
125
109
97 . '
103
_
330
87.6

232

211
Geometric
Standard
Devi nt ion
1.3



1.3
1. 2
1.3
1.4
1.3
1.4
1.4
1,3
1.3

1,6
1.2

1.4

1.7

-------
Table A-2.
DROP DIAMETERS OF THE ENTRAINMENT ENTERING AND
LEAVING THE TEST SECTION (continued)
iixp.
*0.
47
48
49
50
51
52
53
54
55
56
58
59
60
61
63
64
65
66
67
68

Water
Feed Rate
cm3/sec
1.074xl02
9.736X101
7.264X101
3.056xl02
2.833xl02
2.61xl02
2.41xl02
1.914xl02
1.714xl02
1.78xl02
1.267xl02
1.161xl02
1.069xl02
5.472x10*
3.79X101
3.79X101
l.lOSxlO2
l.lOSxlO2
1.074xl02
2.595xl02
i
Water
Pressure
atm, f gauge")
13.6
13.6
13.6
3.40
3.40
3.40
3.40
3.40
3.40
3.40
3.40
3.40
3.40
3.40
13.6
13.6
13.6
13.6
13.6
3.4

Type § No,
of nozzles
M6SS(12)
M6SS(12)
M6SS(12)
M26(12)
M26(12)
M26(12)
M26(12)
M26(9)
M26(9)
M26(9)
M26(6)
M26(6)
M26(6)
M26(3)
M6SS(3)
M6SS(3)
M6SS(9)
M6SS(9)
M6SS(9)
M26(12)

Inlet
Median
Drop Dia-
meter
urn
84
84
84
380
380
*
380
380
380
380
380
380
380
380
380
84
84
84
84
84
380

Geometric
Standard
Deviation
1.3
1.3
1.3
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.3
1.3
1.3
1.3
1.3
1.3

Outlet
Median Drop
Diameter
jim

1377
123
414
317 '
413
1063
300
300
336
392
87
78
308
109
264
389
252
-
109
m
Geometric
Standard
Deviation

2.3
1.4
1.7
1.7
1.8
2.3
1.6
1.6
1.6
1.8
1.3
1.2
1.8
1. 5
1.7
1.9
1.8

1.4


-------
Table A-2.
DROP DIAMETERS OF THE ENTRAINMENT ENTERING AND
LEAVING THE TEST SECTION (continued)
ixp .
4o.
69
70
71
73
74
75

76

77
78
79
80
81
82
83
84
85
86
88
89
90
Water
Feed Rate
cm3/sec
2.333xl02
2.198xl02
2.164x10*
3.881xl02
3.564xl02
1.079xl03

1.459xl03

1.165xl02
1.272xl02
2,027xl02
1.763xl02
1.767xl02
1.761xl02
3.644xl02
3.594xl02
3.439xl02
3.442xl02
A
2.661X102
A
2.567xl02
3.194xl02
	 .
Water
Pressure
atm. f gauge")
3.40
3.40
3.40
3.40
3.40
Type $ No,
of nozzlei
M26(12)
M26(12)
M26(12)
1/8"GG3(12
1/8"GG3(12
3.06 [small gard
fiose (1)
2.04 [large gard
hose (1)
3.40 M26(12)
3.40 M26(9)
3.40 M26(12)
3.40
3.40
3.40
3.40
3.40
3.40
3.40
3.40
3.40
3.40
426(12)
^26(12)
H26(12)
1/8"GG3(12
1/8"GG3(12
1/8"GG3(12
1/8"GG3(12
1/8"GG3(9)
1/8"GG3(9)
1/8"GG3(9)
Inlet
Median
Drop Dia-
meter
urn
380
380
380
) 1,225
) 1,225
sn

sn

380
380
380
380
380
380
) 1,225
) 1,225
) 1,225
) 1,225
1,225
1,225
1,225
Geometric
Standard
Deviation
1.5
1.5
1.5
1.8
1.8
_

-

1.5
1.5
1.5.
1.5
1.5
1.5
1.8
1..8
1.8
1.8
1.8
1.8
1.8
Outlet
Median Drop
Diameter
urn
115

—
«.
-
—

—

1080
798
688
419
634
162
714
3025
1060
981
614
454
511
Geometric
Standard
Devi at ion
1.4

—
_
-
.

_

2 2
£* • £*
1 8
J- • LJ
2.1
1.7
1.6
1.4
1.6
2.4
1.9
1.6
1.7
1.7
1.7

-------
Table A-2.   DROP DIAMETERS OF THE ENTRAINMENT ENTERING AND
            LEAVING THE  TEST SECTION (continued)
Exp.
91
92
93
94

95

97

98

99

100


Water
Feed Rate
cmVsec
3.206xl02
3.192xl02
3.15xl02
1.086xl03

1.069xl03

1.077xl03

1.078xl03

1.454xl03

1.453xl03


Water
Pressure
atm. ("gauge")
3.40
3.40
3.40
3.12

3.20

3.20

3.20

2.04 1

2.04


Type $ No
of nozzlei
L/8"GG3(9)
L/8"GG3(9)
L/8"GG3(9)
small gard
lose (1)
>mall gard
lose (1)
small gardi
lose (1)
>mall gardi
lose (1)
,arge gardi
lose (1)
,arge gardi
lose (1)
'
Inlet
Median
Drop Dia-
meter
urn
1,225
1,225
1,225
m
*'
in





;n

;n


Geometric
Standard
Deviation
1.8
1.8
1.8












Outlet
Median Drop
Diameter
	 um 	
795
696
N.A.
N.A.

95





88

^_


Geometric
Standard
Deviation
1.8
1. 5
N.A.
N.A.

1.3





1. 3





-------
                    Table  A-2.  DROP DIAMETERS OF THE  ENTRAINMENT ENTERING AND
                               LEAVING THE TEST SECTION (continued)
C/4
Bxp.
to.
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
Water
Feed Rate
cm3/sec
1.453xl03
1.449xl03
1.263xl02
1.137xl02
1.137xl02
7.264X101
9. 159x10 l
3.474X101
1.327xl02
3.097xl02
4.453xl02
4.492xl02
4.233xl02
3.050xl02
3.058xl02
3.567xl02
3.878xl02
1.137xl02
1.137xl02
7.264X101
Water
Pressure
atm. (gauge 1
2.041
2.041
13.605
13.605
13.605
13.605
13.605
13.605
3.401
3.401
3.401
3.401
3.401
3.401
3.401.
3.40
3.40
13.61
13.61
13.61
Type § No.
of nozzle*
11-1/2F35
11-1/2F35
M6(12)
M6(12)
M6(12)
M6(6)
M6(6)
M6(3)
M26(12)
M26(12)
GG3(12)
GG3(12)
GG3(12)
GG3(9)
GG3(9)
GG3(12)
GG3(12)
M6(12)
M6(12)
M6(6)
Inlet
Median
Drop Dia-
meter
urn

-
84
84
-
84
84
84
380
380
12
12
12
12
12
12
12
84
84
84
Geometric
Standard
Deviation

-
1.3
1.3
-
1.3
1.3
1.3
1.5
1.5
1.8
1.8
1,8
1.8
1.8
_
-
1.3
1.3
1.3
!
Outlet
Median Drop
Diameter
ym

-
-
69
-
_
-
294
510
-
298
-
.
281
351
277
-
-
-

Geometric
Standard
Deviation

-
-
1. 3
-
_
-
1.6
1.8
-
1.6

-
1.5
1.6
1.6
-
-
-


-------
Table A-2.  DROP DIAMETERS OF THE ENTRAINMENT ENTERING AND
           LEAVING THE TEST SECTION (continued)
Exp.
to.
121
122
123
124
125
126
127
128
130
131
132
133
134
135
136
t
137
138
140
141
142

Water
Feed Rate
cm3/sec
1.137xl02
3.474X101
1.074xl02
1.074xl02
1.074xl02
1.074X102-
1.074xl02
1.074xl02
1.074xl02
1.074xl02
3.494x10*
4.536xl02
4.392xl02
4.261xl02
4.182xl02

1.067xl03
1.069xl03
2.S65xl02
4.185xl02
1.263xl02

	 ,
Water
Pressure
atm. (gauge)
13.61
13.61
13.61
13.61
13.61
13.61-
13.61
13.61
13.61
13.61
3.40
3.40
3.40
3.40
3.40

3.06
3.06
3.40
3.40
13.60

Type § No.
of nozzles
M6(12)
M6(3)
M6(12)
M6(12)
M6(12)
M6(12)
M6(9)
M6(9)
M6(9)
M6(9)
1/8GG3(12
1/8GG3(12
1/8GG3(12
1/8GG3(12
GG3(12)

11-1/2F18
11-1/2F18
M26(12)
GG3(12)
M6(12)

Inlet
Median
Drop Dia-
meter
urn
84
84
84
84
84
84
84
84
84
84
1 1225
I 1225
I 1225
) 1225
1225

-
-
380
1225
84

Geometric
Standard
Deviation
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.8
1.8
1.8
1.8
1.8

-
-
1.5
1.7
1.3

Outlet
Median Drop
Diameter
ym
_
-
798
-
-
-
605
152
-
-
-
-
-
441
472

-
-
-
-
"
t
Geometric
Standard
Deviation
_
-
1.9
-
-
-
1.9
1.5
-
—
-
-
-
1.6
1.6

-
-
-
-



-------
                  Table A-2.   DROP DIAMETERS OF THE ENTRAINMENT ENTERING AND
                              LEAVING THE TEST SECTION (continued)
Exp.
4o.
143
145
146
147
148
149
150
151
152
153
Water
Feed Rate
cm3/sec
I,263xl02
1.390xl02
1.273xl02
1.334xl02
2.353xl02
4.321xl02
4.214xl02
2.118xl02
1.314X102
I,300xl02
Water
Pressure
atm. f gauge ")
13.60
13.60
13.60
13.60
3.40
3.40 "
3.40
3.40
13.60
13.60
Type § No
of nozzles
M6(12)
M6(12)
M6(12)
M6(12)
M26(12)
GG3(12)
GG3(12)
M26(12)
M6(12)
M6(12)
Inlet
Median
Drop Dia-
meter
urn
84
84
84
84
380
1225
1225
380
84
84
Geometric
Standard
Deviation
1.3
1.3
1.3
1.3
1.5
1.8
1.8
1.5
1.3
1.3
Outlet
Median Drop
Diameter
urn
86
87
-
Geometric
Standard
Deviation
1.3
1.3
-
I
M
tn

-------
                  Table A-3.   LIQUID MATERIAL BALANCE
Exp.
No.
1
2
3
4
5
6
-8
9
.12
13
14
15
17
18
19
20
21
22
23
24
Input
cm 3
6.07xl05a
3.329xlOsa
7.61xlOsa
5.36xl05
7.91xl05
7.28xl05
1.367xl06a
1.337xl06
5.076xl05
N.A.
3.741xl05
4.775xl05
5.63xl05
N.A.
L.232xl06
5.12X105
i.481x!05
7.618X105
?.391xl05
5.912xl05
\
i
Before
Test Section
% of Input '
68.2 •
81.3
57.7
84.4
93.9
91.1
64.9
35.6
88.1
3.226xl05
85,0
85.7
7.8
4.42xl05
13.9
18.7
21.1
38.1
41.1
52.0

Test Section
Section I
•6 of Input
17.1
14.2
27.0
10.1
5.8
5.2
18.9
64, Oa
10.9
3.659x10*
10.9
5.4
28.3
5.438xl05
63.3
23.9
49.7
60.4
61.7
65.0

Section .11
* of Input
12.9
0.4
7.4
2,7
0.6
- 0 . 6
8.0
0.3
12.1
3.94x10*
11.9
5.8
16.5
3.31Sxl03
0
23.5
6,7
0.4
0
0

Section III
% of Input
1,7$
. 0
5.46
0
0
0.4
7.33
0
0
0
0
0
19.78
2.805xl033
0
25.93
2.1
0
0
0

Section IV
% of Input
0.043
0
1.63
0.053
0
0
0.83
0
0
0
0
0
0.23
3.545x10*3
0
3.13
1.9
0
0
0

After Test
Section in air
?o of Input
0
0
0
0
N.A, '
2.7a
0
0
0
N.A.
3. 2ct
• *•* w»
3 . 5ct
0
N.A.
0
4.9
N.A.
1.1
N.A.
N.A.

(See notes  on page  A-23)

-------
                 Table A-3.  LIQUID MATERIAL BALANCE .(continued)
Exp.
No.
25
26
27
28
29
30
31
32
.33
34
35
36
37
38
40
41
43
45
46
47
Input
cm3
6.822xl05
5.685xl05
1.137xl06
L.137xl06
1.137xl06
4. 738x10 5
1.3S5xl06
5.917xlOs
L.470xl06
L.481xl06
2.888xl06
L.470xl06
7.954xl05
7.915xl05
2.285xlOs
1.895xl05
1.545xl05
3.568xl05
3. 70 5x10 5
3.754xl05
i
\
I
Before
Test Section
% of Input '
44.3 •
54.4
47.3
35.7
32,8
10.6
41.2
7.6
17.5
26.8
39.4
41.3
67.2
47.5
66.0
92.6
71.0
68.0
67.9
64,0


-
Test Section
Section I
1 of Input
60.3
56.8
50.8
57.4
34.1
31.5
27,4
36.1
62.5
63.5
-47.7
28.9
26.3
21.0
32.0
9.1
15.7
16.0
10.2
20.6



Section J3
% of Input
0
0
0
0.4
16,8
' 29.23
6.63
453 '
18.63
5.53
11.33
27.53
12.3
17.2
0
0
12.8
0
19.33
2.6



section III
% of Input
0
0
0
0.33
9.53
14.83
11.13
0
0.5
0
0.1
0
0
0
0
0
0
0
0
0.06



Section IV
% o£ Inrmt
0 -
0
0
0
6.93
19.23
8. '33
0
0
0.2
0
0.1 '.
0
0
0
0
0
0
0
0



After Test
Section in air
% of Input
N.A.
0
0
6.2
14.9
N.A.
5,3
11.3
0.9
4.1
1.5
2.2
0

r.92a
0
0.5a
16. Oa
2 ,6a
12. 7a



(see notes on page A-23)

-------
                  Table A-3.  LIQUID MATERIAL BALANCE  (continued)
Exp.
No.
48
49
50
51
53
54
55
56
57
58
59
60
61
63
64
65
66
67
68
69


Input
cm 3
3.365xl05
2.499xl05
1.126xl06
1.007xl06
8.567xl05
6.727xl05
6.072xl05
6.289xlOs
6.140xl05
4.402xl05
4,08.2xl05
3.724xl05
L.SOSxlO5
L.192xlOs
U224xl05
3.803xl05
5.840xlOs
3.761xl05
).165xl05
3.259xl05
t

Before
Test Section
% of Input
57.9
67.2
59.7
N.A.
69.5
34.8
60.9
53.4
44.1
53.4
60.5
55.8
43.0
65.2
73.1
68.6
64.0
63.1
60.7
59.4


Test Section
Section I
; of Input
17.7
26.5
32.7
34.2
34.4
28.7
35.4
39.1
35.6
30.2
35.5
39.7
30.0
6.4
12.4
6.7
18.7
24.1
25.6
26.9


Section II
i of Input
8.9
1.6
7.83
12.7
2.13
*' 25.63
1.2
5.23
12.63
24.33
2.0
3.83
12.66
15.03
3.14
28.3
7.63
0.3
33.0
17.0


Section III
% of Input
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0


Section IV
?; of Input
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0


After Test
Section in air
% of Input
IS.Sct
4.7a
0
N.A.
0
10. 9a
2.5a
2.3a
7,7a
0
2.0a
0.7a
14. 4a
13. 4a
11.4
0 .
9.7a
12. 5a
N.A.
0

•
(see notes on page A-23)

-------
                 Table A-3.  LIQUID MATERIAL BALANCE  (continued)
Exp.
No.
70
71
73
74
75
76
77
78
79
80
81
82
83
84
85
86
88
89
90
91
Input
cm 3
7.806X105
7.675xl05
1.386xl06
1.281xl06
3.872xl06
5. .243x10*
4.033xl05
4.438xl05
7.182xl05
6.205xl05
6.207xl05
6.268xl05
1.305x10*
1.278x10*
1.238x10*
1.236x10*
9.418xl05
9.100xl05
1.139x10*
1.147x10*
t
|
*
Before
Test Section
1 of Input
79.2
71.2
30.2
76.0
2.3.
2.9
45.4
57.2
67.4
62.2
53.9
74.9
33.1
14.6
21.3
56.3
20.4
24.2
26.4
38.8



' Test Section
Section I
% of Input
31.5
41.9
46.6
40.9
15.4
25.3
40.4
38.7
37.9
37,3
35,8
25.6
74.2 -
78.8
78.2
53.4
80,2
78.7
80.6
70.8



Section .11
% of Input
1.6
8.5
3.4
0
67,6
60,1
3,3
3.1
0.5
3.4
2.0
0.9
2.4
16.4
9.6
1.0
10.3
8.1
4.3
2.7



Section III
% of Int)ut
0
0.9
2.3
0
6.8
11.9
0
0
0
0
0.1
0
0
0
0
0
0
0.1
0
0



Section IV
% of Innut'
0
0
0
0

0.4
0
0
0
0
0
0
0
0.3
0.1
0
0.1
0.17
0.1
0



After Test
Section in air
% of Incut
N.A.
N.A.
N.A.
N.A.
7.9a
0
10. 9a
l.Oa
0
0
8.2a
0
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.



(see notes on page A-23)

-------
                 Table  A-3.  LIQUID MATERIAL BALANCE (continued)
Bxp.
No,
92
93
94
95
97
98
99
100
Input
cm 3
1.144xl06
1.132xl06
3.892xl06
3.835xl06
3.873xl06
3.880xl06
5.219xlOs
5.448xlOs
Before
Test Section
% of Input
49.7
59.1
2.3
2.1
29.6
44.3
0.9
2.5
Test Section
Section I
of Input
60.9
53.5
29.7
13.3
72.4
57.2
11.6
37.8
section II
' of Input
1,8
0.75
35.5
69.8
0.3
0.17
67.4
51.3
ection III
% of Input
0
0
24.7
15.9
0
0
19.3
4.9
Section IV
% of Input
0
0
12.5
0.6
0
0
1.7
0.4
\fter Test
section in air
% of Input
N.A.
N.A.
N.A.
0
0
0
N.A.
3. la
(see notes  on page A-23)

-------
                  Table A-3.  LIQUID MATERIAL BALANCE (continued)
Exp.
No.
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
Input
cm 3
5.224xl06
5.216xl06
4.526xl05
3.954xl05
4.014xl05
2.473xl05
5.214xl05
L.107xl05
t.635x!05
l.lOSxlO6
L.589xl06
L.607xl06
L.SlOxlO6
L.084xl06
L.088xl06
116 |L.269xl06
117 L.385xlOe
118
119
120
K046xl05
4.007xl05
2.470xl05
Before
Test Section
1 of Input
36.4
50.4
90.3 .
76.8
74.7
61.2
34.3 •
62.4
69.9
85.8
27.1
33.9
21.1
18.4
23.5
17.7
24.4
74.4
75.9
72.8
Test Section
Section I
% of Input
67.5
50.2
44.8
16.3
20.2
14.5
18.1
11.0
23.7
28.5
33.3
58.0
32.4
41.7
34.8
35.4
62.9
14.0
23.8
16.1
Section II
% of Innut
1.6
0.2
0
4.3
0.8
6.7
0
5.5
4.0
0.3
46.9
13.9
52.5
50.9
57.7
60.0
19.9
14.8
0
49.9
Section III
1 of Input
0.09
0
0
0
0
0
0
0
0.2
0
0.4
0
0.2
0.4
0
0.4
0
0
0
0
Section IV
I of Input
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
After Test
Section in air
% of Input
0
0
0
0
0
0
0
0
2.2
0
N.A.
0
N.A.
N.A.
N.A.
N.A.
0
0
0
0
(see notes on page A-23)

-------
                                Table A-3.   LIQUID MATERIAL BALANCE  (continued)
to
t-o
5xp.
No.
121
122
123
124
125
126
127
128
130
131
132
133
134
135
136
137
138
140
141
L42

Input
cm3
.088xl05
1.106xl05
.87xl05
3.86xl05
3.86xl05
3.84xl05
3.56xl05
3.56xl05
3.78xl05
3.85xl05
1.252xl06
L.631xl06
L.574xl06
L.529xl06
S.OOOxlO6
7.627xl06
7.629xl06
..842xl06
S.OOSxlO6
5.876xl05
1
«
i
before
Test Section
1 of Input
75.1
63.8
86.5
68.1
91.9
76.7
67.4 •
66.1
63.6
69.4
69.2
17.4
27.9
17.3
16.6
0.8
0.5
90.2
68.2
58.3


Test Section
Section I
\ of Input
20.0
13.7
28.0
28.8
2.6
19.5
26.9
26.8
21.5
8.2
43.6
57.7
74.5
56.0
59.3
22.0
21.8
17.8
39.2
24.7


ection II
of Input
0
2.1
1.75
0
0
0
1.6
0
0
0
0
29.6
1.1
30.4
29.0
61.3
65.4
0
0
0.3


ection III
% of Input
0
0
0
0
0
0
0
0
0
0
0
0.3
0
0.6
0.9
15.7
13.8
0
0
0


ection IV
?: of Input
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0.2
0.6
0
0
0

fter Test
ection in air
% of Input
0
0
3.59
0
0
0
4.0
6.8
0
0
N.A.
N.A.
N.A.
N.A.
0.1
0.2
N.A.
N.A.
N.A.
0

i
                (see notes on page A-23)

-------
                                 Table A-3.   LIQUID MATERIAL BALANCE (continued)
Exp.
No.
143
145
146
147
148
149
150
151
152
153

Input
cm 3
9.025xl05
9.87xl05
9.160xl05
9.415xl05
1.667xl06
3.099xl06
3.006xl06
L.473xl06
J.454xl05
).365xl05
1
j
«i
Before
Test Section
% of Input
56.7
52.9
82.2
71.9
36.8
16.8
30.4'
61.6
87.9
63.3


Test Section
Section I
\ of Input
26.5
23.3
3.0
8.7
29.0
46.9
10.5
43.9
12.4
19.3


Section .11
; of Input
0
0.2
0.2
1.3
22.3
41.4
65.6
3.2
0
2.8


section III
% of Input
0
0
0
0
0
0
0.2
0
0
0


Section IV
% of Input
0
0
0
0
0
0
0
0
0
0


kfter Test
Section in air
% of Input
0
0.1
0
0.1
0.2
N.A.
N.A.
N.A.
N.A.
0


to
C/4
          a = Obtained by material balance
          3 = Liquid overflowing from previous section
          * = If the liquid input is not available (N.A.) liquid flow is given  in cm3

-------
Table A-4.  PRESSURE DROP DATA
Exp .
No.
i
!
i
1
2
3 '
4
5
6
8
9
11
12
13
14
15
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
System
Pressure
mm Hg gauge
N.A.
N.A,
N.A.
N.A.
-24.36.
-26.39
-25.12
-24.61
-23.09
-23.09
-23.09
-24.87
-26.14
-25.12
. -24.80
-23.60 '
-23.50
-26.80
-23.0
-24.4
-24.3 -
-22.1
-21.9
-19.9
-3.7
-20.5
-22.0
-22.0
-22.6
-32.0
Pressure Drop Over Test Section
AP,
dry
cm W . C .
1.7
0.41
3.0
0.41
0.08
0.12
1.5
0.74
0.29
0.12
0.08
0.12
0.04
1.2
1.20
1.1
1,03
0.58
0.29
0.21
N.A.
0.29
0.04
0.04
0.21
0.29
1.3
1.3
1.3
N.A.
A? ^
wet
cm W.C.
1.7
0.41
3.3
0.41
0.12
0.12
1.5
0.82
0.29
0.16
0.08
0.12
0
1.3
1.4
1.5
2.2
1.3
0.62
0.54
0.21
0.45
0.21
0.29
0.54
0.8
1.6
1.8
1.3
N.A.
            A-24

-------
Table A-4.   PRESSURE DROP DATA (continued)
Exp.
No.
34
35
36
37
38
39
40
41
42
43
45
46
47
48
49
50
51
52
53
54
55
56
58
59
60
61
63
64
65
66
System
Pressure
mm Hg gauge
-22.0
-22.0
-23.0
-23.0
-25.0
-25.5
N.A.
.-23.0
-21.9
-20.5
-23
-23
-23.5
-19
-18
N.A.
-24
-24
-24
-22.8
-23
-23
-20
-20
-22
-21.5
-19
-19
-19
-19
Pressure Drop Over Test Section
AP,
dry
cm w.C.
0.37
0.41
0.12
0.29
1.0
1.1
0.45
0.08
0.04
0.99
0.29
1.0
0.54
0.78
0.61
0.78
0.95
0.66
0.50
1 . 3
0.50
0.79
1.28
0.54
0.83
1.3
1.0
0.74
1.1
0.74
AP «.
wet
cm w.C.
0.37
0.12
0.12
0.54
1.03
1.45
0.62
0.08
0.04
1.4
0.29
1.7
0.87
1.3
0.87
0.87
0.87
0.66
0.50
0.5
0.50
0.79
1.28
0.54
0.91
1.4
1.6
1.1
1.9
1.3
             A-25

-------
Table A-4. PRESSURE DROP DATA (continued)
Exp .
No.
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
88
89
90
91
92
93
94
95
97
98
99
100
-
System
Pressure
mm Hg gauge
-20
-20
-20
-21.5
-20
-18
-19
-19
-19
-20
-19.8
-22
-23
-22.9
-23
-23
-22
-22
-26
-26.
-19
-20
-20
-20
-20
-20
-20
-20.5
-20
-20
-17 •
-17

Pressure Drop Over Test Section
iPdry
cm W.C.
0.45
1.1
0.78
0.45
8.63
0.45
8.6
0.45
9.1
8.7
2.8
2.4
1.7
2.2
2.7
0.54
0.54
2.7
2.1
0.12
2.7
2.0
1.2
0.540
0.25
0.41
2.7
6.1
0.62
0.21
5.9
3.4

AP «.
wet
cm W.C.
0.78
2.0
1.0
0.54
8.9
0.45
9.29
0.37
4.2
9.5
3.2
2.5
1.8
2.4
2.9
0.54
0.54
3.0
2.2
0.45
2.9
2.0
1.2
0.45
0.25
0.330
2.6
N.A.
0.54
0.12
7.6
5rt !
.0
1
             A-26

-------
Table A-4.  PRESSURE DROP DATA (continued)
jExp.
No.
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
130
131
System
Pressure
mm Hg gauge
-17.5
-17.5
-19.0
-18.0
-18,0
-17.0
-17.0
-20.0
-20.5
-20.0
-22.0
-22.0
-18.0
-18.0
-17.0
-17.0
-17.0
-23.0
-23.0
-20.0
-20.0
-20.0
-26.0
-25.0
-23.0
-23.0
-20.0
-20.0
-16.0
-17.0
Pressure Drop Over Test Section
AP,
dry
cm w.C.
0.87
0.21
0.21
6.2
2.21
6.2
2.2
6.2
6.1
3.4
5.9
3.5
5.9
6.1
6.2
6.2
3.6
5.9
2.4
6.2
2.4
6.2
1.1
0-.45
0.04
0.29
1.0
0.79
0.29
0.12
APwet
cm w.C.
0.45
0.17
0.21
6.5
2.2
6.5
2.3
6.6
6.5
3.7
6.7
4.2
6.7
6.6
6.7
7.1
4.3
6.4
2.6
7.3
2.5
6.5
1.9
0.87
0.04
0,29
1.9
1.4
0.45
0.12
                A-27

-------
Table A-4.  PRESSURE DROP DATA (continued)
Exp .
jNo.
132
133
134
135
136
137
138
140
141
142
143
146
147
148
149
150
151
152
153
System
Pressure
mm Hg gauge
-19.0
-17.0
-17.0
-18.6
-23.2
-19.0
-16,8
-17.0
-18.5
-20.0
-20.9
-20.2
-18.5
-14.5
-15.8
-18.0
-16.8
-18.8
-18.7
Pressure Drop Over Test Section
APdry
cm W.C.
0.21
1.]
0.62
1.0
1.0
1.0
1.0
0.12
0.29
0.87
0.62
0.04
0.12
1.2
1.0
0.54
2.60
0.04
5.1
" AP «.
wet
cm W.C.
0.54
1.9
1.5
2.5
2.5
2.9
2.8
0.21
0.62
1.5
0.95
0.04
0.21
1.5
1.2
' 0.79
2.8
0.08
5.4
                 A-28

-------
APPENDIX B
 GLOSSARY

-------
                       GLOSSARY

COLLECTION EFFICIENCY or OVERALL COLLECTION EFFICIENCY
     Collection efficiency or overall collection efficiency
is the mass ratio of net liquid collected in the entrainment
separator to the liquid present in the inlet entrainment.
It can also be expressed as the difference between primary
efficiency and reentrainment.  We use either fraction or
percent, as specified in the text or figure.

PENETRATION
     Penetration is the mass ratio of drops in the outlet
to that of the inlet of the entrainment separator.
Penetration is also equal to "1 - collection efficiency",
if in fractional form.  We use either fraction or percent,
as specified in the text or figure.

PRIMARY COLLECTION
     Primary collection is defined as fractional collection
of the drops present in the original entrainment by various
mechanisms which is reported in terms of mass fraction as
an efficiency.  Primary efficiency includes only the
collection of drops present in the original entrainment.
The reentrainment of these collected drops or the subsequent
collection of these reentrained drops does not affect the
primary collection efficiency.

REENTRAINMENT
     Reentrainment is the  mass ratio of drops entering the
gas from the liquid in the entrainment separator to drops
present in the inlet entrainment.
                        B-l

-------
REENTRAINMENT VELOCITY
     Reentrainment velocity is the gas velocity at which
drops are first observed to become reentrained in the gas.
The reentrainment velocity will vary for different kinds of
entrainment separators and different operating conditions.

SECONDARY COLLECTION
     Secondary collection refers to drops which are
absorbed after having been reentrained.  The mass ratio
of these drops to those present in the inlet entrainment
is the secondary collection efficiency.
                             B-2

-------
APPENDIX C
REFERENCES

-------
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Alia,  P.,  L.  Cravarola, A.  Hassid,  and  E.  Pedrouhi.
Liquid Volume Fraction  in Adiabatic Two Phase Vertical
Upflow-Round  Conduit. CISE  Report R-105. 1965.
Anderson,  J.  D., R. E.  Bellinger, and D. E. Lamb. Gas
Phase  Controlled Mass Transfer  in Two Phase Annular
Horizontal Flow. AIChE  Journal.  10;.640,  1964.

Baker, 0.  Simultaneous  Flow of  Oil  and  Gas. Oil Gas
Journal. 53:185, .1954.

Bell,  C. G. and W. Strauss. Effectiveness  of Vertical
Mist Eliminators in a Cross Flow Scrubber. Journal
of the APCA.  23:967-9.  November  1973.

Bradie, J. K.  and A. N. Dickson. Removal of Entrained
Liquid Droplets by Wire Mesh Demisters.  Paper 24 in Fluid
Mechanics  and Measurements  in Two-Phase  Flow Systems. (A
joint  symposium of the  Inst. of  Mech. Engr. and the Yorkshire
Branch of  the  Inst. of  Chem. Engr.)  24-25. London. September
1969.
Buerkholz, A..Drop Separation on Wire Fitters. Chemie
Ingenieur  Tecknik. 4_2_,  21,  1314-1321, 1970.

Calvert, S. Air Pollution.  Stern, A. C.  (ed.). 3_, Academic
Press, New York. 1968.

Calvert, S.,  J. Goldshmid,  D. Leith, and D. Mehta.
Scrubber Handbook. Prepared for  EPA  Contract No. CPA-70-95.
Vol. I and II, 1972.
Calvert,S. and D. Lundgren. Particle Collection in Closed
Packed Arrays. Presented at AIHA. 1970.

Carman, P.C.  Fluid Flow Through  Granular Beds. Trans.
Inst. Chem. Engr. 15:150, 1937.

Castleman, R.A. Bur. Stand. J. Res.  Washington. 6^:369, 1931.
Carpenter, C.   L. and D.  F. Othmer.   Investigation of Wire
Mesh as an Entrainment Separator. AIChE Journal, p.  549, 1955,
Chien, S. F.  and W. Ibele, Pressure Drop and Liquid Film
Thickness of Two Phase Annular and Annular-Mist Flows.
ASME Paper. 62-WA170.

Chilton, H. Elimination of Carryover from Packed Towers With
Special Reference to Natural Draught Water Cooling Towers.
Trans. ICE. 30, 235.
                         C-l

-------
Collier, J. G. and G. F. Hewitt. Data on Vertical Flow
of Air-Water Mixtures in Annular and Dispersed Flow Regions:
Part II, Film Thickness and Entrainment data and Analysis
of Pressure Drop Measurements. Trans. Inst. Chem. Engr,
3£:127, 1961.
Cousins, L. B., W.H. Denton, and G. F, Hewitt. Liquid Mass
Transfer in Annular Two Phase Flow. Exeter. 21-23, June
1965.

Cousins, L. B. and G. F. Hewitt. Liquid Phase Mass Transfer
in Annular Two Phase Flow-Droplet Deposition and Liquid
Entrainment. AERE-R 5657. 1968.
Davis, R. F. Proc. Inst. Mech. Engrs. 149;148, 1940.
Dombrowski, N. and R. P. Frazer. A Photographic Investigation
into the Disintegration of Liquid Sheets. Phil. Trans.
A924, 247, 101, 1954.

Eckert, J. S. Chem. Engr. Prog. 57_, 9, 54, 1961.

Edgerton, H. E., K. J. Germeshansen, and H. E. Grier.
Photography J. 76^:198, 1936.

Page, A. and F. C. Johansen. Proc. Roy Soc. (London).
116A:170, 1927.
Fairs, G. L. Calder-Fox Scrubbers and the Factors
Influencing Their Performance. Trans. I Chem. E. London.
22, 110.
Foust, A. S., L. A. Wenzel, C. W. Clump, L. Maus, and
L. B. Andersen. Principles of Unit Operations. Toppan Company-
Tokyo. 1959.
Garner, F. H., S. R. M. Ellis, and J. A. Laay. The Size
Distribution and Entrainment of Droplets. Trans. Inst.
Chem. Engr. 3_2:222, 1954.
Gill, L. E., G. F. Hewitt, J. W. Hitchon, and P. M. C. Lacy.
Sampling Probe Studies of the Gas Core in Annular Two
Phase Flow: 1, The Effect of Length on Phase and Velocity
Distribution. Chem. Engr. Sci. 1_8:525, 1963.
Golovin, M. N., and A. A. Putnam. Ind. Engr. Chem. Fund.
1_:264, 1962.
Grimison. Trans. Am. Soc. Mech. Engr. 5_9:583-94, 1937.

Grimley, S. S. Trans. Inst. Chem. Engr. (London). 23, 228-235,
1948.
Haenlein, A. Forsch. Ing. Wes. 2^:139, 1931.
                        C-2

-------
Hall-Taylor, N.  S.  and  R. M. Nedderman.  The  Coalescence
of Disturbance Waves  in Annular Two-Phase  Flow. Chem.
Engr.  Sci.  23^:551-64, 1963.

Hanratty, T. J.  and D.  E. Woodmansee. Stability of the
Interface for a  Horizontal Air-Liquid Flow.  Symposium
on Two Phase Flow.  Exeter. Paper Al, 21-23,  June 1965.

Hinze, J. 0. Forced Deformation of Viscous Liquid
Globules. Appl.  Sci.  Res. Ai.  263-72, 1948.

Hinze, J. 0. Critical Speed  and Sizes of Globules. Appl.
Sci. Res. Al, 275-88, 1948a.

Houghton, J. G.  and W.  H. Radford. Trans. Am.  Inst. of
Ch. E. 35^:427, 1939.

Hughmark, G. A.  Film  Thickness Entrainment,  and Pressure
Drop in Upward Annular  and Dispersed Flow, AIChE Journal.
19, 5, 1062-7, 1973.

Jackson, S. and  S.  Calvert. AIChE Journal. 1,2:1075, 1966.

Jashnani, I. L.  Coalescence  and HTU in Foam  Fractionation
Columns. Ph.D. Dissertation, U. ov Cincinnati. 1971.
Kitchener, J. A. Foams  and Free Liquid Films,  in Recent
Progress in Surface Science. Academic Press. New York. 1964.

Kotov, N. A. Influence  of Spray Entrainment  on Gas Scrubber
Efficiency. Translated  by EPA  from Vodosnabzheniye i
Sanitaria Technika. 7/.31-4,  1972.

Lane, W. R. Shatter of  Drops in Streams of Air. Ind. Engr.
Chem. 43, 1312,  1951.
Lapple, C. E. and C. B.  Shepherd. IEC Ind. 32, 605, 1940.

Leith, D. and W. Licht.  The Collection Efficiency of
Cyclone Type Particle Collectors - A New Theoretical
Approach. Paper presented at San Francisco meeting of
AIChE. December  1971.
Leva. M. Chem. Engr. Prog. Symp. Ser. No. 10, 50,  51,  1954.

Lobo, W. E., L. Friend,  F. Hashmall, and F. A. Zenz.
Trans. AIChE. 41, 693,  1945.

Mercer, T. T. and H. Y.  Chow. J. of Coll. and Interface
Sci.  2.7:75-83', 1968.

Miles, J. W. On the Generation of Surface Waves by Shear
Flows. J. Fluid Mech. 3_, 185, 1957.
Moyers, C. G., Jr. Entrainment Separator Selection and
Evaluation. Engr. Res.  Report ER-60-1010, Union Carbide.
October 1960.
                         C-3

-------
Newitt, D. M., N. Dombrowski, and F. H. Knelman. Liquid
Entrainment: 1 The Mechanism of Drop Formation from Gas
or Vapor Bubbles. Trans. Inst. Chem. Engr. 3^, 244, 1954.
Nukiyama, S..and Y. Tarrasawa. Trans. Soc. of Mech. Engr.
(Japan). 4_, 5_, £, 1938-1940.
Perry, J. H. Chemical Engineering Handbook. 4th Edition.
McGraw-Hill. New York. 1963.
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Rayleigh, Lord, Phil. Mag. 48, 321, 1889.
Roberts, D. C. and D. E. Hartley. A Correlation of Pressure
Drop Data for Two Phase Annular Flows in Vertical Channels.
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                                 TECHNICAL REPORT DATA
                          (Please read Instructions on the reverse before completing}
 1. REPORT NO.
 EPA-650/2-74-119-a
                            2.
                                                       3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
 Entrainment Separators for Scrubbers--Initial
  Report
             5. REPORT DATE
              October 1974
            6. PERFORMING ORGANIZATION CODE
7 AUTHOR(sSeymour Calvert,  Indrakumar L.  Jashnani,
Shuichow Yung,  and Samuel Stalberg
                                                       8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
                                                       10. PROGRAM ELEMENT NO.
 A.P.T. , Inc.
 P. O.  Box 71
 Riverside, CA 92502
              1AB013; ROAP 21ACX-086
             11. CONTRACT/GRANT NO.
              68-02-0637
 12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 NERC-RTP,  Control Systems Laboratory
 Research Triangle Park,  NC 27711
             13. TYPE OF REPORT AND PERIOD COVERED
              Initial;   Through 6/74
             14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
          The report gives results of an evaluation of current technology relating to
 the separation of entrained drops  of liquid from the gas leaving scrubbers.  It includes
 results of experimental studies of entrainment separator characteristics, as well as
 theoretical analysis.  Zigzag baffle, knitted mesh, tube bank, packed bed, and cyclone
 devices were tested.  It reports collection efficiency and reentrainment as  related
 to drop size. Pressure drop as a  function of gas flow rate is also reported.
 Mathematical models for  primary collection efficiency are satisfactory, but useful
 reentrainment models are not yet available. An auxiliary experiment was aimed at
 determining reentrainment from liquid sheets under the influence of an air stream.
 Work is still in progress  on  vertical gas flow systems, solids deposition,
 mathematical modeling, and the development of improved designs.
 7.
                             KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                           b.lDENTIFIERS/OPEN ENDED TERMS
                         c. COSATI Field/Group
 Air Pollution
 Scrubbers
 Entrainment
 Efficiency
 Mathematical Models
Air Pollution Control
Stationary Sources
Entrainment Separators
Collection Efficiency
 13B
 07A
 07D
 14A
 12A
 8. DISTRIBUTION STATEMENT


 Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES

    318
20. SECURITY CLASS (Thispage)
Unclassified
                         22. PRICE
EPA Form 2220-1 (9-73)
                                        C-6

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