c/EPA
           Fnnrt. D * ,-   Industrial Environmental Research  EPA-600/7-78-087
           tnvironmental Protection  Laboratory          June 1978
           A9encV        Research Triangle Park NC 27711
Third Symposium on
Fabric Filters for
Paniculate
Collection
          Interagency
          Energy/Environment
          R&D Program Report
                               ******
                                          *****
                                          *****

-------
                    RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental Protec-
tion Agency, have been grouped into nine series. These nine broad categories were
established to facilitate further  development and application of environmental tech-
nology. Elimination of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The nine series are:

          1. Environmental Health Effects Research
          2. Environmental Protection Technology
          3. Ecological Research
          4. Environmental Monitoring
          5. Socioeconomic Environmental Studies
          6. Scientific and Technical Assessment Reports (STAR)
          7. Interagency Energy-Environment Research and Development
          8. "Special" Reports
          9. Miscellaneous Reports

This report has been assigned to the ENVIRONMENTAL PROTECTION TECHNOLOGY
series. This series describes research performed to develop and demonstrate instrumen-
tation, equipment, and methodology to repair or prevent environmental degradation from
point and non-point sources of pollution. This work provides the new or improved tech-
nology required for the control and treatment of pollution sources to meet environmental
quality standards.
                             REVIEW NOTICE


           This report has been reviewed by the U.S.  Environmental
           Protection Agency, and approved for publication.  Approval
           does not signify that the contents necessarily reflect the
           views and policy of the Agency, nor does mention of trade
           names or  commercial products constitute endorsement or
           recommendation for use.
           This document is available to the public through the National Technical Informa-
           tion Service, Springfield, Virginia 22161.

-------
                                         EPA-600/7-78-087
                                                   June 1978
Third  Symposiym  on  Fabric Filters
      for Particulate Collection
                 Richard Dennis, Compiler

                 GCA Technology Division
                     Burlington Road
               Bedford, Massachusetts 01730
                  Contract No. 68-02-2177
                Program Element No. EHE624
             EPA Project Officer: Dennis C. Drehmel

           Industrial Environmental Research Laboratory
             Office of Energy, Minerals, and Industry
               Research Triangle Park, NC 27711
                      Prepared for
                                           EiwlronmentaJ Prote
           U.S. ENVIRONMENTAL PROTECTION AGENCY  ^°n v>^orzry
              Office of Research and Development     *^'' ciou:--1 - !saiborn Street
                  Washington, DC 20460         Chicago, Illiaoia  60604

-------
                                  ABSTRACT
     The Third Symposium on Fabric Filters for Particle Collection was held on
December 5-6, 1977 in Tucson, Arizona.  The Symposium was sponsored by the
U.S. EPA1 s .Industrial Environmental Research Laboratory and was organized by
GCA/Technology Division.

     The conference was intended to emphasize current field experience and
engineering-oriented research so that potential users may better select
and/or design their control systems.  The technical content of the meeting
focused on fabrics for high temperature filtration, their field behavior with
fly ash and other effluents, design criteria and shakedown experience, and new
filtration concepts that appear amenable to combustion and other process
effluents.
   '             '    '
     This report presents the 17 technical papers presented at the symposium.
  .         •     ' •
                                    111

-------
                                ACKNOWLEDGMENT
     GCA wishes to express its appreciation for assistance in organizing and
conducting this symposium to Dr. Dennis Drehmel, EPA Project Officer.  Members
of the GCA/Technology Division staff who provided assistance were:
Mr. Stephen V. Capone, Dr. Paul F. Fennelly, and Mr. Norman F. Surprenant.
                                       IV

-------
                               TABLE OF  CONTENTS
                                                                          Page
 Abstract  .................                                ...
 Acknowledgments   ...............            ........  .
 List of Figures   .  .  ...............      * . ........ ^±
 List of Tables ................  .  .  .  .        ......


 Paper 1  - Selection Criteria for Emission Control System and
            Status Report of Fabric Filter Performance Testing  ..... 1

 Paper 2  - Modeling Coal Fly Ash Filtration With Glass Fabrics ..... 13

 Paper 3  - A Pilot Plant Study of Various Filter Media Applied
            to a Refuse Boiler  ...............             /-,

 Paper 4  - Field Tests With a Mobile Fabric Filter ........... 75

 Paper 5  - Australian Experience, Filtration of Flyash From Very Low
            Sulfur Coals  ..................             ,Q5

 Paper 6  - Demonstration of a High Velocity Fabric Filtration System
            Used to Control Flyash Emissions
 Paper 7  - Baghouse Performance on a Small Electric Arc Furnace  ....  155
 Paper 8  - Fume  Control at Small Smelters   ...  ..........      167

 Paper 9  - Fabric  Filters  in the Cement  Industry  .  .  ........  .  .  177

 Paper 10 - New Applications for Fabric Filters
 Paper  11 - Effect  of Modified  Cleaning Pulses  on Pulse  Jet  Filter
           Performance    ..................              205

 Paper  12 - Current and  Future  EPA Filtration Research   .........  229

 Paper  13 - Contributing Role of Single Fiber Properties to Nonwoven
           Fabric Performance  ................            235

 Paper  14 - Specific Resistance (K2) of Filter Dust Cakes:  Comparison
           of Theory and Experiments ................      251

 Paper  15 - The Influence of Electrostatically-Induced Cage Voltage
           Upon Bag Collection Efficiency During the Pulse-Jet Fabric
           Filtration of Room Temperature Flyash ... ......        289

Paper 16 - Textile Filter Media Durability ............  .     329

Paper 17 - High-Temperature Filtration ......  ........        331
List of Attendees  ............

-------
                               LIST OF FIGURES


Figure

                                   PAPER 1

  1        Comparison of Costs (%)  	  6

  2        Harrington No.  2 Flue Gas Flow Diagram and
           Monitoring Points 	  11

                                   PAPER 2
  1        Schematic, Dust Accumulation on Woven Glass Fabrics 	  16

  2        Massive Pinhole Leaks With all Multifilament Yarns and
           Large, ~200 ym, pores	17
  3        Typical Drag Versus Loading Curves for Filters With Different
           Degrees of Cleaning and a Maximum Allowable Level for
           Terminal Drag,  S   and Terminal Fabric Loading, WT  	  20

  4        Fly Ash Dislodgement From 10 ft x 4 in. Woven Glass Bag
           (Inside Illumination) 	  21
  5        Fly Ash Filtration With Completely and Partially Cleaned
           Woven Glass Fabric (Menardi Southern)  	  24
  6        Relationship Between Cleaned Area Fraction and Initial
           Fabric Loading.  GCA Fly Ash and Woven Glass Fabric 	  26

  7        Effect of Inlet Concentration on Predicted Outlet Concen-
           trations at a Face Velocity of 0.61 m/min.  GCA Fly Ash
           and Sunbury Fabric	28
  8        Predicted and Observed Outlet Concentrations for Bench
           Scale Tests.  GCA Fly Ash and Sunbury  Fabric	29
  9        System Breakdown for I Bags and J Areas Per Bag	32
 10        NUCLA Baghouse Simulation, Resistance  Versus Time  	  35
 11        Test Run No. 0422 Nucla Baghouse Simulation - Linear
           Penetration Versus Time Graph  	 36

                                   PAPER 3
   1        Schematic Diagram of the Enviro-Clean  RA-1 Dust Collector
           Model 144-RA1-5-104	46
   2        Temperature Profile  for the Enviro-Systems Baghouse  	 47

  3        Fabric Filter Pilot Plant  Installed  at Nashville Thermal
           Transfer  Corp	48
   4        Inlet Particle Size  Distribution for Two  Brinks Impactor
           Runs	52
   5        Outlet Particle  Size Distribution  	 54
   6        Outlet Particle  Size Distribution, Globe  Albany  	 55

                                      vi

-------
                               LIST OF FIGURES
Figure                          PAPER 3 (cont)
                                                                         Page
  7        Outlet Particle Size Distribution for Gore-Tex Fabric .... 57
  8        Comparison of Three (3) Fabrics for Outlet Concentration
           versus Air-to-Cloth Ratio .................. 60
  9        Comparison of Installed Costs for Four (4) Filter Media
           and Electrostatic Precipitators .............      62
 10        Installed Cost Comparisons for Different Air Pollution
           Control Techniques  ...................      64
 11        Comparison of Annual Operating Costs of  Four (4)  Filter
           Media  and ESP Assuming Four Year Bag Life .......... 65
 12        Comparison of Annual Operating Costs of  Four (4)  Filter
           Media  and ESP Assuming Four Year Bag Life ..........  66
 13        Annual Operating  Cost  Comparison for Three Air  Pollution
           Control Techniques  ....... ...........              gg
 14        Comparison of Annual Operating Costs of  Four (4)  Filter
           Media  and ESP Assuming Two  Year Bag  Life   ........  .  .  69
 15         Comparison of Annual Operating Costs of  Four (4)  Filter
           Media  and ESP Assuming Four Year Bag Life  ..........  70
 16         Annualized  Cost for  the Three  Air Pollution  Control
           Techniques  ................                    -,->

                                  PAPER  4
 1        Average Mass Penetration versus  Geometric Mean Particle
          Diameter   ................                      , „.,

                                  PAPER 5
 1        Typical Coal Analysis ...............
 2        ECNSW Fabric Filter Installations .............. 114
 3A       ECNSW Tallawarra Station - Section A Pilot Unit ......  .115
 3B       ECNSW Tallawarra Station - Section A and B Full Scale .... 116
 4        ECNSW Wangi  Station - Units 4,  5,  6 - Pulse Jet Filters .  .  . 117
 5        ECNSW Wangi  Station - Unit 5 PC Boiler - Reverse Air
          Baghouse  Design  Conditions  ...............      118
                                   VII

-------
                               LIST OF FIGURES

Figure                                                                   Page
                                   PAPER 6
  1        SD-10 General Arrangement With Pyramid Hoppers 	  .   123
  2        Fabric Filter Module Cell  ..... 	   124
  3        Baghouse Pictorial Showing Gas Flow  	   126
  4        Step 2 - The Fabric Filter	127
  5        Step 3 - Shock	  .   128
  6        Step 4 - Drag	129
  7        Kerr Pilot Plant Photo 	   131
  8        Outlet Concentration versus Air-to-Cloth Ratio for
           Various Bag Materials  	   132
  9        Comparison of Operating Pressures for Various Bag
           Materials	133
 10        Installed Costs versus Air-to-Cloth Ratio  	   134
 11        Operating Costs versus Air-to-Cloth Ratio  	   135
 12        Teflon Felt - Annual Operating Costs versus Air-to-Cloth
           Ratio for Different Bag Life Assumptions	136
 13        Annualized Cost Comparison   	137
 14        EPA Demonstration of the Enviro-Systems Fabric Filter Sys-
           tem at Kerr Finishing Div. FabricsAmerica, Concord,
           North Carolina	• • •   139
 15        One House on Truck	140
 16        House Being Lifted  Onto Hopper - Far View	141
 17        House Being Lifted  Onto Hopper - Near View	142
 18        Completed System	   143
 19        Control Panel	•   144
 20        Fabric Filter Schematic   	   145
 21        Total Annualized Cost Versus Air-to-Cloth Ratio
           Teflon Felt	150
 22        Annualized Costs Versus Air-to-Cloth Ratio 	   152
 23        Annualized Costs Versus Air-to-Cloth Ratio 	   153
                                    Vlll

-------
                               LIST OF FIGURES

F1Sure                                                                   Page
                                   PAPER 7
  1        Photograph of Side of Fabric Filter .  .  .  .  .........  157
  2        Photograph of End of Fabric Filter  ...............  158
  3        Concentration Versus Process Cycle for 10  ym Particles.  .  .  .  160
  4        Time in Process  Cycle at Which Inlet Samples Were
           Collected
  5        Composited  Differential Size  Distribution  Curves  of
           Baghouse  Inlet Aerosol  ................... 153
  6        Average Outlet Differential Size Distribution Curves   .... 164
  7        Fabric Filter Fractional Penetration Curves  ......... 165
                                  PAPER 10
 1        Flow Sheet
 2        Typical Filter Pressure Loss Curve  ......... .... 193
 3        Coke Oven Exhaust Tar Removal Efficiency  .......... 192
 4        Coke Oven Pilot Unit  .................... 194
 5        Coke Oven Pilot Unit  ............... ..... 195
 6        Galvanizing Line Fabric Filter Operating Conditions ..... 197
 7        Galvanizing Line Fabric Filter Design Features  ....... 197
 8        Sinter Machine Windbox Fabric Filter  ............ 199
 9        Fabric Filter - Nahcolite System  .............. 201
10        s°2 Removal as a Function of Stoichiometric Ratio Under
          Optimum Conditions  .................          202
11        Fabric Filter-Nahcolite System Costs  ............ 203

                                  PAPER 11
 1        Schematic  Drawing  of  Fabric  Filter Apparatus  Used  ......  210
 2         Cumulative Size  Distribution by  Count  for  Fly Ash  ......  211
 3         Valve  Arrangement  for Pulse-Air  Manifold ...........  212
 4         Photograph Tracing of Oscilloscope Display:   Pulse  Pressure
          Versus  Time for Normal Pulse   .  . .  ............    214
                                    ix

-------
                               LIST  OF FIGURES
Figure                         PAPER 11 (cont)                           Page

  5        Photograph Tracing of  Oscilloscope Display:   Pulse  Pressure
           Versus Time for Modified Pulse .	216
  6        Photograph Tracing of  Oscilloscope Display:   Pulse  Pressure
           Versus Time for Modified Pulse With Twice Normal Chamber
           Volume	  217
  7        Penetration Versus Filtration Velocity,  Pulse Type  as
           Parameter	•	220
  8        Penetration Versus Filtration Velocity,  Relative Humidity
           as Parameter	221
  9        Pressure Drop Versus Filtration Velocity, Relative  Humidity
           as Parameter	•	223
                                   PAPER 13

  1        Capture Efficiencies of Three Nonwoven PET Fabrics Made of
           Various Fibers, as Shown, When Filtering a Flyash Aerosol. .   241

  2        Ratios of Outlet Concentrations for Filters Made of Fibers
           With 2, 3 and 5 Lobes to Outlet Concentrations for Round
           Fiber Filter	   242
  3        Capture Efficiencies for Nonwoven Rayon Filters Made of Fibers
           With Various Levels of Crimp as Shown, When Filtering a
           Flyash Aerosol	243
  4        Penetration (Equal to 1-Efficiency) for PET and Polypropylene
           Filters of Constant Weight and Density but Made of Fibers of
           Different Diameters	 •	244
  5        Specific Cake Resistance for the Filters in Figure 4 ....   245

  6        Pressure Drops at Beginning and End of Filter Cycle
           (APj^ and APf) for Conditioned Bags Made of Round and
           Trilobal PET Fibers	246
  7        Outlet Concentration Ratios for Bags in Figure 6  	  247
  8        Single Fiber Efficiencies for Each Layer in Layered Filters
           Made of Round and Trilobal Fibers	248
  9        Calculated Single Fiber Efficiencies for Fibers With Cross
           Sections p = 1 + e Cos m (+C) Where m = Number of Lobes
           and e  Indicates the Lobe Depth	249

-------
                               LIST OF FIGURES

                                                                         Page
                                   PAPER 14
  1        Experimental Apparatus .	      273
  2        Cross Section of Dust Cake on Woven Fabric	275
  3        Dust Cake Shadow Cast on Woven Fabric	  277
  4        Particle Size Distribution	  278
  5        Specific Resistance Versus Solidity  	  282

                                  PAPER 15
  1        Cage Contact	  297
  2        Cage Voltage Forms	     299
  3        Basic Electrical Equivalent Circuit  	  302
  4        Gas Flow Rate Through  One Bag  of  a Four-Row Pulse-Jet
           ArraV	304
  5         Modified Equivalent  Circuit Containing  Distributed
           Components    	             OQ-:
  6         Cage Voltage During  Fly Ash Filtration  At High  Relative
           Humidity	                   314
  7         Cage Voltage Under an  External Bias of  -2000 Volts  	   316

                                  PAPER 17
  1         3-M Company  Thermacomb 	     334
  2         Calculated Performance 3.0  ym Alumina Fiber Bed  	  .   339
  3         D.O.P. Efficiency fn Airflow Velocity   	   341
  4         D.0.0. Efficiency fn Basis Weight	345
  5         Dust Loading of Ceramic Felts	        343
  6         Dust Loading of Ceramic Paper	349
  7        Dust Loading of Woven Ceramic Media	.   350
 8        Saffil Alumina - Post Test Dust Cake	  353
 9        Woven Fiberfrax - Post  Test Dust Cake  ....  	  .    355
10        Fiberfrax Blanket -  Post  Test Dust Calce	  355
                                     xi

-------
                                LIST OF TABLES

Table
                                    PAPER 2
  1       Required Data Inputs for Specific Model Application ...... 33
  2       Predicted and Measured Resistance Characteristics for Nucla
          Filter System	34
  3       Measured and Predicted Values for Filter System Penetration
          and Resistance, Coal Fly Ash Filtration With Woven Glass
          Fabrics	38
                                    PAPER 3
  1       Nashville Thermal Transfer	49
  2       Inlet Emission Profile .  .  .	50
  3       Outlet Concentration and Cumulative %  	 53
  4       Outlet Concentration and Cumulative %  	 56
  5       Outlet Concentration and Cumulative %  	 58
  6       Bag Cost as Percent of Installed Cost	61

                                    PAPER 4
  1       Brass and Bronze Foundry Pulse Cleaning Test Results	89
  2       Brass and Bronze Foundry  Shake Cleaning Test Results	89
  3       Hot Mix Asphalt Plant Pulse Cleaning Test Results  	 90
  4       Coal-Fired Power Plant  (Cyclone-Fired  Boiler) Shake  Cleaning
          Test Results	90
  5       Operating Conditions for  Coal-Fired Power Plant  (Anthracite
          Coal) Tests	91
  6       Coal-Fired Power Plant  (Anthracite Coal) Mass Efficiency Test
          Results	92
  7       Operating Conditions for  Pulp Mill Lime Recovery Kiln Tests  .  . 94
  8       Pulp Mill Lime Recovery Kiln Mass Efficiency Test  Results  ... 95
  9       Pulp Mill Lime Recovery Kiln Fractional Efficiency Test
          Results	96
  10       Pressure Drop Results of  Pulp Mill Lime Recovery Kiln Tests  .  . 97
  11       Operating Conditions for  Coal-Fired Power Plant  (Subbituminous
          Coal) Tests	98
  12       Pressure Drop Results of  Coal-Fired Power Plant  (Subbituminous
          Coal)  Shake  Cleaning Tests	99
                                        XII

-------
                                LIST OF TABLES
Table                           PAPER 4 (cont)                             Page
 13       Pressure Drop Results of Coal-Fired Power Plant (Subbituminous
          Coal) Reverse Cleaning Tests (Teflon/Glass Bags) 	  100
 14       Pressure Drop Results of Coal-Fired Power Plant (Subbituminous
          Coal) Reverse Cleaning Tests (Graphite/Glass Bags)  	  101
 15       Coal-Fired Power Plant (Subbituminous Coal)  Mass Efficiency
          Test Results	102
                                    PAPER 6
  1       Alarms and Shut-Down Functions 	  147
                                    PAPER 7
  1       Average Results  of Total Mass Measurements 	  159
                                    PAPER 8
  1       Fume Control in  Small Smelters 	  175
                                    PAPER 11
  1       Fractional Mass  Penetration/Pressure  Drop, MM Water  Gauge/%
          Relative Humidity 	    219
                                    PAPER 14
  1       Minimum Specific Resistance   	  ,  .   258
  2       Comparison of  Resistance Factors  Predicted by Kozeny-Carman
          Equation and "Free Surface"  Model	   263
  3       Comparison of  D    and D    	268
  4       Porosities and Particle  Diameters for which  C  =1.1  	   271
                                                       s
                                    PAPER 15
  1       Experimental Nomex Test  Bags  (Scrimless Felts)  	   311
  2       Bag  Performance  Series	312
  3       Control  Bag  Performance  Under  Cage Electrical Bias (All Runs
          at 50% Relative  Humidity)	315
  4       Control  Bag  Performance  at Various Cage Electrical Terminations
          (All Runs  at 50% Relative Humidity)	318
  5       Properties of Needled Polyester Felt Fabric	320
  6       Filtration Performance of the Test Polyester  Felts 	   322
                                    xiii

-------
                                LIST OF TABLES

Table                                                                     Page

                                   PAPER 17
  1       Summary of 3M ThermaComb Performance  	   336
  2       Effect of Changing Cleaning Conditions 	  ....   336
  3       Summary Room Ambient Test Data .	   342
                                      xiv

-------
                      SELECTION CRITERIA
                              for
                   EMISSION CONTROL SYSTEM
                              and
                STATUS REPORT OF FABRIC FILTER
                     PERFORMANCE  TESTING
Presented by:                      Presented at:
Jack D. Jones                      Third EPA Symposium
Principal Engineer, Mechanical     on Fabric Filters for
and                                Particle Collection
Kenneth L. Ladd, Jr.               December 5,  1977
benior Environmentalist
Southwestern Public Service Co
Amarillo,  Texas               '     Tucson,  Arizona

-------
                     ABSTRACT
              SELECTION CRITERIA FOR
           EMISSION  CONTROL  SYSTEM AND
STATUS REPORT OF FABRIC FILTER PERFORMANCE TESTING

After studying the technological and economic aspects
of emission control devices for its  secorid coal-fired
generating unit, Southwestern Public Service Company
selected a fabric filter system for particulate con-
trol.  Problems with electrostatic precipitators and
the desire to install an emission control device which
would not require particulate scrubbing prompted South-
western to investigate the feasibility of a fabric filter
installation.  The study revealed that a fabric filter
system would be economically justifiable as well as
technically appropriate for the Company's coal-fired
plant which utilizes low sulfur Western coal.
As a result of its choice, Southwestern, under a contract
with the U. S. Environmental Protection Agency, will con-
duct a study to assess the performance of the fabric fil-
ter system as an emission control device.  Continuous
monitoring of the flue gas emission stream will be made
at five different sampling points.  Special inlet and
outlet sample testing will define the particulate charac-
teristics.  The collected data will be processed into a
determination of the economics and industrial acceptability
of operating and maintaining the commercial emission con-
trol system.   The resultant report should be a guide on
the selection, design, operation and maintenance of a
fabric filter system for Western coal-fired boilers.

-------
         SELECTION CRITERIA FOR EMISSION CONTROL SYSTEM
                            PART  I
      Southwestern Public Service Company is an electric utility
 headquartered in Amarillo, Texas, with 2,240 employees serving
 approximately 280,000 customers in Texas, Oklahoma, New Mexico
 and a small area of Kansas.  The Company has a generating capa-
 city of  2740 MW produced by five major and three smaller power
 stations;  seven of these installations are fueled by natural
 gas.  The number one unit of Southwestern's first coal-fired
 station went on line in July, 1976;  it has a 356 MW capability.
 By July, 1984,  the Company will have approximately 2150 MW of
 coal-fired steam generating capability on line.
      Southwestern Public Service Company designs its own power
 plants  through  the Generation Plant  Design Group,  which is
 part of the System Engineering Department organized in 1945.
 When we began design of our first coal-fired unit,  the Gener-
 ating Plant Design Group had 30 employees,  of whom 12  were
 engineers.   We  now have 87  employees  in plant design,  36  of
 whom are engineers.
      The basic  problem  in designing  the Company's  second  coal-
 fired unit  was  the  selection of a coal-fired furnace flue  gas
 treating and  control  system  which would satisfy EPA's  New
 Source  Standards.   These standards require  that a coal-fired
 facility not  emit more  than  .1  pounds per million Btu  particu-
 late, and emissions cannot exceed 1.2 pounds per million input
 of sulfur dioxide.
     Southwestern Public Service Company looked at the alter-
natives  for controlling  coal-fired boiler emissions and an
effort was made to select a type of emission control device
which would not  require scrubbing for particulate removal.

-------
The 350 MW Harrington Station unit (located near Amarillo,
Texas) uses sub-bituminous low sulfur Western coal,  and,
therefore, the EPA standards for S02 could be met by selecting
low sulfur coal as fuel.
     The primary systems initially studied for particulate con-
trol were electrostatic precipitators.  Since the construction
of Harrington Station Unit #1, electrostatic precipitator guar-
antees, performance and technology had improved to the point
that consideration was given to the purchase of a 99.570 removal-
of-ash electrostatic precipitator.  At the time that a decision
was required by Generation Plant Design staff, numerous utili-
ties were having problems with hot-side precipitators; there-
fore, this type of precipitator was not considered.
     While obtaining bids and information from suppliers of
electrostatic precipitators some mention was made of the use
of fabric filters for particulate control.  The use of this
type of filter system in Southwestern1s service area is very
common  (in the carbon black industry) and we were somewhat
familiar with this application.  After a study was made of
fabric  filters, and how  they were applied at the Sunbury and
NUCLA facilities, a decision was made to compare electrostatic
precipitators with baghouse systems.

     Baghouse vendors were contacted and the only specifica-
tions given these suppliers for preparing their quotations were
flue gas  flow, ash characteristics, and grain loading.  Meetings
were held with fabric filter suppliers to determine a common
base for  comparison with each other and with electrostatic pre-
cipitator proposals.  These comparisons were based on physical
design, physical operation, capital cost and operating cost.
     Comparison Charts:  This comparison chart  (Figure 1) will
show the  comparative costs of three fabric filters and three

-------
 99.5% effective precipitators.   The comparison is in percentages
 with the fabric filter purchased for Harrington Station, Unit #2,
 being the base.  There are two areas in which the competitors
 were lower than the base.   The #3 fabric filter was lower in
 capital cost due to the cost of bag replacement for fabric fil-
 ters being classified as maintenance.   Replacement for the fabric
 filters was based on a two year life of the bags;  however, ex-
 perience at Sunbury indicates that bag life is much longer than
 two years.   From a discounted cash flow analysis it can be seen
 that the fabric filters have less effect on the cost to stock-
 holders than any of the precipitators.   It  should be noted,  how-
 ever,  that the  parameters  used  in this  analysis may not neces-
 sarily apply to other utilities,  or to  other areas.
      Our first  fabric filter was  selected for Harrington Station,
 Unit #2.   For the #3  unit at Harrington we wrote  a set of speci-
 fications  and then negotiated a contract for a fabric filter sys-
 tem to be  supplied by Wheelabrator-Frye,  Inc.   Essentially it  is
 the same as  the system designed for Unit #2.
      The Company's  next  coal-fired  station  will  be ToIk Station
 Units  #1 and #2.   Unit #1  is  scheduled  to go on  line  in June,
 1982.   Southwestern Public  Service  will  prepare  a  set  of speci-
 fications for a fabric filter system based  on  knowledge gained
 from the purchase  and use  of  two  fabric  filter systems  at  our
 Harrington Station,  enhanced by the  knowledge gained in studying
 the  system for  Unit #2.
     In  the  second part of this paper,  Kenneth Ladd will describe
 Southwestern Public Service Company's plans  to obtain this
knowledge.

-------
       COMPARISON  OF COSTS (%)
           FABRIC FILTER
99.5 % PRECIPITATOR
CAPITAL COST


OPERATING COST


MAINTENANCE
COST
COST TO
STOCKHOLPER
BASE
100

too

100

100

2
101

132

101

115

3
86

110

144

105

1
142

228

20

133

2
143

175

20

132

3
166

153

20

148










   FIGURE 1

-------
        SELECTION CRITERIA FOR EMISSION CONTROL SYSTEM
                           PART II
      The preceding comments describe Southwestern Public Ser-
 vice Company's reasons for selecting a fabric filter system
 for emission control.  Because such a small amount of informa-
 tion is available on the performance testing of fabric filters
 at other utility installations, it was necessary for Southwestern
 Public Service to make its own evaluation of emission control de-
 vices for the specified Harrington Station application.
      Southwestern has no previous experience in fabric filter
 system operations so when asked the question,  "Why a baghouse?"
 we encourage each utility to make its  own analysis.   Factors
 to consider are specific requirements,  boiler  design,  fuel,
 and other engineering and economic considerations.   Southwestern
 is not qualified to  present general criteria at this time.
      To assist  in the collection  of information to  formulate  a
 more complete data base for fabric filter performance, South-
 western and EPA have  agreed to  make a  comprehensive  study of  a
 commercial,  operating unit.   The  study will  require  two years
 to complete the collection  and  assessment of one full operating
 year's  worth of data.  After this  experience  and testing, South-
 western Public  Service  can  offer more expert opinion concerning
 fabric  filters.   In the  last part  of this paper, the status of
 the  testing program will be discussed.
     The objective  of the  study is to implement an overall pro-
gram of  testing and evaluation design to  (1) fully characterize
 the fabric filter system applied to Harrington Station, Unit #2;
 (2) study the technical and economic feasibility of the system;
 (3) demonstrate long-term reliability of the system;  and (4)  de-
termine the system's  optimum operating conditions.

-------
     A description of the emission source and the fabric fil-
ter system to be tested is as follows:
     The emission source is a pulverized coal-fired Combustion
Engineering tangentially-fired boiler.  It will use low sulfur
Western coal, supplying steam to a 356 MW rated steam turbine
generator.  The fabric filter is a Wheelabrator-Frye, Inc. unit
with 28 compartments, operating at 313° F, cleaning 2,650,000
acfm at full load; the normal net air-to-cloth ratio is 3.4:1.
The fabric filter cleaning method is reverse air and shaking
with the control flexibility of using either or both.  The
filter medium is fiberglass coated with silicone and graphite.
The bags are 11.5 inches in diameter and 30.5 feet long.
     The test plan will characterize the fabric filter system
by manual sampling and continuous monitoring.  The plan also
calls for analyses of all solids and gases in and out of the
system.  Additionally, data will be collected and recorded
which describes all significant fuel and operation information.
     Major manual sampling and testing of the particulate
entering and leaving the fabric filter system will be used to
determine performance characteristics that cannot be measured
with continuous monitoring equipment.  Three detailed manual
samplings will be equally spaced during the year of operating
tests.  Five sampling ports will be sampled at the same time
to determine mass particulate flow and particle size distribu-
tion down to .01 ym.  The particulate ash will be analyzed for
organic material, elemental constituents, sulfates, sulfites
and nitrates.
     Manual sampling and testing will also be used to determine
flue gas characteristics.  The parameters to be determined are
hydrogen chloride, hydrogen fluoride, oxides of sulfur, oxide
of nitrogen, organic vapors, and elemental constituents.
     All major sampling and testing will be performed according
                              8

-------
  to   EPA and  other  approved  testing procedures.  The manual  sam-
  pling results will be  correlated with operating data  to define
  the  performance of the fabric  filter at full  load on  the system.
      The same five sampling ports will be used to locate the
  continuous monitoring equipment (see Figure 2, Harrington #2
  Flue Gas Flow Diagram and Monitoring Points).
      The parameters listed below will be continuously monitored
  (flue gas stream - at all 5 points):

      !•   S02                           5.   02
      2-   NOX                           6.   Temperature
      3.   Particulate (grain/cu.ft.)     7.   Duct pressure
      4.   Flue gas  flow (acfm)
      Additional operating parameters that  will be  measured or
 calculated on a continuous basis will be pressure  drop across
 the system,  power  consumption,  load  on the unit,  fuel  flow,
 particulate removal,  cleaning mode and frequency and  flue  gas
 flow. There are approximately  30 analog inputs and another  20
 contact  inputs  that will  direct operational  data into  the  plant
 computer.   This data will not be as  specialized as the manual
 sampling information, but rather will  represent every  day  opera-
 tion  of  the  fabric  filter system.  Daily records will  be kept
 of  the maintenance  required  by  the fabric  filter system.
      The test program should produce an assessment of  the per-
 formance of a fabric filter  system that determines particulate
 collection, pressure drop, temperature, energy consumption,
 S02/S03  removal, optimum  cleaning procedures, fabric care and
maintenance,  corrosion, system reliability and bottom line cost
of operation  and maintenance.
     An option for a future study exists which would permit the
determination of operation and maintenance  parameters  for five
years of  operation  after performance  has been defined.
                              9

-------
     During the present study, the fabric filter system will
operate as designed and required for the generation of electric
power from a commercially operating unit.   This limits the
special testing of parameters outside of the normal operation.
Another future option would include special testing of fabrics,
air-to-cloth ratios, or other related research.  These objec-
tives would be accomplished by installing a small slipstream
fabric filter test module (about 10,000 acfm).
     Southwestern Public Service Company wants  to gain experience
in the application of fabric filters as well as provide to other
utilities information which might be useful in their evalua-
tions of their own unique emission control problems.  A per-
formance report submitted by a utility would present utility
knowledge and application to the air quality regulatory groups,
and thus better represent the industry's problems and solutions.
     As a result of the testing program, Southwestern Public
Service Company will, two years from now, be able to make an
assessment based on sound and well-documented operating experienc
                              10

-------

-------
12

-------
MODELING COAL FLY ASH FILTRATION
       WITH GLASS FABRICS
               by


         Richard Dennis
              and
          Hans  Klemm
       GCA CORPORATION
   GCA/TECHNOLOGY DIVISION
   Bedford,  Massachusetts

           13

-------
                                   ABSTRACT
     A new mathematical model for predicting the performance of woven glass
filters with coal fly ash aerosols from utility boilers is described in this
paper.  The data base includes bench and pilot scale studies in which several
dust/fabric combinations were investigated; field data from prior GCA studies
of coal fly ash filtration with glass fabrics; past GCA studies of fabric fil-
ter cleaning mechanisms and a broad-based literature survey.

     Two new concepts were instrumental in model design.  The first relates to
the manner in which dust dislodges from a fabric and its subsequent impact
upon resistance and penetration in a multichambered system.  The second con-
cept is associated with the relatively large fractions of fly ash that pass
with minimal collection through temporarily or permanently unblocked pores or
pinholes.  Additionally, the quantitation of the cleaning action with dust
removal in terms of method, intensity and duration of cleaning was essential
to the overall modeling process.  The examination of specific resistance
coefficient, K2, for the dust layer in the light of polydispersed rather than
monodispersed particle components provided improved estimates of K.2-  Trial
applications of the modeling technique to field filter systems operating at
Sunbury, Pennsylvania and Nucla, Colorado indicate excellent agreement between
theory and practice for both penetration and resistance characteristics.
                                      14

-------
                                    SECTION  1

                                    BACKGROUND
      The prospect of stricter participate emission regulations for coal-fired
 boilers suggests that fabric filtration may be the best control technique for
 many applications.  Limited field experience with large utility boilers1'2 has
 demonstrated that glass fabric filters perform well with respect to moderate
 pressure loss, very high collection efficiency and acceptable service life
 (at least 2 years).  A possible drawback, however, in the eyes of utility
 groups has been the inability to predict accurately how a new filter system
 will perform without extensive pilot testing and field trials.3.4  Only when
 the new plant design replicates an existing (and successful) installation with
 respect to power level,  boiler design and fuel characteristics can the filter
 performance be predicted safely.

      In this paper,  a filtration model is described which,  based upon limited
 field validation,  provides rational estimates for the performance of woven
 glass bags with coal fly ash in real filter systems.4.5  The apparent success
 of the model is attributed to the introduction of three new concepts or ap-
 proaches to the modeling process.

      The first  relates to  the fact that  dust  remaining on a fabric  surface
 after cleaning  is  characterized by a distinctive, nonuniform distribution in
 which the  unique resistance and collection  properties of cleaned  and uncleaned
 areas are  definable  and  thus amenable to  mathematical analysis.       ~ -

      The second approach allows us to quantify the relationship  between the
 amount of  dust  removed from a filter and the  method of cleaning  and the filter
 dust loading prior  to cleaning.5'6

      The _third  approach  centers on the unique dust penetrating properties  ob-
 served  for  fly  ash/woven glass  fabric systems in  which the  failure  to obtain
 rapid and/or complete pore  bridging allows significant direct leakage (bypassing)
 of the  upstream aerosol  to  the clean air side of  the system.  Such penetration
 arises  because  of a characteristic nonuniformity  in both pore dimensions and
 in the  dispersion of the loose fiber substrate that screens the pore openings.4.5
r  K        i    f°r ^ ab°Ve lmPerfecti°ns, a continuous and highly impene-
trable dust layer would form above the substrate as shown in Figure 1.  £n the

tribut?o  'f311 H    Y  ?°r WeaVe C°Upled With a SparSit? and nonuniform dis-
tribution of substrate fibers can lead to the critical pinhole leak problem
illustrated in Figure 2.   The relatively low resistance to gas flow presented
by the larger pores results in the passage of a disproportionately large
                                      15

-------
   YARN
                                   YASN
                           BULKED FIBERS
                           DUST
UNUSED
FABRIC
                                            EARLY  DUST
                                            BRIDGING OF
                                            FIBER  SUBSTRATE
                                              SUB  SURFACE
                                              DUST CAKE
                                              DEVELOPMENT
Figure 1.  Schematic, dust accumulation on woven glass fabrics.

                           16

-------
Figure 2.   Massive pinhole leaks with all multifilament  yarns  and  large,
           -200 ym,  pores.
                                  17

-------
fraction of the uncleaned gas along with most dust particles < 15 ym diameter.
Because the quantity of fly ash penetrating woven glass fabrics via the pore
or pinhole leak route exceeds that which penetrates the unbroken dust cake by
some 100 to 1000 times, the particle size properties of the effluent particles
are essentially the same as those in the entering aerosol.

     The above phenonemon explain why the reported fractional efficiencies for
glass fabric systems often indicate the same degree of collection for all
particle sizes.  It is also pointed out that periodic rear face slough-off
of agglomerated particles due to mechanical vibration or aerodynamic drag may
contribute significantly to the effluent loading.4'7

     Another consideration in the modeling process is the fact that the dust
collection capability for any specified area of a fabric surface depends upon
both the local dust cover and the local filtration velocity.3'4'6'8  Addi-
tionally, the specific resistance coefficient, K2, for a given dust depends
not only upon the physical properties of the particles, gas and bed structure
but also upon the gas velocity at the time of particle deposition.3'5

     Introduction of variables and concepts discussed above into the classical
filtration equations constitutes the basis for a comparatively simple model
which can serve two major roles.  The first application relates to the design
of a filter system based upon specified dust and fabric properties, air to
cloth ratios, proposed frequency and/or intensity of cleaning and pressure loss
constraints.  The second application is that of determining whether the operat-
ing regimen and basic design approach specified by a system designer will allow
the user to meet particle emission requirements while conforming to system gas
flow and resistance requirements.  Thus, the second or diagnostic role of the
filtration model should prove particularly valuable to environmental control
groups who must assess the adequacy of proposed control measures.

     In the following sections, we have outlined briefly the basic structure
and development of the model and its preliminary trial runs.  We have not at-
tempted, however, to describe fine operating details nor the programming rou-
tines per se, both aspects having been dealt with extensively in a recent
study.   Although the basic mathematical model has been established, it is em-
phasized that peripheral modifications in the model with respect to what con-
stitutes direct or indirect data inputs are expected based upon specific user
requirements and precise model applications.
                                      18

-------
                                    SECTION 2

                               MODEL DEVELOPMENT
  BASIC  FILTRATION RELATIONSHIPS

 leads
                                                                 .
the characteristic relationship shown by the solid Curve I  Figure 3
      the CUrvllln                                                  "
                                                                ve      gure
 SP  whef^    the CUrvlllnrr f°™ °f Curve 1 depicts the true residua! drag"






      The linear expression
                                   = SE + K2 W
                   resultant  fllter  dr*S>  SE  the  effective  residual  drag, K2
                   te  coefficient f°r the  dust, and W  the  fabric  surface area
     When a fabric bag is cleaned by bag collapse and reverse flow or bv
mechanical shaking, the dust sloughs off as flakes or slabs with th^separa-
                  f \dUSt/fabric int-face where the adhesive 1^ arT
                  ^shows the appearance of a full scale glass bag (10 ft x
represented by Curves 2 through 4, Figure 3.

PARALLEL FLOW CONCEPT
                        °f *** CU™S'  FlgUre 3'  have sometimes been incorrectly
                                     19

-------
N5

O
          CO

          CO
          <
          oc
          a

          OL
          ui
          UI
          O
          <
          a:
          LJ
                     DESCRIPTION

            MAXIMUM  POSSIBLE  CLEANING

            HIGHLY  EFFICIENT CLEANING

            AVERAGE  CLEANING  RANGE

            (MECHANICAL  SHAKING)

            AVERAGE CLEANING  RANGE

            COLLAPSE  WITH  REVERSE

            FLOW
    Figure 3.
                   AVERAGE  FABRIC  LOADING.W



Typical drag versus loading curves for filters with different degrees of cleaning and

a maximum allowable level for terminal drag,  ST, and terminal fabric loading, WT.

-------
Figure 4.  Fly ash dislodgement from 10 ft x 4 in. woven glass bag
           (inside illumination).

                                 21

-------
pinhole leakage that may divert as much as 20 percent of the approaching gas
flow through as little as < 0.1 percent of the filter face area.4

     The path of these curves is governed by several parallel flow paths in
which the approaching gas stream is apportioned according to the local drag
values at any specified time for cleaned and uncleaned surfaces.3'4'9

                                      Aui          Au.
                                                     \l     A
                                                                           (2)

     In Equation (2), S and,A refer to overall drag and filter area, respec-
tively, i designates the i   fractional area and its associated properties,
n is the total number of filter areas making up the whole surface, and the
subscripts c and u refer to the cleaned and uncleaned filter areas.

     The resulting pressure losses, P, after a time increase, At, for cleaned
and uncleaned filter surfaces are equal and expressable by the following
general relationship:


                     t ~r At        t ~F" At           t 4" At

in which Sg is the characteristic effective residual drag, V the instantaneous
face velocity and W the total surface loading at the time t + At.  Equations (2)
and (3) form the building blocks for the iteration process from which the local
and overall drag and resistance parameters may be estimated by computer for
any time and/or average filter dust loading during a filtration cycle.  Two
critical parameters must be defined, however, before undertaking the modeling
process.

SPECIFIC RESISTANCE COEFFICIENT (K2)

     The first parameter is K2, which has been demonstrated in past and current
studies to increase with the velocity of dust deposition, presumably due to
increased dust layer compaction and hence lower cake porosity.3*4  For many
coal fly ash/woven glass fabric systems, K2 values computed as shown below may
be used in Equation (3):

                        K2 = 1.8 V'5   (Metric units)*                      (4)

     For broader applications, however, Equation (4) is better expressed as
                           (K2)  = (K2)  (V2/Vi                             (5)
                               2       1

when K2 has been measured at a different velocity.  Although several theoretical
approaches have been proposed for the estimation of K2 in terms of particle
 V = face velocity, m/min.  K2 = specific resistance coefficient, N.min/g.m

                                      22

-------
 and fluid parameters,  the direct measurement of K2 is recommended.   In the
 absence of direct measurements,  a modified form of the Carman-Kozeny equation4
 provides a rough (± 25 percent)  estimate of K2; i.e.,


                          K2 = 2.5y (S'0)2 (l-e)/Ppe3                       (6)

 where  y is the gas viscosity,  e the cake porosity,  p  the discrete particle
 density, and S'o the specific surface parameter for  the size distribution as
 a whole, i.e.

                         S'   = ^  particle surface area
                           0   E  particle volume

 for any unit volume of dust cake.   Although cake porosity is a  measureable
 quantity,  it should be noted that  a 10 percent  error in porosity  estimation
 will lead  to a  50 percent error  in the porosity function (l-e)/e3.   Particle
 density measurements over the size spectrum of  polydispersed dusts  such as
 fly ash are also subject to error.   Hence,  there is  a strong argument  for
 direct  measurement of  K2 (and SE)  whenever  possible.

      Use of the parallel flow concept involving Equations (2) and (3)  for
 several partially cleaned fabrics  indicated excellent agreement between ob-
 served  and  predicted drag values.4*5  The modeling process used in  Figure 5
 is  based on the fact that the cleaned area  fraction,  ac,  is always  associated
 with a  characteristic  fabric drag,  S .

 FRACTION OF FILTER SURFACE  CLEANED (ac)

      The fraction of the  filtration  surface cleaned by  the cleaning process,
 ac,  must also be determined  prior  to the  modeling  effort.   In the case  of
 fabric  cleaning by bag  collapse  and  reverse flow,  the amount of dust removed
 can  be  related  to  the  fabric dust  loading immediately before cleaning  (WT),  the
 characteristic  residual dust loading for  the cleaned  region (W  )  and the
 average filter  dust  loading  after  cleaning,  (W  ').            R
                                              R

                                   ,   V  - WR
                              *c = X  - -w—^                            (7)
 or                                        l    R

                   ac = 1.51 x l(T8 WT2'52 = 1.51 x 10~8 Wp2-52              (8)

 in which the fabric  loading prior to cleaning, WT or Wp,  is expressed in
 grams/m  .  Equation  (7) can only be used  to estimate ac when the average  filter
 dust holding after cleaning, WR', is known.  Ordinarily,  such data are obtain-
 able only when special experimental testing procedures are employed.  Hence,
 Equation (8) which depends upon the measureable or readily calculable Wp or
WT term, is chosen to compute the cleaned area fraction, ac.^

     The term Wp has the special significance of identifying the fabric load-
 ing associated with the fabric pressure loss just before initiating the cleaning

                                       23

-------
                                                                        77-32.3
  1,000
    800
     	1	—r	1	1	1——i	1     i     r~

     —A WOVEN  GLASS  FABRIC, COMPLETELY  CLEANED

     —O WOVEN  GLASS FABRIC, PARTIALLY CLEANED

     •--x PREDICTED  CURVE, PARTIALLY CLEANED
         WOVEN  GLASS  FABRIC
UJ
O
2

f
CO
CO
UJ
a:

a
OL
co

g
600
400
    200
    TEST PARAMETERS

PARTIALLY  CLEANED FABRIC

  V=0.6I  m/min

  C0 = 6.9 g/m3

  ac =0.485

  QU S0.5I5

  Sc = 102.4  N min/m3

  Su =1033 N min/m3

  K2 =1-81 V^Nmin/g m
                200
                      400      600       800       1,000

                         AVERAGE  FABRIC  LOADING, g/m2
                 1,200
   Figure 5.  Fly ash filtration with completely and partially cleaned woven glass  fabric

            (Menardi Southern)

-------
 action.   In  many systems,  Wp represents  the fabric  dust loading corresponding
 to  the preset  pressure loss at  which the filter  cleaning cycle is  to be
 activated.

 DUST DISLODGEMENT AND ADHESIVE  FORCES

      Dust separation from  any element of the filter surface is assumed to take
 place when the local separating force equals or  exceeds the local  adhesive
 force bonding  the dust layer to the fabric surface.  The dislodging force
 for bag  collapse-reverse flow systems is that resulting from the tensile or
 shear stresses (assumed to be approximately the  same)  exerted by the local
 surface  loading in mass per unit area, Ma,  in a  gravity field, g.   If the
 system is cleaned by mechanical shaking,  the acceleration,  a, imparted to the
 dust layer by  the mechanical shaking action is substituted  for the gravitational
 acceleration,4»6» 1"

                              "a = 0.75 4 ir2 f2A                             (9)

 such that the  dislodging force  is now defined by the relation Ma'a rather than
 Ma-g.  In Equation (9),  f  refers to the  shaking  frequency and A to the ampli-
 tude (half-stroke) of the  shaker arm motion (assumed to be  essentially hori-
 zontal) .  After  cleaning by the above mechanisms, the  dust  remaining on the
 filter is assumed  to be held by an adhesive force in excess of the computed
 Ma'a or Ma*g values.

      The  relationship between ac and fabric loading shown in Figure 6 is also
 a measure of the distribution of adhesive forces over  the fabric surface.   The
 range of  adhesive  forces encountered exhibits a  pattern similar to that dis-
 played for particle  to particle adhesive forces3'11'12  while the average
 adhesive  forces  binding the cake to the  fabric agree with those described by
 Zimon.13  The  cleaned area values reflect those  to  be  expected after a fabric
 element has  undergone successive flexings.   Recent  measurements have shown
 that  a single  cleaning by  bag collapse and  reverse  flow removes about 67  per-
 cent  of the  dust separable by repeated cleanings at the same initial dust load
 level.1*

 DUST  PENETRATION WITH WOVEN GLASS FABRICS

      Extensive laboratory  and field  measurements coupled  with a detailed
 analysis  of  the  filtration process with  conventional twill-weave glass fab-
 rics  have shown  that  coal  fly ash emissions  are  due mainly  to gas  flow through
 the  low resistance paths afforded by unblocked pores, pinholes  or  other  lead
 regions in a filter.4'5  Furthermore, because  relatively  few particles  are
 removed from the gas  fraction passing through  the pores  (nearly  100  percent
 penetration  for  diameters  <  15  ym),  the particle size distributions  are nearly
 the same  for up- and downstream aerosols  provided that  size measurements  are
made  in the immediate vicinity of  the dirty and cleaned filter  faces.1.4

     The above factors suggest,  therefore, that mass emissions  from  glass fab-
 rics  should depend in part upon  (2)  the inlet  concentration  and  (b)  the total
 remaining unblocked pore region at any time.   The latter  item,  (b),  is governed


                                      25

-------
    10°
       10
          INTERFACIAL ADHESIVE FORCE, dynes/cm2

         I                                       ,«2

o
 , .
O

i-
o
<£
cr.
U.
LU
o:
z !••
UJ
,.J
O
   K^j:

       r
  ~
       i.
      IQ
 Figure 6.
                    l	1	1—i—r~T"T
           ° ' NUCLA   ) HELD
           O 2 SUNBURY/ DATA
           o
              3 BOW
                 )
           oc s|
              ief° w
                          2.52
                              	I	I	L
                                    _i	I,.. ,1	L_.	.

                                          JO3
                                                      .
                                                      j
               FABRIC  LOADING, W-g/m2



      Relationship between cleaned area fraction and initial
      fabric loading.  GCA fly ash and woven glass fabric
                              26

-------
 by the amount of dust  deposited  on the cleaned filter  face following resumption
 of filtration.   Given  a glass  fabric  with no  visible signs of  weave imperfec-
 tions  and with a relatively uniform pore structure,  the relationship between
 outlet concentration,  Co,  and  fabric  dust loading, W,  appears  as  shown in
 Figure 7  for an average filtration velocity of 0.61  m/min (2 ft/min).   After
 fabric loadings increase to 60 to  80  grams/m2,  however,  the direct  proportion-
 ality  between inlet  and outlet concentrations disappears because  of a second
 contributor  to outlet  loading.   The latter is the low  level, essentially
 steady state,  slough-off of agglomerated dust from the downstream region  of
 the dust  deposit as  the result of  aerodynamic reentrainment augmented by
 mechanically generated vibrations.4'7  A conservative  estimate of the magnitude
 of this source strength place  it as less than a 0.5  mg/m3 contributor,  CR, to
 the overall  effluent loading.

     Average face velocity has been shown to  play a  major role in determining
 filter effluent concentrations.  Following deposition  of about 60 to  80 gram/m2,
 Figure 8,  steady state emissions are  seen to  increase  from ~ 0.5  to  150 mg/m3
 over the  face  velocity range of  0.39  to 3.35  m/min (1.3  to 11  ft/min).  This
 relationship indicates that seeking to  reduce collector  size by increasing the
 face velocity  (air to  cloth ratio)  may  lead to  unacceptably high  emission
 levels.

     The  solid  line  curves shown in Figure 8  represent  the best mathematical
 fits to the  indicated  data points.  The outlet  concentration,  Co, is defined
 by the local penetration level (Pn),  the inlet  dust  concentration (C±), and
 the previously  cited residual  concentration,  CR = 0.5 mg/m3.

                               C0 = Pn  C±  + CR                            (10)

 The  formal equation  structures and  the precise manner in which they are applied
 in the modeling process  are  presented in Reference 4.  For present purposes,
 it  suffices  to point out that the following expression

                       Pn  or  C0 *   (((,, Clf W, V, CR)

 describes penetration or effluent concentration as a function of  ,  a parameter
 characterizing the dust/fabric combination under test;  constant inlet and
 residual concentrations, C± and CR, respectively; and the time and position
 dependent variables;  i.e., local face velocity, V, and local fabric  dust
 loading, W.

     The total (and average) filter system penetration, Pn, at  some  time,  t,
 for a system consisting of I compartments and J areal subdivisions per bag is
determined by successive iterations in accordance with the general summation
                                     I
                       Pnt = vTT-j A:   L>  Pnij    vij                   (ID
                              c     i=l   i=l     Jt    Jt
                                     27

-------
 o
o

z
o
I-

ff
H-

UJ
o


I
111


3
                20
40       60       80       100

 FABRIC  LOADING {W),g/m2
120
140
 Figure 7.  Effect of inlet concentration  on predicted outlet concen-

            trations at a face velocity of 0.61  m/min.  GCA fly ash

            and Sunbury fabric.
                                   28

-------
cr.
h-
o
O
o
i-
UJ
h-
O
                                          4.60
                                                         3.55
      j    MCT£5: SOLID  LINES  ARE CURVES  PREDICTED  Bf MODEL.
                SVMBOS..S  REPRESENT  ACTUAL DATA  POINTS.
   10
20        40        60       80  "
              FABRIC  LOADING  (W),
                                                     	l_._
                                                                          I4O
   Figure  8.   Predicted  and observed outlet concentrations for bench
               scale tests.   GCA fly ash and Sunbury  fabric.
                                     29

-------
                                  SECTION 3

                               MODEL CAPABILITY
     In the previous sections, the basic filtration equations and the iterative
approach for treating multicompartment systems have been reviewed.  The follow-
ing discussion is intended to demonstrate how closely the predictive model
describes the overall fly ash filtration processes for utility applications.
The only major constraints for the model are that (1) the inlet aerosol should
consist of or possess the general physical properties of a coal fly ash and
(2) the fabric characteristics be similar to the woven glass media of the types
used in the field.  Within the above framework, the model is sufficiently
flexible to meet the following criteria:

     •    The model is adaptable to either constant flow or constant
          pressure conditions.

     •    The model can accommodate to a continuous cleaning regimen;
          i.e., the immediate repetition of the cleaning cycle follow-
          ing the sequential cleaning of successive individual
          compartments, or

     •    The model can also describe the situation where lengthy
          filtration intervals are encountered between the clean-
          ing cycles.

     •    The model can be used with collapse and reverse flow sys-
          tems and mechanical shaking systems or combinations of the
          above.  It is not intended for use with pulse jet or high
          velocity reverse jet cleaning systems.

     •    The model can be used equally well with pressure or time
          controlled cleaning cycles.

     •    The model provides estimates of average and point values
          of filter drag or resistance for the selected set of
          operating parameters and dust/fabric specifications.

     •    The model provides estimates of average and point values
          for penetration and mass effluent concentration for the
          selected set of operating parameters and dust/fabric
          specifications.
                                      30

-------
                                   SECTION 4

                               MODEL APPLICATIONS


      In Figure 9, a schematic flow diagram is shown for a filtration system
 in which the approaching aerosol is distributed among I separate compartments
 (each containing several bags) and £ separate filtration regions on each bag.
 It is assumed for simplification that the performance of each compartment is
 represented by the behavior of any single bag within the compartment and that
 there are no concentration gradients in the approaching air stream.  Con-
 sequently, the model must describe the integrated effect of many parallel
 flow paths through fabric surface elements bearing different dust loadings.
 The local performance of each element, resistance- and penetrationwise, is then
 defined by the equations presented in earlier sections of this paper.

      An analysis of field measurements performed at the Nucla, Colorado Power
 Station2»4 illustrates how the filtration model can be used to predict system
 performance characteristics.   The data inputs required to model the filtration
 process are summarized in Table 1.   Items 1 through 3 are based upon system
 design or operating data provided by the manufacturer.   The 2-minute minimal
 time interval,  Item 4, was chosen by the model user so that successive stepwise
 iterations would always indicate the maximum,  minimum and average system
 resistance while any one compartment was off-line for cleaning.

      Average face and average reverse flow velocities,  Items 5 and 6,
 respectively,  are operating parameters also selected  by the  filter manufacturer.

      Inlet dust  concentration and average filtration  temperature,  Items 7  and 8,
 are  determined mainly by the  combustion process  and the type of  fuel burned
 The  estimates  of  effective residual  drag (SE), specific  resistance coefficient
 (K2), and  residual  dust loading  (WR)  (Items  9, 10  and 11,  respectively)  are
 best  determined by  direct  measurement  if not already  defined in  the literature
 for  the  dust/fabric  combination  of interest.

      With  respect to  the operating parameters  set  forth  in Table 1,  it  was
 required that the system pressure loss just before fabric cleaning'should not
 exceed a value of 1160  N/m* (4.7  in. water), (Item 12).  Given this  constraint,
 the model  has been used to  determine the frequency of cleaning and  the  operat-
 ing ranges  for overall  system pressure loss and effluent particulate concen-
 trations.   One key input parameter> i.e., the fraction of cleaned filtration
 surface  ac, produced when a given compartment (or bag) is cleaned, is presently
 evaluated outside of the modeling program.  The calculations are performed by
 first estimating Wp from the maximum allowable pressure, P   , by
ment of Equation (1); i.e.,                               max'  y
                                     31

-------
        Co

         V
w
K)
                              i  ll
                             w,,
                                  •12
w,
                                 12
           CU    C2I
W
           U
           W,
                                                     21
                C22
W2
                                   12**_iiFij     V2il  E?
                                 2J

                                     •12
                                                     r3I
                            Figure 9.   System breakdown for I bags and J areas per bag.

-------
                  TABLE 1.   REQUIRED DATA  INPUTS  FOR SPECIFIC  MODEL APPLICATION*
Item
1
2
3
Variable
Number of compartments
Complete cleaning cycle
Cleaning time per
Description
6
24 minutes
4 minutes
Comment
System design parameter.
Time to sequentially clean six compartments.
Indicates total compartment off-line time.
  5

  6


  7

  8

  9



10


11

12
         compartment

       Minimum time increment for
         iterative computations
Average face velocity (v)

Reverse flow velocity (VR)


Inlet dust concentration (C.)

Temperature

Effective (clean)
fabric drag (S,,)
              Ct

 Specific resistance
   coefficient
 Residual dust loading  (WR)


 Cleaned fabric area
         fraction (a )
                                 2 minutes
0.824 m/min

0.0415 m/min
               Provides data points for maximum, minimum
                 and average resistance and penetration
                 during off-line period for on-line
                 compartments.

               Based on total flow and total fabric  area.

               Weighted average velocity over total  (4 min-
                 utes) cleaning interval.
2.6 g/m3
412° K

434 N min/m3
               Average baghouse temperature.

               Based on linear extrapolation of drag versus
                 fabric loading measurements with uniform
                 dust deposit.

0.76 N min/g.m Value determined at 0.61 m/min and 25°C.
50 g/m2


0.375
               Refers to surface loading on freshly cleaned
                 areas only.

               Fraction of cleaned surface exposed when
                 cleaning is initiated with a fabric
                 loading corresponding to a resistance
                 of 1160 N/m2
Modeling of actual field performance of stoker-fired boilers at Nucla, Colorado, Colorado Ute
Electric Association.2'^

-------
                              Wp = (ISS - SE) /K2                        (la)
In Equation (la), Wp is the unique (uniformly distributed) fabric loading
associated with the maximum allowable pressure loss. P
                                                   '  max

     The a  value may then be computed as indicated below:


                           ac = 1.51 x ID"8 Wp2-52                         (8)

With the introduction of ac, the program is ready to generate a tabular and/or
graphical printout that can provide interim, individual compartment, and over-
all system performance parameters.

     Figure 10 shows the predicted and actual filter resistance characteristics
versus operating time, the latter providing a direct measure of fabric dust
loading when volume flow rate and inlet dust loading are constant.  The good
agreement between these curves suggests that the physical concepts used in the
model development are a fair expression of the actual system operation.  A
comparison of selected reference points summarized in Table 2 also illustrates
the degree of success attainable with the model.

     Figure 11 predicts the changes in overall effluent concentrations that
should be expected during periods of filter cleaning and during those periods
when all compartments are on line.  Although there are no field measurements
available to confirm the short term, ~ minutes, predictions for the Nucla
baghouse, the weighted average values derived from these curves, agree will
with the corresponding field measurements.

              TABLE 2.  PREDICTED AND MEASURED RESISTANCE CHARAC-
                        TERISTICS FOR NUCLA FILTER SYSTEM


                                          Actual         Predicted
                                      N/m2   in. H20   N/m2   in. H20
Maximum resistance during
cleaning
Initial resistance follow-
ing cleaning
Maximum resistance just
before cleaning*
Time between successive
cleaning cycles
1700
850
1160
150
6.8
3.4
4.7
min
1520
720
1160
188
6.1
2.9
4.7
min
         *
          Fixed value for predicted conditions.
                                     34

-------
ro
 i
 O
A MEASURED

© PREDICTED
                  100        200

                        TIME , minutes
                                300
400
 Figure 10.  NUCLA baghouse simulation, resistance versus time,
                         35

-------
TEST  RUN «  0422  NUCLfl^pHGHCUSE  S I K'J'.iP.T I CN-L I NEflR
PENETRflTION VS    ••   -    -
                                TIME  GR.-P
ov
                                          280.00   320.00   3BO. 00  400.00   440.00  480.00
               40~00   80~00    120.00  160.00   200.00  240.00   2
                                            TIME MINUTES)


               Figure 11.  Test run No. 0422 Nucla baghouse simulation - linear penetration

                         versus time graph.

-------
     Preliminary model validations were also conducted based upon a combination
of field and laboratory tests relating to the fabric filtration equipment at
the Sunbury Station of the Pennsylvania Power and Light Company1'4  The results
for both Sunbury and Nucla modeling operations are compared with actual test
observations in Table 3.  In view of the early development stage of the model,
the overall agreement between actual and predicted values is considered to be
highly satisfactory.

     The differences between observed and predicted values are attributed to
a combination of factors including simplifications in the modeling mathematics
and uncertainties in some data inputs.  Improvements in model reliability are
expected to result from a sensitivity analysis now in progress and the conduct
of further field and laboratory measurements.

     In the preceeding discussions, the reportings on model structure and its
applications represent but a small part of a very extensive study.4  Although
only the linear model is described here, the computer program is also written
to accept the condition where use of the true residual drag, SR, and a
curvilinear drag/fabric loading relationship may afford better estimates of
filter system performance.   The detailed studies also indicate several tech-
niques whereby the key data inputs can be adjusted to satisfy a broad range
of operating conditions.
                                     37

-------
                 TABLE 3.   MEASURED AND PREDICTED VALUES  FOR  FILTER SYSTEM PENETRATION  AND RESISTANCE,
                             COAL FLY ASH FILTRATION WITH WOVEN GLASS FABRICS
OJ
oo


Data source
Test _ . . . period
Description
case
A Sucla, Colo. 9/21/74
B Sunbury, PA 1/08/75
C Sunbury, PA 3/20/75
to
3/22/75

Penetration


Percent penetration
Bag
service Measured
Average
6 months 0.21
2 years 0.06
1.5 days 0.15

* Predicted

_.Linear model
Average ^Claanin
0.19 1.52
0.20
0.20


.*



Resistance
Test
case
A
B
Measured
Maximum
Average cleaning Maximum
1030 1700 1160§
635 710 710*



Minimum
Average
8505 972
560* 620
Predicted
Linear model
Maximum .
cleaning
1521 1160§
663 663*


Minimum
720§
567*
                              Based on field measurements.  See References 1 and 2.
                              All values listed as average depict overall system performance (penetration and
                              .resistance) for combined cleaning and filtering cycles.
                              All values listed under cleaning describe  performance  parameter during cleaning
                              only.
                              Maximum-minimum with Nucla tests indicate  resistance immediately before and
                              after cleaning.
                              Maximum-minimum with Sunbury tests indicate values for envelope curve.

-------
                                   SECTION  5

                                    SUMMARY


     The mathematical model described here represents  a new and very  effective
 technique  for predicting average and instantaneous resistance  and  emission
 characteristics during the filtration of coal fly ash  with  woven glass  fabrics.

     Two basic concepts used  in the model  design, (1)  the quantiative descrip-
 tion of the filtration properties  of partially cleaned fabric  surfaces  and
 (2) the correct description of effluent particle size  properties for  fabrics
 in which direct pore or pinhole penetration constitutes the major  source of
 emissions, have played important roles in  structuring  the predictive
 equations.

     A third factor in the model development was the formulation of explicit
 functions  to describe quantitatively the cleaning process in terms of the
method, intensity and frequency of cleaning.  By cleaning we refer specifically
 to the amount of dust removed during the cleaning of any one compartment and
 the effect of its removal on  filter resistance and penetration characteristics.

     The success of the model, based upon  limited applications to field data,
 suggests strongly that it be  further evaluated.   Minor changes in existing
compliance type sampling methods and apparatus should provide the key data for
resistance/fabric loading relationships that are fundamental to the applica-
tion of the model.  Additionally,  such measurements should help to confirm
the present observation that electrical charge and/or humidity factors do not
appear to play an important role in fly ash filtration with glass fabrics.
Application of the concepts presented here and in Reference 4 to other dust/
fabric combinations should provide a rational basis for treating heretofore
unresolved problems in many field  filtration applications.
                                     39

-------
 1.    Cass,  R.W.,  and R.M.  Bradway.   Fractional Efficiency of a Utility Boiler
      Baghouse:   Sunbury Steam-Electric Station.  GCA/Technology Division,
      Bedford,  Massachusetts.   Control Systems Laboratory, U.S. Environmental
      Protection Agency, Research Triangle Park, N.C.  Report No. EPA-600/2-76-
      077a (NTIS No.  PB253-943/AS).   March 1976.

 2.    Bradway,  R.M.,  and R.W.  Cass.   Fractional Efficiency of a Utility Boiler
      Baghouse  - Nucla Generating Plant.  GCA/Technology Division, Bedford,
      Mass.   Control  Systems Laboratory, U.S. Environmental Protection Agency,
      Research  Triangle Park,  N.C.  Report No. EPA-600/12-75-013a (NTIS
      No. PB246-641/AS).  August 1975.

 3.    Billings,  C.E., and J.E. Wilder.  Handbook of Fabric Filter Technology,
      Volume I,  Fabric Filter Systems Study:  GCA/Technology Division.  EPA
      No. APTD  0690 (NTIS No.  PB-200-648).  December 1970.

 4.    Dennis, R.,  et  al.  Filtration Model for Coal Fly Ash with Glass Fabrics.
      Industrial Environmental Research Laboratory, U.S. Environmental Protec-
      tion Agency, Research Triangle Park, N.C.  Report No. EPA-600/7-77-084.
      August 1977.

 5.    Dennis, R.,  R.W. Cass, and R.R. Hall.  Dust Dislodgement from Woven
      Fabrics Versus  Filter Performance.  APCA Paper 77-32.3.  Presented at
      the 70th  APCA Annual Meeting,  Toronto, Ontario, Canada.  June 20-24, 1977.

 6.    Dennis, R.,  and J.E.  Wilder.  Fabric Filter Cleaning Studies.  GCA/
      Technology Division,  Bedford,  Mass.  Control Systems Laboratory, Research
      Traingle  Park,  N.C.  Report No. EPA-650/2-75-009.  January 1975.

 7.    Leith, D., and  M.W. First.  Particle Collection by Pulse-Jet Fabric Filter.
      Presented at 68th Annual APCA Meeting, Boston.  1975.

 8.    Ensor, D.S., R.G. Hooper, and R.W. Scheck.  Determination of the Frac-
      tional Efficiency, Opacity Characteristics, and Engineering Aspects of a
      Fabric Filter Operating on a Utility Boiler.  Final Report.  Meteorology
      Research  Inc.,  Altadena, California.  EPRI-FP-297.  November 1976.

 9.    Robinson,  J.W., R.E.  Harrington, and P.W. Spaite.  A New Method for
      Analysis  of Multicompartment Fabric Filtration.  Atmos Environ.
      1:499-508, 1967.

10.    Walsh, G.W., and P.W. Spaite.   An Analysis of Mechanical Shaking in Air
      Filtration.   J  Air Pollut Control Assoc.  12:57, 1962.

11.    LOffler,  F.   Investigating Adhesive Forces Between Solid Particles and
      Fiber Surfaces.  Staub (English Translation).  26:10.  June 1966.

12.    Corn,  M.   The Adhesion of Solid Particles to Solid Surface.  A Review,
      J Air Pollut Control Assoc.  11:523, 1961.

13.    Zimon, A.D.   Adhesion of Dust and Powder.  Plenum Press, New York,
      1969.   p.  112.

                                       40

-------
  A PILOT PLANT STUDY OF VARIOUS FILTER MEDIA

           APPLIED TO A REFUSE BOILER
                       By

                 JOHN C.  MYCOCK
              Paper Presented At

           Fabric Filter Symposium

               Tucson, Arizona

               December 5, 1977
                 Sponsored By

   Federal Environmental Protection Agency
Industrial Environmental Research Laboratory
                       41

-------
                              Acknowledgements

    This program was sponsored by the Federal Environmental Protection Agency
with Nashville Thermal Transfer as the prime contractor and Enviro-Systems and
Research, Inc. as the major subcontractor.

    The author wishes to acknowledge the vital role played by each of the
participants.

    This project has been funded at least in part with Federal funds  from the
Environmental Protection Agency under Contract Number R80-4223. Q)  The con-
tent of this publication does not necessarily reflect the views or policies
of the U.S. Environmental Protection Agency, nor does mention of  trade names,
commercial products or organizations imply endorsement by the U.S.  Government.
                                     42

-------
                                   Abstract,

      A pilot scale investigation was conducted to determine the techno-economic
 feasibility of applying fabric filter dust collectors to solid refuse-fired
 boilers.   The pilot facility,  installed on a slip stream of a 135,000 Ib/hr.
 boiler, was sized to handle a  9,000 ACFM at an air-to-cloth ratio  of 6 to 1.
 Filter media evaluated included PTFE laminate on a woven backing,  woven glass
 and felted glass.

      Overall efficiencies greater than 99.8% were achieved with all  three types
 of filter media tested when operating at air-to-cloth ratios of 6  to 1 or less
 and having  an inlet  loading of  0.5 gr/DSCF.   For the  brief exposure  period
 encountered during the performance testing,  all  three of the bag materials
 tested  indicated no wear problems.

     The pressure drops obtained for the three filter media were within the
 conmercially acceptable range.

     The installed, operating and annualized costs for fabric filters were
developed and compared with the economics of wet scrubbing and electrostatic
precipitation.  This analysis indicated that the annualized costs of the
electrostatic precipitator and the fabric filter are  very close.
                                     43

-------
      In June 1976, an EPA sponsored pilot scale investigation was initiated.
The purpose of the study was to determine the techno-economic feasibility of
.applying fabric filter dust collectors to a refuse-fired boiler.  Included
in the program was the screening of a variety of filter media.  These included
Gore-Tex  (a PTFE laminate on a PTFE woven backing), supplied by W.L. Gore and
Associates, Inc.f a woven glass bag  (22^ oz. with Q78 finish), supplied by
Globe Albany Filtration and. an experimental needled felt glass bag supplied
by the Huyck Corporation.

      The test program was conducted on an existing fabric filter (baghouse)
system that is presently installed on the slip stream of a refuse boiler
owned and operated by the Nashville Thermal Transfer Corporation (NTTC) r a
public authority of the State of Tennessee.  By burning approximately 25%,
the city's daily output of refuse, this plant can supply steam and chilled
water to a number of downtown buildings,, including the State Capitol.

     An experimental program was conducted by NTTC in 1975 for the purpose of
establishing methods of controlling pollution from refuse-fired boilers.
Enviro-Systems & Research was selected to participate in this program and
provided NTTC with a two (2)  module Enviro-Clean RA-1 rectangular dust col-
lector to be used as a vehicle for filter media screening.  A second baghouse,
an Ess Tee pulse jet type was also tested.  Only a very preliminary screening
of filter media was included in this original program which was terminated
due to monetary considerations,  but data obtained indicated that a fabric
filter dust collector was capable of achieving excellent dust collection
efficiencies;  therefore the EPA funded program was instituted to confirm and
validate this data.

     The Enviro-Systems & Research baghouse is designed to contain a total of
1660 square feet of cloth.   The house is subdivided into twelve (12)  separate
cells, each cell having twelve (12)  bags.

     The operation of the baghouse is as follows:   the dirty gases  enter one
end of the unit,  pass through the tapered duct,  into the classifier,  then
through the bags.   The classifier forces the dirty gases to change  direction
90°,  then 18CP.   This quick directional change forces the larger and heavier
                                     44

-------
particles out of the flow so that they will fall directly into the hopper.
Dirty gases enter the classifier through a central duct tapered to feed the
sane quantity of gas into each cell.  The gases are forced through the fabric
filter into the center of the bags.  The cleaned gases are drawn up and out
through the center of the filtering bag into a center exit plenum via an
open damper in the cell above the tube sheet  (to which the bags are locked
on top and bottom via snap rings).

    As solid matter collects on the outside of the filter bag, it builds a
cake or crust which begins to restrict the flow of gases.  The bags are
cleaned one cell at a time by closing off the cell damper.  Clean air enters
through the damper, is forced down the filter bag  (opposite the normal flow
direction), and expands the bag with such a shock that the "cake" is cracked
and particulate matter falls off the bag and into the hopper.  Damper systems
and control panel arrangements allow for variations in main gas volume,
reverse air volume, duration of cleaning and frequency of cleaning.

    The pilot plant was originally installed on one of the NTTC boilers in
September 1975.  The slip stream is a 16 inch duct approximately 250 feet
long with numerous turns.  This duct is covered with 1^ inch metal-skinned
insulation to decrease heat loss.  The outlet and reverse air duct were also
insulated.  A temperature profile (Figure 2) shows a maximum temperature of
350° F in the inlet duct while the maximum at the outlet was 18CP F. Figure
3 is a photograph of the plant.

    An inlet profile was obtained at the beginning of the ES&R program and
again during the testing of the needled glass fabric.  Tables 1 and 2 list
these results.   Although chloride and flouride concentrations could result
in increased bag deterioration, we found no evidence of this during the
program.

    Rigorous sampling indicated that changes in the inlet loading had no
significant effect on outlet loading.  Therefore,  an average inlet concen-
tration was calculated from data obtained during concentrated testing efforts
in March of 1977 and used as the basis for all total mass and fractional
efficiencies.
                                     45

-------
                                 ELEVATION
                                                                      END view
                                  Figure 1




Schematic Diagram of the Enviro-Clean RA-1 Dust Collector Model  144-RA1-5-104

-------
                     Figure 2




Temperature Profile for the Enviro-Systems Baghouse

-------
Figure 3.  Fabric Filter Pilot Plant Installed at
           Nashville Thermal Transfer Corp.
                        48

-------
                                  TABLE 1
                        NASHVILLE THERMAL TRANSFER
 Test Data
 Date
 Gas  Temperature  (avg.  °F)
 Stack Rate  (SCFMD)
 Flue Gas  Composition
     H20 (%)
     02  (%)
     CO  (%)
     C02 (X)
Particulate Concentration
     (Grains/SCFD)
Isokinetic Rate (%)
Cl  (ppm)
F   (ppm)
[house Inlet Gas Stream Profile
1
7/29/76
F) 411
1583
15.94
7.1
12.9
>n
0.72
109.16
84.1
7.09
Run Number
2
7/30/76
443
1581
16.03
7.1
12.9
1.38
109.3
83.7
0.8
3
7/30/76
410
1520
18.68
7.1
12.9
1.76
94.3
68.04
0.61
                                   49

-------
                            TABLE 2
                    INLET EMISSION PROFILE
Date
                                           11/20/76
Stack Temp.  (Avg.°F)
Stack Rate   (SCFMD)
Stack Rate   (ACFM)
Flue Gas Composition
      H20    (%)
       02    (20
      C02    (%)
Metered Gas  Volume (SCFD)
Particulate Concentration
     (Grains/SCFD)
Emission Rates (Ib/Hr)
Isokinetic Rate (%}
F     (ppm)
                                           360°F
                                         2252.2
                                         3826.6

                                            7%
                                       10.88 %
                                        7.25 %
                                          21.90

                                        1.1634
                                         22.46
                                        101.2%
                                          0.2
                              50

-------
      Figure 4  shows the  average  inlet particle size distribution.

                              Needled Glass  Felt

      Outlet particulate  concentrations obtained when varying the apparent
 velocity or more comonly - the  air-to-cloth ratio  (A/c ratio)  for the  glass
 felt are provided in Table 3.  As is  evident in this table,  the needled
 glass felt  proved to be  an extremely  efficient filter media  for this appli-
 cation at all A/C ratios studied.

      Outlet particle size distribution for air-to-cloth ratios  of  3.2,  6.4
 and 8.7 to  1 is graphically displayed in Figure 5.   In  ascending order, the
 percentages of fabric penetration of  particles less than three  (3) microns
 are 50%, 41% and 34% respectively.

                                 Woven Glass
     The woven glass bags were employed at air-to-cloth ratios of 2.75, 4.2
and 6.7.  Figure 6 shows the particle size distribution for the A/C ratios.
The curves also indicate that as the air-to-cloth ratio is increased, the
percentage of sub-micron particles  (when compared to total emissions) also
increases.

     Average outlet concentrations and relative cumulative percentages are
shown in Table 4.  Although not quite as efficient as the other fabrics
tested, woven glass proved more than satisfactory to meet present code
requirements.

                            ;    PTFE Laminate

     The PTFE laminate was employed at air-to-cloth ratios of 4.2, 5.4 and
6.0 and once again the outlet particulate concentrations and particle size
distributions were determined.  Particle size data is shown in Figure 7.
For the lowest air-to-cloth ratio the penetration of sub-micron particles
is 41% of total particulate penetration.   Outlet concentration and cumulative
percentages are listed in Table 5.   While there seems to be no clear correla-
tion between filtration velocity and outlet dust concentration,  it is
                                    51

-------
    30.0
   2t).0
   10.0
IS)
c
o


I   5.0
0)
IM
CO


0)
s_
(O
O-
   1.0
   0.7
                        O Run 2

                        A Run j
                  JL
_L
JL
J_
J_
JL
_L
                              _L
                                                              JL
J
              .512      5    10     20    30   40  50  60  70  80

                    Percent Less Than Size  Indicated
                                 Figure 4


                  Inlet  Particle Size Distribution for Two

                           Brinks  Impactor Runs

                                 (3/33/77)

                                   52

-------
                                                  TABLE  3
Ui
OUTLET CONCENTRATION AND
Air-to-Cloth 3.2/1
Avg. (1) Avg. (2)
Part. Outlet
Diam. Cone.
Microns gr/SCFD
9.33
6.23
4.20
2.77
1.33
0.80
0.57
0.30
0.30
TOTAL
.0001834
.0000657
.0000391
.0000459
.0000744
.0000286
.0000434
.0000455
.0000482

.0005742
Cum % (3)
100.00%
68.04
56.6
49.79
41.8
28.85
23.87
16.31
8.39

Huyck Bags
Air-to-Cloth 6.
Avg.. Avg.
Part. Outlet
Diam. Cone.
Microns gr/SCFD
9.33
6.23
4.20
2.77
1.33
0.80
0.57
0.30
0.30
TOTAL
.0001770
.0000502
.0000592
.0000207
.0000154
.0000302
.0000155
.0000156
.0000494
.0004332
CUMULATIVE %
4/1
Cum %
100.00%
59.02
47.43
33.76
28.99
25.54
18.57
15.0
11.40

Air-to-cloth 8.7/1
Avg. Avg.
Part. Outlet
Diam. Cone.
Microns qr/SCFD Cum £
9.33
6.23
4.20
2.77
1.33
0.80
0.57
0.30
0.30
TOTAL
.0005394
.0002472
.0002162
.0001229
.0000849
.0000697
.0000338
.0000485
.0001073
.0014699
100.00%
63.31
46.49
31 . 78
23.42
17.64
12.9
10.6
7.30

  (1) Corrected for Stack Temperature
  (2  gr/SCFD - Grains Per Standard Cubic Foot Dry (Standard - 7QQF,
  (3) Percent of Total Outlet Concentration Less  Than  Size Indicated
29.92" Hg)

-------
to
•Zi
o
M
i—i

00
a:

-------
     10
   20  30  40  5.0  60  70
% Less Than Size Indicated
80    90
                    Figure 6
Outlet Particle Size Distribution, Globe Albany
                 55

-------
                                                  TABLE  4
                                  Outlet Concentration  and Cumulative %
          Air-to-cloth 2.75/1
  Avg.  (1)  Avg. (2)
  Part.     Outlet
  Diam.     Cone.
  Microns   gr/SCFD      Cum%
  8.85      ^0003446  100.0~OT
                            (3)
Ul
6.03
4.10
2.63
1.33
0.84
0.54
0.17
0.17
TOTAL
.0001473
.0000631
.0000625
.0000417
.0000431
.0000515
.0000493

.0008031
57.09
38.75
30.89
23.11
17.92
12.55
 6.14
Globe
Albany Bags

Air-to-cloth 4.2/1
Avg.
Part.
Diam.
Microns
78.85
6.03
4.10
2.63
1.33
0.84
0.54
0.17
0.17
TOTAL
Avg.
Outlet
Cone.
gr/SCFD
.0001936
.0000647
.0000536
.0000618
.0000601
.0000558
.0000482
.0001009
.0000843
.0007230
Cum%
1075700%'
73.23
64.28
56.87
48.32
40.01
32.29
25.62
11.66
   Air-to-cloth 6.7/1
Avg.-  Avg.
Part. Outlet
Diam-. Cone.
Micron gr/SCFD Cum%
78.85 .0001936  10~0.00%
 6.03 .0000415   91.63
 4.10 .0000411   87.33
 2.63 .0000506   83.07
 1.33 .0000456   77.83
 0.84 .0000828   73.01
 0.54 .0001134   64.44
 0.17 .0002527   52.69
 0.17 .0002563   26.53
TOTAL .0009659
   (1)  Corrected for Stack Temperature
   (2)  gr/SCFD - Grains Per Standard Cubic Foot Dry (Standard - 70°F,  29.92"
   (3)  Percent of Total Outlet Concentration Less Than Size Indicated
                                                                           Hg)

-------
8.0
7.0
6.0
5.0
4.0

3.0
                          A
                                 o
                                             KEY
                                         O  4.2/1
                                         A  5.4/1
                                         06/1
                                  I    l
              10    20   30  40  50  60  70  80     90
                   % LESS THAN SIZE INDICATED
                            Figure 7
       Outlet Particle Size  Distribution for Gore-Tex Fabric
                      57

-------
Ui
CO
     Air-to-cloth  4.2/1
    Avg.     Avg.
    Part.   Outlet
    Diam.   Cone.
    Microns gr/SCFD
8.4
5.7
3.9
2.5
1.2
0.77
0.48
0.41
0.41
            Cum.%
.0001760  100.00%
.0000235   67.28
.0000512
.0000372
.0000666
.0000637
.0000581
.0000221
           .0000402
62.92
53.42
46.52
34.16
22.34
11.56
 7.46
    TOTAL  .0005388
                                                    TABLE  5
                                     Outlet Concentration  and Cumulative %
Gore-Tex Bags
March
Air-to-cloth
Avg.
Part. Outlet
Diam. Cone.
Micronsgr/scFD
8.4
5.7
3.9
2.5
1.2
0.77
0.48
0.41
0.41
TOTAL
.0001628
.0000961
.0002230
.0000564
.0000423
.0000333
.0000179
.0000179
.0000230
.0006727
1977
5.4/1
Cum.%
100.00%
75.71
61.42
28.27
19.93
13.64
8.74
6.08
3.42
Ai
r-to-cloth
Avg. Avg.
Part. Outlet
Diam. Cone.
Microns gr/SCFD
8.4
5.7
3.9
2.5
1.2
0.77
0.48
0.41
0.41
TOTAL
.0001703
.0000605
.0000688
.0000461
.0000251
.0000346
.0000374
.0000213
.0000482
.0005123
6/1
Cum.%
100.00%
66.75
54.94
41.51
32.51
27.61
20.86
13.56
9.40
    1)  Corrected for ;Stack Temperature
    2)  The outlet concentration for the air-to-cloth ratio of 5.4 was not an average of two values
        gr/SCFD - Grains Per Standard Cubic Foot Dry (Standard - 70° F, 29.92" Hg)
    3)  Percent of Total Outlet Concentration Less Than Size Indicated

-------
 evident that the PTFE laminate is extremely efficient at the three air-to-
 cloth levels studied.

      As shown in Figure 8, for air-to-cloth ratios of approximately 3 and 6
 to 1 the felted glass snowed the lowest dust concentrations and the woven
 glass media the highest.  However, as I had stated before, the v.'oven glass
 media was considered more than satisfactory to meet present code requirements
 for this application.

                           Economic Considerations

      The economics of applying fabric filters to the refuse-fired boilers
 were evaluated and comparative costs for an electrostatic precipitator (ESP)
 and wet scrubber were developed.   Installed costs were calculated for a
 fabric filter dust collector sized to handle 140,000 acfm at 46CP F.   The
 costs were developed for four (4)  filter media:   woven glass,  PTFE laminate,
 needled glass felt,  and Teflon felt (style 2663).  Air-to-cloth ratios con-
 sidered were 2.9,5.8,  8.9  and 11.3  Table 6 shows the costs were developed
 from actual bag manufacturer quotes obtained during 1976.

      The installed costs for an electrostatic precipitator capable of  handling
 140,000 ACFM at  98.5% efficiency were also developed.  This cost was developed
 by  adding the flange-to-flange cost (supplied by  a leading ESP manufacturer)
 plus  70% of the  purchase price for erection cost  (the  same figure was  used  in
 the fabric filter case), plus  5% of the purchase  price for fans.

     A graphical  comparison of the  installed costs  for the  four bag materials
 versus  the  installed  costs of  the electrostatic precipitator is shown  in
 Figure  9.  At air-to-cloth ratios of 5.8/1 or greater, the  installed costs
 of  the  fabric filter  (for all bags considered) was lower than the electrostatic
 precipitator.

     Installed costs for a wet scrubber capable of handling 140,000 ACFM with
 99% efficiency and a pressure drop of 30" W.G. were derived by doubling the
 figure of $316,000 for 70,000 ACFM given in the article "Performance and Cost
Comparison between Fabric Filters and Alternate Particulate Control Techniques"2
and adding 12% for escalation.        59

-------
.0014

.0013

.0012

.0011
in
- .0010
CD
 I
C
O
4->
to
o>
(J
c
O)
.0009

.0008

.0007
,§  .0006
   .0005

   .00041-
               O Huyck Experimental
               Q Globe Albany
               A Gore-Tex
              2     3     4     5      67      8
               Air-to-Cloth Ratio   (ACFM/Ft.2)
                                                            10
                                Figure  8
         Comparison of Three  (3)  Fabrics for Outlet Concentration
                          vs. Air-to-Cloth Ratio
                              60

-------
               TABLE  6
Bag Cost as Percent of  Installed  Cost
Globe Albany ($17.25/bag)
2.9
5.8
8.9
11.3
Huyck($32.40/bag)
2.9
5.8
Y1
8.9
11.3
Installed Cost

817,260
421,750
316,734
271,837

928,522
477,381
353,821
301,505
Bag Cost

74,520
37,260
24,840
19,872

139,968
69,984
46,656
37,325
% of Installed
Cost for Bags

9.1
8.8
7.8
7.3

15.1
14.7
13.2
12.4
Gore-Tex/Gore-Tex ($51.50/bag)
2.9 ;
5.8
8.9
11.3
Teflon Felt ($68/bag)
2.9 i
5.8
8.9
11.3
1,068, 792
547,516
400,578
338,912

,189,968
608,104
440,970
371,226
222,480
111,240
74,160
59,328

293,760
146,880
97,920
78,336
20.8
20.3
18.5
17.5

24.7
24.1
22.2
21.1
               61

-------
     1200
     1000   -
     800  _
cc.
i—i

-------
       A comparison of the three methods of particulate control  is  seen  in
  Figure 10.   The fabric filter technique for air-to-cloth ratios of  5.8/1 and
  greater on  all  bags  considered has  the lowest installed cost and  the wet
  scrubber the highest.   However, should an air-to-cloth ratio of 2.9/1  be
  required, fabric filters would be the  most expensive  and the electrostatic
  precipitators the least expensive method.   Development of the operating and
  annualized  costs for the three control techniques, employed the formulae
  published by Edmisten  and Bunyard.3

      Operating costs were developed for the  fabric filters with two and four
 year bag life and compared with those of the electrostatic precipitator.
 Fabric filter costs were  based on pressure drops of 6", 7", 10.5" and 12.5"
 W.G. for air-to-cloth ratios of 2.9, 5.8, 8.9 and 11.3/1 respectively.   Pre-
 cipitator costs were based on a pressure drop of 2" W.G. (all pressure drop
 values included 1.5" W.G. for drop across the inlet duct) and maintenance
 costs of 3% of the flange-to-flange price  (considered higher than average but
 used due to the corrosive elements in the gas stream).  Electrical rates for
 both cases were actuals obtained from NTTC.  These costs presented in Figures
 11 and 12 show the electrostatic precipitator to be less expensive to operate
 than any of  the fabric filter cases  considered.

      While studying these graphs one must remember that in  the  formula  for
 calculating  annual operating costs for  a specific bag  life only two  variables
 exist:

      1.  the number of  bags  (which decrease with increasing A/O.

      2.  the pressure drop (which increases with increasing A/C) .

     It appears that  at  some point in the increase of the air-to-cloth ratio
 for a particular  bag  life, the  effect of the increase in pressure drop out-
weighs the effect of the decrease in number of bags required.

     As I had stated previously all bag materials were treated the sane  with
regard to pressure drop.  Actual pressure drops obtained during the course of
                                     63

-------
                                                     Installed   Costs  x   10    Dollars
     zs
     to
     rt-
     Ol
     CD
     QL
     O
     O
     o
     o
O rt- -"•
— '• -s l/l
-h O O
-+1—13
fD    to
-S  -H
(t>  (D -h
300
c-t- rr -s
     fD
-+> c:

o  

fD

n

fD
1/1
     O
     3
£ N UJ 4^ Ul O
X o o o o o
0 o o o o o
Fabric Electrostatic Wet
Filtration Precipitation Scrubbing
(A/C 5.8/1)
I I if I i
v£>
Globe Albany filters ^°
00
^
Teflon felt filters





•^1 00
0 0
o o
1 1
vO
vO
•
00
^
vO
00
*
Ul
"'^
vO
vO
^


-------
 CO
 o:
 o
 O
 CO

 O
 CO
 CO
 O
UJ

o

_J
<

•z.
2:
«3T
                                                     KEY:


                                                     Teflon  Felt

                                               O   Gore-Tex/Gore-Tex

                                               A   Huyck Glass Felt


                                                    Globe Albany Woven Glass

                                                    ESP (98.5% Efficiency)
                                  6           8

                               AIR-TO-CLOTH  (ACFM/FT.2)
10
12
                                       Figure 11


                   Comparison of Annual Operating Costs of Four (4)
                   Filter Media and ESP Assuming Four Year Bag Life
                                    65

-------
                                                 KEY:

                                         O  Teflon Felt

                                         ^  Gore-Tex/Gore-Tex
                                         A  Huyck Glass Felt

                                         n  Globe Albany Woven Glass

                                        --  ESP C98.5% Efficiency)
 O
 Q
CO
 O
 co
CO
O
CD
DC.
CL.
O
                               6           8            10

                                AIR-TO-CLOTH  (ACFM/FT.2)


                                   Figure  12

               Comparison of Annual Operating Costs of  Four  (4)
               Filter Media and ESP Assuming  Four Year  Bag Life
12
                                 66

-------
  the program, although well within the commercially acceptable range, were not
  vised for this comparison because of the suspected influence of the sub-dew
  point conditions that plagued us throughout the program.

      A comparison of the annual operating costs for the three techniques of
  control is illustrated in Figure 13.  The electrostatic precipitator is seen
  to be the most economical while the wet scrubber seems the most expensive
  approach.

      The annualized costs or total costs of control were developed from the
 preceding installed and operating costs.   These results shown in Figures 14
 and 15 were based on the following assumptions:  First, hardware and instal-
 lation costs are depreciated over fifteen (15)  years.   Second,  the straight
 line method of  depreciation (6  2/3% per year)  is used.   This  method has the
 simplicity of a constant annual write-off.  Third, other costs  called capital
 charges, which  include interest, taxes, insurance and other miscellaneous
 costs  are  assumed equal  to  the  amount of depreciation,  or 6 2/3% of the initial
 installed  costs.  Therefore,  depreciation plus  these other annual  charges
 amount to  13  1/3% of the installed costs.

     As illustrated  in Figures 14 and 15, fabric filters,  at air-to-cloth
 levels of 5.8/1 or greater, and  electrostatic precipitators are extremely
 competitive on an annualized costs basis.

     Figure 16 shows the comparison of the annualized costs of control for
 the three techniques studied.  Once again the wet scrubber is the most expen-
 sive approach, while the costs of the fabric filter and electrostatic precip-
 itator are very close.   This being the case, the need to replace bag life and
pressure drop assumptions in computations  for operating costs  with empirical
 facts is necessary for final selection of  the best alternative.
                                      67

-------
300

200
CO
S-t
£ 100
r-H
a
i
o
r— <
X
50
CO
~LJ
CO
o 40

GO
-S 30
rt
i-i
0)
O 20
r_,
d
3
C
C
10
99%
-



99.8%
-


^
99. 8%



•^










^,
*
^^

CU ro
H ^






98. 5%































































              Fabric
            F iltration
            (A/C  5.8/1)
Electrostatic   Wet
Precipitation    Scrubbing
                      Figure  13

    Annual  Operating  Cost  Comparison for Three Air
             Air Pollution Control Teqhm'ques
                   68

-------
     350
     300
    250
                                           KEY:
                                     O  Teflon Felt

                                     O  Gore-Tex/Gore-Tex

                                     A  Huyck Glass Felt

                                     Q  Globe Albany Woven Glass


                                     —  ESP (98.5% Efficiency)
    200
 GO
 D;
 O
 O
ro
O
oo
O
o
150
~  100
     50
        ,-
                     ^           6           8          10

                         AIR-TO-CLOTH (ACFM/FT.2)


                                   Figure 14


                Comparison of Annual Operating Costs of Four (4)
                Filter Media and ESP Assuming Two Year Bag Life

                                  69
                                                                12

-------
     300
     250
    200
oo
DC
O
Q
    150
      KEY:

O  Teflon  Felt

O  Gore-Tex/Gore-Tex

A  tiuyck Glass Felt

CH  Globe Albany Woven Glass

—  ESP  (98.5% Efficiency)
oo
O
LlJ
t-vl
    100
     50
                                 JL
                                 6           8           10

                               AIR-TO-CLOTH  (ACFM/fT.2)
                            12
                                    Figure 15


                 Comparison of Annual Operating Costs of Four  (4)
                 Filter Media and ESP Assuming Four Year Bag Life
                                 70

-------
 CO
 !-,

 ri
 O
 IH
 4-1
 £3
 O
 O
CO
O
u

T)
0>
N
         350
                                       99%
        300
        250
        200
        150
        100
        50
                               99. 8%
99. 8%
*
i—i
<
a>

•
CO
«•( —.
0) 0)
                                0)
                         98. 5%
                      Fabric;
                     Filtration
                    Electrostatic   Wet
                    Precipitation    Scrubbing
                                Figure  16


     Annualized Cost  for  the Three Air Pollution Control Techniques

                                 71

-------
                                 CONCLUSIONS

     The three filter media tested for dust reiroval capability indicated high
level removal over a range of air-to-cloth ratios  (apparent filtration velo-
city) .  For air-to-cloth ratios of approximately 3 to 1 and 6 to 1 the felted
glass media showed the lowest outlet dust concentration and the woven glass
media was considered more than satisfactory to meet present code requirements
for this application.

     No clear correlation between filtration velocity and outlet dust concen-
tration was demonstrated.  There may well be such a correlation, however,
testing circumstances did not allow for determination of it in this program.

     The three filter media for dust removal capability did not show signs
of wear or weakening during this test program.  It should be noted, however,
that total on-stream time was very limited.

     The pressure drops obtained for the three filter media were within the
commercially acceptable range.

     Generalizations regarding the costs of particulate removal devices are
inherently dangerous, however, it does appear that of the conventional routes
to particulate control, only fabric filters and electrostatic precipitators
are suitable to refuse-fired boilers.  The economic analysis indicates that
the wet scrubber has both higher operating and capital costs (and,  therefore,
higher total annualized costs) than either the electrostatic precipitator or
fabric filter.

     In view of this and considering its potential for corrosion, the wet
scrubber appears to be an unlikely candidate for this application.

     As previously mentioned,  the economic analysis indicate that the annual-
ized costs of the electrostatic precipitator and the fabric filter are very
close.  Final selection of the best alternative can only be made after bag
life and pressure drop assumptions have been replaced with empirical facts.
                                      72

-------
References

1)  J.D. McKenna, J.C. Mycock, R.L. Miller, K.D. Brandt, "Applying Fabric
    Filtration to Refuse Fired Boilers", Report to be published by EPA.

2)  J.D. McKenna, J.C. Mycock and W.O. Lipscomb, "Performance and Cost
    Comparisons Between Fabric Filters and Alternate Particulate Control
    Techniques", JAPCA, V24,  N12 December 1974, P1144.

3)  N.G. Edmisten and F.L.  Bunyard, "A Systematic Procedure for Determining
    the Cost of Controlling Particulate Emissions from Industrial Sources",
    J.  Air Pollution Control  Association V20,  N7, p.446 (1970).
                                     73

-------
74

-------
                FIELD TESTS WITH A MOBILE FABRIC FILTER
                            Dale L. Harmon
                     Particulate Technology Branch
             Industrial Environmental Research Laboratory
                  Research Triangle Park, N. C. 27711
                             December 1977

                               Abstract

     In 1973, EPA funded the design and construction of a mobile fabric
filter unit, the first of a series of three mobile research units built
for the assessment of the collectibility of particulate emissions from
industrial sources.  The mobile filter unit can be adapted to cleaning
by mechanical shaking, pulse jet or low-pressure reverse flow.  Cleaning
parameters can be varied easily over broad ranges.  The paper presents
results of tests completed on a brass and bronze foundry, a hot mix as-
phalt plant, a pulp mill lime recovery kiln, a refuse processing plant
the three coalfired boilers.  The most recent test was at the Amarillo,
Texas Harrington Station generating plant of the Southwestern Public
Service Company.  Low-sulfur subbituminous coal was burned.  Woven Teflon
coated fiberglass and woven graphite - and - silicone - coated fiberglass
bags were tested in shake and reverse air cleaning modes.  Total mass
efficiency for all tests ranged from 99.56% to 99.99% with an overall
average of 99.87%.  Bag blinding problems were encountered with reverse
cleaning.
                                  75

-------
                   FIELD TESTS WITH A MOBILE  FABRIC FILTER
                                Dale L. Harmon
                         Particulate Technology Branch
                  Industrial Environmental Research Laboratory
                      Research Triangle Park, N. C. 27711
                                December 1977
 INTRODUCTION
     The Environmental Protection Agency and predecessor organizations
have been involved in development of systems for control of emissions
from industrial sources for many years.  The EPA R&D program for particulate
control is designed to establish engineering design techniques and
performance models, and to improve the collection capability and economics
of control devices for particulate matter.  The objective is the development
and demonstration of control technologies capable of effectively removing
large fractions of the under 3 micron diameter particles from effluents.

     In 1973, EPA funded the design and construction of a mobile fabric
filter unit, the first of a series of three mobile research units built
for the assessment of the collectibility of particulate emissions from
industrial sources.  These units house the three types of conventional
particulate collectors (fabric filter, wet scrubber and electrostatic
precipitator) that are generally used by industry at the present time.

     Actual  data on particle collection efficiency of conventional
particulate collectors is sparse.  Actual operating data for the optimization
of collection efficiency and cost is not readily available.   Design of
control equipment is presently based on projections from historical data
which has been developed by manufacturers for their own devices and is
proprietary.   This information is not standardized and cannot be extrapolated
to other devices.  On-site testing prior to control  device selection is
seldom attempted and the possibility of alternative devices  is poorly
defined.   The EPA mobile units are highly versatile and will  be used to
investigate the applicability of these control  methods to the control  of
fine particulate emitted from a wide range of sources.   The  relative
capabilities  and limitations of these control  devices  will  be evaluated
                                     76

-------
 and documented.  This  information,  supplemented  by  data  from  other  EPA
 particulate  programs,  will  permit selection  by equipment users  of collection
 systems that are technically and economically optimum  for specific
 applications. Operation of  the mobile  units  will  be coordinated with
 other EPA laboratories and  regions  to  provide, when possible, field data
 on specific  problem sources.

 MOBILE UNIT  DESIGN

      The original mobile fabric filter unit was  built  by  GCA Corporation
 for EPA and was mounted on an open  1360 kg (1.5  ton) truck.  The equipment
 could be operated on the truck or could be removed  and operated at
 locations not accessible to the truck.  The mobile  filter unit  can be
 adapted to cleaning by mechanical  shaking, pulse jet or low-pressure
 reverse flow.  Filtration can be conducted at cloth velocities  as high
 as 0.1  m/s (20 fpm) with a pressure differential  up to 50 cm (20 in.)  of
 water,  and at gas temperatures  up  to 290°C (550°F).   Cleaning parameters
 can be  varied easily over broad ranges.  One to  seven filter bags of any
 fabric  media, 1.2 to 3  m (4 to 10  ft) long and  up to 30 cm (12  in.) in
 diameter may  be  used.   Gas flows used are from 0.012 to 0.13 m3/s (26
 to 280  cfm),  as  determined by  cloth  velocity, bag size and bag number.

     The mobile  fabric filter unit just described operated on  effluents
 from a  brass  and bronze foundry, a hot mix asphalt plant, a coal-fired
 boiler,  a  lime kiln and a  pulp  mill  recovery  boiler.  Operation  of the
 unit from  the open  truck was found to be  extremely inconvenient  and
 detrimental to efficient field  testing,  so the filter system was installed
 in  a 12 m  (40 ft) closed trailer in  October 1976.  Since  then  the unit
 has been used to determine the  performance of a fabric  filter  on the
 effluent from a  cyclone collector used  on  the St.  Louis Refuse Processing
 Plant and a power plant burning a western  subbituminous coal.

     The second mobile unit received by EPA was the  wet scrubber.  This
unit, built by the Naval Surface Weapons Center at Dahlgren, Va., was
delivered in December 1974.  The scrubber unit is in a 12 m  (40  ft)
trailer  and contains a venturi  scrubber and a sieve tray scrubber.
                                     77

-------
 Maximum  gas  flow  rate  through  the  scrubbers  is  0.28 m3/s  (600 cfm).
 Maximum  L/G  ratio is 0.01  m/m  (75  gal./acf).   The unit  can  treat  gas
 at  temperatures up to  480°C  (900°F).

      The mobile electrostatic  precipitator was  delivered  to EPA in
 September 1976.   This  system was also  designed  and  built  by the Naval
 Surface  Weapons Center.  The mobile  ESP  facility consists of  two separate
 units mounted  in  12 m  (40  ft)  freight  vans.   The first unit is the
 process  van  which houses a five-section  ESP  and all  auxiliary equipment.
 Each  section of the ESP has  a  separate power supply which provides  up to
 50,000 volts and  7 milliamps DC.   The  precipitator  is  designed to operate
 at  flow  rates  up  to 1.4 m3/s (3000 cfm)  at temperatures up to 480°C
 (900°F).   The  second unit  is a control/laboratory van  containing all
 process  controls,  monitors and recorders plus provisions  for  an analytical
 laboratory and equipment storage.

 MOBILE FABRIC  FILTER FIELD TESTS

 Tests by GCA/Technology Division

     After designing and building  the  mobile fabric  filter for the
 Environmental  Protection Agency, GCA/Technology Division  conducted field
 tests on the following three sources:

               Secondary brass  and bronze  foundry.
               Hot  mix asphalt  plant.
               Coal-fired  boiler.

 Results  of these  three tests are discussed briefly below:

     Secondary Brass and Bronze  Foundry

     The mobile fabric filter system was operated in the  pulse  jet,
mechanical shake,  and reverse flow cleaning modes on a  secondary  brass
and bronze foundry.  Three pulse cleaning tests using Nomex felt  bags
were conducted. The only parameter varied was the interval between
pulses:   two tests were at a 40 second interval  and one at a 20 second
interval.  Data is summarized in Table 1.  During test  3,   in
                                     78

-------
  which  the  filter  bags  were  cleaned  twice  as  often,  the  average
  pressure drop  across the  filter was  only  13  cm  (5  inches)  as  compared  to
  23 and  25  cm (9 and 10 inches) for  the  first two tests.  However,  increasing
  the cleaning frequency also doubled  the percent penetration.

       Four  shake cleaning  tests using woven Nomex bags were conducted.
  Bag tension, shaking frequency and amplitude, and filtration  velocity
  were varied.  Data is  summarized in Table 2.  Test 4 was designed to
  simulate cleaning parameters for a full scale fabric filter which was
  operating at the test site.   The plant had experienced problems with
  excessive pressure drop across the filter.  This problem was evident
  with the mobile unit during  test 4.   Very little cleaning was accomplished.
  After  2 hours  operation the  pressure drop had increased  to 38 cm (15
  inches)  and even  after  shaking was  only slightly reduced to 33 cm (13
  inches).  Tests 5,  6, and  7  indicate that  increased  shaking frequency
  and  amplitude  (both  contributing to  higher bag acceleration)  reduced the
  filter  pressure drop and increased filtration capacity but  also  increased
  penetration.  This information was helpful in analyzing  the plant's
  problem.

      Only one reverse flow cleaning test was  conducted:  it was primarily
 to state down the mobile fabric filter system in the reverse flow cleaning
 »de.   Data  collected was not sufficient to develop conclusions.

      Hot Mix Asphalt Plant

      Four pulse  cleaning tests  on a  hot  mix asphalt  plant using Nomex
 felt bags were conducted.   Results of  these tests are presented in Table
 3. The pressure  drop performance of the mobile unit was worse than that
 o  a p ant fabric filter  system operating on the source tested.   he
 Plant f,,ter operated at 5  to 8 cm (2 to  3  inches) pressure drop and  had
  reported air consumption of 0.5 to 0.8 JMJ (8 to „ H^"
ft )  versus a 28 to 30 cm (1,  to 12 inch) pressure drop near the en  of

                 "
                                     79

-------
 which may account for the lower pressure drop, although filter geometry
 may have also been an important factor.  The continuous rise in filter
 pressure drop throughout the field test may have been caused by moisture
 problems.

      Coal-Fired Power Plant (Cyclone-Fired Boiler)

      Three shake cleaning tests on a coal-fired power plant with cyclone-
 fired boilers using woven glass bags were conducted.  Results of these
 tests are presented in Table 4.  Pressure drop across the mobile fabric
 filter averaged about 13.7 cm (5.4 inches) after 20 hours of testing at
 a filtration velocity of 1.4 cm/sec (2.7 fpm).   Total mass efficiency
 averaged 99.66%.

 Tests by Monsanto Research Corporation

      Following  completion of the three tests  described above,  operation
 of the  mobile filter  was transferred  to Monsanto  Research Corporation
 (MRC) under  a contract with  EPA's  Industrial  Environmental  Research
 Laboratory at Research Triangle Park  (IERL-RTP) to  maintain and  operate
 various  IERL-RTP field and  laboratory  test facilities.   The following
 tests were completed  by  MRC:

      Coal-Fired  Power  Plant  (Anthracite Coal)

     The  mobile  fabric filter was operated  at the Shamokin  Dam, Pennsylvania,
 generating station of  Pennsylvania Power and Light  Company.2  This
 station was unusual in two respects:   it had a full-scale fabric filter
 operating and it burned  a mixture of anthracite silt  and petroleum  coke.
 An extensive  test was conducted with the mobile filter using three  bag
 types and three cleaning modes over a range of values of air/cloth
 ratio, filtration time, and pulse interval.  Operating conditions for
 the tests are given in Table 5.  Total  particulate collection efficiency
 and penetration  results are given in Table 6.   Fractional efficiency
measurements  were also made for each run.
                                      80

-------
      Based on collection efficiency of particles 5  m and less in size,
 cleaning mode/bag type combinations can be ranked in descending order of
 collection efficiency as follows:

           1)   Reverse clean - Nomex felt bag
           2)   Reverse clean - glass bag
           3)   Shake clean - Nomex felt bag
           4)   Shake clean - Nomex woven bag
           5)   Pulse clean - Nomex felt bag

      This ranking is based on the data at the operating conditions given
 in Table 5 and does not necessarily describe optimum performance achievable
 for each cleaning mode/bag type combination.

      Pulp Mill Lime Recovery Kiln

      The mobile fabric filter was operated at the Weyerhauser Corporation's
 pulp mill  in Plymouth, North Carolina,  on a lime recovery kiln.3  Two
 cleaning modes and two fabric types were used in this test program.
 Operating  conditions are given in Table 7.   Total  particulate collection
 efficiency and penetration results are  given  in Table 8.   Fractional
 efficiency results are given in Table  9.   Overall,  integrated mass
 collection efficiency was 99.98%.   Overall  averages  of mean  fractional
 efficiencies  by size range were as follows:

           size»  yfn            Efficiency,  %        Penetration,  %

             1-3                   99.815               0.185
            4-6                   99.814               0.186
            7-10                  99.918               0.082

     Bag pressure  drop  (AP) data  is summarized  as average  values in
Table 10. The  results show marked  differences in bag AP both within and
between cleaning mode/bag groups.  The variation within groups  is  in the
direction expected in response to  changing test conditions.  A  comparison
of results between cleaning modes  clearly shows shake mode operating at
a significantly lower AP.  in other words, shake appears to provide
                                    81

-------
 considerably more  efficient  cleaning  than  reverse  flow.

      On  the basis  of  collection  efficiency,  it  appears  that  a  high  level
 of  control of  lime recovery  kiln emissions can  be  attained by  a  fabric
 filter.   However,  operating  problems  during  this test program, caused
 by  the high moisture  content in  the flue gas which resulted  in condensation
 and much deposition on  occasion,  discourages the use of a fabric filter
 in  this  application.

      Refuse Processing  Plant

      The mobile  fabric  filter was operated at the  City  of St.  Louis
 Refuse Processing  Plant on the plant's  air density separator cyclone
 exhaust.  The  plant receives raw domestic  solid waste which  is shredded
 in  a hammermill. The  shredded waste is  conveyed in an air classifier
 which separates  heavier particles from  lighter  ones by  gravitational
 settling and vertical pneumatic  conveyance.  The lighter fraction from
 the air  classifier is separated  from  its carrier air stream  in a cyclone
 where the coarse matter settles  out and is collected to  be burned in a
 local power plant.  The cyclone  separator  air is exhausted to  the atmosphere.
 It  is these emissions to which the test was  directed.

      Only the  pulse cleaning mode was used for  this test with  Dacron
 polyester felted bags and one set of  cleaning parameters.  It was necessary
 to  run three 6-hour days in  order to  collect enough material at  the
 filter outlet  to weigh  for mass  and fractional  particulate efficiency
 measurements.  Total mass penetration was  0.05%.   The corresponding mass
 efficiency was 99.95%.

      Coal-Fired Power Plant  (Subbituminous Coal)

      The  mobile fabric  filter was operated at the  Amarillo,  Texas,
 Harrington Station  generating plant of the Southwestern  Public Service
 Company  from May to July 1977.  Harrington Station is the first  coal-
 fired electric generating plant in the Southwestern Public Service
 Company  system.  Unit 1, a 350 MW pulverized coal-fired boiler, went on
 line  in August 1976.  It burns low-sulfur subbituminous  coal  transported
by train  from Wyoming. Harrington Station Unit 2,  almost identical to
                                    82

-------
  Unit 1,  is under construction and is scheduled to go on line in 1978.
  Unit 2 will  employ a fabric filter designed by Wheelabrator-Frye for
  particulate  removal.   Unit 3 is  planned for 1980 and will  also have a
  fabric filter.

       EPA has  funded  a contract with  Southwestern Public Service to
  conduct  an exhaustive 1 year test program  on  the Unit 2 fabric filter  to
  determine  the performance  of a fabric  filter  on  a  large coal-fired
  boiler burning  low-sulfur  coal.   The demonstration  is expected to show
  that  fabric filters  are cost effective  and  show  superior performance for
  collecting particulates from large utility  boilers.   Options to  extend
  the demonstration and  pilot  plant work  beyond  the 1 year base  period are
  included in the  contract.

      The objectives of the mobile fabric filter test  program at the
 Harrington Station were:

      1)   To develop filter operating performance data for input to
           the design of the full  scale filter and development of the
           test program.

      2)   To  provide data  to compare  fabric filter operation  and
           particulate collection  capability for boilers burning
           low-sulfur  western coal  with  those for  boilers burning high-
           sulfur eastern coal.

     Two  bag materials  were  tested:  woven Teflon-coated  fiber  glass and
woven  graphite-and-silicone-coated fiber glass.  The bag  materials were
tested  in shake  and reverse air cleaning modes.  Operating conditions
for the tests  are given in Table 11.  Bags were tested at an air-to-
cloth ratio of 0.0155 m/s (3.05 fpm).  This ratio was  chosen to approximate
that planned for the Unit 2 and Unit 3 fabric filters at Harrington
Station. Bags were cleaned when the bag pressure drop reached  10.2 cm (4
inches).
                                      83

-------
     Shake  cleaning  parameters  were:   frequency  -  6.9  cps,  amplitude
 2.22 cm (0.875  inches),  and  duration  -  10  sec.  These parameters  gave  a
 shaker arm acceleration  of 4.3 g's  and  138 shakes (2  per cycle) per
 cleaning.   Bag  tension was not measured, but  was  estimated at
 0.45 - 0.91  kg  (1-2 lb).  A  delay of  1  min was  used between filtration
 and shaking  and a 2 min  delay  between shaking and filtration to allow
 dislodged  dust  to settle.  Average  filtration time with the Teflon/glass
 shake bags was  219  min,  and  with the  graphite/glass bags was 181  min.

      For the reverse air cleaning tests, the  reverse  air-to-cloth ratio
 was initially set at 0.0102  m/s (2  fpm).   During  fabric filter operation,
 however, bag blinding was observed  with this  reverse  air flow rate.  The
 reverse air-to-cloth ratio was  ultimately  increased to 0.0269 m/s
 (5.3 fpm), the  maximum available from the  reverse air fan  at the  selected
 operating  conditions.  Several  time combinations  were attempted to help reduce
 blinding.  The  combination settled  upon was:  first delay  -  minimum  (5
 sec),  with reverse  air fan on;  reverse  air time - 30  sec;  second  delay -
 1 min,  with  reverse air  fan  shut off  at about 30  sec.  Filtration times
 with the Teflon/glass reverse  air bags  were 20-30 min.  The  filtration
 times  with the  graphite/glass  bags  using reverse  air  cleaning were so
 short  that these bags were tested using alternating shake  and reverse
 air cleaning.   After shaking,  filtration times were 30-60  min; after
 reverse  air  cleaning, filtration times  were 10-28 min with an average  of
 17  min.

      In  all  cases,  new bags were conditioned  a minimum of  24 hours prior
 to  sampling.  Gas temperature  in the  slipstream probe was  usually between
 180  and  200°C (350  and 390°F) during  samplng.  Heat loss through  the inlet
 duct caused  a temperature drop  of 27-32°C  (80-90°F) to the inlet  sampling
 section. The  temperature dropped another 27-32°C  as the gas passed through
 the  bag  compartment  to the outlet sampling section.  Gas pressure in the
 slipstream probe was between 25 and 43 cm  (10 and  17 inches) vacuum.
 Pressure drop in the inlet duct to the inlet sampling  section was  2.5 to
 4 cm (1  to 1.5 inches).  Bag  compartment pressure drop  was  usually  a
maximum of 10.2  cm  (4 inches) except during bag  cake resistance tests.
                                       84

-------
       A  summary  of  shake  cleaning  pressure drop results  is  shown in.Table
  12.  Data  from the  Teflon/glass  shake  bags on  June 9  are questionable due
  to  low  flow  rate during  the  last  few  hours of operation.   Average filtration
  time for  the other 2  days  of particulate  sampling was 3 hrs,  39 min.
  Average effective  residual bag  AP for the last 2  days was  38  mm (1.5
  inches) and  the average  terminal  bag  AP was 107 mm (4.2 inches).

       The  graphite/glass  shake bag average filtration time  was 3 hrs,  1
  min.  Average effective  residual  bag  AP was 44 mm (1.7  inches)  and the
  average terminal bag  AP  was  103 mm  (4.1 inches).

       The  filtration times were shorter and  residual  pressure  drops
  higher with  the graphite/glass bags.  These results  indicate  higher
  particulate  filtration efficiency and less  cake removal during  cleaning.
  The average  boiler load was  slightly higher during sampling of  the
  graphite/glass bags: an average of 336 MW for  the 3  days compared to 331
 MW for the last 2 days with  the Teflon/glass bags.   The small  difference
  in boiler load is not believed responsible  for the difference in results.

      A summary of the reverse cleaning pressure drop results for the
 Teflon glass  bags  is presented in  Table 13.  Bag blinding problems were
 encountered.  In  an  effort to  get better bag cleaning and extend filtration
 time the bags were  sometimes  cleaned 2 or  3 times  before filtration was
 resumed.  Some additional  cleaning  was  accomplished, but  not enough to
 extend the time  between  cleans to  more than 30 min.   Even with multiple
 cleanings, the filtration times  grew shorter as operation continued.
 Extending  the delay or reverse air durations did not  improve cleaning.
 The  reverse air  flow was  1.7  times the forward rate.

      To  determine the  cause for bag blinding,  several factors  were
 invetigated.  First, the  bags  were observed  during cleaning.   The bags
 collapsed  well as the  reverse  air  damper opened  at the start of  the
 first  delay and stayed collapsed until the manual reverse air  gate valve
was closed during the second delay.  The reverse air  fan caused  no
additional  collapse because the negative system pressure pulled  in
reverse air without the fan running.   As filtration resumed, the bags
                                     85

-------
  inflated.  When collapsed, the bags had an hourglass shape between the
  spreader rings.  The bags did not collapse to the point where the reverse
  air flow was choked off due to the bags closing up completely.

      Dust cake removal was observed through the bag compartment hopper
  window.  During the first delay, there was a large quantity of fallout
  immediately when the reverse air gate valve opened.  Most visible particles
  were large flakes.  A fairly large portion exited the hopper entrance
  into the inlet duct.  After the initial puff, flakes settled slowly
  toward the dust collection can, with a portion pulled out through the
  hopper entrance. When the reverse air fan came on, there was a small
  quantity of flaky dust as the fan started—much less than during the
  first delay.  Flakes again settled slowly.  During the second delay, a
  few flakes were dislodged at the start.  Flakes continued settling for
 most of the duration.  As filtration was resumed, a puff of dust entered
 the hopper.   Much of the dust was pulled up into the bags, but did not
 appear to be enough to make much difference in the bag cake or pressure
 drop.   The puff was probably due to the forward air reentraining particles
 that settled in the inlet duct during bag cleaning.

      The reverse air temperature was at least the same as the bag compartment
 outlet temperature at  the start of cleaning and rose about 35°C as
 reverse flow continued.   The reverse air moisture content, measured with
 the wet bulb method, was  found  to be 2 percent by volume less than the
 filtration gas  moisture  content.   Condensation on the  bags was  therefore
 a doubtful cause  of bag  blinding.

     The  bags never completely  relaxed  during  the  delay  between  cleaning
 and the  resumption  of filtration.  This was due  to leakage through  the
 reverse air  gate valve.  To stop  reverse air  leakage,  the  manual gate
 valve was also  shut  about halfway through the  second delay, but bag
 cleaning was not improved.

     On the second day of sampling the Teflon/glass reverse air bags
 the bags were cleaned by shaking prior to sampling.  The first filtration
 time was approximately 2 hours,  but decreased to about 25 min when
operation was stopped at the end of the test.
                                     86

-------
      The pressure drop results for the graphite/glass reverse air bags
 are shown in Table 14.  During bag conditioning, blinding was even more
 severe than with the Teflon/glass reverse air bags.  After only 10 hours
 of operation (having started with new bags), filtration time had decreased
 to less than 4 min. and residual bag AP rose to 81 mm (3.2 inches).

      For particulate sampling, it was decided to use reverse air cleaning
 until the time between cleans decreased to 30 min or less, then shake
 the bags and resume reverse air cleaning.  The result, as shown in Table
 14, was that only every other cleaning was with reverse air.  Even after
 shake cleaning, filtration times were much shorter than when using shake
 cleaning alone.

      Table 15 presents the results of sampling for total  mass concentrations,
 Penetration of  both Teflon/glass bag types was higher than that of the
 graphite/glass  bags.   Penetration was about the same for both cleaning
 modes with the  graphite/glass bags,  possibly influenced by the alternating
 reverse air and shake cleaning employed with the reverse  air bags.

      Figure 1 presents mass penetration versus particle size curves  for
 the four  fabric/cleaning mode combinations tested.   All  four penetration
 curves  exhibit  minima.  The minimum  penetrations of the shake-type bags
 occur at  larger particle sizes than  those of the reverse-air-type bags.
 With  both  the shake and reverse  air  bags,  the minimum penetrations were
 at  smaller  sizes  with  the  graphite/glass  bag  material.  The  maxima for
 the two reverse air curves  at  about  4 Pm  may  not be  real.  It  is suspected
 that  characteristics of the impactors  produced or magnified  these results.
 It  is possible  that the penetrations  actually continue to  increase above
 4 mm.  The graphite/glass shaken bags  had  the lowest  penetrations in
 the particle size range measured.

     Plans are underway to operate the mobile fabric filter at a site
burning eastern  high sulfur coal using the same fabric/cleaning mode
combination as used at Harrington Station so a more direct comparison of
fabric filter performance on high sulfur and low sulfur coal  can be
presented.
                                     87

-------
SUMMARY

     The original objective in building the mobile fabric filter, wet
scrubber and electrostatic precipitator units was to operate all three
units on the same source to compare the relative capabilities and limitations
of the control methods on a given source.  In practice the units, more
frequently, have been used individually to answer specific control
problems. The fabric filter unit has been operated on eight field sources
including three utility boilers.   A second mobile unit was operated at
only two of these sources.   It is anticipated that these mobile units
will  find wide application in the future to meet the original objective
as well  as to answer specific control  problems.
                                      88

-------
Table 1.  BRASS AND BRONZE FOUNDRY PULSE CLEANING TEST RESULTS
Parameter
Inlet dust concentration, g/m3 (grains/scf)
Inlet particle size, ym (mass median)
Avg. filter pressure drop, cm water (inches)
Outlet dust concentration, g/m3 (grains/scf)
Interval between pulses, sec
Penetration, %
Efficiency, %
T 	
3.89 (1.7)
0.5
25 (10)
0.0032(0.0014)
40
0.081
99.919
Fest Number
i 	 *r 	
3.89 (1.7)
0.5
23 (9)
0.0030(0.0013)
40
0.078
99.922
o
3
3.89 (1.7)
0.5
13 (5)
0.0064(0.0028
20
0.15
99.85
Table 2.  BRASS AND BRONZE FOUNDRY SHAKE CLEANING TEST RESULTS
Parameter

Cleaning Parameters
Amplitude, cm (inches)
Frequency, cps
Tension, grams (pounds)
Filtration velocity, cm/sec (fpm)
Maximum pressure drop, cm water (inches)
Average penetration, %

Average outlet dust concentration,
g/m (grains/scf)

••— — — — — — — —

0.95(3/8)
3-6
2270(5)
1.5(3)
38(15)
Ono
. uo
o.oon
(0.0005)
Test Number
5
	

2.2(7/8)
6
908(2)
1.5(3)
33(13)
.14
0.0027
(o; 00121
6

2.2(7/8)
8
454(1)
1.5(3)
30(12)
0.16
0.020
(0.0087)
7

2.2(7/8)
6
454(1)
1.3(2.5)
18(7)
fi n^
0.00069
(0.0003)
                              89

-------
            Table  3.   HOT  MIX ASPHALT  PLANT  PULSE  CLEANING  TEST RESULTS
Parameter
Filtration velocity, cm/sec (fpm)
Avg. filter pressure drop, cm water (inches)
Inlet particle size, ym (mass median)
Inlet dust concentration, g/m (grains/scf)
Outlet dust concentration, " "

Avg. penetration, %
Avg. efficiency, %
Test Number
1
4.1 (8)
11.7(4.6)
12-15
34.1(14.9)
0.066
(0.029)
0.18
99.82
2
4.1 (8)
14.2(5.6)
12-15
35.5(15.5)
0.034
(0.015)
0.10
99.90
3
3.8(7.5)
18.8(7.4)
12-15
35.0(15.3)
0.039
(0.017)
0.13
99.87
4
3.7(7
26.9(1
12-15
36.9(1
0.08
(0.03
0.23
99.7
Table 4.  COAL-FIRED POWER PLANT (CYCLONE-FIRED BOILER) SHAKE CLEANING TEST RESULTS
Parameter
Filtration velocity, cm/sec (fpm)
Avg. filter pressure drop, cm water (inches)
Inlet particle size, pro (mass median)
Inlet dust concentration, g/m (grains/scf)
o
Outlet dust concentration, g/m (grains/scf)
Avg. penetration, %
Avg. efficiency, %
Test Number
1 j
1.4 (2.7)
12.2 (4.8)
5
1.6 (0.7)
0.009(0.004)
0.57
99.43
2
1.4 (2.7)
13.2 (5.2)
5
1.6 (0.7)
0.004(0.0016)
0.23
99.77
3
1.4 (2.7)
13.7 (5.4)
5
1.6 (0.7)
0. 005(0. 002^
0.34
99.66
                                         90

-------
   Table '5.  OPERATING CONDITIONS FOR COAL-FIRED POWER
            PLANT (ANTHRACITE COAL) TESTS
                  Shake Mode
 Filtration period
 1st pause
 Cleaning period
 2nd pause
 Shake frequency
 Amplitude
 Shaker-arm acceleration
 Bag tension
 A/C
                 .Pulse Mode

 Pulse interval
 Pulse duration
 Pulse jet pressure
 A/C
      ——	•	  	
 Filtration period
 1st pause
 Cleaning period
 2nd pause
 Bag tension
 A/C

Reverse flow air  rate
 20 min.
 10 sec
 10 sec
 30 sec
  7 cps
 2.22 cm
 4.4 g's
 0.682 kg
 0.010, 0.015,
 0.020 m/s
 I/  2,  3 min
 0.10 sec
 4.14 x 105 pa
 0.020, 0.031
 (max.) m/s
30,  40,  50  min
30 sec
20 sec
30 sec
0.682 kg
0.010, 0.015,
0.020 m/s
0.045 m3/s
                          91

-------
Table 6.   COAL-FIRED POWER PLANT (ANTHRACITE COAL)  MASS
          EFFICIENCY TEST RESULTS
Run3
S-G-2-20
S-G-3-20
S-G-4-20
Average
S-WN-2-20
S-WN-3-20
S-WN--4--20
Average
S-FN-2-20
S-FN-3-20
S-FN-4-20
Average
P-FN-4-1
P-FN-6.2-1
P-FN-6.2-2
P-FN-6.2-3
Average
R-G-2-30
R-G-3-30
R-G-4-30
R-G--4-40
R-G-4-30
Average
Mass Load
In
2 503
3 108
4 030
3 213
5 828
1 246
1 898
2 991
4 456
4 818
5 299
4 362
3 858
7 855
6 069
7 525
6 325
3 616
3 197
3 075
1 509
1 960
2 672
inq , ma/nH
Ou t
93
I
207
100
14
1
53
23
1
1
1
1
2
35
119
77
58
21
9
8
—
. —
13
Col. Eff. Penetration
% %
96.30
99.97
94.88
97.05
99.76
99.89
97.23
98.96
99.71
99.98
99.98
99.89
99.94
99.56
98.03
98.97
99.13
99.42
99.73
99.74
	
** ^« H
99.63
3.70
0.03
5.12
2.95
0.24
0.11
2.77
1.C4
0.28
0.02
0.02
0.11
0.06
0.44
1.97
1.03
0.88
0.58
0.27
0.26
— «.

0.37
                        (more)
                            92

-------
   Table 6. (Cont'd)  COAL-FIRED POWER PLANT (ANTHRACITE COAL)
                      MASS EFFICIENCY TEST RESULTS
Run3
R-FN-2-30
R-FN-3-30
R-FN-4-30
R-FN-3-40
R-FN-3-50
R-FN'-3-30
Average
Mass Loading, raq/m^

3
4
4
3
4
2
3
In
902
122
282
833
889
352
895
Out
1
5
1
—
3
1
2
Col.
I
99
99
99
_
99
99
99
Eff.
»
>
.99
.88
.99
__
.95
.95
. 95
Penetration
0.
0.
0.
^_
0.
0.
0.
01
12
01
^
05
05
05
Average
3  969
31
99 .18
                                                                0.82
 Run Code
                        Example:     S-G-2-20

        First  letter  =  Cleaning Mode:  S  - Shake

                                      P  - Pulse

                                      R  - Reverse

        Second  letter =  Bag Type:      6  - Glass

                                     WN  - Woven Nomex

                                     FN  - Felted Nomex

        First Number = A/C Ratio, fpm (x  5.08 x 10~3 = m/sec)

        Second Number = Filtration Period, min, for shake and reverse

                     - Pulse Interval,  sec,  for pulse
                              93

-------
Table 7.  OPERATING CONDITIONS FOR PULP MILL LIME RECOVERY  KILN TESTS
                       Shake Mode
Filtration period
First  pause
Cleaning  period
Second pause
Shake  frequency
Amplitude
Shaker-arm acceleration
Bag tension
A/C
30, 50 min
30 s
 5 s
30 s
 7 cps
22.2 mm  (0.875  in.)
43.1 m/s2  (4.4  g's)
0.68 kg  (1.5  Ib)
0.015, 0.025  m/s  (3,  5 fpm)
                      Reverse Mode
Filtration period
First pause
Cleaning period
Second pause
Bag tension
A/C
R.F. air temperature
R.F. air flow
30, 50 min
30 s
 5, 20, 40 s
30 s
0.68 kg (1.5 Ib)
0.015, 0.025 m/s  (3,  5  fpm)
113°C  (235°F)
4.5 x 10-2 m3/s  (95 acfm)
                             94

-------
      Table 8.   PULP MILL LIME RECOVERY KILN MASS EFFICIENCY TEST RESULTS
Grain Loading, g/m3 (qr/sdcf)
Run9
S-WN-3-30-5

S-WN-3-50-5

S-WN-5-30-5

Average
S-FN-3-30-5

S-FN-3-50-5

S-FN-5-30-5

Average
R-V7N-3-30-5

R-WN-3-30-20

R-WN-5-30-5

R-WN-3-50-5

Average
R-FN-3-30-20

R-FN-3-50-40

R-FH-3-30-40

Average
Average
a,.
In
8.65(3.78)
8.65(3.78)
7.83(3.42)
'2.79(1.22)
2.33(1.02)
4.39(1.92)
5.77(2.52)
6.86(3.00)
6.86(3.00)
0.597(0.261)
0.309(0.135)
4.3.5(1.90)
8.21(3.59)
4.53(1.98)
11.2(4.91)
8.58(3.75)
6.80(2.97)
5.95(2.60)
24.9(10.9)
5.84(2.55)
5.88(2.57)
5.95(2.60)
9.40(4.11)
8.56(3.74)
4.97(2.17)
6.80(2.97)
9.15(4.00)
13.9(6.08)
7.94(3.47)
8.56(3.74)
7.24 (3.17)

Out
0.00291(0.00127)
0.00318(0.00139)
0.000191(0.0000835)
0.000149(0.0000649)
0.000359(0.000157)
0.00130(0.000569)
0.00135(0.000589)
0.000613(0.000268)
0.000897(0.000392)
0.000831(0.000363) '
0.000570(0.000249)
0.00220(0.000963)
0.00563(0.00246)
0.00179(0.000783)
0.00102(0.000444)
0.00281(0.00123)
0.00110(0.000482)
0.00105(0.000459)
0.00118(0.000516)
0.00113(0.000492)
0.000755(0.000330)
0.00146(0.000638)
0.00131(0.000574)
0.000931(0.000407)
0.00112(0.000490)
0.000490(0.000214)
0.00166(0.000726)
0.00166(0.000726)
0.00180(0.000788)
0.00128(0.000559)
- — '- ii — ._
0.00142 (0.000622)

Collection
Efficiency,
	 %
99.97
99.96
99.99
99.99
99.98
99.97,
99.98
99.99
99.99
99.86
99.82
99.95
99.93
99.96
99.99
99.97
99.98
99.98
99.99
99.98
99.98
99.97
99.99
99.99
99.98
99.99
99.98
99.99
99.98
99.99
99.98

Penetration,
%
0.0336
0.0368
0.00244
0.00532
0.0154
0.0300
0.0233.
0.00893
0.0130
0.139
0.184
0.0507
0.0685
0.0395
0.00904
0.0328
0.0162
0.0176
0.00471
0.0193
0.0128
0.0245
0.0140
•• -.—.--._
0.0109
0.0226
0.00721
0.0182
0.0119
0.0227
0.0149
0.0222

Run Code - Example:  S-WN-3-30-5
   First Letter - cleaning mode (Shake - S, Reverse - R)
   Second Set of Letters - fabric type (Woven Uomex - WN
   First Number - A/C ratio,  fpm (x 5.08 :< 10~J - m/sec)
   Second Number - filtration period, min          '   '
   Third Number - cleaning period,  sec

                                      95
Felted K7omex - FN)

-------
  Table  9.  PULP MILL LIME RECOVERY KILN FRACTIONAL EFFICIENCY TEST RESULTS
Mass Median
Biamcter, urn
Run3
S-WN-3-30-5

S-WN-3-50-5

S-WN-5-30-5

S-FN-3-30-5

S-FN-3-50-5

S-FN-5-30-5

R-WN-3-30-5

R-WN-3-30-20

R-WN-3-50-5

R-WN-5-30-5

R-FN-3-30-20

R-FN-3-30-40

R-FN-3-50-40
R-FN-3-50-40
_
In
7.7
7.7
7.5
7.4
7.4
8.3
7.7
7.6
0.4
1.2
8.2
8.2
7.8
7.8
7.6
7.5
7.3
7.2
8.4
8.2
7.8
7.6
7.7
7.6

8.0
8.0
Out
3.6
1.1
0.46
0.45
0.5
0.7
0.5
0.5
2.8
0.6
10.0
5.7
4.5
3.2
3.8
4.7
7.1
5.9
7.0
9.6
4.8
4.9
2.3
3.5

3.2
1.9
Fractional Efficiency^
Min
99.61
99.28
c
~c
c
-Q
99.89
99.51
99.80
99.21
99.84
99.20
99.87
99.03
99.89
99.92
99.97
99.97
99.67
_c
99.97
99.85
99.80
97.15

99.95
97.90
Max.
93
@3




@1
@1
@6
@4
(§6
(§3
<§3
(§4
@4
(§3
@4
@5
(§5

@4
(§4
(§3
(§4

(§7
@4
99.99
99.99
_e
-e
c
c
99.99
99.99
99.86
99.99
99.99
99.95
99.99
99.98
99.99
99.99
99.99
99.98
99.96
_C
99.99
99.99
99.99
99.99

99.99
99.99
eio
@10




010
@ 8
@10
@ 8
@ 3
(§10
610
(§10
(^10
(§10
610
(§10
(§1,10

(9 8
@ 8
(§10
610

0 1
610
Mean Fractional Efficiencv
1 -
99
99




99
99
99
99
99
3 ym
.66
.46
C
C
e
-C
.91
.73
.84
.46
.99
99.38
99
99
99
99
99
99
99

99
99
99
99

99
99
.92
.50
.95
.93
.98
.99
.92
_C
.98
.95
.87
.76

.99
.89
4-6 ym
99.85
99.81
C
_^:
C
c
99.99
_a
99.81
99.52
99.86
99.54
99.96
99.55
99.93
99.96
99.98
99.98
99.71
_c
99.98
99.88
99.93
98.94

9.9.96
99.12
7-
99
10 ym
.97
99,99




99
99
99
99
99
99
99
99
99
99
99
99
99

99
99
99
99

99
99
C
IC
_q
-£
.99
.98
.84
.98
.90
.90
.99
.96
.99
.99
.99
.98
.90
_C
.99
.99
.99
.98

.96
.99
a
 See Table S for code explanation

 Number after @ is particle size, ym,  at which minimum or reaximum collection
 efficiency occurs
c
 Test conditions which had apparent fraction efficiencies > 100%

                                       96

-------
    Table TO.   PRESSURE DROP RESULTS OF PULP MILL LIME RECOVERY KILN TESTS
Run a
S-WN-3-30-5
S-WN-3-50-5
S-WN-5-30-5
S-FN-3-30-5
S-FN-3-50-5
S-FN-5-30-5
R-WN-3-30-5
R-WN-3-30-20
R-WN-3-50-5
R-WN-5-30-5
R-FN-3-30-20
R-FN-3-30-40
R-FN-3-50-40
"" 	 ' ' 'I .—
a
See Table 8
b
= Effective
c
= Residual
d
= Effective
AP b
e
- — • 	 • — 	 „
0.60(2.4)
0.52(2.1)
1.44(5.8)
0.17(0.7)
0.32(1.3)
0.67(2.7)
0.65(2.6)
0.90(3.6)
0.85(3.4)
1.84(7.4)
1.54(6.2)
1.94(7.8)
1.97(7.9)
— • ' - ._.-.-..

AP c
r
1.00(4.0)
0.95(3.8)
1.94(7.8)
0.40(1.6)
0.70(2.8)
1.29(5.2)
1-17(4.7)
1.19(4.8)
1.37(5.5)
2.44(9.8)
2.07(8.3)
2.31(9.3)
2.44(9.8)
i 	
e
40.2(0.82)
34.8(0.71)
56.8(1.16)
11.3(0.23)
21.1(0.43)
26.9(0.55)
42.1(0.86)
58.8(1.20)
55.4(1.13)
72.5(1.48)
99.4(2.03)
128.4(2.62)
129.3(2.64)
— " 	 -•
S e
JL
"" ' "" •• ' i inn • i ,M-
65.1(1.33)
61.7(1.26)
75.9(1.55)
26.0(0.53)
45.6(0.93)
50.9(1.04)
76.4(1.56)
78.4(1.60)
89.6(1.83)
96.0(1.96)
135.2(2.76)
153.8(3.14)
159.2(3.25)
— "•— 	 —
for code explanation

pressure drop

pressure drop,

drag = AP/U,

, kPa (in. w

kPa (in. w.

kPa/m/s (in.

•c.)

c.)

w.c./fpm)






                                                                   39,400(33.9)
                                                                   25,100(21.6)
                                                                   18,300(15.7)

                                                                   29,400(25.3)
                                                                   29,400(25.3)
                                                                   28,700(24.7)

                                                                   32,900(28.3)
                                                                   18,700(16.1)
                                                                   19,800(17.0)
                                                                   13,700(11,8)

                                                                   35,100(30.2)
                                                                   25,100(21.6)
                                                                  19,100(16.4)
= Residual drag = AP r/U, kPa/m/s (in. w.c./fpm)

- Cake specific resistance, kPa/m/s • kg • m2 (in. w.c./fpm-lb-ft2)
                                     97

-------
       Table  11.  OPERATING CONDITIONS FOR COAL-FIRED POWER PLANT
                            (SUBBITUMINOUS COAL) TESTS
                               Shake Mode	


                                                                Graphite/Glass Bags
                                    		             	^_         Avg
 Filtration  period, min             166-290      219             152-225        181
 1st  pause,  min
 Cleaning  period,  sec
 2nd  pause,  min
 Shake  frequency,  cps
 Amplitude,  cm
 Shaker-arm  acceleration, g's
 Bag  tension, kg                    0.
 A/C, m/s
	Reverse Mode	'	'


                                   Teflon/Glass Bags             Graphite/Glass Bac
                                     Range       Avg               Range         Avg
 Filtration  period, min               20-30        23               10-28          17
 1st  pause,  sec                         5                             5
 Cleaning  period,  sec                   30                            30
 2nd  pause,  sec                         60                            60
 A/C,  m/s                             0.0155                        0.0155
 Reverse air A/C,  m/s             0.0102-0.0269                 0.0102-0.0269
 a
 •Alternate shake and reverse air cleaning—data reported is for reverse air only
                                         98

-------
         Table 12.  PRESSURE DROP RESULTS OF COAL-FIRED POWER PLANT
                    •/fSUBBITUMINOUS COAL) SHAKE CLEANING TESTS
Date
IT 977)
6-9
6-11
6-13

Avgc
6-22


6-23



6-24




Avg
Fabric Filtration Time
Type (hr:min)
To-firm /rTTTT 	 "~ 	 = — =•= — 	 	
i CT ion/b i ass
Teflon/Glass
Teflon/Glass

Teflon Glass
Graphite/Glass


Graphite/Glass



Graphite/Glass




Graphite/Glass
4:ou
2:46
3:31
3:45
3:36
3* A C
• £1 K
* I W
3:39
3:45
2 A ~7
• LL I
• T-y
2. •*> o
:32
2:52 .
2i— *\
* R <
- Do
2:46
3. r\~?
.u/
3:05
2r* />
: 59

3:05
3f\ r"
:25
3:01
Residual Bag
AP (mm H?0)
14 (43) a
18
30(97)
23
25(66)
28
27
30(53)
*> o
33
20
30(119)
i rt
28
33
32
32(112)
on
OU
36
38
31
Effective
Residual AP
(mm H?0)
33
32
41
36
36
38
38
34

42
46
46

48
43
48
43

43
46
43
44
Terminal
Bag AP
(mn HoO)
746
104
109
102
112
107
102

102
102
104

108
102
102
102

103
i \j-\j
102
103
103
:  Previous  terminal  bag  AP  (nra FLO)

  Shut  down  due  to low flow rate
 'Data  for 6-9-77 not  included  because  of unreliability
                                      99

-------
                 Table 13.  PRESSURE DROP  RESULTS OF COAL-FIRED POWER PLANT
                               (SUBBITUMINOUS COAL) REVERSE CLEANING TESTS
                                          (TEFLON/GLASS BAGS)
Filtration
Date Time, Min

7-15-77 19
15
4
-------
Table 14.  PRESSURE DROP RESULTS OF COAL-FIRED POWER PLANT
             (SUBBITUMINOUS COAL) REVERSE CLEANING TESTS
                       (GRAPHITE/GLASS BAGS)
Filtration
Date Min
7-19-77 44
76
17
64
16
31
17
34
16
55
13
17
55
10
109
28
78
Time, Cleaning
Mode
Shake
Shake
Rev. air
Shake
Rev. air
Shake
Rev. air
Shake
Rev. air
Shake
Rev. air
Rev. air
Shake
Rev. air
Shake
Rev. air
Shake
Residual Bag
AP (mm H00)
23
28
58
29
66
38
67
34
66
25
-
74
25
70
18
61
20
Effective Residual
AP (mm H00)
	 £ 	
61
66
86
74
91
81
88
81
84
71
-
91
71
91
53
88
55
Terminal Bag
AP (mm H00)
102
89
102
102
102
102
102
102
102
102
102
102
102
102
102
99
100
                         101

-------
         Table 15.   COAL-FIRED POWER PLANT  (SUBBITUMINOUS COAL)
                             MASS EFFICIENCY TEST RESULTS
Run3
S-T-6-9
S-T-6-11
S-T-6-13
Average
S-G-6-22
S-G-6-23
S-G-6-24
Average
R-T-7-15
R-T-7-16
Average
R-G-7-19
aRun Code
Example
First Letter =
Mass Loading, mg/m
In
368
4830
1450 *
2216
3940
3590
5130
4220
3530
3600
3570
3690

Out
1.63
5.45
4.31
3.80
1.74
2.18
1.15
1.69
4.44
2.38
3.41
1.05

Collection
Efficiency, %
99.56
99.89
99.70
99.83
99.96
99.94
99.98
99.96
99.87
99.93
99.90
99.97

Penetrati on ,
%
0.44
0.11
0.30
0.17
0.04
0.06
0.02
0.04
0.13
0.07
0.10
0.03

: S-T-6-9
Cleaning
Mode: S - Shake
R - Reverse


Second Letter = Bag Type:  T -  Teflon/glass
                           G -  Graphite/glass
First Number = Month of Test
Second Number = Day of Test
                                    102

-------
          O TEFLON/GLASS SHAKE BAGS
          OGRAfHJTE/GLASS SHAKE BAGS
          A TEFLON/GLASS REVERSE AIR BAGS
          OGPAPHSTE/GLASS REVERSE ASR BAGS
           PC ~ 2,8 tj/«ni3
      	L,
	I	LJ_jJLjJjJjLLL
   2         4      6    8  1.0
                                                            4     6   8  10
                        GEOMETRIC MEAN PARTICLE DIAMETER, ftm
Figure 1.  Average mass penetration vs geometric mean particle diameter.
                                   103

-------
References

     1,   Hall, R. H. and Dennis, R., "Mobile Fabric Filter System
Design and Field Test Results,"  EPA-650/2-75-059, (NTIS No. PB 246-
287/AS), July 1975.

     2.   Opferkoch, R. E., "Particulate Control Mobile Test Units:
First Year's Operation,"  EPA-600/2-76-042, (NTIS No. PB 251-722/AS),
February 1976.

     3.   Zanders, D. L., "Particulate Control Mobile Test Units:
Second Year's Operation,"  EPA-600/2-77-042, (NTIS No.  PB 264-067/AS),
January 1977.
                                     104

-------
AUSTRALIAN EXPERIENCE,  FILTRATION OF




 FLYASH FROM VERY LOW SULFUR COALS
 THIRD SYMPOSIUM ON FABRIC FILTERS




     FOR PARTICLE COLLECTION




 DOUBLETREE INN   TUCSON, ARIZONA




        December 5-6, 1977
                By




         A.  C.  LEUTBECHER




MARKETING MANAGER,  FABRIC FILTERS




 WESTERN PRECIPITATION DIVISION




    Los  Angeles,  California





                105

-------
              BIOGRAPHICAL NOTE
DEL LEUTBECHER is a graduate from Cleveland State



University (1967) with a B.S. desgree in Engineering



Science.  He has also attended Graduate School at



Northern Illinois University, majoring in marketing.



Del has eight years sales and marketing experience



in the air pollution control field, specifically in-



volved with scrubbers and bag filters, and presently



is Marketing Manager, Fabric Filters for Western



Precipitation Division of JOY Manufacturing in Los



Angeles, California.
                       106

-------
AUSTRALIAN EXPERIENCE, FILTRATION OF FLYASH FROM VERY LOW

SULFUR COALS.
          Abstract
          This paper examines the Australian experience
          in applying fabric filters to coal fired boilers
          Consequences of burning very low sulfur coal
          (0.3%-0.4%) are highlighted.  Specific examples
          of shaker, reverse air and pulse jet cleaning
          mechanisms are discussed and experience with
          acrylic filtration media is detailed.
          As can be seen by Fig. 1, Australian coal is quite

different from that mined in the United States.  U. S. coals

classified as low sulfur generally run .7%-1.0% sulfur content.

Coals with sulfur contents on the order of 0.6% to 0.7% are

considered "high sulfur" varieties in Australia.  Low sulfur

coal is defined as containing approximately 0.3% sulfur.  Given

this extremely low sulfur content and the mild Australian cli-

mate, air heater gas outlet temperatures on efficient boilers

can run as low as 220°F.  At these conditions flyash is highly

resistive and precipitator performance has been unsatisfactory.

As an analogous situation opened the door to baghouse applica-

tion for flyash collection in the United States, so, too, are

the Australians turning to fabric filtration.
                           107

-------
          The single factor making the Australian experience
so unique is low gas inlet temperatures to the baghouse.
Inlet temperatures in the 250 OF to 300 OF range are not un-
common.  This phenomenon of low inlet temperatures makes pos-
sible the use of synthetic fibers such as acrylic for filtra-
tion media.

          the Electricity Commission of New South Wales has
taken the technical lead in baghouse applications in Australia.
A listing of experience to date is shown in Figure 2.  This
paper will discuss some of these installations in detail.

          The first significant installation was commissioned
in May of 1972 at the Tallawarra Power Station.  This shaker
type filter was installed on a pulverized fuel boiler and
designed to handle 80,000 ACFM of flue gas at 2700p.  The intent
upon successful operation of this pilot unit was to retrofit the
entire station with baghouses, amounting to four 30 MW boilers
in Section "A" and two 100 MW boilers in Section "B".  Specific
design details of this pilot are shown in Fig. 3A.  As can be
seen, pilot experience was very good with pressure drop main-
tained at 3" W. C. and efficiency at 99.9%.  This was accompli-
shed at a gross filter ratio of 2.23/1 with a cleaning cycle
initiated every thirty minutes.  Based upon successful experience
a 500,000 ACFM full scale baghouse was commissioned at Section "A1
in September of 1974, and four 170,000 ACFM units at Section "B"
                          108

-------
during the period March 1975 to March 1976.  Design details



are shown in Fig. 3B.  Operating experience has been consistent



with that of the original pilot unit.





          Several comments are worthy of mention with regard to



the fabric material utilized.  Polyester bag material was judged



to be unsuitable due to hydrolysis and subsequent acid attack.



Although steps were taken to prevent moisture ingress, the pos-



sibility of accidental wetting such as economizer leaks cannot



be excluded.  In addition, high moisture conditions as occur



during soot blowing have caused polyester hydrolysis.  Acrylic



fibers have demonstrated resistance to hydrolysis and acid attack.



Acrylic fiber is, however, temperature sensitive and will support



combustion.  Necessary steps must be taken to prevent heating



acrylic fiber in excess of 260^F by using air dilution and/or



water sprays.  As protection against air heater failure, bypass



is recommended.  Finally, care must be taken during operation and



maintenance to avoid a dangerous fire as bags burn fairly readily.



A full water spray or CO2 fire protection system is recommended.





          The specific bag recommended by the Commission is



Draylon T, 12 oz/sq yd, 2X2 twill with a permability of 25-33.





          As previously mentioned, there are three pulse jet



installations in Australia at Wangi Station Units 4, 5 and 6.



They are essentially identical installations as shown in Fig. 4.
                           109

-------
          Of the units tested, efficiencies have been in excess



of 99.5%, however, problems have been reported.   Pressure drop



has averaged 5" W.C.  This is primarily due to the high filter



ratio and the Commission is recommending 3.5 - 4.0 ratios to



conserve pressure drop and maximize bag life.  The acrylic bags



have experienced an embrittlement problem.  It has been theorized



that the cold, compressed cleaning air has caused localized



condensation of flue gas and subsequent acid attack.  Bag bleeding



and visible puffing during cleaning have also been reported.  The



acrylic bags used were 18 oz/square yard needled felt with a



permeability of 25 CFM/square foot/V W.G.






          The final pilot installation to be discussed is the



reverse air cleaned baghouse pilot unit at Wangi Station Unit 5.



Design conditions for this baghouse are shown in Fig. 5.  As shown,



this unit has four compartments of six bags each for a total of



twenty-four bags.  The bags are 8-inch diameter by 22-foot long



Menardi 601T fiberglass with 10% Teflon B finish.  Material is



9.5 oz/sq. yd.,3X1 twill with a permeability of 75.






          The baghouse is designed so that one compartment is




always off line in the cleaning mode.  When a section is dampered



off for cleaning  it automatically goes into a 75 second null



period.  The collapse period is adjustable over a wide range,



however, it currently is set very short  (5-8 seconds) with the



intention of providing more residual dust cake for acid dew





                            110

-------
point protection.  After collapse, the compartment goes into

a second null period.  This second null period can be quite

long as all four compartments are never on line at once.


          Overall, the unit has performed extremely well.

Even with the short collapse period, pressure drop is maintained

between 2-3" W.C.  Efficiencies are very high.  After 400 hours

of service, outlet emissions were less than .006 gr/acf.  The

most recent test in October of this year was inconclusive in that

emission levels were so low measurement was impractical.  After

some 3500 hours of operation, including 70 starts and stops

(140 dew point excursions)  the bags show no signs of wear or

deterioration.


          In summary, it is fair to say that since 1972 the tech-

nical experience with baghouses on very low sulfur coal burning

boilers has been good.  This paper has focused on two inter-

related variables:  cleaning mechanism and type of bag material.

With regard to type of cleaning mechanism, the experience has been
                     *
most favorable with the reverse air cleaned baghouse in terms of

low pressure drop and projected bag life, with the shaker a close

second.  The pulse jet experience has not been good, however,

some design modifications would give more favorable results.
                            Ill

-------
          The question of whether to use acrylic or glass bags



is really the central issue as once this selection is made the



cleaning mechanism follows logically.  Acrylic bags have shown



to be suitable at temperatures of 260°F and below.  We can



expect that with acrylic bags some type gas cooling will be re-



quired as well as an emergency bypass and a fire protection



system.  This auxiliary equipment may substantially change the



economic balance, especially at shaker ratios of 3.0 and lower



in favor of reverse air cleaning with glass bags.  Glass bags



with their higher temperature capability of SOO^F are not as



susceptable to temperature variations as may be found in



Australia and do not present the fire hazard.
                           112

-------
                 TYPICAL  COAL ANALYSIS
U. S. LOW SULFUR WESTERN
MOIST %   FIXED CARBON  %    VOLATILE %     ASH %      SULFUR %
8-10      40-50
                 35-40
7-14
                                                      .6-.9
AUSTRALIAN LOW SULFUR
MOIST %   FIXED CARBON %   VOLATILE  %      ASH %      SULFUR %
1-3
60-70
                            20-30
                                 8-12
           0.3-0.5
                           Fig. 1
                             113

-------
ECNSW FABRIC FILTER INSTALLATIONS
Mo/Yr
in
Service
May 1972
Sept 1974
March 1975
Aug 1975
Dec 1975
Jan -1976
Mar 1976
April 1976
June 1976




July 1976

Oct 1976
Station/
Boiler
Tallawarra 4
Tallawarra 1-4
Tallawarra 6B
Tallawarra 6A
Wangi 4
Tallawarra 5A
Tallawarra 5B
Wangi 5
Wangi 1A
Wangi IB
Wangi 6
Wangi 2A
Wangi 2B
Wangi 3A
Wangi 3B
Wangi 5
Gas
Flow
ACFM
80,000
500,000
170,000
170,000
320,000
170,000
170,000
320,000
130,000
130,000
320,000
130,000
130,000
130,000
130,000
1,900
Nom. Gas
Tempera-
ture
290
290
270
270
260
270
270
260
300
300
260
300
300
300
300
270
Gross
Ratio
2.23
2.10
2.4
2.4
6.8
2.4
2.4
6.8
3.5
3.5
6.8
3.5
3.5
3.5
3.5
2.29
Fabric
Type
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Acrylic
Glass
Cleanir
Mechan-
ism
Shake
Shake
Shake
Shake
Pulse
Shake
Shake
Pulse
Shake
Shake
Pulse
Shake
Shake
Shake
Shake
R/A
              Fig. 2
                114

-------
                ECNSW TALLAWARRA STATION

                  SECTION A PILOT UNIT



Gas Volume                    80,000 ACFM

Gas Temperature               270°F

Dust Loading                  13 gr/cubic foot

Particle Size                 4% less than 2.5 microns

Gas Cooling                   Air dilution/water spray

Gross Filter Ratio            2.23/1

Net Filter Ratio              2.98/1  (one out for cleaning)

Number of Bags                330/compartment (1320 total)

Bag Size                      6V dia X 16'-6" long

Bag Material                  Acrylic, Polyester

Cleaning. Mechanism            Shaker
                  OPERATIONAL RESULTS


Pressure Drop                 3" W.C. Flange to Flange

Outlet Emission               Less than .004 gr/ft3(99.9%)

Polyester Bag Life            400 hrs rapid deterioration

Acrylic Bag Life              Good, no acid attack after
                                14,000 hrs/340 starts
                      Fig. 3A

                           115

-------
 ECNSW TALLAWARRA STATION




SECTION A and B FULL SCALE
DESIGN VARIABLE
Gas Volume
Gas Temperature
Gross Filter Ratio
Number of Bags
Bag Size
Bag Material
Cleaning Mechanism
SECTION A
500,000
290
•2.1
7,200
6V X 16'-6"
Acrylic
Shaker
SECTION B
170,000 ea.
270
2.4/1
2,880
6%" X 16 '-6"
Acrylic
Shaker
          Fig.  3B




            116

-------
            ECNSW WANGI STATION




               UNITS 4, 5, 6




             PULSE JET FILTERS
Gas Volume






Gas Temperature






Dust Loading






Median Particle Size






Gas Cooling






Filter Ratio






Number of Bags






Bag Size






BAg Material






Cleaning Mechanism
160,000 ACFM






260°F






10 gr/cubic foot






12 microns






Air Dilution






6.68/1






2,016






42s" dia X 10'-0" long






Draylon T Acrylic





Pulse Jet
                   Fig. 4
                     117

-------
             ECNSW WANGI STATION

              UNIT 5 PC BOILER

             REVERSE AIR BAGHOUSE

              DESIGN CONDITIONS
 Gas Volume

 Gas Temperature

 Dust Loading

 Avg.  Moisture

 Median  Particle Size

 Gas Cooling

 Net Filter Ratio

 Number  of  Bags

 Bag Size

 Bag Material


 Cleaning Mechanism
 1900 ACFM

 260-2700F

 5-6  gr/acf

 4.67%

 2  microns

 none

 2.29/1  (one  out)

 24  (4 compartments)

 8" Dia by 22'-0"  long

 (Menardi  601T glass)
 (with 10%  Teflon  B  finish)

Reverse Air
           OPERATIONAL RESULTS
Pressure Drop

Outlet Emission

Bag Life
.005 gr/acf max.

3500 hrs - no visible
deterioration (70 starts)
                 Fig. 5

                     118

-------
DEMONSTRATION OF A HIGH VELOCITY FABRIC FILTRATION
     SYSTEM USED TO CONTROL FLY ASH EMISSIONS
                      By
                John D.  McKenna
                      and
               Kathryn D. Brandt
                 Presented At
    The  Third Symposium on Fabric Filters for
             Particle Collection
               Tucson, Arizona
             December 5-6, 1977
                       119

-------
                                 ABSTRACT
      As a follow-up to a  pilot plant  study,  a  full  scale investigation  of
 applying high  velocity fabric  filtration  to  coal-fired  boiler fly  ash
 control  was  conducted.  Two  filter systems were separately applied to two
 60,000  Ib./hr. coal  fired boilers.  Performance evaluations conducted over
 the  course of a year included  total mass  removal efficiency and fractional
 efficiencies.  One  filtration  system employed Teflon felt as the filter
 media while  the second system  employed Gore-Tex, a PTFE  laminate on PTFE
 woven backing.  During the course of the year a limited  number of glass
 felt and woven glass bags were introduced into the house containing Gore-
Tex.
     Performance results and economic evaluation indicate this method of
fly ash control  to be an attractive alternate  to electrostatic precipitation.
                                    120

-------
                               INTRODUCTION
     In 1973 Enviro-Systerns & Research, Inc.  was awarded an EPA contract.
The purpose of this contract was to determine the technical and economic
feasibility of employing fabric filter dust collectors for fly ash emission
control, particularly as applied to industrial  boilers.  Initially the
program was jointly funded by the EPA, Kerr Finishing Division of Fabrics-
America and ES&R, Inc.'1)  The Kerr Plant located in Concord, North Carolina,
served as the host site for the program and ES&R manufactured and installed
the pilot facility.  The pilot plant program provided short term performance
data including dust removal efficiencies and pressure drops for a number of
filter media.  '  This data and a preliminary  economic analysis indicated
that long term bag life and performance studies were warranted.  EPA thus
decided to award a contract for the full scale demonstration of this approach
to fly ash control.  The initial demonstration contract awarded to Fabrics-
America with ES&R as the major sub-contractor called for ES&R to design,
fabricate, install and then operate the two fabric filter units for a period
of one year.  Contract options called for subsequent additional long term
operation of the units in order to test other filter media and also to eval-
uate the device as an sulfur oxide removal  system.
                                    121

-------
  KERR - THE HOST SITE
      The Kerr Finishing Division of FabricsAmerica is a textile dye and
  finishing plant located in the textile belt of central North Carolina.

      Kerr's normal production schedule is three shifts per day, five days per
 week with 450-500 employees.  Plant capabilities include processes to bleach,
 mercerize, dye, nap, finish and sanforize both cotton and synthetic fabrics,
 as well as cutting and preparing corduroy.

      Two Babcock & Wilcox steam boilers are in operation at the Kerr facilities.
 Each has a design capacity of sixty thousand pounds  of steam per hour and both
 are equipped  with spreader stokers.  Each boiler has  a two-hour peaking  capac-
 ity of seventy  thousand pounds per hour.   The design  efficiency of these units
 is 82 percent.   Based on the above parameters,  the heat input for these  units
 is 73.2 million  BTU/hr. each.   Both boilers  are equipped with fans for supplying
 draft and unit  number two,  the unit tapped for  the pilot plant  stream, has
 overfire steam  injection for better combustion  control.  In  January,  1973,
 emission tests  had been conducted  on these boilers.   The particulate emission
 rates were  found  to be  approximately 130  pounds/hour  versus  an  allowable  of
 about 25 pounds/hour.   Gas  volumes  were determined to  be about  35,000 ACFM at
 a temperature of about  355°  F.  Thus the  grain  loading measured was about 0.4
 grains per ACFM.   Orsat analysis indicated 9.5% C02,  10% 02,  0% CO and 80.5%
 N2.  Coal analysis  indicated the percent  sulfur to be about  0.6%.

 THE HIGH VELOCITY  FILTER
     A schematic of the  fabric filter dust collector is shown in Figure 1.  As
 shown, the unit is about 10 feet wide by 27 feet high.  It is of modular
 construction and the length increases as the number of modules increase.   Each
 module consists  of two thirty-six bag cells as shown  in Figure-2.  Each addi-
 tional module  adds 3 feet 4 inches  to the length of the house.  One baghouse
 may contain as many as fifteen modules  and thus house 1,080 bags with a total
 of 12,400 square feet of filter media.

     The bags  are 5 inches  in diameter  and 104 inches  long,  giving each bag
 11.5 square  feet of cloth.   The bags are set into the  tube  sheet by the use of
two snap  rings incorporated  into  the bag itself.   The  snap  rings lock  in  place,
                                     122

-------
                       General  Arrangement  SD-IO
Vof For Construction Purposes
                                   Pyramid Hopper
                             **L" FLANGE. TO
                                            Figure 1
                              SD-10 General Arrangement With Pyramid Hoppers

-------
fc

-------
 one above and one below the tube sheet.   A cage is set inside the bag and keeps
 the bag from collapsing.  The dust ladened gas enters one end of the unit, as
 shown in Figure 3, passes through the tapered duct, into the classifier, and
 then through the bags.   The classifier forces the dirty gases to change direc-
 tion 90°, then 180°.   This quick directional  change forces the larger and
 heavier particles out of the flow so that they fall directly into the hopper.
 The gas flows through the fabric filter into  the center of the bags (Figure 4),
 leaving the particulate on the outer surface  of the bags where it is removed
 periodically during the cleaning cycle.   The  clean gas then flows up and out
 through the center of the filtering bag  into  a center exit plenum via an open
 damper in the cell above the tube sheet.   The bags are cleaned one cell  (36
 bags)  at a  time by activating the pneumatic cell  damper.  See Figures 5 and 6.
 When the damper is in the up position,  the flow is through the bags from the
 dirty side  to the center plenum or clean  side.   When the damper is dropped to
 the down position, the  flow is from the cleaning gas plenum through the bags
 to  the dirty side or  hopper.

      The cleaning system employs  a unique hybrid  method referred to as  the
 Shock-Drag  Cleaning System, designed to prolong bag life by minimizing  dis-
 tortion of  the  fibers.

      During the cleaning cycle,  clean gas enters  the cell  through the pneu-
 matic  damper.   The clean gas  is  forced down the filter bag,  opposite to  the
 normal  flow direction.   The bag expands with  a  shock (Figure 5)  so  that  the
 cake  is  cracked and the  particulate  falls  off the  bag  into  the  hopper.   After
 the  shock has expanded   the filter bag and broken  off  the  cake,  the clean  air
 continues to  flow providing a  drag  (Figure 6) which  pushes  and  pulls  the dust
 particles away  from the  fabric.  The smaller  particles  are  thus  forced out  of
 the  fabric  and  fall into  the hopper  for removal from the unit.   Damper system
 and  control panel  arrangements allow for  variations  in main  gas  volume,
 reverse-air volume, duration of cleaning and  frequency of cleaning.

THE PILOT PLANT
     In the summer of 1973 a pilot scale investigation was initiated with the
purpose of determining the techno-economic feasibility of applying a fabric
filter dust collector to coal-fired industrial boilers.  The pilot facility,
                                      125

-------
co

ED
O




CD
O
GO
                                     9ZT
                                                                   >  2
                                                                   ^  a
     fD


     00

-------
Ftgure 4
       127

-------
Figure 5
         128

-------
4
   Figure 6
           129

-------
  installed on a slip stream of Kerr's number two boiler, was to handle 11,000
  acfm when operating at an air-to-cloth ratio of 6/1.  Figure 7 shows the pilot
  facility.  This prototype facility was actually a two module commercial  size
  unit containing five inch diameter 104 inch long bags.  Thus, future scale up
  problems were minimized.

      The filter media evaluated were Nomex(R)  felt, Teflon
-------
PH

4J
 -U
 O
PH
r*»

 0)


I"

-------
                                                      Figure 8
S3
               .020
         CJ
         oo


          l/l
          C
         •r—

          CO


         CD
          ro

         4J
          C
          
.015
               .0.10
              ,005
                                                Outlet Concentration
                                                         vs.
                                     Air-to-Cloth Ratio for Various Bag Materials
                              KEY:
O   Nomex

O   Teflon  Felt  -  Style 2663

Q   Gore-Tex/Nomex

A   Dralon-T
                                            6                  9

                                             Air-to-Cloth Ratio (ACFM/Ft.2)
                                                                  12
                                                                     14

-------
                                                  Figure 9

                              Comparison of Operating  Pressures for Various
                                               Bag  Materials"
LO
Co
           to
           OJ
           o
           e
 03
CO

 in
 to
 o

 u

-------
                                 Figure 10

                   Installed Costs  vs.  Air-to-Cloth  Ratio
    350
in
O
CJ
QJ
    300
(/)
%  250
O
O
    200
   150
   TOO
    50
O
0
A
O
O
KEY;
Nomex Felt
Gore-Tex/Nomex
Gore-Tex/Gore-Tex
Oral on T
Teflon Felt
                              6            8
                         Air-to-Cloth  (ACFM/Ft.2)
      10
              12
                                    134

-------
                                 Figure  11
                   Operating Costs vs. Air-to-Cloth  Ratio
     50
     40
 to
 o
 Q
CO
 o
     30
 
 •*->
 o

 ?   20
 (O
 s_
 
-------
    175
                                     Figure 12

                                    Teflon Felt

                     Annual  Operating Cost vs. Air-to-Cloth  Ratio
                          for Different Bag Life Assumptions
    150
    125
 <0
 o
 Q
CO
 O
 X

 J/l
 o
 C_5
 CD
 01
 CL.
 O
 fO
 3
 C
 c
    100
     75
     50
     25
KEY;
Annual Replacement - Avg. Life 1 Yr.
Replacement Over 2 Yrs. - Avg. Life 1.5 Yrs
Replacement Over 3 Yrs. - Avg.
Replacement Over 4 Yrs. - Avg.
Replacement Over 5 Yrs. -
                                                         Avg.
Life
Life
Life
2 Yrs.
2.5 Yrs,
3 Yrs.
                               _L
                        _L
                               6            8            10
                         Air-to-Cloth Ratio (ACFM/Ft.2)
                                      136
                                     12

-------
Figure 13
Annual i zed Cost Comparison
175 —
I / tJ



150
en 125
o
o
CD
« 100
+J
o
O

-------
 Gore-Tex had torn in a matter of days when used with a  spiral  cage.   This
 problem was overcome by use of a rigid cage.

 FULL SCALE OPERATION
      In 1976, two full  scale fabric filter dust collection  systems were  designed,
 fabricated and installed on each of the two 60,000  Ib/hr  Kerr  boilers  in Concord,
 North Carolina.   In  December of 1976, both dust collectors  were brought  on
 stream under an  EPA  Demonstration Program  (Contract No. 68-02-2148) with
 FabricsAmerica being the prime contractor  and ES&R  the major subcontractor.
 Figure 14 is an  artist  rendition of the full scale  baghouse.   ES&R was con-
 tracted to provide a turn-key system.   This contract  included  system design,
 fabrication of ductwork and baghouses,  supply and installation of all  system
 components,  start-up and testing of the units for a minimum of one year.  The
 system was designed  to  include features accommodating the planned test program.
 Long  straight duct runs  were  provided at both the inlet and outlet, platform
 and stair access  to  all  major test  ports,  a sophisticated separate control
 house and a  penthouse over  both  fabric  filter dust collection  systems were
 provided.   The penthouse  covers  the  outlet test ports, thus allowing testing
 in inclement  weather at  the points where the major share of the testing  is to
 be done.

      Each  unit was constructed of a  10  gauge mild steel  house and 3/16" mild
 steel  hoppers.  Pyramid hoppers were chosen to eliminate potential  problems
 with  screw conveying of the collected'fly ash.   Two inches of Fiberglas insu-
 lation with a sheet metal skin overlay was  installed on  both house  and hopper
 at the factory.  Houses and hoppers were shipped from Roanoke,  Virginia to
 Concord, North Carolina by truck.  Figure 15 shows  one house leaving  the
 factory.  Figures 16 and 17 show one of the houses  being lifted onto  its
 hopper.  Figure 18 shows the system with all major  hardware  elements  complete.
 The common penthouse  is shown covering both baghouses and  in the foreground
 the control house is  seen.  The dust collection  system control  panel  within the
 control house is  shown in Figure 19.  A system schematic is  provided  in Figure
 20.   As is shown  in this figure, the dust collection system  is  brought  on line
 by closing a boiler stack damper and opening a system inlet  damper, the flue
gas  then passes into  the inlet duct, down by an  auxiliary  gas fired heater  into
a center baghouse inlet  plenum, the  dust laden gas then enters  the hopper turns
                                     138

-------
                         Figure 14
EPA  DEMONSTRATION OF THE ENVIRO-SYSTEMS FABRIC FILTER SYSTEM
AT KERR FINISHING DIV.  FA3RICSAMERICA, CONCORD,NORTH CAROLINA

-------

-------
                Figure 16




House Being Lifted Onto Hopper -  Far View
                       141

-------
               Figure 17




House Being Lifted Onto Hopper - Near View
                      142

-------
Co
                                                            n


                                                            1
                                                            M
                                                            CD
                                                            ft
                                                            CD
                                                            CU
                                                            Cfl
                                                            rt

                                                            §
                                                                    CO

-------

-------
                                          TO
      Figure 20




Fabric Filter Schematic

-------
  and comes up to the filter bags.   Once it passes  thru  the  filter media,  the  now
  clean gas passes  into  the  exit plenum thru the  exit  duct,  a  vortex damper and
  out the main system fan  to the dust collection  system  stack.   A  portion  of the
  cleaned flue gas  is  drawn  from the stack  by a separate smaller cleaning  fan  and
  returned to  the system to  be  used  in backflushing the  bags during cleaning.
  The auxiliary heater can be employed to preheat the  house  prior  to  baghouse
  start-up and it can  also be employed to purge the house at shut-down.  The
  vortex  damper is employed  to maintain  a predetermined  pressure at the boiler
  stack in an  attempt  to prevent  the  dust collection system pressure  drop  fluc-
  tucations from  influencing the  boiler  operation.  The control system includes
  automatic preheat, start-up and purge  mode and operation of the vortex is also
  automated.  The system is arranged  so  that the entire operation of both bag-
  houses  is  controlled from the console located in the control house.  When set
  up  for automatic operation, either baghouse can be started and stopped from
  controls located in the boiler house, however, provision  was  included on the
  control  house console for locking-out the boiler house  start  function.   Alarms
 and an automatic shut-down  have been included for  the functions shown on  Table  1
 A number of temperatures  and pressures are permanently  recorded.   These  include
 the inlet and outlet temperature of each  house and the  pressure drop across
 each house and main fan.  One  of the two  houses  is equipped with  an  inlet and
 outlet transmissometer.

      The two  houses  are identical in terms  of the basic hardware.  Each house
 contains eighteen  (18) cells with thirty-six  (36) 5"  dia. X 8'  8"  long bags in
 each cell, thus  both  houses contain  a total of 7,440  square feet of  cloth.
 Initially, House No.  1 contained 648 Teflon felt bags and House No.  2 contained
 648  Gore-Tex  bags.  During the first  year of operation one cell (36 bags) of
 Gore-Tex  was  replaced by an experimental felted glass media and subsequently a
 second cell of Gore-Tex bags was replaced by a 26 oz. woven glass  media.

 DEMONSTRATION PROGRAM PURPOSE AND OBJECTIVES
     The purpose  of the  demonstration program is  the  testing of a  full scale
 demonstration fabric filter  system installed on an  industrial  size coal  fired
 stoker boiler. The baghouse system will be operated  and tested over the  duration
of the program to determine  general  operating parameters,  bag  life data and
economic  factors  necessary for  making techno-economic  evaluations.
                                     146

-------
                           Table  1

                Alarms  and  Shut-Down  Functions
                                                      Alarm &
       Function                      Alarm Only        Shut-Down
 Bag Cleaning on Manual                  X

 Boiler House Stop                                         X

 Control House Stop                                        X

 System Fan Below 1400 RPM                                 X

 RA Fan Off                              X

 Hopper Full                             X

 Heater Off                              X

 Pneumatic Air Low                       X

 Stack Pressure Out of Range                               X

 Phase Monitor Tripped                   X

 Inlet or Outlet Temp. High                                X

 Dryer Off                               X

Alarm Horns Off                         X
                              147

-------
       The objectives of the program are to demonstrate the feasibility of apply-
  ing fabric filtration to industrial size coal fired stoker boilers and to
  accomplish the following:

           Obtain operating data that would be generally useful for appli-
           cation engineering.

           Obtain operating data and bag life  data necessary in making
           techno-economic  evaluations.

           Determination of the  efficiency  of  removal  for  specific
           particle size ranges  as  a function  of filter media on-stream
           duration.

           Determination of filter media property changes as a  function
          of bag on-stream duration.

          An economic evaluation comparing capital, operating and annu-
          al i zed costs of baghouses for the filter media tested.

 RESULTS:   COMPARISON OF  FULL SCALE AND PILOT  UNITS
      The  data  gathered at  this  time indicates similarity  between full  scale  and
 pilot plant operations.  The outlet particle  sizing achieved with  Andersen
 inertia!  impactors seem to approximate  the results obtained with the pilot
 study for Teflon felt; however,  demonstration tests at only one air-to-cloth
 ratio have been  obtained.  Outlet  grain loading values for  Teflon  felt acquired
 via Andersen impactor  confirm pilot plant  results although  four values from
 late  August 1977 were higher.  Andersen outlet grain loadings  calculated for
 the Gore-Tex bags showed results higher and lower than the pilot plant value of
 0.004 grains/SCF but all  values were below 0.01 gr/SCF.   The pressure drop
 across the house is somewhat higher for the full  scale plant than for the pilot
 plant; however, the relative position of the pressure  drop curves for different
 bag materials is very close to the pilot operation. One factor contributing  to
 the higher pressure drop  may be  the removal of the cyclones  which were  present
during the pilot plant studies.   Another consideration is  the  limited on-stream
time of the pilot plant operation.
                                      148

-------
      Hardware problems encountered during the testing program included com-
 pressed air in-line freezing during the extreme cold of January and February,
 1977, and rapid deterioration of silicone rubber gasketing material employed
 around the dampers and hatch covers.  All gasketing material  was replaced with
 asbestos gasketing.  Debugging of the system controls was extensive and plug-
 gage of the boiler stack pressure tap with moisture and ash required subsequent
 installation of a continuous compressed air purge system.

      High pressure drop across both houses appeared to be the result of boiler
 start-up through the  baghouses,  plus a number dew point excursions  occurring
 when the controls were being debugged.  In view of the heavy  dust pearls  on the
 surface of the  bags it was  decided to manually vacuum each  bag.  After vacuuming
 the houses were brought on  stream and the pressure drops  were reduced to  accept-
 able levels.  In the  case of the Teflon felt the  pressure drop across the  bags
 returned to the original clean bag level.   Lab permeability analysis  confirmed
 this.   Subsequent to  bringing  the  houses  on  stream,  failure of the  Gore-Tex
 bags occurred.   At  the  end  of  the  first year of operation about  ten  percent of
 the Gore-Tex  bags  had  failed;  no bag failures  or  obvious  signs of deterioration
 had occurred  with  the  Teflon felt  bags.   The  failure  of the Gore-Tex  bags
 generally  was in  the  form of either  a  small  round  hole, one inch or  less in
 diameter,  or  a  tear about 1/8  to 1/4 inch wide  and one to six inches  long.
 Occasionally  a  bag  would be found  totally shredded.  One possibility  is that the
 impact  of  the PTFE membrane on the tube sheet  during installation and  removal
 initiates  the failure.  Another  contributing factor may be the stress occurring
 as  the  bags shrink on the rigid  cage when going through the temperature eleva-
 tion at start-up each week.

 CURRENT COSTS
     Overall, the economic evaluation executed during the pilot plant program
 remains valid.  For the 70,000 ACFM case, a baghouse outfitted with  Teflon felt
 and assuming a two-year bag  life continues to be a more economically attractive
 alternative than an electrostatic precipitator.  During 1977 a major price
 reduction for Teflon felt occurred.  The installed price was reduced from $75
per bag (5" dia. X 8'  8" long)  to $53 per bag.   The impact of  this price reduc-
tion on annualized cost is shown  in Figure 21.   This  brings  the Teflon felt
                                       149

-------
   90
                  Figure 21
Total  Annualized Cost vs. Air-to-Cloth Ratio
                Teflon Felt
                                                           KEY:

                                                      O   $75/Bag,  Original

                                                      ^\   $53/Bag,  Original
20
                    Air-to-Cloth Ratio (ACfW/Ft.2)
                                   150

-------
alternative in line with the cost of Gore-Tex, as can be seen by reviewing the
pilot study annualized cost comparison, shown in Figure 22, with the current
comparison, shown in Figure 23.

FUTURE PLANS
     EPA has at this time elected to exercise two of the three proposed options,
thus the two demonstration units will continue to be operated and tested
throughout 1978 and 1979.  House No. 1  will continue to be operated with Teflon
felt as the filter media.  The program plan calls for replacement of the Gore-
Tex with a series of other filter media, thus obtaining cost, life and  perform-
ance data on a variety of candidate media considered potentially suitable for
fly ash control applications.   The initial candidate materials include both
woven and felted glass.
                                      151

-------
                               Figure 22
                 AnnualIzed Costs  vs. A1r-to-C1oth  Ratio
                                                 KEY;
                                              O  Teflon
                                              A  Gore-Tex/Gore-Tex
                                              Q  Nomex
                                                  Gore-Tex/Nomex
                                                  Dralon
20
                         Air-to-Cloth (ACFM/Ft.2)
                            152

-------
                                       Annualized  Costs, 103 Dollars
U)
  o
   I
  o
  —I
  o
  rt-
  3"
  5>
  O
                                                                                                CO
                                                                                                o
                                                                                                               o
                                                                                                              —\
                                                                                                                     c
                                                                                                                     oi
                         N
                         ro
                         Q.

                         o
                         o
                                                                          O   0   a   t>   o
                                                                                                                     -s

                                                                                                                     r+
                                                                                                                     O
                                                                                                                     I
                                                                                                                     O

                                                                                                                     o
                                                                                                                     rl-
                         73
                         Oi
                                                                                                                         n>
                                                                                                                         ro
                                                                                                                         co
                                                                           03
                                                                           CU
CD
O
ro
_4
fD
<
=2
O
3
fD
X
V

r^ *
•=z
o
ro
^x
*
•Ml
•vj
•
CO
o
^s.
03
QJ
Id
G">
O
ro
i
ro
x
^"^
CD
O

ro
i
— (
ro
x
—i
ro

o
3
^

cn

•v^
03
CU
(0


                                                                                 CO
                                                                                 cu
                                                                                (£)
en

rn

-------
                                REFERENCES
   J.  D.  McKenna,  "Applying  Fabric  Filtration to Coal Fired Industrial

   ?rl!or^"APrel1m1nary P11ot  Scale  Investigation", July - 1974, EPA
   650/2-74-058.
(2)

  J.  D. McKenna,_J.C. Mycock, and W. 0. Lipscomb, "Applying Fabric Filtra-
                                   154

-------
            BAGHOUSE PERFORMANCE ON A SMALL ELECTRIC ARC FURNACE

                                     by

                              Robert M. Bradway
                           GCA/Technology Division
ABSTRACT

     This paper presents the results of an evaluation of a fabric filter sys-
tem controlling emissions from either one or two 30-ton electric arc furnaces
producing a high-strength, low-alloy specialty steel.  The evaluation involved
measuring the system's total mass collection efficiency and apparent frac-
tional collection efficiency.  Testing involved 8 sampling days with one fur-
nace operating, and 2 days with two furnaces.  Baghouse influent and effluent
streams were sampled with total mass samplers, inertial impactors, a conden-
sation nuclei counter (CNC), and an optical dust counter.  Total mass tests
showed baghouse mean mass efficiency to be 97.9 percent with one furnace op-
erating, and 98.7 percent with two furnaces.  Mean outlet mass concentrations
for one- and two-furnace operation were 0.0014 and 0.0019 grains/dscf, re-
spectively.   Influent impactor tests showed considerable size distribution
differences  as a function of the phase of the process:  the greatest concen-
trations for the particles sized occurred during the first melt.  Effluent
impactor size distribution tests suggested agglomeration.
                                     155

-------
 INTRODUCTION
      The work reported in this paper presents one phase of a program whose
 purpose was to characterize the performance of several industrial size fabric
 filter systems.  The fabric filter tested at the Marathon LeTourneau Company
 in Longview, Texas cleaned the emissions of either one or two 30-ton electric
 arc furnaces which produce a high strength, low-alloy specialty steel.  Each
 furnish is fitted with a side draft hood and a canopy hood which is used only
 during charging and pouring.   The hoods are ducted through a spark arrester
 to a 10-compartment American Air Filter baghouse which utilizes Dacron™ bags.

      The performance of the fabric filter was characterized by determination
 of the particulate removal efficiency as a function of total mass and particle
 size.   The apparent fractional efficiency, defined as the measured change in
 the particulate concentrations as a function of particle size that results
 from the filtration process,  was determined by upstream and downstream sampling
 using  mertial cascade impactors.   The baghouse influent and effluent streams
 were also monitored with a condensation nuclei counter to determine variations
 in submicron particle  concentrations  as a function of the process and the
 cleaning cycle.

 MARATHON LETOURNEAU STEEL MILL

     The steel mill at  Marathon  LeTourneau produces  high strength,  low alloy,
 specialty steel  in two  electric  arc furnaces  of 30 tons  each,  nominal capacity
 The furnaces  are  10,000 kVA swing  roof top charged units  with  individual  com-
 bination side-draft and canopy hooding.   The  side-draft  hoods  operate while
 the furnace  roof  is in  place  and the  canopy hoods  operate when the  roof is re-
 moved  for charging and  tapping.  The  furnaces  use  the  basic  steel making  pro-
 cess with cold number one  oil-free scrap.   The  furnaces must be  back  charged
 once to  reach  holding capacity,  and the  double  slag  method of  refining is
 used.  Additions  of fluorspar  are  commonly  made  for  slag  conditioning and
 oxygen lancing is  used  to  lower  the carbon  content of  the  melt.

     The  furnace hoods  are ducted  to  a  10-compartment American Air  Filter  bag-
 house installed in  1973.   Photographs  of  the baghouse are  presented in Figures 1
 and 2.   The baghouse has a cloth area  of  52,7782 which results in an  air-to-
 cloth ratio of 3.22:1 at the design flow  of 170,000  acfm  at 150°F.  The net
 air-to-cloth ratio  increases to 3.58:1 with one compartment off-line  for clean-
 ing.  The cleaning  cycle is actuated by timer such that there is no delay  time
between cycles.  Each baghouse compart contains 288 Dacron™ filter tubes
which are 5 inches  in diameter by 14 feet long.
                                     156

-------
Figure 1.  Photograph of side of fabric filter.

-------
Ijl
O3
                             Figure 2.  Photograph  of end of fabric filter.

-------
 RESULTS

      The  primary purpose of the  sampling program at Marathon LeTourneau was
 to  define the  total  and  fractional  particulate penetration through a fabric
 filter cleaning  the  emissions  from  an electric arc furnace.   The secondary
 reason for testing was to determine the  effect of approximately doubling the
 particulate loading  to the baghouse on the total and fractional penetration.
 In  addition,  the baghouse inlet  and outlet submicrometer particle concentra-
 tions were measured  as a function of the process cycle and the baghouse
 cleaning  cycle to determine if periods of high penetration are a function of
 the process cycle, the cleaning  cycle or both.   Finally, the inlet particle
 size distributions were  measured as a function of the process cycle.

      Mass Measurements
      The  baghouse  inlet  and  outlet  average  particulate mass  concentrations
 and  the resulting  efficiency penetration results  are  presented in Table 1.
 Examination  of  the table shows  that the  inlet  concentrations for the test
 days  during  which  there  were two  furnaces in operation were  approximately
 twice that of the  runs in which there  was only one  furnace  in operation.
             TABLE  1.  AVERAGE RESULTS  OF  TOTAL MASS  MEASUREMENTS
            Tests
Concentration,
    gr/dscf       Efficiency,   Penetration,
	—     percent       percent
Inlet    Outlet
All
Two furnaces
One furnace
0.0824
0.1472
0.0662
0.0015
0.0019
0.0014
98.18
98.71
97.94
1.82
1.29
2.06

     The mass penetration and the total mass sample outlet concentration  sta-
tistics show that the penetration is lower even though the outlet  concentra-
tion is higher (40 percent) with the two furnaces in operation indicating the
baghouse particulate removal efficiency varies with inlet grain loading.   Thus
the baghouse dampens changes in the outlet concentration or emission rate
caused by variations in the inlet concentration.

     The particle size distribution data was not such a straightforward task
as the total mass measurements, however.  The duration of the inlet impactor
sampling to collect a weighable sample on each stage without overloading  was
quite variable due to differences in the mass concentration as a function  of
the process cycle.  Figure 3 illustrates in a somewhat simplistic way what
happens to the mass concentration as a function of the process cycle for  one
micrometer particle.   Other curves were constructed for two,  four, six, eight
                                     159

-------
       o
       w
             0.10
            0.05
             0.01
       9


       O



       j?  0.005
           0.001
                          I     I
                     FIRST  MELT
                              BACK

                             CHARGE
                                                       I    I
                0
                    J	L
                                          SECOND  MELT
                              TAP
      J	1	1    I	I	L
60            120

CYCLE TIME.minutts
                                                           ISO
Figure  3.   Concentration versus  process cycle for 10 ym particles.
                                  160

-------
 and ten micrometer particles and all showed the same pattern.   The concentra-
 tion is highest during the first melt,  drops dramatically during back charging,
 increases somewhat during the second melt and then decreases again during tap.

      Because of the large temporal changes in concentration, it was important
 that we sample during phases of the cycle.  Figure 4 shows the sequence of
 inlet impactor measurements that were taken, showing that nearly every part
 of the process cycle was  sampled.   These results were the time averaged and
 composited to construct a single curve  for the inlet particle  size distribution
 with our furnace in operation and another for two furnaces in  operation.   These
 curves are shown in Figure 5.   It can be seen from these curves that highest
 inlet concentration occurs at about two micrometers and that two furnace  op-
 eration roughly doubles the concentration over the entire size range covered
 by the impactors.

      The measurement of the outlet particle size distribution  was more straight-
 forward.   Because  of the  very low concentrations, however,  outlet impactors
 were run for 9 to  15 hours each day so  that a weighable amount of particulate
 could be collected on each stage.

      The results of the outlet impactor runs are summarized in Figure 6.   As
 can be seen,  the grain loadings are very low but the particle  size of maximum
 concentration is 4 micrometers  This is compared to a maximum  concentration
 at 2 ym at the inlet,  a phenomenon discussed yesterday by Dick Dennis.

      By comparing  the  inlet and outlet  size distribution curves,  one can  con-
 struct a fractional efficiency curve for the baghouse,  as shown in Figure 7.
 Although we  generally  do  not like  to describe baghouse  collection performance
 in terms  of  fractional  efficiency  because  many of the outlet particles  do not
 directly penetrate the  filter,  it  is a  conventional method  of  describing  col-
 lector performance.   These curves  show  a minimum at about 1 ym,  a maximum at
 about  6 ym and then a  dropoff  to 10 ym.

      Inlet and outlet measurements  were also made in the submicrometer  particles
 with a condensation nuclei counter.   These measurements  showed collection ef-
 ficiencies of 99.23 to  99.86 percent for particles  over  the range of 0.0025  ym
 to about  0.5  ym.   This  device,  when used on the  outlet  gas  stream,  very con-
 sistently showed peaks  in  the  small  particle concentration  immediately  after
 a  compartment  was  cleaned.

      In summary, the baghouse  evaluated controlled  the emissions  to an  outlet
 concentration  of 0.0015 gr/dscf.  This  is  3k  times  below the allowable  concen-
 tration.   The  baghouse  studied  also  was  shown  to  efficiently collect  particles
 over a  very broad  range of  particle  sizes.
     This project has been funded at least in part with Federal funds from the
Environmental Protection Agency under Contract No. 68-02-1438, Task 4.  The
contents of this publication does not necessarily reflect the view or policies
of the U.S. Environmental Protection Agency, nor does mention of trade names,
commercial products, or organizations imply endorsement by the U.S. Government.

                                     161

-------
               INLET
             RUN NO,
                                                                       I	1
a-.
                8
                           h-H-
-H
                10
POWER ON
. 1 ,
1 f 	 1 , 	 ,
BACK CHARGE SLAG OFF
-1 	 Li 	 L 	 1 ill
REBOIL TAP
                       v              eo              iao             iso

                                       CYCLE  TIME, minutes
              Figure 4.  Time  in process cycle at which inlet  samples were collected.

-------
     0.2
u
U)
tn
c
'5
w
0»
0>
O
  O.I
0.09
0.08
0.07

0.06

0.05

0.04


0.03
    0.02
    0.01
        0
              >-ONE  FURNACE  ON
              |-TWO  FURNACES ON
               23456     789
             PARTICLE  AERODYNAMIC  DIAMETER,/im
                                                              10
      Figure 5.  Composited differential  size distribution
                curves of baghouse inlet aerosol.
                            163

-------
     0.002 r
•o
-»*
s
o
o»
O
O
      0.001
    0.0009 I-
    0.0008 h
    0.0007k
    0.0006
2   0.0005
   0.0004
   0.0003
          h
   0.0002
   0.0001
                                                                i
                     >-ONE FURNACE ON
                     I-TWO FURNACES ON
                                  56789|Q
                 PARTICLE  AERODYNAMIC  DIAMETER,
                                                                II
     Figure 6.  Average outlet differential size distribution
                                                    curves.
                              164

-------
0)
Qt
 •»

Z
o
cr
l-
LJ

UJ
Q.
                             -ONE  FURNACE  ON

                             -TWO FURNACES ON
                       34567

                        PARTICLE SIZE./im



      Figure 1.   Fabric filter fractional penetration curves.
                             165

-------
166

-------
                        FUME CONTROL AT SMALL SMELTERS
                              Knowlton J. Caplan
                                   ABSTRACT

     In general, fabric filters are successfully applied to fume control in
small smelters.  Special considerations need to be provided for hot gases,
possible presence of acid (especially S02), high dew points, and sometimes for
fire prevention.  Efficiencies are adequate for present emission standards and
a clear stack is usually obtained.  Air-to-cloth ratios are usually quite con-
servative because the permeability of the dust cake is quite low.  The dust is
somewhat, but not exceedingly, difficult to handle.  A table is provided sum-
marizing the performance of 15 fabric filters in small smelters processing lead,
brass, and copper.
                                      167

-------
                   FUME CONTROL AT SMALL SMELTERS

                                              By Knowlton J.  Caplan11

 Presented at  3rd EPA Symposium on Fabric Filters for Particle Col-
 lection,  December 6,  1977,  Tucson,  Arizona
                            INTRODUCTION

 The  term "small  smelters"  covers  a  very  heterogeneous  and poorly
 described segment  of U.S.  industry.  Almost  all  small  smelters  are
 secondary smelters, that is,  the  raw material  for  the  process is
 recycled scrap.  Obviously, such  industries  provide  a  highly use-
 ful  economic and environmental  function.  Apparently these
 industries are not represented  as such by any  trade  association,
 although they may  be members  of other trade  associations  related
 to the  end uses  of their product.   In a  recent study on economic
 impact  of proposed government regulations on the lead  industry,
 it proved impossible to closely define or accurately count the
 number  of secondary lead smelters.

 With such a heterogeneous  definition of  the  subject, this  paper
 will only cover  part of it, that  part which  is represented in our
 direct  experience.  This paper  is not a  comprehensive  literature
 survey,  but rather a description  of general  operating  characteris-
 tics of  the industry as related to  fume  control.


                     INDUSTRY CHARACTERISTICS

 Secondary Lead Smelters

 Secondary lead smelters are generally centered around  a local
 supply of scrapped automobile batteries and  those batteries are
 the  main  source of feed material to the plant.   Other  forms of
 lead  scrap are handled incidentally.  Such secondary smelters may
 be associated with a battery manufacturing plant which consumes
 the  lead produced,  or may be independent, producing pig lead.
Although a process does exist for charging the drained batteries,
 case and all,  into a melting furnace, that process is not widely
used and most plants operate  by "breaking"  the batteries.  A
mechanical saw or guillotine is used to cut  the case open, the
lead bearing plates are dumped out of the case, allowed to dry in
piles on the floor, and handled by front end loader for manipulatin<
the stock piles and charging the furnace. Various mechanized schem<
  President,  Industrial Health Engineering Associates,  Inc.,
  Minneapolis,  Minnesota.
                               168

-------
have been proposed and tried without notable success.  Obviously
this method of bulk handling is dusty and presents a difficult
occupational health problem, but the dust concentrations are
usually below present emission standards and even if they were
not, the particle size is relatively coarse and collection would
not be difficult.

The major sources of fume in the secondary lead smelter are
either a blast furnace resembling a foundry cupola or a reverb-
eratory furnace, and the associated refining kettles.  These will
be described later.
                       c'
Secondary Copper Smelters

Recycled copper can be recovered by wet chemical methods or by
smelting.  The copper scrap going to a smelter is much more hetero-
geneous than is the case with the lead industry.  The scrap contains
many other metals besides copper and many alloying elements for
copper, so that the metals separation and refining process is much
more complicated.  The same smelter may also receive other non-
ferrous scrap materials involving semi-precious or precious
metals.  As far as the copper scrap is concerned, it is even less
homogeneous than the lead battery scrap and is handled by front
end loader in bulk, with the associated hygiene problems.  The
first process  evolving  fume is the charging of the material to
a blast furnace; from there on the melting process resembles in
its process steps a primary copper smelter, with the major ex-
ception that the sulfur content is low and evolution of SC>2 is
not too significant a problem.

Fabric filters are used for fume collection from the blast furnace,
converter and other associated fume sources.  Our experience in
this particular problem is limited in that the severe depression
of the copper market has delayed our projects in this area.

Brass Recovery

It is our impression that most brass is recycled by brass foundries
or other brass producers, rather than attempting to smelt the
brass to a marketable grade.  Brass melting in brass foundries is
usually conducted in crucible furnaces or in tilting melting fur-
naces using scrap brass of known composition as part of the
charge.  The emission from crucible furnaces is quite low, unless
oily scrap is used.  The emission from direct fired melting furnaces


                                169

-------
 is higher, and causes potential problems of baghouse  fires either
 from carryover of sparks or from finely divided metallics  (es-
 pecially  zinc) that may be generated by the reducing  atmosphere
 and collected in the baghouse.  As far as we know, brass is either
 smelted for its copper content in a copper smelter or directly
 used in the foundry and there are no "brass smelters" as such.

 Secondary Aluminum Smelting

 We have no experience with this particular industrial function
 other than the typical problems associated with aluminum melting
 as practiced in light metal foundries.  The major problem associ-
 ated with fume in such operations arises from the use of chlorine
 as a scavenging gas in the melt, which produces a copious aluminum
 chloride fume.  Treatment of this source has been extensively
 described in literature.
               FABRIC FILTER APPLICATION TO SMELTERS

Table I presents a summary of data available to us concerning the
general operating parameters of fabric filters in small smelters.
Much of the data is missing, as is obvious, since the information
was collected incidentally to other work which may have been on
the baghouse itself or only indirectly related.  Some information
from AP-40 has been included for the sake of completeness.

Most notable among the missing data is particle size information.
Although scientifically this is regrettable, for practical appli-
cation it is not too important.  All the systems are handling a
fine metallurgical fume which would be expected to, and does, have
a mass median aerodynamic diameter of 1 micron or less.  Of
greater practical importance is that the fume is "difficult";
that is, the permeability of the accumulated filter cake is low.
The dust is also, in general, somewhat difficult to handle,
somewhat sticky, etc., as distinguished from a free flowing
granular material.

It will be noted that all the filters except one (which is trouble-
some)  are operating at quite modest air-to-cloth ratios for the
type of filter involved.   Differential pressures across the fabric
are, with the same exception, in the normally expected range even
though accurate data may  not be available due to the large varia-
tions in operating conditions for some filters.


                                170

-------
Efficiencies are usually in the range of 98 to 99% on a weight
basis, the stack is usually visually clear, and the outlet
grain loading is usually comfortably below the present emission
standard for primary lead smelters.  The reason for the efficiency
being somewhat below the 99.9 weight percent that can usually be
expected for a fabric filter is not clear.  The duty conditions
are rather severe,  involving high temperatures and chemical attack
on the fabric.  Furthermore, the baghouses are usually quite
large so that, in view of the high temperatures and noxious con-
ditions, finding and fixing small mechanical leakages through the
fabric is difficult and is not actively pursued as long as the
emissions are satisfactory.

The hot gases from the furnaces may be cooled to suitable bag-
house temperatures by any of the classical methods.  If acid is
present, the most favorable design would be to use radiant coolers
to avoid introduction of additional water vapor.  When water sprays
are used, they are usually used only for partial cooling, the
remainder being by dilution in order to avoid too high a dew point.

If acid gases are present in significant quantity or if water
spray cooling is used, the hoppers of the fabric filter should be
kept above the dew point.  This requires provisions over and above
that required to keep the main housing above the dew point.  With
material collected in the hopper, the collected layer of dust
provides an insulating effect so that the metal temperature may
be far below the gas temperature.  However, the vapors will still
migrate through the bed of dust, condensing on the cold metal
walls and forming a cake or mud.

Blast furnaces or cupola type furnaces can be operated under
significant draft so that there is no escape of fume from the
furnace itself.  There is, of course, fume evolved from the
pouring of the metal or the tapping of slag which should be con-
trolled from a hygiene point of view.  The air from such hoods
is usually only 100 - 150°F and is an economical source for
dilution air since it also requires filtration.

Reverb furnaces on the other hand are typically operated at a few
hundredths of an inch water gage draft in order to conserve fuel.
Such furnaces tend to be somewhat leaky and loss of the draft
will result in leakage of fume from the furnace itself or from
various operating ports.  In some primary smelters, very elaborate,
fast-acting control systems are installed to regulate the furnace


                                171

-------
 draft  in accordance  with  operating  conditions,  the opening of
 charge ports,  etc.   Such  elaborate  controls  are usually not found
 in secondary  smelters.  External  hygiene  control hoods may be
 located over  the  charge ports, metal  and  slag  taps,  and again,
 this contaminant-laden air provides a source of dilution air for
 cooling the furnace  gas on an economic basis.   Such hygiene
 hoods  do not,  however, provide for  maintenance  of adequate furnace
 draft  to prevent  leakage  from the furnace itself.


                  FIRES IN METALLURGICAL BAGHOUSES

 Fires  are not  uncommon in metallurgical baghouses.   They usually
 but not always occur in the hopper  of the baghouse.   However, the
 circumstances  under which they occur  are  highly variable,  and
 immediate investigations following  a  fire usually lack the
 application of scientific expertise.   As  far as we  know,  no
 concerted research has been done  on the subject.

 Fires  occurring in the hopper are almost  always caused by  the
 presence  of finely divided unoxidized metallics of  a  pyrophoric
 nature.   The presence of metallic zinc is  probably  the most common
 source  of such fires, and the presence of  metallic  lead probably
 the second most common source.

 Prevention of fires in baghouse hoppers has  been most  successfully
 accomplished by the addition of an  inexpensive  diluent material.
 The most  common diluent is agricultural lime, it  serving obviously
 as a diluent to the combustible materials  and also, if a fire does
 start,   heat will be absorbed in dehydrating  of  the  lime  thus
 furnishing an additional cooling  effect.   Some  installations  have
 used various carbonates such as soda  ash or  ground limestone, the
 theory  being that the heat of the fire will  release carbon  di-
 oxide which will tend to smother  the  fire.  This latter action
 probably would not be effective for a  fire in the bags  since the
 filtering air flow would rather quickly flush the blanket of
 carbon dioxide away from the combustion area.

There is an empirical test called a "burning test" which is
applied to controlling fires in metallurgical baghouses.  In
general the test consists  of taking a shallow pan full of the
collected dust and attempting to light it at one end by ordinary
means such as  a match or  a burning paper towel.   The time of
burning from one end to the other of the pan is then measured, and

                                172

-------
if it is less than some specified value, the diluent is added to
the duct entering the baghouse so as to mix with, dilute, etc.,
the combustible dust.  The test is strictly empirical and the
parameters need to be developed for each individual plant or bag-
house situation.

One plant used a pan one-half inch deep, 2 inches wide, and 6
inches long.  In this case, the burning was not actually timed;
if the dust burned at all, the diluent was added.  The diluent
was hydrated lime (agricultural lime) and was added in amounts
varying from 5% to 20% of the total dust load.

In another plant the test pan was 1 inch deep, 3 inches wide and
9 inches long.  If the length of time required to burn from one
end to the other was greater than 2 minutes, it was judged
acceptable; if less than 2 minutes, agricultural lime was added
to the flue.

Fires starting on the bags rather than in the hopper are usually
blamed on the carryover of sparks although there are some indi-
cations that these fires also are sometimes started by metallics.
In one interesting case, the bags of a reverse pulse filter with
bottom inlet caught fire at the top of the bags and there was no
fire in the hopper.  Because at times sparks had been observed in
the flue, the fire was blamed on sparks.  It is difficult to
understand how such sparks would preferentially migrate to the
top of the bags.  Another possible explanation would be that the
reverse pulse air, having more energy and physically agitating
the dust cake more at the top of the bags than further down, may
have started the fire in the metallics present.  In any case,
the provision of a spark trap such as a cyclone or a spray cham-
ber would prevent fires from sparks if they cannot otherwise be
prevented.  If both sparks and unoxidized zinc or lead are
present, both types of precautions may be required.


                           DUST HANDLING

The handling of recovered dust in most secondary smelters is a
difficult problem because such plants usually do not have a
multiplicity of processes and options for disposal of such
material.  The material may also have a significant monetary
value.  Its disposal by means other than to the process would be
an obvious problem in solid waste disposal.

                                173

-------
 The  dust  is usually somewhat difficult  to  handle.   It  does  not
 flow readily  from hoppers, etc.,  unless special  provisions  are
 made.   The dust should be capable of conveyance  by  pneumatic
 conveying, but some operators have experienced difficulty with
 this operation due, in our opinion, to  inadequately designed
 systems.  Screw conveyors work, but they must be enclosed and
 dust control  applied.  Belt conveyors or other dusting type of
 material  handling equipment is to be avoided.

 The  dust  is usually significantly different in metallic compos-
 ition to  the  parent material and  metallurgical considerations may
 govern^the point in the process to which it is returned, or even
 if it is  to be returned.  Leaving aside the metallurgical con-
 siderations,  dust returned in that form to a blast  furnace  or
 cupola  is mostly re-entrained and immediately reappears in  the
 baghouse, constituting a circulating dust load.  The circulating
 dust load may be an operating advantage if such  recirculation
 accumulates unwanted impurities so that a bleed-off or programmed
 disposal of the dust can be made.  Otherwise, the dust will be
 recovered more efficiently by returning it to a  different type
 of furnace such as a reverberatory furnace.  Most secondary
 smelters do not indulge in pugging or briquetting of dust to
 reduce  its loss in the furnace.
                              SUMMARY

In general, fabric filters are successfully applied to fume con-
trol in small smelters.   Special considerations need to be pro-
vided for hot gases,  possible presence of acid (especially SO9),
high dew points,  and  sometimes for fire prevention.  Efficiencies
are adequate for  present emission standards and a clear stack is
usually obtained.  Air-to-cloth ratios are usually quite con-
servative because the permeability of the dust cake is quite low.
The dust is somewhat, but not exceedingly, difficult to handle.
                               174

-------
 3:
 a
 5i
3 HI •"

Ml
 U
       8~ll
       En 5 i!
                o  j o
          do  c   fi o
          H  &   &1
        %.S
             c   o
       Si
          o   Q  a
          p  h*   £
               l
     e  ?  ?  p  s-
           u  w
           *J  *>  -a
           ,.s. a  1^
        >1 9
        3 S
  1  I!  |£  Si IE
  ^  C«  fe^  |8« a(^

  5  H ?  J {  I ? S! ; 'I

I  *i T:> r.  !is!3i§3

hs  iPil  ihhij
  j«c j»n s»  3f at SsS
                                       I   Mi   i  Si
                                s  §
                            a
tt®

SI
                                       U
                                     «. S
                                     •-
                                     «  h
                                    o-  B<
                                                 tS
 i
        ?S8SS
                            175

-------
176

-------
                                   rTTCgjrraa

                                   FULLER
                                 COMPANY
                    FABRIC FILTERS  IN  THE CEMENT INDUSTRY
                                N.  D.  PHILLIPS
                           SENIOR  PROJECT ENGINEER

                                      AND

                                W.  C.  BRUMAGIN
                           CHIEF  PRODUCT ENGINEER
                           DUST  PRODUCTS DIVISION
                               FULLER COMPANY
                              FOR  PRESENTATION AT
                      THIRD  SYMPOSIUM ON FABRIC FILTERS
                           FOR  PARTICLE COLLECTION
                               DECEMBER 5-6, 1977
                                TUCSON, ARIZONA
                                     177
P.O. BOX aa. CATASAUQUA, PA. 18O32 TELEPHONE: 215-26-4-6O11 TWX: 51O-651-5B1Q TELEX: 03-4-7443 CABLE: CQLFULLER

                              A GATX  COMPANY

-------
 INTRODUCTION

 Over the last 20 years, cement producers have been under
 considerable pressure to reduce their contributions to the
 air pollution problem of the nation.  In fact, dust col-
 lection equipment has been used for a very long time in
 cement plants,  much longer than the last twenty (20) years
 This has been primarily due to the nature of the materials
 used in the process and the materials produced, as well as,
 the two initial  reasons why any plant will  consider in-
 stallation  of dust collection equipment.  The first being
 recovery of a product that already has an investment in it
 and is usable in the end product of the plant.  The second
 being  the elimination of air-borne dust within the plant
 facilities, thereby extending the life of mechanical equip-
 ment in the plant and reducing housekeeping  expenses in the
 facility.   For  these reasons, 30 or 40 years  ago,  it was
 common to see dust collection equipment within the plant
 venting material  handling  facilities, drying  facilities,
 pyroprocessing  equipment,  and milling equipment.

 There  have  been  two distinct processes used  in the manufacture
 of  cement that  differ primarily in the treatment of the raw
 material Before  pyroprocessing.   The wet process in earlier
^times  being the  most common,  required little  in  the way of
 dust collection  equipment,  until  after the raw feed had been
 dried,  calcined  and clinkered.   The dry  process  plant,  has
 always  required  dust collection  equipment  in  greater degree
 because of  the  crushing, drying,  milling,  and  blending  of  dry,
 relatively  fine  materials.   With  the advent of the  energy
 crisis,  dry plants  in  the  United  States  are becoming  more
 popular,  therefore,  cement  plants  will  be  equipped  with  dry
 filtration  dust  collection  equipment to  a greater  degree  in
 uric,  T u L u v* G »

 In  the  late 1950's,  good neighbor!iness  and the move  to  im-
 prove  the quality  of  our environment,  caused  cement  manufactur-
 ers  to  look at replacing their mechanical separation  equip-
 ment and  electrostatic  precipitators  with more efficient
 devices.  In  the  late  1950's,  fabric  filters  began  to be ap-
 plied  to  the  waste  gases from  long  dry kilns,  the  initial
 small  suspension  preheater  kilns,  and  somewhat later  than
 that,  to  long wet  process kilns.   This came about  largely  be-
 cause  of an  increase  in production  of  fiberglass fabrics and
 tnrn^i1^r°y^ni-ntS  1n.tre?t1n9 fiberglass fabrics with  lubricant;
 to prolong  their service life.  This  development gave cement
manufacturers the  best available filtration efficiency of  the
m.I^nlo a11?wed *hej. *» use a P^ce of equipment that could
?a?e    Prin?  tem+ly* hl?h effici"ency  regardless of production
rate.   Prior  to this time,  plants recovered a substantial amount
of material  from the air stream before it ever got  to the final
discharge.  The installation of higher efficiency filtration
equipment,Required today by EPA, Required in some  cases by
 local law in earlier days,  gave cement manufacturers two ad-
                            178

-------
ditional benefits.  The first, a better rapport with local
neighbors, the second being a cleaner plant environment.  In
early days, it was not uncommon to see roofs of the plant
facilities with 6 to 8" of dust all over them, causing in
some cases structural damage, in others replacement of roofs
at more frequently than normal intervals.

Today, we break up application of dust collection equipment
into two distinct categories.  The first is application of  the
equipment to parts of the process that are largely housekeeping
in nature.  Examples would be ventilation of material  handling
equipment, crushing, storage and withdrawal facilities of both
raw and finished materials, etc.  The second category  is ap-
plication of equipment to the process train and process gas
itself.  Examples here are drying, milling, burning (kiln),
material cooling (clinker coolers), and others.

There are eight (8)  basic processes in cement plants which
require dust collection equipment:

     1)  material handling
     2)  storage and silos
     3)  crushing
     4 )  d ry i n g
     5)  milling
     6)  burning (kiln)
         alkali bypass
         cooler (clinker)
      7)
      8)
 In some cases, the air streams from several of these can be
 combined to form one combination gas stream handled by a
 single piece of equipment.  We will discuss each of these
 separate areas to point out the potential problems for design
 and operation of the dust collection equipment.

 Duct System Design

 An important part of dust ventilation systems is the desiqn
 of the ducts .

 The design of the duct system used for collecting the vent
 air streams and fugitive dust from the material handling equip-
 ment or any of the other equipment to be discussed in this paper
 can follow either of two general  methods of design; each would
 be used for different purposes.

 The first would be a self-cleaning duct system.  This duct
 system would be designed with a maximum velocity of about 2000
 feet per minute.   Because of these low velocities, material  may
 OnnIen?ULon *5? Plpjs..hence all  pipe runs must have a minimum
 slope of 450 with no horizontal runs  whatsoever.   This desiqn
 approach should be considered when handling extremely abrasive
material  in order to reduce wear  on pipe-lines.  It should  also
be considered where there is large inherent variation in the

                           179

-------
 volume within the system,  whereby material  handling velocities
 cannot be guaranteed  for a conventional  high velocity vent
 5 Jr S L ClT) .
                   syltem 1s  expensive  to  install.   This  system
            to  short  horizontal  distances  where  the  dust  col-
               *?*1  as.  close  as  Possible to the sources  being
                ^ !J ' "9  s^stems  also- present  support problems,
  n     noK^  atJtSe  fpex of runs  where the  ductwork must  go
 to  a  90°  bend  and  back  down  to  filtration equipment.

 The advantage  of the  self-cleaning  system is that it provides
 the lowest  operating  static  pressure and  thus the lowest fan
 energy  requirement;  a consideration  that  must be kept  in mind
 today .

 The other general  method of  designing  a vent system  would  be
 to use  conventional  high velocity  ventilation techniques   The
 Jnnn92  Veloc1t1es  for this system would be between  3500 and
 4000 feet per  minute.   These velocities must be maintained to
 prevent any settling  of  dust in any  long  horizontal  runs.  This
 system  can  be  used on any materials, but  abrasive materials,
 such as clinker dust  or  sand will present wear problems; and
!5e + £   i?ystem must  thel"efore be designed to allow  for wear
 at the  elbows  and  any intersections or  transition points.

 inewhirh%h°me Jases.,tn  these various material  venting systems
 in which the material may be hot and moist, and the collected
 air and dust could present a caking problem.  Insulation of
 the ductwork and dust collector or the  admission of supple-
mentary warm air might be required.

 I.  Material Handling

    Since a cement plant is  required to move large quantities
    of- dry materials as  either raw feed or finished  product,
    many belt conveyors  and  bucket elevators are used.   At each
    of the transfer points  onto or off the belt  or from the
    thaJem,',«?°!!e <|ry dust emission ts Priced.   The air volume
    that must be handled is  definitely  related  to  the height  of
    the material  fall.  The  further the material  falls, the
    bigger the  ventilation  problem.  Also  at transfer points,
    there is a  tendency  for  the stream  of  material  to drag  air
    in at the upper end  of  the transfer.  The air  migrates  to
    the lower transfer housing, backing up at the  discharge of
    the lower transfer housing, and causing dusting  primarily
    vMnmlSch01?K F°r  thts  reason>  the primary  ventilation
    volume should  be  removed  from  the lower portion  of  any
    transfer housing.

    If  too high an  air velocity of  the  vent air  is used,  ex-
    ^fh1!Ie^USt  1S transP°rted  f^orn  the point of  transfer
    rather than removing  only the  amount of dust and air  that
    is  generated.   Generally,  the  dryer and finer  the material

                           180

-------
     that is being conveyed, the more fugitive dust that is
     generated at the transfer points.  Belt conveyors require^
     less energy than pneumatic conveying, but have the potential
     of greater fugitive dust production.

     Either small shaker collectors or high ratio pulse type
     collectors are used for these collection points.

11.  Storage and Silos

     Silos are filled by bucket elevators, belts, or pneumatic
     conveying.  At the discharge points of bucket elevators,
     the material is flung  from the buckets.  The volume of air
     to be removed is dependent upon  the cross sectional area
     of the housing and its height.

     The volume of air to be ventilated  from a silo depends upon
     any one or combination of:

     1.  Width and speed of belt conveyor

     2.  Size of bucket elevator

     3.  Air volume capacity of pneumatic  conveying system

         (A surge factor should be included when sizing the
           fan and filter).

     The first two systems  generally  require  the lowest volume
     of  air and  the  least amount of  dust to be collected.   A
     pneumatic conveying system requires the  largest  volume of
     air and generates more dust to  be  collected.

     Silo  venting also applies  to  the homogenizing  (blending)
     silos  for raw feed  in  dry  process  plants.   The  air volume
     is  determined by  the air  supply  required  for  blending.

     Either  intermittent or continuous  collectors  of  the  shaker
     or  pulse  type can  be used.

Ill.  Crushing

     The crushers  used  in a cement plant are  generally selected
     on  the  basis  of  the  type  of  stone  being  used  to  supply raw
     material  for  the  product,  as  well  as, the size  required  for
     further  processing  after  the  crusher.  Commonly,  hammermills
     or  impactors  are  applied  to  limestone today,  and in  many
     existing  plants,  the combination of jaw  crushers, gyratory
     crushers,  and  cone  crushers  have been used.   The fugitive
     dust  problem  in  crushing  operations increases  as  the amount
     of  energy  increases  in the crushing operation.   The  hammer-
     mill  creates  the  most  serious dusting problem as  it  is
     really  analogous  to  a  large  fan, thereby creating motion of
     an  air  stream  by  itself.   The hammermill  has  extremely high

                               181

-------
tip velocities, thus imparting considerable kinetic
energy to the stone being crushed which has to be
"killed" below the crusher and hopefully before the
stone reaches the material handling system below.  This
is not true with the other methods of crushing where air
flow is induced primarily due to the flow of stone by
gravity thru the other crusher designs.

In all cases in the crushing operation, it is preferable
to do all of the venting down below the crushers, either
in chutes or in the material handling system below the
chutes.  The design of the plant can help to reduce a
fugitive dusting problem if rock boxes are included under-
neath the crushers to kill the motion of the moving materia'
before it reaches the material handling system.  A rock box
is a trap, usually formed of concrete that extends the full
width and length of the crusher discharge opening.  In the
bottom of this rock box there is a smaller opening, al-
lowing the passage of material to the subsequent operations
downstream.  The crushed stone is allowed to fill up and
seek its natural angle of repose and thus any additional
stone falling from the crusher must impact on the en-
trapped stone before it can reach the opening in the rock
box passing the material on to the conveying system.

It should be noted that when a crusher is operating with
a choke of material ahead of it, there is usually no dust-
ing on the top side of the crusher; however, when the choke
is no longer ahead of the hammermill, some minor dusting
can occur at the feed opening to a hammermill.

Most crushers are fed with either front end loaders or dump
trucks.  At the time that the crusher is fed with a load
of material, dusting occurs at the initial dump of the
quarried material  into the feed hopper for the crusher.
Ventilation of a condition like this has not been usually
attempted as vast quantities of air are required to adequate
prevent fugitive dust from getting into the ambient air awa^
from the crusher.   Conventionally., feed points of crushers
should be enclosed and usually have been enclosed with a
small  building, open on one side to accept front end loaders
and dump trucks.

Primary crushers usually reduce the quarry-size rock to less
than four inch size, normally, about one inch.

Secondary crushers, generally of the hammermill  type,  re-
duce the rock to 1/4" x 0.   As long as  the feed and pro-
duct are dry, there is no particular problem with dust col-
lection on this installation.

Since  these facilities usually require  large air volumes,
high ratio pulse type collectors are the best selection.

                         182

-------
IV.   Drying

     Drying  of raw feed can be accomplished  in  a  separately
     fired rotary dryer, a rotary dryer utilizing some waste
     kiln gases,  or in a combination dryer-crusher operation.
     The main concern for handling the off-gases  from a dryer
     or crusher/dryer operation is insulation to  prevent any
     dewpoint occurrence in the collector system.  If the off-
     gases are at least 100° above the projected  water dew-
     point of the system, with proper insulation  there should
     be no particular problem.

     Depending upon the gas temperature, the collector could
     be either a  glass bag reverse air cleaned unit, or a
     synthetic bag pulse type collector.  Care should be taken
     in the choice of fabric on drying operations.  Potential
     hydrolysis or chemical attack of fabric may  occur.

 V,   Milling

     In a cement  plant, ball mills are used  to grind finished
     cement to the size distribution required for the specific
     type of cement being produced.  The ball mill and the
     separator are the two main items of process  equipment in
     any milling  circuit whether it be a finished cement circuit
     or a raw feed circuit in a dry process  cement plant.
     Classification of the mill product is done in an air sepa-
     rator where  the fines are separated from the coarse ma-
     terial using principles of Stokes's Law.  The fines are
     discharged to the outer cone of the separator and sepa-
     rated by centrifugal action, and the coarse product is
     returned to  the milling circuit from the inner cone of  the
     separator.

     In a finished cement circuit, there is  a difference in
     the fineness of grinding for different types of cement,
     and therefore there  is a difference in the size distribution
     as well as the amount of material.  Masonry cement and  Type
     III cement are ground to the finest size distribution.   It
     is often necessary  to cool the cement before it is trans-
     ported to storage silos.  This cooling can be done in the
     ball mill by introducing water along with a grinding aid;
     it may be done by introducing substantial quantities of
     cooling air into  the air separator, or independent cement
     coolers may be used  downstream of  the air separator.  Cement
     coolers usually operate under the  principle of cooling  the
     cement with water either by an indirect heat transfer coil
     within the cooler or by allowing a continuous flow of water
     on the outer shell  of a tank containing aerated finished
     cement.

     On the raw feed circuit of a dry cement plant, drying of
     the raw materials may occur in the mill, or by introducing
     preheated air into  the air separator to flash dry  the material

                             183

-------
     Dust collection in a milling circuit for raw feed or cement
     can normally be classified as application of process type
     dust collectors.  Generally, two dust collectors are used,
     one to vent the mill along with all the other ancillary
     ventilation points that occur at both the feed end and the
     discharge of the mill and material handling equipment down-
     stream of the mill.  In cases where either drying or cool-
     ing occurs in the separator, an independent dust collector
     is applied on this portion of the mill circuit.  There are
     two reasons to apply a separate dust collector here, one
     being to take advantage of a fan energy saving as drying
     and cooling circuits and separators generally operate at
     low static pressures; two, if this circuit was applied to
     one general ventilation system for the entire mill room,
     there can be interaction between the mill and the separator
     air volumes that can potentially cause control problems of
     the milling process itself.

     The air streams coming from the ball mills and from the
     separators contain great quantities of material; with the
     exception of a roller mill circuit, these two areas are
     the highest grain load encountered in a cement plant.  Since
     most of the material is very fine, the dust collector catch
     represents a substantial quantity of the finished product
     in the circuit.

     Ther-e are several  things to be very careful of in applicatioi
     of dust collectors in this area.  The extreme amount of
     material  caught from the air stream requires careful  choice
     of the material handling system within the collection equip-
     ment.   Introduction of moisture into the mill, must be made
     known, as this could affect the choice of the filtering equi|
     ment as well  as its size.   If drying is to occur either in a
     mill or in a separator, this must be made apparent as this
     also could affect the choice of fabric applied as well  as th<
     size of the equipment installed.

     Both shaker and pulse type collectors have been successfully
     applied in this system.

VI-  Burning - Kilns

     For venting the burning or calcining equipment, kiln, dif-
     ferent problems are involved in the three types of processes
     wet process,  dry process,  and preheater process.

     Wet Process -  In the wet process kiln, since the feed materic
     is a slurry or wet cake, the off-gases will  contain as  much
     as 35% by volume moisture  producing a high dewpoint temper-
     ature, in the  order of 165°F but with dry bulb temperatures
     of about  SOO°F.   The prime problem in venting this gas  strean
     is the necessary insulation required for the system to  pre-
     vent condensation  which produces extreme corrosion on the
     housing and potential  blinding  of the dust cake on the  filter
     bags.
                             184

-------
Glass bag reverse air units with adequate insulation have
been successfully used for this type of process.

Long Dry Kiln - The off-gases from a long dry kiln are
usually at a temperature of 750 to 1000°F and require
cooling prior to entering the baghouse.  Depending on the
alkali content of the waste kiln gases, a cyclone may be
incorporated at the kiln discharge to collect the coarser
fraction for refiring into the kiln with the raw feed or
by the insufflation technique.  If the dust is high in
alkali content, then the fines, which contain the larger
percentage of alkali can be wasted.  If the alkali content
is low, then the total waste dust stream can be collected
in the fabric filter and returned to the kiln for firing.
Some cooling in the case of the cyclone equipment is
obtained, but, generally, the cooling is accomplished by
water sprays in the discharge end of the kiln.

Water Spray Towers or Air-to-Air Heat Exchangers can be
utilized for cooling of the kiln gases, however, this is
not usually done.

Since the moisture level content of these gases is not of
great concern, generally, uninsulated pressure  type bag-
houses are used, however, fully insulated suction type
houses are also employed.  Both types use glass bags and
reverse air cleaning.

Preheater Kiln - Since the waste gases from the preheater
kiln are used for warming the incoming raw feed, the off-
gas temperatures are lower than for the long dry kiln and
temperature control is usually accomplished by  a bleed-
air damper.  The exit gas temperatures are normally 650°F,
when the preheater is operated at  rated capacity.  Temper-
ing with air brings the gas stream down to 500-550°F allow-
ing application of glass fabric filters.

One variation which can be used with preheater  kilns is
an air-swept in-line roller mill used for grinding the
rock, from the secondary crusher size, plus clay, iron
ore or other additives, to the size necessary for raw
feed.  The ground material goes directly to the homogeniz-
ing silos.

Generally, the in-line roller mill is used as a raw mill
and drying operation, since sufficient heat is  available
in the kiln gases.  The dust  collection problem associated
with  this operation is to  insure adequate insulation to
prevent  possible water dewpoint conditions in the fabric
collector.  Of course, another design consideration must
be for handling the hot gases when the roller mill must  be
bypassed for periods of maintenance or emergency outages.
This  is  generally accomplished with a multi-fan installation
so that  normally one fan provides  the pressure  drop re-

                         185

-------
       quirements of the mill while it is in operation and a
       separate fan provides drop for the collector alone.

       The off-gas from the mill circuit quite often goes thru
       a set of cyclones to collect the majority of the milled
       material, however, this does not always have to be the
       case and the baghouse can handle the total dust load.
       All of the dust collected is then supplied as raw feed
       to the preheater.  If the raw feed contains sufficient
       alkali content that some of the dust must be wasted,
       this is usually handled in the alkali bypass system.

       Fabric collectors for kilns have all been glass bag re-
       verse air cleaned units, of either pressure or suction
       design.  Proper fabric selection depends on the type of
       kiln and type of feed material  being calcined.

 VII.  Alkali Bypass. Preheater Kilns

       In order to control  the alkali  content of the finished
       clinker, when the alkali content of the raw feed is too
       high, a small proportion of the kiln gases are vented at
       the kiln exit prior  to the preheater and are cooled and
       collected in a separate fabric  filter.  Since the gas
       stream leaving the kiln prior to the preheater is in the
       1800°F temperature range, the gases must be quickly quenched
       by either,  or a combination of, air-quenching and water
       spray cooling to reduce the gas temperature to 500 to 550°F
       for collection in the fabric filter.

       Reverse air cleaned  glass bag units are used for this
       system.

VIII.  Clinker Cooler

       The clinker cooler's  main purpose,  of course, is to cool
       the clinker quickly  enough by air-quenching to set the
       chemical  properties  of the clinker.  Another important
       function of the clinker cooler  is  to recover sufficient
       heat in the air stream to assist the combustion and burning
       of the cement rock.   Additional  heat is also utilized for
       the pulverized coal  circuit or  additional  drying operations
       which might be utilized at the  plant.

       There is  always  excess waste hot air from  the clinker which
       must be vented.   The  main problem  in handling this waste
       hot air stream to a  fabric filter  is the temperature control
       required  during  the  flushes  which  occur from the kiln.   The
       temperature can  vary  from less  than 300°F  to 800 or 1000°F.
       Cooling of  this  waste stream can  be accomplished in either
       of two ways:

       1.   Water sprays  in  the cooler  onto the clinker bed
           plus  the  addition  of large  quantities  of dilution

                              186

-------
        air to the vent stream to reduce the temperature
        of the gases sufficient to be handled by the fabric
        filter.

    2.  Air-to-air heat excahngers in which the hot gases
        are cooled to the control temperature by passing
        them thru a tubular heat exchanger cooled from the
        outside by a secondary stream of ambient air moved
        by separate low pressure fans.  This technique can
        produce large volumes of relatively warm air which
        might be useful for warming buildings during the
        wintertime.

    No particular problem is involved in the fabric filters
    for the clinker coolers as long as the temperature control
    and the surge volumes are adequately provided for.  Both Q
    Nomex bags, 425° maximum temperature, and glass bags, 550 F
    limit, have been successfully utilized.  High ratio pulse
    type collectors use Nomex felt bags at the 425°F limit,
    while glass bags are used in reverse air cleaned collectors.

CONCLUSION

As a  reference to define the amount of material to  be handled,
cement plants  producing 1000 ton per  day of  finished product
^require a supply of about 1JTDO ton per day of raw feed materials.
Plants are operating at 3000 TPD production  and others being
built with capacities  up to 7000 TPD.  These, usually dry materials
must  be handled and conveyed many times through the different
processes.  Today plants operate at 99.9998% material efficiency.
This  means more saleable product from the  raw materials.

Federal E.P.A. emission regulations of 0.3  Ib/ton from  kilns  and
0.1 Ib/ton from clinker coolers  are easily met with fabric  filters
when  design consideration of  the process conditions and  proper
selection of  filter media are made.   Test  data  shows  kiln  emissions
to be 0.013 to 0.035 grains/SCFD  (.1  to  .25  Ib/ton) and  cooler
emissions to  be 0.0012 to 0.015  grains/SCFD  (.011 to  .061  Ib/ton)
for a variety  of  plants.

All of the miscellaneous sources  are  regulated  by opacity,  but
with  proper fabric  no  visible  emissions occur.
                             187

-------
188

-------
NEW APPLICATIONS FOR FABRIC FILTERS
           R.  L.  Adams

      Wheelabrator-Frye Inc.
         Pittsburgh, Pa.
          December 1977
                189

-------
                      NEW APPLICATIONS FOR FABRIC FILTERS

           Requirements for improved filtration efficiencies have led to the
 use of fabric filtration in many areas that a few years ago were considered
 the domain of high-efficiency cyclones and low-energy wet scrubbers.  This
 paper will review a few of these new applications for fabric filters.   It is
 recognized that almost any so-called "new" applications will have been tried
 somewhere at some time in the past.  However, we believe that the applications
 discussed herein represent major future potential for fabric filtration and
 that developments over the past year or so in these areas have been significant.
           It should be noted that three of the five applications to be dis-
 cussed employ coated fabric filters.   It is this area that provides great
 potential for expanding the use of the fabric filtration in the future.  The
 applications which are discussed in this paper represent only a few of the many
 potential uses for coated fabric filters.   Expanding research and development
 activity  in  this field will  uncover many more in the near future.
           We have chosen  for discussion  five  new applications.   These  are:
 1)  coke oven emission  sources,  2)  coke oven  combusion stacks, 3)  sinter machine
 windboxes, 4)  galvanizing lines  and 5)  S02  removal.   We  would like  to  give  a
 brief  review of  the  current  state  of the art  in  each of  these areas.   In  some
 cases, the work  has  been  done on  only  a  pilot  scale  in other cases  full-scale
 production units  are in operation.
                          Coke Oven  Emission Controls
           A  unique application of  a fabric filter for coke  oven emission  control
 has  recently been  disclosed by the  Taisei Corporation, Tokyo, Japan.  This  pro-
 cess is covered by United States Patent  4,010,013.   The  process utilizes a
 coated fabric  filter called the PRECO  Filter to  remove particulate and  tars
 from charging, pushing and other coking side operations.  It has not been ap-
 plied to  coke oven combustion stacks and these will be discussed in another
 section of this paper.

           Figure 1 shows a typical flow sheet for the process.  Coal or coke is
passed through a pulverizer and injected onto the filter bags.  Coke oven gas
ventilation sources are then ducted to  the filter.  The fabric filter utilized
                                      190

-------
          FLOW SHEET

              Coal  (Coke Dust)
              Introduction
                                                                                Fan
CD

73
            Hopper
Baghouse
Filter
Precoat Layer
     Adjustment of
     Particle Size
        Larry Car Hood

        Door Leak Hood

        Coke Guide
        Car Hood

        Other Hoods
                                                                    Coal Yard
            Coke Oven

-------
 in this application is a standard filter equipped with polyester filter fabric
 and bag cleaning is accomplished by mechanical shaking.  The protective coating
 of coal or coke dust effectively prevents the adhesion of the tar to the fabric.
 It also serves as a filter aid in that it contributes considerably to the fil-
 tration efficiency of the unit.
          Operation of the unit is somewhat different than operation of a stan-
 dard fabric filter.  Figure 2 shows a typical filter pressure loss curve for
 this operation.  It can be seen that after an extended period of operation,
 breakthrough on the filter aid material is anticipated and substantial increases
 in pressure drop may be encountered.  The operating goal, therefore, is to begin
 cleaning of the filter prior to this time to keep operation on the flat part of
 the curve.  This has been successfully accomplished in a full-scale factility
operating at Tokyo Gas Company.
          Figure 3 shows the extremely high removal efficiencies that have been
obtained in both pilot and full-scale operation.   At the filtration temperatures
employed,  the tars exist in a condensed state as  liquid aerosols and can be effec-
tively removed by the coal  or coke precoat layer.   The collected material  from
the process is returned to the coal  yard, mixed with coal,  and sent to the coke
oven  for reuse.
                                   FIGURE 3
                              COKE OVEN EXHAUST
                            TAR REMOVAL EFFICIENCY
P re coating
Material
Coke
Pulverized
Coal
Pulverized
Coal

Temper-
ature
°F
104
104
248

Tar Concentration
Grains/Cu. Ft.
Inlet Outlet
0.083
0.015
0.049
0.169
0.264
0.084
0.223
— : 	 _j
0.00006
0.00001
0.0001
0.0005
0.00009
0.00003
0.000009
Removal
Efficiency
%
99.93
99.93
99.79
99.70
99.97
99.99
99.99
                                      192

-------
12
o
_l
d)
3
% 8-
0>
a_
$-
r-~
u_
4 -


Inches
2^
4

Introduction of Start of
Tar-Containing Increase
Dust Gas Pressure

/*"
r
Fi

01234
Hours

i
i
|
i
i
i
i
!
i
Sudden /
in
Loss


Iter

5

/Gas intro-
/ duction

j s^
Cleaning

6 7

TYPICAL FILTER PRESSURE LOSS CURVE
            FIGURE 2
                193

-------
          We believe that the Taisei PRECO Filter represents a very new and novel
application for fabric filters.  The fact that the coating material is the raw
material for the ovens and that the collected material may be returned to the
ovens is significant.  We would expect to see application of this type of filter
in the United States in the future.
                         Coke Oven Combustion Stacks
          In many of the older coke ovens, leaks exist between the coking side
and the combustion side of the oven due to deterioration of the bricks.  There-
fore, contaminants such as hydrocarbons and tars leak into the combusion side
of the oven where they are partially burned to produce a finely divided form of
carbon black along with condensibles.  This leakage is generally intermittent
in nature but as the air pollution codes become more stringent, control of this
source is now being required in some areas.
          Early this year, a pilot fabric filter was operated at a major steel
mill.  During operation of the pilot unit, the oven was fired with both coke
oven gas and blast furnace gas.  During firing of coke oven gas, the filter was
operated both with a precoat of limestone and without a precoat.  Performance
with regard to filtration of solid particulate is given in Figure 4.  It should
be noted that the average outlet concentration on solid particulate when using
the coated baghouse was 55% less than when using a noncoated baghouse.
                                   FIGURE 4
                             COKE OVEN PILOT UNIT
   Solid Particulate
       gr./DSCF
     Inlet
       (max.)
       (min.)
       (avg.)
     Outlet
       (max.)
       (min.)
       (avg.)
 Blast Furnace
Gas (noncoated)
   0.1173
   0.0101
   0.0585

   0.0048
   0.0007
   0.0023
   Coke Oven
Gas (precoated)
   0.0958
   0.0219
   0.0657


   0.006
   0.0014
   0.0035
   Coke Oven
Gas (noncoated)
   0.0841
   0.0077
   0.0312

   0.0096
   0.0096
   0.0056
                                       194

-------
          Performance of the unit with regard to condensibles  and  sulphuric acid
Is given in Figure 5.
                                   FIGURE 5
                             COKE OVEN PILOT UNIT
Condensibles
qr./SDCF
Ether Fraction
Inlet
(max. )
( mi n . )
(avg.)
Outlet
(max.)
(min.)
(avg.)
Water Fraction
Inlet
(max. )
( mi n . )
(avg.)
Outlet
(max.)
(min. )
(avg.)
Inlet
(max. )
(mi n . )
(avg.)
Outlet
(max. )
(min.)
(avg.)
Blast Furnace
Gas (noncoatedl


0.0041
0.0014
0.0024

0.0017
0.0003
0.0011


0.1791
0.0225
0.0868

0.0762
0.0077
0.0289

0.1323
0.0166
0.0669

0.0528
0.0047
0.0185
                                           Coke Oven
                                        Gas (precoated)
                                           0.0035
                                           0.0005
                                           0.0015

                                           0.0027
                                           0.0003
                                           0.0013
                                           0.0973
                                           0.0574
                                           0.0685

                                           0.0973
                                           0.0312
                                           0.0422
                                            0.0486
                                            0.0363
                                            0.0432

                                            0.0392
                                            0.0232
                                            0.0282
   Coke Oven
Gas (noncoated)
   0.0081
   0.0000
   0.0028

   0.0046
   0.0000
   0.0018
   0.2366
   0.0503
   0.1322

   0.1356
   0.0122
   0.0724
    0.1636
    0.0244
    0.0978

    0.0728
    0.0260
    0.0529
                                         195

-------
An examination of the data shows that the average ether fraction  condensibles
were 27% lower when using the coated fabric filter and that the outlet concen-
tration of the water fraction condensibles was 42% less when using the coated
fabric filter.  In both cases, either with the use or without the use  of the
precoat, stack opacity was less than 5%.   The portion of the water fraction  of
the condensibles due to sulphuric acid is also given in Figure 5.  Since this
fraction would not occur in those ovens firing sulphur-free gases, the sulphuric
acid fraction may be deducted from the water fraction condensibles to  give a
true picture of the effectiveness of the fabric filter.
          Due to the extremely light grain loading, high air-to-cloth  ratios
were utilized.  Air-to-cloth ratios ranged from 3.0 to 3.5 to 1 when utilizing
a coated fabric filter and 2.5 to 3.0 to 1 when using the noncoated fabric
filter.  The pressure drop using a coated fabric filter was approximately 25%
lower when using the noncoated fabric filter at the same air-to-cloth  ratio.
In either case, bag cleaning was carried out only once every 24 hours.
          The first commercial unit using a fabric filter in this application
is now being built.  We believe that this too represents a major extension of
fabric filters into an area previously considered to be outside of the boundries
of good fabric filter application.
                           Galvanizing Line Control
          There have been infrequent attempts over the years to apply  fabric
filters to fume generated from galvanizing lines.  Some of these  have  met with
limited success and, therefore, strictly speaking this is not a new application.
However, to our knowledge, a pulse-jet filter has not been used for this service
in the United States.  We would like to review the successful application of
this type filter to a galvanizing line.  The unit has been in operation since
June 1977.  It was installed after operation of a pilot unit for ten weeks.
          Figure 6 gives both the design and the actual measured  operating con-
ditions of the unit.  It should be noted that while the actual operating air-to-
cloth ratio is approximately 20% greater than design, pressure drop is in the
design range.  The design features of this unit are shown in Figure 7.  Since
start-up, operation of the unit has been generally satisfactory.   However, it
is essential that the unit be kept completely dry.  The collected material is
                                       196

-------
                                  FIGURE  6
                              GALVANIZING LINE
                     FABRIC FILTER OPERATING CONDITIONS
Design Actual
Gas Volume (ACFM)
Gas Temperature (°F)
Total Cloth Area (sq.
Air-to-cloth Ratio
Pressure Loss (in. w.
Inlet Grain Load (gr.


ft.)

g.)
/ACF)
14,000
250 (max.)
5,040
2.78 to 1
6"
4
16,964
187
5,040
3.37 to 1
6"
2.5
                                  FIGURE 7
                              GALVANIZING LINE
                        FABIRC FILTER DESIGN FEATURES
                      Standard Pulse Jet
                      Two  Modules
                      16 oz. Dacron Si 1 iconized  Finish
                      Stainless  Steel  Cages
                      On-line Pulsing
                      Completely Insulated
                      Material  Collected —
                         Zinc Chloride
                         Aluminum Chloride
                         Ammonium Chloride
                         Elemental  Zinc

hygroscopic and readily  absorbes  moisture  from the atmosphere.   While the material
is light and fluffy in the  dry  state,  the  particles tend to agglomerate as they
take on moisture and become very sticky.
          Almost all of  the operating  problems encountered with this unit have
been due to the nature of the collected material.  Upon first start-up of the
equipment, insulation of the system was not  adequate and the collected material
                                       197

-------
 tended to get wet.  Once the defects in the insulation system were corrected,
 there have been no more problems in this area.   The other areas where difficulties
 have been encountered are in the ductwork leading to the collector where  the
 material tends to fall our or to stick on elbows and other impact  surfaces.  There
 has also been some difficulty in removing the material  from the hopper.   As long
 as the rotary valves are operated continuously,  the material  flows  freely.  If,
 however, the rotary valves are shut down for any extended period,  and  plant oper-
 ations seem to accomplish this in spite of all  instructions  to the contrary, the
 material tends to build up and bridge  in the hoppers.   Even  though  the vanes of
 the rotary valves are teflon coated, the material  also  tends  to stick  to  the vanes
 if hopper storage is attempted.
           This unit shows that a pulse-jet filter operating  at a relatively low
 air-to-cloth ratio represents  an excellent means  for controlling galvanizing
 line  fume.   We would recommend,  however,  that each  galvanizing line be studied as
 there  are individual  differences which  may dictate  the  type of equipment  to be
 employed.   It is  necessary to  use proper  operating  precautions  with this  type of
 equipment to preclude  moisture  in the system and  subsequent problems.
                       Sinter Machine Windbox Ventilation
           Fabric  filters  have been  used for  many years  to ventilate the discharge
 end of sinter machines  in  the steel industry.  In addition, we are aware of at
 least one  installation  utilizing  a woven  fabric filter to ventilate the sinter
 machine windbox.  However, within the past year, a pulse-jet type filter for
windbox  ventilation has been installed and we would like to review briefly the
 design and operation of this unit.
          The  design data is given in Figure 8.   These design parameters were
set after extensive pilot testing of a  pulse-jet collector.  Operation over the
first year has generally been satisfactory but some of the parameters  that have
adversely affected operation should be  reviewed.
                                        198

-------
                                  FIGURE 8
                           SINTER MACHINE WINDBOX
                               FABRIC FILTER
              Gas  Volume  - 200,000 ACFM
              Gas  Temperature  - 260°F
              Inlet  Load  - 0.5 gr./ACF Solid Particulate
                         - 0.02 gr./ACF  Condensible Hydrocarbons
              Filter -  14-module  Pulse Jet
              Cloth  Area  - 35,630 sq. ft.
              Air-to-cloth -  5.6  to 1
              Fabric -  16 oz.  Dacron  Felt ICR  Finish
              Pressure  Drop -  4.5" to 6" w.g.
          Extensive  operating experience indicates that  the most  important
parameter affecting  operation of  the  baghouse  is  the  amount of  oil  being  intro-
duced onto the sinter strands. As you  know, this oil  is  not completely burned
and carries over into the filtration  system in the form  of oil  vapor and, as  it
is cooled, in the form condensed  liquid aerosols. As long as there is sufficient
dry filter cake on the bags,  the  effect of  the condensed oils is  minimal.   However,
since the grain loading can  be light  at times  from the operation  of the sinter
machine, the dust cake on the bags will  be  light  and  in  that case a large quantity
of condensed oils can cause  increased pressure drop  in the fabric filter.
          While this unit has not been  tested, the  discharge stack has  remained
optically clear.  It is expected  that performance tests  will be performed in
January.  However, there would appear to be little  or no problem with condensibles
passing through the baghouse and  later condensing at  the discharge of the stack.
          In spite of the successful  operation of this baghouse,  we would strongly
recommend that most sinter line windboxes be piloted  for an extended period of
time to encounter all expected operating conditions  of the sinter machine prior
to installation of the baghouse.   In  addition  to the  problem of condensibles  noted
above, we have also seen a oilot installation  where  solids such as zinc amnonium
sulphate pass through the baghouse as a vapor at filtration temperatures  and later
desublime into a solid at the discharge stack.  Presence of these materials is
almost impossible to predict from observing sinter machine operation and charging
                                        199

-------
 practices; therefore, a pilot unit is recommended to determine the adequacy of
 a fabric filter for this application.
                                  SOo Removal
           Another novel application for a fabric filter is its use to remove
 gaseous contaminents.  Proper selection of an additive material  allows for
 chemical reaction with certain gaseous contaminents as the gases pass, at  low
 velocity, through the filter cake.   One example of this technology is the  use
 of a fabric filter with the additive Nahcolite, a naturally occuring sodium
 bicarbonate,  for removal of sulphur dioxide from boiler flue gas.
           Figure 9 shows a  typical  design of this type of system.   The flue gases
 from the boiler containing  both  particulate and sulphur dioxide  are conveyed to
 the  fabric filter in  a conventional manner.  A solids  additive system is utilized
 to air convey the reactant  material  into the filter and to utilize this material
 to form part  of the filter  cake  and act as  a reactant.   It is  also possible to
 feed the reactant into the  flue  gas  stream  from the boiler prior to its entry
 into the fabric filter.

           This  "dry scrubbing" system is  capable  of removing up  to 90% of the
 S02  contained in  the  inlet  gas stream.   Figure  10 shows S02  removal  as a function
 of the  stoichiometric  ratio  of Nahcolite  fed into the  fabric filter.  The curve
 shown  is  under  optimum feeding conditions.   It  should  be noted that at a one-to-
 one  stoichiometric  ratio approximately  73%  of the  S02  in the inlet  gas stream
 can  be  removed.   In addition, of course,  the fabric  filter will  remove solid
 particulates with efficiencies in excess of 99%.   Particulate  removal efficiency
 in the  pilot  unit of 99.7% was not considered typical since  the pilot unit was
 operated in a manner which required that the bags be completely cleaned at the
 end  of  each test cycle in order to check material balances.  As a  result of
 this operating procedure, the filter cake was essentially destroyed each time
 the bags were cleaned and this resulted in some inefficiency at the start  of
each cycle with regard to particulate removal.  This would not occur in an
operating unit since filter cake would be retained during each cleaning cycle.
          It may be of interest to examine some estimated costs for the fabric
filter-Nahcolite system.  These costs are given in Figure 11.  The basis of the
costs is a 500 megawatt unti handling 1.5% sulphur coal with S09  reduction
                                       200

-------
                                                                           Cleaned
            Flue Gas
            From Boiler
Nahcolite
Car Unloading
TI
                        Nahcolite
                        Storage






Fabric
F
ilte
	
r









Flue Gas


                                            IGrinding
                                            [Mill
                                                        Air
           Main
           I.D. Fans
       _^ To Waste
          Disposal
Injection
Fan
                                                                                                               Stack
                                     FABRIC FILTER - NAHCOLITE SYSTEM

-------
S3
o
S3
   CD
            100
             90
             80
             70
             60
             50
             40
             30
             20
                      Limit of Removal  for
                      Full Utilization  of
                      HC03 in Nahcolite
                                                              Least Squares Curve
                                                              Fit of these runs
                                                            SO? REMOVAL AS A FUNCTION
                                                             OF STOICHIOMETRIC RATIO
                                                            UNDER OPTIMUM CONDITIONS
             10
                0.2     0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0

-------
 consistent with present EPA requirements limiting SOp emissions to 1.2 Ibs.
 per million Btu's.   It can be seen that this system is estimated to be highly
 competitive with present day S02-particulate removal  systems.   It should be
 noted that a source of Nahcolite material  is not yet available and the future
 of this process hinges upon commitments to begin mining operations by those
 who hold Nahcolite  reserves.
                                   FIGURE 11
                        FABRIC FILTER-NAHCOLITE SYSTEM
                                     COSTS
           Estimated Capital  Costs

                             Annual  Operating  Costs
           Capital  Charges  @  14.9%
           Raw  Material
           Disposal
           Labor, Maintenance,  Utilities  & Misc.
$23,100,000
 $46.20/kw

$ 3,442,000
  3,003,000
  1,010,000
  1,963,000
$ 9,418,000/year
                                                        2.69 mils/kwh
                                  Conclusion
          Examination of the above five applications shows in a general way the
directions of expansion for fabric filter technology.  These five applications
certainly do not represent the only new applications for fabric filters but were
chosen because we believe that they do show the current general directions of
technology expansion.  With the increasing efficiency requirements and with re-
quirements for fine particulate control, which we believe are forthcoming, we
feel that the scope of application of fabric filters will be continually broadened
in the future.
                                        203

-------
204

-------
              Effect  of Modified  Cleaning Pulses
               on Pulse Jet  Filter  Performance

                              by

       David Leith, Melvin W.  First and Dwight  D.  Gibson

                      Harvard  University
                   School of  Public Health
          Department  of Environmental Health Sciences
                     665 Huntington Avenue
                  Boston, Massachusetts 02115
                           Abstract

Dust seepage through a pulse-jet filter can be minimized by
gradually reducing air pressure at the end of the cleaning pulse
instead of using the usual square wave pattern.  This allows the
pulsed bags to return gently to their rigid supporting cages and
avoids driving dust trapped in the fabric into the cleaned gas
stream.  Pulse modification by this method is especially effec-
tive at high filtration velocity but requires 27% more com-
pressed air than normal.  Pressure drop is unaffected.

Increased relative humidity was associated with higher pressure
drop but lower dust penetration.  Higher humidity should cause
stronger bonds between the dust deposit and its substrate.  This
may bring about a thicker dust deposit and thereby cause in-
creased pressure drop as observed.  More tightly bound particles
should be less likely to seep through the fabric> thereby reduc-
ing penetration as was also found.
                              205

-------
 Introduction


      An attractive  feature  of  pulse-jet  filters  is  their  ability


 to  operate  at  higher  filtration  velocities  (air  to  cloth  ratios)


 than do filters  cleaned by  other means.   To  increase  filtration


 velocity further is a tempting goal as the resultant  decrease


 in  installed cost can often more than compensate for  the  in-


 creased operating cost caused  by higher  pressure drop across the


 fabric.   The  filtration velocity associated with least annual-


 ized cost increases as the  number of operating hours  per  year


 decreases,  so  that  for a process operated one shift per day or


 less, relatively high velocities (100 mm/s) at relatively high


 pressure drops (^ 250 mm water)  may be appropriate.1


      However,  as filtration velocity increases penetration in-


 creases  as well  for both pulse-jet cleaned filters2'3 and for

                               ll_7
 filters  cleaned  by other means,  '  and in some cases  the pene-


 tration  increase may  become unacceptable.  Although data are


 few,  bag life may decrease as well at high filtration veloci-

 ties.8


      In a conventional cleaning  pulse, compressed air enters the


 bag  rapidly and pushes the bag outward,  away from its supporting


 cage.  Upon approaching full inflation,  the bag decelerates


 rapidly to a state of metastable rest, during which residual


 pulse air flows through the fabric  and flushes out dust loosened

by this deceleration.


     At the  end of a conventional pulse,  the backflow of pulse


air stops and normal filtration resumes.   The bag accelerates
                              206

-------
back toward its supporting cage and hits it smartly causing a

rapid deceleration analogous to that observed as the bag snaps

open.  This causes additional dust agglomerates and particles

to become loosened.  These, together with the agglomerates and

particles that were loosened but not blown free by the cleaning

phase of the pulse, may now be flushed thrugh the bag to the

cleaned air side by the filtration gas.  Dust penetration by
                                       3
this mechanism has been called seepage.

     Effective cleaning requires interaction between the clean-

ing pulse and the fabric.  The bag must be flexible enough to

inflate rapidly as the pulse begins.  It should not stretch

radially so that the bag may decelerate rapidly as it reaches

full inflation.  However, these same qualities, flexibility and

radial distortion resistance, will also allow the bag to return

to its cage rapidly as filtration resumes and this aggravates

seepage.

     Recently it was shown that almost all the dust that pene-

trates through a pulse-jet filter does so by seepage, and that
                                                      o
seepage increases with increasing filtration velocity.   This

occurs for several reasons.  First, higher filtration velocity

increases the fraction of dust feed by a cleaning pulse that

redeposits on the bags, and decreases the fraction of freed
                              q
dust that falls to the hopper.   This causes a thicker dust

deposit to build up, with more dust available to seep through.

Second, higher filtration velocity drives the cleaned fabric

back to its cage faster, causing it to hit with greater impact.
                               207

-------
 This  drives  through  more  dust.




      Dennis  and  Wilder    placed  a  1.7  liter  damping  tank  after



 the outlet of  the  pulse valve in their single bag, pilot  pulse-



 jet filter and studied the  effect  of this tank on both penetra-



 tion  and  pressure  drop.   They found that for filtration velo-



 cities between 30  and 50  mm/s, penetration was reduced by a



 factor of about  five when damped pulses were used; however,



 pressure  drop  increased about 20%.  Some of the air  released by



 a cleaning pulse was taken  up momentarily by the tank, and the



 transient reverse  pressure  gradient across the bag was somewhat



 reduced.  For  this reason,  bag cleaning was less effective; the



 greater residual dust holding was  thought to account for  the



 higher pressure drop found.  Reduced fabric stretching and



 reduced transient pressure  gradients across the bag were  thought



 to account for the reduced  penetration.



      Ideally,  a cleaning pulse should:   (1)  inflate the bag



 quickly so that it will decelerate rapidly when it snaps  fully



 open,  (2) provide time after inflation for pulse air to flow



 through the bag and flush loosened dust into the housing,  and



 (3)  return the fabric to its cage support gently to prevent



 seepage and excessive fabric wear.   A conventional cleaning



pulse  of  sufficient duration produced by a conventional pulse-



jet  solenoid  valve should satisfy the first  two objectives,  but



does not  satisfy  the  last.  Dennis  and  Wilder's damped pulses10



should satisfy the last  two objectives  but  not  the  first.



    To satisfy all three  objectives  simultaneously,  conven-
                             208

-------
tional cleaning pulses were modified in a way that retained

rapid air delivery to each bag at the pulse beginning but that

gently returned the bag to its cage.  Modified pulses described

here began normally but at the pulse end, pressure trailed off

gradually allowing each pulsed bag to deflate gradually and


return gently to its cage.

Experiments

     To test the effectiveness of modified cleaning pulses, a

three bag pilot filter fitted with polyester felt bags 2.44 m
                                     n
tall and 114 mm in diameter was used.   A schematic drawing of

the apparatus is given in Figure 1.  The test dust was fly ash

with cumulative size distribution by count given in Figure 2.

Mass concentrations of fly ash upstream and downstream of the

fabric filter were found by sampling isokinetically, onto glass


fiber papers.

     Cleaning pulses, either conventional or modified, were

delivered sequentially to each bag once per minute.  The valve

arrangement for the pulse-air manifold is shown schematically in

Figure 3.  Compressed air entered through a regulator which con-

trolled pressure at 6.8 atmospheres gauge and passed into a

reservoir from which it flowed through a normally open solenoid

valve, A, into a 1.6 L pulse air chamber.  This chamber could

be fitted with an extension which doubled its volume.  Chamber

pressure was measured on a Bourdon gauge and by a transducer

connected to an oscilliscope.

     The volumes of compressed air used for a conventional
                              209

-------
PULSE VALVE, 8
                         .PULSE  CHAMBER
                               	CHAMBER ISOLATION VALVE, A
                                      COMPRESSED AIR RESERVOIR

                                      HAMPER.
MANOMETER
FOR FILTER
PRESSURE
DROP
 —r-   BLOWER



DUST FEEDER
                                       MANOMETER FOR VOLUMETRIC
                                       AIR FLOWRATE
                                  FILTHS?
                        .HOPPER
       FIGURE 1.   Schematic drawing  of fabric filter  apparatus used.
                               210

-------
0.08
 0.01

                    J_I_JL_J	1
I	JL
    2          SO        30     SO     70       fO
        FRACTION Of PARTICLES BY COUNT SMALLER THAN
                    STATED  DIAMETER
 FIGURE 2.   Cumulative size distribution by count for fly ash.
                            211

-------
PRESSURE
6AU3E
DH
                            OPTIONAL EXTENSION
                            ISTS GMS.
                      ULSE CHAMBER, 1575CM3

                               NORMALLY OPEN
                               SOLENOID VALVE, A
PRESSURE    /PULSE
TRANSDUCER _/ VALVE
               Bi
J
                 PULSE
                 VALVE
U9f
                                                           COMPRESSOR
                                               PRESSURE
                                               REGULATOR
                                                    RESERVOIR
                                                    .37,OOO CM*
           FIGURE 3.  Valve arrangement for pulse-air manifold.

-------
pulse, a modified pulse, and a modified pulse with chamber ex-



tension were measured by connecting the outlet from each pulse



to a spirometer.  The volume of compressed air per pulse was



found to be 8.6 liters for a conventional pulse, 10.9 liters for



a modified pulse, and 20.7 liters for a modified pulse with



extended chamber volume, all measured at ambient pressure.



     For conventional pulse operation the appropriate pulse



valve, EL, B^, or B-, Figure 3, received an electrical signal



to "open" for 75 milliseconds.  A photograph of the relationship



between chamber pressure and time for a conventional pulse as



shown on the oscilloscope is given in Figure 4.  It shows that



pulse valve B, began to open about 20 ms after receiving an



electrical impulse.  Although the electrical on-time was set at



75 ms, the valve continued to pass air for about 220 ms.  This



occurred because the pneumatic valve took about 150 ms to build



up enough air pressure behind its diaphram to close, although



once closure bagan it was rapid.  Pressure vs. time traces for



valves B, , B?, .and B~, were virtually identical.



     To generate a modified cleaning pulse, one of the pulse



valves (B , Bp, or B.J was opened and 240 ms later solenoid



valve A, Figure 3, was closed causing pressure in the chamber



to drop as air bled from it to the pulsed bag.  This gradual



reduction in pulse pressure allowed the bag to move back to



its supporting cage gently.  After about 560 ms, the pulse



valve closed and pressure within the chamber stabilized.  Some



time later, solenoid A was reopened, refilling the chamber with
                              213

-------
LSE OHAMBE R PRESSURE, PSIG _
P3 * 05 09 O
3 © O © © ©
•- - • • • ..••:• ..-| • ', „•
VALVE "B"
f-OpENS
v^

TTTT

i


i fit


VALVE "B"-
JCLOSES .
^ _J


111!


*p
im
m
M
*•
M
SI |_
m
mm
m
m
m
«•
m
m
mi
a
M
m
P
m
•
w
i«
•*
^
w
IB
TTT
H»
•i
1M
BB
IB
»
IV
N»
•B
•»
BB
bSB



it i











i II I


             O            2OO          4OO          6OO
                   TMIE  SINCE VALVE ACTUATED, IfiSLLfSEOONDS
           800
FIGURE 4.  Photograph tracing of  oscilloscope display:
          for normal pulse.
pulse pressure vs. time
                                    214

-------
compressed air for the next pulse.   A photograph of the oscil-


liscope pressure-time trace for a modified pulse is given in


Figure 5-

     The declining portion of the pressure-time relationship for


the modified pulse, and by inference the speed with which the


bag returns to its cage, are determined by the pulse valve flow


characteristics and the volume of the chamber.  To determine the.


effect of chamber size on filter performance, its volume was


doubled by adding an extension.  The pressure-time trace for


this arrangement is given in the oscilloscope photo shown in


Figure 6.


     The effects of pulse modification on dust penetration and


filter resistance were determined for a range of operating con-


ditions.  Before taking data the fabric filter was operated at


constant conditions until the bags reached pressure drop equili-


brium.  This process took some hours; the length of time neces-


sary depended upon the degree to which experimental conditions


differed from test to test.  Tests were run at filtration velo-


cities of 50, 75, 100, 125 and 150 mm/s, using both conventional


and modified pulses, and for normal and extended chamber vol-


umes,  so that twenty different operating and cleaning  situations


could  be studied.  All tests were replicated and run in random


order  with approximately the same inlet dust mass flux 0.33

    ^
kg/m /hr, so that the amount of dust fed between pulses would be


the same regardless of filtration velocity.


     Increased relative humidity has been shown to reduce both
                               215

-------
              .00
         UJ
         Ul
         DC
         OL
         Ui
         09
         S

         z
         o
         Ui
         0>
                                                          CHAMBER
                                                          REFILLED
                                                                   80O
                         TIME  SINCE VALVE ACTUATED,  MILLISECONDS
FIGURE 5.  Photograph tracing  of  oscilloscope display:  pulse pressure vs.  time

          for modified pulse.
                                     216

-------
100

B

•
•
M
m
•
B
"till
MM
K
•»
^
BV
•••
00


1 1 1 1
1 1 I 1
X.

6


1 M 1
III!


BUI
i 1 1 i
VALVE V
CLOSES^

DO

8
                                                                  00
                    TIME  SINCE VALVE  ACTUATED, MILLISECONDS
FIGURE 6.  Photograph tracing of oscilloscope display:  pulse pressure vs. time
          for modified pulse with twice normal chamber volume.
                                     217

-------
 pressure  drop  and penetration  in a woven  fabric filter cleaned
 by  shaking  the bags.    Bench  scale tests on Nomex  and Dacron
 felts  also  show a decrease  in  pressure drop with increased humi-
     12
 dity.     Although it was not possible to  control the humidity of
 the  air passing through the present apparatus, relative humidity
 was  measured for each test.  Because replicates were taken, the
 data could  be  sorted into "higher" and "lower" relative humidi-
 ties for  each  replicated experimental condition.  The variation
 in relative humidity between replicates ranged from less than 1%
 to 32%.
 Results
     Table  1 shows the fractional mass penetration, equilibrium
 pressure  drop  in mm water column, and per cent relative humidity
 measured  for each test.
     Figure 7  is a plot of penetration against filtration velo-
 city with pulse  type as parameter.   An analysis of variance per-
 formed on the  data after taking logarithms showed that penetra-
 tion increased significantly with increased filtration velocity.
 However, at all velocities tested penetration was significantly
 lower with modified pulses than with conventional pulses.   The
 penetration reduction due to pulse  modification is increasingly
 effective as velocity increased.  Pulse chamber volume within
 the range studied had no significant effect on penetration for
either normal or modified pulses.   Penetration is  plotted
against filtration velocity  with relative  humidity as  parameter
in Figure 8.  The penetration increase  with increasing velocity
                              218

-------
                                             Table 1.
          Fractional Mass Penetration/Pressure Drcjp, MM Water Gauge/$ Relative Humidity
Filtration
Velocity
cm/s
    7-5
   10
   12.5
   15
Relative
Humidity
H/L
Lower
Higher
Lower
Higher

Lower
Higher

Lower
Higher

Lower
Higher
            Normal Pulses
                               Modified Pulses
Std. Pulse
Volume
0.011/35 mm/38$
0.006/65 mm/W
0.011/82.5 mm/ 38$
0.012/225 mm/60$

0.016/80 mm A 3$
0.027/260 mm/53$

0.029/160 mm/52$
0.005/500 T
0.178/680 wm/h9%
0.006/385 mm/70$
2 x iStd.
Volume
0.008/35 mm/38$
0.005/65 mm/5W
O.OlU/75 mm/33$
0.011/97.5 mm/50^

0.023/115 mm
0.
0.083/^00
0.003/385
0.072/^75
0.027/615 mm/60$
Std. Pulse
Volume
                                                                  0.007/35 mm/33$
                                                                  0.007/65 T
0.007/103
0.007/275 mm/ 56$

0.033/150 mm/29$
0.003/230 mm/67$

O.OUl/150 mm/38^
0.005A65
O.OU8/250 mm/55^
0.036/685
2 x Std.
Volume
0.000/75 mm/59$
0.001/70 mm/59^
0.009/70 r
0.007/180

0.032/160 mm/26^
0.007/300 mm/62$
O.OiiO/195
0.009/280 mm/69^'

0.035/625 mm/ 37$
0.033/695

-------
             o
                                                  FRACTIONAL  MASS  PENETRATION
NJ
K>
O
             B
             l-i
             BJ
             rt
            H-
            H1
            rt
            O
            O
            13

            M
            0)
            CD
            m
            13
            CD
            i-i
            ro
            i-i

-------
     0.08
  DC
  u)  0.06
  Ul
  a.
     0.04
£
     0.02
              LOWER  RELATIVE
               HUMIDITY
                                               RELATIVE.
                                               HUMIDITY
                 50              100
                  FILTRATION   VELOCITY
                                                    !30
FIGURE  8.  Penetration vs.  filtration velocity,  relative humidity
          as parameter.
                              221

-------
 is  significantly more rapid at low relative humidity.



     As expected, pressure drop increased rapidly with filtra-



 tion velocity as is shown in Figure 9.  An analysis of variance



 performed on the logarithms of the pressure drop data showed



 that this increase was significant.  There was not a significant



 pressure drop difference between normal and modified cleaning



 pulses, or between normal and twice normal pulse volumes.



     Relative humidity is the parameter against which pressure



 drop and filtration velocity are plotted in Figure 9.  For both



 relative humidity conditions, pressure drop increased with velo-



 city.  However, contrary to observations for collection of fly



 ash on woven bags cleaned by shaking,   pressure drop in the



 pulse- jet filter was significantly higher at higher relative



 humidity .



 Discussion



     Pulse form modification is an effective way to reduce dust



 seepage through a pulse- jet filter, especially at higher filtra-



 tion velocities.  At the highest filtration velocity tested,



 150 mm/s, pulse modification lowered fractional penetration by
     Pulse cleaning effectiveness is associated with fabric



deceleration as the bag snaps fully open, and with pulse dura-



tion sufficient to assure that loosened dust is flushed from the



fabric into the filter housing.   Because the initial part of a



modified and a conventional pulse are the same, they should in-



flate and flush bags equally well.  Modified pulses backflush
                              222

-------
      800f
              HIGHER RELATIVE
               HUMIDITY
                             OV    LOWER RELATIVE
                             ^    HUMIDITY
                   50              100
                     FILTRATION  VELOCITY  MM/SEC.
FIGURE  9.  Pressure drop vs. filtration velocity, relative humidity

          as parameter.
                              223

-------
 bags longer than normal pulses  because  additional  backflow


 occurs while pulse pressure  falls  during  the  final stage  of  the


 modified pulse.   However,  if enough  backflow  occurs  to  move


 loosened dust away from the  fabric,  additional  pulse air  brings


 diminished returns as  has  been  shown by Dennis  and Wilder.10


 For these reasons, pressure  drops  across  bags cleaned by  con-


 ventional and modified pulses were about  the  same.


      There was no difference in penetration between  bags  cleaned


 by  modified pulses from the  1.6 L  pulse chamber and  modified


 pulses  from the  3.2 L  chamber.  This  implies that  chamber size


 might  be  decreased further to save on compressed air, while  re-


 taining the form and effect  of  modified pulses.


     For  a dust  particle or  agglomerate to be separated from the


 fabric,  interparticle  adhesive  forces must be overcome by the


 deceleration  force  acting on dust as  the bag snaps open at the


 beginning  of  a cleaning pulse,  or snaps back onto its cage at


 the end of  the pulse.  In the former  case, the dust flies into


 the housing from which it can fall to the hopper; in the latter


 case, the dust separated from the fabric penetrates the filter


by seepage.  It has been demonstrated that increased relative


humidity leads to stronger particle-to-particle and particle-to-

            12 13
fiber bonds,   '   which should make separation of the dust depo-


sit from the fabric more difficult.  Flay ash  may have adsorbed


sulfuric acid, which absorbs  water at high relative humidities,


there strengthening interparticle  bonds.


     Because the  dust deposit is more firmly anchored to the
                              224

-------
fabric at higher relative humidity,  seepage penetration should


decrease.  The data confirm this trend.   At the same time,


stronger interparticle bonds caused by increased relative humi-


dity should make the dust deposit more difficult to clean from


the fabric.  A dust deposit with higher areal density would


account for the higher pressure drops at high relative humidity


found in these experiments.


     Data for woven fabrics cleaned by shaking   and for bench

               ~i O
scale new felts   show that pressure drop decreases with in-


creasing relative humidity, opposite to the trend found here.


Higher interparticle forces could cause a more porous dust depo-


sit structure,12 one more resistant to compaction with continu-


ous dust addition.  Theory15 confirms that for the same amount


of deposited dust, a thicker, more porous  structure should have


less pressure drop than  a thinner, more dense  one.  However,  in


the pulse-jet filter cleaning is not wholly effective at remov-


ing deposited dust.  The effect of increasing  the amount of dust


retained on the bag at high humidity may be more important than


the effect of the more porous structure which  that dust forms.


Summary


     Pulse-jet  filter show higher seepage  penetration at higher


filtration velocities.   This seepage occurs when the bags return


to and strike their rigid  support cages at the end of a cleaning


pulse, as  loosened dust  is driven from the bags into the  cleaned


gas stream.  Seepage can be reduced by cleaning the bags with


pulses which are identical with conventional pulses at the be-
                               225

-------
 ginning, but which gradually decrease in pressure at the pulse

 end, allowing the bags to return gently to their cages.  Modi-

 fied pulses are increasingly effective at reducing dust penetra-

 tion as filtration velocity increases.  At the highest velocity

 tested, 150 mm/s, modified pulses reduced penetration by 46$ but

 had no effect on pressure drop.

     Increased relative humidity caused significantly lower

 penetration but increased pressure drop.  Because increased

 humidity causes an increase in interparticle bond strength, dust

 collected at high humidity may be bound more tightly in place

 and be less likely to seep through the fabric, causing reduced

 penetration.  However, when dust is tightly bound it becomes

 more difficult to separate from the fabric.  At high humidities,

 an equilibrium dust deposit with higher areal density may build

 up on the bags causing higher pressure drop.

Acknowledgement

     This work was supported by EPA Grant R 804700-01,  Dr.  James

H. Turner,  Project Officer.

References

 1.  Leith,  D.  and M. W.  First, "Pressure Drop in a Pulse-Jet
       Fabric  Filter", Filtration and Separation, l4(5):473
       (1977).                                     —

 2.  Leith,  D.,  S.  N. Rudnick and M.  W.  First, High Velocity,
       High  Efficiency Aerosol  Filtration,  EPA Report EPA 600/
       2-76-020,  Office of Research and Development,  Washington,
       D.C.,  1976.

 3.  Leith,  D.  and M. W.  First, "Performance  of a Pulse-Jet Fil-
       ter at  High Filtration Velocity,  III.  Penetration  by
       Fault  Processes",  J.  Air Poll.  Control Assoc . , _2_7(8) : 754


 4.  Spaite, P. ¥.  and G.  Walsh,  "Effect  of Fabric  Structure  on
       Filter  Performance",  Am.  Ind.  Hyg. Assoc.  J.,  2^:357 (1963)
                               226

-------
 5.  Ensor, D. S., R. G. Hooper and R. W. Scheck, Determination
       of  the Fractional Efficiency, Opacity Characteristics
       Engineering and Economic Aspects of a Fabric Filter
       Operating  on a Utility Boiler.  EPRI Report FP-297,
       Palo Alto, CA, 1976.

 6.  McKenna, J.  D., J. C. Mycock and W. 0. Lipscomb,  "Perfor-
       mance and  Cost Comparisons Between Fabric Filters and
       Alternate  Control Techniques", J. Air Poll. Control
       Assoc., 2J£:ll44  (1974).

 7.  Turner, J. H., "Extending Fabric Filter Capabilities", J.
       Air Poll.  Control Assoc.,  24:1132 (1974).

 8.  Hobson, M. J., "Review  of Baghouse Systems  for Boiler
       Plants", in Proceedings, the User and Fabric Filtration
       Equipment  II, Air Pollution Control Association,  4400
       Fifth Ave., Pittsburgh, PA  (1975).

 9.  Leith, D. and M. W. First, "Performance of  a  Pulse-Jet Fil-
       ter at High Filtration Velocity, II. Filter Cake  Redepo-
       sition", J. Air  Poll. Control  Assoc., 27.(7):636 (1977).

10.  Dennis, R. and J.  Wilder, Fabric Filter Cleaning Studies,
       EPA Report EPA-650/2-75-009, Office of  Research and
       Development, Environmental  Protection Agency,  Washington,
       D.C.  (1975).

11.  Durham  J. F. and R. E.  Harrington,  "Influence of Relative
       Humidity  on Filtration Resistance and Efficiency",  Paper
       4e presented  at  63rd  Annual Meeting of  American Institute
       of Chemical Engineers, Chicago,  IL, 1970.

12.   Ariman,  T.  and  D.  J.  Helfritch,  "How Relative Humidity  Cuts
       Pressure  Drop  in Fabric Filters", Filtration  and Separa-
       tion,  14:127  (1977).

13.   Corn, M.  and F.  Stein,  "Re-entrainment  of Particles from a
       Plane  Surface",  Am. Ind. Hyg.  Assoc.  J'.,  26:325 (1965).

14.   Lflffler,  F., "Investigating  Adhesive Forces Between Solid
       Particles  and  Fiber Surfaces",  Staub  (English Transla-
       tion),  2^6:19  (1966) .

15.   Stephan,  D.  G.,  G. W. Walsh  and  R.  A. Herrick,  "Concepts in
       Fabric  Air Filtration",  Am.  Ind.  Hyg. Assoc.  J.,  21:1
       (I960).
                              227

-------
228

-------
  CURRENT  AND FUTURE  EPA FILTRATION  RESEARCH
                James  H.  Turner
       Environmental  Protection Agency
Industrial  Environmental  Research Laboratory
     Research Triangle Park,  N. C. 27711
        3rd EPA Fabric Filter Symposium
               Tucson, Arizona
             December 5-6, 1977
                         229

-------
               CURRENT AND FUTURE EPA FILTRATION RESEARCH

 Introduction

      The Third EPA Fabric Filter Symposium is itself largely a review of
 current and future EPA filtration research:

      Kenneth Ladd and Jack Smith:  reasons for using a baghouse on a
 large utility boiler burning low sulfur western coal.

      Richard Dennis:   formulation of a mathematical  model  of fabric
 filtration for combustion sources using glass bags.   This  model is based
 on extensive field and laboratory testing.

      John Mycock:   performance of a pilot baghouse on  a trash-to-energy
 incinerator.

      Dale Harmon:    use of a mobile pilot baghouse to  perform field
 tests  and relate  field and laboratory results.

      John McKenna:   demonstration of a high velocity fabric  filter
 system on two  industrial  boilers.

      Robert  Bradway:   performance of a fabric  filter system  on  a  small
 electric  arc furnace.

     Melvin  First,  David  Leith  and  Steven  Rudnick:   high velocity  filtration
 in a pulse-jet baghouse and  fundamentals of fabric filtration and  cake
 formation.

     George Lamb:   effects of  fiber  properties  (rather than fabric
 properties) on filtration  performance.

     Robert Donovan:  electrostatic effects  in a pulse-jet baghouse.

     Dennis Drehmel and Mike Shackleton:  filtration under conditions of
high temperature and high pressure.
                                      230

-------
Purpose

     These various programs all fall into just a few categories:

               Assessment of full scale projects.
               Field and laboratory testing and measurements.
               Fundamental studies.

     Most of the work is done  in external programs; i.e., contracts,
grants or interagency agreements.  The purpose of EPA's fabric  filtration
research is to aid in the improvement of particulate control technology
by supporting appropriate projects.  These projects may originate either
within or outside EPA.

Other Projects

      In addition  to  the  projects identified above,  two others  are being
supported by  IERL-RTP.   These  are  fabric comparisons and math  modeling
being done  in Poland, and work on  electrostatic  effects being  done  at
Carnegie-Mellon University.

      The Polish work is  being  performed  at the  Institute of Cement
Building Materials  (IPWMB)  in  Opole, Poland,  and the Principal  Investigator
is Jan  Koscianowski.  At  the  laboratory and pilot level  he  is directing
an effort to  compare the performance of  both  U.S.  and  Polish  fabrics
in Polish equipment.  There  are several  differences between U.  S.  and
Polish  practice:   the Poles  use fabrics  with  plied  yarns and high  counts;
they clean  (at  least in  this case)  with  a  short stroke,  vertical  shake.
There is  also some work  with reverse air cleaning.   Comparisons are
being made  with cotton,  polyester,  glass and  Nomex  fabrics. As well  as
comparing fabrics,  the Poles are endeavoring  to describe the filtration
process mathematically.   The final  reports for  the  work  should be  available
by mid- to  late 1978.
                                       231

-------
      Probably the most challenging work being done, other than convincing
 the new purchaser that baghouses are the perfect answer, is in the area
 of trying to understand the role and importance of electrostatics in
 fabric filtration.  Gaylord Penney and Edward Frederick (Carnegie-
 Mellon) have been jointly exploring this area:  one from the viewpoint
 of determining basic electrical effects, and the other of empirically
 classifying various dust/fabric systems according to electrostatic
 properties and applying these observations to select the optimum fabric
 to collect a specific dust.  As with the earlier Frederick paper (1),
 the final  report from Carnegie-Mellon (due about April) is bound to be
 read and re-read.

 Future Work

      The work at Southwestern Public Service will  continue for at least
 the next 2 years, and there are options  for extended testing and for a
 slaved pilot baghouse to  test various  operating modes  or fabrics.

      The Dennis  model  for  fabric filtration will  be  tested  against  a
 variety of operating conditions and  also will  be  put in simplified  form
 for use by a greater number of people.  Computer  tapes  of  the  model  will
 be available through the National Technical  Information Service.

      The mobile  baghouse will  be used next  to  compare the filterability
 of eastern  and western  low  sulfur coal flyashes from pulverized coal
 boilers. A  report, based on  tests at Southwestern Public Service Company's
 Harrington Station and  at Michigan State University's boiler house will
 be prepared  during the  summer  of 1978.

     The high velocity  Enviro-Systems baghouse at Kerr  Industries will
 be operated for a second year, and other fabrics (besides the current
 Teflon and GoreTex) will be tested.   There is also an option for SO
 removal using an injected sorbent ahead of the baghouse.

     Fundamental  work on high velocity filtration, mechanisms and fiber
property influence will  continue under the  grants  held by Harvard and
                                      232

-------
the Textile Research Institute.   The in-house work at EPA will continue
on electrostatic effects, new fabric evaluation, and investigation of
fine particle penetration.  Additional work will be done in the area of
high-temperature filtration and high- temperature/high- pressure filtration
both in-house and under contract.

     One new contract that is expected will be for pilot scale assessment
of dry sorbent collection of SOV in a baghouse.  This work will be a
                               A
three party endeavor involving the City of Colorado Springs,  Buell/Envirotech
and EPA.  Given the water problems, high resistivity coal and close
source of a good sorbent  (nahcolite) in the west and southwest, the dry
sorbent/baghouse approach should be attractive.  The pilot assessment
will consider disposal methods for spent sorbent/flyash as well as the
process techniques and economics.  The contract for this work should be
signed in mid-1978.

Summary

     EPA's programs in fabric filtration are meant to encourage development
and dissemination of technology primarily  in areas mandated by the Clean
Air Act and its amendments.  With a few exceptions, the individual
projects are described in detail in other  papers presented at the Third
EPA Fabric Filter Symposium.  Emphasis has been on control of combustion
sources.

     Now that baghouses are beginning to be used on utility and industrial
boilers, perhaps the greatest need, and one voiced by many people at the
Symposium, is for reliable field measurements  to be taken and distributed
to designers and potential users.

References

     1.   Frederick, E. R., "How Dust Filter Selection Depends on Electrostatics,"
Chemical Engineering, pp. 107-114, June 26, 1961.
                                      233

-------
234

-------
      CONTRIBUTING  ROLE  OF  SINGLE  FIBER PROPERTIES  TO
                NONWOVEN FABRIC  PERFORMANCE	

       G.  E.  R.  Lamb,  P. A. Costanza,  and D.  O'Meara

                 Textile Research  Institute
                   Princeton,  New  Jersey
     An early study [1]  established that geometric properties of

the constituent fibers in a nonwoven fabric could affect its

filtration performance.   Table I shows results of a 2* factorial

experiment which examined the effect of cross-sectional shape,

surface roughness, crimp, and fiber diameter.  A second phase [2]

of this work therefore examined these effects over a wider range

of variables.  Figure 1 shows that the effects of surface roughness

and of cross-sectional shape on capture efficiency are evident in

the capture of particles smaller than 1 ym.  Figure 2 shows that

in comparison with a filter made of round fibers, one made of

bilobal fibers is less efficient but one made of tri or pentalobal

fibers is more efficient.  The poor performance of bilobal fibers

appears to be due to the strong dependence of single fiber

efficiency on fiber orientation.  Figure 3 and Table II show  that,

while the presence of crimp gives an advantage over a filter  made

of uncrimped fibers, the crimp frequency does not affect performance,

     Figures 4 and 5 show the effect on penetration and on specific

cake resistance of varying the fiber diameter for two weights of

polyester fabric, at constant fabric density.  Measurements with

fibers having a range of surface roughness were not made because

such fibers are not available.


                             235

-------
     A one-bag baghouse was made and two bags were tested, one
made of round, the other of trilobal polyester fibers.  Figures 6
and 7 show that the trilobal bag gave lower pressure drop and
higher efficiency, the penetration for the trilobal bag being
approximately one half that for the round bag.  This is the only
baghouse-scale confirmation of an effect of fiber geometry.  It
indicates that this approach can be expected to give better
performance in commercial application.  The cost of the modifi-
cation would be almost zero.
     Current efforts are aimed at finding explanations for the
effects described above.  To date, only the effects of cross-
sectional shape have been studied in greater detail.  The effi-
ciency E of a filter is given by In(l-E) = -2ax/(l-a) irR where
unpacking density, x = filter thickness, and R = fiber radius.
Figure 7 shows that the ratio of penetration (round to trilobal)
between two 15-oz. fabrics is about 2.  This would be consistent
with a difference in single fiber efficiency of about 20%, which
is roughly the increase in effective diameter due to the change
in shape.  However, measurements on layered filters indicate that
the different performance is only associated with the presence of
dust deposits.  Figure 8 shows calculated single fiber efficiencies
for the various layers in a 4-layer filter, and the trilobal
efficiency is higher for the trilobal only in the upstream layer,
where the dust cake is located.  An interesting consequence of
this finding is shown in Table III, which compares performance
                             236

-------
of layered fabrics in which the upstream layer was different



from the rest of the filter.  The table shows that the performance



of the filters is dominated by the thin upstream layer.  These



facts prompted a study of dust cake structure, aimed at the



determination of any features of the structure built on different



substrates that would explain the lower pressure drop given in



some cases by trilobal fabrics as well as the higher efficiencies



and the patterns described above.  Microscopical examination has



so far proved unsuccessful in describing any such features.



     In a separate approach, single fiber efficiencies have been



calculated for capture in the presence of an electric  field.



Figure 9 shows collection efficiency for fibers having different



numbers of lobes, and shows that it increases both with increasing



number of lobes and with increasing lobe height.  It is possible



that the effects we have seen may originate  from  interactions of



charged particles with electric fields due to previous deposition



of charged particles.  Experimental verification  of this hypothesis



is the object of  future work.
                             237

-------
                         REFERENCES
1.  B. Miller, G. E. R. Lamb, and P. Costanza, "Influence of
    Fiber Characteristics on Participate Filtration," EPA-650/2-72-
    January 1975.

2.  B. Miller, G. Lamb, P. Costanza, and J. Craig, "Nonwoven Fabri<
    Filters for Particulate Removal in the Respirable Dust Range,"
    EPA-600/7-77-115, October 1977.
                             238

-------
                      FIGURE CAPTIONS
Fig. 1  Capture efficiencies of three nonwoven PET
  fabrics made of various fibers, as shown, when
  filtering a flyash aerosol.
Fig. 2  Ratios of outlet concentrations for filters
  made of fibers with 2, 3 and 5 lobes to outlet
  concentrations for round fiber filter.
Fig. 3  Capture efficiencies for nonwoven rayon filters
  made of fibers with various levels of crimp as shown,
  when filtering a flyash aerosol.
Fig. 4  Penetration (equal to 1-efficiency) for PET
  and polypropylene filters of constant weight and
  density but made of fibers of different diameters.
Fig. 5  Specific cake resistance for the filters in
  Figure 4.
Fig. 6  Pressure drops at beginning and end of filter
  cycle (AP. and AP,.) for conditioned bags made of
  round and1trilobal PET fibers.
Fig. 7  Outlet concentration ratios for bags in Figure 6,
Fig. 8  Single fiber efficiencies for each layer in
  layered filters made of round and trilobal fibers.
                             239

-------
Fig. 9  Calculated single fiber efficiencies  for  fibers
  with cross sections p = 1 + e Cos m  (+c) where m =
  number of lobes and e indicates the  lobe depth.
                             240

-------
CAPTURE EFFICIENCY (Tenth cycle)

           P              P
           bo              c£
                                                        o
  o
  INJ
  •*»
o
                           O x

-------
N)
.0
NJ
        Co (Normalized
             for round)

         5,0
        4.0
        3,0
        2.0
         0
          oh-
G Bllobal
A Trilobal
  Pentalobal
                                                     ©
                  .024  .042   .075   .133   .24   42       i.O   1.6   2.7 4.0

                                     PARTICLE DIAMETER  Cftm)

-------
    O
       CAPTURE EFFICIENCY (%)
                   oo
                   O
O .
r rr,
m

g
>
m
   CM
   '91
       en
                                      GO
                                      c~>
                                      3E
                                           f)
                                           "O
                                           oo
                                           n
                                           3:
                                                12
                                                -o
                                                oo

-------
       th
(I-E)( 15" cycle)
 ,o2
 10
   4
             0 PET
             0 PP
3 oz/yd
                            0
                               20
               FIBER DIAMETER
                                         14 oz/yd
                                                Z
       30
                      244

-------
  K( 15th cycle)
(l04N-s/kq.m)
   14 -
    12
    10
     8
    4
O  PET
A
                      3oz
                   1
                   10            20
                  FIBER DIAMETER (
                                       14 oz/yd'
             30
                       245

-------
  AP
(mmH20)
                                           Round
                                              Round
                                              Trilobal
            15        30       45

               FACE VELOCITY ( mm/s)
60
75
                         246

-------
ISJ
        Cft(trilobol)
         Co(round)
          1.2 r
          1.0
          OB
         0.6
         0.4
          O.2
.01
    30mm/s
    I5mm/s
.024    .04 .06.08.10    .2
                                                   .4   .6 .8  1.0
                                PARTICLE DIAMETER  (ftm)

-------
SINGLE FIBER
  EFFICIENCY
   10
  OB
  0.6
  0.4
           .02
x TRSLOBAL

©ROUND
.04    .06    .08     JO-
DEPTH INTO FILTER  (cm)
                       .12  '   .14
                          248

-------
1.8 r
   0.0  0.05  0.1    0.15   0.2   0.25   0.3
                    249

-------
250

-------
         inocHMc  h'Ci'.Uitanco  (K2)  of  Kilter Dust  Cakou:
              Comparison  of Theory and Experiments

                               by

            Stephen N.  Rudnick* and Melvin W.  First

                       Harvard University
                     School of Public Health
           Department of  Environmental Health  Sciences
                      665 Huntington  Avenue
                   Boston, Massachusetts 02115
                           .Abstract

The specific resistance (K2) of filter cakes formed from elutri-
ated AC-Fine test dust was measured at air to cloth ratios be-
tween 7.1 and 56 mm/s (1.4 and 11 fpm) in an apparatus in which
other operating conditions including aerosol size distribution
remained invariant.  Cake porosity and particle size distribu-
tion, shape, and density, which affect the specific resistance of
dust cakes, were also measured.  It was found that the Kozeny-
Carman equation, which treats a dust cake as a collection of
capillaries, seriously underestimated specific resistance.  It
is believed that this discrepancy occurs because the high poro-
sity of air-deposited filter cakes makes them more closely re-
semble an assembly of individual particles than a collection of
capillary passages.  A simple model based on Stokes' law indi-
cates that the Kozeny-Carman equation predicts K2 values for
air-deposited filter cakes which are less than the minimum theo-
retical specific resistance.  Predictions of K2 made from the
Happel "free surface" model, which treats the dust cake as an
assemblage of particles rather than capillaries, compared favor-
ably with experimental values after accounting for nonuniform par-
ticle size, nonspherical shape, and gas slip.  No empirically
fitted constants derived from the measured values of K2 were re-
quired .
*To whom inquiries should be addressed


                               251

-------
 Nomenclature

 Roman


 a     cloth  area  with  dust  deposit, m2


 A     constant  which characterizes interaction between  gas and
        solid surface,  dimensionless

 B     permeability  coefficient  in Darcy's  equation, m3i-s/kg

 Cs    slip correction  factor, dimensionless

 D     particle  diameter,  ym

 Dg    diameter  of sphere  with same volume  as particle,  ym

 Dp    projected area diameter,  ym

 D     sedimentation diameter, ym


 Dvl   volume-length mean  (sedimentation) diameter in Equation (15),
        ym


 DVS   volume-surface mean diameter in Equation (10), ym

 k     Kozeny constant,  dimensionless

 K2    specific  resistance of dust cake, sec"1

 Kn    modified  Knudsen  number,  dimensionless

 L     dust cake thickness,  m

 m     mass of dust  cake,  kg

 n     number fraction,  dimensionless

 N     number of particles in dust cake

 R     resistance  factor,  dimensionless

 S     specific surface area of particles, m"1

V     superficial velocity, m/s

w    weight fraction,  dimensionless

W    areal density, kg/m2
                              252

-------
Greek

a    solidity, dimensionless

A?   pressure drop, Pa

e    porosity, dimensionless

A    mean free path of gas, m

y    viscosity, Pa-s

p    particle density, kg/m3

T    particle relaxation time, s

T    particle relaxation time based on DVI, s

    shape factor relating D^ to D  in Equation  (19), dimension-
 vl    less                 P     S

     shape factor relating D  to DVS in Equation  (11), dimension-
X    dynamic shape factor, dimensionless

Subscript

i    particle size category
                               253

-------
 Introduction


      Determination of  the  permeability  of porous media  to  fluids

 has  produced a  voluminous  literature1'2 concerned  to  a  large


 extent  with  the prediction of permeability  from the properties

 of the  porous structure  and gaseous medium  and confirmation of

 these relationships by experiment.  Various theories  and empiri-

 cal  formulations have been proposed, but the general  consensus,

 until recently,  has been that the Kozeny-Carman equation^  is the


 most reliable,  and considerable  experimental data  have  been pub-

 lished  to  support  this contention.


     The Kozeny-Carman equation  was first applied  to  the filtra-

 tion of dusts on fabrics by Williams, Hatch, and Greenburg^ and,

 despite a  lack  of  experimental verification, has found wide

 acceptance '  '  .   Generally, only the permeability of the dust

 cake has been measured as  it is  considerably more  difficult to

 determine  the parameters required for insertion in the Kozeny-

 Carman  equation.   In particular, measurement of filter cake

 porosity is  especially difficult because the dust cake is nor-

 mally a very thin,  fragile structure supported on a fabric which

 is not  flat and whose fibers mingle to varying degrees with the

 particles in the cake.   For these reasons,  the porosities of


 dust deposits on operating fabric filters have not  previously
                            o
been measured experimentally .

Darcy's  Law


     The fundamental relationship governing  noncompressible,

creeping flow through porous media,  Darcy's  law,  states  that  the
                             254

-------
rate of flow is directly proportional  to  the  pressure  gradient
causing the flow ,  i.e.:
          V = B^                                           (1)
               LJ
where V is superficial velocity, B is  Darcy's permeability coef-
ficient, AP is pressure drop, and L is thickness of the porous
medium.  Because the thickness of a dust cake is difficult to
measure, Williams, Hatch, and Greenburg4 substituted the areal
density, W,  (i.e., weight of dust on the filter per unit of
cloth  area)  from the following expression:
           T  -    ,w                                          (2)
             -^n^y
where  p   is  the density of  the particles in  the dust  cake and
 e is the  dust  cake porosity (void fraction).  After substituting
 Equation  (2)  into  (1),  Darcy's  law becomes:
           K   - AP                                            (3)
           K2 ~ VW
 where  K2  = [Bp (1-e)]"1.   The  quantity "K2",  the  specific resis-
 tance  of  the dust  cake, has been employed  extensively in  fabric
 filtration studies4'5'7.  It was first  called "K2"  by Billings
 and Wilder9 and this designation has  become  synonomous with spe-
 cific  resistance.   The reciprocal of  K2,  the permeability, of the
 dust cake, has also been used for characterizing  dust cakes .
 Equation  (3) is a definition of specific resistance and Darcy's
 law simply states that it is constant for a  given porous  and
                               255

-------
 flow medium.



 Stokes '  Law



      Because a dust cake is composed of small particles,  Stokes'



 law can be used as a model to predict specific resistance if it



 is assumed that there is no hydrodynamic interaction between



 particles.  For spheres  of uniform size, the sum of the drag



 forces on each particle  in a unit mass  of dust cake is  equal to



 pressure drop per unit of areal  density, or:



           M = Z  Drag Force _ (3TryVD/Cs)N

           W    I,  Mass         7T~1  :                        (**)
                               (^D3pp)N





 where  N  is number of particles in the dust  cake,  y  is gas  visco-



 sity,  D  is particle diameter,  and C   is  slip  correction factor.
                                   O


 Combining Equation (4) with the  definition  of K2  (Equation 3)


 yields:
           (K2)        =        =
             2 minimum   p D^C    rC                         -(5;
                         PS     s




where T =  ppD2/l8y.  Inasmuch as the velocity on the surfaces of



the particles is zero (ignoring slip), as the particle get closer



together the absolute value of the velocity gradient between par-



ticles increases resulting in larger shear stress in the fluid and



greater drag on the particles10.  Therefore, Equation (5) is an ex-



pression for the minimum specific resistance because the particles



are assumed to be far apart (i.e.,  e + 1).  It is also important



to note that the minimum specific resistance is equal to the



reciprocal of the slip-corrected particle relaxation time,  T,
                              256

-------
which plays a prominent role in the mechanics of aerosols.   Al-
though K2 depends on .the density of the particles,  as does  the
terminal settling velocity of a particle, pressure  drop is  inde-
pendent of density.  For a dust cake composed of unit specific
gravity spheres, the minimum specific resistance for ambient air
flow based on Equation (5) is shown in Table I.
     It may be deduced from Equation (5) that smaller values of
the minimum specific resistance will be obtained whenever small
particles accumulate in clusters which mimic larger particles.
As observed by Carman and Malherbe11, this situation can exist
with uncompacted fine powders because of the presence of a rela-
tively  large surface force compared to the gravitational force
on the  particles.  A different  situation exists  in a dust cake
because the flow,  itself, creates  the porous medium.  Therefore,
when flow resistance in one portion of the dust  cake is less
than in another, the flow rate  is  greater in that portion with
lower  resistance,  and  hence a  larger number  of particles will
deposit in  this  region causing  an  increase in  flow resistance.
Consequently,  the  distribution  of  particles  in the dust cake
tends  toward uniformity.  An exception to this  tendency occurs  when
the  aerosol being  filtered  is  composed predominantly  of complex
aggregates  because particle  deposition  in the  internal recesses
of  an  aggregate  may  not be  possible.
      Inasmuch  as Stokes'  law places  a  minimum  constraint on any
model  proposed for predicting  pressure  drop  across  a dust  cake,
                               257

-------
              TABLE I.  Minimum Specific Resistance
                                       Specific Resistance
Particle Diameter, ym          (ms)  1      in.  water/(fpm-lb/ft2)
        50                       0.13               0.013
        10                       3.2               0.32
         5                      13                 1.3
         1                     280                28
         0.5                   980                98
                              258

-------
a new quantity,  the resistance factor,  R,  may  be defined by  the



following equation:





          K2=J                                            (6)
R is a number greater than one which,  when multiplied by the




minimum specific resistance, defined in Equation (5)3 gives



the specific resistance of the dust cake (for C  equal to
                                               S


unity).  R generally is only a function of dust cake porosity,



although the porosity is influenced by the conditions prevailing



when the dust cake is formed (e.g., velocity, humdity) and the



properties of the dust.  The value of T is affected solely by



the properties of the dust.  The slip correction factor, C , is
                                                          S


a function of both particle size distribution and porosity and



will be discussed in detail later.




Kozeny-Carman Equation



     The Kozeny-Carman equation  is a semi-empirical relationship



which assumes that a dust cake can be represented by a collection



of parallel capillaries whose total surface area is equal to the



surface area of the particles and whose total volume is equal to



the void volume of the dust cake.  It can be written as follows:
       .






where k is the Kozeny constant which Carman  determined to be



equal to 4.8 for spheres and 5.0 for various irregularly shaped



particles over a wide range of experimental conditions.  Substi



tuting the former value into Equation (7),  it is found that the





                              259

-------
 oretlcally the Kozeny-Carman equation is  invalid  at  porosities


 greater than 0.92 because  higher porosities  would correspond  to


 a value of R less than unity.


      The porosity above which  the Kozeny-Carman equation is no


 longer useful is  somwhat nebulous.  Billings  and  Wilder12 stated


 that  the Kozeny-Carman equation  does  not  apply to high porosity


 dust  cakes  because  the theory  is  based  on discrete passageways.


 Specifically,  they  suggest  caution  for  porosities in excess of

             13
 0.7.   Carman   contended that  his  theory  does not break  down  until


 porosity exceeds  0.8.


      Although  in  situ  porosities  of dust  cakes on cloth  filters


 have  never  been reported in  the literature, there are some clues


 to the  range  of porosities which  can be expected.  Billings and

       1*1
 Wilder    indicated  that  the  porosities  of granular powders vary


 from  about  0.40 to  0.99.  Orr15 listed porosities  from 0.51 to


 0.94  for  dust  filter cakes composed of particles  with diameters


 from  0.24 to 33 ym.  Although these dusts were collected on fab-


 rics, the porosities were apparently those that resulted when


 the same dusts were placed in glass containers and tapped16.

                 "IV "1 fit
 Kimura and linoya '*   used the Kozeny-Carman equation to back-


 calculate the porosities of dust cakes from experimentally de-


 termined values of specific resistance.   Their calculated poro-


 sities ranged from 0.55 to 0.99.   Because a porosity  greater


 than 0.92 calculated from the Kozeny-Carman equation  is  theore-


tically impossible,  their data is suspect.


     In conclusion,  it is evident that the Kozeny-Carman  equa-
                              260

-------
tion Is probably of limited utility for the prediction of dust



cake specific resistance.   In particular,  at high porosities,  ...



which are not uncommon for dust filter cakes, the Kozeny-Carman



equation will seriously underestimate pressure drop.



"Free Surface" Model



     An alternate approach to a capillary  model is to recognize



that a dust cake consists  of an assemblage of individual parti-



cles subjected to aerodynamic drag which can be represented by



a collection of uniformly  distributed cells, each composed of a



spherical particle and a concentric, fluid-filled envelope of



such proportion that the porosity of the cell and of the entire



granular medium is identical.  If appropriate boundary conditions



are formulated, the Navier-Stokes equation (neglecting Inertial



effects) can be solved rigorously.


           19
     Happel   postulated a "free surface"  cell ; mo die!' in' which the



salient boundary condition is the disappearance of tangential



stress on the surface of the spherical envelope.  If the size of



the spherical envelope is  infinite, the result becomes identical



with Stokes' law.  For prediction of pressure drop through a



dust cake, the "free surface" model of Happel can be written in



terms of the resistance factor as follows:



                           3 + 2(l-e)^3
          R =
              3 - 4.5(1-£)V3 + 4.5(l-e)5/3 - 3(l-e)2



Theoretically, this relationship should be valid for all values



of porosity and it yields the proper limits, i.e., for c = 0,



R Is infinite and for e = 1, R = 1.  It shows good agreement
                              261

-------
 with published experimental data for hindered settling in the
 high porosity range (0.95 to l.O)19; and,  for packed beds in the
 low porosity range (0.30 to 0.60),  it gives results essentially
 identical to those derived from the Kozeny-Carman equation,  as
 shown in Table II.  The close agreement between the semi-empiri-
 cal Kozeny-Carman equation and the  theoretical relationship  of
 Happel in the low porosity range (<.6o) is  striking considering
 that the "free surface" model contains  no empirical constants.
 In the intermediate porosity range  (0.60 to 0.95),  the experi-
 mental results are contradictory, indicating that  porosity does
 not uniquely characterize permeability.  Inasmuch  as  most of the
 data in this porosity  range  come from fluidized  and sedimenting
 particle systems,  circulation and agglomeration  effects would be
 expected to  play  an important role  and  result  in increased per-
 meability.   This  would explain qualitatively discrepancies be-
 tween the  "free surface"  model  and  experimental  results.  The
 "free surface" model,  however,  is in  satisfactory agreement with
 the rather limited  experimental  data  in which  circulation and
 agglomeration  effects  were eliminated or minimized19'20.  It
 seems  likely that there are no agglomeration effects present
 when  a  dust  cake is formed primarily from a nonaggregated aero-
 sol.  As discussed previously, a dust cake forms dynamically and
 it  is reasonable to assume that particle deposition tends toward
 uniformity.
     Inasmuch as the "free surface"  model is theoretically valid
at all porosities, it is tempting to adopt  it for dust filter
                              262

-------
TABLE II.   Comparison of Resistance Factors  Predicted by  Kozeny-Carman
           Equation and "Free Surface"  Model
                                   Resistance Factor (R)
Kozeny-Carman Equation
Porosity (Eq. 7, k =.4.8)
.30
.40
.50
.60
.70
.80
.90
1.00
250
90
38
18
8.4
3.7
1.3
0.0
Happel Model Ratio
(Eq. 8) Happel/Kozeny-Carman
230
85
38
19
10
5.6
3.1
1.0
0.92
0.94
1.0
1.1
1.2
1.5
2.4
oo

-------
 cakes but certain Important considerations remain unresolved.  In
 particular, the "free surface" model assumes uniform spheres, and
 does not indicate how nonuniform particle sizes and nonspherical
 shapes should be handled.  In addition, the "free surface" model
 assumes that particles are sufficiently large that the fluid can
 be considered as a continuum.   This may not be correct for a dust
 cake composed of very small particles.
 Effect of Particle Size Distribution and Particle Shape
      When the Kozeny-Carman equation is employed, the correct
 mean particle diameter as given by  the  hydraulic  radius theory
 is  a function of the   specific  surface  area of the  granules,  S,
 (i.e.,  the  surface area  exposed to  the  fluid per  unit  volume  of
 solid material),  or

          °vs  =  6/S                                          (9)

 where Dys is  the mean  diameter  to be used in the  Kozeny-Carman
        21
 equation  .   This approach automatically corrects for particle
 shape.  For spherical  particles,
          _     En.D.3                                				

where n± is the number fraction and w± the weight fraction of
particles with diameter D±.  Dys is often referred to as volume-
surface mean diameter or the Sauter mean diameter.  For irregu-
larly shaped particles

           vs  ~ *vs  Zn.(Dz).                                 (11)
                              264

-------
where $   is a shape factor which is assumed here to be indepen-
       vs

dent of particle size and D  is the projected area diameter ob-


tained from microscopy.


     Some experimental studies using mixtures of various particle


sizes have shown agreement with the Kozeny-Carman equation when


using D   as the mean diameter22.  Carman  also showed that the
       VS

use of D   gave good results for mixtures of spheres in which
        VS

the diameter ratio was 2:1 whereas when the diameter ratio was


5:1, the calculated value for DVS was not able to compensate

                                                        23
entirely for changes in permeability.  Krumbein and Monk   used


sands having equal mass median diameters but different size dis-


tributions and obtained a significant effect of particle size


dispersity on specific resistance.  Correcting their data to a


constant volume-surface mean diameter does not substantially

                             Oil
change their results.  Carman   stated that whereas the permea-


bility method for measurement of particle size does not require


particles of uniform size, an excessively wide distribution of


sizes should be avoided, and this warning is frequently echoed

        pc
in  texts  .

                                                            19
     In his original "free surface" model derivation, Happel


did not treat nonuniformity in size or nonsphericity, but


later2 , he supported  the use of a volume-surface mean diameter.


Rather then follow this empirical approach, it can be shown that


a mean diameter follows logically from either the Stokes' law or


Happel model.  For illustrative purposes, if Equation  (4), based


on Stokes' law is rewritten to apply to a distribution of irregu-
                               265

-------
 larly shaped particles of various sizes, and if slip is neglected,


 Equation (4) assumes the following form:
           AP = Z Drag Force _

           W    T, Mass       ~ i     ~~r" --                (12)
 where x is a dynamic shape factor defined by Puchs27 as the ratio


 of the resistance of a given particle to that of a spherical par-


 ticle having the same volume, and DS is the diameter of a sphere


 having the same volume as the particle.  Prom the definition of


 the sedimentation (Stokes) diameter, D , it can be shown27
                                       s

 that:



               D2

           X = D^                                            (13)
                s



 Hence,  if it is assumed that x is  independent of particle size,


 substituting Equation (13) into Equation (12)  yields:
           (Ko)         = AZ. =  !8y    -^   »  j-                    ,  . .
              minimum  WV   p    In. (D3).                    (••L^)
                              p     i   s  i


 Comparing  Equations  (14) and  (5),  it will be  seen  that  the  re-


 quired mean diameter  is the volume-length mean diameter based on


 the distribution of  sedimentation  diameters:     ': '


                           1/2
          D
vl
                                                             (15)
Alternatively, pp, can be set equal to unit specific"gravTEy~Ir


Equation  (ilj) and an aerodynamic diameter substituted for the


sedimentation diameter in Equation (15).  The same result is


obtained for the "free surface" model with slip included pro-


vided the dynamic shape factor is not influenced by porosity.


Equation (6) can then be rewritten as follows:


                              266

-------
          K2 -


where
           2
                vl s
          T   =  pvl                                       (17)
           vl
When D T is to be determined by microscopic methods,

                    • ~^ (-p, 3 •>! —| 1/2
          D   = A    __^^                               (18)
          Dvl


where  ,  is a shape factor which is assumed to be independent of
       vl

particle size and porosity and which relates the sedimentation

diameter to the projected area diameter, i.e.,
     Although the volume-length mean diameter, D¥IJ given by

Equation (15) differs from the volume-surface mean diameter, DVS,

given by Equation (10), the difference is small for spherical

particles unless the particle size distribution is fairly broad.

For example, if the particle sizes are log normally distributed,

these two diameters can be related using the Hatch-Choate equa-
    po
tion   as shown in Table.III.  For most of the studies done on

granular media, usage of DTrc, or D , would give nearly the same
                          V S     v _L

results, but for most industrial dust cakes, the difference can

be expected to be large because industrial dusts tend to have a

geometric standard deviation greater than 2.5.

Slip Flow

     When particle diameters in a dust cake become small, the gas
                               267

-------
TABLE III.  Comparison of D   and D
                           vs      vl
Geometric
Standard                      _   _
Deviation                     Dvs/Dvl
   LO                          1.0
   1'5                          1.09
   2.0                          1<27
   2-5                          1.52
   3-0                          !
                268

-------
can no longer be regarded as a continuum and the specific resis-
tance will be less than predicted by theory because the gas velo-
city will not be zero at the particle surface.  Inasmuch as the
derivation given by Happel   does not account for this slip, the
"free surface" model was rederived using the classical slip flow
         29
procedure   in which the Navier-Stokes equation is solved using
boundary conditions which account for noncontinuum effects.  This
method is valid only for small (<0.25) Knudsen numbers (gas mean
free path/particle radius).  The result of this derivation is
given below in terms of the slip correction factor for use in
Equation (16):
               (En.D1)-(	)                     (20)
          C  = 	
               I
                            5/3
                               +
                      2 _ 3a 5/3 + Sa5/3 - 2a* + 6Kn. (l-a1/3-a5/3+a:
                                                 i
where a is dust cake solidity (1-e) and Kn. is a modified Knudsen
number for a particle of size D., i.e., Kn. = ±m.3 where A is a
                               i          1   DJ
number close to unity vwhich "characterizes the interaction of the
gas molecules with the particle surface and A is the mean free
path of the gas.
     From Equation (20), when the Knudsen number approaches zero
(i.e., no slip), the slip correction factor approaches unity.
When porosity is equal to unity and the particles are single-
sized:
          c  _ l+3Kn                                        .  ,
           s " l+2Kn                                        (21)
                              269

-------
 Equation  (21) is identical to the result given by Fuchs30 for

 the slip correction factor for a single particle in an infinite

 medium, which is valid only for small Knudsen numbers and is

 approximately equal to the Cunningham slip correction factor.

      Prom theory, Equation (20) should be valid at all porosities

 (for Knudsen numbers <0.25).   It gives excellent agreement with

 published experimental results for compacted fine powders having

 porosities from Q.H to 0.6* and, as stated above, is  in fair

 agreement with the Cunningham slip correction factor  for porosi-

 ties approaching unity.   If a slip correction factor  = 1.1 is

 ignored,  a 10* error in  the specific  resistance will  be obtained.

 From Equation (20), this  error corresponds  to the particle sizes

 and porosities shown in  Table IV.   When  either porosity or particle

 diameter  becomes  smaller  than the  value  shown in Table IV,

 neglect of the slip correction factor  will  yield a value  for

 specific  resistance from  Equation  (16) that will  exceed the cor-

 rect  value  by  more  than 10*.

 Experimental Apparatus


     Experimental apparatus was  designed to fulfill two key ob-

 jectives:   (1) determination of  filter cake specific resistance,

 and  (2) preparation of filter cakes for porosity measurement.

 Figure  1 shows the bench scale equipment in which dust cakes were

 formed  on various cloth and paper supports at a constant air-to-

 cloth ratio over a wide range of air-to-cloth ratios such that

 other parameters (e.g., aerosol particle size distribution and

relative humidity) could be held ' essentially constant  during a


"pSbl^pi??^ ^ !tatement can be f°urid in Harvard School of
 progress       d^toral dissertation by S.  Rudnick currently in
                              270

-------
TABLE IV.  Porosities and Particle Diameters for which C  =1.1
                                                        o


                                           Particle
                                           Diameter,
          Porosity                            ym

            0.3                              32

            0.4                              22

            0.5                              16

            0.6                              11

            0.7                               8.2

            0.8                               5.7

            0.9                               3.6

            1.0                               1.1
                               271

-------
  a  run  and  from run-to-run.
      As shown In Figure 1, filtered compressed air was fed to a
  Wright31 dust feeder which dispersed the test dust.  The resul-
  tant aerosol passed through an elutrlator In which all particles
  with an aerodynamic diameter greater than 8.4 ym were removed
  before reaching the experimental filter.  Aerosol in excess of
  the amount needed for filtration was vented at the inlet to the
  elutrlator.  To avoid flow disturbances, a circular frustum with
 a 7° half angle was used upstream of the filter.   The filter
 holder was  composed of two cylindrical pieces with large flanges
 between which a supporting substrate such as cloth could be
 clamped with the  cloth acting as  its own leak tight gasket.   Plow
 measuring and controlling  devices,  located downstream from  the
 filter, included  a  manually adusted control  valve  to  giwe con-
 stant  flow  over the  duration  of a run  plus a sensitive  and  accu-
 rate pressure  gauge  placed upstream of  a calibrated critical  ori-
 fice to make  it possible to measure mass flow rate.   The  critical
 orifice also  served  to isolate the  system from downstream dis-
 turbances caused by  the vacuum pump.  The control valve acted as
 a high  flow resistance in  series with the filter so that  changes
 In pressure drop across the filter  cake  had  little  effect on mass
 flow rate.  At face velocities below 50  mm/s (10 fpm) flow rate
remained constant throughout a run without need to readjust the
control valve.  Pressure drop across the filter was recorded con-
tinuously on a chart recorder.  Filter approach velocity was
adjusted by  varying  filter  area,  i.e.,  changing the diameter of
                             272

-------
                              PRESSURE
                              TRANSDUCER

                            (TO  CHART RBOROER)
NJ
•vl
U)
   VERTICAL
   ELUTRIATOR
            COMPRESSED
            AIR»»   —
PRESSURE
REGULATOR
                      PRE- FILTER
                       TEST
                       FILTER
                                                                POST- FILTI
                               INFLOW CONTROL VAU/E
                                                              CRITICAL
                                                              ORIFICE
              XACCUUM
              PUMP
 WALLACE 8 TIERNAN GAUGE

•VENT
                                       WRIGHT
                                        DUST
                                        FEEDER  DUST HOPPER
                                 FIGURE 1.  Experimental Apparatus

-------
  filter holder and connecting pieces.   Inasmuch as  the  filter area


  was always less than the elutriator cross  sectional  area,  the


  aerosol size distribution was not  affected by  changes  in  filter


  face velocity.


  Porosity Determinations


       The porosity  (e) of dynamically formed dust cakes was cal-


  culated from the following working  relationship in terms of  the


  measurable parameters:




           e  = 1 -  m
                   appL                                       (22)




 where Pp Is  the density of individual particles, m is the mass


 of filter cake exclusive of dust retained in the interstices  of


 the fabric, a is area of the dust deposit,  and L ds average thick-


 ness of the dust cake.  Density of particles removed  from filter


 cakes was evaluated by pycnometry using a nonadsorbing  gas, filter


 cake mass was determined by weighing to the nearest tenth  of  a


 milligram,  area  of  the dust deposit  was equal  to the  open  area of


 the filter holder,  and cake thickness was measured  by the  follow-


 ing procedure:   A fracture could  be  induced in  most dust cakes  by


 bending  the cloth and  then the cake  could be removed  cleanly  from


 one side of the  fracture  by tapping.  This  would expose a cross


 section  of the cake such  as that  shown  in Figure 2 on which


 thickness measurements could be made.  During the cleaning cycle


 of  a bag  filter, a similar process of fabric bending and cake


 separation takes place2*.  Alterations of the portion of the dust


cake remaining on the fabric that might  be caused by the bending
                              274

-------
Figure 2.   Cross Section of Dust Cake on Woven Fabric
                         275

-------
 procedure could be detected easily with a stereoscopic microscope.
 Dust cake thickness was measured by three techniques:
      A.  Measuring cake thickness with a calibrated graticule in
 an 84x stereoscopic microscope.   The circular dust cake was al-
 ways flat in the vicinity of its center but it tended  to decrease
 in thickness, near the edge.  /Therefore, dust cake thickness was
 measured as  a function of diameter and converted to a  single
 value of average cake thickness  by graphical integration.   As
 this is a lenghthy procedure,  it was done once at each filter
 velocity and,  thereafter,  an experimentally determined correction
 factor, calculated for each  filter velocity,  was applied to con-
 vert from thickness  at the cake  center to average dust cake
 thickness.             ••'•-•-
      B.   Measuring the shadow  formed in a scanning  electron micro-
 scope using  backscatter electrons,  because  the  edge of  the sha-
 dow  is  cast  on a cleaned portion of  fabric,  this  method  automat-
 ically  compensates  for the unevenness  of  the  fabric.   This  pro-
 cedure  is not applicable to  the flight  microscope  because of in-
 sufficient depth of  field.   A micrograph  of a  shadow cast on a
 woven fabric is  shown  in Figure  3.
      C.   Measuring the  amount of rotation of a calibrated fine
 focusing  adjustment of  a light microscope with a  22x objective
 by focusing first on the cake surface and then on the fabric
 surface.
All of these methods worked reasonably well for flat cake sup-
ports (paper) but for fabrics, method C gave very inconsistent
                              276

-------
   4
     i
   3

 f  2
 4.
s
w
5  s
O  4
-
a  3
                         PARTICLE SIZE  OF AC-FINE TEST OUST
                         PENETRATING A 0229* (9 INCH) DIAMETER
                         VERTICAL  ELUTRIATOR  AT A GAS FLOW RATE
                         OF 2.7 L/«i«
  .05
    0.01
J_
                                                        I  I
                                                    J.
0.1     I         10
  CUMULATIVE PERCENT
   90          90
UNOER8IZE  BY COUNT
                                             96 99  99.8   99.99
                FIGURE 4.   Particle  Size Distribution
                                  277

-------
                                                        100)jm
Figure 3.  Dust Cake Shadow Cast on Woven Fabric
                        278

-------
results.  Methods A and B gave reasonably good agreement.   Method



A is the most accurate and most time consuming.



Characterization of the Aerosol



     Employing the apparatus shown in Figure 1, representative



samples of the aerosol generated from AC-fine test dust (GM



Phoenix Laboratory, Flint, Michigan), were collected on two 0.2



ym diameter Nuclepore filters in series separated by an open



fibrous mat (Nuclepore D24? FOR).  All parameters remained the



same as during dust cake formation except that the concentration



of the aerosol was reduced to produce a deposit suitable for



sizing.  The filter samples were photographed in a scanning



electron microscope at magnifications appropriate for stratified



counting.  Particles were sorted into geometrically spaced size



categories with a transparent overlay patterned after the May-



Porton graticule^.  it was intended that the second Nuclepore



filter would be used to measure the fractional efficiency of



these filters, but no particles were detected on the second fil-



ter.



     The projected area diameter distribution of the aerosol used



in this study is shown on log probability paper in Figure 4.  The



volume-length shape factor,  , (Equation 18), used to convert



projected area diameter to sedimentation diameter, was estimated



based on (1) the? projected area diameter of the largest particles



passing through the elutriator determined for photomicrographs,



and (2) the sedimentation diameter of the largest spherical par-



ticle capable of penetrating the elutriator based on the elutria-
                              279

-------
 tor center-line velocity assuming Poiseuille flow.   This approach


 is likely to give somewhat large values  of $ ,  because the big-


 gest particles penetrating the elutriator may go undetected by


 microscopy due to their scarcity.   The volume-surface shape fac-


 tor, vs (Equation 11), used to convert  projected area diameter


 to volume-surface mean diameter, was  determined from (1) pro-


 jected area diameter distribution,  and (2)  specific  surface area


 measurements on polished cross sections  of particles embedded in


 plastic resin employing the  methods of Chalkley,  Cornfield, and

     34
 Park  .   It was found for the aerosol used in this study that


 4>vl = 0.66 and $vs  = 0.62.   Both are  within the range of values


 cited in the literature for  similarly shaped particles35,36^


 Results



      Elutriated AC-Fine test  dust was collected at various  face


 velocities from 7.1  mm/s  (1.4 fpm)  to 56  mm/s  (11 fpm)  on paper


 and woven fabric  supports  that included Teflon, polypropylene,


 Dacron  (all  3x1  twill,  monofilament yarns),  cotton sateen,  What-


 man 41,  and  8.0  ym Millipore  filter.   Specific  resistance,  K2,


 was  determined  from  the following equation:



           K, -  x  (AP)2-(AP)!
           *2 ~ V     W>¥^	                                (23)



where subscript "1"  refers to the point at which AP became


essentially linear with areal density and subscript "2" refers


to dust flow termination.



     Measured values of solidity (1-e) have been plotted against


experimentally derived values of the specific resistance, K2,
                              280

-------
in Figure 5.  Also included in Figure 5 is a curve showing the



functional relationship between specific resistance and solidity



that we recommend based on Equations (8), (15), (16), (17) and



(20) or their composite given as follows:




                    n, (D ) {3 + 2a5/3 + 6Kn.( 1-a5/3)}
                     _1_  O J_               -L
                    '3 _ 4.5C11/3 + 4.5a5/3 - 3a2 + 9Kn. (l-a^-a^+a2)
                                                   i             	

          K, =      ""
                PpZ[n.(D3).]




The experimental results are in considerably better agreement



with Equation (24) than with the Kozeny-Carman equation also



shown in Figure 5 which greatly underestimated the specific re-



sistance of the experimentally filtered dust cakes.  This was



expected because the porosity of these dust cakes lies outside



the range of validity for the Kozeny-Carman equation.  A large



portion of the Kozeny-Carman curve lies below the minimum possi-



ble specific resistance predicted from the Stokes' law model



shown as a single point in Figure 5.



Discussion



     A filter dust cake can be modeled as a collection of capil-



laries or as an assemblage of particles.  Although the latter is



clearly a more realistic representation, the Kozeny-Carman



equation utilizes the former, and consequently suffers certain



limitations.  In particular, as the porosity of a dust cake



approaches unity, the Kozeny-Carman equation predicts that the



specific resistance (K2) will approach zero, whereas in this



case, the cumulative frictional and form drag of the isolated



particles will define the value of K2.  As a limiting case,



                              281

-------
SPECIF.C RESISTANCE ( K, ),
                            OR
                                                                                                                                       IO"
                                                                           058
o   §    §    3    S    8    8
N)
00
NJ
                                                    O
                                                    13
                                                    (D
                                                    n
                                                    H-
                                                    Hi
                                                    H-
                                                    O
                                                    
                              K  °
                           •"4
                           laS
                           1^
                                                                                                                                 m
                                                                                                                           * V
                                                                                                                              6>
                             35

-------
applying Stokes'  law to flow through a dust cake,  leads  to Equa-
tion (5) which, solely from hydrodynamic considerations, gives
the minimum value of K2 for a given dust.  It is clear from Table
I that the minimum specific resistance for small particles will
be large.  For example, a 0.5 um particle diameter yields a mini-
mum K2 equal to 980/ms (98 in. water/fpm»lb/ft2).   This  example
incorporates an important concept:  the specific resistance for
small particles will always be large, regardless of the magni-
tude of porosity.  A common misunderstanding of fabric filter
vendors and users is that fine fumes produce nonporous filter
cakes with high flow resistance.  Although fine fumes do cause
high flow resistance, the dust cakes are, nonetheless, likely
to exhibit high porosity.  The high flow resistance is due pri-
marily to the small particle size.
     An understanding of minimum specific resistance can be help-
ful in determining whether or not data from lab or field studies
are of the correct order of magnitude.  When K2 values less than
the calculated minimum specific resistance are obtained, the data
must be suspect.
     Although the Kozeny-Carman equation (with a suitable cor-
rection for slip flow) is presumably valid for dust cakes with
porosities less than 0.65, the "free surface" model, modified
to treat nonuniform particle sizes, nonspherical shapes, and slip
flow, is preferable because it gives good agreement with experi-
mental measurements for the entire range of dust cake porosities.
Either model yields essentially the same specific resistance for

                               283

-------
 porosities less than 0.65.  This is fortunate in light of the
 extensive experimental support of the Kozeny-Carman equation at
 these porosities.  But at porosities above 0.65, which are com-
 mon in fabric filter dust cakes, the Kozeny-Carman equation under-
 estimates specific resistance whereas the modified "free surface"
 model gives adequate agreement with experimental results.  This
 is shown in Figure 5.
      Both the Stokes'  law model and the "free surface" model con-
 sider a dust cake to be an assemblage of particles  but the "free
 surface" model differs  because the  drag force on a  particle given
 by Stokes'  law is  multiplied by a factor that is greater than
 unity and increases  as  dust  cake porosity decreases.   When poro-
 sity  approaches  one,  the  two models  become identical.   The mean
 diameter appropriate  for  these models  is  given by Equation (15)
 and is  calculated  directly from the  sedimentation diameter distri-
 bution  or aerodynamic diameter distribution when particle  specific
 gravity  is taken in unity in Equation  (17).   The diameter  distri-
 bution may be  expressed on a number  or weight basis, and can
 often be  measured with the aid  of an inertial sampling device such
 as  an impactor provided particle size is not  too small.  In addi-
 tion to correcting for particle shape based on the aerodynamic
 properties of particles, this measurement method may also compen-
 sate for particle orientation inasmuch as a particle is likely to
remain in an aerodynamically stable  position after incorporation
into the dust cake.
                               284

-------
     Inasmuch as the "free surface" model also predicts the flow

field surrounding a particle in a dust cake, it may be possible

to predict S02 collection efficiency in fabric filters which re-

move S02 in a reacting chemical precoat or upstream injection.
        •37
Pfeffer   derived a solution for heat and mass transfer in par-

ticulate systems based on the "free surface" model which is valid

for high Peclet number.  Although S02 removal in a fabric filter

dust cake usually occurs at low Peclet number, development of an

approach similar to Pfeffer's which can be applied to S02 removal

in a fabric filter, may be possible.  This type of modeling capa-

bility may become very useful if all new coal-fired utility plants

are required to use scrubbers or fabric filters with nahcolite

injection, as appears likely  .

Acknowledgement

     This work was supported in part by Stone & Webster Engineer-

ing Corporation, Boston, Mass.   It was performed in partial ful-

fillment of the requirements for the Sc.D. degree at the Harvard

School of Public Health.

References

 1.   Carman,  P.  C., "Flow of Gases Through Porous Media",
       Academic  Press,  New York, NY, 1956.

 2.   Scheidegger,  A.  E., "The Physics of Plow Through Porous
       Media",  University of Toronto Press,  Toronto,  Canada,
       1974.

 3.   Carman,  P.  C.,  "Fluid Flow Through Granular Beds",  Trans-
       actions - Institution of Chemical Engineers,  15:150-166,
       1937.

 4.   Williams, C.  E., Hatch,  T.  and  Greenburg,  L.,  "Determina-
       tion of Cloth  Area for Industrial  Air  Filters", Heating
       Piping and  Air Conditioning,  12:259-263,  19*10.

                             285

-------
      Silverman, L., "Filtration Through Porous Media",  American
        Industrial Hygiene Association Quarterly,  11:11-20,  1950.

      Stephan, D. G.,  Walsh,  G.  ¥.  and Herrick, R.  A.,  "Concepts
        in Fabric Air  Filtration",  American Industrial  Hygiene
        Association Journal,  21:1-14,  I960.

      Billings,  C.  E.  and Wilder,  J.,  "Handbook of  Fabric Filter
        Technology, Vol.  I,  Fabric  Filter Systems  Study", National
        Technical Information Service,  PB-200  648,  Springfield,
  8.   Ibid.,  p.  2-131.

  9,   Ibid. ,  p.  2-160.

 10.   Fuchs,  N.  A.,  "The  Mechanics  of  Aerosols",  Pergamon Press
        Oxford,  England,  1964,  p.  49.

 11.   Carman,  P.  C.  and Malherbe P.  le R.,  "Routine  Measurement  of
        Surface  of Paint  Pigments  and  Other Fine  Powders",  Journal
        of the Society of Chemical  Industries, London  (Trans-
        actions), England,  69:134-143, 1950.

 12.   Billings,  C. E. and Wilder, J.,  Op. Cit., p. 2-117.

 13.   Carman,  P.  C.,  1956,  Op.  Cit., p. 15.

 14.   Billings,  C. E. and Wilder, J.,  Op. Cit., p. 2-134.

 15.   Orr, C. >Jr.,  "Particulate Technology", MacMillan,  New York,


 16.   linoya,  K. and Yamamura, M. ,_ "Fundamental Experiments With
       Dust-Collectors",  Kagaku Kogaku, Japan, 20:163-171  1956
        (in Japanese) .                                           '

 17.   Kimura,  N. and linoya, K., "Pressure Drop Characteristics
       oo ^t??,,C1°t5 f°? Dust Collecti°n", Kagaku K5gaku, Japan,
       29:166-174, 1965,  (in Japanese) .
18.  Kimura, N. and linoya, K., "Pressure Drop Characteristics
       of Filter Cloth for Dust Collection".; Kagaku KSgaku, Japan,
       3:193-196, 1965, (abridged edition in English).

19.  Happel, J   "Viscous Flow in Multiparticle Systems:  Slow
       f^ion of Fluids Relative to Beds of Spherical Particles",
       A.I.Ch.E. Journal, 4:197-201, 1958.

20.  Happel, J., "Fluid Flow in Multiparticle Systems", Trans-
       actions of the New York Academy of Sciences,  20:404-410,


                              286

-------
21.   Carman,  P.  C.,  1956,  Op_.  Cit.,  p.  11.

22.   Ibid,  p. 18.

23.   Krumbein, W.  C.  and Monk, G.  D.,  "Permeability as a Function
       of the Size Parameters  of Unconsolidated Sand", Trans-
       actions of  the American Institute of Mechanical Engineers,
       151:153-163,  1943.

24.   Carman,  P. C.,  1956, Op.  Cit. , p.  83.

25.   Allen, T., "Particle Size Measurement", Chapman and Hall,
       London, England, 1968.

26.   Happel,  J. and Brenner, H., "Low Reynolds Number Hydrodyna-
       mics With Special Applications to Particulate Media ,
       2nd Ed., Noordhoff International Publishing, Leyden,
       Netherlands,  1973, pp.  395, 4l8.

27.   Fuchs, N. A., Op_. Cit., pp. 39-40.

28.   Silverman, L., Billings,  C. E. and First, M. ¥., "Particle
       Size Analysis in Industrial Hygiene", Academic Press, New
       York,  NY, .1971, p. 242.

29.   Hidy, G. M. and Brock, J. R., "The Dynamics of Aerocolloidal
       Systems", Pergamon Press, Oxford, England,  1970, p. 147.

30.  Fuchs,  N. A., Op_. Cit.,  p. 25.

31.  Wright,  B. M.,  "A New  Dust-Feed Mechanism", Journal of
       Scientific Instruments,  27:12-15, 1950.

32.  Dennis,  R.,  Cass, R. W.  and Hall,  R.  R. ,  "Observed Dust
       Dislodgement  from Woven  Fabrics  and Its Measured and
       Predicted  Effect on  Filter Performance",  Presented  at
       the 70th Annual Meeting  of the  Air  Pollution  Control
       Association,  Toronto,  Canada, June  20-24, 1977-

33.  May,  K.  R.,  "A  New  Graticule  for  Particle Counting and
       Sizing", Journal  of  Scientific  Instruments,  42:500-501
       1965.

34.  Chalkley,  H. W.,  Cornfield,  J. and Park,  H.,  "A Method  for
       Estimating Volume-Surface  Ratios",  Science,  110:295-297,
       1949.'

35.  Mercer,  T. T. ,  "Aerosol  Technology in Hazard  Evaluation",
       Academic  Press,  New  York,  NY, 1973, p.  83.

36.  Herdan,  G.,  "Small  Particle  Statistics",  Academic  Press, New
       York,  NY,  I960,  p. 175-


                              287

-------
37.  Pfeffer, R.,  "Heat and Mass Transport In Multiparticle Systems",
       Industrial  and Engineering Chemistry Fundamentals, 3:380-
       383,  1964.                                        '


38.  Mcllvaine,  R.  W., ed., "Fabric Filter Newsletter", No. 23,
       Mcllvaine Company,  Northbrook,  IL, September 10, 1977,
       p.  8.
                             288

-------
      THE INFLUENCE OF ELECTROSTATICALLY-INDUCED CAGE VOLTAGE
       UPON BAG COLLECTION EFFICIENCY DURING THE PULSE-JET
            FABRIC FILTRATION OF ROOM TEMPERATURE FLYASH
                           R. P. Donovan*
                           R. L. Ogan+
                           J. H. Turner+
*Research Triangle Institute
Process Engineering Department
P. 0. Box 12194
Research Triangle Park, N. C.  27709

+Environmental  Protection Agency
Industrial  Environmental Research Laboratory
Research Triangle Park, N. C.  27711
                               289

-------
                                Abstract

      In a previous paper an experimental arrangement was described
 for measuring the effect of electrostatic charge buildup on fabric
 filters during the room temperature, pulse-jet filtration of re-
 dispersed flyash—flyash which was originally collected by an electro-
 static precipitator scrubbing the effluent of a pulverized coal boiler.
 A prime justification and advantage of that experimental  arrangement
 was that it required only the attachment of one electrical  lead to the
 cage supporting  the bag filter.   This simple modification was assumed
 not to change or influence  the dust/fabric  interaction  being  studied
 in any way.
      From  the qualitative concepts  previously presented,  a  simple
 analog  equivalent circuit is  proposed for relating  the  charge buildup  on
 or in  the  fabric  to  the  cage  voltage  detected by the measuring  technique.
 Since  the  simple  equivalent circuit to be presented explains  at  least
 some of  the cage  voltage features observed so  far,  it is  concluded  to
 be a useful starting  point for modeling  the  interaction.
     A second general goal of the experimental program is to relate
the electrostatic properties of a given dust/fabric system to its per-
formance as a fabric filter.  The initial observation of this portion
of the program concludes the paper.
                                290

-------
                        HISTORICAL BACKGROUND

     At least as long ago as 1913 [Reference 1] experiments were being
performed which showed that raising clouds of dust produced large amounts
of electricity, that the sign of the resultant charge depended on the
dust composition and that particle size affected charge quantity.  The
work included passing particles through metal mesh and light cotton
fabrics, and measuring voltages and signs of charge at the mesh or
fabric surface and beyond.  Passing dust through long tubes (20 feet)*
also generated strong charges.
     By 1926 Deodhar [Reference 2] (and Shaw [Reference 2] in discussion
following Deodhar's paper) showed that temperature and humidity also
affected charge.  The beginnings of a triboelectric series for dusts
were discussed.  In 1950, Kunkel [Reference 3] refined previous work
and presented quantitative information about dust clouds.  With highly
reproducible measurements, he concluded that (1) the particles in a dust
cloud are charged, probably as a result of particle to particle separation
after contact, (2) the clouds have about equal numbers of positively
and negatively charged particles and are therefore neutral (unless a
significant portion of the particles strike a dissimilar material),
(3) the effect holds for at least over the size range from 0.5 to 30 ym,
(4) for the case of metals and insulators being the dissimilar materials,
     *Use of metric units exclusively would seriously inconvenience the
majority of the intended reading audience.   For those readers more familiar
with the metric system a conversion table for changing the British units
used in the report to their metric equivalent appears in the appendix.
                                291

-------
  the  insulator will  invariabley have a predominantly negative charge, and
  (5)  because, at least for the quartz powder studies, a one or two
 molecule thick layer of water remained on the particles even to several
 hundred degrees centigrade (water vapor moisture plays only a minor
 role in the electrification process).
      About this time interest was generated in the deposition of particles
 on fibers (and other surfaces) and the effects of electrostatic pheno-
 mena on the process.  Kraemer and Johnstone [Reference 4]  presented
 equations of motion for a particle influenced by an electrostatic force
 in a resisting fluid,  and equations  for  the electrostatic  force on  a
 particle approaching a  collector  at  constant voltage and for  a  collector
 at constant charge.  Experimentally  they  studied  charged collector  with
 corona-charged OOP,  charged collector with  only naturally  charged
 aerosol,  and grounded collector with corona-charged aerosol.  Their
 results  agreed reasonably well with the various collection parameters
 they  had  presented,  and led to the suggestion of an electrified mat
 filter assumed to yield several orders of magnitude increase in col-
 lection efficiency over its non-electrified analog.  No mention was made,
 however, of collection by cake established on a fiber or fabric support.
      Rossano and Silverman [Reference 5] did experimental  work with charged
 aerosols and/or charged fiber filters (not fabric}.  They used low  concen-
 trations of methylene blue particles (0.1 to 1.7 mg/m3, 2 Pm mass median
diameter [MMD]) and Saran fiber beds 1  in. thick (35 to 70 ym curled fibers
packed to 2.6 lb/ft3).   Filtration velocity was 33 to 66 fpm.   Their
                                292

-------
conclusions were that filtration efficiency increased with increasing
fiber charge and decreasing fiber diameter for a negatively charged
filter and relatively uncharged aerosol.  In the range studied,  velocity
was not a significant variable (contrary to Kraemer and Johnstone's
prediction).  For a negatively charged bed and positively charged
particles, collection efficiency increased with increasing charge and
increasing filter packing density.  It should be pointed out that the
fiber beds were charged by hand carding just prior to each experiment.
An experimental loss in collection efficiency of the bed over a 3 day
period (to 45% from 75%) was presumed to be caused by electrical dis-
charge of the bed.  Further experimentation of particular (and disturbing)
interest to the present work showed that passage of dust through an
uncharged bed produced no measurable charge on the bed.  Methylene blue
at 1.0 mg/m3 at velocities of 33 and 70 fpm, and atmospheric dust at 33
to 364 fpm were used.
     Although of closer interest to the present work and to baghouse
users than much of the preceding work, the Rossano and Silverman experi-
ments still have important differences when compared to fabric filtration.
They used thick, open fiber beds which were not cleaned and had no
appreciable cake.  The fibers were relatively large in diameter and the
aerosol loading was low.  Velocity was an order of magnitude higher than
those used with fabric filters and efficiency much lower (which may be
an unfair criticism in view of the low inlet loading).
                                293

-------
      Rao et al. [Reference  6],  in  a  paper  with  "Fabric  Filtration"  in
 the title, develop a strictly theoretical  description and equations for
 a  particle being  collected  by an array  of  three parallel  cylinders.
 There may  be  some confusion in  the minds of  the authors between fiber
 and fabric filters.   Cleaning and  existence  of  a cake are not mentioned.
      Makino et al.  [Reference 7],  with  a reverse twist, studied removal
 of dust  from  a  filter paper backed up by electrodes.  They filtered dusts
 (Lycopodium,  ABS  and  sinter dust)  through  the filter with no current
 through  the electrodes, then  stopped the dust (but not air) flow, and
 turned on  the electrodes in  order  to remove  dust from the filter (pre-
 sumably  the filter surface  was vertical).  They  used alternating current
 in  three different electrode/filter configurations and concluded that
 removal efficiency was a function  of electrode distance from the filter,
 electrode  diameter, and distance between electrode wires.  They also
 found that  removal efficiency increased as the  initial electric charge
 of  the dust increased and that filtering velocity was not significant
 even up to  about 50 cm/sec.  Optimum removal depended on  frequency, with
 lower frequency being better.  Finally, the authors found that continuously
moving the filter in relation to the electrodes  improved cleaning effi-
ciency (presumably the motion wasn't vigorous enough to approximate
shake cleaning).
     Numerous authors have  studied  particle deposition on fibers with
the influence of charges  or electric  fields.   When  fabrics or filter mats
were used the conclusion  reached is invariably that charging aids filtration
                                 294

-------
The experimental method includes measurement of efficiency for clean
fabric without, and then with, charging.  The efficiency usually goes
from some low value to something in the 90's.  What is not brought out
is the difference between non-cleaned fresh fabrics or mats which
filter without significant cake formation, and cleanable fabric filters
which depend on the dust itself for very high collection efficiency.
     One refreshing change has been the work done by Frederick
[Reference 8], and Penney and Frederick [Reference 9] in exploring
the role of fabric electrical properties and dust electrical properties
in the fabric filtration process.
     The present work is predicated on trying to gain still further under-
standing of electrical effects in an operating fabric filter by taking
measurements in a commercial pulse-jet baghouse operated in a laboratory
atmosphere.
                                 295

-------
               REVIEW OF EPA ELECTROSTATIC EXPERIMENT

      The experimental  apparatus used throughout this work consists of a
 commercially available, nine-bag MikroPul  pulse-jet baghouse.   This unit
 is one of the smallest commercially available baghouses.   Asisuch
 it retains all  the features of fuller sized  units  and lends  itself well
 to laboratory simulation of field experience.
      For the electrostatic  measurements  to be  reported here  (and  as
 reported previously [Reference 10]), the bag mounting technique was
 altered from the  conventional  mounting as  shown  in  Figure  1.  The  at-
 tachment of a banana jack to the  cage is the only change from the  stan-
 dard  bag mounting procedures.   The  purpose of  this  banana  jack  is  to
 allow monitoring  of the  electrostatic properties of the dust/fabric
 system  by using the cage as an  electrode or  electrical contact  to  the
 system.   As  evident in Figure  1,  the cage is electrically  isolated  from
 the baghouse  housing by a single  thickness of fabric.  Since most of the
 synthetic  fabrics  investigated  here have high electrical resistivity, the
 electrical  isolation of the cage  is generally high.  By connecting a high
 impedance electrometer to the cage, the cage  voltage can be monitored
without disturbing or altering the filtration conditions.
                               296

-------
VENTURI
                                        PLENUM  FLOOR
                                      \VENTURI  SHOULDER




                                        HOSE CLAMP






                                        BANANA  JACK
               FIGURE 1.  CAGE CONTACT
                        297

-------
       The primary experimental measurement made in this work has
 been the monitoring of cage voltage as a function of various
 independent parameters of filtration.   As previously described
 [Reference 10], the voltage on the cage typically displays behavior
 similar to that illustrated in Figures 2a and 2b.   Figure 2a,
 showing the cage voltage of a polyester felt bag (Dacron*) filtering
 flyash, typifies the characteristic of a low resistivity fabric.
 Figure 2b, showing the cage voltage of a heat treated experimental
 Nomex* felt bag, presents the characteristics of a higher resistivity
 fabric.  In both voltage traces,  the pulse-jet cleaning of the bags
 produces a sharp voltage spike, especially when  the  row of bags
 pulsed is that  to which  the electrometer is  attached  (Row 1,
 Figure 2a).  When neighboring  rows  are  pulse-cleaned,  the  voltage
 spike  is of opposite  polarity  and reduced  magnitude.   The  time
 constants  associated  with cage voltage  recovery  depend  strongly on
 fabric  resistivity, as is evident in the plots of Figure 2.
      Among  the  conclusions drawn in Reference 1 were  the  following:
       1.  The electrostatic charge originates primarily because of
          triboelectric  interactions between the fabric and the
          dust.  Charges on the dust alone do not dominate the
          observed cage voltage, as is  made evident by the
*Tradename of E.  I.  duPont de Nemours and Company.
                               298

-------
   I20r
    90
uj   60
o
h   30
   -30
   -60
   -90 L-
DACRON FELT (EST. R - 109 OHMS)
DUST FEED RATE: 9 g/m3 (4 grains/ft3)
AIR/CLOTH: 3 em/see (6 fpm)
PULSE PRESSURE: 0.62 N/mm2 (90 psi)
RELATIVE HUMIDITY: 50%
                      2           3             I            2
                           ROW  BEING PULSED
           a)  BAG OF LOW  ELECTRICAL  RESISTANCE (POLYESTER FELT)
   sooor
UJ
UJ
  -5000
             EXPERIMENTAL NOMEX FELT
               (MEASURED R = 5 X 1011 OHMS)
             DUST FEED RATE: 9 g/m3
                                      AIR/CLOTH:  3 cm/sec
                                      PULSE PRESSURE:  0.62 N/mm2
                                      RELATIVE HUMIDITY:  50%
            b)  BAG OF HIGH ELECTRICAL  RESISTANCE (EXPERIMENTAL NOMEX FELT)
                       FIGURE 2.  CAGE VOLTAGE FORMS
                                     299

-------
            dependence of cage voltage upon fabric type.  Switching
            fabrics, while maintaining comparable electrical iso-
            lation and filtration conditions, causes significant
            differences in the observed cage voltage.
       2.   The pulse-cleaning action creates a voltage spike of
            sign and magnitude dependent on the bag charge.  In
            this sense the pulse-jet cleaning enhances the signal-
            to-noise ratio for the detection of electrostatic effects.
       3.   Pulse-jet cleaning removes charge as well as dust from
            the bags during cleaning.  When a neighboring row of
            bags is pulse-cleaned, the shift in bag charge is
            opposite to what it is when the monitored bag's row
            itself is pulse-cleaned.
       4.   Air flow alone produces only small cage vsltages.  With the
            addition of flyash to the air flow (4 gra.ins/acfm), the cage
            voltage increases significantly in magnitude and changes
            sign.
     Further exploration of the relationship between electrostatic
charge buildup and the resultant cage voltage is one of the two
major purposes of this paper and is  discussed next.   Following that,
the final section of the paper relates these cage voltages to fabric
filtration performance,  the second major purpose of  the paper.
                                 300

-------
                    ELECTRICAL EQUIVALENT CIRCUIT

      The measurement of static charges on insulators is most often
performed by an inductive technique such as the Faraday "pail"
method [Reference 11].  In such methods the insulator charges are
not required to move but merely to terminate their lines of force
on charges induced in an adjacent conducting surface.  Since that
surface is a conductor, these induced charges can be measured by
direct coupling to a conventional electrometer and a measure of the
insulator charge is obtained even though no direct contact to it
is established.
      In the baghouse apparatus employed here, the electrically
conductive cage serves as the "adjacent surface" used to detect the
charges on or in the fabric.  The cage, however, is more than
adjacent; it actually makes direct contact with the fabric as well
so that the possibility also exists for direct charge flow from the
fabric to the cage.
      A similar relationship couples the cage charge to the baghouse
housing which is electrically grounded.  Consequently, at a minimum,
the electrical  equivalent circuit should consist of two capacitors
and resistors in series as sketched in Figure 3.
                               301

-------
HOUSING
CAGE
COLLAR
FABRIC
SURFACE
                                                O VELECTROSTATIC
                        CAGE
           FIGURE 3.  BASIC ELECTRICAL EQUIVALENT CIRCUIT
                               302

-------
     The forcing function, V^,   .    .  ..  , represents the voltage
created by two separate actions:
     1.  the electrostatic charge generated on the fabric by the
         dust flow, and
     2.  the fabric motion during the  pulse-cleaning of each
         row of bags.
     If electrostatic charge generation is proportional to gas
flow through the bag, this contribution to the forcing function
could take on a form such as illustrated  in Figure 4.  This plot,
reproduced from Reference 12,  is the calculated gas flow through
one bag of a specific pulse-jet baghouse.  This calculation is
for a 4 x 4 matrix of bags but shows the  variation of gas flow to
be expected in a pulse-jet baghouse in general.  The rapid rise
in flow coinciding with the cleaning pulse comes about because of
the low flow resistance of a freshly cleaned bag--a bag with
little or no filter cake in place.   As the cake rebuilds on the
cleaned bag,.the air flow through it decreases rapidly until the
adjacent row is cleaned.  The rapid increase in gas flow through
this neighboring bag causes a corresponding rapid decrease in
flow through the monitored bag which subsequently recovers as the
flow through the just cleaned row decreases.   And so on for the
remaining rows in the baghouse until the monitored bag is pulse-
cleaned again.
                              303

-------
                    cc
CM
I
a

o
DC
X
                         1,000
o
                       t  500
                    u.

                    o
                    K

                    UJ
                    O
                                                    4                   8
                                                        TIME, MINUTES
                FIGURE 4.  GAS FLOW RATE THROUGH ONE BAG  OF A FOUR-ROW PULSE-JET ARRAY (REF. 12)

-------
      Even without a charge generation function of the form illus-
trated in Figure 4, the pulse-cleaning action should induce a
voltage spike on the cage—simply because of the bag motion during
the cleaning.  Charge in or on the fabric undergoes a change in
position and hence in capacitive coupling to the cage when the bag
is pulse-cleaned.  This action alone causes a cage voltage spike.
In addition the cleaning action can cause a change in the bag
charge; the net bag charge may be changed because of the dust
removed by the cleaning action.
      The cage voltage, therefore, depends upon a number of variables
which are not well defined or easy to measure.  While the initial
simulation of the cage voltage is being carried out with the simple
circuit of Figure 3, additional elements, as illustrated by the
distributed resistances and capacitances sketched in Figure 5, seem
more realistic and will be added as necessary.
      Once having settled upon an adequate equivalent circuit, the
problem becomes one of accurately describing the forcing function.
Many variables could influence the form of the forcing function so
that selecting a realistic representation may be neither trivial
nor obvious.  Further experimentation will be carried out in order
to further define its dependencies.
      Various combinations of equivalent circuits and forcing func-
tions are now being studied on an Electronics Associates 380 analog
computer as preliminary work in the development of a quantitative
model.
                                305

-------
FIGURE 5.   MODIFIED EQUIVALENT CIRCUIT CONTAINING DISTRIBUTED COMPONENTS
                                  306

-------
             RELATIONSHIP BETWEEN FABRIC ELECTROSTATIC
               PROPERTIES AND COLLECTION EFFICIENCY
     Ultimately, interest in the electrostatic properties of a
dust/fabric system depends upon the relationship between these
electrostatic properties and the performance of the fabric as a
filter for the dust.  If electrostatics exert little or no influence
upon filtration performance, interest in the electrostatic
properties of fabric filters will diminish rapidly and rightly
so.  If, however, electrostatics are important or are important
under certain conditions, this information should be better known
and increased study of the interaction is warranted.
     Evidence is slowly accumulating to suggest that electrostatic
interactions can be important second or even first order effects
in fabric filtration performance [Reference 9].  Some additional
data to further support the significance of electrostatic properties
are presented in this section.  Both the data reported here as
well as those in Reference 9 are based on fabric filtration
systems in which the major filtration action comes from conventional,
high performance fabric filters—those which conventionally
filter with collection  efficiencies on the order of 99+%.   Variation
in the electrostatic properties of  the dust/fabric system has
                              307

-------
 been shown in Reference 9 to alter the operating  costs  of filtra-
 tion (by varying the time required between  fabric cleaning cycles;
 i.e., by influencing the drags  and specific cake  resistance
 during filtration).   In this work we  show what  we interpret to  be
 an electrostatic influence upon dust  cake formation with  its
 attendant effect upon dust collection efficiency.
 Collection Efficiency Experiment
      The relationship between electrostatic properties  and collection
 efficiency suggested itself from independent routine laboratory
 evaluation of various fabric filters  [Reference  13].   In  comparing
 the collection efficiency of an experimental  Nomex felt with that
 of a standard Nomex  fabric not  having gone  through the  special
 heat treatment associated with  the  preparation of the experimental
 Nomex,  a  correlation  between  the observed electrostatic properties
 and the collection efficiency was noted.  The experimental  Nomex
 bags exhibited very  high  cage voltages during filtration--the
 highest values seen  in  our measurements.
      At the same time,  they filtered  redispersed flyash with
 uncharacteristically  low  collection efficiency (~97%).   Conventional
 Nomex felt bags routinely  filter this dust source with  efficiencies
 in  excess of  99%.  The fabric manufacturer  (DuPont) expressed
 surprise at this result and cited his own measurements  of collection
 efficiency in which similarly prepared experimental  Nomex bags
 and comparable-weight standard Nomex bags performed similarly
when filtering cement dust.  Both filtered cement dust  with
collection efficiency in excess  of 99%.
                              308

-------
       The  thought  occurred  to  us  then  that  the  significantly
 different  cage  voltage  noted on the  experimental  Nomex was  perhaps
 related  to the  fabric performance as a filter.  The  reason  for  the
 high  cage  voltage  was hypothesized to  be  the  result  of the  heat
 treatment  associated with the  preparation of  these experimental
 fabrics.*   During  the preparation of these  fabrics,  the  fibers  are
 exposed  briefly (2-3 min) to a temperature  of about  315°C (600°F).
 This  heat  treatment probably volatilizes  the  anti-static coatings
 normally found  on  Nomex, rendering the fabric electrical resistance
 much  higher than before the treatment.  As  can  be seen from the
 equivalent circuits proposed in the  previous  sections, increasing
 the resistance  between the cage and  ground  (R-j  in Figure 3) increases
 the magnitude of vCaqe» assuming  all other  parameters, including
 the charge generation function, VE,  remain  constant.
       In order  to  verify the role  of the  anti-static coating, two
 new sets of fabric filters were prepared:
       1.   The first was the control  group,  prepared as before,
           including the heat treating  step.
       2.   The second group was identical  to the first except
           that all  bags were sprayed with an anti-static coating
           after the heat treatment.
*This hypothesis was originated by Dr. H. Forsten, E. I. duPont de
Nemours and Company, Wilmington, Delaware.
                               309

-------
      Table 1 lists the manufacturer's description of the two test
 fabrics.  The fabrics are nominally identical  except for the anti-static
 coating of the second fabric.
 Results
      Electrostatically the two test fabrics,  not surprisingly,  are not
 identical.   The control  bags exhibited cage voltage spikes in excess  of
 1000 volts,  while the maximum  cage voltage of  the coated bags was about
 50 volts.  While not the actual  voltage traces recorded  on these  test
 bags,  the  traces contrasted in Figure 2 correspond roughly to those
 recorded on  the test bags,  Figure  2a  representing the  coated bag  and
 Figure 2b, the  control.
     Table 2 summarizes  the measurements  of collection efficiency and
 outlet concentration.  The  important  conclusion  from the data of  Table 2
 is  that the  addition of  the anti-static coating  (Run No.  1)  improved  bag
 collection efficiency over  that  of the  uncoated  control  bag  (Runs  No.  2
 and  4).  The  run  numbers  correspond to  the  chronological  order  in  which
 the  measurements  were  made.  When  the measurements are made  on  the same
 fabric,  the  run  number tells the order  in which  the run  was  made.   (In
 Table  2, Run  4  followed Run  3 which followed Run  2--all  on the  same set
 of bags.)
     Increasing the  relative humidity from 50% to 70% improved  col-
 lection efficiency even more (Run No. 3).  At 70%, relative  humidity,
 the cage voltage  changes its character significantly from that
 at 50% relative humidity (Figure 2b).  The voltage spikes associated
with the cleaning pulse are reduced in magnitude to the order of
                                310

-------
                                TABLE 1

                    EXPERIMENTAL NOMEX TEST BAGS*

                           (SCRIMLESS FELTS)
                                                     BAG SET 2
                             BAG SET 1          (CONTROL + ANTI-STATIC
                            (CONTROL)              COATING)*

BASIS WEIGHT                   17.0                     17.4
  (oz./yd.2)

THICKNESS                     93                       89
  (mils)

AIR PERMEABILITY              12                       17
(cfm/ft2 at 0.5 in. H20)
v»*
 •Courtesy of H. Forsten, E. I. du Pont
**Sprayed with 1% "Avitex" DN
                                311

-------
                                                  TABLE 2

                                          BAG PERFORMANCE SERIES
 p—'
 K)
    RUN
    NO

     1
    4
             FABRIC

CONTROL WITH ANTI-STATIC COATING
     (50% RELATIVE HUMIDITY)

         CONTROL ALONE
     (50% RELATIVE HUMIDITY)

         CONTROL ALONE
     (70% RELATIVE HUMIDITY)

         CONTROL ALONE
     (50% RELATIVE HUMIDITY)
COLLECT.
 EFF. (%)

  98.7*
  97.1


  99.3


  96.8
OUTLET CONC.
(GRAINS/103 ft3)

     44.6*
                                                                        118
                                                                         28.2
                                                                        128
 BAG PRESSURE
CHANGE DURING
ONE FILTRATION
 CYCLE (in. H20)
     "*! ' APf)
      0.50
   (3.15 - 3.65)

      0.20
   (2.80 - 3.00)

      0.20
   (2.80 - 3.00)

      0.15
   (3.55 - 3.70)
* Average of two runs, 2 days apart

-------
50-70 volts (Figure 6).  What also differentiates this cage voltage
trace from that of Figure 2a is the relatively high steady state
voltage evident in Figure 6.  The cage signal in Figure 6 is still
better isolated electrically from ground than that in Figure 2a.
Whatever else the high relative humidity does, it seems not to
degrade R-, in the elementary equivalent circuit of Figure 3.
     These data immediately suggest that a negative cage bias is a
desirable operating condition.  Such a bias could be externally
applied to the cage via the same leads previously used to monitor
the cage voltage.  The effectiveness of such a bias depends upon
the values of C? and R? (Figure 3) of any given fabric/dust system,
since the voltage appearing at the physically poorly-defined
Electrostatic tern"na^ of Figure 3 1S most likely what the dust
being filtered will sense.
     Any improved collection efficiency anticipated for operation
with a negative bias on the cage did not materialize (Table 3).  A
                                                          g
bias of -2000 volts applied to all nine cages through a 10  series
resistor produced a cage voltage trace as shown in Figure 7.  The
Row 3 cleaning pulse appears to be less effective than those of
Rows 1 and 2, as indicated by the smaller voltage spike associated
with its firing.  This condition was also evident in some of the
data presented in Reference 10, and was attributed to blow pipe
misalignment, pressure leaks,  or some other condition not involving
electrostatics.
                                313

-------
 200

 100

   0
-100

-200
                 EXPERIMENTAL NOMEX FELT
                       I min
UJ
                                  2            3
                                  ROW BEING PULSED
                 DUST FEED RATE: 9 g/m3 (4 grains/ft3)
                 AIR/CLOTH:  3 cm/sec (6 fpm)
                 PULSE PRESSURE: 0.62 N/mm2 (90 psi)
                 RELATIVE HUMIDITY: 70%
 FIGURE 6.  CAGE VOLTAGE  DURING FLY ASH FILTRATION  AT HIGH RELATIVE HUMIDITY
                                      314

-------
OJ
f—'
Ui
                                                TABLES

                           CONTROL BAG PERFORMANCE UNDER CAGE ELECTRICAL BIAS

                                    (ALL RUNS AT 50% RELATIVE HUMIDITY)
                                                                                       BAG PRESSURE
                                          COLLECT.ON             OUTLET CONC           CHANGE «*L HjO)
  RUN MQ.             CAGE BIAS              EFF. (%)              (GRAINS/1Q3 tf) 7          (AP,  A"''	

     6                 FLOATING                96.6                    136                    ^8
                      GROUNDED               98.1
                                                                      75'9
     8                -2000 VOLTS             97.6                     97.0                (4.14-4.31)

-------
                                                                    BAGS
u>
               Id
0
-1000
-2000
-3000
9
9
-2000 V ~O9fl V
1 1 "VW '
1 1 1
1 1 1
	 N *_ _A
23 1
9
9
9

^
2
9
9
9


3
3
2
1
— 1 min 	 »
i i
i 1
. L
1
                                                     PULSING ORDER
                           FIGURE  7.   CAGE VOLTAGE  UNDER AN EXTERNAL BIAS OF -2000 VOLTS

-------
     Table 3 shows that the presence of this electrical bias
doesn't significantly alter the collection efficiency of the
bags--at least not nearly as significantly as the higher humidity
operation did (Run 3, Table 2).  The opposite polarity (+2000
volts on the cage) also produced no significant change in collection
efficiency.
     In spite of this low sensitivity to bias levels, cage electrical
termination is important as the data of Table 4 show.  Low resistance
terminations to the cages are superior to the high resistance,
floating termination; that is, filtration performance with various
cage electrical terminations (Table 4) shows that controlling the
electrical termination of the cage does influence filtration per-
formance.  These data show that the coupling between the fabric
charges (the VE terminal, Figures 3 and 5) and the cage is strong
enough to allow different cage terminations to influence enough
of the active filtering surface as to be detectable by the measurement
of collection efficiency.  Having the bags tied together electrically
(Run 6, Table 4) does not produce a significant change in performance
from operation with each bag electrically floating alone (Run 4,
Table 4).
     The conclusion from the termination and bias  data of Tables
3 and 4 is that having a low leakage path for the  electrostatically
generated cage charges is more important than any  arbitrary  cage
voltage level.   Operating with the  cage at high electrical  isolation
from ground degrades  collection efficiency.   Reducing the cage
electrical  isolation  (whether by humidity, conductive fabrics or
                               317

-------
                                                    TABLE 4

                       CONTROL BAG PERFORMANCE AT VARIOUS CAGE ELECTRICAL TERMINATIONS

                                       (ALL RUNS AT 50% RELATIVE HUMIDITY)
  RUN NO.
00
CAGE ELECTRICAL
  TERMINATION

  FLOATING
                       GROUNDED*


                       FLOATING*


                       GROUNDED*
COLLECTION
  EFF. (%)

   96.8
                            97.9
                            96.6
                           98.1
OUTLET CONC.
(GRAINS/103 ft3)

     128
                             83.8
                            136
                             75.9
 BAG PRESSURE
CHANGE DURING
ONE FILTRATION
 CYCLE (in. H2O)
   (APj - APf)

      0.15
   (3.55 - 3.70)

      0.15
   (3.55 - 3.70)

      0.28
   (4.52 - 4.80)

      0.18
   (4.23-4.41)
     *AII nine bags tied together electrically.

-------
 direct contact to ground) produces superior performance with
 respect to dust collection efficiency.
       Charge generation is also part of the overall effect and the
 influence of each of these "corrective" actions upon charge generation
 is not so clear as their effects upon cage electrical isolation.
 The total problem, therefore, has only been partially considered; the
 influence of these variables upon VE is yet to be determined.
 Polyester Felt Experiment
       To better establish the tentative relationship illustrated by
 the measurements made on the experimental  Nomex fabrics described
 in the preceding sections, the experiment was repeated on two sets
 of felted polyester bags.  Both of these sets of needled Dacron
 felt bags have nominal  properties as listed in Table 5.
       What has been previously shown is that a bag of high electrical
 resistance and relatively low collection efficiency can be converted
 into a bag of lower electrical  resistance  and higher collection
 efficiency by spraying  the bag with an anti-static coating prior to
 the filtration tests.
       With the two sets of polyester bags  (Table 5) the bag electrical
 properties were changed in the opposite direction to that of the Nomex
 experiment.  Initially both sets of bags have been manufactured with
 anti-static coatings, the standard procedure.  With one set of bags this
 anti-static coating was removed, at least partially, by repeated soaking
(no agitation) in perch!oroethylene.  Bag resistance increased as a result
of this soaking, presumably because of coating removal.

                                319

-------
                         TABLE 5

     PROPERTIES OF NEEDLED POLYESTER FELT FABRIC*




         WEIGHT (oz/yd2)                 16.0

         THICKNESS (mils)                 58.0

         AIR PERMEABILITY               25.9
         (pfm/ft2 at 0.5 in. H2O)
•Measurements by FRL, an Albany International Co., Dedham, MA
                       320

-------
      Table 6 shows that the bags from which the anti-static
coating has been removed filter less efficiently than  those standard
bags on which it remains.
      This result corroborates the results of the experimental
Nomex bag, linking the bag electrical resistance to its filtration
performance.   The cage voltage of the soaked polyester felt bags
was, perhaps, an order of magnitude greater than what  has been  seen
on standard polyester felt bags (Figure 2a).  The lone voltage
trace made with the soaked polyester bags was noisier  than typical
but the magnitude of the primary voltage spikes was about 500
volts, as compared with 50-70 volts usually seen on the standard
polyester felt bag.
                             321

-------
                      TABLE 6

 FILTRATION PERFORMANCE OF THE TEST POLYESTER FELTS
       FABRIC TESTED

jj»   STANDARD POLYESTER
           FELT

 STANDARD POLYESTER FELT
   AFTER MULTIPLE SOAKS
   IN PERCHLOROETHYLENE
 ELECTRICAL
 RESISTANCE
OF MOUNTED
 BAGS (ohms)

  108 _109
    > 1010
COLLECT.
 EFF. (%)

  99.8
  97.2
OUTLET CONC.
(GRAINS/103 ft3)

      6.9
     111
 BAG PRESSURE
CHANGE DURING
ONE FILTRATION
 CYCLE (in. H2O)
   (APj - APf)

     0.10
   (1.50- 1.60)
     0.10
   (2.60 - 2.70)

-------
                             CONCLUSIONS

1.   Bag collection efficiency is  highest when:
     a)  Relative humidity is high (70% is better than  50%).
                                     8                       10
     b)  Fabric resistance is low  (10  ohms is  better than  10
         or 10   ohms).
     c)  The cage is electrically  grounded (grounded cage is
         better than floating).
2.   These conclusions are valid only for the redispersed flyash
     used in these experiments and over the specified range of
     the variables considered, but they show that electrostatic
     properties can be important in fabric filtration.
                               323

-------
                           ACKNOWLEDGMENT

      Dr. Herman H. Forsten, Textile Research Laboratory, E.  I.
duPont de Nemours and Company, Wilmington, Delaware, provided advice
and assistance in our attempts to relate the cage voltage measure-
ments to the collection efficiency of flyash.  He arranged for the
fabrication of the Nomex test bags which were donated by DuPont.
He also advised us on methods for removing the anti-static coating
from the Dacron felts.
                             324

-------
                              REFERENCES
1    Rudge, W.  A.  D.,  "On the Electrification  Produced during the Raising
     of a Cloud of Dust," Proceedings  of the Royal  Society. Vol. XC-A,
     pp. 255-272,  1914.

2    Deodhar, G. B., "Electricity of Dust Clouds  -  Part  I," Institute
     of Physics and the Physical  Society.  Proceedings of  the Physical
     Society. Vol. 39, pp. 243-249, 1927.

3.   Kunkel, W. B., "The Static Electrification of  Dust  Particles on
     Dispersion into a Cloud." Journal of Applied Physics, Vol.  21,
     pp. 820-832,  1950.

4.   Kraemer, H. F. and H. F. Johnstone, "Collection of  Aerosol  Particles
     in Presence of Electrostatic Fields." Industrial and  Engineering
     Chemistry, Vol. 47. No. 12, pp. 2426-2434, 1955.

5    Rossano, A. T., Jr. and L. Silverman, "Electrostatic  Mechanisms  in
     Fiber Filtration of Aerosols," Report No. NYO-1954, Harvard School
     of Public Health, 1955.

6.   Rao,  K., S. T. Ariman, K. T. Yang and R.  L. Hosbein,  "Collection of
     Dust  by Fabric Filtration in an Electrostatic Field." 2nd  Annual
     Environmental Engineering and Science Conference, Louisville,
     April 1972.

 7.   Makino, E., K. linoya, M. Shibamoto, S.  Toyama, and F. Ikazaki,
     "Experiments  on  Electrical.Dislodging of.Dust Layers," Trans.  Japan
     Chemical Engineers  Society. Vol 2. No. 1, pp. 31-37,  1976.'

 8.   Frederick, E. R., "How Dust Filter Selection Depends on Electrostatics,"
     Chemical Engineering, pp. 107-114, June 26, 1961.

 9.   Penney, G. W. and E. R. Frederick,  "Electrostatic Effects in Fabric
     Filtration, final report  for  EPA Research Grant No.  R803020, in
     preparation.

 10.  Donovan, R. P.,  R.  L. Ogan, and J. H. Turner, "Electrostatic Effects
     in Pulse-Jet  Fabric Filtration of Room Temperature Flyash,"  pres-
     entation to the  Engineering Foundation Conference, "Theory, Practice
     and  Process  Principles for  Physical Separations," Asilomar Conference
     Grounds, Pacific Grove, California, October 30  - November 4, 1977.

 11.  Hersh,  S.  P.,  "Resistivity  and Static Behavior  of Textile Surfaces,"
     Chapter 6  in  Surface Characteristics of  Fibers  and Textiles. Part 1,
     edited  by  M.  J.  Schick, Marcel Dekker, inc., z/u Madison Avenue,
     New  York,  N.  Y.  10016  (1975).

                                 325

-------
                        REFERENCES (Continued)
12.  Theodore, L., J.  Reynolds, A.  Corvini,  and A.  Buonicore,
     "Particulate Control  by Pulsed-Air Baghouse Filtration:   De-
     scribing Equations and Solution,"  pp. 90-103 in  The User  and
     Fabric Filtration Equipment II.  APCA Specialty Conference Proceed-
     ings, Buffalo, New York, October 1975,  Air Pollution Control Assn.,
     4400 Fifth Avenue, Pittsburgh,  PA  15213 (1975).

13.  Turner,  J. H., "EPA Research in  Fabric  Filtration:   Annual  Report
     on IER1,-RTP In-house Program,"  EPA-600/7-77-042  (NTIS No.  PB
     267441/AS), May 1977.
                               326

-------
To Convert From:
foot
yard

Ib (force)

foot
inch
mil
yard

grain
Ib (mass)

inch of-water  (60°F)
Winch?  (psi)
foot/mi n  (fpm)

foot?
inch.,
yard

oz/yd2

grains/ft
grains/1000 ft
                                APPENDIX
                           CONVERSION FACTORS
  To:
meter,
meter'
meter'
newton
Multiply By:

        ,-2
9.29 x 10
6.45 x 10
8.36 x 10
4.45
                                                                     -4
                                                                     -1
meter
meter
meter
meter
kilogram
kilogram
2
newton/meter^
newton/mete^
newton/meter
meter/sec
3
meter.
meter..
meter
0
kg/nr
kq/m3

g/nr
3.05 x
2.54 x
2.54 x
9.14 x
6.48 x
4.54 x
2.49 x
6.89 x
4.79 x
5.08 x

2.83 x
1.64 x
7.65 x

3.39 x
2.29 x

2.29 x
10_2
10 i
10 1
10"1
"I?
10 '
10t?
10Ii
10 '
io-2
_9
10-5
10-1
10 '
_2
10 d
ID'3
_ J
10 J
                                                             'K = -4 (°F +459.67)
                                  327

-------
328

-------
                        TEXTILE FILTER MEDIA DURABILITY

                               Winston F. Budrow


     In reviewing the requirements for a textile filter media, three basic pri-
mary functions are generated.  The first primary function of the filter media
is to separate and collect suspended particulate matter from a gaseous stream
and allow the cleaned gaseous stream to pass through.

     As the filter media collects particulate matter, the fabric achieves a
diminishing return in which the filter media will no longer pass air through
it at an acceptable level.  At this point, it becomes necessary to remove the
collected particulate matter and regenerate the filtering qualities of the
filter system.  For this reason, cleanability becomes a primary function also.
The filtering and cleaning qualities are referred to as a cycle.  The cycles
of filtering and cleaning must be performed in a repetitive fashion, as dic-
tated by economic factors.  Therefore, the third primary function is determined,
that of durability.  These three primary and equally important functions,
namely:  filterability, cleanability and durability, depict the filter media's
ability to perform.

     This paper concerns itself with the primary function of durability.  Dura-
bility can best be defined as the resistance to the chemical and physical break-
down associated with fabric filtration.

     The physical breakdown results generally from the filtering and cleaning
functions, whereas the chemical breakdown results generally from the chemistry
and thermo characteristics of the environment to which the filter media is
being exposed.

     Chemical breakdown of the filter media is the most common cause of premature
fabric failure in filtration, primarily due to the fact that it is the least un-
derstood.  Synthetic organic fibers are generated through chemical reactions to
form the polymer phase from the monomer phase.  In chemistry, chemical reactions
yield the resultant, which indicates the reactions are reversible.  There lies
the weak link in fabric technology.  Any substance or condition which tends to
reverse or break down the polymer structure of the fiber will cause premature
deterioration of the filter fabric.

     In most filtration systems, the one critical ingredient which activates the
chemistry of the dust and the gases is moisture.  Normally, dust materials, when
in a dry phase or void of moisture, are relatively inactive; whereas, in the wet
phase or presence of moisture, the dust material or gases are liquified and
                                      329

-------
 become  chemically  very  active  and  attack  the  fiber structure,  either  through  a
 direct  reaction  or a  catalytic reaction.  Moisture in itself  can cause  damage
 to  certain filter  media through hydrolysis  or oxidation.   These  reactions  can
 be  catalyzed or  accelerated  due to the  presence  of an acid condition, alkaline
 condition  and/or temperature elevation.

      To combat deterioration situations,  a  proper  fiber  selection most  resistant
 to  the  environmental  conditions is the  first  primary  step.  Secondly, by under-
 standing the potential  chemical activity  of the  gases and  the  dust, one can
 establish  the necessary controls and precautions to be taken  for prolonging the
 durability of the  filter media.

      Physical breakdown of the filter media presents  a different type of fiber
 fatigue or distruction.  All fiber filter media will,  of course,  fail at some
 point due  to use;  however, it  is the extension of  the physical breakdown which
 is  of concern to us.

      Normal  physical  filter  media  breakdown is the  result  of work performed.
 The work performed can  be defined  as the  filtering  actions, cleaning actions,
 and the stress strain associated with those functions.

     The filtering phase is  probably the  most vulnerable to excess physical
 attack,^due  to the  unpredictable aerodynamics of the  air volume.  The air volume
 in combination with the  particulate matter  enters  the  cylindrical filter bag  at
 high velocities.   If the entry  is  not perpendicular,  dust  impingement occurs
 and gives  a  sand blasting effect,  resulting in premature failure.  Even when
 the dust entry is  perpendicular to the bag, however,  attack will  occur  if the
 bag is  not properly installed.   An improperly installed bag will  result in
 fabric  deformation which allows folds or  pleats to be  contacted  by the  high
 velocity dust, resulting in  the same premature failure.

     Naturally,  many forms of excessive physical attack can occur due to the
 variety of baghouse designs,  filter media types and applications.  The  important
message concerning fabric premature deterioration is to detect the condition  and
 correct the  situation.

    ^In summary,  durability  is  a primary  function of filter media performance
 and is the most  important subject  for proper economical baghouse performance.
Filter media life or durability can be substantially extended in most systems
by a complete investigation and evaluation of filter media which could yield
 substantial savings in both the cost of the filter media and the operating costs
 involved with baghouses.
                                     330

-------
                 HIGH-TEMPERATURE  FILTRATION
            Dr. Dennis C. Drehmel
            U.S. Environmental Protection Agency
            Research Triangle Park, N.C.  27711
            Michael A. Shackleton
            Acurex Corporation
            Mountain View, Calif.   94042
                           Abstract

Research on high temperature particle control using ceramic
fiber barrier filtration has shown this technique offers
promise of successful development.  Results of testing of rigid
ceramic membrane structures and of ceramic fiber beds including
woven, paper and felt ceramic filters are presented.
                             331

-------
                  HIGH-TEMPERATURE FILTRATION

 Introduction
        Removal of particles from high temperature gas  streams
 has been studied for many years.   Some of the  motivation for
 this research was the desire to operate coal fired gas tur-
 bines.1   Recently there  is renewed interest  in the utilization
 of  coal.   The processes  most actively being  studied are pres-
 surized  fluid bed combustion (PFBC)  and gasification combined
 cycle (GCC)  plants.   Both processes  are called combined cycle
 since they generate  power by means of gas turbines as  well  as
 steam turbines.
       in  the PFBC,  coal is burned in a fluid  bed of limestone
 (which removes the S02)  and heat  is  transferred to.tubes in the
 fluid bed.   Up to 80% of the recoverable  heat  value of the  coal
 is  removed in the fluid  bed,  and  the  gas  exits at 1500°F and
 10  atm pressure.   The gas  must  now be expanded through a gas
 turbine  to recover the remaining  energy.   However,  previous
 investigations showed that large  particles erode turbine blades
 and  small  particles  cause  deposits that choke  the turbine.   To
 protect  the  turbine,  some  high-temperature particulate control
 is required.   Moreover,  since it  would  not be  economical to
 duplicate  particulate control for environmental  regulations at
 another point  of  the  process, high-temperature control must
 also  meet  new  source  performance  environmental standards for
 coal-fired utilities.  Currently,  this  allows  emissions  to  be
 no greater than 0.1  ft/million Btu.
       To meet both the environmental and turbine  requirements,
 a system consisting of two  cyclones and a filter  is  being
 studied.   The  two cyclones  lower  the  overall particle  concen-
 tration but fail to remove  small particles.  Concentrations
 leaving the second cyclone  can be as high as 1.0 grains/scf
and have a mass median diameter of 5.0  pm.  The  filter can be
a ceramic bag filter, a ceramic membrane, or a granular  bed.
                             332

-------
Research to date has concentrated on the granular bed since it
has been considered available technology.  However, results of
tests at the Exxon PFBG Miniplant have been disappointing.2
The granular beds tested could barely meet the environmental
standard at the beginning of a run and lost efficiency contin-
uously from 95% to as low as 50% within 24 hours.  Although
granular bed filters may still prove to be a solution to high-
temperature particle control, it is now apparent that they will
require more developmental work.
       Alternative high-temperature filters, using either a
ceramic bag or ceramic membrane, are being developed.  The
remainder of this paper will be devoted to describing ongoing
work by the Environmental Protection Agency to assess these
high-temperature filters as part of environmental control for
the PFBC, although it is expected that results can be extrapo-
lated to the GCC or to high-temperature metallurgical operations

Ceramic Membrane Filters
       Several ceramic materials in many configurations were
screened as possible high-temperature filters.   One of the
most promising materials tested was a ceramic cross flow
monolith produced by 3M Company under the trade  name of Therma-
Comb.  This material is composed of alternate layers of corru-
gations separated by thin filtering barriers.  This type of
configuration affords a large amount of  filter surface in a
very small volume.  Figure  1 shows a piece of this material
illustrating the construction.
       Bench side experiments were conducted in  the high-
temperature ceramic test facility at 970°K.  Provisions were
made to blow back from the  clean side and also down the chan-
nels on the dirty side so that various cleaning  schemes could
be investigated.  A sequencer was designed to automatically
start and operate the cleaning cycle.  A 17 cm diameter by
38 cm deep tubular furnace  was used to heat the  filter.  An
additional furnace was added to preheat  the dust-laden air.
                            333

-------
Figure 1.  3-M Company Thermacomb.
              334

-------
       Cascade impactors were used to determine the size dis-
tribution of the test dust (limestone).   The typical mass median
diameter was 1.4 ym and the geometric deviation was 3.0 urn.  There
was some difficulty in maintaining constant feed rate, but dust
                                              3          3
loadings were maintained at levels from 2 gm/m  to 7 gm/m  .
       Typical results for filtering the limestone test dust
with the 3M ThermaComb are summarized in Table 1.  Table 2
shows the effect of varying the initial pressure of a 0.6-
second pulse.  Table 2 also shows the result of a similar  set
of runs except that the pulse time was increased from 0.6
seconds to 5 seconds.  These data show that the length of  the
pulse does not have much effect on the cleaning results.   In
both runs the collection efficiency was very high  (99.6 to
100%) at a linear velocity of 0.41 m/min  (1.33 ft/min).  Using
the 103.4 kPa pressure pulse for cleaning, it was possible to
return to a stable pressure drop across the filter in spite
of the relatively high dust loadings which in these two runs
were 2.6 and 3.75 gm/m .
       Tests using the 3M ThermaComb as a filtering media
showed filtering efficiency to be close to 100% even  though
the test dust had a mass median diameter of 1.4 ym and a sig-
nificant fraction of sub micron material.  Cleanability of the
media was verified in experiments evaluating the effect of
cleaning pulse intensity and duration.  It was determined
that the ceramic filter behaved similarly to fabric filters
in that the pressure drop could be attributed to a residual
pressure drop and that across an incompressible cake.

Ceramic Fiber Barrier Filters
       Ceramic fibers are produced by several manufacturers.
In general, these materials are sold for refractory insulation
applications.  Many of these ceramic fiber materials  are pro-
duced in smaller fiber diameters  (3 ym) than are generally
                             335

-------
         Table  1.   Summary  of  3M ThermaComb Performance
       Flow rate
         3, .
        m /nun
       Filter area
         2
        m
       Inlet/Concentration
        gm/m
       Temperature
        °K
       Efficiency
        Percent
Average     Range Tested
 0.095        0.04  -  0.16

 0.0227
 3.6
990
96.6
2.2 - 5.4
953 - 1088
85 - 99.6
       Table 2.  Effect of Changing Cleaning Conditions
Pulse
Test Pressure
Number KPa
1 34.5
1 69.0
1 103.4
2 103.4
2 103.4
Pulse
Duration
seconds
0.6
0.6
0.6
0.6
5
Cycle
Time*
minutes
2-4
8
12 - 20
12
12
Residual Pressure
KPa
3.5 increasing to
3.0 increasing to
2.8
2.8
2.8
Drop
limit
limit



*as required to lower pressure drop away from the upper limit
available for filtration applications at room temperature  (20 urn)
This smaller fiber diameter, coupled with high temperature and
corrosion resistance characteristics, makes these fibers
intriguing candidates for high-temperature filtration
applications.
                             336

-------
       Available ceramic fiber configurations can be classified
into the following three groups of materials:
       *   Woven structures - cloth woven from long-filament
           yarns of ceramic fibers
       •   Papers — Ceramic structures produced from short
           lengths of fibers, generally held together with
           binders.
       •   Felts — Structures produced to form mats of relatively
           long fibers.  These materials are known as blankets in
           the insulation industry.  They tend to be less tightly
           packed than conventional felt materials.

Theory
       Filtration theory supports the contention that ceramic
fiber filters should perform adequately at high temperatures
and pressures.
       There are three particle collection mechanisms generally
considered to account for the performance of a bed of fibers in
removing particles from gas streams.  These mechanisms are:
direct interception, diffusion, and inertial impaction.  Exam-
ining these mechanisms under high temperature and high pressure
(800°C and 10 atm) indicates that direct interception and dif-
fusion will be roughly the same as their performance at room
temperatures and ambient pressures, while the inertial impac-
tion mechanism will be slightly less effective at high temper-
atures and pressures.  This statement is true when comparing
the performance of a clean filter bed (no dust cake) at low
temperature/pressure and at high temperature/pressure.  This
relatively minor performance reduction can be compensated for
in the design of the filter media.  For example, using smaller
diameter fibers in the filter bed can increase collection
efficiency far more than the viscosity effect of high temper-
ature reduces it.   A fiber bed consisting of 3 ym diameter

                             337

-------
 fibers, as compared with 20 ym fibers, can be expected to pro-
 vide equal collection efficiency with a 3 ym fiber bed weighing
 only one tenth as much on a weight per unit area basis.  Figure
 2 presents a calculated prediction of collection efficiency
 for a 3.0 ym fiber bed, consisting of alumina fibers, collect-
 ing a 0.5 ym fly ash particle from an air stream at 815°C and
 10 atm pressure.  The four curves show that for a decrease in
 solidity* (a)  a reduction in efficiency,  for a given basis
 weight,  should be expected.   Similarly,  an increase in airflow
 velocity causes a small reduction in collection efficiency for
 a given  filter bed (constant basis weight).   Note also that by
 adding fibers  (increasing basis weight),  all of these effects
 can be nullified.

       The magnitude  of predicted efficiency is also interest-
 ing.   This analysis shows that  for a ceramic fiber bed consist-
 ing of 3.0 ym  alumina fibers a  basis weight  of  500-600 g/m2
 should provide 80  to  90 percent collection of a 0.5 ym particle
 even at  the reduced performance levels encountered at high
 temperatures and pressures.
       For comparison,  a  standard filter media  consisting  of
 20  ym  fibers and having a basis weight of 540 g/m2  (16  oz/yd2)
 can be expected to collect only about 20 percent  of 0.5 ym
 particles at room ambient conditions.  Thus, to provide collec-
 tion efficiency performance  equal  to a conventional  filter
 requires only about one-tenth the weight of fibers  for  a 3.0
 ym fiber bed.  Or, put another way, a ceramic fiber bed of
 equal media weight to a conventional filter, but made from 3.0
 ym fibers, will be much more efficient even at high tempera-
 tures and pressures than is normally sufficient in the filtra-
tion industry.
'Solidity (a)  is the fraction of the fiber bed which is solid
            °f °'°2 ±ndicates that 2* °f the bed ifoccupLd
                             338

-------
                                       COLLECTION EFFICIENCY — %


                                      g     g      2           S
"•*)
H-
fD


NJ
o
0)
M
o
ft

ft)
(0
3
0)

E
(D

U)
•c
3

0)
H
d
3
H-
hh
H-
tr
 tr
 (D
  bo o
  
H
(O t
I ~-. 3


Is
   >

   TJ
      O

      m
                                  A-I87O4

-------
Room Ambient Filter Media Tests
       A large number of ceramic fiber filter media candidates
have been subjected to a series of filtration tests at room
ambient conditions.  These tests included some examples of con-
ventional filter media for comparison.  Included among the
tests were:
       •   Dioctylphtalate smoke (D.O.P) penetration as a
           function of air flow velocity
       •   Determination of maximum pore size  (in micrometers)
       •   Measurement of permeability
       •   Flat-sheet dust loading tests using A.C.  Fine test
           dust.  Over-all collection efficiency and dust
           loading required to develop 3.7 KPa (15 in H?0)
           pressure drop are determined from this test which
           is operated at 10 cm/sec  (20 ft/min) Air-to-cloth
           ratio.
Data collected from these tests are summarized on Table 3.
       Penetration tests using D.O.P. smoke measure the ability
of the clean fiber bed to stop fine particles.  The D.O.P.
smoke generator is adjusted to provide a nominal particle size
of 0.3 um diameter which is a "most penetrating" particle size
because of the minimal effect of diffusion and inertial impac-
tion at this particle size.  The D.O.P. test results should
correlate well to the results predicted by analysis since
particle collection is provided only by the fibers and not
by the dust cake.  Figure 3 provides a plot of the OOP effi-
ciency as a function of air flow velocity for all the media
tested.  Ceramic media data are plotted in solid lines and con-
ventional media in dotted lines.  Numbers on the curves refer
to those on Table 3.  Several interesting observations can be
made concerning this data:
       •   Several of the ceramic materials, especially the
           ceramic papers and felts, are capable of higher
                             340

-------
   100
   90
   80
   70
0)
•g  60
V)
a.
O
O
|  50
CO
o
:p   40
    20
    10
     0
                                                                       25
                 34
               15
             Figure  3,
   5                     10
      Airflow Velocity cm/sec
D.O.P.  Efficiency fn   airflow velocity.
           341

-------
                                                                           Table  3





                                                                SUMMARY ROOM AMBIENT  TEST DATA
N>


(W) Woven
(P) Paper
(F) Felt
1. Carborundum Fiberfrax cloth
(W) with nichrome wire insert
2. Zircar Zirconia felt ZFY-100
(F)
3. ICI Saffil alumina paper
(P) with binder
4. ICI Saffil mat
(F)
5. Babcock & Wilcox Kaowool
(F)
6. Carborundum Fiberfrax
(F) durablanket
7. John Mansville Fiberchrome
(F)
8. Stevens Astroquartz
(W) style 581
9. Hitc-0 Refrasil C-100-96
(W) heat cleaned
10. Hitco Refrasil C-100-48
(W) not heat cleaned
11. Stevens Astroquartz cloth
(W) style 570
12. 3M AB-312 basket weave
(W) cloth


Basis
Weight
1366

615

165

355

746

1363

1297

283

1284

667

677

311
Percent
Efficiency
on ACF @
10 cm/sec
(20 ft. min)
96.55

95.64

99.805

98.74

98.464

99.507

99.654

60.77

81.97

83.37

56.83

51.38


Dust Loading
g/m2 to 3.735 KPa
(g/ft2 to 15" H2O)
239.9
(22.2912)
Media Fractured

159.4
(14.81)
Media Fractured

118.2
(10.980)
146.9
(13.6523)
253.9
(23.59)
Test Stopped —
Low Eff.
5.9
(.5482)
11.56
(1.074)
Test Stopped
Low Eff.
Test- Stopped
Low Eff.


Permeability
cm3/sec/cm2 for 0.1245 KPa
(ft3 /miry ft2 for 0.5" #2° AP)
8.687
(17.1)
10.861
(21.38)
9.307
(18.32)
12.395
(24.4)
8.067
(15.88)
5.583
(10.99)
11.897
. (23.42)
37.236
(73.3)
1.240
(2.44)
3.099
(6.1)
22.758
(44.8)
13.553
(26.68)


Maximum
pore size
Micrometers
248.6

59

43

61.1

66.9

68.2

112.3

248.6

112.3

133.8

267.7

870


Percent Efficiency on
0.3 Mm OOP at cm/sec
2.68 5.35 14.22
45 47 50

75 70 72

82 65 62

79 80 73

96.5 93.5 86

97.1 94.6 90.5

78 73 74

0 9 12

0 19 34

0 11 10

0 13 32

0 5 8

-------
                                                                  Table  3  (Continued)
OJ


13.
(W)
14.
(W)
15.
(W)
16.
(W)
17.
(W)

18.
(W)

19.
(W)
20.
(W)

21.
(W)
22.
(F)
23.
(W)

24.
(W)

(W) Woven
(P) Paper
(F) Felt
3M AB-312 twill weave
cloth
HITCO Refrasil cloth
UC-100-48
Zircar Zirconia cloth
ZFY-30A
FMI-Stevens Astroquartz
cloth crowfoot satin
3M AB-312 twill weave
cloth coated with 3M
coating
3M AB-312 basket weave
cloth coated with 3M
coating
3M AB-312 twill weave
cloth Menarde coating
HITCO Kefrasil cloth
UC-100-96 not heat
cleaned
Carborundum Fiberfrax
no insert wire L-126TT
HITCO Refrasil batt B100-1

HITCO Pefrasil standard
not heat cleaned
very thin UC-100-28
HITCO Irish Refrasil
chromized C-1554-48

Basis
Weight
g/m2
231
643

60S

352

227


281


254

1249


1544

807

335


683

Percent
Efficiency
on ACF @
10 cm/ sec
(20 ft. min)
48.55
69.26

99.014

76.19

47.64


45.65


55.078

68.46


99.21

99,229

84.41


81.476


Dust Loading
g/tn2 to 3.735 KPa
(g/ft2 to 15" H20)
Test Stopped
Low Eff. (same)
21.3
(1.98024)
88.1
(8.1853)
91.6
(8.5057)
Test Stopped
Low Eff.

Test Stopped
Low Eff.

Test Stopped
Low Eff.
13.68
(1.2708)

173.5
(16.1213)
169.1
(15.706)
22.88
(2.1257)

11.97
(1.1116)

Permeability Maximum Percent Efficiency on
cm3/sec/cra2 for 0.1245 KPa pore size 0.3 urn DOP at cm/sec
(ft3/"un/ft2 for 0-5" H20 AP> Micrometers 2.68 5.35 14.22
28.448 435 032
(56)
8.687 193.3 043
(17.1)
5.791 248.6 29 37 34
(11.40)
16.556 267.7 056
(32.59)
65.181 870 0 3 10
(128.31)

47.595 __ 580 ' 070
(93.69)

51.211 580 0 6 10
(100.81)
3.414 316 0 11 16
(6.72)

7.447 91.6 55 55 57
(14.66)
8.900 64.4 84 79 72
(17.52)
11.897 139.2 010
(23.42)

5.121 124.3 2 8 10
(10.08)

-------
                                                             Table 3  (Concluded)
                                           Percent
                                         Efficiency

25.
(P)
26.
(P)
27.
(P)
28.
(W)

29.
(W)
30.
(W)
31.
(W)
32.
(W)
33.
(F)
34.
(W)

(W) Woven Basis
(P) Paper Weight
(F) Felt g/m2
Carborundum Piberfrax 604
paper (with binder) 970J
ICI Saffil Zirconia paper 212
(with binder)
Carborundum Fiberfrax 152
paper (no binder) 970-AH
3M AB-312 double thick 1035
plain weave

FMI crowfoot satin cloth 905
astroquartz
3M AB-312 12 harness satin 675
weave
630 Tuflex fiberglass* 564

15-011-020 woven filment* 175
polyester
25-200-070 polyester felt* 524

HITCO Refrasil cloth (std) 637
not heat cleaned, med.
thickness
on ACF @ Dust Loading
10 cm/sec g/m2 to 3.735 KPa
(20 ft. min) (g/ft2 to 15" H2O)
99.99 73.7
(6.8442)
93.20 82.2
*Probable hole (7.6374)
99.91 84.4
(7.8369)
43.86 Test Stopped
Low Eff.

40.08 Test Stopped
Low Eff.
53.73 Test Stopped
Low Eff. ,
93.982 47.6
(4.4187)
96.078 28.0
(2.60163)
99.193 135.3
(12.5688)
48.40 34.5
(3.2063)

Permeability Maximum Percent Efficiency on
cm3/sec/cm2 for 0.1245 KPa pore size 0.3 ym OOP at cm/sec
(ft3/min/ft2 for 0.5" H2O AP) Micrometers 2.68 5.35 14.22
26.899 47.7 99.5 99.0 97.6
(52.95)
8.692 37.4 83 78 74
(17.11)
12.416 43.5 88 - 73
(24.44)
84.836 too large to 0 10 41
(167) measure with
our equipment
62.078 497 0 10 32
(122.20)
75.529 696 0 8 24
(148.68)
16.038 174 10 9 19
(31.57)
6.828 74 604
(13.44)
11.897 128.9 34 24 29
(23.42)
6.934 -
(13.65)

#These materials are conventional  (not ceramic)  media.

-------
           efficiency collection of fine particles than are
           media normally used successively in commercial
           filter units.
       *   Many of the woven ceramic materials had zero D.O.P.
           efficiency at low velocity and higher D.O.P. effi-
           ciency at higher velocity.
           This is contrary to what theory suggests and to the
           behavior normally seen in tests of conventional
           filter materials.  A likely explanation for this
           performance is that it is caused by the presence of
           many large pores in the media.  Examination of the
           pore size data in Table 3 shows that the woven
           ceramic materials as a group are characterized by
           larger pore size than are conventional filter materi-
           als.  Thus, at low airflow velocity, most of the flow
           passes through the large pores and little filtration
           takes place.  As velocity is increased, flow through
           the large pores becomes restricted and some of the
           flow is caused to pass through smaller pores where
           more filtration can take place.
       •   The D.O.P. data also supports the theoretical analy-
           sis.  Efficiency as a function of basis weight for
           selected ceramic materials is plotted in Figure 4.
           The materials selected are ceramic papers and felts.
           These materials provide a fiber bed similar to that
           for which the analysis summarized in Figure 2 was
           based.   Figure 4 shows that the nominally 3 ym fibers
           do indeed provide higher collection efficiency on a
           weight-per-unit area basis than conventional media
           produced with larger diameter fibers.

       Maximum pore size data shows that many of  the woven
ceramic materials  had pores larger than those characteristic

                              345

-------
       200      400       600       800
                       Basis Weight — gm/cm2
                                          1000     1200
                                                           1400
Figure 4.   D.O. P. efficiency  fn   basis weight,
                         346

-------
of filter materials.  Also, many of the felt and paper materials
had pore sizes similar to those of conventional filter materials.
       Permeability is measured as the flow per unit area at a
constant pressure drop.  Thus, a material with low permeability
offers a high restriction to gas flow and one with high perme-
ability allows more gas to penetrate for a given pressure drop.
Table 3 shows that some ceramic materials are available which
have low permeability, while others have high permeability.
Some of the woven materials have low permeability and large
pore size, while others have high permeability and large pore
size.  Most of the paper and felt materials have permeability
similar to that of commonly used filter materials.
       Flat sheet dust loading tests were performed as follows:
A 7.62 cm  (3 inch) diameter disc of media is suspended across
an air stream which is maintained at 10.16 cm/sec  (20 ft/min)
velocity through the filter media.  In this test the media
supports itself against the pressure drop  (no screen is used).
Standard A.C. Fine test dust  (0-80 pm silica) was fed to the
                                    3            3
media at a nominal rate of 0.883 g/m   (0.025 g/ft ) until a
pressure drop of 3.735 KPa (15 in H20) is reached.  Pressure
drop as a function of time is monitored during the test.  This
data is presented in Figures 5, 6, and 7 for selected materials.
                                          2
From the data collected, dust loading  (g/m ) necessary to cause
a given pressure drop 3.735 KPa (15 in H?0) is determined.
Examination of this data in Table 3 shows that some of the woven
materials reached high pressure drops while collecting only a
small weight per unit area of dust.  This is true also of the
commercial woven materials (items 31 and 32).  Other woven
ceramics were penetrated so severely that they would not develop
a pressure drop of 3.735 KPa  (15 in H?0).
       Two of the non-woven samples (which were unsupported)
fractured as a result of the pressure drop across them.  Several
of the ceramic paper and felt materials exhibited dust loading,
similar to that which is expected from conventional filter
papers and felts.

-------
Pressure Drop ~- KPa
                             CD

-------
                                A.C. Fine Test Dust
                                0.883 g/M3
                                A/C 10.16 cm/sec
             10          20

                   Time ~ Minutes
30
40
Figure 6.   Dust loading of  ceramic  paper.

                  349

-------
CO
Ol
o
                                                                                 AC Fine Test Dust
                                                                                 0.883 g/m 3
                                                                                 A/C 10.16 cm/sec


                                                                                 #31, 32 Conventional Woven Filters
                              10
                                        20
30
40        50

Time ~ Minutes
                                                                              60
                                       70
80
                           Figure  7.   Dust loading  of  woven  ceramic media.

-------
       The flat sheet loading tests also provided overall col-
lection efficiency (mass basis)  data for the tested materials.
Dust penetrating the media was collected in an absolute filter
downstream of the test media.  Table 3 reveals that most of
the woven ceramic materials did not achieve high collection
efficiency in this test.  On the other hand, woven commercial
materials were only moderately efficient.  Several of the
ceramic paper and felt materials, however, did provide collec-
tion efficiency of 99 percent or better.  The two materials
which fractured would have provided higher efficiency perform-
ance had they not fractured.  The test was stopped as soon as
the fracture was detected.

General Conclusions  from Room Ambient Tests
       •   Several of the ceramic paper  and  felt materials are
           capable of removing  fine particles at high efficiency
           without excessive filter weights.
       •   The  ceramic  paper and felt materials  have  filtration
           characteristics  and  performed similar to paper  and
           felt commercial  filter  media  in  a series of  filter
           media tests.
       •   The  ceramic  woven materials  in general  were  charac-
           terized  by  large pores  and poor  collection effi-
           ciency in the  dust loading tests.  The  range of
           parameters  exhibited by the  various  materials,  how-
           ever, indicate that  an  acceptable woven ceramic
           filter media can probably  be fabricated,  but such
           a filter media would have  the same limitations as
           currently available  woven  filters.   That is, accept-
           able performance is  only probable at low air-to-
           cloth ratios.
                              351

-------
       *   "Blanket" ceramic fiber materials  (felts) consisting
           of small diameter fibers  (3.0 ym) appear to be the
           most promising materials for high temperature and
           pressure tests because of their combination of good
           filtration performance and relatively high strength.

High Temperature/Pressure Tests
       Two major questions concerning the suitability of ceramic
fibers for filtration need to be answered.  These are:
       1.  How durable are ceramic fiber structures when sub-
           jected to environmental conditions associated with
           filtration applications.
       2.  How well do ceramic fibers perform as filters in the
           HTHP environment.
Some preliminary answers are available concerning the first of
these questions.
       Three ceramic filter media configurations have survived
a test during which the filter elements were subjected to 50,000
cleaning pulses.  The objective of these tests was to simulate
approximately one year of operation of mechanical loads on the
media at high temperature and pressure.  Test conditions were
as follows:
       Temperature — 815°C
       Pressure - 930 KPa
       Air-to-cloth-ratio - 5 to one (2.54 cm/sec)
       Cleaning pulse pressure — 1100 KPa
       Cleaning pulse interval — ~10 seconds
       Cleaning pulse duration — 100 m second
       Dust — recirculated fly ash
The three filter media configurations tested were:
       •   Saffil alumina mat contained between an inside and
           an outside layer of 304 stainless steel knit wire
           screen.   Figure 8 shows how easily the residual
                             352

-------
Figure 8.  Saffil Alumina—Post Test Dust Cake (Clean strip using Vacuum Cleaner)




                                      353

-------
            dust cake was removed from this media after the
            test.
        •   Woven Fiberfrax cloth with nichrome wire scrim
            insert.   Figure 9 shows the dust cake following
            the 50,000 Pulse test.
        •   Fiberfrax blanket contained between an inside and
            an outside cylinder of 304 stainless steel square
            mesh screen similar to common window screen.   The
            ceramic  fiber blanket was held in position between
            the screens with 302ss wire sewn between the  screens.
            This resulted in about 100 penetrations of the ce-
            ramic fiber bed.  Figure 10 shows the dust cake fol-
            lowing the test.
 Pressure drop during the tests was  controlled by the rapid clean-
 ing  pulses  and in general remained  less  than about 5 KPa  (20 in
 H20).

        Dust penetrating the ceramic  test media was collected
 on a high efficiency filter located  downstream (after cooling)
 of the  test chamber.   This  data is not reported for the  Saffil
 Alumina or for  the Woven  Fiberfrax Cloth because of a leak
 discovered in  a gasket  in the  test rig.   This  problem was  cor-
 rected  before  the fiberfrax blanket  test was performed.   Average
 outlet  loading  during  this  test was  0.0055  g/  m3  (0.0024  gr/ ft3).
 Figure  10 shows  that the  dust  was concentrated near the places
 where wire penetrated the  filter  element.   This  concentration
 of dust near the wire penetration points  could be  seen on  the
 inside  of the element also.  Thus, most  of  the  dust which  pene-
 trated  apparently did so  through  the holes made by  the wires.
 It is reasonable to expect  that a filter  element without holes
will experience  less penetration.  Also  a less  frequent clean-
 ing pulse interval will reduce penetration.  Therefore even
better performance than that achieved in  this  test  should  result
from future tests.
                              354

-------
Figure 9.   Woven Fiberfrax - Post Test Dust Cake




                      355

-------
Figure 10.   Fiberfrax Blanket - Post Test Dust Cake




                        356

-------
Conclusions
       Research on bench scale indicates that fine particle
control at high temperature and pressure can be achieved using
barrier filtration by ceramic filter beds.  Evidence in support
of this contention includes the following:
       •   A theoretical basis exists for it.
       •   Room temperature tests show that particles including
           fine particles are collected at high efficiency.
       •   Tests at high temperatures and pressures show that
           several ceramic filter structures are capable of
           surviving in excess of 50,000 cleaning pulses while
           maintaining pressure drop at acceptable levels and
           providing efficiency close to the lowest reported
           turbine requirements.
                          REFERENCES

    Hazard, H. R.,  "Coal Firing for the Open-Cycle Gas Turbine."
    Proceedings of  the Joint Conference on Combustion, 1955, ATME
    and IME.
    Hoke, R.,  "Ducon Gravel Bed Filter Testing," EPA/ERDA Sym-
    posium on High  Temperature/Pressure Particle Control,
    Washington, D.C., Sept. 1977.
                              357

-------
358

-------
                              SYMPOSIUM ATTENDEES
K. P. ANANTH
Midwest Research Institute
425 Volker Blvd.
Kansas City, MO  64110

GRANT D. APPLEWHITE
American Air Filter Co., Inc.
215 Central Avenue
Louisville, KY  40277

MARYLIN ARDELL
Mcllvaine Company
2970 Maria Ave.
Glenview, IL  60025

B. ARNOLD
SF Products Canada Ltd.
4480 Cote de Liesse Road
Montreal, Quebec
Canada  H4N 2R1

PAUL ATLAS
J. P. Stevens & Company
141 Lanza Ave.
Garfield, NJ  07026

JAMES BALL
Midland-Ross Corp.
Capitol Castings Div.
P.O. 750
Phoenix,  AZ  85001

JOHN BARANSKI
General Battery Corporation
Box 1262
Reading,  PA  19603

DUANE BECKNELL
Lear Siegler, Inc.
74 Inverness Drive East
Englewood,  CO  80110

WALLACE P. BEHNKE
E. I. du Pont de Nemours & Co.,  Inc.
701 Bldg. Chestnut Run Location
Wilmington, DE  19898
STEVE BELLMORE
Fabric Filters
525 South Hayden Rd.
Tempe, AZ  85281

LARRY BENNETT
Fabric Filters
525 South Hayden Rd.
Tempe, AZ  85281

ROBERT P. BENNETT
Apollo Chemical Corp.
35 South Jefferson Road
Whippany, NJ  07981

LUTZ BERGMANN
Milliken & Company
1304 Washington Street
LaGrange, GA  30240

CARL H. BILLINGS
Arizona Bureau of Air Quality Control
1740 West Adams St.
Phoenix, AZ  85007

GERRIT W. BLYDORP
Mobay Chemical Corp.
Baytex Fibers Div.
425 Park Avenue
New York, NY  10022

JOHN BRANCACCIO
Western Electric Company
222 Broadway
New York, NY  10038

ROGER I. BRANDSTETTER
Industrial Filtration Inc.
1500 Daisy Ave.
Long Beach, CA  90813

FREDERICK E. BRANDT
Johns-Manville Sales Corp.
Ken-Caryl Ranch
Denver, CO  80217
                                      359

-------
WILLIAM J. BRINKMAN
Magna Copper Co.
P.O. Box M
San Manuel, AZ  85631

PETER R. CAMPBELL
Globe Albany Filtration
2405 West University
Tempe, AZ  85281

J. MICHAEL CANTY
Viking Sales Co.
Box 50025
Tucson, AZ  85703

STEPHEN V. CAPONE
GCA Corporation
GCA/Technology Division
Burlington Road
Bedford, MA  01730

BENGT CARLSSON
Bahco Systems, Inc.
3402 Oakcliff Rd., Suite B-l
(P.O. Box 48116-Atl 30362)
Atlanta, GA  30340

HUNG BEN CHU
Los Angeles Department of
  Water & Power
111 N. Hope St.
Los Angeles, CA  90051

W. A. CHENEY
United Air Specialists
6665 Creek Rd.
Cincinnati, OH  45242

PETER CHMARA
Mines Accident Prevention
  Association of Ontario
290 Second Ave. West
North Bay, Ontario
Canada  P1B 3K9

JACK CLEMENTS
Standard Havens, Inc.
8800 E.  63rd
Kansas City, MO  64133
JOHN F. COBIANCHI
J. P. Stevens & Co., Inc.
1185 Avenue of the Americas
New York, NY  10036

WILLIAM COLUMBUS
Arizona State BAQC
5055 E. Broadway C-209
Tucson, AZ  85204

ROBERT C. COMER
W. W. Criswell Co.
800 Industrial Highway
Riverton, NJ  08077

EDWARD B. COOPER
W. L. Gore & Associates, Inc.
104 Bent Lane,
Newark, DE  19711

FLOYD B. CORONER
State of Utah Department of Health
150 West North Temple
P.O. Box 500
Salt Lake City, UT  84110

RICHARD T. COX
Huyck Felt-Division of Huyck Corp.
Washington Street
Rensselaer, NY  12144

FRED CROWSON
Naval Surface Weapons Center
Code CG-31
Dahlgren, VA  22448

VICTOR M. DAY
Lear Siegler Inc.
74 Inverness Dr. E.
Englewood, CO  80110

EDWARD DE GARBOLEWSKI
W. L. Gore & Associates, Inc.
P. 0. Box 1220, Rt. 213 North
Elkton, MD  21921

RONALD L. DEPOE
J. P. Stevens & Co., Inc.
1185 Avenue of the Americas
New York, NY  10036
                                      360

-------
 GORDON A. DICK
 Wheelabrator - Canada
 235  Speers Rd.
 Oakville, Ontario
 Canada  L6H-2K9

 THOMAS DONNELLY
 Donaldson Company, Inc.
 P.O. Box 1299
 Minneapolis, MO  55440

 DAN  DOYLE
 Flakt, Inc.
 1500 East Putnam Ave.
 Old  Greenwich, CT  06870

 DELMAR J. DOYLE
 American Air Filter Co., Inc.
 215  Central Avenue
 Louisville, KY  40277

 T. REGINALD DRISCOLL
 Globe Albany - Canada
 Morrow
 Barrie, Ontario
 Canada

 STEPHEN B. DUERK
 J. P. Stevens & Co., Inc.
 1185 Avenue of the Americas
 New York, NY  10036

 JOHN M. EBREY
 Lodge-Cottrell
 601  Jefferson
 Houston, TX  77005

 HEINZ ENGELBRECHT
 Wheelabrator-Frye
 600 Grant St.
 Pittsburgh, PA  15219

 DONALD R. ENNS
 Endur Limited
 5379 Fairview St.
 Burlington, Ontario
 Canada  L7L 5K4

 DAVID S.  ENSOR
Meteorology Research,  Inc.
 464 W.  Woodbury Rd.
Altadena, CA  91001
P. S. ESHELMAN
General Motors Corporation
Industrial Hygiene Dept.
GM Technical Center
Warren, MI  48090

REGINALD G. EVANS
Canadian Johns-Manville Co.
P.O. Box 1500
Asbestos, Quebec
Canada  J1T3N2

J. P. PAGAN
E. I. du Pont de Nemours
85 Mill Plain Rd.
Fairfield, CT  06430

L. W. FERGUSON
Owens-Corning Fiberglas Corporation
P. 0. Box 415
Granville, OH  43023

PETER FINNIS
Wheelabrator - Canada
235 Speers Rd.
Oakville, Ontario
Canada  L6H-2K9

E. R. FREDERICK
Air Pollution Control Association
P.O. Box 2861
Pittsburgh, PA  15230

GENE FREDERICK
Clark-Schweble Fiber Glass Corp.
14530 South Anson Ave.
Santa Fe Springs, CA  90670

ROBERT E. FREY
Torit Div. Donaldson
P.O. Box 43217
St. Paul, MN  55164

DALE A. FURLONG
Buell Division of Envirotech Corporation
200 N. Seventh Street
Lebanon, PA  17042

JOHN H. FURSE
Rexnord APC Div.
3300 Fern Valley Rd.
Louisville, KY  40213
                                      361

-------
R. G. GARCIA
Duval Sierrita
Box 125
Sahuarita, AZ  85629

ROGER L. GIBBS
Naval Surface Weapons Center
Code CG-31
Dahlgren, VA  22448

RONALD GITTELSON
Southern Silk Mills
Spring City, TN  37381

HARRY J. GIULIANI
Wheelabrator-Frye Inc.
600 Grant Street
Piitsburgh, PA  15219

A. GOMEZ
Duval Corp.
4715 E. Ft. Lowell Rd.
Tucson, AZ  85712

MANUEL GONZALES
Los Alamos Scientific Laboratory
P.O. Box 1663
Los Alamos, NM  87545

EUGENE E. GRASSEL
Donaldson Co. Inc.
P.O. Box 1299
Minneapolis, MN  55440

PAUL GRIM
Stearn Rogers
700 S. Ash St.
P.O. Box 5888
Denver, CO  80217

THERON GRUBB
Burlington Glass Fabrics Co.
110 Andrew St.
Greenboro, NC  27406

ARNOLD G. GRUSHKIN
Research-Cottrell, Inc.
P.O. Box 750
Bound Brook, NJ  08805
THOMAS L. HARSELL, JR.
Harsell Engineering Corp.
10,000 Santa Monica Blvd., Suite  307
Los Angeles, CA  90067

BARRY J. HASWELL
Blast-Tech Ltd.
1100 Invicta Drive, Unit 12
Oakville, Ontario
Canada  L6H-2K9

TOM HAYES
3M Company
3M Center, Bldg. 230-BE
St. Paul, MN  55101

J. M. HENRICKS
Tucson Gas & Electric
P.O. Box 711
Tucson, AZ  85702

RICHARD B. HOGUE, JR
Viking Sales Co.
Box 50025
Tucson, AZ  85703

MARK HOLCOMBE
Chromalloy, Textile Service Division
900 N. Alvarado
Los Angeles, CA  90026

ROBERT P. HOSEMANN
Pacific Gas & Electric
77 Beale Street
San Francisco, CA  94106

RICHARD G. HOSPER
MRI
464 W. Woodburg Rd.
Altadena, CA  91001

CHARLES B. HOTCHKISS
Menardi-Southern
1201 Francisco St.
Torrance, CA  90502

TOM HOYNE
Buell - Envirotech
7462 N. Figueroa St.
Los Angeles, CA  90041
                                     362

-------
JACK D. JONES
Southwestern Public Service Company
Box 1261
Amarillo, TX  79170

INGEMAR KARVEGARD
Bahco Systems, Inc.
3402 Oakcliff Rd., Suite B-l
(P.O. Box 48116 - Atl. 30362)
Atlanta, GA  30340

MICHAEL T. KEARNS
Air Pollution Sysrems Inc.
1114 Andover Park West
Tukwilla, WA  98188

THOMAS P. KELLY
Clark-Schwebel Fiber Glass Corp.
5 Corporate Park Drive
White Plains, NY  10604

WILLIAM KELLY
Environmental Elements
7249 National Drive
Hanover, MD  21076

STANLEY K. KEMPNER
Western Electric
222 Broadway
New York, NY  10038

THOMAS J. KILEY
Griffin Environmental Company, Inc.
P.O. Box 86
Baldwinsville, NY  13027

JERRY KRAIM
Stansteel Corporation
5001 S. Boyle Avenue
Los Angeles, CA  90058

PAUL LANGSTON
DuPont Co.
114 Mulberry Rd.
Newark, DE  19711

G. D. LANOIS
Wheelabrator-Frye Inc.
600 Grant St.
Pittsburgh, PA  15219
RICHARD C. LARSON
Torit Division
Donaldson Co. Inc.
1133 Rankin St.
St. Paul, MN  55165

JOE LEDBETTER
University of Texas at Austin
Cockrell Hall
Austin, TX  78712

WAYNE H. LEIPOLD
Phelps Dodge
P. 0. Drawer E
Douglas, AZ 85607

BENJAMIN LINSKY
West Virginia University
Fattersall House
Morgantown, WV  26506

W. 0. LIPSCOMB
Acurex/Aerotherm
c/o EPA Research Triangle Park
Durham, NC  27711

JOE LOFLIN
Texas A & M University
Zachery Bid. Ind. Eng.
College Station, TX  77840

ROBERT L. LUCAS
E. I. DuPont
Louviers Bldg.
Newark, DE  19711

CARL E. LUNDBERG
Contamination  Control,  Inc.
1310 Genoa
So. Houston, TX  88587

TSHIEN MA
Buell Div. of  Envirotech
200 North Seventh St.
Lebanon, PA  17042

TERRY MACRAE
Industrial Clean Air
2929 Fifth St.
Berkeley, CA   94710
                                     363

-------
BRIAN MEAD
DuPont Company
PP&R D 13126
Wilmington, DE  19898

MANAN MEHTA
Mikropul Corp.
10 Chatham Rd.
Summit, NJ  07901

ROBERT C. MEYER
Envirotech Corporation
P.O. Box 1211
Salt Lake City, UT  84117

JAMES A. MITCHELL
Lodge-Cottrell-Dresser
601 Jefferson, 27th Floor
Houston, TX  77005

FRED MORENO
Acurex Corporation
485 Clyde Ave.
Mountain View, CA  94042

ANDY MURPHY
Acurex Corporation
3301 Womens Club Drive, Suite 147
Raleigh, NC  27611

WALLACE G. MURRAY
Cities Service Co.
P. 0. Drawer 1149
Franklin, LA  70538

RAYMOND Z. NAAR
Huyck Research Center
Washington Street
Rensselaer, NY  12144

WILLIAM G. NELSON
U.S. Borax
Borax Road
Boron, CA  93516

JOE NOLL
Flakt, Inc.
1500 East Putnam Avenue
Old Greenwich, CT  06870
PETE PETREY
American Air Filter Co. Inc.
215 Central Ave.
Louisville, KY  40277

WALTER PIULLE
EPRI
3412 Hillview Avenue
Palo Alto, CA  94303

CHARLES J. 0'BOYLE
EPA Region VIII
1860 Lincoln St.
Denver, CO  80295

PALMER PARSONS
Filtered Air Corp.
Perry, OH  44081

MUKESH N. PATEL
Illinois Institute of Technology
I. I. T. Centre
Chicago, IL  60616

MICHAEL A. PETRILLI
Monsanto Enviro-Chem Systems
Corporate Square Office Park
Box 14547
St. Louis, MO  63178

THOMAS PLUNKETT
Standard Havens
8800 E. 63rd
Kansas City, MO  64133

ED POLLOCK
SF Products Canada Ltd.
4480 Cote de Liesse Road
Montreal, Quebec
Canada  H4N 2R1

W. WALTER RENBERG
Envirotech Corporation
Two Airport Office Park
400 Rouser Rd.
Pittsburgh, PA  15108

RONALD J. RENKO
C-E Air Preheater
P.O. Box 372
Wellsville, NY  14895
                                     364

-------
LAMSON RHEINFRANK
Standard Havens, Inc.
8800 E. 63rd
Kansas City, MO  64113

DON RICHMOND
C-E Air Preheater
Andover Rd.
Wellsville, NY  14895

ENRIQUE RODRIGUEZ T.
Accion Social Regiomontana A.C.
Box 2034
Monterrey, N.L.
Mexico

RICHARD ROLFE
Joy Manufacturing Co.
4565 Colorado
Los Angeles, CA  90039

DONALD H. RULLMAN
American Air Filter Co., Inc.
215 Central Ave.
Louisville, KY  40291

DOUGLAS RYDER
Globe Albany Corp.
2405 W. University
Tempe, AZ  85281

ALBERTO SABADELL
Mitre Corp.
McLean, VA   22101

CHARLES A.  SALOTTI
University  of Wisconsin - M
P.O. Box
Milwaukee, WI   53201

HARRY N.  SANDSTEDT
DuPont
Centre Rd.  Bldg.
Wilmington,  DE  19898

ROBERT W.  SCHECK
Stearns Roger,  Inc.
Box 5888
Denver, CO   80217
S. P. SCHLIESSER
Acuretex/Aerotherm
c/o EPA Research Triangle Park
Durham, NC  27711

TOM SCHNEIDER
Bay Area Industrial Filtration
6355 Coliseum Way
Oakland, CA  94621

M.P. SCHREYER
Wheelabrator-Frye Inc.
14920 So. Main
Gardena, CA  90248

FREDERICK D. SCHULER
Donaldson Company
P.O. Box 1299
Minneapolis, MN  55440

JOHN H. SCOTT
Donaldson Company, Inc.
P.O. Box 1299
Minneapolis, MN  55440

WILLIAM E. SEBESTA
300 Florence
Bay Village, OH  44140

MIKE SHACKLETON
Acurex Corp. Aerotherm Div.
485 Clyde Ave.
Mountain View, CA  94042

JERRY SHANG
Mitre Corp.
McLean, VA  22101

J. R. SHEPPARD
Milliken & Company
1304 Washington Street
LaGrance, GA  30240
                                       365

-------
 JOE SIBRAVA
 Flakt,  Inc.
 1500 East Putnam Ave.
 Old Greenwich,  CT  06870

 GLENN A.  SMITH,  JR.
 BHA Company  Div.  of Std.  Havens
 8800 E.  63rd Street
 Kansas  City, MO   64133

 GORDON  L.  SMITH
 American Air Filter
 215 Dentral
 Louisville,  KY   40201

 JOHN D.  SQUIBBS
 Ford Motor Company
 Michigan  Casting  Center
 22000 Gibraltar Road
 Flat Rock, MI 48134

 J.  STEPHENSON
 Ontario Hydro, Central Health
  Physics  Services
 757  Mackay Rd.
 Pickering, Ontario
 Canada  L1V  2R5

 SHARON STORY
 Fabric Filters
 525  South  Hayden Rd.
 Tempe, AZ  85281

 EMIL STUDINKA
 Texas A & M  University
 Zachery Bldg. Ind. Eng.
 College Station, TX  77840

 HERB  SUERTH
 CEA  Carter Day Co.
 500  73rd Avenue, NE
Minneapolis, MIN  55432

NORM  Surprenant
GCA Corporation
GCA/Technology Division
Burlington Rd.
Bedford, MA 01730
 ROBERT D.  Button
 Public Service Co.  of Colorado
 5900 E.  39th Avenue
 Denver,  CO  80207

 DONALD P.  TEIXEIRA
 EPRI
 3412 Hillview Avenue
 Palo Alto, CA  94303

 LARRY A. THAXTON
 Buell Emission Control Division
 Envirotech Corporation
 200  N.  7th Street
 Lebanon, PA  17067

 FERNANDO ORTIZ THOMAS
 Cristales  Mexicanos,  S.A.
 Galeana y  Ruiz Cortines
 Monterrey, N.L.
 Mexico

 TIM  THURMAN
 Great Lakes Filter
 18475 Sherwood
 Detroit, MI  48234

 ROBERT TISCONE
 Environmental Elements
 7249 National Drive
 Hanover, MD  21076

 DAVID W. TOWNSEND
 W. W. Criswell Co.
 3901 W. Beech Ave.
 P.O.  Box 130
 McAllen, TX  78501

 JOHN W. VAKLYES, JR.
 C-E  Air Preheater
 Andover Rd.
 Wellsville, NY  14895

 MIGUEL ANGEL VARGAS
 Cristales Mexicanos, S.A.
 Galeana y Ruiz Cortines
Monterrey,  N.L.
Mexico
                                      366

-------
THOMAS C. WAGNER
PPG Industries - Fiber Glass Division
One Gateway Center
Piitsburgh, PA  15222

KEN A. WALKER
Environmental Elements Corp.
Box 1318
Baltimore, MD  21203

JACK A. WAUGH
Kaiser Aluminum & Chemical Corporation
P. 0. Box 98
Ravenswood, W. VA  26164

FRANK T. WEEMS
Envirotech Corporation
3000 Sand Hill Road
Menlo Park, CA  94025

WAYNE .WELLAN
Combustion Equipment Association
502 73rd Avenue, NE
Minneapolis, MN  55432

VINCENT J. WEMLINGER, II
E. I. DuPont F & F Dept.
1007 Market St.
Wilmington, DE  19898

ANDERS WIKTORSSON
AB Svenska Flaktfabrikon
S-35187
Vaxjb, Sweden

CHARLES WRIGHT
Fabric Filter
525 Hayden Road
Tempe, AZ  85281

PAUL YOSICK
American Air Filter
215 Central Ave.
Louisiana, KY  40222

DAVID YOUNG
Bekaert Steel Wire Corporation
800 Third Avenue
New York, NY  10022
JAMES ZARFOSS
Environmental Elements
7249 National Drive
Hanover, MD  21076

JOHN ZUTTERMEISTER
Bechtel Power Corp.
50 Beale Street
San Francisco, CA  94598
                                      367

-------
368

-------
                                TECHNICAL REPORT DATA
                          (Please read Instructions on the reverse before completing)
 1. REPORT NO.
  EPA-600/7-78-087
                           2.
                                                       3. RECIPIENT'S ACCESSION-NO.
 4. TITLE AND SUBTITLE
 Third Symposium on Fabric Filters for Parti culate
  Collection
            5. REPORT DATE
             June 1978
            6. PERFORMING ORGANIZATION CODE
             GCA-TR-78-33-G
 7. AUTHOR(S)
                                                       8. PERFORMING ORGANIZATION REPORT NO,
 N. Suprenant, Compiler
9. PERFORMING ORGANIZATION NAME AND ADDRESS
GCA Technology Division
Burlington Road
Bedford, Massachusetts  01730
            10. PROGRAM ELEMENT NO.
             EHE624
            11. CONTRACT/GRANT NO.

             68-02-2177
 12. SPONSORING AGENCY NAME AND ADDRESS
 EPA, Office of Research and Development
 Industrial Environmental Research Laboratory
 Research Triangle Park, NC  27711
            13. TYPE OF REPORT AND PERIOD CO
             Proceedings; 6/77-3/78
                                                                               VERED
            14. SPONSORING AGENCY CODE
              EPA/600/13
 15.SUPPLEMENTARY NOTES TERL_RTP project officer is Dennis C. Drehmel,  Mail Drop 61,
 919/541-2925.
 16. ABSTRACT
          The report presents the 17 technical papers given at an EPA-sponsored
 symposium, held in December 1977 in Tuscon, Arizona, on fabric filters for particle
 collection.  Emphasis was on current field experience and engineering-oriented
 research so that potential users could better select and/or design particulate control
 systems. Technical content focused on fabrics for  high temperature filtration, their
 field behavior with fly ash and other effluents, design criteria and shakedown exper-
 ience ,  and  new filtration concepts that appear amenable to combustion and other
 process effluents.
17.
                             KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
                                           b.lDENTIFIERS/OPEN ENDED TERMS
                         c. COSATI Field/Group
 Pollution
 Dust
 Dust Filters
 Filtration
 Fabrics
 Fly Ash
Pollution Control
Stationary Sources
Particulate
Fabric Filters
 13B
 11G
 13K
 07D
 HE
 21B
 3. DISTRIBUTION STATEMENT

 Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
 383
                                           20. SECURITY CLASS (Thispage)
                                           Unclassified
                                                                   22. PRICE
EPA Form 2220-1 (9-73)
                                        369

-------