United States
Environmental Protection
Municipal Environmental Research  EPA 600/2-80-1 46
Laboratory           August 1980
Cincinnati. OH 45268
nesearch and Development
Carbon
Reactivation by
Externally-Fired
Rotary Kiln  Furnace

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                 RESEARCH  REPORTING SERIES

 Research reports of the Office of Research and Development, U.S. Environmental
 Protection Agency, have been grouped into nine series. These nine broad cate-
 gories were established to facilitate further development and  application of en-
 vironmental technology. 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 TECH-
 NOLOGY series. This series describes research performed to  develop and dem-
 onstrate instrumentation, equipment, and methodology to repair or prevent en-
 vironmental degradation from point and non-point sources of pollution. This work
 provides the new or improved technology required for the control and treatment
 of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia  22161.

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                                         EPA-600/2-80-146
                                         August 1980
     CARBON REACTIVATION BY EXTERNALLY-FIRED
               ROTARY KILN FURNACE
                       by

                 Ching-lin Chen
                 Leon S. Directo

County Sanitation Districts of Los Angeles County
           Whittier, California  90607
             Contract No. 14-12-150
                 Project Officer

                Irwin J. Kugelman
          Wastewater Research Division
   Municipal Environmental  Research Laboratory
             Cincinnati, Ohio  45268
   MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
       OFFICE OF RESEARCH AND DEVELOPMENT
      U.S. ENVIRONMENTAL PROTECTION AGENCY
             CINCINNATI, OHIO  45268

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                                  DISCLAIMER


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

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                                   FOREWORD
   The  Environmental  Protection Agency was created because of increasing
public and government concern about the dangers of pollution  to  the health and
welfare of the American people.  Noxious air, foul water, and spoiled land are
tragic testimony to the deterioration of our natural  environment. The
complexity of that environment and the interplay between its  components
require a concentrated and integrated attack on the problem.

   Research  and development  is that  necessary  first step in problem  solution
and it involves defining the problem, measuring its impact,  and  searching for
solutions.  The Municipal Environmental Research Laboratory develops new and
improved technology and systems for the prevention, treatment, and management
of wastewater and solid and hazardous waste pollutant discharges from
municipal and community sources,  for the preservation and treatment of public
drinking water supplies, and to minimfze the adverse economic, social, health,
and aesthetic effects of pollution.  This publication is one  of  the products
of that research;  a most vital communications link between the researcher and
the user community.

   One of the  advanced  treatment procedures  is  adsorption on  activated
carbon. After its  capacity is exhausted the carbon is thermally  regenerated.
This report covers studies on regeneration in a rotary kiln furnace  a lower
capital cost system than that conventionally used (multiple hearth furnace).

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                                  ABSTRACT
An externally-fired rotary kiln furnace system has been evaluated for cost-
effectiveness in carbon reactivation at the Pomona Advanced Wastewater
Treatment Research Facility.  The pilot scale rotary kiln furnace was
operated within the range of 682 kg/day (1,500 Ib/day) to 909 kg/day (2,000
Ib/day).

The granular activated carbon used for the furnace evaluation study was ex-
hausted -in a 1.82 m (6 ft) diameter steel carbon adsorption column.  The
column treated the unchlorinated and unfiltered activated sludge effluent
from the 0.44 cu m/sec (10 MGD) Pomona Water Reclamation Plant.  The carbon
adsorption column provided an empty-bed detention time of 10 minutes at a
flow of 6.2 I/sec (100 gpm).

The rotary kiln furnace was found to be as effective as the multiple hearth
furnace in reactivating the exhausted granular activated carbon.  The
operation and maintenance of the rotary kiln system required less operator
skill than the multiple hearth furnace system.  However, the corrosion rate
was higher in the rotary tube than in the multiple hearth furnace.

Cost estimates based on a typical regeneration capacity of 182 kg/hr
(400 Ib/hr) have been made for both rotary kiln and multiple hearth furnace
systems.  These indicate that the capital cost for the multiple hearth
furnace is about two times that of the rotary kiln furnace.  The operation
and maintenance costs for both furnace systems are similar.  The overall
process costs" for the multiple hearth and rotary kiln furnace systems are
estimated to be 33.2 cents/kg (15.1 cents/lb) of carbon regenerated and 29.2
cents/kg (13.3 cents/lb) of carbon regenerated, respectively.

This report is submitted in fulfillment of Contract No. 14-12-150 by the
County Sanitation Districts of Los Angeles County under the partial sponsor-
ship of the U.S. Environmental Protection Agency.  This report covers the
entire project period from November 1975 through January 1978.
                                      IV

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                                  CONTENTS.

                                                                    Page

Foreword   	     i i i
Abstract   	      iv
Figures    	      vi
Tables     	     vii
Acknowledgements ,	   viii

   1.  Introduction    .  .  ,	       1
   2.  Conclusions	       3
   3.  Recommendations 	       4
   4.  Pilot Plant  Description 	       5
   5.  Pilot Plant  Operation	      11
   6.  Pilot Plant  Results and Discussions ....'.	      16

References	      35

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                                FIGURES


Number                                                               Page

   1  Schematic diagram of rotary kiln carbon  regeneration
      system  	     6

   2  Carbon adsorption column  	     7

   3  Rotary kiln  regeneration system   	    10

   4  Carbon adsorption column backwash schedule   	    13

   5  Color  removal  through the carbon column  	    18

   6  Dissolved  COD  removal  through  the carbon  column  	    19

   7  Effect of  carbon  regeneration  on iodine,  molasses, and
      methylene  blue numbers   	    21

   8  DCOD adsorption capacity comparison  among various
      adsorption cycles  	    22

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                                   TABLES
Number                                                               Page

  1   Characteristics of Filtrasorb 300 Granular Activated
        Carbon  	        8

  2   Summary of Pomona Water Reclamation Plant Secondary
        Effluent Water Quality Characteristics (January 1 to
        December 31, 1977)  	       12

  3   Summary of Carbon Adsorption Column Performance During
        Rotary Kiln Regeneration Study  ....  	       17

  4   Results of Carbon Control  Tests During Rotary Kiln
        Regeneration Study  	       20

  5   Summary of Rotary Kiln Furnace Operating Temperatures (F)  .      24

  6   Summary of Rotary Kiln Furnace Operating Conditions ....       25

  7   Summary of Emissions from  the Externally-Fired Rotary
        Kiln Carbon Regeneration System 	       29

  8   Summary of Emissions from  the Multiple Hearth Carbon
        Regeneration Pilot System 	       30

  9   Criteria and  Unit Costs for Carbon Regeneration Cost
        Analysis	       32

 10   Summary of Carbon Regeneration Cost Estimates 	       33
                                    VII

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                              ACKNOWLEDGEMENTS
This study was jointly sponsored by the U.S. Environmental Protection Agency
and the County Sanitation Districts of Los Angeles County.

The untiring efforts of both the operating and laboratory staff of the Pomona
Advanced Wastewater Treatment Research Facility are gratefully acknowledged.
                                     vm

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                                  SECTION  I

                                INTRODUCTION
 The  Sanitation  Districts of  Los Angeles County and the United States
 Environmental Protection Agency have been jointly conducting an intensive
 pilot  plant  study  on  granular  activated carbon adsorption process for waste-
 water  treatment  since 1965.  The  study is conducted at the Sanitation
 Districts' Pomona  Advanced Wastewater Treatment Research Facility, Pomona,
 California.

 The  Pomona carbon  study adopted a multiple hearth furnace system for carbon
 regeneration during the first  10  years of pilot plant operations.  During
 this initial period,  the emphasis of the study was placed on the evaluation
 of the various  treatment process  parameters, such as pretreatment require-
 ments, carbon characteristics, adsorption capacity, backwash requirements,
 hydraulic loading  rates, and mode of regeneration.  The evaluation of dif-
 ferent types of  carbon regeneration furnace systems was not included in
 the  initial period of study.   Nevertheless, the multiple hearth furnace
 system was found to be very  effective and very reliable in regenerating the
 granular activated carbon for  wastewater treatment.  The details of the
 initial carbon  adsorption study results have been published elsewhere
 (1,2,3,4).

 It is  essential  that  every important aspect of any treatment process scheme
 should be thoroughly  studied before the process can be considered to be fully
 investigated.   Carbon regeneration is a major factor in the determination of
 the carbon process feasibility and cost effectiveness for wastewater treat-
ment.  Although  economical regeneration had been achieved with the multiple
 hearth furnace,  it was considered to be capital intensive compared to a
rotary kiln furnace.  Therefore,  the study presented in this report was
 initiated to determine if an externally-fired rotary kiln could be success-
fully utilized for regeneration of granular activated carbon.

Filtrasorb 300 granular activated carbon was exhausted by exposure to second-
ary effluent in  a downflow carbon contactor and then regenerated in the
rotary kiln.  This process was repeated for several cycles.  The performance
of the carbon after regeneration  was evaluated by its adsorption effective-
ness in the next adsorption cycle.  The performance of the rotary kiln
furnace was compared  to that of a multiple hearth furnace which had regen-
erated the same type  of carbon from this same type of pilot carbon contactor
exhausted with the same activated sludge plant effluent.

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The comparison was based on the ability to regenerate the carbon, fuel and
power consumption, ease of control and operation, and extent of carbon
losses.  The studies with the multiple hearth furnace were not in parallel
with those on the rotary kiln but were done at an earlier time.  The com-
parison study was initiated in November 1975, and completed in January 1978.
This report was prepared in May 1979.

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                                 SECTION II

                                CONCLUSIONS


The following conclusions can be drawn from the pilot plant study:


A.  The externally-fired rotary kiln furnace system was effective as the
    multiple hearth furnace system in reactivating granular activated car-
    bons which were exhausted by an activated sludge plant effluent.

B.  The rotary kiln regeneration system required less operational skill
    and maintenance labor than the multiple hearth furnace system.

C.  The usable life span of the rotary kiln was rather short compared
    to the life of the multiple hearth furnace.

D.  The fuel consumption rate averaged 27,520 kJ/kg (11,830 BTU/lb) for the
    externally-fired rotary kiln pilot plant.  This consumption rate was
    about twice that of a multiple hearth system.

E.  Both rotary kiln and multiple hearth furnace systems required an after-
    burner and a venturi wet scrubber for effective control of emissions
    of air pollutants.

F.  The average carbon loss observed in the operation of the rotary kiln
    pilot plant was approximately 7 percent per regeneration cycle.  This
    is equivalent to the carbon loss of a multiple hearth furnace system.

G.  The total process cost for a 182 kg/hr (400 Ib/hr) externally-fired
    rotary kiln system is estimated to be about 29.2 cents/kg (13.3 cents/lb)
    of carbon compared to 33.2 cents/kg (15.1 cents/.lb) of carbon for a mul-
    tiple hearth system with an equivalent regeneration capacity.

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                                 SECTION  III

                               RECOMMENDATIONS
A.  A comparison study of an externally-fired rotary kiln system and an in-
    ternally-fired rotary kiln system should be conducted.

B.  The life of a rotary kiln under steady operating conditions should be de-
    termined.

C.  Evaluation of a more energy saving rotary kiln provided with furnace
    flights, better furnace insulation and heat recovery system should be
    performed.

D.  Optimization of the air pollution control system for rotary kiln furnace
    should be conducted.

E.  Other carbon regeneration systems, such as Shirco infrared moving belt
    system and Westveco moving bed system, should be investigated to provide
    sufficient information for making furnace system selection.

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                                 SECTION IV

                          PILOT PLANT DESCRIPTION
A general layout of the 6.2 I/sec (100 gpm) pilot plant system is shown in
Figure 1.  Basically, the pilot plant consisted of a carbon contacting
column, a carbon dewatering and regeneration system, and an air pollution
control system.

CARBON CONTACTING COLUMN

The carbon contacting column used to provide the exhausted carbon for the re-
generation study is shown in Figure 2.  The column was a steel column with
1.83 m (6 ft) in diameter and 4.88 m (16 ft) in height.  The column was
operated in a downflow gravity mode.  As indicated in the figure, the carbon
bed was supported by a Neva Clog stainless steel screen.  A surface wash
piping system was provided at about 5 cm (2 in) above the surface of the
unexpanded carbon bed in the column.  The interior surface of the steel
column was coated with corrosion-inhibiting bitumastic coal-tar epoxy.  The
column contained about 1,590 kg (3,500 Ibs) of Calgon Filtrasorb 300 (8 x 30
mesh) granular activated carbon.  Table 1 presents the typical characteris-
tics of the carbon.  The depth of the carbon bed in the column was approxi-
mately 1.37 m (57 in) providing an empty-bed contact time of 10 minutes at a
system flow of 6.3 I/sec (100 gpm).

CARBON REGENERATION SYSTEM

The rotary kiln carbon regeneration furnace system was manufactured by the
former T. M. Melsheimer Co., Compton, California.  The furnace system con-
tained two externally-fired rotary kilns with  identical design.  The kilns
were made of Type 309 stainless steel with dimensions of 38.1 cm (15 in) in
diameter and 4.27 m (14 ft) in length.  The rotary kilns_were driven by an
1/3 hp (0.25 kW) drive mechanism and had a common slope 'of 0.008 toward exit
ends.  The furnace was designed for an operating temperature range of 790C
(1,450F) to 960C (1,760'F).  The rotary kiln furnace system had a rated
total regeneration capacity range of 682 kg (1,500 Ibs) to 909 kg (2,000
Ibs) of granular activated carbon per 24 hour period.

The spent carbon was first dewatered in a 61 cm wide by 122 cm long by 122 cm
deep (2 ft X 4 ft X 4 ft)  wood chamber.  The partially dewatered, spent car-
bon was then manually shovelled into the stainless steel feed hoppers.  Each
feed hopper had a nominal  capacity of 230 kg (500 Ibs) carbon.  Each feed
hopper was equipped with an 1/4 hp (0.19 kW) vibrator and a variable speed
screw conveyor   to facilitate the control of the carbon feed rate to each
rotary kiln.
                                      5

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SECONDARY
EFFLUENT
       BACKWASH
         WATER
              r
   CARBON
   COLUMN
       | SPENT
       l_CARBONj
 PRODUCT
  WATER
                    DEWATERING
                      CHAMBER
                      T
                       FEED
                      HOPPER
  TO ATMOSPHERE
                                 FUEL-
      AFTER-
      BURNER
r
            AIR
                                                     r
                        REGENERATED
                       CARBON  HOPPER
I	REGENERATED
     CARBON
         ROTARY KILN FURNACE
            	I
                         I	I
                    TO CARBON
                      _____ 	r, -T11 . ,1||	_|
                      COLUMN
 Figure  I. Schematic diagram  of rotary kiln carbon  regeneration system.

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     FULL OPEN COVER
     WITH 15" PORTHOLE
    20-I" HOLES
u.
10
   WASH
   WATER
   If)
\\ SURFACE WASH
                CARBON BED SURFACE	^
                          - 	->-
                             I  SAMPLING
                               TAPS
                NEVA CLOG
                 SCREEN
                               BOLT RING


                              INFLUENT
                              BACKWASH
                                            CARBON
                                            CHARGE
                                           CARBON
                                           "DISCHARGE
                                          EFFLUENT
                                          BACKWASH
                    I.Oft. = 0.305m
     Figure  2.  Carbon adsorption column.

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                          TABLE 1



CHARACTERISTICS OF FILTRASORB 300 GRANULAR ACTIVATED CARBON
Molasses Number
Iodine Number, mg/g
Apparent Density, g/cc
Methylene Blue Number, mg/g
Ash, %
Mean Particle Diameter, mm
Sieve Analysis:
% retained on
U.S. Sieve No., 8
10
12
14
16
18
20
30
pan
210
1040
0.484
256
6.4
1.44

3.5
12.6
19.2
16.3
15.1
9.0
6.8
11.7
5.8

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As indicated in Figure 3, a total of eight atmospheric gas burners were pro-
vided along both sides of the furnace.  KAO wool and K-20 fire brick were
used to insulate the furnace system.  The KAO wood blanket (in two layers)
covered the entire sides and roof of the furnace interior.  Mineral wool
block was set between the KAO wool blanket and the shell of the furnace for
further insulation.  The insulation was designed to keep the shell below
100C (212F) at normal interior operation temperatures.  The shell was made
of low carbon steel sheet to provide protection and support.

Six sets of thermocouples were provided along the length of each rotary kiln
for monitoring the furnace temperature profile.  The thermocouples were
located at 0.61 m (2 ft) intervals starting at 0.61 m (2 ft) from the carbon
feed end.  The third set of thermocouple at 1.83 m (6 ft) from the carbon
feed end was used as a temperature indicator-controller for controlling the
furnace operating temperature at desired level.  The thermocouples were
located about 2.54 cm (1 in) above the rotary kilns.  The desired amount of
steam was introduced at the exit end of each rotary kiln with a flow measure-
ment and control device.

AIR POLLUTION CONTROL SYSTEM

The rotary kiln furnace pilot system was only equipped with an afterburner
unit for its air pollution control.  This was based on the manufacturer's
claim that such a simple air pollution control system performed satisfac-
torily in a similar application(S).  Two eclipse single stage, low pressure
atmosphere injecting gas burners (Model TR-6 injector with Eclipse ST-206
nozzle) were mounted right above the exits of the exhaust from the two
rotary kilns.  Each of the gas burners had a rated capacity of 58,000
kJ/hr (55,000 BTU/hr).

During the carbon regeneration, the furnace exhaust was burned together with
air by the open-air gas burners.  The burned air-exhaust mixture was dis-
persed through a stainless steel stack at a height of approximately 6.1 m
(20 ft) from the ground level.

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    SPENT CARBON

          FEED
        HOPPER
DEWATERING
 CHAMBER
GAS-
                                  STEAM
                          15" DIAMETER BY 14' LONG
                         STAJNLES S J5TEEL
                          15" DIAMETER BY 14* LONG
                    GAS-
                                 (=*-
                               REGENERATED
                                  CARBON
                                  HOPPERS
                             PLAN
                          l'= 12 = 0.305m
             GAS STACK
                           ^-FLUEGAS
                      HOOD
^
JST
D
mm
^^
GAS TO
^BURNERS
SiiKisiiiKiv
'"''-'''*'-''*'''-
^
J
ii-'iii
                                                 -KAO WOOL
                         STAINLESS STEEL TUBES
                    ^TTTTTTTTTTTTTTTUTTTTTTTTTTT^
                                                       FURNACE
                                                       ENCLOSURE
                  SCREW CONVEYOR
                     -K-20 FIRE BRICK
                          ELEVATION
                          f = 12"= 0.305m
        Figure 3.  Rotary kiln regeneration system.
                              10

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                                   SECTION V

                             PILOT  PLANT OPERATION
 OPERATION  OF  CARBON  CONTACTING  COLUMN

 Carbon Adsorption

 During the carbon regeneration  comparison study, the unchlorinated and un-
 filtered secondary effluent from the Pomona Water Reclamation Plant was
 treated directly by  the carbon  adsorption systems.  The Pomona Water
 Reclamation Plant is a 0.44 cu  m/sec (10 MGD) activated sludge plant.
 The typical water quality produced by the plant is shown in Table 2.

 A  15.2 cm  (6  in) diameter steel pipe was used to transfer the unchlorinated
 secondary effluent from the Pomona Water Reclamation Plant to the Pomona
 Advanced Wastewater  Treatment Research Facility at a maximum total flow rate
 of 37.9 I/sec (600 gpm).  A surge tank at the research site was used to hold
 the secondary effluent for supplying the pilot plant study by an  influent
 pumping system.  The product water from the carbon column and the excess
 water from the surge tank were  discharged together to the creek after
 adequate chlorination.

 The contacting carbon column was operated in a gravity downflow mode at a
 constant rate of 6.3 I/sec (100 gpm) thereby providing a hydraulic loading
 rate of 2.4 1/sec/sq m (3.5 gpm/sq ft) and an empty-bed contact time of
 approximately 10 minutes.  As indicated in Figure 2, the column feed water
 entered the top of the contactor through an annular distribution ring con-
 taining twenty 2.54 cm (1 in) diameter holes around the circumference of the
 contactor.  The entrance annular ring was located about 2.5 m (8.3 ft) above
 the top of the carbon bed, thus providing sufficient space for bed expansion
 during backwashing.

 Backwash of Carbon Bed

 The carbon bed was backwashed daily to maintain good hydraulic conditions
 for operation.  The carbon column-was usually taken off stream for back-
 wash at 8:00 A.M., and it was back on stream at approximately 9:00 A.M.

 The unchlorinated secondary effluent from the Pomona Water Reclamation Plant
 was used as wash water for the  carbon bed backwash operation.  The backwash
 schedule,  as indicated in Figure 4, consisted of a surface wash at a constant
rate of 1.22 1/sec/sq m (1.8 gpm/sq ft) for 10 minutes and a stepwise water
 backwash to a maximum rate of 7.13 1/sec/sq m (10.5 gpm/sq ft) within a total

                                     11

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                              TABLE  2

SUMMARY OF POMONA WATER  RECLAMATION  PLANT SECONDARY EFFLUENT WATER
     QUALITY CHARACTERISTICS  (JANUARY 1 to DECEMBER 31, 1977)
Parameter
Total Cadmium, yg/1
Total Chromium, mg/1
Total Copper, mg/1
Total Iron, mg/1
Total Lead, mg/1
Total Nickel, mg/1
Potassium, mg/1
Total Silver, yg/1
Sodium, mg/1
Total Zinc, mg/1
Total Hardness, mg/1 CaCO^
Total Alkalinity, mg/1 CaC03
Total Dissolved Solids, mg/1
Chloride, mg/1 Cl
Sulfate, mg/1 S04
Nitrate, mg/1 N
Nitrite, mg/1 N
Ammonia, mg/1 N
Organic Nitrogen, mg/1 N
Phosphate, mg/1 P04
Range
1 -
0.01
0.005
0.02
0.01
0.02
10
1
94
0.042
185 -
127 -
479 -
92 -
93 -
0.01 -
0.01 -
0.07 -
0.6 -
17.0 -
6
- 0.02
- 0.020
- 0.14
- 0.04
- 0.08
- 16
- 3
- 121
- 0.160
207
252
667
119
119
20.5
3.65
19.6
2.1
25.2
Mean
2.8
0.01
0.015
0.05
0.02
0.04
11.8
1.4
111
0.081
200
207
567
104
111
2.81
1.11
11.7
1.1
21.6
                                12

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           20
                 I gpm/sq.ft.= 0.68 l/sec/sq. m

                 I gal = 3.79 liters
         *- l5
OJ
         E
         Q.
         O>
<
a:

o
   0
                                                                       ~1
                                                       	l
                                          rJ
                                          I     BACKWASH (5000 GALS.)
                SURFACE WASH
                  (500 GALS.)
             0
                       10
 15        20

TIME, minutes
25
30
35
                Figure 4.  Carbon adsorption  column backwash  schedule.

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 period of approximately 32 minutes.  The total  volumes of water used  for  sur-
 face wash and backwash were equal to 1.89 cu m (500 gallons)  and 18.9 cu  m
 (5,000 gallons), respectively.  The combined total  of water consumed  in back-
 wash was about 4 percent of the total volume of product water.

 During backwashing, the backwash water was discharged into a holding  tank
 designed to capture any accidental carbon spills and to allow visual  ob-
 servation of the clarity of the backwash water.  The backwash water contain-
 ing heavy accumulations of biological floes and some carbon fines  overflowed
 a weir in the holding tank and was pumped into  the  head end of  the primary
 sedimentation tanks of the Pomona Water Reclamation Plant.

 While adequate space was provided above the carbon  bed in the contacting
 column for  bed expansion during backwash cycle, routine column  backwash
 operation was limited to a maximum upflow rate  of 7.3 1/sec/sq  m (10.5 gpm/
 sq ft)  because of the limitation on the structural  strength of  the underdrain
 screen.   At  the backwash rate  of 7.13 1/sec/sq  m (10.5 gpm/sq ft), the
 measured bed expansion was about 10 percent.

 The headloss buildup through  a granular activated carbon  column operated  on a
 packed-bed  and downflow mode,  was found to be  influenced  by such factors  as
 hydraulic surface loading, influent suspended  solids level, carbon particle
 size and the length of filter  run.  The average total  headloss  buildup
 through  the  carbon  bed was about 0.17 kg/sq cm  (2.5 psig)  for a 23 hour
 operation period  during  the study.

 Carbon Transfer for Regeneration

 Normally, the carbon  contacting column  treated  a total  volume of 22,710 cu m
 (6  million gallons)  of Pomona  Water Reclamation Plant  secondary effluent  be-
 fore it  was  taken off stream  in preparation for carbon regeneration.  The
 COD removal  efficiency of  the  carbon column usually reached a leveling off
 value  at  this cut off volume.

 The  spent carbon  was  thoroughly backwashed  before being hydraulical ly trans-
 ferred as a  slurry  to  the  elevated dewatering chamber.  The backwash pro-
 cedure was similar  to  that used  for routine column  backwash except for the
 fact that the  last  backwash step was prolonged  to provide  a total  backwash
 water volume  of about  79.5 cu m  (21,000 gallons).

 CARBON REGENERATION

 The dewatered  spent carbon, with  about  50  percent moisture  content, was
 transferred from  the  feed  hoppers  through  screw conveyors  into  two parallel
rotary kiln furnaces.  The  carbon  feed  rate to  each rotary  kiln was main-
tained at approximately 16  kg/hr  (35  Ib/hr).  The average  steam consumption
rate was 0.3 kg steam/kg carbon.   The kilns were  rotated automatically at an
 average rate of 6 revolutions per  minute.

The regeneration  temperature was maintained at  885C (1,625F)  by  the tem-
perature indicator-controller which  was  located  1.83 m (6 ft) from the


                                     14

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 carbon  feed  end.   The  feed  end  was  usually  about 93C (200F) lower than the
 controlling  temperature.  The regenerated carbon was discharged from the
 rotary  kilns into  two  covered storage  hoppers for carbon cooling.  The
 cooled  carbon was  periodically  shovelled  into 208 1 (55 gallon) drums which
 were  then  emptied  into the  carbon contactor through a hoist system.

 CARBON  MAKE-UP

 After carbon regeneration,  the  regenerated  carbon was put back  in the con-
 tactor  and thoroughly  backwashed with  57  to 76 cu m (15,000 to  20,000 gal-
 lons) of secondary effluent to  remove  carbon fines.  Appropriate amount of
 make-up carbon was then added to replace  the carbon lost during regeneration.
 The contactor, with the added make-up  virgin carbon, was backwashed again
 with  7.6 to  19 cu  m (2,000  to 5,000 gallons) of secondary effluent before
 the contactor was  placed  back in operation.

 SAMPLING AND TESTING

 During  the carbon  adsorption and regeneration cycles, appropriate samples
 were  taken for evaluating the carbon adsorption and carbon reactivation
 efficiencies.   The types, locations, and  frequencies of the various samples
 taken during the study are  described as follows.

 Water Quality Monitoring

 Refrigerated 23 hour composite  samples (9:00 A.M. to 8:00 A.M.  next day) of
 influent and effluent  from  the  carbon  contacting column were collected
 automatically using timer-controlled solenoid valves.  These samples were
 analyzed daily for turbidity and three times a week for total chemical
 oxygen  demand  (TCOD),  dissolved chemical  oxygen demand (DCOD),  suspended
 solids  (SS)  and color.   Determinations for  pH and temperature were performed
 on grab samples three  times a week.  All  analyses were performed in accor-
 dance with the Standard  Methods(S).

 Carbon  Regeneration Control  Test

 In the  course  of carbon  regeneration,  a number of control tests, consisting
 of the  determinations  of  apparent density,  iodine number, methylene blue
 number, and  molasses number, were performed to regulate the regeneration
 process and  monitor the  quality of  the regenerated carbon.  All tests were
 performed using standardized procedures of  the Pittsburgh Activated Carbon
 Company(7).

 The test for  apparent  density was determined routinely every hour whereas the
 tests for  iodine and molasses numbers were  performed every four hours and two
 hours,  respectively.   The six to eight grab samples of spent carbon, col-
 lected during  carbon transfer,  and  the hourly samples of regenerated carbon
 were composited over the regeneration period.  These composited carbon
 samples were  analyzed  for apparent  density, molasses number, iodine number,
methylene blue  number,  ash  content,  and mean particle size.
                                     15

-------
                                  SECTION VI

                       PILOT PLANT RESULTS AND DISCUSSIONS
 PERFORMANCE OF CARBON CONTACTING COLUMN

 Four adsorption cycles were performed with the carbon contacting column  dur-
 ing the entire rotary kiln regeneration study period.  The average values  of
 water quality parameters for each adsorption cycle are presented in Table  3.
 The overall averages for the entire operation are also included  in the
 table.

 As indicated in Table 3, the average volume of secondary effluent processed
 through the carbon  contacting column during each  adsorption  cycle was about
 24,200  cu m (6.4 million gallons).   The average pressure drop  before the
 daily backwash of the carbon column was approximately 0.18 kg/sq cm (2.5
 psig).   The carbon  column with a carbon-bed depth of  1.37 m  (57  in)  seemed to
 be generally effective for suspended solids and turbidity removals.  These
 removals  averaged 83.6 percent and  72.9 percent for the  suspended solids and
 turbidity,  respectively.

 The  removals of color and dissolved chemical  oxygen demand  (DCOD)  by the car-
 bon  column  are illustrated in Figures  5 and 6,  respectively.   Both color and
 DCOD were effectively removed by the carbon in  the early portion  of  each ad-
 sorption  cycle.   As  the  carbon approached  exhaustion,  both color  and DCOD re-
 movals  seemed  to  level off at approximately 40  percent and 30  percent, re-
 spectively.   These phenomena may be attributed  to the  biological  reactions
 taking  place inside  the  carbon bed.   The total  average removals  for  color and
 DCOD  over  an  adsorption  cycle were  54.8 percent and 42.9 percent,  respec-
 tively.   The color removal  seemed to improve  slightly  after  each  carbon  re-
 generation.   This phenomenon  was  accompanied  by a similar trend  of molasses
 number  increase with  the number  of  the  carbon regeneration,  which  is indi-
 cated in  Table  4  and  Figure  7.

 A comparison  of DCOD  adsorption  capacities  with respect  to adsorption cycles
 is presented  in Figure 8.  As  indicated in  the  figure, the DCOD  adsorption
capacity curve for each  adsorption  cycle follows  very  closely to  each other,
especially at low levels of  applied  DCOD.   This similarity adequately demon-
strates that the rotary  kiln  regeneration system  could consistently  restore
the operational carbon adsorption capacity  in its repeated regeneration
cycles.
                                     16

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                                       TABLE 3



SUMMARY OF CARBON ADSORPTION COLUMN PERFORMANCE DURING ROTARY KILN REGENERATION STUDY
Parameter
Total Flow- Processed , MG
Daily Pressure Drop, psig
Suspended Solids, mg/1
Column Influent
Column Effluent
Turbidity, FTU
Column Influent
Column Effluent
Color, color unit
Column Influent
Column Effluent
Total COD, mg/1
Column Influent
Column Effluent
Dissolved COD, mg/1
Column Influent
Column Effluent
PH
Column Influent
Column Effluent
I
Temperature, C
Column Influent
Column Effluent
Operation Period
On
Off
Adsorption
First
4.81
--

12.6
2.8

5.1
1.5

31
15

39.6
17.9

25.3
14.3

7.3
7.3


22.9
22.9

10/29/75
12/31/75
Cycle
Second
6.83
1.9

9.0
2.0

3.7
1.4

33
15

42.4
20.8

32.2
10.6

7.7
7.7


24.5
24.7

9/22/76
11 6/77
Third
6.76
2.7

12.9
1.8

6.0
1.5

31
13

45.1
20.4

28.1
16.2

7.5
7.6


22.0
21.7

1/25/77
4/22/77
Fourth
7.12
2.9

10.4
1.1

4.3
1.0

31
13

40.5
17.3

25.6
14.3

7.4
7.5


27.0
26.8

5/19/77
8/24/77

-------
   100
                               OPERATING CONDITIONS
              Hydraulic Surface Loading Rate = 3.5gpm/sq.ft.(2.4 l/sec./sq.m)
                         Empty-bed Contact Time = 10 minutes
            	 1st  Adsorption  Cycle (Virgin Filtrasorb 300 carbon)
            	  2nd Adsorption  Cycle (Regenerated once thru rotary  kiln)
            A	*  3rd Adsorption  Cycle (Regenerated twice  thru rotary kiln)
            	  4th Adsorption Cycle (Regenerated thrice thru rotary kiln)
    75
                                             ,	TEST SUSPENDED DUE TO
                                                INSTRUMENT  MALFUNCTION,
                                                3rd ADSORPTION CYCLE
   50
   25
8  20
   10
                         2345
                          VOLUME  TREATED, million gallons
  Figure  5.  Color  removal  through  the  carbon  column.
                                     18

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100
                           OPERATING CONDITIONS
           Hydraulic Surface Loading Rate = 3.5 gpm/sq.ft. (2.4 l/sec./sq. m)
                      Empty-bed Contact Time = 10 minutes
         	-fl 1st  Adsorption Cycle (Virgin Filtrasorb 300 carbon)
         	 2 nd Adsorption Cycle (Regenerated once thru rotary kiln)
         A	-A 3rd Adsorption Cycle (Regenerated twice thru rotary kiln)
         	 4th Adsorption Cycle (Regenerated thrice thru rotary kiln)
75
50
25
20
                      2345
                       VOLUME TREATED, million gallons
       Figure  6.  Dissolved  COD  removal through
                     the  carbon   column.
                                 19

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ro
o
                                                     TABLE  4


                       RESULTS  OF  CARBON  CONTROL  TESTS  DURING ROTARY KILN REGENERATION STUDY
Parameter
AD, g/cc
IN, mg/g
MN
MBN, mg/g
Ash, %
MPD, mm
First
Regeneration
S R
0.522
623
155
241
6.5
1.66
0.519
886
210
260
7.3
1.50
Second
Regeneration
S R
0.564
610
142
169
7.2
1.58
0.502
846
220
258
8.4
1.46
Third
Regeneration
S R
0.559
620
206
158
7.4
1.48
0.514
831
241
251
8.2
1.46
Fourth
Regeneration
S R
0.548 0.517
616 773
186 241
163 252
9.7
1.61 1.46
          NOTES:   1.   The data were based on the composite samples of both rotary kilns.


                  2.   S = spent carbon; R = regenerated carbon


                  3.   AD = Apparent density; IN = Iodine number; MN = Molasses number;  MBN  =  Methylene

                           blue number; MPD = Mean particle diameter.

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                    MULTIPLE HEARTH SYSTEM
                       -O REGENERATED CARBON
                       - SPENT CARBON
                      ROTARY KILN  SYSTEM
                  & --- ^ REGENERATED CARBON
                  A --- A SPENT CARBON
1st        2nd        3rd
   REGENERATION CYCLE
                                                  4th
Figure  7.  Effect  of carbon regeneration  on  iodine,
           molasses, and methyiene blue numbers.

-------
ro
no
         AC = ADSORPTION CYCLE
                                                         WITH ROTARY KILN
                                                         REGENERATED CARBON
                                           X>3rd AC
              O-W1TH MULTIPLE HEARTH REGENERATED CARBON (2nd AC)
                                 0.3       0.4       0.5

                                  DCOD APPLIED, Ib/lb C
                 Figure  8.  DCOD adsorption  capacity  comparison

                            among various  adsorption  cycles.

-------
 PERFORMANCE  OF  REGENERATION SYSTEM

 During  initial  operation of the rotary kiln carbon regeneration system, some
 mechanical difficulties were encountered.  The problems were generally in the
 areas of carbon dewatering, carbon  feed, gas burner, steam monitoring, and
 furnace temperature control.  Most  of these problems were associated with im-
 proper designs  in  the  original system.  Several system modifications were
 per formed before  the  layout as shown in Figure 3 was accomplished for
 routine operation.  This system modification had caused a long shut-down time
 between the  first  and  second adsorption cycles, which is indicated in Table
 3.

 Furnace Operating  Temperature

 Usually it required about 90 minutes for the rotary kiln system to reach the
 desired furnace operating temperature.  The actual feeding of the spent car-
 bon into the kilns was  initiated 30 minutes after the preset controlling
 temperature  was reached.

 The average  operating  temperatures  at various thermocouple locations along
 the length of the  rotary kiln system for each regeneration cycle are shown in
 Table 5.  As indicated  in the table, the average temperature at the carbon
 feed end of  the rotary kiln was about 93C (200F) lower than the temperature
 at the location of temperature indicator-controller, which was located about
 half-way of  the length  of the rotary kiln.  The average temperature along the
 rotary kiln  in  the last 3.05 m (10  ft) section ranged from 891C (1,635F) to
 916C (1,681F).   This  relatively small variation seemed to indicate a rather
 uniform temperature distribution along the last 3.05 m (10 ft) section of the
 rotary kiln  system.  The regeneration temperature range of 891C (1,635F) to
 916C (1,681F) in the  rotary kiln  system is slightly lower than the range of
 916C (1,681F) to 932C (1,710'F)  observed in the multiple hearth furnace
 system^3'.

 The temperature at the  temperature  indicator-controller was gradually de-
 creased from an average of 936C (1,716F) in the second regeneration cycle
 to 893C (1,640'F) and  876C (1,608F) for the third and fourth regeneration
 cycles, respectively.  The purpose of this procedure was to determine the
 lower limit of  furnace  operating temperature which would be equally effective
 for carbon regeneration.

 Carbon Feed Rate

 Table 6 summarizes the  rotary kiln  operating conditions for the four carbon
 regeneration cycles.   As indicated  in the table, the average carbon feed rate
 for each rotary kiln ranged form 14.7 kg/hr (32.3 Ib/hr) to 19.0 kg/hr (41.7
 Ib/hr), with an overall average of  16.0 kg/hr (35.1 Ib/hr).  The highest car-
 bon feed rate occurred  in the first regeneration cycle which was considered
 as a shake down operation of the rotary kiln regeneration system.  The aver-
 age travel  time of carbon through the rotary kiln was estimated to be 30
minutes with the kiln  rotated at an average rate of 6 revolutions per minute.
                                     23

-------
                                                     TABLE  5


                           SUMMARY  OF  ROTARY  KILN  FURNACE  OPERATING  TEMPERATURES  (F)
Thermocouple Distance From
Number Feed End, ft
First
1 2
2 4 
3 6 1681
4 8 
5 10
6 12
Regeneration
Second
150*
1670
1716
1755
1741
1720
Cycle
Third
1413
1599
1640
1651
1627
1586
Fourth
1392
1543
1608
1637
1622
1592
Overal 1
Average
1461
1635
1661
1681
1663
1633
NOTES:  1.  All temperature data were based on the average of two rotary kilns.

        2.  Thermocouple Number 3 was used as the temperature indicator-controller.


        3.  (F - 32) X 1 = "C; ft X 0.305 = m
                        9

-------
                                                                       TABLE 6
                                                 SUMMARY OF ROTARY KILN FURNACE OPERATING CONDITIONS
ro
en
Regeneration Cycle
Parameter
Total Carbon Regenerated, Ib
Duration of Regeneration, hr
Carbon Feed Rate, Ib/hr
Steam Used, Ib/lb carbon
Total Fuel Used, BTU/lb carbon
Carbon Loss, %
First
3,420
41.0
83.4
0.24
9,070
12.9
Second
3,420
53.0
64.5
0.31
13,050
6.3
Third
3,010
45.0
66.9
0.30
12,370
6.0
Fourth
3,370
51.5
65.4
0.30
12,820
7.6
Overall
Average
3,305
47.6
70.1
0.29
11,830
6.6
                   NOTE:  1.  Approximately 400  Ibs of carbon were  lost to drain during carbon transfer for
                              third carbon regeneration cycle.

                          2.  Substantial carbon  loss was caused by on-and-off shake-down operations during
                              the first carbon regeneration cycle.  Consequently, the unusually high 12.9%
                              carbon  loss was not  used in the calculation of the overall carbon loss average.

                          3.  The carbon feed rates were based on the  sums of two rotary kiln.

-------
 Steam and Fuel Consumption Rates

 During the regeneration cycle, the steam was continuously injected at the
 exit ends of the rotary kilns at the rate of 4.5 kg/hr (10 Ib/hr) for each of
 the two rotary kilns.  Because of this constant injection rate, the calcu-
 lated steam consumption rate thus varied from 0.24 to 0.31 kilogram of steam
 per kilogram of carbon, depending on the variations of the carbon feed rate.
 This steam consumption rate range was about one-half of the steam consumption
 rate used in the multiple hearth furnace operations having an average carbon
 feed rate of 37.1 kg/hr (81.7 Ib/hr).

 As indicated in Table 6, the total  fuel  consumption rate for the first regen-
 eration cycle was about 21,000 kJ/kg carbon (9,070 BTU/lb carbon), which  was
 about 23 percent lower than the overall  average fuel consumption rate.  Since
 the heat energy required to maintain the furnace operating temperature is
 practically constant and is only slightly affected by the moderate variation
 of carbon feed rate, the calculated fuel consumption rate on unit carbon
 weight will  be affected inversely by the carbon feed rate.  Therefore, the
 lower fuel  consumption rate in the  first regeneration cycle might be caused
 by the relatively higher carbon feed rate in the first regneration cycle,
 which was about 19 percent higher than the average carbon feed  rate for the
 entire study.

 The operation  of the rotary kiln  system  during  the initial eight hours, which
 represented  about 20 percent of the total  regeneration time used in the first
 regeneration  cycle,  was on an on-and-off basis  due to various mechanical  dif-
 ficulties.   This unusual  mode of  operation resulted in a heavy  carbon loss of
 12.9  percent  as indicated  in Table  6.
 The  carbon  losses  in  the subsequent three  regeneration  cycles  were  about  6.3,
 6.0,  and  6.6  percent.   These  levels of carbon  losses  were very similar  to  the
 results obtained from  the multiple hearth  furnace  operation'^'.
 As  indicated  in  Table  6,  about  181  kg  (400  Ibs)  of carbon were  inadvertently
 lost  through  an  open drain  valve  during  the  preparation  of carbon  transfer
 for the third  regeneration  cycle.   This  type  of  carbon loss was not  included
 in  the carbon  loss calculation.

 Carbon Adsorption Capacity

 In  the course  of thermal  regeneration, the organic pollutants on the  surfaces
 of  the external  and pore  areas of carbon  are  oxidized and removed.  However,
 this  oxidation process does not completely remove the adsorbed organics from
 the carbon pores.  Therefore, a certain  amount of theoretical adsorption
 capacity is normally lost in every  thermal regeneration  cycle.  In addition
 to this cause  for capacity  loss, the change of pore size distribution in the
 regeneration process may  also contribute  to the  reduction of theoretical
 carbon adsorption capacity.  The carbon  adsorption capacity recovery can be
monitored by the determinations of  the iodine number, molasses number, and
methylene blue number on both spent and regenerated carbons.  Table 4 sum-
marizes the values of the carbon characteristic  numbers obtained in the
rotary kiln regeneration study.

                                      26

-------
 As  indicated  in  Tables  1  and  4,  the  iodine  number of  the virgin Calgon
 Filtrasorb  300 granular activated  carbon  was  about  1,040 mg/g, and  it was re-
 duced  to  623  mg/g,  a 40 percent  reduction,  at  the end of the first  adsorp-
 tion cycle.   This  reduction  in  iodine  number  was partially recovered from
 623 mg/g  to 886  mg/g in the  first  regeneration cycle  by the rotary  kiln
 system.   A  continuing decrease  in  the  iodine  number with respect to regen-
 eration cycle is apparent from  Figure  7,  although the cyclic thermal regen-
 eration was effective  in  restoring the  operational  adsorption capacity, as
 shown  in  Figure  8.

 On the contrary, the molasses number was  found to be  gradually increased
 with the  number  of  regeneration  cycle.  Since  the molasses number related to
 the surface area of the pores with a diameter  larger  than 28 angstroms, the
 increase  in molasses number  indicated  an  enlargement  of micropore structures
 to macropore  structures in the  carbon during  the repeated thermal regenera-
 tion process.  This shift in  pore  size  distribution also caused a reduction
 of total  surface area of  the  carbon, which  was indicated by the reduction of
 the iodine  number.   The molasses number of  the virgin carbon was about 210,
 and it was  increased to 241,  a  15  percent increase, at the end of the fourth
 regeneration  cycle.  This increase in molasses number seemed to improve the
 color removal  slightly  as shown  in Table  3  and Figure 5.

 Another parameter  used  to measure  pore  enlargement during thermal regenera-
 tion was  the  methylene  blue  number.  This number related to surface area of
 carbon pores  with diameter larger  than  15 angstroms.  As indicated  in Tables
 1 and 4,  the  methylene  blue  number of the carbon after four regeneration
 cycles was  about 252 mg/g as compared to  256 mg/g of  the virgin carbon.

 The ash content  of  the  regenerated carbon,  which measured the buildup of in-
 organic residues,  increased  significantly from a level of 6.4 percent for the
 virgin carbon  to 9.7 percent  for the carbon with four thermal regeneration
 cycles.   The  mean particle diameter seemed  to  maintain at a fairly constant
 level of  1.46mm in  all four regeneration cycles.  Similarly, the apparent
 density of the regenerated carbon  only  fluctuated slightly between 0.502 and
 0.519 g/cu cm, as  indicated  in  Table 4.

 The effects of the  rotary kiln carbon regeneration on the various carbon
 characteristic numbers, as discussed in the above paragraphs, are very simi-
 lar to those  observed in  the multiple hearth carbon regeneration study(^).
 These similarities  are  illustrated in Figure  7.  Apparently, both rotary kiln
 and multiple  hearth  regeneration systems  could restore the carbon adsorption
 capacity  equally well.

 Furnace Life

 After almost  18  months  of installation  and  operation, the interior  surfaces
of both rotary kilns were found  seriously corroded.   One of the two rotary
 kilns actually broke into two sections  during  a special regeneration of some
odor control carbons on June 14, 1977.  This special regeneration might have
enhanced  the corrosion  rate by producing  the  sulfur oxides which might be
converted to corrosive  sulfuric  acid fume.  The corrosion was particularly
                                      27

-------
 serious within the first 1.2 m (4 ft)  section near the carbon  feed  end.   The
 broken kiln was replaced with a similar kiln to complete the fourth regenera-
 tion cycle.

 In comparison with the multiple hearth furnace used in a previous carbon  ad-
 sorption study under similar operating conditions, the useable life for the
 rotary kiln furnace was much shorter than the actual  12 years  of functional
 period for the multiple hearth furnace pilot systenr   .

 PERFORMANCE OF AIR POLLUTION CONTROL SYSTEM

 During the second  carbon regeneration  cycle, the emissions  from the after-
 burner stack of the rotary kin regeneration system were tested by the  South
 Coast Air  Quality  Management District  (SCAQMD).   The  flue gases at  the outlet
 of the afterburner were tested for flow rate, temperature,  particulate
 matter,  carbon monoxide, carbon dioxide, oxygen,  odor number and oxides of
 sulfur.

 Gas  flow measurements  were made with a standard  pitot tube  and a magnetic
 draft gauge.  The  gas  temperature  was  measured  with chromel-alumel  thermo-
 couple and  a portable  potentiometer.   The test  for particulate matter  was
 performed  using  a  wet  impingement  method.   Samples for the  determination  of
 oxides of  sulfur were  collected by an  impinger  train  containing 5 percent
 NaOH.   During  the  test period, gas samples  were  also  collected  and  analyzed
 with  a conventional  Orsat  analyzer for C0~  and  tested with  a Teledyne  oxygen
 analyzer for Op.   A gas chromatograph-comoustion-infrared technique  was used
 to determine tne concentration of  carbon monoxide.

 Table  7  presents a summary of  the  emission  data  from  the  afterburner stack.
 During the  entire  second regeneration,  odors and  smoke were  not detected.  As
 indicated by the data,  the  measured  emissions were within the  allowable
 limits.  However,  it should  be mentioned that because of the configuration of
 the afterburner stack,  an  indeterminate  amount of  ambient air  invariably  pro-
 vided  natural  dilution  of  the  emissions  from the  regeneration  system.  Thus,
 the measured  emissions  reported  in Table 7  represented  the diluted  concentra-
 tion of the  air pollutants.   If an appropriate  air  dilution  factor  were
 applied, the  actual  emission concentration  would  be higher.  Consequently, it
 is most likely that  without  the dilution effect  the actual particulate
 emissions would exceed  the  allowable limits.

 The above concern  has caused the SCAQMD  to  deny the Sanitation  Districts'
 permit application for  further  operation  of  the  rotary kiln  pilot plant.  It
 has been required  to modify the  air  pollution control  system of the  rotary
 kiln furnace to meet the control limits  of  particulates, carbon monoxides and
oxides of sulfur without clean  air dilution.  The  SCAQMD has suggested that a
venturi-scrubber,  a high efficiency  afterburner,  and  a  sulfur  dioxide
scrubber be  added to minimize  the  above  pollutants, respectively.

Table 8 shows the results of the evaluations  of the air pollution control
system of the multiple  hearth  furnace.   The  data  indicated that all  emission
                                     28

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                                                    TABLE 7

              SUMMARY OF EMISSIONS FROM THE EXTERNALLY-FIRED ROTARY KILN CARBON REGENERATION SYSTEM
                         Parameter
                                         SCAQMD
                                        Emission
                                          Limit
  Measured Emissions

From Afterburner Stack
ro
1.   Particulate Matter

    Concentration, grain/SCF
    Emission Rate, Ib/hr

2.   Oxides of Sulfur, (S02)


    Concentration, ppm by volume
    Emission Rate, Ib/hr

3.   Carbon Monoxide (CO)

4.   Odor

    Odor Unit/SCF

5.   Gas Flow

    Temp.,  F 
    Rate, SCFM
                                                          0.196
                                                          0.990
                                                         2000.00
          0.185
          0.700
         67.00
          0.36

         530.00
                                                                                     NONE
                                                                                    415.00
                                                                                    530.00
                NOTES:   1.   SCAQMD = South Coast Air Quality Management District


                         2.   Ib/hr X 0.454 = Kg/hr;  (F - 32) X |  =   C;  SCFM X 0.472 = I/sec;

                             grain/SCF X 2.29 = g/cu m

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CO
o
                                                                       TABLE  8


                            SUMMARY OF  EMISSIONS  FROM  THE  MULTIPLE  HEARTH  CARBON  REGENERATION  PILOT  SYSTEM  (Ref. 3)







1.


2.


3.


4.


5.

6.

7.




APCD
Parameter Emission
Limit


Participate Matter
Concentration, grains/SCF 0.20
Emission rate, Ib/hr 1.00
Oxides of Nitrogen, (NOX)
Concentration, ppm dry 225
Emission rate, Ib/hr
Oxides of sulfur (S0)
Concentration, ppm SO 0.2%
Emission rate, Ib/hr
Hydrocarbons
Concentration, ppm C
Emission rate, Ib/hr C
Carbon Monoxide (CO)
Concentration, % Volume dry
Odor
Odor unit/SCF
Gas Flow
Temperature, *F
SCFM
Measured Emissions
(Test Series I)


Baghouse

Inlet Outlet

0.987 0.298
0.890 0.266

94





3900
0.88

0.56

20,000

354 140
104 104

Measured
Emissions

(Test Series II)


After-
Burner
Outlet

0.046
0.09

166
0.48

217
0.88

660
0.50

0.20

10

1000
392




Baghouse

Inlet

1.82
2.17

40
0.028

nil


740
0.20

1.36

20,000

352
139

Outlet

0.47
0.80

--
--

nil
--

561
0.21

0.86



159
198


After-
Burner
Outlet

0.075
0.24

180
0.40

149
0.57

nil
--

0.11

20

1148
376
                    NOTES:   1. APCO  = Air  Pollution  Control  District  (Los  Angeles  County,  California)

                             2. Ib/hr X  0.454  =  Kg/hr;  (F  -  32)  X | =  "C;  SCFM  X 0.472  =  I/sec;

                               grain/SCF  X 2.29 =  g/cu m

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parameters, such  as participate matter, oxides of nitrogen, oxides of sulfur,
hydrocarbon, and  odor number, were all in full compliance with the local  air
pollution control requirements.

An 182 kg/hr (400 Ib/hr) plant-scale multiple hearth carbon regeneration  sys-
tem has been in operation at the Sanitation Districts' Pomona Water
Reclamation Plant, Pomona, California, since early 1977    .   This furnace is
provided with an  adequate air pollution control system which  consists of  only
a venturi wet scrubber and an afterburner.  The satisfactory results form
this air pollution control system seem to indicate that the same type of  sys-
tem may be able to provide an adequate control of the emissions from the
rotary kiln regeneration system.  The combination of cyclone  and baghouse
used in the pilot-scale multiple hearth regeneration system can reliably be
replaced by the venturi wet scrubber unit(3).

COST ESTIMATE

Criteria for Cost Estimates

An economic analysis has been prepared to compare the carbon  regeneration
costs between a multiple hearth furnace system and an externally-fired rotary
kiln furnace system.  The furnace capacity used for the cost  comparison
analysis is 182 kg/hr (400 Ib/hr).  This capacity is based on the requirement
of a typical 0.44 cu m/sec (10 MGD) carbon adsorption plant with a carbon
exhaustion rate of 75 g/cu m (650 Ib/MG).  Table 9 shows a summary of the
various assumptions used for the preparation of the cost estimates.

Itemized Cost Estimates
The cost estimates for the furnace systems have been divided into two sub-
categories; namely, capital cost, and operation and maintenance costs.  The
equipment cost consists of carbon dewatering and feed system, furnace system
(including steam generator), and air pollution control system (including an
afterburner and a venturi wet scrubber).  Additionally, the capital  cost also
includes the initial engineering cost (10 percent of equipment cost), equip-
ment shipping and installation cost (125 percent of equipment cost), and
contingency (20 percent of equipment cost).  The operation and maintenance
costs include the utilities, operating and maintenance labor, carbon makeup,
maintenance materials, and rotary tube replacement.  A summary of these
various cost items is shown in Table 10.

Cost Comparison

As indicated in Table 10, the capital cost (with a 20 year amortization at an
interest rate of 10 percent) for a multiple hearth furnace is about 7.52
cents per kilogram of carbon regenerated (3.42 cents/lb of carbon), while it
is about 4.20 cents per kilogram of carbon regenerted (1.91 cents/lb of car-
bon) for an externally-fired rotary kiln furnace with an equivalent regenera-
tion capacity.  The major difference (more than 44 percent) in the capital
cost estimates is basically associated with the substantial difference in the
                                     31

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                                TABLE 9

     CRITERIA AND  UNIT COSTS  FOR CARBON REGENERATION COST ANALYSIS
Criteria
1.
2.
3.
4.
Plant flow, MGD (cu m/sec)
Carbon dosage, Ib/MG (g/cu m)
Carbon feed rate, Ib/hr (Kg/hr)
Steam consumption rate, Kg/Kg of carbon
Multiple hearth
Rotary kiln
10 (0.44)
650 (75)
400 (182)
0.6
0.3
5.     Fuel consumption rate (including furnace and
          afterburner), BTU/lb of carbon (kJ/kg of
          carbon)
          Multiple hearth                                4,000 (9,3000)
          Rotary kiln                                    8,000 (18,6000)
6.
7.
8.
Unit Costs
1.
2.
3.
4.
Power consumption rate, KWH/lb of carbon
Carbon loss, %
Labor, man-hr/lb of carbon (man-hr/kg of carbon)
Multiple hearth
Rotary kiln
Carbon, cents/lb (cents/Kg)
Fuel , cents/therm
Power, cents/KWH
Labor, $/man-hr
0.02
7
0.00615 (0.0135)
0.00492 (0.0108)
60 (132)
14
4
10
Other Assumptions
1.
2.
3.
4.
5.
6.
7.
Maintenance materials: 5% of equipment cost/year
Shipping and installation: 125% of equipment cost.
Initial engineering: 10% of equipment cost.
Contingency: 20% of equipment cost.
Amortization: 20 years at 10% interest rate.
All furnace systems are constructed on sites.
Rotary tube is replaced once every three years.

                                32

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                                                                       TABLE 10

                                                    SUMMARY OF CARBON REGENERATION COST ESTIMATES
                         Cost Item
                                                Multiple Hearth

                                          1000 of $        cents/lb carbon
                                                Rotary Kiln

                                     1000 of  $         cents/lb  carbon
CO
CO
1.  Equipment

   a. Carbon dewatering and
      feed system
   b. Furnace system
   c. Air pollution control system

2.  Shipping and Installation
3.  Engineering
4.  Contingency

5.  Total Capital Cost

6.  Capital Amortization

Operation and Maintenance

1.  Utilities

   a. Steam
   b. Power
   c. Fuel
2.  Labor                '
3.  Carbon make-up
4.  Maintenance material
5.  Rotary tube replacement

Grand Total for Process Cost:
 20
236
 15

339
 27.1
 54.2

691.3
                                                                                  3.42
                                                                                  0.11
                                                                                  0.00
                                                                                  0.56
                                                                                  6.15
                                                                                  4.20
                                                                                  0.57
                                                                                 15.09
 20
116
 15

189
 15.1
 30.2

385.3
                                                                                                                          1.91
                                                            0.05
                                                            0.08
                                                            1.12
                                                            4.92
                                                            4.20
                                                            0.32
                                                            0.68

                                                           13.28
                 NOTE: cents/lb carbon X 2.2  = cents/Kg carbon

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 costs for  furnace equipment.  The  rotary  kiln  is a simpler and cheaper
 furnace  system, than  the multiple hearth furnace system.

 Although the  rotary  kiln furnace is simpler  in design and thus less in main-
 tenance  requirement, yet the  life  of the  rotary tube is rather short.  It is
 assumed  that  a replacement of the  rotary  tube  is necessary for every three
 years of operation at  a cost  of 40,000 dollars per replacement.  On the other
 hand, the multiple hearth furnace  has a much longer useable life span which
 is accomplished by a rather costly routine maintenance work.  As a result of
 these differences in furnace  life  span and maintenance requirement, the total
 operation  and maintenance costs for the multiple hearth (25.67 cents/kg of
 carbon or  11.67 cents/lb of carbon) and the rotary kiln (25.01 cents/kg of
 carbon or  11.37 cents/lb of carbon) furnace systems become very close to each
 other, with only 2.6 percent difference.

 Since the capital costs of the furnace systems represent only small fractions
 of the total process costs (22.6 percent  in multiple hearth system and 14.4
 percent  in rotary kiln system), the difference between the total  process
 costs of the two furnace systems is not greatly affected by the difference in
 their capital costs.   The overall  difference in the process cost estimates is
only about 12 percent, with the rotary kiln furnace system slightly cheaper
than the multiple hearth furnace system.
                                     34

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                                  REFERENCES


  1.   Parkhurst,  John  D.,  Dryden,  Franklin  D.,  McDermott,  Gerald  N.,  and
      English,  John  N.,  "Pomona Activated  Carbon  Pilot  Plant,"  Jour.  WPCF,
      Vol.  39,  No.  10,  Part  2 (1967).

  2.   English,  John  N., Masse, Arthur  N.,  Carry,  Charles  W., Pitkin,  Jay B.,
      and Haskins,  James E.,  "Removal of Organics  from  Wastewater by  Activated
      Carbon,"  Chemical  Engineering  Progress Symposium  Series,  Vol. 67,
      No. 107 (1970).

  3.   Directo,  Leon  S.,  Chen,  Ching-lin, and Miele, Robert  P.,  "Two-Stage
      Granular  Activatd  Carbon Treatment,"  EPA-600/2-78-170 (1978).

  4.   Directo,  Leon  S.,  Chen,  Ching-lin, and Kugelman,  Irwin J.,  "Pilot Plant
      Study of  Physical-Chemical Treatment," Jour. WPCF, Vol. 49, No.  10
      (1977).

  5.  Melsheimer, T. M., and  Jurgensen,  Van.  Personal  communications.

  6.  "Standard Methods for the Examination  of  Water  and Wastewater,"  14th
     Edition,  AWWA  and APHA  (1976).

  7.  "Carbon Analysis Methods," Pittsburgh  Activated Carbon Company,
     Pittsburgh, Pennsylvania.

 8.  Hutchins,  R. A., "Activated  Carbon Regeneration : Thermal  Regeneration
     Costs," Chemical Engineering Progress,  Vol.  71, No.  5  (1975).

 9.  Juhola, A.J.,  and Tepper,  F.,  "Regeneration  of  Spent  Granular Activated
     Carbon," Report No. TWRC-7,  Robert A.  Taft Water  Research Center, U.S.
     Department of  the Interior,  Cincinnati, Ohio  (1969).-

10.  Garrison,  Walter, E., Gratteau, James  C., Hansen, Blair E., and
     Luthy, Richard F., Jr.,  "Gravity Carbon Filtration to Meet Reuse
     Requirements," Jour,  of  the  Environmental Engineering Division, ASCE,
     Vol.  104,  No.  F.E6 (1978).
                                      35

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                                    TECHNICAL REPORT DATA
                             (Please read Instructions on the reverse before completing)
  1. REPORT NO.
      EPA-600/2-80-146
                                                            3. RECIPIENT'S ACCESSIOf*NO.
 4. TITLE ANDSUBTITLE
                                                            5. REPORT DATE
     CARBON  REACTIVATION BY EXTERNALLY-FIRED
     ROTARY  KILN FURNACE
                 August 1980 (Issuing  Date)
              6. PERFORMING ORGANIZATION CODE
 7. AUTHOR(S)

     Ching-lin  Chen and Leon S. Directo
                                                            8. PERFORMING ORGANIZATION REPORT NO.
 9. PERFORMING ORGANIZATION NAME AND ADDRESS
                                                            10. PROGRAM ELEMENT NO.
     County  Sanitation Districts of Los Angeles  County
     Whittier,  California   90607
                 1BC611
SOS#5
              11. CONTRACT/GRANT NO.
                                                                 14-12-150
 12. SPONSORING AGENCY NAME AND ADDRESS
     Municipal  Environmental Research Laboratory-Cin.,OH
     Office of  Research and Development
     U.S. Environmental Protection Agency
     Cincinnati,  Ohio  45268
              13. TYPE OF REPORT AND PERIOD COVERED
                Final - 10/75-1/78
              14. SPONSORING AGENCY CODE
                EPA/600/14
 15. SUPPLEMENTARY NOTES
     Project Officer:   Irwin J.  Kugelman   (513)  684-7633
 16. ABSTRACT
       An externally-fired rotary kiln furnace  system has been evaluated for
  cost-effectiveness  in  carbon reactivation at  the  Pomona Advanced Wastewater
  Treatment Research  Facility.  The pilot scale rotary kiln furnace was operated
  within the range  of 682  kg/day (1,500 Ib/day)  to  909 kg/day (2,000 Ib/day).

       The rotary kiln furnace was found to be  as effective as the multiple hearth
  furnace in reactivating  the exhausted granular activated carbon.  The operation
  and maintenance of  the rotary kiln system required  less operator skill than  the
  multiple hearth furnace  system.   However, the  corrosion rate was higher in the
  rotary tube than  in the  multiple hearth furnace.

       Cost estimates based  on a typical regeneration capacity of 182 kg/hr (400
  Ib/hr) have been  made  for  both rotary kiln and multiple hearth furnace systems.
  These indicate that the  capital  cost for the  multiple hearth furnace is about
  two times that of the  rotary kiln furnace.  The operation and maintenance costs
  for both furnace  systems are similar.  The overall  process costs for the multiple
  hearth and rotary kiln furnace systems are estimated to be 33.2 cents/kg (15.1 cents/
  Ib) of carbon regenerated  and 29.2 cents/kg (13.3 cents/lb) of carbon regenerated,
  respectively.	
17.
                                KEY WORDS AND DOCUMENT ANALYSIS
                  DESCRIPTORS
                                              b.lDENTIFIERS/OPEN ENDED TERMS
                           c. COSATl Field/Group
  Activated Carbon Treatment
 Carbon Regeneration
 Physical-Chemical
   Treatment
                                                                             13B
13. DISTRIBUTION STATEMENT
  RELEASE TO PUBLIC
                                              19. SECURITY CLASS {This Report)
                                                UNCLASSIFIED
                           21. NO. OF PAGES
                               44
20. SECURITY CLASS (Thispage)

  UNCLASSIFIED
                                                                         22. PRICE
EPA Form 2220-1 (9-73)
                                             36
                                                                    GQVR\VE%T PPATiSG OFFiCE 1980-657-165/0144

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