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.
-------
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 790°C
(1,450°F) to 960°C (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
100°C (212°F) 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
-------
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
r—J
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 885°C (1,625°F) by the tem-
perature indicator-controller which was located 1.83 m (6 ft) from the
14
-------
carbon feed end. The feed end was usually about 93°C (200°F) 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
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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
-------
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
-------
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
-------
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.
-------
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 93°C (200°F) 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 891°C (1,635°F) to
916°C (1,681°F). 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 891°C (1,635°F) to
916°C (1,681°F) in the rotary kiln system is slightly lower than the range of
916°C (1,681°F) to 932°C (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 936°C (1,716°F) in the second regeneration cycle
to 893°C (1,640'F) and 876°C (1,608°F) 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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
-------
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
GQV£R\VE%T PPATiSG OFFiCE 1980-657-165/0144
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