TECHNOLOGY ASSESSMENT OF

             CARVER-GREENFIELD

      MUNICIPAL SLUDGE DRYING PROCESS
                    by
            Henry C. Hyde, P.E._
         WWI Consulting Engineers
       Emeryville/ California  94608
        EPA Contract No. 68^-03-3016
              Project Officer

            Robert P. G. Bowker
       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
The information in this document has been funded wholly or in
part by the United States Environmental Protection Agency under
Contract No. 68—03—3016 to WWI Consulting Engineers. It has
been subject to the Agency’s peer and administrative review,
and it has been approved for publication as an EPA document.
Mention of trade names or commercial products-does-not consti-
tute endorsement or recommendation for use.

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FOREWORD
The U.S. 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
testimonies to the deterioration of our natural environment.
The complexity of that environment and the interplay of its
components require a concentrated and integrated attack on the
problem.
Research and development are the necessary first steps in
problem solution, and involve defining the problem, measuring
its impact, and s-earching for solutions. The Municipal
Environmental Research Laboratory develops new and improved
technology and systemsto prevent, treat, and manage wastewater
and solid and hazardous waste pollutant discharges from
municipal and community sources, to preserve and treat public
drinking water supplies, and to minimize the adverse economic,
social, health, and aesthetic effects of pollution. This puo—
lication is one of the products of that research and is a most
vital communication link between the researcher and the user
community.
The innovative and alternative technology provisions of
the Clean Water Act of 1977 (PL 95—217) provide financial
incentives to communities that use wastewater treatment alter-
natives to reduce costs or energy consumption over conventional
systems. Some of these technologies have been only recently
developed and are not in widespread use in the United States.
In an effort to increase awareness of the potential benefits of
such alternatives and to encourage their implementation where
applicable, the Municipal Environmental Research Laboratory has
initiated this series of Emerging Technology Assessment re-
ports. This document discusses the applicability and technical
and economic feasibility of using the Carver—Greenfield munici-
pal sludge drying process for municipal wastewater treatment
facilities.
Francis T. Mayo
Director
Municipal Environmental Research
Laboratory
11

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ABSTRACT
The objective of this report is to evaluate the technical
and economic feasibilty o’f using the Carver—Greenfield
municipal sludge drying process for municipal wastewater treat-
ment facilities. This process uses the principle of multi—
effect evaporation and is primarily employed in the food,
pharmaceutical, and industrial wastewater treathent.industries.
The process can dry aqueous solutions or slurries with a wide
range of solids contents (4 to 45 percent). Fluidizing oil is
added to the aqueous slurry before the sludge is introduced
into the first evaporator. The oil maintains the viscosity at
a level that will allow continuous pumping and also facilitate
heat transfer in th later—stage evaporators where the solids
contents are higher as a result of water evaporation. The
fluidizing oil is recovered after drying y mechanical de—
oiling steps such as centrifugation, filter pressing, or
hydroextraction (steam stripping). The result is a dry product
with 90 percent or greater solids content.
The C—G process is patented by Dehydrotech Corporation
(formerly Carver—Greenfield Corporation) and is marketed under
exclusive license arrangements by •the Foster Wheeler Energy
Corporation. The patented process equipment and appurtenant
hardware can be negotiated directly with Dehydrotech.
Associated patent issues may create complications with
federal funding that can cause delay in project implementation.
In addition, use of the process requires a negotiated license
fee. For the City of Los Angeles Hyperion Energy Recovery
System (HERS) project, the license fee was approximately l.4
million or about 8 percent of the equipment capital cost.
Currently, no comparable sludge drying processes are
available. Thermal sludge drying or conditioning processes
(e.g. flash drying, wet—oxidation) are based on different ther-
modynamic principals and are not analagous to the multi—effect
evaporation system. Indirect contact steam dryers are the
closest conventional technology to the C—G process.
The C—G drying process appears to be a cost—effective,
energy efficient method applicable to the wastewater industry.
Research and development for application to municipal waste—
water solids drying has reached the point for full—scale irnple—
- 111-

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rnentaticr . The Citvcf Los Arigele BERS ro ect will be the
first full—scale municipal wastewater solids facility in the
Dnited States using the C—G process when it is placed into
operation in 1985. Trenton, New Jersey is currently under
design and Chicago, Illinois is seriously considering the pro-
cess. Full scale facilities using the C—G process for munici-
pal sludge drying are operating in Japan. -
Based on this assessment, the following recommendations
are made regarding identified needs to continue to develop
this technology for the municipal wastewater industry:
o Municipal wastewater agencies should consider the C—G
process on a site specific basis due to the variable
process configurations, energy and environmental
considerations, and cost. --
o Pilot testing of the C—G process is necessary to
develop specific design criteria to guide full—scale
projects. -- —- -- - - - - •-- -- — - -- — -- —
o The construction cost and operating characteristics
of the C—G facilities for the City of Los Angeles and
City of Trenton should be tracked to compare design
objectives with performance characteristics and cost.
o There is a need to disseminate technical and cost
information on specific C—G projects (e.g. LOS
Angeles, Trenton) addressing the following areas of
concern:
— Municipal wastewater residual solids dewatering/
drying performance.
— Construction and operating cost.
— Patent status of light oil technology.
This report was submitted in fulfillment of Contract No.
b8—03—3016 by WWI Consulting Engineers under the sponsorship of
the U.S. Environmental Protection Agency. This report covers
the period April 1981 to August 1983, and work was completed as
of August 1983.
iv

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CONTENTS
Disclaimer . . . . . . . . . . . . . . . . .
Foreword • • • •
Abstract . . • •
Figures
Tables . . . . . . • • • • • • • S
Acknowledgements . . • . . • • •-•- -.
Section 1.
Section 2. ConclusiEns and Recommendations. . . . . . . . 5
Section 4. Development Status . . . . . . . .
Introcuction . • . • • • . . . . .
Pilot Scale Research . . . . . . . .
City of Los Angeles. . . . . .
Weyerhaeuser Company . . . . .
Adolph Coors Company
LA/OMAProject. •.......
Full Scale Facilities. . .
Adolph Coors Company . . . . .
Sludge Source.
Oil Fluidization . . . . . . .
Steam Source—Temperature/Pressure
Evaporation. . .
Operating Procedures . . . .
Waste Flow
Maintenance. . . . . . . .
. . 1
. . ii
. . 113.
• . vii
• . viii
ix
• . . . 1
• . . . 1
. . .— ._ 4
Technology Description .
Introduction .
Brief History.. . -. • •. •
Section 3.
Detail ed Technology Description.
Evaporators.
Temperature/Level Controls . . .
Exhaust Stream
Product—Oil Separation . . . . .
Clogging of Evaporator Tubes . . . .
Optimized Oil Recovery—HydroeXtraCtiOfl
Oil Fluidizing Benefits. . • . . •
Common Process Modifications . . .
• . • . 7
• . . . 7
• . . . 9
• . . . 9
.10
• . . .11
.11
• . . .11
• . . .12
• . .13
• . .13
• . .14
• • .14
• .15
• • .15
• .16
• . .18
• • .18
• .18
• • .18
• . .18
• . .18
• . .18
• . .24
• . .24
Principal Observations
24

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Allen Products Company
Sludge Source. . . . . .
Steam. . . . . . . . . . .
Principal Operating Features
Maintenance. . . . . .
Principal Observations
City of Fukuchiyama, Japan
Sludge Source. . . . .
Principal Operating Features
Steam Source
Waste Condensate . . .
Oil—Moisture Difficulties.
Boiler Facilities
Maintenance. . . . . .
Principal Observations
Available Equipment/Hardware
25
• . . . .25
• . . . .27
27
• . . . .27
• . . . .27
. . . . .28
28
28
28
• . . . .28
. . . . .30
30
• . . . .30
• ;30
• .31
Technology Evaluation. . . . . . . • .
Process Theory . . .
Process Description. . . . . . . .
Principle of Multiple—Effect Evaporation
Process Capabilities and Limitations •
Design Considerations. . . . . . • • .
Full—Scale Carver Greenfield Process
Design Criteria
Energy Analysis—Requirements and Recovery
Potential . . • . . • . . . . . . . . . .
Operation and Maintenance Requirements
Cost • . . . . . . . . . . . . • . . •
Comparison with Equivalent
Conventional Technology . • . . .
Cost Comparison
Energy • . . . . . . . . . . . . .
National Impact Assessment
Market Potential • . • . • . . • . •
Cost and Energy Impacts. . . • . . .
I • • • • S S • S I • • • • • • S • • • •
.32
.32-
.32
.32
.35
.39
.39
.44
.47
.50
.51
. • .59
• • .59
• • .60
• .62
.62
• .63
• .64
. . S • S
Section 5.
Section 6.
Section 7.
References
vi-

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TABLES
Numbei Pace
1 Analysis of Condensate from C—G Process . . . . 10
2 Carver—Greenfield Plant Installations. . . . . . 19
3 Temperature and Pressure Distribution at Coors
F a cii i ty • • • • • • • , • • • • • • — — • • • . 2 4
4 Temperature and Pressure Profile — Fukuchiyama . 30
Effect of Pressure on Boiling Point of Water ; . 35
6 Suitable Light Oils for C—G Process. 42
7 Carver—Greenfield Dehydration Design Criteria. . 45
8 Operation and Maintenance Requirements . . . . . 50
9 Preliminary Design Criteria for Carver—Greenfield
System, Hyperion Energy Recovery System, City of
LOS Angeles, California. . . . . . . . . . . . . 54
10 Estimated Costs for Los Angeles Carver—Greenfield
Process. . . . . . . . . . . . . . . . . . . . . 57
11 Example Cost Data for Rotary Dryer . . . . . . . 60
12 Energy Requirements. . . . . . . . . . . . . . . .61
vii

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FIGURES
Number Ppqe
Sludge Management System Utilizing the C—G
Process . . . . . • • • 2
2 Typical Carver—Greenfield Drying Process
S cnematic. . . . S I . . . s
3 C—G Process Flow Schematic; Allen Products Company
(ALPO) Allentown, Pennsylvania . . . . . . . . . .26
_4_ C—G Heat Recovery- Process Flow Schematic; City of —
Fukuchiyarrra, Japan, Sewage Treatment Plant . . . .29
5 Carver— reenfield Block Flow Diagram 33
6 Typical Sin le Effect Evaporator — Falling Film
Type . . . . . . . . . . . . . . . . . . . . . . .34
7 Typical Multi—Effect (Triple Effect) Evaporator —
Falling Film Type 36
8 Materials Balance — Four Effect Carver—
Greenfield Process . . . . . . . . . . . . . . . .37
9 Flow Diagram of a Full Scale Four—Effect
Carver—Greenfield Process. . . . . . . . . . . . .40
10 Schematic Flow Diagram — HERS Carver—Greenfie].d
Process. . . . . . . . . . . . . . . . . . . . . .46
11 Carver—Greenfield Thermal Processing System;
Mass and Energy Balance. . . . . . . . . . . . . .46
viii

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ACKNOWLEDGEMENTS
The following members of the WWI Consulting Engineers and U.S.
Environmental Protection Agency staff have participated in the
preparation of this report.
WWI Consulting Engineers
Mr. Henry C. Hyde, P.E.* Project Manager
US Environmental Protection Agency
Mr. John M. Smith, P.E.* : Chief: Urban Systems
Management Section,
Wastewater Research
Division
Mr. Robert P.G. Bowker, P.E.* : Project Officer
Wastewater Research
Division
* Current Affiliation
Henry C. Hyde Henry Hyde & Associates
Star Box 605
Sausalito, C 94963
John M. Smith J.M. Smith & Associates
Robert P.G. Bowker 7373 Beechmont Avenue
Cincinnati. OH 45230
ix

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k TiON .1.
TECHNOLOGY DESCRIPTION
INTRODUCTION
The Carver—Greenfield (C—G) drying process_-uses the prin-
ciple of multi—effect evaporation and is primarily employed in
the food, pharmaceutical and wastewater treatment industries.
This study was conducted to evaluate the technical and economic
feasibility of using the process for municipal wastewater
treatment facilities.
The C—C process is patented by Dehydrotech Corporation
(formerly Carver—Greenfield Corporation), and it can dry
aqueous solutions o - slurries with a wide range of solids
content (4 to 45 percent). Fluidizing oil is added to the
slurry before the sludge is introduced into the first
evaporator. The oil maintains the viscosity at a level that
will allow continuous pumping and also facilitates heat
transfer in the later stage evaporators where the solids con-
tents are higher as a result of water evaporation. The
fluidizing oil is recovered after drying by mechanical de—
oiling steps such as centrifugatiori, filter pressing or hydro—
extraction (steam stripping). The result is a dry product with
90 percent or greater solids content.
A flow diagram describing how the process fits into a
total sludge management system is shown in Figure 1. Sludge to
be processed is first thickened or dewatered to reduce the
amount of water to be evaporated. Thickened sludge is then
mixed with an oil (carrying medium) such as No. 2 fuel oil or
Isopar L (an Exxon product) at a suggested ratio of 1 part dry
solids to 5 to 10 parts oil. By use of an oil, fluidity is
maintained in all effects of the evaporation cycle, and for-
mation of scale or corrosion of the heat exchangers is mini-
mized. The sludge—oil slur ry is then pumped to the multi—
effect evaporator where water. is vaporized. The remaining
solids—oil mixture is subsequently centrifuged to separate the
oil and solids. The oil is recycled and reused, and the dry
solids are discharged for further processing or disposal.
1

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DEWATERING EVAPORATION OF WATER COMBUSTION END PRODUCTS
Partial Water Sludge Drying Energy Recovery For Reu:e
Pelleted
Dry Fuel
Fuel Oil *
For Sale
OliFor *
Reuse
Fertilizer
Sludge (Thickened/Unthickened) Basic Carver—Greenfleld Pyrolyzer I
Multi—Effect Evaporator Boiler And/Or
j With Hydroextractor Gas Turbine
____________ (Optimum oil recovery,
use of light weight oil) Steam For
Dowaterlng Evaporation
Steam For
Electricity
_________ Steam For
* Use of hosvier weight oil only non—hydroextractiOn recovery system Sale
Electricity
For Sale
FIGURE 1. Sludge Management System Utilizing the C-G Process
Ash

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Multi—effect evaporation affords an economy of scale over
single—effect operations through the reuse of heat. The
C—G process employs reverse flow, multi—effect evaporation with
steam being added to the first effect. In a three—effect
system, vapor from the first effect is used to heat the
solution in the second effect, and the vapor from the second
furnishes heat to the first. Vapor from the last effect is
removed, condensed, and discharged. Through the reuse of heat
in the multiple—effect process, the amount of water removed per
pound of steam supplied increases with increasing number of
effects.
In order to understand the thermodynamic principals of
mulitiple effect evaporation and the chemical engineering
terminology used in this report, the reader is referred to
standard texts (e.g. L. McCabe and C. Smith, Unit Operations of
Chemical Engineering, 3rd Edition, McGraw—Hill, 1976).
In its simplest theoretical form, a single—effect
- evaporator can evaporate a maximum of one kilogram of water per
kilogram of steam supplied, and a double—effect evaporator will
evaporate two kilograms of water per kilogram of steam
supplied, etc., beçause of the reuse of heat. Depending on the
number of effects used, the amount of kilojoules (Btu’s) re-
quired per kilogram (pound) of water removed will vary. For a
single—effect unit, about 2300 kilojoules per kilogram (1000
Stu’s per pound) of water removed is required and for a double—
effect unit, 1150 kilojoules per kilogram (300 Bt&s per pound)
of water removed, etc. A vacuum is applied to the various
effects so as to reduce the vaporization temperature require-
ment necessary to vaporize the liquid, and to mainta .n a
positive temperature difference within each effect so that heat
can be transferred. Conventional heat drying processes nor-
mally require 3450 to 4600 kilojoules per kilogram (1500 to
2000 Btu’s per pound) of water removed. Therefore, in com-
parison, the C—G process is an energy efficient sludge drying
process.
It would appear that an infinite economy of scale would
result from the use of an infinite number of effects. Several
factors, however, limit the number of effects practicable in a
system. Each effect of a multiple—effect evaporator operates
only on a fraction of the total temperature drop across the
system. The total drop is seldom larger than that employed in
single—effect evaporation and the capacity per unit area of
heating surface is reduced proportionately. Thus, a savings in
fuel requirements may be realized through multiple—effect
operation but equipment costs will be greater. Currently a
system being designed by the City of Los Angeles will use four
effects. In most cases no more than three or four effects are
3

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economical, but the actual number is largely influenced by.
prevailing fuel costs.
Most proposals on treating municipal sludge with the
C—C process include a combustion reactor to recover the heat
value of the dried product. Theoretically, this is an
attractive combination of processes since water can be
evaporated with multiple—effect efficiency prior to combustion
or gasification. Fuel gases produced during pyrolysis or waste
heat from an incinerator can then be used to supply the energy
requirements of the Carver—Creenfield process. The dried pro-
duct may also be marketed as a soil conditioner.
Currently, there are no comparable sludge drying processes
available or being developed. Thermal sludge drying or
conditioning processes (e.g. flash drying, wet—oxidation) are
based on different thermodynamic principals and are not
analagous to the multi—effect evaporation system. A solvent
extraction drying process called the Basic Extractive Sludge
Treatment- (B.E.S.T.) process -was--tested by Resources
Conservation Co. bufi development was discontinued in 1979 due
to technical and econ.omic problems. Therefore, the Carver—
Greerifield dehyd-ration process is a unique sludge drying
technology. -
The Carver—Greenfield process is proprietary requiring a
license fee or royalty. In addition, portions of the process
are patented. Patent issues create complications with federal
funding for construction projects that may cause significant
delay of project implementation.
BRIEF HISTORY
The initial concept for the C—G process occurred in 1949
during attempts to dry waste emulsions for the recovery of
vitamin oil. Basically, the process is a technique utilizing
the principle of evaporation and involved adding oil to replace
water. Initially, the process concentrated in the food
industry in the 1950’s. The developmental work was performed
under the direction of Charles C. Greenfield while employed by
Fred S. Carver, Incorporated.
In 1964, the C—G process was introducted to the wastewater
treatment field in Hershey, Pennsylvania at the Hershey Cor-
poration. The facility employed three evaporation stages and
ran successfully for ten years. The Hershey facility repre-
sented a milestone for the C—G technology since hydroextraction
was demonstrated on a full—scale basis for the first time.
4

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SECTION 2
CONCLUSIONS AND RECOMMENDATIONS
The C—G solids dewatering/drying process appears to be a
cost—effective, energy—efficient method applicable to the
wastewater industry. -
Research and development for application in the wastewater
industry has reached the point for full—scale implementation.
The City of Los Angeles Hyperion Energy Recovery System project
will be the first full—scale municipal wastewater solids
facility in the United States using the C—G process when placed
into operation. Trent9n, New .Jersey is currently under design
and Chicago, Illinois is seriously considering the process.
Based on this assessment, the following recommendations
are made regarding identified needs to fully develop this
technology for the municipal wastewater industry;
o Municipal wastewater agencies should consider the C—C
process on a site specific basis due to the variable
process configurations, energy and environiner tal
considerations, and cost.
o Pilot testing of the C—G process is necessary to
develop specific design criteria to guide full—scale
proj ects.
o The construction cost and operating characteristics
of the full scale C—C facilities for the City of Los
Angeles and City of Trenton should be tracked. Full
scale construction cost and operating information is
a key need at this time to determine the widespread
viability of the process.
o There is a need to disseminate technical and cost
information on specific C—G projects in the following
areas of concern:
— Municipal wastewater residual solids dewatering and
drying performance.
— Construction and operating cost.
5

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— Patent status of light oil technology.
6-

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SECTION 3
DETAILED TECHNOLOGY DESCRIPTION
As illustrated in Figure 2, in the C—G process the sludge
is fluidized in the fluidizing tank by the addition of oil.
Oil is fed in metered amounts typically ranging between 5 and
10 parts of oil per part of dry sludge solidsby weight._The
oil—sludge mixture is then processed through a grinder and fed
to a surge tank. From the surge tank the mixture is pumped to
the first stage evaporator. The number of evaporators for a
particular installation will depend upon specific design
criteria. Regardless of the number of stages, however,
approximately equal quantities of water are evaporated in each
stage and each evaporator would be of identical design.
Elements of the process and equipment that may be utilized
are discussed below (Reference 1).
EVAPORATORS
The evaporators used are of the conventional falling film
type and function in the following manner:
o Sludge—oil mixture is pumped to the dome of the heat
exchanger or “tube nest” and falls through vertical
tubes as a film on the tube interior. Heat is
transferred from either process steam or hot vapor
to the sludge in the shell of the heat exchanger.
The temperature of the film within the tube in-
creases. The flow of sludge and steam or hot vapor
is counter current from stage to stage.
o When the mixture enters the vapor chamber a portion
of the moisture is driven off as a hot vapor and
serves as the evaporative medium in the preceding
evaporative stage. The only difference between the
operation of any of the stages or effects is that
process steam serves as the evaporative medium in the
last effect while hot vapor is used in all other
effects. Hot vapor condensate front the shell side
(outside of the tubes) of the evaporator is collected
and drained to a hot well.
7

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Exhausi
FIGURE 2. Typical Carver--Greenfleld Drying Proce 9 Schematic (Reference 1)..
((I
II
—I —,
f?1 r -
- il
U i
U
1)
t)
f.)
Ill
I’.
‘ I’
—4
1;)
r ii
‘f)
I Ii
Ill
—1
()
n
I. —I
Dried Product

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The last evaporative stage is usually referred to as the
t ’hot or drying effect”. ere temperatures are maintained at
approximately 120°C (250°F). The temperatures in preceding
effects are progressively lower with increasing vacuum (by
means of the condenser and vacuum pump) applied for
evaporation.
TEMPERATURE/LEVEL CONTROLS
The temperatures in the “hot effect” must be sufficient to
account for the boiling point rise of the mixture. The boiling
point of the mixture increases above that of pure water as the
sludge becomes more concentrated. The boiling point of the oil—
municipal sludge mixture is 232—247°F (111—119°C).
The low temperatures (maximum 120—130°C, 250—260°F) and
decreasing water concentrations as temperatures increase in the
C—G system do not result in solubilization of any of the
organics or denaturization of the sludge protein. The Carver—
Greenfield system is a drying technique but is not analogous to
heat drying or thernTal sludge conditioning.
The level of sludge—oil mixture in the evaporator is
critical to heat transfer and must be maintained within
specific levels. To accomplish this, the output of the
circulating and transfer pumps are automatically throttled in
proportion to a measured level change with the exception of the
last stage which is controlled by flow to the centrifuge. This
has proved to be an effective and uncomplicated means of
‘control for the C—G process.
EXHAUST STEAM
Process steam is introduced into the first effect. The
steam condensate in the first effect is returned to the boiler.
The condensate from tne other effects is returned to a hot
well. The condenser and vacuum pump maintains the pressure in
the vapor chambers well below atmospheric to permit evaporation
at lower temperatures. The vacuum pump also removes any non—
condensable gases that are present.
The vacuum pump exhaust is combusted in the boiler or
treated for odor control as required and exhausted to the
atmosphere. If light fluidizing oils are used, an activated
carbon adsorption system is employed to trap the vaporized
oils. When the carbon is regenerated, the system returns them
to the C—G process. The condensate from the C—G process does
not require any special pretreatment as is the case for heat
treatment processes (Reference 11).

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The condensate does contain volatile acids and ammonia and
a small amount of carrier oil. Considering the small volume
and low BOD load, the condensate can simply be returned to the
head of the treatment works without any deleterious effect on
the treatment process. The condensate represents approximately
5 to 10 percent of the BOD load at a typical facility. Sum-
marized in Table 1 is a comparison of the C—G condensate
analysis from various dewatering devices (Reference 1).
PRODUCT—OIL SEPARATION
The dried mixture from the last (hot) effect is typically
less than 5 percent moisture content. Lower values of moisture
content are easily obtainable depending upon process require-
ments. Oil content at this point is usually in the range of 80
to 90 percent by weight. This oil consists for the most part
of the carrier or fluidizing oil, but also contains oils and
grease originally in the sludge which have been solubilized in
the fluidizing oil. The first stage of oil/solids separation
is usually accomp1is ed by means of a centrifuge. This centri-
fuge step is capable of reducing the oil content to approxi-
mately 30—40 percent by weight. The recovered oil is suitable
for recycling as 1uidizing oil and provides most of the pro-
cess oil requirements. In the case of municipal sludge, the
likely procedure would be to separate the heavy sludge oil
mixture from the fluidizing oil by distillation, recycling the
fluidizing oil for use in the C—G process, and using the sludge
oil mixture as fuel to generate a portion of the process steam.
Table 1. ANALYSIS OF CONDENSATE FROM C-G PROCESS
.
Source
No. of
Samples
SS
ppn
‘IS
ppn
3 N
ppn
BCD
ppn
D*
ppn
Acids
ppn
Oil
ppri
Fukuchiyaina
32
4.5
16.8
109
193
3230
292
1390
1.45
• LA/G Pilot Study
Liquid digested
sludge
69
9.1
—
—
763
201
348
187
—
Dewatered digested
sludge
57
9.7
—
—
1618
3146
1941
1080
—
Thickened waste
activated
15
8.6
—
.
—
642
2015
2076
2003
—
* COD is low with respect to BOD because the addition of
potassium perrnanganate retards oxidation of volatile organic
acids.
10

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CLOGGING OF EVAPORATOR TUBES
A gummy phase and subsequent plugging of heat exchangers
may occur if the action of the fluidizing medium is inhibited.
In this event, the oil to solids ratio becomes unbalanced,.
viscosity increases as drying occurs and scaling results, even-
tually causing clogging of the evaporator tubes. The phenome-
non behind this problem is the formation of an emulsion. It is
an intimate mixture of the oil and water in which the oil
particles are so fine that the fluidizing result is completely
negated. Emulsified material then behaves as it would without
the oil addition. In a four—effect system, for example, about
one—fourth of the total water input to the system will be
evaporated in each effect. Therefore, each effect will operate
at a certain solids to water ratio. Apparently the gummy phase
can occur at both low and high ratios of solid to water. The
actual ratio depends on the sludge type, carrying oil and other
factors. An important part of gummy phase control is the
application of solids addback to reduce the formation of einul—
sions. Addback simply involves recycling dried product,
ideally to the fluidizing tank, to maintain a solids to water
ratio of 1:3 to the first evaporator. Operating and test data
clearly indicates that this technique is extremely reliable and
has recently been incorporated in the C—G system at the Coors
Brewery. It is important to note that standard process
provisions are available to eliminate most gummy phase problems
(Ref erence 1 and 2).
OPTIMIZED OIL RECOVERY—HYDROEXTRACTION
Further oil recovery steps may be desirable depending upon
use of product and the particular economics of the
installation. High pressure filter presses have been utilized
to reduce the oil content to aDproxlmately 10 percent. On the
other hand, if a light hydrocarbon fluidizing oil such as
Isopar AMSCO 140 or Chevron 4lOB were utilized, economical
recovery could be realized by a hydroextraction technique.
The hydroextraction technique can result in almost com-
plete recovery of fluidizing oil and thereby greatly enhance
process economics. The use of light oil such as Isopar
(boiling point 190—200°C, 375—400°F) will, however, increase
the amount of fluidizing oil that distills in the evaporators.
this oil fraction is easily removed from the condensate by
decanting and coalescing.
)IL FLUIDIZING BENEFITS
Two significant limitations of multi—effect evaporation
re increasing viscosity and resistance to heat exchange of the
11

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slurry asit is concentrated. These limitations are eliminated-
by the addition of the fluidizing oil. The fluidizing
technique offers another advantage in that the oil wets the
heat exchanger tubes, thereby decreasing the potential for
corrosion, scaling and abrasion.
COMMON PROCESS MODIFICATIONS -
The basic C—G process is adaptable to modular application
and to a variety of end product uses. For example, the City of
Los Angeles has conducted extensive tests on combustion of the
dried sludge produced by the C—G process. The report
(Reference 13) was actually a Phase II study to develop
detailed criteria for design and air emission data for subse-
quent air quality permits. Other applications include the use
of the rotary hearth furnace as in the case of the Eli Lilly
plant in Elkart, Indiana (Reference 2 and 11). The soil condi-
tioning product market has also been explored. Modifications
of the components within the basic process may be considered
for specific projects by the design engineer. However, the
basic process is pa€ented by Dehydrotech Corporation.
12

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SECTION 4
DEVELOPMENT STATUS
INTRODUCTION
Although there are many Carver—Greenfield (C—G)
installations in operation, they are mostly used in food pro-
cessing, pharmaceutical, or similar industrial operations.
Several of these facilities process sludges from industrial
waste treatment which have characteristics similar to secondary
sewage sludge. There are two installations in Japan that treat
sewage sludge. The Adolph Coors Brewery at Golden, Colorado
has built a C—G plant to process waste activated sludge pro-
duced from their brewe;y waste treatment operation.
The C—C process is not a traditional sewage sludge
handling process, and concerns have been raised about the adap-
tability of this process in municipal sludge treatment
operations. There have been specific areas of concern raised
about this process in recent years. The most frequently
mentioned regards the potential for the heat exchanger tube
clogging, oil losses from the system, quality of the process
sidestream (condensate), and cost of operation. The Cityof
Omaha had to shut down a C—G installation after operating for a
very short period due to severe operating problems. In this
case, the shutdown of the Omaha facility should not be viewed
as a process failure, but rather as poor planning, design or
both. The problems here appear to have been solvable from a
technical standpoint, thus providing additional knowledge or
the elimination of redundancies in future C—G processes
(Reference 2). The potential quality of the process sidestream
has also been debated in recent years. In a report to the New
York——New Jersey Interstate Sanitation Commission, Camp,
Dresser and McKee Inc. (Reference 4), assumed that the quality
of such liquid stream (condensate) is similar in nature to that
expected from conventional heat treatment of sludge. However,
the condensate was a clear liquid and averaged about 2600 mg/i
COD, mostly from low molecular weight volatile acids, and about
1400 mg/i NH when processing dewatered digested sludge. In
the Hyperion ‘ nergy Recovery System (HERS), the condensate from
C—C process will be about 1/10th the COD and NE 3 load of the
sidestream from typical dewatering (centrifugation) operations.
Low condensate CODs (450 mg/i) were also obtained by Villiers-

-------
et al. (Reference 5) in their exploratory studies employing
primary sludge.
PILOT SCALE RESEARCH
City of Los Angeles (References 2, 6)
In 1975, the City of Los Angeles operated a trailer
mounted pilot scale C—G unit at the Hyperion Treatment Plant.
The unit was a single—effect evaporator rated between 200 tc
500 pounds of water per hour and operated as a batcn process.
The types of sludges processed were raw and digested primary
sludges, and a blend of undigested primary and waste activated
sludge. The following observations were reported by the City:
o The process was capable of drying the type of sludges
tested to over 95 percent solids (on moisture content
basis)
o The dewat red solids from centrifugation contained 30
to 40 percent oil.
o The process condensate (liquid sidestream) had the
following constituent concentrations: oil, 2 mg/i;
TDS, 5—16 mg/i; COD, 340 to 1,060 mg/i; NE 3 , 150 to
7,170 mg/i. The report concluded that ammonia and
COD concentrations would actually be lower than these
levels in a four—effect system. This is due to the
fact that in a foi.ir—effect system, evaporation takes
place at a relatively lower temperature in the first
three effects. The report concluded that the higher
temperatures occurring in a single—effect system
would break down more protein, thus releasing more
ammonia.
o The fluidizing oil was progressively contaminated,
picking up solids from the sludge with each pass
through the system.
o Some clogging of the heat exchanger tubes was
noticed. Grinding of primary sludge was felt to be
essential to prevent such clogging. However, no
scaling of the tubes was observed.
o A recommendation was made to test a pilot plant
operated in a continuous mode. It was also concluded
that the pilot plant should include a sludge grinder
and a hydroextraction unit (see LA/OMA Project
below)
14-

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Weyerhaeuser Company (Reterences 2, I)
In 1977, the Weyerhaeuser Company conducted a pilot
single effect C—G demonstration study at their Cosinopolis,
Washington facility. This was done as a part of a series of
pilot tests for dewatering their “bio—pond” sludge. The sludge
was generated from paper pulp processing activities and was not
similar to municipal sludge in characteristics. Therefore
some caution should be exercised in directly applying these
findings to municipal sludge handling operation. The following
conclusions were drawn from the study:
o A dry granular sludge with solids concentration
varying from 42 to 81 percent was obtained.
o Additional processing was recommendia ä edücéthe
residual oil. Steam stripping for volatile oils
(petroleum base) and pressing for non—volatile
(vegetable) oils were thought to be the most
efficient way of achieving this. - -
o Formation o a gummy phase was observed at certain
ratios of solids to water. The first occurred at a
solids content of about 30 percent and another at
about 90 percent total solids (based on moisture
content). However, the report concluded that the
problem could be avoided through proper design and
operation.
o Formation of an undesirable oil—condensate emulsion
was noticed with the use of Isopar (an Exxon product)
as the carrying medium. This was tracked to the
heavy use of surfectants in the main plant which
ended up in the sludge stream.
o An odor problem was presented by the non—condensable
vapor vented by the vacuum pump.
Adolph Coors Company (References 2, 8)
While investigating potential dewatering methods for waste
activated sludge, Adolph Coors Company of Golden, Colorado,
conducted a pilot study of the C—G process.
The C—G’process was selected as the best process to deal
with their waste activated sludge disposal problem.
Recommendations for full—scale construction included use of
vegetable oil as a carrying fluid; pressing for extraction of
oil from dried sludge, and sale of final product as animal
feed. A description of their full—scale plant operation is
included later in this chapter.
15

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LA/OMA Project (RererenCe Z)
A continuous flow pilot—scale demonstration study of the
C—G process was carried out by the City of Los Angeles at their
yperion Treatment Plant under contract with the Los Angeles—
Orange County Metropolitan Area (LA/OMA) Project.
The conclusions derived from the pilot plant demonstration
are given below. The test objectives are shown in conjunction
with the corresponding conclusions.
Objective 1:
To identify operational problems encountered in the
continuous flow system.
Conclusion:
The operating problems encountered during the pilot—plant
investigation were: solids settling out in the mixing
(fluidizing) tank and feed tanks; carry—over from the
vapor chamber to the steam condenser; plugging of sludge—
oil slurry linesL and dust contamination of the hydroex—
tracted oil. Such problems were attributed to the short-
comings of the pilot—plant design and not the C—G process
itself.
Objective 2:
To investigate the efficiency of the hydroextraction pro-
cess for removal of residual oil in the dewatered solids.
Conclusion:
The hydroextraction process was effective in removing
residual oil in the centrifuged solids. Eydroextracted
solids contained 1.2 percent oil or less (based on dry
weight of solids).
Objective 3:
To identify corrosion problems.
Conclusion:
No scaling of the heat exchanger tube inner walls was
observed. It appeared that Isopar L was an effective
fluidizing medium. During the investigation no corrosion
problem was noticed.
Objective 4:
To determine the extent of heat exchanger tube fouling
during continuous operation and the ability of sludge
grinding to mitigate the problem.
16

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Conclusion:
Clogging of the heat exchanger tube nest inlet by fibrous
sludge material was prevented by grinding of the sludge
feed. Primary sludges definitely require grinding; waste
activated sludges may not.
Objective 5:
To determine the characteristics of final products
resulting from the system, including liquid sidestr earns
(i.e., condensate) and exhaust gases.
Conclusions:
o Extracted sludge water (process condensate) contained
TDS between 16 and 22 mg/i, COD between 212 and 4,167
mg/i, nitrogen as ammonia between 464and1,749 mg/i;
and heavy metal concentrations generally below 0.1
mg/i.
o• Dried sludge solids (centrifuged solids) contained
residual oil ranging between 37.2 and 47.4 percent,
total solids between 51.3 and 60.9 percent, and mois-
ture between 1.0 and 7.7 percent. On an oil—free
basis, the-solids concentration ranged between 87.2
and 98.1 percent, with an average value of 95.7
percent.
o Recirculated oil became contaminated with sludge oils
and fine sludge solids. Stripping of the recircu—
lated oil is effective in removing both heavy sludge
oils and sludge solids, and would help control the
inventory of fine solids in the system.
o Based on limited data, pathogen destruction through
the C—G process appeared to be complete.
o System losses of Isopar were due primarily to uncon-
trolled venting. If vent losses are controlled,
potential loss of Isopar should be limited to that
contained in the final solids after hydroextraction.
o Major air emissions of concern with the C—G process
itself are likely to be hydrocarbons resulting from
the volatility of the Isopar. Mix tanks, vacuum
pumps, centrifuge, and solids conveying systems were
identified as the major sources of such emissions.
In a full scale system, provision must be made to
collect these vapors, condense them, and direct re-
maining gases to a boiler or pyrolysis reactor for
combustion.
17

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FULL SCALE FACILITIES (Reference 1)
There are over seventy operating C—G installations. For
the most part they are used in industry for drying various
industrial waste streams. Two plants, the Fukuchiyama City and
Hiroshima plants in Japan, process municipal sludge from con—
ventiorial activated sludge treatment plants.
A list of full—scale C—G installations is included in
Table 2. Three of these installations are discussed.
Adolph Coors Company, Golden Colorado (Reference 1)
Sludge Source . The sludge processed through the C—C pro-
cess is a mixture of primary and waste-acti-vated sludge
generated from the on—site treatment works. The waste acti-
vated sludge is thickened by air flotation and is blended with
the primary sludge. There are no grinding or masceration steps
prior to introduction into the C—G process. The C—G process at
the Coors Brewery_is a four effect system sized for an
evaporative rate of 60,000 lbs (27,200 kg) of water per hour.
Oil Fluidiza’tion . Sludge is fluidized with a petroleum
based oil at a ratio,: by weight, of 6 parts oil to 1 part of
dry solids. The oil is metered by ratio control of sludge
flow.
Steam Source—Teniperature/Pressure . The steam source for
the C—G installation is the brewery boiler plant. High
pressure steam is supplied and reduced through turbine driven
pumps to 344,700 to 413,700 Pa (50 to 60 psi) for feed into the
fourth effect. The steam is fed into the hot effect at 145°C
(290 0 F}. Vacuum in the effects is sustained by a 25 HP vacuum
pump. This results in a temperature and pressure distribution
as indicated in Table 3.
Evapor&tion . The evaporative efficiency of the Coors
facility averages 3.2 This means that 3.2 kg of water are
evaporated for every kg of steam added. In addition, the
protein in the feed sludge passes through the process undamaged
and is available in the end product. All four effects at Coors
are insulated. The insulation appears to be quite effective,
since the vapor chamber operating floor is comfortable. The
insulation also improves the thermal efficiency of this
installation by minimizing heat loss.
Operating Procedures . The typical composition of the oil—
solids mixture leaving the hot effect is 88 percent oil, 9
percent solids and 3 percent water. After centrifuging, the
oil content is reduced to approximately 35 percent. A high
—pressure filter press step following the centrifuge reduces th
18

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TABLE 2. CARVFR-GR((NF 1(LD PLANT INS 1AILATIONS (Reference I)
Hershey (states
Allen Products
Company
El Paso Natural
Gas
Deemnstrat ion Plant
Ebara infilco Co.
City of
Hiroshima
Upjohn
international
Locations
II Phila. Sold business on death
PA of owner (1st coentercial
plant), operated satis-
factorily while in
operation
i rshey PA Oeactlvated since hershey
entered a regional faci-
lity, operated satisfac-
toriiy while in operation
Crete NE Operating satisfactorily
Clinton, IN Expanded plant, pymolysis
added producing fuel gas
for boiler Evaporator
russ essentially self
sutogeneotis, ope ’ ating
satisfactorily
Jal, NH Originally eeperhnntal
pilot plant
Tokyo Used for demonstration
Japan on sewage sludge
Japan Designed and installed by
Licensee Fbara-infiico Co
Operating satisfartorily
Cuernevaca Plant designed, equipu’ent
Hexico purchased and fabricated.
plant not installed
becaase Hexico relaeed
waste treatment laws.
Pharmaceutical plant
wastes at 2-41 coacen-
trat ion
5000 fat Animal feed
2500 2600 solids (poultry)
9000 600 Burned in solids
handling boiler
to produce steam
6000 660 Sale of fat and
solids for animal
feed
6000 660 Same as Crete Plant
80,000 800 Landfill
30,000 600-800 Burnei in boiler
farnro but slag-
ging ,f salts
occur’ed, modified
bf boiier redesign
4 60,000 1200-2000 Operations of pyro-
lyzet aaolds slag-
ging end particulate
problees Ash to
landfill.
Landfill-sealed
csnta I’uers
4 100,000 2000 Burned in solids
handling boiler
2 9000 600 Pyroly.is in the
fetu,
Start up
Date -
1961- 74
Customer
Independent
Hfg Co
Present Day Status
No. of Plaat Capacity
Evap lbs of lbs of
Effects water/hr solids/hr Disposition
Feed iiaterial
fat and bones from
supermarkets and debon- (2 stages)
ing plants 5 tons/hr
25- 351 water
Primary and secondary 3
sludge (trickling
filter) Dow Pat 6-81
air flotation sludge
Dog food wastes by air 2
flotation combined wish
activated sludge at
about 101 concentration
Same as Crete Plant 2
Coffee wastes at 11 4
concentrat ion
Pharmaceutical plant 3
wastes at 2-41 concen-
tration
Allen Products
Allentown
Operating
Company
PA
Nestle Company
Freehold NJ
Concentrated to SOT only
Operating satisfactorily
Eli tilly 8 Co
Clinton lii
Expanded to larger piant
in igi i, see below
1g64-71
1 910
igyo
19 /0
1970- /8
1978
1912
1973
1975
1975
(2 stages)
3
2000
2000
8rackiuh water
Sewage sludge
Sewage sludge
Pharmaceutical wastes
10
100
tn ,,t’A

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TABLE 2. CONTINUED. p.Z
Friendship
Dairy
Soc I eta
Chimica Dauna
(Smogless Co )
Primary and waste acti-
vated sludge at 4.5-5 0%
concentration.
Brewery treatment plant
sludge 41 concentration
60-70% waste act ivate
30-40% primary
Hazelton Plant had reducing sugar Chocolate waste 22
PA problem, problem resolved, concentration
now customer wants more
automatic operation.
plant design being reviewed
for this operation.
Friendship Operating satisfactorily. 1411k whey byproduct from
NY cottage cheese manu-
facture
Fermentation molasses
waste from alcohol pro-
duct Ion.
Petrochemical activated
sludge
Burned in solids 1916
handling boiler
4 60,000 2500 Fuel-start 1977
landfill-present
Animal feed-1960
‘2 1500 30 Burned In eelstii 1978
package boiler
Customer
Pblkerei J.A:
MaggIe
City of
Fukuchiyama
Adolph Coors
Company
Cadbury
(Peter Paul)
Location Present Day Status
Raitinehrlng Pilot Plant
W. Germany
Japan Designed and installed by
Licensee Ebara—Infilco Co.
Operating satisFactorily.
Golden, CO Operating satisfactorily.
Feed Material
Dairy and food products
No. of
Evap.
Effects
Plant Capacity
lbs. of lbs. of
water/hr._solids/hr.
200 200
3
Disposition
Food products
Start up
Date
1975
r ’ )
irldani Co.
(Smogless Co.)
F errara
Italy
Started operating late
1979
Ranfredonia Design and equipment
Italy purchasing
3500 2500 Sold as animal Fe’ 1978
(2 stage) future as a food
product.
2 11,000 12,000 Fuel gas from pyi. 1979
lysis.
3 4000 550 Fertilizer 1980
I.ons a

-------
IABLE 2. CONTINUED. p.3
Customer
Nick Buecher
& Sons
Enterprise Animal
Oil Company
Rookey Packing Co.
Pine States
By-Products
Cul Inteinational
(Utah By-Products)
Cape Charles
(Reedville Oil)
Des Helnes.
IA
S Portland
PIE
Ogden. UI
Cape Charles
VA
Lynchburg,
VA
Hedesto. CA
Green lay
WI
Green they
WI
bntreal
Canada
Crete. HE
No. of
(yap
Effects
2
2
2
4
2
2
2
2
2
2
Plant Capacity
Pounds/Hr.
60.000
10.000
13 .200
40.000
10.000
25.000
Start-up
Date
1965
1965-70
1 916
1966
1 966
1967
Present day Status
locations and Repeat Plants Feed Material
Chicago. II Operating satisfactorily Rendering plant waste
Philadelphia. Sold - no longer in
PA operation; operated
satisfactorily while
in operation
Disposition
Animal Feed
N)
20 .000
9.700
20 .000
50,000
Operated satisfactorily
Operating satisfactorily
Operating satisFactorily
Shut down because of
fish scarcity, operated
satisfactorily while
in operation
Operating satisfactorily
Operating satisfactorily
First plant operating
satisfactorily
Operating satisfactorily
Operating satisfactorily
Operating Satisfactorily
I 965
1965
1066
1966
Kavanaugh industries
(lynchburg)
Noclesto Tallow Co
Packerland
Packing Co
Green Bay Soap Co.
loses Co.
(Longeull Heat
Exporting Co
Midland By-
Products. Inc.
(Swingle)
Milwaukee Tallow
Co. • Inc.
Canada Packers Ltd
Milwaukee, First plant shut down.
WI installed second plant;
operated satisfactorily
Second plant operating
satisfactorily
Toronto Operating Satisfactorily
2
2
2
2
2
40,000
13,200
60 .000
60 .000
20.000
1 967
1 961
1919
19/9
1966
Note: From processing of bones, fat, viscera of beef, fish, poultry and hogs; usual composition - 60% water. 20% solids, 20% fat

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TABLE 2 CONTINUED, p 4
Customer locations
National By-Products Clinton . IA
Norfolk, VA
P4 tchener,
Ont • Canada
Prey Packing Co St Louis, IC
J P Allan 8 Co Stockton. CA
Armour Foods (Wilson) Hereford, TX
Central Ri-Products Redwood Falls, MN
Dubuque Packing Co. Dubuque. IA
Packerland Green Say, WI
Packing Co
Lomex (Longueuii
Meat Company)
Pepcol Packing Co
Prosper DeMulder
Mentreal
Canada
Denver, CO
Warwickshi re,
England
Quincy, MI
Feed Material
See previous description
2 20,000
2 18.500
2 14,500
2 30,000
2 20,000
20,000
2 20,000
2 20,000
2 20,000
2 30,000
2 50,000
2
2 22,000
2 22,000
2 30,000
60,000
2 40,000
2 30,000
2 45.000
Start-up
Date
1968
1968
1968
1969
19)0
19)0
19)0
19 70
19)0
191 1
19 ) 1
19 )1
19)1
19 )2
191 8.
1912
1913
I 9)4
1914
19)4
19)5
Norfolk Tallow Co.
J N Schneider, Ltd
No of
(yap.
Effects
2
Plant Capacity
Posnds/Ilour
25,000
Disposition
Animal Feed
Present Day Status
and Repeat Plants
First plant, operating
satisfactorily
Operating Satisfactorily
Second plant, operating’
satisfactorily
Operating Satisfactorily
First plant, operating
satisfactorily
No longei in business;
eperated satisfactorily
while in operation
Operating satisfactorily
Great Mark Western
Vereinigte Ttermehl-
fabriken 614811
Alberta Processing
Company
Cuyahoga Con , Inc
Fars rs Union
Marketing I Pro-
cessing Assoc
Plymouth Fertilizer
Packerland Packing
2 22,000
Mering
Germany
iieufekd Bad Aibling
Fed Pep of Germany
Westphalia
Germany
Calgary, First Plant, operating
Alberta, CA satisfactorily
Cleveland, Oil Operating satisfactorily
Long Prairie
MN
Plymouth, Ind
Chippewa
Falls, Wia
Third plant-operating
satisfactorily

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TABLE 2. CONTINUED. p.5
Ho of
Present Day Status (yap. Plant Capacity Start-up
Customer Locations and Repeat Plants Feed Material Effects Pounds/hour Disposition Date
Perdue. Inc. Acco.nac, VA Operating satisfactorily See abovedescription 2 35.000 1975
Prosper DeMulder Ings Road Second plant-operating 2 60.000 1915
Doncaster, Yorkshire satisfactorily
England
Wilson Pharmaceutical Chicago. IL Shut down beet operation In 2 60.000 1975
Company Chicago; sold plant to
Darling Bros. Operated
satisfactorily while in
operation. See below.
Darling Delaware. Inc San Francisco. CA Operating satIsfactorily 2 60.000 1977
Purchased from Wilson;
moved to California
Ryder Rendering Matainoras. PA Operating satisfactorily 2 30.000 1975
West Coast Vancouver. B.C. 2 30.000 1975
Reduction
Robert Wilson & Cahir. Ireland 2 60.000 1975
Sons. Ltd.
I ’)
C ) Alberta Processing Calgary. Alberta Second plant, operating 2 45.000 1976
Company Canada satisfactorily.
National By-Products St. Louis, MO 2 30.000 1976
National By-Products Wichita. KS Third plant; operating 2 30.000 1977
satisfactorily
Ontario Rendering Dundas. Ont. Operating satIsfactorily 2 60,000 1977
Cope Rendering Moultrie, GA 2 20,000 1978
been (longueull Montreal Ihird plant, operating 3 30.000 1978
Moat Company) Canada satisfactorily.
Vancouver Processing Canada Operating satisfactorily 2 bO.00 0 1979
Ltd.
B V. Chemiache Holland Started operating 2 25,000 1979
BedriJven Van De Ileb
B. V. fled Theree Holland Started Operating 2 25 .000 1919
Chemische Fabrieken
Prosper Deflulder Yorkshire, Eng. Ihird plant i not completed 2 41.500 1980
Cabota Spain Designed but not constructed 2 1980
Dubuque Packing Co. Dubuque, IA Operating satisfactorily 2 29,000 1970

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TABLE 3. TEMPERATURE AND PRESSURE DISTRIBUTION AT COORS
FACILITY.
Effect No.
Tempe
F 0
rature
C 0
Pressure
io4_
psia
Pa x
1
120
50
1.5— 2 10.3—
13.8
2
150
65
3 — 4 20.7—
27.6
3
200
95
7 — 9 48.3—
62.1
4
275
135
20 —22 137.9—151.7
oil content below 10 percent. The recovered oil is recycled to
the fluidizing tank. The dry material can be conveyed directly
to storage bins or is pelletized prior to storage. Presently
it is trucked to a landfill on a weekly basis. The temperature
in the storage bins are continuously monitored. Operating
records indicate tha± the temperatures have never exceeded 50°C
(120°F)
Wpste Flo . The vacuum pump exhaust leaving the first
stage evaporator is ‘condensed before being discharged to a
natural gas fired odor furnace where combustion temperatures
reach 760°C (1400°F). Plant effluent is used as condenser
cooling w ater. The condensate from the exhaust stream is
combined with condensate from each effect and conveyed to a hot
well. The combined condensate undergoes three stages of treat-
ment or polishing. The first stage is oil—water separation in
an American Petroleum Institute separator. The second is
fabric filtration for suspended solids removal. The third
stage is passage through a coalescer for removal of the trace
amounts of oil. The entire condensate treatment is a closed
system. The condensate is then returned to the treatment
works.
Maintenance . No special maintenance problems associated
with the C—G. system have been reported. Routine maintenance as
is necessary in any system having pumps and valves is
practiced. The most noticeable maintenance item is the
replacement of pump seals.
Principal Observ&tions .
o The C—G process at the Coors Brewery is fully auto-
mated and utilizes standard instrumentation and con-
trol loops.
o The gummy—phase or plugging of the heat exchangers
does not occur when operational parameters are within
24

-------
proper limits and the process is easily controllable
to maintain those limits.
o An add—back feature which involves recycling a
portion of the hot effect discharge to the feed of
the preceding effect has been incorporated into the—
piping to eliminate the gummy—phase even when feed
solids are below limits (design values).
o There are no odors or visible emissions apparent from
the vacuum pump exhaust after treatment.
o The dry material has an odor characteristic of the
materials processed (brewery odor).
o The operators are representative of the type of
operator found in municipal operations. They have
had no special training other than that received in—
house.
o The condensate, although relatively high in COD (5000
mg/l) atid BOD (3000 mg/i) can be freely returned to
the treatment works with no adverse effect on the
treatment process. The BOD of the condensate repre-
sents less than 10 percent of the treatment plant
inf].uent BOD.
o Total destruction of pathogens based on coliform
tests.
Allen Products Company (ALPO), Allentown, Pennsylvania (Refer-
ence 1)
The C—G installation at ALPO was started up in 1970. It
consists of a two—effect evaporator train originally designed
for an evaporative rate of 6,000 lbs (2,720 kg) of water per
hour. The system is presently operated at 8,000 lbs (3,630 kg)
per hour with no difficulty.
The C—C process at ALPO is operated on an as—needed basis.
The process is shut down and started up intermittently. A
schematic of the C—G process at the ALPO facility is
illustrated in Figure 3.
A good quality tallow is recovered from the waste stream
eliminating the need for make up oil. Tallow is also marketed
periodically as storage reserves build up. The feed ratio is 6
parts oil to 1 part dry solids by weight.
Sludge Source . Two separate waste streams feed the C—G
rocess. The proportions of the two wastes vary continuousl
25

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To Atmosphere
FIGURE 3. C—G Process Flow Schematic; Allen Products Company (ALPO)
Allentown, Penn8ylvania (Reference 1).
Storage
Recycled
Oil Storage
Vacuum
Pump
Condenser
Cooling Water
c - b
Process Steam
Storage Tank
Fiuldizing Tank
Feed Pump
Oil Feed Pump

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The first Stream consists primarily of the wastes produced by
the processing of frozen meats. The second component of the
influent is waste activated sludge generated at the on—site
treatment works. The combined feed to the C—G system is at a
solids content of 11 percent, of which approximately half is
fats.
Steam . Process steam from the manufacturing plant boiler
is fed into the hot effect maintaining a temperature ranging
from 110—115°C (230—240°F). The temperature in the cold effect
is approximately 50°C (120°F). The cold effect operates at a
vacuum reading of 9,650 Pa (25 inches Hg or 1.4 psia).
Operating data recorded at ALPO reports an evaporative
efficiency of 80 percent which translates to 1.6 lbs of water
evaporated for every pound of process steam. This value com-
pares well with the design value.
Principal Operatinc Features . The C—G process is run
intermittently as stored sludge volumes dictate. - The only oil
separation step atALPO is removal by batch operation in a
basket type centrifuge. Oil reduction of approximately 50
percent is achieved. The end product has a typical oil content
of 35—40 percent and’ a moisture content of 2 to 3 percent, as
reported by ALPO operators. The dried product is marketed for
eventual use as animal feed.
The vapor stream from the cold effect is passed through a
condenser and exhausted to the atmosphere without further
treatment.. Condensate from the heat exchangers and condenser
is collected in a central channel and returned to the head of
the treatment works.
Maintenance . The only noteworthy maintenance items
reported were similar to those at Coors; that is, pump seal
replacement and periodic cleaning of condenser tubes with an
acid solution.
Principal Observations .
o The vacuum exhaust imparts no noticeable odor to the
surrounding environment. It was reported, however,
that some odor problems do arise if septic sludge is
processed. In addition, there were no visible
emissions during the inspection.
o The condensate, as observed, was clear and odor free.
Condensate is returned to the treatment works without
upsetting the activated sludge process.
o The dry materials handling phase of the process im
parted a mild odor to the building interior.
27

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o The evaporators were not insulated, and high
temperatures were evident in portions of the
building.
o seat excnanger ciogg rig has not oeen experienced.
City of Fukuchiyama, Japan (Reference 1)
The Fukuchiyaina City plant serves a population of 60,000
to 70,000 people. The influent sewage consists of flow from
sewered residential areas, commercial and industrial sources
within the service area and collected night soil”. The plant
is typical of activated sludge treatment plants in the United
States.
The C—G process at the Fukuchiyama City facility is a
triple effect system sized for a evaporative rate of 14,000 lbs
(6,350 kg) per hour. The process is designed for ultimate
operation on a 24—ho.ur basis.
SludQe Source . The sludge processed by the C—G system is
a mixture of primary., and waste activated. The sludges are
thickened separately and blended prior to the fluidizing step.
The primary sludge is thickened by gravity to a solids content
of 8—9 percent. The waste activated sludge is thickened by air
flotation to a solids content of 4.5 percent. The blended
sludge as processed has an average solids content of 5 to 6
percent.
- Principal Operating Features . The C—G process at the
Fukuchiyaina Plant is operated for approximately 8 hours per
day. The process is started up every morning and produces a
dried product within one hour. The sludge is fluidized with a
heavy grade fuel oil. A schematic of the C—G waste heat
recovery system is illustrated on Figure 4.
Steant Source . The source of steam for the C—G process is
the plant boiler which utilizes the dried product for fuel.
Steam is fed to the hot effectat approximately 296,500 Pa (43
psia). The evaporative efficiency at Fukuchiyama City is 75
percent. A typical pressure and temperature profile for the
Fukuchiyama facility is presented in Table 4.
Was e Condensate . The condensate from the effects under-
goes a gravity oil separation step and is then returned to the
aeration tank. The condensate BOD represents approximately 5
percent of the plant influent BOD loading. The condensate is
clear and colorless but does contain volatile organic acids
derived from the sludge.
28

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Vsoooo. P E.h.o.S To eol..
FIGURE 4. C—G Heat Recovery Pr000aB Flow SchematJc City of Fukuchlyamaj Japan,
Sewage Treatment Plant (Reference 1).
V. o. Pomp
‘ .0
Plea... SI... To Almo. .r.
5cn b.,
Ash To
LsItdIlO
R.cpcled OS 0105.9.

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TABLE 4. TEMPERATURE AND PRESSURE PROFILE — FUKUCBIYAMA
Effect
No.
Temper
(°F)
ature
(°C)
Pres
sure
Pa x 10
psia
1
149
65
0.5—0.9
3.4—6.2
2
176
80
3.2—4.5
22.1—31.0
3
212
100
12.5—14.0
86.2—96.5
Oil—Moisture Difficulties . The oil to solids ratio
utilized at Fukuchiyarna is 6:1 oil to dry solids by weight.
This results in a mixture leaving the hot effect ranging
between 75 and 80 percent oil. Data obtainedf ronr the
Fukuchiyalfla City plant shows that an oil content reduction of
approximately 50 percent is obtained by the centrifuge step.
— Boiler-Facilities. - The dried mixture is presentlyinaSS
fired in the boiler-to produce process steam. Auxiliary fuel
is used for process start—up to maintain a minimum boiler
temperature during intermittent operations and whenever steam
production Js insu fficient. Overall, auxiliary fuel
consumption is reported to be less than 0.115 cu m of fuel
oil/metric ton cry solids (25 gallons/ton). Overall oil con-
sumption for the C—G process and boiler operations is reported
to be approximately 0.42 Cu m per metric ton dry solids (100
gallons/ton). The make—up fuel oil is required because of the
relatively low solids content in the C—G process influent.
The boiler exhaust gas control train at Fukuchiyama City
consists of a cyclone and a wet scrubber. The average
particulate emission reported equates to approximately 0.75 kg
particulate per metric ton of sludge solids (1.5 lbs/ton). The
average sO concentration in the exhaust gas is 105 ppm. These
values arewell within the limits imposed by the local
regulatory agencies and are in general conformance with
regulations in effect in many areas of the United States.
Maintenance . The operators of the C—G process at the
Fukuchiyama City plant report that no special maintenance pro-
cedures are required for the facility. The type of maintenance
operations performed are those normally associated with sewage
treatment works.
Principal Observations .
0 Operation of the C—G system at Fukuchiyama City is
handled routinely with all other treatment
operations.
30

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o Odor was not observed to be a problem either in the
liquid or dry materials handling phases.
o The evaporator effects are not insulated and are
installed outside. Insulation would improve thermal
efficiencies.
o The C—G system performs slightly better than design
expectations.
o The gummy—phase has never occurred at Fukuchiyaina.
o The lack of corrosion further supports the theory
that the oil acts as an inhibiting agent.
o Foaming in the effects has not occurred.
o Boiler stack emissions, based on test data, can meet
most pres nt air pollution codes. -
o Condensate is returned to the aeration tank without
any effect o.n the treatment process.
o Make—up fuel oil to the boiler is required because of
the low solids content in the C—G influent.
AVAILABLE EQUIPMENT/HARDWARE
The C—C process is patented y Dehydrotech Corporation
(formerly Carver—Greenfield Corporation) and is marketed under
exclusive license arrangements by the Foster Wheeler Energy
Corporation. The patented process equipment and appurtenant
hardware can be negotiated directly with Dehydrotech.
Currently, Foster—Wheeler is developing plans and specifi-
cations for all C—G equipment.
31

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SECTION 5
TECHNOLOGY EVALUATION
PROCESS THEORY
Process Description (Reference 3)
The C—G process is a drying technique utilizing the prin-
ciple of multi—effect evaporation. Water is extracted from
sludge by evaporation using multiple—effect evaporators. The
sludge to be processed should first be thickened or dewatered
to reduce the amount of water to be evaporated, and thereby
reducing energy con-sumption. Thickened sludge is then mixed
with an oil, such as No. 4 fuel oil or Isopar—L (an Exxon
product), ir t fluidi:ing tank at a suggested ratio of 1
part dry a s .c —l parts oil (see Figure 5). By use of an
oil, fluidity is maintained in all effects of the evaporation
cycle, formation of scale is eliminated and corrosion of the
heat exchangers is minimized. The sludge/oil slurry is then
pumped to the multiple—effect evaporator where water is
vaporized and the remaining solids! oil mixture is first
separated by gravity and then centrifuged to further separate
the oil and solids. An additional step, called hydro—
extraction, is sometimes .used to maximize oil removal by steam
stripping. The oil is recycled and reused while the solids are
discharged for further processing or disposal. Heavy oils
contained in the sludge dissolve in the carrier oil and can be
recovered as fuel oil by simple distillation.
Principle of Multiple—Effect Evaporation (Reference 1)
A schematic diagram of a single effect evaporator is
illustrated in Figure 6. In a single effect evaporator the
liquid to be evaporated is pumped into a heat exchanger
(generally into a tube nest). Steam is also introduced into
the chamber (generally on the outside of the tubes). As heat
is transferred across the tubes from the steam to the liquid in
the tubes, the steam is condensed. The condensed steam is then
removed from the heat exchanger. At the same time, a portion
of liquid within the heat exchanger evaporates and is
transferred into the vapor chamber along with the remaining
liquid phase. In the vapor chamber the gases and liquid phases
32

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Steam
Figure 5. Carver—Greenfield Block Flow Diagram (Reference 3)
are separated. The liquid is withdrawn. The distilled vapor
then flows to a condenser. In the condenser, cold water or
air is used to cool the vapor below its dew point. The conden-
sate and remaining vapor from the condenser are then withdrawn.
In the single effect evaporator, vapor from the boiling
liquid is condensed and usually discarded. The single effect
evaporator does not utilize the heat contained in the vapor and
therefore does not optimize the use of the original process
steam. Single effect evaporators are used predominantly where
the required capacity is small and the process steam
inexpensive.
To evaporate 0.5 kg (one pound) of water from a solution
in a single effect evaporator, approximately 1320 kj (1250
Btu’s) are required. This translates to approximately 0.6 kg
(1.25 ibs) of saturated steam at 861,850 Pa (125 psia). In
order to provide a more economical utilization of steam, the
multi—effect evaporator principle is employed. The first or
“hot effect” of a multi—effect system functions in the same
-m3nner as a single effect evaporator. That is, steam is fed
Recycle Oil
33

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Exhaust
Vacuum Pump
FIGURE 6. Typical
Single Effect Evaporator —
Falling Film Type (Reference 1).
Condenser [ t Cooling Water
Condensate
Feed Pump
Distilled Vapor
( )
I-lest
Exchanger
Ste a in
Steam Condensate
Transfer
Pump
Concentrated Liquid

-------
from an outside source, and by means of heat exchange is used
to evaporate a portion of the water in the solution or slurry.
In the multi—effect evaporator, the vapor is reused in
successive effects as illustrated in Figure 7.
The vapor from each effect is utilized in subsequent-
effects to evaporate a portion of the liquid in that effect.
The temperature of the vapor from the first effect is lower
than that of the process steam. Similarly, the vapor
temperature in each subsequent effect is lower than that of the
preceding effect. To accomplish the desired evaporation, the
pressure in each successive effect must be lowered. At lower
pressures the solvent or water will evaporate at lower
temperatures permitting evaporation even in the last or so
called cold effect”. The effect of pressure—on-the boiling -
point of water is illustrated in Table 5.
TABLE5. EFFECT OF PRESSURE ON BOILING POINT OF WATER,
Pressure
(psia)
(Pa -i
•
Boiling Point
(°F)
Boiling Point
(°C)
1.0
6.9
101.74
38.75
2.0
13.8
126.08
52.25
5.0
34.5
162.24
72.35
10.0
68.9
193.21
89.56
14.7
101.4
212.00
100.00
If the process steam is fed to the first effect of a
multiple—effect evaporator above the boiling point of the
liquid to be evaporated (at a given pressure), then 1.25 kg of
steam will evaporate about 1 kg of water. The water vapor
evaporated will then serve as the steam for the second effect
and so on for each successive effect. The steam requirement of
1.25 kg of steam per 1 kg of water evaporated for single effect
evaporation can be theoretically reduced to 0.42 kg steam per
kg water, 0.31 kg steam per kg water and 0.25 kg steam per kg
water for 3, 4, and 5 effect evaporators respectively. This,
of course, does not consider radiation heat loss and the energy
required to reduce the pressure:in successive stages.
PROCESS CAPABILITIES AND LIMITATIONS
A simplified materials balance for a typical four—effect
C—G process is illustrated in Figure 8.
35.

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Exhaust
Pump
DIstilled Vapor
Heat
Exchanger
(Typ.)
NOTE: THE EVAPORATING LIQUID AND STEAM
GO IN OPPOSITE DIRECTIONS.
Condensate
DIstilled Vapor
(4
o
Distilled Vapor
Steam
Condensate
Steam Condensate
Feed Pump
Transfer
Pump
(Typ.)
Concentrate
Liquid (Typ.)
FIGURE 7. Tvolcal Multi—Effect (Triple Effect) Evaporator - Falling Film Type (Reference 1).

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I


I

ASSUMPTIONS
Capicily SO? S U
SoUd Contenl 1%
Fk,ldlzlno Rello 5 2S
Eli 50%
MoIitie s 0%
IPO Or
t
y Soflda
.
duct
FIGURE 8. MaterIals Balance — Four Effect Carver—Greenfleld Process (Refer pnce 1).
—4
Peocess Ste.
Condensate 28.346 Kg/It.
Tank
P .odoc l

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The capabilities of the C—G process are listed below:
o The C—G process is capable of drying aqueous
solutions or slurries with a wide range of solids
contents (4 to 45 percent). The process can handle
any type of municipal sewage sludge and can be
designed to handle any feed concentration or can
evaporate water to any degree of dryness.
o Because C—G uses multiple effect evaporation, it
consumes only a fraction of the energy required by
other heat drying processes.
o Assuming the dried sludge is used as a fuel, the
process may be self—sufficient in energy. and_in.sOme
cases provides excess energy for export.
o It removes poly—chiorinated bi—phenyls (PCB) which
are destroyed when sewage oil is used as a fuel in a
boiler.
o The C—C process produces a dry, easy—to—riandle pro-
duct which is sterilized by heating to above 120°C
(250°F) during evaporation. All pathogens, viruses,
bacteria, etc. are destroyed.
o Since it operates in a completely closed system,
odors are contained within the system. The odorif-
erous and other non—condensable gases contained in
the sludge feed which evolve during evaporation can
be added t the air intake of the boiler for
combustion.
o The greatly reduced volume of fully dried sterile
product may be safely’ disposed of with minimum land
use, or may be used as a fertilizer and soil
conditioner.
o The dried solid product can be stored for an
indefinite period.
Two significant limitations of multiple—effect evaporation
are increasing viscosity and resistance to heat exchange of the
liquid as it is concentrated. If the increase in viscosity is
sufficient, the material can clog or scale the evaporator tubes
of the heat exchanger and prevent evaporation. To eliminate
this problem, the material must be kept in a fluid state in
each effect. This can be accomplished by using a fluidizing
medium. The incorporation of a fluidizing oil with the
multiple effect evaporators is the basic principle of the
_C—G process.
38

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It would appear that infinite evaporators would result
from the use of an infinite number of effects. Theoretically
for a single—effect unit, 2300 kj per kg of water removed (1000
Btu’s per pound) is required, and for a double—effect unit,
1150 kj are required per kg of water removed (500 Etu’s per
pound), etc. Several factors, however, limit the number of
effects practicable in a system. Each effect of a multi—effect
evaporator operates only on a fraction of the total temperature
drop across the system. Since the total drop is seldom larger
than that employed in single—effect evaporator, the capacity
per unit area of heating surface is reduced proportionately.
Thus, savings in fuel requirements may be realized through
multi—effect operation, but equipment costs will be greater.
Also, heat is lost to the atmosphere through-the-surface-S of
the system, as well as being removed by the product streams.
Usually 3 or 4 effects are economical, but the actual number is
largely influenced by prevailing fuel costs.
DESIGN CONSIDERATIONS
Full—Scale Carver Greerifield Process (Reference 2)
A detailed diagram of a four—effect, full—scale C—G pro-
cess is presented in Figure 9 and is described below. The
system components were assembled by Dehydrotech Corporation and
Foster—Wheeler Energy Corporation at the request of the LA/OMA
Project (Reference 2).
Referring to Figure 9, feed s1u ge enters the fl-uidizing
tank where it is mixed w ith fluidizing oil. The latter is a
mixture of recycle oil and dry sludge slurry obtained from the
fourth stage evaporator. Capability for dry sludge slurry
recycle, referred to as “addback , is included to improve the
suspension qualities of the feed sludge and oil mixture. It
also alleviates problems associated with gummy phase formation.
A ratio of one part feed solid (dry basis) and one part of
recycled dry slurry solids (oil free basis) has been recom-
mended by the manufacturer. This depends in part on the input
solids content.
The slur ned mixture in the fluidizing tank is then pumped
to a grinder having a 1/4—inch size screen. Discharge from
the grinder is fed by gravity to the evaporator feed tank
fitted with an agitator to maintain a uniform slurry
consistency.
Slurry is then pumped to the four effect evaporator
system. In the evaporator system, temperature of the feed
slurry increases from stage to stage whereas the water vapor
39—

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C o g
V.nI-
Cond.ns.,
U:
c i
OIe.
Cond.ns.ts
R.I n
Ta OoI.
SI. po Fast OD
Sto..it.
Cost. u C.,
OU FUt. ,
P .00. .. Coad.AtSte
tOO P IG 81...’ To
P .o .. .. What. Thown
FIGURE 9. Flow Diagram of a Full Scale Four—Effect Carver—$3reenfleid Process (Reference 2).

-------
flowing in the opposite direction decreases in temperature from-
one effect to the next. The evaporation of liquid continues
through the system by maintaining progressively lower pressures
in each effect and, therefore, progressively lower boiling
points.
Slurry in the evaporator feed tank is pumped continuously
to the first stage (fourth effect) where a constant fluid level
is maintained. Each stage has a transfer pump and control
system.
In order to recover heat energy from the hot recycle oil
and from the fourth stage dry recycle slurry at about 125°C
(255°F), three heat exchangers (HEX) are included, as shown in
Figure 9. As a result, temperature of the recycle solids—oil
slurry is reduced from about 125°C to 60°C (255°F to 145°F),
thereby, increasing the temperature of sludge/oil slurry being
transferred between stages.
It has been assumed that Isopar—L , an aliphatic ligh€ oil,
would be used as the fluidizing medium. At one atmosphere
pressure, the oil boils at 190°C to 205°C (375 to 400°F),
decreasing to about 115°C to 125°C (240 to 260°F) at 0.10
atmospheres. The boiling point is considerably greater than
that of water at all pressures which reduces the amount of oil
vaporized along with water in the vapor chambers. However, the
boiling point is sufficiently low that hydroextraction and
steam stripping of Isopar is possible using steam of moderate
temperature and pressure; therefore, dry solids can be produced
which contain only small amounts of the original fluidizing
oil. An Isopar and steam mixture is azeotropic in that the
mixture has a lower boiling point than either individual
component. This is of some help in the hydroextraction arid
steam stripping operation. Since Isopar is a non—polar fluid
it will tend to dissolve grease, fats and oils, and other non-
polar materials contained in the sludge. I opar can be steam
stripped from most of these dissolved oils leaving a residue,
hereinafter referred to as “heavy oil” which can be used as a
fuel.
A review of operating C—C installations indicates that
there are numerous oils suitable for use as fluidizing media.
Tallow, lubricating grade oil, and soybean oil are typical of
oils presently in use. Isopar—L , which has been demonstrated
as suitable for use with municipal sludge as well as other
sludges, has become closely associated with the C—G process in
recent years. Isopar—L was used successfully during pilot
testing conducted as part of the LA/OMA Project. It vaporizes
at 376 to 400 0 F at atmospheric pressure, and has a boiling
point and consistency of quality that makes it highly desirable
for use with the C—C process, particularly when nydroextractiorr
41

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is included. The popularity of Isopar—L, however, is due to
the interest in marketing C—G products such as animal feed from
the Coors facility. In those applications, the purity of
IsoDar—L is very des!rable. For C—G ap lications such as that
proposed icr zna Los Angeles HERS project, any i g t oh w tn
characteristics similar to Isopar—L is suitable. The
characteristics of Isopar—L and similar light oils are shown in
Table 6. - -
Table 6. SUITABLE LIGHT OILS FOR C—G PROCESS
Property
Isopar—L Amsco 160
Chevron 410B
Distillation, ASTM D—86,
0 F
IBP
370
367
368
10 percent
376
372
378
50 percent
382
376
387
90 percent
393
389
402
EP
405
410
417
Flash point, ASTMD—56 .,
°F
144
142
142
Specific gravity at 60°F
0.767
0.7945
0.8034
Viscosity, centipoise at
i00 0 Fa
1.1
1.3
1.3
Cost, $/gaib
1.59
1.38
1.72
a Viscosity based on estimates by Foster Wheeler Energy
Corporation
b Prices are for comparison purposes only.
In most multi—effect systems, it is desirable to evaporate
about equal quantities of water in each stage. However, heat
recovery requirements often dictate varying water evaporation
rates for different stages. In the case of the hydroextraction
steam stripping technique, approximately equal quantities of
water are evaporated in the first three stages and a lesser
amount in the fourth stage whereas for the vacuum stripping and
distillation, a more equal evaporation results in all four
stages.
Condensate collected from the first two evaporation stages
will contain distilled fluidizing oil in amounts up to about 40
percent or higher by weight. Vapor from the fourth stage will
contain distilled oil in amounts up to about 100—150 percent of
42

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the water evaporated depending on the temperature of the slurry-
in the fourth stage.
In a single effect evaporator operating at 72°C (162°F),
the partial pressure of water and Isopar is about 34,500 Pa (5
psia) and 4,140 Pa (0.60 psia), respectively. Since the moles
of gas are proportional to the vapor pressure, the mole
percentage of water to Isopar in the vapor would be about 8.3
to 1. However, actual weight percentage would be about 0.88 to
1 of water to Isopar. Even through the partial pressure of
Isopar is significantly lower than water, the higher molecular
weight results in a large weight percentage being evaporated in
each effect.
The water—oil condensate is decanted in-_small gravity
separation tanks and the oil is returned automatically to the
stage from which it has been evaporated. An interface con-
troller maintains a suitable oil level in each of these decan—
tation tanks. Water is discharged to a larger oil—water
separation tank where a more thorough separation of remaining
oil from water is made. Since this water has been heated
during the evaporation step, recovery of the heat is made by
flashing to the higher vacuum of the preceeding stage. Two
such flash units are employed in a four effect evaporator
system. Trace quantities of oil remaining in the condensate
are removed in a coalescer leaving a high quality water.
A portion of the dry sludge—oil slurry (about one half) is
recycled back though the heat exchangers to the fluidizing tank
and the balance is centrifuged to produce dry solids containing
about 40 percent oil. It is important to note that the dry
sludge—oil slurry also contains the uheavy oil” which is
approximately equal to 10 percent of the digested primary
sludge feed (dry weight basis).
A portion of the recycled oil, approximately 25 percent,
is pumped to the Heavy Oil Separation Still where 80 percent of
the heavy oil is recovered. The balance of the oil is returned
through heat exchangers to the fluidizing tank. Residual
quantities of light oil leaving the Separation Still with the
heavy oil are recovered through a vacuum stripper unit and the
heavy oil is discharged from this unit. Heavy oil may be
filtered depending on the proposed use and is thought to be
suitable for use as a fuel oil. However, oil will not be
filtered in the HERS design since it will be fired in a
fluidized bed incinerator.
If the heavy oil is not separated from the recycled Isopar
the Isopar—heavy oil mixture would reach a saturation level.
The heavy oil will then eventually show up in the centrifuged
-solids. Since only the Isopar, being a light oil, is distilled
43.

-------
off in the hydroextraction process, heavier oils would tend to
stay with the dried sludge. If dried sludge is to be thermally
processed for energy recovery, heavy oil may not need to be
separated from the sludge, and steam required to operate the
C—G process could De supplied from the thermal processing
system. In fact, keeping the heavy oils in the sludge is an
advantage if the product is thermally processed. If separated,
the heavy oil would have to be remixed with the solids or
introduced separately into the pyrolysis unit.
If energy recovery is not a part of the sludge handling
scheme, then separation of the heavy oil becomes more
important. The heavy oil could supplement the fuel requirement
for the boiler operation which supplies steam to the C—C
process in the latter case. -
Centrifuged solids, containing light fluidizing oil and
other dissolved heavy oil, are conveyed to a “Hydroextractor”.
The hydroextractor is a type of indirect steam dryer. Heat is
supplied to the hydroextractor contents by indirect heat ex-
change with steam. Steam is also directly sparged through the
product to steam distill the Isopar at a temperature of about
120°C to 160°C (2 50°F to 325°F) at atmospheric pressure. An
alternate technique is-to distill the Isopar without any direct
steam input at a vacuum of 0.5 atmospheres. Energy required to
raise the temperature of the product to 160°C (325°F) and
provide the heat of vaporization of the oil is obtained by
supplying steam to the internal hollow mixing conveyor flights
and the steam jacket of the hydroextractor unit. Vapors of the
hydroextraction unit enter the Heavy Oil Separation Still to
separa te the oil fractions. Isopar and steam are then returned
to the fourth stage vapor-chamber to recover the heat value.
Dry product is withdrawn from the system after
hydroextraction. Process condensate is recycled back to the
treatment plant. All vent gases after condensation for oil
recovery are combusted in the boiler or thermal reactor.
Design Criteria (Reference 2)
General design criteria are listed in Table 7. The number
of effects and the required evaporation efficiency depend on
the situation. A two—effect system may be most economical in
some cases. Also, redundancy or reliability requirements are
site specific. The Los Angeles design incorporates three
modules, each capable of handling 50 percent of the average
design load. This level of redundancy is dictated by the large
quantity of sludge being processed, the lack of alternative
disposal options in emergency situations, the need to handle
peak sludge production rates, and estimated downtime for
-routine maintenance. The City of Trenton, however, will use a--
44

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single process train, sized for above—average production rates
and designed to operate five days/week. Finally, Isopar will
probably be used as fluidizing oil only where a food grade
product i to b toduc Othe: etroleur based cils are more
readily avallaDle ano le expensive.
TABLE 7. CA.RVER—GREENFIELD DEHYDRATION DESIGN CRITERIA
Item Criteria
Number of Effects 2, 3 or 4
Evaporation Rate 2.3 kg water/kg st-eant
Steam Characteristics 448,200 Pa (65 psia) saturated
Boiler Efficiency 75%
Fuel Value of Extracted
Heavy Oil 41,850 kj/kg (18,000 Btu/lb)
Fluidizing Oil Isopar—L
Fluidizing Oil Make—Up 1% by weight of dry solids fed
(assumes hydroextraction is
employed for oil recovery)
Weight of Isopar—L 766 kg/cu ni (6.388 lbs/gal)
Outfeed 95% solids
Figure 10 shows the four—effect system employing the
hydroextraction process recommended for the Hyperion Energy
Recovery System (HERS) project. The system downstream of wet
cake storage but including the use of digester gas consists of
the following major components (Reference 11):
o C—C dehydration system
o Fluidized bed boiler system
o Fluidized bed air emission control system
o Digester gas cleanup system
o Combined cycle power plant
45

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Steam to other users — Steam to dlgesterS — 1
1,360 Kg/hr 14.500 Kg/hr
Steam - I Mw
8,160 Kg/hr Super—heated steam to C0 — to plant
Kg/hr 15,400 Kg/hr
, RBINES — 3.830 K / hr I
GENERATORS 25.000 1 Proce s steam to 6-0 -
ACK-PRESSURE TURBINE r
12 8 Mw
Gas - (
177.000
m 3 ,day — — 1.9MW +
Evaporate — I I
a.
I OIGESTER J 962 mt/day MAIN
TURBINE
Digesled _____
Wet cake — _____
5.68 /mIn 20% eollde 1241 mt/day 10 3 Mw
SWITCHYARD
udge —
slud e - 1.200 mt/day Dry 5$ DISTRIBUTION
AND
CARVER-
SYSTEM
REENFIELD
Centrate - 6.81 m 3 FmIn EN:n:Y:::ovEnv BU::DING
49,900kg/hr
.f U0E0
FIGURE 10. SchematIc Flow Diagram, HERS Carver-Greenfleld Process.

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The dried sludge product from the C—G process in the HERS
projects will be thermally processed for energy recovery. The
thermal process system selected after a Phase I study resulted
n tne use of a fluidized bed reactor ( eference 13).
ENERGY ANALYSIS— REQUIREMENTS AND RECOVERY POTENTIAL
(Reference 2)
A mass and energy balance for combined C—G drying and
thermal processing is shown in Figure 11 based on the HERS
project design.
In developing the mass and energy balance it was assumed
that any extracted heavy oil from theC—G process is combined
with dry product solids and pyrolyzed in a multiple hearth
furnace (MEF). Low energy fuel gas produced under partial
oxidation conditions in the multiple hearth would be
immediately afterburned and passed through a boiler for steam
production. The m.ass flow and temperature of flue gases
exiting the afterbu ner were calculated from a heat and mass
balance considering the caloric content of the feed and 140
percent stoichiomstric air supply. Steam production was calcu-
lated assuming an exit: gas temperature from the boiler of 204°C
(400°F). Electrical production will include a condensing steam
turbine with an extraction of process steam for the C—G unit at
1140 KPa (165 psia). Higher steam pressures are used in the
HERS design than indicated in Table 7 due to the use of
electrical production turDine exhaust steam.
About 38 percent of the steam produced is required for
operation of the C—G process with the remainder available for
production of electricity. About 6,260 KW of the total 7580 KW
produced results from steam condensed at 22,100 Pa (3.2 psia).
The remainder is derived from that portion of input steam
extracted at 1140 KPa (165 psia). If vacuum hydroextraction is
used, only about 22 percent of the process steam would be
required at 1,140 KPa (165 psia) with the remainder at 550 KPa
(80 psia). If two extractions were made from the turbine, one
each at 550 and 1,140 KPa (80 and 165 psia), electrical pro-
duction could be increased to about 8,019 KW, approximately a 6
percent increase. It should be noted that other steam turbine
configurations are possible; for example, a condensing turbine
with a separate backpressure turbine for steam used in the
C—G. However, electrical production would not differ signifi—
cantly. Therefore, the system shown in Figure 11 represents the
potential energy budget for a combined process of dehydration
and thermal processing using a proven energy conversion system.
47

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FIGURE 11. Carver—Greenfleld Thermal rocessIng System
Mass and Energy Balance ‘leference 1).
WATER
TREATMENT MAKEUP
- __________ WATER
303 kgIIi,
910, OOWH AS
NC(I:SSARY
QEWATERED
SLUDGE CAKE
338 u Ip4 TE
2*6 mlpd VS
*001 mSpd I12O
PROCESS
CONDENSATE
10 PLANT
656 m Ip S H20
ISOPAR
3 1 mipS
ASH 110 dmlpd
*640 kw
TO ATMOSPHERE
I 0• C
*380 kw
(INCLUDE S
FLUE GAS
CLEANUP)
NET OUTPUT
4060 kw
COOLING WATER
2] 6 Cu mlinIn
AI l 1C
SEE N0 ESON NEXT PAGE
28720 kgIhr
CONDENSATE PUMP

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Figure 11 continued
NOTES
a. Feed to MHF contains 197 dmtpd (217 dtpd) of VS @ 21.1x10 3
kJ/kg (9100 BTtJ/lb VS) cornbin d with 21 mtpd (23 tpd) of
extracted heavy oil @ 41.9x10 kJ/kg (18,000 Btu/lb) and
16 mtpd (18 tpd) of residual water.
b. Mass flow and temperature calculated from heat balance
assuming 140 percent stoichiometric air in MEF and
afterburner combined. Flue gas temperature is greater
than 1538°C (2800°F) in this example.
c. High energy venturi scrubber and multipl-e-tray scrubber-
ass urn e d.
d. Steam turbine electrical production at 4.6 kg/hr (10.1
lb/hr) per KW extracted @ 22 KPa (3.2 psia) and 13.3 kg/hr
(29.4 lb/hr) pex KW extracted @ 1,135 KPa (165 psia).
e. Separate backpressure turbine could also be used.
f. With vacuum applied to hydroextraction unit, about 22
percent of steam requirement would be at 116,000 kgs/sq
meter (165 psia) with remainder at 56,250 kgs/sq meter (80
psia). Two extractions from turbine at those pressures
would be possible with some increase in electrical conver-
sion efficiency.
g. Assumes 5 percent consumptive loss of steam in vacuum
hydroextraction and Isopar distillation system. If
hydroextraction conducted at one atmosphere, consumptive
loss could increase to 65 percent of applied steam. Heat
value of this direct steam is recovered in the process in
either case.
49

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OPERATION AND MAINTENANCE REQUIREMENTS (Reference 2)
Table 8 lists the labor, power and chemical requirements
for the C—G process only based on the City of Los Angeles
proposed full—scale Hyperion Energy Recovery System (HERS)
(Reference 11). The design data for HERS is presented in the
cost section.
TABLE 8. OPERATION AND MAINTENANCE REQUIREMENTS
Design
265 dtPda @ 20 percent solids
Labor
10 personnel @ 1500
hrs/yr each
Power used
1900 kW/day
Chemical requiremerits
(carrier oil)
1,200 kg/day or 766
(2,650 lb/day or 15
@ 6.388 lb/gal)
kg/cu in
gal/day
a dry tons per day
b based on total oil loss of 0.5 percent of output of dry
solids
The process is quite flexible in terms of variations
during operation. The heart of the process is the multiple—
effect evaporator train, which consists of feed and circulation
pumps, heat exchanger, vapor chamber and connection piping. As
such, the system is comprised of mostly duplicative equipment
which is non—proprietary and available from more than one
manufacturer. These equipment sections (e.g. an evaporative
effect unit) are amenable to duplication or by—pass arrangement
to assure 100 percent reliability. Thus, an extra evaporative
effect (pumps, heat exchanger, vapor chamber) may be piped in
parallel with the ones in normal operation to provide switch—
over capability in case one of the effects is shut down
temporarily for any reason. A way to assure reliability with-
out extra equipment is to have bypass arrangement such that a
normal 4—effect system can be operated as a 3—effect system by
using slightly more process steam and higher temperature drop
across the system with attendant decrease in efficiency. With
these and certain other essential spare equipment, the Carver—
Greenfield system can cope with upset conditions without having
100 percent redundancy.
50

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The C—G process poses no special maintenance problems.
The maintenance effort required in the dry materials phase and
distillate condensing operations will be greater than in other
process segments. All required maintenance procedures are
within the capabilities of well trained municipal personnel.
Equipment durability and reliability are quite good. The
employment of proper preventive maintenance procedures for the
C—G process can be expected to result in smooth running
operations with long life.
COST
Cost estimating procedures follow the US EPA’S cost—
effectiveness guidelines. Cost—effectiveness is defined to
include monetary cost and environmental and social_impact
assessment. Capital cost estimates are based on the
Engineering News Record Construction Cost Index (ENR CCI) 20
cities average for March 1981 or 3384. Capital costs are based
on an operable system with a 20—year life. If a system has an
expected service life of less than 20 years, the capital cost
includes the present worth of subsequent replacement at current
values, required to obtain a 20—year service life. Salvage
value for estimated, service life beyond 20 years is not
considered.
Capital costs include construction, engineering, legal,
administration and contingencies for all building, equipment
and labor, energy, chemicals and routine replacement of parts
and equipment (when replacement is required at intervals of
five years or less). Equipment cost estimates were based on
preliminary layouts and sizing, and were obtained from the City
of Los Angeles proposed full—scale system (Reference 11).
Basic cost assumptions include:
Service life
Equipment = 20 years
Structures = 40 years
Interest rate (EPA required) = 7 percent
Non—component costs = Piping @ 10%
Electrical @ 8%
Instrumentation @ 5%
Site preparation @ 5%
Total = 28% of
construction cost
Non—construction cost = Engineering and con-
struction supervision
@ 15%
51

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Contingencies @ 15%
Total = 30% of
construction and non—
component costs
Capital cost = Construction cost
plus non—component -
and non—construction
costs
Capital recovery factor = 20 years, 0.09439
40 years, 0.07501
Present worth factor = 20 years, 10.594
40 years, 13.332
ENR CCI (20 cities average = 3384
for March 1981)
Labor Cost. (March 198l = $15/hour
Energy cost March 1981)
Electfici t.y (industrial = $0.014/M 3
rate) - ($0.05/kilowatt—hour)
Gasoline = $0.396/liter
($1 .50/gallon)
Natural Gas = 0.053/cu m
($l.491/l,000 cu ft)
Three parallel, four—effect C—C process trains were
assumed. Each process train would be a complete system
designed to handle 50 percent of the sludge loading. This
would provide 50 percent standby for all equipment based on the
proposed sludge loading rate.
A four effect C—G system is proposed for the HERS systeni
including the following subsystems:
o sludge cake fluidizing
o First stage de—oiling by centrifuge
o Seéond stage de—oiling by hydroextraction
o Light/heavy oil separation
o Sewage oil recovery
52

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o Condensate polishing
o Once—through cooling of condensate using secondary
treated effluent
o Dry product storage
o Pelletizing system
o Oil storage
Table 9 presents the preliminary design criteria for this
system and Table 10 presents the cost breakdown. It should be
noted that, at the time of this writing, these cost estimates
were still in the draft stage and are subject to revision.
Non—component costs are included in the equipment cost
estimates.
Process license fees are included in the cost estimate.
The license fees of aproximately $1.4 million is based on a
formula that accounts for energy savings. The license fee
formula varies from project to project depending upon several
factors including energy savings. For example, the license fee
at Trenton, New Jersey was approximately $0.82 million without
an allowance for energy savings.
53-.

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TABLE 9. PRELIMINARY DESIGN CRITERIA FOR CARVER—GREENFIELD.
SYSTEM, HYPERION ENERGY RECOVERY SYSTEM, CITY OF LOS
ANGELES, CALIFORNIA (Reference 11)
Ite n Preliminary Cesign Criteria
Ntznber of n dules 3
Sludge capacity, tons dry solids/day 135 (each)
Evaporative capacity, lb/hr 63,750 (each)
Oil fludizing subsystem
Makeup oil tank
N riber 2
Diameter, ft 12
Height, ft 30
Materials of construction Carbon steel
Fluidizing tank
Niinber 3
Diameter, ft 8
Height, ft 9
I nk itaxer type - in tabiU.zers
Materials of. construction 304— 5 5
Sludge grinder
3
Materials of construction Carbon steel
Evaporation subsystem
Vapor drums
1st stage
Num r 3
Diameter, ft 6.8
Height (including 60° hopper), ft 29
2nd stage
N iri r 3
Diameter, ft 5.3
Height (including 60° hopper), ft 26.5
3rd stage
NL nter 3
Diameter, ft 4.6
Height (including 600 hopper), ft 24
4th stage
N zn r 3
Diameter, ft 4.6
Height (including 60° hopper), ft 24
Materials of construction (all) Carbon steel
continued
54

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Table 9 (continued)
It n Preliminary sigi Criteria
.1st stage con nser
N nber 3
¶Lype Forced feed circu—
lation, single ss
Tube length, ft 40
Shell diameter, in. 28
Nunber of tubes 365
Heat exchanger area, s ft 3,560
Materials of construction 304L —SS tubes and heads;
car n steel shell
1st to 4th stage heat exchangers
Ni.miber (each stage) 3
Forced feed circulation
- Tube length, ft 20
Shell diameter, in. - 45
N .rnber of tubes 720
Heat exchanger area, s ft 3500
Materials of cons truction 304L—SS tuoes and ‘neaás;
carton steel shell
De-oiling and oil separation subsyst n
3rd arid 4th stage settling tanks
N nber (each stage) 3
Diameter, ft 9
Height (including 45° hopper), ft 22
Materials of construction rhxDn steel
Centrifuge
N nber 3
Type Horizontal, solid b il
Materials of construction rton steel, 304—SS conveyor
Light oil evaporator
NL nber 3
Materials of construction 316L-SS, tubes; carton steel,
shell
Hydroextractor
Nt nber 3
Diameter, ft 4
Length, ft 24
Materials of construction 316 SS clad
Recovered light oil storage tank
Nt ber 2
Storage, thys 3
Materials of construction .rbon steel
continued
55

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T ble 9 (continued)
It n Preliminary esi criteria
Sludge oil storaçe tank
Nzr er 2
Storage, days 3
Materials of construction rbon steel
Pelletizer
Number 3
Rate, tons/day 132.5
Minimum densifi tion factor 2:1
Materials of construction .rbon steel
Pellet storage tanks
Number 3
Storage, days
Pellets 6
P ider 3
Materials of construction ( rbon steel
Standby boiler
Number units 1
Firetube, s fired
Pressure, ig 150
city, lb/rn 50,000
56

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TABLE 10. ESTIMATED COSTS FOR LOS ANGELES CARVER—GREENFIELD.
PROCESS (Reference 11)
Capital Cost ($ ) (installed for 265 dry tons/day)
Equipment (non—component costs included)
Tanks and vessels $1,199,000
Drums 564,000
Beat exchangers and condensers 2,302,000
Pumps 2,011,000
Compressors 249,000
Centrifuges 995,000
Grinders 191,000
Fluidizer tanks 162,000
Hydroextractors 829,000
-Towers and stills 402,000
Oil—water separator 228,000
Pelletizers 402,000
Dust collectors 46,000
Standby boiler 635,000
Piping systems and platforms 2,638,000
Instrumentation 958,000
Conveyors 129,000
Subtotal $13,940,000
Engineering, legal, administration and
contingencies, @ 30%
Process License Fee 1.400.000
Subtotal for equipment 19,522,000
Structures 3,459,000
Engineering, legal, administrative and
contingencies, @ 30% l .038 .000
Subtotal for structures 4,497,000
Total Capital Costs $24,019,000
continued
57

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TABLE 10 (continued)
Annual Capital Cost (S/vear)a
Equipment
Structures
$ 1,843,000
_7 _nnn
Subtotal
2,180,000
O&M Cost ($/year )
Laborb
powerC
Chemicalsd
Maintenance materials e
$ 225,000
832,00 0
167 ,000
362 .000
Subtotal
1,586 ,000
Annual Cost
$ 3,766,000
$/dry ton $
aAnnual capital costs based on 7% interest, 20—year life for
equipment, 40—year life for structures
bLabor cost based on 10 positions at 1,500 hours per year and
$15 per hour
Cpower cost based on $0.05/kW
dchemical cost based .ori carrier oil cost of $0.381 kg
($0.173/lb) with losses of 0.5% in dried product
eAnnual maintenance cost estimated at 2% of equipment cost
39
.58

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SECTION 6
COMPARISON WITH EQUIThLENT CONVENTIONAL TECHNOLOGY
COST COMPARISON
The C—G process is a uniquely designed dehydration
(drying) process. Other heat drying processes include:
o Flash dryers
o Spray dryers
o Rotary dryers
o Multiple hearth dryers
o Indirect steam dryers
o Sonic dryer
Indirect contact steam dryers as manufactured by Bethlehem
or Bepex ate the closest conventional technology to the C—C
process since they are indirectly heated. The LA/OMA Project
conducted an analysis comparing indirect steam dryers with C—G
technology. The following conclusions were drawn from the
comparison between steam drying and dehydration:
o Capital cost of both processes are comparable.
o Steam drying consumes significantly more energy which
results in significantly higher O&M costs.
o Dehydration is less expensive than steam drying on an
overall annual cost basis.
The available information on sludge drying equipment
generally lacks key information necessary to develop accurate
capital and O&M cost curves. Cost information on the flash,
spray and rotary dryers is not readily available and data
presented on multiple hearth dryers deal with the unit
primarily as an incineration process rather than a drying
process.
59-

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The LA/OMA Project obtained cost information from the
manufacturers of rotary dryers. The information was based on
an input of 1,525 wet metric tons per day (1,680 wet tpd) of
sludge at 10 percent solids dried to 73 percent solid concen-
tration. Table 11 presents the cost information for rotary
dryers.
- - Operating costs have wide variations due to fluctuations
in auxiliary fuel requirements for various feed material
characteristics.
TABLE 11. EXAMPLE COST FOR ROTARY DRYER (Reference 11)
Input sludge cake
Metric tons/day (wet) 1,525
Metric tons/day (dry) 152
% solids - 10—
Installed capital cost (@ ENR = 3384) $6,198,000
Annual capital coat 585,000
O&M costs
Labor $ 450,000
Fuel $4 ,525 ,00 U
Annual O&M costs $4,975,000
Total annual cost S5,560,000
$/dry metric ton $ 100
Although the capital cost of rotary dryers is less than
the C—G process, the significantly higher annual O&M cost as a
result of higher energy requirements results in a lower annual
cost for the C—G process ($40 to $60/dry metric ton). These
results are generally correct when comparing the C—G process to
conventional drying technology.
ENERGY
The overall evaporation energy requirement of the C—G
process is less than that of comparable sludge drying processes
as shown in Table 12.
60

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TABLE 12. ENERGY REQUIREMENTS (Reference 3)
Kj Input/Kg of
Unit Water Evaporated
Spray dryer 4,650 minimum
Flash dryer 5,120—6,280
Rotary dryer 5,580—6,510
C—G (4 effect) 810—1,050
Indirect steam 2,900
Other devices that 2,330 (plus heat
use heat for drying lost due to in—
and do not employ efficiencies of
multiple effect system)
eva oration -
Btu Input/lb of
Water Evaporated
2000 minimum
2200—2700
2 40 0—2800
3 50—450
1,250
1000 (plus heat lost
due to inefficiencies
of system)
61

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SECTION 7
NATIONAL IMPACT ASSESSMENT
MARKET POTENTIAL
The cost—effective and energy efficient dewatering/drying
of residual wastewater solids prior to disposal or use is a
major problem facing most municipal wastewater agencies nation-
wide.
Existing mechanical dewatering methods in widespread use
(vacuum filtration, centrifugation, belt filters and filter
presses) are expensive and performance is limited by the
physical/chemical characteristics of residual solids. Heat
treatment (e.g. wet oxidation) and heat drying processes pre-
sent unique problems- :(e.g. odor, sidestream treatment, energy
efficiency). Air drying processes are available for small
plants but, because of land area requirements, are generally
not suitable for large municipalities.
The C—G process apparently does not have the negative
characteristics of existing dewatering/drying technology, is
ôost—effective and is energy efficient. Because of the nation-
wide need of small and large agencies for a more effective and
efficient wastewater residual solids dewatering/drying process
and because the C—G process is modular in design and adaptable
to municipal wastewater facilities of 10 mgd capacity and
greater, it appears that the nationwide market potential is
significant.
Risk factors that currently limit the market potential
include:
o Limited experience with wastewater residual solids.
Although the C—C process has a successful history in
the food processing and other industries, full scale
experience with municipal wastewater residual solids
is limited to two facilities in Japan. There are no
full—scale operating facilities currently processing
municipal wastewater solids in the U.S. The Los
Angeles HERS project is the first full—scale design
in the U.S.
62

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o The C—G process is mechanically complex. History of-
the wastewater treatment industry indicates that
mechanically complex processes are a source of major
operating and maintenance problems. However, the
limited experience with the C—G process in the waste—
water industry to date indicates that operation and
maintenance problems are within the capabilities of
municipal wastewater agencies.
Fcs:e:— r C:: or. ma:t E C— z :
U.S. and can also act as tne designer. However otr ers are not
precluded from designing the system as long as a license fee is
negotiated directly with Dehydrotech. For example, the City of
LOS Angeles license fee has been negotiated directly with
flydrotech without Foster—Wheeler involvement.
There is no sole source equipment or appurtenant hardware
in the C—G system. In the LOS Angeles design, Foster—Wheeler
developed plans and specifications for the C—G equipment while
other consulting engineers prepared the overall system design.
The construction will be competitively bid by general con-
tractors which is normal municipal practice.
COST AND ENERGY IMPACTS
It appears that the cost and energy impacts on a national
level would not be significant but could be significant for a
local agency/municipality. In addition to annual cost and
energy savings for solids dewatering/drying, there would be
significant cost and energy savings associated with the
transport and disposal or- use of the resiaual solids because of
the dryness and, therefore, reduced volume.
In making cost and energy comparisons with other
mechanical, chemical, heat, and air drying methods, it is
important to compare the processes on a wet weight/volume basis
as well as a dry weight/volume basis. The end product wetness
and volume varies with each process and determines the final
cost of disposal or use. Likewise, site specific comparisons
for decision—making should be made on a total system basis
(e.g. dewatering, drying, disposal/use) rather than a unit
process basis.
The C—G process is generally cost—effective in modules to
service a range of treatment plant capacity from about 10 mgd
to over 300 mgd. A.lthough the process has been used on a pilot
scale of 1 mgd capacity or less, it is generally not cost—
effective at less than 10 mgd wastewater plant capacity.
63

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LIST OF REFERENCES
1. Metcalf and Eddy of New York, Inc., Consulting Engineers.
The .Carver—Greenfield Process State—of—the—Art for
janicipal Sludge Manaaernent — An Evaluation . July,
1979.
2. LA/OMA Project, Regional Wastewater Solids Management
Program. Carver—Greenfield Process Evaluation — A
Process for Sludge Drying . December, 1978.
3. Foster Wheeler Energy Corporation. The Carver—Greenfield
Process for Sewage Sludge Disposal . March, 1981.
4. Camp, Dresser & McKee, Inc. and Alexander Potter Asso-
ciates.. Alternatives for Sludge Management in the
New York —New Jersey Metropolitan Area , Report of
the New York—New Jersey Interstate Sanitation Com-
mission. June, 1975.
5. Villiers, R., Grossman, E., and Farrell, J.B. Brief Ex
loratory Study of Distillate Ouality from the
Distillation of an Oil—Primary Sludge Mix-
ture . Technical Memo to Records, National Environ-
mental Research Center, U.S.E.P.A., Cincinnati, Ohio,
January 6, 1976.
6. City of Los Angelesr Bureau of Engineering, Carver—Green—
field Process Applied to Sewage Sludge Dewatering,
Report on Pilot Tests Conducted at Hyperion Treatment
Plant. Playa del Rey. California , February, 1976.
7. Campbell, C.J., A Pilot Demonstration of the Carver—
Greenfield Sludge De ater.inC ProceS. . Weyer-
haeuser Co., Cosmopolis, Washington. February, 1977.
8. Bays, LD., Engineering the Disposal. of Waste Activated
Sludge . International Pollution Engineering Con-
gress, Philadelphia, Pennsylvania. October 22—25,
1973.
9. LA/OMA Project, Regional Wastewater Solids Management
Program, Sludge Processinc and Disposal. A State of
he Art Review , April, 1977.
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10. U.S. Environmental Protection Agency. Process Design
Manual Sludoe Treatment and Disposal . EPA 625/1—79—
00].. September, 1979.
11. Metcalf and Eddy of New York, Inc., Consulting Engineers.
The y erion Energy Recovery S!ste , Report to the
— - City of Los Angeles. October 1981.
12. U.S. Environmental Protection Agency. Innovative and
Alternative Technoloov Assessment Manual . EPA 430/9—
78—009, CD—53. February, 1980.
13. City of Los Angeles, Bureau of Engineering. Fluidized Bed
Combustion of Sludge Derived Fuel , Results of Demon-
stration Studies to Develop Design Criteria and Air
Emission Factors. January, 1982.
65..

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