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 ------- 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. ------- 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 ------- 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- ------- 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 ------- 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 ------- 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- ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- — Patent status of light oil technology. 6- ------- 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 ------- 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 ------- 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). ------- 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 ------- 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 ------- 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 ------- 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- ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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. ------- 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 ------- 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 ------- 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 ------- 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 ------- 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. ------- 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). ------- 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 ------- 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 ------- 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— ------- 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 ------- 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 ------- 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 ------- 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 ------- 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. ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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-. ------- 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 ------- 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 ------- 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 ------- 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 ------- 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 ------- 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- ------- 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 ------- 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 ------- 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 ------- 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 ------- 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. 64 ------- 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.. ------- |