REPORT ON A STUDY

     OF THE ALEXANDRIA, VIRGINIA INCINERATOR



      This report (SW-12ts) was written by
                TOBIAS A. HEGDAHL
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
    Public   Health   Service
          Environmental Health Service
        Bureau of Solid Waste Management
                      1970

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Single copies of this publication will  be distributed as supplies
permit.  Address requests to the Bureau of Solid Waste Management,
Office of Information, 5555 Ridge Avenue, Cincinnati, Ohio  45213-

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                            FOREWORD






     Incineration  is an important method of solid waste processing  in




the United States, and although over 300 incinerators are  in operation,




little information on the performance of these units  is available.   It




is therefore not surprising that the effects of incineration on the




environment are little understood and frequently ignored.




     An incinerator discharges effluents into the environment  in three




states:  solid, liquid, and gaseous.  The sources of  these effluents




are the processes of combustion, gas cleaning, and residue quenching.




Any determination of the pollution contribution to the environment by




incineration must be concerned with all these effluents.




     The Bureau of Solid Waste Management, through the Division of




Technical  Operations, has initiated a testing program to characterize




the performance of incinerators of different designs and configurations.




The primary objectives of this program are to produce basic information




that identifies the results of the incineration process and to develop




reliable sampling methodology.




     During the studies it is considered necessary to make a complete




analysis of all features that affect the operation of the facility as




well as those that influence its potential  for environmental  pollution.




The operation of the facility is not altered in any way unless  specific
                                   i i i

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study objectives dictate a change.  Therefore, no special effort is

made to operate the facility at its design capacity; rather, it is

tested at its "operating" capacity.

     Reports from each study in this program will be prepared primarily

for use by the management of the facility, although they will be

available upon request to other interested technical personnel.  Each

report will  contain only the data obtained during one individual study.

Data comparisons with other studies will not be made in individual

study reports.  Summaries and comparisons of the data from all  studies

will be reported annually.
                                    --RICHARD D. VAUGHAN, Direotov
                                      Bureau of Solid Waste Management

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                            CONTENTS


INTRODUCTION  	    1

SUMMARY 	    3

DESCRIPTION OF ALEXANDRIA, VIRGINIA,  INCINERATOR   	    5

   Operating Procedure  	    5

   Plant Layout	,	    6
                                         «•
   Incinerator Design 	    8

   Maintenance	,	   1*4

METHODS AND PROCEDURES  	   17

   Input and Output Measurements	   17

   Sampling Techniques  	   18

RESULTS	   23

   Overall  Plant Efficiency 	   23

   Stack Tests	   25

   Incoming Solid Waste and Residue Composition 	   27

   Heat Contents and Burning Efficiency  	   27

   Liquid Effluents 	   30

   Cost Analysis  	   32

REFERENCES	   38

ACKNOWLEDGMENTS 	   39

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APPENDICES  ............................   41

   A  Example Calculations for the Ash, Volatile, and
      Heat Content of the Solid Waste  ...............   43

   B  Example Calculations for the Ash, Volatile, and
      Heat Content of the Residue .................   kj

   C  Plant Efficiency Calculations ................   51

TABLES

   1  Incinerator Performance Data  ................   24

   2  Stack Effluent Data .....................   26

   3  Composition of Solid Waste  .................   28

   4  Composition of Residue Samples   ...............   29

   5  Solid Waste, Residue,  and Fly Ash Heat Contents .......   29

   6  Volatile and Ash Content  ..................   30

   7  Liquid Effluent Analysis  ..................   31

   8  Total Annual Cost ......................   33

   9  Annual Operating Cost by Cost Center  ............   35

  10  Breakdown of Annual Repair and Maintenance Cost .......   36

  11  Cost Projections for Full Capacity  .............   37

 A-l  Proximate Analyses of the Combustible Portion
      of the Solid Waste Samples  .................   43
 A-2  Conversion of the Separation Data to a Dry Basis
 B-l  Proximate Analyses of the Unburned Combustibles
      and Fines ..........................  47

 B-2  Conversion of Residue Separation Data to a Dry Basis  ....  48
                                     VI

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FIGURES




   1   General  Layout  of  Alexandria,  Virginia,  Incinerator  	    7




   2   Furnace  Schematic  of  Alexandria,  Virginia,  Incinerator   ...    9




   3   Scrubber Schematic of Alexandria, Virginia,  Incinerator  ...   12




   k   Incinerator  Cost Centers, Alexandria, Virginia   	   3^
                                  VI I

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       REPORT ON A STUDY OF THE ALEXANDRIA, VIRGINIA, INCINERATOR






     The Division of Technical  Operations of the Bureau of Solid Waste




Management provides technical  information and assistance to public and




private agencies, organizations, and individuals throughout the country.




In October 196? Mr. Leroy Stone, Solid Waste Management Representative,




Bureau of Solid Waste Management, Region III was contacted by the City of




Alexandria, Virginia, regarding the possibility of having their incinerator




tested.  The city was interested in finding out if recently made changes




in furnace operation had affected particulate emissions.  Since the




National Air Pollution Control  Administration had conducted stack-emission




tests in April 1967, before the changes in operation were made, a direct




comparison would be possible.




     Testing the incinerator would not only satisfy Alexandria's need for




stack-emission data, it would also further the Division of Technical




Operation's efforts to develop basic information about the environmental




pollution potential of incinerators.  A study was, therefore, conducted




from May 18 to 25,  1968.

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                                 SUMMARY






     The burning rate of each furnace during the study week, May 20-24,




1968, averaged 6.42 tons per hr, slightly more than rated capacity.  The




plant was designed to burn 6.25 tons of solid waste per hr per furnace,




or 300 tons per day for both furnaces, with a heat content of 5,000 Btu




per Ib.  Laboratory analysis revealed that the gross heat content available




in the incoming solid waste averaged approximately 4,300 Btu per Ib.




Annual figures indicate, however,  that based on a 5~day week, the plant




burns an average of 250 tons per day.  This can be explained partly by




the fact that when the supply of solid waste is low, one furnace is shut




down.  When operating, however, the furnaces do burn close to design




capaci ty.




     The average particulate-emission rate with one furnace operating




was 0.88 gr per standard cubic foot (scf)  corrected to 12 percent C0?.




With both furnaces operating, the  average emission rate was 1.12 gr per




scf at 12 percent C02-




     The National Air Pollution Control  Administration had conducted




stack-emission tests on the incinerator in April  1967, before an increase




in underfire air was made to reduce slag buildup  on the grates.   The




average of their three tests with  both furnaces operating was 0.26  gr




per scf at 12 percent CO-.

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     All wastewater from the plant operation is discharged into the




city sewer system.  In both the residue-quench and fly ash scrubber




systems, water is recirculated for 1  week before discharge.  Makeup




water is obtained from the city water supply.  The extreme acidity




that occurs in the fly ash scrubber water necessitates a soda ash




neutralization system to protect equipment from corrosion.




     The plant employs 2k full-time personnel to work the three shifts




each day.  Solid waste is burned Monday through Friday, and the plant is




open until noon on Saturday to receive waste.  The cost of plant operation




was $4.90 per ton of solid waste burned.  The total cost per ton,




including depreciation came to $7.26.




     Total weight-reduction efficiency of the incinerator was approximately




68 percent on a dry basis.  The residue contained an average of 2.0




percent volatiles, and the fly ash had 13.9 percent volatiles.  Total




weight  reduction of volatiles was approximately 99 percent.  Approximately




99 percent of the available heat was released during incineration.




     The operation of the plant was well managed.  Complete records of




the data taken from the  instrumentation are kept on file for possible




future  reference.  The working atmosphere was clean, and employees did




their jobs effectively.

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            DESCRIPTION OF ALEXANDRIA, VIRGINIA,  INCINERATOR






                           Operating Procedure






     The Alexandria, Virginia, municipal  incinerator  is  located  in  the




southeastern section of the city at 5301 Wheeler Avenue.   It was placed




in operation in October 1966 and handles the solid waste generated  by




household, commercial, and industrial sources in Alexandria and Cameron




Station.  The total population served numbers about 100,000.  Operating




funds are provided from the municipal budget.




     Plant operation is under the administrative control of the director




of public works, but the plant superintendent is directly  in charge of




the day-to-day operation.   The plant operates three shifts a day and




requires 2^4 full-time employees.  Both the foreman and the superintendent




have offices at the plant.  Employees understand their jobs and perform




them efficiently.




     All trucks using the incinerator are required to secure a tag  that




is valid for 1  year.  When the tag is issued, the tare weight of the




vehicle is recorded.  A full-time operator is on duty during the hours




the plant is open to receive solid wastes, and all incoming trucks are




weighed on semi-automatic scales of 45,000-lb capacity.  The residue




and fly ash trucks leaving the plant while the operator is on duty are




also weighed.   Normally, estimates are made on the weights of residue

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and fly ash that are removed when the scales are closed.  During the study,




however, all fly ash and residue were weighed to enable reduction-efficiency




calculations to be made.




     The incinerator is open to receive solid waste from 7 am to 5 pm on




weekdays, and from 6 am to 12 noon on Saturday.  Both furnaces are fired




up on Monday morning and are usually run continuously until Wednesday




evening or Thursday morning, when one is shut down because the supply of




solid waste is usually  insufficient to keep both furnaces in operation




all week.  The furnace  is fired up again Thursday evening or Friday




morning, and both furnaces are run continuously until very early Saturday




morning, when the pit is emptied.  The solid waste coming in Saturday




morning remains in the  pit until  operation begins Monday.




     Inflammable liquids and hazardous dusts such as pulverized coal,




flour,  and sawdust are  excluded from the incinerator.  Any material




that the plant foreman  feels may be harmful to the operation is also




rejected and hauled to  a landfill.






                              Plant Layout






     The incinerator is located in an industrially zoned area with no




residences  in the immediate vicinity.  A fence with two lockable gates




borders the entire plant, and the area (Figure 1) is well landscaped




and free of 1i tter.




     The plant structure is of conventional brick design with one storage




pit and a covered, ventilated tipping area that can accommodate eight




trucks at a time.  The  storage pit is 111 ft long, 23.5 ft wide and

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        N
Figure 1.   General  layout  of  Alexandria,  Virginia,  incinerator.

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32 ft deep.  It has a level  capacity of approximately 3,000 cu yd and




is capable of storing 2 days of solid waste.




     The building has four floors.  A large meeting room and the residue




dumping area are on the ground floor, the furnaces and offices are




located on the second floor, the employee facilities are on the third




floor, and the charging hoppers are located on the fourth floor.




     The plant environment is very clean, with a charging floor, tipping




area, furnace room, and residue-disposal  area that are nearly dust and




odor free.  Temperatures are not excessive in any working area.  Drinking




fountains and soft-drink machines are located throughout the plant, and




employees have access to a refrigerator and stove in their lunchroom.  A




large locker room is also available for employees to shower and dress.






                           Incinerator Design






     Furnaces.  The incinerator was designed to burn 300 tons per 2k hr




of operation.  The two identical, continuous-feed furnaces have rocking



grates and a common 200-ft stack (Figure 2).  Each is designed to burn




6.25 tons per hr, or 150 tons per day.  The design was based on a solid




waste heat content of 5,000 Btu per Ib.



     Combustion gases are partially cleaned by passing them through a




water-spray baffle scrubber.  Residue from both furnaces is water-quenched




in a common tank and removed by conveyor.  The highly acidic scrubber




water is neutralized with soda ash before being pumped to a settling




basin, where the resulting sediment is removed with a conveyor.

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     The furnace chambers were manufactured by Plibrico.*  The primary

combustion chamber is approximately 3^ ft long, 8 ft wide, and 8 ft

high.  The brick refractories are 8 in. thick.

     An automatic hydraulic system controls tne three separate sections

of grates (manufactured by Flynn and Emrich), which can be set to rock

at various speeds and in various cycles.  The grates nearest the

residue-quench tank are usually run one-fifth as fast as the middle

grates.  The first section of grates is essentially for drying, and

most of the burning occurs on the next two sections.  Approximately

30 min are required for solid waste to pass from the charging hoppers

to the residue-quench tank.

     A thermocouple located  in the secondary combustion chamber is

connected to a buzzer alarm that rings when the temperature exceeds

1,450 F.  Operating experience has shown that when this temperature

is reached in the secondary combustion chamber, the temperature is

high enough in the primary chamber to cause slagging and refractory

deterioration.  Adjustments are then made in grate speeds and/or

auxiliary air to lower the temperature.

     Each furnace is equipped with underfire and overfire air fans

that are  rated at 19,000 cfm each, with the dampers fully open.  The

underfire air fan is usually run with  the damper half open, which is

equal to  about 75 percent of the available fan capacity.  Overfire

air  fans  are usually operated with the dampers one-eighth open, which

is equal  to about 20 percent of the fan capacity.  A 200-ft stack
      "The mention of commercial products does not imply endorsement by
 the U.S. Public Health Service.
                                      10

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provides the necessary natural draft for removal of combustion gases




from the combustion chamber.




     Charging System.  Solid waste is charged into the furnace hoppers




with a 2.5-cu-yd grapple attached to a P S H overhead crane of ^-ton




capacity.  A standby crane is not available.  The operator sits in an




enclosed moving cab and feeds each furnace through separate charging




hoppers.  The solid waste is fed both by gravity and by the movement




of the furnace grates from the charging hoppers, through the charging




chutes, and into the furnaces.  The charging chutes are water-cooled to




protect them from excessive heat buildup.




     Air Pollution Control Equipment.  After the combustion gases leave




the primary combustion chamber they pass through a flue into the secondary




combustion chamber before entering the spray-baffle scrubber (Figure 3).




A set of pressurized nozzles spray water down the firebrick baffle walls




from above.  The combustion gases make two 90° turns while passing




through the baffle walls, thus causing the particulates to impinge




upon the wetted surfaces where some are entrained in the water droplets.




Water is pumped through the scrubber system at a rate of 500 gpm.   The




scrubber water, laden with fly ash, is processed through a fly ash




settling basin and pumped back to a sump tank for recirculation.   Before




entering the settling basin, however, the water is treated with soda ash




to reduce the extreme acidity of the water.  Sedimentation and neutrali-




zation are the only treatments the scrubber water receives before  its




once-a-week discharge into the city sewer system.   Replacement and make-




up water come from fresh city water.   Make-up water is  pumped through
                                     11

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the charging chute cooling system before  it  is utilized  in  the  scrubber




and residue-quench systems.




     Residue and Fly Ash Removal Systems.  The residue from each furnace




falls off the last section of grates  into a  common quench tank where  it




is removed by conveyor to a truck.  The plant is equipped with a reserve




quench tank and conveyor system.  A movable  flap gate diverts the residue




to one system or the other, and  in this way, plant operation  is not




impeded if a conveyor fails.  The water from the residue-quench tank  is




recirculated at a rate of 300 gpm from a sump tank that  is separate from




the scrubber-water sump tank.  The material  that settles out  in the sump




tank is removed Monday morning when fresh water is added.  The residue-




quench water, untreated except for sedimentation,  is discharged into




the city sewer system at this time.




     The sludge from the bottom of the fly ash settling basin is removed




by conveyor to a truck.  Both residue and fly ash  were weighed during




the study, then hauled to a disposal  site located  on Wheeler Avenue about




i mile from the plant.  The disposal  site is leveled off and covered about




four times a year.




     Instrumentation.  The incinerator is equipped with an upright  Honeywell




instrument panel  located on the furnace floor between the two furnaces.




Controls for regulating the hydraulic grates are  located on  each furnace.




The instrument panel  contains continuous-recording circular  charts  that




record readouts  of  temperatures for each secondary combustion chamber




as well  as the temperature in the stack.  Underfire and overfire air-




pressure gauges  are located on the instrument panel.   Air flow is
                                     13

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regulated by adjusting the dampers.  The stack draft and the vacuum




between the breeching and the combustion chambers are indicated on gauges




located on the instrument panel.  A continuous-recording circular chart




indicating smoke opacity is also on the panel.  Manual  readings of water




temperature in the water-cooled charging chutes are taken hourly with a




thermometer to indicate possible heat buildup in the chutes.




     Each furnace is controlled by an operator who monitors the instrument




panel and makes necessary adjustments in grate speeds and overfire and




underfire air to keep combustion as efficient as possible.  If temperatures




in the secondary combustion chamber become too high (about 1,450 F) ,  a




buzzer alarm rings and necessary adjustments are made.   The degree of




burnout in the residue is observed to determine whether grate speeds




should be changed to vary the residence time of the solid waste in the




furnace.  The furnace temperature and the completeness  of combustion  can




also be regulated by varying the overfire and underfire air.  These




methods are used in combination to obtain the desired operating conditions.



Readings are taken every hour from all instrumentation  and filed for




future reference.  The charts from the continuous recorders are also




kept on file.






                              Mai ntenance
     Minimal corrective maintenance has been required in most aspects of




plant operation, but problems with clinker buildup on the grates did




develop soon after the plant was opened.  The problem was alleviated




by  increasing the underfire air rate.  The increase in underfire air

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resulted in excessive fly ash blowover into the secondary combustion




chamber, which reportedly lowered the pH in the scrubber water.  To




prevent the acidic water from corroding the pumping and settling basin




equipment, a soda ash neutralization system was added.  This treatment




takes place after the water is drained from the scrubbers and before it




enters the settling basin.   The cost of the treatment is about $2,500




per yr.  When the cost of the grate replacement is compared to the cost




of the neutralization system after the underfire air rate was changed,




the expenditure was certainly justified.  However,  as discussed later




under Results, the increased underfire air probably did substantially




increase stack emissions.  During the first year and a half of operation,




a total of 98 grate sections were replaced, but most of them were re-




quired before the changes in the underfire air rate were made.  Each




grate section costs $2^0 and requires about 1  hr to replace.




     Routine maintenance work is done on  Monday mornings before the




furnaces are fired.  The only other maintenance that has been required




has been patchwork on the refractories and frequent repairs on the smoke




opacity meter.
                                     15

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                         METHODS AND PROCEDURES






     The methods and procedures used in this study were designed to give




an overall view of the potential for air, water, and land pollution that




the incinerator has on the surrounding environment.  The study was also




undertaken to provide information on the characteristics of solid wastes.




     During the week of the tests, the incinerator was operated normally,




which meant that one furnace was shut down on Thursday, May 23.  Four




stack tests were performed while both furnaces were operating; two were




performed with one furnace operating.  Sampling of all effluents was




done simultaneously.






                      Input and Output Measurements






     All incoming solid waste is weighed on the incinerator scale before




it is dumped into the storage pit.  Efforts were made to obtain a more




accurate measurement of the charging rate while stack tests were being




conducted Ly weighing the grapple loads on a platform scale before they




were charged into the furnace.  Difficulties were encountered in keeping




the crane cables slack and in keepsng the solid waste in the grapple




while weighing, thus making it impossible to gather more definitive data.




     The average charging rate over the study week was determined by




dividing the total  number of furnace operating hours into the number of




tons of solid waste received and burned from May 18 to 2k,  1968.   The

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residue and fly ash were also weighed during the study week to determine

the reduction efficiencies.


                          Sampling Techniques


     Incoming Solid Waste.  Samples of incoming solid waste were taken

on Monday, Tuesday, and Wednesday.  The solid waste samples were obtained

by dumping a partial grapple load of what was considered typical waste

(determined by visual inspection) onto a plastic drop cloth on the charging

floor.   The sample was then separated into the following nine categories:


          Combustibles:                       Noncombustibles:
          Food wastes                         Metal products
          Garden wastes                       Glass and ceramic
          Paper products                        products
          Plastics, rubber, and               Ash, dirt, and rocks
            leather
          Textiles
          Wood
     After separation, materials in each of the categories were weighed.

The total sample weight was then calculated, and the percent by weight

of each category was determined.  Using these percentages, a 10- to 15-lb

sample was reconstituted by weight from the combustible categories.

Noncombustibles were assumed inert and were excluded from this sample to

make the  laboratory grinding less troublesome.  Laboratory analysis of

the sample included determinations of moisture content, heat content,

percent volatiles, and percent ash.  The analysis indicated that adequate

precautions to protect against moisture loss were not taken, thus making

it necessary  to estimate the moisture content.  Once the sample was

well mixed and dried, the volatile and ash analyses were performed on
                                     18

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a portion of the sample according to procedures outlined  in Appendix  A




of Tentative Methods of Analysis of Refuse and Compost  in Mun icipal




Refuse Disposal.1  The heat content was determined on a well miAed,




dry portion of the sample  in the Parr Adiabatic Calorimeter by  the




method outlined in the Parr Instrument Company's Manual Number  130.2




     Res i due. Furnace residue samples were taken on Tuesday, Wednesday,




and Thursday of the test week for determination of burning efficiency.




Approximately 15 gal of residue were caught in a 30-gal drum as  it was




discharged from the residue conveyor.  The sample was allowed to dry  for




several hours and was then separated by hand Into three categories:




metals, glass and rocks, and unburned combustibles and fines.




     After the larger pieces of unburned combustibles (glass, metal,




and rock)  were removed, the remainder of the sample was sifted  through




a i-in. mesh screen to remove the fines.  The weight of each category




was recorded, and all the unburned combustibles and fines were  returned




to the laboratory for analysis.  The remainder of the sample was discarded




and assumed to contain no heat, moisture, or volatiles.  Laboratory




analysis of the residue was the same as for the Incoming solid waste




except that the moisture content was determined from one sample taken




from the conveyor in a 6-gal plastic container that was tightly sealed




to guard against moisture loss during shipment to the laboratory.




     Fly Ash.  Fly ash samples were taken from the fly ash conveyor.




A 1-gal composite sample was taken for the 3 days of stack testing and




was returned to the laboratory for the same analyses that were made




on the solid waste and residue.

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     S_t£d£jijFfJjjen_tJ._  The majority of time and effort during  the week was




devoted to sampling the stack effluent.  Monday was spent  in  setting up




the sampling equipment.  Two tests were made on both Tuesday  and Wednesday




when both furnaces were operating, and two tests were made on Thursday




when only one furnace was operating.




     The two stack sampling ports were located 100 ft above the ground




and l80 degrees apart.  Equipment was set up on a catwalk  located at this




level,  TVelve points across the diameter of the stack were sampled during




each test.  Each point was sampled for E> min, making a total  sampling




time of 1 hr,  SEX of the points were sampled from each port.  Approximately




15 min were required to move the sampling probe between the ports during




the test.  The sampling was done approximately 10 stack diameters up




from the top of the breeching at the base of the stack.  The  maximum




velocity head encountered during testing was 0.32 in. of water.  A 3/8-




in. diameter nozzle, wa-j used on che sampling probe.  Two particulate




coiU-ction boxes were required per test because of plugging problems




encountered wHh t*e glass fiber filters.  The plugging occurred because




of part i cu i .3i~e huiUup o>'> the filter, which prevented maintenance of




isokinetic sampling conditions.




     The procedures used  in stack sampling are described in the publication




Specifications for  Incinerator Testing at Federal Faci1ities3 and the




addendum  to that publication.  The particulate samples returned to the




laboratory were analyzed  according to the procedures outlined in that




publi cation .
                                     20

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     Liquid Effluent.  Liquid samples of 1 liter were taken from the




residue quench tank and the fly ash settling basin during each day of




stack sampling.  Half of each sample was collected during the mcrning




tests and half during the afternoon tests.  It was not possible to




collect samples of the scrubber water before the neutralization process.




The samples were sealed, labeled, and returned to the laboratory for




determination of solid, chemical, and biological characteristics.  The




samples were analyzed according to procedures  outlined in Standard




Methods for Examination of Water and Waste Water.**  Separate grab samples




were collected and delivered to the Alexandria Sanitation Department




where BOD tests were performed.
                                    21

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                                 RESULTS






                        Overall Plant Efficiency






     During the week of the study, 1,271.8 tons of solid waste were




received and burned.  With the furnaces operating a total of 198 hours,




the average burning rate was 6.1*2 tons per furnace per hour.  The storage




pit was emptied before and after the study week, and all incoming solid




waste and solid effluents were weighed during the week.  The burning




rates of the furnaces could not be determined on a daily basis because




burning was not continuous and the solid waste was not completely burned




until the end of the week.  The moisture contents for the residue and




fly ash were obtained from single samples taken for that purpose.




Laboratory data for the moisture content of the incoming solid waste




were unrealistically low (5 to 15 percent), considering that the wastes




were visibly wet.  This indicates that not enough precaution had been




taken in sealing the sample containers for shipment back to the laboratory.




An estimated moisture content of 20 percent was assumed for all calculations




(Table 1).




     The overall weight reduction efficiency for the week was approximately




68 percent, weight reduction in volatiles was approximately 99 percent,




and the percentage of heat released was approximately 99-  These calcula-




tions are shown in Appendix C.
                                     23

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                               Stack Tests






     A total of six stack tests was conducted during the study week.




The results of the particulate emissions tests are expressed in three




different ways (Table 2.)




     A spectrographic analysis of the particulate matter collected on




the filter paper used during the stack tests was conducted to determine




the metallic elements present in the stack effluent.  The most prominent




elements were aluminum, lead, tin, and zinc, but none were present in




great quantity.




     Because a qualified smoke reader was not available during the study




and the smoke opacity meter on the instrument panel was not functioning,




a comparison of the Ringlemann number to particulate loadings could not




be made.




     The National Air Pollution Control  Administration had conducted




stack-emission tests on the incinerator in April 196?, before the increase




in underfire air was made to reduce slag buildup on the grates.   The




average of their three tests with both furnaces operating was 0.26 gr



per scf at 12 percent carbon dioxide, which may be compared with this




study's average of 1.12 gr per scf at 12 percent carbon dioxide  with




both furnaces operating (Table 2).  The increased turbulence caused by



the additional underfire air appears to have increased particulate




emissions by a factor of approximately four.  The sampling techniques




and equipment used for the two studies were identical  except that  the




National Air Pollution samples were taken at only two points along the




stack diameter, compared with the 12 points used during this study.
                                     25

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              Incoming Solid Waste and Residue Composition






     A total of seven samples was separated (Table 3) on an as received




basis into nine categories during the week of the study.  Three residue




samples were separated to determine their composition during the week of




the study (Table k).






                  Heat Contents and Burning Efficiency






     Laboratory analysis to determine heat content was performed on the




incoming solid waste, residue, and fly ash by standard bomb calorimetry




(Table 5).  The data for the solid waste are representative of the solid




waste as received at the incinerator.  Data for the fly ash and residue




are on a dry basis.  Appendix A shows the methods for calculating the




data for the solid waste, and Appendix B shows the methods for calculating




the data for the residue and fly ash.




     For the three samples analyzed, the incoming solid waste had an




average gross heat content of A,320 Btu per Ib.   This is below the 5,000-




Btu-per-lb design heat-release rate, but the heat content can fluctuate




considerably because of seasonal variation in solid waste composition.




The furnace residue had an average gross heat content of about 200 Btu




per Ib, and the composite fly ash sample contained 180 Btu per Ib.




     The laboratory analyzed the combustible portion of the solid waste




samples for the percent volatiles and ash (Table 6).  The noncombustibles




were discarded in the field after their percentage by weight of the total




sample had been determined.  The percent volatiles and ash for the total
                                     27

-------






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sample (combustibles and noncombustibles) were calculated from laboratory




values by assuming that the noncombustibles contained no moisture, were




completely ash, and contained no heat.






                                 TABLE 4




                     COMPOSITION OF RESIDUE SAMPLES*
Date of sample
Component
Unburned combustibles
and fines
Metal
Glass
Total
5-
Ib
31
9
23
63
21-68
%
1*3.2
14.3
36.5
100.0
5-22-68
Ib
31.8
10.0
21.0
62.8
%
50.6
15-9
33.5
100.0
5-23-68
Ib
38
9
19
66
%
57.6
13.6
28.8
100.0
Average %
52.5
14.6
32.9
100.0
     'Data on a wet basis although the samples were allowed to drain.









                                 TABLE 5




             SOLID WASTE, RESIDUE, AND FLY ASH HEAT CONTENTS
Date
5-20-68
5-21-68
5-22-68
5-23-68
Average
Sol i d waste
(Btu/lb, as
received basis)
4,140
4,260
4,550
---
4,320
Residue Fly ash*
(Btu/lb, (Btu/lb
dry basis) dry basis)
___
180
170
250
200 180
          "A composite sample was  analyzed.
                                    29

-------
                                  TABLE 6

                         VOLATILE AND ASH CONTENT
                                (Dry basis)
Material and date tested
Incoming solid waste:
May 20
May 21
May 22
May 23
Average
Res i due :
May 21
May 22
May 23
Average
Volati les
(*)

65. k
69.0
70.3
---
68.2

1.8
1.8
2.3
2.0
Ash
(°A
\'o)

3^.6
31.0
29.8

31 .8

98.2
98.2
97-7
98.0
     Fly ash:
       May 21-23*                      13-9            86.

          "One composite sample was analyzed.
     The same procedure was used to determine the volatiles and ash  in

the total residue sample, because only the unburned combustibles and fines

were returned and analyzed in the laboratory.  The percentages of glass

and of rocks and metals were determined in the field, and these two

categories were then discarded.  The fly ash sample was returned in  its

enti rety.


                            Liquid Effluents


     Laboratory analysis was also performed on the fly ash scrubber water

and the  residue quench water (Table 7)-  The residue quench water is

recirculated at the  rate of 300 gpm, and the fly ash scrubber water  is
                                      30

-------
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                                               31

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recirculated at 500 gpm.  Both systems are drained and flushed at the




end of each week and replenished with fresh water from the city water




supply.  The acidic water from the fly ash scrubber is neutralized with




soda ash and is then circulated through a settling basin, where the




entrained fly ash is removed.  This water is then pumped to the sump




tank for recirculation.  As stated earlier, it was impossible to get a




sample before the soda ash neutralization process.  The residue quench




water  is recirculated from a separate sump tank with no settlement except




that which takes place  in the conveyor tank and in the sump tank itself.




     the wastewater from the incinerator is discharged to the city sewer




system for treatment.  No additional treatment other than the soda ash




neutralization and sedimentation is performed on the process water before




di scharge.






                              Cost Analysis






     The total annual cost for incinerating 65,000 tons of solid waste




was $^72,082 (Table 8), yielding a unit cost of $7-26 per ton.  This




figure  includes both operating costs, depreciation, and interest costs.




The operating cost amounted to $^.90 per ton, or 67.5 percent of the




total.   Interest and depreciation costs amounted to $2.36 per ton, or




32.5 percent of the total.




     The capital cost of the plant was $1,978,7^0, excluding the cost




of  land.  The depreciation cost was calculated by using a 25-year plant




life and straight-1ine  depreciation.  The yearly interest was determined
                                     32

-------
                                 TABLE 8




                            TOTAL ANNUAL COST
1 tern
Annual operating cost:
Direct labor
Uti 1 i ties
Parts and suppl ies
Vehicle operating expenses
External repair charges
Disposal charges
Overhead
Subtotal
Annual financing and
ownership costs:
Plant depreciation
Vehicle depreciation
1 nterest
Subtotal
Total annual cost
Cost

$197,500
20,000
32,950
7,200
6,250
2,000
52,800
318,700


79,1^9
9,675
61*, 558
153,382
i»72,082
Percent of total

ltl.9
k.2
7.0
1.5
1.3
0.1*
11.2
67.5


16.8
2.0
13.7
32.5
100.0
by retiring the bond over the 25~year plant life at an interest rate of




3.2 percent.




     The operating costs were analyzed by breaking them into functional




cost centers:   receiving, volume reduction, and effluent handling and




treatment (Figure 4).  Operations involved in each cost center are also




shown.  The cost breakdown by cost center is shown In Table 9-




     The total  annual cost of repair and maintenance (Table 10)  for the




three cost centers was $76,7^7-   These repair and maintenance costs (labor,




parts, external charges, and overhead)  were allocated to each of the cost
                                     33

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                                TABLE 10

             BREAKDOWN OF ANNUAL REPAIR AND MAINTENANCE COST


          I tern                    Cost      Percent of total
Actual charge:
Labor
Parts
External charges
Overhead

$29,625
32,950
6,250
7,922

38.6
k2.S
8.2
10.3
   Total                          76,7^7          100.0
Cost center:
  Receiving                       9,112           11.9
  Volume reduction               56,826           7^.0
  Effluent handling
    and treatment                 10,809           1^.1

   Total                         76,7^7          100.0
of 250 tons.  Because the plant was designed to burn 300 tons a day, a

projection was made to estimate what the change in cost would be if the

plant were operated at design capacity (Table 11).  Although the total

annual cost would increase from $^72,082 to $^85,762, savings would be

made on a unit cost basis.  The greatest savings on a per-ton basis wouid

be in direct labor, since no additional men would be required, and in

financing and ownership costs.  The total cost per ton would be reduced

from $7.26 to $6.22.
                                     36

-------




















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-------
                              REFERENCES
1.   American Public Works  Association.   Municipal  refuse  disposal.
      2d ed.  Chicago,  Public Administration  Service,  1966.   p.  375-399.

2.   Parr Instrument Company.   Operating  the adiabatic  calorimeter.
      J^ Oxygen bomb calorimetry and combustion  methods.   Technical
      Manual No.  130.   Moline, 111., I960.  p.  30-32.

3.   National Center for Air Pollution Control.   Specifications  for
      incinerator testing  at  Federal facilities.  Durham,  N.C.,  U.S.
      Department of Health, Education,  and  Welfare,  Oct.  1967-   35  p.

k.   American Public Health Association,  American Water Works  Association,
      and Water Pollution  Control  Federation,   Standard methods  for the
      examination of water and wastewater;  including bottom sediments
      and sludges.  12th ed.   New York,  American Public Health Associa-
      tion, Inc., 1965.  769  p.
                                   38

-------
                             ACKNOWLEDGMENTS






     The author expresses his appreciation for the excellent cooperation




and assistance extended by the Alexandria Incinerator staff.  A special




thank you is extended to Mr.  P. B. Hall, Director of Public Works, Mr. Carl




Struder, incinerator superintendent, and Mr. Harry Dodson, incinerator




foreman, whose efforts were essential in planning and conducting the study.




The laboratory assistance provided by the Alexandria Sanitation Authority




in analyzing liquid samples is also greatly appreciated.




     The author is also grateful  for the aid and support  of the staff of the




Bureau of Solid Waste Management.   The Division of Research and Development




Operations provided the laboratory support for the study.  Members of the




field study team from the Bureau  of Solid Waste Management were:






          James S. Bridges                    Tobias A.  Hegdahl




          Richard A. Carnes                   Billy P.  Helms




          Dennis E. Carruth                   Albert E.  O'Connor




          Clyde J. Dial                       Thomas J.  Sorg




          John J.  Giar                        Charles S.  Spooner




          Robert Griffin                      Morris G.  Tucker
                                     39

-------
APPENDICES

-------
                               APPENDIX A


               Example Calculations for the Ash, Volatile,

                   and Heat Content of the Solid Waste


     Using the data from the laboratory analyses of the solid waste sample

collected on May 20, 1968, these calculations show the methods used to

calculate the ash, volatile, and heat content of the total sample.

     The laboratory analyses (Table A-l)  were performed on a dry basis.

The moisture contents shown are inaccurate and it was assumed that the

solid waste contained 20 percent moisture.  For the following calculation,

the assumptions were made that the noncombustibles contained no moisture,

no heat, and were considered as "ash."
                                TABLE A-l

              PROXIMATE ANALYSES OF THE COMBUSTIBLE PORTION
                       OF THE SOLID WASTE SAMPLES
Date sample
col lected
5-20-68
5-21-68
5-22-68
Moi sture
(%)
8.8
18.5
16.8
Volati le
U)
90.2
86.9
93.0
Ash
(*)
9.8
13.1
7.0
Heat
(Btu/lb)
71^5
7090
7530
     The moisture content of the combustibles is calculated by the following

method:

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  rcent moisture     /,,     .   ... .   \  / .,             \
  in total       =   (lb combust.bles \  f lb moisture   \
  samole             \   lb waste    /  \1b combust.ble/


                                  bustibleJ
Percent moisture
  in tot
  sample


  20.0 (assumed) = (0.78)  [^^i^J^.]  100.0

  Ib moisture    _     20.0
 lb combustible  ~ 100.0 (0.78)


      Because the volatile and ash fractions are calculated on a dry basis,

the percent combustibles must be converted to a dry basis by means of  the

following equation:
Percent
  combus
        dry    _  Mb wet combustibles - Ib moisture in combustibles]   ,nn
        tibles    \                  dry sample wt                  /
      These calculations are summarized in Table A-2.


                                TABLE A-2

            CONVERSION OF THE SEPARATION DATA TO A DRY BASIS


                      Wet weight        Moisture        Dry weight
^UIIIpUMfcJM L
Combustibles
iNoncombus ti bles
Total sample
(lb)
205-0
58.0
263.0
U)
78.0
22.0
100.0
(*)
25.6
0.0*
20 . 0*
(lb)
52.5
0.0
52.5
(Ib)
152.5
58.0
210.5
(%)
72. /t
27.6
100.0
     kAssumed.
      The percent volatiles and ash are calculated by the following method:
Percent volatiles
  in total sample
                      j    lb volat i les    \  Mb dry combustibles]   ,QO Q
                      \lb dry combustibles/  \   lb dry waste     /
Percent volatiles = (     }(    ^ }  >Q = 6
  in total sample

Percent ash in    ^ 100>Q _     ent volatiles
  total sample

Percent ash in    =
  total sample

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     The laboratory reports the heat content on a dry basis  for  the

combustibles only, thus the moisture content and the noncombustibles  in

the total sample must be considered when calculating the heat  content  of

the total sample.  The heat content of the total sample on an  "as  received

basis" was calculated by the following method:
Heat content
  in total
  sample
Btu
Ib dry combustibles
                1  -1
                           f% moisture
                              in total +
                              sample	
                    noncombustibles
                    in total samp 1e
                                100.0
Heat content
  in total   = 7145
  sample
     [.
     1  -
           .O + 22.0
            \
            ;j =
= 7145 (0.58) =
                                     45

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                               APPENDIX B






              Example Calculations for the Ash, Volatile,




              and Heat Content of the Residue and Fly Ash






     Using the data from the laboratory analyses (Table B-l) of  the




residue sample taken on May 21, 1968, these example calculations show




the methods used to calculate the moisture, ash, volatile, and heat




content of the total sample.  For each sample, only the fines and




unburned combustibles were returned for laboratory analyses.  The




laboratory volatile, ash, and heat content data are on a dry basis.






                                TABLE B-l




        PROXIMATE ANALYSES OF THE UNBURNED COMBUSTIBLES AND FINES
Date sample
col lected
5-21-68
5-22-68
5-23-68
Moi sture
(*)
2k. k
20.6
29.9
Volati le
(*)
k.2
k.\
Jt.8
Ash
(*)
95.8
95.9
95.2
Heat
(Btu/lb)
A37
383
513
     An additional sample was taken on May 22, 1968 which was analyzed for




moisture only.  It contained 2^.5 percent moisture and is the value used




in the efficiency calculations (Appendix C) and was assumed representative




of the residue.

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     Because the remaining calculations are on a dry basis,  the  separation

data (Table 4) must be converted to a dry basis by means of  the  following

equation:
Percent dry _  Mb wet component - lb moisture in wet component j  ,_n  -
  component    \              total dry sample wt               /
     It was assumed that all the moisture was  in the fines and unburned

combustibles and that the glass and metals were dry.  These calculations

are summarized in Table B-2.


                                TABLE B-2

          CONVERSION OF RESIDUE SEPARATION DATA TO A DRY BASIS
Component
Fines and unburned
combust! bles
Glass and rocks
Metal
Total sample
Wet weight
(Ib)

31
23
9
63
(%)

49.2
36.5
14.3
100.0
Moi sture
(*)

2lt.lt
0.0*
0.0-
12.1
(Ib)

7.6
0.0
0.0
7.6
Dry weight
(Ib)

23. 4
23.0
9.0
55.4
T°/\
'01

1*2.2
41.6
16.2
100.0
     -'Assumed.


     The percent volatiles and ash are calculated by the following method:


                                                  'lb dry fines and
Percent volatiles     [     lb volatiles       \ I   unburned combustibles
  in total sample     \lb dry fines and        ] \     lb dry  residue
                         unburned combustibles,

Percent volatiles =  (   ^ (Q ^}  ]QQ >Q = ]
  in total sample
                                                                             ioc.;

-------
Percent ash in    = ]QQ>Q _      nt vo]atiles
  total sample

Percent ash in    = 100>Q „ ,<8 = 98-2
  total sample


     The heat content is calculated on a dry basis by  the following method


                                           (\  /lb dry  fines and
                    	Btu	 I I   unburned combustibles
                    lb dry fines and        I I     lb  dry residue
                      unburned combustibles/  \

Heat content in = (ll37) (o>422) = ,8o
  total sample
     The volatile and ash contents of the fly ash as reported by the

laboratory were on a dry basis.  Therefore, no adjustment  is needed.  The

heat content, however, was reported as 1,290 Btu/lb on a moisture and ash

free basis.  The following calculation is used to adjust this value to

only a dry basis:
Heat content
  total sample
in _|	Btu	J  Mb dry volati les j
e   \lb dry volati les/  \ lb dry fly ash /
                                         "•9

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                                    APPENDIX C


                           Plant Efficiency Calculations


          These calculations show the methods used to calculate the  percent

     weight reduction, the percent volatile reduction, and the percent heat

     released.  The following data were used:
      Soli d waste
> ,271,8 tons wet
20 percent moisture
; ,017.4 tons dry
6-3,2 percent volatiles
'i,320 Btu/lb
'98.0 hr of burning time
Parti culate
186 Ib/hr
       Fly ash
       Res i due
31.0 tons wet
69.4 percent moisture
9.5 tons dry
13.9 percent volatiles
180 Btu/lb
399-5 tons wet
24.5 percent moisture
301.6 tons dry
2.0 percent volatiles
200 Btu/lb
                                          51

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-------