EPA  430/09-87-010
                SUMMARY OF THE
            1987 CARVER-GREENFIELD
       SLUDGE DRYING TECHNOLOGY WORKSHOP:
            PROBLEMS AND SOLUTIONS
           Held in Los Angeles, CA
           on March 10 and 11, 1987
                      by


:c:-.n Walker, Office of Municipal Pollution Control

                     and

      John Zirschky, ERM-Southeast, Inc.
         Contract No.  68-01-7108 with
    Environmental Resources Management, Inc.
                James Wheeler
               Project Officer
    Office of Municipal Pollution Control
     U.S.  Environmental Protection Agency
            Washington, D.C.  20460
                            (4- •

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               TABLE OF CONTENTS
                                                   Page

 LIST  OF TABLES                                      i ii
 LIST  OF FIGURES                                      iv
 EXECUTIVE SUMMARY                                     V
 OVERVIEW                                            1-1
 1.1  Introduction                                   1-1
 1.2  Report Format                                  1-2

 THE CARVER-GREENFIELD SLUDGE DRYING PROCESS         2-1
 2.1  Background                                     2-1
 2.2  Multiple Effect System                         2-2
     2.2.1  Process Description                     2-2
     2.2.2  Addback                                2-11
 2.3  Mechanical Vapor Recompression                2-14
 2.4  Light-Oil System                              2-16

 OPERATIONAL EXPERIENCES                             3-1
 3.1  Operating System                               3-1
 3.2  City of Los Angeles Hyperion C-C
        Treatment System                            3-1
     3.2.1   Project History                        3-1
     3.2.2   Cost                                   3-2
     3.2.3   Operational Problems                   3~-2
 3.3  Burlington Industries                          3-5
     3.3.1   System Description                     3-5
     3.3.2   Operational Problems                   3-6
 3.4  LA County Sanitation District
        Pilot System                                3-6
     3.4.1   System Description                     3-6

RECOMMENDATIONS                                     4-1
4.1  Introduction                                   4-1
4.2  Responsibilities for Design and
        Construction                                4-1
4.3  Design                                         4-4
     4.3.1   Philosophy                             4-4
     4.3.2   Plan and Specifications                4-5
     4.3.3   Equipment Selection                    4-5
     4.3.4   Plant Model                            4-7
4.4  Contractor Selection and Construction
        Activities                                  4-8

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                    TABLE OF CONTENTS  (Cont'd)
SECTION
          4.5  Operations
               4.5.1    Personnel  Requirements
               4.5.2    Operator Training
               4.5.3    Start-up and  Solids  Recycle
               4.5.4    Centrate Quality
               4.5.5    Excessive  Loss  of Carrier Oil
               4.5.6    Use  of  Dried  Sludge
               4.5.7    Process Monitoring and Control
          4.6  Innovative/Alternative  Technology (i .;
                  Funding  Issues
          4.7  Future Meetings

          REFERENCES
APPENDIX
   A      Seminar  Attendees
   B      Reviewers  Comments

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                           LIST  OF  TABLES
.Table                        Title                           Page



 2-1      Carver-Greenfield  Light Oil  Plants                  2-3

 2-2      Summary of United  States C-G Light Oil System      2-17

 2-3      Summary of United  States C-G Light Oil Systems
            Operation  Information and  Energy Requirements    2-18

 2-4      Summary of United  States C-G Light Oil Systems -
            System Redundancy                                2-19

 3-1      Process Problems and Corrective Measures;
            Burlington Industries C-G System                 3-7

 3-2      Mechanical and Physical Problems
            and Corrective Measures; Burlington
            Industries C-G System                            3-10

 i-4-^>      FW Scope of  Work Carver Greenfield Facility
 ~"         Step II Design                                   4-2

 C^2)     FW Scope of  Work Carver Greenfield Facility
            Step III Services                                4-3

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                          LIST OF FIGURES

Figure                        Title                         _l£2


 2-1        Process Flow Diagram of  the C-G  System           2-4

 2-2        Process Flow Diagram of  the MVR/C-C  System       2-8

 2-3        Schematic Diagram of the Oil Distillation
               System for the C-G Process                    2-9

 2-4        Addback Solids Flow Diagram for  the
               Multiple Effect C-G Process                  2-12

 2-5        Process Flow Diagram of  the MVR/C-G  System      2-15

 3-1        Schematic Diagram of the Hyperion Sludge
               Process" Facility                              3-3

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     CARVER-GREENFIELD  SLUDGE  DRYING TECHNOLOGY WORKSHOP:
                      PROBLEMS  &  SOLUTIONS

                      EXECUTIVE  SUMMARY


Four municipal wastewater  treatment  authorities have selected
the  Carver-G"°°nf'T1 ^  n ^ ghi" "* "*  sludge  drying  (C-G)  svstert
for  dewatering   their  sewage sludge.    Ocean  County, New
Jersey;theMercerCountyUtilityAuthority   (Trenton, New
Jersey);  the  City of Los Angeles,  California;  and the Los
Angeles,   California,   County   Sanitation   Districts  are
currently designing or  constructing  C-G systems.   The City of
Los  Angeles will  soon  begin operation of  their  265 dry ton
per day C-G system.   This  system will be  the first  municipal
wastewater sludge C-G unit utilizing thp  light oil  syst-pm to
begin operation.  LimifcpH  si-art: — up tests  have been conducted r
and  as  with any  new application  of  a  t-o^hrmi rvrjy f  problems
h_aj£g- been  experienced  in  the  start-up of the  system.   The
problems  encountered  by the  City of  Los  Angeles  have been
aggravated because  of  the v_pry  .ghnri-  <-img period  ava i 1 a,h1Lf=>
f"r  rJP°i7-n—a-»ei—nnnqt-rnnt- i on anH  hppausp   this  sysfprn	i_s—tile
first full-scale  system to be  built.

To minimize start-up  problems  at the remaining  three systems,
the  U.   S.   Environmental  Protection  Agency's   Municipal
Facilities Division (EPA-MFD)  sponsored a  two-day  seminar and
workshop  on  the  C-G  process.   Representatives  from each  of
the  four  wastewater  treatment plants, and C-G  design firm
(Foster-Wheeler USA  Corporation), the patent  holder  of the
system  (Dehydro-Tech),  EPA,  the  state environmental agencies
from CA and NJ, and municipalities  currently considering the
C-G process attended  the seminar.

This report was written to summarize the  considerable amount
of  information  on the  C-G process   that  was  disseminated  at
the workshop.   The objective of this document is  to  summarize
the key points of the seminar  and other follow-up information
to assist both the attendees and other individuals who may be
considering the C-G  process.  Suggestions  for  improving the
design and  construction procedures as  well as  the  EPA/state
funding mechanisms are  included in the report.

The Carver-Greenfield Process  (C-G)  is a  patented system for
drying solids.  It is now  being  applied in the United States
to the drying of  municipal wastewater  treatment plant sewage
sludges.   The  first  step in  the C-G process is  to  mix  a
carrier  (fluidizing)  oil  with wet  sludge  (which  can  have  a
wide range  of  initial  moisture  contents) .   This  fluidized
mixture is then fed into a multi-effect evaporation  system (a
series  of interconnected  evaporators  and  heat exchangers).
The  final solids  end  product is essentially free  of oil and

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water.  The  C-G configuration  (Figure I)  is designed  for
efficient utilization  and reut il i za tion of  heat with  the
carrier  oil   being  recovered and  recycled  repeatedly  in  the
process.   The C-G system is substantially  different  from  any
other   wastewater - slndp-p   processing  systems  hprans.'ff   i t-
yEj,iiz&s _ recyclable   hydrocarbons  to  fluidize  the  solids
Hnrina  frying.     A  C-G   system,   in  fact,   resembles   a
{petrochemical plant more  than a  wastewater  treatment  plant
and  requires  some of  the same  equipment and  _s k i 1 1 s  found  in
petrochemical plants to  properly  operate and  maintain.

There  have been  a  progression of  operating  C-G systems  for
drying different  kinds of solids  dating  back  to 1961.   In  the
mid  1_9 7 0 s , the_ system wa s  modified to  a I low  n^f nf a  1 igh t
 (volatile) fluidizing  oil  (e.g.,  No.  2  fuel  oil).   This
system  is  the basis for four municipal wastewater  treatment
facilities in the United  States — the  City  of  Los Angeles
 (City of  Los Angeles),  the Los Angeles County Sanitation
Districts (LACSD), Mercer County  (Trenton),  KJ  and  Ocean
County,  NJ.    Three of  these fnnr  facilities  are  employing
four   f orced-ci rcul a i- i nn evaporating  units   in  series   for
Hrying t-hta q i . n rig. g» r  and the  fourth — Ocean County,  MJ--is  using
a mechanical  vapor  recompression  evaporator,  followed by  two
forced-circulation  evaporating  units  in  series  for  sludge
drying.  The  first  f ul ly oper£tiiQjia_l.^JLgh^
the  United Sates is being  utilized by  Bur linqton^Industr ies
in Clarksvil 1 e_,_ri _V i r gin i a.. •  The Burlington system  processes to
dryness  both   wool-scouring wastewater  at  0.5  to  1 percent
solids as  well as  a dewatered  solids residue  at 16 percent
solids  from  their wastewater  (finished  wool  cleaning water)
treatment  plant.

•The  light oil  C-G systems must  safely  pump, evaporate.
  para_t^ •qnf^  i-prycle hot oily
      _
water   and  solids   through   .a.._nnmhpr   of   i
c o m P Q n_e_n_t-S..^,  These  task s _have__ posed ^  nnmbejn — o£__dle_JLJJiLP r
co_nstruction,   start-up  and   operational  problems  -f_or  all
qr_oups   involved.     VaTuable  lessons  are  being  learned,
especially   from  the  design,   construction  and  start-up
experiences at the  City  of  Los  Angeles.   Also,  valuable
insjf|hfc  naa  hpen gained f rom  nporat- i nna 1  g xper i gnre-s — o_f _ f.he
jSurlington Industries  light oil  C-CL sygf-pTn and  a pilot pla_nt
testing  program  under^k ^n  in  t-ho_iai-g i g_70s_ by .
The U.  S.  Environmental  Protection  Agency  (US EPA)  wanted to
help  the  municipalities  achieve viable C-G  systems  for cost
effectively  drying  their sludge.   All groups  involved (the
designers,  manufacturers,  and the  municipalities)  wanted  to
find  solutions  to specific problems such as with construction
management,  start-up, grid,  and  portions of  design  that were
not working  well—the goal being to avoid  repeating previous
mistakes and to quickly benefit  from design modifications and

                              vi

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The ERM Group.
     MOIST
     SOLIDS
             FLUIDIZING
               TANK
            CARRIER
              OIL
                                  CARRIER OIL
CARRIER OIL
                                  EVAPORATORS
                                      AND
                                HEAT EXCHANGERS
                                      r
                               DRIED  SOUDS IN OIL
                                 7
                         SEWAGE OIL
                          CARRIER OIL
       SOUDS
      CARRIER OIL
         A
                                                        WATER
                                                        TO
                                                        POTW
                            SEWAGE
                            OIL
                            (FUEL)
       98% SOLIDS
       (FUEL OR
       FERTILIZER)
                              FIGURE  I

        SCHEMATIC  OF  THE CARVER-GREENFIELD  SYSTEM
                                 Vll


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'approaches  that have  worked well.   A  workshop  offered  the
 best    format    for    sharing    information    and    improving
 communications  between all  parties.  This format also seemed
 to  be  an  important way of  focusing  on  difficult problem  areas
 of  the new  C-G technology to  create  an  awareness  and an
 atmosphere  for  finding and  sharing  accelerated   solutions.
 Therefore, a_t-wo-day  workshop was held  in.  Los Angeles in
 March  1987.

 An  excellent  spirit  of  cooperation  and  willingness to  share
 among  all  these groups was established by  the  workshop.
 Communication  among  the groups has  been  excellent.   This
 proceedings of  the workshop, which also  contains considerable
 follow-up   information  from   the   participants,   has  been
 produced  to  summarize  the  findings  and assist  other  groups
 considering  utilization of  this  technology,  as well  as the
 workshop participants.   The  report is divided  into  four major
 parts  as  follows:    (1)  Overview,  (2)  The  Carver-Greenfield
 Sludge  Drying  Process,  (3)  Operational  Experiences,  and  (4)
 Recommendations.

 Many  problems  have been  identified  and overcome.   Other
 identified problems are being worked  on.   These  problems
 include:

     1.   OIL-WATER  SEPARATOR AND EVAPORATORS:  An  oil-water
          separator  and  interconnected  evaporation  system is
          used  for separation and recovery of  the carrier oil
          from  the evaporated water  (not more  than  about 100
          ppm residual  .insoluble  oil in  the water) .

          Problems   with  the   oil   recovery   to  date  have
          included (a) prevention of solids carry-over  to the
          oil-water  separator  from  the  evaporator, and  (b)
          maintaining  reliable   operation  of   the  separator.
          Solids carry-over  at   the  City of  Los Angeles  has
          prevented  formation of a  good oil-water  interface
          in  the  separator  due  to  the  formation  of  an
          emulsig_n.  Oil-water  separation, however,  has  also
          been  inconsistent  where  solids  carry-over  to  the
          separator  has  not   been  a  problem   (e.g.,   at
          Burlington).

          If Oil is  not properly spparafpd and	is carried
          over_  into  the  water,  j, t is wagted aacLgoes back_to
          the head  of  the wastewater treatment  plant.   If
          water  is not sega_r,ated._.fj:om.__.tbje— oil  . the  water, is
          recycled  with the_ ca.rr_i.er oil, to  tihe  fluidizing
          tank  and  can cause   th.e._ formation . of  a  "gumrnv
          phase.''  At  a water  content  in  solids  and  oil  in
          the range  of about  3Q__to   1^ pprr^nt  the  viscosity
          of the solids  slurry greatly increases.   This  high

                             vii i

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     viscosity phase is referred  to  as the gummy phase,
     and  development  of  the  gummy  phase  can  cause
     pumpabilitY   problems   and    plugging    iji   the
     evaporators and heat exchangers.                "~~~"-

2.   ON-LINE MONITORING OF THE  RATIO  OF  SOLIDS TO WATER
     TO CARRIER OIL:  Improvement is needed in automatic
     measurement and control of the  exact amounts  of
     solids,  water  and  carrier  oil  bein_g pumped ajd
     mixed  at critica}  Ipnat-inrrs—in t-ho C-G sysfre,IP-
     TETiis  particularly  critical  because excessive
     carrier oil in  the system  will  reduce the capacity
     because of the  excess oil  that  must  be volatilized
     and recycled.   Too llttlp  r**rr.i.e*r  njj.	may  likely
     result in an  oil-solids mixture  that  is  too  thick
     to pump a solids-water mixture of around  30 percent
     (gummy phase)  or in which can cause  plugging  in the
     heat exchangers"!                           "	

     Manual   sampl ing	and    determination    of  .._the
     solids-to-water-to-oil ratio at half-hour  intervals
     is  being  successfully  used   at  the  Burlington
     Industries C-G facility to  aid  in control.

3.   CENTRIFUGATION:  Centrifugation  is  used after the
     evaporative drying  process to separate  the drv
     sol ids   from   the   carrier   and    sewage   oil.
     Difficulties  experienced  with  centrifugation have
•-7    included   excessive   abrasion   and   insufficient
     c_apture  of  solids fines.   Sufficient capture of
     fines during  centrifugation  depends upon  a  number
     of  factors  including,  proper   rate  of   feed  and
     gravitational force.

     Failure to captur-e sufficient  solids, sav only 9?
     percent  as  compared wil-h—QQ percent,, mpans that
     ther_e will be 3 percent,  in.gi-parl oJL. 1.  percent  fines_
     in the sewage and  carrier oil  going  t-n  t-hp  flash_
     still (not yet  in use by the City of  Los  Angeles) .
     As the carrier oil  is  flashed off of  the sewage oil
                         be
eva
pora
t-i
US-
process L_
1-h
p
so.
JdS in_
t-ho_ e:ow
age ...og
1
     become concentrated.  The resultant  solids content
     would  then  5e  about  50 percent  instead  of  20
     percent.   This higher solids  content  can  cause
     pumpability  problems and clogging  of  the system
     piping.

     DE-OILER   (HYDROEXTRACTOR) :       Another   problem
     encountered by Burlington and now the City of Los
     Angeles has been  solids  cai^ry-over into  vapor lines
     from the de-oiling| process.   Burlington has solved
     this  problem byincreasing the  velocity of  the

                          ix

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     vapor flow in the pipeline  from  the  de-oiler  and by
     manually cleaning any accumulated  solids  out  of the
     line  once each  shift (five  minutes  required per
     shift) .   The City  of Los  Angelas  ig  graying t-i-ia
     problem by  repipinq to gain  an  increased  velocity
     of vapor flow through a  shorter, more direct  oath.
     The  City  ot  Los   ft,pgplgs  i «=;
     installing  a  cyclonic dust  trap  with nitrogen
     Blanketing  as an  ext-ra pn=^an<- i rm  against solids
     bu,.i_ld-up   and   aui-np* idat-i nn.       use    of   the
     distillation system  (not yet used during startup by
     the City  of Los Angeles)  should also reduce the
     fines in the system.

5.   EXCESSIVE  LOSS  OF CARRIER OIL  FROM THE  SYSTEM:
     Carrier oil  losses are thought to  occur  primarily
     (a)   into  wastewater  during oil-water  separation,
     (b)  into  the sewage oil from  the flash  stilling
     process, and  (c)  into  the  solids product  from the
     de-oiling process.   Excessive  loss  of  the carrier
     oil  can be  expensive"^  Burlington  expected a  loss
     of about  3  gallons  per hour but  instead  has  been
     experiencing  a  loss of  9  to 12  gallons  per hour.
     Depending upon the cost of oil, these losses can be
     quite costly.  Costs  for light  oil  in August 1987,
     were about $1.10 per 'gallon.
     PUMPS  AND PUMP  SEALS:   Pnmp  g^al  failures  and
     abrasion  of  pumps has  been a  continuing  problem.
     H_j(jh^r  gna lit-y pumps  with hardened surfaces  ar e
     jTe.e,d,e,d .   Satisfactory service from seals  is  now
     being  obtained  at Burlington   with  changes  needed
     every 3 to 7 months depending upon the type of seal
     and  its  application.   About  one-half day and  two
     men  are  required  for  a seal  change.   Some  of  the
     seals  are quite expensive, and  failure of  seals
     several   times  each   month  was  not  acceptable.
                                          in
    Jiave resulted in be.t£er serving fnr t- h «a f; i±^_njF_r.r>g
    .Angeles.,.,,

    COORDINATED  DESIGN,   CONSTRUCTION   AND  START-UP:
     Unless there  is active and  meaningful  interaction
     among   the  designer,   construction   contractor,
    municipal  owner  and  operations  personnel,  many
    avoidable  time-consuming  and costly  problems  will
    be encountered.

    This has been especially  true for the  City  of Los
    Angeles  wher_e _thjejjt: _ probl gpis  h^ye   also  beejn
    ejcacerba t.e.d._— by— — a - ve ry -- s-h-ox.t-__cjpjur_t::manda ted
    time-frame  for__d,ejs_ign_ and , ^construct ion  
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           fac i LLtx/ _ §L_very  complex  interdependent  expansio n
           of the wastewater  treatment  facility  including  not
           only  the  state of the art  C-G system,  but also
           state of the art systems for  combusting the sludge,
           scrubbing  the  exhaust  gases,  and  cogeneration  of
           power and steam  from  sludge  combustion as  well  as
           burning of gas from the sludge digestor.

 The  use of models and pilot  testing  for  improving the design
 of a C-G  system is often  overlooked.    Benefits  of  a model
 include a  mechanism  for  checking the  design,  for  ensuring
 that  all the pieces will  fit together  and into  the  allotted
 space,  for  assisting the contractor  in construction,  and
 helping with operator  training.    Burlington saved $50,000  in
 construction  costs   and  undoubtedly  saved  much  more   in
 change-order avoidance by paying  $28,000  for construction  of
 their model.  The limited pilot  testing by LACSD helped them
 anticipate many problems.   Many of  the problems encountered
 by the City  of  Los  Angeles  (discussed  in this  report) could
 have  been anticipated  and  resolved  prior to construction  by
 use  of a model  instead  of requiring considerable extra time
 and  cost (millions of  dollars) for modification  of the system
 during  start-up.     I_t   is   important  to  note_  th_a_t  the
                          (not met because of ths[~encountere d
 p rob 1 em s )__f^r__b^q_uiiii_n q  operations  was  a.l so  a  sign i f i c a n t
 factor contributing  to  the  problems  at the  City of  Los
 Angeles'  system.
 Redundancy should  be  considered for any  component  prone to
 failure  or for  which  failure could  pose  a safety  risk.
 Specifications for equipment should be carefully written for
 future systems.   Operational experiencing  ar-gnir^r)  with t-hg
 ejuLsLLLDJI  system  will provide  the data  needed to  prepar e
 bet t ejr_s pe c i f i c a 1 1 o n s .

 The C-G process is, in effect,  a petrochemical type plant and
 not a  conventional  wastewater  type treatment process.   Safe
 and efficient  operation of the  C-G  process  requires qualified
 operators.   Adequate  training must be  provided.   In most
 situations to  date the operator training  may not  have been
 adequate.

 It  is  essential  that any  municipal  wastewater  treatment
 authority  considering   the   C-G   technology   review  the
 experience and performance of the  four municipal C-G systems
 discussed  in  this  report.   Visits  and detailed discussions
 with as many  of  these  four  system  owners as  possible  should
 be conducted  so that the experience gained  from these systems
 can then  be incorporated into new designs.  Pilot testing of
! untried equipment and  modifications to overcome solutions to
i past problems  is  vital.   Accurate  operation  and maintenance
                               XI

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cost data should  also  be available for use  in  estimating
actual  costs  for future systems.
                           XII

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                        SUMMARY REPORT

 WORKSHOP ON THE CARVER-GREENFIELD SLUDGE DRYING TECHNOLOGY:
                    PROBLEMS AND SOLUTIONS

                   Held in Los Angeles, CA
                   on March 10 and 11, 1987

                          SECTION  1
                           OVERVIEW
1.1  Introduction

Four municipal wastewater treatment authorities have selected
the Carver-Greenfield  light oil  sludge drying  (C-G)  system
for dewatering  their  sewage  sludge.   Ocean  County,  New
Jersey;  the  Mercer  County Utility  Authority  (Trenton,  New
jersey);  the  City of  Los Angeles,  California;  and the  Los
Angeles, California County Sanitation Districts are currently
designing or  constructing  C-C  systems.  The City of  Los
Angeles  will  soon  begin operation of  their  265 dry ton  per
day C-G system.   This system  will  be the  first municipal
wastewater sludge  C-G  unit utilizing the  light  oil  system to
begin operation.  Limited start-up tests have been conducted,
and as  with  any  new application  of  a technology,  problems
have been  experienced  in  the  start-up of  the system.    The
problems  encountered  by  the  City of  Los  Angeles have  been
aggravated because of  the very  short  time  period  available
for design and construction and  because  this system is  the
first full-scale municipal system to be built.

To minimize start-up problems at the remaining three systems,
the  U.   S.   Environmental  Protection   Agency's   Municipal
Facilities Division (EPA-MFD)  sponsored a  two-day seminar  and
workshop on  the C-G process.   Representatives from each  of
the four wastewater treatment  plants, the  C-G design  firm
(Foster-Wheeler USA  Corporation),  the  patent holder of  the
system  (Dehydro-Tech),  EPA, the state environmental agencies,
and municipalities  currently  considering  the C-G process
attended  the  seminar.    An  attendance  list  is presented  as
Appendix A.

A considerable amount  of  information on the  C-G  process  was
disseminated  at the workshop.   Suggestions  for  improving  the
design  and construction  procedures as  well  as  the  EPA/state
funding  mechanisms  were  discussed.    The  objective of  this
document is  to  summarize the  key  points  of  the  seminar  and
other  follow-up information to assist both  the  attendees  and
other  individuals who may be considering the C-G process.
                              1-1

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1.2  Report Format

The  workshop  summary has  been  divided into  three major
sections.   Section  2 summarizes  the  C-G process for  those
unfamiliar  with  this process.     In  Section  3,   a  brief
discussion  of  the   operating  experiences  at  several  C-G
wastewater treatment plants  is  presented.    A  summary of the
recommendations presented  at  the  seminar  is presented in
Section 4.
                             1-2

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                          SECTION  2
         THE CARVER-GREENFIELD SLUDGE DRYING PROCESS
2.1  Background

;ln the mid  1940s,  Mr.  Charles Greenfield began  investigating
'processes for separating  vitamin  oils  from  ground fish liver
water slurries for his employer, Vitol Processing Co., in New
Jersey.     Centrifuging,   pH   control,   and   conventional
thickening  operations  all proved ineffective for  drying  and
recoverying the resulting  vitamin oils  and  solids.   However,
using  the  fish  oil  itself  as  a  carrier  medium  in  an
evaporation system  was  found  to  be  an  effective  drying
process.  When  synthetic vitamins displaced  natural vitamin
oils, the Vital Company processing plant was  shut  down.   Mr.
Greenfield  then set  up his  own  pilot  plant  and  laboratory to
study  the  drying  of  edible  rendering  products  and  the
production  of  dry  milk  powder.   This  work  brought  Mr.
Greenfield  into  contact  with  Fred.  S.  Carver,  Inc.  and  in
1955  they entered  into a  long-term contract.   Under  this
association,  the   evaporation  procedure  for  processing  the
vitamin   oils   evolved  into   what   is  now  know   as   the
Carver-Greenfield  (C-G) drying process.

Development work  continued, and in  1961 the  first  C-C plant
was built in  Pennsylvania for  processing inedible  rendering
plant wastes  (waste  fats  and  bones  from  the  meat  processing
industry).    Initial  problems  with  this   system  included
non-uniform  flow  and  poor distribution  through the  1-inch
diameter evaporator  tubes.  These problems  were  mitigated  by
increasing  the  circulation  rate  of   oil   slurry   in   the
evaporator,  maintaining  the oil-to-solids  ratio on a  water
free basis  at about  5.5 to  1  and  devising an  improved  heater
slurry distribution  system.   In  this  plant,  the  fluidizing
agent was tallow.

In  1964,  a  C-G   plant  was  constructed  for   the  Hershey
Corporation to dry solids from their  wastewater  system.  Both
primary and secondary trickling filter sludges were  dried  in
this system.   Problems with  this system included  undesired
thickening of the oil because of  the formation of  soaps  from
fatty acids in  the sludges.   This formation  was intensified
at alkaline pH  values  and  elevated  temperatures.   This
problem   was   lessened,   but   not   totally   overcome,   by
controlling  the pH and by using oils,  in which the  soaps  were
more soluble for fluidizing and carrying  the  sludges through
the evaporators.   A heavy oil was  used as  the fluidizing
agent.     An  expeller  press,   used   after  evaporation  and
centrifugation to  remove the heavy carrier  oil,  never  worked
and was abandoned.  Therefore,  the centrifuged product, which
contained 40 percent  fluidizing heavy oil, was burned.  This

                              2-1

-------
was  not a problem  because  the original  fat  content of the
sludge was  25 percent  and  the  added  heavy oil  used for
fluidizing was readily available  at  a low price during that
period.  The Hershey plant was operated with  relative success
until  it was shut down in 1974.

Additional C-G plants  were built after 1964  in  the  food,
pharmaceutical, and  waste treatment industries.   Several
Japanese  municipalities  purchased   the  C-G  process  for
wastewater  treatment  sludge drying.    All of  these systems
utilized a "heavy"  (non-volatile)  oil for fluidizing the
product to be dried.   Often  the  carrier  oil itself  was
generated from the product being dried.   Problems encountered
included plugging of  evaporator tubes because  of  high  fiber
content of the  sludges  and  a high  oil usage due to  the
inability  to  recover all  of the oil  from  the dewatered
sludge.  Increasing the oil-to-dry solids ratio and grinding
of the sludge prior  to the C-G process  alleviated plugging  of
the evaporator tubes.  Use of "light"  (volatile)  oils,  which
can be more readily recovered  by vaporization,  then was
developed  as  a solution to  high  oil  usage  in  the  C-G*
process.   An  example of  a  light  oil  that might be  used  is
Number  2 fuel  oil,  Exxon's  Isopar* or  Union  Oil's  Amsco*  as
compared with  Number  6 fuel oil.   The light  oil has  a  lower
viscosity,  better  heat  transfer,   is  easier  to recover  and
recycle back  into  the  process,  and  does a  better job  of
removing and  allowing for the  recovery  of  sewage oil  than
does the heavy oil.

The city of  Los Angeles  Hyperion  Wastewater  Treatment  Plant
is the  first municipal wastewater treatment  plant with  a
light oil C-G system in the  United States.  Complete start-up
of the  Hyperion C-G  system  is anticipated  shortly.  Four
other light oil C-G systems are in design, construction, or
operation  in  the  United States  (Table  2-1) .   A general
description of the C-G process  is presented below.


2.2  Multiple Effect System

     2.2.1   Process  Description

A simplified  process  flow  diagram is presented in Figure  2-1.
This  represents the  process used in all but the  Ocean  County,
NJ system.   The Ocean County system is  discussed in  Section
2.3.
*Trade names are given solely for the use of the reader and
 do  not  imply  endorsement  by  the  U.   S.   Environmental
 Protection  Agency.
                             2-2

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                                                       TABLE 2-1

                                          CARVER-GREENFIELD LIGHT-OIL PLANTS
         Location
                        Feed Material
                    Design Capacity
                      (Tons Dry
                      Sol ids/Day)
Disposition of
   Dry Solids
Phase
i
U)
         City of Los Angeles
         Los Angeles, Calif.
Los Angeles, County
Sanitation Districts
Los Angeles, CA

Ocean County Utility
Authority, New Jersey
         Mercer County
         Utility Authority
         Trenton, NJ

         Burlington Industries
         Clarksville, VA.
         F. W. Martinez,  Inc.
         Concord, CA
Primary/secondary     265.0
sanitary sewage
sludge

Primary/secondary     240.0
sanitary sewage
sludge

Pr imary/secondary      50.0
sanitary sewage
sludge

Primary sanitary      118.0
sewage sludge
                        Biological sludge      20.4
                        scouring wastewater
                        from wool washing

                        Alum sludge from       16.0
                        Contra Costa Water
                        District
Burned in boiler
to generate
electricity

Burned in boiler
to generate
electricity

Fertilizer
                                                              Fertilizer
                                      Solids-landfill;
                                      lanolin-burned
                                      and/or sold

                                      Solids-landfill
Construction
Start-up beginning
1/87

Construction
                                                                                            Engineering
                                                                                            Completed
                    Construction
                    Start-up
                    1/88

                    Operating,
                    1983-present
                    Constructed,
                    Start-up beginning
                    8/87

-------
The ERM Group.
             VACUUU SYSTEM
               COOLING
               WATER

             ADOBACK OF
             BOX SOUDS  ,
                OIL      (A
                                                                       DIRECTION Of
                                                                       SOUDS FLOW
                                                           DRECTION OF
                                                           HEAT FLOW
                                      WASTEWATER
                                        VAPOR
    N)
 \f-3Kt
V.
                                                                 WASTEWATER
                                                                                           WASTEWATER
                                                                   EFFECT
            RUIOIBNO •
            TANK
STEAM
CONOENSATE
SECOND
[VAPORATOR
STAGE






                                                                  VAPOR
                                                    CONDENSATE
                                                                                         THIRD
                                                                                      EVAPORATOR
                                                                                         STAGE
                                                                                             VAPOR
                                                                                 STEAM
                                                                              CONDENSATE
                                                                                                       FOURTH
                                                                                                     EVAPORATOR
                                                                                                       STAGE
                                                                                               STEAM
                                                                                             CONDENSATE
                                                                                                                                      SOILDS FOR FUEL
                                                                                                                                      OR FERTILIZER
                                                                                                                                DRY OEOILED
                                                                                                                                BIOMASS •
                                                                                                                                9SX SOUDS
                                                                                                                                       OEOILER
                                                                   CENTRIFUGE
OIL-WATER
SEPARATOR
(SEE FIG.
*>

1^~&
WASTE
WATER
TO POTW

(TO OIL-WATER ^—£\ ^ 	 ^\ ^ 	 £l *~Y
SEPARATOR) C±J CXJ Cr3 £_
S£WAGE « J^^nJfu0"-
/ OIL * WATER) CtNTRATE
CARRIER OIL OIL DISTILLATION _ CARRIER AND SEWAGE OL
-c(T
©
SYSTEM 	 l 	
(ALSO CALLED A
HYDROEX TRACTOR)

• SOUDS FOR
ADD8ACK (60%
SOUDS IN  OJU
SEE F)GUR£
a-4)
                                                                                (SEE FIG. 2-3)

                                          CRITICAL AREAS;  A - AODBACK OF SOUDS TO PREVENT GUMMY PHASE; B - ABRASION AND LEAKING OF PUMP SEALS:
                                                        C - ODORS IN VAPORS; 0 - PRESENCE OF FINES IN CENTRATE; E - ABRASION OF CENTRIFUGE-
                                                        F - CARRYOVER OF FINES INTO VAPOR SYSTEM.                            wuraruuc,
                              FIGURE 2-1.   GENERAL  PROCESS  FLOW  DIAGRAM OF THE  MULTIPLE EFFECT C-G PROCESS.


-------
Wet  sludge from  thickening  after  digestion  is fed  into a
fluidizing  tank.   The  purpose of  the  fluidizing tank  is to
mix  the sludge and carrier  oil  into  a slurry for  further
processing.   QjLL_and  previously  dried sol ids  called addback
are re-mixed with  the  wet  sludge  in the fluidizinq tank.  The
additional  solids  are  added to prevent formation  of  a "cjummy
phase"  in  the evaporators (further discussion of the  gummy
phase  is  presented in  Section 2.2.2).    The  oil-water-solids
mixture   is  pumped   from  the   fluidizing  tank   into  the
four-effect evaporator system.

In  a multiple  effect   forced-circulation evaporating  system
(Figure  2-1)/  high  pressure   steam enters  the steam  jacket
(shell)  of  the first  effect  and evaporates  water   from  the
oil-water-solids  mixture  jUJJ3uo_r_)  inside  the  first  effect
evaporator.   The   incoming  high   pressure  steam condenses  in
the steam jacket in the process of heating  up the liquor,  and
this  condensed water  is  drained out  and returned to  the
boiler  of  the  system.   The water evaporated from the  liquor
in  the first effect,  moves  as  a  vapor  (steam,  at  a  lower
temperature and pressure  than in the  incoming  high  pressure
steam  to  the  first effect)  to the steam jacket  of the  second
effect.  The  vapor from the first effect, in turn, condenses
in  the steam  jacket of  the second effect  in the process  of
heating  up  the   liquor   in   the  second   effect,  and  this
condensed water  is drained out  and  returned  to the  boiler
system.  These processes are  repeated in  the Jbh i r d _ aad__fo,.urth
eff_ec_t	evaporators  with   the   exception   that  the   wajber_
vap_or_l2_ed™"f:rom  the liquor  in  the fnnrth  p.££act  is—caoideKsed
i,n_a	water-cooled  external heat  exchangers-prior to return  to
_the  bo iler.  The  evaporating temperature and pressure  is
lower  in each succeeding effect.

The  liquor  (mixture)   to be evaporated could  move through a
multiple  effect   evaporating system   in  either  the  same
(forward feed) or  opposite (backward feed)  directions as  the
vapor   is  moving.     Forward  feed  results  in  a   simpler
installation  because   liquor  can  be  transferred   between
effects without pumping.   However, it  is  seldom used if  the
liquor  becomes more viscous as it evaporates.   Backward feed
is  then preferred  because the  most	co.ncen-t-r-a~fe@d—iiq-uo-r—is
evajjgrajted  in  the  first  effect  where_ <~h^>—high—t_empj2jia_ture
reduce s  vj.sc o s i ty__ an d  jm i_n imi^ze s_ _Lts__ad-V-exs.e	affect  ,,Qjg__he a t
JLr a n s-f SLT_ c o e f f Tc i e n t s .   In  the Carver-Greenfield  system,
backwardfeed is use.

When backward  feed is  used  in  a multiple  effect  system, a
unique  numbering  system is  used  to  identify  the  vapor and
liquor  streams.   The  term "stage" is  used to  refer to  the
sequential  order  in which the liquor  (the  sludge-oil-water
mixture) moves  through the system.   Thus,  in   a  four-effect
(four evaporator)   system,  wet sludge  liquor enters the  first

                              2-5

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stage   (last   effect — 1 owes t    temperature    and    pressure
evaporator).   This liquor  sequentially flows  through the
second and  third  stage  before  treatment  in and exiting  from
the  fourth  stage   /first-   effect—highest   temperature  and
          evaporator! .   On  the other  hand,  the  previously
described effects  (evaporators) are  numbered  in  the direction
of  heat  flow.   In  the C-G  process,  the  fresh  (highest
temperature and  pressure)  steam  enters  the  first  effect
evaporator  shell  which  is   the  fourth   stage  for  liquor
evaporation  (where the  solid's content  is  the  greatest and
hence the boiling  point  of the liquor  is the  greatest),  jieat
then  s_u_b..s.e.qu.enj:i.ally flows  as vapor through  the  second ,
th_ir_d_, a n d__fjpja_r_t ii __ef_f e c t s .

A multiple  effect evaporator  system may appear  to present a
difficult control  problem due to the number of evaporators to
control  (systems of six evaporators are  common),  but in
actuality,  control of rnul_ti pie, effect systems JLs_jifiJj*.l:j_y_gJ.y
§jjapJ-e..    Liquid  levels  have  to  be  maintained  in  each
evaporator,  &£e_a,m_ must  be  supplied  to  the  first  effect at
                      and  water  must  be   supplied  to  the
water-cooled external condenser at a  reasonably  constant
temperature and adequate flow rate to condense the vapor from
the  last  effect.    Th e  1 i quo r .__j eed ____ _£Lo.w__ r.a t e . __ i.js___ttjen
established   to _  produce   the _______ d,e_si_red-__^jjiaj____^oj.-ija s
concentration.   When t h i s Ti  3orfe7~"aii  of  the intermediate
vapor   temperatures   and  liquor   concentrations   establish
themselves and are not subject. to external control.

A  phenomenon  that   reduces  the   potential  value  of  the
available  temperature  drop  between  the  condensing  steam
entering  the  first  effect  and  the water cooling  the  vapor
from the  fourth effect  is  the boildng point  rise  (BPR)  that
occurs  when  a  liquid  that  contains  dissolved  salts  is
concentrated.  For example, a 22  percent aqueous solution  of
sodium   chloride   boils   at   atmospheric   pressure  at   a
temperature of  222°F, whereas pure  water  boils at  212 F
(therefore, the BPR  is 10°F.)   The vapor evaporating from the
aqueous  sodium  chloride is pure  water  and  will  condense  at
212 F at  atmospheric pressure.   Thus, some  of the available
temperature difference disappears.  There are more losses  in
the available temperature difference when the liquor retains
some superheat after  it passes through the evaporator tubes.

This BPR phenomenon  reduces  the  amount  of  energy  per  hour
that can be exchanged in the system (capacity of the system),
but does not lower the steam economy (kilograms  [kg] of water
evaporated from the  liquor divided by kg of  steam  charged  to
the  first  effect) .    Approximately  one  kg  of  water  is
evaporated from the  liquor for each kg of vapor  condensed  in
each effect (evaporator) , assuming minimal heat loss from the
system  and  adequate  temperatures  and  pressures  in  each

                              2-6

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 effect.   The approximate  steam  economy  is calculated  by
 dividing  the steam used by  a  single effect evaporator  by  the
 number  of effects.   In general,  the multiple effect  systems
 are  designed based upon the amount  of water  to be evaporated.
 An important advantage of  a  multiple effect system is  that
 relatively high rates  .of _ evaporation per __ unit  pf'JKeat  input
 qajLJie^ai^Le.yed .  For  example,  an evaporation to  steam  ratio
 of about  three  can be achieved with  a four effect system.

 in the C-G  system,  not only water,  but  also  some  of  the
 carrier  oil  and sewage oils in the  sludge  will  be  vaporized
 from the  sludge in  each effect.  Condensation  of this  steam
 and  oil  occurs  in the  heat  exchangers  shell section  of  the
 evaporators.   The  condensate  i s . directed _to -An— rv--i-V— ua-h.^r
 separator  which  is  usej3_t-Q_-S-epa-c-ate — water — an-d — recover- — the
 jjjUL.  .Th.e _r e coyer ed_oJJ__i-s — Recycled — to — the — fJoiijiizJJig_tajnk .
                                         ^             t .   The
  _
 location of the oil separation system with respect  to  the C-G
 process  is  shown of Figure 2-1.  A more detailed schematic of
 the water-oil separation system is provided in Figure  2-2.

 After    evaporation,    the   solids-oil    slurry   contains
 approximately liz^.Q.JSeT^en^^solj.o^ in  oil,,   Water content is
 typically on the order of  L^2_ pe r c eritT~~Th e terminology used
 to  refer to  solids concentrations varies  depending upon the
 location of the solids.   The  solids concentration  of the
 sludge  entering the  first-stage evaporator is  measured with
 respect  to  the water content.  Therefore, a 10 percent solids
 concentration fed  to the  evaporators  represents  10 percent
 solids  in water.  Oil is  present at a  ratio of roughly eight
 parts  oil per one  part  dry solids; however,  the  oil content
 is  not  included in expressing  the  solids concentration prior
 to  exiting  the evaporators.   Conversel v_^._o_n.C-e _ t.h.e._s 1 udq e
 e x i t s __t h e_e_va pjorat, pj^s..*_ ,th.e_l 5^-2 0_.p e,r c e n t__solj. d s _c_o n c e n t r a.t ion
 r e far s^fco~the-H3e-r^e^tag-e_oJL_s.o_l_ids  in oil and Jjeg 1 e c t s „ .t h e
 approximately 1-3  percent  water content.

 Approximately one-half of  the  dewatered sludge  flow leaving
 the last stage  (first effect evaporator) is  recycled  to the
 fluidizing  tank in  a process  called addback (see Section
 2.2.2) .   The  oil  present  in the  remaining dewatered  sludge
 must be  removed  from  the solids so that the  oil may  be
 reused.   Bulk separation is accomplished  by ce^n^rjjEuaaJt.ipn to
 increase the solids concentration to approximately j[0__pe_r_cent
 (solids  in  oil, Figure  2-1).  Centrate  from  the  centrifuges
 is  sent  to  a  fJLasti_js±jJLl .   This  still separates  the  sewage
 qil_from the carrier, oil,  thereby allowing the carrier oil to
~               A diagram  of the oil  distillation  system  is
  ___
presented  in  Figure  2-3.

The  ability to recover  the  10-20 percfent content  of sewage
oil  normally  present  is sewage  sludge  is  important  for  at

                               2-7

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The ERM Group.
           OILY WATER
             FROM ALL
         EVAPORATORS
                 FRESH
            CARRIER OIL
     CARRIER OIL TO
         FLUIOIZING.
       EVAPORATION,
     FLUSH SYSTEMS
                                                      OIL FROM
                                                    COALESCER "B"
                                                          WATER FROM
                                                         COALESCER "B"
       OILY WATER
       SURGE TANK
                                 PLATE
                                 TYPE
                                SEPAR
                                 ATOR
                                    OILY H20 TO
              COALESCER ,
                                           PREFILTER  COALESCER
                           RECOVERED
                           OIL PUMP
                                         TO TANK "B
               FRESH/RECOVERED
                OIL SURGE TANK
                                                            DEOILED
                                                           WATER TO
                                                            OUTFALL
      FIGURE  2-2.
SCHEMATIC  DIAGRAM  OF  THE  OIL  RECOVERY SYSTEM  FOR  THE
C-G PROCESS.
                                 - -V" 1 rnifcii .
 TtMERN Group,

-------
The ERM Group.
OIL/WATER VAPOR
      TO STAGE 1
     EVAPORATOR
        HEATERS

      OIL VAPOR
      TO STAGE 4
     EVAPORATOR
        HEATERS
    CENTRATE OIL
           FRO)
     CENTRIFUGES
                       VENT VAPORS
                             VAPOR FROM FIRST STAGE
                           r HYDROEXTRACTORS
                                   VAPOR FROM FLASH
                                             STILL "B"
               CENTRATE
               SURGE TANK

              -  aASH STILL
                  FEED PUMP
      185 PSI STEAM

             STEAM
         CONDENSATE
         TO RECEIVER
      FIGURE 2-3.
                                              FLASH
                                              STILL
t
                                                                  - TO VENT GASES CLEANING SYSTEM
                                                                  -i VAPOR FROM SECOND STAGE HYDROEXTRACTOR
-V VAPOR FROM STRIPPER "B"
                                                         /
                                                          OIL
                                                          STRIPPER
                                                          V/L
                                                          SEPARATOR
                                         FLASH STILL
                                         CIRCULATION
                                         PUMP
                                                                                          SEWAGE OIL
                                                                                          TO STORAGE
                                                        SEWAGE OIL
                                                         DISCHARGE
                                                           PUMP
                                                                                           -?
                                                                                           STRIPPING
                                                                                           STEAM
                     SCHEMATIC DIAGRAM  OF  THE OIL  DISTILLATION SYSTEM
                      FOR THE  C-G  PROCESS.

-------
  least  two reasons.  First,  if  this  oil  is not separated from
  the carrier  oil after centr i f uga tion,  it could  cause the
  formation  of  emuls ions  and  foaming  problems  in the C-G
  system.   Secondly, the sewage J3J.1S can be used to supply heat
  ajid_riowe r .   For example, when separated from sewage sludge at
  the 13 percent sewage  oil  content,  the  sewage oils  can  be
  used as  a  fuel in boilers to generate  100  percent  of the
  steam  needed for  producing steam for  the C-G system.   Khen
  separated at the  16 percent sewage oil  content  from  sewage
  sludge (such as at Trenton,  NJ) , the sewage  oil can be used
  not only  to generate 100 percent of  the steam required  by the
  C-G system, but also to generate 50  percent of the C-G  system
  power  requirements.

  Some solids may be present in the Qent£a_£e, and may interfere
  with the  operation of  the f lash__still ; thus, centrate quality
  is  a potential  concern  (see Section  4.5.5).   Fine  particles,
  in  particular,  are difficult to remove by ^ej3jLr.i.f.aga_tlojj .  As
  the carrier oil is separated from the sewage oil in the flash
  still  (Figure  2-3)  for recycling back  into  the  evaporating
  process,  the solids  in the  sewage  oil become  concentrated.
  The resultant solids content in  the sewage oil is  about ten
  times  the solids content of the  centrate.   Too  high a  solids
  content, such  as  50-60 percent,  is  n_o_t _pjjmpable and the
               a p .     ~~    '
  In  the heavy oil C-G process, additional  oil  recovery  beyond
  centrifugation is  usually accomplished  using  a screw  type
  press.   The oil-solids  mixture is either burned, or  depending
  upon the oil  used, is  used  for  animal  feed  or  fertilizer.
  The cost of oil for a heavy oil  system  for  a  large  plant can
  be  very high.   Use of heavy oils  at  the  Los Angeles Hyperion
  plant,  for  example, would have cost  approximately $3 million
  per year.   Light  oil systems  have therefore  been  specified
  for all  four  municipal wastewater  systems  in  the United
  States.  Oil costs for  these  systems are projected to  range
  from approximately $10,000  (Ocean County)  to $150,000  (LACSD)
  per year.

  In  a light  oil system,  final  oil  removal from the centrifuged
  sludge    takes  place    in   an   unit    operation   called
^xfiydroextract ion,   which   sounds  like  a  misnomer   for   the
  process.   However, since ste_am ___ is  utiLized _ to _vapojLJz.e_ the
  oil and thereby remove   the  light oil  from the solids,  the
  terminology  was utilized.  By  the time  the solids  reach  the
  hydroextractor,  nearly  all  water  has been removed.  Oil,  not
  water,  is then  vaporized from the solids.   Thus,  the  term
  "de-oiler" may also be appropriately  used  as well as the  terra
  "hydroextractor" .

  The hydroextractor is essentially a  two-stage dryer.    Oily
  solids  enter a heated  vessel maintained  under vacuum where

                               2-10

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hollow steam-heated  paddles are  used to mix  and convey  the
solids.   Any  residual  moisture and  the  carrier  oil  are
vaporized thereby  drying de-oiling  the  sludge.   Although a
hydroextractor  somewhat  resembles   a  screw  conveyor,   the
solids actually  flow by  gravity  from  the  first  and second
stage of the hydroextractor.  Approximately  95 percent of  the
oil  is  removed  in  the  first "stage,  with  the  remaining  oil
being removed in the second stage.  The vaporized  oil is then
recondensed  in the  evaporator  system and  reused.   The  final
dry solids product exits the hydroextractor.

Dust carry-over into vapor  lines  is  a potential problem with
the  hydroextractor,  particularly  if   fine  particles  are
present, if  large amounts of steam are used  to reduce the oil
content  to   a  small  amount,   or  if  the  influent  solids
concentration  is   low   (<50  percent) .     At   low  solids
concentration,  the  quantity  of  oil  evaporated  is  high,
creating a  high  vapor velocity.   The high  velocity through
the  hydroextractor  increases  the generation  of dust.   A
ba f f 1 e . i.s_.u^jed_t^_heJ.B_^L]^e^ejit—so. 1 ,ids_aarr-V^a&er .

Odors  are  a  potential  problem  with   any  sludge  drying
operation   including  the   C-G   process.     Hot  wastewater
treatment sludge  has the potential  to  be  very odoriferous.
To minimize  the  potential  for  odors, as  well as  fires,  all
process units in  the C-G system are _seaJLe<3.   Gases  from the
process units are vented into vapoj:__l.ines.   Oil  in the  gases
is recovered from the condensate  of  the  heat exchanger.   The
remaining gases  must then be scrubbed  in the  evaporator  or
are burned  in the boiler to  remove noxious  odors.   Activated
carbon could also be used for odor removal, however,  the cost
for such a  system would  be  expensive.  Therefore,  the vented
gases are typically burned in a  C-G application in the boiler
that produces the steam for. the  system.

     2.2.2  Addback

Addback   (Figure   2-4)   is  the   process   which   dewatered
solids-oil  slurry  from  the  fourth  stage  (first   effect)
evaporator  is recycled  to mix  with fresh sludge in  the
fluidizing tank.   The purpose of  thijs_pj-0£ess__i_s J:o_pr_e_v.snt
formation  of a  "g,nmm.y  phase"  which can be  a significant
operating constraint.

The  fluid properties of  the  solids-water-oil  slurry  change
depending upon the solids to water concentration.  Wet sludge
from the wastewater  treatment system  typically  contains  from
2 to  20  percent  solids  depending  upon  the  prior  dewatering
steps   (e.g.,   belt   press   or   centrifuge).      Solids
concentrations (water  basis)  mixed  in  the  solids-water-oil
slurry  in   this   range  are  pumpable.     As   the   solids
concentration increases  above  20  percent  (water  basis)  the

                             2-11

-------
The ERM Group.
                             WASTE-
                                ER
                                                                    DIRECTION Of
                                                                    SOUDS FLOW
                                                                 DRECTION OF
                                                                 HEAT FLOW
i
i—>
N)
           FE£D
          FLUIOIZJNO
          TANK
                                      4TH
                                      EFFECT
                                                WASTEWATER
                                                                          WASTEWATER
                                                                                                    WASTEWATER
FIRST
VAPORATOfi
STAGE






           •ADOBACK SOUDS AT
           0U SOUDS IN WATER
           (eox SOUDS IN OIL)
                                                                                                                               DRY DEOILED
                                                                                                                                 BIOMASS
                                                                                                                                 PRODUCT
                                                                                                                               (88X SOUDS)
                                                                                                                                      CARRIER OIL
                                                                                                                                      TO RECOVERY
                                                                                                                                      SYSTEM
                                                                                                                                         HOT DRY
                                                                                                                                         BIOMASS AT
                                                                                                                                         60X SOUDS
                                                                                                                                         IN OIL
                                                 EXCHANGER
                                                                                HEAT
                                                                           EXCHANGER
                                                                                                     EXCHANGER
                                      CRITICAL AREAS (NOT SHOWN PREVIOUSLY):  A - PLUGGING OF SPIRAL HEAT EXCHANGER
                                                                        B - VISCOMETER AND RATIO CONTROLLER
                                                                            FOR ADDBACK CONTROL
                                                                                                                      NOTE:
                                                                                                                                         AOOBACK
                                                                                                                            APPROXIMATELY 60 PERCENT
                                                                                                                            OF THE SOUDS ARE RECYCLED
                                                                                                                            AS ADDBACK TO AVOID
                                                                                                                            DEVELOPMENT OF A 'GUMMY
                                                                                                                            PHASE* IN THE EVAPORATORS
  L
          FIGURE  2-4.   ADDBACK  SOLIDS FLOW DIAGRAM  FOR  THE MULTIPLE EFFECT C-G  PROCESS.

-------
solids begin  to coalesce and  become sticky  (hence  the term
"gummy") .  This  sticky or gummy phase  occurs in the range of
ZQ to 30 percent solids  (water basis).   The viscosity of the
"gummy" slurry increases  dramatically, and the slurry becomes
difficult  to  pump.   Once the  solids  concentration increases
past approximately 30  to 35 percent (water basis)  mixed  in
the solids-water-oil  slurry, the  solids again  are dispersed
in the slurry and  are pumpable.

Should the gummy phase occur within any of the process units,
plugging of the  unit  would result.   The  unit would then have
to be  shut down—f^r__cie_an_ing.   Dry  solids and  oil  from the
fourth-stage evaporator are thus  added  back to  the  wet feed
sludge  to  increase  the  solids  content  of the  slurry  to
approximately 35_pejccent  solids in water (Figure 2-4).

The  slurry  of  dry   solids in  oil  from  the  last  stage
evaporator is  very hot  (e.g.,  250 F).   If this slurry were
added directly to  the fluidizing  tank, vaporization  of  water
and oil  would  occur  in  this tank.   Considerable  heat  value
would also be  lost.   Instead of recycling  the  addback solids
directly to  the fluidizing  tank,   the  solids pass through  a
series of  spiral  heat exchangers   (Figure  2-4) .    The  spiral
heat exchangers  are  constructed  of  two parallel  stainless
steel  plates  which   are  rolled   into   a   spiral   cylinder.
Spacers  are  used  to  separate  the plates  during  rolling  to
form two parallel  but separate  flow paths.   Sludge from each
effect is  fed  into one flow path  of  its  corresponding  spiral
heat exchange while the addback solids  are  pumped through the
other  path.   Th_e_axldbacJc__s^_ljLcLs._a,rje__u,s.ed	t_o—pJLeJi.ea.t—Lhe
sludge JLed.	to.?Teac"h"~e"f£ectljH±-h.erj5.by__J.inProving  the ener gy
efficj1ejrcy__gf the  proc_esis,.

Two of  the problems  with  addback are  start-up  and  jp_r.g_cej3s
control.  During start-up of a  new plant, dry solids  will not
have been  generated  to  feed back  into  the  fluidizing  tank.
Compost  or some other  source  of dry  solids will  thus  be
required.  Care should be taken to ensure that  the  compost  or
other  material  is free  of  particles  which  may  clog the
system.  Secondly, care must be taken in  c_Qn.tjc_o,lling__the_ra_te
of addback which can  be difficult.  Typically, about half  of
the  dried   solids   from  the   last   stage  (first  effect
evaporator) are  used  as  addback  (i.e.  a  solids  to  recycle
ratio of 1 to 1)  .  Y.iscomete.r_s__on_the discharge_p.ump.-£roitu±Jije
f luidj.jz.ing.._ tank  are" now recommended  to  control__addjb.aj;k.   If
the  viscosity  increases   (thereby indicating  the   incipient
development of  the  gummy phase), alarms  are  sounded and
additional dry  solids are  fed to the  fluidizing tank.  A
ratio controller is used  to  physically control the amount  of
solids recycled as addback.
                             2-13

-------
2.3  Mechanical Vapor  Recompression

Mechanical  Vapor  Recompression  (MVR)  evaporators offer  an
alternative   to   the   multiple-effect  evaporator   system
described  above.   A  full-scale MVR  C-G  system has  been  in
operation since  1983 in the  Netherlands  in  a  heavy oil
rendering  application.  The  MVR alternative will  be  used  by
Ocean  County,  New Jersey,  which will represent the  first
light  oil  MVR   evaporation  system   for  drying  municipal
wastewater sludge.

In an MVR system, water vapor generated by steam in the first
stage evaporator  is compressed  and  recirculated  to  the  steam
chest  oQf first-stage  evaporator  at  a  temperature of  about
170-180 C and  pressure of about  20  psia  (Figure 2-5) .  The
compressed  water  vapor  condenses and  is removed  providing
enough heat  to vaporize  an  equal  amount of water,  thereby
concentrating the sludge in  the evaporator.

The differential  in temperature between the  compressed  water
vapor  and  the liquor  is  about  15 F.   The  magnitude  of the
temperature difference between the  condensed  steam and the
evaporating water  in  the MVR system  is of prime importance.
The  lower  the   temperature differential,  the  lower  the
electrical  energy  required   f°ro  recompression.     At  a
temperature differential  of  150  F, about  6   to  7  pounds
water per pound of steam equivalent can be removed  in  the MVR
system  compared  with  about   3  Ibs/water/lb/steam   in  the
four-effect evaporating system.   These calculations hold
provided that boiling  point  rise  (BPR)  (previous^ discussed
in Section  2.2)  is not higher  than about 4  or  5 C.   If the
BPR is  not excessive,  the final -  temperature differential at
the exit of the  vaporizer  can be  low and  the  evaporating
capacity  of  the  system  will  be  high.   With  this  low
temperature   differential,   only   a   moderate   amount  of
recompression is  needed to attain the necessary  pressure and
temperatures of  the  saturated  vapor.   At the Ocean  County,
New Jersey, facility,  a  950  HP  (650 KWH)  compressor will be
used for the  MVR  system  in which  there is also  a  two-effect
forced circulation evaporating system  in series  after  the MVR
unit for final drying.

Influent sludge  solids  contents of  not  more  than about  8
percent have been felt important for  the  Ocean County system
largely because  of the ease  thereby  in avoiding the  "gummy
phase".  Addback of partially dried solids can be avoided by
doing the bulk  of  the  evaporating  in  the  MVR unit, provided
the feed  sludge  to be dried is properly metered  into the
sludge-water-oil  slurry  (liquor)  in the  MVR unit  (e.g.,  20
parts liquor at 50 percent solids  to  1 part feed  at 7 percent
solids).    In  this manner, the  percent  solids  (water-solids
basis)    is   then  sufficiently  high  that   the  critical

                             2-14

-------
The ERM Group
     FEED
     BIOMASS
     O 5-15X
     SOLKT
   FLUID TANK
                                                             •VENT
                                                        VACUUM SYSTEM
        CARRIER
        OIL
MECHANICAL
  VAPOR
  RECOM-
  PRESSION
EVAPORATOR 20
                                                 WASTEWATER
                                                   VAPOR
                                   2ND
                                   EFFECT
                                      WASTEWATER
                                                 s&~
  FIRST
:VAPORATOR
 STAGES
                                                                     VAPOR
     1ST
     EFFECT
                                                                   SOLIDS FOR FUEL
                                                                    OR FERTILIZER
                                                SECOND
                                              i VAPORATOR
                                                STAGES
                         ^TC^      J  c
                                                                                              STEAM
               OIL-WATER
               SEPARATOR
               (SEE FIG. 2-2)
WASTE
WATER
TO POTW
                    _  STEAM "-—,—-^    I    STEAM
                    CONDENSATE        J CONDENSATE
                    (TO OIL-WATER V_/TY  (TO OIL-WATER
                    SEPARATOR)      £±_}  SEPARATOR)

              BY-PRODUCT __      DRY
              "   OIL               + OIL
DRY BIOMASS ^NTRjfUGE
                  I MIAI-  |—
                  CARRIER
                  OIL
      OIL DISTILLATION
         SYSTEM
                                                              CARRIER OIL
                      DRY DEOILED
                      BIOMASS O
                      98% SOLIDS
                                                                             (ALSO CALLED A
                                                                             HYDROEXTRACTOR)
                              SEE FIG. 2-3 FOR DETAILS
            FIGURE. 2-5.   PROCESS FLOW DIAGRAM  OF  THE MVR/C-G SYSTEM.

-------
water-solids ratio  is never encountered.  Besides eliminating
addbacks,  considerable  economies can also be  realized  using
the MVR  unit because  only  simplified equipment is needed for
dewatering the sludge prior to C-G processing.  Boiling point
rise  is not  likely  to be  a problem  with  sludges in  MVR
systems until the  solids contents reach about 60 percent
(water basis).

Operating experiences with a  light oil MVR C-G system are not
yet available.  Thus, it is not yet know how  the economics of
an MVR system will  compare with  a  four-effect  system as  well
as  with  other alternatives  for  drying wastewater  treatment
sludges.
2.4  Light-Oil Systems

A summary of  the  C-G  light-oil  systems  in  operation, design,
or  construction  are  presented  in  Table  2-1.    The  four
municipal wastewater treatment authorities: Los  Angeles City;
Los  Angeles  County  Sanitation Districts;  Mercer County,  New
Jersey; and Ocean County, Mew Jersey  are the  only  full-scale
municipal wastewater sewage sludge drying  systems  in design,
construction, or  operation  in the USA.  Table 2-2  provides a
summary of the estimated capital and O&M costs for  these four
systems and  the  Burlington  Industries  system.   AJ..1 	Q_fL_..the
municipal  systems  were  funded  as  IjmQj£a_iJ^Le_,  under  the
Innovative/Alternative  (I/A)  provisions of  the Clean Water
Act.

Dehydro-Tech Corporation through Hanover Research Corporation
owns the patents  for  the C-G process and  licensing fees  are
negotiable.   The estimated  capital and  bid  costs  of  the
Hyperion C-G System were respectively $43.2 and $30 million,
of  which the license fee  will range from $1.4 to  $1.7
million,  depending  upon.jthe._ abil ijty _to  meet performance
guarantees.    The  actual  cost as of  March 1987, was  $43
million  (Table  2-2) .   The  influent  solids  concentratfltmrs-j
projected  energy and  oil requirements,  and the  operating
schedule for the five U. S.  C-G  systems  is  presented in Table
2-3.  The two Los Angeles systems will  operate  continuously.
It is anticipated that  redundancy in  the system (e.g., extra
pumps,  centrifuges,  etc.; Table 2-4)  will  permit routine  and
required  maintenance   to  be   performed   without  adversely
affecting  these  systems.     Operational   experience  will
determine if sufficient redundancy  has been provided.
                             2-16

-------
                TABLE 2-2  SUMMARY OF UNITED STATES C-G LIGHT OIL SYSTEM CAPITOL AND OiM COSTS (IN MILLION



System
City of Los Angeles,
CA. Hyperion Plant
Los Angeles County
Sanitation Districts
Mercer County, NJ
Trenton, NJ
to Ocean Co. Mastewater
1 Authority, NJ
Burlington Industries
Clarksville, VA



Descr iption
4-effect C-G system

4-effect C-G system

4-effect C-G system

MVR 2-effect C-G system

5-effect C-G system

Capital Costa
Carver-Greenfield Total Project


Est. Bid Spent(a) Est. Bid
43.2 30.7 43 224 158

60 54.7 (c) 48.7 120

12 12 35

38 13

3.3 4.23

OtM Costs
Less(b)
OiM Benefit
(5/ton) (5/ton)
40-50

80 7

N/A N/A

N/A N/A

30

Total Costs


(9/ton)
160-200

248

N/A

N/A


-------
                                                            TABLE  2-3

                                         SUMMARY OF  UNITED  STATES C-C LIGHT OIL SYSTEMS
                                        OPERATIONAL  INFORMATION AND  ENERGY REQUIREMENTS






NJ
I
oa

System

City o£ Los Angeles, CA
Los Angeles County
Sanitation District, CA
Mercer County, NJ
Ocean County Wastewater
Authority, NJ
Burlington Industries
Clarksville, VA
Description

4-e££ect C-C
4-effect C-G

4-ef£ect C-G
MVR 2-ef£ect

5-e£fect C-G



system
system

system
system

system

Operational % Solids % Solids Projected Energy Requirements
Days per in water* in oil BTU/LB Make-up Oil**
week in feed in feed water gallons/day
evaporated
7 20 11 363 174
7 19 9 362 264
(2 trains)
5 22 17 363 110
3 7 10 200 44

5 4

 « Composition of outgoing sludges 2.5-3% water,  0.1 to 0.2%  Amsco oil,  1.3  to  2.3%  sewage  oil,  95%  solids.
** Cost per gallon is 51.50 as of March 1987.

-------
                                            TABLE 2-4




                SUMMARY  OF UNITED STATES C-G LIGHT OIL SYSTEMS-SYSTEM  REDUNDANCY
City of LA,CA LA County San. Dist.,CA Mercer Co.,NJ
On Stream Time
Number of Trains
Fluidization
Evaporation
Oil Removal
1° Oil Distillation
Oil Recovery
Dilute Acid
Vent Gas
Ni trogen
Start-up Boiler
Cool ing Tower
Control Approach
Continuous
2 + 1 (a)
1 + 1
2 + 1
2 + 1
1 + 1
1 + 1
1
1 + 1
1
Temporary
None
Semi-Automated
Operation
Continuous
3 +
1 +
3 +
3 +
1 +
1 +
1 +
1
1 +
1
1
Spares
1
Spares
Spares
1
1
1

1


Fully Automated
Operation
5 Days/Week
1
1 + 1
1
1 + 1
1
1
1
1
1
1
W S A C
Semi -Automated
Operation
Ocean Co., NJ
3 Days/Week
1
1 + 1
1
1
1
1
1
1
Bottles
1
1
Semi-Automated
Operation
WSAC
Wet Surface Air Cooler (a) 2+1=2 operational units plus 1 redundant  unit.

-------
                           SECTION 3
                   OPERATIONAL  EXPERIENCES
 3.1 Operating Systems

 The operating  experiences of  three  wastewater C-G  light-oil
 systems  were discussed  during  the  seminar:  1)  the  limited
 start-up experience  of  the City of Los  Angeles  Hyperion
 system,  2)   the  Burlington  Industries  industrial wastewater
 system in Clarksville, Virginia, and 3)  a pilot-scale  system
 operated for  18  months by the  Los Angeles County Sanitation
 District (LACSD).  Brief discussions of some of the  operating
 experiences  at these systems are  presented  in this section.
 More   detailed   discussions   of   specific  problems   and
 recommendationsare  presentedin  Section  4.Discussions of
 the operating  experiences at  other  systems can  be  found in
 Reference 1.
 3.2  City of Los Angeles Hyperion C-G Treatment System

     3.2.1  Project History

 The City  of Los Angeles Hyperion  Wastewater  Treatment Plant
 serves approximately  3.4 million people  in  a  640  square mile
 area.     Approximately  420  million  gallons  per   day  of
 wastewater are treated at this facility.  Since the treatment
 plant  is  subjected to marine  secondary  discharge standards,
 not  all  of  the  wastewater  currently  receives  secondary
 treatment.  Currently, only  about  100  MGD receives secondary
 treatment.    The  combined  plant  effluent of  primary  and
 secondary effluents  is then discharged  to  the  Pacific Ocean
 through   a   five-mile  outfall.     Primary  and  secondary
 anaerobically digested sludge  from the  treatment plant  is
 either landfilled  or  discharged to  the ocean  through  a seven
 mile outfall.

 In the early 1970s,  the city began investigating  alternative
 means  for  sludge disposal.   State  and  federal agencies
 required  that  faster progress be  made towards developing  a
 better sludge management system.  Legal actions  resulted, and
 a Consent Decree was  signed  in  late  1979  or early 1980.   The
 provisions of the  Consent  Decree  specified that  design  of  a
 sludge treatment system had to be completed by December 1982.
 Many fcerbni^]  issues
r e s o lutiogLnf  +•*»**«»  issues required an  additional  two  yea r s
JLQ resolve!   Thus,  the  New Jersey  based engineering  firm,
P^h0r^h^rUrr-^rr"n"ot  able  to begin  design and  detailed
engineering of the C-G system until  February 1982.
                              3-1

-------
 The  Hyperion Energy Recovery System  (HERS) ,  of which  the C-G
 system is a component,  is the  largest  I/A project  funded  to
 date by EPA, and  as  of March 1987, was  98  percent  complete.
 The   HERS  consists   of  several  components:     mechanical
 dewatering  of  the digested sludge  using  centrifuges,  the C-G
 process,  combustion  of  the  sludge  for  steam  and  power
 generation,  and combined-cycle digestor  gas  power  generation
 using  gas   and  steam  turbines.    Figure  3-1  presents   a
 schematic  flow  diagram  of   the  Hyperion  treatment  plant
 including HERS.

      3.2.2   Cost

 Due— t-Q— th.e_JJjgjLted time . _f_rame.-ayailabJ._e for design  imposed by
 t-hj5  C o n s ej^t— Hec-r-e-e-, — a-d-gg+i-a-t-e — te-J-m-e — wa-s — oo-t— -a-v.ajLI.ab _l.e__f o r
 sufficient   quality  control   and  checking  of  the  design
 drawings.  The  initial  estimates  for  the constructon of the
 entire HERS system by  the various design engineers involved
 was  $222 million.   The  construction  bids,  however,  were
 significantly   less,  and  the  project  was  awarded  to the
 general contractor at $158 million.  The lower bid price was
 believed  due    to  bidding   during  a   depressed  time  for
 construction jobs.  Due to factors  such  as  design changes fo_r
                 ^ i i-y  of the system and the insufficient time
     q "*_]_•< <~y  ^nnt-mi — off  the  nriryjnal  design drawings, numerous
change orders  were needed.   Change  orders as  of  February
1987,  have  totaled $58 million.   Thus,  the total project
construction cost as of February 1987, has been $216 million
or  within $6 million  of the  original estimate.   Under  the
construction grants  program, however,  funding for the project
was limited  to the contractor bid of  $158 million  plus  5
percent  for  change orders  totaling  $166 million.   Thus,  the
city  has  had   to  fund   an   additional   $50   million  for
construction of the  system.

     3.2.3   Operational  Problems

Limited  start-up testing has been  conducted  at  the Hyperion
plant,   and   several  problems,  many   of   which  have  been
overcome,  were  encountered   during  this  start-up.     For
example,  compost was  used  to  provide  the solids  needed  to
begin  operation of the system and avoid  the  gummy  phase.
Wood chips  present in some of  the compost were  too  large  to
pass through  the spiral  heat exchanger clearance of 5/16 -inch
to  7/16-inch,  and  the  heat exchanger  became plugged.   The
exchangers were cleaned  and the wood chips were subsequently
screened out.    r_avitation  in  pinch  valves  due  to high
^ ffa^aflHai  pressure  through  the valves was  also a problem.
•Replacement  of these valves  was a rather  simple but very
costlv solution in both  time and money.  Flow measurement  has
been another  problem that is  being approached differently  by
the  various  municipalities. The best  flow metering  solution

                              3-2

-------
Tfi9 ERM Group.
                                    HYPERION ENERGY RECOVERY SYSTEM
 U)
 I

PRIMARY
SLUDGE



•—•*»•
REMOVAL

—
COMPRESSION
DEHYDRATION
FILTRATION

r
ANAEROBIC
DIGESTION
I
-H~

MECHANICAL
DEWATERING

.._.
—


GAS
TURBINES
t
ELECTRIC
POV*R
—

-»*•

WET CAKE
STORAGE

—
^
H
•-ii ^^

HEAT
RECOVERY
STEAM
GENERATION



CARVER-
GREEHnELD
DRYING
PROCESS



DISPERSION
STACK

STEAM
TURBINES
ELECTRIC
POWER
SDF
STORAGE

*-

FLUE CAS
CLEAHUP
t
HEAT
RECOVERY
STEAM
GENERATION
I

THERMAL
PROCESSING
	 A 	 _


WASTE
ACTIVATED
ILUOOC
^


WAS
THICKENING
                                          STEAM FLOW
                                          GAS aow
                                          SLUDGE SOUDS FLOW
            FIGURE 3-1
SCHEMATIC OE  THE  HYPERION  SLUDGE
PROCESSING FACILITY.

-------
 is not  known at  this time.   Mass flow  meters  were used at
 HERS to monitor solids flow  rates  at  key  points.
,Fa^Ture of pump goaig has  been  a  significant  problem.  Due to
 tKe"~~prrs"s i b 1 i ty  for potentially dangerous hot  hydrocarbon
 leaks,  double  mechanical seals  had been  specified.   The
 inside  seal  exposed  to  the  water-solid-oil  slurry usually
 failed  within  3  to 10  days of  installation.   The  use of
 extremely  hard  tungsten carbide  on both  faces  of  the seals
-has   apparently  resolved   the   problem — n?;3r ^-o^m"     5
 non-flammable oil  is  used as  a  gearing and cooling — media
 between the double  seals.   Design engineers have recommended
 that the inside seal, exposed to  the  sludge, be flushed using
 oi_l  as the  flushing   agent.   _TJa.e — pumps — ^lir rpntlv  being
'utilized were  designed  for  more routine  wastewater  sludge
 handling needs.  Precise-tolerance  chemical-quality pumps are"?
 perhaps more appropriate for  a  C-G  system.                 — '

 Another  significant problem  encountered  was smoldering  of
 srTM rig  within  a section of the process  piping.   Because of
 the  problems  encountered  during  construction,  the  steam
 generation system  was  not  on-line  when  the  C-G  process  was
 undergoing start-up.  A  temporary skid-mounted boiler system
 was  thus  installed to  permit  operation  of  the  C-G  system.
 Partial  failure of  the temporary  process boiler allowed a
 section of  pipe  to  cool.   Soli/l*?   in  ^^"3.  pipeline  then
 accumulated  on tb*»  int-pri-ojs — p>pn \jjjTi i_s_.  _Air  subsequently
 entered the pipeline when _a — coal  was  inadvertently  lef-t  out^
 .g£— ±£±_ -L£S££ni ^nrir\a_ routine ' maintenance.  The  air  allowed
 auto-oxidation_of  the fatty acids in  the  solids  on  the  pipe
 walls   to   occur .     This  exothermic   reaction   generated
 sufficient  heat to  oxidize  other  orqanirsr   and  smoldering
 continued.    It is  estimated  that  a  maximum  temperature  of
 1300°F had been reached  in  a  six-foot section  of  pipe  by  the
 time  an  operator  noticed  that  the  pipe  insni*i-inn   was
 saqgjLaa. .   Steam flow was  then increase^ to  cool the pipe
 (steam  is  considerably  cooler  than  1300  F) .   Damage to  the
 system was thereby  limited  to the heated  section  of  pipe  and
 nearby  plastic  valve seats.  Design  engineers stressed  that
 no explosion occurred  and that  other drying technologies
 (e.g., flash dryers, rotary kilns) have a higher  risk of  fire
 or explosion than  the C-G  technology.  After  this  incident,
 this section of the C-G  hydroextraction system was redesigned
 to prevent air from entering vapor transport lines by raising
'fh^_np^r=iting pr^qB-i^" fmm u^nnm  fo_ atmospheric.   Nj.tr ngej
blanketing of  key  processing  units  during  maintenance  was
also added  to reduce fire hazards.

 Pining Changes were also made and were being  implemented  in
March 1987.   Smaller  pipe  sizes  are  being used  t.a  inrrftaae
the flow velocTt7""to"5JL-l^t per  second  or  greater in  the
lpor lines!   Soot blowers  (special cyclonic  dust  collectors)

                               3-4

-------
 are also being  installed  to help clean out vapor lines,   hhen
 the pipe changes  are  constructed,  some loss of flexibility  in
 operation will  result;  however,  safety will be improved.


 3^.3  Burlington  Industries

     3.3.1  System  Description

 The  Burlington   Industries  textile   plant  in   Clarksville,
 Virginia,     investigated     pyrolysis,     multiple    hearth
 incineration, and fluidized bed  incineration  before selecting
 a  five-effect C-G system to  handle  wool scouring wash water
 and  bio-sludge.   Their  reason  for selecting  the C-G system
 was  not justified on  the  basis of  cost per  ton  for  dry
 solids.  Instead, their system was selected to accomplish the
 following objectives:

     1.   To  avoid  the  lagooning of the  malodorous wastewater
          from  wool  scouring  by  drying  the  solids.   The
          resultant dry lanolin  from wool  scouring can now be
          sold  and  the  dried biological  solids  (biosludge)
          from cleaning the finished  wool  are now acceptable
          for disposal at the county landfill.

     2.   The  second  objective  was  to  decrease  chemical
          consumption,  cost and  quantity of resultant solids
          generated     at   the   wastewater  treatment  plant
          because of evaporative drying  capability.

 The  lower  cost  land  application  alternative  for   sludge
 handling was  prohibited by the Virginia  Health Department.
 Furthermore,  air  quality   concerns, eliminated  alternatives
 involving incineration.

 Capital expenditures were $4.13 million  for a five-effect  C-G
 system with an  original design capacity of 20  tons per  day
 solids 3nH w^ter  evaporation rate  of  19_^5.aa_aQJJU3i3s of  water
 per hour.  Currently, the system is required  to  process only
 6.0  dry tons of solids  per day.   Construct ion  began in
 November  1981, and completed  inCJajiua~ry  19JT3T.  A limited
 starf-np ™*s  Conducted in  February  L983;   however., official
 start-up was begun in September  1983.   Annual  operating costs
 are approximately  i? I 8U , UUO "adjusted for  depreciation and
 resource  recovery.   Recovered lanolin is sold  and helps
 offset the cost of operation.  The net cost of the Burlington
 C-G system is  approximately  $430 per  dry  ton which includes a
 cost allowance  for  recovered lanolin.    As  previously  noted,
 the cost per dry ton of solids produced was not the criterion
Burlington used  for  choosing the C-G  technology.  Instead,
Burlington  chose the C-G  system  to  solve their difficult


                              3-5

-------
problem of  recovering very  soluble  solids from  dilute a
wastewater  (0.5  to 1.0 percent solids).

      3.3.2   Operational Problems at Burlington

Process  control was  initially  a  problem as changes  in the
solids   concentrations   interfered  with   the   flow  meter
operation.    Pressure control  helped  overcome  part  of  this
problem.     Major  process   problems  experienced  included
inaccurate  flow  measurement  (corrected  by replacement of some
flow  meters and by manual  half-hourly  solid-water-oil  ratio
determinations) ,  excessive  loss of  the  carrier  oil  (to  be
corrected  by adding  a more efficient  oil-water  separator),
and centrifuge  plugging and wear  (corrected by  flushing the
centrifuge  with carrier  oil  and   installing removable  wear
plates  in  the centrifuge).   Plugging of the vapor lines  with
solids was  also  a  problem.   This problem  has been practically
eliminated  by modifying the piping  to  increase  the  velocity
within  the  vapor lines and  manual  cleaning  of  the five-foot
long  vapor  line between the de-oiler  and the scrubber.   To
clean out  the  small  amount of solids that build up takes
about five  minutes  once during  each  shift.   Additional
operational   problems  and   the   corrective  measures   are
summarized  in Tables  3-1 and 3-2.

Burlington  Industries  reports  that, in  general, their  C-G
system   is   operating  satisfactorily   and  is   currently
encountering  routine  maintenance   problems which   consist
mostly  of   leaks  and  seal  failures.     Burlington  still,
however, is  dealing with excessive pump erosion  problems.


3.4   LA County Pilot  System

      3.4.1   System Description

The Los Angeles  County Sanitation  Districts (LACSD)  operated
a two-effect C-G pilot plant system for  18 months  in  order  to
generate sufficient dry sludge  for combustion and  air quality
testing.   The LACSD  intends to incinerate  the dried  sludge
and needed  to ensure  that the incinerator emissions would not
exceed  air  quality   criteria.     A secondary   purpose of
operating this pilot  plant was  to acquire a greater knowledge
of  the  C-G  process.    This  part of  the pilot  testing was
limited to about 1 of the 18 months and  was mostly incidental
to the primary purpose.  The amount of  dried sludge  required
for test burning was  originally estimated to be  about four to
five  tons  of dry  sludge.    The actual  sludge  requirements
turned out to be on the order of 40 to 50 tons.

Operating costs  for a full-scale C-G system  are estimated to
be $73/dry  ton  based  upon experience  gained with the pilot
                              3-6

-------
                                          TABLE 3-1

                          PROCESS PROBLEMS AND CORRECTIVE MEASURES
                              BURLINGTON INDUSTRIES C-G SYSTEM.
          Process Problems
      Action Taken
1.    Lack of process and operational
     knowledge including
     instrumentation.

2.   Operating parameters and standards
     not established.
      Initial  lack of knowledge of the unknowns. 3,
      For example, how dry the product needed
      to be was  unknown.
      Excessive  carrier  oil  loss  -
      9-12  gph vs  3  gph  std.
      Plugging of 4th  and  5th  stage
      heat exchangers
Resolved with time and
exper ience.


Resolved from pilot data and
field experience - trial and
error.

Handled one by one.  For examples,  it
was important to maintain low water
content in the dry material as well
as a pH of about 5.0.  High water
content would produce materials of
rock like consistency.  Otherwise,
there was great difficulty in handling
the dry product through the centrifuge,
hydroextractor and conveyors.  The
addition of biosludge to the lanolin
rich material between the fourth and
fifth stages of drying helped the
operations.

Tested all known sources for
losses.  However, requires more testing
for oil losses.  Testing other systems
for oil/water separation to improve oil
recovery.

Resolved with time and experience:
a.  Determined proper oil to solids
    ratio @ 7-9:1.
    Additional heat exchangers.
                                                         Removed 90
                                                         exchanger.
                ell in top of heat

-------
                                            TABLE 3-1

                            PROCESS PROBLEMS AND CORRECTIVE MEASURES
                           BURLINGTON INDUSTRIES C-G SYSTEM (Cont'd).
            Process Problems
      Action Taken
       Flow measurement - flow meters
       malfunctioning due to type of
       product.
to
i
00
        Foaming  caused  by  rate  of  throughput
        in  C-G  System and  detergent  in
        product.   Any small  amount of foam tends
        to  emulsify  water  with  oil in the
        oil/water  separator  operations
        and reduce the  capacity of separation.
To maintain adequate control of  the
5th stage, the oil/solids ratio  should
be from 8/1 to 10/1.  It is very
difficult to sense the flow and
consistency of a solids to water to
oil mixture that continually changes.

Using ALPHASOMICS meter in sludge
line - not 100% satisfied.
Controllotron going into fault mode -
unable to contol system automatically
in the 5th stage.  Okay where product
is not too dense.  Tried density meter
without success.

The ratio is currently determined
manually each 1/2 hour by sampling and
separating into fractions with a bench
centrifuge.  A suitable monitoring
device for automatic operation is being
sought.

Problem partially resolved by
requesting cut-back on use of
detergent when foaming occurs and
temporary one hour cut-back on flow
rate of wastes to be dried thorugh the
rate of wastes to be dried.

-------
                                              TABLE 3-1

                              PROCESS PROBLEMS AMD CORRECTIVE MEASURES
                             BURLINGTON INDUSTRIES C-G SYSTEM  (Cont'd),
                     Process Problems
                  Action Taken
    8.   Oil/water  separator  -  capacity, and
         carry  over  of  oil  and  fines.
i
vo
     9.   Moisture/oil in hydroextractor
     10.  Centrifuge plugging.
     11.  Centrifuge erosion.
8.   Present operation is drying 75 GPM
     scouring waste (1/2 to 1% solids) and
     4 GPM 20% solids bio-sludge from
     finished wool cleaning.  This is the
     original design capacity, facilitated
     by modifications made to give more
     evaporation capacity.  Both Burlington
     and Dehydro-Tech are working to reach
     higher capacities.  Further increase in
     throughput rate may be assisted by a
     larger capacity for oil/water
     separation and/or vapor foam
     disengagement.

9.   Problem overcome by improving moisture
     content & quality of feed to
     centrifuge.

10.  Problem resloved by flushing with
     carrier oil when shutting down.

11.  Resolved problem by installing
     removeable wear plates on inside of
     casing.
          Problems not resolved - 4, 6, 7,  and  8

-------
                                           TABLE  3-2

                    MECHANICAL AND PHYSICAL PROBLEMS AND CORRECTIVE  MEASURES
                                BURLINGTON INDUSTRIES C-G SYSTEM.
           Mechanical & Physical
                                                             Action  Taken
to
I
1.   Building size - too small.

2.*  Material of construction -
     CS vs SS piping, tanks, etc.
     Leaks - erosion & corrosion.

3.   Design  changes  - piping,
     equipment,  etc.

     Inadequate  capacity based  on  original
     design  for  80  GPM  (37,000  Ib/hr) at
     3.5%  solids in  the wool  scouring waste
     Actual  solids  content is  1/2  to  1%.
     Needed  capacity is  for  90  to  100 GPM
      (50,000 Ib/hr).

     Hydroextractor -
     a.   Tines  of rotor.
     b.   Tines  drives.
     c.   Propane heater  sink.
     d.   Pluggage in vapor lines.
        e.  Pluggage in scrubber bubble
            trays.
        f.  Plate heat exchanger pluggage,

        g.  Scrubber bottom outlet
            pluggage.
1.    62'  x 52' - too late to correct.

2.    a.  Replacing as required.
     b.  Feeding ammonia to increase pH.
         1.0#/hr. @ 5.0+ pH.

3.    Altered/modified/removed as
     required.

4.    Installed additional small heat
     exchangers to increase capacity.
     a.  Replaced tines with angle
         iron.
     b.  Replaced "Carter" drives.
     c.  Made three pass - modified.
     d.  Increased velocity and in-
         stalled manual rake between
         deoiler and scrubber.
         Modified piping.
     e.  Remove disk on tray opening.

     f.  Replaced with spiral heat
         exchanger.
     g.  Modified bottom of scrubber
         and installed C.O. sparger.

-------
                                          TABLE  3-2

                  MECHANICAL AND PHYSICAL PROBLEMS AND  CORRECTIVE MEASURES
                         BURLINGTON INDUSTRIES C-G SYSTEM  (Cont'd).
          Mechanical & Physical
                                                             Action Taken
6.


7
Agitator maintenance - bottom
bearing and shaft failure.

Pumps - erosion, corrosion.
      Pump  seals  - mechanical  by
      Chesterton.
 9.    Pump impellers  -  wrong  design  •
      should  have  been  open  impeller
 10.*  Leaks - piping.


 11.*  Acid system -  leaks  and  pump
      fa ilure.
 12.* Vacuum system -  replaced.
6.   Replaced with larger agitator and
     shaft - no bottom bearing.

7.   Replacing and changing materials
     of construction - Durco CD4M.
     Fifth stage casing being replaced
     (because of acid attack) with lower
     cost CD4M steel compared with stain-
     less steel.  CD4M impellers holding up
     very well.

8.   a.  Still experimenting.
     b.  Trying bellows vs spring
         loaded seal - Chesterton.
     c.  Trying Sealol bellows type
         seal.
     d.  Both seals holding up very well.

9.   Replacing as required to prevent
     wool, trash, etc. from plugging
     impeller.

10.  Replacing with SS.  pH control with
     ammonia feed.

11.  a.  Replaced piping  with coated
         piping.
     b.  Repair pump as  required.

12.  Replaced liquid ring pump 3  times-
     last pump stainless  steel.

-------
                                          TABLE 3-2

                  MECHANICAL AND PHYSICAL PROBLEMS AND CORRECTIVE  MEASURES
                         BURLINGTON INDUSTRIES C-G SYSTEM  (cont'd).
          Mechanical & Physical
                 Action Taken
13.   Centrifuge.

14.   Pelletizer


15.   Solids handling
      Moyno  Pump  (Sludge)  -  Excessive
      pump maintenance  and high
      pressure  drop.
13.   Factory rebuilt in Jan.  1986.

14.   Never tried to operate -  solids
     too dusty.

15.   Replaced belt conveyors with screw
     conveyors.  Fair service  now.  Will
     replace.

16.   Replaced 4" piping with 6" piping.
 General  Notes;

 *Items  1,  7,  10,  11  &  12  are  corrosion  problems  that occurred  in  the  condensate piping  after
  the 4th stage.   These problems  occurred due  to  sulfuric  acid  added at  that  stage  to permit
  separation of  the lanolin.   The subsequent addition of ammonia after the  5th  stage  should
  eliminate many  of the corrosion problems  encountered  in  the past.
 Ma intenance Costs;

           Direct maintenance $25,000  to  30,000

 1987      Overhaul  type of maintenance,  which
           includes  items such as  vacuum  pump
           changes,  piping, etc.   This type  of
           maintenance should be  reduced  om
           future years.
         $30,000/year

          75,OOP/year
         $105,000/year

-------
                                          TABLE 3-2

                  MECHANICAL AND PHYSICAL PROBLEMS AND CORRECTIVE MEASURES
                         BURLINGTON INDUSTRIES C-G SYSTEM  (cont'd).
          Mechanical & Physical
                 Action Taken
13.   Centrifuge.

14.   Pelletizer


15.  Solids handling
      Moyno  Pump  (Sludge)  -  Excessive
      pump maintenance  and high
      pressure  drop.
13.   Factory rebuilt in Jan.  1986.

14.   Never tried to operate - solids
     too dusty.

15.   Replaced belt conveyors with screw
     conveyors.  Fair service now.  Will
     replace.

16.   Replaced 4" piping with 6" piping.
 General  Notes;

 *Items 1,  7,  10,  11  &  12  are corrosion  problems  that  occurred  in  the condensate piping after
  the 4th stage.   These problems occurred  due  to  sulfuric  acid  added  at that stage to permit
  separation of  the lanolin.   The subsequent addition  of ammonia after the 5th stage should
  eliminate many  of the corrosion problems encountered in  the past.
 Maintenance Costs:

 1986      Direct maintenance $25,000  to  30,000

 1987      Overhaul  type of maintenance,  which
           includes  items such as vacuum  pump
           changes,  piping, etc.   This type of
           maintenance should be  reduced  om
           future years.
         $30,000/year

          75,OOP/year
         $105,000/year

-------
 system.   Including amortization  of  the $120 million capital
 C°S^  3f  «??/*:, Percent  ^terest  for  20 years  yields  a  total
 cost  of  $248/dry ton.  Currently, the LACSD pays $38/dry ton
 for composting and  $50/dry  ton  for landfilling.

 Several  operational  problems  were  experienced  in  the  pilot
 plant   because:   1)  the   pilot  system   was  designed  for
 processing  cattle feedlot manure and not  sludge,  and  2)  the
 age  of the pilot system made maintaining operation  quite
 difficult.       Under   these   circumstances,   considerable
 modification  to  the pilot plant  was  necessary.   For example,
 abrasion of  pump  seals was  a  significant  problem as  the
 original seals lasted only  four to seven days.  This abrasive
 problem was believed  to  be  due to the alignment of the pumps,
 the  nature  of  the seal,  and the  abrasive  nature  of  the
 sludge.   Tungsten carbide  on  tungsten  carbide  seals  with  an
 oil  flush between  the  seals  was  recommended  as an  interim
 improvement  for  future  systems  but was  not believed  to  be  an
 adequate long-term  solution.

 The  LACSD  was  never were able  to  overcome  poor centrate
 quality in  the  recycle stream (i.e.  more  than expected
 quantities  of solids were  carrying  over  into  the centrate.)
 A planned solution  by LACSD is the use of a greater number  of
 smaller centrifuges operating at a lower speed (gravitational
 force).     Lower speeds  also  will  reduce  wear  problems.
 Others,   including  Dehydro-Tech,    believe   that   higher
 gravitational  force is  necessary  to  prepare a good cake  and
 to capture  a  sufficient  amount of the fines.

 Fires   in    the   hydroextractor.  also   occurred.      The
 hydroextractor was  not  air-tight, and on  two occasions,  slow
 smoldering  fires occurred  after  the system  was shut  down.
 Concerns regarding odors  were  also expressed.  The pilot
 system was  1/200  the  size of the  full   scale  plant to  be
 built,  yet  odor  complaints  were received  as far  as  1/4  mile
 away.   Since  a   full-scale C-G  system  is  totally  enclosed,
 except  for  a  limited number  of exhaust vents,  any  possible
 odor  problems  should  be  controllable.

 By far  the  greatest concern expressed by  the  LACSD was  with
 the  solids  handling.   For example,  plugging  o£__the_ hea t_
 exchanger s_wa§_f e 11 to be a  s igjiJULicant., prSSl£JiL~s.in£e__i t
 occurred  continually 3uHng~~their  pilot  operation.     As
 previously pointed  out,  Los Angeles  City  originally  had
 problems  with plugging  of  the  spiral  heat  exchangers  with
 wood  chips.   The  city  later  felt  that  this  problem  was
 overcome  by screening larger  solids  pieces out  of  the  test
 materials being  used  and better  process  control to overcome
 going  into  the "gummy phase".  It is not  yet  known if  other
 problems  will   result   in  plugging  of   the   spiral   heat
'exchangers.

                             3-13

-------
system.   Including  amortization of  the  5120  million capital
cost  at eight  percent interest  for  20 years yields  a  total
cost  of $248/dry ton.  Currently,  the  LACSD pays  $38/dry  ton
for composting and 550/dry ton for landfilling.

Several operational  problems were  experienced  in the  pilot
plant  because:   1)   the  pilot  system  was   designed   for
processing  cattle feedlot  manure and not sludge,  and 2)  the
age of  the  pilot system made  maintaining  operation quite
difficult.       Under   these   circumstances,   considerable
modification to the pilot  plant  was  necessary.  For  example,
abrasion of pump  seals  was a  significant problem as  the
original seals lasted only four to seven  days.   This  abrasive
problem was  believed, to be due to the alignment  of the pumps,
the  nature  of  the  seal,  and  the  abrasive nature  of  the
sludge.   Tungsten carbide  on tungsten  carbide seals  with an
oil  flush between the seals was recommended as  an  interim
improvement  for future systems but was not believed to be an
adequate long-term solution.

The  LACSD  was  never were able  to  overcome poor  centrate
quality  in  the recycle stream (i.e.  more than  expected
quantities  of  solids  were carrying  over  into the centrate.)
A planned solution by LACSD is the use  of a  greater number of
smaller centrifuges operating at a lower  speed (gravitational
force).     Lower  speeds   also  will  reduce  wear  problems.
Others,    including   Dehydro-Tech,   believe   that   higher
gravitational  force is necessary  to  prepare  a good  cake and
to capture  a sufficient amount of the fines.

Fires   in    the   hydroextractor   also   occurred.      The
hydroextractor was not air-tight, and on  two occasions,  slow
smoldering   fires  occurred after  the system was  shut down.
Concerns regarding  odors were  also expressed.  The pilot
system  was  1/200  the size  of  the  full scale  plant to  be
built,  yet  odor complaints were  received as  far as  1/4  mile
away.   Since  a full-scale  C-G  system is  totally enclosed,
except  for  a  limited number  of  exhaust  vents,  any possible
odor  problems  should be controllable.

By far  the greatest  concern  expressed  by the  LACSD  was  with
the  solids  handling.   For  example,  plugging  of___th_e .heat_
exchangers -was felt  to  be_a^3JLULLfl a n t  pAfl&Iam^ 1 nc e_.i t
occurred ^i^l^^^^^J^  Anally  had
previously  pointed  out, LOS  nuycj-c  ,         -J          • ,_,_
^  ,.     ^..'V,  „!,„.„< no of  the  spiral  heat  exchangers  with
problems with  P^1"   later  felt  that this  problem  was
wood  chips.   The city  la* «         .         of  the  fcest
         bv screening  .target  auj.±<^   c
          Lused and  b.tt.r  prcc...  =»tr.l^o ovrcoj.

                             '
exchangers.
                             3-13

-------
The LACSD  also  had plugging of  one-inch  lines in the pilot
operation, yet  the spiral heat  exchanger  specifications for
all four  systems  call for openings of 5/16  to  7/16-inch.
Backflushing  capability  for the  heat, exchangers  could help
alleviate  this  problem    as   could   prescreening  with  a
1/10-inch  mesh  screen and/or  use of a  Muffin Monster  (TM)
with a 1/8-inch mesh screen.  There was also discussion about
the possible  need  for a  Reitz  mill  (a fine grinding  impact
type mill) , but the possible  need for such a device was not
resolved.  A  Reitz mill  would  add  about 150  HP  to the energy
requirements of the system for the City of  Los  Angeles.

LACSD  also recommended that,  if possible, a  municipality
consider  using  the  heavy  oil  system and  eliminate  the
hydroextractors.   The LACSD did  not believe that there was
sufficient knowledge about how light oil systems will perform
and that  new systems  should  not  be designed  until  further
operational experience is gained from the four  plants already
in start-up or  construction.   Foster Wheeler engineers later
noted  that   due   to   the   time   required   for  design,  the
experience gained at the  four  existing municipal  systems/
could  be incorporated into the  design of  any new  systems|
before design of these new systems was completed.
                             3-14

-------
                           SECTION  4
                       RECOMMENDATIONS
4.1  Introduction
Numerous  means  to  improve the  design,  construction,  and
operation  of  the  C-C  system  were  discussed  during  the
seminar.  A brief  discussion of  the major recommendations is
presented herein.
4.2  Responsibilities for Design and Construction

The CG  systems  that appear  to  have had  the  fewest problems
during design  and  construction are  those  systems  which  have
had the  fewest  groups  involved with these  tasks.   The LACSD
and Ocean County  systems,  which have either had one  firm  or
agency in control  of the C-G portion of  the project  or  have
utilized special management techniques, have had fewer design
and construction  problems,  to date,  than  the City  of Los
Angeles  and  Mercer Co.  Th.e  City  of Los  Angeles  has  had  by
• far the  most  complex arrangements   (Tables  4-1  and 4-2) 'with
responsibility  greatly   divided   between   consultants  and
contractors   durj.nq  the__   various   phases  of  design  and
construction.
These experiences  emphasize the essential need  for  a  single
party to have  overall  control  of  th_g, *<=•* ig" — a-R-d construction
to  ensure that meaningful Interface between all parties
involved  with  a C-G  system occurs.   Appointing  one  design
firm as the prime A/E  firm  for a sludge treatment plant could
minimize potential problems and help ensure that good design,
construction,  and start-up  procedures are used.

Foster  Wheeler is  the only  engineering  firm  authorized  by
Dehydro-Tech for the  design C-G systems of with  larger  than
30  dry  tons per  day  drying  capacity.   Typically,  however,
other engineering  firms  are  responsible  for  the design  of
other components of a  total sludge treatment plant which must
mesh  closely  with the  C-G system.   Vertical division  of
design  tasks  appear to  be  superior to  horizontal division.
With vertical  division one firm  designs  ^portion  of  the
plant from the foundations  to the roof.  JU^e-C^ty-^Las.

                                         espo nubilities?)  ajid
                                                          "
                                    with vertical division "of
                                 between  d^er^t-d^ae^
and construction  contractors must  be  carefully managed and
controlled.
                              4-1

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                                           TABLE 4-1

                                        FW SCOPE OF WORK
                                   CARVER GREENFIELD FACILITY
                                         STEP II DESIGN
A-E Consultants
INTERFACES
-Wet Cake
-Dry Product
-Sewage oil
-Utilities
-Electrical
PROGRESS DESIGN
SITE DESIGN
CIVIL DESIGN
STRUCTURAL DESIGN
| ARCHITECTURAL DESIGN
N)
MECHANICAL DESIGN
ELECTRICAL DESIGN
INSTRUMENT DESIGN
CENTRAL CONTROL SYSTEM
SCALE MODEL

BEGIN DESIGN
1001 DESIGN SUBMITTAL
CONSTRUCTION AWARD

OVERALL PROJECT COST
IN MILLION $
C-G FACILITY COST
IN MILLION $
CITY OF L. A.
Montganery-Parsons
(M-P)

CONVEYOR DISCHARGE
SOLIDS COOLER OUTLET
PIPE CONNECTION @ B.L.
OSBL
480V HOC
FW / DTC
M-P
M-P
M-P
LAC

M-P / FW
M-P / FW
M-P / FW / CONTRACTOR
M-P (MP)
AFTER DESIGN (PR MODEL)

FEBRUARY 1982
JANUARY 19B3
OCTOBER 1983

Bid C$15ff)
To date $216
Bid \$2o)

LACSD
None

CONVEYOR DISCHARGE
STORAGE SILOS
STORAGE TANKS
SELF-CONTAINED
12KV FEEDER
FW / DTC
FW / LAC
FW
FW
FW

FW
FW
FW
LACSD (MP)
DURING DESIGN
(COMPLETE MODEL)
OCTOBER 1983
JUNE 1985
MARCH 1986


$120
$50

MERCER COUNTY
Clinton Bogert Assoc
(CBA)

CONVEYOR DISCHARGE
PELLETIZER DISCHARGE
BOILER/TURBINE GENERATOR
SELF CONTAINED
13.2KV SWITCHGEAR
FW /DCT
CBA
CBA
CBA
C fl A

FW
C B A / FW
FW / CONTRACTOR
FW (A)
NONE

MARCH 1982
SEPTEMBER 1983
AUGUST 1984


$35
$12

OCEAN COUNTY
Havens t, Emerson/
Brown & Ca Id well
(H&E / B&C)

PIPE CONNECTION
SOLIDS COOLER OUTLET
PIPE CONNECTION
OSBL
480V MCC
FW / DTC
H&E / B&C
FW
FW
H&E / B&C

FW
H&E / B&C / FW
FW
H&E / B&C (A)
NONE

JUNE 1984
JUNE 1985
BIDS RECEIVED
FEBRUARY 1986

$27
$6

Wheelec
             DTC - Dchydro-Tcch Corporation

-------
                                                       TABLE  4-2

                                                    FW SCOPE  OF WORK
                                               CARVER GREENFIELD  FACILITY
                                                   STEP  III SERVICES
CITY OF L. A.
A-E CONSULTANTS M - P
CONSTRUCTION MANAGEMENT M - P
TECHNICAL REVIEWS FW
FW FIELD REPRESENTATION PARTIAL
DURING CONSTRUCTION
PROCESS OPERATING MANUAL FW
0&M MANUAL M - P
(MECH CATALOGS)
OPERATOR TRAINING M - P w/FW ASSISTANCE
COMMISSIONING M - P w/FW ASSISTANCE
INITIAL START-UP M - P w/FW ASSISTANCE
PERFORMANCE TESTING FW/ DTC
PRIME ENGINEERING M - P
CONSTRUCTION AWARD OCTOBER 1983
MECHANICAL CONSTRUCTION SEPTEMBER 1985
COMPLETION (SCHEDULED)
MECHANICAL CONSTRUCTION JUNE 1987
COMPLETION (FORECAST)
LACSD
NONE
LACSD
FW
FULL TIME
FW
CONTRACTOR
FW
FW
FW
FW
FW
MARCH 1986
SEPTEMBER 1988
SEPTEMBER 1988
TRENTON
C B A
C B A
FW
PARTIAL
FW
C B A / CONTRACTOR
DTC
DTC
DTC
DTC
C B A
AUGUST 1984
JANUARY 1987
JULY 1987
OCEAN COUNTY
HS.E / B4C
0 C U A
FW
NONE
FW
IJ&E / BiC
H&E / B&C
W/FW ASSISTANCE
FW / DTC
FW / DTC
FW / DTC
H&E / B&C
SPRING 1987
FALL 1989
FALL 1989
1. CBA:  Clinton Bogert Assoc.
2. DTC:  Dehydro-Tech Corporation
3. FW:   Foster Wheeler
4. H&E / B&C:  Havens & Bimerson/Brown & Caldwell
5. M-P:  Montgomery-Parsons

-------
All   design  firms  involved  must  understand  the  process
K^Vi"'  *he  Pr°c?ss  strong points  and  limitations,  and
the  influent  and effluent  requirements.   The design  firm
responsible for  conventional  technologies  must  co-ordinate
with  the  C-G design firm to ensure that the sludge treatment
and  initial   dewatering  processes  are compatible.    For
example,  multiple vapor  recompression  C-G systems are thought
to be  more economical for sludges with a high water content
 (e.g., 5 to  10 percent  solids); whereas,  multiple effect
systems  are thought to be more  economical  for dryer sludges
 (e.g.,  15 to  20  percent).   The designers of  the  C-G  system
must, therefore, know the  projected  water content of  the
sludge  to be  produced by the conventional  treatment system.
Conversely,  the designers  of the C-G  system must provide
other design   firms  with  information  on   any  C-G process
streams which  will  be  recycled  to  the  treatment plant.   Thus,
responsibility for  design should be clearly defined.


4.3   Design_

      4.3.1  Philosophy

The  HERS was  originally  designed  to  provide  maximum energy
recovery and  operational  flexibility.   As  a  result,  the
system   components   were   highly  integrated.    Operational
problems  in  one unit could significantly affect the  operation
of all  other units.   The  complexity  of operation was  thereby
increased.      The  HERS  C-G  system   is   currently  being
selectively  redesigned to be  less  integrated.	 Because__the
'C-G  process is new for wastewater .treatment,  the  importance
of  operational  simplicity  versus  maximum energy  usage  and
recovery  should be considered..

Safety  should  also be  a primary concern in design.   Explosion
venting and  nitrogen blanketing were  added to the HERS system
after construction had  begun.   HERS  engineers also  added
instrumentation  and   redundancy  in   both   equipment   and
protective  safeguards.  The LACSD system has  been designed to
shut  down  in  a fail  safe  mode  should  control  problems
develop.   Unplanned combustion  of solids in the  system  has
occurred  in  both pilot and full-scale  systems; thus, safety
is important.

Scheduled downtime for maintenance should be  considered.   The
Burlington  Industries  and two New Jersey systems do  not  or
will  not  operate continuously because  of feed availability.
These  systems  do not operate at least  two days  per week
(generally  weekends).    Regular  maintenance  can  thus   be
conducted   without  disrupting   solids  handling   at  these
facilities.     Time   has   not  been   allotted  for  routine
maintenance  at  either  of  the  Los Angeles  systems.   The  lack

                              4-4

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 hoVH       scheduled maintenance could  become a problem
should  operational   problems   arise.     To  alleviate   this
potential  problem,  redundancy has been provided  so  that,  at
least  in  theory, portions  of a  given  process train can  be
shut  down for  maintenance while  continuing  to  operate  the
remaining  portions  of the  train.   Providing  for at least  2
days  sludge  storage  prior to the C-G process  should also  be
considered.

Any municipal  wastewater  treatment  authority  considering  the
C-C technology,  should review the experience  performance  of
the four  municipal  C-G  systems  discussed in this report.
Visits to and detailed discussions with  as many of these four
system owners  and engineers as possible  should be  conducted
so that the  experience gained  from these  systems  can then be
incorporated  into  their systems.   Accurate  operation and
maintenance  cost data  should  also  be available  for  use   in
determining  real  plant costs.   All these  steps  are  essential
in  weighing  a  possible  committment   to  using  the  C-G
technology.

     4.3.2.  Plans and Specifications

Preparing detailed plans  and  specifications is critical  to a
C-C   project.	Time  constraints  limited  the  time  for
specification  preparation and TPVJPW of i-hg LA  HERS project.
Pages   were   inadvertently   left   out   of    the   project
Specifications    whirh   resulted   In    piping   prnblpma.
Improvements in  the  wording of  the specifications could  also
have  been made.  For example,  the  specifications  for the
spiral heat  exchangers  were  intended to  have been written
such  that a 5/16-inch plate, spacing would be  the  minimum
opening,    including   a tolerance  of  1/8-inch.    Instead,
5/16-inch  became the  nominal size for  the opening,  plus  or
minus  1/8-inch.   The  minimum  opening of  the  heat exchanger
could  have  been  3/16-inch, while the opening  on  the sludge
grinder is 1/4-inch.   This  could  cause  plugging  of the  heat
exchanger.  While  the openings  in  spiral heat  exchangers
could  have been made  larger  (over one  inch  in diameter)  to
avoid  possible plugging,  the larger openings would result  in
larger   less    efficient   units   for   exchanging   heat.
Fortunately;  ^° mannfartnrer of the spiral  heat exchanger.
made  the City OJL r.ns Anaeles  exchangers with  a 5/16  to
7/16-inch opening.

     4.3.3   Equipment Selection

With  new applications of  a  technology,  reliable  process
 nn •; pmant- i«T critical since experience with  operations is not
available—to  help  compensate  for   equipment  limitations.
Desicmers of the  system recommended  that,if  possible,  sole
source  purchasing  should  be  conducted   for  some  process

                              4-5

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 equipment.   The  construction contractor should also be made
 aware  that  a particular manufacturer of a piece of  equipment
 is  preferred if  the  design  of  the  system (e.g.,  piping)  is
 based   upon  this  equipment.     Otherwise,  the   equipment
 purchased  (whether  or not it  is  the  least expensive  to
 purchase)  may not  fit into the space allotted and  could
 require  redesign  of  associated portions of the system.

 Delivery of process  equipment should be scheduled carefully.
 Othewise, process equipment may  arrive  months  or years before
 it  can   be  used.     If  problems   develop  upon  operation,
 difficulty may be encountered  in  having the manufacturer
 honor  the warranty.

 Early  operational experiences  have  shown that problems may
 occur  with pump  seals;  flow meters;  level,  viscosity and
 other  sensors;  valves;  oil/water  separators; centrifuges; the
 hydroextractor   (de-oiler)   and   heat  exchangers.     Solids
 abrasion of  the  seals  causes relatively rapid  breakdown.
 Pump manufacturers may  not  provide any  assistance  should seal
 problems  develop.  Instead,  the  manufacturers may refer the
 owner  to a seal  manufacturer.   H_iqher gnaii.-t-y  pumps wi i-h
 hardened  surfaces  are  apparently  no^H^r?.    Rvpgr -Imgnhai- i on
 w^th pump seals is  si-itJ — underway at Burlington— aud — ttue_Ci±-y_
 of  Los Angeles.  Future systems  should contact the  existing
 s^ys terns   t"o  determine  which  types   of   seals   full-scale
 operational  experiences have shown  to  be  effective.   Double
 mechanical   (tungsten   carbide  on   tungsten  carbide)  seals
 appear to offer the most promise  at  this time.

 Accurately measuring  solids flow  in  the  system  is  very
 important and difficult; thus, mass  flow meters may be needed
 for automated control  along  with manual measurement of the
 solids  to oil  to  water ratios.   Doppler-ef feet flow meters
 may also  prove  to be effective.
Level  control  _jn  j-ho ^ygporn*""1"1 — i-s — v_g>ry  important for
obtaining  good  heat transfer.   Initially,  level sensors in
the  HERS  effects  provided  inaccurate level  data.   As  a
result,  process efficiency  decreased.    Replacement  of the
fluid  in  the  level  controllers  corrected this  problem at the
HERS.

An oil-water  separator,  hooked to an evaporating system, is
needed  for effective  operation that will  routinely permit
essentially complete  recovery of  the carrier  oil (not more
than about 100 ppm residual free oil  in the  water).   The
          t-n ^ate have  been  (a)  to  avoid  solids  Crtrrv-nvftr to
         at-gr separate*- ^rom thfa evaporator,,  and — (h)  reliable
                  sepIrTtor.   This  solids carry-over at the
Cit7~of Los Angeles has prevented the establishment of a good
interface  in  the separator  because  of the  formation  of an
                              4-6

-------
 emulsion.   Separation  has also  been  inconsistent (e.g., at
 Burlington)  where solids carry-over to the separator has not
 been a problem.

 If oil is  not properly  separated and is  carried  over  into the
 water,  the  oil  goes back  to  the head  of  the  wastewater
 treatment  plant  and  is thus   wasted.    If water  is  not
 separated  from the oil,  the water  would  go with the carrier
 oil  to  the  fluidizing  tank and  could  cause  pumpability
 problems and  plugging of the evaporators and heat exchangers
 due to the formation  of  a gummy  phase.

 Both high-  and  low-g centrifuges  have been  recommended  to
 reduce carryover  of  fine solids  into  the centrate.  It is not
 really know at this  time which   will work  best.   Remove able
 wear plates  shoulfl b^ instil grf  in  t-he. ^f-ntri f 'NflS b.^aiiRP- "f
 the abrasive nature of  <-ho maj-oripis  ben ng._ pumped .   Sole
 source  purchasing  of   the  heat   exchangers   as   well   as
 centrifuges  is recommended  by   the  design  engineers  because
 the both pieces  of equipment are very critical  to successful
 operation.

 Normal  pressures in the spiral heat  exchangers initially
 caused  deflection of the endplates at  HERS,  resulting  in
 mixing  of solids  in  the  two   flow  paths.   Manufacturer
 supplied  replacement  gasketing   and strenghtened  endplates
 have corrected this  problem.    Pressure testing  of the  heat
 exchangers is  recommended to ensure  that leakage between  flow
 paths  does   not   occur.     Only one  flow  path  should   be
 pressurized during testing.
 Redundancy  should be nnnsiripred _ fox — any  components — £r_Q_n£ — Lo
 failure  or  for  which  failure  could  pose a  safety risk.
 Specifications  for  equipment  should  HP rar^fnlly  written  for
 fyTture  systems.   Qpgrati,9nal  experiences acquired  wii*"1"1 — tke-
 existing systems will provide  the data  needed  to prepare
 better  specifications.

      4.3.4 Plant  Model

 Constructing  a  scale  model  of  the  C-G system  is highly
 beneficial.   Not only can the  model be  used  for  operator
 training, but  also  for  checking  the  design and  to  assist  the
 contractor in construction.  Burlington Industries found  that
 the  $28,000  required to  construct  the model saved  at  least
 $50,000 in construction.  Models are very useful for ensuring
(the  process  equipment  and  piping  will fit  in  the  available
'space.    Problems  with the  equipment  not fitting in  the
 available space have occurred at  systems where a  model  was
 not  built.
                              4-7

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 4.4  Contractor Selection and Construction Activities

 As   with   any   construction  project,  having  a  qualified
 contractor  is  very important  to the  success of  a project.
 Many  contracts  were required  to construct   the  Los Angeles
 HERS project within  the  time constraints  imposed  by the
 Consent Decree.  One of the prime  contractors,  although not
 the C-G contractor, performed very poorly.    Because the KERS
 was highly integrated,   the  failure  of  this  one contractor
 impacted all components of the  HERS project,  including the
 C-G system.  Under such  conditions,  total  integration of the
 system was actually  a  detriment.   This contractor  is  no
 longer involved in the  project.  Also/ no  liquidated damages
 were  placed on  mp°<"irLg—the . project—g/*hA . f im«a rpnsfra i nt-g
 required for HERS.   Tp  r^t-rngpor-> .r—tk«—actual—elapsed—t-ime
 f-r-om  process selection  j-n sl-arft-^p ._couJLd.  perhaps  have be&n
 reduced had  a  more realistic  schedule been  acceptable fr.om
 the  beginning.^   A  more  realistic  schedule   would  have
 permitted a more careJiuJLLy- controlled design and construction
 approach.~~'~

 The Los  Angeles CSD,  on  the  other  hand,  was not  under  any
 legal  time  contraints  and was  able to proceed  at  a  slower
 B.f3CR>  Fewer prime construction contractors  are  involved  in
 the  construction  of    the  LACSD  system. .    Mercer  County
 expressed  concern  that  their  contractor   did   not  fully
 comprehend  the   project.   As  a  result, the plant was  only  85
 percent completed  by  the  original'  project completion  date.
 It  was felt  that  hiring a contractor  familiar with  chemical
 plant  type  construction may have eliminated  many of  Mercer
 County's construction' delays.

 Ocean County has  attempted  to avoid contractor  and  start-up
 problems by writing the original bid documents in  such  a way
 that  Dehydro-Tech,  the   construction  contractor,   the  design
 engineers,  and  the County are sharing  responsibility  for the
 project until all  testing of  the completed   system has  been
 conducted  and   approved.   Payments  to  the  contractor for
 start-up work are to be  made based upon actual services  being
performed,  rather than  upon a  lump  sum for the entire  task.
Ocean County believes it  saved  an estimated  $500,000  in the
bids it received by using this  approach.

A general  comment made during the  workshop was  that when
compared to a  petrochemical plant,  construction of a C-G
system  is  relatively simple.  Therefore, other treatment
authorities  which  utilize  the  C-G  process  should  consider
selecting  contractors with  petrochemical  plant  construction
experience.
                              4-8

-------
KERS personnel stressed  that  key  individuals  in the proiect  I
must have  time to  review the plans  and specifications  in
detail.     The   LACSD  system  required  approximately  %So
drawings; thus,  a significant  time  for  review is required for
a C-G  system.   These same  individuals  should be  present  or
available   during   construction   to   answer   contractor's
questions and routinely monitor  the contractor's performance.


4.5  Operation

     4.5.1  Personnel Requirements

The  number  of   individuals  required   to  run  a  municipal
wastewater C-G  system is  not  yet accurately  known.   One
operator was  reported  to be  sufficient  for  operating  three
C-G  trains in the  rendering  industry.   Without  computer
control the Burlington Industries'  system requires two people
per shift,  with an  additional person on  day  shift to assist
in routine  maintenance and  solids  truck  loading.   The LACSD
system will be  entirely computer controlled  because  the
operation  of the process  is felt  by  the LACSD to be  too
complex for manual  operation.

Differences in opinions on  the educational and/or experience
level  needed  by an  operator  to  run  a  C-G  system  were
expressed.  The opinion most commonly expressed  was  that
refinery or petrochemical operators and supervisors would be
well  qualified  to  operate a C-G  system.   A significant
difference  in risk  exists between a hot  hydrocarbon  leak from
a  C-G  system  versus  the  relatively  innocuous spills  of
wastewater  and  sludge  with  which  most  wastewater  treatment
plant  operators  are familiar.   Regardless of  the  personnel
background,  it   is   important  that  all  personnel  receive
adequate training and  that  they are able  to  comprehend the
care that needs to be exercised  in working with systems that
involve the use  of  hot hydrocarbons.

     4.5.2  Operator Training

A  key  point made during  the  discussions  was  that the C-G
process is, in effect, a  petrochemical  type plant and  not a
conventional wastewater  type  treatment  process.    Safe and
efficient  operation of  the  C-G process  requires  qualified
operators.  Adequate training  must be provided.  Operators at
the  Hyperion plant  were  scheduled for a  total  of eight days
of  training  from  Foster Wheeler.   There  was  additional
training on specific equipment by vendor  representatives.  In
retrospect,  some individuals associated  with  the  Hyperion
system  believed  that  more  specialized  training  time would
have been beneficial.   Various opinions  on the amount of
training required were voiced and  ranged from three weeks to

                              4-9

-------
three months.   Allowing operators to observe the operation of
other systems  would  be highly beneficial.

To  assist in  training,  a physical  model  of the C-G process
should be constructed.  Due to the relative  complexity of the
system,  a municipality should  also consider contracting or
negotiating  for  (as  part  of the  design cost)  full-time,
on-site  technical support  for the  process  during  start up.
Finally f  a pilot! plnni; gyghg^ ghpuld be operated at least on
£hose  new untried  components of  a_£^G___sxjs££ESL_to ,Determine
they will interact with, t-hg entire pronpfici.  to better a'ssu'Fg
their suitability and  to better  acquaint plant personnel with
the^ design  of  the  process.   Treatment  plant personnel  will
then be  able to have  better input into  the  system  design as
well as  have acquired  valuable training  in operating the C-G
system.

     4.5.3   Start-up and Solids  Recycle

When  a   plant  first begins operation, sufficient  solids  to
avoid  a  gummy phase  will  not  be present.   Thus, another
source  of solids will  be  needed for start-up.   Composted
sludge is one  material recommended for use during start-up if
the compost does  not  contain particles  larger  than  the
clearances  in the process  equipment.   Fine  grinding  and./or
Screening of  the ^ompn ^ figr]  gj^^qo may  a 1 g n  h f*—noo^o(-j  1-n
prevent  wood__pr  fjh^rs _fmm plugging heat  exchangers.   Other
suitable  materials might  include  heat-dried  sludge products
such as milorganite or dried solids  from other C-G systems.

Changes  in particle size occur as  the solids pass through the
C-G system.   Particle  size  may grow  through  the  first  three
evaporators.    In  the   fourth  evaporator,  particle  size  may
decrease  if  forced circulation  evaporation  is  used.   Under
routine  operating conditions particle size  reduction is  not
anticipated  to  be  a  significant  problem.   During start-up
however, solids  will recycle through the system several  times
until the  solids inventory  increases.  A  significant amount
of  fine  solids can thus be generated.   Some of  these  fines
will also be removed   from the system with the  centrate  from
the centrifuges  and from the de-oiler into the vapor lines.

The fines can also be drawn into  the vapor vent lines  from
the hydroextractor..   Then,  if cooling of the  pipes  occurs,
these fines  stick to the  interior pipe walls, and plugging of
the vapor vent lines or fires could result. _ The city of LA
is  solving  the  problems by re-piping to  gain an  increased
vapor  flow velocity   (to a  minimum  of 50 feet per second)
through a shorter more direct path   They are also installing
a  dust  trap   and  nitrogen  gas  blanketing   as   an  extra
precaution against solids build up and auto-oxidation.


                             4-10

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      4.5.4  Cen trate  Qua1i ty

K:hen the LA HERS was initially designed, Foster Wheeler
contacted the  centrifuge manufacturers to  discuss  reasonable
design  specifications  for  their  equipment.   The manufacturers
stated  at that  time  that  a c^nt-rate solids concentration  n€
0.5  percent  solids was feasible.   DurJ_nji_j3ldd_LcLg- of t-h^
project,  however,   manufacturers  would  only  guarantee   1
percent  solids.   As_ a result/ the  centrate qualH-y was  1 PSH
than  originally  designed.   One  percent solids  concentration
are  now  expected under routine operating conditions;  however,
solids  concentrations in  the  centrate may be even higher
during   start-up  due   to  increased  fin^s  r^nH-ir^—from
excessive recycling.

Failure  to  capture  sufficient   solids  (say only  97 percent
compared with 99  percent)  means that  there  will  be  three
percent instead  of  ong pprr-pnt fines  in the sewage  and
carrier  oil going to i-he»  ft a_sJa_« t-ii i .   AS  the  carrier oil is
flashed  off to the sewage  oil so  that it can be  recycled back
into  the evaporating process, the  solids  in the  sewage  oil
become more concentrated.   The resultant solids content would
then  be  about  50  percent instead of 20 percent.   Too high  a
solids  content  is not pumpable  and  the system  plugs  up  and
increased loss  of carrier  oil  could occur.  .Future systems
should  pay  particular  attention to  t_he  performance ... nf  I-HP
centrifuges and_the  effect  t;o _ centrate^ ,q^,a,li ty  QQ frihpi...iiPY'' «-T-ng
systems.

      4.5.5  Excessive Loss  of Carrier Oil

Carrier  oil losses  are  thought  to  occur primarily  (a)  into
wastewater  during  oil-water separation,  (b)  into the  sewage
oil  from the flash stilling process, and  (c) into  the solids
product  from  the de-oiling  process.   Excessive loss of  the
carrier  oil  can  be  expensive.   Improvement  in  the  equipment
and   operation  to   recover  more  of   the   carrier   oil  is
necessary.

      4.5.6  Use of the Dried Sludge

It   is   important  to  anticipate  possible, limitations  on
ultimate use and  disposal  of the dry end product,  including
ash.   in August  1987,  the EPA  was  scheduled  to  issue  new
draft  comprehensive  sludge  management regulations.     The
constituents and concentrations  of these contituents  present
in the sludge will determine the  available options for sludge
disposal.

Dehydro-Tech  engineers  stated   that oil   soluble   organics
should  be  removed  from  the sludge  in the  C-G  process.
Orqanics  including  sewage  oil would be extracted  from  the
sludge by the  carrier oil.   The removed sewage oil  can  be

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monih   „ I        concentration  in  the HERS  is  routinely
monitored to  ensure that  the  PCB levels are acceptable for
incineration  xn  their system.   Pathogens  are killed by the
high  temperatures  and  dehydration  because  of  the  lonq
retention time of the sludge in the C-G system.

Metals  concentrations may  be of  concern as  non-volatile
metals  should remain with  the  solid particles.   Volatile
metals, such as lead and particularly mercury, may be removed
from the sludge, and air pollution control  devices capable of
removing these metals may  be  needed depending upon local air
quality standards and the metal concentrations in the  sludge.
The dried sludge  from  the  HERS is currently classified as  a
hazardous waste  by  California's  Wet  Extraction  Test  (WET)
Procedure due to  cadmium; although,  the  levels  of  cadmium
detected were not hazardous  by the  U. S.  EPA  Extraction
Procedure (EP Toxicity) Test.

Processing differences can have appreciable influence on the
"degree of hazardousness"  of the  C-G end  product.   The
quenching of  the  ash with water,  which  will  occur  at HERS,
should  reduce readily leachable metal  levels per unit  volume.
The  ash from  LACSD is not  expected  to fail the  WET Test
because the lime  used in the  process will  decrease metal
leachability.  Future plants will have the  option to  produce
either  a non-leachable slag or an ash.

     4.5.7  Process Monitoring and Control

Parameters required for process monitoring  are reported to be
few.   pjarc-pnt- so|,irlg i .q  f ppn^; ^d fro  be  the only  routine
monitoring  parameter  for  the  influejit	raw... jE,sed.    Effluent
from  the  fluidizingtan'K  should  be  monitored   for  the
solids/water  and  oil/solids  ratio.    Addback  should  be
monitored (to assure the proper water/solids  ratio)   to avoid
the  gummy  phase.    Temperature  and pressure  can be  used  to
monitor  the   evaporators,  while  percent  oil  should  be
monitored in the dried product.

Actual  process control is more complicated.  Numerous devices
such as flow meters,  viscometers,  level  controllers, and
pressure and temperature gauges  are all  needed  to better
control the operation of a C-G  system.   Problems with all of
these measuring devices or sensors have been experienced.

For  example,   there  is   difficulty   in  being   able  to
automatically  measure  and  control  the  exact  amounts  of
solids, water and carrier  oil being  pumped and  mixed  at
critical locations in  the  C-G system.   This  is particularly
critical because  excessive  carrier  oil in the  system will
reduce   the   capacity   because  the   excess  oil   must  be
volatilized and recycled.  Too  little carrier oil may  likely

                             4-12

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result  in  attaining a water content  in  the  solids  and  oil  of
about 30 percent  which might not be pumpable due to formation
of   "gummy   phase."      Manual   half-hourly  sampling  and
determination  of    the   solids-to-oil   ratio   is   being
successfully  used at  the  Burlington Industries C-G  facility
to aid  in  process control.

Many of the  minor problems, such as  inaccurate  readings from
the  level  controllers,   have   been  corrected   (e.g.,  by
replacing  the fluid in the level controller) .  With  time and
additional  operating  gypprion^o  mrjny existing problems will
be_ corrected,, uh n o  *t—^k^—a^m
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that project and the already invested federal funds.   Whether
or  not those  changes are  federally  funded  is  entirely a
separate  issue  and  immaterial  with respect  to  the grantee's
obligation to make  the changes  at the  time  that  they become
apparent and necessary.

A grantee that fails to make  necessary changes when  they
are apparent, would be liable for charges of  mismanagement or
negligence in the handling  of  federal  funds.  Such a charge
would  seriously impair further  federal  funding and question
those  funds already invested in the project.
M/R  funding
which:
is only  potentially  available  for  a project
          has completed construction,
          has been accepted  by  the grantee,
          has begun a performance period, and
          has failed to meet performance standards.

Until   these   conditions  have  been   met,   there  is   no
demonstration that the I/A technology has failed and that  M/R
funding should be made available.   There also are additional
State  requirments  which place limitations  on M/R funding
availablity even if these conditions are met.

4.7  Future Meetings

The participants  in  the  seminar unanimously  agreed  that  the
seminar was  very  worthwhile.   Many participants  recommend
that  a follow-up  seminar be  held  after more  operational
experiences  is  acquired.   Because  of the  problems  still
unresolved,  many  wanted to have  another meeting  after 6
months, or approximately  in  September  1987.   However, March
1988,  was ultimately proposed as a more suitable time for a
follow-up meeting.
                            4-14

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                          SECTION 5

                          REFERENCES


1.   Hyde,   H.   c.,   1984.      Technology   Assessment   of
     Carver-Greenfield   Municipal  Sludge   Drying   Process/
     EPA-600/2-84-200  (NTIS  PBS5-138634) ,  Water  Engineering
     Research Laboratory/ Cincinnati, OH.

2.   Crumm, J. c. and K. A. Pluenneke, 1984.  "Development  of
     an  Efficient  Biomass  Drying  Process and  its Commercial
     Use  for  Energy Recovery."  Presented at the Institute  of
     Gas  Technology Symposium on  Energy  from Biomass and
     Wastes,  Orlando, Florida, February 1, 1984.

3.   Walters, S., 1985.   "Benefits from Biowaste." Mechanical
     Engineering, pp.70-75,  April  1985.
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