United States
 Environmental Protection
 Agency
 Industrial Environmental Research
 Laboratory
 Research Triangle Park NC 27711
 Research and Development
EPA-600/S7-82-025a  August 1982
 Project Summary
Ammonium Sulfate and
 Bisulfate  Formation in  Air
 Preheaters
J. M. Burke and K. L Johnson
  Nitrogen oxide (IMOX), emissions
from electric utility boilers may be
reduced by 80-90 percent, through
the application of pollution control
technology based on the selective
catalytic reduction of NOxwith ammo-
nia; however, some unreacted ammo-
nia may be emitted from the control
system. This study investigated the
potential impact of these ammonia
emissions on a combustion air  pre-
heater, downstream  of  a selective
catalytic reduction system. Athermo-
dynamic analysis was  conducted
which indicated that both ammonium
sulfate ((NH4)2804) and  ammonium
bisulfate (NHUHSCM could form in the
intermediate and low temperature
zones of an  air  preheater and  that
(NH4)2SO4 was the thermodynamically
favored reaction product. A kinetic
analysis of the NHa-SOs reactions was
conducted which showed that  IMH4
HSOj is the first compound formed
under the time-temperature histories
in an air preheater. This indicates that
the reaction which forms NH4HSO4
from gaseous reactants is more rapid
than that which forms (NH4);>SO4. The
study identified  five  techniques for
minimizing the deposition of ammo-
nium sulfates in  an air preheater. A
technical and economic evaluation of
each solution was conducted: the
results indicate that the use of avail-
able air preheater design options is the
optimum technique for minimizing
deposit formation.
  This Project Summary was devel-
oped by EPA's Industrial Environmen-
tal Research Laboratory, Research
Triangle Park, NC. to announce key
findings of the research project that is
fully documented in,a-separate report
of the same title (see Project Report
ordering information at back).

Introduction
  Currently,  the principal methods of
controlling nitrogen oxide (NOx) emis-
sions from  stationary  combustion
sources are combustion modifications
and flue gas treatment.  Combustion
modifications are  employed  on new
utility boilers and are generally capable
of reducing  NOx emissions up to 50
percent. Flue gas treatment is a technol-
ogy  which is used commercially in
Japan and it is being applied on a limited
basis in the U.S.
  Several flue gas treatment processes
have been developed in Japan. Of these,
only selective catalytic reduction (SCR)
of NOx with ammonia has commercially
demonstrated the capability of limiting
NOx emissions from stationary sources
by 90 percent or more. Because SCR
can  attain such high NOX reduction
efficiencies,  it is receiving increased
attention in the U.S.
  For a utility application of SCR, a
catalytic reactor is located between the
economizer and air preheater sections
of the boiler. At this point, ammonia,
injected into the flue gas upstream of
the  catalyst, reacts with NOx on the

-------
catalyst surface to form  elemental
nitrogen and water. The overall reac-
tions can be represented by:
  4NO + 4NH3 + 02 - 4N2 + 6H20  (1)
  2NO2 + 4NH3 + 02 - 3N2 + 6H20(2)
  Although SCR systems have under-
gone  extensive commercial develop-
ment  in Japan, an unresolved issue is
that of ammonia emissions from the
process and the impact of these emis-
sions  on equipment downstream of the
catalytic reactor. Such equipment can
include air preheaters and other pollu-
tion control  equipment.  This study
specifically addresses  the impact of
ammonia emissions on the operation of
air preheaters downstream of SCR
systems.

Study Objectives and Approach
  This study had three major objectives:
(1) to collect and interpret data on the
thermodynamics and kinetics of NH3-
S03 reactions;  (2) to identify techniques
for minimizing  the deposition of ammo-
nium  sulfates in an air preheater; and (3)
to complete a  technical and economic
evaluation of those techniques.
  The approach used to meet the study
objectives began with a thermodynamic
analysis of possible NH3 reactions  to
identify conditions which favor the
formation of ammonium sulfates.
Experimental data were then compared
to the expected equilibrium  results and
a kinetic model was developed to predict
the formation and deposition of ammo-
nium  sulfates.
   Information was also collected on air
preheater design and operation. These
data were then used, in conjunction with
the results of  the  thermodynamic and
kinetic analyses, to identify techniques
for minimizing the deposition of ammo-
nium  sulfates in  an  air  preheater.
Finally,  a  technical  and economic
evaluation of each technique was
completed.

Problem  Definition
   The problem of  ammonium sulfate
deposition  has several  aspects which
must be defined before solutions can be
identified. The chemistry of the NH3-
S03 reactions must be examined and
the principal causes of deposit forma-
tion pinpointed. In addition, the impact
on operation and maintenance of the air
preheater and the environmental im-
pacts associated with (NH4)2S04/NH4
HSO4 deposition must be considered.

NH3-SO3 Chemistry
   Experience at SCR installations has
demonstrated  that NH3 and SO3 can
 react and deposit in air  preheaters.
 Chemical  analysis  of  the deposits
 indicates that  the principal reaction
 products are (NH4)2S04 and NhUHSCU.
 Other  components  in  the deposits
 include corrosion products (NH4-Fe-SO4
 compounds) and fly ash (Ca, Si, and Al
 compounds). The following discussion
 identifies reactions which can occur in
 an air preheater.1l 2l 3'
   The  NH3-S03 reactions which  can
 take place in  an air preheater  are
 illustrated by:
 2NH3 + S03 + H2O5£(NH4)2S04 (s) (3)
 NH3 + S03+H20*:NH4HS04(I)     (4)
 These reactions can occur as a gas con-
 taining NH3, S03, and H2O is cooled. For
 a flue gas stream, the exact temperature
 at which solid/liquid products begin to
 form or "condense" depends on the
 reaction product(s) formed and on the
 concentration of NH3, S03, and  (to  a
 lesser degree) H2O. In general, as the
 concentrations  of reactants in the gas
 increase,  the temperature at which
, deposits will form also increases.
   Another reaction which occurs as the
 gas is cooled is represented by:
   H2O + S03^:H2S04(g)          (5)
 Formation of  H2S04 lowers   the
 concentration of SO3 available for the
 reaction with NH3 (Equations 3 and 4.)
 This, inturn, reduces the temperatureat
 which either (NHUfeSCu or NH4HSO4 will
 form. Of course, NH3 can react  with
 H2SO4 as illustrated by:
     25O-1
     200-
  1
      750-
      700.
                     2NH3 + H2SO45j:(NH4)2SO4 (s)     (6)
                     NH3+H2S04^NH4HSO4(D       (7)
                   However, these reactions occur at a
                   lower temperature than those of NH3
                   with S03.  As  a result the formation
                   temperatures  for  the  reactions with
                   H2SO4 define a lower limit for formation
                   of (NH4)2S04 and NH4HSO4, while the
                   formation temperatures for the  reac-
                   tions with S03  define an upper limit.
                     Based on evaluation  of NH3-SO3
                   reactions, the  compounds which can
                   form in an air preheater are (NH4)2SO4
                   and NH4HSO4. If only (NH4)2S04 forms,
                   it will exist as  a solid. This compound
                   does  not   melt;  it  decomposes.  If
                   NH4HSO4 or both compounds form, the
                   deposit  may be either solid or liquid,
                   depending on the  deposit composition
                   and the temperature as shown in Figure
                   1. 3'4

                   Ammonium Sulfates and
                   Air Preheater Design
                     Early experience with corrosion and
                   plugging of air preheaters resultedfrom
                   condensation of H2SO4 vapor on the
                   metal surfaces in the preheater. The
                   deposition  of NH3-SO3 compounds  is
                   somewhat  analogous  to the  H2SO<
                   condensation problem. Liquid NH4HSO<
                   or a solution of (NH4)2S04 and NH4HSO4
                   can condense  and deposit in  the  air
                   preheater. Formation of solid (NH4)2S04
                   should not present a problem since the
                   solid should not adhere to the surface as
                                                   A - Solid (NH 4)2804 and
                              B - Solid NH4HSO4 and
                                  Liquid Solution of
                                  (NH4)2S04 and
                                  NH4HSO4
                              C - Solid 
-------
readily  as  a liquid. However,  liquid
(NH4>2S04/NH4HSO4  deposits  can
present problems. They tend to collect
fly ash particles and to react with both
the fly ash and the metal surface in the
air preheater to form a solid deposit.
  Deposition of ammonium  sulfates
presents a  more significant  problem
than H2SO4 deposition. To understand
why,  it is  necessary to examine the
basics of air preheater operation. Most
utility boilers employ regenerative air
preheaters  in which heat  is absorbed
from the flue gas by metal heat transfer
elements. These metal  elements are
then  exposed  to the combustion  air
where they release  the heat absorbed
from  the flue gas.  Subsequently, the
elements are re-exposed to the flue gas,
and the cycle is repeated.
  During the heat transfer cycle  in a
regenerative preheater, the  temperature
of the  metal heat  transfer  elements
changes continuously   as they  are
alternately  exposed to  flue gas  and
combustion air.  Figure 2  is a typical
temperature profile  for a regenerative
air preheater. The center line represents
the average metal  temperature  as a
function of depth through the preheater.
The left- and right-hand lines represent
the low and high metal  temperatures,
respectively.6.
  Some  features of regenerative  air
preheaters  which are used to minimize
the impacts of  H2S04  condensation/
plugging include soot blowers and water
washing equipment. Soot blowing has
been used as an effective technique for
controlling  and  minimizing  deposits.
Soot  blowers direct a  high pressure
stream of either steam  or  air onto the
heat transfer elements where deposits
can  accumulate.  This  dislodges  the
deposits which  are  then entrained by
the flue gas.
  Water washing is  usually required to
supplement soot blowing of the  air
preheater.   Typically,  washing  is
restricted to boiler outages. However,
the frequency  of  water  washing is
ultimately determined by the pressure
drop across the air preheater. Once the
pressure drop   increases  beyond  a
certain level, washing is required.
  The  temperature  profile shown in
Figure  2  indicates  some additional
design features  used to minimize air
preheater plugging  and  corrosion. As
shown, the  fluctuation of metal temper-
atures in the extreme cold end of the air
preheater is less than that in the higher
temperature zones. This tends to limit
H2S04 condensation to the cold end and
is due to the design of the heat transfer
    150 ~
    125 -
    100 -
 1  "-
     50 -
     25 -H
                                            Low Temperature Zone
                  1
                 50
               I         I         I
             100       150      200

                      Temperature, °C
250
300
350
 Figure 2.
Temperature profile of heat transfer elements in a regenerative air
preheater.
elements in the cold end. The cold-end
heat transfer elements are constructed
of heavy-gauge material which allows
the elements to corrode and still retain
the  strength, to  withstand  the soot
blower blast. In addition, the configura-
tion of  the  elements is  different,
consisting  of  spaced,  flat  sheets
oriented parallel to the gas flow. This
permits better penetration of the soot
blower jet into the cold end.  5' 6 These
differences  result  in   the  cold-end
elements having a higher heat capacity
and lower  heat transfer  efficiency
which  in  turn  limits temperature
fluctuations.
  As previously discussed, the deposi-
tion of ammonium sulfates is analogous
to  H2SC>4  condensation  in an  air
                           preheater. However, ammonium sulfates
                           condense at higher temperatures than
                           does  HjSO-t,  presenting significant
                           problems.  Figure  3  illustrates  the
                           relationship between typical H2S04(I),
                           (NH4)2S04, and NH4HSO4 initial forma-
                           tion temperatures and the air preheater
                           temperature profile from Figure 2. As
                           shown,  H2SO4 can form in about 35
                           percent of  the preheater but  only the
                           extreme  cold-end metal temperatures
                           are always below the acid dewpoint. On
                           the  other  hand,  (NH4)2SO4   and
                           NH4HS04 can form in about 50 percent
                           of the air preheater. In this case, some
                           portion of the heat transfer elements in
                           the intermediate zone of the preheater
                           are  always below  the formation
                           temperatures for ammonium sulfates.
                           3

-------
  150 -i
  125 -
 100 -
I
   75 ~
•s
  50 -
   25-
               50
 Figure 3.
      Temperature, °C

NH4HSO4. and HzSO^I) formation temperatures in an
             air preheater.
  The  fact that both  (NH4)2S04 and
NH4HS04 can form and deposit in the
intermediate temperature zone of an air
preheater presents  several problems:
(1)  the  heat transfer elements  in the
intermediate  temperature  zone  are
especially susceptible to corrosion since
they are typically manufactured from
light-gauge carbon steel;  (2) soot
blowing equipment is not as effective in
removing NHa-SOa deposits as it is in
removing H^O* deposits (the blowers
are at the ends of the preheater, while
NHs-SOs  deposits  can form  in  the
center); and (3) since soot blowing will
probably not be effective in controlling
deposit formation in the  intermediate
                zone, water washing may be required
                more  frequently  (this could  require
                either forced boiler outages or periodic
                reductions  in  boiler  load to permit
                washing and thereby maintain accept-
                able air preheater performance).
                 Available  data from  installations in
                Japan  indicate  that  air preheater
                plugging problems do occur. In some
                cases, soot  blowing is ineffective and
                more  frequent  water  washing  is
                required.1' ' 3
                Impact of Deposit Formation
                on Air Preheater Performance
                 Two major aspects  of air preheater
                performance can be  affected by the
deposition  of  ammonium  sulfates
thermal efficiency and pressure drop
Thermal efficiency, a  measure of the
heat transferred from the flue gas to the
combustion air, is significant since £
decline in efficiency (evidenced by ar
increase in flue gas temperature at the
air  preheater  exit) decreases  boilei
efficiency.
  The impact  of (NH4)2SC>2/NH4HSO-
deposition on the thermal efficiency 01
the air preheater is not expected to be
significant.  The  results  of  tests
conducted  by the  Electric  Powei
Development Company (EPDC) in Japar
showed no evidence of a decline in the
thermal efficiency of the preheater.7 Ir
addition,  another  study reported thai
the presence of soot and fly ash deposits
can improve the thermal efficiency ol
the air preheater. This is a result of the
deposits actually  increasing the heat
capacity of the air preheater.8
  Pressure  drop  through the   air
preheater is also an important aspect ol
preheater performance. An increase ir
pressure drop through the  preheatei
can cause a slight decline in the therma
efficiency of the boiler. In addition, if the
increase is too large,  the fans may noi
be able to maintain full flow rates anc
the boiler would  have  to  operate al
reduced load or be shut down to permh
washing of the preheater.
  Japanese experience has shown thai
(NH4)2SO4/NH4HSO4  deposition  car
have an adverse impact on the pressure
drop through  the preheater. In some
cases the air preheater pressure drof
has increased despite the use of soo
blowing,  and  more  frequent  watei
washing of  the preheater  has beer
required.


Environmental Considerations

  Ammonia emitted from SCR systems
can  affect  operation  of downstream
equipment  and may  also have some
environmental impacts. The principa
environmental  impact which is expectec
to result from deposition of (NH4)2SCv
NH4HS04 will be  associated with the
water stream  which  is used to wash
deposits  from the  preheater.  This
stream can contain^issolved, NH4, SO42
Fe+z/3,  and other  compounds whicr
may be present in fly ash.  The actua
composition of the wash water will be
similar to the composition of water f rorr
conventional  air  preheater washing
The principal difference is the presence
of NHj and possibly higher Fe concen
trations than normal.

-------
  Air preheater wash water is classified
 as a metal cleaning waste; as such, it
 must meet the discharge limits which
 are  shown  in Table  I.9 This waste
 stream can be treated separately or it
 may be  combined  with  other  metal
 cleaning  wastes in a single treatment
 facility. The type of treatment employed
 is site specific.
  Typically, metal  cleaning  wastes
 contain copper and iron; depending on
 the cleaning process used, significant
 amounts of NH3 also may be present.
 Some typical boiler cleaning chemicals
 include  ammoniated citric  acid,
 ammoniated  EDTA,  and  ammonical
 sodium bromate. Use of these chemicals
 can result in NH3 concentrations of 700
 - 5200 mg/l  in  the  waste stream.9
 Analysis  of wash water  from  an air
 preheater  downstream  of an  SCR
 system   indicated an  average  NH3
 concentration  of 8   mg/l.  (As  a
 maximum, the  NH3 concentrations in air
 preheater wash water should be less
 than 100 mg/l.) These concentrations
 are less than those expected in typical
 metal cleaning wastes; as a result, the
 most significant impact of NH3 in the air
 preheater  wash  water  will  be to
 increase  the volume of metal cleaning
 waste water which must be treated.

 Thermodynamic and Kinetic
 Analyses of NH3-SO3
 Reactions
  One  objective  of this study was to
 quantify the factors which influence the
 formation  of  (NH4)2S04/NH4HS04
 deposits. To achieve this objective, two
 types of analyses were conducted: (1)
 the thermodynamics of NH3 reactions
 were evaluated  to  identify  which
 reactions can  occur in the preheater;
 and (2) a kinetic analysis was conducted
 to identify the factors which control the
 rate  of (NH4)2SO4/NH4HSO4 formation
 in the preheater.

 Thermodynamics
  The formation of both (NH4)2S04 and
NH4HSO4 are temperature dependent
 reactions which  proceed  as a  gas
containing NH3, SO3, and H2O is cooled.
The  temperature at  which  these
 reactions begin to occur  will  depend
on the concentrations of  reactants in
the  gas  phase and  on the  product
formed.
  To quantify the relationship between
 reactant concentrations,  products
formed,  and temperature, a thermo-
dynamic analysis of the (NhU^SO* and
NH4HS04 formation  reactions was
conducted.  This  analysis  employed
thermodymanic  principles to estimate
the equilibrium concentrations of both
reactants and products. The results of
the analysis  do not  imply  that the
reactions which can occur will proceed
at a rapid or even measurable rate. They
do, however,  identify reactions which
will   not  proceed  under  certain
circumstances.
  The  only significant  NH3 reactions
which can occur in an air preheater are
those  which  form  (NH4)2S04  and
NH4HS04. In addition, H2S04 can form
from the reaction of SO3 and H2O. The
thermodynamic analysis conducted as
part of this study considered only these
reactions.
  Some typical results of  the thermo-
dynamic analysis are present in Figure 4
which  shows the fractional extent of
reaction (E) as a function of temperature
for an  initial S03 concentration  of 10
ppm and various initial NH3 concentra-
tions.  Fractional  extent of reaction is
defined here  as the fraction of the
stoichiometrically limiting  species that
can react for a given temperature and
inlet NHa/S03 concentrations as shown
in Table 2.
  A major result of the thermodynamic
analysis  is  that  (NH4)2S04  is the
principal product at equilibrium for all
the cases examined. This can be seen in
Figure 4 which shows initial (NH4)2S04
formation temperatures that are 20  -
40°C  higher  than  the NH4HSO4
formation temperatures. The reason for
this is that, for a given temperature, the
change in  free energy for (NH4)2S04
formation is greater than the change in
free energy for NH4HS04 formation.
            Another result of the thermodynamic
          analysis is  that  both  (NH4)2SO4  and
          NH4HSO4form in a narrowtemperature
          range. The temperature drop required to
          permit 90 percent reaction of NH3 and
          S03  is  approximately  30°C   and
          approximately  20°C for 80 percent
          reaction. This is significant in terms of
          air preheater operation. It means  that
          most deposition could  be limited  to a
          small region of the preheater.

          Kinetics
            The  results of the thermodynamic
          analysis identify  what  reactions  are
          possible at  a  given  temperature,  but
          they do not provide any information on
          the rate at which the reactions occur.
          Rate  data  can only be obtained by
          experimentation  and   subsequent
          analysis of the experimental results. As
          part  of this   study, Jumpei  Ando
          conducted  laboratory experiments on
          NH3-S03 reactions  and supplied  the
          results of these experiments to Radian.
          A kinetic analysis of Ando's experi-
          mental  results  was  conducted which
          identified possible rate limiting steps in
          the formation of ammonium sulfates in
          a  heat exchanger.  A  model   of
          (NH4)2S04/NH4HS04 formation   and
          deposition  was then developed  and
          applied to Ando's  experiments.
            The three phenomena which can limit
          the rate of (NH4)2S04 and/or NH4HSO4
          formation in a heat exchanger are:
            • Chemical Reaction Rate.
            • Heat Transfer Rate.
            • Mass Transfer Rate.
            The  model developed as part of  this
          study incorporated several assumptions.
          First, NH4HS04  was assumed to be the
          only  compound  found  in   the heat
Table 1.    Discharge Limits for Metal Cleaning Wastes
                                       Emission Limit for New Sources, mg/l
  Stream Pollutant
        Maximum
Average
Total Suspended Solids
Oil and Grease
Copper (total)
Iron (total)
           100
            20
              1
              1
  30
   15
    1
    1
Table 2.    Fractional Extent of Reaction Defined as a Function of Reaction Product
           and NHa/SOa Mole Ratio
                NH3/SO3 Ratio
Bisulfate Formation
Sulfate Formation
       > 1
       < 1
      >2
      <2
 1 / - initial, f - final, and Yz - mole fraction of species a.

                                       5

-------
exchanger. This assumption was made
because analysis of deposits in Ando's
experimental  apparatus  showed  an
NHa/SOs mole  ratio of 1.1  (i.e., the
deposits were 90 percent NH4HSC>4).
Second, the rate of NhUHSCU formation
was assumed to be very rapid, such that
the gas was at equilibrium with respect
to NHUHSC^ formation in all areas of the
heat  exchanger. This  means  that
NhUHSO* can form as either a deposit
on the heat exchanger surface or as an
aerosol  in  the gas  and the rate  of
aerosol/deposit formation is a function
of the rate of heat and mass transfer in
the heat exchanger.
  A model based on these assumptions
was applied  to  Ando's experimental
heat exchanger resulting in a prediction
of deposit and aerosol formation in the
exchanger.  Figure  5 presents  typical
model  results  and  compares those
results with  some  of Ando's  experi-
mental  data. The figure  shows the
fractional amount of NH3 and  H2SO4
converted to NmHSO4 as a function of
distance  in  the experimental  heat
exchanger. The solid line in the figure is
a smooth curve drawn through the data
points  from  Ando's  experimental
results. The dashed lines represent the
theoretical predictions from the model.
The lower dashed line represents only
the amount of  NH4HSO4 predicted  to
form at the heat transfer surface. The
upper dashed line represents the sum of
the condensate and aerosol predicted to
form.
  The  modeling results  in  Figure  5
appear similar to those obtained in the
laboratory experiments, although- the
exact fate of the aerosols  cannot  be
predicted. It does appear, however, that
the assumptions made  in developing
the  model  are  valid.   At  an initial
NHa/SOs mole ratio of 1.0, the principal
reaction  product   appears  to  be
NhUHSCX, and the reaction which forms
this product is very rapid.
  The fact that NhUHSCU is the principal
product formed is in apparent conflict
with  the  thermodynamic predictions
which indicate that (NH4)2S04 should be
the  only compound  which  forms,
regardless of  the   initial  NHs/SOa
stoichiometric ratio. Apparently, the
reaction which forms (NhU^SC^ directly
from gas  phase  reactants is  slow
relative to both the rate at which the gas
is  cooled  from the  sulfate  to the
bisulfate formation temperature and the
rate of the reaction which produces
NH4HSO4. As a consequence, the gas is
cooled below both the (NKUbSCU and
Uj
 1.0

0.9

0.8

0.7

0.6-

0.5-

0.4-

0.3-

0.2-

0.1 -

  0
    KEY
	(NHthSO* Formation
	NH4HSO4 Formation
    ppm at NH3 inlet
 O 700
 D 50
 A 30
 O 10
       230  220  270  200  190   180  170  160   150  140   130   120

                              Temperature, °C


Figure 4.    Thermodynamic equilibria for ammonium sulfate and ammonium
            bisulfate with 10 ppm SOs at inlet.
                                                     KEY
                                                Q Ando's Laboratory Resulti
                                              	Theoretical Predictions
 J2 Q>

 2 >5   0.10 -
                                                  Condensate + aerosol
 Figure 5.
           O   10    20   30   40   50  60   7O   80   90   100  110 12

                                     Distance, cm
            Predicted and actual W/4//SO4 formation for 600 Ncm/sec gas
            with 200 ppm each NH3 and SOa, and 160°C oil bath.
NH4HS04  formation  temperatures
before  appreciable  quantities  of
(NH4)2SO4 can form. At this point, the
formation of NHUHSC^  predominates
due to its more rapid reaction rate. This
is not to imply that no (NhUJzSCU will
                                     form in a preheater. On the contrary,
                                     significant quantities of (NhUfeSC^ will
                                     form in the presence of excess NHs.
                                       In additional experiments using' the
                                     laboratory-scale heat exchanger, Ando
                                     found that the composition of deposits

-------
are related to the stoichiometric ratio of
the reactants. Based on Ando'sdata and
the  results  of the modeling  work,  it
appears that the formation of ammonium
sulfates proceeds via the reaction path
shown in the following equations:
  S03(g) + H20(g)5tH2S04(g)      (8)
  NH3(g) + H2S04(g)3±:NH4HS04(l) (9)
  aNH4HS04(l) + bNH3(g);s-
    (a-b)NH4HS04-(bMNH4)2SO4(l) (10)
  Sulfuric acid vapor is the first product
formed, and this reaction is essentially
complete  at the  NimHSO* formation
temperature. NH3 then  reacts  with
H2S04 to form  liquid  NhUHSCU which
can further react with  NH3 as shown in
Equation 10. The compound shown on
the right side of Equation 10 represents
a  liquid  solution of  NH4HS04 and
(NH4)2S04.
  In  summary,  the   primary  factors
controlling  NH4HS04  and  subsequent
(NH4)2SC>4 formation are the concentra-
tions of the  gaseous reactants and the
system  temperatures.  For given
reactant concentrations, there  is  a
specific  temperature above  which
NH4HS04 will not form. The phenome-
non of NH4HS04 deposition  is more
complex. The relative rates of heat and
mass transfer must be  considered to
predict the amount of deposits.

Techniques for Minimizing
Deposition of
(NH4)2SO4/NH4HSO4

  Solutions to the (NH4)2SO4/NH4HS04
deposition problem should minimize or
eliminate plugging and corrosion of the
air preheater. This can be done in two
ways: (1) modification of air preheater
design  and/or  operation, and  (2)
modification of SGR system design and/
or operation. The following  discussion
presents  specific  techniques  for
minimizing the problem.

Modification of Air Preheater
Design/Operation

  Four  techniques   identified for
minimizing  the   impacts  of  deposit
formation  require modification of air
preheater design or operation:
  • Use  of  Available  Air  Preheater
    Design Options.
  • Heat Cleaning of the Air Preheater.
  • Flue Gas Recirculation for Selective
    Formation of (NH4)2S04.
  • Increased Air Preheater Operating
    Temperature.
  Each technique is discussed in detail
below.
 Use of Available Air Preheater
 Design Options
   One  way  to  limit  the  impact of
 (NH4>2SO4/NH4HSO4 deposit formation
 is  to  use  available  options  when
 specifying  an  air  preheater  design.
 Specifically, this includes:
   • Both hot-  and   cold-end  soot
    blowers.
   • Increased soot blowing  frequency.
   • Increased  soot  blowing steam
    pressure.
   • Provisions  for in-service  water
    washing of the preheater.
   • Use of corrosion resistant material
    in both  the  intermediate  and low
    temperature zones of the preheater.
   • Use of combined intermediate and
    low temperature heat  transfer
    elements.
   Employing  these options minimizes
 any impact associated with (NH4>2SO4/
 NH4HSO4 deposition. Use of combined
 heat transfer elements, increased soot
 blowing  intensity,  and   in-service
 washing should  minimize plugging of
 the preheater, and the use of corrosion
 resistant material  should permit reli-
 able air preheater operation.
   Each option will require some change
 in air  preheater design or operation.
 Unfortunately, very little experience is
 available, and the  effectiveness of the
 air preheater design options in limiting
 deposits is uncertain. However, EPDC
 has recently awarded a contract for two
 Ljunstrom   heat  exchangers to  be
 installed  downstream of  an  SCR
 system.  These air preheaters  incor-
 porate  most  of  the modifications
 recommended here;  based on  pilot-
 scale  tests,  EPDC expects them  to
 operate without problems.2

 Heat Cleaning of the
Air Preheater

  The  fact that (NH4)2SO4/NH4HSO4
deposits  will decompose at elevated
temperatures provides the basis for a
second  solution  to  the   deposition
problem.10 This solution, termed "heat
cleaning," requires that the operating
temperature   in  the  preheater  be
elevated to the point where (NH4)2SO4
and NH4HS04  will  rapidly decompose
(350 - 450°C). Periodic cleaning using
this  technique should help  prevent
deposit buildup.
  Use of the heat  cleaning  technique
has several drawbacks: (1) elevation of
preheater temperatures will  result in a
temporary decrease in boiler efficiency;
(2) the flue gas exiting the preheater
 may  need to  be cooled to prevent
 damaging downstream equipment due
 to the  high  temperature of the gas
 (cooling the gas may also be required to
 recondense the  (NH4)2SO4/NH4HS04
 so these compounds can be collected in
 particulate control equipment);  (3) if
 temperature  gradients  greater  than
 those  encountered  during normal
 operation  of the preheater occur during
 heat  cleaning, differential expansion
 can damage the preheater; and (4) heat
 cleaning   will  effectively  remove
 deposits of NH4-Fe-S04 compounds and
 NH4-fly ash-SO4 compounds which can
 form  in the preheater.
  Use of heat cleaning to minimize air
 preheater deposits requires that several
 modifications be incorporated in the air
 preheater  design. In  particular,  these
 modifications must include provisions
 for  increasing the   cold-end  metal
 temperature.  Examination of air pre-
 heater design characteristics indicates
 that the most promising  technique of
 increasing the cold-end metal tempera-
 ture involves eliminating the flow of air
 to the preheater while reducing the flue
 gas flow rate. This will result in raising
 the preheater temperature to the flue
 gas temperature  with a  minimum of
 problems.  Since no air flows through
 the  preheater during   this period,
 differential expansion  of the preheater
 wheel should be minimized. Also, since
 operation at a reduced flue gas flow will
 minimize the decline in boiler efficiency,
 it may not  be necessary to cool the flue
 gas exiting the preheater  with dilution
 air.
  Note that this technique requires the
 boiler to have more than one preheater.
 Also,  no  data are  available which
 indicate if  heat cleaning  will work or
 how effective it will be. This solution is
 based strictly on engineering judgement
 and  requires  experimental  work  to
 substantiate its feasibility. Technically,
 this solution is considered possible, but
 not proven.

 Flue  Gas Recirculation for
 Selective Formation of
 (IMH4)2S04
  The  results  of  the  thermodynamic
 analysis have identified several useful
facts  concerning  the formation  of
 ammonium sulfates.  First, (NH4)2S04
forms  at  higher  temperatures  than
 NH4HSO4 and exists in pure form only as
 a solid. Second, at 20°C below the initial
formation  temperature, the (NH4)2SO4
formation   reaction  can  proceed  to
approximately 80  percent completion.

-------
By  modification  of the  air preheater
design,  it may be possible to exploit
these facts to selectively form (NH4)2S04
and thereby minimize deposit formation.
  One potential technique for selectively
forming (NH4)2SO4 employs flue gas
recirculation from downstream of the
air preheater to cool  hot flue  gas in a
reaction  chamber. Temperatures are
controlled  in  the chamber  so  that
(NH4)2SO4 (but not NH4HS04) is formed.
The solid (NH4)2SO4 should then  pass
through the preheater and be collected
by paniculate control  equipment.
  Two  preheater designs can  be  used
with flue  gas  recirculation: split and
single.  The split design divides a single
air  preheater into two  preheaters  in
series, separated by a reaction chamber.
The first air preheater is  operated  such
that the cold-end metal temperature is
maintained above the (NH4)2S04 forma-
tion  temperature. Cooled flue gas is
recirculated from downstream of the
second preheater and injected into the
reaction  chamber. The recirculation
rate is  controlled to cool  the flue gas in
the reaction chamber below the forma-
tion temperature of (NH4)2SO4 but not
that of NH4HSO4. This should  result in
the formation of solid (NH4)2S04 only.
  An alternative to the spl it a ir preheater
design is a single air preheater in which
flue gas is recirculated from the  cold-
end to  a reaction chamber upstream of
the hot-end. The recirculation rate is
controlled  to  maintain  the flue gas
temperature entering the preheater
below  the formation temperature  of
(NH4)2S04 but above that of NH4HS04. In
principal, this technique  is identical to
use of a split air preheater. However, in
practice, use  of  a  single preheater
would require recirculation of more flue
gas and a larger preheater.
  Flue gas recirculation  was identified
as a possible solution to  the deposition
problem, based strictly on the thermo-
dynamic   analysis  of  (NH4)2S04/
NH4HSO4 formation. However, there
are factors which make the feasibility of
this solution uncertain. First, there  are
no data on the rate at which (NH4)2SO4
forms  from gas-phase  reactants.  All
experimental data, including analysis of
air preheater  deposits,  indicate that
NH4HSO4 is the first product  to  form
from gaseous reactants.  The results of
Radian's kinetic analysis confirms that
the NH4HSO4 formation reaction occurs
very rapidly, but the (NH4)2S04 formation
rate could not be determined. Therefore,
it may be impossible to selectively form
(NH4)2S04 with a realistically  sized
reaction chamber residence time (i.e., 1
to 2 sec).
  A second problem  associated with
flue gas recirculation is one of process
control. Changes in fuel sulfur content
or excess air to the boiler may change
the S03 concentration, while changes
in flue gas flowrate and NOX concentra-
tion can change the concentration of
NH3 which is emitted from the reactor. If
the air preheater is designed for one
range of NH3-S03 concentrations and a
significant change  in these concentra-
tions occurs, it will be difficult to control
the system to limit (NH4)2S04 formation
to the  reaction chamber and to prevent
NH4HS04 formation. The principal
reason for this is that both NH3 and SOa
must  be  measured continuously to
adjust the recirculation rate  to the
reaction chamber and thus control
formation of (NH4)2S04. Unfortunately,
both  NH3  and  S03  are  difficult to
measure continuously.
   The  problems associated with  use of
flue gas recirculation represent signifi-
cant technical obstacles. No data are
available to indicate whether it  is
possible to selectively produce (NH^^CU
In  addition, the  control problems
associated  with changing NH3-S03
concentrations will be  difficult to
resolve. Therefore, the technical feasi-
bility of using flue gas recirculation to
prevent deposit formation is considered
low.
Increased Air Preheater
Operating Temperature
  The most direct way to minimize the
deposition of ammonium sulfates is to
increase  the  air preheater operating
temperature  above  that  at  which
NH4HS04 forms. This should minimize
plugging  and corrosion  since any
(NH4)2SO4 and/or deposits which form,
will be non-corrosive. These deposits
will occur in the extreme cold-end of the
preheater and should be easily removed
by soot blowing.
  Modification of  the air  preheater
design to permit operation at a higher
temperature should be relatively simple.
The  principal  change required is  a
reduction in thermal efficiency of the
preheater. Efficiency can be reduced by
reducing the size of the preheater so the
cold-end temperature is above that of
NH4HSO4 formation.
  The major impact of increasing the
cold-end metal temperature will be to
decrease boiler efficiency. In addition,
there may be some impacts on down-
stream  equipment and possibly an
environmental impact due to gas-phase
NH3 and SO3 emissions.  For  these
reasons, it may be necessary to cool the
flue gas exiting the preheater below the
NH4HS04 formation temperature.

Modification of SCR
Design/ Operation
  A  second approach  to solving the
(NH4)2S04/NH4HSO4 deposition problem
is to modify  the  SCR system design
and/or  operation.   The  intent of
modifying the SCR system is to reduce
the  NH3 emissions from the reactor,
thereby  reducing  the  formation of
ammonium sulfates  in the preheater.
There is basically one way to modify the
SCR system so that the NH3 emissions
are reduced. Additional catalyst can be
used and the  NH3 injection rate can be
lowered while maintaining the desired
NOX removal  level, thus reducing the
NH3 emissions.
  The  design of  an  SCR  system is
influenced by a trade-off between the
quantity of catalyst in the reactor, the
NH3 injection  rate, and the NOx removal
efficiency of the system. By increasing
the  quantity  of catalyst  and  simulta-
neously reducing the NH3 injection rate,
the NH3 emissions can be reduced while
maintaining a constant NO*  removal
efficiency. This relationship is quantified
in Table 3. As  shown, NH3 emissions for
the base case are 30 ppm. The  use of
about 30 percent additional  catalyst
(Case 2) can  reduce  NH3 emissions to
about 10 ppm while 70 percent more
catalyst  (Case  3) should  effectively
eliminate NH3 emissions.
  The   most   significant impact of
increasing the amount of catalyst in the
reactor  will be to increase the capital
investment and operating costs for the
SCR system.
Table 3. Effect of Increased Catalyst on
Case Base
Relative Catalyst Amount 1.0
NH3/NO* for 90% Removal 1.0
NHs Emissions, ppm 30
NH3 Emissions3' 11
7
1.10
0.98
20
2
1.31
0.95
10
3
1.71
0.92
0
                                  8

-------
Estimated Costs for Proposed
Solutions to the Deposition
Problem
  Cost  estimates  were  prepared  to
determine the incremental capital and
first year annualized  costs  for each
solution  identified  by  this study. The
basis for these estimates is defined in
Table  4.  Incremental  costs  were
determined  for  each  modification
required to  implement  a  proposed
solution using the flowrates,  tempera-
tures, and other characteristics of the
system defined in Table 4. The following
discussion presents the results of the
cost estimates, along  with a specific
definition of the modifications included
in making those estimates.

Air Preheater Design Option
Costs
  Table  5  compares  design options
added  to the  preheater to  minimize
deposit  formation with an unmodified
preheater design. Table 6 contains cost
estimates for the  preheater  design
options. As shown, soot blowing costs
will  increase significantly due to an
increase in both the  number of soot
blowers and the soot blowing frequency.
Also, material  costs  will  increase
significantly  due  to   the  corrosion
resistant material  used in the  inter-
mediate temperature  zone of  the
preheater.

Air Preheater Heat
Cleaning Costs
  Table 7 gives estimated incremental
capital and first year annualized costs
for  air  preheater heat cleaning. The
costs associated  directly with  heat
cleaning include fuel costs which result
from  raising  the  flue gas  exit
temperature from 150  to 350°C for 30
minutes per day at 10 percent of the
maximum flue gas flow rate.

Flue Gas Recirculation  Costs
  Table  8 gives estimated costs for the
two  flue gas  recirculation  options
defined  in this study. The capital costs
shown include the incremental costs for
an additional  or larger air preheater,
recirculation fans,  ducts for  flue gas
recirculation, and a reaction chamber.
Included  in   the  annualized cost
estimates is a heat credit which results
from assuming that flue gas temperature
at the air preheater exit can be reduced
from 150 to 115°C due to neutralization
of H2S04 in the gas.
Table 4.    Basis for Estimating Incremental Costs of Proposed Solution
             Parameter
       Base Value
Boiler Characteristics
  • Size
  • Thermal Efficiency
  • Number of Air Preheaters
  • Flue Gas Flowrate
  • Heat Rate
  • Operating Factor
Flue Gas Characteristics
  • Reactor Inlet
    —/VOx concentration
    —NHz concentration
    —SOa concentration
    —temperature
  • Reactor Outlet
    —/VOx concentration
    —NH3 concentration
    —S03 concentration
  • Air Preheater Outlet
    —/VOx concentration
    —NH3 concentration
    —SOa concentration
    —NHtHSO* concentration
    —temperature
SCR Characteristics
  • Relative Quantity of Catalyst
  • /VOX Removal Efficiency
  • NHa/NO* Mole Ratio
Air Preheater Characteristics
  • Type/Size
  • Number of Soot Blowers
  • Soot Blowing Frequency
  • Soot Blowing Steam Pressure
Cost Characteristics
  • Year
  • Fuel Cost
  • Air Preheater Capital Cost
  • Type of Installation
  • Capital Recovery Factor
       500 MWe
       88%
       2
       620 kg/sec (82.0OO Ib/min)
       9.5 MJ/kWh (90OO Btu/kWh)
       7000 hrs/yr
       350 ppm
       350 ppm
       10 ppm
       350°C

       35 ppm
       30 ppm
       10 ppm

       35 ppm
       20 ppm
       0 ppm
       10 ppm equivalent
       150°C

       1.0
       90%
       1.0

       Ljungstrom Tri-Sector/Size 31
       1 / air preheater    (cold-end)
       3/day
       1.48 MPa (200 psigj

       1979 Capital/1980 annualized3
       $2.37/GJ
       $2,600,000
       New
       14.6% of capital investment
^Annualized costs include annual operating and maintenance costs (including fuel}
 plus capital-related charges such as depreciation,  return-on-investment,  and
 interest-on-debt.
Table 5.    A Comparison of Modified Preheater with Basic Preheater
           Design Specifications
  Specification
      Basic
      Design
                           Modified
                            Design
Number of Soot Blowers

Soot Blowing Frequency
Soot Blowing Steam Pressure
Materials of Construction
  - intermediate temp zone

  - low temp zone
1 - Cold end only   3 Cold end
                  3 Hot end
                  6/day
                  1.82 MPa
3/day
1.48 MPa

Light gauge
carbon steel
Heavy gauge
carbon steel
                  Combined intermediate
                  and low temperature zones
                  304 stainless steel

-------
Increased Air Preheater
Operating Temperature Costs
  Table 9 shows incremental first year
annualized  costs for  increasing the
preheater operating temperature above
the NH4HSO4 and (NH4)2SO4 formation
temperatures. For this study, no change
in capital costs was considered since no
a'dditional  capital expenditures are
required. The annualized costs given in
Table 9 are based on  increased fuel
costs which result from raising the flue
gas  exit temperature  to  230°C and
250°C  for prevention of NhUHSO* and
         formation, respectively.
Increased Catalyst Costs
  Table 10givesthe incremental capital
and annualized costs incurred to reduce
NH3 emissions to 1 0 ppm by increasing
the quantity of catalyst in the reactor.
The  estimates  of  Table 10  include
incremental  capital charges  for  the
initial catalyst charge,  higher reactor
and annual costs for catalyst replace-
ment,  and a credit for reduced NH3
ammonia consumption.

Conclusions
  The major conclusions of this study
are:
  • NH3 leakage from SCR reactors can
    be a  problem for an air preheater
    downstream of the reactor. How-
    ever, operating experience indicates
    that NH3 concentrations below 10
    ppm  at the air preheater entrance
    do not result in serious deposition
    problems. This is probably due to
    the fact that at low NH3 concentra-
    tions, ammonium sulfates form in
    the cold end of the preheater where
    soot blowing equipment effectively
    removes deposits.
  • The effects of the deposition problem
    are limited to plugging of the
    preheater and corrosion  of pre-
    heater materials in the intermediate
    temperature zone. The ability of the
    preheater to transfer heat  should
    not be significantly  impaired by
    deposit buildup. In addition, normal
    corrosion in the extreme cold end of
   /he preheater will be reduced due to
    neutralization  of  SOs-HzSC^ by
    NH3.
  • No significant environmental
    problems will result from washing
    deposits from the air preheater. The
    NH3  levels in the preheater wash
    water will  be lower than  those
    typically encountered in  power
    plant metal cleaning wastes. A
TableG.
  Option
Estimated Capital and First Year Annualized Costs for Air Preheater
Design Options
                   Incremental Capital
                     Costs. $1000's
Incremental Annualized
    Costs, $10OO's
Soot Blowing Modifications
In -Service Washing
Corrosion Resistant Material
TOTAL
158
0
1376
1534
233
18
201
452
Table 7.    Estimated Capital and First Year Annualized Costs for Air Preheater
           Heat Cleaning
                                         Option
                              Incremental Capital     Incremental Annualized
                                Costs, $1000's           Costs, $1000's
Heat Cleaning
Corrosion Resistant Material
TOTAL
                          370
                         1376
                         1746
          70
         201
         271
Table8.
  Method
Estimated Incremental Capital and First Year Annualized Costs for
Flue Gas Recirculation
                   Incremental Capital
                     Costs, $1000's
Incremental Annualized
    Costs, $10OO's
Single Preheater
Split Preheater
                          9690
                          6223
         857
        (198}
Table9.
  Option
Incremental First Year Annualized Costs for Increasing Air Preheater
Operating Temperature
                  Cold End Temperature
                           °C
   Annualized Costs
       $1000's
Prevent NHJiSO* Formation
                Formation
                         230°C
                         250°C
        3098
        4270
Table 10.    Estimated Incremental Capital and First Year Annualized Costs for an
            Increased Catalyst Charge
Catalyst Life
   years
                  Capital Costs
                    $1000's
      Annualized Costs
          $10OO's
     1
     2
                      6054
                      6054
           3640
           2248
    slight increase in waste treatment
    costs may result due to the increased
    volume of wash water. The magni-
    tude of this cost increase is site
    specific and depends on the method
    of waste water treatment employed.
    The problems  associated  with
    deposition of (NhUJaSCVNhUHSCU
    can be minimized or eliminated by
    several  techniques.  A  relative
    technical and economic ranking of
    these techniques is given in Table
    11. As shown,  solutions with the
                                 lower technical feasibility have the
                                 lower costs, while the solutions
                                 with the higher technical feasibility
                                 incur higher costs.
                                 Based on the results in Table 11, it
                                 appears that use  of available air
                                 preheater design options is  the
                                 optimum solution to the deposition
                                 problem both technically and eco-
                                 nomically. However, the solutions
                                 with low technical feasibility could
                                 result in lower annualized costs
                                 and thus merit further investigation.
                                 10

-------
     Table 12 gives the annualized costs
     for various solutions to the deposi-
     tion problem as a percentage of the
     annual revenue requirements for
     SCR. As shown the cost impact of
     the solutions ranges from a 1.6
     percent reduction to a 30 percent
     increase in annualized costs.
 References
 1. Ando, Jumpei. Ammonium Bisulfate
    Problem  with NOX  Reduction by
    Ammonia. Private communication.
    March 1979.
 2. Jones, G.D.  Selective  Catalytic
    Reduction and NOX Control in Japan.
    EPA-600/7-81-030 (NTIS PB81-
    191116),  March 1981.
 3. Ando, Jumpei. NOX Abatement for
    Stationary Sources in Japan. EPA-
    600/7-79-205 (NTIS PB80-113673),
    August 1979.
 4. Castellan, G.W. Physical Chemistry.
    Addison-Wesley Publishing Com-
    pany, Inc. 1971.
 5. MacDuff,  E.J. and N.D. Clark.
    "Ljungstrom Air  Preheater Design
    and Operation." Combustion, pp. 24-
    30. March 1976.
 6. Campbell, H.H.  CE Air Preheater.
    Personal  communication  with J.M.
    Burke. June 25,  1980.
 7. Nakabayashi, Y. and K. Mouri. Test of
    NH3/SOX Compound Deposit  Pro-
    blems on  Air Preheater at Coal-Fir-
    ing Boiler. Electric Power Develop-
    ment Co., Ltd., Thermal Power De-
    partment. Tokyo, Japan. 1977.
 8. Karlsson, J. and S.  Holm. "Heat
    Transfer  and  Fluid Resistances in
    Ljungstrom Regenerative-Type Air
    Preheaters." Transactions of ASME;
    65. pp. 61-72. 1943.
 9. U.S. EPA, Office of Water and Waste
    Management. Development Docu-
    ment for  Proposed Effluent Limita-
    tions Guidelines, New Source  Per-
    formance  Standards and  Pretreat-
    ment  Standards for the Steam
    Electric Point Source Category. EPA-
    440/1-80-029b (NTIS PB81 -
    119075),  September  1980.
10. Kiyoura, R. and K. Urano.  "Mecha-
    nism,  Kinetics, and  Equilibrium of
    Thermal  Decomposition of Ammo-
    nium Sulfate." Industrial  Engineer-
    ing Chemistry, Vol. 9, No. 4. pp. 489-
    494. 1970.
11. Maxwell,  J.D., et al. "Preliminary
    Economic Analysis of NOx Flue Gas
    Treatment Processes." EPA-600/7-
    80-021 (NTIS PB80-176456);
    February  1980.
Table 1 1 .
             Technical  and Economic Ranking of Proposed Solutions to the
                               Deposition Problem
Solution
Air Preheater Design Options
Heat Cleaning
Flue Gas Recirculation
- Single Preheater
- Split Preheater
Increased Cold-End Metal Temperature
Increased Catalyst/ Decreased NHs/NO*
Estimated Incremental
Relative Technical First Year Annualized Costs
Feasibility* 1000's
Intermediate
Low
Low
Low
High
Intermediate
452
271
857
1198)
3,098
3,668*'c
*These are somewhat subjective and based on engineering judgment,
B7/7/s cost is based on reducing NHs emissions to approximately 10 ppm.
cAssumes a 1-year catalyst life (current vendor guarantee for coal-fired applications}.
Table 12.    Estimated Increase in SCR Annualized Costs for Proposed Solutions to
            the (NH^iSO^/NHd-ISOA Deposition Problem

                 Solution                 Increase (Decrease} in SCR Costs, %
Air Preheater Design Options
Heat Cleaning
Flue Gas Recirculation
 - Single Preheater
 - Split Preheater
Increased Cold-End Metal Temperature
Increased Catalyst/Decreased NH3/NO*
                                                         3.7
                                                         2.2

                                                         7.0
                                                        (1.6)
                                                       25.4
                                                       30.0
   J. M. Burke and K. L Johnson are with Radian Corporation, Austin, TX 78766.
   J. David Mobley is the EPA Project Officer (see below).
   The complete report, entitled "Ammonium Sulfate and Bisulfate Formation in
     Air Preheaters," (Order No. PB 82-237 025; Cost: $21.00, subject to change)
     will be available only from:
          National Technical Information Service
          5285 Port Royal Road
          Springfield, VA 22161
          Telephone: 703-487-4650
   The EPA Project Officer can be contacted at:
          Industrial Environmental Research Laboratory
          U.S. Environmental Protection Agency
          Research Triangle Park, NC 27711
                                                                               11

-------
         «
o
5'
3
0)
^

O


•(*
en
M
O)
oo
00   <0
 ni  c
     C5
     m
                                                                              m > -o m

                                                                              5111.
                                                                               i  3 (D  -i

                                                                              8Sg.§
                                                                              oi   03
                                                                                   3  (D

                                                                                      0)

-------