v-xEPA
                                  United States
                                  Environmental Protection
                                  Agency
                                  Industrial Environmental Research
                                 -Laboratory
                                  Research Triangle Park NC 27711
                                  Research and Development
                                  EPA-600/S7-81-030  Aug. 1981
Project  Summary
                                                                                                    i
*
                                  Selective  Catalytic
                                  Reduction  and  NO,
                                  Control  in  Japan
                                  Gary D. Jones
                                    A four-member study team traveled
                                  in Japan during March 1980 to assess
                                  NO, flue gas treatment technology
                                  and related areas. The overall goat of
                                  the study was to obtain new informa-
                                  tion on current issues concerning
                                  application of this technology and
                                  update  information previously  pub-
                                  lished. A total of 28 equipment vendors,
                                  process operators, governmental
                                  agencies, and industry groups were
                                  contacted. There has been substantial
                                  progress recently with regard to com-
                                  mercial applications of selective cata-
                                  lytic reduction (SCR) technology to
                                  gas- and oil-fired boilers. In several
                                  applications, SCR systems are oper-
                                  ated continuously and are successfully
                                  removing 80 percent of NOx from the
                                  flue gas stream. Current development
                                  and demonstration efforts are aimed
                                  at applying SCR technology to coal-
                                  fired  boilers since that fraction of
                                  Japan's total electric power genera-
                                  tion is expected to increase to 12.5
                                  percent in 1995 and since most of the
                                  new, coal-fired boilers will use flue gas
                                  treatment technology for NOX control.
                                  Four SCR systems on coal-fired boilers
                                  are scheduled to start up in 1980 and
                                  81. Thus, the Japanese activity in the
                                  NO* control field should provide valu-
                                  able information to interested parties
                                  in the U.S. in the next 4 years.

                                    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
                                    The Environmental Protection Agency
                                  is investigating methods of controlling
                                  nitrogen oxides (NO*) emissions from
                                  fossil-fuel-fired utility and industrial
                                  boilers since these sources comprise a
                                  major source of NOx emissions. Coal-
                                  fired boilers are of particular interest
                                  since they emit the highest concentra-
                                  tions of NOx. Currently, NOX emissions
                                  are reduced by the use of special "Low
                                  NOx" burners and other combustion
                                  controls. Another technique, developed
                                  primarily in Japan, treats the flue gas to
                                  achieve 80-90 percent NOx removal.
                                  This technique is usually termed selec-
                                  tive catalytic reduction (SCR) or catalytic
                                  de-NOx since it involves injecting am-
                                  monia (NH3) into the flue gas prior to a
                                  catalytic reactor which reduces NOx to
                                  N2 according to the following reactions:

                                     4NO + 4NH3 + 02 - 4N2 +  6H20
                                    2N02 + 4NH3 + 02 - 3N2 +  6H2O

                                    SCR  has been widely applied com-
                                  mercially in Japan to  several  oil- and
                                  gas-fired boilers. Coal-fired applications
                                  will soon be on-line. However,  because
                                  this technology has not been applied in
                                  the U.S., there are several unanswered

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questions  regarding the application of
SCR technology to coal-fired boilers. A
study team consisting of J.David Mobley
of EPA/IERL-RTP, Jumpei Andoof Chuo
University, Gary D. Jones of Radian
Corporation, and J. Douglas Maxwell of
TVA, travelled in Japan during March
1980 to develop answers to these
questions. Information was gathered
from a wide variety  of sources. Equip-
ment vendors included those of SCR
processes, SCR catalysts, other N0»
control processes, air  preheaters, and
instruments. The variety of installations
inspected included utility and industrial
boilers firing gas, oil, or coal. Govern-
mental groups on both the national and
local level were contacted as  well as
industry groups.
  The results of the study can be broken
down into four primary subject areas:
SCR process design, application of SCR,
SCR installations, and additional aspects
of SCR.

SCR Process Design

Catalyst
  The catalyst is the "heart" of an SCR
system and, consequently, is the subject
of many design considerations. Spe-
cially shaped catalysts  that avoid being
plugged by fly ash have been developed
for  use with oil- and coal-fired boilers.
The shapes are typically classified as
honeycomb, plate, or pipe. For gas-fired
applications,  the conventional pellet
shape is preferred.
  The same basic catalyst material is
used by all SCR vendors and consists of
TiOz and VzO5 as major components.
Each vendor also includes some addi-
tional proprietary compounds to affect
special properties, such as the SOz
oxidation  potential. The catalyst ele-
ments can be supplied in  three forms:
composed solely of catalyst material
(homogeneous), or composed of either a
ceramic or metallic substrate that is
coated with catalytic material. There is
no agreement on which type  is best;
each offers unique advantages. Of the
systems currently under construction
on coal-fired  boilers, two are  using a
homogeneous catalyst and two are
using a coated catalyst.
  One aspect  of using  V205 as an SCR
catalyst is that it will also catalyze the
oxidation of S02 to S03; with a V205-rich
catalyst, the conversion can be as high
as 5 percent.  The performance of one
formulation can be shown as a function
of temperature; however,  note that
other factors also affect the rate of S02
oxidation. High SO3 concentrations can
cause  problems  due to ammonium
bisulfate (NH450°C, the catalyst particles  will
undergo sintering and  the  catalyst
activity will be reduced. Low tempera-
tures, <300°C, can allow NH4HS04 to
form on the catalyst if sufficient SO3 is
present. Temperatures <100°C can
allow water deposition which can per-
manently reduce the catalyst activity.
The  desired operating temperature
range is 350 to 400°C: for some applica-
tions a temperature control system is
recommended by the vendor to maintain
a minimum temperature.

/VOX Removal
  NOx  removals  of  90 percent and
higher  are potentially obtainable with
SCR systems, although most systems
installed in Japan  usually operate at 80
percent removal. The vendors indicate
that 90 percent removal can be achieved,
but will cost more since more catalyst
and a higher NH3:NOx mole ratio will be
necessary.

NH3 Emissions
  Increasing MOx removal also has the
effect of increasing NH3 emissions.
Keeping the NH3 emissions low at 90
percent NO. removal levels will require
either additional catalyst or some other
process for NH3 removal. To go from 80
to 90 percent NOx removal without
increasing NH3 emissions is estimated
to require about 30 percent additional
catalyst. The  process vendors indicate
that at either 80 or 90 percent NOx
removal, slip  or unreacted NH3 can be
limited to <10 ppm.

Costs
  The costs quoted for SCR systems by
all of the vendors are similar. Investment
costs for a typical 80 percent control
system applied to an oil-fired boiler are
about 3000 to 4000 yen/kW ($12 to
$16/kW). A similar system applied to a
coal-fired boiler would be about ¥=6000
to 7000 yen/kW ($24 to $28/kW).
These figures are for new units. The
cost of SCR systems installed on existing
boilers can be substantially higher. No
general figures are available for retrofit
systems due to the high variability
between individual installations.
  One vendor indicated that investment
costs for a 90 percent NOx removal
system are 20 to 25 percent higher than
those for an 80 percent system applied
to an oil-fired boiler if increased NH3
emissions are allowable. For 90 percent
NOX control with low NH3 emissions, the
costs will be 40 to 50 percent greater,
rather than 20 to 25 percent.

Application of SCR

Flue Gas Processing
Considerations
  When installing a boiler which in-
cludes an SCR system (or retrofitting an
SCR system to an existing unit), it is
necessary to consider the flue gas
processing system as a whole since the
location of equipment relative to other
pieces can have significant downstream
impacts. The temperature requirements
of the NOx reduction reactions are 370
±~50°C, and economics limit the loca-
tion of the reactor to upstream of the air
preheater. Temperature regulation may
be  necessary to  limit temperature ex-
cursions outside this range. Where
required, temperature control can be
obtained by either load regulation or
bypassing hot floe gas around  the
economizer and mixing it with the main
gas stream.
  In Japan,  the particulate control
devices are almost always electrostatic
precipitators (ESP), installed either
upstream of the SCR system or down-
stream of the  air preheater. This option
results in the two basic arrangements of
flue gas processing equipment, shown
in Figure 1.

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                                              Air
Boiler                   SCR               „  ,   ,
                                           Preheater

Arrangement A.  Cold-Side Paniculate Removal — Example: Chugoku Electric Shimonoseki Power-station
                                                                                                          Stack
      Boiler
                                                             Air
                                                          Preheater
                                                                                         FGD
                             Stack
      Arrangement B.  Hot-Side Paniculate Removal — Example: Electric Power Development Company Takehara
                      Power Station
  Figure  1.    Basic equipment layout options for processing flue gas from a coal-fired boiler.
  In Japan, hot-side ESP's will be used
with most of the SCR systems currently
under construction on coal-fired boilers.
There are several reasons for this: one is
that, when these systems were designed
several years ago, SCR catalysts had not
been adequately proven with high ash
loadings. Other equally important rea-
sons are that cold-side ESP's are not
effective with the low sulfur coal some-
times received in Japan, and the concern
that NH3 compounds in the collected fly
ash will affect by-product utilization.
However, it is anticipated that many
SCR systems currently being designed
will utilize cold-side ESP's.


Downstream Impacts and
Countermeasures
  The SCR  system can  potentially im-
pact the air preheater, ESP, and FGD
system.  The most important of these is
the air preheater. Several plants have
                                  reported problems with air preheater
                                  plugging and corrosion by NhUHSCU,
                                  product of a condensation reaction
                                  between NH3, SOs, and HjO: tn many
                                  cases, more rigorous soot  blowing
                                  procedures have controWed the plugging
                                  to the extent that water washing the air
                                  preheater is only required once per year
                                  during a scheduled boiler outage. In
                                  other cases, however, water washing is
                                  necessary every few months, even with
                                  NHa and SOa concentrations of <4 ppm
                                  and a  temperature of 140°C. The plug-
                                  ging occurs at the interface between the
                                  intermediate- and cold-temperature
                                  elements where the temperature is cool
                                  and soot blowing is least effective.
                                    Where more severe problems are
                                  anticipated,  such  as after a  hot-side
                                  ESP, a modified air preheater design
                                  will be used. This design consists of
                                  combining the intermediate and cold
                                  sections into a single element which
                                  permits more effective soot  blowing
which, for the new design, is done from
both the hot and cold sides. Also, the
large element is made of  corrosion
resistant, coated material  similar to
typical cotd-end elements.
  The  NH3 emitted by SCR systems is
not expected to adversely impact the
operation of a cold-side ESP; on oil-fired
boilers in Japan, NH3 is often injected
upstream of these units for ash condi-
tioning. However, the NH3 can affect the
fly ash utilization in by-products by
depositing on the surface of the fly ash.
The impact of SCR systems on baghouse
efficiency is not known in Japan where
it is being investigated at two pilot units.
  Systems in which a limestone FGD
unit exists downstream of an SCR unit
will be operational in the near future in
Japan. There are no adverse effects of
SCR systems anticipated on the perfor-
mance of-downstream limestone/gyp-
sum FGD systems. The FGD system will
absorb NH3; however*, reliability and

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SOa removal should not be affected.

Environmental Impacts
  SCR systems on gas-  and oil-fired
boilers in Japan emit NH3; however,
since the concentrations are 3-10 ppm,
it is not considered to be a serious air
quality impact. Ammonia  emissions
from full-scale,  coal-fired applications
have not been  quantified; however,
downstream equipment  will probably
mitigate any air  impacts.
  Visible plumes of ammonium sulfite
have been known tooccurduring certain
atmospheric conditions with NH3-based
FGD systems. Based on Japanese ex-
perience with situations in which 10
ppm of NH3 enters the FGD system,
Japanese researchers do not feel that
SCR systems will cause visible plume
formation.
  SCR systems can also have water
impacts  resulting from: NHs in the
leachate from ash that has been used as
landfill,  NH4HS04 in the  air preheater
wash water, NH3 in FGD blowdown, and
ammonia compounds in the water used
to wash gypsum produced  by an FGD
system. Where the concentrations are
high enough to  cause  water pollution
problems, an activated sludge water
treatment system may be  necessary.
Solid waste from SCR systems consists
of spent catalyst material. A definite
disposal method has not yet been estab-
lished primarily because none of the
commercial SCR units have required a
catalyst change. This area requires
further investigation for  U.S. applica-
tions.

SCR Installations

Extent of Application
  SCR systems  have been installed on
many gas- and oil-fired boilers and are
operating successfully. One application
to a coal-fired boiler and four others are
scheduled to startup within a year.
  With all of the coal-fired applications,
the  catalyst and  reactor are designed in
a vertical downflow arrangement to
minimize the potential for plugging by
fly ash. Soot blowers are installed on
some  units above the  beds to control
ash buildup. These are installed as  a
conservative design measure  in case
plugging develops; however, they are
not  expected to be necessary. There are
up  to four beds within the reactor
consisting of one or two layers of
catalyst modules, each of which corf-
tains many catalyst elements.
  In some cases a dummy layer of
catalyst modules is installed at the
reactor inlet to prevent abrasion of the
catalyst surface.

Operation and Maintenance
  The labor requirements of the opera-
ting full-scale systems are  small. No
additional operating personnel are
required and maintenance labor consists
primarily of NH3 and catalyst loading,
and cleaning  the air  preheater during
the annual outage. Since there have
been no catalyst changes to date, the
labor estimates for this work vary widely.
Operators indicate that the SCR  proc-
esses themselves are very reliable,
essentially 100 percent. However, in
some cases, a boiler shutdown has been
necessary where air preheater plugging
has occurred.  In most cases, steps have
been taken to reduce the plugging rate
to the extent that  cleaning  is only
required during normal boiler outages.,

Additional  Aspects of SCR

Government Agencies
  Environmental regulation in Japan is
similar to that in the US in that a federal
agency establishes the minimum re-
quirements for the country as a whole.
Local governments have the option of
adopti ng the federa I sta nda rds or esta b-
lishing their own, more stringent stan-
dards. The Japan Environment Agency
recently modified standards for ambient
air  quality and established three con-
centration ranges based on a  daily
average sample. Above 0.06  ppm NC>2,
countermeasures must be undertaken
to reduce the level to 0.06. Within the
range 0.04 to  0.06 ppm NO2,  no signifi-
cant change  is allowed; areas below
0.04 ppm NC>2 are allowed to deteriorate
to 0.04 ppm. The Environment Agency
also sets emission standards for  point
sources. Emission limits for new sources
are  shown in Table 1.
Table 1.    National Emission Limits for
     The local governments, city and pre-
   fectural, have required many of the SCR
   applications. This occurs primarily when
   the plant  owners negotiate with the
   local governments over a plant siting or
   expansion. Citizen groups appear to
   have a significant voice in these deliber-
   ations. The cooperative spirit which
   exists between the local citizens, the
   plant personnel, and the government
   provides the driving force for the plant's
   compliance with the negotiated emis-
   sion limits and the successful imple-
   mentation of new control technology.
   Further, the local governments utilize
   sophisticated air quality monitoring.
   systems to ensure that the public is
   protected  and  that regulations are
   complied with.


   Industry Groups
     The two industry groups contacted
   are looking to the future when coal will
   be a much more significant energy
   source. Coal-fired boiler capacity is
   expected to increase from 4410 MW in
   1978 to about 34,500 MW by 1995 and
   NOX control will probably be required on
   all of these. They feel that combustion
   modifications and SCR have been suc-
   cessfully demonstrated on gas- and oil-
   fired boilers and that these techniques
   will also be useful on coal-fired units.

   Instrument Design
     The application of SCR systems in
   Japan has necessitated the development
   of instruments  capable of measuring
   NOx and NH3. Coal-fired applications
   present the most difficult situation for
   the instruments since the flue gas
   contains SO2, SO3, and fly ash. Chemi-
   luminescent monitors, most commonly
   used for NO« measurement, apparently
   operate satisfactorily  with coal-fired
   flue gas.
     Usually the NH3 monitor is a chemi-
   luminescent NO monitor with an up-
New Sources
Fuel
Gas



Oil


Coal
Unit Size
WOO Nnf/hr
>500
40 - 500
10-40
<10
>500
10 - 500
<10
All Sizes
Oz Concentration
%
5
5
5
5
4
4
4
6
/Vox
Emission Limit
ppm
60
100
130
150
130
150
180
400

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stream  catalytic converter which con-
verts NH3 to NO. Sulfur oxides apparently
interfere with the monitoring equipment
and there  have been additional prob-
lems with the converters giving incom-
plete NO conversions. An alternative
NH3 emissions  monitor for coal-fired
flue gas has not been perfected; how-
ever, several techniques are being
developed.

Conclusions
  SCR has been applied to many gas-
and oil-fired boilers, both utility and
industrial, and these are operating
successfully. Full-scale tests on coal-
fired utility boilers are just beginning;
several  units will be on-line in the next
year or  two. These full-scale units will
be  incorporating  some new design
features developed specifically to deal
with coal-related problems such as air
preheater plugging and catalyst erosion.
Gary D. Jones is with Radian Corporation, 8501 Mo-Pac Blvd., A ustin, TX 78759.
J. David Mobley is the EPA Project Officer (see below).
The complete report, entitled "Selective Catalytic Reduction and NO > Control in
  Japan," (Order No. PB 81-191 116; Cost: $20.00, subject to change) will be
  available only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA22161
        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
ir U S GOVERNMENT PRINTING OFFICE, 1981 - 757-012/7256

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