United States
               Environmental Protection
               Agency
Air and Energy Engineering
Research  Laboratory
Research Triangle Park, NC 27711
               Research and Development
EPA/600/SR-93/188  December 1993
EPA      Project Summary

               Evaluation  of Simultaneous
               SO2/NOX Control  Technology
               Kevin R. Bruce and Walter F. Hansen
                The Clean Air Act Amendments of
              1990 (CAAA) have led to accelerated
              research into novel sulfur dioxide (SO2)
              and nitrogen oxide (NO) control tech-
              nologies for coal-fired industrial boil-
              ers. One  of these technologies com-
              bines  sorbent injection and selective
              non-catalytic reduction for simultaneous
              SO2/NOx removal. The work presented
              herein concentrated on characterizing
              three process operational parameters
              of this technology: injection tempera-
              ture, sorbent type, and reductant/pol-
              lutant stoichiometric ratio. A slurry com-
              posed of  a urea-based  solution
              (NOxOUT A or NOxOUT A+) and various
              calcium-(Ca-) based sorbents was in-
              jected at a range of temperatures and
              reactant/pollutant stoichiometries in a
              natural-gas-fired, pilot-scale reactor with
              doped pollutants..  Up to 80% reduction
              of SO2 and NOx at reactant/pollutant
              stoichiometric ratios of 2 and 1.5, re-
              spectively, was achieved. SO2 emission
              reductions from slurry injection were
              enhanced moderately when compared
              with dry sorbent injection methods, pos-
              sibly caused by sorbent fracturing to
              smaller, more reactive particles. Emis-
              sions  from  ammonia  (NH3)  slip
              (unreacted  nitrogen-based  reducing
              agent) and nitrous oxide (N2O) forma-
              tion were reduced in comparison with
              other published results,  while similar
              NOx reductions were obtained. In-
              creased carbon monoxide (CO) emis-
              sions, caused by the decomposition of
              urea, were moderate. Emissions of CO,
              NH3, and  NO for the enhanced urea
              solution (NoxOUT A+) were substan-
              tially less than the levels observed dur-
ing urea (NOXOUT A) injection. The in-
jection of the urea-based solution en-
hanced SO removal, probably because
of the formation of (NH^CAfSOJ, H2O.
The  results of this pilot-scale  study
have shown high reduction of both SO,
and NO.
  This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Tri-
angle Park, NC, to announce key find-
ings 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 project work reported here was ini-
tiated through a Cooperative Research and
Development  Agreement (CRADA) be-
tween EPA and Nalco Fuel Tech, a com-
mercial licensor of a urea-based reducing
agent injection technology for NOx  reduc-
tion.
  Experimental  testing of Nalco Fuel
Tech's urea-based  NOxOUT A and
NOXOUT A+ reducing agents for NOx con-
trol, in combination with Ca-based sorbent
injection for SO2 control, was conducted
from June to November 1991. Testing was
performed at  EPA's Environmental Re-
search Center in Research Triangle Park,
NC, in a pollutant-doped, natural-gas-fired
50,000 Btu/h (15 kW) furnace.
  The project scope of work included test-
ing furnace sorbent injection of several
Ca-based sorbents to remove  SO2 from
flue gas. The tested sorbents came from
a single source of commercially prepared
slaked lime [Ca(OH) ], limestone (CaCO3),
and quicklime (CaO). A comparison of
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SO2 removal efficiency was made between
dry and  slurry  injection. The  effect of
CaCO3 sorbent particle size was also stud-
ied.
  Slurry sorbent injection was found to be
superior to dry injection for SO2 removal.
Dry injection of Ca(OH)2 achieved a maxi-
mum of 60% SO  removal (at a Ca/S ratio
= 2), while the Ca(OH)2 slurry  removed
72%. Removal efficiency with Ca(OH) was
superior to that with CaCO3  in both dry
(43%) and slurry (58%) testing.  CaO was
tested  in slurry form  by slaking to form
Ca(OH)2 slurry, and compared to the com-
mercially prepared Ca(OH)2.  The slaked
CaO proved identical in its SO2 removal
performance to the commercially prepared
Ca(OH)2.
  Both  NOXOUT A  and  NO OUT A+
achieved maximum NOx removal when in-
jected at a temperature of about 1,100 °C.
Almost no difference in the two reducing
agents existed at the optimum  tempera-
ture; approximately 80% NOx removal was
observed for both  reducing agents. At tem-
peratures  higher  than the optimum, NOx
removal efficiency  dropped quickly.   At
about 1,170°C, the reducing  agents be-
gan producing NOx, caused probably  by
high temperature oxidation of the NH3 pro-
duced by urea decomposition. At tempera-
tures  lower than the optimum, NOx  re-
moval efficiency gradually decreased!!
  Varying the molar ratb of reducing agent
(urea) to baseline NOx, or N/NOx|( showed
that increasing N/NO^ to a value of near 2
produced significant improvement  in NOx
removal. Further N/NOx| increases had little
or no effect on removal efficiency.
  The  work mentioned above also  en-
tailed  characterizing NH3, N2O, and  CO
emissions produced by injecting the  re-
ducing agent over  a range of tempera-
tures  and N/NOxl.  Each reducing  agent
produced maximum NH3 slip (unreacted
nitrogen-based reducing  agent)  at  the
lower  injection temperatures;  around
821 °C, the amount of slip was about 140
ppm for both NOXOUT A and NOXOUT A+.
As injection temperature increased, NH3
slip for the NOXOUT A decreased quickly,
while slip from NOXOUT A+ dropped  off
almost completely at around 875 °C.   At
900-1,000 °C, slip generated by NOxOUT
A gradually decreased to a level of about
60 ppm.  Throughout this temperature re-
   K. Bruce and W. Hansen are with Acurex Environmental Corp., Research Triangle
      Park, NC 27709.
   Brian K. Gullett is the EPA Project Officer (see below).
   The complete report, entitled "Evaluation of Simultaneous SO2/NOx Control Tech-
      nology," (Order No. PB94-114741/AS; Cost: $27.00; 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:
           Air and Energy Engineering Research Laboratory
           U.S. Environmental Protection Agency
           Research Triangle Park, NC 27711
gime, NOXOUT A+ produced negligible NH3
slip (<10 ppm).
  CO emissions produced by NOxOUT A
rose gradually from about 20  ppm  at
800 °C  to  a maximum of 25  ppm  at
1,100 °C.  NOXOUT A+ produced low CO
at 800-1,000 °C (<10 ppm), with a maxi-
mum of 50 ppm around  1,100 °C.
  NO production by NOxOUT A was neg-
ligible at lower injection temperatures (ap-
proximately 25 ppm), but increased with
injection temperature to a  maximum  of
200 ppm at approximately 1,150 °C, about
42% of the  NOx  reduced.   NOXOUT A+
produced only moderate levelsx of N2O
(typically <40 ppm, less than 20%  of the
NOx reduced) over the entire temperature
range.  A maximum of about 30 ppm was
observed at around 1,150 °C.
  Aqueous ammonia solution was injected
to ensure that these results would  be re-
producible on other facilities. Available data
for NOx  removal using aqueous ammonia
injection showed comparable  results  to
others' work. These data validated improve-
ments  shown by this  work  with  both
NOXOUT solutions and suggested the ap-
plicability of these results to other facilities.

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