United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/S7-88/013 Nov. 1988
Project Summary
Development of Sorbent
Injection Criteria for Sulfur
Oxides Control from Tangentially
Fired Coal Boilers
R. W. Koucky, J. L. Marion, and D. K. Anderson
The report describes a program to
develop design criteria for injection
of dry sorbents into tangentially fired
furnaces for the control of sulfur
oxides (SOX) emissions. The program
included aerodynamic cold-flow
testing and mathematical modeling
of sorbent injection, demonstration
testing of SOX emissions control in a
14.7 MW thermal tangentially fired
Boiler Simulation Facility (BSF), and
development of recommendations for
sorbent injection in a tangentially
fired boiler demonstration of the
process. The Isothermal flow
modeling led to development of
sorbent injection systems for
tangentially fired furnaces which
provide high levels of sorbent
dispersion. A sorbent dispersion
mathematical modeling technique
was developed to support flow
modeling in identifying and
optimizing sorbent injection
locations and methods. Sorbent
injection tests in the BSF
investigated the following variables:
sorbent type, injection location,
injector tilt, injection velocity,
number of injectors, and carrier air
flow rate. Sulfur capture efficiency
up to 50% was achieved at a Ca/S
molar ratio of 2:1 with calcium
hydroxide sorbent treated with
calcium lignosulfonate. A procedure
was developed for specifying sorbent
injection locations and methods for a
full-scale demonstration of the
sorbent injection process in a
tangentially fired utility boiler.
This Project Summary was
developed by EPA's Air and Energy
Engineering Research Laboratory,
Research Triangle Park, NC, to
announce key findings of the research
project that is fully documented in a
separate report of trie same title (see
Project Report ordering information at
back).
Introduction
Furnace sorbent injection is being
developed as an approach for sulfur
dioxide (SOg) control for coal-burning
utility boilers. The process is attractive
for retrofit of existing boilers since the
capital equipment requirements are less
than for other options such as flue gas
desulfurization, and the estimated overall
sulfur reduction cost per ton of sulfur
removed from flue gas is less than for
these options. In the furnace sorbent
injection process, sorbent, usually
calcium hydroxide [Ca(OH)2] or
limestone (CaCOa), is injected above the
flame zone and mixes with flue gas
containing SC>2 The SC>2 reacts
chemically with lime (CaO), formed from
the sorbent, to make solid calcium sulfate
(CaS04). The CaS04 is removed with fly
ash in paniculate collection equipment.
A significant fraction of the existing
boilers in the U.S. that would be
candidates for retrofit with sorbent
injection technology are tangentially fired
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utility boilers. Tangential firing introduces
special considerations for the design of
sorbent injection systems due to the
unique aerodynamics in the sorbent
mixing region of tangentially fired
furnaces. Therefore, a program was
established to address the criteria for the
location and method of sorbent injection
in tangentially fired coal-burning
furnaces in order to provide the most
effective removal of sulfur oxides,
The program included four tasks:
Task A - Cold flow modeling of
sorbent injection systems.
Task B - Mathematical modeling of
sorbent injection systems,
SOa capture performance,
and furnace thermal
performance.
Task C - Combustion testing of
sorbent injection
location/injector design
combinations in a pilot scale
Boiler Simulation Facility
(BSF).
Task D - Sorbent injection system
design recommendations
for a full-scale tangentially
fired boiler demonstration.
Cold Flow Modeling
The cold flow modeling consisted of
three screening levels designed to lead
to the selection of injector design/location
combinations for combustion testing. In
the first screening level, flow visualization
tests of 16 injector configurations were
conducted. Each configuration was
evaluated at up to three injector carrier
air velocities and three injector nozzle tilt
positions. The 11 best injector
configurations from the first screening
level were evaluated in the second
screening level, which consisted of
three-dimensional velocity profile
measurements and mixing studies using
a methane tracer gas measured by a
laser absorption spectrophotometer. In
the third screening level, the five
configurations which demonstrated the
best performance in the second level
testing were tested over a range of
simulated furnace operating conditions
using the same techniques utilized
during the first two screening levels.
The isothermal flow modeling was
performed in the Large Scale Furnace
Aerodynamics Test Facility (LSFATF).
The facility was a 0.46-scale simulation
of the BSF used in Task C. The inflow
modeling tests, supported by
mathematical modeling, developed
several sorbent injection systems which
provide high levels of sorbent dispersion
for a wide range of sulfation tem-
perature windows and corresponding
sorbent injection locations.
Mathematical Modeling
The mathematical modeling effort was
divided into three subtasks. One was
thermal modeling to provide furnace gas
temperature predictions. Thermal
modeling was conducted to design the
BSF, to select candidate sorbent injector
locations for both the isothermal flow
studies and the combustion testing at the
BSF, and to interpret BSF test results in
order to optimize SC>2 capture
performance at the BSF. The second
modeling subtask was sorbent dispersion
modeling which was conducted using a
computational fluid dynamics (CFD)
code. It was shown that CFD can
effectively simulate sorbent mixing in the
upper part of a tangentially fired furnace
and can be an effective design tool for
selecting and optimizing sorbent injector
locations and methods. In the third
mathematical modeling subtask, a SOa
capture performance model was
developed by application of a proprietary
computer code. The model predicts SC>2
capture as a function of furnace
geometry, furnace temperature profile
and operating conditions, sorbent
injection parameters, and the inherent
capture performance of the sorbent.
Combustion Testing
Combustion testing was performed in
a large pilot-scale tangentially fired test
furnace to evaluate and optimize sorbent
injection concepts developed from
isothermal and mathematical modeling
studies. Objectives of the combustion
testing were to:
1. Evaluate SOa capture performance
for various injection locations,
designs, and operating conditions.
2. Evaluate three hydrated lime
sorbents, including a hydrated lime
treated with calcium lignosulfonate.
3. Optimize SOa capture performance.
4. Refine the sorbent injector design
guidelines developed in the cold flow
and mathematical modeling tasks.
5. Create a data base for sorbent
injection system design guidelines
for tangentially fired boilers.
Combustion testing was performed in
C-E's new 14.7 MW thermal (50x106
Btu/hr) BSF. This facility was designed
and built by C-E specifically to support
the sorbent injection design criteria
program. The BSF represents a
significant contribution toward EPA's goal
of commercializing in-furnace sorbent
injection technology for SOa control. Th
facility accurately models th
time/temperature history, volumetric heal
release rate, heat absorption, and
aerodynamic characteristics of a large
utility boiler. Both the lower and upper
furnaces are modeled so that the region
of the boiler where SOa capture reactions
take place is properly represented.
Tests were performed using an eastern
bituminous coal containing 2.7 to 3.2%
sulfur. More than 160 tests were
performed, including baseline tests
upper furnace temperature char-
acterization tests, and NOX mea-
surements as well as sorbent injectior
tests over a range of Ca/S molar ratios
sorbent types, injector tilts, sorben
carrier air velocities, and injectoi
locations. The BSF was found to b«
representative of a large utility boiler ir
terms of operation, heat release, ga;
time/temperature profile, carbon burnout
and NOX/SO2 emissions. With hydratec
lime sorbent treated with calciun
lignosulfonate, SC>2 capture efficiency o
up to 50% was obtained at a Ca/S mola
ratio of 2:1 for selected test conditions.
Design Recommendations
In program Task D, a sorbent injecto
design procedure for tangentially fire<
furnaces was developed. This procedun
applies the design guidelines, experi
mental methods, and computationa
methods developed in the first threi
tasks of the program. By this step-by
step procedure, injector design feature:
are optimized including injector elevation
peripheral location, size and shape, am
operating conditions. This procedure wi
be applied in selecting the sorben
injector designs for the tangentially firei
furnace sorbent injection demonstratio
program.
Conclusions
This program led to the following
major conclusions:
1. Isothermal flow modeling provide
sorbent injector designs fo
tangentially fired furnaces with hig
levels of sorbent dispersion for
wide range of sulfation temperatur
windows and corresponding sorbet
injection locations. Specific design
were selected and tested in the 14.
MW thermal BSF.
2. For furnaces in which the beginnin
of the sulfation temperature windo
is at or near the arch elevatioi
injection from a position low in ft
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front wall provides effective sorbent
dispersion.
For furnaces in which the beginning
of the sulfation temperature window
is below the arch, tangential injection
from the corners of the unit provides
very effective sorbent penetration
and dispersion across the furnace
plan area.
Thermal modeling using proprietary
C-E design codes provided
significant support to the program for
the design of the BSF, selection of
injector locations for both the
isothermal flow studies and BSF
combustion testing, and in
interpretation of BSF test results.
Computational fluid dynamic (CFD)
modeling provides an effective
simulation of the flow patterns and
mixing in the upper part of
tangentially fired furnaces. CFD
simulation in combination with cold
flow modeling can be used to
identify and optimize sorbent injector
locations and operating conditions
for dry sorbent injection systems for
SC>2 control in tangentially fired
furnaces.
6.
7.
A model was developed to predict
SOa capture as a function of furnace
geometry, furnace temperature
profile, operating conditions, sorbent
injection parameters, and the
inherent SO2 capture performance of
the sorbent by application of a
proprietary C-E computer code.
The model will be applied in scaling
up results of this program for a
demonstration of dry sorbent
injection technology in a tangentially
fired utility boiler.
The BSF was found to be
representative of a large utility boiler
in terms of operation, volumetric
heat release, gas time/temperature
history, carbon burnout, and
emissions.
8. Three sorbents were tested at the
BSF firing an eastern U.S.
bituminous coal containing on
average 3% sulfur. Sorbent A was
untreated Black River hydrated lime,
Sorbent B was untreated
Marblehead hydrated lime, and
Sorbent C was Marblehead hydrated
lime treated with calcium
lignosulfonate. SO2 capture varied
with sorbent type. Typical SO2
capture performance results at a
calcium/sulfur molar ratio of 2:1
were: Sorbent A, 25-30%; Sorbent
B, 30-40%; and Sorbent C, 35-
50%.
9. Although most sorbent injection tests
were run for a constant 20-minute
interval, longer tests showed that
S02 capture could be increased by
10 or 20% (or 4 to 10 percentage
points) by extending sorbent
injection to 1 hour. This was due to
deposition of reactive sorbent on
heat transfer surfaces.
10. Optimum S02 capture was obtained
by injection into the region where
furnace gas temperatures range from
1230 to 1290°C.
11. Injector tilt was demonstrated to be
an effective approach for injecting
sorbent into the optimum location.
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R. W. Koucky, J. L. Marion, and D. K. Anderson are with Combustion
Engineering, Inc.. Windsor, CT 06095.
Samuel L Rakes is the EPA Project Officer (see below).
The complete report, entitled "Development of Sorbent Injection Criteria for
Sulfur Oxides Control from Tangentially Fired Coal Boilers," (Order No.
PB 88-238 357/AS; Cost: $32.95, 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
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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