United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 277t t
Research and Development
EPA/600/S7-90/007 June 1990
SEPA Project Summary
Three-Stage Combustion
(Reburning) on a Full Scale
Operating Boiler in the U.S.S.R.
R. C. LaFlesh, R. D. Lewis, and D. K. Anderson
This report gives results of a
program to complete the preliminary
design of a three-stage combustion
(reburn) system for NOX emissions
control on an operating boiler in the
U.S.S.R. This project was sponsored
by the U.S. Environmental Protection
Agency (EPA) in support of the
protocol of the Eleventh Meeting of
the Stationary Source Air Pollution
Control Technology Working Group,
Moscow, U.S.S.R., November 1988.
The program to design the reburn
system consisted of five tasks:
visiting the Ladyzhinskaya host site
to exchange design and operating
information; translating Soviet
documents into English; performing
process calculations; conducting
physical flow modeling; and
developing a preliminary system
design which included general
arrangement drawings and furnace
performance analyses.
The overall preliminary reburn
system design was presented to and
accepted by Soviet representatives
during a June 1989 meeting at the
EPA's Air and Energy Engineering
Research Laboratory (AEERL) in
Research Triangle Park, N.C. It
appears that reburning would be a
viable NOX reduction technology for
the type of boiler that the host
Ladyzhinskaya steam generating unit
represents.
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 the same title (see
Project Report ordering Information at
back).
Introduction
The objective of this program was to
systematically develop a preliminary
design for a three-stage combustion
(reburn) system for the 300 MWe type
77T7T-3I2 Ladyzhinskaya steam generating
unit located in Vinnitsa, U.S.S.R. This
objective has been met and the
preliminary design was accepted by the
Soviet representatives monitoring this
program during a meeting at EPA/AEERL
in June 1989.
Acceptance was qualified, however, in
that the Soviets requested that a
supplemental thermal performance
sensitivity analysis be conducted on the
key reburn process parameters in order
to even further quantify any impacts that
the reburn system would have on normal
boiler operation. In addition, during the
June 1989 meeting the Soviet
representatives presented additional
information and clarification on the. design
and operational assumptions that were
used in developing the preliminary reburn
system design.
Future work on the three-stage
combustion (reburning) demonstration
will include the Soviet side's completing
the detailed design of the system, then
fabricating, retrofitting, and finally testing
the system at the Ladyzhinskaya power
station. Currently, the U.S. side would be
involved in these phases in review and
consultative roles.
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Design Elements
The statements below summarize
major elements of the preliminary design.
(Key findings related to the supplemental
recommendations for the jointly accepted
U.S.S.R. preliminary reburn system
design are included).
• The design is based on: information
transmitted from the Soviet to the U.S.
side during the Ladyzhinskaya plant
tour hosted by the Soviet side in
November 1988; public domain
reburning technology technical
literature; and Combustion Engineer-
ing boiler design methodologies.
• The preliminary design employs
natural gas as the reburn fuel and coal
as the main, burner fuel. The report
highlights potential advantages and
disadvantages of using fuel oil and
coal as reburn fuels.
• The preliminary design meets design
criteria for maximizing NOX reductions
for the process.
• To the extent possible, the preliminary
design was developed consistent with
the Soviet side directive that reburn
system operation cannot affect slag
tapping (wet slag removal from the
furnace bottom), that temperature
growth (with the reburn system in
operation) must be within tube design
limits, and that furnace slagging/
fouling characteristics should not
change. As designers of the
Ladyzhinskaya unit, the Soviet side
must corroborate the above through
application of their own design
methodologies prior to establishing the
final reburn system design.
• The preliminary design identifies
major process flows for the main
burners, reburn fuel injectors, and
burnout air injectors. The total number
of injectors, as well as their elevational
and planar locations and their
approximate free areas (cross
sectional exit areas), have been
established based on stoichiometric/
residence time calculations, physical
flow modeling, and boiler performance
calculations. Detailed mechanical
design of the system is the
responsibility of the Soviet side.
• The preliminary design generally
consisted of 12 reburn fuel injector
windboxes located at elevation 20.3 m,
and 12 burnout air injector windboxes
located at elevation 29.2 m (Figure I).
The reburn fuel (natural gas)
represented 20% of the total heat
input into the boiler. Recirculated flue
gas (FGR) has been employed as a
reburn fuel propelling medium; the
quantity of FGR required was defined
to be 10% by weight of the total boiler
flue gas.
• The reburn fuel and burnout air
injectors identified in the preliminary
design are capable of vertically tilting
and horizontally yawing. This design
feature will enhance system
performance optimization in the host
boiler. Down-tilt of the nozzles
significantly enhanced mixing, as
demonstrated by physical flow
modeling.
• The reburn fuel nozzle configuration
should be designed to achieve a jet
velocity at the nozzle exit of 146-183
ft/sec(45-56 m/sec).
• The burnout air nozzle configuration
should be designed to achieve a jet
velocity at the nozzle exit of 183-229
ft/sec(56-70 m/sec).
• When reburning is employed, gas
temperature in the furnace hopper
should decrease by 50 to IOO°F (28 to
56°C) and the furnace exit gas
temperature should increase by 60 to
70°F (35 to 40°C).
The cumulative waterwall steam heat
absorption was predicted to decrease
by about 4% with natural gas
reburning. The fly ash carbon content
was anticipated to decrease slightly
with natural gas reburning. And finally,
no significant changes were predicted
for the furnace waterwall metal
temperatures.
• A supplemental thermal performance
analysis and sensitivity study, based
on information exchanged by the
U.S./Soviet sides in June 1989,
resulted in several key design recom-
mendations. These recommendations,
if implemented in the Soviet final
system design, will potentially improve
NOX reduction performance and
further minimize the operational
impacts of reburning on the
Ladyzhinskaya boiler.
In particular, it was determined that it
would be desirable to: minimize the main
burner excess air level; minimize the
reburn fuel flow while maintaining the
desired reburn zone stoichiometry;
minimize the reburn injector flue gas
recirculation (FGR) flow while maintaining
effective mixing; and maintaining or
increasing the upper furnace FGR flow
and approximate location.
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Flue Gas
Recirculation
Atozz/es
(6 Rear Wall)
Burnout Air
Injectors
(6 Front Wall)
(6 Rear Wall)
Reburn Fuel
Injectors
(6 Front Wall)
(6 Rear Wall)
Auxilary (Dump)
Burners
(2 Front Wall)
Main Coal
Burners
(S Front Wall)
(8 Rear Wall)
Figure 1. Preliminary reburn system design, Ladyzhinskaya Power Station, Vinnitsa. U.S.S.R.
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R LaFlesh, R. Lewis, and D. Anderson are with Combustion Engineering, ,lnc.,
Windsor, CT 06095.
Robert E. Hall is the EPA Project Officer (see below).
The complete report, entitled "Three-Stage Combustion (Reburning) on a Full
Scale Operating Boiler in the U.S.S.R.," (Order No. PS 90-787 322AS;
Cost: $23.00, 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 ^^
United States Center for Environmental Research
Environmental Protection Information
Agency Cincinnati OH 45268
Official Business
Penally for Private Use S300
EPA/600/S7-90/007
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