&EPA
United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC 27711
EPA-453/R-94-068
Final Report
October 1994
Air
Nitrogen Oxide Emissions and Their
Control From Uninstalled Aircraft
Engines in Enclosed Test Cells
Joint Report to Congress on the
Environmental Protection Agency -
Department of Transportation Study
"S and
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U.S. Environmental
Protection Agency
U.S. Department of
Transportation
JOINT REPORT TO CONGRESS
on the
EPA-DOT
STUDY OF NITROGEN OXIDE EMISSIONS AND THEIR CONTROL
FROM UNINSTALLED AIRCRAFT ENGINES IN ENCLOSED TEST CELLS
by the
Administrator of the Environmental Protection Agency
and the
Secretary of Transportation
Washington, D.C. 20591
September 1994
Report to the United States Congress
Pursuant to Section 233 (a) of the
Clean Air Act Amendments of 1990,
P.L. 101-549
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TABLE OF CONTENTS
LIST OF FIGURES
LIST OF TABLES
EXECUTIVE SUMMARY
v
X
xii
CHAPTER 1 INTRODUCTION AND SUMMARY OF FINDINGS
1.1
1.2
SCOPE OF STUDY . .
SUMMARY OF FINDINGS
1.2.1
1.2.2
.... 1-1
1-2
1-4
Feasibility, Effectiveness, and
Costs of NOX Control Technologies
Applied to Test Cells . . . 1-4
Effects of Test Cell NOX Control
Technologies on Aircraft Engine
Safety, Design, Structure,
Operations and Performance
Testing 1-11
1.2.3 Impact of Not Controlling NOX
Emissions From Test Cells in the
Applicable Ozone Non-Attainment
Areas 1-13
CHAPTER 2 CHARACTERIZATION OF TEST CELLS 2-1
2.1 TEST CELL DESCRIPTION 2-2
2.1.1 Sea Level Test Cell Description . 2-4
2.1.2. Altitude Simulating Test
. Cell Description 2-11
2.1.3 Test Stands • 2-14
2.1.4 Hush Houses 2-14
2.2 AIRCRAFT ENGINES EVALUATED IN TEST CELLS 2-15
2.3 TEST CELL TESTING AND TEST DESCRIPTION . 2-21
2.3.1 Development Testing 2-23
2.3.2 Production/Overhaul Testing'. . . 2-25
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TABLE OF CONTENTS(continued)
2.4 OWNER/OPERATOR PROFILE 2-28
2.4.1 Test Cell Population
Distribution .......... 2-32
2.5 SUMMARY . . . . . . . . . 2-32
2.6 REFERENCES 2-35
CHAPTER 3 MODEL TEST CELL DEVELOPMENT ........ 3-1
3.1 OVERVIEW 3-1
3.2 AIRCRAFT ENGINE EMISSION FACTORS .... 3-3
3.3 TURBOFAN/TURBOJET MODEL TEST
CELL DESCRIPTION 3-5
3.4 OBSERVED TEST CELL DATA . 3-14
3.5 TURBOPROP/TURBOSHAFT MODEL TEST
CELL DESCRIPTION . 3-21
3.6 SUMMARY 3-28
3.7 REFERENCES 3-29
CHAPTER 4 FEASIBILITY OF REDUCING NOX EMISSIONS
FROM TEST CELLS 4-1
4.1 OVERVIEW . . 4-1
4.2 NOX FORMATION MECHANISMS 4-2
4.3 SELECTIVE CATALYTIC REDUCTION (SCR) > .4-5
4.3.1 Feasibility of SCR for
Test Cell Application 4-8
4.4 SELECTIVE NON-CATALYTIC REDUCTION (SNCR) 4-12
4.4.1 Feasibility of SNCR for Test Cell
Application 4-14
4.5 REBURN NOX CONTROL TECHNOLOGY 4-15
4.5.1 Feasibility of Reburning for
Test Cell Application ..... 4-17
4.6 ENGINE MODIFICATION APPROACHES TO
NOX EMISSION REDUCTIONS . . 4-23
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TABLE OF CONTENTS{continued)
4.6.1 Steam/Water Injection Process
Description ....;...••• 4-24
4.6.2 Fuel Emulsion Process
Description 4-25
4.6.3 Feasibility of Water/Steam Injection
and Fuel/Water Emulsion for NOX Control
of Test Cells 4-28
4.7 EMERGING TECHNOLOGIES - • • 4-30
4.7.1 NOX Sorbent Technology 4-30
4.7.2 Low NOX Combustor Technology . . 4-31
4 . 8 EFFECTS OF TEST CELL NOX CONTROL TECHNOLOGIES
ON AIRCRAFT ENGINE SAFETY, DESIGN, STRUCTURE,
OPERATION AND PERFORMANCE TESTING . . . 4-33
4.8.1 Effects of Water or Steam
Injection 4-33
4.8'. 2 Effects of Back Pressure .... 4-34
4.9 REFERENCES . . 4-36
CHAPTER 5. COSTS OF IMPLEMENTING NOX CONTROL
TECHNOLOGIES S"1
5.1 OVERVIEW . . . 5-1
5.2 COST ESTIMATION METHODOLOGY 5-2
5.3 SELECTIVE CATALYTIC REDUCTION COST
COMPONENTS 5-4
5 .4 COST ESTIMATES FOR IMPLEMENTATION OF
SCR TO MODEL TEST CELLS 5-11
5.5 SENSITIVITY OF SCR COST PROJECTIONS . . 5-22
5.6 SELECTIVE NON-CATALYTIC REDUCTION
COST COMPONENTS 5-24
5.7 COST ESTIMATES FOR IMPLEMENTATION OF SNCR
TO MODEL TEST CELLS 5-25
5.8 SUMMARY 5-27
5.9 REFERENCES 5-30
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TABLE OF CONTENTS(continued)
CHAPTER 6.
TEST CELL NOX EMISSION INVENTORY ESTIMATE
6.1 INFORMATION COLLECTION BACKGROUND ' .
6.1.1 Owner/Operator Information
6.1.2 Summary of State and Local
Regulations .
6.2 RESULTS OF TEST CELL INVENTORY , . .
6.3 REFERENCES
Page
6-1
6-1
6-1
6-2
6-5
6-13
APPENDIX A: DEVELOPMENT OF EQUATION 3.1 ... A-l
APPENDIX B: DEVELOPMENT OF EQUATIONS GOVERNING
NOX ESTIMATES . B-l
APPENDIX C: DEVELOPMENT OF EQUATION 3 . 3
C-l
APPENDIX D: SAMPLE COST CALCULATIONS OF
SCR INSTALLATION .....
D-l
IV
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LIST OF FIGURES
Figure
1-1 Annual test cell emissions by ozone non-attainment
status category for test cells located in ozone
non-attainment areas
1-15
1-2 Average annual NOX emission per test cell for
all reported test cells
1-16
2-1 Schematic of a generic test cell 2-3
2-2 Typical sea level test cell (single air inlet
with air flow division) . . :
2-3 Typical sea level test cell (single air inlet)
2-4 Typical sea level test cell (two air inlets) .
2-5 Schematic of F-402 test cell at Cherry Point
Naval Aviation Depot
2-6 Generic schematic of an altitude
simulating test cell
2-5
2-6
2-7
2-10
2-12
2-7 Side view of an F-14A in a hush house . 2-16
2-8 High bypass turbofan engine (PW4000 engine) . . . . 2-17
2-9 Low bypass turbofan engine (JT8D-200
turbofan engine)
2-18
2-10 Turboprop/turboshaft type engine 2-20
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LIST OF FIGURES (continued)
Figure
Page
2-11 Engine test schedule illustrating how engine
load varies with time during cycle .....
2-22
2-12 Typical production run engine test schedule
2-13 Endurance engine test cycle
. . 2-27
. . 2-29
3-1 Schematic of turbofan/turbojet model test cell
(relative dimensions for Model B Test Cell)
3-6
3-2 Predicted engine core exhaust temperature
vs. core thrust by engine
3-3 Predicted stack gas temperature vs. thrust
(augmentation ratio =5.0)
3-10
3-12
3-4 Predicted stack gas temperature at peak thrust
as a function of augmentation ratio
3-5 Predicted stack gas peak mass flow rate as
a function of augmentation ratio . . . . .
3-13
3-15
3-6 Predicted stack NOX concentration by thrust
corrected to 15 percent 02
3-17
3-7 Jet engine test cell/augmenter flow and accompanying
measured static pressure profile . 3-19
3-8 Measured gas temperature profiles at various axial
distances from the engine at 89 percent power . . . 3-20
VI
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LIST OF FIGURES(continued)
Figure
Page
3-9 Measured NOX concentration profiles at
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LIST OP FIGURES(continued)
Figure
Page
5-1 Cost effectiveness of SCR for turbofan/turbojet
model test cells as a function of catalyst material
(augmentation ratio =5.0) 5-12
5-2 Cost effectiveness of SCR for the turbojet/turbofan
model test cells as a function of augmentation ratio
(2" AP/Ti02/V205 catalyst) 5-15
5-3 Total installed cost of SCR for the turbojet/turbofan
model test cells as a function of augmentation ratio
(2" AP,Ti02/V2O5 catalyst) 5-16
5-4 Annual operational costs of SCR for the turbojet/turbofan
model test cells as a function of augmentation ratio
(2" AP,TiO2/V2O5 catalyst) 5-17
5-5 Cost effectiveness of SCR for turboprop/turboshaft
Model E Test Cell 5-19
5-6 Cost effectiveness and total installed cost for
turboprop/turboshaft Model E Test Cell
(2" AP,TiO2/V2O5 catalyst) . . . ,
5-20
5-7 Annual operating cost of SCR for turboprop/turboshaft
model test cell as a function of augmentation ratio
(2" AP,Ti02/V2O5 catalyst) . . 5-21
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LIST OF FIGURES(continued)
Figure
Page
6-1 Annual NOX emission distribution by ozone attainment
status and test cell owner/operator group
6-6
6-2 Test cell distribution by ozone attainment status
and by owner/operator group
6-3 Annual test cell emissions by ozone non-attainment
status category for test cells located in ozone
non-attainment areas
6-7
6-8
6-4 Average annual NOX emission per test cell for all
reported test cells ......
6-10
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LIST OF TABLES
Table
1-1 TEST CELL RELATIVE CONTRIBUTION TO OZONE
NON-ATTAINMENT AREA STATIONARY SOURCE AND
TOTAL ANNUAL NOX EMISSIONS . 1-17
2-1 DISTRIBUTION OF SEA LEVEL AND ALTITUDE SIMULATING
TEST CELLS BY OWNER/OPERATOR CATEGORY 2-33
3-1 EXAMPLE OF GASEOUS EMISSIONS TABLE FROM AN
AESO DOCUMENT FOR THE J52-P-408 ENGINE ....... 3-4
3-2 MODEL TEST CELL POWER SCHEDULE .....' 3-9
3-3 PREDICTED EMISSION CHARACTERISTICS FOR A
TURBO JET/TURBOFAN MODEL TEST CELL . . . 3-16
3-4 PREDICTED EMISSION CHARACTERISTICS FOR A
TURBOPROP/TURBOSHAFT MODEL TEST CELL 3-27
4-1 COST EFFECTIVENESS FOR REBURN NOX CONTROL
APPLIED TO MODEL TEST CELLS 4-22
5-1 SUMMARY OF CATALYST MATERIAL PARAMETERS USED IN
SCR COST ANALYSIS - . . '5-7
5-2 TURBOFAN/TURBO JET MODEL TEST CELL SCR COST MODEL . 5-9
5-3 COST EFFECTIVENESS ($ per ton NOX removed) OF SCR
FOR THE MODEL TEST CELLS AND EACH CATALYST .
(Augmentation Ratio = 5) 5-13
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LIST OF TABLES(continued)
Table
Page
5-4 SCR COST SENSITIVITY FOR LOWEST COST SOLUTION CATALYST
($/ton NOX removed for 2" AP,Ti02/V205 catalyst) . . 5-23
5-5 MODEL TEST CELL SNCR COST MODEL 5-26
5-6 PREDICTED COST EFFECTIVENESS OF SNCR AS A FUNCTION OF
AUGMENTATION RATIO 5-28
6-1 STATE AND LOCAL REGULATORY AGENCIES CONTACTED
6-4
6-2 TEST CELL RELATIVE CONTRIBUTION TO OZONE
'NON-ATTAINMENT AREA STATIONARY SOURCE AND TOTAL
ANNUAL NOX EMISSIONS
6-11
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EXECUTIVE SUMMARY
The Clean Air Act Amendments of 1990 (.CAAA) , Public Law
101-549, requires the Administrator of the Environmental
Protection Agency and the Secretary of Transportation, in
consultation with the Secretary of Defense, to conduct a study
and investigate the testing of uninstalled aircraft engines in
enclosed test cells. Section 233(a) of the Act specifies the
issues the study should address, at a minimum. These issues
are:
"(1) whether technologies exist to control some or all
emissions of oxides of nitrogen from test cells;
(2) the effectiveness of such technologies;
(3) the cost of implementing such technologies;
(4) whether such technologies affect the safety, design,
structure, operation, or performance of aircraft
engines;
(5) whether such technologies impair the effectiveness
and accuracy of aircraft engine safety design and
performance tests conducted at test cells; and
(6) the impact of not controlling such oxides of
nitrogen in the applicable non-attainment areas and
on other sources, stationary and mobile, on oxides
of nitrogen in such areas."
Following completion of the study and submission of the
required Report to Congress, Section 233(b) of the Act
authorizes States to adopt or enforce any standard for
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emissions of oxides of nitrogen from test cells, after issuing
a public notice stating whether such standards are in
accordance with the findings of the study.
Test cells are facilities designed to operate and measure
the performance of uninstalled aircraft engines. Aircraft
engine testing may be categorized as engine development
testing, engine production testing, and testing following
engine repair. Engine tests vary widely depending on the
purpose of the test, the test cell, and the aircraft engine.
Finally, the testing of aircraft engines in test cells results
in emission of oxides of nitrogen (NOX) . NOX contributes to
the formation of ozone in the atmosphere.
The majority of the test cells in the United States are
owned and operated by the Department of Defense and aircraft
engine manufacturers, although airlines and contract repair
stations also own and operate enclosed aircraft engine test
cells. Based on the information provided by test cell owners
and operators, 368 enclosed test cells for testing uninstalled
aircraft engines were identified in the United States. These
368 enclosed test cells were located at 130 test facilities.
Only one of these 130 test facilities is devoted to the
testing of internal combustion type aircraft engines; the
overwhelming majority of test cells are used to test gas
turbine type aircraft engines. Accordingly, the scope of this
report includes only test cells that are used to test gas
turbine type aircraft engines.
Pursuant to §233(a) of the Act, this report focuses on
the testing of uninstalled aircraft engines in enclosed test
cells. However, aircraft engines are also tested in
facilities other than enclosed test cells. Aircraft engines
may be tested using test stands, which are not fully enclosed
structures. Testing is also performed in facilities where the
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engine remains installed on the aircraft. These facilities
are sometimes referred to as hush houses.
Based on information identified during the study of the
issues addressed under Subparts 1 through 6 in §233(a) of the
Act/ the following presents a summary of our findings:
1) Although technologies exist for the control of NOX/
none have been applied (full scale) to aircraft
engine test cells in the United States. The
differences in engines, engine tests, and test_cell
sizes and types complicate the design of applying a
NOX control system to a test cell. Various NOX
control technologies that have been applied to
sources other than test cells are examined in this
report for their applicability to test cells.
2) The effectiveness of add-on NOX control technologies
applied to test cells and other stationary sources
is outlined in this report. However, the
effectiveness of these NOX controls applied to test
cells cannot be determined until after installation
and testing on a full-scale test cell.
3) The costs of applying conventional NOX control
technologies to test cells will be high, ranging
from an estimated $167,000 to over $2.5 million per
ton NOX reduced. Cost estimates are based on the
projected application of NOX controls demonstrated
on other stationary sources to model test cells
developed in the study.
4) The NOX control technologies using water or steam
injection and fuel/water emulsions would directly
adversely affect the safety, design, structure,
operation, or performance of aircraft engines. To
apply these technologies, temporary modifications to
the engine would be required. For this reason, as
well as the effects these technologies would have on
performance tests (see below), water or steam
injection and fuel/water emulsions should not be
considered technically feasible options for
application to test cells.
5) The effects of NOX controls on aircraft engine
safety design and performance tests cannot be fully
addressed until research and development and test
and evaluation programs have been completed. All of
the known potential effects NOX controls may have on
the safety design and performance tests of aircraft
xiv
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engines are addressed in the report. Unwanted back
pressure effects may result from add-on NOX 'control
technologies.
6) The impact of not controlling NOX emissions from
test cells in the applicable ozone non-attainment
areas is addressed by comparing the NOX emissions
from test cells to the non-attainment area
stationary and total NOX emissions. The
contribution of test cells to NOX emissions in ozone
non-attainment areas does not exceed 3 percent of
the stationary NOX and 0.7 percent of the combined
stationary and mobile NOX sources. The vast
majority of test cells contribute less than 1
percent of the stationary source NOX emissions and
less than 0.07 percent of the combined stationary
and mobile source NOX emissions.
xv
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CHAPTER 1
INTRODUCTION AND SUMMARY OF FINDINGS
Section 233 of the Clean Air Act Amendments (CAAA) of
1990, Public Law 101-549, mandates that the Administrator of
the Environmental Protection Agency (EPA) and the Secretary of
Transportation, in consultation with the Secretary of Defense,
conduct a study of uninstalled aircraft engines in enclosed
test cells.
SEC. 233. STATES AUTHORITY TO REGULATE.
(a) Study — The Administrator of the
Environmental Protection Agency and the Secretary of
Transportation, in consultation with the Secretary
of Defense, shall commence a study and investigation
of the testing of uninstalled aircraft engines in
enclosed test cells that shall address at a minimum
the following issues and such other issues as they
shall deem appropriate:
(1) whether technologies exist to control some or
all emissions of oxides of nitrogen from test
cells;
(2) the effectiveness of such technologies;
(3) the cost of implementing such technologies;
(4) whether such technologies affect the safety,
design, structure, operation, or performance of
aircraft engines;
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(5) whether such technologies impair the
effectiveness and accuracy of aircraft engine
safety design and performance tests conducted
at test cells; and
(6) the impact of not controlling such oxides of
nitrogen in the applicable non-attaintment
areas and on other sources, stationary and
mobile, on oxides of nitrogen in such areas.
(b) Report, Authority to Regulate.
Not later than 24 months after enactment of the
Clean Air Act Amendments of 1990, the Administrator
of the Environmental Protection Agency and the
Secretary of Transportation shall submit to Congress
a report of the study conducted under this section.
Following the completion of such study, any of the
States may adopt or enforce any standard for
emissions of oxides of nitrogen from test cells only
after issuing a public notice stating whether such
standards are in accordance with the findings of the
study. '
1.1 SCOPE OF STUDY
This report examines the six areas of investigation
identified in §233(a) of the CAAA of 1990 relating to oxides
of nitrogen (NOX) emissions and the potential control of these
emissions from enclosed test cells capable of testing
uninstalled aircraft engines. It does not address various
other facilities employed to test aircraft engines other than
the enclosed structures examined in this study. For example,
test stands are-facilities which are typically used in long-
term durability testing of aircraft engines. These structures
are not fully enclosed and generally do not treat incoming
engine or exhaust gas for acoustic abatement. Aircraft engine
testing is also performed in facilities where the engine
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remains installed on the aircraft. These facilities, commonly
called "hush houses", are typically used for a brief engine
run-up and final airworthiness evaluation at military
bases.
Enclosed uninstalled aircraft engine test cells (referred
to in this report as test cells) may also be used in the
performance evaluation and development of aircraft auxiliary-
power units (APU's), as well as marine and industrial engines.
Auxiliary power units are turbine type engines used in
aircraft to provide electrical power. Neither APU's nor
marine and industrial engines are aircraft engines and were
not addressed in this study given §233(a)'s limitation to
aircraft engine testing. , Accordingly, the NOX emissions from
facilities devoted solely to the testing of these other
engines, and the portion of the NOX emissions from facilities
covered in this study while testing this type of equipment,
have not been included in the NOX inventory estimates or the
NOX control feasibility assessment presented in this report.
Information provided by test cell owners and operators
identified test cells which are used exclusively, to test
reciprocating aircraft engines, also known as internal
combustion or 1C engines, and test cells which are used to
test both turbine-based and 1C engines. Of the approximately
• 130 test facilities identified from this study, only one
performs 1C aircraft engine testing in test cells. For this
site, operating eight test cells testing 1C engines, it is
estimated that total annual NOX emissions are 250 Ibs. This
represents less than 0.01 percent of the annual NOX emissions
attributed to test cell operation in the United States. Given
this low contribution to overall NOX emission from test cells,
this report focuses on those test cells testing turbine (jet)
type aircraft engines which are used in both commercial and
military aircraft.
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As described in more detail in Chapter 2 of this report,
test cells may be grouped into two categories: sea level
ambient condition testing and altitude simulating. The sea
level test cell is used to evaluate the engine at the ambient
conditions experienced at the time of testing. Test cells
capable of simulating altitude conditions are large, complex
facilities used to test the engine at conditions found in
flight by providing air at controlled temperatures and
pressures. (Of the 368 test cells identified from this study,
35 are altitude test cells.) As a result of the complexity of
altitude test cells, the costs of applying NOX controls to
these types of facilities would be more than the predicted
costs for applying similar technologies to sea level test
cells. Therefore, the focus of this report in assessing the
feasibility and costs of applying NOX controls to test cells
is on sea level test cells.
Finally, it should be noted that the DoD was consulted
extensively in this study. The DoD provided much information
and data, and reviewed and provided comments on drafts of this
report.
1.2 SUMMARY OF FINDINGS
1.2.1 Feasibility, Effectiveness, and Costs of NOX Control
Technologies Applied to Test Cells
Subparts 1-3 of §233(a) of the.Act pertain to the
technical feasibility, effectiveness, and costs of NOX control
technologies for application to test cells. These issues are
addressed in Chapters 4 and 5 of this report and are
summarized as follows.
There are currently no NOX controls applied to test cells
in the United States. Various NOX control technologies that
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have been applied to other stationary combustion sources are
examined in this report for their applicability to test cells.
Potentially applicable control technologies can be categorized
as follows: 1) exhaust gas treatment methods established on
other fossil fuel-fired systems (selective catalytic reduction
(SCR), selective non-catalytic reduction (SNCR) and reburn);
2) emerging technologies (vermiculite-magnesium oxide (MgO)
sorbent bed, low NOX combustors); 3) established NOX control
methods for stationary gas turbines which would reduce
emissions from test cells by temporarily modifying the engine
tested (water/steam injection and water-in-fuel emulsion).
Selective Catalytic Reduction
SCR is a post-combustion NOX control technology whereby
ammonia is injected into the exhaus't gas and reacts with
nitric oxide (NO) to produce nitrogen gas (N2) and water in
the presence of a catalyst. The reaction is strongly
temperature dependent with a narrow temperature operating
range. This report examined two catalysts with temperatures
centered on 490 °F and 650 °F. SCR has been demonstrated with
a NOX removal efficiency of 80 percent when applied to
stationary gas turbines.
It is conceptually possible to design an SCR system using
conventional catalyst materials that could be applied to test
cells. A research and development and evaluation program
would' be required before decisions could be made on design
characteristics for test cells incorporating such a NOX
control system. This would result in test cells which would
control NOX and not affect safety or performance of the
engines when tested or affect subsequent in-flight safety.
Present-day test cells may require major structural
modifications to meet these new design characteristics.
Various considerations, such as site conditions, may limit the
1-5
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practicality of retrofit and necessitate test cell
replacement.
Due to relatively low stack gas temperatures associated
with the operation of test cells, the application of SCR in
most cases would require reheating of the exhaust gas to
maintain the stack gas temperature within the appropriate
catalyst temperature range. Both the duct burner which could
be used to reheat the exhaust gas and the ammonia injection
system must be tightly controlled via the use of feedback
control systems to follow the characteristically rapid
variations in gas temperature, mass flow rate, and NOX
concentration of the test cell exhaust gas. Controllers must
be designed to track the transient conditions, but it is
•uncertain how effective the required feedback systems would be
at tracking such a highly transient emission source. Lag time
in the response of the ammonia injection system to changes in
exhaust gas conditions would result in increased unreacted
ammonia emissions and a decrease in the NOX removal efficiency
of the system.
The cost-effectiveness estimates for SCR applied to test
cells range from $167,000 to $972,000 per ton NOX removed,
assuming the lowest cost solution catalyst and depending on
the test cell size. The primary cost components are the
catalyst and the SCR reactor vessel. Cost elements which have
not been included in the cost analysis are system
design/development costs and the cost of recalibrating the
engine/test cell combination following retrofit to account for
the change in air flow characteristics through the cell. It
is not anticipated that these components will significantly
alter the cost effectiveness estimates. Using the cost
analysis methodology outlined in Chapter 5, every $1 million
of capital investment increases the cost effectiveness
estimates $4,000 per ton NOX removed (cost recovery factor of.
1-6
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0.094 and 24 tons NOX per year). A cost sensitivity analysis
indicated that an increase in catalyst life, an increase in
test cell annual usage, an increase in NOX removal efficiency,
and a decrease in test cell dilution air (augmentation air)
would all decrease the SCR system dollar per ton estimates.
Total capital installed retrofit costs for SCR range from
$1 million to $43 million for the lowest cost solution
catalyst, depending on test cell size and operating
characteristics. Total capital costs for a recently designed
test cell capable of evaluating large turbofan type engines
range from $18 to $20 million. Total capital installed
retrofit cost to incorporate SCR to this test cell is
estimated at $14 million.
Selective Non-Catalytic Reduction
SNCR involves the injection of either ammonia or urea
into the exhaust gas stream. The ammonia or urea reacts with
NO to produce N2 within a temperature range of approximately
1,800 to 2,000 °F. SNCR has been demonstrated on utility
boilers, process heaters and other fossil fuel-fired systems
to achieve up to 50 percent NOX removal.
Due to the low stack gas temperatures associated with the
test cells, application of SNCR will require substantial
reheating with a natural gas duct burner to maintain the stack
gas temperature within the appropriate temperature range.
Similar to SCR, both the duct burner which is used to reheat
the gas and the ammonia or urea injection system.will require
controls capable of tracking the characteristically rapid
variations in gas temperature, mass flow rate, and NOX
concentration. Controllers must be designed to track the
transient conditions, but it is uncertain how effective the
required feedback systems would be at tracking such a highly
transient emission source. Lag time in the response of the
controllers to changes in exhaust gas conditions would result
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in increased unreacted ammonia or urea emissions and a
decrease in the NOX removal efficiency of the system. It is
conceptually possible to design an SNCR system using
conventional materials that could be applied to test cells .
However, until the research and development and test and
evaluation programs have been completed, the safety and
performance issues cannot be fully addressed.
Due to SNCR's lower NOX removal efficiency, and the
emissions from the duct burner, SNCR may actually cause a net
increase in NOX emissions from the test cell under most
operating conditions. At the few operating conditions where
SNCR may cause a net decrease in NOX emissions, the cost-
effectiveness estimate for SNCR ranges from $350,000 to over
$1 million per ton NOX removed. Natural gas reheat fuel is
the primary cost component. Design and development costs have
not been included in the cost effectiveness estimates. It is
not anticipated that these cost components will significantly
alter the cost effectiveness of SNCR. Using the cost analysis
methodology outlined in Chapter 5, every $1 million of capital
investment increases the cost effectiveness estimates $4,000
per ton NOX removed (cost recovery factor of 0.094 and 24 tons
NOX per year) .
Reburn
Reburn is a NOX control technology which removes NOX by
firing natural gas in a second combustion zone to produce
slightly fuel-rich conditions. The reduction of NOX to N2
occurs by reactions with hydrocarbon fragments formed in the
fuel-rich state. This relatively, new technology has been
demonstrated on utility boilers .
Reburning in an oxygen-rich gas such as that from a test
cell exhaust (greater than 15 percent oxygen) is referred to
as lean reburning, where local fuel-rich conditions occur in
an overall fuel-lean exhaust gas. The feasibility of lean
1-8'
-------
reburn was examined at bench-scale as part of a Small Business
Innovation Research (SBIR) effort. The SBIR study showed that
lean reburn can remove NOX at up to 60 percent efficiency at a
NOX inlet concentration of 1000 ppm, and the study documented
the significant decrease in NOX removal efficiency as inlet NOX
concentration dropped from 1000 ppm to 500 ppm. At a NOX
inlet concentration of 500 ppm, the removal efficiency dropped
to 30 percent. The SBIR study did not test for NOX removal at
NOX concentrations more typical of test cell operation (100
ppm or less). It is conceptually possible to design a reburn
system using conventional materials that could be applied to-
test cells. However, until the research and development and
test and evaluation programs have been completed, the safety
and performance issues cannot be fully addressed.
However, cost-effectiveness for reburn applied to test
cells was estimated assuming a NOX removal efficiency of 10
percent, based on a fuel equivalence of 0.8 and an inlet NOX
concentration- of 100 ppm. The high fuel requirement is due to
the high oxygen levels in the test cell exhaust gas. The
cost-effectiveness ranged from $480,000 to $9.4 million per
ton of NOX removed for different sized test cells, assuming
reburn fuel as the only cost element.
Vermiculite - Magnesium Oxide Sorbent Bed
The vermiculite-MgO sorbent bed is a post-combustion
control technology which removes NOX from the gas stream by
adsorption onto the bed material. Unlike SCR, this technology
does not require exhaust gas reheat or ammonia injection.
Short-term testing on a test cell using a 10 percent
slipstream indicated 50 to nearly 70 percent NOX removal.
Long-term pilot-scale testing has not been conducted on test
cells (or other combustion sources), and the technology has
not been demonstrated on a full-scale test cell. There is-a
proposal to further evaluate this approach on a test cell. It
is conceptually possible to design a vermiculite sorbent bed
1-9
-------
that could be applied to test cells. However, until the
research and development and test and evaluation programs have
been completed, the safety and performance issues cannot be
fully addressed. Cost-effectiveness estimates are unavailable
due to limited information on this technology.
Water or Steam Infection
Water or steam injection or water-in-fuel emulsion are
established NOX control technologies for stationary gas
turbines. Water reduces the flame temperature, thereby
reducing thermal NOX formation. The use of either water/steam
injection or water-in-fuel emulsion to reduce NOX from engines
evaluated in test cells would require temporary engine
modifications and would significantly alter the performance
characteristics of the engine under test. See Section 1.2.2
for more details.
Low N(X Combust or s
Although not actually a NOX control technology for test
cells, aircraft engine combustors are being designed to
produce less NOX and thus may ultimately lead to lower test
cell NOX emissions. Low NOX combustor technology has been
developed for stationary gas turbine applications. However,
the transfer of this technology to aircraft engines is not
straightforward. Aircraft engines place demands on the
combustor technology that are not required for stationary gas
turbine applications, such as rapid transient operation with
low risk of flameout. Currently, some jet engine
manufacturers and NASA are developing low NOX combustors for
use on their engines.
1-10
-------
1.2.2 Effects of Test Cell NOX Control Technologies on
Aircraft Engine Safety, Design, Structure,
Operations and Performance Testing
Subparts 4 and 5 of §233(a) of "the CAAA pertain to the
effects that NOX control technologies might have on the
safety, design, structure, operations and performance of
aircraft engines and the impact on the effectiveness and
accuracy of aircraft engine safety design and performance
tests conducted at test cells. All of the known potential
effects that the various control technologies may have on the
engine or the engine test are addressed in Chapter 4 of this
report and are summarized as follows. However, until the
research and development and test and evaluation programs have
been .completed, the safety and performance issues on testing
cannot be fully addressed.
Effects of Water or Steam In-jection
As discussed previously, water or steam injection and
fuel/water emulsion would directly affect the engine and
engine test by altering the performance characteristics during
testing. These modifications would result in the evaluation
of an engine within the test cell which would require further
modification before being returned for in-flight service.
Also, this type of NOX control would result in engines tested
with performance characteristics which are not representative
of the engine when prepared for in-flight service. This alone
defeats the purpose of certification and validation testing
following engine repair. For engine development-related test
cell operation, critical component testing and engine
performance determination would be invalid or provide data for
unrealistic or non-representative engines and operating
conditions.
1-11
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Effects of Back Pressure
The back pressure associated with the post-combustion NOX
control technology equipment, such as catalysts, sorbent beds
and duct burners, would impede the air flow through the test
cell. Using conventional technology, designs can limit back
pressure to 0.1 inch water for a duct burner and 1 to 2 inches
of water for a catalyst bed.
The aerodynamics of the test cell affect the performance
of the engine being tested. An increase in back pressure, as
would occur with an add-on NOX control technology, would also
affect the aerodynamics of the test cell. Air flow
recirculation, causing temperature and pressure distortion of
the engine inlet air, can lead to uncertainty about engine
performance measurements. Engine performance may become
unstable and unrepeatable, leading to test rejection and
possibly unnecessary engine rebuild. Recirculation of air
within the test cell will also affect engine thrust
measurement. In extreme cases, engine inlet air flow
distortion may result in compressor stall and cause severe
engine damage.
An increase in back pressure downstream of the test
engine may reduce the augmentation ratio (an indicator of the
amount of test cell dilution air which bypasses the engine).
This would make it necessary to recalibrate the test cell for
each engine model tested in that test cell. In addition, the
increase in back pressure may make it necessary to decrease
the maximum thrust capability of a test cell to compensate for
the decrease in augmentation air flow. This resultant
decrease in thrust capability would effectively limit the size
of engines that can be tested in the cell. Continued testing
of these engines would require a major modification of the
test cell or construction of a new test cell which would use
1-12
-------
NOX controls and not affect the safety or performance of the
engine.
One modeling study indicates that vortices in the test
chamber may be avoided if the augmentation ratio is kept above
0.8. New test cells are designed so that augmentation ratios
are typically greater than 0.8, and in practice, augmentation
ratios are normally between 1 and 10. Therefore, although the
add-on NOX control technology may lead to a reduced
augmentation ratio, there is some indication that if the new
augmentation ratio remains greater than 0.8, inlet air
vortices may be avoided. However, for low bypass ratio engine
testing and engine core testing, the minimum augmentation
ratio is determined by the cooling requirement on the aft
portion of the engine. For this reason, low bypass ratio
engine testing and engine core testing augmentation ratios
must be maintained much higher than 0.8 to provide sufficient
cooling.
1.2.3 Impact of Not Controlling NOX Emissions From Test Cells
in the Applicable Ozone Non-Attainment Areas
Subpart 6 of §233 (a), of the CAAA pertains to the impact
of not controlling NOX emissions from test cells in the
applicable ozone non-attainment areas. (An area is classified
as non-attainment if it does not meet the national ambient air
quality standard (NAAQS) for the pollutant in question.)
This issue is addressed in Chapter 6 of this report and is
summarized below. An inventory of the test cells in the
United States, along with their annual emission estimates,
serves to address the question of impact.
Results from this study (see Chapter 6) indicate that the
total annual NOX emitted from the current population of 368
test cells in the United States is approximately 2,830 tons.
1-13
-------
Approximately 74 percent (2,070 tons) is emitted into ozone
non-attainment areas. The NOX emissions distribution for test
cells located in ozone non-attainment areas is presented in
Figure 1-1. A significant variation exists in test cell
annual NOX emissions, which are determined in part by the size
of the engines tested within the test cell, the annual hours
of operation, and the test schedules. Figure 1-2 presents the
distribution of average test cell annual NOX emissions.
Data were generated from the average annual facility NOX
emissions divided by the average number of test cells per
facility.
The relative contribution of test cell NOX emissions to
total NOX emissions within the ozone non-attainment areas was
determined by comparison to non-attainment area stationary and
total NOX emissions. This analysis is summarized in Table 1-
1. The data show that the contribution of test cells to NOX
emissions in ozone non-attainment areas does not exceed 3
percent of the stationary NOX and 0.7 percent of the combined
stationary and mobile NOX sources. The data also show that
the vast majority of test cells contribute less than 1 percent
of the stationary source NOX emissions and less than 0.07
percent of the combined stationary and mobile NOX source NOX
emissions.
1-14
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CHAPTER 2
CHARACTERIZATION OF TEST CELLS
Test cells are facilities designed to operate and measure
the performance of uninstalled aircraft engines. The
Department of Defense (DoD), the commercial airline industry,
aircraft engine manufacturers, and contract engine repair
organizations operate test cells to achieve their specific
goals, which include: engine development, maintenance and
repair, and airworthiness evaluation.
Test cell designs vary widely to meet the owner/operator
requirements, although as will be discussed in Section 2.1,
these facilities can be broadly categorized by their ability
to conduct either "altitude simulation" or "sea level"
testing. As will also be discussed in Section 2.1, aircraft
engine testing is performed using facilities other than test
cells, including test stands and hush houses. These two types
of facilities described briefly in Section 2.1 do not conform
to the scope of work in this report and are not included in
either the emission inventory presented in Chapter 6 or the
NOX control feasibility assessment presented in Chapter 4.
The physical size and exhaust gas characteristics
(temperature, flowrate and NOX concentration) of test cells
are determined to a large extent by the engines tested within
the facility. A brief description of the types of engines
typically tested within test cells and their impact on the
test cell exhaust gas characteristics is presented in Section
2.2. The operation of an individual test cell is primarily
determined by the test goals of the owner/operators and can
2-1
-------
vary widely, for example, between aircraft engine development
and commercial airline airworthiness assessments. Section 2.3
presents a discussion of the types and objectives of tests
performed in test cells. The distribution of test cells by
owner/operator within the United States and the role of test
cell operation within the various owner/operator groups is
presented in Section 2.4.
2.1 TEST CELL DESCRIPTION
1, 2, 3, 4, 5
'Test cells are structures designed to hold and operate
aircraft engines; use advanced test instrumentation to measure
and document engine performance; and suppress noise to the
surroundings during engine tests. Test cells may be found at
Air Force, Navy and Army bases, at commercial airline
facilities, NASA, aircraft engine manufacturers' facilities,
and at contract engine repair facilities. Test cells exist in
a large variety of configurations, and generally no two are
exactly alike. However, three principal components found in
all test cells are: (1) a building which encloses the engine
and the instrumentation and provides fuel and structural
support during testing; (2) an augmentation tube; (3) and a
blast room and/or exhaust stack. A schematic of a generic
test cell containing the above mentioned components is shown
in Figure 2-1. Although there is great variety in design,
test cells can be grouped into two categories: sea level •
ambient condition testing and altitude simulating. This
section will discuss the physical properties of, and
differences between, these types of test cells. Engine
testing is also conducted in facilities other than test cells
such as test stands and hush houses. Although these two types
of facilities are not covered by this study, a brief
2-2
-------
Combustion and
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2-3
-------
description of each is provided at the end of this section in
order to distinguish them from test cells.
2.1.1 Sea Level Test Cell Description
The sea level test cell is used to evaluate the engine at
the ambient conditions experienced at the time of testing.
Figures 2-2, 2-3, and 2-4 are schematic diagrams of typical
sea level test cells. While there are fundamental differences
between the facilities shown, these test cell designs are
capable of conducting similar engine tests. The primary air,
which consists of the air that goes into the engine, and the
secondary or augmentation air, which is the air that flows out
the stack but does not flow through the engine, have different
flow patterns through these facilities. In Figure 2-2, the
air enters the facility through a single inlet. The air flow
is divided into the primary air and the secondary/augmentation
air. The augmentation air does not pass through the front of
the engine but is used for the purpose of dilution, cooling,
and to limit the negative pressure in the cell. Figure 2-3
depicts a test cell with a single air inlet without physical
separation of the primary and secondary air. In this design
of test cell, the secondary air is entrained around the engine
by the lower pressures created from the high velocity exhaust
gas (ejector effect). Figure 2-4 shows a test cell that has
two air inlets, one for the primary air and a separate one for
the augmentation air.
Test cells are usually massive reinforced concrete
structures designed to withstand the intense vibrations,
negative pressures generated within the facility, and the heat
generated by the engine. Typically,' air is drawn into the
test cell by..the engine through various kinds of acoustical
2-4
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baffling and/or turning vanes. The test engine is fastened to
a thrust frame which is anchored to the test cell. The thrust
frame incorporates load cells and other instrumentation to
monitor and evaluate the engine during testing. The test cell
also provides the fuel, necessary hardware and controls to
simulate the aircraft for which the engine is used. The
thrust frame and associated instrumentation are used to
measure the observed engine thrust exerted on the frame.
The corrected (actual) thrust is determined using the
observed thrust and the test.cell/engine correction factor.
The correction factor is determined for each specific model of
engine for each test cell by placing a calibrated engine of
the same model with known thrust characteristics in the test
cell and monitoring such items as the observed thrust, fuel
flow rate, and engine rpm. The correction factor relating
observed thrust to actual thrust is required to account for
dissimilar air flow around the engine as well as the effect of
variations in ambient air conditions. Thrust measurement is a
critical parameter in test cell operation; test cell
operational goals include the desire to minimize the required
thrust corrections, and to ensure for test repeatability.
Minor changes to the test cell or mounting arrangement of the
engine within the facility can significantly'impact air flow
around the engine. This change in air flow would necessitate
recalibration and determination of a new thrust correction
factor for each engine tested in the altered test cell.
,In a test cell, the augmenter tube is located behind the
engine. The augmenter tube has two primary purposes: (1) to
reduce negative static pressures in the test cell during the
test by enhancing augmentation air flow; (2) and to promote
air flow around the engine, which cools the engine as if in
flight. ' The air entrained by the engine exhaust which did not
pass through the engine cools and dilutes the engine exhaust.
2-8
-------
This dilution helps to protect the test cell from the heat of
the engine exhaust by maintaining a temperature of typically
less than 400"F in the test cell exit gas.
.Augmenter tube design varies in shape and size. Most
augmenter tubes have a bell mouth at the front to promote
secondary air flow. The engine exhaust gas and secondary air
are mixed and flow down the augmenter tube, usually made of
steel, to a position under the stack. The augmenter tube is
usually perforated at the end to distribute the exhaust gases
in a-uniform manner and to minimize the creation of localized
hot spots which may damage the concrete. Some augmenter tubes
do not have either the bell mouth or the perforated ending to
the augmenter tube. Figure 2-5 shows a schematic diagram of
the F402 test cell at the Naval Aviation Depot Cherry Point.
In lieu of the perforations in the augmenter tube, this
facility has permanently mounted angular slats at the bottom
of the stack in order to direct the exhaust gases. This
particular test cell design incorporates acoustic dampening
along the augmenter tube region, eliminating the need for
sound baffles in the stack.
'In addition to air cooling, test cell designs can
incorporate water sprays to cool the exhaust gases in the
augmenter tube. Water is usually sprayed radially through
spray rings, which are routinely used for test cells testing
military engines that have an afterburning mode. Water
cooling systems can be operated at all power settings above
idle, or automatically triggered when a specific stack
temperature is reached.
2-9
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2.1.2 Altitude Simulating Test Cell Description
Test cells capable of simulating altitude conditions are
large, complex facilities used to test aircraft engines at
conditions found in flight. These facilities not only measure
engine performance as in sea level test cells, but also
provide air at controlled temperatures and pressures to
simulate actual flight conditions. Although individual
facility capabilities can vary, altitudes ranging from sea
level to nearly 70,000 feet, air speeds up to Mach 3, and
inlet air temperatures from below -20 *F to nearly 500*F can be
achieved in several of these type test cells. These
facilities are generally owned and operated by the engine
manufacturer, DoD, or NASA and are used for all types of
testing including certification, fuel economy determination,
and high altitude performance assessment.
When simulating altitude conditions, air flow through the
engine is tightly controlled, with both the engine and
additional exhaust pumps moving the air through the test cell.
Figure 2-6 depicts a generic schematic of an altitude
simulating test cell. In order to simulate flight conditions
at altitude, air pressures must be independently controlled
both upstream and downstream of the engine. This condition
requires that a pressure seal arrangement be used, isolating
these two sections of the test chamber. Typically, the engine
is mounted through a bulkhead and closed off with a pressure
seal. Test cell secondary air, primarily used for cooling, is
introduced behind the bulkhead. ,
Although different altitude test facilities use different
methods and equipment to evacuate the test chamber, the basic
approach remains the same. One or more vacuum pumps driven by
gas or steam drivers or by electric motors are used to pull
air through the test chamber. The test engine exhaust gas
2-11
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stream typically passes through a temperature control device
prior to entering the exhaust vacuum pumps. Modulating
discharge valves are usually included in the ductwork between
the test chamber and the vacuum pumping equipment and are used
in conjunction with the vacuum pump(s) to set air flow rates
and to control pressure. For example, the chamber is
maintained at approximately 1/4 atmosphere pressure to
simulate 35,000 feet altitude conditions. The simulated Mach
number is determined by the ratio of inlet engine pressure to
test chamber air pressure. This ratio is approximately 1.5 to
simulate 0.8 Mach number, which is a typical commercial engine
test condition to demonstrate cruise performance. Modulating
valves upstream of the engine inlet are used to set the
pressure level at the front face of the engine.
.The Willgoos turbine laboratory, owned and operated by
Pratt and Whitney, is an altitude simulating facility.5 The
facility provides air at controlled temperatures and pressures
to simulate actual flight conditions at altitudes ranging from
sea level to 65,000 feet and Mach number up to 3. The
facility uses various combinations of 16 steam turbine driven
compressors and 6 gas turbine driven compressors for several
test cells. The steam turbines are powered by steam from six
marine type boilers.
The auxiliary equipment (steam compressors, gas
compressors, refrigeration system, process heaters, and
conditioning chambers) operates in a transient nature and
responds to sudden upsets in flow as a result of the engine
test; such as simulated flame out testing at altitude which
results in engine discharge temperatures swinging from 1000 °F
to -20 °F.
Due to the overall design of the facility, which
incorporates bypass flows to assist in controlling engine
inlet and exhaust conditions, the swings in auxiliary
equipment throughput are less severe than those experienced by
2-13
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the test engine during normal testing. However, during
simulated or actual test engine flame out, transient
conditions exist in all of the facility's auxiliary equipment.
These transients place significant loads on the auxiliary
equipment, causing rapid changes in the gas and emission
characteristics of the exhaust stream of the equipment and the
test engine.
Test cells capable of altitude simulating tests are used
to fulfill several test requirements in the engine development
cycle including: operability, cruise performance, endurance
certification, and compliance to both commercial and military
contracts and Federal Aviation Administration (FAA)
guidelines. A description of these tests will be discussed in
Section 2.3.
2.1.3
Test Stands
A test stand is a facility typically used for long-term
durability testing of uninstalled aircraft engines. Test
stands differ from test cells in that they are not completely
enclosed and generally do not use the level of instrumentation
found in test cells. Because test stands are not fully
enclosed facilities, they do not experience the negative
pressures found in test cells during engine operation. Test
stands do not typically control the inlet flow or muffle the
engine exhaust noise. Test stands do not conform to the scope
of the work as defined in Chapter 1, and data were not
obtained for these facilities in the NOX inventory as
described in Chapter 6.
2.1.4 Hush Houses
A hush house is a facility designed to test an engine
while still installed on the aircraft. These facilities are
often used in the final test of engine air worthiness.
2-14
-------
The aircraft is moved into a facility and anchored to the
floor during testing. Figure 2-7 shows a side'view of an F-
14A in a hush house located at the Naval Weapons Industrial
Reserve Plant in Calverton, New York. Hush houses do not
conform.to the scope of work as described in Chapter 1, and
data were not obtained on these facilities for the NOX
inventory as described in Chapter 6.
2 .2 AIRCRAFT ENGINES EVALUATED IN TEST CELLS 6< 7
The majority of test cells operated in the United States
are owned and operated by jet engine manufacturers and the DoD
(see Section 2.4). As a result, the current population of
test cells is used to evaluate a variety of turbine-based
aircraft engines. Turbine-based or "jet" aircraft engines
incorporate a variety of engine designs, including turbofan,
turbojet, turboprop, and turboshaft configurations.
Typically, large commercial airlines use high bypass
turbofan engines. Turbofan engines refer to a class of
aircraft engines which derive a portion of engine thrust from
the fan section of the engine, and not solely from the high
velocity, high temperature exhaust exiting the turbine region
of the engine. A high degree of bypass air flow is associated
with an engine incorporating a large fan section, as shown in
Figure 2-8. In this engine, the majority of air entering the
front of the engine does not pass through the compressor
blades, the combustor, or the turbine blades, but.is
compressed in the fan region and throttled out the back of the
engine to create engine thrust. As mentioned above, the
relative level of thrust obtained from the bypass air can
vary. Figure 2-9 illustrates a turbofan engine with
significantly less bypass air flow than the engine shown in
Figure 2-8.
2-15
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A turbojet type engine is distinguished' from the turbofan
engine in that there is no fan region, and all of the engine
thrust is derived from the high velocity, high temperature
exhaust exiting the engine. However, the vast majority of
"jet" engines currently in service incorporate some degree of
bypass flow.
Figure 2-10 illustrates a turboprop/turboshaft type
engine. The turboprop/turboshaft type aircraft engine differs
fundamentally from the turbofan/turbojet style engine in that
work is extracted from the exhaust by high and low pressure
turbine blades to create shaft horse power. Typically, these
engines are used on smaller commercial style propeller
aircraft and helicopters. The primary difference between the
turboshaft and turboprop engine is that the turboprop is used
to power a propeller directly while the turboshaft is used to
drive a gear box, which in turn powers a propeller/rotor
blade.
The exhaust gas characteristics of turbofan, turbojet,
turboprop/turboshaft type engines are different, and therefore
the test cell exhaust gas characteristics testing these
engines will be different. A high bypass, turbofan type
engine significantly cools the hot turbine exhaust gas as it
is mixed with the fan air. The exhaust of a turbojet type
engine would not be subject to this mixing process. For
turboshaft/turboprop type engines, every effort is made to
extract the maximum shaft horsepower from the turbine exhaust.
For test cell operation, turboshaft/turboprop engines are
typically connected to a dynamometer to extract and measure
the horsepower produced by the engine. Test cells testing a
turboprop/turboshaft type engine would have a much lower stack
gas volumetric flow rate, as well as a lower velocity, and do
not typically require the augmenter associated with the
turbofan/turbojet testing test cells.
2-19
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As previously described in Sections 2.1 and 2.1.1, the
. augmentation air cools the test cell exhaust, cools the
engine, and affects test cell negative pressures. However,
depending on the engine type, the minimum amount of
augmentation air required for test cell operation varies
significantly. Test cells testing high bypass turbofan
engines can typically operate with minimum augmentation ratios
around 1 (the augmentation ratio is defined as the ratio of
air flowing into the test cell, but not through the engine, to
the total engine inlet air flow). This, is due in part to the
large amount of fan air available to cool the engine. For
test cells testing low bypass turbofans or turbojet engines,
minimum augmentation ratios of 2 to 3 are required to provide
sufficient cooling on the aft portion of the engine.8
2.3 TEST CELL TESTING AND TEST DESCRIPTION 9' 10- "
Figure 2-11 presents an engine test schedule illustrating
the rapid transient nature of engine testing performed in test
cells. Most owners and operators of test cells have developed
their own test schedules, although engine manufacturers
provide the engine owner with a suggested test program
following repair. The variety of test schedules is diverse,
although within many owner/operator groups the test purpose
remains the same, that is, evaluation of engine performance by
determining critical engine parameters. Parameters which are
used to assess engine performance include but are not limited
to the following: thrust, fuel flow, engine compressor and
turbine rpm, and the engine pressure ratio (engine pressure
ratio, epr, is the ratio of the inlet pressure and the exhaust
pressure immediately behind the turbine blades). For engine
manufacturers, testing involves engine development as well as
basic performance evaluation.
The DoD, commercial airlines, engine manufacturers, the
National Aeronautics and Space Administration (NASA), and
2-21
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engine load varies with time during cycle.
2-22
-------
contract repair facilities have developed test schedules to
fit the purpose of the test. Although the test objective may
be similar, the test schedule will be customized for the
individual test cell and engine undergoing the test.
Aircraft engine testing may be categorized as development
testmg, production testing, and engine testing after an
overhaul. Overhaul testing is performed at engine
manufacturer sites, overhaul sites, government and airline
owned test facilities. Production testing is done by
manufacturers. Development testing is done by manufacturers
and a few of the DOD facilities.
2.3.1 Development Testing
The two major types of development testing are full
engine testing and component testing. Full engine development
testing is performed in both altitude simulating test cells
and sea level test cells. Verification of the altitude
performance of the engine is critical- to determine both
operational safety and operating cost. Altitude simulation
testing in test cells is a critical element in the engine
development cycle, and testing is conducted to evaluate the
following:
.Operability. These tests demonstrate the engine
response to various throttle movements. Aircraft
engine altitude performance and operability require
design tradeoffs. These tradeoffs chosen during the
engine design stage need to be verified to ensure
the best possible fuel efficiency while achieving
stall-free transient operation. Because this
testing requires rapid transients to verify the
engine's stall-free characteristics, this type of
testing places the most demands on the altitude
simulating test cell.
2-23
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Cruise performance. Engine manufacturers typically
guarantee fuel efficiency to their customers, and
therefore, they include a verification of that
performance element as part of the altitude test
process. This is not just a single demonstration
test, but rather a series of back-to-back tests.
These tests evaluate various design configurations
throughout the multi-year engine development cycle
to ultimately end up with the best engine
configuration to provide to the customer at
certification.
Endurance certification. There are several altitude
endurance tests required of engine manufacturers to
verify engine operation at maximum continuous power
for up to 45 hours. These tests are typically
conducted once during the development of a new
engine model.
Compliance. This special altitude test is sometimes
included in military and commercial contracts. It
is a one-time test conducted on one production
engine configuration. Test results can be used in
negotiations for any subsequent engine warranty
claims.
Sea level development testing is performed in both open
and enclosed test cells. The following is a description of
the tests,performed in a sea level test cell for development
testing:
Operabilitv. These tests are similar to the
altitude operability test in that they are used to
verify engine compression system stability during
rapid throttle transient. On a particular engine
2-24
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model, this testing is usually conducted at sea
level before altitude due to relatively lower costs.
Once a particular configuration is chosen that is
best at sea level, it is then verified at altitude.
Performance. Some performance testing can also be
accomplished at sea level, particularly during
configuration optimization testing. Verification is
then done at altitude.
Endurance. Virtually all endurance testing is done
at sea level. This testing is done for various
purposes but, in general, it is done to accumulate
operating time and heat cycles on the engine and all
its components to assess durability. One particular
version of endurance, called Initial Maintenance
Interval (IMI), is conducted to determine
appropriate engine operating intervals prior to
maintenance for the production engines once they are
out in the airline fleet.
Certification. There are many tests conducted as
part of the engine certification process, including
determination of maximum rotor speeds, blade out,
water ingestion, bird strikes, emissions and a 150-
hour engine run. In order to obtain FAA or DoD
certification, each of these tests must be
successfully completed.
2.3.2 Production/Overhaul Testing
Production'testing is almost always related to the
verification that is done on each and every production engine
built by the manufacturer. Each aircraft engine makes at
2-25
-------
least one production test run, typically 4 to 6 hours in
length. Successful completion of these tests results in the
engine's readiness for shipment to the customer. Engines
manufactured early in the production run of a new engine model
go through two engine tests, with substantial engine teardown
between each. As engine maturity is demonstrated, audit
levels are reduced so that only one test run is required if
all other conditions are met.
Overhaul testing is virtually the same as production
testing, except that it is conducted on an engine after it has
been in service and has just completed a major overhaul or
repair. These tests are conducted to determine if the engine
performance is back to pre-overhaul limits so that it can be
re-installed for fleet operation. This testing may be done at
manufacturers' facilities or at overhaul shops owned by the
airlines, the government, or private repair facilities.
Figure 2-12 presents a typical production run engine test
schedule.
Within the categories of production and overhaul engine
testing, specific tests are completed in test cells to achieve
the owner/operator goals. These engine test programs can be
categorized as endurance, performance and special.
Endurance. As mentioned previously, endurance tests
are done to demonstrate engine reliability. Most
endurance tests are done in sea level facilities and
usually incorporate engine thermal cycling.
Typically, cycles consist of allowing the engine to
cool for several minutes at idle, making a rapid
throttle change up to take-off power, and remaining
there for several minutes before rapidly returning
to idle power. Although there are many variations
in cycle detail, all of the engine test cycles of
this kind are designed to simulate some portion of
2-26
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an engine's expected service life. Recent trends,
aimed at providing a mature propulsion package at
fleet introduction, include testing of the entire
engine over the spectrum of expected operating
conditions. This attention to detail during the
development process can reduce the number of
"nuisance" problems traditionally experienced when a
new aircraft engine is introduced into the fleet.
Figure 2-13 presents an example of an endurance engine
test cycle.
Performance. Engine performance testing is
conducted both at altitude and sea level facilities.
Its purpose is to demonstrate the performance of the
engine or its sub-components, or to demonstrate the
relative performance of one engine configuration to
another. This testing is done at sea level where
possible and at altitude if necessary.
Special. There are several types of special tests
including ice ingestion, water ingestion, and bird
ingestion where engine reliability is demonstrated
during simulated events which may occur later during
the engine's service. These tests are performed in
sea level facilities. Other specialty tests include
"blade out" (a fan blade failure during take-off
mode to ensure airplane safety), hot fuel, cold
fuel, hot oil, and altitude restarts.
2.4 OWNER/OPERATOR PROFILE
The DoD uses both altitude simulating test cells and sea
level test cells to conduct a variety of tests. DoD
facilities, primarily Navy and Air Force Bases, conduct some
2-28
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levels of development testing, including altitude simulating
developmental testing. The DoD also performs overhaul testing
at many facilities across the United States. The DoD conducts
endurance tests and performance tests in both altitude
simulating and sea level test cells. The DoD has established
a hierarchial structure to conduct engine repair and testing
to maintain fleet readiness. For example, the Navy has a
repair and maintenance hierarchy to maintain fleet readiness
consisting of three levels (operational, intermediate, and
depot).
The operational ("O") level maintenance is performed by
an operating unit (squadron) on a day-to-day basis. This
maintenance is performed to keep assigned aircraft, engines,
and systems in a fully mission ready status. The engine
maintenance performed at the "0" level is limited to removal
and installation of quick engine change gear (QEC). This type
of maintenance does not require engine verification using a
test cell, although it might require an engine run-up while
installed on the aircraft.
Intermediate ("I") level maintenance is performed at
designated locations to support a group of operational units.
The "I" level mission is to enhance and sustain the combat
readiness of the supported activities (squadrons).
Maintenance at this level is performed to a greater depth than
the "O" level, and is performed both on and off aircraft.
Maintenance at the "I," level is most often limited to hot
section repair (turbine and combustor(s)). At the "I" level,
engine certification is most often conducted using a test
cell, however, it may also be done using an open-air test
stand.
Maintenance at the depot "D" level consists of all "O"
and "I" level activities as well as cold section repair
2-30
-------
(compressor section). Although the work done at the "I" level
is not of the same complexity as work done at the depot level,
both require engine verification. Due to the depth of
maintenance, all depot type repairs and overhauls require full
engine performance verification using test cells. The
operation and use of test cells are a major part of the depot
level of effort. Thirty percent of the DoD test cells are on
this tier of the organizational hierarchy. These test cells
are used for both routine maintenance to major overhaul engine
verifications and air worthiness determinations. The test
cells are required at depots to run a thorough analysis of the
engine before it is returned to fleet service.
Commercial airline use of test cells consists of the same
level of maintenance and repair as the depot level of the Navy
test -cells. The commercial airlines' purpose for testing is
primarily air worthiness determination, engine safety
performance guarantees, and fuel efficiency. Airlines
routinely disassemble an engine to its individual components
for repair and maintenance. Test cells are then used to
determine that the post-maintenance engine performance
capabilities are similar to the pre-maintenance performance
capabilities. Commercial airlines use only sea level test
cells to test the engines and will contract any altitude
simulating testing that may be necessary to,a capable
facility. Specifically,. commercial airlines perform sea level
testing and overhaul testing and use endurance and performance
tests as described above.
The aircraft engine manufacturers use both sea level and
altitude simulating test cells. The manufacturers are the
only owner/operator group that performs all testing and
conducts all tests mentioned above. Production testing is
solely performed by engine manufacturers as are most
specialized tests.
2-31
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The National Aeronautics and Space Administration (NASA)
provides the aeronautic community with testing and evaluation
capability in support of their research and technology
charter. The test cells operated by NASA are used for
performance evaluation, component development/evaluation,
qualification tests, endurance tests, and technology
development.
Independent contract repair facilities use test cells in •
the same manner as the commercial airlines. These facilities
perform sea level overhaul testing and conduct the endurance
and performance tests for engine certification following major
engine maintenance. These facilities do not have altitude
simulating test cell capabilities.
2.4.1 Test Cell Population Distribution
Table 2-1 provides the distribution of sea level and
altitude simulation capable test cells by owner/operator
category. This information was compiled from test cell users
to estimate the NOX emissions from test cells. Based on the
results, there is a total of 368 test cells operated in the
United States. The DoD and the engine manufacturers operate
the largest number of test cells at 50 percent and 40 percent
of the current test cell population, respectively. The Air
Force operates 62 percent of the DoD-owned test cells.
2.5 SUMMARY .
There are 368 test cells operated in the United States.
These facilities are owned and operated by the aircraft engine
manufacturers, DoD, commercial airlines, contract repair
organizations, and NASA. Test cells are used primarily for
aircraft engine developmental testing and air worthiness
assessment following engine repair. Test cell exhaust gas
2-32
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TABLE 2-1. DISTRIBUTION OF SEA LEVEL AND ALTITUDE
SIMULATING TEST CELLS BY OWNER/OPERATOR CATEGORY 1
Owner/ • Sea Level
Operator Test Cell
Commercial Airlines 13
Altitude Simulating
Test Cell
Totals
13
DoD, Total
Navy
Army/Air Force
{169}
57
112
{1.4}
0
14
{183}
57
126
Aircraft Engine
Manufacturers
129
19
148
NASA
Contract Repair
Facilities
21
2
0
3
21
Total
333
35
368
* This table represents a summary of information provided by test cell
owners/operators, 1993.
2-33
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characteristics are controlled by test cell design and
operation of the engine tested within the test cell, and the
test schedule used in the engine test program. Engine test
programs are typically transient in nature, with many rapid
swings in engine throttle position. These engine transients
are accompanied by rapid fluctuations in engine air flow
rates, exhaust gas temperatures, and NOX emissions.
Altitude simulating capable test cells are facilities
which are capable of independently controlling the inlet air
temperature and pressures both upstream and downstream of the
test engine. These test cells are typically large complex
facilities with many subsystems operating in concert with the
engine test schedule. Altitude simulating capable test cells
are primarily used by the DoD and engine manufacturers and
represent approximately 10 percent of the total test cell
population within the United States.
2-34
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2.6 REFERENCES
1.
2.
3.
4.
5.
Blake, D.E., Jet Engine Test Cells — Emissions and
.Control Measures: Phase I. Prepared for the United
States Environmental Protection.Agency, Division of
Stationary Source Enforcement, Technical Support
Branch, by Acurex Corporation, Research Triangle
Park, North Carolina. EPA-340/l-78-011a.
April 1978. pp. 6-19.
Northwest Site Visit Report from Harris, R.E, Energy and
Environmental Research Corporation, to Wood, J.P,
EPA/ESD. April 13, 1993.
Delta Airlines Site Visit Report from Harris R.E, Energy
•and Environmental Research Corporation, to Wood, J.P,
EPA/ESD. April 24, 1993.
Cherry Point Site Visit Report from Harris R.E, Energy
and Environmental Research Corporation, to Wood, J.P,
EPA/ESD. February 4, 1993.
Pratt & Whitney Site Visit Report from Harris R.E, Energy
and Environmental Research Corporation, to Wood, J.P,
EPA/ESD. November 16, 1992.
6.
7.
Pratt & Whitney. Figures 2-8 and 2-9, cutaway views of
Pratt & Whitney aircraft engines, provided to the EPA.
Letter from Spratt, J.J. Allison Gas Turbine Division of
General Motors Corporation, to Donaldson, G.C., EER
Corporation. June 4, 1993. In response to a request for
a cross-sectional view of a turboprop/turboshaft engine.
2-35
-------
8. Meeting minutes. Representatives from the Aerospace
Industries Association, Department of Defense, Federal
Aviation Administration, EPA, and EER. February 3, 1994.
Discussion of technical aspects of and industry concerns
with the Report to Congress.
9. Letter from Dimmock, R.L.,Pratt & Whitney, to Wood, J.P,
EPA/ESD. October 19, 1992. Discussion of test cell
operation descriptions.
10. Johnson, S.A., and C.B. Katz (PSI Technology Company).
Feasibility of Reburning for Controlling NOX Emissions
from Air Force Jet Engine Test Cells. Prepared for Air
Force Engineering & Services Center. Tyndall AFB, FL.
ESL-TR-89-33. June 1989. p 8.
11. Letter from Rountree, G., Aerospace Industries
Association, to Wood, J.P., EPA/ESD. March 13, 1993.
Aerospace Industries. Association information on
test cells used by member companies.
2-36
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CHAPTER 3
MODEL TEST CELL DEVELOPMENT
3 .1 OVERVIEW
Given that it is conceptually .possible to apply NOX
control technologies examined in this study to aircraft engine
test cells, the technical feasibility and cost of implementing
the NOX controls depend on the pollutant concentrations, gas
mass flow rates, gas flow velocities, and gas temperatures
downstream of the engine tested within the test cell. The NOX
mass emissions from a specific test cell for a particular test
are determined solely by the aircraft engine under evaluation
and the test cycle used to evaluate the engine. The test cell
itself does not contribute to the NOX mass emissions. The
stack pollutant concentrations, gas flow rates, gas
velocities, , and gas temperatures downstream of the engine are
determined by the specific engine and test program, as well as
the volume of the air entrained though the test cell. As
discussed in Chapter 2,-the volume of air entrained through
the test cell is governed in part by the engine and setup of
the engine within the test cell', as well as the design and
operation of the test cell itself. Adjusting the stack gas to
a fixed percentage oxygen level (15 percent, for example)
corrects for the dilution effect of the- entrained air and
allows for direct comparison of test cell exhaust
characteristics; however, both total gas volume flow and stack
gas exit temperatures are significantly affected by the
entrained air.
3-1
-------
The EPA has compiled the emission characteristics for a
wide variety of stationary sources,1 including boilers,
heaters, and most other fossil fuel-fired combustion systems.
This body of data is compiled from measured stack test data
and can be readily categorized according to a variety of basic
parameters, including the type of fuel burned and the basic
operating characteristics of the source. For test cells, the
wide range of current engines that can be tested in an
individual cell, the ongoing development of new engines to be
tested, and the variety of engine evaluations required to meet
the test goals preclude this type of characterization.
Additionally, stack emission measurements from test cells are
not routinely made. Therefore, measured test cell stack data
are not widely available to reliably characterize the NOX
emissions of a particular class of test cells.
This chapter describes the development of five model test
cells which are used to estimate the stack exit temperatures,
flow rates, and NOX concentrations necessary to evaluate the
feasibility and cost of implementing NOX controls to a large
portion of the current test cell population. The five model
plants are divided into two main categories according to the
type-of engine tested: turbojet/turbofan test capable test
cells and turboshaft/turboprop test capable test cells. As
discussed in Chapter 2, these engines are primarily
differentiated by the energy in the.exhaust gas. Measured
engine emission data are combined with models of the
temperature rise across the engine and air flow through the
test cell to predict the stack gas conditions. As will be
discussed in Chapter 6, test cells -testing these two -classes
of engines contribute the majority of NOX emissions from the
current population of test cells in the United States.
The stack gas conditions predicted using the model test
cell analysis are supplemented with detailed velocity,
temperature, and NOX concentration data measured in the
3-2
-------
exhaust stream of a test cell testing a military engine.
These measured data provide additional information regarding
the characteristics of the exhaust gas stream that can impact
the feasibility and cost of implementing NOX controls.
Additionally, these measured data are used to verify the
temperature estimates obtained from the model test cell
analysis.
3.2 AIRCRAFT ENGINE EMISSION FACTORS
Aircraft engine NOX emission factors for a large portion
of the existing engine population have been documented.2
Typically, these emission factors are expressed in units of
pounds of NOX per 1,000 pounds fuel consumed and are
determined at several thrust levels. Generally, the emission
factors are determined by the engine manufacturers and the DOD
using core flow measurements (with probes located immediately
behind the engine exhaust), and detailed guidelines for their
determination exist.3 The body of emission factor data for
military service engines is less well developed, although
databases have been developed and many of the more common
engines in service have been characterized.4' 5
Table 3-1 presents a typical emission factor summary.
Several features of jet engine emissions (and therefore test
cell emissions) are displayed in this sheet. NOX emissions
for this particular engine range from a low of 2.38 lbs/NOx
per 1,000 Ibs fuel at idle to a high of 12.32 lbs/NOx per
1,000 Ibs fuel at full military power (maximum thrust). Over
this same range, fuel consumption increases from 779 Ibs/hour
to 9,479 Ibs/hour. These values can be combined to compute
the mass emission rate of NOX per hour of operation. At idle,
this engine produces approximately 1.85 Ibs NOX per hour; at
military power, NOX is produced at a rate of approximately
116.8 Ibs/hour. This significant range in emission output
illustrates the impact that the test cycle used in the engine
3-3
-------
TABLE 3-1.
EXAMPLE OF GASEOUS EMISSIONS TABLE FROM
AN AESO DOCUMENT FOR THE J52-P-408 ENGINE
Power
Carbon
setting monoxide
measured,
Idle
Intermediate 1
Intermediate 2
Normal
Military
ppm
361.98
92.59
44.27
31.59
26.88
Carbon
dioxide
measured ,
2
1:24
1.68
2.82
3.28
3.70
Oxides
of Hydrocarbons Oxygen
nitrogen
measured ,
ppm,
NOX
9.39
31.29
71.08
101.70
137.18
NO
9.20
28.17
67.23
99.11
137.18
measured, Z
Ppm meas. calc.
320.00
20.40
16.30
17.40
18.20
Power Fuel flow, Thrust,
setting Ib/hr Ib
Idle
Intermediate 1
Intermediate 2
Normal
Military
779
2547
5752
8078
9479
548
3420
7629
10142
11349
Speed, Emission index, lb/1000 Ib of fuel
rpm CO
55.96
11.12
3.18
1.95
1.47
C02
3018
3162
3177
3179
3180
NOX
2.38
6.17
8.38
10.29
12.32
Hydrocarbons
28.33
1.40
0.67
0.61
0.57
Power
setting
Idle
Intermediate
Intermediate
Normal
Military
Oxides of nitrogen,
corrected to
3X oxygen, ppm,
meas . calc .
1
2
-
CO
43.6
28.3
18.3
15.7
13.9
Emissions,
C02
2351
8054
18272
25678
30104
pounds per
NO 2
1.86
15.71
48.21
83.13
116.76
hour
Hydro-
carbons
22. 07
3.57
3.85
4.96
5.40
Combustion F/A
efficiency,
Z
0.006
0.008
0.014
0.016
0.018
NOTE: values in this table are taken from Scott Env. Tech., Individual Engine Test
& Model Summary Reports, Mod. 6, Alameda Testing, USAF Contract F29601-75-C-46,
October 20, 1976.
3-4
-------
evaluation can have on both the instantaneous and total stack
emissions during the test. •
Test cell stack NOX concentrations when corrected to a
fixed percentage oxygen level are determined solely by the
engine under test. Engine NOX emission rates (per pound of
fuel consumed) combined with the fuel consumption rate
determine these NOX levels. Observed NOX concentrations and
test cell stack oxygen levels (in the absence of additional
cooling air) are a function of the engine mass emission rate,
as well as the air flow through the engine. As discussed in
Chapter 2, two types of engine air exist: combustion air and
bypass air. The combustion air flow through the engine can be
determined from the fuel rate and the fuel-to-air ratio at the
given thrust level. The bypass air passes through the front
of the engine, is compressed, but is bypassed around the
combustor. Depending on the specific engine design, these gas
streams will begin mixing either downstream of the engine or
just before exiting the engine. Most modern jet engines
incorporate some degree of bypass ,air flow. For military
turbofan engines, typical bypass ratios are between 1 and 2.
For large civilian transport applications, high bypass ratio
turbofan engines are used with up to 6 volumes of air entering
the front of the engine for every 1 volume of air used in
combustion of the fuel. The NOX concentration exiting the
combustor is diluted by.the bypass air flow. In typical test
cell operations, the gas is further diluted by the additional
air entrained through the test cells by the high velocity
engine exhaust. Although the dilution air will increase stack
oxygen levels and reduce observed stack NOX concentrations,
the NOX mass emission rate does not change.
3.3 TURBOFAN/TURBOJET MODEL TEST CELL DESCRIPTION
Four model test cells have been developed to assist in
both the technical and cost assessment of implementing NOX
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controls for test cells capable of testing turbofan and
turbojet type engines. Figure 3-1 presents a schematic
diagram of these model test cells. Although the specific
dimensions will vary with design, the dimensions shown in
Figure 3-1 are associated with a test cell which has a maximum
thrust capacity of 20,000 Ibs. For each model test cell, the
independent parameter in the analysis is the augmentation air
ratio associated with the operation of the test cell.. As
discussed in Chapter 2, the augmentation ratio is defined as
the ratio of air flowing into the test cell but not through
the engine to the total engine inlet air flow. In actual test
cell operation, the augmentation ratio will vary with thrust
setting and critically impacts the accuracy of the thrust
measurements, as well as the negative pressures experienced in
the test cell. In order to simplify the model test cell
calculations, the augmentation ratio is held constant
(independent of thrust). However, the sensitivity of the
predicted test cell stack exit conditions to changes in
augmentation ratio is determined by varying the augmentation
ratio from 1 to 10.
The four individual air-cooled model test cells are
distinguished primarily by the maximum thrust capacity of the
test cell. In the model test cell development, the maximum
thrust, fuel flow, pollutant emissions, engine air flow, and
engine exit temperature, are prescribed by the engine selected
for each of the model plants. The aircraft engines selected
for all of the model test cells are either turbofans or
turbojets and span the thrust ranges and engine types of the
current population of engines in service. The engines
selected for each of the individual model test cells are as
follows:
Model Test Cell (A): This model test cell uses the CF6-80A2
turbofan engine used in the Boeing B-767-200 with a maximum
thrust level of approximately 48,000 Ibs.
3-7
-------
Model Test Cell (B): This model test cell uses the F101DFE
used as the model for the present F-16 Falcon engine with a
maximum thrust of approximately 15,000 Ibs.
Model Test Cell (C): This model test cell uses the J79-GE-10B
turbojet engine, an afterburning engine with a maximum thrust
of 17,000 Ibs used in the F4 Phantom. This test cell is
distinguished by the significant increase in engine exhaust
temperature associated with the injection of raw fuel
(afterburning) into the exhaust of the engine. This has the
effect of significantly increasing engine thrust, and is used
solely on military aircraft engines.
Model Test Cell (D); This model test cell uses the J52-P-6B
turbofan which is currently used in the A-4 Skyhawk with a
maximum thrust of approximately 8,500 Ibs.
Engine data/ including emission factors, fuel flow, and
air-to-fuel ratio, were obtained from an AESO document for the
F101DFE, J79-GE-10B, and the J52-P-6B engines.6 Engine data
for the CF6-80A2 were obtained from the FAA/International
Civil Aviation Organization (ICAO) database.2
Table 3-2 summarizes the power schedule used in the model
test cells required to estimate the total NOX emissions.
Where 'engine emission data were not•available at the exact
intermediate settings, values at thrust settings closest to 30
percent and 80 percent of maximum power were selected. For
Model Test Cell (C), the power schedule is slightly different.
Five percent of the time the engine is operated in afterburner
mode, and 20 percent of the time the engine is operated at the
80 percent thrust level while the other levels remain the
same.
3-8
-------
TABLE 3-2. MODEL TEST CELL POWER SCHEDULE
Percent Maximum Thrust {%)-
100 •
80
30
idle (3-5%)
Percent time at
Thrust Setting (%)
25
25
20
30
The engine core exit gas temperatures for each of the
model test cells are estimated using Equation 3-1. The
development of this equation is provided in Appendix A. '
tC = ta + 1/Cp (LHV*FA - 1/2*(TC/MC)2)
Eq. 3-1
where:
tc: engine core exhaust temperature (°F)
ta: atmospheric temperature (°F)
Cp: heat capacity (BTU/lb °F)
FA: fuel-to-air ratio (Ib fuel/lb air)
Me: core air mass flow rate (Ibs/sec)
Tc: core thrust (lbF)
LHV: jet A lower heating value (18,500 BTU/lb)7
Figure 3-2 presents the computed engine core exhaust
temperatures for the model test cells at the various thrust
settings. During an observed test of a CF6-80-A2 at a thrust
setting of 100 percent, a core exit temperature of 1,440°F was
measured.8 Using Equation 3-1 and the engine specific
parameters, a core exhaust temperature of 1,423°F is
predicted.
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The engine core exhaust gas is cooled as it is mixed with
both the bypass engine air stream and the entrained
augmentation air stream. Equation 3-2 is used to predict the
fully mixed stack gas temperature.
tstack = (tc + BR*tb + (1 + BR)*AR*ta)/(l + BR+(1 + BR)*AR)
Eq. 3-2
where:
tstack: fully mixed stack gas temperature (°F)
tc: engine core exhaust temperature (°F)
BR: engine bypass ratio
tb: bypass flow gas temperature (°F)
ta: atmospheric temperature (°F)
AR: test cell augmentation ratio
Figure 3-3 presents the predicted stack gas temperatures •
for the model test cells operating the engines at the
prescribed throttle settings at an augmentation ratio of 5.
Using a complete set of data acquired for a J79-GE-10B,9 the
stack exit temperature using Equations 3-1 and 3-2 and an
augmentation ratio of 2 is predicted to be 413°F at 100
percent thrust. Actual test data recorded a stack exit
temperature for a J79-GE-10B engine of 413°F in an older model
test.cell that operates with an augmentation ratio of nearly
2. The current model neglects any heat transfer to the
surroundings and assumes constant, temperature-independent
heat capacity values. Despite these simplifications, the
agreement between the measured and predicted temperatures is
quite good and is considered sufficient for the technical and
cost.assessments to be presented in Chapters 4 and 5.
The effect of augmentation air (the independent model
parameter) on stack gas temperatures is presented in Figure
3-4. A significant drop in the stack gas temperature occurs
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as the augmentation ratio is increased from 1 to 3. Beyond
the augmentation ratio of 3, the rate of decrease in stack
temperature is reduced. Figure 3-5 presents the stack gas
mass flow rate as a function of the augmentation ratio for the
model test cells. For Model Test Cell (A) which incorporates
the high bypass engine (CF6-80A2), significant increases in
mass flow occur as the augmentation air ratio is increased.
This is associated with a decreasing effect on the stack gas
temperature as shown in Figure 3-4.
Table 3-3 summarizes the NOX emissions from the four
model test cells calculated using an augmentation ratio of 5
with an annual usage of 200 hours (based on data summarized in
Chapter 6). NOX concentrations have been corrected to a
uniform 15 percent O2. The equations used to predict NOX
levels are summarized in Appendix B. Figure 3-6 presents the
predicted stack NOX concentrations. Stack NOX levels are not
significantly different at peak thrust levels despite the
large variation in engine design used in the analysis. The
exception to this are the NOX emissions calculated for the
Model Test Cell (C) when operating the engine in afterburning
mode. During afterburning operation, large reductions in NOX
levels occur; however, these are generally associated with an
increase in carbon monoxide (CO) production. Predicted annual
total NOX emissions for the model test cell testing the large
civilian CF6 engine are 24.5 tons. Predicted annual NOX
emissions for the Model D testing the smallest
turbofan/turbojet engine are less than 3 tons.
3.4 OBSERVED TEST CELL DATA
The model test cells described in Section 3.3 predict the
resulting stack gas temperatures, NOX emission concentrations,
and total annual NOX emissions. As will be discussed in
Chapters 4 and 5, the technical feasibility and cost of
implementing selective catalytic reduction (SCR), selective
3-14
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TABLE 3-3.
PREDICTED EMISSION CHARACTERISTICS FOR
A TURBOJET/TURBOFAN MODEL TEST CELL
Augmentation Ratio = 5.0 Total Yearly Hours used per Model Test Ceil = 200 hrs Ambient Air Temnerature = Rd'F
Test Cell
Model
Model A
Model B
Model C *
Model D
Inpuie
Thrust
Ibf
48671
41370
14601
1723
15084
13549
1869
628
17500
11248
9000
3381
265
8439
7355
3157
511
dData
Fuel
Ibs/min
298.0
249.3
84.7
19.8
167.9
147.9
25.9
14.5
583.3
166.7
126.3
57.0
20.8
105.8
89.9
38.5
11.9
NOx
Ibs/Mlbs fue
29.6
26.6
10.8
3.4
19.7
16.5
4.4
2.6
4.5
10.3
8.3
4.2
1.3
8.9
7.6
4.5
2.7
Calculated Characteristics
Stack Gas
Temperature, "F
116.3
112.0
91.8
88.4
203.0
199.4
114.6
116.8
257.3
246.9
193.5
153.3
141.9
235.6
224.5
169.2
147.1
Stack Gas
Ibs/second
10123
9808
8924
2913
2017
1820
974
514
4728
1417
1512
1024
439
938
852
568
231
NOx Flow
Ibs/secoM
0.147
0.111
0.015
0.001
0.055
0.041
0.002
0.001
0.044
0.029
0.017
0.004
0.000
0.016
0.011
0.003
0.001
NOx, Tons
Per Year
13.2
9.9
1.1
0.1
24.4
5.0
3.7
0.1
0.1
83
0.8
2.6
1.3
0.3
0.0
4.9
1.4
1.0
0.2
0.1
2 7
Stack
% O2, wet
20.84
20.75
20.91.
20.93
20.06
20.09-
20.73
20.72
19.66
19.73
20.13
20.44
20.52
19.81
19.90
20.31
20.48.
Stack NOx ppmvc
at 15% O2
373.1
185.8
85.6
295
130.9
110.0
30.9
17.9
298 '
67.9
55.0
28.5
9.0
589
50.1
30.3
18.0
NOTE:
Engine Emissions Data for Model Test Cells B, C, and D utilize the following reference:
Aircraft Environmental Support Office, "Summary Tables of Gaseous and Paniculate Emissions from Aircraft Engines,'
AESO Report Number 6-90, San Diego California, June 1990, p.7, 15,22.
Engine Emissions Data for Model Test Cell A are from the following reference:
U. S. Department of Transportaion, "FAA Aircraft Engine Emission Database (FAEED)," Office of Environment
and Energy, Federal Aviation Administration.
* W Afterburner Mode ,
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non-catalytic reduction (SNCR), or other potential NOX
controls to the test cell are strongly influenced by these
parameters. However, the feasibility and cost effectiveness
of potential NOX control strategies can also be affected by
more detailed parameters than can be determined using the
model test cells. Specifically, gas flow velocity, NOX
distribution and gas temperature distribution within the test
cell can all have a significant impact on the feasibility of a
particular NOX control method.
In an effort to assess the viability of implementing SCR,
a 1987 study was conducted to determine detailed gas
characteristics in the exhaust of a test cell.10 Detailed
stack and augmenter tube measurements were conducted at the
Navy facility in Lemoore, California, in test cell #3 (TlO
Type design). The engine used in the study was a General
Electric F404 military afterburning turbofan engine (maximum
thrust of 17,000 Ibs) and is similar in engine specific
parameters to the J79-GE-10B used in Model Test Cell (C) .
Figure 3-7 presents a schematic diagram illustrating the
components of the air flow through the augmenter tube. In
addition, the static pressures associated with these flows are
plotted as a function of position along the augmenter tube.
This figure illustrates the mechanism for the air entrainment
through the test cell, in addition to the potential for
significant variations in velocity, temperature, and pollutant
concentration that can occur in the augmenter tube region.
Figure 3-8 presents a plot of the measured gas
temperature profiles at various locations within the augmenter
tube with the engine operating at 89 percent of maximum power.
The data illustrate the impact of the mixing process on
reducing the engine exhaust gas temperatures. Using the
engine data for a F404 in the test cell model (C) , stack exit
temperatures are predicted to be 180°F at an augmentation
ratio of 7. The DoD has indicated that T-10 test cells
operate at an augmentation ratio of 7. This corresponds with
the fully mixed values of 180°F recorded 55 feet from the
engine.
3-18
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•Figure 3-9 presents the measured NOX concentrations at
various locations within the augmenter tube. This graph
displays similar profiles to the temperature plots (Figure
3-8) and illustrates the impact of mixing the entrained air
with the engine air on the final stack exit NOX
concentrations. The slight skew in the data is attributed to
asymmetries in the augmentation air flow.
The measured temperature and NOX data are indicative of
the large variations that exist within the gas stream as it
passes down the augmenter tube. In the absence of fully mixed
conditions, significant local variations in temperature and
concentrations exist. The effectiveness of NOX controls (for
example, SNCR) within the augmenter tube itself would be
significantly reduced by these variations. ' In addition,
insertion of SNCR within the augmenter tube would have the
potential to impact the pressure profile and resulting rate of
air entrainment through the test cell.
3.5
TURBOPROP/TURBOSHAFT MODEL TEST CELL DESCRIPTION
Turboprop/turboshaft jet engines are distinguished in
part from turbojet/turbofan engines in that the exhaust is a
low energy, typically lower velocity gas stream. As discussed
in Chapter 2, testing of these type engines within test cells
typically involves extracting the engine power using a
dynamometer. Figure 3-10 presents the schematic diagram of a
representative test cell capable of testing
turboshaft/turboprop engines, although other designs and
locations of the dynamometer are possible. Because the
exhaust is a low velocity gas stream, entrained augmentation
air is significantly less than that found in test cells
testing turboprop/turbojet type engines. A single model test
cell has been developed to assist in determining the technical
feasibility and costs of implementing NOX control to test
cells testing turboshaft/turboprop type engines.
3-21
-------
3-22
-------
Front
14' 10'
Air inlet
Engine Support and
Fuel Equipment
Dynamometer
t
Engine
Stack
•10
J
70'
Right Side View
20'
14'
Top View
Figure 3-10. Schematic of turboprop/turboshaft model test cell
(Relative dimensions for Model E Test Cell) .
3-23
-------
Model Test Cell (E): This model test cell uses the T58-GE-8F
turboshaft engine. This engine is used in the Sea King Series
helicopters and delivers approximately 1,400 peak shaft
horsepower. ;
The engine core exhaust temperature is calculated using
Equation 3-3 and the engine specific data.11 The development
of this equation is provided in Appendix C.
tc = ta + 1/Cp (LHV * FA - W/Me)
Eq, 3-3
where:
tc:
ta:
Cp:
LHV:
W:
Me:
Engine core exhaust gas temperature (°F)
atmospheric temperature (°F)
heat capacity (BTU/lb °F)
jet A lower heating value (18,500 BTU/lb)
horsepower of the engine (hp)
engine exhaust mass flow (Ib/sec)
Fully mixed stack temperatures are calculated using
Equation 3-2. Annual NOX estimates from the model test cell
are based on 200 hours/year operation and a power schedule as
shown in Table 3-2. This model test cell's annual utilization
is consistent with the reported utilization of the current
test cell population as reported in Chapter 6. Figure 3-11
presents the predicted stack gas exit temperatures and stack
mass flow rates for the model test cell. A uniform
(independent of thrust) augmentation ratio of 0.2 is assumed.
Predicted peak gas temperatures are generally above those
predicted for the turbofan/turbojet test capable model test
cells and are in the range of 900°F. Stack NOX emissions are
plotted in Figure 3-12. Peak NOX emissions are predicted to
be 62 ppm at 15 percent O2. Annual NOX emissions of much less
than 1 ton are predicted. Table 3-4 summarizes the emission
estimates from Test Cell Model (E).
3-24
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3-27
-------
3 .6 SUMMARY
Five model test cells have been developed to predict the
stack gas characteristics necessary in evaluating the
feasibility and cost of adding NOX controls to those test
cells capable of testing turbojet/turbofan and
turboprop/turboshaft engines. These model test cells utilize
measured data from engines representative of those evaluated
and tested in the current population of test cells.
Additionally, measured data have been presented to both
illustrate the variability of gas temperatures and NOX
concentrations within the augmenter tube region of a test cell
and verify the predictions of the model test cells.
Comparison of the predicted stack gas temperatures with
measured data indicates that the models are sufficiently
accurate for the purpose of this study. As will be discussed
in Chapter 4, these variations of gas temperature and NOX
concentrations within the test cell have a significant impact
on determining the placement and the viability of flue gas NOX
controls.
3-28
-------
3.7 REFERENCES
1. United States Environmental Protection Agency.
Compilation of Air Pollutant Emission Factors, Volume 1:
Stationary Point and Area Sources. Research Triangle
Park, North Carolina. AP-42. Fourth Edition.
September 1985.
2. United States Department of Transportation. FAA Aircraft
Engine Emissions Database (FAEED). Office of Environment
and Energy, Federal Aviation Administration.
3. International Civil Aviation Organization, Annex 16.
Environmental Protection, Volume II. Aircraft Engine
Emissions. June 1981.
4. United States Department of Defense. Software Users
Manual for the Aircraft Engine Emission Database System.
Aircraft Division, Naval Air Warfare Center. Trenton,
New Jersey. August 1992.
5. Aircraft Environmental Support Office. Summary Tables
of Gaseous and Particulate Emissions from Aircraft
Engines. Prepared for the Aircraft Environmental Support
•Office, Naval Aviation Depot. North Island, San Diego,
California. AESO Report No. 6-90. June 1990.
6
7,
8.
'Ref. 5, pp. 7, 15, 22.
Ref. 5, p. 45.
Energy and Environmental Research Corporation. Delta
Airlines Site Visit Report. Prepared for the U.S. EPA.
'Research Triangle Park, North Carolina. ESD Project No
92/20. March 1993. p. 2.
Ref. 5, p. 53.
3-29
-------
10. Stalling, J.H.E., P.A. May, andG.D. Jones (Radian
Corporation). Pilot De-NOx Test Facility for Jet Engine
Test Cells. Prepared for the U.S. EPA. Research
Triangle Park, North Carolina. Draft. September 1987.
11. Ref. 5, p. 30.
3-30
-------
CHAPTER 4
FEASIBILITY OF REDUCING NOX EMISSIONS FROM TEST CELLS
4 .1 OVERVIEW
The technical feasibility of applying a variety of NOX
control technologies to test cells is examined in this
chapter. Flue gas treatment methods, specifically selective
•catalytic reduction (SCR) and selective non-catalytic
reduction (SNCR), are well established technologies for
reducing NOX emissions from a broad range of fossil fuel-fired
systems. The feasibility of these methods for reducing NOX
emissions from test cells is examined in Sections 4.3 and 4.4.
Reburn is a combustion modification NOX control technology
which has recently received considerable testing and
validation on large utility-type boilers. The feasibility of
reburn for NOX control applied to test cells is examined in
Section 4.5. Gas turbines used for power generation,
including aeroderivative models, commonly incorporate either
steam or water injection to reduce NOX emissions. More
recently, fuel emulsifiers have been investigated as a means
of reducing NOX emissions from stationary gas turbines. The
feasibility of these NOX control 'methods (steam/water
injection, fuel emulsifiers) for test cells is examined in
Section 4.6. There has been research conducted through a
series of Small Business Innovation Research (SBIR) awards to
develop a NOX control method solely for test cell application.
This research effort has resulted in development and testing
of a low temperature magnesium-oxide, vermiculite-based
4-1
-------
sorbent for NOX control which does not require chemical
injection. Section 4.7 examines this technology for general
applicability to full-scale test cell operation and also
includes a discussion of low NOX combustor design. As part of
the feasibility assessment of NOX control technologies,
Section 4.8 examines potential effects of the NOX control
technologies on the engine and engine test.
The operational complexity of altitude simulating test
cells, as well as the multitude of subsystems, further
complicates the development of flue gas NOX abatement
techniques. Typically, the altitude facility will have less
available plot space to install NOX control reactors. Large
temperature swings will place greater demands on flue gas
conditioning, and potential failure in temperature control can
result in catastrophic failure in downstream systems due to
the thermal shock. Altitude facilities are less uniform in-
design, and site-specific factors will dominate potential
reactor design. Therefore, the focus of this chapter is on the
feasibility of applying NOX control technologies to sea level
test cells.
4.2
NOX FORMATION MECHANISMS
The NOX emissions from test cells are generated by the
engines tested within the facility. The NOX mass emission
rate is determined solely by the test engine and is unaffected
by the design of the test cell itself. Nitrogen oxides (NOX)
are products of all conventional combustion processes. NOX is
a collective term for nitric oxide (NO) and nitrogen dioxide
(NO2) . NO is the predominate form of NOX produced by aircraft
engines, with lesser amounts of NO2; however, once emitted to
the atmosphere, NO converts to NO2.
• NOX emissions from jet engines are generated in the
primary combustion zone of the engine, located in the forward
4-2
-------
volume of the combustor where the fuel is injected.- Within
the combustor (Figure 4-1), localized regions of
stoichiometric and near stoichiometric fuel/air mixtures exist
at high engine power conditions, resulting in high flame
temperatures. As will be discussed, these high flame
temperatures are responsible for most of the NOX emissions
from,jet engines.
4
The generation of NOX from fuel combustion is a result of
three formation mechanisms, namely thermal NOX formation,
prompt NOX formation, and fuel NOX formation. Thermal NOX is
produced by exposing the nitrogen contained in the combustion
air (ambient air contains 79 percent nitrogen by volume) to
the high temperatures of combustion. Prompt NOX is formed
from the oxidation of hydrogen cyanide, an intermediate
product from the reaction of nitrogen with hydrocarbon. Fuel
NOX is formed when the nitrogen in the fuel is oxidized to NO.
The chemistry associated with formation of thermal NOX is
relatively well understood, especially under fuel-lean
conditions. The controlling chemical reactions are referred
to as the Zeldovich mechanism. The Zeldovich reaction set
predicts a linear dependence between the rate of thermal NOX
formation and the local concentration of oxygen,, atoms. The
main-source of oxygen atoms is the disassociation of O2, which
is exponentially dependent on the flame temperature. The
combined effect is that thermal NOX formation is strongly
dependent on flame temperature, with the rate of NOX formation
increasing by an order of magnitude with approximately every
100°C increase in peak flame temperature.
Fuel NOX is formed when the fuel being burned contains
nitrogen within its chemical structure. Jet fuel is a
composite of light distillate oils. Typically, light
distillate oil contains less than 0.015 percent by weight of
4-3
-------
O
4->
CQ
O
u
(0
o
•H
a
0)
^
en
-H
4-4
-------
chemically-bound nitrogen. Chemically-bound nitrogen is the
nitrogen that is bound to hydrogen atoms (such as amines) or
to carbon atoms (such as cyano compounds) .
The relative contributions of thermal and prompt NOX
versus fuel NOX for turbines burning jet fuel are easily
estimated. For a jet fuel containing 0.015 weight 'percent
fuel-bound nitrogen, complete conversion of the bound nitrogen
equates to an emission factor of 0.5 Ib fuel NOX/1,000 Ibs
fuel. Emission factors for engines used in the model test
cells described in Chapter 5 range from 7.5 to 29.6 Ibs
NOX/1,000 Ibs fuel at 80 percent power. Emission factors
during idle for these engines (where fuel NOX would account
for a more significant fraction due to low combustion
temperatures) range from less than 1.3 to greater than 3 Ibs
NOX/1,000 Ibs fuel. At idle conditions, conversion of the
fuel-bound nitrogen to NOX accounts for a significant portion
of the NOX formed. However, at normal operating conditions
where emission rates are significantly higher, thermal NOX
accounts for more than 95 percent of total NOX emissions.
4.3 SELECTIVE CATALYTIC REDUCTION (SCR)1' 2' 3
SCR is a post-combustion NOX control technology which
employs a highly reaction-specific process to push the
reaction of NO with ammonia towards a thermodynamic
equilibrium:
NO
NH
1/4 02
N
3/2 H2O
The products of the reaction under idealized conditions are
nitrogen and water. However, under practical conditions, the
reaction is not complete and results in some unreacted ammonia
(NH3 slip) and NO in the exiting flue gas.
4-5
-------
The majority of SCR experience in the United States is
with stationary gas turbine applications, primarily firing
natural gas. The largest body of SCR experience with energy
systems firing moderate sulfur oil and coal fuel is in Japan,
where over 40,000 MW of electric power are generated using SCR
as a NOX control method. Catalyst technology is continuing to
develop, and this will impact the viability of SCR as a NOX
control strategy for test cells. Early catalysts were
typically designed to operate between 675 and 750°F, with
space velocities (flue gas volumetric flow rate/catalyst
volume) in the range of 15,000 to 20,000 hrs"1. Currently,
catalysts are available which can operate in the 475 to 550°F
temperature range, with space velocities in excess of 40,000
hrs"1. Demonstrated NOX removal efficiencies range from 80 to
90 percent when applied to stationary gas turbines.
The NOX,reduction efficiency for an SCR System is
influenced by the catalyst material and physical condition,
the reactor operating temperature, the residence time of the
gas within the catalyst reactor, and the molar ratio of
ammonia to NOX (NH3/NOX) . Several catalyst materials are
available, and each has an optimum NOX removal efficiency
range within a specified reaction temperature range.
Proprietary formulations containing titanium dioxide, vanadium
pentoxide, platinum, or zeolite are available to meet a wide
range of operating temperatures.
The NOX removal efficiency gradually decreases over the
operating life of the SCR system due to catalyst masking,
poisoning, or sintering. Catalyst masking involves the
deposition of agents on the catalyst surface, forming a
barrier between the active catalyst surface and the gas. The
effects of the masking can typically be removed by vacuuming,
using soot blowers, or superheated steam to clean the
catalyst. Catalyst poisoning involves a chemical reaction
4-6
-------
between the catalyst and the flue gas. Typically, a poisoned
catalyst cannot be regenerated to perform at design NOX
reduction efficiencies. Sintering results from a physical
change due to overheating of the catalyst. Most catalysts
have porous-type surfaces; sintering causes the surface of the
catalyst to become non-porous and therefore not as effective.
The rate of catalyst performance degradation, either
through masking or poisoning, depends on the flue gas
characteristics and operation characteristics of the system,
and is therefore site specific. However, natural gas-fired
systems incorporating SCR have reported 5 to 10 years of
catalyst life. Coal-fired or heavy fuel oil systems typically
operate 3 to 4 years before significant catalyst performance
degradation.
The space velocity for a particular SCR design is
indicative of the gas residence time within the reactor. The
lower the space velocity, the longer the residence time, and
the higher the potential NOX emission reduction. The distance
between the plates or cells within a catalyst is referred to
as the pitch and affects the overall size of the catalyst
body. The smaller the pitch, the greater the number of rows
or cells that can be placed in a given volume. Both the space
velocity and pitch determine the physical space requirements
necessary to house the catalyst volume required to achieve the
desired NOX reductions.
Ammonia handling, storage and injection grids are
required in addition to the SCR reactor vessel required to
house the catalyst in order to implement SCR. Both anhydrous
and aqueous ammonia are used in SCR designs. Anhydrous
ammonia (usually a liquid under pressure) results in the
smallest storage tankage but represents a potential hazard
4-7
-------
through catastrophic tank failure. Aqueous ammonia (roughly
20 mole percent) storage requires approximately four times the
tank volume but is safer. For both systems, a dilution system
is required, typically air for anhydrous systems and water for
aqueous ammonia systems.
4.3.1 Feasibility of SCR for Test Cell Application
Significant differences exist between the exhaust gas
characteristics of power generating gas turbines and the stack
gas characteristics of test cells. These differences impact
both the SCR system requirements to implement SCR and the
costs associated with the SCR system. As shown in Chapter 3,
the stack gas temperature of test cells is generally below
that suitable for SCR systems incorporating a proven catalyst
material. In addition, the stack gas temperature will vary.
significantly with engine thrust. Furthermore, the NOX mass
emission rate will vary with engine thrust, causing the NOX
concentration entering the SCR reactor to vary. The ammonia
injection system must track NOX molar flow rates. If not,
then NOX reduction efficiencies will be reduced and/or
excessive ammonia slip will occur. Engine testing (as shown
in Chapter 2) requires rapid and frequent changes in engine
output, thus the variations in temperature and NOX emissions
from test cells will place demands on the SCR controller not
found in current SCR installations; and ammonia injection
systems have not been applied to test cells.
The stack gas from test cells can be heated using a duct
burner to elevate and maintain the stack gas temperature to
the catalyst operating temperature. Duct burners are commonly
used on power generation gas turbine installations to increase
the temperature of the flue gas upstream of the heat recovery
steam generator (HRSG) and increase the overall efficiency of
the installation, but they have not been applied to test
cells. However, the use of a duct burner will increase the
4-8
-------
NOX emissions entering the SCR system. The NOX emissions from
the duct burner can be minimized by firing the burner with
natural gas. The operation of the duct burner must be tightly
controlled to ensure a uniform, suitable temperature of the
test cell exhaust gas entering the SCR reactor. This will
require linking the operation of the duct burner to the test
engine power setting, as well as the reactor inlet gas
temperature. For facilities testing afterburning engines, an
additional concern with the duct burner can arise.
Afterburning engines introduce raw fuel downstream of the
combustor. Should, flame out or failure of the afterburner
occur, the potential for ignition by the duct burner and
flashback of this well mixed fuel exists.
In a previous examination of SCR for test cell
application,4 reduction in the level of augmentation air flow
was considered as a means of elevating the exhaust gas
temperature to levels suitable for the SCR catalyst. As
discussed in Chapter 2, the required level of augmentation air
flow is determined from the calibration and cooling
requirements of the test cell; therefore, it is not feasible
to introduce a system to automatically adjust the level of
augmentation air flow to minimize reheat requirements, as well
as maintain the engine test integrity, during the typically
transient test schedule. For this reason, both the SCR and
the SNCR system analysis in the next chapter use reheat to
achieve the suitable exhaust gas temperature.
For an SCR system to effectively reduce NOX emissions, it
is necessary to ensure that the ammonia and NO are uniformly
mixed at the design NH3/NOX molar ratio. As presented in
Chapter 3, a uniform NOX concentration does not occur until
well downstream of the engine exhaust. Injection of the
ammonia at rates based on mean flow NOX levels in the presence
of a-NOx concentration distribution will result in both a
lower NOX removal efficiency and excessive ammonia slip. In
order to ensure adequate mixing and a uniform NOX
4-9
-------
concentration distribution, the injection grids will have to
be placed either at the end of the augmenter tube or in the
stack region of the test cell. For space-limited test cells,
it may be necessary to force the mixing of the augmentation
air with the engine exhaust to ensure a uniform NOX
concentration. However, this will increase the pressure drop
downstream of the engine and therefore increase the back
pressure on the engine tested within the test cell.
As discussed in Chapter 2, the augmentation air flow and
the operation and calibration of the test cell is critically
dependent on the back pressure experienced by the engine
tested within the test cell. Changes in the pressure drop
downstream of the test engine affect the air flow upstream of
the engine and alter the calibration of test cell for that
specific engine. Excessive back pressure will affect flow
patterns upstream of the engine air inlet and can potentially
lead to exhaust gas recirculation and possibly engine stall.5
Additionally, these changed air flow patterns may cause non-
representative test measurements and non-repeatable tests.
However, modeling studies have shown that if an augmentation
ratio of at least 0.8 is maintained, inlet air vortices may be
avoided.6'7 As a result of installing an SCR system to an
existing test cell, the facility will need at a minimum to
recalibrate the test cell for each.engine tested at that test
cell. In addition, the test cell facility may be downsized in
thrust capability as a result of the decrease in augmentation
air flow associated with the increase in engine back pressure
generated by the SCR system. This effect can be minimized by
designing an SCR system with a reduced pressure drop. Recent
SCR installations for power generating gas turbines have been
installed with between 1 and 2 inches of -water gauge pressure
drop across the reactor.8 As will be shown in Chapter 5,
lowering the back pressure impacts the cost of the SCR system.
4-10
-------
Additionally, water vapor in the stack gas from test
cells which incorporate water cooling .may affect the SCR
system. Water cooled test cells have exit moisture contents
on the order of 10 percent. Stationary power generating gas
turbine facilities use SCR in conjunction with water injection
into the combustor. Water injection, as a NOX control
technology, is described in Section 4.6.1. The water-to-fuel
mass ratio of stationary gas turbines which use water
injection is on the order of 1 to 2 pounds of water per pound
fuel. These SCR systems experience moisture on the order of 7
to 9 percent and experience no loss of NOX reduction at these
moisture levels. Therefore, if SCR is applied to a test cell
that uses water cooling, the water vapor should not affect SCR
performance.
The reheat portion of the system would need to be tightly
controlled to ensure a uniform reactor inlet temperature
independent of the rapidly varying engine exhaust gas
temperature and exhaust gas flow rates. For test cells
testing afterburning engines, cooling the gas stream may be
required (most likely water quench) to ensure the integrity
and maintain the appropriate operating temperature of.the SCR
system during afterburning operation. The SCR system would
also require controllers to govern the ammonia injection to
ensure adequate NOX reductions without excessive ammonia slip.
A waste heat recovery system may be part of the design to
reduce stack exit gas temperatures and recover a portion of
the energy used to reheat the stack gas. However, the waste
heat and potential steam generated may not be needed by or
easily incorporated into all test cell facilities. If stack
gas cooling downstream of the SCR system is required, then a
water quench system should be easily incorporated.
4-11
-------
It is conceptually possible to design an SCR system using
conventional catalyst materials that could be applied to test
cells. A research and development and evaluation program
would be required before decisions could be made on design
characteristics for test cells incorporating such a NOX
control system. This would result in test cells which would
control NOX and not affect the safety or performance of the
engines when tested or affect subsequent in-flight safety.
Present-day test cells may require major structural
modifications to meet these new design characteristics.
Various considerations, such as site conditions, may limit the
practicality of retrofit and necessitate test cell
replacement.
4.4 SELECTIVE NON-CATALYTIC REDUCTION (SNCR)
9, 10, 11, 12, 13
SNCR technology provides post-combustion reduction of
nitrogen oxide emissions. Using SNCR technology, chemical
agents are added to the combustion products where they react
at elevated temperatures with NOX to form molecular nitrogen.
Typical agents which have broad industrial applications are
ammonia (NH3) and urea [CO(NH2)2] . However, small-scale
studies have shown that other chemical compounds can also be
used to provide effective NOX control. The primary limiting
factor restricting SNCR application is that it is only viable
over a fairly narrow temperature range and there is the
potential for the production of by-product emissions. For
both ammonia and urea injection, incomplete reactions will
result in ammonia emitted from the stack (referred to as
ammonia slip). Additionally, recent studies have shown that
nitrous oxide (N2O) emissions can increase with urea
injection.
Ammonia injection was developed and patented by Exxon in
the late 1970s as the Exxon Thermal DeNOx® process.
4-12
-------
The overall chemistry for the process can be expressed by two
competing reactions:
NO + NH3 + 1/4 02 —> N2 + 3/2 H2O
NH3 + 5/4 O2 —> NO + 3/2 H20
The first reaction is the desired step causing the reduction
of NO to molecular nitrogen. This reaction occurs in a narrow
temperature range centered at approximately 1,800 to 2,000°F.
If the temperature is more than 100 to 200°F over this range,
the second reaction-dominates and NO is created. At
temperatures below the optimum range, the ammonia will be
unreacted and will exit as ammonia slip. A variety of
promoting agents or compounds have .been developed which will
shift the optimum temperature range down 100 to 300°F.
Urea injection for NOX control was developed and patented
by the Electric Power Research Institute (EPRI). When urea
(CO(NH2)2) is injected into high temperature post-combustion
gases, it decomposes to form ammonia and isocyanic acid
(HNCO). The ammonia formed from the decomposition can then
react with the combustion gas in the same manner as if ammonia
had been injected directly into the gas stream. A key
component of the process is what happens to the isocyanic acid
formed from the decomposition process. This species reacts to
form the NCO radical, which can then form NH or NO. Recent
studies have shown that under certain process conditions, the
NCO radical will react with NO to form N2O. This species is
not presently regulated, but there are growing concerns about
N2O since it may contribute to the greenhouse effect. Recent
studies have identified several chemical agents which can be
added to urea to extend the temperature range over which
injection is effective at reducing NOX emissions.
_
4-13
-------
As with SCR, SNCR requires chemical injection into the
flue gas stream. Chemical handling equipment, including
storage tanks and injection grids, are required. Unlike SCR,
however, a large reactor vessel housing the catalyst is not
required, but the reactor vessel must be able to handle the
increased temperatures associated with SNCR. This removes the
pressure drop and elevated back pressures associated with this
component.
4.4.1 Feasibility of SNCR for Test Cell Application
Many of the factors influencing the technical feasibility
of SCR for application to test cells also apply to SNCR. Test
cell stack gas exit temperatures are significantly below the
reaction temperatures necessary for the application of SNCR,
therefore stack gas reheat is required. In addition, a
uniform NOX concentration distribution and an ammonia or urea
injection system are required to ensure maximum NOX reduction
and minimum ammonia or urea slip.
As with SCR, the temperature of the exhaust gas entering
the SNCR system can be raised using a duct burner. However,
because the reaction temperature of SNCR is significantly
above test cell exit gas temperatures and the NOX reduction
potential using SNCR is less than SCR (50 to 60 percent versus
80 to 90 percent), a potential exists for a net increase in
NOX emissions from the test cell as result of the SNCR
technology. This possibility for a net increase in NOX
emissions arises from the NOX generated by the duct burners
when reheating the gas stream. The reheat requirements are a
function of the test cell operating characteristics and the
engines tested within the facility. As such, the feasibility
of SNCR strongly depends on the specific site. In Chapter 5,
the cost of implementing SNCR is evaluated. In the analysis,
the relative level of NOX generated from the duct burner to
4-14
-------
that removed by the SNCR system is determined. This analysis
indicates that SNCR is conceptually possible (reduces overall
NOX emissions) under a narrow range of test cell operational
characteristics and will be discussed in Chapter 5. This
narrow range severely restricts the use of SNCR technology for
broad application to test cells. It is conceptually possible
to design an SNCR system using conventional materials that
could be applied to test cells. However, until the research
and development and test and evaluation programs have been
completed, the safety and performance issues cannot be fully
addressed.
4 .5 REBURN NOX CONTROL TECHNOLOGY 14- 1S- 16- 17
Conventional gas reburning is a combustion modification
emission control technique which reduces NOX formed in the
main combustion zone by firing natural gas in a second
combustion zone under slightly fuel-rich conditions. NOX is
reduced by reactions with hydrocarbon fragments formed by the
natural gas combustion. Typically, conventional gas reburn as
applied to boilers involves injection of natural gas (at rates
equal to about 15 percent of the total combustion load) into
the region just above the main combustion zone. This is
followed by the downstream introduction of the remainder of
the combustion air. The injection of natural gas is ideally
done with a nearly inert carrier, such as recirculated flue
gas, to produce a slightly fuel-rich region. In that region,
NOX produced by the primary source is "reburned" and reduced
to molecular nitrogen.
Depending on the initial NOX level and the specific
boiler design, NOX emission control in the range of 60 percent
may be achieved. Additional air is added following this
"reburning zone" to complete combustion and return the excess
air levels back to normal values. This transition region is
4-15
-------
also important for NOX control since only a portion of the
fixed nitrogen will be converted back to NOX.
For conventional gas reburning to be effective, it is
necessary to inject the natural gas into the flue gas stream
and mix it rapidly with the combustion products from the
primary combustion zone. Penetration of the natural gas into
the flue gas stream can be improved by increasing the momentum
of the injected natural gas stream via a carrier gas. The
carrier gas should contain minimal oxygen since the objective
of the natural gas' injection is to produce a slightly fuel-
rich zone. For boiler .applications, flue gas is a convenient
carrier because it typically contains only about 7 percent
oxygen and does not require preheating.
For conventional gas reburning, the location, size and
shape of the gas injectors are key to the overall
effectiveness of the natural gas reburning process. These
parameters are site specific and are selected as part of the
process design. Typically, flow modeling (either
computational or reduced scale) is required to reliably design
this component.
As with the natural gas injectors, the location, size,
and shape of the air injection ports are key to the overall
effectiveness of the gas reburning process. The air must be
injected far enough downstream of the reburn gas injectors to
provide adequate residence time for the NOX reduction
reactions while still completing combustion. By adjusting the
designs of the reburn gas injectors and overfire air ports,
NOX emission control, steam temperature, and CO burnout
efficiency can all be balanced in boiler applications.
4-16
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4.5.1 Feasibility of Reburning for Test Cell Application
As part of a series of exploratory studies of novel
technologies to control NOX emissions from engine test
facilities, reburn was evaluated as a potential NOX control
technology for test cell application16. In the study, "lean
reburn" was investigated using a laboratory scale rig to
assess the likely performance and cost for application to a
military test cell. Lean reburn involves utilizing a duct
burner which consumes a portion of the excess oxygen available
in the exhaust of the test cell. Unlike conventional reburn,
burnout air is not added downstream of the burner. Figure 4-2
presents the schematic diagram of the test rig used to
evaluate the technology. Figure 4-3 presents the possible
configurations postulated for application of lean
reburn to the test cell. Figure 4-4 presents the plot of the
measured NOX removal efficiency versus fuel equivalence ratio,
where the fuel equivalence ratio is defined as the actual
ratio of fuel to oxygen divided by the stoichiometric ratio of
fuel 'to oxygen. Plotted in this fashion, values for the fuel
equivalence ratio of less than 1 represent fuel-lean (excess
oxygen) conditions. In the test rig, a 50 percent reduction
in NOX was observed at a fuel equivalence ratio of
approximately 0.8. When the inlet NO concentration was
lowered from 1,000 ppm to 550 ppm at the equivalence ratio of
0.8, the observed NO reduction efficiency was reduced to
approximately 28 percent.
Using methane (CH4) as the reburn fuel, a fuel
equivalence ratio of 0.8 corresponds to an oxygen level of
approximately 4.5 percent in the exhaust. Assuming an inverse
linear relationship between the NOX removal efficiency and the
inlet NOX concentration from Figure 4-4, this would yield a
conservative estimate of a 10 percent NOX reduction at an
inlet NOX concentration of 100 ppm. From Table 3-3, stack 02
levels from the model test cells are in the range of 16.to 20
percent. Therefore, to achieve a 10 percent NOX reduction,
4-17
-------
TO
EXHAUST
HX HX
WATER WATER
OUT ' IN
EXHAUST QUENCH
T/C T/C T/C T/C
tlT HEAT
EXCHANGER
T/C T/C
^COMBUSTION
AIR BLOWER
REBURNEH TEST SECTION
SAMPLE LINE
ICE BATH
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• • • «i ROTAMETERS
GAS
ANALYZERS
•TO
EXHAUST
SAMPLING
VACUUM PUMP
GAS CYLINDERS
Figure 4-2. Reburn test apparatus
4-18
-------
AIR
EXHAUST
A
IHf—
WATER REBURN WATER
SPRAY FUEL SPRAY
INCORPORATE REBURNING INTO AUGMENTER
MAY REQUIRE REPLACING AUGMENTER WITH HIGH-TEMPERATURE ALLOY
WORRY ABOUT VELOCITY/TURBULENCE
r
D
EXHAUST
T.4SO-770T
pH2O SPRAY
REBURN
FUEL
INCORPORATE ^O SPRAYS TO QUENCH VERY HIGH EXHAUST TEMPERATURES IN AUGMENTER
BUILD EXTERNAL REBURN CHAMBER DOWNSTREAM OF EXISTING AUGMENTER TUBE
ADJUST/CONTROL OF BACKPRESSURE?
Figure 4-3. Reburning options
4-19
-------
^ 70
CO
CO
m 60
T
INLET NOX
CONCENTRATION
• 1000 ppm
900 F INLET
15%O2
0.2
0.4 0.6
FUEL EQUIVALENCE RATIO
0.8
1.0
Figure 4-4.
Effect of NOX concentration on
reburning NOX reduction.
4-20
-------
sufficient reburn fuel must be consumed to lower the oxygen
level from between 16 and 20 percent to 4.5 percent. At
stoichiometric conditions, 2 moles of oxygen are required for
every mole of methane burned. At an equivalence ratio of 0.8,
yielding the 10 percent reduction in NOX, 2.5 moles of oxygen
are required per mole of reburn fuel. The methane
requirements necessary to reduce the stack O2 levels to the
required 4.5 percent and achieve the 10 percent reduction in
NOX emissions can be calculated as follows.
Moles (02) / sec = Ms / MWs * [02]
Eq. 4.1
where:
Ms = Test cell stack gas flow rate (Ibs/sec)
MWS = Test cell stack gas molecular weight
[O2] = Test cell stack gas oxygen concentration
The volumetric flow rate of methane required to achieve the 10
percent reduction in NOX is given by:
CH4(ft3/sec) = 379 (Moles/ft3)* (Moles (02) /sec) /2 . 5 Eq. 4.2
Using the above equations and the stack conditions
summarized in Tables 3-3 and 3-4, the methane consumption
necessary to reduce the NOX emissions 10 percent from the
model test cells discussed in the previous chapter is
summarized in Table 4-1. The methane consumption is based on
25 hours per year of test cell operation at maximum engine
thrust. Under this condition, stack exit temperatures are
highest and oxygen levels are lowest, with conditions
favorable for reburn application.
Also provided is an estimate of the cost in $/ton NOX
removed, assuming a methane cost of $3/MSCF. These estimates
4-21
-------
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4-22
-------
range from a low of approximately $480,000 per ton NOX removed
to a.high of over $59 million per ton. These estimates do not
reflect any costs beyond those associated with the methane gas
consumption. In addition, an optimistic 10 percent reduction
in NOX was assumed based on an estimate of mean stack NOX
concentration levels of 100 ppm. Actual stack NOX
concentrations are a function of the augmentation air flow and
can be less than 100 ppm.
The assumption that lean reburn can achieve even a 10
percent reduction in NOX emissions has not been proven at
inlet conditions similar to those found in test cells. For
this reason, lean reburn cannot be considered a proven
technology for test cell application. It is conceptually
possible to design a reburn system using conventional
materials that could be applied to test cells. However, until
the research and development and test and evaluation programs
have been completed, the safety and performance issues cannot
be fully addressed. In the event that the lean reburn
technology would achieve this level of NOX reduction
performance, the methane consumption alone drives the cost
effectiveness in $/ton NOX removed above those anticipated for
SCR (Chapter 5).
4.6
ENGINE MODIFICATION APPROACHES TO NOX EMISSION REDUCTIONS
Temporarily modifying the engine during the test to
reduce engine NOX emissions is a potential approach to
reducing NOX emissions from test cells. However, as will be
discussed in Section 4.6.3, the engine modifications necessary
to reduce the NOX emissions significantly alter the engine
performance characteristics.
4-23
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4.6.1 Steam/Water Injection Process Description
18, 19
Steam or water injected into the primary combustion zone
of a gas turbine engine provides a heat sink which lowers the
flame temperature and thereby reduces thermal NOX formation.
This injection is described by the water-to-fuel ratio (WFR)
evaluated on a mass basis (Ib water or steam injected per Ib
fuel consumed). For water injection, the control system would
require a water purification system, pump(s), water metering
valves and instrumentation, turbine-mounted injection nozzles,
and any necessary interconnecting piping. A steam injection
system would require the same items except a steam generator
would replace the pump(s).
The WFR is the most important factor affecting the
performance of steam or water injection. The injection rate
is directly related to the NOX abatement potential. The
higher the WFR, the higher the possible NOX abatement. For
the gas turbine industry, WFR's range from 0.46 to 2.28 to
achieve controlled NOX emission levels for oil-fired units
ranging from 42 to 110 ppmv, corrected to 15 percent oxygen.
Water-based WFR's are usually lower than the steam WFR for the
same NOX abatement. The latent heat associated with water
injection increases the heat sink capability of water
injection and therefore lowers the required WFR for a given
NOX reduction level. From available stationary gas turbine
data, steam/water injection is used to achieve NOX removal
efficiencies of 70 'to over 85 percent from uncontrolled
levels.
The type of fuel burned in the turbine affects the
performance of steam or water injection. In general, lower
controlled NOX emission levels may be achieved with gaseous
fuels than with oil fuels. For turbines firing distillate oil
fuels, steam/water injection has the effect of increasing the
4-24
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conversion of fuel-bound nitrogen to NOX (Figure 4-5). This
would not be anticipated to affect the engines tested within
test cells which burn fuels with fuel-bound nitrogen levels of
typically less than .015 percent.
4.6.2 Fuel Emulsion Process Description 20- 21
The use of a water-in-fuel emulsion is a more recent NOX
control technique developed for stationary gas turbines.-The
process reduces NOX by lowering the peak flame temperature in
precisely the same manner as steam/water injection discussed
in the previous section. The water-in-fuel suspension allows
a more ideal heat absorption to occur due to both the
homogeneous nature of the emulsion and the ideal location of
the water in close vicinity to the burning fuel droplet.
Additionally, the process creates the emulsion prior to
injection and combustion. In contrast, the steam/water
injection fluid forms a heterogeneous post-combustion mixture
where fuel predominates in some areas of the flame and the
steam/water predominates in others.
The fuel emulsion homogeneous mixture allows for a lower
WFR than in traditional steam/water injection. The emulsion
WFR ranges from 20 to 50 percent and is stabilized with
chemical additives to maintain the emulsion at the high
temperature and pressure associated with injection. The
process uses similar hardware as water injection with
additional equipment for the emulsification, chemical
stabilizer, storage, and injection systems (including metering
valves and instrumentation). This system can be retrofitted
onto existing fuel delivery systems.
Nalco Fuel Tech has developed an emulsion technology for
distillate oil-fired stationary gas turbines. The technology
has been tested in both short-term and long-term tests.
4-25
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The short-term tests were conducted at Public Service and Gas
Company's (PS&G) Kearney Generating Station on a single TP&M
A4 engine operated as part of a twinpak consisting of two gas
turbine engines and one generator. NOX emission reductions
ranging from 8 to 68 percent, with water weight percents of
4.4 to 36, respectively, were achieved. The short-term
emulsion tests caused no observable detrimental effects to the
gas* turbine engine.
A long-term demonstration of the Nalco Fuel Tech NOX
emissions reduction process was later conducted on PS&G Edison
Station Unit #!._ The unit consists of four twinpaks for a
combined unit output of 76 MW. The twinpak engines are FT4
A-9 aeroderivative gas turbines and are dual-fuel capable.
Four separate emulsification systems.were installed, one to
service each twinpak. Tests were conducted over a 60-day
period on one of the four engines with emission measurements
of NOX/ CO, 02, and unburned hydrocarbon (UHC). During the
testing, the water content of the emulsion varied from 0 to
0.65 water/oil weight ratio, with the ratio at 0.65, a
reduction in NOX emissions of close to 70 percent was
observed.
Water-in-fuel emulsion lowers the flame temperature and
therefore is an effective thermal NOX control for gas turbine
engines. This approach has the initial apparent advantage
over the more traditional steam/water injection method in that
injection nozzles mounted within the combustor are not
required. However, for both water in fuel emulsion and
steam/water injection, the impact on engine performance will
be similar, and hardware modifications to the engine under
test would be required that would,not be used during in-flight
service.
4-27
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4.6.3 Feasibility of Water/Steam Injection and Fuel/Water
Emulsion for NOX Control of Test Cells
As described in Chapter 2, the owner/operators of test
cells utilize the facilities for either engine development or
certification and evaluation following engine repair. The use
of either water/steam injection or water-in-fuel emulsion
would require temporary .engine modifications and would
significantly alter the performance characteristics of the
engine under test. These modifications would result in the
evaluation of an engine within the test cell which would
require further modification before being returned for
in-flight service. Additionally, the operating
characteristics of the modified engine will be significantly
different in all of the critical areas used to evaluate the
performance of the engine within the test cell. The use of
either water/steam injection or water-in-fuel emulsion will
impact the engine under test as follows.
For a given turbine inlet temperature, there will be
an increase of fuel usage related directly to the
latent and sensible heat of the water.
The increased fuel flow and water flow will cause
increased mass flow through the turbine, which will
increase turbine rotor speed and engine thrust.
An increase in turbine speed will increase
compressor speed and result in increased air flow
through the compressor and an increase in engine
pressure ratio.
Increased air flow drives conditions in the
combustor more fuel-lean.
4-28
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Engine tests to a specific thrust condition can be
reached at lower turbine inlet temperatures due to
increased mass flow through the turbine..
Engine tests to a specific thrust condition can be
reached at reduced fan speeds. This would limit
information regarding blade failures, vibration, and
tip clearance variations.
The change in specific gravity from as little as a
10 percent water emulsion may require modification
to some engines' fuel control system (i.e., pump and
fuel lines).
Changes to fuel flow and pressure drop across fuel
nozzles would greatly impact fuel atomization and
the details of the burning process. This might
impact the relight capability, blow-out performance,
and flame stability.
All of the changes arising as a result of the NOX
controls applied to the engine will affect performance
parameters which are critical in assessing engine integrity,
including fuel 'efficiency, thrust, and temperature
calibration. Engine testing with'either steam/water injection
or fuel emulsion installed following repair would require
subsequent alterations to the engine before returning the
engine to service. These additional alterations and
modifications would raise air-worthiness concerns.
The use of temporary modifications to the engines tested
within test cells would result in engines tested with
performance characteristics which are not representative of
the engine when prepared for in-flight service. This
condition alone defeats the purpose of certification and
4-29
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validation testing following engine repair. For engine
development related test cell operation, critical component
testing and engine performance determination would be invalid
or provide data for unrealistic or non-representative engines
and operating conditions. For these reasons, as well as
safety concerns that would certainly be raised, water/steam
injection and water-in-fuel emulsion technology for test cell
applications should not be considered technically viable
options.
4.7 EMERGING TECHNOLOGIES
4.7.1 NOX Sorbent Technology
22, 23, 24, 25, 26, 27
The Air Force has directed a series of efforts focused on
developing a control technology to reduce NOX emissions from
test cells. Phase I and Phase II investigations involved
laboratory screening of 25 variations of a coated vermiculite
substrate sorbent, bench-scale testing of the most promising
options, slipstream tests, and finally prototype development
for testing on a test cell.
The NOX control technology selected for prototype testing
was a magnesium oxide-coated (MgO) vermiculite bed preceded by
either another uncoated vermiculite or an activated carbon
bed. As the exhaust gas passed through the sorbent beds, the
NOX was adsorbed onto the bed material, which effectively
acted as a NOX "filter". Two engines, one a 2,200 Ibf thrust
and the other 930 Ibf thrust, were tested in the facility.
Temperatures at the filter inlet fluctuated between 170 and
210°F at 80 percent engine thrust. The system was designed
such that the filter could be exposed to the entire exit gas
flow from the facility. However, due to excessive pressure
drop across the NOX control -system, only a small portion of
the gas stream was subjected to the sorbent beds. The data
4-30
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suggest that only 10 percent of the exit gas stream passed
through the sorbent beds, while the remaining gas flow went
through slot doors placed adjacent to the NOX control system.
A NOX removal efficiency ranging from 40 to 75 percent was
reported using the upstream bed of virgin vermiculite. A
slight improvement in NOX removal efficiency was reported when
incorporating the activated carbon bed.
The vermiculite sorbent technology operates in a
temperature region more suited for test cell application than
either SCR or SNCR. However, insufficient testing of this
technology on either test cells or other NOX emission sources
has been completed to document the performance of the •
technology for extended operation. There is an approved
proposal to further evaluate this approach on a test cell.
It is conceptually possible to design a vermiculite sorbent
bed that could be applied to test cells. However, until the-
research and development and test and evaluation programs have
been completed, the safety and performance issues cannot be
fully addressed.
4.7.2 'Low NOX Combustor Technology 28
As described in Chapters 2 and 3, the NOX emission rates
from test cells are a direct function of the engine under
test. Jet-type aircraft engines designed and installed in the
1970s burned cooler and less completely than the current
generation of aircraft engines. This resulted in lower NOX
emission factors and higher carbon monoxide (CO) and total
hydrocarbon (THC) emission factors (emission factor is defined
as Ibs of pollutants per Ibs fuel burned). Engine and
combustor development focused on improving engine performance
and efficiency has altered these characteristics considerably.
Current jet-type aircraft engines have relatively lower CO and
THC emission factors and higher NOX emission factors at full
4-31
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and flight power. Presently, there is a considerable effort
being made to lower the NOX emission factors from aircraft
engines while still maintaining the reduced CO and THC
emission factors.
Dry low NOX combustor technology has been developed for
stationary gas turbine applications. In this technology,
combustors are designed to minimize NOX production without the
use of steam/water injection. Stationary gas turbines
incorporating dry low NOX combustors primarily fire natural
gas, whereas aircraft engines burn liquid fuel. The
combustion characteristics of liquid fuels are significantly
different than those of gaseous fuels and typically result in
higher NOX emissions. .Aircraft engines require rapid
transient operation with a low risk of flame out. When flame
out does occur, easy restart is required. These requirements,
place further demands on the combustor technology which are
not required in stationary gas turbines. Currently, there are
two basic aircraft engine low NOX combustor designs under
research by manufacturers and NASA. They are the lean
pre-mixed/prevaporized(LPP) and the rich-burn/quick-
quench/lean-burn (RQL).
The development of low NOX combustion technology for
aircraft engines may ultimately'reduce NOX emissions from the
test cell population. The development and sale of aircraft
engines with reduced NOX emission rates will be followed by a
transition period as these engines progress onto their
aircraft fleet.
4-32
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4.8 EFFECTS OF TEST CELL NOX CONTROL TECHNOLOGIES ON AIRCRAFT
ENGINE SAFETY, DESIGN, STRUCTURE, OPERATION
AND PERFORMANCE TESTING 6' 7
Subparts 4 and 5 of §233 (a) of the CAAA pertairi to the
effects that NOX control technologies might have on the
safety, design, structure, operation and performance of
aircraft engines and the impact on the effectiveness and
accuracy of aircraft engine safety design and performance
tests conducted at test cells. All of the known potential
effects that the various control technologies may have on the
engine or the engine test are addressed in the following
sections. However, until the research and development and
test and evaluation programs have been completed, the safety
and performance issues on testing cannot be fully addressed.
4.8.1 Effects of Water or Steam Injection
As discussed previously, water or steam injection and
fuel/water emulsion would directly affect the engine and
engine test by altering the performance characteristics during
testing. These modifications would result in the evaluation
of an engine within the test cell which would require further
modification before being returned for in-flight service.
Also, this type of NOX control would result in engines tested
with performance characteristics which are not representative
of the engine when prepared for in-flight service. This alone
defeats the purpose of certification and validation testing
following engine repair. For engine development-related test
cell operation, critical component testing and engine
performance determination would be invalid or provide data for
unrealistic or non-representative engines and operating
conditions.
4-33
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4.8.2 Effects of Back Pressure
Back pressure resulting from add-on NOX controls may also
affect the engine or engine test. The back pressure
associated with the post-combustion NOX control technology
equipment, such as catalyst and sorbent beds, and duct burners
would impede the air flow through the test cell. Using
conventional technology, designs can limit back pressure to
0.1 inch water for a duct burner and 1 to 2 inches of water
for a catalyst bed.
The aerodynamics of the test cell can affect the
performance of the engine being tested. In turn, an increase
in back pressure, as would occur with an add-on NOX control
technology, would affect the aerodynamics of the test cell.
Air flow recirculation, causing temperature and pressure
distortion of the engine inlet air, can lead to uncertainty
about engine performance measurements. Engine performance may
become unstable and unrepeatable, leading to test rejection
and possibly unnecessary engine rebuild. Recirculation of air
within the test cell will also affect engine thrust
measurement. In extreme cases, engine inlet air flow
distortion may result in compressor stall and cause severe
engine damage. .
An increase in back pressure downstream of the test
engine may reduce the augmentation ratio (an indicator of the
amount of test cell dilution air which bypasses the engine).
This would make it necessary to recalibrate the test cell for
each engine model tested in that test cell. In addition, the
increase in back pressure may make it necessary to decrease
the maximum thrust capability of a test cell to compensate for
the decrease in augmentation air flow. This resultant decease
in thrust capability would effectively limit the size of
engines that can be tested in the cell. Continued testing of
4-34
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these engines would require a major modification of the test
cell or construction of a new test cell that would use NOX
controls and not affect the safety or performance of the *
engine.
One modeling study indicated that vortices in the test
chamber may be avoided if the augmentation ratio is kept above
0.8. New test cells are designed so that augmentation ratios
are typically greater than 0.8, and in practice, augmentation
ratios are normally between 1 and 10. Therefore although the
add-on NOX control 'technology may lead to a reduced
augmentation ratio, there is some indication that if the new
augmentation ratio remains greater than 0.8, inlet air
vortices may be avoided. However, for low bypass ratio engine
testing and engine core testing, the minimum augmentation
ratio is determined by the cooling requirement on the aft
portion of the engine. Subsequently, low bypass ratio engine
testing and engine core testing augmentation ratios must be
maintained much higher than 0.8 to provide sufficient cooling.
4-35
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4.9 REFERENCES
1. United States Environmental Protection Agency.
Alternative Control Techniques Document--NOX Emissions
from Stationary Gas Turbines. Research Triangle Park,
North Carolina. Publication No.' EPA-453/R-93-007.
January 1993. pp. 5-63 to 5-82.
2. Sidebotham, G.W., and R.H. Williams. Technology of NOX
Control for Stationary Gas Turbines. Prepared for Center
for Energy and Environmental Studies, Princeton
University. Princeton, New Jersey. Draft.
January 1989. pp. 21-25
3. Rosenberg, H.S., J.H. Oxley, and R.E. Barrett (Battelle).
Selective Catalytic Reduction for NOX Control at
Cogeneration Plants. Proceedings from the 1992 ASME
Cogen-Turbo Conference. .IGTI-Vol. 7. pp. 409-417.
4. Stelling, J.H.E., P.A. May and G.D. Jones (Radian
Corporation). Pilot De-NOx Test Facility for Jet Engine
Test Cells. Prepared for the United States EPA.
Research Triangle Park, North Carolina. Draft.
September 1987.
5. Memorandum from Harris, R.E., Energy and Environmental
Research Corporation, to Wood, J.P., EPA/ISB. Northwest
Airlines Site Visit Report for Enclosed Uninstalled
Aircraft Engine Test Cell Study. March 26,.1993 .
6. Design Considerations for Enclosed Turbofan/Turbojet
Engine Test Cells. Prepared by SAE EG-1E Subcommittee,
Gas Turbine Engine Test Facilities and Equipment for
Project No. EG-1E87-3. Presented at the SAE-EG-1
Meeting, No. 131. Hartford, Connecticut. October 1993.
pp. 19-22.
4-36
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7. Rudnitski, D.M. Experience in Developing an Improved
Ground-level Test Capability. Presented at the Advisory-
Group for Aerospace Research and Development Lecture.
Lecture Series No. 169, Comparative Engine Performance
Measurements, North Atlantic Treaty Organization.
8. Memorandum from Lee, S.Y., Energy and Environmental
Research Corporation, to Painter, D., EPA/ISB. Ocean
State Power Site Visit Report for Gas Turbine NSPS
Revision Effort. September 1992.
9. Lyon, R.K., and J.E. Hardy (Exxon Research and
Engineering Co-.}. Discovery and Development of the -
Thermal NOXProcess. I&EC Fundamentals. 25:19-24. 1986.
10. Gomaa, H.M., L.G. Hackemesser, and D.T. Cindric (M.W.
Kellogg Co.). NOX/CO Emissions and Control in Ethylene
Plants. Environmental Progress. 10:267-272.
November 1991.
11. Hurst, B.E (Exxon Research and Engineering Co.).
Improved Thermal DeNOx Process for Coal-Fired Utility
Boilers. Presented at llth Annual Stack Gas/Coal
Utilization Meeting. Paducah, KY. October 6, 1983.
12. Chen, S.L., R.K. Lyon, and W.R. Seeker (EER Corporation),
Advanced Non-Catalytic Post Combustion NOX Control.
Presented at AFRC International Symposium. San
Francisco, California. October 1990.
13.• Energy and Environmental Research Corporation. Kinetic
Modeling Studies. Contract No. DE-AC22-88PL88943.
Prepared for the United States Department of Energy.
4-37
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14. Lanier, W.S., J.A. Mullholland, and J.T. Beard.
Reburning Thermal and Chemical Processes in a Two-
Dimensional Pilot-Scale System. Proceedings from the
21st Symposium (International) on Combustion/The
Combustion Institute. 1986. pp. 1171-1179.
15. Chen, S.L., et al. (EER Corporation). Bench and Pilot
Scale Process Evaluation of Reburning for In-Furnace NOX
Reduction. Proceedings from the 21st Symposium
(International) on Combustion/The Combustion Institute.
1986. pp. 1159-1169.
16. Energy and Environmental Research Corporation. Gas
Reburning Technology Review. Prepared for the Gas
Research Institute. Chicago, Illinois. July 1991.
17. Johnson, S.A., and C.B. Katz (PSI Technology Company).
Feasibility of Reburning for Controlling NOX Emissions
from Air Force Jet Engine Test Cells. Prepared for Air
Force Engineering & Services Center. Tyndall AFB, FL.
ESL-TR-89-33. June 1989.
18. Ref. 1, pp. 5-5 to 5-35.
19. Ref. 2, pp. 25-30.
20. Ref. 1, p. 5-7.
21. Brown, D.T. (PSE&G) and A.S. Dainoff (Nalco). Long-Term
NOX Control Demonstration TurbiNOx™ Light Oil Emulsion
Process in Oil and Dual Fueled Combustion Turbines.
Proceedings from the 1992 ASME Cogen-Turbo Conference.
IGTI-Vol. 7. pp. 521-527.
4-38
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22. Nelson, B.W., D.A. Van Stone, and S.G. Nelson (Sorbent
Technologies Corp.). Development and Demonstration of a
New Filter System to Control Emissions during Jet Engine
Testing. Prepared for Air Force Civil Engineering
Support Agency. Tyndall AFB, FL. CEL-TR-92-49.
October 1992.
23. Lyon, R.K. (EER Corporation). New Technology for
Controlling NOX from Jet Engine Test Cells. Prepared for
, Air Force Engineering and Services Center: Tyndall AFB,
FL. ESL-TR-89-16. May 21, 1991.
24
Ham, D.O., G. Moniz, and M. Gouveia (PSI Technology Co.)
Additives for NOX Emissions Control from Fixed Sources.
Prepared for Air Force Engineering and Services Center.
Tyndall AFB, FL. ESL-TR-89-24. December 1989.
25. Sorbent Technologies Corporation. A Proposal for a
Facility to Control Emissions during Jet-Engine Testing
at McClellan Air Force Base. Prepared for McClellan Air
Force Base. November 4, 1992.
26. Letter from Nelson, S.G., Sorbent Technologies
Corporation, to Wood, J.P., EPA/ISB. Capital Costs and
Annual Operating Costs for Sorbtech Sorbent Technology.
27. Wander, J.D., and S.G. Nelson. NOX Control for Jet
Engine Test Cells. Presented at the 86th Annual Meeting
and Exhibition of the Air and Waste Management
Association. Denver, Colorado. June 13-18, 1993.
28. Ref. 1, pp. 5-36 to 5-50.
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CHAPTER 5
COSTS OF IMPLEMENTING NOX CONTROL TECHNOLOGIES
5.1 OVERVIEW
The costs of implementing selective catalytic reduction
(SCR) and selective non-catalytic reduction (SNCR) NOX
controls to the model test cells developed in Chapter's are
presented in this chapter. As discussed in Chapter 3, these
model test cells are representative of the current population
of test cells within the United States. As discussed in
Chapter 4, SCR and SNCR are well-established control
technologies for other fossil fuel-fired NOX sources; as such,
many of the cost components associated with implementing each
of these methods are readily defined. However, due to the
unique nature of test cell operation, there are several
aspects of the costs associated with implementing SCR and SNCR
which would typically not be found for other more traditional
SCR/SNCR installations.
Section 5.2 describes the methodology used in the cost
analysis. Section 5.3 describes the components of the SCR
cost model as applied to the five model test cells developed
in Chapter 3. In Section 5.4, the cost estimates of
implementing SCR to the five model test cells are presented.
The costs of implementing SCR are strongly dependent on
several parameters, including the desired level of NOX
emission reduction. In Section 5.5, the sensitivity of the
cost projections to changes in this value, as well as the
other major cost elements, are examined. The cost components
5-1
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of implementing SNCR are described in Section 5.6. The cost
estimates of implementing SNCR to the five model test cells
are presented in Section 5.7.
5.2 COST ESTIMATION METHODOLOGY
The costs of implementing both SCR and SNCR NOX controls
to test cells can be divided into two major cost categories —
capital investment costs and annual operating and maintenance
(O&M) costs. Capital costs consist of the total investment
necessary to purchase, construct, and make operational a
control system. Operating and maintenance costs are the total
annual costs necessary to operate and maintain the control
system.
Capital costs of NOX controls include both direct and
indirect cost components. Direct capital costs are expenses
required to purchase equipment for the control system as well
as those expenses required for installing the equipment.
Indirect capital costs are those costs entailed in the
development of the overall control system.
Annual O&M costs are also classified as either direct or
indirect annual costs. For this analysis, O&M costs are
considered to be costs resulting from the operation of the NOX
control equipment and do not include the annual O&M costs of
operating the test cell without NOX controls.
Using the Office of Air Quality Planning and Standards
(OAQPS) EPA costing methodology, total capital investment and
annual O&M costs may be combined to give a total annualized
cost.1 Total capital investment is converted to a uniform
5-2
-------
annual capital recovery -cost by multiplying the total capital
investment by the capital recovery factor given by:
CRF =
Eg. 5.1
where:
n
i
Economic life (years).
Pretax marginal rate of return on private
investment.
For the analysis presented in this chapter, a 20-year life
expectancy is used. This is combined with a value of 7
percent for the pretax marginal rate of return (i) and results
in a cost recovery factor of 0.094.
As described in Chapter 4, selective catalytic reduction
of NOX utilizes a catalyst whose reactivity decreases over
time. This loss of catalyst activity has the effect of
reducing the performance of the SCR system. Typical vendor
guarantees of the reactor catalyst life when applied to gas
fired boilers, heaters and power generating turbines range
between 3 and 5 years, although actual data indicate that
little reduction in reactor performance occurs before 6 to 10
years. Traditional SCR systems have never been implemented on
test cells; therefore, actual life expectancy data are
unavailable. However, it is likely that the thermal cycling
associated with the operation of test cells will have a
detrimental effect on the life of the reactor catalyst.
Additionally, due to the low sulfur content "of Jet A (the fuel
primarily burned by the engines tested within the test cells),
it is unlikely that catalyst "poisoning" will occur, and in
the absence of other factors an extended catalyst life on the
order of 6 to 10 years would be expected. Because of these
5-3
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two competing conditions, a life expectancy of 5 years has
been chosen for the reactor catalyst.
The cost effectiveness of implementing SCR and SNCR can
be determined by dividing the total annualized cost by the
anticipated NOX emission reduction (in tons) to generate a
$/ton NOX removed ratio. The calculation of the cost
effectiveness ($/ton) not only allows comparison of cost
effectiveness between SCR and SNCR when applied to test cells,
but can be used to compare the cost effectiveness of
implementing NOX controls to sources other than test cells
within a specific geographical region. As discussed in
Chapter 4, the application of SCR and SNCR to test cells
requires significant reheating of the stack gas to the
operating temperature range of the control technology. This
reheating has the effect of increasing the amount of NOX
entering the control system. In the cost analysis presented
in this chapter, the tons of NOX removed used in the cost
effectiveness calculation is taken as the difference between
the uncontrolled model test cell NOX emissions and the NOX
emissions following application of the NOX control system.
The removal of NOX generated by reheating of the test cell gas
is not credited in the cost-benefit calculation.
Additionally, the cost effectiveness calculation for both SCR
and SNCR predicted negative cost effectiveness values at some
operating conditions. A negative cost effectiveness results
from the control technology forming more NOX than it can
remove.
5.3 SELECTIVE CATALYTIC REDUCTION COST COMPONENTS
The SCR cost model is based on the SCR system described
in Chapter 4 applied to the model test cells described in
Chapter 3. The cost elements are derived from a conceptual
design of the system, supported with typical costs of SCR when
5-4
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applied to other gas-fired systems. As described in Chapter
4, the SCR reactor would be located in the stack region of
test cells. The main components of any SCR NOX control system
include: the ammonia tank, the ammonia vaporization system and
injection grids, the catalyst reactor vessel, catalyst, and a
controller. In addition to these elements, application of SCR
to the model test cells requires the use of duct burners to
reheat the gas stream to the operating temperature of the
catalyst material. Conceptually, the duct burners must be
located upstream of the ammonia injection grid, either at the
base of the stack or at the end of the augmenter tube region
of the test cell. The catalyst vessel can be located within
or on top of the stack, either in place of the exit baffles or
within the exit baffles if they exist.
Typically, the primary cost element of an SCR NOX control
system is the catalyst. Final selection of both the catalyst
material and the desired NOX emission reduction impacts other
costs associated with installing and operating an SCR system,
including those related to the reactor vessel, construction
and contingency (indirect capital costs), reheat fuel
requirements, and chemical costs. Cost elements which have
not been included in the cost analysis are system
design/development costs and the cost of recalibrating the
engine/test cell combination following retrofit to account for
the change in air flow characteristics through the cell. It
is not anticipated that these components will significantly
alter the cost effectiveness estimates. Using the cost
analysis methodology outlined in Section 5.2, every $1 million
of capital investment increases the cost effectiveness
estimates by $4,000 per ton NOX removed (cost recovery factor
of 0.094 and 24 tons NOX per year) .
There are a variety of catalyst materials commercially
available for use in SCR NOX control systems. Selection of a
5-5
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particular catalyst material defines the required operating
temperature range of the reactor vessel. Selection of a
pressure drop across the reactor vessel combined with a
desired level of NOX emission reduction are the principle
elements in determining the space velocity of the catalyst
material. The space velocity is defined as the volumetric gas
flow rate divided by the catalyst volume (ftVhr/ft3) and has
units of hrs'1. The space velocity is inversely related to the
residence time required for the stack gas to remain over the
catalyst material in order to achieve the desired level of NOX
emission reduction. Early SCR NOX systems were developed
using a titanium/vanadium-based (TiO2/V2O5) system. For gas-
fired systems, space velocities were typically on the order of
15,000 hrs-1 to 20,000 hrs'1. Currently, for the same level of
NOX emission-reduction, gas-fired boilers, heaters, and power
generating turbines are using titanium/vanadium-based SCR
systems with space velocities in the 30,000 hrs'1 to 50,000
hrs'1 range. More recently, platinum-based catalysts have been
developed with operating temperatures significantly below
those found in the titanium/vanadium-based systems. In
applying SCR to the model test cells of Chapter 5, -several
catalyst systems were considered. The catalyst materials and
their operating characteristics are summarized in Table 5-1.
The costs per cubic foot of catalyst presented in Table 5-1
are derived from recent vendor quotes of catalyst systems to
be installed in a variety of natural gas-fired industrial
boilers and process heaters. These gas-fired systems were
operating with stack NOX conditions on the order of 33 ppm
(at 15 percent O2) . The space velocities summarized in Table
5-1 are based on NOX emission reductions of 80 percent for all
catalyst materials.
As previously discussed, the operating characteristics of
the individual catalyst material affects the costs of
installing SCR to test cells beyond the purchase cost of the
5-6
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catalyst itself. The platinum catalyst, which has the lowest
operating temperature (490°F), will require less reheat fuel
to elevate the stack gas temperature to the catalyst operating
temperature than required for the titanium/vanadium-based SCR
systems. Additionally, this reduction in reheat fuel
consumption reduces the ammonia requirements necessary to
maintain the prescribed NOX emission reduction since the duct
burners will contribute less to the NOX load entering the SCR
reactor. However, as will be presented in the next section,
these benefits of the reduced,operating temperature associated
with the platinum catalysts do not exceed the increase in
catalyst purchase cost.
The required catalyst volume necessary to achieve the
target NOX emission reductions is determined by the space
velocity for the individual catalyst system and the stack gas
volume flow rate from the model test cells. As described in
Chapter 3, the stack gas volume flow rate is a function of the
specific engine used in the model test cell and the
augmentation ratio.
Table 5-2 presents a copy of a portion of the spreadsheet
used to calculate the costs associated with implementing SCR
to the turbofan/turbojet model test cells using the titanium/
vanadium-based catalyst. The required catalyst volume is
computed using the stack gas flow rate and the required space
velocity for the particular catalyst material from Table 5-1.
The cost of purchasing the catalyst is calculated using the
required catalyst volume and cost per cubic foot (Table 5-1) . ,
As discussed in Section 5.2, the catalyst is modeled with a
5-year life expectancy and annualized using the cost recovery
factor of 0.24 (5 years, 7 percent).
The capital cost of the reactor vessel used to house the
catalyst is estimated at 10 percent of the catalyst cost.
5-8
-------
TABLE 5-2. TURBOFAN/ TURBO JET MODEL TEST CELL SCR COST MODEL
..
SCR Catalyst Type
Model Test Cell
Pressure Drop of Catalyst Bed, " wg
Temperature of Catalyst, °F
Space Velocity of Catalyst Bed, hrM
Peak Gas Flow, Ibs/sec
Peak ACFS at Catalyst Operating Temp.
Required Catalyst Volume, ft3
Catalyst Cost, S/ft3
Direct Capital Costs (5 years, 7%)
SCR Catalyst Cost
Cost Recovery Factor
Anmialized Cost
Direct Capital Costs (20 years, 7%)
SCR Reactor Vessel ( 10% Can Costs)
TiO2/V2O5
A
65
5665
1012:
27380;
1740C
$1,200
$20,879,601
.24:
$5,073,743
TiO2/V2O5
B
I
3 65
5665
• 201'
5454;
346(
$1,200
$4,159,667
.24;
51,010,799
52,087,960
1 Ammonia Tank $14 QOO
CEM/Contol Systems
Duct Burners
Ammonia Vaporization System
Total
Indirect Capital Costs (20 years, 7%)
Contingency (3% Direct Capital Cost)
Constuction (20% Direct Capital Cost)
. Total
Total Capital Costs (20 Years, 7%)
Cost Recovery Factor
Annualized Cost
Total Installed Cost
Total Annualized Capital Cost
Annual Operating
Ammonia, (S200/ton 25% wt sol.)
Reheat (NG), (S3 .5/MMBtu)
Labor (10% Operating Costs)
Total
Total Annual Cost
Cost Effectiveness
Engine NOx Emissions, tons/yr
Duct Burner NOx Emissions, tons/yr
Total Tons NOx Emitted per year
Total Tons NOx Removed (80%) per year
Net Tons Emitted per year
Net Tons Removed per year
Total ($/Net ton NOx removed)
$175,000
520,000
515,000
52,311,960
569,359
5462,392
5531,751
$2,843,71
0.094
• 5267,309
$23,723^12
$5,341,052
$19,707
$2,958,091
$297,780
$3,275^78
$8,616,630
24397
42.258
66.656
53.32
13.33
11.07
$778,655
$415,96'
$14,OOC
$175,OOC
$20,OOC
$15,00(
5639,967
$19,195
$127,993
$147,192
$787,159
0.09'
573,993
$4,946,826
$1,084,792
54,466
5439,059
544,352
5487,877
$1,572,669
8.832
6.272
15.104
12.08
3.02
5.81
$270,636
T5O2/V2O5
C
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51,200
$9,751,490
.24:
$2,369,612
5975,149
514,000
$175,000
$20,000
515,000
51,199,149
$35,974
5239,830
5275,804
51,474,953
0.094
5138,646
$11,226,444
$2,508,258
$2,917
$344,503
$34,742
$382,163
$2,890,420
4.946
4.921
9.867
7.89
1.97
297
$972379
' 2
) 650
56651
938
25373
1612
$1,200
$1,934,841
.243
$470,166
5193,484
$14,000
5175,000
$20,000
$15,000
$417,484
$12,525
$83,497
596,021
$513,505
0.094
$48^70
$2,448347
$518,436
$1,630
$197,296
$19,893
$218,818
$737,254
2695
2.819
5.513
4.41
1.10
1.59
$463,068
5-9
-------
The contingency and construction costs (indirect capital
costs) are based on a percentage of those direct capital costs
which are annualized over 20 years. The contingency costs are
estimated to be 3 percent of the direct capital costs. The
construction costs are estimated to be 20 percent of the
direct capital costs. As discussed in Section 5.2, the
annualized capital costs are determined using the cost
recovery factor computed using a 20-year life and an interest
rate of 7 percent. The total installed cost is calculated as
the cost of purchasing the catalyst plus the direct and
indirect capital costs.
The annual operating costs are dependent on both the
catalyst material and the individual model test cell operating
characteristics. The temperature difference between the
operational temperature of the catalyst (Table 5-1) and the
model test cell stack temperature is used to estimate the heat
input required from the duct burner. The annual heat input
estimate incorporates the engine power schedule for the model
test cells and the total operating hours of the model test
cell as described in Chapter 3. The costs of reheating the
stack gas is based on a natural gas cost of $3.50/MMBtu. The
duct burner contributes additional NOX loading on the SCR
reactor. A NOX emission factor of 0.1 Ibs NOX per million Btu2
is used in the calculation, which is consistent with the
performance of natural gas-fired burners. The required
ammonia flow rate is then calculated using the NOX mass flow
rate determined in the model test cell and the additional NOX
from the duct burners and a NH3/NOX molar ratio of 1. The cost
of the ammonia is based on the use of an aqueous ammonia
solution (25 wt percent NH3) with a price of $250/ton of
solution.
The cost effectiveness of SCR in $/ton NOX removed is
determined by summing the annual operating costs and the
5-10
-------
annualized capital costs (including the catalyst cost) and
dividing by the total annual tons of NOX removed by the SCR
system. As discussed in Section 5.2, the .NOX removed by the
SCR system originating from the duct burner is not included in
this calculation.
A complete sample calculation of the costs associated
with implementing SCR is presented in Appendix D.
5.4 COST ESTIMATES FOR IMPLEMENTATION OF SCR TO
MODEL TEST CELLS
Figure 5-1 and Table 5-3 present the cost effectiveness
estimates for installing SCR to the turbofan/turbojet model
test cells. For each model test cell there is a significant
range in the predicted cost effectiveness estimates arising
from the catalyst material and the test cell operating
characteristics. For all model test cells, the most cost
effective installation of SCR uses the titanium/vanadium
catalyst with the 2-inch pressure drop across the reactor
vessel (2" AP,TiO2/V205) . The highest costs are predicted
using the platinum-based catalyst with the 1-inch pressure
drop across the reactor vessel. The most cost-effective
installations of SCR on the turbofan/turbojet model test cells
range from a low of $270,000/ton NOX removed for Model Test
Cell B to a high of $972,000/ton NOX removed for Model Test
Cell C at an augmentation ratio of 5 (an augmentation ratio of
5 was chosen as the median of the augmentation ratios
examined). The EPA has estimated the cost effectiveness of
implementing SCR to land-based, gas-fired power generating
turbines of similar size to those engines used in the model
test cells to be in the range of $6,000 to $10,000 per ton of
NOX removed.3 This large difference in cost effectiveness is a
direct result of significantly lower annual NOX emissions from
the model test cells with similar peak gas volume flow rates. -
5-11
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TABLE 5-3. COST EFFECTIVENESS ($ Per ton NOX removed) OF SCR
FOR THE MODEL TEST CELLS AND EACH CATALYST (Augmentation ratio = 5)
Catalyst
Platinum
1" AP
Platinum
2" AP
Ti02/V205
1" AP
Ti02/V205
2" AP
Model A
$2,576,000
$1,224,000
$1,069, 000
$779,000
Model B
$1,097,000
$511,000
$380,000
$270,000
Model C
$4, 667,000
$2,089, 000
$1,477,000
$972,000
Model . D
$1,772,000
$827,000
$650,000
$463,000
5-13
-------
As discussed in Chapter 3, the augmentation ratio is the
independent parameter in the model test cells and affects the
volume flow rate of stack gas. Figure 5-2 presents the
predicted cost effectiveness of installing the most cost
effective SCR system (2" AP,Ti02/V2O5) to the turbof an/turbo jet
model test cells as a function of the augmentation ratio. The
increase in the predicted cost effectiveness ($/ton) with the
augmentation ratio results from the increased volume flow rate
of gas entering the SCR system and the associated increase in
catalyst volume and reheat fuel consumption.
Figure 5-3 presents the predicted total installed cost of
applying the most cost effective SCR system (2" AP, Ti02/V2O5)
to the turbofan/turbojet model test cells as a function of the
augmentation ratio. Total installed costs range from
$1,012,000 for Model Test Cell D at an augmentation ratio of 1
to $43,000,000 for Model Test Cell A at an augmentation ratio
of 10. The total capital cost for a recently designed test
cell capable of evaluating large turbofan type engines (80,000
Ibs thrust) ranges from $18 to $20 million. The total
installed cost to incorporate SCR to this test cell is
estimated at $14 million.4
Figure 5-4 presents the predicted annual operating cost
of the most cost effective SCR system (2" AP,TiO2/V2O5) to the
turbofan/turbojet model test cells as a function of the
augmentation ratio. Annual operating costs are predicted to
range from $10,000 for Model Test Cell D at an augmentation
ratio of 1 to $6,000,000 for Model Test Cell A at an
augmentation ratio of 10. '
The turboprop/turboshaft model test cell differs from the
four turbofan/turbojet model test cells primarily in the
reduced level of volume flow of stack gas and the total annual
NOX emissions. The reduced stack gas volume flow decreases
5-14
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the catalyst volume requirements and the resulting capital
costs. This is offset in the cost effectiveness calculation by
a reduction in annual NOX available for removal by the SCR NOX
control system.
Figure 5-5 presents the cost effectiveness estimates of
applying the four SCR catalyst systems to the turboprop/
turboshaft model test cell. The cost effectiveness ranges
from a low of $167,000/ton to a high of $425,000/ton,- for an
augmentation ratio equal to 0.2 (an augmentation ratio of 0.2
is representative of turboprop/turboshaft test cell
operation). The titanium/vanadium SCR system with the 2-inch
pressure drop across the reactor vessel (2" AP,TiO2/V2O5) is
predicted to be the most cost effective SCR installation.
Figure 5-6 presents the cost effectiveness and total
installed costs of installing the (2" AP,TiO2/V205) SCR system
to Model Test Cell E as a function of the augmentation ratio.
For augmentation ratios between 0 and 1, total installed costs
range from $313,000 to $348,000, while cost effectiveness
estimates range from $167,000 to $219,000 per ton NOX
removed.
Figure 5-7 presents the corresponding predicted annual
operating costs as a function of the augmentation ratio.
Annual operating costs are predicted to be less than $2,000
under all conditions. This significant reduction in the
annual operating costs over the turbojet/turbofan test cells
is a direct result of the elevated exhaust gas temperatures,
lower exhaust flow, and low NOX emissions associated with the
operation of the turboprop/turboshaft test cell.
5-18
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5.5 SENSITIVITY OF SCR COST PROJECTIONS
As discussed in Section 5.3, the cost of implementing SCR
to the model test cells is strongly dependent on both the life
of the catalyst material and the level of NOX emission
reduction required from the SCR system. The cost
effectiveness (S/ton) is driven by both the total annualized
costs and the total tons of NOX removed. Table 5-4 summarizes
the results of a sensitivity analysis examining the costs of
implementing SCR to the five model test cells to changes in
these cost elements. The cost effectiveness of installing the
titanium/vanadium-based SCR system with 2 inches of water
pressure drop across the reactor is provided as the baseline
case. As presented in the last section, this SCR system
represents the lowest cost (in $/ton NOX removed) solution of
installing SCR to the model test cells as defined in Section
5.3. As expected, the sensitivity analysis indicates that
increasing the catalyst life from 5 to 10 years lowers the
predicted cost effectiveness estimates. This reduction in the
cost effectiveness is approximately 30 percent from baseline
for Model Test Cells A, B, C, and D, and a reduction in the
cost effectiveness is approximately 10 percent from baseline
for Model Test Cell E.
Increasing the model test cell hours of operation from
200 to 400 hours doubles the total annual NOX emissions from
the model test cells. Peak gas flow rates remain unchanged,
and total capital costs remain constant from the baseline
case; however, the increase in test cell utilization increases
the annual ammonia and reheat gas requirements to achieve the
same 80 percent NOX emission reduction. The resulting cost
effectiveness ($/ton NOX removed) of installing the SCR system
under these conditions is reduced by approximately 40 percent
from baseline for all model test cells.
5-22
-------
TABLE 5-4. SCR COST SENSITIVITY FOR LOWEST COST SOLUTION CATALYST
($/ton NOX removed for the 2" AP TiO2/V2O5 catalyst)
Varied Caharacteristic
Baseline
40% NOx Reduction
Increase operational
hours to 400 hours per
year
Increase catalyst life
to 10 years
Model A
$779,000
NCE
$537,000
$558,000
Model B
$270,000
NCE
$177,000
$199,000
Model C
$972,000
NCE
$550,000
$641,000
Model D
$463,000
NCE.
$300,000'
$340,000
Model E
$175,000
$303,000
$88,000
$156,000
NOTE: NCE = Negative cosf effectiveness
5-23
-------
A decrease in the target NOX emission reduction level
from 80 to 40 percent reduces the volume of catalyst required
in the SCR system by 50 percent, thereby reducing the catalyst
costs by the same amount. However, the other fixed capital
costs (including ammonia tank, controller, and duct burners)
are not reduced as significantly. The change in capital costs
is combined with the reduction by 50 percent in annual tons of
NOX removed. As a result of the drop in SCR effectiveness,
the cost sensitivity analysis predicted negative cost
effectiveness values for Model Test Cells A, B, C, and D,
meaning that the NOX emitted by the duct burner exceeded the
total NOX removed by the SCR system. The cost sensitivity
analysis for Model Test Cell E, however, predicted a 73
percent increase in the cost effectiveness of SCR from the
baseline case.
5.6 'SELECTIVE NON-CATALYTIC REDUCTION COST COMPONENTS
The SNCR cost model is based on the SNCR system described
in Chapter 4 applied to the model test cells outlined in
Chapter 3. As with the SCR cost model, the cost elements of
SNCR are derived from a conceptual design of the system,
supported with typical costs of SNCR when applied to other
gas-fired systems. As discussed in Chapter 4, the SNCR system
would be located in the stack region of the model test cells.
The main cost elements of the system are the duct burners
required to heat the stack gas to the suitable temperature
range, and the ammonia injection and vaporization system. As
with the SCR system, the duct burners would be located near
the bottom of the stack and the ammonia injection grid would
be located just downstream of the duct burners. The capital
cost components of the SNCR system are the ammonia storage,
vaporization and injection system, duct burners and the
control system.
5-24
-------
As discussed in Section 5.3, the principal cost element
of implementing SCR to the model test cells is the catalyst.
In the absence of the catalyst material (which is not used for
SNCR), the principle cost element is the annual usage of
reheat fuel required to elevate the stack gas temperature to
the required reaction temperature (1700°F). The increase in
reheat fuel consumption over that used by the SCR system is
associated with an increase in the NOX which must be removed
by the SNCR system. The annualized costs for SNCR are
determined in precisely the same manner used in the SCR
analysis. Total capital costs are annualized using the cost
recovery factor and combined with annual operating costs.
Design and development costs have not been included in the
cost effectiveness estimates. It is not anticipated that
these cost components will significantly alter the cost
effectiveness of SNCR. Using the cost analysis methodology
outlined in Section 5.2, every $1 million of capital
investment increases the cost effectiveness estimates by
$4,000 per ton NOX removed (cost recovery factor of 0.094 and
24 tons NOX per year) . A 50 percent reduction in the NOX level
entering the SNCR system is used to estimate the cost
effectiveness. This is consistent with those reductions found
on industrial applications of SNCR to other fossil fuel-fired
systems.
5.7 COST ESTIMATES FOR IMPLEMENTATION OF SNCR TO
MODEL TEST CELLS
Table 5-5 summarizes the cost model and resulting cost
estimates for implementing SNCR to the five model test cells
(augmentation ratio = 5 for Models A, B, C, and D and 0.2 for
Model E). Note that for Model Test Cells A through D, the
annual tons of NOX per year emitted by the duct burner exceed
the total NOX eliminated by the SNCR controls. This is
indicated as a negative cost effectiveness. As a result,
application of SNCR under these conditions increases the net
5-25
-------
TABLE 5-5. MODEL TEST CELL SNCR COST MODEL
II
Model Test Cel " '
JSNCR Operating Temperature 'F
[Augmentation Ratio
Direct Capital Costs (20 years. 7%)
II Ammonia Tank
II CEM/Cohtol Systems
Ammonia Vaporization System
Indirect Capital Costs (20 years. 7%)
Contingency (3% Direct Capiial P»ct^
II Constuoion (20% Direct Capital Costs)
1 Cost Recovery Factor
II Annualized Capital Cost
(Annual Operating ~
1 Ammonia, (S200/ton 25% wt sol .)
Reheat (NG). (S3.S MMBtu)
Labor (10% of operating Costs)
Total — r
[Total Annual Cost
Cost Effectiveness '
I Engine NOx Emissions, tons/yr
1 Duct Burner NOx Emissions, tons/yr
| Total Tons NOx Emitted per year
1 Total Tons NOx Removed (50%) per year
Net Tons Emitted per year
1 Net Tons Removed per year i
Total ($/Net ton NOx removed)*
* Values in parenthesis are negative
A
— — — _ __ ^___ _
1700
$14.000
$175.000
S15.000
S224.000
$6,720
$44.800
$51.520
$275.520
.094
$25,899
$44.334
$8,789.016
$883,335
$9716 685
S9.742.584
24.397
125.557
149.955
74.977
74.977
-50.580
($192,617)
'
B
1700
5
$14,000
$175 000
$20,000
$15.000
$224.000
$6,720
$44,800
$51,520
$275,520
.094
$25,899
$8,678
$1,436,491
$144,517
$1,589 686 I
$1,615,585
8.832|
20.521
29.353
14.677
14.677
-5.845
($276,418)
===•=-
C
1700
5
$14,000
$20,000
$224,000
$6,720
$51,520
.094
$25,899
7
$6.01 P"
$1,323,153_[
$132,916 1
$1,462,080 |
$1,487,979 :
4.946 j
20.332
10.166)
-5.220,1
($285.042)!
:
D
1700
5
$14,000
$20,000
$224.000
$6.720
$51,520
$275,520
.094
$25,899
$3,659
$677,610
$68,127
" ~ "$749,396 ',
~Tl""~f
$775,295 [_
j.
— - ....2.6951.
9.6801
12.375!
6.1871
6.187]
-3.493J
($221,976)1
: 1
E |
1700
0.2
$14,000
$175,000
$20,000
$15,000
$224,000
$6,720
$44,800
$51,520
$275,520
.094
$25.899
$115
$9.031
$9151
$10,061 1
$35,959]
— , . If
0-259
0.1 29)
0.388
0.194
.- -0-'94
0.065)
.... $554,857
5-26
-------
NOX emissions from the model test cells. Model E predicted a
cost effectiveness of over a half of a million dollars per ton
NOX removed. The NOX generated in the reheat of the stack gas
is a direct function of both the volume flow rate of stack gas
and the temperature rise required across the duct burner.
Model Test Cells A, B, C, and D are predicted to have
negative cost effectiveness values at augmentation ratios of 2
or higher. At an augmentation ratio of 1, Model Test Cells B
and C are predicted to have cost effectiveness values of
$350,000 and $1.5 million/ton NOX removed, respectively.
Model Test Cells A and D are predicted to have negative cost
effectiveness values at an augmentation ratio of 1. However,
turbofan/turbojet test cells (Model Test Cells A through D)
would typically be run with an augmentation ratio above 1.
Model Test Cell E would typically be run with an
augmentation ratio of around 0.2. Under these conditions, the
predicted cost effectiveness is just over $550,000/ton NOX
removed. Table 5-6 summarizes the predicted cost
effectiveness of implementing SNCR to Model Test Cell E as a
function of augmentation ratio. Where the SNCR controls would
result in a negative cost effectiveness, it is indicated in
the table as NCE.
5.8 SUMMARY
. Cost models for SCR and SNCR have been developed and
applied to the model test cells described in Chapter 3.
Several catalyst materials with a wide range of operating
characteristics were incorporated into SCR cost projections.
The most cost effective implementation of SCR to the model
test cells would utilize a titanium/vanadium-based catalyst
incorporating a 2-inch water gage pressure drop across the SCR
reactor vessel. The cost effectiveness of installing this SCR
5-27
-------
r
TABLE 5-6.
PREDICTED COST EFFECTIVENESS OF SNCR AS A
FUNCTION OF AUGMENTATION RATIO
Augmentation
Ratio
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9 '
1.0
Model E
$384,000
$458, 000
$555, 000
$688, 000
$881, 000
$1, 188, 000
$1,752,000
$3, 132, 000
$11, 695,000
NCE
NCE
NOTE: NCE = Negative cost effectiveness
5-28
-------
system to the five model test cells ranged from $167,000 to
$972,000 per ton NOX removed, operating Model Test Cells A
through D at an augmentation ratio of 5 and Model Test Cell E
at an augmentation ratio of 0.2.
A brief sensitivity analysis was conducted to determine
the impact of changes in the principle cost components of SCR
to the predicted cost effectiveness. This analysis indicated
that reductions of approximately 30 percent in the cost
effectiveness ($/ton) estimates would result from extension of
the catalyst life from 5 to 10 years. Reductions in the cost
effectiveness estimates of approximately 40 percent from the
baseline value were predicted with an annual utilization
increase from 200 to 400 hours in the model test cells. The
effect of decreasing the target NOX emission reductions from
80 percent to 40 percent was also investigated. At 40 percent
NOX removal efficiency, the cost effectiveness ($/ton)of
installing SCR is predicted to be negative for Models A, B, C,
and D. For Model E, the cost effectiveness is predicted to
increase 73 percent from the baseline conditions.
The technical analysis of installing SNCR on five model
test cells indicates that SNCR reduces NOX emissions from the
model test cells only under limited operating conditions. In
most cases, it is predicted that the NOX emissions from the
duct burner used with SNCR would exceed the NOX removed by
SNCR. For Model Test Cell E, the predicted cost effectiveness
values range from $384,000 to $11,700,000 ton/NOx removed
depending on the augmentation ratio. Model Test Cells B and C
have predicted cost effectiveness values of $350,000 and
$1,500,000 ton/NOx removed, respectively, at an augmentation
ratio of 1 and a net increase in NOX emissions for
augmentation ratios of 2 or higher. Model Test Cells A and D
are predicted to have a net increase in NOX emissions at all
augmentation ratios.
5-29
-------
5.9 REFERENCES
3.
4.
Office of Air Quality Planning and Standards. OAQPS
Control Cost Manual. United States Environmental
Protection Agency. Research Triangle Park, North
Carolina. EPA 450/3-90-006. January 1990.
Office of Air Quality Planning and Standards.
Alternative Control Techniques Document — NOX Emissions
from Stationary Gas Turbines. Research Triangle Park,
North Carolina. ' EPA-453/R-93-007. January 1993.
pp 5-76 and 5-77.
Ref. 2,
6-27.
Letter from Sumner, J., General Electric Aircraft
Engines, to Wood, J.P., EPA/BSD, February 10, 1994
Capital costs of a new test cell.
5-30
-------
CHAPTER 6
TEST CELL NOX EMISSION INVENTORY ESTIMATE
In this chapter, total annual NOX emissions attributed to
test cell operation are categorized by owner/operator group
and by their location within ozone attainment or ozone non-
attainment areas. The distribution of NOX emissions from test
cells within ozone non-attainment areas is further subdivided
by non-attainment classifications. In addition, the NOX
emissions from test cells within ozone non-attainment areas
are compared to both total stationary source NOX emissions, as
well as to combined total stationary and total mobile source
NOX emissions within that area.
6.1 INFORMATION COLLECTION BACKGROUND
6.1.1 Owner/Operator Information
The information presented in this chapter, as well as the
owner/operator summary presented in Chapter 2, was compiled
from information provided by test cell owners and operators.
The following is a list of companies and organizations
that provided information for the study.
Engine Manufacturers:
United Technologies, Pratt & Whitney
General Electric Aircraft Engines
6-1
-------
Allied Signal Aerospace
Textron Lycoining
Allison Gas Turbines
Repair Facilities:
Williams International
Ryder Aviall Inc.
Airwork
Pacific Airmotive Corporation
Airlines:
American Airlines
United Airlines
US Air
Delta Airlines
Northwest Airlines
Organizations:
National Aeronautics & Space Administration (NASA)
Department of Defense (DoD)
AIA
Total annual NOX emission estimates for each facility
operating test cells were provided by the owner/operators. In
addition, information related to fuel consumption, hours of
operation, number of test cells, and test cell physical
arrangement was obtained.
6.1.2 .Summary of State and Local Regulations
State and local air pollution control agencies were
contacted to obtain information on emission regulations and
6-2
-------
current permitting practices for test cells. Information
requested of the state or local regulatory agencies included
permitting practices for test cells and identification of any
specific regulations pertaining to test cells. Table 6-1
presents a listing of all state and- local regulatory agencies
which were contacted in this effort.
None of the state or local air pollution control agencies
contacted have specific regulations concerning NOX emissions
from test cells. Several agencies indicated that the
permitting of test' cells would use a maximum allowable
emission standard to regulate atypical point sources.
Emissions from jet aircraft engines are currently regulated by
the EPA Office of Mobile Sources. Pollutants covered by the
standards include total hydrocarbons and particulate
emissions. Oxides of nitrogen from aircraft engines are
currently not regulated. In addition, these regulations do
not apply to the testing and maintenance of jet engines.
Without specific regulatory guidelines, several agencies
were found to use worst-cases scenarios to determine the
maximum allowable NOXemissions-of the test cell. For example,
test cells that actually operate 200 to 400 hours per year are
permitted based on 8,760 hours of operation. Several agencies
were found to regulate other operational characteristics of
the test cell. Maximum operational hours per year or per day
and fuel type are the most common regulated characteristics.
More.than 50 percent of the military test cells located in the
survey, all of the commercial, and two-thirds of the engine
manufacturers' facilities are permitted with operational
restrictions.
6-3
-------
TABLE 6-1. STATE AND LOCAL REGULATORY AGENCIES CONTACTED
Regulatory agency
Contact and Phone Number
California, Bay Area Air Quality Management District
California, San Diego County Air Pollution Control District
California, San Jaoquin Valley Unified Air Pollution Control District
California, South Coast Air Quality Management District
Connecticut, Bureau of Air Manangement
Florida, Duval County Air Quality Division
Georgia, Air Protection Branch
[ndiana, Ciy of Indianapolis Air Quality Management District
Maine, Department of Environmental Protection
Maryland, Department of the Environment
New York, Department of Environmental Conservation
North Carolina, Air Quality Division
Ohio, Sate of Ohio Environmental Protection Agency
Oklahoma, Tulsa City County Health Department
Pennsylvania, Bureau of Air Quality Control
Pennsylvania, Department of Environmental Resources
Pennsylvania, AUeghany County Health Department
Tennessee, Air Pollution Control Division
Texas, Air Control Board
Texas, Air Control Board
Virginia, Department of Air Pollution Control
Washington, Department of Ecology, Air Program
Washington, Northwest Air Pollution Authority
Ellen Linder (451) 771-6000
Kim Cresencia (619) 694-3307
Dave Warner (209) 497-1000
Ranjit Vishwanath (714) 396-2000
Ernest Bouffard (203) 566-8230
Ronald Roberson (904) 530-3660
Ronald Methier (404) 656-4713
Matt Mosier (317) 327-2270
Rick Creswell (207) 289-2437
Craig Holdefer (410) 631-3215
Randy Orr (518) 457-7230
Charles Yirka (919) 733-3340
Jim Braun (614) 644-3617
Ray Bishop (918) 744-1000
George Mentzer (717) 787-9256
Tom McGinley (215) 832-6224
Mark Schooley (412) 578-8117
Greg Forte (615) 741-3931
Mike Coldiron (512) 908-1260
Kevin Bloomer (512) 908-1514
Art Escobar (804) 786-5783
Sally Otterson (206) 459-6256
Jamie Randies (206) 428-1617
6-4
-------
6.2 .RESULTS OF TEST CELL INVENTORY
The compilation of data indicates that annual NOX
emissions from the current test cell population total
approximately 2,830 tons. Approximately 67 percent of the
test cells (249 out of a total of 368) are located in ozone
non-attainment areas, with these test cells emitting 74
percent of the total test cell annual NOX emissions.
Figure 6-1 presents a distribution of annual NOX
emissions by owner/operator group and by attainment .or non-
attainment status. Engine manufacturers operating test cells
emit•the majority of NOX in ozone.non-attainment areas,
while test cells operated by the DoD emit the majority of NOX
in attainment areas. Total annual NOX emissions from test
cells owned and operated by aircraft engine manufacturers in
ozone non-attainment areas are approximately 1,650 tons.
Annual NOX emissions from the DoD test cells are more evenly
split between non-attainment and attainment areas, with
approximately 513 tons out of a total of 845 tons produced in
non-attainment areas. Figure 6-2 presents the corresponding
test cell population distribution. The data indicate that'
engine manufacturers operate nearly 140 test cells in ozone '
non-attainment areas, while the DoD operates just over 100
test cells in ozone attainment areas and nearly 80 in non-
attainment areas.
Figure 6-3 presents the NOX emissions distribution for
test cells located in ozone non-attainment areas. Within the
ozone non-attainment areas, moderate and serious non-
attainment areas account for 90 percent of the total NOX
emitted by test cells.
6-5
-------
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Figure 6-4 presents a distribution of average annual test
cell NOX emissions. The Model Test Cells A through E
described in Chapter^ emit 25, 10, 5, 2, and 0.3 tons of NOX
per year, respectively. These model test cell emission levels
correspond well with the distribution of average annual test
cell emissions identified in this survey.
The impact of not controlling NOX emissions from test
cells can be examined by comparing annual NOX emissions from
test cells to the total annual NOX emissions in the area.
Table 6-2 presents the relative contribution of NOX emissions
from test cells to the total stationary source NOX emissions
and the combined total stationary source and mobile source NOX
emissions for those test cells located within ozone non-
attainment areas.
Total annual stationary source and mobile source NOX
emissions used in generating Table 6-2 were extracted from
recent EPA compilations of NOX source emissions.1'2 The
majority of the test cell facilities located within ozone non-
attainment areas have less than a 1 percent contribution to
the stationary source NOX totals. Only two non-attainment
areas have a contribution from test cell operation of more
than 1 percent of the stationary source NOX emissions. These
areas are Phoenix, Arizona, at 2.66 percent, and the greater
Connecticut area at 2.49 percent. None of the ozone non-
attainment areas have NOX contributions from test cells which
are greater than 0.7 percent for the total NOX emitted into
that area, and only two locations are greater than 0.07
percent of the total NOX contributed to an ozone non-
attainment area.
Test cells contribute only slightly to the total NOX
emissions within non-attainment areas. Total annual NOX
emitted from test cells located in non-attainment areas is
6-9
-------
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just under 2,100 tons. These NOX emissions account for less
than 0.14 percent of the total stationary source NOX emissions
and 0.04 percent of the total NOX emitted into those ozone
non-attainment areas.
6-12
-------
6.3 REFERENCES
1. United States Environmental Protection Agency. Regional
Interim Emission Inventories, Volume II. Research
Triangle Park, North Carolina. Publication No. EPA-
454/R-93-021b. May 1993.
2. United States Environmental Protection Agency.
Development of an Interim 1990 Emission Inventory --
Ozone Non-Attainment Area Summary Table. Prepared by
E.H. Pechan and Associates, Inc., for EPA/OAQPS/TSD/
SRAB. July 1993.
6-13
-------
-------
APPENDIX A: DEVELOPMENT OF EQUATION 3.1
The first law of thermodynamics can be applied to a
control volume surrounding the engine mounted in the test
cell. The resulting energy equation neglecting heat transfer
from the surroundings to the control volume is given by:
dm/dt (hi + Vi2/2) = -dE/dt + dm/dt (he + Ve2/2) + dW/dt
where
dm/dt
he
Ve
dW/dt
-dE/dt
Rate of -mass addition to the control volume.
Enthalpy of gas entering control volume.
Velocity of gas entering the control volume.
Enthalpy of gas leaving the control volume.
Velocity of gas leaving the control volume.
Shaft power removed from the control volume,
Rate of change of energy within the control
volume.
For the turbojet/turbofan engines, the work extracted is
zero. Assuming the exit velocity is significantly greater
than the inlet velocity, the change in enthalpy through the
control volume can be expressed as:
(he - hi) = (dmf/dt)/(dm/dt) * LHV - (l/2)Ve2
where
dmf/dt
LHV
Fuel flow rate per unit time.
Lower heating value.
A-l
-------
Assuming a constant heat capacity value across the control
volume gives:
(te - ti) = (1/Cp) [ FA * LEV - (1/2)(Tc/(dm/dt))2 ]
where
Cp
Tc
LHV
te
ti
FA
Heat capacity.
Engine core thrust.
Fuel lower heating value.
Temperature of gas leaving the control volume.
Temperature of gas entering the control volume,
Fuel-to-air-ratio.
If the inlet temperature is at atmospheric conditions, then
the engine core exit temperature can be expressed as:
tc = ta + (1/Cp)[ FA * LHV - (1/2)(Tc/(dm/dt))2 ]
where:
tc:' Engine core exhaust temperature.
Tc: Engine core thrust.
ta: Atmospheric temperature.
A-2
-------
APPENDIX B: DEVELOPMENT OF EQUATIONS GOVERNING NOX ESTIMATES
The governing ideal combustion equation is given by:
CH2 + (a) (3/2) (02 + (79/21)N2) -» CO2 + H2O +
(a) (3/2) (79/21)N2 + (a-l)(3/2)O2
where :
a = EA + 1
and :
EA is the excess air level defined as:
EA = (total air - theoretical air)/theoretical air
The excess air level is related to the engine air to fuel
ratio (AF) by:
EA = (AF-14.7J/14.7
The moles of combustion products (MCP) per mole of fuel burned
is given by:
MCP = (7.14)(a) + 0.5
The moles of bypass air flow (MB) per mole fuel burned is
given by:
MB = (BP) (a) (3/2) (1 + 79/21)
MB = (7.14/14.7) * (AF)(BP)
where the bypass ratio (BP) is defined as the volume of air
entering the front of the engine which does not pass through
the combustor divided by the volume of air used in combustion.
B-l
-------
The moles of augmentation air (MA) are equal to the
augmentation ratio (AR) times the sum of the total air flow
entering the front of the test engine.
MA = (AR)[(BP)(AF)(7.14/14.7) + (a)(7.14)]
MA = (AR) (AF) (7.14/14.7) (BP + 1)
Total stack mole flow per mole fuel combusted (TSM) is given
as the sum of the augmentation mole flow and total engine
exhaust flow: . . .
TSM = MA + MB + MCP
The moles of NOX (as N02) per mole of fuel burned (MNX) is
given by:
MNX = EF * (14/46)
where ' •
EF : Engine NOX emission factor (Ibs NOx/lb fuel)
The NOX concentration in ppm at the stack exit is given by:
ppm NOX = Ie6 * (EF) (14/46) / (TSM)
The percent oxygen concentration at the stack exit is given
by:
02 {%) = 100 * [ 0.21 * (MA + MB) + (a-1)(3/2 ]/(TSM)
The NOX concentration in the stack corrected to 15 percent O2
is given by:
•ppm NOX (@ 15% 02) = (ppm NOX) * (20 . 98-15) / (20 . 98-O2%)
B-2
-------
Sample Calculation;
Consider the emissions from a model test cell operating
the CF6-80A2 at maximum thrust:
AF = 55 (from engine specific data)
EF = 29.6 Ibs NOX per 1000 Ibs fuel
The moles of combustion products (MCP) is given by:
MCP = (7.14) (a) + 0.5
MCP =27.2
where :
a = AF/14.7
a = 3.74
The moles of bypass (MB) air flow with a bypass ratio (BP =
5. 17) is given by:
MB = (7.14/14.7) * (AF) (BP)
MB = 138.1
The moles of augmentation air at an augmentation ratio (AR) of
5 is given by:
.MA = (AR) (AF) (7.14/14.7) (BP + 1)
MA = (5) (55) (7.14/14.7) (5.17 + 1)
MA = 824.1
The stack NOX concentration is given by:
ppm NOX = Ie6 * (EF) (14/46) / (TSM)
ppm NOX = Ie6 *(29. 6/1000) (14/46)/(27. 2
+ 824.1)
ppm NOX = 9.1
138.1
B-3 .
-------
The stack oxygen concentration is given by:
02 (%) = 100 * [ 0.21 * (MA + MB)+ (a - 1)(3/2)]/(TSM)
02 (%) = 100 * (0.21 * (160.3 +-133.6) + (55/14.7 -
1) (3/2))/989.4
02 (%) =20.84
The NOX concentration corrected to 15% O2 is given by:
ppm NOX (@ 15% 02) = (ppm NOX) * (20 . 98-15) / (20 . 98-O2%)
ppm NOX (@ 15% 02) = 28.05 * (20 . 98-15) / (20 . 98-20 . 84)
ppm NOX (@ 15% O2) = 373.1
B-4
-------
APPENDIX C : DEVELOPMENT OF EQUATION 3.3
The first law of thermodynamics can be applied to a
control volume surrounding the engine mounted in the test
cell. The resulting energy equation neglecting heat transfer
from the surroundings to the control volume is given by:
dm/dt
+ Vi2/2) = -dE/dt + dm/dt (he + Ve2/2) + dW/dt
where
dm/dt
ve
dW/dt
-dE/dt
Rate of mass addition to the control volume,
Enthalpy of gas entering control volume.
Velocity of gas entering the control volume,
Enthalpy of gas leaving the control volume.
Velocity of gas leaving the control volume.
Shaft Power removed from the control volume.
Rate of change of energy within the control
volume.
For the turboprop/ turboshaft engines, the work is
extracted using a dynamometer, resulting in the exhaust energy
which is significantly reduced relative to the
turbo jet /turbo fan type engines. Assuming the exit velocity is
zero, the change in enthalpy through the control volume can be
expressed as:
(he -
= (dmf/dt)/ (dm/dt) * LHV - (dW/dt )/ (dm/dt )
where :
dmf/dt :
•LHV :
Fuel flow rate per unit time.
Lower heating value.
C-l
-------
Assuming a constant heat capacity value across the control
volume gives:
(te - ti) = (1/Cp) [ FA * LHV - (dW/dt)/(dm/dt)]
where
Cp
dW/dt
LHV
te
ti
FA
Heat capacity.
Shaft power extracted from the engine.
Fuel lower heating value.
Temperature of gas leaving the control volume.
Temperature of gas entering the control volume,
Fuel-to-air-ratio.
If the inlet temperature is at atmospheric conditions, then
the engine core exit temperature can be expressed as:
tc = ta + (1/Cp)[ FA * LHV - (dW/dt)/(dm/dt)]
where :
tc :
Tc :
FA :
ta :
Engine core exhaust temperature.
Engine core thrust.
Fuel-to-air-ratio.
Atmospheric temperature.
C-2
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APPENDIX D: SAMPLE COST CALCULATIONS OF SCR INSTALLATION
Basic Catalyst Parameters (Table 5-1):
Material:
Pressure Drop:
Space Velocity:
Temperature (TC):
Cost:
Platinum
1" water gauge
27,000 hrs'1
490 °F
4,100 $/ft3
Model Test Cell (A) parameters extracted from Chapter 3 data:
Thrust (%) Stack Temp
°F
100
80
30
Idle
116.3
112.0
91.8
88.4
% Utilization
25
25
20
30
Stack
Flow
(Ibs/sec)
10123
9808
8924
2913
Annual NOX emissions: 24.4 tons/year
The catalyst volume is calculated using the peak stack
volume flow rate at the catalyst operating temperature, and
the catalyst space velocity as:
Peak stack actual ftVsec (acfs) (@490 °F) = (Max. test
cell Ibs/sec) /(p.)
where:
Ps
and: ps
Gas density at catalyst operating temperature
(0.076) * (5407(460 + Tc))
where:
Tc = 490 °F (from Table 5-1 and above)
Peak Stack ACFS (@ 490 °F) = 10123/0.0432
Peak Stack ACFS (@ 490 °F) = 234,340 ftVsec
D-l
-------
The required catalyst volume (CV) is computed using the
peak stack acfs at the catalyst temperature and the catalyst
space velocity as:
CV (ft3) = 234,340 acfs * 3,600 sec/hr /27,000 hrs'1
= 31,245 ft3
The catalyst cost is given by:
Catalyst Cost = 31,245 ft3 * 4,100 $/ft3
Catalyst Cost = $128,105,933
The reheat fuel flow rate is calculated using the
temperature difference between the catalyst operating
temperature and the test cell stack gas temperature, the heat
capacity of the gas stream, and the heating value of the fuel
(natural gas). The reheat fuel flow rate is given by:
mf = (ms) (Cp) (AT)/[(Cp) (Tc) - LHV]
'where:
mf
ms =
Cp
(AT)
LHV
Tc =
Reheat fuel flow rate (Ibs/sec)
Model test cell stack gas flow rate (Ibs/sec)
Stack gas heat capacity (Btu/lb/F)
Catalyst temperature - test cell stack temp. (°F)
Lower heating value of reheat fuel (Btu/lb)
Catalyst temperature
At 100% thrust, the reheat fuel flow rate is given by:
mf = (10,123) * (0.28) * (116.3-490)/[(0.28)
* (490) - 21,500]
mf = 178,600 Ibs/hr
D-2
-------
At 80% thrust, the reheat fuel flow rate is given by:
mf = (9808) * (0.28) * (112.0-490)/[(0.28)
* (490) - 21,500]
mf = 174,900 Ibs/hr
At 30% thrust, the reheat fuel flow rate is given by:
mf = (8924) * (0.28) * (91.8-490)/[(0.28)
* (490) - 21,500]
mf = 167,700 Ibs/hr
At idle, the reheat fuel flow rate is given by:
mf = (2,913) * (0.28) (88.4-490)/[ (0.28) (490)
- 21,500]
mf = 55,200 Ibs/hr
The thermal input is given by the product of the fuel
flow and the heating value of the reheat fuel. The
calculation utilizes the power schedule of the test cell and
is given by:
total BTU's = (total hours/year)'* LHV * [(mf(100%) *
0.25 + mf (80%)* 0.25 + mf (30%) * 0.2 + mf(idle) * 0.3 ]
Total Btu's = 5.95 *. 105 MMBTU'S
The cost of reheat is estimated at the natural gas price of
$3.5/MMBtu4.
D-3
-------
Reheat Costs = Total Btu's * 3.5 $/MMBtu
= 5.95 x 105 * 3.5
= $2,084,000
The NOX generated by the duct burner is given by:
NOX (duct burner ) = (MMBtu's reheat) * 0.1 Ibs NOx/MMBtu)
= 5.95 * 105 * 0.1 .
NOX (duct burner ) =29.7 tons/yr
The ammonia used by the SCR system is determined from the
annual NOX emission per year and the molar ratio of ammonia to
NOX (1) . The annual consumption of ammonia (NH3) is given by:
Tons Ammonia. = Tons NOX * (molecular wt. NH3/molecular
wt. NO2)
= (29.7 + 24.4) * 17/46
= 20
The annual requirement of 25% weight ammonia solution is
4 times the tons of ammonia or 80 tons of a 25% solution. The
annual chemical cost is then:
Ammonia Cost
= 80 tons * 200 $/ton
= $16,000
D-4
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TECHNICAL REPORT DATA
(Please read Instructions on reverse before completing)
1. REPORT NO.
EPA-453/R-94-068
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE Nitrogen Oxide Emissions and Their Control
From Uninstalled Aircraft Engines in Enclosed Test Cells
Joint Report to Congress on the Environmental Protection Agency
- Department of Transportation Study
5. REPORT DATE
September 1994 (date of submittal
to Congress)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Emission Standards Division
Industrial Studies Branch
Research Triangle Park, NC 27711
10. PROGRAM ELEMENT NO.
Emission Standards Division 92-20
11. CONTRACT/GRANT NO.
Radian 68-D1-0177
12. SPONSORING AGENCY NAME AND ADDRESS
Director
Office of Air Quality Planning and Standards
Office of Air and Radiation
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Department of Transportation
Federal Aviation Administration (FAA)
Office of Environment and Energy
800 Independance Av SW
Washington DC 20591
13. TYPE OF REPORT AND PERIOD COVERED
Final - Report to Congress
14. SPONSORING AGENCY CODE
EPA/200/04
15. SUPPLEMENTARY NOTES
EPA project manager: Joseph Wood (919) 541-5446. FAA Contact: Edward McQueen (202) 267-3560
Subcontractor for Radian Corp. was Energy and Environmental Research Corp.
16. ABSTRACT
This report was submitted to the Congress under mandate of Section 233 of the Clean Air Act
Amendments of 1990. The report provides a characterization of aircraft engine test cells and their
emissions. The majority of the test cells in the U.S. are owned and operated by the Department of
Defense, aircraft engine manufacturers, and the airlines. There are 368 enclosed aircraft engine test
cells in the U.S. No technologies to control NOx emissions have been applied to full-scale test cells.
Various NOx control technologies that have been applied to combustion sources other than test cells are
examined in the report for their applicability to test cells. The effectiveness of NOx controls applied to
test cells is uncertain. It is estimated that the costs of applying conventional NOx controls to test cells
would range from $167,000 to over $2.5 million per ton NOx reduced. Effects of NOx controls on the
aircraft engine and aircraft engine test are also addressed. Finally, annual emissions from test cells are
estimated and compared to total NOx emissions in the applicable ozone non-attainment areas.
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17. KEY WORDS AND DOCUMENT ANALYSIS
», DESCRIPTORS
Aircraft engine test cells
nitrogen oxide emissions
NOx emission control
Costs for NOx emission controls
18. DISTRIBUTION STATEMENT
Release Unlimited
b. IDENTIFIERS/OPEN ENDED TERMS
Air Pollution control
19. SECURITY CLASS (Report)
Unclassified
20. SECURITY CLASS (Page)
Unclassified
c. COSATI Field/Group
21. NO. OF PAGES
195
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE
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