SEPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600 7-80-038
March 1980
Photochemical Study of
IMOx Removal from
Stack Gases
nteragency
Energy/Environment
R&D Program Report
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RESEARCH REPORTING SERIES
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EPA-600/7-80-038
March 1980
Photochemical Study of NOx
Removal from Stack Gases
by
John R. Richards and Donald L. Fox
University of North Carolina
School of Public Health
Chapel Hill, North Carolina 27514
Grant No R804740
Program Element No. INE623
EPA Project Officer: Joseph A. McSorley
Industrial Environmental Research Laboratory
Office of Environmental Engineering and Technology
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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ABSTRACT
The technical feasibility of a photochemical pretreatment system
for NO control at coal-fired boilers was evaluated. This approach uti-
n
lizes reaction mechanism similar to those responsible for photochemical
oxidant incidents. The reactions are initiated under controlled condi-
tions while the pollutants are at high concentration and while the reac-
tion products can be removed. Results indicated that under time limited
and light limited conditions, it is possible to quench the photochemical
reactions at the NOo peak and prior to the formation of ozone, aerosols,
and other secondary products.
Energy and hydrocarbon requirements were estimated in a series of
159 experimental runs. The optimal operating conditions were identified
as a NO /C3H6 stoichiometric ratio of 1 and an N02 photolysis rate of
1 to 1.5 reciprocal minutes which is equivalent to approximately 3 to 5%
station power. These conditions allowed for an &3% oxidation of NO with
an exit concentration of NO less than 100 ppm. Variation of the energy
input levels or the propylene injection rates resulted in NO oxidation
efficiencies of 10 to 99%. Photochemical oxidation of NO was insensitive
to SOp concentration and C02 concentration. Conversion was enhanced at
low initial NO levels, high temperatures, and high CO concentrations.
J\
Oxygen concentrations above 2% were necessary. The photochemical system
appears compatible with conditions resulting from combustion modifica-
tions to suppress NO generation.
A
Reactor products consisted primarily of NOg. formaldehyde, acetalde-
hyde, and acetic acid all of which should be removed in the downstream
flue gas desulfurization system. Mass spectrometer analyses indicated
the presence of a large number of organic compounds; nevertheless, all
of these were present in only trace quantities. A major fraction of the
injected propylene was also emitted. It was concluded that propylene is
not sufficiently reactive for the photochemical system. Other hydrocar-
ii
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bons are recommended for further study.
Capital and annuallzed cost estimates have been prepared for a
model coal-fired power plant of 500 MW generating capacity. Depending
on the extent of NO oxidation desired, the capital costs v*ry from $37/
KW to $50/KW. These estimates include the photochemical reactor with
mercury lamps, and the propylene storage and distribution system. The
annualized costs estimates range from 3.8 to 5.6 mills/kWh. The upper
value corresponds to &500 ppm NO while the lower value is for A200 ppm
NO.
The cost estimates are considered high due to the poor reactivity of
propylene and the low efficiency of presently available lamps. Further
bench scale testing could conceivably yield a photochemical system re-
quiring only 1/2 the annualized cost of the present system. Even with
the present limitations, the costs for the photochemical system are com-
petitive with other control techniques involving NO gas phase oxidation
followed by N02 absorption. Costs for alternative approaches such as
selective noncatalytic reduction, however, are substantially lower. It
is concluded that the photochemical system will not be commercially com-
petitive unless serious operational problems limit the-alternative tech-
niques or unless the photochemical system can be refined to reduce cost.
This report was submitted in fulfillment of Grant No. R804740
by the Department of Environmental Sciences and Engineering of the Uni-
versity of North Carolina. The study was performed under the sponsor-
ship of the Industrial Environmental Research Laboratory of the U.S.
Environmental Protection Agency. This report covers the period of
December 27, 1976, to December 27, 1978, and work was completed as of
February 28, 1979.
ill
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ACKNOWLEDGMENTS
This report was prepared for the Industrial Environmental Research
Laboratory of the U.S. Environmental Protection Agency. The EPA Project
Officer was Mr. Joseph McSorley. UNC appreciates the direction and as-
sistance provided by Mr. McSorley.
The authors gratefully acknowledge the assistance of Mr. Frank
Malcolm in the fabrication of the reactor assembly and the gas blending
equipment. X-ray fluorescence analyses and liquid chromotography tests
of the Millipore filter samples were performed by the U.S.E.P.A. Environ-
mental Research Laboratory. The GC mass spectrometer tests were done
under contract at Research Triangle Institute by Dr. E. Pellizzari.
The principal investigator was Dr. Donald L. Fox. The co-principal
investigator and principal author of the report was Mr. John Richards.
Consulting support was provided by Dr. Harvey Jeffries, Dr. E. Stahel,
and Dr. Parker Reist.
iv
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CONTENTS
Page
Abstract ii
Acknowledgments iv
Figures vii
Tables x
1. Introduction 1
2. Summary and Conclusions 4
3. Recommendations 8
4. Background 9
NO Control Techniques 9
/\
Photochemical NO Control Techniques 26
J\
5. Experimental 43
General Design Objectives 43
Reactor Design and Performance 45
Acti nometry L5
Reactant and Product Measurement f8
Gas Handl ing Apparatus 62
Experimental Design ("6
Test Procedure £7
6. Results and Discussion 71
Spectral Effects ^
Hydrocarbon Requirements 79
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Variables Influencing NO Oxidation 91
Reaction Products 102
Cost Estimates 117
References 126
Appendices
vi
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FIGURES
Number Page
1. Trends in the emissions of NOX from stationary sources 10
2. Possible formation mechanism for fuel NOV 14
/\
3. Effect of excess air on NOo emissions 16
4. Effect of secondary air addition on NOX emissions 17
5. Classification of NOX flue gas treatment processes 20
6. Effect of temperature on NOX removal in the selective
noncatalytic reduction process 23
7. Photochemical system conceptual design 29
8. Absorption coefficients of flue gas components 33
9. Power requirements as a function of net product quantum
yield 35
IQa. Photostationary state reactions 37
lOb. Simplified olefin/NOx photochemical reactions 37
lOc Simplified aldehyde photochemical reactions 37
11. Typical pollutant concentration-time profile for
photochemical reactions in batch reactor 40
12a. View of quartz reactor on support rod 46
12b. View of outer CSTR 46
13. Mercury doped xenon arc output spectra 47
14. Light distribution in quartz reactor 49
15. N(>2 photolysis rate as a function of lamp current 51
16. Initial inlet configuration 54
vil
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Number pdge
16b. Reactor inlet configuration • 54
17. Gas analyzers for NOV, SO?, and condensation nuclei 59
A ^-
18. Gas analyzers for hydrocarbons 59
19. Influence of N02 on pulsed fluorescent S02 readings 61
20. Side view of reactor and spectrometer 63
21. Front view of blending box 63
22. Gas flow system 65
23. Influence of middle ultraviolet light on NO oxidation 73
24. Typical comparative spectra; during and after
experimental run 75
25. Influence of NOX on absorption spectra 76
26. Influence of $62 on NO oxidation 78
27. NO oxidation, influence of initial propylene concentration
and light intensity. Low initial NOX concentration 81
28. NO oxidation, influence of initial propylene concentration
and light intensity. High initial NOX concentration. ... 82
29. NO oxidation, influence of initial propylene concentration
and light intensity. Low initial NOx concentration 83
30. NO oxidation, influence of initial propylene concentration
and light intensity. High initial NOx concentration. ... 84
31. Comparason of propylene and ethylene 86
J2. Unreacted propylene concentration at various inlet NOX
levels and light intensities 88
33. NO oxidation and propylene consumption as a function of N02
photolysis rate 89
34. Effect of oxygen content on NO oxidation 92
35. Effect of CO concentration on NO oxidation 96
36. Effect of initial NOX concentration on NO oxidation 99
viii
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Number Page
37. Effect of C02 concentration on NO oxidation 101
38. Influence of temperature on NO oxidation 103
39. Nitrate deposits iny
40. Sulfate deposits Ill
41. Typical gas chromatograph output Ill
42. Aldehyde/propylene decay in sampling bags 11^
lx
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TABLES
Number Page
1 Typical Flue Gas Composition of Coal -Fired Boilers ............. 11
2 Effect of Combustion Modification Techniques on the Emission
of Polycycl i c Organi c Matter ................................ 21
3 Photochemi cal Reactor Desi gn Assumptions ....................... 30
4 Effluent Gas Composition Assumptions ........................... 30
5 Energy Del ivery in Model System ................................ 34
6 Comparison of Experimental System and Full Scale Systems ....... 44
7 Tracer Results ................................................. 53
8 Experimental Design ............................................ 68
9 Influence of Oxygen Content on Propylene Consumption ........... 94
lOa Nitrogen Material Balance, [NO ]0 ^600 PPM ..................... 105
/\
lOb Nitrogen Material Balances, [NO ]0 ^1200 PPM (v/v) ............. 105
A
11 Nitrate Aerosol Quantities Compared with NO Oxidation .......... 108
12 Sulfur Material Balance ........................................ 108
13 X-Ray Fluorescent Sulfur Measurement Expressed as APPM S02 ..... 112
14a Carbon Material Balances, [N0v]0 ^QQ PPM (v/v) ................ 112
A
14b Carbon Material Balances, [NO ]0 V1200 PPM (v/v) ............... 112
A
1 5 Carbon Bal ance Correct! ons for Al dehydes ....................... 114
16 Relationship Between Aldehyde Formation and NO Oxidation ....... lie
17 Major Organic Compounds Determined in GC/MS Tests, PPM (v/v) ---- -113
X
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Number Page
18. Capital Cost Estimates 122
19. Annualized Cost Estimates 123
20. Comparison of Costs for Flue Gas Treatment Processes 124
B-l. Experimental Data, Influence of Middle UV Filter
on NO Oxidation 136
B-2. Experimental Data,Influence of Sulfur Dioxide on NO
Oxidation 138
B-3. Experimental Data, Influence of Propylene Concentration
and UV Light Intensity on NO Oxidation 141
B-4. Experimental Data, Comparison of Ethylene and Propylene .. 166
B-5. Experimental Data, Influence of Oxygen Content on
NO Oxidation 168
B-6. Experimental Data, Influence of CO on NO Oxidation 170
B-7. ExDerimental Data, Influence of Initial NOX Concentration
on NO Oxidation 171
B-8. Experimental Data, Influence of C02 Concentration
on NO Oxidation 173
B-9. Experimental Data, Influence of Gas Temperature
on NO Oxidation 174
xi
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CHAPTER 1
INTRODUCTION
GENERAL
Both utility and industrial boilers are major sources of anthropo-
genic nitrogen oxide emissions, contributing over 40% of total yearly
emissions in the United States. These primary nitrogen oxides (NOX)
emissions react chemically with hydrocarbons in the ambient air through
a set of partially understood photochemical reaction mechanisms. Conse-
quences of these reactions include elevated ozoria levels and potentially
toxic secondary pollutants. Previous photochemical oxidant control stra-
tegies directed only at hydrocarbon reduction may be set aside in
favor of more balanced NOX and hydrocarbon control. In fact, there is
growing awareness that elevated photochemical oxidant levels in some non-
urban areas are sensitive primarily to NOX concentration.
Strict NO control will be required in order to reduce the impact of
J{
photochemically generated secondary pollutants such as ozone. Coal-fired
boilers will receive a disproportionate share of the control burden since
centralized stationary sources are administratively easier to regulate
than motor vehicles and since the shift in national energy policy toward
greater reliance on domestic coal supplies will result in increased NO
rt
emissions from this source category.
Unfortunately, combustion modifications which substantially reduce
NO generation in oil- and gas-fired boilers are not nearly as success-
/\
ful when applied to coal-fired boilers. Such techniques are limited to
30 to 50% NO reduction and sometimes result in reduced boiler perfor-
X
mance. It is probable that combustion modification alone will not be
adequate. There is a need for "add-on" control technology which supple-
ments combustion modifications so that much greater N0x reductions can
be achieved.
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A photochemical process is a possible solution. This approach
takes advantage of chemical reactions analogous to those culpable ambi-
ent reactions leading to photochemical oxidants. The reactions are ini-
tiated while the pollutants are still highly concentrated within the flue
gas. In this manner, control is maintained over the reaction conditions
and collection of reaction products is possible.
There are a number of advantages inherent in photochemical control
of NO from coal-fired boilers. Since the photochemical system is oper-
/\
ated downstream of the boiler, there is no adverse impact on the boiler
energy efficiency or on boiler maintenance costs. The stoichiometric re-
quirements of hydrocarbons are much lower than equivalent requirements
for ozone or other dark phase oxidizing agents. As a concentration de-
pendent approach, energy requirements are limited to that increment nec-
essary to maintain compliance with applicable standards. By using NO
7\
outlet concentration monitor feedback control of lamp power, it is pos-
sible to follow rapid fluctuations in boiler NO emissions, thereby in-
A
suring continuous compliance and avoiding expensive over-control. Under
light-limited and time-limited conditions, it is possible to selectively
oxidize NO to N0? and then quench the reactions before most of the unde-
sirable secondary products form.
PURPOSE
The purpose of this study is to evaluate the technical and economic
feasibility of photochemical pretreatment for NO control. It is a bench
J\
scale analysis emphasizing those basic chemical reaction mechanism para-
meters which influence costs and performance. It is recognized that a
certain amount of engineering development is also necessary with respect
to lamp optimization and reaction product collection. These subjects are
necessarily reserved for later work on a pilot scale.
Specifically, the study is designed to evaluate the efficiency of
the reaction mechanisms in the high concentration pollutant gas mixtures
characteristic of coal-fired boilers. Relationships between nitric oxide
oxidation and energy consumption under various physical conditions are
obtained in order to define the limits of the control technique. Molar
ratios of SO^, NO and hydrocarbons are varied to consider the effect of
2
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initial concentrations on t.ie type and extent of the secondary chemical
reactions. Major reaction products are identified.
APPROACH
A flow reactor system was designed to simulate stack concMiions and
to allow rapid turnaround for maximum experimental runs. Simulated flue
gas was blended externally and then irradiated inside a quartz reactor
using a high pressure xenon arc. This UV lamp was a compromise choice
o
having moderate energy output in the 2400-3000 and 3000-4000 A spectral
bands of interest, and also having reasonable temperature stability.
o
Light intensity in the 3000-4000 A spectral band was routinely measured
using N02 photolysis. The outer chamber was used as a mounting frame,
light shield and heater for the inner reactor. In this manner, the walls
of the quartz reactor could be maintained slightly above the internal
gas temperature to minimize wall deposition of aerosols. The outer cham-
ber was constantly purged with N2 to reduce the possibility of 0~ leak-
age.
Gas analyzers operating off a common outlet manifold with a short
residence time were used to measure reactant and product concentrations
on a continuous basis. Millipore filter samples were taken for subse-
quent analysis of possible aerosols. After dark phase steady state con-
ditions matched planned conditions, the xenon arc was turned on. The
reactor was allowed to achieve steady state conditions at which
time all appropriate data was recorded. The difference between dark and
light phase steady state conditions was used as a measure of NO oxida-
tion at the various run conditions.
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CHAPTER 2
SUMMARY AND CONCLUSIONS
This study was performed to determine the technical and economical
feasibility of a photochemical technique for the oxidation of NO. This
approach takes advantage of chemical reactions similar to those responsi-
ble for ambient photochemical smog incidents. The reactions are initiat-
ed while the pollutants are still highly concentrated within the flue
gas and while the reaction products can be safely collected. With care-
fully controlled light limited and time limited conditions, it is possi-
ble to maintain good control on the extent of NO oxidation and the reac-
tion products. Photochemical pretreatment for NO oxidation was proposed
as a near term solution for the need for supplemental NO control tech-
/\
nology for coal-fired boilers.
The experimental program has been designed to address five specific
questions concerning photochemical system operating characteristics and
cost. One of the principal issues is the total energy requirement. The
present analyses are necessarily restricted to the commercially available,
low efficiency, laboratory-scale, ultraviolet lamps. Energy requirements
using these lamps were anticipated to be high. A second issue concerns
the possible need for injected hydrocarbons to sustain the photochemical-
ly initiated free radical chain reactions. Propylene has been arbitrar-
ily chosen for study since it is a readily available hydrocarbon of low
cost. The fraction of hydrocarbon consumed is the third issue of impor-
tance since the hydrocarbon is itself a criteria pollutant. A number of
chemical and physical conditions could conceivably influence the extent
of NO oxidation and the study of these variables constitutes the fourth
major work area. The quantities and chemical characteristics of reaction
products are the remaining issues addressed in the experimental program.
A continuous stirred tank reacfor was designed to simulate coal-
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fired power plant stack conditions and to allow rapid turnaround for
maximum experimental runs. Simulated flue gas was blended externally
and then irradiated inside a quartz reactor using a high pressure mercury-
doped xenon arc. Light intensity in the 3000 to 4000 A spectral band was
routinely measured using NOo photolysis. Gas analyzers optraiing off a
common outlet manifold with a short residence time were urc.d to measure
reactant and product concentrations on a continuous basis. Millipore
filter samples were taken for subsequent analysis of possible aerosols.
Strong spectral effects were identified. Ultraviolet light in the
o
middle ultraviolet spectrum of 2400 to 3000 A appeared to be particularly
effective in NO oxidation. It was determined that SO^ was not responsi-
ble for this phenomenon, despite the fact that it was the strongest mid-
dle UV absorber in the system. NO conversion actually improved as the
S02 concentration decreased. The enhancing effect was probably due to
the photolysis of aldehydes, nitrous acid and hydrogen peroxide; however,
definitive conclusions could not be reached on the basis of available
data.
The effect of UV light intensity and propylene concentration were
tested in a large series of tests. NO oxidation in the absence of UV
light was essentially zero in all runs tested. There was measurable NO
oxidation in the absence of hydrocarbon; however, the efficiency of con-
version was limited to approximately 10% of the inlet NO . A series of
/\
NO conversion isopleths were defined for the various levels of the two
principal variables. The relationships were characterized by distinct
light sensitive zones, hydrocarbon sensitive zones and a ridge between
the two in which both variables were important. Generally, it appeared
necessary to use propylene at a stoichiometric ratio of 1 to 2, depending
on the light intensity. The required light energies appeared to be equi-
valent to 3 to 5% of station power for tests done with inlet NO concen-
y\
trations of 600 ppr.i (v/v). System performance at higher NO levels of
A
1200 ppm (v/v) was considerably poorer than those at the low concentra-
tions.
A comparison of system performance using propylene and ethylene in-
dicated that the reactivity of the hydrocarbon is an important limitation
on the amount of NO oxidized. Except at high concentrations, the NO con-
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version was substantially higher with propylene. This work was consis-
tent with results of the S02 sensitivity tests which indicated that com-
petition for hydroxv radicals suppresses system performance.
A major problem involved in the use of the photochemical system with
propylene appears to be the fraction of injected hydrocarbon which is not
consumed in the reactor. In the experimental runs, over 50% of the mate-
rial was released without reacting.
Due to the favorable cost, it is assumed that combustion modifica-
tions will be used to the maximum extent possible before the use of a
flue gas treatment system will be considered. Therefore, it is important
that the system be compatible with the conditions resulting from such
modifications. Tests with various excess air levels confirms that the
photochemical systems performs adequately down to oxygen concentrations
of 2 to 3%. Also, the efficiency of the reaction mechanisms appears to
increase at lower initial NOX concentrations. It is proposed that the
latter phenomenon is due to the consumption of hydroxy radicals by N02>
nitrous acid, and nitric acid, which would otherwise react with propy-
lene in radical branching reactions. Since combustion modifications
could conceivably lead to increased carbon monoxide concentrations, a
small test series was performed to test the influence on the system. As
expected, the hydroxy radical reaction with CO leading to a hydroperoxy
radical appears to enhance conversion of NO. Carbon dioxide at concen-
trations of up to 20% did not have any measurable influence on the sys-
tem.
Aerosols were not generated in measurable quantities in any of the
runs. Condensation nuclei counter readings were consistently at back-
ground levels. X-ray fluorescence tests of the Mi 11ipore filter samples
indicated that less than 1% of the sulfur was present as aerosol. Minor
quantities of deposited nitrate and sulfate material were occasionally
visible on the inner surfaces of the reactor and in the effluent lines.
Generally, the sulfur material balance could account for 97 to 99%
of the input quantities. Unaccountable nitrogen quantities reached 15%
of input values for the very reactive conditions, presumable because the
system had proceeded beyond the N02 peak and substantial quantities of
nitric acid and organic nitrate compounds had begun to form. Between
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25 and 50% of the input carbon cculd not be accounted for as propylene.
The principal reaction products included formaldehyde and acetaldehyde.
Mass spectrometer analyses of a selected group of runs suggest that an
extremely large group of organic coumpounds can form at trace levels. The
najor compounds identified in the GC-mass spectrometer tests included
acetic acid and acetaldehyde. Other compounds present in the range of
1 to 2 ppm included nitromethane, methyl formate, methyl nitrate, butyl
formate, toluene, and acetophenone.
Capital and annualized costs were estimated for a model plant. Re-
sults indicate that capital costs could be in the range of $37 to $50 per
kW, and that the annualized costs would be 3.8 to 5.6 mills/kWh. The
range in values reflects the variation in cost as a function of the de-
sired NO conversion efficiency. These costs are lower than for some costs
of comparable systems. Catalytic reductions systems and NH3 injection
systems, however, have reported costs approximately % those for the
photochemical system. It is concluded that the photochemical system
based on propylene will be used only if the alternative processes cannot
be adapted for coal-fired boilers, or if there are operational problems
with such systems when used in full-scale systems.
The principal conclusion of the study is that photochemical control
techniques, as presently conceived, are not competitive. Additional
bench-scale study of different hydrocarbons and improved lamps, however,
could conceivably yield a system considerably better than the alterna-
tive flue gas denitrification systems.
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CHAPTER 3
RECOMMENDATIONS
1. It is recommended that the present experimental system be uti-
lized to evaluate the system performance with acetone and formaldehyde.
Both compounds participate in primary photochemical processes and should,
therefore, be less susceptible to the reactivity problem identified with
propylene.
2. Further studies should also be done to test system efficiency at
lower initial NOX levels. The experimental tests in this project sugges-
ted improved NO oxidation efficiency at lower NOX concentrations. The
600 ppm level used in most of the present work is higher than would be
expected for coal-fired boilers modified for reduced NOX generation.
Accordingly, the cost estimates could be high.
3. The analytical capability of the system should be improved so
that better nitrogen balances could be prepared. The response of the
chemiluminescent analyzer to nitrous acid and to nitric acid should be
determined.
4. The performance of the photochemical system at temperatures of
700 to 800°F should be analyzed to determine if the irradiation could be
one downstream from a hot side electrostatic precipitator.
5. A kinetic simulation model should be used as an aid to under-
standing the reaction system.
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CHAPTER 4
BACKGROUND
NO CONTROL TECHNIQUES
/\
The photochemical process for NO control is being developed in an-
A
ticipation of a need for control of coal-fired utility boiler emissions.
In this section, the growing importance of coal-fired boiler NO emis-
/\
sions is discussed. NO formation mechanisms in the combustion process
A
are briefly addressed to indicate the potential benefits of modified
operating conditions for NO suppression. It is concluded that such
A
"combustion modification techniques" are economical and effective; how-
ever, these may not be adequate to achieve the very stringent NO emis-
/\
sion levels being considered by EPA. Accordingly, some type of supple-
mental control technology may be necessary. Competitive add-on tech-
niques are briefly described so that the photochemical process studied
in this project can be critically evaluated.
Coal-Fired Boilers as Sources of Nitrogen Oxides
Constantly growing energy demands, coupled with the shift toward
greater national dependence on available coal supplies, will result in a
major increase in NO emissions from coal-fired boilers in the next 20
A
years (Acurex, 1977). As shown in Figure 1, the NO emissions from
A
stationary sources (point and area) have increased from 3.9 Tg/Yr in
1950 to a present rate of 12 Tg/Yr and will probably reach 17 Tg/Yr by
1990. Coal-fired boilers are responsible for approximately 30% of these
emissions, and thus, represent the largest source category ( Salvesenejt
§1., 1978).
The typical flue gas composition of coal-fired boilers is provided
in Table 1. This is based on 3.5% sulfur, 16% ash coal, 10,500 Btu/Lb.
and an excess air rate of approximately 25%. Note that there is a wide
-------
17.
15.O
112.5
iio.o
7.5
2.5L
1 Acurex. 1978
? NAS, 1977
3 Kemp «nd Dykema, 1977
« Rlccl. 1977
5 Acurex, 1977
6 Salvesen. 1978
Stationary Sources
Combined Total
Coal-Fired
Utility Boilers
rear:
1960
1970
1980
1990
2000
Figure 1. Trends in the emissions of NOX
from stationary sources.
10
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TABLE 1. TYPICAL FLUE GAS COMPOSITION
OF COAL-FIRED BOILERS
Contaminants
Horizontally Opposed Firing3 400- 900 ppm
Tangential Firing3 300- 600 ppm
Front Wall9 400- 850 ppm
Cyclone9 500-1200 ppm
S02 1000-3000 ppm
S03 5- 30 ppm
HC 1- 100 ppm
CO 10- 50 ppm
Major Components
N2 74%
02 4%
C02 13%
H20 9%
Reference - Acurex, 1978.
11
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variation in the initial NOX levels for common firing modes. Tangential
units presently comprise 35% of the utility boiler population and will
represent a greater share in the future due, partially, to the favorable
NOX emission rates. Cyclone boilers represent only 10-30% of present
coal-fired generating capacity but are responsible for over 19-22% of
the NOX emissions from this source category (Ctvrtnecek and Rusek, 1977).
These boilers connot achieve the required 0.7 IBs./MMbtu NOX emission
rate3 due to the high heat release rates characteristic of the cyclone
boilers. Because of this problem very few cyclone boilers have been
ordered since 1974 (Batayko, 1979) despite the slight energy efficiency
advantage over other types of boilers, and the ability to burn high ash-
low fusion temperature coals.
The NO control requirements will probably be set as low as possible
/\
considering available technology due to the increasing concern over NO
X
participation in oxidant formation and the health implications of NOp.
EPA has informally stated control technology goals of 200 ppm (v/v) in
1980 and 100 ppm (v/v) in 1985 for pulverized coal-fired boilers (McCut-
chen, 1977).
Control will be achieved by use of combustion modification tech-
niques, add-on control processes or a combination of the two. To date,
most of the research has been devoted to the development of combustion
control due to low inherent costs (Ricci, 1977). There is growing reali-
zation, however, that such techniques are limited with respect to NO
J\
reduction in coal-fired boilers and can have some adverse impact on
boiler performance when applied zealously.
Combusion Modifications for Control of Nitrogen Oxides
There are two general formation mechanisms leading to the generation
of NO during the combustion of coal. "Thermal" NO results from the
x x
high temperature fixation of molecular nitrogen. "Fuel" NO results
/>
from the oxidation of organically bound nitrogen. The relative impor-
tance of each mechanism cannot be determined with presently available
aStandard of Performance for New Sources (NSPS), a regulation prom-
ulgated by the U.S. Environmental Protection Agency.
12
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information (Armento, 1975); however, it is believed that fuel NO com-
X
prises 50 to 100% of the total NO (Dykema, 1978). Nitric oxide (NO)
J\
is the predominant species in each case, with less than 5 to 10% nitrogen
dioxide (N02). While N0£ is the thermodynamically favored form at stack
temperatures, the formation mechanisms are quenched before significant
conversion of NO can occur in the boiler.
Fuel nitrogen oxidation is a complex physiochemical process governed
primarily by the local conditions surrounding the initial combustion zone
(Acurex, 1977). As shown in Figure 2, the nitrogen in the coal is parti-
tioned into a vapor fraction and a char fraction upon injection into the
boiler. A portion of the volatile fraction is oxidized to NO, some of
which escapes the fuel rich reducing conditions of the burner flame (Heap
et al., 1976). The nitrogen compounds remaining on the char particle are
oxidized at a slower rate. The NO formed on the particle surface must
penetrate the boundary layer before it is reduced to N~. The NO yield
£ X
of this set of simultaneous oxidation mechanisms is fortuitously only 10
to 40% with the lowest yields at the higher fuel nitrogen levels (Faucett
et al., 1977).
Thermal NO results from a partially understood set of free radical
J\
reactions operative throughout the high temperature zone of the boiler.
During the early combustion stage, a super equilibrium level of free rad-
icals leads to the rapid formation of NO in a process which is sometimes
termed "prompt" NO . In the later stages of fuel oxidation, a slower
A
equilibrium moderated set of reactions represented by the Zeldovich mech-
anism (Reactions 1 to 3).
N2 + 0 + NO + N (1, a & b)
M + 02 + M + 20 (2, a & b)
N + 02 - NO + 0 (3, a & b)
These reactions have a strong temperature dependence due to the high
activation energy of reaction 1. The role of oxygen in a free radical
transfer step explains the strong effect of available oxygen on the ex-
tent of thermal NOX formation.
A number of combustion modification techniques have been developed
in order to interfere with the fuel and thermal NOV formation processes.
J\
13
-------
ash
virtual
nitrogen
free
Reduction
in
ayer
Escape
from
Boundary
Layer
Oil
Droplet
or
oal Particle
Volatile
raction
Reduced in Hea
Releasp
Zone
Source: Acurex 1977
Figure 2. Possible formation mechanism for fuel NO .
14
-------
These include: (1) low excels air, (2) off-stoichiometric combustion,
(3) reduced air preheat, and (4) advanced burner design. Flue gas recir-
culation, a technique proven useful for gas- and oil-fired systems is
not considered acceptable for coal-fired boilers (Armento, 1975) due pos-
sibly to the importance of fuel nitrogen oxidation and the insensitivity
of fuel nitrogen to temperature reduction schemes.
The most successful techniques appear to be low excess air combus-
tion and off-stoichiometric combustion (Armento, 1975; Selker, 1975).
The positive effect of these two approaches is partially because the
restricted oxygen level in the high temperature fuel oxidation zone inhi-
bits both fuel and thermal NOX formation ( Armento, 1975).
Low excess air combustion is sometimes considered just good oper-
ating practice which should be used at all boilers regardless of NOX re-
duction requirements. When the excess air is maintained in the 15 to
25% range, the flue gas volume is minimized and sensible heat loss is
minimized. Boiler energy efficiency can be improved more than 1% in this
manner. At lower levels of excess air, localized reducing conditions can
lead to increased slagging. The potential benefit of low excess air is
illustrated in Figure 3. Generally, the effectiveness of low excess air
alone is limited to a maximum 20% NO reduction (Acurex, 1978).
/N
Off-stoichiometric combustion may be accomplished in several ways
depending on whether the boiler is new or is an existing unit which re-
quires retrofit. For the latter case, selected burners can be operated
with air only so that others can be operated fuel rich. This minimizes
thermal and fuel NOX formation mechanisms in the high temperature zones.
With biased firing in this manner, boiler derating is necessary. For a
new boiler, the same result can be accomplished without derating penal-
ties by including a set of overfire air ports. The potential NOX reduc-
tion available by means of off-stoichiometric combustion is limited to
less than 40% (Acurex, 1978) as shown in Figure 4. New unit design
equipped with overfire air ports show typical NOX reductions of about
50% (Lachapelle, 1979).
A third approach for NOV suppression which appears useful is the
^
use of advanced burners. Pilot-scale tests have suggested that 200 ppm
levels are achievable with low NOX burner designs. Demonstration of
this equipment on full-scale boilers is in progress (Lachapelle, 1979).
15
-------
Normal Firing
178-227 MW
600
500
Biased Firing
166-210 MW
400
Q.
D-
300
X
o
Coal-Fired, Front Wall
Boiler
200
Source: Crawford etal., 1977
100
1
J_
23
Average % Oxygen in Flue Gas
Figure 3. Effect of excess air on
emissions
16
-------
800 -
CO
CO
CM
O
ro
600
500
400
300
200
100
Full Load, High Excess Air
Reduced Load
Normal Excess Air
1 Load, Normal
Excess Air
Coal-Fired Utility
Boiler, Crawford et al .."
1977
I
I
Figure 4.
20 40 60
Ov erf ire Air Dampers - % Open
80
Effect of secondary air'addition on NO emissions,
1\
17
-------
A number of other combustion modifications have been tested and
found less desirable than low excess air, off-stoichiometric combustion,
and advanced burner designs. These techniques include: flue gas recirc-
ulation, reduced air preheat, load reduction, and use of low nitrogen
coal. All except the last involve energy penalties. These approaches
generally provide much less than 20% NOX reduction and probably will not
be used substantially in the near future.
A coal-fired boiler utilizing the low excess air firing and/or off-
stoichiometric combustion will probably have flue gases with 2 to 3% oxy-
gen and 300 to 500 ppm (v/v) NOX. The predominant chemical composition
of the NOX will continue to be NO. It is probable that all new boilers
and most existing units less than 10 to 20 years old will include ad-
vanced combustion control techniques due to the inherent low cost. The
use of low excess air involves no significant capital cost and provides
a slight benefit in energy efficiency. The use of off-stoichiometric
combustion does require additional burner ports and other equipment;
however, retrofit capital costs remain at a very modest $1 to $2/kW
(Mason et al., 1977).
There are several practical limitations to the use of combustion
modification techniques due simply to the fact that boiler equipment was
designed to operate under oxidizing conditions. As excess air and burner
conditions are increasingly optimized for low NOX boilers, operational
problems appear. One of the most common of these is the reduction of ash
fusion temperature near the base of the boiler which can lead to in-
creased slagging (Crawford et al, 1977). Other potential problems in-
clude generation of carbon monoxide and high carbon carryover. The lat-
ter condition is important primarily because it represents a loss of
boiler energy efficiency. An optimized level on NOX control can minimize
these side effects.
Potential aggravation of polycyclic organic matter concentration (POM)
is an important disadvantage of combustion modifications. In one study
done by Thompson and McElroy (1976), the use of staged combustion and
flue gas recirculation resulted in a 40% increase in boiler POM emissions.
It is apparent in Table 2 that some of the individual hydrocarbons such
as pyrene and methyl anthracene exhibited dramatic increases when these
18
-------
combustion modifications were used. Considerably more experimental evi-
dence is necessary to document the relationship between POM generation
and NO combustion controls.
/\
Flue Gas Treatment for Nitrogen Oxides Control
While the need for flue gas denitrication cannot be corcl»
-------
Selective Catalytic Reduction -
Selective Noncatalytic Reduction - 1
Nonselectlve Catalytic Reduction - 1
Radiation - 1
Adsorption - 1
Liquid Phase Oxidation - 4
Liquid Phase Reduction - 5
Liquid Phase Oxidation - 3
Liquid Phase Reduction - 5
Figure 5. Classification of NOX flue gas treatment processes,
-------
TABLE 2. EFFECT OF COMBUSTION MODIFICATION TECHNIQUES
ON THE EMISSION OF POLYCYCLIC ORGANIC MATTER
Compound
Anthracene/ PI enanthrene
Methyl Anthracenes
Fluoranthracenes
Pyrene
Total
% of Baseline
Baseline
115.0
34.4
33.2
9.7
192.3
100
Biased Firing
119.5
32.3
73.5
34.7
260.0
135
Concentration
[yg/dscm]
15« Recirculation
92.8
57.1
15.8
14.9
180.6
94
Biased Firing &
Recirculation
157.3
65.0
28.9
31.0
277.2
144
From: Thompson and McElroy, 1976.
-------
Within a very narrow flue gas temperature range, reaction 4 is favored
over reaction 5, thereby providing an opportunity for a net reduction in
NO. Applied improperly, however, there is the potential for an increase
in total NO levels. Unless injection is done within 150°F temperature
/\
range (Muzio and Arand, 1976), a number of undesirable conditions can re-
sult, including: (1) incomplete reduction of NO, (2) emission of excess
NH-, and (3) increase in total NO emissions due to NH, oxidation. This
tj A O
narrow optimum temperature range is illustrated in Figure 6. While it is
possible to modify this temperature zone by combined use of NH_ and H»,
3 t-
the safety problems involved in the use of a highly explosive gas in a
boiler may hamper H2 use (Faucett et a! . , 1977). Thus, there Is a seri-
ous unresolved problem. Further, gas temperature at any one injection
port in the convective region of a boiler experiences swings of more
than 200°F as boiler load varies in diurnal and seasonal cycles (Muzio
and Arand, 1976).
Exxon, a developer of one such process, has estimated annual ized
costs for a 1000 MW coal-fired boiler with an initial NO level of 300
^
ppm (v/v) and a final desired level of 100 ppm (v/v) at 4.76 to 10.2
million dollars per year (Lyon as reported by Muzio and Arand, 1976).
This is equivalent to 0.75 to 1.6 mills per kWh assuming an average ca-
pacity factor of 75% for a base loaded unit. Capital costs would be low
since equipment requirements are limited to an NH, storage and distribu-
O
tion system. The principal operating cost is for NH-, which is dependent
on the rapidly rising cost of natural gas. The estimates of annual ized
costs provided above are for an ideal NO inlet concentration. Costs
/\
should rise proportionally to the inlet level of NO .
/\
While this approach is the most straightforward, it is apparent
that some serious operational problems and high operating costs discour-
age use in this country. Since NO reduction is limited to 50 to 70%,
/\
even at very high NH?/NOy ratios of 3 to 4 (Faucett et al . . 1977), it is
possible that this approach will serve primarily oil-fired boilers.
Selective Catalytic (Dry. Gas Phase) Reduction
This category includes the majority of processes under development,
as demonstrated in Figure 5. Reduction of NOX occurs in a catalytic re-
22
-------
350
300
250
200
§. 150
CL
ro
:r
100
50
I
NH
Source: Faucett et al
1977
Figure 6.
_J I ^
12001400 1600 1800
Gas Temperature, °F
Effect of temperature on NO removal in the selective
noncatalytic reduction process.
23
-------
actor downstream of the boiler. By using a catalyst, it is possible to
avoid the potentially crippling temperature sensitivity problems and
fouling problems which plague the selective noncatalytic process per-
formed in the boiler superheater. These catalytic reactions require only
a 0.9 to 1.2 NH3/NO stoichiometric ratio, thus minimizing sensitivity to
rising NH., costs.
The two sets of composite reactions shown below generally illustrate
the type of overall reactions responsible for NO reduction in the various
catalytic processes (Faucett et al . , 1977). The catalyst and design char-
acteristics affect the actual overall stoichiometry of the processes.
4NH3
4 NH-
3
(g)
(g)
6 N0(g)
6 NO-
2
4 NH,
3
(g)
(g)
+
+
+
+
+
2
4
4
8
3
N02
NO,
NH3
NH,
3
0.
(g)
\
g)
(g)
(g)
+ 0 na^.ja,.
2(g)
+ Catalyst
2(g)
Catalyst
Catalyst
Catalyst
'(g)
3N2
4 N0
2
5 N2
/ 1 » o
2
2 N0
2
(g)
(g)
(g)
(g) "
H
(g)
f 6
* 6
^ 6
h i;
H 6
H2
U
2
H2
? H
H-
2
Q
Q
(g)
°(9)
-0,
2 (g
Q
(g)
(1Q)
The catalytic process generally requires a high efficiency electro-
static precipitator on the "hot" side (before air preheater) to protect
the catalyst from potential poisons and flyash coating. Malfunctions of
these precipitators represent a serious threat to the catalyst life and
long term NO reduction performance. In addition to the precipitator, a
A
catalyst-containing reactor operating in a temperature range of 300 to
500°C is necessary. For these reasons, the capital costs for catalytic
systems will probably be much higher than the previously discussed non-
catalytic approach. A recent compilation of these processes include
capital costs estimates ranging from $10 to $36 per kW (Mason et al . .
1977). To put these numbers in perspective, consider that the boiler-
turbine assembly costs $400 to $600 per kW and nonregenerative SO,, con-
trol systems cost $50 to $150 per kW. The NO costs are low but cer-
^\
tainly not insignificant. Annualized cost estimates range from a very
low 0.2 mills per kWh to a moderate level of 1.8 mills per kWh. The
lower NH-, requirements offsets the higher capital costs involved in
24
-------
catalytic approach. There is very little meaningful data concerning the
possible useful life of the catalyst under conditions similar to coal-
fired boilers, since almost all experimental work has concerned oil-fired
boilers.
Radiation Oxidation
The EBARA-JAERI process is of interest in this report primarily be-
cause of the superficial similarity to the photochemical process. Acutal-
ly, the two radiation techniques are quite different with respect to chemi-
cal mechanisms used and to reaction products formed. The flue gas from
the air preheater is treated in a cold side (after air preheater) elec-
trostatic precipitator and then irradiated by electron beams to yield a
highly corrosive particulate. This material is removed from the gas
stream in a second precipitator (Acurex, 1977; Machi et al, 1975). Costs
for this highly complex process range from a moderately high $100 per kW
to a phenomenal $1000 per kW. The high value is probably most realistic
for coal-fired boilers. Power plant derating of approximately 3.3% is
required to satisfy energy demand. Due to limited size of presently
available electron beam accelerators, large numbers (100 to 500 ) would
be required for average sized coal-fired power plant applications.
It is readily apparent that this process is not a prime candidate
for control of coal-fired boilers. The only advantage to the approach
is the freedom from chemical additives and the simultaneous S02 and NOX
control without the use of wet scrubbers. It is doubtful that these
advantages will outweigh the high costs and potential operational diff-
iculties of electron beam accelerators.
Absorption of NO
There are at least eight processes under development which first
absorb NO and then attempt to oxidize or reduce the nitrites and nitrates
in solution. Very large absorbers are required to overcome the poor
solubilities of NO. Performance appears partially sensitive to the
highly Variable S02 concentrations and to 02 concentrations (Faucett
et al, 1977). To date, this group of processes has only been studied
on the bench and pilot scales. Development work has been directed
toward oil-fired boilers.
25
-------
Preliminary cost estimates suggest capital costs of $65 to $130 per
kW and annualized costs ranging from 4.8 to 7.4 mills per kWh (Faucett
et al, 1977). These represent ideal costs based on an absolute minimum
NOX reduction requirement of 125 ppm. All of these costs are for oil-
fired boiler applications.
Oxidation of NO with Liquid Phase Oxidation or Reduction
This category of control techniques is most similar to the photo-
chemical technique being studied. In each process, an additive is in-
jected into the flue gas directly downstream of the air preheater. Addi-
tives such as ozone and chlorine dioxide are used to oxidize the NO to
N02 while minimizing formation of N,>05 and other nitrogen compounds. By
converting the very insoluble NO to the relatively soluble form of NO,,,
it is possible to use much smaller absorbers than necessary for the di-
rect NO absorption processes. This cost saving is partially offset by
the much higher cost of the gas pnase oxidant. Harrison (1976) has
estimated the capital and operating costs of an ozone plant for a 500 MW
coal-fired power plant with 600 ppm inlet NOX concentration at $57.60/kW
and 4.7mills/kWh respectively. Due to the cooling requirements of the
ozone plant, the flue gas from the processes is increased by as much as
10%. The high concentration ozone stream presents serious safety problems
which may not be adequately reflected in these costs.
Absorption processes range from $84/kW to $134/kW (Acurex, 1977).
Corresponding annualized costs vary from 6.7 mills/kWh to 8.9 mills/kWh
(Acurex, 1977). All of these costs are for oil-fired applications which
require considerably less NO reduction than coal-fired boilers. Most
A
of these processes have an optimal control efficiency of 60 to 70%. The
potential for toxic secondary product formation due to ozone or chlorine
dioxide side reactions has not yet been addressed.
PHOTOCHEMICAL NO CONTROL TECHNIQUES
A
A conceptual design of a photoc
trol at a coal-fired utility boiler is analyzed in this section. Based
A conceptual design of a photochemical control system for NO con-
A
26
-------
on anticipated light absorption characteristics and commercial lamp emis-
sion spectra, the potential energy requirements are calculated as a func-
tion of the net product quantum yield of the various photochemical reac-
tions.
The reaction products and N0? quantum yields of four possible sets
of reaction mechanisms are reviewed in this section. It is concluded
that photochemical systems could be economically competitive. Major is-
sues which need to be resolved in the experimental phase of the project
are identified. Previous studies of photochemical techniques are dis-
cussed briefly to clarify possible reasons why this control approach has
not been studied earlier.
Previous Studies
General Electric (Browne and Stone, 1965) tested the SO^ control ef-
ficiency of ultraviolet light and corona discharges. Unfortunately, the
energy calculations were not corrected for the 2% UV light absorption
which occurred in the small diameter tubular reactor (path length of 1
inch). Because of this error, it was concluded that costs for a photo-
chemical system were not competitive. Westinghouse (Hamm, 1965)
performed a screening study of possible physiochemical means to collect
sulfur dioxide, and photochemistry was only one of a large number of ap-
proaches tested. The researchers restricted the study to the infrared
spectrum and not surprisingly reached the conclusion that "photochemis-
try" was not sufficiently energy efficient for use in S0? control. This
study is of interest only because it may have limited research interest
in the further evaluation of more reasonable photochemical techniques.
Neither of the above studies considered NOX control since at that time
it was assumed that combustion modification techniques would be adequate
for the modest NOX reductions considered necessary.
Dols and Boknoven (1974) described a process for the oxidation of NO
in coke oven gas to prevent pipeline gumming. This appears to be the
first process developed for the photochemical oxidation of NO for
commercial purposes. Oxidation is accomplished using a butadiene/NO
ratio of two. The initial NO concentration is reported to be only
o.25 ppm (v/v), three orders of magnitude less than levels in coal-fired
27
-------
boilers. The gas stream was irradiated in the 2050 to 2200 A absorption
band of the butadiene. For these reasons, the system appears to be quite
different from the photochemical system studied in this project.
Machi et al. (1975) developed a process for the simultaneous control
of S0? and NO using either ionizing radiation or ultraviolet light.
C, A
This process is the basis for the EBARA-JAERI system described earlier.
This is probably the first photochemical-type system proposed for control
of NO from a power plant. Irradiation is done with an electron beam
/\
which presumably results in hydroxyl and hydroperoxy radical formation
by the dissociation of water vapor.
It is apparent that photochemical techniques have not been studied
extensively. The work to date has been limited to several specialized
or exotic applications. Considering the widespread nature of photoche-
mical smog incidents involving the ambient level oxidation of nitrogen
oxides, it is surprising that a system based on conventional smog-type
reaction mechanisms has not been proposed.
Photochemical System Conceptual Design
A flowsheet for a photochemical treatment system on a coal-fired
boiler is shown in Figure 7. This includes the existing equipment'for
particulate and sulfur dioxide collection plus the equipment needed to
photochemically treat the nitrogen oxides. The photochemical reactor has
been located downstream of the electrostatic precipitator in order to re-
duce erosion of lamp optical surfaces. Using a cylindrical design with
the lamps centrally located, it is possible to achieve reasonable light
absorption. The dimensions of the reactor are selected to obtain ade-
quate path length and gas retention time. Irradiated effluent is then
sent to the flue gas desulfurization system where the SOo and N0? are ab-
sorbed in an alkaline slurry. The lamps are mounted on vertical support
rods running parallel to the reactor centerline. Due to the limited size
of presently available ultraviolet lamps, over 700 units (length, b feet;
diameter, 6 inches) would be required to get the intensities considered
necessary. The average superficial gas velocity has been set at 5 feet
per second so that the necessary retention time can be achieved without
excessive reactor heights. Other assumed design parameters are summa-
rized in Tables 3 and 4.
28
-------
ro
Stack
Liquor/Propyl ene stream
Flue Gas Streams
Reactor
Flue Gas from
Air Preheater
Electrostatic
Preci pita tor
Participate Control System
Photochemical System
Sludge Treatment Equip.
Flue Gas Desulfurization System -»-»•
Figure 7. Photochemical system conceptual design.
-------
TABLE 3. PHOTOCHEMICAL REACTOR DESIGN ASSUMPTIONS
Boiler Rating
Capacity Factor
Gas Flow Rate at Full Load
Gas Temperature
Gas Retention Time
Gas Flow Characteristics
Lamp Type
Lamp Efficiency
Light Path Length
500 MW
60% ,
1x10° scfm
275°F
6 seconds
Well mixed
Mercury doped xenon arc
20%
10 feet
TABLE 4. EFFLUENT GAS COMPOSITION ASSUMPTIONS^-
Pollutant
NO
N02
HNO
RCHOb
°3
so2
Inlet
150"
50
0
0
10
1500
Outlet
TGCf
400
50
100
50
1500
— All concentrations in ppm.
^ Includes formaldehyde and acetaldehyde
30
-------
Photochemical System Operating Characteristics
The feasibility of photochemical systems is dependent on the effi-
ciency of energy delivery/utilization and on the characteristics of the
reaction products. These two subjects are reviewed using the conceptual
design in the preceding section.
Energy Delivery Efficiency--
The energy cost of a photochemical system is the product of the en-
ergy delivery efficiency and the absorbed energy utilization efficiency.
This is expressed in Equation 1.
\
f* •*»
Mnox
V
P_ (Equation 1)
c
Where: C = the total electrical power cost
MNOX = moles of NOX treated per unit time
$ = net product quantum yield of the combined reaction mecha-
P nisms
E = energy delivery efficiency for the specific reactor system
and effluent gas composition
P = energy cost
Equation 1 indicates that energy cost is an inverse function of the net
product quantum yield and the energy efficiency of generation/absorption.
If either of these factors approach zero, the energy cost of a photoche-
mical system would become prohibitive. Obviously, this is the case when
deactivation of excited species occurs without chemical reaction and when
there is a poor match between lamp emission spectrum and absorption bands
of effluent compounds. Equation 1 also indicates that the energy is a
linear function of the pollutant concentration. This is somewhat mis-
leading since the energy delivery efficiency, E, should also be a func-
tion of the pollutant concentration in some cases. For example, if NO
/\
compounds are involved in an important primary photochemical process,
then a reduction of the NO inlet concentration could reduce the overall
J\
energy delivery effectiveness. This would partially offset the cost sav-
ings of the initial NO inlet reduction.
y\
31
-------
In equation 2, the energy delivery efficiency factor has been ex-
panded to specifically include the lamp generation efficiency across the
middle and near UV spectrum, the average reactor pathlength, and the pol-
lutant extinction coefficients. The net product quantum yield factor has
been kept outside the summation sign since it is not strictly wavelength
dependent.
A = 12500 A
A = 1800 A (Equation 2)
where S = fraction of lamp input power emitted at wavelength A
a. = extinction coefficient of species i
c. = concentration of species i
L = average pathlength for reactor
The parameter 4> -E has been estimated for the reactor configuration
and effluent composition presented earlier. The data provided in Tables
3 and 4 has been combined with typical mercury-doped xenon arc emission
spectra and the absorption spectra of the absorbing species (Figure 8).
The results of the energy delivery calculations are shown in Table 5.
The energy delivery to each of the absorbing species has been provided
along with the total energy input to the gas stream. Almost complete
light absorption is expected in the middle UV band of 2000 to 3000 A,
while only 60% absorption is achieved in the near UV band of 3000 to
3650 A.
It is apparent that at the assumed pollutant concentrations, the
aldehydes cannot compete effectively for the limited light available
within its absorption spectrum. The middle ultraviolet band will be
dominated by sulfur dioxide and ozone photolysis while the near ultra-
violet band will be dominated by nitrogen dioxide photolysis.
The energy delivery estimates have been substituted back into equa-
tion 2 to derive a preliminary estimate of the net product quantum yield
necessary for an economical control system. The desired energy demand is
in the range of 0.5 to 2% of total station. It is apparent that the net
product quantum yield must be greater than 0.5 to ensure reasonable
32
-------
I I I I
I I I I
OJ
co
1000
100
o>
o
o
o
c
o
Q.
s-
o
to
_O
-------
TABLE 5. ENERGY DELIVERY IN MODEL SYSTEM3
uv
B^nd
rim
185-210
210-240
240-260
260-280
280-300
300-320
320-340
340-380
s
A
Quanta/
Min
0
26
46
39
29
74
9
85
c
N09
c
-
_3
1.5x10
3.9xlO"4
5.2xlO"4
_4
7.7x10
_3
1.0x10
1.8xlO"3
2.6xlO"3
.a. (moles/1
HN09
d.
-
-4
6.4x10
2.9xlO"4
6.5xlO"4 1
-4
3.2x10 2
.5
4.8x10 2
6.7xlO"6
Neg.
iter x 1
RCHOb
-
Neg.
Neg.
.4xlO"5
c
.6x10"°
_5
.0x10
Neg .
Neg .
iters/mol e
0,
3
-
_3
3.2x10 J
9.6xlO"3
6.4xlO"3
-4
9.6x10
_5
3.2x10
Neg .
Neg .
)
SO
2
_
_T
7.7x10
2.9xlO"3
9.6xlO"3
T
9.6x10"
_•>
1.9x10 J
l.OxlO"4
Neg.
E
Quanta/
Eff. Min
-
0.99 26
0.99 46
0.99 39
0.99 29
0.65 48
0.47 4
0.80 68
E , Quanta/Min
i
NO,
2
3
1.4
1.2
2.0
16.4
4.0
51 .6
HNCL
2
1 .3
1.0
0.1
0.1
0.8
0
17.0
RHCOb 00
3
0 6.4
0 33.5
0 15.0
0.1 2.4
0.3 0.5
0 0
0 0
S00
2
15.3
10.1
22.6
24.4
30.2
0.2
0
Applicable to 500 MW station, 2% derating for lamp power and 20% lamp efficiency in spectral band <4000 A
blncludes formaldehyde and acetaldehyde
-------
10
00
r
OJ
I
OO
:
01
CT
01
01
Near UV Photolysis only
Optimum
Operating
Band
Near and Middle
V .Photolysis,,
I
i
3456
Net Product Quantum Yield
Figure 9. Power requirements as a function of net product quantum yield.
-------
energy demands. If N02 photolysis is the only important reaction mech-
anism, then the product quantum yield requirements are considerably more
severe as indicated by the upper curve. Without any contribution from
reactions initiated in the middle UV, the quantum yield of NC^ photolysis
reactions must be greater than 5.
Energy Utilization--
The preceding section concerned the problems in the delivery of en-
ergy to an effluent gas stream. Results of this analysis indicate that
the economical feasibility of photochemical systems depends directly on
the net product quantum yield which can be achieved. The reaction mech-
anisms which will be initiated in such a system are now reviewed with
respect to the possible product quantum yields and with respect to the
possible types of reaction products.
It should be noted that the term reaction mechanism is used in a
very broad sense. It applied to an entire assembly of reactions initi-
ated by the absorption of ultraviolet light in a specific spectral band
by a specific compound. Some of the possible mechanisms are identified
in the list below:
Absorbing
Mechanists Spectral Band Species
1. Vacuum UV Reactions 1700 - 2000 A 02, H20
2. Excited State Chemistry 2400 - 12500 A S02, N02, 02
3. Molecular Complex Photolysis 2400 - 3400 A EDA Complexes
4. N02 Photolysis 2400 - 4000 A N02> HCHO, CH3CHO
tach of these "mechanisms" could consist of thousands of individual chem-
ical reactions involving large numbers of distinct species. N02 photo-
lysis 1s emphasized since it is possibly the dominant reaction mechanism
in the photochemical system.
NCL Photolysis—The irradiation of coal-fired boiler effluent in the
near UV spectral band can promote several simultaneous cyclic free radi-
cal processes. Simplified illustrations of the three major sets of reac-
tions are provided in Figures lOa, b, and c.
36
-------
A\ denotes reaction number
i
Figure lOa. Photostationary state reactions.
RCHO
HCHO
RH
Figure IQb. Simplified olefin/NO photochemical reactions,
OH RCHO
HCHO
Figure lOc. Simplified aldehyde photochemical reactions.
37
-------
In the absence of appreciable olefin concentration, the reactions
are limited to the photostationary state conditions of Figure lOa. Reac-
tions 11 to 13 are involved in this cycle.
N00 + hv(3000-4000 A) -> NO + 0(3P) (11)
00 + M -> 0, + M (12)
0, (13)
0(3P)
0.
2
+ NO
N0
Unless there is sink for the ozone formed in reaction 12, there is little
change in the N0/N0? ratio. The N0? product quantum yield of this set of
reactions is zero.
When olefins are added to the flue gas, several additional free rad-
ical cycles are initiated. Basic elements of these processes are the hy-
droxy radical attack on virgin olefin and the peroxy radical oxidation of
NO to yield N02 plus additional hydroxy and peroxy radicals. Three gen-
eral types of reactions are listed below:
•OH + C0Hr
R-
RQ2,
RQi
+ NO
*• + H20 (14)
R02- (15)
OH-
RO-
ROS
RCHO
HCHOJ
f N02 (16)
Reaction 14 involves addition of the OH- group to the olefin. The
resulting radical will react with oxygen to yield the peroxy radical.
The oxidation of NO in reaction 16 can result in the formation of one or
more of the products listed in the brackets. The organic radicals can
undergo further reaction with oxygen to give additional peroxy radicals.
While hydroxy attack of propylene accounts for most of the olefin
consumption, the reaction with ozone also could yield many similar organ-
ic radicals.
The aldehydes formed in reaction 16 can photolysis directly if there
is sufficient energy available in the 2400 to 3400 A band. As shown in
reactions 17 and 18 , the products include the formyl radical, or simply
ethane and CO. The latter reaction becomes important only at the high
energy side of the absorption spectrum. The aldehydes may also react
38
-------
with hydroxy radicals by means of hydrogen abstraction to give products
analogous to those formed in reaction 17. Due to the limited light
available in the middle UV, reaction 19 will probably be the principal
reaction path for the aldehydes.
RCHO + hv(2400-3400 A) + R« + HCO- (17)
RCHO + hv(2400-3400 A) + R- + R. + CO 08)
RCHO + OH- .> RQ. + H20 (19)
The aldehyde reactions listed above could be important free radical
propagation reactions.
The N02 product quantum yield of the N0x-olefin reaction system can
conceivably be high. As shown in the propylene and aldehyde degradation
steps, the attack of one ozone molecule or one hydroxy radical can result
in the direct oxidation of NO and can result in the formation of numerous
hydroperoxy radicals. The latter react almost exclusively with NO to
yield N02- While the yield is a function of olefin and total NOX
concentration, the value at high concentrations could be in the range of
2 to 10.
The combined result of these free radical cycles is a gradual
depletion of the NO and the formation of N02- Once the NO is exhausted,
ozone is no longer consumed in reaction 13, it builds up to appreciable
concentrations. Other stable secondary products such as peroxyacyl
nitrate, nitric acid and organic aerosols also accumulate in the latter
stages of the reactions. An example concentration profile during the
course of the photochemical reactions is provided in Figure 11.
With time limited and light limited conditions, it should be
possible to avoid the latter stages of the overall process during which
most of the toxic secondary products are formed. By designing the
reactor to reach the N02 peak, an optimum reaction product composition
should be obtained. At this stage of the reaction, however, there
potentially is incomplete consumption of the olefin. Some olefin could
be emitted from the process.
Vacuum ultraviolet reactions -- Both water vapor and oxygen compounds
o
absorb strongly in the 1700 to 1900 A band and undergo dissociation to
39
-------
c
o
tO
i-
O
C
o
CJ
-M
C
-------
yield free radical species. The applicable reactions are presented below.
H20 + h, (1700 - I960 A)-^H' + OH' (20)
H- + 02 — ^H02- (21)
02 + h (1700 - 1900 A)-*-2 0(3P) (22)
0(3P) + 02 + M -MJa + M (23)
These reactions could result in the oxidation of NO to N02 with or without
the addition of olefins. In the absence of hydrocarbons, the NO? product
quantum yield would be in the range of 1 to 2 assuming that radical
recombination is not a serious problem. With olefins, the product
quantum yield and the reaction products would be very similar to those
discussed in the previous section.
Molecular complex photolysis — The formation of molecular complexes
between S02 and either NO or NOp would create the possibility of a
primary photochemical process involving absorption within the charge
transfer band. Based on a review of the ionization potentials of the NOX
compounds, it has been suggested (Richards, Fox, and Reist, 1976) that
this absorption could be in the middle UV band. The reactins involved
are entirely speculctive at this t;i:e since ci.ly one S02 gas phase
complex has been studied (Christian and Grundnes, 1967). The importance
of this reaction mechanism depends on the equilibrium constant of the
complex and the extinction coefficient of the complex, neither of which
are presently known. The product quantum yields of these reactions are
probably less than 1 since non-volatile reaction products are formed.
There is no reason to believe that a free radical chain reaction process
can be initiated by molecular complex photolysis.
Excited state reactions— The absorption of long wavelength UV
and visible light could result in the formation of various excited
state species. Generally, these species revert rapidly to the ground
state and do not participate in chemical reactions. The product quan-
tum yields for the possible reactions would be quite low unless at high
concentrations the excited species are temporarily stabilized within a
cluster or a complex.
-------
Study Requirements
The preliminary analyses suggest that photochemical systems are
an economically viable technique for NOV control assuming that the net
A
product quantum yield of the combined reaction mechanisms is in the range
of 1 to 5. Factors which influence quantum yields, such as olefin
concentration and pollutant concentrations are potentially important.
The extent of hydrocarbon consumption at the point of optimal N02
concentration is a third possible issue.
42
-------
CHAPTER 5
EXPERIMENTAL
GENERAL DESIGN OBJECTIVES
The experimental apparatus was designed to simulate anticipated
field conditions. An artificial flue gas and components more sophisti-
cated than necessary for a full system were used to gain maximum control
of the independent variables.
A continuous stirred tank reactor (CSTR) was chosed as the irradia-
tion chamber since this was most compatible with the geometric configura-
tion of the high quality ultraviolet (UV) lamps. Light absorption path
length and light distribution are more favorable in a CSTR than in a plug
flow reactor (PFR). Due to the offsetting factors of holding time and
light intensity in the CSTR, it was possible to match light energy per
gram mole levels in this study with levels considered achievable in
commercial units. Thus, the CSTR results can be related to conditions
to be expected in larger systems. Risks inherent in scale-up are also
minimized since non-zero order reactions proceed more rapidly in real
gas streams represented by dispersed plug flow conditions than in the
well-mixed conditions of this study.
Conditions within the experimental unit and those expected on a
commercial scale are compared in Table 6. Two typical utility boilers
have been listed: one without NO controls and one with state-of-the-art
A
combustion controls. With two exceptions, all variables are adequately
represented in the quartz CSTR system. Despite its high concentration
in flue gases, C02 was not considered important either as a third body
or as a direct photochemical reactant; and therefore, it was omitted.
Humidity was purposely minimized since the reactants would have been
partially removed in the impingers. Preliminary test work indicated
that the reactions are not highly sensitive to humidity.
43
-------
TABLE 6. COMPARISON OF EXPERIMENTAL SYSTEM AND FULL SCALE SYSTEMS
Parameter
Dominant Flow
Characteristics
Gas Retention Time,
Seconds
Gas Flow Rate, SCFM
Flue Gas Composition
co2, %
o2, %
H20, %
NOX, PPM
S02, PPM
HC, PPM
CO, PPM
Particulate, qr/dscf
Gas Temperature, °F
UV Absorption, % Inp
2400-300C A
3000-4000 A
Watts UV Absorbed pe
Gram Mole NO
/^
N02, Photolysis Rate
Kr min"1
Quartz Reactor
Bench Scale System
Completely Mixed
45
0.04
0
0-8
1-3
0-2000
0-3000
0-2000
0-3000
0
250-350
Jt
20
6
r
0-100
»
0-5.0
Util
Full
Uncontrolled
Dispersed
Plug Flow
6-12
2xl05-2xl06
11-15
4-8
3-8
400-1200
1000-3000
10-100
10-200
0.5-2
250-325
99
70
50-100
0.2-2.0
ity Boiler
Scale System
State of the Art
Combustion Controls
Dispersed
Plug Flow
6-12
2xl05-2xl06
11-15
2-5
3-8
300-600
1000-3000
10-100
10-2000
0.5-2
250-325
99
70
50-100
0.2-2.0
44
-------
REACTOR DESIGN AND PERFORMANCE
The dual CSTR system shown in Figure 12 was used in this study. The
outer reactor is a 22" diameter, 1/2" thick titanium sphere originally
built for use as a helium storage tank for a NASA Lunar Rover. Access
holes were cut in the sphere and brass flanges were permanently mounted
using Armstrong 612 Epoxy resin. A front brass plate was built to serve
as the lamp house and reactor carrier. A 1/2" diameter SS 304 support rod
attached to this front plate was used to mount and align the inner reactor.
Whenever cleaning of the inner reactor was necessary, it was possible to
remove the entire assembly from the outer sphere without disconnecting
any gas lines, lamp power cords or thermocouple leads.
The inner reactor had an internal volume of 1.39 liters and was com-
posed of commercial grade quartz. The front and back windows were made of
o
Suprasil 2 quartz with UV transmission extending down to 1800 A. A ground
glass fitting was mounted on the back extension of the reactor so that the
inner surfaces of the reactor could be flushed with distilled water for
cleaning.
Light Source
An Illumination Industries model XL-2009-150 mercury-doped xenon arc
was used as a light source. This was selected after a preliminary survey
of various high pressure mercury arcs, compact xenon arcs and mercury-
doped xenon arcs. The latter group was found to be highly temperature
dependent with strong shifts in output spectrum with only 5-10°F changes
in lamp house temperature. Standard xenon arcs without mercury-doping had
insufficient energy output despite superior temperature stability and
start-up characteristics. The mercury-doped xenon lamp was a compromise
choice that allowed reasonable energy output with only minor temperature
dependence. None of the lamps had any significant output in the 1700 to
O
1850 A band; therefore, study of vacuum ultraviolet reaction mechanisms
was impossible. The spectrum of the mercury-doped xenon arc as measured
by an Optronic Model 400 Radiometer is illustrated in Figure 13. It ex-
hibits the peaks characteristic of mercury, specifically 2537, 2860, 2960,
3030, 3130 and 3660 A. Small quantities of 1930 A light are also emitted
45
-------
Figure 12a. View of quartz reactor on support rod.
Figure 12b. View of outer CSTR.
46
-------
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
22C
i i
-
-
A.
- -f
CNi
1
o
- X
O)
QJ
^J
c
0}
c
^_
O)
Q.
CO
_ +J
4_>
IT3
)0 2400 2600
|_j~n J I—
i
2800
•^
i l
J-
t
1MB
1
•
3000 3200
1 J
-
1 ^
-
-
-
-
_
—
3400 3600 380(
Wavelength Nanometers
Figure "\2. Mercury doped xenon arc output spectra.
-------
due to the choice of Suprasil quartz lamp envelopes. This type of lamp
achieves 90% full output in 2 minutes and 98% in 3 minutes based on radio-
meter and spectrometer readings. An Electronic Measurements Model 308
Power Supply was used to operate the lamp. Starting voltages were appro-
ximately 35 kv and operating conditions were 20vdc and 6-8 amps. The
lower value was used in most of the tests so that the 150-watt lamp was
actually operating at 120-130 watts. This minimized temperatures at the
base of the xenon arc and at the nylon insulators surrounding the anode.
Lamp House
The xenon arc lamp is mounted with the anode 10° off vertical which
is within the manufacturer's specifications. The lamp bulb is 1-3/8"
from the front window of the inner CSTR.
A polished aluminum conical reflector is located directly behind the
xenon arc to improve energy delivery to the reactor. N02 photolysis tests
indicated that 40 to 60% of the total near UV energy absorbed in the re-
actor was reflected from the aluminum cone. Aluminum was chosen due to
its high reflectivity in the middle UV band. The lamp bulb was never
touched or cleaned with solvents. A dry piece of lens tissue was used
daily to clean the bulb.
The distribution of light within the quartz reactor was measured
qualitatively using thermocouples mounted on a flexible, movable rod.
The millivolt difference between a black thermocouple directly in the
light path and a white thermocouple shielded from direct light was tak-
en as a measure of light intensity. Due to the mounting equipment neces-
sary to support the thermocouple rod inside the quartz reactor, it was
impossible to perform the light distribution tests inside the large sphere.
Reflected light from the titanium surfaces may moderate the light inten-
sity gradients shown in Figure 14. It is apparent that light intensity
is low near the walls of the quartz reactor.
Lamp operating currents were monitored with a Simpson Microampmeter
connected parallel to a 0.25 ohm shunt. Meter values represent 1.7xlO~
of actual currents.
A set of 3 aperture plates was constructed of multiple layers of
decorative metal foil of 1/16" thickness. The conventional diaphragyi
aperture was considered inappropriate since the intense lamp house tem-
48
-------
VO
1.1 REAR
2.2
1.
1.0
i
1.0
SHOWN ACTUAL SCALE
Light distribution expressed as difference in
exposed thermocouple and shielded thermocouple
at locations shown
Figure 14. Light distribution in quartz reactor.
-------
peratures would have vaporized the lubricating oil and warped the shutter
blades. NO- photolysis tests on various occasions indicated the follow-
ing intensity ratios:
Plate 1 0.16
Plate 2 0.30
Plate 3 0.57
Open (Basis) 1 .00
These plates were used to select the general light intensity range de-
sired.
The lamp electrodes extended through the interior walls of the fil-
ter house. Cylindrical nylon was used to prevent sparkover of the high
voltage starting pulse. A constant stream of commercial grade N? at a
rate of 15-20 liters per minute aided lamp house heat dissipation and
precluded ozone formation. The N? flowed axially around the lamp, per
manufacturer's recommendations. During certain tests when heat dissipa-
tion was inadequate, slight vaporization of the nylon insulators occurred.
This was readily apparent on the relatively "cold" surfaces within the
filter house such as the aluminum reflector and the interior brass walls.
No discoloration was ever noted on the lamp or reactor face.
For certain runs, it was necessary to filter out a portion of the UV
emission spectrum. A 3" O.D. Suprasil quartz window was used for full
o
spectrum (>1800 A) runs and a commercial glass window was used to iso-
late the near UV (>3200 A).
Lamp current was the principal independent variable affecting ultra-
violet energy output. The k, data for both lamps used in the experimen-
tal run indicated a consistent relationship with lamp current. The
linear regression equation representing this data of Figure 15 is shown
below. This equation was calculated after throwing out the March 16th
and March 18th data points. These low values were contributed to visi-
y = 0.96 + 2.52 (x-10)
where: y = k,, min
x = lamp current, amps
(as read by Simpson
Microampmeter.)
50
-------
c
i
X 3
0)
to 0
>> 2
'o
•V
o
£
D.
I
I
L
<>• March 16
March 18
10.0
Figure 15.
10.2 10.4 10.6
Lamp Current, Amps
10.8
11 .0
N02 photolysis rate as a function of lamp current.
-------
ble deposits on the inner surfaces of the reactor during high S0? con-
centration runs (>3000 ppm SCL). The slope of the k, plot of Figure 15
is slightly higher than corresponding plot of total UV volts versus cur-
rent as determined by the Radiometer.
Reactor Gas Flow Characteristics
The gaseous mixing characteristics determine the average local re-
actant concentrations in the reactor zones where secondary thermal reac-
tions are proceeding. The resulting influence on competitive reaction
mechanisms is prejudiced against second and third order reactions when
non-plug flow conditions occur (Levenspiel, 1972). The inner reactor
was purposely designed with minimum possible plug flow conditions since
this minimizes several non-photochemical NC^ formation reactions and
since it represents the slowest possible reaction times for all mecha-
nisms.
A set of tracer tests were performed in order to evaluate flow pat-
tern characteristics as a function of flow rate. The procedures of Wolf
and Resnick (1963) were used. After a steady state NOV concentration was
A
established in the reactor for a period of five bed volumes, the NO flow
A
was abruptly stopped. The response to this step change in inlet NO flow
A
was measured using the TECO chemiluminescent monitor. The basic equation
(3) of Wolf and Resnick was used to analyze the data.
F(t) = 1 - exp
(Equation 3)
where: F(t) = fraction of material which remains in the reactor
f = fraction of gas flow short circuiting
d = fraction of reactor volume with only diffusion mass
transfer (dead space)
r = residence time correction factor
a = fraction of non-dead space which is well mixed
p = fraction of non-dead space which is in plug flow
e = average residence time
t = elapsed time
L = lag
m = lag factor
52
-------
By assuming lag is negligible and that the average residence time is
known, Equation 3 can be rearranged to give Equation 4. This was used
to match results from the tracer tests.
[~T
[l^jl
+ (Equation 4)
Since one equation with three independent variables cannot yield a unique
solution, some judgment is necessary to derive a reasonable solution.
The reactor configuration studied in these tracer runs is shown in Fig-
ure 16. The small diameter Teflon tube on the inlet side was added af-
ter preliminary tracer work indicated serious short circuiting. This
tube plus the outlet tubing leading to the NO instrument added a plug
/\
flow section to the "reactor". The long neck near the outlet tube intro-
duces a potential dead space of up to 5 percent. These factors were con-
sidered in the trial and error solutions.
Results are summarized in Table 2. Corresponding graphs illustra-
ting the match between Equation 4 values and the observed l-F(t) versus
t/9 curves are provided in Appendix A.
TABLE 7. TRACER RESULTS
Flow Rate
(1pm)
1.0
1.5
2.0
2.5
3.0
% CSTR
92
91
92
85
72
% Plug
Flow
8
9
8
15
28
% Dead
Space
2
2
2
4
8
% Short
Circuiting
6
6
6
1
1
Mixing characteristics within the 1 to 2 Iiters-per-m1nute range
closely approach design objectives. Dead zones are somewhat smaller than
expected while shortcircuiting is slightly greater. At the higher flow
rates, it is apparent that some plug flow character can be maintained
across the quartz sphere. An increase in dead space at 3.0 liters per
minute is probably due to isolation of gases in the outlet neck. Over
the range of flow rates used in the study, CSTR conditions can be as-
sumed to prevail with only slight error.
53
-------
Suprasil Window
Suprasil Window
1/4" O.D. Inlet-
Extension
•1/4" O.D. Outlet
Extension
Figure 16a. Initial inlet configuration.
1/8" O.D.
Teflon Tubing
1/4" O.D.
Inlet
Extension
1/8" O.D. Teflon Tube
NOTE: Drawings not to scale
Figure 16b. Reactor inlet configuration.
54
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ACTINOMETRY
The experimental apparatus included actinometer systems for both
the near UV (3000 to 4000 A) and the middle UV (2400 to 3000 A) spectral
bands. The function of these actinometry systems was to provide a mea-
sure of light absorption so that the N0? net product quantum yield de-
fined in equation 1 could be calculated. Quantum yield can be related
_
N°? TIN - +fi - JTET (Equation 5)
LV NEAR MIDDLE" J
where: NNQ = Gram moles of N02 formed in CSTR
NNEAR = Quanta of uv ]l"9ht absorbed in the 3000 to 4000
A band.
NMfnm r - Quanta of UV light absorbed in the 2400 to 3000
pIIUULL — o
A band.
t = Unit of time
to the overall energy requirements using the lower curve in Figure 9.
The rate of N02 formation in the CSTR (numerator of Equation 5) can be
calculated using the steady state N02 concentration in the reactor efflu-
ent and the effluent flow rate. This is shown in Equation 6.
n /I gram mol e
N02
iu /+\ - (r 1 iters^ (7Q°F\ fcram Mol es . . ,\
(NNO? } " 1G ""Tnj \T~j \22.4 liters totalj
* l
C -~
SS/ 10b ppm N02
(Equation 6)
where: G = the CSTR effluent flow rate
T = the gas temperature at the reactor outlet
^ 2'ss = steady state N02 concentration in the reactor
Acetone photolysis was used to measure middle UV energy penetrating
through the quartz sphere. The difference between runs with and without
reactive gases in the quartz sphere served as a measure of the N..Trjrj, r
term of Equation 5.
The acetone pressure was chosen to maximize UV absorption within the
o
outer CSTR. Over the 2400 to 3000 A spectral range, UV absorption ranged
55
-------
from 75 to 94%. The results of Howe and Noyes (1936) indicate that the
CO quantum yield of the overall set of reactions is approximately equal
to one at the acetone vapor pressure, gas temperatures and UV spectral
bands used in the actinometry system. Thus, with only minor corrections
the CO yield provided a direct measure of middle UV energy input to the
quartz sphere. The CO was measured in a Miran Dispersive Infrared Analy-
zer. A complex system of dry ice and liquid nitrogen baths were used to
remove interfering vapors, particularly acetone. Numerous cold trap de-
signs were evaluated, however, none could operate for longer than 45 min-
utes without plugging due to acetone freezing. Because of this problem
the middle UV actinometry system was abandoned.
The inability to measure light absorption in the middle UV forced a
redefinition of the NOp product quantum yield term to be measured in the
study. This new definition is given in Equation 7. Since the contribu-
tion of middle UV light is ignored in the revised definition, the calcu-
lated product quantum yield should be greater than or equal to the actual
o
quantum yield for the entire UV spectrum of 2400 to 4000 A. The values
would be equal only in the case that UV absorption in the middle UV band
does not enhance or reduce N02 formation.
* -
N02(calc) IMU2 (Equation 7)
H(ca1c) >} (Equations)
The revised definition of N02 product quantum yield can be related
to the overall energy requirements of the system using the upper curve of
Figure 9. This approach overestimates the actual energy requirements by
the factor represented by the ratio of quantum yields (Equation 8).
The NNEAR term was determined using the N02 photolysis procedures
of Sickles and Jeffries (1975). The N0£ photolysis is measured by
irradiating a N02-N2 gas stream and observing the steady state
56
-------
concentrations of NO and N02 in the reactor effluent. The photolysis
rate, k-, is calculated using Equation 9 provided in their paper.
A[NOJ f Ro([NO]o + A[NOJ)]
Klss=^^A7L1 +Rl [N02]ss J Aquation 9)
where: A(N02) = the drop in N02 concentration between inlet and outlet
streams
(NO.,),. = the steady state N00 concentration in the reactor
i. SS £.
average residence time
(NO)Q = concentration of NO in the reactor influent
R1 = 0.27
R2 = 0.25
The k-j tests were done in the actual CSTR to account for internal
light reflection and the non-ideal light distribution conditions discussed
earlier. Tests were done at least once per day. An attempt was made to
perform the k, determination at the temperatures expected in the runs,
however, some deviation generally existed. Results of three successive
tests indicate a drop in observed k, values of 20% over a temperature
range of 275 to 125°F. Based on these results, corrections were consi-
dered unnecessary for the relatively small temperature variation between
the runs and the applicable k, test.
The k.j value was used in Equation 10 to calculate the NN™R term
of the product quantum yield. Substitution of the right side of this
equality and the right side of Equation 6 leads to a very simple defini-
tion of the N02 product quantum yield.
/-mo A A- i< i -r *. t \ /Gram Mole NO,
/N /tx_,, /70°FVGram Moles Total
^EAR71;"MitersI T A 22.4 Liters
«e"N02) Cation ,0)
where: k, = the NO^ photolysis rate
T = the gas temperature in the CSTR
V * the volume of the CSTR
57
-------
*Mn = G/V-k = 1/rk, (Equation 11)
NU2(calc) ' '
Equation 11 suggests that the N02 product quantum yield is a depen-
dent variable of the N02 photolysis rate, k,. This unusual condition re-
sults because the photochemical system utilizes NCL photolysis to produce
N02. Equation 11 provides a very convenient means to relate the observed
steady state NC^ concentration with the energy requirements of the system
as indicated on the upper curve of Figure 9.
REACTANT AND PRODUCT MEASUREMENT
The diluted effluent stream in the outlet manifold was analyzed with
a set of gas analyzers shown in Figures 17 and 18. All of these instru-
ments were calibrated by preparing a known gas concentration in a 40-liter
Teflon bag. In initial tests, all the components in the system used were
mixed together during calibration. There appeared to be essentially no
interferences at the undiluted concentrations of initial components.
Nitrogen Oxides Analysis
A Thermo Electron Model 10A Chemiluminescent NO-NO Analyzer was
/\
used. This instrument utilizes the reaction between NO and 00 which re-
o o
suits in light emission at 3100 A. The light intensity measured by the
photomultiplier assembly is linearly related to the concentration of NO.
The concentration of combined NO species is determined by reduction to
A
NO in a metal coil at 650°C-700°C. The difference between the NO and
N0x values is representative of the N02 concentration plus an unknown
number of other species such as nitrous acid, nitric acid and peroxyacyl-
nitrate.
The Chemiluminescent instrument was calibrated routinely using Tef-
lon bag mixtures containing known quantities of NO, CL, S02 and propylene.
The instrument was operated using laboratory air instead of 02 since the
diluted outlet concentrations rarely exceeded 500 ppm.
Sulfur Dioxide Analysis
It was necessary to use a pulse fluorescent technique in order to
ensure S02 specificity. A Thermo Electron Model 40 Analyzer was chosen.
58
-------
Figure 17. Gas analyzers for NOX, S02» and
condensation nuclei.
Figure 18. Gas analyzer for hydrocarbons.
59
-------
It operates by excitation of SO, to the singlet state by irradiation at
o £
2200-2300 A using a pulsed UV source. The excited molecules decay to the
o
ground state by two possible pathways - fluorescent at 3400 A and quench-
ing. Light from the fluorescence reaction is linearly related to the SOp
concentration.
S02 -i- hv(2200-2300 A) S02* (24)
S02* -*- S02 + hv (25)
S02* + m +-r S02 + m (26
Using the Teflon bag mixtures with typical (diluted) reactor efflu-
ent, it was observed that the fluorescence is sensitive to N02 concentra-
tion, a product of the photochemical reactions. The significance of this
interference is illustrated in Figure 19. It is proposed that this pre-
viously unreported negative interference is due to increased quenching ef-
ficiency via a contact molecular complex, as indicated in reactions 27
and 28.
S02* +N02- [(S02)(N02)]* (27)
[(S02)(N02)]* + m + S02 + N02 + m1 (28)
The molecular complex would provide additional vibrational degrees of
freedom which would facilitate radiationless decay. It was necessary to
adjust observed S02 values according to the prevailing N02 concentration
due to the negative interference.
Hydrocarbon Analysis
Gas chromatography analyses were performed on a routine basis using
a Varian Series 2440 Analyzer equipped with a fame ionization detector.
A 10 cc sample loop was purged continuous with outlet manifold gas and in-
jections were then done twice during each irradiation period. A polypax 3
meter column at 80°C was used for separation. Calibration was again done
using Teflon bag samples of known concentrations.
Condensation Nuclei Analysis
An Environment/One Rich 100 condensation nuclei monitor was used to
evaluate possible aerosol formation. For a portion of the irradiation
period, the Millipore filter was taken off line to permit unfiltered gases
60
-------
-40
(VI
I
c
0)
o
0)
Q.
-30
-20
-10
I
I I
100 200 300 400 500 600 700 800 900 1000 1100 TJOO 1300 1400
[N02] PPM
Figure ID. Influence of NOo on pulsed fluorescent SO^ Readings
-------
to enter the outlet manifold. This instrument exposes the sample gas to
a 300% supersaturated condition which causes condensation of water vapor
on condensation nuclei. A portion of these grow into the light scatter-
ing size region causing a reduction in light transmission in a tubular
cell. This instrument qualitatively indicated the presence or absence of
large quantities of condensation nuclei.
Spectral Analysis
A number of spectral changes were anticipated due to aging of quartz
windows, lamp deterioration and reactor cleanliness. The k, responds to
a relatively broad spectral band and would not serve as a useful indica-
tor of such developing problems. For this reason, a Heath Model 703 IR/UV
spectrometer was used. The PM tube detector module was placed on the cen-
terline defined by the xenon arc and reactor (see Figure ?0). A Hewlett
o
Packard x-y plotter was used to record spectra from 2400 to 3700 A for N?
and during actual test situations. A set of spectra was generally taken
once per run. Relative peak height values on the N? spectra revealed the
deterioration effects listed earlier. The differences in the two spectra
indicated major absorbing species.
GAS HANDLING APPARATUS
The experimental apparatus was designed to maximize flexibility in
and to facilitate routine checks for nonoptional performance caused by
leaks, surface mediated catalytic reaction or other factors. The system
was composed of a number of separate units including:
(1) gas blending
(2) heaters
(3) temperature measurement
(4) ventilation
(5) humidification
Gas Blending
The simulated flue gas was prepared by blending of pollutant
gases and oxygen into a nitrogen carrier gas stream. This permitted
complete flexibility in the concentrations of all components. The
blending box is shown in Figure 21. All gas lines from the cylinders
G2
-------
Figure 20. Side view of reactor and spectrometer.
Figure 21. Front view of blending box.
63
-------
to the blending box and within the blending box were Teflon so that hy-
drocarbon contamination could be minimized. As shown in Figure 22, the
N2 and 02 were mixed first followed by humidification in Greenberg-Smith
impingers filled with distilled water. Part of the humidified gas stream
was drawn off to a Dew Point Hygrometer for measurement of humidity. The
N,-0,> stream was mixed with S09, NO and hydrocarbon lines to complete
tL c. £ X
the blending process. All flows were monitored with calibrated rotameters
shown in Figure 21.
The simulated flue gas stream was split in half with one portion
going to the reactor via a tube furnace and the other half proceeding di-
rectly to the outlet manifold solenoids. A pressure gauge on the reactor
side of the line served as a very sensitive indicator of flow variations.
The gas stream entering the outlet manifold was diluted a factor of
2 to 5 by dried laboratory air. This was necessary to support the large
flow requirements of the gas analyzers feeding off of the outlet monitor.
The complete gas flow system is illustrated in Figure 22.
Heaters
A tube furnace shown in the center of Figure 21 served as the ini-
tial reactor gas heating system. The temperature of the heated gas gene-
rally was 125-150° Fat the front flange of the large reactor.
A series of seven 100-watt power resistors were mounted in the outer
CSTR. By varying the voltage from 0 to 85 V.A.C. across the parallel
circuit, it was possible to control gas temperatures inside the quartz
CSTR from 125°F to >300°F. By heating from the outside walls of the
quartz CSTR, it was possible to keep the reactor walls at least 10°F
higher than the inner gas temperature. This minimized deposition of
aerosols on the reactor's inner walls.
Temperature Measurement
The gas temperature inside the quartz reactor was measured using a
Chromel-Constantin thermocouple (Type E thermocouple). The zero to 10
multivolt signal generated were measured on a Model 10A Fluke digital
Multimeter (see top right, Figure 21).
The thermocouple probe was located on the quartz reactor center!ine,
64
-------
CJ1
9 Pressure
Gauge
uosi
to Hooc!
1
ik
1
'
Monitor
, 1 '
Monitor
Mon1 tor
r
1
h
&
To *od
To Hood F To Hood r To Hood^
Rotaneter
Ur1er1te
Column
Figure 22. Gas flow system.
-------
directly above the gas exit port. The probe was loosely wrapped with
several layers of white Teflon tape so that radiant energy would not
bias the results.
Humidification
The combined N2 and 02 streams were humidified in a set of 2 500-ml
impingers filled with distilled water. Desired humidities were achieved
by bypassing some of the gas around the impingers. Treatment of the simu-
lated flue gas would have allowed higher humidity; however, the reser-
voirs would have collected soluble gases such as S02 and N02.
EXPERIMENTAL DESIGN
A preliminary test series was performed to aid in the preparation
of the experiments. Considering that over 10 major variables were con-
sidered of possible importance, a complete factorial design was not con-
sidered feasible. Even with the rapid turnaround capabilities of CSTR
systems, the maximum number of tests which could reasonably be done with
available resources was estimated to range from 150 to 200. It was nec-
essary to screen the variables and subdivide the test program so that
this limitation was not exceeded.
The very rough initial tests indicated that the variables of most
importance with respect to NO oxidation were the UV light intensity and
the hydrocarbon concentration. Accordingly, a 5 x 5 x 2 factorial design
was used to study these variables at NO levels of 600 and 1000 ppm (v/v).
/\
The ranges of the variables roughly approximate the levels considered
achievable in commercial systems. Hydrocarbon concentrations well-be-
yond stoichiometric requirements were used in order to identify the
point, if any, that the system becomes hydrocarbon insensitive. Speci-
fics concerning this major test series are provided in Table 8. The
test series was repeated once so that interactions among these three
variables could be identified.
A number of small factorial test series were devoted to secondary
variables also observed to influence NO oxidation in the preliminary
test work. These runs were done at equal light intensities and hydro-
carbon levels so that the sensitivity of the system to each variable
-------
could be qualitatively compared. Specifics concerning these studies are
also covered in Table 8.
Most of the series in Table 8 provided information concerning varia-
tions expected in commercial systems. The range in SC^ levels, 02 levels
and gas temperatures were selected to correspond to the anticipated levels
at utility boilers. The spectral characteristics study (series 5) was in-
tended to aid in the selection of lamps for subsequent pilot plant stu-
ies. The hydrocarbon comparison study (series 6) served to evaluate
relative advantages of each compound in terms of NO conversion
efficiency. This information would be of use in cost estimation and
design of subsequent work.
Despite the high concentrations of C02 in boiler effluent it was
assumed that there would be no relationship between the NO oxidation ef-
ficiency and the level of C02- Series 7 was included in the study to
check this assumption. The possible beneficial impact of carbon monoxide
was studied in Series 8.
TEST PROCEDURE
Each run consisted of three distinct phases: (1) establishment of
dark phase steady state conditions with respect to gas flow rates, re-
actor temperature and pollutant concentrations, (2) a 15- to 20-r,iinute
irradiation period, and (3) a recheck of dark phase steady state condi-
tions. In this manner, it was possible to check for drift of pollutant
concentrations, temperature, and other factors which would have influ-
enced the reactions during the irradiation period. During the initial
dark phase period the rotameter readings, temperatures, and gas analy-
zer values were recorded along with information concerning the run. Af-
ter this data was recorded in the project notebook, the lamp was started.
Immediately after lamp start-up, the reactor effluent was diverted to the
Millipore filter. After a warm-up period of 4.0 minutes, the Heath Spec-
o
trometer was started on a scan beginning at 2450 A and extending to 3700
o
A. The complete scan required 11 minutes. At the 5.0-minute point after
lamp start-up, a GC injection was made and the NOX and S02 analyzer data
was recorded. Rotameter settings, temperatures, lamp currents, and other
67
-------
TABLE 8. EXPERIMENTAL DESIGN
O>
Series
No.
1
2
3
4
5
Variable
1
Light
Intensity
[S0~]o
c.
[02]
£.
Tempera-
ture
Spectral
Charac-
teristics
Variable
Levels 2
0 (min"1)
0.25
0.50
1.00
2.00
0 ppm [NOjo
500 x
1000
1500
3000
0 % [NOjo
1
3
5
10 %
125°F [NOjo
175 x
225
275
2400A Light
3200A ^tensity
Total
Number
Variable of
Levels 3 Levels REPS Tests
0 [NO ]0 600 2 100
250 x 1000 ppm
500
1000
2000 ppm (v/v)
600 - 1 10
1000
600 - 1 10
1000
600 - - 1 8
100
0 (min"1) - 1 1Q
0.25
0.50
1.00
2.00
-------
TABLE 8 (continued)
01
UD
Series
No.
6
7
8
Variable
1
Hydro-
carbon
Tvpe
[co2]
CO
Variable
Levels 2 Levels
Propylene Hydrocarbon 250
Ethyl ene Concentration 500
1000
2000
0%
8
12
20
0 -
1000 ppm
1500
2500
Total
Number
Variable of
3 Levels REPS Tests
1 8
1 4
1 4
-------
data of interest was then checked. At the 10.0 minute point, another
GC injection was made and the NO and S0? analyzer data was recorded.
/\ L-
Rotameter settings, temperatures, lamp currents and other data of
interest was then checked. Near the completion of the irradiation period,
the Millipore filter was taken off line to prevent exposure to dark phase
conditions. The CN counter was observed for several minutes to determine
if aerosol formation was detectable. When all necessary data had been
recorded, the lamp was shut down and time was allowed to reestablish dark
phase steady state conditions. All flow rates, and pollutant concentra-
tions, and gas temperatures were then rechecked and recorded.
After each run, the lamp filters and/or aperture plates were changed.
At the beginning of each day, the lamp condition was checked using the k,
level. After each day's run, cumulative lamp operating hours and the
number of starts was recorded. The xenon-mercury arc was replaced when
operating time exceeded 100 hours or when the number of starts exceeded
200.
70
-------
CHAPTER 6
RESULTS AND DISCUSSION
The experimental program has been designed to address five basic
factors concerning photochemical system operating characteristics and
cost. These principal issues are listed below:
1. What is the relative importance of UV absorption in the middle
UV spectrum?
2. What olefin concentrations are necessary to achieve adequate
NO oxidation?
3. At the point of optimal NOp formation, what fraction of the ole-
fin has not reacted?
4. To what extent do the flue gas chemical and physical characteris-
tics affect the photochemical system performance?
5. What secondary products are emitted from the reactor?
Data from the 159 runs performed have been divided into five sec-
tions, each one of which is devoted to one of the issues listed above.
These analyses culminate in an assessment of order-of-magnitude annua-
lized costs.
While the primary purpose of this project is simply to evaluate the
competitive potential for photochemical NOV control , some attention is
A
also given to the identification of possible reaction mechanisms. This
is useful in transferring information gained in this study to consider
other industrial applications.
SPECTRAL EFFECTS
NO Oxidation Effectiveness
Filters were used to test the relative effectiveness of near UV and
middle UV light. A standard piece of window glass was used to eliminate
light of wavelengths 3000 A and a piece of SuprasiT^or quartz was used
71
-------
for full spectrum tests. Use of a Suprasil quartz filter was not strict-
ly necessary since the front window of the CSTR is composed of similar
material. The filter was added to equalize the effects of light reflec-
tion. Each of these filters were 1/4" thick, 2" diameter ?nd were
placed between the lamp and the CSTR front window.
Heath Spectrometer scans indicated that the window glass filter re-
duced UV light of <2960 A by 99%. It also significantly reduced radia-
o o
tion of 3030 A and 3130 A (two major peaks in the lamp output spectra) and
it moderately attenuated the entire near UV spectrum entering the CSTR.
This unintended impact on the near UV band was quantitatively accounted
for by performing k, tests with each of the filters. The ratio between
the observed k] values was 2.04 (>1800 A/>3000 A) ±0.40 based on 3 sepa-
rate determinations done over a 4-week period.
Differences in NO Oxidation
The extent of NO oxidation at equivalent k, levels is the criteria
used to evaluate spectral effects. The aperature plates were used to
vary the incident light intensities to give 4 distinct levels. Results
of eight tests, four with each filter, are presented in Figure 23. The
upper curve is the NO conversion in ppm (v/v) using the Suprasir^
quartz filter while the lower curve is the NO conversion using the win-
dow glass filter. Other variables such as propylene concentration, oxy-
gen concentration and gas temperature were held relatively constant as
indicated by the data summary table included within Figure 23. The
eight tests were performed in random order.
The shaded region between the two curves represents the contribu-
tion of middle UV light. At the UV light intensities which will be ty-
pical of commercial installation, namely 0.2 to 0.4 mirr' adjustrd k-, the
middle UV appears responsible for 65 to 85% of the NO converted. This is
remarKaole considering that the middle UV output from a mercury doped
xenon arc is only 15% of the output in the near UV band (see Section 4,
Figure 13).
The $.,-. / -, \/$wn factor introduced earlier appears to be a func-
iiUn^caicj NUp
tion of the total light intensity entering the reactor. At low levels of
72
-------
500
400
i
s.
a
r—i
O
z
l__l
<
300
200
100
Variable
NOn, ppm
rt
C3Hg, ppm
S02, ppm
02,. %
Temp., °F
T , ' m i n .
Min
596
1302
1312
3.8
251
0.737
Mean
627
1377
1428
4.4
273
0.760
Max
665
1441
1500
4.7
295
0.783
0.20 0.40 0.60
NO, Photolysis Rate, Min";
0.80
1.00
Figure 23. Influence of middle ultraviolet light on NO oxidation,
-------
light, this ratio is 1 to 3. The ratio approaches 1 at very high light
intensities presumably because reactions initiated in the near UV are
sufficient to convert the available NO. This revised data indicates that
the k-j must be in the range of 0.2 to 0.4 min in order to keep energy
demand less than 2% of station power.
Possible Causes of Spectral Effects
The Heath Spectrometer was used to identify possible absorbing
species in the middle ultraviolet band of 2400 to 3000 A which could be
responsible for the enhanced NO conversion. It was necessary to analyze
experimental runs performed without the filters.
Figure 24 includes two separate spectra; one taken during the
actual run and one taken after all gas streams except the dry N2 stream
have been turned off. Strong UV absorption is apparent in the band from
o
2600 to 3030 A. This set of comparative spectra is characteristic of
virtually all spectra obtained during the experimental program. For a
small set of the runs, however, attempts were made to determine what
fraction of the middle UV absorption could be assigned to S02 and what
fraction was the result of other primary absorbers such HCHO, CH3CHO,
HN02, and EDA Complexes. This was accomplished by modifying the procedure
used in taking the second, "baseline" spectra. In this set of runs, the
S02 injection rate was kept constant and only the NOX inlet stream was
turned off. Since the latter volumetric flow rate was quite small
relative to the total, the S02 concentration in the "baseline" spectra
was almost equal to that used in the run. The result of these comparative
spectra is shown in Figure 25. S02 obviously accounts for essentially
all middle UV absorption measurable by means of the Heath Spectrometer.
Considering the apparent dominance of S02 absorption, it is logical
to propose that S02 participates in one or more primary photochemical
processes which contribute to MO oxidation. Possible reaction mechanisms
include EDA comples reactions and singlet S02 reactions (excited state
possibly stabilized within a complex or cluster). A series of 10
experimental runs were performed to check for the role of S02 in the
overall reaction scheme. The S02 content in the reactor influent was
varied from 0 to 3000 ppm to correspond to the general range in coal-
fired boilers of 500 to 3000 ppm. The tests were divided into five low
74
-------
100 -
80 -
01
60
40..
20,-
2550
Wavelength A
2675
2800
2925
3050
3175
Spectra, N2 Purge
Spectra, Reactive
Gas Mixture (S02
NOX, C3H6)
NOTE: Spectra,,
merge at 3150 A
3300
3425
3550
Figure 24. Typical comparative spectra; during and after experimental run.
-------
100
80
60
en
40
20
C
-------
NOX inlet runs and five high NOX inlet runs. The results of interest
were the extent of NO oxidation across this wide range of S0£ concentra-
tions. These are presented in Figure 26 along with a summary of the
variability of other factors.
The upper line of Figure 26 is the observed SOg effect on NO oxida-
tion with the inlet NOX concentrations averaging 544 ppm. While there
may be a discernable association, the influence of S0£ on this type of
system is insignificant. In the case of the high NOX inlet tests
( average of 1165 ppm), there is a definite suppression of NO oxidation
at the higher S02 concentrations. This is contrary to the trend which
could be inferred from the spectral band tests. The probable reason for
the negative effect of S02 on the overall system is the hydroxv radical
reaction listed below:
•OH + S02 + OHS02 (29)
This reaction would compete with hydroxy attack on the propylene which is
important in maintaining the free radical chain process resulting in NO
oxidation. The HOS02 radical formed in the above reaction would react
further to form probably sulfuric acid, peroxysulfuric acid, and related
compounds according to the reactions proposed by Calvert et a!. (1977).
At the high S02 concentrations tests, aerosol deposits containing con-
siderable sulfur were observed. This confirms that S0« is being oxidized
and the above reaction is the only known reaction fast enough to account
for the conversion to aerosol precursors.
The S02 test series demonstrate that S02 absorption is not respon-
sible for the strong effect of middle UV light. Based on these results,
it appears very unlikely that EDA complexes composed partially of S02 or
that excited S02 reactions have a significant impact on NO conversion.
It is necessary to identify other possible middle UV absorbers to account
for the spectral effects. Three possible species are 03, HN02 and H20,>.
All of these absorb strongly in portions of the middle UV spectrum, and
the photolysis reaction yield free radicals which could enhance the
oxidation process. The reactions are provided below:
77
-------
90
80
70
60
Low Inlet NOX Tests
High Inlet NOX Tests.
oo
o
o
o
40
30
20
10
500
Variable
NO -low, ppm
NO -high
k, , min
C3H ppm
3
(v/9)
mm max mean
506 577 544
1068 1248 1165
4.2 4.7 4.32
4.1 4.63 4.49
543 990 808
1000
2000
2500
1500
SO?, ppm
Figure 26. Influence of S02 on NO oxidation
3000
-------
hv(2400-2800 A)-^20n> 1 •** 203 (30)
hv(2400-3600) — «-OH- + NO (31)
hv(1900-4000) -*-20H- (32)
The presence of these absorbing species cannot be dismissed on the
basis of the comparative spectra discussed earlier. A check of the Heath
Spectrometer using Equation 12 indicates that the minimum detectable
concentrations are quite high. For this analysis, minimum detectable
was arbitrary (MDC) defined as the concentration which would result in
2% transmittance change at a specific wavelength. The results indicates
that the MDC's for 03 is 17 ppm, for HN02 is 145 ppm and for H2<32 is
740 ppm.
Ln(0.98) = C (Equation 12)
a2660 L
It is conceivable that one or more of the above species does exist at
steady state concentrations below those detectable, and that these pho-
tolyze to produce free radicals which support NO oxidation.
In summary, the analyses of possible causes of the middle UV en-
hancement did not conclusively indicate what species were responsible.
It is clear, however, that S02 does not participate in any primary pho-
tochemical processes which significantly effect the overall system.
HYDROCARBON REQUIREMENTS
The energy requirements and the hydrogen requirements are considered
two major components of the photochemical system operating costs, A
large test matrix was performed to determine the extent of NO oxidation
over wide ranges of both variables. These tests were done using propy-
lene. The relative effectiveness of ethyl ene and propylene was tested
in a separate set of tests.
Propylene Tests
The efficiency of NO oxidation at 5 levels of hydrocarbon
concentration and 5 levels of UV light intensity were tested in two sets
79
-------
of matrices. One set was done at an approximate inlet NOX concentration
of 600 ppm which is representative of many coal-fired boilers without
combustion modifications for NOX suppression. The second set of tests
was done at an inlet NOV concentration of approximately 1200 ppm which
A
is an upper limit concentration probably representative of cyclone
fired boilers or units firing coal of very high fuel nitrogen content.
The entire test series was repeated.
Propylene was a convenient hydrocarbon to use since the reactions
are fairly well understood and since it does not degrade into light
scattering aerosol which could deposit on the optical surfaces within
the CSTR. Propylene is also an attractive candidate for commerical
systems, because it is a readily available bulk chemical of reasonable
cost.
Results are presented in a series of 4 figures (27 to 30). The
first and the third are for the low NOX tests and the second and the
fourth are for the high NOX tests. In each case, the observed NO is
plotted with respect to the prevailing k-, level and the inlet propylene
concentration. Isopleths have been drawn to indicate conditions of
equal NO oxidation.
There are several outlying points in each of the four figures. It
is believed that this is due to errors inherent in the k, measurement and
in the propylene measurement. Light deposits on the inside window of the
CSTR could reduce k1 values by as much as 50% based on N02 photolysis
tests before and after reactor cleaning. There were also random fluctua-
tions in the lamp current caused by variation of lamp operating tempera-
ture. After the first 40 runs, a series of electrical problems caused
by construction in adjacent labs resulted in the premature failure of
the xenon-mercury arc. It was replaced by a supposedly identical unit;
however, operating characteristics were different. Due to a higher oper-
ating temperature, it was necessary to reduce the lamp current so that
volatilization of the nylon insulator around the lamp electrodes would
not significantly affect the light intensity levels.
Gradual deterioration of the capillary used to inject the gas sam-
ple to the Varian Gas Chromatograph resulted in some error in the propy-
lene measurement. Calculated propylene concentration based on the cali-
80
-------
CO
re
a:
1.5
1.0
o
o
£ 0.5
CM
O
CO
o
o
• 37
\
o
o
• 342
\
• 480
• 505
Runs 19-43
Numbers next to data points
indicate APPM at specified
experimental conditions
400
•23 .155.0,
200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400
[C3H ], PPM
Figure 27. NO oxidation, influence of initial propylene concentration and light intensity,
low initial NO concentration (-v600 ppm (v/v))
A
-------
1.5
00
PO
10
cc
in
o
4->
O
.c
O_
CNJ
O
i.o L
0.5 I
Numbers next to data points
indicate ANO at specified
*532 conditions
• 153
• 103
Figure 28.
~80U~
[C3Hg] ppm (v/v)
NO oxidation, influence of initial propylene concentration
and light intensity, high initial NOX concentration ( 1200 ppm v/v)
-------
1.5 -
00
u>
ce
42 1.0
M
O
a.
CM
o
0.5
Runs 69-93
Numbers next to data points
[ndicate Appm NO at speci-~
ied experimental condi
tions.
1600 1800 2000
I200 1400
ppm, v/v
Figure 29. NO oxidation, influence of initial propylene concentration
and light intensity, low initial NOX concentration ( 600 ppm v/v)
-------
1.5
co
c
•r-
s:
*
CU
4J
CO
CU
o
•M
o
CM
o
594
•
Runs 94-118
Numbers next to data points
indicate Appro' NO at specified
xperimental conditions.
1.0 -
0.5 ~
•477
400 600
800 1000 1200 1400
[C3H6J ppm v/v
600 1800 2000
Figure 30, NO oxidation, influence of initial propylene concentration
and light intensity, high initial NOY concentration ( 1200 ppm v/v)
A
-------
brated rotameter values indicated up to a 25% error due to these problems.
The low N0x inlet ^-olefin plots have three distinct regions, (1)
an area of apparent UV light insensitivity below 500 ppm (v/v) of olefin,
(2) an area of olefin insensitivity at UV intensities below 0.5 k, , and
(3) a central region where both variables exert an influence.
The lignt insensitive region is obviously unattractive due to the
high cost of electrical power. Selection of an optimum operating point
in the remaining two regions depends on the necessary control efficiency
and the relative costs of propylene and energy. To achieve an outlet NO
concentration of 100 ppm it appears necessary to use propylene concentra-
tions greater than 500 ppm with k-j values of approximately 1 to 2.
A comparison of the high and low NO test series shows the efficien-
/\
cy of NO conversion appears to be 10 to 25% better in the low NOX tests.
Because of this unexpected result, an additional series of tests were
performed to study the relationship between inlet NO concentration and
J\
the efficiency of NO oxidation. These runs are described in a later sec-
tion.
In the high NO series, there is a light insensitive region; however,
/\
there does not appear to be a propylene insensitive region. At the same
stoichiometric NO/C3Hg ratio; however, the UV light requirements are
close to those for the low NO test program.
/\
Comparison of Propylene and Ethylene Effectiveness
One of the principal design requirements is the selection of the
most effective hydrocarbon on a cost per unit NO converted basis. A
screening of possible hydrocarbons is beyond the scope of this project;
nevertheless, tests using ethylene were considered useful to evaluate
the differences in performance.
A set of eight runs were performed, four with propylene and four
with ethylene. The extent of NO conversion is presented in Figure 31
along with a summary of variability in the run conditions. There is a
clear difference between the two compounds on a Appm NO basis. This
could be due to the reactivity of the alkyl radical in the propylene
reactions or due simply to a difference in the reaction rate constants
85
-------
800
600
00
CTl
Q.
Q-
X
o
400
200
1
JL
600
800
1000 1200 1400
Olefin Concentration, ppm (v/v)
600
1800
Figure 31. Comparison of propylene and ethylene
-------
of the two compounds with hydroxy radicals. The convergence of the two
curves of Figure 31 supports the reaction rate explanation. At the high
olefin concentrations, there should be more effective competition for the
reactive species.
Utureactod Hydrocarbon Emissions
The environmental acceptability of the photochemical process is
partially dependent on the fraction of injected olefin which does not
react and is emitted from the control system. The downstream flue gas
desulfurization system would not be effective in removing these hydro-
carbons.
The fraction of propylene consumed at various light intensity levels
and various inlet propylene concentrations was evaluated using the data
of runs 74 to 93. The purpose was to determine if there was an optimal
operating range in which the emission of unreacted hydrocarbon is not a
problem. The data are displayed in Figures 32a-d, each of which presents
results at a distinct k-j level. The top line of these figures is the
inlet propylene concentration and the bottom line is the reactor outlet
concentration. Unreacted olefin is represented as the shaded portion.
The run number adjacent to each data point corresponds to the run
summaries of Appendix B.
Unreacted propylene emissions are a significant problem across the
range of propylene inlet concentrations used in these runs. Even at
very low concentrations, a major fraction of the olefin remains uncon-
sumed. Light intensity does have a favorable impact as demonstrated by
the shrinking unreacted hydrocarbon concentrations evident by comparing
Figures 32a-d. Based on these results, it appears that control of the
hydrocarbon/NO stoichiometric ratio is not effective in preventing the
J\
emission of unreacted hydrocarbon. There are only three options remain-
ing: (1) increase light intensity, (2) alter propylene reactivity, and
(3) select more reactive hydrocarbon. The first option can be evaluated
using the same data set presented in Figure 32.
The percent propylene consumption derived from the data of Figure 32
has been combined with the observed percent NO oxidation for the same runs
to derive a second set of four Figure 33a-d. The purpose of these is to
determine operating point of the system with respect to the NO^ peak (re-
87
-------
2000
1500
1000
average k, - 0.25 Mi
Inlet
h
,
r^ 500
2000
1500-
100C -
50C
83
average k] = 0.48 Min~y/ s*
500 1000 1500 2000
Initial C$\6 , ppm v/v
Figure 31a
500 1000 1500 2000
Initia'i 03^ , ppm v/v
Figure 31b
88
>
>
ID
2000
1500
1000
500
average k : 0.66 Min
-1
87.
Tnlet
•2000
1500
1000
500
I
I
average k,
1 .57 Min
500 1000 1500 2000
Initial C3H6 , ppm v/v
Figure 31c
500 1000 1500 2000
Initial C3Hg , ppm v/v
Figure 31d
Figure 32. Unreacted propylene concentration at various inlet
NOX levels and light intensities
-------
1 UU
o
1 75
C
o
^ 50
0~>
°a
I "
+->
ro
T3
X
o
o
s* Figu
— _^l UU
o..
E
average [C^] = 316 g 75
m
" 50
C
0
| 25
— .
— average [C^H^] = 640
/i ill
0.5 1 .0 1.5 2.0 0.5 1 .u ] _5 2.
re 33a. N0? photolysis Figure 33b. N0? photolysis
rate,
rate, mirr'
o
4->
CL
c
O
X
o
100 r-
75
50 -
25 -
0.5 1.0 1.5
Figure 33c. N09 photolysis
= 2026
C3H6
I
2.0
0.5 1.0 1.5 2.0
Figure 33d. NCL photolysis
C- 1
rate, .inn~ '
Figure 33. NO oxidation and propylene consumption as a function of
NO,, photolysis rate.
89
-------
fer to Figure 11), and to extrapolate the possible light energy require-
ments to achieve low olefin emissions. On these graphs, the point of
NO-NOo crossover is shown as a horizontal line at the 5Q% conversion le-
vel and the point of the NOp peak is arbitrary shown as a horizontal
line at the 95% conversion level.
At the low propylene concentration test series, Figure 33a, it is
apparent that the reaction system does not begin to even approach the
NO-NO/, crossover point. The extrapolated light requirements approach
positive infinity since tne operating conditions are within the nght
insensitive region described in the previous section. As the propylene
concentration is increased stepwise in the set of four figures, it is ap-
parent that the operating point approaches and then goes beyond the point
of the N02 peak. The extrapolated light energy requirements gradually
decrease to a level of k1 =1.5 mlrf^this can be converted to station
power retirements using Figure 9). In the case of propylene^control of
unreacted emissions using increased light energy requires undesirably
high energy levels.
Assuming that the energy costs were tolerable, use of increased
light energy to control hydrocarbon emissions entails a second risk. As
illustrated in Figure 11 of Chapter 4, secondary reaction products form
readily when ambient-type photochemical systems pass the N02 peak. Some
of the compounds which could be expected include peroxyacylnitrate (PAN),
ozone (Oo)» nitric acid (HNO.J and hydrogen peroxide (H^Oo). Fine par-
ticulate composed of sulfates, nitrates, and organic particulate could
also form. All of these reaction products would strain the control capa-
bility of the scrubbers used the downstream flue gas desulfurization sys-
tems. The fine particulate would be especially difficult to remove. In
the case of propylene, the data presented in Figures 33a-d. demonstrates
that control of unreacted emissions using light energy is done at the
risk of secondary pollutant generation, assuming that reaction schemes
at stack concentrations generally resemble those at ambient concentra-
tions.
Solutions more fundamental than just control of the C,H,/NOv stoi-
•JO A
chiometric ratio or the increased use of light appear necessary to pre-
vent emissions of unreacted hydrocarbons. The alteration of effluent
90
-------
conditions to improve the propylene competition for reactive species
such as 63 and OH will be analyzed in a subsequent section. Generally,
the reaction rates with OH radicals, ozone or atomic oxygen increase
with the molecular weight of the hydrocarbon; however the potential for
aerosol formation also increases. Presumably, a compromise choice will
be required.
VARIABLES INFLUENCING NO OXIDATION
The effect of various physical and chemical variables are analyzed
to determine the operating limitations of the photochemical system and
to evaluate the extent to which propylene reactions can be optimized.
Possibly the most important variable is the oxygen concentration since
this is essential to the free radical chain reactions and since NO sup-
J\
pression techniques can lead to reduced flue gas oxygen content. Such
modifications can also lead to increased CO levels; therefore, this is
examined over the concentration range anticipated. Due to the unexpected
difference between the high and low NO test series discussed in a pre-
A
vious section, a set of tests have been devoted to this subject. Other
variables considered are effluent gas temperature and C02 concentration.
All of the experiments described in this section were done at reaction
conditions resembling as close as possible those used in the large test
matrices of runs 19 to 118. Each test program is discussed with respect
to the influence of the NO conversion efficiency and with respect to the
possible underlying chemical reasons for the observed effect.
Influence of Oxygen Content
The principal questions of interest are: (1) whether the reduced
oxygen content of NO suppressed boilers interferes with photochemical
oxidation, and (2) whether the increase of oxygen would reduce the unre-
acted propylene concentration. These were evaluated in a set of 10 runs
(numbers 127 to 136), five of which were done at high NO levels and five
A
of which were done at moderate NO levels. The oxygen content of the
/\
reactor feed stream was modified by adjusting the balance between the
91
-------
1200
1000
800
0.
Q.
600
Variable
N0v0
X
C^H,
3 6
so2
kl
Temp
T
Min
1020
569
1252
4.5
256
0.738
Max
1101
702
1347
4.5
295
0.784
Mean
1080
636
1304
4.5
271
0.763
400
200
Variable
NV
C3H6
so2
k!
Temp.
-T
Min
515
569
1260
4.5
261
0,738
Max
604
695
1465
4.5
295
0.772
Mean
563
621
1348
4.5
272
0.7R1
% Op (volume)
8
Figure 34. Effect of oxygen content on NO oxidation
92
-------
dry nitrogen and dry air streams in the blending box. The prevailing
oxygen concentrations were calculated based on the rotameter values as
calibrated at the operating pressure of the particular run. Other varia-
bles were held as constant as possible in the set of runs.
The results are presented in Figure 34. For each set of five, the
average inlet NO concentration is shown as a horizontal line. The typi-
A
cal oxygen contents for high NOX emitting boilers are shown as a range of
3 to 5% by volume. The corresponding values for more typical boilers
with and without NOX suppression capability are shown as a range of "\h
to 4%. Those units with low excess air capability would be in the low
end of the range and unmodified boilers would be close to the 3 to 4%
range. With respect to the lower curve, it is apparent that below an
oxygen concentration of 2% there is rather severe oxygen starvation of
the free radical cycles. However, within the region typical of most
installations, this loss in NO oxidation capability is limited to 5 to
15%. This is a very important result in that it appears that a photo-
chemical system is compatible with low excess air combustion modifications,
It is desirable, but not necessary, to add oxygen through flue gas
dilution.
At high inlet N0tf levels, the extent of oxygen starvation is severe
]\
throughout the range studied. NO oxidation effectiveness is impaired to
the extent of 10 to 90% with the latter value occurring at extremely low
oxygen content. For such applications, it may be advantageous to either
reduce inlet NO concentrations and/or dilute the effluent stream prior
4\
to the photochemical reactor.
The influence pf oxygen content on the utilization of propylene is
unclear. The data presented in Table 9 indicate that the untreated ole-
fin concentration varies from 67 to 95% of the inlet concentration over
the oxygen range of 0 to 7%. High oxygen content such as in run 128 did
not significantly improve the propylene emissions problem. In fact, the
extent of propylene conversion at the k, level of 2.84 min'1 appears to
be slightly lower than comparable values discussed in the previous sec-
tion (refer to Figures 32a-d). Conversely, low oxygen content did not
drive propylene emissions any higher than would be expected for the quan-
tity of NO oxidized.
93
-------
TABLE 9. INFLUENCE OF OXYGEN CONTENT ON PROPYLENE CONSUMPTION
Oxygen Unreacted C-H,
Content C~Hfi Emissions ANO
(X by Vol.) (fern) (% of [C3H6]0) (ppm)
High 0 102 82 126
[NOjo 0.86 108 83 404
Tests 2.54 234 67 626
3.88 N/D N/D 781
6.14 210 70 990
Low 0 26 95 120
[NO ]0 0.81 117 79 392
Tests 2.45 190 67 558
4.43 157 78 493
7.42 N/D N/D 559
94
-------
The NO oxidation in the absence of 02 (runs 133 and 134) is inter-
esting because it indicates the extent of conversion possible in the ab-
sence of the free radical chain reaction mechanisms and other mechanisms
dependent on oxygen. One possible reaction mechanism is the oxidation of
NO by atomic oxygen as shown in reactions 33 to 38,
N02 + hv(3000-4000 A) •> NO + 0(3P) (33)
0(3P) + NO % N02 (34)
0(3P) + C3H6 + C"H2CH = CH2 + OH (35)
+ -C3H60- (36)
C"3H60 + NO + C3H6ONO (37)
0(3P) + N02 + NO + 02 (38)
The N02 product quantum yield for such a mechanism must be small due
to the rate of the reverse reaction, 38.
Influence of Carbon Monoxide Concentration
The typical levels of carbon monoxide in the effluent of coal-fired
boilers is 10 to 50 ppm. With certain combustion modifications for NOX
suppression, however, increased CO levels can result. The maximum expect-
ed concentration is 2000 ppm since above this point there is probably un-
acceptable carbon carryover and there is a risk of explosive conditions
(Acurex, 1978). A set of four runs (numbers 137 to 140) were performed
to examine the possible effect of CO within the 0 to 3000 ppm range. The
purposes of this work was to determine the extent to which CO enhances
the NO conversion efficiency and to determine if unreacted hydrocarbons
are reduced at high CO levels.
CO was injected into the influent gas stream using the S02 line, and
the prevailing CO concentration was calculated based on the rotameter cal-
ibration. Except for the absences of SCL, the effluent conditions were
similar to those used in the large test series (runs 19 to 118). The
variability of reaction conditions is presented in the table included
with Figure 35. This figure illustrates the NO oxidation effectiveness
in terms of ppm NO converted at the corresponding CO inlet concentration.
The run numbers shown adjacent to each of the data points corresponds to
the data compilation in Appendix B.
95
-------
800
600
Cu
a.
400
200
Variable
[NOX]0
[C3H]
Cso2]
-Co2]%
kl
Temp.
T
Min
842
1137
0
4.5
1.55
266
0.764
Max
896
1180
0
4.7
1.95
269
0.765
Mean
865
1152
0
4.6
1.65
267
0. 767
1000
2000
[CO], PPM +
Figure 35. Effect of CO on NO oxidation
"OTT
96
-------
The results displayed in Figure 35 show that CO enhances the oxida-
tion of NO. There is a 22% increase in the ppm of NO converted at 3000
ppm CO relative to 0 ppm CO. This effect is attributed to the reaction
of CO with hydroxy radicals which ultimately results in the hydroperoxy
radical attack of NO.
CO + OH- -> C0? + H. (39)
02 + H. SHOg (40)
NO + H02-+ N02 + OH- (41)
The effectiveness of the chain process is limited by the competition
for the hydroxy radicals. This competition primarily comes from the reac-
tions listed below:
(42)
(43)
(44)
The fraction of hydroxy radicals retained in the CO chain reaction
can be approximated using the ratio of Equation 13. The summation term
in the denominator accounts for OH sinks not expressly considered in the
above set of reactions.
OH- +C3H6+
OH- -i- N00 +
2
OH- + NO ->
CH3CHOH=CH2
HNOo
3
HN02
c __ _ _
•"OH k[CO] + k[C3H6] + k[N02] + k[NO] + " k^]
1=1
where: Fn,, = the fraction of hydroxy radicals reacting according to
un reaction 39
k. = the rate constant for the reaction number i
Assuming that the summation term is neglible, and using the reaction 39
rate constant of 2.50 x 102 ppm"1 min"1 and constants of Demerjian, Kerr
and Calvert (1975) for the other hydroxy reactions, indicates that CO uti-
lizes 5% of the hydroxy radicals at 3000 ppm. This small fraction appar-
ently accounts for the 22% increased in NO oxidation. These results con-
firm previous conclusions that hydroxy radical utilization is an impor-
tant factor in the overall reaction scheme active in the photochemical
process. CO has a moderate influence on NO conversion due to its OH
reaction and resulting free radical chain reactions. This positive ef-
97
-------
feet again demonstrates that the photochemical system is compatible with
conditions expected at boilers modified to suppress NOX generation.
The high concentrations of NO and N02 in addition to the large rate
constants for hydroxy radical reaction may hinder the optimal utilization
of hydroxy radicals. In time-limited and light-limited conditions, both
reactions 43 and 44 may represent free radical termination steps. The
adverse impact of high NOx levels on system performance has already been
discussed earlier concerning the large test series and is evaluated
specifically in the next section.
Influence of Initial NO Concentration
/\
During the course of other experimental subsets, it was observed that
there was a moderate negative correlation between the extent of NO conver-
sion and the initial NO concentration. This was studied in a special ser-
ies of runs with initial concentrations varying from 400 to 2000 ppm. Ob-
viously, the high levels are not representative of any commonly encoun-
tered fossil-fuel fired boiler. Unlike most of the experimental work,
this set of tests has been done specifically to evaluate mechanistic ques-
tions and not to evaluate technical/economic feasibility of the technique.
A series of 7 runs (numbers 141 to 147) were performed under nearly
identical conditions. The influence of initial NOX concentration was in-
dicated by the difference in ppm NO converted. Results are presented in
Figure 36. The probable reasons for the negative slope are the reactions
1 isted below:
OH- + N02 +HN03 (43)
OH- + NO 2HNO- (44a,b)
OH- + HN02 +N02- + H30 (45)
OH + HN03 +N03 + H20 (46)
HN02 + hv(<4000 A) +NO + OH- (47)
HN03 + hv(<3400 A) +N02 + OH- (48)
Reactions 43 and 44 should be important sinks for the hydroxy radicals.
With the time and light limited conditions, it is unlikely that the pho-
tolysis of nitrous acid and/or nitric acid would significantly offset the
overall dampening effect of increased NO .
98
-------
1000 -
800
/
/
Hi I
600
Q.
a.
O
z
<3
400
200
Min
904
1582
4.5
1 .55
261
0.758
Mean
959
1709
4.55
1.55
269
0.764
Max
1183
2086
4.7
1.55
272
0.771
200 400 600 800 1000 1200 1400 1600 1800 2000 2200
[NOXL, PPM
Figure 36. Effect of initial NOX concentration
on NO oxidation
99
-------
It should be noted that this is not a problem for the photochemical
system since both nitrous acid and nitric acid should be effectively
removed downstream in the flue gas desulfurization system. These results
could suggest that the difference between the high concentration runs
and the low concentration runs is partially due to the increased presence
of nitrous acid and nitric acid in the high concentration tests.
Influence of Carbon Dioxjde
The simulated flue gas streams used in this project did not include
C0? since photolysis was negligible in the lamp emission spectra and since
C0? does not actively participate in known dark phase reactions. Sus-
pected chemical activity is limited to enhancement of the atomic oxygen-
nitric oxide reaction (Demerjian et al., 1975). This relatively minor
third body activity did not warrant the additional complexity involved
with adding another component to the reactor influent stream. This as-
sumption was tested in a set of four runs (numbers 148 to 151) done at
C02 concentrations ranging from 0 to 20%. Typical C02 levels are in the
range of 10 to 15%.
The influence of C02 was measured with respect to the change in NO
concentration at various CO- levels. The results of the four tests are
presented in Figure 37. Variability of experimental conditions is re-
ported in the table enclosed within this Figure.
The observed NO concentration drop varied 3% for the tests and
there is no apparent trend. It is concluded that CO,, does not exert
any appreciable influence on the overall photochemical process and that
the system can in fact be operated successfully in the high C02 environ-
ment of coal-firea boiler effluent.
Influence of Gas Temperature
There are three possible locations where hydrocarbons could be in-
jected and the irradiation performed: following the FGD system presatu-
rator, preceding the presaturator, and preceding the air preheater. A
series of tests were done to evaluate system performance at the various
temperature levels characteristic of these possible locations. Due to
physical limitations of the reactor, it was impossible to approach the
500-700°F range representative of the air preheater inlet. In these runs,
100
-------
500 i i_.
400
300
OJ
TJ
*¥—
X
O
200
100
Variable
N0x
C3H6
so2
ki
Temp.
Min
846
855
0
1 .55
261
0.768
Max
898
1018
0
1.55
264
0.771
Mean
866
960
0
1.55
262
0.770
R^
15
20
% CO,
Figure 37. Effect of CC>2 concentration on NO oxidation
101
-------
the gas temperature was varied from a low of 115 F to a high of almost
300 F. The latter value is characteristic of older boilers with minimal
air preheater surface areas. Newer boiler designs have maximized thermal
efficiency by reducing air preheater exit temperature from 300 to 275 F.
This is possible due to the common use of low sulfur western coals with
low acid dewpoint. After the presaturator, which sometimes accompanies a
flue gas desulfurization system, the gas temperature is reduced to
adiabatic saturation levels of approximately 125 F. These two common
temperature ranges are illustrated on Figure 38. Effluent temperature
between these two regions is uncommon. Data points have been taken in
this temperature range only to obtain a clearer picture of the relation-
ship between the extent of NO oxidation and the gas temperature.
The test series was divided in high N0tf and low NO subsets. The
A X
flow rate of the blended gas stream to the reactor was adjusted to ac-
count for the density changes occurring upon heating in the tube furnace
and CSTR. The purpose of this was to ensure that the energy per gram
mole of gas was approximately equal for the eight tests. The runs (num-
bers 152-159) were performed in random order.
The results are presented in terms of percent NO oxidation. This
was chosen instead of change in NO concentration since there was consi-
derable unintentional variation 1n the Initial NO concentrations as indi-
A
cated in the tables provided with Figure 38. Conversion of NO at high
temperatures is obviously favored. There is a considerable loss of sys-
tem effectiveness as the temperature if reduced; therefore, the preferred
location for the system is prior to the presaturator. It is conceivable
that performance could be improved with the reactor on the "hot side" of
the air preheater if the observed trend continues. This should be exa-
mined in subsequent bench scale tests.
REACTION PRODUCTS
The quantities and characteristics of the photochemical system reac-
tion products will partially determine the commercial acceptability of
the technique. Ideally, the system would operate at the point of the NOp
peak and there would be a minimum of secondary reaction products such as
ozone, PAN, and aerosols. The formation of submicron aerosols would be
102
-------
Runs 152 to 159
1000
800
Q.
*
O
C
o
X
o
600
Variable
[NOX].
r H
L3H6
so2
°2
T2
Min
1190
541
1232
3.8
0.742
Mean
1294
677
1396
4.3
0.753
Max
1543
849
1637
5.0
0.772
400
200
Variable
[N0x],
CoHc
3 6
so2
°2
kl
Min
547
541
1284
3.8
0.8
Mean
579
573
1380
4.0
1 .15
Max
651
625
146E
4.4
1.5!
I
I
I
120 140 160 180 200 220 240 260 280
Gas Temperature, F
Figure 38. Influence of temperature on NO oxidation
103
-------
particularly unfortunate since the collection of most scrubbers used in
FGD systems are at a minimum in the 0.2 to 0.7 microns. A net increase
in the levels of ROM's and other potentially toxic organic compounds
would also reduce the appeal of a photochemical approach.
The generation of secondary reacuon products has been evaluated by
performing nitrogen, sulfur, and carbon material balance calculations a-
round the quartz CSTR and determining the fraction unaccountable. This
represented the maximum quantity of material which could be in the form
of toxic secondary products. Millipore filter samples were analyzed with
x-ray fluorescence and ion chromotoaraphy to evaluate the fraction of
missing sulfur and nitrogen which were in the form of sultate and nitrate
aerosols. The sulfate and nitrate content of wash waters of the reactor
and effluent gas lines was also added to complete the material balances
of sulfur and nitrogen.
For selected runs, samples of the reactor effluent were taken in 40-
liter Teflon bags and were analyzed at the UNC Pittsboro research site
where it was possible to convert the formaldehyde to CO for analysis in
the gas chromotography. For the same set of runs, gas samples were taken
in Tenax columns for GC-mass spectrometry. The purpose of these runs was
to identify possible toxic organic products present at low concentrations,
Nitrogen Balances
The fraction of the nitrogen compounds measurable with the chemilumi-
nescent analyzer are reported in Table 10. Low light and/or low propy-
lene conditions provide only limited photochemical activity; therefore,
most of the initial nitrogen can be accounted for as NO or measurable
NO compounds. As reactivity increases, it is apparent that the portion
A
of unaccountable nitrogen increases to 10 to 20% of the initial NO con-
A
centration. One possible reason for this is that the system has the
capability to proceed beyond the peak where some of the NO has been con-
A
verted to gaseous or aerosol forms which cannot be measured by the TECO
instrument. This unaccountable nitrogen amounts to a maximum of 120 ppm.
To determine the fraction of the nitrogen present as aerosol, some
of the Millipore filters (see Chapter 4, Figure 22} were analyzed using
ion chromotography. The oxygen test series (runs 127 to 136) which
104
-------
TABLE lOa. NITROGEN MATERIAL BALANCE, [NO ]0 ^600 PPM
Relative
Light Level
0
1/4
1/2
3/4
1
0 250
Hydrocarbon
1 .00
1.00
1.00
0.99
1.00
1.00
1 .06
0.96
0.92
0.94
500
Target
PPM (v
1.00
0.95
0.97
0.92
0.87
1000 1500
Concentration,
/v)
1.00
0.94
0.93
0.98
0.82
1.00
0.97
0.93
0.86
0.87
Runs
69 to 73
74 to 78
79 to 83
84 to 88
89 to 93
TABLE lOb. NITROGEN MATERIAL BALANCES, [NOV]0 =1200 PPM (v/v)
A
Relative
Liqht Level
0
1/4
1/2
3/4
1
0 250
Hydrocarbon
1.00
1.00
1.02
1.00
1.01
1 .00
0.99
0.98
0.95
0.99
500
Target
PPM (v
1 .00
1.00
0.95
0.97
0.97
1000 1500
Concentration,
/v)
1.00
0.97
0.95
0.96
0.90
1 .00
0.99
0.94
0.95
0.90
Runs
94 to 98
99 to 103
104 to 108
109 to 113
114 to 118
105
-------
exhibited substantial variability In NO conversion were used to identify
the possible range in quantities of nitrate aerosol. It should be noted
that the gas temperature at the filter point had generally cooled to
ambient levels; therefore, it is likely that most of the nitrate had con-
densed prior to collection. Observed nitrate levels expressed in terms
of ppm of NO are in the range of 1 to 5, trivial when compared with the
total NO unaccountable. The variability of the nitrate concentrations
in Table 11 does not appear correlated with the extent of NO conversion.
At regular intervals, the reactor was flushed with distilled water
to measure quantities of deposited material and to prevent major changes
in the light transmission properties of the CSTR. Deposits were highly
water soluble. Wet chemical analyses of the samples indicated very small
quantities of nitrates as indicated on Figure 39. Considering that ap-
proximately 30 runs were performed between each washing, the quantities
of nitrate represent less than 1% of the unaccountable fraction. Analy-
sis of the line rinse water at the end of the experimental program also
indicated that very little of the nitrates materials were deposited.
It is concluded that most of the unaccountable nitrogen is present
as gaseous material which is not adequately reduced in the converter of
the chemiluminescent analyzer. Possible compounds include, but are not
limited to, nitric acid, nitrous acid, and organic nitrates. Since the
chemical composition is uncertain and the concentrations may exceed 100
ppm, it must be concluded that some nitrogen compounds may represent
toxic reaction products.
Sulfur Balances
Very little change in $02 concentrations was observed during the
change from dark phase to light phase conditions in each of the runs.
As indicated in Table 12, the maximum drop was 5% and the normal drop
was in the range of 1 to 3%. These relatively small fractions represent
the maximum amounts of potentially toxic sulfur compounds formed in the
reactor. These quantities could be even smaller than suggested by the
material balance since NO,, formed during irradiation suppresses the S02
signal in the pulse fluorescent analyzer (refer to Chapter 4). Correct-
ing the light phase S02 concentrations according to the steady state N02
106
-------
Line Deposits (4-28-78)
Gram Moles N00"
Line 1
Sample 1
Sample 2
Line 2
Sample 1
Sample 2
Line 3
Sample
0
0
5.8x10
1.1x10
-5
-5
Quartz Reactor
L-Line 1
Teflon, 1/4" O.D
Reactor
Gram Mol
Date of Wash
3-15-78
3-23-78
4-5-78
4-14-78
4-27-78
Deposits
es N03"
2.9xlO~j?
5.0x10";?
7.0x10"^
1.4x10"°
3.0x10"°
Line 3, Teflon, 1/4
Figure 39. Nitrate deposits
-------
TABLE 11. NITRATE AEROSOL QUANTITIES COMPARED WITH NO OXIDATION
Run
127
128
129
130
131
132
133
134
135
136
90
91
114
115
116
117
118
ANO as
N03-, ppm
2.39
3.00
2.12
1.42
2.15
1.87
1 .96
1.98
2.52
2.50
3.05
4.78
2.91
2.08
1.44
1.78
2.22
ANO
ppm
404
990
493
626
392
558
126
120
559
781
285
464
27
247
339
517
594
ANO
%
37
95
98
61
69
95
12
24
96
69
44
76
3
25
34
51
60
TABLE 12. SULFUR MATERIAL BALANCE
Relative
Light Level
0
1/4
1/2
3/4
1
SULFUR MATERIAL BALANCE, CORRECTED
AND UNCORRECTED
Hydrocarbon Target Concentration,
PPM (v/v)
0 250 500 1000 1500
N.D. N.D. N.D. 1.00 1.00
N.D. N.D. N.D. 1.00 1.00
1.00 0.99 0.98 0.99 1.00
1.00 1.00 1.00 1.01 1.03
0.98 0.98 0.99 0.97 0.98
1.00 1.00 1.01 1.00 1.02
0.97 0.97 0.99 0.95 1.00
0.98 0.99 1.00 1.00 1.04
0.97 0.97 0.95 0.97 0.98
0.97 1.00 0.99 1.02 1.00
Runs
69 to 73
74 to 78
79 to 83
84 to 88
89 to 93
108
-------
levels and the relationship of Figure 18 accounts for most of the observed
SO,,. These corrected sulfur material balances are reported as the second
entry for each of the runs covered in Table 12. The amount of sulfur un-
accountable is very small and approaches the inherent errors involved in
reading the S0~ analyzer analog scale.
X-ray fluorescent tests for sulfur have been performed for all of
the runs of the experimental program. Results for runs 68 to 93 are pre-
sented in Table 13 in terms of the Appro of SCU. The very low quantities
of sulfate aerosol confirm expectations of insignificant S0? conversion.
This conclusion was checked further by performing ion chromatography
analyses on a selected group of the Millipore filters. Results present-
ed in Appendix B for each of the runs indicate that the sulfate levels
are conceivably 50% lower than those suggested by x-ray fluorescence.
No attempt was made to determine the most accurate analytical approach
due to the small quantities of sulfur in the aerosol form.
There was an order of magnitude more sulfate material than nitrate
material present in the reactor deposits and in the effluent handling
lines. The measured quantities have been expressed in terms of gram moles
of sulfate in Figure 40. These quantities are equivalent to approximately
3% of the sulfur unaccountable over the combined set of experimental runs.
It is concluded that sulfate aerosol or toxic sulfur compounds are not
formed in significant quantities in the photochemical system.
Carbon Material Balances
The extent of propylene consumption was a strong function of the
light intensity and the initial propylene concentration. With reactive
conditions 25 to 50% of the propylene reacted to form one or more degra-
dation products. The fraction accountable as propylene for runs 68 to
118 is presented in Table 14. This set of runs was chosen since the
quality of the Varian GC data was considered the best.
Possible reaction products accounting for the missing carbon include,
but are not limited to, formaldehyde, acetaldehyde, carbon dioxide, car-
bon monoxide, and organic aerosols. The Varian gas chromotograph res-
ults (a sample run output is shown in Figure 41) suggests that only one
or two major reaction products were formed. The large peak following
109
-------
Line Deposits
(4-28-78)
Line 1
Wash 1
Wash 2
Line 2
Mash 1
Wash 2
Line 3
Wash 1
Gram Moles
so4=
2.0x10"?
7.2X10"5
4.1xlO~a
1.0x10
l.SxlO"4
Line 2
SS, V O.D.
Line 1
Teflon, V O.D.
Reactor
Date of Wash
3-15
3-23
4-5
4-14
4-27
Deposits
Gram Moles
so4 =
4x1 0"J
2.7xlO"J
3.3x10": -
4.4xlO"r
1.7xlO~3
Line 3-
Teflon, V O.D.
Figure 40. Sulfate deposits
-------
60
50
•§, 40
•f~
0)
2:
eo
30
20
10
1 I i I I
Initial Dark Phase Injections
Propylene Propylene
Final Dark Phase
Injection
Light Phase Injection
Propylene
:etalde-
lend Acetaldehyde
Attenuation 32
ATT-32 Att-2 Att-32 Att-2
Time -*-*•
Figure *1. Typical gas chromatograph output
-------
TABLE 13. X-RAY FLUORESCENT SULFUR MEASUREMENT EXPRESSED AS APPM SO
Hydrocarbon Target Concentrations,
Relative PPM (v/v)
Light Level 0 250 500 1000 1500
0
1/4
1/2
3/4
1
0.80
N.D.
0.21
0.25
0.40
0.33
0.45
1.53
1.59
1.48
0.11
0.10
0.09
0.22
1,03
N.D.
0.18
0.12
0.37
0.80
N.D.
0.13
0.73
0.25
0.97
Runs
69 to 73
74 to 78
79 to 83
84 to 88
89 to 93
TABLE 14a. CARBON MATERIAL BALANCES. [NQ..]0 ^600 PPM (v/v)
Hydrocarbon
Relative
Light Level 0 250
0
1/4
1/2
3/4
1
N/A
N/A
N/A
N/A
N//L
1
0
0
0
0
.CO
.83
.73
.68
.51
Target Concentration,
PPM (v/v)
500 1000 1500
1
0
0
0
0
.00
nc
.OD
.83
.76
.50
1
0
0
0
0
.00
.91
.85
.73
.58
1.00
0.91
0.85
0.78
0.76
C9
74
79
84
89
Runs
to
to
to
to
to
73
78
83
88
93
TABLE 14b. CARBON MATERIAL BALANCES, [NOV]0 ^1200 PPM (v/v)
A
Hydrocarbon Target Concentration,
Relative PPM (v/v)
Light Level 0 250 500 1000 1500 Runs
0
1/4
1/2
3/4
1
N/A
N/A
N/A
N/A
N/A
N.D.
0.85
0.80
0.70
0.58
1.00
0.90
N.D.
0.76
0.56
0.99
0.89
0.86
0.76
0.60
1.00
0.93
0.89
0.82
0.65
94 to 98
99 to 103
104 to 108
109 to 113
114 to 118
112
-------
the propylene was identified as acetaldehyde and the very small peak di-
rectly proceeding it was presumed to be formaldehyde. Due to the limited
ability of the Varian to detect formaldehyde, bag samples were taken for
a limited group of runs so that the effluent could be analyzed at the
UNC Pittsboro research site. The formaldehyde was converted to carbon
monoxide and the treated effluent was analyzed on a Carle II gas chroma-
to graph. The result of the special GC tests are presented in Table 15.
The total aldehyde concentration (formaldehyde and acetaldehyde) account-
ed for 20 to 50% of the missing carbon. The major product was the for-r
maldehyde which was generally present at concentrations of 1 to 3 times
the levels of the acetaldehyde. The observed aldehyde concentrations
displayed a strong correlation with the extent of NO conversion indica-
ting that these are principal reaction products in propylene degradation
and that the subsequent reaction of the aldehydes is incomplete. This
is consistent with the observations in previous sections that aldehydes
would compete only weakly for hydroxy radicals and would not photolyze
rapidly under light limited conditions.
It is possible that the actual aldehyde concentrations are somewhat
higher than indicated in Table 15. The observed propvlene concentrations
were approximately 50% lower than the corresponding values measured dur-
ing the run using the Varian GC. Part of this difference could be due to
decay by further reaction of the gas mixture during transport to the
Pittsboro site. Elapsed times of 2 to 4 hours occurred between the time
of sample acquisition and analysis due to the 18 mile distance between
the labs and the difficulty in coordinating the runs with the transpor-
tation. The importance of this delay was evaluated by taking repeated
readings on a bag sample which was not transported. The rate of propy-
lene and acetaldehyde decay are apparent in Figure 42. Both compounds
exhibit a first order rate of decay of 5% which is represented by the
dotted line. If this is characteristic of the other bag samples, the
aldehyde concentrations reported in Table 15 could be 10 to 15% higher.
While decay of the samples accounts for some of the difference in
observed propylene concentrations there remains some difference between
the two sets of GC data. The Varian data is considered more reliable
113
-------
TABLE 15. CARBON BALANCE CORRECTIONS FOR ALDEHYDES
Run
%C Unaccounted for as C^Hg
APPM C as C3Hg
Measured [C3Hg]ss vs. Actual [C3Hg]ss ,
Measured HCHO, ppmC
Measured CH3CHO, ppmC
Total RCHO, ppmC
%C Unaccounted for as RCHO
%C Unaccounted, Corrected for RCHO
102
10.9
600
% 54
250
58
308
51
5.4
107
13.6
540
46
N.D.
32
32
6
12.8
112
24.4
1035
62
325
114
439
42
14.1
115
42.1
372
100
195
60
255
69
13.2
116
44.4
840
51
186
104
290
35
29
117
40.5
1602
N.D.
315
42
357
22
32
118
35.0
1941
N.D.
348
212
610
31
24
-------
20
10
NOTE: Curves represent calculated first
order decay rate of 0.05/nT1
I
I
I
8 PM 12 PM 4 AM 8 AM 12 Noon
Figure 42. Aldehyde/propylene decay in sampling bags
115
-------
TABLE 16. RELATIONSHIP BETWEEN ALDEHYDE FORMATION AND NO OXIDATION
HCHO CH.CHO ANO
Run ppm ppm ppm
102 250 58 156
107 N.D. 32 219
112 325 114 334
115 195 60 247
116 186 315 339
117 315 42 517
118 398 212 594
116
-------
since the absolute values agree within 10% of the propylene tank concen-
tration and the observed gas stream flow rates.
Following inclusion of the aldehydes, the carbon material balances
approach 80 to 95%. It is conceivable that the remaining fraction is
partially composed of polycyclic organic matter and/or other potentially
toxic organic compounds. To evaluate this possibility, a selected series
of runs were performed with Tenax sampling columns. These were analyzed
using a GC mass spectrometer at the Research Triangle Institute. The prin-
cipal compounds identified in the 10 test samples are reported in Table
IT. In all of these tests, acetaldehyde and acetic acid were present in
small but nevertheless significant quantities. The other compounds were
present on an irregular basis and generally in much smaller quantities.
It is very unlikely that some of the observed compounds actually
originated in the photochemical system. For example, methylene chloride
is used in the extraction step of the Tenax column treatment. Also, there
are not halogenated precursors which could explain the presence of hexa-
fluorobenzene and trichloroethylene. It must be assumed that these com-
pounds and possibly some of the others in the upper group actually entered
by way of the dilution air stream (refer to Figure 22) or were contami-
nants in the GC mass spectrometry laboratory.
The main conclusion drawn from the mass spectrometer results is that
a large number of organic compounds are formed; however, the total concen-
tration of such compounds measurable by the GC mass spectrometer is very
small.
COST ESTIMATES
Photochemical system capital and annualized cost estimates have been
prepared based on the experimental results discussed earlier. The basis
of these calculations is the model system presented in Chapter 4. The
cost estimates are indicative only of a propylene system as studied in
this project. A more reactive hydrocarbon could conceivably allow a more
economical system without the problem of unreacted hydrocarbon emissions.
Development of improved ultraviolet lamps and reflectors could also have
a major impact on the capital and annualized costs. For these reasons,
the propylene system costs are considered a maximum cost for a photo-
117
-------
TABLE 17. MAJOR ORGANIC COMPOUNDS DETERMINED IN GC/MS TESTS. PPM (y/y)
CO
acetoni trite
acetaldehyde
C^HgO isomer
pfopylene oxide
nitromethane
4-methyl-l ,3-dioxolane
acetic acid
acetone
methyl formate
methyl nitrate
butyl formate
ethyl ene
pro penal -Hn ethyl ether
toluene
xylene isomer
alkyl dioxolane
acetophenone
methyl ene chloride
hexafluorobenzene
m-hexane
trichloroethylene
RUN
117 115 118 117- 107
3.1 1.4 4.8 1.2 4.7
1.1 0.5 2.3 0.7
0
1.3 0.44 2.1
24.8 13.2 1.6 1.6 3.2
1.1 1.1
2.0
1.1
0.4
107 101 116
4.8 2.4
1.6
2.8 3.6 2.3
1.0
1.7
1.8
0.18
>3000 A filter in place.
-------
chemical system for NO oxidation.
Model Plant Characteristics
The cost estimates have been prepared for a 500-megawatt base
loaded coal-fired boiler. It is assumed that no combustion modifications
have been made to suppress NO formation end that the average inlet concen-
A
tration is 600 ppm (v/v). Cost estimates were not prepared for the 1200
ppm (v/v) case since the results indicated maximum NO oxidation efficien-
cies of only 50%.
Irradiation of the effluent gas stream is accomplished in a set of
cylindrical reactors (stainless steel) with medium pressure mercury arc
lamps mounted on vertical supports along the centerline of the reactor.
Baffles are included to improve mixing of the gas stream. The reactors
are connected in parallel directly following the electrostatic preci pita-
tor so that flyash abrasion of the optical surfaces is minimized. A sys-
tem of propylene distribution pipes is located in the breeching leading
to the reactor. Liquified propylene is stored in spherical tanks (stain-
less steel). Sufficient supply for 2 months continuous operation is kept
on site.
Absorption of the N02 formed in the photochemical reactor would be
accomplished in conventional flue gas desulfurization system. It is as-
sumed that absorption occurs according to reactions 49 and 50. Unlike
nitric acid absorption towers, there does not appear to be any NO regene-
ration.
2N02(g) + 350-^, £* ZNOj^j + 2HSO;|,j + SO^, , + 2H+ (49)
4S03~fl) + 2N02(1)~ %) *«»i?l) (50)
Approximately 10 to 50% of the absorbed N02 is ultimately corrected to
N03" salts (Faucett et al . , 1977). Presumably, the remainder is absorbed
according to reaction 50. Laboratory scale work done by Chappel (1973)
indicates that sulfite scrubbing liquors such as used in some FGD systems
provide high efficiency NOg removal. Based on this work complete N02 ab-
sorption will be assumed. No credit will be taken for possible NO absorp-
tion which in some cases appears to reach 10 to 20% (Chappel, 1973). Due
to the very high solubilities of nitrites and nitrates, it is unlikely
119
-------
that any scaling will occur in the FGD system as a result of the photo-
chemical system. Disposal of the nitrites and nitrates will be done at
the same time that the calcium sulfite and calcium sulfate sludges are
treated.
The system costs are limited to only those items needed in addition
to the conventional FGD system. These include the propylene storage and
distribution system, the photochemical reactor and lamps, and the elec-
trical costs.
Model Plant Costs
The dominant cost components are the propylene cost and the electri-
cal power costs. The latter were calculated from the k, level using
equation 1 developed in Section 5. Based on the spectral effects runs
(numbers 1 to 8), it was apparent that the $Ng ca-|c/*Ng factor is in the
range of 3 to 5. A value of 3 was used in conjunction #ith Figure 9,
which relates the product quantum yield with the required electrical
power. This biases the results high with respect to electrical costs.
Results of the propylene test series (runs 19 to 118) indicate that
the desired NO reduction could be achieved at various combinations of
propylene and UV light intensities. The possible operating conditions
are indicated as isopleths on Figures 28 to 31. For several levels of
NO control, the optimum operating point with respect to combined energy
and propylene cost was determined by trial and error methods. The opti-
mal operating conditions are the high UV light/low propylene regions of
Figures 27 to 30. This is desirable in another sense since unreacted
hydrocarbon emissions are also minimized in these regions. For these
reasons, operating points shown in Table 18 have been selected for the
cost evaluations.
The cost of propylene is based on reports in the Chemical Marketing
Reporter (1979). The quoted price has been stable for over a year. An
excess supply is forecast for at least the next 2 years (Ponder, 1978);
therefore, it is unlikely that substantial price increases will occur.
The quantities for the model plant represent 0.00075 of the national pro-
duction rate.
Electrical costs have been assumed to be 30 mills per kWh. This is
120
-------
equivalent to the purchase of power for some utilities. The relatively
high costs have been used to account for use of gas turbines to supple-
ment generating capacity during peak periods.
The installed capital costs of the reactors and the storage tanks have
bee based on the costs reported in Peters and Timmerhaus (1968). These
have been updated to January 1979 using the CE factors as reported in
Chemical Engineering (1979). The lamp and power supply costs are based
on Canrad Hanovia lamp HST. These costs have also been updated
The calculated costs have been reported in Tables 18 and 19. Each
of these includes four separate columns for various levels of NO oxida-
tion. It is assumed that in most cases it would be desirable to reduce
the NO by 500 PPM in order to achieve the stated EPA objectives. The
other columns are presented to indicate the sensitivity of cost to NO
control level and to facilitate comparisons with cost estimates of other
systems most of which are applicable to 300 pprn NO oxidation. The capi-
tal cost estimates range from 37 to $50 per KW, depending on the number
of UV lamps required. This is approximately 1/2 the cost for a limestone
based flue gas desulfurization system (PEDCo., 1975). The annualized
costs range from 3.8 to 5.6 mills per kWh. This is higher than origi-
nally anticipated due partially to poor propylene reactivity. A compari-
son of the reported costs for various flue gas treatment processes is
presented in Table 20. The photochemical system is obviously much less
costly than the various NO oxidation-N02 absorption processes. The
reason that photochemistry is more attractive than the latter is the high
cost of the ozone generating facility ($40/kW and 2.7 mills/kWh). The
NH- injection technique is considerably more attractive based on the
present cost estimates. These two systems, however, are subject to
serious operational problems which have been discussed in earlier sec-
tions.
Based on the photochemical system cost estimates, it appears that a
system based on propylene is only marginally competitive. Commercial
utilization of the process would be unlikely unless there were serious
operational problems in the selective noncatalytic and selective cataly-
tic reduction techniques. Several improvements in the photochemical sys-
tem could substantially improve the marketability of the technique. For
121
-------
TABLE 16. CAPITAL COST ESTIMATES
ro
ro
Cost Component
Direct Costs
Lamp and Power Supplies
Propylene Distribution
Subtotal Direct
Indirect Costs (42% Direct
Cost)
Subtotal Direct and
Indirect Costs
Contingency and Fees (25%
Direct and Indirect Costs)
Subtotal (lamps and
distribution system)
Subtotal (reactors)
Subtotal (propylene
stage)
TOTAL
$/kW
COST, $
500
5,300,000
1,000,000
6,300,000
2,646,000
8,946,000
2,236,500
11,182,500
12,380,000
1,343,283
24,905,783
50
A PPM NO
400 300
4,321,540
1 ,000,000
5,321,540
2,235,046
7,556,586
1,889,146
9,445,733
12,380,000
1,343,283
23,169,017
46
3,261 ,540
1 ,000,000
4,261,540
1,789,847
6,051,387
1,512,846
7,564,234
12,380,000
1,343,283
21,287,518
43
200
1,793,846
1,000,000
2,793,846
1,173,415
3,967,261
991,815
4,959,076
12,380,000
1,343,283
18,682,359
37
-------
TABLE 19. ANNUALIZED COSTS
ro
CO
ANO, ppm A500-
A.
B.
C.
D.
E.
F.
Raw Materials
Utilities 5,031,000
Operating Labor
Direct
Supervision
Subtotal
Maintenance
Labor and
Materials
Supplies
Subtotal
Overhead
Plant
Payrol 1
Subtotal
Fixed 5,058,205
TOTAL 14,579,370
MILLS/kWh 5.65
A400
1 ,800,000
4,102,200
175,200
26,280
201,480
1,389,900
208,489
1,598,389
900,000
40,300
940,300
4,705,627
13,347,966
5.15
A30(£ A20(£
3,096,000 1,548,000
4,323,495 3,794,307
11,914,630 9,832,387
4.62 3.81
^Detailed cost components not shown. These can be calculated as a ratio of
A400 values.
-------
TABLE 20. COMPARISON OF COSTS FOR FLUE GAS TREATMENT PROCESSES
Technique
Photochemical System
Selective Non-Catalytic
Reduction
Selective Catalytic
Reduction
Radiation Oxidation
NO Oxidation/NO,, Absorption
NO Absorption, liquid
phase condition
£ ppm NO
500
400
300
200
200
200-300
200-300
200-300
125
Capital
Cost
$/kW
50
46
43
37
N.D.
10-36
100-1000
84-134
65-130
Annual i zed
Cost
Mills/kWh
5.65
5.15
4.62
3.81
0.75-1.60
0.20-1.80
N.D.
6.7-8.9
4.8-7.4 ~
N.D. - NO Data Available
124
-------
example, development of more efficient lamps or lamps with effective re-
flectors could allow installation of the lamps in the electrostatic pre-
' )f»i »'iM/f •.. UH-M-K/ 'illowlri'j «•! irnj nation of the very expensive reactors.
This would have a secondary benefit since the reaction products would
serve to reduce resistivity. Use of a more reactive hydrocarbon would
reduce hydrocarbon demand and possible reduce the light energy require-
ments. A photochemical system based on hexene or acetone could concei-
vably operate at capital and annualized costs less than 1/2 those pre-
sented here for the propylene system.
125
-------
REFERENCES
1. Acurex Corporation (1977). EPA Stationary Source Combustion Control
Technology Program - FY1976. EPA Publication EPA-600/7-77-077,
July 1977.
2. Acurex Corporation (1978). Control Techniques for Nitrogen Oxides
Emissions from Stationary Sources - Second Edition. EPA Publication
EPA-650/2-76-001, January 1978.
3. Armento, W. J. (1975). Effects of Design and Operating Variables on
NOX from Coal-Fired Furnaces - Phase II. EPA Publication EPA-650/2-
74-002b, February 1975.
4. Browne, W. R. and Stone, E. E. (1965). Sulfur Dioxide Conversion
Under Corona Discharge Catalysis. Final Report, U. S. Public Health
Service Contract No. PH 86-67-2, March 1965.
5. Batayko, R. (1979). Personal Communication, March 1979.
6. Calvert, J. G., Su, F., Bottenheim, J. W., and Strauss, 0. P. (1977).
Mechanism of the Homogeneous Oxidation of Sulfur Dioxide in the
Troposphere. Atmospheric Environment, Volume 12, Pages 197-226,
February 1977.
7. Canrad Hanovia (1973). Publications B0238 and L0238, November 1973.
8. Chappell, 6. A. (1973). Development of Aqueous Processes for Removing
NOX from Flue Gases. EPA Publication EPA-R2-73-051, June 1973.
9. Anonymous (1979). Economic Indicators. Chemical Engineering, Volume
86, No. 2, Page 7, January 15, 1979.
10. Anonymous (1979). Current Prices. Chemical Marketing Reporter,
Volume 215, No. 4, Page 45, January 22, 1979.
11. Christian, S. D. and Grundnes, J. (1967). Charge Transfer Complex
Between Sulfur Dioxide and Trimethyl amine in the Gas Phase and in
Heptane. Nature, Volume 214, Pages 1111-1112. 1967.
12. Corbett, W. E. Jones, G. D., Micheletti, W. C., Wells, R. M., and
Wilkens, G. F. (1978). Assessment of the Need for NOX Flue Gas
Treatment Technology. EPA Publication EPA-600/7-78-215, November, 1978.
126
-------
13. Crawford, A. R., Manny, E. H., and Bartok, W. (1977). "Application
of Combustion Modifications to Power Generating Combustion Sources"
in Proceedings of the Second Stationary Source Combustion Symposium;
Volume II, Utility and Large Industrial Boilers. EPA Publication
EPA-600/7-77-073b, Pages 3-40, July 1977.
14. Ctvrtnicek, T. E., and Rusek, S. N. (1977). "Cyclone Boilers - Their
Emissions and Population" in Proceedings of the Second Stationary
Source Combustion Symposium-, Volume II, Utility and Large Boilers.
EPA Publication EPA_600/7-77-073b, Pages 123-142, July 1977.
15. Demerjian, K. L., Kerr, J. A., and Calvert, J. 6. (1975). "The
Mechanism of Photochemical Smog Formation" in Advances in Environmental
Sciences and Technology, Volume 4, Pages 1-213, 1975.
16. Dols, M. 0. and Boknoven, C. (1974). Process for the Photochemical
Oxidation of NO to N02. U. S. Patent 3,120,479, Issued February 4.
1979.
17. Dykema, 0. W. (1978). Combustion Modification Effects on NOX Emissions
from Gas-, Oil-, and Coal-Fired Utility Boilers. EPA Publication
EPA-600/2-78-217, December 1978.
18. Faucett, H. L., Maxwell, J. D., and Burnett, T. A. (1977). Technical
Assessment of NOX Removal Processes for Utility Applications. EPA
Publication EPA-600/7-77-127, November 1977.
19. Hamm, J. R. (1965). Study of Physiochemical Techniques for Removal
of S02 from Stack Gases. Final Report, U.S Department of Health,
Education and Welfare Contract, November 1978.
20. Harrison, L. J. (1976). Technology and Economics of Flue Gas NOX
Oxidation by Ozone. Final Report, EPA Contract 68-02-1325, November
1976.
21. Heap, M. P., Tyson, T. J., Carver, G. P., Martin, G. B., and Lowes,
T. M. (1976). "The Optimization of Burner Design Parameters to
Control NOX Formation in Pulverized Coal and Heavy Oil Flames" in
Proceedings of the Stationary Source Combustion Symposium EPA
Publication EPA-600/2-76-152b, June 1976.
22. Howe , J. P., and Noyes, W. A. Jr. (1936). Photochemical Studies
XXIII, The Photochemical Decomposition of Acetone Vapor Near 1900 A.
A Comparison with the Decomposition at Longer Wave Lengths. Journal
of The American Chemical Society, Volume 58, Pages 1404-1412, 1936.
23. Jeffries j n.E. Photochemical Kinetic Simulation System, Version 2a.
Unpublished Report. June 1977.
24. Kemp, V. E., and Dykema, 0. W. (1977). "Inventory of Atmospheric
Emissions from Stationary Point Sources" in Proceedings of the Second
Stationary Source Combustion Symposium, Volume II, Utility and Large
Boilers. EPA Publication EPA-600/7-77-073b, Pages 257- 278, July 1977.
127
-------
25. Lachapelle, D. (1979). Personal Communication, May 1979.
26. Levenspeil, 0. (1972). Chemical Reaction Engineering. John Wiley
and Sons Publishing Co, New York, 1972.
27. Machi, S., Kawamura, K., Dawaakami, W., Aoki, S., Hashimoto,S.,
Yotamoto, K., and Sunaga, H. (1975). Process for the Photochemical
Oxidation of NO to N02« U. S. Patent 3,869,362, Issued February 4
1975.
28. Mason, H., Shimiza, A., Ferrell, J., Poe, G., Waterland, L., and
Evans, R. (1977). Preliminary Environmental Assessment of Combustion
Modification Techniques; Volume II, Technical Results. EPA Publica-
tion EPA-600/7-77-119b, October 1977.
29. McCutchen, G. P. (1977). NOx Emission Trends and Federal Regulation.
Chemical Engineering Progress, Page 38, August 1977.
30. Muzio, L. J., and Arand J. K. (1976). Homogeneous Gas Phase De-
composition of Oxides of Nitrogen. Electric Power Research Institute
Publication FP-253, August 1976.
31. National Academy of Sciences, Subcommittee on Nitrogen Oxides (1977).
Ozone and Other Photochemical Oxidants. EPA Publication EPA-600/ 1-
77-013, February 1977.
32. PEDCo Environmental (1975). Flue Gas Desulfurization Process Cost
Assessment. Final Report, Environmental Protection Agency Contract
No. 68-01-3150, May 1975.
33. Peters M. S., and Timmerhaus, K. D. (1968). Plant Design and
Economics for Chemical Engineers. Second Edition.McGraw Hill Book
Company, 1968.
34. Ponder T. (1978). U. S. Propylene: Demand vs. Supply. Hydrocarbon
Processing, Volume 57, Number 7, Pages 186-188, July 1978.
35. Ricci, L. J. (1977). Nixing NOX Emissions. Chemical Engineering,
Volume 84, Number 4, Pages 84-89, April 11, 1977.
36. Richards, J., Fox, D., and Reist, P. (1976). The Influence of
Molecular Complexes on the Photooxidation of Sulfur Dioxide.
Atmospheric Environment, Volume 10, Pages 211-217, 1976.
37. Salvesen, K. G., Wolfe K. J., Chu, E., and Herther, M. A. (1978).
Emission Characterization of Stationary NOX Sources; Volume I, Results,
EPA Publication EPA-650/7-78-120a, June 1978.
38 Selker, A P. (1975). Program for Reduction of NOX from Tangential
Coal-Fired Boilers, Phase II. EPA Publication EPA-650/2-73-005a,
June 1975.
128
-------
39. Sickles, J. E. II, and Jeffries , H. E. (1975). Development and
Operation of a Device for the Continuous Measurement of ka for
Nitrogen Dioxide. University of North Carolina at Chapel Hill,
Department of Environmental Sciences and Engineering Publication
ESE-396, June, 1976.
40. Thompson, R. E.,and McElroy, M. W. (1976). Effectiveness of Gas
Recirculation and Staged Combustion in Reducing NOX on a 560 MW
Coal-Fired Boiler. Electric Power Research Institute Publication
FP-257, September 1976.
41. Wolf, D., and Resnick, W. (1963). Residence Time Distribution in
Real Systems. Chemcial Engineering Progress, Volume 2, Pages 283-
293, 1963.
42. Yeager, K E., and Teixeira, D. P. (1977). "The EPRI Program on NOX
Control Using Combustion Modification Techniques" in Proceedings of
the Second Stationary Source Combustion Symposium; Volume II, Utility
and Large Boilers. EPA Publication EPA-600/7-77-073b, July 1977.
129
-------
APPENDIX A
Reactor Flow Characterization
130
-------
I I I I
0.1
0.01
Tracer Curve for 3.0 LPM
Observed Data Points
Calculated Curve
I I I I
I
Calculated
Results
I I
I I I tilll
i
0.2 0.4 0.6 0.8 1.0 1.2
t/t •*-*
1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
Appendix A Curve 1
-------
CO
INJ
0.0
Tracer Curve for 2.0 LPM
Observed data points
Calculated curve
I
J_
I
_L
I
Calculated Results
a = 0.92
p = 0.08
d = 0.02
.f = 0.06
I
I
I
I
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
t/t-^
Appendix A Curve 2
2.8 3.0
-------
1.0
-l->
u_
I
0.1
CO
0.01 —
I I
Tracer Curve for 1.5 LPM
uoserved Data Points
calculated Curve
J
I
1
L
1
1
Calculated Results
a = 0.91
p = 0.09
d = 0.02
f = 0.06-
i.
J
L
0 0.2 0.4 0.6 0.8 1.0 1.2 1-4 ] 6 ] >8 2.0 2.2 2.4 2.6 28 30
t/t
Appendix A Curve 3
-------
1.0
I
I
I
Calculated Results
a = 0.92
p = 0.08
d = 0.02
f = 0.06
0.1
Tracer Curve for 1.0 LPM
Observed Data Points
Calculated Curve
0.01
I I
0 0.2 0.4 0.6 P.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
Appendix A Curve 4
-------
APPENDIX B
Experimental Results
135
-------
TABLE B-l. EXPERIMENTAL DATA, INFLUENCE OF MIDDLE UV
FILTER ON NO OXIDATION.
Run Number
Chronological No.
Conditions
[N0]0» ppm
[C3Hg]0, ppm
[S02J0> ppm
[02L %
k, , min
T, min
Temp., °F
Filter >
Gas Analyses
ANO, ppm
NO Oxid., %
[N02J, ppm
[NOX]/[NOXL
AC-H.., ppm
6 0
ANO/A C3H6
ASOp, ppm
S0? Oxid., %
Filter Analysis
XRF, ppm S02
1
81
596
N.D.
1500
4.5
0.124
0.783
251
o
1800, A
223
37.5
202
0.929
N.D.
N.D.
64
4.3
0.01
2
84
665
1441
1478
4.7
0.248
0.758
274
0
>1800 A
367
55.2
283
0.929
168
2.18
37
2.5
0.01
3
79
626
1355
1339
4.5
0.34
0.760
272
o
>3000 A
108
17.3
92
0.957
194
0.56
27
2.0
0.01
4
77
637
1390
1485
4.0
1.20
0.755
277
o
>1800 A
599
95.6
535
0.88
256
2.34
86
5.8
0.07
136
-------
TABLE B-l (continued)
Run Number
Chronological No
Conditions
[N0]0, Ppm
[C3Hg]0, ppm
[S02L ppm
[o2], %
k, , min"
T, min
Temp., °F
Filter
Gas Analyses
ANO, ppm
NO Oxid., %
[NOJ, ppm
[NO 1/[NO 0]
A A
AC3H6, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
5
. 82
608
N.D.
1457
4.5
0.08
0.764
269
o
>3000 A
16
2.6
31
1.00
N.D.
N.D.
16
1.1
N.D.
6
83
655
1302
1460
4.7
0.158
0.760
272
o
>3000 A
36
5.5
41
0.982
77
0.47
26
1.8
N.D.
7
80
610
1415
1393
4.4
0.68
0.758
274
0
>1800 A
567
93.0
481
0.832
281
2.02
108
7.8
0.04
8
78
616
1360
1312
3.8
0.60
0.737
295
0
>3000 A
448
72.7
394
0.895
161
2.78
59
4.5
0.03
137
-------
TABLE B-2. EXPERIMENTAL DATA, INFLUENCE OF SULFUR DIOXIDE
ON NO OXIDATION. uiuAiut
Run Number
Chronological No.
Conditions
[NOX]0, ppm
[C3H,]0, ppm
[S02]0, ppm
[02L %
k, , min"
, min
Temp., °F
Gas Analyses
NO, ppm
NO Oxid., %
[N02L ppm
[NOx]o/[NOx]0
C_H, , ppm
NO/ C,HR
•3 D
S02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
9
49
1068
837
510
4.3
4.1
0.768
266
902
88.8
807
0.861
300
3.0
48
9.4
0.08
10
50
550
990
540
4.4
4.52
0.758
274
541
99.2
462
0.836
376
1.44
92
16.9
0.08
11
51
550
819
1066
4.3
4.52
0.753
279
526
98.8
464
0.855
N.D.
N.D.
44
4.2
0.07
12
52
577
790
0
4.2
4.52
0.753
279
555
98.4
493
0.869
N.D.
N.D.
0
0
N.D.
(continued)
138
-------
Run Number
Chronological No.
Conditions
[NOjo. PPm
X
[CoH/-]o ' PP"1
[S02]0, ppm
[02], I
k, , min~
T, min
Temp. , °F
Gas Analyses
AND, ppm
NO Oxid., %
[N02], ppm
[NOx]/[NOx]0
AC3H6, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid. , %
Filter Analyses
XRF, ppm S02
13
53
1203
790
1119
4.5
4.52
0.753
279
928
77.4
804
0.893
359
2.58
62
5.6
0.15
14
1248
818
3241
4.0
4.51
0.750
282
857
69.2
675
0.847
321
2.67
133
4.1
0.04
15
55
506
877
1332
4.3
4.52
0.767
266
479
98.2
426
0.860
189
2.54
67
5.0
0.08
16
56
528
819
3197
4.3
4.63
0.767
266
497
97.4
448
0.874
N.D.
N.D.
133
4.2
N.D.
(continued)
139
-------
TABLE B-2 (continued)
Run Number
Chronological No.
Conditions
[N0x]0, ppm
[C3H6L, ppm
[S02]0, ppm
[0?], %
*- _i
k, , min
, min
Temp. , °F
Gas Analyses
NO, ppm
NO Oxid., %
[N02L ppm
[NOj0/[NOjo
A A
C-jHg, ppm
NO/ C.,H_
•j b
S02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
17
57
1199
643
1368
4.7
4.52
0.758
274
972
87.6
861
0.889
N.D.
N.D.
71
5.2
N.D.
18
58
1106
702
0
4.2
4.52
0.764
269
941
86.9
826
0.276
219
4.30
0
0
0.02
140
-------
TABLE B-3. EXPERIMENTAL DATA, INFLUENCE OF PROPYLENE CONCENTRATION
AND UV LIGHT INTENSITY Oil ON OXIDATION.
Run Number
Chronological No.
Conditions
[NOX]0 ppm
[C3H6]0 ppm
[so2]0
[02] %
k, , min"
1
T, min
Temp., °F
Gas Analyses
AND, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC3H6, ppm
ANO/AC-H,
«J O
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
19
39
592
0
1492
4.3
0
0.794
241
0
0
14
1.00
0
_
N.D.
N.D.
0.01
20
47
569
331
1374
4.5
0
0.786
248
0
0
9
1.00
16
0
N.D.
N.D.
N.D.
21
28
548
475
1772
4.6
0
0.788
246
0
0
14
1.02
N.D.
N.D.
0
0
N.D.
22
18
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
141
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0x]0 ppm
[C~H ]0 ppm
[so2]0
c.
[02] I
k, , min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid. , %
[N02], ppm
[NOx]/[NOx]0
AC^H, , ppm
ANO/AC-Hg
A Qft n run
n ou n > p pin
SO, Oxid., %
<:
Filter Analyses
XRF, ppm S02
23
34
557
1856
1446
4.5
0
0.813
225
0
0
14
1.00
N.D.
N.D.
N.D.
N.D.
0.04
24
40
597
0
1492
4.6
0.10
0.781
253
23
3.8
27
0.992
0
-
9
0.6
0.02
25
7
542
246
1487
4.2
0.10
0.750
282
155
0.289
115
0.918
0
-
44
3.0
N.D.
26
23
512
394
1386
4.3
0.38
0.758
274
155
31.4
155
0.967
N.D.
N.D.
0
0
0.01
(continued)
142
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0x]o» ppm
[C3H5L, ppm
[S02]0, PPf"
[02L °/°
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, min
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC3H6> ppm
ANO/AC3H6
AS02, ppm
so2, %
Filter Analyses
XRF, ppm S09
L.
27
17
497
905
1439
4.5
0.38
0.794
241
244
50.5
222
0.929
0
-
44
3.0
0.02
28
6
529
1788
1615
4.8
0.38
0.764
269
356
67.2
300
0.942
80
4.45
94
5.8
0.02
29
25
529
0
1431
4.3
0.96
0.758
274
37
7.0
32
0.982
0
-
37
2.6
N.D.
27
566
247
1558
4.2
0.96
0.767
266
183
33.1
159
0.933
N.D.
N.D.
5
0.3
0.03
(continued)
143
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOX]0, ppm
[C3H6L, ppm
[S02]oi Ppm
[02L %
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, min
NO Oxid., %
[N02], ppm
[NOx]/[NOx]0
AC3H6, ppm
ANO/AC-H,.
AS02, ppm
so2, %
Filter Analyses
XRF, ppm S02
31
7
566
519
1700
4.0
0.72
0.764
269
269
47.5
222
0.958
74
3.61
71
4.2
0.02
32
36
561
979
1333
4.3
0.33
0.767
266
363
66.4
331
0.918
280
1.30
68
5.1
0.03
33
44
565
1850
1275
4.3
0.47
0.774
259
454
81.5
398
0.886
162
2.81
34
2.7
N.D.
34
45
565
0
1425
4.2
0.41
0.764
269
39
6.9
34
0.977
0
-
47
3.3
N.D.
(continued)
144
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NO ]0» PPm
X
[C-jHglo, ppm
[S02]0> PPm
[o2], %
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
[NOX]/[NOX]0
AC,H,-> ppm
ANO/ AC^ H£
j b
ASO~, ppm
L.
S0? Oxid. , %
Filter Analyses
XRF, ppm S02
35
41
555
331
1381
4.5
1.37
0.768
264
262
48.0
226
0.920
126
2.08
4
0.3
0.05
36
33
524
475
1550
4.6
1.83
0.758
274
317
61.6
262
0.877
N.D.
N.D.
46
3.0
0.03
37
46
586
475
1395
4.5
1.11
0.760
272
471
81.5
411
0.883
153
3.07
51
3.7
N.D.
38
15
606
2108
1761
5.3
1.37
0.783
251
585
98.4
528
0.889
0
-
71
4.1
0.16
(continued)
145
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NO lo, ppm
X
[C3H6L, pom
[S02]o, ppm
[02L %
k , min ,
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOXL
AC-jHg, ppm
ANO/AC3H6
ASOp, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm SO 2
39
31
538
475
1498
4.9
3.68
0.750
282
61
11.5
61
0.983
N.D.
N.D.
37
2.5
0.44
40
38
505
344
1465
4.6
3.21
0.745
287
342
57.9
275
0.880
200
1.70
71
4.8
0.07
41
35
524
475
1460
4.5
2.40
0.764
269
389
75.4
344
0.897
283
1.38
18
1.2
0.02
42
22
502
979
1442
4.2
3.21
0.774
259
481
98.3
418
0.850
N.D.
N.D.
64
4.3
N.D.
(continued)
146
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0x]o, PP
[C3H6]0, ppm
[S02]0» Ppm
[o2], %
k, , min
T, min
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
[NO l/[NOy]0
A A
AC3Hg, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
43
12
534
1738
1685
4.0
3.21
0.772
505
0.973
440
0.851
217
2.33
47
2.8
0.11
44
32
1150
0
1481
4.5
0
0.788
0
0
9
1.00
N.D.
N.D.
0
0
0.04
45 46-
30
955
265
1488
4.6
0
0.797
0
0
14
N.D.
N.D.
N.D.
N.D.
N.D.
N.D.
missng
(continued)
147
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOX]0, Ppm
[C3H6]0, ppm
[S02]0, ppm
[OJ, %
_]
k,min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
[NOX]/[NOX]0
AC3H6, ppm
ANO/AC3H&
ASOp, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
47
42
1055
1072
1386
4.3
0
0.810
9
0.8
17
1.00
0
0
f!.r;.
N.D.
N.D.
48
48
1327
2066
1340
4.7
0
0.792
9
0.6
21
1 .00
N.D.
N.D.
N.D.
N.D.
N.D.
49
3
1217
0
1615
4.3
0.32
0.758
274
0
0
23 ,
1.00
0
0
19
1.2
0.01
50
13
1030
243
1615
4.8
0.18
0.768
264
103
10.1
103
0.990
0
-
23
1.4
0.01
(continued)
148
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOX]0, ppm
[C3H6]0, ppm
[S02]0» PP1"
[02], %
k, , min"
T, min.
Temp., °F
Gas Analyses
AND, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC3Hg, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
51
14
1095
562
1714
4.8
0.18
0.794
241
138
12.8
133
0.983
0
•-
0
0
0.01
52
21
1018
937
1576
4.5
0.25
0.783
251
158
16.6
200
0.975
0
-
64
4.1
0.02
53
16
1028
1917
1547
4.3
0.38
0.768
264
271
26.8
262
0.977
0
-
24
1.5
0.02
54
5
1123
1886
1451
4.
0.
0.
269
460
41
398
0
98
4
70
4
0
8
72
,764
.0
.917
.69
.8
.05
(continued)
149
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOjo, ppm
A
[C,H,]0, ppm
O 0
[S00]0, ppm
L.
[o2L %
k, , min
T, min
Temp., °F
Gas Analyses
ANO, min
NO Oxid., %
[N02J, pom
[NOX]/[NOX]0
AC3Hg, ppm
ANO/AC0H,
o b
ASO?, ppm
so2, %
Filter Analyses
XRF, ppm S07
55
20
980
265
1555
4.5
0.72
0.768
264
145
15.4
153
0.970
0
21
1.4
0.03
56
29
1025
475
1460
4.6
0.96
0.781
253
187
18.5
178
0.977
N.D.
N.D.
42
2.9
0.02
57 58
9
1040
1016
1627
4.6
1.14
0.760
272
312
30
249
0.972
157
1.99
45
2.8
0.03
(continued)
150
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOX]0. ppm
[C3H63o. ppm
[S02]0, PF
[023. *
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N023, PPm
[NOX3/[NOX]0
AC3Hg, ppm
ANO/AC3H&
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
59 6(
24
949
0
1344
4.5
1.83
0.755
277
29
3.3
67
0.991
0
-
34
2.5
0.02
£ 61
19
963
380
1541
4.2
1.37
0.764
269
201
21.7
214
0.978
0
-
43
2.8
0.05
62
2
1035
740
1541
4.3
1.85
0.745
287
391
37.8
345
0.933
73
5.36
69
4.5
0.06
missng
(continued)
151
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOjo, Ppm
X
[C-jHglo, ppm
[SOplo. ppm
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
*[NOX]/[NOX]0
ACgHg, ppm
ANO/AC-jH,.
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S0?
63
1
1150
1587
1472
4.6
2.34
0.767
272
552
48.0
460
0.920
253
2.18
46
3.1
0.33
64
26
1063
0
1509
4.5
3.21
0.747
285
41
4.0
60
0.996
0
-
28
1.8
0.08
65
43
976
255
1361
4.3
3.21
0.760
272
295
30.8
218
0.904
142
2.08
86
6.3
4.13
66
4
1147
543
1755
4.7
3.21
0.750
282
445
38.8
328
0.878
136
3.28
140
8.0
0.33
(continued)
152
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOjo, ppm
X
[C3Hg]0, ppm
[so23<,, ppm
[02]. J
k, , min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N023, ppm
[NOX]/[NOX]0
AC3Hg, ppm
ANO/AC3H6
ASO?, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
67
37
1175
979
1424
4.3
2.80
0.750
282
601
53.2
511
0.885
519
1.16
86
6.0
0.06
68
10
977
1856
1554
4.5
5.00
0,740
292
932
96.7
755
0.805
257
3.62
111
7.1
0.40
69
121
658
0
1984
4.64
0
0.772
261
0
0
16
l.QO
0
N.A.
0
0
0.08
70
157
460
480
1770
4.17
0
0.774
259
0
0
5
N.D.
0
N.A.
N.D.
N.D.
N.D.
(continued)
153
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOL, ppm
[C3H6L, ppm
[S02]0, ppm
[Q2], %
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Ox id., %
[N02L ppm
[NOX]/[NOX]0
AC-jHg, ppm
ANO/AC-.H..
o o
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm SO.
c
71
156
443
540
1701
4.64
0
0.774
259
0
0
5
N.D.
0
-
N.D.
N.D.
N.D.
72
144
612
1415
1835
4.64
0
0.774
259
0
0
11
0.994
0
-
10
0.5
0.18
73
128
625
1970
1792
4.64
0
0.774
259
0
0
11
1.00
0
™
0
0
0.11
74
120
614
0
1934
4.56
0.27
0.752
280
11
1.78
27.4
1 .00
0
N.A.
0
0
N.D.
(continued)
154
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOX]0, ppm
[C3H6]0, ppm
[S02]0, PP
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0]o, ppm
[C3Hg]0, ppm
[S02]0, ppm
[02], %
k, , min~
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
([NO] + [N02]/
[NOD
AC-)H,-, ppm
36
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
79
133
570
0
1907
4.48
0.49
0.777
256
44
7.7
44
0.983
0
N.A.
33
1.7
0.27
80
108
626
303
2035
4.70
0.48
0.76
269
192
30.9
184
0.980
81
2.39
38
1.8
1.08
81
124
652
620
1912
4.64
0.47
0.764
269
252
38.6
225
0.991
106
1.80
16
0.9
(Both sides)
0.15/0.19
82
139
583
1300
1825
4.47
0.47
0.760
272
367
63.0
324
0.973
196
2.04
9
2.7
N.D.
(continued)
156
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NOJo. Ppm
X
[C3H6]0, ppm
[S02]0» ppm
[02], *
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NO 1/LNOlo
A A
ACoH,-, ppm
36
ANO/AC3Hg
AS02, ppm
S02 Oxid. , %
Filter Analyses
XRF, S02 ppm
83
113
619
2005
1911
4.56
0.48
0.745
287
416
67.3
384
0.977
305
1.36
44
2.3
3.80
84
135
616
0
1809
4.47
0.58
0.760
272
54
8.8
49
0.970
0
N.A.
54
3.0
0.82
85
145
617
370
1863
4.64
0.63
0.769
264
183
29.7
133
0.902
120
1.31
44
2.4
1.15
86
116
641
630
1902
4.64
0.91
0.755
277
323
50.4
285
0.940
161
2.48
22
1.15
0.35
(continued)
157
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0]0, ppm
[C0HC]0, ppm
o u
[S02]0, ppm
[02], %
k, , min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC0HC, ppm
36
ANO/AC3H6
AS02, ppm
SQp Oxid. , %
Filter Analyses
XRF, S02 ppm
87
118
614
1270
1896
4.56
0.63
0.755
277
449
73.1
449
0.954
343
1.04
87
4.6
0.25
88
148
548
2040
1836
4.56
0.63
0.750
282
482
88.0
405
0.845
452
0.89
0
0
0.81
89
154
592
0
1808
4.46
1.55
0.747
285
38
6.5
38
0.982
0
N.A.
54
3.0
0.28
90
126
647
350
1819
4.64
1.55
0.760
272
285
44.0
247
0.910
170
1.67
55
3.0
2.19
(continued)
158
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0]0, ppm
[C.jHx.]o» ppm
[S02]0» ppm
[02L %
k, , min"
T, min
Temp., °F
Gas Analyses
AND, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC3H6, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
91
136
610
680
1809
4.47
1.55
0.758
274
464
76.0
383
C.949
342
1.29
92
5.1
5.67
92
112
635
1320
1880
4.64
1.59
0.75
279
603
94.9
504
0.976
550
1.10
60
3.2
N.D.
93
109
606
2120
1995
4.64
1.59
0.75
282
596
98.3
532
0.894
N.D.
N.D.
37
1.8
1.07
94
127
992
0
2000
4.64
0
0.777
256
0
0
16
N.D.
N.D.
N.A.
N.D.
N.D.
0.70
(continued)
159
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[NO ]0, ppm
X
[C.,Hfi]0, ppm
[S02L, ppm
[02L %
k, , min~
T, min
Temp., °F
Gas Analyses
AND, ppm
NO Oxid., %
[N02L ppm
[NOX]/[NOX]0
AC3Hg, ppm
ANO/AC,HC
J D
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S0?
95
129
943
320
1748
4.64
0
0.781
253
0
0
16
1 .00
0
-
0
0
0.41
96
125
1008
670
1852
4.64
0
0.788
246
0
0
22
0.991
0
-
16
0.9
0.75
97
115
1162
1320
1857
4.64
0
0.771
262
0
0
22
1.00
17
0
0
0
N.D.
98
in
1090
1927
1852
4.64
0
0.77
259
6
0.55
29
1.00
0
-
0
0
N.D.
(continued)
160
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0]0, PPm
[CgHgL, ppm
[S02L, Ppm
[02L %
k, , min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
[NOX]/[NOX]0
AC3H6, ppm
ANO/AC3Hg
AS09, ppm
u
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
99
117
1178
0
1956
4.56
0.27
0.769
264
6
0.51
33
0.994
0
N.A.
11
0.6
N.D.
100
131
992
310
1765
4.48
0.31
0.764
269
93
9.4
88
0.991
45
2.1
16
0.9
0.95
101
157
1014
720
1874
4.64
0.20
0.753
279
82
8.1
88
0.984
72
1.0
22
1.2
0.25
102
143
1006
1415
1835
4.64
0.18
0.769
264
156
15.5
128
0.957
200
0.78
11
0.6
0.59
(continued)
161
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0]0» ppm
[C3Hg]0, ppm
[S02]0> ppm
[02], %
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
AC3H6, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
103
149
1014
2040
1863
4.56
0.18
0.755
277
170
16.7
137
147
0.74
33
1.8
0.31
104
134
1026
0
1874
4.47
0.47
0.764
269
19
1.8
38
0
N.A.
22
1.2
0.42
105
130
937
320
1754
4.48
0.47
0.767
266
148
15.8
121
64
11
0.6
3.20
106
no
1138
^670
1942
4.64
0.48
0.75
282
250
22.0
218
N.D.
N.D.
48
2.5
0.25
(continued)
162
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0]0, ppm
[C3H6]0, ppm
[S02]0, Ppm
[OJ, %
k. , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC-H/-, ppm
3 o
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
107
152
1008
1320
1841
4.64
0.33
0.772
261
219
21.7
164
180
1 .22
71
3.9
0.83
108
138
1010
2030
1809
4.47
0.47
0.758
274
367
36.3
308
235
0.94
54
3.0
1.78
109
142
1006
0
1846
4.64
0.764
269
39
3.9
39
0.984
0
N.A.
0
0
0.42
no
137
1021
370
1793
4.47
0.88
0.755
277
200
19.6
146
0.927
110
1.54
32
1.8
2.65
(continued)
163
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0]o, ppm
[C3H6J0, ppm
[S02]0, ppm
[02L %
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC3Hg, ppm
ANO/AC3H6
AS02> ppm
S02 Ox id., %
Filter Analyses
XRF, S02 ppm
111
150
1014
720
1874
4.64
0.63
0.750
282
197
19.5
164
0.942
170
1.0
38
2.0
0.76
112
141
1001
1415
1910
4.64
0.63
0.786
248
334
33.3
295
0.930
345
0.97
73
3.8
1.00
113
119
1222
2035
1869
4.56
0.88
0.747
285
477
39.0
444
0.962
363
0.94
71
3.8
0.54
114
153
948
0
1814
4.46
1.30
0.747
285
27
2.9
33
0.988
0
N.A.
60
3.3
0.53
164
-------
TABLE B-3 (Continued)
Run Number
Chronological No.
Conditions
[N0v]0, ppm
X
[CoH,- Jo » ppm
[S02]0» ppm
[02], %
k, , min ,
1 ' -1
T, min
Temp., °F
Gas Analyses
AND, ppm
NO Oxid., %
[NO ], ppm
[NOX]/[NOX]0
AC^H,, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, ppm S02
115
123
1200
270
1923
4.56
0.47
0.750
282
236
19.6
219
0.980
124
1.82
38
2.0
0.57
116
122
1174
630
1918
4.64
1.55
0.758
274
378
32.2
340
0.977
280
1.35
60
3.1
1.43
117
146
1012
1320
1812
4.64
1.10
0.755
277
517
51.0
417
0.882
534
0.89
78
4.3
2.94
118
147
983
1848
1728
4.56
1.75
0.747
285
594
60.4
497
0.886
647
2.59
76
4.4
2.91
(continued)
165
-------
TABLE B-4 EXPERIMENTAL DATA, COMPARISON OF ETHYLENE
AND PROPYLENE
Run Number
Chronological No.
Conditions
[NO Jo, ppm
X
[OlefinL, ppm
[S00]0» ppm
L -I
k, , min"
T, min
Temp., °F
Olefin
Gas Analyses
AND, ppm
NO Oxid., %
[N02L ppm
AOlefin, ppm
ANO/A Olefin
AS09, ppm
c.
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
119
92
913
1326
1600
1.8
0.764
269
C3H6
593
65.0
511
516
1.15
46
2.9
0.23
120
90
960
759
1553
1.8
0.769
264
C2H4
243
25.3
206
242
0.76
83
5.3
0.08
121
86
917
1048
1582
1 .8
0.769
264
C2H4
330
36.0
262
335
0.68
131
8.3
0.12
122
87
901
1886
1651
1.8
0.767
266
C2H4
744
82.6
561
581
1.09
162
9.8
0.11
(continued)
166
-------
TABLE B-4 (Continued)
Run Number
Chronological No.
Conditions
[N0x]o, ppm
[Olefin], ppm
[S02]0, ppm
[02]0» PPm
k, , min"
T, min
Temp., °F
Olefin
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AOlefin, ppm
ANO/AOlefin
ASOo> ppm
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
123
91
898
1393
1610
1.8
0.764
269
C2H4
521
48.0
439
412
1.26
88
5.4
0.06
124
85
865
482
1609
4.6
1.8
0.774
259
C3H6
314
36.3
241
0.958
194
1.62
68
4.2
0.26
125
89
954
980
1598
4.5
1.8
0.767
266
C3H6
487
51.1
409
0.961
371
1.31
62
3.9
0.06
126
88
927
1624
1614
4.7
1.8
0.769
264
C3H6
686
74.1
561
0.916
566
1.21
136
8.4
0.27
167
-------
TABLE B-5 EXPERIMENTAL DATA, INFLUENCE OF OXYGEN CONTENT
ON NO OXIDATION.
Run Number
Chronological No.
Conditions
[NOX]0, ppm
[CgHgL, ppm
[S02]0, ppm
[02], J
k, , min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC3H6, ppm
ANO/AC3H6
ASOp, ppm
S02 Oxid. , %
Filter Analyses
XRF, S02 ppm
127
66
515
569
1371
0
4.5
0.738
295
120
23.5
44
0.845
26
4.64
9
0.6
0.06
128
63
580
569
1260
0.81
4.5
0.768
264
392
68.5
300
0.827
117
3.34
52
4.1
0.05
T29
64
597
569
1317
2.45
4.5
0.758
274
558
94.8
462
0.825
190
2.94
118
8.9
0.13
130
61
519
702
1328
4.43
4.5
0.772
261
493
98.2
444
0.872
157
3.14
40
3.0
0.12
168
-------
TABLE B-5 (Continued)
Run Number
Chronological No.
Conditions
[N0xlo. ppm
[C3H6]0, ppm
[S02]0, ppm
[Op], %
-1
k, , min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC-jHg, ppm
ANO/AC-H,
o o
ASO^, ppm
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
131
67
604
695
1465
7.42
4.5
0.767
266
559
95.5
506
0.882
N.D.
N.D.
49
3.3
0.09
132
65
1020
569
1347
0
4.5
0.738
295
126
12.4
44
0.914
102
1.23
9
0.6
0.08
133
59
1101
637
1314
0.86
4.5
0.764
269
404
37.1
2GO
0.875
109
3.70
49
3.7
0.06
134
62
1043
702
1296
2.54
4.5
0.784
256
626
61.3
484
0.842
231
2.71
N.D.
N.D.
0.08
169
-------
TABLE B-6 EXPERIMENTAL DATA, INFLUENCE OF CO
ON NO OXIDATION.
Run Number
Chronological No.
Conditions
[NOXJ0, ppm
[C3H6]OJ ppm
[S02L, ppm
[02L %
k, , min"
T, min
Temp., °F
[CO], ppm
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
[NOX]/[NOX]0
AC3Hg, ppm
ANO/AC^H,.
o b
AS09, ppm
C.
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
137
106
875
1137
0
4.5
1 .55
0.764
269
0
680
81.3
653
0.926
N.A.
N.A.
N.A.
N.A.
N.D.
138
105
848
1180
0
4.7
1 .45
0.764
269
1124
718
86.4
621
0.866
N.A.
N.A.
N.A.
N.A.
N.D.
139
107
842
1137
0
4.5
1.65
0.767
266
1985
783
95.4
707
0.885
N.A.
N.A.
N.A.
N.A.
N.D.
140
104
896
1180
0
4.7
1 .95
0.764
269
3000
832
96.2
718
0.837
N.A.
N.A.
N.A.
N.A.
N.D.
170
-------
TABLE B-7 EXPERIMENTAL DATA, INFLUENCE OF INITIAL NOX
CONCENTRATION ON NO OXIDATION.
Run Number
Chronological No.
Conditions
[NO ]0, ppm
A
[C3H6], ppm
[S02]0. ppm
[02], I
— 1
k , min
1
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
[NOX]/[NOX]0
AC3Hg, ppm
ANO/ACgHg
ASOp. ppm
S02 Oxid., %
Filter Analyses
XRF, S02 pom
141
97
445
1183
1582
4.5
N.D.
0.771
261
430
100.0
372
0.835
N.D.
N.D.
73
4.6
N.D.
142
98
770
917
2086
4.5
N.D.
0.764
269
519
68.8
445
0.884
N.D.
N.D.
73
3.5
N.D.
143
100
1231
917
1614
4.5
N.D.
0.758
274
445
37.0
377
0.923
N.D.
N.D.
63
3.9
N.D.
144
102
1001
904
1719
4.7
N.D.
0.764
269
482
49.5
419
0.911
N.D.
N.D.
37
2.1
N.D.
171
-------
TABLE B-7 (Continued)
Run Number
Chronological No.
Conditions
[NOX]0, ppm
[C3Hg]0, ppm
[S02]OJ ppm
[02L %
I
k, , min
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[N02L ppm
[NOX]/[NOX]0
AC^Hg, ppm
ANO/AC3Hg
AS02, ppm
S02, Oxid., %
Filter Analyses
XRF, S0? ppm
145
103
1467
904
1729
4.7
N.D.
0.764
269
445
30.9
367
0.929
N.D.
N.D.
47
2.7
N.D.
146
101
1886
872
1651
4.5
N.D.
0.767
266
367
20.0
341
0.958
N.D.
N.D.
52
3.2
M r>
n . L/ .
i in
147
99
2017
1019
1582
4.5
N.D.
0.760
272
367
18.7
341
0.961
N.D.
N.D.
37
2.3
N.D.
••»•— •H^B— -••—
172
-------
TABLE B-8 EXPERIMENTAL DATA, INFLUENCE OF
CONCENTRATION ON NO OXIDATION.
Run Number
Chronological No.
Conditions
[NO¥L, ppm
A
[C3H6]0, ppm
[SO^loi ppm
[02], %
k, , min"
T, min
Temp., °F
[C02]0. %
Gas Analyses
ANO, ppm
NO Oxid., %
[N02], ppm
[NOX]/[NOX]0
AC3H6' ppm
ANO/AC0H,
3 0
ASOp, ppm
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
148
94
862
1018
0
4.2
1 .55
0.768
264
0
501
59.1
428
0.898
N.D.
N.D.
N.A.
N.A.
149
93
859
966
0
4.4
1 .55
0.771
261
6.3
477
57.2
409
0.890
N.D.
N.D.
N.A.
N.A.
150
96
898
1000
0
4.5
K55
0.771
261
12,6
506
58.0
439
0.897
N.D,
N.D.
N.A.
N.A.
151
95
846
855
0
4.2
1 .55
0.768
264
18.5
470
56.9
413
0.908
N.D.
N.D.
N.A.
N.A.
173
-------
TABLE B-9 EXPERIMENTAL DATA, INFLUENCE OF GAS TEMPERATURE
ON NO OXIDATION.
Run Number
Chronoloqical No.
Conditions
[NO ]0, ppm
[C.Hg]0, ppm
[S02]0» ppm
[02L %
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[NOX]/[NOX]0
AC3Hg, ppm
ANO/AC0HC
J D
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
152
73
547
548
1387
3.7
1.55
0.772
115
453
84.9
0.844
199
2.28
100
7.2
0.33
153
74
572
541
1385
4.2
1.45
0.760
187
542
97.3
0.845
90
6.09
44
3.2
0.53
154
71
547
625
1/165
4.4
0.8
0.747
214
498
93.2
0.851
74
6.75
63
4.3
N.D.
155
76
651
579
]?.M
4.2
1.45
0.753
285
600
94.7
0.829
77
7.80
N.D.
N.D.
0.16
174
-------
TABLE B-9 (Continued)
Run Number
Chronological No.
Conditions
[NOXL, ppm
[C-,Hg]0» PP111
[S02]0, Ppm
[02], %
k, , min"
T, min
Temp., °F
Gas Analyses
ANO, ppm
NO Oxid., %
[NOX]/[NOX]0
AC3H6, ppm
ANO/AC3H6
AS02, ppm
S02 Oxid., %
Filter Analyses
XRF, S02 ppm
156
70
1543
849
1359
5.0
1.45
0.742
132
703
46.8
0.911
100
-7.04
98
7.2
0.25
157
75
1203
584
1232
3.8
1.55
0.763
198
631
C3.5
0.881
N.D.
N.D.
59
. 4.8
0.08
158
69
1190
734
1357
4.3
1.45
0.753
214
790
68.0
0.912
145
5.34
143
10.5
0.17
159
72
1238
541
1637
4.0
1.23
0.753
295
823
67.8
0.885
127
6.70
100
6.1
0.15
175
-------
APPENDIX C
Kinetic Model
176
-------
APPENDIX C - KINETIC MODELING
A preliminary attempt was made to adapt a propylene/NOx kinetic
mechanism developed by Jeffries (1977) for use in analyzing experimental
results with the Photochemical Kinetics Simulation System (PKSS) also
developed by Jeffries. This kinetic mechanism had successfully been used
to simulate smog chamber results at the UNC research facility. Since
these tests were conducted in a batch reactor and at ambient conditions,
some mechanism modifications were necessary.
One change was to operate the program so as to simulate a CSTR using
dilution and continuous mass input. By balancing these two factors it
was possible to simulate the CSTR conditions at an average reactor residence
time of 0.75 minutes. Model runs under dark phase conditions confirmed
that the concentrations of NO, S02, and 03^ remained constant.
Initial simulation runs indicated that certain reactions were too
rapid for the time scale chosen. Rescaling of the variables was necessary
to simulate the short time scale events; the units used in the rescaling
were one-thousandth of a minute. These units required no change in the
second order rate constants. It was necessary to divide the first order
rate constants (including k-|) by a factor of 1000 and multiply the third
order rate constants by a factor of 1000. The resulting mechanism is
shown in the attached sample computer printout. The basic PKSS program
was not changed, therefore, the units continued to be printed in units of
"minutes" while the actual time was "minutes x 10~3".
There are several obvious deficiencies in this mechanism: (1) ozone
-propylene reactions were inadvertently omitted, (2) no attempt was made
to adjust photolysis rates of aldehydes due to middle UV light, and (3)
photolysis rates were not adjusted to reflect absorbance changes as a
function of temperature.
The NO conversion estimates of the sample run are approximately 15%
of the actual results based on runs 44 to 68. The primary reason for the
177
-------
difference is probably the first error identified above. Other possible
contributing factors are listed below:
(1) Aldehyde photolysis in the middle UV
(2) Photolysis of species other than aldehydes in the middle UV
(3) Improper selection of composite reactions due to high gas
temperature and/or low oxygen concentration.
(4) Improper selection of photolysis rates due to temperature
effects and/or middle UV light.
(5) Improper use of kinetic model
(6) Improper mechanism for high concentration, high temperature
system
Although, initial attempts at modeling the experimental results with
PKSS were not successful, there is no apparent reason why this mechanism
can not be improved so that PKSS could be used to simulate a system such
as that used in the project. It is recommended that modeling efforts be
emphasized in future work.
178
-------
~P" H u T~0~~C" H C M~~I~C~J~TK I N E TIC ^ SIMULATION S Y S T E~~M
VERSION 003A CREATED 07/12/77
............ USE* GOCUxCNTATION
IHIS JS A TEST RUN
U5I»»;-Ti~ROT HCCFWT5M BA5LD UN KLC£N' FINDINGS INCLUDING!
II NEW RATES FOR H02tOH WITH NO » N02 GIVING HN02. HN03. I
TTO2W07T~iHICH HAS HIGR'
?) NEW 03 I OLEFIN CHEF; CREGIEE "ECH. STABLE BIRAOICALS, HOT
ftLCTK 8C1U.
si NEW PAN CHEH: EITHER HCNDRY«S RATES OR cox«s RATES.
» HAS UNntHGONE SUCEb^IVL HLVIS10N AS> L'OXPARISON HKOCEED—
I ADDED R02 + NOOKETONE+HN02 TO PROPY CHEM
VLRSION 6B
THL WnXJMUM NU"HLH OF:
SPECIES IS "»0l
REACTIONS I!> 75T
TABLE VALUES ISIT!
ITEMS IU BL' SAVED 15 ZOo-NO SELCCTIvC pUNCHlMC OF OUTPUTS
DILUTION HATE PROFILE" FRUHlgnNSTANT DILUTION OF 1.5E-3 USED TO SIMULATE TAU OF 0.75
"INITIAL CONCLNTHA1I9N OF NU
INITIAL CdNCtNTRATfON OF NO2=0.1
"IW1TIAL eftNCLNTRAtlON OF PflOPTLsl.O
'INITIAL CJivCtNTRATION OF 03 =0.05
INITIAL CONtLNTRTTiON OF SO?=2.5
INITIAL CONCENTRATION OF HCHT=0.1
RATION or 02 =<«o.
INITIAL CONCLNTRATION OF N20n=i.oc-5
INITIAL CONC(.NTRATION OF NDS =i.OE-5
INITIAL CONCINTRATION OF HNO?=i.oE-"r
INITIAL CONCtMTRATlON of CCwi =TT."5
INITIAL coNCtNTRATiorj OF coo =l.oC-7
ToNcENTRTfjiiV o? fcbi "=i.ot^T
^ INITIAL cm
-------
INITIAL" cnNCtNTRaTioN
INIHAL CONCENTRATION
INITIAL CONCENTRftTION
OPTIONS SELECTED:
CNSTOIL
TtlAX
CNSTCAT
CNSTTf"
CNSTH2
CUSUI
C«">TFI
Hh4X
»RTST£P 50
PLTSTEP so
END
THIS RUS u«;cs CONSTANT
Of H02 =l.?E-6
OF o =i.:->io
OF PAN =l.:E-3
0.0015
no oo.
1.
itOO.
10.
0.0017 '- —
20.
LIGHT INTEMSITY EOU4L TO 1.70000E-03
THIS RUN USES CONSTANT TEHPEHiTURE EQUAL TO t.OOOOOE*OZ
THIS RON USES CONSTANT yjitER cONC E8U»L TO 1.00000E*01
THIS RuN USCS CONSTANT CATALYSIS CO'JC EQUAL TQ 1.00000E*00
THIS RUN USES CONSTANT DILUTI'lM RATE COUOL TO 1.50000E-03
-------
»• t c"
"A N i " s *
00
1)
( 2)
31
« 31
7)
( 6)
91
<
10t
13 1
15 (
( 261
t
THIS is- » ™ ST "UN
N02 --HV-->
03 "HV-->
o >
N03 * NO >
N03 + N02 >
N205 >
rj205 >
03 --HV-->
010 >
010 ...... >
n* + — --^L
05 + OH >
OH » NO >
HNO2 --HV-O
OH « N02 >
OH » HN03 ->
03 « HO? >
H02 + NO? >
H02U02 >
HO2 * N03 -._-.->
Mn? » H02 -•-».->
H20? --HV-O
1.00 NO * 1.00 0
1.00 010
1.00 03
1.00 N02
1.00 NO?
1.00 NO
1.00 N03
1.00 N03
2.00 N02
1.00 N205
1.00 NO 3 « 1.00 NO?
2.00 WHN03
0.11 01D + 0.89 0
1.00 0
2.00 OH
1.00 HO?
1.00 HN02
1.00 NO * 1.00 OH
1.00 HN03
1.00 N03
1.00 OH
1.00 N02 * 1>00 OH
1.00 H02N02
1.00 N02 •> 1.00 H02
1.00 HN03
1.00 H202
2,00 OH
2.00 NO?
1.000E«00 <
l.OOOE+00 <
. .«.OOE*02^E<°( 5.10E»02/TX
1.3iOF*03»Ei(«l-1.20E«03/TX
«.!i«nr»os <
1.360E»OH <
3.610E*03 <
1.77nE + 02»E«P(-2.i»5E + 03/TX
2.808E+OM <
2.187E»02»E*P( 8.61E*02/T)<
7.<-1.03E*Oi»/TX
(H20I* 8.000E-07 <
(E)» 5.380C-02 <
8.5tOE-01 <
(H2CI. 9.110E.06 <
H.620E-07 <
2.217E«03«EXP(-1.00E«03/T)<
3.859E + 02»E*P( 1.11E+03/TK
5.000E-01 <
1.UOOC*04 <
8.868E*02«EXP(-'t.OOE*02/TX
1.079E«02»EXP(-1.28E + 03/TX
1.182E + 01* <
9.000E»03 <
H.500E«m»E«°(-1.17E + OH/TX
2.500E*03 <
lt.B9'»E»Ot»CX<>(-5.mE*02/TX
l.OOOE-01 <
2.5?ffE-05»EX»( 5.30E«02/T)<
e.85«*02>
2.371E«Ol>
3.500t«03>
1 .SSOEtOO
3.6
i
2.808E«0«>
I
3.933E«03>
6.85tE»00> <
a.OOOE-03>
^.382E-02>
8,5tOE-01> . r
_5jltOE-02>
it.620C.07>
7.73HE*01>
1.600C«0
2.
l.«OOE*0»>
2.317E*02>
1 .H96E+00>
1.182E*0
•J.OOOEt-OS)
..20fcE-OS>
2.500E403>
7.980E«03>
l.»9?E.O»> ,
-------
00
30T
31 1
32)
33)
' 311
351
(
ib)
' r§7>
38)
(
vr\
t ••„,
"It
f
";?)
*- U3'
r
"it
' "61
NO V NOZ --> 2
HNOZ + HlMUZ ------> J
OH » CO } 1
HCMU --HV > -1
CCHO" --HV--> 1
CrOS » M02 > 1
> 1
> 1
> 1
> 1
N03 * PROPYL > 1
63 + PROPYL > I
7THJ
vmr
.08
.00
rmr
.00
.00
.OS
.00
.00
.06
.00
.08
.80
.00
.66
.00
HNOZ " IH20)
NO « I.Ofl-NOS ' .
H02
CO + 0.5B— HO?
Hos + i.oo-cn
CO « 1.00"H05 + 0.99 COD
CC03
N02 + 1.00 COO
PAN
PROCTL
0?
NO
N02
S02
N02
HCHO * 6.20 CCH02 »' O.«0 MOCMO,
CCHO + 0.20 HO2 + 0.70 CO
?,
1
u
(CJ» Z
T
(c>» u
.300E-I
;TTBOE-I
)3
< ?.?DOE-05>
< 1.300E-"D5>
)} ( H.DUnL*U^^
3?
[>«-
;onoE-02
< K.buoi--o»^
C I.9ZOE OZ>
"
1
1
6
1
1
3
7
U
14
**
03
;560C«"OS
73DOT-ir3
^OITOC.
.500E-
,4601-
.700C-
,820E«
.siof*
02
03
05
03
00
00»E«°<-1
.510E«00«Ex°(-l
< 1
f^S
< i
* J
< 3
< 7
,90E+03/T)< 7
;?f6rnrr5
. OOOE-OZ>
.500E-dS>
.500E-05>
.700E-03>
,8ZOE»00>
,677E-03>
(
r
*•
r
.90E»03/T)< 7.677E-OS>
U7|
«8|
a,,
50)
511
521
531
C3OHO?
C3OHO?
MO
»0
OH
TJOH02
C30H02
+
+
•
+
+
•*
+
H02
C30H02
N02
M02
NO
NO
— >
---> 2
.--•> 1
---> i
— > i
---> i
• --> i
.00
.00
.00
.00
.00
.00
CCHO *
MON02
HCHO *
C30H02
N02 »
N02 »
2.00
1.00
2.00
2.00
'HCHO » 270FT?05"
HM02
HCHO + 2.00 H02
CCHO
8.0CCE»03 < 8.000E»03>
5,00:E«02 < 5.000E«OZ>
lf5CCE*0« < 1.500E«OH>
*.uc:E»o3 < •..»noi.oS>
3.7<-;E»0'» < 3.7»OE + 0*>
fe.OCCC«03 < 6.000E+03>
6,c::E«03 < 6.000E»03>
(
(
c
vn
55)
561
^71
58)
59)
CC03
coo
coo
coo
coo
02
» H02
+ NO
+ NO
+ H02
* con
+ MO
> 1
> 1
> 1
> l
.00
.00
.50
.00
N02 » 1.00 MO
HCHO » 1.00 HN02
MO
HCHO + 1.00 H02
6«C-CC+03 ^6»
9«fct"E*03 ^9»
2.*::r4os < 2.
8.~t~C*G3 ^8.
e.:trr»03 < 8,
i.c:cE»oo < i.
OOOE+03>
600E*03>
tOOE*
Hoof*
03>
03>
OOOE«03>
OOOE*
oo>
- s\
O
-------
-> 1.00 NO? * 1.00 CC6T"
^> 1.30 R03
1.190E*lB.E«»l-1.33t*0«»/T)<
621
50?
* r<03
'.• H8?
-> 1.00 S03 * 1.00 N02
-> 1.06 OhT
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
. REPORT NO.
EPA-600/7-80-038
1. RECIPIENT'S ACCESSION NO.
. TITLE AND SUBTITLE
Photochemical Study of NOx Removal from
Stack Gases
. REPORT DATE
March 1980
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
John R. Richards and Donald L. Fox
8. PERFORMING ORGANIZATION REPORT NO.
. PERFORMING ORGANIZATION NAME AND ADDRESS
University of North Carolina
School of Public Health
Chapel Hill, North Carolina 27514
10. PROGRAM ELEMENT NO.
INE623
11. CONTRACT/GRANT NO.
Grant No. R804740
2. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 1/77 - 3/79
14. SPONSORING AGENCY CODE
EPA/600/13
5. SUPPLEMENTARY NOTES JERL-RTP project officer is Joseph A. McSorley, Mail Drop 63,
919/541-2745.
. ABSTRACT The report gives results of an evaluation of the technical feasibility of a
photochemical pretreatment system for NOx control at coal-fired boilers. The ap-
proach utilizes reaction mechanisms similar to those responsible for photochemical
oxidant incidents. The reactions are initiated under controlled conditions while
the pollutants are at high concentration and while the reaction products can be remo-
ved. Results indicate that, under time- and light-limited conditions, it is possible to
quench the photochemical reactions at the NO2 peak and prior to the formation of
ozone, aerosols, and other secondary products. Energy and hydrocarbon require-
ments were estimated in a series of 159 experimental runs. The optimal operating
conditions were identified as a NOx/C3H6 stoichiometric ratio of 1 and an NO2 photo-
lysis rate of 1 to 1. 5 reciprocal minutes (equivalent to 3 to 5% station power). These
conditions allowed for an 83% oxidation of NO with an exit concentration of NO less
than 100 ppm. Variation of the energy input levels or the propylene injection rates
resulted in NO oxidation efficiencies of 10 to 99%. Photochemical oxidation of NO
was insensitive to SO2 concentration and CO2 concentration. The photochemical sys-
tem appears compatible with conditions resulting from combustion modifications
to suppress NOx generation".
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
Pollution Combustion
Photochemical Reactions
Oxidation Boilers
Flue Gases Propylene
Nitrogen Oxides
Coal
b. IDENTIFIERS/OPEN ENDED TERMS
Pollution Control
Stationary Sources
COSATI Field/Group
13B
07E
07B,07C
21B
21D
13A
13. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThtsReport)
Unclassified
21. NO. OF PAGES
200
20. SECURITY CLASS (Tkit pagej
Unclassified
23. PRICE
EPA Form 22ZO-1 (*-73)
189
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