U.S. Environmental Protection Agency Industrial Environmental Hfs-'areh
Office of Research and Development Laboratory
Research Triangle Park. North Carolina 27711
EPA'600/7-76-03'
TECHNOLOGY AND
ECONOMICS OF
FLUE GAS NOX OXIDATION BY
OZONE
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been .grouped into seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The seven series
are:
1. Environmental Health Effects Research
2. Environmental Protection Technology .
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from
the effort funded under the 17-agency Federal Energy/Environment
Research and Development Program. These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally—compatible manner by providing the necessary
environmental data and control technology. Investigations include
analyses of the transport of energy-related pollutants and their health
and ecological effects; assessments of, and development of, control
technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
REVIEW NOTICE
This report has been reviewed by the participating Federal
Agencies, and approved for publication. Approval does not
signify that the contents necessarily reflect the views and
policies of the Government, nor does mention of trade names
or commercial products constitute endorsement or recommen-
dation for use.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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EPA-600/7-76-033
December 1976
TECHNOLOGY AND ECONOMICS
OF FLUE GAS NO
A
OXIDATION BY OZONE
by
J.W. Harrison
Research Triangle Institute
P. O. Box 12194
Research Triangle Park, NC 27709
Contract No. 68-02-1325, Task 38
Program Element No. EHE624
EPA Task Officer: Richard D. Stern
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
-------
TABLE OF CONTENTS
LIST OF FIGURES iv
LIST OF TABLES v
INTRODUCTION 1
EXECUTIVE SUMMARY 3
ESTIMATE OF OZONE REQUIREMENT .... 6
OZONE GENERATION TECHNOLOGY AND ENERGY REQUIREMENTS..... 11
Corona Discharge Generation of Ozone 11
Ozone Generation Systems , 14
Utility Requirements 18
ECONOMICS OF OZONE PRODUCTION ., 23
FORECAST FOR IMPROVEMENTS 29
APPENDIX A. OZONE REACTION KINETICS 31
Ozone Thermal Decomposition 31
Reaction with Nitric Oxide 33
Reaction with Nitrogen Dioxide 33
Summary 38
APPENDIX B. DETERMINATION OF OZONE DEMAND 40
Model Reactor 40
Approximate Equations 42
Solution of Approximate Equations 45
Steady State Approximation 51
APPENDIX C. ECONOMIC ANALYSIS 57
Capital Costs 57
Operating Costs 61
REFERENCES 65
iii
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LIST OF FIGURES
Page
Figure 1. Required ozone mass flow rate for oxidation of NO at
various concentration at typically flue gas flow
rates 10
Figure 2. Welsbach ozonator (Type C) 13
Figure 3. Effect of varying oxygen flow 15
Figure 4. Ozone production versus cooling water inlet temperature
(air and oxygen feed) 16
Figure 5. Ozone generation systems 17
Figure 6. Utility'requirements, power, water, and supply air for
ozonator using air feedstock 20
Figure 7. Utility requirements, power and water, and oxygen feed
rate for ozonator and oxygen plant combined.. 21
Figure 8. (Concentration,^time) curves for ozone + S02 reaction
showing H^O^ aerosol formation on the addition of
ci s-pent-2-ene 37
Figure 9. Elemental reaction volume in plug-flow reactor model 41
Figure 10. Relation between NO, N02 and N205 concentrations and
the fraction of ozone used for oxidation for initial
conditions [03]/[NO] = 0.5 and [N02]/[NO] = 0.05 47
Figure 11. Relation between NO, N02 and N205 concentrations and the
fraction of ozone used for oxidation for initial condi-
tions [03]/[NO] = 0.9 and [N02]/[NO] = 0.05. 48
Figure 12. Relation between NO, N02 and N20c concentrations and
the fraction of ozone used for oxidation for initial
conditions [03]/[I\IO] = 1.0 and [N02]/[NO] = 0.05 49
Figure 13. Relation between NO, N02 and N20c concentrations and
the fraction of ozone used for oxidation for initial
conditions [03]/[NO] = 1.0 and '.[N02]/[NO] = 0.05 50
Figure 14. Relation between NO and N02 concentrations and the
fraction of ozone used for initial conditions [03]/[NO.] =
1.0 and [N02]/[NO] = 0.05 with steady state assumption
for [N.205] 54
Figure 15. Cost of cooling water versus flow rate 62
IV
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LIST OF TABLES
Page
Table 1. Summary of Capital and Operating Costs and Energy,
Requirements for Flue Gas NO Oxidation by Ozone for
500 MW Oil-Fired and Coal-Fired Plants 4
Table 2. Estimated Flue Gas Compositions for Power Units without
Emission Control Facilities... 7
Table 3. Power Plant Flue Gas Emission Rates 9
Table 4. Ozone Generation by Various Methods, Best Reported
Results , 12
Table 5. Utility Requirements for Ozone Generation for NO
Oxidation in Flue Gas from 500 MW Oil-Fired and Coal-
Fired Stations 22
Table 6. Assumed Power Plant Capacity Schedule 24
Table 7. Cost Items and Estimated Total Capital Investment for
Ozonation Facilities for 500 MW Coal-Fired and Oil-
Fi red Generati on Stati ons 26
Table 8. Annual Operating Costs, First Year, 7,000 Operating
Hours for Oxidation of NO in Flue Gas of 500 MW
Generating Units 27
Table 9. Size of Reaction Rate Values at 60° and 149°C 43
Table 10. Numerical Estimates for Initial Values at 149°C of
Terms in Rate Equations at Stoichiometric Ozone Feed
from Both Ai r Stock and Oxygen Stock 44
Table 11. Estimated Direct Capital Costs for Ozone Generation for
NO Oxidation in 500 MW Generating Stations 59
Table 12. Indirect Investment and Allowance Factors 60
Table 13. Project Expenditure Schedule 60
Table 14. Direct Cost Elements for Operation of Ozonators and
Oxygen Plant 63
Table 15. Annual Capital Charges for Power Industry Financing 64
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INTRODUCTION
Stationary combustion sources contribute about one-half of the
man-made nitrogen oxides (NO ) emitted to the atmosphere in the
• A
United States. Because these emissions contribute to adverse health
effects, EPA is pursuing a vigorous program of research into cost-
effective, commercially viable methods for controlling these emissions.
Two branches of control technology are being addressed: (1) control
of the combustion process (combustion modification) and (2) control of
post-combustion products (flue gas treatment-FGT). Due to recent
emphasis on NO emission control and because FGT can be employed as
A
an "add-on" technology, particularly when high removal efficiencies
are required or when combustion modification is inappropriate, there
has been an increased activity of EPA research in this area.
Flue gas from combustion processes contains NO which is predomi-
A
nantly in the form NO. Although N02 is to some extent soluble in water
or aqueous solutions, NO is practically insoluble as far as conventional
scrubbing processes are concerned. Therefore, for effective removal NO
must be either reduced to elemental nitrogen, or oxidized to N02 or N^O,-.
This leads to two types of control options: NO reduction or NO oxidation
followed by N0£ scrubbing.
At normal flue gas exit temperatures (about 300°F or 150°C) the
oxidation of NO by atmospheric oxygen is kinetically controlled at too
low a rate for practical conversion to NO^ or NoOr. Therefore, some
strong oxidant such as ozone or chlorine dioxide must be used to insure
a practical reaction velocity. The resulting reaction products have,
at present, little or no commercial value to offset expensive, relatively
complex equipment required and the projected high operating costs.
Despite these drawbacks, however, processes involving NO oxidation
followed by NOp wet scrubbing are being developed in Japan due to
the more stringent regulations on NOY control and the potential for
A 11
simultaneous S0? and NO removal.
£. A
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This report analyzes one of the NO oxidation process options
which involves the conversion of NO to N0£ or N205 by gas phase
reaction with ozone. The objectives of the analysis are: to
determine the amount of ozone required per unit of NO in a typical
flue gas stream; to determine the costs and energy requirements
of ozone generated using current technology; and to determine
whether or not any significant improvements in ozone generation
technology can be forecast. This information provides the basis for
assessment of whether or not this method of NO .oxidation is cost-
effective and commercially viable when compared to alternative
oxidation methods.
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LXECUTIVE SUMMARY
Consideration of the reactions that take place between ozone (O.J
and nitric oxide (NO), nitrogen dioxide (NC^) and sulfur dioxide (SCL)
in a typical flue gas stream from a generation unit indicate that to a
good approximation only an amount of. ozone stoichiometric with the NO
J\
is required to achieve essentially complete conversion of NO to either
NOp or NpOr, both of which may be subsequently scrubbed from the gas
stream. The reaction with S02 is negligible.
The only viable method currently available for large scale ozone
generation is the corona discharge. Either air or oxygen can be used
as feedstock to the ozone generator. With oxygen feed the output ozone
concentration is approximately twice that with air feed and the electrical
energy required per kilogram of ozone produced is approximately half that
with air feed. However, when the energy required to produce ,oxygen from
air is taken into account, the total energy requirement using oxygen feed
is found to be higher than that for air feed.
The energy requirements and the capital and operating costs were
examined for ozone generation with air and oxygen as feed for a 500 MW
oil-fired and coal-fired unit. The results are summarized in Table 1.
Approximately 13% more energy is required for generation from oxygen.
Even with air feed the energy penalty for ozone oxidation of NO is sizeable,
From 3% to over 9% of the total energy generated by the plant may be
required for ozone generation, depending upon the NO concentration.
In addition to a higher energy penalty, both capital investment
and operating costs are much higher for ozone generated from oxygen than
from air. As can be seen from Table 1, the capital investment for ozone
generation from oxygen feed is about three times as large as that required
for air feed. For the NO concentrations typical for an oil-fired unit
approximately $56 of capital investment is required per kWh of generating
capacity for an oxygen feed ozonator compared to about $18 per kWh
capacity for an air feed unit. At the much higher NO levels typical of
coal-fired generating stations the capital investment jumps to about
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Table 1. Summary of Capital and Operating Costs and Energy Requirements
for Flue Gas NO Oxidation by Ozone for 500 MW Oil-Fired and
Coal-Fired Plants
Item
Capital Investment
$/kg 03/yr
$/KW capacity
Operating Rates
$/kg 03 produced
mil/kWh produced
Energy
kWh/yr 03 production
% Energy for 03
production
Oil Fired (200 ppm NO)
Air Feed
1.85
17.60
1.48
2.0
1.1 x 108
3.1
Oxygen Feed
5.90
56.20
2.76
3.8
1.25 x 108
3.6
Coal Fired (600 ppm NO)
Air Feed
1.84
52.60
1.16
i .
4-7
3.3 x 108
9.4
Oxygen Feed
5.34
152.40
2.24
9.1
3.75 x 108
10.7
-------
$152 per-kWh capacity when oxygen feed is used compared to about $53 per
kWh for air feed.
There is a similar disparity in operating costs. As can be seen
from Table 1, operating costs for oxygen feed ozonators are approximately
twice as large as those for air feed units. For oil-fired units the
operating rates are 3.8 mil per kWh produced when oxygen feed is used
compared to 2 mil per kWh when air feed is used. Again, for the higher
NO concentrations typical of coal-fired generators, operating rates for
these installations would be much higher, 9.1 mil per kWh for oxygen feed ,
or 4.7 mil per kWh for air feed. The economic and energy penalties
associated with large scale ozone generation increase with increasing
NO content. The use of combustion modification technology to reduce
NO concentration prior to post combustion FGT processes, such as the
oxidation process analyzed in this report, would be highly desirable, if
not obligatory, if ozone oxidation is to be seriously considered. In
this connection, it must be emphasized that the costs and energy require-
ments have been determined exclusively for the generation of ozone for
supply to the flue gas stream. They do not include the cost of building
and operating scrubbers for NOp removal.
At present the only practical improvement in ozone generation
technology appears to be the possibility of reducing the energy required
by eliminating the necessity for air preparation (filtering, dehumidifying)
prior to induction into the ozonator. A process for this has reportedly
been developed in Japan, but is not yet available in this country. The
energy required per kilogram of ozone produced is about two-thirds that
now required. Elimination of the air clean-up equipment should also
provide a savings in capital investment and, possibly, reduced maintenance
costs. Until such a system is proved in large scale operation, however,
it appears that the use of ozone for NO oxidation will be very expensive.
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ESTIMATE OF OZONE REQUIREMENT
A recent report on NO abatement for stationary sources in Japan
A
has given some details on the use of ozone to promote NOV removal in
A
two pilot plant evaluations. Both of these plants use ozone to oxidize
NO to N02 or t^Og followed by scrubbing to remove the higher oxides
from the treated gas stream. Although some economic data are given the
model upon which the estimates are based is not given, making it difficult
to extrapolate to typical full-sized generation units. In order to make
a realistic assessment of the ozone requirements for a typical power plant
in the United States, a model situation will be analyzed in this report.
The physical situation assumed is that the ozone is generated on-site and
injected into the flue gas stream where the gas phase reactions of ozone
(0,) with other chemical species in the gas stream occur in a manner that
2
is typical of "plug-flow" reactors . This model assumes that conversion
of reactants at the walls is negligible compared to the gas phase reaction
rates and that these gas phase reactions occur as the reactants are trans-
ported in the streaming gas.
The flue gas will contain appreciable amounts of Np, COo, and HLO
vapor, smaller amounts of Op, and even smaller amounts of S02, NO and
N02. (See Table 2). Typically the injected ozone stream will consist
of about 1 to 2% of ozone in either air or oxygen, depending on which
gas is used as feedstock for the ozone generator. Among these gas phase
constituents the major conversion mechanisms for ozone are thermal
decomposition, oxidation of NO to N02 (the desired reaction), oxidation
of N02 to NpOg, catalyzed decomposition of ozone by N205 and oxidation
of SOo to SO.,. These reactions and their relative rates are discussed
in Appendix A. Under the conditions assumed, the conversion of NO to
N02 and the conversion of N02 to N205> followed by reaction of NO with
N20^, are the predominant reactions.
The plug-flow model reactor analysis detailed in Appendix B, using
the reaction rate data given in Appendix A, indicates that the amount of
ozone required for essentially complete removal of NO from the gas stream
-------
Table 2. Estimated Flue Gas Compositions for Power Units without Emission
Control Facilities. 3 .
Coal -fired boiler
Fuel and pulverized coal (hori-. Oil-fired boiler , .
boiler type zontal , frontal-fired)^ ' (tangential-fired)^'
°f ' 2.0 3.5 5.0 1.0 2.5 4.0
Flue gas composition,
% by volume
Nitrogen
Carbon dioxide
Oxygen
Water
Sulfur dioxide
Nitrogen oxides
Fly ash loading
Grains/scf dry
Grains/scf wet
74.
12.
4.
7.
0.
0.
4.
3.
62
57
86
77
12
06
11
79
74.
12.
4.
7.
0.
0.
4.
3.
55
55
86
76
22
06
11
79
74.49
12.54
4.85
7.75
0.31
0.06
4.11
3.79
73.
12.
2.
11.
0.
0.
o.
0.
83
52
55
03
05
02
036
032
73.
12.
2.
IT.
0.
0.
0.
0.
73
37
55
19
14
02
036
032
73
12
2
11
0
0
0
0
.64
.21
.54
.37
.22
.02
.036
.032
(1) Pulverized coal, 20% excess air to boiler, 13% additional air leakage
at heater assumed.
(2) Assumed 5% excess air to boiler and 10% air leakage to preheater.
-------
by conversion to N02 is that required by the stoichiometric equation
NO + 03 = N02 + 02 . (1)
This conclusion allows an estimate of the amount of ozone that must be
used for a given plant size.
An equation is derived in Appendix B for the mass flow rate of
ozone required for a given flue gas flow rate and NO concentration.
This equation is
wn = 2 x 10~6Q,;n kg/s
°3 F (2)
3
where QF is the flue gas flow rate in m /s at the standard condition of one
atmosphere and 21°C (about 70°F), and n is the NO concentration in ppm.
Table 3 shows flue gas flow rates typical of 200 MW, 500 MW and 1000 MW
power plants. For purposes of estimating, the respective flow rates
will be taken as 188 m3/s (4 x lo5 SCFM), 472 m3/s (1 x lo6 SCFM) and
3 6
944 m /s (2 x 10 SCFM). Using these nominal rates the ozone require-
ment as a function of NO concentration is given in Figure 1.
As pointed out in Appendix B, this estimate does not take into
account ozone lost due to catalyzed decomposition on the hot surfaces
of the duct in which the gas streams are mixed and the reaction takes
place. However, it does provide a reasonable basis for assessing the
size of ozone generation plant required to produce ozone at the rates
necessary for present day electrical generating stations in the United
States. The next section examines current ozone generation technology
in order to determine the capability of generating ozone in the large
amounts required and the price to be paid in terms of energy and
dollars for NO oxidation by this method.
8
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3
Table 3. Power Plant Flue Gas Emission Rates.
Stack
Power plant Type gas flow ,
size, MW plant acfm (310°F) scfm (70°F) rr/s(21°C)
Coal-fired units
200 New 630 x 103 630 x 103 203
500- New 1,540 x 103 1,060 x 103 500
1,000 New 2,980 x 103 2,060 x 103 972
Oil-fired units
200. New 530 x TO3 364 x 103 172
500 New 1,300 x 103 908 x 103 428
1,000 New 2,510 x TO3 1,720 x 103 812
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2.0
1.8
1.6
1.44
1.2
to
CD
o
«/>
to
I 0.8
N
O
0.6
0.4.
0.2.
472 m3/s (1 x IQ6 SCFH)
188 m3/s (4 x 105 SCFM)
190.5
..142.8
95.2
c
o
O
CO
CO
to
OJ
c
o
.. 47.6
100 200
300 400 500 600 700 800 900 1000
NO Concentration (ppm)
Figure 1. Required ozone mass flow rate for oxidation of NO at various
concentrations for typical flue gas flow rates.
10
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OZONE GENERATION TECHNOLOGY AND ENERGY REQUIREMENTS
Generation of ozone from a gas containing oxygen requires a rupture
of the 02 bond. At 25°C the bond dissociation energy is about 5.2 electron
volts (8.3 x 10 Joule per molecule or about 5 x 10 Joules/mole).
Several methods of producing this dissociation, followed by the generation
step
0 + 2 0 + 0 + 0 (3)
are summarized in Table 4 along with the yield in kilograms of ozone
5
per kilowatt-hour of energy input. Also shown is the ozone concentration
available in the output stream. It should be noted that the maximum
yields are obtained by operating at much less than the maximum output
ozone concentrations. This will be discussed further in the next section.
Of all of these methods, the only one currently viable for large scale
generation of ozone is the corona discharge.
Corona Discharge Generation of Ozone
The status of large scale ozone generation technology ca. 1973 has
been surveyed by Klein ejt a_l_. According to Klein the large scale units
all use a corona discharge method. For this method the major design
parameters are air gap, pressure, temperature, dielectric covering the
electrodes, electric power voltage and frequency, feed gas composition
and output ozone concentration. Typically the latter varies from less
than 0.5% to as high as 10% by weight for a well designed generator
operating under ideal conditions. There is an inverse relationship
between power efficiency (kgO^/kWh) and ozone concentration.
5
A typical large scale ozonator is shown schematically in Figure
2. The outer tubes, end plates and pressure vessel are stainless steel.
The inner tubes are glass, coated internally with either graphite or
metal for the second electrode. The applied potential is 15,000-19,000
volts at 60 Hz. The power density is 650-1300 Watts per square meter
of electrode area. Either air or oxygen is used as a feed, supplied with
11
-------
5
Table 4. Ozone Generation by Various Methods, Best Reported Results.
Yield, kgCL/kWh Ozone Concentration
3 (% Volume)
theoretical 0.346
corona discharge in air up to .150 up to 6%
or oxygen
electrolysis of water up to .012 up to 20%
photochemical
-2537 A up to .025 up to 0.25%
1400-1700 K ' up to 3.5%
radiochemical
using 02 gas .220 .006%
using liquid Oo -108 5%
thermal .056 0.33%
*
Maximum yields can, of course, only be obtained by operating at much
less than the maximum ozone concentrations.
12
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Transformer
Oione
out
ABC
Air or
-\-\-_-
Oiygin In
Figure 2 . Welsbiach ozonator (Type C). Legend: A, cooling water; ,
B, stainless-steel tube; C, discharge gap; D, glass tube.
13
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with a dewpoint of at least -60°C. Internal pressure is maintained
at 1-2 atmospheres to optimize the conversion efficiency. With air
feed, the output ozone concentration is typically about 1% by weight
at a yield of 0.05-0.06 kgOykWh. with oxygen feed the output ozone
concentration is typically 1.5-2.0% by weight at a yield of 0.11-0.13
kgOg/kWh. These yield figures are only for the ozonators. They do
not include energy for pumping and drying air (for air feed) or
liquefaction (for oxygen feed).
Electrode gap spacing must be large enough not to cause too high
a pressure drop as feed gas is pumped through the reactor, but not too
large, since a higher supply voltage -- and hence more expensive
transformer -- is required as the gap spacing increases. The feed gas
must be thoroughly dried to prevent sparking and ozone decomposition.
Another problem with air feed is that small quantities of ^Oj- are
generated, typically 1-2% of the ozone concentration , which can combine
with water vapor to form nitric acid unless the air is thoroughly dried.
Part of the spacing between electrode surfaces is taken up by a dielectric
(typically glass) which serves to limit the discharge current, preventing
high current areas which would destroy the electrode surfaces.
The power consumption of an ozonator is directly proportional to
the frequency and the peak voltage used. If the input power is increased
to increase the output ozone rate, the latter will not be proportional
unless the feed rate is also increased to hold the output ozone con-
centration constant. This is illustrated in Figure 3. Since 85-95%
of the input electrical power is dissipated as heat in the discharge
space, increased power requires concomitant increase in coolant flow
to avoid excessive temperature rise, which as discussed in Appendix A,
can lead to more rapid ozone decomposition. The effect of increasing
inlet temperature of cooling water on ozone production at a given
oxygen or air feed rate is shown in Figure 4. It can be seen that an
adequate supply of cooling water is necessary for efficient operation.
Ozone Generation Systems
Basic process flow diagrams for two types of ozone generation
systems are shown in Figure 5. When air is used as the feedstock it
14
-------
o
'o 4
o
o ,
o Z
o
3
0.2
5 0.1
0.2
O.I
c
UJ
A* Ozone Concentration
B - Ozone yield
C * Energy yield
I
I
10 IS 20 25
Oxygen flow, Ib/hr
30 38
Figure 3 . Effect of varying oxygen flow."
15
-------
80
40
Figure 4.
60 80 TOO
Cooling Water Inlet Temperature,
Typical effect on ozone production of cooling water inlet
temperature (air and oxygen feed). 7
16
-------
Compressor .
Air-J-Q
s
1 1
I
J
Air
0- + Air
to
Process
Filter
Coolers Driers
Ozonator
OZONE FROM AIR
Air-
Oxygen
Plant
to
Process
Ozonator
OZONE FROM OXYGEN
Figure 5. Ozone generation systems.
17
-------
must be filtered to remove participate matter, cooled to minimize
thermal decomposition of ozone in the ozone generator (ozonator) and
dried to remove practically all of the moisture prior to insertion
into the corona discharge unit.
For large scale generation from oxygen feedstock, a plant
producing oxygen from air must be used. This has the advantage of
producing a higher percentage of ozone in the output stream of the
ozonator for a given flow rate, but this advantage is offset by the
increased complexity, capital and operating costs of the oxygen plant.
Only if the oxygen is used in some other manner, for instance by
recycling, as is commonly used in water treatment, can the increased
costs be justified. For flue gas treatment this is obviously
impractical.
Standard commercial ozone modules are available typically to
o
about 560 kg/day maximum. For larger demands parallel modules must
be used. As will be discussed in the next section, an ozone demand
of as much as 0.6 kg/s or 51,840 kg/day could be required. This
would employ 93 parallel units at the present module size limit.
When oxygen feed to the ozonator is considered at 1.7% (weight)
ozone output,an oxygen feed rate of about 33 kg/s would be required.
This corresponds to a daily rate of 2.85 x 10 kg/day (about 3140 tons/day),
The largest oxygen plant built to date in the U. S. has a capacity of
21 kg/s (2000 tons/day). These size comparisons are made to emphasize
that the quantities of ozone projected in this report will require a
sizable extrapolation of present technology, both in ozone generation
and in oxygen liquefaction (should this be used). This extrapolation
should be kept in mind when the economics of ozone production are
discussed in a subsequent section.
Utility Requirements
Using the ozone mass flow requirement data from Figure 1 along
with typical yield figures for ozone generators and typical cooling
water flow rates, an estimate can be obtained for the electrical
energy, water and air (or oxygen) demands which these ozone flow rates
imply.
18
-------
The electrical power required, both for ozone generation and for
air induction and conditioning, is typically 23.15 kWh/kgCU for 1%
8
(weight) ozone output when air is used as a feedstock to the ozonator.
Required power as a function of ozone mass flow rate is plotted in
Figure 6. Also shown in this figure are the cooling water flow rate
required, based on an estimate of .0162 £/s per kgCL produced , and
the flow rate of air required, based on the weight fraction.
For oxygen feed to the ozonator, approximately the same cooling
water flow would be required but the power requirement would be reduced
to about 8.3 kWh/kg03 for 1.7% (weight) ozone output. The power and
cooling water requirements for the oxygen plant must be added to these
figures. For a typical plant producing 98% oxygen by volume, the power
and water requirements are about 0.31 kWh/kg02 and 0.039 m /kgOp,
respectively. Since the flow rate of oxygen will be about 50 times that
of the ozone output, these requirements will be substantial. The
combined power and cooling water demand and oxygen demand are plotted
versus ozone mass flow rate in Figure 7. Comparison with Figure 6
shows that the higher ozone generating efficiency when using oxygen
is more than offset by the power required to extract oxygen from air
to obtain the feedstock to the ozonator. Utility requirements for
ozone generation are summarized in Table 5.
19
-------
Power Air Flow
(MW) (m3/s)
50
0
0
0.5
47.6
1.0 1.5
95.2 142.8
Ozone Feed Rate
Water Flow
(m3/s) (Gal/min)
126 --2000
063- -1000
2.0 kg/s
190.5 tons/day
Figure 6. Utility requirements, power, water, and supply air for
ozonator using air feedstock.
20
-------
Power O Flow
(MW>
250 .,.125
200-
Ozone Feed Rate
Water Flow
(m3/s) (Gal/min)
10.0,
"100,000
80,000
-60,000
-40,000
• 20,000
2.0 kg/s
190.5 tons/day
Figure 7. Utility requirements, power and water, and oxygen feed rate
for ozonator and oxygen plant combined.
21
-------
Table 5. Utility Requirements for Ozone Generation for NO Oxidation
in Flue Gas from 500 MW Oil-fired and Coal-fired Stations.
Item
Power (MW)
kWh/yr 0,
production
% Energy for 0.,
production
Cooling water
(m3/s)
Air Flow (m3/s)
Oxygen Feed
Rate (kg/s)
Oil -Fired (200 ppm NO)
Air- Feed
15.8
1.1 x 108
3.1
.011
15.7
~
Oxygen Feed
18
1.25 x 108
3.6
.437
-
n
Coal -Fired (600 ppm NO)
Air- Feed
47.5
3.3 x 108
9.5
.033
/
47
™
Oxygen Feed
54
3.75 x 108
10.8
1.31
-
33
22
-------
ECONOMICS OF OZONE PRODUCTION
The economics of integrated ozone water treatment systems has been
treated by Rosen, who has discussed the tradeoffs between air feed
and oxygen feed systems. However his analysis must be considerably
modified for application to power plant FGT systems because oxygen
recycle is not possible. Since the ozone FGT systems would be installed
primarily in private utility owned electrical generation plants, the
guidelines appropriate to regulated private utility-type costing should
be employed. These guidelines have been applied to economic evaluations
of the costs of power plant flue gas desulfurization processes by
3
McGlamery ejt aK Their procedure is applicable to the economic evaluation
of ozone FGT processes and will be used.
Based on Federal Power Commission guidelines a new fossil-fueled
power generation unit has an expected operating life of 30 years. The
utilization factor over this period declines rapidly after the first
10 years, as shown in Table 6, which is based on TVA operating data.
Recently there has been some discussion of reducing the depreciation
15
lifetime to 20 years in order to internally generate more capital,
but whether or not this might occur in the near future is doubtful.
Although an analysis could be performed to project operating costs over
a 20 year lifetime as well as a 30 year lifetime, at the present exploratory
stage of considering the economic viability of the use of ozone to oxidize
NO to N0£ neither course seems justified. Rather, it appears that an
assessment of first year costs is all that is needed at present.
In order to provide such an assessment, two model situations are
used. The first case is an oil-fired 500 MW unit which is assumed to have
an NO concentration of 200 ppm (cf. Table 2). The second is a coal-
fired 500 MW unit which is assumed to have an NO concentration of 600 ppm
(cf. Table 2). A cost estimate analysis is performed for each case for
both air feed and oxygen feed to the ozone generator. Details of this
procedure are given in Appendix C.
Capital cost estimates for ozone generators were obtained from a
8
manufacturer. Capital costs for the required oxygen plants were based
23
-------
Table 6. Assumed Power Plant Capacity, Schedule.
Operating year
1-10
11-15
16-20
21-30
Average for 30 year life
t
Capacity factor % *
(nameplate rating)
80
57
40
17
48.5
Annual
kWh/kW
capacity
7,000
5,000
3,500
1,500
4,250
100% =8,760 hours/yr
24
-------
on manufacturer's data (1974) updated to 1976 dollars using Chemical
Engineering magazine cost indic<
standard cost-capacity relation
12
Engineering magazine cost indices. Size was updated using the
C2 = (^(QyQ (4)
where C~ is the cost of a plant with capacity (^ and C^ is the cost
of a plant with -capacity Q-, . The exponent N has the capacity of 0.72
13
for oxygen plants in the range .01 to 15.8 kg/s (1 to 1500 tons/day).
Because the size of plant required for the coal-fired case was approximately
double the upper limit of this range, this limit was used in equation (4)
and then the cost was doubled.
Indirect costs covering engineering design and supervision, contractor
fees, contingencies and construction field expense were added, as was an
allowance for start-up and modification and interest on funds borrowed
difring the construction phase (assumed to last three years). The resulting
total capital costs are given in Table 7
Operating costs, based on 7000 hours of operation in the first
year were calculated for direct, indirect and fixed elements. The
direct costs were estimated from the utility data presented in the
preceding section and from manufacturer's information and/or estimates
of operating labor and maintenance costs. Indirect costs were based
on the assumption of a plant overhead rate of 20% of the direct costs
and an administrative overhead of 10% of the labor cost. Fixed costs
were comprised of depreciation (over a 30 year period), replacement,
insurance, debt service (10%) equity return (14%) and taxes. Application
of these elements give the first year operating costs shown in Table 8.
In both the oil-fired (200 ppm NO) and coal-fired (600 ppm NO)
cases the capital and operating costs of using oxygen feed are consider-
ably higher than when air feed to the ozone generator is used. A
comparison of the costs for the oil-fired case with those for the coal-
fired case show a direct relationship with NO content. This dramatically
emphasizes the desirability of using combustion modification controls to
reduce NO content prior to flue gas treatment. However, even if combustion
25
-------
Table 7. Cost Items and Estimated Total Capital Investment for Ozonation Facilities for 500 MW Coal-
Fired and Oil-Fired Generating Stations
Item
Direct Costs
Indirect Costs:
Engr. Design and Supv.
Construction Field Expense
Contractor's Fee
Contingency
Total Direct and Indirect Costs
Allowance for Start-up and
Modification (8%)
Interest During Construction
(12%)
Estimated Total Capital
Investment (1976 $)
Unit Costs
$/kg03 (first year)
$/KW capacity
Oil Fired (200 ppm NO)
Air Feed
$5.4M
.49M
.59M
.27M
.54M
$7.3M
.58M
.88M
$8.8M
1.85
17.60
Oxygen Feed
$17. 3M
1.56M
1.90M
.87M
1.74M
$23. 4M
1.87M
2.81M
$28. 1M
5.90
56.20
Coal Fired (600 ppm NO)
Air Feed
$16. 2M
1.46M
1.78M
.81M
1.62M
$21. 9M
1.75M
2.63M
-$26. 3M
1.84
52.60
Oxygen Feed
$47. OM
4.23M
5.17M
2.35M
4.70M
$63. 5M
5.1M
7.6M
$76. 2M
5.34
152.40
ro
-------
Table 8. Annual Operating Costs, First Year, 7,000 Operating Hours, for Oxidation of NO in Flue
Gas of 500 MW Generating Units
Item
Direct Costs
Electrical
Water
Labor
Maintenance
Total Direct Cost
Indirect Cost
Fixed Cost
Total
Unit Costs
$/kg 0- produced
mil/kWh produced
Oil Fired (200 ppm NO)
Air Feed
$3.305M
0.1 58M
0.149M
0.324M
$3.936M
0.802M
2.291M
$7.029M
1.48
2.0
Oxygen .Feed
$3.806M
0.221M
0.298M
0.519M
$4.844M
0.999M
7.314M
S13.157M ,
2.76
3.8
Coal Fired (600 ppm NO)
Air Feed
$6.624M
0.159M
0.298M
0.972M
$8.053M
1.641M
6.846M
$16.540M
1.16
4.7
. Oxygen Feed
$7.616M
0.663M
0.447M
1.410M
$10.136M
2.072M
19.835M
$32.043M
2.24
9.1
ro
-------
modification could reduce the NO content of flue gas from a coal-fired
unit to the level now typical of an oil-fired unit, the capital and
operating costs would still be significant.
28
-------
FORECAST FOR IMPROVEMENTS
Until.recently the energy required for large scale generation of
ozone at about 1% weight concentration with air feed ranged from about
5 14
17 to about 20 kWh/kg03. It has been reported that an improved
version of the corona discharge system has been developed in Japan,
based on a concept produced by the Grace Company. This involves re-
design of the ozone generator to handle unprocessed air, thereby
eliminating the equipment required for air preparation. The energy
required is reported to be 11-13 kWh/kg03. Negotiations are currently
being conducted by Union Carbide to secure licensing rights to produce
ozonators using this process for the U. S. Market.
Recently there have been developments in the combined use of nuclear
radiation and electric discharge in order to increase the attainable
output concentration of ozone and to improve the energy efficiency. A
Japanese patent has described the use of gamma radiation from a Cobalt-60
source to increase the 0., concentration from 3.5%, for electric discharge alone,
to 7% in an oxygen feed stream. The energy per unit mass of ozone produced
was decreased from 5.6 kWh/kgO^ for the electric discharge alone to
3.5 kWh/kgO- for the combined nuclear radiation-electric discharge process.
It should be pointed out, however, that this was bench scale demonstration.
The use of nuclear radiation for ozone production has been studied
in this country for a number of years. Steinberg has summarized much
of this research and has examined the economics of "chemonuclear" ozone
compared to standard electric discharge plants, using as the basis a
400 ton/day plant. The cost analysis assumed that the nuclear radiation
is available from "waste radiation" from an existing nuclear reactor.
The use for the ozone generated was assumed to be for waste water treatment.
In order to put into perspective the size of radioactive source required
when a nuclear reactor is not available, Steinberg estimates that in order
to generate 907 kg03/day a 19.3 Megacurie Cobalt-60 source would be required.
A source of this size would present extremely impractical shielding problems.
The chemo-nuclear approach does not use electric discharge to augment the
production of ozone.
29
-------
In summary, it appears that in the foreseeable future the only
practical improvement that can be expected in large scale ozone generation
technology is a reduction in the generating power to about two-thirds
of the amount now required, based on the W. R. Grace development.
30
-------
APPENDIX A. OZONE REACTION KINETICS
The use of ozone to oxidize flue gas NO to more readily absorbed
A
species requires the generation of large quantities of ozone. In order
to model the process to ascertain the energy efficiency and cost and to
forecast the possibility of technological improvements, the reactions
and kinetic factors involved in the generation, transport, mixing, and
reaction of ozone must be considered.
Ozone Thermal Decomposition
Even as ozone is being generated and transported to the region where
it will be used, ozone is in the process of decomposing due to collisions
with other gas phase species. The sequence of reactions leading to this
decomposition is believed to be
Kl
03 + M -* 02 + 0 + M (A.I)
K2
02 + 0 + M-+03 + M (A.2)
K3
0 + 03 -> 2 02 . (A.3)
In these equations M represents a third collision partner, of any type
molecule present in the gas mixture. The concentration of M is equal to
the number density of gas molecules and is therefore proportional to the
total pressure of the gas mixture containing the ozone and oxygen. These
are uncatalyzed gas phase reactions. The rate equation for the decay of
ozone concentration is
-d[03J 2K1K3[03]2[M]
~~ =
dT~ K^p} + K3[03] ' (A'4)
31
-------
In a practical ozone system the concentration of oxygen is large compared
5
to that of ozone, and the total pressure is usually one to two atmospheres.
Comparing the two terms in the denominator at 300°K under typical operating
conditions
K2[02][M] = 2.2 x 105 sec"1
K3[03] = 6.1 x 102 sec"1 .
Therefore, to a good approximation
-d[0,]
= 2K1K3[03r/K2[02] . (A.5)
or
.d[00
= K5[03]/[02]
where21 «5 = 4.55 x 1015 exp (-15,400/T) sec"1. Note that since [M] no
longer appears in the equation, the ozone decomposition rate is not
explicitly a function of the total pressure and depends only upon the
ozone and oxygen concentrations.
The inverse dependence of decay rate on oxygen concentration sug-
gests the use of oxygen rather than air as the source gas in the ozone
generating system. Another reason for not using air is the possibility
of catalyzed decomposition of ozone by N90K through a cyclic process
5
which regenerates N^Gg while destroying ozone, which is considered
subsequently in this Appendix.
Many solid surfaces catalyze the decomposition of ozone. Catalytic
activity depends upon the physical and chemical state of the solid surface
5
as well as upon the presence of moisture. Ozone decomposition in aqueous
solutions is much more rapid than in the gaseous state because it is
catalyzed by hydroxyl ions.
32
-------
Reaction with Nitric Oxide
Ozone reacts with nitric oxide to give either electronically excited
* +
p or vibrationally excited NOo as
*
NO + 03 -*• N02 + 02 (A. 6)
K7
NO + 03 -»- N02 + 02 (A. 7)
with rate constants18 of Kc = 7.8 x io5 exp (-2103/T) m3/mole-sec and
c 3
K7 = 4.3 x 10 exp (-1173/T) m /mole-sec. The electronically excited N02
relaxes to ground state either through chemiluminescence or collisional
energy transfer, while N02 relaxes only by the latter mechanism. The
combined rate equation for N02 is
= Kg [N0][03] , (A.8)
where KQ = (Kg + K7). This is also the loss rate for ozone due to N02
formation.
Reaction with Nitrogen Dioxide
Ozone reactions with nitrogen dioxide yield N00,- through the reac-
19
tion sequence
Kg
N02 + 03 -*• N03 + 02 (A.9)
K10
N02 + N03 -s- N205 , (A. 10)
the first of which is rate limiting. The rate constant of (A.9) is given
by Kg = 5.9 x 106 exp (-3523/T) m /mole-sec. The N2Q5 molecules so formed
33
-------
can thermally decompose and participate in cyclic reaction sequence which
20 21
decomposes ozone. The complex sequence has been studied in detail '
22
and elucidated by Johnson. It involves
ai(M)
N205 + M - >• H2o£ + M (A. 11)
g + M - > N205 + M (A. 12)
N2°5* — " N02 + N03
i*
N02 + N03 — * N20j (A. 14)
K15
N02 + N03 — >• NO + 02 + N02 (A. 15)
K16
NO + N03 — ^ 2 N02 (A. 16)
K17
N03 + N03 — * 2 N02 + 02 (A. 17)
Kg
N03 + 02 (A.9)
The superscript i* indicates one of the excited states of N20g. Reaction
rates for the individual reactions are appropriately summed over the
excited states in order to obtain the overall reaction rate. The rate
constants a^M) and b.(M) depend upon the collision partner species M.
Johnston has considered four overall reaction sequences involving
(A.9 - A.17). These are, with stoichiometric equations
34
-------
1. the decomposition of nitrogen pentoxide,
2 N205 = 4 N02 + 02 (A.18)
2. the decomposition of nitrogen pentoxide in the presence of
nitric oxide,
NO + N205 = 3 N02 (A.19)
3. the decomposition of ozone in the presence of nitrogen
pentoxide,
2 03 + N205 = 3 02 + N205 (A.20)
4. the formation of nitrogen pentoxide from ozone and nitrogen
dioxide
2 N02 + 03 = N205 + 02 . (A.21)
All of these mechanisms should be considered in the process under investi-
i
gation. The second reaction above must be considered when
K16[NO] » K15[N02]
or (A.22)
K,
[NO] » ^ [N0?] .
K16 *
35
-------
Johnston has estimated that, at 300°K, K,c = 7 x lo8 and K1C > 1013.
lo ID
Therefore, it appears that even trace quantities of NO serve to catalyze
the decomposition of NpO,-. The decay rate is, at the pressure of
practical interest,
-K(2) " • (A-23)
?n -i
The value of K^ ' at 300°K is given by Johnston at 0.29 sec with an
activation energy of (8.8 ±0.84) x 10 Joule/mole.
The reaction sequence of ozone decomposition by nitrogen pentoxide
is given by Johnston as
- -dT C°3] = K{3) tN205]2/3 [03]2/3 (A.24)
where K^ has the value of 2.6 (mole/m3)1/3 sec"1 at 300°K with an
activation energy of (8. 6 ±0.42) x 10 Joule/mole.
Reaction with Sulfur Dioxide
The reaction of S02 with 03 is very slow unless catalyzed by other
species. The reaction
S02 + 03 -»• S03 + 02 (A. 25)
=.K21[S02][03] (A. 26)
23 -3 3
has been found to have a rate constant of about 6 x 10 m /mole-sec at
360°K and about 1.2 x 10 m /mole-sec at 300°K. In a study of the mecha-
24
nism of aerosol formation, it was found that the reaction of S02 and 03
at about 0.1 ppm concentrations in air were very slow until olefins were
added to the gas mixture. Then the reaction rates were dramatically
increased, leading to the formation of H2SO» aerosol as SO-, combined with
water vapor. This is illustrated in Figure 8. Since it is doubtful that
36
-------
.SflRm 2-penl-2>cne
added
time/min
Figure 8. (Concentration, time) curves for ozone + SC^ reaction showing
HSO aerosol formation on the.addition of cis-pent-2-ene.
37
-------
any such species would be present in the flue gas, it appears that the
oxidation of S02 by 03 represents a negligible depletion of the ozone.
Therefore, reaction rate (A.26) will not be included with the other
kinetic terms.
Summary
Ozone generation by electrical discharge has poor energy efficiency.
Large-scale ozone generator outputs are typically a few percent by weight
of ozone at most. Once generated, ozone starts to decay spontaneously at
a rate given by
d[03]
(- ? 1
= 4.55 x I0n exp (-15,400/T)[03r/[02] moles/m -sec (A.27)
which rapidly increases with temperature. Ozone also decomposes in reac-
tions which are catalyzed by moisture, certain types of surfaces, and by
certain gaseous species.
The primary reaction of interest for NO removal is the oxidation of
/\
NO to N02 by ozone, which occurs at a rate proportional to the gas phase
concentration of both NO and 03, given by
d[NO?] , ,
d1/ = [7.8 x 10b exp (-2103/T) + 4.3 x TO* exp (-1173/T)]
x [N0][03] moles/m3-sec . (A.28)
Ozone also reacts with N02 to produce N205 at a rate proportional to both
the N02 and 03 concentrations, given by
d[N?0,] , ^
—|p- = 5.9 x 10° exp (-3523/T)[N02][03l moles/m -sec . (A.29)
The product N205 is in turn decomposed at a rate which is enhanced by
even trace quantities of NO, given by
38
-------
4 •
= 5.77 x 1014 exp (-10,568/T)[N205] moles/in -sec . (A.30)
In addition, NpO,- participates in a cyclic reaction sequence described by
equations (A.11) through (A.17) which tends to decompose ozone at a rate
giyen by
--gjr- = 2.23 x lo13 exp (-10,316/T)[N205]2/3[03]2/3 mole/m3-sec .
(A.31)
Compared to reactions with NO , the gas phase reaction of ozone with S09
A £
is relatively slow. Even though SOp typically occurs at concentrations
of as much as five to ten times that of NO in flue gas from oil- and
A
coal-fired boilers, the rate of loss of ozone due to S02 oxidation is
negligible compared to other losses.
The rate equations (A.27) through (A.31) are used in Appendix B,
evaluated at temperatures typical of flue gas streams, in order to esti-
mate the amount of ozone required to oxidize NO at a given input concen-
tration in order to facilitate later removal by various scrubbing processes.
39
-------
APPENDIX B. DETERMINATION OF OZONE DEMAND
In order to obtain a quantitative estimate of the amount of ozone
required to convert NO to N0~ or N^Or in a flue gas stream, a model will
be developed for the process. Then the model will be used to estimate
the amount of Og required for various flue gas rates and NO concentra-
tions.
Model Reactor
The classical reactor situation of "plug flow" will be used for the
model. As shown in Figure 9, an elemental volume, dV, in the reactor is
considered. The total volume rate of flow, q, is considered constant
into and out of the volume. Each species under consideration moves into
dV at a rate qC., where C. represents the volume concentration, in
3
moles/m , of species i. In dV chemical reactions occur which change the
concentration by AC. so that the exit flow rate from dV is q(C. + AC.)-
1 f\ 1 1
For each dV the continuity relation for each species is :
(accumulation).. = (input)^ - (output^ + (generation)..
(B.I)
- (recombination). .
Since there is no provision for mass storage, the left hand side of
(B.I) is identically zero. The modeling method consists of setting up
the simultaneous equations of the form (B.I) with appropriate terms for
each species and solving these, subject to the appropriate boundary
conditions on input, in order to determine, for a given total reaction
volume, V , the value of the concentrations of each species at the
output.
In terms of rates, equation (B.I) can be written as
9C. 9C.
40
-------
Cross Section A
dz
qC1
dV
q(C1
Figure 9. Elemental reaction volume in plug-flow reactor model.
where A is the cross-sectional area of the reactor. If the lineal
velocity of transport is assumed to be a constant, u, over A, this can
be written as
dC.
~3T
3C.
3C,
gain
'loss-
(B.3)
for the four species of interest, with the notation
o
C, = ozone concentration, [Oo], moles/m
3
C0 = nitric oxide concentration, [NO], moles/m
3
C3 = nitrogen dioxide concentration [NCL], moles/m
C. = nitrogen pentoxide concentration [N20c], moles/m^
The simultaneous equations are:
3C
=
- K8C2C1 - K9C3C1
(B.4)
41
-------
3C,
(B.5)
£. - |/ r f oi/ r r 4. 't\/\f-lr ^R K\
~T— - Ngl'oi'i ^^Q^O^I ^^a, ^/i \D-Dy
o£ Obi Z/ O I T
u -3F = Wl * K- C4 '
where 1C = Kg/tOp]'. These are obviously nonlinear. Rigorous solution is
difficult, if not impossible. However, by considering the relative size
of the terms involved, it may be possible to neglect some terms in order
to get an approximate solution without too much difficulty.
Approximate Equations
Two situations will be considered. First, the flue gas is initially
cooled to 60°C--the situation used in Japanese pilot plant operations --
and second, the flue gas is not cooled from its normal exit temperature of
about 149°C. Values for the rate coefficients in equations (B.4) - (B.7)
corresponding to these two temperatures are shown in Table 9. It is
obvious that the "worst case" of the two situations as far as possible
retention on the nonlinear terms in (B.4) - (B.7) are concerned is the
higher temperature situation, which will be taken.
In order to test for the relative size of the rate terms, two cases
will be considered. For both it will be assumed that the flue gas feed
is at 472 m3/s with 600 ppm NO and 30 ppm N02 at 149°C. These condi-
tions are typical for a coal-fired 500 MW generation unit. The first
case assumes that the added ozone is at 1% by weight in air and the feed
rate gives an ozone/nitric oxide mole ratio of 1.0. The second case
assumes that the added ozone is at 1.7% by weight in oxygen. The initial
value of N^Oj- is assumed to be zero for both cases. The resulting values
for the rate terms in equations (B.4) - (B.7) are shown in Table 10.
It is obvious that the effect of gas phase thermal decomposition of
2
ozone, the term KgC-j, is small initially even at 149°C and will become
even smaller as the ozone concentration decreases due to reactions with
the nitrogen oxides. Therefore, this term can be dropped from equation
(B.4) with negligible error. It also appears that, as a first approxi-
mation, the interactions of N^O,- formation and reaction with NO and 03
42
-------
Table 9. Size of Reaction Rate Values at 60° and 149°C.
Reaction
Rate
Pre-exponential
Factor
Exponential
Argument
Value at 60°C Value at 149°C
Units
to
9
(3)
4.55 x 1015/[02]
7.8 x 105
4.3 x lo5
5.9 x 10'
2.23 x 10
13
-15,400/T
- 2,103/T
- 1,173/T
- 3,523/T
-10,316/T
3.7 x 10~5/[02] 0.64/[02] Sec
1.41 x 10
1.5
0.784
3.2 x 10
1.4
540
-1
m /mole-sec
m /mole-sec
(m3/mole)+1/3 sec"1
,(2)
5.77 x 10
14
-10,568/T
9.5
7.68 x 10"
Sec
-1
-------
Table 10. Numerical Estimates for Initial Values at 149°C of Terms in
Rate Equations at Stoichiometric Ozone Feed from Both Air
Stock and Oxygen Stock
Terms
1 ?
Vi
K8C2C1
K9C3C1
K(3)c 2/3 c 2/3
K(2)c
Feed Composition
1% (wt) 1.7% (wt)
Ozone in Air Ozone in Oxygen
3.1 x 10"4 1.2 x 10"4
8.1 8.9
8.9 x 10"3 9.7 x lo"3
0 0
0, 0
44
-------
can be neglected. This assumption will be tested after the simplified
reaction equations are used to model the system.
The approximate rate equations can be written in the form
dC1
~dT = "aC!C2 " bC!C3
(B.8)
~dT
(B.9)
dC
= aC!C2 ' 2bClC3
dC^
dz
(B.10)
(B.ll)
where a = Kg/u and b = Kg/u.
Solution of Approximate Equations
These coupled nonlinear equations would still be extremely difficult
: ^ 25
to solve by conventional means. However, Benson has discussed a method
that provides a convenient way to assess the ratios of species concentra-
tions when the reactions are allowed to proceed to a given extent. Using
this method, it can be shown that the reactant concentrations can be
written in the forms
10
10
30_
C30/C20
+ 0.5
(B.12)
(B.13)
45
-------
and
'30
3oy
20,
(B.14)
where C
,Q,
and C3Q are the initial concentrations of ozone, nitric
oxide, and nitrogen dioxide, respectively. It has been assumed that the
initial concentration of N?0r is zero. The parameter K is given by
= L-
(B.15)
These equations can be used, with appropriate values for the initial
concentrations of reactants, to determine the course of the reactions
as NO and N02 are oxidized.
Numerical evaluations for the conditions:
T =
C30/C20
C10/C20
422°K (149°C)
30/600 =0.05
0.5, 0.9, 1.0, and 1.1
are presented graphically in Figures 10, 11, 12, and 13. For the NO
* r\
concentration ratio assumed, exact stoichiometry would require C-,n/C?n
to be 1.025. Comparison of the curves indicates that as far as NO oxida-
tion in concerned, there is little advantage in exceeding the stoichiometric
ratio. An increase of 10% added ozone, going from Cif/Con = 1-0 to
CIQ/CPQ =1.1, results in only a slight increase in amount oxidized--i.e.,
from 96% to 98%. Most of the extra ozone is consumed in the production of
N205.
Checking the assumption that led to dropping the C« terms from
equations (B.4) - (B.7), consider the data of Figure 12 for the case
where 90% of the ozone has been depleted. The rate terms of (B.4) - (B.ll)
are, for the case of air feed,
46
-------
C3Q/C20 = 0.05
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Figure 10. Relation between NO, N02 and N205 concentrations and the
fraction of ozone used for oxidation for initial conditions
[03]/[NO] = 0.5 and [N02]/[NO] = 0.05.
47
-------
C10/C2Q = 0.9
o
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
(c10-Cl)/c10
Figure 11. Relation between NO, N02 and NpOr concentrations and the
fraction of ozone used for oxidation for initial conditions
[03]/[NO] = 0.9 and [N02]/[NO] = 0.05.
48
-------
c10/c20 = i.o
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
(cio-ci)/cio
Figure 12. Relation between NO, N02 and N20^ concentrations and the
fraction of ozone used for oxidation for initial conditions
[03]/[NO] = 1.0 and [N02]/[NO] = 0.05.
49
-------
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Figure 13.
Relation between NO, N02 and N2o5 concentrations and the
fraction of ozone used for oxidation for initial conditions
[03]/[NO] = 1.1 and [N02]/[NO] = 0.05.
50
-------
= 0.111
K]C1C3 = 0.0146
K(2)C,, = 2.73
oo 4
K(3)(C1C4)2/3 = 0.0367 .
Thus, it appears that the assumption was not justified by these results
because of the rapid build-up of N^O,- as the ozone nears depletion. The
question arises as to whether or not such a build-up will occur since,
according to equation (B.7),
the rate of increase of C. will be limited by its conversion to N02
through reaction with NO. As discussed in Appendix A, in connection
with the inequality (A.22), as long as even small amounts of NO are
present, they will rapidly react with N^O,- to produce NOo. In the words
of Benson, "NO acts as an efficient scavenger for NpOg."
Steady State Approximation
Taking this into account an alternative approach is to invoke the
25
"steady-state hypothesis" for the species N205. This hypothesis
assumes that there is a rapid build-up of N^O^ to a concentration value
where the two opposing rate terms in (B.7) balance to give a net rate of
zero. When (and if) this occurs, the dynamic equilibrium value of C is
Defining f = IO3'/u and g
be written in the form
, the rate equations (B.4) - (B.7) can
dc
- bC]C3 -
51
-------
- ,gC
dC, . .
-^ = aCjCg - 2 bC1C3 + 3 gC4
dC4
-^= bC1C3 - gC4 = 0.
Solving equation (B.16) for C4 and substituting this into (B.13) - (B.15)
gives
dC
- bC]C3 (B.18)
Again using the situation of air feed to the ozone generator and a flue
gas temperature of 149°C, the rate terms in the above equation can be
compared for the situation where the C,, Co. and C3 concentrations are
near their initial value and C4 has achieved its steady-state value of
_
/2\ C-.C., = 1.16 x 10 moles/m
l\
The rate terms are
aC!C2 = n C1C2 = 8J1/U
bC!C3 = IT C1C3 = 8'86 x 10"3/u
52
-------
f(C1C4)2/3 = ^- (C^)273 = 3.82 x 10'3/u .
The last term is certainly negligible with respect to the first term,
initially. As the concentration of NCL, C3, increases, the first term
will decrease and the second term will increase, but not rapidly, since
the build-up of C^ is countered by the decrease of C-.. It will be
assumed that the third term remains negligible and this assumption will
be tested when the consequences are evaluated. With this modification,
equations (B.17) - (B.19) are equivalent to
dC2/dC1 = 1 (B.20)
dC3/dC] = -1 . (B.21)
Using the initial conditions
Cl C10
C2 = C20
at z = '0 (t = 0) , (B.22)
the NO and N02 concentrations are given by
C2/C2Q = 1 - (C10/C2())(C10 - Cl)/C10 (B.23)
C3/C2Q = (C30/C20) + (C10/C20)(C10 - Cl)/C1(J . (B.24)
A plot of these relations for the case Cig/C™ =1.0 and Con/Con =
0.05 is given in Figure 14.
2/3
Testing the assumption that the rate term f(C-,Cj remains
negligible with respect to the other terms in equation (B.17), at
99% ozone use,
53
-------
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Figure 14.
Relation between NO and NOp concentrations and the fraction
of ozone used for initial conditions [03]/[NO] = 1.0 and
[N02]/[NO] = 0.05 with steady state assumption for [N205].
54
-------
(C1Q - C^/Cjg = 0.99 C2 = 0.01 C2Q
^ = 1.04 C,
2(J
= 8.11 x 10"4/u
bC]C3 = 1.84 x 10"2/u
f(C1C4)2/3 = 1.77 x 10"4/u .
The N205 catalyzed decomposition of ozone accounts for only about 1% of
the ozone depletion rate at this point. Therefore, the assumption that
this term remains negligible was justified.
The conclusion reached from this analysis is that the amount of ozone
required for oxidation of NO to N02 is the amount required by the
stoichiometric equation
03 + NO = N02 + 02 .
3
For a flue gas flow rate of QF m /sec and an NO concentration of n ppm,
the mass flow rate of ozone required is
w0 = $= 2 x 10"6 QFn. kg/sec (B.25)
where Qr is the flue gas rate under the industrial standard condition of
21°C (~70°F). For a 500-MW plant with a nominal flue gas flow rate of
6 3
1 x 10 SCFM or 472 m /sec with an NO concentration of 600 ppm, an ozone
feed rate of 0.566 kg/sec or 53.9 tons/day is required. The ozone require-
ments for various flue gas flow rates at various NO concentrations have
been plotted in Figure 1 of this report.
55
-------
In closing, it should be re-emphasized that this model is for gas
phase reactions only and does not account for wall losses of ozone.
Inherent assumptions are those for the classical "plug flow" model--
i.e., a uniform velocity across the reactor cross-section, good initial
mixing of the reactants, and negligible axial diffusion effects;
56
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APPENDIX C. ECONOMIC ANALYSIS
In order to determine the cost of oxidizing NO to NOp using ozone,
the initial capital investment required for the construction of a suit-
ably sized ozone generation plant must be estimated. Then the costs
associated with amortization of the capital investment, labor, utilities,
maintenance, etc., must be estimated and averaged over the amount of NO
oxidized and over the amount of electric power generated over some suit-
able period of time. These measures can then be compared to other per
unit generation cost measures in order to assess the economic viability
of this method of NO oxidation vis-a-vis other methods.
Capital Costs
Capital investment cost can be estimated for both air feed and oxygen
feed plants as follows. For tonnage-sized ozone plants the current costs
of equipment plus direct construction costs run about $330 per kg ozone
0
per day ($300,000/ton/day) using air feed. This cost includes all of
the air induction, drying, and cooling equipment necessary to condition
the feed to the ozonators.
For oxygen feed there are two cost components, the ozone generation
Q
system and the oxygen plant. The ozone generation costs are estimated
to be $177 per kg 03 per day ($160,000/ton/day). To this must be added
the cost of building an oxygen plant to supply the feed. Oxygen plant
cost can be estimated by obtaining a cost figure, C-j, for a plant of
capacity Q, and extrapolating by the well-known cost-capacity relation
(C.I)
where C~ is the cost of a plant of capacity Qo and N is an exponent for a
••'•??
given class of equipment or process plant. The value of this exponent is
determined by plotting cost-versus-size data on a log-log scale. Tables
are published from time to time in various magazines and books germane to
chemical engineering, which give values of N over a suitable size range
for various equipments. In addition to the size factor of cost, there is
57
-------
a price escalation factor which must be taken into account. The cost C-j
is for some base year with a cost index I-p Plant of cost C2 is to be
built in a year with a cost index 1^, giving an updated cost of
C2 = Cglg/Ij = C] ^ (CyQ^ . . (C.2)
For the current analysis a 1976 cost index is used for I9. For oxygen
fi
plants in the range of about 900 kg/day to about 1.4 x 10 kg/day,
13
Zimmerman has given a value for N of 0.72, which is used in this
analysis. Cost index data are obtained from Chemical Engineering
magazine.
For a 500-MW coal-fired plant with a nominal NO concentration of
600 ppm, the required ozone is, from the analysis of Appendix B,
49,000 kg/day (53.9 tons/day). For a 500-MW oil-fired plant with a
nominal concentration of 200 ppm, the requirement is about 16,300 kg/day
(18 tons/day). Assuming 1.7% by weight ozone when oxygen is used as
a feedstock to the ozonators, the required oxygen plant capacities are
2.9 x 106 kg/day (3180 tons/day) and 9.67 x 105 kg/day (1060 tons/day),
respectively. The latter figure lies within the range given by
Zimmerman corresponding to N = 0.72 for the cost capacity equation (C.I).
The larger plant, however, is over twice the size of the upper range
limit. For the cost estimate for this size plant, it will be assumed
that two parallel plants at the upper limit (or only slightly above)
are to be built as a unit to obtain a direct cost figure. Using data
for a mid-1974 oxygen planl
the oxygen plant costs are
for a mid-1974 oxygen plant of 7.89 x 10 kg/day (870 tons/day) capacity,
Oil-fired case: C2 = $11 x 106 (^-) ' = $12.7 million
Coal -fired case: C2 = 2 x $11 x 106 fij^-) ' = $34 million
These direct costs, updated to first quarter 1976 dollars using Chemical
Engineering magazine indices, are given in Table 11 along with the ozone
generator direct costs.
58
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Table 11. Estimated Direct Capital Costs for Ozone Generation for NO
Oxidation in 500-MW Generating Stations
Type /NO
Concentration
Oil Fired/
200 ppm
Coal Fired/
600 ppm
Ozone
Required
(kg/day)
16,300
49 ,000
Direct Capital Costs
Air Feed
$ 5.4 M
$16.2 M
Oxygen Feed
Ozonator
$2.9 M.
$8.6 M
02 Plant
$14.4 M
$38.4 M
Total
$17.3 M
$47 M
In addition to these direct costs, which include equipment, instal-
lation, labor and materials, and construction facilities, there are
indirect project costs that must be added into the total investment.
These costs include engineering and design supervision, construction
field expense, contractor's fees, contingency, allowance for start-up
and modification, and interest during construction. The figures used
3
for these items, shown in Table 12 taken from McGlamery et_al_., are
representative of those expected for power industry equipment installa-
tion. In addition to the percentage contributions shown in Table 11,
it is standard practice to include an allowance for start-up and modifi-
cation costs, which will be taken as 8% of the subtotal direct plus
indirect investment, and to include the interest costs during construc-
tion. The interest cost is estimated to be 10% per year, and the
construction is assumed to take place over a three-year period, giving a
cumulative rate of 12% direct plus indirect investment.
3
McGlamery et al. assumed a capital structure of 50% equity - 50%
debt for their calculations with a three-year project expenditure schedule.
This does not agree with recent practice. In 1974 only 33% of construc-
tion funds were provided internally with the percentage expected to rise
26
to about 41% by 1979.tu Using 40% equity - 60% debt financing at
simple interest, the project expenditure schedule is as shown in Table 13.
the cumulative debt financing is equivalent to 12% of the total expendi-
ture, which was the value used to compute the interest during construction
costs in Table 7.
59
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Table 12. Indirect Investment and Allowance Factors
Power unit size and status
Engineering design and
supervision
Construction field expense
Contractor's fees
Contingency9
Total in directs
Percentage
New
9
11
5
10
35
of direct investment
500 MW
Existing
10
13
7
11
41
aBased on proven design rather than a "first of a kind" installation; a
minimum amount of contingency is included. For a "first of a kind"
installation, contingency would normally be greater than that shown
above.
Table 13. Project Expenditure Schedule
Year
Item
Total
% of expenditure as borrowed
funds
Simple interest at 10%/year
as % of total expenditure
Year 1 debt
Year 2 debt
Year 3 debt
Accumulated interest as %
of total expenditure
15
1.5
1.5
30
1.5
3.0
4.5
15
1.5
3.0
1.5
6.0
60
4.5
6.0
1.5
12.0
60
-------
It has been assumed that the plant equipment shown in Table 11 will
be installed only in new plants. Based on this assumption and the use
of the corresponding percentages for indirect costs shown in Table 12,
the estimated total capital investment is as shown in Table 7 of the
text. These estimates are in 1976 dollars.
Operating Costs
For an estimation of operating costs, the procedure that will be
13
used will generally follow the method of McGlamery et al. The cost
elements will be divided into three categories: direct costs, indirect
costs, and fixed costs (average capital charges). Direct cost elements
for the process options are given in Table 13. The cost of power is
taken as 2 cents/kWh for coal-fired units and 3 cents/kWh for oil-fired
27
units. The cost of cooling water depends on the usage rate. A plot
27
of cost versus rate is shown in Figure 15. Costs were taken to nearest
cent from this data. The indirect costs are figured on the basis of a
plant overhead, 20% of the total direct costs, and an administrative
overhead, 10% of the direct labor cost. The average capital charges
which constitute the fixed costs are compiled in Table 15. These differ
somewhat from the figures used by McGlamery et al. because the capital
structure is assumed to be 60% debt - 40% equity rather than 50/50.
In addition, it is assumed that 0.5% of the original investment will
be allowed for interim replacements rather than 0.6%.
Based upon these cost elements, calculations were made of operating
costs for the first year on the basis of 7000 hours of operation
(cf. Table 6). During this first year, the fixed costs are at a maximum
because the base is the initial investment. The figures for each cost
element, as well as unit costs, in terms of dollars per kg of 0^
produced and in terms of mils per generated kilowatt-hour, are given in
Table 8 of the text.
61
-------
4-r
•3-
QJ
'c£.
U-
S-
OJ
"la .5-
3
c' .4-
o
o
o
.3
.2
10
-1
.1
.2
.5
Cost (Cents/m3)
Figure 15. Cost of cooling water versus flow rate.
62
-------
Table 14. Direct Cost Elements for Operation of Ozonators and Oxygen Plant
Ozonators (Air Feed):
Electric Power: 23,148 (IOOQ ^g Q ) x Capacity ( day
kWh 100° k9 °
x days of operation
— — yp — -
3
Cooling Water: 1,400 (1QOQ kg Q ) x Capacity (
x days of operation
mj yr
Labor: 48 ^=- x 365^ays x ^L. (oil-fired)
96 „ 3^, „ , (coal.f1red)
Maintenance: 6%/yr of direct investment cost
Ozonators (Oxygen Feed) and Oxygen Plant:
100°
Electric Power: [8267(1000g QJ x Capacity (
kWh 100°
^
kwh.
1000 kg 02 day
x days of operation
- — c -
3 1000 kg 03
Cooling Water: [ 1,400 (100Q kg Q ) x Capacity ( - ^ - )
m3 1000 kg
1000 kg 0> x Capac1ty ( day
-~ x days of operation
m . yr
Labor: 96 . 365 days x (o11.f1ped)
yr
144 ^^ x 365 days x ^± (coal-fired)
yr
Maintenance: 3%/yr of direct investment cost
63
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Table 15. Annual Capital Charges for Power Industry Financing
Item As % Original Investment
Depreciation-straight line basis 3.33
Interim replacements 0.5
Insurance 0.5
Total applied to 4.33
original investment
Item As % Outstanding Depreciation Base*
Cost of capital
60% debt - bonds at 10% 6.0
40% equity - 14% return 5.6
Taxes
Federal (50% of gross return) 5.6
State (National average) 4.5
Total applied to 21.7
depreciation base
*Applied on an average basis over 30 years, the total annual % of fixed
investment would be 4.33% + 1/2 (21.7%) = 15.18%.
64
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REFERENCES
1. J. Ando, H. Tohata, and G. A. Issacs, "NOX Abatement for Stationary
Sources in Japan," Final Report on EPA Contract No. 68-02-1321,
Task 6. EPA-600/2-76-013b. PEDCo Environmental Specialists, Inc.,
Cincinnati, Ohio, January 1976.
2. D. M. Himmelbau and K. B. Bischoff, Process Analysis and Simulation
Deterministic Systems, John Wiley and Sons, New York, pp. 25-28.
3. G. G. McGlamery, et al., "Detailed Cost Estimates for Advanced
Effluent Desulfurization Processes," EPA-600/2-75-006, U.S. Environ-
mental Protection Agency Office of Research and Development, Washington,
D.C., January 1975
4. J. A. Kerr and A. F. Trotman-Dickinson, "Strengths of Chemical Bonds,"
page F-149 in R. C. Weast (Ed.), Handbook of Chemistry and Physics,
48th Edition, The Chemical Rubber Co., Cleveland, Ohio, 1967.
5. T. C. Manley and S. J. Niegowski, "Ozone," pp. 410-432 in K. Othmer
(Ed.), Encyclopedia of Chemical Technology. 2nd Edition, Volume 14,
Interscience Publishers, New York, 1967.
6. M. J. Klein, et al.. "Generation of Ozone," pp. 1-9 in R. G. Rice
and M. E. Browning (Eds.), First International Symposium on Ozone for
Water and Wastewater Treatment, International Ozone Institute,
Waterbury, Conn. 1975.
7. "Ozone Generation for Industrial Application," Bulletin 201, The
Welsbach Corporation, Ozone Processes Division, Philadelphia, Pa.,
May 1965.
8. Estimate by Mr. Carl Nebel, Welsbach Corporation, Ozone Processes
Division, Philadelphia, Pa., June 2, 1976 and August 30, 1976.
9. J. F. Potter, Linde Division, Union Carbide, private communication,
September 8, 1976.
10. H. M. Rosen, "Integrating Ozone Systems," pp. 843-851 in Rice and
Browning, op cit.
11. Federal Power Commission, "Hydroelectric Power Evaluation," FPC P-35
(1968) and Supplement No. 1, FPC P-38 (1969), Superintendent of
Documents, U.S. Government Printing Office, Washington, D.C.
12. Chemical Engineering, p. 7, May 24, 1976.
13. 0. T. Zimmerman, "Capital Investment Cost Estimation," pp. 301-337 in
F. C. Jelen (Ed.), Cost and Optimization Engineering, McGraw-Hill,
New York, N.Y., 1970.
65
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14. Private communication, Dr. Harvey Rosen, Union Carbide, February, 1976.
15. N. Okada, et al., "Preparation of Ozone," Japan Kokai, 73, 39,
p. 391, June 9, 1973. (Chemical Abstracts. 79, P94131, 1973.)
16. M. Steinberg, et al., "Large Scale Ozone Production in Chemo-Nuclear
Reactors for Waste Treatment," pp. 10-39 in Rice and Browning, 0£
cit.
17. S. W. Benson and A. E. Axworthy, "Mechanism of the Gas Phase, Thermal
Decomposition of Ozone," J. Chem. Phys., 26_, 1718 (1957).
18. M. Gauthier and D. R. Snelling, "Possible Production of 02 ('Ag)
and 02 ('£q) in the Reaction of NO with 03," Chem. Phys. Letters.
20, 178 (1973).
19. J. A. Ghormley, et al., "Reaction of Excited Oxygen Atoms with Nitrous
Oxide. Rate Constants for Reaction of Ozone with Nitric Oxide and
Nitrogen Dioxide," J. Phys. Chem., 77^ 1341 (1973).
20. H. S. Johnson, "Four Mechanisms Involving Nitrogen Peroxide," J. Amer.
Chem. Soc.. 73_, 4542 (1951).
21. G. Schott and N. Davidson, "Shock Waves in Chemical Kinetics:
Nitrogen Peroxide," J. Amer. Chem. Soc.. 80, 1841 ( 1958).
22. H. S. Johnson, Gas Phase Reaction Theory, The Ronald Press Co.,
New York, N.Y., 1966. pp. 14-32.
23. D. D. Davis, et al., "Stop Flow Time of Flight Mass Spectrometry
Kinetics Study. Reactions of Ozone with Nitrogen Dioxide and Sulfur
Dioxide," J. Phys. Chem., 78^, 1775 (1974).
24. R. A. Cox and S. A. Paukett, "Aerosol Formation from Sulfur Dioxide
in the Presence of Ozone and Olefinic Hydrocarbons," J. Chem. Soc.,
Faraday.Transactions I. 68, 1735 ( 1972).
25. S. W. Benson, The Foundation of Chemical Kinetics, McGraw-Hill Book
Co., New York, N.Y., 1960. Also see S. W. Benson, "The Induction
Period in Chain Reactions," J. Chem. Phys.. 20_, 1605 (1952).
26. Federal Power Commission, "National Power Survey - The Financial
Outlook for the Electric Power Industry," FPC P87 Report and
Recommendations of the Technical Advisory Committee on Finance,
Superintendent of Documents, U.S. Government Printing Office,
Washington, D.C., December 1974.
27. Private communication, D. Mobley, EPA-NERC, Research Triangle Park,
N. C., August, 1976.
66
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/7-76-033
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Technology and Economics of Flue Gas NOx Oxidation
by Ozone
5. REPORT DATE
December 1976
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
J.W. Harrison
B. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Research Triangle Institute
P.O. Box 12194
Research Triangle Park, NC 27709
10. PROGRAM ELEMENT NO.
EHE624
11. CONTRACT/GRANT NO.
68-02-1325, Task 38
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT ANDPERIOD COVERED
Task Final; 7-10/76
14. SPONSORING AGENCY CODE
EPA-ORD
is.SUPPLEMENTARY NOTES ffiRL-RTP task officer for this report is R.D. Stern, 919/549-8411
Ext 2 915, Mail Drop 61.
16. ABSTRACT
repOrt gives results of an investigation of the kinetics of oxidation of
NO by ozone and concludes that a stoichiometric amount of ozone is required when
oxidation occurs at flue gas temperatures typical for electrical generating stations.
It also surveys the state of current technology for large-scale ozone generation and
concludes that electrical discharge is the only feasible method at present. The
report also presents results (on a per unit basis) of calculations of the energy con-
sumption and economics of ozone generation at rates sufficient to oxidize NO at flue
gas flow rates and at nitrogen oxides (NOx) concentrations typical for 500 MW coal-
and oil-fired boilers. Stationary combustion sources contribute about half the man-
made NOx emitted to the atmosphere in the U.S. Flue gas from combustion proces-
ses contains NOx which is predominantly in the form of NO. Although NO2 is to some
extent soluble in water or aqueous solutions , NO is practically insoluble when conven-
tional scrubbing processes are used. For effective removal, the NO must either be
reduced to elemental nitrogen or oxidized to NO2 or higher oxides which can be
removed by scrubbing.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATl Field/Group
Air Pollution
Flue Gases
Nitrogen Oxides
Oxidation
Ozone
Kinetics
Electric Power Plants
Coal
Fuel Oil
Air Pollution Control
Stationary Sources
13B
2 IB
07B
20K
10B
2 ID
18. DISTRIBUTION STATEMEN1
Unlimited
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
72
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
67
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