United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S7-84-053 May 1984
&ER& Project Summary
Flare Efficiency Monitoring by
Remote Infrared Sensing:
A Feasibility Demonstration
Merle J. Persky and Robert L. Spellicy
Passive infrared methods have been
evaluated for use in remotely monitor-
ing the efficiency of industrial flares. To
perform this evaluation, field tests were
conducted using a general infrared
measurement device, EPA's ROSE (Re-
mote Optical Sensing of Emissions)
Fourier transform infrared (FTIR) sys-
tem. With this system, infrared emis-
sions arising from the gaseous exhaust
products of a small-scale industrial flare
were observed under a wide range of
operating conditions, at several posi-
tions in and above the combustion
zone. A procedure was developed by
which carbon monoxide (CO) and car-
bon dioxide (CO2) concentrations could
be determined from these emissions
and the results used to estimate flare
efficiency. The procedures developed
utilize basic spectroscopic principles,
mainly the use of the vibration-rotation
lines of the CO fundamental emission
band to calculate an approximate gas
temperature, followed by a "best-fit"
matching of computer-modeled CO
and COz synthetic spectra to the meas-
ured spectra in order to determine CO
and COa concentrations. These concen-
trations are then combined to estimate
flare efficiency.
Major results of this study include: (1)
the collection of a data base on flare
emissions for a typical flare at several
flow rates of propylene, steam, and
nitrogen; (2) the comparison of three
specific runs with simultaneous extrac-
tive probe measurements indicating
comparable CO and CO2concentrations
(to within 10 to 30 percent), but sig-
nificantly different temperatures (differ-
ing by a factor of 2 to 4); (3) the
determination of a better than 20 ppm
detection threshold for CO using FTIR;
and (4) the conclusion that the most
serious uncertainties are the spatial
distributions of temperature and gas
concentration, and the detectability of
hydrocarbon species.
This Project Summary was developed
by EPA's Industrial Environmental Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering in-
formation at back).
Introduction
Flares are used by several industries
for the disposal of waste gases by combus-
tion. The total amount of gas flared in the
U.S. has not been measured accurately,
but one estimate is 16 million tons per
year. Since large amounts of gases are
flared, both the Government and associ-
ated industries have a vital interest in
ensuring that the design and operation of
flare systems are optimum in order to
minimize the production of undesirable
by-products.
Therefore, an effective way to monitor
flare efficiency needs to be developed.
Two potential measurement approaches
for determining flare efficiency are: (1)
point sampling of combustion products
using extractive probes, and (2) remote
sensing of combustion products using
infrared spectroscopic techniques.
Each approach has strengths and weak-
nesses. The extractive probe provides
localized data on a large number of exhaust
species in a very direct manner; however.
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the local nature of the probe measure-
ment makes it vulnerable to wind effects
unless compensation is provided by in-
cluding a tracer gas or by using the ratios
of combustion products rather than abso-
lute values. That is, variations in con-
centrations observed with a probe could
be caused by the wind's moving the
combustion products relative to the probe,
or by spatial variations in the plume itself.
In addition, since the probe is a direct
measurement device (required to be at
the flare itself), it may introduce inter-
ferences with plant operation.
The remote sensing concept utilizes
the fact that the exhaust products em-
ployed in the efficiency calculation are
infrared-active: i.e., each has its own
unique radiant emission (or signature) in
the infrared region of the spectrum. This
signature, being related to the concentra-
tion of the product, allows infrared spec-
troscopy to be used to determine flare
efficiency by measuring these radiant
emissions remotely and non-obtrusively.
The infrared method is also more global in
the sense that a spatial averaging is
obtained. Consequently, it may provide a
more representative measure than a
localized probe.
Scope of Study
As suggested above, remote optical
sensing offers great promise for flare
efficiency monitoring. While numerous
previous efforts have demonstrated its
value for the general field of air pollution,
only limited efforts have been undertaken
to evaluate it specifically for flare effi-
ciency measurements. Therefore, meas-
urements and analyses were performed
to demonstrate and develop remote opti-
cal sensing, specifically infrared spectro-
scopy, for application to this monitoring
problem.
Infrared spectroscopic data were col-
lected at the John Zink Company, Tulsa,
OK, from June 17 to 24, 1982. The
measurements were made in conjunction
with a series of flare tests. The instru-
mentation used was the EPA ROSE
(Remote Optical Sensing of Emissions)
system, a versatile spectroscopic meas-
urement tool containing a Fourier trans-
form infrared (FTIR) spectrometer as well
as computer-based data collection and
processing equipment.
In addition to the infrared measure-
ments, coincident extractive probe meas-
urements were obtained that could be
used for comparison. These measure-
ments provided localized data on gas
temperatures as well as on the concen-
trations of various combustion products,
including CO, C02, hydrocarbons, and
particulates. Since these probe meas- *
urements represent the current state-of-
the-art in flare emission monitoring, they
were compared with the FTIR results to
estimate the basic validity of the infrared
approach. To facilitate these compari-
sons, the majority of the remote infrared
data was taken at the same position and
at the same time as that of the probe.
A further comparison of FTIR and probe
data was performed using a set of five
"unknown" calibration gases whose iden-
tities and concentrations were deter-
mined both by the extractive probe anal-
ysis methods and by absorption measure-
ments using the ROSE FTIR. These com-
parisons were used to determine the
inherent agreement between the two
measurement methods, independent of
flare or atmospheric influences.
Program Results
Experimental data were collected on a
small-scale industrial flare using remote
IR methods. These data were then used to
develop a baseline analysis procedure for
determination of specie concentrations
required for the evaluation of flare com-
bustion efficiency. Once developed, these
baseline methods were applied to four
specific tests and the results compared
with point-sampling measurements to
determine the basic applicability of the IR
approach.
In general, the results of these compar-
isons clearly indicate that IR methods are
applicable to the problem of combustion
efficiency monitoring and, in many in-
stances, they can offer substantial advan-
tages over currently available methods.
Even with the limited developmental
work possible in this study, baseline
procedures could be formulated which
allowed for evaluation of plume temper-
ature, CO concentration, and C02 con-
centration based solely on the IR spectra.
With these values, estimates of efficiency
could then be made using the approx-
imate relationship, which at high effi-
ciency gave values in good agreement
with the point sampled results (see Table
1). The only major shortcoming of the IR
approach was its inability to determine
total hydrocarbon concentrations which
are necessary for monitoring lower effi-
ciency flares. This was in part tht, result of
using a general IR instrument not specifi-
cally tailored to this measurement prob-
lem and in part the result of looking at a
small flare whose limited optical depth
rendered the detection of weaker IR
emitters difficult. Given a solution to this
problem, however, IR methods look attrac-
tive because they allow for remote, non-
hazardous, non-intrusive monitoring of
industrial flares from as far as a quarter to
half a mile (0.4 to 0.8 km). The method-
ologies developed also look straightfor-
ward enough that they could be imple-
mented on field hardware, allowing for
near-real-time in-situ results. In addition,
it is highly probable that less costly and
more selective IR equipment could be
developed for use in monitoring the
specific species of interest.
General Applicability of FTIR to
Flare Monitoring
From the experience and results of this
program, the FTIR approach, although not
fully developed, has some distinct advan-
tages over conventional monitoring meth-
ods:
1. The operation is remote and pas-
sive. It therefore minimizes poten-
tially objectionable interference
with normal plant operation, elimi-
nates the need for personnel being
near a large industrial flare, and
makes possible sampling of ele-
vated flares from off-site.
2. The approach allows for great flexi-
bility in choosing operational param-
Table 1. Comparison of Remote Sensing Extractive Probe Sampling*
CO CO2 TMC
Test No. Temp. (K) Concen. (ppm) Concen. Ippm) Concen. (ppmj Efficiency (%)
FTIR Probe FTIR Probe FTIR Probe FTIR Probe FTIR Probe
50
53
55
59°
920
1400
683
2500
416
387
344
421
<20
-27
155
1350
35
10
125
80
6000
2900
1800
>6OOO
5382
2438
1371
5965
b
fa
b
b
17
7
475
63
>99.67
99.08
92.07
>81.63
99.1
99.0
69.7
97.7
"Probe data are background corrected, over the same observation time as the FTIR values.
"Not measurable by FTIR.
CFTIR in combustion flame, probe above; both above flame in others.
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eters. For example, the spectral
resolution, collecting area, spectral
range, and measurement time can
be easily adjusted in real-time to
accommodate variations in flare
operation, as well as to facilitate
both local and spatially averaged
observations.
3. Several separated flares can be
monitored in a timely manner from
a central measurement facility.
4. FTIR can accommodate a variety of
flare sizes. The performance will in
fact increase with size since, for the
same spectrometer sensitivity, a
longer optical path results in a
lower detection threshold.
5. Monitoring equipment can be oper-
ated by one person, and there is
potential for automated, in-situ
data analysis. Therefore, labor costs
are minimal, even though initial
equipment costs may be relatively
high.
Confidence in the results and conclu-
sions derived from FTIR data is provided
by the fact that the basic principles and
methods are well established, although
the specific analysis techniques are not
yet perfected for application to flares. The
greatest uncertainty in this regard is the
lack of an accurate knowledge of the
spatial distributions associated with
temperature and specie concentrations
for a "typical" flare.
M. PerskyandR. Spellicyare with Opt/Metrics, Inc., Bedford, MA 01730 and Las
Cruces, NM 88001, respectively.
Bruce A. Tichenor is the EPA Project Officer (see below).
The complete report, entitled "Flare Efficiency Monitoring by Remote Infrared
Sensing: A Feasibility Demonstration," (Order No. PB 84-187 566; Cost:
$11 .SO, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
U S GOVERNMENT PRINTING OFFICE- 1984 — 759-015/7714
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