METHOD
3 - GAS ANALYSIS FOR THE
DETERMINATION
OF DRY MOLECULAR WEIGHT
NOTE: This method does not include all of the
specifications (e.g.,
equipment and supplies) and procedures (e.g., sampling) essential to its performance.
Some material is incorporated by reference from other methods in this part.
Therefore, to obtain reliable results, persons using this method should also
have a thorough knowledge of Method 1.
8.0 Sample Collection,
Preservation, Storage, and Transport.
8.1 Single Point, Grab
Sampling Procedure.
8.2 Single-Point,
Integrated Sampling Procedure.
8.3 Multi-Point,
Integrated Sampling Procedure.
10.0 Calibration and
Standardization.
11.3 Integrated Sample
Analysis.
11.5 Leak-Check
Procedure for Orsat Analyzer.
12.0 Calculations and
Data Analysis.
13.0 Method
Performance. [Reserved]
14.0 Pollution
Prevention. [Reserved]
15.0 Waste Management.
[Reserved]
17.0 Tables, Diagrams,
Flowcharts, and Validation Data.
1.0 Scope and Application.
1.1 Analytes.
1.2 Applicability.
This method is
applicable for the determination of CO2 and
O2 concentrations and dry molecular weight
of a sample from an effluent gas stream of a fossilfuel combustion process or
other process.
1.3 Other methods, as well as modifications to the procedure described herein, are also applicable for all of the above determinations.
Examples of
specific methods and modifications include: (1) a multi-point grab sampling
method using an Orsat analyzer to analyze the individual grab sample obtained
at each point; (2) a method for measuring either CO2 or O2 and
using stoichiometric calculations to determine dry molecular weight; and (3)
assigning a value of 30.0 for dry molecular weight, in lieu of actual
measurements, for processes burning natural gas, coal, or oil. These methods
and modifications may be used, but are subject to the approval of the
Administrator. The method may also be applicable to other processes where it
has been determined that compounds other than CO2,
O2, carbon monoxide (CO), and nitrogen (N2) are not present in concentrations
sufficient to affect the results.
1.4 Data Quality Objectives.
Adherence to
the requirements of this method will enhance the quality of the data obtained
from air pollutant sampling methods.
2.0 Summary of Method.
2.1 A gas
sample is extracted from a stack by one of the following methods: (1)
single-point, grab sampling; (2) single-point, integrated sampling; or (3)
multi-point, integrated sampling. The gas sample is analyzed for percent CO2 and percent O2. For dry molecular weight determination,
either an Orsat or a Fyrite analyzer may be used for the analysis.
3.0 Definitions. [Reserved]
4.0 Interferences.
4.1 Several compounds
can interfere, to varying degrees, with the results of Orsat or Fyrite
analyses. Compounds that interfere with CO2 concentration
measurement include acid gases (e.g., sulfur dioxide, hydrogen chloride); compounds that
interfere with O2
concentration measurement
include unsaturated hydrocarbons (e.g., acetone, acetylene), nitrous oxide, and ammonia. Ammonia
reacts chemically with the O2 absorbing
solution, and when present in the effluent gas stream must be removed before
analysis.
5.0 Safety.
5.1
Disclaimer. This method may involve hazardous materials, operations, and
equipment. This test method may not address all of the safety problems
associated with its use. It is the responsibility of the user of this test
method to establish appropriate safety and health practices and determine the
applicability of regulatory limitations
prior to
performing this test method.
5.2 Corrosive
Reagents.
5.2.1 A
typical Orsat analyzer requires four reagents: a gas-confining solution, CO2 absorbent, O2 absorbent, and CO absorbent. These
reagents may contain potassium hydroxide, sodium hydroxide, cuprous chloride,
cuprous sulfate, alkaline pyrogallic acid, and/or chromous chloride. Follow
manufacturer's operating instructions and observe all warning labels for
reagent use.
5.2.2 A
typical Fyrite analyzer contains zinc chloride, hydrochloric acid, and either
potassium hydroxide or chromous chloride. Follow manufacturer's operating
instructions and observe all warning labels for reagent use.
6.0 Equipment and Supplies.
NOTE: As an alternative to the sampling
apparatus and systems described herein, other sampling systems (e.g., liquid displacement) may be used,
provided such systems are capable of obtaining a representative sample and
maintaining a constant sampling rate, and are, otherwise, capable of yielding
acceptable results. Use of such systems is subject to the approval of the
Administrator.
6.1 Grab Sampling
(See Figure 3-1).
6.1.1 Probe.
Stainless
steel or borosilicate glass tubing equipped with an in-stack or out-of-stack
filter to remove particulate matter (a plug of glass wool is satisfactory for
this purpose). Any other materials, resistant to temperature at sampling
conditions and inert to all components of the gas stream, may be used for the
probe. Examples of such materials
may include aluminum, copper, quartz glass, and Teflon.
6.1.2 Pump.
A one-way
squeeze bulb, or equivalent, to transport the gas sample to the analyzer.
6.2 Integrated Sampling
(Figure 3-2).
6.2.1 Probe.
Same as in
Section 6.1.1.
6.2.2 Condenser.
An air-cooled
or water-cooled condenser, or other condenser no greater than 250 ml that will
not remove O2, CO2,
CO, and N2, to remove excess moisture which would
interfere with the operation of the pump and flowmeter.
6.2.3 Valve.
A needle
valve, to adjust sample gas flow rate.
6.2.4 Pump.
A leak-free,
diaphragm-type pump, or equivalent, to transport sample gas to the flexible
bag. Install a small surge tank
between the pump and rate meter to eliminate the pulsation effect of the
diaphragm pump on the rate meter.
6.2.5 Rate Meter.
A rotameter,
or equivalent, capable of measuring flow rate to ± 2 percent of the selected
flow rate. A flow rate range of 500 to 1000 ml/min is suggested.
6.2.6 Flexible Bag.
Any leak-free
plastic (e.g.,
Tedlar, Mylar, Teflon) or plastic-coated aluminum (e.g., aluminized Mylar) bag, or equivalent,
having a capacity consistent with the selected flow rate and duration of the test
run. A capacity in the range of 55 to 90 liters (1.9 to 3.2 ft3) is suggested. To leak-check the bag,
connect it to a water manometer, and pressurize the bag to 5 to 10 cm H2O (2 to 4 in. H2O). Allow to stand for 10 minutes. Any
displacement in the water manometer indicates a leak. An alternative leak-check
method is to pressurize the bag to 5 to 10 cm (2 to 4 in.) H2O and allow to stand overnight. A
deflated bag indicates a leak.
6.2.7 Pressure Gauge.
A water-filled
U-tube manometer, or equivalent, of about 30 cm (12 in.), for the flexible bag
leak-check.
6.2.8 Vacuum Gauge.
A mercury
manometer, or equivalent, of at least 760 mm (30 in.) Hg, for the sampling
train leak-check.
6.3 Analysis.
An Orsat or
Fyrite type combustion gas analyzer.
7.0 Reagents and Standards.
7.1 Reagents.
As specified
by the Orsat or Fyritetype combustion analyzer manufacturer.
7.2 Standards.
Two standard
gas mixtures, traceable to National Institute of Standards and Technology
(NIST) standards, to be used in auditing the accuracy of the analyzer and the
analyzer operator technique:
7.2.1. Gas
cylinder containing 2 to 4 percent O2 and
14 to 18 percent CO2.
7.2.2. Gas
cylinder containing 2 to 4 percent CO2 and
about 15 percent O2.
8.0 Sample Collection, Preservation, Storage, and Transport.
8.1 Single Point, Grab Sampling Procedure.
8.1.1 The
sampling point in the duct shall either be at the centroid of the cross section
or at a point no closer to the walls than 1.0 m (3.3 ft), unless otherwise
specified by the Administrator.
8.1.2 Set up
the equipment as shown in Figure 3-1, making sure all connections ahead of the
analyzer are tight. If an Orsat
analyzer is used, it is recommended that the analyzer be leak-checked by
following the procedure in Section 11.5; however, the
leak-check is optional.
8.1.3 Place
the probe in the stack, with the tip of the probe positioned at the sampling
point. Purge the sampling line long enough to allow at least five
exchanges. Draw a sample into the
analyzer, and immediately analyze it for percent CO2 and percent O2 according to Section
11.2.
8.2 Single-Point, Integrated Sampling Procedure.
8.2.1 The
sampling point in the duct shall be located as specified in Section 8.1.1.
8.2.2
Leak-check (optional) the flexible bag as in Section 6.2.6.
Set up the equipment as shown in Figure 3-2. Just before
sampling, leak-check (optional) the train by placing a vacuum gauge at the
condenser inlet, pulling a vacuum of at least 250 mm Hg (10 in. Hg), plugging
the outlet at the quick disconnect, and then turning off the pump. The vacuum
should remain stable for at least 0.5 minute. Evacuate the flexible bag.
Connect the probe, and place it in the stack, with the tip of the probe
positioned at the sampling point. Purge the sampling line. Next, connect the bag, and make sure
that all connections
are tight.
8.2.3 Sample
Collection. Sample at a constant rate (± 10 percent). The sampling run should
be simultaneous with, and for the same total length of time as, the pollutant
emission rate determination. Collection of at least 28 liters (1.0 ft3) of sample gas is recommended; however,
smaller volumes may be collected, if desired.
8.2.4 Obtain
one integrated flue gas sample during each pollutant emission rate
determination. Within 8 hours after the sample is taken, analyze it for percent
CO2 and percent O2 using either an Orsat analyzer or a
Fyrite type combustion gas analyzer according to Section
11.3.
NOTE: When using an Orsat analyzer, periodic Fyrite
readings may be taken to verify/confirm the results obtained from the Orsat.
8.3 Multi-Point, Integrated Sampling Procedure.
8.3.1 Unless
otherwise specified in an applicable regulation, or by the Administrator, a
minimum of eight traverse points shall be used for circular stacks having
diameters less than 0.61 m (24 in.), a minimum of nine shall be used for
rectangular stacks having equivalent diameters less than 0.61 m (24 in.), and a
minimum of 12 traverse points shall be used for all other cases. The traverse
points shall be located according to Method 1.
8.3.2 Follow
the procedures outlined in Sections
8.2.2 through
8.2.4, except for the following: Traverse all sampling points, and sample at
each point for an equal length of time. Record sampling data as shown in Figure 3-3.
9.0 Quality Control.
10.0 Calibration and Standardization.
10.1 Analyzer.
The analyzer
and analyzer operator's technique should be audited periodically as follows:
take a sample from a manifold containing a known mixture of CO2 and O2,
and analyze according to the procedure in Section 11.3.
Repeat this procedure until the measured concentration of three consecutive
samples agrees with the stated value ± 0.5 percent. If necessary, take
corrective action, as specified in the analyzer users manual.
10.2 Rotameter.
The rotameter
need not be calibrated, but should be cleaned and maintained according to the
manufacturer's instruction.
11.0 Analytical Procedure.
11.1 Maintenance.
The Orsat or
Fyrite-type analyzer should be maintained and operated according to the
manufacturers specifications.
11.2 Grab Sample Analysis.
Use either an
Orsat analyzer or a Fyrite-type combustion gas analyzer to measure O2 and CO2 concentration
for dry molecular weight determination, using procedures as specified in the
analyzer user's manual. If an Orsat analyzer is used, it is recommended that
the Orsat leak-check, described in Section 11.5, be performed before this
determination; however, the check is optional. Calculate the dry molecular
weight as indicated in Section 12.0. Repeat the sampling, analysis, and
calculation procedures until the dry molecular weights of any three grab
samples differ from their mean by no more than 0.3 g/g-mole (0.3 lb/lb-mole).
Average these three molecular weights, and report the results to the nearest
0.1 g/g-mole (0.1 lb/lb-mole).
11.3 Integrated Sample Analysis.
Use either an
Orsat analyzer or a Fyrite-type combustion gas analyzer to measure O2 and CO2 concentration
for dry molecular weight determination, using procedures as specified in the
analyzer user's manual. If an Orsat analyzer is used, it is recommended that
the Orsat leak-check, described in Section 11.5, be performed before this
determination; however, the check is optional. Calculate the dry molecular
weight as indicated in Section 12.0. Repeat the analysis and calculation
procedures until the individual dry molecular weights for any three analyses
differ from their mean by no more than 0.3 g/g-mole (0.3 lb/lb-mole). Average
these three molecular weights, and report the results to the nearest 0.1
g/g-mole (0.1 lb/lb-mole).
11.4 Standardization.
A periodic
check of the reagents and of operator technique should be conducted at least
once every three series of test runs as outlined in Section 10.1.
11.5 Leak-Check Procedure for Orsat Analyzer.
Moving an Orsat analyzer frequently causes it to leak. Therefore, an Orsat analyzer should be thoroughly leak-checked on site before the flue gas sample is introduced into it. The procedure for leak-checking an Orsat analyzer is as follows:
11.5.1 Bring
the liquid level in each pipette up to the reference mark on the capillary
tubing, and then close the pipette stopcock.
11.5.2 Raise
the leveling bulb sufficiently to bring the confining liquid meniscus onto the
graduated portion of the burette, and then close the manifold stopcock.
11.5.3 Record
the meniscus position.
11.5.4 Observe
the meniscus in the burette and the liquid level in the pipette for movement
over the next 4 minutes.
11.5.5 For the
Orsat analyzer to pass the leak-check, two conditions must be met:
11.5.5.1 The
liquid level in each pipette must not fall below the bottom of the capillary
tubing during this 4-minute interval.
11.5.5.2 The
meniscus in the burette must not change by more than 0.2 ml during this
4-minute interval.
11.5.6 If the
analyzer fails the leak-check procedure, check all rubber connections and stopcocks
to determine whether they might be the cause of the leak. Disassemble, clean,
and regrease any leaking stopcocks. Replace leaking rubber connections. After
the analyzer is reassembled, repeat the leak-check procedure.
12.0 Calculations and Data Analysis.
Md = Dry molecular weight, g/g-mole
(lb/lb-mole).
%CO2 = Percent CO2 by volume, dry basis.
%O2 = Percent O2 by
volume, dry basis.
%CO = Percent
CO by volume, dry basis.
%N2 = Percent N2 by
volume, dry basis.
0.280 =
Molecular weight of N2
or CO, divided by 100.
0.320 =
Molecular weight of O2
divided by 100.
0.440 =
Molecular weight of CO2
divided by 100.
12.2 Nitrogen,
Carbon Monoxide Concentration. Determine the percentage of the gas that is N2 and CO by subtracting the sum of the
percent CO2 and percent O2 from 100 percent.
12.3 Dry
Molecular Weight. Use Equation 3-1 to calculate the dry molecular weight of the
stack gas.
NOTE: The above Equation 3-1 does not consider
the effect on calculated dry molecular weight of argon in the effluent gas. The
concentration of argon, with a molecular weight of 39.9, in ambient air is
about 0.9 percent. A negative error of approximately 0.4 percent is introduced.
The tester may choose to include argon in the analysis using procedures subject
to approval of the Administrator.
13.0 Method Performance. [Reserved]
14.0 Pollution Prevention. [Reserved]
15.0 Waste Management. [Reserved]
16.0 References.
1. Altshuller,
A.P. Storage of Gases and Vapors in Plastic Bags. International Journal of Air
and Water Pollution. 6:75-81. 1963.
2. Conner,
William D. and J.S. Nader. Air Sampling with Plastic Bags. Journal of the
American Industrial Hygiene Association. 25:291-297. 1964.
3. Burrell
Manual for Gas Analysts, Seventh edition. Burrell Corporation, 2223 Fifth
Avenue, Pittsburgh, PA. 15219. 1951.
4. Mitchell,
W.J. and M.R. Midgett. Field Reliability of the Orsat Analyzer. Journal of Air
Pollution Control Association. 26:491-495. May 1976.
5. Shigehara,
R.T., R.M. Neulicht, and W.S. Smith. Validating Orsat Analysis Data from Fossil
Fuel-Fired Units. Stack Sampling News. 4(2):21-26. August 1976.
17.0 Tables, Diagrams, Flowcharts, and Validation Data.
Figure
3-1. Grab-Sampling Train.
Figure
3-2. Integrated Gas-Sampling Train.
Figure
3-3. Sampling Rate Data.
