METHOD 6 - DETERMINATION OF SULFUR DIOXIDE EMISSIONS FROM STATIONARY SOURCES
NOTE: This method does not include all of the
specifications (e.g.,
equipment and supplies) and procedures (e.g., sampling and analytical) 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 have a
thorough knowledge of at least the following additional test methods: Method 1, Method 2, Method 3, Method 5, and Method 8.
4.2 Water-Soluble
Cations and Fluorides.
5.2.1 Hydrogen Peroxide
(H2O2).
5.2.2 Sodium Hydroxide
(NaOH).
6.1.1.2 Bubbler and
Impingers.
6.1.3 Vacuum Gauge and
Rotameter.
7.1.2 Isopropanol, 80
Percent by Volume.
7.1.3 Hydrogen Peroxide
(H2O2), 3 Percent by Volume.
7.1.4 Potassium Iodide
Solution, 10 Percent Weight by Volume (w/v).
7.2.2 Isopropanol, 80
Percent by Volume.
7.3.2 Isopropanol, 100
Percent.
7.3.4 Barium Standard
Solution, 0.0100 N.
7.3.5 Sulfuric Acid
Standard, 0.0100 N.
7.3.6 Quality Assurance
Audit Samples.
8.0 Sample Collection,
Preservation, Storage and Transport.
8.1 Preparation of
Sampling Train.
8.2 Sampling Train
Leak-Check Procedure.
10.0 Calibration and
Standardization.
10.1.2 Post-Test
Calibration Check.
10.1.3 DGM as a
Calibration Standard.
10.5 Barium Standard
Solution.
12.0 Data Analysis and
Calculations.
12.2 Dry Sample Gas
Volume, Corrected to Standard Conditions.
12.4 Relative Error for
QA Audit Samples.
14.0 Pollution
Prevention. [Reserved]
15.0 Waste Management.
[Reserved]
16.2 Critical Orifices
for Volume and Rate Measurements.
16.2.1 Preparation of
Sampling Train.
16.2.2 Selection of
Critical Orifices.
16.3 Elimination of
Ammonia Interference.
18.0 Tables, Diagrams,
Flowcharts and Validation Data.
1.0 Scope and Application.
1.1 Analytes.
1.2 Applicability.
This method applies
to the measurement of sulfur dioxide (SO2)
emissions from stationary sources.
1.3 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 the sampling point in the stack. The SO2 and the sulfur trioxide, including those fractions in any sulfur
acid mist, are separated. The SO2 fraction is measured
by the barium-thorin titration method.
3.0 Definitions. [Reserved]
4.0 Interferences.
4.1 Free Ammonia.
Free ammonia
interferes with this method by reacting with SO2 to
form particulate sulfite and by reacting with the indicator. If free ammonia is
present (this can be determined by knowledge of the process and/or noticing
white particulate matter in the probe and isopropanol bubbler), alternative
methods, subject to the approval of the Administrator are required. One
approved alternative is listed in Reference 13 of Section
17.0.
4.2 Water-Soluble Cations and Fluorides.
The cations and
fluorides are removed by a glass wool filter and an isopropanol bubbler;
therefore, they do not affect the SO2 analysis.
When samples are collected from a gas stream with high concentrations of
metallic fumes (i.e., very
fine cation aerosols) a high-efficiency glass fiber filter must be used in
place of the glass wool plug (i.e.,
the one in the probe) to remove the cation interferent.
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 to establish appropriate safety and health practices
and determine the applicability of regulatory limitations before performing
this test method.
5.2 Corrosive reagents.
The following
reagents are hazardous. Personal protective equipment and safe procedures are
useful in preventing chemical splashes. If contact occurs, immediately flush
with copious amounts of water for at least 15 minutes. Remove clothing under
shower and decontaminate. Treat residual chemical burns as thermal burns.
5.2.1 Hydrogen Peroxide (H2O2).
Irritating to eyes,
skin, nose, and lungs. 30% H2O2 is a strong oxidizing agent. Avoid contact with skin, eyes, and
combustible material. Wear gloves when handling.
5.2.2 Sodium Hydroxide (NaOH).
Causes severe damage
to eyes and skin. Inhalation causes irritation to nose, throat, and lungs.
Reacts exothermically with limited amounts of water.
5.2.3 Sulfuric Acid (H2SO4).
Rapidly destructive
to body tissue. Will cause third degree burns. Eye damage may result in
blindness. Inhalation may be fatal from spasm of the larynx, usually within 30
minutes. May cause lung tissue damage with edema. 1 mg/m3 for 8 hours will cause lung damage or, in higher concentrations,
death. Provide ventilation to limit inhalation. Reacts violently with metals
and organics.
6.0 Equipment and Supplies.
6.1 Sample Collection.
The following items
are required for sample collection:
6.1.1 Sampling Train.
A schematic of the
sampling train is shown in Figure 6-1. The sampling
equipment described in Method 8 may be substituted in place of the midget
impinger equipment of Method 6. However, the Method 8 train must be modified to
include a heated filter between the probe and isopropanol impinger, and the
operation of the sampling train and sample analysis must be at the flow rates
and solution volumes defined in Method 8. Alternatively, SO2 may be determined simultaneously with particulate matter and
moisture determinations by either (1) replacing the water in a Method 5
impinger system with a 3 percent H2O2 solution, or (2) replacing the Method 5 water impinger system with
a Method 8 isopropanol-filter-H2O2 system. The analysis for SO2 must be
consistent with the procedure of Method 8. The Method 6 sampling train consists
of the following components:
6.1.1.1 Probe.
Borosilicate glass or
stainless steel (other materials of construction may be used, subject to the
approval of the Administrator), approximately 6 mm (0.25 in.) inside diameter,
with a heating system to prevent water condensation and a filter (either
in-stack or heated out-of-stack) to remove particulate matter, including
sulfuric acid mist. A plug of glass wool is a satisfactory filter.
6.1.1.2 Bubbler and Impingers.
One midget bubbler
with medium-coarse glass frit and borosilicate or quartz glass wool packed in
top (see Figure 6-1) to prevent sulfuric acid mist carryover, and three 30-ml
midget impingers. The midget bubbler and midget impingers must be connected in
series with leak-free glass connectors. Silicone grease may be used, if
necessary, to prevent leakage. A midget impinger may be used in place of the
midget bubbler.
NOTE: Other collection absorbers and flow rates may be
used, subject to the approval of the Administrator, but the collection efficiency
must be shown to be at least 99 percent for each test run and must be
documented in the report. If the efficiency is found to be acceptable after a
series of three tests, further documentation is not required. To conduct the
efficiency test, an extra absorber must be added and analyzed separately. This
extra absorber must not contain more than 1 percent of the total SO2.
6.1.1.3 Glass Wool.
Borosilicate or
quartz.
6.1.1.4 Stopcock Grease.
Acetone-insoluble,
heat-stable silicone grease may be used, if necessary.
6.1.1.5 Temperature Sensor.
Dial thermometer, or
equivalent, to measure temperature of gas leaving impinger train to within 1 ¡C
(2 ¡F).
6.1.1.6 Drying Tube.
Tube packed with 6-
to 16-mesh indicating-type silica gel, or equivalent, to dry the gas sample and
to protect the meter and pump. If silica gel is previously used, dry at 177 ¡C
(350 ¡F) for 2 hours. New silica gel may be used as received. Alternatively,
other types of desiccants (equivalent or better) may be used, subject to the approval
of the Administrator.
6.1.1.7 Valve.
Needle valve, to
regulate sample gas flow rate.
6.1.1.8 Pump.
Leak-free diaphragm
pump, or equivalent, to pull gas through the train. Install a small surge tank
between the pump and rate meter to negate the pulsation effect of the diaphragm
pump on the rate meter.
6.1.1.9 Rate Meter.
Rotameter, or
equivalent, capable of measuring flow rate to within 2 percent of the selected
flow rate of about 1 liter/min (0.035 cfm).
6.1.1.10 Volume Meter.
Dry gas meter (DGM),
sufficiently accurate to measure the sample volume to within 2 percent,
calibrated at the selected flow rate and conditions actually encountered during
sampling, and equipped with a temperature sensor (dial thermometer, or
equivalent) capable of measuring temperature accurately to within 3 ¡C (5.4
¡F). A critical orifice may be used in place of the DGM specified in this
section provided that it is selected, calibrated, and used as specified in Section 16.0.
6.1.2 Barometer.
Mercury, aneroid, or
other barometer capable of measuring atmospheric pressure to within 2.5 mm Hg
(0.1 in. Hg). See the NOTE in
Method 5, Section 6.1.2.
6.1.3 Vacuum Gauge and Rotameter.
At least 760-mm Hg (30-in.
Hg) gauge and 0- to 40-ml/min rotameter, to be used for leak-check of the
sampling train.
6.2 Sample Recovery.
The following items
are needed for sample recovery:
6.2.1 Wash Bottles.
Two polyethylene or glass bottles, 500-ml.
6.2.2 Storage Bottles.
Polyethylene bottles, 100-ml, to store impinger samples (one per sample).
6.3 Sample Analysis.
The following
equipment is needed for sample analysis:
6.3.1 Pipettes.
Volumetric type, 5-ml, 20-ml (one needed per sample), and 25-ml sizes.
6.3.2 Volumetric
Flasks. 100-ml size (one per sample) and 1000-ml size.
6.3.3
Burettes. 5- and 50-ml sizes.
6.3.4 Erlenmeyer
Flasks. 250-ml size (one for each sample, blank, and standard).
6.3.5 Dropping
Bottle. 125-ml size, to add indicator.
6.3.6 Graduated Cylinder.
100-ml size.
6.3.7
Spectrophotometer. To measure absorbance at 352 nm.
7.0 Reagents and Standards.
NOTE: Unless otherwise indicated, all reagents must
conform to the specifications established by the Committee on Analytical
Reagents of the American Chemical Society. Where such specifications are not
available, use the best available grade.
7.1 Sample Collection.
The following
reagents are required for sample collection:
7.1.1 Water.
Deionized distilled
to conform to ASTM Specification D 1193-77 or 91 Type 3 (incorporated by
reference - see ¤60.17). The KMnO4 test for
oxidizable organic matter may be omitted when high concentrations of organic
matter are not expected to be present.
7.1.2 Isopropanol, 80 Percent by Volume.
Mix 80 ml of isopropanol
with 20 ml of water.
7.1.2.1 Check each
lot of isopropanol for peroxide impurities as follows: Shake 10 ml of
isopropanol with 10 ml of freshly prepared 10 percent potassium iodide
solution. Prepare a blank by similarly treating 10 ml of water. After 1 minute,
read the absorbance at 352 nm on a spectrophotometer using a 1-cm path length.
If absorbance exceeds 0.1, reject alcohol for use.
7.1.2.2 Peroxides may
be removed from isopropanol by redistilling or by passage through a column of
activated alumina; however, reagent grade isopropanol with suitably low
peroxide levels may be obtained from commercial sources. Rejection of
contaminated lots may, therefore, be a more efficient procedure.
7.1.3 Hydrogen Peroxide (H2O2), 3 Percent by Volume.
Add 10 ml of 30
percent H2O2 to 90 ml of water.
Prepare fresh daily.
7.1.4 Potassium Iodide Solution, 10 Percent Weight by Volume (w/v).
Dissolve 10.0 g of KI
in water, and dilute to 100 ml. Prepare when needed.
7.2 Sample Recovery.
The following
reagents are required for sample recovery:
7.2.1 Water.
Same as in Section
7.1.1.
7.2.2 Isopropanol, 80 Percent by Volume.
Same as in Section
7.1.2.
7.3 Sample Analysis.
The following
reagents and standards are required for sample analysis:
7.3.1 Water.
Same as in Section
7.1.1.
7.3.2 Isopropanol, 100 Percent.
7.3.3 Thorin Indicator.
1-(o-arsonophenylazo)-2-naphthol-3, 6-disulfonic
acid, disodium salt, or equivalent. Dissolve 0.20 g in 100 ml of water.
7.3.4 Barium Standard Solution, 0.0100 N.
Dissolve 1.95 g of
barium perchlorate trihydrate [Ba(ClO4)2 3H2O] in 200 ml water, and dilute to 1 liter with
isopropanol. Alternatively, 1.22 g of barium chloride dihydrate [BaCl2 2H2O] may be used instead of the barium perchlorate
trihydrate. Standardize as in Section 10.5.
7.3.5 Sulfuric Acid Standard, 0.0100 N.
Purchase or
standardize to ± 0.0002 N against 0.0100 N NaOH which has previously been
standardized against potassium acid phthalate (primary standard grade).
7.3.6 Quality Assurance Audit Samples.
When making
compliance determinations, audit samples, if available must be obtained from
the appropriate EPA Regional Office or from the responsible enforcement
authority and analyzed in conjunction with the field samples.
Note: The responsible enforcement authority should be
notified at least 30 days prior to the test date to allow sufficient time for
sample delivery.
8.0 Sample Collection, Preservation, Storage and Transport.
8.1 Preparation of Sampling Train.
Measure 15 ml of 80
percent isopropanol into the midget bubbler and 15 ml of 3 percent H2O2 into each of the first two midget impingers.
Leave the final midget impinger dry. Assemble the train as shown in Figure 6-1.
Adjust the probe heater to a temperature sufficient to prevent water condensation.
Place crushed ice and water around the impingers.
8.2 Sampling Train Leak-Check Procedure.
A leak-check prior to
the sampling run is recommended, but not required. A leak-check after the
sampling run is mandatory. The leak-check procedure is as follows:
8.2.1 Temporarily
attach a suitable (e.g., 0-
to 40-ml/min) rotameter to the outlet of the DGM, and place a vacuum gauge at
or near the probe inlet. Plug the probe inlet, pull a vacuum of at least 250 mm
Hg (10 in. Hg), and note the flow rate as indicated by the rotameter. A leakage
rate in excess of 2 percent of the average sampling rate is not acceptable.
NOTE: Carefully (i.e., slowly) release the probe inlet plug before
turning off the pump.
8.2.2 It is suggested
(not mandatory) that the pump be leak-checked separately, either prior to or
after the sampling run. To leak-check the pump, proceed as follows: Disconnect
the drying tube from the probe-impinger assembly. Place a vacuum gauge at the
inlet to either the drying tube or the pump, pull a vacuum of 250 mm Hg (10 in.
Hg), plug or pinch off the outlet of the flow meter, and then turn off the
pump. The vacuum should remain stable for at least 30 seconds. If performed
prior to the sampling run, the pump leak-check shall precede the leak-check of
the sampling train described immediately above; if performed after the sampling
run, the pump leak-check shall follow the sampling train leak-check.
8.2.3 Other
leak-check procedures may be used, subject to the approval of the
Administrator.
8.3 Sample Collection.
8.3.1 Record the
initial DGM reading and barometric pressure. To begin sampling, position the
tip of the probe at the sampling point, connect the probe to the bubbler, and
start the pump. Adjust the sample flow to a constant rate of approximately 1.0
liter/min as indicated by the rate meter. Maintain this constant rate (± 10
percent) during the entire sampling run.
8.3.2 Take readings
(DGM volume, temperatures at DGM and at impinger outlet, and rate meter flow
rate) at least every 5 minutes. Add more ice during the run to keep the
temperature of the gases leaving the last impinger at 20 ¡C (68 ¡F) or less.
8.3.3 At the
conclusion of each run, turn off the pump, remove the probe from the stack, and
record the final readings. Conduct a leak-check as described in Section 8.2.
(This leak-check is mandatory.) If a leak is detected, void the test run or use
procedures acceptable to the Administrator to adjust the sample volume for the
leakage.
8.3.4
Drain the ice bath, and purge the remaining part of the train by drawing clean
ambient air through the system for 15 minutes at the sampling rate. Clean
ambient air can be provided by passing air through a charcoal filter or through
an extra midget impinger containing 15 ml of 3 percent H2O2. Alternatively, ambient air without
purification may be used.
8.4 Sample Recovery.
Disconnect the
impingers after purging. Discard the contents of the midget bubbler. Pour the
contents of the midget impingers into a leak-free polyethylene bottle for
shipment. Rinse the three midget impingers and the connecting tubes with water,
and add the rinse to the same storage container. Mark the fluid level. Seal and
identify the sample container.
9.0 Quality Control.
10.0 Calibration and Standardization.
10.1 Volume Metering System.
10.1.1 Initial Calibration.
10.1.1.1 Before its
initial use in the field, leak-check the metering system (drying tube, needle valve,
pump, rate meter, and DGM) as follows: Place a vacuum gauge at the inlet to the
drying tube and pull a vacuum of 250 mm Hg (10 in. Hg). Plug or pinch off the
outlet of the flow meter, and then turn off the pump. The vacuum must remain
stable for at least 30 seconds. Carefully release the vacuum gauge before
releasing the flow meter end.
10.1.1.2 Remove the
drying tube, and calibrate the metering system (at the sampling flow rate
specified by the method) as follows: Connect an appropriately sized wet-test
meter (e.g., 1 liter per
revolution) to the inlet of the needle valve. Make three independent
calibration runs, using at least five revolutions of the DGM per run. Calculate
the calibration factor Y (wet-test meter calibration volume divided by the DGM
volume, both volumes adjusted to the same reference temperature and pressure)
for each run, and average the results (øYi). If any
Y-value deviates by more than 2 percent from (øYi),
the metering system is unacceptable for use. If the metering system is acceptable,
use (øYi) as the calibration factor for subsequent test
runs.
10.1.2 Post-Test Calibration Check.
After each field test
series, conduct a calibration check using the procedures outlined in Section
10.1.1.2, except that three or more revolutions of the DGM may be used, and
only two independent runs need be made. If the average of the two post-test
calibration factors does not deviate by more than 5 percent from øYi, then øYi
is accepted as the DGM calibration
factor (Y), which is used in Equation 6-1 to calculate collected sample volume
(see Section 12.2). If the deviation is more than 5
percent, recalibrate the metering system as in Section 10.1.1, and determine a
posttest calibration factor (øYf). Compare øYi and øYf; the smaller of the two factors is accepted as
the DGM calibration factor. If recalibration indicates that the metering system
is unacceptable for use, either void the test run or use methods, subject to
the approval of the Administrator, to determine an acceptable value for the
collected sample volume.
10.1.3 DGM as a Calibration Standard.
A DGM may be used as
a calibration standard for volume measurements in place of the wet-test meter
specified in Section 10.1.1.2, provided that it is calibrated initially and
recalibrated periodically according to the same procedures outlined in Method
5, Section 10.3 with the following exceptions: (a) the DGM is calibrated
against a wet-test meter having a capacity of 1 liter/rev (0.035 ft3/rev) or 3 liters/rev (0.1 ft3/rev) and
having the capability of measuring volume to within 1 percent; (b) the DGM is
calibrated at 1 liter/min (0.035 cfm); and (c) the meter box of the Method 6
sampling train is calibrated at the same flow rate.
10.2 Temperature Sensors.
Calibrate against
mercury-in-glass thermometers.
10.3 Rate Meter.
The rate meter need
not be calibrated, but should be cleaned and maintained according to the
manufacturer's instructions.
10.4 Barometer.
Calibrate against a
mercury barometer.
10.5 Barium Standard Solution.
Standardize the
barium perchlorate or chloride solution against 25 ml of standard sulfuric acid
to which 100 ml of 100 percent isopropanol has been added. Run duplicate
analyses. Calculate the normality using the average of duplicate analyses where
the titrations agree within 1 percent or 0.2 ml, whichever is larger.
11.0 Analytical Procedure.
11.1 Sample Loss Check.
Note level of liquid
in container and confirm whether any sample was lost during shipment; note this
finding on the analytical data sheet. If a noticeable amount of leakage has
occurred, either void the sample or use methods, subject to the approval of the
Administrator, to correct the final results.
11.2 Sample Analysis.
11.2.1 Transfer the
contents of the storage container to a 100-ml volumetric flask, dilute to
exactly 100 ml with water, and mix the diluted sample.
11.2.2 Pipette a
20-ml aliquot of the diluted sample into a 250-ml Erlenmeyer flask and add 80 ml
of 100 percent isopropanol plus two to four drops of thorin indicator. While
stirring the solution, titrate to a pink endpoint using 0.0100 N barium
standard solution.
11.2.3 Repeat the
procedures in Section 11.2.2, and average the titration volumes. Run a blank
with each series of samples. Replicate titrations must agree within 1 percent
or 0.2 ml, whichever is larger.
NOTE: Protect the 0.0100 N barium standard solution
from evaporation at all times.
11.3 Audit Sample Analysis.
11.3.1 When the method
is used to analyze samples to demonstrate compliance with a source emission
regulation, an audit sample, if available, must be analyzed.
11.3.2 Concurrently
analyze the audit sample and the compliance samples in the same manner to
evaluate the technique of the analyst and the standards preparation.
11.3.3 The same
analyst, analytical reagents, and analytical system must be used for the
compliance samples and the audit sample. If this condition is met, duplicate
auditing of subsequent compliance analyses for the same enforcement agency
within a 30-day period is waived. An audit sample set may not be used to
validate different sets of compliance samples under the jurisdiction of
separate enforcement agencies, unless prior arrangements have been made with both
enforcement agencies.
11.4 Audit Sample Results.
11.4.1 Calculate the
audit sample concentrations and submit results using the instructions provided
with the audit samples.
11.4.2 Report the
results of the audit samples and the compliance determination samples along
with their identification numbers, and the analyst's name to the responsible
enforcement authority. Include this information with reports of any subsequent
compliance analyses for the same enforcement authority during the 30-day
period.
11.4.3 The
concentrations of the audit samples obtained by the analyst must agree within 5
percent of the actual concentration. If the 5 percent specification is not met,
reanalyze the compliance and audit samples, and include initial and reanalysis
values in the test report.
11.4.4 Failure to
meet the 5-percent specification may require retests until the audit problems
are resolved. However, if the audit results do not affect the compliance or
noncompliance status of the affected facility, the Administrator may waive the
reanalysis requirement, further audits, or retests and accept the results of
the compliance test. While steps are being taken to resolve audit analysis
problems, the Administrator may also choose to use the data to determine the
compliance or noncompliance status of the affected facility.
12.0 Data Analysis and Calculations.
Carry out
calculations, retaining at least one extra significant figure beyond that of
the acquired data. Round off figures after final calculation.
12.1 Nomenclature.
Ca = Actual concentration of SO2 in audit
sample, mg/dscm.
Cd = Determined concentration of SO2 in audit
sample, mg/dscm.
CSO2 = Concentration of SO2, dry basis, corrected to standard conditions, mg/dscm (lb/dscf).
N = Normality of barium
standard titrant, meq/ml.
Pbar = Barometric pressure, mm Hg (in. Hg).
Pstd = Standard absolute pressure, 760 mm Hg (29.92
in. Hg).
RE = Relative error
of QA audit sample analysis, percent
Tm = Average DGM absolute temperature, ¡K (¡R).
Tstd = Standard absolute temperature, 293 ¡K (528
¡R).
Va = Volume of sample aliquot titrated, ml.
Vm = Dry gas volume as measured by the DGM, dcm (dcf).
Vm(std)= Dry gas volume measured by the DGM, corrected
to standard conditions, dscm (dscf).
Vsoln = Total volume of solution in which the SO2 sample is contained, 100 ml.
Vt = Volume of barium standard titrant used for the sample (average of
replicate titration), ml.
Vtb = Volume of barium standard titrant used for the
blank, ml.
Y = DGM calibration
factor.
12.2 Dry Sample Gas Volume, Corrected to Standard
Conditions.
where:
K1 = 0.3855 ¡K/mm Hg for metric units,
= 17.65 ¡R/in. Hg for
English units.
12.3 SO2 Concentration.
where:
K2 = 32.03 mg SO2/meq for metric units,
= 7.061 x 10-5 lb SO2/meq for English
units.
12.4 Relative Error for QA Audit Samples.
13.0 Method Performance.
13.1 Range.
The minimum
detectable limit of the method has been determined to be 3.4 mg SO2/m3 (2.12 x 10-7 lb/ft3). Although no upper limit has been established, tests have shown
that concentrations as high as 80,000 mg/m3 (0.005
lb/ft3) of SO2 can be
collected efficiently at a rate of 1.0 liter/min (0.035 cfm) for 20 minutes in
two midget impingers, each containing 15 ml of 3 percent H2O2. Based on theoretical calculations, the upper
concentration limit in a 20 liter (0.7 ft3) sample
is about 93,300 mg/m3
(0.00583 lb/ft3).
14.0 Pollution Prevention. [Reserved]
15.0 Waste Management. [Reserved]
16.0 Alternative Procedures.
16.1 Nomenclature.
Same as Section 12.1,
with the following additions:
Bwa = Water vapor in ambient air, proportion by
volume.
Ma = Molecular weight of the ambient air saturated at impinger
temperature, g/g-mole
(lb/lb-mole).
Ms = Molecular weight of the sample gas saturated at impinger
temperature, g/g-mole
(lb/lb-mole).
Pc = Inlet vacuum reading obtained during the calibration run, mm Hg
(in. Hg).
Psr = Inlet vacuum reading obtained during the
sampling run, mm Hg (in. Hg).
Qstd = Volumetric flow rate through critical orifice,
scm/min (scf/min).
_
Qstd = Average flow rate of pre-test and post-test
calibration runs, scm/min (scf/min).
Tamb = Ambient absolute temperature of air, ¡K (¡R).
Vsb = Volume of gas as measured by the soap bubble
meter, m3 (ft3).
Vsb(std)= Volume of gas as measured by the soap bubble
meter, corrected to standard conditions, scm (scf).
2 = Soap bubble
travel time, min.
2s = Time, min.
16.2 Critical Orifices for Volume and Rate Measurements.
A critical orifice
may be used in place of the DGM specified in Section 6.1.1.10, provided that it
is selected, calibrated, and used as follows:
16.2.1 Preparation of Sampling Train.
Assemble the sampling
train as shown in Figure 6-2. The rate meter and surge
tank are optional but are recommended in order to detect changes in the flow
rate.
NOTE: The critical orifices can be adapted to a Method
6 type sampling train as follows: Insert sleeve type, serum bottle stoppers
into two reducing unions. Insert the needle into the stoppers as shown in Figure 6-3.
16.2.2 Selection of Critical Orifices.
16.2.2.1 The
procedure that follows describes the use of hypodermic needles and stainless
steel needle tubings, which have been found suitable for use as critical
orifices. Other materials and critical orifice designs may be used provided the
orifices act as true critical orifices, (i.e., a critical vacuum can be obtained) as
described in this section. Select a critical orifice that is sized to operate
at the desired flow rate. The needle sizes and tubing lengths shown in Table 6-1 give the following approximate flow rates.
16.2.2.2 Determine
the suitability and the appropriate operating vacuum of the critical orifice as
follows: If applicable, temporarily attach a rate meter and surge tank to the
outlet of the sampling train, if said equipment is not present (see Section
16.2.1). Turn on the pump and adjust the valve to give an outlet vacuum reading
corresponding to about half of the atmospheric pressure. Observe the rate meter
reading. Slowly increase the vacuum until a stable reading is obtained on the
rate meter. Record the critical vacuum, which is the outlet vacuum when the
rate meter first reaches a stable value. Orifices that do not reach a critical
value must not be used.
16.2.3 Field Procedures.
16.2.3.1 Leak-Check
Procedure. A leak-check before the sampling run is recommended, but not
required. The leak-check procedure is as follows: Temporarily attach a suitable
(e.g., 0-40 ml/min) rotameter and surge tank, or a soap bubble meter and surge
tank to the outlet of the pump. Plug the probe inlet, pull an outlet vacuum of
at least 250 mm Hg (10 in. Hg), and note the flow rate as indicated by the
rotameter or bubble meter. A leakage rate in excess of 2 percent of the average
sampling rate (Qøstd) is not acceptable. Carefully release the probe
inlet plug before turning off the pump.
16.2.3.2 Moisture Determination.
At the sampling location, prior to testing, determine the percent moisture of
the ambient air using the wet and dry bulb temperatures or, if appropriate, a
relative humidity meter.
16.2.3.3 Critical
Orifice Calibration. At the sampling location, prior to testing, calibrate the
entire sampling train (i.e.,
determine the flow rate of the sampling train when operated at critical
conditions). Attach a 500-ml soap bubble meter to the inlet of the probe, and
operate the sampling train at an outlet vacuum of 25 to 50 mm Hg (1 to 2 in.
Hg) above the critical vacuum. Record the information listed in Figure 6-4. Calculate the standard volume of air measured
by the soap bubble meter and the volumetric flow rate using the equations
below:
16.2.3.4 Sampling.
16.2.3.4.1 Operate
the sampling train for sample collection at the same vacuum used during the
calibration run. Start the watch and pump simultaneously. Take readings
(temperature, rate meter, inlet vacuum, and outlet vacuum) at least every 5
minutes. At the end of the sampling run, stop the watch and pump
simultaneously.
16.2.3.4.2 Conduct a
post-test calibration run using the calibration procedure outlined in Section
16.2.3.3. If the Qstd
obtained before and after the test
differ by more than 5 percent, void the test run; if not, calculate the volume
of the gas measured with the critical orifice using Equation 6-6 as follows:
16.2.3.4.3 If the
percent difference between the molecular weight of the ambient air at saturated
conditions and the sample gas is more that ± 3 percent, then the molecular
weight of the gas sample must be considered in the calculations using the
following equation:
NOTE: A post-test leak-check is not necessary because
the post-test calibration run results will indicate whether there is any
leakage.
16.2.3.4.4 Drain the
ice bath, and purge the sampling train using the procedure described in Section 8.3.4.
16.3 Elimination of Ammonia Interference.
The following
alternative procedures must be used in addition to those specified in the
method when sampling at sources having ammonia emissions.
16.3.1 Sampling.
The probe shall be
maintained at 275¡C (527¡F) and equipped with a high-efficiency in-stack filter
(glass fiber) to remove particulate matter. The filter material shall be
unreactive to SO2. Whatman 934AH (formerly Reeve Angel 934AH)
filters treated as described in Reference 10 in
Section 17.0 of Method 5 is an example of a filter that has been shown to
work. Where alkaline particulate matter and condensed moisture are present in
the gas stream, the filter shall be heated above the moisture dew point but
below 225¡C (437¡F).
16.3.2 Sample Recovery.
Recover the sample
according to Section 8.4 except for discarding the contents of the midget
bubbler. Add the bubbler contents, including the rinsings of the bubbler with
water, to a separate polyethylene bottle from the rest of the sample. Under
normal testing conditions where sulfur trioxide will not be present
significantly, the tester may opt to delete the midget bubbler from the
sampling train. If an approximation of the sulfur trioxide concentration is
desired, transfer the contents of the midget bubbler to a separate polyethylene
bottle.
16.3.3 Sample Analysis.
Follow the procedures
in Sections 11.1 and 11.2, except add 0.5 ml of 0.1 N
HCl to the Erlenmeyer flask and mix before adding the indicator. The following
analysis procedure may be used for an approximation of the sulfur trioxide
concentration. The accuracy of the calculated concentration will depend upon
the ammonia to SO2 ratio and the level of oxygen present in the gas
stream. A fraction of the SO2 will be counted as
sulfur trioxide as the ammonia to SO2 ratio and
the sample oxygen content increases. Generally, when this ratio is 1 or less and
the oxygen content is in the range of 5 percent, less than 10 percent of the SO2 will be counted as sulfur trioxide. Analyze the peroxide and
isopropanol sample portions separately. Analyze the peroxide portion as
described above. Sulfur trioxide is determined by difference using sequential
titration of the isopropanol portion of the sample. Transfer the contents of
the isopropanol storage container to a 100-ml volumetric flask, and dilute to
exactly 100 ml with water. Pipette a 20-ml aliquot of this solution into a
250-ml Erlenmeyer flask, add 0.5 ml of 0.1 N HCl, 80 ml of 100 percent
isopropanol, and two to four drops of thorin indicator. Titrate to a pink
endpoint using 0.0100 N barium perchlorate. Repeat and average the titration
volumes that agree within 1 percent or 0.2 ml, whichever is larger. Use this
volume in Equation 6-2 to determine the sulfur trioxide concentration. From the
flask containing the remainder of the isopropanol sample, determine the
fraction of SO2 collected in the bubbler by pipetting 20-ml
aliquots into 250-ml Erlenmeyer flasks. Add 5 ml of 3 percent H2O2, 100 ml of 100 percent isopropanol, and two to
four drips of thorin indicator, and titrate as before. From this titration
volume, subtract the titrant volume determined for sulfur trioxide, and add the
titrant volume determined for the peroxide portion. This final volume
constitutes Vt, the volume of barium perchlorate used for the
SO2 sample.
17.0 References.
1. Atmospheric
Emissions from Sulfuric Acid Manufacturing Processes. U.S. DHEW, PHS, Division
of Air Pollution. Public Health Service Publication No. 999-AP-13. Cincinnati,
OH. 1965.
2. Corbett, P.F. The
Determination of SO2
and SO3 in Flue Gases. Journal of the Institute of Fuel. 24:237-243.1961.
3. Matty, R.E., and
E.K. Diehl. Measuring Flue-Gas SO2 and SO3. Power. 101:94-97. November 1957.
4. Patton, W.F., and
J.A. Brink, Jr. New Equipment and Techniques for Sampling Chemical Process
Gases. J. Air Pollution Control Association. 13:162. 1963.
5. Rom, J.J.
Maintenance, Calibration, and Operation of Isokinetic Source Sampling
Equipment. Office of Air Programs, U.S. Environmental Protection Agency.
Research Triangle Park, NC. APTD-0576. March 1972.
6. Hamil, H.F., and
D.E. Camann. Collaborative Study of Method for the Determination of Sulfur
Dioxide Emissions from Stationary Sources (Fossil-Fuel Fired Steam Generators).
U.S. Environmental Protection Agency, Research Triangle Park, NC.
EPA-650/4-74-024. December 1973.
7. Annual Book of
ASTM Standards. Part 31; Water, Atmospheric Analysis. American Society for
Testing and Materials. Philadelphia, PA. 1974. pp. 40-42.
8. Knoll, J.E., and
M.R. Midgett. The Application of EPA Method 6 to High Sulfur Dioxide
Concentrations. U.S. Environmental Protection Agency. Research Triangle Park,
NC. EPA-600/4-76-038. July 1976.
9. Westlin, P. R.,
and R. T. Shigehara. Procedure for Calibrating and Using Dry Gas Volume Meters
as Calibration Standards. Source Evaluation Society Newsletter. 3(1):17-30.
February 1978.
10. Yu, K. K.
Evaluation of Moisture Effect on Dry Gas Meter Calibration. Source Evaluation
Society
Newsletter.
5(1):24-28. February 1980.
11. Lodge, J.P., Jr.,
et al. The Use of Hypodermic
Needles as Critical Orifices in Air Sampling. J. Air Pollution Control
Association. 16:197-200. 1966.
12. Shigehara, R.T.,
and C.B. Sorrell. Using Critical Orifices as Method 5 CalibrationStandards.
Source Evaluation Society Newsletter. 10:4-15. August 1985.
13.
Curtis, F., Analysis
of Method 6 Samples in the Presence of Ammonia. Source Evaluation Society
Newsletter. 13(1):9-15 February 1988.
18.0 Tables, Diagrams, Flowcharts and Validation Data.
TABLE
6-1. APPROXIMATE FLOW RATES FOR VARIOUS NEEDLE SIZES.
Figure
6-1. Sulfur Dioxide Sampling Train.
Figure
6-2. Sulfur Dioxide Sampling
Train Using a Critical Orifice.
Figure
6-3. Critical Orifice
Adaptation for the Method 6 Sampling Train.
Figure
6-4. Critical Orifice Calibration Data Sheet.
