Pt. 63, Subpt. DDDD, App. A
Appendix A to Subpart DDDD of Part 63
—Alternative Procedure To Determine Capture Efficiency From Enclosures Around Hot Presses in the Plywood and Composite Wood Products Industry Using Sulfur Hexafluoride Tracer Gas
1.0Scope and Application
This procedure has been developed specifically for the rule for the plywood and composite wood products (PCWP) industry and is used to determine the capture efficiency of a partial hot press enclosure in that industry. This procedure is applicable for the determination of capture efficiency for enclosures around hot presses and is an alternative to the construction of temporary total enclosures (TTE). Sulfur hexafluoride (SF6) is used as a tracer gas (other tracer gases may be used if approved by the EPA Administrator). This gas is not indigenous to the ambient atmosphere and is nonreactive.
This procedure uses infrared spectrometry (IR) as the analytical technique. When the infrared spectrometer used is a Fourier-Transform Infrared spectrometer (FTIR), an alternate instrument calibration procedure may be used; the alternate calibration procedure is the calibration transfer standard (CTS) procedure of EPA Method 320 (appendix A to 40 CFR part 63
). Other analytical techniques which are capable of equivalent Method Performance (Section 13.0
) also may be used. Specifically, gas chromatography with electron capture detection (GC/ECD) is an applicable technique for analysis of SF6
2.0Summary of Method
A constant mass flow rate of SF6
tracer gas is released through manifolds at multiple locations within the enclosure to mimic the release of hazardous air pollutants during the press process. This test method requires a minimum of three SF6
injection points (two at the press unloader and one at the press) and provides details about considerations for locating the injection points. A GC/ECD is used to measure the concentration of SF6
at the inlet duct to the control device (outlet duct from enclosure). Simultaneously, EPA Method 2 (appendix A to 40 CFR part 60
) is used to measure the flow rate at the inlet duct to the control device. The concentration and flow rate measurements are used to calculate the mass emission rate of SF6
at the control device inlet. Through calculation of the mass of SF6
released through the manifolds and the mass of SF6
measured at the inlet to the control device, the capture efficiency of the enclosure is calculated.
In addition, optional samples of the ambient air may be taken at locations around the perimeter of the enclosure to quantify the ambient concentration of SF6 and to identify those areas of the enclosure that may be performing less efficiently; these samples would be taken using disposable syringes and would be analyzed using a GC/ECD.
Finally, in addition to the requirements specified in this procedure, the data quality objectives (DQO) or lower confidence limit (LCL) criteria specified in appendix A to 40 CFR part 63
, subpart KK, Data Quality Objective and Lower Confidence Limit Approaches for Alternative Capture Efficiency Protocols and Test Methods, must also be satisfied. A minimum of three test runs are required for this procedure; however, additional test runs may be required based on the results of the DQO or LCL analysis.
3.1Capture efficiency (CE). The weight per unit time of SF6 entering the control device divided by the weight per unit time of SF6 released through manifolds at multiple locations within the enclosure.
3.2Control device (CD). The equipment used to reduce, by destruction or removal, press exhaust air pollutants prior to discharge to the ambient air.
3.3Control/destruction efficiency (DE). The volatile organic compound or HAP removal efficiency of the control device.
3.4Data Quality Objective (DQO) Approach. A statistical procedure to determine the precision of the data from a test series and to qualify the data in the determination of capture efficiency for compliance purposes. If the results of the DQO analysis of the initial three test runs do not satisfy the DQO criterion, the LCL approach can be used or additional test runs must be conducted. If additional test runs are conducted, then the DQO or LCL analysis is conducted using the data from both the initial test runs and all additional test runs.
3.5Lower Confidence Limit (LCL) Approach. An alternative statistical procedure that can be used to qualify data in the determination of capture efficiency for compliance purposes. If the results of the LCL approach produce a CE that is too low for demonstrating compliance, then additional test runs must be conducted until the LCL or DQO is met. As with the DQO, data from all valid test runs must be used in the calculation.
3.6Minimum Measurement Level (MML). The minimum tracer gas concentration expected to be measured during the test series. This value is selected by the tester based on the capabilities of the IR spectrometer (or GC/ECD) and the other known or measured parameters of the hot press enclosure to be tested. The selected MML must be above the low-level calibration standard and preferably below the mid-level calibration standard.
3.7Method 204. The U.S. EPA Method 204, “Criteria For and Verification of a Permanent or Temporary Total Enclosure” (40 CFR part 51
, appendix M).
3.8Method 205. The U.S. EPA Method 205, “Verification of Gas Dilution Systems for Field Instrument Calibrations” (40 CFR part 51
, appendix M).
3.9Method 320. The U.S. EPA Method 320, “Measurement of Vapor Phase Organic and Inorganic Emissions by Extractive Fourier Transform Infrared (FTIR) Spectroscopy” (40 CFR part 63
, appendix A).
3.10Overall capture and control efficiency (CCE). The collection and control/destruction efficiency of both the PPE and CD combined. The CCE is calculated as the product of the CE and DE.
3.11Partial press enclosure (PPE). The physical barrier that “partially” encloses the press equipment, captures a significant amount of the associated emissions, and transports those emissions to the CD.
3.12Test series. A minimum of three test runs or, when more than three runs are conducted, all of the test runs conducted.
There are no known interferences.
Sulfur hexafluoride is a colorless, odorless, nonflammable liquefied gas. It is stable and nonreactive and, because it is noncorrosive, most structural materials are compatible with it. The Occupational Safety and Health Administration Permissible Emission Limit-Time Weighted Average (PEL-TWA) and Threshold Limit Value-Time Weighted Average (TLV-TWA) concentrations are 1,000 parts per million. Sulfur hexafluoride is an asphyxiant. Exposure to an oxygen-deficient atmosphere (less than 19.5 percent oxygen) may cause dizziness, drowsiness, nausea, vomiting, excess salivation, diminished mental alertness, loss of consciousness, and death. Exposure to atmospheres containing less than 12 percent oxygen will bring about unconsciousness without warning and so quickly that the individuals cannot help themselves. Contact with liquid or cold vapor may cause frostbite. Avoid breathing sulfur hexafluoride gas. Self-contained breathing apparatus may be required by rescue workers. Sulfur hexafluoride is not listed as a carcinogen or a potential carcinogen.
6.0Equipment and Supplies
This method requires equipment and supplies for: (a) the injection of tracer gas into the enclosure, (b) the measurement of the tracer gas concentration in the exhaust gas entering the control device, and (c) the measurement of the volumetric flow rate of the exhaust gas entering the control device. In addition, the requisite equipment needed for EPA Methods 1-4 in appendix A to 40 CFR part 60
will be required. Equipment and supplies for optional ambient air sampling are discussed in Section 8.6
6.1Tracer Gas Injection.
6.1.1Manifolds. This method requires the use of tracer gas supply cylinder(s) along with the appropriate flow control elements. Figure 1 shows a schematic drawing of the injection system showing potential locations for the tracer gas manifolds. Figure 2 shows a schematic drawing of the recommended configuration of the injection manifold. Three tracer gas discharge manifolds are required at a minimum.
6.1.2Flow Control Meter. Flow control and measurement meter for measuring the quantity of tracer gas injected. A mass flow, volumetric flow, or critical orifice control meter can be used for this method. The meter must be accurate to within ±5 percent at the flow rate used. This means that the flow meter must be calibrated against a primary standard for flow measurement at the appropriate flow rate.
6.2Measurement of Tracer Gas Concentration.
6.2.1Sampling Probes. Use Pyrex or stainless steel sampling probes of sufficient length to reach the traverse points calculated according to EPA Method 1 (appendix A to 40 CFR part 60
6.2.2Sampling Line. Use a heated Teflon sampling line to transport the sample to the analytical instrument.
6.2.3Sampling Pump. Use a sampling pump capable of extracting sufficient sample from the duct and transporting to the analytical instrument.
6.2.4Sample Conditioning System. Use a particulate filter sufficient to protect the sampling pump and analytical instrument. At the discretion of the tester and depending on the equipment used and the moisture content of the exhaust gas, it may be necessary to further condition the sample by removing moisture using a condenser.
6.2.5Analytical Instrument. Use one of the following analytical instruments.
184.108.40.206Spectrometer. Use an infrared spectrometer designed to measuring SF6
tracer gas and capable of meeting or exceeding the specifications of this procedure. An FTIR meeting the specifications of Method 320 in appendix A to 40 CFR part 63
may be used.
220.127.116.11GC/ECD. Use a GC/ECD designed to measure SF6 tracer gas and capable of meeting or exceeding the specifications of this procedure.
6.2.6Recorder. At a minimum, use a recorder with linear strip chart. An automated data acquisition system (DAS) is recommended.
6.3Exhaust Gas Flow Rate Measurement. Use equipment specified for EPA Methods 2, 3, and 4 in appendix A to 40 CFR part 60
for measuring flow rate of exhaust gas at the inlet to the control device.
7.0Reagents and Standards
7.1Tracer Gas. Use SF6
as the tracer gas. The manufacturer of the SF6
tracer gas should provide a recommended shelf life for the tracer gas cylinder over which the concentration does not change more than ±2 percent from the certified value. A gas mixture of SF6
diluted with nitrogen should be used; based on experience and calculations, pure SF6
gas is not necessary to conduct tracer gas testing. Select a concentration and flow rate that is appropriate for the analytical instrument's detection limit, the MML, and the exhaust gas flow rate from the enclosure (see section 8.1
.1). You may use a tracer gas other than SF6
with the prior approval of the EPA Administrator. If you use an approved tracer gas other than SF6
, all references to SF6
in this protocol instead refer to the approved tracer gas.
7.2Calibration Gases. The SF6
calibration gases required will be dependent on the selected MML and the appropriate span selected for the test. Commercial cylinder gases certified by the manufacturer to be accurate to within 1 percent of the certified label value are preferable, although cylinder gases certified by the manufacturer to 2 percent accuracy are allowed. Additionally, the manufacturer of the SF6
calibration gases should provide a recommended shelf life for each calibration gas cylinder over which the concentration does not change more than ±2 percent from the certified value. Another option allowed by this method is for the tester to obtain high concentration certified cylinder gases and then use a dilution system meeting the requirements of EPA Method 205, 40 CFR part 51
, appendix M, to make multi-level calibration gas standards. Low-level, mid-level, and high-level calibration gases will be required. The MML must be above the low-level standard, the high-level standard must be no more than four times the low-level standard, and the mid-level standard must be approximately halfway between the high- and low-level standards. See section 12.1
for an example calculation of this procedure.
If using an FTIR as the analytical instrument, the tester has the option of following the CTS procedures of Method 320 in appendix A to 40 CFR part 63
; the calibration standards (and procedures) specified in Method 320 may be used in lieu of the calibration standards and procedures in this protocol.
7.2.1Zero Gas. High purity nitrogen.
7.2.2Low-Level Calibration Gas. An SF6 calibration gas in nitrogen with a concentration equivalent to 20 to 30 percent of the applicable span value.
7.2.3Mid-Level Calibration Gas. An SF6 calibration gas in nitrogen with a concentration equivalent to 45 to 55 percent of the applicable span value.
7.2.4High-Level Calibration Gas. An SF6 calibration gas in nitrogen with a concentration equivalent to 80 to 90 percent of the applicable span value.
8.0Sample Collection, Preservation, Storage, and Transport
8.1.1Determination of Minimum Tracer Gas Flow Rate.
18.104.22.168Determine (via design calculations or measurements) the approximate flow rate of the exhaust gas through the enclosure, actual cubic feet per minute (acfm).
22.214.171.124Calculate the minimum tracer gas injection rate necessary to assure a detectable SF6
concentration at the exhaust gas measurement point (see section 12.1
126.96.36.199Select a flow meter for the injection system with an operating range appropriate for the injection rate selected.
8.1.2Determination of the Approximate Time to Reach Equilibrium.
188.8.131.52Determine the volume of the enclosure.
184.108.40.206Calculate the air changes per minute of the enclosure by dividing the approximate exhaust flow rate (220.127.116.11 above) by the enclosed volume (18.104.22.168 above).
22.214.171.124Calculate the time at which the tracer concentration in the enclosure will achieve approximate equilibrium. Divide 3 by the air changes per minute (126.96.36.199 above) to establish this time. This is the approximate length of time for the system to come to equilibrium. Concentration equilibrium occurs when the tracer concentration in the enclosure stops changing as a function of time for a constant tracer release rate. Because the press is continuously cycling, equilibrium may be exhibited by a repeating, but stable, cyclic pattern rather than a single constant concentration value. Assure sufficient tracer gas is available to allow the system to come to equilibrium, and to sample for a minimum of 20 minutes and repeat the procedure for a minimum of three test runs. Additional test runs may be required based on the results of the DQO and LCL analyses described in 40 CFR part 63
, subpart KK, appendix A.
8.1.3Location of Injection Points. This method requires a minimum of three tracer gas injection points. The injection points should be located within leak prone, volatile organic compound/hazardous air pollutant (VOC/HAP) producing areas around the press, or horizontally within 12 inches of the defined equipment. One potential configuration of the injection points is depicted in Figure 1. The effect of wind, exfiltration through the building envelope, and air flowing through open building doors should be considered when locating tracer gas injection points within the enclosure. The injection points should also be located at a vertical elevation equal to the VOC/HAP generating zones. The injection points should not be located beneath obstructions that would prevent a natural dispersion of the gas. Document the selected injection points in a drawing(s).
8.1.4Location of Flow Measurement and Tracer Sampling. Accurate CD inlet gas flow rate measurements are critical to the success of this procedure. Select a measurement location meeting the criteria of EPA Method 1 (40 CFR part 60
, appendix A), Sampling and Velocity Traverses for Stationary Sources. Also, when selecting the measurement location, consider whether stratification of the tracer gas is likely at the location (e.g.
, do not select a location immediately after a point of air in-leakage to the duct).
8.2Tracer Gas Release. Release the tracer gas at a calculated flow rate (see section 12.1
for calculation) through a minimum of three injection manifolds located as described above in 8.1.3. The tracer gas delivery lines must be routed into the enclosure and attached to the manifolds without violating the integrity of the enclosure.
8.3.1Location of Sampling Point(s). If stratification is not suspected at the measurement location, select a single sample point located at the centroid of the CD inlet duct or at a point no closer to the CD inlet duct walls than 1 meter. If stratification is suspected, establish a “measurement line” that passes through the centroidal area and in the direction of any expected stratification. Locate three traverse points at 16.7, 50.0 and 83.3 percent of the measurement line and sample from each of these three points during each run, or follow the procedure in section 8.3
.2 to verify whether stratification does or does not exist.
8.3.2Stratification Verification. The presence or absence of stratification can be verified by using the following procedure. While the facility is operating normally, initiate tracer gas release into the enclosure. For rectangular ducts, locate at least nine sample points in the cross section such that the sample points are the centroids of similarly-shaped, equal area divisions of the cross section. Measure the tracer gas concentration at each point. Calculate the mean value for all sample points. For circular ducts, conduct a 12-point traverse (i.e.
, six points on each of the two perpendicular diameters) locating the sample points as described in 40 CFR part 60
, appendix A, Method 1. Perform the measurements and calculations as described above. Determine if the mean pollutant concentration is more than 10 percent different from any single point. If so, the cross section is considered to be stratified, and the tester may not use a single sample point location, but must use the three traverse points at 16.7, 50.0, and 83.3 percent of the entire measurement line. Other traverse points may be selected, provided that they can be shown to the satisfaction of the Administrator to provide a representative sample over the stack or duct cross section.
8.4CD Inlet Gas Flow Rate Measurements. The procedures of EPA Methods 1-4 (40 CFR part 60
, appendix A) are used to determine the CD inlet gas flow rate. Molecular weight (Method 3) and moisture (Method 4) determinations are only required once for each test series. However, if the test series is not completed within 24 hours, then the molecular weight and moisture measurements should be repeated daily. As a minimum, velocity measurements are conducted according to the procedures of Methods 1 and 2 before and after each test run, as close to the start and end of the run as practicable. A velocity measurement between two runs satisfies both the criterion of “after” the run just completed and “before” the run to be initiated. Accurate exhaust gas flow rate measurements are critical to the success of this procedure. If significant temporal variations of flow rate are anticipated during the test run under normal process operating conditions, take appropriate steps to accurately measure the flow rate during the test. Examples of steps that might be taken include: (1) conducting additional velocity traverses during the test run; or (2) continuously monitoring a single point of average velocity during the run and using these data, in conjunction with the pre- and post-test traverses, to calculate an average velocity for the test run.
8.5Tracer Gas Measurement Procedure.
8.5.1Calibration Error Test. Immediately prior to the emission test (within 2 hours of the start of the test), introduce zero gas and high-level calibration gas at the calibration valve assembly. Zero and calibrate the analyzer according to the manufacturer's procedures using, respectively, nitrogen and the calibration gases. Calculate the predicted response for the low-level and mid-level gases based on a linear response line between the zero and high-level response. Then introduce the low-level and mid-level calibration gases successively to the measurement system. Record the analyzer responses for the low-level and mid-level calibration gases and determine the differences between the measurement system responses and the predicted responses using the equation in section 12.3
. These differences must be less than 5 percent of the respective calibration gas value. If not, the measurement system must be replaced or repaired prior to testing. No adjustments to the measurement system shall be conducted after the calibration and before the drift determination (section 8.5
.4). If adjustments are necessary before the completion of the test series, perform the drift checks prior to the required adjustments and repeat the calibration following the adjustments. If multiple electronic ranges are to be used, each additional range must be checked with a mid-level calibration gas to verify the multiplication factor.
If using an FTIR for the analytical instrument, you may choose to follow the pretest preparation, evaluation, and calibration procedures of Method 320 (section 8.0
) (40 CFR part 63
, appendix A) in lieu of the above procedure.
8.5.2Response Time Test. Conduct this test once prior to each test series. Introduce zero gas into the measurement system at the calibration valve assembly. When the system output has stabilized, switch quickly to the high-level calibration gas. Record the time from the concentration change to the measurement system response equivalent to 95 percent of the step change. Repeat the test three times and average the results.
8.5.3SF6 Measurement. Sampling of the enclosure exhaust gas at the inlet to the CD should begin at the onset of tracer gas release. If necessary, adjust the tracer gas injection rate such that the measured tracer gas concentration at the CD inlet is within the spectrometer's calibration range (i.e., between the MML and the span value). Once the tracer gas concentration reaches equilibrium, the SF6 concentration should be measured using the infrared spectrometer continuously for at least 20 minutes per run. Continuously record (i.e., record at least once per minute) the concentration. Conduct at least three test runs. On the recording chart, in the data acquisition system, or in a log book, make a note of periods of process interruption or cyclic operation such as the cycles of the hot press operation. Table 1 to this appendix summarizes the physical measurements required for the enclosure testing.
If a GC/ECD is used as the analytical instrument, a continuous record (at least once per minute) likely will not be possible; make a minimum of five injections during each test run. Also, the minimum test run duration criterion of 20 minutes applies.
8.5.4Drift Determination. Immediately following the completion of the test run, reintroduce the zero and mid-level calibration gases, one at a time, to the measurement system at the calibration valve assembly. (Make no adjustments to the measurement system until both the zero and calibration drift checks are made.) Record the analyzer responses for the zero and mid-level calibration gases and determine the difference between the instrument responses for each gas prior to and after the emission test run using the equation in section 12.4
. If the drift values exceed the specified limits (section 13), invalidate the test results preceding the check and repeat the test following corrections to the measurement system. Alternatively, recalibrate the test measurement system as in section 8.5
.1 and report the results using both sets of calibration data (i.e.
, data determined prior to the test period and data determined following the test period). Note: If using an FTIR for the analytical instrument, you may choose to follow the post-test calibration procedures of Method 320 in appendix A to 40 CFR part 63
.2) in lieu of the above procedures.
8.6Ambient Air Sampling (Optional). Sampling the ambient air surrounding the enclosure is optional. However, taking these samples during the capture efficiency testing will identify those areas of the enclosure that may be performing less efficiently.
8.6.1Location of Ambient Samples Outside the Enclosure (Optional). In selecting the sampling locations for collecting samples of the ambient air surrounding the enclosure, consider potential leak points, the direction of the release, and laminar flow characteristics in the area surrounding the enclosure. Samples should be collected from all sides of the enclosure, downstream in the prevailing room air flow, and in the operating personnel occupancy areas.
8.6.2Collection of Ambient Samples (Optional). During the tracer gas release, collect ambient samples from the area surrounding the enclosure perimeter at predetermined location using disposable syringes or some other type of containers that are non-absorbent, inert, and that have low permeability (i.e., polyvinyl fluoride film or polyester film sample bags or polyethylene, polypropylene, nylon or glass bottles). The use of disposable syringes allows samples to be injected directly into a gas chromatograph. Concentration measurements taken around the perimeter of the enclosure provide evidence of capture performance and will assist in the identification of those areas of the enclosure that are performing less efficiently.
8.6.3Analysis and Storage of Ambient Samples (Optional). Analyze the ambient samples using an analytical instrument calibrated and operated according to the procedures in this appendix or ASTM E 260 and ASTM E 697. Samples may be analyzed immediately after a sample is taken, or they may be stored for future analysis. Experience has shown no degradation of concentration in polypropylene syringes when stored for several months as long as the needle or syringe is plugged. Polypropylene syringes should be discarded after one use to eliminate the possibility of cross contamination of samples.
9.1Sampling, System Leak Check. A sampling system leak check should be conducted prior to and after each test run to ensure the integrity of the sampling system.
9.2Zero and Calibration Drift Tests.
||Quality control measure
||Zero and calibration drift tests
||Ensures that bias introduced by drift in the measurement system output during the run is no greater than 3 percent of span.
10.0Calibration and Standardization
10.1Control Device Inlet Air Flow Rate Measurement Equipment. Follow the equipment calibration requirements specified in Methods 2, 3, and 4 (appendix A to 40 CFR part 60
) for measuring the velocity, molecular weight, and moisture of the control device inlet air.
10.2Tracer Gas Injection Rate. A dry gas volume flow meter, mass flow meter, or orifice can be used to measure the tracer gas injection flow rate. The selected flow measurement device must have an accuracy of greater than ±5 percent at the field operating range. Prior to the test, verify the calibration of the selected flow measurement device using either a wet test meter, spirometer, or liquid displacement meter as the calibration device. Select a minimum of two flow rates to bracket the expected field operating range of the flow meter. Conduct three calibration runs at each of the two selected flow rates. For each run, note the exact quantity of gas as determined by the calibration standard and the gas volume indicated by the flow meter. For each flow rate, calculate the average percent difference of the indicated flow compared to the calibration standard.
10.3Spectrometer. Follow the calibration requirements specified by the equipment manufacturer for infrared spectrometer measurements and conduct the pretest calibration error test specified in section 8.5
.1. Note: if using an FTIR analytical instrument see Method 320, section 10 (appendix A to 40 CFR part 63
10.4Gas Chromatograph. Follow the pre-test calibration requirements specified in section 8.5
10.5Gas Chromatograph for Ambient Sampling (Optional). For the optional ambient sampling, follow the calibration requirements specified in section 8.5
.1 or ASTM E 260 and E 697 and by the equipment manufacturer for gas chromatograph measurements.
The sample collection and analysis are concurrent for this method (see section 8.0
12.0Calculations and Data Analysis
12.1Estimate MML and Span. The MML is the minimum measurement level. The selection of this level is at the discretion of the tester. However, the MML must be higher than the low-level calibration standard, and the tester must be able to measure at this level with a precision of ≤10 percent. As an example, select the MML as 10 times the instrument's published detection limit. The detection limit of one instrument is 0.01 parts per million by volume (ppmv). Therefore, the MML would be 0.10 ppmv. Select the low-level calibration standard as 0.08 ppmv. The high-level standard would be four times the low-level standard or 0.32 ppmv. A reasonable mid-level standard would then be 0.20 ppmv (halfway between the low-level standard and the high-level standard). Finally, the span value would be approximately 0.40 ppmv (the high-level value is 80 percent of the span). In this example, the following MML, calibration standards, and span values would apply:
MML = 0.10 ppmv
Low-level standard = 0.08 ppmv
Mid-level standard = 0.20 ppmv
High-level standard = 0.32 ppmv
Span value = 0.40 ppmv
12.2Estimate Tracer Gas Injection Rate for the Given Span. To estimate the minimum and maximum tracer gas injection rate, assume a worst case capture efficiency of 80 percent, and calculate the tracer gas flow rate based on known or measured parameters. To estimate the minimum tracer gas injection rate, assume that the MML concentration (10 times the IR detection limit in this example) is desired at the measurement location. The following equation can be used to estimate the minimum tracer gas injection rate:
((QT-MIN × 0.8)/QE) × (CT ÷ 100) × 106 = MML
QT-MIN = 1.25 × MML × (QE/CT) × 10−4
QT-MIN = minimum volumetric flow rate of tracer gas injected, standard cubic feet per minute (scfm);
QE = volumetric flow rate of exhaust gas, scfm;
CT = Tracer gas (SF6) concentration in gas blend, percent by volume;
MML = minimum measured level, ppmv = 10 × IRDL (for this example);
IRDL = IR detection limit, ppmv.
Standard conditions: 20 °C, 760 millimeters of mercury (mm Hg).
To estimate the maximum tracer gas injection rate, assume that the span value is desired at the measurement location. The following equation can be used to estimate the maximum tracer gas injection rate:
((QT-MAX × 0.8)/QE) × (CT ÷ 100) × 106 = span value
QT-MAX = 1.25 × span value × (QE/CT) × 10−4
QT-MAX = maximum volumetric flow rate of tracer gas injected, scfm;
Span value = instrument span value, ppmv.
The following example illustrates this calculation procedure:
Find the range of volumetric flow rate of tracer gas to be injected when the following parameters are known:
QE = 60,000 scfm (typical exhaust gas flow rate from an enclosure);
CT = 2 percent SF6 in nitrogen;
IRDL = 0.01 ppmv (per manufacturer's specifications);
MML = 10 × IRDL = 0.10 ppmv;
Span value = 0.40 ppmv;
QT = ?
Minimum tracer gas volumetric flow rate:
QT-MIN = 1.25 × MML × (QE/CT) × 10−4
QT-MIN = 1.25 × 0.10 × (60,000/2) × 10−4 = 0.375 scfm
Maximum tracer gas volumetric flow rate:
QT-MAX = 1.25 × span value × (QE/CT) × 10−4
QT-MAX = 1.25 × 0.40 × (60,000/2) × 10−4 = 1.5 scfm
In this example, the estimated total volumetric flow rate of the two percent SF6 tracer gas injected through the manifolds in the enclosure lies between 0.375 and 1.5 scfm.
12.3Calibration Error. Calculate the calibration error for the low-level and mid-level calibration gases using the following equation:
Err = |Cstd−Cmeasverbar; ÷ Cstd × 100
Err = calibration error, percent;
Cstd = low-level or mid-level calibration gas value, ppmv;
Cmeas = measured response to low-level or mid-level concentration gas, ppmv.
12.4Calibration Drift. Calculate the calibration drift for the zero and low-level calibration gases using the following equation:
D = |verbar;Cinitial − Cfinal |verbar; ÷ Cspan × 100
D = calibration drift, percent;
Cinitial = low-level or mid-level calibration gas value measured before test run, ppmv;
Cfinal = low-level or mid-level calibration gas value measured after test run, ppmv;
Cspan = span value, ppmv.
12.5Calculate Capture Efficiency. The equation to calculate enclosure capture efficiency is provided below:
CE = (SF6-CD ÷ SF6-INJ) × 100
CE = capture efficiency;
SF6-CD = mass of SF6 measured at the inlet to the CD;
SF6-INJ= mass of SF6 injected from the tracer source into the enclosure.
Calculate the CE for each of the initial three test runs. Then follow the procedures outlined in section 12.6
to calculate the overall capture efficiency.
12.6Calculate Overall Capture Efficiency. After calculating the capture efficiency for each of the initial three test runs, follow the procedures in 40 CFR part 63
, subpart KK, appendix A, to determine if the results of the testing can be used in determining compliance with the requirements of the rule. There are two methods that can be used: the DQO and LCL methods. The DQO method is described in section 3 of40 CFR part 63
, subpart KK, appendix A, and provides a measure of the precision of the capture efficiency testing conducted. Section 3 of40 CFR part 63
, subpart KK, appendix A, provides an example calculation using results from a facility. If the DQO criteria are met using the first set of three test runs, then the facility can use the average capture efficiency of these test results to determine the capture efficiency of the enclosure. If the DQO criteria are not met, then the facility can conduct another set of three runs and run the DQO analysis again using the results from the six runs OR
the facility can elect to use the LCL approach.
The LCL method is described in section 4 of40 CFR part 63
, subpart KK, appendix A, and provides sources that may be performing much better than their regulatory requirement, a screening option by which they can demonstrate compliance. The LCL approach compares the 80 percent lower confidence limit for the mean measured CE value to the applicable regulatory requirement. If the LCL capture efficiency is higher than the applicable limit, then the facility is in initial compliance and would use the LCL capture efficiency as the capture efficiency to determine compliance. If the LCL capture efficiency is lower than the applicable limit, then the facility must perform additional test runs and re-run the DQO or LCL analysis.
13.1Measurement System Performance Specifications.
13.1.1Zero Drift. Less than ±3 percent of the span value.
13.1.2Calibration Drift. Less than ±3 percent of the span value.
13.1.3Calibration Error. Less than ±5 percent of the calibration gas value.
13.2Flow Measurement Specifications. The mass flow, volumetric flow, or critical orifice control meter used should have an accuracy of greater than ±5 percent at the flow rate used.
13.3Calibration and Tracer Gas Specifications. The manufacturer of the calibration and tracer gases should provide a recommended shelf life for each calibration gas cylinder over which the concentration does not change more than ±2 percent from the certified value.
14.0Pollution Prevention [Reserved]
15.0Waste Management [Reserved]
1. 40 CFR part 60
, appendix A, EPA Method 1—Sample and velocity traverses for stationary sources.
2. 40 CFR part 60
, appendix A, EPA Method 2—Determination of stack gas velocity and volumetric flow rate.
3. 40 CFR part 60
, appendix A, EPA Method 3—Gas analysis for the determination of dry molecular weight.
4. 40 CFR part 60
, appendix A, EPA Method 4—Determination of moisture content in stack gases.
5. SEMI F15-93 Test Method for Enclosures Using Sulfur Hexafluoride Tracer Gas and Gas Chromotography.
6. Memorandum from John S. Seitz, Director, Office of Air Quality Planning and Standards, to EPA Regional Directors, Revised Capture Efficiency Guidance for Control of Volatile Organic Compound Emissions, February 7, 1995. (That memorandum contains an attached technical document from Candace Sorrell, Emission Monitoring and Analysis Division, “Guidelines for Determining Capture Efficiency,” January 9, 1994).
7. Technical Systems Audit of Testing at Plant “C,” EPA-454/R-00-26, May 2000.
8. Material Safety Data Sheet for SF6 Air Products and Chemicals, Inc. Website: www3.airproducts.com. October 2001.
17.0Tables, Diagrams, Flowcharts, and Validation Data
Table 1 to Appendix A—Summary of Critical Physical Measurements for Enclosure Testing
|Tracer gas injection rate
||Mass flow meter, volumetric flow meter or critical orifice
||Injection manifolds (cylinder gas).
|Tracer gas concentration at control device inlet
||Infrared Spectrometer or GC/ECD
||Continuous (at least one reading per minute) for a minimum of 20 minutes
||Inlet duct to the control device (outlet duct of enclosure).
|Volumetric air flow rate
||EPA Methods 1, 2, 3, 4 (40 CFR part 60, appendix A)• Velocity sensor (Manometer/Pitot tube)
||Each test run for velocity (minimum); Daily for moisture and molecular weight
||Inlet duct to the control device (outlet duct of enclosure).
||• Midget Impinger sampler
||• Orsat or Fyrite