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where: Pr=dynamic parameter specification, de

termined empirically, to insure complete reaction of the available Os,

ppm-minute (NORC=NO concentration in the reaction

chamber, ppm R=residence time of the reactant gases in

the reaction chamber, minute (NO)stp=concentration of the undiluted

NO standard, ppm Fro=NO flowrate, scm3/min Fo=0, generator air flowrate, scm/min Vre=volume of the reaction chamber,

scm 1.4.2 The flow conditions to be used in the GPT system are determined by the following procedure:

(a) Determine Ft, the total flow required at the output manifold (Fy=analyzer demand plus 10 to 50% excess).

(b) Establish (NOJout as the highest NO concentration (ppm) which will be required at the output manifold. (NOJOur should be approximately equivalent to 90% of the upper range limit (URL) of the NO, concentration range to be covered.

(c) Determine Fxo as

Verify that tx < 2 minutes. If not, select a reaction chamber with a smaller Ver(g) Compute the diluent air flowrate as Fo=F1-FF

(8) where:

Fo=diluent air flowrate, scm3/min

(h) If Fo turns out to be impractical for the desired system, select a reaction chamber having a different Vec and recompute F and Fo.

NOTE: A dynamic parameter lower than 2.75 ppm-minutes may be used if it can be determined empirically that quantitative reaction of O, with NO occurs. A procedure for making this determination as well as a more detailed discussion of the above requirements and other related considerations is given in reference 13.

1.5 Procedure.

1.5.1 Assemble a dynamic calibration system such as the one shown in Figure 1.

1.5.2 Insure that all flowmeters are calibrated under the conditions of use against a reliable standard such as a soap-bubble meter or wet-test meter. An volumetric flowrates should be corrected to 25° C and 760 mm Hg. A discussion on the calibration of flowmeters is given in reference 13.

1.5.3 Precautions must be taken to remove O, and other contaminants from the NO pressure regulator and delivery system prior to the start of calibration to avoid any conversion of the standard NO to NO,. Failure to do so can cause significant errors in calibration. This problem may be minimized by (1) carefully evacuating the regulator, when possible, after the regulator has been connected to the cylinder and before opening the cylinder valve; (2) thoroughly flushing the regulator and delivery system with NO after opening the cylinder valve; (3) not removing the regulator from the cylinder between calibrations unless absolutely necessary. Further discussion of these procedures is given in reference 13.

1.5.4 Select the operating range of the NO/NO,/NO, analyzer to be calibrated. In order to obtain maximum precision and ac. curacy for NO, calibration, all three channels of the analyzer should be set to the same range. If operation of the NO and NO, channels on higher ranges is desired, subsequent recalibration of the NO and NO, channels on the higher ranges is recommended.

Note: Some analyzer designs may require identical ranges for NO, NO,, and NO. during operation of the analyzer.

1.5.5 Connect the recorder output cable(s) of the NO/NO/NO, analyzer to the input terminals of the strip chart recorder(s). All adjustments to the analyzer should be performed based on the appropri

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ate strip chart readings. References to analyzer responses in the procedures given below refer to recorder responses.

1.5.6 Determine the GPT flow conditions required to meet the dynamic parameter specification as indicated in 1.4.

1.5.7 Adjust the diluent air and O, generator air flows to obtain the flows determined in section 1.4.2. The total air flow must exceed the total demand of the analyzer(s) connected to the output manifold to insure that no ambient air is pulled into the manifold vent. Allow the analyzer to sample zero air until stable NO, NO, and NO, responses are obtained. After the responses have stabilized, adjust the analyzer zero control(s).

NOTE: Some analyzers may have separate zero controls for NO, NOx, and NO2. Other analyzers may have separate zero controls only for NO and NO,, while still others may have only one zero control common to all three channels.

Offsetting the analyzer zero adjustments to +5 percent of scale is recommended to fa. cilitate observing negative zero drift. Record the stable zero air responses as Zxo, ZNOX, and ZNO,.

1.5.8 Preparation of NO and NO, calibration curves.

1.5.8.1 Adjustment of NO span control. Adjust the NO flow from the standard NO cylinder to generate an NO concentration of approximately 80 percent of the upper range limit (URL) of the NO range. This exact NO concentration is calculated from:

only for NO and NO,, while still others may have only one span control common to all three channels. When only one span control is available, the span adjustment is made on the NO channel of the analyzer. If substantial adjustment of the NO span control is necessary, it may be necessary to recheck the zero and span adjustments by repeating steps 1.5.7 and 1.5.8.1. Record the NO concentration and the analyzer's NO response.

1.5.8.2 Adjustment of NO, span control. When adjusting the analyzer's NO, span control, the presence of any NO, impurity in the standard NO cylinder must be taken into account. Procedures for determining the amount of NO, impurity in the standard NO cylinder are given in reference 13. The exact NO, concentration is calculated from:

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where: (NO)out=diluted NO concentration at the

output manifold, ppm Sample this NO concentration until the NO and NO, responses have stabilized. Adjust the NO span control to obtain a recorder response as indicated below: recorder response (percent scale)

NOTE: If the analyzer has only one span control, the span adjustment is made on the NO channel and no further adjustment is made here for NOX If substantial adjustment of the NO, span control is necessary, it may be necessary to recheck the zero and span adjustments by repeating steps 1.5.7 and 1.5.8.2. Record the NO, concentration and the analyzer's NO, response.

1.5.8.3 Generate several additional con. centrations (at least five evenly spaced points across the remaining scale are suggested to verify linearity) by decreasing Fro or increasing F. For each concentration generated, calculate the exact NO and NO, concentrations using equations (9) and (11) respectively. Record the analyzer's NO and NO, responses for each concentration. Plot the analyzer responses versus the respective calculated NO and NO, concentrations and

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NO concentration determined in step 1.5.9.1. After the analyzer responses have stabilized, record the resultant NO and NO, concentrations as (NO) rem and (NO, Treme

1.5.9.3 Calculate the resulting NO, concentration from:

draw or calculate the NO and NO, calibra. tion curves. For subsequent calibrations where linearity can be assumed, these curves may be checked with a two-point calibration consisting of a zero air point and NO and NO, concentrations of approximate ly 80% of the URL.

1.5.9 Preparation of NO, calibration curve.

1.5.9.1 Assuming the NO, zero has been properly adjusted while sampling zero air in step 1.5.7, adjust F, and F, as determined in section 1.4.2. Adjust Fxo to generate an NO concentration near 90% of the URL of the NO range. Sample this NO concentration until the NO and NO, responses have stabilized. Using the NO calibration curve obtained in section 1.5.8, measure and record the NO concentration as (NO)orig. Using the NO, calibration curve obtained in section 1.5.8, measure and record the NO, concentration as (NO,Jorice

1.5.9.2 Adjust the O, generator to generate sufficient O, to produce a decrease in the NO concentration equivalent to approximately 80% of the URL of the NO, range. The decrease must not exceed 90% of the

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((NO2lou recorder response (% scale) =

URL

(14)

NOTE: If the analyzer has only one or two span controls, the span adjustments are made on the NO channel or NO and NO, channels and no further adjustment is made here for NO2. If substantial adjustment of the NO, span control is necessary, it may be necessary to recheck the zero and span adjustments by repeating steps 1.5.7 and 1.5.9.3. Record the NO, concentration and the corresponding analyzer NO, and NO, responses.

1.5.9.4 Maintaining the same Fxo, Fo, and Fp as in section 1.5.9.1, adjust the ozone generator to obtain several other concentrations of NO, over the NO, range (at least five evenly spaced points across the remaining scale are suggested). Calculate each NO, concentration using equation (13) and record the corresponding analyzer NO, and NO, responses. Plot the analyzer's NO, responses versus the corresponding calculated NO, concentrations and draw or calculate the NO, calibration curve.

1.5.10 Determination of converter effi. ciency.

1.5.10.1 For each NO, concentration generated during the preparation of the NO2 calibration curve (see section 1.5.9) calculate the concentration of NO, converted from:

(NO,Iconv=[NO_Jout"( [NO,Jorix'[NO]rem)

(15) where: (NO)conv=concentration of NO, convert

ed, ppm (NO, Jorix = original NO, concentration prior

to addition of O,, ppm [NO,]rem=NO, concentration remaining

after addition of Os, ppm NOTE: Supplemental information on calibration and other procedures in this method are given in reference 13. Plot (NO2)cony (y-axis) versus [NO]out (xaxis) and draw or calculate the converter efficiency curve. The slope of the curve times 100 is the average converter efficiency, Ec The average converter efficiency must be greater than 96%; if it is less than 96%, replace or service the converter.

2. Alternative B-NO, permeation device. Major equipment required: Stable O, generator. Chemiluminescence NO/NO,/NO, analyzer with strip chart recorder(s).

NO concentration standard.
NO, concentration standard.

2.1 Principle. Atmospheres containing accurately known concentrations of nitrogen dioxide are generated by means of a

permeation device. (10) The permeation device emits NO, at a known constant rate provided the temperature of the device is held constant (+0.1° C) and the device has been accurately calibrated at the temperature of use. The NO2 emitted from the device is diluted with zero air to produce NO, concentrations suitable for calibration of the NO, channel of the NO/NO/NO, analyzer. An NO concentration standard is used for calibration of the NO and NO, channels of the analyzer.

2.2 Apparatus. A typical system suitable for generating the required NO and NO2 concentrations is shown in Figure 2. All connections between components downstream from the permeation device should be of glass, Teflon ", or other non-reactive materi

al.

2.2.1 Air Now controllers. Devices capable of maintaining constant air flows within +2% of the required flowrate.

2.2.2 NO flow controller. A device capable of maintaining constant NO flows within +2% of the required flowrate. Component parts in contact with the NO must be of a non-reactive material.

2.2.3 Air flowmeters. Calibrated flowmeters capable of measuring and monitoring air flowrates with an accuracy of +2% of the measured flowrate.

2.2.4 NO flowmeter. A calibrated flowmeter capable of measuring and monitoring NO flowrates with an accuracy of +2% of the measured flowrate. (Rotameters have been reported to operate unreliably when measuring low NO flows and are not recommended.)

2.2.5 Pressure regulator for standard NO cylinder. This regulator must have a non-reactive diaphragm and internal parts and a suitable delivery pressure.

2.2.6 Drier. Scrubber to remove moisture from the permeation device air system. The use of the drier is optional with NO, permeation devices not sensitive to moisture. (Refer to the supplier's instructions for use of the permeation device.)

2.2.7 Constant temperature chamber. Chamber capable of housing the NO, permeation device and maintaining its temperature to within +0.1°C. 2.2.8 Temperature measuring device.

ce capable of measuring and monitoring the temperature of the NO, permeation device with an accuracy of +0.05°C.

2.2.9 Valves. A valve may be used as shown in Figure 2 to divert the NO, from the permeation device when zero air or NO is required at the manifold. A second valve may be used to divert the NO flow when zero air or NO, is required at the manifold.

The valves should be constructed of glass, Teflon , or other nonreactive material.

2.2.10 Mixing chamber. A chamber constructed of glass, Teflone, or other nonreactive material and designed to provide thor

ough mixing of pollutant gas streams and diluent air.

2.2.11 Output manifold. The output manifold should be constructed of glass, Teflonk, or other non-reactive material and should be of sufficient diameter to insure an insignificant pressure drop at the analyzer connection. The system must have a vent designed to insure atmospheric pressure at the manifold and to prevent ambient air from entering the manifold.

2.3 Reagents.

2.3.1 Calibration standards. Calibration standards are required for both NO and NO2. The reference standard for the calibration may be either an NO or NO, standard. The reference standard must be used to certify the other standard to ensure consistency between the two standards.

2.3.1.1 NO, concentration standard. A permeation device suitable for generating NO, concentrations at the required flowrates over the required concentration range. If the permeation device is used as the reference standard, it must be traceable to a National Bureau of Standards NO, Standard Reference Material (SRM 1629) or NO in N, Standard Reference Material (SRM 1683 or SRM 1684). If an NO cylinder is used as the reference standard, the NO, permeation device must be certified against the NO standard according to the procedure given in reference 13. The use of the permeation device should be in strict accordance with the instructions supplied with the device. Additional information regarding the use of permeation devices is given by Scaringelli et al. (11) and Rook et al. (12).

2.3.1.2 NO concentration standard. Cylinder containing 50 to 100 ppm NO in N2 with less than 1 ppm NO2. If the cylinder is used as the reference standard, it must be traceable to a National Bureau of Standards NO in N, Standard Reference Material (SRM 1683 or SRM 1684) or NO, Standard Reference Material (SRM 1629). If an NO, permeation device is used as the reference standard, the NO cylinder must be certified against the NO, standard according to the procedure given in reference 13. The cylinder should be recertified on a regular basis as determined by the local quality control program. A procedure for determining the amount of NO, impurity in the NO cylinder is also given in reference 13.

2.3.3 Zero air. Air, free of contaminants which might react with NO or NO, or cause a detectable response on the NO/NO,/NO, analyzer. When using permeation devices that are sensitive to moisture, the zero air passing across the permeation device must be dry to avoid surface reactions on the device. (Refer to the supplier's instructions for use of the permeation device.) A procedure for generating zero air is given in reference 13.

Dev

diluent air flowrate, F, to provide zero air at the output manifold. The total air flow must exceed the total demand of the analyzer(s) connected to the output mani. fold to insure that no ambient air is pulled into the manifold vent. Allow the analyzer to sample zero air until stable NO, NO.. and NO2 responses are obtained. After the responses have stabilized, adjust the analyzer zero control(s).

NOTE: Some analyzers may have separate zero controls for NO, NO,, and NO2. Other analyzers may have separate zero conti only for NO and NO,, while still others may have only one zero common control to all three channels. Offsetting the analyzer zero adjustments to +5% of scale is recommended to facilitate observing negative zero drift. Record the stable zero air responses as Zxo, Zxox, and Zgoz.

2.4.8 Preparation of NO and NO, calibration curves.

2.4.8.1 Adjustment of NO span control. Adjust the NO flow from the standard NO cylinder to generate an NO concentration of approximately 80% of the upper range limit (URL) of the NO range. The exact NO concentration is calculated from:

2.4 Procedure.

2.4.1 Assemble the calibration apparatus such as the typical one shown in Figure 2.

2.4.2 Insure that all flowmeters are calibrated under the conditions of use against a reliable standard such as a soap bubble meter or wet-test meter. All volumetric flowrates should be corrected to 25° C and 760 mm Hg. A discussion on the calibration of flowmeters is given in reference 13.

2.4.3 Install the permeation device in the constant temperature chamber. Provide a small fixed air flow (200-400 scm'/min) across the device. The permeation device should always have a continuous air flow across it to prevent large buildup of NO, in the system and a consequent restabilization period. Record the flowrate as FP. Allow the device to stabilize at the calibration temperature for at least 24 hours. The temperature must be adjusted and controlled to within +0.1°C or less of the calibration temperature as monitored with the temperature measuring device.

2.4.4 Precautions must be taken to remove O, and other contaminants from the NO pressure regulator and delivery system prior to the start of calibration to avoid any conversion of the standard NO to NO2. Failure to do so can cause significant errors in calibration. This problem may be minimized by

(1) Carefully evacuating the regulator, when possible, after the regulator has been connected to the cylinder and before opening the cylinder valve;

(2) Thoroughly flushing the regulator and delivery system with NO after opening the cylinder valve;

(3) Not removing the regulator from the cylinder between calibrations unless absolutely necessary. Further discussion of these procedures is given in reference 13.

2.4.5 Select the operating range of the NO/NO,NO, analyzer to be calibrated. In order to obtain maximum precision and accuracy for NO, calibration, all three channels of the analyzer should be set to the same range. If operation of the NO and NO, channels on higher ranges is desired, subsequent recalibration of the NO and NO, channels on the higher ranges is recommended.

NOTE: Some analyzer designs may require identical ranges for NO, NO,, and NO, during operation of the analyzer.

2.4.6 Connect the recorder output cable(s) of the NO/NO,/NO, analyzer to the input terminals of the strip chart recorder(s). All adjustments to the analyzer should be performed based on the appropriate strip chart readings. References to analyzer responses in the procedures given below refer to recorder responses.

2.4.7 Switch the valve to vent the flow from the permeation device and adjust the

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