4. Procedure. 4.1 Guidelines for source testing are detailed in the following sections. These guidelines are generally applicable; however, most sample sites differ to some degree and temporary alterations such as stack extensions or expansions often are required to insure the best possible sample site. Further, since mercury is hazardous, care should be taken to minimize exposure. Finally, since the total quantity of mercury to be collected generally is small, the test must be carefully conducted to prevent contamination or loss of sample. 4.2 Selection of a sampling site and minimum number of traverse points. 4.2.1 Select a suitable sampling site that is as close as is practicable to the point of atmospheric emission. If possible, stacks smaller than 1 foot in diameter should not be sampled. 4.2.2 The sampling site should be at least eight stack or duct diameters downstream and two diameters upstream from any flow disturbance such as a bend, expansion or contraction. For rectangular cross section, determine an equivalent diameter from the following equation: _2LW ' ., eq. 102-1 where: D.=equivalent diameter. L=length. W=width. 4.2.3 When the above sampling site criteria can be met, the minimum number of traverse points is four (4) for stacks 1 foot in diameter or less, eight (8) for stacks larger than 1 foot but 2 feet in diameter or less, and twelve (12) for stacks larger than 2 feet. . 4.2.4 Some sampling situations may render the above sampling site criteria impractical. When this is the case, choose a convenient sampling location and use figure 102–3 to determine the minimum number of traverse points. However, use figure 102-3 only for stacks 1 foot in diameter or larger.. 4.2.5 To use figure 102–3, first measure the distance from the chosen sampling location to the nearest upstream and downstream disturbances. Divide this distance by the diameter or equivalent diameter to determine the distance in terms of pipe diameters. Determine the corresponding number of tray. erse points for each distance from figure 102-3. Select the higher of the two numbers of traverse points, or a greater value, such that for circular stacks the number is a mul: tiple of four, and for rectangular stacks the number follows the criteria of section 4.3.2. 4.2.6 If a selected sampling point is closer than 1 inch from stack wall, adjust the location of that point to insure that the sample is taken at least 1 inch away from the wall. 4.3 Cross-sectional layout and location of traverse points. 4.3.1 For circular stacks locate the traverse points on at least two diameters according to figure 102-4 and table 102-1. The traverse axes shall divide the stack-cross section into equal parts. 4.3.2 For rectangular stacks divide the cross-section into as many equal rectangular areas as traverse points, such that the ratio of the length to the width of the elemental areas is between one and two. Locate the traverse points at the centroid of each equal area according to figure 102-5. 4.4 Measurement of stack conditions. 4.4.1 Set up the apparatus as shown in figure 102–2. Make sure all connections are tight and leak free. Measure the velocity head and temperature at the traverse points specified by section 4.2 and 4.3. 4.4.2 Measure the static pressure in the stack. 4.4.3 Determine the stack gas moisture. 4.4.4 Determine the stack gas molecular weight from the measured moisture content and knowledge of the expected gas stream composition. Sound engineering judgment should be used. 4.5 Preparation of sampling train. 4.5.1 Prior to assembly, clean all glassware (probe, impingers, and connectors) by rinsing with wash acid, tap water, 0.1M ICI, tap water, and finally distilled water. Place 100 ml of 0.1M ICI in each of the first three impingers, and place approximately 200 g. of preweighed silica gel in the fourth impinger. Save 80 ml of the 0.1M IC1 as a blank in the sample analysis. Set up the train and the probe as in Figure 102–1.. 4.5.2 Leak check the sampling train at the sampling site. The leakage rate should not be in excess of 1 percent of the desired sampling rate. Place crushed ice around the impingers. Add more ice during the run to keep the temperature of the gases leaving the last impinger at 70° F or less. 4.6 Mercury train operation. 4.6.1 Safety procedures. It is imperative that the sampler conduct the source test under conditions of utmost safety, since hydrogen and air mixtures are explosive. The sample train essentially is leakless, so that attention to safe operation can be concentrated at the inlet and outlet. The following specific items are recommended: 4.6.1.1 Operate only the vacuum pump during the test. The other electrical equipment, e.g. heaters, fans and timers, normally are not essential to the success of a hydrogen stream test. 4.6.1.2 Seal the sample port to minimize leakage of hydrogen from the stack. 4.6.1.3 Vent sampled hydrogen at least 10 feet away from the train. This can be accomplished easily by attaching a 12-in i.d. Tygon tube to the exhaust from the orifice meter. 4.6.2 For each run, record the data required on the sample sheet shown in figure 102–6. Take readings at each sampling point at least every 5 minutes and when significant changes in stack conditions necessitate additional adjustments in flow rate. 4.6.3 Sample at a rate of 0.5 to 1.0 cfm. Samples shall be taken over such a period or periods as are necessary to accurately determine the maximum emissions which would occur in a 24-hour period. In the case of cyclic operations, sufficient tests shall be made so as to allow accurate determination or calculation of the emissions which will occur over the duration of the cycle. A minimum sample time of 2 hours is recommended. In some instances, high mercury concentretions can prevent sampling in one run for the desired minimum time. This is indicated by reddening in the first impinger as free iodine is llberated. In this case, a run may be divided into two or more subruns to insure that the absorbing solutions are not depleted. 4.6.4 To begin sampling, position the nozzle at the first traverse point with the tip pointing directly into the gas stream. Immediately start the pump and adjust the flow to isokinetic conditions. Sample for at least 5 minutes at each traverse point; sampling time must be the same for each point. Maintain isokinetic sampling throughout the sampling period, using the following procedures. Figure 102-4. Cross section of circular stack showing location of traverse points on perpendicular diameters. Figure 102-5. Cross section of rectangular stack divided into 12 equal. areas, with traverse points al centroid of each area, Table 102-1, Location of traverse points in circular stacks Figure 102-8. Field data 4.6.4.1 Nomographs which aid in the rapid the meter box. Convert the hydrogen AP to adjustment of the sampling rate without an equivalent value for air by multiplying by other computations are in APTD-0576 and a ratio of the molecular weight of air to byare avallable from commercial suppliers. The drogen at the stack moisture content. Insert avallable nomographs, however, are set up this value of AP onto the nomograph and for use in air streams, and minor changes are road off AH. Again, convert the AH, which is required to provide applicability to hydrogen. an air equivalent value, to the AH for hydro 4.6.4.2 Callbrate the meter box orifice. Use gen by dividing by 13. This factor includes the techniques as described in APTD-0576. the ratio of the dry molecular weights and a 4.6.4.3 The correction factor nomograph correction for the different orince calibration discussed in APTD-0676 and shown on the factors for hydrogen and air. This procedure reverse side of commercial nomographs will is diagrammed below: not be used. In its place, the correction factor /MW air will be calculated using equation 102–2. Observe AP-Multiply (MWH, nomograph. ÁHO PM, eq. 102-2 where: C=Correction factor. Read off AH-Divide by 13-WH to be used on meter box. Cp=Pitot tube coefficient. M.=Mole fraction dry gas. 4.6.4.6 Operate the sample train at the calculated AH at each sample point. P=Stack pressure, inHg. Pm=Meter pressure, inHg. 4.6.5 Turn off the pump at the conclusion Tm=Meter temperature, "R. of each run and record the final readings. M.=Molecular weight of stack gas (from Immediately remove the probe and nozzle 4.4.4), lb/lb mole. from the stack and handle in accordance with AH@=Meter box callbration factor, ob the sample recovery process described in sec tion 4.7. tained in step 4.6.4.2. 4.7 Sample recovery. 4.6.4.4 Set the calculated correction factor 4.7.1 (All glass storage bottles and the on the front of the operating nomograph. graduated cylinder must be precleaned as in Select the proper nozzle and set the K-factor section 4.5.1). This operation should be peron the nomograph as detalled in APTD-0576. formed in an area free of possible mercury 4.6.4.5 Read the velocity head in the stack contamination. Industrial laboratories and at each sample point from the manometer in ambient air around mercury-using facilities 5. Calibration.-5.1 Sampling Train. 5.1.1 Use standard methods and equipment as detailed in APTD-0576 to callbrate the rate meter, pitot tube and dry gas meter. Recali. braate prior to each test series. 5.2 Analysis.-5.2.1 Prepare a calibration curve for the spectrophotometer using the standard mercury solutions. Plot the peak heights read on the recorder versus the concentration of mercury in the standard solutions. Standards should be interspersed with the samples since the calibration can change slightly with time. A new callbration curve should be prepared for each new set of samples run. 6. Calculations—6.1 Average dry gas meter temperature, stack temperature, stack pressure and average orifice pressure drop. See data sheet (fig. 102-6). 6.2 Dry gas volume.-Correct the sample volume measured by the dry gas meter to stack conditions by using equation 102-3. are not normally free of mercury contamination. When the sampling train is moved, care must be exercised to prevent breakage and contamination, 4.7.2 Disconnect the probe from the impinger train. Place the contents (measured to +1 ml) of the first three impingers into a 500 ml sample bottle. Rinse the probe and all glassware between it and the back half of the third impinger with two 50 ml portions of 0.1M ICI solution, Add these rinses to the first bottle. For a blank, place 80 ml of the 0.1M ICI in a 100 mi sample bottle. Place the silica gel in the plastic jar. Seal and secure all containers for shipment. If an additional test is desired, the glassware can be carefully double rinsed with distilled water and reassembled. However, if the glassware is to be out of use more than 2 days, the initial acid wash procedure must be followed. 4.8 Analysis—4.8.1 Apparatus preparation.-Clean all glassware according to the procedure of section 4.5.1. Adjust the instrument settings according to the instrument manual, using an absorption wavelength of 253.7 nm. 4.8.2 Analysis preparation.-Adjust the air delivery pressure and the needle valve to obtain a constant air flow of about 1.3 1/min. The analysis tube should be bypassed except during aeration. Purge the equipment for 2 minutes. Prepare a sample of mercury standard solution (3.4.2) according to section 4.8.3. Place the analysis tube in the line, and aerate until a maximum peak height is reached on the recorder. Remove the analysis tube, flush the lines, and rinse the analysis tube with distilled water. Repeat with another sample of the same standard solution. This purge and analysis cycle is to be repeated until peak heights are reproducible. 4.8.3 Sample preparation. Just prior to analysis, transfer a sample aliquot of up to 50 ml to the cleaned 100 ml analysis tube. Adjust the volume to 50 ml with 0.1M ICI if required. Add 5 ml of 10 N sodium hydroxide, cap tube with a clean glass stopper and shake vigorously. Prolonged, vigorous shaking at this point is necessary to obtain an accurate analysis. Add 5 ml of the reducing agent (reagent 3.3.2), cap tube with a clean glass stopper and shake vigorously and immediately place in sample line. 4.8.4 Mercury determination.-After the system has been stabilized, prepare samples from the sample bottle according to section 4.8.3. Aerate the sample until & maximum peak height is reached on the recorder. The mercury content is determined by comparing the peak heights of the samples to the peak heights of the calibration solutions. It collected samples are out of the linear range, the samples should be diluted. Prepare a blank from the 100 ml bottle according to section 4.8.3 and analyze to determine the reagent blank mercury level. eq. 102-3 where: Vm=Volume of gas sample through the dry gas meter (stack conditions), ft. Vm=Volume of gas sample through the dry gas meter (meter conditions), fta. To=Average temperature of stack gas, oR. T'm=Average dry gas meter temperature, OR. Phar=Barometric pressure at the orifice meter, inHg. AH=Average pressure drop across the ori fice meter, inH,O. 13.6=Specific gravity of mercury. Pe=Stack pressure, Pbar +static pressure, InHg. 6.3 Volume of water vapor. Vtotal =Vm, +Vw, eg. 102-5 where: Veotal= total volume of gas sample (stack conditions), fts. V., Volume of gas through dry gas meter (stack v conditions), its. V., Volume of water vapor in gas sample (stack conditions), 10%. |