1094 STACK SAMPLING INTRODUCTION It is frequently necessary to determine the amount, con- centration, or rate of emission of various pollutants in the exhaust streams from industrial or commercial processes. Because this generally involves the sampling and eventual analysis of the gas flowing through a stack into the outside air, it is usually called “stack emission sampling”, or more simply, “stack sampling”. In most cases, it is not possible or practical to collect all of the gases emitted to the outside air over any reasonable time period. Therefore, it is necessary to collect only a frac- tion of the overall gas stream. A representative side stream is isolated from the main flow (usually by removing it from the stack altogether) and processed in some way. The gas stream may be filtered, condensed, bubbled, adsorbed, bottled, or pumped through an automatic analyzer. The equipment used for this purpose is called the sampling train. The end result of this step is usually an assessment of the contents of the stream. Meanwhile, an assessment is made about the other characteristics of the stack gas itself, such as temperature and flow rate. The information from these two assessments is then combined to produce a measure of the emissions from the stack in the desired units, such as pounds per hour, grains/dry standard cubic foot, kg/kg of fuel burned, and so on. Generally, the units are chosen to conform with appli- cable regulations. Of course, the testing must include all of the pollutants that are of interest, under all of the process conditions that are needed. This must also include a wide range of checks and balances, often termed Quality Control (QC) and Quality Assurance (QA) to ensure and measure the reliabil- ity of the results. Most importantly, it all must be based on a well reasoned plan, called a Stack Test Protocol or Quality Assurance Project Plan (QAPP) that is written ahead of time and approved by all interested parties. Finally, these results must be reported in a way that fairly represents what was done, to allow regulators and/or the sources to make informed decisions. A prime criterion for method selection is that the method must produce data useful for the purpose intended. For example, is the detection limit of the method low enough to prove compliance with the emission standard, or is the method able to measure and/or account for cyclonic flow in the stack, or is it able to differentiate between similar chemi- cal species, or is that necessary? These sorts of questions fall into a general category called QA. They can be restated as six data quality parameters: P Precision Repeatability A Accuracy Bias, closeness to “correct” R Representativeness Typical of actual stack gas C Comparability Similar to other data C Completeness Enough information S Sensitivity Low enough detection levels These so-called PARCCS Parameters are simply ways to ensure that the results of a sampling project will yield useful results. When methods published by EPA are used, the PARCCS parameters have already been determined and are built into the methods. For novel methods, the PARCCS parameters must be determined, at least qualitatively. This is well beyond the scope of this chapter but must be borne in mind should new methodology need to be developed to fit a specific circumstance. This leads to the most important warning concerning stack testing. In all but the most dire emergencies, stack test- ing projects should be planned and carried out by trained, experienced stack testing teams. No one should believe that even a close reading of this chapter would provide sufficient background to plan or perform stack tests. There are four recent advances in the stack testing field that rate special mention. The first is the increasing reliance on external quality assurance, as embodied in audit samples and devices. Several agencies and organiza- tions, particularly the Emissions, Monitoring and Analysis Division in USEPA’s North Carolina facility, are now pro- ducing reliable Performance Evaluation (PE) audit samples that can be obtained for the purpose of checking analytical accuracy at the time of sample analyses. They are avail- able for many parameters, as listed in the specific Test Methods. The second major recent advance in stack testing is the development and proliferation of reliable continuous emis- sion monitoring systems (CEMS). CEMS are generally electronic analyzers that determine and record instantaneous concentrations of given parameters continuously. For example, a CEMS for stack gas opacity, termed a transmissometer, shines a light beam through the stack gas and measures the fraction of light transmitted, taking a reading C019_003_r03.indd 1094C019_003_r03.indd 1094 11/18/2005 11:07:13 AM11/18/2005 11:07:13 AM © 2006 by Taylor & Francis Group, LLC STACK SAMPLING 1095 every few seconds. A CEMS for SO 2 extracts a small sample of stack gas and sends it to a monitor outside the stack for analysis and recording. The CEMS records present an excel- lent picture of the continuing status of compliance of the stack gas, reveal any inconsistencies, failures of control devices, or process upsets, and allow plant operators to act immediately when any anomaly appears. It is likely that more and more CEMS will be required as they become available. CEMS are becoming more available for mercury, particulate matter and ammonia. While detailed discussion of CEMS technology, proce- dures, and operation cannot be presented here, the Performance Specifications for the CEMs currently required by USEPA may be found in Appendix B to 40 CFR Part 60, immediately following the Test Methods. A third major advance in stack testing is the introduc- tion of the 300 series methods found in 40 CFR Part 63 Appendix A. In an effort to measure the hazardous air pollut- ants to demonstrate emission reductions pursuant to MACT requirements, EPA has introduced a number of 300 series methods. Some of these methods are specific for pollutants from specific sources. Method 301, which is undergoing revi- sion in 2005, is a field validation procedure that will enable source owners to validate their own test methods in the absence of a recognized EPA method. The fourth is the rewrite of the manual methods into a standard format. The instrumental methods are being rewrit- ten in 2005, along with some major changes. The following sections of this chapter will deal with the selection of sampling and analytical methods, followed by some general information on protocol and final report preparation. Selection of a Sampling Method The choice of stack sampling methodology is most strongly dependent on the pollutants to be measured. In many cases, similar pollutants can be measured with the same or slightly modified methods, while dissimilar pollutants may require totally different methods. The most obvious categorization of pollutants is based on their physical state: gaseous, liquid, or solid. Gaseous pollutants are generally easier to sample and can be collected using one of a few simple train configurations. Liquid and solid pollutants, usually lumped into a single category called particulates, require a totally different collection concept. The following sections will describe the generalized methods employed for collecting particulate and gaseous stack samples. These are followed by more detailed descrip- tions of methods to be used for specific compounds, or groups of compounds. When the U.S. Environmental Protection Agency (EPA) has designated a method as a Test Method, it is required by EPA and by most states for compliance determi- nations. For convenience, the appropriate EPA designations are indicated. When a Test Method is used in establishing an emission limit and is specified by a regulation that method is called the Reference Method. Particulate Sampling When the pollutant of interest is or is attached to solid par- ticles or liquid droplets at stack conditions, it is necessary to select a method that physically traps the particles. But the first step must be the selection of a side stream that is truly representative of the stack exhaust gases. A representative sample of the stack exhaust gas will look and behave like a small-scale version of the actual exhaust gas. It will contain the same fraction of particulates as the main stream (including the same ratios of large and small particles) and will contain a fair share of material from each part of the stack cross section. (This is necessary because gases flow faster near the center of a stack and slower near the walls due to friction). In addition a representative sample must be taken at a location that is free of unusual flow patterns, such as cyclonic flow (in which a significant component of the flow is not along the axis of the stack) or stratified flow (in which the particulates are bunched along one side of the stack). This is because it is very difficult to figure out the actual aver- age flow rate and particulate rate when the measurements are all skewed by the flow anomalies. In most cases, flow abnormalities are caused by recognizable disturbances, such as bends, fans, expansions, contractions, or shape changes in the duct. These disturbances, whether upstream or down- stream from the sampling location, have the potential for making useful testing very difficult, or even impossible. For that reason, the first criterion for good particulate testing is to find a location that is sufficiently far from flow distur- bances. Extensive testing has shown that a sampling location 8 stack diameters downstream from any disturbance and 2 diameters upstream from any disturbance is sufficiently far. In this measurement, the term stack diameter is used liter- ally for circular stacks. For rectangular stacks, an equivalent stack diameter is calculated. In some cases, it is impossible to find a location in the stack or in any straight duct leading to the stack that satisfies these criteria. It is possible to use a location closer to distur- bances. However, other provisions must be taken to account for the possible inaccuracies introduced by the disturbed flow. All of this is described in detail in Test Method 1. Once a sampling location is selected, it is necessary to collect samples of the gas stream that are representative of the gas flowing by that location. This is achieved by sam- pling for a short time at each of several points across the stack cross-section. In practice, two or more holes, or ports, are cut in the stack wall and a sampling probe inserted. The probe is essentially a hollow tube shaped like a shepherd’s crook with the short end, or nozzle, facing into the gas stream. The gas stream is then pumped by suction from the main stream through the nozzle and probe into the collection part of the sampling train located outside the stack. The probe is held in one spot, aligned into the main stream, for a specified time. It is then moved to another point and held for the same time. This process is repeated along the line between the port and the opposite wall. The process of moving the probe along C019_003_r03.indd 1095C019_003_r03.indd 1095 11/18/2005 11:07:14 AM11/18/2005 11:07:14 AM © 2006 by Taylor & Francis Group, LLC 1096 STACK SAMPLING this line is called a traverse, and the individual sampling points termed traverse points. The configuration of the ports and the traverse points is generally chosen according to Test Method 1. Three additional considerations must be addressed in order for the sample to be considered representative. First, the particulate-laden gas stream entering the nozzle must be typical of the stream flowing by it. Second, the makeup of the gas stream leaving the probe and entering the rest of the sampling train must be substantially the same as it was when it entered the nozzle. Third, sampling must be conducted at a time and for sufficient duration to cover any inconsistencies in the pollution emission rate. The first of these conditions may sound like overkill. However, the previous work was to ensure the representa- tiveness of the location. This part concerns the representa- tiveness of the gas collected there. This is ensured by careful design of the nozzle and control o the side stream flow rate. The opening of the nozzle is designed with sharply tapered edges. The nozzle itself is shaped to minimize deposition of particulates on the inside walls as the stream turns 90°. The sampling stream flow rate is extremely important because of the difference in aerodynamics and inertial effects of particles. Very small particles tend to behave like gas mol- ecules and tend to follow gas flow stream lines. For these particles, sample flow rates are not critical. Large particles, however, do not necessarily follow the gas flow streamlines. Instead, their flow is controlled more by their inertia. In other words, they tend to keep going in straight lines. Thus, if the flow rate into the sampling nozzles is different than the local gas flow rate, the gas itself and the fine particles will be skewed, either into or out of the nozzle, depend- ing on the relative rates. The large particles, however, will continue along their straight paths. Those, and only those, in direct line with the nozzle face will enter. This can have a significant effect on the measured particulate concentra- tions, depending on the degrees of error in the nozzle flow rate and on the fraction of particulate mass attributable to the large particles. Sampling at exactly the right flow rate is termed iso- kinetic sampling. Sampling at too great a velocity is called superisokinetic, while sampling at too low a velocity is called subisokinetic. Generally, superisokinetic sampling results in an underestimation of the actual particulate con- centration (termed a low bias), while subisokinetic sam- pling results in an overestimation (high bias). Test Method 5 contains instructions for choosing the appropriate nozzle size and sampling flow rate to ensure isokinetic sampling. Sample flow rate and nozzle size are based on the volume of sample gas that needs to be collected and on the flow rate in the stack gas. The needed sample volume is based on the amount of particulate needed for the physical or chemical analyses to be conducted, and will be discussed in the analysis section. The stack gas flow rate is determined according to procedures described in Test Method 2. The procedure involves the measurement of linear flow rate by means of the relationship between the static and dynamic pressure in the gas stream. The static pressure is the pressure of the gas stream, as measured by a pressure tap perpendicu- lar to the flow. The dynamic pressure is the pressure exerted by the flowing stream and is indicative of the flow velocity. It is measured by a pressure tap facing directly into the flow stream. In practice, a device called an “S-type pitot tube” is used to measure static and dynamic pressure at a single loca- tion. Standard calculations are then used to compute the flow rate. By moving the pitot tube across a stack cross section, the flow rate at each point can be determined. All of this is described in detail in Test Method 2. Next, it is necessary to assure that the sample gas stream does not change substantially between the time it enters the nozzle and leaves the probe for the collection part of the sam- pling train. This is accomplished by ensuring that the construc- tion and operation of the probe do not interfere physically or chemically with the flowing sample stream. The nozzle and probe must be made of materials, such as stainless steel, glass, or teflon, that are smooth and do not react with the stream. In addition, the probe may be heated to ensure that vapors in the stream do not condense on the walls of the probe. A stainless steel nozzle and a glass-lined probe heated to 120 Ϯ 14ºC (248 Ϯ 25ºF) will suffice for most situations. However, spe- cial construction materials and/or probe temperature settings may be required for sampling exhaust streams from certain source types of containing certain contaminants. The appro- priate sections of this chapter should be consulted in detail before any decisions are made. The third and final consideration for ensuring represen- tative particulate sampling is that the sampling is conducted at a time and over a sufficient time period to account for variabilities in the exhaust steam. In general, it is desirable to measure the maximum possible emissions, so as to deter- mine compliance under so-called worst case conditions. This is accomplished by first determining the stage or stages in the plant process mot likely to produce the greatest emis- sion rate. This might require preliminary testing, or it may be specified in the applicable regulations. Once the time for testing is selected, it is necessary to decide the duration of each sample run and the number of runs to be performed. Generally, this is specified in the applicable regulation or in the Test Methods. However, in some cases, it may be necessary to select different sampling periods. The basic reason for sampling for any given time is to account for temporal variability in the emissions. Very few processes produce emission streams that are truly con- stant over more than a few minutes at a time. In most cases, though, an hour or two-hour sampling period will be suf- ficient to smooth out any inherent variation in the exhaust stream. In practical terms, this is accomplished by pumping the sample stream through the filter, solutions, or sorbents for the full sampling period. This effectively averages the collected sample over the entire time period. Of course, it is possible that variations in the emission rate with time could mean that higher concentrations are measured at one point in a traverse, such as near one stack wall, etc. However, in most cases, these variations are not significant. The individual regulations or Test methods usually state the required sampling duration. There are two reasons that C019_003_r03.indd 1096C019_003_r03.indd 1096 11/18/2005 11:07:14 AM11/18/2005 11:07:14 AM © 2006 by Taylor & Francis Group, LLC STACK SAMPLING 1097 the sampling duration might be changed. First, if the source is known to vary over a longer or shorter cycle, such that a different sampling period would be likely to yield more meaningful results. Second, with some state operating per- mits establishing very low emission limits, sampling times are increased to provide adequate quantification limits. At this point, the sample gas stream should be as repre- sentative as can be collected using these methods. However, there is still the inherent variability of the methods them- selves. To account for this, most testing programs include a series of three or more test runs in a single test. Depending on the underlying regulations, the results of the test runs can be used independently or averaged to reach a final emission measurement. Once an appropriate sample gas stream has been extracted from an exhaust stream, it must be collected in some way for subsequent analysis. Most particulate sam- pling trains separate the particulate matter from the rest of the gas stream, saving the particulates and exhausting the particulate-free gas sample stream. This separation can be accomplished physically, chemically, or both. Examples of physical separation are filtration, inertial separation (using a “cyclone”), or condensation. Examples of chemical separa- tion include dissolving into solution, adsorption, or chemical reaction into a solution. One or more of these separation techniques may be appropriate for a given particulate material or under given process and/or stack conditions. The specific technique to be used and the limiting conditions may be found under the specific Test Methods described later in this Section. The essence of each is to ensure that all of the particulate matter flowing through the nozzle and probe is actually collected for subsequent analysis. The following is a brief list of these particulate sampling principles, rearranged in an order that might be followed for an actual test. 1) Select a sampling location far from disturbances. 2) Determine traverse point locations. 3) Select appropriate nozzle, probe, heater, and so on. 4) Determine appropriate time for testing (worst case, etc.) 5) Determine isokinetic sampling rates. 6) Select sample train configuration. 7) Perform test runs. Gaseous Sampling When the pollutant of interest is a gas at ambient pressure, sampling is much easier and more straightforward than for particulate samples. This is because gas streams are almost always well mixed across the stack and are not subject to the internal considerations at the nozzle or in the probe. As a result, there is usually no need to worry about the sample location, traversing the stack cross-section, or isokinetic sam- pling. An exception is the measurement of nitrogen oxides from gas turbines using method 20. This method requires a stratification study. The only real concern is that the probe be constructed of materials that will not react with or adsorb contaminants from the sample stream. Sampling is usually performed by inserting a probe at a convenient location and sampling at the centroid of the cross-section. As with particulate sampling, it is important to measure the gas flow rate in the stack to allow calcula- tions of emission rate. This is done in the same way as for particulate sampling using Test Method 2. Protocol and Final Report Preparation A stack sampling project, like most other investigative work, is not likely to succeed unless it is well planned and documented. The Stack Test Protocol, or Quality Assurance Project Plan, is the means used to document the planning of the project. The more detail that can be included in the protocol, the better the likelihood that the test will suc- ceed the first time. Most EPA Regions and State Agencies have specific protocol formats and require specific types of information. Therefore, the project manager should contact the Agency well before the projected test date to obtain the format and to discuss any special conditions that need to be included, such as audit samples. The final Stack Test Report is just as important as the Protocol. It is the means by which the testing team documents what they did and their results. If the Report does not fairly report what actually happened on the stack, in the laboratory and in the calculations, the entire test might well be wasted. Again, it is advisable for the project manager to contact the regulatory agency well before the test to obtain information of acceptable report formats and special information that might be needed. It is likely, though, that the Agency will require copies of all field data sheets, lab data sheets and print-outs, calculation procedures, examples, and results, diagrams, etc. A fourth advance has been made in the dis- semination of stack testing information through EPA’s elec- tronic bulletin board. The Emission Measurement Technical Information Center (EMTIC) bulletin board is available as part of the Technology Transfer Network Bulletin Board Service (TTNBBS). The EMTIC bulletin board includes promulgated methods, proposed methods, some state test methods, papers on stack analysis, a data base on validated methods for various compounds, etc. It can be used to get answers to specific questions. Access to the TTNBBS is available through the Internet at “http://www.epa.gov//ttn” Stack Test Guidance is available at http://www.epa.gov/ Compliance/assistance/air/index.html This his document does not address test methods. However, it does provide a good discussion of regulatory requirements for stack testing, including notifications, time frames, observation by regulatory agencies, and reporting. TEST METHOD DESCRIPTIONS The main body of this chapter includes brief descriptions of selected current U.S. EPA Test Methods. These are the C019_003_r03.indd 1097C019_003_r03.indd 1097 11/18/2005 11:07:14 AM11/18/2005 11:07:14 AM © 2006 by Taylor & Francis Group, LLC 1098 STACK SAMPLING TABLE 1 Parameters Test methods Conditions Arsenic 108, 108A−C Beryllium 103, 104 103 Screening Carbon Disulfide 15 Carbon Monoxide 3, 10 Carbon Dioxide 3, 3A, 3B, 3A Instrumental 3C, 20 Carbonyl Sulfide 15 Condensible PM 202 Chromium 306, 306A Electroplating Dioxins 23 Dry Molecular Weight 3 Excess Air 3 Field Validation 301 Flow Rate 2 Volumetric Flow Rate 2A Small stacks Flow Rate 2B Gasoline Vapor Incin Flow Rate 2C For small ducts Flow Rate 2D For small ducts Flow Rate 2E Landfill gas production Fluoride (total) 13A, B, 14 AL plants Fugitive Emissions 22 Gasoline Vapors 27 Leaks from Tanks Halogenated Organic 307 Vapor from solvent cleaning Hydrogen Chloride 26 Hydrogen Sulfide 11, 15 Lead 12 Inorganic (continued) methods approved by U.S. EPA for testing emissions from sources subject to the New Source Performance Standards (NSPS), found in 40 CFR Part 60, and the National Emissions Standards for Hazardous Air Pollutants (NESHAPS), found at 40 CFR Parts 61 and 63. The methods themselves can be found in the appendices to those regulations. The U.S. EPA Test Methods may, of course, be used for purposes other than NSPS or NESHAPS. However, their applicability and validity may be unsure. The same is true for methods developed by the states or by others. Many meth- ods are completely appropriate for a given circumstance for which they have been extensively verified (as have the EPA methods for NSPS and NESHAPS). However, their validity under other circumstances should always be questioned until and unless their performance can be confirmed. The descriptions presented here are valuable for develop- ing general understanding of the equipment and procedures. However, the methods should never be attempted without a thorough reading and understanding of the methods them- selves. Stack Testing is still a very complex process that requires experience if useful results are to be obtained. To assist in the selection of a Test Method, Table 1 lists the parameters that can be measured, along with the appro- priate methods. Test Method 1 Test Method 1 is used to determine representative traverse points for measuring solid or liquid pollutants and/or deter- mine total volumetric flow rate from a stationary source. The procedures described in this method are used to determine the minimum number of points, the location of these points, and whether the chosen points are free from cyclonic flow. The Method contains a rote procedure for choosing point locations that are at the centroids or equal area portions of the stack cross section. This ensures equal weighting of all flows into the average flow rate determination. The minimum number of sampling points is determined from Figure 1. This figure is applicable to both round and rectangular ducts based on the distance from the nearest dis- turbance, bend, exit o other obstruction which might disrupt the flow of gas through the duct. The ducts must be at least C019_003_r03.indd 1098C019_003_r03.indd 1098 11/18/2005 11:07:14 AM11/18/2005 11:07:14 AM © 2006 by Taylor & Francis Group, LLC STACK SAMPLING 1099 TABLE 1 (continued) Parameters Test methods Conditions Leaking Gasoline Tank Organics 27 Leaks—Organic 21 Mercury 101, 101A, 102, 101A From Incinerators 102 In hydrogen Mercury 105 In Sewage Sludge Metals 29 Moisture 4 Nitrogen Oxides 20 Nitrogen Oxides 7, 7A−E Different methods Nonmethane Organics 25 Organics—Leaking 21 Organics (gaseous) 18, 25A−B A-B-different analyzers Organics 25C Landfill gas Organics 25D Waste samples Organics 25E Waste samples Organics 304A−B Biodegradation Organics 305 Individual organics in waste Organics 311 Hazardous air pollutants in paints Oxygen 3, 3A, 3B, 3C, 20 3A instrumental Particulates 5, A-I A-I Specif Facials, 17 In stack filter PM 10 201 OR 201A, and 202 Polonium-210 III Sampling Site I Sulfur Dioxide 6, 6A−C, 8 A—Fossil fuel, B—daily average, C—instrumental Sulfur Compounds 15A, 16, 16A 16A Total Reduced, 16—Semicontinuous Sulfuric Acid Mist 8 Surface Coatings 24, 24A Volatiles, water, density, solids Surface Tension 306B Chromium electroplating Organics (gaseous) 18 Traverse Point 1 Traverse Points 1A For small ducts Velocity 2, 2A-2H Vinyl Chloride 107 In Wastewater, 107A resin slurry Vinyl Chloride 106 Visible Emissions 9, 9-Alt, 303, 9-Alt-Lidar, 303A, 22 fugitives Volatile Organics Capture Efficiency(VOCs) 204 et al. Wood Heaters 28 Certification and auditing Wood Heaters 28A Air to fuel ratio C019_003_r03.indd 1099C019_003_r03.indd 1099 11/18/2005 11:07:14 AM11/18/2005 11:07:14 AM © 2006 by Taylor & Francis Group, LLC 1100 STACK SAMPLING 12 inches (0.3 m) in diameter or 113 in 2 (0.071 m 2 ) cross- sectional area. Sampling ports must not be within 2 duct diameters downstream or half a diameter upstream from any flow disturbance. Sampling points are then determined by dividing the stack into equal area sections as shown in Figures 2 and 3. A table is provided in the Method which gives the percentage of the stack diameter from the inside wall to each traverse point. For stacks greater than 24 inches in diameter, no point should be closer than 1 inch from the wall; for smaller stacks, no closer than 0.5 inch. Once these criteria are met measurement of the direction of flow is made to insure absence of significant cyclonic flow. The angle of the flow is determined by rotating a Type S pitot tube until a null or zero differential pressure is observed on the manometer. The angle of the pitot tube with the stack is then measured. This procedure is repeated for each sampling point and the average of the absolute values of the angles calculated. If the average angle is greater than 20º, the sampling site is not acceptable and a new site must be chosen, the stack extended, or straightening veins installed. A few unusual cases have been accounted for by the method. If the duct diameter or size is smaller than that required by Method 1, Method 1A can be used. For cases where 2 equivalent stack diameters downstream or a half diameter upstream are not available, a directional velocity probe can be used to determine the absence of cyclonic flow, as described in Method 1. If the average angle is less than 20º, then the sampling site is satisfactory; however a greater number of points must be used. Test Method 2 Test Method 2 is used to determine the average velocity in a duct by measuring the differential pressure across a Type S (Stausscheibe) pitot tube. The Type S pitot tube is preferable to the standard pitot tube when there are particles that could cause plugging of the small holes in the standard pitot tube. Measurement sites for velocity determination are chosen as described in Method 1, that is, required number of sites and absence of cyclonic or swirling flow. The type S and standard pitot tubes are shown in Figure 4. When the Type S pitot tube has been correctly manufactured and installed on a probe as shown in Figure 5, there is no interference and calibration is not necessary. A pitot tube constant of 0.84 is assumed. If the criteria for interferences are not met, the method discusses the necessary calibration procedures. DUCT DIAMETERS DOWNSTREAM FROM FLOW DISTURBANCE* (DISTANCE B) 2 0 10 20 30 40 50 0.5 1.0 1.5 2.0 2.5 34 5 67 8 9 10 20 24 OR 25 a 8 OR 9 a 16 12 STACK DIAMETER = 0.30 TO 0.61 m (12-24 in) STACK DIAMETER > 0.61 m (24in) *FROM POINT OF ANY TYPE OF DISTURBANCE (BEND, EXPANSION, CONTRACTION, ETC.) a HIGHER NUMBER IS FOR RECTANGULAR STACKS OR DUCTS DUCT DIAMETERS UPSTREAM FROM FLOW DISTURBANCE* (DISTANCE A) MINIMUM NUMBER OF TRAVERSE POINTS DISTURBANCE MEASUREMENT SITE DISTURBANCE B A FIGURE 1 Minimum number of traverse points for particulate traverses. C019_003_r03.indd 1100C019_003_r03.indd 1100 11/18/2005 11:07:14 AM11/18/2005 11:07:14 AM © 2006 by Taylor & Francis Group, LLC STACK SAMPLING 1101 Velocity, as measured with a pitot tube, is proportional to the square root of the differential pressure across the two sides of the pitot tube and the density of the stack gas. Most sampling trains use a combination inclined–vertical manom- eter to measure the velocity head, or ∆p. These manometers usually have 0.01 inch of water subdivisions from 0−1 inch of water. The vertical section has 0.1 inch divisions from 1−10 inches of water. This type of gauge provides sufficient accuracy down to 0.05 inches; below that a more sensitive gauge should be used. The temperature of the gases is usually measured using a type K (Chromel-Alumel) thermocouple mounted on the probe. The absolute pressure is calculated by adding the static pressure in the stack to the barometric pressure. The molecu- lar weight of the stack gases is determined using Methods 3 and 4. Velocity is calculated by the equation below: V s ϭ K p C p (∆p 0.5 ) avg {T s(avg) /(P s M s )} 0.5 where: K p = Velocity equation constant K 34.97 m sec (g/g - mole)(mmHg) ( K)(mmH O) metric p 2 0.5 ϭ ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ K 85.49 ft sec (lb/lb - mole)(in.Hg) ( R)(in.H O) Eng p 2 0.5 ϭ ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ llish C p ϭ Pitot tube Coefficient (0.84 for S Type without interferences) ∆p ϭ pressure difference across the two sides of the pitot tube (velocity head of the stack gas) P s ϭ Absolute pressure of the stack, mm Hg or in. Hg M s ϭ Molecular weight of the wet stack gases, g/g mole or lb/lb mole T s ϭ Absolute stack temperature, ºK (273 + ºC) or ºR (460 + ºF) The average dry volumetric stack flow is: Q sd ϭ 3,600(1 − B ws )V s A(T std /T s(avg) )(P s /P std ) where: Q sd ϭ Average stack gas dry volumetric flow rate B ws ϭ Water vapor in the gas stream from Method 4 or 5 V s ϭ Average stack gas velocity A ϭ Cross-sectional area of the stack T std ϭ Standard absolute temperature 293ºK or 528ºF P std ϭ Standard absolute pressure 760 mm Hg or 29.92 in. Hg 1 2 3 4 5 6 TRAVERSE POINT DISTANCE, % of diameter 1 2 3 4 5 6 4.4 14.6 29.6 70.4 85.4 95.6 FIGURE 2 Example showing circular stack cross section divided into 12 equal areas, with location of traverse points indicated. FIGURE 3 Example showing rectangular stack cross section divided into 12 equal areas, with a tra- verse point at centroid of each area. C019_003_r03.indd 1101C019_003_r03.indd 1101 11/18/2005 11:07:14 AM11/18/2005 11:07:14 AM © 2006 by Taylor & Francis Group, LLC 1102 STACK SAMPLING SECTION AA CURVED OR MITERED JUNCTION 90° BEND A A D STATIC HOLES (~0.1D) IN OUTSIDE TUBE ONLY HEMISPHERICAL TIP IMPACT OPENING- INNER TUBE ONLY 60 (MIN.) 80 (MIN.) MANOMETER Standard pitot tube design specifications. 1.90–2.54 CM (0.75–1.0 IN.) 7.62 CM (3 IN.)** TEMPERATURE SENSOR TYPE S PITOT TUBE L* GAS FLOW FLEXIBLE TUBING 6.25 MM (1/4 IN.) LEAK-FREE CONNECTIONS MANOMETER *L = DISTANCE TO FURTHEST SAMPLING POINT PLUS 30 CM (12 IN.) **PITOT TUBE - TEMPERATURE SENSOR SPACING Type S pitot tube-manometer assembly. FIGURE 4 Type S pitot tube-manometer assembly. C019_003_r03.indd 1102C019_003_r03.indd 1102 11/18/2005 11:07:15 AM11/18/2005 11:07:15 AM © 2006 by Taylor & Francis Group, LLC STACK SAMPLING 1103 Other methods 2A through 2H are used for specific conditions. Test Method 3 Test Method 3 is used to determine the oxygen (O 2 ) and carbon dioxide (CO 2 ) concentration from combustion gas streams for the determination of molecular weight. The method can also be used for other processes where compounds other than CO 2 , O 2 , CO or N 2 are not present in concentrations that will affect the results significantly. The O 2 and CO 2 can then be used to calculate excess air, molecu- lar weight of the gas, or to correct emission rates as specified by various subparts of 40 CFR Part 60. Method 3 can also be used to determine carbon monoxide when concentrations are in the percent range. Two types of analyzers can be used depending on the use intended for the data. Both analyzers depend on the absorp- tion of components in the combustion gases by specific chemicals. The Orsat Analyzer sequentially absorbs CO 2 , O 2 , and CO. The change in sample volume is measured with a gas burette after each absorption step. Potassium hydrox- ide solution is used to absorb CO 2 , forming potassium car- bonate. When no further change in volume is noted, the difference from the starting volume is the amount of CO 2 present. Since the starting volume in the burette is usually 100 ml, the difference in ml is also the concentration of CO 2 in percent. The absorbent solution for O 2 is a solution of alkaline pyrogallic acid or chromous chloride. The CO absorbent is usually cuprous chloride or sulfate solution. The Fyrite type analyzers are available for either CO 2 or O 2 , however they do not provide the accuracy of the Orsat Analyzer, using Method B. Test Method 3A Test Method 3A is an instrumental method for determin- ing O 2 and CO 2 . From stationary sources when specified in the applicable regulations. Calibration procedures are similar to those dis- cussed in Method 6C. Test Method 3B The Orsat analyzer is required for emission rate correc- tions and excess air determinations. Concentration values from 3 consecutive analyses must differ by no more than 1 D t D n TYPE S PITOT TUBE SAMPLING NOZZLE x > 1.90 cm (3/4 in.) for D n = 1.3 cm (1/2 in.) (a) BOTTOM VIEW: SHOWING MINIMUM PITOT-NOZZLE SEPARATION. SAMPLING NOZZLE SAMPLING PROBE D t TYPE S PITOT TUBE. NOZZLE OPENING IMPACT PRESSURE OPENING STATIC PRESSURE OPENING (b) SIDE VIEW: TO PREVENT PITOT TUBE FROM INTERFERING WITH GAS FLOW STREAMLINES APPROACHING THE NOZZLE, THE IMPACT PRESSURE OPENING PLANE OF THE PITOT TUBE SHALL BE EVEN WITH OR DOWNSTREAM FROM THE NOZZLE ENTRY PLANE FIGURE 5 (a) Bottom view: showing minimum pitot-nozzle separation. (b) Side view: to prevent pitot tube from interfering with gas flow streamlines approaching the nozzle, the impact pressure opening plane of the pitot tube shall be even with or downstream from the nozzle entry plane. C019_003_r03.indd 1103C019_003_r03.indd 1103 11/18/2005 11:07:15 AM11/18/2005 11:07:15 AM © 2006 by Taylor & Francis Group, LLC [...]... (VCM) in stack gas It does not measure VCM in particulate matter Stack gas is withdrawn from the centroid of the stack into a tedlar bag using the bag-in-a-box technique that isolates the sample from the pump The sample is then analyzed directly using a gas chromatograph-flame ionization detector (GC-FID) The sampling probe for this method is a standard stainless steel probe The rest of the sampling. .. i.e the amount of moisture and the effect of other compounds competing for the adsorbent © 2006 by Taylor & Francis Group, LLC C019_003_r03.indd 1113 11/18/2005 11:07:17 AM 1114 STACK SAMPLING The EPA Test Method 18 write-up and the QA Handbook Section 3.16 contain detailed instructions for sampling, analysis and calibrations, along with a list of references for many organic compounds of interest Both... effluent velocity in the roof monitor A standard pitot tube is used for the velocity measurement of the air entering the nozzles because the standard pitot obstructs less of the cross section than a Type S pitot tube The EPA Test Method 14 write-up contains detailed instructions for the set-up, calibration, and use of permanent manifolds for sampling emissions from potroom roof monitors at aluminum plants... specifications and the test procedures are followed The following Measurement System Performance Specification must be passed by the instrument before actual environmental samples are analyzed: 1) Analyzer Calibration Error must be less than Ϯ 2% of the span for the zero, mid-range, and highrange calibration gases 2) Sampling System Bias must be less than Ϯ 5% of the span for the zero, mid-range, and high-range... less than Ϯ 3% of the span over the period of each run 4) Calibration Drift must be less than Ϯ 3% of the span over the period of each run The analytical range must be selected such that the SO2 emission limit required of the source is not less than 30% of the instrument span Any run in which the SO2 concentration in the stack gas goes off-scale must be repeated The EPA Test Method 6C write-up contains... volume of solids, and weight of solids of surface coatings This method applies to paints varnish, lacquer, and other related coatings American Society of Testing Methods (ASTM) procedures have been incorporated by reference into this test method Test Method 24A Test Method 24A is not a stack test method Instead, it is used to determine the volatile organic content (VOC) and density of printing inks and. .. exit gas temperature of at least 129ºC (266ºF) The filter is heated in a chamber capable of maintaining a gas temperature of 121 Ϯ 3ºC (250 Ϯ 5ºF) The sample tank must be leak checked and cleaned by the procedures described in the method The pressure of the sample tank is measured before and after sampling, and this information is used to determine the amount of sample collected After sampling the sample... STACK SAMPLING The following Measurement System Performance Specification must be passed by the instrument before actual environmental samples are analyzed: 1) Analyzer Calibration Error must be less than Ϯ 5% of the span for the zero, mid-range, and high-range calibration gases 2) Zero Drift must be less than Ϯ 3% of the span over the period of each run 3) Calibration Drift must be less than Ϯ 5 of. .. trained and experienced with the equipment being used Test Method 27 Test Method 27 is used for determining leaks from gasoline delivery tank trucks or rail cars It does not involve actual measurements of gasoline emissions Instead, it involves the pressurization and/ or evacuation of the tank and the subsequent measurement of the pressure and/ or evacuation of the tank and the subsequent measurement of the... factor of 10 or so of the level of interest (such as a regulatory emission standard), the test would normally be repeated using Method 104, which is much more reliable, if more expensive Method 103 uses a rough isokinetic sampling procedure, in which a sample probe is placed at only three locations along a stack diameter The sample train consists of a nozzle and probe connected to a filter and a meter-pump . less than Ϯ 2% of the span for the zero, mid-range, and high- range calibration gases. 2) Sampling System Bias must be less than Ϯ 5% of the span for the zero, mid-range, and high-range calibration. selection of a side stream that is truly representative of the stack exhaust gases. A representative sample of the stack exhaust gas will look and behave like a small-scale version of the actual. generally involves the sampling and eventual analysis of the gas flowing through a stack into the outside air, it is usually called stack emission sampling , or more simply, stack sampling . In