CHAPTER 2 STACK SAMPLING FACILITIES General Most sampling for representative results requires minimum sampling facilities for which the Texas Natural Resource Conservation Commission (TNRCC) has established the guidelines presented in this chapter. Stack sampling operations utilize a system of equipment to traverse a cross-section of the stack or duct through ports located such that a representative sample can be obtained. Normally, a monorail structure is erected so the cross-section of the stack may be traversed on two diameters for circular stacks and on a matrix layout for rectangular or other shaped stacks. These guidelines cannot anticipate all situations, and special cases will occur. Non-standard or alternate installations are therefore evaluated on an individual basis, and in such instances detailed plans should be sent to the TNRCC for review and approval before the construction of stack sampling facilities is initiated. Existing sources with stack sampling facilities approved previously by the TNRCC may not normally be required to meet these additional specifications described in this chapter. The 220-volt, 50-amp electrical outlet at the stack base as described in the Power Supply section of this chapter may, however, be necessary in certain cases due to the increased power requirements of TNRCC monitoring systems. The following guidelines constitute minimum requirements for safe and accessible stack sampling facilities: Physical Features Before consideration is given to the installation of sampling ports and platforms, certain dimensions and other features of the stack and stack gas must be verified in order that a representative sample is possible. Stack diameter must be at least one foot. Stack gas velocity head must be at least 0.1 inches of water. The stack must have at least 2-1/2 diameters of uniform undisturbed cross-section. Sampling Ports Port location The optimum location of sampling ports is at least eight stack diameters downstream of any bends, inlets, constrictions, abatement equipment, straightening vanes, or other flow disturbance; and at least two stack diameters upstream of the stack exit or other flow disturbance. Hydraulic diameter is used for non-circular stacks and is defined later in this chapter. This location permits a sample traverse to be taken using a minimum of twelve sampling points. A greater number of sampling points is necessary on stacks which fail to meet this location criteria. For a valid sample traverse to be obtained, however, sampling ports must be located at least two stack diameters downstream and at least one-half stack diameter upstream from any disturbance. If a 2-1/2 diameter length of uniform undisturbed stack cross-section is not available, stack modification must be made or an alternate sampling location must be chosen which will satisfy this criteria. To minimize the increase in the number of sampling points required on stacks with undisturbed cross-section less than 10 but greater than 2-1/2 stack diameters in length, the sampling ports should be located such that the distance from the ports to the nearest upstream disturbance is four times the distance from the ports to the nearest downstream disturbance (see Figure 2-3 for minimum number of sampling points required). The 2-1/2 diameter criteria must be met; the 4:1 distance ratio is a recommendation. Port Size Ports are minimum three-inch ID standard industrial flanged pipe with six-inch bolt circle diameter and closed by a removable blind flange. Larger port sizes are necessary on large diameter, double-walled stacks which necessitate longer ports. These ports should also be standard industrial flanged pipe. Ports no smaller than four inches inside diameter must be provided on stacks greater than ten feet in diameter. Port Installation Port shall be installed flush with the interior stack wall and shall extend outward from the exterior stack wall no less than three inches nor more than eight inches unless additional length is required for gate valves. Gate valves should be installed only when extreme stack conditions and/or the presence of hazardous materials require such devices for the safety of personnel. Ports shall be installed no less than five feet nor more than six feet above the floor of the platform and the clearance zone described later in this chapter must be maintained. Number and Location of Ports on Circular Stacks A minimum of two ports shall be installed on diameters 90ø apart if the stack diameter plus one port length (stack inside wall to end of port extension) is less than ten feet. Four ports shall be installed on diameters 90ø apart if the stack diameter plus one port length is equal to or greater than ten feet. Number and Location of Ports on Non-Circular Stacks The same upstream and downstream distance requirements discussed previously apply to non-circular stacks. The hydraulic diameter (four times the area divided by the perimeter) is used in place of the circular diameter. This becomes (2AB)/(A+B) for a rectangular stack, where A and B are the cross-sectional dimensions of the stack. The streamwise location of the sampling ports is determined in the same manner as for circular stacks using the hydraulic diameter. The hydraulic diameter is used only for determining the location of sampling ports and the required number of sampling points. Hydraulic diameter is not used in data reduction. The cross-stream location of the sampling ports is dependent upon the total number of sampling points required. Figure 2-3 is used to determine the required minimum number of sampling points by reading the curve corresponding to the number of upstream hydraulic diameters (B) and downstream hydraulic diameters (A) and selecting the higher number. The stack cross-section of square or rectangular stacks is divided into a matrix (i,j) of equal area rectangles such that i = j or i = j + 1 and i + j is equal to or greater than the total number of sampling points required. The number of sampling ports required is either i or j located along one side of the stack such that the centerline of each port is colinear with the centroid of each row of sampling points. Stacks with cross-sections which are not circular or rectangular must be equipped with an adequate arrangement of sampling ports so that the stack cross-section may be divided into a sufficient number of area increments for a representative sample. If equal area increments are not possible, time weighting of the sample at the various sampling points may be necessary. Detailed plans of such installations should receive advance approval by the TNRCC. Monorail Support Structure The installation of a permanent monorail support structure is recommended to reduce set-up time and to eliminate the load-bearing requirements for the sampling ports. Figure 2-1 shows a drawing of the monorail support structure including the relative position of the bracket to the sampling port. This bracket is intended to be compatible with several types of sampling equipment. The loading requirements for ports or the monorail support structure are shown below. Port or Monorail Support Loading The port or monorail support installation shall be capable of supporting the following loads: Vertical load of 200 pounds Horizontal load of 200 pounds Radial load of 1,000 pounds (along stack diameter) Work Platform A work platform shall be provided around the stack circumference between the sampling ports and extending at least three feet beyond each port. If four ports are required, the work platform shall extend around the entire circumference of the stack. The minimum platform width shall be at least three feet measured radially with stack diameter. The work platform must be capable of supporting at least 2,000 pounds. Safe and easy access to the work platform shall be provided via ladder, stairway, or other suitable means. Safe guardrails shall be provided around the platform. Angular rather than round rail members should be used if possible. No open ladder well, stairwell, or other such opening shall be located within three feet of any sampling port. Ladder wells shall be covered at the platform and any opening to the platform shall be equipped with a safety bar or chain at the opening. A temporary work platform for sampling operations is acceptable if proper safety and accessibility is provided. All other requirements detailed in this chapter such as for monorails, ports, loading, clearance and power must be met by the temporary facilities. Clearance Zone A three-dimensional obstruction-free clearance zone shall be provided around each sampling port. The zone shall extend one foot above the port, two feet below the port, and two feet to either side of the port. The zone shall extend outward from the exterior wall of the stack at least one stack diameter (or stack radius if four ports are provided), plus one port length (inside wall to end of port extension) plus three feet. Although this clearance zone is adequate for TNRCC sampling equipment, sampling contractors may have other clearance needs. The clearance zone is illustrated in Figure 2-2. Power Supply Electrical power outlets shall be provided as follows: Platform One 115-volt, 15-amp, single phase, 60 hertz alternating current circuit with a grounded two-receptacle weather-proof outlet. Receptacles shall accept standard three-prong grounded household-type plugs or suitable adapters shall be provided. Stack base Two 115-volt, 15-amp, single phase 60 hertz alternating current circuits with grounded two-receptacle weather-proof outlets. Receptacles shall accept standard three-prong grounded household-type plugs or suitable adapters shall be provided. One 220-volt, 50-amp, single phase alternating current circuit with standard 50-amp plug or suitable adapters capable of being wired to TNRCC power cord. Vehicle Access and Parking The stack sampling will be coordinated and controlled from a van or trailer parked near the base of the stack for the duration of the sampling except for situations in which sampling operations must be conducted from a rooftop or other location. Vehicle access and parking space must be provided since various umbilical, communications and equipment transport lines will be strung from the van or trailer to the stack platform and will remain in position throughout the sampling period. Gaseous Sampling - Concentration Only Standard sampling ports and platforms are normally necessary for gaseous sampling because a velocity traverse is needed for flow rate determination in most cases. In sampling situations for which only pollutant concentration is needed or for which an accurate flow rate is available by other approved means, less elaborate sampling facilities may be acceptable. All facilities must, however, meet strength and safety requirements. Gaseous sampling facilities for concentration only shall be sufficient for collection of a sample of stack gas according to standard gaseous sampling procedures. Adequate minimum facilities such as a one-inch nipple shall be installed in the stack at a location where sufficient turbulence exists (no stratification) to insure a representative sample. Proper clearance must be provided for sampling operations or a permanent probe and sample line can be installed at the port location and extended to a more accessible sampling location. The probe and sample line must be installed so that leak checks can be made. Permanent Monorail Systems Source operators are encouraged to install permanent monorail systems on large stacks. Monorails must extend the full radial length of the clearance zone described previously and must be capable of supporting a 200 pound load anywhere along the monorail track. Rollers must be properly lubricated and maintained in working condition. The sample box attachment hooks should be six inches above the port centerline. If the monorail is installed with the hooks more than six inches above the port centerline, suitable adapters must be provided. Miscellaneous Requirements In addition to the specific requirements detailed in this chapter, other miscellaneous requirements are as follows: Power hoists shall be provided for sampling platforms 200 feet or more above ground level. Non-circular horizontal ducts should have provisions for vertical sampling. Circular horizontal ducts should have one vertical and one horizontal port. Suitable work platforms are necessary in both cases. Heat insulation shall be installed as necessary on high temperature stacks for safety in the vicinity of the work platform. The source operator is responsible for maintaining all sampling facilities in safe, useable condition at all times. Excess Air Additional facilities may be necessary for determining the composition and flow rates of feed stock and fuel on certain processes such as incinerators. This information, obtained at the time of sampling, is necessary to calculate the amount of air in the stack effluent in excess of stoichiometric. Cyclonic Flow Cyclonic or swirling flow may be encountered in a stack or duct due to certain circumstances such as cyclone collectors or tangential duct entry. Corrective measures such as straightening vanes may be necessary to alleviate the cyclonic condition. The existence of cyclonic flow may be determined as described in Chapter 4. A method for sampling cyclonic flow is described in Appendix H, but advance approval should be obtained concerning its applicability for determining compliance status.