chap2.txt
chap2.txt
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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 90
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 90 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.