United States
Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park, NC
EPA 340/1-92-015f
September 1992
Revised March 1993
Stationary Source Compliance Training Series
&EPA COURSE #345
EMISSION CAPTURE AND
GAS HANDLING SYSTEM
INSPECTION
Reference Volume 2 -
Guide On Measurement Ports
Location And Design
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EPA 340/1-92-01 5f
Revised March 1993
Course Module #345
Emission Capture And
Gas Handling System Inspection
Reference Volume 2 -
Guide On Measurement Ports Location And Design
Prepared by:
Crowder Environmental Associates, Inc.
2905 Province Place
Piano, TX 75075
and
Entrophy Environmentalist, Inc.
PO Box 12291
Research Triangle Park, NC 27709
Contract No. 68-02-4462
Work Assignment No. 174
EPA Work Assignment Manager: Kirk Foster
EPA Project Officer: Aaron Martin
US. ENVIRONMENTAL PROTECTION AGENCY
Stationary Source Compliance Division
Office of Air Quality Planning and Standards
Washington, DC 20460
September 1992
Revised March 1993
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EPA-340/1-84-017
Guidelines on Preferred Location and
Design of Measurement Ports for Air
Pollution Control Systems
Prepared by:
Richards Engineering
2605 Tanglewood Road
Durham, North Carolina 27705
and
JACA Corporation
550 Pinetown Road,
Fort Washington, Pennsylvania 19034
EPA Project Officer: John Busik
EPA Task Manager: Kirk Foster
Contract No. 68-01-3962
Prepared for:
Stationary Source Compliance Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Washington, D.C. 20460
September 1984
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DISCLAIMER
This final report is furnished to the U.S. Environmental Protection Agency
by JACA Corporation of Fort Washington, Pennsylvania and Richards Engineering
of Durham, North Carolina. The opinions, findings and conclusions are those
of the authors and not necessarily those of the U.S. Environmental Protection.
Any mention of products does not constitute endorsement by Richards Engineering,
JACA Corporation, or the U.S. Environmental Protection Agency. Parts and
fittings equivalent to those listed on measurement port drawings are available
from a number of suppliers.
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ACKNOWLEDGEMENTS
JACA Corporation and Richards Engineering would like to thank Mr. Kirk
Foster of the U.S. Environmental Protection Agency for this assistance during
this project. The assistance of Mr. R. Stroup and Mr. S. Schleisser of Nutech
Corportation in providing details concerning the replaceable tip S-type pitot
tube is also gratefully acknowledged.
Mr. R. C. Richards, P.E. of Richards Technical Services and Mr. J. R.
Richards, P.E. of Richards Engineering prepared the measurement port designs.
Final drawings were prepared by Ms. Kathy Butz of Graphic Associates and by
Mr. R. C. Richards. Mr. Uday Patankar, P.E. of JACA Corporation served as
Project Director.
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TABLE OF CONTENTS
1.0 Introduction 1-1
1.1 Background l"-"-
1.2 Scope l~1
2.0 Measurement Requirements and Problems 2-1
2.1 Static Pressure 2-1
2.2 Gas Temperature 2-5
2.3 Gas Stream Oxygen and Carbon Dioxide Concentrations 2-7
2.4 Gas Flow 2-8
3.0 Port Design and Location 3-1
3.1 Limitations of Existing Ports 3-1
3.2 Recommended Port Designs 3-4
3.3 Port Designs 3-6
3.4 Port Locations 3-21
References 4—1
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TABLE OF FIGURES
Number Title
2-1 Aspiration Effect
2-1 Use of Sanding Disk to Seal Ports
3-1 Port Located Near Burn Hazard
3-2 Clean-out Port for D/P Transmitter
3-3 1/4 Inch Diameter Measurement Ports
3-4 1/4 Inch Diameter Measurement Port with Extension Tube 3-10
3-5 Modified S-Type Pitot Tube 3-12
3-6 Pitot Tube Port and Sleeve 3-13
3-7 Pitot Differential Pressure Gauge Shelter 3-14
3-8 Modified Stack Sampling Ports 3-16
3-9 S-Type Pitot Tube with Replaceable Tip Shown
with Alignment Sleeve 3-17
3-10 Modified Stack Sampling Port and S-Type Pitot Tube 3-19
3-11 Pitot Tube Mounting Bracket 3-20
3-12 Location of Ports on Outlet Duct of Fabric Filter 3-22
3-13 Instrument Port Location for Pulse Jet
and Plenum Pulse Baghouses 3-24
3-14 Location of Ports on Reverse Air Fabric Filter,
(Outside-to-Inside Flow) 3-25
3-15 Location of Ports on Reverse Air and Shaker
Fabric Filters 3-26
3-16 Location of Ports on a Spray Tower Scrubber 3-28
3-17 Location of Ports on Packed Bed, Moving Bed
and Tray Type Scrubbers 3-30
3-18 Location of Ports on Gas-Atomized Scrubbers 3-31
3-19 Location of Ports on Inlet Duct to Gas-Atomized
Scrubbers 3-32
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1.0 INTRODUCTION
Portable instrumentation is useful in evaluating the performance of air
pollution control systems during both regulatory agency compliance inspections
and source operator routine maintenance checks. However, the use of instrumen-
tation, such as static pressure gauges, thermocouples, oxygen analyzers and
pitot tubes has been limited by the lack of adequate measurement ports on the
existing control systems. This report examines the data requirements and
provides recommendations on measurement port design and location.
1.1 BACKGROUND
The U.S Environmental Protection Agency has been actively involved in the
development of new and more detailed equipment inspection procedures. These
are intended to provide regulatory agencies with the capability of identifying
emerging problems before there is serious community impact and before the
equipment deteoriation demands expensive repair. Equally important is the need
to have complete technical information when negotiating compliance programs
with sources experiencing chronic compliance problems. While these new pro-
cedures are being developed primarily to aid regulatory agencies, they will
also aid sources operators.
The use of portable instruments such as static pressure gauges, thermo-
couples, gas analyzers and pitot tubes is often necessary when evaluating the
performance of air pollution control systems. Unfortunately, many existing
systems have been installed without any measurement ports or with ports in
improper locations. This has limited both the regulatory agency inspector and
the equipment operator.
As regulatory agencies adopt these new inspection procedures, there will
be a need to reach agreement with source operators concerning the types of
ports to be installed and concerning the most favorable locations for these
ports on specific units. The recommendations presented in this report are
intended to serve as a starting point for agency and source personnel in
discussing port requirements. Specific designs are proposed which should
minimize common measurement errors. Potential safety factors which must be
taken into account are also discussed.
1.2 SCOPE
The specific types of control equipment addressed include fabric filters,
wet scrubbers, mechanical collectors, absorbers, and electrostatic precipita-
tors. The types of measurements necessary to evaluate performance of each of
these types of collectors are briefly summarized and more detailed information
is provided in References 1, 2 and 3. The instrumentation required for each
measurement is introduced primarily to illustrate the type of probe required
and the necessary access to the port area. Common problems which can occur
while attempting to use existing ports are also covered. These problems can
seriously affect the accuracy of the measurement and can also lengthen the time
required to make' reasonable measurements.
1-1
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There can be a number of serious safety problems associated with improper-
ly located measurement ports. The most obvious of these are falls due to
ports situated in precarious locations. Other common problems include pollu-
tant accumulation in poorly ventilated areas in the vicinity of the ports, hot
surfaces adjacent to the ports, and static charge accumulation on the probes.
Static charge accumulation is very common downstream of electrostatic precipi-
tators, but can also occur in any gas stream in which the relative humidity is
low and the particulate concentration is high.
Specific port designs are proposed in this report. Drawings and general
specifications are provided to facilitate the location and installation of the
ports on the types of control devices listed above. They have been designed
in a manner to minimize measurement problems while using commonly available
parts and materials. It is possible to install these ports economically. The
specifications have been prepared to include some flexibility. However, it
is easy to modify these designs to satisfy site specific conditions.
Most of the measurement port designs presented in this report are too
small for the EPA Reference Method test equipment. The optimum locations for
emission testing are usually different than the optimum locations for control
system performance diagnosis. Also, the stack sampling ports are too large
for the types of probes used with the portable inspection instruments. It
must be understood that both stack sampling ports AND inspection ports are
necessary in most cases.
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2.0 MEASUREMENT REQUIREMENTS AND PROBLEMS
The instruments used to analyze the performance of air pollution control
equipment measure basic parameters such as gas static pressures, gas tempera-
tures and gas flow rates. None of the instruments are exotic and all have
been in common use for a number of years. Only their use by regulatory agen-
cies is relatively new. All of the instruments are small and easily carried.
Despite the familar nature of the instruments, there has been very little
written about measurement techniques and common measurement errors. The
following section addresses the data which is necessary for system evaluation
and some of the common measurement problems which have been encountered with
existing ports. This section provides the basis for later discussions
concerning specific port configurations and locations.
2.1 STATIC PRESSURE
The static pressure of a gas stream is simply the pressure exerted in
all directions by the fluid, measured in a direction normal to the flow. It
is similar to the barometric pressure which is the pressure exerted by the
atmosphere on the surface of the earth. When the static pressure is greater
than the barometric pressure, it is called "positive" pressure and when it is
lower it is called "negative" pressure. Both positive and negative pressures
are common in air pollution control systems. The measurement problems and
potential safety hazards, however, are quite different for each..
2.1.1 Reasons for Measuring Static Pressure
The gas stream static pressure drop while going through an air pollution
control system is a measure of the amount of energy removed from the gas
stream. This parameter can be used in a number of ways to identify control
system problems as indicated in the brief summary provided below:
Particulate Wet Scrubbers -
Fabric Filters
Static pressure drop can be indirectly
related to the particulate removal
efficiencies for most common types of
scrubbers. Demister pluggage and severe
air infiltration can also be identified.
The pressure drop across each compartment
provides useful information concerning
the dust layer on the bags and the gas flow
through the compartment. If the static
pressure drop is higher than normal,
cleaning system problems or fabric
blinding are probable.
The static pressure drop across a
fabric filter which has been isolated
for cleaning provides an indication
of the damper operation and condition.
2-1
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Mechanical Collectors - The static pressure drop provides an
indication of any problems which change
the gas flow resistance. Most such
problems lead to increased emissions.
Electrostatic - Static pressure drop is not a meaning-
Precipitators ful operating parameter.
Absorbers - Static pressure drop changes provide
indications of gas flow rate changes,
liquor flow rate changes, and poor gas-
liquor distribution. The data can also
be used to identify demister pluggage
and severe air infiltration.
There is a static pressure decrease whenever gas is accelerated in a hood
from essentially zero velocity to the duct transport velocity. This is due to
the conversion of potential energy to kinetic energy in the duct and due to
frictional energy losses. This hood static pressure drop is proportional to
the gas flow rate, thereby making this a useful qualitative indication of total
hood capture effectiveness. A decrease in the hood static pressure often
indicates severe air infiltration in the downstream ductwork or a change in the
fan operating conditions.
There is also a static pressure decrease whenever gas is passing through
a duct. This is due primarily to the conversion from potential energy to
frictional heat. The changes are normally too small to be of diagnostic use.
However, the inlet static pressure to the control device can be used as a
pseudo hood static pressure. If the absolute value of this static pressure has
decreased, the gas flow rate to the collector has probably decreased.
2.1.2 Instruments Used to Measure Static Pressure
Instruments used to measure static pressure are listed in Table 2-1 along
with the generally accepted meter operating ranges. The inclined manometer is
used primarily for pitot traverse velocity pressure measurements due to its
limited range. This instrument has the best resolution of any of the gauges
and does not need to be calibrated. The slack tube could theoretically be
used for any range. However, practical considerations limit the normal range
to about 36 inches of water. The diaphragm gauge can be used over a very wide
range. These gauges must be regularly calibrated against a slack tube or
inclined manometer.
There is no gas flow through any of these instruments. Therefore, no
pumps or power supplies are necessary to operate the gauges. Most of the
instruments are easily carried with the only exception being the rather bulky
inclined manometer. Generally, it is necessary to lift the inclined manometer
to the port location using a rope.
The static pressure measurements can be made in several locations: (1) the
interior surface of the duct or collector, (2) the middle of duct, and (3)
several locations along a traverse of the duct. Interior surface measurement
2-2
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is the only option for collectors due to the presence of internal components.
These surface measurements are also appropriate for ducts in which the gas
velocity is low. However, errors are possible at normal duct velocities with
this style of port.
Table 2-1. INSTRUMENTS USED TO MEASURE STATIC PRESSURE
Instrument Operating Range Resolution Accuracy
Inches of Water Inches of Water
Inclined Manometer 0 to 5 0.05 1-2%
Slack Tube Manometer 0 to 36 0.20 1-3%
Diaphragm Gauges 0 to 150 1.00 3 - 5%
In ducts, the surface irregularities around the port and flow patterns
within the duct can lead to some variation between surface static pressures and
the true static pressure within the gas stream. A more accurate measurement is
possible by moving away from the inner surface of the duct and into the main
flow stream. To do this, the gauge can be connected to a section of I/A inch
O.D. tubing. The instruments can also be connected to the downstream side of
an S-type pitot tube. With this approach it is possible to traverse the entire
duct and average the static pressure measurements. The latter is the preferred
approach for field inspection. However, it is more time consuming and diffi-
cult to get a pitot tube to the measurement port than it is to move the very
small diaphragm gauges around.
2.1.3 Possible Errors in the Measurement of Static Pressure
One of the major errors involved in static pressure measurement is the
aspiration effect in negative pressure ducts and vessels (Reference 2). If the
port is not entirely sealed around the probe there can be high velocity gas
"jets" through the open areas. If these pass by the opening of the probe as
shown in Figure 2-1, the jets can induce negative static pressures. The mea-
sured value is then the true negative static pressure plus the aspiration
induced negative static pressure. While this is usually insignificant below 10
inches of water, it is definitely important at -20 inches of water and above
(higher negative pressures). For -example, it is possible to measure a -25
inches in a duct where the true static pressure is actually -20 inches. At the
very high negative pressure of -100 inches, it is possible to induce additional
suction to yield measured values as high as -150 inches W.C.
One common way of sealing a port is to use a cloth or glove around the
probe. This is done at the risk of losing the material into the duct where
it could damage downstream equipment such as fans and air pollution control
devices. To illustrate the forces across the port, the data in Table 2-2
contains the calculated static pressures in pounds force across the area of
the port.
2-3
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NEGATIVE
PRESSURE
OUCT
-20"
AIP INFILTRATION
COPPER PROBE
RUBBER STOPPER
Figure 2-1. Aspiration Effect
SANDING DISK
COPPER TUBE
RUBBER STOPPER
-DUCT WALL
Figure 2-2. Use of Sanding Disk to Seal Ports
2-4
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Table 2-2. FORCES ACROSS OPEN MEASUREMENT PORTS
Port Diameter Static Pressure Total Pressure
Inches Inches of Water Pounds
1 10 0.31
1 25 0.78
1 100 3.10
A 10 4.58
A 25 11.45
A 100 45.82
Basis: Open Area of 1 Inch Port equals 0.864 square inches
Open Area of 4 inch port equals 12.73 square inches
(Assuming Schedule 40 IPS Pipe)
It is obvious from the data in Table 2-2 that the slightest moment of
inattention will allow the cloth or glove to be sucked into the duct or vessel
being tested. One way to eliminate this problem is to use a flat rubber
sanding disk (available for most hardware stores) which has a diameter of at
least one inch greater than the port being used. This is shown in Figure 2-2.
Another approach is to use a large rubber stopper, drilled out to
allow movement of the port. Both this and the rubber sanding disk provide a
seal against infiltration around the probe. However, there can be gas leakage
on positive pressure equipment. Also, the seal inherently isolates the probe
from the duct. Therefore ,the dissipation of static charges which develop on
the probe is inhibited.
2.2 GAS TEMPERATURE MEASUREMENT
2.2.1 Reasons for Measuring the Gas Temperatures
Gas temperature data is often essential in the evaluation of air pollu-
tion control system performance. In some cases, the performance of the con-
trol device is directly related to the gas temperatures existing at the inlet
of the collector. On control devices operating at elevated temperatures, the
changes in the gas temperature from inlet to outlet provide one indication of
air infiltration, which is one of the insults which can gradually harm the
physical condition of control equipment. Closely associated with air infiltra-
tion is the localized condensation of acidic vapors and water, both of which
attack system components. The temperature data is also necessary to determine
if high temperature excursions have probably damaged temperature sensitive com-
ponents of the control system. A brief summary of the most common uses of gas
temperature measurements is provided in the list below for each major type of
control system:
Particulate Wet Scrubbers - Measured to determine if the gas stream
is saturated after the scrubber and to
determine if changes in the inlet gas
temperature have changed the quantity of
condensed particles.
2-5
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Fabric Filters
Mechanical Collectors
Electrostatic
Precipitators
Absorbers
Measured to determine if high temperature
limits of fabric are being exceeded. The
outlet temperature is measured to determine
if air infiltration is significant or if
there is some potential for acid vapor
condensation.
Measured to determine if air infiltration
is significant or if there is some potential
for acid vapor condensation. It is also
measured to correct the static pressure
drop for gas density changes since the
baseline period.
Measured to determine if resistivity changes
or severe resistivity differences have been
caused by temperature changes. It is also
measured to determine if the start-up periods
are excessive.
Measured to determine if there have been
major changes in the equilibrium curve.
2.2.2 Instruments Used to Measure Gas Temperature
The equipment generally available for temperature measurement includes:
(1) dial-type thermometers, (2) thermisters, (3) fixed position thermocouples,
and (A) portable thermocouples. The thermisters will not be discussed further
since they have an operating limit of approximately 150°F after which the
response is nonlinear. Both the dial-type thermometers and fixed position
thermocouples can indicate lower than actual temperatures since they must be
mounted close to the duct wall. Some ducts can have a substantial difference
between the gas temperature close to the duct wall and that in the center of
the duct.
In addition to the limited reach of the dial-type thermometer, the
inherent design renders the unit susceptible to a bias to lower than actual
temperatures. Heat can be conducted up the metallic stem to the large
circular face plate outside of the gas stream. This serves as a very
effective heat exchanger.
The probe portion of the dial-type thermometer is the bimetallic coil
sealed in the end of the stem. Commercial units are generally 1/4 inch in
diameter. The probes for the thermocouples can be a variety of sizes ranging
from the bare bead to several sizes of thermowells. The bare bead type
thermocouple probe has a diameter of approximately 1/8 inches.
2.2.3 Measurement Problems
If the distribution of temperatures is large enough, errors in operation
of the control system are possible. For example, if a fixed position thermo-
couple on a baghouse inlet indicates 500 °F, the actual gas stream temperature
2-6
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in the duct center could be 525 °F. The higher temperature exceeds the normally
accepted limit of 500 °F. For this reason, it is sometimes necessary' to
traverse the gas stream to determine both the average temperature and the
temperature distribution. This can only be done using a portable thermocouple.
Since a flexible thermocouple probe is the easiest to transport around a con-
trol device, there must be ways to fix the probe at the desired positiion in
the duct. For small ducts, the probe can be threaded through I/A inch O.D.
tubing as long as the wall thickness does not exceed 1/16 of an inch. This is
adequate as long as the duct is small or a complete traverse is not necessary.
For for more demanding situations, the probe can be wired or taped (depending
on temperature) to an S-type pitot tube.
By placing the thermocouple probe well inside the duct or by performing a
complete traverse of the duct, it is possible to avoid the errors due to air
infiltration through the port. Note that the 1/4" tube can be bent slightly so
that when close to the duct wall, it is out of the path of cold ambient air
leaking through the port. The complete traverse is useful when accuracy is very
important and a significant temperature variation is expected.
Another common problem is the impaction of water droplets. If the gas
stream is not saturated, this will cause rapid fluctuations between the dry
bulb and wet bulb temperatures.
2.3 GAS STREAM OXYGEN AND CARBON DIOXIDE CONCENTRATIONS
These measurements are valuable when inspecting air pollution control
systems serving stoker fired coal boilers, oil-fired boilers and other fuel
combustion sources.
2.3.1 Reasons for Measuring the Oxygen and Carbon Dioxide Concentrations
The control device inlet conditions help to determine if the combustion
conditions have deteoriated to the point that excess emission conditions are
possible. The difference between the oxygen levels measured before and after
the collector clearly show the extent of air infiltration into the collector.
With such information, the inspector can evaluate whether or not the corrective
actions proposed by the operator have a reasonable chance of succeeding.
2.3.2 Instruments in General Use
Instruments generally used for this purpose include: (1) Orsat Analyzers
(2) Specific Gas Absorbers, and (3) Electroconductivity Analyzers. The
first two are similar in that the gas sample is mixed with chemicals which
absorb one component of the gas sample. The change in the height of a column
of liquid is proportional to the concentration of the absorbed gas. The Orsat
instrument measures oxygen, carbon dioxide and carbon monoxide from a single
gas sample. The specific gas absorbers measure either the carbon dioxide or
oxygen concentration. Both the Orsat and Specific Gas Absorbers are manually
operated, wet chemical analyzers. The electroconductivity instrument is a
standard line powered unit which senses the oxygen concentration in a contin-
uously extracted gas sample. The electroconductivity unit is generally consid-
ered as accurate as the Orsat and less time consuming. The specific gas
absorbers are very portable and simple to use, but are slightly less accurate
2-7
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than the other two approaches. The common element of all three approaches is
that the sample can be easily acquired through a 1/4" O.D. tube inserted in the
gas stream. Again, if there is a need to traverse a large duct, the pitot tube
can serve as a sampling tube.
2.3.3 Possible Errors in the Measurement of Oxygen and Carbon Dioxide
The major error possible in the measurement of oxygen and carbon dioxide
concentrations is the inadvertent inclusion of inleaking ambient air with the
sample. This is avoided by placing the sampling probe upstream from the port
or by extending the probe well into the duct. This is identical to the steps
taken to minimize air infiltration related static pressure and gas temperature
measurements errors.
Downstream of wet scrubbers, the gas stream oxygen and carbon dioxide
concentrations are difficult to interpret due to the partial absorption of
both in the scrubber. Accordingly, the data can not be used to indicate air
infiltration or to identify major changes in process operation.
2.4 GAS FLOW MEASUREMENTS
Gas flow data is measured less frequently than the data discussed
previously. It is necessary to confirm problems suspected from the initial
evaluation of inspection .data.
2.4.1 Reasons for Measuring Gas Flow Rate
For all pollution control systems, the measurement of gas flow rate at the
inlet of the unit demonstrates whether or not the proper gas flow rate from the
process equipment is being delivered. A drop in the flow rate could be due to a
change in fan operation or severe air infiltration into the ductwork downstream
from the sampling point. The difference in the gas flow rates before and after
the collector provides an estimate of the air infiltration rate (after correct-
ion for gas density changes.)
2.4.2 Instruments Used to Measure Gas Flow Rate
The standard instrument for measuring the gas flow rate is the pitot
tube. The Standard pitot tube does not need to be calibrated. However, the
small static pressure ports are vulnerable to pluggage when used on the inlet
side of many particulate control devices. For this reason, the S-type pitot
tube is used most often by inspectors.
The dimensions of the pitot tube are partially fixed by EPA Reference
Method 1 and partially determined by customer specifications. The width of the
sensor portion of the tube must be not exceed 1 and 1/2 inches. The diameter
of the tubes is generally 3/8 inches and the tubes are tack welded together
at several spots. A thermocouple well may also be included along the pneumatic
tubes.
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2.4.3 Measurement Problems
Port air infiltration is as much of a problem with this measurement as
it was with the previously discussed instruments. It is necessary to seal the
port adequately to prevent erroneous measurements at the traverse points close
to the port.
Orientation of the probe is important. If it is allowed to dip or float
in the gas stream, a lower than actual velocity pressure is indicated. This
type of error is especially difficult to avoid when the probe is extended well
into the gas stream and the operator has only limited leverage. The second
orientation error is simply a matter of carelessness. If the tube is twisted
in the gas stream, significant positive or negative errors are possible. Such
errors are not common on stack sampling tests since the probe is rigidly
mounted on the main sampling tube which is securly hung from the boom. How-
ever, in the case of the field inspector, the individual is generally working
with only a pitot tube and at a location where the pitot must be hand held.
The inspector is also working either alone or with plant personnel who are not
familiar with the techniques.
2-9
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3.0 PORT DESIGN
This section examines some of the major limitations and potential safety
hazards of existing ports. Its purpose is to compile a list of criteria which
define an acceptable inspection/measurement port for air pollution control
systems. Port designs have been developed during this project based on these
criteria. They could be installed on many systems with little or no modifica-
tions. In other cases, these designs will serve as a useful starting point in
developing the necessary ports. Siting recommendations for major categories of
control systems have also been proposed.
3.1 LIMITATIONS OF EXISTING PORTS
Because of the relatively limited use of portable instruments on air
pollution control systems, little effort has been spent previously on the
design and location of ports. Some of these are located in completely in-
accessible locations and some have been placed in unrepresentative locations
along the ductwork. A variety of safety hazards may be present in the
Immediate vicinity of the ports.
3.1.1 Port Pluggage
This is a very common problem which plagues measurement ports of
practically all sizes and descriptions. The recesses which are inherent to the
port provide an ideal location for the accumulation of sludge and solids.
While pluggage can not be avoided entirely, common sense should be used
on port location. Ports should be located in a area protected from the
natural drainage of water and sludge. They should also be placed in portions
of the duct or collector which are usually free of dust accumulation. Due to
these problems, the ports should not be on the lower sides of ducts.
Due to plugging tendencies, access to the port area is necessary so that
the deposits can be rodded out prior to the measurement. Long tubing runs
from the port to an accessible location should be avoided since it is sometimes
difficult to clear the deposits using compressed air.
3.1.2 Oversized Port Fumigation
Large 4 inch diameter ports are common since these are large enough for
standard stack sampling probes. With positive pressure conditions, however,
there can be substantial gas flow out of the port into the immediate vicinity
of the inspector. Inhalation hazards can be created if the persons involved do
not have the appropriate respirators or if ventilation is poor. Chemical
and physical asphyixants can also accumulate within the breathing zone.
The pollutant concentrations can exceed the capability of most cartridge
and canister type respirators. In some cases, combinations of pollutants would
pose a threat even at lower concentrations since each type of respirator is
3-1
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effective only for a single pollutant. Therefore, it is important to avoid use
of an open positive pressure port.
Large ports are not desirable for inspection measurements since all of
the probes discussed in the previous section were relatively small. The
largest probe used is the pitot tube which has a width of less than 1 and 1/2
inches (with the exception of the model with the replaceable tip). In some
cases, all measurements can be made through 1/4 inch diameter ports. There is
no advantage to the large ports and there can be significant safety problems
involved when the pressures are even slightly positive.
3.1.3 Ports in Partially Confined Areas
Inhalation hazards similar to those possible with large positive pres-
sure ports occur when the ports are located in portions of the collector with
inherently poor ventilation. This is most common in large multi-compartment
fabric filters where the measurement ports and instrumentation are mounted in
the walkways between rows of compartments. Gas leakage out of access hatches,
weld gaps, and ductwork expansion joints can accumulate to high concentrations
during periods of low ambient wind speed. Partially confined areas are also
common on wet scrubber systems since they are often inside to minimize freezing
conditions during off-line periods. The ports on these scrubbers are often
located in areas with very little natural ventilation. Partially confined
areas are common to all types of air pollution control systems.
3.1.A Static Charge Accumulation
Particles striking a probe within a gas stream result in some static
charge on the probe. If this is not dissipated, it is conceivable that the
electrical charge will accumulate to a sufficient voltage to arc over to a
grounded portion of the duct wall. This could initiate an explosion within the
duct due to the presence of either suspended particulate matter in the gas
stream or small deposits of dust at the bottom of the duct. While a search of
the literature and numerous contacts with instrument manufacturers has failed
to uncover any published reports of static accumulation, unpublished data com-
piled by the authors of this report indicates that such charges do accumulate
under certain conditions.
Considering the explosive nature of many common dusts such as metallic
dusts, grain and flour dusts and coal dust, a cautious approach is necessary
with regard to static. All probes should be electrically bonded to a grounded
component of the control system to dissipate the electrical charge as it
develops.
3.1.5 Burn Hazards
Many gas streams treated in air pollution control systems are very hot.
The ductwork surfaces and measurement ports are often more than 500 °F. There-
fore, direct contact can quickly lead to a painful burn. The port shown in
Figure 3-1, is located between the side wall and a large flange. A painful
burn could occur while opening the port since both the side wall and the flange
are above 400 °F. Unfortunately, many ports are located in such a manner that
a burn is likely while working with portable instrumentation. The port should
3-2
-------
preferably be located away from hot surfaces. A short extension nipple moves
the inspector away from the hot surface of the duct itself and also moves
activity away from hot adjacent surfaces. A layer of insulation on the duct
reduces the chances of direct contact while also reducing the radiant energy
from the duct.
Figure 3-1. Port Located Near Burn Hazards
3.1.6 Transducers
The ports must not be mounted along with differential pressure (D/P)
transducers. Figure 3-2 illustrates a D/P transducer with a 1" line leading to
the port and a 2" pipe welded to the side of the wet scrubber. While the 2"
plug on the front side of the tee looks like a useable port, opening it would
affect the pressure sensed by the transducer. It is quite possible that the
low pressure signal generated by the transducer could be interpreted as a major
upset by the automated process control system which would then trip off the
system components. Actually, the 2" plug is not intended as an inspection
measurement port but rather as a means for routine cleaning of the port
deposits. The inspection port should be located away from the transducer port
so that false static pressure signals are not transmitted.
Figure 3-2. Clean-out Port for D/P Transmitter
3-3
-------
3.1.7 Stuck Port Caps
The most difficult part of any sampling or measurement exercise is the
removal of the large 4" pipe caps often used to close off the port. Normally
these must be removed by heating with a torch or by use of a large pipe wrench
with a several foot pipe extender. The latter approach is taken at the risk of
ripping off the entire port nipple.
3.2 RECOMMENDED PORT DESIGNS
Port design and siting criteria have been compiled which should minimize
the measurement problems and safety hazards of many existing ports. These
criteria should be satisfied to the extent possible on all new systems and on
existing collectors where ports are being installed. The recommended port
designs presented later in this section satisfy these criteria.
3.2.1 Criteria of Good Inspection Measurement Ports
The general criteria for good measurement ports are described here. Due
to the different types of measurements required at different locations in an
air pollution control system, it is necessary to list somewhat different
criteria for ports mounted on the walls of the collector and ports mounted on
ducts before and after the collector.
3.2.1.1 Ductwork Ports - These ports must accomodate a pitot tube which is
used not only for gas flow measurement but also: (1) as a thermocouple support
when traversing the duct, (2) as a static pressure probe when traversing the
duct, and (3) as a sampling tube when analyzing gas stream oxygen, carbon
dioxide and carbon monoxide levels. The general guidelines regarding ductwork
ports are discussed below.
!• Accessibility - Access platforms and ladders should meet
OSHA requirements.
2. Port Locations - The ports should be located at least 2 duct
diameters downstream and at least 1/2 duct diameter upstream from
any flow disturbances. The ports should be as far from the flow
disturbances as conveniently and economically possible to minimize
the number of sampling points necessary to characterize flow and
composition.
3. Port Spacing on Rectangular Ducts - The number of ports necessary
on a rectangular duct depends on the distances from the upstream and
downstream disturbances. EPA Reference Method 1 requirements should
be satisfied.
4, Port Diameter - The ports should not have an internal diameter
exceeding 2 inches. All probes can fit through a port of this size.
Larger ports have greater air infiltration (negative static pressure)
or greater potential for pollutant exposure (positive pressure).
3-4
-------
5. Partially Confined Areas - The ports should not be located in
areas which are prone to pollutant accumulation due to poor natural
ventilation.
6. Large Rectangular Ducts - Ports are needed on each vertical side
which exceeds 6 feet. The maximum extension distance of pitot
tubes in common use is 6 feet.
7. Round Ducts - Two ports spaced 90° apart should be located on
round ducts. If they exceed a diameter of six feet, then four ports
spaced equally around the duct are necessary due to pitot tube reach
limits.
8. Exposed Locations - The ports should not be located above plant
equipment or vents which could suddenly release either steam or
pollutant laden gases which could engulf the sampling area. The
ports should not be in the immediate vicinity of components of the
ductwork prone to leakage, such as expansion joints.
9. Hot Surfaces - Hot surfaces in the vicinity of the port should be
insulated to reduce the chance of direct contact and to reduce the
radiation rate.
10. Port Caps - Easily removed port caps should be used.
11. Static Electricity Bonding - The port must be designed to inher-
ently provide a bonding path from the probe to the duct. There must
also be provisions for the use of a grounding/bonding cable.
12. Pluggage - The port should be located in areas which are not
prone to pluggage. Orientation of the port should minimize build-up
of material.
13. Port Sealing - There must be effective ways to minimize gas flow
out of positive pressure ports during the use of the portable
instruments. There must be effective ways to minimize air
infiltration into negative pressure ports.
3.2.1.2 Collector Wall Ports - The ports used on the walls of the air
pollution control device are quite different since there is rarely a need to
traverse the internal space. All of the measurements done on fabric filters,
mechanical collectors, and wet scrubbers can be done using only a 1/4 inch
diameter probe. The criteria for these ports are presented below:
1. Accessibility - There must be safe and convenient access
to the port location on the collector wall so that it is possible
to rod out the port prior to the measurement. All ladders and
platforms should meet OSHA requirements.
2. Connecting Tubing - There should be no permanently mounted
connecting tubing from the port to a "convenient" measurement
location. It is impossible to obtain representative temperature
data after the gas passes through the long tubing.
3-5
-------
3. Differential Pressure Transducers - The port should not be
directly connected to a differential pressure transducer. Opening
the port to make the measurement could result in a false signal to
the process control equipment.
4. Extension Tubing - When extension tubing inside the unit is
necessary to connect a port to an internal area of the collector,
this tube should be straight so that it can be rodded out prior
to the measurement.
5. Size - The port should have an internal diameter between 1/4
inch and 1 inch. It should be only as large as necessary to accept
the specific probes to be used.
6. Partially Confined Areas - To the extent possible, the ports
should be located in well ventilated areas, where accumulation of
pollutants is unlikely.
7. Pluggage - The ports should not be located in areas prone to
pluggage. Orientation of the port should minimize the accumulation
of materials in the port recess.
8. Moving Equipment - The ports should not be located near moving
equipment such as shaker assemblies and fan sheaves.
9. Air Infiltration - To the extent possible, the ports should be
located away from common sites of air infiltration such as large
access hatches.
10. Hot Surfaces - To the extent possible, the port should extend
outward away from hot collector wall surfaces to minimize the risk
of direct contact.
3.3 PORT DESIGNS
Ports which satisfy the criteria presented earlier are discussed in this
section. Several relatively large ports are proposed for areas where a
complete traverse of a gas stream is necessary. A simple 1/4 diameter port is
proposed for collector walls and other areas where measurements close to the
interior surface are sufficient. A special port which has interior extension
tubing is also proposed for certain types of fabric filter systems. This is
presented since this design would permit the installation of ports in safe
locations without the need for additional ladders and platforms, both of which
can be expensive.
3.3.1 Small Ports
These ports are intended for static pressure, gas temperature and
oxygen/carbon dioxide measurements at various positions on the control systems
listed in Table' 3-1.
3-6
-------
Table 3-1. Locations for Small Ports
Application Location of Ports
1. Pulse Jet Fabric Filters Above and Below Tube Sheet
2. Mechanical Collectors Above and Below Clean Side
(Multi-Cyclone Designs) Tube Sheet -
3. Particulate Wet Scrubbers Before and after Trays,
Beds, and Restricted Throats
Before and After Demisters
4. Reverse Air Fabric Filters Above and Below Tube Sheet
(Cylindrical Shell, Outside-
to-Inside Flow Designs)
5. Hoods Immediately After
Converging Section.
6. Ductwork Various locations
A sketch of the recommended port configuration for these applications is
presented in Figure 3-3a.. This is constructed of a Swagelok pipe weld con-
nector. A 3/16 inch weld around the circumference provides a gas tight seal and
holds the port fitting to the collector wall. The compression of the 0-ring
against the probe and against the fittings prevents any leakage of gas out of
the port. Air infiltration in negative pressure situations is also
negligible.
For areas where sludge or liquids occassionaly accumulate on the inner
surface of the duct, the port can be inclined to facilitate drainage. This is
illustrated on the upper right side of Figure 3-3b. A port cap, as shown
in the lower right of Figure 3-3c, can be used to seal the I/A inch port.
This prevents material accumulation in the port recess when the port is closed
and it also prevents air infiltration (negative pressure situations) into the
collector. In the case of fabric filters, this localized air infiltration
could cause some corrosion and some acid condensation related bag damage.
3.3.2 Small Ports with Extension Tubes
There are several common types of fabric filters for which it is very
difficult to arrange the measurement ports. In the large, multi-compartment
reverse air (inside-to-outside flow) and shaker collectors, the tube sheet
separating the "clean" from the "dirty" side is mounted directly above the
hoppers. The walkways are almost always above the elevation of the tube sheet.
Therefore, the ports must supposedly be below the walkway. There is often an
elbow fitting below the walkway which connects the port to a tube leading above
the walkway area. This does not satisfy one of the main criteria in that
accessibility to the port is not available. Since this part of the hopper area
is prone to solids accumulation, this failing is especially troublesome.
3-7
-------
INSTRUMENT
SWAGELOK PLUG # SS-600-P
L...
,-J
PARKER O-RING
SIZE 2-202
-SWAGELOK NUT
*SS-602-I
SWAGELOK MALE CONNECTOR
SS-600-V8MPW
OUTSIDE
INSIDE
Figure 3-3b. 1/4" Port With
Standard Plug
SS FLAT HEAD RIVET
,1 1/4" X 1 3/4*
SWAGELOK NUT *SS-602'I
SWAGELOK TO MALE
PIPE WELD CONNECTOR
*SS-600-!-8MPW
Figure 3-3a. 1/4" Port With
Seal Nut Clamp
: SWAGELOK MALE CONNECTOR
1 SS-600-1-8MPW
Figure 3-3c. 1/4" Port With
Stem Type Cap
Figure 3-9. 1/4" Measurement Port
3-8
-------
The recommended means for installing the port for these types of collect-
ors is shown in Figure 3-4. In this case, the port is mounted on a section of
3/8 inch IPS Schedule 40 pipe which extends inside the fabric filter from below
the tube sheet to a position outside the collector shell. The pipe terminates
at a position above the walkway so that there is good accessibility for rodding
out the extension pipe. The extension pipe must be positioned so that it
passes between the bag thimble or snap ring connections on the tube sheet. The
60° angle minimizes the length of pipe needed and ensures that the port will
not extend very far out into the walking area.
The pipe must be welded completely around the circumference on the lower
side of the tube sheet. Failure to do this will result in dust leakage through
the gap and may invite crevice corrosion. The pipe must also be welded on the
outside of the collector wall. A mounting plate has been provided at this
position to facilitate the welding. The remainder of the fittings and the cap
are identical to that described earlier for standard small ports. The 0-ring
seal provides the necessary protection against positive pressure gas leakage.
The "clean" side port for the compartment should be mounted horizontally
in the same general vicinity of the "dirty" side port shown in Figure 3-4.
This is a standard small port without any extension pipe.
A port similar to that described in Figure 3-4 can be used for top access
type pulse jet fabric filters. With these collectors, the tube sheet which
separates the "clean" side from the "dirty" side is mounted close to the top of
the baghouse. There is good accessibility to the top of the unit due
to the need to routinely service the diaphragm valves and to replace bags.
However, there is rarely any access to the side of the collector where the
ports should logically be placed. Nevertheless, some ports have been installed
along the side, usually in a spot that can not be reached through the ladder
cage.
An alternative design for these ports is similar to that shown in Figure
3-4. In this case, both of the ports are located on the roof of the pulse
jet baghouse. The "dirty" side port has an extension pipe which passes through
the roof of the collector, down through the clean air plenum, and through the
tube sheet. The tube is welded entirely around the circumference of the tube
sheet to prevent gas leakage. The cap with an 0-ring seal is identical to
that described in Figure 3-3. The "dirty" side port is located directly above
a portion of the tube sheet which is equidistant from the bags and bag clamps.
By placing the port between the access hatches, the port should not present a
trip hazard. The "clean" side port is located close to the "dirty" side port.
It consists of a fitting identical to that shown in Figure 3-3. The main
disadvantages of this arrangment include burn hazards on the access hatch and
potential errors due to air infiltration. These are outweighed by the improved
accessiblity available at this location.
3.3.3 Standard Large Inspection Measurement Ports
These ports accept pitot tubes either for gas flow measurement or for
traverse checks of static pressure, gas temperature or gas composition. They
would be used on all ducts greater than 2 feet diameter.
3-9
-------
SWAGELOK NUT*SS-602-I
CO
I
COLLECTOR SHELL
TUBE SHEET
DUST HOPPER
7/8" DIA HOLE IN TUBE SHEET
ARRANGEMENT OF INSTRUMENT PORT
SWAGELOK FEMALE CONNECTOR
*SS-600-7-6
— I 3/4" DIA
HOLE IN
SHELL
1/4" DIA PROBE
PARKER
0 RING*2-2O2
-BURN PIPE CLEARANCE
FRONT AND BACK.
3/4"
DIA BURN-l
I to
3"
3/8 IPSflPE-SCHED 40 X 12" LONG
DETAIL OF FACE PLATE
3" SO X 1/4 BAR
ENLARGED DETAIL OF PORT TUBE
NOTE: ALL WELDS 3/16"
Figure 3-4. 1/4" Port With Extension Tube
-------
A description of the S-Type Pitot Tube must be presented before the large
port design can be discussed. The modified S-Type Pitot Tube is shown in
Figure 3-5. This consists of the typical 3/8 inch diameter parallel tubes
with a flared sensor end having a width between 1 and 1 and 1/2 inches. There
is also a 3/16 inch diameter thin wall tube which protects the permanently
mounted thermocouple wire. The major difference between this pitot tube and
conventional pitot tubes is the 1 and 5/16 inch O.D. tube which encloses the
pitot pneumatic lines and thermocouple line. The outer tube facilitates use of
an 0-Ring seal described in a later drawing. This tube can fit over an exist-
ing pitot tube. To prevent gas leakage up through the tubes, bulkhead fittings
should be welded to either end. A support bulkhead is also necessary in the
middle of the pitot tube. This sleeve adds less than 1 pound per foot to the
pitot tube weight.
The pitot alignment sleeve and port are shown in Figure 3-6. The port
is a 4 inch section of 1 and 1/4 inch IPS pipe having a wall thickness of
0.140 inches. It is welded to the duct wall on one end. The other end is
welded to a 1/4 inch thick mounting flange. The pitot is supported in an
outer flange with a 1 and 3/8 inch hole through the center. As shown in
Figure 3-6, a thumb screw is mounted at the top of the outer flange to hold
the pitot at a designated measurement point. The outer flange collar has
score marks 20° in either direction from the vertical so that the pitot tube
rotation can be checked while making minor adjustments for cyclonic flow. The
bolts should be tack welded to the inner flange so that they do not have to be
removed while opening the port. The nuts on the outer flange should be coated
with an anti-seizing compound.
The port and pitot tube collar maintain the pitot tube in a level position
so that pitch error is negligible even when the pitot tube is fully extended.
The score marks on the collar also help the inspector to avoid any yaw errors.
The 0-ring seal resting on the shoulder of the inner flange provides a gas
tight seal while the instrument is inside the port. During times when the port
is being opened and closed there obviously is no way to prevent some gas leak-
age. However, with this small port design, the quantity of gas flowing outward
(positive pressure situations) would be less than 10% of that for conventional
4 inch ports.
The port can be sealed during periods of nonuse with a 4 and 1/2 inch
piece of stainless steel bar, 1 and 5/16 inches in diameter. This completely
fills the port recess so that solids and sludge can not accumulate. This
should also be coated with a small quantity of anti-seizing compound. This
bar is welded to a small flange which attaches to the inner flange of the
port.
While the measurement is being made, the entire port recess is filled.
This reduces the possibility of unusual flow patterns close to the port area
due to the disturbance caused by the discontinuous inner surface of the duct.
Therefore, this arrangement causes less aerodynamic disturbance than typical
stack sampling ports.
The pitot tube is self supporting, thereby freeing the inspector's hands
for recording data. A convenient shelter for mounting the inclined manometer
or low range diaphragm gauge is shown in Figure 3-7. There are small magnets
3-11
-------
H
•SUPPORT BULKHEADS
(APPROX. 3'O.C.)
LBULKHEAD
'•*• (WELD GAS
TIGHT)
-=r
BULKHEAD^
•z
NOTE: 3/16 a i 5/ie SLEEVES
ADD 1 LB/FT OF LGTH
'APPROX.
SS TUBE 3/16" O.D. X .035" WALL-
SS TUBE 1.315" O.D. X .065" WALL-
1
8 TK
1/4" DRILL
VIEW I-I
SECTION IE-I
BULKHEAD DETAIL
MODIFICATION OF 3/8" STANDARD S-TYPE PITOT TUBE
NOTE: 3/1 e" a i s/ie" O.D. SLEEVES ADD LESS THAN I*/FT OF PITOT
TUBE LENGTH
Figure 3-5. Modified S-Type Pitot Tube
3-12
-------
O-RING 1 11/16 O.D. X 1 5/16" I.D. X 3/16"DIA.
4"
U:
1/4"- 20 THUMB SCREW X 1" LG
5/16" PROBE SHELL
SCORE COLLAR
SPOT WELD
^ r, „,
LSS PIPE-1
(2) 3/8 HEX HD BOLT X l" LG
W1TH HEX NUT
-SS BAR-1 5/16 "Dl A X 4 1/2" LG
gl/GAS TIGHT
PITOT TUBE PORT WITH PLUG
Figure 3-6. Pitot Tube Port and Sleeve
3-13
-------
SHELTER (16 GA SHEET)
-MANOMETER
1/4" SO. HD. BOLT 8 WING NUT
_ TT
H ($
LJ £&~ LJ
HAND HELD DIGITAL THERMOMETER
TO PITOT TUBE\ PROV|DE HOOK OR BASKET FOR SUPPORT
THERMOCOUPLE CABLE
Figure 3-7. Pitot Differential Pressure Gauge Shelter
3-14
-------
for leveling the inclined manometer. This shelter is an optional feature
which is helpful when frequent pitot traverse are anticipated.
It should be noted that all commercially available pitot tubes could be
used in these ports, with or without the mounting collar and sleeve. The
advantages of the modifications shown are a substantial reduction in pitch and
yaw errors, facilitation of checks for cyclonic flow, and protection from toxic
pollutants under positive pressure conditions. These modifications to typical
pitot tubes would increase the cost slightly due to more difficult fabrication
steps. The total additional weight would be less than 1 pound per foot.
Therefore, the portability of the pitot tube is not affected. The permanent
parts included in each of the ports can be easily constructed out of commer-
cially available fittings and materials. While more costly than the simple 4
inch IPS pipe nipples in common use, this port design provides for more accur-
ate measurement and safer working conditions.
3.3.4 Modified Stack Sampling Ports
In some plants, existing stack sampling ports are at some of the locations
useful for evaluation of system conditions. It is also possible that plants
will want the flexibility to conduct EPA Reference Method stack tests at the
locations chosen for inspection measurement ports. It is also possible that
the plants will want the capability to use pitot tubes with replaceable
tips. This section presents recommendations for ports which satisfy most of
the design criteria discussed earlier, while allowing for large stack sampling
probes and/or replaceable tip S-type pitot tubes.
The port design is illustrated in Figures 3-8 a,b and c. The top sketch,
Figure 3-8 a, is the port which would be used in a location where there is no
existing 4 inch port. An 11 inch piece of IPS Schedule 40 pipe is welded to a
flange constructed of 1/2 inch plate. A 4 inch diameter hole is made in this
flange and the surface is hand ground to be flush with the inner surface of
the pipe. After burning or cutting the necessary hole in the collector or
duct wall, the 4 inch IPS Schedule 40 pipe with flange is welded to the
exterior of the wall. Both of the welds should be 1/4 inch gas tight welds.
The pipe flange includes two 1/2 inch - 13 NC x 2 inch long square head
bolts. These are tack welded to the back side of the pipe flange so that
they do not have to be removed when opening and closing the port.
When there are existing 4 inch ports in the desired location, it is a
simple matter to modify these to facilitate inspection measurements. For
those with a female IPS pipe thread, 4 inch IPS Schedule 40 pipe with one end
threaded can be used. This is illustrated in Figure 3-8b. As before, a
flange is installed on the other end to accept the pitot fittings discussed in
later sketches. Existing ports having a 4 inch male IPS fitting can be
converted using a 4 inch standard pipe coupling, as shown in Figure 3-8c.
Again it is necessary that the main body of the port be a 4 inch pipe with one
end threaded. The coupling should be allowed to seize or corrode into posi-
tion since it will not be removed and since rotation is not desired.
A drawing of the replaceable tip S-type pitot tube is provided in Figure
3-9. It has two unions connecting the 3/8 inch O.D. tubes. This allows for
3-15
-------
9/16" DRILL-2 HOLES
10 5/8
FOR 7 1/2" STD S-TYPE PITOT TUBE TIP
r
4" IPS PIPE X .238 WALL
rl
•*-4"DIA BORN -SHELL
\ HAND GRIND INSIDE SURFACE
-FLUSH WITH SHELL i.D.--Kx
i
GAS TIGHT 1/4" V
NEW PORT INSTALLATION
i_j
L
r4" IPS FEMALE THREAD PIPE
(EXISTING)
4" IPS PIPE.SCHED 40-
GAS TIGHT 1/4"
ALTERATION OF EXISTING PORT
4" IPS FEMALE THREADED PIPE
r4" IPS MALE THREAD PIPE PORT
(EXISTING)
4" IPS PIPE ,SCHED 40
ALTERATION OF EXISTING PORT
4" IPS MALE THREADED PIPE
l/2"-!3HEX NUT
BRASS
l/2"-l3 SQ.HDBOLT X 2"
LONG
"-SPOT WELD-OPPOSITE SIDES
OF FLAT HEADS
ENLARGED DETAIL
(TYPICAL)
NOTES IN TEXT:
PL.FLANGE MUST BE SQUARE
WITH AXIS OF PORT
NEVER-SEEZ^BOLTS BEFORE
LEAVING SITE
Note:
Figure 3-8a is on the top left
Figure 3-8b is on the middle left
Figure 3-8c is on the lower left
Figure 3-8. Modified Stack Sampling Ports.
3-16
-------
LO
I
7 1/2" STD REPLACEABLE TIP
THERMOCOUPLE
WIRE AND CONNECTOR
-SLEEVE-SEE DETAILS BELOW
-THUMB SCREW
-304SS TUBE 3/16"O.D. X.035" WALL
I
FIXED LENGTH SPECIFIED BY CUSTOMER
304SS X 24 GA TIE WIRE-ANNEALED
(SPIRAL WOUND BY CUSTOMER)
3/8
*•
n
-'i
5 15/16" j
i
1/16 R (TYP)X
1"
* 1/8 KERF
-SAW CUT
7/32"
/'I
^y
1 ! V™-*
it h 7/32 R
1 1
t *
''row
I "^
'eg
rO
NOTE: CLAMP SLEEVE HALVES ON
PITOT TUBE AND SPOT WELD
2 PLACES EACH SIDE OF JOINT
GRIND WELDS FLUSH.
# 21 DRILL 10- 32 TAP
FOR THUMB SCREW
•THERMOCOUPLE WIRE SLEEVE
,3/8" OD. PITOT TUBES
LSLEEVE-SS304
FLAT BAR I"X2"X 12" LG
(MAKES 2 PIECES)
SPOT WELD 3/8 TUBES
ON SIDE OPPOSITE SLEEVE
SECTION I-I
VIEW n-n
— I/8"X 45°(TYP)
MODIFICATION OF STANDARD 3/8" S-TYPE PITOT TUBE
Figure 3-9. S-Type PiLot Tube with Replaceable Tip Shown
With Alignment Sleeve
-------
replacement of the tip in the event that it is damaged during use or shipment.
The distance from the tip to the end of the caps (which attach to the unions)
is approxiamately 7 and 1/2 inches. The width of the pitot tube at the unions
is approximately 2 and 1/8 inches. It is this width which prevents use of the
replaceable tip S-type pitot tubes in the port described in Figure 3-4. The
long port bodies presented in Figure 3-8 were sized so that the wide portion
of the pitot tube around the union fittings would fit within the port recess.
Alignment and support necessary to prevent measurement errors are now accom-
plished by an external mounting sleeve.
The manner in which an S-Type pitot tube would be mounted in the port is
shown in Figure 3-10. A pitot mounting bracket is secured to the port flange
by means of the two 1/2 inch bolts. This bracket includes a square sleeve
which extends backward 5 inches. This is designed to hold the mounting sleeve
attached to the pitot tube.
The pitot mounting bracket, shown in Figure 3-11, is a piece that would be
brought by the inspector to the plant, assuming that the plant is using the
standard fittings and port design shown. It consists of a 9 inch diameter 1/4
inch thick plate with a hole of 2 and 1/4 inches cut through it. A 5/8 inch
section of 3 and 1/2 inch IPS Schedule 40 pipe is welded to the back side of
the plate to serve as a guide as it is inserted into the pipe flange shown in
Figure 3-9. The front of the flange has a 5 and 1/2 inch long piece of 2 and
1/2 inch square tubing. It is this square tubing which serves as the holder
for the pitot tube sleeve. The square tube is welded entirely around the
circumference while the 3 and 1/2 inch round pipe is simply tack welded at four
locations.
The pitot sleeve is illustrated in Figure 3-9. This is simply a 5 and
5/16 inch long, 2 and 1/2 inch diameter square bar which has holes for the
pitot tube and thermocouple wire tube. This is placed around the pitot tube
and the two halves are tack welded together. The pitot tube should move
freely through this sleeve. Gas flow leakage through the gap will be minimal
under moderate positive pressure conditions.
The mounting flange includes the enlarged bolt holes so that it is
possible to rotate the probe slightly in the event of cyclonic flow. There is
also a neoprene gasket to seal off any leakage around the mounting flange.
There are two alternatives for closing the modified stack sampling ports
when not in use. An insert as shown in Figure 3-10 can be used to completely
fill the recessed area. This is simply a 4 inch IPS Schedule pipe welded to a
blank 1/4 inch thick plate. This front plate has two 5/8 inch holes so that it
can be mounted on the protruding 1/2 inch bolts welded to the permanent port
body. At the end of the 4 inch port plug, there is a 3 and 5/8 inch diamter
1/4 inch plate which blanks off the end pointed toward the duct. In this way,
there is no recess to allow the build-up of solids and sludge. To prevent
corrosion of this pipe insert, an anti-seizing compound should be applied. For
severe corrosion conditions when gas temperatures are below 500 °F, the insert
can be constructed of teflon.
The second alternative is simply a 1/4 inch thick plate identical to that
shown in Figure 3-10. Instead of being welded to the 4 inch pipe insert, it
3-18
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SLEEVE
'-MODIFIED 3/8" STANDARD S-TYPE PITOTTUBE
— THUMB SCREW-SLEEVE RETENTION
MAXIMUM FOR TRAVERSE
PORT AND PITOT TUBE ASSEMBLY
PORT PLUG
PORT AND PLUG ASSEMBLY
Figure 3-10. Modified Stack Sampling Port and S-Type Pitot Tube
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NJ
O
2 1/4" DIA HOLE
1/4- 20 SQ.NUT
SPOT WELD-2 FLATS
3/8" DRILL TUBE
2 1/2 SO TUBE X .238 WALL
5/8 SLOTS
SPOT WELD
4 PL ACES-90 "APART
NOTE: STRAIGHTEN FLANGE AFTER
WELDING
3 1/2" IPS PIPE X .226" WALL
Figure 3-11. Pitot Tube Mounting Bracket
-------
is attached directly to the port. This provides an easily removed seal. How-
ever, it does not prevent materials from accumulating in the port recess.
The parts chosen to seal the port during nonuse must be provided by the
source. The mounting bracket and the mounting sleeve are brought by the in-
spector. Therefore, relatively few of these must be made. The total weight of
the mounting bracket and mounting sleeve are estimated at 10 pounds. While
this assembly greatly reduces the errors involved in pitot traverse and simpli-
fies traverses for other measurements, it does require a port which extends out
from the wall a distance of 11 inches. The is considerably greater than most
present ports. Whenever possible, the smaller port described in section 3.3.3
should be used.
3.4 Port Locations
This section illustrates the preferred locations for the various types of
measurement ports presented in Section 3.3. The control devices illustrated
in the following drawings represent most of the common types of commercially
available units.
3.A.I Duct Ports
The pitot tube ports (see sections 3.3.2 and 3.3.3) should be placed in
locations as far as possible from flow disturbances. On circular ducts which
are equal to or less than 6 feet diameter (inside dimensions), there should be
at least two pitot tube ports spaced 90° apart. On larger circular ducts it is
necessary to have A ports spaced 90° apart so that conventional pitot tubes can
be used. The number and spacing of pitot tube ports on rectangular ducts
should be consistent with the requirements of EPA Reference Method 2. Again,
it is necessary to include ports on both sides of the ducts if the width
exceeds 6 feet.
A possible location for ports on the outlet duct of a pulse jet baghouse
is shown in Figure 3-12. This has been located close to the ground to
minimize the cost of the ladder and access platform. However, it must be far
enough away from the fan to avoid flow disturbances caused by the duct elbow
and the inlet damper of the fan. In the plan view sketch on the left side of
Figure 3-12, it is apparent that there are two pitot tube ports spaced 90°
apart and a small I/A" port between these pitot tube ports. The small port
is to facilitate gas temperature, static pressure, and oxygen concentration
measurements. Similar pitot tube ports could be installed in the outlet
ductwork of most other types of air pollution control systems.
The sketch on the right side of Figure 3-12 illustrates the arrangement
of pitot tube ports in the stack. These are located A5° degrees from the
platform center line so that there is adequate clearance for both ports.
They should be located well upstream of the gas inlet to the stack. However,
they should not be so high in the stack that downmixing is possible. The
position shown in Figure 3-12.is the maximum height normally possible.
3.A.2 Port Locations for Fabric Filters
The types.of ports used on fabric filters include both the standard I/A"
port and the I/A" port with the extended tube. Good accessibility to the
3-21
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r-BAGHOUSE
PITOT TUBE PORTS
EXHAUST FAN
1/4" INSTRUMENT PORT
STACK
PITOT
TUBE PORTS^i
45
LOCATION OF PORTS
FOR INDUCED DRAFT FAN SYSTEM
ALTERNATE PORT LOCATION
Figure 3-12. Location of Ports on Outlet Duct of Fabric Filter
3-22
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port area is necessary so that it can be rodded out prior to the measurement
and so that accurate gas temperature measurements can be made.
3.4.2.1 Pulse Jet Fabric Filters - The locations for 1/4" instrument ports
for conventional top access pulse jet baghouses are illustrated in Figure 3-13.
There are two "clean" side ports which pass through the top shell of the
baghouse and terminate in the clean air plenum of the unit. Between these two
is another 1/4" port which extends down through the tube sheet. These ports
sense "dirty" side conditions. There is convenient access to these ports since
it is necessary to perform all service work from the roof. It is easy to rod
out the "dirty" side port since the extension tube is straight. They do not
present a trip hazard and do not present an obstacle to bag maintenance and
replacement. These ports must be located at a position which is opposite to
the direction which the hatches swing when opened. This varies from unit to
unit.
The only disadvantage of this location is the potential for burns on the
hand while removing the port caps on baghouses operating at elevated tempera-
tures. This problem is easily avoided by wearing gloves. The gloves are
necessary for other inspection activities. Therefore, this is not a burden
for regulatory agency personnel.
For pulse jet baghouses having "dirty" side access only, there must be a
platform near the access hatch. The standard 1/4" ports should be installed
above and below the tube sheet which is normally slightly above the top of the
access hatch. In fact, this is the location selected by manufacturers of
these baghouses. The only disadvantage of this location is that the
inspectors must exercise restraint when rodding out the "dirty" side port since
it is possible to puncture a bag near the port.
3.4.2.2 Reverse Air (Outside-to-Inside Flow) Fabric Filters - These units
often have a rotating cleaning arm in the clean air plenum. This precludes the
use of the extender pipe shown in the pulse jet baghouse sketch. The "dirty"
side port location must be below the elevation of the tube sheet, as shown in
Figure 3-14. This means that a small platform must be provided in the area of
the port. The "clean" side port can be cut through the top shell since this
will not interfere with the bag cleaning equipment. Since bags hang in the
proximity of the "dirty" side port, it is again necessary to rod out this port
carefully. It should be noted that the ladder to the top of the baghouse is
necessary for general maintenance. Only the small lower platform must be
added.
3.4.2.3 Shaker and Reverse Air (Inside-to-Outside Flow) Fabric Filters -
These fabric filters generally have a number of individual compartments. The
small ports must be placed on each of these, as shown in Figure 3-15. The
"clean" side port is the standard 1/4" fitting mounted on the exterior wall
above the tube sheet. It should be placed at elevation which is convenient
for using the portable instruments. The "dirty" side port must include an
extension tube which passes through the clean gas plenum and terminates below
the tube sheet. It must have a gas tight weld on the lower side of the tube
sheet to prevent gas- sneakage through gaps. A straight tube is used so that
it can be easily cleaned out before any measurement. The entire assembly is
oriented on a -60° angle so that the port cap does not extend into the normal
3-23
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GAS INLET-
ACCESS HATCHES-
1/4" INSTRUMENT PORTS
ACCESS HATCH
GAS OUTLET
GAS INLET-
GAS OUTLET
1
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TUBE SHEET
1/4" INSTRUMENT PORTS
1/4" INSTRUMENT PORT WITH
CROSS PLENUM PIPE
HANDRAIL
1/4" INSTRUMENT PORT WIT
CROSS PLENUM PIPE
Figure 3-13.
Instrument Port Location for Pulse Jet (or Plenum Pulse)
Baghouse
3-24
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REVERSE AIR
BLOWER
HAND RAIL
/4" INSTRUMENT PORT
1/4" INSTRUMENT PORT
1/4" INSTRUMENT PORT
CELL PLATE
1/4" INSTRUMENT PORT
FABRIC FILTER DUST COLLECTOR
REVERSE JET CLEANING TYPE
Figure 3-14.
Location of Ports on Reverse Air Fabric Filter
(Outside-to-Inside Flow)
3-25
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GAS OUTLET
COMPARTMENT-
GAS INLET
1/4" INSTRUMENT PORT
ELEVATION
SHAKER OR REVERSE AIR BAGHOUSE
l/4"-60 INSTRUMENT PORT
ENLARGED DETAIL
Figure 3-15. Location of Ports on Reverse Air and Shaker Fabric Filters
3-26
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walking area. As shown in the side elevation view, these ports are located on
each of the compartments in the unit. Not shown here are the pitot tube ports
which would be necessary on the inlet ductwork to this collector.
3.4.3 Ports for Electrostatic Precipitators
Ports should not be installed on or near the shells of electrostatic
precipitators. A high voltage arc to a probe could occur if the port were
close to the energized portion of the precipitator. Measurement ports can be
located only in the inlet and outlet ductwork or in the stack. All downstream
ports should be equipped with grounding taps and cables since the charged
particles passing the probes can result in very high static charges on these
probes.
In the very large majority of cases, there are adequate stack sampling
ports before the precipitator and in the stack. These should be used, if
possible. The modified port design illustrated in Figures 3-8 to 3-11 will
aid accurate pitot tube traverses and minimize the exposure to potentially
toxic pollutants.
3.4.4 Ports for Mechanical Collectors
Small ports should be installed above and below the "clean" side tube
sheet of multi-cyclone collectors. The platforms should allow safe access to
the ports. It is generally necessary to include 6" extension pipes on the
exterior of the unit to penetrate insulation around the mechanical collector.
The end of the pipe should resemble the port shown in Figure 3-3.
Pitot tube ports should be installed upstream and downstream of the unit
at locations where there is safe access. The downstream port should be
before the induced draft fan, if possible. The upstream port should be close
to the multi-cyclone collector inlet so that the measurements can isolate
air infiltration and gas flow resistance for only the collector and not other
common components such as economizers and air preheaters.
3.4.5 Ports for Wet Scrubbers
A combination of small 1/4 inch ports and pitot tube ports is used to
evaluate wet scrubber performance. The small ports are placed between all
beds and stages to measure static pressure changes across each. These are
also used before and after demisters to identify demister pluggage. The pitot
tube ports are located on the ductwork before and after the scrubber vessel.
They are used to measure gas flow rates, to evaluate scrubber vessel air
infiltration, and to conduct reentrainment tests.
3.4.5.1 Spray Tower Scrubbers - The inlet ductwork pitot tube ports should
be situated upstream of any spray headers in order to minimize droplet impac-
tion on the probes and to minimize pluggage of the ports. A parallel set of
small ports is provided along side the pitot tube ports so that some measure-
ments can be made without opening the larger ports. This is particularly
important when the unit is under positive pressure. The small ports do not
add any significant cost to the small platform assembly shown in Figure 3-16.
3-27
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LIQUOR INLET
DEMISTER
/4" INSTRUMENT PORT
PITOT TUBE PORT
1/4" INSTRUMENT PORT
l/4"-30° INSTRUMENT
PORT
CENTRIFUGAL CYCLONIC SCRUBBER
Figure 3-16. Location of Ports on a Spray Tower Scrubber
3-28
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There is another set of small ports located immediately upstream and
downstream of the demister. These provide a means of identifying demister
pluggage. Obviously, only one of these ports would be needed on a unit which
does not have a demister.
3.4.5.2 Packed Bed, Moving Bed and Tray_ Tower Scrubbers - Preferred port
locations for this large group of scrubbers is illustrated in Figure 3-17.
Small instrumentation ports are provided between each bed or tray and before
and after the demister. All of these are inclined 30° to facilitate drainage
from the port (see Figure 3-3). Pitot tube ports are present in the ductwork
before and after the scrubber. Due to the small scale of most systems, a
single port is normally adequate and this minimizes the cost of the top plat-
form. For large systems, two ports spaced 90° apart should be used.
3.A.5.3 Gas-Atomized Scrubbers - A typical venturi scrubber is shown in
Figure 3-18. The small measurement ports are installed Immediately upstream
of the point of liquor injection, on the horizontal duct leading to the
cyclonic chamber, and above the demister. In this case, the static pressure
drop can be determined using the middle port and the port above the demister.
The pressure drop across the throat can be estimated using the initial port
and the middle port.
It is important that the middle port be in the middle or upper portion of
the horizontal duct. This is an area very prone to port pluggage due to the
turbulent motion of the liquor droplets coming from the venturi throat. There
is also a layer of liquor flowing on the sloped bottom of this duct.
Pitot tube ports similar to those illustrated in Figure 3-4 should be
installed in the ductwork upstream and downstream of the venturi scrubber
vessel. These should be located as far from flow disturbances as possible.
The outlet duct ports should be located before an induced draft fan. However,
if this is not possible, the stack ports can be used.
Figure 3-19 illustrates the pitot tube ports which are appropriate for
most gas-atomized scrubbers. There are two separate ports spaced 90° apart,
each of which is 45° off the center line of the platform. This allows access
to both ports with an economical platform.
3-29
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PITOTTUBE PORT
1/4" INSTRUMENT PORT
PITOT TUBE PORT
1/4" INSTRUMENT PORT
DEMISTER
1/4" INSTRUMENT
PORTS (3)
IMPINGEMENT TRAYS
{3 STAGES SHOWN)
SPRAY MANIFOLD
IMPINGEMENT TRAY TYPE SCRUBBER
Figure 3-17.
Location of Ports on Packed Bed, Moving Bed and Tray Type
Scrubbers
3-30
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1/4" INSTRUMENT PORT
1/4" INSTRUMENT PORT
VARIABLE VENTURI
1/4" INSTRUMENT PORT
DEMISTER
HIGH ENERGY VENTURI SCRUBBER
Figure 3-18. Location of Ports on .Gas-Atomized Scrubbers
3-31
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LJ
T
IT IT
1/4" INSTRUMENT PORT-
r-PITOT TUBE PORTS (2)
4-
DEMISTER
1/4 INSTRUMENT PORT
ORICLONE TYPE VENTURI SCRUBBER
Figure 3-19. Location of Ports on Inlet Duct to Gas-Atomized Scrubber
3-32
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REFERENCES
1. Richards, J. and R. Segall. Wet Scrubber Performance Evaluation. EPA
Publication No. 340/1-83-022. September, 1983.
2. Richards, J. and R. Segall. Advanced Inspection Techniques Workshop,
Student Manual (Draft). Report to the U.S. Environmental Protection
Agency under Contract No. 68-01-6312. May, 1984.
3. Richards, J. Chapter 8, Baseline Inspection Techniques. In: Air
Compliance Inspection Manual (Draft). Report to U.S. Environmental
Protection Agency under Contract No. 68-02-3960. September, 1984.
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