Series 1 - 300 - 7/82
^f W
.0)
8 EVALUATION OF STATIONARY
.2
"a.
o
O
o
o
3
O
(0
O
SOURCE PERFORMANCE TESTS
Special Problems and Concepts
US ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF AIR, NOISE AND RADIATION
STATIONARY SOURCE COMPLIANCE DIVISION
WASHINGTON DC 20460
CM
8 US ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF AIR, NOISE AND RADIATION
STATIONARY SOURCE COMPLIANCE DIVISION
WASHINGTON DC 20460
-------
DRAFT
EVALUATION OF STATIONARY
SOURCE PERFORMANCE TESTS
Special Problems and Concept
Prepared by
PEDCo Environmental, Inc.
505 S. Duke St., Suite 503
Durham, North Carolina 27701
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF AIR, NOISE AND RADIATION
STATIONARY SOURCE COMPLIANCE DIVISION
WASHINGTON, D.C. 20460
July 1982
-------
INTENDED PURPOSE
This is not an official policy and standards document. The opinions,
findings, and conclusions are those of the authors and not necessarily those
of the Environmental Protection Agency. Every attempt has been made to repre-
sent the present state of the art as well as subject areas still under eval-
uation. Any mention of products or organizations does not constitute endorse-
ment by the United States Environmental Protection Agency.
This document is issued by the Stationary Source Compliance Division,
Office of Air Quality Planning and Standards, USEPA. It is for use in work-
shops presented by Agency staff and others receiving contractual or grant
support from the USEPA. It is part of a series of instructional manuals
addressing compliance testing procedures.
Governmental air pollution control agencies establishing training pro-
grams may receive single copies of this document, free of charge, from the
Stationary Source Compliance Division Workshop Coordinator, USEPA, MD-7,
Research Triangle Park, NC 27711. Since the document is specially designed
to be used in conjunction with other training materials and will be updated
and revised as needed periodically, it is not issued as an EPA publication
nor copies maintained for public distribution.
iii
-------
CONTENTS
Page
Section A. Unconfined Flow (Lecture 301) A-l
1. Procedures for sampling sources not confined to
a duct A-3
2. Slides A-9
Section B. High Temperature Sources (Lecture 302) B-l
1. Problems associated with sampling high tempera-
ture sources B-3
2. Slides B-9
Section C. High Moisture Content (Lecture 303) C-l
1. Sampling methods for stacks with high moisture
content C-3
2. Slides C-17
Section D. Low Velocity Flow (Lecture 304) D-l
1. A survey of commercially available instrumenta-
tion for the measurement of low-range gas
velocities D-3
2. Velocity measurements at low flow rates D-21
3. Slides D-29
Section E. Cyclonic Flow (Lecture 305) E-l
1. Isokinetic particulate sampling in nonparallel
flow systems-cyclonic flow E-3
2. Techniques to measure volumetric flow and partic-
ulate concentrations in stacks with cyclonic flow E-25
3. Slides E-35
Section F. Condensibles (.Lecture 306) F~l
1. Condensibles, reactive compounds,. and effect of
sampling train F-3
2. Effects of sampling train configuration and
analytical procedures on particulate catch F-10
3. Slides F-27
Section G. Fluctuating Velocity (Lecture 307) G-l
1. Slides G-3
v
-------
CONTENTS (continued)
Page
Section H. Soot Blowing (Lecture 308) H-l
1. Particulate source sampling at steam generators
with intermittent soot blowing H-3
2. Slides H-23
Section I. Sampling Port Location (Lecture 309) 1-1
1. Access problems 1-3
2. Guidelines for sampling in tapered stacks 1-27
3. Sampling in ducts less than twelve inches in
diameter 1-32
4. Slides 1-47
Section J. Intermittent Process Operation (Lecture 310) J-l
1. Slides j-3
-------
SECTION A. UNCONFINED FLOW
Subject Page
1. Procedures for sampling sources not confined to a duct A-3
2. Slides A-9
A-l
-------
PROCEDURES FOR SAMPLING SOURCES NOT CONFINED TO A DUCT
by
Walt Smith
INTRODUCTION
Most sources of air pollution emissions travel through stacks or duct
work on their way to the atmosphere from the point of generation. Conven-
tional source test methods are based upon this fact. Occasionally, though,
an unconfined source may be encountered. Adapting current methods or
devising a new method to handle such a source raises a multitude of ques-
tions concerning the method's equivalency with accepted procedures. A
simpler approach entails modifying the source so that approved methods may
be employed.
CONFINING A SOURCE
When no flue or ductwork is present at a source, a temporary or permanent
flue should be affixed if at all possible. Care should be taken that an
effective seal is achieved at the interface between flue and source. Sheet
metal is a good material for the extension, due to its resistance to high
temperatures, its rigidity and its relatively light weight. Plywood is often
employed when high temperature is not a factor. Some examples of temporary
flues are shown in Figure 1.
In order to conform to EPA's Method 1 guidelines, the extension should
have a length equal to about ten times its own diameter. Obviously, the
smaller the diameter the more manageable the apparatus becomes. A lower
limit of about 18" in diameter should be observed, however, so that flue gas
acceleration due to probe blockage will not become a factor during sampling.
Exit velocity of the effluent must also be considered, as S type pi tot tubes
are unreliable at flow significantly below 600 feet per minute. If possible,
the flue diameter should be chosen such that this minimum velocity condition
is met.
If a high degree of turbulence is expected, as with an exhaust fan,
straightening vanes can be installed as a built-in feature of the extension.
As an added dividend, the vanes will lend rigidity to sheet-metal cyclinders.
A-3
-------
>2d
Ports
'&s
sLx^xi'
Straightening
Vanes (optional)
Ports
Seal Carefully
Carefully
Existing Structures
Temporary Extensions
Examples of temporary ducts for sampling unconfined sources
-------
Sampling ports can be cut ahead of time if their location are known in
advance.
WHEN CONFINING ISN'T PRACTICAL
The foregoing discussion presumes that the installation of a flue at
the point of emission is a practical matter. Some sources are too large or
irregular for such modification. One approach to sampling these sources is
to confine a small portion of the flow at a time, rather than the entire
volume.
In one instance, an open-faced grain dryer was to be sampled for partic-
ulate emissions. The geometry of the exit grating was such that total con-
finement was impractical (Figure 2). A cylindrical "stack" was affixed to
the end of a standard Method 5 sampling probe, such that the nozzle was
aligned along the axis of the eyeliner (Figure 3). The face of the dryer was
partitioned at the centroids of these areas. Placement of the open-ended
cylinder directly against the screen covering the face of the dryer blocked
out the effects of ambient air motion.
When a stack extension is not feasible and a method such as the one out-
lined here must be resorted to, all.equipment and procedures used in sampling
and analysis should be discussed with and agreed upon by appropriate repre-
sentatives of the firm being tested and the regulatory agency involved.
A-5
-------
o
00
o
no
•
Sketch of an open faced grain dryer
showing multi-faceted exhaust area.
A-6
-------
Open-ended Cylinder Attached
To Probe For Sampling Uncon-
fined Sources.
A-7
-------
SLIDE 301-0
NOTES
UNCONFINED EMISSIONS
SLIDE 301-1
SOURCES
1. Pressurized Baghouses
2. Roof Monitors
3. Open-faced Grain Dryers
SLIDE 301-2
A-9
-------
SLIDE 301-3
NOTES
SLIDE 301-4
(picture of grain dryer)
SLIDE 301-5
SAMPLING CONDITION I
CONFINE THE SOURCE
o Obtain effective seal at
interface between flue and
source
o Determine if modification
affects emissions from source
A-ll
-------
SLIDE 301-6
RECTANGULAR UNCONFINED SOURCE
tijj| EXISTING STRUCTURES
I J TEMPORARY EXTENSIONS
NOTES
SLIDE 301-7
CIRCULAR UNCONFINED SOURCE
mm) EXISTING STRUCTURES
I 1 TEMPORARY EXTENSIONS
STRAIGHTENING
VANES
(OPTIONAL)
A-13
-------
SLIDE 301-8
NOTES
SLIDE 301-9
SAMPLING CONDITION I I
CONFINING SOURCE IMPRACTICE
Equipment and procedures used
in sampling and analysis should
be agreed upon by representatives
of:
o organization being tested
o regulatory agency involved
SLIDE 301-10
A-15
-------
SLIDE 301-11
NOTES
GRAIN DRYER
30-80 ft
SLIDE 301-12
CYLINDER ATTACHED TO PROBE
A-17
-------
SECTION B. HIGH TEMPERATURE SOURCES
Subject Page
1. Problems associated with sampling high temperature
sources B-3
2. Slides B-9
B-l
-------
PROBLEMS ASSOCIATED WITH SAMPLING HIGH-TEMPERATURE SOURCES
by
Jim Peeler
Testing teams are encountering increasing numbers of high-temperature
sources. Municipal incinerators and gas turbines, for example, usually emit
effluents well in excess of 750°F; temperatures 2000°F have been encountered
on occasion.
Standard, commercially available EPA Method 5 train sampling equipment
is not designed for use at stack temperatures much above 700°F. Clearly,
modifications are required when temperatures higher than this are expected.
THE PROBE AND PROBLEMS
Most problems arising from high-temperature sources involve the one
element of the train whch is in constant, direct contact with the gas stream—
the probe. A standard EPA shielded probe is unsatisfactory above 800°F, for
a variety of reasons.
An early problem in high-temperature sampling was achieving a seal be-
tween the nozzle and the probe lines which would remain air-tight at the
sampling temperature. Viton V rings and Teflon seals are useless at temp-
eratures above 450°F, necessitating the use of asbestos string as a gasket
material. Asbestos does not have the resiliency to fill the gap which opens
as the glass probe liner and metal sheath expand at different rates. In addi-
tion, asbestos is characterized by a lack of cohesion. Stray filters may
find their way into the train and contaminate the particulate sample. Despite
these drawbacks, asbestos string can be, and has been, used with success.
At temperatures above 800°F, the difference between the coefficients of
thermal expansion of glass and stainless steel begins to have a large effect.
The probe sheath may bend as it expands, due to uneven heating and/or the
presence of attachments such as pi tot lines, causing glass liners to break.
Another frequently encountered problem is breakage of the glass liner near
the nozzle connection. As the sheath expands, the liner becomes unseated
at this connection; following the test, probe cooling and contraction causes
breakage as the liner fails to reseat itself.
B-3
-------
Use of stainless steel (or other alloy) liners is one solution to thermal
expansion problems. However, metal probe liners introduced a major problem
of their own. At temperatures sufficiently high to require their use, there
is almost a certainty that substances in the effluent gas will react with
sample-exposed metal surfaces. Solid waste incinerators, for example, can be
expected to emit large amounts of chlorides from plastic materials.
In general, the standard EPA probe is limited to applications below 750°F.
The stainless steel probe sheath will expand and distort above this temperature.
Softening of the nozzle and pitot openings may affect their calibrations, as
well.
THE PROBE AND SOLUTIONS
Given the fact that standard probes are unusable at sampling temperatures
above 750°F, what sort of probe will do the job? There are two basic approaches
to fabricating high-temperature probes: 1) devise a cooling system which will
allow use of standard stainless steel and/or glass components or 2) construct
the probe of materials able to withstand the temperatures expected.
Probe cooling is accomplished by constructing a jacket around the probe
and circulating a liquid or gas through it. Coolants which have been used
include ambient air, water, and steam. Gaseous coolants are usually vented
into the stack; liquids are recirculated.
Cooled probes present the immediate disadvantage of requiring support
equipment. This is usually expensive and bulky, and will require maintenance.
Malfunction of the cooling system during a run will necessitate a delay at
best, and perhaps abandonment of.the test.
When liquid coolants are used, the formation of vapor pockets inside
the jacket must be considered. Pop-off valves should be installed, and the
probe should be aligned during operation so that gases can be vented as needed.
Otherwise, rupturing of the jacket is a very real possibility.
Care must be taken with regards to the placement of gas coolant vents or
liquid coolant pop-off valves near the nozzle end of the jacket. Venting must
not bias results obtained from the pitot lines or the thermocouple, and the
sample entering the nozzle must not be diluted.
Even with an efficient cooling system in operation, some softening of
the outside surface of the jacket can occur. Similarly, the protruding tips
B-4
-------
of the nozzle and pitot tubes may be sugject to softening. While these
eventualities are unlikely, they should not be dismissed out of hand.
Thus far, the disadvantages of cooled probes which have been discussed
are not prohibitive problems. Rather, they are drawbacks which can be sur-
mounted or tolerated. However, there are other problems introduced by
cooled probes which are not as easily dismissed.
The nozzle of a cooled probe will be at a lower temperature than the
stack gases. Even if the nozzle itself is not directly Involved in the
cooling, one must consider conduction to the cooler parts of the probe. This
being the case, a question arises as to the effects of a "cold" nozzle on
stack gas flow around the nozzle tip. Will contraction of gases in and
around the nozzle be as sufficient to affect isokinetics? If so, by how
much? Will the pitot openings be similarly affected? These questions need
further study.
Another adverse effect can be predicted with greater certainty. With
the probe liner cooled significantly below the temperature of the gas sample,
condensation in the probe must be expected. This complicates cleanup as well
as decreasing the assurance of obtaining representative data.
Despite these questions regarding the validity of the data obtained,
cooled probes have been used successfully in high-temperature applications;
air-cooled probes have been used at temperatures of at least 1000°F, water-
cooled probes at 1700 F, and a steam-cooled probe was effective at well over
2000°F. Steam offers an advantage over other coolants in that sample gases
will not be overcooled on their way to the filter, thus satisfying Method 5
requirements for probe temperature.
As an alternative to complicated cooling systems, one may instead con-
struct the probe using materials which will withstand high temperatures.
Special alloys, as mentioned before, may react with stack gases, and to a
largely unpredictable extent.
Probes constructed of quartz ($102) have been used successfully, though
quartz has its own drawbacks. These probes are unsheathed, and the nozzle
is an extension of the quartz tubing, making a one-piece "L" shaped construc-
tion.
Quartz is considerably harder than glass—and considerably more brittle.
Extreme care must be taken in handling the probe, as there is no protective
B-5
-------
sheath. Contact with liquids, such as raindrops, can suddenly shatter a hot
probe. Moreover, probe lengths greater than about five feet are impractical.
One-piece construction dictates a fixed nozzle size of a given probe.
Absence of the stainless steel sheath means that pi tots, thermocouples, etc.
cannot be directly attached to the probe. Standard S-type stainless steel
pitot tubes can be used separately to get "quicker" readings at the nozzle
location.
Quartz probes should be about a foot longer than necessary for the tra-
verse of the duct. This will leave part of the probe exposed to ambient
conditions at all times so that the sample will be cooled somewhat. Care
should still be taken that the filter is not burned.
Thus, each approach to fabricating a high-temperature probe nas numerous
disadvantages. Which approach to use to solve a given high-temperature problem
will be dictated by the particulars of that problem and by the relative merits
of the two types of probes.
Cooled probes offer the principal advantage of durability. Length is
not severely limited; a water-cooled probe 20 feet in length has been used
successfully. Breakage is not an overriding concern. Cooling of the sampled
gases also ensures that the filter temperature can be maintained within operat-
ing limits. Sensing lines can be included inside the cooling jacket, so contin-
uous velocity and temperature readings are not a problem.
In the case of quartz probes, perhaps the most significant advantage is
the assurance that the effluents will not react with the probe during sampling.
This is a major consideration at high temperatures. Incinerators represent a
large number of high temperature sources, and caustic substances in their ef-
fluents must be expected.
The absence of a cooling system with its attendant pump, tubing, connec-
tions and heat exchanges, simplifies the sampling process and precludes me-
chanical failure. Not having to deal with a heavy, bulky probe is also a con-
sideration.
Condensation in the probe will not be a probem with an uncooled quartz
probe. Cleanup is also simplified considerably. There are no leak problems,
as the probe and nozzle are one piece. Gases are not in danger of being
cooled below 250°F, a situation which may happen with cooled probes and which
violates Method 5 guidelines. Heat expansion and possible distortion of the
probe and nozzle are no longer problems.
B-6
-------
MISCELLANEOUS PROBLEMS
Certain hazards and problems inherent in high-temperature sampling must
still be dealt with regardless of the type of probe selected. It is espe-
cially important that these be anticipated, and advance preparations made to
lessen their effects.
If the pitot lines are not included in a cooling jacket, discrete veloc-
ity measurements may be necessary to avoid sagging of stainless steel pitot
tubes. A thermocouple can be attached to the pitot tubes also, and the assembly
hand-held in the stack just long enough to get reliable readings.
Heat radiated directly from the process heat source will affect thermo-
couple readings if the source is within line-of-sight of the sampling location.
Opaque shielding around the hot junction will guard against erroneous high
readings.
Sampling teams should also be prepared to deal with an abnormally hot
ambient environment. Conditions around the duct or stack should enter into
the selection of the sampling site (Method 1, Section 2.1). The impinger ice
bath and other equipment may need shielding from the stack wall. Asbestos
panels may be useful as insulation material around the work area. Fans, plenty
of drinking water, and salt tablets could come in prove quite useful for per-
sonnel welfare.
CONCLUSION
High-temperature stack sampling is not impossible; it is merely difficult.
But the problems can be solved and the hazards avoided with the proper equip-
ment, thoughtful preparation, and a liberal dose of ingenuity.
B-7
-------
SLIDE 302-0
HIGH TEMPERATURE SOURCES
NOTES
SLIDE 302-1
HIGH TEMPERATURE SOURCES
o Municipal Incinerators
o Gas Turbines
o Glass Furnaces
o Other Sources
SLIDE 302-2
B-9
-------
SLIDE 302-3 NOTES
THE PROBE
(Unsatisfactory above 800°F)
PROBLEMS
o achieving airtight seal
between nozzle and probe liner
o breakage of glass probe liner
due to different coefficients
of thermal expansion between
probe liner and stainless
steel jacket
Note: Teflon ferrels and Viton-O rings must not be
used at temperatures exceeding their softening point.
Also, the organic material in the glue of the tape
used to wrap the heating wire on the probe can burn
off and bias the test. The probe should be free of
tape since there is no need to heat the probe.
SLIDE 302-4
SLIDE 302-5
METAL PROBE LINERS
At high temperatures, reactive
substances in effluent gas will
react with exposed surfaces of
metal liners
High effluent gas temperatures
could cause softening of the
nozzle and pitot tube
B-ll
-------
SLIDE 302-6
NOTES
SLIDE 302-7
CONSTRUCTION OF HIGH
TEMPERATURE PROBES
Devise a cooling system
allowing use of standard
material. Coolant may be:
o ambient air
o water
o steam
Construct probes of materials
which can withstand high
temperatures. Materials may
be:
o special alloys
o quartz
(SI02)
B-13
-------
SLIDE 302-8
SLIDE 302-9
NOTES
USE OF PROBE COOLING TECHNIQUES
ADVANTAGES
0 durability of probe
0 unrestricted probe length
0 cooling of gases ensures that filter
temperature can be maintained within limits
0 sensing lines can be included within cooling
jackets
DISADVANTAGES
0 requires structural support equipment
0 vapor pockets may form which may rupture
jacket
0 venting may bias results or dilute sample
0 cooler nozzle/pitot tube gives variable
effects on stack gas flow
0 consdensation in probe
SLIDE 302-10
B-15
-------
SLIDE 302-11
NOTES
SLIDE 302-12
QUARTZ PROBE
ADVANTAGES
o effluents will not react with
probe during sampling
o absence of bulky cooling system
o no condensation in probe
o probe and nozzle are one piece
eliminating leaks
o no heat expansion and distor-
tion of probe and nozzle
o gases not cooled below 250°F
SLIDE 302-13
DISADVANTAGES
o very brittle/no protective
sheath
o fixed nozzle size
o pitot tube and thermocouple
cannot be attached
o probe lengths greater than
5 ft are impractical
o potential for burning the
filter
B-17
-------
SLIDE 302-14 NOTES
MISCELLANEOUS SAMPLING
PROBLEMS
o sagging of stainless steel
pitot tube
o heat radiation from process
affects temoerature measurement
B-19
-------
SECTION C. HIGH MOISTURE,CONTENT
Subject Page
1. Sampling methods for stacks with high moisture content C-3
2. Slides C-17
C-l
-------
SAMPLING METHODS FOR STACKS WITH HIGH MOISTURE CONTENT
by
Robert A. Estes
INTRODUCTION
In most sampling situations, EPA Method 5 is prescribed as
the accepted method for measuring particulate emissions. However,
if the moisture content of the sampled gas is significantly
above 50%, Method 5 may give unreliable results or become com-
pletely unworkable. Examples of such high-moisture sampling
situations are ammonium nitrate prilling facilities, lime-
hydrators, evaporators, and coke oven quench towers. The purpose of
this paper is to present the three most noted approaches to
sampling high moisture stacks. These methods were developed by
JACA Corporation, the EPA, and Entropy Environmentalists.
BACKGROUND
Before dealing with the individual methods, some background
information is in order. Method 5 is generally becoming the
most widely accepted method for determining particulate emission
rates. Proper use of Method 5 depends upon the relationship
established by the nomograph equation:
AH = D"
1TK C
P P
4K
m
2
Md(1-Bws)2
Md(1-Bws> + ""W
T P
m s
T P
s m
Ap
CD
This equation relates the pressure differential across the pitot
tube (used to determine local stack velocity) to the pressure
drop across the orifice meter (used to determine sampling rate)
in maintaining isokinetic sampling conditions. With a given set
of equipment and stack conditions that can be assumed constant,
Equation (1) can be reduced to the form:
AH = KAp (2)
The pressure drop across the orifice meter is measured after the
sample gas has been filtered and the moisture removed by the
impingers and the silica gel. The remaining dry gas is metered to
determine the total volume sampled and to determine overall
C-3
-------
isokinetics by post-test calculations.
In stacks with a low moisture content, the percent moisture
may be provided by plant data, determined by Method 4, or
simply estimated. The effect of an error in determining mois-
ture at low moisture levels is relatively small. However, as
the moisture content increases, the effects of error increase.
Eventually, a point may be reached where a 2% error (or a 2%
change in the moisture content from the initial value) will
result in a sampling rate outside of the allowed ± 101 range
from 100% isokinetic sampling. This is due to the non-linearity
of the correction factor for water removal found in the nomo-
graph equation and represented by the term:
)2
ws
Md(1-Bws> + 18Bws (3)
found in Eq.(1).
As sample gas from a stack at nearly 100% moisture passes
through the impingers (condenser) of a Method 5 train, the
majority of the sample is left behind as condensed water. There
is very little dry air exiting the impingers. In a standard
Method 5 train, the impingers are followed by the pump, control
valves, dry gas meter, and orifice flow meter. With only a
small fraction of the gas volume entering the nozzle being
passed through these components, three problems become apparent.
First, the low flow rate through the orifice may give rise
to erroneous readings. An orifice meter only gives linear
results over a given operating range. Low gas flow can fall
outside of the operating range over which the orifice was
calibrated. Second, with very little gas passing through the
pump and control valves, the sampling rate cannot be accurately
controlled. Finally, even if the sample contains enough dry
gas to enable accurate orifice readings and flow control, fluc-
tuations in the moisture content of the stack gas will still
upset isokineticity. In cases where there is a large variation
C-4
-------
in moisture content, such as during a coke oven quenching
operation, measurement and control of the dry gas fraction of
the total sample volume will be insufficient to detect and
make allowances for the fluctuations in the total gas flow
rate (including water vapor) through the nozzle. Should post-
test calculations demonstrate 100 ±10% isokinetics in spite
of these uncontrolled fluctuations, the fact that the sampling
rate was substantially over-and under-isokinetic at various
times during the sampling run could void the test results.
Due to these problems a standard Method 5 particulate
sampling train is inappropriate for sampling effluents with
a high moisture content, meaning those significantly above
50% water vapor by volume.
A COMMON APPROACH
The common approach to these problems is the placement of
the orifice meter before the impingers, where condensation of
the moisture occurs. This allows the total sample volume to
be passed through the orifice. The significance in this place-
ment is that the moisture content does not have to be known
beforehand, nor do changes in moisture content affect the
isokinetic sampling rate. The mathematical significance of
this orifice placement is the elimination of the correction
factor (Eq. 3) in the standard EPA Method 5 nomograph equation,
yielding the relationship:
fs. AP (4)
p
31
The above equation is the isokinetic relationship between the
pressure differential across the pitot tube and the pressure
drop across the orifice meter, upon which all three high mois-
ture methods are based.
JACA CORP. METHOD FOR PARTICULATE SAMPLING OF HIGH-MOISTURE STACKS
The design chosen by JACA to measure particulate matter
in high moisture stacks resembles a Method 5 train. The major
exception is that the orifice meter is placed in the heated box
C-5
H -
D4
n
TTK C
P P
L4Km.
2 T
m
T
s
-------
with the filter assembly. The orifice design was chosen to
encompass typical sampling volumetric flow rates (centered
around .7 acfm). JACA concluded that the risks of orifice
fouling, and thereby of change in the calibration coefficient,
were high enough to warrant placement of the orifice after the
filter. The advantage of this placement is the prevention of
condensation at the orifice (hot box temperature: 250 F) and
protection from particulate fouling of the orifice. The dis-
advantage of this placement is that the meter pressure (Pm) is
not constant as in Method 5 because of the changing pressure
drop induced by the glass frit and particulate build-up on the
filter. The absolute pressure at the meter must be monitored
and compensated for in the isokinetic equation (Eq.4).
A technical paper was presented at the June 20-24, 1977
annual APCA meeting by Uday Patankar and Wayne Ott of the JACA
Corporation on the use and performance of the JACA method. The
authors acknowledged two problems which occurred during sampling
on their first test (a lime-hydrator). First, a great deal of
condensation occurred in the manometer lines from the orifice.
It was felt that much of this had to do with the incorrect
sizing of the nozzle, leading to excessively high flow rates.
Second, controlling the sampling train to match the prescrubed
isokinetic sampling rates was difficult. The sampling team
had to settle for maintaining an average flow rate. Fortunately,
the velocity profile of the stack was fairly flat and allowed
the test to maintain an overall +J10% isokinetic sampling rate.
A second test was performed on a concentrator/evaporator
for diagnostic purposes. It was felt that the solution to both
the problems encountered previously hinged mainly upon attaining
more manageable flow rates by use of a smaller nozzle size. The
difference in the total gas volume sampled by the smaller nozzle
was balanced by longer sampling times at each point along the
traverse. Also, U-tube condensate traps were placed on the
manometer lines to allow accurate manometer readings to be ob-
tained. These traps could be periodically emptied as needed.
C-6
-------
JACA reported no significant problems on the second test.
The sampling was reported to be controllable and post-test
calculations indicated that the ± 10% overall isokinetic require-
ment had been met.
EPA METHOD FOR PARTICULATE SAMPLING OF HIGH-MOISTURE STACKS
The EPA method was developed for use in sampling ammonium
nitrate production facilities for the determination of particulate
(ammonium nitrate) emissions from neutralizers, evaporators, and
prilling towers. However, this method should be able to sample
most high moisture stacks or those with wide variation in stack
gas moisture content with relatively few problems. (This method
2
is currently under technical review by EPA.)
The EPA method incorporates an in-stack orifice of a third
generation design which allows interchangeability of the orifice
plate. A venturi design was considered because it has the same
operating characteristics as an orifice. However, an orifice
is easily fabricated and can be changed to allow for different
flow rates.
The first-generation design incorporated the orifice in the
sampling nozzle. However, this design was unusable in standard
three-inch ports. It also showed different calibration co-
efficients depending on whether dry room air or a flowing stream
was used in the calibration procedure. The source of this problem
was not determined, though it was felt that the proximity of the
nozzle to the orifice was a contributing factor. The second
generation design placed the orifice meter between the nozzle
goose-neck and the probe. The present third-generation design
provides an easier way of accomodating different flow rates by
changing the orifice plate rather than changing the entire meter
assembly as in the second-generation meter. In the second and
third generation designs no significant difference was found in
the orifice coefficient when calibrated with dry room air or a
flowing stream.
C-7
-------
Since the sampling train is designed to sample ammonium
nitrate, the design takes advantage of the hygroscopic nature
of ammonium nitrate by capturing it in the impinger water.
A filter at 250° would tend to allow ammonium nitrate to pass
through. Thus, the filter is placed before the impinger con-
taining the silica gel. The probe is heated to prevent conden-
sation prior to the impingers.
The in-stack orifice meter is not heated and thereby samples
at stack conditions. The isokinetic sampling equation now
becomes:
2
AH = D
4
n
UK C
P P
4K
m
Ap (S)
Problems with controlling the sampling rate and condensation of
moisture in the manometer lines did occur, though not as acutely
as experienced with the JACA Method.
The EPA method has only been used in short 20-30 minute
diagnostic runs. However, no major problems are foreseen if this
method is approved for use at ammonium nitrate production facilities
With minor modifications, this method should be usable in most
other sampling situations where high moisture content is encountered
ENTROPY ENVIRONMENTALISTS HIGH MOISTURE PARTICULATE SAMPLING METHOD
The method developed by Entropy Environmentalists, Inc. has
been used successfully at an ammonium nitrate production facility.
The sampling train has been designed with the .flexibility to meet
any sampling situation encountered by allowing use of either an
orifice or venturi meter (in high particulate loadings), and an
option in filter placement dependent upon the source tested. The
meter, however, is not as easily interchangeable as the orifice
in the EPA method.
The Entropy method incorporates the orifice meter in the
heated filter box, followed by a sampling valve. Under circum-
stances where a non-hygroscopic particulate is encountered in a
C-8
-------
high moisture stack, the filter would be placed between the
orifice and the sampling valve. This would allow particulate to
be defined as in Method 5: that which can be captured on a
specified filter type at 250°F. The advantage to having the
orifice in front of the filter assembly is that filter loading
and the glass frit have no effect on meter pressure, which remains
constant and does not require monitoring. The disadvantage is
that precautions must be taken to prevent orifice fouling, which
would change the orifice calibration. As mentioned above, a ven-
turi may replace the orifice since it would tend to foul less and
has the same general operating characteristics. Another alterna-
tive is to place a coarse filter of glass wool before the orifice,
which would protect the orifice and not affect meter pressure. In
situations where particulate loadings are exceptionally high, both
a coarse filter and venturi meter could be used.
The Entropy method employs a sampling valve in the hot box,
before condensation takes place in the impingers. This allows
for positive flow control of the total sample rather than just
control of the smaller amount of dry air leaving the impingers.
Since condensation in the manometer lines was seen to be a
common problem, a system utilizing solenoid operated 3-way T-
valves connected to the manometer lines \vith a small pressurized
air supply was utilized to clear the lines periodically. The
volume of air thus introduced into the sample line is insignificant
when compared to the total sample volume.
PROBLEMS COMMON TO ALL THREE METHODS
When sampling sources with high moisture content, a problem
which must be considered is the possibility of entrained water
droplets. Generally, sources of high moisture content will have
sampling conditions of approximately atmospheric pressure and
temperatures above 220°F. This is high enough above saturation
conditions that water droplets should not pose any problem.
However, as saturation conditions are approached, special care
must be taken.
C-9
-------
If water droplets are encountered when sampling using Method
5 the sample gas stream is usually assumed saturated, and wet
bulb/dry bulb measurements are taken to determine the saturated
water volume. Any excess water captured must be accounted for
as entrained water droplets. Saturated volumes from wet bulb/
dry bulb data may be found by psychrometric charts or by partial
pressure calculations. This procedure cannot be applied to any
of the high moisture methods.
Water droplets that enter the nozzles of any of the moisture-
method sampling trains will cause a problem with the isokinetic
sampling rate. Fouling of the orifice would also be a problem
for the EPA method. The water droplets would vaporize in the probe
and hot box of the JACA and Entropy methods, affecting the iso-
kinetic sampling rate. This effect would not be obvious from post-
test calculations, because total volume sampled and total water
captured in the impingers are used to determine the overall
isokinetics. The sampling would take place under-isokinetically
though calculations indicate otherwise. A way has not yet been
developed for these high moisture methods to sample in situations
where both high moisture content and entrained water droplets are
encountered? Fortunately, most high most high moisture processes
are designed to prevent condensation.
A second problem common to all the high moisture methods is
condensation in the manometer lines. Diffusion is the initial
driving force for placing water vapor in the manometer lines.
Water vapor changes its volume approximately 1600 times in con-
densing, and the condensation thereby creates a vacuum. This
draws in more water vapor, which condenses and continues the cvcle.
It would seem that this problem may be more severe in the EPA
method because of the long manometer lines running along the probe
from the in-stack orifice. However, this problem did not appear
severe in the test runs performed. In any case, the manometer
lines must be "running uphill" or incorporate a c.ondensate trap
to prevent condensed water vapor from running into the manometers.
A means for periodically clearing the lines should also be included.
C-10
-------
Another problem can arise if the ice around the impingers
is allowed to melt completely. If the temperature in the last
impinger rises above 90°F, the silica gel will saturate quickly.
The high rate of condensation in the impingers releases a great
amount of heat, consuming a great deal of ice. The remedy is
to have plenty of ice on hand and to monitor the impingers closely
draining water as necessary, or perhaps adding salt, to keep the
exit gas temperature around 70° F or less.
The JACA method is intended to handle all sampling situations
of high moisture content with one train design, while the Entropy
method allows flexibility in filter placement and meter type, which
is dependent upon sampling requirements and source type. The EPA
method, with certain modifications, should be usable in sampling
situations other than ammonium nitrate production facilities.
The Entropy design is the only one capable of controlled sampling
in a 100% moisture stack. It should be noted at at 100% moisture
conditions there would be no dry gas to control beyond the im-
pingers, and the control valves and pump would become useless.
Condensation (heat transfer) would become the driving force and
rate determining factor. Without a control valve prior to the
impingers, isokinetic sampling could not occur. Therefore,
the Entropy method would allow positive control at 100% moisture
conditions (assuming the rate of heat transfer within the
impingers was high enough).
Few 100% moisture sources exist, and under less severe
conditions there is no reason why the results from one sampling
train design should differ significantly from the results of
another. One would simply have to consider the advantages, dis-
advantages, and operating characteristics of each design.
C-ll
-------
NOMENCLATURE
B = Mole fraction, water in stack gas, dimensionless
iV 5
C = pitot tube coefficient, dimensionless
D = nozzle diameter, in.
T^ *
n
ft3 /
K = orifice calibration, -0.72+0.05 ±£- J
171 f-nnefanf 5eC »
lb
. «. -,-„ . lb-moleDR
constant
K = units conversion constant, 85.48 j^ Vlb-mole°R
AH = orifice pressure differential, in. f^O
M, = molecular weight of stack gas, dry, Ibs/lb-mole
Ap = pitot tube pressure differential, in. H20
m = absolute pressure of dry gas meter, in. Hg.
P _ absolute pressure in stack, in. Hg,
T = meter temperature, °R
m
T = stack temperature, °R
18 = molecular \veight of H20, Ibs/lb-mole
C-12
-------
JACA HIGH MOISTURE SAMPLING TRAIN
MANOMETER
NOZZLE
n
i
M
UJ
PROBE
TnU tichnlctl dlt>, fumilhld unitr Uni«4 St>t» Cot,t th» vrltltn f.t»,.Jion of J»C* Curs,.
b< tithtr [«) uixi. rtUtiid or tra-
•en« «h«r« t>i< tlH or proem concirntil 1> not o(hrnil>« riuonibi/
>viiU61i to tr.ibtt tUtly p«rfor»«nee of th< »er> fn*it?i thi: thi r«-
lti« or ditclour* dtrrtof ovtiUc tilt tovtmitn? »h«U B« M^I lub'jcl
to • proMbllion ijilnit furthtr u»«, rtUm, or ducloiun, or (li)
r«U«i« to i foriiin lovinntra, n th« internt of th» Unit»« Snt«
•»/ rK).lri, for ««t,-|«ncf rtpatr or o«
-------
EPA HIGH MOISTURE SAMPLING TRAIN
PROBE
O
THERMOMETER-x CHECK
1 VALVE
VACUUM
LINE
AIR-TIGHT
PUMP
FIGURE 5-2.
-------
ENTROPY HIGH MOISTURE SAMPLING TRAIN
PROBE
n
COMP. AIR
PURGE
SYSTEM
ORIFICE
HOT
BOX
-44
1
L
f-
1
1
1
THERMOMETER-x CHECK
VALVE
_
IMPINGERS
i
•f RATtT-1
ICE BATH
99
-T f
O
RY TEST
METER
BY-PASS VACUUM
VALVE GAUGE
rC£h T O
. *^^ ^ t^L* T^
O
MAIN
VALVE
VACUUM
LINE
AIR-TIGHT
PUMP
FIGURE 5-3.
-------
SLIDE 303-0 NOTES
HIGH MOISTURE CONTENT
SLIDE 303-1
SAMPLING METHODS FOR STACKS
WITH HIGH MOISTURE CONTENT
HIGH MOISTURE SOURCES
O Ammonium Nitrate Prilling
Facilities
o Lime Hyrators
o Evaporators
o Coke Oven Quench Towers
SLIDE 303-2
(picture of high moisture source)
C-17
-------
SLIDE 303-3
NOTES
THE PROBLEM
AH=Dn4
4K
T.P
AP
m
SLIDE 303-4
SAMPLING PROBLEMS
o erroneous readings due to low
flow rate through orifice
o inaccurate control of sampling
rate due to small volume of gas
passing through control valves
o non-isokinetic sampling due to
, fluctuations in moisture content
of stack gas
SLIDE 303-5
SOLUTION
PLACE ORIFICE METER BEFORE
IMPINGERS
o total sample volume passes
through orifice meter
o moisture content measurement
unnecessary
o isokinetics not affected by
moisture changes
C-19
-------
SLIDE 303-6
NOTES
THE SOLUTION
AH = D,
4
4Km
TmPs
T,Pm
AP
SLIDE 303-7
HIGH MOISTURE CONTENT
SAMPLING METHODS
o JACA Corporation Method
o EPA Method
o Entropy Method
SLIDE 303r8
JACA HIGH MOISTURE SAMPLING TRAIN
MANOMETER
CONOENSATE TRAP
MI2LE
PROSE
•\ CH£«
1 VALVE
C-21
-------
SLIDE 303-9
JACA CORPORATION METHOD
Orifice meter is located in
heated sample box behind filter
ADVANTAGES
o prevention of condensation at
orifice
o protection from particulate
fouling
DISADVANTAGES
o orifice meter pressure does
not remain constant
SLIDE 303-10
EPA HIGH MOISTURE SAMPLING TRAIN
NOTES
CHECK
»AIVE
~""" ~~" Irr mtvu _i
SLIDE 303-11
EPA METHOD
o developed for use at ammonium
nitrate facilities
o consists of an in-situ orifice
with a changeable orifice plate
o filter located before silica
gel impinger
o probe heated to prevent
condensation
C-23
-------
SLIDE 303-12
NOTES
EPA METHOD
Isokinetic Sampling Rate Equation
AH = Dn<
AP
SLIDE 303-13
ENTROPY HIGH MOISTURE SAMPLING TRAIN
HMK
CHECK
VALVE
SLIDE 303-14
ENTROPY METHOD
o used at ammonium nitrate
facility
o orifice or venturi meter
located in heater box
o sample control valve located
in back of metering device
o manometer lines cleaned by
pressurized air
C-25
-------
SLIDE 303-15
NOTES
(picture of needle valve on probe)
SLIDE 303-16
PROBLEMS COMMON TO
ALL THREE METHODS
1. Entrained water droplets
2. Condensation in manometer
lines
3. Improper condensation in
impingers
SLIDE 303-17
C-27
-------
SLIDE 303-18
NOTES
SLIDE 303-19
MOISTURE EQUATION - PARTIAL PRESSURE
S.V.R
Where: Bws = proportion (by volume) of water
vapor in a gas mixture
S.V.R = saturated vapor pressure of water
at average stack temperature
P = absolute pressure of the stack
C-29
-------
SECTION D. LOW VELOCITY FLOW
Subject Page
1. A survey of commercially available instrumentation
for the measurement of low-range gas velocities D-3
2. Velocity measurements at low flow rates D-21
3. Slides D-29
D-l
-------
A SURVEY OF COMMERCIALLY AVAILABLE INSTRUMENTATION
FOR THE MEASUREMENT OF LOW-RANGE GAS VELOCITIES
Robert F. Vollaro
INTRODUCTION
Gas velocities in industrial smokestacks and ducts typically range from
about 1000 to 5000 ft/min; velocities in this range can be measured satis-
factorily with a Type-S pi tot tube and gauge-oil manometer. Stacks are
occasionally encountered, however, in which the velocities are consistently
below 1000 ft/min. Measurement of gas velocity is less straightforward below
1000 ft/min than in the 1000 to 5000 ft/min range, because most gauge-oil
manometers are not sensitive enough to give accurate low-range readings. The
purpose of this paper is to evaluate several commercially available instru-
ments which are capable of measuring gas velocities below. 1000 ft/min.
SURVEY OF LOW-RANGE VELOCITY INSTRUMENTATION
The following paragraphs provide a brief description and evaluation of
11 commercially available instruments, along with cost data. A summary of
the descriptive information is presented in Table 1.
1. Instrument and Manufacturer: Inclined manometer, Model 125-AV
(Figure 1) manufactured by Dwyer Instruments, Inc., Michigan City, Indiana.
a. Operating principle - A differential pressure signal from a
primary sensing element (e.g., a Type-S pitot tube) causes a positive dis-
placement of gauge fluid along a calibrated, inclined scale.
b. Velocity range - The full-scale range of the manometer is
0 to 1 in. water column; the scale divisions are 0.005 in. FLO. The manometer
is readable to the nearest 0.003 in. H20.
D-3
-------
Table 1. LOW-RANGE VELOCITY INSTRUMENTATION
Instrument and
manufacturer
Inclined Manometer *
Model 125-AV
Dwyer Instruments, Inc.
Micromanometer *
Model 10133
Ther mo-systems. Inc.
Microtector *
Hook Gauge
Dwyer Instruments, Inc.
Electronic Manometer *
Model 1023
Datametrics, Inc.
Mechanical
Vane Anemometer
Davis Instrument Co.
Extended Range
Propeller Anemometer
R.M. Young Co.
Hot-wire Anemometer
Model VT-1610
Thermo-Systems, Inc.
Hot-film Wedge Sensor
Model 1234-H
Thermo-Systems, Inc.
Fluid* Velocity Sensor
Model 308 R
Fluidynamtc Devices, Ltd.
Stack Velocity Sampler *
Model GSM-1D5K
Teledyne Hastings- Raydist
Differential Pressure *
Transmitter
Brandt Industries, Inc.
Lower
velocity
limit, ft/min
700
700 in field
400 in lab
700 in field
100 in lab
700 in field
100 in lab
70
75
30
60
200
100
150
Temperature
range
Same as
primary
sensor
Same as
primary
sensor
Same as
primary
sensor
Same as
primary
sensor
To 250°F
(est.)
To180°Ffor
continuous
duty
To212°F
To 570°F
To 450°F
Same as
primary
sensor
Same as
primary
sensor
Resistance
to
paniculate
Same as
primary
sensor
Same as
primary
sensor
Same as
primary
sensor
Same as
primary
sensor
Fair
Fair
Fair
to
good
Good
Fair
to
good
Excellent
Excellent
Applications
Industrial stacks, ducts, vents;
also lab applications; air or
non-air streams
Lab applications; limited use
in industrial stacks, ducts,
vents; air or non-air streams
Lab applications; limited use
in industrial stacks, ducts,
vents; air or non-air streams
Lab applications; limited use
in industrial stacks, ducts,
vents; air or non-air streams
Industrial vents and grilles;
special calibration needed for
non-air streams
Roof monitors and vents; spe-
cial calibration needed for
non-air streams
Industrial stacks, vents, ducts;
lab applications; special cali-
bration needed for
non-air streams
Industrial stacks, vents, ducts,
lab applications; special cali-
bration needed for
non-air streams
Industrial stacks, vents,
ducts; air or non-air streams
Industrial stacks, vents,
ducts; air or non-air streams
Industrial stacks, vents,
ducts; air or non-air streams
Must be used in conjunction with a Type - S pitot tube or other appropriate primary sensing element.
D-4
-------
229
Figure 1. Dwyer inclined manometer, mode! 1 25-AV, connect-
ed to a Type-S pitot tube.
MICROMETER
DIAL
Figure 2. Thermo-Systems micromanometer, model 10133,
connected to a Type-S pitot tube.
D-5
-------
c. Temperature range - The operating temperature range of the
manometer is the same as that of the primary sensing element.
d. Resistance to particulate matter - Governed by particulate
resistance of primary sensor.
e. Evaluation - As previously noted, the manometer has scale divi-
sions of 0.005 in. H20, and is readable to the nearest 0.003 in. H20. Thus,
it has greater sensitivity than most inclined manometers, which have 0.01 in.
H20 divisions and are readable to 0.005 in. H20. Therefore, with the 125-AV,
accuracy of better than 10 percent in velocity head (AP) readings can be
ensured, provided that the manometer is not used to measure values of AP
lower than about 0.03 in. hLO (which corresponds to a velocity of about
700 ft/min for air flowing at 70°F).
f. Cost - Approximately $125.
2. Instrument and Manufacturer: Micromanometer, Model 10133 (Figure 2),
manufactured by Thermo-Systems, Inc., St. Paul, Minnesota.
a. Operating principle - A differential pressure signal from a
primary sensing element causes a displacement of gauge fluid along a
calibrated, inclined scale.
b. Velocity range - The full-scale range of the micromanometer is
0 to 1.2 in. water column. The scale divisions are 0.01 in H20, but the
instrument has a micrometer dial, making it possible to read velocity head
to the nearest 0.001 in. HgO.
c. Temperature range - Governed by the primary sensing element.
d. Resistance to particulate matter - Same as primary sensor.
e. Evaluation - The Model 10133 micro-manometer is better suited
for laboratory work than for source-sampling applications, particularly at
D-6
-------
velocities below 700 ft/min. The reason is that the performance of the
manometer is adversely affected by flow pulsations, vibrations, etc. Even
when it is in a vibration-free environment, the instrument cannot be used to
read AP values below 0.01 in. H20, if AP readings within +_ 10 percent of true
are desired.
f. Cost - $200 or less (estimated).
3. Instrument and Manufacturer: Micro-tector Hook Gauge (Figure 3),
manufactured by Dwyer Instruments, Inc., Michigan City, Indiana.
a. Operating principle - A differential pressure signal from a
primary sensing element causes a slight displacement of gauge fluid. A
metal "hook" mounted in a micrometer barrel is carefully lowered until its
point "just" contacts the gauge fluid. The instant of contact with the fluid
is detected by completion of a low-power AC circuit. On indication of contact,
the operator stops lowering the hook, and reads the micrometer to determine AP.
b. Velocity range - The full-scale range of,the gauge is 0 to 2 in.
water column. The micrometer scale is readable to the nearest 0.00025 in. ^0.
c. Temperature range - Governed by primary sensing element.
d. Resistance to particulate matter - Same as primary sensor.
e. Evaluation - The manufacturer's estimated readability (to the
nearest 0.00025 in. hUO) implies that one should be able to read AP values
as low as 0.0025 in. hUO with +_ 10 percent confidence. In practice, however,
this readability is only possible if the instrument is perfectly leveled and
used in an absolutely vibration-free environment. Generally, the hook gauge
will not be a useful field instrument for measuring velocities lower than
about 700 ft/min.
f. Cost - About $200.
D-7
-------
MICROMETER
BARREL
HOOK
Figure 3. Dwyer microtector hook gauge, connected
to a Type-S pitot tube.
TRANSDUCER
Figure 4. Datametrics electronic manometer, model 1023, connected to a Type-S
pitot tube.
D-8
-------
4. Instrument and Manufacturer: Electronic Manometer, Type 1023
(Figure 4), manufactured by Datametrics, Inc., Wilmington, Massachusetts.
a. Operating principle - A differential pressure signal from a
primary sensing element is converted to an electrical signal by transducers.
The output signal can, if desired, be read on a digital voltmeter or
recording chart.
b. Velocity range - The manometer is useful over a wide range of
velocities because of its multi-scale readout system. The least sensitive
scale is 0 to 100 in. water column, and the most sensitive is 0 to 0.01 in.
H«0, full-scale. The rated accuracy of the manometer is 2 percent of full-
scale for all operating ranges.
c. Temperature range - Governed by the primary sensing element.
d. Resistance to particulate matter - Same as primary sensor.
e. Evaluation - The 1023 manometer is a high-precision instrument;
if zeroed with a digital voltmeter, it is capable of measuring velocity heads
aS low as. 0.001 in. HgO with acceptable accuracy. Note, however, that read-
ings made on the most sensitive (0 to 0.01 in. h^O) scale are adversely affected
by connecting-line vibrations; thus, the lines from the primary sensor to the
transducer must be perfectly still during use in this range. The manometer is,
therefore, better suited for laboratory, rather than field, applications for
measuring AP values below 0.01 in. H20.
f. Cost - About $1000.
5. Instrument and Manufacturer: Mechanical Vane Anemometer (Figure 5),
manufactured by Davis Instrument Co., Baltimore, Maryland.
D-9
-------
a. Operating principle - A gas stream flowing through the anemometer
(see Figure 5), causes the propeller blades to rotate. The propeller rpm is
proportional to the velocity of the flowing gas. The readout is in linear
feet; dividing this readout by the total measurement time gives the gas
velocity in ft/min.
b. Velocity range - The anemometer can measure velocities between
70 and 5000 ft/min with acceptable accuracy.
c. Temperature range - (The author does not have a reliable estimate
of the instrument's temperature capabilities; however, there seems to be no
reason why the anemometer could not be used in gas streams as hot as 200 or
250°F.)
d. Resistance to parti oilate matter - The propeller blades provide
fairly good resistance to particulate matter, especially when the instrument
is used for brief periods of time.
e. Evaluation - A mechanical vane anemometer is best suited for
making a "quick check" of the exit velocities from a vent or grille. The
anemometer is calibrated for use in air streams; special calibration is needed
for use in non-air streams. Although the anemometer can accurately.measure
velocities in the 70 to 700 ft/min range (out of range of most primary sensor-
manometer combinations) , the instrument can only be used for a short time
before it must be stopped, reset, and restarted manually. Thus, the anemometer
is not easily adaptable for use in source-sampling applications.
f. Cost - Estimated at $100 or less.
6. Instrument and Manufacturer: Extended Range Propeller Vane Anemometer
(Figure 6), manufactured by R. M. Young Co., Traverse City, Michigan.
D-10
-------
Figure 5. Mechanical vane anemometer,
manufactured by Davis Instruments, Inc.
ABS THERMOPLASTIC
PROPELLER
TO RECORDER
Figure 6. Extended-range propeller vane anemometer, manu-
factured by R.M. Young Company.
D-ll
-------
a. Operating principle - Flowing gas causes the propeller (see
Figure 6) to turn at a rate proportional to the gas velocity. The propeller
shaft is coupled to a d.c. generator. The generator output is an analog
voltage, proportional to shaft rpm. The output: signal is monitored contin-
uously by means of a recording chart.
b. Velocity range - The velocity range for the anemometer is 75
to 6000 ft/min; 75 ft/min is the threshold velocity at which the propeller
begins to turn.
c. Temperature range - With an ABS thermoplastic propeller, the
anemometer can be used continuously in gas streams as hot as 180°F and,
intermittently, in streams as hot as 300°F.
d. Resistance to particulate matter - The propeller blades provide
fairly good resistance to particulate matter.
e. Evaluation - Because it cannot be used for extended periods of
time at temperatures above 180°F, the anemometer is of limited value for
source-sampling applications. It would probably be useful for continuous
velocity measurement in roof monitors. The anemometer is calibrated for use
in air streams; special calibration is required for use in non-air streams.
f. Cost - About $700 with recording chart.
7. Instrument and Manufacturer: Velocity Transducer, Model 1610,
manufactured by Thermo-Systems, Inc., Minneapolis, Minnesota.
a. Operating principle - The VT-1610 measures the velocity of a
flowing gas stream by sensing the cooling effect of the stream as it moves
over the heated surface of the sensor, the "hot-wire" principle. The output
signals from the sensor are electrical and non-linear. A signal conditioner
D-12
-------
is available to linearize the output. The output signals are temperature
compensated so that the readings will be in ft/min, corrected to 70°F.
b. Velocity range - The instrument can measure velocities as low
as 30 ft/min (on the low scale) and as high as 12,000 ft/min (on the high
scale), with acceptable accuracy (+ 2 percent).
c. Temperature range - The instrument can be used in gas streams
as hot as 212°F.
d. Resistance to particulate matter - Unlike many hot-wire devices,
the VT-1610 sensor is ruggedized and has fairly good resistance to partic-
ulate matter.
e. Evaluation - It appears that the VT-1610 would be most suitable
for short-term use in low-temperature air streams, particularly when velocities
are too low (under 700 ft/min) to be measured with most primary sensor-
manometer combinations. If used continuously in a dusty environment, the
instrument will tend to foul after several hours. The sensor is calibrated
for use in air streams; special calibration is required if it is to be used
in non-air streams.
f. Cost - About $1000 for sensor and signal conditioner.
8. Instrument and Manufacturer: Wedge Hot-Film Sensor, Model 1234-H
(Figure 8), manufactured by Thermo-Systems, Inc., Minneapolis, Minnesota.
a. Operating principle - The 1234-H measures the velocity of a flow-
ing gas stream by sensing the cooling effect of the stream as it moves over
the heated sensor surface, the "hot-film" principle. The output signal is
electrical and can be read continuously on a recording chart, if desired.
When used with a temperature compensator, the readout will be in ft/min,
corrected to 70°F.
D-13
-------
Figure 7. Thermo-Systems hot-wire anemometer, model VT-1610.
SENSOR
Figures. Thermo-Systems hot-film wedge sensor, model 1234-H.
D-14
-------
b. Velocity range - The sensor can measure velocities as low as
60 ft/min (on the low-scale) or as high as 12,000 ft/min (on high-scale),
with acceptable accuracy (+_2 percent).
c. Temperature range - The sensor can be used in gas streams as
hot as 570°F.
d. Resistance to particulate matter - The sensor is ruggedized
and offers good resistance to particulate matter.
e. Evaluation - The 1234-H is best suited for short-term use in
air streams, particularly when velocities are too low to be measured with
primary sensor-manometer combinations. It may prove to be useful for measur-
ing total flow rate from roof monitors, because several sensors, positioned
at different points along a roof vent, can be connected to a multi-channel
readout system. Like the VT-1610, the 1234-H requires special calibration
for use in non-air streams.
f. Cost - About $1500, for one temperature-compensated sensor and
readout system; about $500 for each additional sensor.
9. Instrument and Manufacturer: Fluidic Velocity Sensor, Model 308R
(Figure 9), manufactured by FluiDynamics, Ltd., Ontario, Canada.
a. Operating principle - The following description refers to
Figure 9: A free jet of supply fluid (air or N«) is issued from a nozzle
(point B), and impinges on two pick-up ports (point C). At zero cross-flow
velocity, the differential pressure across the pick-up ports is zero. Any
cross-flow causes the supply air jet to deflect, yielding a differential
pressure signal proportional to the velocity. The output signal can be read
with a differential pressure gauge or transducer.
D-15
-------
TO
SUPPLY FLUID
DIFFERENTIAL PRESSURE
GAUGE
SENSING HEAD
PROBE
FLOW
Figure 9. Fluidic velocity sensor, model 308R, manufactured by FluiDynamic
Devices, Ltd.
PURGE
GAS
Figure 10. Stack velocity sampler, model GSM-1D5K manufactured by Teledyne
Hastings-Raydist.
D-16
-------
b. Velocity range - The sensor has a full-scale velocity range
of 0 to 3600 ft/nrin. The accuracy of the sensor is about +_3 percent for
velocities above 600 ft/nrin, and +_ 5 to 10 percent for velocities below
600 ft/nrin.
c. Temperature range - The sensor can be used in gas streams as
hot as 450°F.
d. Resistance to particulate matter - The sensor has fairly good
resistance to particulate matter.
e. Evaluation - One of the outstanding features of the sensor is
that it has a linear, high-amplitude output signal, even at low velocities.
For example, when the cross-flow velocity (VG) is 600 ft/min, the sensor
output is about 12 in. H20; at VG = 200 ft/min, the output is about 4 in. H20.
Note, however, .that the sensor is difficult to zero; for-this reason, its
accuracy falls off appreciably for v < 200 ft/min. The sensing head is
mounted on a cylindrical probe, making it convenient to use in source-sampling
applications. The sensor can be used in non-air streams, provided that the
gas density is known.
f. Cost - About $2000.
10. Instrument and Manufacturer: Stack Velocity Sampler, Model GSM-1D5K
(Figure 10), manufactured by Hastings-Raydist, Hampton, Virginia.
a. Operating principle - The following description refers to
Figure 10: At zero cross-flow, supply fluid (air or N«) is continually purged
at equal rates, out of both impact openings of the Type-S pi tot tube. Any
cross-flow velocity causes a back-pressure against the purge gas, at point A.
The back-pressure signal is proportional to the fluid velocity; thermoelectric
D-17
-------
sensors (transducers) interpret and convert this signal. The output voltage
from the transducers is linear over about 90 percent of the scale; output
voltage can be read with a digital voltmeter or recording chart, if desired.
b. Velocity range - The velocity range is 0 to 1500 ft/min, full
scale. The lower limit of readability is about 100 ft/min.
c. Temperature range - The instrument is operable at all tempera-
tures at which a Type-S pi tot tube can be used.
d. Resistance to particulate matter - The continuous-purge principle
of the sensor gives it excellent resistance to particulate matter.
e. Evaluation - The most outstanding feature of the Hastings
instrument is that it works with a Type-S pi tot tube; thus, it is easily
adaptable for use with conventional source-sampling equipment. The volt-
meter on the control panel is adequate for reading velocities between 200 and
1500 ft/min. To read accurately velocities between 100 and 200 ft/min, a
digital voltmeter or sensitive chart recorder is needed. The sensor can be
used in non-air streams if the density of the gas is known. Note that the
instrument must be calibrated exactly as it is to be used, because different
calibration curves will be obtained for different pi tot tube and connecting-
line lengths.
f. Cost - About $1500 to $2000.
11. Instrument and Manufacturer: Differential Pressure Transmitter
(Figure 11), manufactured by Brandt Industries, Inc., Raleigh, North Carolina.
a. Operating principle - The following description refers to
Figure 11: Supply fluid (air on N«) exhausts equally out of both sides of
the pi tot tube at zero cross-flow velocity. Any cross-flow will cause a
D-18
-------
Figure 11. Differential pressure transmitter, series 200; manufactured by Brandt Industries, Inc.
D-19
-------
back-pressure against the purge gas at point A. The magnitude of the back-
pressure signal is proportional to the fluid velocity. Transducers receive
and convert the back-pressure signal. The output signal from the transducers
is pneumatic and linear; the output can be read continuously on a pneumatic
recorder if desired.
b. Velocity range - The full-scale range of the transmitter is 0
to 0.05 in. water column. The accuracy of the transmitter is estimated at
+ 2 percent of span.
c. Temperature Range - The transmitter can be used at any tempera-
ture at which the primary sensing element (pitot tube or other sensor) can
be used.
d. Resistance to particulate matter - The continuous-purge action
of the supply fluid gives the sensor excellent resistance to particulate
matter.
e. Evaluation - The Brandt'transmitter is a versatile device; it
can be used as a single-point sensor, or adapted for multipoint sensing
(e.g., it can be used with a pitot "rake"). The transmitter is easily adapt-
able for use with conventional source-sampling equipment. An especially
attractive feature of the transmitter is a damping control5 which allows
true, time-integrated average velocity head readings to be made. Velocities
as low as 150 to 200 ft/min can be read with acceptable accuracy. The instru-
ment can be used in non-air streams if the gas density is known. One draw-
back of the instrument is that there is a practical upper-limit (30 ft) on
the length of the connecting lines; note, also, that the connecting lines
are somewhat vibration-sensitive and should be still when measurements are
made.
D-20
-------
VELOCITY MEASUREMENTS AT LOW FLOW RATES
by
Robert F. Vollaro
INTRODUCTION
Accurate determination of the volumetric flow rate of a gaseous effluent
is one of the most important measurements the stack sampler has to make. Flow
rate is usually calculated from the mean velocity of the effluent stream and
the cross-sectional area of the duct. For velocity determinations, the S-type
pitot tube in combination with a pressure differential measuring device, usually
an incline manometer or magnehelic gauge, has become the standard of the stack
sampling industry.
In rare cases, stack gas velocities will be so low that the velocity head
does not register on these pressure gauges. The lower limit for a 0- .25 inch
water manometer, for instance, is 0.0025 inches, and the accuracy in this region
is questionable. Roughly speaking, S-type pitot tubes are ineffective at veloc-
ities below 600 feet per minute.
When velocities below 600 feet per minute are encountered or expected, an
alternative approach to velocity measurement must be devised. These alternatives
fall into three categories: use of velocity measurement techniques other than
pitot tubes, modification of the source to effect a sufficiently high velocity
for using pitots, and computational methods.
ALTERNATIVE VELOCITY MEASUREMENTS TECHNIQUES
Methodologies for measuring gas stream velocities fall into five general
categories, based on their principle of operation: measurement of a pressure
drop, measurement of a temperature differential, measurement of a mechanical
displacement, measurement of the progress of a tracer inserted into the gas
stream, and measurement of the amount of dilution of an indicator material.
Numerous mechanisms have been developed for making each of these measurements.
Many of these are discussed below, arranged categorically by operating principle.
A. Measurement of a Pressure Drop - In a flow measuring device which incorp-
orates a tube with a constriction, the gas velocity through the device is
proportional to the pressure drop across the constriction. For incompressible
fluids, the flow rate is given by an equation of the type.
D-21
-------
Q = CA ^ Ap
where
3
Q = volumetric flow rate, in /sec
C = flow coefficient of the measuring device, dimension!ess
2
A = cross-sectional area at minimum diameter, in
2
g = acceleration due to gravity, 386 in/sec
3
Y = fluid density, Ib/in
2
Ap = pressure drop across the constriction, Ib/in . (2)
Three types of constriction meters useful in. gas flow measurements are the
venturi meter, the orifice meter, and the laminar flow meter. With these
devices, all the gases must pass through the meter.
Venturi meters—Venturi meters consist of a conical converging nozzle, a cylin-
drical throat about 1/3 the pipe diameter and no longer than its own diameter,
and a diverging section. Static pressure taps are located upstream of the con-
vergence and at the throat. Venturi meters offer high accuracy and relatively
low head loss, and are highly resistant to abrasion from entrained particulates
and the resultant alteration of performance characteristics. However, they are
impractical for large diameter ducts.
Orifice meters — An orifice meter consists of a plate placed across a duct,
with a small, sharpd-edged opening at its center. Pressure taps are on either
side of the plate. Orifice meters are cheaper than Venturis and more readily
adaptable to larger diameter ducts. Limitations include considerable head
loss and sensitivity to abrasion or corrosion.
Laminar flow element—Driscoll (3) describes a device which can be used
when the pressure drop associated with the venturi and orifice meters is un-
acceptable. A bundle of 3/4" by 15" steel tubing was brazed into a duct, and
the pressure drop across the element measured.- Flow is related to this pressure
drop by the equation
D-22
-------
where
Q = flow rate
K = calibration factor of the flow element
yo = gas viscosity at calibration conditions
V = gas viscosity at measurement conditions, and
Ap = pressure drop.
This device was demonstrated experimentally to be an excellent gas flow meter
at flow rates well below 100 cfm.
These devices yield a total volumetric flow rate measurement. They are
applicable only if all gases can be passed through the meter. In many in-
stances, as with large ducts, ducts with irregular cross-sections, or cases
when the back pressure associated with these devices is undesirable, use of a
pressure drop device to measure flow rates is precluded.
B. Measurement of a Temperature Differential - The principle in operation here
is that the rate of transfer of heat from a stationary heat source to a gas
stream is related to the velocity of the stream. (3) Instruments which employ
this principle include hot-wire anemometers, thermistor anemometers, and hot
film anemometers.
Hot-wire anemometers—Hot-water anemometers operate in one of two ways. Gas
velocity is determined either from temperature change in a resistance wire, or
by the amount the passing gases are heated. In the second instance two temp-
erature-sensing elements are employed, one upstream, heated, and one downstream,
unheated. An accurate determination of the flue gas temperature is necessary
to use these instruments.
Thermistor^ anemometers--The thermistor anemometer, identical in principle to the
hot-wire anemometer, uses thermistors rather than resistance wires as heating
and sensing elements. Gases pass into a small opening, are heated by the first
resistor, and the temperature increase determined by the second resistor. While
hot-wire instruments have been found to be accurate at velocities down to 100
feet per minute, thermistor anemometers are sensitive to velocities of less than
20 feet per minute.
Hot-film anemometers—Hot-wire and thermistor anemometers are subject to a
serious drawback insofar as stack sampling field application is concerned;
they lose accuracy when coated with particulate. Shielded hot-wire anemometers
D-23
-------
are commercially available, which return to calibration when the shield is wiped
clean. The hot-film anemometer is one such instrument, with the sensing element
coated with with a protective film. Participates which impinge on the element
can be removed, restoring the instrument to calibration. Shielded, or not,
hot-wire anemometers are subject to inaccuracies when used in particulate-laden
streams. They are quite useful for measuring low flows in clean gas streams.
C. Measurement by Mechanical Displacement - Numerous devices for the determi-
nation of gas velocities operate on the principle that mechanical displacement
due to the impact pressure of a moving gas is proportional to the gas velocity.
Among these are rotating vane and swinging vane anemometers, and drag body meters.
Rotating vane anemometers—These instruments consist of a series of radially-
mounted, diagonal vanes which rotate when a gas stream moves past the unit.
The rotating vanes either deive a series of dials which measure the mount of gas,
in units of length, passing the meter, or provide a direct velocity readout
through the use of magnetic pickups. Rotating vane anemometers are subject to
damage and/or loss of accuracy in wet or dirty gas streams.
Swing vane anemometers--In this device, the gas stream impinges upon a metal
strip vane connected at one end to a meter. The amount of deflection of the
vane is proportional to the impact pressure, which in turn is related to the
gas velocity. A direct readout for velocity is usually provided. As with the
rotating vane type, swinging vane anemometers should not be sued at elevated
temperatures or in dust-laden gases. (1)
Drag body meters--The drag force on a body inserted into a gas stream can be a
very accurate measurement of the flow rate. A fixed body is usually mounted on
a support incorporating a strain gauge in order to measure the drag force. With
a symmetrical body, this meter works for flows in either direction. However,
these instruments are ineffective below about 150 feet per minute. (2)
D. Injection of a Tracer Material - This technique is a simple one: introduce
a readily identifiable tracer material into the gas stream a known distance up-
stream of a detection device, and measure the amount of time required for the
tracer to traverse that distance. Tracers which have been used successfully
include ballons, colored smoke, chemicals, and radioactive materials. (1)
Ballons—Balions can be added to a duct and then spotted downstream at a window
or at the duct exit. The gases cannot be so hot as to rupture the ballons, a
severe limitation. Additionally, errors can be introduced due to the inertia!
properties of the ballons and due to their bouyance (positive or negative).
D-24
-------
Colored smoke — Colored powders are injected into the gas stream with a squeeze
bulb, and the time required for the smoke cloud to exit the stack is measured.
This is a simple method, useful in plumes which are not extremely dense.
Chemi cal s— Instead of colored powder, a chemical which will react with a sub-
stance in the gas stream to form a visible cloud can be injected. Ammonium
hydroxide, for example, will react with sulfur dioxide to form a white aerosol.
In the absence of sufficient quantities of S02, hydrochloric acid can be in-
jected along with the ammonium hydroxide. This method will not work in saturated
stacks, as the white cloud cannot be easily seen.
Radioactive materials — Radioactive isotopes, detected with a geiger counter,
have been used to measure stack flows, but this method is not highly recommended.
It requires complicated and expensive equipment, highly trained personnel, and
elaborate safety precautions, and provides no better results than colored powders
or chemical reagents.
E. Dilution of an Indicator Material - The dilution technique is useful when
measurements with pitot tubes or other devices is impractical, as when highly
turbulent flow cannot be avoided. A tracer gas, preferably one not already
present in the stack gas, is introduced at a known concentration and rate into
the flue. The concentration of the injected gas is then measured at a point
far enough downstream for complete mixing to have taken place. (3) Volumetric
flow can then be calculated using the equation:
where
Q = stack gas flow rate
Q. = indicator gas injection rate
C. = indicator gas concentration at injection
C = indicator gas concentration at sampling.
Ethane, methane, and propane have been used with success, the downstream con-
centration monitored with a hydrocarbon analyzer. Expense of instrumentation
and portability problems restrict this method; the latter can be circumvented
by collecting grab samples for analysis in a laboratory. Radioactive materials
(carbon-14, radioactive krypton, etc.) have also been utilized. (1)
D-25
-------
SOURCE MODIFICATION TO ACHIEVE INCREASED VELOCITY
At a constant volumetric flow rate, the velocity of a gas stream confined
to a duct is inversely proportional to the cross-sectional area of the duct.
An increase in the velocity of flue gases can be effected by a reduction in
the cross-sectional area. An extension, either temporary or permanent, which
tapers from the duct size to an appropriate smaller cross-section is constructed
and affixed to the duct opening. A velocity traverse of the smaller section can
then be performed using a pitot tube.
The extent of the cross-sectional reduction will depend on the original
velocity of the gas; an increase to above 600 feet per minute should be achieved.
A lower area limit of about one square foot should be observed to avoid biased
velocity readings due to probe blockage in the extension.
This method is limited in its application only by the size of the duct and
the accessibility of its terminus.
COMPUTATIONAL METHODS
Within any given fuel category, the ratio of the quantity of dry effluent
gas generated by combustion to the gross calorific value of the fuel is a con-
stant. This ratio is known as the dry F (Fd) Factor. Values for Fd for num-
erous types of fuel, from coal and oil to shoe leather, have been computed
and can be obtained from a table. Knowing this value, along with the heat in-
put rate and dry oxygen concentration of the effluent gas, the volumetric flow
rate is obtainable through the relationship
Qsd = QH x Fd x 20.9 - %Q2
where
3
0 , = dry volumetric flow rate of stack gas, ft /hr
6
Qu = heat input rate, 10 Btu/hr, and
36
F. = dry F Factor for fuel being burned, ft 710 Btu.
d
The term AA l0'9^ is a correction factor for excess air.
cU.y - *Up
Wet effluent flow rate, Qsw, can be calculated using a separate wet F
Factor, F , and incorporating the moisture fraction in the ambient air (Bwa)
in the excess air correction factor. The above equation then becomes
20.9
Qsw " QH x hw x 20.9(1 - Bwa) -
D-26
-------
Experience has shown that these calculated flow rates are significantly lower
than measured rates. Aerodynamic interferences and pitot tube misalignment are
factors which can produce measured values higher than the actual flow rate.
Stoichiometric calculations are quite useful, though, when instrument measure-
ments are not possible. (4)
CONCLUSIONS
There is almost no end to the range of devices and techniques available
for measuring the rate of flow of a gas stream. Of the types discussed here,
each is most useful under particular conditions of flow rate, temperature,
dust and moisture concentration, and so on. Many of the techniques were devel-
oped for specific applications, taking into account the peculiarities of the
source to be measured, yet are applicable to other similar situations. Table 1
lists the performance characteristics of these types of low measurement devices.
TABLE 1. PERFORMANCE CHARACTERISTICS OF FLOW MEASUREMENT DEVICES
Type
Venturi
Orifice
Laminar flow
Hot-wire
Thermistor
Hot-film
Rotating vane
Swinging vane
Drag body
Approximate range
100
50
5
~10
~10
10
<100
20
5
- 500,000 cfm
- 100,000 cfm
100 cfm
- >2,000 ft/mi n
? ft/mi n
- >2,000 ft/mi n
- >2,000 ft/min
- >2, 000 ft/min
100 cfm
Accuracy
%
1 - 2
1 - 2
1 - 2
~2
~1
~2
~1
~3
0.5 - 2
Calibration
stability
in dust
good
fair
good
poor
fair
good
good
fair - good
good
With such a wide range of devices.and techniques for measuring gas flow rates,
plus the fact that the development of new techniques is limited only one one's
ingenuity, it is virtually inconceivable that a source test should have to be
abandoned due to an inability to determine the volumetric flow rate of the
effluent gases. Should flows be too low for pi tot tubes to provide this data,
a host of alternatives are at the stack sampler's disposal.
D-27
-------
REFERENCES
1. Cooper, H.B.H., Or. and A.T. Rossano, Jr. Source Testing for Air
Pollution Control, Environmental Research and Applications, Inc.,
197T
2. Cook, M.H. and E. Rabinowicz. Physical Measurement and Analysis.
(Reading, Massachusetts, Addison-Wesley Publishing Company, Inc.),
1963.
3. Driscoll, J.N. Flue Gas Monitoring Techniques. (Ann Arbor, Ann
Arbor Science Publishers, Inc.), 1974.
4. Shigehara, R.T., R.M. Neulicht, W.S. Smith, and J.W. Peeler. "Summary
of F-Factor Methods for Determining Emissions from Combustion Sources".
Entropy Environmentalists, Inc., Research Triangle Park, North Carolina,
1976.
D-28
-------
SLIDE 304-0 NOTES
VELOCITY MEASUREMENT
TECHNIQUES AT
LOW GAS FLOWS
SLIDE 304-1
VELOCITY
o used to determine nozzle size
o used to obtain k-factor for
setting isokinetics
VOLUMETRIC FLOW
o used to determine mass emissions
SLIDE 304-2
THE PROBLEM
o pressure differential devices
insensitive below 1000 ft/min
o unreliable pitot tube accuracy
below 400 ft/min
D-29
-------
SLIDE 304-3
NOTES
SLIDE 304-4
(picture of scale divisions of
above manometer)
SLIDE 304-5
D-31
-------
SLIDE 304-6
SLIDE 304-7
SLIDE 304-8
NOTES
D-33
-------
SLIDE 304-9 NOTES
SLIDE 304-10
ALTERNATIVE APPROACHES FOR
LOW VELOCITY MEASUREMENTS
1. The use of techniques other
than pitot tubes
2. Modification of the source to
effect a sufficiently high
velocity for using the pitot
tube
3. Measure velocity at a different
location and use data to cal-
culate velocity at sampling site
4. Compute flow and velocity using
process parameters
SLIDE 304-11
TECHNIQUES OTHER THAN
PITOT TUBES
PRESSURE DROP MEASUREMENT DEVICES
o Venturi Meters
o Orifice Meters
o Mass Flow Meters
D-35
-------
SLIDE 304-12
NOTES
SLIDE 304-13
SCHEMATIC OF HASTING METER
SLIDE 304-14
TEMPERATURE DIFFERENTIAL
MEASUREMENT DEVICES
o Hot Wire Anemometer
(accuracy greater than 100 FPM)
o Thermister Anemometer
(velocity sensitive less than 20 FPM)
o Hot Film Anemometer
D-37
-------
SLIDE 304-15
NOTES
SLIDE 304-16
SLIDE 304-17
MECHANICAL DISPLACEMENT
MEASURING DEVICES
o Rotating Vane Anemometer
o Swinging Vane Anemometer
o Drag Body Meters
D-39
-------
SLIDE 304-18
NOTES
SLIDE 304-19
SLIDE 304-20
MODIFICATION OF SOURCE
TO INCREASE VELOCITY
Increase velocity by reducing
the cross-sectional area using
stack extension
Velocity should be increased
to above 600 ft/min
A lower area limit of approxi-
mately 1 ft2 to avoid bias due to
probe blockage
D-41
-------
SLIDE 304-21 NOTES
COMPUTATIONAL METHOD
("F" FACTOR)
o Dry "F" factor
o - o x F x 20-9
Qsd ~ QH x Fd x 20.9 - %02
o Wet "F" factor
20.9
n - n x F x _
Qsw ~ QH w 20.9(1 - B) - %0
2
D-43
-------
SECTION E. CYCLONIC FLOW
Subject Page
1. Isokinetic particulate sampling in nonparallel flow
systems-cyclonic flow E~3
2. Techniques to measure volumetric flow and particulate
concentrations in stacks with cyclonic flow E-25
3. Slides E~35
E-l
-------
ISOKINETIC PARTICULATE SAMPLING IN NON-PARALLEL
FLOW SYSTEMS- CYCLONIC FLOW
by
Jim Peeler
In most stationary sources, the direction of gas flow is
essentially parallel to the stack axis. Examples of non-parallel
flow systems are flow immediately following a bend or turn in the
ductwork, flow in a convergent or divergent section, and cyclonic
(tangential) flow. Cyclonic flow most often occurs after inertial
demisters following wet scrubbers, in stacks with tangential in-
lets, and after axial fans. Method 1—Sample and Velocity Traverses,
and Method 2—Determination of Stack Gas Velocity and Volumetric
Flow Rate, are not applicable to stacks with cyclonic flow. Method
1 (2.4), gives explicit instructions for determining when unac-
ceptable flow conditions exist. In short, the angle (between the
pitot orientation and the plane perpendicular to the stack axis)
required to produce a null reading is measured for each sampling
point. If the average of the absolute values of the angles is
greater than 10°, unacceptable flow conditions exist.
In many cases, particulate sampling is required even though
the appropriate reference methods are not applicable due to non-
parallel flow. This situation occurs more frequently at existing
sources than at new sources, since sources subject to NSPS are
required to provide sampling locations which permit sampling
according to the appropriate reference methods. There are
three possible alternatives when unacceptable flow conditions
exist:
(1) modify the sampling methodology to obtain accurate results
E-3
-------
(2) use standard or alternate methodology which gives results
biased high (in the agency's favor), or (3) modify the source
to permit standard sampling procedures to be used. This paper
discusses three sampling procedures which have been commonly
proposed. Also, source modifications which can be employed are
described. Current studies on tangential flow may provide better
solutions in the future.
BACKGROUND INFORMATION
In order to determine the biases of various sampling tech-
niques in non-parallel flow systems, it is necessary to under-
stand the requirements of proportional sampling and the errors
associated with pitot tube measurements.
Proportional Sampling - Source sampling is conducted to
determine the concentration of a particular pollutant in an
effluent stream. The concentration of component Z which is re-
presentative of the effluent is, (1)
£• = volume of component Z _ CZ x v(ft/sec) * A(ft2) x e(sec)
Z total volume of effluent ~ ,rfc<., ^ .,- ,. : :
V(ft/sec) x A(ft2) x e(sec)
GZ = %, if component Z is a gas
GZ = Ibs/ft , if component Z is particulate
For a steady state source with spatial variations in concen-
tration and velocity, Equation (1) can be expressed as,
C_ = 'A -Z-- (2)
'z
E-4
-------
Evaluation of Equation (2) requires knowledge of concentration
and velocity as functions of location across the stack cross
section. In practice, the integrals in Equation (2) are
approximated by sampling at a finite number of points,
SC. V.A.e.
.1111
r - ,. f3^
^Z ZV. A. 6. *• }
.111
In the application of standard EPA methods, equal areas are
sampled for equal times. Equation (3) becomes,
It is not feasible to determine the concentration (C.) at each
sampling point. However, the quantity [zC.V^] can be evaluated
by collecting a single integrated sample where the sampling rate
is weighed proportionally to the stack velocity at each sampling
point. This procedure of sampling at a rate which is related to
the stack velocity by a constant is referred to as proportional
sampling. In the preceding discussion it has been assumed that
the velocity of the effluent stream is parallel to the stack
axis. In non-parallel flow systems, the sampling rate should
be weighted proportionally to the component of the velocity
parallel to the stack axis.
When sampling for particulates it is necessary to sample
isokinetically to obtain a representative sample. For sources
where the velocity is parallel to the stack axis, isokinetic
sampling is a special case of proportional sampling where the con-
stant relating the sampling velocity to the stack velocity is 1.
E-5
-------
Thus, in parallel flow systems, isokinetic sampling auto-
matically satisfied proportional sampling requirements. For
non-parallel flow systems, isokinetic sampling conditions must
be based on the velocity vector, however, proportional sampling
conditions must be based on the component of velocity parallel
to the stack axis. This creates considerable difficulty in
sampling non-parallel flow systems.
Pitot Tube Errors - Pitot tube errors arise when the pitot
tube is not oreinted correctly with respect to the gas stream
velocity vector. Two types of pitot tube misalignment are shown
in Figure.4-4. Figures 4-5 8 4-6 show the % error in the velocity
vector measurement as a function of yaw and pitch angles for
a S-Type pitot. When the S-Type pitot is part of a probe
assembly, the % error has even greater dependence on pitch and
yaw angles.
A '!*
Yaw Angle Misalignment Pitch Angle Misalignment
Figure 4-4. Types of Pitot Tube Misalignment
E-6
-------
Figure 4-5 Velocity Errors from Yaw Angle Misalignment
Figure 4-6 Velocity Errors from Pitch Angle Misalignment
E-7
-------
SAMPLING TECHNIQUES FOR NON-PARALLEL FLOW SYSTEMS
When attempting to sample a source with non-parallel flow,
several problems are encountered; (1) velocity measurements
are subject to pitot tube errors, (2) volumetric flow rate
determinations are difficult, (3) problems arise relating to
the alignment between the sample nozzle and flow stream, (4)
proportional sampling conditions are difficult to maintain; and
(5) the inertial properties of the dust particles introduce
biases of unknown magnitude. These problems are discussed as
they effect three sampling techniques.
Before discussing individual sampling techniques, a bias
which is common to all sampling methods for non-parallel flow
systems should be considered. All of the approaches which will
be described assume that a sample which is collected isokineti-
cally and weighted proportionally to the axial velocity will
accurately reflect the particulate concentration in the effluent
stream. The methods for determining isokinetic and proportional
sampling conditions are based on measurements of gas velocity.
It should be noted that non-parallel flow systems are created by
inertial forces acting on the gas stream as the effluent moves
through the stack or ductwork system. Since dust particles are
subject to much greater inertial affects than are gas molecules,
the actual velocities of the particles and the gas stream will
not be the same under cyclonic or other non-parallel flow con-
ditions. In almost all cases, the greater inertial affects on
particles will create larger angles between the particle velocities
and the stack axis than between the gas velocity and the stack
E-8
-------
axis. This introduces a low bias of unknown magnitude in the
measured concentration due to misalignment of the sampling
nozzle with respect to the particle velocities. This bias in-
creases as the particle size increases.
Criteria for determining the minimum number of sampling
points and for locating the sampling points in non-parallel
flow systems must be developed since Method 1 is not applicable
in these cases. It is recommended that 48 sampling points (the
maximum specified by Method 1) be used until applicable criteria
can be developed. All of the sampling techniques which will be
presented assume that sampling is conducted at points repre-
senting equal areas of the stack cross-sectional area. The pro-
cedures in Method 1 for locating sampling points should be em-
ployed.
Blind Man's Approach--The blind man's approach is so named since
the standard test methods are applied and the non-parallel flow
situation is simply ignored. This procedure is subject to
multiple biasing affects.
Since the nozzle is not aligned with the direction of the
flow, the apparent or effective area of the nozzle opening is
reduced. If the angle between the flow direction and the per-
pendicular to the nozzle opening is $, then the area of the
nozzle opening perpendicular to the flow stream is reduced by
cos . (Figure 4-7).
E-9
-------
J ?
actual area A =ir[ - ]
effective area = A cos<|>
Figure 4-7.
Reduction of effective area of nozzle not aligned
with direction of flow.
E-10
-------
In this approach, the sampler has no knowledge of the angle *
and therefore the sampling rate will be overisokinetic by an
amount directly proportional to cos f.
Figures 4-5 and 4-5 show that the pitot tube gives incorrect
readings when not aligned with the flow. For all yaw angles
where -40° < e < 40° and for all positive pitch angles the
pitot gives higher than real readings. Thus for three out of
four cases of misalignment the pitot gives high readings which
creates overisokinetic sampling conditions. It should be noted
that the pitot readings will be further influenced when the an-
gle of the flow is such that the pitot is effectively on the down-
stream side of the sampling nozzle. In this situation the noz-
zle disturbs the flow stream and introduces additional velocity
measurement errors.
The effects of the reduced effective nozzle opening, and,
in most cases, the effects of the pitot error, contribute to
overisokinetic sampling. Overisokinetic sampling biases the
concentration measurement low. The degree of the bias increases
as the particle size increases.
In the blind man's approach, the sampling rate is weighted
proportionally to the magnitude of the velocity vector. In
order to meet the constraint of proportional sampling, the
sampling rate should be weighted proportionally to the component
of the velocity vector parallel to the stack axis. Therefore, if
the angle between the velocity vector and the stack axis varies
across the cross section of the stack, then proportional sampling
conditions are not maintained. The bias which results from
E-ll
-------
non-proportional sampling increases as the variations in velocity
and concentration across the stack increase. The direction of the
bias is not easily determined.
If sampling is conducted to determine compliance with a mass
emission rate standard, (Ibs/hr), the total volumetric flow rate
must be determined. Misalignment to the pitot with the flow re-
sults in errors in determining the magnitude of the velocity vec-
tor. A second error in determining the volumetric flow rate arises
because the velocity vector is not parallel to the axis of the
stack. The axial velocity vector component is equal to the velocity
vector times the cos $ , (where $ is the angle between the velocity
vector and the stack axis). The errors in determining the axial
velocity component due to pitot misalignment error, and due to ve-
locity direction error can be combined, and are shown in Figures
4-8 and 4-9. From these figures it is apparent that the axial velocity
and thus the volumetric flow rate are overestimated. The degree
of the bias cannot be estimated since, in the blind man's approach,
the sampler has no knowledge of the angle between the velocity
and the stack axis.
The mass emission rate is the product of the concentration
measured by the sampling train and the total volumetric flow rate.
The concentration is biased low and the volumetric flow rate
is biased high. The two errors tend to offset each other; however,
it is not possible to determine the net affect due to the unknown
extent of the biases. In addition, the magnitude and direction of
the bias due to non-proportional sampling is unknown.
In some stacks, negative velocities are encountered at
particular sampling points. When negative velocities are
E-12
-------
Figure 4-8. Axial Velocity Component Error due to Yaw Angle Misalignment
Figure 4-9. Axial Velocity Component Error due to Pitch Angle Misalignment
E-13
-------
encountered, no sampling should be conducted. This biases the
concentration determination high if the negative flow region
contains any particulate material. When determining the vol-
umetric flow rate for use in calculating a mass emission rate,
the negative pitot reading(s) should be used to calculate the
quantity of negative volumetric flow which should then be sub-
tracted from the positive volumetric flow. It should be remem-
bered that negative velocity measurements are subject to similar
errors as positive velocity measurements. Neglecting the pitot
errors, the mass emission rate will be biased high due to the
high bias in the concentration measurement created by negative
flow.
Alignment Approach--The alignment approach invloves determina-
tion of the direction of flow at each sampling point (by means
of three dimensional pitot sensor or similar device). The
sampling nozzle and pitot are then aligned with the flow direction
at each sampling point.
For standard Method 5 particulate sampling equipment, it
is easy to rotate the sampling probe for different yaw angles.
However, it is not possible to align the sampling nozzle and
pitot for different pitch angles. Therefore, the alignment
method is not applicable to sources where pitch angle misalign-
ment exists. Figures 4-10 and 4-11 show pitch and yaw angles for
a typical stack with cyclonic flow.
In the alignment method, the sampling rate must be based on
the magnitude of the velocity vector at each sampling point to
maintain isokinetic sampling conditions. If the yaw angle varies
E-14
-------
Stack Wall
10°-
10° ^
20° _
30° _
Center of Stack
Stack Wall
Figure 4-10. Typical Pitch Angle Profile in Stack with Cyclonic Flow.
Data near Walls and at Center is Unreliable.
Current
Stack Wall
40C
50C
60<
70° .
80° -
90° J
Center of Stack
Stack Wall
Figure 4-11.
Typical Yaw Angle Profile in Stack with Cyclonic Flow.
Data near Walls and at Center is Unreliable.
E-15
Current
-------
across the stack cross section, then the sampling velocity is
not weighted proportionally to the axial component of the
velocity vector. In this situation, proportional sampling
requirements can be satisfied by adjusting the sampling time
for each sampling point such that the volume of sample collected
is related by a constant to the axial velocity component at each
sampling point. This can be accomplished by weighting the
sampling time at each point by cos (where <)> is the angle between
the velocity vector and the stack axis):
02 = B! cos<{> (5)
6, = nominal sampling time per point
62 = actual sampling time at a point
= misalignment angle at a point
The sampling team should be careful in selecting the nominal
sampling time per point to ensure collection of the minimum
required sample volume since application of Equation 5 will re-
duce the actual sampling time.
In sampling to determine compliance with a mass emission
rate standard the volumetric flow rate must be determined. Since
the angle of the velocity vector (with respect to the stack
axis) must be determined to apply the alignment approach, the
axial volumetric flow rate can be calculated as:
N
Z (X/AP. COS*.)
i <«
E-16
-------
where: Q = stack volumetric flow rate (ft /sec)
actual conditions
K = 85.48
C = pitdt tube coefficient
P
2
A = stack cross-sectional area (ft )
T = average stack temperature (°R)
P = absolute stack pressure (in. Hg)
M = molecular weight of stack gas, wet
5 (Ib/lb-mole)
A = pitot reading (in H90)
P *
4> = angle between velocity vector and stack axis
N = number of sampling points
No additional biases are introduced when calculating the volu-
metric flow rate if the angles <|>. are accurately known.
No sampling should be conducted at sampling points where
negative velocities are observed. There is no way to assign
a negative value to the quantity C.V. when the velocity is
negative since the sampling train obtains an integrated sample,
[Z C-V,]. The fact that negative flows are not sampled biases
the concentration measurement high if the negative flows contain
any particulate matter. When determining a mass emission rate,
the negative volumetric flow rate should be calculated based on
the negative axial velocity component. The net volumetric
flow rate,(positive volumetric flow rate minus negative volu-
metric flow rate), must be used to calculate the mass emission
rate. Where negative velocities are encountered, the mass
emission rate will be biased high due to the bias in the
concentration measurement.
E-17
-------
Compensation Approach - The compensation approach requires
determination of the direction of flow at each sampling point,
(by means of a three dimensional pitot sensor or similar device),
and measurement of the velocity vector at each sampling point.
In the compensation approach, the sampling nozzle is aligned with
the stack axis as in the blind man's approach. This method is
applicable to sources with both pitch and yaw angle misalignment
if a separate pitot and sampling probe are used.
The nozzle is not aligned with the flow direction; therefore
the effective nozzle area is reduced by cos<|> , Figure 4-12. In
the compensation approach, the angle is known and the sampling
rate is reduced by cos to maintain isokinetic sampling conditions.
The use of the nozzle area correction requires that the isokinetic
sampling rate is proportional to both the velocity vector V and
cos4> . Since the axial velocity component V is Vcos(J> , the
3.
nozzle area correction also weights the sampling rate proportion-
ally to the axial velocity. Therefore the requirements of
proportional sampling are satisfied.
The compensation approach is subject to biases when the
angle between the nozzle and the flow stream becomes sufficient-
ly large. For very large angles of misalignment, the flow
around the nozzle will create aerodynamic interferences with the
isokinetic sampling. In general, these interferences will bias
the concentration measurement low. The degree of the bias will
increase as the velocity increases and as the angle of misalign-
ment increases. Further study is required to determine at what
angle these affects become significant and the extent of the
biases on the sampling results.
E-18
-------
actual nozzle opening
area, A
effective area, EA
EA = A cos
Figure 4-12. Compensation Approach
E-19
-------
When sampling to determine a mass emission rate, the
volumetric flow rate should be determined as :
N
as in the alignment approach. No additional biases are intro-
duced in calculating the volumetric flow rate if the angles
are determined accurately.
As in the alignment approach, no sampling should be con-
ducted at sampling points where negative velocities are ob-
served. Again, this biases the concentration high if the
negative flow contains particulate matter. To calculate the
net volumetric flow rate where negative flows are encountered,
Equation 6 can be used by adding a negative sign to cos<|>
where 4> is negative, or the negative volumetric flow can be
subtracted from the positive volumetric flow. Where negative
flows are encountered the mass emission rate will be biased
high due to the high bias in the measured concentration.
SOURCE MODIFICATIONS
In some non- parallel flow situations, modifications to
the source can be made which permit application of the stan-
dard sampling methodology. The simplest source modification is
to move the sampling site to an alternative location and there-
by avoid the problem altogether. This option is generally not
available since anticipated non-parallel flow conditions should
have been a major consideration in the selection of the origi-
E-20
-------
nal sampling site. A second modification is to employ
straightening vanes to eliminate the non-parallel flow.
Straightening vanes can be fabricated of almost any material
(depending on the temperature encountered). In most cases, a
single vane or a pair of vanes at 90°, extending across the
stack are sufficient to eliminate the flow problem. The
straightening vanes should be at least 1/2 stack diameter in
length, (parallel to axis of stack).
At some sources, particularly at asphalt plants, a stack
with cyclonic flow functions as part of the inertial demister
system for wet scrubbers. Straightening vanes employed in
this situation would eliminate the stack's function as a con-
trol device and thereby greatly increase emissions. In most
cases, a stack extension equippped with straightening vanes
can be employed (Figure 4-13). Straightening vanes are used
to create a flow disturbance which improves the flow condi-
tions downstream at the sampling site. The flow disturbance
from straightening vanes also propagates upstream to an un-
known extent. It should also be noted that straightening vanes
exert work on the effluent stream which is evidenced by a
pressure drop across the vanes. In most cases, the straighten-
ing vanes will have little affect on the volumetric flow rate
through the system since the pressure drop across the vanes
is small compared to other pressure drops in the effluent
handling system. Ideally, any modifications which are employed
should not affect the flow pattern in stacks which function
as part of the control system. Any affects on the flow pat-
tern in the existing stack will generally reduce the cyclonic
E-21
-------
flow and increase the emission rate. Adherence to the follow-
ing criteria will minimize the affects of a stack extension
and straightening vanes.
1. the stack extension should be the same diameter
as the existing stack
2. the straightening vanes should be at least 1/2
stack diameter downstream from the exit of the
existing stack
3. the extension must be at least 2 1/2 diameters in
length after the straightening vanes.
A second type modification which can be used for stacks with
cyclonic flow is essentially the addition of a tangential
outlet duct (Figure 4-14) . Although this type of extension is
more difficult to construct, there is less affect on the flow
pattern in the existing stack and straightening vanes in the
extension may not be necessary. In some cases, the diameter
of the extension may be smaller than the existing stack which
reduces the actual length of the extension. In any case, the
extension must be at least 2 1/2 diameters in length to
satisfy the minimum requirements of Method 1.
E-22
-------
\
\
>l/2d
>2d
>l/2d
>l/2d
"i
Figure 4-13. Stack
Extension With Straightening
Vanes
TOP VIEW
Figure 4-14. Temporary Tangential
Outlet
E-23
-------
CONCLUSIONS
When particulate sampling is required and where non-
parallel flow conditions are encountered, a decision must
be made to either modify the source to eliminate the un-
acceptable flow situation or apply one of the special
sampling procedures which have been discussed. Source modi-
fications should be employed when feasible since they will
reduce the complexity and difficulty in obtaining a repre-
sentative sample. Modifications to sources where stacks with
cyclonic flow function as part of the control system should
be carefully planned.
Where source modifications can not be employed and special
sampling procedures are to be used, either the alignment
approach or the compensation approach should be used. The
blind man's approach should not be used due to the many
problems which are encountered which result in unknown biases
in the sampling results. The alignment approach is limited
to non-parrallel flow situation where only yaw angle misalign-
ment exists. The compensation method can be used in any non-
parallel flow situation, however a low bias in the sampling
results may occur for large angles of misalignment. Both the
alignment appeoach and the compensation approach allow a
particulate sample to be obtained isokinetically and both
approaches satisfy the requirements of proportionally weighting
the sampling relative to the stack axial volumetric flow rate.
Application of either the alignment or compensation approach
will require considerably more time and effort to obtain valid
sampling results than is encountered in the application of
standard particulate sampling procedures.
E-24
-------
Project Summary
TECHNIQUES TO MEASURE VOLUMETRIC FLOW AND PARTICULATE CONCENTRATIONS
IN STACKS WITH CYCLONIC FLOW
by
J. Douglas Sterrett, Allen R. Barbin, Joe W. Reece
W. Glenn Carter and Bruce B. Ferguson
Harmon Engineering and Testing, Inc.
Auburn Industrial Park
Auburn, AL 35810
Contract No. 68-02-3215
Project Officer: William J. Mitchell
Quality Assurance Division (MD-77)
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
ENVIRONMENTAL MONITORING SYSTEMS LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
E-25
-------
ABSTRACT
The ability of a venturi to accurately measure volumetric flow in
cyclonic flow situations was examined. A mathematical model, which was
developed to describe the effect of the venturi on the flow, correctly
predicted the intensification of the swirling motion in the venturi
throat and an interesting acceleration of the axial velocity component
in the core of the flow field. Experimental results showed that the
venturi can accurately measure volumetric flow, even in the presence of
fairly strong swirling flow. An analysis of the effect of a venturi on
particulate distribution showed that, even though the venturi converging
section directed particles toward the center of the venturi throat, the
intense swirl present in the venturi throat quickly convected the particles
back to the wall.
Both egg crate and e'toile devices were evaluated to determine their
ability to straighten swirling flow. It was found that the egg crate flow
straightener would effectively straighten swirling flow when the length of
the straightener was equal to or greater than its cell size. It was also
determined that significant energy savings could result if cyclonic flows
were straightened at the base of tall stacks. Empirical equations were
developed to predict the head losses for the various egg crate assemblies
studied. A field study to determine the effect of an egg crate device on
particulate distribution across the stack gave inconclusive results.
INTRODUCTION
Cyclonic flows are frequently encountered in the exhaust stacks of
stationary sources which come under present Federal and state emissions
regulations. Particles in a cyclonic flow are subject to a strong radial
acceleration field and many are convected to the stack wall where they
E-26
-------
cannot be quantitatively collected with conventional sampling techniques.
It has been suggested (1) that an in-stack installed venturi by itself
might straighten cyclonic flow and redistribute the particulate suffi-
ciently to render it samplable with conventional methods such as EPA
Method 5.
The initial objective of this study was to determine the validity of
this theory through laboratory and field measurements. The results showed
that the venturi was not adequate for this purpose. Thus, additional work
was conducted to evaluate the ability of other devices such as low-pressure
drop egg crates to straighten the flow and simultaneously move the particu-
late back towards the center of the stack.
EXPERIMENTAL
The wind tunnel shown in Figure 1 was used to investigate the effects
of the venturi on cyclonic flow. Air enters this wind tunnel through a
conical flow regulator, passes through a set of honeycomb straightening
vanes, and then flows through a carefully calibrated Herschel-type venturi.
The air then enters the suction side of a centrifugal blower. Immediately
downstream from the blower the air enters a tangential admittance swirl
generator, which cascades the air into the test section through four
longitudinal slots externally adjustable. Hinged vanes located in these
slots allow the angle of admittance to be controlled so that very intense
swirling flows can be generated.
This swirl generator was also used to evaluate the ability pf various
low-head loss straightening vanes (Figure 2) to straighten cyclonic flow.
Starting with an overall straightener length, L, of two pipe diameters,
each straightening device was tested at flow rates of 7, 10, and 13 m3/s.
E-27
-------
At each of these flow rates, head loss data were recorded for five different
swirl intensities. If the device straightened the cyclonic flow, its length
was shortened and the device retested. This process continued until the flow
field was no longer straightened.
After the wind tunnel studies were completed, the ability of the egg
crate to straighten cyclonic flow and to redistribute the particulate was
evaluated at a fertilizer plant. The stack at the plant was 76 cm in
diameter and 11 m high. Stack temperature was 32 °C, moisture was 5% and
the axial volumetric flow was approximately 127 m3/min. Exhaust gases from
the fertilizer blending operation entered tangentially at the base of the
stack and then passed through a water spray chamber and a turning vane to
produce swirling flow. The swirling flow caused particulate laden water
droplets to move to the stack wall where they drained downward and exited
with the scrubber water.
A galvanized steel egg crate of cell size D/4 (19 cm) and length D/2
(38 cm) was installed in the stack at a point seven pipe diameters downstream
of the turning vane (four pipe diameters from the stack exit). Particulate
and velocity measurements were made through sampling ports located two pipe
diameters downstream and two pipe diameters upstream from the center of the
egg crate. EPA Methods 1 (sampling point selection), 2 (velocity and volu-
metric flow), and 5 (particulate sampling) were used in the testing. Flow
angle with respect to the stack longitudinal axis was measured using a
United Sensor 3-dimensional pitot tube.
RESULTS AND CONCLUSIONS
Venturi Studies
It was found that an in-stack venturi designed as described in this study
will accurately measure volumetric flow in cyclonic flow situations. However,
E-28
-------
it will not straighten cyclonic flows nor redistribute the participate
because the total angular momentum is conserved as the gas passes through
the venturi throat. It was also found that the characteristic region of
low axial velocity in the center of the gas stream is accelerated in the
venturi throat to give a nearly rectangular velocity profile in the venturi
throat, itself.
Some possible benefits of an in-stack installed venturi designed
according to the specifications developed in this study are:
• Properly calibrated, a venturi can stand alone as a volume flow
measuring device;
• The increased velocity in the venturi throat could make possible
more accurate sampling in stacks with low velocities since most
pi tot tubes are inaccurate below 10 ft/s.
Flow Straightener Studies
Egg crate flow straighteners were found to be effective in removing
the swirl component of the flow at lengths equal to or greater than the
cell size. The straightening effectiveness was greatly reduced when the
length was reduced below the cell size.
The e'toile type Straightener was able to straighten swirling flow, but
the overall effective length requirements were greater than for the egg crate
and the head loss across the e'toile straighteners was also higher. For
example, the minimum effective length for an eight-vane e'toile Straightener
was two stack diameters.
The field testing results were inconclusive in relation to the ability
of the egg crate to redistribute the flow back towards the center of the
stack. However, the egg crate did destroy the strong swirling flow present
(Table 1) since the flow angle at all twenty traverse points downstream
of the egg crate deviated less than 4° from the stack axis. Also, static
E-29
-------
pressure measurements upstream and downstream of the egg crate were identical,
demonstrating that the head loss was negligible. Thus, we conclude that the
egg crate can be a cost-effective means to destroy cyclonic flow patterns.
In the particulate testing, eight, 60-min sampling runs were accomplished
using two Method 5 trains sampling simultaneously. (Train A sampled two pipe
diameters downstream of the egg crate and Train B sampled two pipe diameters
upsteam.) In the first three runs, each train sampled a total of 20 points
(10 points on each diameter). In these and the other five runs, Train A
sampled with its nozzle and pi tot tube aligned with the stack axis, while
Train B sampled with its nozzle and pitot tube aligned with the direction
of the gas flow at the sampling point. (Train B sampling time at each point
was adjusted so that the ratio of the volume of gas collected at each point
to the total axial volumetric flow in the stack remained constant.)
In the last five runs single-point sampling rather than traversing
was employed. In these runs, Train A sampled at the same point - a point
58 cm in from the port hole, but Train B sampled a different point in
each run, i.e., Run 4 (71 cm), Run 5 (67 cm), Run 6 (63 cm), Run 7 (58 cm),
and Run 8 (49 cm). The objective of these five runs was to determine the
particulate distribution upstream of the egg crate in relation to the
concentration at a specific point downstream of the egg crate.
The results of the eight runs (Table 3) show that in all runs the par-
ticulate concentration determined upstream compared well with that determined
downstream. Further, the close agreement between the two trains in the last
five runs shows that the particulate concentration was evenly distributed up-
stream of the egg crate. This demonstrates that the swirling flow effectively
removed large particles, i.e., the remaining particles were small enough to
follow the gas flow lines. Thus, the degree of redistribution of particulate
by the egg crate cannot be determined from these results. Resource limitations
E-30
-------
and the fact that no additional sources were available for testing prevented
conducting additional field tests.
REFERENCE
1. Mitchell, W. J., B. E. Blagun, D. E. Johnson, and M. R. Midgett. Angular
Flow Insensitive Pitot Tube Suitable for Use With Standard Stack Testing
Equipment, EPA-600/4-79-042. U.S. Environmental Protection Agency,
Research Triangle Park, North Carolina 27711, 1979.
E-31
-------
TABLE 1. FLOW ANGLES MEASURED DOWNSTREAM OF THE EGG CRATE
Distance from
Stack Wall (cm)
2.5
7.6
12.7
17.8
22.8
27.9
33.0
38.1
43.2
48.3
53.3
58.4
63.5
68.6
73.7
Flow Angle
Port A (6)
46
52
58
65
68
57
0
-54
-52
-46
-40
-34
-28
-20
-20
Flow Angle
Port B (9)
45
47
50
50
53
56
58
-1
-45
-44
-41
-37
-37
-32
-26
TABLE 2. COMPARISON OF PARTICULATE CONCENTRATIONS AND VOLUMETRIC FLOW UPSTREAM
AND DOWNSTREAM FROM THE EGG CRATE
Run
Number
1
2
3
AVERAGE
4
5
6
7
8
AVERAGE
Concentration
Upstream
130
147
26
1ST
22
31
103
35
64
"47
(mg/m3)
Downstream
130
154
22
102
18
31
86
33
55
~43
Volumetric
Upstream
137
138
115
130
Flow (mVmin)
Downstream
125
120
115
120
E-32
-------
Conical Flow
Regulator
5.5*
Test Venturl
(Dimensions In centineters)
Flow Rate Venturl
•Blower
Flow Straightening Vents
Flow
£
-------
J. Douglas Sterrett, Allen R. Barbin, Joe W. Reece, W. Glenn Carter, and
Bruce B. Ferguson are with Harmon Engineering and Testing, Inc., Auburn
Industrial Park, Auburn, AL 35810
Dr. William J. Mitchell is the EPA Project Officer (see below).
The complete report, entitled "Techniques to Measure Volumetric Flow and
Particulate Concentrations in Stacks with Cyclonic Flow," (Order No.
PB ; Cost: $ , subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: (703) 487-4650
The EPA Project Officer can be contacted at:
Quality Assurance Division (MD-77)
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
E-34
-------
SLIDE 305-0
NOTES
CYCLONIC
OR
NON PARALLEL FLOW
SLIDE 305-1
DEFINITION OF CYCLONIC FLOW
Cyclonic, swirling, or nonparallel flow is defin-
ed to exist in the stack when the average flow at
designated sample points in the stack average
greater than 10° off parallel with stack walls
SLIDE 305-2
E-35
-------
SLIDE 305-3
ESTABLISH A NONPARALLEL
FLOW TESTING PROTOCOL
• determine whether emission regulation is a con-
centration or mass emission regulation
• determine if purpose of test is to prove com-
pliance or show violation
• determine whether burden of proof is with the
agency or facility
• determine suitable test method(s) to accomplish
above goals
• provide facility with alternatives when a known
high bias on test results is suggested by agency
NOTES
SLIDE 305-4
KNOWN FACTS WHEN SAMPLING IN
NONPARALLEL FLOW
• measured particulate concentration will be biased
low (less than true value); non-parallel flow does not
affect measured gaseous concentration
• measured stack gas volumetric flow rate will be
biased high (greater than true value)
SLIDE 305-5
EXAMPLE VELOCITY PROFILE FOR
CYCLONIC FLOW
Axial Velocity Across a Traverse
Axial
Velocity
Percent Diameter
E-37
-------
SLIDE 305-6 NOTES
SAMPLING APPROACHES FOR
CYCLONIC FLOW
1. Blind Man's Approach
2. Alignment Approach
3. Compensation Approach
4. Source Modification
SLIDE 305-7
BLIND MAN'S APPROACH
PROCEDURE
• testing is performed in the normal manner and the
angular flow variations and biases are ignored
RESULTS
• participate concentration is biased low
• volumetric flow rate is biased high
• mass emission rate bias cannot be determined
SLIDE 305-8
ALIGNMENT APPROACH
PROCEDURE
• nozzle is pointed into direction of flow in an effort to
compensate for angular misalignment; angle is re-
corded at each point
• sample time at each point is compensated for mathe-
matically by cosine of misalignment angle
• mathematic compensation is made on flow readings
using velocity pressure and alignment angle
E-39
-------
SLIDE 305-9 NOTES
t' - t(cos 0)
Examples:
• 10° misalignment & 2 min./pt
f = 2(cos10°) = 1.97min.
• 45° misalignment & 2 min./pt.
t' = 2(cos 45°) = 1.41 min.
where:
t' = actual time sampled per point
t = sample time per point with no misalignment
6 = misalignment angle
SLIDE 305-10
(cont.) RESULTS
• testing is very difficult and time consuming
• particulate concentration contains less bias with
two exceptions: 1) nozzle is not corrected for
the angular misalignment in both planes and 2)
particulate does not follow flow pattern
• flow rate will be more accurate, however, a Type
S pitot tube also can only correct for the flow
misalignment in one plane
• mass emission rate may contain less bias, how-
ever, readjustment of nozzle angle at every point
can possibly introduce greater biases through
probe breakage and sample train leakage
E-41
-------
SLIDE 305-11
NOTES
COMPENSATION APPROACH
PROCEDURE
• testing is performed in normal manner with
exception that a larger nozzle is used to correct
for misalignment error and higher than true flow
rate
RESULTS
• particulate concentration is less biased
• volumetric flow rate is biased high
• mass emission rate is biased high
SLIDE 305-12
CORRECTING NOZZLE DIAMETER FOR
COMPENSATION APPROACH
TWO ERRORS MUST BE COMPENSATED FOR
• misalignment of particulate approaching nozzle
• higher than true velocity reading
SLIDE 305-13
REDUCED EFFECTIVE NOZZLE OPENING
ACTUAL AREA A - n[ | ]2
E-43
-------
SLIDE 305-14
REDUCED EFFECTIVE NOZZLE OPENING
NOTES
EFFECTIVE AREA = A cos*
SLIDE 305-15
ERROR DUE TO YAW ANGLE MISALIGNMENT
+150
+100
+50
-80
-60 -40
-20 0 +20
8, degrees
+40 +60
SLIDE 305-16
CORRECT THE NOZZLE DIAMETER
AS FOLLOWS
1. determine ideal nozzle diameter in normal manner with
velocity traverse
2. record all misalignment angles during velocity traverse
3. divide ideal nozzle size by cosine of average angle of
misalignment (equ. 1 )
4. select nozzle that is closest to this diameter for use
5. multiply actual nozzle diameter by cosine of average
angle of misalignment and use calculated value on data
sheet for isokinetic calculations and to set nomograph
(equ. 2)
+80
E-45
-------
SLIDE 305-17 NOTES
n' - n.
II, — ": 7T (equ. 1)
(cos 6)
Examples:
• 10° misalignment & 0.29" diameter nozzle
0.29
• (cos 10°)
45° misalignment & 0.29" diameter nozzle
where:
n,' = adjusted ideal nozzle diameter used to select
actual nozzle for compensation method sampling
n< = ideal nozzle diameter determined using average
velocity pressure with type "S" pitot tube oriented
normally (parallel to stack walls)
0 = average or maximum misalignment angle
SLIDE 305-18
nr = na(cos0)
(equ. 2)
Examples:
•10° misalignment & 0.375" diameter nozzle
n/ = (0.375)(cos 10°) = 0.369"
•45° misalignment & 0.375" diameter nozzle
n,' = (0.375)(cos 45°) = 0.265"
where:
n' = nozzle size used for setting nomograph and cal-
culating isokinetic rate
rt = actual nozzle diameter used on sampling train
0 = average or maximum misalignment angle
E-47
-------
SLIDE 305-19
SOURCE MODIFICATION
OPTION 1
Procedure:
• place a flow straightening device in stack to
interrupt cyclonic flow
• test in normal manner on parallel flow
Results:
• participate concentration should be accurate
representation
• flow rate should be more accurate
Note: flow straighteners can cause the source
to emit more particulate emissions due to lack
of cyclonic separation
NOTES
SLIDE 305-20
FLOW STRAIGHTENERS
SLIDE 305-21
SOURCE MODIFICATION
OPTION 2
Procedure:
» place an involute or exit duct on top of a small stack;
sample involute duct in normal manner
Results:
* particulate concentration, volumetric flow rate and mass
emission rate will all be accurate
E-49
-------
SLIDE 305-22
NOTES
INVOLUTE SYSTEM
o
o
INVOLUTE OR
SKIMMER
CYCLONE INLET
SLIDE 305-23
CONCLUSIONS
RANKING OF APPROACHES FOR
FACILITY TESTED SOURCES
• use flow straighteners or involute system if source will
not be affected and approach is feasible
• use compensation method for concentration emissions
regulation
• use blind man's approach for mass emission regulation
SLIDE 305-24
(cont) RANKING OF APPROACHES FOR
AGENCY TESTED SOURCES
• use source modification when it is certain that source will not
be affected and approach is feasible
• use blind man's approach for concentration emission
regulations '
• use blind man's approach for particulate concentration measure-
ment and measure volumetric flow at a more accurate location
for mass emission regulation
E-51
-------
SECTION F. CONDENSIBLES
Subject Page
1. Condensibles, reactive compounds, and effect of
sampling train F-3
2. Effects of sampling train configuration and analytical
procedures on particulate catch F-10
3. Slides F-27
F-l
-------
CONDENSIBLES, REACTIVE COMPOUNDS, AND EFFECT OF
SAMPLING TRAIN CONFIGURATION
*>y
Guy Oldaker
As source sampling technology has changed over the years,
the definition of what constitutes "particulate matter" has
been revised to reflect these changes. This definition is
crucial to the determination of what pollutants are controllable
and are thus subject to study and possible regulation.
A by-product of this situation is the problem of estab-
lishing sampling and analytical procedures which will reliably
collect those pollutants once they have been defined. Several
factors enter into the determination of exactly what kind of
data a given stack test will produce. These include the tem-
perature of the stack gas at the moment of filtration, the
location of the filter in the sampling train, and the analytical
methods used to retrieve the sample from the train for quanti-
fication. The existence of condensible and reactive particulate
has had a major part in determining the methodology used for
particulate sampling for NSPS sources and in state regulations
for existing sources. With the establishment of sampling train
design parameters, and analytical procedures begins the argu-
ment of the "representativeness" of the captured sample.
DEFINITION OF A PARTICULATE
The typical definition of particulate matter in most state
regulations reads something like "Any solid or liquid emission
except uncombined water at standard conditions." In most states
F-3
-------
EPA Method 5 is the predominant sampling method for determining
participate emission rates from sources. Method 5 defines parti-
culate as that which is captured by the probe and filter at 120°C.
Thus, many states use a Method that is inconsistent with their
legal definition of particulate.
On the Federal level, in the NSPS regulations concerning
particulate matter, the emission levels acceptable, and the methods
used to determine emission levels, are consistent with another
definition: "any finely divided solid or liquid material other
than uncorabined water as measured by Method 5 'or any equivalent or
alternative method." This avoids legal inconsistencies.
The question of inclusion of condensible material, and the
problems created by reactive particulate matter, have influenced
the development of the Reference Methods for use on NSPS sources.
As proposed in the Federal Register, August 17, 1971, for three
affected NSPS source classifications,the full EPA Method 5 train
(front and .back half) would have been used to determine particu-
late emission nates. Proposed allowable emission limits were based
on the results from use of the full EPA Method 5 drain.
The response to the proposed regulations challenged the
'representativeness' of the particulate sample captured in the
impingers. The full EPA Method 5 train was designed to attempt
to capture particulate as was defined at that time (particulate
existing @ 20°C and later). Questions were raised regarding
oxidation and condensation of sulfates as well as reaction
of sulfates on the filter and in the impingers, with respect to
whether these same reactions occur after dispersion into ambient
air. F_4
-------
As noted, factors such as filter type, placement and temper-
ature, and sample recovery techniques influence the quantity of
particulate captured. The development of the Method 5 train re-
flected an attempt to have a sampling method consistent with the
definition of particulate at that time. However, the arguments
put forward against back-half analysis carried a considerable
amount of weight when coupled with the lack of studies on reaction
and dispersion characteristics of particulates upon exiting the
stack. The EPA engineers determined that the material collected
in the impingers was usually (though not in every case) a consis-
tent fraction of the total particulate catch. In fossil-fuel ed
steam generators this fraction was approximately 50 percent, while
in the case of incinerators 20 to 30 percent of the total parti-
culate catch was found in the impingers. The EPA chose to use only
the front half of the Method 5 train to determine the particulate
emission rate, making a corresponding reduction in the allowable
emission limit.
BACK-HALF ANALYSIS
As noted, a considerable amount of thought has gone into what
constitutes a "particulate" and whether the captured sample is
representative of what the control equipment sees or what occurs
at ambient condition after dilution and cooling. The full EPA
train (front and back-half) seems to represent sampling conditions
consistent with many state regulations. Eleven states allow for
the reporting a back-half analysis in some form.
F-5
-------
Going to the CRC Handbook of Chemistry and Physics, one can
find some 180 inorganic and organometallie compounds which boil
or sublime above 20°C but below 120°C. Though these compounds
would be included in the legal definition of'particulate" in 48
states, they will pass through the heated filter of a standard
Method 5 train.
The two major compound groups which are most discussed when
considering back-half analysis are sulfates and organics. The de-
gree to which these groups condense or react in the impingers ap-
pears to be dependent upon the source. However, in each source
category the percentage of the total particulate tends to be con-
sistent. The condensation and reaction of SO compounds has been
A
a subject of much discussion. EPA engineers have determined for
NSPS sources this reaction does not necessarily play a large part
in the back-half catch. Hydrocarbons (organics) play a larger role
at sources such as wood veneer plants, coffee roasters, and some
asphalt plants. Back-half catch may account for 50% or more or the
total catch. Clearly, this is a significant fraction. (See
Table 6.1).
Analysis procedures are important when back-half catch is
desired. Simple boil-down of the impinger water would result
in the loss of these organic compounds. The usual procedure
would be an ether-chloroform extraction with a boil-down at am-
bient conditions. The remaining inorganic salts and acids could
be boiled down as usual. In the source categories noted above,
the organic catch will have a greater impact of the total catch
than the inorganics.
F-6
-------
Back-half analysis raises the possibility that results could
be biased slightly high through inclusion of dissolved or hydrated
gases (HC1 readily combines with impinger water) which, by them-
selves, are gaseous at room temperatures. Sulfates may be formed
as a pseudo-particulate by reaction in the impinger water such as:
NH3 + S02 + H20 -* (NH4)2503 (1)
or
S03 + H20 H. H2S04 (2)
(unbalanced equations)
The question of these reactions affecting the total particulate
catch is still unanswered. However, these biases will tend to be
insignificant when compared to the amount of genuine particulate
caught.
The central question in dealing with condensibles and re-
active compounds is defining what constitutes a particulate. In
the majority of states there is an inconsistency between the legal
definition and the particulate sampling methodology. The parti-
culate catch depends on the sample train configuration and sampling
temperature.
In the NSPS regulations, particulate is defined by the meth-
odology used. By specifying Method 5 & 120°C (160°C for fossil-
fuel-fired steam generators) a common basis is drawn for comparison
of allowable emission levels with particulate sampling data. (The
current Method 5 is front-half analysis only.)
The cost of controlling the particulates which exit at stan-
dard conditions could be prohibitive. In setting NSPS emission
F-7
-------
levels, the best available control technology (considering cost)
must be taken into consideration by the EPA administrator. By
selecting sampling methodology and emission levels that demonstrate
the level achievable by this control technology, the EPA avoids the
problem of considering the representativeness of the samples when
condensibles and reactive compounds are excluded. The questions
about the reactions which occur in the back-half, and whether these
take place beyond the stack exit, still exist and are a subject
of further research.
F-8
-------
Table 6-1
Source Category % of Total Catch Collected
In Back Half
Fossil Fuel Fired Steam Gen. : 50%
Incinerator - 20-30%
Conventional
Asphalt Hot Mix overall 41-48%-86%
w/ scrubber 4 -29 - 56
w/ Baghouse 30-66 - 86
Drum-Mix (Preliminary)
Uncontrolled - 26%
Venturi control (Scrubber) : 9%
Wet Scrubber Fan ~ 17%
Asphalt Roofing ?
Petroleum Refineries 36- 56 - 83
Lead Smelter 36- 77- 83
Secondary Brass and Bronze 17- 38 - 58
BOF (Steel and Iron) 14- 30 - 40
Electric Arc
Inlet Baghouse 1-2 - 4
Outlet Baghouse 40- 57 - 76
F-9
-------
13
Effects of Sampling Train Configuration
and Analytical Procedures on Particulate Catch
BY
Walter S. Smith
Robert A. Estes
F-10
-------
As source sampling technology has changed over the years,
the definition of what constitutes "particulate matter" has
been revised constantly to keep up with those changes. This
definition is crucial to the determination of what pollutants
are controllable and are thus subject to study and possible
regulation.
A by-product of this situation is the problem of establish-
ing sampling and analytical procedures which will reliably col-
lect those pollutants once they have been defined. Several
factors enter into the determination of exactly what kind of
data a given stack test will produce. These include the temp-
erature of the stack gas at the moment of filtration/ the loca-
tion of the filter in the sampling train, and the analytical
methods used to retrieve the sample from the train for quanti-
fication. The effects of these factors on the particulate catch
warrant close examination.
Defining a Particulate
In the beginning, definitions of particulate matter were
largely empirical. "Solids, in the form of dust or fume, which
pass with the gases through a flue or stack" seemed reasonable
enough in 1920. By 1957, the American Society of Mechanical
Engineers was using "particles of gas-borne solid matter larger
2
than one micron mean diameter," which, if anything, is less
comprehensive than its predecessor.
F-ll
-------
As concern of the quality of the environment escalated
during the past decade, an attempt was made to extend the scope
of source sampling beyond an evaluation of the best available
control equipment toward complete emissions inventories. Corre-
spondingly, there was a general broadening of the definition of
particulates by state agencies. A definition similar to "any
material, except uncombined water, which exists in a finely
I • 3
divided form as a liquid or solid at standard conditions" cur-
rently appears in the regulations of all but two states.
In the Federal Register, June 14, 1974, EPA states that
"particulate matter means any finely divided solid or liquid,
other than uncombined water, as measured by Method 5... or an
4
equivalent or alternative method." In other words, a particu-
late is now anything which is caught by the sampling apparatus
used, and then detected by the analytical methods employed.
Sampling Train Development
As noted, different sampling trains and analytical methods
can yield different results. A major variable is the config-
uration of the sampling train. The location of the collection
filter, the temperature at which it is maintained during a test,
and the selective inclusion or exclusion of elements of the
sample train in total catch analysis are important factors in
ascertaining particulate catch.
Early methods of determination of dust concentration in
gas streams, notably Western Precipitation Company's WP-50 (1920)
and the ASME's Power Test Code 21 (1941) employed instack filters
F-12
-------
for particulate collection (Figure 1). One such filter, the
Alundum Thimble/ is a relatively coarse filter medium which is
maintained in the stack at stack temperature. Penetration of
particulate through the thimble was at that time considered to
be a negligible problem.
As particulate collection devices such as electrostatic
precipitators, became widely used, the importance of catching
smaller particles increased. A more comprehensive sample than
was provided by a heated filtration medium was also desired.
In 1963/ the Los Angeles Air Pollution Control District
devised a sampling train in an effort to achieve a complete
emissions inventory. Three Greenberg-Smith impingers in series,
the first two prefilled with 100 ml. distilled water and the
third dry, serve as particulate collectors. Normally, the im-
pinger train is backed up by a single thickness paper extraction
thimble in order to collect any particulate matter that may have
passed through the impingers (Figure 2). If particulate wetting
is undesirable, an Alundum Thimble, substituted for the paper
thimble, may precede the impingers (Figure 3) . In all cases,
analysis of the impinger water by extraction, boil-down and
weighing is specified. This method will hereafter be referred
to as the LA Method.
Eight years later, the Method 5 sampling system guidelines
were promulgated by the EPA. Method 5 retained the concept of
out-of-stack filtration introduced in the LA Method, but in a
different format (Figure 4). A glass mat filter was placed
F-13
-------
before the impinger train, and the filter maintained at about
250°F. Heating of the probe was also specified, such that the
temperature of the gas sample would not fall below 250 prior
to filtration. Impinger water analysis was retained as a part
of the sample recovery procedure.
In the Method 5 train, as originally proposed, effluents
which condense above 250 F should be caught on the heated filter;
those which condense between 250°F and 70°F should be caught in
the condensers. The filter catch is then determined gravi-
metrically, and the water in the condensers is analyzed for par-
ticulate content. These determinations, taken together, comprise
a sample which attempts to include all substances which are
particulate standard conditions.
Back Half Analysis
Method 5 currently calls for removing particulates from
sample - exposed surfaces ahead of the filter frit with an
acetone rinse. The acetone is then evaporated at ambient
temperature and pressure, desiccated, and weighed. This defines
particulate catch at the temperature of the filter during samp-
ling or at room temperature, whichever is higher. However,
some water of hydration might be included in that catch.
Since most stack temperatures are well above room tempera-
ture, the practical problem of excessive drying time leads many
to dry the sample at the temperature at which the filter was
maintained during the test. This should not affect results,
as long as drying temperature does not exceed the sampling temp-
erature.
F-14
-------
Analysis of the impinger water, as noted previously, is
necessary to account for any effluents which are gaseous at the
filter temperature but which condense at the temperature of the
impingers. At present, eleven states require analysis of the
impinger catch, though the methods of analysis vary. Federal
regulations currently omit the back half entirely.
According to the CRC Handbook of Chemistry and Physics
there are some 180 inorganic and organometallic compounds which
boil or sublimate above standard temperature but below 250°F.
Though these compounds would be included in the legal definition
of "particulate" in 48 states, they will pass through the heated
filter of a standard Method 5 train.
Simple boiling down of the water would result in the loss
of those effluents that volatilize at the temperature employed.
Simple extraction will remove some of the volatiles, yet solubles
are left behind. Therefore, the reasonable procedures would be
extraction with a solvent (e.g., ether-chlorofom), followed by
boil-down. This procedure would remove most everything, depend-
ing on the solubility of the volatiles in extraction. For trains
with the filter after the impingers (Figure 2), filtration is
needed to remove solids in the impinger water prior to extrac-
tion .
Back half analysis raises the possibility that results
could be biased slightly on the high side through the inclusion
of dissolved and hydrated gases which, by themselves, are gas-
eous at room temperature. An example would be hydrated HCl
F-15
-------
derived from HCl gas and the water in the impingers. Additional
positive error can be introduced through the formation of pseudo-
particulates in the impinger water, e.g.,:
NH3 + SO2 + H20 -»• (NH4)2S03 .
This particular action ultimately takes place in the atmosphere,
but whether or not it should be included in the particulate
catch is a question as yet unanswered.
Nevertheless, any such positive bias will likely be insig-
nificant relative to the amount of genuine particulate which is
caught by the impingers. With the collection filter maintained
at 250°F during a test, the amount of particulate matter in the
impinger water will certainly be significant and should not be
overlooked.
Filter Location and Temperature
In-stack filtration methods, by maintaining the filter
medium at the temperature of the stack gas, define particulates
as substances which are solid or liquid at that temperature.
This data, while useful for control equipment design, is of
little value in the context of environmental impact assessment.
Since emissions caught by the filter consist only of substances
which are particulates at the stack temperature, these emissions
will change from source to source, perhaps even fron run to run,
as the definition of particulate varies with fluctuations in
stack gas temperature.
Whereas in-stack filters define particulates at stack temp-
erature, Method 5 defines particulates at the temperature of the
F-16
-------
out-of-stack filter. This temperature is nominally 250°F, but
regulations allow for a range of +25°F, and temperatures up to
320°F are permitted in the case of fossil-fuel fired steam gen-
erators .
Effluents emitting from high-temperature sources may not
cool to 250 F before filtering, depending on such factors as
ambient temperature, wind speed, and probe length. On the other
hand, effluents which enter the probe at less than 250°F will
be heated to some extent prior to reaching the filter medium.
Another angle to consider, though minor, is what might
happen if the probe were not as hot as the filter, causing the
stack gas sample to be cooled and then reheated. Should this
occur, there is the possibility that some substances which are
gases at the filter temperature would cool enough to form partic-
ulate in the probe. These may not evolve back into the gaseous
state upon reheating.
To avoid heating a sample above its stack temperature,
maintaining the filter at 250°F or stack temperature, whichever
is lower, is sometimes proposed. This broadens somewhat the
definition of a particulate in the case of effluents at less
than 250°F, but reintroduces the original problem of having the
definition of the particulate collected based on a variable.
While the temperature of the heated box can be maintained
in the neighborhood of 250°F, or any other arbitray figure, the
crucial factor, namely the temperature of the sample at the
moment of filter penetration, remains difficult to monitor and
control with current Method 5 hardware.
F-17
-------
Placement of the filter after the impingers, as in the LA
Method or in EPA Method 13 (Figure 5) , leaves all of the problems
involved in back half analysis unsolved, while introducing addi-
tional ones. Collection of basic materials in the impinger
water increases the likelihood of trapping acid gases. In addi-
tion, the fact that carbon does not wet poses clean-up problems.
In a few instances the use of filters in both places is
specified (Figure 6). Experience has indicated, however, that
the use of filters both before and after the impinger train does
not yield results significantly different from those obtained
by an unmodified Method 5 train (Figure 4).
As to the actual sampling train, then, it can be said that
the Method 5 system as originally proposed, is, if not perfect,
the most effective method devised to date. Ideally, all sub-
stances in the effluent stream which are solid or liquid at stan-
dard conditions are caught on the filter or in the water impin-
gers. This arrangement comes close to catching particulates
as defined at standard conditions.
Keep in mind the difference between what the train actually
catches, and what is retrieved from the train and reported as
the particulate catch. How the results of a test are analyzed
determines how accurately the reported catch represents the
actual catch.
F-18
-------
Conclusions
Total assessment of environmental impact was close to
reality with the original Method 5 system. Economic factors
entered the picture at this point, however. Arguing that
the cost of total control technology would be prohibitive at
this point, industries campaigned for removal of the condenser,
or back half, analysis from the total catch. This eliminates,
for example, measurement of SO-, emitted by fossil-fuel fired
installations.
So it has come to pass that Method 5 currently ignores the
back half catch in its determination of particulate emissions.
The consequences of ignoring this part of the train are signifi-
cant, since the nature of the catch—and thus the working defi-
nition of a particulate—now rests solely upon what is caught
by the heated filter. All states currently accept EPA Method 5
particulate data in some applications; most accept this data for
all particulate emissions tests. As we have seen, a disparity
exists between the nature of particulates collected by Method 5
and the nature of particulates as defined by law in no less than
48 states. By accepting data produced by the current Method 5
those states are, in effect, contradicting their own statues.
Thus, inclusion or exclusion of the back half analysis, in
conjunction with the temperature at which the filter is main-
tained during sampling, unquestionably affect the results ob-
tained during a particulate test. If the back half is ignored,
as is currently the case with Method 5, the operating tempera-
ture of the front half of the train becomes very significant in
F-19
-------
determining what is caught by the heated filter and thus per-
ceived as particulate emissions.
Method 5 is now specified as the procedure to be used when
making particulate mass emission measurements for compliance
with performance standards. These standards have been formulated
bearing in mind "the degree of emission reduction which (taking
into account the cost of achieving such reduction), the Admini-
strator determined has been adequately demonstrated."
In other words, despite the advances in stack sampling
technology in recent years, we are still evaluating the best
available control technology. Testing and regulation of total
environment impact of effluent gases is not yet a reality.
F-20
-------
FIGURE 2
PROBE
THIMBLE
HOLDER
ICE BATH
1 IMPINGERS
METERING
SYSTEM
Figure 2. L.A. method particulate train with paper thimble after water Impingers.
-------
FIGURE 3
PROBE
THIMBLE
HOLDER
ICE BATH j
I
METERING
SYSTEM
Figure 3. L.A. Method participate train with ceramic thimble
preceding water impinger.
-------
FIGURE 4
i
NJ
10
-FIL
PROBE IHO
,,. - I /
•*-. . 1 1 /
(
TER-,
LDER
nr\ •
in
^ ' i V i
1 1
HEATED BOX
CONDENSER
METERING
SYSTEM
Figure 4. EPA Method 5 particulate train with heated glass mat
filter preceding condenser.
-------
FIGURE 5
l
to
PROBE
FILTER
HOLDER
I
ICE BATH I
IMPIIMGERS
-1 I
METERING
SYSTEM
Figure 5. EPA Method 13 train with glass mat filter following impingers.
-------
FIGURE 6
,- FILTER -,
PROBE iHOLDER|
J
I
HEATED BOX
CONDENSER
FILTER
HOLDER
METERING
SYSTEM
to
Figure 6. Participate train with glass mat filters
before and after condenser.
-------
FIGURE 7
NOZZLE
i
to
PROBE
IN-STACK
FILTER
HOLDER
CONDENSER
METERING
SYSTEM
Figure 7. In-stack participate sampling train.
-------
SLIDE 306-0 NOTES
CONDENSIBLE
MATTER
SLIDE 306-1
DEFINITION OF CONDENSIBLE MATTER
Condensible matter or condensible particulate
is usually defined as any matter that is in gaseous
phase at stack temperature
SLIDE 306-2
BIASES FROM CONDENSIBLES
POSITIVE
Some condensibles that are not intended to be
regulated condense below stack temperature and are
collected on heated filter
NEGATIVE
Some condensibles that are to be regulated do not
condense at filter temperature and pass through filter
F-27
-------
SLIDE 306-3
NOTES
CONDENSIBLE MATTER
SOURCE
CATEGORY:
• fossil fuel fired gen.
• incinerator
• asphalt plant
• smelters
% OF TOTAL CATCH
IN BACK HALF:
«50
20-30
40-85
35-85
SLIDE 306-4
I^J
PROBE
J V 1 1
IN-STACK
FILTER
i if\i r^i-r»
Pfil\inFIM<»FR
LrVsIM L/ClvOCrl
METERING
SYSTEM
FIRST GENERATION LA. SAMPLE TRAIN
SLIDE 306-5
PROBE
r\
i
ICE BATH j
1
J. —
".
THIMBLE
HOLDER
IIN=»=
METERING
SYSTEM
j_jMP|NGERS ,
SECOND GENERATION LA. SAMPLE TRAIN
F-29
-------
SLIDE 306-6
PROBE
NOTES
THIMBLE
HOLDER
METERING
SYSTEM
ICE BATH!
THIRD GENERATION LA. SAMPLE TRAIN
SLIDE 306-7
PROBE
ir~ 1
.-FILTER-,
(HOLDER
1 rfFh '
£ 1 , w i-
1 1
HEATED BOX
omVincMocD
IrUIMUklMohn
METERING
SYSTEM
EPA METHOD 5 SAMPLE TRAIN
SLIDE 306-8
PROBE
FILTER
HOLDER
ICE BATH
METERING
SYSTEM
EPA METHOD 13 SAMPLE TRAIN
F-31
-------
SLIDE 306-9
NOTES
PROBE
HP> L_
>-*
,-FILTER-,
i HOLDER |
n ' /IFh i
=* — i — MLK — i —
L J
HEATED BOX
l^/^&ir%rM|c«r**ri
CONDENSER
HLTER
HOLDER
t
METERING
SYSTEM
EPA METHOD 13 SAMPLE TRAIN
SLIDE 306-10
NOZZLEf
XTK PROBE
1
1
IN-STACK
FILTER
HOLDER
rnrunPMQPP
vrVylllL/dMOun
METERING
SYSTEM
EPA METHOD 17 SAMPLE TRAIN
SLIDE 306-11
STEPS TO HANDLE CONDENSIBLES
•determine if condensibles are to be regulated by
applicable emissions regulations
•design proper sampling and analytical procedures to
match intention of the regulation
F-33
-------
SLIDE 306-12 NOTES
REMOVAL OF SULFATE CONDENSIBLE
FROM THE PARTICULATE CATCH
•heat sample train filter and probe above sulfate
dewpoint
Sample to a specified temperature {i.e..
F,450°F) for 4 hours in a furnace
•IPA rinse recovered sample and titrate for free acid
(H2SO4- 2H20)
•water rinse recovered sample and titrate for acid and
sulfates (H2SO4- 2H2O)
SLIDE 306-13
INCLUSION OF SULFATE WITH
PARTICULATE EMISSIONS
OPTION 1
• ensure probe and filter temperature do not
exceed specified temperature (i.e., 250°F, 320°F)
• do not allow any posttest heating of the
recovered sample
OPTION 2
• use Methods 5 and 8 sampling trains
• remove all sulfates from Method 5 sample as
previously cited and then add sulfate results
from Method 8 train
SLIDE 306-14
EXCLUSION OF OTHER INORGANIC
CONDENSIBLES FROM PARTICULATE CATCH
OPTION 1
• use an in stack filter sample train
OPTION 2
• maintain probe and filter temperature above dewpoint of
condensibles during testing
OPTION 3
• determine exact amount of condensible in sample by analytical
means and subtract from catch
F-35
-------
SLIDE 306-15 NOTES
USE OF IMPINGERS TO COLLECT
CONDENSIBLES
ETHER-CHLOROFORM EXTRACTION
TECHNIQUE
Problems with technique:
• pseudopartlculates may be formed in the impingers
• ether-chloroform extraction can be highly dependent
on pH of sample
SLIDE 306-16
(cont) Elimination of problems with technique:
• allow source to determine and subtract any pseudo-
pa rticulates
• standardize pH for extraction when non-extractables
are not to be included
• have published procedures that are applied uniformly
SLIDE 306-17
CAUTIONS ON CONDENSIBLE
SAMPLING TECHNIQUES
• EPA Reference Method 5 sample box temperature may
not be an accurate indication of sample gas temperature
• condensed particulate matter may change its chemical
composition after condensation
• although temperature is major parameter for collection
of condensibles, several other factors can greatly affect
condensibles, i.e.. moisture content, dilution air, pre-
sence of other compounds
F-37
-------
SECTION G. FLUCTUATING VELOCITY
Subject page
1. Slides G_3
G-l
-------
SLIDE 307-0 NOTES
FLUCTUATING VELOCITY
SLIDE 307-1
TYPES OF FLUCTUATING VELOCITY
o minor variations at short time
intervals (seconds)
o major variations at short time
intervals (seconds)
o minor variations at long time
intervals (minutes)
o major variations at long time
intervals (minutes)
SLIDE 307-2
MINOR VARIATIONS AT
SHORT TIME INTERVALS
o add extra lengths of tubing
(i.e., 100 ft) to pitot tube
lines
o add capillary tube to impact
line
G-3
-------
SLIDE 307-3
NOTES
SLIDE 307-5
MAJOR VARIATIONS AT
SHORT TIME INTERVALS
1. Add extra length of pitot
tube lines
2. Make flow adjustments at 2
minute intervals and ignore
at other times
3. Calculate the impact of
variation with preliminary
velocity traverse and make
appropriate adjustments in
isokinetic rates
G-5
-------
SLIDE 307-6 NOTES
MINOR VARIATIONS AT
LONG TIME INTERVALS
o change isokinetic sampling rate
whenever Ap changes by more than
20%. Mentally time weight both
the Ap and AH and record their
time weighted readings
SLIDE 307-7
MAJOR VARIATIONS AT
LONG TIME INTERVALS
o change isokinetic sampling rate
whenever Ap changes by more than
20%. Mentally time weight both
the Ap and AH and record their
weighted readings
o allow testing to proceed if the
large variation in Ap forces the
train out of its range of main-
taining isokinetic
o do not change nozzles during
a sample run
G-7
-------
SECTION H. SOOT BLOWING
Subject Page
1. Particulate source sampling at steam generators
with intermittent soot blowing H-3
2. Slides H-23
H-l
-------
PARTICULATE SOURCE SAMPLING AT
STEAM GENERATORS WITH
INTERMITTENT SOOT BLOWING
OCTOBER 1, 1978
PREPARED FOR:
KIRK FOSTER
DIVISION STATIONARY SOURCE ENFORCEMENT
PREPARED BY:
JAMES W. PEELER
ENTROPY ENVIRONMENTALISTS, INC.
H-3
-------
PARTICULATE SOURCE SAMPLING AT
STEAM GENERATORS WITH INTERMITTENT
SOOT BLOWING
Introduction
At fossil-fuel fired steam generators which utilize intermit-
tent soot blowing practices, a major contribution to the total
particulate emissions from the facility often occurs during
relatively short duration soot blowing periods. Since emissions
during soot blowing periods can be quite significant, a procedure
is needed for conducting performance tests and weighting the
test results in a manner which will accurately reflects the
total emissions from the source. The major problem areas encount-
ered in developing such a procedure include: (1) establishing
a workable definition of "representative" emission values which
is directly comparable to the applicable emissions standard;
(2) determining representative source operation conditions for
conducting the performance test, (both for normal operating
conditions and soot blowing conditions); and (3) collecting
particulate samples which accurately reflect the emissions for
both source operating modes. This paper discusses these problem
areas and outlines methods which may be employed to determine
representative emission values for fossil-fuel fired steam gen-
erators with intermittent soot blowing. It should be noted that
some control agencies enforce emission standards which are effec-
tively "never to exceed" emission limitations. In this situation,
sources must comply with the emission standards during soot
blowing and testing must be conducted to reflect the maximum emis-
sions from the source. Other control agencies may exclude soot
blowing from all performance tests as a non-representative opera-
ting condition. This paper does not attempt to address either of
these issues.
H-4
-------
Soot Blowing Practices / Effluent Characteristics
Soot blowing practices are highly variable between sources and
are subject to change both with time and with operating conditions
at any specific source. The frequency. and duration of soot blow-
ing periods is dependent on many factors including: boiler
design, firing method, furnace operating conditions, combustion
efficiency, type of fuel, ash content of fuel, operating load,
and the frequency/magnitude of load fluctuations. Soot blowing
may be conducted as a regularly scheduled intervals or may be
initiated as necessary when indicated by operating parameters
such as increased pressure drop across the furnace and heat
exchanger surfaces, or decreased heat transfer efficiency.
Some modern large scale generators blow soot continuously. For
steam generators with intermittent soot blowing, the frequency
of the cleaning periods ranges from once per 24 hours to nearly
continuously. Both manual and automatic soot blowing systems
are used at steam generators.
The soot blowing process employs a number of lances to remove
accumulated material from the heat exchange surfaces in the fur-
nace, boiler, superheater, and air preheater while the boiler is
operating. The lances travel across the heat exchange surfaces
and remove the deposits by means of high pressure jets of steam
or air. The effectiveness of the lances is dependent on (1)
spacing of the lances, (2) nozzle design and angle of attack,
(3) air or steam pressure, (4) lance-to-tube speed, (5) frequency
and duration of operation, and (6) the nature of the deposits
on the tube surfaces.
The particulate concentration of the uncontrolled effluent stream
is subject to large temporal variations during the soot blowing
period due to the nature of the tube cleaning process. For a
specific lance, most of the accumulated material is removed
from the tube surfaces on the instroke of the lance. The re-
maining deposits are removed as the lance is retracted. In
addition, the cleaning process is usually initiated at the heat
H-5
-------
exchange surfaces nearest the burners and moves downstream,
finally cleaning the air preheater. Since deposits on the various
heat exchange surfaces are generally not uniform, this method
of cleaning adds to the temporal variations in the uncontrolled
particulate concentration during the soot blowing period. The
variations in the particulate concentration during soot blowing
may be minimized or "smoothed" to some extent by the particulate
control device and effluent handling system.
For the purposes of conducting particulate emission performance
tests, steam generators utilizing intermittent soot blowing
practices should be treated as cyclic or batch processes where
each cycle consists of a period of normal operation and a period
of soot blowing. The normal operation period is characterized
by steady-state source operation and relatively constant emission
levels over the duration of the performance tests. In contrast,
the soot blowing period is characterized by increased particulate
emissions and large fluctuations in the emission values over a
relatively short time period.
Representative Emission Values
Isokinetic sampling for particulate matter automatically integrates
or averages the particulate concentration of the effluent stream
over the duration of the sampling run. Thus, at most sources, the
time period for averaging emission values is indirectly defined by
the duration of the sampling run. Three sample runs are averaged
to determine the performance test results. For steam generators
with intermittent soot blowing, the fluctuations in particulate
concentration are relatively large and the interval between soot
blowing periods may be considerably greater than the duration of
the sampling runs. Therefore, at these sources, alternate sampling
procedures and alternate averaging or weighting procedures must be
employed to determine representative emission values.
For the purposes of this discussion, "representative" emissions
are considered to be the emission values which would be measured
if, for a given time period, the entire effluent stream could be
H-6
-------
collected, well mixed, and then sampled. Employing this defini-
tion, the representative emission rate for a steam generator with
intermittent soot blowing is equivalent to the emission rate from
a steady-state source which would produce the same net pollutant
mass emissions over the time period being considered.
Consider the simplest case where independent sampling runs are
conducted to determine the pollutant mass rate at normal operating
conditions and during soot blowing. If multiple sampling runs
are performed at either operating condition, then the averages of
the samples at each operating condition should be used to determine
the representative emission rate. The pollutant mass emission
rate which is representative of the emissions from the source,
(pmr), may be calculated from the following equation:
pmr =(pmr1t1 + pmr2t2) x 100 (1)
where: pmr.. = average pollutant mass rate of
samples at normal operating
conditions
pmr- = average pollutant mass rate of
samples during soot blowing
t1 = percent of source operation time
at normal operating conditions
t2 = percent of source operation time
blowing soot
The volumetric flow rate, (dry, standard conditions) and percent
excess air are not expected to vary significantly between periods
of normal operation and periods of soot blowing. Therefore, a
representative mass concentration, (C),or representative specific
emission rate, (E, lbs/10 Btu), may also be determined by simply
time weighting the measurements at each condition;
H-7
-------
" =
= (C1t1 + C2t2) x 100 (2)
C + Ct) x. 100 x ( ° )
where: C, = average particulate concentration
of samples at normal operating
conditions
C~ = average particulate concentration
of samples during soot blowing
It should be emphasized that if the volumetric flow rate varies
significantly between normal operation and soot blowing periods,
then alternate equations should be employed to determine repre-
sentative particulate concentrations and representative specific
emission rates. In addition, if the percent excess air varies
significantly between the two source operating modes, then alter
nate equations must be employed to determine representative spe-
cific emission rates. These equations are derived in Appendix A
of this paper.
As an alternate to conducting independent sampling runs during
normal operations and soot blowing periods, a representative
emission rate may be determined if sampling runs are conducted
at normal operating conditions and additional sampling runs are
conducted which include both normal operation and soot blowing.
In this case, the representative pollutant mass rate may be
calculated as:
p = Pmr1(t1- t2) + pmrx (p)t2 x 100 *(4)
where:
pmr^ = average pmr of sample (s) at normal operating
conditions
pmrx = average pmr of sample(s) containing soot blowing
*This equation was developed by C. L. Goerner of the Texas Air
Control Board. See Appendix B for details.
H-8
-------
t^ - percent of source operating time at normal
operating conditions
t2 = percent of source operating time blowing soot
A = hours of soot blowing during sample(s)
B = hours not soot blowing during sample(s)
containing soot blowing
The above equation may be employed to determine a representative
particulate concentration, (U) or representative specific emission
rate, (E) provided that the volumetric flow rate remains constant,
and in the case of the specific emission rate, the excess air also
remains constant. It should be noted that Equation 4 may be
employed even when independent sampling runs are conducted at
normal operating conditions and during soot blowing. In this
situation, B=0 and pmr = pmr2. Thus Equation 4 reduces to
Equation 1.
Sampling Strategies
Due to the variability of both operating conditions and soot
blowing practices between sources, an appropriate sampling strat-
egy should be devised for each source based on the source -
specific conditions encountered. It is essential that the source
operating conditions and soot blowing practices are clearly unde'r-
stood and well documented in order to conduct performance tests
which are representative of emissions from the source. Factors
such as normal maximum operating load, frequency of soot blowing
periods, duration of soot blowing periods, and methods or para-
meters employed to initiate soot blowing should be considered.
Data from installed transmissometers may provide the most useful
information for establishing the conditions at which the source
should operate during the performance tests. The source should
note all periods of soot blowing on the permanent data record of
the transmissometer measurements. A comparison of the plant pro-
duction rate records and transmissometer data will then provide
a simple means for determining both the frequency and duration of
typical soot blowing periods while the source is operating at the
maximum normal production rate or other conditions which the con-
H-9
-------
trol agency may specify as representative conditions for conducting
the performance tests. In addition, assuming that a linear corre-
lation between the optical density and mass concentration of the
effluent exists, it provides a rough estimate of the relative
particulate emissions levels during soot blowing. Such an esti-
mate is useful in evaluating the significance of temporal varia-
tions during the soot blowing period and in determining the level
of effort which should be expended in sampling the soot blowing.
For example, if the transmissometer data indicates that the part-
iculate concentration is much greater during soot blowing and if
soot blowing constitutes a significant fraction of the total
source operating time, then more emphasis should be placed on
sampling the soot blowing period than would be expended in sampling
soot blowing periods at a source where the apparent particulate
concentration is not drastically increased during cleaning, or
where the cleaning periods are infrequent or of short duration.
For sources where the interval between soot blowing periods is
relatively short, performance tests should be conducted such that
each sampling run spans an entire cycle of normal operation and
soot blowing. Each sample traverse should be intitated at either
a different sampling point or at a different time in the operating
cycle so that the composite sampling during the soot blowing periods
is representative of the effluent across the entire stack or duct
cross section. The agency should not allow the source to schedule
sampling such that sampling at a point of minimum velocity or
minimum particulate concentration is always coincident with the
soot blowing portion of the plant cycle. The average of three
sampling runs should provide a representative emission value.
For sources where the interval between soot blowing periods is too
long to permit sampling runs to be conducted over the entire oper-
ating cycle, two options are available: (1) separate sampling runs
may be conducted during normal operation and during soot blowing
to determine the parameters required for calculation of represen-
tative emission values; or (2) sampling runs may be conducted at
normal operating conditions and additional runs may be conducted
which include both normal operation and soot blowing to allow
"Use of In-stack Transmissometer in Manual Source Sampling for
Particulate Mass Concentration Measurements", K.Foster, N.White,
Presented at East Central Section, APCA Annual Meeting, Dayton,
Ohio, September 17-19, 1975.
H-10
-------
calculation of a representative emission value according to
Equation 4. The number of sampling runs used to determine values
for the appropriate parameters directly affects the accuracy of
the calculated emission rates. At a minimum, two runs should be
conducted during normal operating conditions and one run should
be conducted during or containing soot blowing. For sources where
soot blowing constitutes a very significant portion of the total
emissions from the source, it may be necessary to conduct more
than one sampling run during or. containing soot blowing. Essen-
tially, the number of runs conducted at each operating condition
should be directly dependent on the fraction of emissions arising
during each operating condition. Sampling runs conducted during
soot blowing should span the entire blowing period due to the
existence of temporal variations in the effluent particulate
concentration over the cleaning cycle.
If independent sampling run(s) are to be conducted during the soot
blowing period, the short duration of typical soot blowing periods
will usually prohibit completion of a full sampling traverse during
the cleaning cycle. When a short duration soot blowing period re-
quires a reduced number of sampling points, all of the sampling
points should lie on the same stack or duct diameter to allow con-
tinuous sampling during the blowing period without interruption of
sampling to change ports. Ideally, the sampling points which are
selected would be representative of both the average particulate
concentration and average volumetric flow rate in the stack or
duct. However, the sampler and agency observer have no prior
knowledge regarding the particulate concentration variation across
the stack with the exception of those cases with obvious flow
disturbances. Sampling sites where the velocity profile is fully
developed and where the particulate concentration is relatively
uniform reduce the significance of measurement errors arising from
traversing only a portion of the stack. Single point particulate
sampling should always be avoided but may be necessitated at sources
with very short duration soot blowing periods. A point of repre-
sentative velocity should be selected when single point sampling is
required. When this situation is encountered the errors in the
H-ll
-------
calculated emission rate due to sampling at a single point will
be minimized due to the relatively small fraction of the total
emissions occurring during the short soot blowing period. If more
than one soot blowing period is to be sampled, the sample traverses
should be initiated at different sampling points, (or conducted
at different sampling points for single point sampling) to mini-
mize the effects of concurrent spatial and temporal variations.
The effluent velocity must be measured at the point(s) sampled
during soot blowing runs in order to maintain isokinetic sampling
conditions. These velocity measurments should be compared to
the values measured at the same points during normal operation
sampling runs to check the validity of assumptions regarding con-
stant volumetric flow rate during both operational conditions.
For sources subject to specific emission standards, (mass per
unit of heat input) measurements of $C02 and/or %02 during soot
blowing periods should be used to determine if the excess air
varies significantly between soot blowing and normal operation.
The equations in Appendix A should be employed to determine
representative specific emission values for sources where sig-
nificant variations in the percent excess air are encountered.
H-12
-------
APPENDIX A
H-13
-------
It should be noted that the method for determining a representa-
tive emission value is in some cases dependent on the applicable
emission standard, (i.e., mass emission rate, concentration, or
specific emissions standard - lbs/10 Btu) . Each case is consid-
ered separately in the following sections. The following nomen-
clature is employed.
C^ - effluent particulate concentration during normal
operating conditions, (dry standard conditions)
C- - effluent particulate concentration during soot
blowing, (dry standard conditions)
Q-^ - effluent volumetric flow rate during normal operating
conditions, (dry, standard conditions)
Q2 - effluent volumetric flow rate during soot blowing
(dry, standard conditions)
^ - pollutant mass rate during normal operating conditions
K
- pollutant mass rate during soot blowing
T.. - amount of time source operates at normal operating
conditions
T - amount of time source blows soot
H-14
-------
Case I - Representative Mass Emission Rate, pmr
total mass emissions
pmr = total time
The general equation for N operating modes is ;
.
For a FFFSG with intermittent soot blowing, N = 2, then;
Pmrl ^1 + Pmr7 T? ^l^l^l + C?Q->T0
pmr T+T T + T ^~~*
•If the volumetric flow rate does not change during soot
blowing, then;
pnr T + T
Al 2
Q = constant
H-15
-------
Case II - Representative Concentration, C
_ total mass emissions A-5
C = total volume of effluent
The general equation for N operating modes is,
N N
£ pmr.t.
/•• - 1~ 1
A"6
N
N
For a FFFSG with intermittent soot blowing, N = 2, then;
TI ^ pn.r2 TZ _ C1Q1T1 ^ C,QT
_
If the volumetric flow rate does not change during soot
blowing, then;
- C1T1 + C2T? A- 8
C = V . T - Q = constant A tt
!1 2
H-16
-------
Case III - Representative E, (lbs/10 btu)
_ total mass emissions
E = total heat input A"9
N
E
A-10
E = N
H. t.
11
i=l
where: H = heat input rate
Since considerable difficulty is encountered in attempting to
measure heat input rates and/ or total heat input, the F- factor
method is usually employed. Therefore, a different approach
should be used to determine E, based on the parameters which
are actually measured.
F = r P / 20.9 \ A- 11
E u r I 20. 9 - %0 J
Define Z such that equation 11 can be written in generalized
form, . •? x -i
6 ft stoichA , /ft • A-12
E (lbs/10 Btu) = c F ,
^ ° 5
10 Btu / \ft stoich.
Since F is a constant, equation 10 can be written as;
_ / total mass emissions _ \ 1 A- 13
CZ ( total stoichiometric effluent volume j I
Note that § = Q
M 5
where Q = stoichiometric volume flow rate
O
A general equation for N operating modes can be written as;
N
^ C--Q t-
or = F i=l i is i A.14
N
QI .
^1 Zi ^ L 'si'i
H-17
-------
For a FFFSG with intermittent soot blowing, N = 2
E = F
ClVl +
QT
11
A-15
If the volumetric flow rate does not change during soot
blowing, then,
E = F
" r T +
Vi
Tl +
- z7
C2T2l
T2
Z-
Q = constant
A-16
If the excess air does not change during soot blowing, then
• E = FZ
+ C:Q2T2'
Z = constant
A-17
If both the volumetric flow rate and excess air do not
change during soot blowing, then;
E = FZ
L
C2T2'
Q = constant
Z = constant
A-18
For almost all steam generators with intermittent soot blowing
practices, the volumetric flow rate (dry standard basis) and the
quantity of excess air are not expected to vary between periods
of normal operation and periods of soot blowing. Therefore, simply
time weighting the emission values can be employed to determine
the representative pollutant mass rate (eq. 4), representative
concentration (eq. 8), and the representative specific emission
rate, E (eq • 18). Where the volumetric flow rate, and in the
case of the specific emission rate E, the quantity of excess air
vary significantly during soot blowing,the general form of the
equations should be employed to determine representative emission
values.
K-18
-------
APPENDIX B
H-19
-------
8520 SHOAL CREEK BOULEVARD
AUSTIN. TEXAS 78758
JOHN L. BLAIR 512/451-5711 WILLIAM N. ALLAN
Chairman y^t^jfey JOE C. BRIOGEFARMER. P. E.
CHARLES R.JAYNES /V*Qp*£fc\\ FRED HARTMAN
Vice Chairman / n^^
-------
Averaging Soot Blowing in Stack Samples
PMRAVG(R) = PMRSfi(S) + PMRNOSB(R-S) (1)
PMRSBR(A+B) = PMRSB(A) + PMRNOSB(B) (2)
Solving equation (2) for PMRSfi;
PMRSB = [PMRSBR(A + B) - PMRNQSB(B)] /A (3)
Substitute equation (3) into equation (1) yields;
PMRAVG(R) = [PMRSBR(A + B) - PMRNOSB(B)] f + PMRNOSB(R-S) (4)
Collecting terms yields;
PMRAVG(R) - PMRSBR(A + B)| + PMRCR-S-) (5a)
or;
- PMR
SBR
PMR = Pollutant Mass Rate (Ib/hr)
PMR.y- = Average PMR for daily operating time
PMR
riiKSB = PMR while blowing soot
= Average PMR of sample (s) with no soot blowing
= Average PMR o.f sample(s) containing soot blowing
A = Hours soot blowing during sample (s)
B = Hours not soot blowing during sample (s) containing
soot blowing
R = Average hours of operation per 24 hours
S = Average hours of soot blowing per 24 hours
H-21
-------
SLIDE 308-0 NOTES
INTERMITTENT
SOOT
BLOWING
SLIDE 308-1
DETERMINE TYPE OF EMISSIONS REGULATION
THE REGULATION MAY REQUIRE
• addition of soot blowing on a daily basis
since it is a normal part of operation
• testing at worst case since the regulation is
never to exceed limitation
• the exclusion of soot blowing from the
regulated emission
SLIDE 308-2
INTERMITTENT SOOT BLOWING
DAILY AVERAGING TECHNIQUE
1. Determine normal cycle and duration
of the soot blowing.
2. Determine the locations of soot
blowing
• boiler tubes
• superheater tubes
• air preheater
Note: All boilers do not contain all of
these heat exchangers
H-23
-------
SLIDE 308-3 NOTES
SOOT BLOWING TEST PROTOCOL
• A separate run should be performed during soot
blowing.
• The run should be conducted for the same
length of time as the normal soot blowing.
• The run should be made as nearly as possible to
the correct soot blowing interval cycle.
• The criteria for minimum points and sample
volume should be waived.
Note:The "separate run" may be the third run or the
agency may require a fourth run.
SLIDE 308-4
SOOT BLOWING AVERAGING TECHNIQUES
MASS EMISSION RATE BASIS
pmr = (pmnt! + pmr2t2) x 100
where
pmr, = average pollutant mass rate ol
samples at normal operating
conditions
pmr2 = average pollutant mass rate of
samples during soot blowing
I, = percent of source operation time
at normal operating conditions
\t » percent ol source operation tome
blowing soot
SLIDE 308-5
AVERAGING TECHNIQUE FOR lb/10a Btu
Convert to an Emission Rate Basis:
'20.9.-%(V
20.9
where
pmr - pollutant mass rate. ttVhr
E = lb/10*Btu
o, = flue gas flow rate, scfm
F = f factor used to determine lb/10* Btu
%02 = percent oxygen during sample run
H-25
-------
SLIDE 308-6 NOTES
The resulting mass emission rates from
Equation 2 along with their corresponding
time can be averaged using Equation 1. The
results wiH be on a mass emission rate basis.
SLIDE 308-7
AVERAGE TECHNIQUE USING MEASURED
CONCENTRATION (C) TO CONVERT TO lb/106 Btu (E)
N
S
N
2
where:
E = lb/106 Btu
C = concentration, Ib/dscf
Q = flue gas flow rate, dscfh
Z = excess air correction
t = percentage of time during day
F = F factor
SLIDE 308-8
AVERAGING TECHNIQUE USING 1b/10* Btu (E)
N Q,
2 EI t where
_ 1 = 1 Z,
E = E = 1b/106 Btu
N Q, Q = flue gas flow rate, dscfh
2 t Z = excess air correction
i = 1 Z, t = percent of time
H-27
-------
SLIDE 308-9 NOTES
LETS TAKE AN EXAMPLE
Run 1 0.095 lb/10* Btu 3,650,000 scfh 10.2 %0a
Run 2 0.087 lb/108 Btu 3,540,000 scfh 8.9 %«,
Run 3 0.091 lb/106 Btu 3,930,000 scfh 9.3 %0,
Run 4 0.330 lb/10* Btu 3,810,000 scfh 10.8
Soot blowing=45 minutes each tor 3 times a day
SLIDE 308-10
CALCULATE PERCENT OF TIME (t)
Sample Runs = ™0'*3 = 30.2% = I,, t2, & fe
SLIDE 308-11
CALCULATE STOICHIOMETRIC VOLUMETRIC
FLOW (a)
20.9
= 2,033,000 scfh
0.3 = 2,181,000 scfh
O« = 1,841,000 scfh
H-29
-------
NOTES
SLIDE 308-12
CALCULATE AVERAGE E
N
2
N
Q*.,
SLIDE 308-13
CALCULATE AVERAGE E
= _ (0.095) (1.869) (30.2) + (0.087) (2.033) (30.2) +
E = (1.869) (30.2) + (2.033) (30.2) +
(0.091) (2.181) (30.2) + (0.33) (1.841) (9.375)
(2.181) (30.2) + (1.841) (9.375)
E = 0.111 Ib/KFBtu
Note: All flue gas flow rates have
been divided by 1,000,000 to
allow the data to be. more
easily placed on one slide
H-31
-------
SLIDE 308-14 NOTES
APPROXIMATING AVERAGING TECHNIQUE
When a._ and %O2 are faMy constant:
"C = (C^, + Cata) x 100
20.9
E = FfC,!, + CM x 100 x
wners
average partlculate concentration of
samples at normal operating conditions
average partlculate concentration of
samples during soot blowing
SLIDE 308-15
CONCLUSIONS
determine how soot blowing should be handled
for emission regulation
establish soot blowing testing protocol
evaluate the testing results to ensure a correct
representation of soot blowing data
H-33
-------
SECTION I. SAMPLING PORT LOCATION
Subject Page
1. Access problems 1-3
2. Guidelines for sampling in tapered stacks 1-27
3. Sampling in ducts less than twelve inches in diameter 1-32
4. Slides 1-47
1-1
-------
ACCESS PROBLEMS
by
Walt Smith
In general terms, "access" as it applies to source sampling
means everything of a physical nature that the tester requires of
the source in order that a valid test may be performed. This
includes:
1) being physically able to get necessary men and equip-
ment to the sampling port location;
2) having enough room and freedom from obstructions for
safe performance and observation of a valid test;
3) having necessary support items (e.g. electricity);
4) not being denied use of any of the above.
The question of access should be covered at the pre-test
meeting, if such a meeting is held, so that these items will be
available at the time testing is to be done. Not all situations
can be anticipated at the pre-test meeting, and some questions
that are "answered" (proper number and location of sampling ports)
may still cause a problem (port caps frozen by rust) on the date
of the test. Nonetheless, it is important that certain points
be covered prior to the test. The pre-test meeting provides
the best opportunity for this, since all parties are represented
and the sampling site is (presumable) available for inspection.
If no pre-test meeting has been held, these items must be covered
immediately prior to the test.
The general requirements that the tester makes of the source
in order to satisfy the predetermined test protocol will depend
on the type of source, the tester and his equipment, and the
protocol. The inspector should know what to look for as
1-3
-------
indicators that these requirements will be met on the test date.
A comprehensive site inspection, conducted by the inspector in
conjunction with representatives of the source and the testing
firm, takes only a short time a^d substantially diminishes the
chance of access problems interfering with the execution of test
protocol.
Items to be inspected or discussed fall into three basic
categories. The first and most extensive inspection is of the
sampling site, to determine whether a valid test can be performed
there;. The observer should then discuss with the testing firm
representative the nature of his equipment and his plans for
adapting, if necessary, to unusual sampling site configurations.
Finally, all potential safety problems should be covered. The
source representative should be able to relay all safety rules
relevant to the areas of the plant where personnel involved in
the testing effort will be working. OSHA regulations should
also be considered. These will pertain to ladders, platforms,
hand rails, and so forth. Following is a detailed discussion of
what to look for in each of these areas during the pre-test in-
spection.
THE SAMPLING SITE
As the agency observer, the tester, and the source repre-
sentative approach the sampling site, the tester may be looking
for such things as vehicular access, unloading area, and means
for transporting sampling equipment from his vehicle to the
sampling site. The source representative will aid him in working
1-4
-------
out these matters of logistics; you needn't worry about such
problems.
Upon arriving at the actual sampling site, a few preliminary
observations are in order. (If you are not familiar with the
requirements for an acceptable sampling site, go back and re-
view EPA Method 1). Make certain that there are at least two
equivalent duct diameters form the sampling port location to
the nearest disturbance upstream, and at least one-half diameter
downstream to the nearest disturbance or the stack exit. These
distances are absolute minima. A test performed at a site which
does not meet both of these requirements will not be considered
an acceptable demonstration of compliance or violation. Ideally,
there should be eight diameters upstream and two diameters down-
stream of straight, undisturbed flow.
SAMPLING PORTS
After establishing the straight-run distances upstream and
downstream of the port location, determine the number of sampling
k
points needed according to the Method 1 formulae. See that there
are enough sampling ports provided, and they are installed in the
proper locations, to enable this particular requirement of Method
1 to be met.
(NOTE: Reference methods 1-8 have been revised since the
December 1971 promulgation. In particular, the requirements
for point locations in a rectangular cross-section have been
changed, as have minimum stack diameter requirements. The in-
spector should be familiar with the most recent versions, pro-
mulgated on August 18, 1977, of the reference methods.)
1-5
-------
If the sampling site and/or port locations do not meet the
requirements of method 1, you may require the source to make
necessary modifications. In borderline cases, consider that
working with a cooperative source will be helpful on the test
date, before demanding costly modifications. Make sure that the
requests you make of the source are reasonable in light of the
goal of meeting the testing objectives.
Having located all ports, make sure each can be opened.
A typical sampling port consists of a 4-inch hole in the duct
wall, a 4-inch diameter pipe extension (nipple) generally be-
tween four and 24 inches in length, and a threaded metal cap
which screws onto the nipple to seal the port when it is not
in use. Frequently, these caps will become frozen in place
by rust; this is particularly true if the ports have not been
opened for some time. Try to get all ports open--this will save
time on the day of the test. If one or more caps will not come
off with a pipe wrench, try the following measures:
"Slip a length of 2-inch pipe over the wrench handle to
increase the length of the lever arm.
'Beat on the sides of the cap with a hammer or other heavy
object, to break the threads free.
'Heat the cap (but not the nipple) with a torch; it may
expand enough to loosen.
If these measures succeed, coat the threads with an anti-
seize compound before replacing the cap. If the cap still re-
fuses to loosen, more drastic measures are called for:
'Cast metal caps can be broken apart by repeated blows with
a hammer.
1—6
-------
"Use a cutting torch to cut off the nipple around the
base of the cap.
*If feasible, cut a new port (this is the very last resort).
Bear in mind that these remedies preclude resealing the port
with the cap. It may be desirable to wait until the test date
before destroying or altering a port.
After locating and opening each port, check with the tester
to be sure the ports are of sufficient diameter to accommodate
whatever instruments will be placed in the stack. This will
rarely be a problem, as most sampling equipment is designed to
fit ports as small as 3 inches in diameter. Check to be sure
that the nipples are flush with the inside wall of the duct. If
the pipe extends even a fraction of an inch into the duct, a flow
disturbance has been introduced which will affect any sampling
points near the duct wall. Also, measuring the depth of the
nipple along its inner surface and assuming that the inner end
of the nipple is flush with the stack wall will yield an erroneous
value for the duct diameter, dislocating the sampling points cal-
culated from that value.
Often, sampling ports will have deposits of some sort along
their inner surfaces. This may be in the form of loose particu-
late, hard cake, or rust and scale. Suggested that the source deposits
from all ports. This procedure may have to be repeated at the
time of the test, but clearing the ports now will eliminate delays
later in cases where deposits are difficult to remove.
It is desirable to minimize the length of the sampling tra-
verse as much as possible. This is the distance from a sampling
1-7
-------
port to the most distant sampling point that must be reached
from that port. The reason for this stipulation is that sam-
pling probes will sag noticeably when the length of probe ex-
tended into the stack exceeds ten feet or so. If an in-stack
filter assembly (or other heavy attachment) is affixed to the
probe tip, the sagging will be more pronounced.
At existing sampling sites, the ports are fixed in number
and arrangement and not easily or cheaply relocated. However,
be sure that existing ports are used in the most efficient way.
On round ducts of large diameter, access through four ports spaced
90° apart reduces the needed probe length to less than half the
duct diameter (there are no sampling points in the middle 20%
or more of the diameter). If such a duct has four accessible
ports installed, suggest use of all four. Rectangular ducts less
than eight feet in the short dimension are best sampled using
ports along the long dimension. If both dimensions exceed 8
feet, access from opposite sides will help.
Generally, the sampling team will have to adapt to whatever
port arrangement is provided. The observer should be aware of
the likelihood of probe sag when the sampling traverse exceeds
eight or ten feet. If the direction of probe sag is upstream,
the pitot velocity readings will be higher than real. If the
direction of probe sag is downstream, the velocity readings will
be low. If the probe sags across the streamlines, the readings
may be correct, but the probe tip will not be at the sampling
point. Sagging would have to cause a misalignment of more than
30 in the first case, and more than 15° in the second case before
the velocity error exceeded ten percent.
1-8
-------
Errors in the velocity measurements create anisokinetic
sampling conditions. Higher than real pitot readings create
overisokinetic sampling conditions which bias the concentration
measurement low. Similarly, lower than real pitot readings create
underisokinetic sampling which biases the measured concentration
high. Errors in velocity measurements introduce an additional
bias when mass emission rates are calculated, due to the error
in the volumetric flow rate, a determination also based on pitot
velocity measurements.
DUCTWORK
The tester will probably want to measure certain duct
dimensions in order to determine what sort of equipment he will
need to bring to perform the test. He will be measuring the
traverse distance, the distance from a given port to the opposite
duct wall. This dimension is used to calculate the sampling
point locations and to determine the probe length necessary to
reach all of those points.
If the duct is circular, suggest that the tester measure
two perpendicular diameters. Should they differ by more than
5$, two different sets of sampling points should be used, each
determined by one of the diameters. (If four ports will be used,
one set of points will suffice.) If the cross-sectional area of
the duct must be determined (the applicable standard is in terms
of pollutant mass rate rather than pollutant concentration),
measure the circumference in the plane of the sampling points
and calculate the area based on the assumption that the duct is
circular. The calculated area will thus be equal to or greater
1-9
-------
than the actual area; any bias introduced by the stack being
out of round will favor the agency, not the source.
For rectangular ducts, particularly at steam generators,
remember to consider the thickness of insulating material when
computing the internal dimensions from measurements of external
dimensions. Measurement of two adjacent sides will suffice un-
less the duct is noticeably asymmetrical. As with round ducts,
assuming the cross-section is rectangular and calculating the
area accordingly will bias pollutant mass rates in favor of the
agency, if at all.
Should a source representative challenge the assumption of
roundness or rectangularity, ask him for his figure for the cross-
sectional area. He should be able to support this figure to your
satisfaction before it is used in further calculations.
The newly promulgated (August 18, 1977) Reference Method 1
prohibits use of the method in ducts of less than 0.071 m
2
(113 inches ) cross-sectional area. This corresponds to a cir-
cular duct of 0.30 m (12 inch) diameter. Do not allow velocity
measurements or particulate sampling in ducts which do not meet
this minimum size requirement without consulting Chapter 3.
Inspect the ductwork in the area of the sampling ports
visually, checking the condition of the wall material. In
particular, look for possible leaks. Deteriorated duct walls
indicate a possibility of leakage which could compromise the
validity of the test. This is most important in cases where
the duct is under a negative pressure, since leaks will cause
ambient air to be drawn into the gas stream, diluting the sample
1-10
-------
and disrupting stream lines. If positive pressure exists in the
duct, leakage will be in the form of stack gases escaping into
the ambient environment. This probably will not effect the
samples, unless a significant percentage of the stream is es-
caping. Be aware of the possibility of toxic or noxious fumes
in the work area (see section on Safety below).
Any duct which carries a particulate-laden or corrosive gas
stream will probably have deposits along its inner surfaces. In
vertical ducts or stacks, deposits may be limited to rust or
scale. Loose particulate may build up in ports, on ledges, or
at any other irregularity in the walls. In horizontal ducts,
the problem of particulate deposition may be severe, amounting
to a considerable percentage of the cross-sectional area.
Ask the source representative to see that the internal sur-
faces of ducts to be sampled are lanced (cleaned with an air
jet) not less than 24 hours before the testing is to be done.
It is the responsibility of the source to see that this is done.
Be absolutely sure, before testing starts, that deposits in the
bottom of horizontal ducts have been removed. These deposits
are sometimes so deep that a probe (inserted from either the
side or the top of the duct) may plow into the dust layer,
vacuuming up large quantities of particulate and instantly
ruining the sample. Merely taking care to avoid getting the
nozzle in the dust layer is insufficient precaution. Re- entrain-
ment of particulate at the boundary between dust layer and moving
gas stream will create higher-than-real particulate concentrations
near the top of the dust layer. Although the bias thus introduced
1-11
-------
will be in the agency's favor, its magnitude is unpredictable
and potentially great.
Internal obstructions, if they are present, can affect test
results by introducing flow disturbances. Checking for these
obstructions can be difficult, but there are a few approaches.
Scan the outside of the duct for evidence of structures which
may pass through the walls to the inside. A good example of this
would be an in-situ gas monitor, which has a tube permanently
mounted across the stack. Ask the source representative for
engineering drawings of the duct. These may indicate straighten-
ing vanes, dampers, structural members, etc. inside the duct.
Finally, if a light is available, look into the ports and in-
spect visually the interior of the duct for as far as you are
able to see.
If the tester has brought along the proper instruments, or
if .gauges are mounted on the duct, record the temperature and the
static pressure of the gases. These will be of use on the date
of the test, when they may be compared against the conditions in
the stack at that time.
WORK AREA
For the purposes of this section, "work area" means the
immediate vicinity of the sampling ports, from which the testing
and observing personnel and their equipment will be operating.
This includes platforms, scaffolds, the outer wall of the duct
or stack, and any nearby areas which may be used for such pur-
poses as sample recovery and equipment storage.
1-12
-------
In general, see that there is room for all personnel to
do their jobs effectively. The tester will determine his needs
in terms of his men and equipment. The observer should see that
he will have access to both the port area and the meter box lo-
cation, taking into consideration the amount of "elbow room"
needed by the testing crew.
The observer should also make sure that there are no fea-
tures of the site which will jeopardize the fulfillment of the
test objectives as set forth in the protocol. Check for obstruc-
tions in front of the sampling ports. Most particulate sampling
equipment, with the probe connected to the sample box (containing
the heated filter compartment and the impinger ice bath), requires
a clearance of about one foot beyond the probe length. This
clearance is measured from the outer end of the nipple perpendi-
cularly from the stack wall to the nearest obstruction. The
tester will be able to determine if there are any clearance
problems, based on his knowledge of his equipment.
Have the source representative point out the nearest source
of llOv, 60-cycle electricity. With his assistance and that of
the tester, locate a suitable clean-up area, where particulate-
laden filters may be transferred to storage containers with a
minimum danger of sample loss. (Many testers perform clean-up
procedures in their van or truck, with the doors closed to deflect
wind.) If testing is expected to take more than one day, suggest
that the tester and the source representative work out procedures
and locations for overnight storage of the sampling equipment.
1-13
-------
RIGGING
The term "rigging," as it is used in this section, means the
physical apparatus used to support and maintain the sample box-
pitobe assembly at the proper locations and attitudes for execu-
tion of a valid test. Support for the pitobe and sample box
typically consists of an overhead monorail from which the sample
box is suspended at one or two points by rollers. The most common
alternative is placement of the sample box on a table of some sort.
Rigging set-ups will vary as widely as do site configurations,
and are not limited to standard equipment and procedures. The
ingenuity of the test crew is often called upon, and the results
are often unique. Whatever the rigging arrangements, the set-up
should:
1) allow positioning of the nozzle at each sampling point
and perpendicular to the gas stream lines
2) provide stability during sampling
3) minimize opportunities for sample loss or contamination
4) not hinder the test team (or observer) in the performance
of their duties
5) not introduce unsafe conditions (see section on safety)
In most sampling situations, the probe is in a horizontal
position. For this reason, most sample box-pitobe assemblies
are designed for use in this configuration. Vertical traversing
requires some degree of adaptation; this situation will be dis-
cussed later.
Determine the alignment of the sampling traverses as dictated
by the sampling port locations. Make sure that probe supports
1-14
-------
can properly be attached to the stack, or that a table or tray
can be placed in front of each port at the proper height. The
tester will be able to make these determinations based on his
familiarity with his particular equipment. Whatever means of
support is proposed, ensure that the nozzle opening can be
positioned at each sampling point with reasonable accuracy;
that the plane of the nozzle opening will be perpendicular to the
gas stream lines; and that support will be steady, such that there
is no tendency toward deviation from either of these criteria,
even if the sample box-pitobe assembly is left unattended during
sampling.
When sampling a rectangular duct which runs horizontally,
the ports may be across the top or bottom of the duct rather than
down the side. Sampling downward from the top of a duct poses
few problems, assuming that the sampling equipment being used is
adaptable to this type of traverse (this is not always the case).
The main consideration again is the probability of particulate
deposits in the bottom of the duct.
Sampling upward from the bottom of a duct poses more serious
problems. Most sampling equipment cannot be modified for this
type of traverse. Even if it can, there are more problems. In
a typical sampling probe, the glass (or stainless steel) liner
is held in place by the gasket and ferrules at the nozzle end
and by the filter glassware connections at the sample box end.
When the probe is inserted in the duct, heat expansion will cause
the metal ferrules to ease their grip on a glass liner. With the
probe in a horizontal or nozzle-downward position, the only danger
1-15
-------
in this is the possible loss of seal between nozzle and liner.
When the probe is used nozzle-upward, however, ferrule expansion
may cause the liner to become completely unseated from the nozzle,
and possibly to fall out of the probe altogether. Sampling up-
ward should be avoided if at all possible; if such traverses are
unavoidable, some means will have to be devised to prevent the
liner from coming unseated as the ferrules expand.
Ocassionally, a horizontal duct may be encountered which
is circular. If ports are not already installed, or if new ports
are easily cut, have them situated as shown in Figure 2-1. This
arrangement eliminates the need for disconnecting and reconnecting
the probe from the sample box in the middle of a run. (This
maneuver should be avoided in any sampling situation if at all
possible, as it introduces a high probability of sample loss.)
Ask the tester if his sample box will function properly when
situated with the probe angled 45° downward. As a bonus, this
sampling configuration will greatly reduce the possibility of
dipping the nozzle in deposits of loose particulate which may
exist in the bottom of the duct.
SAFETY
Source testing is, by nature, a potentially hazardous
undertaking. Work is typically conducted at elevated locations,
often upon temporary platforms or scaffolding. Electrically-
powered equipment will be in use. Testers may be exposed to
noxious gases, dust, loud noise, hot objects, and weather. By
working at industrial sites, stack samplers are also subject to
the safety hazards of the particular facilities to which their
1-16
-------
job may take them. Despite these aspects of source testing,
almost any job can be done in safety if it is carefully planned
and conscientiously executed.
Unsafe conditions will be generally related to one of two
areas: the sampling site and its environs, and the testing equip-
ment and procedures. Potential hazards that arise from conditions
at the plant or sampling site should be corrected by plant personnel.
They will possess the necessary knowledge of the plant and the
, process. Neither source testers nor agency observers are empowered
with the the authority to single-handedly effect alterations or
modifications to someone else's plant or process.
Factors associated with working at elevated sites perhaps
constitute the most evident safety problems. Access ladders,
stairways, and the work area should comply with OSHA standards.
There are specifications for ladders and ladder cages, safety belts, steps,
railings and footplates along stairways and around platforms, and
for temporary scaffolding. These and other related standards may
be found in 29 CFR Part 1910, available at nominal cost from your
state's Department of Labor.
Care should be exercised when working at elevated sites to
avoid dropping objects, or causing them to fall. Recommend that
the tester minimize the amount of equipment hoisted to an elevated
platform. Spare parts, back-up equipment, clean-up materials,
etc. could be left in the truck. Platforms cluttered with un-
necessary equipment are crowded, and chances are increased of some-
one tripping over something, thus breaking equipment, injuring
himself, or knocking objects over the side.
1-17
-------
Testing personnel should see that all items of testing
epuipment at the site are placed in secure positions. Heavy
boxes should not be placed where they can fall over, glass should
be protected from accidental breakage, and rigging should support
their intended loads with a considerable margin for safety. Ropes
and chains should be visually inspected before use.
Meter boxes, thermocouples, pumps, and other items of sampling
equipment require 110-volt electric current. Be sure all electric
lines and equipment are grounded. Exercise particular care when
wet areas are encountered at a sampling site.
Before sampling is commenced, the locations of any adjacent
power lines should be determined and relayed to all personnel. A
minimum clearance of at least ten feet must be allowed between
s
power lines and any equipment. Assume all power lines are "hot";
do not take anyone's word that a wire is not live.
Placement of a metal probe into a moving gas stream will
often generate a substantial static charge in the probe. If the
gas stream has just exited an electrostatic precipitator, the
charging effect will be particularly strong. Probe sheaths should
be grounded to prevent static buildup. This grounding will also
prevent shocking in case the heater wires inside the probe short
out against the sheath.
The problem of electric shocks, particularly static shocks,
may not appear to be serious. Remember that not only is there
danger from the shocks themselves, but also from the involuntary
reactions shocks will cause. Such a reaction may result in
dropped objects, and possibly a serious fall.
1-18
-------
Noxious gases and dust should be anticipated at all sampling
sites. This is particularly true when the duct being sampled
is under a positive pressure. Ports should be opened only when
necessary, and carefully sealed around instruments placed in them.
If the work area is inclosed, make provisions for ventilation.
Remember that the sampling train exhaust (in the meter box) will
be a source of stack gas fumes. If high concentrations of toxic
gases are expected, frequent spot checks with detector tubes or
other detection equipment should be made. If high concentrations
are found, appropriate masks or respirators should be worn by all
personnel who will be continuously in the work area. In all cases,
when such symptoms as dizziness, headache, eye irritation, nausea,
or breathing difficulty occur, assume the presence of gaseous
toxicants and take appropriate action. Should dust be an air
comtaminant of concern, eye protection and masks should be avail-
able for use at personal discretion.
Heat is a frequently encountered sampling safety problem
which manifests itself in two ways. First, sampling probes are
always hot to some degree, and hottest when just removed from a
heated gas stream. Care should be taken when handling probes to
avoid burns. A more serious problem is that of elevated ambient
temperatures in the work area. If hot summer weather, heat rad-
iating from duct surfaces, or a combination of these factors can
be expected, be sure to have an adequate supply of drinking fluids
on hand. Salt tablets are also useful. If possible, have plant
personnel arrange to ventilate the site. One small fan can make
a large difference in comfort.
1-19
-------
Noise is another environmental irritant which can manifest
itself in two ways. Many sampling sites are constantly noisy,
due to proximity to fans or other loud equipment. Ear protection
should be a part of each man's personal safety gear. Nearby
sources of sudden noises, such as sirens, whistles, and relief
valves, should be pointed out by plant personnel. Activation of
these devices could cause at least an involuntary reaction, and
at worst hearing damage.
All personnel-testers and observers-should always be wearing
hard hats and steel-toed boots. Additional safety gear, such as
goggles, ear protection, respirators, etc., should be carried
along in case they become necessary. Follow plant rules and the
recommendations of the source representative at all times. Most
s
plants have learned from experience what types of safety equipment
and procedures should be followed. Specialized safety gear, such
as safety belts for climbing, grounding straps, or chemically-
resistant clothing, will usually be provided by the plant.
Have the source representative point out the locations of
nearby safety equipment. This equipment includes eye baths,
safety showers, fire-fighting equipment, and first-aid equipment.
The meaning of emergency signals employed b^ the plant should be
understood by all parties involved in the testing.
Most test teams will carry their own first-aid kit; an
agency representative frequently employed in observing source
tests should also consider carrying along his own personal kit.
It should go without saying that a thorough familiarity with the
kit's contents and use is a must.
1-20
-------
DUCT
NAILS
)\
Lx4
J SAMPLE
TRA^RSE BQ\RD
Figure 2-1. Suggested Port Location in Horizontal Round Ducts
1-21
-------
ESTABLISHING SAMPLING POINT LOCATIONS IN
DUCTS WITH ECCENTRIC CROSS-SECTIONS
by
Giuseppe J. Schiappa
In the vast majority of stack sampling situations, the duct
carrying the effluent to be sampled is circular or rectangular in
cross-section. Reference Metho'd 1 is written on the assumption
that all ducts to be sampled will be circular or rectangular; the
possibility that a duct may have a cross-section of some other
shape is not considered. Field experience has shown that eccent-
ric-shaped cross-sections, though rare, are encountered on occa-
sion. In these cases, Method 1 guidelines do not specify precisely
how to determine the optimum sampling location, the number of tra-
verse points needed, or the cross-sectional layout of these points.
Strategies for making these determinations will have to be devel-
oped for each eccentric duct encountered in light of the particular
shape of the duct cross-section. These strategies should embody
the principle and intent of Method 1, extending them beyond cir-
cular and rectangular ducts to encompass the particulars of the
sampling situation at hand.
DETERMINATION OF OPTIMUM SAMPLING LOCATION
Method 1 guidelines with regard to selection of the optimum
sampling site location in a duct can be applied directly to the
case of eccentric ducts. The sampling site ideally should be at
least eight equivalent diameters downstream and two equivalent
diameters upstream from the nearest flow disturbances. In no case
should the site be less than two diameters downstream or one-half
diameter upstream from disturbances. Simply stated, the procedure
1-22
-------
for determining the optimum sampling site location in a given
duct is to find the largest accessible section of straight run
between any two flow disturbances, and to locate the sampling
ports in that section such that 80% of the straight run is on the
upstream side, and 20% is on the downstream side of the ports.
A problem arises in determining the "equivalent diameter" of
a duct with an irregular cross-section, so that the distances to
the upstream and downstream disturbances may be expressed in terms
of duct diameters. If the cross-section is an aberration of a
circle, calculate a mean diameter. If the cross-section is
trapezoidal or polygonal, the equivalent diameter is determined
by the equation:
where
De = 4
D = equivalent diameter
A = cross-sectional area
P = perimeter
The perimeter should be determined by measurement, and the area
may be calculated using appropriate geometric formulas.
Having established the distances from the chosen measurement
site to the nearest upstream and downstream disturbances, the
minimum number of traverse points may be determined according
to Section 2.2 of Method 1.
CROSS-SECTIONAL LAYOUT AND LOCATION OF TRAVERSE POINTS
In mapping out a given number of equal areas within an
eccentric-shaped cross-section, one's ingenuity will frequently
be called upon. The more irregular the shape encountered, the
1-23
-------
more subjective the process of laying out the equal areas. There
is often more than one acceptable way to divide up a duct cross-
section. What is offered here are guidelines, first for aberrated
circular ducts (ellipsoidal), and then for trapezoids and polygons.
For ducts whose cross-sections are variations on a circle,
treat the duct as circular for purposes of locating traverse points
If ports are not installed, have them located one-quarter of the
duct circumference apart. One should be in the plane of the
greatest expected concentration variation. Extend axes from each
port through the geometric center of the cross-section. Use the
length of each of these axes to determine a set of point locations,
using Table 1-2 in Method 1. If the axes are of different lengths,
this will yield two separate sets of traverse point markings. Be
sure to keep track of which set of points applies to which
port.
If the cross-section in question is a trapezoid or other
irregular polygon, a.graphic method of point distribution should
be employed. Draw the duct cross-section to scale on graph paper,
and determine the total number of squares covered. Dividing this
number by the minimum number of sample points required yields the
number of squares to be covered by each equal area. Remember that
more than the minimum number of sampling points may be used.
The layout of these equal areas will be dictated by several
factors. The locations of the sampling ports, if they are already
present, must be taken into consideration. 'Extend a line from the
i
center of each port, perpendicular to the wall in which the port
is located, to the opposite side of the duct. The areas should be
1-24
-------
arranged such that as many sampling points as possible lie along
these lines. (Pivoting of the probe from side to side to reach
sampling points should be avoided as much as possible, due to the
inherent inaccuracies in locating the nozzle near a point using
this method.) Figures 3-1 § 3-2 are examples of this graphic method.
Figure 3-1 is of an ammonium nitrate prilling tower. The "duct"
cross-section is a metal grating across the top of the tower, which
is square. Testing personnel were able to enter the tower and walk
around on the grating; hence, access to the points was not diffi-
cult. The dark circle in the center is the spray head location,
an area which could not be sampled at the grating level. In
Figure 3-2, a trapezoid, note that every point is on or near a
perpendicular drawn through a port.
1-25
-------
Figure 3-1.
Figure 3-2
Examples o£ Sampling point distributions in Eccentric Ducts
1-26
-------
GUIDELINES FOR SAMPLING IN TAPERED STACKS
T. J. Logan and R. T. Shigehara
Tapering of the inside diameter of stacks is occasionally
done when designing natural draft stacks, when there are special
flow or structural considerations, and for pressure recovery.
These tapers seldom exceed a few degrees. Although guidelines
for the selection of a sampling site to aid in the extraction of
a representative sample are given in Method 1 of the August 18,
1977 Federal Register, no mention is made about tapered stacks.
The purpose of this paper is to provide the necessary background
on how to deal with tapered stacks.
In order to obtain a representative sample, the particles
must be extracted at an isokinetic flow rate. The condition of
isokineticity demands that the particles and gases flow directly
into the sampling nozzle and that the velocity be accurately
measured. Therefore, two factors must be considered: (1) the
effect of the taper on flow conditions within the stack and (2)
the effect of the taper on velocity determination and particulate
matter collection.
Effect £f_ Taper on Stack Flow Conditions
About the only information related to this area was the
work done with venturi meters. The ASME Research on Fluid Meters
cites that beyond a convergent included angle of 21 and a diver-
gent included angle of 15° gas separation from the walls is ex-
pected to occur. This is undesirable as eddies would be formed
causing particles and gases to flow in undeterminable directions.
1-27
-------
From a physical standpoint, convergent angles of 15 or 21
would not likely occur in stacks due to the tremendous increase
in velocity. If the larger stack diameter D is used, a tapered
stack meeting the minimum 2.5 D requirement of Method I would
cause an increase in velocity of about 8.6 times at the outlet for
a 15° included angle and 186 times for the 21 included angle.
Such an increase would require considerable additional power and
would be impractical and uneconomical.
One builder of chimneys related that convergent stacks gener-
2
ally do not exceed 0.5 in. per foot. This corresponds to an in-
cluded angle of about 4.8° for convergent stacks. Divergent
stacks are normally designed at about 5 - 15 .
Based on the above, the 15° included angle can be considered
the maximum limit for both convergent and divergent stacks, with
the understanding that the 15° angle will be very unlikely in
convergent stacks. The purpose for making this statement is to
form the limit and basis for evaluating the effect of the taper
on the velocity determination and the particulate matter collection.
.Effect p_f Taper on Velocity and Particulate Concentration
Convergent or divergent stacks would cause an angle of attack
by the gases and particulate on the pitot tube and particulate
sampling probe nozzle. Data presented by Grove and Smith show
that such an angle will result in velocity measurements with a
type-S pitot tube being biased,, usually high. This higher ap-
parent velocity also causes particulate sampling to be in error
because isokinetic sampling requires that the sample gas velocity
be made equal to the stack gas velocity, which is in error since
1-28
-------
it is measured by the misaligned pitot tube. In addition to the
sampling rate being over-isokinetic, the misalignment of the probe
nozzle with the stack gas stream results in a reduction in the
effective nozzle area.
The magnitude of the effect on the particulate concentration
by being over-isokinetic and having a reduced nozzle area is a
function of particle size. For particles of less than 1 micron,
the concentration will not be affected. However, with the larger
particles of greater than 50 - 75 microns, the sampled concentra-
tion will be low. In a practical case, where there is a distri-
bution of particle sizes, the error will be somewhat less, and
for well-controlled sources where the majority of the particles
are characteristically small (<2 microns) the error will be small.
The effects of these errors on pollutant mass rate deter-
mination are not easily ascertained. The error of the higher
measured volumetric flow rate and the error of the lower measured
particulate concentration will act in opposite directions. The
magnitudes of each of these errors is difficult to determine, and
varies with the situation; therefore, no consistent rule for
determining the direction or the magnitude of the consequent error
in the pollutant mass rate can be established.
RECOMMENDATIONS
Based on the above discussion, the following guidelines
are recommended:
1. Consider all stacks with the total included angle of
1-29
-------
<^ 15° as straight stacks.
2. Use the maximum diameter (diameter at upstream dis-
turbance if stack is convergent; diameter at downstream distur-
bance if stack is divergent) for determining the distances from
the sampling site to upstream and downstream disturbances and
the minimum number of sampling points. Use the diameter at the
sampling site for determining the sampling point locations.
3. If the taper exceeds an included angle of 15°, consider
it a flow disturbance and:
a) modify the stack by adding a straght section at least
2.5 times its own diameter in length, or
b) treat the gas flow as non-parallel (see section on
non-parallel flow).
1-30
-------
REFERENCES
Fluid Meters, Their Theory and Application, Report of ASME
Research Committee on Fluid Meters, 5 Ed, ASME, N.Y., 1959,
Personal Communication with Richard Lohr, Vice president,
International Chimney Corporation.
Grove, J.D. and W.S. Smith, Pitot Tube Errors Due to Mis-
alignment and Nonstreamlined Flow, Stack Sampling News,
Volume 1, No. 5, pages 7 - 11, November, 1973.
1-31
-------
SAMPLING IN DUCTS LESS THAN TWELVE
INCHES IN DIAMETER
by
Robert F. Vollaro
With the August 18, 1977 revisions to Reference Methods
1-8, use of Methods 1,2,5, or 8 is not permitted in ducts less
2 2
than 0.30 m (12 inches) in diameter or 0.071 m (113 in. ) in
cross sectional area. This is due to the fact that, in ducts smaller
than these limits, a standard probe assembly will block more than
10% of the cross-sectional area of the duct when fully inserted
(Figure 3-4) As the velocity of the flowing gases in inversely
proportional to the effective cross-sectional area of the duct,
velocity readings taken by an s-type pitot tube attached to the
probe will be biased high. At maximum probe insertion, this bias
will be more than 10%.
!-•
If a duct smaller than twelve inches in diameter is en-
countered, there are three options which may be followed in order
to obtain a valid test. These are: sampling at a constant
rate, adding a stack extension, and taking remote velocity
measurements. The latter method was devised by Robert F. Vollaro
of the EPA, and his description of the method is appended to this
section.
SAMPLING AT A CONSTANT RATE
For small ducts where the flow is expected to be uniform,
velocity measurements and sampling may be done at the same site.
Measure the velocity prior to testing, and base the sampling rate
on that measurement. The velocity should be checked again fol-
lowing the test. If the before and after measurements differ by
1-32
-------
more than ten percent the test results should be discarded.
Monitoring of the probe's pitot lines — even .though they are
providing erroneous velocity readings— is useful to indicate
any unexpected fluctuations in velocity during the test.
ADDING AN EXTENSION
For stacks with high flow rates, an extension 24 inches
diameter will enable sampling with a standard pitobe assembly.
Since this expanded extension introduces a flow disturbance,
it should have a length equal to at least 2%, and preferably 10,
times its diameter. Stack gas velocity, which is inversely pro-
portional to the diameter squared, must be at least 600 feet per
minute in the extension to enable use of s-type pitot tubes.
REMOTE VELOCITY MEASUREMENTS
To conduct representative sample traverses in ducts having
diameters between 4 and 12 inches, it is recommended that the
arrangement shown in Fig. 3-5 be used, in which velocity head CAP)
readings are taken downstream of the actual sampling site.
The straight run of duct between the sampling and velocity measure-
ment sites is necessary in order to allow the flow profile, tempo-
rarily disturbed by the sample probe, to redevelop and stabilize.
The pitot tube and sampling nozzle shown in Figures 3-6 and 3-8
from those of a conventional pitobe assembly ; construction
details of these components are discussed below:
A. Pitot tube
A standard (Type-P) pitot tube shall be used, instead
of a Type-S, to monitor stack gas velocity. When D
is less than 12 inches, a Type-S pitot tube can block
1-33
-------
a significant part of the duct cross-section, and
yield pseudo-high values of velocity head CAP)• Cross
section blockage is not a serious problem with a
standard pitot tube, however, for two reasons: 1)
the impact and static pressure sensing holes of a standard
pitot tube, unlike those of a Type-S, follow a 90°
bend, and are located well upstream of the tube;
2) when properly aligned, the sensing head of a standard
pitot tube is parallel, not perpendicular, to the flow
streamlines in the duct.
The preferred design for the standard pitot tube is
the Prandtl hemispherical-nosed design (Figure 3-6). Pitot
tubes constructed according to the criteria illustrated
in Figure 3 will have coefficients of 0.99 ± 0.01. 2'3
Note, however, that for most convenient tubing diameters
(dimension "D", Figure 3-6) , the static and impact sensing
holes of the Prandtl-type pitot tube will be very small,
thus making the tube susceptible to plugging in particulate
or liquid droplet-laden gas streams. Therefore, whenever
these conditions are encountered, either of the following
can be done: 1) a "back purge" system of some kind can be
used to clean out the static and impact holes periodically
during sampling; 2) a modified Prandtl pitot tube (Figure
3-7) which features enlarged impact and static pressure
holes, can be used instead of the Prandtl-type. It has
recently been demonstrated that the coefficients of the
Prandtl and modified Prandtl pitot tubes are essentially
4
the same.
1-34
-------
B. Sampling nozzle
The sampling nozzle can either be of the button-
hook or elbow design. The nozzle shall meet the
general design criteria specified in section 2.1.1
of the revised version of EPA Method 5, except
that the entry plane of the nozzle must be at
least 2 nozzle diameters (i.d.) upstream of the
probe sheath blockage plane (see Figure 3-8).
The following procedures shall be used to perform sample
traverses using the arrangement illustrated in Figure 3-5:
A. Location of sampling site.
Select a sampling site which is at least 8 duct
diameters downstream and 10 diameters upstream
from the nearest flow disturbances; this allows
the velocity measurements site to be located 8
diameters downstream of the sampling location and
2 diameters upstream of the nearest flow distur-
bance. For rectangular stacks, use an equivalent
diameter, calculated from the following equation,
to determine the upstream and downstream distances
D = 2LW
e L + W
Where:
D = Equivalent diameter
G
L = Length of cross-section
W = Width of cross-section
If sampling site located 8 diameters downstream
and 10 diameters upstream from the nearest dis-
1-35
-------
turbances is not available, select a site which
meets these criteria as nearly as possible. Under
no circumstances, however, shall a sampling site
be chosen which is less than 2 diameters down-
stream and 2.5 diameters upstream from the nearest
disturbances; this guarantees a minimum of 2
diameters of straight run between the sampling and
velocity measurement sites, and 0.5 diameters
between the velocity measurement site and the
nearest flow disturbance.
B. Number of traverse points
The correct number of traverse points shall be
determined from Figure 3-9. To use Figure 3-9, pro-
ceed as follows: first, determine the three
distances, "A", "B", and "C", and express each
distance in terms of duct diameters; second,
read from Figure 3-9,the number of traverse points
corresponding to each of these three distances;
third, select the highest of the 3 numbers of
traverse points, or a greater number, so that
for circular ducts the number is a multiple of 4;
for rectangular ducts, the number should be
chosen so that the criteria of section "D" be-
low can be met.
C. Location of traverse points, circular cross-sections
For circular stacks, locate the traverse points
according to section 2.3.1 or Method 1. Any
1-36
-------
traverse point located less than l/z"from
the stack wall will not be acceptable for
use as a sampling point; all such traverse
points shall be "adjusted" by relocating them
to a distance of exactly 1/2 inch from the wall.
In some cases, this relocation process may
involve combining 2 adjusted traverse points
to form a single "adjusted" point; thus, in
some instances, the number of points actually
used for sampling may be less than the number
of traverse points obtained from Figure 3-9.
D. Location of traverse points, rectangular cross-sections
For rectangular stacks, divide the cross-section
into as many equal rectangular elemental areas
as traverse points. Follow Table 1-1 in Method 1
(August 18, 1977) to determine the arrangement
of the equal areas. Locate a traverse point at
the centroid of each elemental area.
E. Sampling
Sample at each non-adjusted traverse point for the
time interval specified in the method being used
(e.g. Method 5). Sample at each "adjusted" point
for the appropriate integral multiple of the sam-
pling time at a non-adjusted point. For example,
if the adjusted point represents the combination
of two traverse points, sample twice as long at the
adjusted point as at the non-adjusted points. During
1-37
-------
each sample run, velocity head (AP) readings
shall be taken at points downstream of, but
directly in line with, the sampling points. The
sampling rate through the nozzle shall be set
based upon the AP readings; if a nomograph is
used, be sure when setting it to use the correct
value O0.99) of the pitot tube coefficient.
1-38
-------
REFERENCES
1. Martin, Robert M. Construction Details of Isokinetic Source-
Sampling Equipment. Environmental Protection Agency, Publication
No. APTD-0851. Research Triangle Park, N.C. April, 1971.
2. Perry, Robert H., Cecil H. Chilton, and Sidney D. Kirkpatrick
(editors) . Chemical Engineers' Handbook, Fourth Edition. McGraw-
Hill Book Company. New York, 1963.
3. Fluid Meters, Their Theory and Application. Published by the
American Society of Mechanical Engineers. 5th Edition. New
York, 1959.
4. Vollaro, R. F. Evaluation of Modified Prandtl-Type Pitot Tube,
interoffice memorandum. U. S. Environmental Protection Agency.
Emission Measurement Branch. Research Triangle Park, North
Carolina. November 28, 1975.
5. Shigehara, R. T. Adjustments in the EPA Nomograph for Different
Pitot Tube Coefficients and Dry Molecular Weights. U.S. Environ-
mental Protection Agency. Emission Measurement Branch. Research
Triangle Park, N. C. August, 1974.
1-39
-------
H
I
Estimated
. Sheath
Blockage
x w
Duct Area
x 100
Figure 3-3. Projected-area models for typical pitobe assemblies;
shaded area represents approximate average sheath
blockage for a sample traverse.
-------
H
1
Flow
disturbance
[<: 2 Dg ^~
8
Standard
Pitot
Tube
/»
Triujjornturo
8
Snmpl ing
Probe
Flow
Dioturbnnco
Figure 3-4 .Recommended sampling arrangement, when h" <_ D < 12",
-------
H
I
8 Static holes
* 0.1 D
Impact
opening
0.4D
Figure 3-5. Prandtl hemispherical-nosed standard pitot tube
-------
i
*>
U)
TF
A
Static Holes
3/8 D
Impact Opening
1/2 D
10. D
o --f
4 D
Figure 3-6. Modified Prandtl hemispherical-nosed standard pitot tube,
-------
H
I
Plane of
sheath
blockage
Figure 3-7. Recommended sampling nozzle design for use
when V < Dc < 12".
— s
-------
Number of Duct Diameters Between Velocity
Measurement Site and Nearest Disturbance
(Distance C)
1.5
Flow
Disturbance
Number of Duct Diameters Between Sampling Site and
Nearest Disturbance, (Distance A)
or
Number of Duct Diameters Between Sampling and Velocity
Measurement Sites, (Distance B)
Figure 3-8. Minimum number of traverse points, 4"<_ Dg< 12".
1-45
-------
SLIDE 309-0 NOTES
SAMPLING POINT LOCATION
SLIDE 309-1
METHOD 1 - CRITERIA FOR NUMBER
OF SAMPLING POINTS
VELOCITY
minimum = 12
maximum = 24
PART1CULATES
minimum = 12
maximum = 48
SLIDE 309-2
RATIONALE FOR INCREASING THE NUMBER
OF SAMPLING POINTS FOR NON-IDEAL
SAMPLING LOCATIONS
In general, the more variation in any parameter-being
measured, the greater the number of readings required to
obtain desired precision
1-47
-------
SLIDE 309-3
NOTES
FACTS ABOUT SAMPLING IN
NONPARALLEL FLOWS
measured participate concentration will be biased low
(less than true value)
measured volumetric flow rate will be biased high
(greater than true value)
measured mass emission rate will have an undeter-
mined bias
measured gases pollutant concentration will not be
biased
SLIDE 309-4
EXAMPLE STACK
CONTROL
DEVICE
LOCATION
B
LOCATION
A
SLIDE 309-5
EXAMPLE STACK SOLUTIONS
SAMPLING POINTS REQUIREMENTS
location A — 48 sampling points
location B — 12 sampling points
RESULTS
location A — measured concentration likely lower
— measured flow rate likely higher
1-49
-------
SLIDE 309-6 NOTES
RESULTS FROM INCREASING NUMBER
OF SAMPLING POINTS
• will likely give a more precise measurement
• does not remove measurement bias
• makes the source test and agency observer more
fatigued
Note: Never do less points than is
legally required by the method
SLIDE 309-7
OPTIONS FOR TESTING AT SAMPLING
LOCATIONS THAT DO NOT MEET
METHOD 1 CRITERIA
option 1 — move to a new location
option 2 — sample in normal manner and results will
be biased as previously noted
option 3 — use a compensation approach
SLIDE 309-8
COMPENSATION APPROACH
Agency should use all the same rationale and
procedures as described in the cyclonic flow
lecture
1-51
-------
SLIDE 309-9 NOTES
NOTES OF INTEREST
EPA plans to reduce maximum number of
sampling points required for paniculate testing.
Number will likely become the same as is now
required for volumetric flow rate determination
SLIDE 309-10
RANKING OF OPTIONS
1. Change to an acceptable sampling location
when feasible
2. Test in normal manner when agency must prove
violation
3. Test using compensation approach when source
must prove compliance
SLIDE 309-11
CONCLUSION
Suitability of sample location is more important
than increasing above 24 the number of sampling
points.
NOTE: this lecture assumes that there is no
secondary paniculate formation in the
stack after sample location
1-53
-------
SECTION J. INTERMITTENT PROCESS OPERATION
Subject Page
1. Slides J-3
J-l
-------
SLIDE 310-0
NOTES
INTERMITTENT PROCESS OPERATION
SLIDE 310-1
SLIDE 310-2
ESTABLISH INTERMITTENT PROCESS
OPERATION TESTING PROTOCOL
1. determine requirements and definitions of applicable
emission regulation(s)
2. determine requirements and definitions of applicable
test method(s)
3. determine source's normal or future normal mode of
operation
4. establish testing protocol
J-3
-------
SLIDE 310-3 NOTES
GENERALLY ACCEPTED "NO-NO'S"
WHEN TESTING INTERMITTENT PROCESSES
DO NOT:
• start, stop, and restart sample run to select only
certain portions of process cycle
• sample less than minimum sample volume or time
requirement (usually one hour minimum)
• require source to modify normal operations to
increase emissions
Note:The start, stop and restart technique may be used,
but only in conjunction with mathematical correc-
tion of the final results for non-sampling time.
SLIDE 310-4
BEST SOLUTIONS FOR TESTING
INTERMITTENT PROCESS OPERATION
• publish general procedures for sampling intermittent
process operation
• publish specific procedures for every type of inter-
mittent source category
SLIDE 310-5
TESTING COMPLETE PROCESS CYCLES
set up sample time and points to complete run for
minimum process cycle
after all sample points have been tested, continue to
sample at as many additional points as required to
complete actual process cycle or normal process cycle
J-5
-------
SLIDE 310-6 NOTES
CONCLUSIONS
• sampling protocols for intermittent sources are
more of a legal decision than a technical one
• ensure support of agency attorney in testing
protocol prior to actual test
J-7
------- |