United States
Environmental Protection
Agency
Environmental Monitoring Systems- ,'-, "•'"
Laboratory * p£ A
Research Triangle Park NC 27711 fi\*
xvEPA
Research and Development
EPA-600/S4-82-062 Oct. 1982
Project Summary
Techniques to Measure
Volumetric Flow and
Particulate Concentrations in
Stacks with Cyclonic Flow
J. Douglas Sterrett, Allen R. Barbin, Joe W. Reece, W. Glenn Carter,
and Bruce B. Ferguson
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 the 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
that were studied. A field study to
determine the effect of an egg crate
device on particulate distribution
across the stack gave inconclusive
results.
This Project Summary was
developed by EPA's Environmental
Monitoring Systems Laboratory,
Research Triangle Park. NC. to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
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
cannot be quantitatively collected with
conventional sampling techniques.
Mitchell et al.* suggested that an in-
stack installed venturi by itself might
•Mitchell, W J , B. E Blagun, D. E. Johnson, and
M R. Midgett. Angular Flow Insensitive PitotTube
Suitable for Use with Standard Stack Testing
Equipment EPA-600/4-79-042, U.S. Environ-
mental Protection Agency, Research Triangle Park,
NC, 1979
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straighten cyclonic flow and
redistribute the particulate sufficiently
to sample it 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 particle 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
the 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 longitud-
inal and externally adjustable slots.
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
elevate the ability of 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,
Conical Flow
Regulator
Flow Rate Venturi
45.7
and 13 mVs. 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 percent, and the
axial volumetric flow was approxi-
mately! 27 mVmin. 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 thetesting. Flow
45.7
Test Venturi
(Dimensions in centimeters/
Flow Straightening Vents
Flow
7.62m
1.5ml
Electric Motor
• Swirl Generator
Figure 1. Experimental facility plan review.
2
See Detail Above -
angle with respect to the stack
longitudinal axis was measured using a
United Sensor® 3-dimensional pttot
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, it will
neither straighten cyclonic flows nor
redistribute the particulate 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 m 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 m-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; and
• The increased velocity in the
venturi throat could make more
accurate sampling in stacks with
low velocities since most pitot
tubes are inaccurate below 10ft/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
Figure 2. Egg crate and 8-vane etoile-
type flow straighteners.
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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 those for the egg
crate; 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 20 traverse
points downstream of the egg crate
deviated less than 4° from the stack
axis. Also, static 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 paniculate 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 upstream.) 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 pilot tube
aligned with the stack axis, while Train
B sampled with its nozzle and pilot 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 pointtothetotal
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 paniculate 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 2)
show that in all runs the particulate
concentration determined upstream
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 (9)
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
A verage
4
5
6
7
8
A verage
Concentration (mg/m3)
Upstream Downstream
130
147
26
101
22
31
103
35
64
47
130
154
22
102
18
31
86
33
55
45
Volumetric
Upstream
137
138
115
130
Flow (m3/min)
Downstream
125
120
115
120
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 upstream 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 and the fact that no additional
sources were available for testing pre-
vented conducting additional field tests.
field tests.
Reference
1. Mitchell, W. J., B. E. Blagun, D. E.
Johnson, and M. R. Midgett.
Angular Flow Insensitive Pilot Tube
Suitable for Use with Standard
Stack Testing Equipment. EPA-
600/4-79-042, U.S. Environmental
Proteclion Agency, Research
Triangle Park, North Carolina,
1979.
* US. GOVERNMENT PRINTING OFFICE: 1982-559-017/0848
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J. Douglas Sterrett. Allen R. Barbin. Joe W. Reece, W. Glenn Carter, and Bruce B.
Ferguson are with Harmon Engineering and Testing, Inc., Auburn, AL 35810.
William J. Mitchell is the EPA Project Officer (see below).
The complete report, entitled "Techniques to Measure Volumetric Flow and
Paniculate Concentrations in Stacks with Cyclonic Flow," (Order No. PB
82-259 789; Cost: $10.50, 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:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
PS 0000339
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