U.S. Patent Dec. 13, 2022 Sheet 18 of 48 US 11,525,840 B2

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184

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Pitch, [deg]

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FIG. 18

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U.S. Patent Dec. 13, 2022 Sheet 39 of 48 US 11,525,840 B2

3 +

A)

B)

1.20 +
30-20 -10 0 10 20 30

Pitch, [deg]

FIG. 39


U.S. Patent Dec. 13, 2022 Sheet 35 of 48

US 11,525,840 B2

4

ri LDA
3
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thermal anemomete!

FIG. 35


U.S. Patent Dec. 13, 2022 Sheet 44 of 48 US 11,525,840 B2

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FIG. 44


U.S. Patent Dee. 13, 2022 Sheet 12 of 48 US 11,525,840 B2

301; receiving, by an analyzer, differential pressure signal 214.0, differential pressure signal 214.1,
differential pressure signa! 214.2, and differential pressure signal 214.3

302: producing zeroth calibrated pressure CPO from differential pressure signal 214.0, first
calibrated pressure CPi from differential pressure signal 214.1, second calibrated pressure CP2
from differential pressure signal 214.2, and third calibrated pressure CP3 from differential pressure
signal 214.3

removing a dependence of a pressure PO of a reference gas from zeroth calibrated pressure
CPO, first calibrated pressure CPi, second calibrated pressure CP2, and third calibrated pressure
CP3 to produce, respectively, first adjusted pressure API, second adjusted pressure AP2, and third
adjusted pressure AP3
ifey pair-wise subtracting CPi from CPO // te provide for off-axis velocity vector

304; combining first adjusted pressure AP1, second adjusted pressure AP2, and third adjusted
pressure AP3 to obtain a pseudo-dynamic pressure scalar

305: individually normalizing first adjusted pressure API, second adjusted pressure AP2, and third
adjusted pressure AP3 with the pseado-dynamic pressure scalar to produce, respectively, first
reduced pressure RP1, second reduced pressure RP2, and third reduced pressure RP3

306: determining real dynamic pressure 307: determining a yaw angle or a pitch
from first reduced pressure RPI, second angle of the gas flow from first reduced
reduced pressure RP2, and third reduced pressure RPI, second reduced pressure
pressure RP3 RP2, and third reduced pressure RP3

31: determining velocity

FIG. 12


US 11,525,840 B2

47

9. The non-nulling gas velocity measurement apparatus of
claim 8, further comprising a controller in communication
with each gas valve and that:

produces a plurality of valve control signals; and

communicates the valve control signals, such that each

gas valve receives one of the valve control signals from
the controller and produces valve-selected gas based on
the valve control signal.

10. The non-nulling gas velocity measurement apparatus
of claim 9, wherein the controller further produces a control
signal; and communicates the control signal to the analyzer,
such that the control signal indicates whether each gas valve
produces valve-selected gas from the stagnant gas or the
reference gas.

11. The non-nulling gas velocity measurement apparatus
of claim 1, wherein the gas source is an emission stack.

12. The non-nulling gas velocity measurement apparatus
of claim 1, wherein the aerodynamic flow head comprises a

hemispherical surface over which gas flow flows to be 2

received by the entrant aperture that are arranged in the
hemispherical surface.

13. The non-nulling gas velocity measurement apparatus
of claim 1, wherein the aerodynamic flow head comprises a
conical surface over which gas flow flows to be received by
the entrant aperture that are arranged in the conical surface.

14. The non-nulling gas velocity measurement apparatus
of claim 1, wherein the differential pressure signal from the
plurality of differential pressure transducers provide a deter-
mination of gas velocity parameters that comprise turbu-
lence intensity, velocity vector, static pressure, or density of
gas flow.

15. The non-nulling gas velocity measurement apparatus
of claim 1, wherein the gas flow comprises a Mach number
from 0.01 to 0.3 at a velocity that is from 5 m/s to 100 m/s.

16. A process for performing non-nulling measurement of
gas velocity parameters, the process comprising:

receiving, by an analyzer, a zeroth differential pressure

signal, first differential pressure signal, a second dif
ferential pressure signal, and third differential pressure
signal;

producing a zeroth calibrated pressure CPO from the

zeroth differential pressure signal, a first calibrated
pressure CPI from the first differential pressure signal,
a second calibrated pressure CP2 from the second
differential pressure signal, and a third calibrated pres-
sure CP3 from the third differential pressure signal;
removing a dependence of a reference gas pressure PO of
areference gas from the zeroth calibrated pressure CPO,
the first calibrated pressure CP1, the second calibrated
pressure CP2, and the third calibrated pressure CP3 to
produce, respectively, a first adjusted pressure API, a

second adjusted pressure AP2, and a third adjusted
5

pressure AP3;

combining the first adjusted pressure API, the second

adjusted pressure AP2, and the third adjusted pressure
AP3 to obtain a pseudo-dynamic pressure scalar;

individually normalizing the first adjusted pressure AP1,
the second adjusted pressure AP2, and the third
adjusted pressure AP3 with the pseudo-dynamic pres-
sure scalar to produce, respectively, a first reduced
pressure RPI, a second reduced pressure RP2, and a
third reduced pressure RP3;

determining a real dynamic pressure from the first
reduced pressure RP1, the second reduced pressure
RP2, and the third reduced pressure RP3;

48
determining a yaw angle or a pitch angle of the gas flow
from the first reduced pressure RP1, the second reduced
pressure RP2, and the third reduced pressure RP3; and
determining velocity of the gas flow from the real
dynamic pressure to perform non-nulling measurement
of gas velocity parameters.
17. The process for performing non-nulling measurement
of gas velocity parameters of claim 16, further comprising:
disposing a non-nulling pitot probe in an emission stack
such that a central entrant aperture of the non-nulling
pitot probe is aligned with a stack axis of the emission
stack, the non-nulling pitot probe comprising:
an aerodynamic flow head comprising a plurality of
entrant apertures that comprises the central entrant
aperture and a plurality of peripheral entrant aper-
tures arranged radially from the central entrant aper-
ture, the peripheral entrant aperture comprising a
first peripheral entrant aperture, a second peripheral
entrant aperture, and a third peripheral entrant aper-
ture:
an entrant body tube disposed on the aerodynamic flow
head;
an extensor body tube disposed on the entrant body
tube such that the entrant body tube is interposed
between the aerodynamic flow head and the extensor
body tube, such that extensor body tube is arranged
at an oblique angle to the entrant body tube: and
a plurality of pressure channels disposed in the aero-
dynamic flow head, the entrant body tube, and the
extensor body tube, such that each entrant aperture is
separately and independently in fluid communication
with one of the pressure channels, and each pressure
channel independently receives and communicates
the gas flow as stagnant gas from the entrant aperture
of which the pressure channel is in communication;
receiving, by the entrant apertures, the gas flow;
producing, by the central entrant aperture, a zeroth stag-
0 nant gas from the gas flow;
producing, by the first peripheral entrant aperture. a first
stagnant gas from the gas flow;
producing, by the second peripheral entrant aperture, a
second stagnant gas from the gas flow;
producing, by the third peripheral entrant aperture, a third
stagnant gas from the gas flow; and
obtaining the zeroth differential pressure signal, the first
differential pressure signal, the second differential pres-
sure signal, and the third differential pressure signal
respectively from the zeroth stagnant gas, the first
stagnant gas, the second stagnant gas, and the third
stagnant gas.
18. The process for performing non-nulling measurement
of gas velocity parameters of claim 16, further comprising:
disposing a non-nulling pitot probe in an emission stack
such that a central entrant aperture of the non-nulling
pitot probe is not aligned with a stack axis of the
emission stack, the non-nulling pitot probe comprising:
9 an aerodynamic flow head comprising a plurality of
entrant apertures that comprises the central entrant
aperture and a plurality of peripheral entrant aper-
tures arranged radially from the central entrant aper-
ture, the peripheral entrant aperture comprising a
first peripheral entrant aperture, a second peripheral
entrant aperture, and a third peripheral entrant aper-
ture:

0

&

50



US 11,525,840 B2

11

Reference pressure source 210 provides reference gas 211
and can be a pressurized vessel, gas generator, and the like.
Reference gas 211 can be a gas at reference gas pressure PO.
Exemplary reference gases 211 include air, an inert gas,
nitrogen, and the like. Reference gas pressure PO is sufli-
ciently great enough to provide a stable differential pressure
reading by differential pressure transducer 213 and can be
from 1 Pa to 100 MPa, specifically 100 Pa to 1 MPa, and
more specifically from 5 kPa to 1 MPa

In an embodiment, with reference to FIG. 11, non-nulling
pitot probe 201 is disposed in emission stack 235 that is
disposed on and in fluid communication with emission
source 243. Emission source 243 can be a refinery, com-
bustion chamber, chemical processor, and the like that
produces emissions that are communicated to emission stack
235 as gas flow 206 that can include particulates, gas, liquid,
or a combination thereof. Emission stack 235 has a stack
axis along which gas flow 206 flows away from emission
source 243 and includes flange 236 that provide a fixed

height test point at height H from emission source 243 for 2

disposing non-nulling pitot probe 201 in emission stack 235.
Aerodynamic flow head 207 is selectively positioned at
various radial locations, as measured from the stack axis
centerline of emission stack 235, such as first radial position
R1, second radial position R2, and the like. A number of
radial positions can be selected to provide a full character-
ization of gas velocity parameters 216 of gas flow 206
throughout emission stack 235 at height H. It should be
appreciated that non-nulling pitot probe 201 is constructed
and configured so that non-nulling pitot probe 201 fully
characterizes gas velocity parameters 216 of gas flow 206 in
absence of rotating non-nulling pitot probe 201 in emission
stack 235. Instead of rotating non-nulling pitot probe 201 to
obtain data for determination of gas velocity parameters
216, central entrant aperture 238 of non-nulling pitot probe
201 can be aligned to be parallel to stack axis of emission
stack 235. In case of disposition of non-nulling pitot probe
201 with central entrant aperture 238 of non-nulling pitot
probe 201 not aligned parallel to stack axis of emission stack
235, data from non-nulling pitot probe 201 can be corrected
to account for the angle at which non-nulling pitot probe 201
is disposed relative to the stack axis.

In an embodiment, with reference to FIG. 9, FIG. 10, and
FIG. 11, control system 247 provides data acquisition and
control and interface of components of non-nulling gas
velocity measurement apparatus 200. Control system 247
receives stack signal 244 from non-nulling pitot probe 201
that can be disposed in emission stack 235. Stack signal 244
provides electrical signals, e.g., voltages, that indicate

whether emission stack 235 is subject to purge such that gas 5

valve 209 should isolate non-nulling pitot probe 201 from
differential pressure transducer 213 as well as a radial
position of aerodynamic flow head 207 of non-nulling pitot
probe 201 in emission stack 235. Control system 247

includes switcher 231 that receives stack signal 244 from s

non-nulling pitot probe 201 or emission stack 235 and splits
stack signal 244 into stack radial p
purge signal 234. It should be appreciated that st
244 can be produced by a user or automated proces
a mechanical, electrical, or optical system. Stack radial
position signal 233 indicates the radial position of aerody-
namic flow head 207 of non-nulling pitot probe 201 in
emission stack 235, wherein stack radial position signal 233
can be an analog voltage from 0 volts (V) to 10 V. Non-
nulling pitot probe 201 can be positioned, e.g., at a minimum
of four radial positions per quadrant of emission stack 235.
Purge signal 234 indicates whether emission stack 235 is

&

12

subject to purge so that gas valve 209 can isolate non-nulling
pitot probe 201 from differential pressure transducer 213,
wherein purge signal 234 can be a digital voltage such as a
5 VDC digital signal that indicates to connected non-nulling
pitot probe 201 via gas valve 209 to differential pressure
transducer 213 such that a signal HI indicates a condition
that is safe to connect differential pressure signal 214 to
non-nulling pitot probe 201, and a signal LOW indicates a
condition isolate non-nulling pitot probe 201 from differen-
tial pressure signal 214 by gas valve 209, as controlled by
valve control signal 227. In an embodiment, with reference
to FIG. 10, switcher 231 includes data receiver 232 that
receives stack signal 244, e.g., by a receptacle for receipt of
a cable or other electrical signal communication medium
and sends stack signal 244 to signal splitter 246. Signal
splitter 246 splits stack signal 244 into stack radial position
signal 233 and is in electrical communication with voltage
divider 245 that produces purge signal 234.

Control system 247 also can include controller 226 in
electrical communication with switcher 231. Controller 226
includes various electrical components that receive and
handle electrical signals and process instructions. Controller
226 can be a data acquisition card or similar device for

5 electrically interfacing with the various components of con-

trol system 247. Controller 226 receives purge signal 234
from switcher 231 and controls electronic relay 225 to
produce valve control signal 227 that is communicated to
gas valve 209. Electronic relay 225 receives electrical power
from power supply 229, and the electrical power is switch-
ably transmitted by electronic relay 225 to gas valve 209 to
select reference flow configuration or sample flow configu-
ration of individual gas valves 209. Controller 226 receives
valve-selected gas 212 from differential pressure transducer
213. Differential pressure transducer 213 is powered by
power supply 229. Controller 226 collates and communi-
cates signals including the radial position of non-nulling
pilot probe 201 in emission stack 235, the purge status of
emission stack 235, differential pressure signal 214, and the
like to communication interface 230. Communication inter-
face 230 can be a computer interface bus that provic
connection points for electrical communication cabling
between controller 226 and analyzer 215. Analyzer 215
receives data, including differential pressure signal 214 from
communication interface 230 and determines gas velocity
parameters 216 that include turbulence intensity, velocity
vector, static pressure, or density of gas flow 206 from such
data. Analyzer 215 can include a computer processor, field
programmable gate array, and the like that can perform data
manipulation according to electronic circuitry configuration
or instructions, ¢.g., from computer code, executable pro-
gram, or program script. Analyzer 215 can receive data via
communication line 218, which can be a hardwire or wire-
less electronic or optical communication line.

Non-nulling gas velocity measurement apparatus 200 and
non-nulling pitot probe 201 can be made in various ways. It
should be appreciated that non-nulling gas velocity mea-
surement apparatus 200 includes a number of optical, elec-
trical, or mechanical components, wherein such components
can be interconnected and placed in communication (e.
optical communication, electrical communication, mechani
cal communication, and the like) by physical, chemical,
optical, or free-space interconnects. The components can be
disposed on mounts that can be disposed on a bulkhead for
alignment or physical compartmentalization. As a result,
non-nulling gas velocity measurement apparatus 200 can be
disposed in a terrestrial environment or space environment.



US 11,525,840 B2

7

209 communicates valve-selected gas 212 to differential
pressure transducer 213; receives valve-selected gas 212
from gas valve 209; receives reference gas 211 at reference
gas pressure P0; compares a pressure of valve-selected gas
212 to reference gas pressure PO; and produces a differential
pressure signal 214 from comparison of the pressure of the
valve-selected gas 212 to the reference gas pressure.

In an embodiment, non-nulling gas velocity measurement
apparatus 200 includes a plurality of stagnant gas lines 217,
such that each stagnant gas line 217 separately interconnects
one pressure channel 205 with one of the gas valves 209 for
communicating gas flow 206 received by the respective
entrant aperture 202 to the respective gas valve 209 as
stagnant gas 208.

In an embodiment, non-nulling gas velocity measurement
apparatus 200 includes a plurality of valve outlet gas lines
224, such that each valve outlet gas line 224 separately
interconnects one gas valve 209 with one of the differential
pressure transducers 213 for communicating valve-selected
gas 212 from gas valve 209 to the respective differential
pressure transducer 213.

In an embodiment, non-nulling gas velocity measurement
apparatus 200 includes reference gas line 223 in communi-
cation with each gas valve 209 and that communicates
reference gas 211 to gas valves 209

In an embodiment, non-nulling gas velocity measurement
apparatus 200 includes reference gas line 223 in communi-
cation with each differential pressure transducer 213 and that
communicates reference gas 211 to differential pressure
transducers 213.

In an embodiment, non-nulling gas velocity measurement
apparatus 200 includes reference pressure source 210 that
provides reference gas 211 to each gas valve 209.

In an embodiment, non-nulling gas velocity measurement
apparatus 200 includes reference pressure source 210 that
provides reference gas 211 to each differential pressure
transducer 213.

In an embodiment, non-nulling gas velocity measurement
apparatus 200 includes analyzer 215 in communication with
each differential pressure transducer 213 and that: receives
each differential pressure signal 214 from each differential
pressure transducer 213; and produces gas velocity param-
eters 216 from differential pressure signal 214.

In an embodiment, non-nulling gas velocity measurement
apparatus 200 controller 226 in communication with each
gas valve 209 and that: produces a plurality of valve control
signals 227; and communicates valve control signals 227,
such that each gas valve 209 receives one of valve control
signals 227 from controller 226 and produces valve-selected

gas 212 based on valve control signal 227. In an embodi- 5

ment, non-nulling gas velocity measurement apparatus 200
controller 226 produces control signal 228 and communi-
cates control signal 228 to analyzer 215, such that control
signal 228 indicates whether each gas valve 209 produces

valve-selected gas 212 from stagnant gas 208 or reference

gas 211.

Non-nulling gas velocity measurement apparatus 200 can
be made from various elements and components. With
reference to FIG. 3, FIG. 4, FIG. 5, FIG. 6, and FIG. 7,
non-nulling pitot probe 201 receives gas flow 206 at acro-
dynamic flow head 207 that includes a plurality of entrant
apertures 202, wherein entrant apertures 202 include central
entrant aperture 238, referred to a zeroth entrant aperture
202.0, around which is disposed a plurality of peripheral
entrant apertures 239, referred to as first entrant aperture
202.1, second entrant aperture 202.2, . . . , to n-th entrant
aperture 202.7, wherein n is an arbitrary integer. A number

20

3

&

&

8

of peripheral entrant apertures 239 is arbitrary but selected
to adequately characterize gas flow 206. At a minimum,
three peripheral entrant apertures 239 are included as shown
in FIG. 7C, for characterization of gas flow 206. Peripheral
entrant apertures 239 are disposed at radial distance R with
respect to a center of central entrant aperture 238 that is
centrally position on aerodynamic flow head 207 and can be
spaced apart by an equal amount of space at a selected pitch,
such as for a distribution of four peripheral entrant apertures
239 for a total of five entrant apertures 202 as shown in FIG.
7D or for a distribution of eight peripheral entrant apertures
239 for a total of nine entrant apertures 202 as shown in FIG.
7E. Radial distance R can be selected based on a size, e.g.,
a diameter, of aerodynamic flow head 207 and diameter D of
individual entrant apertures 202. It is contemplated that
radial distance can be from 1 micrometer (um) to 1 meter
(m), specifically from 1 millimeter (mm) to 50 centimeters
(cm), and more specifically from 1 mm to 10 cm. Diameter
D is selected to maximize acceptance of gas flow 206 by
each entrant aperture 202 while being connecting each
pressure channel 205 to a stagnant gas line 217. Diameter D
can as large as possible without interference among adjacent
entrant apertures 202 so that individual entrant apertures 202
are physically separate, including the particular pressure

5 channel 205 that is in fluid communication with the indi-

vidual entrant aperture 202. Diameter D can be from 1
micrometer (jm) to 1 meter (m), specifically from 1 mil
meter (mm) to 50 centimeters (cm), and more specifi
from 1 mm to 10 cm.

Gas flow 206 received by entrant apertures 202 is com-
municated to pressure channels 205, wherein each entrant
aperture 202 is connected to one pressure channel 205 in an
absence of fluid communication among pressure channels
205. That is, pressure channels 205 are isolated from one
another, Pressure channel 205 extends from entrant aperture
202 in aerodynamic flow head 207 through entrant body
tube 203 and terminates at extensor body tube 204 disposed
distal from aerodynamic flow head 207.

Non-nulling gas velocity measurement apparatus 200,
including aerodynamic flow head 207, entrant body tube
203, and extensor body tube 204, be made of a material
that is physically or chemically resilient in an environment
of the source of gas flow 206 such as emission stack 235.
Exemplary materials include a metal (¢.g., nickel, stainless
steel, and the like), ceramic, thermoplastic, glass, and the
like. Aerodynamic flow head 207, entrant body tube 203,
and extensor body tube 204 can be made of the same or
different material and can be monolithic in a single physical
body or can be separate members that are physically joined.
‘An aerodynamic shape of aerodynamic flow head 207 as
experience by gas flow 206 can be selected to not cause
disruption of gas flow 206 over aerodynamic flow head 207
or creation of eddies from gas flow 206. The shape can be,
e.g., hemispherical as shown in FIG. 3, FIG. 4, FIG. 5, and
FIG. 7A or conical as shown in FIG. 6 and FIG. 7B. For a
conical aerodynamic flow head 207, the surface of aerody-
namic flow head 207 can have an arbitrary conical angle
with respect to a length axis of entrant body tube 203, the
conical angle can be from slightly greater than 90° to slightly
less than 180°, specifically from 95° to 175°, and more
specifically from 95° to 135°,

Entrant body tube 203 is interposed between aerodynamic
flow head 207 and extensor body tube 204 and communi-
cates gas flow 206 received by entrant aperture 202 via
pressure channel 205. Extensor body tube 204 is arranged at
an oblique angle to entrant body tube 203, which can be
around 90°, specifically from 60° to 120°. It is contemplated

lly



US 11,525,840 B2

19

sured at prescribed points in the stack cross section. These
velocity measurements are made using EPA-approved dif-
ferential pressure probes such as the 2-hole S-probe or the
5-hole spherical probe. Measurements using the more accu-
rate 5-hole spherical probes require a time-consuming rota-
tion (or nulling) of the probe to find the yaw angle. We
developed a time-saving non-nulling technique using a
spherical probe that measures all 3 components of velocity
and therefore provides better accuracy than an S-probe. We
compared the non-nulling technique with the BPA Method
2F nulling technique at both high (16 m/s) and low (7 m/s)
loads in a coal-fired powerplant smokestack. Their excellent
mutual agreement (within 0.3% of the flow) demonstrates
that the non-nulling technique accurately measures flue gas
flows.

Greenhouse gases and other pollutants from coal-fired
power plants (CFPPs) are quantified by continuous emission
monitoring systems (CEMS) permanently installed in
exhaust stacks. CEMS equipment measures the concentra-
tion of each pollutant as well as the total flow. The accuracy
of CEMS flow monitors are evaluated following an EPA
procedure known as a relative accuracy test audit (RATA).
Flow RATAs are performed using any of 3 EPA approved
differential-pressure (pitot) probes along with their corre-

sponding protocols including EPA Method 2, Method 2F, 2

Method 2G, and Method 1 (EPA 2017c, 2017d, 2017e,
20178).

In this example, we present a non-nulling flow RATA
procedure that can reduce RATA measurement times and
simultaneously increase their accuracy. We developed the
Non-Nulling Method using conventional spherical probes.
FIG. 15A shows a spherical probe. We tested the Non-
Nulling Method by performing a 16-point flow RATA in the
exhaust stack of a CFPP as illustrated in FIG. 15B. The
average axial velocity measured by the Non-Nulling Method
Vay Was compared 10 Vay the average axial velocity
determined using the EPA-approved Method 2F nulling
protocol. We compared Vy with Vyyoy-at two average stack
velocities (16 m/s and 7 m/s) corresponding to the power
plant’s high and low loads. We found excellent mutual
agreement between the Method 2F and the non-nulling
average velocities: the differences were less than 1001V yop!
Var lI<0.3%.

For several decades, S-probes have been differential pres-
sure probes for flow RATAs. These probes continue to be
used even though they can overpredict the flow by as much
as 10% or more when non-axial velocity components are
significant. EPA-approved five-hole probes (such as the
spherical probe in FIG. 15A) can provide better accuracy,

but they are rarely used because flow RATAs conducted with 5

these probes are more costly and, in many cases, more
time-consuming than RATAS performed with S-probes. In
CFPPs that have wet scrubbers, an $-probe RATA using
Method 2 (EPA 2017c) or Method 2G (EPA 2017e) is

generally less time consuming than a S-hole probe RATA 5

since the 2 pressure ports on the S-probe are larger and do
not plug as frequently as the smaller ports on the 5-hole
spherical probe. In any case, whether one uses an S-probe to
measure 2 components of velocity vector at each traverse
point (EPA 2017e) or a 5-hole probe to measure the entire
velocity vector (EPA 2017d), a significant fraction of the
measurement time is spent rotating the probe about its axis
searching for the null condition. The null condition is
satisfied when the differential pressure between two of the
probe’s ports is zero. For example, a five-hole probe must be
rotated about its axis until the differential pressure between
ports 2 and 3 is zero. When P,5=0, all three velocity

3

&

20

components can be determined from measuring the differ-
ential pressures between other ports on the spherical probe
as specified in Method 2F (EPA 2017d). Because all the
velocity components are measured, the result is more accu-
rate than the S-probe. However, finding the null condition
can take several minutes at each traverse point, especially in
stacks with significant yaw and/or in wet stacks that require
frequent purging of the spherical probe’s 5 pressure ports to
remove water droplets and particulates. In this example, we
show that the Non-Nulling Method accurately determines
the axial velocity without rotating the probe. Therefore,
non-nulling measurements are faster than corresponding
Method 2F measurements, but with comparable (or probably
better) accuracy.

‘The accuracy of the Non-Nulling Method was previously
demonstrated in a Scale Model Smokestack Simulator
(SMSS). The SMSS facility uses air as a surrogate for flue
gas and generates asymmetric swirling flows in its 1.2 m
diameter test section. Yaw-null angles are almost 40° near
the wall. A key element of the SMSS facility is that flow
measurements are traceable to NIST primary standards. A
NIST-calibrated flow meter installed in an upstream section
of piping (that is not subjected to the flow distortions present
in the test section) measures the flow at a 0.7% uncertainty.
Unless otherwise stated, all uncertainties in this paper are
expanded standard uncertainties with coverage factor k=2
corresponding to a 95% confidence limit. By comparing the
Non-Nulling Method to the calibrated flow meter, we found
agreement of 0.8%.

The measurements described in this example demonstrate
that the Non-Nulling Method agrees with the EPA-approved
Method 2F (EPA 2017d) in the harsh conditions of a CFPP
stack. To provide a rigorous test of the Non-Nulling Method
we intentionally selected a CFPP known to have a complex
velocity field in its stack. The selected stack’s RATA mea-
surement platform was only 3.8 stack diameters ( 8 m)
downstream of a 90° elbow. Moreover, upstream of the
elbow, flow from two wet scrubbers merged into a single
stream. The velocity profile at the measurement platform
was skewed and had large negative yaw-null angles of
nearly -30° at the stack wall. To add to this complexity,
repeated flow RATAs showed spatially localized transients
at certain traverse points that were characterized by changes
of 10% or more in the axial velocity. Because the Non-
Nulling Method provided accurate results for these chal-
lenging measurement conditions, we expect it will also
perform well in stacks with less complicated velocity fields.

With regard to calculating the spatially averaged axial
velocity in the stack, FIG. 15B is a diagram the stack
cross-section used for the flow RATA. A spherical probe was
installed in each of four flanges on the wall of the stack. As
illustrated in the figure, each probe measures the axial
velocity Vixjaz, Of the four points on its radius. (The
adjacent radii are at right angles to each other.) The traverse
points are located at the centroids of equal area so that the
average RATA velocity is determined by the arithmetic
mean of the N=16 axial velocity measurements,

w

The desired volumetric flow is Vx.4z4 multiplied by the
stack’s cross-sectional area, We used the spatially averaged
axial velocity Vir to compare Method 2F with the Non-


US 11,525,840 B2

27

in the wind tunnel at the probe's location. For most probe
geometries, P,,(IVI, Tu, 0, B) is too complex to predict
accurately. Complexities, particularly at large values of « or
B, include excess noise and, for low values of Tu, hysteresis
generated by boundary layer separation.

NIST’s updated air-velocity calibration system spans the
ranges: yaw angle +180°; pitch angle #45°: airspeed 1 m/s
to 30 m/s; turbulence intensity 0.0007 to 0.25; average data
rate: 300 points/hour at fixed Tu. These specifications
include the measurement ranges that are used for smoke-
stack measurements: 5 m/ss|V|<30 m/s and Tu about 0.1.

For airspeeds that NIST determines using its laser doppler
anemometer (LDA), the system’s expanded uncertainty cor-
responding to 95% confidence interval is U,(V,)=0.004xV,
where V, is the component of V perpendicular to LDA’s
interference fringes. For airspeeds that NIST determines
using a calibrated pitot tube: U,(IVI)=0.0044xIVI+(0.013
m’/s*/IV1). The expanded uncertainty of the pitch and yaw
angles is 0.3° and the expanded uncertainty of the measure-
ments of turbulence intensity is U(Tu)-0.03xTu_ for
0.03sTus0.1. NIST’s calibrations of P,,(/VI, Tu, ot, B) are
traceable to the International System of Units. Such trace-
ability is essential to eam international recognition of
NIST’s new capability for calibrating angle- and turbulence-
dependent responses of diverse anemometers.

National Metrology Institutes (NMIs) has posted calibra-
tion capabilities for diverse anemometers. However, none of
the posted capabilities consider Tu, @., and B as independent
variables. Therefore, the results of any one these interna-
tionally-recognized calibrations can be summarized in a
small table listing the anemometer’s response at, perhaps, 10
to 20 airspeeds. All the NMIs calibrate anemometers in
low-turbulence air flows at ambient temperature and pres-
sure. Prior to calibrations, those anemometers that have
direction-dependent responses to the air flow are aligned
with the air flow. For example, the axis of a propeller
anemometer is aligned parallel to the air stream. In the range
0.5 m/s to 38 m/s, the smallest claimed expanded uncertainty
was |V1)=0.0025xIVI. The uncertainties for the present
4-variable calibrations are only 1.6x larger calibrations
obtained under the restricted conditions: a=$=0 and Tu~0,

Regarding the wind tunnel, FIG. 21 shows the wind
tunnel with its higher-speed test section installed. Here, we
describe the tunnel’s operation when turbulence generators
are absent. The wind tunnel is a closed loop contained within
a footprint 43.5 m long and 8.9 m wide. The fan that drives
the airflow is on the opposite side of the loop from the test
section that contains the working airspeed standards and any
instrument under test IUT. From the fan, the airflow passes

through two sets of turning vanes and into a large-cross- 5

section, screen-filled “settling” chamber that reduces the
fan-generated turbulence and swirl. The test section shown
in the side view in FIG. 21 is used for calibrations spanning
the range 0.15 m/s to 75 mis. It is 12 m long and 1.5 m wide.

‘Along the flow direction, the test section’s height forms a

venturi-like duct. The height gradually contracts from 2.1 m
to 1.2 m. Thea, it is constant for a length of 2 m. Finally, the
height gradually returns to 2.1 m. In the test section, the
longitudinal free-stream turbulence level is 0.001 over most
of the airspeed range with a transverse airspeed gradient of
less than 1% within a working area of 90% for all test section
areas. Using an LDA, we mapped the airspeed in a vertical
plane that passed through the geometric center of the test
section. In 0.4 m wide by 0.4 m high subsection of the map,
the maximum airspeed difference from the center of the test
section was 0.10% in the vertical direction and 0.15% in the
horizontal direction at the airspeed 10 m/s. Therefore, any

20

&

28

TUT can be accurately calibrated if it is located anywhere in
the subsection. If an IUT is located closer to the test
section’s wall during a calibration, the calibration must
account for the boundary layers attached to the wind tun-
nel’s walls.

While making the airspeed map, the airspeed was kept
constant using a PID control loop linked to an L-shaped pitot
tube placed on the side of the wind tunnel, as shown in FIG.
22. For normal calibrations, data are taken when the PID
loop indicates that [VI is controlled within the larger of 0.01
m/s or 0.002|V| for the range 5 m/ss|V/=40 m/s. The noise
in the PID loop corresponded to air speed fluctuations of
0.01% rms, when averaged over 50 seconds. We did not map
the airspeed below 5 m/s because, at lower airspeeds, the
uncertainty of the pitot tube measurements is larger than the
uncertainty of the map. Above 20 m/s, the increasing Reyn-
olds number increases flatness of the airspeed map in the
wind tunnel’s cross-section.

The LDA probe is permanently installed on the outside
surface of the roof of the wind tunnel. When a turbulence-
generating device (grid or flag array) is installed in the wind
tunnel, it is located 1 m to 3.5 m upstream of the sensing
volume of the LDA, depending on the turbulence intensity
desired at the probe’s location.

‘Two L-shaped pitot tubes are permanently mounted in the
wind tunnel. One pitot tube serves as the airspeed sensor in
a feedback loop that controls the power supply that drives
the fan. It is located near the test point, but not so near that
it interferes with the flow around the IUT. A second pitot
tube serves as a check standard for the entire airspeed
calibration system. It also monitors the static air pressure in
the wind tunnel. The static pressure is combined with data
from temperature and the humidity sensors to calculate the
density of the air in the wind tunnel.

The test point (the leading surface of the probe being
calibrated) is usually 12 cm downstream from LDA. This
ensures the blockage of the flow by the IUT has only a small
effect on the airspeed at the LDA. We measured the blockage
by moving the probe downstream, as suggested by the
dashed outline of a probe in FIG. 22

FIG. 23 shows the two coordinat ms used during
calibrations. One coordinate system is attached to the wind
tunnel. Its origin is the test point which is usually located 12
cm downstream from the sensing volume of the LDA. This
coordinate system is right-handed. Its X-axis is parallel to
the wind; its Z-axis points up; and the Y-axis points to the
right when looking into the wind.

‘The second coordinate system rotates with the probe as its
orientation with respect to the wind velocity changes during
calibrations. Its origin is the symmetry point on the probe’s
head facing into the wind. Its orientation with respect to the
wind velocity is specified by the pitch and yaw angles, as
defined in FIG. 23. The pitch angle a is in the XY plane. The
angle o. increases from zero as the probe’s support tube is
rotated from the Y-axis in the direction of the arrow “A”. The
yaw angle specifies the orientation of the probe’s head in
the plane that pa: through both the Z-axis and the
centerline of the probe’s head. When centerline is in the
pitch plane, B=0; the angle P increases as the support tube
is rotated about its axis in the direction of the arrow “B”.

NIST calibrates probes that have support tube with
lengths ranging from 60 cm to 250 cm. Calibrations are
conducted at user-selected pitch angles -45°sas+45° and
yaw angles -180°s0+180° with an angular resolution of
03°.

As shown in the top panel of FIG. 24, NIST uses two
rotational stages on top of two translational stages to orient



US 11,525,840 B2

3

FIG. 9 shows a configuration of gas valve and differential
pressure transducer for a non-nulling gas velocity measure-
ment apparatus;

FIG. 10 shows a switcher for communication with con-
troller in a non-nulling gas velocity measurement apparatus:

FIG. 11 shows side view in panel A and a plan view in
panel B of non-nulling pitot probe disposed on an emission
stack in communication with an emission source;

FIG. 12 shows steps in a process for performing non-
nulling measurement of gas velocity parameters;

FIG. 13 shows steps in a process for performing non-
nulling measurement of gas velocity parameters;

FIG. 14 shows steps in a process for performing non-
nulling measurement of gas velocity parameters:

FIG. 15 shows a spherical probe in panel A and test
configuration in panel B;

FIG. 16 shows a calibration setup:

FIG. 17 shows RATA velocities determined by Method 2F
and by the Non-Nulling Method for 6 repeated runs at low

flow and 4 repeated runs at high flow according to Example 2

1;

FIG. 18 shows graphs of flow parameters versus distance;

FIG. 19 shows a graph of pitch angle versus collection
time;

FIG. 20 shows a multi-hole differential-pressure probe,
wherein during the probe's calibration, it was attached to a
1 mong, 25.4 mm O.D. steel support tube. The support tube
enclosed narrower, pressure-transmitting tubes that con-
nected the ports in the probe's head with differential-
pressure gauges located several meters away;

FIG. 21 shows a top view of recirculating wind tunnel,
with the low speed test section in place; and a side view of
settling chamber and high-speed test section;

FIG. 22 shows a configuration of a wind tunnel test
section, as viewed from above, during the calibration of a
multi-hole, differential-pressure probe in accordance with
Example 2;

FIG. 23 shows the wind tunnel coordinate system. The
origin of the coordinate system is the “test point” which is
usually set ~12 cm downstream from the LDA’s sensing
volume. BOTTOM: Coordinate system for orienting a
multi-hole pressure probe. The pitch angle a is in the XY
plane. The angle @ increases from zero as the probe’s
support tube is rotated from the Y-axis in the direction of the
arrow “A”. The yaw angle B specifies the orientation of the
center-line of probe’s head in the plane that includes both the
Z-axis and the center-line. When the center-line is in the
pitch plane, B=0; B increases as the support tube is rotated
about its axis in the direction of the arrow “B”. The axes X'
and Y" are attached to the probe being calibrated;

FIG. 24 shows: (TOP) Schematic diagram of two trans-
lation stages and two rotation stages that orient probe-
support tube at designated angles without moving the test
point. MIDDLE: The rotation and translation stages are

mounted on the outside of the wind tunnel’s wall. BOT- s

TOM: Probe support tube is mounted on the stages and
passes through a horizontal slot in the wind tunnel’s wall.
The brush covering the slot reduces unwanted air flow from
the laboratory into wind tunnel;

FIG. 25 shows: (TOP) coordinate systems for the wind
tunnel and a probe during a calibration with turbulence. The
probe’s support tube is clamped to a carbon fiber pipe that
leads to the translation/rotation stages outside the wind
tunnel. The test point does not move when the angles a and
B are changed by rotating the carbon fiber pipe about the Y'
or Z axes. BOTTOM: Experimental probe connected to a
carbon fiber pipe by a diagonal transition tube. By design,

3

&

&

4

the diagonal transition tube ensures that the test point does
not translate when the carbon fiber pipe is rotated about its
axis during a calibration;

FIG. 26 shows a graph of normalized disk speed versus
time for LDA using the spinning disk standard. The k=2,
‘Type A, uncertainty of each calibration is indicated by a
vertical bar. The solid horizontal line at 1.0051 is the
unweighted average of the four calibrations plotted. The
dashed lines bracket the k=2 uncertainty 0.41%;

FIG. 27 shows: (LEFT) removable turbulence-generating
wooden grid installed in NIST’s wind tunnel. The wooden
cylinders have diameters of 2.54 cm and are spaced 12.7 em
between centers. RIGHT: Removable turbulence-generating
“flag” array in the wind tunnel. The flags were sewn onto
ropes that are tied to a frame 1.25 m wide and 0.95 m high,
An L-shaped pitot tube and the green light from the LDA are
visible downstream from the flags;

FIG. 28 shows a graph of flow velocity as a function of
the Y coordinate at fixed distances downstream from the
turbulence-generating grid. The black circles indicate the Y
coordinates of the grid’s vertical cylinders. The average
airspeed was 9.6 m/s. However, negative (upstream) air-
speeds were measured near the vertical cylinders on the 13
cm traverse, as suggested by the arrows on the upper panel;

FIG. 29 shows graphs of turbulence intensity Tu vs
distance X downstream from the grid at airspeed 10 m/s.
Data span cross-stream distances: -17sY/cms7. The dashed
horizontal lines at (1.004+0.046) Tu indicate the standard
deviations of the data from the formula Tu=4.55(X/em)-°32
in the range: 66<X/cms176. The upper horizontal Tu scale
indicates that the values of X corresponding to
0.06sTus0.14;

FIG. 30 shows turbulence intensities Tu measured with 4
instruments. The intensity ratios TUyjn-jote/TUzp4 and
TUporwie!TUzp4 are near 1.0, independent of airspeed and
turbulence fraction. The ratios Tuy, pijo/TUzp4 range from
0.19 to 0.37 (dashed lines), depending on airspeed;

FIG. 31 shows: (Top) measured airspeed as a function of
two probes’ distances downstream from the LDA. Bottom:
Subset of data from top as a function of inverse distance. The
dotted curve and solid line show extrapolations to infinite
distance. The vertical dashed lines at 12 cm indicate the
position of a typical probe during a calibration;

FIG. 32 shows turbulence dependence of blockage by an
EPA-accepted multi-hole probe measured at 10 m/s. The
uncertainty bars represent the standard deviation of the mean
of 5 independent measurements. The dashed line represents
the uncertainty-weighted mean of the plotted points. The
data are consistent with the blockage being independent of
the turbulence intensity;

FIG, 33 shows: (Top) 5-hole spherical probe with labels
‘on pressure-sensing ports. Bottom: Pressure difference
between ports P, and P as a function of pitch and yaw
angles. Data were taken at intervals of 2° at 5 m/s;

FIG. 34 shows pitch dependence of the calibration factor
of a vane anemometer at an air speed near 10 m/s;

FIG. 35 shows a calibration factor of a thermal anemom-
eter at an air speed near 10 m/s;

FIG. 36 shows panels A, B, and C for the 3 EPA-
sanctioned RATA probes including A) the S-probe, B) Prism
probe, and C) Spherical Probe. The hemispherical and
conical probes shown in D) and B), respectively are custom-
made probes designed for non-nulling.

FIG. 37 shows normalized flow velocity (Vard/Vcxnes)
for Method 2F (M2F) and for the non-nulling method at zero
yaw angle (NN, f=0) at a high load of 16 mvs and a low load
of 7 ms.



U.S. Patent Dec. 13, 2022 Sheet 22 of 48 US 11,525,840 B2

ipitot tube: check standard) | pitot tube: |

i ard static pressure | flow control!

C

x

aaa ie

x

TM &
cd

ve

o

=

a 3
g Hi 3
LDA sensing | S
volume | oe

FIG. 22


U.S. Patent Dec. 13, 2022 Sheet 40 of 48 US 11,525,840 B2

FIG. 40


US 11,525,840 B2

45

cannot occur, and that the description includes instances
where the event occurs and instances where it does not. As
used herein, combination is inclusive of blends, mixtures,
alloys, reaction products, collection of elements, and the
like.

As used herein, a combination thereof refers to a combi-
nation comprising at least one of the named constituents,
components, compounds, or elements, optionally together
with one or more of the same class of constituents, compo-
nents, compounds, or elements.

All references are incorporated herein by reference.

The use of the terms “a,” “an,” and “the” and similar
referents in the context of describing the invention (espe-
cially in the context of the following claims) are to be
construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by con-
text. It can further be noted that the terms first, second,
primary, secondary, and the like herein do not denote any

order, quantity, or importance, but rather are used to distin- 2

guish one element from another. It will also be understood
that, although the terms first, second, etc. are, in some
instances, used herein to describe various elements, these
elements should not be limited by these terms. For example,
a first current could be termed a second current, and,
similarly, a second current could be termed a first current,
without departing from the scope of the various described
embodiments. The first current and the second current are

both currents, but they are not the same condition unless
3

explicitly stated as such.

The modifier about used in connection with a quantity is
inclusive of the stated value and has the meaning dictated by
the context (e.g., it includes the degree of error associated
with measurement of the particular quantity). The conjune-
tion or is used to link objects of a list or alternatives and is
not disjunctive; rather the elements can be used separately or
can be combined together under appropriate circumstances.

What is claimed is:

1. A non-nulling gas velocity measurement apparatus for
performing non-nulling measurement of gas velocity param-
eters, the non-nulling gas velocity measurement apparatus
comprising:

a non-nulling pitot probe comprising:

an aerodynamic flow head comprising a plurality of
entrant apertures that comprises a central entrant
aperture and a plurality of peripheral entrant aperture
arranged radially from the central entrant aperture,

such that the entrant apertures receive a gas flow 5

from a gas source;

an entrant body tube disposed on the aerodynamic flow
head;

an extensor body tube disposed on the entrant body

tube such that the entrant body tube is interposed 5

between the aerodynamic flow head and the extensor
body tube, such that extensor body tube is arranged
at an oblique angle to the entrant body tube; and
plurality of pressure channels disposed in the aero-
dynamic flow head, the entrant body tube, and the
extensor body tube, such that each entrant aperture is
separately and independently in fluid communication
with one of the pressure channels, and each pressure
channel independently receives and communicates
the gas flow as stagnant gas from the entrant aperture
of which the pressure channel is in communication;
and

.

10

4

4

46
a plurality of gas valves such that each gas valve:

is in fluid communication with a different entrant
aperture of the non-nulling pitot probe via a different
pressure channel;

receives stagnant gas from the respective entrant aper-
ture;

receives a reference ga

receives a valve control signal; and
produces a valve-selected gas based on the valve con-
trol signal, the valve-selected gas consisting essen-
tially of the reference gas or the stagnant gas: and
plurality of differential pressure transducers, such that
each differential pressure transducer:

is separately and independently in fluid communication
with a different gas valve, and that gas valve com-
municates the valve-selected gas to the differential
pressure transducer;

receives the valve-selected gas from the gas valve:
receives the reference gas at a reference gas pressure:

compares a pressure of valve-selected gas to the refer-
ence gas pressure; and

produces a differential pressure signal from comparison

of the pressure of the valve-selected gas to the
reference gas pressure.

2. The non-nulling gas velocity measurement apparatus of
claim 1, further comprising a plurality of sample gas lines,
such that each sample gas line separately interconnects one
pressure channel with one of the gas valves for communi-
cating the gas flow received by the respective entrant
aperture to the respective gas valve as the stagnant gas.

3. The non-nulling gas velocity measurement apparatus of
claim 1, further comprising a plurality of valve outlet gas
lines, such that each valve outlet gas line separately inter-
connects one gas valve with one of the differential pressure
transducers for communicating the valve-selected gas from
the gas valve to the respective differential pressure trans-
ducer.

5

4. The non-nulling gas velocity measurement apparatus of
claim 1, further comprising a reference gas line in commu-
nication with each gas valve and that communicates the
reference gas to the gas valves.

5. The non-nulling gas velocity measurement apparatus of
claim 1, further comprising a reference gas line in commu-
nication with each differential pressure transducer and that
communicates the reference gas to the differential pressure
transducers.

6. The non-nulling gas velocity measurement apparatus of
claim 1, further comprising a reference pressure source that
provides the reference gas to each gas valve.

7. The non-nulling gas velocity measurement apparatus of
claim 1, further comprising a reference pressure source that
provides the reference gas to each differential pressure
transducer.

8. The non-nulling gas velocity measurement apparatus of
claim 1, further comprising an analyzer in communication
with each differential pressure transducer and that:

receives each differential pressure signal from each dif-

ferential pressure transducer; and

produces a gas velocity parameters from the differential

pressure signal.


U.S. Patent Dee. 13, 2022 Sheet 3 of 48 US 11,525,840 B2

(B) 201 [204

x
202.0, 238
{ Dp <—
Zz 20
202.230

wer

202,

i; | 239
205,
240 i
i 205,
203-~ | 241
AL i”
205,
241
pep pape pe pm em
¥ v
A A
FIG. 3



US 11,525,840 B2

49

an entrant body tube disposed on the aerodynamic flow
head;
an extensor body tube disposed on the entrant body
tube such that the entrant body tube is interposed
between the aerodynamic flow head and the extensor
body tube, such that extensor body tube is arranged
at an oblique angle to the entrant body tube; and
plurality of pressure channels disposed in the aero-
dynamic flow head, the entrant body tube, and the
extensor body tube, such that each entrant aperture is
separately and independently in fluid communication
with one of the pressure channels, and each pressure
channel independently receives and communicates
the gas flow as stagnant gas from the entrant aperture
of which the pressure channel is in communication;
receiving, by the entrant apertures, the gas flow:
producing, by the central entrant aperture, a zeroth stag-
nant gas from the gas flow;

s

producing, by the first peripheral entrant aperture, a first

stagnant gas from the gas flow;
producing, by the second peripheral entrant aperture, a
second stagnant gas from the gas flow; and
producing, by the third peripheral entrant aperture, a third
stagnant gas from the gas flow; and

obtaining the zeroth differential pressure signal, the first 25

differential pressure signal, the second differential pres-
sure signal, and the third differential pressure signal
respectively from the zeroth stagnant gas, the first
stagnant gas, the second stagnant gas, and the third
stagnant gas.
19. The process for performing non-nulling measurement
of gas velocity parameters of claim 18, further comprising
determining a non-axial orientation factor for a non-axial
angle with respect to the stack axis at which non-nulling
pitot probe is disposed in the emission stack.
20. The process for performing non-nulling measurement
of gas velocity parameters of claim 18, further comprising

50

correcting the real dynamic pressure with the non-axial
orientation factor prior to determining the velocity of the gas
flow.

21. A non-nulling pitot probe comprising:

an aerodynamic flow head comprising a plurality of

entrant apertures that comprises a central entrant aper-
ture and a plurality of peripheral entrant aperture
arranged radially from the central entrant aperture, such
that the entrant apertures receive a gas flow from a gas
source;

an entrant body tube disposed on the aerodynamic flow

head;

an extensor body tube disposed on the entrant body tube

such that the entrant body tube is interposed between
the aerodynamic flow head and the extensor body tube,
such that extensor body tube is arranged at an oblique
angle to the entrant body tube; and

a plurality of pressure channels disposed in the aerody-

namic flow head, the entrant body tube, and the exten-
sor body tube, such that each entrant aperture is sepa-
rately and independently in fluid communication with
one of the pressure channels, and each pressure channel
independently receives and communicates the gas flow
as stagnant gas from the entrant aperture of which the
pressure channel is in communication.

22. The non-nulling pitot probe of claim 21, wherein the
aerodynamic flow head comprises a hemispherical surface
over which gas flow flows to be received by the entrant
aperture that are arranged in the hemispherical surface.

23. The non-nulling pitot probe of claim 21, wherein the
aerodynamic flow head comprises a conical surface over
which gas flow flows to be received by the entrant aperture

that are arranged in the conical surface.

24. The non-nulling pitot probe of claim 21, wherein a

diameter of the entrant apertures is from 1 millimeter to 50
centimeters.


U.S. Patent Dec. 13, 2022 Sheet 33 of 48 US 11,525,840 B2

FIG. 33


U.S. Patent Dec. 13, 2022 Sheet 19 of 48 US 11,525,840 B2

307 z

20; &oe
aus 3 SN
2 vg 3 #@. #
‘= oP t oe e e*
ef -10] e a

20: Ls *e

¥
«30+ 3 7. T 4

0 2 4 6 8 10
Collection Time, [s]

FIG. 19


US 11,525,840 B2

Sheet 25 of 48

Dec. 13, 2022

U.S. Patent

|
Pe ae
Se ee

/
 .

_

—
_
| _

oF

tion stages |

carbon fiber pipe to

ransiat

fonirota’

t

wd

ng

us

pitch pls pe.

transnt

a

probe support tube 5
S flexible pressure

i
ie

FIG. 25


U.S. Patent Dee. 13, 2022 Sheet 21 of 48 US 11,525,840 B2

FIG. 21


U.S. Patent Dec. 13, 2022 Sheet 34 of 48 US 11,525,840 B2

= ®
4.01 . e* e
® @ e
@ 1.00 + °
2 e
~ 0.99
2
~ 0.98 /*
98 sa
new
0.97 Ll j j | j | l
10 ze) i) § 10 18 20

pitchangle [degrees]

FIG. 34


U.S. Patent Dec. 13, 2022 Sheet 16 of 48 US 11,525,840 B2

FIG. 16


US 11,525,840 B2

23

the high-pressure side of each differential pressure trans-
ducer to ports I through 5 on the spherical probe (FIG. 15A).
The low-pressure side of each transducer was open to the
ambient pressure herein denoted P,,. In this way, we mea-
sured the flue gas pressure at all 5 ports on the spherical
probe head, minus the ambient reference pressure, Pg
located in the case. The required differential pressures for
the non-nulling algorithm (P,>, P13, Py4: Ps) and for
Method 2F (P33, P12, P4s) were calculated by subtracting the
appropriate pressure measurements. For example, the yaw
pressure was determined by subtracting the pressure mea-
sured at port 2 from the pressure at port 3: P3,=(P,-P,.,)—
(P3-Prep)-

Method 2F determines the average axial velocity and
pitch angle from pressure averages. Specifically, we calcu-
lated Py> 4g and P4s,qyg5 Which are arithmetic averages of
P,, and P,; sampled at 10 Hz for 10 sec. In contr:
implementation of the Non-Nulling Method determines the
average axial velocity V
sured values of P,,, P,;. P,4, and P,, are updated, In
particular, the differential pressures are used in conjunction
with the Non-Nulling curve fits to calculate the dynamic
pressure (P,,,,). yaw-null angle (B,,,,:). and pitch angle («.),

which in turn are used in Eg (2) to determine Vy, At the 2

end of the 10 sec collection interval, we calculate the
arithmetic average of the 100 values of Vyw,, By logging
the time history during the 10 sec collection we were able to
ify transient behavior in @, B,,,. and Vyyx,,, that could
not be observed using Method 2F. See FIG. 19 below.
Although we purged the 5 pressure lines connected to the
spherical probe every 60 sec, we still had problems with
plugging, especially at the low flow condition (7 m/s).
During normal data acquisition, the pressure signals are
noisy with fluctuations of the same magnitude as the signal
average; when a port is plugged, fluctuations are reduced.
We measured the noise of the pressure signals at each of the
5 pressure ports to identify data affected by plugging.
FIG. 17 lists average flow results for the low (7 m/s) and
high (16 m/s) flow RATAs. For both the low and high flow
RATAs the run-averages were in excellent mutual agree-
ment: -0.3% and 0.1%, respectively. The non-nulling mea-
surements have less scatter than the Method 2F measure-
ments as evidenced by the smaller standard deviations. The
standard deviation of the Non-Nulling velocities was one-
third of the standard deviation of the Method 2F velocities
at low load, and the ratio reduced to one-ninth at high load
The larger scatter in the Method 2F data is attributed to the
different null pressures P,, for each of the measurements.

Despite using an automated traverse system, transients in the

velocity field (see FIG. 19) made it infeasible to perfectly
null the probe, and as a result P,, was close to zero but not
identically zero for each run. Nevertheless, the excellent
agreement between Vyy2,-and V yy is solid evidence that the

Non-Nulling Method is at least as accurate as EPA’s Method

2F. Moreover, the data for the Non-Nulling Method was
acquired in only 4” of the time needed for Method 2F and
has a consistently lower relative variation. Because this is
the first field test using the Non-Nulling Method, we expect
its speed advantage over Method 2F can be improved. The
Non-Nulling Method only requires 10 sec at each traverse
point while Method 2F times required from 15 sec to 300 sec
(i.e., 10 sec for data collection and the balance of time to find
the null position). The shorter Non-Nulling times limit the
opportunity for the pressure ports to plug. Consequently, we
should not need to purge as frequently when performing the
Non-Nulling Method. Moreover, the purging process can be

,, every 0.1 sec when the mea- 2

&

&

24

performed while the probe is moving from one traverse
point to the next to save additional time.

FIG. 18A through FIG. 183C shows graphs to compare
the high-flow RATA results for Method 2F (®) and the
Non-Nulling Method (4). Specifically, we compare the
following parameters: 1) the axial velocity V.,.,,2,, in FIG.
18A; 2) the yaw-null angle f,,,,; in FIG. 18B, and 3) the pitch
angle a in FIG. 18C. These parameters are plotted against
the normalized distance y/D where D is the diameter of the
stack, and y is the distance along a chord measured from the
stack’s wall, as shown in FIG. 15B. Similar results (not
shown herein) are found when these parameters are plotted
versus x/D.

In FIG. 18A, the open circles (O) connected by dashed
lines are Method 2F data from each of the 4 high flow runs.
The spacings between the dashed lines indicate the profile
variations we measured for the 4 Method 2F runs over a
duration of 3600 sec. Despite these variations, the flow
velocity of each Method 2F run is stable as shown in FIG.
17. The standard deviation was 1.8% of the average flow
velocity. The solid circles (#) and solid triangles (4) in
FIG. 18A are the averages of the Method 2F runs and the
non-nulling runs, respectively. The solid lines connecting
the averaged points are close to each other. This displays the
good agreement of the Method 2F velocity profile with the
non-nulling velocity profile. FIG. 17 shows that the differ-
ence in the averaged flow velocity is only 0.1%. The
variations of the flow field near y/D=0.8 in FIG. 18A might
be due to vortices from the elbow 3.8 D upstream of the
measurement platform. We are confident that they are not
artefacts of the measurements (e.g., caused by plugging)
because the average flow velocity for each run is stable.

FIG. 18B shows that the yaw-null angles determined by
Method 2F (@) and by the Non-Nulling Method (@ ) are in
good agreement. Both methods show the yaw-null angles
are most negative near the wall with a value of nearly -30°.
The yaw-null angle is less negative as one moves away from
the wall toward the center of the stack. The differences
between Method 2F and the Non-Nulling Method are small-
est near the center of the stack and increase to maximum of
only 7° in the worst

FIG. 18C show profiles of the pitch angles determined by
Method 2F (@) and by the Non-Nulling Method (@). We
found the same characteristic profiles independent of flow
load and method. Although we hoped to assess the Non-
Nulling Method in a stack with high pitch, the largest pitch
angle was only about 6°. This maximum pitch angle
occurred on the x-axis chord (not shown).

FIG. 19 plots the yaw-null angle during a typical 10 sec
collection time with the probe oriented at B=f,,,,;. Because
the probe was nulled, the Non-Nulling algorithm measures
Braz the yaw-null angle relative to the rotated probe ori-
ented at B. In a steady flow with low turbulence we expect
B,.z0° throughout the 10 sec collection. We observed
(FIG, 19) the sine-like oscillations with an amplitude of
nearly 30° and period of approximately 4.5 sec. Surpris-
ingly, the integrated average of B,,,, is -1.5°, which is close
to zero. This data demonstrated that the yaw-null angle was
not stationary. That is, the location of the yaw-null angle
changes during the 10 sec collection. As such, the yaw-null
angle determined by Method 2F is not unique; one can find
a range of yaw angles that satisfy P,,-0 depending on the
measurement time.

There is time dependence of ,,,. shown in FIG. 19. If
similar oscillations appear in future RATAs, we could obtain
more-accurate average values of f,,,, either by averaging
over more cycles (thereby increasing the measurement time)



U.S. Patent Dec. 13, 2022 Sheet 8 of 48 US 11,525,840 B2

(A) 209 — Reference flow configuration

211 208
222
227
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I~ 219
212—~_J oo
W220
(B) 209 Sample fi
21i— 208
227
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222 224
219
212
220

FIG. 8


U.S. Patent Dec. 13, 2022 Sheet 31 of 48 US 11,525,840 B2
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US 11,525,840 B2

37

Using NIST’s wind tunnel and NIST’s smokestack simu-
lator, we developed non-nulling algorithms for the spherical
probe in FIG. 36C and for the two custom probes shown in
FIG. 36D and FIG. 36E. At NIST, we calibrated these probes
using our non-nulling method and also EPA’s Method 2F,
and then we used these probes to measure the flow velocity
in a CFPP stack.

For assessing the accuracy and limitations of the non-
nulling method, we selected a CFPP stack known to have
complex flows. The selected stack’s RATA measurement
platform was only 3.8 stack diameters (D=6.8 m) down-
stream of a 90° elbow. Moreover, upstream of the elbow,
flow from two wet scrubbers merged into a single stream.
Not surprisingly, the flow at the RATA platform had signifi-
cant yaw-null angles that were nearly -30° at the stack wall.
The flue gas was saturated with water from the wet scrub-
bers. The wet, particle-laden gas frequently plugged the 3-D
probes; plugging increased the duration of the tests and
resulted in false high (or low) axial velocity measurements

both for Method 2F and the non-nulling method. We devel- 2

oped a statistical method based on the noisiness of the
measured pressure signals to identify data affected by plug-
ging.

The CFPP stack was equipped with an X-pattern ultra-
sonic flow meter system, which was used as the CEMS flow
monitor. The CFPP provided us with minute by minute
CEMS flow velocity data (Vexs,s) for the duration of the
On average, the stability of Vezyzs during the flow
RATAs was better than 1.5%. We performed a 16-point flow
RATA using both Method 2F and the non-nulling method.
The flow RATAs were performed at two loads, a high load
with a flue gas velocity of 16 nV/s, and at a low load of 7 m/s

The non-nulling method and Method 2F showed agree-
ment for the spherical probes. As indicated in the last
column, the difference at high load was -0.1% and at low
load the difference was 0%. The flow results from the
non-nulling method were consistent throughout the test. The
percent difference of Vyx/Verys determined with the
spherical probes and the custom probes was only -0.4% at
high load and -2.3% at low load. Vax/Veryys i8 close to
unity in all cases, This agreement between Vy and Vexxgs
is better than expected. The values of Vegas are based on an
earlier S-probe RATA calibration that used the conventional
nulling method. Our values of Vy are based on a 16-point
traverse that did not account for the lower velocities near the
wall. If we had accounted the lower velocities, we would
have found Vyy<Vexrgs We measured pitch angles less
than 5°, so that S-probe errors related to pitch angle are
negligible in this stack. The results of Method 2F and the

non-nulling method showed poor agreement for the custom

probes: the differences are 5.9% at high load and 10% at low
load. These results are erroneous for the following reasons:
a) the non-nulling results were consistent for all tests and
agreed with the results obtained with the EPA-sanctioned

spherical probe, b) in cases where RATAs based on Method 5

2F disagree with the S-probe nulling method, the Method 2F
results are typically lower due to inherent positive biases in
the S-probe.

We calibrated all 3 probe types in NIST’s wind tunnel
using both Method 2F and the non-nulling method. Calibra-
tions were performed in the wind tunnel’s rectangular test
section (1.5 mxl1.2 m) using NIST’s Laser Doppler
Anemometer (LDA) working standard. The metrological
traceability of the LDA working standard is documented. We
use the LDA velocity (U,p,) in conjunction with air density
(Buz) in the wind tunnel to determine the dynamic pressure,
Pj PureUrp/2. The wind tunnel is equipped with an

&

&

5 evaluate at P,.

38

automated traversing system, which positions the pitot
probes to prescribed pitch angles () and yaw angles (B) in
the test section. The expanded uncertainty of wind speed is
less than 1%, and the expanded uncertainties of pitch and
yaw angles are 0.5°.

We calibrated four spherical probes, two hemispherical
probes, and two conical probes. All the probes were cali-
brated at 11 velocities ranging from 5 m/s to 30 m/s in steps
of 2.5 m/s, and at 17 pitch angles ranging from -20° to 20°
in steps of 2.5°. Thus, for each probe we measured 187
combined velocity and pitch angle set points. We used curve
fitting to determine the pitch calibration factor, F,, and the
velocity calibration, F, at the null condition (P,,-0). The
curve fit method does not require rotating the probe to the
exact position where P,,=0; instead the pitch pressure ratio,
P4s/P,>, and the velocity pressure ratio, [P,,,/P,2]°2, are
measured over a narrow range of yaw pressures surrounding
P,,=0. By definition, the pitch pressure ratio and the velocity
pressure ratio equal the respective calibration factors,
F,=P,,/P,, and F,=[P,,,,/P,2]"” at zero yaw pressure, P,~0.
The measured values of the pitch pressure ratio and the
velocity pressure ratio values are fit by either a 2” or 3
degree polynomial function of the yaw pressure, which we
to determine the respective null param-

eters, F, and Fy.

FIG. 38 and FIG. 39 shows plots for the calibration
parameters F, and F, as functions of the pitch angle for a
hemispherical probe (FIG. 36D) and a conical probe (FIG.
36E). The circles are data taken at the 11 different velocities
ranging from 5 m/s to 30 m/s. For both probes, F, is nearly
independent of velocity, but F, exhibits a small, systematic
velocity dependence. The solid lines are curves fitted to the
data. The pitch angle (a) is fitted by a 6” degree polynomial
of independent variable F,, and F, is fit to 6” degree
polynomial of «.

As observed in FIG. 38B and FIG. 39B, the curve fit of
F, appears as an average of the velocity data at each pitch
angle. This approximate method of accounting for the veloc-
ity dependence is consistent with the Method 2F protocol.

For flow RATAs performed using Method 2F, we deter-
mined the axial velocity at each traverse point using the
following procedure. First, we nulled the probe and mea-
sured the yaw-null angle (f,,,,,) with an inclinometer. Next,
we determined the pitch calibration factor, F,=P45/P,>, from
the measured mull pressures P,; and P,>. We use the 6”
degree polynomial determined during calibration, a=a(F,)
(here expressed in generic functional form) to determine a.
Then, the calculated a is used to determine the velocity
calibration factor using the fitted curve F;=F,(a.) developed
during calibration. The differential pressure between ports 1
and 2 on the probe head along with the velocity calibration
factor determine the dynamic pressure, P.,,,/-Fs°P,>.
Finally, the axial velocity at each traverse point is deter-
mined as a function of the 1) dynamic pressure, 2) yaw-null
angle, and 3) pitch angle using

_

w

cos( Bru — Bo}eos(@)

wherein B, accounts for any yaw angle offset (or misalign-
ment) when probes are installed into the automated traverse
system used to perform the flow RATA. We followed EPA
Method 4 to measure the flue gas moisture, and we used EPA
Method 3A to determine the molar mass. The flue gas


US 11,525,840 B2

4

We processed the data after the field tests were completed.
We used the time stamps provided by the MAP system to
identify the non-nulling and Method 2F pressure data. For
the low loads, approximately 20% of the data could not be
found at the indicated time stamps. At the high load less than
5% of the data was unaccounted for.

FIG. 37 summarizes the average flow results. It provides
solid evidence that the non-nulling method has the potential
to make efficient, accurate stack flow measurements. We
compare the profiles of velocity, yaw-null angle, and pitch
angle determined by Method 2F to those determined by the
non-nulling method.

The flow RATAs were performed along 2 orthogonal
axes. We denote the axis extending from port 1 to port 3 in
FIG. 4 as the “x-axis”. The y-axis extended from port 2 to
port 4. Each axis included 8 traverse points. The traverse
points are located at the centroids of equal area, so that flow
velocity of each run is calculated by averaging the axial

velocities measured at 16 traverse points. The axial velocity, 2

yaw-null angle, and pitch angle are plotted on the x/D and
y/D axes, respectively, where D is the diameter of the stack.

Regarding axial velocity profiles, FIG. 42A and FIG. 42B
show that while the load remained constant, the flow profile
had large variations (greater than 10%) at particular loca-
tions. FIG. 42 is a plot of the normalized axial velocity
(Vaeri!V ceass) measured using the spherical probes at high
load as functions of x/D and y/D, respectively. The open
circles (OQ) connected by dashed lines are Method 2F data
from each of the 4 runs. The spacings between the dashed
lines indicate profile variations. Despite these variations, the
flow velocity of each Method 2F run is stable as shown in
FIG. 43. The standard deviation expressed as a percent was
only 2.1%.

We observed similar profile variations (not plotted) in the
4 non-nulling runs even though the standard deviation of the
average velocity was only 0.4%.

The localized variations in the flow field indicated in FIG.
42A and FIG. 42B might be due to vortices. They are not
artifacts of the measurements (e.g., caused by plugging or
filtering the data) because the average flow velocity for each
run is stable.

The solid circles and solid triangles in FIG. 42 are the
averages of the Method 2F runs and the non-nulling runs,
respectively. In FIG. 42A and FIG. 42B, the solid lines
connecting the averaged points are close to each other. This
agrees with Method 2F velocity profiles with the non-nulling
velocity profiles. FIG. 43 shows that the difference in the
averaged flow velocity is only -0.1%. Normalized velocity

profiles measured at both high and low loads were similar to 5

the profiles observed in FIG. 42A and FIG. 42B.

Regarding yaw angle profiles, FIG. 44 shows average
yaw-null profiles for the spherical probe at high load. The
Method 2F data (circles) and non-nulling data (triangles)

yaw-null angles show the same trend and agree in FIG. 44A.

and FIG. 44B. Both methods show the magnitudes of
yaw-null angles are largest near the wall with a value of
nearly 30°. The magnitude yaw-null angle decreases mono-
tonically as one moves away from the wall toward the center
of the stack. The differences between Method 2F and the
non-nulling method are smallest near the center of the stack
and increase to maximum of approximately 7° near the wall
in the worst case.

Yaw-null profiles were nearly identical at low load. The
same trends occurs as shown in FIG. 44A and FIG. 44B
independent of probe type (i.e., spherical or custom) and
method (i.e., non-nulling or Method 2F).

&

&

a2

FIG. 45 shows plots for the yaw-null angle during a
typical 10 s collection time with the probe oriented at
B=B,,,z Because the probe was nulled, the non-nulling
algorithm measures ',,,; defined by Eq. (2). Ina steady flow
with low turbulence f',,,, would have a constant value close
to 0° during the 10 s collection. In contrast, FIG. 45 has
sine-like oscillations with an amplitude of nearly 30° and a
period of approximately 4 s. Surprisingly, the integrated
average of ',,; is -1.5°, which is close to zero. This
time-dependence of f',,,,; is evidence that the flow field in
the CFPP stack had large transients. FIG. 42A and FIG. 42B
are additional evidence for large transients. Better averages
could be obtained by averaging over more cycles (ie.,
longer collection times) or by averaging over the 4 s period

Regarding pitch angle profiles, FIG. 46A and FIG. 46B
show profiles of the pitch angle determined by Method 2F
(indicated by circles) and by the non-nulling algorithm with
Y° (indicated by triangles). These results correspond to
Test #1 specified in FIG. 41. The pitch angles determined by
Method 2F and by the non-nulling algorithm agree with each
other and have similar, asymmetric dependences on x/D and
y/D. We found the same characteristic profiles independent
of flow load, probe type, and method. Although we hoped to
perform the test in a stack with high pitch, the largest pitch

5 angle was only about 5°

Regarding troubleshooting plugging problems, to miti-
gate plugging we purged the probe pressure ports every
60 s. Nevertheless, we still had problems with plugging.
Plugging issues were most severe for spherical probe 2
during Test #4 in Table 2. The 4 traverse points in port 1
seemed to be the most impacted by plugging problems.

One way to detect plugging is to evaluate the consistency
of repeated axial velocity measurements made at the same
traverse point. If significant deviations are found at the same
traverse points from run to run, then plugging could be the
culprit. We used a simple statistical approach to find outliers
in the data caused by plugging.

‘The pressure signals (P,, ,., n=l to 5) for the five pressure
ports on the probe head’ were noisy. That is, pressures
fluctuations during non-nulling and during Method 2F were
usually larger than the mean of the pressure signal. The noise
could decrease if a pressure port on the probe head was
plugged. For each 10 s collection time, we computed the
standard deviation of the pressure signal from each pressure
port on the probe head. If the standard deviation was below
the typical noise level by a statistically defined threshold, we
assumed that the port was plugged.

FIG. 47 shows data obtained for the statistical approach to
detect plugged pressure ports. This example focuses on the
non-nulling measurements made at low load using spherical
probe 2. The 24 set points on the x-axis correspond to the 4
traverse points for port 1 multiplied by the 6 repeated runs
(see Test #4, FIG. 41). The y-axis is the standard deviation
of the pressure signals o,,=a(P,,,...) measured at the n=1 to
5 pressure ports on the probe head. We considered a pressure
port plugged if the standard deviation was below the statis-
tical limit indicated by the dashed line (--). For simplicity
FIG. 9 only shows a single limit; however, in practice we
used separate limits for each of the 5 pressure signals. The
statistical limit for the n” probe was

limit,-(o,,)-ko(@,) )

wherein (o,,) is the average of the 24 values of o,; a(6,,) is
the standard deviation of the 24 values of o,,; and k is the
coverage factor which we set equal to 1.5. The computed
normalized velocities had only a weak sensitivity to the
value of k.


US 11,525,840 B2

43

FIG. 48A compares two normalized velocity profiles, one
affected by plugging, and the other calculated excluding the
subset of data affected by plugging. The figure corresponds
to traverses performed at low load using the spherical
probes. The velocity (Vp4z,) was determined using the
non-nulling algorithm with the probe oriented at zero yaw
angle. Fach open triangle is the average of 6 repeated runs.
The dashed line connecting the triangles shows the normal-
ized axial velocity profile of the 8 traverse points between
port I and port 3 (ie., the x-axis). The first 4 points along
x/D are traversed by the spherical probe 2 installed in port
1, The statistical approach illustrated in FIG. 47 might
indicate that several of these points were affected by plug-
ging. If these points are omitted when calculating the
a ixial velocity at each traverse point, we obtain the
solid triangles. The solid line connecting the solid triangles
shows the normalized velocity profile corrected to account
for plugging.

If the normalized velocity profile (indicated by filled

triangles) in FIG. 48 is correct, one might find the same 2

profile at low load independent probe type (ie., spherical or
custom) and independent of the method (i.e., non-nulling or
Method 2F). Moreover, for these high Reynolds number
flows (3x10° to 6.5x10°) we expect that the high load
normalized velocity profile will have essentially the same
shape as the low load. FIG. 48B shows that all normalized
profiles agree with the corrected profile. The agreement of
these profiles provides evidence that we successfully iden-
tified and removed data affected by plugging, and that the
non-nulling method performed well independent of probe
type and flow load

This example shows results that the non-nulling method
accurately measured complex flows in CFPP stacks. We
conducted 16-point flow RATAs 3.8 stack diameters down-
stream of the 90° elbow at the stack inlet, and we measured.
yaw-null angles approaching -30° near the stack wall. We
found excellent agreement between the non-nulling method
and Method 2F using spherical probes. The results from
FIG. 37 show agreement of -0.1% at a high load of 16 m/s
and 0.0% at a low load of 7 m/s. Similar levels of agreement
occurred between Method 2F and the non-nulling method
when we conducted flow RATAs in NIST Scale-Model
Smokestack Simulator (SM: The non-nulling method
gives the same flow results but is more time and cost
efficient than Method 2F.

The SMSS facility uses air as a surrogate for flue gas and
has a 1.2 m diameter test section. The facility can generate
complex flows that have yaw-null angles of almost 40° at the
wall. The excellent non-nulling flow results found in the

SMSS are analogous to those found in this study of a CFPP 5

stack. Thus, the SMSS facility is a satisfactory research
facility for characterizing probes used for flow RATAs,
ultrasonic CEMS, and other flow monitors for use in CFPP
stacks,

We developed hemispherical and conical non-nulling s

pitot probes and compared their performance in a CFPP
stack with the EPA-sanctioned spherical probe using the
non-nulling method. The non-nulling flow velocities at high
and low loads were consistent for all probe types. After
normalizing the measured axial velocities by the CEMS
velocity, we found essentially the same characteristic pro-
files at low and high loads across both orthogonal chords.
The normalized Method 2F axial velocities also exhibited
the same profiles across the chords.

‘The non-nulling method measured consistent pitch and
yaw-null angles using all the probe types at both high and
low loads. Therefore, in future flow RATA testing, a hybrid

44

non-nulling method can be implemented. That is, if while
performing a flow RATA using the non-nulling method one
has reason to question the axial velocity measurement, the
RATA tester can rotate the probe to the calculated yaw-null
angle and take a Method 2F measurement

The non-nulling method requires bidirectional, fast
response differential pressure transducers. We used indus-
trial grade differential transducers for our stack measure-
ments, We measured the pressure (minus a common refer-
ence pressure) at each of the 5 ports on the 3-D probe.
Pressure measurements were sampled at 10 Hz. They
revealed periodic pressure fluctuations with periods ranging
between 3 s and 5 s. These transients could not be observed.
or adequately accounted for (e.g., averaging over the peri-
ods) using Method 2F. In contrast, the non-nulling data
processing could easily be modified to perform averages
over the period.

We used an automated traverse system to reduce the
RATA times and to improve the accuracy of nulling the
probes. The benefits of automated traverses are less impor-
tant for the non-nulling method than for nulling methods
because the non-nulling method does not rotate the probe
rotation and eliminates errors from imperfect nulling.

Despite purging every 60 seconds, conventional spherical
probes became plugged most frequently at low load. We did
not experience the same difficulties with the two non-nulling

urate flow measurements, we distinguished fluc-
tuations of the axial velocity from plugging of one or more
pressure ports by detecting the reduction in the pressure
noise that occurs when a pressure port is plugged. Without
plugging, the fluctuations of the pressure signals were ofien
larger than their mean values. For each pressure signal,
during each 10 s data collection period, we used the standard
deviation of the pressure from its mean as a measure of its
noise. We did not process the noise data in real time. After
all the measurements were completed, we used a statistical
criterion to discard data corrupted by plugging. We can
process the noise data as they are acquired during a RATA.
If the noise indicates plugging the probe can be purged and
the data retaken. Thus, the noise measurements can be a
diagnostic to guide the data acquisition and not to discard
data.

This example describes a 3000-point calibration on each
probe used for the non-nulling measurements. Such an
extensive calibration may not be practical for routine flow
RATAs. A baseline non-nulling calibration can be applied to
all probes of the same type such that a calibration can be
done to correct for slight manufacturing differences.

While one or more embodiments have been shown and
described, modifications and substitutions may be made
thereto without departing from the spirit and scope of the
invention. Accordingly, it is to be understood that the present
invention has been described by way of illustrations and not
limitation. Embodiments herein can be used independently
or can be combined.

All ranges disclosed herein are inclusive of the endpoints,
and the endpoints are independently combinable with each
other. The ranges are continuous and thus contain every
value and subset thereof in the range. Unless otherwise
stated or contextually inapplicable, all percentages, when
expressing a quantity, are weight percentages. The suflix (s)
as used herein is intended to include both the singular and
the plural of the term that it modifies, thereby including at
least one of that term (e.g., the colorant(s) includes at least
one colorants). Option, optional, or optionally means that
the subsequently described event or circumstance can or



U.S. Patent

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air speed, mis

20

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3.8

Dec. 13, 2022

Sheet 28 of 48

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US 11,525,840 B2

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transverse distance, cm

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19



U.S. Patent Dec. 13, 2022 Sheet 5 of 48 US 11,525,840 B2

201
— xX
Hemispherical aerodynamic flow head
zZ*
202.4, Y
239 202.1, 239
202.0, 238
202.3,
239

FIG. 5


U.S. Patent Dee. 13, 2022 Sheet 4 of 48 US 11,525,840 B2

(B) 201 205, (C) 201 205, ~~]

207

205,
241

(A) 201 1

y ’
202.0, 238
202.1239 7
Ce 202.3, 239

poe ee eee

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U.S. Patent Dec. 13, 2022 Sheet 17 of 48 US 11,525,840 B2

Run No. Vor Vn % Diff °

Low Load (7 m/s)

I 7.09 | 7.06 0.4

2 7.04 | 7.18 -1.9

3 7.06 | 7.21 21

4 7.10 | 7.17 -1

5 7.03 | 7.21 2.5

6 = 7.50 | 7.14 5.0

Avg") 744 | 7.16 -0.3
% Std Dev” — 2.5 0.8
High Load (16 m/s)

1 16.44 | 16.29 0.9

2 16.48 | 16.24 1.5

3 15.84 | 16.23 24

4 16.37 | 16.27 0.6

Avg") 16.28 | 16.26 0.1
% Std Dev” — 1.8 0.2

a) Avg is the average of the 4 or 6 runs

b) % Std Dev= 100x(Std. Dev. of 4 or 6
runs)/Avg

ce) % Diff = 100(Vvr/ Van -1)

FIG. 17


U.S. Patent

(A) 201
Hemispherical
207

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203 |

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(Cj 201 Four-aperture

202.1,
239

202.0,238

239

({E) 201

Dec. 13, 2022

Sheet 7 of 48

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207

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US 11,525,840 B2

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| ‘ angle
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{D) 201 Five-aperture

202.4,
239,

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202.0, 238 +—
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Nine-aperture 207
202.8, 239 wai
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202.7,
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202.1,
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202.2,
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202.1, 239
202.2, 239

292.3, 239

202.4, 239


U.S. Patent

‘wind direction |

Dec. 13, 2022

Sheet 23 of 48 US 11,525,840 B2

test point

descents

LDA sensing |

volume |

¥

_tubes to differential
L pressure gauges |

FIG. 23


a2) United States Patent

Shinder et al.

US011525840B2

US 11,525,840 B2
Dec. 13, 2022

(10) Patent No.:
(45) Date of Patent:

G4)

ay

(72)

(73)

()

(21)
(22)

(65)

(60)

(51)

NON-NULLING GAS VELOCITY
MEASUREMENT APPARATUS AND
PERFORMING NON-NULLING
MEASUREMENT OF GAS VELOCITY

PARAMETERS

Applicant:

Inventors:

Assignee:

Notice:

Appl. No.:

Filed:

US 2021/0325421 Al

Government of the United States of
America, as represented by the
Secretary of Commerce, Gaithersburg,
MD (US)

losif Isaakovich Shinder, Gaithersburg,
MD (US); Aaron Nathaniel Johnson,
Gaithersburg, MD (US); Bernard
James Filla, Nederland, CO (US)

GOVERNMENT OF THE UNITED
STATES OF AMERICA, AS
REPRESENTED BY THE
SECRETARY OF COMMERCE,
Gaithersburg, MD (US)

Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 56 days.

17/231,468

Apr. 15, 2021

Prior Publication Data
Oct. 21, 2021

Related U.S. Application Data
Provisional application No. 63/011,004, filed on Apr.

16, 2020.

Int. Cl.

GOIP 5/16 (2006.01)

GOIP 5/165 (2006.01)
(Continued)

(52) US. Cl.
cpc

GOIP 5/16 (2013.01); GOIF 1/34
GOLF 1/46 (2013.01); GOP 5/165
(2013.01)

(2013.01);

m Search

(58) Field of Classific:
USPC. esonee soseesnesaneeennees 702/50
See application file for complete search history.

(56) References Cited
U.S. PATENT DOCUMENTS.
3,318,146 A 5/1967 De Leo et al.

5,423,209 A 6/1995. Nakaya et al.

(Continued)
OTHER PUBLICATIONS
US. EPA, “Preliminary Test Method 007 for the Determination of
Cyclonic Flow Velocity Components Using a Calculation Approach

to Method 2F”, doi: https://www3.epa.govittneme0 l/prelim/pre-
007 pat.

Primary Examiner — Paul D Lee
(74) Attorney, Agent, or Firm — Office of Chief Counsel
for National Institute of Standards and Technology

(57) ABSTRACT

A non-nulling gas velocity measurement apparatus performs
a non-nulling measurement of gas velocity parameters and
includes: a non-nulling pitot probe; gas valves in fluid
communication with a different entrant aperture of the
non-nulling pitot probe via a different pressure channel;
receives stagnant gas from the respective entrant aperture;
receives a reference gas; receives a valve control signal; and
produces a valve-selected gas based on the valve control
signal, the valve-selected gas consisting essentially of the
reference gas or the stagnant gas; and a plurality of differ-
ential pressure transducers, such that each differential pres-
sure transducer: is separately and independently in fluid
communication with a different gas valve, and that gas valve
communicates the valve-selected gas to the differential
pressure transducer; receives the valve-selected gas from the
gas valve; and produces a differential pressure signal from
(Continued)



U.S. Patent Dec. 13, 2022 Sheet 46 of 48 US 11,525,840 B2

@ M2F & NN@Oyaw

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21

Nulling Method. Although errors in the cross-sectional area
impact the calculated volumetric flow and its uncertainty
budget, the cross-section area was the same for both meth-
ods so that the comparison is not sensitive to it.

The axial velocity at each point was determined using a
modified version of the Bernoulli equation

Q
c0s(Bruit ~ Bo)eos(a).

Here, P,,,, is the dynamic pressure (equal to the flue gas’s
kinetic energy per unit volume); ct is the pitch angle, which
is non-zero when the flue gas has a component of velocity
along the spherical probe’s ports 4 and 5 (FIG. 15A); Bua
is the yaw-null angle, which is non-zero when the flue gas
has a component of velocity directed along ports 2 and 3; p
is the mass density of flue gas; and By is a parameter that was
determined during each probe's calibration to account for
any yaw angle misalignment (or offset). A misalignment
occurs when the yaw angle corresponding to P,,=0 diflers
from the zero-yaw angle marking (or scribe line) on the
probe.

‘To implement Method 2F, we developed probe calibration
curves that determine P,,,, and c as a function of other
differential pressure measurements after f,,,,,; has been deter-
mined by the nulling procedure. In contrast, for the Non-
Nulling Method we develop calibration curves for Pins
Bye and ct in the wind tunnel that can be applied without
nulling the probe. For both the Non-Nulling Method and
Method 2F, the same procedures were used to determine p
and B, in eq 2. The values of B, for each probe are
determined during calibration and remain fixed throughout
the flow RATA.

With regard to probe calibrations for non-nulling and
Method 2F, we calibrated each of the 4 spherical probes in
the wind tunnel in accordance with Method 2F and the
Non-Nulling Method. Probes were installed in the wind
tunnel’s rectangular cross-section (1.5 m wide by 1.2 m
high) and calibrated one at a time against NIST’s Laser
Doppler Anemometer (LDA) working standard

The top-view of the calibration setup is shown in FIG. 16.
‘An automated traverse system (not shown in the figure)
moves the probe to specified values of pitch (a) and yaw
angles (f). The distance in the x-direction between pressure
port 1 on the spherical probe and the LDA sensing volume
is maintained fixed for all probe orientations. The uncer-
tainty of wind speed is 0.4%, and the uncertainties of pitch
and yaw angles are 0.5°.

With regard to Method 2F probe calibrations, the spheri-
cal probes were calibrated at 3 velocities 9 m/s, 18 m/s, and
27 m/s, and at 21 pitch angles ranging from -12° to 12° in
steps of 2°. Thus, for each of the 4 spherical probes we

measured 39 combined velocity and pitch angle set points.

At each set point we used the Curve Fit Method (Shinder et.
al., 2018) to determine the pitch calibration factor, F,=P45/
P,, and the velocity calibration factor, F,=[P,,,//P,2]', at
the null condition (P.,=0). Here, the dynamic pressure is
defined by Puy. PanUzp./2 where Uzp, is the velocity
measured by the LDA and p,,, is the air density in the wind
tunnel. The measured calibration factors were fit to 4”
degree polynomials represented herein by o=a(F,) and
",=F,(a). The standard deviations of the respective fit
duals were 0.3° and 0.37%.

During the flow RATA at the CFPP, we followed the
EPA-approved Method 2F protocol (EPA 2017d) to deter-

re

20

3

4

45

6:

22

mine the axial velocity. First, we nulled each probe to
determine B,,,,;,- With the probes nulled we determined the
pitch calibration factor, F,=P,/P, , from the measured null
pressures P,; and P,,. The calibration curve a=ca(F,) was
used to determine the pitch angle, which we used as an input
to calculate the velocity calibration factor, F,=F,(a). Next,
the measured P,, and F, were used to determine the dynamic
pressure, P,,,.-F,°P,>. Finally, the Method 2F axial velocity
at each traverse point is determined using Pj, By,» and
in eq 2.

‘The non-mulling method correlates Pj. By,» and. with
the differential pressures P,>, P,3, P14, and P,, measured
across the probe ports. We measured more than 3000 data
points spanning the velocity range from 5 m/s to 30 m/s,
pitch angles from -20° to 20°, and yaw angles from -42° to
42°. The calibration curve for each parameter P jy» By,an and
@ is a fifth-degree polynomial of the four independent
variables: P,>, P13. P14, and Ps. The residual standard
deviations of each parameter were comparable for all 4
spherical probes. On average, the residual standard devia-
tions were 1.3%, 0.5°, and 0.75° for Pass Bruce and
respectively. -

With regard to a test protocol for stack flow measure-
ments, the test protocol was performed by a certified RATA

5 tester who used commercially available RATA equipment

called a “Multiple Automated Probe System” (MAPS) to
perform five functions: 1) move all 4 probes simultaneously
to specified points; 2) supply bursts of high pressure gas to
purge water droplets or particulates plugging any of the 5
pressure ports on the spherical probe head at one minute
intervals; 3) implement the Method 2F nulling procedure to
determine f,,,,;; at each traverse point; 4) provide time stamps
at the start and stop of the Non-Nulling and Method 2F
measurement intervals, and 5) determine the flue gas density
(p) using EPA-approved methods 4 and 3A (EPA 2017a,
2017b).

A MAPS unit containing a spherical probe was installed
in each flange on the stack wall. The MAPS units simulta-
neously moved all 4 probes to the specified traverse point
and rotated each probe to a zero yaw angle (8=0°). After a
3 sec stabilization period, the axial velocity Vyy,, was
measured for 10 sec using the Non-Nulling Method with the
probe oriented at B=0°. Next, each MAPS unit nulled its
probe (i.e., rotated probe until P,=0) and recorded By...
After another 3 sec stabilization period, we measured the
axial velocity Viger, for 10 sec via Method 2F. On average.
the Method 2F measurements (including the nulling proce-
dure) took 60 sec at each traverse point. After measuring the
axial velocities Viwy,, and Vaysp,, at all 16 traverse points, we
used eq I to determine respective flow RATA velocities, Vy,
and Vyyo;» for the completed run. We completed a total of 4
runs (Velocity profiles) at the high load (16 m/s) and 6 runs
at the low load (7 mvs).

With regard to a data acquisition system and differential
pressure measurements, to collect non-nulling and Method
2F data, we designed and assembled four custom data
acquisition systems that were connected to a single laptop
computer, Each system included industrial-grade, difleren-
tial pressure transducers, which we sampled at 10 Hz. The
transducers were bidirectional with a full-scale of 1240 Pa
and a specified response time faster than 1 ms. We used
pneumatically actuated valves to isolate the differential
pressure transducers during gas purging to clear probe ports
of contaminants. The transducers and valves for each system.
were housed in a weather-proof case located on the mea-
surement platform just below the MAPS units. We used 5
nylon tubes (13 m long; inner diameter 6.35 mm) to connect



U.S. Patent Dec. 13, 2022 Sheet 42 of 48 US 11,525,840 B2

OM2F runs @M2F & NN@Oyaw

1.3

1.2

1.1

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U.S. Patent

Dec. 13, 2022

Sheet 30 of 48 US 11,525,840 B2

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U.S. Patent Dec. 13, 2022 Sheet 47 of 48 US 11,525,840 B2

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Te

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US 11,525,840 B2

35

vector and can give biased results if the stack flow has
significant yaw and pitch angles. Furthermore, S-probe
measurements are time intensive, requiring probe rotation
(or nulling) at each traverse point to find the yaw angle. The
only EPA-sanctioned alternatives to the S-probe are 5-hole
probes (i.e., the prism probe and spherical probe) that also
require yaw-nulling. We developed a non-nulling technique
applicable to the spherical probe and two custom designed
S-hole probes that reduce testing time and may improve
measurement accuracy. The non-nulling technique measures
all 3 components of velocity without rotating the probe. We
assessed the performance of these 5-hole probes in a coal-
fired stack at the high-load (16 m/s) and the low-load (7
m/s). For the spherical probes, the non-nulling results and
the nulling results were in excellent mutual agreement
(<0.1%). For the custom probes, the non-nulling and nulling
results were inconsistent: the differences were 5% at the high
load and 10% at the low load. The non-nulling technique can
accurately measure flue gas flows in a coal-fired stack.

Combustion gases from coal-fired power plants (CEPPs) 2

are exhausted into large diameter (>5 m), vertically oriented
smokestacks, which emit pollutants into the atmosphere. To
quantify the amount of pollutants released into the atmo-
sphere, the total flow in these stacks must be accurately
measured; however, accurate stack flow measurements are
difficult. Stacks are fed by a network of elbows, reducers,
fans, etc. which generate complex, difficult-to-measure
flows. The flue gas itself causes additional difliculties
because it can be hot (as high as 120° C.), acidic, asphyxi-
ating, and in some cases saturated with water vapor. Nev-
ertheless, accurate measurements of the total flue gas flow
are essential to monitor emissions of greenhouse gases
(GHGs) and other hazardous pollutants.

Pollutant emissions from CFPPs are quantified by con-
tinuous emission monitoring systems (CEMS) permanently
installed in the stacks. The CEMS equipment measures the
concentration of each regulated pollutant as well as the total
flow. Federal regulations require annual calibration of the
CEMS flow monitors and concentration equipment. These
calibrations are performed using an EPA protocol called a
relative accuracy t udit (RATA). The flow portion of the
calibration is herein referred to as the flow RATA.

Regarding how stack flows are conventionally measured,
the flow RATA maps the axial stack velocity measured along
two orthogonal chords in the stack cross-section. A pitot
probe is inserted into the flow through ports on the stack
wall. On each chord, measurements are made at discrete
points located at the centroids of equal area. The discrete
velocity measurements are integrated to determine the flow

velocity, which in turn, is used to determine the correction 5

factor for the CEMS flow meter.

FIGS. 36A, B, and C show the three RATA probe types
sanctioned by the EPA including A) the S-probe, B) the
prism probe, and C) the spherical probe. All 3 probes use the

same measurement principle. The axial velocity is correlated. 5

to differential pressure measurements made across the
probe’s pressure ports. Both the prism and the spherical
probe have 5 pressure ports and both measure the entire
velocity vector including the pitch, yaw, and axial velocity
components. In contrast, the S-probe measures only the yaw
and axial velocities, and has been shown to give flow
velocities that are biased high if significant pitch and yaw are
present in the flow.

‘About the nulling method, the 3 EPA-sanctioned probes
use a yaw-nulling method to determine the angle of off-axis
flow in the yaw direction, which we call the yaw-null angle
(Byun) At each point on the RATA map, the probe is nulled

&

&

36

by rotating it about its axis until the vector sum of the yaw
and axial velocities align with pressure port 1. For a 3-D
probe the nulling procedure can be accomplished in a single
rotation. The S-probe requires 2 rotations. First the S-probe
is nulled by rotating it about its axis until P,,=0. A second
90° rotation orients port 1 so that it faces into the flow. Once
the probe is nulled, the probe calibration parameters are used
to determine the dynamic pressure (P,,,,), and for 3-D probes
the pitch angle («). -

About errors due to imperfect nulling, if the null condition
is not satisfied, significant flow measurement errors can
occur. The nulling errors increase with the ratio AP, ,/Pyns
where the null-differential-pressure AP,,,-P2; for 3-D
probes and AP,,,,-P,» for the S-probe. The errors become
significant when AP,,,,,/P.,,,, is not small relative to unity. In
most cases the nulling procedure is performed manually. A
person rotates the probe while reading a differential pressure
gauge to determine the exact yaw angle for which AP,,,,-0.
However, transients in stack flows, noisy pressure signals,
and human errors make nulling imperfect and introduce
unquantified bias (e.g. high for an S-probe) into the mea-
surement process.

When the velocity field has a significant yaw component,
nulling the probe can be time-intensive and, consequently,
expensive. When mapping the flow field, several iterations
are generally required to find the yaw-null angle at each
traverse point. The nulling time increases in wet stacks since
stack testers must frequently interrupt the measurement
process to purge the probe’s pressure ports of droplets or
particles. Because 3-D probes have more pressure ports than
S-probes, and because the diameters of these ports are
smaller than the ports of S-probes, 3-D probes are more
susceptible to plugging. Consequently, 3-D probes generally
require more time than the S-probe to complete the flow
RATA. Historically the stack flow measurement community
has opted to use the more robust and economical, but less
accurate, S-probe.

About a non-nulling method, non-nulling methods deter-
mine the axial velocity without rotating the probe at cach
traverse point to find §,,,,. Instead, the axial velocity, the
pitch angle, and the yaw-null angle B,,,,, are determined with
the probe oriented at zero yaw angle (i.c., B=0° such that
port 1 on the probe is aligned with the stack axis). Compared
with nulling methods, non-nulling methods reduce the time
needed to perform flow RATAs. CFFPs are concerned about
the duration of flow RATAs because they must maintain
loads stipulated by the RATA instead of loads dictated by
customer supply and demand.

The non-nulling method also has the potential to improve
flow measurement accuracy compared with nulling meth-
ods. First, the S-probe measures only 2 components of the
velocity vector while the non-nulling method applies to 3-D
probes and thereby measures the entire velocity vector.
Second, Method 2F, which is the EPA nulling method for
3-D probes, does not address errors resulting from imperfect
nulling, as discussed above

In this example, we describe accurately determining the
total flow in a CFPP stack using a non-nulling method and
commercially available flow RATA equipment. In previous
work, we achieved 1% accuracy when we performed flow
RATAs in NIST’s Scale-Model Smokestack Simulator
(SMSS) using a spherical probe, even with highly-distorted
flows. However, the SMSS facility uses ambient air as
surrogate for flue gas and performs flow RATAs under
laboratory conditions using laboratory grade instrumenta-
tion.



U.S. Patent Dec. 13, 2022 Sheet 6 of 48 US 11,525,840 B2

201 Conical aerodynamic flow head

202.2,
239

FIG. 6


U.S. Patent Dec. 13, 2022 Sheet 20 of 48 US 11,525,840 B2

FIG. 20


US 11,525,840 B2

17

ventional EPA protocols have been established for deter-
mining p given tp, and temperature.

Coefficients a,7,.47,9 are determined by fitting wind tun-
nel data to the polynomial for each output tp,. Sufficient wind
tunnel data are collected as a function of pitch, yaw, air-
speed, and turbulence intensity and the degree of the poly-
nomial for the intended application. For stack applications
using a 5-port probe (i.e., 4 exterior ports and 1 central port
202), 500 wind tunnel points can specify about 100 coefli-
cients for a 5” degree polynomial fit.

Non-nulling gas velocity measurement apparatus 200 and
processes disclosed herein have numerous benefi uses
including robust, faster and more accurate emissions mea-
surements as described below. Advantageously, non-nulling
gas velocity measurement apparatus 200 overcomes limita-
tions and technical deficiencies of conventional devices and
conventional processes. It should be appreciated that non-
nulling pitot probe 201 overcomes clogging issues of con-
ventional pitot probes in a way that has heretofore been
taught away such as in U.S. Pat. No. 5,423,209 that teaches
that conventional multi-hole spherical pitot tube probe
includes pressure holes for detecting the direction of wind
that constitute small holes in four directions of the spherical
surface. Further, this patent teaches that if the pressure hole
is only one small hole, in the case where even one hole
becomes clogged with insects, a cloud of dust and so on, the
probe possibly fails to function. This patent also teaches that
in the multi-hole spherical pitot tube probe described in the
patent, the arrangement of pressure holes on the curved
surface for detecting the direction of wind and the diameter
of holes influence on the accuracy of detection of wind-
direction. That patent concludes that, if the hole diameter is
large, an error in pressure detection increases, thus posing a
problem in that the hole diameter cannot be made large in
order to prevent clogging.

Advantageously, non-nulling fluid velocity measurement
apparatus 200, non-nulling pitot probe 201, and processes
herein provide multi-hole pitot probes that involve a non-
nulling method, ie., no need to rotate non-nulling pitot
probe 201, to measure the static pressure. the entire velocity
vector and the turbulence intensity of fluid flow. Non-nulling,
pitot probe 201 provide better accuracy than EPA-sanc-
tioned probes and measurements can be performed much
faster than conventional probes, resulting in significant
financial savings for powerplants, more accurate hazardous
emissions measurements for the general public. The fluid
velocity is calculated from measurements of the turbulence
intensity in conjunction with differential pressure measure-
ments. Performing non-nulling measurement of gas velocity

parameters can be applied to typical and extreme stack 5

conditions. Geometric features of include shape, hole size,
and hole location that are provide robust and accurate
velocity measurements in harsh stack conditions, e.g., high
temperatures, solid and liquid impurities in the flue gas,

highly 3-D dimensional velocity field, high turbulence inten- 5
sities, and the like.
Beneficially, has a selected geometry of multi-holes, i.e.,

entrant apertures 202. Performing non-nulling measurement
of gas velocity parameters includes calculation of 3-D
velocity and turbulence intensity from differential pressure
measurements at EPA-compliant locations in emission stack
235. Non-nulling gas velocity measurement apparatus 200
includes hardware to measure differential pressures. The
hardware can acquire data, e.g., at two acquisition rates
including a slow rates (e.g., 10 Hz) for accurate 3D velocity
determination or a fast rate (e.g., 1.0 kHz) for turbulence
intensity measurements. The hardware is compatible with

20

3

&

&

18

standard probe purging methods used by stack testing indus-
try. Electronics and software for data analysis and calcula-
tions in real time are included in non-nulling gas velocity
measurement apparatus 200. Further, performing non-null-
ing measurement of gas velocity parameters includes cali-
bration of 3-D probes in a wind tunnel that corrects for
turbulence and blockage effects.

Conventional flow monitors that measure hazardous
emissions from powerplant smokestacks are calibrated
annually using EPA-sanctioned pitot probes. These conven-
tional probes measure the flue gas velocity at prescribed
points along two orthogonal, diametric chords in a cross-
section of the stack, Conventionally, the flow is calculated
by averaging the axial velocity components and multiplying
this result by the stack cross-sectional area. Conventionally,
velocities are determined using a nulling method, which
requires rotating the conventional probe about its axis to
align an impact pressure port with two components of the
velocity vector. Once the conventional probe is oriented at
the nuil angle, the measured pressure differences between
the pressure ports are combined with other data to calculate
the gas velocity.

Beneficially, non-nulling pitot probe 201 measures veloc-
ity faster and more accurately than conventional EPA-
sanctioned probes and perform better in performing non-
nulling measurement of gas velocity parameters than
conventional EPA-sanctioned spherical probe. Stack flow
monitors can be calibrated in /sth the time, not including
setup time, using non-nulling pitot probe 201 instead of a
conventional EPA-sanctioned probe. The time savings pro-
vided by non-nulling pitot probe 201 reduces the time a
power plant must operate at loads dictated by EPA test
protocol and increases the time the plant can operate at
profitable loads, based on customer demand. Further, non-
nulling pitot probe 201 is superior to conventional EPA-
tioned probes because non-nulling pitot probe 201 has
better reliability and accuracy. Entrant aperture 202 Of
non-nulling pitot probe 201 can be, e.g., three to six 3 to 6
times larger than ports in conventional EPA-sanctioned
probes and mitigate erroneous velocity measurements due to
port plugging from particles or water droplets in gas flow
206 such as flue gas. Non-nulling pitot probe 201 avoids
errors resulting from imperfect execution of conventional
nulling methods. The complex, turbulent velocity fields in
smokestacks may inaccurately measure the null angle,
which can result in unquantified errors in the velocity
measurement. Non-nulling pitot probe 201 can include a
correction to the measured velocity from the turbulent
intensity of gas flow 206. Ignoring this correction, such as in
conventional nulling procedures, can lead to over-estimating
stack emissions by 5%, when the turbulence intensity is
10%.

Non-nulling gas velocity measurement apparatus 200 and
processes herein unexpectedly provides accurate 3-D veloc-
ity measurements including the turbulence intensity, accu-
rate static pressure, reduced measurement time by a factor of
5 (or more) greater accuracy than conventional devices and
processes, and minimizes clogging the probe pressure ports.
The result being accurate flow measurements in harsh stack
conditions, which could not be obtained with currently used
probes and methods.

The articles and processes herein are illustrated further by
the following Examples, which are non-limiting.

EXAMPLES

Example 1. Faster, More Accurate, Stack-Flow
Measurements

Exhaust flows from coal-fired electricity-generating
plants are determined by averaging flue gas velocities mea-


US 11,525,840 B2

31

for the fan and the spinning disk, (2) generation of the oil
droplets entrained in the air flow, and (3) the protocol for
integrating over the LDA’s sensing volume. To re-calibrate
the LDA, we replaced the spinning disk described in with an
optical chopper. The chopper enabled us to calibrate the
LDA while it was installed on the roof of the wind tunnel.
This change saved time and eliminated possible calibration
changes that might occur as the LDA was removed and
reinstalled on the roof of the wind tunnel.

The LDA measures only the component of the air velocity
vector that is perpendicular to the surfaces of the interfer-
ence fringes generated where the laser beams intersect in an
ellipsoidal “sensing” volume. When the LDA was installed
on the roof of the wind tunnel, it was aligned so that the
surfaces of the interference fringes were parallel (+0.5°) to
the YZ plane of the wind tunnel. With this orientation, the
LDA measures the downstream (X) component of the air
velocity incident on the IUT. The downstream component of
the velocity is exactly what is required to map gas flows in
smokestacks using multi-hole differential-pressure probes.

NIST’s LDA uses a solid-state laser with a wavelength of
513.5 nm. The output lens of the LDA has a focal length of
1200 mm and the laser beams intersect at the angle 3.46°.
The LDA’s sensing volume extended 13 mm along the Z
axis and 0.39 mm along the X and Y axes. The sensing
volume’s dimensions are weakly dependent on the settings
of the burst spectrum analyzer and the laser’s intensity.

With regard to generating turbulence, generating turbu-
lence occurred by placing grids across the flow a wind
tunnel. Grids generate nearly homogeneous turbulence with
eddies no larger than the elements of the grid; therefore, the
length scale of the generated turbulence increases with the
size of the grid.

We assembled the grid shown in FIG. 27 using 25 mm
diameter wooden cylinders arranged to form square open-
ings 10 cm ona side. During normal, turbulence-dependent
calibrations, the grid was fastened upstream of the test point
at one of three locations: —1.06 m, -2.00 m, or -3.56 m
where the corresponding values of the turbulence intensity
were Tu=0.094, 0.056, or 0.028.

FIG. 28 shows that the influence of the grid on the
X-component of the flow velocity exceeds 1% even 159 em
downstream from the grid. To minimize the effects of this
dependence, we tightly control the location of the test point
and we took data only when X260 cm.

FIG. 29 displays the X- and Y-dependences of Tu mea-
sured using a multi-hole probe and with the grid located at
the indicated distances upstream of the test point. Immedi-
ately downstream of the grid, the values of Tu in planes

perpendicular to the flow have the periodicity of the grid. Ins

these planes, Tu maxima occur where (V,) have minima,
i.e. in the “wake” of the grid’s cylinders. The periodicity
attenuates as the X (downstream) coordinate increases. As
evident in FIG. 29, when X>~60 cm, the periodicity is

smaller than the noise of the Tu measurements. In this range, 5

the standard deviation of Tu measurements is 0.046 Tu, as
indicated by the dashed lines in FIG. 29.

When X>=60 cm, Tu is a function of X alone: Tu=4.55
(X/cm)~°**? in the range 66<X/cms176, which corresponds
to 0.06sTus0.14.

On the rare occasions when calibrations are desired at
intensities greater than 0.14, the grid was replaced with an
array of “flags” on a frame that was easily installed and
removed from the wind tunnel. See FIG. 27, right. Each flag
had been sewn around a rope that was tied to a frame. At
airspeeds below 3 m/s, the flags moved only slightly and
generated little turbulence. At airspeeds near 5 m/s, the flags

4

4

0

32

generated turbulence with a wide frequency spectrum and
with superimposed peaks near 5 Hz and its harmonics.
Above 5 Hz, the peaks moved to higher frequencies and
became less prominent.

At airspeeds above 15 m/s, the flags began to fray. To
stabilize the flags, we trained the assembled flag array for
approximately 30 minutes at 25 mvs. After the training,
turbulence intensity measured 50 cm downstream from the
array was stable with the value Tu-0.20 in airspeeds ranging
from 5 m/s to 35 m/s.

Regarding measuring turbulence, we tested four methods
of measuring turbulence intensity: (1) Laser Doppler
anemometer, (2) high-frequency, 3-D, multi-hole pressure
probe with integrated pressure sensors, (3), constant-tem-
perature hot-wire, anemometer and (4) an L-shaped pitot
tube. As shown in FIG. 30, methods (1), (2), and (3) were in
mutual agreement (within the bounds +0.10 Tu) in the range
0.02sTus0.20 and airspeeds from 5 m/s to 25 m/s. In
contrast, the turbulence intensity ratios determined with the
L-shaped pitot tube were only a fraction (0.19 Tuz 4 to 0.37
Tuzp,) of the values determined methods (1), (2), and (3).
We did not study the origin of this difference. The high-
frequency pressure fluctuations at the pitot tube’s port might
have been attenuated by the response time of the differential-

5 pressure gauge and by the time constant associated with flow

in the tube connecting the differential pressure gauge to the
pitot tube. It is contemplated that, the pitot tube, together
with its pressure transducer and the connecting tubes, could
be calibrated as a unit to measure turbulence intensity.

To determine Tu and its standard uncertainty u(Tu) from
the LDA, we recorded the data from the burst spectrum
analyzer and computed the average value of the X-compo-
nent of the velocity (V,) and its relative standard deviation
On=(V2)'7/(V,). It is an approximation to replace
(V,) with (V) because (V,)>>(V,) and (V,)>>(V.). We
assume that G,, has two, uncorrelated sources: (1) back-
ground velocity fluctuations with the relative standard devia-
tion Gy, . that are always present, even in the absence of
turbulence-generating grids, and (2) grid-generated fluctua-
tions with the relative standard deviation 64,9, (The
background fluctuations occur because the spacing of the
interference fringes generated by the LDA varies by
approximately +3% across the sensing volume and because
the tracer oil droplets pass through the sensing volume at
random values of the Y- and Z-coordinates.) The grid-
generated turbulence is isotropic; therefore, we will simplify
the notation by replacing 0, »¢ and Oy5,gia With Ope and
Gg,a We computed the turbulence intensity Tu from each
burst spectrum by subtracting the background velocity fluc-
tuations from the velocity fluctuations when the grid was
present:

To determine the statistical contribution to the standard
uncertainty u(Tu) we must measure Tu many times and
characterize its fluctuations. This leads us to determine the
standard deviation of Tu (itself a relative standard deviation)
from a sequence of burst spectra using:

r

Opg))”

When the turbulence-generating grid was placed at three
locations upstream of the test point (X=-3.56 m, -1.06 m,
-2.00 m) the turbulence intensities and their expanded
uncertainti were TusU(Tu)=0.025820.0026,
0.053220.0032, 0.0950:0.0051, respectively.

Regarding blockage corrections to LDA measurements. to
calibrate probes, NIST measures the probe’s response to a



U.S. Patent

Dec. 13, 2022 Sheet 37 of 48

US 11,525,840 B2

Probe Types

NN
(B= 0)

M2F/NN-1

Spherical
Probes (SP)

0,994

OEY

Custom

Probes (CP)

CPSP

Spherical

Probes (SP)

Custom

Probes (CP)

CP/SP-1

Low | 86%

-2.3 %

NumberoF- ERAT, forth teat thy £1
a} Number-of repeated RATA traverses forthe same probe at the same fe
bj) Standard deviation of normalized RATA velocity expressed as a percent
¢) Percent difference computed using 100 (M2F/NN -1)

(4) The CFPP test results are summarized in Table 1. The tabulated RATA velocities are normalized by
the CEMS velocity (Vara/Vcems) to help account for flow variations during and between
measurements. The data in column “M2F” are the normalized flow velocities for Method 2F; the data in
column “NN ( = 0)” are the normalized non-nulling velocities obtained with the probe at a zero yaw

FIG. 37



U.S. Patent Dec. 13, 2022 Sheet 38 of 48 US 11,525,840 B2

|

2

1

B)

30 -20 -10 0 10 20 30
Pitch, [deg]

FIG. 38


US 11,525,840 B2

9

that, no matter the oblique angle between entrant body tube
203 and extensor body tube 204, central entrant aperture 238
and its pressure channel 205 can be aligned to be coaxial,
e.g., with a stack axis of emission stack 235. Length L1 of
entrant body tube 203 can be long enough to ensure non-
‘eddy formation of gas flow 206 as residual gas flow 206 not
received through entrant apertures 202 flows over external
surface of non-nulling gas velocity measurement apparatus
200. Length L1 can be, e.g., from 1 cm to 10 m, specifically

from 5 cm to 1 m, and more specifically from 10 cm to 100 |

cm.

Extensor body tube 204 provides interconnection of non-
nulling pitot probe 201 to differential pressure transducer
213, reference pressure source 210, and the like. Moreover,
non-nulling pitot probe 201 can be mounted to a flange or
other bulkhead member for disposal of non-nulling pitot
probe 201 in a test configuration such as a gas source, ¢.g..
emission stack 235, via extensor body tube 204, Length L2

of extensor body tube 204 can be long enough to ensure 2

disposal of aerodynamic flow head 207 at selected positions
in a sampling environment such as various radial locations
(e.g. first radial position R1, second radial position R2, and
the like) in emission stack 235 as shown in FIG. 11. Length
L2 can be, e.g., from 1 cm to 10 m, specifically from 5 cm
to 1 m, and more specifically from 10 cm to 100 cm
Non-nulling pitot probe 201 can include additional hard-
ware accoutrements including sensor port 242 disposed on
extensor body tube 204 for receiving various instrumenta-
tion such as a temperature probe, ¢.g., a thermocouple.
Pressure channel 205 provides unobstructed fluid com-
munication of gas flow 206 from entrant aperture 202 to gas
valve 209. In this manner, pressure channel 205 propagates
a pressure of gas flow 206 from, e.g., in emission stack 235,
‘as sampled by the entrant aperture 202 to which pressure
channel 205 is connected to gas valve 209 as stagnant gas
208 via sample gas line 217. Accordingly, pressure channel
205 has a diameter appropriate for transmitting stagnant gas
208 with fidelity and in an absence of modifying such. It
should be appreciated that entrant aperture 202 receives gas
flow 206 and communicates such as stagnant gas 208 to
pressure channel 205 so that stagnant gas 208 is the portion
‘of gas flow 206 sampled by entrant aperture 202, and
stagnant gas 208 includes all gas flow properties as gas flow
206 received by entrant aperture 202. With reference to FIG.
3 and FIG. 4, each pressure channel 205 is in fluid commu-
nication with one entrant aperture 202. Indeed, central
pressure channel 240 is a pressure channel 205 that com-
municates stagnant gas 208 from gas flow 206 received by

central entrant aperture 238. Similarly, peripheral pressure 5

channel 241 is a pressure channel 205 that communicates
stagnant gas 208 from gas flow 206 received by peripheral
entrant aperture 239.

It is contemplated that gas flow 206 is a fluid that can be

a gas or liquid. Exemplary gas flows 206 include effluent

from an industrial emission stack 235, molecular or atomic
gas sources, liquid supplies, and the like. A pressure of ga
flow 206 can be from 1 pascal (Pa) to 100 megapascal
(MPa), specifically 100 Pa to 1 MPa, and more specifically
from 5 kilopascals (kPa) to 1 MPa. A temperature of gas flow
206 can be any temperature as long as stagnant gas 208 can
be communicated through pressure channel 208. Gas flow
206 can have a Mach number from 0.01 to 0.3 at a velocity
that is from 5 m/s to 100 m/s. A density of gas flow 206 can
be from 107° grams/milliliter (g/mL) to 20 g/mL, specifi-
cally from 10-* g/mL to 10 g/mL. and more specifically 10-*
g/mL to 2 g/mL. As used herein, stagnant gas 208 refers to

&

&

10

the pressure induced on the entrant aperture 202 due to gas
flow 206 incident at entrant apertures 202.

Sample gas line 217 receives stagnant gas 208 from
pressure channel 205 and communicates stagnant gas 208 to
gas valve 209. Sample gas line 217 is constructed of a
material that withstands a temperature, chemical, or pressure
demand of the flow environment such as emissions stack
235. Exemplary materials for sample gas line 217 include
metals, plastics, and the like.

Gas valve 209 is in fluid communication with non-nulling
pitot probe 201 via sample gas line 217 and receives
stagnant gas 208 and reference gas 211. Further, gas valve
209 can be controlled by valve control signal 227 to select
output of gas valve 209 between stagnant gas 208 and
reference gas 211 based on valve control signal 227. With
reference to FIG. 8, gas valve 209 can have a reference flow
configuration as in panel A or sample flow configuration as
shown in panel B. When valve control signal 227 provides
a first signal, e.g., a low voltage, gas valve 209 obtains
reference flow configuration, wherein reference valve line
221 of gas valve 209 flows reference gas 211 through gas
valve 209 to provide reference gas 211 as valve-selected gas
212, and sample valve line 222 provides stagnant gas 208 as
exhaust flow 219, e.g., to sink 220. Sink 220 can be a plug

5 that blocks fluid flow or other hardware. When valve control

signal 227 provides a second signal, e.g., a high voltage, gas
valve 209 obtains sample flow configuration, wherein ref-
erence valve line 221 of gas valve 209 flows reference gas
211 through gas valve 209 to provide reference gas 211 as
exhaust flow 219, and sample valve line 222 provides
stagnant gas 208 as valve-selected gas 212. Gas valve 209
can be a pneumatic valve, e.g., a two-position, four-way
valve, or the like. In an embodiment, gas valve 209 isolates
differential pressure signal 214 from non-nulling pitot probe
201 so that emission stack 235 can be purged with a high
pressure. In this manner, differential pressure signal 214 is
protected from potential damage from high pressure or
sudden pressure changes that can damage certain compo-
nents of differential pressure signal 214 such as a diaphragm.
Moreover, an additional gas line can be connected to non-
nulling pitot probe 201 to provide positive pressure in
pressure channel 205 while differential pressure transducer
213 is isolated from pressure channel 205 by gas valve 209
so that entrant aperture 202 can be unclogged should a clog
of entrant aperture 202 occur. Because each entrant aperture
202 is connected to a different gas valve 209 that is inde-
pendently controlled by a separate valve control signal 227,
individual entrant apertures 202 are selectively addressable
and can be subjected to individual pressurization and flow.
Valve outlet gas line 224 receives valve-selected gas 212
from gas valve 209 and communicates valve-selected gas
212 to differential pressure transducer 213. Valve outlet gas
line 224 is constructed of a material that withstands a
temperature, chemical, or pressure demand of the flow
environment such as emissions stack 235. Exemplary mate-
tials for valve outlet gas line 224 include metals, plastics,
and the like.
Differential pressure transducer 213 receives and com-
pares valve-selected gas 212 and reference gas 211 to
produce differential pressure signal 214. Differential pres-
sure signal 214 can be made with reference to a calibrated
pressure range or can be a raw signal that is proportional to
a difference in pressure between valve-selected gas 212 and
reference gas 211. Accordingly, differential pressure signal
214 can be a voltage with an amplitude that corresponds to
the difference in pressure or can be a voltage signal that
provides absolute pressure for valve-selected gas 212.



U.S. Patent Dec. 13, 2022 Sheet 26 of 48 US 11,525,840 B2

1.02
=
a
Pa
=)
wok
=
S a a ee ae |
2 1.00
ww
ae
2
=
ao he a ae ot a a be #
2013 2015 2017 2019 2021

date of calibraton [year]

FIG. 26


US 11,525,840 B2

15

including a plurality of entrant apertures 202 that includes
central entrant aperture 238 and a plurality of peripheral
entrant apertures 239 arranged radially from central entrant
aperture 238, peripheral entrant aperture 239 including first
peripheral entrant aperture 239.1, second peripheral entrant
aperture 239.2, and third peripheral entrant aperture 239.3;
entrant body tube 203 disposed on aerodynamic flow head
207; extensor body tube 204 disposed on entrant body tube
203 such that entrant body tube 203 is interposed between
aerodynamic flow head 207 and extensor body tube 204,
such that extensor body tube 204 is arranged at an oblique
angle to entrant body tube 203; and a plurality of pressure
channels 205 disposed in aerodynamic flow head 207,
entrant body tube 203, and extensor body tube 204, such that
each entrant aperture 202 is separately and independently in
fluid communication with one of pressure channels 205, and
each pressure channel 205 independently receives and com-
municates gas flow 206 as stagnant gas 208 from entrant
aperture 202 of which pressure channel 205 is in commu-
nication; receiving, by entrant apertures 202, gas flow:
producing, by central entrant aperture 238, zeroth stagnant
gas 208.0 from gas flow; producing, by first peripheral
entrant aperture 239.1, first stagnant gas 208.1 from gas flow
206; producing, by second peripheral entrant aperture 239.2,
second stagnant gas 208.2 from gas flow 206; and produc-
ins
gas 208.3 from gas flow 206; and obtaining zeroth differ-
ential pressure signal 214.0, first differential pressure signal
214.1, second differential pressure signal 214.2, and third
differential pressure signal 214.3 respectively from zeroth
stagnant gas 208.0, first stagnant gas 208.1, second stagnant
gas 208.2, and third stagnant gas 208.3, ¢.g., by transducing
an electrical signal from a mechanical deflection of a dia-
phragm in the differential pressure transducer 213 caused by
a change in the differential pressure across the diaphragm.
In an embodiment, performing non-nulling measurement
of gas velocity parameters includes determining a non-axial
orientation factor for a non-axial angle with respect to the
stack axis at which non-nulling pitot probe 201 is disposed
in emission stack 235. Here, adjusted pressures (APL.
APN) are mapped into turbulence intensity correct
dynamic pressures, yaw angle, pitch angle, and static pres-
sure. The mapping is accomplished using an N”-degree
multivariable polynomial having reduced pressures (RP1,
RP2, and the like) as independent variables.
Pseudo-dynamic pressure is a root-sum-square of the
adjusted pressures (API, ... , / APN). For definiteness, the
pseudo dynamic pressure and outputs (.g., dynamic pres-
sure, yaw angle, pitch angle, and static pressure) for a probe
with four exterior pressure ports (e.g., 202.1, 202.2, 202.3,
and 202.4) surrounding central entrant aperture 202.0 is

Pay NV
Reduced pressures are obtained by normalizing each

adjusted pressure P,,=P,,/P,,,, by the pseudo dynamic pres-
3, 4, and 5. The adjusted pressures are x,=P,>.

Ps Ps

roe KP, 5, R-P,4. and the like.

"Seafar« Output variables are y, wherein subscript i=1 to 4
specifies dynamic pressure when i=1; the yaw angle when
the pitch angle when i=3; and the static pressure when
i-4. The outputs y, are determined by an N degree poly-
nomial of the 4 reduced pressures

On Os

‘

oo + dco +e, TH) -

by third peripheral entrant aperture 239.3, third stagnant 5,

4s and x,=P,., and the reduced pressures are s

0

&

50

6:

16

-continued
(CPO+ Prep Wit

wherein 8, is the Kronecker delta function defined by

[lis
B= ho Gey
0 ie]

Anaad, ate polynomial coefficients determined by curve

fits 10 wind tunnel data for each 1p,, and Q, are upper limits
of respective summations wherein

Qe=N= Ba) 4s-Oeatdes)12~ rates Oe)T,

so that Q,=N-q3-q,-q,, Q;=N-q.-q,, Q.=N-q,, and
QEN.

The effect of turbulent flow on the velocity is accounted
for in the dynamic pressure y, by multiplying the N” degree
polynomial by a single variable function of turbulence
intensity (Tu), wherein c, and c, are fit coefficients to wind
tunnel data. The turbulence intensity of the flow is measured.
independent of this analysis. Static pressure 1p, includes the
difference between the static pressure and the central pres-
sure port (202.0) determined by N” degree polynomial; the
difference between the central port and the reference pres-
sure, i.e., CP0; and the reference pressure, reference pressure
source 210 as P,.p

The analysis can be extended to Mz3 variables by defin-
ing the outputs yp, by

(1454 (co-+ 61TH?) ~ (CPO Prep in

wherein upper limits of the summations are defined by

Sim92 — > Sim

met

Qar = N = ear gu—1 — (Oxat + See )9t-2 = oe =

and the Pseudo dynamic pressure is

In an embodiment, performing non-nulling measurement
of gas velocity parameters includes correcting the real
dynamic pressure with the non-axial orientation factor prior
to determining the velocity of gas flow 206, wherein the
axial velocity is determined by

Vax = ¥ 7H cosipa)eosids)
P

such that fluid density p is determined using an appropriate
equation of state using as inputs static pressure y, and
temperature of gas flow 206. In stack measurements, con-


US 11,525,840 B2

33

uniform flow in the X-direction as a function of (V,), Tu, a.
and B. The widely-used, uniform-flow convention is appro-
priate for mapping the flow in cross-sections of power-plant
stacks with diameters that are much larger than the dimen-
sions of the probe and its supports. In the absence of
grid-generated turbulence, NIST’s wind tunnel generates an
excellent approximation to a uniform flow _ field.
(ACV,)/(V,)<0.002 over an area of 0.4 mx0.4 m in the Y-Z
plane. However, the uniformity of the flow field is destroyed
when any bluff object (such as pressure probe undergoing
calibration) is inserted into the flow. For an accurate cali-
bration, the probe must be “distant” from the sensing volume
of the LDA that determines (V,). Alternatively, the LDA-
determined values of (V,) must be corrected to account for
probe-generated non-uniformity in the flow field. This cor-
rection is called a “LDA sensing volume blockage correc-
tion”. This blockage correction is independent of the bound-
ary layers separating the walls of the wind tunnel from the
average flow in the tunnel.

FIG. 31 displays measurements of the blockage effect for
two test objects: (1) a 2.54 cm diameter, hemispherical
differential-pressure probe and (2) a 12.7 cm diameter
sphere. Each of these objects was mounted on a carbon fiber
tube (2.54 cm diameter) that extended from the center of the

wind tunnel to the translation-rotation stages outside the 2

tunnel. To vary the blockage, the tube was translated in the
‘X-direction, as indicated by the dashed outline in FIG. 22.
During these measurements, the wind tunnel did not contain
turbulence-generating structures and the air speed was main-
tained near 10 m/s.

The upper panel of FIG. 31 is a plot of the ratio of two
LDA-determined velocities Vp4/Vip, 66 om 28 a function
of the distance measured on a streamline between the
sensing volume of the LDA and the spherical surface of the
test object. (The subscript “66 cm” indicates V,,,, measured
66 cm upstream from the test object.) The legend of FIG. 31
identifies the data sets by their free-stream velocity Vz 4, -
‘At small distances from the hemispherical probe, V;,,/
Vis, oo om has a strong dependence on Vzp,, x. The
dependence on V;,4, .. attenuates with increasing distance
as emphasized in the lower panel of FIG. 31. The lower
panel of FIG. 31 expands the vertical scale of the upper
panel by a factor of 80 and replaces the horizontal axis by
the reciprocal of the distance. The reciprocal-distance facili-
tates extrapolating the data to determine V4, ... For flows
ranging from 5 m/s to 30 m/s and at distances greater than
8 cm, the data for the hemispherical probe are independent
of V;p4, « and they are consistent with the linear function:
Vial ipa, 66 on=1-0019-0.120x(distance/em)"".

FIG. 31 shows that, at 10 m/s, blockage effects for the 5

12.7 cm diameter sphere are much larger than those for the

2.54 cm probe and they are consistent with the empirical

funetion: Vn4/V 4, 65 on=1-003~7.1x(distance/em)-'°’.
When a turbulence-generating grid is present in NIST”:

s

wind tunnel, (V,) in most of the Y-Z plane has the period-

icity of the grid. (Near the walls of the wind tunnel, (V,) has
additional significant variation.) Therefore, calibrations in
high turbulence require the instrument under test (IUT) to be
located directly downstream from the LDA. Fundamentally,
blockage effects depend on the ratio of the air speed to the
rate pressure waves propagate (i.e, Mach number), and
should be independent of the level of turbulence intensity.
Nevertheless, we searched for a turbulence-dependence of
the blockage, by installing an EPA-accepted multi-hole
probe just downstream of the LDA with an air speed of 10
mm/s. The turbulence-generating grid was placed at three
locations upstream of the test point (X=-1.06 m, -2.00 m,

20

3

&

34
or -3.56 m). As shown in FIG. 32, the blockage was
independent of the turbulence, within the noise of the
measurements.

Regarding calibration data for multi-hole differential
pressure probe, for faster, more accurate, flue gas flow
measurements in power plants, we acquired data displayed
in FIG. 33. The displayed data are a small fraction of the data
that are needed to characterize the response of a S-hole
spherical probe for flue gas measurements. The full data set
comprises the pressures measured at all 5 ports (relative to
the static pressure) at pitch and yaw intervals of 2° at air
speeds of 5 m/s, 10 m/s, 20 m/s, and 30 m/s and at 4
turbulence intensities. Routine acquisition of such large data
sets for customer-provided probes is prohibitively expen-
sive, even using a fully automated calibration system. One
thrust of our research is to document methods of character-
izing multi-hole spherical (and other) probes with much
smaller data seta. This might be done by comparing the
responses of each customer's probe to the corresponding
responses of a nominally-identical “master” probe under
only a few calibration conditions. Alternatively, the master
probe could be replaced with a numerical and/or analytical
model for the responses of an ideal probe.

Regarding a vane anemometer, an anemometer including
“vanes” or a “propeller” or an “impellor” rotates about an
axis parallel to the wind direction. FIG. 34 is a sample of
calibration data for a rotating vane anemometer with a
protective cylindrical ring (or frame) surrounding the vanes.
In FIG. 34, the zero on the pitch axis is arbitrary because no
effort was made to align the anemometer’s rotation axis with
the axis of the wind tunnel. The plotted data show that the
calibration factor V2.7/V yzsr is insensitive to small changes
of the pitch angle « at approximately a=4°. This angle was
used to calibrate the IUT as a function of air speed. FIG. 34
also shows that the factor steps up when the pitch
angle jumps decreases near @=~1° or increases near c=12°.
We speculate that the frame begins to shadow the vanes at
these angles.

With regard to thermal anemometer, FIG. 35 displays
some of the calibration data for a thermal anemometer that
was designed to be insensitive to its orientation with respect
to the average wind speed. This anemometer’s calibration
factor was remarkably insensitive to the yaw angle; how-
ever, it did have an easily measured dependence on the pitch
angle.

Regarding uncertainties, we tabulated uncertainty contri-
butions from misalignment of the spinning disk with respect
to the LDA, thermal expansion of the disk, the LDA’s
optical system, the clock of the burst spectrum analyzer, and
of the LDA the clock, and the alignment of the TUT with
respect to the LDA. All these uncertainty contributions were
negligible in comparison with the (k=2, expanded) 0.41%
uncertainty of the calibration factor of the LDA relative to
the spinning disk standard in range 0.2 nvs to 10 mis.
Blockage effects can be significantly larger than the uncer-
tainty of the LDA calibration factor; however, we correct for
blockage.

Example 3. Non-Nulling Measurements of Flue
Gas Flows in a Coal-Fired Power Plant Stack

Exhaust flows from coal-fired stacks are determined by
measuring the flue gas velocity at prescribed points in the
stack cross section. During the last 30 years these velocity
measurements have been made predominantly using S-type
pitot probes. These probes are inexpensive: however,
S-probes measure only two components of the velocity


U.S. Patent Dee. 13, 2022 Sheet 2 of 48 US 11,525,840 B2

200
Win
27
208.1 208.2 1208.3 208.4
2T—) 217-~J 217~] g
2 7 4 208.0~
al 223 217 ~~
209.1 209.2 209.3 209.4 209.0
> 223
ay “A 21204
| eo
| i
RF 22 1212.3 212.4
L224 b hLLag L224 W224 224
| /
213.1 213.2 2133 213.4 213.0
214.1 h214.2 214.3 214.4
218 218—~) 218 —~ 218] 214.0~J
218—~]
215
216

FIG. 2


U.S. Patent Dec. 13, 2022 Sheet 45 of 48 US 11,525,840 B2

0 2 4 6 8 10
Collection Time, [s]

FIG. 45


U.S. Patent Dec. 13, 2022 Sheet 43 of 48 US 11,525,840 B2
Run wie angen % Diff’
No cEMS cEMS
1 1.008 0.999 0.9%
2 1.009 0.993 16%
3 0.965 0.991 -2.6 %
4 0.988 0.992 -0.4 %
Avg? 0.993 0.994 -0.1 %*
“Std 2.1% 0.4%
| a) Avg is the average of the 4 runs
b) %Std Devis 100 times the standard deviation of the 4 runs dividing by the average
co “Diff is calculated by 100(Vyax/ Vancoyaw-1)

FIG. 43


US 11,525,840 B2

39

density (p) was determined via Method 2F using pressure,
temperature, and molar mass measurements.

Regarding non-nulling probe calibrations, the non-nulling
method can also use Eq. (1) to determine the axial velocity
at each traverse point. A difference is that P,y,,,. B,,.7 and a
are determined by fitting 3000 or more data points acquired
in NIST’s wind tunnel. These data span velocities from 5
m/s to 30 m/s, pitch angles from -20° to 20°, and yaw angles
from -42° to 42°. The fitted calibration curve is a fifth-
degree polynomial of the four independent variables: P,.,
Pi5, Pia, and Pi5.

For the non-nulling method, there is no need to rotate the
probe. However, since scenarios could arise where rotating
the probe is beneficial (e.g., the predicted value of 8,7
exceeds the curve fit limits), we discuss a more general
application of the non-nulling method. First the probe is
rotated to a user-selected yaw angle (3). Next, we simulta-
neously measure the four input pressures: P,, Py3, Py4. and
P,;, and use the non-nulling calibration curve fits to calcu-
late Pj, B'y.a» and ot. Here, B',,27 is the calculated yaw-null
angle relative to the rotated probe position at B. The absolute
yaw-null angle is the sum of the probe yaw angle and the
yaw-null angle determined from the non-nulling algorithm,

Brut BB att

If the probe is oriented at a zero yaw angle (B-0°), then
the yaw-null angle determined by the non-nulling algorithm
equals the yaw angle measured from the stack axis,
B uc-Bnua Alternatively, if one rotates the probe to the
yaw-null angle, B=,,,,;. then f',,,, would be zero, ideally. In
this case any changes in f',,,, would provide an indication of
how the yaw-null angle fluctuates while the probe is oriented
at the yaw-angle.

Regarding a test protocol for stack flow measurements,
we conducted 16-point flow RATAs using multiple probe
types. We used a set of 4 spherical probes (see FIG. 36C),
and we also used a combination of the 2 custom probes
shown in FIG. 36D and FIG. 36E. We tested each probe type
at 2 loads, a high load with a nominal flow velocity of 16
m/s, and a low load of 7 m/s. The test matrix shown in FIG.
41 lists the probes used for each test, the flow loads, and the
number of repeated runs. The diagram in FIG. 40 shows the
cross-sectional view of the setup. The probe installed in each
port measures the axial velocity of the nearest 4 points as
illustrated in the figure. A complete traverse, herein called a
run, includes all 16 points shown in the figure. We com-
pleted 4 runs for each probe type at the high load and 6 runs
for each probe type at the low load.

Our test protocol was conducted with RATA equipment

2

that include a multiple automated probe system (MAP) to 5

perform five functions: 1) move all 4 probes simultaneously
to specified points; 2) periodically supply high pressure gas
to purge droplets or particles plugging any of the 5 pressure
ports on the probe head; 3) send a DC voltage to the data

acquisition system 5 s prior to starting a purge, 4) implement

the Method 2F nulling procedure including the measurement
of By and By; and 5) provide time stamps at the start and
stop of each non-nulling and Method 2F measurement
intervals.

To collect non-nulling and Method 2F data, we designed
and assembled four data acquisition systems that were
connected to a single laptop computer. Each system included
inexpensive, industrial-grade differential pressure transduc-
ers, which we sampled at 10 Hz. The transducers were
bidirectional with a full-scale of 1244 Pa and a time response
faster than 1 kHz. We used pneumatically actuated valves to
isolate the differential pressure transducers during purge

40

events. The transducers and valves for each system were
housed ina weather-proof case. Each case was placed on the
floor of the RATA measurement platform just below the port
where the corresponding probe was installed. Fach case
contained 5 pressure transducers that were connected to the
5 pressure ports on the 3-D probe using 6.35 mm inner
diameter tubes approximately 13 m long. In this way, we
measured the flue gas pressure (minus a near ambient
reference pressure, P,. located inside the case) at all 5
pressure ports on the probe head. The required differential
pressures for the non-nulling algorithm (i.¢., P,>, Pia. Phas
P,;) and for Method 2F (i.e., P23, Py2. P4s) were calculated
by subtracting the appropriate pressure measurements. For
example, the yaw pressure was determined by subtracting
the measured pressures on port 2 from port 3, P3,=(P2-
Pre (P3—P rep)

Each of the 4 tests listed in FIG. 41 began by starting the
data acquisition unit. Pressure data were collected through-
out the test except during purge events, which occurred
approximately once every minute. During purge events,
valves isolated the transducers from the purge pressure
while simultaneously re-zeroing the transducers to the com-
mon reference pressure.

The same measurement protocol was followed at each
traverse point. The MAP system simultaneously moved the
4 probes to the specified traverse point and rotated each
probe to a zero yaw angle. After a 3 s stabilization period,
the axial velocity (Viyyoyaw) Was measured for 10 s using
the non-nulling algorithm. Next, the MAP system nulled
each probe and recorded its f,,,,. After another 3 s stabili-
zation period we measured the axial velocity for 10 s via
Method 2F (Vygr) and the non-nulling method (V yyaynut)
Thus, we measured 3 velocities at each traverse point: 1)
non-nulling with the probe at zero yaw: Vyycoyaw 2)
Method 2F at the yaw-null angle; Vy, and 3) a second
non-nulling measurement coincident with Vy where the
probe is oriented at the yaw-null angle; Vea The
second non-nulling measurement provided insight regarding
the steadiness of the yaw-null angle, and could be directly
compared to Vyyor since both measurements were made
simultaneously.

The 3 axial velocities (.e., Vexaovan Vers and
Vuncaonut!) Measured at each traverse point are all calculated
using Eq. (1). However, the algorithms for determining P,,,,.
Byun and ct. differ for the non-nulling method and Method
2F.

Method 2F determines the average axial velocity and
pitch angle from pressure averages. Specifically, we calcu-
lated Py> ag and Ps... Which are arithmetic averages of
P,, and P,; sampled at 10 Hz for 10 s.

In contrast, our implementation of the non-nulling method
determines the average dynamic pressure (P,,,,). yaw-null
angle (B,,,,,) and pitch angle («) from time averages. These
quantities are calculated every 0.1 s when P,>, P13, Py, and
P,, are updated. At the end of the 10 s collection interval, we
calculate the arithmetic average of the 100 values of P,,,,.
Brus and ct, As expected for the steady flows in NIST’s wind
tunnel, the values of P.s,,. Bruce and @ computed from the
pressure averages and the time averages were indistinguish-
able. If transients are present in the stack flow, a time
average may be more accurate than a pressure average. In
the CFPP stack, we compared the axial velocities V,,,;.:
determined from pressure averages and time averages in a
few cases. For most of the comparisons, the values of V j.jar
agreed to better than 1%; in a few cases Vixjq) differed by
10% or more.



U.S. Patent

we
IS
iS

Dec. 13, 2022

Sheet 13 of 48

US 11,525,840 B2

301: receiving,

by an analyzer, differential pressure signal 214.0, differential pressure signal 214.1,
differential pressure signal 214.2, and differential pressure signal 214.3

signal 214.3

302: producing zeroth calibrated pressure CPO from differential pressure signal 214.0, first
calibrated pressure CP! from differential pressu
from differential pressure signal 214.2, and third calibrated pressure CP3 from differential pressure

re signal 214.1, second calibrated pressure CP2

adjusted pressure AP3

/iby pair-wise subtracting CPi from CPO. // to pro’

303: removing a dependence of a pressure PO of a reference gas from zeroth calibrated pressure
CPO, first calibrated pressure CP1, second calibrated pressure CP2, and third calibrated pressure
CP3 to produce, respectively, first adjusted pressure AP, second adjusted pressure AP2, and third

Wide for off-axis velocity vector

304: combining first adjusted pressure API, second adjusted pressure AP2, and third adjusted
pressure AP3 to obtain a pseudo-dynamie pressure sealar

305

individually normalizing first adjusted pressure API, second adjusted pressure AP2, and third
adjusted pressure AP3 with the pseudo-dynarnic pressure scalar to produce, respectively, first
reduced pressure RP1, second reduced pressure RP2, and third reduced pressure RP3

306: determining — real
dynamic pressure from first
reduced pressure RP1, second
reduced pressure RP2, and
third reduced pressure RP3

307; determining a yaw angle
or a pitch angle of the gas flow
from first reduced pressure RPI,

second reduced pressure RP2,
and third reduced pressure RP3

3LL: determining velocity

FIG. 13

: disposing non-nulling
pitot probe 201 in emission
stack 235 such that central
entrant aperture 218 of non-
nulling pitot probe 201 is
aligned with the stack axis



US 11,525,840 B2

13

In an embodiment, a process for making non-nulling gas
velocity measurement apparatus 200 includes: connecting
non-nulling pitot probe 201 in communication with gas
valve 209 by durable, flexible rubber tubing with air-tight
and vibration-resistant connectors; connecting gas valve 209
in communication with reference pressure source 210 by
flexible rubber or plastic tubing with air-tight and vibration
resistant connectors; connecting reference pressure source
210 in communication with differential pressure transducer
213 by flexible rubber or plastic tubing with air-tight and
vibration-resistant connectors; connecting gas valve 209 in
communication with differential pressure transducer 213 by
flexible rubber or plastic tubing with air-tight and vibration-
resistant connectors; connecting solid-state relay 225 in
communication with controller 226 by a 5 vde digital control
line; connecting solid-state relay 225 in communication with
gas valve 209 by 24 vde wiring providing an energizing
Voltage to switch the gas valve 209 state; and connecting
controller 226 to analyzer 215 by USB or ethernet line 214

through communication interface 230. The process also can 2

include connecting analyzer 215 in communication with
differential pressure transducer 213 by insulated copper
twisted-pair wiring.

Inan embodiment, a process for making non-nulling pitot
probe 201 includes providing a stock material for entrant
body tube 203, extensor body tube 204, and aerodynamic
flow head 207, wherein such components can be formed
from a same piece of material or separate pieces; forming
entrant body tube 203, extensor body tube 204, and aero-
dynamic flow head 207 from the stock material by removing
excess material such as by machining that can include using
a lathe or CNC; and forming pressure channel 205 in entrant
body tube 203, extensor body tube 204, and aerodynamic
flow head 207 by drilling.

Non-nulling gas velocity measurement apparatus 200 has
numerous advantageous and unexpected benefits and uses.
In an embodiment, with reference to FIG. 12, FIG. 13, and
FIG. 14, a process for performing non-nulling measurement
of gas velocity parameters includes: receiving, by an ana-
lyzer, after converting measured voltages into scaled pres-
sure units, a zeroth differential pressure signal 214.0, first
differential pressure signal 214.1, a second differential pres-
sure signal 214.2, and third differential pressure signal
214.3: producing a zeroth calibrated pressure CPO from the
zeroth differential pressure signal 214.0, a first calibrated
pressure CP1 from the first differential pressure signal 214.1,
a second calibrated pressure CP2 from the second differen-
tial pressure signal 214.2, and a third calibrated pressure
CP3 from the third differential pressure signal 214.3 by

calibrated measurement corrections specific to each differ- 5

ential pressure sensor; removing a dependence of a reference
gas pressure PO of a reference gas 211 from the zeroth
calibrated pressure CPO, the first calibrated pressure CP1,
the second calibrated pressure CP2, and the third calibrated

pressure CP3 to produce, respectively, a first adjusted pres-

sure API, a second adjusted pressure AP2, and a third
adjusted pressure AP3 by subtracting CP1 from CPO to
obtain the value APL, subtracting CP2 from CPO to obtain
the value AP2, and subtracting CP3 from CP0 to obtain the
value AP3; combining the first adjusted pressure AP1, the
second adjusted pressure AP2, and the third adjusted pres-
sure AP3 to obtain a pseudo-dynamic pressure scalar by
taking the square root of the sum of the squares of AP1, AP2,
and AP3; individually normalizing the first adjusted pressure
API, the second adjusted pressure AP2, and the third
adjusted pressure AP3 with the pscudo-dynamic pressure
scalar to produce, respectively, a first reduced pressure RP1,

&

&

14

asecond reduced pressure RP2, and a third reduced pressure
RP3 by dividing AP1 by the pseudo-dynamic pressure to get
RPI, dividing AP2 by the pseudo-dynamic pressure to get
RP2, dividing AP3 by the pseudo-dynamic pressure to get
RP3; determining a real dynamic pressure from the first
reduced pressure RP1, the second reduced pressure RP2, and
the third reduced pressure RP3 by applying the NN algo-
rithm based on a second degree (or higher) polynomial of
three or more variables using calibration coefficients for
reduced real dynamic pressure to obtain a reduced real
dynamic pressure, wherein the reduced real dynamic pres-
sure is then multiplied by the pseudo-dynamic pressure and
the turbulence factor to get the real dynamic pressure;
determining a yaw angle or a pitch angle of the gas flow
from the first reduced pressure RP1, the second reduced
pressure RP2, and the third reduced pressure RP3; and
determining velocity of gas flow 206 from the real dynamic
pressure by applying the NN algorithm based on a second
degree (or higher) polynomial of three or more variables
using calibration coefficients for either yaw or pitch, respec-
tively to perform non-nulling measurement of gas velocity
parameters.

In an embodiment, performing non-nulling measurement
of gas velocity parameters also includes disposing non-

5 nulling pitot probe 201 in emission stack 235 such that

central entrant aperture 238 of non-nulling pitot probe 201
is aligned with a stack axis of emission stack 235; non-
nulling pitot probe 201 including: aerodynamic flow head
207 including a plurality of entrant apertures 202 that
includes central entrant aperture 238 and a plurality of
peripheral entrant apertures 239 arranged radially from
central entrant aperture 238, peripheral entrant aperture 239
including first peripheral entrant aperture 239.1, second
peripheral entrant aperture 239.2, and third peripheral
entrant aperture 239.3; entrant body tube 203 disposed on
aerodynamic flow head 207; extensor body tube 204 dis-
posed on entrant body tube 203 such that entrant body tube
203 is interposed between aerodynamic flow head 207 and
extensor body tube 204, such that extensor body tube 204 is
arranged at an oblique angle to entrant body tube 203; and
a plurality of pressure channels 205 disposed in aerody-
namic flow head 207, entrant body tube 203, and extensor
body tube 204, such that each entrant aperture 202 is
separately and independently in fluid communication with
one of pressure channels 205, and each pressure channel 205
independently receives and communicates gas flow 206 as
stagnant gas 208 from entrant aperture 202 of which pres-
sure channel 205 is in communication; receiving, by entrant
apertures 202, gas flow 206; producing, by central entrant
aperture 238, a zeroth stagnant gas 208.0 from the gas flow
206; producing, by first peripheral entrant aperture 239.1,
first stagnant gas 208.1 from gas flow 206; producing, by
second peripheral entrant aperture 239.2, second stagnant
gas 208.2 from gas flow 206; producing, by third peripheral
entrant aperture 239.3, third stagnant gas 208.3 from gas
flow 206: and obtaining zeroth differential pressure signal
214.0, first differential pressure signal 214.1, second difler-
ential pressure signal 214.2, and third differential pressure
signal 214.3 respectively from zeroth stagnant gas 208.0,
first stagnant gas 208.1, second stagnant gas 208.2, and third
stagnant gas 208.3

In an embodiment, performing non-nulling measurement
of gas velocity parameters includes disposing non-nulling
pitot probe 201 in emission stack 235 such that central
entrant aperture 238 of non-nulling pitot probe 201 is not
aligned with a stack axis of emission stack 235, non-nulling
pitot probe 201 including: aerodynamic flow head 207



US 11,525,840 B2

25
or by averaging over an integer multiple of the period of the
oscillation (4.5 sec in FIG. 19).

We performed a 16-point flow RATA at a CEPP at high
(16 m/s) and low (7 m/s) loads using a Non-Nulling Method
that we developed for a spherical probe. We compared the
non-nulling flow results with the EPA-approved Method 2F
and obtained mutual agreement of -0.3% at the low load and
0.1% at the high load, respectively. This good agreement
was obtained in a stack with complex flow conditions,
including an asymmetric velocity profile (FIG. 18A), a large
negative yaw-null angle of nearly -30° at the wall (FIG.
18B), significant fluctuations in the axial velocity (FIG.
18A) and in the yaw-null angle (FIG. 19) in certain regions
of the stack cross-section. Because we obtained good results
under these diflicult flow conditions, we expect that the
Non-Nulling Method would perform equally-well or better
in more favorable flow conditions.

An advantage of the Non-Nulling Method includes its
speed and accuracy. Flow RATAs performed using the
Non-Nulling Method are at least as accurate as Method 2F, 2
but can be performed significantly faster. Here, we estimate
that the acquisition of the non-nulling data took /5” of the
time needed for the Method 2F data. (The same setup times
apply to Non-Nulling and Method 2F measurements.) Addi-
tional stack testing is needed to provide a more rigorous 25
assessment of the time savings.

The Non-Nulling Method has 2 diagnostic features that
help ensure its accuracy. First, since the Non-Nulling
Method measured yaw-null angles (8,,,,;°8) consistent with
Method 2F values. one can rotate the probe to fi. and
measure the axial velocity using Method 2F. The Method 2F
measurement can then be used to cross check the non-
nulling result. This hybrid Non-Nulling Method bypasses
the need to search for the yaw-null angle, which is the part
of Method 2F that takes the most time. Second, since the 35
Non-Nulling Method measures the pressure at all 5 ports on
the spherical probe, a significant decrease in the noise levels
of these measurements can be used to help troubleshoot
plugging problems as was done in this example.

In this example, we performed a 3000-point calibration on
each probe used for the non-nulling measurements. Such an
extensive calibration is not practical for routine flow RATAs.

The benefits of automated traverses are less important for
the Non-Nulling Method since its accuracy does not depend
on satisfying the null condition P,,—0. In contrast, Method 4
2F benefits substantially from an automated traverse unit. In
the present work the automated traverse unit was able to null
(i.e., find the angle where P,,~0) despite transient pressure
fluctuations with amplitudes nearly equal to the time-aver-
aged signal and periods ranging between 3 s and 5s. We note 5
that many flow RATAs are performed manually, and such
transients could result in imperfect nulling (.c., P23#0),
which can introduce unquantified errors in the Method 2F
velocity measurements. Currently, the Method 2F protocol
does not specify acceptable values of P; when using nulling 5:
methods.

This example demonstrates that the Non-Nulling Method
is viable for fast, a flow RATA measurements.
Here, we showed the Non-Nulling Method gave analogous
results to EPA-approved Method 2F in a CFFP stack. The 6
‘agreement between the methods was 0.3% at the plant's low
load of 7 m/s and 0.1% agreement at a high load of 16 m/s;
however, the Non-Nulling data acquisition only took 4” the
time of Method 2F data acquisition. Given the harsh flow
conditions for this initial test we are confident the Non- 6!
Nulling Method will give similar (or better) results in less
complex stack flows.

&

26

Example 2. Air-Velocity Calibration System for
Large, Turbulent Flows

NIST’s airspeed calibration service calibrates anemom-
eters as a function of airspeed vector and turbulence inten-
sity (Tu). The vector (sometimes called “3-D”) capability is
particularly important for calibrating multi-hole differential
pressure probes that are often used to comply with regula-
tions limiting pollution emitted by smokestacks of coal-
burning electric power plants. To achieve these capabilities
starting with a conventional “1-D” wind tunnel, we installed
translation/rotation stages and turbulence generators that use
removable grids or flags. The calibration ranges are: yaw
angle +180°; pitch angle +45°; airspeed 1 m/s to 30 mis;
turbulence intensity 0.07<Tus0.25; average data collection
rate: 300 points/hour at fixed Tu. The system’s expanded
uncertainties corresponding to 95% confidence level are:
airspeed 0.0045xIV1+(0.036/IVI)° where IVI is the magni-
tude of the airspeed in m/s; pitch and yaw angles 0.3°; and
turbulence intensity 0.03 Tu. The airspeed working standard
is a Laser Doppler Anemometer that is traced to SI unit of
velocity via a spinning disk. Calibrations are performed in
the 1.5 mx1.2 m rectangular test section of NIST’s wind
tunnel and are corrected for blockage by the instrument
under test and its supports.

‘Accurate measurements of outdoor air flows and of gas
flows in large conduits and stacks are needed by weather
services and diverse industries ive, aircraft,
wind-power, fossil-fueled electricity-generating). These
large flows have spatial and temporal non-uniformities
described as “swirls”, “eddies”, and “turbulence”. Often,
these complicated flows are quantified by using well-char-
acterized anemometers to map (or “velocity profile”) a
cross-section of the flow and then integrating the map. To
accurately characterize anemometers for velocity profiling,
we modernized NIST’s wind tunnel that had been built in
1967. This example describes how a non-nulling pitot probe
and non-nulling gas velocity measurement apparatus
improved the wind tunnel’s hardware, software, and cali-
bration capabilities.

NIST’s updated air-velocity calibration system can char-
acterize pitot tubes, multi-hole differential-pressure probes,
thermal and ultrasonic anemometers, and anemometers that
depend upon rotating cups, vanes, and the like. In this
example, we emphasize the calibration of multi-hole differ-
ential-pressure probes that are often used to comply with
regulations limiting pollution emitted by smokestacks of
coal-burning electric power plants. Calibrated probes can
reduce the cost of velocity-profile-based emission measure-
ments while increasing the accuracy of the maps because the
calibrations now account for the pitch («) and yaw (B)
angles that specify the probe’ orientation with respect to the
average flow velocity vector V and for the turbulence
intensity Tu. The quantity that we call “turbulence intensity”
is the dimensionless ratio Tu=(V,)"7/(V,) where V, is
instantaneous velocity component measured by the laser
Doppler anemometer (LDA) when the LDA is aligned with
the velocity vector V; “( )” denotes a time average (typically
5s) and (V,2)"? is the standard deviation o(V,) measured
by the LDA (after correcting for o(V,) in the absence of
turbulence).

FIG. 20 shows a non-nulling pitot probe, also referred
herein as a multi-hole differential-pressure probe, that was
calibrated. A detailed calibration of such a probe generates
hundreds or thousands of values of P,,(IV1, Tu, ct, f)), where
P, =P, -P, is the pressure difference between port | and port
i of the probe and |V| is the magnitude of the airspeed vector



U.S. Patent Dec. 13, 2022 Sheet 15 of 48 US 11,525,840 B2

Spherical Probe
Test Locations

Outer wall

{b)

FIG. 15


U.S. Patent Dec. 13, 2022 Sheet 1 of 48 US 11,525,840 B2

200
210
21
e
206 208 212
} Z
ats 201 209 213
~~ 227 214~

228

226 215

FIG. 1


U.S. Patent Dec. 13, 2022 Sheet 36 of 48 US 11,525,840 B2

FIG. 36


U.S. Patent Dec. 13, 2022 Sheet 24 of 48 US 11,525,840 B2

SSR

FIG, 24


US 11,525,840 B2
Page 2

comparison of the pressure of the valve-selected gas to a

reference gas pressure.

24 Claims, 48 Drawing Sheets

(51) Int. Cl.
GOIF 1/46 (2006.01)
GOIF 1/34 (2006.01)
(56) References Cited

U.S, PATENT DOCUMENTS
7,212,953 BL* 5/2007 Artiuch
2015/0377662 AL* 12/2015 Ray

201810259380 A1* 9/2018 Birch

* cited by examiner

GOLF 25/15
702/100
GOIP 5/14
73/861.47
AGIB 5/087


U.S. Patent Dec. 13, 2022

Sheet 48 of 48

US 11,525,840 B2

A LL Sphere & LL Sphere
(Plugged) (Corrected)
1.4
Port 1 data
2
Fd
»¥
*
e
$
0.87
A)
0.6 f r t t
00 O02 04 06 O08 1.
xiD
4.4
NN LL
» 1.27 ur LL Sphere
= phere
§ _
~ 1.04 sag
g FP NN HL
x 0.87 NNLL Sphere Custom
Custom
B)
0.6 . t
00 02 04 06 08 1.0
xD

Normalized axial velocity profiles plotted against the dimensionless distance from port | to port 3:

A) & Low Load Spherical profile with plugged probe ports; & same profile recalculated with plugged
data removed.

B) Five profiles not significantly affected by plugging:

1) @ NN LL Custom non-nulling low load,
2) @ NN HL Custom non-nulling high:

3) ® NN HL Sphere non-nulling high load,
4) ® M2F LL Sphere, Method 2F low load
5) & NN LL Sphere, non-nulling, low load

FIG. 48


U.S. Patent Dec. 13, 2022 Sheet 32 of 48 US 11,525,840 B2

O.042

6.090

0.008 b=

6.006 p

6.004

Vins. item / Viva,

0.002

9.000 i i ! i
0.00 0.02 0.04 0.06 0.08 0.40

turbulence intensity

FIG. 32


U.S. Patent Dec. 13, 2022 Sheet 41 of 48 US 11,525,840 B2

Test Probe Repeat
Load Port | Port 2 Port 3 Port 4
No. ‘Tynes Runs
Spherical
1 High 4 Sphere 2 | Sphere 3 | Sphere 5 Sphere 6
Probes
Custom Hemi- Hemi-
2 High 4 Conical 1 Conical 2
Probes sphere | sphere 1
Custom Hemi- Hemi-
3 Low 6 Conical 1 Conical 2
Probes sphere | sphere 1
Spherical
4 Low 6 Sphere 2 | Sphere3 | Sphere5 | Sphere 6
Probes

FIG. 41


U.S. Patent Dec. 13, 2022 Sheet 27 of 48 US 11,525,840 B2

ECCCCC Cen

‘Se EN A a

FIG. 27


U.S. Patent Dec. 13, 2022 Sheet 11 of 48 US 11,525,840 B2

(A) Stack axis
> Saat Fixed height test point
i t Y
: LA
AAA AT
wo tttt | |
boii
poaitod '
1 tpt t {
fo ofptod 1H
poait od i
bobibod i
potibod }
poai tod i
Poti bod {
poaibod '
poaitod '
botibod {
Z pier
L.. 243

(B)

FIG. 11


US 11,525,840 B2

29

the IUT in the wind tunnel while maintaining the test point
12.0+0.3 cm downstream from the sensing volume of the
LDA. The translation/rotation stages are mounted on the
outside wall of the wind tunnel’s test section. (See FIG.
24FIG. 5.) The support tube of a multi-hole probe (or any
other IUT) is clamped to the top stage. The support tube
extends from the stages into the wind tunnel by passing
through a brush that covers a slot in the test section’s wall
With the brush in place, the flow of laboratory air into wind
tunnel has a negligible effect at the test point, as we
confirmed by measurements.

Fach translation and each rotation stage is driven by a
servo motor. Each stage contains an absolute encoder that is
read to determine the stage’s position. All four servos are
controlled by a deterministic PID-based master control unit,
using stage position set-points calculated by the main air-
speed DAC program. The stage positions are based on user
requested values of pitch and yaw, or absolute stage posi-
tions. The main airspeed program then continuously collects
encoder readings to confirm, and correct if necessary, the
true position for each stage. During normal operation, the
main program and master control unit maintains the trans-
lation stages within 0.02 mm (8 encoder steps) of their set
points and the rotation stages are maintained within 0.03°
(15 encoder steps)

As mentioned above, in low turbulence, the airspeed is
nearly independent of location in the YZ plane. Therefore,
the uncertainty of a calibration is not increased if the test
point is displaced a few centimeters from the streamline
passing through the sensing volume of the LDA. This will
occur, as in the lower panel of FIG. 23 when the probe head
is far from the axis of the probe support tube. When the
turbulence-generating grid is in the wind tunnel, the flow
through the YZ plane varies with the 12.7 cm periodicity of
the grid. Therefore, the most accurate calibrations involve
the test point to remain close to the streamline from the
LDA, even as the probe rotates. In a worst-case scenario
(Tu=0.1) a 2 cm uncertainty in Z will lead to a 0.5%
uncertainty in the velocity.

FIG. 25 shows two possible methods of fixing the test
point during a calibration in a turbulent flow. In the upper
panel of FIG. 25, a carbon fiber pipe is clamped to the probe
support tube and to the translation/rotation stages outside the
wind tunnel. The clamp, acting as a spacer, is adjusted until
test point is colinear with the carbon fiber pipe. During a
calibration, the pipe rotates about its symmetry axis; how-
ever, the test point does not translate off the axis. This
arrangement enables calibrations in turbulent flows of cer-
tain probes with shapes that are fixed by regulations.

The lower panel of FIG. 25 shows a diagonal transition 5

pipe connecting an experimental probe to a carbon fiber
pipe. The dimensions of diagonal transition were chosen so
that the test point was colinear with the carbon fiber pipe.
Again, the test point does not translate when the carbon fiber
pipe is rotated.

In response to aerodynamic forces, the test point on a
typical probe is deflected much further than the tight toler-
ances maintained by the translation/rotation stages. We
measured the motion of a test point on a carbon fiber tube by
fastening a pointer to the tube’s end and moving the stages
until the pointer barely obstructed the LDA’s sensing vol-
ume, as detected by the LDA’s burst spectrum analyzer
(BSA). We increased the airspeed to bend the tube and
programmed the stages to return the pointer to the LDA’s
sensing volume. The test point’s deflection was the negative
of the programmed changes in the stages’ positions. Near the
pitch angle a=0, the downstream deflection was

20

&

35

30
AX/cm=0.00099x{(V,)/(n/s)}? in the range 5<(V,)/(m/s)
30 with the standard deviation o=0.013 cm. Under the
same conditions, the tube’s angular deflection was Aa=-
0.00040°x{(V,)/(m/s)}?. These values of AX and Ac. are
20% larger than we estimated from the tube’s dimensions
(unsupported length L=143 em; O.D.=25.4 mm; 1.D.=23.4
mm) and literature data for elastic constants and for the
aerodynamic drag on a cylinder. We concluded that drag
accounts for most of AX and Ac: perhaps small contribu-
tions to AX and Ac result from play in the stages’ bearings
and deflections of the wind tunnel’s walls. If a typical probe
were attached to the tube, the drag might double. If so,
AX~1.7 cm and Ac=0.7° at (V,)=30 m/s. If necessary, we
can use the stages and the BSA to measure and compensate
for AX and Aa.

With regard to traceable low-turbulence airspeed mea-
surements in the wind tunnel, in low turbulence, the cali-
bration chain starts with length and time standards that
determine the diameter and rotation frequency of a spinning
disk. The periphery of the disk carries a 5 m-diameter wire
that simulates tracer particles entrained in flowing air. At a
well-defined, rotation-dependent speed, the wire passes
through the crossed, focused laser beams comprising the
sensing volume of the LDA. Some of the incident laser beam

5 is scattered and doppler shifted by the wire and then detected

by the BSA. NIST has used a protocol that integrates the
weighted LDA velocity measurements and position of the
wire over the entire sensing volume at every velocity. To
conduct the integration, the LDA optical probe was mounted
on an automated traverse system that moved the laser’s
sensing volume relative to the wire.

The response to aerodynamic forces, the same measure-
ments established AY=0 with an estimated uncertainty of
less than 1 mm for pitch angles ranging from -20° to +20°.
These measurements did not establish a tight bound on AZ,
because the translation/rotation stages could not change the
Z coordinate. However, we expect AZ resulting from aero-
dynamic forces will be on the same order as AY.

When LDA is correctly aligned and the spinning disk is
operating correctly, a plot of LDA-indicated velocity as a
function of position has a well-defined rectangular shape
that has no irregularities in the sensing volume. If the
sensing volume has small departures from symmetry, the
calibration results may be irregular. Poorly aligned LDA
beams can generate sensing volumes that contain major
defects such as asymmetry or non-parallel interference
fringes. If such defects are present, attempts to align the
spinning disk and the LDA may produce erratic, unrepeat-
able, and puzzling results such as changes in the sign of the
derivative of the LDA reading with respect to sensing
volume position.

The ratio (disk speed)/(LDA speed) is independent of the
airspeed in the range 0.2 m/s to 30 m/s within the k=2
expanded relative uncertainty U,(ratio)=0.0041.

The wind tunnel was seeded with droplets of di-ethyl-
hexyl-sebacate (DEHS, CAS #122-62-3). When droplets
pass through the sensing volume of the LDA, they scatter
and doppler-shift the laser light. The mean droplet diameter
is 1.1 um with a standard deviation of 0.1 jm. The droplets
are small enough that their velocity approaches that of the air
flow with a time constant about 2 jis. The droplets were
generated by an atomizer.

FIG. 26 demonstrates long-term stability of the LDA
calibration relative to the spinning disk standard. Earlier
LDA calibration data, spanning the years 1997 to 2013, are
consistent with FIG. 26, albeit with larger uncertainties. We
reduced the uncertainties by improving: (1) speed controls



US 11,525,840 B2

1
NON-NULLING GAS VELOCITY
MEASUREMENT APPARATUS AND
PERFORMING NON-NULLING
MEASUREMENT OF GAS VELOCITY
PARAMETERS:

CROSS REFERENCE TO RELATED
APPLICATIONS

‘The application claims priority to U.S. Provisional Patent
Application Ser. No. 63/011,004 filed Apr. 16, 2020, the
disclosure of which is incorporated herein by reference in its
entirety.

STATEMENT REGARDING FEDERALLY
SPONSORED RESEARCH,

This invention was made with United States Government

support from the National Institute of Standards and Tech- 5,

nology (NIST), an agency of the United States Department
of Commerce. The Government has certain rights in the
invention. Licensing inquiries may be directed to the Tech-
nology Partnerships Office, NIST, Gaithersburg, Md..
20899; voice (301) 975-2573; email tpo@nist.gov; refer-
ence NIST Docket Number 20-040US1.

BRIEF DESCRIPTION

Disclosed is a non-nulling gas velocity measurement
apparatus for non-nulling measurement of gas velocity
parameters, the non-nulling gas velocity measurement appa-
ratus comprising: a non-nulling pitot probe comprising: an
aerodynamic flow head comprising a plurality of entrant
apertures that comprises a central entrant aperture and a
plurality of peripheral entrant aperture arranged radially
from the central entrant aperture, such that the entrant
apertures receive a gas flow from a gas source; an entrant
body tube disposed on the aerodynamic flow head; an
extensor body tube disposed on the entrant body tube such
that the entrant body tube is interposed between the aero-
dynamic flow head and the extensor body tube. such that
extensor body tube is arranged at an oblique angle to the
entrant body tube; and a plurality of pressure channels
disposed in the aerodynamic flow head, the entrant body
tube, and the extensor body tube, such that each entrant
aperture is separately and independently in fluid communi-
cation with one of the pressure channels, and each pressure

channel independently receives and communicates the gas_5

flow as stagnant gas from the entrant aperture of which the
pressure channel is in communication; and a plurality of gas
valves such that each gas valve: is in fluid communication
with a different entrant aperture of the non-nulling pitot

probe via a different pressure channel; receives stagnant gas

from the respective entrant aperture; receives a reference
ives a valve control signal; and produces a valve-
selected gas based on the valve control signal, the valve-
selected gas consisting essentially of the reference gas or the
stagnant gas; and a plurality of differential pressure trans-
ducers, such that each differential pressure transducer: is
separately and independently in fluid communication with a
different gas valve, and that gas valve communicates the
valve-selected gas to the differential pressure transducer;
receives the valve-selected gas from the gas valve; receives
the reference gas at a reference gas pressure; compares a
pressure of valve-selected gas to the pressure of the refer-

&

2

ence gas; and produces a differential pressure signal from
comparison of the pressure of the valve-selected gas to the
reference gas pressure.

Disclosed is a process for performing non-nulling mea-
surement of gas velocity parameters, the process compris-
ing: receiving, by an analyzer, a zeroth differential pressure
signal, first differential pressure signal, a second differential
pressure signal, and third differential pressure signal; pro-
ducing a zeroth calibrated pressure from the zeroth differ-
ential pressure signal, a first calibrated pressure from the first
differential pressure signal, a second calibrated pressure
from the second differential pressure signal, and a third
calibrated pressure from the third differential pressure sig-
nal; removing a dependence of a reference gas pressure of a
reference gas from the zeroth calibrated pressure, the first
calibrated pressure, the second calibrated pressure, and the
third calibrated pressure to produce, respectively, a first
adjusted pressure, a second adjusted pressure, and a third
adjusted pressure; combining the first adjusted pressure, the
second adjusted pressure, and the third adjusted pressure to
obtain a pseudo-dynamic pressure scalar; individually nor-
malizing the first adjusted pressure, the second adjusted
pressure, and the third adjusted pressure with the pseudo-
dynamic pressure scalar to produce, respectively, a first

5 reduced pressure, a second reduced pressure, and a third

reduced pressure; determining a real dynamic pressure from
the first reduced pressure, the second reduced pressure, and
the third reduced pressure; determining a yaw angle or a
pitch angle of the gas flow from the first reduced pressure,
the second reduced pressure, and the third reduced pressure;
and determining velocity of the gas flow from the real
dynamic pressure to perform non-nulling measurement of
gas velocity parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

The following description cannot be considered limiting
in any way. With reference to the accompanying drawings,
like elements are numbered alike.

FIG. 1 shows a non-nulling gas velocity measurement
apparatu

FIG. 2
apparatus;

FIG. 3 shows a plan view of a non-nulling pitot probe in
panel A and, in panel B, a cross-section along line C-C of the
non-nulling pitot probe in panel

FIG. 4 shows, in panel A, a side view of the non-nulling
pitot probe shown in B of FIG. 3; in panel B, a cross-section
along line A-A of the non-nulling pitot probe shown in panel
A; and in panel B, a cross-section along line B-B of the
non-nulling pitot probe in panel A;

FIG. 5 shows a non-nulling pitot probe including a
hemispherical aerodynamic flow head;

FIG. 6 shows a non-nulling pitot probe including a conical
aerodynamic flow head;

FIG. 7 shows a hemispherical aerodynamic flow head of
a non-nulling pitot probe in panel A; a conical aerodynamic
flow head of a non-nulling pitot probe in panel B; a plan
view of an aerodynamic flow head of a non-nulling pitot
probe that has four entrant apertures in panel C; a plan view
of an aerodynamic flow head of a non-nulling pitot probe
that has five entrant apertures in panel D; and a plan view of
an aerodynamic flow head of a non-nulling pitot probe that
has eight entrant apertures in panel E;

FIG. 8 shows a gas valve in a reference flow configuration
in panel A; and a gas valve in a stagnant flow configuration
in panel B;

ows a non-nulling gas velocity measurement



US 11,525,840 B2

5

FIG. 38 shows hemispherical probe F, and F, calibration
parameters plotted versus pitch angle. The circles are data
points taken at 11 different velocities and the solid line is a
curve fitted to the points;

FIG. 39 shows conical probe F, and F, calibration param-
eters plotted versus pitch angle. The circles are data points
taken at the 11 different velocities and the solid line is a
curve fitted to the points;

FIG. 40 shows a cross-section of stack showing probes,
port numbers and 16 traverse points located at centroids of
equal stack area;

FIG. 41 shows Test matrix for 16-point flow RATAs
performed in CFPP stack.

FIG. 42 shows Flow RATA for spherical probes at high
load: Plots of normalized axial velocity versus A) x/D, and
B) yD.

FIG. 43 shows normalized flow velocities determined by
Method 2F and by the non-nulling method for the 4 repeated
runs measured with spherical probe at high load (16 m/s);

FIG. 44 shows yaw-null profiles determined using
Method 2F (circles) and non-nulling with B=0° (triangles)
along A) port 1 to port 3, and B) port 2 to port 4;

FIG. 45 shows sine-like oscillations of yaw-null angle
during 10 s Method 2F data collection, wherein a Spherical
probe was oriented at the yaw-null angle, and f'',,,,., was
determined every 0.1 s using the non-nulling algorithm;

FIG. 46 shows Pitch angle profile for Test #1 according to
Example 3;

FIG. 47 shows standard deviation of pressure signals (o,,)
at n=1 to 5 pressure ports on the spherical probe head,
wherein values of o,, below the dashed line indicate that port
n was plugged; and

FIG. 48 shows normalized axial velocity profiles plotted
against the dimensionless distance from port 1 to port 3: A)
Open triangles indicate low load spherical profile with
plugged probe ports; closed triangles indicate the same
profile recalculated with plugged data removed. B) Five
profiles not significantly affected by plugging.

DETAILED DESCRIPTION.

A detailed description of one or more embodiments is
presented herein by way of exemplification and not limita-
tion.

‘Accurately quantifying hazardous emissions from indus-
trial emission stacks involves accurate gas velocity mea-
surements made at various points on a cross-section of the
emission stack. Conventional probes for such measurement
involve a time-consuming nulling procedure, wherein the

conventional probe is rotated about its axis at each point tos

find a yaw component of velocity at that point. It should be
appreciated that non-nulling gas velocity measurement
apparatus 200 and process for performing non-nulling mea-
surement of gas velocity parameters that reduces time and

cost of such measurements as compared with conventional

probes. Non-nulling pitot probe 201 measures the velocity
more accurately than conventional probes, including con-
ventional probes sanctioned by the US Environmental Pro-
tection Agency (EPA). A diameter of pressure-sensing holes
in non-nulling pitot probe 201, referred to as entrant aper-
tures 202, can be three times to six times larger than
pressure-sensing holes in conventional EPA-sanctioned
3-dimensional probes, and the size increase in non-nulling
pitot probe 201 mitigates plugging of the holes that occur
when flue gas has water droplets or other particles. Con-
ventional EPA-sanctioned probes are calibrated in laminar
wind tunnel flows and are used in turbulent stack flows

20

4

&

6

without accounting for turbulence intensity, but this over-
estimates stack emissions by 5%, e.g., when the turbulence
intensity is 10%. Non-nulling gas velocity measurement
apparatus 200 and process for performing non-nulling mea-
surement of gas velocity parameters determine the turbu-
lence intensity of the flue gas velocity and correct the
measurements for the turbulence intensity.

Non-nulling gas velocity measurement apparatus 200
performs non-nulling measurement of gas velocity param-
eters of gas flow 206. In an embodiment, with reference to
FIG. 1, non-nulling gas velocity measurement apparatus 200
includes: non-nulling pitot probe 201 that receives gas flow
206 and produces stagnant gas 208 from gas flow 206;
reference pressure source 210 that produces reference gas
211; controller 226 that produces valve control signal 227
and control signal 228; gas valve 209 in fluid communica-
tion with non-nulling pitot probe 201 and reference pressure
source 210 and in electrical communication with controller
226 and that receives stagnant gas 208 from non-nulling
pitot probe 201, receives reference gas 211 from reference
pressure source 210, receives valve control signal 227 from
controller 226, and produces valve-selected gas 212 that
includes reference gas 211 or stagnant gas 208 based on
valve control signal 227; differential pressure transducer 213

5 in fluid communication with reference pressure source 210

and gas valve 209 and that produces differential pressure
signal 214 by comparing valve-selected gas 212 with refer-
ence gas 211; and analyzer 215 in electrical communication
with differential pressure transducer 213 and controller 226
and that receives differential pressure signal 214 from dif-
ferential pressure transducer 213 and control signal 228
from controller 226 and produces gas velocity parameters
216 from analysis of differential pressure signal 214 in view
of control signal 228.

In an embodiment, with reference to FIG. 1, FIG. 2, FIG.
3, and FIG. 4, non-nulling gas velocity measurement appa-
ratus 200 includes: a non-nulling pitot probe 201 including:
aerodynamic flow head 207 including a plurality of entrant
apertures 202 that includes central entrant aperture 238 and
a plurality of peripheral entrant aperture 239 arranged radi-
ally from central entrant aperture 238, such that entrant
apertures 202 receive gas flow 206 from a gas source;
entrant body tube 203 disposed on aerodynamic flow head
207; extensor body tube 204 disposed on entrant body tube
203 such that entrant body tube 203 is interposed between
aerodynamic flow head 207 and extensor body tube 204,
such that extensor body tube 204 is arranged at an oblique
angle to entrant body tube 203; and a plurality of pressure
channels 205 disposed in aerodynamic flow head 207,
entrant body tube 203, and extensor body tube 204, such that
each entrant aperture 202 is separately and independently in
fluid communication with one of pressure channels 205, and
each pressure channel 205 independently receives and com-
municates gas flow 206 as stagnant gas 208 from entrant
aperture 202 of which pressure channel 205 is in commu-
nication; and a plurality of gas valves 209 such that each gas
valve 209: is in fluid communication with a di
aperture 202 of non-nulling pitot probe 201 via a different
pressure channel 205; receives stagnant gas 208 from the
respective entrant aperture 202; receives reference gas 211;
receives valve control signal 227; and produces valve-
selected gas 212 based on valve control signal 227, valve-
selected gas 212 consisting essentially of reference gas 211
or stagnant gas 208; and a plurality of differential pressure
transducers 213, such that each differential pressure trans-
ducer 213: is separately and independently in fluid commu-
nication with a different gas valve 209, and that gas valve



U.S. Patent

Dec. 13, 2022 Sheet 14 of 48

301: receiving, by an analyzer, differential pressure signal 214.0, differential pressure signal 214.1,
differential pressure signal 214.2, and differential pressure signal 214.3

302: producing zeroth calibrated pressure CPO from differential pressure signal 214.0, first
calibrated pressure CPI from differential pressure signal 214.1, second calibrated pressure CP2
from differential pressure signal 214.2, and third calibrated pressure CP3 from differential pressure
signal 2143

303: removing a dependence of a pressure PO of a reference gas from zeroth calibrated pressure
CPO, first calibrated pressure CP1, second calibrated pressure CP2, and third calibrated pressure
CP3 to produce, respectively, first adjusted pressure API, second adjusted pressure AP2, and third
adjusted pressure AP3
doy pair-wise subtracting CPi from CPO // to provide for off-axis velocity vector

304: combining first adjusted pressure API, second adjusted pressure AP2, and third adjusted
pressure AP3 to obtain a pseudo-dynamic pressure scalar

US 11,525,840 B2

uatly normalizing first adjusted pressure API, second adjusted pressure AP2, and third
sre AP3 with the pscudo-dynamic pressure scalar to produce, respectively, first
reduced pressure RP, second reduced pressure RP2, and thitd reduced pressure RP3

306: determining — real
dynamic pressure from first
reduced pressure RP], second
reduced pressure RP2, and
third reduced pressure RP3

307: determining a yaw angle or
a pitch angle of the gas flow
from first reduced pressure RP1,
second reduced pressure RP2,
and third reduced pressure RP3

3 disposing non-nulling
pitot_ probe 201 in emission
stack 235 such that central
entrant aperture 218 of non-
nulling pitot probe 201 is not
aligned with the stack axis

: determining velocity

310: correcting the real

dynamic pressure with the non-
axial orientation factor

312: determining a non-axial
orientation factor for the non-
axial angle

FIG. 14