U.S. patent number 3,895,233 [Application Number 05/445,588] was granted by the patent office on 1975-07-15 for gas analyzer.
This patent grant is currently assigned to Bailey Meter Company. Invention is credited to Richard H. Boll, John E. Tozier.
United States Patent |
3,895,233 |
Boll , et al. |
July 15, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Gas analyzer
Abstract
A gas analyzer for determining the concentration of a
constituent gas in a mixture of gases carrying solid particulate
matter in suspension. The analyzer includes a first and a second
radiation source which emit radiation of different wave lengths
having different absorption coefficients for the constituent gas
but virtually identical absorption coefficients for the solid
particulate matter. Radiation pulses from the first and second
sources are alternately passed through the gas mixture to a
phototransducer generating output signals which input to a
computing circuit, the output signal from which is in substantially
linear proportion to the constituent gas concentration and which is
unaffected by the solid particulate matter suspended in the mixture
of gases. A monitoring phototransducer also receiving the radiation
pulses from the radiation sources generates output signals which
input to the computing circuit to compensate for deterioration and
other changes in the outputs of the radiation sources.
Inventors: |
Boll; Richard H. (Alliance,
OH), Tozier; John E. (Solon, OH) |
Assignee: |
Bailey Meter Company
(Wickliffe, OH)
|
Family
ID: |
26972219 |
Appl.
No.: |
05/445,588 |
Filed: |
February 25, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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301209 |
Oct 26, 1972 |
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Current U.S.
Class: |
250/373; 250/573;
356/437; 250/432R; 356/435; 356/441 |
Current CPC
Class: |
G01N
21/314 (20130101); G01N 21/534 (20130101); G01N
2021/151 (20130101) |
Current International
Class: |
G01N
21/53 (20060101); G01N 21/47 (20060101); G01N
21/31 (20060101); G01n 021/26 (); G01n
023/12 () |
Field of
Search: |
;250/373,573,432,339,345
;356/206,207,76 ;73/23 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Grigsby; T. N.
Attorney, Agent or Firm: Luhrs; John F.
Parent Case Text
This is a continuation-in-part of application Ser. No. 301,209
filed Oct. 26, 1972, now abandoned.
Claims
We claim:
1. A gas analyzer for determining the concentration of a
constituent gas in a mixture of gases containing interfering
material comprising, a first and a second radiation source which
emit radiation of different wave lengths having different
absorption coefficients for the constituent gas and virtually
identical absorption coefficients for said interfering material,
means generating electric control pulses having a predetermined
time period, a first means responsive to said control pulses
generating a first pulse burst having a time duration substantially
less than said time period, means responsive to the pulses in said
first burst energizing one of said radiation sources to produce
radiation pulses, a second means responsive to said control pulses
for sequentially generating a second pulse burst having a time
duration substantially the same as said first burst, means
responsive to the pulses in said second burst energizing the other
of said radiation sources to produce radiation pulses, means
passing said radiation pulses through said mixture of gases to a
first phototransducer producing signals proportional to the
radiation received from said first and second sources, and a
computing circuit responsive to said signals generating an output
signal corresponding to the concentration of the constituent
gas.
2. A gas analyzer according to claim 1 further including, a second
phototransducer receiving said radiation pulses and producing
signals corresponding to the magnitude thereof, said computing
circuit responsive to said last named signals and modifying said
output signal in accordance therewith.
3. A gas analyzer as set forth in claim 2 further including a
beam-splitter located proximate to said radiation sources whereby
radiation pulses therefrom are split, part being transmitted to
said first phototransducer and part being simultaeously transmitted
to said second phototransducer.
4. A gas analyzer as set forth in claim 2 further including a first
narrow band pass filter disposed between said radiation sources and
said first phototransducer to block radiation of undesirable wave
lengths from impinging on said first phototransducer and a second
narrow band pass filter disposed between said radiation sources and
said second phototransducer to block radiation of undesirable wave
lengths from impinging on said second phototransducer.
5. A gas analyzer as set forth in claim 1 wherein said constituent
gas is sulphur dioxide, and said first radiation source is a
hollow-cathode lamp whose cathode is formed from the group
consisting of iridium and magnesium and said second radiation
source is a hollow-cathode lamp whose cathode is formed from the
group consisting of gallium, tin and lead.
6. A gas analyzer as set forth in claim 1 further including a first
means responsive to the pulses in said first burst generating a
signal controling the response of said computing circuit to the
signals proportional to the radiation received from said first
radiation source and a second means responsive to the pulses in
said second burst controling the response of said computing circuit
to the signals proportional to the radiation received from said
second radiation source.
7. A gas analyzer as set forth in claim 1 wherein said first and
second means generate output signals having a predetermined time
duration less than the time duration of the pulses in said first
and second pulse bursts respectively.
8. A gas analyzer as set forth in claim 1 further including means
continuously energizing said first and second radiation source
below their firing potential and wherein said means responsive to
said control pulses increases the potential across said sources
above the firing potential.
Description
BACKGROUND OF THE INVENTION
This invention relates to gas analyzers generally and in particular
to a gas analyzer for determining the sulphur dioxide concentration
in waste gases carrying solid particulate matter in suspension such
as discharged to the atmosphere from industrial processes and
fossil fuel fired furnaces or produced in industrial processes,
such as gases produced in sulphuric acid manufacture, pulp
manufacture and the like. Heretofor the concentration of SO.sub.2
and other deleterious constituents in waste gases has received
little attention, emphasis being placed on gas analyses which are
indicative of the completeness or efficiency of combustion or of
the process. Emphasis, however, has recently been placed on
instruments which will continuously analyze for the concentration
of deleterious constituent gases in waste gases. Of major
importance among such deleterious constituent gases is sulphur
dioxide.
Sulphur dioxide analyzers presently available are predominantly of
the sampling type wherein a sample of the waste gases is
intermittently or continuously withdrawn, cleaned of solid
particulate matter and then analyzed by one means or another. Such
analyzers are unsatisfactory for industrial purposes in that their
use involves drawing the sample through a sampling line to the
analyzer. Such a sampling line ordinarily must be heated to prevent
water vapor or sulphuric acid condensation and it must be
periodically purged to prevent plugging by solid particulate
matter. Furthermore, care must be taken in selecting the materials
of the sampling line lest it act as a catalyst to convert SO.sub.2
to S0.sub.3 and thus give an erroneous analysis. Furthermore,
deposits of particulate matter in the sampling line can act as a
catalyst for conversion of S0.sub.2 to S0.sub.3. Such instruments
draw the sample from a particular point in the flowing stream of
gases and are therefor subject to error due to stratification of
the S0.sub.2 within the stream. Finally it may be said that such
instruments are deficient for industrial use in that they give
history rather than news. There is an unavoidable time lag in
drawing the sample through a sample line, so that what is exhibited
is not the S0.sub.2 concentration presently existing but that which
existed some time previously.
SUMMARY OF THE INVENTION In its broader aspects the present
invention is directed to a gas analyzer for determining the
concentration of a constituent gas in a mixture of gases carrying
solid particulate matter in suspension. More particularly it is
directed to a gas analyzer for determining the concentration of
S0.sub.2 in a mixture of gases carrying solid particulate matter in
suspension.
IN THE DRAWINGS
FIG. 1 is a schematic illustration showing an in-situ application
of our gas analyzer.
FIG. 2 is a cross-sectional view taken along the line 2--2 in the
direction of the arrows in FIG. 1.
FIG. 3 is a schematic illustration showing in block diagram one
form of computing circuit.
FIG. 4 is a schematic illustration showing in block diagram a
modification of a part of the computing circuit shown in FIG.
3.
FIGS. 5A, 5B, 5C and 6A, 6B, 6C are graphs useful in explaining the
operation of the modified computing circuit shown in FIG. 4.
DETAILED DESCRIPTION
For purposes of description we have chosen to illustrate and
describe our invention as applied to the in-situ determination of
S0.sub.2 in waste gases flowing through a duct. However, our
invention has a wide variety of other applications and may be used,
for example, to determine the S0.sub.2 concentration in gases
regardless of whether or not the analysis is made in-situ. Our
invention may also be used to determine the S0.sub.2 concentration
in gases produced for use in industrial processes to aid in
maximizing the efficiency of production or to aid in maintaining
the S0.sub.2 concentration at, or below, or above a predetermined
value.
Referring to FIG. 1 there is shown a duct 2 through which waste
gases flow in the direction of the arrow. Mounted transversely in
the duct is a light pipe 4 which may be of the type illustrated and
described in copending application Ser. No. 348,876 filed in the
U.S. Pat. Office on April 9, 1973. As shown in FIG. 1, taken in
conjunction with FIG. 2, the light pipe is provided with slots 6 of
predetermined length and width through which the waste gases
pass.
Mounted on one end of the light pipe 4 is a housing indicated at 8
in which is mounted a hollow-cathode lamp 10 which may be from the
group comprising iridium and magnesium, and of that group
preferably magnesium. Also mounted in the housing 8 is a
hollow-cathode lamp 12 which may be from the group comprising
gallium, tin or lead, and of that group preferably gallium.
A beam-splitter 14 is disposed within the housing 8 so that
radiation emitted from the lamps 10 and 12 is split, part being
transmitted through the light pipe 4 to a phototransducer 16 and
the remainder to a phototransducer 18. A lens, such as shown
schematically at 20 may be mounted within the light pipe 4 to
collimate the light from lamps 10 and 12. The lamp 10 when
energized emits, predominatly, radiation having a wave length of
approximately 2852 Angstroms whereas the lamp 12, when energized,
emits radiation of approximately 2874 Angstroms. Both lamps when
energized emit some radiation of other undesirable wave lengths. To
block this undersirable radiation from impinging on phototransducer
18 there is mounted within the housing 8 a narrow band pass filter
22 which peaks at 2,850A.+-.50A and has a half band width of 300A
or less. A substantially identical filter 24 is disposed in the
light pipe 4 to block any stray light and the radiation of
undesirable wavelengths from the lamps 10 and 12 impinging on
phototransducer 16. Windows such as shown at 25 may be mounted
within the light pipe 4 to isolate the waste gases and which may be
maintained free of deposits of particulate matter by maintaining a
flow of bleed air through ports such as shown at 26.
The lamps 10 and 12 are connected by lines 28 and 30 respectively
to a power supply and control unit 32 which alternately energizes
the lamps for short time increments whereby radiation pulses are
transmitted sequentially from lamps 10 and 12 to phototransducers
16 and 18. As the lamps 10 nd 12 are energized impulses are
simultaneously sent along lines 34, 36 from the power supply 32
indicating the lamp fired.
In operation, the power supply and control unit 32 energizes,
cyclically, for a short increment of time, the gallium lamp 12
causing it to emit a radiation pulse having a wavelength of
approximately 2,874A and simultaneously emits a signal along line
34 indicating that this lamp is energized. The radiation pulse from
the lamp 12 impinges on the beam-splitter 14 and is both
transmitted through the beam-splitter to the phototransducer 16 and
reflected by the beam-splitter 14 to the phototransducer 18. During
alternate increments of time, the power supply and control unit 32
energizes the magnesium lamp 10 causing it to emit a radiation
pulse having a wavelength of approximately 2,852A and
simultaneously emits a signal along line 36 indicating that this
lamp was energized. The radiation pulse from lamp 10 impinges on
the beam-splitter 14 and is both transmitted therethrough to the
phototransducer 18 and reflected thereby to the phototransducer 16.
In the foregoing description reference has been made specifically
to gallium and magnesium lamps. It is apparent, however, that
either or both lamps may be replaced by other members of their
respective groups.
Radiation traveling through the light pipe 4 will be absorbed to
some extent by the particulate matter suspended in the flowing
stream of waste gases as well as the S0.sub.2 present therein, with
the unabsorbed portion being received by the phototransducer 16
which produces a signal along line 38 proportional to the intensity
of the unabsorbed radiation. The phototransducer 18 produces a
signal proportional to the radiation to which it is exposed which
is transmitted along line 40. Since there is no absorptive media
between the lamps 10, 12 and phototransducer 18, changes in the
output signal therefrom are indicative of deterioration or changes
in the outputs of the lamps.
Referring now to FIG. 3 there is shown in block diagram one type of
computing circuit whereby an output signal corresponding to
S0.sub.2 concentration in the flowing stream of waste gases can be
generated. It should be understood however that the computing
circuit shown is for illustrative purposes only, it being evident
that any computing circuit either analog or digital may be
incorporated in our invention which functions substantially in
accordance with the following:
In the presence of both a gaseous absorbent and particulates, the
attenuation of monochromatic light is described by: ##EQU1## where:
I = intensity of light reaching phototransducer 16, watts
I.sub.o = intensity of light reaching phototransducer 16 in the
absence of absorbing gas and particulate material, watts
k = absorption coefficient of absorbing gas, cm.sup..sup.-1
C.sub.s = concentration of absorbing gas, mol fraction
L = light pathlength through gas, cm
.phi. = extinction coefficient for particulate material, cm.sup.2
/gm
C.sub.p = concentration of particulate material, gm/cm.sup.3
Where light of two different wavelengths is concerned, for example
that coming from lamps 10 and 12, respectively, this equation
applies separately for both wavelengths: ##EQU2## where the a and b
subscripts merely denote one or the other of the two wavelengths.
If the wavelengths are very close together, .phi..sub.a will be
very nearly equal to .phi..sub.b no matter what the nature of the
particulates. For example, as a practical matter, if one wavelength
is 1 percent than the other, then the two particulate extinction
coefficients will differ by at most 4 percent, even under the most
adverse conditions. Thus, as a practical matter, .phi..sub.a =
.phi..sub.b and equations (2) and (3) may be solved simultaneously
to give: ##EQU3## However, as practically, it is difficult to
measure I.sub.ao and I.sub.bo ; I.sub.am and I.sub.bm that are
proportional thereto may be substituted therefor:
I.sub.ao = .alpha. I.sub.am ; I.sub.bo = .beta. I.sub.bm 5
where .alpha. and .beta. are proportionality constants whose values
depend upon the characteristics of beam-splitter 14. The
concentration of absorbing gas is, then, given in terms of I.sub.am
and I.sub.bm by: ##EQU4## The values of I.sub.am and I.sub.bm are
measured by phototransducer 18. The term ln .alpha..beta. is merely
a constant, or a zero adjustment, that is inputed into the
computing circuit so as to get zero output for zero concentration
of the absorbing gas.
As shown in FIG. 3 the signals generated by phototransducer 16
input to a logarithmic amplifier 46, whereas the signals generated
by phototransducer 18 input to a logarithmic amplifier 48. The
output signals from logarithmic amplifier 46 are applied along line
50 to storage registers 52 and 54. Registers 52 and 54 are also
connected to the power supply and control unit through lines 36 and
34 respectively. The registers 52 and 54 are connected through
lines 56, 58 respectively to a difference amplifier 60 connected to
an algebraic summing amplifier 62 by way of line 64. The output
signals from logarithmic amplifier 48 are applied along a line 66
to storage registers 68 and 70. Registers 68 and 70 are also
connected to the power supply and control unit 32 through lines 36
and 34 respectively. The registers 68 and 70 connected through
lines 72 and 74 respectively to a difference amplifier 76 connected
to algebraic summing amplifier 62 by way of line 78. The output
signal from algebraic summing amplifier 62 may be transmitted to an
appropriate indicating, recording and/or controlling device such as
shown at 80.
The algebraic summing amplifier 62 may be provided with a
calibration input 82 which may be used, to properly adjust for the
constant ln .alpha./.beta. of equation (6).
In operation, the computing circuit, as shown in FIG. 3, whenever
the power supply and control unit 32 energizes the lamp 10 the
signal indicating such actuation is transmitted along line 36 to
the registers 52, 68 causing them to receive the signals supplied
from the phototransducers 16 and 18 respectively. Similarly when
the power supply actuates the lamp 12 the signal indicating such
actuation is transmitted along line 34 to the registers 54, 70
causing them to receive the signals then supplied from the
phototransducers 16 and 18 respectively. Thus after one cycle of
operation, the logarithms of values of the unabsorbed radiation
from lamps 10 and 12 are stored in registers 52, 54 and the values
of the logarithms of the radiation emitted from lamps 10 and 12 are
stored in registers 68, 70. These values are the values of ln
I.sub.a, ln I.sub.b, ln I.sub.am and ln I.sub.bm in equation (6)
for C.sub.s.
The registers 52, 54 provide the inputs to the difference amplifier
60 while the registers 68, 70 provide the inputs to the difference
amplifier 76. The outputs of the amplifiers 60, 76 provide the
inputs to the summing amplifier 62. The amplifier 62 thus provides
an output along line 84 that is virtually linearly proportional to
the concentration of S0.sub.2 in the waste gases passing through
the duct or stack 2 and which is substantially independent of
particulate matter concentration.
From the foregoing, it is obvious that choosing the wavelengths of
the hollow-cathode lamps 10 and 12 sufficiently close together will
eliminate interference from particulate matter, so that a correct
result is obtained regardless of the amount of particulate matter.
Moreover, it will also be recognized that the same kind of
compensation is afforded for interfering gases that happen to have
the same absorption coefficient for both wavelengths. This is,
indeed, the case with ozone, which is slightly absorbed at
wavelengths in the order of 2,850A, but with substantially the same
coefficient for the radiations from both lamps. It is also obvious
that gases that do not absorb appreciably in this wavelength
region, for example, water vapor, carbon dioxide, oxygen, nitrogen,
etc., will have no effect upon the accuracy of the analyzer. As
heretofor described the power supply and control unit 32 cyclically
energizes, for short increments of time, the lamp 12, and during
alternate increments of time, the lamp 10. Such supervision by the
power supply and control unit 32 is graphically illustrated by
trace 95 in FIG. 5A. During a complete cycle of operation the unit
32 produces a positive square wave for one-half cycle having a
desired time duration and a negative square wave during the
following one-half cycle having the same time duration. Directly or
indirectly, through conventional circuit components, the positive
wave energizes the lamp 12. Simultaneously the unit generates a
control signal which is transmitted along line 34 to storage
registers 54 and 70. During alternate half cycles the negative wave
energizes the lamp 10 and the unit simultaneously generates a
control signal transmitted along line 36 to storage registers 52
and 68. Thus the lamps 10 and 12 have a 50 percent duty cycle each
being energized one-half the time, regardless of the length of a
complete cycle of operation.
In FIG. 4 there is shown in block diagram a modification of the
circuit shown in FIG. 3 which, while retaining all of the desirable
features of the latter, may be adjusted to give maximum lamp life
by further reducing the lamp cycle duty, or by operating the lamps
intermittently. In the latter, the lamps are energized by a
periodic burst of electrical pulses, each burst of sufficient time
duration to provide sample averaging, thus compensating for
momentary excursions in system parameters, such as a puff of smoke,
followed by a dead time period of length consistent with the
exigencies of a particular application. As an order of magnitude
our invention comprehends operating the lamps at an overall 1% duty
cycle or even less, as we have found that the life of the lamps is
increased in inverse proportion to the reduction in duty cycle.
Further we have found that in most industrial processes the
composition of the gases changes relatively slowly, so that the
reduction in duty cycle does not adversely affect accuracy.
Referring to FIG. 4 the square wave described in reference to FIG.
5A is transmitted along line 84A from the power supply and control
unit 32 to a pulse shaping and firing unit 86A which at the start
of each positive cycle, as shown by trace 96 in FIG. 5B generates a
pulse which is transmitted along line 87A to the base of a
transistor 88A. As evident, the unit 86A may be designed to
generate a pulse of desired time duration which may be, for
example, in the order of 1 percent of a complete cycle of
operation.
The square wave from the power supply and control unit 32 is also
transmitted along line 84B to a delay unit 89 and thence to a pulse
shaping and firing unit 86B, identical with unit 86A, which
following the time delay established by unit 89, as shown by trace
97 in FIG. 5C, usually corresponding to the time duration of the
pulse generated in unit 86A, generates a similar pulse which is
transmitted along line 87B to the base of a transistor 88B.
Except for the duration of the pulses generated in units 86A and
86B, the lamps 10 and 12 are preferably maintained energized below
the threshold potential necessary to fire, by a divider network,
which in the case of the lamp 12 comprises a resistor 90A connected
to a positive voltage source and a resistor 91A connected to
ground. A similar divider network comprising resistors 90B and 91B
is provided for the lamp 10.
Transistors 88A and 88B are normally non-conducting, however, upon
receiving a pulse from unit 86A or 86B respectively are rendered
conducting, shorting out the resistor 91A or 91B as the case may
be, thereby firing the lamp 12 or 10 to provide the intermittant
and sequential operation heretofore described.
In the modification shown in FIG. 4 the control signals indicating
the firing of the lamp 10 or the lamp 12 are not transmitted
directly from the power supply and control unit 32, but are derived
from the pulses from the unit 86A or the unit 86B. In the case of
lamp 10, the pulses transmitted along line 87B are transmitted to a
pulse shaping unit 92B which generates a control signal,
transmitted along the line 36, to the storage registers 52 and 68.
Similarly, in the case of lamp 12 the shaped pulses transmitted
along line 87A are transmitted to a pulse shaping unit 92A which
generates a control signal transmitted along line 34 to the storage
registers 54 and 70.
The pulse shaping units 92A and 92B may, depending upon the firing
characteristics of lamps 12 and 10 and circuit factors, be arranged
to generate control signals having a time duration the same as, or
shorter than, the time duration of the pulses generated in units
86A and 86B. We have found, however, that the control signals
should preferably have a time duration which is a fraction of the
time duration of the pulses. As an order of magnitude, we have
found it desirable that if the pulses generated in units 86A and
86B have a time duration of 0.003 seconds, the control signals
should have a time duration of approximately 0.0003 seconds at a
selected point in the time span of the pulses, thus introducing
into the storage registers 52, 54, 68 and 70 output signals from
phototransducers 16 and 18 having maximum integrity and eliminating
spurious signal components due to the firing characteristics of
lamps 10 and 12 and other factors which may be conveniently
referred to as system noise.
As illustrated graphically in FIG. 6A, the power supply and control
unit 32 may be arranged to generate momentary pulses 98 of any
desired time period T. Each pulse so generated, transmitted along
lines 84A and 84B, triggers the pulse shaping and firing units 86A
and 86B to generate a burst of pulses 99 as shown in FIG. 6B, and a
burst of pulses 100 as shown in FIG. 6C respectively. Each burst
has a total time duration t. During a burst of pulses each lamp may
be considered as having a 50 percent duty cycle, however, as the
total time duration t and the number of pulses in a burst may be
adjusted to the minimum required to produce an average sample
during each sampling period and which is followed by a dead time
period which may be, as an order of magnitude one hundred times or
more in time duration than the sampling period, the overall duty
cycle of lamps 10 and 12 is thus minimized, maximizing lamp
life.
While as an aid to understanding our invention we have at times in
the foregoing description used specific figures, it should be
recognized that these are by way of example only and not by way of
limitation.
* * * * *