Note: Descriptions are shown in the official language in which they were submitted.
llal62~7
The present invention relates to gas sampling
systems generally and particularly to closed loop gas sampl-
ing systems which return the sample to the area from which
the sample was taken.
The control of various processes such as steel
making as well as combustion control systems is dependent
upon an accurate monitoring and analyzing of process gases
such as combustion flue gases. These gases are normally
analyzed for concentrations of various elements such as
oxygen, carbon monoxide, carbon dioxide, sulfur dioxide, and
: other combustibles. Usually, individual analyzers are
provided to measure the oxygen concentration as well as the
combustibles concentration in the process gases.
The mentioned individual sampling systems usually
had their own indicators for providing an indication of a
plugged sample inlet line. Plugging occurs due to the dirty
environment of the flue and such plugging must be taken into
consideration to insure the continuous accurate operation
of the analyzing system. The usual type of such flow in-
dicator has been a pressure switch operating on negative
pressure that is tied into the sampling system. Thus, as
the inlet line is plugged up to a predetermined amount,
negative pressure increases in the system eventually causing
the switch to close a contact and indicate the malfunction.
The use of the aforementioned individual sampling
systems for oxygen and combustibles resulted in a great
duplication of parts and required more mounting space and
installation time to be adapted to the duct. What was needed
was a single sampling system which would check for both
oxygen and combustibles level as well as providing a single
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indication of proper flow through the sample line.
The present invention relates to an indicator
assembly for providing an indication of a blocked inlet
line of a gas analyzing assembly comprising:
a source of gas to be analyzed;
an inlet line connected to said gas source to
convey said gas therethrough;
a gas analyzing assembly connected to said
inlet line;
a supply air powered first aspirator assembly
connected to said gas analyzing assembly to draw sample gas
from said inlet line through said gas analyzing assembly;
a second aspirator assembly connected to said
inlet line to draw sample gas through itself under normal
operating conditions and to draw supply air from said
first aspirator assemrbly through said gas analyzing assembly
- whenever said inlet line is blocked a predetermined amount.
The present invention solves the previously dis-
cussed problems of the prior art sampling systems as well
as others by providing a single gas sampling system which
is able to provide an indication of not only the oxygen
content in the duct but also the combustibles level or
content therein. To accomplish this, an oxygen detector as
well as a combustibles detector are connected to a common
sample inlet line communicating with the gases in the duct.
The flue gases from the duct are individually drawn from
this common sample line through both the oxygen detector
and the combustibles detector by individual aspirator units
connected to the oxygen detector and the combustibles detec-
tor which have their outlets exhausting into a common out-
let line which feeds the sampled gases back into the duct.
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In another embodiment of the present invention,
the oxygen detector is utilized to provide an indication of
a blocked condition in the sample inlet. To accomplish
this, the two mentioned aspirators are sized so as to have
the one aspirator overpower the second aspirator associated
with the oxygen detector whenever the common sample line is
blocked. The overpowering of the oxygen analyzer associated
aspirator causes supply air to flow through the oxygen
detector and the oxygen detector to then indicate an
abnormally high oxygen level. This pins the indicator which
signal may then be utilized to provide an alarm condition
indicative of a blocked sample inlet.
From the foregoing it will be seen that one
aspect of the present invention is to provide a sampling
system which will establish a control signal indicative of
a blocked sample l,ine condition.
These and other aspects of the present invention
will be more clearly understood after a review of the
following description of the preferred embodiment of the
invention when considered in conjunction with the accompanying
drawings.
Fig. 1 is a schematic representation of the
sampling system within which the preferred embodiment is
used showing sample gas flow under normal conditions.
Fig. 2 is the schematic of Fig. 1 showing the
modified flow of system gas during a blocked sample inlet
condition.
Fig. 3 is a graph indicating the flow characteristics
of the pair of aspirators of the sampling system of Fig. 1.
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Referring now to the drawings it will be understood
that the showings therein are for the purpose of illustrating a
preferred embodiment of the present invention and the invention
is not limited thereto.
As may be best seen with reference to Fig. 1, a sampli~g
system 10 is mounted to a duct or boiler wall 12 to draw process
gas from the inside of a duct 14 and to exhaust it back thereto
after analyzing the process gas for both oxygen and combustibles.
The process gas sample is taken from an inlet line 16 extending
through the duct wall 12 and having a filter 18 mounted to the
end thereof. The analyzed sample is then exhausted back into the
duct 14 through an outlet line 20 extending through the duct wall
12 downstream of the inlet line 16. This relative positioning
of the inlet line 16 and the outlet line 20 is done to insure
that the exhaust will not interfere with the inlet of a
representative sample gas.
The gas sampling system 10 includes an oxygen detector 22
and a combustibles detector 24 both of which are connected to
the inlet line 16 by respective oxygen detector inlet line 26 and
combustibles detector inlet line 28. The sample gas from the
mentioned inlet lines 16, 26, 28 is drawn through the oxygen
detector 22 by an aspirator 30 while the sample is drawn
through the combustibles detector 24`by an aspirator 32. The
aspirators 30 and 32 are powered by supply air from a common
supply air line 34 which has parallel trunk lines 36 and 38
supplying aspirators 32 and 30 respectively. The outputs of the
aspirators 30 and 32 are exhausted to the exhaust line 20 by
respective output lines 40 and 42 communicating with the
exhaust line 20.
The aspirators 30 and 32 as well as the various inlet
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and outlet lines associated therewith are all enclosed in a
heated block 44 which has an electric heater mounted therein
(not shown) to maintain the temperature at approximately 400F
well above the dewpoint of any flue gases or supply air to
prevent condensation thereof. The supply air line 34 has a
section 46 formed sinusoidally within the heated block 44 to delay
the transport time of supply air to the aspirators to thereby
insure that any supply air provided to the aspirators 30 and 32
will be sufficiently heated to prevent condensation. It should
be noted that the inlet line 28 supplying gas to the combustibles
detector 24 is similarly formed in a sinusoidal manner. The
oxygen detector 22 is enclosed in a second heated block 48 mounted
proximate to the heated block 44 and having a separate auxiliary
heater (not shown) which maintains the oxygen detector at approxi-
mately 1500F, the operating temperature of a Zirconium Oxide
oxygen detector. The combustibles detector 24 is enclosed in yet
another separate heated block 50 which also has its own separate
heater (not shown) which maintains the combustibles detector at a
temperature of approximately 800F.
Turning next to the particular operation and description
of the oxygen detector 22, it will be understood that the oxygen
detector 22 is a well-known heated Zirconium Oxide oxygen detector
which is sufficently described in U.S. Patent No. 3,960,500
entitled "GAS SAMPLING ANALYZING SYSTEM". The reader is referred
thereto for further details of such oxygen detector. In operation,
the aspirator 30 draws the flue sample from the duct 14 into
itself through a pair of parallel lines 52 and 54 having the
oxygen detector 22 located in line 52. The operation of the
oxygen detector 22 in such a closed loop system and the function
of the parallel line 54 is more than adequately described in the
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mentioned U.S. Patent No. 3,960,500 and will not be recited
herein for the sake of conciseness and readability.
The combustibles detector 24 may be any one of a number
of well-known combustible detectors. An example of one such
combustible detector is described in U.S. Patent No. 4,063,898,
entitled "COMBUSTIBLE GASES DETECTOR". The sample from the inlet
line 16 is drawn through the combustibles detector 24 by virtue
of aspirator 32 drawing the sample from inlet line 16 through
combustibles inlet line 28 and into the combustibles detector 24.
It will be noted that the combustibles detector 24 dilutes the
sample from line 28 with an equal amount of supply air from
sample line 34 prior to entering the combination into the
combustibles detector 24. To insure that the dilution is in the
1 to 1 ratio of supply air to sample gas a flow regulator 56 is
mounted in the supply air line 34 prior to the combustibles inlet
line 28. The aspirator 32 then exhausts the sample and the
dilution air along with its own supply air into exhaust line 42
which ultimately feeds into exhaust liné 20 and back into the
duct 14.
Turning now particularly to Fig. 1, it may be seen
that the operation of the sampling system under normal operating
conditions is as follows: the aspirator 30 as well as the
aspirator 32 establish a negative pressure at their inlet lines
58 and 60 respectively which induces a flow of sample gas to
inlet lines 26, 28 causing the sample to flow through the oxygen
analyzer 22 and the combustibles detector 24. A bypass line 54
is also operated by the aspirator 30 to induce a greater quantity
of sample from the inlet line 16 to thereby speed the reaction
time of the oxygen detector 22 to a change in any conditions of the
duct 14. Supply air is drawn through the regulator 56 and mixed
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with the sample gas from inlet line 28 into the combustibles
detector 24.
As may be seen from Fig. 3, the aspirators 30 and 32 are
sized so as to have aspirator 32 more efficient than the aspirator
30. The aspirator 32 is capable of developing a significantly
higher negative pressure at its sample inlet 60 than the aspirator
30. This sizing becomes critical in providing a blocked inlet 16
indication in the sampling system 10. Referring now with particu-
lar emphasis to Figs. 2 and 3, it will be seen that when the inlet
line 16 becomes blocked due to a clogging of the filter 18 or the
lodging of foreign particles in the actual inlet line 16, gas flow
through the inlet line 16 will drop down to a level as indicated .
at point A on the chart of Fig. 3.to a point where there will be
insufficient gas flow to supply both the aspirators 30 and 32. ¦
At this point, the aspirator 30 supplying the oxygen detector 22
:lwill have insufficient negative pressure capability to draw any of
jthe sample gas through itself and only the hi~h negative pressure I ¦
aspirator 32 will be able to draw any sample through itself. To
compensate for the lack of sample gas, the aspirator 32 will now
start drawing supply air from the aspirator 30 in a reverse di-
rection from that shown in Fig. 1 through the oxygen detector 22,
the bypass line 54, and into the combustibles detector supply
line 28. Thus, we can see that now instead of sample duct gases
being drawn through the oxygen detector.22, supply air originat-
ing at line 38 to feed the operation of the aspirator 30 will
now be drawn through the sample inlet 58 of the aspirator 30 by
the aspirator 32 and through the oxygen detector 22. Since the
supply air is abnormally high in oxygen when compared to the
oxygen content of the duct 14 gas, the oxygen detector 22 will
start indicating this abnormally high oxygen content and will
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cause the voltmeter 62 which is calibrated to provide an indi-
cation of the oxygen content to be pinned or go off-scale.
This off-scale reading of the indicator 62 can be used to pro-
vide a control signal indicative of a blocked inlet line 16
which can sound an alarm to indicate that the line must be
cleaned either by replacing the filter 18 or backblowing
supply air through it to dislodge any particles that may have
become entrained in the inlet line 16.
From the foregoing it can be seen that the Applicants
have provided a gas sampling system which indicates not only
the oxygen content in a flue, but also the combustibles content
therein. This sampling system furthermore utilizes the oxygen
detector to establish a control signal indicative of a blocked
inlet line 16 whenever the oxygen detector 22 goes out of range.
Certain modifications and improvements will occur to
those skilled in the art upon reading this specification. As
an example, individual exhaust lines could be run directly into
the duct rather than a single manifolded exhaust line. It will
be understood that all such improvements and modifications have
been deleted herein for the sake of conciseness and readability
but are intended to be within the scope of the appended claim.
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