Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for
detecting internal leakage between streams in fluid processing equipment.
Various methods have been proposed for detecting leaks between
internal streams in fluid processing systems such as heat exchangers,
incinerators, etc. Generally, such conventional leak detection operations
require that all or a part of the processing system be shut down before the
leak detection procedure can be undertaken. Some leak detection procedures
employ radioactive substances, necessitating the use of specially trained
personnel and elaborate safety precautions. Although radioactive tracer
leak detection operates successfully, the inconvenience associated with the
use of radioactive materials has provided an incentive to seek alternative,
superior methods for detecting leaks in processing equipment.
Sulfur hexafluoride has been suggested for use as a tracer in
detecting leaks in buried gas pipelines. A quantity of sulfur hexafluoride
is introduced into the pipeline, and the soil adjacent to the pipeline is
tested for the presence of sulfur hexafluoride by digging test holes and
sampling the air in the holes. Several types of apparatus for detecting
sulfur hexafluoride in very small quantities in other gases such as air are
commercially available, most if not all of them including some form of
electron capture detection cell for measuring the amount of sulfur hexa-
fluoride in a gaseous atmosphere. Other electron-capturing gases such as
organic chlorides and organic fluorides have also been used for the same
purpose.
SUMMARY OF THE INVENTION
In an embodiment, the present invention relates to apparatus for
detecting leakage through a partition separating a portion of a first path
fram a portion of a second path in a fluid processing system, while opera-
tion of the system is continued, the apparatus comprising in combination:
means for introducing a known quantity of sulfur hexafluoride into fluid
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flowing in the first path upstream of the partition; means for continuously
removing a sample of fluid flowing in the second path at a locus downstream
of the partition; means for removing normally liquid components from the
sample; means for testing the sample to determine the presence of sulfur
hexafluoride therein; and means for indicating the amount of sulfur hexa-
fluoride in the sample. Preferably the apparatus as defined above further
includes means for introducing a known quantity of sulfur hexafluoride into
the second path at a locus upstream of the partition.
According to another aspect of the present invention there is
provided in a fluid processing system wherein fluids flow in a first path
and a second path, with a partition separating a portion of said first path
from a portion of said second path, the method for detecting leakage through
said partition while continuing operation of said system, which comprises
the steps of:
(a) introducing sulfur hexafluoride into said first path upstream of
said partition;
(b) withdrawing a sample of fluid in said second path at a sampling
locus downstream of said partition;
(c) testing said sample for the presence of sulfur hexafluoride; and
(d) determining the period of time after step (a) until the presence
of sulfur hexafluoride is detected in step (c).
In addition to the steps mentioned above, the method employed
according to the present invention preferably includes the further steps,
carried out prior to step (a), of:
(1) introducing sulfur hexafluoride into the second path upstream of
the partition;
(2) continuously sampling fluid at the sampling locus;
(3) testing the resulting sample for the presence of sulfur hexa-
fluoride; and
(4) measuring the period of time after step ~1) until the presence of
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sulfur hexafluoride is detected in step ~3), for estimating the period of
time required for sulfur hexafluoride introduced in step (a) to reach the
sampling locus if an opening exists between the first and second paths
through the partition.
One preferred type of fluids processing equipment in which the
present invention can be employed is heat exchangers.
DESCRIPTION OF THE DRAWING
- The attached Figure sho~s a schematic representation of preferred
embodiment of the apparatus of the present invention and illustrates its
use according to the method of the invention in detecting a leak in a heat
exchanger employed in a fluid hydrocarbon processing system.
DETAILED DESCRIPTION OF THE INVENTION
The present invention can best be understood by reference to the
attached drawing. It will be understood that the invention is not thereby
limited to the specific embodiment shown, and that the scope of the inven-
tion includes the alternatives, modifications and equivalents of the depict-
ed embodiment which are encompassed in the appended claims.
Turning to the drawing, there is shown a hydrocarbon conversion
system 1, into which a fluid hydrocarbon-containing feed is introduced by
way of a first path in the system via a conduit 3. The feed stream passes
into a heat exchanger 5, and is partially heated by passing it through a
plurality of heat exchange tubes 6 in the heat exchanger 5. Feed is with-
drawn from the exchanger 5 and passed through a conduit 7 into a furnace 9.
The feed is heated to the desired reaction temperature in the furnace 9 and
is then passed through a conduit 11 into a hydrocarbon conversion reactor
13. After the hydrocarbons have been processed in the conversion reactor
13, which may contain a conversion catalyst, a product stream is removed
into a second path in the processing system through a conduit 15 and is
passed into the exchanger 5. The relatively hot reacter effluent fluid is
0 then heat exchanged with the relatively cold feed from the conduit 3 by
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flowing the hotter fluid around the heat exchange tubes 6 within the
exchanger 5. The heat exchange tubes 6 act as a partition, separating the
cooler fluid in the first path in the tubes 6 from the hotter fluid in the
second path around the tubes 6 in the exchanger 5. After the heat exchange
procedure has been carried out, the partially cooled product stream is then
removed from the system for further treatment via a conduit 17.
It will be apparent that the heat exchanger 5 is an integral part
of the processing system 1, and that shutting down the heat exchanger 5
would necessitate shutting down the whole system if it were necessary to
remove the heat exchanger 5 from service in order to check for leakage
therein. Unfortunately, in a typical hydrocarbon conversion system of the
type shown, leakage of fluid from the feed stream into the product stream
results in contamination of the product stream with unprocessed, unconverted
hydrocarbons. Thus, for example, lower-octane feed components in the hydro-
carbon feed stream can contaminate a higher-octane product stream, adversely
affecting the quality of the product. In this type of operation, when
analysis of the product stream shows that the product quality is lower than
is to be expected, the cause of the drop in product quality may be found in
one or more of several sources, e.g., catalyst failure, feed contamination,
control failure, etc., in addition to the possibility of a leak in the heat
exchanger 5 from the feed stream into the product stream. Thus, it is
desirable to be able to determine if leakage is present from the feed stream
in the tubes 6 into the product stream in the exchanger 5, and , if so, what
the size of leak is. It is also desirable to determine whether leakage has
occurred without shutting down the whole system, as a complete shutdown has
serious adverse economic consequences.
According to the invention, apparatus is provided for detecting
leakage through the heat exchange tubes 6 from the fluid flowing into the
tubes 6 into fluid flowing around the tubes 6 within the exchanger 5. Means
are provided for introducing a known quantity of sulfur hexafluoride into
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the feed flowing in the conduit 3, such as a cylinder 18 filled with a
measured amount of sulfur hexafluoride under a pressure higher than the
pressure in the conduit 3. The cylinder 18 is connected via conduit 19 to
the conduit 3, with a valve 20 operatively connected into the conduit 19.
The cylinder 18 includes valves 21 and 22 at either end. The cylinder 18 is
connected by a conduit 23 to an inert gas cylinder 24, which has a valve 25
connected therein. The inert gas cylinder is used for introducing the
sulfur hexafluoride into the line 3, as more fully described below. The
cylinder 24 contains an inert gas such as nitrogen, helium or argon at a
pressure higher than the pressure in the conduit 3. Means are also provided
for continuously removing a sample of the product fluids flowing within the
conduit 17, such as a conduit 26 attached to the conduit 17 with a valve 27
operatively connected into the conduit 26. When the valve 27 is opened,
fluids are conducted through the conduit 26 to means which are provided for
removing normally liquid components from the sample, such as a cooler 29,
connected by a conduit 31 to a liquid-vapor separator vessel 33. Liquid
components gravity-separating in the vessel 33 are removed through a conduit
35 and may be discarded. The conduit 35 has a valve 36 connected therein,
so that a liquid level seal can be maintained in the vessel 33 to prevent
gas from flowing through the conduit 35. The gaseous sample is then passed
through a conduit 37 to means provided for testing the sample to determine
the presence of sulfur hexafluoride therein, such as an electron-capture
measurement cell and indicator 39, which is connected to an indicator and
recorder 41, for visually indicating and recording the relative concentration
of sulfur hexafluoride in the sample. The use of the sulfur hexafluoride
detector and the recorder allows the amount of sulfur hexafluoride in a
sample to be determined on an absolute basis, after the instruments have been
calibrated in a manner to be described hereinafter. For calibrating the
testing and indicating apparatus 39 and 41, means are provided for introduc-
ing a known quantity of sulfur hexafluoride into the fluid flowing within the
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conduit 15 at a point upstream of the heat exchanger 5, such as a cylinder43 which is filled with a measured amoun~ of sulfur hexafluoride under a
pressure higher than the pressure of the fluids flowing in the conduit 15.
The cylinder 43 is connected to the conduit 15 by way of a conduit 45, with
a valve 47 opPratively connected into the conduit 45. The cylinder 43 in-
cludes valves 49 and 51 therein. The cylinder 43 is connected by a conduit
53 to an inert gas cylinder 55 which has a valve 57 connected therein. The
cylinder 55 contains an inert gas at a pressure higher than the pressure in
the conduit 15.
In operation of the apparatus according to a preferred embodiment
o the method, prior to carrying out tests with sulfur hexafluoride, it is
advantageous to line out the readings from the testing device 39 to establish
a base line reading on the recorder 41 in the absence of any sulfur hexa-
fluoride. The valve 27 is adjusted to permit a sample of the fluid in the
conduit 17 to flow continuously through the conduit 26 at the desired rate.
Condensable components in the sample are continuously removed therefrom by
cooling the sample in the cooler 29 and separating liquids in the gravity
separator vessel 33. A level of liquid is maintained in the bottom of the
separator vessel 33 by adjusting the valve 36 on the line 35. This prevents
2Q the gaseous sample from being lost through the conduit 35. The continuously
~lowing gaseous sample is then conducted to the electron-capture measurement
and indicating device 39, in wh~ch the sample is continuously tested for the
presence of sulfur hexa1uoride, with the result being continuously read out
on the recorder 41 for visual inspection.
According to the invention, the response of the instruments 39 and
41 to a measured concentration of sulfur hexafluoride in the fluids in the
conduit 17 is preferably determined. The fluid in the condult 17 ls continu-
ously sampled at any convenient rate. The valves 57 and 51 are opened,
allowing the high pressure inert gas in the cylinder 55 to flow through the
conduit 53 into the sulfur hexafluoride cylinder 43. The valves 47 and 49
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are then opened for a period of time sufficient for the inert gas to carry
substantially all the sulfur hexafluoride from the cylinder 43 through the
conduit 45 into the conduit 15, allowing a measured quantity of sulfur
hexafluoride to flow in a pulse through the conduit 45, the conduit 15,
and the heat exchanger 5 into the conduit 17, while the fluid in the conduit
17 is being continuously sampled as indicated above. The response of the
sulfur hexafluoride measurement instrument and indicator 39 in the recorder
41 to the pulse of sulfur hexafluoride in the calibration sample, is then
determined, and the amplitude of the response of the devices to the
calibration pulse of sulfur hexafluoride of known size allows establishment
of a quantitative standard for determining the size of any leak thereafter
detected by the amount of sulfur hexafluoride in the sample. The use of
the pulsed calibrating sample supplied from the cylinder 43 is also useful
for estimating the period of time required for sulfur hexafluoride to
travel in the fluids flowing through the system from the exchanger 5 through
the conduit 17 to the sampling point at the conduit 26. Such a determination
is desirable in cases, such as in the embodiment depicted, in which some of
sulfur hexafluoride from the leak-testing sulfur hexafluoride pulse (which
is discharged from the cylinder 24 through the conduit 3) may reach the
fluid to bs sampled for sulfur hexafluoride (if it is not decomposed in the
system) after a certain period of time, generally much longer than the
period of time required for sulfur hexafluoride to reach the detection
apparatus via a leak. This may occur via feed-effluent heat exchange,
effluent recycle, etc.
After the pulse of sulfur hexafluoride has been passed into the
conduit 15, the valves 47, 49, 51 and 57 are closed, halting the flow of
inert gas from cylinder 55.
After calibration and response period estimation have preferably
been carried out, the test for leakage in the heat exchange tubes 6 is
commenced. The fluid in the conduit 17 is sampled, preferably continuously,
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at a convenient rate. The valves 25 and 22 are opened, allowing the high
pressure inert gas in the cylinder 24 to flow through the conduit 23 into
the sulfur hexafluoride cylinder 18. The valves 20 and 21 are then opened
for a period of time sufficient for the inert gas to carry all the sulfur
hexafluoride from the cylinder 18 through the conduit 19 into the conduit
3, introducing a predetermined amount of sulfur hexafluoride into the con-
duit 3. After the pulse of sulfur hexafluoride has been passed into the
conduit 3, the valves 20, 21, 22 and 25 are closed, halting the flow of
inert gas from the cylinder 24. The sulfur hexafluoride pulse is carried
through the conduit 21 and the heat exchange tubes 6. If a leak exists
in the tubes 6, some sulfur hexafluoride will pass through the tubes 6,
enter the hotter fluid, and exit the heat exchanger 5 into the conduit 17.
A sample of this sulfur hexafluoride-containing fluid then passes through
the conduit 25. After preferably being cooled and having liquid components
removed therefrom, it is tested in the electron-capture measurement and
indicator instrument 39, with the amount of sulfur hexafluoride in the
sample being shown by the size of the response which can be read out on
the recorder 41.
A preferred embodiment of the method and apparatus of the invention
having been described, a variety of equivalents, modifications, and
alternatives within the spirit of the present invention and within the
scope of the following claims will be apparent to those skilled in the art.
