Note: Descriptions are shown in the official language in which they were submitted.
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APPARATUS AND PROVES S
FOR DISPENSING AN ABRASIVE INTO A GAS STREAM
Background of the Invention
Field of the Invention
The invention relates to the dispensing of
particles into a gas stream.
Description of the Prior Art Apparatus
Apparatus comprising a gas supply line,
means for controlling the extent of the stream of
gas, a supply container for particles, such as
abrasives, dispensing means coupled to the gas
supply line, and a discharge line for discharging
the gas stream laden with particles is generally
known in the art. Such apparatus is disclosed in
Dutch Patent Application No. 7708990, and is
designed for cleaning and/or decoying the interior
of pipelines, tubes or other conduits. For this
purpose, the stream of gas laden with abrasive is
introduced into the pipeline to be cleaned by means
of a suitable injection head, the abrasive impinging
on the pipe wall to be cleaned at a high radial
velocity owing to turbulential and vertical
components in the stream of gas. For the cleaning
of pipes, use can be made of abrasive materials
having sharp edges, such as sand and steel grit, but
abrasive or cleaning materials in the form of steel
balls, i.e. steel shot, or other cleaning materials,
can also be employed.
It has been found that the decoying and
cleaning of such pipelines having a relatively large
diameter, as to be found in hydrocarbon furnaces in
refineries and the like, can be achieved in a
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particularly effective way, it being possible for
such pipelines to be internally stripped of every
kind of deposits. It has also been found, however,
that the cleaning of pipelines having a small
diameter, i.e. on the order of one or a few
centimeters, is often impossible or impractical,
using available apparatus because the small amount
of abrasive or other cleaning materials that must be
supplied to the stream of gas for the cleaning of
these pipelines cannot be properly dosed using the
available apparatus. In fact, in prior art
apparatus, the abrasive is dosed by means of a plate
provided with a suitable aperture that would have to
be so small, for the quantity of abrasive required
for cleaning thin, i.e. small diameter, pipelines
and tubes, that the aperture would immediately
become clogged with abrasive.
Small diameter pipelines and tubes,
however, are very widely used as, for example, in
existing heat exchangers in refineries and
processing industries. In these heat exchanger
pipes, carbonaceous, corrosion and/or chemical
precipitate layers can be deposited in the course of
time, adversely affecting heat trays or and material
flow. Accordingly, such layers must be removed
after some period of use. Pipe banks in heat
exchangers have hitherto been cleaned typically by
means of water under high pressure. One
disadvantage of this technique is that cleaning with
water generally leaves residues of the layers in the
tubes. Another disadvantage is that the water
issues with great force from the end of the pipe
bank, said water being greatly contaminated, and
causing a major water burden.
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It is, accordingly, an object of the
present invention to provide an apparatus and
process for dispensing an abrasive or other cleaning
materials into a stream of gas, whereby it is
possible to accurately dose small quantities of
abrasive into the gas stream.
It is another object of the invention to
provide an improved apparatus and process for
metering a controlled amount of abrasive or other
cleaning material into a propelling gas stream.
Summary of the Invention
For such purposes, the invention provides
an apparatus and process in which the dispensing
means may comprise a conveyor means to which an
abrasive or other particles can be supplied from a
container, the conveyor means being capable of
transporting the abrasive to a supply orifice in the
gas supply line. A pressure equalizing conduit is
positioned between the interior of the container and
the gas supply line, the equalizing conduit being
coupled with the gas supply line at a point
intermediate the propelling gas control means and
the particle supply orifice.
Brief Description of the Drawings
The invention will be described
hereinbelow, by way of example, with reference to
the accompanying drawings relating to a particular
embodiment of the invention in which:
Fig. 1 shows a diagrammatic elevation Al
view of an embodiment of the dispensing apparatus
according to the invention;
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Fig. 2 shows a cross-sectional view of a
detail of Fig. l; and
Fig. 3 is an elevation Al view taken on line
III-III of Fig. 2.
Detailed Description of the Invention
It has been found that, by controlling the
rate of circulation of a conveyor belt, it is
possible to supply even the smallest possible
desired quantity of abrasive or other particles to a
propelling gas stream in a highly accurate,
reproducible manner. In cleaning the piping in a
heat exchanger or in other cleaning applications, a
stream of gas is subject to a varying
counter-pressure in the discharge conduit of the
apparatus for every pipe or conduit being cleaned.
It is necessary to provide means for ensuring that,
nevertheless, the correct quantity of abrasive or
other particles can be supplied to the gas stream
regardless of every possible counter-pressure. For
this purpose, there is provided a direct,
self-compensating, equalizing conduit coupled, on
the one hand, to the interior of the particle supply
container and, on the other hand, to the gas supply
line at a point intermediate the propelling gas
control means and the supply orifice for the
abrasive or other particles. A portion of the gas
from the total gas stream flows in the equalizing
conduit, which gas is thus supplied to the
container. Inasmuch as the pressure at the point
where the equalizing conduit is coupled to the gas
supply line will be a little higher than the
pressure at the point of the supply orifice for the
abrasive or other particles, a minor gas stream is
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generated from the particle supply container to the
supply orifice This minor gas stream ensures that,
irrespective of the counter-pressure experienced,
abrasive or other particles can be continually
supplied to the propelling stream of gas.
In Fig. 1, a gas supply line, designated by
the numeral I is connected to a source of gas (not
shown) for supplying a suitable propelling gas, e.g.
nitrogen or air, stream for the abrasives or other
cleaning particles. Provided in gas supply line 1
are, successively, a shut-off valve 2, a control
valve 3/ and aperture plate 4. Furthermore, a
pressure gauge 5 is coupled to the line intermediate
control valve 3 and the aperture plate 4. The
aperture plate 4 is dimensioned so that a critical
pressure is generated, so that the position of
control valve 3 is proportional to the velocity of
the gas. Connected to line 1 at some distance from
aperture 4 is a particle supply inlet 6 for the
supply of abrasive or other particles. This supply
inlet preferably tapers towards line 1.
A particle container 7 for abrasive or
other cleaning materials is closed at the top in a
gas-tight manner, by means of a cover. Container 7
desirably has a funnel-shaped bottom to optimize
flow of the abrasive Connected to the bottom of
the container is supply conduit 8, which terminates
a short distance above a conveyor belt 9, which is
preferably channel-shaped. The shape of conveyor
belt 9, and the shape of the mouth of the supply
conduit, are best shown in Figures 2 and 3, which
illustrate details of the area where the supply
conduit terminates at the conveyor belt.
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Conveyor belt 9 may be connected in the
usual way with a prime mover, such as a motor, for
movement over two pulleys 10 and 11. In operation,
belt 9 circulates in a clock-wise direction, as
viewed in Fig. 1. The right-hand pulley 11 is so
positioned that the point where the abrasive or
other particles lying on the belt leaves the same
under the influence of gravity is located over the
center of supply orifice 6 in gas line 1. The
supply conduit 8, conveyor belt 9 and pulleys 10 and
11 are all housed in a gas-tight housing coupled at
the top with particle container 7 and at the bottom
terminating in the, preferably tapered, supply
orifice 6.
In order to ensure that, at any
counter-pressure encountered at the effluent end of
line 1, the desired quantity of abrasive or other
particles is supplied to the gas stream, there is
provided an equalizing conduit 13. Conduit 13 is
connected, on the one hand, with the interior of
said container 7, preferably at the top thereof,
and, on the other hand, with the gas supply line 1,
at a location intermediate the supply orifice 6 and
the aperture plate 4. Equalizing conduit 13
preferably terminates in gas line 1 with a mouth
located in the direction of flow of the gas, so that
the conduit captures a little of the gas supplied.
As a result, via the equalizing conduit, a pressure
can be generated within container 7, said pressure
being a little higher than the pressure in conduit 1
adjacent to supply orifice 6. The result is a
positive pressure for the introduction of the
abrasive or other particles into the stream of gas,
independent of the counter-pressure experienced by
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the gas. Those skilled in the art will appreciate
that the counter-pressure is determined by the
diameter and the degree of fouling of the pipe being
cleaned. The particle supply orifice 6 preferably
also terminates in supply line 1 via a mouth
extending at an angle, whereby the abrasive or other
particles are essentially supplied in the direction
of flow of the gas. Vortices adjacent to the
abrasive supply inlet orifice are thereby
substantially prevented.
In order that abrasive or other particles
may be supplied from the container to the conveyor
belt without any problems even at low velocities of
the conveyor belt, it has been determined that it is
beneficial-to bevel the end of supply conduit 8
relative to the supporting surface of the conveyor
belt, as is clearly shown in Figures 2 and 3.
It has been found that, by means of the
dispensing apparatus according to the invention,
even small quantities of abrasive or other particles
can be supplied to a stream of gas in a highly
accurate manner. The quantity of abrasive to be
dispensed depends on the gas throughput, and can be
controlled by adapting the velocity of the conveyor
belt. The propelling gas laden with abrasive or
other particles is supplied via a discharge conduit,
not shown, to a suitable injection nozzle.
It has also been found that by means of
the apparatus and process of the invention, pipes
having a diameter ranging between 0.5 and 7.5 cm can
be cleaned in an extremely effective manner without
there being any residual carbonaceous, corrosion
and/or precipitate layers in the pipes.
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Although the invention has been described
in the foregoing with reference to an exemplary
embodiment it is noted that the invention is not so
limited to the particular details of the illustrated
embodiment. Various modifications can be made
without departing from the scope of the invention
For example, various means, well known to those
skilled in the art, can be used for the control of
the gas stream in gas line 1, and for delivering
particles from container 7 to particle supply
orifice 6. In place of conveyor belt 9, for
example, a transporting wheel, mounted for rotation
under supply conduit 8 and provided with recesses
along its circumference for receiving particles and
transporting said particles to supply orifice 6, can
be employed. For this purpose the transporting
wheel must be capable of rotating in the same plane
as, e.g. pulley 10. It will be appreciated that
other means can be utilized for the delivery of
particles in a controlled manner from container 7 to
particle supply orifice 6. When employed, the
conveyer belt may be flat instead of channel shaped,
and there are also various obvious design
alternatives for the shape of container 7, supply
conduit 8, and supply orifice 6.
The invention as disclosed herein can be
used to effectively control the rate at which
abrasives or other cleaning materials, or other
desired particles, are metered into a propelling gas
stream. While the invention is particularly
advantageous in the metering of small quantities of
particles into propelling gas streams for injection
into small diameter heat exchanger tubes and the
like, it will be appreciated that the invention can
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also be advantageously employed for the controlled
injection of cleaning materials into propelling gas
streams for introduction into larger sized furnace
tubes to be decoyed and cleaned, pipelines to be
cleaned and dried, and other such applications in
which the direct, self-compensating pressure
equalizing conduit described above can assure that a
desired quantity of particles can be supplied to a
propelling gas stream regardless of the varying
counter-pressure that may be operative in the
downstream pipe or other conduit into which the
article entrained propelling gas stream is being
introduced through a discharge conduit and injection
head. The invention thus enhances the effectiveness
of the use of particles entrained in a gas stream in
such applications, by insuring that a controlled
quantity of particles can be employed in a desired
manner in accordance with established procedures and
experience pertaining to the treatment of such
tubes, pipelines or other conduits.
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