Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
218627~
METHOD AND APPARATUS FOR TAKING GAS SAMPLES FROM CONTAINERS
The invention relates to a method for taking a
gas sample from containers carried past a sampling station
by means of a conveyor device, in which a medium is
injected into each container and the gas thereby expelled
from the container is at least partially received into a
throughflow collecting chamber and drawn off to at least
one analysing unit. The invention also relates to an
apparatus for carrying out the method, according to the
introductory part of claim 9.
A method as described above, and such apparatus
are known from DE-C 4225984. This is intended to provide a
simple way of taking a gas sample from eontainers, in
particular from returned multi-trip bottles. With the
method and apparatus according to the prior art, however,
the mechanical simplification which the invention sets out
to, and does, achieve is associated with a very short gas
withdrawal time, and this may have unsatisfaetory results,
especially if the bottles are being conveyed at high speed.
WO-A 93/24841 discloses a method and an apparatus in which
the same problems basically occur.
The later-published DE-A 4427314 discloses an
arrangement in which there is no extraction from a
collecting chamber, the expelled gas being conveyed
directly through a conduit to a measuring cell, and then
being released to atmosphere.
Accordingly a principal object of the present
21~6~75
,
invention is to improve the known method so that gas
samples for analysis can be reliably taken even under
difficult conditions, for example with a high bottle
throughput.
This object may be realised in the abovementioned
method by effecting the inflow of gas into the collecting
chamber over a longer section of the conveyor path than is
required for the outflow of gas from the collecting
chamber.
It has been found that the problem indicated can
be solved by such a step, in which the gas expelled from
the container is collected over a relatively extended
section of the conveyor path and is focussed on a
relatively small space in the region of the outflow
opening. For each container, the gas sample ~xpelled from
the container by the injected air is available over a
section of the conveyor path, not just at a specific point
on the conveyor path as in the prior art.
Also, extraction of the gas sample is
advantageously effected above the outflow opening of the
collecting chamber. This ensures that the flow of the gas
which has been collected in the chamber is not disturbed by
the extraction element, which is optimally positioned
within the gas flow, thus assisting extraction of a gas
sample suitable for analysis.
It is also advantageous if injection of the
medium (usually compressed air) likewise takes place over a
section of the conveyor path, whicll may be of the same
2186~75
length as, or longer than, the inflow opening of the
collecting chamber. Shorter injection is also possible,
but is not preferred.
The apparatus for carrying out the method has the
characterising features of claim 9, in order to realise the
abovestated object.
The invention will now be described in detail
with reference to the embodiments illustrated by way of
example in the drawings, in which:
Fig. 1 shows schematically the neck and mouth
region of a bottle, to illustrate the method:
Fig. 2a shows schematically a collecting chamber
according to the invention, viewed in side elevation,
Fig. 2b shows schematically the arrangement of
Fig. 2a, viewed in the conveying direction,
Fig. 3 is a perspective view of the collecting
chamber with its injection nozzle,
Fig. 4 is a schematic illustration of a purging
air arrangement,
Fig. 5 is a diagram showing the effect of the
purging air, and
Fig. 6 is a view of the mouth region of a
container illustrating another air and gas flow
arrangement.
Fig. 1 shows schematically the upper part of a
container 1, eg. a bottle. The injection of a jet 3 of
rnedium into this container by rneans of a nozzle 2 is known
from the state of the art. The mediurn will usually be air,
2 i 8~275
although some other gaseous medium may also be used. The
medium is injected over part of the cross-section of the
opening of the container 1. As is also known, the
injection of the medium causes the gas present in the
bottle to be expelled through displacement by the injected
medium. For a certain time this expulsion takes place with
practically no dilution by the injected medium. In Fig. 1
the expelled gas is illustrated as a flow 5. It is also
known that this flow 5 can be collected in a round
collector pipe and part of this gas flow can be extracted
from the interior of the collector pipe in order that the
gas can be analysed for residues and a judgement made as to
the reusability of the container. The containers 1 are
conveyed on a conveyor device and pass a sampling station
where the gas flow 5 passes into the collector pipe at a
point location.
In accordance with the present invention, the
intake of the gas expelled from the bottle 1 occurs not at
a single point on the conveyor path but over an extended
section thereof which is longer than the gas outflow
opening at the top of the collecting chamber. In Figs. 2a
and 2b this is illustrated schematically, with Fig. 2a
showing a side view of the collecting chamber, the bottles
being conveyed in the direction of the arrow B on a known
conveyor device which is not shown, while in Fig. 2b the
same collecting chamber 4 is viewed in the direction of the
arrow A in Fig. 2a, that is to say in the conveying
direction of the containers.
2 ~ 86~75
In Fig. 2a a container 1 is shown in three
different positions through which it passes as it is being
conveyed past the collecting chamber. The three positions
illustrated are designated 1,1' and 1". The gas flows
escaping from the container in these positions are
accordingly designated 5,5' and 5". In Fig. 2a the medium
injected into the bottles is not shown. However, this will
be apparent from Fig. 2b, which will be explained
presently. From Fig. 2a, it can be seen that the
collecting chamber 4 has an inflow opening 14 for the gas
flows 5 which extends over a larger section of the conveyor
path than the outflow opening 13 for the gas flows escaping
from the collecting chamber, which are designated 5"'. In
the example shown, the collecting chamber 4 is bounded by
two baffle elements or collector elements constructed eg.
as deflector plates 10 and 11 whose bottom ends are further
apart from each other than their top ends, those bottom and
top ends defining the inflow opening 14 and the outflow
opening 13 respectively. The collecting chamber may be
closed off on one side with a wall 12, or closed off with
walls on both sides, or open on both sides.
It can be seen that the configuration of the
collecting chamber in this embodiment of the invention
allows the gas escaping from an individual container 1 to
be collected over a conveying distance b. It has been
found that a gas flow 5 which is essentially undiluted by
the injected medium, flows out of the bottle for a
sufficient enough length of time. The specified
~1 8~275
.
configuration of the collecting chamber 4 causes the gas
flows 5,5' and 5" from the bottle to be focussed at the
outflow opening 13 of the collecting chamber. The gas flow
at the outflow opening is designated 5"'. The configuration
of the collecting chamber 4 has also been found to cause
the gas flow 5 to be only slight]y diluted with ambient
air, as essentially only air expelled from the container is
conveyed through the collecting chamber 4 to the outflow
opening 13.
The portion of the gas flow which is to be
supplied to the analysing unit is preferably extracted
above the outflow opening 13. For this purpose, a suction
pipe 7 is provided, which draws off part of the gas flow 5"'
and supplies it as a flow 8 to an analysing unit, which is
not shown. This arrangement for the extraction of the
sample gas flow 8 above the collecting chamber 4 has the
advantage that there is no disturbance of the flow in the
collecting chamber itself, thus further avoiding the
ingress of ambient air. The sample gas flows 5,5' and 5"
are focussed at the outflow opening 13 of the collecting
chamber 4, whose outlet diameter a is small in relation to
the distance b, so that the gas sample 8 removed above the
opening 13 is a representative, only slightly diluted,
sample of gas from the container 1, and is available for
analysis during a time span which is prolonged by
approximately the ratio b : a.
The injection - not illustrated in Fig. 2a - of
the jet 3 of compressed air to displace the gas present in
21 86~75
the container can be seen in detail in Fig. 2b. The nozzle
2 to introduce the compressed air jet 3 is, accordingly,
located behind the collecting chamber 4, in the direction
of view of Fig. 2a. The nozzle 2 is preferably a nozzle
which extends over the entire length b of the inflow
opening of the collecting chamber 4. The nozzle 2 may,
however, be longer than the distance b, so that injection
commences before the bottle mouth arrives in the region of
the collecting chamber 4. It is also possible to make the
nozzle 2 shorter than the distancè b if this should prove
advantageous for a particular application. In the
illustration in Fig. 2b, the reference symbols used in Fig.
2a designate the same parts.
Fig. 3 shows a perspective view of a similar
configuration to Figs. 2a and 2b of the apparatus for
carrying out the method. The mouth of a container 1, which
is being conveyed in the direction of the arrow B, is again
shown. The collecting chamber 4, again bounded by two
deflector plates 10 and 11, and also having a back wall 12,
is arranged above the container 1. For its part, the back
wall 12 forms part of the air nozzle 2, which is
constructed with a slit-form opening 15 producing a flow 3
in the form of an air curtain entering the container 1
throughout the time during which the container is being
conveyed under the collecting chamber 4. For the sake of
clarity, the gas 5 flowing out of the container 1 is
illustrated only at the container mouth in ~ig. 3, and not
inside the collectiny chamber. The pattern of gas flow is,
2 1 86~75
.
however, essentially as illustrated in Fig. 2a. An
extraction element 7, which is shown removing part of the
gas flow 5 as a flow 8, and which feeds the flow to the
analysing station, is located above the outflow opening of
the collecting chamber 4. In the example shown, air outlet
openings 16 are also illustrated in the side wall 12; the
function of these openings will be explained presently.
The embodiment shown in Fig. 3 may be modified in
a variety of ways. For example, the shape of the deflector
plates 10 and 11 may be other than rectangular as
illustrated. Furthermore, instead of being straight, these
deflector plates may be curved, with the convex side
towards the container mouth or facing the other way. Also,
as already mentioned, the back wall 12 of the collecting
chamber is not obligatory. The collecting chamber could be
open at the rear, as well as at the front. In this case,
the air supply to the nozzle 2 would be close to its
discharge opening 15, and not above the deflector plates 10
and 11. If the back wall 12 were omitted, the deflector
plates would be secured above the conveyor device by other
means, eg. by supporting bars. In all embodiments, the
flow and/or pressure of the medium 3 is either set at a
constant level or varied to suit operating parameters, such
as the conveying speed for example.
The entire apparatus forming the collecting
chamber and extractor is moreover preferably made
vertically adjustable so that the height of the sampling
station above the conveyor device can be adjusted to adapt
21 ~6275
the apparatus to different containers. The slit form
opening 15 of the nozzle 2 may be replaced with a series of
individual openings. In this case, instead of the
continuous injection resulting from an unbroken air curtain
(which is preferred), a series of continuously flowing air
columns, arranged side by side, are formed, whose effect on
the passing bottle is that of a pulsed injection.
Furthermore it is possible to provide not ~ust a single
nozzle for injection into one segment of the circular area
of the mouth, but two nozzles, injecting into two segments.
Such a method of injection is shown schematically in Fig.
6, in which one nozzle produces an air curtain 3 injecting
into the segment 18 of the circular mouth of the container
1 (as is also the case in Fig~ 3), and an additional nozzle
now injects an air curtain 3' into a segment 19. The
emerging gas flow 5 will then lie centrally between the two
air curtains 3 and 3'. A corresponding modification of eg.
the embodiment shown in Fig. 3 is easily realised. of
course, another arrangement, in which the injection is made
centrally, is also possible, with a nozzle e~tending above
the centre of the circular opening of the container, and
with gas 5 passing via lateral segments into the collecting
chamber. In this case, if the need arises, there may be
provided two separate collecting chambers which join
together in the region of their outflow opening. The
entire gas sampling unit can moreover be heated to prevent
gas from the containers from condensing on the unit.
A further embodiment will now be described with
2~6275
reference to Fig. 4. In Fig. 4, the collecting chamber 4
is again illustrated schematically, and bounded by
deflector plates 10 and 11, with the extractor pipe 7
arranged at its outflow opening. Here the gas emerging
from the container 1 is illustrated by an arrow 25 drawn as
a broken line which represents the normal direction of the
gas outflow. In the embodiment of Fig. 4, a purging
airflow 17 is produced approximately at right angles to the
conveying direction of the containers, causing a slight
deflection of the gas outflow from the bottle 1. The gas
flow which is actually established as a result of the
crossflow 17 is indicated by the arrow 5 drawn as an
unbroken line. This gas flow also reaches the extractor
pipe 7, that is to say, the flow 17 is made sufficiently
weak to ensure that the gas flow 5 stays within the
collecting chamber. The purpose of this purging airflow 17
is to purge the gas collecting chamber 4 before the arrival
of the next bottle 1 sufficiently to ensure that when the
next bottle 1 releases its gas flow into the collecting
chamber only insignificant amounts of the gas flow from the
previous container remain in the collecting chamber, in
order that the analysis is not vitiated by the so-called
memory effect of the collecting chamber.
Fig. 5 shows as an example the output signal of
an analysing station which analyses the extracted gas flow,
over time t. The curve 20 represents the output signal
yielded by analysis of the gas flow of a first container,
whi:le the output signal 20' is the signal yielded by
21 ~6275
analysis of the following container. The curve 20 shows
the profile of the signal obtained without the use of the
purging air flow. It will be seen that in that period t2,
when the following container is being analysed and the
output signal 20' is being generated on the basis of the gas
outflow from that container, signal components 22
originating from the gas flow of the container previously
analysed in the period tl are still being detected. With
the use of purging air, the resulting curve is not curve
20, but curve 21, from which it is apparent that the gas
components from the previous container have largely been
purged away by the period t2, so that they will not have an
unacceptable influence on the analysis of the contents of
the second container.
The pu;-ging airflow 17 may be produced by a
separate blower or a separate compressed air connection.
The velocity and rate of the purging airflow are preferably
adapted to the specific container conveying speed and/or
container type Fig. 3 shows the air out]et openings 16
(already referred to) in the back wall 12 of the collecting
chamber, which are used in this example to produce the
transverse purging airflow. The purging airflow is in this
example drawn directly from the injection airflow 3, and
diverted into the collecting chamber.
