Note: Descriptions are shown in the official language in which they were submitted.
CA 02256137 1998-12-16
P.6857/Ke/Pa
Maschinenfabrik Sulzer-Burckhardt AG, CH-4002 Basel (Switzerland)
Arrangement for the determination of the mass through-flow of a ~ase-
ous medium
The invention relates to an arrangement for the determination of the
mass through-flow of a gaseous medium.
The determination of the mass through-flow of a gaseous medium such
as natural gas, and in particular compressed natural gas, receives a
particular importance in gas tanking plants. Above all, compressed
natural gas is becoming increasingly more important as an alternative
fuel for motor vehicles. In order to enable a satisfactory range with vehi-
cles powered by natural gas and at the same time to keep the dimen-
sions of the gas supply container in the motor vehicle within reasonable
bounds, these supply containers are typically filled with natural gas up
to pressures of about 200 bar. Filling procedures and installations have
been developed for this which enable a very simple and rapid filling of
motor vehicles of this kind - comparable to filling up with petrol. A
method of this kind or an installation of this kind respectively is de-
scribed in detail for example in EP-A-653 585.
In order to fill in and sell natural gas into motor vehicles at natural gas
filling stations or filling pumps it is necessary to determine exactly the
amount of gas filled in. It is generally agreed that the mass of the gas
and not its volume is the quantity which is to be charged to the cus-
tomer. There thus results the necessity of determining the mass
through-flow of the compressed natural gas sufficiently precisely, i.e.
with an error of at most ~1% to ~2%. This is however relatively compli-
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Gated and expensive in particular when the gas is under high pressure,
for example in the range from about 100-300 bar.
For the determination of the mass through-flow in gas filling installa-
tions, such as for example filling pumps, through-flow measurement
apparatuses are often used which are based on the Coriolis principle. In
apparatuses of this kind, one or more tubes through which the gas
flows are set into oscillation. Through this a Coriolis force acts on the
flowing gas, which has as a result that the oscillations of the tube or
tubes changes in a manner which is dependent on the mass flow. The
Coriolis measurement apparatuses thus permit a direct measurement of
the mass flow of the gas. Pulses are produced by electronic means
which are proportional to the mass of the gas flowing through and
which then for example are supplied to a filling pump counter appara-
tus. Mass through-flow meters of this kind, which are based on the
Coriolis principle, are however very complicated and cost-intensive ap-
paratuses, which in addition react relatively sensitively to external dis-
turbances. They represent a considerable cost factor for gas filling in-
stallations.
The object of the invention is therefore to provide an arrangement for
the determination of the mass through-flow of a gaseous medium which
is very simple and economical and nevertheless permits an exact deter-
mination of the mass of gaseous medium flowing through. In particular
the arrangement should also be suitable for gases which are under high
pressure.
The arrangement for the determination of the mass through-flow of a
gaseous medium satisfying this object is characterised by the features
of the independent patent claim 1.
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26380-49
3
In <~ccordance with the invention there is provided
arrangement fc~r the determinat,yon o.f the mass through-flow of a
gaseous medium comprising an apparatus (2) for the
determination of the density of. the gaseous medium, an
apparatus (3) for the determination of the volumetric through-
flow of the g~~seous medium, and a connection line (4) between
these two app;~ratuses (2, 3), wherein the apparatus (2) for the
determination of the density comprises a weighing device (22)
and a container (21) with a constant volume which has an inlet
(23) and an outlet (24) for the gaseous medium, with the
container (21) being arranged in such a manner that its current
weight - incl,asive of the gaseous medium located in the
interior of t:ze container (21) - can be determined by; means of
the weighing device (22).
In 'the arrangement in acr_ordance with the invention
the determination of the mass through-flow is not carried out
by a direct m~=asurement, but rather in two steps: On the one
hand the curr~=nt density or the operating density of gaseous
flowing medium is deterrr;i.ned, and on the other hand a
volumetric through-flow measurement is carried out. The mass
through-flow can be determined from these two quantities.
Thr~~ugh this rrceasure the arrangement in accordance
with the invention is particularly simple and economical, in
particular in comparison with the measurement apparatuses based
on the Coriolis principle.
The determination of the density of the gaseous
medium preferably takes place through a weighing of a precisely
known volume through which the gaseous medium flows.
The volumetric through-flow measurement is preferably
done by means of a rotor' which is arranged in the gas flow,
which has a plurality of blades and which comprises a magnetic
CA 02256137 2001-06-08
26380-49
3a
fields, e.g. through a H=all sensor, the rotational movement of
the blades is converted into electrical signals so that the
speed of rotation of the rotor and thus the volume through-flow
can be determined.
The arrangement. in accordance with the invention is
particularly suitable f.:or gas filling stations.
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Further advantageous measures and preferred embodiments result from
the subordinate claims.
The invention will be explained in the following in more detail with ref-
erence to an exemplary embodiment and with reference to the drawings.
Shown in the schematic drawings, which are not to scale, are:
Fig. 1: a schematic representation of an exemplary embodiment of
the arrangement in accordance with the invention, and
Fig. 2: a sectional representation of an exemplary embodiment of
the apparatus for the determination of the volumetric
through-flow.
In the following description of the invention, reference is made by way of
example to the use, which is important in practice, in which the ar-
rangement in accordance with the invention is a part of a gas filling
station such as is disclosed in the already mentioned EP-A-653 585.
The arrangement in accordance with the invention is then e.g. the com-
ponent which is provided with the reference numeral 8 in Figs. 2a, 2b
and 2c of EP-A-653 585 and is designated as a "mass through-flow ap-
paratus".
Fig. 1 shows in a schematic illustration an exemplary embodiment of
the arrangement in accordance with the invention for the determination
of the mass through-flow of a gaseous medium, which is designated in
its entirety by the reference numeral 1. The arrangement 1 comprises
an apparatus 2 for the determination of the density of the gaseous me-
dium, an apparatus 3 for the determination of the volumetric through-
flow of the gaseous medium, and a connection line 4 between these two
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apparatuses 2, 3.
The apparatus 2 for the determination of the density comprises a
weighing device 22 and a container 21 with a constant and known vol-
ume. The container 21 has an inlet 23 and an outlet 24 for the gaseous
medium and is arranged in such a manner that its current weight, by
which is meant in the operating state the sum of its own or empty
weight and the weight of the gaseous medium located in the interior of
the container 21, can be determined by the weighing device 22. In the
exemplary embodiment described here the weighing device 22 is de-
signed as a platform on which the container 21 rests so that it loads the
platform with its weight. In or on the platform 22, at least one force
sensor, such as for example a strain gauge or a strain gauge bridge cir-
cuit, is provided in order to enable a precise determination of the cur-
rent weight of the container 21. The measurement data determined by
means of the weighing device 22 are transmitted via one or more signal
lines 7 to an evaluation unit 5 where the data are e.g. further processed
and evaluated.
The inlet 23 of the container 21 is connected to a supply line 9 and the
outlet 24 to a flow-off line 4. The supply line 9 leads for example to a
storage unit 6 in which the gaseous medium is kept. In the embodiment
of the gas filling station the storage unit 6 is the supply vessel from
which the gas flows out during the filling of the vehicle into its tank,
and thus corresponds to the storage unit which is provided with the ref-
erence numeral 3 in EP-A-653 585. It is self evident that in such uses
in which the gas is under pressure, the lines 4, 9 and the container 21
are made pressure resistant. In addition these lines 4, 9 are designed
flexibly and/or are flexibly connected to the inlet 23 and the outlet 24
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respectively of the container 21 so that they cause no substantial dis-
turbance in the weighing of the container 21. In the exemplary em-
bodiment described here the flow-off line 4 forms the connection line
which connects the two apparatuses 2, 3.
In principle all volumetric through-flow measurement apparatuses
which are known per se are suitable as an apparatus 3 for the determi-
nation of the volumetric through-flow. In the following a particularly
preferred embodiment is described with reference to Fig. 2 in which a
pressure resistant non-magnetic, in particular a metallic, housing 31 is
provided in which a rotor 32 with a plurality of blades 33 which com-
prises a magnetic material is arranged. The apparatus 3 further has a
transducer, preferably a Hall sensor 35, which is sensitive to magnetic
fields and which converts the movement of the blades 33 into electric
signals which are fed via signal lines 10 to the evaluation unit 5 (Fig. 1).
For practical reasons the Hall sensor 35 is preferably arranged at the
outside of the housing 31. In the embodiment illustrated in Fig. 2 the
rotor 32 is designed as an axial turbine. It is naturally also possible to
form the rotor 32 as a vaned wheel turbine. The rotor 32 runs out at
both ends in the axial direction into a shaft 34. The shafts 34 are in
each case held by a non-illustrated pin bearing. The rotor 32 is set into
rotation by the flowing gaseous medium, of which the flow direction is
indicated by the arrows F. The blades 33 or the entire rotor 32 are mag-
netisable or have permanent magnetic properties. The rotor 32 with the
blades 33 can for example be manufactured of a plastic, with the plastic
having magnetic materials, e.g. in the form of particles, embedded
and/or provided at its surface. At least the blades 33 of the rotor 32
must be designed in such a manner that they permanently produce a
magnetic field (in the operating state). In the operating state the rotor
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32 in the housing 31 is set into rotation by the flowing medium, with
the speed of rotation of the rotor 32 being substantially proportional to
the volume of the gas flowing through. If the rotor 32 rotates, then the
rotating past of the blades 33 at the Hall sensor 35 can be measured by
the latter so that the speed of rotation of the rotor 32 and thus the
volumetric through-flow of the gaseous medium can be determined.
The gas flows into the housing 31 through the opening in the housing
31 which is on the left in the illustration (Fig. 2) in the operating state.
This opening is connected to the outlet 24 of the container 21 by means
of the connection line 4 (Fig. 1). Through the opening in the housing 31
at the right in accordance with the illustration in Fig. 2, the gaseous
medium flows out of the latter and arrives at the motor vehicle to be
filled via a pressure line 11 (Fig. 1).
The operating state of the arrangement will now be explained with refer-
ence to the example of the use in which a motor vehicle is filled with
compressed natural gas. The precise procedure of the filling can for ex-
ample be carried out as described in EP-A-653 585. In the following,
therefore, only the aspects which are essential for the mass determina-
tion of the output gas will be discussed.
The compressed natural gas is typically under an operating pressure of
greater than 100 bar, for example between 200 and 300 bar (with refer-
ence to a temperature of 15°C), in the storage unit 6. The components
of
the arrangement 1 through which the natural gas flows, e.g. the con-
tainer 21 and the lines 9, 4 and 1 l, are designed in such a manner that
they withstand this pressure. During the filling the compressed gas
flows, as is indicated symbolically by the arrows without reference sym-
bols in Fig. 1, out of the storage unit 6 through the supply line 9,
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through the container 21, which is designed for example as a pressure
bottle, through the connection line 4, through the apparatus 3 for the
determination of the volumetric through-flow and through the pressure
line 11 into the supply container of the vehicle to be filled. Since the
container 21 through which the gas flows has a constant and precisely
known volume, the same volume of gas is always present in its interior
during the filling process. By means of the weighing device 22 the cur-
rent weight of the container 21 - that is, its own weight and the weight
of the gas momentarily present in it - is continuously determined.
Since the volume of the quantity of gas present in the.container is con-
stant and known, the momentary density or operating density of the
flowing gas can be determined in a very simple manner from the
weighing, taking into consideration the likewise known proper weight of
the container 21. Through the flexible design of the supply and flow-off
lines 9, 4, that is through their flexible connection to the container 21 it
is ensured that the lines 4, 9 have practically no disturbing influence on
the weighing.
After flowing through the container 21 the gas flows at substantially the
same pressure and the same temperature through the housing 31 of the
apparatus 3 and thereby sets the rotor 32 in rotation. By means of the
Hall sensor 35 the speed of rotation of the rotor 32 is determined, from
which the volumetric through-flow of the natural gas can be deter-
mined. In the evaluation unit 5, then, the mass through-flow is calcu-
lated from the current density of the natural gas and the volumetric
through-flow and, for example, is fed to a display device of the gas filling
station via a signal line 8.
Preferably the evaluation unit 5, which receives signals both from the
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apparatus 2 for the determination of the density and from the appara-
tus 3 for the determination of the volumetric through-flow, comprises
electronic means for the multiplication of the current density signal by
the volumetric through-flow signal in order thus to determine the signal
for the mass through-flow.
The two apparatuses 2 and 3 and the connection line 4 are designed
and arranged relative to one another in such a manner that no sub-
stantial pressure gradient and no substantial temperature gradient are
present between the inlet of the container 21 and the outlet of the
housing 31 of the apparatus 3 so that the natural gas flows through the
two apparatuses 2 and 3 substantially under the same pressure and at
the same temperature.
The inlet 23 and/or the outlet 24 of the container 21 are preferably de-
signed in such a manner that the recoil effect caused by the flowing
gaseous medium is a minimum. For this, for example, as illustrated in
Fig. 1, the inlet 23 is designed in such a manner that it first extends as
a tube into the interior of the container 21 and has there a T-shaped
end with two inlet openings 23a and 23b. The two inlet openings are
thus arranged in such a manner that the gas flowing through the one
inlet opening 23a flows substantially in the direction opposite to gas
flowing through the other inlet opening 23b. Through this measure the
recoil effect effected by the inflowing gas can at least be significantly re-
duced, which has a positive effect on the precision of the weighing.
In order to further increase the precision of the mass through-flow de-
termination, in particular that of the weighing, it is advantageous if the
container 21 has a ratio of proper weight to volume which is less than 1
kg/1, in particular less than 0.5 kg/1. Containers 21 which fulfil this
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condition and which are also suitable for the above mentioned high op-
erating pressures, e.g. up to 300 bar, are known from the prior art, for
example as so-called composite bottles. These are pressure bottles
which have a thin aluminium bottle (a so-called liner) which is sur-
rounded by high strength fibres, e.g. carbon fibres, with these fibres
being cast in an epoxy resin. Bottles of this kind are typically used as
respiratory air bottles. Their ratio of proper weight to volume is par-
ticularly low, for example 0.3 kg/1.
Numerous variants of the described exemplary embodiment are possi-
ble, of which only two will be mentioned here in a non-exhaustive list.
Thus for example the relative arrangement of the two apparatuses 2 and
3 with respect to one another in the flow direction of the gaseous me-
dium can be reversed so that the gaseous medium first flows through
the apparatus 3 for the determination of the volumetric through-flow
and then through the apparatus 2 for the determination of the density.
The apparatus 2 for the determination of the density can also analo
gously be designed in accordance with the principle of a bending beam
or a beam balance, with the container 21 then being suspended from
the balance.
In regard to a precision of the weighing which is as high as possible it is
advantageous if the container 21 is arranged to be as freely standing or
as freely hanging respectively and as friction-less as possible.
Through the invention a particularly simple and economical arrange-
ment is proposed by means of which the mass through-flow of a gase-
ous medium, in particular a gaseous medium under high pressure, can
be very precisely and reliably determined in a simple manner. This ar-
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rangement is suitable in particular for gas filling stations and especially
those for the output of compressed natural gas, e.g. in the pressure
range from 200 - 300 bar (referred to a temperature of 15°C).
