AU1130399A

AU1130399A - Arrangement for the determination of the mass throughflow of a gaseous medium

Info

Publication number: AU1130399A
Application number: AU11303/99A
Authority: AU
Inventors: Heinz Mutter
Original assignee: GreenField AG
Current assignee: Atlas Copco Schweiz AG
Priority date: 1998-01-20
Filing date: 1999-01-13
Publication date: 1999-08-12
Anticipated expiration: 2019-01-13
Also published as: AR014287A1; EP0936450A1; CA2256137A1; AU745300B2; CA2256137C; DE59813966D1; EP0936450B1; ATE359495T1; NZ333338A; KR19990068023A; BR9900117A; JPH11271127A

Description

MIUMU 1 2WW519 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

S

S S SS Application Number: Lodged: Invention Title: ARRANGEMENT FOR THE DETERMINATION OF THE MASS THROUGH- FLOW OF GASEOUS MEDIUM The following statement is a full description of this Invention, including the best method of performing it known to us:- P.6857/Ke/Pa Maschinenfabrik Sulzer-Burckhardt AG, CH-4002 Basel (Switzerland) Arrangement for the determination of the mass through-flow of a gaseous 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- S"cles powered by natural gas and at the same time to keep the dimensions 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 described 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 customer. 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 to This is however relatively compli- -2cated 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 installations, 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 S 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 apparatus. Mass through-flow meters of this kind, which are based on the Coriolis principle, are however very complicated and cost-intensive apparatuses, which in addition react relatively sensitively to external disturbances. They represent a considerable cost factor for gas filling in- S°o°0o 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 determination 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.

-3- In accordance with the invention the arrangement thus comprises an apparatus for the determination of the density of the gaseous medium, an apparatus for the determination of the volume through-flow of the gaseous medium and a connection line between these two apparatuses.

In the arrangement in accordance with the invention the determination of the mass through-flow is not carried out by a direct measurement, but rather in two steps: On the one hand the current density or the operating density of gaseous flowing medium is determined, and on the other hand a volumetric through-flow measurement is carried out. The S mass through-flow can be determined from these two quantities.

Through this measure the arrangement in accordance with the inveno* tion 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 material. Through a transducer which is sensitive to magnetic fields, e.g. through a Hall 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 for gas filling stations.

-4- Further advantageous measures and preferred embodiments result from the subordinate claims.

The invention will be explained in the following in more detail with reference 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 arrangement 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 component 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 apparatus".

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 medium, an apparatus 3 for the determination of the volumetric throughflow of the gaseous medium, and a connection line 4 between these two 5 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 volume. 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 designed 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 circuit, is provided in order to enable a precise determination of the current 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.

°o°°o S* 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 reference 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 -6respectively of the container 21 so that they cause no substantial disturbance in the weighing of the container 21. In the exemplary embodiment 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 determination 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 comprises 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 magnetisable 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 -7- 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. 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 reference 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 example be carried out as described in EP-A-653 585. In the following, therefore, only the aspects which are essential for the mass determination 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 reference 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 container 21 and the lines 9, 4 and 11, 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 symbols in Fig. 1, out of the storage unit 6 through the supply line 9, 8 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 current weight of the container 21 that is, its own weight and the weight Sof the gas momentarily present in it -is continuously determined.

Since the volume of the quantity of gas present in the container is constant 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 S.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 determined. In the evaluation unit 5, then, the mass through-flow is calculated 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 -9apparatus 2 for the determination of the density and from the apparatus 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 substantial 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 designed 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 reduced, which has a positive effect on the precision of the weighing.

In order to further increase the precision of the mass through-flow determination, 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 10 condition and which are also suitable for the above mentioned high operating 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 surrounded 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 particularly low, for example 0.3 kg/l.

Numerous variants of the described exemplary embodiment are possible, of which only two will be mentioned here in a non-exhaustive list.

SThus for example the relative arrangement of the two apparatuses 2 and 3 with respect to one another in the flow direction of the gaseous medium 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- S. 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 arrangement is proposed by means of which the mass through-flow of a gaseous medium, in particular a gaseous medium under high pressure, can be very precisely and reliably determined in a simple manner. This ar- 11 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 0

C).

"Comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

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Claims

2. Arrangement in accordance with claim 1, in which 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- inclusive of the gaseous medium located in the interior of the container (21) can be determined by means of the weighing device (22).
3. Arrangement in accordance with one of the preceding claims, in which the inlet (23) of the container (21) is connected to a supply line and the outlet (24) to a flow-off line with both lines 9) 99 9° being designed flexibly and resistant to pressure, and with one of .9 the two lines forming the connection line
4. Arrangement in accordance with one of the preceding claims, with the container (21) having a ratio of its own weight to its volume which is less than 1 kg/l, in particular is less than 0.5 kg/l. Arrangement in accordance with one of the preceding claims, with the inlet (23) and/or the outlet (24) of the container being designed in such a manner that the recoil effect caused by the flowing gase- ous medium is a minimum. 13
6. Arrangement in accordance with one of the preceding claims, with the apparatus for the determination of the volumetric through- flow having a pressure resistant, non-magnetic, in particular a me- tallic, housing (31) in which a rotor (32) with a plurality of blades (33) which comprises a magnetic material is arranged, and with the apparatus further comprising a transducer (35) which is sensi- tive to magnetic fields and which converts the movement of the blades (33) into electric signals. C.o
7. Arrangement in accordance with claim 6, with the transducer C* SO being arranged at the outside of the housing (31). C@@
8. Arrangement in accordance with claim 6 or claim 7, with the trans- ducer being executed as a Hall sensor
9. Arrangement in accordance with one of the preceding claims which is designed for an operating pressure of over 100 bar, in particular of 200 to 300 bar. S•10. Arrangement in accordance with one of the preceding claims com- prising an evaluation unit which receives signals both from the apparatus for the determination of the density as well as from the apparatus for the determination of the volumetric through- flow, with the evaluation unit comprising electronic means for the multiplication of the current density signal by the volumetric through-flow signal in order thus to determine a signal for the mass through-flow.
11. Gas filling station with an arrangement in accordance with one of the preceding claims. DATED this 13th day of January 1999. MASCHINENFABRIK SULZER-BURCKHARDT AG WATERMARK PATENT TRADEMARK ATTORNEYS ~H'X if 1 122.