Compact device for metering gas at variable pressure

Details Compact device for metering gas at variable pressure Compact device for metering gas at variable pressure

1998-05-20

2001-03-13

Patel, Harshad (Department: 2855)

Measuring and testing

Volume or rate of flow

Using turbine

C073S195000

Reexamination Certificate

active

06199434

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a compact variable-pressure gas metering device for metering a volume of gas flowing along a pipe, downstream from an expander-regulator, and comprising in succession a flow straightener, a velocity-measuring flowmeter, and a silent flowrate limiter.
The invention relates more particularly to a device applicable to a gas distribution station performing the functions of expanding and regulating the delivery pressure of gas and of metering the volumes of gas delivered.
BACKGROUND OF THE INVENTION
In a conventional solution, as shown in
FIG. 2
, the gas flowing in a pipe
6
A at an upstream pressure Pe is expanded from the upstream pressure Pe to a regulated downstream pressure Pa in an expander-regulator
1
A which receives a control signal via a line
4
A starting from a segment of pipe
3
A situated downstream from the expander-regulator
1
A. A meter
2
A is disposed between pipe segment
3
A and a downstream distribution pipe
7
A. The meter
2
A meters the volume of gas consumed at the downstream pressure Pa, which pressure depends only on the fixed set point of the regulator
1
A that serves to keep said downstream pressure constant. To ensure that the metering is reliable, it is necessary to have good flow conditions in the pipe segment
3
A between the expander-regulator
1
A and the meter
2
A. For this purpose, the segment of pipe
3
A must comprise substantial rectilinear lengths L. The high level of disturbance that exists in the vicinity of the release valve of the pressure regulator leads to the gas flowmeter device being placed at a distance from the expander-regulator that corresponds to several times the diameter of the pipe interconnecting these two elements. This gives rise to non-negligible bulk.
In another known solution, as shown in
FIG. 3
, a gas meter
2
B is installed upstream from an expander-regulator
1
B, which is provided with a link
4
B coming from the downstream pipe
7
B to receive information concerning the regulated downstream pressure Pa. Under such circumstances, pipe segment
5
B between the meter
2
B and the expander-regulator
1
B can be relatively short and the maximum flow rating of the meter
2
B can be small. In this solution, the meter is not subjected to the disturbances generated by the expander-regulator.
However in solution A (metering downstream from expansion) as in solution B (metering upstream from expansion), the link pipes connecting the inlet of the station or the pressure expander-regulator to the meter, e.g. a spinner meter, generally adds additional disturbances due to the particular shape of the link pipes and to the accessories that may be mounted on the link pipes. The flowmeter can thus receive a flow of gas whose velocity profile is deformed or which has a gas stream that is subject to rotation, which is prejudicial to the quality of metering. In addition, the operating dynamic range of stations fitted in those manners, i.e. the ratio between the maximum flow rate Qmax and the minimum flow Qmin between which compliance with legal weights-and-measures regulations guarantees good metering accuracy at low pressure, is of the order of 20 to 30 for volume-measuring meters. Such dynamic ranges are sometimes too small to cover all of the flow rates applicable to certain public distribution stations, or certain industrial customers. This leads to low flow rates being metered poorly. Furthermore, the rules governing dimensioning of delivery stations generally lead to expander-regulators being installed that are of a capacity that is very much greater than that of the meters, under normal operating conditions. Consequently, in certain situations, there is a risk of the meter being damaged by its maximum flow rate being temporarily exceeded.
Proposals have also been made, in particular in document EP-A-0 337 887, for a multifunction integrated expansion station for feeding gas to a secondary network. In that case, the expander-regulator
1
C, a straightener element
8
C, a meter
2
C, and a flowrate limiter
9
C (
FIG. 4
) are all incorporated in a single outer body extending over a distance
5
C and connected firstly to an upstream pipe
6
C in which there obtains an upstream pressure Pe, and secondly to a downstream pipe
7
C in which there obtains a regulated downstream pressure Pa. The link
4
C enables a control signal to be applied to the expander-regulator
1
C representing the downstream pressure Pa. Metering is performed at a variable metering pressure Pv which differs from the regulated downstream pressure, given the presence of the flowrate limiter
9
C which develops headloss. This leads to the dynamic range of the meter
2
C being increased, while also protecting the meter against possible excess flowrate.
A variable pressure meter of that type is advantageous because of the increase in dynamic range that it makes possible and because of its compactness. Nevertheless, it must be specially designed since the various elements of the expansion station must be integrated in a common housing. This leads in particular to a special and relatively complex design for the flow straightener
8
C and the limiter
9
C, in particular.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention seeks to remedy the above-mentioned drawbacks and to make it possible to implement a gas distribution station and a gas metering device which are compact while also being modular, suitable for easily incorporating conventional expander-regulators or conventional meters, and implementing gas flow straightener elements or flowrate limiters of a structure that simplifies manufacture while guaranteeing robustness and a high level of safety in operation.
These objects are achieved by a compact variable-pressure gas metering device for metering a volume of gas flowing along a pipe, downstream from an expander-regulator, and comprising in succession: a flow straightener, a velocity-measuring flowmeter, and a silent flowrate limiter; wherein the straightener is disposed between a flange of an upstream pipe for coupling to the expander-regulator, and an upstream flange of the meter, wherein the limiter is disposed between a downstream flange of the meter or of an extender associated with the meter, and a flange of a downstream pipe, wherein the straightener comprises a support ring in which there are mounted a first perforated plate perforated by holes together with a first porous plate and a spacer in the form of an annulus co-operating with the first perforated plate, and wherein the limiter comprises an upstream web defining a second perforated plate perforated by a defined number of calibrated holes of total flow section that is much less than the flow section of the first perforated plate, a second porous plate, and a downstream web defining a third perforated plate perforated by holes of total flow section that is much greater than the total flow section of the second perforated plate of the upstream web.
Advantageously, the holes of the first perforated plate are distributed uniformly over the entire area of said first plate.
According to a particular characteristic of the straightener, the support ring has, in the vicinity of its downstream face, a shoulder projecting radially inwards from the support ring, and the first perforated plate is placed directly in contact with said shoulder.
In which case, advantageously, the first perforated plate, the first porous plate, and the spacer constitute a stack coming into abutment against the shoulder of the support ring, and the sum of the thicknesses in the axial direction of the first perforated plate, of the first porous plate, and of the spacer is slightly greater than the distance in the axial direction between the downstream shoulder of the support ring and the upstream face of said support ring in such a manner that clamping the stack between the flange of the upstream connection pipe and the upstream flange of the meter compresses the first porous plate to a small extent. As a result, any possibility of slack between the various e

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