GB2204363A

GB2204363A - Metering liquid or thick substances

Info

Publication number: GB2204363A
Application number: GB08809110A
Authority: GB
Inventors: Jean-Marie Chauveau
Original assignee: HASLER FRERES INTERNATIONAL SA
Current assignee: HASLER FRERES INTERNATIONAL SA
Priority date: 1987-05-05
Filing date: 1988-04-18
Publication date: 1988-11-09
Also published as: FR2614983A1; GB8809110D0; IT1217413B; IT8820194A0; DE3815034A1

Description

2 2 0 4 3 6 J.31 PROCESS FOR METERING LIQUID OR THICK SUBSTANCES AND

INSTALLATION FOR CARRYING OUT THIS PROCESS This invention relates to a process for metering liquid or thick substances.

It also relates to an installation for metering liquid or thick substances enabling the above process to be carried out and having a supply vat containing the substances to be metered, means for tapping predeterm ined masses or volumes of these substances and means for discharging said predetermined masses or volumes in a controlled way.

Traditionally pumps are used for regulating the flow of liquids to be metered. The use of a tank supported by a weighing machine enables the weight of liquids to be metered to be regulated and thus the duty of the pump to be associated with the desired loss in weight per unit of time. Such appliances are known by the name of regulateddrainage hoppers or differential gravimetric flow control devices.

In these installations, pumps are weak components which may leak, which are likely to pollute the metered liquid and which in all cases require a lot of maintenance.

Moreover, viscous or thick substances generally cannot be metered in installations of this type.

The object of this invention is to remove the above drawbacks by developing a process and perfecting an in stallation for metering liqiid or thick substances with out a pump.

To this end, the process according to the invention is characterised in that predetermined masses or volumes of substances to be metered are tapped, in that these predetermined masses or volumes are temporarily stored 2 in at least one intermediate storage tank of known weight and/or volume, in that these predetermined masses or volumes are subjected to the pressure of a gas and in that the opening of a,relief valve and/or the press ure of said gas in said tank is regulated so that the flow of said predetermined masses or volumes occurs within a given time.

According to a preferred embodiment, two intermediate storage tanks arranged in parallel are used and one of these intermediate storage tanks is filled during at most a part of the time required to empty the other.

Means for filling and emptying intermediate storage tanks are preferably designed so that one of these tanks can be filled within a period of time less than the minimum time required to empty the other tank.

The weight of predetermined masses of substances con tained in the intermediate storage tanks is preferably determined by weighing said tanks.

During the emptying of the tank, the variation in weight of the tank containing the substances to be metered is preferably regulated continuously and the discharge flow of these substances is regulated by adjusting the pressure of the gas injected into the tank and/or the opening of the relief valve.

According to an advantageous embodiment, metering is carried out as follows:

- the supply valve of the previously filled intermediate tank is closed, the escape valve of this tank is opened, - the tank is pressurised, - a chain for measuring the weight of the two tanks is activated, 3 the relief valve of the filled tank is progress ively opened and the relief valve of the emptied tank is progressively closed, the chain for measuring the weight of the filled tank is activated, - the inlet o. f the pressurised gas into the empty tank is closed, the supply valve of the empty tank is opened, the weight of this tank is regulated as it is filled so as to ascertain the moment when it is regarded as being full, and the corresponding supply valve is closed.

The installation according to the invention is character- ised in that the means for tapping said predetermined masses or volumes and the means for discharging them comprise at least one intermediate storage_tank, a pressurised gas generating device for subjecting the substances contained in this tank to the pressure of this gas, at least one relief and/or control valve mounted on a drainage line of this tank and elements for reg ulating and controlling the pressurised gas generating device and the opening of the relief and/or control valve.

According to a first preferred. embodiment of this installation, it comprises two intermediate storage tanks connected in parallel to the supply vat and a dis charge circuit comprising two relief and control valves respectively connected to each of the two tanks.

According to a second preferred embodiment, it comprises two intermediate storage tanks connected in parallel to the supply vat and a discharge circuit comprising two relief valves respectively connected to each of the two tanks and a single control valve.

4 Each intermediate storage tank is advantageously conn ected to a weighing machine designed to measure the weight of this tank containing a predetermined mass of substance to be metered. The control valve is preferably of the type having a pneumatic 0-ring.

The present invention and its various advantages will be better understood by reference to the description of a preferred exemplified embodiment and of the attached drawing in which the single figure represents the install ation according to the invention in diagrammatic form.

With reference to the figure, the installation described comprises a supply vat 10 containing a liquid or thick substance 11 to be metered, two intermediate storage tanks 12 and 13 connected in parallel by means of lines 14 and 15 to supply vat 10 and two discharge lines 16 and 17 connected between them and to an outlet line 18.

Supply valves 20 and 21 are respectively mounted on supply lines 14 and 15 and relief and/or control valves 22 and 23 are respectively mounted on discharge lines 16 and 17.

An air compressor 24, which could be replaced by var ious other pressurised gas sources, is connected to a pressure distributor 25 itself coupled to the two inter mediate storage tanks 12 and 13. Each of these tanks is connected to a weighing machine 26 and 27 respect ively. Moreover, intermediate storage tank 12 is fitted with an escape or pressurised gas discharge valve 28.

Similarly, intermediate storage tank 13 is also fitted with a valve 29 having the same functions.

The operating principle of the device according to the invention is as follows: the two intermediate storage tanks 12 and 13 are alternately filled and emptied.

While one of the tanks is emptied via the discharge line, by the corresponding relief valve, the other intermediate storage tank is filled. The emptying of the first tank is controlled as a function of the w6ight loss measured by means of the weighing machine corr esponding to the respective tank. The regulation of the discharge of the liquid or thick substances con tained in the tank is effected by controlling the pressure of the gas injected into said tank. This gas may be a neutral gas, a mixture of gas, air, steam or any other gas not reacting with the substances contained in the tank. The regulation may also be effected by controlling the relief valve which is advantageously formed by a pneumatic 0-ring.

When the substances to be metered are formed by easily flowing liquids, the supply vat is connected to the intermediate storage tank and the liquid flows by grav ity into said tank, the section of the supply line being chosen so that the tank is filled over a period of time substantially equal to 80 % of the minimum time required to ensure the other tank is emptied. On the other hand, if the substance contained in the supply vat is viscous or thick, this vat is pressurised to ensure the forced filling of the intermediate storage tanks. The filling of these intermediate storage tanks 12 and 13 is facil itated by two escape valves 28 and 29 ensuring the re moval of the air initially contained in the tank, at the moment of this filling. The tank containing a pre determined volume of substance to be metered is w6ighed; when the upper level is reached, the supply valve is closed.

At the same time the other intermediate storage tank was emptied as a preliminary, this emptying being con trolled as a function of the weight loss of the tank, which is measured by the corresponding weighing machine.

6 This regulation is carried out by controlling the pressure of the gas injected into the intermediate storage tank during the emptying operation, and the said pressure is intended more or less to force sub s stance towards the relief valve. Bearing in mind the elasticity of the gases, this method may have a tendency to vary with respect to the flow if the variations are rapid. However it has the advantage of not having any moving part in contact with the liquid, and this removes any risk of pollution.

Furthermore relief and/or control valves 22 and 23 preferably comprise a circular aperture closed by a holl ow 0-ring made of elastic material and supplied with a liquid which can be injected under pressure. The opening of the relief valve is directly associated with the pressure of the liquid injected into said ring.

It is clearly understood that these relief valves having a pneumatic ring could be replaced by a needlp valve or any other equivalent device. It is also possible to place a single control valve 19 on outlet line 18, in this case the only function of valves 22 and 23 being to shut. As above, no moving part dis turbs the liquid as it is drained from the tank be ing emptied.

It is as well to note that the pressurising of the intermediate storage tank being emptied does not sig nificantly influence the weight of said tank. In fact, the weight of the volureof pressurised air or gas injected into the tank is practically negligible.

with respect to the weight of the liquid or thick substance contained in said tank. For this reason it is possible to regulate the weight loss of the tank during emptying.

7 When the tank being emptied reaches the lower level, an automatic control and operating device 30 ensures the switching of supply and relief valves so that a new filling and emptying cycle can be started.

To carry out metering, the following procedure is used:

- the supply valve of the previously filled inter- mediate tank is closed, - the escape valve of this tank is opened, - the tank is pressurised, - a chain for measuring the weight of the two tanks is activated, - the relief valve of the filled tank is progress- ively opened and the relief valve of the emptied tank is progressively closed, - the chain for measuring the weight of the filled tank is activated, - the inlet of the pressurised gas into the empty tank is closed, - the supply valve of the empty tank is opened, - the weight of this tank is regulated as it is filled so as to ascertain the moment when it is regarded as being full.

- and the corresponding supply valve is closed.

It is obvious that if the installation only has a single intermediate storage tank, it is hardly possible to ensure the continuous metering of substances in- itially contained in supply vat 10. The preferred refinement comprises two intermdiate storage tanks.

one of which is being filled while the other is being emptied and enables continuous metering of substances 11 to be ensured.

8 As mentioned above, this installation and the pro- cess which it ensures enables liquid or thick sub- stances to be metered without the use of a pump.

This invention is not limited to the embodiments described above but may undergo various modifications and may be presented in various ways obvious for a person skilled in the art. Inter alia, the weighing machine may be replaced by measuring the flow in line by -the control valve, by an ultrasonic or Corriolis ef f ect flowmeter or by any other appliance. Furthermore, it will be noted that if the substances treated so require, it is also possible to provide the install ation with a thermostat. This is particularly ad vantageous if viscous substances have to be treated at ambient temperature. This installation enables liquids to be "pumped" upwards. It also enables dangerous liquids and explosive substances-to be treated by appropriately dimensioning the vat and the intermediate tanks.

9

Claims

1. Process for metering liquid or thick substances, characterised in that predetermined masses or volumes of these substances are sequentially tapped, in that these predetermined masses or volumes are temporarily stored in at least one intermediate storage tank of known weight and /or volume, in that these predeterm ined masses or volumes are.subjected to the pressure of a gas and in that the opening of a relief valve and/or the pressure of said gas in said tank is reg ulated so that the flow of said predetermined masses or volumes occurs within a given time.

2. Process according to Claim 1, characterised in that two intermediate storage tanks arranged in parallel are used and in that one of these intermediate storage tanks is filled during At most a part of the time required to empty the other tank.

3. Process according to Claim 2, characterised in that means for filling and emptying these intermediate storage tanks are designed so that one of these tanks can be filled within a period of time less thc,n the minimum time required to empty the other tank.

4. Process according to Claim 1, characterised in that the weight of said predetermined masses of sub stances is determined by weighing the tank.

5. Process according to any one of the above claims, characterised in that, while the tank is being emptied, the variation in weight of the tank containingsubstances to be metered is regulated continuously and in that the discharge flow of these substances is regulated by adjusting the pressure of the gas injected into the tank and/or the opening of the relief valve.

- lO -

6. Process according to Claim 1, characterised in that metering is carried out as follows:

- the supply valve of the previously filled inter- mediate tank is closed, - the escape valve for this tank is opened, - the tank is pressurised, - a chain for measuring the weight of the two tanks is activated, - the relief valve of the filled tank is progressively opened and the relief valve of the emptied tank is progressively closed, - the chain for measuring the weight of the filled -- tank is activated, - the inlet of the pressurised gas into the empty tank is closed, - the supply valve of the empty tank is opened, - the weight of this tank is regulated as it is filled so as to ascertain the moment when it is regarded as being full, - and the corresponding supply valve is closed.

7. Installation for metering liquid or thick substances, enabling the process according to any one of the above claims to be carried out, comprising a supply vat (10) containing the substances (11) to be metered, means for tapping predetermined masses or volumes of these sub stances, and means for the controlled discharge of said predetermined masses or volumes, characterised in that the means for tapping said predetermined masses or volumes and the means for discharging them comprise at least one intermediate storage tank (12 or 13), a pressurised gas generating device (24)-for putting the substances contained in this tank under the pressure of this gas, at least one relief and/or control valve (22 or 23) mounted on a discharge line (16 or 17) of this tank and control and operating elements (30) for the pressurised gas generator and of the relief and/or control valve (22 or 23).

8. Installation according to Claim 7, character ised in that it comprises two intermediate storage tanks (12 and 13) connected in parallel to the supply vat (10) and a discharge circuit comprising two relief and control valves (22, 23) respectively conn ected to each 'of the two tanks.

9. Installation according to Claim 7, character ised in that it comprises two intermediate storage tanks (12 and 13) connected in parallel to the supply vat (10) and a discharge circuit comprising two relief valves (22, 23) respectively connected to each of the two tanks and a single control valve (19).

10. Installation according to Claim 7, character ised in that each intermediate storage tank is connected to a weighing machine (26, 27) for measuring the weight of this tank containing a predetermined mass of the substance to be metered.

11. Installation according to any one of the above claims, characterised in that the control valves (22, 23, 19) are of the type having a pneumatic 0-ring.

12. A process for metering liquid or thick substances, or an installation enabling the process to be carried out, substances hereinbefore described with reference to the accompanying drawing.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WClR 4TP. Purther copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed b.v Multiplex tecbniaues ltd. St Marv Crav. Kent. Con. 1/87.