GB2219105A

GB2219105A - Controlling a property of a mixture

Info

Publication number: GB2219105A
Application number: GB8909541A
Authority: GB
Inventors: Kolbj Rn Elvebu
Original assignee: Ulstein Nor A S
Current assignee: Ulstein Nor A S
Priority date: 1988-04-29
Filing date: 1989-04-26
Publication date: 1989-11-29
Anticipated expiration: 2009-04-26
Also published as: NO881908D0; GB8909541D0; NO881908L; NO172266C; NO172266B; GB2219105B

Abstract

To control a property such as the density of drilling mud or other mixture supplied from a container 6, the density is measured at 17, 18 or at 25, and a level sensor 23 measures the quantity of mixture in the container. A control unit 22 then calculates how much of an additive in storage tank 3 needs to be added to a set fraction e.g a third of the measured quantity to bring the density of that fraction to a desired level. The calculated amount is then dispensed by reference to weighing cells 19 and mixed with the mixture. The resultant density and quantity are then measured again and the whole process is repeated until the density falls within determined limits. <IMAGE>

Description

A METHOD AND A DEVICE FOR AUTOMATIC PRODUCTION OF A MIXTURE COMPRISING AT LEAST TWO FLOWABLE COMPONENTS The invention relates to a method and a device for automatic production of a mixture comprising at least two flowable components, and having certain desired properties, where it is possible to vary the properties of the mixture by varying the ratio of mixture.

The invention is intended for use especially in connection with preparation of drilling mud which is used in connection with oil drilling, more precisely, in connection with dosing weighting materials which are added to achieve a desired density. The invention may, however, also be used in mixing powders and mixtures, e.g. in paint producing industry, or processing industry.

Automatic mixing devices for drill mud are previously known, where discharge of free-flowing or bulk material from the tanks depends on the material flowing freely out of the tank, without any actuation by vibrating devices or the like. This condition, however, is not always achieved which will cause failures. Furthermore, a discharge valve is known which comprises a bucket wheel to provide volumetric control of the discharge. Such valves are more complicated than, e.g. simple valves of the flap valve kind and render the plant more expensive. It is previously known to use radioactive isotopes for determining the density of ? mixture. Besides being an indirect measuring method, this is also a comparatively expensive method.

The known methods of the kinds mentioned above basically require that the added components after, e.g. only one determination of density, will cause the mixture to achieve the desired density. Depending on the accuracy of determination of density, determination of the volume of the mixture, and the volume of discharge, the achieved density of the mixture may correspond to the desired density to a varying degree. It is, thus, not ensured that this method will result in the actual density of the mixture converging towards the desired density.

It is an object of the invention to provide a method and a device of the above mentioned kind which does not have the above disadvantages. The characterizing features of said method and device will appear from the claims.

In the following, the invention is disclosed in more detail with reference to the single Figure of the drawing which shows an embodiment of a device according to the invention.

The mixture may comprise a liquid, and the shown embodiment comprises a device for supplying bulk material to such a mixture.

Above a tank 3 a storage bunker 1 is provided for bulk material which may flow down into tank 3, via a bunker valve 2. From tank 3 the bulk material may flow on to a container 6, via a tank valve 4, and a mixing chamber 5.

An agitator 7 may be provided in container 6 for mixing the components, and the mixture may be supplied to the users from container 6, via a user's pipeline circuit 8, shown in dashed lines. Said pipeline circuit may, e.g. comprise a pump 9, and if the mixture is to be returned to container 6, the circuit may comprise a return pipe 10. Container 6 may, furthermore, comprise a level gauge 23 for determining the surface level and, thus, the volume of mixture in container 6.

One or a number of sensors 25 may be provided in container 6 for determining the value of the property parameter to be varied by addition of the bulk material to the container. If it is important to have the mixture at rest during determination, the device may, as shown, comprise a measuring pipe circuit 11 with a pump 12 to pump mixture from the tank and return it to the tank through a main pipe 13, mixing chamber 5, and the pipe through which bulk material is supplied from the mixing chamber and to container 6.

A bypass 14 forming a parallel circuit with main pipe 13, is connected with the latter at two separate locations in the flow direction. Between said connections a choke means 24, which may, if desired, be adjustable may be provided to retain mixture flowing through the main pipe. In bypass 14 a closing valve 15, and 16, respectively, may be provided at one or both connections and, e.g. in the central portion of bypass 14 one or more sensors, e.g. two sensors 17, 18 may be provided.

For measuring the total content of the tank 3 in order to determine whether it is necessary top up with bulk material from bunker 1, or for measuring the quantity of discharged bulk material from the tank, the latter may be supported by weighing means 19, e.g. weighing cells.

Since bulk material may tend to agglomerate and stick to the tank walls, the tank may be provided with a means known per se, for creating a fluidized bed in the tank. In this manner bulk material can readily readily pass through valve 4. Valve 4 may, thus, be a simple and inexpensive flap valve, or the like. Such a means for producing a fluidized bed may comprise a compressed-air tank 20, and a pipeline extending from tank 20 to tank 3, with an air valve 21 provided in said pipeline.

For automatic discharge of bulk material from tank 3 a control unit 22 is provided and is designed to receive information on the value of the determined property parameters, on the weight of the bulk material in tank 3, and on the level and, thus, volume of the mixture in container 6, from sensors 17, 18, and if desired, 25, weighing means 19, and level gauge 23, respectively. Furthermore, tank valve 4 and air valve 21 are provided with maneuvring means which may be actuated by control unit 22. Bunker valve 2 and closing valves 15, 16 are also provided with such maneuvring means, if such valves are provided.The control unit is designed to receive and store data on the desired density of the mixture, and permitted maximum and minimum values of the weight of the bulk material in the tank, and to transmit actuating signals to bunker valve 2 to open or close said valve if the weight falls short of the minimum value, or exceeds the maximum value, respectively. Furthermore, the control unit is designed to calculate the volume of the mixture in container 6 by the aid of signals received from level gauge 24, and to transmit signals to closing valves 15, 16 at predetermined intervals to close said valves and then open them after a predetermined interval.

Assuming that container 6 initially contains drilling mud of too low a density, i.e. of a density lower than a predetermined desired value set in the control unit, and that bunker 1 contains a bulk material which can increase the density of the drilling mud by addition to such mud, the device functions as follows. It is also assumed, in the following, that pump 12 continuously pumps mixture through measuring pipeline circuit 11, and that the latter comprises the bypass 14.

Given the above conditions the drilling mud mixture will be pumped into pipeline circuit 11, and if closing valves 15, 16 are open, choke means 24 will cause part of the mixture to flow through bypass 14. After the mentioned interval closing valves will close, and the property parameter of interest (in this case the density) of the mixture in bypass 14 between valves 15 and 16 will be measured by sensors 17, 18. Because the liquid in bypass 14 between valves 15 and 16 is at rest, erroneous measurements due to movement of the liquid are avoided. For measuring the density of the liquid the longitudinal axis of bypass 14 may extend vertically, two sensors 17, 18 being provided at a vertical distance from one another and serving to measure the pressure of the liquid in the bypass at the respective different levels of the sensors 17, 18.On the basis of the vertical distance between sensors, and the difference between pressures measured by the sensors 17, 18, the control unit calculates the density of the mixture in branch pipe 14. On the basis of the signal emitted from the level gauge the control unit calculates the volume of mixture in container 6, and sets a volume (herein referred to as the set volume), which is, for certain, smaller than the calculated volume, for example which is one third of the calculated volume. Then the control unit calculates the quantity of bulk material which it would be necessary to mix with this set volume, at the density calculated from the signals from sensors 17, 18, to bring this volume to the predetermined desired density.

To discharge said calculated quantity of bulk material the control unit transmits an actuating signal for opening air valve 21 and, at the same time or later, it transmits an actuating signal for opening tank valve 4. Bulk material then flows down into mixing chamber 5, where it is gradually mixed with the mixture in measuring pipeline circuit 11, and then flows down into container 6.

When the calculated quantity of bulk material has been discharged control unit 22 transmits closing signals to the open valves 4, 21. Agitator 7 ensures a homogeneous consistency of the mixture and prevents sedimentation of the bulk material.

Then closing valves 15, 16 are closed and the volume of the mixture is measured once more in the same way as before. The control unit sets a new set volume of mixture which is smaller than the new measured volume and which new set volume may be equal to the previous set volume, or may be slightly larger than the previous set volume, for example one incremental value larger than the first volume, or which may be the same proportion, e.g. one third, of the new measured volume as the previous set volume was of the previous measured volume. The control unit then calculates the quantity of bulk material which it would be necessary to mix with the new set volume, at the most recently measured density, to bring this volume to the predetermined desired density, and this quantity of bulk material is added to the mixture in the container in the same way as before.By repeating the above mentioned process it is possible to achieve a gradual increase of the density of the drilling mud to the desired value.

This dosing method is based on an algorithm which is known from mathematical approaches and is called functional iteration. By utilising said method in the above context a gradual approximation of a property parameter to a desired value may be achieved with an accuracy which is, in practice, only limited by the operating accuracy of the device.

If the property parameters are not influenced by whether the mixture is at rest during determination, the sensor or sensors may instead be provided in main tube 13 or in container 6, as indicated by reference numeral 25.

The device is described above with only one tank 3 and discharge and determining means provided for said tank. It is, however, possible to provide a plurality of tanks 3 with associated means for different components of the mixture which influence various properties of the mixture. If tanks are provided for liquid components, e.g. the device for creating a fluidizing bed will, obviously, be omitted.

Claims

CLAIMS:

1. A method for automatic production of a mixture comprising at least two flowable components and having certain desired properties, where the properties of the mixture may be varied by variation of the ratio of mixture, whereby a first quantity of mixture which may, but need not have approximately the desired properties is initially prepared, and the momentary total quantity and the property parameters of the mixture are determined, c h a r a c t e r i z e d i n that a) a second quantity of mixture which is smaller than the momentary total quantity of mixture is determined, b) the quantities of components which would have to be supplied to the second quantity of mixture for the latter to show the desired values are calculated, and said quantities of components are supplied, c) the momentary total quantity of mixture is determined, d) another second quantity of mixture which is smaller than the momentary total quantity of mixture, and which may. be increased by an incremental value to be larger than the last calculated second quantity of mixture is determined, e) the property parameters of the mixture are determined, and f) steps b-e are repeated until the value of property parameters is within determined limits.

2. A device for use by the implementation of the method according to claim l, comprising - a separate storing tank (3) for each of the flowable components, - a discharge pipe for each tank (3) connecting the tank (3) with a container (6) for mixing of the components, - a discharge valve (4) provided in each discharge pipe and - a control system (22) for controlling discharge of the content of the tank(s) dependent on measured values of property parameters to change the ratio of mixture, c h a r a c t e r i z e d i n that it comprises a device (20, 21) for producing a fluidized bed in the tank(s) (3) and a weighing means (19) for current measurement of the weight of the content of the tank(s), whereby the control system comprises a control unit (22) which is connected with the device (20, 21) for producing a fluidized bed, the discharge valve (4) and the weighing means (19), and is adapted to provide opening and closing of the discharge valve (4) and at the same time starting and stopping respectively of the device (20, 21) for producing a fluidized bed and thus to control the discharge of calculated quantities of the content of the tank(s) (3) based on the current measurement of the weight thereof.

3. A device according to claim 2, c h a r a c t e r i z e d i n that the discharge valve (4) is butterfly valve, a ball valve or the like.

4. A method according to claim 1 and substantially as hereinbefore described with reference to the accompanying drawing.

5. Apparatus for use in producing a controlled mixture of flowable components, substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

6. Any novel feature or combination of features described herein.