WO1991010116A1 - A method and a device for determining the positions of boundary layers - Google Patents

Abstract

A method and a device for determining vertical distribution of one or a plurality of media (14, 15) surrounding a measuring device (1-6), and where the positions (31) of boundary layers may be determined from the difference of an arrangement of one or a plurality of thermal sensor elements (1) which have direct or indirect thermal connection with the medium to be measured (14, 15), via an external partition (5), and where a temperature sensitive self-regulating material is used for said element or elements, preferably an electrically conductive composite material, power being supplied to the element or elements, and said position(s) being recorded as a function of the power consumed by element (1), i.e. as a function of the mangnitude of the effect absorbed by the measured medium at the measuring point (its heat conductivity).

Description

A method and a device for determining the positions boundary layers

The present invention relates to a method for determini vertical distribution of one or a plurality of med surrounding a measuring device, and by which the positions boundary layers may be determined on the basis of differen in the arrangement of one or a plurality of thermal sens elements having a direct or Indirect thermal coupling to t medium to be measured, via an external partition, with pow being supplied to said element or elements, and with sa position or positions being recorded as a function of t magnitude of the power absorbed by the medium to be measur at the measurement point (its heat conductively).

In connection with continuous monitoring of tanks and stora spaces constant monitoring of the position and extension boundary layers, as well as any formation of sludge zones i required. By a slugde zone is meant a mixture zone of t substantially adjacent substances, but certain deposits m also be admixed, like wax and other pollutions having specific gravity which lies between that of both adjacen main media, like crude oil and water in the present case. Th boundary layers may consist of various kinds of liquids granules, gases, and a combinationt thereof. A specia object is a measuring device for determining the positions o boundary layers in storage tanks for crude oil in case o production or storage at sea or in connection with larg storage spaces in rock.

In said storage systems the boundary layers substantiall comprise oil/water, but transitional layers of liquid/gas an liquid/sediments or other kinds of deposits are not uncommon Additionally, transitional zones are often formed, especiall about boundary layer positions, which substantially const itute a composition of two or more of the components to b stored. They form so-called slugde zones with consequent formed deposits which may adversely influence measuri devices or the like.

Furthermore, installations in the above mentioned situatio are such that maintenance, replacement, cleaning or ot kinds of service present great difficulties of access high costs.

There are various sensor systems based on thermal effect European Patent Application No. 0052215 from VDO in German filed in 1981 may be mentioned as an example. Here, principle is shown according to which a pattern of resistan elements is etched out from a substrate which is suppli with constant current. The voltage drop across the resis ance elements will be higher or lower dependent on wheth the element is submerged in a liquid or not.

Signal processing electronics successively connect t elements, voltage is recorded, and the level of volt determines whether the element is completely or part submerged in liquid. In case an element is partly submer the additional level is achieved by the aid of interpolati between the fraction of voltage drop in air and the p centage of voltage drop from the portion of the elem which is submerged in liquid.

A number of similar level measuring systems is disclose especially in connection with fuel tanks on vessels, in whi resistance elements in the form of metal wire or vari kinds of thin film/thick film techniques are in dir contact with the medium to be measured, as will also app from French Patent No. FR 8215 750, Pras Jean Claude. detailed description is also found in VDI-Berichte No. 5 1984, pp 235-242. It is common to the above mentioned principles of measurem that they are mainly intended for level measurement in f tanks containing pure products, and that the measurement made to determine the boundary layer between air and liqui Also, the self-regulating elements are required to be direct contact with the medium to be measured, and lo connector lines to the individual measuring elements must avoided, since such lines easily contribute to errors. Th means that signal processing should occur in the immedia vicinity of the self-regulating element.

Among other known level measuring systems which utili thermal effects to detect level and boundary layers, vario discrete point level measuring means should be mentioned, which the heat transport from a heating element to a medi which is to be measured is measured by the aid of a diffe encial recording temperature measurement system which mainly based on a thermopile comprising a large number thermoelements which are serially connected.

Due to the fact that the separate points of measurement a successively connected to a suitable signal processing uni the thermal transport at each point of measurement will be expression of the nature of the surrounding medium. Amo the patent literature it may be referred to NO-PS No. 1 517, GB Patent Application No. GB-A 2 134 260, US-PS Nos. 2 702 476, 3 280 627, and German OS No. 1 959 04

It is common to measuring devices of the above mentioned ki that each point of measurement is relatively expensive a complicated, especially if a useful contrast between signa from different measured media is to be achieved. Comprehen ive and expensive signal conditioning will be require especially when low signal levels are to be transmitted, vi long cables. Additionally, good thermal control of the he source and the thermal masses incorporated in the system wil be required, as well as stabilization of the temperature o the medium to be measured.

The method according to the invention is characterized i that for the mentioned element of elements a temperatur sensitive self-regulating material is used, preferably a electrically conductive composite material, that said powe is electrical power which is supplied directly to th element, and that said position or positions are recorded a functions of the electrical power consumed by the element.

The measuring device according to the invention is charac terized in said element or elements consisting of temperature sensitive self-regulating material, preferably o an electrically conductive composite material (1), e.g consisting of a polymer with a carbon compound having goo mechanical and electrical coupling to metallic, paralle connectors (2,3) by the aid of which one or a plurality o elements are designed to be selectively connected to input of a signal processing unit (40), and that said element o elements are arranged substantially vertically, so that or a such a mutual distance that one or a plurality of boundar layers may be recorded.

Further characterizing features of the method and measurin device will appear from the following claims and th disclosure below.

According to the invention great flexibility is achieved a regards resolution and signal effect, as well as a sub stantial cost saving effect both as regards manufacture an installation. Supplied electric power to the sensor poin depends on the dissipated thermal effect, which in tur depends on the thermal condition of the surrounding medium An essential advantage is that the sensor signal in the for of supplied power and necessary heating of the element ma occur over the same connector lines. The invention is based on thermal principles, heat bei transported to the medium to be measured from a heati element which is strongly self-regulating, i.e. suppli power is a function of the power loss to the medium to measured. In this manner a heating source and a sensor ar somehow combined in one and the same unit, which is in thi disclosure designated a self-regulating element, the self regulating element regulating the supplied electrical powe as a function of the temperature of the element, and th temperature, in turn, depending on the heat dissipation t the surrounding medium. By recording supplied power at an time a signal effect is achieved which is an expression o the composition of the surrounding medium based on therma properties.

The sensing effect is achieved by the fact that the activ element in the sensor is manufactured from a polymer with a admixed conductive carbon material forming a large number o parallel electric connections between substantially paralle connectors which are integrated in the element and form th points of connection for the connector lines between separat sensor points and the signal processing unit.

Due to the fact that power is supplied to the connecto lines, the intermediate semi-conductive core material i heated and a microscopic expansion occurs with a subsequen increase of resistance, which will in turn result in reduction of delivered power.

In the same manner a temperature reduction will caus contraction of the material and, thus, reduction of resist ance, resulting in an increase of delivered power. In thi manner the self-regulating effect is achieved which forms th sensor signal proper. In the market there are various manufacturers of heati elements based on plastic materials which show the abo mentioned effect due to admixture of conductive material carbon, metal particles, or the like, and which may adapted to a sensor element as to shape and size. Terminati of the connector lines to individual sensor elements, bo mechanically and electrically, is of great importance achieve a stable element. In the presently disclosed examp of a sensor system embodiment there is, for practical reaso used the material of a heating cable, which has the abo mentioned regulation properties, and the termination betwe said material and the connector lines show a suitable desig

The above mentioned example of application of the material the self-regulating element is only given to show a practic design without this being considered a limitation to oth materials having the same properties, but with differe design, termination, etc. Among known product names Raych has a comprehensive spectrum of heating cable products whi are adapted to various objects as regards operation voltag temperature range, power per unit length with various kin of mechanical, electrical, and chemical protection.

A sensor system will basically comprise a series of discre self-regulating elements with a suitable vertical distribu ion. The connector lines connect each individual sel regulating element with a connector means enabling ea individual element to be connected to a clrcuittry in whi the supplied power is measured as to magnitude and time f each separate element.

In larger sensor systems comprising a large number measuring points it may be advantageous to distribu connectors for separate measuring points in suitable group matrix, or other known designs for addressing certa elements or groups over a minimum of connector lines. T simplest design would be a larger or smaller group of sel regulating elements with a common connection, whereas t others are extended separately to the connector means. certain cases it may be suitable to integrate connector mea together or closely to the self-regulating elements, so th the separate elements may be connected to the common pow supply which is controlled via signal lines, and will th reduce the connector line connection between sensor a connector module.

Determination of boundary layers occurs by sensor elemen being successively connected to a power source in a suitabl sequence. Supplied power is recorded, and based on knowled of the power characteristic of the sensor element as function of temperature, the thermal properties and, thus positions of the surrounding medium are determined.

A special embodiment of a self-regulating element consists o a vertical distribution of the active sensor material with cable-like design and with two connector lines for connectio of a power source. The supplied power will commonly regulat on the average value of the total extension of the element The sensor may, thus, comprise one or a plurality of self regulating element(s), or a combination of short punctiform as well as elongate elements to cover special requirement of a tank measuring system.

Due to a certain thermal transition resistance between th element and the medium a temperature differential will occu between element and medium. This will vary vertically i case the self-regulating element is in a transitional zon between two or a plurality of media which are to be measure and have different thermal properties. By the aid o temperature sensors which are suitably distributed verticall and with good thermal connection closest to the medium to b measured, one or a plurality of transitional zones or passage thereof may be recorded within one and the same self regulating element. A microprocessor controls signal processing and will on t basis of measurement data provide unambiguous informati about the measured medium surrounding the sensor, as regar thermal properties of said medium, which determines the pow delivered by the self-regulating element.

The invention is now to be disclosed in more detail wi reference to the attached drawings representing non-limiti embodiments of the invention.

Figure 1 shows the active self-regulating element connection with a measuring point. Figure 2 shows an example of the relationship of pow and temperature. Figure 3 shows the active self-regulating element plac

Inside a protective tube. Figure 4 shows a sensor with an elongate self-regulati element with temperature sensors. Figures 5-8 show further examples of the arrangement of t active self-regulating element. Figure 9 is a sectional view along the section IX-IX

Figure 8. Figure 10 shows an example of grouping connector lines separate self-regulating elements. Figure 11 shows an example of a complete sensor install

In a storage tank for oil and water. Figure 12 shows a block diagram of connections betwe sensors and signal processing and display.

In Figure 1 an embodiment is shown of the active sel regulating element with active material 1 forming a lar number of parallel paths of power between connector lines and 3. The material has an enclosing mantle of an ele trically well insulating material 4. Emitted power per un length is a function of the composition and temperature the material. In Figure 2 an example of a typical characteristic illustrated, showing the ratio between supplied power ( W/ft) and temperature (degrees F) of various mixtures of t active material, marked a, b, c, and d.

Figure 3 shows an example of how the self-regulating eleme 1 is thermally connected to the inside of a tube wall 5 the aid of a material 6 showing good thermal conductivity f optimalization of the thermal contact between the sel regulating element and the tube wall. The connecting materi 6 may be of metal or a similar conductive material, desired, a glue or paste showing good thermal conductivit The self-regulating element may show a certain vertic extent which may, in fact, constitute an independent syste It may, if desired, form a measurement point with a certai vertical extent, but which in a larger measuring system, e. of more than 100 meters, will be considered a measurin point.

In Figure 4 an example is shown of how a plurality o measuring points may be established along the extent of self-regulating element due to the fact that a self-regulat ing element 1, which has a certain vertical extension an will maintain a constant temperature within its regulatio area due to its self-regulating function. In the Figure thre separate connectors 11, 12, 13 are shown, each of which form a separate thermal connection with media 14, 15 to b measured. The latter, in turn, have different therma properties. Medium 15 which may be water, may e. g. exhibit higher heat sink effect than medium 14, which may e.g. b oil. The temperature differencial across respective connec tors 11, 13, which is recorded by the aid of temperatur sensors 7, 9, will thus be different. The difference will b proportional to the difference of thermal conductivity an capacity of the media to be measured. Connector 12 wil transfer thermal power to both media, 14 and 15. This mean that the temperature difference as measured at 8 is high than 15 and lower than 14 in water and oil, respectivel Temperature measurements 7, 8, 9 are conveyed to sign processing unit 40 and are indicated to be differe temperature gradients on display 45 in the form of diagra 43.

Figure 5 shows an embodiment with the self-regulating eleme being provided in good thermal contact with a connect material 16 on the inside of a tube-shaped barrier. In th manner a radial thermal contact with the medium to measured is achieved through the tube, at the same time the vertical extent of the sensor point is limited. T central portion 18 of connector material 16 provides spa for extending connector lines from self-regulating elemen which are located lower (not shown in Figure 5). Thus, figu represents a variant of that shown in Figure 4 and in t following Figures 8-11.

In Figure 6 a flat design is shown, in which the sel regulating element 1' is in thermal contact with two later faces 19, 19' of the barrier. In this manner the therm contact between sensor element 1 and the surrounding medi to be mesured is enhanced, via connector elements 20, 20' a barrier 19, 19'. Connector elements 20, 20' may be of material showing good thermal conductivity. Voids 21 provi space for electric connections 22 to the self-regulati elements.

Figure 7 is substantially like the embodiment shown in Figu 6, apart from the fact that sensor element 1'' has mo horizontal extension to provide for limited vertic extension of the measuring point (sensor point) in order increase the vertical resolution for level indication.

Figure 8 shows a flexible sensor device in which sel regulating elements 1"' are provided on a flexible tube-li core 23 which also forms a channel for conveying of conduct lines 2, 3. Barrier 24 consists of a flexible material, e. polyethylene or the like. In connection with large lengths may be suitable to integrate a flexible member 25, e.g. steel, Kevlar® or another material with tensile strength order to absorb tensile forces and to render the sens length stable to achieve vertical measurement accuracy.

In an Integrated embodiment, in which sensors and feed lin in principle form a cable-like design, a uniform sens system is achieved without any hazard of liquid intrusio which is especially suited for underwater storage syste where an inaccessible termination point between sensor a cable is located in water of somewhat high pressure.

Figure 9 is a sectional view along section IX-IX of Figure

In Figure 10 an example is shown of how various self-regulat ing elements 1"" may be terminated in groups 26, inter ali to distribute supplied power in a suitable manner. Connec tions 2 and 3 to the separate sensors are quite dependent o the applied method of addressing. In the shown embodiment th sensors are supplied with d.c. power, and in order to preven undesirable parallel connections a blocking diode 27 i provided in connector line 2 to each separate element.

Figure 11 shows an example of a sensor installation in storage tank 38 for oil 29 and water 30, respectively, wit a transition zone 31. Self-regulating elements 1'" may have suitable vertical distribution, e.g. different mutua distance, and are surrounded by a steel tube 32. The senso ends in a sensor head 33 with termination 34 of the electri connections to sensor points 1"'.

In Figure 12 a simple block diagram is shown of connection between sensors and associated units. Separate sensors 35 35', 35" are connected, via multiwire cables 36, with connector module 37, which connects the individual sel regulating elements 1"' in sensors 35, 35', 35^H successivel or in groups to a power supply 38. Supplied power to t individual self-regulating elements is measured and converte in an A/D converter 39. The signals are processed in a sign processing unit 40 and are compared with measurement valu in a calibration table. Control of connector module 37 i achieved, via the signal processor, which may on the basis o the result of measurement influence the connection separate self-regulating elements in a suitable manner, e. in groups, as a function of level position and direction well as supplied power. A display unit 41 is an example possibility of presenting a survey of the positions 42 respective transition zones. Temperature gradient 43 may an integrated part of the display unit.

The self-regulating element or elements may function li temperature resistors to measure the vertical distribution temperature of the surrounding medium to be measured. This i an Important feature, since the temperatures of the liqui may initially be different, which will strongly enhance t effect of measurement. This is the case, especially connection with the main application of the present syste i. e. storage tanks on a production platform, in whi differences in temperature between oil and water may reach degrees or more. By the aid of the signal processing un this information is extracted and may be displayed on displ 41 in the form of temperature gradient curves 43. Th should not be mixed up with Figure 4, in which the tempera ure is obtained by the aid of special temperature senso which only react to temperature.

An example of an application of said system is a producti platform where crude oil is temporarily stored in lar storage cells which contain oil and water at a vertic distribution. The extent of the sensors comprises the total area measurement of the respective transistion zone. The vertic distribution of measuring points may be adapted to t requirement of resolution. The separate self-regulati elements are connected to power supply 38 individually or i groups, whereas power supplied to each element is measur and converted in A/D converter 39 to digital form for furthe signal processing in signal processor 40. The magnitude o supplied power is a function of the temperature of th element which is, in turn, influenced by thermal propertie of the surrounding medium.

Since there is less thermal dissipation from sensor to oi than to water, there will be more supplied electric power i water than in oil. The relative difference between senso points in oil and water, respectively, are essentially give by the temperature gradient in respective media to b measured, and to a certain degree by production tolerances o various self-regulating elements.

The sensitivity characteristics of the individual self regulating elements as a function of temperature in a know medium to be measured, e.g. water, may be incorporated as calibration value of the complete sensor forming a referenc table.

With said reference table being included in the signa processing, it is possible to discriminate between variou media and the vertical temperature gradients along th surface of the sensor. By the aid of slightly more sophisti cated signal processing, motions of various transition zone in the storage cells may be monitored, so that only th adjacent self-regulating elements are activated at any give time, at the same time as the magnitude and character o signal levels relative to reference values and the positio of the boundary layer will be an expression of the conditio of the measurement point with respect to formation o coating, e.g. formation of wax. Also, it will be possible discriminate between upper and lower limit of a bounda layer zone, especially when it passes one or a plurality sensor points, e.g. when the tank is filled or emptied.

In case a coating, e.g. wax formation, Is recorded about t sensor point, more power is applied for some time and/or magnitude, which will, in turn, cause a higher surfa temperature and prevent formation of wax. This may manually controlled or constitute part of the sign processing routine. Especially in connection with stora cells the sensors will be subjected to deposition of wax. will then be important to be able to control supplied pow by the aid of the sensors to prevent such deposition. T self-regulating element, thus, has three functions, viz: to record transition zones based on thermal properties of t media, 2) to record the temperature (gradients) of media, a 3) to prevent and/or remove wax deposits.

The composition, consistency, and temperature of the medi to be measured is substantially determining the magnitude a duration of applied power. In addition there is the requir ment of time for response.

There are two alternative ways of controlling the sensors:

a. Using the dynamic, and statistical portion, respectivel of the supplied power characteristic, with the dynamic portion representing the drop characteristic of decreas as a function of time subsequent to the connection of t self-regulating element, whereas the statistical portion is represented by the stable power level which t sensor adopts after a certain period of time. In this ca the sensors or groups thereof will be constantly activat (heated), at the same time as applied power on individu elements is recorded successively. This method provid for the quickest updating time (response time) and t highest sensitivity against changes of the therm properties of the medium. However, correspondingly hi amounts of applied energy will be required due to t large number of sensors connected at the same time.

b. Alternatively, the self-regulating elements are connect separately, and the dynamic process from the moment connection until a given point of time is an expression the response by the sensor, as a composite function of t thermal properties both of the sensor and of the surroun ing media. The thermal properties of the sensor are kno according to a calibration table (reference values) an may, thus, in principle be subtracted from the measure value to permit determination of the thermal properties o the surrounding medium to be measured.

The same method may, obviously, be used for measurin transition zones, temperature gradients of other media an combinations as those mentioned above, provided they hav different thermal properties.

Claims

PATENT CLAIMS: 1. A method for determining vertical distribution of one or plurality of media surrounding a measuring device, and b which the positions of boundary layers may be determined o the basis of difference in the arrangement of one or plurality of thermal sensor elements having a direct o indirect thermal coupling to the medium to be measured, vi an external partition, with power being supplied to sai element or elements, and with said position or position being recorded as a function of the magnitude of the powe absorbed by the medium to be measured at the measuremen point (its heat conductivity), c h a r a c t e r i z e d i n that for the mentione element or elements a temperature sensitive self-regulatin material is used, preferably an electrically conductiv composite material, that said power is electrical power whi is supplied directly to the element, and that said positio or positions are recorded as functions of the electric power consumed by the element.

2. A method according to claim 1, c h a r a c t e r i z e d i n that a combination o discrete points and continuous measurement is provided b making the elements cover different vertical length units.

3.

A method according to claim 1 or 2, c h a r a c t e r i z e d i.n that the vertical di tribution of temperature of the surrounding medium i measured by letting the elements function as temperatu dependent resistors.

4.

A method according to one or several of claims 1 - 3, c h a r a c t e r i z e d i n that the elements besid having their measuring effect also prevent formation of w as a consequence of the heat power delivered thereby to t surroundings.

5.

A method according to one or several of claims 1 - 4, c h a r a c t e r i z e d i n that a sludge layer, I.e. zone in which both media to be measured in the boundary zo are mixed in a ratio which follows a certain vertic gradient, is recorded by interpolation between media, a with the gradient being recorded by one or a plurality measurement points being passed in a situation of loading unloading said media to be measured in a storage container.

6.

A method according to one or several of claims 1 - 3, and 5, c h a r a c t e r i z e d i n that information recorde by said elements is extracted both in a statistic and dynamic portion of signals delivered by said elements.

7. A method according to one or several of the preceding claims c h a r a c t e r i z e d i n that one or a plurality o temperature sensitive means are provided closer to the mediu to be measured than said elements in order to record th gradient of the relative distribution of the therma transport along the extension of the elements.

8.

A device for determining the vertical distribution of one o a plurality of media surrounding a measuring device, wher the positions of boundary layers may be determined fro differences in thermal conditions and properties, where a arrangement of one or a plurality of thermal sensor element having a direct or indirect thermal coupling to the medi to be measured, via an external partition, are used, whe power is supplied to the element or elements, and whe said position or positions are recorded as a function of t magnitude of the power absorbed by the medium to be measur at the measurement point (its heat conductivity), c h a r a c t e r i z e d I n said element or elemen consisting of a temperature sensitive self-regulati material, preferably of an electrically conductive composi material (1), e.g. consisting of a polymer with a carb compound having good mechanical and electrical coupling metallic, parallel connectors (2, 3), by the aid of which o or a plurality of elements are designed to be selectivel connected to inputs of a signal processing unit (40), a that said element or elements are arranged substantiall vertically, so that or at such a mutual distance that one a plurality of boundary layers may be recorded.

9. A device according to claim 8, c h a r a c t e r i z e d i n that each element is independent self-regulating heating element, e.g. in a cabl like design, in which each element has its said metall connectors (2, 3) connected to a power source (38).

10.

A device according to claim 8 or 9, c h a r a c t e r i z e d i n that the elements a surrounded by a barrier (5; 10; 19, 19') of a suitab material forming a protection against the medium to measured, e.g. made from acidproof steel or plastic materia e.g. Teflon, nylon, polyethylene, or the like.

11. A device according to one or a plurality of claims 8 - 10, c h a r a c t e r i z e d i n that one connector (2) the elements is common, whereas the other connector (3) the elements permits selective connection of the elements I dividually by the aid of a suitable connecting modu (Figure 10).