DE2800157A1 - DEVICE FOR MONITORING THE ELECTROSTATIC CHARGE TRANSPORTED BY A FLOATING MATERIAL - Google Patents

Description

PATBNTAHWALT DIPL. ING. K. HOLZEK PHILIPPINE -WELSEB -BTHABBM 14

8900 AUGSBUKG

TELEFOIf B16475 TELEX 63310S P * <al d

W.263

Augsburg, January 2, 1978

National Research Development Corporation, Kingsgate House, 66-74 Victoria Street, London SWl,

England

Device for monitoring the electrostatic charge transported with a flowing material

The invention relates to a device for the continuous monitoring of the with one through a pipeline flowing, flowable electrically insulating material per unit of time transported amount of electrostatic charge.

The creation and transport of electrostatic charge through electrically insulating, through a conveyor system

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flowing material is a general Ue driving especially when handling volatile hydrocarbon fuels or fuels is important. üs is aesnalb It is important to be able to monitor the charge density in order to neutralize the charge using methods known per se to be able to.

When considering possible means of measurement, lnuio jedoen the inaccuracy of the term "isolating" in context must be taken into account with the flowing insulating material. It can therefore, for example, a type of Monitoring device should be considered, which is suitable for materials, of which iovor gangs during the heating only a very small amount of charge is delivered to the wall of the heating chamber. Such materials have a long relaxation time.

Other materials such as certain types of liquid fuels for which the On the other hand, they actually show a long relaxation time based on conventional conductivity measurements a comparatively quick relaxation.

The invention is based on the object of designing a device of the type mentioned at the outset in such a way that

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They are particularly useful for monitoring the electrostatic Loading of materials of the latter type is suitable.

This object is achieved according to the invention by the arrangement specified in the characterizing part of the main claim solved.

The relationship between the current measured in the ground line and the respective charge density leaves for every material from the knowledge of the volumetric Derive Kengenstromes.

Preferably the heating chamber is essentially complete enclosed by a grounded electrostatic shield.

The heating chamber can have an essentially cylindrical shape, the ratio of the inner diameter of its enlarged section to the inner diameter of the inlet being in the range from 1/2 : 1 to 1/2 : 1. The square root form of the ratios is chosen in order to emphasize the respective cross-sectional ratio represented by the root radical.

Preferably the length of the flow chamber is in view on the properties of the flowing to be monitored

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_ ₇ _ 280Q157

Material selected so that the dwell time of an element of the flowing material in the measuring chamber is considerably shorter than is the relaxation time constant of the material.

The research literature relating to the electrical properties of, for example, liquid fuels flowing in pipelines shows that there are complex and incompletely known relationships for the charge exchange between an insulating fluid and the flow channel wall. According to the invention, the measuring chamber is designed and the measuring arrangement made so that the
respective charge density in the flowing insulating material can be reliably derived from a given relationship between the charge density and the measured charge current to the iießkammer-Viand.

It is not necessary to consider in detail the various mechanisms that are responsible for the uptake and release of electrostatic charge by one in contact with the
electrically conductive, but insulated viand of a pipeline flowing medium can be made responsible.
These mechanisms usually result in a charge of the fluid, the charge increase in the fluid being referred to as "flow stream".
Because the influence of the surface contact is important or even

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is predominant for the charging mechanism of the fluid, the flowing mass of material can only then can be considered electrically homogeneous when the flow is turbulent. This state can of course only be used for pipelines be accepted with high conveying speed. Will the flow stream in a very long pipe with i., the linear flow velocity with u and the inner diameter of the pipeline with d, so can the flow stream through the following, in general express recognized relationship:

= ku ^a d ^b

The exponents a and b are each greater than one and can in turn be derived from the values of u and d be dependent. Exact values are not essential for the explanation of the invention, which is why it is assumed that a = b = 2, so that

= ku ² d ² (1)

In the flowing medium therefore accumulates in every area in which a flow stream in the material flow takes place inside, a progressively increasing charge. The at each point along the length of the

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Pipeline charge density achieved in each case by the accumulating charge can be denoted by dq. the Charge accumulation speed may be non-uniform, as flow obstacles such as filters arranged in the pipeline are particularly productive charge sources represent. The term "flow stream" is sometimes used to refer to Designation of the product dqx (where χ is the volumetric flow rate) used; however, this product is in the referred to in the present description as the amount of cargo transported per unit of time.

Discharge represents an equally complex process when a stationary volume of flow medium with a Charge density dq of an electrically conductive, grounded Wall is exposed. If the fluid is viewed as a dielectric, there is an exponential decrease in the charge density to be expected, which depends on the ratio of the conductivities and the relative dielectric constants. For fuels of high purity, this ratio would result in a very long time constant. In the In practice, certain processes such as ion recombination may occur, which is the actual time constant reduce to values in the range of 1 s. The actual course of waste therefore no longer needs to be strict to be exponential, however, it is convenient to have a

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Time constant (or relaxation time) T in the conventional Sense to use. Accordingly, the charge density dq, achieved after the lapse of a period of time t is through given the following expression:

e " ^{fc / T} (2)

The relaxation must be taken into account in a similar way if the generation of a flow stream i ^ in

a short pipe section at ground potential is looked at. Equation 1 is then to be added to the following equation:

i _s = k uV (1 - e) ₍₃₎

where t is now the time required by the flow to flow through the pipeline.

An embodiment of the invention and the use of equations 2 and 3 to determine the charge density in a Iießkamriier is referred to below with reference to the attached drawings described in detail. It shows:

ilg. 1 into a fuel delivery tube

line built-in device according to the invention, and

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Pig. 2 schematically the in .tf'ig. 1 shown

Equipment with additional components to neutralize the charge of the in the pipeline flowing fuel.

According to Fig. 1, a substantially cylindrical, metal measuring chamber 10 is at one end with an inlet port 12 and at its other end with a similar outlet connection 16 for connection to a pipe 14 Mistake. The inlet port 12 and the outlet port 16 are each mounted in insulating sleeves 18 so that the keßkammer 10 is also electrically isolated after installation in the pipeline 14.

In addition, one with the measuring chamber 10 is coaxial and essentially complete on the insulating bushes 18 surrounding electrostatic shield 20 mounted, which, however, is electrically isolated both from the measuring chamber 10 and from the pipeline 14. The shield is provided with an earthing connection 22. The measuring chamber is also provided with a terminal 24 from which an electrical line through one in the shield formed wall duct is passed.

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The measuring chamber is for a pipe 14 with designed with a certain inner diameter. The connecting pieces 12 and Io of the measuring chamber have the same inner diameter like the pipeline 14, while the heating chamber 10 has a larger, three times the pipe diameter Has inner diameter. The transition between the diameter of the inlet port 12 and the larger diameter of the enlarged section of the measuring chamber 10 occurs abruptly, as the shape of the transition section 25 shows, its cone half-angle is preferably greater than 60 and in which any streamlined shape of the transition profile is avoided should.

The design of the flow chamber 10 for a specific clear pipe diameter implicitly includes the design for a specific range of flow velocities. The length of the heating chamber 10 is preferably calculated from these data in such a way that the dwell time of an element of the material flow entering the measuring chamber 10 at the mean flow velocity in the measuring chamber is considerably shorter than the relaxation time of the fluid. A flow meter 26 of conventional design is also arranged in the pipeline lh , so that the volumetric flow rate during the charge measurement

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can be measured. In Fig. 1 is the flow meter arranged downstream of the measuring chamber 10, but it can just as well be upstream of the heating chamber.

To carry out the measurement, an electrometer 28 is connected between the connection 2 4 of the measuring chamber 10 and earth, after which the fluid is allowed to flow through the heating chamber 10 for a sufficiently long period of time, that the charge distribution can stabilize. The magnitude of the current indicated by the electrometer 28 and the measured flow rate are then recorded. For calibration purposes, at least one direct measurement of the charge density is required using conventional means for the same fluid and to compare with the corresponding current display of the electrometer 28. Measurements taken at different times are included if air is trapped in the measuring chamber 10 can, not necessarily comparable with each other. In order to rule out this problem, it is therefore desirable to use the To arrange measuring chamber 10 vertically, with the inlet end facing downwards.

Fig. 2 shows schematically an embodiment of a Control system, which is connected to the pipeline 14 measuring chamber 10 with an electrostatic shield 20, an electrometer 28 and a flow meter 26

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according to the arrangement in rig. 1 has. The pipe 14 also runs through a charge neutralizer 30, which is arranged upstream of the measuring chamber IC. The iteutralizer works in a manner known per se as a function of the output signal a control unit 32 and neutralizes the respectively measured charge of the material flow. The control unit 32 receives signals via converter or amplifier components that may be required, which on the one hand the strength of the current flowing through the electrometer 28 and, on the other hand, that measured by the flow meter 26 Represent mass flow. The control unit 32 contains means to derive an output signal from the two input signals, which is used to compensate for the total amount of charge or the degree of neutralization required to reduce the amount of charge to a safe level.

Experiments have the relationship between the size of eggs Charge density in the medium flowing in the pipeline and the current intensity indicated by the electrometer 2 8 for Proven a fuel of medium conductivity, which however is still not completely a theoretical one Analysis is accessible. For discussion purposes there are two Mechanisms are viewed as if they were effective independently of one another, but the possibility must not be disregarded let there be an interaction between these

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consists of both mechanisms. Such an interaction can, for example, have an effect that an imaginary Value for T is introduced which deviates considerably from the value normally taken into account. One possible cause of the interaction is the increased turbulence resulting from the intentionally non-streamlined Entrance section of the measuring chamber results. In particular, it should be noted that with the aid of the invention The results obtained in the measuring chamber are not indicative of those which are uniform with an insulated pipe section Inside diameter in which the flow is turbulent are results obtained.

The two mechanisms are grounded by the electrometer displayed captured currents i and i.

O X

From the above explanation it can be seen that before the entry of the flowing medium into the chamber 10 The accumulated charge in the medium is withdrawn by a relaxation current i collected by the measuring chamber, which however, by a new component of the flow stream i

which can be generated when the medium flows through the measuring chamber. The volume flow is denoted by v ¹ and the charge density of the in the

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Measuring chamber 10 entering medium with dq, so is

i _c = ν

By substituting equations 2 and 3 and inserting the corresponding values U ₁ and d. for the linear flow velocity in the measuring chamber 10 or the inner diameter of the heating chamber one obtains:

i _c = (V 'dq ₀ - k U ₁ ² U ₁ ² ) (1 - e " ^{t / T} )

It turns out that depending on the exponential

2 decrease, since the value of U ₁ depends on IZd ₁ , an almost direct proportionality of the size of i to

Charge density can be brought about by making the diameter dl large. The length of the measuring chamber 10 is best chosen so that the residence time of an element of the flowing medium in the measuring chamber is considerable is smaller than the relaxation time constant of the medium. The influence of each element of the flowing medium is then only subject to the measurement during the initial phase of the relaxation curve when the discharge speed is at is highest.

A consideration of the factors determining the size i has shown theoretically that the invention

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as measured, represents the accumulated charge density by a current draw, which is generally small and depends on the ratio t / T, and that the flowing medium decreased with the amount of charge removed original charge continues to flow.

The measurement of the collected current for a particular fuel has shown, however, that a current i is observed which is of such a size that the expected value of i cannot be identified therein

can. It must be taken into account that such measurements are afflicted with an error which can amount to up to 20% and therefore covers i. The value of i actually seems to correspond to the total amount of charge transported in the main flow per unit of time, 'the

ix = v ¹ dq

which can be determined by direct measurement of the charge density in the pipeline. Besides, none seem Reduction of the charge density in the flow emerging from the measuring chamber to occur, which indicates a charge displacement process suggests.

The result can also be due to induction influences by the moving, with the flowing medium to the downstream

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Charge transported towards the end of the measuring chamber to be brought. When the flow velocity changes there is an almost linear change in i, which indicates the lack of a substantial one

exponential decay component of the current.

Regardless of which of the two mechanisms is predominant in the formation of the diverted current appears (and in what form would one or the other Mechanism depends on the properties of the flowing medium), the measurement can be made according to the same, below summarized measuring procedures are carried out:

1) For calibration purposes, the relationship between the charge density of the main flow and the trapped Current determined for the flowing medium under consideration.

2) It is ensured that the charge densities in Inflow and outflow are not significantly different from each other are different. The relationship t / T is then satisfactory, regardless of whether the actual value of T is known or not.

3) The volumetric flow rate of the flowing medium is measured.

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4) The dissipated current is measured and the charge density or the amount of charge transported per unit of time is derived from equations 1 and 3.

As already mentioned, the inner diameter d is in the described heating arrangement. the keßkammer 10 considerably larger than the inner diameter d of the pipeline. This results in a reduction in the generation of a flow

2 2 current to a fraction d / d .. of that in the pipeline generated flow stream and also brought about turbulent flow conditions allow a useful measurement of the charge density. Though at any diameter ratio d./d, which is greater than 1, a certain advantage is achieved, this is significantly below the The diameter ratios lying in the value n / 2 are small and can be made possible by diameter ratios significantly above the value \ / ΐθ ~ can no longer be increased significantly. Similarly, the length of the measuring chamber should be advantageous can be chosen so that the value of t is below 0.5T, although the calibration process is of course different Values allowed.

The point of view of the profitability of refueling systems requires the use of the smallest possible pipe

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- On lines and noons of daily flow velocities in areas of electrical safety. Nevertheless, there is a particular danger here, and the use of a measuring device of the type described enables continuous monitoring of the charge density in the fuel or the amount of charge transported per unit of time, a person supervising without special qualifications being sufficient to initiate a warning when a danger occurs. The monitored parameters may, of course, as an input signal for an automatic warning system or for automatically controlling a Ladun ₀ 3neutralisation or other suitable iiaßnahmen find application. A closed loop control is shown in Figure 2; alternatively, a neutralizer located downstream of the IfeJüSteile can be used in an open control circuit.

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Blank

Claims (1)

.to. ten c auo., r lic: ie Means ^, for kontxnuxerlicaen monitoring aer with a flowing through a pipeline fliewfähi _to en electrically insulating Katerial per unit time transported electrostatic charge quantity, characterized by a Invitation (12) and a capacity utilization (Ιό) having, in the course of the pipeline (lh) eihscaaltuare heating chamber (10) with electrically conductive, insulated ή on ei, v / ob ei the rieiäkammer has an extended section extending at least over part of its length with a light cross-section that is larger than the clear pipe cross-section and a light cross-section designed in this way between the invitation and the extended section Transition section (25) is arranged that the kateriaiströmung when entering the enlarged section is significantly slowed down and put into a turbulent state, and a grounding line (2h) is connected to the let chamber wall, in which an ammeter (2 8) for measuring the in the ground wire flowing current is set as hatred for the amount of electrostatic charge transported per unit of time in the pipeline with the material. 2. Device according to claim 1, characterized in that that the measuring chamber (10) from a grounded electrostatic 809829/0690 BATH ORIGINAL Isolation un ^ (2u) irr. "Eaentlicnen 'vollstcLnai _t; is enclosed. 3. The device according to claim 1 or 2, characterized in that the poor (10) has an essentially cylindrical mandrel and the ratio of the inside diameter of the enlarged body to the inside diameter of the chamber inlet is large from \ / ~ 2 ~ : 1 to n / TC ': 1 lie ^ t. 4. Execution. according to one of claims 1 to 3 _3, characterized in that the length of the, ie, icapimer (lü), according to the properties of a flowing material, is such that the dwell time of an element of the flowing material in the new chamber is smaller is known as the relaxation ze itkonstante of materials. 5. Device according to one of claims 1 to 4, characterized in that the transition is conical is formed, the between its wall and the otrcinungsaciise included in the iliac kidney (10) Conical angle is not smaller than όθ. and device according to one of claims 1 to 5, characterized by a volumetric flow meter (26) for ..measuring the per unit of time through the pipe (14) 809829/0690 2AD ORiQt _NAL 280Ü157 flowing through]! ^ 'aterialTnenge and through one of it and determining the charge density in the flowing material from the measured amount of electrostatic charge per unit of time Component. 7. device according to one of the sprints 1 to o, characterized by an electrostatic stress level measured as a function of the respective time limit _or . oteuerkomjjonente work from the electrostatic leakage density, which controls an electrically neutralizing the material flowing in the liohrleitunö iie ut rails ati onseinrichtung (30). 809829/0690 - BAD ORsGUNAL