GB2211302A - Process and device for measuring a two-phase gas-solid or liquid-solid flow rate - Google Patents

Abstract

In a process for the determination of the mass flow rate of a pulverulent or granular solid product in an installation for handling by fluid current, a measurement is made of the total loss of charge Pt existing between two pressure sensors 13, 14 spaced by the distance L within an ascending vertical duct transporting the fluid charged with the pulverulent mixture. A determination or a calculation is moreover made of the loss of charge Pg due to the fluid alone between these same sections, of diameter D and of cross-section S. As a function of the constant g of the acceleration due to gravity, of the coefficient of friction fs of the particles and of the average speed of the solid particles Us determined by intercorrelation using capacitive sensors 10, 11, a calculation is made of the mass flow rate of solid particles Ms. <IMAGE>

Description

Process and device for measuring a two-phase gas-sot id or liquid-solid flow rate.

The invention relates to the determination of the mass or of the mass flow rate of a pulverulent or granular solid product carried in a pneumatic or hydraulic handling installation.

It is known that the total mass carried can be obtained by integration with respect to time, if the mass flow rate of solid products is known at each instant.

On the other hand, it is known that this mass flow rate of solid products may be determined if the capability is present to determine separately the average speed of the solid particles and the concentration of these particles, that is to say the mass of solid particles which is contained within an element of volume of piping, the cross-section of which is known.

The measurement of the average speed of the solid particles is a problem which is completely resolved in a simple andveffective manner by the known process of intercorrelation as described, for example, in British Patent G8-A-1,235,856.

On the other hand, the direct and effective measurement of the concentration of solid product is not at all easy.

A known process consists in deducing this concentration fro the measurement of the electrical capacitance of a capacitor formed of two electrodes separated by the solid-fluid mixture. However, such a measurelent is not at all reliable, and it is greatly affected, in particular, by the humidity of the solid product.

Another known process consists in measuring the absorption undergone by a beam of ultrasonic waves or, more generally, an ionizing radiation, but the implementation and the calibration of such a process are extremely problematic.

The object of the invention is to implement a process for measuring the mass flow rate of solid product, and more particularly for measuring the concentration of this product, which uses only a current and simple technology, which is easy to implement and which nevertheless is extremely reliable, especially in relation to the humidity of the product.

The invention consists in measuring, within a pipe portion where the regime is established, on the one hand, the average speed of the particles by the known process of intercorrelation and, on the other hand, the total loss of charge existing between two sections of the pipe, the loss of charge due to the fluid alone between these same sections of the pipe being likewise measured or calculated, and in then calculating the mass flow rate of solid product as a function of these quantities and of constant values determined in advance, such as the diameter and the cross-section of the pipe, the distance between the two sections of the pipe where the loss of charge is measured, the acceleration due to gravity and a coefficient of friction of the solid particles which is determined empirically.

In fact, the loss of charge measured in this way is directly a function of the concentration and independent of the humidity of the product; this permits release from this variable. Moreover, the determination of a pressure difference may be obtained by a technology which is relatively simple and easy to inpleoent.

In particular, the operation is preferably carried out on an ascending verticle element of the transport conduit, inserting therein, in proximity to one another, two special sensors each consisting of a flexibLe elastic sleeve of the same internal diameter as the duct, this sleeve being contained within a rigid casing and surrounded by an incompressible fluid which transmits the pressure difference to a differential manometer, the electrodes for the determination of the speed by intercorrelation consisting of two annular rings surrounding the sleeve in the vicinity of its two ends and electrically connected to the electronic device for determining the speed.

Other particular features of the invention will become evident in the description which will follow, of an embodiment and a mode of implementation taken by way of example and represented in the accompanying drawing, in which: Figure 1 represents the general diagram of the process; Figure 2 represents, in axial cross-section, one of the particular sensors of the invention; and Figure 3 diagrammatically represents the connection of the two sensors.

In the text which follows, it is assumed that what is involved is an installation for the pneumatic handling of a pulverulent or granular solid product, but the invention would be applicable just as well to a hydraulic transport.

The pulverulent solid to be transported is initially contained in a reservoir 1, in which it may advantageously be fluidized by a secondary gas circuit comprising an inlet 2 and a compensating piping 3, and an installation (not represented) supplies a gas flow rate Mg in the principal inlet duct 4.

A set of valves 5 permits the regulation of the gas flov rate as well as the excess pressure necessary for the possible secondary fluidization circuit.

A measuring device 6 permits the determination of this flow rate in a direct form or in the form of a loss of charge, as will be seen hereinbelow.

The solid fluidized in this manner flous from the reservoir 1 through the duct 7 and is mixed with the gas in the horizontal section 8 of the gas duct, the latter then comprising a preferably vertical section 9, in which the remainder of the measuring apparatus is inserted.

The latter comprises, in the principle thereof, two electrodes 10 and 11 surrounding the flow and connected to an electronic device 12 permitting, by the known process of intercorrelation to which reference is made hereinabove, the determination of the speed Us of the solid particles.

Moreover, according to the invention, two sensors 13 and 14 are used, which are separated by a distance L, and permitting the determination, by means of a differential manometer 15, of the total pressure difference, or total loss of charge Pt between the two sections 13 and 14, of diameter D and of cross-section S.

An appropriate computer 16, preferably electronic, receives at 17 the indication of the gas flow rate, permitting the calculation of the loss of charge Pg due to the gas alone in the two sections 13 and 14 separated by a distance of L. In a variant, the device 6 may directly measure this loss of charge or a proportional value, multiplied by the desired constant in order to obtain the value Pg. The computer 16 receives, on the other hand, via 18, the value of the total loss of charge Pt and via 19 the average speed of the solid particles Us.

As a function of these various variables and constants as vell as of the constant of the acceleration due to gravity g, the computer 16 determines the mass flow rate of pulverulent solid product Ms by the following formula:

in which fs represents, in principle, the coefficient of friction of the solid particles contained within the hopper, and which consequently depends essentially on their physical characteristics.

This coefficient may be determined experimentally by using a calibration bench on which measurements are made, on the one hand, of the flow rate Ms and, on the other hand, of the abovementioned variables Pt, Pg and Us, and the value of fs, extracted from the abovementioned formula, is deduced therefrom.

If the mass flow rate Ms is constant throughout a duration T, the total mass transported by the installation is obtained by forming the product of this flow rate and this time. If, on the other hand, this flow rate Ms varies with time in the course of the transport, the computer 16 permits the evaluation, constantly in real time, of the values of this flow rate, and the total mass transported is obtained by integration, with respect to time, over the duration T, as illustrated by the computer 20 in Figure 1.

The implementation of the process according to the invention thus consists essentially in arranging the sensors 10, 11, 13 and 14 on the vertical duct 9.

As represented in Figure 2, each sensor 13 or 14 comprises a rigid body 21 in which a tubular sleeve 22 of very flexible rubber or the like is mounted. The latter is mounted in a sealing manner at its two ends in the body 21 by virtue of rigid connecting pieces 23 fixed by screws 24. This sealing connection thus completely encloses an annular chamber 25 surrounding the sleeve 22 within the body 21.

Within this annular chamber 25 and at the two ends of the latter there are placed insulating annular supports 26, each supporting one of the metallic electrodes 10 and 11, which are themselves annular and electrically connected by sealing connections 27 and 28 represented only in Figure 3.

As represented in Figure 3, two identical sensors 21 are disposed at the average distance L to constitute the sensors 13 and 14 indicated previously.

The flanges 29 terninating each one of the bodies 21 permit the connection to the duct 9 comprising a section 9a situated between the sensors. This section 9a may, in particular, serve as support for the computer 12, connected by the wires 27 and 28 to the electrodes 10 and 11 of one of the bodies 21, and likevise for the differential manometer 15 which is connected by hydraulic ducts 30 respectively to one of the connections 31 of each one of the bodies 21. All the space formed by the recesses 25, the ducts 30 and the differential manometer 15, on both sides of the single diaphragm, is filled with the aid of a fluid which is incompressible and non-reactive with the rubber sleeve, such as a solicone oil, and is completely purged of its air, by using for this purpose the other connection 31 which is then closed in a sealing manner.

The internal dianeter of the sleeves 22 and the quantity of incompressible liquid enclosed in this manner are determined in such a manner that at rest the internal diameter of the sleeve is precisely that of the remainder of the duct 9 and 9a in order to avoid the introduction of any disturbance in the flow.

The measuring electrodes 10 and 11 act, consequently, through the wall of the deformable sleeve 22, and permit the measureeent, in a capacitive manner, of the irregular variations of concentration in the flow, in order to deduce therefrom, by intercorrelation of the signals, the speed of the particles by the known process to which reference is made hereinabove.

The flow meter according to the invention is thus relatively simple, easy to implement, and is extremely reliable, supplying, in particular, a measurement of the mass flov rate which is independent of the possible humidity of the product.

Claims (5)

1. Process for the determination of the mass flow rate of a pulverulent or granular solid product in an installation for handling by fluid current, in which process the average speed of the solid particles is determined by intercorrelation on the basis of capacitive sensors (10,11) spaced in the flow, characterized in that a measurement is made of the total loss of charge Pt existing between two sections (13, 14) spaced by the distance L in an ascending, preferably vertical duct transporting the fluid-solid mixture, in that a determination or a calculation is moreover made of the loss of charge Pg due to the fluid alone between these same sections, of diameter 0 and of cross-section S, and then in that, as a function of the constant g of the acceleration due to gravity and of the average speed of the solid particles Us determined by intercorrelation, a calculation is made of the mass flow rate of solid particles Ms by the following formula:

in which the coefficient fs is determined empirically by previous calibration and is dependent only upon the nature of the particles.

2. Device for carrying out the process according to Claim 1, characterized in that at each one of the sensing sections (13,14) there is disposed a pressure sensor (21) comprising essentially a tubular sleeve of flexible material (22) of the sane average internal diameter as the vertical ascending duct (9), this sleeve closing in a sealing manner on its exterior an annular chamber (25) filled entirely with an incompressible liquid and connected by a duct (30) to a differential manometer (15) permitting the determination of the total loss of charge between the two sections (13,14).

3. Device according to Claim 2, characterized in that the electrodes (10,11) for sensing the speed of the particles by intercorrelation consist of annular metallic electrodes disposed within the said annular chamber (25) at the ends of the latter, in at least one of the sensor bodies (21).

4. Device according to one of Claims 2 and 3, characterized in that a computer (16) permanently receives the indications of loss of charge (Pg) due to the gas alone, of total loss of charge (Pt) and of average speed (Us) of the particles, and calculates in real time the mass flow rate (Ms) of solid particles, this mass flow rate being possibly integrated with respect to time in order to determine the mass of solid particles which is transported.

5. Device according to one of Clains 2 to 4, characterized in that the flexible sleeve (22) of each one of the sensors (21) is made of rubber of great flexibility, and in that the inconpressible liquid which surrounds it is silicone-based.