WO2007080618A2

WO2007080618A2 - Method and instrument for detecting air and/or other gases inside transiting liquids

Info

Publication number: WO2007080618A2
Application number: PCT/IT2007/000009
Authority: WO
Inventors: Marco Profeti; Luca Bozzi
Original assignee: S.A.M.P.I. S.P.A.
Priority date: 2006-01-11
Filing date: 2007-01-05
Publication date: 2007-07-19
Also published as: ITFI20060009A1; WO2007080618A3

Abstract

Acoustic waves in the ultrasonic range are transmitted through the transiting mass to be examined and attenuation of the incident energy during transit through said mass is mesured.

Description

"METHOD AND INSTRUMENT FOR DETECTING AIR AND/OR OTHER GASES INSIDE TRANSITING LIQUIDS"

DESCRIPTION

The object of the present invention is to provide an instrument for con- tinuously detecting the presence of air and/or gas inside liquids. One of the main applications of said instrument is found in systems for measuring hydrocarbons or liquids in general, in which measurement of liquid alone must be guaranteed.

The ways in which a specific liquid transferring and measuring system can use the information deriving from the instrument of the invention will not be described hereunder. In fact, these systems can be designed in many ways, the variation of which also implies variation in the way the instrument under consideration is applied. In a typical case - such as the one mentioned above - the information relating to the presence of air and/or gas can be used simply to close a valve an^ shut off passage of the product through the measuring device. Otherwise, it may be useful not to close said valve completely but to throttle closing it, so that delivery of the product is not interrupted. In other cases, it is possible to switch off the transfer pump either in combination with or separately to closing of the supply valve. In yet other cases, the flow can be diverted upstream of the measuring device, returning it to the suction of the pump.

In all the aforesaid cases, the systems as a whole can differ greatly from one another; however, there is no change to the instrument according to the invention, which has the object of supplying information regarding the presence of air and/or gas inside the liquid it is measuring. This information can be supplied in various typical modes, such as with voltage free contacts, by communication on the serial and/or parallel protocol, with a voltage or current signal proportional to the percentage of air and/or gas, or yet other modes.

A subject of the invention is a method for detecting air and/or other gases inside transiting liquids, according to which acoustic waves - in particular in the ultrasonic range - are transmitted through the mass to be examined, and attenuation of the incident energy during transit through said mass is measured.

Another subject of the invention is an instrument for detecting air and/or gas inside transiting liquids, which comprises an emitter of acoustic waves - in particular in the ultrasonic range - and a receiver of said acoustic waves, placed on a measurement section perpendicular, or in any case inclined, with respect to the direction of the flow to be examined.

Other features of the invention are defined in the dependent claims. The instrument is based on the transmission of acoustic waves - in the ultrasonic range - between an emitter and a receiver placed on a measurement section perpendicular, or in any case oblique, with respect to the flow of the liquid. The two sensors can be mounted in various ways, in particular in the three ways shown in Figure 1, Figure 2 and Figure 3. According to Figure 1, there is provided an emitter 11 and a receiver 13 of acoustic waves in diametrically opposed positions with respect to the duct 15 through which the fluid to be examined flows. The gaseous bubbles tend to concentrate in the central area, and they are well intercepted by the flow of acoustic waves, as the emitter and receiver are facing each and operate by transparency.

According to Figure 2, the emitter 21 and the receiver 23 are positioned so that the flow of acoustic waves is subjected to a reflection and consequently describes two oblique portions (oblique reflection).

According to Figure 3, the emitter and the receiver are combined in 31, so that the flow of acoustic waves describes two coincident diametrical portions, i.e. with coupled reflection.

The choice of the type of mounting depends on the dimensions of the pipe and on the sensitivity that the instrument must have in detecting the presence of air or gas present in the liquid and entrained by the liquid. By way of example, some criteria for choice are indicated.

The "Oblique Reflection" type according to Figure 2 should be preferred in the case of large pipes (over 8"), while the "Coupled Reflection" type according to Figure 3 should be preferred in applications in which maximum sensitivity is required. The solution in Figure 1 with simple crossing is the conceptual ap- plication.

The transmitter/receiver pair can normally be mounted on an appropriate flange or on a section of pipe, but can also be mounted on equipment of existing transfer and measurement systems when these directly guarantee the paths of the ultrasonic waves conforming to one or other of the solutions in Figures 1, W _, -

2 and 3.

As already indicated, the instrument is based on the physical principle of attenuation" of the incident energy during passage of the ultrasonic waves through fluids with different acoustic impedance, as in the case of liquids and 5 gases. In fact, the energy that reaches the receiver decreases in relation to the increase in ihe difference between the acoustic impedance of the fluids passed through and that of the transmitter-receiver pair. The parameter that measures this attenuation is the "Transmission Coefficient T".

Indicating: io the density with p in g/cm³ the longitudinal Drooaqatiqn velocity with v in cm/s the acoustic impedance generically with Z = pxv in g/cm² s the acoustic impedance of the sensor with Z₈ ; the acoustic impedance of the fluid with Z_f ; 15 the transmission coefficient T is expressed by

AxZ xZ

T = f

(z_s+z_ff

Considering on average the following values of acoustic impedance: Z, =1,7x10⁶

20 Z_f = 0,13xl0⁶ in the case of diesel oil

Z_f - 150 in the case of air the Transmission Coefficient (expressed in percentage) varies between: 26% in the case of transmission between sensor and diesel oil 0.035% in the case of transmission between sensor and air.

25 By normalizing the two values calculated above at 100, a Normalized

Transmission Coefficient varying from 100 to 0.13 is obtained. The dynamics associated with this indicator is therefore 769. Using this important variation, it is easy to assess not only whether there is air and/or gas in the liquid, but also to assess the quantity thereof.

30 To measure the Transmission Coefficient the schematic diagram in Figure 4 can be used. Pulses of a predetermined duration schematically shown at / are fed to the emitter 11 or 21 or 31 at fixed intervals by the microprocessor card 51 by means. The signal R received by the receiver is rectified and subsequently sent to a peak detector RP for the purpose of obtaining the measurement value "V" (analog or digital signal at the output of RP). This value V is compared with the value Vt (obtained during initial calibration of the instrument) to obtain the value "T%": The percentage thus obtained is processed by the Microprocessor that supplies the output U, which is used in any case, and in particular to control the components to intercept the flow. Processing of the value "7" can be carried out in analog mode or in digital mode. Analog Processing

The signal downstream of the "rectifier + peak detector" RP stage is passed by a low-pass filter with cut-off frequency suitable to obtain the desired dynamics (a response time of 0.3 to 0.5 s is normally sufficient). The output from the filter is acquired by the microprocessor 51 which compares it with a predetermined threshold. This system is suitable when it is not necessary to detect a continuous percentage of air and/or gas present in the liquid, but on the contrary an on/off signal is sufficient. Digital Processing

In this case, at each transmission cycle of the signal from the transmitter to the receiver, downstream of the "rectifier + peak detector" RP stage the microprocessor 51 performs sampling of the value of "V". After a certain number of samples, "T" is calculated through the ratio between the average of the "V" values and the calibration value Vt. This procedure is necessary as - above all when the percentage of air and/or gas is very low - the passage of bubbles through the section involved by transmission of the ultrasonic waves has an irregular trend. Therefore, the need to assess the quantity of air and/or gas passing through the instrument on a statistical basis is evident. This approach is fundamental when the precision of the liquid measurement system requires indication also in the case of even the smallest quantities of air and/or gas passing through. In this case, the signal output from the instrument can be of two types: - a double contact to manage throttling of the flow on two stages as a function of the quantity of air present in the flow;

- a continuous current or voltage signal or in any case through communication on serial or parallel protocol for continuous throttling control.

Claims

. _CLAIMS

1. An instrument for detecting air and/or other gases inside transiting liquids, characterized in that it comprises an emitter of acoustic waves and a receiver of said acoustic waves placed on a measurement section perpendicu- lar, or in any case inclined, with respect to the direction of the flow to be examined.

2. Instrument as claimed in claim 1, characterized in that two sensors (emitter and receiver) are mounted in positions approximately diametrically opposed in a section of duct for flow of the fluid to be examined (facing each other in transparency).

3. Instrument as claimed in claim 1 , characterized in that the two sensors (emitter and receiver) are mounted in a section of duct through which the fluid to be examined flows, so that the acoustic waves are subjected to at least one reflection.

4. Instrument as claimed in claim 3, characterized in that emitter and receiver are positioned at an angle (with oblique reflection).

5. Instrument as claimed in claim 3, characterized in that emitter and receiver are combined, and the reflection is such as to obtain return in the same direction as the emitter.

6. Instrument as claimed in at least one of the previous claims, characterized in that it comprises means to power the emitter at fixed intervals, means to rectify the signals detected by the receiver, and a peak detector to obtain an output value "V" to be compared with a calibration value Vt; the percentage thus obtained being processed by a control logic.

7. Instrument as claimed in at least one of the previous claims, characterized in that the transmitter/receiver pair is normally mounted on an appropriate section of pipe or on equipment of existing transfer and measurement systems.

8. Method for detecting air and/or other gases inside transiting liquids, characterized in that acoustic waves are transmitted through the mass to be examined and attenuation of the incident energy during transit through said mass is measured.

9. Method as claimed in claim 8, characterized in that the acoustic waves are in the ultrasonic range. _ _

10. Method as claimed in claim 8 and/or 9, characterized in that said transmission is performed through a flowing mass.

11. Method as claimed in at least one of claims 8 and subsequent, characterized in that transmission is performed between an emitter and a receiver and in the presence of at least one reflection.

12. Method as claimed in at least one of claims 8 and subsequent, characterized in that the transmission coefficient is measured, and the value measured is processed in analog mode.

13. Method as claimed in at least one of claims 8 to 11 , characterized in that the transmission coefficient is measured, and the value measured is processed in digital mode.

14. Method as claimed in at least one of claims 8 and subsequent, characterized in that an average value is measured in a predetermined transit time of the fluid, calculated on a statistical basis.

15. Method and instrument for detecting air and/or other gases inside transiting liquids; all as described above and represented by way of example in the accompanying drawing.