EP0843644A1

EP0843644A1 - Process for the recovery of steam emitted in a liquid distribution plant

Info

Publication number: EP0843644A1
Application number: EP96927121A
Authority: EP
Inventors: Jacques Fournier
Original assignee: Itron Soluciones de Medida Espana SA; Schlumberger SA
Current assignee: Tokheim Services France SAS
Priority date: 1995-08-10
Filing date: 1996-07-29
Publication date: 1998-05-27
Anticipated expiration: 2016-07-29
Also published as: CA2227874A1; FR2737717B1; US6047745A; ATE197586T1; EP0843644B1; FR2737717A1; DE69610985T2; DE69610985D1; WO1997006095A1; CA2227874C; ES2153969T3

Abstract

PCT No. PCT/FR96/01217 Sec. 371 Date Feb. 3, 1998 Sec. 102(e) Date Feb. 3, 1998 PCT Filed Jul. 29, 1996 PCT Pub. No. WO97/06095 PCT Pub. Date Feb. 20, 1997A method of recovering vapor emitted in a liquid dispensing installation comprising: liquid dispensing means (PL) adapted to cause said liquid to flow with a liquid flowrate QL; vapor recovery means (PV) adapted to cause said vapor to flow with a vapor flowrate QV along a pipe (120), said vapor flowrate QV being controlled by a parameter G. According to the invention, the method includes the following steps: establishing an equation G=F (QV, {pi}) relating the parameter G to the vapor flowrate QV and to parameters pi characteristic of the recovery means and said pipe (120); determining an initial value {pi}o of the parameters pi; on each dispensing k of liquid: measuring the liquid flowrate QLk and determining a value Gk of the parameter G from the equation: Gk=F (QLk, {pi}k-1); determining a new value {pi}k of the parameters pi to be used for the next dispensing k+1 of liquid. Application to dispensing fuel for motor vehicles.

Description

PROCESS FOR RECOVERING VAPOR EMITTED FROM A LIQUID DELIVERY SYSTEM

The present invention relates to a process for recovering vapor emitted in a liquid distribution installation during the distribution of said liquid inside a tank.

The invention finds a particularly advantageous application in the field of fuel distribution for motor vehicles for example, in order to recover the hydrocarbon vapors escaping from the tank of said vehicles as the latter fills with liquid fuel.

A liquid dispensing installation such as fuel for motor vehicles generally comprises means for dispensing said liquid essentially constituted by pressure meters fitted with pumps capable of circulating the fuel with a liquid flow rate QL between a tank storage and tank vehicles. The meters also include a liquid meter connected to a pulse generator allowing a computer to establish the volume and the price of the fuel delivered, which appear in clear on a display with which the meters are equipped.

In addition, when it is intended to recover the vapors of hydrocarbons emitted, said installation comprises recovery means capable of circulating said vapors with a vapor flow rate Qv along a pipe, between the vehicle tank and a recovery tank, the storage tank for example, the vapor flow rate Qv being controlled by a quantity G characteristic of said recovery means so as to maintain a proportional relationship Qv = k between the vapor flow rate Qv and the liquid flow rate QL QL with k equal to or close to 1.

Most often, said recovery means are constituted by a pump sucking the vapors from the tank to discharge them into the hydrocarbon storage tank. The characteristic magnitude G is then the speed w of rotation of said pump, which is controlled by the pulse generator of the distribution means.

However, in most cases, it is not possible to simply impose a pump speed w proportional to the liquid flow rate QL-

In fact, the operating conditions can be very different from one installation to another by: the pressure losses on the recovery pipe, upstream and downstream of the pump, - the possible presence of calibrated valves at the recovery tank which can generate in it a pressure different from atmospheric pressure and corresponding to an additional hydraulic resistance on the recovery pipe, - the internal leakage of the recovery pump, depending on the pressure difference upstream-downstream, which affects its effectiveness.

In summary, to obtain a given vapor flow rate Qv, it is necessary to impose on the recovery pump a speed w of rotation which depends on the installation. In order to take into account the parameters mentioned above, it is common to carry out a calibration of the complete installation when it is installed on site. During this calibration, a speed w of the recovery pump is fixed and the corresponding vapor flow Qv is measured using a flow meter or a gas meter. A table (w, Qv) is thus established connecting the speed w and the vapor flow rate Qv with a sufficient number of points to define the characteristic of the pump under these operating conditions. This table is stored in a microprocessor.

In normal operation, the flow meter is removed and, during a distribution of hydrocarbons at a liquid flow rate QL, the microprocessor searches the table for the speed w to be imposed on the recovery pump so that Qv = QL-

This known recovery method however has the following drawbacks: the pressure losses on the recovery pipe can change over time due to: a gradual partial sealing by dust, the change in section of the elastomer pipes with the prolonged presence of hydrocarbons. This is the case in particular of the pipe part located upstream of the pump, generally consisting of an elastomer tube surrounded by pressurized liquid, this part representing the core of a coaxial hose. - the internal leakage of the pump can evolve due to wear, as in vane pumps for example, the density of the vapors is variable with the hydrocarbons and the temperature of the tanks of the vehicles, which modifies the influence of the losses of upstream and downstream load. - the vapor pressure in the recovery tank can also vary with the hydrocarbons and the temperature. Also, the technical problem to be solved by the object of the present invention is to propose a method for recovering vapor emitted in a liquid distribution installation during the distribution of said liquid inside a tank, said installation comprising : means for distributing liquid capable of circulating said liquid with a liquid flow rate Q _L between a tank and said tank, means of vapor recovery capable of circulating said vapor with a vapor flow rate Qy along a pipeline, between said tank and a recovery tank, said vapor flow Qy being controlled by a quantity G characteristic of said recovery means, a process which, taking into account the slow evolution of the parameters characteristic of the circulation of vapor along the pipeline recovery, would allow a delayed recalibration of the characteristic quantity G as a function of the vapor flow rate eur Qv-

The solution to the technical problem posed consists, according to the present invention, in that said method comprises the steps consisting in: build a relationship

G = F (Q _γ , ^}) connecting the quantity G to the vapor flow rate Qy and to parameters p ^ characteristic of the recovery means and said pipe, determine an initial value {p _j } ₀ of the parameters p _j , at each liquid distribution k: measure the liquid flow rate Q ^ and determine a value G ^ of the quantity G to be imposed on the recovery means by the relation: determine a new value (p ^} ^ of the parameters p _j to be used for the following distribution k + 1 of liquid.

Thus, during a liquid distribution, on the one hand, a value determined from parameters calculated during the previous distribution is used for the characteristic quantity G, and, on the other hand, at least one measurement is carried out making it possible to calculate new values for said parameters which will be used for the following distribution. As will be seen in detail below, two particular, but not exclusive, modes of implementing the method according to the invention are proposed.

According to a first embodiment, the recovery means comprising a pump, said quantity G is the speed w of rotation of said pump.

According to a second embodiment, the recovery means comprising a pump and a solenoid valve, said quantity G is the hydraulic resistance imposed by said solenoid valve, the speed w of rotation of the pump being constant. In a first approximation, the different parameters pj characteristic of the recovery means and the pipeline will be considered to be independent of the vapor flow rate Qy. However, it may happen that some of these parameters vary with said vapor flow rate. This is particularly the case for the internal leakage coefficient α of vane pumps when the vane is not guided with precision. The method of the invention must then be adapted to this particular situation. This is why, according to the invention, it is expected that a parameter p among the parameters p _j varying with the vapor flow rate Qy: an initial table is established [poJ, Qv-J] (j = 1, .. ., N) connecting N values of the parameter p to N values of vapor flow rate Qy, to each distribution k of liquid:

. we use in the relation Gk - F (Q _Lk , {p _i > _k _ ₁ ) a value pi _k _ ι of the parameter p such that [pJ _k - 1, QV = ^ Lk ^

. the steam flow rate Qy ^ is measured and a corresponding value p _k of the parameter p is determined,

. we calculate a coefficient A _k such that

^A k = Pk / pj ^' o ^with [pJ'o.QJ'v = ^Q Vkl. we set up a new table

[pJk _> QJy] with p ⁾ _k = A _k pJ ₀ for all j.

The description which follows with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be implemented. Figure 1 is a general diagram of a liquid distribution installation implementing a vapor recovery process according to the invention.

Figure 2 is a diagram of the vapor recovery circuit of Figure 1 in the case where the recovery pump has no internal leakage.

Figure 3 is a diagram of the vapor recovery circuit of Figure 1 in the case where the recovery pump has a non-zero internal leak.

Figure 4 is a diagram of the vapor recovery circuit of Figure 1 using two pressure regulators.

FIG. 5 is a diagram of a vapor recovery circuit with two recovery channels delivering through a common pipe. Figure 6 is a diagram of the vapor recovery circuit of Figure 1 with an adjustment valve downstream of the recovery pump.

The diagram in FIG. 1 shows an installation for distributing liquid, for example fuel, inside the tank of a vehicle, not shown.

This installation comprises fuel distribution means essentially constituted by a pump PL capable of circulating said fuel L with a liquid flow rate QL between a storage tank 100 and said tank along a pipe 110, up to a gun. 111 distribution.

As already mentioned above, a volume counter

112, possibly including the liquid pump PL, comprises a measurer 113 placed on the pipe 110 in series with the pump PL so that a pulse generator 114, coupled to said measurer

113, provides an impulse signal representative of the liquid flow rate QL which a computer 115 then translates in terms of volume and price to a display 116.

The installation of FIG. 1 also includes means for recovering the vapor V emitted during the distribution of the liquid in the tank of the vehicle. In the example of FIG. 1, said recovery means mainly consist of a pump Pv capable of circulating said vapor with a vapor flow rate Qv along a pipe 120 between the tank, passing through the gun 111 of distribution, and a recovery tank 100 which, in the case of FIG. 1, is none other than the storage tank for liquid fuel.

In general, the recovery method of the invention consists in imposing on a quantity G characteristic of the recovery means, the speed w of rotation of the pump Pv in the example of FIG. 1, a value such that the flow rate resulting vapor Qv is as close as possible to the liquid flow rate QL-

For this purpose, we establish and store in the memory of a circuit

121 for controlling the motor Mv of the pump Pv a relation G ≈ F fQy, ^}) connecting the quantity G to the vapor flow rate Qv and to parameters Pj characteristic of the recovery means and of the recovery pipe 120, these parameters will be explained in the following case by case. Then, after having determined an initial value {p _j } ₀ of the parameters p ^, the liquid flow rate QLk at is measured at each distribution k of liquid. using the information supplied by the pulse generator 114 to the motor control circuit 121 Mv- The value G _k of the quantity G to be imposed on the recovery means is then determined by the relation where {p ^} p, _ _j represents the value of the parameters p ^ calculated during the previous distribution k- 1 of liquid.

During this same liquid distribution k, a new value {p ^} ^ is determined. parameters p to be used for the following distribution k + 1 of liquid.

It will be understood that the recovery process according to the invention is based on the idea of a deferred updating of the parameters governing the circulation of vapor in the recovery pipe 120. However, as the updating takes place from one distribution of liquid to the next, the systematic error inherent in the process remains negligible given the very slow drift in time of the parameters p which are essentially linked to the steam pump Pv and to the pressure drops in the pipe 120. A first example of application of the method of the invention is given in FIG. 2. In this example, the recovery means comprise the steam pump Pv whose speed w of rotation constitutes the quantity G controlling the vapor flow rate Qv-

Assuming that the pump Pv has a zero internal leakage coefficient α, that the vapor recovery takes place at atmospheric pressure P ^ and that the recovery tank 120 is also at atmospheric pressure PA (zero pressure or vacuum ΔPo), the relation between the speed w of rotation of the pump Pv and the vapor flow is written: w = Qv / V _G (P '/ PA) (1) where VQ is the geometric cyclic volume of the pump and F the pressure at the inlet of the pump.

If R 'is the hydraulic resistance in the upstream part of the recovery pipe 120, we have: P _A - F = R' Q _v n (2) n being equal to 7/4, but which can also be taken equal to 2 for reasons of simplification.

The relation (1) is then written: w = Q _v / v _G (iR ^' Qv ⁿ / PA) which represents the general formula G = F (Qv, {P _j }), the parameters pj being the geometric cyclic volume VQ and the upstream hydraulic resistance R '. The VQ parameter is constant and can be measured once and for all at the factory. The initial value R'o of the parameter R 'is determined by means of the relation (2) by imposing any speed w of rotation on the pump Pv and by measuring the pressure F using a pressure sensor 122 and optionally a flow meter, not shown, which supplies the corresponding vapor flow rate Qv. After this initialization phase, the flow meter is deleted. The values of VQ and R'o are stored in a memory of the circuit 121 for controlling the motor Mv of the pump Pv-

At the first liquid distribution, said control circuit calculates the speed wj to be imposed on the pump from the values VQ, R'o previously measured and the liquid flow rate QLI received from the pulse generator 1 14 by the relation: _{W l} = QLI / VQ (l-R'oQn _L ι / P _A )

During this first distribution, a measurement F l of the pressure F is carried out, which makes it possible to calculate the new value R '1 of R' using the two relations: Qvl = wι VQ PVPA

R 'ι will be used during the second distribution, and so on. The diagram in FIG. 3 relates to a steam pump Py having a coefficient of non-zero internal leakage α.

The general equation of the vapor recovery circuit is written: w = Q _V / V _G (F / P _A ) + αΔP (3) ΔP being the pressure difference across the pump Pv- ΔP is connected to the vapor flow Qv by: ΔP = (R '+ R ") Q ⁿ _v = RQ ⁿ v

R "being the downstream hydraulic resistance of the recovery line 120.

Given the fact that we always have P _A - F = R 'Q ⁿ v equation (3) is then written: w = Q _v / V _G (lR ^' Qv ⁿ / PA) ⁺ (αR) Qv ¹¹ The parameters pj characteristic of the recovery circuit are therefore VQ, R 'and αR. As before, the constant geometric cyclic volume VQ of the pump is measured at the factory. As for the parameters R 'and αR, they can be determined using a sensor 122 of upstream pressure F and a flow meter 123 placed at the inlet of the pump Pv which makes it possible to measure the vapor flow rate Qy. In reality, the flow rate Q _1U supplied by the flow meter 123 must be corrected by the pressure F:

Qv = Qiu (P '/ PA)

This operation is carried out automatically by the circuit 121 for controlling the motor Mv which, in addition to the liquid flow information QL, also receives P 'and Qι _u .

Under these conditions, the values of R 'and αR are related to Qv and P' by:

R = (P _A - F) / Q ⁿ _v (αR) = [w - Q _v / VQ (1 - R 'Qn _v / P _A )] / Q * V

The initial values R'o and (αR) o can be determined during a first distribution k = o during which the speed w of rotation of the pump Pv is measured.

If one wants to know the value of the downstream hydraulic resistance R "to follow for example the evolution of the state of the pipe 120 downstream of the pump or to detect an anomaly, one can place at the output of the pump Pv a pressure sensor P ", not shown. We deduce R "by:

R "= (P _A - P") / Q ⁿ _v The variant embodiment shown in the diagram in FIG. 4 aims to simplify the operations for updating the parameters pj. To do this, the pressure sensor 122 F and possibly that giving the pressure P "are deleted, and there are pressure regulators 124 and 125 respectively at the inlet and at the outlet of the pump Pv. The regulator 124 is adjusted to a set value corresponding to a pressure F such that PA ^_ P 'is constant whatever the vapor flow rate Qy. Similarly, the regulator 125 imposes a pressure P "such that P" -PA is independent of Qy. conditions for the proper functioning of this system are:

P _A - F>R'Qv ¹¹ P "- P _A >R" Q _v ⁿ

As long as these conditions are fulfilled, general equation (3) is written:

or

The only parameters pj to take into account are VQ and α, R 'and R "no longer participating in the equation of the recovery circuit. VQ is determined in the factory, while α can be calculated at each distribution by the relation α = (w - Q _V P _A / V _G P.) / (P "-F) or α = (w - Qi _u / V _G ) / (P" -F)

It can also occur that the pressure inside the recovery tank 100 is not equal to atmospheric pressure PA and has a pressure difference ΔPo, positive or negative, due for example to the presence of a valve 130 shown in Figure 1.

In this case, the general relation (3) becomes: w = Q _V P _A / V _G P + αRQ ⁿ _{v +} αΔPo

The last term αΔPo is a corrective term equivalent to an initial speed wi. This can be determined during the waiting periods between two distributions as the minimum speed to be applied to the pump Pv to obtain a non-zero vapor flow rate Qy. Then the quantity w-wi is treated as above with ΔPo = 0.

FIG. 5 shows the diagram of an installation where two steam pumps Pva, Pvb deliver in a common pipe 12 of small diameter. This is particularly the case in fuel distribution stations where, to limit the costs associated with the installation for recovering hydrocarbon vapors, a flexible tube is slid into the suction pipe for the return of the vapors to the recovery tank 100. This tube is generally common to two pumps, and has a common hydraulic resistance R _c which can be significant.

The two channels a and b of the circuit of Figure 5 being symmetrical, we will only deal with channel a.

The general relation governing the circulation of vapor in channel a is written: ^w a "Qlua / ^v Ga ^{+ α} a ΔPa with ΔPa = R _a Q _V ⁿ _a ^{+ Rc} (Qva ⁺ QVG) ^Π and Ra = R'a + R "a taking for n the approximate value of 2, we obtain:

W _a = Qlua / VQa ⁺ ≈a ( ^R a ⁺ Rc) QVa ⁺ <* a * c (QVb ⁺ 2Q _V a Qvθ) The first two terms correspond to a simple path of hydraulic resistance R _a + R _c and the third term is a corrective term related to channel b.

When only the way to deliver the liquid while it was QVB ⁼ O, I ^e third term is zero. From the first two terms we deduce α _a (R _a + Rc) always by measuring the flow rate Qι _ua (or Qva) and the pressure Fa using the flow meter 123a and the pressure sensor 122a.

If the two channels a and b deliver liquid simultaneously, the measurements of vapor flow and pressure on the channels a and b, associated with the term α _a (R _a + Rc) calculated previously, make it possible to deduce α _a R _c .

The diagram in FIG. 6 illustrates a variant implementation of the vapor recovery process, object of the invention. According to this variant, the circulation of steam in the recovery pipe 120 is ensured by a pump Pv at speed w ₀ of fixed rotation, controlled by a motor Mv-

The vapor flow rate Qy is adjusted by a solenoid valve 126 disposed downstream of the pump Pv and having a variable hydraulic resistance Rx, the value of which is imposed by a control circuit 121.

In this example, the quantity G characteristic of the recovery means is Rx, connected to the speed wo of the pump Pv and to the vapor flow rate Qy by: Rx = (WO-QV / VQ (1 - R'Qn _v / P _A ) - (αR) Q ⁿ y) / aQ * y with R = R '+ R "

The parameters pj to be determined are VQ, R ', R and α. Apart from VQ, constant and measured in the factory, the other three parameters can be calculated from the measurements of the flow meter 123, and the pressures F and P "given by the sensors 122 and 126. We have indeed:

R = R ^'+ (P ^" - P _A -RχQ ² _v ) / Q ⁿ V α = (wo - Q _V / V _G (lR ^' Q ² v / PA) / (RQ ⁿ v ⁺ R _a Q ² v )

Of course, one could just as easily place the solenoid valve 126 upstream of the steam pump Pv, which would lead to a system of relationships which are different but equivalent to those which have just been established.

Similarly, taking into account a recovery tank pressure different from atmospheric pressure as well as that of a return tube common to two pumps apply in the same way to the embodiment which has just been described. using a solenoid valve.

In all of the foregoing, no account has been taken of any variation with the vapor flow rate Qy of the characteristic parameters governing the circulation of vapor in the recovery pipe. However, it is known that for certain types of pumps the coefficient of internal leakage α depends on said vapor flow rate. In this case, we establish an initial table obtained by on-site calibration, noted [(αR) ol, QyJ] of the parameter αR, for example, connecting N values (j = l, ...., N) of αR to N corresponding values of Qy:

At the first distribution k = 1 of liquid, knowledge of the liquid flow rate Q _Lj makes it possible to determine the value (αR) jJ to be used in the general flow relationship, namely:

During this same distribution, we measure the vapor flow rate Qyi from which we deduce, on the one hand using flow relationships, a value (αR) j of the parameter αR, and, on the other hand using the initial table a value (αR) r _j J ^• It may happen that the QLI and Qvi values do not exactly correspond to Qy ⁾ values of the table. We will then proceed by linear interpolation.

We deduce a coefficient Aj = (αR) ι / (αR) J ₀ allowing to update the whole table which will be used for the following distribution by multiplying each value (αR) oJ by the coefficient Al- The new table is written: [(αR) i-î, QyJ] with (αR) iJ = A i (αR), ^ ^' for all j.

The same procedure is followed for each distribution, updating the table with respect to the initial table which is kept in memory.

Claims

1. Method for recovering vapor emitted in a liquid distribution installation during the distribution of said liquid inside a tank, said installation comprising: liquid distribution means (PL) capable of circulating said liquid with a liquid flow Q ^ between a tank

(100) and said tank, means (IV; 126) of vapor recovery able to circulate said steam with a vapor flow Qy along a pipe (120), between said tank and a tank (100) of recovery, said vapor flow rate Qy being controlled by a quantity G (w; R _x ) characteristic of said recovery means, characterized in that said method comprises the steps consisting in: establishing a relationship

G = F (Qy, {p;}) relating the quantity G to the vapor flow rate Qy and to parameters p _j characteristic of the recovery means and of said pipeline, (120) determining an initial value {p _j } ₀ of the parameters p ^, at each liquid distribution k: measure the liquid flow rate Q ^ and determine a value G _k of the quantity G to be imposed on the recovery means by the relation:

G _k = F (Q _Lk , {Pi} _k _ι) determine a new value {p _j J ^ of the parameters p ^ to be used for the following distribution k + 1 of liquid.

2. Method according to claim 1, characterized in that a parameter p among the parameters p ^ varying with the vapor flow rate

Q _V : we establish an initial table [poï, Qv-J] (j =! ”•• -, N) connecting N values of the parameter p to N values of vapor flow rate Qy, at each distribution k of liquid:. we use in the relation

^ "F WLk 'iPi hc- l) a value pJ _k _ j of the parameter p such that [pJ _k . I, QJy _ Q _Lk ]

. we calculate a coefficient A _k such that

Ak = Pk / PJ ^' O ^with [pJ'o "0 ^, " v = ^Q Vkl. We establish a new table

[pJk »CJy] with pi _k = A _k pJ _{0 for all} j.

Method according to one of claims 1 or 2, characterized in that, the recovery means comprising a pump (P _v ), said quantity G is the speed w of rotation of said pump.

4. Method according to claim 3, characterized in that, the pump (P _v ) having a coefficient of zero internal leakage α, said relation w = F (Qy, {p-}) for a recovery tank (100) at atmospheric pressure is given by:

V _G being the geometric cyclic volume of the pump (P _v ), R 'the hydraulic resistance of the pipe (120) upstream of the pump, n a coefficient equal to 7/4, and PA the atmospheric pressure, and in this that said parameters p ^ being constituted by the parameters V _G and R ', the parameter VQ, constant, is determined by an initial calibration of the pump (P _v ), the value R' _k of the parameter R 'at each distribution k being determined from the measurement of the pressure F at the pump inlet (P _v ) by the relationships:

Qvk = w _k VQ F _k / P _A R ^' k = (PA- P ^' k) / Q ⁿ vk 5. Method according to claim 3, characterized in that, the pump (Pv) having a non-zero coefficient of internal leakage α, said relation w = F (Q _v , {p _j }) is given by: w = Q _V / ^ G (lR ^' Qv ⁿ / PA) ⁺ (αR) Qv ¹¹

VQ being the geometric cyclic volume of the pump (P _v ), R 'the hydraulic resistance of the pipe (120) upstream of the pump, n a coefficient equal to 7/4, PA the atmospheric pressure and R the total hydraulic resistance of the pipeline, equal to the sum of the upstream hydraulic resistance R 'and the hydraulic resistance R "of the pipeline (120) downstream of the pump (P _v ), and in that said parameters p ^ being constituted by VQ , R 'and αR, the constant parameter VQ is determined by an initial calibration of the pump (P _v ), the values R' _k and (αR) _k of the parameters R 'and αR at each distribution k being determined from measurements of the vapor flow rate Q _v and of the pressure F at the inlet of the pump (P _v ) by the relationships:

R'k = (PA - P'k) / Q ⁿ vk

(αR) _k = [w _k - Q _vk / VQ (1 - R ' _k Q ⁿ _vk / P _A )] / Q ⁿ v _k

6. Method according to claim 5, characterized in that the value R ^" _k of the hydraulic resistance R" downstream of the pump (P _v ) at each distribution k is determined by measuring the pressure P "at the outlet of the pump by the relation: R " _k - (PA" P "k) / Q ⁿ vk

7. Method according to claim 3, characterized in that, the pump (Pv) having a coefficient of non-zero internal leakage α and the pressures F and P "at the inlet and outlet of the pump (P _v ) being maintained constants using pressure regulators (124, 125), said relation w = F (Q _v , {p ^}) is given by:

VQ being the geometric cyclic volume of the pump (P _v ) and PA the atmospheric pressure, and in that said parameters p {being constituted by the parameters VQ and α, the parameter VQ, constant is determined by an initial calibration of the pump (P _v ), the value α _k of the parameter α at each distribution k being determined at from the measurement of the vapor flow rate Qy of the pump (P _v ) by the relation: α _k - (wfc - Qvk PA / VQF) / (FF)

8. Method according to any one of claims 4 to 7, characterized in that said recovery tank (100) having a pressure difference ΔP ₀ relative to atmospheric pressure, is added to the calculated values of the speed w of the pump (Pv) a quantity WJ equal to the minimum speed to be applied to the pump to obtain a non-zero vapor flow rate Qv, said quantity w ₀ being measured between two distributions of liquid.

9. Method according to one of claims 1 or 2, characterized in that, the recovery means comprising a pump (Pv) and a solenoid valve (126), said quantity G is the hydraulic resistance R _x imposed by said solenoid valve, the pump rotation speed w being constant.

10. Method according to claim 9, characterized in that, said solenoid valve (126) being arranged downstream of the pump (P _v ), said pump having a coefficient of non-zero internal leakage α, said relation R _x = F (Qv , {p _j }) is given by: Rx = [wo - Qy / V _G (l-R'Qn _v / P _A ) - ( _α R) Q ⁿ _V ] / αQ ² _V VQ being the geometric cyclic volume of the pump (Pv), R ′ the hydraulic resistance of the pipe (120) upstream of the pump, n a coefficient equal to 7/4, PA the atmospheric pressure,

R the hydraulic resistance of the pipe, equal to the sum of the upstream hydraulic resistance R and the hydraulic resistance R "downstream of the pump (P _v ), and in that said parameters Pj being constituted by VQ, R ', R and α, the parameter V _G , constant, is determined by an initial calibration of the pump (Pv), the values R'k " ^R k ^{and α} k of the parameters R ', R and α at each distribution k being determined from the measurements of the vapor flow rate Qy and of the pressures F and P" at the inlet and at the outlet of the pump by relationships:

R ^' k - (PA - P ^' k) Q ⁿ v _k

R _k - R ^' _k ⁺ (P'k - PA - RχkQ ² vk) / Q ⁿ vk α _k = [wo - Qvk / VQ (l-R'kQ ⁿ Vk / PA)] / (RkQ ⁿ Vk ⁺ RχkQ ² Vk)