EP0629175B1 - Treatment of petrol vapours in service stations - Google Patents

Abstract

A process is disclosed for preventing environmentally harmful effects in service stations and for the controlled treatment of excess, environmentally harmful petrol vapour/air mixtures. For that purpose, the pressure in the fuelling system is measured, any excess exhaust vapours are exchanged with the environment through a defined opening and the physical conditions prevailing in the atmosphere of the fuelling system are adjusted for the various modes of operation of the fuelling system. Also disclosed are the physical calculation of gas quantities and a device for carrying out the process.

Description

The invention relates to a method according to the preamble of claim 1 and a device according to the preamble of claim 31 for carrying out the method.

Such a control of the excess vapors and a treatment of the different gas quantities which arise in the course of the different operating states of a gas station with gas recirculation is e.g. from US-A-4 009 985, whereby special measures must be taken to make the fundamental technical difference, namely the open connection between the nozzle and vehicle tank compared to the prior art with a gas-tight connection (see page 4, lines 59 and 60 and page 5, lines 34 to 38).

Furthermore, it is advantageous not only to consider the current operating pressure before starting treatment (combustion) of an excess gas volume, but also to generally take into account the resulting gas volume, which is due to the size of the free space V (see equation (6)) in a system of storage tanks is available.

In addition, the measuring device according to the prior art with pressure sensors (see. 51, 73, 81, 95 and page 13, line 2, 3.. As soon as a preselected pressure is determined, ..) is constructed so that each sensor in the sense of a function provides a pressure-controlled alarm (PA pressure alarm), from which the previous pressure value can be recognized, but from which a direct change in the treatment of the gas volume is triggered. However, the measuring device is not suitable for measuring a pressure curve or a pressure display / control (PIC - pressure-indicating-controlling), or perform a pressure display / recording (PIR). Only one operating point can be identified for each pressure sensor, and when the operating point is reached, the relay (51) changes the operating conditions at the measuring point for the other pressure sensors (73, 81, 95), so that the pressure values of the individual pressure sensors cannot be compared with one another.

The disadvantage of this sensor-controlled measuring device PA according to the prior art can be seen regularly in certain, recurring operating conditions. If the storage tanks (18) are full after filling, the volume V above the liquid level (19) of the storage tanks (18) is very small. Already at a negative pressure of -0.2 inch WC to -0.5 inch WC (page 7, line 62) the sensor (51) PA reports an excess volume and the combustion is started; although there is still no excess in the small volume V or, if saturation occurs, it can develop appreciably. (see equation (6) of the patent application)

Based on this prior art, the invention is based on the task of monitoring the return of the correct amount of gas from the car tank to the underground tank and the excess vapors which occur during the refilling processes and during re-evaporation in the various operating states of a petrol station result in tank operation, to be recorded and discharged from the tank system via a defined opening.

According to the invention, this object is achieved by the method according to claim 1 or the device according to claim 31. Further refinements of the method and the device are given in subclaims 2 to 30 and 32 to 35.

It is from DE-A-40 00 165 (cf. there in particular also page 5, lines 45 to 47) and from US-A-4 009 985 (cf. there 51, 73, 81, 95) for decanting gasoline-like Liquids are known to measure a pressure value and use pressure-controlled relays to treat the excess vapors; wherein in the prior art according to DE-A-40 00 165 on the at each pressure nozzle δp measured individual gas nozzle, the density of the gas (see there page 3 equation (2)) is calculated and according to the prior art according to US-A-4 009 985 reaching a certain pressure by triggering one or more pressure switches (51, 73, 81, 95) is recognizable. However, a combination of the different measuring techniques for a central pressure measurement, PIC and / or PIR, and at one point in the underground tank for carrying out the method and for forming the device according to claim 31 was not suggested.

It is also known from US Pat. No. 4,063,874 (cf. there in particular page 3, lines 36 to 39) and from DE-A-40 00 165 (cf. page 1, lines 36 and 37), that excess air is sucked in at the filler neck; wherein in the prior art according to US-A-4 063 874 the excess steam / air mixture is first cleaned in an absorber (28, 29) and the condensed hydrocarbons intermittently with fresh air in a burner (44), just as in the prior art according to US-A-4 009 985; and in the prior art according to DE-A-40 00 165 the excess gasoline vapors are recovered in a vapor liquefaction unit (29), an absorber. From DE-A-26 15 144 it is known to treat excess vapors; whereby no vapors with inert air components are taken over from the car tank, only pure vapors (see page 15, lines 4 to 6 and valve 158) and the possible excess is partially condensed by means of cooling condensation (120). Even in the case of a combination of the various possibilities for the treatment of the excess steam / air mixtures, it is not advisable to design the method in such a way that the gasoline vapor / air mixture is cleaned in a washer known per se with diesel fuel as the washing liquid according to patent claims 28 to 30.

The invention is explained in more detail below with reference to FIGS. 1 and 2 and the diagram in FIG. 3.

• Fig. 1 Druckaufzeichnungen aus dem Erdtank;
• Fig. 2 Dampfdruckkurven verschiedener Benzinqualitäten;
• Fig. 3 die schematische Darstellung einer Tankstelle mit Gasrückführung.

Show it:

• Fig. 1 pressure records from the underground tank;
• Fig. 2 vapor pressure curves of different gasoline qualities;
• Fig. 3 shows the schematic representation of a gas station with gas recirculation.

• Kurve A, zeigt den Einfluß eines Tankvorganges ab der Minute 6,
• Kurve B, zeigt den Druckanstieg im Erdtank in der Pause zwischen 2 Tankvorgängen,
• Kurve C, zeigt den Einfluß einer Betankung von 2 Pkw gleichzeitig, ebenfalls ab der Minute 6 für die Dauer von 30 sek.

Die untere Kurve D gehört zu einer anderen Tankstelle mit einer dezentralen Pumpe, die im Gegensatz zur zentralen Pumpe nicht kontinuierlich, sondern nur während des Tankvorganges arbeitet. Bei einem idealen Tankvorgang mit Gasrückführung wird das aus dem Erdtank entnommene Benzinvolumen gerade durch das zurückgeführte Gasvolumen ersetzt. Hierbei spricht man von einer 100 % -Gasrückführung. Für diesen Tankvorgang bleibt der Druck im Erdtank konstant oder die Druckänderung ist gleich 0. Speziell unter Berücksichtigung der in Deutschland gültigen Gesetze kann dieser Tankvorgang als ideal bezeichnet werden. Die Druckmessungen entsprechend Kurve A über den Tankvorgang von 1,25 Minuten zeigen also, daß aufgrund des Druckabfalles das zurückgeführte Gasvolumen kleiner als die getankte Menge ist, also zu klein ist.
Der Druckverlauf unter Kurve C fällt bei dem relativ kurzen Betanken von 2 Pkw noch steiler und weiter ab. Dies zeigt, daß auch hier die zurückgeführte Gasmenge zu klein ist und daß die notwendige doppelte Saugleistung der zentralen Pumpe für diesen Betriebsfall nicht verfügbar ist.
Kurve B ist die charakteristische Druckzunahme im Erdtank, die u.a. durch den kontinuierlichen Betrieb der zentralen Vakuumpumpe im Erdtank entsteht. Bei dem vorhandenen Freiraumvolumen im Erdtank von 13,5 m3 errechnet sich nach der unten aufgeführten Gleichung (6) eine Volumenzunahme von ca 430 l/h.
Demgegenüber ist der Verlauf der Kurve D für diskontinuierlichen Pumpenbetrieb wesentlich flacher und entspricht bei einem Freiraum von 12,9 m3 nur einer Volumenzunahme von 60 l/h.The measuring method has meanwhile been used at various petrol stations with facilities for gas recirculation. In Fig. 1 the result is plotted as a pressure curve in the underground tank over time and in different operating states. The print recordings start consistently after 4.5 minutes and last up to the 9th minute. The measurement was carried out using a U-tube or inclined tube manometer in the free space of the floor tank. The 3 upper pressure curves come from a gas station with a central vacuum pump for gas recirculation.

• Curve A, shows the influence of a refueling process from minute 6,
• Curve B, shows the pressure increase in the underground tank during the break between 2 refueling processes,
• Curve C shows the influence of refueling 2 cars at the same time, also from minute 6 for a period of 30 seconds.

The lower curve D belongs to another petrol station with a decentralized pump which, in contrast to the central pump, does not work continuously, but only during the refueling process. In an ideal refueling process with gas recirculation, the volume of petrol taken from the underground tank is currently being replaced by the volume of gas returned. This is called 100% gas recirculation. For this refueling process, the pressure in the underground tank remains constant or the change in pressure is 0. This refueling process can be described as ideal, especially taking into account the laws applicable in Germany. The pressure measurements according to curve A over the refueling process of 1.25 minutes therefore show that, due to the pressure drop, the returned gas volume is smaller than the tanked amount, ie it is too small.
The pressure curve under curve C drops even more steeply and further with the relatively short refueling of 2 cars. This shows that here too the amount of gas returned is too small and that the necessary double suction power of the central pump is not available for this type of operation.
Curve B is the characteristic pressure increase in the underground tank, which is caused by the continuous operation of the central vacuum pump in the underground tank. With the existing one Free space volume in the underground tank of 13.5 m3 is calculated according to equation (6) below, an increase in volume of approx. 430 l / h.
In contrast, the course of curve D is significantly flatter for discontinuous pump operation and corresponds to a volume increase of 60 l / h with a free space of 12.9 m3.

• Während des Tanken wird viel zuwenig Gas aus dem Pkw abgesaugt, sodaß der Tankkunde den schädlichen Gasen ausgesetzt ist.
• Während der übrigen zeit ist in dem Erdtank ein großes überschüssiges Volumen, das über das Ventil in der Entlüftungsleitung in die Atmosphäre entweicht und an der Grundstücksgrenze die Nachbarschaft belastet.
• Vor einer Benzin-lieferung muß der Tankwart den Füllstand im Erdtank kontrollieren und den Anschlußstutzen für die Benzinleitung öffnen. Beide Male baut sich über die Öffnung der Druck im Bodentank ab und der Bedienungsmann steht in einem gesundheits-schädlichen Gasstrom, der mit über 20 m/s ihm ins Gesicht bläst.

The measurements carried out show that even in modern systems, the gas recirculation during refueling leads to completely uncontrolled harmful environmental effects at different times:

• Too little gas is sucked out of the car during refueling, so that the tank customer is exposed to the harmful gases.
• During the rest of the time, there is a large excess volume in the underground tank, which escapes into the atmosphere via the valve in the ventilation line and pollutes the neighborhood at the property boundary.
• Before delivering petrol, the petrol station attendant must check the level in the underground tank and open the connection for the petrol line. Both times, the pressure in the floor tank is reduced through the opening and the operator is in a gas flow that is harmful to health and blows in his face at over 20 m / s.

• daß der Ermittlung der Rückführrate der Vorzug vor der Volumenrate, welche den idealen Tankvorgang beschreibt, gegeben wird,
• die Meßstelle, durch die Messung am offenen Tankstutzen, außerhalb der Tankstation ist, und meßtechnisch nur Bruchteile der Betriebszeit einer Tankstelle erfaßt werden,
• die Volumenrate im wirklichen Tankbetrieb als Funktionskontrolle nicht gemessen werden kann und
• Messungen innerhalb der Tankanlage nicht vorgesehen sind.
  Unter der Volumenrate versteht man das Verhältnis:
• rückgeführtes Gasvolumen/Volumen des getankten Kraftstoff x 100.

With the device according to the invention, the causes of these typical disadvantages are to be recognized in order to avoid the disadvantages in the environmentally friendly operation of a petrol station.
A procedure for assessing gas recirculation systems is described in research project No. 104 08 508 by the Federal Environment Agency in Berlin. Here, TÜV Rheinland presents a measuring method to determine the efficiency of the recirculation using the gas recirculation system examined above.
With this method, the emission at the tank neck is measured with and without gas recirculation. Emission reduction with gas recirculation is a measure of the recycle rate.
However, the process has the disadvantages

• that the determination of the return rate is given preference over the volume rate, which describes the ideal fueling process,
• the measuring point, due to the measurement at the open tank neck, is outside the filling station and only a fraction of the operating time of a filling station is measured,
• the volume rate in real tank operation as a function check cannot be measured and
• Measurements within the tank system are not provided.
  The volume rate is the ratio:
• Returned gas volume / volume of fuel tanked x 100.

Based on this measuring method as the state of the art, the object of the invention is to centrally monitor the individual tank processes with gas recirculation and the formation of excess vapors in the underground tank via a measuring point.

According to the invention, this object is achieved by the method according to claim 1 or the device according to claim 31.

2 shows the vapor pressure curves of 3 gasoline mixtures which influence the formation of harmful emissions at petrol stations.
The upper curve with the highest vapor pressure belongs to a winter fuel.
The mean vapor pressure curve corresponds to summer gasoline.
The lower vapor pressure curve belongs to a gasoline, from which the low boilers are partially evaporated. It is the remaining gasoline in the empty car tank.

Fig. 3 is a schematic representation of the function of a gas station, including refueling with gas recirculation (stage 2) and gasoline delivery with gas swing (level 1). 3 the device for carrying out the measurements is entered schematically.
The tank system consists of the underground tank 11 with the ventilation line 14, which is optionally closed with a so-called pressure vacuum valve 15 as a safety valve. The tank 11 is partially filled with gasoline. The free space with the gasoline vapor / air mixture is located above the liquid level 13. The connecting lines for the petrol delivery and the petrol withdrawal are supplied via the dome shaft, not shown.
The gasoline is withdrawn via the gasoline pump 5 in the liquid line 4, which ends with the fuel nozzle, not shown. The amount of gasoline is measured in the petrol pump and written down on the gasoline meter 6 as a (FIR) flow indicator. The line 3 for gas recirculation begins at the fuel nozzle and ends in the collecting line 7, which is usually laid underground.
In active systems, a gas pump 8 generates a negative pressure in the gas return line 3 when refueling, so that the gas mixture can be sucked out of the car tank. The pressure drop in line 3 and thus the delivery capacity of pump 8 can be set via a throttle valve 9. Several fueling points can be connected to the gasoline line 3 and the collecting line 7. The nozzle 16 shows the possibility of connecting several underground tanks.
The underground tank 11 has 3 further closable connections, the connection 17 for the gas-tight holding of the measuring rod and the 2 pipe connections with the removable covers for the temporary connection of the pipes for gasoline unloading with gas oscillation.
A control valve 18 is installed in the collecting line 7, by means of which the returned gas quantity (volume rate) can be regulated. The pressure in the free space of the underground tank 11 is measured as a pressure display control (PIC) 19, for example in the ventilation line 14. The pressure measurement and control will be described later in connection with the individual operating states.
When removing petrol, refueling, the vehicle tank 10 is connected to the petrol station via the fuel nozzle.

The line 20 on the detachable connection between the tank 10 and the line 3 symbolizes the gas exchange in the area of the tank nozzle 21 with the environment.
When installing active systems, characterized by the index (a), a pump 8 is installed in line 3 to generate a negative pressure. In this case, not enough extracted gas can escape via line 20, and fresh air can also be drawn in additionally.
When installing passive systems, characterized by the index (p), a seal is to be created between the line 3 and the tank neck 21 by means of a sealing collar (not shown) in order to displace the gas portion from the tank 10 into the underground tank 11 when filling with gasoline . Particularly at the beginning of the tank, however, due to volume peaks, there can be a considerable increase in pressure and a release of vapors containing gasoline via the symbolized line 20, ie the sealing point (not shown).
To deliver fuel, the tank 12 of the tank truck (Tkw) is connected to the underground tank 11 via the line 22 for liquid and the line 23 for the gas-containing air. The tank 12 is normally designed as a case tank and is only suitable for operation at atmospheric pressure. The pressure safety device 24 ensures that any overpressures or underpressures that occur are compensated for with the surroundings without damage to the tank. At the end of refueling and at the end of gasoline deliveries, the connections to the surroundings, in the fuel nozzle and the nozzles in the cathedral shaft are closed.

While in the measuring method according to the invention the typical operating data can be recorded over the entire operating time, the method according to the prior art only allows an assessment over the short period of time of a refueling operation, that is to say a total of about 5% of the total time.
In practice, this operating state is called refueling with gas recirculation as stage 2. The delivery of gasoline with gas recirculation in the tanker truck is referred to as level 1 and takes about 1/10 of level 2, i.e. 0.5%.
The operating conditions at a petrol station in the remaining part of a 24-hour day are referred to below as level 0. As was determined in the measurements in Fig. 1, is subject to a tank system during this period considerable pressure fluctuations, which can lead to harmful environmental effects. The gasoline vapors from the vehicle contain namely at 80% saturation and 40 ° C and 5 vol. % Benzene in the remaining gasoline approx. 30 g benzene / m3. The permissible TRK value (technical standard concentration) for the carcinogenic benzene is only 15 mg / m3. In typical summer conditions, with the same saturation and 20 ° C, the vapors contain 700 g / m3 of petrol. The permissible MAK value (max. Workplace conc.) For the vapors of the petrol components is 0.3 - 2 g / m3 for n-paraffins. In addition to this direct danger to humans, these vapors contribute greatly to the formation of smog and ozone.

The invention is explained below taking into account the 3 different operating conditions for stages 2, 1 and 0.
The general state of knowledge regarding the evaluation of emissions from refueling was developed by Dr. H. Waldeyer, in "Emission reduction when refueling", published by TÜV Rheinland, 1990, and was published as part of a research project by the Federal Environment Agency in Berlin under No. 104 08 504.
The empirical calculation methods for emissions from refueling listed in the appendix have the disadvantage that the modern engine design cannot yet be included in the empirical calculation approaches.
Modern vehicles today have much better engine compartment insulation to improve the function of the exhaust gas catalytic converter, for example during a cold start. The increasing introduction of the catalyst has the consequence that the gasoline in the cycle of a tank filling is increasingly depleted of low boilers by pumping over the injection pump. So today there are significantly more air components and less gasoline vapors in the empty tank than in the past with the now outdated technology.
The basis for the theoretical basis has already been withdrawn from the evaluation of emissions during refueling according to the state of the art (No. 104 08 504).
In addition, the introduction of stage 2 will mean that the spread of catalytic converters in the affected regions will have progressed.

• die gasseitige Volumenentwicklung des durch das eingefüllte Benzin verdrängten Gasvolumen,
• ausgehend von einem Zustand 1 und einer Gaszusammensetzung in dem leeren Tank über dem Restbenzin,
• bei einem Zustand 2 und nach der Sättigung über dem Benzin im Lagertank, berücksichtigt wird.

In diesem Fall wird davon ausgegangen, daß das Fahrzeug vollgetankt wird. Bei einer physikalischen Betrachtung wird die Entwicklung des Volumens der inerten Luftanteile im leeren Pkwtank und über dem an Leichtsieder armen Benzin (untere Kurve in Fig. 2), bei einer bestimmten Sättigung über dem frischen Kraftstoff, der mehr Leichtsieder enthält, verfolgt. Es wird also zunächst die wirkliche Volumenbildung beschrieben, welche gemäß der Erfindung überwacht wird.
Diese Volumenentwicklung unterliegt den allgemeinen Gesetzen des Stoffaustausches aus der physikalischen Chemie. Für die unterschiedlichen Gasgemische gilt das Gesetz von DALTON. Da diese physikalisch definierbaren Volumenberechnungen eine Voraussetzung für den Nachweis von schädlichen Umwelteinwirkungen sind und diese speziell nach dem Stand des Wissens bei der Betrachtung bisher nicht berücksichtigt werden, wird im folgenden zunächst die physikalische Grundlage für die Berechnung näher dargestellt.
Hierzu wird der zu füllende Tank 10 jeweils mit dem Index 1 und der Tank 11 mit der Kraftstoffentnahme oder der Gaszufuhr mit dem Index 2 bezeichnet.
Bei Tankbeginn oder vor Herstellung der Verbindung zwischen dem leeren Tank 10 und dem Lagertank 11 besteht über den Spiegeln der Flüssigkeit Atmosphärendruck. Über der Flüssigkeit ist ein Gemisch aus Luft und Benzindämpfen, wobei die Luftanteile gegenüber den kondensierbaren Dämpfen als inert zu bezeichnen sind. Der zusätzlich in der Luft enthaltene Wasserdampf ist gering und wird bei der folgenden Betrachtung nicht berücksichtigt.It is a further object of the invention to avoid this disadvantage for the future operation of stage 2.
This object is achieved according to the features of claim 3 in that
to calculate the vapors generated for level 2

• the gas-side volume development of the gas volume displaced by the filled gasoline,
• starting from a state 1 and a gas composition in the empty tank above the remaining gasoline,
• in a condition 2 and after saturation above the gasoline in the storage tank, is taken into account.

In this case it is assumed that the vehicle is filled up with fuel. From a physical point of view, the development of the volume of the inert air components in the empty car tank and above the gasoline poor in low boilers (lower curve in FIG. 2) is followed, with a certain saturation, over the fresh fuel which contains more low boilers. The actual volume formation, which is monitored according to the invention, is therefore first described.
This volume development is subject to the general laws of mass transfer from physical chemistry. The law of DALTON applies to the different gas mixtures. Since these physically definable volume calculations are a prerequisite for the detection of harmful environmental impacts and these have not been taken into account in the consideration up to now, especially according to the current state of knowledge, the physical basis for the calculation is presented in more detail below.
For this purpose, the tank 10 to be filled is designated with the index 1 and the tank 11 with the fuel removal or the gas supply with the index 2.
At the beginning of the tank or before the connection between the empty tank 10 and the storage tank 11 is established, atmospheric pressure exists above the levels of the liquid. Above the liquid there is a mixture of air and gasoline vapors, the air fractions being inert to the condensable vapors. The additional water vapor contained in the air is low and is not taken into account in the following consideration.

The mass transfer processes during the refueling process and their influence on the volume in the individual tank chambers 10 and 11 are therefore subject to the laws of the general gas equation and the law according to DALTON. According to the idea of the invention, it should therefore be determined which space or volume the inerts from the tank 10 occupy above the gasoline mixture from the tank 11. The general gas equation is as follows: $$\text{p ∗ V = m ∗ R ∗ T; or m ∗ R = p ∗ V / T;}$$

The above equations apply to the gas mixture and, according to DALTON, also to the individual components with the corresponding partial pressures.

bezogen auf den Tank 2 gilt entsprechend: $${\text{m}}_{\text{(i2)}}{\text{∗ R}}_{\text{(i2)}}{\text{= p}}_{\text{(i2)}}{\text{∗ V}}_{\text{(i2)}}{\text{/ T}}_{\text{(i2)}}\text{;}$$

In relation to the inerts in tank 1, the following therefore applies: $${\text{m}}_{\text{(i1)}}{\text{∗ R}}_{\text{(i1)}}{\text{= p}}_{\text{(i1)}}{\text{∗ V}}_{\text{(i1)}}{\text{/ T}}_{\text{(i1)}}\text{; and}$$

in relation to tank 2, the following applies accordingly: $${\text{m}}_{\text{(i2)}}{\text{∗ R}}_{\text{(i2)}}{\text{= p}}_{\text{(i2)}}{\text{∗ V}}_{\text{(i2)}}{\text{/ T}}_{\text{(i2)}}\text{;}$$

T₁ ist die Temperatur im Tank 1 in Kelvin, T₂ ist die Temperatur im Tank 2. Je nach der Art des Betankungsvorganges, mit einem kalten oder warmen Fahrzeug, sind die Temperaturen nur gering unterschiedlich.
Die Partialdrücke p_(i1) und p_(i2) sind die Drücke der Inerten im Tank 1 und Tank 2.
Das Volumen V₁ entspricht bei einem Auffüllen des Tank 1 dem getankten Flüssigkeitsvolumen.Since the amount of inert is by definition not changing during the refueling process, the product of m _i ∗ R _{i is also} constant. The following equation applies to volume development: $${\text{V}}_{\text{(2)}}{\text{= V}}_{\text{(1)}}{\text{∗ p}}_{\text{(i1)}}{\text{/ p}}_{\text{(i2)}}{\text{∗ T}}_{\text{(i2)}}{\text{/ T}}_{\text{(i1)}}\text{;}$$

T₁ is the temperature in tank 1 in Kelvin, T₂ is the temperature in tank 2. Depending on the type of refueling process, with a cold or warm vehicle, the temperatures are only slightly different.
The partial pressures p _(i1) and p _(i2) are the pressures of the inerts in tank 1 and tank 2.
The volume V₁ corresponds to the tanked liquid volume when filling the tank 1.

Since the majority of gasoline contains only air and gasoline components, the following equation applies according to DALTON: $${\text{p}}_{\text{(i)}}{\text{= p}}_{\text{(total)}}{\text{- P}}_{\text{(Petrol)}}\text{;}$$

If the partial pressures above the liquids are known, the partial pressures p _{(i) of} the inerts can be calculated according to equation (2).
Equation (2) further shows that if the partial pressures of the gasoline change, the partial pressures of the inert p _(i) will change accordingly. The total pressure p (g) remains constant under the usual operating conditions, namely approx. 1 bar to 1 atm depending on the location of the tank system and the current weather conditions.
In accordance with the concept of the invention, the operational evaporation of the low boilers in the tank 10 results in an increased partial pressure p _{(i) of} the inerts. Thus, according to equation (1) and for stage 2, there is an increase in volume in the gas recirculation.
The calculation method according to the invention thus has the advantage over the empirical method that the possible environmental impact during the refueling of modern vehicles according to stage 2 can be determined mathematically as a result of the increase in volume.
The metrological determination of the ideal fueling process with 100% gas recirculation (volume rate) by pressure measurement has the advantage that each gas recirculation of any refueling can be clearly defined. The excess gas volume will escape at the tank neck of the car, as is also the case without gas recirculation. In contrast, an inadequate emission reduction would be determined with a test method according to the prior art under these conditions, which are ideal for gas recirculation.
In the course of stage 2, the returned small gas volume enters the large free space of the tank 11 of a few cbm (m3).
As a result of the mixing, the saturation takes place very slowly. The saturation is determined as a pressure increase in the closed system of stage 0 as part of the pressure measurement.
The excess volume that forms in the course of stage 2 arises from the change in the composition of the fuel and the increase in the vapor pressure when fresh fuel is fed into the tank 10. This vaporizes spontaneously low boilers and cause the volume to increase. While a calculation of the excess volume is not possible according to the state of the art according to 104 08 508, the volume development can be calculated according to equation (1). The partial pressures in tank 11 can be determined with knowledge of the Benz composition, but in tank 10 they depend on the past driving mode. A simple way to determine the condition in tank 10 is a gas analysis, especially by determining oxygen (O2). The oxygen content can be determined within seconds using the Dräger analysis tubes.
Due to the oxygen content, the corresponding air content is also known. This proportion of air can be converted into volume% or weight% and in m _(i) as kg / m3.

Using this quantity, the following equation applies: $${\text{p}}_{\text{(i)}}{\text{= m}}_{\text{(i)}}{\text{∗ R}}_{\text{(i)}}{\text{∗ T}}_{\text{(i)}}\text{/ V;}$$

If the volume V = 1 is set, the partial pressure of the inerts in the tank chambers 10 and 11 can be calculated via an oxygen measurement. R (i), the gas constant of air, and T (i) are both known.
Of particular importance is the development of the volume to prevent harmful environmental effects when the tank is half full. On the one hand, part of the volume in the tank 10 is displaced and conveyed back into the tank 11. At the same time, the composition of the gasoline in the tank 10 changes, associated with a considerable increase in the partial pressure due to the low boilers supplied in the fuel. On the other hand, the calculated volume increase due to the increase in partial pressure relates to the total gas volume that was present in tank 10 before the tank started. The development of the excess volume is equivalent to that when filling the tank, but the tank was only filled up to half the volume.
As a precaution against harmful environmental effects, it is therefore strongly recommended that the customer refuel fully.
Selling the petrol via automated teller machines, eg 14 l for 20 DM, prevents the more environmentally friendly refueling and results in additional volume.
For delivery and decanting with gas oscillation (level 1) it is important that at the end of level 0 there is no excess pressure in the floor tank. When checking the fill level or opening the flange cover, the tank atmosphere would blow out. At least at this point in time the pressure equalization must already have taken place.
The refilling process of stage 1 is subject to the same physical laws and process data as stage 2, with the difference that the delivery tank is largely emptied and the large volume of the returned gas decisively determines the conditions in the delivery tank.

The procedure for limiting emissions when refilling and storing petrol is described in the 20th Ordinance of the Federal Immission Control Act of October 1992 in the FRG. This regulation regulates the procedure for gas exchange under § 3 and describes the procedure in such a way that no fuel vapor is released into the environment during operation. The Air Pollution Control Ordinance (LRV), which is valid in Switzerland, is partially coordinated with the FRG and also prescribes a closed system for the transfer of fuel.
Both regulations assume a volume flow to be returned, which is identical to the amount of petrol refilled.

No vapor emissions are released in such a filling process. If, however, the storage of the liquids, i.e. level 0 or the fuel transport in the truck, takes place normally at atmospheric pressure, the decanting process is only completed when the pressure and volume balance with the environment has been established.

• sie die beim Umfüllen gegebene Druck- und Volumenänderung nicht berücksichtigen,
• und den Ausgleich der Gasseite mit der Umgebung unkontrolliert beim Öffnen der Verbindungsleitungen herstellen.

The known systems for decanting the liquids therefore have the disadvantage that

• they do not take into account the change in pressure and volume during transfer,
• and balance the gas side with the environment in an uncontrolled manner when opening the connecting lines.

In the event of overpressure, the operator is in the escaping, harmful and explosive volume flow when loosening the connecting line. On the one hand, the permissible workplace concentrations for the vapors of petrol and benzene are exceeded many times over. Gasoline and benzene can even be present as an aerosol. On the other hand, the volume can spread in the area of the tanker vehicle (Tkw) and ignite when sparking due to spark formation.
It is further possible that when the pressure drops to the response pressure of the safety valve 15, when the liquid line 22 is loosened, the remaining excess pressure is released by spouting gasoline and the operator receives a gasoline shower.
It has already been shown in practice that the above regulation does not yet provide adequate precautionary measures against harmful environmental effects.

It is the object of the invention to avoid these disadvantages for the operation of stage 1, to restore the operating state in the filled tank for the usual storage conditions of stage 0 and to take into account the volume changes resulting during a transfer operation.

This object is achieved by carrying out the refilling process in accordance with the features of claim 9.

When the regulation was passed, the legislature assumed that the same physical conditions exist in the residual gasoline and in the atmosphere above as in the storage tank of the truck.
In reality, the temperature in the underground tank is relatively even and only slowly follows the fluctuations over the course of a day. The temperature of the fresh fuel, however, is determined by the external conditions. When delivered from the refinery, the temperature can be up to 20 ° C higher than that in the underground tank. This also applies to the unloading of residual amounts after intense sun exposure on warm days.
It can be seen from the vapor pressure curves in FIG. 2 that the vapor pressure doubles at a temperature gradient of 20.degree.

The method prescribed in accordance with the above regulation therefore has the disadvantage that it does not take into account the actual operating conditions and thus does not take into account the harmful additional environmental effects.
The worst case is the first delivery of winter fuel on a warm autumn afternoon. These conditions and the physical calculation are taken into account in accordance with the features of claim 10. In the equations listed, the same designations are used as in above, index 1 for the tank to be filled and index 2 for the delivery tank.
Since the possible excess vapors can be particularly harmful to the operating personnel in the event of contact, the possible volume and pressure development in the course of stage 1 is also explained in more detail. The partial pressures of the gasoline mixtures are assumed to be known for the fresh fuel and the refilling process of stage 1.
With the simplification that the total barometric pressure is pg = 1 bar and by inserting p _i = p _g - p _d into equation (1) equation (4) applies $${\text{V}}_{\text{2nd}}{\text{= V}}_{\text{1}}{\text{(1 - p}}_{\text{d1}}{\text{) / (1 - p}}_{\text{d2}}{\text{) (T}}_{\text{2nd}}{\text{/ T}}_{\text{1}}\text{);}$$

The development of a volume in a transfer process with gas recirculation therefore depends on the differences in the vapor pressures of the liquids and the associated temperatures. The equation applies to constant pressure or an open system.

Für den Druck der Inerten (Luft) im Zustand 2 gilt.. $${\text{p}}_{\text{i2}}{\text{= p}}_{\text{i1}}{\text{(T}}_{\text{2}}{\text{/T}}_{\text{1}}{\text{) ; mit p}}_{\text{i1}}{\text{= p}}_{\text{g1}}{\text{- p}}_{\text{d1}}\text{folgt..}$$

$${\text{p}}_{\text{g2}}{\text{= (p}}_{\text{g1}}{\text{- p}}_{\text{d1}}{\text{) (T}}_{\text{2}}{\text{/T}}_{\text{1}}{\text{) + p}}_{\text{d2}}{\text{; mit p}}_{\text{g1}}\text{= 1 bar gilt Gleichung}$$

$${\text{p}}_{\text{g2}}{\text{= (1 - p}}_{\text{d1}}{\text{) (T}}_{\text{2}}{\text{/T}}_{\text{1}}{\text{) + p}}_{\text{d2}}\text{;}$$

DALTON applies the composition of the partial pressures in a closed system or constant volume. $${\text{p}}_{\text{g2}}{\text{= p}}_{\text{i2}}{\text{+ p}}_{\text{d2}}\text{;}$$

The following applies to the pressure of the inert gases (air) in state 2 .. $${\text{p}}_{\text{i2}}{\text{= p}}_{\text{i1}}{\text{(T}}_{\text{2nd}}{\text{/ T}}_{\text{1}}{\text{); with p}}_{\text{i1}}{\text{= p}}_{\text{g1}}{\text{- p}}_{\text{d1}}\text{follows ..}$$

$${\text{p}}_{\text{g2}}{\text{= (p}}_{\text{g1}}{\text{- p}}_{\text{d1}}{\text{) (T}}_{\text{2nd}}{\text{/ T}}_{\text{1}}{\text{) + p}}_{\text{d2}}{\text{; with p}}_{\text{g1}}\text{= 1 bar equation applies}$$

$${\text{p}}_{\text{g2}}{\text{= (1 - p}}_{\text{d1}}{\text{) (T}}_{\text{2nd}}{\text{/ T}}_{\text{1}}{\text{) + p}}_{\text{d2}}\text{;}$$

The development of the total pressure in a decanting process with gas recirculation therefore depends on the differences in the vapor pressures of the liquids and the associated temperatures. The simplified equation applies to the rough estimate of the pressure development during a transfer process: $${\text{p}}_{\text{g2}}{\text{= p}}_{\text{g1}}{\text{+ (p}}_{\text{d2}}{\text{- p}}_{\text{d1}}\text{);}$$

• die vergleichende Messung der Emissionen am Pkwtank für einen Tankvorgang über eine Stunde dauert und die zurückgeführte Gasmenge entweder nicht gemessen wird oder zu wenig beachtet wird. Als Folge daraus entsteht bei der Vorsorge für die Allgemeinheit der große Nachteil,

daß die Gefahren infolge der Gasrückführung für die Zeit nach dem Tankvorgang nicht erkannt werden.
Diese Nachteile hat das Verfahren nach dem Hauptanspruch nicht: Die Druckmessung ermöglicht eine Schnellanalyse über den Tankvorgang mit Gasrückführung.
Sie ermöglicht die Feststellung von schädlichen Betriebszuständen bei der Durchführung der Stufe 1.
Sie ermöglicht die Beobachtung der Zustände im Erdtank während der übrigen Betriebszeit.The pressure development in the course of stage 1 can thus be tracked via the pressure measurement in the underground tank. From a certain point in time or a change in pressure, the pressure compensation with the environment can be established by opening a valve. The pressure measurement according to the invention and the procedure according to claim 9 therefore have the advantage that when the connecting line is released, the operator no longer has the excess gases or fuel flowing out of the filling line.
Stage 1 is therefore only completed when the operating pressure matches the pressure of stage 0 and stage 2 again.
This pressure compensation in the underground tank must be set before creating and before disconnecting the line connection for stage 1.
The pressure curves in FIG. 1 show that even in the operation of stage 0, the development of an excess volume can be observed in the quiescent state due to the re-evaporation. As part of the legal precaution against harmful environmental effects, it must at least be ensured that the excess vapors escape in a controlled manner. Reference should be made here to the past catastrophes in Luisville, Kentucky and 1992 in Guadalachara. The uncontrolled safety valve 15 in the vent line 14 enables an overpressure of up to 250 mm water pressure in the underground tank. In the case of the examined gas station with central pump curves A and C in Fig. 1, there is obviously a leak on the suction side in the gas return line. Through this possible opening, the entire excess volume that arises at level 0 during the period of inactivity overnight can escape. After the Presentations and tests of the prior art, this pump is in a shaft and this is connected to the sewer.
As part of precautionary measures, it should be borne in mind that 1 m3 of gas (m3) escaping from the underground tank into a sewer system can produce 25 m3 of ignitable gases when diluted with air. Flammable mixtures can accumulate over days and weeks, leading to the disasters mentioned above. The test method according to the prior art therefore has the technical disadvantage that

• the comparative measurement of the emissions from the car tank for a refueling process takes over an hour and the amount of gas returned is either not measured or is neglected. As a result, there is a major disadvantage in providing for the general public,

that the dangers due to gas recirculation are not recognized for the time after the refueling process.
The method according to the main claim does not have these disadvantages: the pressure measurement enables a quick analysis of the refueling process with gas recirculation.
It enables the determination of harmful operating conditions when performing level 1.
It enables the conditions in the underground tank to be observed during the remaining operating hours.

According to the invention, by opening the ventilation line contrary to the state regulation, the volume and pressure can be equalized with the surroundings. The renewed risk to individual groups of people in the gas stations with gas exchange is thereby reduced. The ideal fueling process and the determination of the ideal volume rate (level 2) must, however, be determined by measuring the pressure with a closed underground tank.

The installation and function of the measurement and control technology is therefore described below.
The vent line 14 of the floor tank 11 can be operated according to the invention for the operation of stage 1 with a free opening to the atmosphere. When the opening is closed with a safety valve, the pressure change in the tank 11 be measured. The pressure measurement 19 (PIC) is used for this purpose, implemented as a pressure display (PI) or as a pressure display / control (PIC). The line 25 with the valve 26 enables the pressure equalization of the tank 11 with the environment.
In the case of existing systems, a pressure indicator, for example as a U-tube manometer and the valve 26 as a manual valve, can be designed to protect the operating personnel, which is opened in the event of pressure differences from the environment before the flange connections on the tank 11 are opened.
The continuous measurement can be carried out by means of a pressure transmitter, for example from Rosemount. A current of 4 to 20 mA (milliampere) is the measure for the pressure difference to the environment. The measurement signal can be processed via the controller 27 and the valve 26 can be controlled in one embodiment as a control valve.
With a certain signal from the controller 27, the pressure compensation can be established via the line 25 with the atmosphere.
At the gas station there is a need to monitor the mechanical function. Using the pressure display (PI), for example on a screen as a digital value, it is possible for the operating personnel to continuously check the function of the gas recirculation (level 2). With ideal gas recirculation, the scale value remains constant over the duration of the refueling process, i.e. it does not change.
At the gas station there is a need to control the suction power of the pump 8. If excess volume occurs as a result of the gas recirculation of stage 2, excess pressure forms in the closed tank 11. This increase in pressure can be clearly defined. Small pressure differences can be measured exactly. The pressure increase is a pure function of the additional air components supplied and the given saturation of the gasoline vapor / air mixture from the tank 10.

For the pressure rise in the closed tank 11 or for the partial pressure portion of the excess gas mixture, the following applies according to DALTON: $${\text{V ∗}}_{\text{(delta)}}{\text{p = (m}}_{\text{i}}{\text{∗ R}}_{\text{i}}{\text{+ m}}_{\text{b}}{\text{∗ R}}_{\text{b}}\text{) T;}$$

For the volume development in the open tank 11 or for the actual volume of the excess gas mixture at atmospheric pressure, the following applies according to DALTON: $${}_{\text{(delta)}}{\text{V ∗ p = (m}}_{\text{i}}{\text{∗ R}}_{\text{i}}{\text{+ m}}_{\text{b}}{\text{∗ R}}_{\text{b}}\text{) T;}$$

The right-hand side is identical in both equations, so the following applies to the conversion of the pressure difference in a closed system into the volume development of an open system: $${}_{\text{(delta)}}{\text{V = V ∗}}_{\text{(delta)}}\text{p / p;}$$

The volume V is the freeboard in the closed tank 11. The pressure difference (delta) p is measured over a certain period of time in which a known amount of petrol has been filled. The pressure p is the total barometric pressure of the gas. The dependency shown applies in the same way to negative pressure changes, i.e. for insufficient gas recirculation. The calculated difference (delta) V can be related to the amount of fuel indicated at 6. The quotient (delta) V / FIR * 100 is the deviation of the volume rate from the ideal volume rate of 100%.

At the petrol station there is a need to have recurring checks carried out. The measuring procedure, which is simple due to the pressure measurement, is especially suitable for the first-time and recurring control of the installation at the petrol stations. These controls are necessary in accordance with the 21st BImschV (Federal Immission Control Ordinance).
At the gas station, there is a need to set the gas quantity very precisely in tank operation. By using this simple measuring principle, it is possible to set the recirculated gas quantity correctly when starting up the system and to provide functional evidence in accordance with § 6 of the regulation.
An increasing pressure in line 14 shows that clearly not too little gas is being returned. A negative pressure gradient at the start of a measurement is therefore an indication that the emissions from the fuel nozzle can be reduced by increasing the suction power.
The adjustment of the gas quantities and the uniform setting of the volume quantity is possible through the control valve 9 in line 3.
The accuracy of the pressure measurement depends on the selected measuring range and, according to equation (6), on the free volume V in the tank 11. The deviation of the operating pressure in the tank 11 from the ambient pressure can, for example, exceed the desired small measuring range of 2 to 5 mbar for the pressure measurement. For this type of operation, an alternative measurement setup is drawn in the vent line 14 on the flange 28.
As a connection flange in existing installations, one of the flanges in the dome shaft for level 1 gas oscillation or the flange 17 for the dipstick can also be used. The measuring setup consists of a measuring container 29 which is installed in the line 30 between two valves 31 and 32.
When measuring the pressure curve, the valve 32 is closed to the environment and the connection to the tank 11 is initially opened. The pressure measurement 33 is connected to both sides of the valve 31. At the start of a measurement, this valve 31 is closed and the pressure deviation (PIR) from the initial state can be measured and, for example, printed out as a document.
The conditions in the measuring container 29 should remain as constant as possible. A cylindrical or glass design is possible.

At the petrol station there is a need for recurrent leak tests. With the comparative pressure measurement in line 30, it is possible to carry out the prescribed tightness checks in the tank system. According to equation (6), the decrease in pressure is the measure for the leakage quantities.

• 1. die Verdrängungsarbeit zum Aufblasen gegen die Atmosphäre,
• 2. das Eigengewicht der Folie, welche auf das Gasvolumen in der Folie einwirkt,
• 3. der Einfluß des Winddruckes (Staudruck) auf der Folie,
• 4. der dynamische Anteil der Fällgeschwindigkeit.

The pressure measurement Pi or pressure control PIC described above can also be used for the treatment of the excess gas quantities during stage 0.
The gas returned during stage 2 causes a dilution of the gasoline vapors in the tank 11 due to the inert content. In the course of stage 0, re-evaporation occurs with a further increase in pressure in the closed system. In this case, the pressure control can open the valve 26 or in one longer break over night it can generally be open. This can prevent the uncontrolled escape of vapors in the earth's area.
These questions of shifting emissions through the recirculation of gasoline-containing air were also addressed in the test procedure, Chap. 5, examined according to the prior art. The excess vapors are collected here in a foil bag with a capacity of 90 l.
This measuring method has the disadvantage that neither the volume nor the total pressure remains constant during the measurement, and that the pressure change is not measured over the duration of the measurement. Filling the foil bag requires an increase in pressure in the underground tank for several reasons:

• 1. the displacement work to inflate against the atmosphere,
• 2. the dead weight of the film, which acts on the gas volume in the film,
• 3. the influence of wind pressure (dynamic pressure) on the film,
• 4. the dynamic proportion of the rate of felling.

The volume measurement in the film bag according to the prior art must therefore be supplemented by a pressure measurement according to the invention. The actual volume increase in the underground tank can then be calculated using equation (6) according to claim 16 plus the volume in the foil bag.

The test method according to the state of the art therefore does not take the conditions in the floor tank into account in the measurements on the fuel nozzle and in the measurements on the ventilation mast in order to fulfill the precaution against harmful environmental effects.

At the petrol station there is a need to regulate the amount of gas returned in the future. The pressure records in Fig. 1 about the filling process for the TÜV-tested system drop so much that it can be assumed that in the actual filling operation other influences influence the returned gas volume, which cannot be recognized with the test method according to the prior art are.
The described system from Scheidt & Bachmann works with a central vacuum pump that is constantly in operation. During the breaks between refueling, the pump is switched off by the Frictional losses heated up considerably. The heat energy stored as latent heat in the pump heats up the gas entering at the beginning of stage 2, which increases the volume flow to be pumped in the pump by up to 20%. However, the pump has a constant delivery volume, so that the amount sucked off at the tank neck is too small and the vacuum at the suction neck of the pump breaks down. If the pump is operated for a long time or several refueling cycles in succession, it cools down and the effective delivery volume increases.
The examined central gas pump therefore has an unsteady delivery characteristic that does not deliver enough output at the beginning of the refueling process. An error that cannot be determined with the test method according to the state of the art. However, it shows that the ideal gas recirculation in certain systems can only be achieved by regulation.
For this reason, one possibility is shown in FIG. 3 for using the pressure measurement as the actual value for regulating the gas quantity. For this purpose, a control valve 18 is installed in the manifold 7. This valve is fed by the controller 27. If the pressure rises, the pressure loss in the control valve 18 is increased to reduce the volume flow. If the pressure drops, the pressure loss in line 7 is reduced by opening the valve accordingly.

At the gas station there is a need to clean the excess volume.
The above description of the invention shows that the harmful environmental effects arise from the excess gas volume. It is therefore of interest to take a holistic view of the volume formation at a petrol station, starting from the refueling process and the condition in the car tank up to the delivery of petrol with the condition in the tanker truck. The following initial conditions are realistic according to FIG. 2: Car Temperature 10 ° C Vapor pressure 0.15 bar Truck Temperature 30 ° C Vapor pressure 0.5 bar According to equation (4), for V2 = 1.82 V1;
The excess volume is therefore 82% of the fuel quantity. To avoid undetected damage It is therefore important to properly discharge the volume into the atmosphere, taking into account the state regulations. According to the invention, further cleaning of the excess volume is also possible. According to the features of claim 29, this cleaning is carried out by washing the gasoline-containing gases with diesel fuel.
Diesel fuel has a vapor pressure of 5.5 mm WS at 20 ° C. This requires a hydrocarbon content of 4 g / m3. The diesel fuel is the solvent for the gasoline vapors, so that the gasoline can be washed out to a residual content of 10 to 20 g / m3. The vapors are fed into the scrubber from below via line 25. The cleaned gases can be fed to the tank for diesel fuel. The washing liquid is fed to the washer from above. To achieve the required number of separation stages of 5, an orderly packing is installed in the scrubber. The overall height of the pack is in the range of 1 m. The washing liquid is removed from the tank for diesel fuel and also fed back into it. A possible place for an installation site is at the vent line 14. The execution of such a washer is described in the applicant's German application DE 39 16 073.
Future developments may require the use of a bayonet lock when refueling. The excess volume flow can then escape via line 25. The regulation in the line enables controlled further treatment.
With the new process, it is possible to identify harmful environmental effects on gas stations with gas recirculation and to operate the tank systems in an environmentally friendly manner in accordance with § 23 of the BImschG (Federal Immission Control Act).
With the measuring device described, it is possible to carry out the necessary checks, such as a leak test and functional test of the gas return, at different petrol stations.
The personnel are given the opportunity to protect themselves from the harmful gases.
The petrol station customers can get the information they need on how to avoid further emissions by filling up regularly.
The analysis for oxygen enables a statistical recording of the initial conditions in the empty car tank. This could result in further improvements when refueling cars.

Claims (35)

1. Method for precaution against harmful environmental effects at filling stations having a filling system with gas displacement devices and for the controlled treatment of an excessive and environmentally harmful petrol-vapour/air mixture (vapours) which occurs in the tank atmosphere during the storage of carburettor fuels, here designated as stage 0, as result of the supply of non-saturated air fractions and may be supersaturated in respect of the higher boilers, such as octane and benzene, and which, during the filling of the storage tank, designated as stage 1, or the extraction of fuel, designated as stage 2, in each case occurs in conjunction with the gas displacement or gas return, the filling station having

   - an installation for the return of the vapours (stage 2), for example by means of a gas suck-off (3, 8, 9, 7), from the passenger car tank (10) into the filling system (11, 16),

   - an installation for transferring the vapours (stage 1), for example by means of a gas displacement line (23), from the filling system (11, 16) to the delivery tank (12), and

   - a closable orifice (14, 15; 25, 26; 28, 30, 31, 32) for the discharge of excess vapours,

   characterized in that,

   - to monitor excessive vapours and to prevent an uncontrolled release of the vapours,
   the pressure (19, 33) in the filling system is measured periodically or permanently and consequently a trend of the pressure is determined,

   - the excess vapours occurring are recorded in a documentable manner by means of the pressure measurement, and - an orifice is provided for the exchange of vapours with the environment.
2. Method according to Claim 1, characterized in that the pressure measurement for the individual stages 0, 1 and 2 takes place, in the case of one storage tank, at a common measuring point and, in the case of a plurality of tanks which are connected to form a system, in one tank.
3. Method according to Claims 1 and 2, characterized in that, to calculate the vapours occurring for stage 2,

   - the gas-side volume expansion of the gas volume displaced by the introduced petrol is taken into account,

   - starting from a state 1 and a gas composition in the empty tank, via the residual petrol, and,

   - in the case of a state 2 and after saturation, via the petrol in the storage tank.
4. Method according to Claim 3, characterized in that

   - in the physical observation of the operation, the behaviour of the inert fractions is taken into account,

   - the behaviour of the inert fractions is described by means of the general gas equation and Dalton's law, and

   - the following equation $$\text{V(2) = V(1) ∗ p(i1)/p(i2) ∗ T(i2)/T(i1) ;}$$

   

   is derived from this for the volume expansion.
5. Method according to Claims 3 and 4, characterized in that the partial pressure p(i) of the inert fractions is determined by the determination by measurement of the air fractions, for example by means of oxygen measurement, and by calculation according to the equation $$\text{p(i) = m(i) ∗ R(i) ∗ T(i)/V ;}$$

   
6. Method according to Claims 3-5, characterized in that, in the case of a filling operation with incomplete filling of the tank, the gas-side volume expansion is also taken into account in that part of the tank which is not filled by the introduced petrol.
7. Method according to Claims 3 - 6, characterized in that the results and findings from the method of calculation are used for the practical filling work and the filling-station customer is referred, generally by an operating instruction, to the possibility of precaution against harmful environmental effects by filling of the tank.
8. Method according to Claims 1 - 7, characterized in that the excess vapours from the operation of stage 2 and from a system with vacuum assistance come into exchange with the environment via an orifice (20) at the non-gastight connection between the pump nozzle and vehicle tank.
9. Method according to Claims 1 and 2, characterized in that in the operation of stage 1, in respect of the excess vapours,

   - the effect of the physically different conditions via the fluid (2) on the original gas volume is taken into account via the fluid (1), and

   - the transfer operation is carried out in 2 work processes,

   - the actual transfer operation with simultaneous gas return, and

   - the equalization of the atmosphere changing in the tank (1) and (2) with the environment.
10. Method according to Claim 9, characterized in that the change in the atmosphere is determined according to Dalton's physical laws,

    - in the case of the assumption of a constant pressure, as the change in the volume, taking into account the dependencies of the equation $$\text{V2 = V1 (1 - pd1)/(1 - pd2) (T2/T1) ;}$$

    

    - in the case of the assumption of a constant volume, as the change in the pressure, taking into account the dependencies of the equation $$\text{pg2 = (1 - pd1) (T2/T1) + pd2 ;}$$

    
11. Method according to Claim 1 and Claim 9, characterized in that the commencement in time of the exchange with the environment is regulated via a control valve, for example in the vent line.
12. Method according to Claim 1 and Claim 9, characterized in that, to avoid high pressure fluctuations in the delivery tank, the vent line is connected to this tank (12).
13. Method according to Claims 1 - 12, characterized in that, to avoid a vapour escape harmful to health at the commencement and/or at the end of stage 1 via the connecting orifices in the dome shaft, in each case an equalization of the pressure in the filling system with the ambient pressure takes place before the opening of the flanged connection in the buried tank and, for this purpose, an orifice is provided for pressure equalization in the vent line (25, 28).
14. Method according to Claim 1, characterized in that the excess vapours from the operation of stage 0 are dissipated via the pressure-controlled adjusting valve (26) or via a permanent orifice in the vent line.
15. Method according to Claims 1 - 8, characterized in that the return of the desired gas volume in the course of stage 2 is controlled via the pressure measurement in the buried tank.
16. Method according to Claim 1 and claim 15, characterized in that, to carry out the volume determination, the vent line is closed, for example by means of a pressure vacuum valve,

    the determination of the volumetric excesses as a result of gas displacement takes place via a pressure measurement in the gaseous tank volume,

    and the volume difference is calculated according to the equation $$\text{(delta)V = V ∗ (delta)p / p ;}$$

    
17. Method according to Claim 1 and Claims 15 and 16, characterized in that, for a gas return of equal volume or a volume rate of 100%, the desired value of the pressure change is zero.
18. Method according to Claim 1 and Claims 15 to 17, characterized in that, for the measurement of small pressure differences, an additional measuring vessel (29) is connected to the filling system or part thereof on the gas side and, after the connecting line (28, 30) has been shut off, the pressure trend is determined in relation to the measuring vessel.
19. Method according to Claim 1, characterized in that the measurement of the pressure trend is used for a tightness test.
20. Method according to Claim 1, characterized in that the pressure trend is used as an actual value for the mechanical operating check of the gas return.
21. Method according to Claim 1, characterized in that the pressure trend is used as an actual value for checking and setting the suck-off capacity at the pump nozzle.
22. Method according to Claim 1, characterized in that the pressure trend is used as an actual value for the acceptance checks and recurring checks.
23. Method according to Claim 1, characterized in that the pressure trend is used as an actual value for the regulation of the returned gas volume (volume rate).
24. Method according to Claims 1 - 23, characterized in that, if a plurality of pumps are working and if a standard volume rate is set for each pump, the volume rate is regulated as a sum via a regulating valve (18) in the gas return line (7).
25. Method according to Claim 1 and Claims 19 - 24, characterized in that the pressure trend is plotted graphically for preparing the test or acceptance reports.
26. Method according to Claim 1, characterized in that the measurement of the pressure trend is used to improve volume determination by means of the foil bag.
27. Method according to Claims 1 - 26, characterized in that the pressure trend is used as an actual value for regulating the excess volume at stage 0 or stage 1.
28. Method according to Claims 1 - 27, characterized in that the excess vapours are supplied to a washing stage for the separation of the vaporous hydrocarbons.
29. Method according to Claim 28, characterized in that the vapours are washed with diesel fuel as a solvent.
30. Method according to Claim 28 and Claim 29, characterized in that the cleaned vapours and the spent washing fluid are supplied to the storage tank for diesel fuel.
31. Apparatus for carrying out the method according to Claim 1 and according to one of Claims 19 - 30 in the course of the operation of the individual stages 0, 1 and 2 at filling stations with gas return devices, to monitor excess vapours and to prevent an uncontrolled release of the vapours by means of a periodic or permanent measurement of the pressure in the filling system and a determination of the trend of the pressure in the filling system,

    to guarantee an orifice the exchange of excess vapours with the environment,

    to carry out pressure equalization in the buried tank with the environment, consisting of

    a closable vent line (14, 15; 25; 28, 30) and of a device for measuring the pressure (19, 33) in the filling system (11, 16), characterized in that

    - the vent line (14, 15; 25; 28, 30) can be closed by means of at least one shut-off valve (26; 31) for the measurement of pressure changes in the case of a constant volume and can be opened for pressure equalization with the environment,

    - the measurement of the pressure takes place continuously by means of a pressure transmitter, the measuring head of which is connected to the filling system (11, 16, 14, 28) and the measurement signal of which is transmitted via a current of 4 to 20 mA to an associated pressure indicator (PI - pressure indicating),

    - and means are provided for recording the trend of the pressure in a documentable manner.
32. Apparatus for carrying out the method according to Claim 18 and for the measurement of small pressure changes σp in the filling system, consisting of

    an apparatus according to Claim 31, characterized in that,

    to form a constant reference volume relative to the volume at the measuring point (19, 33), a measuring vessel (29) is built into the vent line (30) downstream of the shut-off valve (31) and a shut-off valve (32) is built into the vent line (30) downstream of the measuring vessel (29),

    the measuring head of the pressure transmitter (33) is connected on both sides of the shut-off valve (31),

    and, after an equalization of the volumes (14, 29) by means of the closing of the shut-off valve (31), pressure changes can be measured with a small measuring range.
33. Apparatus for recording (PIR) the measurement results according to Claim 25, consisting of an apparatus according to Claim 31 or 32 and of a recording instrument (printer/chart recorder), characterized in that,

    after the electronic transmission of the measurement signal, the latter can be recorded and documented graphically on paper (curves A, B, C, D).
34. Apparatus for recording (PIR) the measurement results according to Claim 25, consisting of an apparatus according to Claim 31 or 32 and of an electronic data memory, characterized in that,

    after the electronic transmission of the measurement signal, the latter can be filed in an electronic data memory.
35. Apparatus for carrying out the method according to Claim 1, at the same satisfying special safety requirements, consisting of the apparatus according to Claim 31, characterized in that

    a flame trap is built into the connecting line upstream of the measuring head as explosion protection.

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