EP0629175A1

EP0629175A1 - Treatment of petrol vapours in service stations.

Info

Publication number: EP0629175A1
Application number: EP93903833A
Authority: EP
Inventors: Fritz Curtius
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-03-08
Filing date: 1993-02-28
Publication date: 1994-12-21
Anticipated expiration: 2013-02-28
Also published as: EP0629175B1; ATE138352T1

Abstract

L'invention concerne un procédé de prévention des effets préjudiciables à l'environnement dans les stations-service et de traitement contrôlé des mélanges air/vapeurs d'essence excédentaires nocifs pour l'environnement. Le procédé consiste à mesurer la pression dans le système de distribution, à faire entrer les éventuelles vapeurs excédentaires en échange avec le milieu ambiant par l'intermédiaire d'un orifice défini et à ajuster les conditions physiques dans l'atmosphère du système de distribution en fonction des différents modes de fonctionnement du dispositif de distribution. L'invention concerne en outre le calcul physique des volumes de gaz ainsi que le dispositif permettant la mise en oeuvre dudit procédé.The invention relates to a method for the prevention of harmful effects on the environment in service stations and for the controlled treatment of excess air/gasoline vapor mixtures which are harmful to the environment. The process consists of measuring the pressure in the distribution system, introducing any excess vapors in exchange with the ambient medium through a defined orifice and adjusting the physical conditions in the atmosphere of the distribution system by depending on the different operating modes of the dispensing device. The invention also relates to the physical calculation of the volumes of gas as well as the device allowing the implementation of said method.

Description

«4.

Treatment of gasoline vapors at petrol stations.

The invention relates to a method for precautionary measures against harmful environmental effects on petrol stations which are operated with devices for gas recirculation. The invention relates in particular to a method and the device for measuring and monitoring the excess gas quantities. Furthermore, the metrological acquisition of the data is supplemented by the associated physical calculation method.

In order to protect the general public, modern petrol stations must be operated with facilities for gas recirculation. The time for refueling with gas recirculation only takes about 1 hour per day at petrol stations with normal sales, and fuel is only replenished every few days. For the rest of the day from 23 h the petrol station is either ready for operation or for certain times e.g. closed overnight. In the context of the present invention, the excess amounts of gas which occur in the remaining time of 95% of the period are also taken into account.

The invention enables continuous monitoring of the operation of a petrol station and the possible excess amounts of gas that can escape from the underground tank as a harmful environmental impact. The pressure curve in the underground tank is used as a measurable variable for this. With the device according to the invention, the pressure in the underground tank is measured.

The measuring method has meanwhile been used in various

Gas stations measured with gas recirculation devices. In

Fig. L is the result as a pressure curve in the underground tank above

Time and applied in different operating conditions. The

Print recordings start consistently after 4.5 minutes

-4- and last up to the 9th minute. The measurement was made using

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 a

100% gas recirculation. For this refueling process, the pressure in the underground tank remains constant or the change in pressure is 0.

Especially taking into account the valid in Germany

By law, this fueling process can be described as ideal.

The pressure measurements according to curve A over the refueling process from

So 1.25 minutes show that due to the drop in pressure, the returned gas volume is smaller than the tanked amount, ie it is too small.

The pressure curve under curve C falls with the relatively short one

Refuel 2 cars even steeper and further. This shows that here too the amount of gas returned is too small and that the necessary double suction power of the central pump for this

Operating case is not available.

Curve B is the characteristic pressure increase in the underground tank, which among other things through the continuous operation of the central

Vacuum pump in the underground tank is created. 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

1 / h.

In contrast, the course of curve D is discontinuous

Pump operation much flatter and corresponds to one

Free space of 12.9 m3 only an increase in volume of 60 1 / h. 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:

- During refueling, far too little gas is sucked out of the car, 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.

With the pressure measurement according to the invention in the free space of the underground tank, the causes of these typical disadvantages are to be recognized, in order to eliminate the disadvantages in the environmentally compatible operation of a

To avoid gas station.

A procedure for assessing gas return systems is in research project No. 104 08 508 of the Federal Environment Agency

Berlin described. Here, TÜV Rheinland provides a measuring method based on the gas recirculation system examined above

Determination of the return efficiency before.

In this method, the emission at the tank neck is measured with and without gas recirculation. The emission reduction with

Gas recirculation is a measure of the recycle rate.

However, the method has the disadvantages that the determination of the return rate is preferred over the

Volume rate, which describes the ideal refueling process, is given, the measuring point, by measuring 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 cannot be measured in real tank operation as a function check and

Measurements within the tank system are not provided. The volume rate is understood as the ratio: returned gas volume / volume of fuel tanked x 100.

After not only the above-described system for gas recirculation but also all other systems in Germany are tested with this test method from TÜV Rheinland, it is the task of the invention not only to avoid the disadvantages of this test method, but above all also the consequences thereof, especially the to avoid uncontrolled harmful environmental effects in practical operation.

This object is achieved in that

- the pressure in the underground tank system (storage tank) is measured temporarily or permanently to avoid uncontrolled release of vapors,

- the occurring excess vapors exchange with the environment via a defined opening,

- The operating conditions in the underground tank are approximated in the course of or when changing between one of the stages 0, 1 and 2 in relation to the physical state of the tank atmosphere.

The invention is described below with reference to FIGS. 1 to 1. 3 described.

Fig. 1 is an example of the actual pressure curve in a system that was tested according to the ideas of the German authorities using the test procedure of TÜV Rheinland.

2 shows the vapor pressure curves of 3 gasoline mixtures which influence the formation of the harmful emissions at petrol stations.

The upper curve with the highest vapor pressure belongs to one

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 that

Residual 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 oscillation (stage 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, e.g. in the vent line 14. The pressure measurement and control will be described later in connection with the individual operating states.

When petrol is withdrawn, refueling, the vehicle tank 10 is connected to the petrol station via the fuel nozzle.

^• 'S- 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 gasoline-containing vapors via the symbolized line 20, i.e. the sealing point not shown come. 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 approximately 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 to 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 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 during refueling is described by Dr. H. Waldeyer, in "Emission reduction when refueling", published by TÜV Rheinland, 1990. The theoretical and practical studies presented here were also published as part of a research project by the Federal Environment Agency in Berlin under the number 104 08 504. The empirical calculation methods for emissions from refueling listed in the appendix have the disadvantage that today's modern engine design cannot yet be included in the empirical calculation approaches.

Modern vehicles today have much better engine compartment insulation in order to function as an exhaust gas catalytic converter e.g. improve on 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 assessment of emissions when refueling carried out by the TÜV.

In addition, the introduction of stage 2 will mean that the spread of catalytic converters in the affected regions will have progressed. It is a further object of the invention to avoid this disadvantage for the future operation of stage 2, especially for the TÜV-tested systems.

This object is achieved in accordance with the features of claim 3 in that for the calculation of the vapors formed for stage 2

- the gas-side volume development of the gas volume displaced by the filled gasoline,

- starting from a condition 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 low 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 Geset :: from DALTON applies to the different gas mixtures. Since these physically definable volume calculations are a prerequisite for the detection of harmful environmental effects 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 first described 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 extraction 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. _ _, g— 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:

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.

Based on the inertness in tank 1, the following therefore applies:

m (iι) * R (ii) = p (ii) * V (ii) / T (ii); and

in relation to tank 2, the following applies accordingly:

m (i2) * R (i2) = p (i2) * V (i2) / T (i2);

Since, by definition, the amount of the inert does not change during the tank process, the product of mi * Ri is also constant. The following equation applies to volume development:

V (2) = V (l) * p (il) / p (i2) * T (i2) / T (il), * (1)

Ti 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 (iι) and p (i2) are the pressures of the inerts in

Tank 1 and Tank 2.

The volume Vi 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:

-5- p (i) = p (total) - P (gasoline); (2)

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 (l) 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.

As part 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 in the course of the pressure measurement in the closed system of stage 0 as an increase in pressure. 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, whereas due to the TÜV publications it is not possible to check the excess volume by calculation, the volume development can be calculated according to equation (1). The partial pressures in the tank 11 can be determined with knowledge of the gasoline composition, but in the tank 10 they depend on the past driving operation. A simple way of determining the state in tank 10 is a gas analysis, above all by determining oxygen (02). The oxygen content can be determined within seconds using the Dräger analysis tubes. Because of 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:

p (i) = m (i) * R (i) * T (i) / V; (3)

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 impacts when the tank is half full. Here, on the one hand, part of the volume in the tank 10 is displaced and reclaimed in 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, e.g. 14 1 for DM 20, 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 level 1 refilling process is subject to the same physical laws and process data as level 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 Federal Republic of Germany. 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, has been partially agreed with the FRG and also prescribes a closed system for the refilling of fuels. Both regulations are based on a volume flow to be returned which is identical to the amount of petrol refilled.

No vapor emissions are released in a filling process carried out in this way. However, if the storage of the liquids, i.e. level 0 or the fuel transport in the truck, takes place normally at atmospheric pressure, the refilling process is only completed when the pressure and volume balance with the environment has been established.

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

- they at the. Do not take into account the change in pressure and volume,

- and establish the balance of 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 uniform 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 reach 20 ° C. over which lie 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. A - 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 as in above are used, 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 pi = pg - pd into equation (1) equation (4) applies

V2 = VI (1 - pdl) / (l - pd2) (T2 / TD; (4)

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.

According to DALTON, the composition of the partial pressures in a closed system or constant volume applies.

pg2 = pi2 + pd2;

The following applies to the pressure of the inert gases (air) in state 2 ..

pi2 = pii (T2 / T1); with pii = pgi - pdi follows ..

pg2 = (pgi - pdi) (T2 / T1) + pd2; with pgi = 1 bar

Equation (5) ... pg2 = (1 - pdi) (T2 / T1) + pd2; (5)

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:

pg2 = pgi + (pd2 - pdi);

The pressure development in the course of stage 1 can thus be tracked via the pressure measurement in the underground tank. From a certain

Time or a change in pressure can be made by opening one

Valves that equalize pressure with the environment are established.

The pressure measurement according to the invention and the procedure according to claim 9 therefore have the advantage that the operator no longer has excess when loosening the connecting line

Gases or the fuel flows counter to the filling line.

Stage 1 is therefore only completed in terms of time when, according to the feature of the main claim, 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 the stage

0 So the development of an excess volume can be observed in the idle 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. Here are the past

Disasters in Luisville, Kentucky and referred to Guadalachara in 1992. The unregulated safety valve 15 in the

Vent line 14 allows overpressure in the underground tank

250 mm WS. In the case of the examined petrol station with a central one

There is obviously a leak on the suction side in the pump

Gas return line. Via this possible opening, the entire excess volume that is at level 0 in the period of

Silence occurs overnight, escape. After the

-ΛS- This is presentations and tests of the state of the art

Pump in a shaft and this connected to the sewer.

As part of the precautionary measure, it should be borne in mind that from 1 cbm of gas (m3) escaping from the underground tank into a sewer system, one

Dilution with air can produce 25 m3 of ignitable gases. about

Flammable mixtures can accumulate for 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 emissions from a car tank for one

Refueling takes over an hour and the returned

The amount of gas is either not measured or is neglected. As a result of this arises in the provision for the

In general, the great disadvantage 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 via the

Refueling with gas recirculation.

It enables the determination of harmful operating conditions when performing level 1.

It enables the monitoring of conditions in the underground tank ^'during the remaining operating time.

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 existing systems, in order to protect the operating personnel, a pressure display can be implemented, for example as a U-tube manometer and the valve 26 as a manual valve, 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 e.g. 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 petrol station, the need to monitor the mechanical function is via the pressure display (PI) e.g. On a screen as a digital value, the operating personnel are able to continuously monitor the function of the gas recirculation (level 2). In the ideal gas pressure guide, 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 rise is a series function of the additional air portions 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:

V * (delta) p = (mi * Ri + mb * Rb) 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:

(delta) V * p = (mi * Ri + mb * Rb) 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:

(delta) V = V * (delta) p / p; (6)

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 (deita) 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 correctly set the amount of gas returned when starting up the system and to provide functional evidence in accordance with Section 6 of the Ordinance. 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 nozzle can be reduced by increasing the suction power.

-λtL - The adjustment of the gas quantities and the uniform setting of the

Volume is possible through the control valve 9 in line 3.

The accuracy of the pressure measurement depends on the selected one

Measuring range from and according to equation (6) from the free space volume V in the tank 11. The deviation of the operating pressure in the tank 11 from the ambient pressure can e.g. the desired little one

Exceed measuring range of 2 to 5 mbar for pressure measurement.

For this type of operation, an alternative measurement setup is in the

Vent line 14 located on the flange 28.

As a connection flange in existing installations, one of the flanges in the dome shaft can also be used for the gas oscillation of the stage

1 or the flange 17 can be used for the dipstick.

The measuring setup consists of a measuring container 29, which is between 2

Valves 31 and 32 is installed in line 30.

When measuring the pressure curve, the valve 32 is closed

Environment closed and the connection to the tank 11 first opened. The pressure measurement 33 is connected to both

Side of the valve 31. At the start of a measurement, this will

Valve 31 closed and the pressure deviation (PIR) from that

Initial state can be measured and e.g. can be printed out as a document. .

The conditions in the measuring container 29 should remain as constant as possible. A cylindrical or glass version

Metal is possible.

At the petrol station there is a need for periodic 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.

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 liters.

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 pouch causes 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 part of the filling speed.

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 state-of-the-art test method therefore does not take the conditions in the floor tank into account to the extent that the precautionary measures against harmful environmental effects are taken into account in the measurements on the fuel nozzle and in the measurements on the ventilation mast.

At the petrol station, there is a need, which will be returned in the future

Regulate the amount of gas. The print records in Fig. 1 on the

The refueling process for the TÜV-tested system drops so much that one can assume that there are others in the real refueling operation

Influences that influence the returned gas volume, which cannot be recognized with the test method according to the state of the art.

The described system from Scheidt & Bachmann works with a central vacuum pump that is constantly in operation. In the

The pump is stopped by the pump

-10- 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 negative pressure at the suction neck of the pump breaks down. During longer operation or several refueling processes in succession, the pump cools down and the effective delivery volume increases.

The examined central gas pump therefore has an unsteady delivery characteristic, which at the beginning of the refueling process has too little delivery capacity. 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 with 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 steam pressure 0.15 bar Truck temperature 30 ° C steam pressure 0.5 bar According to equation (4), for V2 = 1.82 VI; The excess volume is therefore 82% of the fuel quantity. To avoid undetected damage

-1 Λ - 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 dictate 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 method 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 Section 23 of the BlmschG (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 gas station customers can get the desired information, such as other emissions ^"can be avoided by regularly filling up. 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.

-2 -

Claims

Process for precaution against harmful environmental effects on petrol stations with gas pendulum devices and for the controlled treatment of an excess and environmentally harmful gasoline vapor / air mixture (vapors), which is referred to as stage 0 when storing petrol, due to the supply of unsaturated air divide occurs in the tank atmosphere and can be supersaturated with regard to the higher boilers such as octane and benzene, and which when filling the tank, referred to as level 1, or the removal of fuel, referred to as level 2, in each case in connection with the gas oscillation or gas recirculation, characterized in that

- The pressure in the tank system (storage tank) is measured temporarily or permanently to avoid an uncontrolled release of vapors,

- the excess vapors which occur occur via a defined opening i exchange with the environment,

- The operating conditions in the tank system are approximated in the course or when changing between one of the stages 0, 1 and 2 in relation to the physical state of the tank atmosphere.

2. The method according to claim (l), characterized in that the pressure measurement for the individual stages 0, 1 and 2 takes place in a tank in a storage tank in a common measuring point and in several tanks which are connected to form a system.

3. The method according to claim (1 - 2), characterized in that for the calculation of the vapors formed for stage 2

- based on a condition and a gas composition in the empty tank above the remaining gasoline,

4. The method according to claim (l - 3), characterized in that - when considering the physical process, the behavior of the inert components is taken into account,

- the behavior of the inert components is described with the general gas equation and the law of DALTON and

- from this the following equation for the volume development

V (2) = V (ι) * p (ii) / p (i2) * T (± 2) / T (ii); (1) is derived.

5. The method according to claim (1 - 4), characterized in that the partial pressure p (i) of the inert gases via the measurement of the air fractions e.g. by means of oxygen measurement and using the calculation according to the equation p (i) = m (i) * R (i) * T (i) / V; (3) is determined.

6. The method according to claim (l - 5), characterized in that the gas-side volume development in that part of the tank that is not filled by the filled gasoline is also taken into account in a tank process with incomplete filling of the tank.

7. The method according to claim (l - 6), characterized in that the results and findings from the calculation process for practical tank operation are used and the petrol station customer is generally referred to the possibility of precautionary measures against harmful environmental effects by filling up with an instruction manual.

8. The method according to claim (1 - 7), characterized in that the excess vapors from the operation of stage 2 and a system with negative pressure support via the non-gas-tight connection between the fuel nozzle and vehicle tank come into exchange with the environment.

9. The method according to claim (l - 8), characterized in that in the operation of stage 1 in relation to the excess vapors

- The effect of the physically different conditions above the liquid (2) on the original gas volume above the liquid (l) is taken into account and - the transfer process is carried out in two work processes,

- The actual transfer process with simultaneous gas recirculation and

- the balance of the changing atmosphere in the tank (l) and (2) with the environment.

10. The method according to claim (1 - 9), characterized in that the change in the atmosphere according to the physical laws of DALTON,

- assuming a constant pressure, as the change in volume taking into account the dependencies of the equation

V2 = Vl (1 - pdl) / (l - pd2) (T2 / TD; (4)

- assuming a constant volume as the change in pressure taking into account the dependencies of the equation pg2 = (1 - pdi) (T2 / T1) + pd2; (5)

is determined.

11. The method according to claim (1 - 10), characterized in that the timing of the exchange with the environment via a control valve e.g. is regulated in the vent line.

12. The method according to claim (1 - 11), characterized in that the ventilation line is connected to this tank 12 to avoid large pressure fluctuations in the delivery tank.

13. The method according to claim (l - 12), characterized in that in order to avoid a harmful vapor outlet at the beginning and / or at the end of stage l via the opening in the manhole, a pressure equalization with the in each case before opening the flange connection in the underground tank Environment is established via a ventilation line.

14. The method according to claim (l - 13), characterized in that the excess vapors are discharged from the operation of stage 0 via the pressure-controlled control valve or via a permanent opening in the vent line.

15-. Method according to claim (1-14), characterized in that the return of the desired gas volume in the course of stage 2 is controlled via the pressure measurement in the underground tank.

16. The method according to claim (1 - 15), characterized in that, for carrying out the. Volume determination of the ventilation line e.g. is closed with a pressure vacuum valve, the determination of the volumetric excesses as a result of the gas oscillation takes place via a pressure measurement in the gaseous tank volume and the volume difference according to the equation

(delta) V = V * (delta) p / p; (6) is calculated.

17. The method according to claim (1 - 16), characterized in that for a volume-equal gas recirculation or a volume rate of 100%, the target value of the pressure change is zero.

18. The method according to claim (l - 17), characterized in that for the measurement of small pressure differences on the tank system or parts thereof, an additional measuring container is connected on the gas side and after shutting off the connecting line, the pressure curve relative to the measuring container is determined.

19. The method according to claim (1 - 18), characterized in that the measurement of the pressure curve is used for a leak test.

20. The method according to claim (1 - 19), characterized in that the pressure curve is used as the actual value for the mechanical function control of the gas recirculation.

21. The method according to claim (1 - 20), characterized in that the pressure curve is used as the actual value for the control and adjustment of the suction power at the nozzle istole.

22. The method according to claim (l - 21), characterized in that the pressure curve is used as the actual value for the acceptance controls and recurring controls.

23. The method according to claim (1 - 22), characterized in that the pressure curve is used as the actual value for the regulation of the recirculated gas volume: (the volume rate).

24. The method according to claim (l - 23), characterized in that the operation of several taps and the setting of a uniform volume rate for each tap, the volume rate is controlled as a sum via a control valve in the gas return line.

25. The method according to claim (1 - 24), characterized in that for the creation of the test or acceptance reports the Druckveriauf is graphically plotted.

26. The method according to claim (l - 25), characterized in that the measurement of the pressure curve is used to improve the volume determination with the film bag.

27. The method according to claim (l - 26), characterized in that the pressure curve is used as the actual value for controlling the excess volume at level 0 or level 1.

28. The method according to claim (l - 27), characterized in that the excess vapors for the separation of the vaporous hydrocarbons are fed to a washing stage.

29. The method according to claim (l - 28), characterized in that the vapors are washed with diesel fuel as the solvent.

30. The method according to claim (1 - 29), characterized in that the cleaned vapors and the used washing liquid are fed to the storage tank for diesel fuel.

-IS-

31. Measuring device for carrying out the method according to claim (1-30) for recording the differential pressure in the tank system of a petrol station or in parts of the system relative to the pressure in the environment, consisting of

- a shut-off valve to create a constant volume at the measuring point by installing it in the open ventilation line,

- a pressure transmitter for connection to the measuring point,

- and a pressure display.

32. Measuring device for performing the method according to claim (1 - 31) for measuring small pressure changes in a closed system, consisting of

- a connector for the measuring device,

a closed measuring container, connected to the connecting piece, to form a constant comparison volume with the volume of the measuring point,

- A shut-off valve, installed between the connector and the measuring container, in the connecting line and

- a pressure transmitter, for connection to the 2 constant volumes that result from the closing of the shut-off valve.

33. Measuring device consisting of a device according to claims (31 or 32) and an electronic forwarding of the measurement signal and storage of the measurement data.

34. Measuring device according to claim (33) and a connected printer for graphical documentation of the system function.

35. Measuring device according to one of the preceding claims (31 - 34), characterized in that a permanent fla mens barrier is installed in the connecting line in front of the measuring head as explosion protection.

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