FR2701470A1 - Process for the recovery of hydrocarbon vapour in service stations and system in which it is applied - Google Patents

Abstract

Process for separating the volatile hydrocarbon components from a gaseous mixture drawn in during a filling of a vehicle tank and escaping through a vent in a liquid hydrocarbon vessel, characterised in that the gaseous mixture is guided to flow into liquid hydrocarbon present in a separator in order to cause the liquid to absorb the said volatile components.

Description

The invention relates to a method and a system for separating the components of hydrocarbon vapors in service stations.

More specifically, the invention relates to a process for the separation of volatile hydrocarbon components from a gaseous mixture aspirated during filling of a tank of a vehicle and escaping through a vent in a tank of liquid hydrocarbon as well as an apparatus system by applying.

It is known that such recovery of the hydrocarbon vapors emitted into the atmosphere during the filling of vehicle tanks is generally obtained either by suction pumps with a gas flow regulation system proportional to the flow of the liquid delivered, or by an overpressure generated in the tank by adding liquid.

These methods are not yet satisfactory. In particular, the latter method then makes use of guns provided with sealing bellows which it is difficult to apply correctly in practice.

Either by a poor seal of the bellows, or in systems assisted by a poor adaptation of the gun to the tank which can let them escape. We never recover all of the evaporated hydrocarbons. Air is sucked in place of the hydrocarbon vapors.

Once discharged into the underground storage tank, this air generates additional pollution by its progressive saturation with gaseous hydrocarbons during the partial pressure balancing period.

As they evaporate, these hydrocarbons increase the total gas volume in the tank and the excess is then expelled by the vent which, as a safety measure, flows the tank to the atmosphere.

An effective way to increase the recovery efficiency at the level of the vehicle tank is to very strongly increase the suction with the gun, but has the serious drawback of sucking in large quantities of air which will cause unacceptable pollution at the level of the vent.

To remedy these drawbacks, in particular to avoid serious pollution of the atmosphere, it is the object of the present invention to separate most of the volatile hydrocarbons from the gaseous mixture which escape through the vent of the tank.

In order to achieve this object, the invention provides a process for separating volatile hydrocarbon components from a gaseous mixture drawn in during filling of a tank of a vehicle and escaping through a vent in a tank of liquid hydrocarbon characterized in that the gas mixture is guided to pass through liquid hydrocarbon contained in a separator in order to cause said volatile components to be absorbed by the liquid.

It is a device for trapping only hydrocarbons leaving through the vent, the air contained in the mixture being able to escape freely.

In principle, the invention makes use of known physical phenomena and characteristics of fuels.

It is known that at room temperature, the vapor pressure of fuels whose molecular mass of the vapors is close to 66 g / mol is of the order of 0.4 bar.

The vapors in equilibrium with the liquid phase essentially consist of butane and pentane, the heavier components remaining more easily in the liquid phase.

An approximate calculation then shows that the two main gaseous constituents each have a partial vapor pressure of the order of 0.2 bar, the rest (0.6 bar) coming from the mixed air.

When the butane + pentane + air mixture leaves the vent, the first two components must be trapped and the air alone allowed to escape.

Cold condensation would allow this, but to obtain a good yield, it would be necessary to compress the gas or lower the temperature of the mixture considerably, for example until the vapor pressure of butane (liquid) is significantly lower than 0.2 bar which implies temperatures of - 60 C minimum. And it is obvious that this is not practicable.

The process according to the invention then consists in cold dissolving the volatile hydrocarbon components (pentane and butane) in liquid fuel cooled to considerably lower temperatures, but such as the vapor pressure of the constituents normally present at- above the cold liquid and in equilibrium with it is much lower than the partial pressure of the gases to be trapped.

According to a preferred embodiment of the invention, a permanent fuel flow rate of the order of a few liters per minute is created by a pump which sucks from the underground storage tank. This fuel passes through at least one heat exchanger, preferably a refrigerator exchanger to be cooled there to -30 C for example, then directed towards a heat-insulated enclosure into which the gases escaping through the vent are injected.

By bubbling or by simple contact, the hydrocarbons are dissolved in the cooled fuel liquid. Only air can escape into the atmosphere, being not significantly soluble.

Indeed, the vapor pressure which overcomes the cold hydrocarbon is then very low, of the order of 10 to 20 mbar, while the vapor pressures of the gaseous hydrocarbons still free are much higher.

Once in contact with the cold flowing fuel, they are trapped and remain dissolved. They are then entrained and return with the solvent fuel to the underground storage tank.

In addition, the invention can be easily adapted to each application where it is sought to establish a very high suction of the hydrocarbon mixture at the vehicle tank, intentionally greater than 100%, for example 130% (of the liquid supplied for filling the tank) with the maximum flow or more, preferably without any proportional regulation. This permanent flow will be obtained by a pump started as soon as a fuel meter delivers its counting pulses.

This can be achieved in a manner known per se, for example by means of a pump in continuous operation connected to the suction pipe with or without restrictions of the diaphragm type.

We will adjust, for example, a permanent gas flow of around 55 1 / my for any fuel flow up to 40 I / min.

In all cases, we immediately see the advantages of the system * no regulation of the vapor suction rate at
vehicle tank level, * possibility of using small pipes for
vapor return pipes to the tank
storage, their high and fluctuating pressure drop
always being compensated by a powerful vacuum cleaner, * very high vapor recovery efficiency at
level of the gun, * a single hydrocarbon trapping system which is
then installed on a vent common to all tanks, * cooling obtained by refrigeration
traditional, not requiring temperatures
very low and modest power.

Other advantageous features of the invention will appear in the claims.

The invention will be better understood on reading the description below of several embodiments of the invention, given by way of nonlimiting examples.

The description refers to the appended figures in which
Figure 1 illustrates a first embodiment of a
apparatus according to the invention in diagram and
Figure 2 illustrates a second embodiment of a
apparatus according to the invention.

An underground storage tank 1 contains liquid fuel 2. This is sucked by a line 3 by means of a pump 4 (followed by its meter not shown) and discharged under pressure by a flexible hose 5 recovering steam to a pistol 6 with recovery.

The vapors containing an excess of air are sucked at at least one opening 7 when a steam pump 8 is running. The vapors are then directed to the top of the tank 1 by a pipe 9.

On the right of the diagram in Figure 1 we distinguish
A line 10 plunging into the liquid fuel of the tank 1. By this a pump 11 sucks fuel and discharges it through a first heat exchanger 12 then a second heat exchanger 13 to an absorber separator 14. It returns by gravity for example, by a pipe 16 to the exchanger 12 then by a pipe 18 to a water condenser 17 and finally to the storage tank by a pipe 19.

A refrigerator 15 cools the fuel which arrives through the line 10 in the exchanger 13.

The excess gas sucked through the opening 7 of the gun 6 and that created by the evaporation of the hydrocarbons flows through a pipe 20 mounted on a vent 21 of the tank 1 and passes through the water condenser 17 maintained at a temperature slightly above OC or the gas abandons its humidity. The water 23 is collected at the bottom. From a certain level a valve 24 ensures the emptying.

After drying, the vapors flow towards the separator-absorber 14 as soon as a slight overpressure allows the opening of the valve 31.

In the separator-absorber 14, in contact with the cold liquid which arrives via the line 10, the gaseous hydrocarbons dissolve in the liquid by rising through baffles 22. The fuel in circulation finally drives them towards the tank 1 via the return line 16 to the exchanger 12 to pre-cool the fuel and minimize heat losses, then through the channel 18 to the exchanger 17 where it still produces enough cold to condense the water on the exchanger 17.

The air collects at the top of the separator-exchanger 14 and flows through the vent 28 to the outside, into the atmosphere. Of course, all parts of the system where the temperature is below the ambient are insulated.

To facilitate the absorption of gaseous hydrocarbons in the liquid hydrocarbon solvent, the invention also provides for prior compression of the gases. As illustrated in figure 2 (if they are the same elements, the same reference numbers are used as in figure 1).

For this purpose, a compressor 25 followed by cooling fins 27 is inserted into the pipe 20. The compressor 25 is started as soon as a certain pressure is reached in the tank 1.

A sensor 26 then supplies a signal to a motor of the compressor 25 for starting up in order to inject pressurized gases into the separator-absorber 14. An air discharge valve 29 is controlled by the level of the liquid in the separator-absorber 14.

The entire circuit of the liquid aspirated by the pump 11 is under pressure and a restriction 30 regulates the flow of solvent liquid. In this way, the dissolution and absorption of gaseous hydrocarbons will be effective at even lower temperatures and the efficiency of the inventive system is higher.

Claims (14)

1) A process for the separation of volatile components  of hydrocarbon from a gas mixture sucks up for a  filling a tank of a vehicle and  escaping through a vent in a hydrocarbon tank  liquid characterized in that the gas mixture is  guide to go through liquid hydrocarbon  contained in a separator to absorb  said volatile components by the liquid. 2) Method according to claim 1 characterized in that  the liquid hydrocarbon in the separator comes from the  tank and is cooled. 3) Method according to claim 2, characterized in that  that the liquid hydrocarbon in the separator is cooled  in two steps before entering the separator. 4) Method according to claim 3, characterized in that  that the first cooling step is obtained  letting the liquid hydrocarbon pass through a  first heat exchanger or hydrocarbon  liquid is cooled by the already cold liquid returned  by the separator in the tank. 5) Method according to one of claims 3 or 4  characterized in that the second stage of  cooling is obtained by leaving the hydrocarbon  liquid pass through a second heat exchanger  where the liquid fuel is cooled by a  fridge. 6) Method according to one of claims 2 to 5,  characterized in that the escaping gas mixture  from the tank goes into a condenser where the mixture  gas is cooled by the cold liquid from the separator  in order to separate the water from said gas mixture. 7) Method according to one of the preceding claims,  characterized in that the gas mixture is compressed  in a compressor before entering the  separator. 8) Apparatus for separating volatile components  of hydrocarbon from a gas mixture aspirated during  filling a tank of a vehicle and  escaping through a vent in a hydrocarbon tank  liquid characterized in that the apparatus comprises  a separator which is partially filled  liquid hydrocarbon and in which the mixture  gaseous pass in order to make the said components absorb  volatile by the liquid. 9) Apparatus according to claim 8 characterized in  what it has a heat exchanger where  the liquid hydrocarbon coming from the tank is cooled and  then guided in the separator 10) Apparatus according to claim 9, characterized in  that it is provided with two heat exchangers which  cool the liquid hydrocarbon in two stages  before entering the separator. 11) Apparatus according to claim 10, characterized in  what in the first heat exchanger, the  gas mixture is cooled by the already cold liquid  returned by the separator to the tank. 12) Apparatus according to one of claims 10 or ll  characterized in that in the second heat exchanger  thermies, the gas mixture is cooled by a  fridge. 13) Apparatus according to one of claims 9 to 12,  characterized in that it also includes a  capacitor where the gas mixture is cooled by the  cold liquid from the separator to separate the water  of said gas mixture. 14) Apparatus according to one of claims 8 to 13,  characterized in that it is provided with a compressor in  which the gas mixture is compressed before  enter the separator.