GB2277131A

GB2277131A - Device for use with petroleum products storage tanks

Info

Publication number: GB2277131A
Application number: GB9407175A
Authority: GB
Inventors: De Las Heras Gonzola Lopez
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-04-12
Filing date: 1994-04-12
Publication date: 1994-10-19
Also published as: ES2062953A2; GB9407175D0; ES2062953R; ES2062953B1; FR2703982A1

Abstract

Losses by evaporation from all types of tanks for storing petroleum products are prevented and a means for discharging said products is provided by a device consisting of a compressor 1 equipped with regulating means for introducing air at specific pressure into the tank above the level of the interior liquid and maintaining said pressure at a value greater than the vapour tension of the liquid in order to prevent the evaporation thereof. Calibrated valves 5 permit the exit of air when the pressure is greater than that required and they close when it is less, the internal pressure thereby being always constant and sufficient for the discharge of the tank without the use of auxiliary pumps of any type. <IMAGE>

Description

DEVICE FOR USE WITH PETROLEUM PRODUCTS STORAGE TANKS FIELD OF APPLICATION OF THE INVENTION The novel device for preventing losses by evaporation in all types of tanks for storing petroleum products and for dispensing with pumps for discharging said products, to which this invention refers, applies to the entire petroleum industry, equally in factories, refineries and in service stations, and even in oil tankers in which use is made of tanks of greater or lesser capacity for the storage of such products, with the aim of completely eliminating the serious drawback which currently exists of losses by evaporation, which are of considerable size in some cases, leading to a loss, for this reason, of up to 10 % of the liquid stored, and with the possibility of dispensing with motorized pump units for the loading of tanker lorries, trucks, vessels, etc.

STATE OF THE ART There is currently no device specially designed to prevent the evaporation of petroleum products stored in tanks of large or average capacity. Attempts have been made, by means of the special domed shape of the covers of said tanks, only to collect said vapours and subsequently condense them, in order to recover, at least in part, some of the evaporated product, but these attempts have not achieved an effect which is sufficiently satisfactory to be able to be considered as genuinely useful, and this is, in addition, a very costly system which is practically impossible for large-capacity tanks in which, owing to their dimensions, there would be a requirement for structures of great complexity and cost.

DESCRIPTION OF THE INVENTION The novel device in question for preventing losses by evaporation in all types of tanks for storing petroleum products and for dispensing with pumps for discharging said products, is based essentially on the introduction into the tank, which is totally sealed in order to prevent leaks, above the existing liquid level, of a certain quantity of dry, filtered, low-temperature pressurized air, this pressure being such that it is slightly greater than the vapour tension of the liquid, whereby evaporation is halted owing to the existence, above the liquid surface, of a pressure greater than that of the vapour of the liquid, this air pressure being maintained by means of a series of calibrated valves located in the top part of the tank and which permit the exit of the air when its pressure is greater than that mentioned, and a compressor system equipped with a pressure-sensitive device which prevents the pressure exceeding a suitable value above the surface of the tank and which introduces air as the pressure owing to discharge of the tank, decreases thereby obtaining, at all times, a stable and fixed pressure which completely eliminates evaporation of the liquid contained in the tank.

This being the basis of the device, its embodiment is simple in that it is unnecessary to do more than fit an inlet pipe above the maximum liquid level in the tank, which pipe communicates with a compressor equipped with the means for regulating, stopping and starting which are generally used in this type of element, for there always to be maintained, inside the tank, a pressure generally calculated at being approximately 1.5 kg.cm2 whenever the vapour tension of the petroleum products is between 1.2 and 0.8 kg.cm2 depending on the temperatures and atmospheric pressure corresponding to the installation site.

One or more calibrated valves are coupled to the cover of the tank and, in a normal manner, maintain adequate internal pressure, opening when said pressure increases or closing when it decreases, as a function of the level reached inside the tank.

In the event of underground tanks of the type used in service stations, this inlet tube can be coupled at the manhole which all such tanks have, the charging orifice having a relief valve so that, once the compressor has been stopped, the orifice can open for charging or measurement of the tank with no risk of the internal pressure being able to displace the charging valve in a violent manner. Similarly, in service stations, provision is made for the use of a calibrated valve at the outlet of the relief or ventilation pipe existing in all of them, so that, inside the tank, the pressure necessary for eliminating evaporation of the product stored in the tank is kept stable and does not alter.

A detailed description of the novel device which is mentioned will be given below with reference to the drawing which accompanies it, which represents a preferred embodiment capable of any variations in detail which do not constitute a fundamental alteration of the essential characteristics of the device.

Said drawing illustrates: In Figure 1: diagram showing installation in a storage tank for large installations.

In Figure 2: diagram showing installation in an underground storage tank corresponding to a service station.

According to the embodiment shown, the novel device for preventing losses by evaporation in all types of tanks for storing petroleum products and for dispensing with pumps for discharging said products, which is proposed, consists of the installation of a compressor with a pressure-sensitive device (1) calibrated to the appropriate pressure and coupled to a pipe (2) of material and diameter suitable for each case, as a function of the capacity of the storage tank or tank (3) in question, which pipe has its end inside the tank above the level (4) of the liquid contained.

On the upper face of the tank, provision is made for the installation of calibrated valves (5) which open when the internal pressure is above that which is required and which close when it is below said pressure, unlike the regulating system of the compressor (1) which starts up whenever the internal pressure is below that which is required,, or shuts down if it is higher.

Similarly, the valves will have a relief system for depressurizing the tank if it is to be measured.

In the case of an underground storage tank, as used in service stations, the compressor (1) and pipe (2) are installed in such a manner that the entry is via the manhole (6) laterally with respect to the charging valve (7), on which provision is made for the installation of a second relief valve (8) which opens after the compressor has stopped, and, before proceeding to open, halts the charging or useful measurement of the storage tank (3).

The discharge pipes (9), for places for charging tankers, in the case of a factory, or to the supply nozzles (10), in the case of a service station, emerge from the storage tank or tank (3) in question, provision being made, in the case of service stations, for the pipe (11) which goes to the relief outlet or breather (12) which is equipped at its outlet with a calibrated valve (13) which prevents the exit of the air when the internal pressure is that which is required for operation of the device, or which opens if said pressure is above that which is required.

Organized in this manner, the novel device which is mentioned, with the compressor, proceeds to introduce air into the storage tank (3) above the surface (4) of the existing liquid until a pressure is achieved which is slightly greater than the vapour tension of the petroleum product in question, thereby preventing evaporation thereof.

This pressure is always kept constant by the effect of the aforementioned calibrated valves (5 and 13), whilst, inside the storage tank, there is always sufficient pressure for discharge of the tanks to take place, either via the tanker-charging pipe or via the supply nozzles of the service station, without the need for pumps of any type, since, even when the liquid level is descending, the compressor continues to maintain the required high pressure, and the exit of the liquid will always be constant and regular.

In this manner, not only is evaporation of the petroleum product in question eliminated, but also discharge pumps are dispensed with, with the resulting economic advantage that this involves.

It should be noted that the compressors must be equipped with a device permitting the introduction of pressurized cold air, with an integral thermostat, for ensuring that the maximum temperature of the air introduced at pressure is approximately 100C, since this temperature for the pressurized air is the most suitable for eliminating possible evaporation, since the vapour tension at this temperature is minimal and easier to eliminate by means of the pressure of the air introduced.

When commencing the operation in a recently filled tank, this cold air is introduced initially keeping the ventilation valves open, in order to entrain the gases existing to the outside and, once it has been verified that no type of gas is exiting, these valves are then closed in order to obtain the established internal pressure.

It is obvious that, in all cases, whether dealing with fixed or underground tanks or with vessels, it is necessary for these to be completely and absolutely sealed at all points where there might be an exit of pressurized air, since the opposite case would involve a loss and virtual continuous operation of the compressors.

The location of the calibrated valves on fixed tanks may be variable and they may even be provided on the measurement covers in order to depressurize the tank and permit measurement if this is to be performed manually, even though, currently, owing to the use of electronic means for measurement, installation at such points would not be necessary.

In the tanks mentioned, which may also be those for petroleum-carrier vessels, the calibrated valves could be installed on the measurement covers or in proximity thereto, since this would not vary the essential nature of the invention, as could the necessary compressors with their corresponding thermostats and pressure-sensitive devices.

Another major advantage of this device consists in that, if there is a leak of liquid owing to perforation of the tank, a porosity existing therein, etc., this will immediately be detected since, if the compressor has to operate constantly, even when no tank discharge operation is taking place, this is a signal that there is a leak of liquid at some point because, in order to maintain constant pressure, the compressor has to operate continuously and it is thereby easy to detect leaks, which are always dangerous and polluting owing to the nature of the petroleum products for which the device mentioned is intended.

The form, materials and dimensions may vary together with, generally, all accessory and secondary aspects, provided this does not alter, change or modify the essential nature of the novel device which has been described.

Claims

1. Novel device for preventing losses by evaporation in all types of tanks for storing petroleum products and for dispensing with pumps for discharging said products, characterized by the provision of a regulated compressor system, fitted by means of a pipe of diameter and strength suitable for each case, to the inside of the tank in question, with entry above the level of the liquid contained, introducing air at sufficient pressure so that it is greater than the vapour tension of the product contained, thereby preventing the evaporation of the product in question.

2. Novel device for preventing losses by evaporation in all types of tanks for storing petroleum products and dispensing with pumps for discharging said products according to Claim 1, characterized in that, in order to maintain the necessary internal pressure to eliminate evaporation, provision is made for a number of calibrated valves which open, when the pressure increases above the required value, and which close when it descends, the compressor coming into operation and reestablishing the required pressure in each case.

3. Novel device for preventing losses by evaporation in all types of tanks for storing petroleum products and for dispensing with pumps for discharging said products according to Claim 1 or Claim 2, characterized in that, in the underground tanks of service stations, the entry of pressurized air is provided via the manhole and in that a relief valve is located on the discharge valve in order to eliminate the internal pressure before opening the valve in order to charge the tank.

4. Novel device for preventing losses by evaporation in all types of tanks for storing petroleum products and for dispensing with pumps for discharging said products according to any of the preceding claims characterized in that the internal pressure in the tank in question dispenses with the use of pumps for discharging said tank, the exit being produced due to the said pressure, which is always constant.

5. A novel device for preventing losses by evaporation in all types of tanks for storing petroleum products and for dispensing with pumps for discharging said products, the device being substantially as herein described and illustrated in the accompanying drawings.