FR2789762A1 - Leakage detection system, e.g. for hydrocarbons from storage facilities, comprises barrier containing emitter and receiver to measure rate of absorption of electromagnetic radiation - Google Patents

Abstract

A detection system is installed to supply to the user information indicating the concentration of the substance in several ranges of concentration, from very low to high concentrations. The detection system is a barrier containing an emitter and a receiver to measure the substance's rate of absorption of electromagnetic radiation, preferably in the infrared. Surveillance and detection of substances, in particular hydrocarbon or other issues escaping from containers or tanks mounted on transport devices or fixed, in an enclosure or in free air, comprises the use of a detection system having high and low thresholds in each range, each threshold triggering a particular action and controlled by taking into account a unit of length. The low concentration range uses ppm per meter and the high concentration range uses Low explosion threshold (LIE) x meters and/or % LIE. The set-up and installation of the system are simplified, principally by indicating the correct relative alignment between the emission cell and the reception cell. At least one element in the detection system has an indicator of the concentration of the detected substance. The system includes means of automatically controlling defaults which can affect the correct functioning of the system.

Description

The present invention relates to a method for monitoring and

  detection of gases, in particular from hydrocarbons or others, escaping from confinement modules or tanks mounted on a means of locomotion or fixed, being in a confined enclosure

or in the open air.

  It aims more particularly to allow the detection of liquefied petroleum gas (LPG) or natural gas for vehicle (CNG) which are liable to escape at any point from the storage installation or from the tank located on a vehicle, Of type

especially city buses.

  Indeed, the use of gaseous fuels is increasingly encouraged by the public authorities as

  fuel for city vehicles.

  We know that these fuels, which are free from sulfur components unlike traditional fossil fuels, offer almost stoichiometric combustion with oxidant such as air, which generates non-polluting atmospheric emissions (dioxide of

carbon, and water).

  In addition, this type of fuel, which is in fact a mixture of butane, propane, as well as some traces of other organic hydrocarbons (propene, butene,

  ethane, ....), is neither toxic nor corrosive.

  On the other hand, its main danger is linked to its flammability of between 2 and 9% by volume in the air. Loss of gas containment G.P. L. or G.N.V. in suspension can therefore lead to an explosion, either of a gas cloud in the event of a leak, or of a storage tank in the event of external aggressions, linked to natural phenomena (climatic conditions, lightning, flood, earthquake ... ) or to human activity (interventions on one of the links in the gas distribution), this explosion being explained by the conjunction of two independent causes:

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  - an air / hydrocarbon mixture between the lower explosion limit (L.I.E.) and the upper explosion limit (L.S.E.); a calorific contribution in the form of heat or spark at a temperature greater than or equal to the flash point. In addition, the vapor density of G.P.L. (1.8) as well as their low temperature, following the evaporation of the G.P.L., risks creating a phenomenon of accumulation at

  ground level, under the influence of gravity effects.

  This accumulation increases the risk of explosion in the event of containment because the potential ignition points

are located at ground level.

  If G.N.V. is used as a gaseous fuel, the risks are quite similar to those associated with the use of G.P.L. except that the accumulation zones are rather located in height due to the density of the

  G.N.V. which is lower than that of air.

  The present invention therefore aims to provide a process which makes it possible to take into account the risks introduced by the use and conditioning of a gaseous fuel such as in particular G.P.L. or G.N.V., for a fleet of vehicles whose operation is likely to create a leak and a loss of containment which may

lead to an explosion.

  To this end, the process for monitoring and detecting substances, in particular from hydrocarbons or others, escaping from confinement modules or reservoirs mounted on a means of locomotion or fixed, being in a confined enclosure or at l open air, is characterized in that it consists in providing, in the environment of storage areas, maintenance areas or more generally in any operating area which is likely to contain molecules of the substance, a system of detection of the substance capable of providing the user with information relating to the concentration of said substance, according to several concentration ranges, on the one hand in the

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  domain of very low concentrations, and on the other hand

  in the area of high concentrations.

  Other features and advantages of this

  invention will emerge from the description given below.

  According to a preferred embodiment of an installation for implementing the process which is the subject of the invention, it consists: - in taking into account during its construction, design and prevention options for the storage of LPG , making it possible to avoid the risks of explosion and loss of containment on the tanks, - to grasp the dangers presented by the packaging of LPG linked to a loss of product containment, by taking preventive and safety measures linked to the exploitation of this type of gas, in particular by installing gas detection and ventilation systems during product transfer, - to make special provisions to minimize the risk of gas accumulation and failure of gas storage enclosures during maintenance and storage of vehicles powered by this type of fuel. In this context linked to the introduction of a potentially explosive gas inside premises, installations are carried out which essentially consist in providing in the environment storage zones, maintenance zones or more generally in any zone of which is likely to contain LPG gas molecules in suspension, a system of

gas detection.

  According to a characteristic of the invention, this system for detecting a substance and in particular a gas is based on the principle of absorption of electromagnetic radiation whose wave range is located

  especially in the infrared domain.

  In fact, the C-H chemical bonds characteristic of hydrocarbons have the property of absorbing electromagnetic radiation located in the infrared and

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  which on the other hand are insensitive to the dust rejected by

  exhaust gases (CO, C02, NOx, heavy metals ...).

  These detection systems are produced in the form of barriers, each of them comprising a transmitter and a receiver. The transmission and reception device forming the barrier is provided with means, of the electronic type in particular, which make it possible to simplify the initialization and installation of said device, consisting mainly of indicating the correct position of relative alignment between the cell d and the reception cell. In addition, at least one of the elements of the barrier includes an indicator of the concentration of the detected gas. These means also allow self-checking of faults which may affect the correct functioning of the barrier (fouling of the optics, interruption of the beam with triggering of timed alarms, etc.). These barriers are arranged so as to cover the extent of the surface to be detected and in the case of a

  detection of G.P.L., these are placed close to the ground.

  In an application for detecting a gas with a density lower than air, these barriers will be positioned at a

greater height.

  In addition, provision is also made to have in confinement zones that are not easily accessible to general ventilation, or that cannot be covered by a technology using the barriers, a plurality of point detectors that can also work according to the

  infrared absorption technology.

  Furthermore, it is expected that this gas detection system, either with barriers or with point detectors, can work according to several concentration ranges: very low concentrations (range of p.p.m. x meter) as in the field of high concentrations (range of

L.I.E. x meter and% of L.I.E.).

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  Each of the ranges (ppm x meter, LEL x meter and% of LEL) can also be subdivided into several scales comprising high thresholds and low thresholds, each triggering a particular action, each threshold being adjusted taking into account a length unit. Thus, the output of the sensors forming the barriers or the point detectors provides a

  information which is expressed in p.p.m. x meter or in L.I.E.

x meter or as a% of L.I.E.

  Thus, by way of example, a first threshold set very low makes it possible to inform the manager in order to trigger investigations and the first necessary actions. We can give in particular as a nonlimiting adjustment threshold, 250 p.p.m. for a length of 2 meters (500 p.p. m. X meter), or 50 p.p.m. for a length of 10 meters (500

p.p.m. x meter).

  A second threshold, higher than the previous one, triggers for example a visual alarm, an opening of doors or hatches to the outside, or even the forced ventilation of the enclosure, likewise this threshold value can possibly be set to 100 ppm for a

  length of 20 meters (2000 p.p.m. x meter).

  Of course, it goes without saying that these two thresholds, in the range of p.p.m. x meter, are adjustable according to the

  applications targeted by the process which is the subject of the invention.

  These thresholds, for the% L.I.E. of the point detector, can correspond for a setting threshold of in particular 15%, for example to an audible alarm, an evacuation of the personnel, a general power cut, it being understood that the supply of the forced ventilation takes place upstream of the cut

general current.

  Another adjustment threshold expressed in% of L.I.E. is still available and may correspond, for example, to the establishment of evacuation plans for the surrounding population, information from the competent administrative authorities.

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  The barrier detection system and fixed point detectors can usefully be supplemented by a mobile detection system. This detects small quantities

  gas, especially from 0.1 p.p.m.

  Whatever the type of gas detection system (barrier technology and / or point detectors), all of these sensors are connected to a PLC or a computer system comprising one or more display units responsible for report information on screens and generate alarm histories, so that the user is informed of events and can make the necessary decisions and initiate useful actions. These PLCs also ensure the triggering of alarms as well as the actions to secure the

the installation.

  The invention as described above offers multiple advantages because it allows both point detection of gas and peripheral detection, which ensures greater coverage of the enclosure, precisely when the point detectors are too far apart. These enclosures can be constituted in particular by a bus maintenance center, a factory or a workshop for the manufacture and / or assembly of buses, trucks, cars or any other machine (forklift) running on gas, a factory or a workshop for transforming this type of vehicle, air or covered parking, public or private, any factory or industry whose fleet of vehicles is fueled by gas, a tunnel

  receiving traffic from this type of vehicle.

  Finally, the detection and monitoring process is not only applied to G.P.L. gas. or G.N.V., but also it makes it possible to monitor the presence of poisons in catalysts, splashes of water, temperatures

extremes.

  Obviously, the present invention is not limited to the embodiments described and

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  shown above, but that it encompasses all variants.

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Claims (6)

  1 - Process for monitoring and detecting substances, in particular from hydrocarbons or others, escaping from confinement modules or tanks mounted on a means of locomotion or fixed, being in a confined enclosure or in the open air , characterized in that it consists in providing, in the environment of the storage areas, maintenance areas or more generally in any operating area which is likely to contain molecules of the substance, a system for detecting a substance capable of providing the user with information relating to the concentration of said substance, according to several concentration ranges, on the one hand in the field of very low concentrations, and   on the other hand in the area of high concentrations.   2 - Monitoring method according to claim 1, characterized in that the detection system is positioned so that it can cover the extent of the surface to be monitored, in a perimeter and point configuration. 3 - Monitoring method according to one of the   Claims 1 or 2, characterized in that the system for   detection provides information relating to the concentration of the substance detected in each of the ranges and according to several scales comprising high and low thresholds, these thresholds each triggering a particular action, each of the thresholds being further adjusted by   taking into account a unit of length.   4 - Installation for the implementation of the process   according to any one of claims 1 to 3,   characterized in that the detection system is a barrier comprising at least one transmitter and one receiver, placed in the surface area to be monitored, this detection system providing a measurement as a function of the rate of absorption by the substance of a electromagnetic radiation. 9 2789762   - Installation according to claim 4, characterized in that the wave range of the electromagnetic radiation is located in the infrared range. 6 - Installation according to any one of   Claims 4 or 5, characterized in that the system of   detection uses low concentrations as a range p.p.m. per meter.   7 - Installation according to any one of   Claims 4 or 5, characterized in that the system of   detection uses high concentrations as a range the L.I.E. x meter and / or% L.I.E ..   8 - Installation according to any one of   Claims 4 to 6, characterized in that the system for   detection is provided with means making it possible to simplify the initialization and installation of said system, consisting mainly in indicating the correct position of relative alignment between the emission cell and the reception cell.   9 - Installation according to any one of   Claims 4 to 8, characterized in that at least one   elements of the detection system includes an indicator   concentration of the detected substance.   - Installation according to any one of   Claims 4 to 9, characterized in that the system of   detection includes means for performing self-checking of faults that may affect operation correct of said system.