Patent Application
20240353064
The present invention deals with harmful gas leaking at substantially atmospheric pressure from industrial plants, and in particular it relates to a method and to an apparatus to prevent the leaked gas from being released into the atmosphere.
As well known, industrial plants processing chemicals in the gaseous state comprise pipe and equipment connections through which small gas leaks are likely to occur at a substantially atmospheric pressure. In particular, such leaks may take place through sealing elements of moving parts of the equipment used to convey a gas, such as compressors. Other leaks at atmospheric pressure can occur when taking samples of a process fluid for process control purposes. Occasional atmospheric pressure gas leaks at may also occur due to defected sealing of connections between plant equipment, such as piping, vessels and instruments.
In many instances, the processed gas is environmentally harmful and/or and/or flammable or capable of forming explosive mixtures with the air surrounding the leakage point.
As well known, a gas released at substantially atmospheric pressure cannot be admitted as such into a flare for combustion. Therefore, in these cases, in order to restore safety for people and animals, a “safe” area is normally identified, i.e., a place close to the plant, if any, where people and animals do not use to stay, and/or no sources of ignition are present, such as hot surfaces or electrical equipment with no suitable protection for an explosive atmosphere. A device is then provided for collecting and conveying the leaked gas from the leaking points to the safe area, as schematically shown in
However, a safe area is not always easily available. Moreover, with the above systems, the leaked streams are released as such into the atmosphere, which is particularly critical if the leaked gas includes greenhouse chemical such as methane and hydrocarbons in general. The problem is not negligible, as installations handling hydrocarbon gases, such as pipelines, chemical plants, power stations and the like, are widespread.
There is therefore a need for an apparatus and a method to collect gas streams leaking through sealing and connection elements in a gas-treating industrial plant, and released at substantially atmospheric pressure, in particular, hydrocarbon gases, to avoid their emission into the atmosphere.
A vent fluid handling assembly including a vent fuel recovery piping is disclosed, and a method for operating the same, are disclosed, for instance, in US 2019/0323464 A1.
It is therefore an object of the present invention to provide an apparatus and a method for collecting a gas leaked at a substantially atmospheric pressure in a gas-treating industrial plant, in particular hydrocarbon gases, without releasing the collected gas into the atmosphere.
It is also an object of the present invention to provide such an apparatus and a method that enable leaked gas collection without creating an excessive vacuum at the leakage points, in order not to suck too much ambient air along with the gas, and in order not to promote leakage by the vacuum.
It is a particular object of the invention to provide such apparatus and method that allows releasing the leaked gas in a safe area in the case of a failure of the apparatus itself, or of a power supply interruption.
These and other objects are achieved by an apparatus and a method for collecting leaked gas streams at a substantially atmospheric pressure from an industrial plant and conveying the collected gas to a reception body pressurised at a predetermined reception pressure, as defined by claims 1 and 11, respectively. Particularly advantageous embodiments and modifications of the apparatus and of the method are defined in the dependent claims.
According to one aspect of the invention, the apparatus comprises:
According to another aspect of the invention, the method comprises the steps of:
Preferably, the minimum pressure is between −200 and −100 Pa, in particular the minimum pressure is about −150 Pa. The target pressure value is advantageously set between −50 Pa and the minimum pressure.
This way, by accurately controlling the partial vacuum, or negative relative pressure, created by compressor, in particular, in the collector container, the leaked gas can be regularly and selectively removed from the leakage points. More in detail, if such a control unit were not associated with the compressor, an excessive suction and/or vacuum degree would be created at the leakage points. In the former case, an undesirable amount of ambient air would be withdrawn at the collection points along with the leaked gas, which could lead to an explosive mixture and/or make it impossible to recover the gas for any technical use. In the latter case, which may occur if the leakage point is associated to a local collection container, an excessive local vacuum could paradoxically cause further leakage.
The apparatus and the method of the invention can be used, for instance, in such a plant as a compressor station of a pipeline, and the reception body of the collected and compressed leakage gas can be the pipeline itself. More in general, any plant including a compressor can advantageously use the apparatus of the invention, and the reception body can be any vessel, equipment, or pipeline to which compressor sends a compressed gas.
Advantageously, the pressure sensor/transducer is also arranged to detect a current value of the ambient atmospheric pressure and to generate the suction pressure signal as a differential pressure signal related to a difference between the atmospheric pressure and compressor suction pressure.
This way, the suction pressure control accuracy can be further improved, which is an advantage in connection with the above-mentioned desired low absolute values of the suction relative pressure.
Advantageously, the collector container is provided with a safety vent device configured to release the leaked gas, which is present in the collector container, into the atmosphere if the pressure of the collected leaked gas exceeds a predetermined maximum safety threshold value higher than the atmospheric pressure. In particular, the safety vent device can comprise an pressure relief valve, for example a counterbalance valve, arranged along a vent pipe leading to a safe area. In particular, the safety vent device, i.e., a pressure relief valve, is configured to release the collected leaked gas when the pressure of the collected leaked gas exceeds a safety maximum threshold value set between 1 mbar and 10 mbar.
This way, if an equipment failure occurs such as a sudden compressor failure or stop, or if a manoeuvre error is made when actuating a shut-off valve along compressor suction or delivery pipe, the safety level of the prior technology is restored, since the gas is released into the atmosphere in a safe area, which can be accepted in such an exceptional condition.
Preferably, a heat exchanger device is provided along the recirculation duct, the heat exchange device configured to cool the recirculation portion of the leaked gas conveyed to the collector container. This prevents the temperature of the gas collected in the collector container from reaching excessively high values, which would be inappropriate for admission to compressor, due to a hot recirculating gas portion entering the collector container.
A check valve can be arranged along the delivery pipe of compressor in order to prevent any pressurised-gas backflow from the pressurised reception body to the compressor and the collector container via the recirculation duct, if a compressor shutdown occurs, due for instance to a power failure, a compressor fault or an operator's mistake. Advantageously, the delivery pipe comprises a restricted-section pipe portion serially arranged to this check valve, e.g., downstream thereof, in order to limit such a pressurised-gas backflow if, besides a compressor fault, the check valve remains blocked at an open position.
In one embodiment, the apparatus comprises a second compressor arranged in parallel to the above-mentioned compressor, hereinafter referred to as the first compressor, and the pressure controller is configured to start the second compressor or the first compressor in addition to the first compressor or the second compressor, respectively, if the suction pressure becomes higher than a predetermined maximum operating threshold value.
The condition in which only one compressor is running can be restored manually. As an alternative, the pressure controller is configured to stop one between the first compressor and the second compressor if the suction pressure becomes lower than a predetermined switch-off threshold value that is in turn lower than or at most equal to the above maximum operating threshold value.
The invention will be illustrated below with a description of some embodiments and modifications thereof, by way of example and not of limitation, with reference to the accompanying drawings, in which
With reference to
Apparatus 100 comprises a gas-capturing means, not shown, for capturing gas streams 11,12,13 . . . 1n, or is associated with a gas-capturing means existing in the industrial plant, as it is provided in the conventional technique. A gas-capturing means may comprise a chamber encircling a possible leakage points of the plant, such as a vent of a gas sealing system, a stuffing box of a rotating or otherwise movable organs, a sampling sockets, a flange connection, and the like.
Apparatus 100 further comprises a preferably elongated vertical collector container 10 of leaked gas streams 1j, j=1 . . . n, pneumatically connected with the gas-capturing means through collection pipes 2j, j=2 . . . n. This way, streams 1j form a collected leaked gas 1 that is conveyed into collector container 10. The collector container can be a reservoir 10, as shown, and/or a simple manifold. Collector container 10 advantageously comprises a drain nozzle 11 with a drain valve 12 for periodically removing any liquid present in collected leaked gas 1 and accumulated in the bottom of collector container 10.
Apparatus 100 further comprises a compressor 20, preferably a diaphragm compressor, or a compressor of any type from which substantially no gas is likely to leak.
Compressor 20 has a suction mouth 25 pneumatically connected with collector container 10 via a suction pipe 3, and a delivery mouth 26 pneumatically connected with reception body 9 via a delivery pipe 6. Shut-off valves 21,23 can be arranged along suction pipe 3 and delivery pipe 6. These valve are preferably manually operated and are maintained open during normal operation of apparatus 100. Shut-off valves 21,23 can be closed to isolate compressor 20 or apparatus 100 from the rest of the system in case of maintenance or replacement of compressor 20.
Compressor 20 is arranged to compress collected leaked gas 1 up to reception pressure Pr of reception body 9, generally set between a few bars and a few tens of bars. Compressor 20 is also arranged to maintain a suction pressure Ps, in particular the pressure in collector container 10, at a value of about few millibars below atmospheric pressure Patm.
To this purpose, according to the invention, delivery mouth 26 of compressor 20 is also connected with collector container 10 through a recirculation duct 4, and a pressure control unit 40 is provided to control suction pressure Ps of compressor 20, comprising a control valve 41 arranged along recirculation duct 4.
Control unit 40 further comprises a pressure sensor/transducer 47 arranged to detect pressure Ps at the suction to compressor 20 and to generate a suction pressure signal 46. As shown
Control group 40 further comprises a pressure controller 45, preferably an electronic controller, configured to receive pressure signal 46 from pressure sensor/transducer 47, and to generate an open/close signal 43 for an actuator 49 of control valve 41. Actuator 49 is arranged to modify the opening of control valve 41 responsive to pressure signal 46, in order to maintain suction pressure Ps at a target pressure value between atmospheric pressure Patm and a predetermined minimum pressure Pm. In practice, by recirculating a part of the flow of leaked gas 1 back into collection container 10, a balance is established between the flow rate of leaked gas 1 from the leakage points and the flow rate delivered by compressor 20 at reception pressure Pr.
Preferably, the minimum relative pressure Pm is set between −200 Pa and −100 Pa, in particular Pm is about to −150 Pa. The target pressure value, as a gauge pressure, is preferably set between a maximum gauge pressure of e.g., −50 Pa and the minimum gauge pressure Pm.
Advantageously, pressure sensor/transducer 47 is a differential pressure transducer arranged between a location upstream of compressor 20 and the atmosphere, for example between collection container 10 and the atmosphere, and is configured to measure both positive relative pressures and negative relative pressures, generally in a measuring range of −20 mbar÷+20 mbar (−2 kPa÷+2 kPa). In other words, pressure sensor/transducer 47 is arranged to detect a current value of atmospheric pressure Patm in addition to suction pressure Ps of compressor 20, and is configured to generate suction pressure signal 46 as a differential pressure signal related to a difference between atmospheric pressure Patm and suction pressure Ps of compressor 20.
Besides controlling suction pressure Ps of compressor 20, recirculation duct 4 serves to make the compressor start-up easier.
With reference to
In an apparatus 101 according to one embodiment of the invention, a check valve 22 is preferably arranged along delivery pipe 6 of compressor 20 in order to prevent pressurised-gas backflow from pressurised reception body 9 towards compressor 20 and collector container 10 via recirculation duct 4 if a shutdown of compressor 20 occurs, typically a shutdown due to a sudden compressor failure or to a sudden power supply interruption. Moreover, a restricted-section pipe portion 29, such as a calibrated orifice, can advantageously be serially arranged to check valve 22 along delivery pipe 6, preferably downstream of check valve 22, in order to limit the pressurised gas flow from pressurised reception body 9 towards compressor 20 and towards collector container 10 if check valve 22 does not close or does not close completely in case of a sudden stop of compressor 20.
In an apparatus 102 according to another embodiment, collector container 10 is provided with a safety vent device 5,50 for releasing collected leaked gas 1 from collector container 10 into the atmosphere in a safe zone 7, only if pressure Ps of collected leaked gas 1 exceeds a predetermined safety maximum threshold value PMs higher than atmospheric pressure Patm, due to any breakdown or failure of apparatus 102. In particular, as shown in
Moreover, in an improved modification of apparatus 102, the safety vent device comprises a bypass pipe 5′ connected between upstream and downstream of pressure relief valve 50, and first and second shut-off valves 51,52 arranged along vent pipe 5 and bypass pipe 5′, respectively. First and second shut-off valves 51,52 are operated as a normally closed valve and a normally open valve, respectively, during normal operation of apparatus 102. This valve arrangement is useful to allow maintenance of pressure relief valve 50 while continuing to remove gas 1j from the plant and releasing it into safe area 7 also during the short time required by the maintenance.
In a further embodiment, an apparatus 103 comprises a safety valve 24 having an inlet port pneumatically connected with delivery mouth 26 of compressor 20.
In a modification of this apparatus 103, further including the above-described safety vent device 5,50 of apparatus 102, a discharge port of safety valve 24 is pneumatically connected with vent pipe 5, downstream of overpressure valve 50.
In an apparatus 104 according to a further embodiment, a heat exchange device 42 is provided along recirculation duct 4, preferably downstream of control valve 41. Heat exchange device 42 is configured to cool the gas recirculating back to collection container 10, so that leaked gas 1 in collection container 10 does not attain a temperature too high for admission to compressor 20.
In an apparatus 105 according to a further embodiment, control valve 41 is associated with a positioning device 48 including a position sensor configured to detect the position of a plug member of control valve 41 and to generate a position signal 49′ for modifying the position of the plug member and the opening degree of control valve 41. Pressure controller 45 is configured to receive position signal 49′ in addition to suction pressure signal 46, and to modify open/close signal 43 based on position signal 49′.
With reference to
Similarly to apparatus 100 shown in
With reference to
In an apparatus 201 according to one embodiment of the invention, a check valve 52 is preferably arranged along common delivery pipe 6 of compressors 20 and 30 in order to prevent pressurised-gas backflow from pressurised reception body 9 towards compressor 20 and collector container 10 via recirculation duct 4 if a shutdown of compressor 20 or 30 occurs, typically a shutdown due to a sudden compressor failure or to a sudden power supply interruption. A similar flow-limiting function can have check valves 22,32 arranged on respective Moreover, a restricted-section pipe portion 29, such as a calibrated orifice, can advantageously be serially arranged to check valve 52 along common delivery pipe 6, preferably downstream of check valve 52, in order to limit the pressurised gas flow from pressurised reception body 9 towards compressor 20 and collector container 10 if check valve 52 does not close or does not close completely in case of a sudden stop of compressor 20 or 30.
An apparatus 202 according to another embodiment comprises a safety vent device 5,50 for releasing collected leaked gas 1 from collector container 10 into the atmosphere, if the pressure of collected leaked gas 1 exceeds a predetermined safety maximum threshold value PMs higher than atmospheric pressure Patm, as in apparatus 102 of
An apparatus 203 according to a further embodiment comprises two safety valves 24,34 to prevent exceeding the maximum operating pressure of compressors 20,30, each safety valve 24,34 having its inlet port pneumatically connected with delivery mouths 26,36 of compressors 20 and 30 respectively, and with its outlet port pneumatically connected with emergency vent pipe 5, if present.
An apparatus 204 according to a still further embodiment comprises a heat exchange device configured to cool the gas recirculating to collector container 10, such as the apparatus 104 of
In an apparatus 205 according to a still further embodiment, a control valve 41 comprises a positioning device 48, as in apparatus 105 in
The above description of embodiments and modifications of the invention is capable of showing the invention from a conceptual point of view in such a way that others, using the known technique, will be able to modify and/or adapt in various applications such specific embodiments without further research and without departing from the inventive concept, and, therefore, it is understood that such adaptations and modifications will be considered as equivalents of the modifications and specific embodiments. The means and materials for realising the various functions described may be of various kinds without departing from the scope of the invention. It is understood that the expressions or terminology used are purely descriptive and, therefore, not limitative.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021000030173 | Nov 2021 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/061452 | 11/27/2022 | WO |
