A method and an apparatus for recovering a leaking gas from an industrial plant

Abstract

In an apparatus (11) for conveying a leaking gas (1) leaking from an industrial plant (8) into a receiving body (9) pressurized to a predetermined receiving pressure (Pr), a first compression stage (100), a second compression stage (200) are provided, as well as a transit container (150) pneumatically connected downstream of the first compression stage (100) and upstream of the second compression stage (200). The first compression stage (100) comprises a gas collecting means (C) for collecting the leaking gas (1), a collection container (10) pneumatically connected thereto and configured to form a collected leaking gas (1a) therein, a first-stage compressor (20) having a suction side connected to the collection container (10) and a delivery side connected to the transit container (150) and arranged to compress the collected leaking gas (1a) to an intermediate pressure (P), resulting in a compressed leaking gas (1b) in the transit container (150); a first control unit (40), configured to maintain the suction pressure (Ps) of the first-stage compressor (20) at a target value between the atmospheric pressure (Patm) and a predetermined minimum pressure (Pm). The second compression stage (200) comprises an inlet duct (59) from the transit container (150); an outlet duct (69) pneumatically connected to the receiving body (9); a second-stage compression chamber (68) arranged between the inlet duct (59) and the outlet duct (69); a compression piston (67) configured to compress the second-stage compression chamber (68) so as to convey a further-compressed leaking gas (1c) into the outlet duct (69); an actuation group (70) of the compression piston (67). The actuation group (70) includes a pressure sensor (71a) arranged to measure the pressure (P) of the compressed leaking gas (1b) that is present in the transit container (150) and to output a pressure signal (73) related to the measured pressure (P), and is configured to actuate the compression piston (67) based on the pressure value (P) of the gas present in the transit container (150).

Description

A METHOD AND AN APPARATUSFOR RECOVERING A LEAKING GAS FROM AN INDUSTRIAL PLANTDESCRIPTIONScope of the Invention

[0001] The present invention relates to an apparatus andmethod for preventing vent gas to be released into atmosphere by an industrial plant.

[0002] Moreover, the invention relates to an apparatus for actuating such a method, in particular for the so-called "oil & gas" sector.Prior art - Technical problem

[0003] As is well known, in gas-processing plant, connections are present through which some gas almost unavoidably is lost, released at a substantially atmospheric pressure. In particular, those gas losses can consist of gas leaking through sealing systems of machines whose moving members are moved by external motors, which is the case of most compressors. Further systematic atmospheric pressure gas losses consist of used gas samples from in-line analysers. More or less occasional atmospheric pressure gas losses can take place through defective sealing elements of joints between plant components such as piping, equipment and instruments.

[0004] Among the gases released by atmospheric pressure leakage, particularly critical are those involving risks for health and / or flammable gases and / or gases capable of forming explosive mixtures with the air surrounding the leakage area are. In this case, safety is restored by identifying a so-called 'safe' area, i.e. one that is normally not frequented by people or animals and is free of sources of ignition such as overheated surfaces or inadequately protected electrical devices, and by providing a device for collecting and conveying the gas losses to the safe zone.

[0005] However, in this way, leaking gases are emitted as such into the atmosphere. As is well known, since these gases are released from the plant at an essentially atmospheric pressure, they cannot be admitted as such into a flare for combustion. Moreover, greenhouse gas emissions issues are involvedfor a large variety of hydrocarbons gases, in particular for methane, with the well-known harmful global consequences. The problem cannot be neglected, as installations handling hydrocarbon gases are widespread, e.g. pipelines, chemical plants and power plants.

[0006] W02023095079A1 describes an apparatus and a method for collecting gas streams, in particular hydrocarbon gas streams, leaking through sealing systems of industrial plants and released at essentially atmospheric pressure, in order to prevent the gases to be released into atmosphere. The collected gas is compressed to such a low pressure that it can be collected and stored, but cannot be directly fed back into systems operating at a higher pressure.Summary of the invention

[0007] It is therefore an object of the present invention to provide an apparatus and a method for collecting a gas leaking at a substantially atmospheric pressure from an industrial plant, which prevent said gas, or combustion products thereof, from emitted into atmosphere, and which allow to convey the lost gas to a pressurized receiving body.

[0008] It is also an object of the present invention to provide an apparatus and a method for evacuating a gas from a section of a plant, such as a gas pipeline, which makes it possible to collect and re-use the evacuated gas.

[0009] The above and further object are achieved by an apparatus and a method as described in claims 1 and 15, respectively. Particular modifications and advantageous embodiments of the method and the apparatus are defined in the respective dependent claims.

[0010] In a first aspect of the invention, there is provided an apparatus for conveying at least one stream of a leaking gas leaking from an industrial plant to a receiving body, said at least one stream of said leaking gas released at a substantially atmospheric pressure, said receiving body pressurized to a predetermined receiving pressure, wherein the apparatus comprises a first compression stage, a transit container and a second compression stage, wherein the transit container is pneumatically connected downstream of the first compression stage and upstream of the second compression stage,wherein the first compression stage comprises: a gas-collecting means for collecting the at least one leaking gas stream; a collection container of the stream of the leaking gas pneumatically connected to the gas-collecting means and configured in such a way that the at least one stream of said leaking gas forms a collected leaking gas in the collection container; a first-stage compressor having a suction port pneumatically connected to the collection container; wherein the first-stage compressor has a delivery port pneumatically connected with the transit container, through a delivery pipe of the first compression stage, wherein the first-stage compressor is arranged to compress the collected leaking gas to an intermediate pressure, resulting in a compressed leaking gas collecting in the transit container; a first control unit of a suction pressure of the first-stage compressor, said first control unit comprising: a pressure sensor / transducer configured to detect the suction pressure of the first-stage compressor and to generate a suction pressure signal; a regulation member configured to modify the suction pressure of the first-stage compressor; a pressure regulator configured to receive the pressure signal and to generate a regulation signal to operate the regulation member based on the pressure signal, so as to maintain said suction pressure at a target pressure value between the atmospheric pressure and a predetermined minimum pressure, wherein the second compression stage comprises an inlet duct coming from the transit container an outlet duct pneumatically connected to the pressurized receiving body; a second-stage compression chamber arranged between the inlet duct and the outlet duct; a compression piston of the second-stage compression chamber configured to compress the second-stage compression chamber so as to send a further-compressed leaking gas into the outlet duct;an actuation group of the compression piston, wherein said actuation group includes a pressure sensor arranged to measure the intermediate pressure of the compressed leaking gas that is present in the transit container by generating a pressure signal related to the measured intermediate pressure, and is configured to actuate the compression piston based on the measured intermediate pressure value of the compressed leaking gas that is present in the transit container.

[0011] In a second aspect of the invention, a method for conveying to a receiving body at least one stream of a leaking gas leaking from an industrial plant, released at a substantially atmospheric pressure, said receiving body pressurized to a predetermined receiving pressure, comprises a first gastreatment step of treating the leaking gas, obtaining a collected leaking gas, a step of temporarily accumulating the collected leaking gas in a transit container obtaining a compressed leaking gas, and a second gas-treatment step of treating said compressed leaking gas, wherein the first gas-treatment step comprises the steps of: capturing the stream of the leaking gas; collection of the stream of the leaking gas into a collection container, forming said collected leaking gas; in a first compressor, a first gas compression step of compressing the collected leaking gas to a predetermined intermediate pressure, thereby obtaining said compressed leaking gas; conveying said compressed leaking gas into the transit container; measuring a suction pressure of said first-stage compressor; regulating said suction pressure to a target pressure value between the atmospheric pressure and a predetermined minimum pressure wherein the second gas-treatment step comprises the steps of: measurement of the intermediate pressure of the compressed leaking gas that is present in the transit container; conveying the compressed leaking gas from the transit container into a compression chamber of a second compressor;second compression of the compressed leaking gas into the compression chamber of the second compressor, thus obtaining a further-compressed leaking gas stream, wherein the second compression step comprises a step of adjusting a compression ratio according to an intermediate pressure measurement of the compressed leaking gas, so that the further-compressed leaking gas stream has a pressure at least equal to the receiving pressure; conveying the further-compressed leaking gas stream into the pressurized receiving body.

[0012] The industrial plant for which the apparatus and the method are used for collecting and treating the leaking gas can be a compressor. ]For example, such compressor is arranged along a pipeline. However, the compressor can be of various types, such as a reciprocating compressor or a rotary-vane compressor, a rotary-lobe compressor, a rotary-screw compressor and so on. In this case, the pressurized receiving body is pneumatically connected to a suction mouth of such a compressor. Therefore, the step of conveying the further-compressed leaking gas stream includes a step of suctioning the further- compressed leaking gas stream by the compressor.

[0013] More in general, the industrial plant using the apparatus and the method of the invention can be, for instance, a natural-gas compression station along a pipeline, and the receiving body of the further-compressed leaking gas can be the pipeline itself. More in general, the user plant can comprise a compressor, and the receiving body can be an apparatus or pipeline to which the compressor sends a compressed gas.

[0014] ]ln particular, the compression piston of the second compression step is connected to a compressed-air-driven motor, for example a double-diaphragm pneumatic motor, provided with a compressed air inlet and with a spent compressed air outlet, and the actuation group further comprises a regulation valve arranged upstream of the compressed air inlet. In such a case, the second compression step comprises steps of admitting and discharging compressed air into / from an actuation chamber of a pneumatic motor, and a step of adjusting the flow rate of compressed air based on the pressure measurement of the compressed leaking gas that is present in the transit container.

[0015] In one embodiment, the pressure sensor is configured to generate a pressure signal selected between a low-pressure signal and a high-pressure signal according to whether the measured intermediate pressure of the compressed leaking gas is equal to or lower than a predefined minimum pressure or is equal to or higher than a predefined maximum pressure, respectively, and the regulation valve is provided with an actuator, in particular a two-position actuator, configured to open or close the regulation valve upon receipt of the low-pressure signal or the high-pressure signal, respectively. From another point of view, the step of measuring the pressure of the gas that is present in the transit container involves, besides detecting the pressure value, also comparing the measured pressure value with at least two minimum and maximum pressure values, respectively, and the step of adjusting the flow rate of the compressed air involves starting and stopping the supply of a predetermined flow rate of compressed air into the actuation chamber, according to whether the measured pressure value becomes equal to or lower than the minimum value, or becomes equal to or higher than the maximum value, respectively.

[0016] In another embodiment, the pressure sensor is configured to generate a continuous pressure signal, and the regulation valve is provided with a modulating actuator arranged to increase or decrease the opening of the regulation valve according to whether the continuous pressure signal increases or decreases with respect to a predetermined target pressure value. From another point of view, the compressed air flow rate regulation step involves increasing or decreasing the compressed air flow rate according to whether the measured pressure value increases or decreases with respect to a predetermined target pressure value.

[0017] Preferably, the compression chamber is provided with a safety valve having a delivery port pneumatically connected to a suction port of the first-stage compressor.

[0018] ]ln a preferred embodiment, the first compression stage further comprises: a recycling pipe pneumatically connecting the delivery port of the first- stage compressor with the collection container, so that a recycling phasecan be carried out of a recycling portion of the leaking gas compressed by the first-stage compressor back into the collection container; wherein the regulation member of the first stage control unit is a regulation valve arranged along the recycling pipe, and the pressure regulator is configured and to generate the regulation signal as an open / close signal to modifying an opening of the regulation valve based on the pressure signal, so as to maintain the suction pressure at a target pressure value between the atmospheric pressure and a predetermined minimum pressure.Thus, under such conditions, the main and recycling portions of the compressed leaking gas that are conveyed to the transit container and back to the collection tank, respectively, are established responsive to the pressure measured at the suction side of the first-stage compressor unit, so as to maintain such suction pressure at a target pressure value set between the atmospheric pressure and a predetermined minimum pressure Pm.

[0019] In another embodiment, the first-stage compressor is a rotary compressor; the regulation member of the first stage is an inverter arranged to modify the rotation speed of the rotary compressor.

[0020] By controlling the negative pressure created by the first-stage compressor, in particular, in the collection container, it becomes possible to remove regularly and selectively the leaking gas at the various leakage points. An excessive negative pressure, which would occur without any pressure control unit associated to the compressor, i.e., without recycling an appropriate portion of the compressed gas back to the collection container, would in fact lead to an unwanted air suction at the collection means. Moreover, if a leakage point is enclosed in a leaking gas collection chamber, an excessive vacuum could even increase the extent of the leakage.

[0021] Advantageously, the pressure sensor / transducer is further arranged to detect a current value of the atmospheric pressure and to generate the suction pressure signal. In particular, said suction pressure signal is a differential pressure signal related to a difference between the atmospheric pressure and the compressor suction pressure.

[0022] The above allows an accurate control of the suction pressure, in view of the desired low absolute values of the negative pressure.

[0023] ]Advantageously, the collection container is provided with an emergency vent device, configured to release the leaking gas collected in the collection container into the atmosphere when the pressure of the collected leaking gas exceeds a predetermined maximum safety threshold value higher than the atmospheric pressure. ]ln particular, the emergency vent device comprises a pressure-relief valve, for example a counterbalance pressure-relief valve, arranged along a vent pipe having an outlet port in a safe zone. In particular, the emergency vent device, i.e. the pressure-relief valve, is configured to release the collected leaking gas when the pressure of the collected leaking gas exceeds a maximum safety threshold value between 1 mbar and 10 mbar.

[0024] In this way, in case of fault of the apparatus, for example, if the compressor suddenly stops, or if a shut-off valve along the compressor suction or delivery pipe is incorrectly operated, a safety level as in the prior art is restored, by releasing the collected leaking gas into atmosphere in a safe zone.

[0025] Preferably, a heat exchange device is provided along the recycling pipe, said heat exchange device configured to cool the recycling portion of the leaking gas conveyed back into the collection container. This prevents an excessive increase of the temperature of the gas collected in the collection container due to the gas recycled back into the collection container, a condition that would be unsuitable for admission to the compressor,

[0026] A non-return valve can be arranged along the delivery pipe of the first compression stage in order to prevent the pressurized from flowing back from the transit container to the first-stage compressor and to the collection container, via the recycling pipe, if the compressor shuts down, which could be due, for instance, to power failure, machine failure, or maneuver error. Advantageously, the cross-sectional area of the delivery pipe progressively decreases downstream of the non-return valve, in order to limit such a pressurized gas backflow if, the first-stage compressor shuts time and, at the same time, the nonreturn valve is blocked in an open condition.

[0027] In one embodiment, the first compression stage of the apparatus comprises a second first-stage compressor parallelly arranged to the above- mentioned first-stage compressor, hereinafter referred to as the first first-stage compressor. In this case, the pressure regulator can be configured to start thesecond first-stage compressor or the first first-stage compressor in addition to the first first-stage compressor or the second first-stage compressor, respectively, if the suction pressure becomes higher than a predetermined maximum operating threshold value. A condition in which only one first-stage compressor is running can be restored manually or, as an alternative, the pressure regulator is configured to stop only one between the first and the second first-stage compressors, when the suction pressure becomes lower than a predetermined cut-off threshold value below or at most equal to the maximum operating threshold value.

[0028] It falls within the scope of the present patent application also an apparatus, as well as a method, as defined above, in which the industrial plant is a movable compressor unit associated with an internal combustion engine, i.e., a movable compressor unit driven by an internal combustion engine, wherein the engine is configured to receive a fuel gas feed at the receiving pressure in its own gas supply chamber, and the pressurized receiving body comprises the gas supply chamber.Brief description of the drawings

[0029] The invention will hereinafter be illustrated by a description of certain embodiments, made by way of example and not limitation, with reference to the appended drawings, wherein:Fig. 1 is a flow diagram of an apparatus according to the first aspect of the invention;Fig. 2 is a flow diagram of the first compression stage of the apparatus of Fig. 1 ;Fig. 3 is a flow diagram of an apparatus according to the first aspect of the invention, in an application to a compressor;Fig. 4 is a flow diagram of an apparatus according to an embodiment of the first aspect of the invention, in which the second-stage compressor is an air-driven compressor, and the actuation compressed air is supplied through an ON-OFF regulation valve;Fig. 5 is a flow diagram of an apparatus according to an embodiment of the first aspect of the invention, in which the second-stage compressor isan air-driven compressor, and the actuation compressed air is supplied through a modulating regulation valve;Figs. 6 and 7 show flow diagrams of the first compression stage according to two different embodiments each providing a suction pressure control unit;Fig. 8 is a flow diagram of the first compression stage showing different features according to different embodiments;Fig. 9 is a flow diagram of the first compression stage, according to an embodiment in which two first-stage compressors are parallelly arranged with each other;Fig. 10 is a flow diagram of a first compression stage according to the embodiment shown in Fig. 9, and in which different features are shown according to different modifications thereof.Description of preferred embodiments

[0030] With reference to Fig. 1 , an apparatus 1 1 is described for conveying at least one stream of a leaking gas 1 released at a substantially atmospheric pressure from an industrial plant 8, for example a natural-gas compression station along a pipeline, into a receiving body 9 pressurized at a predetermined receiving pressure Pr. In the above example, receiving body 9 can be the pipeline itself at its own operating pressure Pr.

[0031] Apparatus 1 1 comprises a first compression stage 100 according to various embodiments corresponding to those of apparatus 1 1 , which are shown in Figs. 2 and 6-10.

[0032] Apparatus 1 1 further comprises a transit container 150 and a second compression stage 200. Transit container 150 is pneumatically connected downstream of first compression stage 100 and upstream of second compression stage 200.

[0033] As shown in Fig. 2, first compression stage 100 essentially comprises a gas-collecting means C for at least one leaking gas stream 1 , which can in turn be formed by a plurality of leaking gas streams 11, 12, .... 1 n, or is associated with pre-existing gas-collecting means C of the industrial plant, according to the conventional art. Gas-collecting means C is not described in detail as it is well known to a person skilled in the art. Briefly, it can consist of a leaking gascollection chamber arranged around possible leakage points of the plant, such as vents of gas flushed seals, stuffing boxes of rotating or otherwise mobile members, in-line gas sampling points, flanged or other pipe connections, and the like.

[0034] First compression stage 100 further comprises a preferably elongated and vertically-arranged collection container 10 for leaking gas stream 1 , pneumatically connected with gas-collecting means C via a collection pipe 2 of leaking gas stream 1 or via a plurality of collection pipes 2i, 22, .... 2nof respective leaking gas streams 11, 12, .... 1 n. Thus, a collected leaking gas 1 a is formed in collection container 10. Collection container 10 can comprise a vessel 10 as shown in the figures or, in embodiments not shown, can simply be a collector tube. Collection container 10 advantageously comprises a drain 18 provided with a drain valve 19 for continuous or periodic removal of a liquid which can be present in collected leaking gas 1 a and which accumulates in the bottom of collection container 10.

[0035] First compression stage 100 further comprises a first-stage compressor 20, preferably a diaphragm compressor, or other type of gasleakage free compressor.

[0036] First-stage compressor 20 has a suction port 25 pneumatically connected to collection container 10 via a suction pipe 3. First-stage compressor 20 then has a delivery port 26 pneumatically connected with transit container 150 (Fig. 1 ) via a delivery pipe 6. Preferably manually-operated upstream and downstream shut-off valves 21 ,23 can be arranged along suction pipe 3 and delivery pipe 6, respectively. The shut-off valves are kept open during operation of first compression stage 100 and can be closed to isolate first-stage compressor 20 or first compression stage 100 from the rest of the plant in case of maintenance or replacement of first-stage compressor 20.

[0037] First-stage compressor 20 is arranged to compress collected leaking gas 1 a to an intermediate pressure P, which is the pressure of the compressed leaking gas 1 b that is collected within transit container 150. Intermediate pressure P is generally in the order of a few bars or a few tens of bars. First- stage compressor 20 is also arranged so as to maintain the suction pressure Ps, more specifically the pressure within collection container 10, at about few millibars below atmospheric pressure Patm.

[0038] Still with reference to Fig. 1 , second compression stage 200 comprises a second-stage compression chamber 68 arranged between an inlet duct 59 from transit container 150 and an outlet duct 69 pneumatically connected to pressurized receiving body 9.

[0039] A compression piston 67 is arranged within second-stage compression chamber 68 so as to modify the internal volume of second-stage compression chamber 68. In particular, a compression stroke of compression piston 67 allows a further-compressed leaking gas 1 c to be formed within compression chamber 68 and to be sent into outlet port 69. To this purpose, compression piston 67 is functionally connected to an actuation group 70 comprising a pressure sensor 71 that is arranged to measure intermediate pressure P of compressed leaking gas 1 b present within transit container 150 and that is arranged to generate a pressure signal 73 related to measured intermediate pressure P. Moreover, actuation group 70 is configured to actuate compression piston 67 based on pressure signal 73, i.e. on measured intermediate pressure P.

[0040] Fig. 3 schematically shows apparatus 11 as used to recover vents released at a substantially atmospheric pressure from an industrial plant 8 comprising a compressor 8a of any type, such as a reciprocating compressor or a rotary vane compressor, a lobe compressor, a screw compressor and so on. For example, compressor 8a can be arranged along a pipeline conveying a flammable gas or in any case a compressor handling a combustible gas. In this case, in a variant not shown, it can be advantageous to combine the further- compressed leaking gas 1 c produced by second compression stage 200 with the flammable gas feeding compressor 8a. To this purpose, pressurized receiving body 9 can be pneumatically connected to a suction port of compressor 8a.

[0041] First compression stage 100 can further comprise, a control unit 40 for controlling suction pressure Ps of first-stage compressor 20. The control unit is not shown in Fig. 2 but two different embodiments thereof are depicted in Figs.6 and 7.

[0042] Figs. 4 and 5 refer to apparatuses 1 1 , according to respective embodiments of the invention, in which compression piston 67 of second compression stage 200 is connected to a compressed-air-driven motor 61supplied through an inlet 61 a and discharged as spent compressed air through an outlet 61 b. Moreover, actuation unit 70 includes a compressed air regulation valve 72a, 72b arranged upstream of inlet 61 a. For instance, compressed-air- driven motor 61 can be a double-diaphragm pneumatic motor.

[0043] In apparatus 1 1 of Fig. 4, pressure sensor 71 a is configured to generate a pressure signal which can be a low-pressure signal 73' or a high- pressure signal 73" depending on whether measured intermediate pressure P in transit container 150 is not higher than a predefined minimum pressure Pi or is not lower than a predefined maximum pressure P2, respectively. In such a case, regulation valve 72a is configured to be fully open or fully closed, and is provided with an actuator 74a, for example a two-position actuator, configured to fully open or fully close regulation valve 72a upon receiving low-pressure signal 73’ or high-pressure signal 73”, respectively.

[0044] As an alternative, in apparatus 1 1 of Fig. 5, pressure sensor 71 b is configured to generate a continuous pressure signal 73b, i.e. a signal expressing at any time the value of intermediate pressure P inside transit container 150. In such a case, regulation valve 72b is configured to be partially and variably opened responsive to the value of intermediate pressure P, more specifically, regulation valve 72b is provided with a modulating actuator 74b configured to increase or decrease the opening of regulation valve 72b according to whether continuous pressure signal 73b increases or decreases with respect to a predefined target pressure value or set-point PR.

[0045] In an embodiment of first compression stage 100, as shown in Fig. 6, delivery port 26 of first-stage compressor 20 can further be connected with collection container 10 via a recycling pipe 4 and a control unit 40 of suction pressure Psof first-stage compressor 20 can be provided, including firstly a regulation valve 41 a arranged along recycling pipe 4, in order to adjust suction pressure Psof first-stage compressor 20.

[0046] In this same embodiment, control unit 40 further includes a pressure sensor / transducer 47 arranged to detect suction pressure Ps at first-stage compressor 20 and to generate a suction pressure signal 46. As shown in the figure, pressure sensor / transducer 47 can be arranged on collection container 10. As alternative, not shown, pressure sensor / transducer 47 can be arranged along suction pipe 3.

[0047] Control unit 40 further comprises a pressure regulator 45, preferably an electronic regulator, configured to receive pressure signal 46 to be controlled from pressure sensor / transducer 47, and to generate an open / close signal 43 intended for an actuator 49 of regulation valve 41 a. Actuator 49 is arranged to modify the opening status of valve 41 a based on pressure signal 46, so as to maintain suction pressure Ps at a target pressure value between atmospheric pressure Patm and a predetermined minimum pressure Pm. In practice, by recycling to collection container 10 a portion of the flow rate of compressed leaking gas 1 b, said portion indicated hereinafter as recycling portion 1d of compressed leaking gas 1 b, an equilibrium is achieved between the flow rate of leaking gas 1 from the various leakage points and the flow rate suctioned by first-stage compressor 20 at the desired pressure Pr.

[0048] Preferably, minimum relative pressure Pm is set between -200 Pa and -100 Pa, in particular it is close to -150 Pa. The target pressure value, as a relative pressure, is preferably set between a maximum relative pressure, e.g. -50 Pa, and a minimum relative pressure Pm.

[0049] Advantageously, pressure sensor / transducer 47 is a differentialpressure transducer 46 arranged between a point at the suction to first-stage compressor 20 and the atmosphere, for instance between collection container 10 and the atmosphere, and is configured to measure both positive relative pressures and negative relative pressures, generally, in a range of -20 mbar + +20 mbar (-2 kPa + +2 kPa). In other words, pressure sensor / transducer 47 is arranged to detect, besides the value of suction pressure Psat first-stage compressor 20, a current value of atmospheric pressure Patm and to generate suction pressure signal 46 as a differential pressure signal related to a difference between atmospheric pressure Patm and suction pressure Psat first-stage compressor 20.

[0050] Besides allowing adjustment of suction pressure Psat first-stage compressor 20, recycling portion 1 d of compressed leaking gas 1 b flowing back into collection container 10 through recycling pipe 4 makes it easier to start first- stage compressor 20.

[0051] In another embodiment of first compression stage 100, as shown in Fig.7, control unit 40 provided for controlling suction pressure Psof first-stagecompressor 20 can include an inverter 41 b arranged to vary the RPM of first- stage compressor 20.

[0052] Even in this embodiment, control unit 40 includes a pressure sensor / transducer 47 for detecting suction pressure Psat first-stage compressor 20 and for generating a suction pressure signal 46, said sensor / transducer arranged, for instance, on collection container 10 or along suction pipe 3. Control unit 40 further comprises a pressure regulator 45, preferably an electronic regulator, configured to receive pressure signal 46 to be controlled from pressure sensor / transducer 47, and to generate a control signal 43 that is intended, in this case, for inverter 41 b of control unit 40. The assembly formed by inverter 41 b and first-stage compressor 20 is configured to vary the RPM of first-stage compressor 20 based on pressure signal 46, so as to maintain suction pressure Psat a target pressure value between atmospheric pressure Patm and a predetermined minimum pressure Pm.

[0053] Even in this embodiment, minimum relative pressure Pm is preferably set between -200 Pa and -100 Pa, and the target pressure value is preferably set between a maximum relative pressure, for example -50 Pa, and minimum relative pressure Pm.

[0054] Even in this embodiment, pressure sensor / transducer 47 is a differential-pressure transducer with respective pressure ports at a point at the suction of first-stage compressor 20, for example on collection container 10, and at the atmosphere, and is configured to measure pressures generally in a range of -20 mbar + +20 mbar.

[0055] With reference to Fig. 8, first compression stage 100 according to certain embodiments of the invention can further comprise respective features that are described in the following paragraphs. Although such individual features are depicted in the same Fig. 8, they can be present independently of each other, each alone or according to combinations of some of said features.

[0056] In one embodiment, a non-return valve 22 is preferably arranged along delivery pipe 6 of first-stage compressor 20 of first compression stage 100 in order to prevent backflow of pressurized gas from transit container 150 (Fig. 1 ) back to first-stage compressor 20 and to collection container 10 via recycling pipe 4 if first-stage compressor 20 shuts down, typically in the event of a shutdown due to power supply sudden failure or interruption. Moreover, asection restriction 29, for example in the form of a calibrated orifice, can be advantageously provided along delivery pipe 6 serially to non-return valve 22, in particular, downstream of non-return valve 22. This serves to limit the backflow of pressurized gas from transit container 150 towards first-stage compressor 20 and collection container 10 if, in the case of a sudden shutdown of first-stage compressor 20, non-return valve 22 does not close or does not completely close.

[0057] In another embodiment, collection container 10 of first compression stage 100 is provided with an emergency vent device 55 for releasing collected leaking gas 1 a that is present in collection container 10 into atmosphere if the pressure of collected leaking gas 1 a exceeds a predetermined maximum safety threshold value PMS higher than atmospheric pressure Patm, due to any first- stage compressor fault. In particular, emergency vent device 55 comprises a vent pipe 5 having an outlet to atmosphere in a safe zone 7. A pressure-relief valve 50, such as a counterbalance pressure-relief valve, is arranged along vent pipe 5. In particular, emergency vent device 55, i.e. pressure-relief valve 50, is configured to release collected leaking gas 1 a that is present within collection container 10 when the pressure of collected leaking gas 1 a exceeds a predetermined maximum pressure PMS set between 1 and 10 mbar (100-1000 Pa), for example a pressure of 2 mbar (200 Pa).

[0058] Moreover, emergency vent device 55 of a modification of first compression stage 100 can comprise a bypass pipe 5' connected between upstream and downstream of pressure-relief valve 50, and at least two shut-off valves 51 ,52 respectively arranged on vent pipe 5 and on bypass pipe 5’ serially to pressure-relief valve 50, said valves maintained closed and open, respectively, during normal operation of first compression stage 100, in order to allow maintenance on pressure-relief valve 50.

[0059] In a further embodiment, first compression stage 100 comprises a safety valve 24, also shown in Fig. 2 as an optional feature, having its inlet port pneumatically connected with delivery port 26 of first-stage compressor 20, preferably through a portion of delivery pipe 6. In a modification, also shown in Fig. 8, in which emergency vent device 55 is also provided, the outlet port of safety valve 24 is pneumatically connected with said vent pipe 5, downstream of pressure-relief valve 50.

[0060] In a further embodiment, along recycling pipe 4 of first compression stage 100, preferably downstream of regulation valve 41 a, a heat exchange device 42 is provided, also shown in Fig. 2 as an optional feature, configured to refrigerate the recycle gas to collection container 10 so that collected leaking gas 1 a present in collection container 10 does not reach excessive temperatures for admission to first-stage compressor 20.

[0061] In a further embodiment, regulation valve 41 a of first compression stage 100 is provided with a positioner device 48 comprising a position sensor, not shown, configured to detect the position of a stopper member 40 of he regulation valve and to output a position signal 49' related to the stopper member, and pressure regulator 45 is configured to receive position signal 49’ and modify open / close signal 43 directed to actuator 49 based on position signal 49’.

[0062] Referring to Fig. 9, a first compression stage 100 according to an embodiment of the invention comprises multiple first-stage compressors parallelly arranged with respect to each other, in particular a first first-stage compressor 20 and a second first-stage compressor 30. Similarly to first first- stage compressor 20, second first-stage compressor 30 has a suction port 35 pneumatically connected with collection container 10 through a suction pipe 3", 3 as well as a delivery port 36 pneumatically connected with transit container 150 through a delivery pipe 6", 6. In this case, a logic is advantageously provided, not shown, configured to automatically start second first-stage compressor 30 or first first-stage compressor 20 in addition to first first-stage compressor 20 or to second first-stage compressor 30, respectively, already in operation, if suction pressure Psof two first-stage compressors 20,30 exceeds a predetermined maximum operating threshold value PMe. This can occur, for example, in case of fault of first or second first-stage compressor 20 or 30 already in operation. The logic of the control unit can also be configured to automatically stop only one of first and second first-stage compressors 20,30 when suction pressure Psbecomes lower than a predetermined shutdown threshold value PR lower than or at most equal to maximum operating threshold value PMe. In such circumstances, alternatively, once the fault has been corrected, one of two first- stage compressors 20,30 can be manually shut down by an operator.

[0063] The logic of the control unit can comprise pressure regulator 45, described above, and / or can be configured to receive a high-pressure signal and possibly a reset pressure signal generated by pressure regulator 45 when suction pressure Psbecomes higher than the maximum operating pressure PMe or lower than the reset pressure PR, respectively.

[0064] Similarly to what is shown in Fig. 1 , each first-stage compressor 20,30 can be equipped with a respective upstream shut-off valve 21 ,31 arranged along its own suction branch 3', 3" and with a respective downstream shut-off valve 23,33 arranged along its own discharge branch 6', 6" to allow maintenance while the plant and first compression stage is 100 running. Delivery branches 6’, 6” merge together and form delivery pipe 6, along which an additional shut-off valve 53 can be provided.

[0065] With reference to Fig. 10, apparatus 100 according to some embodiments of the invention can further include respective features described in the following paragraphs. Although said features are depicted in the same Fig. 10, they can be present independently of each other, each \alone or according to combinations of some of said features. More precisely, a first compression stage 100 according to one embodiment comprises non-return valves 22,32 arranged along discharge branches 6’ and 6" of first-stage compressors 20 and 30, respectively, in order to prevent backflow of pressurized gas from transit container 150 (Fig. 1 ) towards first-stage compressor 20 or 30 and towards collection container 10 through recycling pipe 4, in the case of a shutdown of first-stage compressor 20 or 30, and of manual actuation of back-up first-stage compressor 30 or 20. An additional non-return valve 52 can be provided along common delivery pipe 6, with a function similar to non-return valves 22,32 described above. Section restriction 29, in the form of a calibrated orifice, can be provided on delivery pipe 6, as shown, or, in a variant not shown, on each delivery branches 6', 6" of the two first-stage compressors 20,30; a first compression stage 100 according to another embodiment comprises an emergency vent device 55 of collection container 10, as in first compression stage 100 of Fig. 8;a first compression stage 100 according to a further embodiment comprises two safety valves 24,34 to prevent exceeding the maximum operating pressure of first-stage compressors 20,30, each safety valve 24,34 having an inlet port pneumatically connected with delivery port 26,36 of first first-stage compressor 20 and second first-stage compressor 30, respectively, and having an outlet port preferably pneumatically connected with emergency vent pipe 5, if present; a first compression stage 100 according to another embodiment comprises a heat exchange device 42 configured to refrigerate the recycling gas portion flowing towards collection container 10, as in the first compression stage 100 of Fig. 8; in a first compression stage 100 according to another embodiment, regulation valve 41 a is provided with a positioner device 48, as in first compression stage 100 of Fig. 8.

[0066] It falls within the scope of the present patent application also an embodiment of the apparatus and of the method, not shown but readily implementable in the light of the present description by a person skilled in the art, in which industrial plant 8 is a movable compressor unit associated with an internal combustion engine, not shown, configured to receive a fuel gas feed at receiving pressure Pr in its own gas supply chamber, not shown, wherein pressurized receiving body 9 comprises said gas supply chamber.

[0067] The above description of embodiments and variants of the invention embodiment will so fully reveal the invention according to a conceptual point of view, so that others, by applying current knowledge, will be able to modify and / or adapt such specific embodiments and variants for various applications, without further research and without departing from the inventive concept, and, therefore, it is understood that such modifications and adaptations will be considered as equivalent to the variants and of the specific embodiments. The means and materials for putting into practice the various functions described can be of various kinds without departing from the scope of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

Claims

CLAIMS1. An apparatus (1 1 ) for conveying at least one stream of a leaking gas (1 ) leaking from an industrial plant (8) into a receiving body (9), said at least one stream of said leaking gas (1 ) released at a substantially atmospheric pressure (Patm), said receiving body (9) pressurized to a predetermined receiving pressure (Pr), wherein said apparatus (1 1 ) comprises a first compression stage (100), a transit container (150) and a second compression stage (200), said transit container (150) pneumatically connected downstream of said first compression stage (100) and upstream of said second compression stage (200), wherein said first compression stage (100) comprises: a gas-collecting means (C) for collecting said stream of said leaking gas (1 ); a collection container (10) of said at least one stream of said leaking gas (1 ) pneumatically connected to said gas-collecting means (C) and configured in such a way that said at least one stream of said leaking gas (1 ) forms a collected leaking gas (1 a) in said collection container (10); a first-stage compressor (20,30) having a suction port (25,35) pneumatically connected to said collection container (10) ; wherein said first-stage compressor (20,30) has a delivery port (26,36) pneumatically connected with said transit container (150), through a delivery pipe (6) of said first compression stage (100), wherein said first-stage compressor (20,30) is arranged to compress said collected leaking gas (1 a) to an intermediate pressure (P), resulting in a compressed leaking gas (1 b) collecting in said transit container (150); a first control unit (40) of a suction pressure (Ps) of said first-stage compressor (20,30), said first control unit comprising: a pressure sensor / transducer (47) configured to detect said suction pressure (Ps) of said first-stage compressor (20,30) and to generate a suction pressure signal (46) ;a regulation device (41 a, 41 b) configured to modify said suction pressure (Ps) of said first-stage compressor (20,30); a pressure regulator (45) configured to receive said pressure signal (46) and to generate a regulation signal (43) to operate said regulation device (41 a, 41 b) based on said pressure signal (46), so as to maintain said suction pressure (Ps) at a target pressure value between the atmospheric pressure (Patm) and a predetermined minimum pressure (Pm), wherein said second compression stage (200) comprises an inlet duct (59) coming from said transit container (150); an outlet duct (69) pneumatically connected to said pressurized receiving body (9); a second-stage compression chamber (68) arranged between said inlet duct (59) and said outlet duct (69); a compression piston (67) of said second-stage compression chamber (68) configured to compress said second-stage compression chamber (68) so as to send a further-compressed leaking gas (1 c) into said outlet duct (69); an actuation group (70) of said compression piston (67), wherein said actuation group (70) includes a pressure sensor (71 , 71 a, 71 b) arranged to measure said intermediate pressure (P) of said compressed leaking gas (1 b) that is present in said transit container (150) by generating a pressure signal (73, 73', 73") related to said measured intermediate pressure (P), and said actuation group (70) is configured to actuate said compression piston (67) based on said measured intermediate pressure (P) of said compressed leaking gas (1 b) that is present in said transit container (150).

2. The apparatus (11 ) according to claim 1 , wherein said industrial plant is a compressor (8), and wherein said pressurized receiving body (9) is pneumatically connected with a suction mouth of said compressor (8).

3. The apparatus (11 ) according to claim 1 , wherein said compression piston (67) of said second compression stage (200) is connected to acompressed-air-driven motor (61 ) provided with an of compressed air inlet (61 a) and an outlet (61 b) of exhausted compressed air, and said actuation group (70) further includes a regulation valve (72a, 72b) arranged upstream of said compressed air inlet (61 a).

4. The apparatus according to claim 3, wherein said compressed-air-driven motor (61 ) is a double-diaphragm pneumatic motor.

5. The apparatus (1 1 ) according to claim 3, wherein said pressure sensor (71 a) is configured to generate a pressure signal selected between a low- pressure signal (73') and a high-pressure signal (73") according to whether said measured intermediate pressure (P) is respectively equal to or lower than a predefined minimum pressure (Pi) or is equal to or higher than a predefined maximum pressure (P2), and said regulation valve (72a) is provided with an actuator configured to open or close said regulation valve (72a) upon receiving said low-pressure signal (73') or said high-pressure signal (73"), respectively.

6. The apparatus (1 1 ) according to claim 3, wherein said pressure sensor (71 b) is configured to generate a continuous pressure signal (73b), and said regulation valve (72b) is provided with a modulating actuator (74b) arranged to increase or decrease the opening of said regulation valve (72b) according to whether said continuous pressure signal (73b) increases or decreases with respect to a predefined target pressure value (PR).

7. The apparatus (1 1 ) according to claim 1 , wherein said first compression stage (100) further comprises: a recycling pipe (4) pneumatically connecting said delivery port (26) of said first-stage compressor with said collection container (10), so as to convey a recycling portion (1 d) of said compressed leaking gas (1 b) from said first-stage compressor (20,30) back into said collection container (10); wherein said regulation device of said first control unit (40) is a regulation valve (41 a) arranged along said recycling pipe (4), and said pressure regulator (45) is configured to generate said regulation signal (43) as an open / close signal (43) to modify an opening of said regulation valve (41 a) based on said pressure signal (46), so as to maintain said suction pressure(Ps) at a target pressure value between the atmospheric pressure (Patm) and a predetermined minimum pressure (Pm).

8. The apparatus (1 1 ) according to claim 1 , wherein said first-stage compressor is a rotary compressor, and said regulation device of said control unit (40) is an inverter (41 b) arranged to modify the rotation speed of said rotary compressor (20).

9. The apparatus (1 1 ) according to claim 1 , wherein said pressure sensor / transducer (47) is further arranged to detect a current value of said atmospheric pressure (Patm) and to generate said suction pressure signal (46) as a differential pressure signal related to a difference between said atmospheric pressure (Patm) and said suction pressure (Ps) of said first- stage compressor (20,30)10. The apparatus (1 1 ) according to claim 1 , wherein said collection container (10) is provided with an emergency vent device (55) configured to release said collected leaking gas (1 a) that is present in said collection container (10) into the atmosphere when said suction pressure (Ps) of said collected leaking gas (1 a) exceeds a predetermined maximum threshold safety value (PMS) higher than said atmospheric pressure (PAtm),11. The apparatus (1 1 ) according to claim 10, wherein said emergency vent device (55) comprises a pressure-relief valve (50) arranged along a vent pipe (5) having an outlet port in a safe zone (7).

12. The apparatus (1 1 ) according to claim 7, wherein along said recycling pipe (4) a heat exchange device (42) is provided that is configured to refrigerate said recycling portion (1 d) conveyed back into said collection container (10).

13. The apparatus (1 1 ) according to claim 7, wherein along said delivery pipe (6, 6', 6") of said first-stage compressor (20,30) a non-return valve (22,32) is arranged to prevent a backflow of pressurized gas from said transit container (150) towards said first-stage compressor (20,30) and towards said collection container (10), through said recycling pipe (4), if said first- stage compressor (20,30) stops.

14. The apparatus (1 1 ) according to claim 1 , wherein said first-stage compressor (20) is a first first-stage compressor (20) and said first compression stage (100) comprises a second first-stage compressor (30)parallelly arranged to said first first-stage compressor (20) and said pressure regulator (45) is configured to start said second first-stage compressor (30) or said first first-stage compressor (20) in addition to said first first-stage compressor (20) or to said second first-stage compressor (30), respectively, if said suction pressure (Ps) becomes higher than a predetermined maximum operating threshold pressure value (PMe ).

15. A method for conveying at least one stream of a leaking gas (1 ) leaking from an industrial plant (8) into a receiving body (9), said stream of said leaking gas (1 ) released at a substantially atmospheric pressure (Patm), said receiving body (9) pressurized to a predetermined receiving pressure (Pr), wherein said method comprises a first gas-treatment step of treating said leaking gas (1 ), thereby obtaining a collected leaking gas (1 a), a step of temporarily accumulating said collected leaking gas (1 a) in a transit container (150), thereby obtaining a compressed leaking gas (1 b), and a second gas-treatment step of treating said compressed leaking gas (1 b), said first gas-treatment step including the steps of: capturing said stream of said leaking gas (1 ); collecting said stream of said leaking gas (1 ) into a collection container (10), forming said collected leaking gas (1 a); in a first-stage compressor (20,30), a first gas compression step of compressing said collected leaking gas (1 a) to a predetermined intermediate pressure (P), thereby obtaining said compressed leaking gas (1 b); conveying said compressed leaking gas (1 b) into said transit container (150); measuring a suction pressure (Ps) of said first-stage compressor (20,30); regulating said suction pressure (Ps) to a target pressure value between the atmospheric pressure (Patm) and a predetermined minimum pressure (Pm), wherein said second gas-treatment step comprises the steps of: measurement of said intermediate pressure (P) of said compressed leaking gas (1 b) present in said transit container (150);conveying said compressed leaking gas (1 b) from said transit container (150) into a compression chamber (68) of a second compressor (60); second compression of said compressed leaking gas (1 b) in said compression chamber (68) of said second compressor (60), thus obtaining a further-compressed leaking gas stream (1 c), wherein said second compression step comprises a step of adjusting a compression ratio based on said measurement of said intermediate pressure (P) of said compressed leaking gas (1 b), so that said further- compressed leaking gas stream (1 c) has a pressure (P') at least equal to said receiving pressure (Pr) ; conveying said further-compressed leaking gas stream (1 c) into said pressurized receiving body (9).

16. The method according to claim 15, wherein said industrial plant is a rotary compressor (8), and said step of conveying said further-compressed leaking gas stream (1 c) comprises a step of suctioning said further- compressed leaking gas stream (1 c) by said rotary compressor (8) .

17. The method according to claim 16, wherein said rotary compressor (8) is arranged along a pipeline.

18. The method according to claim 15, wherein said second compression step comprises steps of admitting compressed air (2a) and discharging exhausted compressed air (2b) into / from an actuation chamber (64) of an pneumatic motor (61 ), and a step of adjusting a flow rate of said compressed air (2a) based on said measurement of said intermediate pressure (P) of said compressed leaking gas (1 b) present in said transit container (150).

19. The method according to claim 15, wherein said first gas-treatment step further comprises the steps of: recycling a recycling portion (1 d) of said compressed leaking gas (1 b) back into said collection container (10), wherein a main portion and said recycling portion (1 d) of said compressed leaking gas (1 b) are determined according to said measured suction pressure (Ps), so as to maintain said suction pressure (Ps) at a targetpressure value between said atmospheric pressure (Patm) and said predetermined minimum pressure (Pm).

20. The method according to claim 15, wherein said industrial plant (8) is a transportable compression unit associated with an internal combustion engine, wherein said internal combustion engine is configured to receive a fuel gas fed at said receiving pressure (Pr) into its own gas supply chamber, wherein said pressurized receiving body (9) comprises said supply chamber.

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