Patent Application
20230366389
The present invention relates to a method and to a device for changing the compression ratio of a reciprocating compressor and, in particular, it also relates to a compression unit comprising said reciprocating compressor and equipped with said device.
The invention also relates to a process and to an apparatus for evacuating a valuable and/or harmful gas from a closed space, and for transferring the gas into a delivery environment at a predetermined pressure.
As well known, reciprocating compressors, in particular piston compressors, are normally used when relatively small gas streams must be compressed, and high compression ratios are required. In order to obtain a predetermined compression ratio, compression units including a plurality of serially connected cylinder-piston units are often used. It is rather easy to regulate the flowrate of a reciprocating compressor, by somehow modifying the number of intake-compression cycles per time unit, or by adjusting the stroke length of the piston. On the contrary, the compression ratio of such an equipment is much harder to change. Several reciprocating compressors have been proposed allowing to change the compression ratio, see for instance KR101352805 B1, JPH0849653 A, CN109973374 A and US2019032553 A1. However, these solutions are difficult to manufacture, involve high manufacture/maintenance costs, and do not always allow a real-time compression ratio change, as required in some processes.
For example, the need to change the compression ratio of a reciprocating compressor arises if the compressor is used, in a substantially continuous service, to transfer a gas from a suction environment to a delivery environment, when the suction pressure and/or the delivery pressure remarkably change during the transfer, which requires adapting the compression ratio provided by the compressor.
A variable compression ratio is also required when the reciprocating compressor is used to evacuate a valuable and/or harmful gas from a closed space and to transfer the gas into a delivery environment at a predetermined delivery pressure, for example at a substantially constant delivery pressure, i.e. at a delivery pressure that remains substantially unchanged during the evacuation/transfer operation.
In particular, this is the case when a plant section, such as a compression section of a gas pipeline, must be evacuated, for example, if a stop condition of the gas pipeline main compressor has occurred, or if the main compressor must be stopped for maintenance, or due to a gas request decrease from the network.
In such conditions, a gas substantially consisting of methane must be removed from the involved plant section. The evacuated gas is normally released into the environment as such or is burnt in a chimney. In both cases, a greenhouse effect gas is emitted into the environment. This is particularly serious in the first case, since methane is much more harmful than carbon dioxide as a greenhouse effect gas. In the latter case, instead, the emissions can also contain nitrogen oxides. In both cases a financial loss is involved, which depends not only on the intrinsic value of the gas that is directly emitted or burnt, but on the higher and higher taxes imposed in an increasing number of states to the users of plants even occasionally releasing greenhouse effect gases.
It is worthwhile to note that the temporary stop of a compression facility can occur even daily, in particular, due to commercial dynamics.
The need is therefore felt to prevent harmful and/or valuable gas to be emitted into the environment from normally pressurized plant sections when these plant sections are temporary or definitely put out of service.
In the exemplary case of a gas pipeline compression facility, the solution to such a problem could consist in introducing the evacuated gas into the gas pipeline itself again. However, in order to put such a solution into practice, the gas must be conveyed from a closed space at a pressure Psc that decreases as the gas is evacuated, into a reception space, in this case the gas pipeline, that is at a predetermined working pressure Pe. At the beginning of the evacuation, the pressure in the closed space PSC is close to the working pressure Pe of the gas pipeline, and the compression unit used for this service is required to provide a compression ratio Pe/Psc of about 1. As the evacuation proceeds, pressure PSC in closed space decreases, while the working pressure Pe remains substantially unchanged, so the compression unit is required to provide an increasing compression ratio Pe/Psc. The lower the residual pressure tolerated in the closed space or in the plant section to be evacuated, the higher is the final compression ratio. This admissible residual pressure is normally about a few tenths of bar above the atmospheric pressure, so as to minimize the net residual emissions.
During the evacuation, the flowrate demand to the compression unit can remarkably decrease. The compression unit is advantageously sized to allow flowrate evacuation values high enough to complete the evacuation in an acceptable time.
Preferably, the above-described service can be carried out by a reciprocating compression unit, in particular by a piston compression unit. In fact, in comparison with the rotating compressors, this type of equipment is better suited for a discontinuous service and reaches more easily the steady operating conditions. Moreover, the required flowrates normally fall within the flowrate field in which the reciprocating compressors are preferable to the rotating compressors.
Briefly, there is the need for a method and a device for changing the compression ratio of a reciprocating compression unit, in particular from values of about 1:1 up to values of about 50:1 and also up to 100:1, taking into account, for example, the common gas pipelines operating pressures. It is also relevant that such method and device allow a quick compression ratio adjustment, so as to adapt the pressure ratio to the upstream pressure change and to the downstream pressure change in particular cases of continuous gas transfer.
As an example, in order to describe the technical problems, reference has been made till now to a gas pipeline compression facility as a closed space to be evacuated. However, similar reasonings can be made for any facility in which a harmful and/or valuable pressurized gas is treated, for instance natural gas liquefaction facilities, CO2 recovery and storage plants, technical gas production and storage/distribution plants, chemical and petrochemical plants, such as polyolefin production facilities, in which pressurized gaseous polyolefins are manipulated. In fact, in all these cases, the release and/or the combustion of the evacuated gas causes a financial loss or harm to the environment to such an extent depending on the gas value/harmfulness. Moreover, in all these cases a pressurized reception space can be identified, such as a storage unit, or a distribution pipe network, into which the evacuated gas can be conveyed.
US 2016/0123314 A1 describes a compressor of a refrigeration plant including multiple compression chambers that can be connected to each other in different configurations by suitably opening and closing a plurality of valves, so as to compress the refrigerant fluid in different numbers of compression steps. The passage from one configuration to another configuration is controlled by a control module responsive to the cooling power required to the refrigeration plant and, accordingly, responsive to a corresponding flowrate of the refrigerant fluid to be compressed.
WO 2012/021928 A2 describes a compressor for compressing air in a plant for making articles such as PET bottles, configured to provide a plurality of serially arranged compression steps and to sequentially activate/deactivate the compression steps as the high-pressure air request increases/decreases.
It is therefore a feature of the present invention to provide a method and a device for changing the compression ratio of a new or existing reciprocating compressor, from a value of about one to a value of some tenths or even one hundred.
It is a particular feature of the present invention to provide a method and an apparatus for evacuating a valuable and/or harmful gas from a closed space into a delivery environment at a predetermined pressure, which allows an amount of gas left in the closed space corresponding to a pressure of at most 0,1 bar gauge, at the end of the gas compression/transfer.
It is also a feature of the invention to provide a compression unit which carries out the method, or that comprises such device associated to a reciprocating compressor.
It is a particular feature of the invention to provide such a device for changing the compression ratio, which allows a reciprocating compressor to continuously convey a gas from a suction environment at a suction pressure into a delivery environment at a delivery pressure, in which the suction pressure and/or the delivery pressure can suddenly and unpredictably change to a relevant extent.
These and other objects are achieved by a method and by a device for changing the compression ratio of a reciprocating compressor, the reciprocating compressor comprising an inlet port for a gas to be compressed and an outlet port for a compressed gas, and a plurality of piston-cylinder units defining a plurality of compression chambers that are pneumatically connected between the inlet port and the outlet port, as defined in claims 1 and 8, respectively, and by a compression unit comprising said device, as defined in claim 11. Advantageous modifications of the method and advantageous exemplary embodiments of the device are defined by respective dependent claims.
According to one aspect of the invention, a method is provided comprising the steps of:
The method also comprises the steps of:
This way, the step of causing the plurality of commutation valves to switch from the first open and/or closed state combination to the second open and/or closed state combination, or in any case from a possible combination to another combination corresponding to a larger number of serially connected compression chambers, is carried out when the overall pressure ratio becomes higher than said overall threshold value, while the step of causing the plurality of commutation valves to switch from the second open and/or closed state combination to the first open and/or closed state combination, or in any case from a possible combination to another combination corresponding to a smaller number of serially connected compression chambers, is carried out when the overall pressure ratio becomes lower than this threshold value.
In an advantageous exemplary embodiment, the method comprises the steps of:
According to another aspect of the invention, a device is provided comprising a plurality of commutation valves for changing the number of compression steps, each commutation valve configured to switch from a respective open status to a respective closed status, and vice-versa,
wherein the commutation valves are arranged to switch:
In other words, the first and the second open and/or closed state combinations of the commutation valves define two different numbers of paths for the gas to be compressed, and the gas passes through a different number of compression chambers, in particular in the path or paths corresponding to the second state combination the gas passes through a number of compression chambers that is larger than the number of compression chamber through which the gas passes in the paths corresponding to the first state combination. Therefore, by the second state combination, the gas is subjected to a larger number of compression steps and is compressed up to a higher pressure than by the first open and/or closed state combination of the valves.
In other words, by the second open and/or closed state combination the compression ratio of the compressor unit is higher than by the first open and/or closed state combination.
Obviously, embodiments are possible in which more than two open and/or closed state combinations of the commutation valves are defined and, accordingly, more than two connection modes of the compression chambers are possible corresponding to respective numbers of compression steps of the gas, each connection mode corresponding to a compression ratio of a plurality of compression ratios that can be provided by the reciprocating compressor unit, thanks to the device according to the invention.
Moreover, the device comprises:
These features define an automatic way to change the number of compression steps to which the gas to be compressed is subjected and, accordingly, an automatic way to switch among the multiple compression ratios that can be provided by a reciprocating compressor equipped with the device. This automatic switch mode is advantageous in the case of normally unmanned installations, such as remotely controlled gas pipeline compression facilities.
In an advantageous exemplary embodiment, the device also comprises an upstream pressure sensor and a downstream pressure sensor arranged upstream and downstream of each compression chamber, respectively, and the control unit is configured to:
It also falls within the scope of the invention a reciprocating compression unit comprising the reciprocating compressor and the above-described device for changing the compression ratio thereof, associated to the compressor.
The gas to be compressed can be withdrawn, for instance, from a closed space from which the gas contained therein has to be evacuated, from an initial pressure to a final pressure, and the compressed gas is sent to a reception space at a predetermined working pressure that remains substantially unchanged at least during the compression steps of the gas to be compressed. As the gas evacuation proceeds, the pressure in the closed space, which is hermetical to the external gas apart from a connection with the inlet port of the compressor, decreases, while the pressure downstream of the reciprocating compressor remains unchanged. Therefore, as the evacuation proceeds, a continuously increasing compression ratio is required to the reciprocating compressor.
In a particular but common case, the closed space to be evacuated comprises a portion of a gas pipeline compression facility, typically including a main compressor of the gas pipeline, and the reception space is the gas pipeline itself, i.e. a section of the gas pipeline downstream of or in any case outside of the portion of the compression facility to be evacuated. The reciprocating compressor equipped with the device according to the invention makes it possible to recover the evacuated gas without substantially emitting it into the atmosphere, which is an economical and environmental advantage, for the reasons explained at the beginning of the present description.
In the case of a gas pipeline compression facility, the device can be associated to a possibly existing reciprocating compressor arranged to recover a lost gas leaking from the main compressor of the gas pipeline, in particular a lost gas leaking from a compressor seal, or in any case from possible leakage points of any closed space, during normal operation of the plant, or in any case while the reciprocating compressor performs an operation different from an evacuation of the closed space. Normally, the pressure of the leaked gas is only slightly higher than the atmospheric pressure. Therefore, a high compression ratio is required to compress the leaked gas up to the normal gas pipeline pressure and to introduce the leaked gas again into the pipeline. Therefore, during the substantially continuous step of recovering the leaked gas, the commutation valves are advantageously arranged in the second open and/or closed state combination, so as to obtain the maximum compression ratio that the reciprocating compressor can provide.
However, the device can be advantageously associated to any process plant reciprocating compressor that is installed between a suction environment at a suction pressure and a delivery environment at a delivery pressure, wherein the suction and delivery pressures can change to such an extent and in such a way that the pressure ratios changes in turn by at least one order of magnitude, and that a significant change of the compression ratio is required to the reciprocating compressor.
In an exemplary embodiment, the commutation valves are at least in part check valves, in particular disc check valves.
The device can comprise a housing box enclosing the commutation valves and configured to be mounted to the compressor. This makes it possible to easily associate the device of the invention to an existing reciprocating compressor, for example to a reciprocating compressor that is already in use in a gas pipeline compression facility for recovering leaked gas streams, as explained above. In particular, the connections to the compressor ducts are available on such a housing box. The control unit can be also arranged within the housing box, in which the electric and/or pneumatic connections required to operate the commutation valves are available.
The invention is shown hereinafter through the description of some exemplary embodiments, exemplifying but not limitative, in which:
With reference to
Device 4 comprises a plurality of commutation valves V for changing the number of compression steps to which a same volume of gas is subjected by reciprocating compressor 3. Commutation valves V are arranged in such a way that the number of serially connected compression chambers 2i increases when turning from a first open and/or closed state combination to a second open and/or closed state combination of the valves, and therefore the number of parallel connected compression chambers 2i decreases.
In particular, in
A second open and/or closed state combination of valves V corresponds to the path marked by a dashed line. In those conditions, all four compression chambers 2i are serially connected to each other, and there are no parallel connected compression chambers. In this case, a same volume of gas to be compressed 8 coming from suction environment 80 through inlet port 40 of reciprocating compressor 3 is subjected to four compression steps by sequentially crossing all four compression chambers 2i. In other words, with this open and/or closed state combination of valves V, compression units 100 and 101 are in a four-compression-steps configuration.
For the sake of simplicity,
As shown in
Opening/closing signals 47 are configured in such a way that the commutation valves switch from the first to the second above-mentioned open and/or closed state combination when the overall pressure ratio becomes higher than a predetermined overall threshold value, and switch from the second to the first open and/or closed state combination when, on the contrary, the overall pressure ratio becomes lower than a predetermined overall threshold value. These open and/or closed state combination can be combinations corresponding to a one-compression-steps configuration and to a two-compression-steps configuration, respectively, or corresponding to a two-compression-steps configuration and to a three-compression-steps configuration, respectively, or corresponding to a three-compression-steps configuration and to a four-compression-steps configuration, respectively.
In this case, more in detail, device 4 comprises a plurality of further upstream pressure sensors 42i, i=2 . . . 4 and a plurality of further downstream pressure sensors 44i, i=1 . . . 3 in addition to first pressure sensor 421 upstream of reciprocating compressor 3, i.e., upstream of first compression chamber 21, and in addition to second pressure sensor 44N downstream of compressor 3, i.e., downstream of Nth, i.e. of fourth compression chamber 2N, where N=4, so that N upstream pressure sensors 42i and N downstream pressure sensors 44i are overall provided upstream and downstream of each compression chamber 2i, respectively. Moreover, control unit 60 is configured to receive upstream pressure signals 45i from each upstream pressure sensor 42i and downstream pressure signals 46i from each downstream pressure sensor 44i, and to calculate single-step pressure ratios, i.e. downstream-to-upstream pressure ratios, for each compression chamber 2i, between each downstream pressure signal 46i and corresponding upstream pressure signal 45i. Control unit 60 is also configured to generate opening/closing control signals 47 of commutation valves V responsive to the calculated single-step pressure ratios, and to transfer opening/closing control signals 47 to actuator elements of commutation valves V. Opening/closing signals 47 are configured in such a way that commutation valves V switch from the first to the second above-mentioned open and/or closed state combination, when at least one of the single-step pressure ratios becomes higher than a predetermined single-step threshold value, and switch from the second to the first open and/or closed state combination when, instead, at least one of the single-step pressure ratios becomes lower than a predetermined single-step threshold value. The threshold values of the two switches can be different from each other. In particular, these threshold values are about 3.
In
The compression chambers can be compression chambers of respective single-action piston-cylinder units 1 or, advantageously, they can be two-by-two coupled as compression chambers of a same double-action piston-cylinder unit, as described hereinafter with reference to
Moreover, the invention is not limited to the preferred exemplary embodiment of
Even in this case, a first open and/or closed state combination of valves V corresponds to the path marked by a continuous line. In these conditions, all at least six compression chambers 2i are parallel connected to each other, so the number N of serially connected compression chambers 2i is one. In this case, a same volume of gas coming from suction environment 80 through inlet port 40 of reciprocating compressor 3 is subjected to a single compression step in a respective compression chamber 2i. In other words, by this open and/or closed state combination of valves V, compression unit 103 comprising compressor 3 and device 4 is in a single-compression-steps configuration.
A second open and/or closed state combination of valves V corresponds to the path marked by a dashed line. In those conditions, all at least six compression chambers 2i are serially connected to each other, and there are no parallel connected compression chambers. In this case, a volume of gas coming from suction environment 80 through inlet port 40 of reciprocating compressor 3 is subjected to at least six compression steps crossing in turn all six or more compression chambers 2i. In other words, by this open and/or closed state combination of valves V, compression unit 103 is in a six(at least)-compression-step configuration.
Even in this case, advantageously, only the configurations are shown that correspond to the minimum number of compression steps, i.e., 1, by the continuous line, and to the maximum number of compression steps, i.e., 6, by a dashed line, since the other possible configurations can be easily deducted from the drawing.
As diagrammatically shown in
As an example, in the following part of the description, reference is made to a closed space 80 that is a section of a compression facility of a gas pipeline comprising a main compressor, while reception space 90 is the gas pipeline itself, at working pressure Pe, which remains substantially unchanged. However, closed space 80 can also be a section of an LNG plant, or of a CO2 recovery and storage plant, or of any technical gas production and storage/distribution plant, or even of a chemical or petrochemical plant, such as a polyolefin production facility, or of any plant where a high-pressure harmful or valuable gas is treated.
In all those applications, initial pressure Psc,0 in closed space 80, i.e., the initial suction pressure of compression unit 104, can be a value set between 25 and 60 bar, in particular 30 and 50 bar, depending on the plant. The predetermined final pressure P* at the end of the evacuation is normally set between 0,1 and 0,2 bar gauge. Pressure Pe in reception space, for example in gas pipeline 90, i.e., the delivery pressure required to compression unit 104, is generally set between 40 and 200 bar gauge. Therefore, as the evacuation of closed space 80 proceeds, the required compression ratio changes from a value R0=Pe/Psc,0, which is generally slightly higher than one, or is the same order of magnitude as one, at the beginning of the evacuation, up to a value R*=Pe/P*, which is generally a few tenths and in some instances about 100, to be achieved at the end of the gas evacuation and conveying process.
As the evacuation proceeds, the evacuation flowrate changes as well. The flowrate can be predetermined by selecting the size of compressor 3, so as to obtain, taking into account the size of plant section 80 to be evacuated, a predetermined total evacuation time t*, which is normally set between 4 and 24 hours. Normally, this flowrate is lower than 500 Kg/h at the beginning of the evacuation.
As shown in
Pistons 14, 24 are preferably connected to a crankshaft, not shown, through respective connecting rods 15, 25, in a conventional way. Accordingly, pistons 14, 24 are arranged to define compression chambers 12, 17 and 22, 27 within cylinders 19, 29, respectively, and to reciprocate within cylinders 19, 29 opposite to each other. In other words, when piston 14 compresses the volume of compression chamber 12 opposite to connecting rod 15 (direct stroke), piston 24 compresses the volume of compression chamber 27 on the same side as connecting rod 25 (backstroke). On the contrary, when piston 14 compresses the volume of compression chamber 17 on the same side as rod 15 (backstroke), piston 24 compresses the volume of compression chamber 22 opposite to connecting rod 25 (direct stroke).
In addition to cylinder-piston units 10, 20, compression unit 105 can comprise a feed tank 41, a shut-off valve V1 arranged upstream of feed tank 41, configured to remain open in any working condition of compression unit 105, a plurality of heat exchangers 43, 48, 52, 57 arranged to cool the gas leaving respective compression chambers 12, 17, 22, 27, and a conventional recycle valve V12 to maintain the pressure upstream of the reciprocating compressor of compression unit 105 above a predetermined value. Recycle valve V12 can be a modulating regulation valve whose opening degree is normally set responsive to the gas intake pressure of compression unit 105, typically by a pressure sensor 42 arranged on feed tank 41 and associated to a pressure regulator PIC.
For example, commutation valves V2-V11 are configured to open and close in such a way to set a two-compression-steps working condition, i.e. a condition in which a same intake gas volume is subjected to two compression steps, or a four-compression-steps working condition, i.e. a condition in which a same intake gas volume is subjected to four compression steps. More in detail, in the two-compression-steps working condition:
This way, two paths are defined for the gas fed through shut-off valve V1 and feed tank 41.
In fact, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a backstroke and a direct stroke, respectively, an amount of gas is withdrawn from feed tank 41 into compression chamber 12 through intake valve 11, while the gas present in compression chamber 17 is transferred into compression chamber 27 through open valves 18, V3, V4, V6 and 26, and the gas present in compression chamber 22 is expelled out of compression unit 105 through valves 23 and V10. Instead, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a direct stroke and a backstroke, respectively, an amount of gas is withdrawn from feed tank 41 into compression chamber 17 through valves V2 and 16, while the gas present in compression chamber 12 is transferred into compression chamber 22 through open valves 13, V4 and 21, and the gas present in compression chamber 27 is expelled out of compression unit 105 through valves 28, V7 and V10.
Therefore, a same volume of gas sucked into compression chamber 12 passes through a first path sequentially defined by elements 11, 12, 13, V4, 21, 22, 23, V10 and is subjected to two compression steps in compression chambers 12 and 22 during the three subsequent backstroke-direct stroke-backstroke of piston 14, while a same volume of gas sucked into compression chamber 17 passes through a second path sequentially defined by elements V2, 16, 17, 18, V3, V4, V6, 26, 27, 28, V7 and V10 and is subjected to two compression steps in compression chambers 17 and 27 during the three subsequent direct stroke-backstroke-direct stroke of piston 14. Therefore, with this open and/or closed state combination of commutation valves V2-V11, the gas withdrawn by compression unit 105 from tank 41 is subjected in any case to two compression steps.
Instead, in the four-compression-steps working condition:
In fact, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a backstroke and a direct stroke, respectively, an amount of gas is withdrawn from feed tank 41 into compression chamber 12 through intake valve 11, while the gas present in compression chamber 17 is transferred into compression chamber 22 through open valves 18, V11, 22 and the gas present in the compression chamber 26 is expelled out of compression unit 105 through valves 28 and V8. Instead, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a direct stroke and a backstroke, respectively, the gas present in compression chamber 12 is transferred into compression chamber 17 through valves 13, V5 and 16, V2 and 16, while the gas present in compression chamber 12 is transferred into compression chamber 22 through open valves 13, V4 and 21, and the gas present in compression chamber 27 is expelled out of compression unit 105 through valves 28, V7 and V10.
Therefore, with this open and/or closed state combination of commutation valves V2-V11, a same volume of gas sucked into compression chamber 12 from tank 41 passes through a single path sequentially defined by elements 11, 12, 13, V5, 16, 17, 18V11, 21, 22, 23, V9, 26, 27.28, V8, in five subsequent backstroke-direct stroke-backstroke-direct stroke-backstroke of piston 14 and is subjected to four compression steps.
Besides cylinder-piston units 10, 20 and feed tank 41, compression unit 106 comprises a delivery tank 49, two shut-off valves W7 and W6 arranged respectively upstream of feed tank 41 and downstream of delivery tank 49, configured to remain open in any working condition of compression unit 106, and also comprises a plurality of heat exchangers, not shown, arranged to cool the gas coming out from respective compression chambers 12, 17, 22, 27. A conventional recycle valve W8 is also provided for maintaining the upstream pressure of the compressor of compression unit 106 above a predetermined value. Recycle valve W8 can have the shape of a modulating regulation valve whose opening degree is normally set responsive to the gas intake pressure of compression unit 106, typically by a pressure sensor arranged on feed tank 41 and associated to a pressure regulator PIC.
Compression unit 106 also comprises a plurality of check valves C1-C7, preferably disc-type check valves.
Commutation valves W1-W5 are configured to open and close in such a way to select, for instance, a single-compression-step working condition, i.e., a working condition in which a same volume of sucked gas is subjected to a single compression step, or a two-compression-steps working condition, i.e., a working condition in which a same volume of sucked gas is subjected to two compression steps, or even a four-compression-steps working condition, i.e., a working condition in which a same volume of sucked gas is subjected to four compression steps.
More in detail, in the single-compression-step working condition, all commutation valves W1-W5 are closed. This way, four paths are defined for the gas fed through shut-off valve W7 and feed tank 41.
In fact, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a backstroke and a direct stroke, respectively, an amount of gas is withdrawn from feed tank 41 into compression chambers 12 and 27 directly and through check valve C6, respectively, while the gas present in compression chambers 17 and 22 is pushed into delivery tank 49 at the outlet of compression unit 106 through check valves C5 and C4, respectively. Instead, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a direct stroke and a backstroke, respectively, an amount of gas is withdrawn from feed tank 41 into compression chambers 17 and 22 through check valve C3 and directly, respectively.
Therefore,
Therefore, with this open and/or closed state combination of commutation valves W1-V5, the gas withdrawn by compression unit 106 from tank 41 is subjected in any case to a single compression step.
Instead, in the two-compression-steps working condition:
In fact, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a backstroke and a direct stroke, respectively, an amount of gas is withdrawn from feed tank 41 into compression chamber 12 through intake valve 11, while the gas present in compression chamber 17 is transferred into compression chamber 27 through open valves 18, W5, 26, and the gas present in compression chamber 22 is expelled out of compression unit 106 through valves 23 and C4. Instead, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a direct stroke and a backstroke, respectively, an amount of gas is withdrawn from feed tank 41 into compression chamber 17 through valves C2 and 16, while the gas present in compression chamber 12 is transferred into compression chamber 22 through open valves 13, W4 and 21, and the gas present in compression chamber 27 is expelled out of compression unit 106 through valve 28.
Therefore, a same volume of gas sucked into compression chamber 12 passes through a first path sequentially defined by elements 11, 12, 13, W4, 21, 22, 23, C4 and is subjected to two compression steps in compression chambers 12 and 22, during the three subsequent backstroke-direct stroke-backstroke of piston 14, while a same volume of gas sucked into compression chamber 17 passes through a second path sequentially defined by elements C2, 16, 17, 18, W5, 26, 27, 28 and is subjected to two compression steps in compression chambers 17 and 27, during the three subsequent direct stroke-backstroke-direct stroke of piston 14. Therefore, with this open and/or closed state combination of commutation valves W1-V5, the gas withdrawn by compression unit 106 from tank 41 is subjected in any case to two compression steps.
Instead, in the four-compression-steps working condition:
In fact, when pistons 14, 24 of the first and of the second cylinder-piston units 10, 20 perform a backstroke and a direct stroke, respectively,
Therefore, with this open and/or closed state combination of commutation valves W1-V5, the gas withdrawn by compression unit 106 from tank 41 is subjected in any case to four compression steps.
In compression unit 106, a cross arrangement of the compression steps is preferred, in order to balance at best the forces exerted by the pistons on the compressor structure.
As shown in
In particular, control unit 60 of compression unit 105 of
In a conceptually similar way, control unit 60 of compression unit 106 of
In
Moreover, in
For instance, compression unit 105, 106 according to the invention can be reserved to the evacuation of a closed space 80. In this case, compression unit 105, 106 will operate in an intermittent service, for example, in connection with plant shutdowns for production or maintenance reasons.
As an alternative, compression unit 105, 106 according to the invention can be also used for other services, in a mixed service including substantially continuous steps for such further services, in a working condition with a suitable number of compression steps selected among the available conditions, and occasionally occurring steps in which a closed space 80 is evacuated.
For example, if closed space 80 include the main compressor, not shown, of a natural gas compression facility, during normal operation of the latter, compression unit 105, 106 can be also used in a substantially continuous service to recover a gas that unavoidably leaks from the compressor seal and, more in general, to recover any plant vent (flare down), and to convey these vent into gas pipeline 90 (
Since the above-mentioned plant vents are normally available at a pressure about 0,2-0,8 bar gauge, which is the same order of magnitude as the pressure in closed space 80 at the end of the evacuation, in the substantially continuous steps of recovering the vents compression units 105, 106 advantageously operate in the same working condition as at the end of an evacuation step, i.e., in both cases, a four-compression-steps working condition.
In the case of compression unit 105 of
In the case of compression unit 106 of
In a further alternative embodiment, compression units 105, 106 equipped with device 4, according to the invention, for changing the compression ratio thereof, can be used in a continuous service as a process compressor, when a gas has to be conveyed from a suction space 80, at a suction pressure, to a delivery space 90, at a delivery pressure, wherein the suction pressure and/or the delivery pressure can change significantly.
With reference to
The foregoing description of exemplary embodiments of the invention will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt these embodiments for various applications without further research and without parting from the invention, and, accordingly, it is meant that such adaptations and modifications will have to be considered as equivalent to the exemplary embodiments. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the scope of the invention. It is to be understood that the phraseology or terminology that is employed herein is for the purpose of description and not of limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020000022762 | Sep 2020 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2021/058871 | 9/28/2021 | WO |
