Patent Description:
Pipeline systems are used to transport fuels such as natural gas or oil from the extraction point to the point of consumption. This consisting mainly of transportations pipelines and distribution pipelines; transportation pipelines are characterized by long pipes with large diameters, transporting fuel between cities, countries and continents, while distribution pipelines comprise pipes with smaller diameter, delivering fuel from transportations pipelines to points of consumption.

The fuel is moved through the transportation pipelines by compression stations along the pipeline which increase the fuel pressure at the station outlet to overcome frictions and losses along the pipeline. The location of the compression stations and the pressure at the station outlet depend on the type of fuel being transported.

The global trend in recent years is to reduce the fossil fraction of fuels to increase the clean fraction of fuel, such as blending natural gas with hydrogen or the use of hydrogen as fuel, wherein the hydrogen can be produced using renewable energy sources or from fossil hydrocarbons wherein the carbon dioxide produced during the reforming process is captured; in these ways, the release of carbon dioxide during the subsequent combustion can be limited or eliminated. Consequently, nowadays gas pipelines need also to be suitable for transporting pure hydrogen or natural gas blended with hydrogen.

However, pure hydrogen has a density that is about one-eighth that of methane (the hydrogen molecular mass is about <NUM> and the methane molecular mass is about <NUM>). So, to transport the same energy as natural gas, pure hydrogen requires more than three times the natural gas volumetric flow and approximately five times the compression power.

Typical drivers employed to drive compressors in gas pipeline compressor stations are: electric motor, reciprocating gas engines, gas turbine engines. For location not served with reliable electro-ducts, the electric motor are not a viable option, and the choice remains between reciprocating engines (for the low power range, typically below 5MW) and gas turbine engines (for the high power range, typically above 5MW). <CIT> discloses a load compressor driven by a gas turbine with a rotor shaft extending through the gas turbine and the load compressor. <CIT> discloses a thermoacoustic driven compressor. <CIT> discloses a turbine-driven reciprocating compressor.

The difference in molecular weight results in an achievable pressure ratio per centrifugal compression stage that is much lower for pure hydrogen than the one achievable with natural gas, thus requiring more compression stages of centrifugal compressors. For this reason, in order to reduce the number of compression stations and the number of compression stages per station, it is possible to use a single reciprocating compressor rather than several centrifugal compressors, driven by a gas turbine engine, to compress pure hydrogen or mixtures of natural gas with hydrogen.

This configuration highlights the problem of the transmission of pulsating torque between the reciprocating compressor and the gas turbine engine. In fact, even if multiple cylinder reciprocating compressors are used in boxer configuration, where each pair of opposed cylinders moves inwards and outwards at the same time, not all reciprocating forces are balanced and torque pulsations are transmitted from the reciprocating compressor to the rotary machine, i.e. the gas turbine.

Finally, considering the lower density of pure hydrogen, at same volumetric flow as natural gas, there are less friction and losses transporting hydrogen and consequently longer distance between gas pipeline compression stations could become possible, in combination with higher compressor discharge pressure of hydrogen (normal gauge pressure of <NUM> bar) than natural gas (normal gauge pressure of <NUM>-<NUM> bar).

Therefore, it would be desirable to have gas pipeline compression stations located at very long distance (><NUM> up and beyond <NUM>), in particular for hydrogen transport in remote location. It would also be desirable to have efficient gas pipeline compression stations from a mechanical and/or emissions points of view. It would further be desirable to have a self-energized gas pipeline compression stations, so that gas transportation is not dependent on external source of energy.

The subject-matter disclosed herein relates to a gas compression system to compress gas transported by a gas pipeline. Gas compression systems are used to recover the pressure loss of the gas pipeline to convey the gas flowing through it to the next gas compression system (or to the end user). The gas compression system disclosed herein compresses the gas by using at least one reciprocating compressor driven by a gas turbine engine advantageously fueled by the same gas transported in the gas pipeline. The gas turbine engine has a high-pressure turbine section and a low-pressure turbine section wherein the low-pressure turbine section is mechanically coupled to the crankshaft of the reciprocating compressor by a mechanical connection such that it minimizes the torque pulsations that the reciprocating machine may transmit to the rotary one, i.e. to the low-pressure turbine section of the gas turbine engine, due to the reciprocating motion. The mechanical connection comprises a gearbox, an elastomeric coupling and a flywheel so that the driver may be well adapted to the load; through the gearbox the rotational speed of the turbine may be adapted to the rotational speed of the reciprocating compressor; through the elastomeric coupling the torque may be transmitted more smoothly considering that the reciprocating compressor offer a non-strictly-constant) torque load; through the flywheel speed oscillations of the reciprocating compressor may be attenuated.

The gas turbine engine has further a combustor section configured to receive the gas transported by the gas pipeline, for example hydrogen, and use it as a fuel, so that the gas compression system may be self-energized by the gas pipeline itself, without the need of an external energy supply. Advantageously, the combustor section is also configured to receive injection of a diluent to reduce reaction zone temperature, and thus reducing thermal NOx formation. More advantageously, the diluent is demineralized water from an external utility source or recovered from air inlet humidity or recovered from the gas turbine exhaust gases.

The subject matter herein disclosed relates to an innovative gas compression system for a gas transported by a gas pipeline that is able to reduce the torque pulsations transmitted between a reciprocating compressor and a gas turbine engine driving the reciprocating compressor. This is achieved by mechanically decoupling a low-pressure turbine section and a high-pressure turbine section of the gas turbine engine but maintaining a fluid coupling between these two sections. Furthermore, the subject matter herein disclosed relates to an innovative gas compression system wherein the gas turbine engine is fueled by gas transported by a gas pipeline.

Reference now will be made in detail to embodiments of the disclosure, examples of which are illustrated in the drawings. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope of the disclosure.

<FIG> schematically shows, for example and without limitation, of an innovative gas compression system generally indicated with reference numeral <NUM>.

According to this example, the gas compression system <NUM> comprises a gas turbine engine <NUM> and a reciprocating compressor <NUM> fluidly connected to a gas pipeline <NUM>; advantageously, the gas pipeline <NUM> may be configured to transport natural gas or hydrogen or natural gas blended with hydrogen.

It is to be noted that the gas transported by the gas pipeline <NUM> may not be a pure gas, for example pure hydrogen, but it may also contain certain percentages of other components. For example, hydrogen can be part of a mixture that also contains ammonia, or hydrogen may be used to blend natural of gas, resulting in a mixture of hydrocarbons (in particular methane, ethane, propane, and higher hydrocarbons in minor percentage), inert gases (in particular nitrogen and carbon dioxide) and hydrogen. The blend of hydrogen (H2) to natural gas (NG) in volume can vary from <NUM>% H2-<NUM>% NG to <NUM>% H2-<NUM>% NG, advantageously the blend is <NUM>% H2-<NUM>% NG.

The gas turbine engine <NUM> and the reciprocating compressor <NUM> are coupled together by a mechanical connection <NUM>. The gas turbine engine <NUM> coupled to the mechanical connection <NUM> may transmit a rotational motion to a crankshaft <NUM> of the reciprocating compressor <NUM>; the crankshaft <NUM> may performs a conversion of the rotational motion transmitted by the gas turbine engine <NUM> to the reciprocating motion of the reciprocating compressor <NUM>. In other words, the gas turbine engine <NUM> may drive the reciprocating compressor <NUM>.

As it will be apparent from the following, the mechanical connection <NUM> is located between the gas turbine engine and the reciprocating compressor <NUM> and is designed in such a way as to minimize the mechanical stresses, in particular torque pulsations, which may be transmitted by the reciprocating compressor <NUM> to the gas turbine engine <NUM> due to reciprocating motion of reciprocating compressor <NUM>.

According to a specific embodiment, the reciprocating compressor <NUM> may have four cylinders, in particular two pairs of opposed cylinders, where each pair of opposed cylinders moves inwards and outwards at the same time with respect to a of the crankshaft <NUM>, which is central with respect to each pair of opposed cylinders; this configuration is known as "boxer configuration". It is to be noted that according to other embodiments, the reciprocating compressor may have a different number of cylinders and/or a different configuration.

Advantageously, each cylinder of the reciprocating compressor <NUM> has a piston connected to the crankshaft <NUM>; each piston is connected to the crankshaft <NUM> by means of a connecting assembly, typically composed by a connecting rod, a crosshead assembly and a piston rod, which may transmit the motion from the crankshaft <NUM> to the piston of the cylinder in order to perform a compression of the gas inside the cylinder. Advantageously, the pistons of the reciprocating compressor <NUM> are each double-acting piston (i.e. the piston compress both in the outward stroke and in the inward stroke with respect to the crankshaft <NUM>).

The big arrow in <FIG> departing from gas pipeline <NUM> indicates that the reciprocating compressor <NUM> is arranged to be fluidly coupled to the gas pipeline <NUM>. For example, considering <FIG>, the gas transported by the gas pipeline may be supplied to the reciprocating compressor <NUM>, in particular to each cylinder of the reciprocating compressor <NUM>, which performs a compression of the gas in order to increase the gas pressure; in other words, the reciprocating compressor <NUM> is arranged to receive and process natural gas or hydrogen or natural gas blended with hydrogen from the gas pipeline <NUM>. It is to be noted that the gas from gas pipeline <NUM> may be split into several streams, each stream being directed to a cylinder of the reciprocating compressor <NUM>. Advantageously, after compression, the gas at the outlet of reciprocating compressor <NUM>, in particular at the outlet of each cylinder of reciprocating compressor <NUM>, is collected and supplied to the next pipe <NUM> of the gas pipeline <NUM> which convey the gas to the next compression station of the gas pipeline or to an end user.

The gas turbine engine <NUM> is the driver of the reciprocating compressor <NUM>, as described above. With non-limiting reference to <FIG>, the gas turbine engine <NUM> comprises an axial compressor section <NUM> that is configured to suck inlet air from the surrounding ambient air and to generate a compressed air flow at an outlet of the axial compressor section <NUM>. Advantageously, air filters are located upstream the axial compressor section to capture smaller contaminants particles or droplets to prevent erosion and/or corrosion and/or fouling of axial compressor section <NUM> and in general of gas turbine engine <NUM>.

The compression section <NUM> of gas turbine engine <NUM> is fluidly coupled to a combustor section <NUM>, located downstream the compressor section <NUM>; in particular, the combustor section <NUM> is configured to receive the compressed air flow from the outlet of the axial compressor section <NUM>.

Advantageously, the combustor section <NUM> is further configured to receive the gas transported by the gas pipeline <NUM> and use it as a fuel, so that the gas turbine engine <NUM> does not require an external source of energy; in other words, the combustor section <NUM> is further configured to receive and process natural gas or hydrogen or natural gas blended with hydrogen from the gas pipeline <NUM>. It is to be noted that the gas received may be injected directly in a combustion chamber of combustor section <NUM> (this is a type of combustion known as "diffusion flame") or may be pre-mixed with the compressed air flow in an area of combustor section <NUM> not yet affected by the flame (this is a type of combustion known as "premixed flame"), depending on the gas received. For example, hydrogen is extremely reactive during combustion, so the simplest technological solution may be to have a diffusion flame instead of a premixed flame depending on the percentage of hydrogen contained in the gas transported by gas pipeline <NUM>. However, the diffusion flame generates higher reaction temperatures with respect to premixed flame and therefore a greater formation of NOx. Hence, the reduction of emission, in particular of NOx, becomes of great importance and can be carried out as explained below.

The combustor section <NUM> of the gas turbine engine <NUM> is fluidly coupled to a turbine section <NUM> located downstream the combustor section <NUM>; in particular, the turbine section <NUM> is configured to receive burned gases from the combustor section <NUM>, as shown in <FIG> by the thin arrow which connects the combustor section <NUM> and the turbine section <NUM>, and perform a first expansion of gases.

The turbine section <NUM> comprises a high-pressure turbine section <NUM> and a low-pressure turbine section <NUM> located downstream the high-pressure turbine section <NUM>. The high-pressure turbine section <NUM> is fluidly coupled to the combustor section <NUM> and has a shaft <NUM>-<NUM> mechanically coupled to a shaft <NUM>-<NUM> of the axial compressor section <NUM>; in other words, the shaft <NUM> has two ends, a first end <NUM>-<NUM> is connected to the axial compressor section <NUM> and a second end <NUM>-<NUM> is connected to the high-pressure turbine section <NUM>, so that the high-pressure turbine section <NUM> may drive the axial compressor section <NUM>.

As shown in <FIG> by the thin arrow which connects the high-pressure turbine section <NUM> and the low-pressure turbine section <NUM>, the high-pressure turbine section <NUM> is fluidly coupled to the low-pressure turbine section <NUM>; in particular, the low-pressure turbine section <NUM> is configured to receive exhaust gases from the high-pressure turbine section <NUM> and perform a second expansion.

The low-pressure turbine section <NUM> has a shaft 21which has a first end <NUM>-<NUM> connected to the low-pressure turbine section <NUM>. The shaft <NUM> is mechanically coupled to the crankshaft <NUM> of reciprocating compressor <NUM>; in particular, the low-pressure turbine section <NUM> may drive the crankshaft <NUM>. It is to be noted that the shaft <NUM>-<NUM> of the low-pressure turbine section <NUM> is mechanically decoupled from the shaft <NUM>-<NUM> of the high-pressure turbine section <NUM> (while they are fluidly coupled), so that only the low-pressure turbine section <NUM> of gas turbine engine <NUM> is mechanically coupled to the reciprocating compressor <NUM> (in particular, only to the reciprocating compressor through other components, e.g. a gearbox and an elastomeric coupling and a flywheel); therefore, the low-pressure turbine section <NUM> may be considered a so-called "free turbine"; advantageously, mechanical torques and motions are only transmitted between the low-pressure turbine section <NUM> and the reciprocating compressor <NUM>, in particular by the shaft <NUM> and the crankshaft <NUM>.

It is to be noted that the high-pressure turbine section <NUM> and the low-pressure turbine section <NUM> may operate at different rotational speed and that these speeds can vary relative to each other. Advantageously, sliding is possible between the shaft <NUM> and the shaft <NUM>, even for long times (minutes).

With non-limiting reference to <FIG>, the gas compression system <NUM> comprises a mechanical connection <NUM> that is mechanically coupled between the low-pressure turbine section <NUM> and the reciprocating compressor <NUM>. Advantageously, the mechanical connection <NUM> is arranged to transmit a rotation motion from the low-pressure turbine section <NUM> to the reciprocating compressor <NUM>, in particular to the crankshaft of the reciprocating compressor <NUM>. Advantageously, the mechanical connection <NUM> is also arranged to dampen and/or minimize the torque pulsations that the reciprocating compressor <NUM> may transmits to the low-pressure turbine section <NUM>, due to the reciprocating motion.

In particular, the mechanical connection <NUM> comprises a gearbox <NUM>; advantageously, the gearbox <NUM> has a first shaft <NUM>-<NUM> on a first side and a second shaft <NUM> on the opposite side to the first side. As shown in <FIG>, the first shaft <NUM>-<NUM> is mechanically coupled to the shaft <NUM>-<NUM> of the low-pressure turbine section <NUM> and the second shaft <NUM> is mechanically coupled to the crankshaft <NUM> of the reciprocating compressor <NUM>; in other words, the shaft <NUM> has a first end connected to the low-pressure turbine section <NUM> and a second end connected to the gearbox <NUM>.

The gearbox <NUM> may be configured to reduce rotational speed of the shaft <NUM> of low-pressure turbine stage <NUM> to the low speed requested by the crankshaft <NUM>. Typically, the speed requested by the crankshaft may be less than <NUM> rpm (rpm=revolutions per minute) and the rotational speed of the low-pressure turbine stage <NUM> may be in the order of <NUM> rpm. Advantageously, the gearbox <NUM> reduces the rotary speed of the shaft <NUM> by at least a <NUM>: <NUM> ratio, preferably by a <NUM>:<NUM> ratio. For example, the rotary speed of the shaft <NUM> may be <NUM> rpm and the rotary speed of the shaft <NUM> may be <NUM> rpm. Advantageously, the gearbox <NUM> is an epicyclic gearbox. More advantageously, the gearbox <NUM> is an epicyclic gearbox with double step of speed-reduction. Advantageously, the gearbox <NUM> may reduce the rotary speed of the shaft <NUM> by a <NUM>:<NUM> ratio, using an intermediate shaft, and then reduce the rotary speed of the intermediate shaft by a <NUM>:<NUM> ratio, corresponding to the rotary speed of the shaft <NUM>. For example, the rotary speed of the shaft <NUM> may be <NUM> rpm, the rotary speed of the intermediate shaft may be <NUM> rpm and the rotary speed of the shaft <NUM> may be <NUM> rpm.

In particular, the mechanical connection <NUM> comprises further an elastomeric coupling <NUM>; advantageously, the elastomeric coupling <NUM> has two connecting elements: a first element that is connected to the second shaft <NUM> of the gearbox <NUM> and a second element that is connected to the crankshaft <NUM>; advantageously, the elastomeric coupling <NUM> has an elastomeric damper located between the first element and the second element, in order to isolate the torque pulsations on the reciprocating compressor <NUM> side only. It is to be noted that the connecting elements of the elastomeric coupling <NUM> may be for example metal hubs or flanges.

In particular, the mechanical connection <NUM> comprises further a flywheel <NUM>; advantageously, the flywheel <NUM> is located between the elastomeric coupling <NUM> and the crankshaft <NUM>; advantageously, the flywheel <NUM> is configured to attenuate speed oscillations of the reciprocating compressor <NUM>. In particular, the flywheel <NUM> is a balanced flywheel optimized to harmonize the rotational effects transmitted between the gas turbine engine <NUM> and the reciprocating compressor <NUM>.

<FIG> and <FIG> refer respectively to a first embodiment <NUM> and a second embodiment <NUM> of a gas compression system. Advantageously, the combustor section <NUM>, <NUM> of the gas compression system <NUM>, <NUM> is configured to receive a diluent to perform low NOx combustion. It is to be noted that NOx gases are a well-known product of combustion, usually produced from the reaction among nitrogen and oxygen during combustion of fuels in air. It is also to be noted that in some countries NOx gases production is restricted, for example by NOx emission limits established by each country.

Typically, NOx gases are produced especially at high temperatures. Advantageously, the injection of a diluent in the combustor section <NUM>, <NUM> of the gas compression system <NUM>, <NUM> lowers the adiabatic flame temperature and influences the formation mechanism of NOx, limiting NOx gases production. It is to be noted that the diluent may be injected directly in the combustor section <NUM>, <NUM>, in particular in the combustion chamber of combustor section <NUM>, <NUM>, or alternatively may be first mixed with the compressed air flow received from the axial compressor section <NUM>,<NUM> or with the gas transported by the gas pipeline <NUM>,<NUM> that is used as fuel.

Advantageously, the diluent is water, in particular demineralized water. Advantageously, the water is recovered from the gas compression system. Additionally or alternatively, the water is supplied from an external source, for example a reverse osmosis system which may perform a water purification process to obtain demineralized water.

A first embodiment <NUM> of a gas compression system will be described in the following with the aid of <FIG>. It is to be noted that elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> in <FIG> may be identical or similar respectively to elements <NUM> (axial compressor section), <NUM> (combustor section), <NUM> (shaft), <NUM> (high-pressure turbine section), <NUM> (low-pressure turbine section), <NUM> (shaft), <NUM> (gearbox), <NUM> (shaft), <NUM> (flywheel), <NUM> (elastomeric coupling), <NUM> (reciprocating compressor), <NUM> (crankshaft), <NUM> (gas pipeline) and <NUM> (next pipe of the gas pipeline) in <FIG> and perform the same or similar functions.

The gas compression system <NUM> of <FIG> comprises a chilling system <NUM> arranged to recover demineralized water from humidity of inlet air flow. Advantageously, the chilling system <NUM> is located upstream the axial compressor section <NUM>. Advantageously, the chilling system <NUM> is located between air filters and the axial compressor section <NUM>.

Typically, in a chilling system, an inlet air flow passes through chilled coils, the air is cooled through indirect heat exchange with a cooling fluid and air humidity condensate on chilled coils when air is cooled below the wet bulb temperature. With non-limiting reference to <FIG>, the chilling system <NUM> has an inlet <NUM> arranged to receive an inlet air flow, in particular an inlet air flow sucked by the axial compressor section <NUM> from the surrounding ambient air; advantageously, the inlet air flow is filtered before entering the chilling system <NUM>.

Advantageously, the chilling system <NUM> has at least two outlets: a first outlet <NUM> is fluidly coupled to the combustor section <NUM> and a second outlet <NUM> is fluidly coupled to the axial compression section <NUM>. Through the first outlet <NUM> the chilling system <NUM> may inject demineralized water in the combustor section <NUM>; advantageously, demineralized water is recovered from condensation of inlet air humidity; advantageously, the demineralized water flow is regulated by at least a valve <NUM> and a pump <NUM>. Through the second outlet <NUM> the chilling system <NUM> may supply cooled inlet air flow to the axial compressor section <NUM>.

Alternative or additionally, the gas compression system <NUM> comprises further a condensate separator arranged to recover demineralized water from humidity of exhaust gases flow.

Advantageously, the condensate separator has at least an inlet fluidly coupled to the low-pressure turbine stage <NUM> and is arranged to receive an inlet exhaust gases flow from the low-pressure turbine stage <NUM>; advantageously, the condensate separator has at least an outlet fluidly coupled to the combustor section <NUM> in order to inject demineralized water in the combustor section <NUM>; advantageously, the demineralized water flow is regulated by at least a valve and a pump.

Alternative or additionally, with non-limiting reference to <FIG>, the gas compression system <NUM> comprises further a reverse osmosis system <NUM> arranged to perform a water purification process to obtain demineralized water. Typically, a reverse osmosis system <NUM> has an inlet <NUM> arranged to receive a water flow and pushes it through a semi-permeable membrane. Advantageously, the reverse osmosis system <NUM> has an outlet <NUM> fluidly coupled to the combustor section <NUM>, in order to inject demineralized water in the combustor section <NUM>.

It is to be noted that demineralized water may be injected in the combustor section in the form of steam.

A second embodiment <NUM> of a gas compression system will be described in the following with the aid of <FIG>. It is to be noted that elements <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> in <FIG> may be identical or similar respectively to elements <NUM> (axial compressor section), <NUM> (combustor section), <NUM> (shaft), <NUM> (high-pressure turbine section), <NUM> (low-pressure turbine section), <NUM> (shaft), <NUM> (gearbox), <NUM> (shaft), <NUM> (flywheel), <NUM> (elastomeric coupling), <NUM> (reciprocating compressor), <NUM> (crankshaft), <NUM> (gas pipeline) and <NUM> (next pipe of the gas pipeline) in <FIG> and perform the same or similar functions.

The gas compression system <NUM> of <FIG> comprises further a steam generator <NUM> arranged to provide heat to the demineralized water. Advantageously, the steam generator is located upstream the combustor section <NUM>; in particular, the steam generator <NUM> has an outlet <NUM> fluidly coupled to the combustor section <NUM>, the outlet <NUM> being arranged to supply steam to the combustor section <NUM>.

Advantageously, the steam generator <NUM> has a first inlet <NUM> fluidly coupled to at least a demineralized water source, for example a chilling system <NUM> or a reverse osmosis group <NUM>.

Advantageously, the steam generator <NUM> has a second inlet <NUM> fluidly coupled to the low-pressure turbine stage <NUM>, in particular to the low-pressure turbine stage outlet where typically exhaust gases are discharged in the surrounding ambient. It is to be noted that exhaust gases may have residual thermal capacity that can be exploited.

Advantageously, the steam generator <NUM> exploits heat from exhaust gases of the low-pressure turbine stage <NUM> and is arranged to provide heat to the demineralized water to generate steam. Steam generator <NUM> may have a second outlet <NUM> where cold exhaust gases are finally discharged in the surrounding ambient.

Claim 1:
A gas compression system (<NUM>) for compressing gas transported by a gas pipeline (<NUM>),
wherein the gas compression system (<NUM>) comprises a gas turbine engine (<NUM>) and a reciprocating compressor (<NUM>),
wherein the gas turbine engine (<NUM>) comprises an axial compressor section (<NUM>), a combustor section (<NUM>), and a turbine section (<NUM>),
wherein the turbine section (<NUM>) comprises a high-pressure turbine section (<NUM>) and a low-pressure turbine section (<NUM>) located downstream the high-pressure turbine section (<NUM>), wherein the low-pressure turbine section (<NUM>) is fluidly coupled to the high-pressure turbine section (<NUM>),
wherein the high-pressure turbine section (<NUM>) has a shaft (<NUM>-<NUM>),
wherein the low-pressure turbine section (<NUM>) has a shaft (<NUM>-<NUM>) mechanically coupled through a mechanical connection (<NUM>) to a crankshaft (<NUM>) of the reciprocating compressor (<NUM>) so to transmit a rotation motion from the low-pressure turbine section (<NUM>) to the reciprocating compressor (<NUM>),
wherein the mechanical connection (<NUM>) comprises a gearbox (<NUM>),
wherein the shaft (<NUM>-<NUM>) of the low-pressure turbine section (<NUM>) is mechanically decoupled from the shaft (<NUM>-<NUM>) of the-high-pressure turbine section (<NUM>) whereby the low-pressure turbine section (<NUM>) operates as a free turbine,
the gas compression system (<NUM>) being characterised in that the mechanical connection (<NUM>) further comprises an elastomeric coupling (<NUM>) and a flywheel (<NUM>).