Patent Description:
<CIT> discloses a centrifugal compressor with a balancing piston. <CIT> discloses a multistage compressor. <CIT> discloses a centrifugal compressor. <CIT> discloses a cooling circuit for an integrated motor compressor with the features of the preamble of claim <NUM>.

Referring to <FIG>, an integrated motor compressor comprises a common case <NUM> which is tight to the gas handled by the motor compressor, in which are placed an electric motor <NUM> and a compressor group <NUM>, for example a multistaged group comprising a set of impellers <NUM>, <NUM>, <NUM> and <NUM> carried by a shaft <NUM>. The motor <NUM> drives in rotation a rotor <NUM> coupled to the shaft <NUM> of the compressor group <NUM>. Bearings <NUM>, <NUM>, <NUM> and <NUM> are used to support the shaft line of the motor compressor and a thrust balancing and sealing piston <NUM> is mounted on the shaft <NUM>.

The motor compressor <NUM> furthermore comprises a gas suction line <NUM>, a discharge line <NUM>, and an intake line <NUM> for cooling gas extracted from the outlet of the motor compressor.

The torque balancing and sealing piston <NUM> comprises a balancing piston <NUM> to compensate for the differential pressure applied to the impeller wheels <NUM>, <NUM>, <NUM> and <NUM> between the suction pressure and the discharge pressure, and a sealing device <NUM> surrounding the balancing piston <NUM> to render the end of the shaft tight by generating pressure losses.

A leakage flow passes through the piston <NUM> axially and is expelled from the case <NUM> by a leakage line <NUM> connected to the suction line <NUM>.

The gas collected by the leakage line <NUM>, having been compressed by the compressor <NUM>, is at a higher temperature than the temperature of the gas in the suction line <NUM>.

In general, the temperature of the gas admitted at the inlet of the motor compressor is on the order of <NUM> to <NUM> and the temperature of the leakage gas is on the order of <NUM>.

The leakage gas thus increases the temperature of the gas circulating in the suction line <NUM>, reducing the efficiency of the compressor <NUM>.

The discharge line <NUM> is generally connected to a cooler <NUM> in order to cool the compressed gas.

A fraction of the gas leaving the cooler <NUM> is extracted and injected into the case <NUM> by the cooling gas admission line <NUM>. Internally, this line <NUM> is connected to cooling means <NUM> of the case <NUM> in order to cool the electric motor <NUM> and the bearings <NUM>, <NUM>, <NUM> and <NUM>.

In a variant, a fraction of gas leaving a wheel is extracted, cooled, and then injected into the case <NUM>.

The compressed gas extracted at the outlet of the cooler <NUM> or at the outlet of a wheel recirculates in the motor compressor <NUM>, decreasing the efficiency of the motor compressor and reducing the flow rate of gas leaving the cooler.

It is thus proposed to mitigate the drawbacks associated on the one hand with the recirculation of the leakage flow of the thrust balancing and sealing piston and on the other hand the cooling of the motor compressor.

Other characteristics and advantages of the invention will appear upon reading the following description of embodiments of the invention, given solely as nonlimiting examples and referring to the drawings, in which:.

Refer to <FIG>, which illustrates a first embodiment of an integrated motor compressor <NUM>.

The integrated motor compressor <NUM> comprises a common tight case <NUM> in which are placed an electric motor <NUM> and a compressor group <NUM> comprising for example a compression section having a set of impeller wheels <NUM>, <NUM>, <NUM> and <NUM>, carried by a shaft <NUM>. The motor <NUM> drives the rotation of a rotor <NUM> coupled to the shaft <NUM> of the compressor group <NUM>. Bearings <NUM>, <NUM>, <NUM> and <NUM> are used to support the shaft line of the motor compressor, and a balancing and sealing piston <NUM> mounted at one end of the shaft <NUM>.

This piston <NUM> is designed to balance the thrusts acting on the compression stages of the motor compressor under the effect of the differential pressure and to ensure the tightness of the compression section.

The motor compressor <NUM> further comprises a gas suction port <NUM> and a compressed gas discharge port <NUM>, a cooling port <NUM> connected to cooling means <NUM> of the electric motor <NUM> and bearings <NUM>, <NUM>, <NUM> and <NUM>, and a leakage port <NUM> connected to the suction port <NUM>.

The cooling means <NUM> deliver cooling gas.

A leakage flow passes axially through the thrust balancing and sealing piston <NUM> and is expelled from the case <NUM> by the leakage port <NUM>.

The bearings <NUM>, <NUM>, <NUM> and <NUM> may comprise electromagnetic bearings so that the shaft <NUM> is supported when the motor compressor <NUM> is working.

The balancing and sealing piston <NUM> comprises a balancing piston <NUM> to compensate for the differential pressure being applied to the wheels of the compressor <NUM> between the suction pressure and the discharge pressure, and a sealing device <NUM> surrounding the balancing piston <NUM> to render the end of the shaft tight by generating pressure losses.

The piston <NUM> further comprises a gas extraction port <NUM>.

The axial position of the extraction port <NUM> is determined such that the pressure value of the extracted gas is equal to a predetermined value Pext less than the value of the discharge pressure.

The sealing device <NUM> comprises a toothed labyrinth comprising disks which are hollow at their center, distributed along an axial direction so as to create a pressure loss between two adjacent disks, the gas extraction port <NUM> being situated between two adjacent disks.

In a variant, the sealing device <NUM> comprises a seal with a honeycomb geometry, the gas extraction port <NUM> being situated at the center of the seal.

The quantity of hot gas circulating through the leakage port <NUM> is diminished by the quantity of gas extracted by the extraction port <NUM>.

Consequently, the temperature of the gas at the suction port is lower than that in the case of a thrust balancing and sealing piston not having an extraction port.

The efficiency of the motor compressor is improved.

The motor compressor <NUM> further comprises a cooling circuit comprising the balancing and sealing piston <NUM>, a gas cooler <NUM> whose one inlet is connected to the extraction port <NUM> and an outlet is connected to an inlet of a filter <NUM>, one outlet of the filter being connected to a regulating valve <NUM> connected to the cooling means <NUM>.

The cooler <NUM> cools the gas circulating at its inlet.

The cooling circuit further comprises temperature sensors <NUM>, <NUM>, and <NUM> measuring the temperature of the electric motor <NUM> and that of the bearings <NUM> and <NUM>, a processing unit <NUM> controlling the regulating valve <NUM> and receiving the temperature information transmitted by the temperature sensors.

In a variant, each bearing may be equipped with a temperature sensor.

The filter <NUM> filters the gas at the outlet to eliminate particles and water contained in the gas.

The processing unit <NUM> regulates the flow rate of gas injected into the cooling circuit of the motor compressor by the regulating valve <NUM> so that the temperature detected by the temperature sensors <NUM>, <NUM>, and <NUM> is equal to a setpoint temperature Tcons chosen so as not to degrade the electric motor <NUM> and the bearings.

The cooling circuit comprises a temperature control loop.

The processing unit <NUM> is realized for example by a microprocessor.

It may be any device able to control the regulating valve <NUM> such that the temperature detected by the temperature sensors <NUM>, <NUM>, and <NUM> is equal to the setpoint temperature Tcons.

The predetermined value Pext1 of the gas pressure extracted at the extraction port <NUM> is at least equal to the value of the pressure losses generated by the cooling means <NUM>, the cooler <NUM>, the filter <NUM> and the regulating valve <NUM>. It is assumed that the pressure losses generated by the lines connecting the elements of the cooling circuit are negligible as compared to the pressure losses generated by said elements.

In a variant, the cooling circuit does not have a filter <NUM>. The predetermined value Pext2 of the gas pressure extracted at the extraction port <NUM> is at least equal to the value of the pressure losses generated by the cooling means <NUM>, the cooler <NUM> and the regulating valve <NUM>.

According to other embodiments, the cooling circuit does not have a valve <NUM>. The predetermined value Pext3 of the gas pressure extracted at the extraction port <NUM> is equal to the predetermined value Pextl minus the value of the pressure losses generated by the valve <NUM> if the circuit includes the filter <NUM> or to the predetermined value Pext2 minus the value of the pressure losses generated by the valve <NUM>.

The cooling means <NUM> inject the leakage gas escaping from the piston referenced as <NUM>.

Consequently, the cooling gas is not extracted at the discharge port <NUM> or at one of the wheels <NUM>, <NUM>, <NUM> and <NUM>, reducing the recirculation of the gas. The efficiency of the motor compressor is improved.

Refer now to <FIG>, which illustrates a second embodiment of an integrated motor compressor <NUM>.

In the following, the elements identical to those previously described are identified by the same numerical references.

This embodiment differs from the first embodiment in that the cooling circuit further comprises a second cooler <NUM>, whose one inlet is connected to the discharge port <NUM>, and a second regulating valve <NUM> connected to an outlet of the second cooler <NUM>.

In a variant, the inlet of the second cooler <NUM> is connected to the outlet of a wheel <NUM>, <NUM>, <NUM> or <NUM> of the compression section.

The second cooler <NUM> cools the gas leaving the compressor <NUM>.

According to other embodiments, the second regulating valve <NUM> is connected directly to the discharge port <NUM> or to the outlet of a wheel <NUM>, <NUM>, <NUM> or <NUM> of the compression section.

The second regulating valve <NUM> is further connected to the cooling port <NUM>.

The processing unit <NUM> further controls the second regulating valve <NUM> so that when the temperature detected by the temperature sensors <NUM>, <NUM> and <NUM> is greater than the setpoint temperature Tcons and the flow rate of gas injected by the first regulating valve <NUM> is equal to a predetermined maximum flow rate, the flow rate of supplemental gas injected by the second regulating valve in the cooling means <NUM> diminishes the temperature detected by the temperature sensors until it is equal to the setpoint temperature Tcons.

The predetermined maximum flow rate is the maximum flow rate of gas passing through the first regulating valve <NUM>.

In a variant, if the cooling circuit does not contain the first regulating valve <NUM>, the processing unit <NUM> controls the second regulating valve <NUM> so that when the temperature detected by the temperature sensors <NUM>, <NUM> and <NUM> is greater than the setpoint temperature Tcons, the supplemental flow rate of gas injected by the second regulating valve in the cooling means <NUM> diminishes the temperature detected by the temperature sensors until it is equal to the setpoint temperature Tcons.

In this embodiment, if the leakage gas flow rate extracted at the extraction port <NUM> is not sufficient to cool the motor <NUM> and the bearings to the setpoint temperature Tcons, a supplemental gas flow is extracted at the discharge port <NUM>.

The cooling capacity of the cooling circuit is improved.

Since the supplemental gas flow extracted at the discharge port is negligible as compared to the gas flow leaving the compressor <NUM>, the efficiency of the motor compressor is not degraded.

According to other embodiments, the motor compressor <NUM> may comprise several compression sections mounted on its shaft, each compression section being connected to a thrust balancing and sealing piston.

Claim 1:
A cooling circuit for an integrated motor compressor (<NUM>), the cooling circuit comprising:
a balancing and sealing piston system comprising :
- a balancing piston (<NUM>) designed to be mounted on a shaft (<NUM>) of the motor compressor to compensate for the differential pressure being applied to the wheels (<NUM>, <NUM>, <NUM>, <NUM>) of a compression section of the motor compressor between the suction pressure and the discharge pressure; and
- a sealing device (<NUM>) surrounding the balancing piston and designed to be mounted on the case (<NUM>) of the motor compressor (<NUM>) to render the compression section tight,
being characterised in that the balancing and sealing piston system furthermore comprises a gas extraction port (<NUM>), the axial position of the extraction port being determined such that the pressure value of the extracted gas is equal to a predetermined value (Pext) less than the value of the discharge pressure;
- a gas cooler (<NUM>) comprising an inlet connected to the gas extraction port (<NUM>) and an outlet; and
- cooling means (<NUM>) for bearings (<NUM>, <NUM>, <NUM>, <NUM>) and for an electric motor (<NUM>) connected to the outlet of the gas cooler;
the pressure value of the extracted gas (Pext) at the gas extraction port (<NUM>) being at least equal to the value of the pressure losses generated by the gas cooler (<NUM>) and the cooling means (<NUM>).