Subsea motor-turbomachine

Abstract

Subsea pressure booster comprising an electric motor ( 2 ) and a compressor ( 3 ), multiphase pump or pump driven by the electric motor, for boosting the pressure of a subsea flow comprising petroleum gas or liquid, distinctive in that the pressure booster comprises a common pressure housing ( 1 ) for the electric motor and compressor, multiphase pump or pump; a diaphragm separating the common pressure housing into two compartments, one compartment for the electric motor and one compartment for the compressor; multiphase pump or pump; a shaft connecting the electric motor to the compressor, multiphase pump or pump; and at least one oil lubricated mechanical shaft seal arranged between the shaft and diaphragm; and bearings on the shaft, preferably at least two radial and one axial oil lubricated bearings ( 4, 4′, 4 ″) for an oil filled or gas filled motor compartment or magnetic bearings or oil lubricated bearings for a gas filled motor compartment.

1 . A subsea pressure booster comprising:
 an electric motor;   a compressor, multiphase pump or pump driven by the electric motor, for boosting a pressure of a subsea flow comprising petroleum gas or liquid;   a common pressure housing for the electric motor and the compressor;   a diaphragm separating the common pressure housing into a first compartment for the electric motor and a second compartment for the compressor;   a shaft connecting the electric motor to the compressor; and   at least one oil lubricated mechanical shaft seal arranged between the shaft and the diaphragm; and   a plurality of bearings disposed on the shaft.   
     
     
         2 . The subsea pressure booster according to  claim 1  wherein a lube oil pressure in the at least one seal between the first compartment and the second compartment is higher than both a compressor suction pressure and an internal motor pressure. 
     
     
         3 . The subsea pressure booster according to  claim 2  wherein the internal motor pressure is a pressure of a first compressor impeller which internal motor pressure is transmitted into the electric motor by a tube. 
     
     
         4 . The subsea pressure booster according to  claim 2  wherein the internal motor pressure is equal to the compressor suction pressure which internal motor pressure is transmitted to the electric motor by a tube. 
     
     
         5 . The subsea pressure booster according to  claim 3  wherein a cooler is disposed in a tube or and arranged such that condensate does not flow into the electric motor but into the compressor. 
     
     
         6 . The subsea pressure booster according to  claim 1  wherein gas pressure above a lube oil in a lube oil tank is equal to a pressure of a first impeller, which pressure is transmitted to the to the lube oil tank from the first impeller by a tube. 
     
     
         7 . The subsea pressure booster according to  claim 1  wherein the pressure above a lube oil in a lube oil tank in the motor is supplied from a nitrogen reservoir. 
     
     
         8 . The subsea pressure booster according to  claim 1  comprising an arrangement for handling oil drained out of the electric motor and the compressor. 
     
     
         9 . The subsea pressure booster according to  claim 8  wherein oil that has leaked into the electric motor is pumped back to a lube oil circuit. 
     
     
         10 . The subsea pressure booster according to  claim 1  wherein a oil lubricated step-up gear is arranged between the electric motor and the compressor on a motor side of the at least one seal. 
     
     
         11 . The subsea pressure booster according to  claim 1 , wherein the electric motor is operatively connected to drive the compressor directly via at least one of a common shaft, a coupling, or a gear coupling connecting a motor shaft to a compressor shaft;
 wherein the compressor comprises at least one oil lubricated mechanical shaft seal;   wherein a lube oil pressure means providing control of a lubrication oil pressure the lubrication oil pressure is higher than or equal to a motor housing pressure and a compressor suction pressure at all operating conditions.   
     
     
         12 . The subsea pressure booster according to  claim 1 , wherein the motor housing is filled with a gas. 
     
     
         13 . The subsea pressure booster according to  claim 12 , comprising a motor gas means controlling a pressure and reducing a humidity of the gas. 
     
     
         14 . The subsea pressure booster according to  claim 11 , wherein the motor and the compressor are connected via at least one shaft;
 a common pressure housing encapsulates the motor and the compressor;   a partition in the common pressure housing separates the common pressure housing into a motor housing and a compressor housing;   a lubrication oil tank is arranged at a higher elevation than the common pressure housing;   lubrication oil lines are arranged from a lower oil filled part of the lubrication oil tank to mechanical seals at either end of the shaft and at either side of the partition;   a line is arranged from a first stage of the compressor to an upper gas filled part of the lubrication oil tank;   the elevation of the lubrication oil tank and variable overpressure provided by the line from the compressor first stage provide an automatically adjustable lubrication oil overpressure;   the motor housing is operatively connected to a lubrication oil drain tank;   a pressure balancing line is arranged from the first stage of the compressor to the motor housing; and   a gas drying device such as a sea water cooled heat exchanger and a MEG injection means is arranged in or operatively connected to the pressure balancing line.   
     
     
         15 . The subsea pressure booster according to  claim 1 , wherein the mechanical shaft seals comprise a spring or another biasing element which together with lube oil pressure means provide closing of the seal dependent on the rotations per minute (rpm) of the shaft, from a closed position at 0 rpm to a maximum open position at maximum rpm. 
     
     
         16 . The subsea pressure booster according to  claim 1 , wherein a lubrication oil tank has ROV-operable connections and lifting means in order to be replaceable by an ROV (Remotely Operable Vehicle). 
     
     
         17 . The subsea pressure booster according to  claim 1 , comprising lube oil pressure means as a separate lubrication oil tank arranged at a higher elevation than the compressor pressure housing for each mechanical seal or group of mechanical seals operating at common pressure;
 a lubrication oil line is via an oil filled part of a piston cylinder arranged from a lower oil filled part of the lubrication oil tank to the or each mechanical seal;   a one way valve is arranged in the lubrication oil line between a cylinder and the lubrication oil tank;   the valve is directed to open up for lubrication oil supply from the lubrication oil tank only when a seal pressure is below a tank pressure;   a line is arranged from a first pressure stage of the compressor to an upper gas filled part of the lubrication oil tank;   a line is arranged from a second pressure stage to a gas filled side of a piston cylinder, the piston cylinder may include a spring providing a minimum overpressure of the mechanical seal or the pressure of the second pressure stage minus the first pressure stage may provide the overpressure, said overpressure being in the range 40-0 bar.   
     
     
         18 . The subsea pressure booster according to  claim 1 , wherein a lube oil tank can be arranged beside or under the electric motor if pressure above a lube oil is supplied from a compressor impeller.