Apparatus and Method For Controlling Supply of Barrier Gas in a Compressor Module

Abstract

An apparatus for controlling the supply of barrier gas to a compressor module includes a pressure housing containing an electric motor which via a shaft is drivably connected to a compressor. The shaft is supported by magnetic bearings and at least one axial seal around the shaft which divides the pressure housing into first and second compartments including the motor and compressor, respectively. The second compartment has fluid inlet and outlet. A line is fluid-connected to the first compartment for barrier gas from a reservoir, with a flow restriction element between the reservoir and first compartment. The apparatus facilitates a method for controlling the supply of barrier gas based on gas velocity through the seal and pressure in the second compartment. An overpressure can be set in the reservoir. A controlled supply of barrier gas to at least the first compartment is effected via flow restriction in the feed pipe.

1 . An apparatus for controlling the supply of barrier gas to a compressor module comprising a pressure housing ( 3 ) containing an electric motor ( 1 ) which via a shaft ( 8 ) is drivably connected to a compressor ( 2 ), wherein the shaft ( 8 ) is supported by magnetic bearings ( 11 ,  21 ) and an axial seal ( 31 ) around the shaft ( 8 ) divides the pressure housing into a first compartment ( 10 ) comprising the motor ( 1 ) and a second compartment ( 20 ) comprising the compressor ( 2 ), the second compartment ( 20 ) comprising an inlet ( 4 ) and an outlet ( 5 ) for fluid that is to be compressed, characterised by a line ( 7 ) fluid-connected to the first compartment ( 10 ) for the supply of barrier gas from a reservoir ( 6 ), and a control device ( 71 ) in the line between the reservoir ( 6 ) and the first compartment ( 10 ). 
   
   
       2 . An apparatus for controlling the supply of barrier gas to a compressor module comprising a pressure housing ( 3 ) containing an electric motor ( 1 ) which via a shaft ( 8 ) is drivably connected to a compressor ( 2 ), wherein the shaft ( 8 ) is supported by first magnetic bearings ( 11 ) and at least one second magnetic bearing ( 21 ) on the opposite side of the compressor in relation to the first magnetic bearings ( 11 ), and an axial seal ( 31 ) around said shaft ( 8 ) divides the pressure housing into a first compartment ( 10 ) comprising the motor ( 1 ) and a second compartment ( 20 ) comprising the compressor ( 2 ), the second compartment ( 20 ) comprising an inlet ( 4 ) and an outlet ( 5 ) for fluid that is to be compressed, and wherein a further axial seal ( 32 ) is fitted around the shaft ( 8 ) between the compressor ( 2 ) and the said second magnetic bearing ( 32 ), thereby forming a third compartment ( 30 ), characterised by a line ( 7 ) fluid-connected to the first compartment ( 10 ) and a line ( 7 ′;  7 ″) fluid-connected to the third compartment ( 30 ), wherein the lines ( 7 ,  7 ′;  7 ″) are arranged for the supply of barrier gas from a reservoir ( 6 ), and respective control devices ( 71 ,  71 ′) in the line between the reservoir ( 6 ) and the first compartment ( 10 ) and the third ( 30 ) compartment, respectively. 
   
   
       3 . An apparatus according to  claim 1 , characterised in that the barrier gas is any gas mixture that is dry, free of particles (as low a particle content as practically possible), and which is inert with respect to the materials in the motor and the magnetic bearings. 
   
   
       4 . An apparatus according to  claim 3 , characterised in that the barrier gas is hydrogen. 
   
   
       5 . An apparatus according to  claim 1 , characterised in that the reservoir ( 6 ) comprises a supply line ( 9 ) connected to another gas source. 
   
   
       6 . An apparatus according to  claim 1 , characterised in that the control device ( 71 ;  71 ′) is a flow restriction means. 
   
   
       7 . An apparatus according to  claim 1 , characterised in that the control device ( 71 ;  71 ′) comprises a plurality of chokes ( 79 ′) arranged in parallel. 
   
   
       8 . A method for controlling the supply of barrier gas to a compressor module as disclosed in  claim 1 , characterised by, on the basis of required barrier gas velocity (v g ) through the seal ( 31 ;  32 ) and the pressure (p s ) in the second compartment ( 20 ), setting an overpressure (p a ) in the reservoir ( 6 ), and effecting a controlled supply of barrier gas to at least the first compartment ( 10 ) by means of the flow restriction ( 71 ;  71 ′) in the feed pipe ( 7 ;  7 ′). 
   
   
       9 . A method according to  claim 8 , characterised in that the flow restriction ( 71 ;  71 ′) is controlled so that it provides a volume flow of barrier gas into at least the first compartment ( 10 ), which at least provides the necessary barrier gas velocity (v g ) through the seal. 
   
   
       10 . A method according to  claim 8 , characterised in that the choke ( 71 ;  71 ′) is controlled so that it gives a fixed mass flow of barrier gas into at least the first compartment ( 10 ), which at least provides the required barrier gas velocity (v g ) through the seal. 
   
   
       11 . A method according to  claim 10 , characterised in that the overpressure (p a ) in the reservoir ( 6 ) is kept constant, and that the flow restriction is controlled on the basis of pressure drop across a metering orifice. 
   
   
       12 . A method according to  claim 8 , characterised in that the flow restriction is kept constant and that the overpressure (p a ) in the reservoir ( 6 ) is adjusted in response to a change in the pressure (p s ) in the second compartment ( 20 ). 
   
   
       13 . A method according to  claim 8 , characterised in that the overpressure (p a ) in the reservoir is kept constant and the flow restriction is adjusted on the basis of measured pressure droop across the restriction ( 71 ;  71 ′). 
   
   
       14 . An apparatus according to  claim 2 , characterised in that the barrier gas is any gas mixture that is dry, free of particles (as low a particle content as practically possible), and which is inert with respect to the materials in the motor and the magnetic bearings. 
   
   
       15 . An apparatus according to  claim 2 , characterised in that the reservoir ( 6 ) comprises a supply line ( 9 ) connected to another gas source. 
   
   
       16 . An apparatus according to  claim 2 , characterised in that the control device ( 71 ;  71 ′) is a flow restriction means. 
   
   
       17 . An apparatus according to  claim 2 , characterised in that the control device ( 71 ;  71 ′) comprises a plurality of chokes ( 79 ′) arranged in parallel. 
   
   
       18 . A method for controlling the supply of barrier gas to a compressor module as disclosed in  claim 2 , characterised by, on the basis of required barrier gas velocity (v g ) through the seal ( 31 ;  32 ) and the pressure (p s ) in the second compartment ( 20 ), setting an overpressure (p a ) in the reservoir ( 6 ), and effecting a controlled supply of barrier gas to at least the first compartment ( 10 ) by means of the flow restriction ( 71 ;  71 ′) in the feed pipe ( 7 ;  7 ′).