Centrifugal separator for separating a liquid mixture with positive displacement pumps respectively downstream of outlets

1 . A centrifugal separator for separation of a liquid mixture comprising:

a stationary frame, a rotatable assembly and a drive unit for rotating the rotatable assembly relative the frame around an axis of rotation,

wherein the rotatable assembly comprises a rotor casing enclosing a separation space in which a stack of separation discs is arranged to rotate around a vertical axis of rotation, and further comprises an exchangeable separation insert and a rotatable member, said exchangeable separation insert comprising said rotor casing and being supported by said rotatable member,

said rotor casing further comprising:

a mechanically hermetically sealed inlet for supply of said liquid mixture to said separation space; and

a first liquid outlet that is mechanically hermetically sealed and arranged for discharge of a separated liquid phase and a second liquid outlet that is mechanically hermetically sealed and arranged for discharge of a separated heavy phase, said heavy phase having a density that is higher than said liquid phase;

at least one second positive displacement pump arranged downstream of said second liquid outlet for transporting the separated heavy phase from said separation space; and

at least one first positive displacement pump arranged downstream of said first liquid outlet for transporting the separated liquid phase from said separation space,

wherein each of said at least one first positive displacement pump and said at least one second positive displacement pump is a peristaltic pump, and

wherein the centrifugal separator is configured such that supply of the liquid mixture to the separation space is solely driven by a suction force generated by at least one of said at least one first positive displacement pump and said at least one second positive displacement pump.

2 . The centrifugal separator according to claim 1 , wherein the at least one second positive displacement pump arranged downstream of said second liquid outlet is configured for stopping the flow of separated heavy phase when not in operation.

3 . The centrifugal separator according to claim 2 , wherein the centrifugal separator is free of any valves between the second liquid outlet and the at least one second positive displacement pump arranged downstream of said second liquid outlet.

4 . The centrifugal separator according to claim 1 , wherein each of the at least one first positive displacement pump and the at least one second positive displacement pump is configured for providing a suction force and/or a counter pressure.

5 . The centrifugal separator according to claim 1 , wherein the centrifugal separator further comprises at least one pressure sensor arranged downstream of said second liquid outlet and a regulating valve arranged downstream of said first liquid outlet, and wherein said valve is configured to operate based on data generated by said pressure sensor.

6 . The centrifugal separator according to claim 1 , wherein the centrifugal separator further comprises at least one pressure sensor arranged downstream of said second liquid outlet, and wherein the at least one second positive displacement pump arranged downstream of said second liquid outlet is configured to operate based on data generated by said pressure sensor.

7 . The centrifugal separator according to claim 1 , wherein the centrifugal separator is free of any valves between the first liquid outlet and the at least one first positive displacement pump arranged downstream of said first liquid outlet.

8 . The centrifugal separator according to claim 1 , wherein the rotatable assembly further comprises at least one outlet conduit for transporting separated heavy phase from the separation space, said conduit extending from a radially outer position of said separation space to said second liquid outlet, said conduit having a conduit inlet arranged at the radially outer position and a conduit outlet arranged at a radially inner position.

9 . The centrifugal separator according to claim 1 , wherein said hermetically sealed inlet is arranged at a first axial end of said rotor casing and arranged so that the liquid mixture to be separated enters said rotor casing at the rotational axis, and

wherein said second liquid outlet is arranged at a second axial end of said rotor casing opposite said first end and arranged so that said separated heavy phase is discharged at the rotational axis.

10 . The centrifugal separator according to claim 1 , wherein the centrifugal separator further comprises a first rotatable seal for sealing and connecting said inlet to a stationary inlet conduit, wherein at least a part of said stationary inlet conduit is arranged around the rotational axis.

11 . The centrifugal separator according to claim 1 , further comprising a second rotatable seal for sealing and connecting said second liquid outlet to a stationary outlet conduit arranged around the rotational axis, and wherein said at least one second positive displacement pump is configured for providing a flow of separated heavy phase in said stationary outlet conduit.

12 . The centrifugal separator according to claim 1 , wherein the exchangeable insert is a disposable insert adapted for single use.

13 . A method for separating a liquid mixture comprising the steps of:

a) providing the centrifugal separator according to claim 1 ;

b) supplying said liquid mixture to be separated to said inlet; and

c) discharging a separated heavy phase via said second mechanically hermetically sealed liquid outlet and a liquid phase via said first hermetically sealed liquid outlet,

wherein the step b) of supplying the liquid mixture to be separated is at least partly performed by applying a suction force and/or a counter pressure with said at least one second positive displacement pump arranged downstream of said second liquid outlet and/or said at least one first positive displacement pump arranged downstream of said first liquid outlet.

14 . The method according to claim 13 , wherein step b) of supplying the liquid mixture to be separated is solely performed by applying a pressure with said at least one second positive displacement pump arranged downstream of said second liquid outlet and/or said at least one first positive displacement pump arranged downstream of said first liquid outlet.

15 . The centrifugal separator according to claim 2 , wherein each of the at least one first positive displacement pump and the at least one second positive displacement pump is configured for providing a suction force and/or a counter pressure.

16 . The centrifugal separator according to claim 3 , wherein each of the at least one first positive displacement pump and the at least one second positive displacement pump is configured for providing a suction force and/or a counter pressure.

17 . The centrifugal separator according to claim 1 , wherein the peristaltic pump comprises a flexible tube connected to a tubing or pipe through which the separated heavy phase is discharged and a rotor with a number of elements arranged for compressing the flexible tube upon rotation.

18 . The centrifugal separator according to claim 1 , wherein the rotor casing includes an axially upper end and an axially lower end, the separation space is defined by a frustoconical portion with a peripheral surface and an imaginary apex pointing toward the axially lower end of the rotor casing, and includes a heavy phase collection space extending from a lower axial position of the peripheral surface to an upper axial position of the peripheral surface, an inner diameter of the heavy phase collection space increases continuously from the lower axial position to the upper axial position, and a radially outermost circumference of the entire stack of separation discs is positioned between the lower axial position and the upper axial position.