Cyclone separator for high gas volume fraction fluids

1. A cyclone separator for separating a heavy fraction from a multiphase fluid comprising a mixture of the heavy fraction, a medium fraction and a light fraction, the cyclone separator including:

an elongated cyclone tube which comprises a fluid inlet, a heavy fraction outlet and a flow bore that extends between the fluid inlet and the heavy fraction outlet;

a tubular mandrel which is positioned concentrically within the cyclone tube, the mandrel comprising a central axis, a first end which is located proximate the fluid inlet, a second end which is located between the first end and the heavy fraction outlet, a light fraction outlet that extends generally axially through the mandrel, an outer diameter surface that together with the cyclone tube defines an annular flow path for the multiphase fluid which extends between the fluid inlet and the flow bore, and a discharge port that extends along the central axis through the second end of the mandrel and connects the light fraction outlet with the flow bore;

the outer diameter surface comprising a generally cylindrical section which extends from proximate the fluid inlet toward the second end, and a convergence section which extends between the cylindrical section and the discharge port;

the mandrel further comprising a plurality of discharge holes which extend through the convergence section between the flow path and the light fraction outlet;

wherein in operation of the cyclone separator, the multiphase fluid flows through the fluid inlet and the flow path and is separated into the light fraction, the medium fraction and the heavy fraction, and wherein the light fraction flows through the discharge holes and is discharged through the light fraction outlet, the medium fractions flows through the discharge port and is discharged through the light fraction outlet, and the heavy fraction flows through the flow bore and is discharged through the heavy fraction outlet.

2. A method for separating a heavy fraction from a multiphase fluid comprising a mixture of the heavy fraction, a medium fraction and a light fraction, the method comprising:

providing a cyclone separator which includes an elongated cyclone tube having a fluid inlet, a heavy fraction outlet and a flow bore that extends generally axially from the fluid inlet to the heavy fraction outlet;

positioning a tubular mandrel concentrically within the flow bore, the mandrel comprising a central axis, a first end which is located proximate the fluid inlet, a second end which is located between the first end and the heavy fraction outlet, a discharge port which extends along the central axis through the second end, a cylindrical section which extends from proximate the fluid inlet toward the second end, and a convergence section which extends between the cylindrical section and the discharge port;

introducing the multiphase fluid into the flow bore through the fluid inlet;

rotating the multiphase fluid to cause it to separate into the heavy fraction, the medium fraction and the light fraction;

discharging the heavy fraction through the heavy fraction outlet;

discharging the medium fraction through the discharge port; and

discharging the light fraction through a number of discharge holes which extend through the convergence section of the mandrel.

3. The method of claim 2 , wherein the light and medium fractions are discharged through a light fraction outlet which extends through the mandrel and is connected to both the discharge port and the discharge holes.

4. A method for retrofitting an existing cyclone separator comprising a cyclone tube and a tubular mandrel which is positioned concentrically within the cyclone tube, the cyclone tube including a fluid inlet, a heavy fraction outlet and an axial flow bore extending between the fluid inlet and the heavy fraction outlet, and the mandrel including a light fraction outlet and a substantially solid outer surface which extends from proximate the fluid inlet toward an outlet port that connects the flow bore to the light fraction outlet, the method comprising:

removing the mandrel from the cyclone tube; and

replacing the mandrel with a modified tubular mandrel which comprises a light fraction outlet that extends axially therethrough, central axis, a first end located proximate the fluid inlet, a second end located between the first end and the heavy fraction outlet, a substantially solid outer surface which extends from proximate the first end to the second end, a discharge port that extends along the central axis through the second end of the mandrel and connects the flow bore to the light fraction outlet, and a number of discharge holes which connect the flow bore to the light fraction outlet between the discharge port and the fluid inlet;

wherein the outer surface of the modified mandrel comprises a cylindrical section extending from adjacent the first end and a convergence section extending between the cylindrical section and the discharge port; and

wherein the discharge holes are located in the convergence section upstream of the discharge port.