Source of power in a hydrocarbon well facility

An apparatus for providing a source of power, the apparatus comprising:

• a rotor having external blades for use in causing rotation of the rotor, and internal blades for use in propelling a fluid through the rotor during rotation of the rotor;
• a fluid circuit coupled with the rotor, wherein rotation of the rotor propels fluid in the fluid circuit through the fluid circuit;
• a power device configured to use the fluid propelled through the fluid circuit as a power source;
• wherein the rotor is in a flow path for a second fluid, the rotor being rotatable by the flow of the second fluid through the path;
• a stator in the rotor, such that the first fluid can be propelled between the rotor and the stator;
• wherein the stator has a plurality of external blades interleaved with the internal blades of the rotor so that rotation of the rotor causes the fluid to be propelled between the internal and external blades;
• wherein the volume between adjacent internal blades of the rotor and external blades of the stator decreases in the direction in which the fluid is propelled between the rotor and the stator;
• and
• wherein the rotor is in a flow path for hydrocarbon fluid in a subsea hydrocarbon well facility, the power device using the fluid propelled through the circuit as a power source for the well facility.