Active thrust management of a turbopump within a supercritical working fluid circuit in a heat engine system

A turbopump system for circulating or pressurizing a working fluid within a working fluid circuit, comprising:

• a turbopump comprising:
• a drive turbine configured to convert a pressure drop in the working fluid to mechanical energy;
• a pump portion configured to circulate or pressurize the working fluid within the working fluid circuit;
• a driveshaft coupled to and between the drive turbine and the pump portion, wherein the drive turbine is configured to drive the pump portion via the driveshaft;
• a thrust bearing circumferentially disposed around the driveshaft and between the drive turbine and the pump portion, the thrust bearing further comprises:
• a cylindrical body having a central axis and containing an inner portion and an outer portion aligned with the central axis;
• a pump-side thrust face comprising a plurality of pump-side bearing pockets extending below the pump-side thrust face and facing the pump portion;
• a turbine-side thrust face comprising a plurality of turbine-side bearing pockets extending below the turbine-side thrust face and facing the drive turbine;
• a circumferential side surface extending along the circumference of the cylindrical body and between the pump-side thrust face and the turbine-side thrust face;
• and
• a central orifice defined by and extending through the cylindrical body along the central axis and configured to provide passage of the driveshaft therethrough;
• a housing at least partially encompassing the driveshaft and the thrust bearing;
• a bearing fluid supply line fluidly coupled to the housing and configured to provide a bearing fluid into the housing;
• a bearing fluid drain line fluidly coupled to the housing and configured to remove the bearing fluid from the housing;
• a turbopump back-pressure regulator valve fluidly coupled to the bearing fluid drain line and configured to control flow through the bearing fluid drain line, a turbopump back-pressure regulator valve fluidly coupled to the bearing fluid drain line and configured to control flow through the bearing fluid drain line;
• a process control system operatively connected to the turbopump back-pressure regulator valve, configured to:
• adjust the turbopump back-pressure regulator valve with a control algorithm embedded in a computer system;
• and
• monitor the turbine-side pocket pressure ratio (P1), the pump-side pocket pressure ratio (P2), a bearing fluid supply pressure, and a bearing fluid drain pressure;
• wherein the control algorithm comprises:
• a primary governing loop controller configured to modulate the turbopump back-pressure regulator valve while adjusting a pump-side pocket pressure ratio (P2);
• a secondary governing loop controller configured to modulate the turbopump back-pressure regulator valve while adjusting a turbine-side pocket pressure ratio (P1);
• and
• a tertiary governing loop controller configured to modulate the turbopump back-pressure regulator valve while adjusting the bearing fluid supply pressure to be at or greater than a critical pressure value for the bearing fluid to maintain the bearing fluid in a supercritical state.

A method for lubricating a turbopump in a heat engine system, comprising:

• circulating a working fluid throughout a working fluid circuit with the turbopump, wherein the working fluid circuit has a high pressure side and a low pressure side and at least a portion of the working fluid is in a supercritical state;
• transferring thermal energy from a heat source stream to the working fluid through at least one heat exchanger, wherein the heat exchanger is fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit and fluidly coupled to and in thermal communication with the heat source stream;
• monitoring a turbine-side pocket pressure ratio (P1), a pump-side pocket pressure ratio (P2), a bearing fluid supply pressure, and a bearing fluid drain pressure via a process control system operatively coupled to the working fluid circuit, wherein P1 equals the pocket pressure on a turbine-side thrust face in the turbine-side bearing pocket minus the drain pressure of the bearing fluid divided by the supply pressure of the bearing fluid minus the drain pressure of the bearing fluid and P2 equals the pocket pressure on a pump-side thrust face in the pump side bearing pocket minus the drain pressure of the bearing fluid divided by the supply pressure of the bearing fluid minus the drain pressure of the bearing fluid, and
• wherein the turbine-side pocket pressure ratio (P1) is monitored in at least one turbine-side bearing pocket of a plurality of turbine-side bearing pockets disposed on the turbine-side thrust face of a thrust bearing within the turbopump, the pump-side pocket pressure ratio (P2) is monitored in at least one pump-side bearing pocket of a plurality of pump-side bearing pockets disposed on a pump-side thrust face of the thrust bearing, the bearing fluid supply pressure is monitored in at least one bearing supply pressure line disposed upstream of the thrust bearing, and the bearing fluid drain pressure is monitored in at least one bearing drain pressure line disposed downstream of the thrust bearing;
• controlling a turbopump back-pressure regulator valve by a primary governing loop
• controller embedded in the process control system, wherein the turbopump back-pressure regulator valve is fluidly coupled to a bearing fluid drain line disposed downstream of the thrust bearing and the primary governing loop controller is configured to modulate the turbopump back-pressure regulator valve while adjusting the pump-side pocket pressure ratio (P2);
• controlling the turbopump back-pressure regulator valve by a secondary governing loop controller embedded in the process control system, wherein the secondary governing loop controller is configured to modulate the turbopump back-pressure regulator valve while adjusting the turbine-side pocket pressure ratio (P1);
• and
• controlling the turbopump back-pressure regulator valve by a tertiary governing loop controller embedded in the process control system, wherein the tertiary governing loop controller is configured to modulate the turbopump back-pressure regulator valve while adjusting the bearing fluid supply pressure to be at or greater than a critical pressure value for the bearing fluid to maintain the bearing fluid in a supercritical state.