Controlling turbopump thrust in a heat engine system

Abstract

A heat engine system and a method are provided for generating energy by transforming thermal energy into mechanical and/or electrical energy, and for controlling a thrust load applied to a turbopump of the heat engine system. The generation of energy may be optimized by controlling a thrust or net thrust load applied to a turbopump of the heat engine system. The heat engine system may include one or more valves, such as a turbopump throttle valve and/or a bearing drain valve, which may be modulated to control the thrust load applied to the turbopump during one or more modes of operating the heat engine system.

We claim: 
     
         1 . A heat engine system, comprising:
 a working fluid circuit having a high pressure side and a low pressure side and being configured to flow a working fluid therethrough, the working fluid being at least partially in a supercritical state and comprising carbon dioxide;   a heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit, the heat exchanger fluidly coupled to and in thermal communication with a heat source and configured to transfer thermal energy from the heat source to the working fluid within the high pressure side of the working fluid circuit;   an expander fluidly coupled to and disposed between the high pressure side and the low pressure side of the working fluid circuit and configured to convert a pressure drop in the working fluid to mechanical energy;   a recuperator fluidly coupled to the working fluid circuit and operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit;   a cooler in thermal communication with the working fluid in the low pressure side of the working fluid circuit and configured to remove thermal energy from the working fluid in the low pressure side of the working fluid circuit;   a turbopump fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit and configured to circulate the working fluid through the working fluid circuit;   a turbopump throttle valve coupled to the high pressure side of the working fluid circuit and configured to control a flow of the working fluid to the turbopump, thereby at least partially controlling a thrust load applied to the turbopump;   a bearing housing substantially encompassing one or more bearings contained within the turbopump;   a charging pump fluidly coupled with the working fluid circuit and configured to transfer the working fluid to an inlet of the bearing housing; and   a bearing drain line fluidly coupled to an outlet of the bearing housing, the bearing drain line including a bearing drain valve coupled thereto and configured to control a flow of the working fluid therethrough, thereby at least partially controlling the thrust load applied to the turbopump.   
     
     
         2 . The heat engine system of  claim 1 , further comprising a mass management system fluidly coupled to the working fluid circuit, the mass management system comprising:
 a mass control tank fluidly coupled to the low pressure side of the working fluid circuit and the charging pump, the mass control tank configured to receive the working fluid from the working fluid circuit and to transfer the working fluid to the charging pump.   
     
     
         3 . The heat engine system of  claim 1 , further comprising a bearing gas supply line fluidly coupled to and between the charging pump and the inlet of the bearing housing, the bearing gas supply line including a bearing gas supply valve coupled thereto and configured to control the flow of the working fluid from the charging pump to the bearing housing. 
     
     
         4 . The heat engine system of  claim 1 , wherein the turbopump comprises a pump portion coupled with a drive turbine via a driveshaft, the pump portion coupled between the low pressure side and the high pressure side of the working fluid circuit and configured to be driven by the drive turbine and to circulate the working fluid through the working fluid circuit. 
     
     
         5 . The heat engine system of  claim 4 , wherein the drive turbine is fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit and configured to drive the pump portion by mechanical energy generated by the expansion of the working fluid flowing therethrough. 
     
     
         6 . The heat engine system of  claim 5 , wherein the turbopump throttle valve is configured to control the flow of the working fluid to an inlet of the drive turbine, thereby at least partially controlling the thrust load applied to the turbopump. 
     
     
         7 . The heat engine system of  claim 1 , wherein the bearing drain valve is modulated to at least partially control a pressure of the working fluid contained in the bearing housing to at least partially control the thrust load applied to the turbopump. 
     
     
         8 . The heat engine system of  claim 1 , wherein the bearing drain valve is modulated such that at least a portion of the working fluid in the bearing housing is in a supercritical state. 
     
     
         9 . The heat engine system of  claim 1 , further comprising a process control system operatively and communicably coupled with the bearing drain valve and configured to modulate the bearing drain valve, thereby providing an active thrust control of the turbopump. 
     
     
         10 . The heat engine system of  claim 1 , further comprising a process control system operatively and communicably coupled with the turbopump throttle valve and configured to modulate the turbopump throttle valve, thereby providing an active thrust control of the turbopump. 
     
     
         11 . A heat engine system, comprising:
 a working fluid circuit having a high pressure side and a low pressure side and configured to flow a working fluid therethrough, wherein the working fluid comprises carbon dioxide and is at least partially in a supercritical state;   a heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit, the heat exchanger fluidly coupled to and in thermal communication with a heat source and configured to transfer thermal energy from the heat source to the working fluid within the high pressure side of the working fluid circuit;   an expander fluidly coupled to and disposed between the high pressure side and the low pressure side of the working fluid circuit and configured to convert a pressure drop in the working fluid to mechanical energy;   a recuperator fluidly coupled to the working fluid circuit and operative to transfer thermal energy between the high pressure side and the low pressure side of the working fluid circuit;   a cooler in thermal communication with the working fluid in the low pressure side of the working fluid circuit and configured to remove thermal energy from the working fluid in the low pressure side of the working fluid circuit;   a turbopump comprising a pump portion coupled with a drive portion via a driveshaft, the pump portion coupled between the low pressure side and the high pressure side of the working fluid circuit and configured to be driven by the drive turbine and to circulate the working fluid through the working fluid circuit, the drive portion fluidly coupled between the low pressure side and the high pressure side of the working fluid circuit and configured to drive the pump portion by mechanical energy generated by the expansion of the working fluid flowing therethrough;   a turbopump throttle valve coupled to the high pressure side of the working fluid circuit and configured to control a flow of the working fluid to an inlet of the drive turbine, thereby at least partially controlling the thrust load applied to the turbopump;   a bearing housing substantially encompassing one or more bearings of the turbopump;   a charging pump fluidly coupled with the working fluid circuit and configured to transfer the working fluid to an inlet of the bearing housing; and   a bearing drain line fluidly coupled to an outlet of the bearing housing, the bearing drain line including a bearing drain valve coupled thereto and configured to at least partially control the thrust load applied to the turbopump.   
     
     
         12 . The heat engine system of  claim 11 , further comprising a process control system operatively and communicably coupled with the bearing drain valve and configured to modulate the bearing drain valve, thereby providing an active thrust control of the turbopump. 
     
     
         13 . The heat engine system of  claim 11 , further comprising a process control system operatively and communicably coupled with the turbopump throttle valve and configured to modulate the turbopump throttle valve, thereby providing an active thrust control of the turbopump. 
     
     
         14 . A method for controlling a thrust load applied to a turbopump of a heat engine system, comprising:
 circulating a working fluid through a high pressure side and a low pressure side of a working fluid circuit with the turbopump, wherein at least a portion of the working fluid is in a supercritical state;   transferring thermal energy from a heat source to the working fluid by a heat exchanger fluidly coupled to and in thermal communication with the heat source and the high pressure side of the working fluid circuit;   flowing the working fluid into an expander and converting the thermal energy from the working fluid to mechanical energy of the expander;   flowing a portion of the working fluid from the working fluid circuit through a charging pump to an inlet of a bearing housing substantially encompassing bearings of the turbopump;   modulating a turbopump throttle valve to control a flow of the working fluid to a drive turbine of the turbopump, thereby at least partially controlling the thrust load applied to the turbopump; and   modulating a bearing drain valve to control a flow of the working fluid through a bearing drain line fluidly coupled to an outlet of the bearing housing, thereby at least partially controlling the thrust load applied to the turbopump.   
     
     
         15 . The method of  claim 14 , further comprising:
 flowing a portion of the working fluid from the low pressure side of the working fluid circuit to a mass control tank fluidly coupled to the working fluid circuit; and   flowing the working fluid from the mass control tank to the charging pump.   
     
     
         16 . The method of  claim 14 , wherein modulating the bearing drain valve to at least partially control the thrust load applied to the turbopump further comprises determining an optimum bearing drain pressure to minimize the thrust load applied to the turbopump. 
     
     
         17 . The method of  claim 16 , wherein determining the optimum bearing drain pressure comprises determining the thrust load applied to the turbopump from a pocket pressure ratio thereof. 
     
     
         18 . The method of  claim 16 , further comprising modulating the turbopump throttle valve with a process control system operatively and communicably coupled therewith to minimize the thrust load applied to the turbopump. 
     
     
         19 . The method of  claim 16 , further comprising modulating the bearing drain valve with a process control system operatively and communicably coupled therewith to minimize the thrust load applied to the turbopump. 
     
     
         20 . The method of  claim 16 , further comprising modulating the bearing drain valve such that the working fluid contained in the bearing housing is in a supercritical state.