Bypass and throttle valves for a supercritical working fluid circuit

Abstract

Aspects of the invention disclosed herein generally provide heat engine systems and methods for recovering energy, such as by generating electricity from thermal energy. Generally, the heat engine system has a working fluid circuit containing a working fluid (e.g., sc-CO 2 ) for absorbing thermal energy from the heat source stream via a heat exchanger. In one aspect, the method includes controlling a power turbine by modulating a turbo pump throttle valve and a power turbine bypass valve to adjust the flowrate of the working fluid entering the power turbine while monitoring and controlling process operation parameters of the heat engine system to synchronize the frequency of the power generator to the frequency of the electrical grid during a synchronization process.

1 . A method for generating electricity with a heat engine system, comprising:
 circulating a working fluid within a working fluid circuit by a turbo pump, wherein the working fluid comprises carbon dioxide and the working fluid circuit has a high pressure side and a low pressure side and at least a portion of the working fluid circuit contains the working fluid in a supercritical state;   transferring thermal energy from a heat source stream to the working fluid by at least a primary heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit;   flowing the working fluid into a power turbine and transferring the thermal energy from the working fluid to the power turbine while converting a pressure drop in the working fluid to mechanical energy, wherein the power turbine is disposed between the high pressure side and the low pressure side of the working fluid circuit and fluidly coupled to and in thermal communication with the working fluid;   converting the mechanical energy into electrical energy by a power generator coupled to the power turbine;   transferring the electrical energy from the power generator to a power outlet, wherein the power outlet is electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid;   controlling the power turbine by modulating a turbo pump throttle valve and a power turbine bypass valve by adjusting a flowrate of the working fluid entering the power turbine, wherein:
 the turbo pump throttle valve is fluidly coupled to the working fluid circuit upstream of an inlet of a drive turbine of the turbo pump and configured to modulate a flow of the working fluid into the drive turbine; and 
 the power turbine bypass valve is fluidly coupled to a power turbine bypass line extending from a point disposed upstream of the inlet of the power turbine and to a point disposed downstream of an outlet of the power turbine, and the power turbine bypass valve is configured to modulate a flow of the working fluid through the power turbine bypass line for controlling the flowrate of the working fluid entering the power turbine; and 
   monitoring and controlling process operation parameters of the heat engine system via a process control system operatively connected to the heat engine system, wherein the process control system is configured to synchronize a generator frequency of the power generator to a grid frequency of the electrical grid.   
     
     
         2 . The method of  claim 1 , further comprising synchronizing the generator frequency of the power generator to the grid frequency of the electrical grid with the process control system by controlling the power turbine via operation of the turbo pump throttle valve and the power turbine bypass valve, wherein the flow of the working fluid is modulated by the power turbine bypass valve to control the flowrate of the working fluid entering the power turbine, and the flow of the working fluid is modulated by the turbo pump throttle valve to control the flowrate of the working fluid entering the drive turbine. 
     
     
         3 . The method of  claim 1 , further comprising:
 transferring thermal energy from the heat source stream to the working fluid by a secondary heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit; and   flowing the heated working fluid from the secondary heat exchanger to the drive turbine of the turbo pump via the turbo pump throttle valve.   
     
     
         4 . The method of  claim 1 , further comprising transferring thermal energy from the heat source stream to the working fluid via the primary heat exchanger and a secondary heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit. 
     
     
         5 . The method of  claim 4 , wherein the primary heat exchanger is fluidly coupled to the working fluid circuit upstream of the power turbine and downstream of a recuperator. 
     
     
         6 . The method of  claim 5 , wherein the recuperator is fluidly coupled to the working fluid circuit and configured to transfer thermal energy from the working fluid within the low pressure side to the working fluid within the high pressure side of the working fluid circuit. 
     
     
         7 . The method of  claim 4 , wherein the secondary heat exchanger is fluidly coupled to the working fluid circuit upstream of an outlet of the pump portion of the turbo pump and downstream of the inlet of the drive turbine of the turbo pump, and the turbo pump throttle valve is fluidly coupled to the working fluid circuit downstream of the secondary heat exchanger and upstream of the inlet of the drive turbine of the turbo pump. 
     
     
         8 . The method of  claim 4 , further comprising a recuperator is fluidly coupled to the working fluid circuit downstream of an outlet of the pump portion of the turbo pump and upstream of the secondary heat exchanger and configured to transfer thermal energy from the working fluid within the low pressure side to the working fluid within the high pressure side of the working fluid circuit, wherein the secondary heat exchanger is fluidly coupled to the working fluid circuit upstream of the outlet of the pump portion of the turbo pump and downstream of the inlet of the drive turbine of the turbo pump, 
     
     
         9 . The method of  claim 1 , further comprising controlling the power turbine by modulating the turbo pump throttle valve, the power turbine bypass valve, and a turbo pump bypass valve by adjusting the flowrate of the working fluid entering the power turbine. 
     
     
         10 . The method of  claim 9 , wherein the process control system is configured to synchronize the power generator to the electrical grid by controlling the power turbine while operating the turbo pump throttle valve, the turbo pump bypass valve, and the power turbine bypass valve to adjust the flow of the working fluid. 
     
     
         11 . A method for generating electricity with a heat engine system, comprising:
 circulating a working fluid within a working fluid circuit by a turbo pump, wherein the working fluid contains carbon dioxide and the working fluid circuit has a high pressure side and a low pressure side;   transferring thermal energy from a heat source stream to the working fluid by at least one heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit;   flowing the working fluid through a power turbine and converting the thermal energy in the working fluid to mechanical energy in the power turbine;   converting the mechanical energy into electrical energy by a power generator coupled to the power turbine;   transferring the electrical energy from the power generator to an electrical grid electrically coupled to the power generator; and   synchronizing a generator frequency of the power generator to a grid frequency of the electrical grid by modulating a turbo pump throttle valve and a power turbine bypass valve during a synchronization process.   
     
     
         12 . The method of  claim 11 , wherein the synchronization process further comprises:
 adjusting a flowrate of the working fluid entering the power turbine by modulating the turbo pump throttle valve and the power turbine bypass valve;   adjusting the rotational speed of the power turbine by adjusting the flowrate of the working fluid entering the power turbine;   adjusting the rotational speed of the power generator by adjusting the rotational speed of the power turbine; and   adjusting the generator frequency to be synchronized with the grid frequency by adjusting the rotational speed of the power generator.   
     
     
         13 . The method of  claim 11 , further comprising synchronizing the generator frequency of the power generator to the grid frequency of the electrical grid by modulating the turbo pump throttle valve, the power turbine bypass valve, and a turbo pump bypass valve during the synchronization process. 
     
     
         14 . The method of  claim 13 , wherein the process control system is configured to synchronize the power generator to the electrical grid by controlling the power turbine while operating the turbo pump throttle valve, the turbo pump bypass valve, and the power turbine bypass valve to adjust the flow of the working fluid during the synchronization process. 
     
     
         15 . A heat engine system for generating electricity, comprising:
 a working fluid circuit containing a working fluid and having a high pressure side and a low pressure side, wherein the working fluid comprises carbon dioxide and at least a portion of the working fluid circuit contains the working fluid in a supercritical state;   a primary heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit, configured to be fluidly coupled to and in thermal communication with a heat source stream, and configured to transfer thermal energy from the heat source stream to the working fluid;   a power turbine disposed between the high pressure side and the low pressure side of the working fluid circuit, fluidly coupled to and in thermal communication with the working fluid, and configured to convert thermal energy to mechanical energy by a pressure drop in the working fluid flowing between the high and the low pressure sides of the working fluid circuit;   a power generator coupled to the power turbine and configured to convert the mechanical energy into electrical energy;   a power outlet electrically coupled to the power generator and configured to transfer the electrical energy from the power generator to an electrical grid;   a turbo pump comprising a drive turbine and a pump portion, wherein:
 the pump portion is fluidly coupled to the low pressure side of the working fluid circuit by an inlet configured to receive the working fluid from the low pressure side of the working fluid circuit, fluidly coupled to the high pressure side of the working fluid circuit by an outlet configured to release the working fluid into the high pressure side of the working fluid circuit, and configured to pressurize or circulate the working fluid within the working fluid circuit; and 
 the drive turbine is fluidly coupled to the high pressure side of the working fluid circuit by an inlet configured to receive the working fluid from the high pressure side of the working fluid circuit, fluidly coupled to the low pressure side of the working fluid circuit by an outlet configured to release the working fluid into the low pressure side of the working fluid circuit, and configured to rotate the pump portion of the turbo pump; 
   a turbo pump throttle valve fluidly coupled to the working fluid circuit upstream of the inlet of the drive turbine of the turbo pump and configured to modulate a flow of the working fluid flowing into the drive turbine;   a power turbine bypass line fluidly coupled to the working fluid circuit upstream of an inlet of the power turbine, fluidly coupled to the working fluid circuit downstream of an outlet of the power turbine, and configured to flow the working fluid around and avoid the power turbine;   a power turbine bypass valve fluidly coupled to the power turbine bypass line and configured to modulate a flow of the working fluid flowing through the power turbine bypass line for controlling the flowrate of the working fluid entering the power turbine; and   a process control system operatively connected to the heat engine system, wherein the process control system is configured to adjust the turbo pump throttle valve and the power turbine bypass valve while synchronizing the power generator to the electrical grid.   
     
     
         16 . The heat engine system of  claim 15 , further comprising a secondary heat exchanger fluidly coupled to and in thermal communication with the high pressure side of the working fluid circuit, configured to be fluidly coupled to and in thermal communication with the heat source stream, and configured to transfer thermal energy from the heat source stream to the working fluid. 
     
     
         17 . The heat engine system of  claim 16 , wherein the primary heat exchanger is fluidly coupled to the working fluid circuit upstream of the power turbine and downstream of a recuperator, and the recuperator is fluidly coupled to the working fluid circuit and configured to transfer thermal energy from the working fluid within the low pressure side to the working fluid within the high pressure side of the working fluid circuit. 
     
     
         18 . The heat engine system of  claim 16 , wherein the secondary heat exchanger is fluidly coupled to the working fluid circuit upstream of an outlet of the pump portion of the turbo pump and downstream of the inlet of the drive turbine of the turbo pump, and the turbo pump throttle valve is fluidly coupled to the working fluid circuit downstream of the secondary heat exchanger and upstream of the inlet of the drive turbine of the turbo pump. 
     
     
         19 . The heat engine system of  claim 16 , further comprising a recuperator is fluidly coupled to the working fluid circuit downstream of an outlet of the pump portion of the turbo pump and upstream of the secondary heat exchanger and configured to transfer thermal energy from the working fluid within the low pressure side to the working fluid within the high pressure side of the working fluid circuit, wherein the secondary heat exchanger is fluidly coupled to the working fluid circuit upstream of the outlet of the pump portion of the turbo pump and downstream of the inlet of the drive turbine of the turbo pump. 
     
     
         20 . The heat engine system of  claim 15 , further comprising a process control system operatively connected to the heat engine system and configured to individually adjust one or more valves while synchronizing the power generator to the electrical grid, wherein the one or more valves is selected from the turbo pump throttle valve, the power turbine bypass valve, a turbo pump bypass valve, a power turbine throttle valve, a power turbine trim valve, or combinations thereof.