Process for controlling a power turbine throttle valve during a supercritical carbon dioxide rankine cycle
View Patent ↗Embodiments of the invention generally provide a heat engine system, a method for generating electricity, and an algorithm for controlling the heat engine system which are configured to efficiently transform thermal energy of a waste heat stream into electricity. In one embodiment, the heat engine system utilizes a working fluid (e.g., sc-CO 2 ) within a working fluid circuit for absorbing the thermal energy that is transformed to mechanical energy by a turbine and electrical energy by a generator. The heat engine system further contains a control system operatively connected to the working fluid circuit and enabled to monitor and control parameters of the heat engine system by manipulating a power turbine throttle valve to adjust the flow of the working fluid. A control algorithm containing multiple system controllers may be utilized by the control system to adjust the power turbine throttle valve while maximizing efficiency of the heat engine system.
1. A method for generating electricity with a heat engine system, comprising:
circulating a working fluid within a working fluid circuit having a high pressure side and a low pressure side, wherein 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 by a first heat exchanger fluidly coupled to and in thermal communication with the heat source stream and the high pressure side of the working fluid circuit;
transferring the working fluid from the first heat exchanger to a first recuperator fluidly coupled to the high pressure side and the low pressure side of the working fluid circuit, wherein the first recuperator is fluidly coupled to the first heat exchanger within the high pressure side of the working fluid circuit;
transferring thermal energy from the working fluid in the low pressure side to the working fluid in the high pressure side by the first recuperator;
transferring the working fluid from the first recuperator to a second heat exchanger fluidly coupled to and in thermal communication with the heat source stream and the high pressure side of the working fluid circuit;
transferring thermal energy from the heat source stream to the working fluid by the second heat exchanger;
transferring the working fluid from the second heat exchanger to a power turbine;
transferring 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 working fluid from the power turbine to the first recuperator;
transferring the working fluid from the first recuperator to a second recuperator fluidly coupled to the high pressure side and the low pressure side of the working fluid circuit;
transferring thermal energy from the working fluid in the low pressure side to the working fluid in the high pressure side by the second recuperator;
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 operating a power turbine throttle valve to adjust a flow of the working fluid, wherein the power turbine throttle valve is fluidly coupled to the working fluid in the supercritical state within the high pressure side of the working fluid circuit upstream from the power turbine; and
monitoring and controlling process operation parameters of the heat engine system, wherein monitoring and controlling the process operation parameters comprises:
adjusting the flow of the working fluid by modulating the power turbine throttle valve to control a rotational speed of the power turbine while synchronizing the power generator with an electrical grid; and
adjusting the flow of the working fluid by modulating the power turbine throttle valve to adaptively tune the power turbine while maintaining a continuous power output from the power generator.
2. The method of claim 1 , wherein the electrical grid contains at least one alternating current bus, alternating current circuit, alternating current grid, or combinations thereof.
3. The method of claim 1 , wherein the working fluid comprises carbon dioxide and at least a portion of the carbon dioxide is in a supercritical state.
4. The method of claim 1 , wherein a generator control module provides an output signal in relation to a phase difference between a generator frequency of the power generator and a grid frequency of the electrical grid.
5. The method of claim 1 , further comprising closing a breaker on the power generator once the power turbine is synchronized with the power generator.
6. The method of claim 1 , further comprising:
monitoring the power output from the power generator; and
modulating the power turbine throttle valve to adaptively tune the power turbine in response to the power output.
7. The method of claim 1 , further comprising monitoring and detecting a reduction of pressure of the working fluid in the supercritical state within the working fluid circuit during a process upset.
8. The method of claim 1 , further comprising monitoring and detecting an increase of rotational speed of the power turbine, the power generator, or a shaft coupled between the power turbine and the power generator during a process upset.
9. The method of claim 8 , further comprising detecting the increase of rotational speed and subsequently adjusting the flow of the working fluid by modulating the power turbine throttle valve to reduce the rotational speed.