Intercooled Cascade Cycle Waste Heat Recovery System

Abstract

Provided herein is a power generation system and method for transforming thermal energy, such as waste heat, into mechanical energy and/or electrical energy. The system employs features designed to accelerate start times, reduce size, lower cost, and be more environmentally friendly. The system may include multiple compressors on separate pinion shafts with multiple expanders, a temperature valve upstream of compressors with a mass management system downstream, an intercooler between compressors, and a cascade exchanger. In one embodiment, the system is configured to drive a synchronous generator, with the separate pinion shafts rotating at two separate, but constant, speeds.

1 - 7 . (canceled) 
     
     
         8 . A supercritical Brayton cycle power generation system comprising:
 a first compressor for compressing working fluid;   a second compressor for compressing working fluid, wherein the second compressor is fluidly connected with the first compressor;   an inter-stage cooler, wherein the inter-stage cooler is downstream of the first compressor and upstream of the second compressor such that working fluid is cooled by way of the inter-stage cooler prior to the inlet of the second compressor;   a primary expander for generating work, wherein the primary expander is downstream of and fluidly connected with the second compressor;   a cascade expander for generating work, wherein the cascade expander is downstream of and fluidly connected with the primary expander; and   a cascade heat exchanger positioned downstream of the primary expander and upstream of the cascade expander such that excess heat from the primary expander is transferred to the working fluid entering the cascade expander.   
     
     
         9 . The system of  claim 8 , further comprising:
 at least one temperature control valve located upstream of the first compressor;   at least one temperature control valve located upstream of the second compressor and downstream of the first compressor;   a mass management system located downstream of the first and second compressors, the mass management system comprising a pressure control valve for adding mass to the power generation system and a backpressure control valve for removing mass from the power generation system; and   at least one stall margin control valve located downstream of the first and second compressors and configured to control the stall margin of the first and second compressors.   
     
     
         10 . The system of  claim 8 , further comprising:
 a primary heat exchanger positioned downstream of the second compressor and upstream of the primary expander;   at least one waste heat flow modulating valve configured to modulate the working fluid flow through the primary heat exchanger; and   at least one bypass valve configured to redirect the working fluid around the primary and cascade expander.   
     
     
         11 . The system of  claim 8 , further comprising:
 a first pinion shaft connecting the cascade expander to the first compressor; and   a second pinion shaft connecting the primary expander to the second compressor.   
     
     
         12 . The system of  claim 11 ,
 wherein the cascade expander and first compressor have a first rotational speed,   wherein the primary expander and second compressor have a second rotational speed, and   wherein the first rotational speed is different than the second rotational speed.   
     
     
         13 . The system of  claim 12 , wherein the first pinion shaft and the second pinion shaft are connected through a bull gear. 
     
     
         14 . The system of  claim 8 , wherein the working fluid has a critical temperature less than 200 degrees Celsius. 
     
     
         15 . The system of  claim 8 , wherein the working fluid is supercritical carbon dioxide. 
     
     
         16 . The system of  claim 8 , further comprising:
 a bypass valve configured to redirect the working fluid around the primary and cascade expanders,   wherein the system is configured to be started up by rotation of the generator while the bypass valve is closed.   
     
     
         17 . A supercritical Brayton cycle power generation system comprising:
 a cascade expander connected to a first compressor through a first pinion shaft;   a primary expander connected to a second compressor through a second pinion shaft,   c. wherein the first pinion shaft and second pinion shaft are connected through a gear; and   a generator connected to the first and second pinion shafts.   
     
     
         18 . The system of  claim 17  wherein, during steady state operations, the cascade expander and first compressor rotate at a first speed, the primary expander and second compressor rotate at a second speed, the generator rotates at a third speed, and wherein all three speeds are constant. 
     
     
         19 . The system of  claim 17 ,
 wherein the primary and cascade expanders are axial turbines, each turbine having a working fluid inlet location and an outlet location, and   wherein the inlet location is distanced farther from the gear than the outlet location.   
     
     
         20 . The system of  claim 17 , further comprising:
 a working fluid,   wherein the working fluid has a critical temperature less than 200 degrees Celsius.   
     
     
         21 . A supercritical Brayton cycle power generation system comprising:
 a first compressor;   a second compressor downstream of and fluidly connected with the first compressor;   a primary expander downstream of and fluidly connected with the second compressor;   a cascade expander downstream of and fluidly connected with the primary expander; and   an inter-stage cooler positioned downstream of the first compressor and upstream of the second compressor, wherein the inter-stage cooler is configured to cool working fluid prior to an inlet of the second compressor.   
     
     
         22 . The system of  claim 21 , further comprising a cooler positioned upstream of the first compressor, wherein the cooler is configured to cool working fluid prior to an inlet of the first compressor. 
     
     
         23 . The system of  claim 21 , further comprising a first temperature control valve positioned downstream of the first compressor and upstream of the second compressor, wherein a first working fluid path between the first and second compressors passes through the inter-stage cooler, and wherein a second working fluid path between the first and second compressors passes through the first temperature control valve. 
     
     
         24 . The system of  claim 23 , further comprising a second temperature control valve positioned upstream of the first compressor. 
     
     
         25 . The system of  claim 21 , further comprising a primary heat exchanger positioned downstream of the second compressor and upstream of the primary expander. 
     
     
         26 . The system of  claim 25 , further comprising a cascade heat exchanger positioned downstream of the primary expander and upstream of the cascade expander. 
     
     
         27 . The system of  claim 21 , further comprising a mass management system located downstream of the first and second compressors, the mass management system comprising a pressure control valve for adding mass to the system and a backpressure control valve for removing mass from the system.