Electricity generation device and method

Abstract

The present invention relates to electricity generation devices and methods that use a cryogenic fluid such as liquid nitrogen or liquid air and a source of low grade waste heat, and means of increasing the efficiency of energy recovery from such devices by combining Rankine and Brayton cycles.

1 . An energy generation device comprising:
 a storage tank for storing a cryogenic fluid,   a fluid pump for compressing cryogenic fluid taken from the storage tank to a high pressure,   an evaporator for evaporating the high pressure cryogenic fluid, to provide a high pressure gas,   a first expansion turbine for expanding the high pressure gas and extracting work from the high pressure gas;   a first reheater for reheating gas exhausted from the first expansion turbine using ambient or waste heat;   a second expansion turbine for expanding working fluid exhausted from the first reheater and extracting work from the working fluid exhausted from the first reheater; wherein   the second expansion turbine has an exhaust outlet which is split into first and second paths such that the working fluid exhausted from the second expansion turbine is divided into first and second portions, wherein the first portion of working fluid is directed along the first path to ambient through a first exhaust, and the second portion of working fluid is directed along the second path to an inlet of the evaporator such that the second portion of working fluid exchanges thermal energy with the high pressure cryogenic fluid within the evaporator; and   a first compressor for compressing the second portion of working fluid after it has passed through the evaporator, wherein an exhaust outlet of the compressor is connected with an exhaust outlet of the first expansion turbine such that the second portion of working fluid and the gas exhausted from the first expansion turbine are combined and directed into the first reheater to be reheated using the ambient or waste heat.   
     
     
         2 . The device of  claim 1  wherein at least one of the first and second expansion turbines is used to drive a generator to produce electricity. 
     
     
         3 . The device of  claim 1  wherein the fluid pump provides for compressing the cryogenic fluid to a pressure of at least 50 bar. 
     
     
         4 . The device of  claim 1 , further comprising a superheater for heating high pressure working fluid output from the evaporator to a high temperature using a source of heat from a co-located process. 
     
     
         5 . The device of  claim 4 , wherein the co-located source of heat is at least one of the ambient environment, the atmosphere, the ground, river, sea or lake water, and waste heat from a power station or industrial plant. 
     
     
         6 . The device of  claim 1 , wherein the first expansion turbine is mounted on a same power shaft as the first compressor. 
     
     
         7 . The device of  claim 1 , further comprising:
 a third expansion turbine and a second reheater positioned between the evaporator and the first expansion turbine, and   a fourth expansion turbine and a third reheater positioned between the first reheater and the second expansion turbine.   
     
     
         8 . The device of  claim 7  wherein the first and third expansion turbines are mounted on a same power shaft as the first compressor. 
     
     
         9 . The device of  claim 1 , further comprising a second compressor for compressing the second portion of the working fluid after it has passed through the evaporator a first time and directing the second portion of the working fluid back through the evaporator a second time before the second portion of the working fluid is compressed by the first compressor. 
     
     
         10 . The device of  claim 9  further comprising:
 a third expansion turbine and a second reheater positioned between the evaporator and the first expansion turbine, and 
 a fourth expansion turbine and a third reheater positioned between the first reheater and the second expansion turbine, 
 wherein the first and third expansion turbines are mounted on a same power shaft as the first and second compressors. 
 
     
     
         11 . A cryogenic energy storage system having a power recovery component comprising the device of  claim 1 . 
     
     
         12 . A method of generating energy comprising:
 storing a cryogenic fluid in a storage tank;   extracting the cryogenic fluid from the storage tank and compressing the cryogenic fluid to a high pressure using a fluid pump;   evaporating the high pressure cryogenic fluid in an evaporator to provide a high pressure gas;   expanding the high pressure gas using a first expansion turbine and extracting work from the high pressure gas;   reheating gas exhausted from the first expansion turbine using a first reheater and ambient or waste heat;   expanding working fluid exhausted from the first reheater and extracting work from the working fluid exhausted from the first reheater using a second expansion turbine; wherein   the second expansion turbine has an exhaust outlet which is split into first and second paths such that the working fluid exhausted from the second expansion turbine is divided into first and second portions, wherein   the first portion of working fluid is directed along the first path to ambient through a first exhaust, and the second portion of working fluid is directed along the second path to an inlet of the evaporator such that the second portion of working fluid exchanges thermal energy with the high pressure cryogenic fluid within the evaporator; and   using a first compressor to compress the second portion of working fluid after it has passed through the evaporator, wherein an exhaust outlet of the compressor is connected with an exhaust outlet of the first expansion turbine such that the second portion of working fluid and the gas exhausted from the first expansion turbine are combined and directed into the first reheater to be reheated using the ambient or waste heat.   
     
     
         13 . The method of  claim 12  further comprising using at least one of the first and second expansion turbines to drive a generator and produce electricity. 
     
     
         14 . The method of  claim 12 , further comprising using a superheater and a source of heat from a co-located process to heat high pressure working fluid output from the evaporator to a high temperature. 
     
     
         15 . The method of  claim 12 , further comprising:
 expanding the high pressure gas using a third expansion turbine;   reheating gas exhausted from the third expansion turbine using a second reheater; and   expanding the working fluid exhausted from the first reheater using a fourth expansion turbine; and   reheating the gas exhausted from the fourth expansion turbine using a third reheater.   
     
     
         16 . The method of any of  claim 12 , further comprising using a second compressor to compress the second portion of working fluid after it has passed through the evaporator a first time and directing the second portion of working fluid back through the evaporator a second time before it is compressed by the first compressor. 
     
     
         17 . The method of  claim 12 , wherein the cryogenic fluid comprises at least one of liquid nitrogen, liquid air and liquid natural gas. 
     
     
         18 . The device or method of  claim 15  further comprising using a second compressor to compress the second portion of working fluid after it has passed through the evaporator a first time and directing the second portion of working fluid back through the evaporator a second time before it is compressed by the first compressor. 
     
     
         19 . The device of  claim 4  further comprising:
 a third expansion turbine and a second reheater positioned between the evaporator and the first expansion turbine, and 
 a fourth expansion turbine and a third reheater positioned between the first reheater and the second expansion turbine 
 
     
     
         20 . The device of  claim 4  further comprising a second compressor for compressing the second portion of the working fluid after it has passed through the evaporator a first time and directing the second portion of the working fluid back through the evaporator a second time before the second portion of the working fluid is compressed by the first compressor.