Hybrid thermal cycle with low pressure boiler

Abstract

Work is produced from heat in a continuous cycle. The cycle involves communicating a first flow of a first working fluid to a low pressure boiler. The low pressure boiler forms a first flow of first working fluid vapor by using a low temperature thermal source. A second flow of the first working fluid is provided to a high pressure boiler to produce a second flow of first working fluid vapor at a pressure higher than the low pressure boiler. A second working fluid in vaporous form is compressed, after which a third working fluid is formed by mixing the first flow of first working fluid vapor, the second flow of second working fluid vapor, and the second working fluid. Thermal energy is transferred directly between one or more of the working fluids in the mixing chamber exclusive of any intervening structure.

We claim: 
     
         1 . A method for producing work from heat in a continuous cycle, comprising:
 communicating a first flow of a first working fluid in liquid form to a low pressure boiler;   setting a pressure of said low pressure boiler below a vaporization pressure of the first working fluid at the temperature of a low temperature thermal source;   heating said first flow of said first working fluid in said low pressure boiler using said low temperature thermal source to form a first flow of first working fluid vapor;   providing a second flow of said first working fluid in liquid form to a high pressure boiler to produce a second flow of first working fluid vapor at a pressure higher than said low pressure boiler, using a high temperature thermal source having a temperature higher than said low temperature thermal source;   compressing a second working fluid in vaporous form;   forming a third working fluid by mixing said first flow of first working fluid vapor, said second flow of second working fluid vapor, and said second working fluid which has been compressed;   transferring thermal energy directly between said second working fluid and at least one of said first flow of first working fluid vapor and said second flow of first working fluid vapor, exclusive of any intervening structure;   expanding said third working fluid to perform useful work after or during said transferring;   cooling said third working fluid to extract said first working fluid, in the form of a condensate, and a residual portion of said third working fluid from which said condensate has been extracted; and   repeating said continuous cycle using said first working fluid recovered in said cooling step and using said residual portion to form at least part of said second working fluid.   
     
     
         2 . The method according to  claim 1 , wherein said low temperature thermal source is comprised of thermal energy that is waste or rejected from a process that operates at a higher temperature as compared to the heating in said low pressure boiler. 
     
     
         3 . The method according to  claim 2 , wherein said process that operates at said higher temperature is said production of said second flow of first working fluid vapor in said high pressure boiler 
     
     
         4 . The method according to  claim 1 , further comprising expanding said second flow of first working fluid vapor prior to said mixing. 
     
     
         5 . The method according to  claim 1 , wherein said first and second flows of said first working fluid are communicated to said low pressure boiler and said high pressure boiler by utilizing a pump. 
     
     
         6 . The method according to  claim 1 , further comprising compressing said third working fluid prior to said cooling step. 
     
     
         7 . The method according to  claim 1 , wherein said cooling step further comprises using at least a portion of said third working fluid as a refrigerant to cool said third working fluid. 
     
     
         8 . The method according to  claim 7 , wherein said second working fluid is said residual portion. 
     
     
         9 . A system for producing work from heat in a continuous cycle, comprising:
 a low pressure boiler;   a pump configured to provide a first flow of a first working fluid in liquid form to said low pressure boiler, said low pressure boiler having an internal pressure below a vaporization pressure of the first working fluid at the temperature of a low temperature thermal source and configured to heat said first flow of said first working fluid using said low temperature thermal source to form a first flow of first working fluid vapor;   a second flow of said first working fluid in liquid form provided by said pump to a high pressure boiler, said high pressure boiler configured to produce a second flow of first working fluid vapor at a pressure higher than said low pressure boiler, using a high temperature thermal source having a temperature higher than said low temperature thermal source;   a compressor configured to compress a second working fluid in vaporous form;   a mixing chamber configured to form a third working fluid by mixing said first flow of first working fluid vapor, said second flow of second working fluid vapor, and said second working fluid which has been compressed, and configured to facilitate a transfer of thermal energy directly between said second working fluid and at least one of said first flow of first working fluid vapor and said second flow of first working fluid vapor, exclusive of any intervening structure;   an expander configured to expand said third working fluid after or during said transfer of thermal energy; and   a condenser configured to cool said third working fluid to extract said first working fluid, in the form of a condensate, and a residual portion of said third working fluid from which said condensate has been extracted;   wherein said second working fluid is comprised of said residual portion, and said first working fluid recovered as condensate in said condenser is re-circulated by said pump to said high pressure boiler and said low pressure boiler.   
     
     
         10 . The system according to  claim 9 , wherein said low temperature thermal source is comprised of thermal energy that is waste or rejected from a process that operates at a higher temperature as compared to the heating in said low pressure boiler. 
     
     
         11 . The system according to  claim 10 , wherein said process comprises production of said second flow of first working fluid vapor in said high pressure boiler 
     
     
         12 . The system according to  claim 9 , further comprising a second expander configured to expand said second flow of first working fluid vapor prior to said second flow entering said mixing chamber. 
     
     
         13 . The system according to  claim 9 , further comprising a second compressor configured to compress said third working fluid to facilitate said cooling step. 
     
     
         14 . The system according to  claim 9 , wherein said condenser comprises a heat exchanger configured to use at least a portion of said third working fluid as a refrigerant to cool said third working fluid. 
     
     
         15 . The system according to  claim 14 , wherein said second working fluid is said residual portion. 
     
     
         16 . A method for producing work from heat in a continuous cycle, comprising:
 communicating a first flow of a first working fluid to a low pressure boiler;   setting a pressure of said low pressure boiler below a vaporization pressure of the first working fluid at the temperature of a low temperature thermal source;   heating said first flow of said first working fluid in said low pressure boiler using said low temperature thermal source to form a first flow of first working fluid vapor;   providing a second flow of said first working fluid to a high pressure boiler to produce a second flow of first working fluid vapor at a pressure higher than said low pressure boiler, using a high temperature thermal source having a temperature higher than said low temperature thermal source;   compressing a second working fluid in vaporous form;   forming a third working fluid by mixing said first flow of first working fluid vapor, said second flow of second working fluid vapor, and said second working fluid which has been compressed;   transferring thermal energy directly between one or more of said second working fluid, said first flow of first working fluid vapor and said second flow of first working fluid vapor, exclusive of any intervening structure.   
     
     
         17 . The method according to  claim 16 , further comprising expanding said third working fluid to perform useful work after or during said transferring. 
     
     
         18 . The method according to  claim 17 , further comprising cooling said third working fluid to extract said first working fluid, in the form of a condensate. 
     
     
         19 . The method according to  claim 18 , further comprising obtaining as part of said cooling step, a residual portion of said third working fluid from which said condensate has been extracted. 
     
     
         20 . The method according to  claim 19 , further comprising repeating said continuous cycle using said first working fluid recovered in said cooling step and using said residual portion to form at least part of said second working fluid. 
     
     
         21 . The method according to  claim 16 , further comprising providing at least a third flow of said first working fluid to a third pressure boiler to produce a third flow of first working fluid vapor at a pressure different from said low pressure boiler and said high pressure boiler, using a thermal source having a temperature different compared to said low temperature thermal source and said high temperature thermal source. 
     
     
         22 . A system for producing work from heat in a continuous cycle, comprising:
 a low pressure boiler having an internal pressure below a vaporization pressure of a first working fluid at the temperature of a low temperature thermal source and configured to heat a first flow of said first working fluid using said low temperature thermal source to form a first flow of first working fluid vapor;   a high pressure boiler configured to heat a second flow of said first working fluid using a high temperature thermal source having a temperature higher than said low temperature thermal source, to produce a second flow of said first working fluid vapor at a pressure higher than said low pressure boiler;   a compressor configured to compress a second working fluid in vaporous form; and   a mixing chamber configured to form a third working fluid by mixing said first flow of first working fluid vapor, said second flow of second working fluid vapor, and said second working fluid which has been compressed, and configured to facilitate a transfer of thermal energy directly between one or more of said second working fluid, said first flow of first working fluid vapor, and said second flow of first working fluid vapor, exclusive of any intervening structure.   
     
     
         23 . The system according to  claim 22 , further comprising an expander configured to expand said third working fluid after or during said transfer of thermal energy. 
     
     
         24 . The system according to  claim 23 , further comprising a condenser configured to cool said third working fluid to extract said first working fluid, in the form of a condensate, and a residual portion of said third working fluid from which said condensate has been extracted. 
     
     
         25 . The system according to  claim 24 , wherein said second working fluid is comprised of said residual portion. 
     
     
         26 . The system according to  claim 25 , wherein said pump is configured to recirculate said first working fluid recovered as condensate in said condenser to said high pressure boiler and said low pressure boiler. 
     
     
         27 . The system according to  claim 22 , further comprising at least a third pressure boiler configured to receive a third flow of said first working fluid, and configured to produce a third flow of first working fluid vapor at a pressure different from said low pressure boiler and said high pressure boiler, said third pressure boiler configured to use a thermal source having a temperature different compared to said low temperature thermal source and said high temperature thermal source.