Power generation from low-temperature heat

Abstract

The invention relates to a method for converting heat energy into mechanical energy by means of a Rankine cycle. In the Rankine cycle the circulating working fluid is pumped to a pressure above its critical pressure prior to heat exchange with an external medium. During the heat exchange with the external medium, the working fluid is heated to a temperature above its critical temperature and sufficiently high for the working fluid to expand without partial condensation. The working fluid is then expanded and condensed. The maximum pressure of the working fluid is controlled by means of an expander controllable with regard to the mass flow rate of the working fluid and/or a pump controllable with regard to the mass flow rate of the working fluid.

1 . A method for converting heat energy into mechanical energy by means of a Rankine cycle, said method comprising:
 pumping a working fluid circulating in a Rankine cycle to a pressure above the critical pressure of said working fluid prior conducting heat exchange between said working fluid and an external medium and   heating said working fluid during said heat exchange with said external medium to a temperature above the critical pressure of said working fluid, said temperature being at least sufficiently high for the working fluid to expand without partial condensation,   expanding said working fluid in, and   condensing the expanded working fluid,   wherein the maximum pressure of said working fluid is controlled by means of an expander (X 1 ) controllable with regard to the mass flow rate of the working fluid ( 5 ) and/or a pump (P 1 ) controllable with regard to the mass flow rate of the working fluid ( 1 ).   
     
     
         2 . The method according to  claim 1 , wherein the maximum pressure of said working fluid is controlled by means of an expander (X 1 ) controllable with regard to the mass flow rate of the working fluid ( 5 ). 
     
     
         3 . The method according to  claim 1 , wherein the maximum pressure of said working fluid is controlled by means of a pump (P 1 ) controllable with regard to the mass flow rate of the working fluid ( 1 ). 
     
     
         4 . A method according to  claim 1 , wherein expander controllable with regard to the mass flow rate of the working fluid comprises an adjustable inlet guide vane. 
     
     
         5 . A method according to  claim 4 , wherein the adjustable inlet guide vane comprises a nozzle ring at the inlet of the expander. 
     
     
         6 . The method according to  claim 1 , wherein said working fluid ( 3 ) is further heated by an additional heat exchange during start-up and/or during part load operation (E 4 ). 
     
     
         7 . The method according to  claim 1 , wherein expanded working fluid ( 5 ) is used to preheat (E 3 ) said working fluid ( 1 ). 
     
     
         8 . The method according to  claim 6 , wherein expanded working fluid ( 5 ) is used to preheat (E 3 ) said working fluid ( 1 ) in said additional heat exchange. 
     
     
         9 . The method according to  claim 1 , wherein expanded working fluid ( 5 ) is condensed (E 2 ), but not subcooled. 
     
     
         10 . The method according to  claim 1 , wherein the pressure of said working fluid ( 4 ) at the inlet of said expander (X 1 ) is at least 30%, above the critical pressure of said working fluid. 
     
     
         11 . The method according to  claim 10 , wherein the pressure of said working fluid ( 4 ) at the inlet of said expander (X 1 ) is 40 and 50% above the critical pressure of said working fluid. 
     
     
         12 . The method according to  claim 1 , wherein said working fluid is propane, propylene or a mixture of propane and propylene. 
     
     
         13 . The method according to  claim 1 , wherein the temperature of said external medium is 120-200° C. 
     
     
         14 . The method according to  claim 13 , wherein the temperature of said external medium is 130-160° C. 
     
     
         15 . A method according to  claim 1 , wherein said working fluid is water or ammonia.