Process, plant and thermodynamic cycle for production of power from variable temperature heat sources

Abstract

A cascade process for the production of power from variable temperature heat sources, includes: circulating a main working fluid selected from perfluorinated compounds (like Perfluoro-2-methylpentane/Perfluoro-i-hexane) in a main circuit according to a main supercritical organic Rankine cycle, operatively coupling in a boiler a variable temperature heat source with the main working fluid of the main circuit to heat and vaporize the main working fluid; circulating an auxiliary working fluid in an auxiliary circuit according to an auxiliary Rankine cycle; thermally coupling in cascade the expanded main working fluid of the main Rankine cycle with the auxiliary working fluid of the auxiliary Rankine cycle, in order to cool the main working fluid and heating the vaporizing the auxiliary working fluid by heat transfer from the main Rankine cycle to the auxiliary Rankine cycle before the expansion of the auxiliary working fluid in an auxiliary expander.

1 . A cascade process for the production of power from variable temperature heat sources, comprising:
 circulating a main working fluid selected from the perfluorinated compounds in a main circuit according to a main organic supercritical Rankine cycle, wherein said main working fluid is heated and vaporized, expanded into a main expander, enslaved to an electric generator or to a mechanical user, cooled, condensed and heated and vaporized again;   operationally coupling in a boiler a variable temperature heat source to the main working fluid of the main circuit to perform said heating and vaporization of the main working fluid;   circulating an auxiliary working fluid in an auxiliary circuit according to an auxiliary Rankine cycle, wherein said auxiliary working fluid is heated and vaporized, expanded into an auxiliary expander, enslaved to an auxiliary electric generator or to an auxiliary mechanical user, cooled, condensed and heated and vaporized again;   thermally coupling the expanded main working fluid of the main Rankine cycle to the auxiliary working fluid of the auxiliary Rankine cycle, in order to cool the main working fluid and to heat and vaporize said auxiliary working fluid by heat transfer from said main Rankine cycle to said auxiliary Rankine cycle before the expansion of the auxiliary working fluid into the auxiliary expander.   
     
     
         2 . The process according to  claim 1 , wherein the main working fluid is preheated in a main recuperator. 
     
     
         3 . The process according to  claim 1 , wherein the main working fluid and the auxiliary working fluid are the same fluid and the auxiliary circuit is a branch of the main circuit; wherein the thermal coupling of the main working fluid to the auxiliary working fluid is performed in a second recuperator located downstream of the main expander and upstream of the auxiliary expander. 
     
     
         4 . The process according to  claim 3 , wherein the auxiliary working fluid is separated from the main working fluid upstream of the main expander and the auxiliary expander and to re-join the auxiliary working fluid and the main working fluid downstream of the main expander and the auxiliary expander. 
     
     
         5 . The process according to  claim 3 , wherein the auxiliary working fluid re-joins the main working fluid in the main recuperator. 
     
     
         6 . The process according to  claim 1 , wherein the main working fluid and the auxiliary working fluid are fluidly separated; wherein the plant comprises a heat exchanger; wherein the main working fluid and the auxiliary working fluid are thermally coupled in the heat exchanger. 
     
     
         7 . The process according to  claim 6 , wherein the auxiliary working fluid is different from the main working fluid. 
     
     
         8 . The process according to  claim 7 , wherein the auxiliary working fluid is an organic fluid, preferably selected from the group comprising: cyclopentane, isopentane, isohexane, hexane, pentane, R245fa, R1234yf. 
     
     
         9 . The process according to  claim 1 , wherein the main working fluid selected from the perfluorinated compounds comprises: Perfluoro-2-methylpentane/Perfluoro-i-hexane (Flutectm PP1), Perfluoro-methylcyclohexane (PP2), Perfluoro-1,3-dimethylcyclohexane (PP3), hexafluorobenzene. 
     
     
         10 . A cascade plant for the production of power from variable temperature heat sources, comprising:
 a main circuit comprising:   a boiler operatively coupled to a variable temperature heat source;   a main expander;   a main recuperator;   a main condenser;   a main pump;   main pipes connecting each other the boiler, the main expander, the main recuperator, the main condenser and the main pump;   a main working fluid selected from the perfluorinated compounds and flowing in the main circuit so as to implement a supercritical organic Rankine cycle;   at least one auxiliary circuit thermally coupled to the main circuit and comprising an auxiliary expander; wherein an auxiliary working fluid enters the auxiliary expander after exchanging heat with the main working fluid exiting the main expander.   
     
     
         11 . The plant according to  claim 10 , wherein the auxiliary circuit is a branch of the main circuit and the auxiliary working fluid is the main working fluid; wherein the plant further comprises a second recuperator located on the main circuit and downstream of the main expander and placed on the auxiliary circuit and upstream of the auxiliary expander; the heat between the main working fluid and the auxiliary working fluid being exchanged in the second recuperator. 
     
     
         12 . Plant The plant according to  claim 11 , wherein the auxiliary circuit branches from the main circuit at a point located between the main recuperator and the boiler and re-joins the main circuit in the main recuperator. 
     
     
         13 . The plant according to  claim 11 , wherein the main expander and the auxiliary expander are integrated in a single radial outflow turbine comprising a single rotor disc provided with a front face and a rear face; wherein ring-shaped arrays of blades are arranged concentrically on the front face to define a first radial path for the working fluid and ring-shaped arrays of blades are arranged concentrically on the rear face to define a second radial path for the working fluid; wherein the main expander is defined by the first radial path and the auxiliary expander is defined by the second radial path. 
     
     
         14 . The plant according to  claim 10 , wherein the auxiliary circuit is fluidly separated from the main circuit; wherein the plant comprises a heat exchanger; wherein the main circuit and the auxiliary circuit are thermally coupled in the heat exchanger. 
     
     
         15 . The plant according to  claim 14 , wherein the auxiliary circuit comprises:
 an auxiliary recuperator;   an auxiliary condenser;   an auxiliary pump;   auxiliary pipes connecting each other the auxiliary expander, the auxiliary recuperator, the auxiliary condenser and the auxiliary pump;   wherein the heat exchanger is placed on the main circuit between the main expander and the main recuperator and is placed on the auxiliary circuit between the auxiliary recuperator and the auxiliary expander.   
     
     
         16 . A cascade thermodynamic cycle for the production of power from variable temperature heat sources, comprising:
 a supercritical main Rankine cycle with an organic main working fluid selected from the perfluorinated compounds; wherein the main Rankine cycle receives heat from a variable temperature heat source;   an auxiliary Rankine cycle with an auxiliary working fluid; wherein the auxiliary cycle is thermally coupled to the main cycle to receive heat from said main cycle after an expansion of the main working fluid and before an expansion of the auxiliary working fluid;   wherein in the main cycle:   a reduced temperature of the main working fluid immediately before the main expansion is between 1.1 and 1.7;   wherein a reduced pressure of the main working fluid immediately before the main expansion is between 1 and 2.5;   wherein a reduced condensation temperature of the main working fluid is between 0.6 and 0.9;   wherein a reduced condensation pressure of the main working fluid is between 0.005 and 0.3.   
     
     
         17 . The cycle according to  claim 16 , wherein in the auxiliary cycle:
 a reduced temperature of the auxiliary working fluid immediately before the auxiliary expansion is between 0.8 and 1.2;   wherein a reduced pressure of the auxiliary working fluid immediately before the auxiliary expansion is between 0.3 and 1.2;   wherein a reduced condensation temperature of the auxiliary working fluid is between 0.5 and 0.75;   wherein a reduced condensation pressure of the auxiliary working fluid is between 0.001 and 0.1.   
     
     
         18 . The cycle according to  claim 16 , wherein in the main cycle:
 a main working fluid temperature immediately before the main expansion is between 250 ° C. and 400 ° C.;   wherein a main working fluid pressure immediately before the main expansion is between 25 bar and 50 bar;   wherein a condensation temperature of the main working fluid is between 10° C. and 50° C.;   wherein a condensation pressure of the main working fluid is between 0.1 bar and 1 bar.   
     
     
         19 . The cycle according to  claim 16 , wherein in the auxiliary cycle:
 a temperature of the auxiliary working fluid immediately before the auxiliary expansion is between 150° C. and 300 ° C.;   wherein an auxiliary working fluid pressure immediately before the auxiliary expansion is between 20 bar and 50 bar;   wherein a condensation temperature of the auxiliary working fluid is between 10° C. and 50° C.;   wherein a condensation pressure of the auxiliary working fluid is between 0.1 bar and 2 bar.