Method of generating power using a combined cycle

Abstract

The invention provides a method of generating power using a combined cycle, comprising operating a first power system in which fuel is burned to generate primary power and a flue gas stream at a flue gas temperature greater than 450° C., and operating a second power system to generate secondary power from the heat comprised by the flue gas stream, the second power system comprising a waste heat recovery heat exchanger. The method further comprises passing the flue gas stream through the waste heat recovery heat exchanger, passing a pressurized waste heat recovery fluid through the waste heat recovery heat exchanger to receive heat from the flue gas stream thereby obtaining a pressurized vaporous waste heat recovery fluid having a temperature in the range of 350° C.-500° C. The waste heat recovery fluid comprises more than 75 mol % of fluorinated ketones.

1 . A method of generating power using a combined cycle, 
       the method comprising:
 operating a first power system in which fuel is burned to generate primary power and a flue gas stream at a flue gas temperature greater than 450° C., 
 operating a second power system to generate secondary power from the heat comprised by the flue gas stream, the second power system comprising a waste heat recovery heat exchanger, 
 the method further comprising: 
 passing the flue gas stream through the waste heat recovery heat exchanger,
 passing a pressurized waste heat recovery fluid through the waste heat recovery heat exchanger to receive heat from the flue gas stream thereby obtaining a pressurized vaporous waste heat recovery fluid having a temperature in the range of 350° C. 500° C., 
 
 wherein the waste heat recovery fluid consists of fluorinated ketones. 
 
     
     
         2 . The method according to  claim 1 , wherein the waste heat recovery fluid comprises more than 90 mol % dodecafluoro-2-methylpentan-3-one. 
     
     
         3 . The method according to  claim 1 , wherein operating the second power system comprises circulating a working fluid through a heat engine cycle. 
     
     
         4 . The method according to  claim 3 , wherein the heat engine cycle is a Rankine cycle. 
     
     
         5 . The method according to  claim 3 , wherein the working fluid circulated through the heat engine cycle is the waste heat recovery fluid. 
     
     
         6 . The method according to  claim 1 , wherein the pressurized vaporous waste heat recovery fluid has a temperature in the range of 400° C. 500° C. 
     
     
         7 . The method according to  claim 1 , wherein the heat engine cycle comprises a condenser in which the waste heat recovery fluid is condensed against an ambient cooling stream, the ambient cooling stream being an ambient air stream or an ambient (sea) water stream. 
     
     
         8 . The method according to  claim 1 , wherein the working fluid is cooled to a temperature in the range 15° C.-80° C. in the condenser. 
     
     
         9 . The method according to  claim 1 , wherein operating the second power system comprises circulating the waste heat recovery fluid as working fluid through a heat engine, such as a Rankine cycle, by simultaneously:
 passing the pressurized waste heat recovery fluid through the waste heat recovery heat exchanger to receive heat from the flue gas stream thereby obtaining a pressurized vaporous waste heat recovery fluid having a temperature in the range of 350° C. 500° C.,   expanding the pressurized vaporous waste heat recovery fluid over an expander, thereby obtaining the secondary power and an expanded lower pressure vaporous waste heat recovery fluid,   passing the expanded lower pressure vaporous waste heat recovery fluid through a condenser to obtain a liquid waste heat recovery fluid, and   passing the liquid waste heat recovery fluid through a pump to obtain the pressurized liquid waste heat recovery fluid.   
     
     
         10 . The method according to  claim 1 ,
 wherein operating the second power system comprises circulating a working fluid through a heat engine, such as a Rankine cycle, to generate the secondary power, the heat engine comprising a heat source heat exchanger and a heat sink heat exchanger,   wherein the method comprises
 passing the waste heat recovery fluid through the heat source heat exchanger, 
 passing the working fluid through the heat source heat exchanger to obtain a heated working fluid by receiving heat from the waste heat recovery fluid. 
   
     
     
         11 . (canceled) 
     
     
         12 . A system for generating power, the system comprises:
 a first power system comprising a fuel burning stage arranged to burn fuel to generate primary power and a flue gas stream at a flue gas temperature greater than 450° C.,   a second power system arranged to generate secondary power from the heat comprised by the flue gas stream, the second power system comprising a waste heat recovery heat exchanger and a waste heat recovery fluid,   wherein the waste heat recovery heat exchanger comprises a first fluid path arranged to receive and convey at least part of the flue gas stream, and a second fluid path arranged to receive and convey the waste heat recovery fluid,   the first and second fluid paths being separated by a heat exchange wall,   the heat exchange wall being suitable to be exposed to the flue gas stream at a flue gas temperature in the range of 450° C.-650° C., and the heat exchange wall being suitable to be exposed to the waste heat recovery fluid at a temperature in the range of 350° C.-500° C.,   wherein the working fluid comprised by the second power system consists of fluorinated ketones.   
     
     
         13 . The system according to  claim 12 , wherein the heat exchange wall is a single layer wall. 
     
     
         14 . The system according to  claim 12 , wherein the system further comprises a heat engine, such as a Rankine cycle, comprising the waste heat recovery heat exchanger, an expander, a condenser and a pump, wherein the condenser is arranged to condense the waste heat recovery fluid against an ambient cooling stream. 
     
     
         15 . The method according to  claim 1 , wherein the waste heat recovery fluid comprises more than 95 mol % dodecafluoro-2-methylpentan-3-one. 
     
     
         16 . The method according to  claim 1 , wherein the waste heat recovery fluid comprises more than 98 mol % dodecafluoro-2-methylpentan-3-one. 
     
     
         17 . The method according to  claim 1 , wherein the waste heat recovery fluid comprises 100 mol % dodecafluoro-2-methylpentan-3-one. 
     
     
         18 . The method according to  claim 1 , wherein the pressurized vaporous waste heat recovery fluid has a temperature in the range of 450° C.-500° C.