Cascaded organic rankine cycle (orc) system using waste heat from a reciprocating engine

Abstract

A method and system for operating a cascaded organic Rankine cycle (ORC) system ( 100 ) utilizes two waste heat sources from a positive-displacement engine ( 106 ), resulting in increased efficiency of the engine ( 106 ) and the cascaded ORC system ( 100 ). A high temperature waste heat source from the positive-displacement engine ( 106 ) is used in a first ORC system ( 102 ) to vaporize a first working fluid ( 118 ). A low temperature waste heat source from the positive-displacement engine ( 106 ) is used in a second ORC system ( 104 ) to heat a second working fluid ( 130 ) to a temperature less than the vaporization temperature. The second working fluid ( 130 ) is then vaporized using heat from the first working fluid ( 118 ). In an exemplary embodiment, the positive-displacement engine ( 106 ) is a reciprocating engine. The high temperature waste heat source may be exhaust gas and the low temperature waste heat source may be jacket cooling water.

1 . A method of operating a cascaded organic Rankine cycle (ORC) system, the method comprising:
 vaporizing a first organic working fluid in a first ORC system using a high temperature heat source from a positive-displacement engine;   heating a second organic working fluid in a second ORC system using a low temperature heat source from the positive-displacement engine; and   vaporizing the second organic working fluid using heat from the first organic working fluid, wherein the first organic working fluid has a higher critical temperature than the second organic working fluid.   
     
     
         2 . The method of  claim 1  wherein the positive-displacement engine is a reciprocating engine. 
     
     
         3 . The method of  claim 1  wherein the high temperature heat source is exhaust gas, and the low temperature heat source is jacket cooling water. 
     
     
         4 . The method of  claim 1  wherein a temperature of the high temperature heat source is between approximately 475 and 540 degrees Celsius, and a temperature of the low temperature heat source is between approximately 100 and 110 degrees Celsius. 
     
     
         5 . The method of  claim 1  wherein vaporizing the second organic working fluid is performed by a heat exchanger configured to condense the first organic working fluid and to vaporize the second organic working fluid. 
     
     
         6 . The method of  claim 1  wherein heating the second organic working fluid in the second ORC system is performed by a heat exchanger configured to extract heat from the low temperature heat source and to preheat the second organic working fluid. 
     
     
         7 . The method of  claim 1  wherein the first organic working fluid is selected from a group consisting of siloxanes, toluene, isobutene, isopentane, n-pentane and 4-trifluoromethyl-1,1,1,3,5,5,5-heptafluoro-2-pentene ((CF 3 ) 2 CHCF═CHCF 3 ). 
     
     
         8 . The method of  claim 1  wherein the second organic working fluid is selected from a group consisting of R123, R134a, R236fa and R245fa. 
     
     
         9 . The method of  claim 1  further comprising:
 heating an external source using heat from the second organic working fluid.   
     
     
         10 . (canceled) 
     
     
         11 . A waste heat recovery system comprising:
 a first organic Rankine cycle (ORC) system configured to vaporize a first organic working fluid using a high temperature waste heat source from a reciprocating engine, and to generate power using the first organic working fluid;   a second organic Rankine cycle (ORC) system configured to receive heat from the first organic working fluid to vaporize a second organic working fluid, and to generate power using the second organic working fluid; and   a heat exchanger configured to increase a temperature of the second organic working fluid using a low temperature waste heat source from the reciprocating engine and prior to vaporizing the second organic working fluid, wherein a critical temperature of the first organic working fluid is greater than a critical temperature of the second organic working fluid.   
     
     
         12 . The waste heat recovery system of  claim 11  wherein the high temperature waste heat source passes through an evaporator of the first ORC system to vaporize the first organic working fluid. 
     
     
         13 . The waste heat recovery system of  claim 12  wherein the first organic working fluid passes through a condenser located downstream of the evaporator of the first ORC system to condense the first organic working fluid and vaporize the second organic working fluid. 
     
     
         14 . The waste heat recovery system of  claim 11  wherein the heat exchanger is located downstream of a condenser of the second ORC system and upstream of an evaporator of the second ORC system. 
     
     
         15 . The waste heat recovery system of  claim 11  wherein the high temperature waste heat source is exhaust gas from the reciprocating engine, and the low temperature waste heat source is jacket cooling water from the reciprocating engine. 
     
     
         16 . (canceled) 
     
     
         17 . The waste heat recovery system of  claim 11  further comprising:
 a heat sink configured to receive heat from the second organic working fluid and to provide heating to an external source.   
     
     
         18 . A method of operating a cascaded organic Rankine cycle (ORC) system having a first ORC system configured to circulate a first working fluid and a second ORC system configured to circulate a second working fluid, the method comprising:
 vaporizing the first working fluid in an evaporator of the first ORC system using exhaust gas from a reciprocating engine;   heating the second working fluid upstream of an evaporator of the second ORC system using cooling water from the reciprocating engine; and   vaporizing the second working fluid in the evaporator of the second ORC system using heat from the first working fluid of the first ORC system, wherein a critical temperature of the first working fluid is greater than a critical temperature of the second working fluid.   
     
     
         19 . The method of  claim 18  wherein the evaporator of the second ORC system is configured as a condenser of the first ORC system. 
     
     
         20 . The method of  claim 18  wherein the first working fluid is selected from a group consisting of siloxanes, toluene, isobutene, isopentane, n-pentane and 4-trifluoromethyl-1,1,1,3,5,5,5-heptafluoro-2-pentene ((CF 3 ) 2 CHCF═CHCF 3 ), and the second working fluid is selected from a group consisting of R123, R134a, R236fa and R245fa. 
     
     
         21 . The method of  claim 18  wherein a temperature of the exhaust gas exiting the reciprocating engine is between approximately 475 and 540 degrees Celsius, and a temperature of the cooling water exiting the reciprocating engine is between approximately 100 and 110 degrees Celsius. 
     
     
         22 . The method of  claim 18  further comprising:
 heating an external source using heat from the second working fluid in the second ORC system.