Triple expansion waste heat recovery system and method

Abstract

A waste heat recovery system is provided. The waste heat recovery system includes a Rankine cycle system for circulating a working fluid. The Rankine cycle system includes at least one first waste heat recovery boiler configured to transfer heat from a heat source to the working fluid. The Rankine cycle system also includes a first expander configured to receive the heated working fluid from the at least one first waste heat recovery boiler. Further, the Rankine cycle system includes a second expander and a third expander coupled to at least one electric generator. The waste heat recovery system also includes a condenser configured to receive the working fluid at low pressure from the first expander, the second expander and the third expander for cooling and a pump connected to the condenser for receiving a cooled and condensed flow of the working fluid from the condenser.

1 . A waste heat recovery system comprising:
 a Rankine cycle system for circulating a working fluid and comprising:
 at least one first waste heat recovery boiler configured to transfer heat from a heat source to the working fluid; 
 a first expander configured to receive the heated working fluid from the at least one first waste heat recovery boiler; and 
 a second expander and a third expander coupled to at least one electric generator; 
   a condenser configured to receive the working fluid at low pressure from the first expander, the second expander and the third expander for cooling; and   a pump connected to the condenser for receiving a cooled and condensed flow of the working fluid from the condenser, wherein the pump is configured for pumping the condensed working fluid to a primary flow of the working fluid into the first waste heat recovery boiler, a secondary flow of the working fluid into the second expander and a tertiary flow of the working fluid into the third expander.   
     
     
         2 . The waste heat recovery system of  claim 1 , wherein the working fluid is carbon dioxide. 
     
     
         3 . The waste heat recovery system of  claim 1 , wherein the first waste heat recovery boiler comprises a heat exchanger section configured to transfer heat from a first stream of hot gases or a first flow of flue gases to the primary flow of the working fluid entering the first expander. 
     
     
         4 . The waste heat recovery system of  claim 1 , wherein the Rankine cycle system comprises a first recuperator configured to transfer heat from the primary flow of the working fluid exiting the first expander to the secondary flow of the working fluid prior to entering into the second expander. 
     
     
         5 . The waste heat recovery system of  claim 4 , wherein the first recuperator is an intermediate temperature recuperator. 
     
     
         6 . The waste heat recovery system of  claim 1 , wherein the Rankine cycle system comprises one second waste heat recovery boiler configured for heating the secondary flow of the working fluid exiting the first recuperator prior to entering the second expander. 
     
     
         7 . The waste heat recovery system of  claim 6 , wherein the one second waste heat recovery boiler comprises a heat exchanger section configured to transfer heat from a second stream of hot gases or a second flow of flue gases to the secondary flow of the working fluid exiting the first recuperator prior to entering the second expander. 
     
     
         8 . The waste heat recovery system of  claim 1 , wherein the Rankine cycle system comprises a second recuperator configured to transfer heat from a secondary flow of the working fluid exiting the second expander to the tertiary flow of the working fluid prior to entering into the third expander. 
     
     
         9 . The waste heat recovery system of  claim 5 , wherein the second recuperator is a low temperature recuperator. 
     
     
         10 . The waste heat recovery system of  claim 1 , wherein the Rankine cycle system comprises an auxiliary cooler for precooling a combined flow of the primary flow of working fluid, the secondary flow of working fluid and the tertiary flow of the working fluid after exiting from the first expander, the second expander and the third expander respectively prior to entering the condenser. 
     
     
         11 . The waste heat recovery system of  claim 1 , wherein the Rankine cycle system comprises a combined heat and power (CHP) system for providing heat for external processes from precooling a combined flow of primary flow of the working fluid, the secondary flow of working fluid and the tertiary flow of the working fluid exiting from the first expander, the second expander and the third expander respectively. 
     
     
         12 . The waste heat recovery system of  claim 11 , wherein the combined heat and power (CHP) system is configured to transfer heat attained from precooling to the primary flow of working fluid for preheating prior to entering the waste heat recovery boiler. 
     
     
         13 . The waste heat recovery system of  claim 1 , wherein the condenser cools the working fluid and the pump compresses a cooled gas rather than pumping a liquid. 
     
     
         14 . A waste heat recovery system comprising:
 a Rankine cycle system for circulating a working fluid and comprising:
 at least one first waste heat recovery boiler configured to transfer heat from a stream of hot gases or flue gases to the working fluid; 
 a first expander configured to receive the heated working fluid from the at least one first waste heat recovery boiler; and 
 a second expander and a third expander coupled to at least one electric generator; 
   a condenser configured to receive the working fluid at low pressure from the first expander, the second expander and the third expander for cooling;   a pump connected to the condenser for receiving a cooled flow of the working fluid from the condenser, wherein the pump is configured for pumping the working fluid to a primary flow of the working fluid into the first waste heat recovery boiler, a secondary flow of the working fluid into the second expander via a first recuperator and a tertiary flow of the working fluid into the third expander via a second recuperator; and   at least one second waste heat recovery boiler configured for heating the secondary flow of the working fluid exiting the first recuperator prior to entering the second expander.   
     
     
         15 . The waste heat recovery system of  claim 14 , wherein the working fluid is carbon dioxide. 
     
     
         16 . The waste heat recovery system of  claim 14 , wherein the at least one first waste heat recovery boiler or the at least one second waste heat recovery boiler is configured to transfer heat from a stream of hot gases or flue gases to the primary flow of the working fluid entering the first expander or the secondary flow of the working fluid entering the second expander. 
     
     
         17 . The waste heat recovery system of  claim 14 , wherein the first recuperator is an intermediate temperature recuperator configured to transfer heat from the primary flow of the working fluid exiting the first expander to the secondary flow of the working fluid prior to entering into the second expander. 
     
     
         18 . The waste heat recovery system of  claim 14 , wherein the second recuperator is a low temperature recuperator configured to transfer heat from a secondary flow of the working fluid exiting the second expander to the tertiary flow of the working fluid prior to entering into the third expander. 
     
     
         19 . The waste heat recovery system of  claim 14 , wherein the Rankine cycle system comprises an auxiliary cooler or a combined heat and power (CHP) system for precooling a combined flow of the primary flow of working fluid, the secondary flow of working fluid and the tertiary flow of the working fluid after exiting from the first expander, the second expander and the third expander respectively prior to entering the condenser. 
     
     
         20 . A method of recovering waste heat for power generation using a working fluid in a Rankine cycle, the method comprising:
 pumping a primary flow of the working fluid though at least one first waste heat recovery boiler for transferring heat from a stream of hot gases or flue gases to the working fluid;   expanding the heated primary flow of the working fluid through a first expander;   diverting a secondary flow of the working fluid from the primary flow through a second expander;   diverting a tertiary flow of the working fluid from the primary flow through a third expander; and   passing a combination of the primary flow of the working fluid, the secondary flow of the working fluid and the tertiary flow of the working fluid exiting the first expander, second expander and the third expander respectively through an auxiliary precooler and a condenser for condensing the combination of the working fluid and further directing the working fluid to a pump.   
     
     
         21 . The method of  claim 20 , further comprising passing the secondary flow of the working fluid through a first intermediate temperature recuperator for preheating before delivering into the second expander. 
     
     
         22 . The method of  claim 20 , further comprising passing the secondary flow exiting the first recuperator into a second heat waste recovery boiler before delivering into the second expander. 
     
     
         23 . The method of  claim 21 , further comprising passing the tertiary flow of the working fluid through a second low temperature recuperator for preheating before delivering the tertiary flow of the working fluid into the third expander.