Embodiments disclosed herein relate generally to the field of power generation and, more particularly, to a system and method for recovering waste heat from a carbon dioxide removal process. Carbon dioxide (CO2) emissions from power plants utilizing fossil fuels are increasingly penalized by national and international regulations, such as the Kyoto protocol and the European Union Emission Trading Scheme. With the increasing cost associated with the emission of CO2, the importance of CO2 emission reduction to economical power generation is increasing. However, due to the energy that must be utilized in order to accomplish CO2 emission reduction by conventional methods, overall power plant efficiency is reduced, in some cases by about 10%. Increasing the efficiency of power plants utilizing CO2 emissions reduction technology is therefore of interest. In one aspect, a system, such as a power plant, is provided, the system including a process fluid cooler, a carbon dioxide removal system, a compression system, and a heat engine. The process fluid cooler can be configured to receive a process fluid including carbon dioxide and to extract thermal energy from the process fluid. The carbon dioxide removal system can include an absorber and a stripper. The absorber can be configured to receive the process fluid from the process fluid cooler and to transfer carbon dioxide from the process fluid to a removal fluid (e.g., a solvent, such as amine). The stripper can be configured to receive the removal fluid from the absorber and can include a reboiler and a stripper condenser. The reboiler can be configured to heat the removal fluid (e.g., by receiving steam) so as to cause carbon dioxide to be released from the removal fluid and outputted as part of a reboiler output stream. The reboiler can also output a heating fluid, such as water. The stripper condenser can be configured to extract thermal energy from the reboiler output stream so as to cause condensation of water associated with the reboiler output stream and to remove carbon dioxide therefrom. The compression system can be configured to receive carbon dioxide from the stripper condenser and to remove thermal energy from the carbon dioxide. The heat engine can be configured to operate according to an organic Rankine cycle and further configured to receive thermal energy from the heating fluid and/or extracted at the process fluid cooler, at the stripper condenser, and/or at the compression system. The heat engine may include a working fluid such as, for example, carbon dioxide, R245fa, and/or butane. The heat engine may also include a secondary condenser configured to extract thermal energy from a working fluid. A second heat engine can be included and configured to operate according to an organic Rankine cycle, receiving thermal energy extracted at the secondary condenser. The system may also include a combustion chamber configured for combustion of a fossil fuel so as to produce the process fluid. The combustion chamber may be configured to direct the process fluid to the process fluid cooler. An exhaust gas recirculation system may also be provided. The exhaust gas recirculation system may be configured to recirculate flue gases back to a main combustion zone of the combustion chamber. The exhaust gas recirculation system can include an exhaust gas recirculation cooler configured to extract thermal energy from the recirculated flue gases, and the heat engine can be configured to receive thermal energy from the exhaust gas recirculation cooler. The system may further include a primary heat engine configured to operate according to a Rankine cycle with water as a working fluid. The primary heat engine may be configured to receive thermal energy from the combustion chamber, and may include a primary condenser configured to extract thermal energy from the working fluid of the primary heat engine. The heat engine can then be configured to receive thermal energy from the primary condenser. In another aspect, another system is provided. The system can include a process fluid cooler configured to receive a process fluid including carbon dioxide and to extract thermal energy from the process fluid. The system can also include a carbon dioxide removal system including an absorber and a stripper. The absorber can be configured to receive the process fluid from the process fluid cooler and to transfer carbon dioxide from the process fluid to a removal fluid. The stripper can be configured to receive the removal fluid from the absorber. The stripper can include a reboiler configured to heat the removal fluid so as to cause carbon dioxide to be released from the removal fluid and outputted as part of a reboiler output stream. The reboiler may also output a heating fluid. The stripper can also include a stripper condenser configured to extract thermal energy from the reboiler output stream so as to cause condensation of water associated therewith and to remove carbon dioxide therefrom. The system can further include a compression system configured to receive carbon dioxide from the stripper condenser and to remove thermal energy from the carbon dioxide, and also a first heat engine configured to operate according to an organic Rankine cycle. The first heat engine can include a first condenser configured to extract thermal energy from a first working fluid and a first evaporator configured to receive thermal energy from at least one of the heating fluid or the thermal energy extracted at the process fluid cooler or the stripper condenser or the compression system. A second heat engine can be configured to operate according to an organic Rankine cycle and can include a second working fluid and a second evaporator configured to receive thermal energy from the first condenser and from at least one of the heating fluid or the thermal energy extracted at the process fluid cooler or the stripper condenser or the compression system. In some embodiments, the first heat engine can include at least one of R245fa or butane as the first working fluid and the second heat engine can include carbon dioxide as the second working fluid. In other embodiments, the first evaporator is configured to receive at least some of the thermal energy extracted at the process fluid cooler and the second evaporator is configured to receive thermal energy from the heating fluid and the thermal energy extracted at the stripper condenser. In yet another aspect, a method is provided, which method includes receiving a process fluid including carbon dioxide and extracting thermal energy from the process fluid. The process fluid may be produced, for example, by combusting fossil fuel. Carbon dioxide can be transferred from the process fluid to a removal fluid. The removal fluid can be heated so as to cause carbon dioxide to be released from the removal fluid and included as part of a mixture including steam and so as to produce an output stream of a heating fluid. Thermal energy can be extracted from the mixture of carbon dioxide and steam so as to cause condensation of the steam and to remove carbon dioxide therefrom, creating a carbon dioxide gas stream. Thermal energy can be extracted from the carbon dioxide gas stream. A heat engine can be operated according to an organic Rankine cycle, and thermal energy can be provided to the heat engine from the heating fluid and from that extracted from the process fluid and the carbon dioxide gas stream. In some embodiments, thermal energy may be extracted from an exhaust gas recirculation cooler and provided to the heat engine. In other embodiments, a primary heat engine may be operated according to a Rankine cycle with water as a working fluid, and thermal energy may be provided from the combustion of fossil fuel to the primary heat engine. Thermal energy can be extracted thermal energy from the working fluid of the primary heat engine and provided to the heat engine. In some embodiments, operating a heat engine according to an organic Rankine cycle can include extracting thermal energy from a working fluid of the heat engine. A second heat engine can be operated according to an organic Rankine cycle, and thermal energy extracted from the working fluid of the heat engine can be provided to the second heat engine. The working fluid of the heat engine can be heated so as to cause evaporation thereof, and a working fluid of the second heat engine can be heated so as to cause evaporation thereof. Thermal energy can be provided to the second heat engine from at least one of the heating fluid or the thermal energy extracted from the process fluid or the carbon dioxide gas stream.
Heat engine and method for operating the same
TOLA, VITTORIO;
2011-01-01
Abstract
Embodiments disclosed herein relate generally to the field of power generation and, more particularly, to a system and method for recovering waste heat from a carbon dioxide removal process. Carbon dioxide (CO2) emissions from power plants utilizing fossil fuels are increasingly penalized by national and international regulations, such as the Kyoto protocol and the European Union Emission Trading Scheme. With the increasing cost associated with the emission of CO2, the importance of CO2 emission reduction to economical power generation is increasing. However, due to the energy that must be utilized in order to accomplish CO2 emission reduction by conventional methods, overall power plant efficiency is reduced, in some cases by about 10%. Increasing the efficiency of power plants utilizing CO2 emissions reduction technology is therefore of interest. In one aspect, a system, such as a power plant, is provided, the system including a process fluid cooler, a carbon dioxide removal system, a compression system, and a heat engine. The process fluid cooler can be configured to receive a process fluid including carbon dioxide and to extract thermal energy from the process fluid. The carbon dioxide removal system can include an absorber and a stripper. The absorber can be configured to receive the process fluid from the process fluid cooler and to transfer carbon dioxide from the process fluid to a removal fluid (e.g., a solvent, such as amine). The stripper can be configured to receive the removal fluid from the absorber and can include a reboiler and a stripper condenser. The reboiler can be configured to heat the removal fluid (e.g., by receiving steam) so as to cause carbon dioxide to be released from the removal fluid and outputted as part of a reboiler output stream. The reboiler can also output a heating fluid, such as water. The stripper condenser can be configured to extract thermal energy from the reboiler output stream so as to cause condensation of water associated with the reboiler output stream and to remove carbon dioxide therefrom. The compression system can be configured to receive carbon dioxide from the stripper condenser and to remove thermal energy from the carbon dioxide. The heat engine can be configured to operate according to an organic Rankine cycle and further configured to receive thermal energy from the heating fluid and/or extracted at the process fluid cooler, at the stripper condenser, and/or at the compression system. The heat engine may include a working fluid such as, for example, carbon dioxide, R245fa, and/or butane. The heat engine may also include a secondary condenser configured to extract thermal energy from a working fluid. A second heat engine can be included and configured to operate according to an organic Rankine cycle, receiving thermal energy extracted at the secondary condenser. The system may also include a combustion chamber configured for combustion of a fossil fuel so as to produce the process fluid. The combustion chamber may be configured to direct the process fluid to the process fluid cooler. An exhaust gas recirculation system may also be provided. The exhaust gas recirculation system may be configured to recirculate flue gases back to a main combustion zone of the combustion chamber. The exhaust gas recirculation system can include an exhaust gas recirculation cooler configured to extract thermal energy from the recirculated flue gases, and the heat engine can be configured to receive thermal energy from the exhaust gas recirculation cooler. The system may further include a primary heat engine configured to operate according to a Rankine cycle with water as a working fluid. The primary heat engine may be configured to receive thermal energy from the combustion chamber, and may include a primary condenser configured to extract thermal energy from the working fluid of the primary heat engine. The heat engine can then be configured to receive thermal energy from the primary condenser. In another aspect, another system is provided. The system can include a process fluid cooler configured to receive a process fluid including carbon dioxide and to extract thermal energy from the process fluid. The system can also include a carbon dioxide removal system including an absorber and a stripper. The absorber can be configured to receive the process fluid from the process fluid cooler and to transfer carbon dioxide from the process fluid to a removal fluid. The stripper can be configured to receive the removal fluid from the absorber. The stripper can include a reboiler configured to heat the removal fluid so as to cause carbon dioxide to be released from the removal fluid and outputted as part of a reboiler output stream. The reboiler may also output a heating fluid. The stripper can also include a stripper condenser configured to extract thermal energy from the reboiler output stream so as to cause condensation of water associated therewith and to remove carbon dioxide therefrom. The system can further include a compression system configured to receive carbon dioxide from the stripper condenser and to remove thermal energy from the carbon dioxide, and also a first heat engine configured to operate according to an organic Rankine cycle. The first heat engine can include a first condenser configured to extract thermal energy from a first working fluid and a first evaporator configured to receive thermal energy from at least one of the heating fluid or the thermal energy extracted at the process fluid cooler or the stripper condenser or the compression system. A second heat engine can be configured to operate according to an organic Rankine cycle and can include a second working fluid and a second evaporator configured to receive thermal energy from the first condenser and from at least one of the heating fluid or the thermal energy extracted at the process fluid cooler or the stripper condenser or the compression system. In some embodiments, the first heat engine can include at least one of R245fa or butane as the first working fluid and the second heat engine can include carbon dioxide as the second working fluid. In other embodiments, the first evaporator is configured to receive at least some of the thermal energy extracted at the process fluid cooler and the second evaporator is configured to receive thermal energy from the heating fluid and the thermal energy extracted at the stripper condenser. In yet another aspect, a method is provided, which method includes receiving a process fluid including carbon dioxide and extracting thermal energy from the process fluid. The process fluid may be produced, for example, by combusting fossil fuel. Carbon dioxide can be transferred from the process fluid to a removal fluid. The removal fluid can be heated so as to cause carbon dioxide to be released from the removal fluid and included as part of a mixture including steam and so as to produce an output stream of a heating fluid. Thermal energy can be extracted from the mixture of carbon dioxide and steam so as to cause condensation of the steam and to remove carbon dioxide therefrom, creating a carbon dioxide gas stream. Thermal energy can be extracted from the carbon dioxide gas stream. A heat engine can be operated according to an organic Rankine cycle, and thermal energy can be provided to the heat engine from the heating fluid and from that extracted from the process fluid and the carbon dioxide gas stream. In some embodiments, thermal energy may be extracted from an exhaust gas recirculation cooler and provided to the heat engine. In other embodiments, a primary heat engine may be operated according to a Rankine cycle with water as a working fluid, and thermal energy may be provided from the combustion of fossil fuel to the primary heat engine. Thermal energy can be extracted thermal energy from the working fluid of the primary heat engine and provided to the heat engine. In some embodiments, operating a heat engine according to an organic Rankine cycle can include extracting thermal energy from a working fluid of the heat engine. A second heat engine can be operated according to an organic Rankine cycle, and thermal energy extracted from the working fluid of the heat engine can be provided to the second heat engine. The working fluid of the heat engine can be heated so as to cause evaporation thereof, and a working fluid of the second heat engine can be heated so as to cause evaporation thereof. Thermal energy can be provided to the second heat engine from at least one of the heating fluid or the thermal energy extracted from the process fluid or the carbon dioxide gas stream.
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