TRIPLE EXPANSION WASTE HEAT RECOVERY SYSTEM AND METHOD |
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申请号 | US13538323 | 申请日 | 2012-06-29 | 公开(公告)号 | US20140000261A1 | 公开(公告)日 | 2014-01-02 |
申请人 | Sebastian Walter Freund; | 发明人 | Sebastian Walter Freund; | ||||
摘要 | 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. | ||||||
权利要求 | |||||||
说明书全文 | The present application relates generally to power generation and, more particularly, to a system and method for recovering waste heat from a plurality of heat sources having different temperatures for the generation of electricity. Many industrial power requirements could benefit from power generation systems that provide electricity or mechanical power with minimum environmental impact and that may be readily integrated into existing power grids or rapidly sited as stand-alone units. Combustion engines such as gas turbines or large reciprocating engines are suitable for power generation in industrial applications but rely on increasingly costly fuel and also generate emissions and waste heat. One method to generate electricity from the waste heat of a combustion engine without increasing the output of emissions and without requiring additional fuel is to apply a bottoming cycle. Bottoming cycles use waste heat from a heat source, such as an engine, and convert that thermal energy into electricity. Rankine cycles are often applied as the bottoming cycle for large combustion engines. Rankine cycles are also used to generate power from geothermal or industrial heat sources. A fundamental Rankine cycle includes a turbogenerator, a boiler, a condenser and a feed pump. In one conventional system provided to generate electricity from waste heat, a Rankine cycle system using carbon dioxide as working fluid is used along with a recuperator. However, the amount of heat that can be recovered from the waste heat source is limited as a boiler inlet temperature of the working fluid increases after passing the recuperator. The boiler efficiency declines and the heat input as well as power output is limited. There is therefore a need for an efficient Rankine cycle system that utilizes the most waste heat and generates an increased net power output. In accordance with an embodiment of the invention, 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, 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. In accordance with an embodiment of the invention, 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 stream of hot gases or flue gases 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 coupled to the first expander and a third expander coupled to the second expander such that the first expander, the second expander and the third expander are coupled directly or indirectly to each other in series and further coupled to a 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. Further, the waste heat recovery system includes 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 via a first recuperator and a tertiary flow of the working fluid into the third expander via a second recuperator. Furthermore, the waste heat recovery system includes 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. In accordance with an embodiment of the invention, a method of recovering waste heat for power generation using a working fluid in a Rankine cycle is provided. The method includes 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. The method also includes expanding the heated primary flow of the working fluid through a first expander. Further, the method includes pumping a secondary flow of the working fluid through a second expander and pumping a tertiary flow of the working fluid through a third expander. Finally, the method includes 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 passing to a pump. These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Any examples of operating parameters are not exclusive of other parameters of the disclosed embodiments. In one embodiment, the first waste heat recovery boiler 16 includes a heat exchanger section configured to transfer heat from a first stream of hot gases or a first flow of flue gases 17 to the primary flow (indicated by arrow 30) of the working fluid 14 entering the first expander 18. As shown in Furthermore, in one embodiment, the Rankine cycle system 12 includes an auxiliary cooler 40 for precooling a combined flow of the primary flow 30 of working fluid 14, the secondary flow 32 of working fluid 14 and the tertiary flow 34 of the working fluid 14 after exiting from the first expander 18, the second expander 20 and the third expander 22 respectively prior to entering the condenser 26. In a combined heat and power (CHP) system, the heat attained in the auxiliary cooler 40 from precooling may be used for an external process. In one embodiment, the auxiliary cooler 40 utilizes the heat attained from precooling in the Rankine cycle system 12 by transferring the heat to the primary flow 30 of the working fluid 14 for preheating prior to entering the waste heat recovery boiler 16. As shown in Advantageously, the present invention utilizes carbon dioxide as the working fluid which can be heated to very high temperatures, leading to high efficiency of the waste heat recovery system. Also, carbon dioxide is non-toxic and thermally stable working fluid. The present system and method using a triple expansion process using three expanders with cascaded recuperators extracts maximum power out of the available waste heat directed in the present system. Moreover, the heating of the secondary flow of the working fluid in the second waste heat recovery boiler can lead to a thermodynamic advantage that allows for higher efficiency at lower peak temperature of the waste heat recovery system. Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. |