Claims:CLAIMS
1. An energy recovery system, comprising:
a heat exchanger 18 configured to convert a partially heated fluid A to a high temperature fluid B, while generating a partially cooled waste heat stream X;
a fluid expander 20 configured to expand the high temperature fluid B into an expanded fluid C; and
a multi-stream heat exchanger 22 configured to transfer heat from the expanded fluid C and the partially cooled waste heat stream X to a high-pressure low temperature fluid F to generate the partially heated fluid A, while cooling the expanded fluid C to a partially cooled fluid D, wherein the partially cooled fluid D is cooled and pressurized to generate the high-pressure low temperature fluid F.

2. The energy recovery system of claim 1, wherein the fluid expander comprises a power turbine.

3. The energy recovery system of claim 1, comprising a fluid cooling system 24 configured to cool the partially cooled fluid D to generate a cooled fluid E.

4. The energy recovery system of claim 3, comprising a pressure building system 26 configured to pressurize the cooled fluid E to generate the high-pressure low temperature fluid F.

5. The energy recovery system of claim 1, wherein the multi-stream heat exchanger 22 comprises any of a shell and tube heat exchanger, a micro shell and tube heat exchanger, a plate-fin heat exchanger, or a printed circuit heat exchanger (PCHE).
6. A method of operating an energy recovery system, comprising:
converting a partially heated fluid A to a high temperature fluid B, while generating a partially cooled waste heat stream X;
expanding the high temperature fluid B into an expanded fluid C;
transferring heat from the expanded fluid C and the partially cooled waste heat stream X to a high-pressure low temperature fluid F for generating the partially heated fluid A, while cooling the expanded fluid C for generating a partially cooled fluid D; and
cooling and pressurizing the partially cooled fluid D for generating the high-pressure low temperature fluid F.

7. The method of claim 6, wherein converting a partially heated fluid A comprises converting a partially heated fluid A via a heat exchanger 18.

8. The method of claim 6, wherein expanding the high temperature fluid B comprises expanding the high temperature fluid B via a fluid expander 20.

9. The method of claim 6, transferring heat from the expanded fluid C and the partially cooled waste heat stream X comprises transferring heat via a multi stream heat exchanger 22.

10. The method of claim 6, cooling and pressurizing the partially cooled fluid D comprises cooling the partially cooled fluid D via a fluid cooling system 24 for generating a cooled fluid E.

11. The method of claim 10, cooling and pressurizing the partially cooled fluid D comprises pressurizing the cooled fluid E via a pressure building system 26 for generating the high-pressure low temperature fluid F.

12. An energy recovery system, comprising:
a first multi-stream heat exchanger 30 configured to convert a partially heated fluid A to a high temperature fluid B, while generating a partially cooled waste heat stream X;
a first fluid expander 32 configured to expand the high temperature fluid B into a first expanded fluid G, wherein the first multi-stream heat exchanger 30 is further configured to transfer heat to the first expanded fluid G to generate a first heated fluid H;
a second fluid expander 34 configured to expand the first heated fluid H into an expanded fluid C;
a multi-stream heat exchanger 22 configured to transfer heat from the expanded fluid C and the partially cooled waste heat stream X to a high-pressure low temperature fluid F to generate the partially heated fluid A, while cooling the expanded fluid C to a partially cooled fluid D, wherein the partially cooled fluid D is cooled and pressurized to generate the high-pressure low temperature fluid F.

13. The energy recovery system of claim 12, wherein the first multi-stream heat exchanger 30 comprises any of a shell and tube heat exchanger, a micro shell and tube heat exchanger, a plate-fin heat exchanger, or a printed circuit heat exchanger (PCHE).

14. The energy recovery system of claim 12, wherein the first fluid expander 32 comprises a power turbine and the second fluid expander 34 comprises a power turbine.

15. The energy recovery system of claim 12, comprises a fluid cooling system 24 configured to cool the partially cooled fluid D to generate a cooled fluid E, wherein a pressure building system 26 pressurizes the cooled fluid E to generate the high-pressure low temperature fluid F.

16. The energy recovery system of claim 12, wherein the multi-stream heat exchanger 22 comprises any of a shell and tube heat exchanger, a micro shell and tube heat exchanger, a plate-fin heat exchanger, or a printed circuit heat exchanger (PCHE).

17. An energy recovery system, comprising:
a heat exchanger 18 configured to convert a partially heated fluid A to a high temperature fluid B, while generating a partially cooled waste heat stream X;
a fluid expander 20 configured to expand the high temperature fluid B into an expanded fluid C; and
a multi-stream heat exchanger 22 configured to transfer heat from the expanded fluid C and the partially cooled waste heat stream X to a second high pressure low temperature fluid L to generate the partially heated fluid A, while cooling the expanded fluid C to a partially cooled fluid D;
a second multi-stream heat exchanger 36 configured to transfer heat from the partially cooled fluid D to generate a first cooled fluid I;
a first pressure building system 38 configured to pressurize the first cooled fluid I to generate a first pressurized fluid J; wherein the first pressurized fluid J is further cooled in the second multi-stream heat exchanger 36 to generate a second cooled fluid K; and
a second pressure building system 40 configured to pressurize the second cooled fluid K to generate the second high pressure low temperature fluid L.

18. An energy recovery system, comprising:
a heat exchanger 18 configured to convert a partially heated fluid A to a high temperature fluid B, while generating a partially cooled waste heat stream X;
a fluid expander 20 configured to expand the high temperature fluid B into an expanded fluid C; and
a multi-stream heat exchanger 22 configured to transfer heat from the expanded fluid C and the partially cooled waste heat stream X to a third high pressure low temperature fluid Q to generate the partially heated fluid A, while cooling the expanded fluid C to a partially cooled fluid D;
a third multi-stream heat exchanger 42 configured to transfer heat from the partially cooled fluid D to generate a third cooled fluid M;
a first pressure building system 38 configured to pressurize the third cooled fluid M to generate a third pressurized fluid N; wherein the third pressurized fluid N is further cooled in the third multi-stream heat exchanger 42 to generate a third cooled fluid O; and
a second pressure building system 40 configured to pressurize the third cooled fluid O to generate a fourth pressurized fluid P, wherein the fourth pressurized fluid P is further cooled in the third multi-stream heat exchanger 42 to generate the third high pressure low temperature fluid Q. , Description:BACKGROUND
[0001] The invention relates generally to the field of heat engines and, more specifically, to waste heat recovery systems.
[0002] A device that converts heat to work is called a heat engine. Heat engines operate on a working fluid to convert heat to work. Many energy-intensive industrial sectors such as cement, fertilizer, aluminum, textile, and paper industries generate large amounts of waste heat which is converted to usable electricity using steam turbines. As technologies for recovering waste heat improves, the use of higher efficiency working fluids compared to steam, such as carbon dioxide in its supercritical phase (sCO2), is being considered. Switching over from steam to sCO2 cycles has a lot of advantages. It has a compact turbo-machinery footprint; has comparable performance relative to steam cycles; has quicker start-stop operations cycle response; and erosion of turbine blade is absent.
[0003] While numerous thermodynamic cycles are known for waste heat recovery, all of them utilize multiple heat exchangers, turbo-machinery, and flow splitters that are employed after compression. It would be appreciated by one of ordinary skill in the art that as the number of heat exchangers and turbine units reduce, the efficiency of the system would improve, as would the economy of the architecture. Similarly, the presence of flow splitters would introduce additional difficulties in real-time control during power generation.
[0004] Therefore, there is a need for a simple and compact thermodynamic cycle architecture that not only improves the efficiency of waste heat recovery but also obviates the need for multiple equipments.

SUMMARY
[0005] A compact energy recovery system is described. The energy recovery system includes a heat exchanger that transfers heat from a waste heat source to a pre-heated high temperature compressed fluid while generating a high temperature fluid and a partially cooled waste heat stream. A high temperature fluid expander expands the high temperature fluid to generate a high temperature expanded fluid. A multi-stream heat exchanger simultaneously transfers heat from the high temperature expanded fluid and the partially cooled waste heat stream to a low temperature, high pressure fluid while generating a low temperature waste heat stream, low temperature expanded fluid and a high temperature compressed fluid. The low temperature expanded fluid is subsequently cooled in a heat exchanger and is compressed using a pressure raising system to produce a low temperature, high pressure fluid. The low temperature, high pressure fluid is fed into the multi- stream heat exchanger to complete the cycle. A method of operating the compact energy recovery system is also described. Other embodiments of the energy recovery system are also described in which the fluid expansion or the pressure building processes are done in two stages, or where both the fluid expansion and the pressure building processes are done in two stages.
[0006] These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is an illustrative representation of a system including a novel energy recovery system in accordance with an embodiment of the invention.
[0008] FIG. 2 is a schematic representation of an exemplary energy recovery system in accordance with one aspect of the present technique.
[0009] FIG. 3 is another embodiment of the energy recovery system in accordance with aspects of the present technique
[0010] FIG. 4 is yet another embodiment of the energy recovery system in accordance with aspects of the present technique
[0011] FIG. 5 is still another embodiment of the energy recovery system in accordance with aspects of the present technique
[0012] FIG. 6 is yet another embodiment of the energy recovery system in accordance with aspects of the present technique
[0013] FIG. 7 is yet another embodiment of the energy recovery system in accordance with aspects of the present technique
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0014] FIG. 1 is a diagrammatical view of a system 10 including a waste heat source 12 and an exemplary energy recovery system 14 in accordance with one aspect of the present technique. The waste heat source 12 provides a heated fluid from which heat is recovered by the energy recovery system 14. During this process, a part of the heat is rejected to the surroundings. The heat energy that is recovered by the energy recovery system 14 is converted to work, which is high-grade energy, via a power generator 16.
[0015] It may be noted that in various embodiments, the waste heat source may include hot gaseous or fluid flow from gas turbines, hot air evacuation chimneys, furnaces, boilers, heat exhausted from industrial processes such as steel plant operation, cement kilns, brick kilns or glass making, combustors, nuclear reactors, gas turbine exhaust from naval vessels, as a by-product of power plants and other manufacturing operations among other diverse waste heat or low-grade heat sources. Further, low-grade heat from solar thermal sources or geothermal sources can also be utilized in the system 10 while keeping within the scope of the techniques described herein. It would be appreciated by one of ordinary skill in the art that often such generated heat is wasted away or dissipated or removed and is therefore lost.
[0016] The energy recovery system 14 includes one or more heat exchangers configured to recover heat energy from the waste heat source 12 efficiently and feed it into a system of fluid expanders in order to convert the heat energy to work by the power generator 16. The power generator 16 uses the recovered heat to convert it into mechanical energy, or to drive electrical generator, or to store power in chemical or battery-based power storage systems. In various embodiments, the power generator 16 may include alternators as well.
[0017] Referring generally to FIG. 2, an exemplary energy recovery system 14 is illustrated in accordance with one embodiment of the present technique. Hot exhaust gases from a waste heat source 12 enters a heat exchanger 18. The waste heat source 12 is thermally coupled to the heat exchanger 18 so that the high temperature exhaust gases pass through the heat exchanger 18. The heat exchanger 18 receives a partially heated fluid, flowing in direction A, which is utilized to extract heat from the high temperature exhaust gases in the heat exchanger 18. Subsequently, the partially heated fluid having extracted the heat achieves a high temperature, flow of which is generally shown by arrow B. The hot exhaust gases that entered heat exchanger 18 from the waste heat source 12 leave the heat exchanger stack at a lower temperature, as a partially cooled waste heat stream generally shown by arrow X. While the above waste heat source 12 has been described with hot exhaust gases, the waste heat source may include other fluids or other forms of heat energy, such as for example solar heat, which can be equally utilized by the heat exchanger 18 to extract heat, as previously noted.
[0018] Heat energy from the waste heat source 12, in the form of heat, is thus partially extracted by the heat exchanger 18 and the extracted heat in the form of the high temperature fluid, flowing in direction B, enters a fluid expander 20. The fluid expander 20 reduces the temperature and pressure of the high temperature fluid B which leaves the fluid expander 20 at an intermediate temperature as an expanded fluid denoted by arrow C.
[0019] The expanded fluid C and the partially cooled waste heat stream X then pass through a multi-stream heat exchanger 22, which transfers the heat energy to a high-pressure low temperature fluid flowing in direction F into the multi-stream heat exchanger 22. Thus, the high-pressure low temperature fluid F gains in temperature in the multi-stream heat exchanger 22 and subsequently flows as fluid A.
[0020] In the multi-stream heat exchanger 22, the partially cooled waste heat stream X and the expanded fluid C are cooled resulting in streams denoted by arrows Y and D respectively. Stream Y represents the fully cooled waste heat stream and is ejected to the ambient surroundings. The partially cooled fluid D passes through a fluid cooling system 24, which rejects heat to the surroundings bringing down the temperature to near ambient levels. It may be noted at this point that the fluid cooling system 24 may be configured to reduce the temperature of the partially cooled fluid D depending on the ambient temperatures. For example, in regions with low ambient temperatures such as between 18°C and 25°C, the fluid cooling system 24 may be set up to reduce the temperature of the partially cooled fluid D to temperatures close to that, such as about 20°C to 28°C. In tropical regions with higher ambient temperatures, say between 35°C and 50°C, the fluid cooling system 24 may be designed to reduce the temperature of the partially cooled fluid D closer to such temperatures, such as about 40°C to 60°C. In other words, the fluid cooling system 24, and therefore the entire energy recovery system 14, may be configured to operate at any ambient conditions.
[0021] After losing its heat in the fluid cooling system 24, the partially cooled fluid D emerges as cooled fluid E. The cooled fluid denoted by E coming out from the fluid cooling system 24 is then fed into a pressure building system 26. The pressure building system 26 pressurizes the cooled fluid E into a high-pressure low temperature fluid F, which may be in a liquefied state, a gaseous state or supercritical state, in various embodiments, depending upon the fluid and the phase of fluid used. As earlier noted, this high-pressure low temperature fluid F is fed into the multi-stream heat exchanger 22 to complete the cycle. Thus, this configuration obviates the need for splitting of the fluid flow at any stage of the cycle. Therefore, unlike the existing systems, this configuration does not require any flow splitters.
[0022] As would be appreciated by one of ordinary skill in the art, fluid expander 20 may be a power turbine, such as for example, a steam power turbine wherein the fluid is steam operating at superheated temperatures, a gas power turbine, or a supercritical carbon dioxide (sCO2) power turbine, where the operating fluid is carbon dioxide (CO2) with pressure and temperature optimized for maintaining CO2 at supercritical conditions. While sCO2 is preferred as working fluid, other pure fluids, such as but not limited to, hydrocarbons (such as methane, ethane or propane), Nitrogen, Helium or fluid mixtures such as a mixture of hydrocarbons and CO2 may also be used with appropriate operating pressures. As illustrated in FIG. 2, fluid expander 20 may drive a power generator 16 to produce any form of high-grade energy as described with reference to FIG. 1.
[0023] The fluid cooling system 24 may include a low temperature heat exchanger, a gas cooler, or a condenser, etc. Similarly, in various embodiments, the pressure building system 26 may include a compressor or a pump depending upon the phase of fluid used and may be driven by an electrical motor 28. For example, in case the fluid is in gaseous or supercritical phase, a compressor may be used, while if the fluid is in liquid phase, a pump may be used. The multi-stream heat exchanger may be of various types, such as but not limited to, shell and tube heat exchangers, micro shell and tube heat exchangers, plate-fin heat exchangers, printed circuit heat exchanger (PCHE), and the like.
[0024] Referring generally to FIG. 3, another embodiment of the energy recovery system is presented in accordance with aspects of the present technique. In this embodiment, the fluid expansion happens in two stages. Fluid A passes through a first multi-stream heat exchanger 30 and is heated to obtain a high temperature fluid B. The high temperature fluid B is expanded first using a first fluid expander 32 to obtain a first expanded fluid G. The first expanded fluid G is fed into the multi-stream heat exchanger 30 and heated to obtain a first heated fluid H. The first heated fluid H expands in a second fluid expander 34 to generate an expanded fluid C. As would be appreciated by one of ordinary skill in the art, the first fluid expander 32 and the second fluid expander 34 may together drive a single power generator 16, via shafts coupled to each, to produce any form of high-grade energy. The expanded fluid C then passes through the multi-stream heat exchanger 22 and cools down to generate a partially cooled fluid D. The partially cooled fluid D is then passed through the fluid cooling system 24 to generate cooled fluid E, which is further pressurized in the pressure building system 26 driven by an electrical motor 28 into a high-pressure low temperature fluid F. As in the previous embodiment of FIG. 2, the high-pressure low temperature fluid F extracts heat energy from the expanded fluid C and the partially cooled waste heat stream X in the multi-stream heat exchanger 22 to generate the partially heated fluid A.
[0025] FIG. 4 illustrates another embodiment of the energy recovery system in accordance with aspects of the present technique. In this embodiment, the pressure building process is done in two stages. The partially cooled fluid D passes through a second multi-stream heat exchanger 36 and is cooled to obtain a first cooled fluid I. The first cooled fluid I is pressurized first using a first pressure building system 38 to obtain a first pressurized fluid J. The first pressurized fluid J is again fed into the second multi-stream heat exchanger 36 and cooled to obtain a second cooled fluid K, as illustrated. The second cooled fluid K is again pressurized using a second pressure building system 40 to obtain a second high-pressure low temperature fluid L. The second high-pressure low temperature pressurized fluid L is fed into the multi-stream heat exchanger 22 to generate the partially heated fluid A and the process of heat transfer and expansion continues, as described with reference to FIG. 2. For example, the second high-pressure low temperature fluid L gains heat energy in the multi-stream heat exchanger 22 to generate the partially heated fluid A. The partially heated fluid A extracts heat from the waste heat source 12 in the heat exchanger 18 to generate a high temperature fluid, flowing in direction B. The fluid expander 20 reduces the temperature and pressure of the high temperature fluid B which leaves the fluid expander 20 at an intermediate temperature as an expanded fluid denoted by arrow C. The expanded fluid C along with the partially cooled waste heat stream X from the heat exchanger 18 then pass through the multi-stream heat exchanger 22, and transfer heat energy to the second high-pressure low temperature pressurized fluid L flowing into the multi-stream heat exchanger 22. As previously noted, the second high-pressure low temperature fluid L gains in temperature in the multi-stream heat exchanger 22 and subsequently flows as the partially heated fluid A.
[0026] Turning now to FIG. 5, yet another embodiment of the energy recovery system is presented in accordance with aspects of the present techniques. As previously described with reference to FIG. 2, the partially heated fluid A extracts heat from the waste heat source 12 in the heat exchanger 18 to generate a high temperature fluid, flowing in direction B. The fluid expander 20 reduces the temperature and pressure of the high temperature fluid B which leaves the fluid expander 20 at an intermediate temperature as an expanded fluid denoted by arrow C. The expanded fluid C along with the partially cooled waste heat stream X from the heat exchanger 18 then pass through the multi-stream heat exchanger 22, and transfer the heat energy to a third high-pressure low temperature fluid Q flowing into the multi-stream heat exchanger 22. After passing through the multi-stream heat exchanger 22, the expanded fluid C cools down to partially cooled fluid D. In this embodiment, the pressure building of the partially cooled fluid D is performed in two stages. The partially cooled fluid D is passed through a third multi-stream heat exchanger 42 to generate a third cooled fluid M, which is first pressurized in a first pressure building system 38 driven by electrical motor 28 into a third pressurized fluid N. The third pressurized fluid N is fed into the third multi-stream heat exchanger 42 to cool and generate a third cooled fluid O. The pressure of the third cooled fluid O is further increased using a second pressure building system 40, driven by the electrical motor 28, to obtain a fourth pressurized fluid P. The fourth pressurized fluid P is fed into the third multi-stream heat exchanger 42 and is cooled to obtain the third high-pressure low temperature fluid Q. As noted before, the third high-pressure low temperature fluid Q is fed into the multi-stream heat exchanger 22 to obtain the partially heated fluid A and the process of heat transfer and expansion continues.
[0027] FIG. 6 illustrates yet another embodiment of the energy recovery system in accordance with aspects of the present technique. One of ordinary skill in the art would appreciate that the teachings of the techniques described with reference to FIG. 3 and FIG. 4 may be combined together to arrive at FIG. 6. Therefore, in this embodiment, both the pressure building process and the expansion process are performed in two stages, thus combining the procedures elaborated with reference to FIG. 3 and FIG. 4.
[0028] Moving over to FIG. 7, still another embodiment of the energy recovery system is illustrated in accordance with aspects of the present technique. As would be appreciated, the teachings of the techniques described with reference to FIG. 3 and FIG. 5 may be combined together to arrive at FIG. 7. In other words, in this embodiment, the pressure building process and the expansion process are each performed in two stages, thus combining the procedures elaborated with reference to FIG. 3 and FIG. 5.
[0029] The various embodiments of the proposed invention described from FIG. 3 to FIG. 7 describe techniques to further increase the efficiency of power production based on the teachings of FIG. 2. These modifications may be implemented based on the desired recovery of waste heat. Applications for embodiments of the invention may be found in combined cycle systems or waste heat recovery systems where waste heat is recovered and utilized to drive power generators to convert low-grade energy (heat) to high-grade energy (work). Teachings of the present techniques can be used to build power systems and power plants where waste heat is available at any ambient temperature.
[0030] While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.