Supercritical CO2 generation system for series recuperative type

Abstract

The present invention relates to a supercritical CO.sub.2 power generation system of a series recuperative type. According to an embodiment of the present invention, an inlet temperature of a turbine can be increased to increase a work of the turbine, thereby realizing a cycle design having improved turbine efficiency. Further, the number and diameter of pipes connected to a heat exchanger using an external heat source can be reduced to reduce the plumbing related costs, thereby improving economical efficiency.

Claims

1. A supercritical CO2 generation system, comprising: a compressor configured to compress a working fluid; a plurality of heat exchangers configured to heat the working fluid using a heat supplied from an external heat source: a plurality of turbines driven by the working fluid; a plurality of recuperators configured to exchange heat between the working fluid having passed through the plurality of turbines and the working fluid having passed through the compressor to thereby cool the working fluid having passed through the plurality of turbines, wherein the plurality of recuperators are installed in series with each other; and a pre-cooler configured to cool the working fluid primarily cooled by the plurality of recuperators, and supply the pre-cooled working fluid to the compressor, wherein temperatures of the working fluids respectively introduced into the plurality of turbines are different from each other, wherein the supercritical CO2 generation system further comprises a mixer configured to mix the working fluid heated by a cold side heat exchanger among the plurality of heat exchangers after having passed through the compressor and having been branched to the cold side heat exchanger with the working fluid having been branched from a cold side recuperator among the plurality of recuperators into the mixer after having passed through the cold side recuperator, such that the working fluid heated by, and having passing through, the cold side heat exchanger is supplied to a hot side heat exchanger among the plurality of heat exchangers without branching required for being supplied to the hot side heat exchanger, wherein the mixer is installed at a downstream end of a separator such that the working fluid, which has passed through the cold side heat exchanger, is mixed with the working fluid, which is branched from the separator after having passed through the cold side recuperator, wherein the separator is disposed at a downstream end of the cold side recuperator, and configured to respectively branch the working fluid heated via the cold side recuperator to (i) a hot side recuperator among the plurality of recuperators and (ii) the mixer such that the working fluid mixed at the mixer is supplied to the hot side heat exchanger, wherein the working fluid branched to the cold side recuperator is heated via the cold side recuperator and then branched to the hot side recuperator among the plurality of recuperators and the hot side heat exchanger among the plurality of heat exchangers, wherein the working fluid branched to the hot side heat exchanger is mixed with the working fluid heated by the cold side heat exchanger to be supplied to the hot side heat exchanger and reheated, and is then supplied to a hot side turbine among the plurality of turbines, wherein the working fluid branched to the hot side recuperator is heated via the hot side recuperator and then supplied to a cold side turbine among the plurality of turbines.

2. The supercritical CO2 generation system of claim 1, wherein the working fluid having passed through the compressor is branched to the cold side heat exchanger among the plurality of heat exchangers and the cold side recuperator among the plurality of recuperators from a downstream end of the compressor, respectively.

3. The supercritical CO2 generation system of claim 1, wherein a flow rate of the working fluid supplied to the hot side turbine via the hot side heat exchanger is set to be larger than that of the working fluid supplied to the cold side turbine via the hot side recuperator.

4. The supercritical CO2 generation system of claim 3, wherein the working fluid supplied to the hot side turbine is transmitted to the hot side recuperator after the hot side turbine is driven and exchanges heat with the working fluid supplied to the hot side recuperator via the compressor to be primarily cooled.

5. The supercritical CO2 generation system of claim 4, wherein the working fluid cooled by the hot side recuperator is mixed with the working fluid via the cold side turbine to be supplied to the cold side recuperator.

6. The supercritical CO2 generation system of claim 5, wherein the working fluid supplied to the cold side recuperator via the hot side recuperator exchanges heat with the working fluid via the compressor to be secondarily cooled, and the working fluid cooled by the cold side recuperator is supplied to the pre-cooler.

7. The supercritical CO2 generation system of claim 1, wherein the flow rate of the working fluid supplied to the hot side turbine via the hot side heat exchanger is 50% to 60% of a total flow rate of the working fluid having passed through the compressor.

8. A supercritical CO2 generation system, comprising: a compressor configured to compress a working fluid; a high temperature heater and a low temperature heater configured to heat the working fluid using a heat supplied from an external heat source; a high temperature turbine and a low temperature turbine driven by the working fluid; a plurality of recuperators configured to exchange heat between (i) the working fluid having passed through the high temperature turbine and the low temperature turbine and (ii) the working fluid having passed through the compressor to thereby cool the working fluid having passed through the high temperature turbine and the low temperature turbine, wherein the plurality of recuperators are installed in series with each other; and a pre-cooler cooling the working fluid primarily cooled by the plurality of recuperators and supplying the pre-cooled working fluid to the compressor, wherein the temperatures of the working fluids introduced into the high temperature turbine and the low temperature turbine are different from each other, wherein the supercritical CO2 generation system further comprises a first mixer configured to mix the working fluid heated by the low temperature heater after having passed through the compressor and having been branched to the low temperature heater with the working fluid having been branched from a low temperature recuperator among the plurality of recuperators into the first mixer after having passed through the low temperature recuperator, such that the working fluid heated by, and having passing through, the low temperature heater is supplied to the high temperature heater without branching required for being supplied to the high temperature heater, wherein the first mixer is installed at a downstream end of a second separator such that the working fluid, which has passed through the low temperature heater, is mixed with the working fluid, which is branched from the second separator after having passed through the low temperature recuperator, wherein the second separator is disposed at a downstream end of the low temperature recuperator, and configured to respectively branch the working fluid heated via the low temperature recuperator to (i) a high temperature recuperator among the plurality of recuperators and (ii) the first mixer such that the working fluid mixed at the first mixer is supplied to the high temperature heater, wherein the working fluid having passed through the high temperature turbine is cooled by sequentially having passed through the high temperature recuperator and the low temperature recuperator and then supplied to the pre-cooler, wherein a downstream end of the compressor is provided with a first separator, and the working fluid having passed through the compressor is branched to the low temperature heater and the low temperature recuperator, respectively, wherein a downstream end of the low temperature heater is provided with the first mixer, and the working fluid branched to the low temperature heater is primarily heated by the low temperature heater and is then mixed with the working fluid from the low temperature recuperator by the first mixer, and wherein the working fluid mixed by the first mixer is reheated by the high temperature heater to be supplied to the high temperature turbine.

9. The supercritical COz2 generation system of claim 8, wherein the working fluid branched from the second separator to the high temperature recuperator is secondarily heated by the high temperature recuperator and then supplied to the low temperature turbine.

10. The supercritical COz generation system of claim 9, wherein a second mixer is provided between the high temperature recuperator and the low temperature recuperator, and the working fluid via the high temperature turbine exchanges heat with the working fluid via the second separator from the high temperature recuperator to be primarily cooled and then supplied to the second mixer.

11. The supercritical CO2 generation system of claim 10, wherein the working fluid having passed through the low temperature turbine is mixed with the working fluid having passed through the high temperature recuperator by the second mixer, supplied to the low temperature recuperator, and exchanges heat with the working fluid having passed through the first separator to be secondarily cooled and is then supplied to the pre-cooler.

12. The supercritical CO2 generation system of claim 8, wherein a flow rate of the working fluid mixed by the first mixer to be supplied to the high temperature heater is set to be larger than that of the working fluid branched to the high temperature recuperator and supplied to the low temperature turbine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and other objects, features and other advantages will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 is a schematic diagram showing the existing EPRI proposed cycle;

(3) FIG. 2 is a schematic diagram showing a cycle of a supercritical CO.sub.2 generation system for a series recuperative type according to an exemplary embodiment;

(4) FIG. 3 is a comparison graph of temperature characteristics of a cycle of FIG. 1 and a cycle of FIG. 2;

(5) FIG. 4 is a comparison graph of net power of the cycle of FIG. 1 and the cycle of FIG. 2;

(6) FIG. 5 is a comparison graph of inlet temperatures of low temperature turbines of the cycle of FIG. 1 and the cycle of FIG. 2;

(7) FIG. 6 is a comparison graph of a sum of flow rates of connection plumbings of the cycle of FIG. 1 and the cycle of FIG. 2; and

(8) FIG. 7 is a comparison graph of flow rates of first mixers of the cycle of FIG. 1 and the cycle of FIG. 2.

DETAILED DESCRIPTION

(9) Hereinafter, a supercritical CO.sub.2 generation system for a series recuperative type according to an exemplary embodiment will be described in detail with reference to the accompanying drawings.

(10) Generally, the supercritical CO.sub.2 generation system configures a closed cycle in which CO.sub.2 used for power generation is not emitted to the outside, and uses supercritical CO.sub.2 as a working fluid to construct a single phase generation system. The supercritical CO.sub.2 generation system uses the CO.sub.2 as the working fluid and therefore may use exhaust gas emitted from a thermal power plant, etc., such that it may be used in a single generation system and a hybrid generation system with the thermal generation system. The working fluid of the supercritical CO.sub.2 generation system may also supply CO.sub.2 separated from the exhaust gas and may also supply separate CO.sub.2.

(11) A working fluid in a cycle that is a supercritical CO.sub.2 becomes a high temperature and high pressure working fluid while passing through a compressor and a heater to drive a turbine. The turbine is connected to a generator and the generator is driven by the turbine to produce power. Alternatively, the turbine and the compressor may be coaxially connected to each other, and then the compressor may be provided with a gear box or the like to be connected to the generator. The working fluid used to produce power is cooled while passing through heat exchangers such as a recuperator and a pre-cooler and the cooled working fluid is again supplied to the compressor and is circulated within the cycle. The turbine or the heat exchanger may be provided in plural.

(12) The supercritical CO.sub.2 generation system according to various exemplary embodiments refers to a system where all the working fluids flowing within the cycle are in the supercritical state as well as a system where most of the working fluids are in the supercritical state and the rest of the working fluids are in a subcritical state.

(13) Further, in various exemplary embodiments, the CO.sub.2 is used as the working fluid. Here, CO.sub.2 refers to pure carbon dioxide in a chemical meaning as well as carbon dioxide including some impurities and even a fluid in which carbon dioxide is mixed with one or more fluids as additives in general terms.

(14) FIG. 2 is a schematic diagram showing a cycle of a supercritical CO.sub.2 generation system for a series recuperative type according to an exemplary embodiment. Referring to FIG. 2, the generation cycle includes two turbines 410a and 430a (400a) for producing electric power, a pre-cooler 500a for cooling a working fluid, and a compressor 100a for increasing a pressure of the cooled working fluid, thereby forming high temperature and high pressure working fluid conditions. In addition, two waste heat recovery heat exchangers 300a (hereinafter, low temperature heater 330a and high temperature heater 310a) separated for effective waste heat recovery are provided and two recuperators 200a (hereinafter, low temperature recuperator 230a and high temperature recuperator 210a) for heat exchange of the working fluid are provided. The waste heat recovery heat exchanger 300a and the recuperator 200a are provided in series, and a plurality of separators and mixers for distributing a flow rate of the working fluid are provided.

(15) A high temperature turbine 410a and the low temperature turbine 430a are driven by the working fluid. First, the high temperature and high pressure working fluid is supplied to the high temperature turbine 410a via transfer pipe 1. A mid-temperature and mid-pressure working fluid that drives the high temperature turbine 410a and is expanded is transmitted to the hot side of the high temperature recuperator 210a via transfer pipe 2 and exchanges heat with the working fluid passing through the compressor 100a and the low temperature recuperator 230a. A rear end of the recuperator 210a is provided with the second mixer M2 and the working fluid that is cooled after heat exchange is transmitted to the second mixer M2 via transfer pipe 3. The working fluid cooled by the high temperature recuperator 210a is mixed with the working fluid that is expanded by passing through the low temperature turbine 430a and has the reduced temperature by the second mixer M2 and is transmitted to the hot side of the low temperature recuperator 230a via transfer pipe 4. That is, the working fluid transmitted to the low temperature recuperator 230a becomes a sum of the working fluids passing through the high temperature turbine 410a and the low temperature turbine 430a. The working fluid once again cooled by the low temperature recuperator 230a is transmitted to the hot side of the pre-cooler 500a via transfer pipe 5. The working fluid cooled by the pre-cooler 500a is transmitted to the compressor 100a via transfer pipe 6.

(16) The low temperature and high pressure working fluid having flow rate m that is cooled by the pre-cooler 500a and compressed by the compressor 100a is transmitted to the separator S1 provided at a rear end of the compressor 100a via transfer pipe 7. The working fluid is branched from the separator S1 to the low temperature heater 330a and the low temperature recuperator 230a, respectively, and branched through transfer pipes 8 and 14, respectively.

(17) The low temperature heater 330a and the high temperature heater 310a are external heat exchangers that heat a working fluid using an external heat source of a cycle such as waste heat, and use gas, as a heat source (hereinafter, waste heat gas) having waste heat such as exhaust gas emitted from a boiler of a generator. The low temperature heater 330a and the high temperature heater 310a serve to exchange heat between the waste heat gas and the working fluid circulated within the cycle, thereby heating the working fluid with heat supplied from the waste heat gas. As the heat exchanger approaches the external heat source, the heat exchange is made at a higher temperature, and as the heat exchanger approaches an outlet end through which the waste heat gas is discharged, the heat exchange is made at a low temperature. The waste heat gas is introduced into the high temperature heater 310a from the high temperature heater via transfer pipe A, introduced into the low temperature heater 330a through the high temperature heater 310a via transfer pipe B, and then discharged to the outside through the low temperature heater 330a via transfer pipe C. Therefore, the high temperature heater 310a is a heat exchanger close to the external heat source, and the low temperature heater 330a is a heat exchanger far away from the external heat source and the high temperature heater 310a.

(18) The working fluid having flow rate mf1 branched to the low temperature heater 330a exchanges heat with the waste heat gas to be primarily heated and is then transmitted to the first mixer M1 installed at the downstream end of the low temperature heater 330a via transfer pipe 9. A second separator S2 is installed between the low temperature recuperator 230a and the mixer M1. The working fluid, which has passed through low temperature recuperator 230a, is branched to the mixer M1 and the high temperature recuperator 210a. The working fluid, which is branched from a second separator after having passed through the low temperature recuperator 230a via the compressor 100a, is transmitted to the first mixer M1 in order to be supplied to the high temperature heater 310a. The flow rate of the working fluid mixed by the first mixer M1 corresponds to the flow rate m of the entire system, and the branched working fluid is supplied to the high temperature recuperator 210a via transfer pipe 15. In the second separator S2, the working fluid is branched to the mixer M1 via transfer pipe 16 and then transferred through the mixer M1 to the high temperature heater 310a via transfer pipe 10 and heated and then supplied to the high temperature turbine 410a via transfer pipe 1, and is branched even to the high temperature recuperator 210a via transfer pipe 15.

(19) If the flow rate branched to the high temperature heater 310a is mf2, the flow rate of the working fluid branched to the high temperature recuperator 210a via the second separator S2 becomes m (1f2). On the other hand, the working fluid branched to the high temperature recuperator 210a exchanges heat with the working fluid passing through the high pressure turbine 410a to be heated via transfer pipe 15, and is then transmitted to the low temperature turbine 430a via transfer pipe 11. The working fluid that drives the low temperature turbine 430a is transmitted to the second mixer M2 as described above via transfer pipe 12.

(20) The flow rate mf2 of the working fluid supplied to the high temperature turbine 410a through the high temperature heater 310a is preferably set to be larger than the flow rate (m (1f2)) of the working fluid supplied to the low temperature turbine 430a via the high temperature recuperator 210a. By the process, the working fluid is circulated within the cycle to drive the turbine and to generate the work of the turbine.

(21) The difference between the existing cycle and the supercritical CO.sub.2 generation system of a series recuperative type according to the exemplary embodiment having the above configuration will be described in detail as follows. In all cases, the inlet temperature of the high temperature turbine, the flow rate of the entire working fluid, and the heat capacity introduced from the external heat source are fixed as the same value.

(22) FIG. 3 is a comparison graph of temperature characteristics of a cycle of FIG. 1 and a cycle of FIG. 2. FIG. 4 is a comparison graph of net power of the cycle of FIG. 1 and the cycle of FIG. 2. FIG. 5 is a comparison graph of inlet temperatures of low temperature turbines of the cycle of FIG. 1 and the cycle of FIG. 2. FIG. 6 is a comparison graph of a sum of flow rates of connection plumbings of the cycle of FIG. 1 and the cycle of FIG. 2. FIG. 7 is a comparison graph of flow rates of first mixers of the cycle of FIG. 1 and the cycle of FIG. 2.

(23) As shown in FIG. 3, when delta t1 ( t1, the temperature difference in the cold side outlets between the low temperature recuperator and the low temperature heater, the temperature difference between transfer pipe 13 and transfer pipe 9) is changed, in the EPRI proposed cycle as shown in FIG. 1, delta t2 (temperature difference in the cold side inlets between the high temperature recuperator and the high temperature heater, the difference between temperature of transfer pipe 15 and temperature of transfer pipe 10) is always maintained to be 0 C. However, in the cycle of the present disclosure, the delta t2 may have a value other than 0 C. Accordingly, since the temperatures of the working fluids introduced into the high temperature recuperator 210a and the high temperature heater 310a are different (transfer pipes 10 and 15), it is possible to design a cycle in which the inlet temperature of the turbine is increased to increase the work of the turbine.

(24) As shown in FIG. 4, the delta t1 is greater than or equal to 0 C., and as the value increases, the proposed cycle of the present disclosure is more superior in net power, compared to the existing EPRI proposed cycle. That is, the proposed cycle of the present disclosure can achieve a higher output in the capacity of the given external heat source, compared with the existing EPRI proposed cycle.

(25) As shown in FIG. 5, as the design is implemented by increasing the delta t1, the inlet temperature of the low temperature turbine in the proposed cycle of the present disclosure is increased, compared to the EPRI proposed cycle, which leads to the increase in the net power.

(26) A typical waste heat recovery generation system may be classified into a waste heat recovery heater block (portion connected from the external heat source to the high temperature and low temperature heaters) for recovering waste heat from the external heat source, a power block including the recuperator and the turbine (generation system portion other than the waste heat recovery block), in which these two blocks are installed at a physical distance. At this time, as the connection plumbing between the two blocks is getting simpler and smaller, the economical efficiency is increased. As shown in FIG. 6, the proposed cycle of the present disclosure can reduce the plumbing diameter because the sum of the flow rates of the connection plumbing between the two blocks is about 60% compared to the EPRI proposed cycle, thereby saving the plumbing costs.

(27) Further, as shown in FIG. 7, since the proposed cycle of the present disclosure has about 50% to 60% of the flow rate of the working fluid introduced into the first mixer, compared to the EPRI proposed cycle, the first mixer and the plumbing before and after the first mixer can be relatively smaller than before. Accordingly, it is possible to save the plumbing related costs.

(28) The supercritical CO.sub.2 power generation system of the series recuperative type according to an exemplary embodiment can increase the inlet temperature of the turbine to increase the work of the turbine, thereby realizing the cycle design having the improved turbine efficiency. Further, the number and diameter of pipes connected to the heat exchanger using the external heat source can be reduced to reduce the plumbing related costs, thereby improving the economical efficiency.

(29) The various exemplary embodiments described as above and shown in the drawings should not be interpreted as limiting the technical spirit of the present invention. The scope of the present disclosure is limited only by matters set forth in the claims and those skilled in the art can modify and change the technical subjects of the present invention in various forms.