KR102122945B1 - Transcritical carbon dioxide power generation system - Google Patents

Abstract

Heat source; Pump; turbine; And a cooler; is connected to the flow path to form a closed circuit, the closed circuit, carbon dioxide; And one or more selected from the group consisting of organic refrigerants and organic solvents; a supercritical carbon dioxide power generation system characterized in that the circulating mixed working fluid.

Description

Transcritical carbon dioxide power generation system

It is about a transcritical carbon dioxide power generation system.

A supercritical carbon dioxide generation system is a power generation system using supercritical carbon dioxide as a working fluid. Carbon dioxide has a high density and low compressibility coefficient near the critical point (31°C and 7.377 MPa), which can reduce the compression work consumed when compressing near the critical point. Therefore, the supercritical carbon dioxide power generation system constituting the compression process near the critical point has an advantage in terms of thermal efficiency.

In addition, since the specific volume is maintained lower than that of other power generation systems throughout the power generation system, there is an advantage of reducing the size of heat exchangers, compressors, and turbines, which are major components. Based on this, research on power generation systems in connection with various heat sources such as thermal power, solar heat, geothermal heat, fuel cells, and industrial waste heat is ongoing.

However, the supercritical carbon dioxide power generation system is a system operating at 31°C or higher, which is the critical temperature of carbon dioxide, and has a limit of the critical temperature (31°C) at the minimum operating temperature during system design or operation. This minimum operating temperature requires a large amount of cooling flow or a large size heat exchanger to dissipate the waste heat in warm areas due to the small difference in temperature from the atmospheric or sea water, the ultimate heat sink.

Republic of Korea Registered Patent No. 10-1691908

The present invention has been made in view of the above-described problems, and an object of the present invention is to mix the carbon dioxide used as a working fluid with at least one of an organic refrigerant and an organic solvent to change the characteristics of the working fluid to change the critical temperature of carbon dioxide ( It is possible to liquefy even above 31℃), and it is an advantage of using a liquid pump rather than gas compression when compressing liquid, and it improves system performance and lowers technical difficulty by increasing power system efficiency, simplifying maintenance of components, and simplifying maintenance. There is a purpose.

In order to achieve the above object, in one aspect of the present invention

Heat source; Pump; turbine; And cooler; is connected to the flow path to form a closed circuit,

The closed circuit,

carbon dioxide; And an organic refrigerant and at least one selected from the group consisting of organic solvents. A supercritical carbon dioxide power generation system is provided, wherein a mixed working fluid containing circulates.

In addition, in another aspect of the present invention

Heat source; Pump; turbine; cooler; And a recuperator connected to a flow path to form a closed circuit,

The closed circuit,

carbon dioxide; And an organic refrigerant and at least one selected from the group consisting of organic solvents. A supercritical carbon dioxide power generation system is provided, wherein a mixed working fluid containing circulates.

The transcritical carbon dioxide power generation system provided in one aspect of the present invention, when toluene and R-32 presented as examples are mixed with carbon dioxide at a mass fraction of 32% (carbon dioxide (68%): toluene (32%)), (carbon dioxide ( 68%):R-32 (32%)) It is possible to liquefy from 190℃ and 36℃, respectively, replacing the mechanical limitations and losses in the high pressure gas compression method with the liquid pump method, enabling efficient and simple operation. There is.

In addition, by lowering the minimum pressure from the critical pressure of carbon dioxide (7.4 MPa) to 5.53 MPa and 5.37 MPa, respectively, it is possible to lower design difficulty and manufacturing cost by lowering design consideration pressure when manufacturing low-pressure devices (pumps, coolers, recuperators, etc.). , This can increase the amount of power generation by increasing the pressure ratio of the power generation system to maintain the pressure of the high-pressure part the same as the existing pure carbon dioxide supercritical power generation system.

Furthermore, unlike a single fluid, the mixed fluid is advantageous for heat transfer because the temperature is not kept constant in the isothermal cooling process (condensation process) including phase change, and it is possible to reduce the volume and manufacturing cost due to less loss when designing the heat exchanger.

In addition, the transcritical carbon dioxide power generation system through mixing of one or more of organic solvents and organic refrigerants with carbon dioxide can control the mixing fluid (carbon dioxide and organic solvent/organic refrigerant) and the mixing ratio according to the applied heat source. Through this, it is possible to construct a small power generation system below 300°C and a sub power generation system for load control of a large power generation system, and it is expected to be used to improve performance by adjusting the mixing ratio according to changes in operating conditions (de-design operation).

1 and 2 are schematic diagrams showing an example of a transcritical carbon dioxide power generation system;
3 and 4 are graphs showing the Ts diagram of the transcritical carbon dioxide power generation system;
5 and 6 is a graph showing the change in efficiency according to the mixing ratio of carbon dioxide and R-32 or carbon dioxide and toluene;
7 is a schematic diagram showing the simulation equipment of KAIST-SCO ₂ PE power generation system used for experimental verification;
8 and 9 are graphs showing the pressure ratio or pressure difference between the pump inlet and the outlet generated through the pump experiment.

In one aspect of the invention

Heat source; Pump; turbine; And cooler; is connected to the flow path to form a closed circuit,

The closed circuit,

carbon dioxide; And an organic refrigerant and at least one selected from the group consisting of organic solvents. A supercritical carbon dioxide power generation system is provided, wherein a mixed working fluid containing circulates.

In addition, in another aspect of the present invention

Heat source; Pump; turbine; cooler; And a recuperator connected to a flow path to form a closed circuit,

The closed circuit,

carbon dioxide; And an organic refrigerant and at least one selected from the group consisting of organic solvents. A supercritical carbon dioxide power generation system is provided, wherein a mixed working fluid containing circulates.

At this time, Figure 1 and Figure 2 is a schematic diagram showing an example of a transcritical carbon dioxide power generation system provided in one aspect of the present invention,

Hereinafter, the supercritical carbon dioxide power generation system provided in one aspect of the present invention will be described in detail with reference to the schematic diagrams of FIGS. 1 and 2.

In the present invention, in the working fluid used in the supercritical carbon dioxide power generation system, due to the critical points (31°C and 7.377 MPa) of the carbon dioxide, liquefaction is impossible above the critical point. As working fluid, carbon dioxide, organic refrigerant and organic solvent 1 Mixing more than one species increases the critical point and enables liquefaction even at the lowest temperature of the existing power generation system, thereby improving power generation efficiency.

Accordingly, the mixed working fluid of the transcritical carbon dioxide power generation system provided in one aspect of the present invention is used, and the mixed working fluid is a mixture of carbon dioxide, an organic refrigerant, an organic solvent, or an organic refrigerant and an organic solvent.

In addition, the organic refrigerant may be an organic refrigerant of the R series, and specific examples include R-32 (CH ₂ F ₂ ), R-123 (CHCl ₂ CF ₃ ), R-134a (CF ₃ CH ₂ F) and R22. (CHClF ₂ ), and the most preferred example may be R-32 in consideration of environmental pollution, toxicity, and economics.

Furthermore, the organic solvent may be toluene, benzene, dimethyl ether and propane, and may be toluene as a most preferred example.

In addition, the mixed working fluid is more than 50% by weight to less than 100% by weight of carbon dioxide; And 0% by weight to less than 50% by weight of at least one selected from the group consisting of organic refrigerants and organic solvents; and 55 to 100% by weight of carbon dioxide; And 0% to 45% by weight of at least one selected from the group consisting of organic refrigerants and organic solvents; and 60% to 75% by weight of carbon dioxide; And 25% by weight to 40% by weight of one or more selected from the group consisting of organic refrigerants and organic solvents.

Further, the critical point of the mixed working fluid may be more than 31°C to less than 320°C and more than 4 MPa to less than 17 MPa, the critical temperature may be 32°C to 200°C, and may be 100°C to 180°C, and the critical pressure May be 3 MPa to 5.8 MPa, and may be 4 MPa to 5.5 MPa.

1 is a schematic diagram of a supercritical carbon dioxide power generation system provided in one aspect of the present invention, wherein the supercritical carbon dioxide power generation system 100 includes a heat source 10 for heating a mixed working fluid containing carbon dioxide; A pump 20 that pressurizes and discharges the mixed working fluid; A turbine 30 into which the mixed working fluid heated from the heat source flows; And a cooler 40 for cooling carbon dioxide discharged from the turbine.

In the transcritical carbon dioxide power generation system 100 provided in one aspect of the present invention, the inflow temperature of the working fluid flowing into the pump 20 may be 30°C to 60°C.

In addition, the inlet pressure of the working fluid flowing into the pump 20 may be greater than 4.5 MPa to less than 7.5 MPa.

2 is a schematic diagram of a transcritical carbon dioxide power generation system provided in another aspect of the present invention, wherein the transcritical carbon dioxide power generation system 100 includes a heat source 10 for heating a mixed working fluid containing carbon dioxide; A pump 20 that pressurizes and discharges the mixed working fluid; A turbine 30 into which the mixed working fluid heated from the heat source flows; A recuperator 50 in which heat exchange between the mixed working fluid discharged from the turbine and the mixed working fluid discharged from the pump is performed; And a cooler 40 for cooling the mixed working fluid discharged from the turbine and flowing through the recuperator.

In the transcritical carbon dioxide power generation system 100 provided in one aspect of the present invention, the inflow temperature of the mixed working fluid flowing into the pump 20 may be 30°C to 60°C.

In addition, the inlet pressure of the working fluid flowing into the pump 20 may be more than 5 MPa to less than 7.5 MPa.

Hereinafter, the present invention will be described in detail through the following experimental examples.

However, the following experimental examples are only for explaining the present invention, and the contents of the present invention are not limited by the following experimental examples.

< Experimental Example 1> Thermodynamic analysis

In order to design and analyze the supercritical carbon dioxide power generation cycle, a thermodynamic analysis in the supercritical carbon dioxide power generation cycle according to the present invention was performed using a code (KAIST_CCD) developed by the KAIST research team, and the performance was compared with a pure supercritical carbon dioxide power generation system. .

The cycle was calculated while maintaining the lowest temperature at 30° C. and the efficiency of each component was set identically as summarized in Table 1 below. The efficiency of the components was chosen as a conservative value and the pressure drop was ignored for simplicity.

System type Trans-critical cycle Recuperated Trans-critical cycl Working Fluid CO ₂ +R-32 CO ₂ +Toluene Thermal input 1 MW _th 1 MW _th Mass flow rate 4-5 kg/s 4-5 kg/s Maximum Pressure 20.0 MPa 20.0 MPa Maximum Temperature 150 ℃ 300 ℃ Minimum Temperature 30 ℃ 30 ℃ Compressor Efficiency 80% 80% Turbine Efficiency 90% 90% Recuperator effectiveness - 90% Pressure Losses 0% (Neglected) 0% (Neglected)

The maximum temperature of the system to which the mixed working fluid of carbon dioxide and R-32 or toluene according to the present invention was applied was set at 150°C and 300°C to ensure thermal stability. In addition, the system to which the mixed working fluid of carbon dioxide and R-32 was applied was performed in the same configuration as the schematic diagram of FIG. 1, and the system to which the mixed working fluid of carbon dioxide and toluene was applied was used in order to utilize the high turbine outlet temperature in the system. It was performed in the same configuration as the schematic diagram of FIG. 2, and the Ts diagram of each power generation system is shown in FIGS. 3 and 4, and the efficiency change according to the mixing ratio of carbon dioxide and R-32 or carbon dioxide and toluene is shown in FIGS. It is shown in 6.

From the thermodynamic calculations, we analyzed the change in power generation system efficiency for different working fluid compositions, and the efficiency of the system is the first law thermal efficiency expressed by Equation 1.

<Equation 1>

As shown in FIGS. 3 and 5, it can be seen that the system using the working fluid in which R-32 and carbon dioxide are mixed has an increased efficiency compared to the system in which pure carbon dioxide is applied as the working fluid when the highest temperature is 150°C. In particular, when the mass fraction of R-32 in the mixed working fluid is 32%, it was confirmed that the efficiency increased by 0.46%p.

In addition, as shown in FIGS. 4 and 6, the system to which the toluene and carbon dioxide mixed working fluid was applied was found to have superior efficiency compared to the system to which pure carbon dioxide was applied as the working fluid when the maximum temperature was 300°C. At the maximum mixing ratio (the mass fraction of toluene is 32%), the system efficiency was 30.02%, which was 5.2%p higher than that of a pure carbon dioxide power generation system. As a result of conservative calculation, it was confirmed that the system efficiency can be reached up to 35% through the improvement of the performance of the component in the future.

< Experimental Example 2> Power system analysis

In order to verify the experiment of the supercritical carbon dioxide power generation system according to the present invention, a power generation system as shown in FIG. 7 was constructed, and compression performance experiments were performed using a working fluid in which carbon dioxide and R-32 were mixed at a mass fraction of 88:12. , The results are shown in Figure 8, Figure 9 and Table 2 below.

Specifically, a compression performance test was conducted with a carbon dioxide and R-32 (88:12 mass fraction) mixed working fluid using a KAIST-S-CO ₂ PE facility. As shown in FIG. 7, the device configuration was configured to have a simple Brayton cycle layout, and a centrifugal pump, a pre-cooler of a PCHE (printed substrate type heat exchanger) type was used. A 26 kW centrifugal pump was used to compress and circulate the working fluid, and a shroud type impeller with a diameter of 234 mm was operated at a constant speed of 3600 rpm for compression performance testing.

Test case
# T
[℃] P [MPa] CO ₂ CO ₂ + R-32
( 0.88:0.12 )

Mass flow rate [kg/s] PR ₁
Pressure ratio [-] Mass flow rate [kg/s] PR ₂
Pressure ratio [-] 4-1 31 8.4 3.96 1.11 4.15 1.12 1.007 4-2 2.97 1.12 2.96 1.12 1.007 4-3 2.00 1.11 1.93 1.12 1.005 5-1 29.2 7.7 3.94 1.12 3.91 1.13 1.010 5-2 2.99 1.12 2.99 1.14 1.009 5-3 2.02 1.12 2.02 1.13 1.008 7-1 37 8.4 3.88 1.11 3.82 1.12 1.008 7-2 3.16 1.08 3.09 1.11 1.021 7-3 2.29 1.08 2.27 1.11 1.020 7-4 1.61 1.08 1.57 1.1 1.020 7-5 0.82 1.08 0.80 1.1 1.018 10-1 33 7.4 2.81 1.11 2.81 1.12 1.006 10-2 2.09 1.11 2.02 1.12 1.005 10-3 1.35 1.11 1.35 1.11 1.005 10-4 0.65 1.10 0.64 1.11 1.004

As shown in Table 2, when a working fluid containing carbon dioxide and R-32 is applied (CO ₂ + R-32), a pressure ratio of 0.5% to 2% higher than when applying pure carbon dioxide as a working fluid (CO ₂ ) It can be confirmed that indicates.

To clarify the increase in the pressure ratio, referring to FIGS. 8 and 9 showing the pressure ratio and the pressure difference between the pump inlet and the outlet, the red mark indicates a case where a mixed working fluid (CO ₂ + R-32, 0.88: 0.12 mass fraction) is applied. It can be seen that the results tend to be similar to experimental results of the same density as the previous pure carbon dioxide. Therefore, it can be understood that the pressure ratio increases by 1% to 2% as the pump inlet density increases by 10% to 40%.

The amount of performance improvement may appear relatively small due to the limitations of low speed centrifugal compressors, but the difference may be larger in high performance high speed compressors. Conversely, if the carbon dioxide power generation system is designed with a mixed working fluid, less work or less rotational speed would be required to increase the same pressure.

In conclusion, through experiments, it was confirmed that the mixed working fluid was liquefied by carbon dioxide even at a temperature of 31° C. or higher, and that there was little uncertainty in thermodynamic analysis and use of physical properties. In addition, it was confirmed that there were no unusual phenomena or problems when operating the experimental device. The transcritical carbon dioxide power generation system of the present invention to which a carbon dioxide-based mixed working fluid is applied not only improves system efficiency, but also mechanical problems of the existing supercritical carbon dioxide power generation system can be solved by replacing the compressor with a relatively simple pump.

100: Transcritical carbon dioxide power generation system
10: heat source
20: pump
30: turbine
40: cooler
50: recuperator

Claims (8)

Heat source; Pump; turbine; And cooler; is connected to the flow path to form a closed circuit,
The closed circuit,
carbon dioxide; And a toluene organic solvent; the mixed working fluid consisting of circulates,
The mixed working fluid comprises 60% to 75% by weight of carbon dioxide; And 25% by weight to 40% by weight of an organic solvent that is toluene.
The critical temperature of the mixed working fluid is 32℃ to 200℃, and the critical pressure is 3 MPa to 5.8 MPa.
Heat source; Pump; turbine; cooler; And a recuperator connected to a flow path to form a closed circuit,
The closed circuit,
carbon dioxide; And a toluene organic solvent; the mixed working fluid consisting of circulates,
The mixed working fluid comprises 60% to 75% by weight of carbon dioxide; And 25% to 40% by weight of toluene organic solvent; and
The critical temperature of the mixed working fluid is 32℃ to 200℃, and the critical pressure is 3 MPa to 5.8 MPa.
delete delete delete delete The method according to claim 1 or 2,
Transcritical carbon dioxide power generation system, characterized in that the inlet temperature of the working fluid flowing into the pump is 30 ℃ to 60 ℃.
The method according to claim 1 or 2,
The transcritical carbon dioxide power generation system, characterized in that the inlet pressure of the working fluid flowing into the pump is greater than 4.5 MPa to less than 7.5 MPa.

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