Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a Rankine cycle system with higher operation efficiency.
The Rankine cycle system comprises a medium loop formed by sequentially connecting a heater, a working device, a cooler and a pressurizing device, wherein a circulating medium circularly flows in the medium loop, the circulating medium flowing out of the heater is in a supercritical state, the three-phase point temperature of the circulating medium is lower than 0 ℃, the three-phase point pressure of the circulating medium is higher than standard atmospheric pressure, the circulating medium flowing out of the cooler is in a saturated liquid state, the temperature T1 of the circulating medium is 0-20 ℃ higher than the three-phase point temperature Tgls ℃, and the pressure P1 of the gaseous circulating medium flowing out of the working device is equal to the saturated steam pressure of the circulating medium at the temperature T1. According to the technical scheme, firstly, in the Rankine cycle system provided by the invention, a circulating medium reaches a supercritical state in a heating device, when the circulating medium is in the supercritical state, the density is higher, and the turbine stage number required by expansion work is relatively smaller, so that the turbine equipment is more compact than the turbine structure in the existing steam Rankine cycle in the invention, and the smaller turbine equipment volume means smaller factory building area and more compact circulating flow.
Second, from a thermodynamic standpoint, increasing the heat source temperature during the cycle and decreasing the heat sink temperature during the cycle may further increase the cycle efficiency. However, when the temperature is below the triple point, constant pressure cooling will cause the circulating medium to sublimate directly from the gaseous state to the solid state without undergoing a liquid phase zone. However, the utilization capacity of the cold source provided by the cooler by the circulating medium in the Rankine cycle is limited by the three-phase point temperature of the circulating medium because the solid circulating medium cannot flow, so according to the Carnot principle, the circulating medium is heated to a supercritical state higher than the gaseous state, and is cooled to a temperature slightly higher than the three-phase point (namely, higher than the three-phase point by 0 ℃ to 20 ℃) in the cooler, the saturated steam pressure of the circulating medium corresponding to the temperature is the exhaust pressure of the final-stage acting device, the working efficiency of the Rankine cycle system can be improved to the greatest extent, and further, the three-phase point temperature of the circulating medium is lower than 0 ℃, the circulating medium can be reduced to a lower temperature, and the three-phase point pressure is higher than the standard atmospheric pressure, so that the vacuum in the condenser is not required to be maintained by external equipment in the condensation process, and the leakage of air into the condenser is avoided, and the circulating efficiency can be improved greatly from the thermodynamic aspect after the high-quality low-temperature cold source is combined and utilized.
Preferably, the rankine cycle system further comprises a regenerator, wherein a hot side inlet of the regenerator is communicated with a medium outlet of the acting device, a hot side outlet of the regenerator is communicated with a hot side inlet of the cooler, a cold side inlet of the regenerator is communicated with a medium outlet of the supercharging device, and a cold side outlet of the regenerator is communicated with the heater.
According to the technical scheme, in the Rankine cycle system, the heat regenerator is added, the gaseous state circulating medium at the outlet of the acting device enters the heat regenerator to exchange heat with the liquid state circulating medium after cooling and compressing in the heat regenerator, so that the gaseous state circulating medium is cooled in the heat regenerator in advance and then is led into the cooler to be cooled, and the liquid state circulating medium after being pressurized by the pressurizing device is heated in advance in the heat regenerator before entering the heater, so that the waste heat of the circulating medium after the acting device can be utilized, the energy required by the heater and the cooler is reduced, and the operating efficiency of the Rankine cycle system is improved.
The heat regenerator preferably comprises a high-temperature heat regenerator and a low-temperature heat regenerator, wherein a hot side inlet of the high-temperature heat regenerator is communicated with a medium outlet of the power device, a hot side outlet of the high-temperature heat regenerator is communicated with a hot side inlet of the low-temperature heat regenerator, a cold side outlet of the high-temperature heat regenerator is communicated with the heater, a cold side inlet of the high-temperature heat regenerator is communicated with a cold side outlet of the low-temperature heat regenerator, a cold side inlet of the low-temperature heat regenerator is communicated with a medium outlet of the supercharging device, and a hot side outlet of the low-temperature heat regenerator is communicated with the cooler.
The rankine cycle system further comprises a first three-way valve, a second three-way valve and a compressor, wherein the first three-way valve is respectively communicated with the compressor outlet, the cold side outlet of the low-temperature heat regenerator and the cold side inlet of the high-temperature heat regenerator, and the second three-way valve is respectively communicated with the compressor inlet, the hot side outlet of the low-temperature heat regenerator and the hot side inlet of the cooler.
According to the technical scheme, the heat regenerator is further arranged to be the high-temperature heat regenerator and the low-temperature heat regenerator, so that waste heat of a working medium flowing out of the working device can be further utilized, and part of circulating medium flowing out of the low-temperature heat regenerator is divided, is directly compressed by the compressor without passing through the cooler and is collected with a liquid circulating medium after cooling and pressurizing and then flows to the heating device, so that the cold source loss of the Rankine cycle system can be reduced, and the working efficiency of the Rankine cycle system is further improved.
Preferably, the working device comprises a first turbine, a second turbine and a third turbine, wherein the first turbine uses the enthalpy change of the supercritical state circulating medium to do work externally, the second turbine receives the supercritical state circulating medium from the first turbine and uses the phase state transition of the circulating medium from the supercritical state to the gaseous state to do work externally, and the third turbine receives the gaseous state circulating medium from the second turbine and uses the enthalpy change of the gaseous state circulating medium to do work externally.
According to the technical proposal, the working device is set as the multi-stage turbine, so that the heat energy transmitted to the circulating medium in the heater is fully converted into mechanical energy through the multi-stage turbine, the operation efficiency of the whole circulating system is improved, when the multi-stage turbine is three-stage transparent, the circulating medium in the first turbine is kept in a supercritical state, at the moment, the density of the circulating medium is higher, the structure of the first turbine can be more compact, the circulating medium enters the third turbine after being changed from a supercritical state into a gas state after being further subjected to adiabatic expansion in the second turbine, and the waste heat of the circulating medium is further utilized in the third turbine, so that the overall operation efficiency of the circulating system is increased.
Preferably, the circulating medium of the rankine cycle system is CO2.
According to the technical scheme, the application of the CO2 as the circulating medium mainly comprises the advantages of high cycle efficiency of a supercritical CO2 (S-CO 2) Brayton cycle and high temperature heat source of the S-CO2 Brayton cycle, low compression power consumption, compact structure, small occupied area, low corrosiveness and the like, and is one of potential choices of efficient power generation of exhaust waste heat of a gas turbine. However, in the supercritical CO2 (S-CO 2) Brayton cycle, the cold source temperature must not be lower than the CO2 critical temperature (31.1 ℃) which limits the operating efficiency of the supercritical CO2 (S-CO 2) Brayton cycle system.
Further, the three-phase point of the H2O is 0.01 ℃ and 610.75Pa, the temperature of the cold end of the H2O can be reduced to more than 0 ℃ at the lowest, and the three-phase point pressure of the H2O is too low (less than 1 kPa), and the H2O is open circulation, if the H2O is reduced to be close to the three-phase point pressure, a vacuum pump is required to perform air extraction work, so that the improvement of the circulation efficiency is limited. In contrast, the three-phase point of CO2 is-56.6 ℃ and 0.52MPa, the temperature of a cold source can be reduced to be lower, the pressure of the three-phase point is higher than the atmospheric pressure, the circulation mode is closed circulation, and a vacuum pump is not needed to be used for vacuumizing, so that the whole circulation is above the atmospheric pressure, and the permeation of non-condensable gas at the low-pressure part of the circulation is avoided. Thus, the circulation efficiency can be greatly improved from the thermodynamic aspect after the combination of the high-quality low-temperature cold source.
Finally, compared with H2O steam, the corrosiveness of the CO2 circulating medium is much more moderate, and the corrosion resistance requirement on the materials of high-temperature parts and equipment can be greatly reduced.
The organic medium Rankine cycle loop comprises an organic medium heater and an organic medium cooler, wherein the external heat source flows through the heater and then enters the organic medium heater, and the external heat source is respectively communicated with the cooler and the organic medium cooler.
According to the technical scheme, higher circulation efficiency can be realized by adopting a circulating mode of combining the Rankine cycle and the organic Rankine cycle, and for the same heat source, more generated energy can be realized and the energy utilization rate can be improved by using the combined circulating system.
Wherein, the temperature of the external cold source is preferably-162 ℃ to 0 ℃. According to the technical scheme, the gaseous circulating medium can be rapidly cooled to the vicinity of the three-phase point by using the cold source with lower temperature, and the low temperature of the cold source is beneficial to improving the operation efficiency of the Rankine cycle system.
Preferably, the external heat source is a gas unit, and the external cold source is liquefied natural gas.
According to the technical scheme, the gas turbine unit is used as a heat source, namely, surplus heat (such as high-temperature flue gas) generated by the gas turbine unit is reused, and in addition, the cold source temperature of the liquefied natural gas is about 162 ℃ below zero, so that gaseous circulating medium can be rapidly cooled to a saturated liquid state near a three-phase point, the low cold source temperature is beneficial to improving the working efficiency of a Rankine cycle system, and further, the liquefied natural gas is used as a cold source to be introduced into a cooler to exchange heat with the circulating medium and then can be continuously introduced into the gas turbine unit to be used as fuel, and the surplus heat generated by the gas turbine unit can be used as an external heat source to supply heat to circulation, so that the full and reasonable utilization of cold source materials is realized.
Detailed Description
The present invention will be described in further detail with reference to the following specific examples and drawings. The implementation of the present invention is not limited to the following embodiments, and various modifications, changes, combinations and improvements of the technical concept of the present invention, which are adopted within the knowledge of those skilled in the art, are all within the scope of the present invention.
1. Integral structure
As shown in fig. 1, the rankine cycle system provided by the embodiment includes a heater 1, a working device 2, a regenerator 5, a cooler 3 and a pressurizing device 4, which are sequentially connected to form a medium loop, wherein the circulating medium circulates in the medium loop, specifically, the three-phase point temperature of the circulating medium is lower than 0 ℃, the three-phase point pressure of the circulating medium is higher than standard atmospheric pressure, the circulating medium absorbs heat energy in the heater 1 and becomes a supercritical fluid, and then flows into the working device 2to expand and do work, so that the heat energy is converted into mechanical energy which is more convenient to use, the gaseous circulating medium passing through the working device 2 enters the regenerator 5, the waste heat of the circulating medium is recycled and then enters the cooler 3 to cool, the gaseous circulating medium is cooled to saturated liquid with the three-phase point temperature of slightly higher than the three-phase point temperature Tgls (Tgls < Tgls +20 ℃) of the circulating medium, the circulating medium enters the pressurizing device 4 to pressurize, the pressurized liquid circulating medium enters the heater 5 to absorb the waste heat of the exhaust of the working device, and then enters the heater 1 to be newly circulated into the regenerator 1 to heat energy.
It should be noted that, in this embodiment, the structure of each device or apparatus is not limited, for example, the working device 2 may be a rotating turbine in some embodiments, and in other embodiments, the working device 2 may also be a cylinder device with a transmission rod, which does not deviate from the protection scope of the present invention, and similarly, the device or apparatus in the present invention is simply replaced.
In addition, it will be understood by those skilled in the art that the regenerator 5 is a device for reusing the waste heat after the working device 2 in this embodiment, that is, a preferred embodiment of the rankine cycle to which the regenerator 5 is added is illustrated in this embodiment, but it will be understood by those skilled in the art that the rankine cycle system provided by the present invention may not include the regenerator, but may be directly formed by sequentially connecting the heater 1, the working device 2, the cooler 3, and the supercharging device 4.
In this embodiment, first, the three-phase temperature of the circulating medium is lower than 0 ℃, a cold source medium with a lower temperature can be utilized, and the three-phase pressure is higher than the standard atmospheric pressure, so that the vacuum in the condenser is not required to be maintained, the energy consumption is saved, and meanwhile, the leakage of external air into the circulating system is avoided, so that after the high-quality low-temperature cold source is utilized in a combined way, the circulating efficiency can be greatly improved according to the carnot principle.
Secondly, the circulating medium reaches a supercritical state in the heating device, when the circulating medium is in the supercritical state, the density is higher, the turbine stage number required by expansion work is relatively smaller, so that the high-pressure turbine equipment in the embodiment is much more compact than the turbine structure in the existing steam Rankine cycle, and the smaller turbine equipment volume means smaller factory building area and more compact circulating flow.
Finally, the temperature of the supercritical circulating medium is higher than that of the gaseous circulating medium, so that according to the carnot principle, under the condition that a cold source provided by the cooler 3 is fixed, the circulating medium in the Rankine cycle system provided by the invention can reach higher initial temperature, namely, the working efficiency of the Rankine cycle system is higher.
Preferably, the circulating medium of the rankine cycle system is CO2.
In the embodiment, the application of CO2 as a circulating medium mainly comprises the supercritical CO2 (S-CO 2) Brayton cycle, and the S-CO2 Brayton cycle has the advantages of high-temperature heat source circulating efficiency, small compression power consumption, compact structure, small occupied area, small corrosiveness and the like, and is one of potential choices of efficient power generation of exhaust waste heat of a gas turbine. However, in the S-CO2 Brayton cycle, the cold source temperature must not be below the CO2 critical temperature (31.1 ℃) which limits the operating efficiency of the S-CO2 Brayton cycle system.
Further, the three-phase point of H2O is 0.01 ℃ and 610.75Pa, the temperature of the cold end of the H2O can be reduced to more than 0 ℃ at the lowest, and because the pressure of the three-phase point of H2O is too low (less than 1 kPa), and the circulation mode is open circulation, if the H2O is cooled to the pressure close to the three-phase point, a vacuum pump is required to be used for pumping work, so that additional energy consumption is increased, and the improvement on the circulation efficiency is limited. In contrast, the CO2 circulation mode is closed circulation, a vacuum pump is not needed to be used for vacuumizing, the three-phase point of CO2 is-56.6 ℃ and 0.52MPa, the temperature of a cold source can be reduced to be lower, the pressure of the three-phase point is higher than the atmospheric pressure, and leakage of non-condensable air outside a condenser to the inside of the circulation is avoided. Thus, the circulation efficiency can be greatly improved from the thermodynamic aspect after the combination of the high-quality low-temperature cold source.
In addition, compared with H2O steam, the corrosiveness of the CO2 circulating medium is much more moderate, and the corrosion resistance requirement on the materials of high-temperature parts and equipment can be greatly reduced.
Finally, the specific volume of the CO2 circulating medium is much smaller than that of H2O, so that the size of working equipment can be greatly reduced, and the factory area is saved.
Next, the rankine cycle device provided in the present embodiment will be described in more detail.
1. Heater 1
In this embodiment, the heater 1 may be any device capable of heating a circulating medium, specifically, the heater 1 may be a heat exchanger that heats a circulating medium by using an external heat source 6, one end of the heat exchanger is led into the external heat source 6, and the other end of the heat exchanger is led into the circulating medium, so that the circulating medium absorbs heat of the external heat source 6 through heat exchange to raise temperature and convert phase so as to facilitate subsequent work, preferably, the external heat source 6 may be solar energy, nuclear energy, fossil fuel, and the like, and further, the external heat source 6 is a gas turbine unit, thereby reusing waste heat of high-temperature flue gas after combustion in the gas turbine unit and saving resources.
2. Working device 2
In the present embodiment, the working device 2 may be a device capable of converting thermal energy into mechanical energy by using expansion work of a circulating medium, for example, a cylinder structure that drives a transmission rod to reciprocate by using gas expansion, or a rotary turbine structure that performs work by using gas expansion rotation, and the present embodiment will be further described by taking the working device 2 as a rotary turbine as an example.
Preferably, the rotary turbine includes a first turbine 21, a second turbine 22 and a third turbine 23, the first turbine 21 uses the change of the enthalpy of the supercritical state circulation medium to do work to the outside, the second turbine 22 receives the supercritical state circulation medium from the first turbine 21 and uses the phase transition of the circulation medium from the supercritical state to the gaseous state to do work to the outside expansion, and the third turbine 23 receives the gaseous state circulation medium from the second turbine 22 and uses the change of the enthalpy of the gaseous state circulation medium to do work to the outside.
In this embodiment, the working device 2 is configured as a multi-stage turbine, so that the heat energy transmitted to the circulating medium in the heater 1 is fully converted into mechanical energy through the multi-stage turbine, so as to improve the operation efficiency of the whole circulating system, but it can be understood by those skilled in the art that the effect that the circulating medium performs work in the working device 2 can be achieved by setting a single or other number of permeable averages, and the protection scope of the invention is not exceeded, wherein when the multi-stage turbine is three-stage permeable, the circulating medium in the first turbine 21 is kept in a supercritical state, the density of the circulating medium is higher at this time, the structure of the first turbine 21 can be more compact, the circulating medium is further adiabatically expanded in the second turbine 22, then enters the third turbine 23 after being changed from the supercritical state into a gaseous state, and the residual heat of the circulating medium is further utilized in the third turbine 23, so as to improve the operation efficiency of the whole circulating system.
3. Regenerator 5
In this embodiment, the regenerator 5 may be a device having two cold and hot flow paths and performing heat exchange on the medium in the two flow paths, specifically, the hot side inlet of the regenerator 5 may be in communication with the medium outlet of the working device 2, the hot side outlet of the regenerator 5 is in communication with the hot side inlet of the cooler 3, the cold side inlet of the regenerator 5 is in communication with the medium outlet of the supercharging device 4, and the cold side outlet of the regenerator 5 is in communication with the heater 1.
In this embodiment, the gaseous circulation medium at the outlet of the working device 2 enters the regenerator 5 to exchange heat with the liquid circulation medium after cooling and compression in the regenerator 5, so that the gaseous circulation medium is cooled in advance in the regenerator 5 and then is led into the cooler 3 to be cooled, and the liquid circulation medium pressurized by the pressurizing device 4 is heated in advance in the regenerator 5 before entering the heater 1, so that the waste heat of the circulation medium after the working device 2 can be utilized, the energy required by the heater 1 and the cooler 3 is reduced, and the operation efficiency of the rankine cycle system is improved.
Further, as shown in fig. 2, the regenerator 5 includes a high-temperature regenerator 51 and a low-temperature regenerator 52, the hot side inlet of the high-temperature regenerator 51 is communicated with the medium outlet of the working device 2, the hot side outlet of the high-temperature regenerator 51 is communicated with the hot side inlet of the low-temperature regenerator 52, the cold side outlet of the high-temperature regenerator 51 is communicated with the cold side inlet of the heater 1, the cold side inlet of the high-temperature regenerator 51 is communicated with the cold side outlet of the low-temperature regenerator, the cold side inlet of the low-temperature regenerator 52 is communicated with the medium outlet of the supercharging device 4, the rankine cycle system further includes a first three-way valve 91, a second three-way valve 92 and a compressor 8, the first three-way valve 91 is respectively communicated with the compressor 8 outlet, the cold side outlet of the low-temperature regenerator 52, the cold side inlet of the high-temperature regenerator 51, and the second three-way valve 92 is respectively communicated with the compressor 8 inlet, the hot side outlet of the low-temperature regenerator 52 and the hot side inlet of the cooler 3.
As an operation example, as shown in fig. 2, in the rankine cycle system, a circulating medium firstly enters a cold side inlet of the heater 1, high-temperature exhaust gas of the gas turbine unit enters a hot side inlet of the heater 1, heat exchange is realized by two streams in the heat exchanger, cooled flue gas is discharged through a hot side outlet of the heat exchanger, and heated circulating medium flows out from a cold side outlet of the heat exchanger and continuously enters the working device 2 to perform expansion work. The working device 2 is provided with three turbines, and the circulating medium at the outlet of the first turbine 21 and the outlet of the second turbine 22 enters the heater 1 again to be heated and then enters the second turbine 22 and the third turbine 23 respectively to be expanded again to do work. The circulating medium at the outlet of the third turbine 23 enters the hot side of the high-temperature heat regenerator 51, exchanges heat with the circulating medium at the cold side of the high-temperature heat regenerator 51 for cooling, enters the hot side of the low-temperature heat regenerator 52 again after the circulating medium subjected to primary cooling, exchanges heat with the cold side stream of the low-temperature heat regenerator 52 for cooling, then is divided into two parts by the second three-way valve 92, namely, the circulating medium of the main stream is cooled to be liquid state by the cooler 3, enters the supercharging device 4 for supercharging, then enters the low-temperature heat regenerator 52 for heat regeneration and heating, and the circulating medium of the auxiliary stream directly enters the compressor 8 for supercharging. Then, the two circulating mediums are converged into one flow through the first three-way valve 91, and then enter the cold side of the high-temperature heat regenerator 51 for heat regeneration and temperature rise, and then enter the heater 1 for absorbing heat, and the circulating process is continued.
In the present embodiment, the regenerator 5 is further provided as the high-temperature regenerator 51 and the low-temperature regenerator 52, so that the waste heat of the working medium flowing out of the working device 2 can be further utilized, and the circulating medium flowing out of the low-temperature regenerator 52 is split, and a part of the circulating medium is compressed by the compressor 8 without passing through the cooler 3 and then is integrated with the cooled and compressed liquid circulating medium to flow into the heating device, so that the heat loss of the rankine cycle system can be reduced, and the working efficiency of the rankine cycle system can be further improved.
4. Cooler 3
In this embodiment, the cooler 3 may be any device capable of cooling the circulating medium, specifically, the cooler 3 may be a heat exchanger that cools the circulating medium by using the external cold source 7, one end of the heat exchanger is led into the external cold source, and the other end of the heat exchanger is led into the circulating medium, so that the gaseous circulating medium is subjected to heat exchange, self heat is absorbed by the external cold source, the circulating medium is cooled to a position near a three-phase point thereof, so that subsequent heat absorption is facilitated, and the temperature difference between the cold end and the hot end of the rankine cycle is improved, thereby improving the circulation efficiency.
The temperature of the external cold source is-162 ℃ to-0 ℃, the gaseous circulating medium can be rapidly and fully cooled to the vicinity of the three-phase point by using the cold source with lower temperature, the low temperature of the cold source is beneficial to improving the operation efficiency of the Rankine cycle system, and the external cold source 7 can be liquefied natural gas. The cold source temperature of the liquefied natural gas is about 162 ℃ below zero, which is favorable for improving the operation efficiency of the Rankine cycle system, in addition, the liquefied natural gas can be further introduced into a gas unit as fuel after heat exchange with a circulating medium in the cooler 3, and the generated high-temperature flue gas can be used as an external heat source 6, so that the recycling of the high-quality external cold source material of the liquefied natural gas is realized.
5. Supercharging device 4
In the present embodiment, the pressurizing device 4 may be a liquid booster pump, and specifically, the pressurizing device 4 pressurizes a saturated liquid circulation medium flowing out of the cooler 3 and having a temperature near a triple point of the circulation medium. Because the pressure of the circulating medium is close to the three-phase point, the energy converted by the expansion work of the circulating medium in the working device 2 in the primary Rankine cycle system is exerted as much as possible.
Preferably, as shown in fig. 3, the rankine cycle system further includes an organic medium rankine cycle circuit, the organic medium rankine cycle circuit includes an organic medium heater 1a and an organic medium cooler 3a, the external heat source 6 flows through the heater 1 and then enters the organic medium heater 1a, and the external heat sink 7 is communicated with the cooler 3 and the organic medium cooler 3 a.
Further, the organic medium rankine cycle system may also include other devices in the rankine cycle system, as shown in fig. 3, where the organic medium rankine cycle further includes an organic medium working device 2a, an organic medium supercharging device 4a, and an organic medium regenerator 5a, and a flow mode of a circulating medium in the organic medium rankine cycle system is consistent with a flow mode of the rankine cycle system provided by the present invention, which is not described herein.
In the embodiment, higher cycle efficiency can be realized by adopting a cycle mode of combining the Rankine cycle and the organic Rankine cycle, and for the same heat source, more generated energy can be realized and the energy utilization rate can be improved by using the combined cycle system.
In addition, in the present embodiment, there is also provided a rankine cycle method applied to the rankine cycle system, including the steps of:
The method comprises a heating step of providing an external heat source 6 and a circulating medium, heating the circulating medium by using the external heat source 6 to enable the circulating medium to be heated to a supercritical state, a working step of working the circulating medium in the supercritical state to the outside to change the circulating medium into a gaseous state close to the three-phase point pressure of the circulating medium, a cooling step of providing an external cold source 7, cooling the gaseous circulating medium by using the external cold source 7 to obtain a saturated liquid circulating medium close to the three-phase point temperature which is lower than 0 ℃, and a compression step of pressurizing the liquid circulating medium.
Those skilled in the art will appreciate that the specific features of the various embodiments may be adaptively split or combined. Such splitting or combining of specific technical features does not cause the technical solution to deviate from the principle of the present invention, and therefore, the technical solution after splitting or combining falls within the protection scope of the present invention.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
Thus far, the technical solution of the present invention has been described in connection with the embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of protection of the present invention is not limited to these specific embodiments. Equivalent modifications and substitutions for related technical features may be made by those skilled in the art without departing from the principles of the present invention, and such modifications and substitutions will fall within the scope of the present invention.