JP2551703B2 - Circulating method of working fluid in low boiling medium system - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for circulating a working fluid in a low boiling point medium system such as a heat pump or a binary cycle, and more particularly, to use a binary non-azeotropic mixture medium as the working fluid. In this case, the performance is improved.

[0002]

2. Description of the Related Art A binary power generation system shown in FIG. 3 as an example of a low boiling point medium system will be described. An evaporator 2, a turbine 4, a condenser 6 and a pump 8 are connected in series to form a closed loop 10. . The working fluid circulating in the closed loop 10 first removes heat from the heat source fluid in the evaporator 2 and evaporates, and the generated steam is the turbine 4
Is supplied to. This steam expands in the turbine 4 and serves to drive the generator 12. The steam discharged from the turbine 4 is deprived of heat by the cooling water in the condenser 6 and condensed. The condensate is sent to the evaporator 2 again by the pump 8.

By the way, in such a heat cycle such as a binary cycle or a heat pump, a Lorentz cycle may be constituted by using a non-azeotropic mixed medium as a working fluid in order to improve efficiency. For example, the binary cycle is basically a Rankine cycle, and when the working fluid is a single medium, as shown in FIG.
-Indicates isothermal changes. However, Freon R
When a mixed medium such as a mixture of 123 and R22 is used as the working fluid, the saturation temperature changes, the evaporation temperature rises in the evaporator 2 and the condensation temperature decreases in the condenser 6, as shown in FIG. . This forms a Lorentz cycle and improves system efficiency.

FIG. 6 shows the simplest temperature-composition relationship of a two-component liquid-vapor system with the horizontal axis representing the mole fraction of the low-boiling component. G and L are single phases, respectively, a gas phase and a liquid phase, and a region of L + G is a two-phase region where a liquid and a vapor coexist. If the temperature of a liquid mixture of 60 mol% (mol fraction = 0.60) of the low boilers is increased under constant pressure, the change in this system can be considered along a straight line ab'cd "e.
At low temperatures, only a liquid phase exists, but a vapor phase appears at point b '. The composition of this vapor phase is given by the point b ", and the two conjugate phases are connected by an equilibrium connection line b" b 'in the figure. Increasing the temperature will produce more steam, in which case
Due to the high concentration of low boiling components in the vapor, this component is relatively reduced in the liquid phase, the composition of the liquid changes along b'c'd ', while the composition of the vapor is b "c" It changes along the d ". At the temperature t ° C, the total composition of the system in the two-phase region is represented by the point c, but the vapor composition and the liquid composition are both ends of the equilibrium connecting line passing through the point c," Given by points and c'points. The relative amounts of the two phases are determined from the principle of leverage in physics. That is, the ratio of the number of moles of vapor to liquid is represented by the ratio of the length of cc 'to c "c. As the temperature is further increased, more and more vapor is generated, and d"
At the point, the liquid phase almost disappears, and when the temperature becomes higher than this, the liquid phase disappears and only the vapor phase (d "point) remains. Even if the temperature is further raised (along d" e) Does not happen.

[0005]

In the vapor phase of the working fluid at the outlet of the condenser, the low boiling point component has the highest concentration in the system, and the gas having the low boiling point component stays near the condensation heat transfer surface. Therefore, in FIG.
As shown in (3), the low-boiling component exists in the condenser in the same manner as the non-condensable gas that impedes mass transfer and heat transfer, and reduces the heat transfer performance.

Therefore, the object of the present invention is to:
Decrease the concentration of uncondensed low-boiling component gas on the outlet side of the condenser,
It is an object of the present invention to provide a method for circulating a working fluid in a low boiling point medium system that uses a binary non-azeotropic mixed medium as a working fluid, which can improve heat transfer performance of a condenser.

[0007]

In order to achieve the above-mentioned object, the present invention provides a method for circulating a working fluid in a heat cycle in which a binary non-azeotropic mixed medium is used as a working fluid. The working fluid is separated into an uncondensed gas and a condensate on the outlet side, and then the separated uncondensed gas is mixed with the condensate and supplied to an evaporator. An ejector can be used as a means for mixing the uncondensed gas with the condensate. It should be noted that although it is possible to employ other means such as a pump or a compressor that exerts a function equivalent to that of the ejector when sucking gas into the liquid, the ejector is advantageous in that it does not require any additional power. .

[0008]

[Operation] In a heat cycle using a non-azeotropic mixed medium as a working fluid, a low boiling point component is likely to evaporate earlier in the evaporator than a high boiling point component, and a low boiling point component is less likely to be condensed in the condenser than a high boiling point component Therefore, the vapor on the outlet side of the condenser has a higher concentration of low-boiling components than the inlet side, and the condensate has a higher concentration of high-boiling components.The concentration of the low-boiling components separated from the condensate on the outlet side of the condenser By mixing the high-concentration uncondensed gas with the condensate having a high boiling point component concentration, the uncondensed gas is dissolved in the condensate. As a result, the concentration of uncondensed low boiling point components near the working fluid outlet of the condenser is reduced, mass transfer and heat transfer are facilitated, and heat transfer performance of the condenser is improved. Further, the pressure also decreases as the concentration of the low boiling point component gas decreases. Therefore, the condensing pressure is lowered, which also helps improve the efficiency of the cycle.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The case of application to the above-mentioned binary power generation system shown in FIG. 3 will be explained as an example. As shown in FIG. 1, a drain pot 14 for separating uncondensed gas is provided at the outlet side of the condenser 6. Is installed, and the working fluid outlet of the condenser 6 is connected to the drain pot 14. The liquid phase below the drain pot 14 is connected to the circulation pump 8. The ejector 16 is attached to the discharge side of the circulation pump 8, and the gas phase above the drain pot 14 is connected to the suction port of the ejector 16.

The working fluid vapor generated in the evaporator 2 is supplied to the turbine 4 to perform work, and then the condenser 6 removes heat from the cooling water to condense it. The condensed drain and the uncondensed gas flow into the drain pot 14. In the drain pot 14, the liquid and the gas are separated, and the liquid is sent to the evaporator 2 via the ejector 16 by the circulation pump 8. When the liquid discharged from the pump 8 passes through the ejector 16, a low pressure portion is generated in the throat portion of the ejector 16 and sucks gas from the drain pot 14. The low-boiling component gas thus sucked is caught in the liquid and absorbed.

Explaining with the vapor-liquid equilibrium diagram of FIG. 2, when the condensation end temperature Tc is the same, the ejector 16 causes the drain pot 14 to operate.
If the vapor inside is sucked in, the concentration of the low boiling point component in the vapor will decrease. Then, the low boiling point component concentration of the liquid also decreases in a form of equilibrium with the low boiling point component concentration of the vapor. The arrow from the solid circle to the dotted circle in the figure indicates this. In this way,
As a result of mixing the liquid having a low low boiling point component concentration and the vapor having a high low boiling point component concentration, a liquid having the same concentration as the supply concentration D is discharged from the ejector 16. At this time, the vapor phase line and the liquid phase line are respectively located at dotted lines, which means that the pressure is reduced.

FIG. 8 shows an embodiment in which a heat pump is used. This system is a system in which vapor generated in the evaporator 2 is pressurized by a compressor-4 'and sent to the condenser 6, high-pressure liquid is decompressed by an expansion valve 16', and latent heat of vaporization is taken by the evaporator 2. . Therefore, since the evaporator 2 has a lower pressure than the condenser 6, it is not necessary to provide the ejector 16 as in the embodiment of FIG. 1, and the drain pot 14 from the drain pot 14 is provided on the secondary side of the expansion valve 16 '. The same operation as in the case of the embodiment shown in FIG. 1 can be obtained simply by connecting the pipes. Incidentally, the present invention is not limited to the above-mentioned embodiment at all, and for example, when the working fluid is sufficiently separated into the uncondensed gas and the condensed liquid on the outlet side of the condenser, the use of the drain pot is not required. It can be omitted. Further, if the separated uncondensed gas can be sucked and mixed with the condensate, it can be replaced with a means other than the ejector.

[0013]

As described above, according to the present invention, in a working fluid circulation method in a heat cycle using a binary non-azeotropic mixed medium as a working fluid, the working fluid is not condensed on the outlet side of the condenser. Separated into gas and condensate, then
Since the separated uncondensed gas is mixed with the condensate and supplied to the evaporator, the concentration of the uncondensed low-boiling-point component gas near the condenser outlet decreases, facilitating mass transfer and heat transfer, and heat transfer performance of the condenser. Is improved. Further, since the pressure also decreases as the concentration of the low boiling point component gas on the outlet side of the condenser decreases,
It also helps improve cycle efficiency by reducing the condensation pressure.

[Brief description of drawings]

FIG. 1 is a flow sheet of a binary power generation system showing an embodiment of the present invention.

FIG. 2 is a vapor-liquid equilibrium diagram of a working fluid in a condenser.

FIG. 3 is a flow sheet of a binary power generation system showing a conventional example.

FIG. 4 is a TS diagram of Rankine cycle.

FIG. 5 is a TS diagram of the Lorentz cycle.

FIG. 6 is a vapor-liquid equilibrium diagram showing a temperature-composition relationship of a binary mixed medium.

FIG. 7 is a cross-sectional view of a condensation heat transfer surface.

FIG. 8 is a flow sheet of a heat pump.

[Explanation of symbols]

 2 Evaporator 4 Turbine 6 Condenser 8 Circulation pump 10 Closed loop 12 Generator 14 Drain pot 16 Ejector

Claims (2)

(57) [Claims] 1. A method of circulating a working fluid in a thermal cycle using a binary non-azeotropic mixed medium as a working fluid, wherein the working fluid is separated into an uncondensed gas and a condensed liquid at an outlet side of a condenser, Then, the separated non-condensed gas is mixed with a condensate and supplied to an evaporator. 2. The ejector is a means for mixing the separated uncondensed gas with the condensate.
A method of circulating a working fluid in a low boiling medium system as described.