JPH04298607A - Evaporator for non-azeotropic mixture - Google Patents

Abstract

PURPOSE:To operate an evaporator at the optimum condition so as to maintain the maximum performance by adjusting the amount of circulation liquid so that the difference in temperature between at the inlet and outlet of hot water becomes equal to the difference in boiling point temperature between at the inlet and outlet of non-azeotropic mixture by adjusting the level of evaporation liquid. CONSTITUTION:The amount of circulation liquid changes by modifying the level of evaporation liquid, that is, the liquid level of non-azeotropic mixture in an evaporator 2 by adjusting power of a circulation pump 8 or opening degree of a valve 18. Since the difference in temperature of hot water becomes equal to the difference in boiling point temperature of non-azeotropic mixture, it is possible to operate the evaporator at the optimum condition and maintain the maximum performance.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION This invention relates to evaporators for non-azeotropic mixtures used as working fluids in low-boiling media systems such as heat pumps and binary cycles.

0002

2. Description of the Related Art Regarding a binary power generation system shown in FIG. 4 as an example of a low boiling point medium system, an evaporator 2, a turbine 4, a condenser 6 and a medium pump 8 are connected in series to form a closed loop 10. are doing. 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 supplied to the turbine 4. This steam expands within the turbine 4 and performs work to drive the generator 12. turbine 4
The steam discharged from the condenser 6 receives heat from the cooling water and condenses. The condensate is sent again to the evaporator 2 by means of a medium pump 8.

By the way, in thermal cycles such as binary cycles and heat pumps, a Lorentz cycle is sometimes constructed by using a non-azeotropic mixture as a working fluid in order to improve efficiency. For example, a binary cycle is basically a Rankine cycle, and when the working fluid consists of a single component, the TS diagram shows ■'-
■, ■−■ indicate isothermal change. However, when a non-azeotropic mixture (such as a mixture of Freon R123 and R22) is used as the working fluid, the saturation temperature changes even at the same pressure, and the evaporation temperature in the evaporator 2 increases, as shown in FIG. The condensing temperature decreases. This creates a Lorentz cycle and improves system efficiency.

FIG. 7 shows the temperature-composition relationship of the simplest two-component liquid-vapor system, with the mole fraction of the low boiling component plotted on the horizontal axis. G and L are single phases, a gas phase and a liquid phase, respectively, and the L+G region is a two-phase region where liquid and vapor coexist. If 60 mol% of low-boiling components (mol fraction = 0.60
) is raised under constant pressure, the change in this system can be thought of along the straight line ab'cd''e. At low temperatures, only the liquid phase exists, but at point b', vapor phase appears. The composition of this vapor phase is given by point b'', and the two conjugate phases are connected by the equilibrium connection line b''b' on the diagram.If the temperature is further increased, more vapor is produced. However, in that case, since the concentration of low-boiling components in the vapor is high, this component is relatively reduced in the liquid phase, and the liquid composition becomes b'c'd'
while the composition of the vapor varies along b"c"d". At temperature t°C, the total composition of the system in the two-phase region is represented by point c, but the vapor composition, The liquid composition is given by points c'' and c', respectively, at both ends of the equilibrium connection line passing through point c. The relative amounts of the two phases are determined by the lever principle of physics. That is, the ratio of moles of vapor and liquid is cc'
It is expressed as the ratio of the length of c" and c".As the temperature is further increased, more and more vapor is generated, and when the temperature reaches point d, the liquid phase almost disappears.If the temperature is increased any higher, the liquid phase disappears and vapor is formed. Only the phase (d” point) remains. Beyond this point, the temperature should be changed to (d” point).
”), nothing happens.

[0005]

In the Lorentz cycle, the optimum condition for the evaporator is when the temperature change of hot water is equal to the difference in boiling point temperature of the non-azeotropic mixture. The aim of the invention is therefore to maintain optimal conditions in such an evaporator.

[0006]

[Means for Solving the Problems] According to the present invention, by adjusting the evaporation liquid level, the amount of circulating liquid is adjusted so that the temperature difference between the hot water and the non-azeotropic mixture becomes equal.

[0007]

[Operation] Lowering the evaporation level reduces the amount of circulating liquid, which lowers the evaporator inlet temperature of the non-azeotropic mixture and reduces the boiling point temperature difference. Conversely, when the evaporation liquid level is raised, the amount of circulating liquid increases, so the evaporator inlet temperature of the non-azeotropic mixture increases, and the boiling point temperature difference increases. By adjusting the evaporation liquid level in this way, the amount of circulating liquid can be adjusted so that the temperature difference of the non-azeotropic mixture is equal to the temperature difference of hot water, and the evaporator can be operated under optimal conditions.

[0008]

[Embodiment] To explain the application to the binary power generation system shown in FIG. 4 as an example, as shown in FIG. , the liquid phase is connected to a tank 16 provided on the inlet side of the evaporator 2. The working fluid exiting the evaporator 2 is separated into vapor and evaporation residual liquid by the mist separator 14.
The evaporation residual liquid is returned to the tank 16. The steam is supplied to the turbine 4 to do work, and then is condensed in the condenser 6, where cooling water removes heat, and the condensed liquid is returned to the tank 16 by the circulation pump 8.

By adjusting the power of the circulation pump 8 or the opening degree of the valve 18 to change the evaporation liquid level, that is, the liquid level of the non-azeotropic mixture in the evaporator 2, the amount of circulating liquid is changed. When the amount of circulating liquid changes, the evaporation temperature in the evaporator 2 changes. To explain specifically according to FIGS. 2 and 3, the evaporator inlet temperature of the non-azeotropic mixture is T2
When the outlet temperature is TE, the temperature difference ΔTW of hot water and the boiling point temperature difference ΔTR of the non-azeotropic mixture become equal (ΔTR
= ΔTW ), when ΔTW > ΔTR, the evaporator inlet temperature of the non-azeotropic mixture will decrease from T2 to T1 by lowering the evaporating liquid level and reducing the amount of circulating liquid.
Since the boiling point temperature difference ΔTR increases as the temperature decreases in the direction, the condition ΔTR =ΔTW can be satisfied. In addition, when ΔTW <ΔTR, by raising the evaporating liquid level and increasing the amount of circulating liquid, the evaporator inlet temperature of the non-azeotropic mixture increases from T2 to T3, and the boiling point temperature difference Δ
Since TR becomes small, the condition of ΔTW =ΔTR can be satisfied. In this way, by adjusting the evaporation liquid level and the circulating liquid amount, ΔTW = ΔTR
The evaporator can be operated under optimal conditions by satisfying the following conditions.

0010

As described above, the present invention adjusts the amount of circulating liquid so that the temperature difference ΔTW of hot water and the boiling point temperature difference ΔTR of the non-azeotropic mixture become equal by adjusting the evaporation liquid level. Therefore, ΔTW can be easily
By satisfying the condition of =ΔTR, the evaporator can be operated under optimal conditions and maximum performance can be maintained.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of the present invention.

FIG. 2 is a vapor-liquid equilibrium diagram of a non-azeotropic mixture.

FIG. 3 is a temperature gradient diagram in an evaporator.

FIG. 4 is a flow sheet of a binary power generation system.

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

FIG. 6 is a TS diagram of a Lorentz cycle.

FIG. 7 is a temperature-composition diagram of a binary mixed medium.

[Explanation of symbols]

2 Evaporator 4 Turbine 6 Condenser 8 Circulation pump 12 Generator 14 Mist separator 16 Tank 18 Valve

Claims (1)

[Claims] 1. An evaporator for non-azeotropic mixtures, characterized in that the circulating liquid amount is adjusted by adjusting the evaporation liquid level so that the temperature difference of hot water and the boiling point temperature difference of the non-azeotropic mixture are equalized. .