JPS6312509B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new working fluid for Rankine cycles. Mechanical energy is obtained by heating and evaporating a liquid medium using thermal energy and expanding it in an expansion device.Then, this medium is then condensed and pressurized by a pump to become a liquid medium.The cycle is repeated to convert thermal energy into mechanical energy. In the Rankine cycle for energy conversion, water is almost the only medium that has traditionally been used as a working fluid for the Rankine cycle. Water as a working fluid has been used in steam engines for a long time. However, water has a high freezing point and a large vapor specific volume, which limits its range of use.Especially when using a low-temperature heat source, the disadvantage is that the equipment becomes bulky and efficiency decreases, and furthermore, when used at low temperatures, it tends to freeze. Therefore, there is a limit to the operating temperature. Many organic working fluids have been proposed to improve the drawbacks of water, but many are flammable or corrosive.
I have not yet found anything that I can use with satisfaction. However, among these, trichlorofluoromethane (hereinafter referred to as Freon-11) is one that has been put into practical use, but the Rankine cycle working fluid made of Freon-11 has the disadvantage of low conversion efficiency from thermal energy to mechanical energy. There is.
Since Freon-11 has the above-mentioned drawbacks, it is hoped that a working fluid with high energy conversion efficiency will emerge. The inventors of the present invention have conducted various studies in response to such demands, and have found that although all conventional working fluids have been researched and used with a single substance, a mixed system in which substances with different characteristics are mixed has been developed. We have discovered that a mixture of trichlorofluoromethane (hereinafter referred to as Freon-11) and difluoroethane (hereinafter referred to as Freon-152) exhibits superior properties compared to single substances, and has demonstrated extremely superior properties as a working fluid for the Rankine cycle. The present invention was completed based on the discovery that the present invention has the following properties. The mixed system of Freon-11 and Freon-152 of the present invention has the following characteristics as a working fluid for Rankine cycle. First, in the Rankine cycle using a mixed system of Freon-11 and Freon-152, the mechanical energy obtained from the heat source energy, that is, the energy conversion efficiency, -114 (dichlorotetrafluoroethane), Freon-152 and 1,1,2-trichloro- described in U.S. Pat. No. 4,055,049
1,2,2-trifluoroethane (Freon-113)
an azeotrope of 1-chloro-2,2,2-trifluoroethane (Freon-133) and octafluorocyclobutane (Freon-C-318) described in U.S. Pat. No. 4,057,974. , is superior to the mixture of diclodifluoromethane (Freon-12) and Freon-11 described in US Pat. No. 4,285,211. Second, Freon-152 is flammable.
However, when mixed with Freon-11, its flammability decreases, and if the mixture ratio of Freon-11 is 69% or more, it will not burn at all. Also, the mixing ratio of Freon-11
At 69% to 50%, the flammability is very small and does not pose a major problem in practical use. In addition, 95 to 50% by weight of Freon-11, Freon-11
In particular, a remarkable improvement in output efficiency is obtained when the mixing ratio of 152 is in the range of 5 to 50% by weight. Figure 1 shows the pressure of the mixture of Freon-11 and Freon-152 of the present invention (mixing ratio 70% by weight/30% by weight).
This is an enthalpy diagram (PH diagram), and the points A, B, C, D, and E drawn in the diagram are respectively explained in the following Figures 2 and 3 of the Rankine cycle implemented in the following example. corresponds to each state point of the Rankine cycle. Figure 2 is a Rankine cycle system diagram for converting thermal energy into mechanical energy.
The figure shows a Rankine cycle plotted on a temperature entropy diagram using a mixture of Freon-11 and Freon-152 as the working fluid. In addition,
Symbols (A to E) in FIG. 2 correspond to state points indicated by symbols (A to E) in FIG. 3. The working fluid heated by the steam generator 4 evaporates and becomes high-temperature, high-pressure steam. This state is shown in FIG. 3 by the changes in D, E, and A. During this time, the liquid working fluid is heated, its temperature rises, and the entire amount begins to boil. This working fluid vapor then enters the expansion device 1, undergoes adiabatic expansion, lowers its temperature and pressure, and performs work between A and B shown in FIG.
The working fluid, which has performed work in the expansion device 1 and has become low temperature and low pressure, then enters the condensation device 2 and flows through B-C in Fig. 3.
It condenses and liquefies as shown in . This liquefied working fluid enters the pump 3, is pressurized, enters the steam generator 4 again, and the cycle as described above is repeated. In Figure 3, point a indicates the state of the hot water when it enters the Rankine cycle steam generator, and point b indicates the state of the hot water when it leaves the steam generator. The arrow on the straight line drawn from point a to point b indicates the direction of flow of hot water. In addition, points d and e indicate the state of the cooling water in the condenser, d indicates the state of the cooling water at the condenser inlet, and e indicates the state of the cooling water at the condenser outlet.A straight line drawn from point d to point e The arrow above indicates the direction of cooling water flow. As the expansion device used for the above-mentioned Rankine cycle, a rotary or reciprocating positive displacement expander or a turbine expander can be used, and the steam generator is of the same type as the boiler used to generate steam. It is also possible to use a condensing device of the type used in refrigeration equipment. As the pump, an organic solvent pressurized liquid pump commonly used in chemical equipment can be used. The Rankine cycle working fluid of the present invention can be used alone, but other additives can be added as necessary. For example, Freon-152 is flammable and has a lower boiling point than Freon-11, so
In the gas phase, the proportion of Freon-152 is large, making it highly flammable. Therefore, other fluorocarbon gases, such as fluorocarbons,
114, Freon-12, Freon-22 or Freon-
Flammability can be suppressed by adding 13BI.
The amount added is usually 50% by weight based on the amount of Freon-152.
The following are preferred. Next, the present invention will be explained using examples, comparative examples, and various test examples. The blending ratio of each component is expressed in weight %. Examples 1 to 3 and Comparative Example 1 According to the Rankine cycle shown in FIGS. 1 to 3 above, mixtures of Freon-11 and Freon-152 of the present invention at various mixing ratios and Freon-114 were used as working fluids in the same apparatus. This cycle was run by: The operating conditions are that the temperature of the hot water at point a in Figure 3 is 120°C, and the temperature of the cooling water at point d is 25°C. The output characteristics during power generation were determined, and the results shown in Table 1 were obtained. Note that the evaporation temperature in this cycle is 80°C and the condensation temperature is 42°C.

[Table] From the results in Table 1, it is clear that the output characteristics of the mixed system of Freon-11 and Freon-152 are significantly improved compared to the case of Freon-11 alone, and the mixing ratio of Freon-152 is 5 to 5. An increase in output is observed within a range of 50% by weight. In addition, the mixed system of Freon-114 and Freon-152 was found to have a small pressure difference between the evaporator and condenser, requiring less pump power. Next, Freon-11 alone and Freon-11/of the present invention
A working fluid of Freon-152 (weight ratio 70/30) was sealed together with iron and lubricating oil in a glass shield tube, and after heating at 150℃ for 100 hours, the halogen concentration and decomposition generation of the working fluid in the shield tube were determined. The amount of material was measured by gas chromatography. The results are shown in Table 2.

[Table] As shown in Table 2, compared to the working fluid of Freon-11 alone, the mixed system of Freon-11 and Freon-152 of the present invention produces less halogen ions at high temperatures, and is less detected by gas chromatography analysis. There are fewer decomposition products. Freon-11/Freon-
In the case of the 152 mixed system, the small amount of halogen produced at high temperatures means that it is less likely to corrode the metal materials of the equipment, and the fact that there are almost no decomposition products means that the decomposition products are not produced during use. This means that the thermodynamic properties of the working fluid for the Rankine cycle are prevented from changing or the efficiency is prevented from decreasing. As mentioned above, Freon-11 and Freon-
The mixed system with 152 is superior to conventional fluorocarbons in many aspects such as energy conversion efficiency, heat exchange characteristics, and thermal stability.
11, and can be used as an excellent working fluid for Rankine cycles. Reference example Freon-152 43% by weight and Freon-113 57% by weight
(A), an azeotrope (B) of 22% by weight of Freon-133 and 86% by weight of Freon-C-318, a mixture of 20% by weight of Freon-12 and 80% by weight of Freon-11.
A Rankine cycle was operated in the same manner as in Examples 1 to 3 using each of (C). The results are shown in Table 3.

[Table] Comparing Tables 1 and 3, it is clear that the working fluid of the present invention significantly improves the output characteristics.

[Brief explanation of the drawing]

Figure 1 shows the pressure of the Freon-11/Freon-152 mixed system, which is the working fluid for the Rankine cycle of the present invention.
The enthalpy diagram, Figure 2 is a systematic diagram of the Rankine cycle, and Figure 3 is a temperature-entropy diagram of the Rankine cycle using a Freon-11/Freon-152 mixed system as the working fluid.

Claims (1)

[Claims] 1. A working fluid for Rankine cycle consisting of a mixture of trichlorofluoromethane and difluoroethane. 2. The working fluid for the Rankine cycle according to claim 1, comprising a mixture of 95 to 50% by weight of trichlorofluoromethane and 5 to 50% by weight of difluoroethane.