JPS6128709B2 - - 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 pseudo-condensed, and thermal energy is obtained by repeating the cycle of pressurizing it with a pump and turning it into a liquid medium. In the Rankine cycle, which converts mechanical energy into mechanical energy, almost the only medium that has traditionally been used as a moving fluid for the Rankine cycle is water. Water as a working fluid has been used in steam engines for a long time. However, water has a high pseudo-solid 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; There is a limit to the temperature at which it can be used because it freezes. 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 working fluid for the Rankine cycle, which is made of Freon-11, has the disadvantage of low conversion efficiency from thermal energy to mechanical energy. There is.
Therefore, the emergence of a dynamic fluid with high energy conversion efficiency and good heating stability is expected. 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 isobutane exhibits superior properties compared to single substances, and that a mixture of trichlorofluoromethane (hereinafter referred to as Freon-11) and isobutane has extremely excellent properties as a working fluid for the Rankine cycle. Heading: We have completed the present invention. The mixed system of Freon-11 and isobutane of the present invention has the following characteristics as a working fluid for Rankine cycle. The Rankine cycle using a mixed system of Freon-11 and isobutane has characteristics that the mechanical energy obtained from the heat source energy, that is, the energy conversion efficiency, is sufficiently higher than that of Freon-11, which is conventionally known as a working fluid for the Rankine cycle. ing. Furthermore, when used as a working fluid, the range of use is severely limited if it is combustible or explosive, but a mixture of Freon-11 and isobutane with a 50% isobutane mixture will combust, but Its explosive range is narrow and its danger is much smaller than that of isobutane, so it can be put to practical use. Generally, a remarkable improvement in output efficiency can be obtained especially when the mixing ratio is in the range of 95 to 50% by weight of Freon-11 and 5 to 50% by weight of isobutane. Figure 1 is a pressure-enthalpy diagram (P-H diagram) of a mixture of Freon-11 and isobutane of the present invention (mixing ratio 70% by weight/30% by weight), and points A, B, C, D, and E respectively correspond to each state point of the Rankine cycle explained in FIGS. 2 and 3 below of the Rankine cycle implemented in the following example. Figure 2 is a Rankine cycle system diagram for converting thermal energy into mechanical energy.
The figure shows a Rankine cycle using a mixture of Freon-11 and isobutane as the working fluid, plotted on a temperature entropy diagram. Note that this corresponds to each state point indicated by symbols A to E in FIG. 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, reduces temperature and pressure, and performs work between A and B shown in FIG. 3.
The working fluid that 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.
Note that in FIG. 3, point a is a heat source. b shows the state of the hot water when it enters the Rankine cycle steam generator, and b shows the state of the hot water when it leaves the steam generator, drawn from point a to point b. Arrows on straight lines indicate 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 pseudo-condenser outlet. The arrow on the straight line indicates the direction of the flow of cooling water. 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. 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, this was carried out using the same apparatus using a mixture of Freon-11 of the present invention and isobutane at various mixing ratios and Freon-11 as working fluids. I drove a cycle. As for the operating conditions, the temperature of the hot water at point a in Figure 3 is set to 120°C, the temperature of the cooling water shown at point d is set to 25°C, and the mechanical energy obtained from the thermal energy of 1000 t/hour of the hot water is Therefore, 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 a mixed system of Freon-11 and isobutane are significantly improved compared to when Freon-11 is used alone. An increase in output is observed within the range. Next, Freon-11 alone and Freon-11 of the present invention/
A working fluid of isobutane (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 products of the working fluid in the shield tube were determined. The amount 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 isobutane of the present invention generates less halogen ions at high temperatures, and is detected by gas chromatography analysis. Fewer decomposition products. In the case of a Freon-11/isobutane 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 there is no problem during use. This means that the thermodynamic properties of the working fluid for the Rankine cycle are prevented from changing and the efficiency is prevented from decreasing due to an increase in decomposition products. As described above, the mixed system of CFC-11 and isobutane of the present invention has many advantages over conventional CFC-11 in many aspects such as energy conversion efficiency, heat exchange characteristics, and thermal stability.
It can be used as an excellent working fluid for Rankine cycle.

[Brief explanation of the drawing]

Figure 1 is a pressure-entapy diagram of a Freon-11/isobutane mixed system, which is the working fluid for the Rankine cycle of the present invention, Figure 2 is a system diagram of the Rankine cycle, and Figure 3 is a Freon-11/isobutane mixed system. It is a diagram in which the Rankine cycle used as a working fluid is plotted on a temperature-entropy diagram.

Claims (1)

[Claims] 1. A working fluid for a Rankine cycle, characterized in that trichlorofluoromethane is mixed with isobutane. 2. The working fluid for Rankine cycle according to claim 1, characterized in that 95 to 50% by weight of trichlorofluoromethane and 5 to 50% by weight of isobutane are mixed.