JP2507446B2 - Hot water turbine plant - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a hot water utilization turbine plant that uses hot water such as geothermal water and waste heat water as a heat source.

(Prior art) As the need to develop new energy to replace fossil fuels has been exclaimed, it has been aimed at the utilization of relatively low-temperature hot water, such as geothermal water and waste hot water, which have not been regarded as heat sources in the past. Is directed. When using hot water at such a temperature level as a heat source of Rankine cycle, a medium having a low boiling point is naturally selected as the working fluid, and hydrocarbons or freons are preferably used. FIG. 4 shows a turbine plant using hot water which uses such hydrocarbons and freons as a working fluid, and the liquid working fluid stored in the full liquid type evaporator 1 is supplied from the outside by a pump or the like. It is heated by hot water and evaporated to be saturated steam, which is sent to the turbine 2.
The working fluid expands in the turbine 2 to rotate its impeller, and drives the generator 3 directly connected to the impeller. After this, the expanded working fluid flows to the condenser 4, where it is cooled by the cooling water sent from the outside to be condensed, further extracted by the working fluid pump 5 and supplied to the preheater 6, where it is warmed by the warm water. After that, the liquid is sent to the full liquid type evaporator 1 to complete the cycle. In addition, the code | symbol 7 in the figure has shown the steam control valve.

(Problems to be solved by the invention) As described above, in the turbine plant utilizing hot water, due to the restriction on the temperature of the hot water used as the heat source, the working fluid of the Rankine cycle uses a low boiling point medium such as hydrocarbon or freon. On the other hand, two media with different characteristics are used.
There is also a movement to construct a Rankine cycle by using a non-azeotropic mixture in which more than one kind is mixed and aim for a more efficient plant. However, when a non-azeotropic mixture is used as the working fluid, compared with the conventional case where it was sufficient to handle a single component,
Technical difficulties double. For example, when a non-azeotropic mixture undergoes a phase change from a liquid phase to a gas phase, temperature and concentration changes locally near the heat transfer surface, and the liquid phase and the gas phase may have different concentrations. The difficulty of handling is not the ratio of single components.

Hereinafter, this point will be described in detail with reference to FIGS. 5 and 6.

FIG. 5 shows the relationship between the temperature of hot water and the temperature of the working fluid and the amount of heat exchanged when heat is exchanged using the above-described liquid-filled evaporator 1. The dashed line is for the case where the working fluid is a single component fluid, while the solid line is for the non-azeotropic mixture. That is, when the full liquid evaporator 1 is used, the boiling point temperature can be raised to T _{3 in the} case of a single component fluid, whereas the boiling point temperature can be raised only to T _{1 in} the non-azeotropic mixture. In the figure, T ₄ is the evaporator inlet hot water temperature, and T ₅ is the preheater inlet working fluid temperature. Of course, if the heat transfer area of the evaporator is made much larger than that of the evaporator for single component fluid, the boiling point temperature can be increased, but this leads to neglect of economic efficiency and is not realistic. .

Let us now consider why such a difference in boiling point temperature occurs. Non-azeotropic mixtures differ in equilibrium vapor and liquid concentration at the same pressure and temperature. This state is shown in FIG. 6 as a schematic equilibrium diagram. Under a certain pressure,
For example, at P _{1 and} at temperature T ₁ , substantial heat and phase transfer of substances do not occur in the gas-liquid coexisting state, that is, the concentrations of the liquid phase and the gas phase in the equilibrium state are C ₁ and C ₂ , respectively. However, when heat is applied to the liquid phase from hot water or the like through the heat transfer surface in the heat exchanger, the temperature of the liquid phase near the heat transfer surface rises. Then, when the heat continuously flows into the liquid phase, the temperature reaches the local temperature T ₃ , whereupon bubbles are generated along the heat transfer surface. In other words, boiling begins. While constantly boiling of T _2, respective concentrations at the interface of the liquid and gas phases that form bubbles has a C ₃ and C _4. At this time, the temperature and concentration of the liquid (bulk liquid) apart from the bubble interface remain at T ₁ and C ₁ . The reason why such a large density difference occurs is as follows. That is, at the bubble interface, the temperature C _{4 of} the substance that moves from the liquid phase to the gas phase is different from the concentration C _{3 of the} liquid phase, so that the liquid side of the bubble interface is deficient in low-boiling components, and conversely high-boiling components are Too much. The deficient low boiling point component moves from the bulk liquid to the bubble interface by diffusion. A concentration gradient is required for this migration to occur. Therefore, when boiling constantly occurs, the concentrations of the bulk liquid and the liquid at the bubble interface are different. Also, when the heat transfer surface temperature is considerably high, the bubble interface temperature also rises to a temperature of T ₃ at maximum, and heat and mass transfer become the most active. That is, the temperature of the steam generated when the heat flux is higher than a certain level becomes higher than the temperature of the bulk liquid. However, the temperature of the steam does not exceed the temperature of the heat transfer surface. The reference symbols T ₁ ^- and T ₃ ^- indicate that the pressure is P
The boiling point and the dew point temperature when ₂ (P ₂ > P ₁ ) are shown, respectively, and the symbol C ₅ shows the concentration of the liquid phase at the temperature T ₃ .

Thus, the situation shown in FIG. 5 occurs, but if the boiling point temperature of the non-azeotropic mixture remains at T ₁ , the advantage of using the non-azeotropic mixture is almost eliminated, and the efficiency of the hot water utilization turbine plant is reduced. Attempts to improve will also be dismissed.

Therefore, an object of the present invention is to provide a hot water utilization turbine plant capable of increasing the temperature of a working fluid in a cycle using a non-azeotropic mixture to be higher than that of a single-component fluid to further improve efficiency.

[Structure of the Invention] (Means for Solving the Problems) In the hot water utilization turbine plant according to the present invention, the total amount of evaporation is reduced in the hot water path configured as a heat source for evaporating the non-azeotropic mixture as the working fluid in the Rankine cycle. On the other hand, a first evaporator and a second evaporator, which generate steam at a predetermined rate, are sequentially provided, and the second evaporator to which the working fluid is first introduced is the second evaporator to which the working fluid is introduced and the second fluid to which the working fluid is introduced next. The evaporator No. 1 is characterized in that heat is transferred by pool boiling.

(Operation) The working fluid is heated by hot water from the inlet to the outlet of the preheater to raise the temperature to near the saturated liquid. continue,
The working fluid is sent to a forced convection evaporator, where it receives heat from hot water and is evaporated until the steam flow rate (quality) reaches a predetermined value. Further, the working fluid flows from the forced convection evaporator to the liquid-filled evaporator, and is heated by hotter hot water to evaporate the remaining portion. The relationship between the temperature of the hot water and the working fluid and the amount of heat exchanged at this time is shown in FIG.
That is, this figure shows the following. The point where the temperature difference between the hot water and the working fluid is the smallest (pinch point) is the point where the saturation temperature of the working fluid is reached. The evaporator is arranged such that the heat transfer from the hot surface to the working fluid is performed not only by boiling but also by convection. In this forced convection evaporator, when evaporation progresses in the flow direction of the working fluid and the quality increases, the heat transfer surface does not come into contact with the liquid, that is, dryout occurs, so the operation is performed with low quality maintained. . On the other hand, in a region where the temperature difference between the hot water and the working fluid is sufficiently large, a full liquid type evaporator is used, which efficiently performs pool boiling heat transfer. This avoids the occurrence of dryout in the high quality range, which is a problem with forced convection evaporators. Thus, according to the above-mentioned configuration of the present invention, the pinch point temperature difference can be reduced, and the evaporation temperature of the working fluid can be maintained at a high value.

Embodiment An embodiment of the present invention will be described below with reference to FIG. The same parts as those shown in FIG. 4 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, in the present embodiment, a full liquid type evaporator 1, a forced convection evaporator 8 and a preheater 6 are sequentially provided in the flowing direction of hot water. Here, the forced convection evaporator 8 and the preheater 6 are configured such that the flowing direction of the hot water and that of the working fluid are countercurrent.

In the above configuration, the working fluid is heated by hot water from the inlet to the outlet of the preheater 8 to raise the temperature to near the saturated liquid. Subsequently, the working fluid is sent to the forced convection evaporator 8 where it receives heat from hot water and is evaporated to a quality of about 0.5. Further, the working fluid flows from the forced convection evaporator 8 to the full-fill type evaporator 1 and is heated by higher temperature hot water to evaporate the remaining portion.

If such forced convection evaporator 8 is used, even a non-azeotropic mixture can be efficiently evaporated with a small temperature difference, and the pinch point temperature difference can be reduced. However, if the quality becomes too high in this process, dryout will occur, so the evaporation limit is limited to about 0.5. After that, the working fluid is transferred to the liquid-filled evaporator 1 and the remaining liquid is also evaporated by the pool boiling heat transfer. At this time, since the low boiling point component concentration of the liquid is lower than that of the initial liquid, as shown in FIG. 2, the liquid temperature T ₁ ″ and the vapor temperature T ₃ ″ are respectively the initial boiling temperature of the liquid. Higher than T ₁ ′ and dew point temperature T ₃ ′. However, the temperature difference between the hot water and the working fluid can be made sufficiently large here, so that the pool boiling heat transfer is efficiently performed.

Further, FIG. 3 shows another embodiment of the present invention. In this embodiment, in addition to the forced convection evaporator 8 of the above embodiment, a separator 9 is provided in the path for transferring the working fluid from the forced convection evaporator 8 to the full-fill type evaporator 1. The separator 9 separates the gas-liquid two-phase flow of the working fluid partially evaporated in the forced convection evaporator 8 into a vapor and a liquid, and supplies only the liquid to the full liquid evaporator 1. When the separator 9 is installed in this way, the flow state of the working fluid inside the liquid-filled evaporator 1 becomes stable and the volumetric flow rate becomes small, so the liquid-filled evaporator 1
Can be made smaller.

[Effects of the Invention] As is clear from the above description, the present invention has a predetermined ratio with respect to the total evaporation amount in the hot water passage configured as a heat source for evaporating the non-azeotropic mixture as the working fluid in the Rankine cycle. First and second evaporators that generate steam are sequentially provided, and the second evaporator is a forced convection boiling
Further, since the heat transfer is performed by pool boiling in the first evaporator, the temperature of the working fluid in the cycle using the non-azeotropic mixture can be kept higher than that of the single component, and the turbine using hot water can be used. It is excellent and useful because it can improve plant efficiency.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a hot water utilization turbine plant according to the present invention, FIG. 2 is a diagram showing the relationship between the temperature of hot water and working fluid and the amount of heat exchanged according to the present invention, and FIG. 3 is the present invention. FIG. 4 is a configuration diagram showing another embodiment of the present invention, FIG. 4 is a configuration diagram showing a conventional hot water utilization turbine plant, and FIG. 5 is a diagram showing the relationship between the temperature of hot water and working fluid and the heat exchange amount when the conventional configuration is used. The diagram shown in FIG. 6 is a schematic view of the vapor-liquid phase equilibrium state of the non-azeotropic mixture. 1 ... Fluid-type evaporator 2 ... Turbine 4 ... Condenser 5 ... Working fluid pump 6 ... Preheater 8 ... Forced convection evaporator 9 ... Separator

Claims (4)

(57) [Claims] 1. A hot water utilization turbine plant using a non-azeotropic mixture as a working fluid in a Rankine cycle, wherein a predetermined amount is predetermined for a total amount of evaporation in a hot water path configured as a heat source for evaporating the non-azeotropic mixture. A second evaporator to which the working fluid is first introduced is provided by forced convection boiling and a first fluid to which the working fluid is next introduced. The hot water turbine plant is characterized in that the evaporator is configured to transfer heat by pool boiling. 2. The hot water turbine plant according to claim 1, wherein the first evaporator is a full liquid evaporator. 3. The hot water utilization turbine plant according to claim 1, wherein the second evaporator is a forced convection evaporator. 4. The hot water utilization turbine plant according to claim 1, wherein a separator is provided in a working fluid transfer path from the second evaporator to the first evaporator.