JPS622128B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides waste heat from steel plants, cement factories, etc.
It relates to a method for recovering power from relatively low-temperature heat sources such as geothermal heat, and in particular combines a hydrothermal turbine process and a fluorocarbon turbine process, resulting in synergistic effects such as improved heat recovery efficiency and miniaturization of equipment. This aims to promote the effective use of low-temperature heat sources.

Conventionally, the methods for obtaining power by recovering heat from low-temperature heat sources of around 200℃ to 350℃, such as waste heat from steel plants, have been based on methods using hydrothermal turbines and low-enthalpy heat media such as chlorofluorocarbons, isobutane, and toluene. There is a method using an organic media turbine using .

The former type of hydrothermal turbine is a turbine that is driven by hot water obtained by heating water under pressure.
This is a two-phase flow turbine that simultaneously introduces steam and hot water generated by flashing hot water to the blade rows. The reason for using a hydrothermal turbine is that sensible heat exchange using hot water has a higher heat recovery rate than latent heat exchange including an evaporation process. In other words, in the case of latent heat exchange, the temperature of the heat source in the heat exchanger varies from the inlet temperature _T1 to the outlet temperature, as shown in Figure 1, which shows the relationship between temperature and heat amount.
Descend almost linearly to T ₂ . On the other hand, water, which is a working fluid, is in a liquid state at a temperature of t ₁ at the inlet. When it is preheated and reaches the saturation temperature _tp , it begins to evaporate and absorbs latent heat. The temperature difference between the temperature curve L ₁ of the heat source and the temperature curve L ₂ of the water becomes the minimum Δt at the saturation temperature t. Such points are called pinch points. Therefore, the temperature difference between the two at the pinch point (T-t=Δt) is the minimum temperature difference. In order to ensure this minimum temperature difference, the temperature difference (approach) between the heat exchanger outlet temperature T ₂ of the waste heat source and the heat exchanger inlet temperature T ₁ of the water must be large, and in order to lower the former temperature Restrictions arise. As a result, a large amount of heat ends up being wasted without being able to be used. Using a latent heat exchange process in this manner is disadvantageous when recovering power from a low temperature heat source. For the above reasons, it is advantageous to use hot water turbines that use as working fluid hot water obtained by absorbing heat from a heat source by pressurizing the water to an extent that it does not evaporate. Since this is a sensible heat exchange during the heating process of hot water, the temperature of the heat source changes as shown in Figure 2.
The calorific properties of L ₁ and hot water temperature L ₂ are almost parallel.

Therefore, if the inlet temperature t ₃ of the hot water is lowered as necessary, the outlet temperature T ₄ of the heat source is also lowered accordingly, so that the heat of the low-temperature heat source can be used effectively. In other words, since there is no restriction on the amount of heat recovered due to the pinch point temperature difference in the evaporator of the working fluid in the steam turbine, the sensible heat exchanger outlet temperature of the low-temperature heat source and
The temperature difference (approach) between pressurized cold water and the inlet temperature of the exchanger can be reduced, and the heat of the former can be recovered to a low temperature, resulting in a large amount of recovered heat. Furthermore, since the sensible heat exchanger does not have an evaporation phase, a liquid recirculation section such as a gas-liquid separation drum or a downcomer pipe is not required, making the structure and handling simple and inexpensive. Furthermore, since heat is transported using high-temperature liquid, the diameter of the piping can be made small, which is particularly advantageous for distributed heat sources. However, on the other hand, since the hot water turbine is a two-phase flow turbine as described above, it is difficult to obtain efficiency equivalent to that of a single-phase flow turbine due to reasons such as droplets adhering to the turbine blades.

On the other hand, organic media turbines that use a series of halogenated hydrocarbon compounds such as Freon-11 and Freon-114 as working media have high cycle efficiency and turbine efficiency as long as they are used at low temperatures of about 150℃ to 100℃. Obtainable. Especially when using Freon-11 or Freon-114 as the organic medium,
It is more advantageous than other organic media such as toluene, pyridine, and florinol in terms of safety such as non-toxicity and nonflammability. However, in the case of fluorocarbons, there are not only advantages; when applied to waste heat sources of about 350℃ to 200℃, the thermal decomposition temperature is at most about 140℃ or less, so the maximum cycle temperature cannot be higher than that, and the cycle It also has limited efficiency and is difficult to use properly. Also, as mentioned above, due to the pinch point temperature differential constraint in the evaporator, the amount of heat recovered is less than with hot water recovery. Furthermore, if heat from a distributed heat source or the like is concentrated and economies of scale are expected from a single large-capacity turbine, the heat transport piping becomes long and the pipe diameter becomes large for steam transport. Moreover, the amount of medium filled into the pipe is large, resulting in excessive medium costs.

Therefore, the first object of the present invention is to focus on the fact that the temperature ranges in which a hydrothermal turbine and a fluorocarbon turbine can be advantageously used are different, and to organically combine the two under certain conditions, thereby eliminating the conventional system of either one alone. It can be effectively used in temperature ranges that were difficult to apply in the past.
Another purpose is to improve the overall cycle efficiency and increase the amount of recovered heat.

In other words, if the back pressure of the hydrothermal turbine is set to slightly exceed atmospheric pressure, the temperature of the discharged hot water and saturated steam will be the saturation temperature corresponding to the back pressure, for example, 100°C and 6 atm at atmospheric pressure. The temperature is as low as 160℃. The front turbine cycle has the highest cycle efficiency in this temperature range, and can be used stably without the risk of thermal decomposition.

Therefore, the present invention achieves the above object by combining a fluorocarbon turbine so that the hot water and saturated steam discharged from the hot water turbine are used as heat sources. Further, reducing the pressure to a high vacuum using only a hot water turbine causes droplets to adhere to the turbine blades, resulting in a decrease in turbine efficiency, as described above. Therefore, it is possible to improve the efficiency of the hot water turbine by making the hot water turbine a back pressure type and increasing the temperature of the hot water at the turbine outlet. In fact, experiments have shown that, as shown in FIG. 5, when a hot water turbine is of a back pressure type and the outlet temperature is increased, the turbine efficiency is improved. Here, D is the diameter of the droplet. The reason for this is as follows.

In other words, a hydrothermal turbine is a two-phase flow turbine, and the turbine blade row contains a mixture of steam and liquid droplets.
enter in. Steam flows along the turbine blades and efficiently imparts momentum to the blades, but since the droplets have a large mass, their inertia force causes them to stick to the blades instead of bending along the blades. This is a particularly noticeable tendency when the turbine back pressure is low, but as the back pressure increases, the steam density increases,
This is thought to be because the shape resistance of the droplets increases, the tendency of the droplets to follow the steam flow increases, and the number of droplets that pass through without adhering to the turbine blades increases, allowing them to efficiently impart momentum to the blades. .

Figure 6 shows this situation. However, back-pressure hot water turbines only partially utilize the available work (enthalpy change in isentropic change) of hot water. For example, high pressure hot water at 250℃
Comparing the available work when expanding to 0.075at and when expanding to 6at, the ratio is 54 to 11, respectively.
If a back pressure of 6 at is applied, only about one-fifth of the work is done when expanded to a high vacuum, and four-fifths of the heat is wasted.
The problem then is how to effectively utilize this four-fifth amount of heat. From this point of view, conventionally, as shown in Figure 3, exhaust gas from a back pressure hot water turbine A is introduced into a steam separator B to be separated into steam and hot water, and the hot water is introduced into a multistage flusher C. Steam D obtained by
Depending on the situation, there is a method of driving a flash steam turbine F to generate electricity. In this case, the amount of heat that could not be utilized by the back pressure hot water turbine A is used, but the flash steam turbine F can only expect a turbine efficiency of about 75% due to the wet components in the steam. Furthermore, the temperature of the water at the outlet G of the multistage flusher C is about 28°C, and even if it is combined with the water I from the condenser H, the temperature _t3 at the inlet K of the heat exchanger J that generates hot water is at most 28°C. It can only be cooled to about 60-70℃. Therefore, the exit temperature of the heat source due to the sensible heat exchange shown in FIG. 2 cannot be lowered very much, and heat recovery from the low-temperature heat source itself is restricted.
This leads to a decrease in the basic amount of recovered heat,
This is extremely disadvantageous as a method of recovering power from a low-temperature heat source.

Therefore, a second object of the present invention is to increase the amount of heat recovered from a low-temperature heat source by combining a hydrothermal turbine cycle and a freon turbine cycle.

Furthermore, in the conventional method using a flash turbine shown in Fig. 3, in order to obtain steam to be supplied to the flash turbine, a multi-stage flasher C is necessarily required, and at the same time, a steam/water separator is required. It is uneconomical as a necessity.

Therefore, the third object of the present invention is to reduce the cost of the entire power recovery device by easily obtaining separated hot water and steam from a hot water turbine without requiring a steam separator or the like. The point is to aim for it.

Furthermore, in the case of an organic medium turbine cycle, there is a problem of a reduction in the amount of recovered heat due to the restriction of the pinch point temperature difference in the evaporator as described above.

Therefore, the fourth object of the present invention is to improve the heat recovery rate of the fluorocarbon cycle by appropriately combining the fluorocarbon cycle and the hot water cycle, improve the turbine efficiency of the fluorocarbon turbine, and increase the overall power recovery rate. It is about increasing.

Next, embodiments embodying the present invention will be described in detail with reference to the accompanying drawings starting from FIG. FIG. 4 is a circuit diagram of a turbine cycle schematically showing an example of a power recovery method according to an embodiment of the present invention. As shown in FIG. 4, water pressurized by a water pump 5 is heated in a hot water generator 1, which is a type of heat exchanger, with a low-temperature heat source of, for example, 350°C to 200°C. It becomes hot water. The water pump 5 pressurizes water in the hot water generator 1 to an extent that evaporation does not occur. The hot water obtained by the hot water generator 1 is sent to the hot water turbine 2 to drive the hot water turbine 2. A constant back pressure is applied to the hot water turbine 2,
From the outlet of the hot water turbine 2, steam and hot water at a constant temperature are separated and discharged. Since this hot water and steam are in a saturated state, their temperature is uniquely determined by determining the back pressure of the turbine. Hot water turbine 2
The back pressure is determined to be such a pressure that the fluorocarbon used in the fluorocarbon cycle described below gives the discharged hot water a temperature within a range that does not cause thermal decomposition in the fluorocarbon evaporator.
The temperature of this hot water is about 110°C for Freon-11 and about 140°C for Freon-114. In this cycle, hot water and steam are separated in the hot water turbine 2 by centrifugal force or swirling airflow caused by rotation of the turbine. An example of such a hot water turbine will be explained with reference to FIG. 7.

In the seventh example, reference numeral 10 denotes a rotor blade provided on a turbine shaft 12 supported by bearings 11, 11. The hot water supplied from the inlet 13 is blown onto the rotor blades 10 through the nozzle 14, at which time a part of it evaporates and turns into water vapor. When passing through the rotor blades 10,
The hot water with a large specific gravity is blown toward the outer circumference by the centrifugal force caused by the swirling air current or the rotation of the rotor blades, and after adhering to the casing wall 15, it flows down under its own weight from the hot water primary separation port 16 to the hot water receiving part 17. Inflow. A portion of the hot water and steam that cannot be recovered in this primary separation passes through the turbine diffuser sections 18 and 19 and bends toward the turbine outlet 20. During this bending, the hot water with a heavy mass collides with the pipe wall 21 or 22, and after adhering to the pipe wall 21 or 22, it slides down due to its own weight and passes from the hot water secondary separation port 23 to the hot water receiving part 17.
flows into. The separated steam of the hot water is guided to the fluorocarbon evaporator 3, where the condensed water 24 and the hot water obtained in the hot water receiving section 17 are combined and guided to the fluorocarbon preheater 4. The flow of hot water is shown by solid line arrows, the flow of water vapor is shown by broken line arrows, the flow of fluorocarbon liquid is shown by a dashed line, and the flow of fluorocarbon vapor is shown by a chain double dotted line.

The steam thus separated in the hydrothermal turbine is
The water is led to a fluorocarbon evaporator 3 that evaporates fluorocarbons, and exchanges heat with the fluorocarbons to become hot water. This hot water is combined with the hot water directly obtained by the hot water turbine and is supplied to the freon preheater 4. Since the heat exchange within the freon preheater 4 is sensible heat exchange, the temperature of the discharged water can be arbitrarily adjusted by the inlet temperature of the supplied freon. The water coming out of the freon preheater is
The water is pressurized by the water pump 5 as described above and circulated to the hot water generator 1. An accumulator is provided between the hot water generator 1 and the hot water turbine 2 to stabilize the hot water turbine inlet pressure.

Next, the cycle of the freon turbine 6 connected to the hot water turbine 2 in series as shown in the figure or in parallel via gears or the like will be explained. The fluorocarbons discharged from the fluorocarbon turbine 6 are cooled in the fluorocarbon condenser 7 and become 100% liquid fluorocarbons. As mentioned above,
The temperature of this liquid Freon determines the temperature of the water supplied to the hot water generator, and the temperature of this water determines the amount of heat recovered from the low temperature heat source. Therefore, the specifications of the fluorocarbon condenser 7 are determined so that the temperature of the liquid fluorocarbon discharged from the fluorocarbon condenser 7 is as low as, for example, 35°C. The liquid Freon discharged from the Freon condenser is pressurized by the Freon pump 8.
Sensible heat is exchanged with the hot water through the freon preheater 4, and the water is heated until just before evaporation. Next, the fluorocarbon heated by water vapor passes through the fluorocarbon evaporator 3, becomes dry or superheated steam, and is supplied to the fluorocarbon turbine 6. After driving the fluorocarbon turbine 6,
It returns to the freon condenser 7. Reference numeral 9 denotes a generator driven by the fluorocarbon turbine 6 and the hot water turbine 2.

In the case of the hot water turbine shown in FIG. 7, the dryness at the outlet of the rotor blades 10 is 25 to 30%.
Therefore, the amount of hot water A entering the hot water receiving part 17 in FIG.
is 70 to 75% of the total, and the amount of hot water B flowing back from the fluorocarbon evaporator 3 is 25 to 30%. Since B is considerably smaller than A, the hot water receiving part 17 itself is used as a fluorocarbon preheater. The freon preheater 4 shown in FIG. 7 can be omitted. The hot water turbine shown in FIG. 8 is an example of such a case. As is clear from the figure, a fluorocarbon preheating tank 25, which is a type of fluorocarbon preheater, is provided at the lower part of the hot water receiving section 17 and is directly connected to the hot water receiving section 17. The warmed fluorocarbon liquid further passes through the fluorocarbon evaporator 3 and is vaporized. Condensate 24 condensed in the fluorocarbon evaporator 3 is returned to the fluorocarbon preheating tank 25 through a pipe 27.

Moreover, what is shown in FIG. 9 is an example of a hard shaft type hot water turbine. In this case, the turbine shaft 12' is vertical, and a ring-shaped groove 28 is provided at the lower outer circumference of the rotor blade 10' provided on the turbine shaft 12'.
The hot water thrown out in the outer circumferential direction by the rotation of the rotor blade 10' accumulates in this groove 28 and is taken out from the hot water primary separation port 16' communicating with the groove 28. In addition, the hot water collected at the bends of the turbine differential users 18' and 19' passes through the outlets 29 and 30, joins with the hot water taken out from the primary separation port 16', and is supplied to the fluorocarbon preheater. be done.

As described above, the present invention organically combines a hydrothermal turbine cycle driven by a low-temperature heat source and a fluorocarbon turbine cycle under appropriate conditions, and provides an appropriate back pressure to the hydrothermal turbine. to improve the turbine efficiency of hydrothermal turbines,
In addition, it is possible to select a temperature range in which the fluorocarbons used do not cause thermal decomposition and the cycle efficiency of the fluorocarbon turbine is high, which improves the cycle efficiency of the entire cycle and dramatically increases the amount of recovered heat. do. Moreover, since it is a combination of a fluorocarbon turbine and a conventional wet steam turbine, which has poor turbine efficiency in the low temperature range, for the hydrothermal turbine cycle, even if only the fluorocarbon turbine section is taken out, the turbine The exchange rate can be expected to be over 80%, improving the overall turbine exchange rate. This is because the freon turbine can obtain dry, saturated or superheated steam at the turbine outlet even in a low temperature range. In addition, by combining a fluorocarbon turbine that can be used at low temperatures, we were able to dramatically lower the temperature of the water flowing into the hot water generator, increasing the amount of heat recovered from the low-temperature heat source and improving the turbine efficiency and cycle as described above. Along with improved efficiency, recovery power has increased significantly.

Furthermore, in the present invention, the hot water and steam phases are separated within the hot water turbine by the centrifugal force generated by the hot water turbine itself, similar to a cyclone separator. Since there is no need for this, the cost reduction is significant.

Furthermore, in the present invention, heat exchange is performed in two stages: fluorocarbons are preheated using hot water separated by a hydrothermal turbine, and evaporated from fluorocarbons using similarly separated steam. The temperature difference in heat exchange can be reduced without being constrained by point temperature differences, reducing thermodynamic irreversible loss, further improving the heat recovery efficiency of the fluorocarbon cycle and the turbine efficiency of the fluorocarbon turbine. Moreover, since the heat exchange is liquid-to-liquid phase and condensation to evaporation, the heat transfer coefficient is increased and the heat transfer area can be reduced.

Furthermore, the dimensions of these devices are controlled by the turbine exhaust capacity, but organic medium vapor such as chlorofluorocarbons has a high saturation pressure and a small specific volume at the cooling water temperature. For this reason, when using a freon turbine and condenser, the dimensions are smaller than when using a conventional steam turbine and condenser whose saturation pressure is lower than atmospheric pressure. Furthermore, since CFC is used as the organic medium, the cost is lower than when using organic media such as toluene, pyridine, and florinol.
It is the most advantageous in terms of safety, hygiene, corrosion resistance, etc.

[Brief explanation of the drawing]

Figure 1 is a heat exchange characteristic diagram in latent heat exchange, Figure 2 is a heat exchange characteristic diagram in sensible heat exchange, Figure 3 is a circuit diagram using a conventional hot water turbine and a steam turbine, and Figure 4. 5 is a circuit diagram of a turbine cycle schematically showing an example of a power recovery method that is an embodiment of the present invention, and FIG. 5 is a graph showing the influence of back pressure and turbine outlet hot water temperature on turbine efficiency and dryness. . FIG. 6 is a graph showing the relationship between back pressure and droplet adhesion amount. 7 to 9 are schematic side sectional views showing various structures of a hot water turbine that can be used in the present invention. (Explanation of symbols), 1... Hot water generator, 2... Hot water turbine, 3... Freon evaporator, 4, 25...
Freon preheater, 5... Water pump, 6... Freon turbine, 7... Freon condenser, 8... Freon pump.

Claims (1)

[Claims] 1 A hot water turbine is driven using hot water heated under pressure by a low-temperature heat source, and the hot water and steam discharged from the hot water turbine are separated within the hot water turbine, and the separated heat is The water is supplied to the Freon preheater and the separated steam is supplied to the Freon evaporator to exchange heat with the Freon. After this heat exchange, the water is pressurized and heated again with a low-temperature heat source. The fluorocarbon turbine is driven by the fluorocarbon gas, the fluorocarbon gas discharged from the hot water turbine is cooled and pressurized, and then heated through the fluorocarbon preheater and fluorocarbon evaporator. A method for recovering power from a low-temperature heat source, characterized in that a back pressure is applied to an outlet of a hot water turbine within a range in which the temperature of hot water and steam does not exceed the thermal decomposition temperature of the fluorocarbon used.