JPS61237804A - Power system - Google Patents

Abstract

PURPOSE:To raise the energy efficiency, by combining plural Rankine cycles which are different from each other their actuation enthalpy ranges, with a single reverse Rankine cycle, and taking outward the energy at the polytropic expansion process of each of the Rankine cycles. CONSTITUTION:A reverse Rankine cycle in which a fluid A circulates through a compressor 3, a high temperature side heat exchanger 1, an expansion valve 4, a low temperature side heat exchanger 2 and a super-heater 9, and plural Rankine cycles in which fluids B, C circulate, are combined with each other. The temperature of the fluid in the heating process of each Rankine cycle is kept lower than the temperature of the fluid in the cooling process of the reverse Rankine cycle, and that in the cooling process of each RAnkine cycle is kept higher than that in the heating process of the reverse Rankine cycle. The end temperature of the heating process of the RAnkine cycle whose actuation enthalpy range is the lowest, is kept lower than the end temperature of the cooling process of the reverse Rankine cycle. Then, power is taken out from an expansion turbine 8 of each Rankine cycle.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power system that supplies thermal energy from the outside and recovers energy in the form of power, and particularly to a power system that is useful for energy saving and environmental protection.

Traditionally, power systems such as power generation systems that generate power from thermal energy obtained by burning fuels such as oil, coal, and nuclear have been burned in Rankine cycle boilers equipped with turbines, or gas It is burned in a gas turbine in a combined cycle of turbine and Rankine cycle.
The generated thermal energy is extracted as power by an expansion turbine rotated by steam or the like, and in one power generation system, this power is converted into electrical energy by a generator.

The steam, whose temperature and pressure have decreased due to expansion, is cooled in a condenser and turned into water, which is then used for circulation. However, the heat released from the steam during the cooling process is released into the seawater and the atmosphere without being used. thrown into the air.

As a result, the energy efficiency of the power system decreases, including the mechanical efficiency of the equipment and friction losses of the piping.

It becomes only about 40 to 42%. On the other hand, the heat abandoned in the ocean and the atmosphere increases the energy in the natural environment,
This results in changes in the environment.

In view of the above-mentioned problems of power systems such as conventional Rankine cycle power generation systems, the present inventor has developed a system that has high energy efficiency and that utilizes the sensible heat of seawater, which has not been used in the past, and wastewater from power plants, factories, etc. For the purpose of providing a power system that utilizes heat, reduces the consumption of valuable fuel, and is useful for preserving the natural environment, we first combined a single rank cycle and a 1-cascade cycle, The heat released during the Rankine cycle cooling process is
It is supplied to the fluid in the temperature raising process of the cascade cycle, and in addition to the heat input from an external heat source in the temperature raising process of the Rankine cycle.
We proposed a power system that improves energy efficiency by returning the heat previously given to the fluid in the cascade cycle.

Its structure and operation will be explained with reference to the drawings.

3 and 4 are a Mollier diagram and a system diagram, respectively, of an example of a power system configured by combining a single Rankine cycle and a single cascade cycle.

The horizontal axis in FIG. 3 is enthalpy and the vertical axis is pressure.

The cycle indicated by →→O→■ in the figure is a Rankine cycle, and the cycle indicated by ■→■→■→■ is a cascade cycle.6 In the system diagram in Figure 4, the loop on the left shows the path of a cascade cycle. , the loop on the right shows the path of the Rankine cycle. Symbols shown next to the route ■, ■,...
. . , ■, ■, . . . indicate positions corresponding to each state in the Mollier diagram of FIG. The fluids used in the Rankine cycle and the cascade cycle may be the same or different.

Each cycle will be explained with reference to FIGS. 3 and 4. In the Rankine cycle, O→■ is the cooling process, ■→Q is the pressure increase process,
■→◎ is the temperature raising process, 0→ is the expansion process, ■→■ of the cascade cycle is the compression process, ■→■ is the cooling process,
→■ is an expansion process, and ■→■ is a temperature raising process. The vapor-liquid equilibrium curve shown by a solid line in FIG. 3 is for a fluid flowing through a Rankine cycle, and the vapor-liquid equilibrium curve shown by a broken line is for a fluid flowing through a cascade cycle.

As shown in FIG. 3, the temperature T2 of the fluid in the cooling step of the cascade cycle is higher than the temperature TH of the fluid in the temperature raising step of the Rankine cycle, and the temperature TL of the fluid in the cooling step of the Rankine cycle is higher than that in the temperature raising step of the cascade cycle. The starting point temperature TM of the temperature raising step 0→O of the Rankine cycle is higher than the fluid temperature T□ at , and lower than the ending point temperature T of the cooling step ■→■ of the cascade cycle. Also, the fourth
As shown in the figure, a high-temperature side heat exchanger 1 is installed between the flow path for the cooling process ■→■ of the cascade cycle and the flow path for the temperature increase process 0→■ of the Rankine cycle. ■Flow path and cascade cycle heating process■→■
A low temperature side heat exchanger 2 is provided between the flow path and the flow path.

A compressor 3 is installed in the compression step ■→■ of the cascade cycle, and when energy E1 is input to the motor to drive the compressor, the gas state of the fluid flowing through this cycle changes to ■ (enthalpy, pressure, temperature). are respectively i■, P
■, T■; The following states also change from ■ to ■. ■
The gas in the state loses heat to the Rankine cycle side by the high temperature side heat exchanger 1 and is cooled down to a temperature T2.When it is further cooled, it starts to liquefy while maintaining the temperature T2, and the enthalpy changes from i to i ■Changes to. In this case, it is not necessarily necessary to liquefy the entire amount, but as shown in FIG. 3, when the entire amount is liquefied beyond the saturated liquid line, the temperature becomes T. An expansion valve 4 is provided in the path from expansion step ■ to ■, and the liquid in state (2) undergoes isenthalpic expansion and becomes a low pressure state (2).

When heat is applied to the liquid in this state from the Rankine cycle side via the low-temperature side heat exchanger 2 to raise the temperature, the liquid becomes gaseous, increasing its enthalpy, and reaches a gas state of 2.

On the other hand, in the Rankine cycle, the low-temperature gas in the fluid in state (■) is liquefied by dissipating heat to the cascade cycle side via the low-temperature side exchanger 2 in the cooling process, and is completely liquefied in (2) when it exceeds the saturated liquid line. It is stored in the receiver 5 and is boosted by the boost pump 6 to reach the high pressure state (1).Then, heat is received from the cascade cycle via the high temperature side heat exchanger 1, and heat is further supplied from an external heat source by the heat exchanger 7. The temperature rises. In the temperature raising process, the fluid is initially in a liquid state, and the temperature rises from TM to TH. In the gas-liquid mixing zone, it is gasified at isothermal TH, and after the entire amount is gasified, the temperature is raised again to reach the temperature of T. The high-temperature, high-pressure gas outputs energy E2 to the outside through the expansion turbine 8 during the expansion process, and becomes the low-temperature, low-pressure gas in the state of ■.

Repeat this cycle.

As described above, in this power system, the energy released from the fluid in the Rankine cycle during the cooling process is not discarded into the seawater or the atmosphere.
Heat is given to the fluid in the cascade cycle to raise its temperature, and it is returned from the fluid in the Rankine cycle in the heating process O → ◎, so heat is radiated into the seawater or the atmosphere in the conventional cooling process. Energy efficiency will be improved compared to the previous model, and the effect of preventing temperature rise in the natural environment will also be improved.

In this system, the energy E□ input in the compression process of the cascade cycle consumes a part of the output energy E2 in the expansion process of the Rankine cycle, so
The subtracted output energy is E2-El, and the energy efficiency η is as follows.

However, considering the mechanical efficiency and friction loss of the device, the efficiency of the entire system will be lower than this, so although this is somewhat improved over conventional systems, it is still inadequate for practical use.

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, it is an object of the present invention to provide a power system with further excellent energy efficiency.

In order to achieve the above object, the present invention combines a Rankine cycle with a cascade cycle, and transfers the heat of the fluid in the cooling process of the cascade cycle to the fluid in the heating process of the Rankine cycle through a heat exchanger. The heat of the fluid in the cooling process of the Rankine cycle is given to the fluid in the heating process of the cascade cycle via a heat exchanger, and the heat of the fluid in the heating process of the Rankine cycle is given from the outside to raise the temperature of the Rankine cycle. In a power system that applies heat to the process fluid from the outside and extracts energy to the outside through the polytropic expansion process of the Rankine cycle, multiple Rankine cycles with different actuation enthalpy regions are combined with a single cascade cycle, and each Rankine cycle's The fluid temperature in the heating process is kept lower than the fluid temperature in the cooling process of the cascade cycle, and the fluid temperature in the cooling process of each Rankine cycle is kept higher than the fluid temperature in the heating process of the cascade cycle. It is characterized in that the temperature at the starting point of the temperature raising step of the lowest Rankine cycle is kept lower than the temperature at the end point of the cooling step of the cascade cycle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the present invention will be explained in detail below using drawings showing embodiments.

FIG. 1(a) is a Mollier diagram of an embodiment of the power system of the present invention, and FIG. 2 is a system diagram thereof.

■'→■'→■'→■'→■' in Figure 1 is a cascade cycle, and ''→''→■'→σ→'' and ■''
→@'→■1→◎'→' are two Rankine cycles with different activation enthalpy regions.

The vapor-liquid equilibrium curves and Mollier diagrams of fluids A, B, and C used in these cascade cycles and the two Rankine cycles are shown in Fig. 1(b), (c), and (d), respectively. (a) shows the Mollier diagrams of the cascade cycle and two Rankine cycles superimposed on the same coordinates.

The temperature raising cycle of the cascade cycle may be supplemented by superheating using a heating medium such as waste heat.

The fluid temperatures TH' and THll in the heating step of the two Rankine cycles are smaller than the fluid temperature in the cooling step of the cascade cycle (T2' in the gas-liquid mixed state, smaller than that in the gas state), and The fluid temperatures TL〆 and T L s in the cooling process are the fluid temperatures in the temperature raising process of the cascade cycle (T in the gas-liquid mixed state).
The temperature at the starting point 0' of the Rankine cycle's heating step e'→◎', which is held higher than i' (in the gas state, smaller than that) and has a lower operating enthalpy region, is the temperature at the starting point 0' of the cascade cycle's cooling step ■'→■ ′ is kept lower than the temperature at the starting point ■′.

Figure 2 is a system diagram of this power system, where the loop shown by a single solid line on the left side of the figure is a cascade cycle in which fluid A flows, and the loop shown inside the right side by a double line of solid and broken lines. This is a Rankine cycle in which fluid B flows, and the loop shown by a double solid line on the outside is a Rankine cycle in which fluid C flows. The symbols shown next to these paths correspond to the symbols showing the states of each cycle in FIG.

The equipment arranged in the cascade cycle is the same as the example shown in Fig. 4, but the high temperature side heat exchanger 1 has a Rankine cycle 2
The low-temperature heat exchanger 2 is configured to sequentially exchange heat with the fluid C of the Rankine cycle 1 and the fluid B of the Rankine cycle 1, and the low temperature side heat exchanger 2 sequentially exchange heat with the fluid B of the Rankine cycle 1 and the fluid C of the Rankine cycle 2. In addition, the low temperature side heat exchanger 2
A super heater 9 is provided between the compressor 3 and the compressor 3 to input heat such as factory waste heat. On the other hand, the configuration and arrangement of the devices of the two Rankine cycles 1 and 2 are the same as those of the Rankine cycle shown in FIG. 4, so the explanation will be omitted.

The expansion turbine 8 provided in the expansion step of the Rankine cycle 1 of the fluid B outputs energy E2, and the turbine 8 provided in the expansion step of the Rankine cycle 2 in which the fluid C flows outputs the energy E.

Therefore, the energy efficiency η of this system is as follows.

By comparing equations (1) and (2), it can be seen that the system of the present invention has improved energy efficiency than the previously proposed system.

In the above embodiment, for one cascade cycle, 2
Although an example in which one Rankine cycle is provided has been shown, energy efficiency is further improved when three or more Rankine cycles are provided for one cascade cycle.

In addition, as shown in FIGS. 5(a) and 5(b), the pressure in the cooling process of the cascade cycle is changed in the middle, or
As shown in Figure (c), the pressure in the temperature raising step of the cascade cycle is changed in the middle, the compression step or expansion step is divided into two stages, and the temperature raising step or cooling step of the Rankine cycle is made to follow this. In this case, the purpose of utilizing heat dissipation from the cooling process in the temperature raising process is achieved.

FIGS. 5(d), (e), and (f) show that when the pressure of the cooling step or the heating cycle of the cascade cycle is changed in the middle, the present invention can create multiple (
It is a Mollier diagram of an example in which two Rankine cycles are provided in the illustrated example.

Each of the above-mentioned embodiments shows the basic concept, and descriptions of auxiliary equipment such as buffer equipment, valves, and meters necessary for each system are omitted.

Further, a system in which a plurality of the above-mentioned systems are combined, a system in combination with other energy systems, or a mixed liquid used in each cycle also belong to the scope of the present invention.

As described above, according to the present invention, a power system with excellent energy efficiency can be obtained, and it is also effective in preventing destruction of the heat balance of the natural environment.

[Brief explanation of drawings]

FIG. 1(a) is a Mollier diagram of a cascade cycle and a Rankine cycle that constitute a system according to an embodiment of the present invention.
(b), (C), and (d) are diagrams showing individual Mollier diagrams and vapor-liquid equilibrium curves of the fluid used for each Rankine cycle, Figure 2 is a system diagram of the example, and Figure 3 is Mollier diagram of the power system proposed earlier by the inventor, No. 4
The figure shows the system diagram, Figure 5 (a), (b), (c)
Figure 5(d) is a Mollier diagram showing the idea of changing the pressure in the cooling process or heating process in the middle of the cascade cycle.
, (e) and (f) are Mollier diagrams of an embodiment in which the present invention is applied to this idea. ■′→■′→■′→■′→■′・・・Cascade cycle ■′ →■′ →O′ →[F]′ →■′. ■“→の′→0”→O′→■′・・・Rankin cycle ■′ →■′ , ■′ →■′ , ■″→■″・・・Cooling process ■′→■′, C′→ O', 0''→0''... Temperature raising process 1.2.7... Heat exchanger 3... Pressure machine 4... Expansion valve 6... Pressure boost pump 8... Expansion turbine bow
D'J D enthalpy
i 5th N (b) (e) (c)
(f) Enthalpy 1
Enthalpy 1 Procedural Amendment February 28, 1986

Claims (1)

[Claims] A cascade cycle that combines a cascade cycle that has a series of steps of compressing, cooling, expanding, and increasing the temperature of a fluid, and a Rankine cycle that has a series of steps of increasing pressure, increasing temperature, polytropic expansion, and cooling a fluid. The heat of the fluid in the cooling process of the cycle is given to the fluid in the heating process of the Rankine cycle via a heat exchanger, and the heat of the fluid in the cooling process of the Rankine cycle is transferred to the fluid in the heating process of the cascade cycle via the heat exchanger. In a power system, heat is given externally to the fluid in the temperature raising process of the Rankine cycle, and energy is extracted externally in the polytropic expansion process of the Rankine cycle. Multiple Rankine cycles with different operating enthalpy regions are combined into a single cascade. In combination with the cycle, the fluid temperature in the heating step of each Rankine cycle is kept lower than the fluid temperature in the cooling step of the cascade cycle, and the fluid temperature in the cooling step of each Rankine cycle is kept lower than the fluid temperature in the heating step of the cascade cycle. The power system is characterized in that the temperature at the starting point of the heating step of the Rankine cycle, which has the lowest operating enthalpy region, is kept lower than the temperature at the end point of the cooling step of the cascade cycle.