JPS6256421B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating and cooling system in which a heat pump cycle is driven by a Rankine cycle heat engine, and more specifically to a Rankine cycle heat engine in which a positive displacement fluid machine is used as an expander. This relates to control of heat pump cycles.

Conventionally, Rankine cycle heat engines have been positioned as large-scale constant-load power plants, as exemplified by steam turbine cycles in thermal power plants. However, in recent years, there has been a new use for small thermal power engines, namely waste heat utilization.
Solar heat utilization. Rankine cycle engines are being reconsidered from external combustion engines. For this reason, instead of conventional high-speed fluid machines such as large steam turbine engines, positive displacement expanders and the like, which are suitable for producing an output of several horsepower and have excellent workability, are attracting attention.

The present invention analyzes the inherent problems when a displacement fluid machine is adopted as the output mechanism of a Rankine cycle engine, and discloses various measures for freely controlling the Rankine cycle engine according to the load. .

First, prior to a detailed explanation of the invention, some characteristics of the current combination of the Rankine cycle and a speed-type fluid machine such as a turbine will be explained. Figure 1 shows the basic system of the Rankine cycle in a typical thermal power plant. In the figure, 1 is a working fluid pump 2
3 is a steam turbine; 4 is a condenser; and 5 is a generator. FIG. 2 shows the Rankine cycle of the system shown in FIG. 1 as a pi diagram (Molier diagram). Figure 3 shows the Rankine cycle as a PV diagram. Next, to explain in more detail the characteristics of the Rankine cycle using the velocity type fluid machine shown in FIGS. 1 to 3, the working fluid liquid pump 1 has a low pressure (condensation pressure _P The working fluid is suctioned and pressurized to form a high-pressure (generated pressure P _G ) liquid, which is led to the generator 2 . In the generator 2, the working fluid is heated by a thermal burner 6, and finally leaves the generator 2 in a high-pressure superheated steam state, passes through a flow control valve 7, and is guided to a steam turbine 3, which is a speed type engine. The steam turbine 3 usually includes a plurality of stages of impellers, and is provided with a reheater (not shown) or the like as necessary. The output shaft of the turbine 3 drives the generator 5 via a speed reduction mechanism or the like as necessary to generate power and transmit the power to the power transmission line. The low-pressure superheated steam, which has been decompressed and expanded to a condensing pressure P _C in the turbine 3 to extract effective work, is cooled by seawater or the like in the condenser 4 and liquefied, and then sucked into the liquid pump 1 again. In this way, the Rankine cycle constitutes a closed cycle of 1'-2'-3'-4'-1' in the Mollier diagram of FIG. That is, in FIG. 2, the product of the enthalpy difference between points 3' and 2' and the amount of working fluid circulating is the amount of heat supplied to the cycle in generator 2, and the product of the enthalpy difference between points 3 and 4 and the amount of working fluid circulating is the amount of heat supplied to the cycle in generator 2. The product of represents the output output from the Rankine cycle to the output shaft. Further, the output extracted from the Rankine cycle can also be expressed as a PV diagram in FIG. That is, the generated pressure P
_G. Condensing pressure P _C . Adiabatic index of working fluid. A closed-loop PV diagram can be obtained from the working fluid circulation amount, and the output of the turbine 3 can be expressed as the area within the diagram (indicated by diagonal lines or dotted lines in FIG. 3). In Fig. 3, a is a partial load state,
b indicates full load condition. As a characteristic of the Rankine cycle employing such a speed type fluid machine, when the load capacity such as the power generation capacity fluctuates, the output power of the Rankine cycle is controlled as follows. That is, due to the characteristics of a generator, it is necessary to keep the output frequency constant and the rotational speed is kept constant. Therefore, controlling the output power means controlling the output torque. In a turbine, which is a speed-type fluid machine, this output torque is controlled by changing the velocity of the inflowing working fluid, that is, it is controlled by increasing or decreasing the amount of working fluid circulating. In other words, this is shown in Figures 2 and 3.
To explain with reference to the figures, in the Mollier diagram in Figure 2, there is no basic change in the operating state on the diagram, and in the PV diagram in Figure 3, for example, for partial load state a (shaded area), When the output increases, the output work area increases and output torque control is performed as in full load state b (stippling portion).

That is, output control when employing a velocity type fluid machine is achieved by controlling the circulation amount of a cycle in which the pressure condition of the cycle is constant.

On the other hand, output control in a Rankine cycle in which a positive displacement fluid machine is used instead of the turbine 3 is performed in a completely different manner. That is, as shown in the PV diagram in Figure 4 when a positive displacement fluid machine is used, for example, when the condensing pressure P _C is constant, the reference generated pressure that generates the reference output torque is P _GA . In this case, the output torque changes as shown in FIG. 4 when the load torque increases. In other words, when the rotation speed is constant, the inlet volume V ₁ and the outlet volume V ₂
In a positive displacement fluid machine in which the pressure is fixed, the standard output L _A shown by the shaded area changes to the high load output L _B as the generated pressure _PGA rises and moves to P _GB . Similarly, when the load torque decreases, the generated pressure decreases to P _GC and low load output L _C to complete a cycle.

In this way, when adopting a positive displacement fluid machine,
Rankine cycle output control is performed by changing the pressure setting of the cycle.

That is, as shown in Fig. 6, when a speed-type fluid machine is adopted in the Rankine cycle, the balance point B _S of the operating differential pressure (P) and the working fluid circulation amount (Q) in the working fluid pump is the load power. Constant pressure changes according to fluctuations in flow direction (horizontal direction in the figure)
Move to. In addition, as shown in Figure 6, when a positive displacement fluid machine is used, the operating balance point B _Y of the liquid pump moves in the direction of constant flow rate and variable pressure (vertical direction in the figure) according to fluctuations in the load power. . This difference in the movement characteristics of the operating point during load fluctuations is the most important difference in Rankine cycle control.

FIG. 7 shows a configuration example of a vane rotary expander as an example of a constant volume fluid machine. This vane rotary type expander has a cylinder 11 and a rotor 1.
2. It is composed of vanes 8 (plurality) that slide along the inner surface of the cylinder 11 inside the rotor 12, and the reference volume when the vane 8 closes the high pressure gas inflow port 9 is V ₁ , and the vane 8 closes the low pressure gas outflow port 10. The reference volume when is opened is _V2 . Therefore, V ₁ and V ₂ are values determined from the shape and are unrelated to the operating state of the Rankine cycle.

In addition, as another conventional example, in positive displacement fluid machines, as typified by steam locomotives, there are examples in which the inflow reference volume V ₁ is made variable by timing control of the inflow valve, but in this case, the control characteristics are Since it is similar to that shown in FIG. 5 and basically corresponds to the control characteristics of a velocity type fluid machine, it is the control characteristics before the present invention.
Therefore, in the following description of the present invention, a positive displacement fluid machine refers to a constant volume fluid machine.

The control system of the present invention will be explained in more detail below. Fig. 8 shows a single-fluid type Rankine system incorporating the present invention. An example of the structure of a heat pump cycle, FIG. 9 shows a Mollier (pi) diagram of the above-mentioned one-fluid cycle, and FIG. 10 similarly shows a PV diagram.

In FIG. 8, an outdoor heat exchanger 13 acts as a condenser for the Rankine cycle and the heat pump cycle during cooling, and as an evaporator for the heat pump cycle during heating. Reference numeral 14 denotes an indoor heat exchanger which acts as an evaporator of the heat pump cycle to cool indoor air during cooling, and acts as a condenser of the Rankine cycle and heat pump cycle to heat indoor air during heating. Reference numeral 15 denotes a working fluid pump having a capacity control mechanism using, for example, a variable speed motor 32, which performs capacity control so that the rotation speed detected by the rotation speed sensor 33 is constant. 16 is a generator, 17 is a positive displacement expander,
These are connected as appropriate to form a Rankine cycle. Further, 18 is a compressor driven by the expander 17, and its discharge side is connected to the expander 17.
After being connected to the outlet side of the pump, it is connected to a four-way valve 19 that switches the flow of the working fluid as shown by the solid line in the figure during cooling and as shown by the broken line in the figure during heating. This compressor 1
8, a four-way valve 19, an indoor heat exchanger 14, an outdoor heat exchanger 13, and a throttle mechanism 20 constitute a heat pump cycle. In addition, 21 and 22 are check valves that control the flow of refrigerant for cooling and heating, 23 is a heating source that heats the generator 16, 24 is a blower for the outdoor heat exchanger,
25 is an indoor heat exchanger blower. In other words, the load fluctuation of the compressor 18 in the heat pump cycle is detected based on the rotation speed of the rotation speed sensor 33, and it is determined whether the load increases or decreases, and when the load increases, the discharge pressure and discharge amount of the working fluid pump 15 are increased. and when the load decreases, the working fluid pump 15
Means is provided for controlling the capacity of the working fluid pump 15 so that the rotational speed detected by the rotational speed sensor 33 is always constant by reducing the discharge output and the amount of liquid discharged. Fig. 9 is a Mollier diagram showing the cycle of Fig. 8, and Fig. 10 is a Mollier diagram showing the cycle of Fig. 8.
Expander output in the figure. It is a PV diagram showing compressor input.

To further explain the characteristics of the single-fluid Rankine heat pump cycle shown in FIG. 8 using the PV diagram in FIG. Determined by outside air conditions at That is, the compression load work L _COMP is determined as shown in FIG. 10 by the evaporation pressure P _E , the condensing pressure P _C , and the compressor reference volume V _COMP . Accordingly, the expander 17 must generate a work amount equal to this work L _COMP ,
As is clear from the above description, the generated pressure P _G is determined from the expander reference volume V _EXP , the condensing pressure P _C , and the expansion generated work L _EXP (=L _COMP ). In addition, for convenience of explanation, each efficiency (expansion, compression efficiency, mechanical efficiency, volumetric efficiency) in the expander 17 and compressor 18 is omitted. In this way, when a positive displacement fluid machine is used as the expander 17, the inherent characteristic that the generated pressure P _G responds to the load on the heat pump cycle side has become clear. As a characteristic, it is desirable to keep the operating speed of the entire system constant regardless of load fluctuations in the heat pump cycle. The present invention makes it possible to control the system so that it can operate steadily while taking into account the unique characteristics of the above-mentioned positive displacement fluid machine.

Although it has already been shown that the generated pressure P _G changes depending on the load of the heat pump cycle, the following problem occurs with the change in the operating pressure specific to this positive displacement fluid machine. That is, as shown in FIG. 9, as a characteristic of gases in general, as the generated pressure P _G increases, the gas specific volume V at the inlet of the expander 17 decreases. As a result, expander 1
The working fluid circulation amount per rotation of 7 is the generated pressure P _G
The pressure increases as the heat pump increases, that is, the generated pressure changes according to the heat pump load, and at the same time
7. The amount of working fluid circulating per revolution also changes.

Figure 11 shows the working fluid pump standard (P
- Q characteristic standard) Standard balance point B _YR shows how it moves according to the system load when the system rotation speed is constant. In the figure, the balance point moves to the upper right when the load increases and to the lower left when the load decreases.

As described above, when a displacement type fluid machine is employed in the Rankine cycle, the operating pressure of the system increases when the load increases, unlike when a conventionally known velocity type fluid machine is employed. In order to operate the system at a steady speed in response to this pressure increase, the working fluid pump of the cycle is controlled so that the discharge pressure and discharge flow rate increase when the load increases, as shown in Figure 8, and when the load decreases. It is necessary to control the discharge pressure and the discharge flow rate to decrease. That is, by controlling the working fluid pump as described above, it becomes possible to operate the system at a steady speed even when the load power of the compressor changes in the Rankine cycle using a positive displacement fluid machine for the first time.

Additionally, as a matter of course, the amount of heat added to the Rankine cycle in the generator and the amount of heat released from the Rankine cycle (and heat pump cycle) in the condenser change as the amount of circulation changes, and the amount of heat input to the generator changes. It is also necessary to consider the control and heat radiation amount control in the condenser at the same time. In a generator, the amount of heat generated by a burner, etc. can be automatically controlled to maintain a constant degree of superheating of the working fluid at its outlet, while in the case of a condenser, the condensing pressure itself changes slightly depending on the heat radiation and amount. The condensing temperature changes so that the amount of heat released to the outside air is balanced. However, this condensing temperature change is normally a minute change, and the equilibrium point change characteristics shown in FIG. 11 basically do not change.

There are many methods for controlling the capacity of the working fluid pump, such as rotational speed control using a variable speed motor, etc., as in the embodiment, or bypass control using a bypass circuit, bypass valve, etc., but any method may be used. In addition, as a load power detection method, it is possible to directly detect the joint shaft torque of the compressor and expander, or to detect the rotation speed or, conveniently, to detect the outside air. Atmosphere conditions such as room temperature may also be detected.

As a positive displacement fluid machine, any type such as a reciprocating piston type, a vane rotary type, a scroll type, a rolling piston type, or a screw type may be adopted. Note that although the PV diagrams all show the case of a vane rotary type, the present invention does not change in any way regardless of the type.

According to the present invention, the working fluid pump of the Rankine cycle is provided with a capacity control mechanism, and the capacity of the liquid pump is controlled according to the load fluctuation of the compressor of the heat pump cycle, and when the load increases, the liquid pump discharge pressure and discharge flow rate are adjusted. By providing a mechanism for controlling the discharge pressure and discharge flow rate to increase and decrease the discharge pressure and discharge flow rate when the load decreases, the operating speed of the constant volume fluid machine can be maintained constant, and by controlling the working fluid pump, the Rankine This provides an excellent effect of allowing operation at a steady speed even when the load power of the compressor changes during the cycle.

[Brief explanation of the drawing]

Figure 1 is a Rankine cycle diagram using a conventional velocity type fluid machine, Figure 2 is a Mollier diagram of the cycle in Figure 1, Figure 3 is the same PV diagram, and Figure 4 is a constant volume fluid machine. An explanatory diagram showing changes in the P-V line in a machine. Figure 5 is an equilibrium point movement characteristic diagram of the P-Q diagram when a velocity-type fluid machine is used. Figure 6 is a diagram showing the P-V line when a displacement-type fluid machine is used. -Equilibrium point movement characteristics of Q diagram, Figure 7 is a sectional view showing an example of the configuration of a constant volume fluid machine, and Figure 8 is a single-fluid Rankine heat pump cycle showing an example of the air conditioner of the present invention. 9 is a Mollier diagram of the cycle shown in FIG. 8, FIG. 10 is a PV diagram thereof, and FIG. 11 is a PQ diagram of the pump control according to the present invention. 13... Outdoor heat exchanger, 14... Indoor heat exchanger, 15... Working fluid liquid pump, 16... Generator, 17... Positive displacement expander, 18... Compressor, 1
9... Four-way valve, 20... Throttle mechanism, 23... Burner, 32... Variable speed motor, 33... Rotation speed sensor.

Claims (1)

[Claims] 1 A steam generator heated by a heat source, a positive displacement expander, a four-way valve, an outdoor heat exchanger, and a working fluid pump having a capacity control mechanism using a variable speed motor etc. are connected in a circulating manner. , a compressor driven by the positive displacement expander and an indoor heat exchanger are provided between the four-way valve and the outdoor heat exchanger, and a rotation speed sensor is provided to detect the rotation speed of the positive displacement expander. , detecting the load fluctuation of the compressor of the heat pump cycle based on the rotation speed of the rotation speed sensor and determining whether the load increases or decreases, and increases the discharge pressure and discharge amount of the working fluid pump when the load increases, An air conditioner comprising means for controlling the capacity of the working fluid pump so that the rotation speed detected by the rotation speed sensor is always constant by reducing the discharge pressure and discharge volume of the working fluid pump when the load decreases. .