JPS6157446B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power generation plant, particularly a plant that generates electricity by transferring heat from a heat source to a working medium and driving a turbine with the working medium, wherein the temperature level of the heat source is relatively low. energy sources, e.g. geothermal,
The present invention relates to a low boiling point medium turbine plant that can be suitably used to utilize factory waste heat.

Conventionally, this type of power generation plant using low-quality energy includes a plant devised to increase the heat recovery rate by using a substance with a boiling point lower than water as a working medium. The prior art will be explained with reference to FIG. Heat is recovered from the high-temperature heat source 1 and the turbine working medium 4 by a preheater 6 and an evaporator 7, and the generated working medium steam and liquid are separated by a gas-liquid separator 8, and the turbine 10 is rotated by the steam. and is converted into electricity by a generator 11. The steam that has worked in the turbine is sent to the condenser 12
The liquid enters the water, is liquefied by the cooling water 13, is pressurized by the pump 5, and then enters the preheater 6 again. This cycle is represented on a temperature-enthalpy and temperature-enthalpy diagram as shown in FIGS. 2 and 3. In the figure, 51 is a high heat source temperature, 52 is a working medium saturated liquid line, 53 is a working medium wet vapor region, and 54
is a working medium saturated vapor line, 55 is an isopressure line, and 56 is an isenthalopic line. In FIG. 2, a sensible heat source such as geothermal water is taken as an example of a high-temperature heat source, and a line 51 shows changes in the state of temperature and enthalpy of the high-temperature heat source on the same graph as the cycle CDEFG of the working medium. However, since the flow rates of water and working medium are generally different, the horizontal axis is the enthalpy corrected for the ratio.

If the temperature T ₁ of the high heat source is relatively low, the second
As shown in the figure, the temperature change line AB of the high heat source and the state line CDE during heating of the working medium are converged at the center, and the distance on the temperature axis at this time, that is, the pinch point temperature difference, is the heat exchange This will affect the size of the vessel and, by extension, the construction cost of the plant. For economic reasons, the pinch point temperature difference needs to be large to a certain extent. Therefore, when the steam temperature of the working medium is increased, the outlet temperature of the high heat source temperature (point B
temperature) increases, and the recovery efficiency decreases.

On the other hand, the amount of energy that can be effectively extracted by the turbine is a part of the amount of recovered energy, and the area surrounded by CDEFG in Figure 3 is the turbine internal loss,
It shows the effective energy when mechanical losses such as generator losses are ignored. The reactive energy discarded into the cooling water in the condenser is expressed by the area of CGFHIJ,
It can be seen that when the condensate temperature Tc is held constant and the steam temperature is increased, the effective energy ratio increases, that is, the cycle efficiency increases.

The above is illustrated in Figure 4,
The generating end output is approximately equal to the recovery rate η and the cycle efficiency η
Since it is proportional to the product of +h, there is a steam temperature that changes as shown by the broken line in the figure and maximizes the output. At this time, both the recovery rate and cycle efficiency are smaller than their maximum values. In other words, in the conventional technology, the system must be operated at values lower than the maximum values for both the recovery rate and the cycle efficiency, mainly because the pinch point temperature difference has to be a positive finite size. The disadvantage was that the output could not be made sufficiently high.

The purpose of the present invention is to utilize the fact that if the steam of the working medium is generated in a supercritical pressure region, both the recovery rate and the cycle efficiency increase, and to create a system that can be pressurized to supercritical pressure to generate steam. , to provide a low boiling point medium turbine plant that can obtain maximum output.

The feature of the present invention is to take advantage of the property that as the pressure increases in the supercritical pressure region, the isobar line on the temperature-enthalpy diagram approaches a straight line sloping upward to the right, to bring the steam of the turbine working medium to supercritical pressure. Therefore, there is a turbine plant using a low boiling point medium that aims to improve the heat recovery rate from a high heat source.

An embodiment of the present invention will be described with reference to the drawings. In this example, as a high temperature heat source, the temperature is 140℃
geothermal water, using refrigerant R-12 as the working medium. In FIG. 5, geothermal water is taken in from inlet 1, and cooled by refrigerant R-1 as a working medium in once-through boiler 22.
2 (fluorocarbon), then exits to the outside world from boiler outlet 2. The low-pressure Freon is pressurized by the pump 5 and heated by the hot water 1 in the once-through boiler 22, but the pressure is lowered by the pressure reducing valve 18 to a point where it does not enter the wet region even if expanded. The fluid is expanded and then led to the reheater 23 where it is heated again by geothermal water to become a supercritical pressure fluid.When it is expanded in the high pressure turbine 10, it becomes low pressure fluorocarbon vapor as work, and is released into the fluorocarbon condenser 12. A closed cycle system is constructed in which the liquid is liquefied by the cooling water 13.

According to the above embodiments of the present invention, the following effects are achieved. FIG. 6 shows a temperature-enthalpy diagram of refrigerant R-12. High heat source temperature
When T ₁ is kept constant and the pressure is increased to supercritical pressure, it can be seen that the temperature at the heat source port decreases as the pressure increases. In other words, in the figure, the line 6 rising to the right
1 is an isobar line, and if P ₁ < Perit < P ₃ < P ₄ , the minimum value of the difference between the heat source temperature T ₁ and the temperature of the working medium R-12 is the pinch point temperature difference Δθp
The inlet and outlet temperatures of a high heat source are T ₁ '', T ₂ '' when P=Perit, T ₁ ′, T ₂ ′, and P=P when P=P ₃ for each pressure. ₄ , T ₁ and T ₂ and the outlet temperature decreases, that is, the heat recovery rate improves. In other words, 62 is a line obtained by adding Δθp to the P ⁴ (supercritical pressure) line, and 63 is a line obtained by adding Δθp to the P 4 (supercritical pressure) line.
This is a line obtained by adding Δθp to the (critical pressure) line.

On the other hand, if the above cycle is plotted on a temperature-entropy diagram, it becomes as shown in Figure 7, and as the pressure increases, the effective energy (7 when P = P ₃ )
(area surrounded by 6, 74″, 73, 77, 78)
Reactive energy for (76, 78, 77, 7 between saturation pressure P of condensate temperature Tc = P ₀ and absolute zero
The ratio of the area surrounded by 7', 78', and 76' gradually increases, and when expressed as cycle efficiency, it becomes as shown in FIG.

As can be seen from the temperature-enthalpy diagram (Figure 6), the state point of the supercritical fluid at the outlet of a once-through boiler moves to the left side of the diagram (lower enthalpy side) as the pressure is increased when comparing at the same fluid temperature. Under conditions where the pinch point temperature difference is kept constant, the heat source outlet temperature can be lowered. In other words, the recovery rate can be improved, but on the other hand, in the temperature-enthalpy diagram in Figure 7, the higher the pressure, the more the adiabatic expansion line (vertical line in the diagram) enters the moist region. It has properties. in general,
During the expansion process in the turbine (approximately regarded as an adiabatic expansion line), if the turbine enters a humid region, problems such as erosion of the turbine blades due to droplets and a decrease in efficiency due to a reduction in steam flow rate will occur. The aim is to expand it to 74" before entering it, and then reheat it to state 73. If low-quality energy with a low temperature level is used, the amount of work due to expansion from 74 to 74" is Since the amount of effective energy is often small compared to the amount of effective energy of the entire Rankine cycle, the throttle valve 18 is provided to only increase the recovery rate. If the thermal drop due to expansion is large, it may be possible to replace the throttle valve with a high-pressure turbine to generate electricity.

Therefore, in addition to the property that the maximum point appears in the output in the region below supercritical pressure (subcritical pressure) as described in the conventional example, the recovery rate and power generation across the entire subcritical and supercritical pressure ranges. When the terminal output is determined, it is as shown in Fig. 9. The recovery rate decreases as the pressure increases in the subcritical region, but increases in the supercritical region, and the cycle efficiency tends to increase as the pressure increases. It has a maximum value at , and shows a monotonous increasing tendency in the supercritical pressure region. At this time, when the pressure becomes sufficiently high, both the recovery rate and the efficiency tend to reach a plateau, so the rate of increase in the power generation output also decreases. In the figure, the pump power and cooling water pump power required to circulate the working medium at the same time are determined, and the sum is used as the station power, and the value obtained by subtracting the station power from the generating end output is the sending end output. It was written as.

As a power generation plant, it should be evaluated based on the maximum output at the sending end, but as shown in Figure 9,
When the pressure of the working medium is changed for the same heat source temperature, the maximum value of the power transmission end output appears in the subcritical region and the supercritical region, respectively. Therefore, a plant with good output performance can be provided by setting and operating the working medium pressure so that the pressure at which the maximum transmission end output is obtained according to the heat source temperature is achieved. In order to achieve this, this embodiment employs a control method as shown in FIG. That is, the heat source inlet temperature is detected by the thermometer 19, and the control device 17 is controlled according to the heat source inlet temperature T so that the thread pressure becomes the optimum pressure Pm (a function of the heat source temperature T) determined in advance by the analysis program. The number of revolutions of the pump 5 is controlled so as to always obtain the maximum output at the power transmission end. The rotational speed and discharge pressure of the pump 5 are detected by a tachometer 20 and a pressure gauge 16, respectively, and fed back to the control device 17. These control devices 17 include, as shown in FIG. 10, an arithmetic device 17a that calculates an optimum pressure Pm at which the vapor of the low boiling point medium reaches a supercritical pressure from the heat source inlet temperature T detected by the thermometer 19;
A calculation device 17 that sets the pressure P ₀ of the low boiling point medium supplied to the through boiler 22 according to the optimum pressure Pm.
b, a comparison device 17c that compares the discharge pressure P of the pump 5 detected by the pressure gauge 16 and the pressure P ₀ ;
and a controller 17d that calculates a control signal c to the pump 5 based on the pressure comparison value p.

FIG. 11 shows another embodiment of the present invention. It was explained in the previous embodiment that in order to increase the enthalpy at the inlet of the turbine to a region within the turbine that does not enter the wet region during the expansion process, it is necessary to include the expansion and reheating processes. In the previous embodiment, the heat drop due to expansion on the high pressure side was often small, so the expansion was performed using a throttle valve and the energy recovery (power generation) there was omitted, but in this embodiment, instead of this, the high pressure turbine 10a is used. and was intended to be used in the generator 10b. In addition, the reheater 23
The low-boiling point medium steam that has been pressurized to supercritical pressure through the process is used to perform work in a low-pressure turbine 10b having a generator 11b, and the other configurations are the same as those of the previous embodiment, so explanations are omitted. do. According to this system, depending on whether the heat drop on the high pressure side is large or not, this embodiment may be advantageous depending on the balance between the equipment cost of the high pressure turbine and the profit generated therefrom. It goes without saying that the control device shown in FIG. 11 can also be applied to this embodiment. According to the present invention, since the steam of the turbine working medium can be generated in a supercritical pressure region, the heat recovery rate of the plant can be improved and the low boiling point medium turbine can obtain the maximum output of the plant. The effect of realizing a plant is achieved.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing a conventional low boiling point medium turbine plant system, Figures 2 and 3 are thermodynamic diagrams to explain the cycle of the conventional system, and Figure 4 is a conventional cycle diagram. 5 is a schematic diagram showing a system of a low boiling point medium turbine plant showing an embodiment of the present invention, and FIG. 6 is an explanatory diagram showing the output performance in the subcritical pressure region of the present invention. Figure 7 is a thermodynamic diagram showing the reason why the heat recovery rate improves in a medium turbine plant.
The figure is an explanatory diagram similarly showing the pressure dependence of cycle efficiency, Fig. 9 is an explanatory diagram quantitatively showing the effect on output according to an embodiment of the present invention, and Fig. 10 is an explanatory diagram showing the control device of Fig. 5. FIG. 11 is a schematic diagram showing a system of a turbine plant using a low boiling point medium, which is another embodiment of the present invention. 1... High temperature heat source, 5... Pump, 10... Turbine, 10a... High pressure turbine, 10b... Low pressure turbine, 11... Generator, 11a, 11b...
Generator, 12... Condenser, 23... Reheater, 11
6...Pressure gauge, 17...Control device, 19...Thermometer.

Claims (1)

[Scope of Claims] 1. A heat exchange device that recovers heat from a high-temperature heat source into a low-boiling point medium, a turbine driven by the steam of the low-boiling point medium that has passed through the heat exchange device, and a condensation device that condenses the low-boiling point medium that has passed through the turbine. A low-boiling point medium turbine plant comprising a condenser that allows the condensation to be carried out, and a pump that feeds the low-boiling point medium condensed in the condenser to the heat exchange device, further comprising an expansion means for expanding the low-boiling point medium that has passed through the heat exchange device. Further, another heat exchanger is provided for heating the low boiling point medium expanded by the expansion book means to generate steam from the low boiling point medium in a pressure range above the critical pressure, and pressurizing with the heat exchanger. A low-boiling point medium turbine plant, characterized in that the low-boiling point medium vapor produced by the boiling point is introduced into the turbine. 2. The low boiling point medium turbine plant according to claim 1, wherein the other heat exchanger is incorporated into the heat exchange device and heated by the same high-temperature heat source. 3. The low boiling point medium turbine plant according to claim 1 or 2, wherein the expansion means is a pressure reducing valve. 4. The low boiling point medium turbine plant according to claim 1 or 2, wherein the expansion means is another turbine device. 5. The low boiling point medium turbine plant according to claim 1 or 2, wherein a substance having a critical pressure lower than the inlet temperature of the high temperature heat source is used as the low boiling point medium. 6. A control device for controlling the discharge pressure of the pump so that the vapor pressure of the low-boiling medium generated in the other heat exchanger can be adjusted according to the inlet temperature of the high-temperature heat source. A low boiling point medium turbine plant according to range 1 or 2 or 3 or 4.