JPS61152916A - Binary cycle power generation plant - Google Patents

Abstract

PURPOSE:To enable the evaporation temperature of a medium to be kept within the limit of thermal stabilization by making heat exchange through an intermediate medium positioned between a heat source and an operating medium when the temperature of a high-temperature heat source fed to an evaporator is high. CONSTITUTION:A heat source fluid fed through a conduit pipe 1 into a heater 2a provides an intermediate medium with the heat there are then is fed into a preheater 4. The intermediate medium heats an operating fluid to boil in a heater 2b, and then returns to the heater 2a by did of an intermediate medium circulating pump 9. The amount of circulation of an intermediate medium is obtained through the quantity of the heat exchanged between a high-temperature heat source and the intermediate medium, after the temperature of an intermediate medium, at which its heat load is not more than the maximum point, is obtained through the evaporation temperature of an operating medium and the quantity of the heat exchanged between the high-temperature heat source and the intermediate medium. Thereby, the evaporation temperature of a medium can be kept within the limit of thermal stabilization so that a heat source energy can be used effectively.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a binary-cycle power plant using a low-boiling organic medium as the working medium.

Conventional binary-cycle power plants typically
As shown in the figure, a high-temperature heat source (such as geothermal heat or factory waste heat) fluid is led to an evaporator 2 through a conduit 1, and after heating and boiling a low boiling point working medium on the secondary side, it is supplied to a preheater 4. The working medium exiting the condenser is preheated to near saturation temperature and is discharged outside the system (reduction well, atmosphere, pipe). On the other hand, the working medium boiled in the evaporator 2 is supplied to the turbine 5 via a stop valve and a control valve, and after being expanded, it is cooled and liquefied in a condenser 6.
The working medium circulation pump 7 sends the preheater 41C to form a secondary closed loop.

In such a binary cycle power plant, there is an optimum evaporation temperature of the working medium at which the maximum output can be obtained for a high-temperature heat source at a certain temperature, and from the viewpoint of effective energy use and economic efficiency, this temperature is generally determined. The evaporation temperature near the maximum power point is selected as the design point.

This optimum evaporation temperature increases as the temperature of the high temperature heat source increases. However, low-boiling point organic media that have good thermal properties, are highly safe, and are inexpensive generally have a low thermal stability limit temperature, and once this temperature is exceeded, the media begins to deteriorate and decompose, producing noncondensable gases and improving plant performance. decomposition products may react with other molecules to become corrosive substances, rapidly increasing the possibility of corroding plant components.

On the other hand, media with a high thermal stability limit temperature generally have poor thermal properties and are not easily available, making them expensive. The use of such expensive media increases the operating and maintenance costs of the binary cycle power plant, and if the thermal characteristics are poor, it may be necessary to increase the size of heat exchange equipment or use specially shaped heat exchanger tubes. Therefore, as mentioned earlier, the thermal stability limit temperature is relatively low.
Commonly used media, such as R-114 (D
ichlorotetrafluoroethane)
, R-113 (Trichlorotrifluoro
ethane), R-11 (Trichlorof
It is desirable to use a medium that is inexpensive, easily available, and highly safe, such as luoromethane.

For this reason, when the temperature of the high-temperature heat source increases, it is necessary to keep the evaporation temperature below the thermal stability limit temperature of the medium used, even if it sacrifices some benefits in terms of thermal cycles, that is, even if it deviates from the optimum evaporation temperature mentioned above. There is.

In that case, as the difference between the temperature on the high-temperature heat source side and the working medium evaporation temperature increases, the difference between the evaporator heat exchanger tube surface and the saturation temperature of the working medium increases, and the maximum heat load point a as shown in Fig. 7 increases. When the temperature exceeds 100% and enters the transition boiling region, the stability of boiling heat transfer is impaired, the heat load rapidly decreases, and the heat transfer characteristics of the evaporator also deteriorate. Here, the heat load corresponds to the amount of heat flowing from the heat source fluid to the working medium through the heat transfer tube. Possible countermeasures to this problem include lowering the temperature of the high-temperature heat source by mixing it with the discharge side, or adding a recovery cycle for degraded media, but the former results in a lot of wasted heat source energy, while the latter As the power increases, so does the cost of the exchange medium, making operational management complex and time-consuming.

[Purpose of the invention]

An object of the present invention is to reduce the temperature of the heat source in a binary cycle power plant even when the temperature of the heat source is high, without using an expensive medium with poor thermal characteristics or wastefully discarding heat to lower the heat source temperature. It is an object of the present invention to provide a heat exchange device that can obtain sufficient reliability and performance using a medium that is easily available at 1fffi.

[Summary of the invention]

In order to achieve the above object, the binary-cycle power plant of the present invention interposes an intermediate medium between the heat source and the working medium when the temperature of the high-temperature heat source supplied to the evaporator is high,
By performing heat exchange through this, the evaporation temperature of the medium is kept within the thermal stability limit, thereby making effective use of the heat source energy.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG. In Fig. 1, the same parts as in Fig. 6 are given the same reference numerals, and their explanations are omitted. There is.

Heat source stream, body (hot water, exhaust gas, etc.) supplied from conduit 1
) first enters the heater ZaK, gives heat to the intermediate medium, and then is supplied to the preheater 4. The intermediate medium given heat by the heater 2a is supplied to the evaporator 2b via the conduit 13 to heat and boil the working medium, and is returned to the heater 2a by the intermediate medium circulation pump 9.

Note that depending on the arrangement of the heater 2a and the evaporator 2b, the circulation pump 9 can be eliminated by using a head difference (the evaporator 2b is made higher than the heater 2a). The intermediate medium preferably has good heat transfer characteristics, large specific heat, and low density in order to reduce heater cost and circulation pump power, but from the viewpoint of economy and handling, water, air, etc. are preferable. The circulating amount of the intermediate medium is determined by determining the intermediate medium temperature that is below the maximum heat load point from the evaporation temperature of the working medium and the amount of heat exchange between the high temperature heat source and the working medium. The 0 operation recommended medium evaporation temperature determined from the above (same as for the medium) is determined by the lower of the thermal stability limit temperature and the optimum evaporation temperature mentioned above. Heated objects with maximum heat load,
The temperature difference in the heating medium can be determined by experiment or approximate calculation.

FIG. 2 shows a heat distribution diagram showing the effect of the present invention in the case where both the heat source and the intermediate medium are water. The vertical axis is the fluid temperature, and the horizontal axis is the amount of heat absorbed by each working fluid. The arrows also indicate the direction of progress of this cyclic process.

The thick solid line shows the process according to the present invention, and the thick broken line shows the process according to the conventional method.

In FIG. 2, the positions on the system showing each state in FIG. 1 are shown with the same numbers. The two solid lines on the left side of Fig. 2 indicate the exchange of heat between the heat source fluid and the intermediate medium 8 in the heater 2aK. The temperature is increased from 12 to 13. The right side of the figure shows the exchange of heat between each fluid in the evaporator 2b and preheater 4. In the evaporator 2b, the intermediate medium is 13
The temperature drops from 15 to 12 (thermally the same as 12), and the working medium is heated and boiled from near saturated liquid 15 to saturated steam 14 using the amount of heat. The boiled working medium enters the turbine 5 and expands to generate shaft power.Q in FIG. 2 indicates the amount of heat that is effectively converted into power. On the other hand, the heater 2a
The heat source fluid exiting the condenser 6 enters the preheater 4 and preheats the working medium exiting the condenser 6 from 17 to 15.

However, in the conventional cycle process, the temperature of the heat source fluid 1 must be lowered to near 13, and the evaporation temperature also has to be lowered due to the constraints of the evaporator pinch point, as shown by the broken line in Figures 2 and 3. When the effective heat drop becomes red, the power conversion energy also decreases from Q to Q. As another example, in an industrial process waste heat recovery plant where the temperature of a high-temperature heat source fluctuates greatly, connecting pipes 18, 19 and valves 20 to 25 as shown by broken lines in FIG. 4 are additionally provided, If the temperature of the high temperature heat source is low, valve 20.22.23
．． 25 is closed and valve 21.24 is opened to perform the same cycle process as before, and when the temperature of the heat source increases, valve 21.
．． By closing valve 24 and opening valves 20, 22, 23, and 25 to switch to a cyclic process using an intermediate medium, the range of efficient operation is increased.

FIG. 4 shows a case in which a conventional cycle process is performed, and the black valves are shown in a closed state. In this case, it is desirable that the heat source fluid and the intermediate medium be of the same type, but they may be of different types.

As yet another embodiment, in case the temperature of the heat source continues to rise during operation of the heat exchanger of the above two embodiments,
As shown in FIG. 5, the temperature Tmea of the inlet temperature of the intermediate medium to the evaporator 2b (point 13 in FIG. 1, which is the same as the outlet temperature of the heater 2a) is detected by the temperature detector 26,
7 K, calculate the deviation from the set value Tset, calculate the amount of rotational speed change of the intermediate medium circulation pump 9 necessary to make this deviation zero using the calculator 28, and issue a command to the controller 29. The same controller controls the rotation speed of the pump 90. Therefore, by changing the circulation rate of the intermediate medium and adjusting the inlet temperature of the evaporator 2 & of the intermediate medium 8 to be within the set value, a given plant system can be operated. It is possible to operate efficiently in near-optimal conditions without exceeding the thermal stability limit of the medium, and the burden on the operator is greatly reduced. The intermediate medium circulation amount can also be adjusted by using a regulating valve instead of the pump rotation speed and changing its opening degree. In this case, the controller 29 calculates the amount of change in the opening degree of the regulating valve, and operates the opening degree of the regulating valve (not shown) based on the command.
Become. The present invention is applicable not only to single boiling systems (with only one type of evaporator), but also to dual boiling systems (with two types of evaporators, high pressure and low pressure), dual Rankine cycles, and two-fluid cycles.

〔Effect of the invention〕

As described above, according to the present invention, even when the temperature of the high heat source is high, efficiency can be improved over a wide temperature range by using a highly safe organic medium that is inexpensive, easily available, and has well-known characteristics. A high binary cycle power plant can be provided.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a binary-cycle power generation plant showing an embodiment of the present invention, Fig. 2 is a graph for explaining the normal state of the thermal cycle process shown in Fig. 1, and Fig. 3 is a diagram of the present invention. A graph showing the i-8 line showing the expansion of the working medium in the turbine in the invention, FIG. 4 is a block diagram of a binary cycle power plant showing another embodiment of the invention - FIG.
The figure is a block diagram showing the control circuit applied to the present invention shown in Figs. 1 and 4, Fig. 6 is a diagram showing a conventional binary-cycle power generation plant, and Fig. 7 is a diagram showing the heat exchanger tube surface temperature and liquid 2 is a graph showing a boiling curve showing a change in heat load (heat exchange amount) with respect to a difference from a saturation temperature. 2... Evaporator, 2a... Heater, 2b... Evaporator, 4... Preheater, 5... Turbine, 6... Condenser, 7... Working medium circulation pump, 9... Intermediate medium circulation pump 10... Heater inlet point of high temperature heat source fluid, 11.
...Heater exit point of high temperature heat source fluid, 11...Evaporator inlet point of high temperature heat source fluid, 12...Heater inlet point of intermediate medium, 12'...Evaporator exit point of intermediate medium, 13 ...Heater exit point of intermediate medium (evaporator inlet point), 14... Evaporator exit point of working medium, 14'... Turbine inlet point of working medium, 15... Evaporator of working medium Inlet point, 16...Turbine outlet point of working medium (condenser inlet point)
, 17... Preheater inlet point of working medium, 18.19... Communication pipe for high temperature heat source fluid, 20.21.
22.23.24.25... Stop valve, 26... Temperature detector, 27... Comparator, 28... Arithmetic unit, 29.
・・Controller, agent Patent attorney Noriyuki Chika
(1 other person) 1st m 21! 1 Yield Figure 3 Entropy (s)-1 Figure 5

Claims (1)

[Claims] 1. A binary cycle power generation plant that uses a low boiling point organic medium as a working medium, applies heat from a high-temperature heat source to it, evaporates it in an evaporator, supplies it to a turbine, expands it, and generates power. In order to lower the temperature on the heat source side that heats and boils the working medium, a heater is provided in parallel to the evaporator using another intermediate medium, and this heater applies heat from the high-temperature heat source to the intermediate medium, A binary cycle power generation plant characterized in that an intermediate medium is supplied to an evaporator to heat and boil a working medium. 2 The heater inlet pipe for the high-temperature heat source and the evaporator inlet pipe for the intermediate medium are connected via a valve, and the heater outlet pipe for the high-temperature heat source and the intermediate medium evaporator outlet pipe are connected via a valve. between the connection point of the former communication pipe and the heater inlet pipe to the heater inlet, between the connection point of the former communication pipe and the evaporator inlet pipe to the heater outlet, and with the latter communication pipe. Valves are provided between the connection point with the heater outlet pipe and the heating outlet, and between the connection point with the latter communication pipe and the evaporator outlet pipe and the heater inlet, and when the temperature of the high-temperature heat source is low, the evaporation 2. The binary cycle power generation plant according to claim 1, characterized in that the system for only a heater is switched to a system for both a heater and an evaporator for operation when the temperature is high. 3. When both the heater and evaporator systems are in operation, a means for measuring the temperature of the intermediate medium at the heater outlet or evaporator inlet, and comparing the measured concentration with the set temperature,
Claim 2, characterized in that it is equipped with calculation means for calculating the intermediate medium circulation amount to eliminate the deviation, and control means for controlling the flow rate of the intermediate medium so that the circulation amount becomes the above-mentioned circulation amount. Binary cycle power plant.