CA1273496A - Geothermal energy utilization system - Google Patents
Geothermal energy utilization systemInfo
- Publication number
- CA1273496A CA1273496A CA000506235A CA506235A CA1273496A CA 1273496 A CA1273496 A CA 1273496A CA 000506235 A CA000506235 A CA 000506235A CA 506235 A CA506235 A CA 506235A CA 1273496 A CA1273496 A CA 1273496A
- Authority
- CA
- Canada
- Prior art keywords
- hot water
- geothermal
- equipment
- temperature
- power generation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/10—Geothermal energy
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- Engine Equipment That Uses Special Cycles (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A system for utilizing the thermal energy of a geothermal fluid produced by a geothermal production well includes direct power generation equipment for generating electric power directly by using the geothermal fluid, indirect power generation equipment for generating electric power through heat exchange with the geothermal fluid using carbon dioxide as a heat transfer medium, refrigeration equipment for cooling water by an absorption refrigeration method, and hot water utilization equipment for hot spring and other purposes. The arrangement is such that high-temperature geothermal fluid is supplied to the direct power generation equipment to be used for the generation of electric power, intermediate-temperature geothermal fluid is supplied to the indirect power generation equipment to be used for the generation of electric power, and hot water recovered at a low temperature following its use in cooling and air conditioning performed by the refrigeration equipment is utilized at the hot water utilization equipment for a hot spring and other purposes.
A system for utilizing the thermal energy of a geothermal fluid produced by a geothermal production well includes direct power generation equipment for generating electric power directly by using the geothermal fluid, indirect power generation equipment for generating electric power through heat exchange with the geothermal fluid using carbon dioxide as a heat transfer medium, refrigeration equipment for cooling water by an absorption refrigeration method, and hot water utilization equipment for hot spring and other purposes. The arrangement is such that high-temperature geothermal fluid is supplied to the direct power generation equipment to be used for the generation of electric power, intermediate-temperature geothermal fluid is supplied to the indirect power generation equipment to be used for the generation of electric power, and hot water recovered at a low temperature following its use in cooling and air conditioning performed by the refrigeration equipment is utilized at the hot water utilization equipment for a hot spring and other purposes.
Description
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TITLE OF T~IE INVENTION
GEOTHERMAL ENERGY UTILIZATION SYSTEM
BACKG~OUND OF THE INVENTION
This invention relates to a geo-thermal energy utilization system in which a geo-thermal fluid is introduced to a plurality of thermal energy utilization facilities in a sequence depending upon the thermal energy possessed by the fluid, and in which each facility is operated by exploiting the -thermal energy delivered thereto to make possible the overall effec-tive utilization of the geo-thermal energy.
Geothermal energy is a naturally occurring form of energy which, as a resource, is available in fairly great abundance in comparison with solar heat and wind energy. Since it is also an inexhaustable and domes-tically available energy source, there are great expectations for its effective utilization. At the present time, geothermal energy is utilized almost entirely for power generation. Several geothermal power generation plants have been put into operation so far and for the most part rely upon so-called dry steam as the geothermal fluid. Dry steam is physically favorable in -that it has almost no moisture content at temperatures above 150C. Geothermal energy also finds some limited application in agriculture, heating and cooling and in the melting of snow, depending upon the tempera-ture of the geothermal fluid and its chemical properties, such as acidity. Cases in which the . ~
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~Z7~4~96 thermal energy oE a geothermal Eluid can be used for power generation or in applications other than power generation are categorized according to the temperature of the geothermal fluid reservoir.
Geothermal fluids do not always accumulate in the earth in the form of layers as does petroleum but of-ten collect in highly porous rock or in multiple rock fractures. Geothermal energy reserves are expressed by the tempera-ture of the fluid in the particular reservoir and -the amount of thermal energy possessed by the fluid, and the method in which the fluid is used is determined by whether it exists in the form of hot water or steam. It is believed that the amount of -the resource available in the form of such physically favorable steam as dry steam occupies about 10~ of the total geotherl~al resource. Further, well production, namely the amount of geothermal fluid which flows out of a geothermal production well per hour, differs greatly from well to well and the amount of thermal energy possessed by a unit weight of the geothermal fluid varies depending upon the weight of steam contained in the unit weight of fluid.
When attempting to utilize a geothermal fluid, thereEore, various restric-tions come to bear depending upon the method of u-tilization and the properties, both chemical and physical, of the geothermal fluid obtained. Matching the type of geothermal fluid with the particular manner of utilization is a difficult '~ ,, ' -~ Z73~
task. For example, even if a geothermal fluid reservoir is discovered with the intent of utilizing its energy for power generation, the reservoir may never be used if the particular geothermal fluid is found to be unsuitable for power generation purposes. Accordingly, there are many cases where only those production wells that produce a gecthermal fluid suitable for a specific utilization are kept for use, with all other production wells being destroyed.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the foregoing circumstances.
According to the present invention, there is provided a system for utilizing in equipment stages the thermal energy of a geothermal fluid produced by a geothermal production well. An equipment stage is selected in accordance with the amount of heat energy possessed by the geothermal fluid. The system may include direct power generation equipment for generating electric power directly by using the ~ ~
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geothermal fluid, indirect power generation equipment for genera-ting electric power through heat exchange with the geothermal fluid using carbon dioxide as a heat -transfer medium, refrigera-tion equipment Eor cooling water by an absorption refrigeration method, and hot water utiliza-tion equipment for hot spring and other purposes. The arrangement is such that high-temperature geothermal fluid is supplied to the direct power generation equipment -to be used for the generation of electric power, intermediate-temperature geothermal fluid is supplied to the indirect power generation eguipment to be used for the generation of electric power, and ho-t water recovered at a low temperature following its use in cooling and air conditioning performed by the refrigeration equipment is utilized at the hot water utilization equipment for hot spring and other purposes.
Thus, according to the present invention r a geothermal fluid extracted from a production well is utilized several times for such purposes as power generation and cooling until it is finally used as hot water. This makes it possible to effectively utilize the thermal energy of the fluid without wasteful radiation of the energy.
O-ther fea-tures and advan-tages of the present invention will be apparent from the :Eollowing description taken in conjunction with the accompanying drawings, in which like reference characters designate .
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the same or simi]ar par-ts -throughout the figures thereoE.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is block diagram useful in describing an embodiment of a geothermal energy utilization system according to the presen-t invention;
Fig. 2 is a schematic view illustrating the arrangement of hot water energy combining units and direct power genera-tion equipment according to the embodiment of the present inven-tion;
Fig. 3 is a schematic view for describing an ejector used in the hot water combining units of Fig.
TITLE OF T~IE INVENTION
GEOTHERMAL ENERGY UTILIZATION SYSTEM
BACKG~OUND OF THE INVENTION
This invention relates to a geo-thermal energy utilization system in which a geo-thermal fluid is introduced to a plurality of thermal energy utilization facilities in a sequence depending upon the thermal energy possessed by the fluid, and in which each facility is operated by exploiting the -thermal energy delivered thereto to make possible the overall effec-tive utilization of the geo-thermal energy.
Geothermal energy is a naturally occurring form of energy which, as a resource, is available in fairly great abundance in comparison with solar heat and wind energy. Since it is also an inexhaustable and domes-tically available energy source, there are great expectations for its effective utilization. At the present time, geothermal energy is utilized almost entirely for power generation. Several geothermal power generation plants have been put into operation so far and for the most part rely upon so-called dry steam as the geothermal fluid. Dry steam is physically favorable in -that it has almost no moisture content at temperatures above 150C. Geothermal energy also finds some limited application in agriculture, heating and cooling and in the melting of snow, depending upon the tempera-ture of the geothermal fluid and its chemical properties, such as acidity. Cases in which the . ~
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~Z7~4~96 thermal energy oE a geothermal Eluid can be used for power generation or in applications other than power generation are categorized according to the temperature of the geothermal fluid reservoir.
Geothermal fluids do not always accumulate in the earth in the form of layers as does petroleum but of-ten collect in highly porous rock or in multiple rock fractures. Geothermal energy reserves are expressed by the tempera-ture of the fluid in the particular reservoir and -the amount of thermal energy possessed by the fluid, and the method in which the fluid is used is determined by whether it exists in the form of hot water or steam. It is believed that the amount of -the resource available in the form of such physically favorable steam as dry steam occupies about 10~ of the total geotherl~al resource. Further, well production, namely the amount of geothermal fluid which flows out of a geothermal production well per hour, differs greatly from well to well and the amount of thermal energy possessed by a unit weight of the geothermal fluid varies depending upon the weight of steam contained in the unit weight of fluid.
When attempting to utilize a geothermal fluid, thereEore, various restric-tions come to bear depending upon the method of u-tilization and the properties, both chemical and physical, of the geothermal fluid obtained. Matching the type of geothermal fluid with the particular manner of utilization is a difficult '~ ,, ' -~ Z73~
task. For example, even if a geothermal fluid reservoir is discovered with the intent of utilizing its energy for power generation, the reservoir may never be used if the particular geothermal fluid is found to be unsuitable for power generation purposes. Accordingly, there are many cases where only those production wells that produce a gecthermal fluid suitable for a specific utilization are kept for use, with all other production wells being destroyed.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the foregoing circumstances.
According to the present invention, there is provided a system for utilizing in equipment stages the thermal energy of a geothermal fluid produced by a geothermal production well. An equipment stage is selected in accordance with the amount of heat energy possessed by the geothermal fluid. The system may include direct power generation equipment for generating electric power directly by using the ~ ~
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geothermal fluid, indirect power generation equipment for genera-ting electric power through heat exchange with the geothermal fluid using carbon dioxide as a heat -transfer medium, refrigera-tion equipment Eor cooling water by an absorption refrigeration method, and hot water utiliza-tion equipment for hot spring and other purposes. The arrangement is such that high-temperature geothermal fluid is supplied to the direct power generation equipment -to be used for the generation of electric power, intermediate-temperature geothermal fluid is supplied to the indirect power generation eguipment to be used for the generation of electric power, and ho-t water recovered at a low temperature following its use in cooling and air conditioning performed by the refrigeration equipment is utilized at the hot water utilization equipment for hot spring and other purposes.
Thus, according to the present invention r a geothermal fluid extracted from a production well is utilized several times for such purposes as power generation and cooling until it is finally used as hot water. This makes it possible to effectively utilize the thermal energy of the fluid without wasteful radiation of the energy.
O-ther fea-tures and advan-tages of the present invention will be apparent from the :Eollowing description taken in conjunction with the accompanying drawings, in which like reference characters designate .
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the same or simi]ar par-ts -throughout the figures thereoE.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is block diagram useful in describing an embodiment of a geothermal energy utilization system according to the presen-t invention;
Fig. 2 is a schematic view illustrating the arrangement of hot water energy combining units and direct power genera-tion equipment according to the embodiment of the present inven-tion;
Fig. 3 is a schematic view for describing an ejector used in the hot water combining units of Fig.
2;
Fig. 4 is a block diagram showing an embodiment of indirect power generation equipment according to the present invention;
Fig. 5 is a thermodynamic diagram useful in describing the cycle of the power generation equipment shown in Fig. 4;
Fig. 6 is a diagrammatic view showing the arrangement of refrigeration equipment according to the embodiment of the present invention;
Fig. 7 is a diagrammatic view showing the arrangement of a water-wheel generator annexed to the power generation equipment of a geothermal energy utilization system according to the embodiment of the present invention;
Fig. 8 is a diagrammatic view for describing an `' " ~ ~', " ' ~''"' ~ ,, , `' '' ::lLZ7~9~i embodiment oE a vacuum conveyance system applied to the present invention; and Figs. 9(A), ~B), (C) are views for describing an embodiment of a hot wa-ter conveyance path applied to the present invention.
DESCRIPTION OE THE PREFERRED EMBODIMEN_ An embodimen-t of -the present invention will now be described with reference to the accompanying drawings.
Fig. 1 is a block diagram illustrating an embodiment of a geo-thermal energy utilization system according to the present invention. The system includes units 11, 1~ each for combining hot water energy from several production wells, direc-t power generating equipment 12, indirect power generating equipment 13, refrigeration equipment 14, and hot water utilization equipment 15. The combining units 11, 16 combine and extract hot water energy from a plurality of production wells so as to make effective overall use of the energy. The direct power generating equipment 12 uses high-temperature geothermal fluid to directly drive a turbine for power generat1on. Examples of this equipment used conventionally are a steam generator, flash generator and total flow generator. The most suitable power generator is selected depending upon the contents of the geothermal fluid extracted from the hot water energy combining unit. Alternatively, a plurality oE thesè power generators may by used in a parallel configuration. The only power generation .-: ,. . :
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.... ~ . , ~lZ73~96 whlch takes place in the prior art uses steam having a temperature above 150C, as men-tioned above. ~owever, by employing an atmospheric pressure turbine which uses saturated steam at a temperature of 100C as the input energy, the direct power generating equipment 12 in accordance with the present invention generates power by utilizing the heat energy of steam the temperature whereof drops to that usable by the indirect power generating equipment 13, which is the next stage. The indirect power generating equipment 13 employs carbon dioxide as a medium and drives a turbine by raising the temperature and pressure of the carbon dioxide to 65C
and 130 kg/cm , respectively, through indirect contact between this medium and the geothermal fluid having an intermediate temperature of 50 - 80C. Like the indirect power generating equipment 13, the refrigeration equipment 14 uses the intermediate temperature geothermal fluid to effect cooling and reErigeration by an absorption refrigeration method.
The hot water utilization equipment 15, an example of which is a hot spring or heating equipment, utilizes hot water of comparatively low temperature which - results from earlier use in the indirect power genera-ting equipment 13 and refrigeration equipment 14.
The geothermal fluid is broadly classified according to the amount of its heat energy. The intermediate- and low-temperature geothermal fluid may be introduced into the system at intermediate points through the combining .
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- , ~ : ' ~2734~?6 unit 16, as illustrated in Fig. 1.
A specific embodiment of each item of equipment shown in Fig. 1 as well as the geothermal fluid conveyance system will now be described.
Fig. 2 is a schematic view illustrating the arrangement of a hot water energy combining unit and the direct power generation equipment according to the embodiment of the present invention. Fig. 3 is a schematic view for describing an ejector used in the hot water combining unit of Fig. 2. As shown in Fig.
2, the arrangemen-t includes geothermal production wells 21, 22, 23, a silencer 24, ejectors 25, 26, a steam separator 27, a steam conveyance pipe 28, a turbine 29, a power generator 30, a pump 31, an injection condenser 32, a hot water tank 33 and a nozzle 34. The production wells 21, 22, 23 are for generating hot water at high, intermediate and low pressures~
respectively. In order that the low-pressure hot water may be successively drawn out by ejection of the high-pressure hot water, the high-pressure production well 21 is connected to the intermediate-pressure production well 22 through the ejector 25, and the intermediate-pressure production well 22 is in turn connected to the low-pressure production well 23 via the ejector 25. The hot water combined by the ejectors 25, 26 is delivered to the steam separator 27. Here steam is separated from the hot water and is then fed to the turbine 29 through the steam conveyance pipe 28.
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"' - . , ~ ' '. - -~2734~6 g The turbine 29 is driven by -the steam delivered thereto, after which the steam i5 condensed by the injection condenser 32. The resul-ting condensate collects in the hot water tank 33 whence it is introduced to the geothermal energy utilization equipment, which is the next stage. Any uncondensed gas is released to the atmosphere.
As shown in Fig. 3, the ejector 25, which combines the high-pressure hot water from the production well 21 and the intermediate-pressure hot water from the production well 22, is adapted to form the high-pressure hot water into a jet by the nozzle 34 and eject the high-pressure hot water toward the low-pressure production well 23 while the intermediate-pressure hot water is drawn into the flow at theinterfacial boundary thereof. A similar construction is adopted for the ejector 2~, which combines the ejected hot water from the ejec-tor 25 and the low-pressure hot water from the production well 23.
According to the method adopted in the prior art, the steam from a plurality of production wells is combined with the steam from the production well having the low well head pressure so that the energy from the production well having the high steam pressure is used after it is effectively reduced. The energy is thus used in a wasteful manner. One reason for adopting this method is that in an arrangement where a plurality of production wells are connected in series, the ... :
''"`' ~' ' ; ', 73~36 low-pressure steam is suppressed by the high-pressure steam, so that the only solution was -to combine the high-pressure steam with the low. A consequence of this conventional approach is a relatively lower input pressure applied to the turbine, as a result of which the latter operates inefficien-tly. By contrast, in accordance with the present invention, the ejectors 25, 26 are employed to connect a plurality of production wells having different geothermal temperatures and the hot water from -the low-pressure production well is successively drawn up by the ejection of the hot water from the high-pressure production well and combined therewith. This enables a large quantity of steam to be supplied to the turbine at the higher pressure rather than the lower so that the turbine can be operated more efficiently.
Fig. 4 illustrates an embodiment of the indirect power generation equipment according to the present invention. The equipment includes a hot water supply unit 41, a preheater/evaporator 42, a turbine 43, a power generator 44, a compression pump 45, a condenser 46, and a medium pump 47. Carbon dioxide, which is used as the heat transfer medium, is fed into the preheater/evaporator 42 by the medium pump 47. The preheater/evaporator 42 is also supplied by the hot water supply unit 41 with geothermal fluid at a low temperature of 65 - 80C. The supply unit 41 receives the hot water from a geothermal production well or from .. ..
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~2 7~4~6 the direct power generation e~uipment, which is the preceding stage. A heat exchange between the carbon dioxide heat transfer medium and the low-temperature (65 - 80C) geothermal :Eluid takes place inside the preheater/evaporator 42. The carbon dioxide heat transfer medium has a critical temperature of 35C, 70 kg/cm and remains stable without undergoing thermal decomposition even if it is raised to a temperature of 65C and a pressure of 130 kg/cm2. By making effective use of the nature of stable carbon dioxide having the critical temperature of 35C, 70 kg/cm2, the carbon dioxide heat transfer medium is raised to a temperature and pressure of 65C and 130 kg/cm2, respectively, by the indirect contact with the geothermal fluid inside the preheater/evaporator 42 before being supplied to the turbine 43. As a result, the turbine 43 is driven into operation so that the power generator 44 generates electric power. Low-temperature geothermal fluid discharged from the preheater/evaporator 42 is introduced to a hot spring or other hot water utilization system. Following its use in operating the turbine 43, the carbon dioxide is cooled and compressed by the compression pump 45 to be converted into a liquid before being re-turned to the condenser 46. The carbon dioxide heat medium is then resupplied to the preheaterJevaporator 42 from the condenser 46 by the medium pump 47. Circulation of the carbon dioxide is thus accomplished.
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Fig. 5 is a thermodynamic diagram useful in describing the cycle of the power generation equipment shown in Fig. 4. Temperature T is plotted along the vertical axis, and enthalpy h (kcal/kg) is plotted along the horizontal axis. The curves plotted include a geothermal fluid temperature change curve 51 and a C2 saturated steam curve 53 for a case where carbon dioxide is used as the heat transfer medium, and a geothermal fluid temperature change curve 52 and a fron satura-ted steam curve 5~ for a case where fron is used as the heat transfer medium. Where fron is used, the medium is elevated in pressure from point a to point b by a pump and is thereafter heated by a geothermal fluid whose temperature changes from ~ ' to ~ , thereby increasing enthalpy to effect preheating and evaporation from b to c' to c". In the turbine, expansion occurs from c" to d so that work is performed, i.e., so that the turbine is driven.
Cooling and condensation occur from d to e to a, ~ ~-whereby the initial state is restored. Where carbon dioxide is used as the heat transfer medium, the medium is elevated in pressure from point a to point b by a pump and is thereafter heated by a geothermal fluid whose temperature changes from ~ to ~ , -thereby increasing enthalpy to effect preheating and evaporation from b to c. Accordingly, in a case where the outlet temperature of the geothermal fluid is the same, i.e., t3, the inlet temperature t2 of the :
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geothermal fluid where carbon dioxide is used as the medium is much lower than the inlet temperature tl oE
the geothermal medium where ~ron is used as the medium.
Accordingly, excellent results are obtained in terms of the usable temperature range of t2 t3, as opposed to tl - t3, and in terms of the ratio of maximum output to the amount of heat emitted by the geothermal fluid (the ratio of c" - d to tl - t3 and of c - d to t2 ~ t3).
In cases where the temperature of the geothermal fluid is not very high or where reliability becomes a problem because the geothermal fluid is strongly acidic and the material constituting the casing or blades of the steam turbine is not sufficiently corrosion resistant, binary cycle power generation using a working medium is adopted. In binary cycle power : generation, the heat energy of the geothermal fluid is transmitted to the working medium to effect its evaporation, the turbine is driven by the steam from the working medium, and electric power is produced by the generator connected to the turbine. With conventional power generation, the geothermal steam temperature inevitably is greater than 150C, with power being generated at low efficiency if the geothermal steam temperature is ~n the order of 80C.
For this reason, geothermal steam at this temperature has not been considered to be usable for power generation. According to the present invention, however, carbon dioxide is used as the heat medium and i. , .
~273496 is raised in temperature and pressure to 65C and 130 kg/cm2, respectively, to drive the turbine. This makes it possible to fully utilize even a geothermal fluid whose temperature is 65 to 80C. Further, iE the geothermal fluid used has a temperature higher than the critical temperature (35C) of the carbon dioxide heat medium, even a geothermal fluid whose temperature is 50C can be employed. Specifically, since this medium can be elevated in temperature and pressure beyond its cri-tical state, the turbine can be driven even by using geothermal fluid of considerably reduced temperature that results from previous use in power generation by the direct power generation equipment.
Fig. 6 is a diagrammatic view showing the arrangement of refrigeration equipment according to the embodiment of the present invention. The equipment includes an evaporation tank 61, a condensation tank 62, refrigerants 63, 64, a pump 65, and a pan 66. The refrigerants 63, 64 consist oF a mixture of a lithium bromide hydrate (Li-Br 2H2O) and an alcohol solution such as ethanol or methanol. The evaporation tank 61 contains the refrigerant 63 under a vacuum oE about 75 mmHg, and the condensation -tank 62 contains the refrigerant 64 under a vacuum of about 7 mmHg. ~ pipe for refluxing hot water in the form of steam from a steam well passes through the refrigerant 63 contained in the evaporation tank 61 in order to hea-t the refrigerant 63 under the vacuum oE 75 mmHg. Since it : .,. ~ . . : : :
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~Z73496 contains the alcohol solution, the refrigerant 63 has a low boiling point and is boiled into a vapor by steam or hot water having a temperature even an low as 65C.
Arranged in -the evaporation tank 61 above the surface of the refrigerant 63 is a pipe for refluxing water Erom an out-of-door cooler. The pan 66 is disposed undernea-th this pipe. Here water vapor obtained from the boiling and evaporation oE the refrigerant 63 is collected in the form of moist steam which is then refluxed from the pan 66 to the condensation tank 62, in the course of which cold water is produced by adiabatic expansion. The cold water is introduced in-to the upper part of the condensation tank 62 to cool an air conditioner water pipe before merging with the refrigerant 64. Water refluxed through the air conditioner water pipe is thus cooled from 12C to 7C.
In the above process, the refrigerant 63 becomes more concentrated due to boiling and evaporation, whereas the refrigerant 64 becomes less concentrated owing to the inflow of the cold water. This makes it necessary to introduce some of the refrigerant 63 into the refrigerant 64 of condensation tank 62 and to reElux some of the refrigerant 64 to the refrigerant 63 in evaporation tank 61 by using the pump 65 so that the concentration of the refrigerants will be maintained at a predetermined value at all times.
Thus, in -the refrigeration equipment as described above, lithium bromide hydrate whose boiling point is - . , . :
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lowered by the addition of an alcohol solution is used as a refrigerant, the water content thereof is evaporated and condensed in the evaporation tank 61, cold water is produced from -the condensate by adiabatic expansion, and the cold water is used to cool the water refluxed through the air conditioner water pipe. This makes it possible to effectively exploit even a low-temperature heat source that was difficult to utilize in the prior art. Further, in the arrangement of Fig. 6, the cooling water regulated to a temperature of 32C by the out-of-door cooler is for auxiliary cooling of the steam in the evaporation tank 61 and the refrigerant 64 in the condensation tank 62 and thus improves the condition in these tanks. More specifically, cooling and condensing some of the steam in the evaporation tank 61 by the water from the cooler to produce wet stearn enhances the adiabatic expansion effect. In the condensation tank 62, the water from the cooler lowers the temperature of the refrigerant 64 so that the discharge temperature of the water refluxed through the air conditioner water pipe will not be raised owing to the refrigerant refluxed from the evaporation tank~61 at a high temperature.
Geothermal energy may be tapped in various forms such as steam, hot water and fluids which are a mix-ture thereof, and the temperature of these geotherrnal fluids varies over a wide range of from high to low -temperatures. Nevertheless, the geothermal energy ::
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~73~g6 sources utilized in the prior ar-t generally give an inlet -temperature of no less -than 80C, with fluids exhibiting a lower tempera-ture having been considered unusable. Even with refrigeration equipment utilizing this conventional geothermal fluid, fresh water at a temperature of 90C is converted into hot wa-ter having a temperature of 95C and this is used as a heat source for producing cold water exhibiting a tempera-ture of from 5 to 10C. Accordingly, with this refrigeration equipment, even when low-temperature hot water is available i-t cannot be utilized if it is below the abovementioned temperature, and even though a heat source having a low temperature of less than 80C is actually usable, the coefficient of performance obtained is only 3 or 4, thus rendering effective utilization impossible. According to the present invention, however, use is made of the mixture of lithium bromide hydrate (Li-Br ~2) and alcohol solution to enable operation of a refrigerator using even low-temperature hot water at 65 to 68C as the energy source. Exploiting such a heat source effectively was difficult in the prior art. Moreover, the presen-t invention makes it possible to attain a coefficient of performance of 7 or 8, which is approximately twice the coefficient of performance of 3 or 4 obtained conventionally. It is thus possible to utilize a much wider range of thermal energies possessed by low-temperature geothermal fluids.
, ' -~2734~6 Fig. 7 is a diagrammatic view showing the arrangement of a water-wheel generator annexed to -the power generation equipment of a geothermal energy utilization system according to the embodlment of the present invention. The arrangment includes a condenser main body 71, an upper liquid reservoir 72, a central liquid reservoir 73, a lower liquid reservoir 74l a hot water bath 75, a wa-ter-wheel turbine 76, and a power genera-tor 77. The condenser in the present example is a barometric condenser. Steam supplied to a steam turbine to perform work as mentioned earlier is cooled and converted into water by the condenser 71. Some of this water is fed to a cold water column for being cooled by the atmosphere and is then utili~ed as cooling water by the condenser 71. The remainder of the water is pooled in the hot water bath 75. More specifically, in the barometric condenser, steam from the steam turbine contacts jets of cold water ejected downwardly from a multiplicity of water holes provided in the bottom of the central liquid reservoir 73, the steam is condensed by such contact and the resulting condensate is collected in the lower liquid reservoir - 74. Steam which has not been condensed by the above process is condensed by cold water jets falling from the upper liquid reservoir 72. ~ny uncondensed gas that still remains is vented from a discharge port located at the upper portion of the condenser 71. Hot water which has collected in the lower liquid reservoir~
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74 is pooled in the hot water bath 75, whence the hot water can be introduced -to the next stage of geothermal energy utilization equipment. To utilize the hot water even more effectively, however, the hot water which collects in the hot water bath 75 is provided with a head by piping or the like and is introduced to the water-wheel turbine 76. Owing to the head developed, greater negative pressure is produced in the condenser and the water-wheel turbine 76 is driven. Though the pressure in the condenser main body 71 is decided by the sum of a head H between the liquid level of the water bath 75 and a standard liquid level and the depth h of the low liquid reservoir 74, negative pressure can be generated inside the condenser by introducing the hot water pooled in the hot water bath 75 to the water-wheel turbine by discharge piping. This makes it possible to dispense with or reduce the capacity of a vacuum pump provided in the prior art for the purpose of preventing partial loss of vacuum (0.1 - 0.3 ata).
Thus, rather than simply conveying the hot water in the hot water bath 75 to the next stage of utilization equipment, after power is generated by the steam turbine the electrical potential energy thereof is effectively exploiting and -the head is utilized to provide the hot water pooled in the condenser with a head so that the water-wheel turbine may generate electric power, thus enhancing the power generating efficiency of the overall system. The end result is .
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~Z7~34~
much more efficient utilization of geothermal energy.
In the geothermal energy utilization system of the presen-t invention, the aim is to improve the overall effective utilization of heat energy by arranging the utilization equipment in dependence upon the amount of heat energy possessed by the geothermal fluid, as shown in Fig. 1. When conveying the geothermal fluid from one stage of utilization equipment to the next, therefore, it is important to minimize loss and improve conveyance efficiency in the conveyance path between stages. An example of such conveyance means well-suited to the present inven-tion will now be described.
Fig. 8 is a diagrammatic view for describing an embodiment of a vacuum conveyance system applied to the present invention. The system includes a hot water supply pipe 81, a hot water feed pump 82, a hot water reservoir column 83, refrigeration equipment 84, a conveyance pipe 85, a vacuum pump 86, geothermal energy utilization equipment 87, a hot water level detector 88, a level controller 89, and a drain valve B. Hot water is fed by the hot water feed pump 82 from the hot water supply pipe 81 to the hot water reservoir column 83 where -the hot water is pooled. Connected to the hot water storage column 83 is the conveyance pipe 85, which is Eor feeding hot water to the geothermal ener~y utilization equipment 87, which is the next stage. The vacuum pump 86 is connected to the terminus of the , .. : . : ~:
,, : ~. ,. ~ : :
.. . .. : ~ - -73~6 conveyance pipe 85. The hot water storage column 83 is provided with the detector 88 for detecting the level oE -the hot water, and the drain valve ~ for extracting ho-t water as well as impurity deposits and the like from the bo-ttom of the column. The level controller 89, which is connected between the detector 88 and the drain valve B, is Eor controlling the opening and closing of the valve B in dependence upon the hot water level detected by the detector 88. More specifically, the level controller 89 is set to upper and lower limit values, with a certain control level serving as a reference value. The level controller 89 opens the drain valve B -to discharge the hot water and settled impurities from the bottom of the hot water reservoir column 83 on the condition that the detected hot water~
level attains the upper limit value, and closes the drain valve B on the condition that the detected hot water level attains the lower limit value. An alternative method ~is to set solely a drainage start value as the reference value and have the level controller 89 open the drain valve B only for a predetermined period of time on the condition that the detected level attains the drainage start valueO Other control methods are of course possible. The heat energy which radiates from the conveyance pipe 85 in the course of conveying the hot water is effectively utilized for heating and cooling by the refrigeration equipmen-t 84.
: :.
1~73~96 The system shown in Fig. 8 is set into operation by driving the hot water feed pump 82 to supply ho-t to -the hot water reseroive column 83, the internal pressure of which is reducecl by operating the vacuum pump 86. As result, -the hot: water fed into the column 83 is flashed into steam which, free of impurities, is conveyed smoothly and automatically through the conveyance pipe 85. As the steam is being conveyed through the pipe 85, thermal energy leaking to the exterior of the pipe through its wall is utilized by the refrigeration equipment 84. Steam conveyed to the hot water utilization equipment 87 at the terminus of the conveyance pipe 85 is condensed and utilized as a hot spring, by way of example. Meanwhile, when the level of the hot water in the reservoir column 83 rises and is detected to reach a predetermined level (reference level) by the level detector 88, the latter issues an output signal to which the level controller 89 responds by opening the drain valve B. As a result, excess hot water collected in the reservoir column 83, as well as impurities which precipitate and settle in the hot water, is discharged from -the column. Thus, impurities contained in the hot water and left behind in the reservoir column 83 by flashing are discharged through the drain valve B at prescribed times.
In the prior art, situations where piping is of great length due to a long conveyance dis-tance or where piping is of a complex configuration are dealt with by ~:.. '' :, .
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.
~273~6 -~3-increasing the motive power for conveyance. This makes it necessary to install a fairly large pump for conveyance pipes of larger diameter or length or for piping of some complexity. 'rhe disadvantageous result is greater cost for equipment, operation and maintenance. In addition, since the hot wate:r is conveyed by ordinary piping, the impurities contained in the hot water are also fed through the piping.
These impurities form scale which deposits on the piping walls and eventually blocks the piping flow path. The scale may also attach itself to the interior of the equipment that utilizes the hot water and thus cause equipment damage or failure. Removing such scale demands even more equipment and extra expense.
In the system of the present invention, however, the vacuum pump 86 is operated at the terminus of the conveyance pipe 85 to evacuate the interior of the pipe 85 and the interior of the hot water reservoir column 83, thereby flashing -the hot water and conveying the same automatically in the form of steam, as set forth above. As a result, 90 to 95~ of the impurities can be removed by being forced to remain in the hot water left :
in the reservoir column. Moreover, since the system functions by relying solely upon operation of the vacuum pump 86, conveyance of the steam can be accomplished at 30% of the power used conventionally to transport hot water thanks to the expansion of the hot water steam, even if the hot water .has a comparatively ~2~3~96 low temperature of 50 - 60C.
Figs. 9(A), (B), (C) are views for describing a embodiment of a hot water conveyance path applied to the present invention. The arrangement includes a concrete frame 91, a conveyance pipe 92, a flexible pipe 93, an insulating air layer 94, an insulator 95, a support 96, a channel 97 and a drain 98.
As shown in Fig. 9(A), the conveyance pipe 92 constitutes a concrete pipe through which hot water is passed. The flexible pipe 93 covers the conveyance pipe 92 and is constituted by a plastic conduit (e.g, of the type manufactured by Furukawa Denko). The insulating air layer 94 is formed between the conveyance pipe 92 and flexible pipe 93 and is filled with air for insulating purposes. The space between the flexible pipe 93 and concrete frame 91 is filed with the insulator 95. The flexible pipe 93 is fixedly positioned in the concrete frame 91 by the support 96.
Fig. 9(B) is a sectional view taken along line A-B of Fig. 9(A) and showing the portion at which the support 96 is provided.
Since the hot water conveyance path having the construction shown in Figs. 9(A), (B) has the insulating air layer 94 interposed between the conveyance pipe 92 and the plastic, flexible pipe 93, the pipe 92 is capable of maintaining heat resistance.
In addition, if hot water should leak from the conveyance pipe 92, expansion of the insulating air - .
.,.
~27;34~
layer 9~ due to a rise in temperature resul-ts in the production of pressure that acts to impede leakage.
Even if hot water should manage to leak out of the conveyance pipe 92, the fact that the flexible pipe 93 is made of water--tight plastic assures that the hot water will remain in the insulating air layer and not reach the insulator 95. Since the insulating mechanism thus remains unaffected, a drop in temperature is prevented from occurring. Further, since the hot water leakage does not permeate and degrade the insulator 95 as is common in the prior art, the quality of the insulator can be maintained. It is also unnecessary to use an insulator of high cost.
Various methods of conveying a geothermal fluid, mainly hot water, are known in the prlor art. One method involves covering the channel conveying the hot water with concrete and passing the hot water through the channel to achieve conveyance. Another method is to cover a concrete channel with a glass wool insulator (or a double layer of urethane) and convey the hot water through the concrete channel. However, these conventional methods of hot water conveyance often demand use of a structure of the type in which an iron pipe is laid in a trench formed in the earth, and the cost of maintaining a temperature drop of no more than 0.1 - 1C/km is considera~le. This has delayed the development of conveyance systems for multi-purpose use. More specifically, when hot water leaks from the - . ...~'~ ~
-: , 1~73~?6 concrete pipe, permeates the insulator and eventually destroys it owiny to attendant expansion caused by the hea-t ~rom the water, the abovementioned temperature drop can no longer be maintained. Insufficient insulation can result in a large drop in temperature, especially where the atmospheric temperature is low, thus leading to a significant loss of effective energy.
According to the above-described hot water conveyance path of the present invention, however, leakage from the conveyance pipe 92 of concrete or the like is prevented from reaching the insulator layer 94 by the flexible pipe 93 made of plastic. This assures that the insulator will not be adversely affected by the leakage. Accordingly, the insulating effect can be fully maintained even if an inexpensive insulator is used. Further, the insulating effect is enhanced and leakage is either blocked or limited by virtue of the insulating air layer 94 furnished between the :~
conveyance pipe 92 and the flexible pipe 93.
Thus, as is evident from the foregoing description, the present invention makes it possible to exploit virtually all of the heat energy possessed by geothermal fluids ranging from hi~h-temperature geothermal fluids to those of low temperature utilizable for hot springs. Geothermal energy can thus be utilized with a very high efficiency overall. In addition, since utilization equipment may be installed over a number of stages, ordinary electricity, the -- . . .: .
1273~
energy for hea-ting and cooling and the requirements for a hot spring can be provided for by the heat energy extracted from a geothermal production well. This is highly conducive to conservation of energy resources.
As many apparently widely different embodiments of the present inven-tion can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as de-fined in the appended claims.
-: ;
Fig. 4 is a block diagram showing an embodiment of indirect power generation equipment according to the present invention;
Fig. 5 is a thermodynamic diagram useful in describing the cycle of the power generation equipment shown in Fig. 4;
Fig. 6 is a diagrammatic view showing the arrangement of refrigeration equipment according to the embodiment of the present invention;
Fig. 7 is a diagrammatic view showing the arrangement of a water-wheel generator annexed to the power generation equipment of a geothermal energy utilization system according to the embodiment of the present invention;
Fig. 8 is a diagrammatic view for describing an `' " ~ ~', " ' ~''"' ~ ,, , `' '' ::lLZ7~9~i embodiment oE a vacuum conveyance system applied to the present invention; and Figs. 9(A), ~B), (C) are views for describing an embodiment of a hot wa-ter conveyance path applied to the present invention.
DESCRIPTION OE THE PREFERRED EMBODIMEN_ An embodimen-t of -the present invention will now be described with reference to the accompanying drawings.
Fig. 1 is a block diagram illustrating an embodiment of a geo-thermal energy utilization system according to the present invention. The system includes units 11, 1~ each for combining hot water energy from several production wells, direc-t power generating equipment 12, indirect power generating equipment 13, refrigeration equipment 14, and hot water utilization equipment 15. The combining units 11, 16 combine and extract hot water energy from a plurality of production wells so as to make effective overall use of the energy. The direct power generating equipment 12 uses high-temperature geothermal fluid to directly drive a turbine for power generat1on. Examples of this equipment used conventionally are a steam generator, flash generator and total flow generator. The most suitable power generator is selected depending upon the contents of the geothermal fluid extracted from the hot water energy combining unit. Alternatively, a plurality oE thesè power generators may by used in a parallel configuration. The only power generation .-: ,. . :
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.... ~ . , ~lZ73~96 whlch takes place in the prior art uses steam having a temperature above 150C, as men-tioned above. ~owever, by employing an atmospheric pressure turbine which uses saturated steam at a temperature of 100C as the input energy, the direct power generating equipment 12 in accordance with the present invention generates power by utilizing the heat energy of steam the temperature whereof drops to that usable by the indirect power generating equipment 13, which is the next stage. The indirect power generating equipment 13 employs carbon dioxide as a medium and drives a turbine by raising the temperature and pressure of the carbon dioxide to 65C
and 130 kg/cm , respectively, through indirect contact between this medium and the geothermal fluid having an intermediate temperature of 50 - 80C. Like the indirect power generating equipment 13, the refrigeration equipment 14 uses the intermediate temperature geothermal fluid to effect cooling and reErigeration by an absorption refrigeration method.
The hot water utilization equipment 15, an example of which is a hot spring or heating equipment, utilizes hot water of comparatively low temperature which - results from earlier use in the indirect power genera-ting equipment 13 and refrigeration equipment 14.
The geothermal fluid is broadly classified according to the amount of its heat energy. The intermediate- and low-temperature geothermal fluid may be introduced into the system at intermediate points through the combining .
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- , ~ : ' ~2734~?6 unit 16, as illustrated in Fig. 1.
A specific embodiment of each item of equipment shown in Fig. 1 as well as the geothermal fluid conveyance system will now be described.
Fig. 2 is a schematic view illustrating the arrangement of a hot water energy combining unit and the direct power generation equipment according to the embodiment of the present invention. Fig. 3 is a schematic view for describing an ejector used in the hot water combining unit of Fig. 2. As shown in Fig.
2, the arrangemen-t includes geothermal production wells 21, 22, 23, a silencer 24, ejectors 25, 26, a steam separator 27, a steam conveyance pipe 28, a turbine 29, a power generator 30, a pump 31, an injection condenser 32, a hot water tank 33 and a nozzle 34. The production wells 21, 22, 23 are for generating hot water at high, intermediate and low pressures~
respectively. In order that the low-pressure hot water may be successively drawn out by ejection of the high-pressure hot water, the high-pressure production well 21 is connected to the intermediate-pressure production well 22 through the ejector 25, and the intermediate-pressure production well 22 is in turn connected to the low-pressure production well 23 via the ejector 25. The hot water combined by the ejectors 25, 26 is delivered to the steam separator 27. Here steam is separated from the hot water and is then fed to the turbine 29 through the steam conveyance pipe 28.
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"' - . , ~ ' '. - -~2734~6 g The turbine 29 is driven by -the steam delivered thereto, after which the steam i5 condensed by the injection condenser 32. The resul-ting condensate collects in the hot water tank 33 whence it is introduced to the geothermal energy utilization equipment, which is the next stage. Any uncondensed gas is released to the atmosphere.
As shown in Fig. 3, the ejector 25, which combines the high-pressure hot water from the production well 21 and the intermediate-pressure hot water from the production well 22, is adapted to form the high-pressure hot water into a jet by the nozzle 34 and eject the high-pressure hot water toward the low-pressure production well 23 while the intermediate-pressure hot water is drawn into the flow at theinterfacial boundary thereof. A similar construction is adopted for the ejector 2~, which combines the ejected hot water from the ejec-tor 25 and the low-pressure hot water from the production well 23.
According to the method adopted in the prior art, the steam from a plurality of production wells is combined with the steam from the production well having the low well head pressure so that the energy from the production well having the high steam pressure is used after it is effectively reduced. The energy is thus used in a wasteful manner. One reason for adopting this method is that in an arrangement where a plurality of production wells are connected in series, the ... :
''"`' ~' ' ; ', 73~36 low-pressure steam is suppressed by the high-pressure steam, so that the only solution was -to combine the high-pressure steam with the low. A consequence of this conventional approach is a relatively lower input pressure applied to the turbine, as a result of which the latter operates inefficien-tly. By contrast, in accordance with the present invention, the ejectors 25, 26 are employed to connect a plurality of production wells having different geothermal temperatures and the hot water from -the low-pressure production well is successively drawn up by the ejection of the hot water from the high-pressure production well and combined therewith. This enables a large quantity of steam to be supplied to the turbine at the higher pressure rather than the lower so that the turbine can be operated more efficiently.
Fig. 4 illustrates an embodiment of the indirect power generation equipment according to the present invention. The equipment includes a hot water supply unit 41, a preheater/evaporator 42, a turbine 43, a power generator 44, a compression pump 45, a condenser 46, and a medium pump 47. Carbon dioxide, which is used as the heat transfer medium, is fed into the preheater/evaporator 42 by the medium pump 47. The preheater/evaporator 42 is also supplied by the hot water supply unit 41 with geothermal fluid at a low temperature of 65 - 80C. The supply unit 41 receives the hot water from a geothermal production well or from .. ..
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~2 7~4~6 the direct power generation e~uipment, which is the preceding stage. A heat exchange between the carbon dioxide heat transfer medium and the low-temperature (65 - 80C) geothermal :Eluid takes place inside the preheater/evaporator 42. The carbon dioxide heat transfer medium has a critical temperature of 35C, 70 kg/cm and remains stable without undergoing thermal decomposition even if it is raised to a temperature of 65C and a pressure of 130 kg/cm2. By making effective use of the nature of stable carbon dioxide having the critical temperature of 35C, 70 kg/cm2, the carbon dioxide heat transfer medium is raised to a temperature and pressure of 65C and 130 kg/cm2, respectively, by the indirect contact with the geothermal fluid inside the preheater/evaporator 42 before being supplied to the turbine 43. As a result, the turbine 43 is driven into operation so that the power generator 44 generates electric power. Low-temperature geothermal fluid discharged from the preheater/evaporator 42 is introduced to a hot spring or other hot water utilization system. Following its use in operating the turbine 43, the carbon dioxide is cooled and compressed by the compression pump 45 to be converted into a liquid before being re-turned to the condenser 46. The carbon dioxide heat medium is then resupplied to the preheaterJevaporator 42 from the condenser 46 by the medium pump 47. Circulation of the carbon dioxide is thus accomplished.
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Fig. 5 is a thermodynamic diagram useful in describing the cycle of the power generation equipment shown in Fig. 4. Temperature T is plotted along the vertical axis, and enthalpy h (kcal/kg) is plotted along the horizontal axis. The curves plotted include a geothermal fluid temperature change curve 51 and a C2 saturated steam curve 53 for a case where carbon dioxide is used as the heat transfer medium, and a geothermal fluid temperature change curve 52 and a fron satura-ted steam curve 5~ for a case where fron is used as the heat transfer medium. Where fron is used, the medium is elevated in pressure from point a to point b by a pump and is thereafter heated by a geothermal fluid whose temperature changes from ~ ' to ~ , thereby increasing enthalpy to effect preheating and evaporation from b to c' to c". In the turbine, expansion occurs from c" to d so that work is performed, i.e., so that the turbine is driven.
Cooling and condensation occur from d to e to a, ~ ~-whereby the initial state is restored. Where carbon dioxide is used as the heat transfer medium, the medium is elevated in pressure from point a to point b by a pump and is thereafter heated by a geothermal fluid whose temperature changes from ~ to ~ , -thereby increasing enthalpy to effect preheating and evaporation from b to c. Accordingly, in a case where the outlet temperature of the geothermal fluid is the same, i.e., t3, the inlet temperature t2 of the :
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geothermal fluid where carbon dioxide is used as the medium is much lower than the inlet temperature tl oE
the geothermal medium where ~ron is used as the medium.
Accordingly, excellent results are obtained in terms of the usable temperature range of t2 t3, as opposed to tl - t3, and in terms of the ratio of maximum output to the amount of heat emitted by the geothermal fluid (the ratio of c" - d to tl - t3 and of c - d to t2 ~ t3).
In cases where the temperature of the geothermal fluid is not very high or where reliability becomes a problem because the geothermal fluid is strongly acidic and the material constituting the casing or blades of the steam turbine is not sufficiently corrosion resistant, binary cycle power generation using a working medium is adopted. In binary cycle power : generation, the heat energy of the geothermal fluid is transmitted to the working medium to effect its evaporation, the turbine is driven by the steam from the working medium, and electric power is produced by the generator connected to the turbine. With conventional power generation, the geothermal steam temperature inevitably is greater than 150C, with power being generated at low efficiency if the geothermal steam temperature is ~n the order of 80C.
For this reason, geothermal steam at this temperature has not been considered to be usable for power generation. According to the present invention, however, carbon dioxide is used as the heat medium and i. , .
~273496 is raised in temperature and pressure to 65C and 130 kg/cm2, respectively, to drive the turbine. This makes it possible to fully utilize even a geothermal fluid whose temperature is 65 to 80C. Further, iE the geothermal fluid used has a temperature higher than the critical temperature (35C) of the carbon dioxide heat medium, even a geothermal fluid whose temperature is 50C can be employed. Specifically, since this medium can be elevated in temperature and pressure beyond its cri-tical state, the turbine can be driven even by using geothermal fluid of considerably reduced temperature that results from previous use in power generation by the direct power generation equipment.
Fig. 6 is a diagrammatic view showing the arrangement of refrigeration equipment according to the embodiment of the present invention. The equipment includes an evaporation tank 61, a condensation tank 62, refrigerants 63, 64, a pump 65, and a pan 66. The refrigerants 63, 64 consist oF a mixture of a lithium bromide hydrate (Li-Br 2H2O) and an alcohol solution such as ethanol or methanol. The evaporation tank 61 contains the refrigerant 63 under a vacuum oE about 75 mmHg, and the condensation -tank 62 contains the refrigerant 64 under a vacuum of about 7 mmHg. ~ pipe for refluxing hot water in the form of steam from a steam well passes through the refrigerant 63 contained in the evaporation tank 61 in order to hea-t the refrigerant 63 under the vacuum oE 75 mmHg. Since it : .,. ~ . . : : :
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~Z73496 contains the alcohol solution, the refrigerant 63 has a low boiling point and is boiled into a vapor by steam or hot water having a temperature even an low as 65C.
Arranged in -the evaporation tank 61 above the surface of the refrigerant 63 is a pipe for refluxing water Erom an out-of-door cooler. The pan 66 is disposed undernea-th this pipe. Here water vapor obtained from the boiling and evaporation oE the refrigerant 63 is collected in the form of moist steam which is then refluxed from the pan 66 to the condensation tank 62, in the course of which cold water is produced by adiabatic expansion. The cold water is introduced in-to the upper part of the condensation tank 62 to cool an air conditioner water pipe before merging with the refrigerant 64. Water refluxed through the air conditioner water pipe is thus cooled from 12C to 7C.
In the above process, the refrigerant 63 becomes more concentrated due to boiling and evaporation, whereas the refrigerant 64 becomes less concentrated owing to the inflow of the cold water. This makes it necessary to introduce some of the refrigerant 63 into the refrigerant 64 of condensation tank 62 and to reElux some of the refrigerant 64 to the refrigerant 63 in evaporation tank 61 by using the pump 65 so that the concentration of the refrigerants will be maintained at a predetermined value at all times.
Thus, in -the refrigeration equipment as described above, lithium bromide hydrate whose boiling point is - . , . :
.
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~27;~4~
lowered by the addition of an alcohol solution is used as a refrigerant, the water content thereof is evaporated and condensed in the evaporation tank 61, cold water is produced from -the condensate by adiabatic expansion, and the cold water is used to cool the water refluxed through the air conditioner water pipe. This makes it possible to effectively exploit even a low-temperature heat source that was difficult to utilize in the prior art. Further, in the arrangement of Fig. 6, the cooling water regulated to a temperature of 32C by the out-of-door cooler is for auxiliary cooling of the steam in the evaporation tank 61 and the refrigerant 64 in the condensation tank 62 and thus improves the condition in these tanks. More specifically, cooling and condensing some of the steam in the evaporation tank 61 by the water from the cooler to produce wet stearn enhances the adiabatic expansion effect. In the condensation tank 62, the water from the cooler lowers the temperature of the refrigerant 64 so that the discharge temperature of the water refluxed through the air conditioner water pipe will not be raised owing to the refrigerant refluxed from the evaporation tank~61 at a high temperature.
Geothermal energy may be tapped in various forms such as steam, hot water and fluids which are a mix-ture thereof, and the temperature of these geotherrnal fluids varies over a wide range of from high to low -temperatures. Nevertheless, the geothermal energy ::
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~73~g6 sources utilized in the prior ar-t generally give an inlet -temperature of no less -than 80C, with fluids exhibiting a lower tempera-ture having been considered unusable. Even with refrigeration equipment utilizing this conventional geothermal fluid, fresh water at a temperature of 90C is converted into hot wa-ter having a temperature of 95C and this is used as a heat source for producing cold water exhibiting a tempera-ture of from 5 to 10C. Accordingly, with this refrigeration equipment, even when low-temperature hot water is available i-t cannot be utilized if it is below the abovementioned temperature, and even though a heat source having a low temperature of less than 80C is actually usable, the coefficient of performance obtained is only 3 or 4, thus rendering effective utilization impossible. According to the present invention, however, use is made of the mixture of lithium bromide hydrate (Li-Br ~2) and alcohol solution to enable operation of a refrigerator using even low-temperature hot water at 65 to 68C as the energy source. Exploiting such a heat source effectively was difficult in the prior art. Moreover, the presen-t invention makes it possible to attain a coefficient of performance of 7 or 8, which is approximately twice the coefficient of performance of 3 or 4 obtained conventionally. It is thus possible to utilize a much wider range of thermal energies possessed by low-temperature geothermal fluids.
, ' -~2734~6 Fig. 7 is a diagrammatic view showing the arrangement of a water-wheel generator annexed to -the power generation equipment of a geothermal energy utilization system according to the embodlment of the present invention. The arrangment includes a condenser main body 71, an upper liquid reservoir 72, a central liquid reservoir 73, a lower liquid reservoir 74l a hot water bath 75, a wa-ter-wheel turbine 76, and a power genera-tor 77. The condenser in the present example is a barometric condenser. Steam supplied to a steam turbine to perform work as mentioned earlier is cooled and converted into water by the condenser 71. Some of this water is fed to a cold water column for being cooled by the atmosphere and is then utili~ed as cooling water by the condenser 71. The remainder of the water is pooled in the hot water bath 75. More specifically, in the barometric condenser, steam from the steam turbine contacts jets of cold water ejected downwardly from a multiplicity of water holes provided in the bottom of the central liquid reservoir 73, the steam is condensed by such contact and the resulting condensate is collected in the lower liquid reservoir - 74. Steam which has not been condensed by the above process is condensed by cold water jets falling from the upper liquid reservoir 72. ~ny uncondensed gas that still remains is vented from a discharge port located at the upper portion of the condenser 71. Hot water which has collected in the lower liquid reservoir~
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74 is pooled in the hot water bath 75, whence the hot water can be introduced -to the next stage of geothermal energy utilization equipment. To utilize the hot water even more effectively, however, the hot water which collects in the hot water bath 75 is provided with a head by piping or the like and is introduced to the water-wheel turbine 76. Owing to the head developed, greater negative pressure is produced in the condenser and the water-wheel turbine 76 is driven. Though the pressure in the condenser main body 71 is decided by the sum of a head H between the liquid level of the water bath 75 and a standard liquid level and the depth h of the low liquid reservoir 74, negative pressure can be generated inside the condenser by introducing the hot water pooled in the hot water bath 75 to the water-wheel turbine by discharge piping. This makes it possible to dispense with or reduce the capacity of a vacuum pump provided in the prior art for the purpose of preventing partial loss of vacuum (0.1 - 0.3 ata).
Thus, rather than simply conveying the hot water in the hot water bath 75 to the next stage of utilization equipment, after power is generated by the steam turbine the electrical potential energy thereof is effectively exploiting and -the head is utilized to provide the hot water pooled in the condenser with a head so that the water-wheel turbine may generate electric power, thus enhancing the power generating efficiency of the overall system. The end result is .
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~Z7~34~
much more efficient utilization of geothermal energy.
In the geothermal energy utilization system of the presen-t invention, the aim is to improve the overall effective utilization of heat energy by arranging the utilization equipment in dependence upon the amount of heat energy possessed by the geothermal fluid, as shown in Fig. 1. When conveying the geothermal fluid from one stage of utilization equipment to the next, therefore, it is important to minimize loss and improve conveyance efficiency in the conveyance path between stages. An example of such conveyance means well-suited to the present inven-tion will now be described.
Fig. 8 is a diagrammatic view for describing an embodiment of a vacuum conveyance system applied to the present invention. The system includes a hot water supply pipe 81, a hot water feed pump 82, a hot water reservoir column 83, refrigeration equipment 84, a conveyance pipe 85, a vacuum pump 86, geothermal energy utilization equipment 87, a hot water level detector 88, a level controller 89, and a drain valve B. Hot water is fed by the hot water feed pump 82 from the hot water supply pipe 81 to the hot water reservoir column 83 where -the hot water is pooled. Connected to the hot water storage column 83 is the conveyance pipe 85, which is Eor feeding hot water to the geothermal ener~y utilization equipment 87, which is the next stage. The vacuum pump 86 is connected to the terminus of the , .. : . : ~:
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.. . .. : ~ - -73~6 conveyance pipe 85. The hot water storage column 83 is provided with the detector 88 for detecting the level oE -the hot water, and the drain valve ~ for extracting ho-t water as well as impurity deposits and the like from the bo-ttom of the column. The level controller 89, which is connected between the detector 88 and the drain valve B, is Eor controlling the opening and closing of the valve B in dependence upon the hot water level detected by the detector 88. More specifically, the level controller 89 is set to upper and lower limit values, with a certain control level serving as a reference value. The level controller 89 opens the drain valve B -to discharge the hot water and settled impurities from the bottom of the hot water reservoir column 83 on the condition that the detected hot water~
level attains the upper limit value, and closes the drain valve B on the condition that the detected hot water level attains the lower limit value. An alternative method ~is to set solely a drainage start value as the reference value and have the level controller 89 open the drain valve B only for a predetermined period of time on the condition that the detected level attains the drainage start valueO Other control methods are of course possible. The heat energy which radiates from the conveyance pipe 85 in the course of conveying the hot water is effectively utilized for heating and cooling by the refrigeration equipmen-t 84.
: :.
1~73~96 The system shown in Fig. 8 is set into operation by driving the hot water feed pump 82 to supply ho-t to -the hot water reseroive column 83, the internal pressure of which is reducecl by operating the vacuum pump 86. As result, -the hot: water fed into the column 83 is flashed into steam which, free of impurities, is conveyed smoothly and automatically through the conveyance pipe 85. As the steam is being conveyed through the pipe 85, thermal energy leaking to the exterior of the pipe through its wall is utilized by the refrigeration equipment 84. Steam conveyed to the hot water utilization equipment 87 at the terminus of the conveyance pipe 85 is condensed and utilized as a hot spring, by way of example. Meanwhile, when the level of the hot water in the reservoir column 83 rises and is detected to reach a predetermined level (reference level) by the level detector 88, the latter issues an output signal to which the level controller 89 responds by opening the drain valve B. As a result, excess hot water collected in the reservoir column 83, as well as impurities which precipitate and settle in the hot water, is discharged from -the column. Thus, impurities contained in the hot water and left behind in the reservoir column 83 by flashing are discharged through the drain valve B at prescribed times.
In the prior art, situations where piping is of great length due to a long conveyance dis-tance or where piping is of a complex configuration are dealt with by ~:.. '' :, .
, - ' -: : ' : ~ :, ~ , , -. .
.
~273~6 -~3-increasing the motive power for conveyance. This makes it necessary to install a fairly large pump for conveyance pipes of larger diameter or length or for piping of some complexity. 'rhe disadvantageous result is greater cost for equipment, operation and maintenance. In addition, since the hot wate:r is conveyed by ordinary piping, the impurities contained in the hot water are also fed through the piping.
These impurities form scale which deposits on the piping walls and eventually blocks the piping flow path. The scale may also attach itself to the interior of the equipment that utilizes the hot water and thus cause equipment damage or failure. Removing such scale demands even more equipment and extra expense.
In the system of the present invention, however, the vacuum pump 86 is operated at the terminus of the conveyance pipe 85 to evacuate the interior of the pipe 85 and the interior of the hot water reservoir column 83, thereby flashing -the hot water and conveying the same automatically in the form of steam, as set forth above. As a result, 90 to 95~ of the impurities can be removed by being forced to remain in the hot water left :
in the reservoir column. Moreover, since the system functions by relying solely upon operation of the vacuum pump 86, conveyance of the steam can be accomplished at 30% of the power used conventionally to transport hot water thanks to the expansion of the hot water steam, even if the hot water .has a comparatively ~2~3~96 low temperature of 50 - 60C.
Figs. 9(A), (B), (C) are views for describing a embodiment of a hot water conveyance path applied to the present invention. The arrangement includes a concrete frame 91, a conveyance pipe 92, a flexible pipe 93, an insulating air layer 94, an insulator 95, a support 96, a channel 97 and a drain 98.
As shown in Fig. 9(A), the conveyance pipe 92 constitutes a concrete pipe through which hot water is passed. The flexible pipe 93 covers the conveyance pipe 92 and is constituted by a plastic conduit (e.g, of the type manufactured by Furukawa Denko). The insulating air layer 94 is formed between the conveyance pipe 92 and flexible pipe 93 and is filled with air for insulating purposes. The space between the flexible pipe 93 and concrete frame 91 is filed with the insulator 95. The flexible pipe 93 is fixedly positioned in the concrete frame 91 by the support 96.
Fig. 9(B) is a sectional view taken along line A-B of Fig. 9(A) and showing the portion at which the support 96 is provided.
Since the hot water conveyance path having the construction shown in Figs. 9(A), (B) has the insulating air layer 94 interposed between the conveyance pipe 92 and the plastic, flexible pipe 93, the pipe 92 is capable of maintaining heat resistance.
In addition, if hot water should leak from the conveyance pipe 92, expansion of the insulating air - .
.,.
~27;34~
layer 9~ due to a rise in temperature resul-ts in the production of pressure that acts to impede leakage.
Even if hot water should manage to leak out of the conveyance pipe 92, the fact that the flexible pipe 93 is made of water--tight plastic assures that the hot water will remain in the insulating air layer and not reach the insulator 95. Since the insulating mechanism thus remains unaffected, a drop in temperature is prevented from occurring. Further, since the hot water leakage does not permeate and degrade the insulator 95 as is common in the prior art, the quality of the insulator can be maintained. It is also unnecessary to use an insulator of high cost.
Various methods of conveying a geothermal fluid, mainly hot water, are known in the prlor art. One method involves covering the channel conveying the hot water with concrete and passing the hot water through the channel to achieve conveyance. Another method is to cover a concrete channel with a glass wool insulator (or a double layer of urethane) and convey the hot water through the concrete channel. However, these conventional methods of hot water conveyance often demand use of a structure of the type in which an iron pipe is laid in a trench formed in the earth, and the cost of maintaining a temperature drop of no more than 0.1 - 1C/km is considera~le. This has delayed the development of conveyance systems for multi-purpose use. More specifically, when hot water leaks from the - . ...~'~ ~
-: , 1~73~?6 concrete pipe, permeates the insulator and eventually destroys it owiny to attendant expansion caused by the hea-t ~rom the water, the abovementioned temperature drop can no longer be maintained. Insufficient insulation can result in a large drop in temperature, especially where the atmospheric temperature is low, thus leading to a significant loss of effective energy.
According to the above-described hot water conveyance path of the present invention, however, leakage from the conveyance pipe 92 of concrete or the like is prevented from reaching the insulator layer 94 by the flexible pipe 93 made of plastic. This assures that the insulator will not be adversely affected by the leakage. Accordingly, the insulating effect can be fully maintained even if an inexpensive insulator is used. Further, the insulating effect is enhanced and leakage is either blocked or limited by virtue of the insulating air layer 94 furnished between the :~
conveyance pipe 92 and the flexible pipe 93.
Thus, as is evident from the foregoing description, the present invention makes it possible to exploit virtually all of the heat energy possessed by geothermal fluids ranging from hi~h-temperature geothermal fluids to those of low temperature utilizable for hot springs. Geothermal energy can thus be utilized with a very high efficiency overall. In addition, since utilization equipment may be installed over a number of stages, ordinary electricity, the -- . . .: .
1273~
energy for hea-ting and cooling and the requirements for a hot spring can be provided for by the heat energy extracted from a geothermal production well. This is highly conducive to conservation of energy resources.
As many apparently widely different embodiments of the present inven-tion can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as de-fined in the appended claims.
-: ;
Claims (10)
1. A geothermal energy utilization system in which heat energy possessed by a geothermal fluid produced by a geothermal production well is utilized in equipment stages selected in accordance with the amount of heat energy possessed by the geothermal fluid.
2. The system according to claim 1, comprising:
direct power generation equipment for generating electric power directly by using the geothermal fluid;
indirect power generation equipment for generating electric power through heat exchange with the geothermal fluid using carbon dioxide as a heat transfer medium;
refrigeration equipment for cooling water by an absorption refrigeration method; and hot water utilization equipment for hot spring and other purposes;
wherein comparatively high-temperature geothermal fluid is supplied to said direct power generation equipment to be used for generation of electric power, intermediate-temperature geothermal fluid is supplied to said indirect power generation equipment to be used for generation of electric power, and hot water recovered at a comparatively low temperature following its use in cooling and air conditioning performed by said refrigeration equipment is utilized at said hot water utilization equipment.
direct power generation equipment for generating electric power directly by using the geothermal fluid;
indirect power generation equipment for generating electric power through heat exchange with the geothermal fluid using carbon dioxide as a heat transfer medium;
refrigeration equipment for cooling water by an absorption refrigeration method; and hot water utilization equipment for hot spring and other purposes;
wherein comparatively high-temperature geothermal fluid is supplied to said direct power generation equipment to be used for generation of electric power, intermediate-temperature geothermal fluid is supplied to said indirect power generation equipment to be used for generation of electric power, and hot water recovered at a comparatively low temperature following its use in cooling and air conditioning performed by said refrigeration equipment is utilized at said hot water utilization equipment.
3. The system according to claim 2 , wherein said direct power generation equipment is driven by an atmospheric pressure turbine provided with input energy in the form of saturated steam at a temperature of 100°C.
4. The system according to claim 2 or claim 3, wherein said indirect power generation equipment drives a turbine by raising the temperature and pressure of the carbon dioxide heat transfer medium to 65°C and 130 kg/cm2, respectively, through indirect contact with the intermediate-temperature geothermal fluid the temperature whereof is 50 to 80°C.
5. The system according to any of claims 1, 2 OR 3, further comprising water-wheel power generation equipment for providing discharge water produced in a condenser with a head to increase negative pressure inside the condenser and drive a water-wheel turbine to generate electric power.
6. The system according to claim 2 or claim 3, wherein said refrigeration equipment uses a refrigerant comprising a mixture of lithium bromide hydrate and an alcohol solution to obtain a high coefficient of performance even with an intermediate-temperature heat source.
7. The system according to any of claims 1, 2 or 3, wherein the geothermal fluid is extracted by connecting a plurality of geothermal production wells in succession from geothermal production wells of higher pressure to geothermal production wells of lower pressure, successively drawing up hot water from the geothermal production wells of lower pressure by ejection of hot water from the geothermal production wells of higher pressure, and combining the hot water so obtained from each of the geothermal production wells.
8. The system according to claim 2, wherein a vacuum pump is connected to a terminus of a conveyance pipe and the interior of the conveyance pipe and the interior of a hot water reservoir column in which hot water is pooled are evacuated by using said vacuum pump, whereby the hot water in said hot water reservoir column is flashed to steam and automatically conveyed.
9. The system according to claim 8, wherein said refrigeration equipment is installed in an intermediate section of said conveyance pipe.
10. The system according to any of claims 1, 2 OR 3, wherein hot water is conveyed by a hot water conveyance path obtained by covering said conveyance pipe with a flexible pipe comprising a water-tight plastic and filling a space between said conveyance pipe and said flexible pipe with air to form an insulating air layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP60101762A JPS61261679A (en) | 1985-05-14 | 1985-05-14 | Utilizing system of terrestrial heat |
| JP101762/1985 | 1985-05-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1273496A true CA1273496A (en) | 1990-09-04 |
Family
ID=14309241
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000506235A Expired - Fee Related CA1273496A (en) | 1985-05-14 | 1986-04-09 | Geothermal energy utilization system |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS61261679A (en) |
| CA (1) | CA1273496A (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH0419367A (en) * | 1990-05-15 | 1992-01-23 | Nkk Corp | Electric-power generator with use of subterranean heat |
| JP4533669B2 (en) * | 2004-05-31 | 2010-09-01 | 南光物産株式会社 | Production method of hot spring mud using geothermal steam |
| JP5829120B2 (en) * | 2011-12-23 | 2015-12-09 | 株式会社ターボブレード | Thermal steam generator |
| CN103398456A (en) * | 2013-08-19 | 2013-11-20 | 吉林澳奇机电集团有限公司 | Energy-saving device and energy-saving method utilizing ground source heat pump |
| CN105890673B (en) * | 2016-06-23 | 2018-05-01 | 南开大学 | A kind of online wide range dynamic water table-temperature measurement system of underground heat well |
-
1985
- 1985-05-14 JP JP60101762A patent/JPS61261679A/en active Granted
-
1986
- 1986-04-09 CA CA000506235A patent/CA1273496A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPS61261679A (en) | 1986-11-19 |
| JPH0526953B2 (en) | 1993-04-19 |
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