Power plants – Utilizing natural heat – Geothermal
Patent
1992-01-21
1993-04-20
Ostrager, Allen M.
Power plants
Utilizing natural heat
Geothermal
165 45, F03G 0704
Patent
active
052031730
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a device for utilization of geothermal energy, wherein a conveyor tube is sunk into the earth's crust for the purpose of raising a medium located therein that is heated by geothermal energy, and possibly transported in vapor form.
Devices for utilization of geothermal energy have been known for a long time. However, they frequently work with systems that are not closed, wherein a fluid is pumped into hot rock and, partially at other places, is again transported to the surface after heating. Here, the fluid pressure arising by heating, in the example with water for example also the water-vapor pressure, is frequently used for forcing upward. For example, a process of this type is known from DE-OS 29 04 140, in which a working fluid consisting of water and of a ketone is introduced into a filler shaft and, after it has passed a geothermal storage formation, is again recovered in a delivery shaft and converted to vapor (steam). A process of this type, in particular when further mixed with a ketone, has the strong disadvantage that only part of the working fluid introduced will be recovered again, and that, because of the open circuit, impurities can possibly be carried into the recovered working fluid. This is highly undesirable, in particular in the case of use of turbines that are to convert the vapor energy into electrical energy. The impurities would lead to deposits and abrasions.
Another disadvantage of such open systems is that the potential energy that must be applied for bringing up the vapor is not correspondingly utilized also when bringing down the working fluid. This type of utilization of the potential energy, which, in particular, appears in the form of a very high fluid pressure at the lower end of a fluid column, is used by way of example in DE-OS 29 07 338 in which a so-called deep-shaft-drop power system is described. However, that installation is highly complicated, includes an internal combustion engine, and does not take into account that heating of the working fluid is already possible by means of geothermal energy (even though in lesser measure). Hence, even with knowledge of the device proposed there, it is not possible to use geothermal energy in a simple manner together with the potential energy that is released with ascent of the medium. In particular, in the case of an installation of this type, it has been demonstrated that raising the temperature of water to 150.degree. C. at a given depth of the shaft does not suffice for generating a vapor (steam), since there prevails a pressure such that conveyed fluid medium does not become vapor-forming at this temperature.
Therefore, the attempt has been made to use fluids other than water. In so doing, proposed, for example in DE-OS 28 18 001, has been Frigen 22 (monochlorodifluoromethane) having a boiling point of about -41.degree. C., which would vaporize already with the heating taking place at lower depths. A working fluid of this type, which can not be used in large plants because of its lacking compatibility with the environment, could find application based on the reverse principle of the cooling chamber. However, also described with this is essentially only a customary type heat exchanger. The special problems and possibilities that occur by using geothermal energy at greater depths, namely raising the pressure in a column of liquid in comparison to the pressure at the surface of the earth and the considerable temperature at greater depths of the earth's crust, are neither resolved by the system nor have they been recognized at all.
Also working based on the same principle is the process described in DE-OS 30 15 307 for converting heat into mechanical energy. It is only that propane, among others, has been proposed as a medium, which in the case of large installations harbors within itself safety risks.
Still to be mentioned also is DE-OS 34 33 057, in which a process and an arrangement for recovering electrical or mechanical energy from hot geothermal beds based on a Rankine process is described. However,
REFERENCES:
patent: 4364232 (1982-12-01), Sheinbaum
patent: 4512156 (1985-04-01), Nagase
patent: 4912941 (1990-04-01), Buchi
Alfred Buch, Energie, vol. 28, No. 10, pp. 278-280; Oct. 1976.
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