Power plants – Utilizing natural heat – Geothermal
Patent
1986-02-04
1987-02-24
Davis, Jr., Albert W.
Power plants
Utilizing natural heat
Geothermal
165 45, 16510425, 16510426, F03G 704
Patent
active
046447504
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to the recovery of geothermal energy. It is well-known that very hot strata can be found at relatively small depths below the surface of the earth. Volcanic phenomena are the most obvious example, although perhaps the least amenable to exploitation. Hot springs are exploited of course, but they are rare.
TECHNICAL BACKGROUND
It has been proposed to create a form of hot spring by pumping water through hot strata fractured by drilling and explosive blasting. Whilst this certainly works, it is not very efficient due to the need to have two spaced-apart bore holes, one to supply relatively cold water and the other to recover it after passage through the hot strata. Also it is necessary to use considerable energy in circulating the water, not just through the strata, but also through the great lengths of pipe needed to reach the latter.
It has been proposed that these problems can be at least mitigated by using a single bore hole provided with two tubes assembled in concentric relation, with one tube being used to supply cold water and the other used to recover it. This certainly avoids the need to drill a second bore hole, but it creates an even bigger problem due to the absolute necessity to have a very efficient heat exchanger at the bottom of the bore hole, since the heat must now be recovered from that relatively limited portion of the hot strata in the immediate vicinity of the bottom of the tube assembly. Where, for example, water is circulated through the latter using the single bore hole system the overall efficiency is quite low.
There is still the problem of the energy needed to circulate the water.
DISCUSSION OF THE PRIOR ART
In order to overcome the above problems it has been proposed that geothermal heat should be recovered by means of a passive heat pipe. U.S. Pat. No. 3,911,683 proposes such a system based on a conventional heat pipe scaled up in dimensions, most particularly in length. Whilst the high thermal efficiency of heat pipes is well-established, the practical problems of such scaling have not been addressed. Unless high thermal efficiency can be retained in the scaled-up version, the resultant arrangement will at best show no advantage over prior systems. At worst, it will not work at all due to the losses involved at the extreme length-to-diameter ratios involved.
DISCUSSION OF THE INVENTION
According to the present invention, a method of recovering geothermal energy comprises the steps of inserting a closed tube into a bore hole extending from the surface into a zone of relatively hot strata so that one end of said tube is at or adjacent the surface and the other end is in said zone, providing heat exchange means in operative contact with said one end, before or after evacuating the closed tube and introducing a quantity of a working fluid thereinto, followed by operating said heat exchange means to recover energy from said working fluid, characterised by the step of providing said tube in the form of an assembly of two tubes disposed in concentric relation, the inner tube being constituted by a relatively small diameter capillary for the return of working fluid to the vicinity of the zone of relatively hot strata.
PREFERRED FEATURES OF THE INVENTION
The method preferably includes the step of providing means such as a pump operable to positively assist the return of the working fluid under gravity. A third and outermost tube is advantageously provided to surround the two tubes in spaced relation thereto, as a means of reducing conduction losses into the cooler strata above the relatively hot strata. Where three tubes are used, the method preferably includes the steps of inserting the third tube into the bore hole first, followed by inserting into it the other two tubes which together constitute the closed tube itself, this second insertion step being carried out so that the closed tube projects from the bottom, downhole end of the third tube into the zone of relatively hot strata. The method then preferably also includes the
REFERENCES:
patent: 3844342 (1974-10-01), Eninger et al.
patent: 3857244 (1974-12-01), Faucette
patent: 3913665 (1975-10-01), Franklin et al.
patent: 4094356 (1978-06-01), Ash et al.
patent: 4290266 (1981-09-01), Twite et al.
patent: 4470450 (1984-09-01), Bizzell et al.
Lockett George E.
Thurston Robert D.
Davis Jr. Albert W.
Energy Soft Computer Systems Limited
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