GEOTHERMAL GROUT HAVING ENHANCED THERMAL CONDUCTIVITY

COULIS GEOTHERMIQUE AVEC CONDUCTIVITE THERMIQUE AMELIOREE

English Abstract

A geothermal grout contains aluminum oxide in the amount of about 65 percent
by weight
but can contain up to 90 percent by weight of aluminum oxide. The remainder of
the grout can be
wholly composed of bentonite or can contain bentonite and any one or more of
the following
ingredients: aluminum oxide, copper sulfate, iron oxide and iron

Claims

I claim:
1. A geothermal grout containing aluminum oxide in the amount of not more than
90
percent by weight.
2. The geothermal grout of claim 1 in which the content of aluminum oxide does
not exceed
about 65 percent by weight.
3. The geothermal grout of claims 1 or 2 which contains essentially only
bentonite and
aluminum oxide.
4. A geothermal grout comprising: bentonite and a substance selected from the
group
comprising: aluminum oxide, copper sulfate, iron oxide and iron.
5. The geothermal grout of claim 4 wherein said substance comprises not more
than about
90 % by weight of said geothermal grout.
6. The geothermal grout of claim 4 wherein said substance comprises not more
than about
65 % by weight of said geothermal grout.

Description

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It is well known that the temperature of fluids can be raised by means of
geothermal
energy from the heat of the earth. The temperature of earth rises with
increasing depth from the
surface and the temperature of liquids likewise rises as the depth of their
surroundings under-
ground increases. When the liquid is extracted from the earth, its thermal
energy can be har-
nessed in ways that depend upon the depth at which the liquid is situated. For
example, water at a
depth of about 2.5 km, is generally in the form of steam. In areas of volcanic
activity and thermal
springs, steam occurs at considerably lesser depths. The steam when extracted
from the earth can
be injected directly onto the blades of a turbine in order to drive a
generator.
It is also known that the temperature of fluids can be lowered by geothermal
means. For
example, hot water from an air conditioner or refrigerator can be circulated
into the earth in order
to cool the water to the temperature of the earth.
In its simplest form, geothermal energy is produced by causing a liquid to
flow downward
from the surface of the earth through a bore hole to a predetermined depth.
The heated liquid is
then returned to the earth's surface through another bore hole and, where its
temperature is raised
in the earth, its heat or thermal energy is extracted and harnessed for the
production of energy.
Alternatively where the temperature of the liquid is lowered in the earth, the
liquid can flow to an
air conditioner, refrigerator or other cooling device where its low
temperature can be harnessed
for cooling purposes.
Geothermal heating and cooling is carried out in various known apparatus. Heat
pumps
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and compressors, for example are used both for heating and cooling. Glycol or
a mixture of
glycol and water is frequently used as the heating and cooling medium.
Typically the fluid flows
through pipes in the ground where it picks up heat from the surrounding earth
or gives it up to the
earth. The pipes are located in vertical wells or horizontal drill holes or
ditches.
The pipe must have good contact with the ground to provide an efficient
transfer of heat
to or from the fluid which flows in it. Grout is used to ensure that there is
such contact. Grout
also acts to protect the pipe from movement of the ground and from corrosive
liquids in the
ground. It also acts as a sealant to prevent contamination of the liquid
within the pipe and
contamination of ground water by the liquid in the pipe.
The grout is poured in the space between the outer wall of the pipe and the
wall of the
hole in which the pipe is located. Typically, dirt, clay, sand, cement,
graphite, bentonite and even
water are used as grout but other substances are also used for this purpose.
Grout is also used in other applications. Electricity generating plants encase
wires in con-
crete in order to insulate the surrounding earth from the heat of the wires.
Cable companies also
use grout to fill the space around their wires and pipes.
The thermal conductivity of the grout has a significant impact on the required
depth of the
pipe and hence the cost of its installation. The more efficient the heat
transfer between the liquid
in the pipe and the earth surrounding the pipe, the shorter the length of pipe
required to provide a
given transfer of heat. A grout that does not effectively conduct heat can act
as an insulator and
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inhibit the transfer of heat to the liquid.
It is known to use clay such as bentonite as a grout in geothermal
applications. Bentonite
contains up to about 10 percent by weight aluminum oxide. Compounds of iron
such as iron
oxide, and oxides of copper are also found in bentonite. Bentonite has
relatively good dimen-
sional stability and bonding characteristics which are important qualities of
grout used for geo-
thermal purposes. Bentonite however generally has relatively low thermal
conductivity compared
to other substances which are commonly used as grout. .
I have found that if additional aluminum oxide is combined with bentonite to
increase
the overall quantity of aluminum oxide to as high as 90 percent by weight but
preferably not
more than 65 % by weight, the thermal conductivity of the grout increases
significantly. The
resulting grout is easy to mix and pump using conventional equipment and meets
the generally
recognized standards required for grout such as satisfactory permeability,
minimum shrinkage,
satisfactory bonding, durability, ease of handling and so on.
The thermal conductivity of other substances commonly used as grout such as
concrete is
also enhanced by the addition of aluminum oxide. If sufficient aluminum oxide
is combined with
such substances to produce a product having about 25 to 30 percent by weight
aluminum oxide,
there is a significant improvement in the thermal conductivity in the product.
The grout of the invention can include additional components including a
thermoplastic
air entraining agent, latex, a shrinkage reducing admixture, calcium oxide or
combinations
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thereof.
It will be understood, of course, that modification can be made in the
composition of the
grout of the invention without departing from the scope of the invention as
defined in the
appended claims.
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