GEOTHERMAL ENERGY

PURPOSE OF THE INVENTION

The present invention refers to a system for extraction of geothermal energy and can be used both for heating of buildings and producing of electric power.

BACKGROUND OF THE INVENTION

Geothermal energy can be extracted by 2 basic methods: utilisation of hot fluids, steam or water coming from the underground to the surface by drilled wells (hydrothermal energy), and using the heat energy of hot rocks (petrothermal energy). The heat flow of petrothermal energy in high temperature areas is 60-100 MW/m ² . This is an unlimited source of energy produced by 1300 ^° C hot magma 24 hours a day, all year round, providing the users real independence from market fluctuations of fuel and gas prices. The temperature rises about 1 °C per each 28 m in depth. Therefore, in the areas of high subterranean heat 100-180°C can be reached in the depth of 2-3km. (L. Anions ..Applied physics" part 2, 1995., RTga, Zvaigzne ABC, 287.- 294.lpp.), http://www. Ivportals. Iv/likum i-prakse. php?id=229943

One of the methods known until now is based on using of natural subterranean water or steam at seismic activity areas. Hot liquids are pumped to the surface through several boreholes - this is called the open geothermal system. Though, the natural water and steam contains dangerous chemical compounds, which can cause environmental pollution by flowing into soil, rivers and lakes. The aggressive chemical compounds like salt or acid can damage the pumps and other technical equipment of the circulation system. High costs of research and drilling and a long time of the project development (up to 10 years) are considered as the disadvantages of this system. Another method of utilization of subterranean heat is based on the circulation of the heating fluid within parallel or coaxial pipes placed into unused gas or oil pumping wells - this is called a closed geothermal system. The effectiveness of this system is 8 times lower comparing to the open system due to a limited contact between heating liquid and hot rocks, caused by the vertical placement of the pipe and void spaces around it. http://www.gtr.ethz.ch/kohl www/PDF Paper/WGC Weissbad.pdf DESCRIPTION OF THE INVENTION

The present invention provides environment-friendly utilisation of subterranean heat from hard hot rocks without the exposure of natural subterranean liquid or gas. The technical purpose of the invention is to improve the efficiency of heat exchange between heat source and heated fluid (for example, pure water) in a closed circuit of coaxial pipes. The presently known arrangement methods of coaxial pipes are descripted by patents RU 2288413 C1 , US4512156 and abandoned application EP 1808652. The methods and materials described in these patents provide the thermal insulation and mechanical strength of the pipes, but do not improve the process of thermal exchange.

The principle of the present invention is shown in the drawings. Fig.1 shows the longitudinal section of the whole system, Fig.2 - the cross section of the system in the cold layers of the earth, Fig.3 - the cross section of the system in the hot layers of the earth, Fig.4 - the longitudinal section of the underground part of the system. The system contains the following elements: V - a vertical borehole in the cold levels of the earth, 1 " - a directed borehole in the hot levels of the earth, 2 - an external pipe, 3 - insulation of the external pipe, 4 - an internal pipe, 5 - insulation of the internal pipe, 6 - a material of increased thermal conductivity, 7 - a downgoing flow of heated liquid, 8 - an upgoing flow of heated liquid, 9 - a mouth of the internal pipe, 10 - a heat exchanger, 1 1 - a connecting pipe, 12 - a pump, 13 - a pipe to the heat consumer, 14 - a pipe from the heat consumer, 15 - the surface of the ground, 16 - cold layers of the ground, 17 - hot layers of the ground, 18 - an occluding block of the external pipe.

The essence of the method is the following: 1) A vertical borehole perpendicular to the surface of the earth is made to reach the hot layers of the earth. Approaching the hot layers of the ground (17), the borehole is directed at an angle of 30-90° against vertical direction for the maximum use of geothermal heat flow according to the depth of the borehole, length and diameter of the pipe.

2) After drilling the remains of the ground and technological drilling liquids are washed out of the borehole under pressure through the occluding block (18) of the external pipe. At the same time the fractured pieces of rocks around the pipe are washed out from natural holes and fractures. The void spaces around the external pipe (6) will be filled by a material of increased thermal conductivity.

3) The external circulation pipe (2) is placed into the borehole (1 ). The external surface of the external pipe (2), is bonded with hot rock (17), by the material of increased thermal conductivity (for example, cement containing admixture of aluminum shavings, flint dust or carbon fibres) (6), filling all natural fractures and the borehole (1 ) around the external pipe (2), providing maximum thermal contact between the surface of the external pipe (2) and the hot rock (17). The material of increased thermal conductivity spreads deeply in the hot rock (17), collecting the heat from wide area and dividing it equally to the whole surface of the pipe (2).

4) After that the end of the pipe (2) is closed by the occluding block (18), forming a closed-loop system. The internal pipe (4) is inserted into the pipe (2), in a free or coaxially fixed position, forming a loop of downgoing and upgoing flow (7, 8). The mouth (9) of the internal pipe (4) is located near the occluding block (18).

The liquid flows downwards (7) the external pipe (2). The heat is transferred from the hot rocks (17) to the cementing material of increased thermal conductivity (6), then to the external pipe (2), then to liquid (7). The heated liquid enters the internal pipe (4), through the mouth (9). Thermal energy is carried to the surface by upgoing flow (8). The heated liquid goes to the heat exchanger (10), transfers the heat to the consumer and then through the connecting pipe (1 1 ) and pump (12) returns to the downgoing pipe (2) for recurrent heating. The insulation layer (5) provides insulation between the pipes (2) and (4), the insulation layer (3) - insulation between the surface of the external pipe (2) and the cold layers of the ground (16).