RU2683059C1 - Method of extraction and use of geothermal heat for cooling soils around subway tunnels - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to methods of using the extracted geothermal heat to cool the soil around the subway tunnels and transform it to heat water in a hot water system. Geothermal heat is extracted from the soils surrounding the subway tunnels with a ground-based low-temperature heat exchanger buried in the ground, which is a set of plug-in circuits made of 32–40 mm diameter polyethylene pipes without butt joints. Contours are laid flat spiral-helical coils at a depth of 2–4 m from the earth's surface below the depth of freezing over the arches of the underground tunnels with a pitch of 0.7–0.8 m, the diameter of the coils is 800–1,000 mm. Number of contours is determined by calculation. Length of the connected circuits made the same 100–120 m. Heat recovered is accumulated in the coolant, which is an ice-free thirty-percent propylene glycol aqueous solution pumped into the pipe under a pressure of 4 atm, circulating at a speed of at least 0.3 m/s over a closed external circuit. Coolant enters the collecting manifolds, from where it is pumped to the heat pump, which transfers heat from the coolant to the water flowing through the pipe from the water supply system and heats it for use by consumers in the hot water system.EFFECT: lowering the temperature of the ground around the underground tunnels, increasing heat transfer through the tunnel walls, using the extracted heat for the needs of hot water supply systems.1 cl, 2 dwg

Description

1. The technical field

The invention relates to methods for using the extracted geothermal heat to cool the soils around the subway tunnels and transforming it to heat water in the hot water supply system of the underground metro premises using a heat pump.

2. The prior art

Known METHOD FOR REMOVING GEOTHERMAL HEAT [1] using a heat carrier circulating in a closed circuit, heated in a well with a temperature gradient, and cooled using a heat pump.

Bibliographic data [1]: METHOD FOR REMOVING GEOTHERMAL HEAT [Text]: pat. 2288413 ROS. Federation: F24J 3/08 (2006.01) / Nikolay Ivanovich Stoyanov (RU), Johann Arestagesovich Geyvandov (RU), Alexander Ilyich Voronin (RU); applicant and patent holder: State educational institution of higher professional education "North Caucasian State Technical University" (RU); - No. 2005113114; declared 04/29/2005; 11/27/2006 Bull. No. 33.

The use of special wells with a depth of 300 m and a diameter of 150 mm for the location of the heat pump probes is not possible during the construction and operation of the subway.

The closest solution to the technical nature and the totality of technical features is the METHOD FOR COMPLETE USE OF THE GEOTHERMAL HEAT USING THE STEAM EJECTIVE HEAT PUMP [2], which includes supplying the cooled heat carrier to the well, after which the heated heat carrier transfers heat to the consumer using a heat pump using a heat pump coolant.

Bibliographic data [2]: METHOD FOR COMPREHENSIVE USE OF GEOTHERMAL HEAT USING A VEHICLE HEAT PUMP [Text]: US Pat. 2528213 Ros. Federation: F24J 3/08 (2006.01) / Stoyanov Nikolay Ivanovich (RU), Voronin Alexander Ilyich (RU), Geyvandov Johann Arestagesovich (RU), Smirnov Stanislav Sergeevich (RU); applicant and patent holder: North-Caucasian Federal University (RU) Federal State Autonomous Educational Institution of Higher Professional Education; - No. 20111140370; declared 10/04/2011; 09/10/2014, Bull. Number 25.

The technical solution is not intended to prevent overheating of the subway tunnels during operation, heated water from the well is used in the generator of the absorption heat pump to operate the heat pump directly, and then to reheat the tap water in the DHW system preheated in the absorber. In addition, the use of an absorption (diffusion) heat pump is less effective than a compression one, since its conversion coefficient is lower due to large losses in the elements of the absorption circuit. The complexity of the design of the unit itself and the high corrosion load require the use of expensive and difficult to handle corrosion-resistant materials.

3. Disclosure of the invention

3.1. The result of solving a technical problem

It has long been known that soil is the most versatile source of dissipated heat. It accumulates solar energy and part of the excess heat generated in the tunnels. At the same time, it is able to give off heat, regardless of the weather. Indeed, at a depth of already 5-7 m, the temperature is almost constant throughout the year. For central Russia, it is 5-8 ° C. The average estimated temperature of the soil around the subway tunnels is 9-12 ° C. These are very suitable conditions for the operation of a heat pump.

In the warm season, the supply air temperature often exceeds the calculated values and additional heat enters the underground structures with the air, which increases the heat load on the soil, which does not allow direct-flow ventilation systems to assimilate the heat in the required amount and provide the normative heat and humidity mode (TVR) (temperature from 18 to 28 ° C, relative humidity 15-75% according to SP 120.13330.2012 “Metro” and SP 2.5.1337-03 “Sanitary rules for the operation of subways”).

The influence of heat from outside air and solar radiation is observed in the surface soil layer to a depth of 15 m. In addition, soils are heated by heat from absolute sources in subway tunnels.

Over a period of 10-15 years, the temperature of soils around the subway tunnels rises according to statistics by 2-3 ° C, which leads to an increase in the temperature of the air coming from the tunnels to the station platform platform.

The technical task is to increase the heat storage capacity of soils in order to avoid overheating of the tunnels during operation in order to maintain normalized meteorological conditions at the stations through the use of naturally cheap low-temperature sources.

EFFECT: lowering the temperature of soils around the subway tunnels at the station, increasing heat transfer through the walls of the tunnel, using extracted heat for the needs of domestic hot water systems.

The solution of the technical problem and the technical result are achieved due to the fact that geothermal heat is extracted from the soils surrounding the subway tunnels, with a ground low-temperature heat exchanger buried in the ground, which is a set of connected circuits made of polyethylene pipes with a diameter of 32-40 mm without butt joints. The contours are laid with flat spiral-helical turns at a depth of 2-4 m from the surface of the earth below the freezing depth around the arches of the subway tunnels in increments of 0.7-0.8 m, the diameter of the turns is 800-1000 mm. The number of circuits is determined by calculation. The length of the connected circuits is the same 100-120 m.The accumulated heat is accumulated in a coolant, which is a non-freezing thirty percent aqueous propylene glycol solution, pumped into the pipe under a pressure of 4 atm, circulating at a speed of at least 0.3 m / s in a closed external circuit. From the circuits, the coolant enters the prefabricated collectors, from where it is pumped to the heat pump evaporator. In the evaporator, the coolant transfers heat to the refrigerant circulating in the internal circuit of the heat pump, where the refrigerant boils and passes into a gaseous state, after which the refrigerant is supplied to the compressor, which compresses it to high pressure, which further increases its temperature. Hot gaseous refrigerant is supplied to the condenser, in which heat of the refrigerant is transferred to the water entering the pipe from the water supply, and heats it for use by consumers in the hot water supply system. The daily unevenness of water consumption for hot water supply is leveled with the help of storage tanks. When cooling, the refrigerant circulating in the internal circuit of the heat pump goes into a liquid state, passes through a pressure reducing valve, losing pressure, from where it is supplied to the evaporator. Then, the cooled coolant along the external circuit is returned to the pump for a new portion of heat, lowering the temperature of the soil around the subway tunnels at the station.

4. Brief Description of the Drawings

THE METHOD FOR REMOVING AND USING THE GEOTHERMAL HEAT FOR COOLING SOIL AROUND THE METRO TUNNELS is illustrated by the following drawings:

In FIG. 1 is a schematic diagram of the operation of a soil cooling system around subway tunnels (section),

In FIG. Figure 2 shows the plan of the operation of the soil cooling system around the subway tunnels, where

1 - subway tunnel; 2 - the surface of the earth; 3 - soil low-temperature heat exchanger; 4 - pump; 5 - evaporator; 6 - compressor; 7 - throttle; 8 - capacitor; 9 - DHW consumer; 10 - heat pump; 11 - the direction of movement of the coolant; 12 - axis of the tunnel; 13 - station; 14 - contour of the soil low-temperature heat exchanger; 15 - prefabricated collector soil low-temperature heat exchanger; 16 - internal circuit of the heat pump refrigerant; 17 - pipe with water coming from the water supply network.

5. The implementation of the invention

The necessary energy is extracted from low-potential (cold) sources - soils surrounding the subway tunnels (1), by an underground low-temperature heat exchanger (3), buried in the ground, enveloping the tunnel structure at a depth below the level of soil freezing.

The low-temperature ground heat exchanger (3) is a set of plug-in circuits (14) made of PE PND6 polyethylene pipes with a diameter of 32-40 mm without butt joints laid by flat spiral-screw coils at a depth of 2-4 m from the earth's surface (2) below the depth freezing over the arch of underground tunnels (1) in increments of 0.7-0.8 m, diameter of turns is 800-1000 mm. The number of circuits (14) is determined by calculation for specific tunnels. The length of the connected circuits (14) should be approximately the same for the hydraulic connection of the system and is 100-120 m.

The extracted heat is accumulated in the heat carrier. As such an energy carrier, a non-freezing environmentally friendly liquid is used - a thirty percent aqueous propylene glycol solution, pumped into the pipe under a pressure of 4 atm., Circulating at a speed of at least 0.3 m / s in a closed external circuit. From the circuits (14), the coolant enters the prefabricated collectors (15), from where it is pumped (4) to the evaporator (5) of the heat pump (10).

In the evaporator (5), the coolant transfers heat to the refrigerant (ozone-safe freon R410A) circulating in the internal circuit (16) of the heat pump (10), which boils and passes into a gaseous state.

After boiling, the refrigerant is supplied to an electric compressor (6), which compresses it to high pressure, which further increases its temperature.

Hot gaseous refrigerant is supplied to the next heat exchanger-condenser (8), in which the refrigerant gives off heat to the heat carrier - water entering the pipe (17) from the water supply system and heats it for use by consumers (9) in the domestic hot water system. The daily unevenness of water consumption for hot water supply is leveled with the help of storage tanks.

When cooling, the refrigerant circulating in the internal circuit (16) of the heat pump (10) goes into a liquid state, passes through a pressure reducing valve, losing pressure, from where it is supplied to the evaporator.

The cooled coolant along the external circuit is returned to the pump for a new portion of heat, lowering the temperature of the soil around the subway tunnels at the station.

6. Best Mode for Carrying Out the Invention

To implement the method, polyethylene pipes are laid with flat helical spirals.

The working fluid (30% aqueous propylene glycol solution) circulates through an external closed circuit through a heat pump (10) of the compressor type. Transformable heat is used to heat water for the hot water supply system in the residential premises of the subway.

Using a geothermal heat pump to cool the soil around the subway tunnels can significantly reduce the temperature of the air coming from the tunnels to the station platform.

Heat removal from each meter of linear pipe depends on many parameters: laying depth, groundwater availability, soil quality, etc. Tentatively, we can assume that for horizontal collectors it is 20 watts. m.p. More precisely: dry sand - 10, dry clay - 20, wet clay - 25, clay with a high water content - 35 watts. m.p. The difference in temperature of the coolant in the forward and reverse lines of the loop in the calculations, is taken equal to 3 ° C. No structures are being erected on the collector’s part of the metro technical zone, and the energy source is replenished with energy due to solar radiation and heat from absolute sources in the subway tunnels.

In the first few years of operation, the system enters a quasistationary mode when the temperature of the soil mass around the heat exchanger becomes 1-2 ° C lower than the initial one. Building heating systems using low-grade heat from the earth are a reliable source of energy that can be used for a long time.

The cost of operating traditional heat sources - heaters, boilers operating on various types of fuel, etc. is increasing every year, hot water is becoming more expensive. The economic benefits of using heat pumps are evident due to their high efficiency and fairly cheap operation.

The largest share of capital investment is the cost of excavation. The construction of metro stations is an open method, the versatility and ease of installation in the pit are the advantages of the method.

Since the circuit for extracting heat is closed, the following are excluded: pollution of the coolant from the soil; coolant leaks into the ground; The pump head is used only to overcome the hydraulic resistance in the system, which is comparable to the hydraulic resistance in conventional heating networks.

Claims (1)

A method of extracting and using geothermal heat for cooling soils around subway tunnels includes supplying a cooled heat carrier to the soil with a temperature gradient, transferring heat to the consumer using a heat pump operating on a refrigerant pair — a low boiling heat carrier, characterized in that geothermal heat is extracted from the soil, the surrounding subway tunnels, with a low-temperature soil heat exchanger buried in the ground, which is a sub-set contours made of polyethylene pipes with a diameter of 32-40 mm without butt joints, the contours are laid with flat spiral-helical turns at a depth of 2-4 m from the surface of the earth below the freezing depth above the arches of the subway tunnels in increments of 0.7-0.8 m, the diameter of the turns is 800-1000 mm, the number of circuits is determined by calculation, the length of the connected circuits is the same 100-120 m, the extracted heat is accumulated in the coolant, which is a non-freezing thirty percent aqueous propylene glycol solution, pumped into the pipe under 4 atm pressure, circulating at a speed of at least 0.3 m / s in a closed external circuit, the coolant enters the prefabricated collectors, from where it is pumped to the heat pump evaporator, in the evaporator the heat transfer heat to the refrigerant circulating in the internal circuit of the heat pump, where the refrigerant boils and goes into a gaseous state, after which the refrigerant is supplied to the compressor, which compresses it to high pressure, which further increases its temperature, hot gaseous refrigerant is fed to the condenser, in The heat of the refrigerant is transferred to the water entering the pipe from the water supply pipe and heats it for use by consumers in the hot water supply system, the daily unevenness of water consumption for hot water supply is leveled with the help of storage tanks, cooling down, the refrigerant circulating in the internal circuit of the heat pump goes into liquid state, passes through a pressure reducing valve, losing pressure, from where it is supplied to the evaporator, then the cooled coolant along the external circuit is returned to the pump wail portion of the heat by lowering the temperature of soil around the station subway tunnels.

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