RU2288413C1 - Method of using geothermal heat - Google Patents

Abstract

FIELD: heat supply systems.

SUBSTANCE: method comprises supplying cooled heat-transfer agent to the casing pipe by means of the heat pump and rising the heated heat-transfer agent in the tube mounted concentrically in the casing pipe.

EFFECT: enhanced environmental protection and reduced cost.

1 cl, 1 dwg

Description

The invention relates to methods for extracting and using geothermal heat, in particular, extracting heat from dry deep rocks.

A known method of extracting heat from the bowels of the earth by using geothermal sources / Dvorov I.M., Dvorov V.I. Thermal waters and their use. M., Enlightenment, 1976. - 128 p., Nathanov H.Kh. Preparation of geothermal water for use. M., Stroiizdat, 1980 .-- 80 p. /.

The disadvantages of this method are: geothermal sources are located in places of increased geological activity, in which construction is limited, which complicates their use; high salinity of geothermal waters, which leads to deposits on the surfaces of heat-using equipment; environmental pollution around the well with mineralized geothermal waters; high pressure at the wellhead, which increases the cost of equipment.

There is also a method of extracting heat from the bowels of the earth by creating a thermal "boiler", in which two wells are drilled at a certain distance from each other and using an nuclear explosion they create an artificial cavity between them / Dvorov I.M., Dvorov V.I. Thermal waters and their use. M., Enlightenment, 1976.- 128 p. /. Cold water is injected into one of the wells, and heat transfer in the form of steam or hot water to the consumer is discharged through the other. With this method of heat recovery, the well can be located near the heat consumption object.

The disadvantages of this method are: the possibility of contamination of the coolant and its loss due to leaks; high cost of implementing the method.

Closest to the proposed method is the extraction of geothermal heat, including the drilling of two wells, the hydraulic connection between which is ensured by the convergence of their lateral branches of the wells for the formation of connecting zones of crushing and cracking. When moving through wells and when filtering in the connecting zones, the injected water is heated as a result of contact with a high-temperature rock mass and is brought to the surface through the well and delivered to the consumer / Dvorov I.M., Dvorov V.I. Thermal waters and their use. M., Enlightenment, 1976. - 128 p., Nathanov H.Kh. Preparation of geothermal water for use. M., Stroiizdat, 1980. - 80 pp., Internal sanitary-engineering devices. At 3 h. 4.1. Heating / V.N.Bogoslovsky, B.A. Krupnov, A.N. Skanavi and others; Ed. I.G. Staroverova and Yu.I. Schiller. M., Stroyizdat, 1990 .-- 344 p. /.

The disadvantages of this method are: the possibility of contamination of the coolant and its loss due to leaks; high cost of implementing the method.

The technical result of the claimed invention is to increase environmental friendliness and reduce the cost of extracting geothermal heat.

The specified technical result is achieved in a method of extracting geothermal heat from a well with a temperature gradient through the casing using a heat carrier circulating in the circuit and used for heat supply needs, in that the heat carrier cooled by means of a heat pump is supplied to the casing, and the heated one rises along concentrically lowered into the casing pipe and transfers heat to the consumer.

In the warm period, the consumer uses heat for the needs of cold supply.

The drawing shows a diagram of a device for extracting heat from the bowels of the earth by the proposed method. The scheme includes the following elements: well with casing 1; lifting pipe 2; heat pump 3; heat consumer 4; cold consumer 5.

The method is as follows.

Chilled water from the consumer with a temperature of t _{2 is} fed through the annulus to the well. Water is heated from the walls of the casing, and then heated to a temperature of t ₁ - is supplied to the consumer. Since the temperature of the heated water t ₁ , depending on the temperature gradient, may not be high enough for direct use in the heat supply system, the use of a heat pump can increase the heat transfer of the well by lowering the temperature of the return water t ₂ pumped into the well. This eliminates the need for thermal insulation of the head of the well (in the prototype, the wells are insulated to a depth of 300 m to prevent heating of the upper layers of the earth's crust). The well is intended for year-round use: in the cold period - for production needs and household (heating, ventilation and hot water supply); in the warm period - for industrial needs, household (hot water) and cold supply. Because the circuit for extracting heat is closed, the following are excluded: pollution of the coolant from the soil; coolant leak into the ground. It is not necessary to create pressure with a pump for pumping coolant into the reservoir; 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.

An example implementation of the method.

For an example of the method, a mathematical model and calculation program are developed. The calculation was made for well No. 6 s. Praskoveyskoe Stavropol Territory.

Mathematical model.

To develop a mathematical model, the following assumptions are made:

- The earth is considered as a sphere with a hard shell;

- within the local geothermal zone has constant values of the heat flux density q and geothermal potential grad T;

- the model can be considered without taking into account the curvature of the solid.

The equations of heat transfer and heat balance in partial derivatives:

where Q ₁ is the amount of heat received by the coolant moving in the annulus from the soil per unit time;

Q ₂ - the amount of heat received by the coolant moving in the annulus from the coolant moving along the inner pipe;

K _1i , K _2i - heat transfer coefficients through the walls of the outer and inner pipes;

Θ _1i , Θ _2i - temperature head, determined by the formulas:

t _gri - soil temperature at the border of contact with the outer pipe;

t _2i is the temperature of the coolant in the annulus;

t _1i is the temperature of the coolant in the inner pipe;

m and C _p1 , C _p2 - mass flow rate and heat capacity of the coolant in the annulus and in the inner pipe;

W ₁ , W ₂ - water equivalents.

According to the law of conservation of energy when cooling an elementary volume of soil with an internal heat source

where q is the density of the geothermal heat flux;

ρ _gri , C _gri - soil density and its heat capacity;

r is the current cylindrical coordinate of the heat-affected zone of the well;

dτ is an infinitesimal period of time equal to

f ₁ , f ₂ - the cross-sectional area of the annular space and the inner pipe;

ρ ₁ , ρ ₂ is the density of the coolant in the annulus and in the inner pipe;

- изменение температуры грунта во времени, определяемое из дифференциального уравнения теплопроводности:

- change in soil temperature over time, determined from the differential heat equation:

- коэффициент температуропроводности грунта;

- coefficient of thermal diffusivity of the soil;

λ _gri is the thermal conductivity of the soil;

dr is the elementary increase in the heat-affected zone of the well during the time dτ.

To solve the equation, it is necessary to establish the boundary conditions.

The temporary boundary conditions are the values:

τ = 0 and

At τ = 0, the initial conditions will be as follows:

- return water temperature - t ₂ ;

- the initial distribution of soil temperature along the depth of the well t _gri = (z _i -L _n ) · grad T + 15 ° С;

for z _i = L, t _2i = t _1i , a Θ _2i = 0;

for t _2i = t _gri , Θ _1i = 0.

At τ _n → ∞, Q ₁ = qπr ² and the stationary mode of heat transfer from the soil to the well is established.

Calculation results

Well Depth L, m 3600 Well thermal power Q, kW 398.8 Water temperature t ₁ , ° С 59

When using a heat pump with lowering the temperature of the return water to 15 ° C, the thermal power of the well increases to 3.2 MW.

For the refrigeration system, absorption or steam-ejection refrigerators are used that carry out the “direct” conversion of heat into cold.

Claims (2)

1. A method of extracting geothermal heat from a well with a temperature gradient through the casing using a heat carrier circulating in the circuit and used for heat supply needs, characterized in that the coolant cooled by means of a heat pump is supplied to the casing, and the heated one rises along a concentrically lowered into casing pipe and transfers heat to the consumer. 2. The method according to claim 1, characterized in that the geothermal heat is used in the warm period for cold supply needs.