Geothermal loop in-ground heat exchanger for energy extraction
A geothermal loop in-ground heat exchanger for energy extraction including an outer tubular casing and an inner tubular portion spaced from the outer tubular casing to define an injection space wherein a working fluid is injected into the injection space at a first temperature, T 1 while the heat exchanger is located in a geothermal heat reservoir and the working fluid exits through the inner tubular portion at a second temperature, T 2 which is greater than T 1 .
1. A geothermal loop in-ground heat exchanger for energy extraction including:
an outer tubular casing bounded by a horizontal lower wall and an inner tubular portion spaced from the outer tubular casing to define an intervening injection space between the outer tubular casing and the inner tubular portion;
wherein a working fluid is injected into the injection space at a first temperature, T 1 , while the heat exchanger is located in a geothermal heat reservoir and the working fluid exits through the inner tubular portion at a second temperature, T 2 , which is greater than T 1 ;
a counter current heat shell is provided external to the outer tubular casing to enhance heat transfer to the working fluid;
wherein the counter current heat shell is an annular shell, closed at an upper end by a transverse upper wall and having a lower end, the countercurrent heat shell bounded laterally by a vertical side wall;
a reinjection port located on the vertical side wall below the transverse upper wall of the counter current heat shell;
entry openings are spaced evenly over the length of the counter current heat shell between the lower end of the countercurrent heat shell and the reinjection port; and
wherein the reinjection port allows a heat carrier to exit the counter current heat shell and the entry openings allow the heat carrier to enter the counter current heat shell.
2. The geothermal loop in-ground heat exchanger as claimed in claim 1 wherein a well bore houses the heat exchanger into which the working fluid is injected from the ground surface into the injection space such that heat is laterally transferred from the geothermal heat reservoir across the outer tubular casing of heat exchanger to the working fluid.
3. The geothermal loop in-ground heat exchanger as claimed in claim 1 wherein the heat exchanger is sized to provide sufficient contact area with the working fluid to partially or completely vaporize the working fluid.
4. The geothermal loop in-ground heat exchanger as claimed in claim 1 wherein the inner tubular portion is partially insulated in an upper zone of the heat exchanger to mitigate heat loss to the injection space.
5. The geothermal loop in-ground heat exchanger as claimed in claim 1 wherein mechanical supports are provided between the inner tubular portion and the outer tubular casing allowing the inner tubular portion to expand and contract independently of the outer tubular casing.
6. The geothermal loop in-ground heat exchanger as claimed in claim 1 wherein a lower end of the inner tubular portion is open and spaced from the horizontal lower wall of the outer tubular casing in order to provide an inversion space to allow the working fluid to enter the inner tubular portion from the injection space.
7. The geothermal loop in-ground heat exchanger as claimed in claim 1 wherein the counter current heat shell is a cylindrical shape.
8. The geothermal loop in-ground heat exchanger as claimed in claim 1 wherein the reinjection port is coupled to an elongate conduit in order to return spent or depleted heat carrier to the geothermal heat reservoir.
9. The geothermal loop in-ground heat exchanger as claimed in claim 8 wherein the elongate conduit extends laterally away from the heat exchanger and is shaped to reinject the spent or depleted heat carrier into a portion of the geothermal heat reservoir.
10. The geothermal loop in-ground heat exchanger as claimed in claim 9 provided with more than one reinjection portion and elongate conduit in order to allow an operator to shift a reinjection location and/or depth in order to maintain a useable heat gradient in the geothermal heat reservoir.
11. The geothermal loop in-ground heat exchanger as claimed in claim 1 further including an expanded lower heat shell portion in addition to the counter current heat shell, the expanded lower heat shell portion extending generally downwardly from the counter current heat shell at the bottom of the heat exchanger.
12. The geothermal loop in-ground heat exchanger as claimed in claim 11 wherein the expanded lower heat shell portion is a closed shell in communication with the counter current heat shell and having entry openings spaced over the length of the expanded lower heat shell portion allowing the heat carrier to enter the lower heat shell portion.
13. A method of energy extraction from a geothermal heat reservoir including the steps of:
providing a geothermal loop in-ground heat exchanger having an outer tubular casing bounded by a horizontal lower wall and an tubular portion spaced from the outer tubular casing to define an injection space;
providing a counter current heat shell external to the outer tubular casing to enhance heat transfer to a working fluid;
wherein: the counter current heat shell is an annular shell closed at an upper end by a transverse upper wall and having a lower end, and bounded laterally by a vertical side wall,
a reinjection port located on the vertical side wall below the transverse upper wall of the counter current heat shell allowing a heat carrier to exit the counter current heat shell, and
entry openings are spaced evenly along the counter current heat shell between the reinjection port and the lower end of the countercurrent heat shell, the entry openings allowing the heat carrier to enter the counter current heat shell;
locating at least a portion of the heat exchanger in a geothermal heat reservoir;
injecting a working fluid at a first temperature, T 1 , into the injection space; and
drawing off the working fluid from the inner tubular portion at a second temperature, T 2 , greater than T 1 .
14. The method of energy extraction from a geothermal heat reservoir as claimed in claim 13 including the additional steps of: utilizing the heat of the working fluid at the second temperature, T 2 , in an appropriate thermodynamic recovery cycle in order to capture energy from the working fluid; and returning the working fluid to the heat exchanger at a temperature lower than the second temperature, T 2 .
15. The method of energy extraction from a geothermal heat reservoir as claimed in claim 13 wherein if a naturally occurring geothermal heat reservoir does not containing at least 10 percent fluid by volume, the method further includes the step of injecting a fluid into the reservoir to provide at least 10 percent water by volume to maintain adequate heat transfer from the reservoir to the outer tubular casing.
16. The method of energy extraction from a geothermal heat reservoir as claimed in claim 13 further including the step of stimulating the geothermal heat reservoir in order to encourage heat flow about the heat exchanger.
17. The method of energy extraction from a geothermal heat reservoir as claimed in claim 16 wherein sequenced stimulation of particular heat zones in multiple steps is used in order to provide a systematic and more sustainable heat gradient.