Steam power plant with a ground heat exchanger

Abstract

A Steam power plant comprising a steam turbine (3) and a condenser (5), wherein the condenser (5) is disclosed, comprising a first heat sink being a ground heat exchanger (29) is connected to the condenser during times when ground temperature is lower than air temperature; and a second heat sink being an above-ground heat exchanger is connected to the condenser during times when ground temperature is not lower than air temperature.

Claims

1. A steam power plant comprising: a steam turbine; a condenser; a first heat sink; and a second heat sink, wherein the first heat sink is a ground heat exchanger and the second heat sink is an above-ground heat exchanger, wherein the steam power plant is operational in at least two modes: an operational mode with the first heat sink and second heat sink connected in a serial connection with the condenser; and another operational mode with the first heat sink in both fluid and thermal communication with the condenser when a ground temperature is less than an air temperature and with the second heat sink in both fluid and thermal communication with the condenser when the ground temperature is not less than the air temperature.

2. The steam power plant according to claim 1, wherein the ground heat exchanger is vertically or horizontally oriented.

3. The steam power plant according to claim 1, wherein the above-ground heat exchanger is an indirect cooling system.

4. The steam power plant according to claim 1, wherein the steam power plant comprises at least one solar collector.

5. The steam power plant according to claim 4, wherein the least one solar collector is installed above the ground heat exchanger.

6. A method for operating a steam power plant comprising a water-steam-cycle, a steam turbine and a condenser for condensing the steam escaping from the steam turbine, the method comprising the steps of: providing a heat carrier fluid from the condenser to a first heat sink comprising a ground heat exchanger and to a second heat sink comprising an above-ground heat exchanger; and operating the steam power plant in at least two modes: an operational mode with the first heat sink and second heat sink connected in a serial connection with the condenser; and another operational mode with the first heat sink fluidly connected to the condenser when a ground temperature is lower than an air temperature and the second heat sink fluidly connected to the condenser when the ground temperature is not lower than the air temperature.

7. The method according to claim 6, wherein the above-ground heat exchanger is a cooling tower, and that the condenser is directly or indirectly coupleable to the cooling tower.

8. A cooling system for a steam power plant comprising: a condenser; a first heat sink comprising a ground heat exchanger; and a second heat sink comprising an above-ground heat exchanger; wherein the steam power plant is operational in at least two modes: an operational mode with the first heat sink and second heat sink connected in a serial connection with the condenser; and another operational mode with the first heat sink in thermal communication with the condenser during times when a ground temperature is lower than an air temperature and with the second heat sink in thermal communication with the condenser when the ground temperature is not lower than the air temperature.

9. The system of claim 8, wherein the above ground heat exchanger provides indirect cooling.

10. The system of claim 8, wherein the ground heat exchanger is a vertically aligned ground heat exchanger.

11. The system of claim 8, further comprising: at least one solar collector; wherein the at least one solar collector provides thermal energy to the steam power plant and shadows the ground surrounding the ground heat exchanger to minimize the penetration of solar radiation into the ground.

12. The system of claim 11, wherein the at least one solar collector is a parabolic trough solar collector.

13. The steam power plant according to claim 1, wherein the steam power plant comprises a plurality of solar collectors, the solar collectors disposed above the ground heat exchanger and being configured to shadow the ground surrounding the ground heat exchanger to minimize the penetration of solar radiation into the ground.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 A circuit diagram of a conventional steam power plant and

(2) FIGS. 2 and 3 embodiments of steam power plants according to the invention.

DETAILED DESCRIPTION

(3) In FIG. 1 a steam power plant is represented as block diagram. The steam power plant can be designed as conventional steam power plant fuelled with fossils or with biomass. Alternatively the steam power plant can be designed as solar-thermal steam power plant where the energy supplied to the water-steam-cycle is generated in a collector field (cf. FIG. 2) out of solar radiation. The invention can also be used for hybrid forms, where the required energy is provided by combustion of fossil and/or organic fuels and, if available, by solar collectors.

(4) FIG. 1 essentially serves for designating the individual components of the power plant and representing the overall context of the water-steam-cycle, as for clarity-reasons in the following figures only the parts of the water-steam-cycle essential to the invention are represented.

(5) In a steam generator 1 utilizing fossil fuels or biomass out of the feed water live steam is generated, which is expanded in a steam turbine 3 and thus drives a generator G. The turbine 3 can be separated into a high-pressure part HD, a medium-pressure part MD and several low-pressure parts ND.

(6) After expanding the steam in the turbine 3, it streams into a condenser 5 and is liquefied therein. For this purpose a cooling medium, as e. g. cooling water, is conveyed to the condenser 5. This cooling water is cooled in a cooling tower (not represented) or by a river in the vicinity of the power plant (not represented), before it enters the condenser 5.

(7) The condensate generated in the condenser 5 is conveyed by a condensate pump 7 to several preheaters VW.sub.1, with i=1 . . . n. In the shown embodiment a feed water tank 8 is arranged after the second preheater VW.sub.2. After the feed water tank 8 a feed water pump 9 is provided.

(8) In the context of the invention it is of significance that the condensate out of the condenser 5 is preheated with steam beginning in the first preheater VW.sub.1 to the last preheater VW.sub.5. Wherein the temperature of the condensate resp. feed water increases from preheater to preheater and correspondingly the temperature of the steam used for preheating also has to increase.

(9) In the represented example the preheater VW.sub.5 is heated with steam from the high-pressure part HD of the steam turbine 3, whereas the first preheater VW.sub.1 is heated with steam from the low-pressure part ND of the steam turbine 3.

(10) The third preheater VW.sub.3 arranged in the feed water tank 8 and the forth preheater VW.sub.4 are heated with steam from the medium-pressure part MD of the turbine 3.

(11) When in the represented water-steam-cycle solarly generated energy/heat is injected, this energy can be injected everywhere in the water-steam-cycle between the condenser 5 and the steam turbine 3. The claimed invention is concerned with the heat dissipation from the condenser 5 and is therefore independent of the details of the water-steam-cycle.

(12) In FIG. 2 the condenser 5 from FIG. 1 is shown. The condenser 5 is connected to a further heat exchanger in the form of a cooling tower 25 via a feed line 21 and a return line 23. In the feed line 21 as well as the return line 23 a heat carrier circulates, as e. g. water, being conveyed by a pump 27. This system is a so-called indirect air cooling; indirect for the reason that the condensation heat emitted in the condenser 5 is transported via the heat carrier circulating in the lines 21 and 23 to the cooling tower 25 and there emits its heat to the ambient air.

(13) According to the invention it is now provided that additionally or alternatively to the cooling tower 25 a ground heat exchanger 29 is arranged in the direct vicinity of the steam power plant. The ground heat exchanger 29 according to the invention is only shown schematically in FIGS. 2 and 3. They can be any kind of ground heat exchanger, either ground heat exchangers vertically driven into the ground, as they are e. g. known for heating buildings or as heat source for heat pump installations. Alternatively it is also possible to design the ground heat exchanger 29 as more or less plane construction being arranged in a constant distance of e. g. 5 m in the ground below the surface.

(14) All embodiments have in common that the ground heat exchanger 29 is streamed through by the heat carrier circulating in the feed line 21 and the return line 23 and thus emits heat to the ground surrounding the ground heat exchanger 29.

(15) In FIG. 2 a method of operation is shown wherein the further heat exchanger 29 resp. the cooling tower 25 and the ground heat exchanger 29 according to the invention are connected in series.

(16) The heat carrier leaves the condenser 5 with a temperature T3. The heat carrier with the temperature T3 is cooled to a temperature T1 in the cooling tower 25. Then the heat carrier streams into the ground heat exchanger 29 according to the invention with this temperature T1 as entry temperature and therein is further cooled to a temperature T2. The temperature T2 is lower than the temperature T1, as the heat carrier in the ground heat exchanger 29 emits heat to its surrounding ground. With the temperature T2 the heat carrier re-enters the condenser 5 and therein absorbs the condensation heat of the steam leaving the steam turbine 3. As the temperature T2 with which the heat carrier enters the condenser 5 due to the serial connection is lower than the exit temperature T1 of the heat carrier out of the cooling tower 25, the degree of efficiency of the power plant is increased.

(17) Exemplary values for the temperatures T1 to T3 are enlisted in the following:

(18) T1 40° C. to 45° C.

(19) T2 35° C. to 40° C.

(20) T3 50° C. to 55° C.

(21) ΔT.sub.K: Temperature increase of heat carrier in condenser

(22) TL: Ambient Air Temperature and

(23) G.sub.T: Temperature difference in cooling tower

(24) By means of FIG. 2 it is indicated that the power plant according to the invention can also comprise a field of solar collectors 31 which are schematically designed as parabolic trough solar collectors. On the one hand these solar collectors 31 contribute to the reduction or complete compensation of the demand of fossil fuels or biomass as fuel. At the same time however concerning the ground heat exchanger 29 according to the invention they have the advantage of shadowing the ground surrounding the ground heat exchanger 29 and thus preventing resp. minimizing the penetration of solar radiation into the ground undesirable in this case.

(25) In FIG. 3 an alternative operation mode is represented. With this operation mode according to FIG. 3a the heat carrier is exclusively cooled via the ground heat exchanger according to the invention and the cooling tower 25 is not active. This signifies that the degree of efficiency of the ground heat exchanger 29 according to the invention with otherwise identical conditions must generally be somewhat larger in order to be able to provide the temperature T2 of the heat carrier.

(26) This operation condition e. g. can be sensible when the outer temperatures are very high so that a nameable contribution of the cooling tower 25 for the emission of the condensation heat cannot take place. Generally in sunny regions this will be the case in daytime.

(27) In FIG. 3b the operation during the night resp. with low outer temperatures is shown. In this case the condenser 5 is exclusively connected with the cooling tower 25 and the ground heat exchanger 29 according to the invention is not active. During these times, which generally occur at night, the ground surrounding the ground heat exchanger 29 can cool again. Thus the efficiency of the ground heat exchanger 29 for the following day is reestablished.

(28) Of course hybrid forms of the operation modes represented according to the FIGS. 2 and 3 are also possible. Especially it is also possible to use the ground heat exchanger 29 according to the invention predominantly in hot seasons and to regenerate in the cold season by not operating it. Then over weeks or even months the ground surrounding the ground heat exchanger 29 can emit heat to further distant regions and to the ambience through the surface of the ground. Thus the temperature of the ground sinks and the efficiency of the ground heat exchanger 29 according to the invention is reestablished.

(29) Alternatively to the described follow-up variation it is possible under circumstances, to select the ground cooling as sole cooling-method. In this case a conventional cooling is dispensed with and only the ground heat exchanger serves as heat sink for condensation. In this case as cooling medium the water of a secondary cycle or air is imaginable.

(30) Depending on the local situation and the regional temperature profile in the ground the ground heat exchanger can also be designed two-dimensionally with rather horizontal orientation or going into the deep.

(31) If necessary, the ground cooling can also be used for conventional power plants in regions with a high temperature difference between day and night (subtropical climate). In the day heat the ground is used for cooling and at night the power plant is operated by surrounding air-cooling and the ground can cool down.