Power plant for generating electrical energy and method for operating a power plant

Abstract

A power plant for generating electrical energy comprises at least a heat storage device (100) for storing electrical energy in heat energy, comprising: an electrical heater (10) for converting electrical energy in heat energy; a heat storage body (30, 31) for receiving and storing heat energy of the electrical heater (10); a heat exchanger (50) for receiving heat energy from the heat storage body (30, 31). The power plant further comprises a turbine (120) and a generator (123). A heat storage fluid circuit (130) connects to the heat exchanger (50) or the heat exchangers (50) and a working fluid circuit (140) connects to the turbine (120). A fluid circuit heat exchanger (131) transfers heat from the heat storage fluid to a working fluid in the working fluid circuit (140).

Claims

1. A power plant for generating electrical energy, comprising: at least one heat storage device for storing electrical energy as heat energy, including at least one heat storage unit, wherein each of the at least one heat storage unit comprises: an electrical heater for converting electrical energy into heat energy; at least one heat storage body for receiving and storing heat energy from the electrical heater; a heat exchanger for receiving heat energy from the at least one heat storage body, wherein the heat exchanger comprises heat exchanger tubes for guiding a heat storage fluid; a first turbine; a generator coupled with the first turbine for generating electrical energy from a rotational movement provided by the first turbine; a heat storage fluid circuit which is connected with the heat exchanger tubes of the heat exchanger of the at least one heat storage device; a working fluid circuit which is connected with the first turbine; a first fluid circuit heat exchanger for transferring heat from the heat storage fluid to a working fluid in the working fluid circuit; a second turbine and a second fluid circuit heat exchanger; the second turbine is coupled with the generator to drive the generator; the first turbine is arranged downstream of the first fluid circuit heat exchanger in the working fluid circuit; the second fluid circuit heat exchanger is arranged downstream of the first turbine; the second turbine is arranged downstream of the second fluid circuit heat exchanger; the first and the second fluid circuit heat exchangers are arranged in the heat storage fluid circuit in two lines which are parallel to each other; further comprising a control device in the heat storage fluid circuit which is configured to variably set distribution of the heat storage fluid to the first fluid circuit heat exchanger and/or the second fluid circuit heat exchanger.

2. The power plant of claim 1, further comprising a first bypass along the first fluid circuit heat exchanger in the working fluid circuit to guide working fluid to the first turbine, bypassing the first fluid circuit heat exchanger, and a first bypass control device configured to variably set distribution of the working fluid to the first fluid circuit heat exchanger and/or to the first bypass.

3. The power plant of claim 1, further comprising a second bypass along the second fluid circuit heat exchanger in the working fluid circuit to guide working fluid to the second turbine, bypassing the second fluid circuit heat exchanger, and a second bypass control device configured to variably set distribution of the working fluid to the second fluid circuit heat exchanger and/or to the second bypass.

4. The power plant of claim 1, further comprising an electrical control unit configured to variably set whether momentarily more electrical energy is taken from an external power grid through the electrical heater of the at least one heat storage device or whether more electrical energy is output to the external power grid by the generator.

5. The power plant of claim 1, the at least one heat storage device comprising a plurality of heat storage devices of which at least some are arranged parallel to each other such that the corresponding heat exchanger tubes are parallel to each other in the heat storage fluid circuit.

6. The power plant of claim 1, the at least one heat storage device comprising a plurality of heat storage devices of which at least some are serially arranged such that the corresponding heat exchanger tubes are serially arranged in the heat storage fluid circuit.

7. The power plant of claim 6, the serially arranged heat storage devices including an anterior heat storage device and a posterior heat storage device, the power plant further comprising a control device configured to operate the anterior heat storage device over a larger temperature range than the posterior heat storage device.

8. The power plant of claim 6, wherein an anterior heat storage device of the serially arranged heat storage devices comprises more heat storage units than a posterior heat storage device of the serially arranged heat storage devices.

9. A method for operating a power plant to generate electrical energy, the method comprising the following steps: converting electrical energy into heat energy with an electrical heater of a heat storage unit of at least one heat storage device; receiving and storing heat energy of the electrical heater with at least one heat storage body of the heat storage unit; transferring heat energy of the at least one heat storage body to a heat storage fluid by a heat exchanger which comprises heat exchanger tubes for guiding the heat storage fluid; guiding the heat storage fluid along a heat storage fluid circuit which comprises a first fluid circuit heat exchanger and a second fluid circuit heat exchanger which are parallel to each other; transferring heat energy from the heat storage fluid to a working fluid, by the first fluid circuit heat exchanger and/or the second fluid circuit heat exchanger; guiding the working fluid in a working fluid circuit to a first turbine for driving the first turbine and to a second turbine for driving the second turbine, wherein the first turbine is located downstream from the first fluid circuit heat exchanger in the working fluid circuit, the second turbine is located downstream from the second fluid circuit heat exchanger in the working fluid circuit, and the second fluid heat exchanger is located downstream of the first turbine; generating electrical energy from a rotational movement provided by the first turbine and the second turbine by a generator coupled with the first turbine and the second turbine, wherein the second turbine drives the generator.

10. The method of claim 9, further comprising at least the following steps: operating a working fluid pump to pressurize the working fluid in the working fluid circuit; operating a heat storage fluid pump to pressurize the heat storage fluid in the heat storage fluid circuit; operating the working fluid pump and the heat storage fluid pump such that the pressure of the working fluid is higher than the pressure of the heat storage fluid.

11. The method of claim 9, further comprising at least the following steps: guiding the heat storage fluid in liquid form to and through the at least one heat storage device, wherein the heat storage fluid is not vaporized; guiding the working fluid through the first fluid circuit heat exchanger and/or the second fluid circuit heat exchanger, wherein the working fluid is vaporized.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further characteristics and advantages of the invention are described in the following with reference to the attached schematic figures.

(2) FIG. 1 shows a heat storage device of a power plant of the invention in a perspective view.

(3) FIG. 2 shows the heat storage device of FIG. 1 in a sectional view.

(4) FIG. 3 shows an exemplary embodiment of a power plant of the invention, comprising the heat storage device of the FIGS. 1 and 2.

(5) Similar and similarly acting components are generally indicated in the Figures with the same reference signs.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) An exemplary embodiment of a power plant 110 of the invention is schematically shown in FIG. 3.

(7) The power plant 110 comprises a first turbine 120 and may comprise a second turbine 121 or also further turbines (not depicted). The turbines 120, 121 are driven by a working fluid passing through the turbines. The working fluid may be a vapor, for example water vapor. A generator 123 is coupled with the turbines 120, 121 and converts the rotational energy which is provided by the turbines 120, 121 into electrical energy. The electrical energy is then output to an external power grid.

(8) The power plant 110 is used to reduce variations in the amount of electrical energy in the external power grid. To this end, the power plant 110 shall take electrical energy from the external power grid in particular if there is an oversupply. In case of an oversupply, electricity costs may temporarily be very low or even negative, rendering the intake of electrical energy almost cost-free or in some cases even lucrative as such. The received electrical energy shall be stored in the power plant 110 and output again as electrical energy at another time. An electrical control unit 150 is configured to variably set whether momentarily more electrical energy is taken from the external power grid by the electrical heater(s) 10 (only a single control connection is illustrated for clarity) or more electrical energy is output to the external power grid through the generator 123.

(9) For this temporary energy storage, the power plant 110 comprises at least one heat storage device 100. In the example of FIG. 3, several heat storage devices 100 are provided. A heat storage device 100 is shown in more detail in the perspective view of FIG. 1 and in the sectional view of FIG. 2. Each heat storage device 100 comprises at least one, preferably several, heat storage units 1 which are stacked on top of each other. Each heat storage unit 1 comprises an electrical heater 10. The electrical heater 10 converts electrical energy into heat energy, preferably substantially completely, i.e., more than 90% of the energy consumed by the electrical heater 10 is converted into heat energy. The electrical energy is received from the external power grid. Each heat storage unit 1 furthermore comprises at least one, in particular exactly two, heat storage bodies 30, 31. These may be metal bodies or metal plates which serve for storing heat energy. The heat storage bodies 30, 31 are arranged next to the electrical heater 10 to receive heat energy from the electrical heater 10. Each heat storage unit finally also comprises a heat exchanger 50 comprising several heat exchanger pipes/tubes 51. Each heat exchanger 50 neighbors at least one of the heat storage bodies 30. In this way, heat energy is transferred from the heat storage body 30 to the heat exchanger pipes and a heat storage fluid transported therein. Through a distributor pipe 45, the heat storage fluid is distributed to the different heat exchangers 50. After passing through the heat exchanger 50, the parts of the heat storage fluid are joined in a collector pipe 55.

(10) The heat energy of the heat storage fluid may now be used to generate electrical energy. As an essential idea of the invention, the heat storage fluid is, however, not led through the turbines 120, 121. Rather, the heat from the heat storage fluid is transferred to another working fluid which is transported in a separate circuit, i.e., the working fluid circuit 140. The heat storage fluid circulates in its own circuit, i.e., the heat storage fluid circuit 130.

(11) This overcomes several disadvantages which would occur if only one circuit were used: Water vapor is often used for driving the turbines; if water were used as the heat storage fluid, it would be vaporized by the heat storage units. With such a phase transition, particularly large amounts of heat energy are taken from the heat storage unit at the edge of the heat storage unit (i.e., its entrance region at which heat storage fluid reaches the heat storage unit). In this way, the heat storage would be unevenly discharged and material wear would be significant. Furthermore the pressure of the fluids at the turbine must be relatively high. With a single circuit this would have the consequence that all lines to the heat storage units must also be designed for higher pressures. The temperature of the heat storage fluid also depends on the momentary temperature of the heat storage units and thus varies. Turbines have, in contrast, a maximal efficiency only for specific temperature/pressure characteristics of the impinging fluids.

(12) These disadvantages are completely or at least partially overcome by using two distinct circuits, i.e., the working fluid circuit 140 and the heat storage fluid circuit 130.

(13) A heat storage fluid pump 125 is arranged in the heat storage fluid circuit 130 to circulate the heat storage fluid in the circuit 130. Furthermore, a working fluid pump 145 is arranged in the working fluid circuit 140 to circulate the working fluid in the circuit 140. The working fluid pump 145 provides a significantly higher pressure than the heat storage fluid pump 125; the pressure may be, for example, at least 10 times as large.

(14) The heat storage fluid may have a higher boiling point than the working fluid so that the heat storage fluid is liquid and not vaporized with heat from the heat storage units. By contrast, the working fluid is vaporized by heat energy from the heat storage fluid and, after passing the turbines 120, 121, it is liquified in a condenser 124. The condenser 124 may comprise, as shown, a heat exchanger through which heat from the working fluid is removed, for example to a liquid which may then be further used, for example for heating purposes. By not vaporizing the heat storage fluid, the above-described disadvantage is avoided that a vaporization abruptly takes large amounts of energy from a part of the heat storage body 30. The heat storage fluid may, for example, be an oil whereas the working fluid may be water or an aqueous solution.

(15) For transferring heat energy from the heat storage fluid to the working fluid, at least a first fluid circuit heat exchanger 131 is provided. In the depicted example, also a second fluid circuit heat exchanger 132 is provided. Through each of these heat exchangers 131, 132, working fluid and separately thereto also heat storage fluid is guided, wherein the respective pipes are thermally coupled to each other for a high heat transfer. A control device 133 is provided in the heat storage fluid circuit 130, which is configured to variably set how heat storage fluid is distributed to the first fluid circuit heat exchanger 131 and the second fluid circuit heat exchanger 132.

(16) The first fluid circuit heat exchanger 131 is arranged upstream of the turbine 120 with regard to the working fluid circuit 140. The second fluid circuit heat exchanger 132 is, by contrast, arranged between the two turbines 120, 121 with regard to the working fluid circuit 140. The working fluid circuit 140 includes a first bypass 141 along the first fluid circuit heat exchanger 131 to guide working fluid to the first turbine 120, bypassing the first fluid circuit heat exchanger 131. A first bypass control device 143 is configured to variably set how working fluid is split towards the first fluid circuit heat exchanger 131 and the first bypass 141. The working fluid circuit 140 includes a second bypass 142 along the second fluid circuit heat exchanger 132 to guide working fluid to the second turbine 121, bypassing the second fluid circuit heat exchanger 132. A second bypass control device 144 is configured to variably set to which parts working fluid is guided to the second fluid circuit heat exchanger 132 and to the second bypass 142.

(17) The two fluid circuit heat exchangers 131, 132 may be arranged parallel to each other with regard to the heat storage fluid circuit 130. A line of the heat storage fluid may fork into two lines 135, 136 before the two fluid circuit heat exchangers 131, 132, wherein the two lines 135, 136 lead through one of the two fluid circuit heat exchangers 131, 132, respectively. Thereafter the two lines 135, 136 merge.

(18) As depicted, at least some of the heat storage devices 100 may be arranged in lines that are parallel to each other. This has the advantage that the heat storage devices 100 arranged parallel to each other are basically similarly discharged, i.e., in particular basically similar amounts of energy are transferred to the passing heat storage fluid. This avoids that a heat storage device 100 reaches a maximal temperature and is thus not able to receive and store further energy from the external power grid, while others of the heat storage devices 100 are further below their maximal temperature. If many of the heat storage devices 100 are able to receive electrical energy simultaneously, a maximal possible intake of electrical energy is advantageously larger.

(19) Furthermore, some of the heat storage devices 100 may be arranged in the heat storage fluid circuit 130 one after the other so that heat storage fluid passes through them consecutively. Here, the discharge (i.e., the heat transfer to the heat storage medium) varies for the consecutively arranged heat storage devices 100. However, this arrangement also has advantages: The heat storage fluid should not fall below a minimal temperature (low temperature threshold), resulting in a minimal temperature for a heat storage device 100. However, it is desirable that a minimal temperature of the heat storage device 100 is low as this increases a possible temperature difference of the heat storage device 100 and thus increases its storage capacity. If two or more heat storage devices 100 are arranged behind each other, they can be operated with different minimal temperatures. An anterior (front) heat storage device of these heat storage devices 100 may have a lower minimal temperature than a posterior (back) heat storage device of these heat storage devices 100. The posterior heat storage device 100 ensures a desired minimal temperature/low temperature threshold of the heat storage fluid. The anterior heat storage device 100, by contrast, may be operated over a very large temperature range (i.e., over a larger temperature range than the posterior heat storage device 100) and thus has a particularly high storage capacity. Alternatively or in addition, also the respective maximal temperatures of the consecutively arranged heat storage devices 100 may be different.

(20) In other words, a control device may be provided and configured to operate an anterior heat storage device 100 of the consecutively arranged heat storage devices 100 over a larger temperature range than a posterior heat storage device 100.

(21) In addition to the temperature range of the heat storage body 30, i.e., the range between the minimal and maximal temperatures used in operation, also the total mass of their heat storage bodies 30 is relevant for the total storage capacity of a heat storage device 100. If a posterior heat storage device 100 of several consecutively arranged heat storage devices is in any case only operated over a smaller temperature range, it is expedient if the mass of its heat storage bodies is chosen smaller than the mass of the heat storage bodies of the anterior heat storage device 100. This may be realized, for example, in that the anterior heat storage device comprises more heat storage units than the posterior heat storage device; apart from that, the heat storage units of the anterior and the posterior heat storage devices 100 may be similar.

(22) In addition to the depicted components, the power plant 110 may also comprise a burner for a (fossil) energy carrier, for example for burning coal, natural gas or syngas. The heat thus released may also be transferred to the working fluid or the heat storage fluid. Provision may be made to control a power of the burner dependent of an electrical power consumption/intake by the electrical heater 10. Electrical power is consumed in particular (or exclusively) if there is an oversupply of electrical energy. During such periods it is thus desirable if less electrical energy is generated and the power of the burner is accordingly reduced. The power of the burner can thus be decreased to a reduced value when the heat storage devices 100 are charged, in particular when their electrical power intake surpasses a predefined threshold. By contrast, the power of the burner is not decreased to the reduced value but is maintained at a higher value if the power intake by the electrical heater does not surpass the threshold.

(23) With the power plant of the invention, large amounts of electrical energy may be stored as heat energy and then converted back into electrical energy in an easy and cost-efficient way.