WO2016034754A1

WO2016034754A1 - Heat storage method and system for a solar steam generation plant and solar steam generation plant

Info

Publication number: WO2016034754A1
Application number: PCT/ES2015/070645
Authority: WO
Inventors: Aleix JOVÉ LLOVERA; Cristina PRIETO RÍOS; Carlos RUBIO ABUJAS; Alfonso Rodríguez Sánchez; María ALGUACIL CUBERO
Original assignee: Abengoa Solar New Technologies, S.A.
Priority date: 2014-09-05
Filing date: 2015-09-02
Publication date: 2016-03-10
Also published as: ES2565690A1; ES2565690B1

Abstract

The invention relates to a heat storage method and system for a steam generation plant, and to the solar plant comprising said system. The method according to the invention minimises the charging and/or discharging effect in conditions that differ from the nominal conditions by means of a system consisting of three blocks: i) a saturating block based on phase-change materials, ii) an over-heating block that increases the temperature of the steam of the heat-transfer fluid to the desired values, and iii) a pre-heating block that increases the difference in temperature between a cold tank and a hot tank of a heat storage material without phase change.

Description

DESCRIPTION

Method and thermal storage system for solar steam generation plant and solar steam generation plant

Field of the Invention The present invention is framed in the field of solar thermal power generation, specifically in the configuration of direct steam generation plants and corresponding thermal storage systems.

In particular, it refers to the configuration and sizing of thermal storage systems within a direct steam generating solar thermal plant. The configuration and the proposed method allow to store heat thanks to the steam produced during the day and deliver this heat when necessary, producing superheated steam at the most similar conditions possible to those of nominal operation of the plant.

The configuration of the proposed storage systems has application both in solar thermal power plants for steam production, and in production processes where heat storage can be a differentiating factor from the point of view of energy and economic efficiency.

Background of the invention

The most commonly used thermal storage materials in known solar thermal plants are molten salts and thermal oil. The former can create problems in operation such as the risk of freezing the salts in the different parts of the installation and the latter represent a very important cost of the plant in addition to not allowing to reach high temperatures (about 400 ° C) which implies low efficiency in the subsequent steam cycle. Even so, both technologies have thermal storage systems based on heat accumulation in double tank systems of molten salts.

Solar thermal direct generation superheated steam plants are presented as an alternative to technologies that use oils and salts to reduce the costs of generating electricity. This type of plant simplifies the design by using steam as a thermal transfer fluid, which allows the elimination of steam exchanger / generator systems in the installation. The main disadvantage of this Technology is that there is no competitive storage system with large capacities.

The power cycles of these superheated steam plants are usually Rankine cycles with or without overheating, with operating pressures between 100 bar and 170 bar and with overheating temperatures between 585 ° C and 360 ° C. In addition, these cycles are usually designed for daily operation by providing a configuration of extractions and recuperators that maximizes their performance while the plant operates during the day, generating electricity and in parallel charging the storage system during daylight hours, in case there is . The known storage systems associated with these plants are divided into: a) thermal storage systems that store heat from exclusively saturated steam, b) thermal storage systems that store heat from saturated and superheated steam at the same time. In these systems the performance of the cycle in the case of the discharge is penalized by the fact of discharging the steam at pressures and / or temperatures significantly below the nominal ones.

The systems in case a) can operate exclusively with saturated steam cycles (turbines that only accept saturated steam). Even so, they allow a range of operation at different pressures as long as the steam enters the cycle in a saturated state. It should be said that each cycle is designed for its nominal operation at a certain pressure (the maximum) and as this pressure decreases, the performance decreases.

The systems in case b) can operate with superheated steam cycles (turbines that only accept superheated steam). If an overheated steam turbine is used, the discharged steam must ensure a minimum superheat temperature for each operating pressure, usually 50 ° C above the saturation temperature. Due to this there are also many combinations of operation, however, and as in the previous case, moving away from the nominal pressure and temperature conditions decreases the cycle performance.

So far these steam plants are designed with thermal storage systems based on saturated steam accumulators, the so-called Ruth's tanks. These tanks can accumulate steam at the same pressure with which they are loaded, but only allow the discharge at a pressure significantly lower than the nominal one, either with sliding pressure or with constant pressure steps in the saturation module. A thermal storage configuration without steam accumulation with two salt tanks, a cold tank and a hot tank is also known. This configuration includes a heat exchanger connected between the two tanks where, in the case of the discharge, the water from the power cycle evaporates and overheats thanks to the salts that pass from the hot tank to the cold through the heat exchanger. During charging, superheated steam is introduced into the heat exchanger that cools and partially condenses by exchanging heat with the salts that pass from the cold tank to the hot tank through the heat exchanger. This configuration also includes a heat recuperator that takes advantage of the heat of the outgoing water flow of the salt exchanger in the load. This recuperator is necessary to completely condense partially condensed steam in the heat exchanger. This configuration with the recuperator implies the modification of the conditions of the extractions of the power cycle, thus moving away from the nominal operation and with it the maximum possible performance. Description of the invention

The present invention minimizes the effect of loading and / or unloading in conditions that differ from the nominal ones by proposing a system consisting of three blocks: i) a saturation block based on phase change materials and ii) an overheating block that raises the steam temperature of a thermal transfer fluid up to the desired values and iii) a preheating block that increases the temperature difference between a cold tank and a hot tank of a thermal storage material without phase change.

This application refers to a thermal storage material without phase change as a material that can be solid, liquid or gas, which stores heat by increasing its temperature, without changing phase under system conditions. In an exemplary embodiment this type of material may be molten salts.

Likewise, thermal transfer fluid means the fluid that circulates from the solar field to the cycle and is returned to the solar field and which could optionally also be used in an electrical generation system. The saturation block is based on the latent heat of a phase-changing material at a temperature similar to that of saturated steam. The thermal energy transmission is carried out in an isothermal process, allowing saturated steam to be generated at constant pressure. In this way the hysteresis between loading and unloading pressures is minimized. The superheat block is responsible for raising the temperature of the steam coming from the saturation block until it reaches temperature values as close to the nominal one.

The preheating block allows, in the case of the discharge, the thermal exchange between the thermal storage material without phase change from a superheater and the thermal transfer fluid from the power cycle. In this way the thermal storage material without phase change reduces its temperature to the minimum values that it allows without changing phase. This increase in the temperature difference in the thermal storage material without phase change between the cold tank and the hot tank up to maximum values allows the use of a smaller amount of said material taking advantage of the entire available temperature range thereof and with it reduce investment both in the material itself and in volume of the tanks and foundations.

The present invention proposes a configuration of a storage system for direct steam generation technology based on a phase change system and a double tank system of thermal storage material without phase change. This configuration allows the system to be downloaded maximizing the performance of the discharge power cycle.

The invention consists in the method for carrying out the heat exchange between thermal storage materials and the thermal transfer fluid both in the loading and unloading process, in the system for carrying out said method and in a solar power plant. thermal storage comprising said system.

As discussed above, the proposed configuration consists of a phase change module, a cold tank of thermal storage material without phase change (cold tank), a hot tank of thermal storage material without phase change (hot tank) , a superheater that performs the heat exchange between the thermal storage material without phase change and the thermal transfer fluid in superheated steam state and a preheater that performs an exchange between the thermal storage material without phase change and the flow fluid thermal transfer in subcooled liquid state. In the discharge, following the thermal transfer fluid circuit, both exchangers are mounted in series with the phase change module and in the direction of lower to higher temperature we would find: preheater, phase change module and superheater. The phase change module is used to evaporate the liquid or condense the steam as the system is in discharge or load mode respectively and can be designed to further heat subcooled liquid to saturation conditions in the discharge. To implement this configuration, it will be necessary to include a piping system that allows the preheated liquid from the preheater to circulate in the discharge to the phase change module and in the load the saturated thermal transfer liquid leaving the phase change module directly to the solar field, not circulating this current to the preheater.

In the circuit of the thermal storage material without phase change and from lower to higher temperature (in the case of discharge) we find the cold tank, the preheater, the superheater and the hot tank. In the case of the load the circuit would be cold tank, superheater and hot tank. The piping system in the load must circulate the thermal storage material without phase change from the cold tank to the hot tank through the superheater while in the discharge the piping system circulates the thermal storage material without changing the phase of the tank heat the cold tank through superheater and preheater.

According to the above, the thermal storage method is characterized by comprising the following steps:

In the load, in the thermal transfer fluid circuit the steam coming from the solar plant is superheated and is cooled in the superheater until it is transformed into saturated steam and subsequently introduced into the phase change module where it is transformed into saturated liquid while that in the circuit of the thermal storage material without phase change, all the thermal storage material without phase change leaving the cold tank is heated in the superheater and stored in the hot tank. The cold tank can be emptied totally or partially, but always the entire thermal material without phase change leaving the cold tank is stored in the hot tank.

In the discharge, the thermal transfer fluid under conditions of subcooled liquid is preheated in the preheater, increasing its temperature and maintaining under conditions of subcooled liquid. It is subsequently introduced into the phase change module where it is transformed into saturated liquid and subsequently saturated steam and is finally superheated to superheated steam in the superheater. While in the material circuit of Thermal storage without phase change, all said material leaving the hot tank, is cooled in the superheater and then in the preheater and finally stored in the cold tank. As with the load, the hot tank can be emptied totally or partially, but always all the thermal material without phase change leaving the hot tank is stored in the cold tank.

And therefore, the system is characterized in that it comprises the module with the phase change material, the thermal transfer fluid circuit and the thermal storage material circuit without phase change, the circuits being configured so that they are different in the case of loading and unloading the system, where,

On the load

- the thermal transfer fluid circuit comprises the superheater in connection with the solar plant and with the phase change module, and

- the circuit of thermal storage material without phase change comprises the superheater, the cold tank and the hot tank, the cold tank, the superheater and the hot tank being configured so that the entire thermal storage material without phase change coming from the cold tank passes to the hot tank through the superheater.

In the discharge - the thermal transfer fluid circuit comprises the phase change module, the superheater and the preheater, being configured so that the preheater is arranged followed by the phase change module and followed by the superheater and the preheater being configured to raise the temperature of the thermal transfer fluid without reaching saturation conditions and the phase change module to perform both the heating of the thermal transfer fluid to the saturation conditions and its phase change to saturated steam,

- the circuit of thermal storage material without phase change comprises the cold tank, the hot tank, the superheater and the preheater, being configured so that the hot tank is arranged followed by the superheater in turn followed by the preheater and followed by the tank cold and passing all of the thermal storage material without phase change from the hot tank to the cold tank through the superheater and preheater so that the entire material of Thermal storage without phase change leaving the hot tank passes to the cold tank through the superheater and preheater.

The method and configuration of the invention allow obtaining the minimum possible temperature in the cold tank and the maximum possible temperature in the hot tank. The energy stored in a phase change storage system is directly proportional to the latent heat of phase change of the phase change material itself, so it is directly proportional to the amount of this material. The energy storage in the phase change system occurs because the phase change module maintains a condensation-solidification temperature such that it allows a thermal gradient with the thermal transfer fluid under conditions of liquid-vapor saturation that ensures the transfer of hot. In an exemplary embodiment this thermal gradient is at least 2 ° C.

The energy stored in a double tank system of thermal storage material without phase change can be calculated as follows: Stored energy = Amount of thermal storage material without phase change * Specific heat * ΔΤ

Then, to store the maximum possible energy with the least amount of thermal storage material without phase change, the maximum ΔΤ or maximum temperature difference between the cold tank and the possible hot tank must be achieved. A larger ΔΤ allows the thermal storage material tanks to be sized without phase change of a smaller size to store the same amount of energy.

In the loading mode the thermal storage material without phase change at the minimum possible temperature that allows its operation circulates from cold tank to hot tank through the superheater. This thermal storage material without phase change gains the heat transferred by the thermal transfer fluid under conditions of superheated steam circulating from the solar field to the superheater.

At the outlet of the superheater the superheated thermal transfer fluid acquires saturated steam quality thanks to having yielded the sensitive heat corresponding to the superheated part to the thermal storage material without phase change. The thermal transfer fluid already in saturated steam conditions passes through the phase change module condensing and giving all the heat of its condensation to the phase change material. The latter gains the heat ceded by the thermal transfer fluid and It changes phase. This heat exchange is due to the existence of a thermal gradient between the phase change material and the thermal transfer fluid under saturated liquid-vapor conditions.

The thermal transfer fluid, in a saturated liquid state, leaving the phase change module is circulated to the process under saturation conditions to be again vaporized and superheated in the solar field receiver.

In the download process the circuit is different. The thermal transfer fluid under conditions of subcooled liquid passes through the preheater and increases its energy, leaving the preheater with a degree of subcooling less than at its inlet. Subsequently, it is introduced in the phase change module, where the thermal transfer fluid in the subcooled liquid state increases its energy and changes phase until it exits in saturated steam conditions. This heat exchange is due to the existence of a thermal gradient between the phase change material and the thermal transfer fluid under saturated liquid-vapor conditions. Finally it passes through the superheater and increases its energy, leaving in a state of superheated steam.

The thermal storage material without phase change of the hot tank passes through the superheater yielding part of its sensible heat. This same storage material without change of phase at its outlet of the superheater is introduced into the preheater so that it continues to transfer energy to the thermal transfer fluid in the subcooled liquid state, in this way the minimum temperature is reached, achieving a greater temperature difference between the cold and hot tank. Subsequently the thermal storage material without phase change is housed in the cold tank.

In the discharge, the thermal transfer fluid in the state of subcooled liquid from the cycle does not reach saturation conditions at the outlet of the preheater, this fluid actually gains heat by raising its temperature but always in the range of subcooled liquid. The temperature reached by the thermal transfer fluid at the outlet of the preheater is determined by the heat transferred by the flow of thermal storage material without phase change from the superheater. Said flow delivers only part of the power that the thermal transfer fluid would require under conditions of subcooled liquid to achieve saturation conditions in the preheater. This is because the thermal energy required to pass from subcooled liquid to saturation conditions in the Preheater is greater than the thermal energy that is capable of transmitting the thermal storage material flow rate without phase change, since this flow rate is the same as exchanging heat in the superheater.

According to the above, the same flow of thermal storage material is maintained without phase change through the superheater and preheater, this having the advantage that it allows to take advantage of the entire operating range of the thermal storage material without phase change. This also avoids the need for an intermediate tank that stores the excess thermal storage material without phase change that would be necessary in the preheater to bring the thermal transfer fluid from subcooled liquid conditions to saturation conditions. In addition, by preheating the thermal transfer fluid of subcooled liquid conditions in the preheater, with the thermal storage material stream without phase change coming from the hot tank through the superheater the temperature of the thermal storage material is decreased without changing phase maximizing the temperature difference between hot and cold tank.

According to the above, the thermal storage material tanks without phase change yield energy to two different processes: i) to bring the thermal transfer fluid from subcooled to subcooled liquid conditions with a lower degree of subcooling through the preheater; and also ii) to bring the thermal transfer fluid in saturated steam conditions to superheated conditions through the superheater.

Finally, the solar steam generation plant comprising a thermal storage system as described above is also object of the invention.

Description of the figures To complete the description and in order to provide a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate embodiments of the invention.

Figure 1 shows a schematic representation of an exemplary embodiment of the plant configuration object of the invention. Figure 2 shows the temperature (T) - heat (Q) graph of the loading process of the storage system of the plant configuration corresponding to Figure 1. Figure 3 shows the temperature (T) - heat (Q) graph of the unloading process of the storage system of the plant configuration corresponding to figure 1.

Detailed description of the invention

An embodiment of the object of the invention is shown in Figure 1. In the exemplary embodiment, the thermal transfer fluid is water. A solar field (10) and a power block (70) are shown. Figure 1 represents the power block (70) only by means of a turbine although it would comprise the elements of a power element. The system consists of a preheating system comprising a preheater (40) and two salt tanks: a cold tank (50) and a hot tank (60), an evaporation system consisting of a module (30) for changing the phase and an overheating system, consisting of a superheater (20).

In the process of loading the thermal storage system, steam is circulated from the solar field (10) to the inlet of the superheater (21), subsequently directed from the outlet of the superheater (22) to the inlet of the module (31) of phase change where its heat yields to the phase change material. From the output of the phase change module (32) the water, already condensed, is recirculated back to the solar field (10). In the discharge process, the water coming from the power block (70) is directed to the preheater inlet (42), in the preheater (40) it receives heat from the salts coming from the hot tank (60) through the superheater ( twenty). Next, it goes to the phase change module (30) where it experiences the passage of subcooled liquid water to saturated steam of quality X = 1, subsequently entering the superheater (20), where it is carried from saturated steam to superheated steam thanks to the heat transferred by the salts from the hot tank (60). Finally said steam is turbinated in the power block (70), producing electricity.

The thermal transfer fluid exits the superheater charge (20) under conditions of superheated steam with a degree of superheat that is lower than that of its entrance to the superheater (20).

Figures 2 and 3 show the thermal cycle experienced by steam and salts in the exemplary embodiment shown in Figure 1. The preferred embodiment of the present invention is developed for a direct superheated steam generation plant of 530 ° C at 130 bar pressure. The proposed phase change module (30) is a module with a phase change temperature preferably of 312 ° C. The subcooled return water temperature of the power block (70) is considered 232 ° C. The minimum operating temperature of molten salts is set as 265 ° C.

With the described steam conditions and the thermal nature of the steam and molten salts, the load graph of Figure 2 is obtained where a indicates water circuit, s indicates the salt circuit and m the phase change material circuit . The saturation temperature of the steam at 130 bar is 331 ° C, so the condensation of this steam is represented at the constant temperature of 331 ° C. By having a phase change material that melts at 312 ° C, the temperature gradient between 331 ° C and 312 ° C allows for a thermal transfer between the heat of the condensing steam and the melting phase change material. The temperature of the hot tank (60) is represented as 522 ° C since due to the thermal nature of the salts and superheated steam it is the maximum temperature that can be achieved respecting a minimum thermal gradient between salts and steam of 5 ° C ( represented in the graph as p). Thus, a minimum thermal transfer between steam and salts is always ensured due to this gradient of 5 ° C. The loading procedure of the system described above would then be according to Figure 2:

1) Steam enters at 530 ° C and 130 bar (point 21 a in Figure 2) into the superheater (20) from the solar field (10).

2) The steam passes through the superheater (20) giving heat to the molten salts and reaching saturation conditions at the outlet thereof, temperature of 331 ° C and pressure of 130 bar (point 22a of Figure 2).

3) The molten salts gain the heat ceded by the superheated steam while also passing through the superheater (20) from the cold tank (50) to 265 ° C to the hot tank (60) where they reach 522 ° C (points 22s and 21 s of figure 2). 4) The steam coming from the superheater (20) under saturation conditions 331 ° C and 130 bar (point 22a of figure 2) is introduced to the phase change module (30) condensing completely (point 32a of figure 2).

5) The phase change module (30) gains the heat ceded by the steam condensing and passes from solid to liquid state (line between points 32m and 31m in Figure 2).

6) The condensed water (point 32a of Figure 2) from the phase change module (30) is returned to the solar field (10) to be evaporated and superheated again. With the fully charged system, cold tank (50) at 265 ° C, hot tank (60) at 522 ° C and phase change module (30) completely molten at 312 ° C, it is discharged obtaining steam at 97 bar (Tsat = 308 ° C) and 517 ° C. The process is structured according to the graph in figure 3 where again indicates the water circuit, s indicates the salt circuit and m the phase change material circuit. The thermal exchange in the preheater (40) implies the thermal transfer of heat from the salts to the subcooled water: the salts would reduce their temperature from 315 ° C (point 41 s of Figure 3) temperature at which they are at superheater output (20) up to 265 ° C (point 42s in figure 3) which is when they are poured into the cold tank (50). The subcooled water gains temperature from 232 ° C (point 42a of figure 3) at its entrance to the preheater (40), coming from the power block (((70), up to 266 ° C (point 41 a of the figure 3), temperature at which it is at its outlet from the preheater (40) At all times there is a high temperature gradient that allows efficient thermal transfer.

As you can see the steam in saturation conditions at 97 bar (horizontal section of line 30a of Figure 3) has a saturation temperature of 308 ° C and the phase change module solidifies at 312 ° C ( line between points 31 m and 32m) so there is also a minimum gradient of 4 ° C that allows the thermal transfer of the phase change module (30) to the liquid water / steam first being subcooled water heating from 266 ° C up to 308 ° C and then evaporating completely at 308 ° C.

Already at the exit of the phase change module (30) where all the water is saturated steam at 308 ° C (point 22a of figure 3), this same steam passes to the superheater (20) where it is superheated to 517 ° C (point 21 a of figure 3) thanks to the heat ceded by the sales (line between points 21 s and 22s of figure 3). In this exchange and by thermal nature of steam and salts, a minimum of 5 ° C of thermal gradient between the salts and steam is also maintained. This minimum thermal gradient occurs between the superheated steam at its outlet of the superheater (20) and the salts at its entrance to it (20), which is reflected precisely between points 21 s and 21 a of Figure 3.

So the download process is developed in the following steps:

1) Subcooled water enters 232 ° C (point 42a in Figure 3) into the preheater (40), coming from the power block (70).

2) Water enters through the preheater (40) and gains heat from salts that circulate in the opposite direction by passing the water from a temperature of 232 ° C to 266 ° C (line from 42a to 41a of Figure 3) .

3) In the same equipment the salts yield heat to the subcooled water, passing the salts at a temperature of 315 ° C to 265 ° C (points 41s and 42s of Figure 3).

4) The subcooled water from the preheater (40) is introduced to the phase change module (30) gaining heat up to 308 ° C of saturation temperature and subsequently evaporating completely (line between points 41 a and 22a of Figure 3) .

5) The phase change module (30) gives heat to the subcooled water in a first stage and then to the saturated water, evaporating completely. The phase change material passes from a liquid state (point 31 m of figure 3) to a solid state (point 32m of figure 3).

6) Saturated steam at the output of the phase change module (30) is introduced to the superheater (20) where it gains temperature by overheating up to 517 ° C (line between points 22a and 21a of Figure 3) thanks to the heat ceded by salts from the hot tank (60) which pass from 522 ° C to 315 ° C (line between points 21 s and 22s of Figure 3).

7) The hot salts of the superheater (point 22s of figure 3) are directly transferred to the inlet of the preheater (40) (point 41 s of figure 3).

The system proposed in the invention, thanks to the phase change module (30), the tanks (50, 60), the preheater (40) and the superheater (20), circulates in discharge the same flow of salts per preheater (40) and superheater (20), obtaining at the same time a maximum temperature difference in the double tank system (50, 60). It does not therefore require the use of intermediate tanks that store the surplus of salts that would originate if their flow through preheater (40) and superheater (20) were different.

The commissioning, in the download mode is carried out according to two possible options of initial system status:

• First embodiment: Subcooled water from the power block (70) is circulated through the preheater (40) through which no salts pass at an initial moment. The subcooled water passes to the phase change module (30) where saturated steam is produced which passes to the superheater (20) from which it is superheated again towards the power block. The salts can follow two routes:

^■ 1A. The salts leave the hot tank (60) and circulate to the superheater (20), from this they pass to the preheater (40) and to the outlet of the preheater

(40) are circulated to the cold tank (50).

^■ 1 B. The salts leave the hot tank (60), pass through the superheater

(20) and at their exit they circulate to the cold tank (50).

• Second embodiment: Subcooled water from the power block (70) is introduced to the phase change module (30) from which it exits under saturated steam conditions and circulates to the superheater (20) from which it is superheated again to The power cycle The sales circuit can also follow two options:

^■ 2A. The salts leave the hot tank (60) and circulate to the superheater (20). From this they pass to the preheater (40) and to the outlet of the preheater

(40) are circulated to the cold tank (50).

^■ 2B. The salts leave the hot tank (60), pass through the superheater

(20) and at their exit they circulate to the cold tank (50).

Another alternative of operation: during loading, the steam leaves the superheater under slightly superheated steam conditions and is introduced to the phase change module providing heat in it, producing the fusion of the phase change material and leaving the same saturated liquid. This implies an increase in the power of the phase change module to allow storing the fraction of energy corresponding to the overheating fraction of this steam. The flow of salts that is needed to exchange energy in the preheater (40) and in the superheater (20), is lower than in the case where the steam reaches saturation conditions at the outlet of the superheater (20).

This embodiment introduces a degree of freedom since the saturation state of the liquid and vapor is not conditioning at the input or output of the phase change module (30) and therefore the system is more versatile against changes in temperature and pressure getting greater flexibility in plant control.

Claims

1. - Thermal storage method for solar steam generation plant comprising a circuit of a thermal transfer fluid and a circuit of a thermal storage material without phase change, characterized in that it comprises the following steps: in loading, In the circuit of the thermal transfer fluid the steam coming from the solar plant is superheated and is cooled in a superheater (20) until its transformation into saturated steam and subsequently introduced into a phase change module (30) where it is transformed into liquid while in the circuit of the thermal storage material without phase change, all the thermal storage material without phase change from a cold tank (50) is heated in the superheater (20) and stored in a hot tank ( 60), and in the discharge the thermal transfer fluid in the subcooled liquid state is preheated in a preheater (40) inc rementing its temperature and keeping under conditions of subcooled liquid and subsequently it is introduced in the phase change module (30) where it is transformed into saturated liquid and subsequently into saturated steam and is finally superheated until superheated steam in the superheater (20) while in the circuit of thermal storage material without phase change, all said material from the hot tank (60), is cooled in the superheater (20) and then in the preheater (40) and finally stored in the cold tank ( fifty).

2. - Thermal storage method for solar steam generation plant, according to claim 1, characterized in that the phase change module (30) maintains a condensation-solidification temperature that allows a thermal gradient with the thermal transfer fluid under conditions of liquid-vapor saturation to ensure heat transfer between the phase change module (30) and the thermal transfer fluid.

3. Thermal storage method for solar steam generation plant, according to claim 2, characterized in that the gradient is at least 2 ° C.

4. Thermal storage method for solar steam generation plant, according to claim 3, characterized in that the gradient is 4 ° C.

5. - Thermal storage method for solar steam generation plant according to claim 4, characterized in that the phase change module (30) has a phase change temperature of 312 ° C for water as transfer fluid thermal

6. - Thermal storage method for solar steam generation plant, according to any one of the preceding claims, characterized in that the thermal transfer fluid exits the superheater load (20) under superheated steam conditions with a degree of superheating lower than that of its entrance to the superheater (20).

7. - Thermal storage method for solar steam generation plant, according to any one of the preceding claims, characterized in that the commissioning in the discharge mode is carried out by circulating thermal transfer fluid under conditions of liquid subcooled by the preheater (40) which subsequently passes to the phase change module (30) where it acquires steam conditions that passes to the superheater (20) while the thermal storage material without phase change leaves the hot tank (60) and circulates to the superheater ( 20), from this it passes to the preheater (40) and to the outlet of the preheater (40) it is circulated to the cold tank (50).

8. - Thermal storage method for solar steam generation plant, according to any one of the preceding claims 1-6, characterized in that the commissioning in the discharge mode is carried out by circulating the thermal transfer fluid under liquid conditions subcooled by the preheater (40) subsequently passing to the phase change module (30) where it acquires steam conditions that passes to the superheater (20) while the thermal storage material without phase change leaves the hot tank (60), passes through the superheater (20) and at its exit circulates to the cold tank (50).

9. - Thermal storage method for solar steam generation plant, according to any one of the preceding claims 1 -6, characterized in that the thermal transfer fluid is introduced during commissioning under conditions of subcooled liquid to the module (30 ) phase change from where it exits under saturated steam conditions and circulates to the superheater (20) from where it exits superheated while, in the circuit of thermal storage material without phase change, this material leaves the hot tank (60) and circulates to the superheater (20), passes to the preheater (40) and to the outlet of the preheater (40) is circulated to the cold tank (50 ).

10.- Thermal storage method for solar steam generation plant, according to any one of the preceding claims 1 -6, characterized in that the thermal transfer fluid is introduced during commissioning under conditions of subcooled liquid to the module (30) phase change from where it exits under saturated steam conditions and circulates to the superheater (20) from which it exits superheated while in the thermal storage material circuit without phase change, this material leaves the hot tank (60), passes through the superheater (20) and at its exit circulates to the cold tank (50).

1 1. Thermal storage method for solar steam generation plant, according to any one of the preceding claims, characterized in that the thermal transfer fluid is water.

12. Thermal storage method for solar steam generation plant, according to any one of the preceding claims, characterized in that the thermal storage material without phase change are molten salts.

13.- Thermal storage system for solar steam generation plant characterized in that it comprises a module (30) with a phase change material, a circuit of a thermal transfer fluid and a circuit of a thermal storage material without change phase circuits being configured so that they are different in the case of loading and unloading the system, where, in the load, the thermal transfer fluid circuit comprises a superheater (20) in connection with the solar plant and with the module (30) phase change, and the thermal storage material circuit without phase change comprises the superheater (20), a cold tank (50) and a hot tank (60), the cold tank (50) being the superheater (20) and the hot tank (60) configured so that all thermal storage material without phase change from the cold tank (50) passes to the hot tank (60) through the superheater (20) , in the download, The thermal transfer fluid circuit comprises the phase change module (30), the superheater (20) and the preheater (40), being configured so that the preheater (40) is arranged followed by the change module (30) phase and followed by the superheater (20) and the preheater (40) being configured to raise the temperature of the thermal transfer fluid without reaching saturation conditions and the phase change module (30) to perform both the heating of the transfer fluid thermal to saturation conditions such as its phase change to saturated steam, the thermal storage material circuit without phase change comprises the cold tank (50), the hot tank (60), the superheater (20) and the preheater ( 40), being configured so that the hot tank (60) is arranged followed by the superheater (20) in turn followed by the preheater (40) and followed by the cold tank (50) so that the entire m Thermal storage unit without phase change leaving the hot tank (60) passes to the cold tank (50) through the superheater (20) and the preheater (40).

14.- Thermal storage system for solar steam generation plant, according to claim 13, characterized in that the thermal transfer fluid exits the superheater load (20) under conditions of superheated steam with a degree of superheat lower than at of its entrance to the superheater (20).

15.- Solar steam generation plant, characterized in that it comprises a thermal storage system according to any one of claims 13 or 14.