ES2543975B1 - Solar steam generator-separator - Google Patents

Abstract

The invention describes a solar-powered steam generator-separator (1) comprising at least one reflecting surface (2) and a receiving tube (3), wherein: the receiving tube (3) is inclined and comprises a portion (3s ) with an upper end provided with a liquid inlet (4) and a steam outlet (5) and a lower end portion (3i) provided with a liquid outlet (6), such that when liquid is introduced, said liquid it forms a falling film from the inlet (4) in the upper end portion (3s) to the outlet (6), while the heat received by the receiving tube (3) due to solar radiation reflected by the surface or surfaces ( 2) reflector (s) causes the evaporation of steam and its ascent until leaving through the outlet (5).

Description

5

10

fifteen

twenty

25

30

35

STEAM GENERATOR-SEPARATOR BY SOLAR ENERGY

DESCRIPTION

OBJECT OF THE INVENTION

The present invention belongs to the field of renewable enemas, and more specifically to solar energy.

The object of the present invention is a new device specially designed to generate steam from a fluid substance, and separate it from the corresponding liquid portion from thermal solar energy. It is a device especially useful for use in combination with absorption machines used as heat pumps, either to achieve a cooling or heating effect, although not exclusively. It is also especially useful in combination with thermal motors for the production of useful work.

BACKGROUND OF THE INVENTION

Absorption machines are thermal thermal machines that pump heat from a heat source to a heat sink at a higher temperature. These are energy-efficient machines to be able to recover residual heats or use renewable heat, such as geothermal, or heat obtained from solar radiation by means of thermal solar collectors. The absorption machines base their operation on the affinity of certain substances of high temperature of evaporation by other pure substances that change phase at the temperatures of interest, for example water or ammonia, called natural refrigerants. Thus a solution of the refrigerant in the solvent is formed inside the machine. However, although they have been in existence for more than a century, absorption machines lack the enormous diffusion of mechanical compression heat pumps due to their greater cost, weight and volume.

In its simplest design, called simple effect, its basic operation is described below with reference to Fig. 1. Firstly an activation heat is applied to the solution inside a generator (G), and as consequently the vapor of the most volatile component, called refrigerant, is separated from the solution (P2). Then, due to the evacuation of heat to an external high temperature sump carried out in a condenser (C), connected to the generator, the refrigerant vapor condenses at high pressure (P3). This evacuated heat constitutes part or all of the useful effect when the machine acts exclusively as a heat pump of heat effect. The refrigerant in

5

10

fifteen

twenty

25

30

35

The liquid state is then expanded in an expansion valve (VE) and, once its pressure is lower (P4), it is evaporated at low pressure in an evaporator (E) to reach the inlet (P1) of an absorber (A) to which it is connected. In the evaporator (E) the heat absorption of the low temperature external focus is produced, achieving the cooling effect of the absorption machine when it is configured exclusively as a cooling heat pump. This evaporated refrigerant (P1) enters an absorber (A) where it joins with the liquid portion of the solution leaving the generator (G) at higher pressure, which has previously exchanged heat with the incoming to said generator (G) and once it has passed through a valve (V), its pressure drops to that of the absorber. The heat evacuated from the absorber (A) is part or all of the useful effect when the pumping machine is set to heat or it is evacuated to the environment, together with the heat of condensation if the machine is configured as refrigerating. The solution, together with its vapors constitutes the working fluid of the cycle.

Currently, a known way of feeding heat to the absorption machine is the use of thermal solar energy. In this case, an external closed circuit is used, called the primary circuit, which takes heat from a thermal collector by means of a heat transfer fluid other than the working fluid of the machine. The heat transfer fluid is generally water based and, since it has to withstand freezing temperatures resulting from the weather without freezing, it usually incorporates an antifreeze additive that is expensive, frequently polluting, and has a finite life. Optionally this primary circuit transfers the heat to a secondary circuit, which usually incorporates an accumulation tank. This serves to store sensitive and / or latent heat and thus activate the absorption machine through a third circuit, called tertiary, at times when the solar input is insufficient, to do so by lowering the energy level of the accumulating substance that It lies inside. The system may lack the secondary circuit, activating the machine directly with the primary connected to the tertiary through a heat exchanger, with or without storage tank, or even the primary can reach the machine directly.

There is a great diversity of configurations of the absorption heat pump cycles. They share the generation and separation of a vapor from a liquid solution. Within this diversity you can find cycles, called hybrids, that provide work in the form of steam compression to facilitate operation. There are also hybrid cycles that seek, in addition to the cooling or heating effect or both at the same time, produce work, only or at the same time with one or both of the above. They are based on the expansion of steam produced in a turbine or expander, subtracting steam from the heat pump cycle. In some cycles, such as Kalina, a solution is used, similar to that used in

5

10

fifteen

twenty

25

30

35

absorption heat pumps, but with the sole or main purpose of producing useful work.

In short, it would be interesting from many points of view to be able to feed the absorption machine with the heat of the sun in a direct way, eliminating steps and intermediate fluids, directly heating the working fluid. This would result in greater simplicity and lower installation costs. The separation of steam from the liquid is usually carried out in the absorption machines in an additional element to the generator, integrating it into the supposes an advantage of weight, cost and efficiency.

On the other hand, the plants of production of useful work, called thermoelectric, make use of solar energy for the production of heat in an installation outside the thermodynamic cycle of power production, called thermal motor. In order to achieve the same advantages as those mentioned above, it is sought to generate this heat in the same working fluid of the cycle instead of in a heat transfer intermediate fluid. In these plants, the working fluid consists of a pure substance, which, due to the heat input, changes from a liquid state to a gaseous state, separating itself from the remaining liquid. This steam is expanded in a turbine or expander to obtain useful work, which is usually exported from the plant in the form of electricity. Steam is produced in horizontally arranged or slightly inclined tubes. Such a provision is known as "Direct Steam Generation" or GDV. Currently this technology is subject to intense research to achieve high reliability and efficiency at a cost that is competitive, although it faces difficulties, such as instabilities of the biphasic flow that is established inside the tubes and tube breaks due to thermal stresses. . They usually have liquid vapor separators external to the tube. The interest of the GDV is to avoid long circuits of a monophasic heat transfer fluid, usually thermal oil, which captures the heat of the sun optically concentrated and transports it to a heat exchanger with the function of evaporator of the pure substance that constitutes the fluid of work of the thermodynamic cycle of power production, or thermal engine.

It would be interesting, from many points of view, to be able to configure the GDV in a stable and controlled way by means of a durable device that produces steam and separates it from the incoming liquid in an effective and integrated way.

In short, whether it is power cycles, absorption cycles, refrigerators or heat or both at the same time, as if it is hybrid cycles with a combination purpose of the previous ones, the direct production of steam with solar energy and its separation of the liquid, it is of great interest that it is produced more conveniently than the current one.

5

10

fifteen

twenty

25

30

35

DESCRIPTION OF THE INVENTION

The present invention describes a new device capable of generating steam and separating this vapor from the solution that carries it, or separating it from its liquid phase, directly using the heat effect resulting from absorbing solar energy. This avoids the use of a heat transfer fluid that, through an entire installation outside the cycle of interest, transmits the heat obtained by solar energy to the absorption machine, to the thermal motor of production of useful work or to the warm cycle of purpose multiple. The set is much simpler, cheaper, compact and efficient. It also eliminates the risk of leakage and freezing of heat transfer fluids, as well as the need to perform maintenance on the installation outside the absorption machine or outside the thermal engine. It also avoids the consumption of water or the heat transfer substance used, related to the renewal of the heat transfer fluid, as well as heat loss.

The present invention takes advantage of the existing relatively mature technology in relation to the usual solar-parabolic-type solar collectors in solar thermal or Fresnel-type plants. The use of this technology, currently in rapid development, predicts a reduction in its manufacturing and use, contributing to lower the cost of the solar installation - which is proposed. The parabolic trough and Fresnel-type collectors use mirrors to concentrate solar radiation and are currently used profusely to heat a fluid and thus feed the thermodynamic cycle for the production of work in the so-called solar thermal power plants. A parabolic trough sensor comprises a reflecting surface, usually of a parabolic trough or Fresnel type (divided into parts), which concentrates solar radiation, directly or with the aid of additional (secondary) optics, along a receiving tube rectum located near the optical focus of said reflective surface. A coaxial outer glass tube surrounds the receiver tube, a forge (much lower pressure than atmospheric pressure) between them in order to minimize heat losses. For the same purpose, the receiver tube outside is covered with an optically selective layer, which allows to increase the overall absorptivity of solar radiation while minimizing the global emittance at operating temperatures. The whole assembly formed by the reflecting surfaces and the receiving tube can rotate in a convenient way to follow the sun's path and thereby maintain the concentration of the radiation on the receiving tube, or they can only rotate only some of the reflecting surfaces around an axis parallel to the axis of the receiver tube to gain simplicity.

In this document, the terms "lower end portion" and "end portion

5

10

fifteen

twenty

25

30

35

upper "refers respectively to the lower and upper end section of the inclined receiving tube. The terms" lower end "and" upper end "refer specifically to the respective end points of the receiving tube.

A first aspect of the invention is directed to a steam generator-separator by means of solar energy comprising at least one reflective surface that concentrates solar radiation on the surface of a receiving tube that is inclined and comprising an upper end portion provided with an inlet of a fluid in a liquid state (for example, the dissolution of a refrigerant in another substance, called a solvent, or a pure fluid), and a generated steam outlet. It also comprises a lower end portion provided with a fluid outlet remaining in the liquid state. When the fluid is introduced in a liquid state through the corresponding inlet, said liquid fluid forms a falling film from the entrance in the upper end portion to the outlet in the lower end portion, while the heat received by the receiving tube Due to the solar radiation reflected by at least one reflective surface it causes the evaporation of steam and its ascent until it exits through the outlet in the upper end portion.

According to a preferred embodiment of the invention, the steam outlet is located in the receiver tube at a higher height than the liquid inlet to allow steam overheating. Thus, the steam goes through a final section in which it does not share the internal volume of the receiving tube with the liquid, so that the heat absorbed by said receiving tube in that section serves to overheat the steam.

This can be implemented in different ways. In a preferred embodiment the liquid inlet is implemented by a conduit outside the receiving tube that is connected to said receiving tube. The introduction of the liquid thus occurs at a point lower than that corresponding to the upper end of the tube itself, the section between said point and the upper end being free of liquid.

In another particular embodiment, the liquid inlet is implemented by an inner conduit to the receiving tube. The effect is the same as that achieved according to the previous embodiment, with the difference that in this case it is not necessary to perform a perforation or inlet port in the receiving tube, but rather that the conduit is introduced through its end and travel a section from the upper end of the receiving tube before discharging the liquid.

The angle of inclination of the receiving tube with respect to the horizontal, and therefore of the entire generator-separator of the invention, may be between 5 degrees and 90 degrees,

5

10

fifteen

twenty

25

30

35

depending on the latitude of the site, the thermo-fluid dynamic processes that develop inside, construction needs and the time of the year. This inclination may be fixed, although preferably the generator-separator of the invention comprises means for modifying the inclination of the receiving tube for the purpose of optimization. The variation of the inclination can be continuous or have several fixed positions.

In addition, in order to prevent the introduction of the receiving tube in the event that the liquid flow is excessive, the invention further comprises a liquid level control means, located in the lower end portion of the receiving tube.

Preferably, the inner surface of the receiving tube comprises a plurality of protuberances that modify the downward trajectory of the liquid in order to favor separately or jointly the stability of the liquid-vapor interface, the distribution of the liquid on the inner surface of the tube and / or the slowing down of the natural sliding of the liquid in a downward direction, favoring the heat transfer by convection and / or radiation between the tube and the liquid and / or the liquid with the steam by means of extended surfaces. These protrusions could be, for example, fins, bars, plates, steps, fixed or mobile inserts, barriers, etc. In this regard, note that in the event that there is a final stretch of steam overheating, such a section may have a different configuration than the rest of the tube, since as previously mentioned, due to the overheating section, no film of liquid.

The section of the receiving tube can be circular, oval, rectangular or in the most convenient way to its function. It can even be of variable section along its length.

As for the reflecting surface, it adopts an essentially cylindrical shape with an axis parallel to the axis of the receiving tube, not necessarily coaxial. Its section by a plane perpendicular to the axis could be parabolic, composed of several parabola sections or formed by flat or slightly curved sections, or Fresnel type, in order to optimize the solar collection, facilitate its manufacture, lower its cost, lower its weight, improve stiffness, increase its duration, improve its cleanliness or vary the angle of acceptance of solar radiation, jointly or interchangeably, among other purposes. These concentrating surfaces may be complemented by one or more additional surfaces, close to the receiving tube, optically in series with them, whose mission may be to favor the concentration of solar radiation, avoid optical losses, homogenize the light intensity around the receiving tube, improve efficiency, reduce cost or simplify its constitution, among others.

5

10

fifteen

twenty

25

30

35

Preferably, the reflective surface is rotatable about an axis parallel to that of the receiving tube to optimize the concentration of the solar radiation on the receiving tube throughout the day. This rotation of the reflecting surface could be of the set of the reflecting surfaces forming a rigid solid or of a set of surfaces that rotate individually together, around axes parallel to each other, called Fresnel type.

A second aspect of the invention is directed to an absorption machine comprising a steam generator-separator as previously described. In this case it would be a conventional absorption machine but where the conventional steam generator that works thanks to the heat provided by an external circuit has been replaced by the steam generator-separator described in this document.

A third aspect of the invention is directed to a thermal engine for the production of useful work comprising a steam generator-separator as described above. In this case it would be a conventional useful power production cycle but where the conventional steam generator that works thanks to the heat provided by an external circuit has been replaced by the steam generator-separator described in this document.

A fourth aspect of the invention is directed to the use of a steam generator-separator as described above for obtaining and separating steam from liquid.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1 shows a scheme of an absorption machine according to the prior art.

Fig. 2 shows a steam generator-separator according to the invention, connected to an absorption machine.

Figs. 3a and 3b show two details of the upper end portion of a tube, according to the invention.

PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of the invention is described below with reference to

5

10

fifteen

twenty

25

30

35

The attached figures.

As previously mentioned, Fig. 1 corresponds to the scheme of a conventional absorption machine. The generator-separator (1) of the present invention may perform the function of the conventional generator (G) shown in this Fig. 1, which requires an external circuit with an intermediate heat transfer fluid to receive the heat Q'in.

Fig. 2 shows a steam generator-separator (1), by solar energy according to the invention, connected to an absorption machine (10). As can be seen, the generator-separator (1) in this representation is mainly formed by a reflecting surface (2) and a receiving tube (3) that are arranged according to a certain inclination in relation to the horizontal. In the upper end portion (3s) of the tube (3), in this example specifically at the upper end of the tube (3), there is an inlet (4) of fluid in the liquid state and an outlet (5) of generated steam , while in the portion (3i) of the lower end of the tube (3), in this example specifically at the lower end of the tube (3) there is an outlet (6) of remaining liquid.

The operation of this new generator-separator (1) is essentially the following: from the inlet (4) of liquid downwards, a descending liquid film is formed on the inner surface of the tube (3). This liquid is partially evaporated by the effect of solar heat received by the tube (3) in its outer part when the sun's rays are concentrated by the effect of the represented reflecting surface (2). The generated steam rises freely through the inside of the tube (3), since the liquid does not fully occupy the section of the tube (3), and exits through the outlet (5) located at the upper end of the tube (3 ). At the same time, through the outlet (6) arranged at the lower end of the tube (3), the remaining liquid that has descended along it is collected. It is thus possible to simultaneously generate steam and separate it from the liquid.

The inclination of the tube (3) and the formation of a thin film descending liquid against the current of the vapor stream prevent the formation of waves, bubbles and other transient instabilities that compromise the duration of the tube (3) and a stable operation of the Absorption machine (10) to which it activates. In addition, the thinness of the film minimizes the amount of liquid needed.

The reflecting surface (2) in this representation is rotatable about an axis parallel to the axis of the receiving tube (3) to follow the sun in its daily trajectory, from the ortho to the sunset, with the purpose of concentrating the light along the tube (3) continuously. The inclination of the tube (3) on the horizontal is done in approximately direction towards the equator

5

10

fifteen

twenty

25

30

to approximate the direction of the Earth's axis of rotation (polar tracking axis), improving the use of solar radiation because the opening area is more perpendicular to the sun's rays and making the rotation speed necessary for solar tracking Be more constant. In addition, a voluntary blur of the reflecting surface (2) allows to avoid overheating easily and quickly.

The generator-separator (1) also comprises a control means (7) located in the lower end portion of the tube (3) to control the liquid level.

Figs. 3a and 3b show two details of the upper end portion (3s) of the tube (3) where it is appreciated how it is possible to arrange the liquid outlet (4) below the steam inlet (5) in order to create a section for steam overheating, if this process is required.

In Fig. 3a, the liquid inlet (4) is implemented by means of a conduit (8a) that enters through the upper end of the tube (3) and travels a section of its interior until the liquid is discharged through an inlet (4) located at a point lower in the upper portion (3s) of the tube (3). As a consequence, the upper section of the tube (3) that goes from the inlet (4) to the upper end of the tube (3) where the steam outlet (5) is located constitutes an optional superheat section for the steam.

Another similar way of implementing this is shown in Fig. 3b, where a conduit (8b) travels part of the upper end portion (3s) of the tube (3) on the outside and connects to it to form the inlet (4 ) of liquid at a point lower than the upper end itself where the steam outlet (5) is located. Similarly, a final section of tube (3) is created where steam overheating occurs.

In order to increase the power, it is possible to use several steam generators-separators (1) of the type described to simultaneously feed the same absorption machine (10), the inlet flow being distributed among different generator-separators (1) by means from a distributor and collecting by means of a collector, both the vapor and the liquid.

Claims (15)

5 10 fifteen twenty 25 30 35 1. Steam generator-separator (1) by means of solar energy, which comprises at least one reflecting surface (2) that concentrates solar radiation on the surface of a receiving tube (3), characterized in that: - the receiver tube (3) is inclined and comprises an upper end portion (3s) provided with an inlet (4) of a fluid in a liquid state and an outlet (5) of generated steam, and an end portion (3i) bottom equipped with an outlet (6) of fluid remaining in the liquid state, - such that when the fluid is introduced in a liquid state, said liquid fluid forms a falling film from the inlet (4) in the upper end portion (3s) to the outlet (6) in the end portion (3i) lower, while the heat received by the receiver tube (3) due to the solar radiation reflected by the at least one reflecting surface (2) causes the evaporation of steam and its rise until it exits through the outlet (5) in the (3s) upper end portion. 2. Generator-separator (1) according to claim 1, wherein the steam outlet (5) is located in the receiver tube (3) at a higher height than the liquid inlet (4) to allow steam overheating . 3. Generator-separator (1) according to claim 2, wherein the liquid inlet (4) is implemented by a conduit (8a) outside the receiving tube (3) that is connected to said receiving tube (3). 4. Generator-separator (1) according to claim 2, wherein the liquid inlet (4) is implemented by a conduit (8b) inside the receiving tube (3) 5. Generator-separator (1) according to any of the preceding claims, wherein the inclination of the receiver tube (3) is between 5 ° and 90 °. 6. Generator-separator (1) according to revindication 5, which also includes means for modifying the inclination of the receiving tube (3). 7. Generator-separator (1) according to any of the preceding claims, which further comprises a means (7) for controlling the level of the liquid located in the lower end portion of the receiving tube (3). 8. Generator-separator (1) according to any of the preceding claims, 5 10 fifteen twenty 25 where the inner surface of the receiver tube (3) comprises a plurality of protuberances that modify the downward trajectory of the liquid. 9. Generator-separator (1) according to claim 8, wherein the protuberances are chosen from the following list: fins, bars, plates, steps, fixed or mobile inserts and barriers. 10. Generator-separator (1) according to any of the claims above, where the section of the receiver tube (3) is variable along its length. 11. Generator-separator (1) according to any of the preceding claims, wherein the section of the receiver tube (3) is circular, rectangular or oval. 12. Generator-separator (1) according to any of the claims above, where the at least one reflecting surface (2) is rotatable about an axis parallel to that of the receiving tube (3) to optimize the concentration of the solar radiation on the receiving tube (3). 13. Absorption machine (10) comprising a steam generator-separator (1) according to any of the preceding claims. 14. Thermal engine comprising a steam generator-separator (1) according to any of the preceding claims. 15. Use of a steam generator-separator (1) by solar energy according to any of claims 1-14 for obtaining and separating steam from a fluid in a liquid state.