A HEAT COLLECTOR TUBE Field of Invention

The present invention relates to heat collector tubes used in solar thermal energy systems and to solar energy systems in which heat collector tubes are used. Prior Art

In solar thermal energy systems, rays from the sun are sent to a heat collector tube by reflector surfaces so that a fluid passed through the heat collector tube is heated up. Solar energy systems are basically divided into two groups according to the type of the fluid passed through the heat collector tube. In the first type of system, a fluid with high heat retention capacity and temperature resistance is passed through the heat collector tube. According to this type, after the fluid heated up is outlet from the solar energy system, it heats the water (or a similar fluid) so as to produce steam having a high temperature and pressure. The steam, in turn, is used to run a steam turbine, for instance, to generate electrical energy. In the second type of system, on the other hand, water (or a similar fluid) is passed through the heat collector tube so that directly steam with high temperature and pressure is obtained. As is disclosed in the patent document WO2013045721 A1 according to the prior art, the approach by which direct hot steam is obtained from a heat collector tube is named as direct steam generation (DSG).

In order to reach high efficiency in a solar thermal energy system, the temperature of the fluid passed through the heat collector tube has to be kept at the highest temperature possible. Therefore, the heat collector tube is coated using special materials in order to absorb the sunrays received from the reflectors in an efficient manner. With the advancing technology, the temperature of the fluid passed through the heat collector tube can be increased up to 550-600°C by virtue of said coatings. However, the costs are high of applying the coating process according to the present coating technology to tubes with a thickness above 5 mm. Therefore, the thickness of heat collector tubes is kept below certain limits. Additionally, since the wall thickness of heat collector tubes used particularly in the direct steam generation method is low, the pressure of the fluid should be below a certain level. This also causes the steam obtained from the solar energy system to have a low pressure. Since the steam outlet from a single heat collector tube is not adequate to operate a steam turbine, it is not feasible to obtain high efficiency from this type of solar energy systems.

Brief Description of Invention A heat collector tube according to the present invention is suitable for use in a direct steam generation-type solar thermal energy system, and heats a fluid which is passed through the heat collector tube by the sunrays reflected thereon by means of at least one reflector. The heat collector tube comprises at least one inner tube of high heat conductivity, through which the fluid by which steam is generated is passed, and at least one spacer tube which surrounds the inner tube leaving a gap there between, on which sunrays fall, through which the gap made with the inner tube at least one other fluid is passed, and which heats the fluid passed between itself and the inner tube by means of the sunrays falling thereon. A solar thermal energy system in which the heat collector tube is used comprises at least one solar panel by which the rays from the sun are sent onto the heat collector tube; at least one fluid tank in which the fluid to be heated by means of sunrays is contained; at least one circulation line by which the fluid in the fluid tank is sent to the spacer tube and the fluid received from the spacer tube is sent to the fluid tank; at least one pump by which the fluid is moved in the circulation line; at least one temperature control valve measuring the temperature of the fluid transferred from the spacer tube to the fluid tank and controls the temperature of the fluid by limiting the flow-rate of the fluid flowing through the circulation line according to the measured temperature; at least one heating line by which the fluid received from the fluid tank is transferred to the inner tube; and at least one other pump by which the fluid is moved in the heating line. Object of Invention

The object of the present invention is to develop a heat collector tube suitable for use in solar thermal energy systems in which direct steam generation is performed. Another object of the present invention is to develop a heat collector tube enabling a fluid passed through the heat collector tube to reach high temperature levels.

A further object of the present invention is to develop a heat collector tube enabling a fluid passed through the heat collector tube to reach high pressure levels.

Still a further object of the present invention is to develop an efficient and reliable heat collector tube. Yet a further object of the present invention is to develop a solar energy system in which the heat collector tube according to the present invention is used.

Description of Figures Representative embodiments of the heat collector tube developed according to the present invention are illustrated in the accompanying figures briefly described below.

Figure 1 is a cross-sectional side view of a heat collector tube according to the present invention.

Figure 2 is a cross-sectional perspective view of the heat collector tube according to the present invention.

Figure 3 is a cross-sectional perspective view of a coupling detail of the heat collector tube according to the present invention.

Figure 4 is a block diagram of a solar energy system in which the heat collector tube is used.

The parts in the figures are individually designated as following.

Heat collector tube (T)

Solar thermal energy system (S)

Inner tube (1)

Spacer tube (2)

Outer tube

Vacuum gap Expansion bellows (4, 4a)

Connection member (5)

Spacer tube outlet (6)

Temperature control valve (7)

Pressure control valve (8)

Pump (9)

Heat storage unit (10)

Fluid tank (11)

Circulation line (12)

Heating line (13)

Description of Invention

In solar thermal energy systems, sunrays are sent to a heat collector tube by means of reflectors. Thus, a fluid passed through the heat collector tube is heated up. In order to increase the temperature of the heated fluid to higher values (e.g, 600°C), the heat collector tubes comprise a coating absorbing the sunrays. According to currently-available coating technologies, the cost of applying a coating to tubes with a thickness above 5 mm is high. When the thickness of the heat collector tube is low, particularly in the direct steam generation-type solar energy systems in which water (or a similar fluid to be steamed) is passed through the heat collector tube, it is not feasible to produce steam at a high pressure. For this reason, a heat collector tube for obtaining steam of a high pressure and temperature and a solar thermal energy system comprising said heat collector tube are developed according to the present invention.

As illustrated in figures 1-3, the heat collector tube (T) developed according to the present invention comprises at least one inner tube (1) of high heat conductivity, through which a fluid by which steam is generated is passed, and at least one spacer tube (2) which surrounds the inner tube (1) leaving a gap therebetween, on which sunrays fall, through which the gap to the inner tube (1) at least one other fluid is passed, and which heats the fluid passed between itself and the inner tube (1) by means of the sunrays falling thereon. The pressure of the fluid passed through said inner tube (1) is preferably higher than 200 bars (specifically 250 bar). Additionally, the pressure of the fluid while it passes through the gap between the inner tube (1) and the spacer tube (2) is preferably lower than 50 bars (preferably 20 bar). In the heat collector tube (T) developed according to the present invention, the fluid passing through the gap between the inner tube (1) and the spacer tube (2) is heated by means of the sunrays falling on the spacer tube (2). The fluid passing through the inner tube (1), in turn, is heated by means of the inner tube (1) with the increasing temperature of the fluid passing through the gap between the inner tube (1) and the spacer tube (2). Here, since the energy of the sunrays is efficiently absorbed by the spacer tube (2) and the energy obtained is transferred to the fluid passing through the inner tube (1) by means of the inner tube (1), the wall thickness of the inner tube (1) may be selected at any desired value. Thus, the fluid can be passed through the inner tube (1) at any desired pressure (e.g. above 200 bars) by selecting a higher wall thickness for the inner tube (1).

According to another preferred embodiment of the present invention, the heat collector tube (T) comprises at least one outer tube (3) which is disposed out of the spacer tube (2) so as to cover the spacer tube (2) and has a vacuum gap (3a) between the spacer tube (2) and itself. According to this embodiment, said outer tube (3) is preferably made of glass (or from another material having high sunray transmission). Thus, sunrays are transmitted onto the spacer tube (2) without energy loss. The outer tube (3) preferably comprises at least one expansion bellows (4) on at least one end thereof by which it is connected to another outer tube (3) and/or to a fixed floor. Thus, when the size of the outer tube (3) changes due to temperature differences, the outer tube (3) is prevented from damages.

According to a further preferred embodiment of the present invention, the spacer tube (2) comprises at least one thermal coating to provide a better absorption of the sunrays. Thus, the amount of energy obtained from the sunrays is increased. Since the sunrays are absorbed by the spacer tube (2) according to this embodiment, there is no need to provide a similar coating on the inner tube (9). The use of a coating on the heat collector is not a preference, but an obligation.

According to a further embodiment of the present invention, the heat collector tube (T) comprises at least one other expansion bellows (4a) having at least one end connected to the spacer tube (2) and at least another end connected to a spacer tube outlet (6) which is immovable (it may be fixed to a floor or to a unit). According to this embodiment, when the length of the spacer tube (2) changes due to temperature changes, the side of the spacer tube (2) connected to the expansion bellows (4a) can displace so as to come closer to and move away from the tube outlet in a safe manner. According to this embodiment, the heat collector tube (T) preferably comprises at least one connection element (B) which connects the spacer tube (2) and the expansion bellows (4a) so that the spacer tube (2) can rotate on the longitudinal axis with respect to the expansion bellows (4a). Thus, in case the solar energy system, in which the heat collector tube (T) is used, makes a rotational movement on the longitudinal axis of the heat collector tube according to the position of the sun, the spacer tube (2) can move with respect to the immovable spacer tube outlet (6) in a safe manner.

As illustrated in the block diagram in figure 4, a solar thermal energy system (S) according to the present invention in which said heat collector tube (T) is used comprises at least one solar panel (not illustrated in the figures) by which the rays from the sun are sent onto the heat collector tube (T); at least one fluid tank (10) in which the fluid to be heated by means of sunrays is contained; at least one circulation line (12) by which the fluid in said fluid tank (11) is transferred to the spacer tube (2) and the fluid received from the spacer tube (2) is transferred to the fluid tank (11); at least one pump (9) by which the fluid is moved in the circulation line (12); at least one temperature control valve (7) which measures the temperature of the fluid transferred from the spacer tube (2) to the fluid tank (11) and controls the temperature of the fluid by limiting the flow-rate of the fluid flowing through the circulation line (12) according to the measured temperature; at least one heating line (13) by which the fluid received from the fluid tank (11) is transferred to the inner tube (1); and at least another pump (9) by which the fluid is moved in the heating line (13). According to this embodiment, the temperature of the fluid passed through the gap between the inner tube (1) and the spacer tube (2) can be kept at a desired temperature range by means of said temperature control valve (7). Thus, the fluid passed through the gap between the inner tube (1) and the spacer tube (2), and the fluid which is heated by the former fluid and passed through the inner tube (1) are prevented from reaching unfavorable temperatures (e.g. high temperatures which can damage the system to which the fluid outlet from the inner tube is transferred).

According to another embodiment of the present invention, the solar thermal energy system (S) comprises at least one pressure control valve (8) controlling the pressure of the fluid circulated in the circulation line (12). Thus, the fluid circulated in the circulation line (12) is prevented from reaching to unfavorable pressure levels and damage the spacer tube (2). According to a further embodiment of the present invention, the solar thermal energy system (S) comprises at least another pressure control valve (8) controlling the pressure of the fluid passed through the heating line (13). Thus, the fluid is passed through the inner tube (1) at a desired pressure level. According to another preferred embodiment of the present invention! the solar thermal energy system (S) comprises at least one heat storage unit (10) disposed at the circulation line (12) (preferably between the spacer tube (2) and the fluid tank (11)). Said heat storage unit (10) stores the energy of the fluid circulated in the circulation line (12) at times when sunrays fall on the solar energy system (S) (e.g. during daytime). At times when no sunrays fall on the solar thermal energy system (S), in turn, the fluid circulated in the circulation line (12) can be heated by means of the energy stored in the heat storage unit (10). Thus, the fluid passed through the inner tube (1) can be heated in an uninterrupted manner. According to alternative embodiments of the present invention, either a single fluid tank

(11) can be used to supply fluid to the circulation line (12) and the heating line (13), or an individual fluid tank (11) for each line (12, 13). In an embodiment involving individual fluid tanks (11), different fluids can be supplied to the circulation line (12) and the heating line (13).

According to a preferred embodiment of the present invention, the solar energy system (S) comprises at least another pump (9) for transferring fluid from at least one fluid source to the fluid tank (11). Thus, when the amount of the fluid in the fluid tank (11) is reduced, an adequate amount of fluid is supplied to the fluid tank (11).

According to a representative embodiment of the present invention, water with a pressure of 20 bars and of 250 bars is circulated in the circulation line (12) and in the heating line (13), respectively. According to this embodiment, the water circulated in the circulation line

(12) can be heated up to 580-600°C by means of the sunrays falling on the spacer tube (2). The water circulated in the heating line (13), in turn, can be heated up to 560-580°C the inner tube (1).