DE102008018433A1 - Solar updraft tower for converting flow energy of air into drive energy of rotating machine, has heating zone integrated in driving region of air guide and operating in flow path in machine arrangement - Google Patents

Abstract

The plant has a tube arrangement opened at top and bottom and provided with a heating region, and a machine arrangement extracting energy from air flow. A heating zone is integrated in a driving region of air guide, and operates in a flow path in the machine arrangement. A heat exchanger for heat transmission is operated with a heat carrier, and heats inner surfaces of the pipe arrangement, where temperature of the heat carrier lies above an air temperature. A heat storage is attached at a line network of the heat exchanger.

Description

The The invention relates to a Aufwindkraftwerk with energy supply to the flowing Air over heat exchanger in the lower tower section and achieved by increased flow velocity as a result of high air heating in conjunction with reduced air resistance a high power density. The construction related costs are thereby reduced. By limiting the height and Measures for the tower construction will be the wind resistance promoted the plant.

State of the art

Chimney power plants are based on the use of air as a resource and use the sun's heat as energy for generating wind in one tubular tower.

It The rule is that with increasing height of the tower the Print offer for the turbine arranged in the lower area increased, the flow velocity and with it the Performance can be increased. With this assessment There are several suggestions for optimization. There were tower structures with sheet metal coating, as well as inexpensive Concrete pipes and plastic pipe elements for the construction of tall towers considered. After experiments with a prototype system in Spain (Almeria) showed that at high tower constructions quite considerate of the aggravating Problem of the wind loads is to take and this all the more, the more slender the tower is.

The Heat is supplied by the classically designed system according to Prof. Schlaich before the air enters the tower, in which lower area turbine and generator are arranged. A kind of glass or foil roofing conveys the heat transfer in the horizontal area. The necessarily large-scale Plant does not provide one for the flowing air negligible flow resistance and forces the tower height to increase for given performance. Visible align the low rate of heat radiation and the upstream of the heat transfer the Pay too much attention to the execution of tall towers with a high degree of slimming, but obviously as a result of itself peak wind load at uneconomically high investment costs to lead.

Vice versa is having a connection of energy transfer area with the flow system of the tower to benefits for lead the flow. With lower pressure loss then there is the possibility for smaller tower height to achieve the same performance. Also against the disadvantage of having the low energy transfer density is given are To take action.

It Thus, the object of the invention is to the updraft power plant to reduce the investment costs thereby to optimize that the supply of energy to the flowing air predominantly in the tower area, after the exit of the air from the turbine, relocated and thus a reduction of the flow resistance he follows; in addition, an intensification of heat transfer provided by various measures, so that with limited Turmhöhe an increase in the print offer comes about and by choosing a large hydraulic diameter the flow the target of high speed and thus high power density is supported.

The Collection of heat radiation takes place outside of the tower in a separate plant by means of a heat carrier, the preferably water or steam or other suitable medium which will be brought to a temperature that is noticeably higher is the temperature of the locally flowing air in the tower. Within of the tower, heat exchangers serve the efficient transfer the heat from the heat transfer medium to the flow medium. They are integrated into the wall area and carry only slightly to increase the flow resistance at.

Across from previously described solutions will be a significant increase the power density due to increased flow velocity while reducing the ratio of tower height aimed at to diameter.

embodiments

The Solution of the task is through a detailed Text representation and explained with reference to several figures.

The characteristics of the updraft

The Aim of high power density with limited tower height can, as mentioned, by reducing the flow resistance and simultaneously increase the heat input be achieved for a limited flow volume.

As 1 represents the system consists of the lower part A1 with turbine and generator, the heated tower center part A2 and the unheated spire A3. The above-demanded special features reduced flow resistance and heating Unte ren tower section are thus made visible. The three tower sections M1, M2, M3 are based on the guide elements Le on the bottom plate B. The lower section A1 is with the influx of air L to the turbine T and the inflow into the Heating area A2 marked. The turbine T is connected via a shaft W to the generator Ge. The bearing La receives above and beyond the generator radial and axial forces in particular from the turbine and supports them. The shape of the vanes Le and their position are chosen so that the incoming air can enter the turbine without major impact losses and reduces the friction losses, which corresponds to an increase in the efficiency of the turbine. By choosing large cross sections in the area of the guide vanes Le, the friction losses are low there.

2 shows as an example a three-bladed turbine T, which is surrounded by 8 vanes Le. The latter are dimensioned so that they can take over the support function for the tower.

The heating zone provided in section A2 of the tower comprises a plurality of sections, wherein the individual sections are assigned to both the inner shell of M2 and the four central webs Sh with the corresponding exchange surface Hs. This increases the heating surface by about a factor of 1 + π / 4. The middle bridges Sh also improve the bending and buckling resistance of the tower. Thus, with large diameters D _r , significantly increased strength data can be achieved with limited material expenditure.

In 1 is further shown that the required for the heating zone cycle of the heat carrier z. B. can each consist of 3 units, the heat input Q to the heat carrier z. B. by solar radiation, and the heat transfer medium is guided by the pump K to the heat exchanger within the section A2 by means of a pipeline.

In 4 is drawn over the flow path, the distribution of air temperature. The heat supply is made clear by temperature increase. It is distributed over the zones 1-3 and characterized by the maximum value θ _p . In the tower section A3, the temperature is kept constant; it is waived here on energy. Accordingly, a simplified interior is possible in this tower section. It can thus easily performed stiffening elements, eg. B. in a star-shaped arrangement, are used. Depending on the achieved velocity of the flow, the core of the flow prevails also outside the tube region of M3, in comparison to a substantially quiet outer zone up to the final dissolution point. The ascending flow medium of the heated zone is the average temperature θ _m attributed. For the buoyancy decisive is the temperature difference to the average ambient temperature θ _o . It is denoted by Δθ and is in 4 detected accordingly: The temperatures to the heat transfer within the 3 exchanger areas are referred to as θ _w1 to θ _w3 , it being assumed that the flow medium is guided in the countercurrent principle. For approximate buoyancy calculation, the length h _r is available as an approach for the flow core (limited to the warm zone). Here, the same cross-section is required. For the friction losses, the proportion of the section A1 must be taken into account and introduced into a corresponding length l, sh. 4 ,

With the mass reduction related to the flow volume of the air equal to the unheated volume Size can be the generated buoyancy force or a corresponding buoyancy pressure can be determined.

5 shows the temperature-induced specific pressure increase as a function of αΔθ. This size is designated by ε. It initially grows proportionally to Δθ and approaches asymptotically the value 1 when strongly heated. The parameter α lies at 0.0036 K ^-1 at temperatures not too high ( L. Prandtl, Fluid Mechanics, Vieweg and Son Braunschweig, 1949 ). For reasons of effort limitation for the heat exchanger and the heat provided by the transducer Q and the heat transfer medium whose maximum temperature is recommended to limit to about 250 ° C. On the buoyancy causing temperature difference Δθ thus eliminates a temperature range of 150 ÷ 200 K. For the heat carrier water vapor, its pressure level in the warmest stage can be kept approximately in the range of 10 bar.

6 The upper curve shows the lift pressure reduced by the friction losses, while the lower curve shows the pressure applied by the turbine. The intersection of both curves represents the operating point and defines the operating speed v _s . For a given range of flow, the friction pressure p _{r is set} proportional to v ² . Apart from the proportions at the inlet and outlet of the flow, p _{r is} the ratio l / D _H with D _H the hydraulic diameter, sh. also 3 , proportional. Another important factor in the tube friction coefficient equation is the surface roughness detected by the factor λ. For wavy roughness and high speed, λ values are less than 10 ^-3 , while for granular surfaces, ratios of 0.05 are given.

The pressure available at the operating point of the turbine drops accordingly 6 , after a reversed parabola. The underlying assumption that the operating pressure is half of the buoyancy pressure appears as a special case.

The power density of the system

Table 1 shows the relationships between forces and flow velocity in the formula lines 1-4. In formula line 1, the buoyant force F _{o is shown as a} function of the specific weight γ of the air and the tower dimensions as well as the lift coefficient ε. The diagram 6 Correspondingly, the speed v _{s can be determined as a} function of the pressures p _o and p _r , the friction pressure.

The power P _{s associated with} the flow follows from the product of effective force (F _o -F _r ) and v _s .

Taking into account the turbine and generator efficiency η _T and η _G , the output generator power can be determined to be P _G = η _T · η _G · P _s .

It is advantageous that the air turbine is not limited in its efficiency by the Carnot process. η _T can thus be about 60% for high-speed wind turbines.

If one relates the flow rate P _s to the volume of the tower, the equation in formula line 5 follows for the "power density" of the power plant. Apart from the energy supply part, the construction cost of the power plant is approximately proportional to the volume of the tower. The power density equation thus also gives indications of the most important optimization variables with regard to the system costs. It should be noted that v _{s is} a function that increases with ε ^0.5 and, in addition, the quotient l / D _H and the coefficient of friction λ should assume the smallest possible values.

High power densities can obviously be achieved with the intensively heated tower of limited height with relatively large D _H. Initially, independent of the turbine, this also speaks for the use of large-volume systems and great overall performance. So can be z. B. with a tower height of h _r = 250 m and an inner diameter D _r = 100 m at a temperature increase Δθ _m = 150 K with ε = 0.35 achieve a flow rate of about 75 m / s, resulting in a flow rate of P _s = 480 MW leads. The power density is 120 W / m ³ for this example, and assuming an efficiency of η _T · η _G = 0.5, the electric power density follows 60 W / m ³ . The performance data determined according to these design requirements show the potential of a very significant increase in performance and power density increase with limited tower height. Due to the high flow rate with the help of intensified energy supply within the tower area, the cost share per power unit can be greatly reduced.

Results of design studies and more features

The equations derived in Table 1, and in particular the equation for power density, show advantages for systems with limited ratio I / D _H. Since the warm-up only takes effect after the turbine outlet, there is basically nothing to prevent the use of high buoyancy characteristics ε. The limit, however, finds this intensification approach where high temperatures of the air and the heat transfer medium, the heat resistance of the material or the pressure associated with the temperature by the heat transfer medium leads to problems. It can be seen that the depiction of the heat transfer in section A2 is favored by the fact that apparently very high air velocities and with them very high heat transfer coefficients between hot wall and turbulent flowing air are achieved. They are in the range of 180-200 W / m ² K, so that the transmission can take place with relatively small areas. From the area close to the wall, the heat is quickly transferred to the center of the flow through intensive exchange of momentum between the flowing vortex packets. For the design of the inner pipe architecture, the idea of pipe stiffening, such as the additional installation of elements of the heat exchanger, must be given space.

The Separation of the air heating section from the horizontal turret and its installation inside the tower proves to be an important measure to increase performance and allows the compression of the heat supply and their restriction on the lower part of the tower. It continues to open the free Choice of the type of energy supply for the energy source.

Naturally it is obvious to the application of the radiation energy of the sun to think with the already recognized as efficient parabolic trough to be used as energy concentrator. She is in the USA and in Germany been tested by DLR. Here, the radiation is on Water or steam-carrying metal tube, the focal point area the gutter is led, concentrated. The temperature increases can be determined by the flow rate of the heat carrier regulate. By connecting several sections result high temperatures at high pressures. Guide values for the required projection area of the irradiated Gullies are dependent on the known geographical factors and the orientation of the gutter to the sun. A following the position of the sun Location tracking can be found in grooves in a horizontal arrangement relatively easy to do.

Of the Advantage of energy conversion in a wind turbine with wind turbine lies opposite the steam turbine concept, which is based on the Carnot efficiency is bound to the abolition of this limit and to the relative simple machine equipment.

In 7 It is pointed out that to minimize the on-site costs also concept modifications 1 are to be considered. Thus, use can be made of the fact that, in order to increase the security against tower deformation, its internal structure can be constructed starting from a central core part Sm. This element is continuously available in height and anchored in the foundation. With him star-shaped, bending-resistant approaches Sh are connected, which are also supported on the foundation and connected to the mantle. The shape of the shell is executed in cross-section as a polygon; the tower cross-section is similar to a truss, sh. 8th , With large cross-sectional area, the number of subdivisions, the fan, can be further increased. Similar to the arrangement after 1 In the tower section A2, the heating zones are formed by units of the heat exchangers Hm and Hs. Again, it is obvious to adapt the modular framework of the tower cross section to a modularized machine arrangement. The turbine T with the generator Ge is driven by the air flow in the inlet region of the feed pipe R. According to the number of tower compartments 4 supply pipes R are present in the example. The attachment of the machines T and Ge via molded parts Le, which take over the function of guide elements. The subdivision of the machines into several individual units can have advantages for assembly, installation and transport, if it is a question of large system capacities.

Around with limited mass with very large machine diameter a high conversion efficiency for generating the electrical Ensuring energy, special magnetic circuit arrangements are recommended after 10 2007 042 935.7 and 10 2007 016 879.0 15. Here are by using permanent magnets in flux concentration form especially high magnetic field densities available. you are the basis for increasing the efficiency of energy conversion.

Aufwindkraftwerk with heat storage

The after 1 illustrated conception of the heat coupling using a liquid or vapor heat carrier allows the possibility to connect to the temporary operation of the system without solar radiation through the pipe network of the heat storage heat storage, and thus to keep the temperatures of the heat carrier at a high level. The operation of the power plant is thus independent of the intensity and duration of direct sunlight. It is to be regarded as a particular advantage that the storage function is based on the same technology as the provision of energy for the heat exchangers in the tower zone A2.

Of the Heat transfer medium of both subsystems is the same. The connection of a memory requires actuators, such as valves or slide to open and close hot water leading lines. Further, it is obvious, as an example described technique of radiation concentration in the form of mirror grooves to provide the storage of heat in the store. It is not excluded, for heating the storage medium also additional possibilities of preheating use. The coupling of the power plant with an effective heat storage increases the functionality and the possibilities of use to a great extent.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - L. Prandtl, Fluid Mechanics, Vieweg and Son Braunschweig, 1949 [0017]

Claims (7)

Aufwindkraftwerk for the implementation of flow energy the air in drive energy of rotating machinery, consisting enclosed by a volume of air heated by heat in an upright, up and down open tube arrangement with a heating area and an airflow energy withdrawing machine assembly, wherein the heating zone is integrated in the buoyancy area of the air duct and after the machine arrangement in the flow path effective becomes. Aufwindkraftwerk according to claim 1, characterized that the heat exchanger used for heat transfer is operated with a heat transfer medium whose temperatures over the air temperatures reached in the respective sections are and he according to the inner surfaces of the pipe assembly heated. Aufwindkraftwerk according to any one of the above claims, characterized in that a part of the heat exchangers associated with the star-shaped tower compartments, which serve to stiffen the tower structure. Aufwindkraftwerk according to any one of the above claims, characterized in that as a heat source for heating the heat carrier used the solar radiation and concentration possibilities of the radiation energy in Form of mirrors parabolic type used Aufwindkraftwerk according to any one of the above claims, characterized in that a heat accumulator to the mains network the heat exchanger is connected, its function also on the principle of heating the heat carrier based. Aufwindkraftwerk according to any one of the above claims, characterized in that as a turbomachine high-speed Wind turbines find use and guide elements are used which also take over other functions. Aufwindkraftwerk according to any one of the above claims, characterized in that for converting the mechanical rotational energy in electrical energy generators with particularly high efficiency can be used, whose exciter field generated by permanent magnets becomes.