Patent Application
20140238386
Not applicable
This invention relates to a field of solar energy usage and, particularly, to solar systems, which operate on the base of concentration of direct solar radiation. In addition, the invention can be used for superheating steam in thermal power plants.
This invention relates to a field of solar energy usage and, particularly, to solar systems, which operate on the base of concentration of direct solar radiation.
The solar systems may be used as a source of thermal energy in power plants, or as a source of thermal energy for carrying out thermo-chemical processes.
There are three main types of the solar concentrating systems, which may put into practice the proposed invention:
1. Parabolic trough collectors (PTCs);
2. Solar thermal collectors with application of linear Fresnel reflectors (LFRs).
3. An array of flat or slightly concave mirrors, or heliostats, which is used to reflect their incident direct solar radiation onto a central receiver mounted on a tower (STP) or on the ground.
PTCs can effectively produce heat at temperatures between 50° C. and 400° C. Concentrating mirrors of PTCs are made by bending sheets of reflective material into a parabolic shape (a trough shape). A receiver is designed as a metal tube with a radiation absorbing coating on its external surface; the metal tube is arranged in a glass tube with the evacuated space between this metal tube and the glass tube.
The receiver is placed along the focal line of the parabolic mirrors.
When the parabolic trough-wise reflector is pointed towards the sun, parallel rays incident on the parabolic trough-wise reflector are reflected onto the receiver tube. It is sufficient to use a single axis tracking of the sun and thus long collector modules are produced. The collector can be orientated in an east-west direction, tracking the sun from north to south, or orientated in a north-south direction and tracking the sun from east to west.
LFR technology relies on an array of linear mirror strips which concentrate light onto a fixed receiver mounted on a supporting construction. Concentrated radiation receivers have a same design as in the case of the PTCs.
It is widely recognized that application of concentrating solar collectors with direct steam generation (DSG) instead of heating thermal oil allows significant diminishment of electricity generation cost in the concentrating solar power plants and, at the same time, to achieve higher efficiency.
Detailed discussion regarding solar power plant with direct steam generation is presented in an article: J. Birnbaum et al. “A Concept for Future Parabolic Trough Based Solar Thermal Power Plant”, PREPRINT-ICPWSXV, Berlin, Sep. 8-1, 2008.
For extremely high inputs of radiant energy, an array of flat or slightly concave mirrors, or heliostats, is used to reflect their incident direct solar radiation onto a central receiver mounted on a tower or on the ground. In such a way, this combination of the tracking mirrors and the central receiver serves as a source of thermal energy in the solar tower power plant (STP).
The concentrated solar radiation absorbed by the central receiver is transferred into thermal energy of a circulating heat transfer medium.
The solar concentrating system, which includes the heliostat achieve concentration ratios of 300-1500 and so are highly field, may efficient both at collecting energy and at converting it to electricity.
There are two technical problems in operation of the receivers of the PTC, LFR and STP systems.
Uneven heating of radiation absorbing pipes in their circumferential direction by concentrated radiation and, as result, their deformation.
This deformation is expressed in bending the radiation absorbing pipes out of their position in the focal areas and diminishment of their efficiency. In addition, it can cause mechanical failure of the receiver, especially, for PTC and LFR systems.
An additional technical problem for PTC, LFR and STP systems is relatively low values of heat transfer coefficients for gaseous heat transfer medium flowing in the radiation absorbing pipes.
It requires operation with high temperature drops between the outer surfaces of the radiation absorbing pipes and the gaseous heat transfer medium. This causes elevation of heat losses mainly by thermal radiation and, in turn, diminishes additionally efficiency of PTC, LFR and STP systems, when they are used for superheating steam, heating the pressurized air or heating a gaseous medium for execution of thermo-chemical reactions.
There are some patents and patent applications intended to solve these problems.
A solar fluid heater device is disclosed in U.S. Pat. No. 1,575,309 to Anderson. The efficiency of heat transfer is enhanced in this device by use of heat transfer baffles disposed within a fluid conveying pipe and extending longitudinally thereof.
U.S. Pat. No. 4,026,273 describes a trough-concentrating system with a radiation absorbing pipe with a plurality of convective heat transfer fins within the radiation absorbing pipe; these heat transfer fins are arranged longitudinally.
However, the longitudinal heat transfer fins cannot enhance the internal surface of the radiation absorbing pipe in fife-to-one ratio or more and, at the same time, to increase significantly the heat transfer coefficient for the fins themselves as for pin-wise fins. At the same time such enhanced heat transfer is required for the radiation absorbing pipe in PTC, LFR and STP systems.
U.S. Pat. No. 5,460,163 discloses a trough-shaped solar radiation collector intended for steam generation. A trough-shaped mirror extending in a longitudinal direction receives and reflects radiation onto an absorber line enclosing within its interior a steam generator tube in which water is heated, vaporized and superheated. Heat is transferred transversely from the absorber line to the steam generator tube by heat pipe segments spaced longitudinally along the absorber line.
It is clear, that this technical solution does not solve the problem of low values of the heat transfer coefficient for heat transfer from the internal surface of the steam generator tube, when the generated saturated steam to be superheated.
WO 2011101485 describes a solar heat receiver tube for direct steam generation, comprising at least one outer absorber tube with an internal absorber tube space and at least one inner water tube with an internal water tube space for carrying water. The inner water tube is arranged in the internal absorber tube space. The outer absorber tube and the inner water tube are formed and arranged such that solar energy can be absorbed by the outer absorber tube and absorbed solar energy can be transferred from the outer absorber tube to the inner water tube for the steam generation within the internal water tube space. Inside the water tube liquid water can be transformed into vaporous water.
This technical solution is analogical to U.S. Pat. No. 5,460,163.
U.S. Pat. No. 5,465,708 describes a trough-shaped collector with an absorber pipe member; this absorber pipe member has an interior with a vaporizer tube having an essentially round cross section, which extends in the interior of the absorber pipe member for transporting heat in the longitudinal direction, and the vaporizer tube is thermally coupled to the absorber pipe member via a heat transport medium presented between the vaporizer tube and the absorber screen for transporting heat transversely to the longitudinal direction.
This technical solution is analogical to U.S. Pat. No. 5,460,163.
U.S. Pat. No. 5,860,414 (DE 43 31 784) discloses a trough-shaped mirror extending in longitudinal direction and reflecting the radiation into a focus region, and an absorber line extending in longitudinal direction through the focus region of the trough-shaped mirror and having a guide tube for the heat transport medium and an absorber pipe surrounding the guide tube such that an annular chamber is formed between guide tube and absorber line, with which the problems existing as a result of the uneven irradiation of the absorber line are also reduced or eliminated, it is suggested that an annular passage medium flow in the annular chamber and that the annular passage medium couple the guide tube thermally to the absorber pipe.
This patent does not solve the problem of enhancing heat transfer for the internal surface of the guide tube.
US patent application No. 20100236239 describes a method for generating steam for a turbine electric power plant, which uses solar radiation. Solar radiation is directed onto a solar receiver. The solar receiver includes a first section, which receives feedwater input and is arranged to heat the feedwater input to generate steam using the directed solar radiation. Feedwater flows through a feedwater vessel to serve as feedwater input to an inlet of the first section of the receiver. Water is separated from the steam in a steam separation vessel, which is in fluid communication with an outlet of the first section of the receiver. The feedwater input may be selectively preheated by a source of preheat other than solar energy in response to system operating conditions, predicted insolation schedule, or an electrical energy tariff schedule.
We see that this patent application does not solve the problem of steam superheating.
US patent application No. 20110239651 discloses heat transfer pipes, which uniformly heat a compressible working fluid passing there through with a simplified supporting structure and reduced manufacturing costs. A solar central receiver on top of a tower on the ground includes heat transfer pipes arranged in the south-north direction; and a casing accommodating the pipes and has a solar radiation inlet through which sunlight reflected by heliostats on the ground is transmitted to the lower surface side of the pipes. The pipes are at equal intervals on a solar radiation receiving surface parallel to a heliostat field on which the collectors are, or inclined with respect to the heliostat field on which the collectors are, and the diameters of the pipes are substantially inversely proportional to the shortest distance from the inlet to the central axes of the respective pipes in the longitudinal direction.
US patent No. 20090261591 application describes a solar power generation system, which includes a solar receiver disposed on a tower that receives radiant heat reflected from a field of solar collectors. The solar receiver includes an evaporator having a plurality of vertically oriented tubes to form a panel for receiving a fluid, such as water and/or steam, wherein the tubes have a rifled internal surface. The fluid within the tubes has a mass flow greater than 0.2.times.10.sup.6 lb/hr/ft.sup.3 at a pressure in the range of 100-2850 psia, wherein radiant heat fluxes on the outside of the tubes exceed 185,00 but/hr/ft.sup.2.
The proposed rifled internal surface of the tubes does not provide a required enhancement of the heat transfer coefficient for steam superheating.
US patent application No. 20080302314 describes a solar concentration plant, which uses water/steam as a heat-carrying fluid; in any thermodynamic cycle or system for the exploitation of process heat, which is comprised of an evaporation subsystem, where saturated steam is produced under the conditions of pressure of the system, and a superheating subsystem through which the steam reaches the required conditions of pressure and temperature at the turbine inlet.
This patent application does not give any technical solution for enhancement of the heat transfer coefficient in the steam superheating unit.
US patent application No. 20080078378 describes a solar tower central receiver with a separated boiler and a super-heater allowing better control on the output steam's temperature. The boiler takes higher solar flux density and works at lower temperature while the super-heater takes lower solar flux and works at high temperature to optimize the cost to performance ratio. The boiler consists of parallel pipes as solar absorber and the super-heater consists of helix parallel pipes as a solar absorber.
We see that this patent application does not give any technical solution for enhancement of the heat transfer coefficient in the steam superheating unit.
EP2372265 describes a thermal solar energy collector with a solar radiation absorption panel, inside which the heat-conducting fluid flows; this solar radiation absorption panel is situated inside a parallelepipedal box with an opening having a transparent cover at the front; the rear wall of the box has a system of seals and reservoirs, which accommodate the expansion and contraction of vertical tubes of the panel and horizontal connections by means of gentle changes in the curvature of the tube bends and slight rotations of the reservoirs, with the addition of a system for filling the box with an inert gas.
In addition, some patent application should be mentioned, such as WO Nos. 20111044281, 201103033, 2010132849, 2010093235, EP 2000669.
These patent applications do not give any technical solution for enhancement of the heat transfer in the steam superheating unit.
There are some US patents and patent applications, which are related to plate dish heat exchangers and their constructions somewhat resemble a receiver of solar concentrated radiation, which is proposed in this invention.
For example, U.S. Pat. Nos. 7,717,164, 7,533,717, 7,426,957, 6,546,996, 5,927,394, 5,099,912, 4,892,136, 4,708,199, 4,561,494, US patent applications Nos. 20030106679, 20070084809, German patents DE-A 43 14 808, DE-A 195 11 991 or DE-A 197 50 748 are related to this technical field. However, these patents and patent applications describe heat exchangers intended to cool oil by a cooling liquid and they do not suitable for heating a gaseous medium by concentrated solar radiation.
This invention is based on possibility to achieve enhancement of heat transfer from a heat sourcing member to a gaseous heat transfer medium flowing along it by extending the internal surface of the heat sourcing member and by generation of multi jet flow between fins, which present structural units of this extended internal surface. It is known, that application of multi-jet flow allows to obtain very high values of the Nusselt number, i.e.—high values of the heat transfer coefficient. For example, the article: Dae Hee Lee et al. “Heat transfer enhancement by the perforated plate installed between an impinging jet and the target plate”; Int. Journal of Heat and Mass Transfer, 45 (2002) pp. 213-217 describes this phenomena.
More specifically, this invention proposes a new method of an internal finning of a solar radiation absorbing tube placed in the focal areas of solar radiation concentrating systems applying tracking trough parabolic mirrors or tracking one-curvature Fresnel mirrors. In addition, such solar radiation absorbing tubes may be used in solar concentrating systems based on application of tracking heliostats, when concentrated solar radiation is absorbed by a bank of solar radiation absorbing tubes, which are situated in a radiation receiving chamber (STP system).
The outer surface of the solar radiation absorbing tube (or tubes in the case of STP system), which is provided preferably with an outer selective radiation absorbing coating, plays a role of the abovementioned heat source member.
An extended heat transferring structure according to this invention is formed by stacked metal perforated plates, preferably, of the circular shape; each metal perforated plate is provided with an inclined rim or an upright two-step rim.
In the case of usage of the upright two-step rim, the difference between the outer radii of both steps of the rim approximates that of the rim width. The adjacent metal perforated plates in their stacked assembly are sealingly jointed by brazing or welding.
The perforations of the metal plates can be executed by different technological methods; for example, by piercing or scrapless piercing, drilling, punching, photochemical milling and electroforming. The perforations in the metal plates can be of the circular shape, the oval shape, the slot shape etc.
In addition, the adjacent circular metal plates may be mutually turned through a certain angle in such a way that the axes of perforations of one circular metal plate intersect the bridges of the adjacent metal circular plates.
In order to achieve higher stiffness of the obtained tubular piece, a set of metal longitudinal rods can be joined with it by brazing or welding.
The external surface of the obtained tubular unit is covered with a solar radiation absorbing coating. This coating has preferably selective optical characteristics.
In such a way, a solar radiation receiver for PTC and LFR systems comprises:
In such a way, the second section of the radiation receiving metal pipe serves for heating and evaporation of the most fraction of the feedwater, and the first section formed from the stacked perforated plates serves mainly for superheating the saturated steam obtained in the second section.
It should be noted, that the stacked perforated plates of the second section play a role of a demister.
In the case of application of solar collectors of PTC and LFR types for superheating steam or heating a gaseous heat transfer medium (for example, the air), the metal pipes of their solar radiation receivers consist of only the first type sections formed by stacking and joining the perforated circular plates with their rims, as it has been described previously.
In the case of a central receiver mounted on a tower (STP) with an array of tracking heliostats, which reflect solar radiation on this central receiver, this central receiver comprises a radiation receiving chamber with at least one glazed aperture intended for entering concentrated solar radiation into the internal space of the radiation receiving chamber.
The internal space of the radiation receiving chamber consists of one or more rows of parallel metal radiation receiving pipes, wherein each metal radiation receiving pipe has a first section manufactured from stacked perforated metal plates with inclined or upright two-step rims; these stacked perforated metal plates are sealingly joined by brazing or welding.
A second section of each metal radiation receiving pipe is a common metal pipe, which is joined by brazing or welding with the first section formed from the stacked perforated plates; two fittings are joined with the free ends of each pair of the first and second pipe sections. The free ends of the fittings are joined with metal bellows.
There are lower and upper headers; the lower header serves for intake of feedwater from an outside delivery unit and its distributing through the bellows and their fittings into the second sections of the metal radiation receiving pipes; the upper header serves for intake of the superheated steam from the first section of the metal radiation receiving tubes and its delivery to an outside consumer.
Selective absorptive coatings cover the outer surfaces of the first and second pipe sections of the metal radiation receiving pipes. It should be noted that these selective absorptive coatings can cover only the outer areas of the first and second pipe sections, which are radiated by concentrated solar radiation.
In the case of application of a solar collectors of STP type for superheating steam or heating a gaseous heat transfer medium (for example, the air), the radiation receiving metal pipes situated in the radiation receiving chamber consist of only the first type tubular sections formed from stacking the perforated circular plates with their rims, as it has been described previously.
It should be noted, that the proposed pipes formed from the stacked metal plates may be applied in radiant or combine superheating units of steam generators operating by combustion of gaseous, liquid or solid fuel.
a and
c and
a and
a and
c and
a and
a and
a,
d,
a and
The perforated metal circular plate 100 comprises a flat member 101, circular perforations 102 and an inclined rim 103.
c and
The perforated circular metal plate 104 comprises a flat member 105, circular perforations 106 and an upright two-step rim with its lower and upper sections 108 and 107.
a and
The perforated circular plate 200 comprises a flat member 201; circular perforations 202 terminated on one side with nipples 204 and an inclined rim 203, which is oriented in the same direction as nipples 204.
a and
The perforated metal circular plate 300 comprises a flat member 301, sharp-leaved perforations 302 and an inclined rim 303.
c and
The perforated circular metal plate 304 comprises a flat member 305, sharp-leaved perforations 306 and an upright two-step rim with its lower and upper sections 308 and 307.
a and
The perforated circular metal plate 400 comprises a flat member 401, circular perforations 402, an inclined rim 403 and a central rectangular opening 404.
The perforated circular metal plate 405 comprises a flat member 406, circular perforations 407, an inclined rim 408 and a central rectangular opening 409, which is angularly shifted with respect to the other circular openings in comparison with the perforated circular metal plate 400.
a and
a demonstrates flat circular plates 502 with sharp-leaved perforations 507, inclined rims 503, fitting 504, fitting 505 and welds 506.
b demonstrates flat circular plates 508 with sharp-leaved perforations 511, lower sections 510 and upper sections 509 of upright two-step rims, fitting 512, fitting 513 and welds 514.
The solar radiation receiver 600 comprises:
a,
The radiation receiving chamber 700, which is installed on tower 703, comprises:
d,
