Ultra-compact, linear, solar-thermal steam generator

Abstract

Direct solar thermal steam generator with an ultra-compact linear Fresnel reflector field that has “travel and turn” capability by means of independent linear and rotational motion of reflectors. Method of positioning and orienting the reflectors of the traveling field such that the reflected energy of the field is maximized at all times Crescent like rotational support rail of the reflector with its gravitational center in the center of the crescent. The curvature of the reflector is customized for each row of the field Ultra-light, collector-absorber structure, with cable suspended arch-like tubular absorber, wide aperture, and secondary reflector with optimized light entrapment Flow distribution and control method of the large horizontal solar thermal steam generation field.

1 . A solar thermal steam generation system (STSG), comprising:
 a plurality of solar reflectors lined up and connected in a row, and a plurality of parallel rows located in proximity with the ground, whereas the cross sectional profile of the reflectors is flat (linear) and/or slightly curved, and   a plurality of collector rows located above and in parallel with the solar reflectors, such to collect and absorb the solar energy directed to them by the reflectors and directly transfer it to thermal energy of steam flow, whereas one collector is to collect energy from multitude of reflectors.   
     
     
         2 . The solar thermal steam generating system of  claim 1 , wherein the reflectors have two independent positioning degrees of freedom: one rotational along the longitudinal axis, and one linear, parallel with the ground and perpendicular to their longitudinal axis. The combination of rotational and linear movement of the reflectors is used to track the Sun and maintain reflection of incident light to one of the collectors on either side of the reflector as well as to position the reflector in the space between two adjacent collectors such that the total reflected energy of the field is maximized in all positions of the sun during the year. 
     
     
         3 . The STSG of  claim 1 , wherein the ratio of reflectors to collectors is typically between 8 to 24 and the collection angle (between the reflected Sun-rays from the furthest pro- and the furthest contra-solar reflectors) is between 70° and 110° 
     
     
         4 . The STSG of  claim 1 , wherein each of the plurality of collectors comprising of plurality of metal tubes (forming an absorber tube-bundle) containing water in liquid or in vapor form, wherein the tubes are arranged in an ach shape by gravitation, suspended freely on a cable suspension. 
     
     
         5 . The cable suspended tube bundle of  claim 4 , wherein the portion of the cable supporting the tube-bundle is filled with freely rotating hollow “beads” of cylindrical or curved profile. Whereas the arch shape of the tube-bundle is further secured by a pre-formed metal bracelet over and across the top of the tubes to the cable. Whereas further to the support of the tube-bundle, a singularity or plurality of hollow rollers on pins is installed between a singularity or plurality of the tubes supported from the bracelet and the suspension cable. 
     
     
         6 . The dual function traveling—rotating reflector support carriage comprising: a base plate mounted on plurality of freely rotating wheels, whereas the support carriage rolls on the wheels on an approximately flat horizontal rail located on the ground and whereas the carriage is guided by guiding-plate or rollers preventing derailing or lifting the carriage from the rail. 
     
     
         7 . The reflector of  claim 1  wherein the reflector mirror is slightly curved for focus, wherein the curvature of each reflector is customized for its distance from the targeted collector. 
     
     
         8 . The reflector of  claim 1  is supported by truss-bridge sub-structure with two circular arch-shaped end-pieces also referred as crescent-rails. The crescent rail is formed from angle iron. Whereas the width of the reflector of  claim 1  extends over the diameter of the crescent-rail. 
     
     
         9 . Carriages of  claim 6  support the reflector sub-structure through the crescent-rail end pieces of  claim 8 . The plurality of reflector-structures of  claim 1  is connected chain-like in a row. Wherein one carriage support is shared by two adjacent reflector-structures in the middle of the row. The carriage located on the end of the reflector row supports only one crescent-rail. 
     
     
         10 . The tube bundle of  claim 5 —functioning as absorber of solar energy into water flow—further comprising of:
 one or plurality of supply tubes enabling the flow of inlet (liquid or vapor) water in the same direction and   plurality of return tubes enabling the flow of outlet (liquid or vapor) water in the same direction.   Whereas the supply and return tubes of the bundle form a two-pass coil system also referred as absorber coils.   
     
     
         11 . A method of steam generation in horizontal tube bundles extended over large areas by capturing the Sun's thermal energy, comprising:
 Flowing all feedwater through each of the plurality of solar collector absorber coils in series—collectively also referred as feedwater heater section; wherein the inlet water temperature is substantially below the boiling temperature and wherein the outlet water temperature is substantially close but slightly below boiling temperature.   Flowing all water leaving the feedwater section into plurality of solar collector absorber coils in parallel—that is to say that the total flow is evenly divided between the number of the coils, wherein the even flow distribution is ensured by a self balancing arrangement known in the art as “reverse-return” system The absorber coils connected in this parallel manner are referred as pre-evaporator section, wherein the inlet water is substantially liquid (has no vapor content) and wherein the outlet water has vapor-phase fraction of approximately from 40% to 80%.   Flowing all water leaving the pre-evaporator section into a separator vessel to separate the liquid phase from vapor phase by reduced speed and by gravity.   Flowing the liquid portion of the total flow, leaving the separator vessel into plurality of solar collector absorber coils in parallel—also referred as evaporator or evaporator-superheater.   Wherein the inlet water has substantially no vapor content and is at boiling temperature and wherein the outlet water is fully evaporated and is slightly or substantially above boiling temperature.   
     
     
         12 . The method of steam generation of  claim 11  wherein the steam flow output of the STSG is controlled by a level control loop, modulating the feedwater flow either by control valve or other means and wherein the quality of the supply steam leaving the STSG is controlled by modulating the liquid water inlet flow to the evaporator/superheater section, and wherein the control loop maintains the temperature of the outlet steam at the desired set-point. 
     
     
         13 . The carriage of  claim 6  further comprises of plurality of roller-wheels mounted on the base plate, whereas the rollers symmetrically support the circular-arch crescent rails of  claim 8  providing stability and free rotational-pivotal movement (degree of freedom). 
     
     
         14 . The carriage of  claim 6  further comprises of 2 guiding plates of “T” shape secured to the base plate, whereas the horizontal plate portions extends over the horizontal arm of the angle iron of the rotating crescent-rail of  claim 8 , preventing derailing or lifting the reflectors from the carriage. 
     
     
         15 . The carriage of  claim 6  further comprises of dual function drive train, whereas the source of driving motion is an electric step-motor mounted on the base plate of the carriage. Whereas the motor has two independent shafts engaged one at a time and whereas one sprocket is mounted on each of the shafts and whereas one sprocket is smaller than the other. 
     
     
         16 . The dual function drive train of  claim 15 . further comprises of pivotal rotation drive, whereas the smaller sprocket of  claim 15 . is engaged with a roller chain mounted on the rim of the Crescent-Rail of  claim 8  and whereas in the rotational motion mode the step motor of  claim 15  engages the shaft with the smaller sprocket and turns the Crescent Rail rolling on the symmetrical rollers of  claim 13  through the roller chain on the crescent. 
     
     
         17 . The dual function drive train of  claim 15 . further comprises of linear motion drive, whereas the larger sprocket of  claim 15 . is engaged—through a set of two transmission sprockets and a transmission roller chain—with a roller chain mounted on the rim of the flat horizontal rail of  claim 6 . 
     
     
         18 . A method of positioning the reflectors by “turn and travel” for maximum reflected energy for the diurnal procession and analemma (Sun's apparent movement on the sky) comprising of:
 Method of “W sandwiching” that is the orientation of reflectors located between two adjacent collectors, whereas a pro-solar reflector may be sandwiched between two counter-solar reflectors (on the counter-solar portion of the field, next to the median reflector) and a counter-solar reflector may be sandwiched between two pro-solar reflectors (on the pro-solar portion of the field, next to the median reflector)—for the purpose of minimizing optical interference (shadowing and blocking the incident or reflected sunlight).   Method of sizing the distance between two adjacent collectors that is based on the position of the Sun at noon on the day of the Equinox, whereas the shadowing/blocking effect is zero and the unutilized reflector gap (space between reflectors that incident sunlight is not reflected but available otherwise) is also zero and whereas the described configuration would form the reflectors in a “W” shape in and around the median reflector located between two collectors.   Method for summer, when the space available for positioning the reflectors is larger than the one required for zero shadowing/blocking, whereas the first priority of the method is to eliminate the “W” shadowing from the middle section of the field between two adjacent collectors as much as possible, and whereas the second priority of the method is to cluster the pro-solar reflectors as close to contra-solar collectors—and conversely cluster the contra-solar reflectors as close to pro-solar collectors—as possible, while maintaining zero shadowing/blocking, whereas the middle section between the collectors may be left for concentration of reflector-gaps.   Method for winter when the space available for positioning the reflectors is smaller than the one required for zero shadowing/blocking; whereas the first priority of the method is to orient an additional pro-solar reflector, in the next available spot (sandwiched) in the contra-solar portion of the field; whereas the second priority of the method is to sacrifice shadowing/blocking surfaces of reflectors in reverse order of effectiveness (sacrificing pro-solar reflector surfaces staring from the furthest); wherein the sacrificing means positioning the reflectors as close to each other as required and possible and losing some effective reflecting surfaces.