Systems and methods for producing steam using solar radiation

Abstract

Methods and systems for generating steam using solar energy are provided here. The methods and systems can be used to generate steam of a desired quality, e.g. about 70%, or superheated steam. Some methods for producing steam of a desired quality comprise flowing water into an inlet of receiver in a linear Fresnel reflector system, wherein the receiver comprises multiple parallel tubes t i connected in parallel, and i=1,k, and irradiating each tube t i along its respective length L i with solar radiation so that solar radiation absorbed at each tube generates thermal input along its length and so that water begins to boil in at least one of the tubes at a point λ i along its length. The methods comprise using one or more temperatures T i in an economizer region of a tube t i or one or more changes in length of the tubes as input to a controller that controls mass flow of water into each of the multiple tubes, thereby controlling quality of steam exiting the receiver.

1 . A method for producing steam, the method comprising:
 flowing water through an inlet to enter a tube of length L under pressure;   irradiating the tube along its length with solar radiation so that solar radiation absorbed at the tube generates thermal input to the tube along its length and so that steam exits the tube; and   providing a control variable as input to a controller that controls mass flow of water through the inlet, thereby controlling quality of steam exiting the tube.   
     
     
         2 . The method of  claim 1 , wherein the control variable comprises a change in tube length. 
     
     
         3 . The method of  claim 1 , wherein the control variable comprises a temperature in an economizer region of the tube. 
     
     
         4 . The method of  claim 3 , wherein a temperature setpoint of the control system depends on the position of the temperature measurement relative to the tube inlet, tube length L, and a desired output steam quality. 
     
     
         5 . The method of  claim 1 , wherein:
 the tube has a transverse dimension W orthogonal to length L;   irradiating the tube comprises rotating a reflector to direct solar radiation to irradiate the tube along its length L; and   the method further comprises adjusting a thermal input to the tube by rotating a position of the reflector to control the quality of steam exiting the tube.   
     
     
         6 . The method of  claim 1 , wherein the control variable comprises predictive information associated with thermal input. 
     
     
         7 . The method of  claim 6 , further comprising separating water that exits the tube from the steam using a separator, and wherein the predictive information comprises thermal input that is based on steam flow out of the separator. 
     
     
         8 . The method of  claim 7 , wherein the separator comprises a steam drum. 
     
     
         9 . The method of  claim 1 , wherein the desired steam quality is 70% or higher. 
     
     
         10 . The method of  claim 1 , adapted for producing superheated steam. 
     
     
         11 . A method for producing steam, the method comprising:
 flowing water into an inlet of a solar receiver in a linear Fresnel reflector system, wherein the receiver comprises multiple tubes connected in parallel;   irradiating each tube along its respective length with solar radiation so that solar radiation absorbed by each tube generates thermal input along its length and so that steam exits the tube; and   using one or more control variables associated with one or more tubes as input to a controller that controls mass flow of water into each of the multiple tubes, thereby controlling steam quality exiting the receiver.   
     
     
         12 . The method of  claim 11 , wherein the one or more control variables comprise one or more temperatures measured in an economizer region of the one or more tubes. 
     
     
         13 . The method of  claim 11 , wherein the one or more control variables comprise a change in tube length of the one or more tubes. 
     
     
         14 . The method of  claim 11 , wherein the one or more control variables comprise predictive information associated with thermal input. 
     
     
         15 . The method of  claim 11 , wherein:
 the receiver has a length L and a transverse dimension W orthogonal to L;   irradiating each tube along its respective length with solar radiation comprises rotating one or more rows of linear Fresnel reflectors in a field of reflectors about an axis to direct solar radiation to irradiate the tubes along length L; and   the method further comprises adjusting thermal input to the multiple parallel tubes along the transverse dimension W by rotating one or more of the reflector rows about the axis to control the steam quality.   
     
     
         16 . A solar boiler comprising:
 a tube having an inlet for receiving water and an outlet;   a control valve capable of regulating flow of water into the inlet; and   a controller for controlling a position of the control valve to control flow of water into the inlet based at least in part on a control variable to control a steam quality at the outlet.   
     
     
         17 . The solar boiler of  claim 16 , wherein the control variable comprises a temperature in an economizer region of the tube. 
     
     
         18 . The solar boiler of  claim 16 , wherein the control variable comprises predictive information associated with thermal input. 
     
     
         19 . The solar boiler of  claim 16 , wherein:
 the tube is anchored at a position P between the inlet and the outlet, the position P extending further from the inlet than a boiling boundary in the tube;   the tube is relatively free to expand at the inlet; and   the control variable comprises a measurement of a change in length of the tube between the inlet and position P.   
     
     
         20 . A solar boiler comprising:
 an elevated receiver comprising multiple parallel tubes extending along the length of the receiver;   a plurality of linear Fresnel reflectors configured to rotate about an axis to track diurnal motion of the sun;   a control valve associated with each of the tubes to regulate mass flow of water into the tubes; and   a controller for adjusting a position of the control valve associated with each tube based at least in part on one or more control variables associated with one or more tubes so as to control mass flow of water into each tube and to control steam quality output from the receiver.   
     
     
         21 . The solar boiler of  claim 20 , further comprising one or more temperature sensors positioned to sense fluid temperature in the economizer region of the one or more tubes, wherein the one or more control variables comprise output from the one or more temperature sensors. 
     
     
         22 . The solar boiler of  claim 20 , wherein the one or more control variables comprise predictive information associated with thermal input. 
     
     
         23 . The solar boiler of  claim 20 , wherein the one or more control variables comprise a change in length of the one or more tubes.