Abstract:
A fluidized-bed concentrating solar power plant comprises a particle receiver configured to contain solid state particles, wherein the particle receiver heats the solid state particles by transferring thermal energy from sunlight to the solid state particles. The plant also comprises a first silo configured to receive and store heated solid state particles from the particle receiver; a heat exchanger configured to receive the heated solid state particles from the first silo and generate a fluidized mixture comprising the heated solid state particles suspended in a gas; and a second silo configured to feed cooled solid state particles to the particle receiver, the cooled solid state particle extracted from the fluidized mixture. The first silo and the second silo each comprise a foundation comprising a base supported by a plurality of micropile units. Each micropile unit comprises a plurality of micropile columns coupled to a support block which supports the base.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of: 
         [0002]    U.S. Provisional Application No. 61/715,747 entitled “Solid Particle Thermal Energy Storage Design For A Fluidized-Bed Concentrating Solar Power Plant” and filed on Oct. 18, 2012, (Applicant Docket No. NREL PROV/12-73) , which is incorporated herein by reference in its entirety; 
         [0003]    U.S. Provisional Application No. 61/619,317 entitled “Gas-Solid Two-Phase Heat Transfer Material CSP Systems and Methods” and filed on Apr. 2, 2012, (Applicant Docket No. NREL PROV/11-92) which is incorporated herein by reference in its entirety; 
         [0004]    U.S. Provisional Application No. 61/715,751 entitled “Fluidized-Bed Heat Exchanger Designs for Different Power Cycle in Power Tower Concentrating Solar Power Plant with Particle Receiver and Solid Thermal Energy Storage”, filed on Oct. 18, 2012, (Applicant Docket NREL PROV/12-74), which is incorporated herein by reference in its entirety; and 
         [0005]    U.S. Provisional Application No. 61/715,755, entitled “Enclosed Particle Receiver Design for a Fluidized Bed in Power Tower Concentrating Solar Power Plant”, filed on Oct. 18, 2012, (Applicant Docket NREL PROV/13-05), which is incorporated herein by reference in its entirety. 
         [0006]    Attorney Docket No. NREL 12-73 1 
     
    
     CONTRACTUAL ORIGIN 
       [0007]    The United States Government has rights in this invention under Contract No. DE-AC36-08G028308 between the United States Department of Energy and the Alliance for Sustainable Energy, LLC, the Manager and Operator of the National Renewable Energy Laboratory. 
     
    
     BACKGROUND 
       [0008]    Concentrating Solar power (CSP) systems utilize solar energy to drive a thermal power cycle for the generation of electricity. CSP technologies include parabolic trough, linear Fresnel, central receiver or “power tower,” and dish/engine systems. Considerable interest in CSP has been driven by renewable energy portfolio standards applicable to energy providers in the southwestern United States and renewable energy feed-in tariffs in Spain. CSP systems are typically deployed as large, centralized power plants to take advantage of economies of scale. A key advantage of certain CSP systems, in particular parabolic troughs and power towers, is the ability to incorporate thermal energy storage. Thermal energy storage is often less expensive and more efficient than electric storage and allows CSP plants to increase capacity factor and dispatch power as needed—for example, to cover evening or other demand peaks. Improved plant structural designs are needed, however, to support improvements in CSP systems utilizing thermal energy storage. 
         [0009]    The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings. 
     
    
     
       DRAWINGS 
         [0010]    Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting. 
           [0011]      FIG. 1  is a diagram of one embodiment of an exemplary storage silo. 
           [0012]      FIGS. 2A-2D  depict exemplary layouts of micropile units within a foundation base. 
           [0013]      FIG. 3  depicts one embodiment of an exemplary micropile unit. 
           [0014]      FIG. 4  depicts one embodiment of an exemplary micropile column. 
           [0015]      FIGS. 5A-5B  depict embodiments of exemplary reinforced concrete. 
           [0016]      FIG. 6  is a cross-section view of an exemplary post-tension strand bundle. 
           [0017]      FIG. 7  is a block diagram of one embodiment of an exemplary concentrating solar power plant. 
           [0018]      FIG. 8A  is a cross-section view of an exemplary coned bottom for a silo. 
           [0019]      FIG. 8B  is a top view of the exemplary coned bottom in  FIG. 8A . 
           [0020]      FIGS. 9A and 9B  are cross-section views of exemplary reinforced concrete for a coned bottom of a silo. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized. The following detailed description is, therefore, not to be taken in a limiting sense. 
         [0022]      FIG. 1  is a diagram of one exemplary embodiment of a storage silo  100  for storage of solid particles (e.g., sand or ash) used in a fluidized-bed concentrating solar power plant, such as the power plant described below with respect to  FIG. 7 . Silo  100  is configured to meet the demands of storing solid particles for use in a fluidized-bed concentrating solar power plant. For example, the storage silo  100  is configured to store thousands of tons of sand up to a temperature range of approximately 800°-900° C. Additionally, the storage silo  100  is configured to accommodate different types of environmental conditions such as, but not limited to, high wind loads, seismic activity, and/or varying soil conditions. Additionally, in some embodiments, the silo  100  is made of concrete with a refractory liner for heat resistance and insulation using materials known to one of skill in the art. 
         [0023]    The exemplary storage silo  100  in  FIG. 1  is comprised of a foundation  102  and a hollow cylinder  104 . The cylinder  104  has a height  101  and a diameter  103  which define a volume for storing the solid particles. The environment of the volume defined by the cylinder  104  is inert with only hot air in this example. For instance, there are no combustion gases in this example. 
         [0024]    In the examples described herein, the diameter  103  is measured from the center of the wall of the cylinder  104 . For example, in this embodiment, the cylinder  104  is comprised of a wall having a thickness of approximately 12 inches. The diameter  103  is, therefore, measured from a point six inches deep into the wall of the cylinder  104  in this example. However, it is to be understood that other thicknesses of the wall can be used in other embodiments and that the diameter can be measured from an inner surface or exterior surface of the wall of the cylinder  104 . Table 1 provides exemplary values for the height, diameter, and corresponding storage capacity of solid particles. It is to be understood that the values in Table 1 are provided by way of example only and that other dimensions can be used in other embodiments. For example, in some embodiments, a height-to-diameter ratio of approximately 3:1 is used in determining the dimensions of the silo. 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 DIAMETER 
                 HEIGHT 
                 CAPACITY 
               
               
                   
               
             
             
               
                 45 ft 
                 130 ft 
                  6,250 tons 
               
               
                 50 ft 
                 148 ft 
                 12,500 tons 
               
               
                 55 ft 
                 165 ft 
                 17,000 tons 
               
               
                 65 ft 
                 230 ft 
                 34,000 tons 
               
               
                   
               
             
          
         
       
     
         [0025]    In this example, a cover or dome  106  is optionally located at one end of the cylinder  104  to enclose the volume defined by the cylinder  104  at the end of the cylinder  104 . The cover  106  is comprised of the same material as the cylinder  104 . For example, in this embodiment, the cover  106  and cylinder  104  are comprised of steel-reinforced concrete, as described in more detail below. The foundation  102  is located at the end of the cylinder  104  opposite from the cover  106 . The foundation  102  includes a plurality of micropile units  108 . Each micropile unit  108  includes a plurality of micropile columns  109  and a footing or block  111  surrounding one end of the respective micropile columns. The micropile columns  109  have a length  110  which extends into the ground or soil  116 . In this embodiment, the length  110  of the micropile units  108  is 50 feet. However, it is to be understood that the length  110  can be different in other embodiments. Additionally, all of the micropile units  108  do not, or may not have the same length in other embodiments. The micropile units  108  are used to anchor the foundation  102  and stabilize against seismic and surcharge loads from the earth as described in more detail below. The foundation  102  also includes a slab or base  112  having a thickness  114  placed on top of the footings  111 . 
         [0026]    In some embodiments, the slab  112  is at least partially submerged in the soil  116 . In addition, the thickness  114 , in some embodiments, is 18 inches. However, other thickness can be used in other embodiments. The base  112  is concentric with the cylinder  104 . As measured from the center of the base  112 , the base  112  has the same wall-center to wall-center diameter as the cylinder  104  in this example. However, the base  112  may have a wider outside diameter than the cylinder  104 , as shown in this example. The micropile units  108  are formed in a pattern and are located under the wall of the cylinder  104 . For example,  FIGS. 2A-2D  depict a top view of exemplary layouts of micropile units. 
         [0027]      FIG. 2A  depicts an exemplary layout of micropile units  208  for a cylinder having a diameter of 45 feet. The circle  204  depicts the location of the cylinder  104  on the base  212  above the pattern of micropile units  208 . As shown in  FIGS. 2A-2D , the cylinder  104  is concentric with the slab  212  and therefore is located at approximately the center of the slab  212 . As mentioned above, the slab  212  may, however, have an outside diameter that is wider than the cylinder  104 &#39;s outside diameter.  FIG. 2B  depicts an exemplary layout of micropile units  208  for a cylinder having a diameter of 50 feet, as shown by circle  204 .  FIG. 2C  depicts an exemplary layout of micropile units  208  for a cylinder having a diameter of 55 feet, as shown by circle  204 .  FIG. 2D  depicts an exemplary layout of micropile units  208  for a cylinder having a diameter of 65 feet, as shown by the circle  204 . 
         [0028]    As can be seen, each exemplary layout includes a plurality of rows of micropile units  208 . The number of rows and the number of micropile units  208  in each row depends on the maximum load or weight to be supported by the corresponding silo. Hence, as the diameter of the corresponding silo and foundation base  212  increases, the maximum load to be supported also increases. Hence, the number of micropile units  208  is also increased accordingly. 
         [0029]    For example, in  FIG. 2A  there are 3 rows of micropile units  208 , whereas in  FIG. 2D  there are 4 rows of mircopile units  208 . Similarly, the total number of micropile units  208  increases with increasing diameter of foundation base  212 . In some embodiments, each of the micropile units  208  is located at least 2 feet from another micropile unit  208 . Separating each micropile unit  208  by at least 2 feet helps the micropile units  208  resist surcharges produced by loading the silo. Table 2 below provides exemplary values for the number of micropile units  208  to be used based on the diameter of the foundation base  212  and corresponding silo. It is to be understood that the number of micropile units in Table 2 are provided by way of example only. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Number of Micropile units 
                 Diameter 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 55 
                 45 feet 
               
               
                   
                 102 
                 50 feet 
               
               
                   
                 136 
                 55 feet 
               
               
                   
                 264 
                 65 feet 
               
               
                   
                   
               
             
          
         
       
     
         [0030]      FIG. 3  depicts an exemplary embodiment of a micropile unit  308 . Micropile unit  308  can be used for each of the plurality of micropile units  108  in  FIGS. 1 and 2 . Micropile unit  308  includes a plurality of micropile columns  309  and a support block  311  which encases or surrounds one end of the micropile columns  309 . The support block  311  can be comprised of concrete and has a height  331 , a width  333 , and a depth  335 . In one embodiment, the height  331  is approximately 4 feet, the width  333  is approximately 8 feet, and the depth  335  is approximately 8 feet. In this example, four micropile columns  309  are used to form micropile unit  308 . However, it is to be understood that more or fewer than four micropile columns  309  can be used in other embodiments. For example, in one alternative embodiment, a fifth micropile column is placed in the center of the other four micropile columns. In addition, the micropile columns  309  are placed relative to one another so that they resist loads from all directions. For example, as shown in the example of  FIG. 3 , each micropile column  309  is placed near a corner of the concrete block  311 . However, other arrangements of the micropile columns  309  can be used in other embodiments. Each micropile column  309 , in this example, is placed at a non-zero angle  339  relative to a plane perpendicular to the bottom of the block  311 . In this example, the angle  339  is 10 degrees. However, other angles greater or less than 10 degrees can be used in other embodiments. 
         [0031]    An exemplary micropile column  409  is depicted in  FIG. 4 . As shown in  FIG. 4 , each micropile column is comprised of a column of grout  413  having a steel reinforcing bar  415  placed within the grout  413 . For example, a column can be dug in the soil. The steel reinforcing bar  415  is placed in the column and then the grout  413  is placed into the column under pressure. In particular, in this example, the grout  413  is compressed into the column under 5,000 pounds per square inch (psi), and the steel reinforcing bar  415  is a #20, 150 Grade steel bar. In other embodiments, other grout pressures and reinforcing bar materials may be used. A plurality of centralizers can be used to assure that the bar  415  is centrally placed in the column in some embodiments. For example, in some embodiments, centralizers can be placed at 10 foot centers along each bar  415 . Each micropile column  409 , in this example, is 50 feet long and has a diameter of 12 inches. In addition, in some embodiments, more than one steel reinforcing bar  415  is used in each column  409 . For example, in one embodiment, a plurality of bars  415  can be evenly distributed in a column  409  having a diameter of 12 inches with a distance between any two bars in the range of approximately 2.8 inches to approximately 4 inches. Furthermore, in some embodiments, each individual column  409  includes a steel plate at the top of the column  409 . The plate extends the tributary area of the respective column  409 . As the tributary area increases, the capacity for the respective column  409  to resist direct loading becomes more effective. 
         [0032]      FIGS. 5A and 5B  depict exemplary embodiments of reinforced concrete which can be used in implementing the wall of a silo such as silo  100 . For example, the reinforced concrete described in  FIG. 5A  or  5 B can be implemented in the cylinder  104  and cover  106 . In both  FIG. 5A  and  FIG. 5B , vertical steel reinforcing bars (rebar)  520  are used for vertical reinforcement of the concrete  530 . As used herein, the term ‘vertical’ refers to a direction that is parallel with the axis of the silo&#39;s hollow cylinder. Similarly, the term ‘horizontal’ refers to a direction that is perpendicular with the axis of the silo&#39;s hollow cylinder. 
         [0033]    In some embodiments, # 10  rebar having a diameter of 1.25 inches is used. However, in other embodiments, vertical rebar  520  having other sizes are used. In the examples shown in  FIGS. 5A and 5B , the vertical reinforcing bars  520  have an approximately uniform horizontal separation distance  525  throughout the silo wall. In some embodiments, the separation distance  525  is selected from the range of approximately 6 inches to approximately 12 inches. However, it is to be understood that other values of the separation distance  525  can be used in other embodiments. 
         [0034]    In  FIG. 5A , horizontal reinforcing bars  540  are also placed horizontally and used for periphery reinforcement of the concrete  530 . In particular, as shown in  FIG. 5A , two columns  541 - 1  and  541 - 2  of horizontal reinforcing bars  540  are used. A first column  541 - 1  is located on a first side of each of the vertical reinforcing bars  520  and a second column  541 - 2  is located on a second side of each of the vertical reinforcing bars  520 . The horizontal reinforcing bars  540  in each column are separated vertically by a vertical separation distance  545 . In addition, the columns  541 - 1  and  541 - 2  of horizontal reinforcing bars  540  are separated horizontally from one another by a horizontal separation distance  547 . In some embodiments, the vertical separation distance  545  is approximately 6 inches. Additionally, in some embodiments, the horizontal separation distance  547  is approximately 5 inches. However, it is to be understood that other values for vertical separation distance  545  and horizontal separation distance  547  can be used in other embodiments. In addition, the vertical separation distance  545  can increase from a first value near the bottom of the silo to a second value near the top of the silo, in some embodiments. 
         [0035]    In  FIG. 5B , post-tension strand bundles  560  are used as the horizontal reinforcement in lieu of horizontal reinforcing bars  540 . The post-tension strand bundles  560  extend in a direction approximately perpendicular to the vertical steel reinforcing bars  520 . Each post-tension strand bundle  560  is a bundle of a plurality of steel strands that is located in a corresponding hole in the concrete  530  and tightened by pulling on both ends of the bundle  560 . For example, in one embodiment, after the concrete  530  is cured, the strand bundles  560  are tensioned to 270 kilopounds per square inch (ksi).  FIG. 6  is a cross-section view of an exemplary post-tension strand bundle  660 . As shown in  FIG. 6 , the exemplary strand bundle  660  includes six strands. Each strand, in some embodiments, has a diameter of 0.75 inches. However, it is to be understood that each strand can have a different diameter in other embodiments. In addition, the number of strands in each strand bundle  560  is dependent on the size of the corresponding silo. The size of the silo is represented in Table 3 by the amount of solid particles which can be stored therein. For example, Table 3 lists exemplary silo sizes and an exemplary corresponding number of strands used in each strand bundle  560 . However, the silo size can also be measured in terms of the diameter of the silo, as discussed above with respect to Table 1. Table 3 also includes an exemplary total number of strand bundles based on the silo size. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 SILO SIZE 
                 NUMBER OF STRANDS 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                  6,250 tons 
                 5 
               
               
                   
                 12,500 tons 
                 6 
               
               
                   
                 17,000 tons 
                 7 
               
               
                   
                 34,000 tons 
                 12 
               
               
                   
                   
               
             
          
         
       
     
         [0036]    As shown in Table 3, as the size of the corresponding silo increases, the number of strands, per ton of material, in each strand bundle decreases. For example, the number of strands in each bundle  560  for a silo size of 6,250 tons is 5. If the same number of strands, per ton of material, in each strand bundle  560  was used for a silo size of 12,500 tons, then each strand bundle  560  would have 10 strands. However, as shown in the exemplary Table 3, the number of strands, per ton of material, in each strand bundle  560  is 6 for a silo size of 12,500 tons. Thus, the cost for horizontal reinforcement per ton of material contained decreases as the silo size increases. As a result, the cost of a post-tension strand horizontally reinforced silo may be up to 10% lower than the cost of a steel-rebar horizontally reinforced silo due to savings on the material. 
         [0037]    Each strand bundle  560  is separated vertically from other strand bundles  560  by a vertical separation distance  565 . In some embodiments, the vertical separation distance  565  is uniform throughout the silo. However, in other embodiments, the vertical separation distance  565  varies as a function of height. That is, the vertical separation distance  565  has an initial value at the end of the silo cylinder near the foundation and a second final value at the opposite end of the silo cylinder. For example, in some such embodiments, the vertical separation distance  565  between two strand bundles  560  near the cover of the silo is greater than the vertical separation distance  565  in the middle of the silo which, in turn, is greater than the vertical separation distance  565  near the foundation of the silo. In other words, the vertical separation distance  565  for a given strand bundle  560  increases as the respective height of the given strand bundle  560  increases. The vertical separation distance  565  can increase with height in some embodiments because the load due to the stored solid particles decreases with height. In some embodiments, the initial vertical separation distance  565  at the foundation of the silo is approximately 12 inches and increases with height. For example, in one embodiment, the separation distance  565  between strand bundles  560  is 12 inches near the bottom of the silo and changes proportionally to 20 inches near the top. 
         [0038]    The silo structure described above can be implemented in a concentrating solar power plant, such as the exemplary power plant  700  shown in  FIG. 7 . The exemplary system  700  includes an array  702  of heliostats  703 . Each heliostat  703  includes a mirror  705  which reflects light from the sun toward a receiver  704 . In addition, each heliostat  703  is configured to turn its respective mirror  705  to compensate for the apparent motion of the sun in the sky due to the rotation of the earth. In this way, each respective mirror  705  continues to reflect sunlight toward the receiver  704  as the position of the sun in the sky changes. 
         [0039]    The combined sunlight reflected from the plurality of heliostats  703  in the array  702  provides temperatures of approximately 500-1000° C. at the receiver  704 . The receiver  704  is configured to transfer the solar heat from the combined sunlight to a heat transport material adapted to store thermal energy such as molten salts or other particles. The heated particles are passed from the receiver  704  to a hot silo  706 . The hot silo  706  is implemented using a silo construction as described above with respect to  FIGS. 1-6 . In some embodiments, the hot silo  706  has a cone bottom as shown and described below with respect to  FIG. 8A-9B . A cone bottom helps enable the hot silo  706  to dispense the stored particles using gravity flow. 
         [0040]    Heated particles from the hot silo  706  are delivered via a conveyor  708  to a heat exchanger  710  as needed. In this embodiment, the heat exchanger  710  is implemented as a fluidized-bed heat exchanger having three stages. In particular, the heat exchanger  710  includes a super heater  711 , an evaporator  713 , and a preheater/economizer  715 . However, it is to be understood that other types and configurations of heat exchangers can be implemented in other embodiments. 
         [0041]    A pump  712  compresses gas and delivers the compressed gas to the heat exchanger  710  where the pressure of the compressed gas suspends the heated particles in the gas. The fluidized mixture of compressed gas and heated particles is moved through the stages of the heat exchanger  710  to transfer heat from the heated particles to a working fluid, such as but not limited to water or ammonia. It is to be understood that, in other embodiments, other working fluids can be used. For example, other working fluids include, but are not limited to, hydrocarbons (e.g., butane, propane, propylene, etc.) and liquid fluorocarbons (e.g., tetrafluoroethane). 
         [0042]    The transfer of heat to the working fluid vaporizes the working fluid. The vaporized working fluid is passed to a vapor turbine  714 . The pressure of the vapor turns the vapor turbine  714 , which is coupled to and drives the generator  716  to produce electricity. The vaporized working fluid is then expelled from the vapor turbine  714  and condensed again in condenser  718 . In particular, the remaining heat from the vaporized working fluid is transferred to a cooler  720  coupled to the condenser  718 . The removal of heat from the vaporized working fluid causes the working fluid to condense to a liquid state. A pump  722  is then used to move the working fluid back into the heat exchanger  710  where it is vaporized by the transfer of heat from the heated particles occurring in the heat exchanger  710 . 
         [0043]    After the particles pass through the heat exchanger  710 , the resulting fluidized mixture is then passed to a cyclone  724  (also referred to as a particle separator). In the cyclone  724 , the solid state particles are separated from the gas particles. The solid particles are then stored in a cold silo  726  for later use. The cold silo  726  is also constructed using the silo structures discussed above with respect to  FIGS. 1-6 . In some embodiments, the cold silo  726  has a flat bottom as opposed to a coned bottom. An elevator or conveyer  728  then moves the solid particles as needed from the cold silo  726  to the receiver  704  where the solid particles are again heated. 
         [0044]      FIG. 8A  depicts a cross-section side view of one example of a coned bottom  800  for a silo, such as silo  100 .  FIG. 8B  depicts a top view of the exemplary coned bottom  800 . As shown in  FIGS. 8A and 8B , the coned bottom  800  has a first diameter  850  at a first end and a second diameter  852  at a second end. In addition, the walls of the coned bottom  800  have a width  856  and are formed at an angle  854  to a horizontal plane parallel with the bottom of the coned bottom  800 . In this example, the first diameter  850  is 50 feet and the second diameter  852  is 3 feet. In addition, in this example, the angle  854  is 45 degrees and the width  856  is 2 feet. However, it is to be understood that other diameters and angles can be used in other embodiments. The height of the coned bottom  800  is dependent on the values for the first diameter  850 , the second diameter  852 , and the angle  854 . 
         [0045]      FIG. 9A  is a cross-section view of a segment of an exemplary reinforced concrete wall  900  for a coned bottom of a silo. As shown in  FIG. 9A , in this example, the wall  900  has a thickness  962  and includes a plurality of vertical reinforcement bars  972 . Each vertical bar  972  has a diameter  970 . In some embodiments, the vertical reinforcement bars  972  are implemented using #10 bars. Thus, the diameter  970  is 1.25 inches in such embodiments, as discussed above. The wall  900  also has embedded within it a plurality of post-tensioned strand bundles  974  in the horizontal direction. In some embodiments, the post-tensioned strand bundles  974  are tensioned to 270 ksi. The vertical bars  972  are evenly displaced in the wall  900  and separated from one another by a distance  964 . In some embodiments, the distance  964  is 1 foot. The strand bundles  974  are located at a distance  968  such that they are placed approximately in the center of the wall  900  in this example. For example, in some embodiments, the thickness  962  is 2 feet and the distance  968  is 1 foot. The strand bundles  974  are also separated from one another by a distance  966 . In some embodiments, the distance  966  is 1 foot. 
         [0046]      FIG. 9B  is a cross-section view of the segment of the exemplary reinforced concrete wall  900 . The view in  FIG. 9B  has been rotated from the view of  FIG. 9A  as indicated by the change in the coordinate axes shown with the respective figure. As shown in  FIG. 9B , rows of vertical bars  972  are evenly spaced throughout the wall  900  by a distance  980 . In some embodiments, the distance  980  is 4 inches. For purposes of explanation,  FIG. 9B  depicts one of the vertical bars  972  without the surrounding concrete. However, it is to be understood that each of the vertical bars  972  is embedded within the wall  900 . 
         [0047]    While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.