Abstract:
A lateral circulator for generating agitation or circulation in a cultivation pond is disclosed. The circulator comprises at least a drive pulley and a secondary pulley, both oriented vertically and placed in the pond separated from one another along the length of the pond. The drive pulley is coupled to a motor, or to a drive train that is itself coupled to the motor. An endless belt is trained over the drive pulley and the secondary pulley. A plurality of cleats is provided along the exterior of the belt. The cleats are typically angled and serve to drive water as the belt rotates through the water. Typically, the belt would extend over much of the length of the cultivation pond, providing agitation and circulation over an extensive, continuous area of the cultivation pond.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application No. 62/257,578, filed Nov. 19, 2015, the contents of which are incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
       [0002]    The invention relates generally to circulating and agitating equipment for pond cultivation, and more particularly, to a circulator and agitator for cultivating algae. 
       2. Description of Related Art 
       [0003]    From time immemorial to the present, humans have cultivated microorganisms—sometimes for processes like fermentation, and sometimes to create a biomass from which nutrients and other valuable chemicals can be extracted. While classic fermentation processes—for example, to produce alcohol or to leaven bread—often rely on simple eukaryotes like  S. cerevisiae,  over the last few decades, a great deal of attention has been focused on the cultivation of algae. 
         [0004]    Algae is a general term for a diverse group of autotrophic, photosynthetic organisms, most of which are aquatic. These organisms may be cultivated for a variety of reasons, and to generate a variety of end products. For example, algae have become an important source of the so-called “omega-3” fatty acids, which are important in human nutrition. Algae are also cultivated to extract their oils, which can be processed into biodiesel and other forms of fuel. Beyond products and byproducts, cultivated algae can also be used in processes like wastewater treatment. 
         [0005]    Cultivation of algae can be done in any number of ways, but is typically done in long, shallow ponds of water. Among other things, most cultivation ponds include an agitator or circulator to circulate the water. In a still pond, the water may stratify, with deeper water having less dissolved oxygen than water nearer the surface, and other nutrients and treatments may not reach the entire volume of the pond, leading to uneven algae growth and reduced yield. The agitator or circulator addresses these issues. Additionally, agitation or circulation can ensure that most of the algae get periodic exposure to strong sunlight, as they are brought toward the surface, followed by darker periods as they sink back toward the bottom, a light-dark pattern that has been found by some researchers to be beneficial. Beyond specific effects on algae, water circulation also maintains homogeneity of the water-nutrient mixture, and can help prevent putrefaction and reduce the growth of unwanted, invasive organisms. 
         [0006]    For many decades, the paddlewheel has been the typical agitator used in cultivation ponds. An example of this can be found in U.S. Pat. No. 4,217,728 to Shimamatsu et al., a 1980 patent, the contents of which are incorporated by reference in their entirety. While a paddlewheel does provide agitation, it is a point source; it drives the water in the pond from a single location. In order to provide agitation for an entire pond—which may be quite large—paddlewheel agitation both uses and wastes a large amount of energy, and may not provide uniform agitation over the entire volume of the pond. 
       SUMMARY OF THE INVENTION 
       [0007]    One aspect of the invention relates to a lateral circulator for a cultivation pond. The lateral circulator comprises at least one drive pulley oriented vertically, at least one second pulley, also oriented vertically, and an endless belt trained over the pulleys and oriented such that its breadth extends vertically. The belt has a series of cleats attached to it, typically arranged at a regular pitch and angled at an angle between 0° and 90°, for example, between 10° and 45°. In use, the circulator would typically be positioned in the center of a cultivation pond, leaving approximately equal channel widths on either side and, in most cases, at the ends. 
         [0008]    Another aspect of the invention relates to methods for circulating water in cultivation ponds. These methods comprise circulating water in a cultivation pond using an endless belt trained over at least one driving pulley and at least one driven pulley such that the breadth of the belt extends vertically along a substantial portion of the length of the cultivation pond. The belt thus provides circulation not as a point source, but as a continuous source that extends over much of the cultivation pond. Because of the extent of the circulator, in many embodiments, relatively slow velocities of the belt are sufficient to create turbulent lateral circulation (i.e., between the belt and the sidewalls of the cultivation pond), which may reduce power requirements. 
         [0009]    Other aspects, features, and advantages of the invention will be set forth in the following description. 
         [0010]    BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0011]    The invention will be described with respect to the following drawing figures, in which like numerals represent like features throughout the description, and in which: 
         [0012]      FIG. 1  is a perspective view of a cultivation pond with a continuous lateral circulator according to one embodiment of the invention; 
         [0013]      FIG. 2  is an elevational view of the lateral circulator of  FIG. 1  in isolation; 
         [0014]      FIG. 3  is a cross-sectional view of one of the cleats on the lateral circulator of  FIG. 1 ; 
         [0015]      FIG. 4  is a schematic view of the belt of the lateral circulator and one of its cleats, illustrating the forces generated by it; 
         [0016]      FIG. 5  is a schematic top plan view of the cultivation pond of  FIG. 1 , illustrating the circulation therein; 
         [0017]      FIG. 6  is a schematic end elevational view of the cultivation pond of  FIG. 1 , illustrating the circulation therein; 
         [0018]      FIG. 7  is an elevational view of a portion of a circulator belt constructed of individual segments, according to another embodiment of the invention; 
         [0019]      FIG. 8  is a top plan view of the circulator belt of  FIG. 7  engaged by a pulley with a sprocket; and 
         [0020]      FIG. 9  is a top plan view of a cultivation pond with a circulation system comprised of a number of shorter conveyor belts operating together. 
     
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  is a perspective view of a continuous lateral circulator, generally indicated at  10 , installed within a cultivation pond  12 . The continuous lateral circulator  10  has the general form of a conveyor belt turned on its side, such that the breadth of the belt  14  extends vertically. The belt  14  is endless and is trained over two vertically-extending pulleys  16 ,  18 . A motor  20  coupled to one of the pulleys  16  drives the belt  14  in a loop. A series of angled cleats  22 , arranged at a regular pitch along the length of the belt  14 , help to push the water in the pond as the belt  14  is driven. 
         [0022]    The pond  12  itself is typical for a cultivation pond, and as can be seen in  FIG. 1 , the circulator  10  is installed in the center of it and extends substantially the entirety of the length of the pond  12 , evenly spaced between the sides and the two ends. For example, if the pond  12  is 1,000 feet (305 meters) long and 100 feet (30 meters) wide, the circulator  10  may be approximately 900 feet long, leaving an equal distance at each end. Of course, the circulator  10  need not be perfectly centered in the pond  12  in all embodiments, and ponds  12  may be of any size. As will be described below in more detail, one advantage of circulators  10  according to embodiments of the present invention is that they may remove agitation-based size restrictions on cultivation ponds  12 , thereby allowing for larger ponds. The pond  12  may be of any depth, although typical cultivation ponds are relatively shallow—depths of less than 1 foot (0.3 meters) are common. 
         [0023]    As shown in  FIG. 1 , the circulator  10  in the illustrated embodiment is taller than the illustrated depth or water level of the pond  12  in which it is placed. That is, the illustrated water level in the pond  12  is lower than the top of the belt  14  and pulleys  16 ,  18 . In most embodiments, the circulator  10  will extend at least substantially the entire depth of the pond  12 , and in many of those embodiments, the circulator  10  may be taller than the average expected pond depth. The extra height allows the water level in the pond  12  to be increased, as might be done for temperature control and for various other reasons known to those skilled in the art. As one example, if a typical water height of a pond  12  is about 12 inches (30 cm), the circulator may be about 18 inches (46 cm) tall. While the cultivation pond  12  illustrated in  FIG. 1  is uncovered and open, cultivation ponds  12  may be covered and closed, as is known in the art. 
         [0024]    There is no particular limitation to the height of the belt  14  and its pulleys  16 ,  18 , or to the length of the belt  14 . Particularly with long belts, it may be helpful to include idler pulleys or rollers, also oriented vertically, which would provide support along the length of the belt  14 . Additionally, the circulator  10  may include belt tensioners and other such devices. The length of the belt  14 , its height, and the speed at which it is to be driven are among the factors that dictate how much power is required to drive the belt  14 . In the illustrated embodiment, a motor  20  directly drives one of the pulleys  16  to move the belt  14 . That motor  20  may, in some embodiments, be as small as ½ horsepower or, in other embodiments, as large as 10 horsepower. The placement of the motor  20 , however, is not critical. In some embodiments, the motor  20  may be placed on the other pulley  18 . In yet other embodiments, the motor  20  may be located elsewhere, and one or both pulleys  16 ,  18  may be driven by a drive-train connected between the motor  20  and the pulleys  16 ,  18 . Generally speaking, various methods of driving conveyor belts are known, and any compatible method may be used in embodiments of the present invention. 
         [0025]    In  FIG. 1 , the circulator  10  is relatively narrow, with nothing between the two sides of the belt  14 . That may not be the case in some embodiments. In some cases, the belt  14  may be arranged around a berm, wall, or other structure, with more pulleys or rollers, if needed, to dictate its path around that structure. For example, many cultivation ponds have walls and other dividing structures, and a belt  14  may be arranged around those walls and structures. As another example, a belt  14  may be placed around a pair of parallel walls that are about as high as the belt  14  and are spaced from each other at a distance of about 3 feet (1 meter). Such walls could be used, for example, to support an elevated horizontal walkway, located between the two sides of the belt  14 , that allows maintenance workers to walk along the center of the pond  12  in order to service the circulator  10  or the pond  12  itself. 
         [0026]    Additionally, while the belt  14  of  FIG. 1  is trained over the pulleys  16 ,  18  such that it has two long sides that are parallel to one another, that need not be the case in other embodiments. Instead, the belt  14  may be trained over any number of pulleys, rollers, idlers, and other structures to have any desired shape, e.g., polygonal or serpentine, if the geometry of the cultivation pond or other factors dictate it. 
         [0027]      FIG. 2  is a side elevational view of the circulator  10  in isolation. In  FIG. 2 , the evenly-spaced cleats  22  can be seen. Cleats  22  are used to drive the water in the pond  12 . In the illustrated embodiment, each cleat  22  is a continuous bar of constant cross-section that extends across the height of the belt  14  at an angle. The cleats  22  of the illustrated embodiment overlap such that if one draws a straight line down the belt  14 , that line may intersect several cleats  22 , e.g., 4-6 cleats, depending on their number and angle. The cleats  22  are arranged at a regular pitch, which will vary from embodiment to embodiment, but may be on the order of, e.g. 3-6 inches. It should be understood that for reasons of legibility and ease in illustration, the drawing figures show fewer cleats at a greater pitch than would be used in most typical operational embodiments. 
         [0028]      FIG. 3  is a cross-sectional view of one of the cleats  22 . As shown, it has a generally trapezoidal cross-section in the illustrated embodiment, such that it is narrower at the top (i.e., the outermost point) than it is at the base. In a typical embodiment, a cleat  22  might have a height in the range of about 1-2 inches (2.5-5 centimeters), and a width in that range as well. The cleat  22  of  FIG. 3  has a base of about 1 inch (2.5 centimeters) and an outward extent of about 2 inches (5 centimeters). It may be helpful if the cleats  22 , taken together, have at least the same effective surface contact area as a paddlewheel suitable for use in the same size of cultivation pond  12 . (“Effective surface contact area” in this context refers to the area that actually contacts and drives water at any point in time.) In some cases, if numerous cleats  22  are on the belt  14 , the effective surface area of those cleats  22  may be greater than that of a paddlewheel that would be used in the same pond, which may allow the belt  14  to move more slowly and provide the same quality of effective circulation. 
         [0029]    Of course, the cleats  22  may vary in form and arrangement from embodiment to embodiment, depending on any number of factors. For example, the cleats may instead have a rectilinear cross-section, but may curve downwardly as they extend outwardly from the belt  14 . Ultimately, the cleats  22  are present to push water, and any cross-sectional shape that accomplishes that purpose may be used. Additionally, the cleats  22  need not be continuous bars, they may have different cross-sectional shapes, and they may be inclined at different angles. 
         [0030]    The forces developed by each cleat  22  are shown in  FIG. 4 , a schematic view of the belt  14  with only a single cleat  22 . If the belt  14  is driven forward with a longitudinal velocity V L , the cleat  22  will generate a forward force (F L ) and a forward velocity (V L ), as well as a downward force (F D ) and a downward velocity (V D ). The amount of forward versus downward force (i.e., the forward and downward components of the overall force vector) is in proportion to the inclination angle of the cleat, θ, and can be readily determined trigonometrically. In most embodiments, the angle θ will be in the range of about 10-45°, although a more preferable range for at least some embodiments might be 10-30°, and in some cases, the range might be narrower still, e.g., 18-22°. The cleat of  FIG. 4  is inclined at an angle of 22°, although it should be understood that the angles shown and described above assume that it is desirable to push the water down; if one wished to push the water up, instead of down, the orientation of the cleats  22  would be reversed. In some embodiments, the ratio of V D  to V L  may be, e.g., 3:1, 4:1, etc. 
         [0031]      FIG. 4  is a two-dimensional schematic illustration of the effect of the cleats  22  on the water. The cross-section of the cleats  22  may be chosen specifically to cast water outward, away from the belt  14 .  FIG. 5  is a top plan view of the pool  12  and the circulator  10 . As shown in  FIG. 5 , the belt  14  is driven forward at some longitudinal velocity, V L , that is aligned with the central long axis of the pond. However, the motion of the belt  14  also drives water forward, down, and away from the belt  14 , creating continuous lateral circulation (i.e., in the direction indicated by arrows V T ) between the circulator  10  and the sides and the bottom of the pool  12 .  FIG. 6  is a schematic end-elevational view of the pool  12  illustrating the circulation from that perspective. 
         [0032]    As  FIGS. 5 and 6  make clear, the circulator  10  is not a point-source agitator placed, for example, on one end of the pond  12 . Rather, by extending over virtually the entire length of the pond  12 , it provides continuous circulation and agitation energy to essentially the entirety of the pond  12 . In so doing, it may remove agitation-based size restrictions on cultivation ponds  12 . While in many cases, the circulator  10  will be operated continuously, in this context, the term “continuous circulation” to the fact that the circulator  10  spans and is physically continuous over substantially the entirety of the pond  12 . The circulation or agitation in the pond  12  is distributed across almost the entire pond  12 ; the circulator  10  is not a point source for agitation, like a paddlewheel. 
         [0033]    In a typical scenario, the belt  14  is driven and the cleats  22  are adapted to ensure a relatively mild turbulent flow in the direction of belt movement, but a relatively strong turbulent flow in the lateral direction. With conventional ponds that use paddlewheels as point-source agitators, Reynolds numbers of 60,000 or more are commonly achieved, indicating very strong turbulent flow. However, large amounts of energy are expended in maintaining those flow conditions, and some of the invested energy may be lost. By contrast, with lateral circulators  10  according to embodiments of the present invention, Reynolds numbers of 15,000-30,000 in the lateral (i.e., transverse) direction may be more commonly used. The belt  22  itself may be driven at relatively low velocity longitudinally, e.g., on the order of 2 inches (5 cm) per second. 
         [0034]    As those of skill in the art will realize, the velocity at which the belt  14  is driven and the velocity of the water around the belt  14  are, in many cases, two different things. The degree to which the belt  14  pushes the water, the momentum imparted, and the direction will vary with the drive velocity; the orientation, number, and shape of the cleats  22 ; and a number of other fluid-dynamic factors. As those of skill in the art might also appreciate, even without cleats  22  to aid in moving water, a belt  14  driven at a high enough velocity could probably produce a desired lateral velocity of the water, but the fraction of that energy that would be transferred to the water would likely be much less than it would be with cleats  22 . Ultimately, the desired water velocities will also depend on non-mechanical factors, such as the type of algae or other organism, and the presence of wind and other environmental factors. 
         [0035]    As was described above, the belt  14  will typically be given a longitudinal velocity, referred to in this description as V L . While that velocity may be continuous over long periods of time, it need not necessarily be. The overall velocity may be varied from moment to moment, if necessary, based on conditions within the cultivation pond  12 , the needs of the particular organism being cultivated, and environmental factors that affect the pond  12 . It should also be understood that the speed at which the motor  20  runs may not be equal to V L ; in most cases, gearing or a drive train between the motor  20  and the pulley  16  that it drives will alter the speed of the motor  20 . In many cases, a gearbox may be integrated into the motor. 
         [0036]    Beyond imparting motion to the belt, other drive signals may be used, and in some cases, superposed on the main drive signal that creates the longitudinal velocity of the belt  14 . For example, it has long been known that vibrations introduced into mechanical systems can help to prevent friction and make mechanisms operate more smoothly—a technique called dithering. Embodiments of the present invention may use dithering—for example, by altering the velocity, acceleration, or direction of the belt  14  at a rate that is significantly different than the velocity of the belt  14  or the rate at which it drives the water. For example, if V L  is selected to drive the water at a rate of 1 Hz, a lower-amplitude, low frequency signal equivalent to about 0.1 Hz may be used for dithering. The resulting movement may be an oscillation, a vibration, or a non-cyclic pattern of acceleration, velocity, or directional changes. The nature and amplitude of the dithering may vary from embodiment to embodiment, and is not particularly limited, so long as the dithering does not detract from the primary motions that the moving belt  14  is to impart to the water. 
         [0037]    Of course, depending on the belt velocity and other factors, dithering may not be required. In a typical embodiment, the turbulent flows that surround the belt  14  and impinge on it during operation may vibrate the circulator  10  in the same way that dithering would—without the need to drive the belt  14  in any special way. 
         [0038]    The belt  14  itself may be made in any of a variety of ways. For example, the belt may be made of a rubber, or of a rubberized or coated fabric or other textile. As was described above, the exterior of the belt  14  has cleats in order to better interact with the water in the cultivation pond  12 . The inward-facing side of the belt  14  may also have grooves, cleats, or other features in some embodiments. Because the belt  14  is mounted vertically, slippage of the belt  14  on the pulleys  16 ,  18  may be more of an issue than in a belt  14  of similar dimensions that is mounted horizontally. Thus, grooves, cleats, or other inward-facing gripping features may be helpful in retaining the belt  14  on the pulleys  16 ,  18 . For example, the belt  14  and pulleys  16 ,  18  may have the cleats and pulley-grooves shown in U.S. Pat. No. 4,011,939 to Conrad, the contents of which are incorporated by reference in their entirety. 
         [0039]    Additionally, while the pulleys  16 ,  18  in the illustrated embodiment are rounded, additional features may be included to prevent slippage or other tracking problems. In some cases, sprockets mounted near or at the edges of the pulleys  16 ,  18  may be made to insert into series of complementary slots cut or formed in coincident positions near the edges of the belt  14 . In other words, the belt  14  and pulleys  16 ,  18  may have male and female complementary engaging structures to prevent belt slippage and so-called tracking problems. In some cases, the male structures may be carried by the belt  14  and the female structures may be carried by the pulleys  16 ,  18 , while in other cases, the opposite may be true. 
         [0040]    Belts  14  may also be made of a number of rigid sections of plastic, rubber, or metal connected together to articulate or flex. As one example of this,  FIG. 7  is an elevational view of a section of a belt  100 , that is comprised of a number of modular sections  102 ,  104 ,  106 ,  108 ,  110 ,  112 , each of which is rigid or semi-rigid. The sections  102 ,  104 ,  106 ,  108 ,  110 ,  112  have edges that define a series of complementary projections and grooves, allowing the sections  102 ,  104 ,  106 ,  108 ,  110 ,  112  to be essentially enmeshed in one another. A series of openings  114 , which line up when the sections  102 ,  104 ,  106 ,  108 ,  110 ,  112  are enmeshed, allow for the insertion of pins  116 , about which the sections  102 ,  104 ,  106 ,  108 ,  110 ,  112  hinge to allow the belt  100  to flex. 
         [0041]    In the description above, it was briefly explained that the cleats  22  need not be continuous bars. On the belt  100 , the cleats are not only discontinuous, but portions of them are carried by different sections  102 ,  108 ,  110 . More specifically, in the illustration of  FIG. 7 , three cleat sections  118 ,  120 ,  122  are each carried by a different section  102 ,  108 ,  110  of the belt. The cleat sections  118 ,  120 ,  122  have the inclination angle described above, and may have the cross-sectional shape described above or any other desirable shape. As shown, when the sections  102 ,  108 ,  110  are assembled, the cleat sections  118 ,  120 ,  122  roughly line up, although there may be some discontinuity. 
         [0042]    Additionally, the two segments  102 ,  104  that define the top of the belt  100  and the two segments that define the bottom of the belt  100  in the illustration of  FIG. 7  include a series of slots  124  at a regular pitch positioned to engage a drive sprocket on one of the belt-drive pulleys.  FIG. 8  illustrates the engagement of the belt  100  trained over a pulley  130  with sprockets  134 . 
         [0043]    In the description above, a single circulator  10  with a single belt  14 ,  100  spans the length of the cultivation pond  12 . However, that need not be the case in all embodiments. Instead, in some embodiments, multiple circulators arranged in series or, in some cases, in parallel, may be used.  FIG. 9  is a top plan view illustrating three circulators  10   a ,  10   b ,  10   c  arranged in series, aligned end-to-end, to cover the same length of a cultivation pond  12 . Each of the circulators  10   a ,  10   b ,  10   c  has its own endless belt  14 , trained over its own set of pulleys  18 ,  20 . The ends of the circulators  10   a ,  10   b ,  10   c  are spaced closely together, although the spacings may be modified to effect control over circulation in the areas between the circulators  10   a ,  10   b ,  10   c . Of course, any number of circulators  10   a ,  10   b ,  10   c  may be used to cover any desired length or distance. 
         [0044]    Smaller circulators  10   a ,  10   b ,  10   c  may be used in parallel when the cultivation pond, or a channel within the pond, is particularly wide. Circulators  10   a ,  10   b ,  10   c  may also be used in parallel when the pond  12  is divided or partially divided such that a single circulator  10  or in-series line of circulators  10   a ,  10   b ,  10   c  is unlikely to produce a lateral circulation that will reach essentially the entire pond. 
         [0045]    Although this description places some emphasis on the circulator  10  providing continuous circulation or agitation across an entire cultivation pond  12 , and that arrangement has a number of advantages, it need not be used in that way in all embodiments to be effective. In some cases, a lateral circulator may be considerably shorter than the circulator  10  of  FIG. 1 . In cases where the circulator is relatively short or small compared to the size of the cultivation pond  12 , that circulator essentially becomes a point source for circulation or agitation, in which case, its longitudinal velocity may be significantly greater than a circulator  10  with a more extensive area in order to achieve the same degree of circulation or agitation. 
         [0046]    While the invention has been described with respect to certain embodiments, the description is intended to be exemplary, rather than limiting. Modifications and changes may be made within the scope of the invention, which is defined by the appended claims.