Abstract:
A vertical wave powered air compressor where different parts of the structure are at different depths (and hence static pressures). A plurality of compression stages are stacked one below the other. Each level has two or more chambers. The chambers have a series of check valves or water seals between them. Each passing wave raises and lowers the entire stack. As the stack moves downward, increased water pressure causes water to enter the first chambers at each level compressing the air inside. As the stack returns upward, the decreased water pressure causes water to leave the first chambers allowing the air therein to expand. However, the check valves prevent the air in the second chambers from expanding or escaping back into the first chambers. Another set of check valves allow the air in the second chambers, as it expands, to be forced downward into the next lower first chamber. With each upward and downward movement of the stack, as waves pass, a quantity of air moves downward from stage to stage until, at the bottom, the lowest stage discharges compressed air into a return pipe.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to capturing energy from waves on bodies of water such as the ocean and more particularly to an apparatus and method for compressing air using power from waves. 
     2. Description of the Prior Art 
     A typical ocean wave in deep water is around 9 feet high with a period of around 8 seconds. In some areas, at some times, 30 foot waves are not uncommon. It is well known that such waves carry considerable energy. For centuries, man has desired to somehow capture and make use of this energy as a source of power. 
     Numerous attempts have been made in the art to capture the energy inherent in ocean waves (or waves on other bodies of water). In U.S. Pat. No. 4,418,286 Scott teaches a counterbalance to generate electricity from waves. In U.S. Pat. No. 4,781,023 Gordon teaches a floating raft that moves up and down with respect to the ocean bottom. In U.S. Pat. No. 4,077,213 Hagen teaches a system of different size floats. In U.S. Pat. No. 3,879,950, Yamada teaches using compressed air and superheated steam as a means of storing wave energy. In U.S. Pat. No. 1,757,166 Brady uses floats and pontoons to capture wave energy. In U.S. Pat. No. 6,956,299, Molina et al. use floating bodies to produce pneumatic and/or hydraulic pressure. Labrador, in U.S. Pat. No. 5,094,595 uses horizontal pistons to compress air from waves. Hambley in U.S. Pat. No. 4,613,287 uses two or more stages mounted on a horizontal shaft. Bolding in U.S. Pat. No. 4,013,379 uses a compressor piston which is sea water itself that can be attached to a sea wall or the like. Compression comes from the horizontally moving wave mass of incoming waves. Bolding does not discuss interference from ebbing waves that reflect from the device. Perkins Jr. in U.S. Pat. No. 4,078,871 also uses horizontal momentum directed to travel up a ramp. 
     None of the above-mentioned inventions take advantage of static water pressure as a result of depth as well as wave motion to compress air. Also, none of them can be submerged conveniently to weather storms or high seas. It would be especially advantageous to have a wave-driven system that compresses air that captures energy from ocean waves using static pressure from depth, and which can be easily submerged to weather high sea and storms. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward a wave powered air compressor that is structured vertically so that different parts of the structure are at different depths (and hence static pressures). A plurality of compression stages are stacked one below the other. Each stage generally has two or more chambers. A compressed air return pipe can run up the center of the stack also acting as a structural member to support the stack. The chambers also have a series of check valves or water seals between them. Each passing wave raises and lowers the entire stack. As the stack moves downward, increased water pressure causes water to enter the first chambers at each level compressing the air therein. Some of the compressed air passes through the check valves into the second chambers. The air in the first chambers at each depth will be at a pressure equal to the water pressure at that depth. As the stack returns upward, the decreased water pressure causes water to leave the first chambers allowing the air therein to expand. However, the check valves prevent the air in the second chambers from expanding or escaping back into the first chambers. Another set of check valves allow the air in the second chambers, as it expands, to be forced downward into the next lower first chamber when the stack has risen high enough so that pressure in a second chamber exceeds the pressure in the next lower first chamber. With each upward and downward movement of the stack, as waves pass, a quantity of air moves downward from stage to stage until, at the bottom, the lowest stage discharges into the central return pipe. Air pressure in this return pipe will be equal to the water pressure at the lowest stage. Compressed air can be continuously taken from the return pipe to perform useful work as long as the take off does not exceed what is being compressed by the wave action. 
     In the event of an impending storm or high seas that might break the moorings or damage the device, it can be taken out of service by simply reducing the take off pressure. This reduces the amount of air volume in the entire stack reducing its buoyancy so that it no longer floats. To restore the stack to normal, air pressure above normal operating pressure can be supplied into the return pipe overcoming sea water pressure as well as check valve pressure thus refloating the stack. 
    
    
     
       DESCRIPTION OF THE FIGURES 
       Attention is now called to several drawings which aid in understanding the features of the present invention: 
         FIG. 1  shows an underwater horizontal view of a simplex and duplex stack arrangement. 
         FIG. 2  shows an embodiment of the invention in a downstroke. 
         FIG. 3  shows the embodiment of  FIG. 2  in an upstroke. 
         FIG. 4  shows a section of  FIG. 2 . 
         FIG. 5  shows airflow in the embodiment of  FIGS. 2-4 . 
         FIG. 6  shows an alternative embodiment of the invention. 
         FIG. 7  shows a section of  FIG. 6   
     
    
    
     Several illustrations and drawings have been presented to better describe the present invention. The scope of the present invention is not limited to what is shown in the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention relates to an ocean wave air compressor. While ocean waves have been described, the present invention can be used on any body of water having wave action. The ocean is generally preferred because of the usually larger size of waves in many areas. 
     Turning to  FIG. 1 , a horizontal, primarily underwater view can be seen of several embodiments of the present invention. Vertical stacks of cascaded chambers  1 ,  7 ,  8  can be seen. Stacks can be either simplex or duplex as shown. Each stack has a top end  2  that floats on the surface of the water. Each stack also has either a take off hose  3 ,  4  from its bottom end or a surface take off  11  from its top. The take off hoses supply compressed air from the device back to shore or to a floating platform where it can be used to perform work such as running a turbine or where it can be stored. Each stack can be tethered  5  to an anchor point  6  on the bottom. Stabilization lines  10  can secure the bottoms of the stacks. In the case of a bottom take off  4 , the hose can be coiled  3  to allow up-down movement of the stack. In the case of a surface takeoff  11 , floats  12  can be used to hold the hose on the surface. 
     As previously stated, the up-down motion of the stacks act to compress air in chambers within each stack level as will be described. The final take off pressure is equivalent to the depth of the lowest chamber. The air temperature of the take off air is approximately that of the surrounding ocean since the generally cold water quickly absorbs any heat generated by compressing causing the device to generally be isothermal. Expansion of the compressed air taken off can provide refrigeration as well as power. 
     It is well known that air in normal pressure and temperature ranges behaves very closely to an ideal gas. It is also known that for an ideal gas undergoing an isothermal compression, the final pressure over the final volume equals the initial pressure over the initial volume. It is also known that if a container partially containing air is submerged with its bottom open to the sea, the air inside is reduced in volume due to the increasing hydrostatic pressure caused by depth. By the gas law, as the volume decreases, the pressure increases. The applied hydrostatic pressure at any given depth is equal to the density of the fluid times the gravitational constant (generally g at sea level) times the depth. Quite generally, water pressure increases by about 1 atmosphere for every 33 feet increase in depth. Hence, a certain amount of air in such a container at the surface will have approximately ½ the volume and twice the pressure at around 33 feet. 
     The present invention works on the following principle. A downstroke in a wave trough and an upstroke in a wave crest uses the sea as a piston at different depths to compress air. Due to inertia, mass and depth related buoyancy, vertical travel of an actual stack will be out of phase with the wave undulations, and vertical travel will be less than the wave height profile. These differences allow air to enter the top stages. Each level in the stack has two chambers, an A chamber and a B chamber (it is within the scope of the present invention to have any number of chambers). The chambers are connected at each level by a one-way check valve that allows air to flow from chamber A to chamber B, but not back. Each B chamber is also connected through a one way check valve to the A chamber below it so that air can flow downward, but not upward. On the down stroke, sea water compresses the air in the A chambers. Some of this compressed air passes through the check valves to the corresponding B chambers. On the upstroke, the remaining air in the A chambers expands, but the air that passed into the B chambers cannot return. Thus the final pressure in the A chambers is less than it was when the downstroke started. This causes air to flow into the A chamber from the B chamber above it through the second set of check valves. Air in the final B chamber at the bottom can be taken off through a take off hose or routed upward though the center of the stack in a take off pipe. The final pressure of the compressed air will approximately equal the static water pressure at the depth of the bottom chambers. Actual pressure will also depend on how much air is being drawn off as well as the size of the chambers, the size and frequency of the waves and other factors. 
       FIG. 2  shows an embodiment of the present invention in a downstroke, while  FIG. 3  shows the same embodiment in an upstroke. Each level has a series of A chambers  11  labeled, A 1  A 2 , A 3 , . . . and a series of B chambers  23  labeled B 1 , B 2 , B 3 , . . . connected by one way water seals C 1 , C 2 , C 3  . . . from A 1 -&gt;B 1 , A 2 -&gt;B 2 , etc. Each B chamber (except the very bottom one) is connected to a second series of one way water seals D 1 , D 2 , D 3  . . . so that B 1 -&gt;A 2 , B 2 -&gt;A 3 , etc. The chambers are shown as cylindrical; however, they can have any shape. A return pipe  19  passes up the center from the lower-most chambers. 
     Turning to  FIG. 2 , as a downstroke begins, each A chamber contains an amount of air. As the structure sinks downward, water enters the A chambers  13  from the bottom  12  compressing the air in each A chamber in the stack to a pressure equal to the water pressure at the particular depth. An optional screen  16  in each A chamber allows water and air to pass; however, prevents entry of any debris or foreign objects. As the air in each A chamber compresses, the water seals C allow some of the air to flow through the seal into the corresponding B chamber through the C vertical columns  15 . For example, some of the air compressing in chamber A n  flows around the water seal C n  into chamber B n . On the A chamber side, there is a vertical column  15 . For air to backflow from B n  into A n , the pressure in B n  would have to be great enough to push all of the C n  water up the vertical column. This cannot happen since when the B n  pressure reaches a certain value it flows through the D n  seal through vertical columns  18  to the top  14  next lower A n+1  chamber rather than pushing the water up the C n  column. The D seals have vertical columns  18 . The seals are thus designed so that air passing in the desired direction displaces a lesser head of water than would be required for air to pass in the undesired direction. Thus, on the downstroke, air compresses in each A chamber with some of it passing through the C seals into the corresponding B chamber. 
       FIG. 3  shows the upstroke. As water leaves the A chambers, the air in the A chambers expands. The air in the B chambers cannot return through the C seals, and rather, expands through the D seals into the next lower A chamber when the pressure in that next lower A chamber has been reduced to the point where the B pressure in the chamber above it exceeds it. With each upward and downward movement of the stack, as waves pass, an additional quantity of air moves downward from stage to stage until the final or lowest stage discharges air into the return pipe  19  at a pressure corresponding to the water pressure at the depth of the final stage. This air can be routed upward at about this pressure to be taken off  20  for use. The maximum pressure is approximately the pressure at the depth of the lowest stage. 
     A cross section taken at X-X in  FIG. 2  or  FIG. 3  is shown in  FIG. 4 . The outer chamber structure  11  can be seen. The A chamber  13  is outermost and surrounds the B chamber which is above it and cannot be seen in the section of  FIG. 4 . The C chamber is formed between an outer wall  21  and an inner wall  22 . The wall of the upper D chamber  25  is above this cross-section and shown in dotted lines. The inner wall  22  of the C chamber is the outer wall of the rising column  18  of the D chamber. The take off pipe  19  is in the center. 
       FIG. 5  shows by means of arrows the airflow from the top of the column to the bottom and back up the take off pipe. 
       FIG. 6  shows an alternate embodiment using mechanical non-return valves rather than water seals with chambers of diminishing volume with depth (to reduce weight of the structure to be lifted). If this type of structure is submerged (say during a storm), a float chamber (not shown) needs to be added to an upper stage and supplied remotely with compressed air to float or control the chamber. This embodiment has A chambers  26  and B chambers  27 , as before, with a central return pipe  29 . Identical mechanical check valves  28  can be used at each level. A hole  35  aligns with a port  33  ( FIG. 7 ) in check valve  28 . 
       FIG. 7  is a cross section at Y-Y from  FIG. 6  showing a rubber band valve  28  with ports  33  that open and close as the structure rises and falls subsequently allowing air from the A chamber to move to the B chamber and then from the B chamber to the next lower A chamber. The central pipe  29  is surrounded by a solid region  30  with ports  33 . A rubber band  32  surrounds the solid region  30 . The rubber band  32  will expand to allow air to escape outward though the ports  33 , but will not allow air to flow inward through the ports  33 . The region  31  belongs to the A or B chamber above, while the region  34  belongs to the A or B chamber below. The functioning is as follows: If holes are placed in a tube with a closed end, and the holes are covered with a rubber band or strap, air being forced into the tube will escape through the holes by expanding the rubber band. However, if the pressure is lowered in the tube, air cannot come in through the holes because the rubber band holds the holes closed. While, this type of check valve and previously a water seal have been used to allow forward (downward) flow of air, but not reverse flow (upward), any type of one-way valve can be used and is within the scope of the present invention. 
     While specific embodiments show a particular number of chambers, or particular shapes and/or sizes of chambers and valves, any number of chambers, based on chamber size and available depth may be used. Also, any shape or size of chamber may be used. The apparatus may be simplex, duplex as shown in  FIG. 1 , or have more than two parts. Any number of parts in tandem is within the scope of the present invention. 
     An example of an application of the present invention is as follows: In a typical deep sea application, with 9 foot waves having a period of 8 seconds, an embodiment of the present invention with a 10 foot diameter initial stage that rises and falls 2 feet with each passing wave would have a terminal pressure of 3 atmospheres and an approximate horse power of 75 (55950 watts). These numbers are for example only and are approximate. 
     As previously stated, the present invention can be used to provide refrigeration since the temperature of the compressed air taken off is approximately that of the surrounding water. If this air is expanded as is known in the art, the resulting temperature drop will provide refrigeration. One way to provide expansion with a drop in temperature is through a valve, throttling device or other mechanism that allows a reduction of pressure in a controlled volume. Also, venting compressed air through a nozzle or venturi at a particular flow rate (where velocity increases) causes a drop in temperature. Given enough pressure, and depending on the water temperature, the exhaust can be below freezing. 
     Several descriptions and illustrations have been provided to aid in understanding the present invention. One skilled in the art will realize that numerous changes and variations are possible without departing from the spirit of the invention. Each of these changes and variations is within the scope of the present invention.