Abstract:
An electric generator is driven by a gas turbine by using the impelling power of subatmospheric pressure hydrogen/deuterium released from hydrogen storage alloy contained in a first container and heated by indirect heat exchange with a heating medium while reabsorbing the hydrogen discharged from the gas turbine in a second hydrogen storage alloy contained in a second container and cooled by indirect heat exchange with a cooling medium. Alternately switching heating and cooling media contact with the hydride alloys maintains hydrogen gas flow as it is the pressure differential between the inlet pressure and the outlet pressure that is performing the work. Great volumes of hydrogen throughput, at subatmospheric pressures, operate the turbine. Electric energy is continuously and efficiently obtained from the electric generator. The principles can also be applied to other metal hydrides devices, e.g., pumps, compressors etc.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a non-provisional of provisional application Ser. No. 62/000,926, filed on May 20, 2014, the entire specification of which is incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to devices using low grade low grade heat from solar thermal, geothermal, ocean thermal, waste heat (“latent” or “waste” heat”) sources to manipulate hydrogen and metal hydrides and thereby to provide for electricity generation and also to a method of generating electric energy through operation of latent or waste heat on a hydrogen storage alloy system. 
         [0004]    2. Background Art 
         [0005]    Thermal hydrogen compressors for a broad range of applications have been known for over twenty years. Thermal compression of hydrogen using reversible metal hydride alloys offers an economical alternative to traditional mechanical hydrogen compressors. Hydride compressors are compact, silent, do not require dynamic seals or excessive maintenance and can operate unattended for long periods. Hydride compressors compress hydrogen and can also compress the hydrogen isotope Deuterium. The use of Deuterium is useful in the present invention due to the ability to enhance expansion efficiency because of the higher molecular weight of Deuterium relative to Hydrogen. In referring herein to hydrogen herein, the term “hydrogen” means isotopes, deuterium and hydrogen. 
         [0006]    The hydrogen compressors are powered by latent or low grade heat, that is, heat that is excess heat derived from other processes as latent or waste heat that is a usually unwanted by-product that would otherwise be vented to the ambient environment. Such latent or waste heat can also be derived from other types of low grade thermal energy, such as ocean heat, geothermal or solar energy. Because the total energy consumption utilized for thermal hydrogen compression is only a fraction of that required for mechanical compression, using hydrogen will reduce the cost of hydrogen production and increase energy use efficiency. The simplicity and passive operation of the thermal compression process offer many advantages over mechanical compressors. Hydrogen compressors of this type are described in U.S. Pat. No. 4,282,931 and commonly owned U.S. Pat. Nos. 4,402,187; 4,505,120; 5,450,721; 4,781,246; 4,884,953; 5,623,987; 6,508,866, and U.S. Pat. No. 8,114,363, all the disclosures of which are incorporated by reference herein, as appropriate. 
         [0007]    Additionally, other patents and applications utilize the principles and features of a hydride bed heat exchanger to provide either heating or cooling for buildings, automobiles and other enclosed spaces. For example, U.S. Pat. No. 6,520,249 describes a low temperature waste heat gas driven refrigeration system using hydrides to pump hydrogen between hydride beds and thus to provide a cooling capacity for refrigeration. U.S. Pat. No. 4,436,539 provides air conditioning by using a hydrogen heat pump; U.S. Pat. No. 4,439,111 describes a solar pumping installation utilizing hydrides. 
         [0008]    Common to all of the heretofore known hydride compressor technologies is the use of metal hydrides to absorb and release hydrogen at appropriate times in the hydriding-dehydriding cycle so as to compress the hydrogen to ever higher pressures in a stairstep way by undergoing continual and repeated absorption/desorption steps. Hydrogen pressure in a metal hydride is known to increase exponentially with increasing temperature. The pressure rise generated in a single stage hydride heat exchanger heated with low-grade heat may be as high as 300%. Although theoretical pressure increases have been calculated to be as much as 500%, the effect of natural inefficiencies, such as heat transfer resistance and hydrogen pressure drop, tends to reduce the available pressure increase in actual practice. 
         [0009]    Additional uses of hydride storage alloy systems as described above include methods and apparatus for generation of electrical energy. For example, U.S. Pat. No. 4,739,180, entitled “Method and apparatus for generating electric energy using hydrogen storage alloy” was issued to Yonoma et al. on Apr. 19, 1988. While these types of uses have been developed and expanded upon, they transfer hydrogen gas within a closed system at higher pressures. Because of the small relative size of the hydrogen atoms, and of hydrogen molecules, the hydrogen gas is more prone to find even miniscule leak paths which can lead to the possibility of leaking hydrogen to the atmosphere, both losing the hydrogen gas as a resource and possibly leading to unintended events. 
         [0010]    Hydrogen gas streams utilized in other than metal hydride battery systems require modifications to these systems toward providing greater energy use efficiencies. For example, in aforementioned U.S. Pat. Nos. 5,450,721 and 5,623,987, drawn to an air conditioning system and a modular manifold hydrogen gas delivery system, respectively, a hydride compression arrangement utilizing several steps in a hydrogen compression process is described. 
         [0011]    Heretofore, generation of electric power by means of a gas turbine using a source of heat having middle to low temperatures levels has been effected by evaporating a pressurized, condensable heat transfer medium such as water, Freon® gas or natural gases. The process includes introducing the resulting vapor into the gas turbine and impelling the gas against vanes connected to a shaft for driving same, condensing the vapor discharged from the gas turbine, and reheating the condensed liquid heat transfer medium for vaporization and for recirculation into the gas turbine. Conventional methods require the use of a heat transfer medium whose boiling point is considerably lower than the temperature of the heat source being used because the boiling point of the gas is constant under constant pressure. In order to condense the vapor of the heat transfer medium discharged from the gas turbine at high efficiencies, the temperature at which the heat transfer medium is condensed must be considerably higher than the temperature of a cooling source. For the above reasons, it is necessary that the difference in temperature between the heating and cooling sources in most gas turbine/generator combinations is large. The difficulty in driving a gas turbine in the above-described manner results in efficiency costs when using a heat source of middle-low levels (50°-150° C.) and a cooling source of about 10°-30° C. 
         [0012]    Systems utilizing recapture “low grade” heat require a source of heat that is otherwise radiated or vented to the environment, or removed by a heat sink or other similar device, or is available as latent or ambient heat, for example, solar or geothermal. Other sources of low grade or ambient heat may also come to mind, so long as it can be utilized to provide the driving force in a thermal hydriding-dehydriding system. 
         [0013]    None of the heretofore known devices have considered the use of gas at low pressure or subatmospheric pressure for providing the motive force for powering a generator. Low and ultralow pressures have not been considered for the most part because low pressures are not considered to have high motive power for driving turbines. This has been the general past experience when designing engines using the Carnot cycle and other known fuel combustion engines. 
         [0014]    Although devices have been described in which solar energy is used to generate and store hydrogen in a storage vessel, for example in U.S. Pat. Nos. 5,512,145 and 6,610,193, for later use in an energy producing device, for example, in a fuel cell, none of the devices heretofore known are capable of directly producing electrical power through a generator motor or turbine driven by low, subatmospheric pressure hydrogen gas moving therethrough. 
       SUMMARY OF THE INVENTION 
       [0015]    Continuous pressure differentials in hydrogen pressure provide the motive power for the generator shaft, and the amount of power available from the lower pressures is compensated by an increase in the volume of the hydrogen flow. The pressure differential is produced by providing two identical hydride heat exchanges alloy storage “beds”, and utilizing simple and reliable one-way hydrogen check valves between the beds, in an arrangement such as is disclosed in commonly owned U.S. Pat. No. 6,042,960, described in greater detail below. When one of the hydride beds is heated and the other bed is cooled, hydrogen absorption and compression occurs simultaneously in different parts of the closed system. Following completion of the hydrogen transfer between two separated beds, the heat source is exchanged at the source or the flow is reversed, for example, the hot and cold water flow is reversed, and hydrogen absorption and compression, again, occurs simultaneously, except hydrogen flow occurs in the opposite direction before the reversal. 
         [0016]    Alternatively, and in accordance with the teaching of U.S. Pat. No. 4,739,180, a simple switching of the check valves permitting the gas to flow in opposite directions provides for the gas flow reversing function. The use of one-way hydrogen check valves, such as one of the two valves illustrated and described in commonly owned U.S. Pat. No. 6,042,960, prevents the hydrogen from back flowing to the hydride bed from which the hydrogen was desorbed in the previous portion of a cycle. The procedure in a simple and passive process allows the hydrogen to flow through the turbine at a low or ultra low pressure whenever a small pressure differential capable of opening the one way check valve (about 1 psi) is present. 
         [0017]    In another aspect of the invention, an inventive configuration of check valves, such as those described in commonly assigned U.S. Pat. No. 6,042,960, permits the essentially automatic operation of the device so that the flow of hydrogen, controlled by the relative pressures in the various pipes of the system, is always in a single direction providing the necessary flow across the gas expansion turbine to drive impellers and a shaft thereby to generate electricity. The automatic operation can be effectuated by pressure sensors in the pipes of the system to recognize the optimal timing for when to switch the flow of heating and cooling media to build-up pressure through desorption and to reduce pressure through absorption by the respective hydride alloys in the hydride beds in the at least two containers therefor. 
         [0018]    In accordance with one aspect of the present invention, there is provided a method of generating electric energy, comprising the steps of providing a gas expansion turbine, an electric generator operatively connected to said gas turbine and capable of generating electric energy when the gas turbine is driven, and a plurality of zones each containing a hydrogen storage alloy capable of absorbing hydrogen upon being cooled and of releasing the absorbed hydrogen upon being heated, heating the hydrogen storage alloy in at least one of the plurality of zones while cooling the hydrogen storage alloy in at least one of the other zones, so that the heated hydrogen storage alloy releases hydrogen into the system, impelling the released hydrogen into the gas turbine to drive the shaft, and feeding the hydrogen used for driving the gas turbine to at least one of the other zones containing a hydrogen storage alloy being cooled to allow the released hydrogen to be reabsorbed thereby. 
         [0019]    Low or ultralow, including subatmospheric, pressures of hydrogen in conjunction with metal hydrides used as a motive power can be expanded beyond generators. For example, metal hydride pumps, compressors, purification devices and other hydrogen-hydride devices are known, and described in numerous articles and patents, including commonly assigned U.S. Pat. Nos. 4,505,120, 4,884,953, 7,736,609 and 8,114,363. The benefits and advantages deriving from the present invention will be evident to a person having skill in the art so that these types of devices will be readily modified for operation in ultralow or subatmospheric pressures, as described herein for generators. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The present invention will now be discussed in further detail below with reference to the accompanying figures in which: 
           [0021]      FIG. 1  is a schematic drawing showing the concepts present in a generator turbine combination according to the present invention. 
           [0022]      FIG. 2  is a fluid flow schematic diagram of a simplified hydride heat pump according to the present invention showing the hydride heat exchanger beds, valving, turbine generator, piping and fluid flow pathways that are generally needed to generate electricity using a metal hydride system; 
           [0023]      FIG. 3  is very similar to the fluid flow schematic diagrams for  FIG. 2  but with the addition of dual check valve arrangement having fluid valves, and is useful in illustrating how electricity generating operation, can be employed in the same device. 
           [0024]      FIG. 4  illustrates in graphical form the efficiency and effect of utilizing deuterium in respect to the pressures generated and the maximum permissible RPMs as a result of limitations therein resulting from the use of foil bearings. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    The description below should be understood in the context of general principles of metal hydride alloy technology. It is well known that metal hydrides have a capability to absorb (charge) and desorb (discharge) hydrogen gas as a function of temperature. It should be recognized that the generation of electricity using these types of systems and using specific are described elsewhere, including in the above mentioned patents and applications to which reference is made, which provide for a more detailed description of metal hydride alloys and metal hydride technology, fluid flow and valve positioning for most efficient operation. 
         [0026]      FIGS. 1 through 3  generally relate to each other in describing the operation of a generating plant utilizing known metal hydride systems. Referring now to  FIG. 1 , the reference numeral  10  denotes a generating system according to the present invention, including a generator  12 , a gas turbine  14 , and a shaft  16  mechanically connecting gas turbine to generator  12 . As the turbine  14  rotates the shaft  16 , it generates electricity in the generator  12  which is drawn off for use in an electrical grid through electrical connectors  11  on the generator  12 . The general operation of the generator  12  is known and not a significant part of this invention. 
         [0027]    Turbine  14  is a gas turbine of known construction, but has a plurality of vanes  18  that are attached to shaft  16  in a concentric relationship. As gas at a higher pressure flows into the gas turbine  14  through the inlet pipe  20  and manifold  22 , the gas is directed to impel the vanes  18  and so rotate the shaft  16  in a desired direction. Manifolds for delivery of hydrogen gas are known and described, for example in commonly assigned U.S. Pat. No. 5,623,987. These manifolds enable the distribution of hydrogen gas to numerous ports at essentially the same pressure before entry into the gas turbine  14 . 
         [0028]    After the gas completes the impelling function in the gas turbine  14 , it is collected at a lower pressure relative to the inlet pressure at the outlet manifold  24 . Then it is directed to the outlet pipe  26  for directing back to the hydride beds  80 ,  80 ′ ( FIG. 2 ), thereby to provide a higher pressure gas in a continual cycle as is explained in greater detail below. 
         [0029]    Referring now to  FIG. 2 , a first heat exchange zone, generally a heat exchanger  40 , accommodating a bed  80  of a hydrogen storage alloy which has absorbed hydrogen, provides a heat source that selectively heats and cools the metal hydride bed  80 . A second heat exchange zone  40 ′, similar to the first heat exchange zone  40 , accommodates a bed  80 ′ of a hydrogen storage alloy which is generally the same as the alloy in the first heat exchange zone  40  and which has released hydrogen in a cycle. The first and second heat exchangers  40 ,  40 ′ generally comprise first and second sealed, closed containers  46  and  46 ′, respectively, in which first and second heat transfer members, such as heat transfer pipes  42 ,  42 ′, respectively, are disposed for heating or cooling the hydrogen storage alloy beds  80 ,  80 ′ contained in the first and second containers  46  and  46 ′. The heat exchange process is performed by indirect heat exchange with heat transfer media flowing through the heat transfer pipes  42 ,  42 ′. The heat transfer media are introduced in the first and second heat transfer pipes  42 ,  42 ′ through feed conduits  50 ,  50 ′, respectively. 
         [0030]    The gas turbine  14  is connected through a transmission shaft  16  to an electric generator  12  so that, as the shaft  16  of generator  12  is rotated by the turbine  14 , it generates electric energy or power. The gas turbine  14  has a hydrogen inlet conduit  20  which is connected, via three-way valve  32 , to both the heat exchangers  40 ,  40 ′ through pipes  20 ,  22 ,  24  and  26 . The gas turbine  14  also includes a hydrogen outlet conduit  24  connection, via three-way valve  34 , both to the first heat exchanger  40  through pipes  28  and  21  and to the second heat exchanger  40 ′ through pipes  30  and  27 . 
         [0031]    The apparatus constructed operates as follows. While maintaining the three-way valves  32  and  34  in their closed positions, the hydrogen storage alloy in bed  80  in the first heat exchanger  40  is heated by introducing a heating medium such as a flow of water or other heat transfer means which has been heated by a solar collector or from low grade heat. The heat medium flows through the line  50  into the first heat transfer pipe  42 . The hydrogen gas previously absorbed in the hydride alloy of bed  80  is thus released from the bed  80  and the first container  46  and the pipes  21 ,  20  and  28  are filled with hydrogen at a temperature of T 1  and a pressure of P 1 . At the same time, the hydrogen storage alloy in bed  80 ′ is cooled indirectly by introducing a cooling medium for example, water taken from a cool reservoir, into the second heat transfer pipe  42 ′ through the line  50 ′, so that the hydride bed  80 ′ inside the second container  46 ′ has a temperature T 2  and a pressure P 2 . 
         [0032]    The three-way valves  32  and  34  are then actuated to selectively communicate the inlet conduit  22  with the pipe  28  and to selectively communicate the outlet conduit  24  with the pipe  26 . As a result, the higher pressure hydrogen is introduced into the gas turbine  14  through lines  21 ,  20  and  22  and, thereby impelling the vanes  18  ( FIG. 1 ) and rotationally driving the shaft  16  of gas turbine  14  and the electric generator  12 . Then the hydrogen gas at a lower pressure passes through outlet lines  24 ,  30  and  27  to the second container  46 ′ of the second heat exchanger  40 ′ where the hydrogen is reabsorbed by the alloy bed  80 ′. In this case, there are maintained relationships of P 1  &gt;P 2  and T 1  &gt;T 2  while the alloy in bed  80  in the first heat exchanger  40  releases the absorbed hydrogen and the alloy in bed  80 ′ absorbs the released hydrogen returning at the lower pressure. Therefore, the gas turbine  14  continues to operate and the shaft  16  rotates the within the generator  12  to produce electricity until the gas in system arrives at an equilibrium pressure. 
         [0033]    When desorption of hydrogen gas from the alloy in bed  80  in the first heat exchanger  40  diminishes as pressure equilibrium is reached, the valves  32  and  34  are again closed. Then, the heating medium is supplied to the second heat transfer pipe  42 ′ while the cooling medium is introduced into the first heat transfer pipe  42  so that the hydrogen gas, absorbed in the previous step in the alloy bed  80 ′ in the second heat exchanger  40 ′, is desorbed therefrom and fills the lines sequentially  27 ,  26  and  22  and the gas in container  46 ′ reaches as new equilibrium at a temperature of T 2 ′ and a pressure of P 2 ′. The valves  32  and  34  are then opened to permit flow of hydrogen through the pipe  26  and into line  22  and the line  24  into the line  28 . This results in the introduction of the hydrogen at T 2 ′ and P 2 ′ into the gas turbine  14 , thereby continuing the impelling and driving of electric generator  12  operatively connected to the gas turbine  14  through shaft  16 . The hydrogen gas then flows through lines  24 ,  28  and  21 , to the first heat exchanger  40  where it is absorbed by the alloy in bed  80  in the first heat exchanger  40  at a temperature of T 1 ′ and a pressure of P 1 ′. Since P 1 ′&lt;P 2 ′ and T 1 ′&lt;T 2 ′, the gas turbine  14  is driven with the higher pressure hydrogen serving as the working gas. 
         [0034]    The operational steps as described above are repeated to continuously drive the shaft  16  and thereby to obtain electric energy from the generator  12 . In this case, since the efficiency in the turbine  14  depends upon the difference in temperature in the incoming hydrogen and the exhaust hydrogen, it may be more effective to provide a heater (not shown) in the hydrogen inlet conduit  22  to improve the operation efficiency of the gas turbine  14 . 
         [0035]    “Volumetric efficiency” in an expansion device, such as turbine  14 , for use with a generator  12  using ultra low pressures requires the system to utilize a high volume of hydrogen throughput. Ideally, use of low pressure can be subatmospheric and a negative pressure environment, relative to ambient, may be used to generate electrical power from latent or solar heat. 
         [0036]    The better the volumetric efficiency, the more work is obtained from a similar volume of gas. Since hydrogen gas has a low MW (2.016), it is liable to leak past seals, blades, vanes more (or easier than) than higher MW gases like steam (MW=18) or Dichlorodifluoromethane (Freon®, MW=102), thereby reducing the volumetric efficiency. It has been found that a marked increase in the volumetric efficiency of hydrogen in an expansion device can be achieved by operating at very low or subatmospheric pressures. Hydrogen volume at very low pressure is so high, that the percentage of hydrogen that leaks past internal seals or leaks out of the closed system  10  without doing any work is reduced, thereby substantially increasing volumetric efficiency and increasing overall expansion efficiency. 
         [0037]    It has also been disclosed that deuterium can replace hydrogen as a diffused gas in metal hydrides. While the increase in volumetric efficiency provides a benefit when using molecular hydrogen, added or enhanced efficiencies may result from the use of deuterium instead of hydrogen while maintaining the functionality of the metal hydride to absorb deuterium. The added molecular weight of deuterium molecules, effectively twice that of hydrogen molecules, provides additional gravitational forces that more effectively impel the vanes of an expansion turbine, such as gas turbine  14 . Thus, use of deuterium is considered to add significantly to the volumetric efficiency of the turbine and thus of the generator in general. 
         [0038]    Collateral benefits of utilizing these type of devices include low pressure construction (less material and less rugged elements are needed to withstand the pressure), lower rotational speed for practical electrical generation, lower rotational speed reduces stress on rotating materials, allowing lighter weight/less expensive construction. Low pressure operation does not reduce the work obtained form the system, since it can be done at the same expansion ratio as higher pressure machines as it is the inlet-to-outlet pressure ratio that performs the work, not the absolute pressure of any one chamber or pipe. Just like the known steam turbine, as described in U.S. Pat. No. 1,089,710, hydrogen volume at ½ atmosphere (7.3 psi) is twice that at atmospheric pressure, at ¼ atmosphere (3.65psi) is 4 times that at 1 atm., at ⅛ atmosphere (1.82 psi) is 8 times more than at 1 atm. and at 1 psia is 14.7 times more than at 1 atm. Thus, multiple expanders, each having several vanes  18  in the same turbine  14 , are provided to accommodate the high gas volume of the hydrogen throughput that must go from higher, albeit still subatmospheric, pressure to lower pressure. Higher volume provides for better performance with a low MW fluid, such as hydrogen, which is ideal for this purpose. Prior efforts, for example using steam, sacrifice efficiency when using the volume to extract the last few BTU&#39;s from steam before condensation. 
         [0039]    Referring now to  FIG. 3 , a second embodiment of the device  110  is shown using an expansion turbine  14 . In this embodiment, like parts will be identified by like numerals, only different elements having a like function will be identified by a different number having a different initial digit. The embodiment of a gas generator turbine  110  shown in  FIG. 3  has a first heat exchange zone, generally a heat exchanger  40 , accommodating a bed of a hydrogen storage alloy  80  which has absorbed hydrogen (or deuterium). The heat exchanger  40  provides a heat source that selectively heats and cools the metal hydride alloy  80 . 
         [0040]    A second heat exchange zone  40 ′, similar to the first heat exchange zone  40 , accommodates a bed of a hydrogen storage alloy  80 ′, which is generally the same as the alloy  80  in the first heat exchange zone  40  and which has released hydrogen therefrom. The first and second heat exchanger zones  40 ,  40 ′ generally comprise first and second sealed, closed containers  46  and  46 ′, respectively, in which first and second heat transfer members, such as heat transfer pipes  42 ,  42 ′, respectively, are disposed for selectively heating or cooling the hydrogen storage alloys  80 ,  80 ′ contained in the first and second containers  46  and  46 ′. This is generally done by indirect heat exchange with heat transfer media flowing through the outlet pipes  42 ,  42 ′, and inlet feed conduits  50 ,  50 ′, which in turn are connected to sources of low grade heat, as described above, and a cooling source, respectively, not shown in  FIG. 3 . 
         [0041]    The heat transfer media are introduced in the first and second heat transfer pipes  42 ,  42 ′ through feed conduits  50 ,  50 ′, respectively. The flow of the heating and cooling media through the pipes  42 ,  42 ′ and through-feed conduits  50  are controlled by several three way cut-off valves  32  that provide for the desired fluid flow direction of the cooling and heating fluids, essentially as in the embodiment of  FIG. 2 . 
         [0042]    A gas turbine  14 , to which an electric generator  12  is connected through a transmission shaft  16 , operates to generate electric energy or power upon rotation of the shaft  16  by the gas turbine  14 . The gas turbine  14  has a hydrogen inlet conduit  120  which is connected, via inlet/outlet pipes  122 ,  124  and going through specified grouping of one valves  132 , referred to herein as the dual check valve arrangement  130 . The operation of the one-way valves  132  follows the teaching of commonly assigned U.S. Pat. No. 6,042,960, with respect to the dual check valve arrangement  130  to produce a continuous flow of higher, albeit subatmospheric, pressure hydrogen in one flow direction. The disclosure of U.S. Pat. No. 6,042,960 is incorporated by reference, as if fully set forth herein. The resulting flow-through of the lower pressure hydrogen from the expansion turbine  14  reaches the point between the two check valves  132  and the valve  132  that will open is the one that has lower pressure on the other side than is in the return conduit  121 , as will be explained below with respect to the device operation. 
         [0043]    Both heat exchangers  40 ,  40 ′ provide fluid communication to the containers  46 ,  46 ′ only through the pipes  122  and  124 . The gas turbine  12  also has a hydrogen outlet conduit  121  which is connected, via dual check valve arrangement  130 , to both the first heat exchanger  40  through pipe  122 , and to the second heat exchanger  40 ′ through pipe  124 . 
         [0044]    The apparatus  110 , thus constructed, operates as follows. While maintaining the dual check valve arrangement  130  in a static position, the hydrogen storage alloy  80  in the first heat exchanger  40  is heated by introducing a heating medium such as a flow of warm water or other heat transfer means which has been heated by a solar collector or from a low grade heat source, flowing through the line  50 . As result of the heating of the hydride bed  80 , the hydrogen absorbed in the hydride alloy  80  is thus released therefrom and the first container  46  and the pipe  122  are filled with hydrogen at an increased temperature of T 1  and pressure of P 1 . As temperature T 1  and pressure P 1  increase, the pressure will continue to rise until it is greater than the pressure P 2  in the pipe  126  (P 1 &gt;P 2 ). As this occurs, at some point the one-way valve  132  between pipes  122  and  126  will open to permit the hydrogen to flow from pipe  122  and into pipe  126  and thereby into conduit  120 , thus powering the expansion turbine  14  by the hydrogen flow and impelling the turbine vanes through expansion from the higher pressure to the lower pressure. 
         [0045]    At the same time, the hydrogen storage alloy  80 ′ is cooled indirectly by introducing a cooling medium, for example, water taken from a cooling reservoir, into the second heat transfer pipe  50 ′ and removing it through the conduit  42  so that the inside of the second container  46 ′ has a temperature T 3  and a pressure P 3 . As the pressure is reduced to that below the pressure P 2 , that is, P 2  &gt;P 3,  the valve  132  between pipes  124  and  126  closes of the hydrogen flow from pipe  126  into pipe  124 . As result of the configuration of dual check valve arrangement  130 , valves  132  permit the flow of hydrogen into the conduit  120  at the appropriate times for the operation to continually flow in a single direction at a relatively constant rate, and thereby to continue the generation of electrical power at low pressures but at high efficiency. 
         [0046]    Simultaneously to this process, the second portion of the dual check valve arrangement  130 , having two additional one way valves  132 , oppositely oriented in respect to fluid flow to those above described, also operate to provide hydrogen gas flow in the opposite direction, that is, from expansion turbine  14  to the hydride bed  80 ′ in container  46 ′. The dual check valve arrangement  130  is automatically actuated to selectively communicate the inlet conduit  121  with the pipe  124  to provide for absorption of the hydrogen gas by the hydride bed  80 ′. That is, as the pressure P 4  in the pipes  121 ,  128  exceeds the pressure P 3  in pipe  124  the one-way valve  132  between these pipes opens and communications is open for hydrogen flow to commence from expansion turbine  14  to hydride bed  80 ′. Simultaneously, because the pressure P 1  is greater than the pressure P 4 , valve  132  between pipes  122  and  128  shuts off the hydrogen flow therebetween. When the pressures begin to approach equilibrium, the three way valves are simply switched, and in the arrangement shown, switched automatically, so that the pipes that were carrying cooling medium begin to provide heated medium to the hydride beds  80 ,  80 ′, and vice versa. 
         [0047]    As a result, the higher pressure hydrogen is introduced into the gas turbine  14  through pipe  120  and, after impelling the vanes  18  ( FIG. 1 ) and driving the shaft  16  of gas turbine  14  and the electric generator  12 , the hydrogen gas at a lower pressure passes through pipe  121  to the appropriate container  46 ,  46 ′ of the appropriate heat exchanger  40 ,  40 ′ where the hydrogen is reabsorbed by the respective alloy  80 ,  80 ′. Therefore, the gas turbine  14  continues to operate without slowing down and shaft  16  rotates the within the generator  12  to produce electricity until the system arrives at an equilibrium and the flows of the two cooling and heating media are reversed. 
         [0048]    One distinct advantage of the device  110  shown in  FIG. 3  is the operation of the valves  132  is essentially automatic, and need not be controlled by the system in any way. That is, the relative pressures of the hydrogen gas in the pipes controls the hydrogen flow, and he pressures are regulated by the cooling and heating media that provide the heat of desorption and cool to provide absorption of the hydrogen gas by the respective hydride beds  80 ,  80 ′. Thus, as pressure sensors in the respective pipes can be utilized to provide an algorithm for the optimal moments in which to switch the direction of flow of the heating and cooling media, the low subatmospheric pressure, albeit at higher than standard volumes, can be used to provide a continuous impelling force on the vanes and a continuous driving of the shaft  16  to generate electrical power from generator  12 . 
         [0049]    The operation as described above are repeated to continuously obtain electric energy from the generator  12 . In this case, since the efficiency in the turbine  14  depends upon the difference in temperature in the incoming hydrogen and the exhaust hydrogen, it may be more effective to provide a heater (not shown) in the hydrogen inlet conduit  122  in improving the operation efficiency of the gas turbine  14 , but this is not a requirement. It should be understood that use of an arrangement with a heater (not shown) will result in a decrease in efficiency because of the power necessary to heat the fluids. 
         [0050]    Foil bearings have been known for use in high or ultrahigh rotational speeds and operations, e.g. U.S. Pat. No. 4,445,792. Operating turbines at sub-atmospheric pressures is desirable because of limitations placed on foil bearings. Foil air bearings, unlike contact-roller bearings, utilize a thin film of pressurized air between relatively moving or rotating surfaces to provide an exceedingly low friction load-bearing interface. The two relatively moving or rotating surfaces are non-contacting because of the air gap formed therebetween during operation. Being non-contacting, foil bearings avoid the traditional bearing-related problems of friction, wear, particulates, and lubricant handling, and offer distinct advantages in precision positioning, such as lacking backlash and stiction (static friction), as well as in high-speed applications. Foil bearings excel where high temperature and high rotational speed bearings are needed. Working in sub-atmospheric pressures permits for superior performance. 
         [0051]    A direct correlation exists between the effects of low pressures and turbine revolution speeds as measured by revolutions per minute (RPMs). The maximum permissible RPMs for foil bearings is around 60,000 RPMs (line  85  in  FIG. 4 ), which speeds are only achievable if the turbines operate at gas inlet pressures below 15 pounds per square inch (psia), which represents atmospheric pressures at seal level. Thus, the use of sub-atmospheric pressures is necessary for the shaft speeds to be less than 60,000 RPMs in using most gasses.  FIG. 4  shows in graph form how a four stage, 3/1 expansion ratio, 20 kW turbine/generator designed for either Hydrogen gas (black line  89 ) or Deuterium gas (broken line  99 ). The graph illustrates that for those embodiments using deuterium gas as the working gas, the shaft speed will only be reduced to 60 k RPMs if operation of the turbine at gas inlet pressures is below 15 psia. Thus sub-atmospheric gas pressures will be a crucial requirement for use of these types of electric generators. 
         [0052]    Other types of low grade heat sources may be used to recapture the low grade heat that would otherwise be dissipated into the environment. These sources may be used to transfer the heat energy into other types of energy, for example, electrical power, that may be immediately used as needed, or alternatively, may be stored for later use, for example, in hydrogen storage vessels commercially available from Ergenics Corporation of Ringwood, N.J., USA. 
         [0053]    Other modifications will be readily apparent to one having ordinary skill in the art. For example, the hydride bed arrangement described above may require make up sources of hydrogen gas if a hermetic sealed system is not provided. Thus, the invention illustrated and described in the above embodiments is thus understood to be for exemplary purposes only, and is not to be limited by the examples of the embodiments shown and described therein, but the invention is to be limited only by the elements and limitations recited in the following claims and their equivalents.