METHOD AND APPARATUS FOR GENERATING ELECTRIC ENERGY USING HYDROGEN STORAGE ALLOY

Abstract: An electric generator (4) operatively connected to a gas turbine (3) is driven by driving the gas turbine (3) with high pressure hydrogen released from a hydrogen storage alloy (MH) which is contained in a first zone (1) and which is heated by indirect heat exchange with a heating medium (18) while reabsorbing the hydrogen discharged from the gas turbine (3) in a hydrogen storage alloy (M) which is contained in a second zone (2) and which is cooled by indirect heat exchange with a cooling medium (19). By switching the flows of the heating and cooling media alternately, an electric energy may be continuously obtained from the electric generator (4).

Description: This invention relates to a method of generating electric energy using a hydrogen storage alloy. Heretofore, generation of electric power by means of a gas turbine using a source of heat of middle-low temperature levels has been effected by evaporating a pressurized, condensible heat transfer medium such as water, freon gas or natural gases, introducing the resulting vapor into the gas turbine 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. The conventional method, however, requires the use of a heat transfer medium whose boiling point is considerably lower than the temperature of a heat source because the boiling point is constant under constant pressure. Further, in order to condense the vapor of the heat transfer medium discharged from the gas turbine with high efficiency, the temperature at which the heat transfer medium is condensed is required to 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 is considerably large. Thus, it is actually difficult to drive a gas turbine in the above-described manner with practically acceptable efficiency and cost when using a heat source of middle-low levels (50 - 150 °C) and a cooling source of about 10-30 °C. It is also known from e.g. US-A-4085590 and US-A-4358931, to generate electricity using a gas turbine which is driven by hydrogen gas which is cyclically desorbed from and then re-absorbed by a so-called hydrogen storage alloy. The desorption stage of the hydrogen cycle is effected using a heating medium. A system of this kind provides potentially an effective method of generating electric energy using a heat source of a middle to low temperature. However, the known systems for generating electricity using hydrogen storage alloys are not as efficient as is desired. In accordance with the present invention there is provided a method of generating electric energy, comprising the steps of: providing a gas turbine, an electric generator operatively connected to said gas turbine and capable of generating an electric energy when said gas turbine is driven, and first and second hydrogen absorbing and desorbing systems each including a plurality of heat exchange zones each containing a hydrogen storage alloy capable of absorbing hydrogen upon being cooled and of releasing the absorbed hydrogen upon being heated; supplying a heating medium to said first system for heating the hydrogen storage alloy in at least one of said plurality of heat exchange zones of said first system by indirect heat exchange therewith so that the heated hydrogen storage alloy in said first system releases hydrogen, while supplying a cooling medium to said first system for cooling the hydrogen storage alloy in at least one of the other heat exchange zones of said first system by indirect heat exchange therewith; introducing said released hydrogen in said first system into said gas turbine to drive same; discharging from said first system the heating medium which has been used for said heating of the hydrogen storage alloy in said first system and introducing same into said second system for heating the hydrogen storage alloy in at least one of said plurality of heat exchange zones of said second system by indirect heat exchange therewith so that the heated hydrogen storage alloy in said second system releases hydrogen, while supplying the cooling medium to said second system for cooling the hydrogen storage alloy in at least one of the heat exchange other zones of said second system by indirect heat exchange therewith; introducing said released hydrogen in said second system into said gas turbine at an intermediate position downstream from the port through which said released hydrogen from said first system is introduced into said gas turbine; and feeding the hydrogen used for driving said gas turbine to said at least one of the other zones of said first and second systems containing the hydrogen storage alloy being cooled to allow the released hydrogen to be reabsorbed thereby. The method of the present invention, by providing an additional hydrogen absorbing and desorbing system where the waste heating medium is utilized for hydrogen desorption, permits the temperature of the heating medium exhausted from the apparatus to be lowered. The present invention will now be described in detail below with reference to the accompanying drawings, in which: Fig. 1 is a flow chart of an apparatus illustrating the principles of generating electricity using hydrogen storage alloys; and Fig. 2 is a flow chart of apparatus for carrying out a preferred embodiment of the method according to the present invention. Referring first to Fig. 1, the reference numeral 1 denotes a first heat exchange zone, generally a heat exchanger, accomodating a bed of a hydrogen storage alloy MH which has absorbed hydrogen, 2 denotes a second heat exchange zone, similar to the first heat exchange zone, accomodating a bed of a hydrogen storage alloy M which is generally the same as the alloy in the first heat exchange zone 1 and which has released hydrogen. The first and second heat exchangers 1 and 2 are generally composed of first and second closed containers 24 and 25, respectively, in which first and second heat transfer members, such as heat transfer pipes 5 and 6, respectively, are disposed for heating or cooling the hydrogen storage alloy contained in the first and second containers 24 and 25 by indirect heat exchange with heat transfer media flowing therethrough. The heat transfer media are introduced in the first and second heat transfer pipes 5 and 6 through feed conduits 18 and 19, respectively. Designated as 3 is a gas turbine to which an electric generator 4 is connected through a transmission shaft 16 so that the generator 4 operates and generates electric energy or power upon driving of the gas turbine 3. The gas turbine 3 has a hydrogen inlet conduit 14 which is connected, via three-way valve 12, both to the first heat exchanger 1 through pipes 8 and 7 and to the second heat exchanger 2 through pipes 10 and 17. The gas turbine 3 also has a hydrogen outlet conduit 15 which is connected, via three-way valve 13, both to the first heat exchanger 1 through pipes 9 and 7 and to the second heat exchanger 2 through pipes 11 and 17. The apparatus thus constructed operates as follows. The hydrogen storage alloy MH in the first heat exchanger 1 is heated, while maintaining the three-way valves 12 and 13 in closed state, by introducing a heating medium through the line 18 into the first heat transfer pipe 5, so that the hydrogen absorbed in the alloy MH is released therefrom and the first container 24 and the pipes 7, 8 and 9 are filled with hydrogen at a tempeature of T₁ and a pressure of P₁. At the same time, the hydrogen storage alloy M is cooled indirectly be introducing a cooling medium into the second heat transfer pipe 6 through the line 19 so that the inside of the second container 25 has a temperature T₂ and a pressure P₂. The three-way valves 12 and 13 are then actuated to selectively communicate the inlet conduit 14 with the pipe 8 and to selectively communicate the outlet conduit 15 with the pipe 11. As a result, the high pressure hydrogen is introduced into the gas turbine 3 through lines 7, 8 and 14 and, after driving the gas turbine and the electric generator 4, passed through lines 15, 11 and 17 to the second container 25 of the second heat exchanger 2 where the hydrogen is reabsorbed by the alloy M. In this case, there are maintained relationships of P₁ > P₂ and T₁ > T₂ while the alloy MH in the first heat exchanger 1 releases the absorbed hydrogen and the alloy M absorbes the released hydrogen. Therefore, the gas turbine 3 continues driving until the system arrives at an equilibrium. When the desorption of hydrogen from the alloy in the first heat exchanger 1 ceases, the valves 12 and 13 are closed. Then, the heating medium is supplied to the second heat transfer pipe 6 while the cooling medium is introduced into the first heat transfer pipe 5 so that the hydrogen absorbed, in the previous step, in the alloy in the second heat exchanger 2 is desorbed therefrom and fills the lines 10, 11 and 17 and the container 25 at a temperature of T₂' and a pressure of P₂'. The valves 12 and 13 are then opened to communicate the line 10 with the line 14 and the line 9 with the line 15. This results in the introduction of the hydrogen at T₂' and P₂' into the gas turbine 3, thereby driving the electric generator 4 operatively connected to the gas turbine 3. The hydrogen is then fed, through the lines 15, 9 and 7, to the first heat exchanger 1 and is absorbed by the alloy in the first heat exchanger 1 at a temperature of T₁' and a pressure of P₁'. Since P₁' < P₂' and T₁' < T₂', the gas turbine 3 is driven with the high pressure hydrogen serving as a working gas. The operations as described above are repeated to continuously obtain electric energy from the generator 4. In this case, since the efficiency in the turbine 3 depends upon the difference in temperature in the incoming hydrogen and the exausted hydrogen, it is effective to provide a heater (not shown) in the hydrogen inlet conduit 14 in improving the operation efficiency of the gas turbine 3. Fig. 2 depicts one embodiment of apparatus for carrying out the method of the present invention and in which two sets of absorbing/desorbing systems I and II, each of the kind shown in Fig. 1 are used. In Fig. 2 valves are omitted from the illustration for the convenience of explanation and similar component parts are designated by the same reference numerals. A heating medium having a temperature of, for example, 120°C is first fed through a line 18 to a heat exchange zone 1 of the first system I for heating a hydrogen storage alloy contained therein and, thereafter, discharged from the heat exchange zone 1. The discharged heating medium having a temperature of, for example, 80°C is then introduced into a heat exchange zone 1' of the second system II for heating a hydrogen storage alloy contained therein. The hydrogen generated in the first system I is introduced through a line 8 into a gas turbine 3 for driving an electric generator 4 while the hydrogen from the second system II, which has a lower pressure than that from the first system I, is introduced through a line 8' into an intermediate stage of the turbine 3, i.e. at a location downstream from the inlet connected to the line 8. The hydrogen is then discharged from the turbine 3 through a line 15 and is reabsorbed by the metals in heat exchange zones 2 and 2' of the first and second systems I and II cooled by a cooling medium supplied through lines 19 and 19', respectively. Practically, each of the hydrogen absorbing and desorbing systems I and II of Fig. 2 may be formed of six or more heat exchangers, in a similar manner to that shown in Fig. 2 of the 'A' publication of this Application (and now the subject of European Patent Application No. 89203332 , divided herefrom). The hydrogen obtained in the system II is desirably heated before introduction into the gas turbine 3. When the gas turbine 3 is provided with a reheater 23 such as shown in Fig. 2 of said divisional application, the hydrogen from the system II is preferably fed to the reheater 23. Any known hydrogen storage alloy may be suitably used for the purpose of the present invention. Representative alloys to be used for the present invention may be selected appropriately in consideration of, for example, the temperature of a source of the heating medium to be utilized for heating the alloys. The same hydrogen storage alloy is generally used in each of the heat exchange zones, though different kinds of hydrogen storage alloys may be used if desired. In accordance with the present invention, electric energy may be efficiently generated using a source of heat of low levels that could not be used heretofore for electric generation. Unlike conventional techniques, no pump is required for pressure elevation and neither condenser for gases discharged from a turbine nor circulating devices for condensed gases are required, thereby rendering the electric energy generation system simple and economical. The present invention has great industrial significance because electric energy can be advantageously generated using geothermal heat or exhaust heat of low levels produced by chemical plants or other manufacturing plants.

Claims: A method of generating electric energy, comprising the steps of: providing a gas turbine, an electric generator operatively connected to said gas turbine and capable of generating an electric energy when said gas turbine is driven, and first and second hydrogen absorbing and desorbing systems each including a plurality of heat exchange zones each containing a hydrogen storage alloy capable of absorbing hydrogen upon being cooled and of releasing the absorbed hydrogen upon being heated; supplying a heating medium to said first system for heating the hydrogen storage alloy in at least one of said plurality of heat exchange zones of said first system by indirect heat exchange therewith so that the heated hydrogen storage alloy in said first system releases hydrogen, while supplying a cooling medium to said first system for cooling the hydrogen storage alloy in at least one of the other heat exchange zones of said first system by indirect heat exchange therewith; introducing said released hydrogen in said first system into said gas turbine to drive same; discharging from said first system the heating medium which has been used for said heating of the hydrogen storage alloy in said first system and introducing same into said second system for heating the hydrogen storage alloy in at least one of said plurality of heat exchange zones of said second system by indirect heat exchange therewith so that the heated hydrogen storage alloy in said second system releases hydrogen, while supplying the cooling medium to said second system for cooling the hydrogen storage alloy in at least one of the other heat exchange zones of said second system by indirect heat exchange therewith; introducing said released hydrogen in said second system into said gas turbine at an intermediate position downstream from the port through which said released hydrogen from said first system is introduced into said gas turbine; and feeding the hydrogen used for driving said gas turbine to said at least one of the other zones of said first and second systems containing the hydrogen storage alloy being cooled to allow the released hydrogen to be reabsorbed thereby. A method as claimed in claim 1, further comprising heating said released hydrogen in said second system before introducing same into said intermediate portion of said gas turbine.

Inventors: SAKAGUCHI, JUNICHI, YANOMA, AKIRA
Applicants: CHIYODA CHEMICAL ENGINEERING & CONSTRUCTION COMPANY LIMITED
Application year: 1987
Main classification: F01K25
IPC codes: F02C1, F01K25