Patent Publication Number: US-2012037153-A1

Title: System for producing energy from hydrogen, in particular for residential buildings

Description:
DESCRIPTION OF THE INVENTION 
     1. Field of application 
     The present invention refers to a system for producing energy from hydrogen, in particular for residential buildings, according to the preamble of claim  1 . 
     2. Prior art 
     As known, hydrogen can be used to produce, for example for residential buildings, heat energy through hydrogen catalytic burners (WO 2006/136316 A1 of the applicant) or through electrical energy through fuel cells (US 2010/0164287 A1). 
     Catalytic burners of the applicant have been used over the years and the fuel cells, i.e. the hydrogen cells, currently have extremely advanced technologies. 
     In catalytic burners, the generated heat energy is used, through a heat exchanger, for heating the water of, for example, a heating system of a residential building and for heating domestic water, or for other heating purposes, for example for heating greenhouses and so on and so forth. 
     The hydrogen for supplying the burner is preferably produced through electrolysis, where the required electrical energy is advantageously produced by renewable sources, such as for example a photovoltaic plant. Hydrogen could also be produced by means of a reformer, or generated by methane gas. 
     Different control components, for example a pressure reducer, a control unit, a battery with battery charger and so on and so forth are associated to the burner. 
     Fuel cells were developed in particular for the automotive industry, and they provide optimal levels both in terms of performance and duration. They can also be used for producing electrical energy in residential buildings. 
     It is also known that fuel cells, during operation thereof, produce heat, which is generally dispersed into the environment. 
     From the abovementioned US 2010/0164287 A1 there is known a system for supplying electric power between a vehicle, comprising a fuel cell and a house. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is that of providing a system for producing energy from hydrogen capable of supplying, for example to a residential building, the required energy whether heat and electrical energy so as to make said residential building independent from the electrical power and gas supply system, wherein—at the same time—the operative synergy between the components of the system which improves the performance of the system is exploited. 
     Such object is attained, according to the invention, by means of system for producing combined energy from hydrogen having the characteristics of claim  1 . 
     Further developments of the invention are observable from the dependent claims. Numerous and significant advantages are obtained from the system for producing energy from hydrogen according to the invention. 
     Firstly, integration—in the system for producing energy according to the invention—of a catalytic burner and a fuel cell both of which can be supplied with hydrogen, advantageously produced through in situ electrolysis, allows the unit to use two sources, i.e. the source of heat energy and the source of electrical energy, in a manner entirely independent from the other, and thus modulate both the electric power and the heat power so as to regulate the relative consumption depending on the contingent needs, wherein the use of hydrogen both for the burner and for the fuel cell allows having a system for producing entirely zero-emission energy, given that both the fuel cell and the burner generate water vapour alone and thus no carbon dioxide and nitrogen oxides. Given that the two sources of energy (burner and fuel cell) operate independently from each other, production of electrical energy is not subordinated to that of heat energy, and vice versa. At the same time, different circuit components already required for the burner can be advantageously used at the same time also for the fuel cell. The system for producing energy according to the invention also allows improving the overall performance of the system. For example, the air used for cooling the fuel cell, available at about 40-45° C., can be used for heating the air entering the burner, thus boosting the efficiency of the latter. As outlined hereinafter, same case applies also regarding water-cooled fuel cells. 
     In the plant for producing combined energy according to the invention using the fuel cell, the plant can operate without being connected to the electrical power supply system, thus the system operates autonomously upon starting. This constitutes an important advantage with respect to the prior art heat generators, in that the prior art methane-powered heat generators do not operate in absence of electrical power. Having the electrical power supply system, a power outlet for possible supply from the power system and for recharging the battery of the auxiliary components in case of discharge thereof for any reason whatsoever, is however recommendable. 
     Associating—in the system—a hydrogen catalytic burner and a fuel cell boosts the efficiency of the latter in that it can recover the heat generated by the same during operation, instead of dispersing such heat. 
     Associating—to the system for producing combined energy according to the invention—a high efficiency heat pump allows obtaining further advantages. Such association—using an assembly of highly efficient technologies—would even allow recovering the energy used for producing hydrogen by electrolysis. 
     Actually, in practice, currently a heat pump has a coefficient of performance (COP) normally comprised between 3 and 4 values, wherein—for the sake of simplicity—a 3.5 COP is considered. A fuel cell has a yield of about 40%, hence the association of the two systems provides an overall value of 1.4 and, thus, greater than one unit. Considering that production of hydrogen through electrolysis (performance of about 75%), then the total performance would reach the value of about 1.05. This means that this system, coupled with a heat pump and with generation of hydrogen through electrolysis, allows recovering more energy with respect to that used initially, hence making it extremely advantageous. Then if the input energy is collected and stored at the right time (for example, in case of connection to the power supply system, at night when it might cost less) or if it comes from a renewable and free source (for example photovoltaic solar), the system according to the invention becomes even more convenient and advantageous. 
     The figures indicated above refer to products currently normally available in the market, and more precisely considering a qualitatively “average” range of products. Therefore, it can be expected that the abovementioned products may in future be replaced by other more efficient ones, hence the total yield is bound to increase and overcome the value indicated previously. 
     Production of hydrogen through electrolysis and using an electric heat pump however allows the obtained system to maintain a strongly “ecological and environmental” value in that it preserves the zero-emission characteristic thereof 
     According to a particular aspect of the invention, the system for producing electrical and heat energy according to the invention can constitute an autonomous unit adapted for the production of emergency electrical and/or heat energy for example in case of natural disasters, earthquakes and the like. 
     A further advantage of the invention lies in the fact that the circuit for the two sources of heat and electrical energy supplied with hydrogen and the single components are partly shared and thus the resulting circuits are much simpler and require fewer components with respect to two independent source systems. 
     Particular use of a system or unit for producing combined energy supplied with hydrogen for residential buildings not served by the electrical and gas supply system is also advantageous. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further characteristics, advantages and details of the system for producing combined energy according to the invention shall be clearer from the following description with reference to some embodiments provided solely by way of example in the attached schematic drawings, wherein: 
         FIG. 1  shows a system for producing electrical and/or heat energy from hydrogen with the respective distribution and control circuits, 
         FIGS. 2 ,  3  and  4  show variant embodiments of the system for producing energy according to the invention, and 
         FIG. 5  shows a system for combined energy comprising a heat pump. 
     
    
    
     Description of the preferred embodiments 
     Unless otherwise specified, identical parts have identical reference numbers in the various figures in order to avoid repetition. 
     With reference to  FIG. 1  the system for combined heat and/or electrical energy from hydrogen is indicated in its entirety with  1  and, in the illustrated example, it is housed, as a unit, in a casing  2  indicated with dotted lines. The hydrogen inlet is indicated with A and the circuit  3  for supplying hydrogen to a catalytic burner  4  and to a fuel cell  5  comprises a shared reducer R. Electronic control modulating solenoid valves  6  and  7 , which are controlled by a special CPU  14  with programmable software, wherein said valves  6  and  7  are followed in series respectively by a fine regulation valve  8 ,  9 , for example of the mechanical type, are respectively provided for downstream of the reducer R in the two branches  3 A and  3 B respectively supplying the burner  4  and the fuel cell  5 . 
     B is used to indicate an inlet of the electrical power supply system while  10  and  11  are used to respectively indicate a battery charger and a buffer battery, while  12  is used to indicate an inverter connected to the fuel cell  5  and to the battery charger  10 . The inverter  12  converts the produced direct current into an alternating current with a voltage upon exit C of, for example, 220V and 50 Hz, as usually provided for residential buildings in Europe. 
     D and E are respectively used to indicate the inlet and outlet, for example, of a heat exchanger, not illustrated, associated to the burner  4  and connected with a heating system, not illustrated. 
     A cooling fan  13  controllable by the CPU is associated to the fuel cell  5 . The hot air  15  coming from the cooling of the fuel cell  5  is directly conveyed to the suctioning element  16  of the burner  4 . This allows recovering the heat contained in the cooling air  15  without requiring further heat exchange means or devices. This cooling air  15 , having a temperature of about 40-45° C., allows increasing the temperature on the catalyst, not illustrated, of the catalytic burner  4 , but without exceeding the limiyt thereof 
     The efficiency of the burner  4  shall be maximum for heating water in particular for the low temperature radiant heating systems, operating with water at a maximum of about 40-45° C. The burner  4  in any case is also capable of bringing the water temperature to about 60° C., the ideal temperature for producing hot domestic water. 
     In the illustrated examples, the electrical power inlet B from the power supply system is provided for supplying the auxiliary components of the system and for charging the battery  11 . The battery  11  can also be charged by the fuel cell  5  when it is operative and thus it allows an off-grid operation, i.e. independent, of the entire system  1 , thus also in case of power failure. 
     The dashed lines from the CPU  14  to the valves  6 ,  7  and to the fans  13  and  16  indicate the signals subjected to the control of the CPU, which can simply be of the on/off or modulated type, depending on the degree of optimization intended to be attained, as well known to a man skilled in the art. 
     For the sake of representation clarity, the exiting “moist” air (containing water generated by the reaction between hydrogen and oxygen) produced by the fuel cell  5  and by the catalytic burner  4  is not illustrated in the casing  2 , just like an air inlet is not illustrated. 
     Both the operation of catalytic burners and fuel cells is known from the prior art, hence a detailed description of the same shall not be provided herein. 
     Example 
     Provided hereinafter is an example for dimensioning a system for producing electrical energy and heat energy according to the invention. 
     It is intended for providing a system or unit comprising a 1 kW fuel cell  5  and a catalytic burner  4  formed by a 5 kW module of the Applicant, i.e. of the type indicated in WO2006/136316 A1. 
     Such power allows meeting basic energy needs of a small residential buidling. 
     The burner  4  for providing the indicated nominal power requires the following hydrogen flow rate: 
       5 kW/3 kWh/Nm 3 =1.67 Nm 3 /h 
     in which the nominal power is divided by the lowest calorific value of hydrogen. 
     Regarding the fuel cell  5  there is assumed an overall performance of 40% (as provided for with PEM fuel cells currently available in the market), hence hydrogen consumption shall be equivalent to: 
       (1 kW/3 kWh/Nm 3 )/0.4=0.833 Nm 3 /h 
     value provided for by the data on the plate of the fuel cells currently available in the market. 
     However, from the fuel cell  5 —during operation—there also develops heat, which can be quantified as follows: 
       (0.833 Nm 3 /h*3 kWh/Nm 3 )—1 kW=1.499 thermal kW.
 
     This heat is usually dispersed by the fan  13  arranged in proximity to the stack, in case of air cooling. 
     In order to increase the efficiency of the system according to the invention this heat, previously dispersed, and whose temperature is in the order of about 40° C., is recovered. 
     A first solution, as illustrated in  FIG. 1 , is that of conveying this hot air  15  directly onto the suction fan  16  of the burner  4 . This allows using the direct passage of the hot air coming from fuel cell  5  to the fan  16  without an intermediate heat exchange. 
     There is assumed a 75% recovery of such heat by the burner  4 . Given that the latter behaves like a normal condensation boiler, it is capable of recovering part of the latent heat of the exhaust “fumes”. Experimental tests indicated a performance equivalent to 
     The overall thermal potential of the system is thus equivalent to 
       5 kW*1.07+1.499 kW*0.75=6.474 kW. 
     The theoretical potential instead amounts to: 
       (1.67+0.833)Nm 3 /h*3 kWh/Nm 3 =7.509 kW. 
     The overall performance of the system according to the invention shall thus be: 
       (6.474 kW+1 kW)/7.509 kW*100=99.53%. 
     The integration of a fuel cell  5  to the burner  4  allowed obtaining an increase of the thermal potential of the system by about 16%, without reducing the yield of the burner  4  per se extremely high (exceeding 100% with reference to the lowest calorific power). In the fuel cell  5  instead, following heat recovery, the yield increases considerably and reaches the value of about 85%, i.e. more than twice the nominal value. 
     Without the heat recovery of the fuel cell  5  the grouping of the burner  4  and of the fuel cell  5  as indicated would have lead to the following total performance: 
       (0.4*1.07)*100=42.8%. 
     Embodiments according to  FIGS. 2 to 4 . 
     The system or unit  1 , respectively  2 , for producing combined energy from hydrogen according to the invention illustrated in  FIG. 1  can advantageously be modified for use in particular applications. 
     For example,  FIG. 2 , for a back-up function, the system according to the invention may provided—therein—for a small tank  18  for storing hydrogen to guarantee operation in any case for a preset number of hours. 
     For such purpose, the most efficient technical solution would be that of providing—in the system  1 —the tank  18  for storing hydrogen in form of metal hydrides, inserted as observable in  FIG. 2 . This solution allows having a good hydrogen reserve within a relatively small space, this type of storage however requiring heat so as to supply the hydrogen contained therein. For this purpose, according to the invention, the heat of the cooling air  15  recovered by the the fuel cell  5  is used. Such device is preferred to the burner for various reasons: the recovery heat would however be obtained in any case with the fuel cell  5  operating and, due to the cost of the hydrides, it is preferable to have a back-up only on the electrical part instead of also on the heat part, even though this argument lose its effectiveness depending on the applications provided for, i.e. considered. 
     As illustrated in  FIG. 2 , the loading of hydrogen into the hydride occurs directly on a branch  20  connected upstream of the reducer R, i.e. with a higher hydrogen pressure with respect to that present downstream of the reducer R, where such higher value can be set at about  15  bars. Hydrogen is instead released through the outlet section  21  connected to the branch  3 B for supplying the fuel cell  5 . The hydrogen release pressure shall thus be lower than the hydrogen loading pressure following the hysteresis of the metallic hydride  18 . The two lines  20  and  21  are provided with a check-valve  22  and  23  so as to obtain the correct direction of the hydrogen flows under any condition. 
     The internal storage  18  allows transferring the system  1  according to the invention from one point or station of loading hydrogen into the metallic hydride  18  and then transferring the system to a place where the electrical and/or heat energy is required, like a normal generator. In any case, the internal storage  18  of hydrogen could also serve for an emergency operation, for any reason, in case of a sudden failure of the source of hydrogen, i.e. the electrolysis device, not illustrated. 
     The further variant illustrated in  FIG. 3  refers to a direct current production, for example for supplying a system or several apparatus that can be supplied in direct current. In this variant, the inverter  12  is replaced by a DC/DC convertor  25  for setting the output voltage to the desired value, where indicated in the figure is a value of  24  Vdc on the output C. Thus, in this case there are no performance drops due to the inverter  12  of the previous variants, such inverter reducing the performance of the fuel cell, in case of increase of the electrical performance. 
     The system  1  according to the invention illustrated in the variant of  FIG. 4  provides for the use of a water-cooled fuel cell  5 . Heat recovery improvements can be obtained in this case. In this case, heat recovery is obtained by means of a heat exchanger  27 , whose primary circuit  28  is traversed by the cooling water of the fuel cell  5  and whose secondary circuit  29  transfers the thermal flow rate from the water cell to the inlet E of the burner  4 , as illustrated in  FIG. 4 . In other words the heat provided by the fuel cell  5  is used for preheating the delivery of a heating system, not illustrated. 
     Two distinct water circuits are preferably provided for a better management of the flows. Furthermore, this variant allows eliminating the risk of “contaminating” the fuel cell  5  with water coming from the heating system, which could contain various types of impurities. 
     Temperature flows can be controlled by switching the pump  30 —for circulating water in the circuit of the cooling water of the fuel cell  5 —on and off A more accurate control can be carried out by modulating the speed of the pump  30 , i.e. the flow rate thereof  FIG. 5  lastly shows a system  1  according to the invention, comprising a burner  4  and a fuel cell  5 , associated to such system  1  being a heat pump  31 , which is supplied with electrical energy provided by the fuel cell  5  and which in turn supplies thermal energy for a unit  32  which receives—likewise—thermal energy from the burner  4 . 
     Thus, this embodiment allows obtaining the functional behaviour described previously with the relative further improved performance. 
     The structural and functional description of the various systems for producing combined energy from hydrogen according to the invention, show that the same allow efficiently attaining both the main object of the present invention and the previously mentioned advantages. 
     Providing systems for producing combined energy from hydrogen jointly applying the single characteristics of the illustrated embodiments at will falls within the scope of protection of the invention. 
     The invention may be subjected—by those skilled in the art—to various modifications and variants, such as for example providing for hydrogen supply from cylinders with reducer, for example for emergency systems and units, or providing for internal hydrogen tanks of the pressurized type, proposing uses alternative to the use in residential buildings, such as for example for heating greenhouses, industrial sheds and so on and so forth, without departing from the scope of protection of the present invention, as claimed in the claims that follow.