Domain of the invention

The invention relates generally to a method to produce electrical power to be used by local systems such as charging points operators or other consumers of the equivalent power levels. It also relates to an autonomous electrical power production system implementing said method.

The state of the art

A fuel cell system can refer to a configuration of one or more fuel cells configured to produce electrical power. The individual fuel cells, such as solid oxide fuel cells, can be arranged to form fuel cell stacks. A fuel cell stack can refer to a plurality of individual fuel cells which are electrically connected in series. The number of individual fuel cells which make up a given fuel cell system can depend on the amount of electrical power which the given fuel cell system is intended to generate. Alternatively, a fuel cell system may include any other configuration of individual fuel cells, as disclosed in EP2258017B1.

Current-voltage characteristics of the fuel cells depend on for example reactant compositions, mass flow, temperature and pressure. Electrochemical reactions in the fuel cell react quickly to fluctuations in the fuel cell load. However, the response capacity of reactants input system is typically much slower, meaning response times of seconds or even minutes. When trying to obtain more efficiency out of fuel cells than the prevailing input of reactants allows, is caused a weakening of fuel cell voltages, and even an irreversible deterioration of fuel cells is possible. In addition, load changes cause rapid temperature changes in the fuel cell, which especially in high temperature fuel cells cause harmful thermomechanical stress, resulting in significant reduction of performance and lifetime of fuel cells. Thus, fuel cell systems must be designed so that the load of each fuel cell is kept as constant as possible and a possible change in the load is tried to be carried out as controllable as possible, as disclosed in EP 2377226B1.

Fuel cell systems typically work on gaseous fuel sources such as hydrogen, ammonia, natural gas or biogas. These fuel sources require compression of the gases for storage or a complex piping infrastructure for the delivery of the gas. with additional risk of leakage and greenhouse effect. Other systems using liquid fuel sources are highly dangerous to humans such as methanol that can cause blindness ingesting as little as 10ml. The problem to solve is to maintain the high temperature fuel cell, such as a Solid Oxide Fuel Cell (SOFC) in temperature whatever the climatic situation and power output.

Summary of the invention

According to the invention, a method is proposed to produce electrical power in an autonomous stationary situation using a chemical fuel obtained from organic source, including steps for: reforming the chemical fuel to produce syngas, injecting said syngas into a high temperature fuel cell to produce electric power, said fuel cell comprising a plurality of stacks, processing said electric power to generate a nominal electric power adapted to the required voltage and current for the consumer, storing in a storage unit a part of electric power not used by the consumer characterized in that it further includes a step for managing the stacks so that some of said stacks are switched off in function of the level of required output while other are maintained as operative and/or used to heat said switched-off stacks.

The fuel cell stack managing step can advantageously comprise: a step for processing data on the instantaneous power demands, a step for determining a number of FC stacks matching the power demands, a step for switching off unused FC stacks, a step for maintain said switched off FC stacks at a predetermined temperature.

The step for maintaining the switched-off FC stacks at a predetermined temperature can be achieved by transferring heat generated by active FC stacks.

The step for maintaining the switched-off FC stacks at a predetermined temperature can be achieved by generating heat from electric energy derived from the active FC stacks.

The method according to the invention can further include a step for controlling the power output of one or more FC stacks from the plurality of FC stacks, as a function of the instantaneous required electric energy, and a step for processing data to anticipate power demands based on recorded or external data. The chemical fuel can comprise ethanol.

According to another aspect of the invention, there is proposed a system to produce electrical power in an autonomous stationary situation using a chemical fuel obtained from organic source, including: means for storing a chemical fuel means for reforming the chemical fuel to produce syngas, means for providing syngas to a plurality of FC stacks within a high temperature fuel cell to produce electric power, means for recycling syngas in excess to heat (or re-insert syngas in) said reforming means, means for processing said electric power to generate a nominal electric power adapted to required voltage and current for a consumer, means for storing a part of electric power which is not used by the consumer characterized in that it further includes means for managing the FC stacks, said managing means comprising (i) means for switching off some of said stacks in function of the level of required output and (ii) means for adjusting active stacks output power so as to be operational and/or used to heat said switched-off stacks.

The fuel cell stack managing means can include processing means programed for: processing data on the instantaneous power demands, determining a number of FC stacks matching the power demands, controlling said switching-off means and said stack power-adjusting means.

The fuel cell can comprise SOFC fuel cells and a pre-reformer to convert the chemical fuel into syngas.

The system according can further comprise communication means to centralize operating data needed to maintain the fuel cell generator system operational.

The claimed solution lies in a variation or the SOFC power combined with the use of a SOFC for maintaining the other SOFC in thermal condition. The power is produced by a fuel cell system. The power is delivered as direct current or alternate current. The fuel consumed by the fuel cell system is Ethanol.

The invention provides sufficient energy storage allowing for a standalone operation without the need to be connected to an energy infrastructure or pipeline. The storage of that fuel is done in a safe manner using a nontoxic organic fuel source that is liquid at ambient storage conditions.

The fuel efficiency is achieved by a fuel cell device for producing electrical power. The fuel cell is based on a SOFC technology that operates at elevated temperature. By adapting the fuel flow in real time and controlling the temperature of the fuel cell system, electrical power is varied based on the demand.

A battery set constitutes temporary energy storage that can deliver instantaneously the power during the transitional phases of the fuel cell system, this to ensure even faster response time of the fuel cell generator system. The energy is stored in the form of a liquid nontoxic fuel source that delivers the electrical power through an electrochemical reaction. Ethanol is preferably used as the liquid fuel source. Ethanol is abundantly available and is an organic molecule.

Description of the drawings

FIG. l illustrates the architecture of an embodiment of an electrical energy production system according to the invention,

FIG. 2 features an embodiment of a FC stacks management unit implemented in a system according to the invention,

FIG.3 features main steps of an electrical energy production method according to the invention,

FIG.4 features an example of heat transfer from a small FC stack to two switched-off FC stacks within an energy-production system according to the invention,

FIG.5 is a flowchart of an embodiment of the electrical energy production method according to the invention.

Detailed description

Referring to Figure 1, an autonomous system for producing electrical energy according to the invention 1 comprises a tank 3 for storing a chemical fuel obtained from an organic source such as ethanol, a unit of pre-reforming 4 provided to receive (9) fuel from tank 3 and transform this fuel into syngas which is then delivered (10) to a group 2 of SOFC fuel cells 21,22,23 provided to deliver an output voltage 12 applied ( 12) at the input of a voltage conversion unit 5 designed to deliver a suitable output voltage (13) to a load 8 such as a set of charging stations for electric vehicles. A gas recycling loop 11 is provided between the fuel cell group 2 and the pre-reforming unit 4.

The autonomous electric energy production system 1 further comprises an electric storage unit 6 such as a set of batteries connected (16) to the voltage conversion unit 5, and a fuel cell management unit 7 provided to communicate (15) with a remote data center 14 and with the fuel storage tank 3, the pre-reforming unit 4, the fuel cell group 2 and the voltage conversion unit 5, respectively via 110,120,130,140 link bus.

The fuel cell management unit 7 comprises, with reference to FIG. 2, a data processing unit 70 and a real-time optimization unit 75 provided to communicate with a fuel input control unit 71, a unit 72 for controlling the pre-reformer, and a unit 73 for controlling the fuel cells via link buses 102,103,104 respectively, as well as with the data processing unit 70 via a link bus 101. The respective fuel inlet control units 71,72,73, control of the pre-reformer and control of the fuel cells are connected via the respective buses 110, 120, 130 for connection to the fuel storage tank 3, to the pre-reforming unit 4 and to the group of fuel cells 2, while the data processing unit 70 is connected via the link bus 140 to the voltage conversion unit 5.

With reference to FIG.3 and 4, a method to produce electrical power in an autonomous stationary situation using a chemical fuel obtained from organic source, includes a step 30 for pre-reforming the chemical fuel provided from a fuel tank 3 to produce syngas, a step 31 for injecting said syngas into a high temperature SOFC fuel cell to produce electric power, said fuel cell comprising a plurality of stacks, a step 41 for recycling syngas in excess from fuel cell into the pre-reformer, a step 32 for processing said electric power to generate a nominal electric power adapted to he required voltage and current for the consumer, a step 33 for storing in a storage unit apart of electric power not used by the consumer, and s step 34 for managing the stacks so that some of said stacks are switched off in function of the level of required output while other are maintained as operative and/or used to heat said switched-off stacks.

The fuel cell stack managing step 34 comprises a step 35 for processing data on the instantaneous power demands, a step 36 for determining a number of FC stacks matching (for adjusting, see claim 9) the power demands, a step 37 for switching off unused FC stacks, and a step 38 for maintaining said switched off FC stacks at a predetermined temperature.

The step 38 for maintaining the switched-off FC stacks at a predetermined temperature is achieved by transferring heat generated by active FC stacks, and/or by generating heat from electric energy derived from the active FC stacks.

The method according to the invention can further include a step 39 for controlling the power output of one or more FC stacks from the plurality of FC stacks, as a function of the instantaneous required electric energy or customer demand 40, and a step 42 for processing data to anticipate power demands based on recorded or external data.

With reference to FIG.4, assuming that the FC stacks management unit 7 has determined that the absence of customer demand should require to switch-off FC stacks 23,24, FC stack 25 is maintained switched-on to produce heat and to transfer said heat to the FC stack 23,24 so as to maintain said switched-off FC stacks to a predetermined temperature. As soon as a customer demand is detected and processed by the FC stacks management unit 7, FC stacks 23,24 are switched on again to provide electric power to the customer load 8.

By way of non-limiting example, FC stack 25 can be designed as a small-power FC compared to the nominal power of FC stacks 23,24. In an exemplary embodiment of the method for producing electrical energy according to the invention, illustrated by FIG. 5, this method comprises a step I of the initial start-up procedure followed by a step II in which a main fuel cell operates at a level depending on the demand for the use of electrical energy.

A step VIII is performed in the background within the data processing unit 70 to determine whether at least one of the conditions for stopping the main fuel cell or all of the fuel cells is met. These conditions are: an electrical consumption demand is less than a predetermined percentage x% compared to a nominal consumption value, the voltage level of the batteries 6 is less than a predetermined percentage y% with respect to a nominal value of the battery voltage, a major failure of the main fuel cell has been detected.

If at least one of these conditions is met, this has the effect of controlling a step IV for stopping the main fuel cell or a step V for stopping the entire group of fuel cells which leads to a step Power generation system shutdown procedure VI 1.

In the configuration where only the main fuel cell has to be stopped, a step VII is provided to drive a secondary fuel cell to a level depending on the internal heat demand required to maintain the fuel cell at a predetermined temperature.

A step IX is implemented within the data processing unit 70 to determine whether the main fuel cell should be restarted according to the consumption demand. In the event of a start-up decision, a stage III is provided to restore the operation and control of the main fuel cell.

As a way of non-limitative example, an electric energy production system according to the invention can handle nominal electric power in the range [10; 1000] kW. A small-size SOFC stack can be for example designed to heat a large-size SOFC stack with a nominal power ratio comprised in the range [1%; 25%]. For example, the fuel consumption of an energy production system according to the invention can be comprised in the range [0.1; 10] liters/minute. The tank of ethanol can be for example comprised in the range [1’000; 50’000] liters.

Of course, this invention is not limited to the above-described embodiments and many other embodiments can be designed without departing from the scope of the invention.