WO2015169979A1

WO2015169979A1 - System for generating electric power

Info

Publication number: WO2015169979A1
Application number: PCT/ES2015/000061
Authority: WO
Inventors: José Manuel ANDUJAR MARQUEZ; Francisca SEGURA MANZANO
Original assignee: Universidad De Huelva
Priority date: 2014-05-06
Filing date: 2015-05-05
Publication date: 2015-11-12
Also published as: ES2553303A1; ES2553303B1

Abstract

The invention relates to a system for generating electric power, which has a series of PEM cell stack modules (1), supplied by a source of hydrogen (8), the pressure of which must be adjusted preferably to almost atmospheric pressure. The system also includes a subsystem for controlling and monitoring each stack, which can activate and deactivate same individually. The control and monitoring subsystem can monitor the modules by receiving, from each module, the signal from an ammeter and a voltmeter of the stack, as well as from a subsystem for detecting cell voltage for each cell of the module stack. Said reception can take place in a first level of the control and monitoring subsystem, via local controllers for each module, which are coordinated at a higher level by a single higher control unit. A cell management subsystem uses said signals to verify that the cell is not exposed to corrosion currents.

Description

ELECTRICAL POWER GENERATION SYSTEM

TECHNICAL SECTOR The present invention relates to a regulated, modular and non-polluting regulated power generation system, based on the modular implementation of stacks of PEM-type fuel cells powered by hydrogen, together with instrumentation, control and monitoring systems included It is applicable in the electricity generation sector.

STATE OF THE TECHNIQUE

The operation of the proton exchange membrane (PEM) cells stacked to generate electrical energy from hydrogen suffers from problems that deteriorate them, which causes their lifetime to be relatively short (on average between 4,000 and 5,000 hours) .

The known PEM cells are cooled by water and require a very high pressure hydrogen supply (5-10 bar), which only in some designs is able to be reduced to 2 bars. Water cooling requires a complex, bulky, heavy and expensive thermal management mechanism. Water is not only the product of the electrochemical reaction of the stack, but it is also critical to ensure efficient and stable operation. Therefore, by simplifying the thermal management system, costs and complexity would be reduced.

As for the feeding of hydrogen at high pressures, it implies a higher design cost as well as a greater risk of leakage and explosion.

Similarly, electric power generation systems by stacking known fuel cells are rigid management elements, as they do not allow to vary their capacity quickly, sometimes causing overloads that damage the cells.

There is also no known system that allows managing the operating hours of the different stacks, distributing the generation of electricity to reduce the chances of deterioration or depletion of the operating life time. l BRIEF EXPLANATION OF THE INVENTION

The invention consists of an electric power generation system, which produces electric power regulated directly from hydrogen by means of an electrochemical reaction, which is intrinsically more efficient than combustion and minimizes the adverse effects associated with the combustion process (among others , excessive noise, polluting emissions and maintenance). The system can operate continuously (24h / day for 365 days a year), that is, for as long as hydrogen is supplied, so unlike other sources of renewable energy, the production of electrical energy from the System object of the invention is independent of the weather conditions.

The system comprises a series of modules, so that it can work with the number of them required at any time, which allows it to generate a regulated power in its range from 0 to "n * p", being "n "the number of modules and" p "the power of each of them assumptions all the same. If this were not the case, it could be from 0 to (p1 + p2 + ... + pn).

In order to increase its lifetime, the system object of the invention monitors each of its cells (voltage and current measurements) to, by means of the control system incorporated, manage and mitigate its aging.

The developed system also has two additional features that make it especially simple: it is air-cooled and does not require high hydrogen supply pressure, since it can actually operate at ambient pressure (similar to 1 bar). For this, the bipolar plates that delimit each cell of the stack will be carried out properly, with mechanized channels whose geometric configuration and diameter will allow this low pressure. The first of the features allows that there are no moving or liquid parts in the cooling system, facilitating and simplifying their integration. The second provides security to the system as it is not necessary to work with high hydrogen pressures. Both features provide reduced volumes, weights and costs and simplify the design.

The invention is, therefore, an electrical power generation system with a series of modules, at least two, but preferably more, each with a stack of Proton exchange membrane (PEM) cells and other necessary subsystems, individual or shared by several stacks. The set of modules is fed by a hydrogen source or several, which are part of a hydrogen subsystem (preferably at near ambient pressure (close to 1 bar) and with a purge line).

The system of the invention comprises a control and monitoring subsystem of each module, which controls them, being able to activate and deactivate them individually.

As described, each module can have the same power, which facilitates the management, or different powers, which provides flexibility to activate the modules at their nominal power when the electric charge requires power levels below the maximum.

The control and monitoring subsystem can monitor each stacking of each module by receiving, for each stacking, the signal of an ammeter and a voltmeter, as well as a cell voltage detection system for each stacking cell. This reception can be done at a first level of the control and monitoring subsystem, by means of local controllers for each module, which are coordinated at a higher level by a single higher control unit.

The cell voltage detection system will communicate, through the control and monitoring subsystem, with a cell management system, capable of detecting its anomalous operation to act accordingly, for example by communicating it to the upper control unit. Preferably, the control and monitoring subsystem is accessible online, either by a local network or by internet.

More preferably, when the power requirement is lower than the maximum, the upper control unit will homogeneously distribute the operating hours among all the modules so that the aging of their stacks is similar.

It is preferred that the modules have their respective oxygenation / cooling subsystems that provide air to the cells, with the dual function of refrigerant and oxygen supply to the cathode. The system is complemented by a simulator of the operation (non-linear) of the system. Preferably it will be able to simulate faults and breakdowns.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, the following figures are included.

Figure 1: represents a schematic of a module, which comprises the stacking of cells and the oxygenation / cooling, hydrogen and electrical subsystems.

Figure 2: represents the general scheme of the control and monitoring subsystem for each module and the complete system.

Figure 3: represents a connection scheme for the case where a conditioning subsystem with multiple inputs is used.

EMBODIMENTS OF THE INVENTION Next, an embodiment of the invention will be described briefly as an illustrative and non-limiting example thereof.

The system of the invention is based on a series of modules (1) consisting of stacks of proton exchange membrane cells (2), preferably air-cooled to avoid the need for external humidification, in addition to the corresponding sub-systems of oxygenation / cooling, hydrogen and electric. In essence, each module (1) is made up of a scheme similar to that of Figure 1, although they can share elements, for example, the source of hydrogen (8) can be shared by all or part of the modules (1).

Air cooling is carried out by means of an oxygenation / cooling subsystem, which on the one hand provides oxygen from the air to the cathode, and on the other hand is responsible for cooling the cell stack. The amount of air injected into the cell stack must be such that it guarantees that it works at its optimum operating temperature. This requires a temperature sensor of operation (3) of each cell stack (2), an incoming air temperature sensor (4), and a ventilation (5) or air extraction system with the ability to adjust the flow of injected or extracted air from each stacking of cells, and modifying the relationship between the volume of air aspirated and the volume theoretically necessary for a correct reaction (lambda parameter λ).

Preferably it will incorporate an oxygen sensor (6), which will send information to the control system described below to avoid situations of low oxygen concentration in the surrounding atmosphere, and therefore insufficient oxidant in the cathode of each stacking cell, and a relative humidity sensor (7) to avoid extreme environmental conditions.

Hydrogen is fed to the anode of each cell (2) in the stack by the hydrogen subsystem. This comprises a source of hydrogen (8), and a conduction line to each cell stack (2), with its supply valves (9), pressure gauges (10) and pressure regulators (11) for control. The hydrogen source (8) can be individual or shared by all or part of the modules (1). The pressure regulator (11) will be necessary when the high pressure of the hydrogen stored in the bottle must be regulated at the low supply pressure, but it is not necessary if the hydrogen source (8) already supplies the hydrogen at the required pressure.

Hydrogen must be supplied to the anode of each cell stacking module at the corresponding pressure and flow. In practice, not all of the hydrogen that enters each anode is consumed. In the anodes water vapor, nitrogen and other inert gases accumulate, so it is advisable to purge them periodically.

Therefore, two hydrogen lines will normally be installed: one for the entry of the latter in each stack and another for the purge of the same. A purge valve (12) is required in the outlet or purge line of each cell stack to expel unused hydrogen along with the inert gases into the surrounding environment. In addition, it is desirable to add a hydrogen sensor (13) to avoid concentrations in the surrounding air that pose a risk of being within the limits considered in an explosive atmosphere (less than a quarter of the lower flammability limit).

The use of the electrical power generated by each stack (2) is carried out by means of the electrical subsystem. This subsystem connects the stacking of cells to an electric load (14), providing a contactor (15) by stacking to isolate it from the electric load (14) and a blocking diode (16) to avoid reverse currents that can damage the stacking. As protection measures for cell stacking (2), it can also have a stacking ammeter (17) and a stacking voltmeter (18), which is connected to the electrical terminals of each cell stacking (2), as well as a voltage monitoring subsystem of each cell individually (not shown) connected to all stacking cells.

The cell monitoring system monitors that no cell goes into reverse operation, which would significantly damage it. On the other hand, the ammeter and the voltmeter of the cell stack (17,18) allow the control and monitoring subsystem to have information and act so that each stack, designed to operate within a range of current and voltage values, is not degrade if these ranges are exceeded.

In addition, the combination of the cell stacking voltmeter (18) and the cell voltage detection subsystem ensure that none of the cells that make up each stacking operate in reverse, with a voltage equal to or less than zero volts.

Each module (1) will have a battery (not shown) to power the different elements of it at the start of the module. This battery can be recharged with part of the power generated by the module itself. The invention can also comprise a control and monitoring subsystem, which guarantees the optimal operation of the system. For this, it will control the modules (1) of which the system is composed, so that they are active depending on the demand requested by the load and its state of use. This will bring the following benefits: · Each module will only be active when the load demands it, which will result in a smaller number of hours of operation and, therefore, in a longer overall duration of the system, prolonging its life time, fundamentally of Your cell stacking.

• Each module will operate at nominal power, which will mean better performance and use of each operating time. • The modules can operate a similar number of hours, with which the natural wear of the system, mainly from the stacking of cells of each module, will be balanced. · The modules can be not only launched on demand, but also interconnected according to requirements.

• In the event that any module deteriorates, with more probability its stacking of cells, the system may operate with the rest, provided that the maximum power required does not exceed that available.

With this control and monitoring subsystem, the system object of the invention provides a regulated power in the range from 0 to "n * p", "n" being the number of modules and "p" the power of each , assumptions all the same. If this were not the case, it could be from 0 to (p1 + p2 + ... + pn).

The control element is configured in two levels: a first level consisting of the local controllers (20) of each module (1), which control the oxygenation / cooling, hydrogen and electrical subsystems and their power conditioner, and a unit of superior control (21) that supervises and governs each local controller (20) according to the general requirements of the system.

The upper control unit (21), depending on the requirements requested to the system, will connect or disconnect each module (1) of the hydrogen supply line and the electrical connection line to the load.

With regard to monitoring, this control and monitoring subsystem measures all the variables of interest, stores them for consultation by the user and supplies them to the control. On the other hand, it allows online access (referring to real-time access through the Internet-network (23) and / or local network-through a computer application as a virtual instrument) to the system. In addition, the monitoring of the system is completed with the visualization of alarms through the computer application (22), which will notify the user of anomalous situations (excess or defect of pressure or temperature, excessive demand for current, reduced operating voltage, etc.). The electrical power generated in each module (1) may not have the necessary quality to feed the electric load (14), so it can be inserted in parallel, between the stacking of cells (2) and the load (14 ), an electrical power conditioning subsystem (24) that ensures that the electrical output of each module (or the complete system of Figure 2, according to the possible connections for the modules described below) is a regulated electrical power suitable for Power any electric charge. This regulation may be DC / DC or include a DC / AC investment.

This subsystem is of specific design for the system object of the invention, since it has to govern the electrical output of each module to be able to supply at all times the changing requirements of regulated electrical power demanded by the load.

For the electric power conditioning subsystem (24) different basic configurations of connection of batteries or modules can be applied: in series, in parallel, in series / in parallel and connected to a conditioning subsystem with multiple inputs. Each with the advantages known to a person skilled in the art. For the series system, higher output voltage and the same current are obtained in all cells. The parallel system allows only one module to work. The series / parallel system allows different voltage and output current configurations, while a subsystem with different inputs (Figure 3) allows one or more modules to work, each at a different operating point. Only two stacks have been represented in this figure, but can be applied to any other number.

To control the effects of deterioration of the modules (mainly their cell stacks), it will be complemented with a cell management subsystem for monitoring and control of the different effects that contribute to the deterioration of the stacks and, therefore, of the modules that contain them. This subsystem works from the data supplied by the control and monitoring subsystem. As an example of the interest of this subsystem, it can be mentioned that the corrosion current in the cells that form each stack can cause a reduction in the cell voltage, even reaching 0 V. This is a serious problem for the affected cell which can lead to irreversible deterioration. However, the reduction of the cell voltage may be caused by a non-harmful effect, such as the high demand for load current. This has to be able to detect the cell management subsystem. This specific design subsystem is able to detect if the reduction in cell voltage is caused by a harmful effect that must be avoided or by another that disappears over time without causing damage. If the design and control of the different subsystems that complement the stacking of cells of each module is not done correctly, or the possible adverse effects are not known in detail, the cell voltage can decrease up to 0.8 V. Knowing that the maximum voltage of a cell (open circuit voltage) is 1 V and the minimum (full load voltage = maximum power) of 0.5 V; The deterioration of several cells in the same stack has significant negative effects on their electrical behavior. The two main causes of deterioration that contribute to the loss of 0.8 V / cell are the corrosion of the carbon used to deposit the catalyst and the starvation of fuel.

The first is due to the fact that in a PEM type fuel cell, in the Electrolyte-Membrane-Electrolyte structure, the catalyst that favors the dissociation of hydrogen is suspended in a thin layer of carbon that covers the membrane on both sides. When this carbon layer disappears (as a result of its reaction with water to form C02, H + ions and electrons), the hydrogen-oxygen interface (hereinafter hydrogen-air since the oxygen with which the fuel cell reacts it comes directly from the surrounding air) that exists in the membrane, becomes oxygen-oxygen (hereinafter air-air). In this case two zones of different voltage and therefore a current called corrosion current are generated. This corrosion current appears during the starting of the battery (degradation by start / stop), and also appears if there are fuel leaks, or if the supply valve or the purge valve are leaking.

The corrosion current also has the effect of consuming the carbon from the catalyst layer.

The cell management subsystem must detect that air-to-air regions have been produced to allow corrective action. For this, it detects that the voltage produced by the cell is lower than the theoretical one, due to the presence of the two air-air and hydrogen-air regions. Thus, in the case of corrosion currents, the cell voltage will be 0.2V or similar instead of approximately 1V. On the other hand, if there are fuel leaks in the valve, the cell will produce tension with the hydrogen valve closed, even after completely consuming the remaining hydrogen that may remain in the circuit (approximately 30 minutes). In the case of starting the cell after being stopped for a while, until the remaining hydrogen has been consumed, the start / stop corrosion currents will be unavoidable, so the system must recognize that this is the case.

Starvation or lack of fuel causes an effect similar to corrosion currents on a fuel cell. When there is not enough hydrogen to react with, it is replaced by the carbon in the catalyst layer, so that the carbon reacts with the water to generate protons and electrons, in order to supply the demand of the charge. In this situation, the cell voltage can drop below 0 V, reaching an irreversible inverse situation that will result in the definitive disabling of it.

For the implementation of the cell management subsystem, a measuring device formed by the cell voltage detection system has been developed, which is not the subject of the invention. The connection with each module together with the development of the virtual instrument for monitoring are not part of the invention.

It is especially interesting to complement the invention with a simulation device implemented by means of hardware and / or software, which can work at both the module (1) and the complete system level (corresponding to Figure 2), and which allows the operation to be replicated. real (nonlinear) of the system object of the invention, and which also allows to simulate failures and breakdowns. This provides the simulator with great value possibilities: training, security, cost savings, etc .; also providing the system object of the invention with a great added value.

The operation procedure begins with the start of the power supply: switching on and adjusting the battery, then adjusting hydrogen, opening the supply valve (9) and its flow. Finally the adjustment of the oxygenation / cooling subsystem, setting the lambda parameter, λ.

During the operation and generation of electrical power, the sensors carry out continuous checks, the result of which may lead to the control and monitoring subsystem to the activation of alarms and even to shutdown due to failure, which would activate an inactive module (1), if any, to supply the missing power. The shutdown of the modules (1) is carried out with the closing of the corresponding valves and actuators, so that the detection of an abnormal condition would also lead to the activation of alarms.

Claims

1- Electric power generation system characterized in that it comprises at least two modules (1) of stacks of proton exchange membrane cells (2), fed by at least one source of hydrogen (8), from a subsystem hydrogen, and because it has a control and monitoring subsystem of each module (1) and each stack, which controls the modules (1) and with the ability to activate and deactivate the modules (1) individually. 2- Electric power generation system according to claim 1, characterized in that each module (1) has a different power.

3- Electric power generation system, according to any of the preceding claims, characterized in that the control and monitoring subsystem receives from each module (1) the signal of a stacking ammeter (17) and a stacking voltmeter (18 ) as well as a cell voltage detection subsystem in each of the cells (2) of the stack.

4- Electric power generation system according to claim 3, characterized in that the cell voltage detection system is communicated with a cell management system, capable of detecting the abnormal operation of the cell and alerting the control subsystem and monitoring.

5- Electric power generation system, according to any of the preceding claims, characterized in that the control and monitoring subsystem has a first level formed by a local controller (20) for each module and a higher level formed by a control unit superior (21) that coordinates the local controllers (20).

6- Electric power generation system, any of the preceding claims, characterized in that the control and monitoring subsystem is accessible online.

7- Electric power generation system, any of the preceding claims, characterized in that the control and monitoring subsystem homogeneously distributes the operating hours among all modules (1) when the requested power is less than the maximum. 8- Electric power generation system, any of the preceding claims, characterized in that the modules (1) comprise an oxygenation / cooling subsystem that provides air to the cells (2) as refrigerant and as oxygen supply to the cathode.

9- Electric power generation system, any of the preceding claims, characterized in that the hydrogen subsystem provides hydrogen at ambient pressure to the cells (2).

10- Electric power generation system, any of the preceding claims, characterized in that the hydrogen subsystem comprises a purge line of the module (1). 11- Electric power generation system, any of the preceding claims, characterized in that it comprises simulation equipment to replicate the operation of said system.