Tuesday, April 1, 2008 - 6:30 PM

Conditioning Gases System and Cooling System for a 8 kW PEM Fuel Cell

Veronica Mesa, Belén Sarmiento, Inmaculada Gonzalez, and Covadonga García. Hynergreen Technologies, S.A.

Fuel cells are electrochemical devices able to produce electrical energy from a fuel, mainly hydrogen, and an oxidant, oxygen, usually coming from air.   The proper operation of a fuel cell, as a device that can deliver electricity with almost only water as by-product (if the hydrogen used is pure), involves the development of different auxiliaries.   Thus, for the right operation of these devices, it is necessary that the feeding gases have an appropriate temperature and humidity characteristics and it is also necessary to adequate the temperature of the system: to heat the stack during the start-up and to cool it down during its operation, due the temperature increase occurred because of the exothermic reaction that take place.   Most typical auxiliaries are the humidification system for reactants, the cooling system for the stack, the control system that coordinate the operation of the whole subsystems, etc. with all their components (valves, pumps, compressors, sensors, controllers, etc.).   The development of these auxiliaries or BoP has to take into account not only operation conditions of the fuel cell but also other complementary requirements due to the final application (size, power consumption, weight, etc.).   An optimum and well designed system or BoP with these auxiliaries will allow extending the lifetime of the stack reducing the cost of its maintenance.   The main objectives of the project are the development of both cooling and humidification systems for adapting not only the temperature and humidity of the reactant gases for feeding a fuel cell, but also the temperature of the own stack.   The system developed in Hynergreen keeps a constant temperature of 60 ºC in the fuel cell and a 100 % humidity for the fuel and has a cooling power up to 10,000 W.   For running the fuel cell, the temperature of the fed gas has to be in the range of the temperature of the fuel cell and thus it has to be preheated. A prerequisite to initiate the process is to heat up the whole unit to 60 ºC using heating devices that are able to do it within 15 minutes. When the temperature is reached, this heating system is switched off.   An approach to humidify and preheat the hydrogen gas is to flow the gas into hot water and then supply this gas to the fuel cell. This treatment can be done in several stages if necessary, and the temperature and humidity can be measured.  

The cooling system is formed of two loops. In the primary one, where the fuel cell is, the heat exchanger is connected with a pump and a tank. The secondary loop consists of a cooler with fans, a pump and an expansion tank.With this system it is possible to condition the gases at the inlet of the fuel cell in terms of temperature and humidity and to heat/cool the system to feed a 8 kWe fuel cell with a steady consumption lower than 500 W.


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