Fuel cell system PEMFC

A fuel cell system for automobile application is shown in Figure 1.5 [41]. At the rated power, the PEMFC stack operates at 2.5 atm. and 80°C to yield an overall system efficiency of 50% (based on lower heating value of hydrogen). Compressed hydrogen and air are humidified to 90% relative humidity at the stack temperature using process water and heat from the stack coolant. A lower system pressure is at part load and is determined by the operating map of the compressor-expander module. Process water is recovered from spent air in an inertial separator just downstream of the stack in a condenser and a demister at the turbine exhaust. 

The utilization principles are shown in Figure 6, where the typical examples are enumerated. Hydrogen turbine has been studied by Japanese WE-NET project and the achieved energy efficiency was as high as about 60 %, which can be competitive with fuel cell system. One of the typical direct energy conversion systems, which have no movable parts and no noise, is fuel cell. Today topics of clean cars have been focused to the cars with PEMFC as was mentioned previously. 

For the stationary generation of heat and power the PEMFC is also in development. Fuel cell systems for combined heat and power generation mostly run on natural gas, and sometimes on biogas. Reformate is fed to the anode in these stationary systems. Only for backup power systems, which are designed for only a limited operating time, is pure hydrogen often used as fuel for the anode. 

The PEMFC is technically in quite an advanced status. Fuel cell systems for both transport as well as stationary applications exist in a wide variety and are being operated in demonstration programs under practical conditions [57]. For large-scale market introduction, cost has to be reduced significantly, and durability must be improved. Both items cannot be solved by clever engineering only -new materials are also required. 

The advantages of PEMFCs over the other fuel cell systems are as follows (Chau-rasia et al., 2003) ... 

Garch, J., Jorissen, L., PEMFC fuel cell systems, in Vielstich, W., Lamm, A.,... 

Stationary power generation on a large scale may use either low- or high-temperature fuel cell systems, and several systems rated at up to a few hundred kW have been operated (Barbir, 2003 Bischoff et ah, 2003 Veyo et ah, 2003). The systems comprise the basic units of PEMFC, MCFC or SOFC as described in Chapter 3, combined with fuel preparation and exhaust clean-... 

Fuel cells, especially PEMFCs, can be used for various applications ranging from portable power supply for use in consumer electronic devices to stationary deployment for combined heat and power generation. Another potential application is transportation, in which fuel cell systems are developed for the propulsion of cars. The performance, operating conditions, costs, and durability requirements differ depending on the application. Transportation applications demand stringent requirements on fuel cell systems. Only the durability requirement in the transportation field is not as rigorous as the stationary application, although cyclic durability is necessary. 

This article reviews fundamental knowledge and understanding of PEMFC. It is hoped that this review has provided useful information for PEMFC researchers and others who are interested in fuel cell systems. It is possible that power generation via fuel cells will become as common as that at present via heat engine that could provide substantial economic and environmental benefits. 

DMFCs have potential near-term applications mainly in the portable power source market, as they are smaller, lighter, simpler, and cleaner than conventional batteries. Liquid methanol is consumed directly in a DMFC, which implies a higher energy density of the fuel cell system. But the power densities achievable with state-of-the-art DMFCs are still very small in comparison to hydrogen-fuelled PEMFCs. One of the major problems lies in the use of liquid methanol solution on the anode of the DMFC, which, on the one hand, keeps the ionomeric membrane water saturated (and thus no humidification is needed) but, on the other hand, does not keep fuel (methanol or any other organic fuel, e.g., formic acid, ethanol) and water from permeating to the cathode side, since the basic PFSA membranes are permeable to both methanol and water. - The fuel and water crossover from anode to cathode hampers the performance of the air cathode. 

High temperature polymer electrolyte membrane fuel cells (HT-PEMFC) operate in a temperature range of 160 to 180 °C. For the HT-PEMFC the hydraulic system of a house is at any time a heat sink. HT-PEMFC based fuel cells can be used in hydraulic systems of new and existing buildings. Furthermore, the HT-PEMFC requires less effort to cleanup the synthesis gas of the fuel processor. But the HT-PEMFC is only demonstrated in few applications so far and the development status is not so advanced as for the LT PEMFC. 

James, B.D., Moton, B.D., Colella, W.G. Mass Production Cost Estimation of Direct H2PEM Fuel Cell Systems for Transportation Applications 2013 Update, http //energy.gov/sites/prod/ files/2014/ll/fl9/fcto sa 2013 pemfc transpoitation cost analysis.pdf, last viewed Jan... 

A PEMFC uses a solid membrane that conducts protons as the electrolyte. Since it can start at ambient temperatures instantly, it is ideal for backup, portable, and motive power applications. The most important technologies concern the stack (like the heart of a human being) and the system controls (like the brain of a human being). The key components in a stack include the catalyst, PEM, GDM, plates, and gasket, while the controls include the operation algorithm, software, and electronic circuits. A fuel cell also needs various auxiliary components such as fans, blowers, compressors, pumps, heat exchangers, humidifiers, converters, valves, sensors, and batteries to work. A fuel cell system involves multidisciplinary skills and knowledge, and therefore it requires a team effort to develop. 

Balancing water is the most difficult task for a PEMFC due to the high water production rate and the various water movement possibilities. Although a previous estimate is very helpful in determining the values of certain key parameters, such as the reactant humidification temperature, the stack inlet and outlet temperatures, the coolant flow rate, and the reactant stoichiometric ratio (mainly air), automatic adjustment by the fuel cell system itself is important in achieving the optimal operation conditions, especially if the fuel cell is in the load-following mode. 

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