Analysis of the Energy Efficiency of Fuel Processor - PEM Fuel Cell Systems (original) (raw)

As the world moved into the 21 st century, a rapid development in industrial and transportation sectors and improvements in living standards have been observed, leading to a strong growth in the energy demand and in global emissions (Song, 2002). In this context, fuel cell technology has been receiving an increasing attention, thanks to its lower emissions and potentially higher energy efficiency if compared with internal combustion engines. A fuel cell is defined as an electrochemical device in which the chemical energy stored in a fuel is converted directly into electricity. Among all fuel cells, low temperature Proton Exchange Membrane Fuel Cells (PEMFC) are promising devices for decentralized energy production, both in stationary and automotive field, thanks to high compactness, low weight (high power-to-weight ratio), high modularity and efficiency, fast start-up and response to load changes. The ideal fuel for PEMFC is hydrogen with low carbon monoxide content to avoid poisoning of the fuel cell; in this way, PEMFC can achieve efficiency up to 60%, far higher if compared to 20-35% efficiency of an internal combustion engine. Hydrogen, though, is not a primary source. It is substantially an energy carrier, that can be stored, transported and used as gaseous fuel, but, it needs to be produced from other fuels. Today most of the hydrogen produced is obtained by hydrocarbons in large industrial plants through the well-known Steam Reforming and Autothermal Reforming processes. However, hydrogen distribution from industrial production plants to small-scale users meets some limitations related to difficulties in hydrogen storage and transport. For its chemical and physical properties, indeed, the development of an hydrogen infrastructure seems to be not feasible in short term, while more reasonable seems to be the concept of decentralized hydrogen production; in this way, an hydrogen source, such as methane, is distributed through pipelines to the small-scale plant, placed nearby users, and the in situ produced hydrogen is fed directly to the energy production system, avoiding hydrogen storage and transportation. In this sense, a compact fuel processor, capable of generating a hydrogen rich stream from an easily transportable fuel, is a potential root to accelerate PEMFC deployment in the near future. A typical fuel processor is constituted by a reforming unit coupled with a CO clean-up section, introduced to guarantee hydrogen production with a CO content compatible with