Alternatives for Micropower Generation Processes

Abstract

Currently, the predominant technologies for autonomous portable power supply are batteries. Alternatives in the range 0.1-10 W are explored in this work, focusing on the combination of fuel processing with fuel cells. A methodology for the comparison of different alternatives for micropower generation processes based on a process superstructure, including hundreds of different designs, is formulated, and the first implementations of system simulation are presented. A comparison between a variety of processes under different constraints is presented, and the influence of heat losses, scale, fuel cell efficiency, and conversion as well as recycling on the performance of the processes is discussed. Conditions under which the technologies considered are a promising alternative to batteries are identified. IntroductionThe widespread use of portable electric and electronic devices increases the need for efficient autonomous man-portable power supplies. 1,2 Portability limits the mass of the power generation system to a few kilograms and the volume to a few liters at most and consequently to power supplies of up to 50 W. Currently, batteries are the predominant technology in most applications. However, batteries have a large environmental impact, high cost, and relatively low gravimetric (Wh/kg) and volumetric (Wh/L) energy density. State-of-the-art primary batteries reach up to 1300 Wh/L and 700 Wh/kg and rechargeable batteries reach up to 400 Wh/L and 300 Wh/kg 3,4 , and the upper limit on performance is now being reached as most of the materials that are practical for use as active materials in batteries have already been investigated and the list of unexplored materials is being depleted. 2,3 Many alternatives are in theory possible, such as electrochemical conversion of fuels in fuel cells, thermophotovoltaic cells, 5,6 a microturbine driving a generator, 7 or even exploiting nuclear power, e.g., with thermoelectrical elements. 8 The electrochemical conversion of common fuels and chemicals, such as hydrocarbons or alcohols, in fuel cells has the potential to yield much higher energy densities than state-of-the-art batteries, provided that the power generation equipment can be miniaturized to such an extent that the weight/volume of the fuel dominates. This approach is very promising because on one hand the above-mentioned fuels have very high energy contents ( Figure 1) and on the other hand fuel cells can in principle achieve very high efficiencies. Direct fuel cells running on methanol, formic acid, or medium-sized hydrocarbons are currently associated with many technological problems including coking, low catalytic activity, fuel crossover, and polarization losses. 9,10 An alternative is fuel processing for hydrogen or syngas generation and subsequent oxidation of the hydrogen or syngas in a fuel cell. This paper analyses different alternatives for syngas generation in combination with electrochemical conversion in fuel cells. A number of different fuels are being considered: hydrocarbons, alcohols, ammonia, as ...

Biofuel cells and their development

“…Some theoretical treatment of mediated bioelectrocatalysis is included Kano and Ikeda (2003) An update of the themes of the previous (2001) paper and describing an ambient temperature, neutral pH biofuel cell The current 'standard text' on the subject covering both microbial and enzymatic biofuel cell systems, updated slightly from an older online review. The content in parts focuses strongly on the authors' own specialisms, slightly at the expense of other approaches Wong and Schwaneberg (2003) Applications of protein engineering to bioelectrocatalysis, with particular reference to rational design and directed evolution processes Calabrese A very clear summary of the state of research into enzyme based biofuel cells for implantable and microscale devices Heller (2004) A summary of the rationale behind the design and the projected capabilities of the two fibre glucose/O 2 biofuel cell concept for powering implantable biosensors Mitsos et al (2004) An overview of competing non-biological approaches to using fuel cells for micropower generation comparing a variety of fuels Palmore (2004) Comments on a recently described (Chaudhuri and Lovley, 2003) microbial biofuel cell, and the implications of its high performance Shukla et al (2004) A brief introduction biofuel cells including a long view of their eventual applications or even permanent power supply for such devices as pacemakers, glucose sensors for diabetics or small valves for bladder control. The early goal of powering an artificial heart has been abandoned as the difficulty of realising a functioning implant has become more apparent.…”

“…Other fuels, such as other lower order alcohols and alkanes, are also used, but they are frequently reformed to produce hydrogen before the fuel cell process (Mitsos et al, 2004;Vielstich et al, 2003).…”

Optimal start-up of micro power generation processes

“…A very promising process for micro power generation is the partial oxidation of butane, with subsequent electro-chemical conversion of the generated syngas in a Solid Oxide Fuel Cell (SOFC) (Mitsos et al, 2004a); one of the main advantages of this process is that butane has a very high energy content, and partial oxidation is an exothermic reaction. Therefore, oxidation of the fuel cell effluents is sufficient to overcome the heat losses at steady-state operation.…”

Designing man‐portable power generation systems for varying power demand

“…[10][11][12] Not only the fabrication and modeling of each component, but also careful system design is necessary to obtain superior performance from a microfabricated fuel cell. 13 Microscale and macroscale process design are significantly different. In microscale design, tight spatial integration of components necessitates the simultaneous consideration of component layout and process selection.…”

“…A superstructure representing plausible process alternatives has been proposed. 13 The superstructure has been used to make comparisons between different processes, as well as to study the effect of heat losses, scale, fuel efficiency and conversion. Layout options have been investigated within the superstructure approach.…”