Luca Micoli

The Effect of Biogas Impurities on SOFC

This chapter treats the effect of biogas impurities on the performances of a solid oxide fuel cell (SOFC). Biogas contains mainly CH4 and CO2 and can be easily produced by several processes. It can be fed to a SOFC to produce electric energy and heat with high efficiency thanks to internal reformer of the fuel cell. Some contaminants are present in the raw biogas with concentrations that can reach values up to 20,000 ppm: sulfur compounds (the most abundant being H2S and mercapatans), halogens, and siloxanes. The quantification of these harmful compounds contained in biogas is specifically treated. The interaction of these compounds with the Ni-based electrodes and the electrolyte dramatically affects the performances of SOFC. The poisoning mechanism and their detrimental effect on SOFC are described in detail. An effective removal of such contaminant (up to concentration lower than 1 ppm for sulfur compounds and 5 ppm for halogens) is needed to guarantee long-term performance of SOFCs.

Processes of Biogas Production: Anaerobic Digestion and Thermal Gasification

This chapter reviews the biogas production by anaerobic digestion (AD) and thermal gasification (TG) processes. The different steps of the AD and the characteristics of the biogas obtained from kinds of biomass carefully have been described. Some attention is devoted to the study of the conditions and techniques proposed in literature to improve the biogas production from organic waste, also analyzing the treatments of the biomass, such as ultrasound, heating, microwave, and chemicals. The co-digestion technique and the design and operating conditions of digesters have been also taken into account. The TG has been treated describing the whole process and the influence of the operating variables, such as temperature and pressure and gasifying agents. Some examples of the type gasifiers are also given.

The Effect of Sulfur Compounds on MCFC

This chapter deals with the effect of sulfur compounds on the performances of molten carbonate fuel cells (MCFC). The chapter comprises a brief description of the main components of MCFCs, electrodes and electrolyte. The effects of sulfur compounds on porous nickel-based anode and porous nickel oxide-based cathode are described taking into account also the mechanisms of the interaction electrodes/sulfur compounds, in particular H2S. The interaction of H2S with carbonates of the electrolyte leading to a reduction of active charge carriers has been discussed considering the mechanisms of deactivation.

Use of a Metal Organic Framework for the Adsorptive Removal of Gaseous HCl: A New Approach for a Challenging Task

In this work, the potentialities of the amino-functionalized, chromium-based MIL-101 metal organic framework (NH2-MIL-101) as a high capacity, fully regenerable hydrogen chloride adsorbent have been proved by a thorough adsorption thermodynamics investigation. The chosen adsorbent showed high gaseous HCl adsorption capacities and, to the best of our knowledge, it is the first example of a totally regenerable substrate for this kind of adsorbate, as evidenced by both experimental and modeling results. This paves the way to the implementation of greener, more energetically efficient pressure/temperature swing adsorption processes to purify biogas feeds for high-temperature fuel cells.

Fuel Cells Challenges

This chapter gives a state-of-art of the commercialization process of fuel cells. Fuel cell technology is well established in niche market (military, aerospace) since the second half of nineteenth century, while the commercialization in a larger market is going slowly. Fuel cell systems have been under development for several decades and their applicability has been demonstrated worldwide both in small and in large scale. Nevertheless, successful commercialisation of this technology requires to overcome some barriers. This chapter reviews the main challenges related to the diffusion of fuel cells: low costs, quality and acceptance by end-users. Costs are related to the hydrogen production and manufacturing and depend also by Government’s supports. Technical issues are mainly linked to the robustness, reliability and durability of a fuel cell especially compared to internal combustion or turbine engines. Fortunately, the public acceptance of fuel cell could be easier considering that it is an environment-friendly technological alternative.

The Effects of Siloxanes on High-Temperature Fuel Cells

In this chapter the effects of siloxanes on high-temperature fuel cells have been treated. Siloxanes represent the second largest family of contaminants present in biogas. They derive from a variety of cosmetics, pharmaceuticals, and antifoam products largely and are found mainly in biogas obtained from landfills and wastewater plants. The chemical properties of siloxanes and their concentration in biogas according to site and season variability (typically in the range 2–80 mg/Nm3) have been reported. Most abundant siloxane compounds present in biogas are hexamethyldisiloxane (L2), hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5). Siloxane impurities can reach downstreams and cause degradation of cell performances due to silica deposition. The mechanisms of silica formation and its interaction with electrodes are illustrated. Among the different techniques for siloxane removal the adsorption is the most practical one today. The commonly used solids, active carbon silica gel, and zeolites are described with several examples giving information on adsorption capacity and breakthrough behavior.

The Use of Biogas in MCFCs and SOFCs Technology: Adsorption Processes and Adsorbent Materials for Removal of Noxious Compounds

Fuel cells are highly efficient and very low emissions power generation systems. The molten carbonate (MCFCs) and solid oxide fuel cells (SOFCs) are emerging in the field of stationary power production as a true alternative to combustion heat engines for the production of electrical power, cogeneration, and tri-generation. They can be fed with different kinds of fuels including biogas. This chapter illustrates the characteristic of biogas depending on the different substrates used in anaerobic digestion process. The processes for upgrading the biogas to biomethane are also treated describing the methodologies to removal several compounds, such as air, O2, water, and CO2. This chapter reviews the techniques for H2S removal (the most abundant harmful compound) during digestion and after digestion. Particular attention is given to the adsorption process for removal of sulphur compounds and siloxanes, describing in detail the adsorbing material proposed in literature, such as activate carbons and zeolites.