Operating Microtubular SOFCS With Hydrogen Chloride and Hydrogen Sulfide Containing Fuels and Synthetic Wood Gas

Abstract

Solid oxide fuel cells are known to be able to handle a large variety of different fuels. Because of the greenhouse effect the use of carbon dioxide neutral gases or liquids are of special interest. In this context wood-gas has a big potential to be an alternative fuel for solid oxide fuel cells (SOFCs). The gas is generated by a fluidized bed steam gasifier and consists of various components such as 25 Vol % carbon monoxide, 20 Vol % carbon dioxide, 10 Vol % methane, 2.5 Vol % ethylene, 0.5 Vol % propylene, 2 Vol % nitrogen, and the rest hydrogen (values in dry state). The water concentration of the original pyrolysis gas is about 35 Vol %. Besides these main ingredients there are of course many impurities like dust, tars, ammonia, hydrogen sulphide, and hydrogen chloride present in the product gas. Especially the last two ones may lead to degeneration of the fuel cell anode and must therefore be almost totally removed before feeding the gas into the cell. In order to reduce energy losses, hot gas cleaning systems are favored. This, however, limits the possibility to reduce the impurity concentrations to very low levels. Therefore the aim of this work is to define the maximum acceptable output concentrations for the hydrogen chloride adsorber also in combination with hydrogen sulphide, since for a micro-tubular SOFC there are as yet hardly any data available. In order to determine the influence of the hydrogen chloride on the performance of the fuel cell, different concentrations of this impurity were fed to the cell. Here, also the flow rate was changed while the electrochemical output was determined. In addition it was analyzed if there were any effects when changing from pure hydrogen to the HCl containing fuel. This was investigated at 1123 K and 1173 K, which are the preferred working temperatures for our cells. Cooling down as well as heating up procedures were tested with cells between 1173 K and 573 K. In a second series of experiments, combinations of hydrogen chloride and hydrogen sulphide of variable concentrations were tested. As before, changing between pure hydrogen and the acid containing fuel at above given temperatures was analyzed by determining the cell performance. In parallel to the above experiments, synthetic wood gas was used for operating the microtubular fuel cell while monitoring the electrochemical output with time.

A transient analysis of a micro-tubular solid oxide fuel cell (SOFC)

“…Although significant amount of work exist on micro-tubular SOFCs [9][10][11][12][13][14][15][16], these devices are not employed in any practical applications yet due to lack of operation optimization to maintain electrochemical performance and mechanical durability simultaneously. This is also related to the difficulty in experimentation as the data such as temperature and current distribution, is not so easily measurable due to the smaller dimensions and elevated operating temperatures.…”

Effect of H2S and HCl contaminants on nickel and ceria pattern anode solid oxide fuel cells

“…To the best of the authors' knowledge, pattern electrode cells have never been tested in an HCl environment, so no direct comparison can be made. Otherwise, in relevant studies conducted with cermet cells, no or insignificant effect on the cell performance has been reported for HCl concentration below 50 ppm [13][14][15]30,65,66]. Both reversible [16,17] and permanent [18] performance loss have been reported at higher concentrations.…”

Long‐Term Stability Studies of Anode‐Supported Microtubular Solid Oxide Fuel Cells

“…For intermediate operating temperatures around 550ºC the most widely used materials are NiO-GDC (gadolinia-doped ceria) for the anode; GDC for the electrolyte and LSCF (lanthanum strontium cobalt ferrite) for the cathode. Some features of mSOFCs comprising their performance under hydrocarbon fuel operation [5,6,7], the resistance to anode redoxcycling [8,9] and thermal cycling [10,11], the effect of gas pressurization [12], the development of hollow fibres [13], and the microtubular stack modelling and design [14,15] have been widely studied. However, there are relatively few studies reported in the literature related to long-period testing of anode-supported mSOFCs under operating conditions.…”