Study On Carbon Fuel Cells Operating On Purified Coal

Coal is currently the second largest primary energy source after oil in the world,and it will remain a major energy source in the coming decades due to its extensive reserves.wide distribution and low cost.Conventional coal-fired power generation is the primary application of coal.However,the major drawbacks of conventional coal-fired power generation are low conversion efficiencies?30-40%?and a large quantity of CO₂ emissions?².7 kg of CO₂per kg of coal?and other pollutants,such as SO_x,NO_x and dust.Solid oxide fuel cells?SOFCs?are all solid-state power generation devices that directly convert the chemical energy of fuel into electricity.The fuels have many advantages,such as high energy conversion efficiency,low pollutant emission,friendly environment,no moving parts,low operating noise,etc.SOFCs are expected to become a new power generation technology which can achieve the efficient and clean usages of coal.Shanxi Province possesses abundant coal resources in China with the high-quality anthracite reserves over 50 billion tons of reserve,which accounts for about 40%of the whole globle reserve of anthracite.However,the reserve of high-quality coal continues shrinking with the extraction and consumption on a large scale.Naturally,more and more attentions have been attracted to the utilization of low-rank coals,such as high-sulfur coals.Therefore,this paper studies the suitability of anthracite and high-sulfur coal as fuels for SOFCs.Nickel-based cermets is the classic anode material for SOFCs owing to their superior performance in terms of catalytic activity,electronic conductivity,and thermo-mechanical compatibility with electrolytes.However,the nickel cermet anodes are prone to sulfur poisoning when using coal-derived carbonaceous fuels,resulting in the anode deactivation and the cell performance degradation.Faced with this challenge,on one hand,tremendous efforts have been devoted to improve the sulfur tolerance of the nickel cermet anodes via various strategies.On the other hand,the desulfurization of the coal-derived carbonaceous fuels is a more direct way to alleviate the sulfur poisoning of the anodes.Shanxi Province possesse abundant resources.Herein,the desulfurization of the high sulfur coal from Shanxi Jincheng was performed by the molten caustic leaching method?MCL?.The compatibility of the pristine and purified coal samples with the nickel cermet anode SOFCs was investigated.The results showed that the MCL method could remove 60%of the sulfur in the high-sulfur coal.The purified high sulfur coal had a more advantageous structure and higher Boudouard reactivity,which was suitable as a fuel for fuel cells.The purification treatment not only made the peak power density of SOFCs improve from 66 mW cm^-22 to 110 mW cm^-22 at 850?,which improved 93pecentage of the PPD,but also extended their stable operating time from 1.7h to 11.2 h under a current density of 50 mA cm^-22 at 850?with a fuel availability increasing from 6.25%to 40%.Meanwhile,the content of sulfur and deposited carbon on the anode surface of cells was decreased by 68%and49%,respectively.The anthracite sample from Shanxi Jincheng was used in this work,as a kind of high-quality coal with medium degree of coalification,high-chemical activity,no burning smoke,and 7.12 wt%of the ash content.Therefore,effects of the ash in the anthracite on the electrochemical performance of cells have become an important research topic.In the paper,we treated the anthracite with acid-alkali?NaOH-HCl?method and studied the effects of the ash in the anthracite on the electrochemical performance of DC-SOFCs.The results showed that the acid-alkali method not only removed most of the ash components with Si and Al in the anthracite,but also made its structure looser.After the removal of ash,the cell's peak power density was improved from129 mW cm^-22 to 159 mW cm^-22 at 850?,i.e.an increase of 23.3%was gained,and the cell's OCV increased from 0.928 V to 0.931 V.Meanwhile,the stable operating time was extended from 14 h to 20 h under a current density of 50mA cm^-22 at 850?along with a fuel availability increasing from 44.1%to62.9%.