Systems And BoP - Desulferization Flashcards
What is the limit of the amount of suffer in FCs?
Above one ppm, fuel cells generally show signs of aging. Therefore, the desulphurization requirement is observed and desulphurization conducted to a level of about one ppm.
What are the sulfur compounds present in Natural gas?
Natural gas also contains natural sulfur-containing components, but its concentration is relatively low and most often it is in the form of hydrogen sulphide, which is easy to remove. In order to guarantee safety, especially in domestic applications, sulfur compounds are later added to the natural gas. They induce a strong, unpleasant odor with a lower odor threshold. These additives are usually mercaptans or thiophenes.
What are the properties of Hydrogen Sulfide (H2S)?
Very toxic, water soluble, perception limit 0,1vppm, maximum level of exposure for personnel over a whole workday under German regulations is 10 ppmv
Danger: not perceptible above 200 ppm
What are the properties of Mercaptane (R—SH)?
Toxic, disgusting smell, very low level of perception
In what form is Mercaptane present in fuels?
Ethane thiol used for odorization of liquid natural gas LNG
Methane-thiol gaseous; higher thiols are liquid or solid at room temperature
How does the desulfurisation of H2S work?
Adsorption on active carbon; reaction with ZnO
How does the desulfurisation of Mercaptane work?
Adsorption, reaction with ZnO
What are the properties of Thiohene (C4H4S)?
Hetero cyclic compound; very toxic; not water soluble; liquid
How does the desulfurisation in Thiohene work?
Cracking of the molecule w/ hydrogen, formation of H2S; Raney Nickel as catalyst
What are the methods of desulfurisation in gases?
The easiest means of gas phase desulfurization is adsorptive removal on an activated carbon bed or activated alumina. This can be used to remove hydrogen sulfide and mercaptans, but not thiophenes. In this case, prior hydrogenation of the thiophene to hydrogen sulfide is necessary. Another possibility is the chemical reaction with zinc oxide to form zinc sulfide. This is the usual procedure for large-scale processes, but has limits in decentralized applications, given that zinc is a heavy metal and therefore toxic and has a high mass. Another method is direct conversion to elemental sulfur in the Claus reaction. This is a process that is very well controlled on an industrial scale, but which cannot be executed at the required pressures and temperatures in small systems.
