Hydrogen-deficient star radii. Hydrogen deficiency results from stellar evolution. Over the course of a star's evolution, both the consumption of hydrogen in nuclear fusion and the removal of hydrogen layers by explosive processes can lead to a deficiency of hydrogen in its atmosphere. Detailed theoretical models are still in their infancy. Modeling of hydrogen-deficient star evolution involves either a single-star approach or a binary-star approach. For example, there have been two theories put forward to explain the formation of extreme helium stars. The helium final flash scenario is a single-star approach in which a helium flash serves to consume the hydrogen from
Acid gas hydrogen sulfide and/or carbon dioxide can be used, the raw gas must be treated to reduce impurities to acceptable levels and this is commonly done with an amine gas treating process. The removed HS is most often subsequently converted to by-product elemental sulfur in a Claus process or alternatively converted to valuable sulfuric acid in a WSA Process unit. Processes within oil refineries or natural-gas processing plants that remove mercaptans and/or hydrogen sulfide are commonly referred to as 'sweetening' processes because they result in products which no longer have the sour, foul odors of mercaptans and hydrogen sulfide. Hydrogen sulfide