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Sulfur recovery using the Claus process

Premium Engineering offers four basic Claus-based processes for sulfur recovery from the sour components of natural gas and plant gas:

  • Straight-through (burn all of the gas)
  • Split-flow
  • Split-flow with air and sour gas preheating
  • Direct oxidation

  1. The straight-through Claus process (burning all of the gas) is used for sour gas streams containing above 50% vol. of H2S and less than 2% vol. of hydrocarbons. Thereby all the gas is fed for burning in the thermal stage reacting furnace of the Claus unit, which is integrated with the reboiler. The temperature in the reacting furnace is as high as 1100-1300°С; sulfur recovery is up to 70%. The further conversion of H2S into sulfur occurs in two or three stages in the presence of a catalyst, at a temperature of 220-260°С. Downstream of each stage the vapor of the recovered sulfur condenses in the surface condensers. The heat released in the process of H2S combustion and sulfur vapor condensation is used to produce high and medium pressure steam. Sulfur recovery in this process is as high as 96-97%.
  2. At a lower H2S content (30-50% vol.) and a hydrocarbon content up to 2 % vol. in the sour gas, the split-flow Claus process is used. According to this scheme, one third of the sour gas is burned to produce sulfur dioxide, while two thirds of the sour gas stream are fed to the catalytic stage bypassing the reacting furnace. Sulfur is recovered at the catalytic stage by the reaction of the sulfur dioxide with H2S contained in the rest (2/3) of the feed sour gas stream. Sulfur recovery in this process is as high as 94-95%..
  3. At a H2S content of 15-30% vol. in the sour gas, when the minimal allowable temperature in the reacting furnace (930°С) cannot be reached using the one third-two thirds scheme, the split-flow with air and sour gas preheating scheme can be used.
  4. H2S content of 10-15% vol. in the sour gas, the straight-through scheme is used, which does not include the high-temperature oxidation (combustion) stage. The sour gas is mixed with the stoichiometric quantity of air and fed directly to the catalytic conversion stage. Sulfur recovery in this process is up to 86%.

To attain a sulfur recovery of 99,0-99,7%, Claus tail gas clean-up techniques are used which fall into three groups:

  • A process based on further processing using Claus reaction, i.e. reaction between H2S and SO2 on a solid or liquid catalyst to yield elemental sulfur.
  • A process based on the reduction of all of the sulfurous compounds to hydrogen with its subsequent extraction.
  • A process based on the oxidation of all of the sulfurous compounds to SO2 or to elemental sulfur with their subsequent extraction.