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Selection of a suitable sulphur recovery process for small to medium acid gas quantity

Selection of a suitable sulphur recovery process for small to medium acid gas quantity

Shantanu Gaurav Srivastava (shantanu57@gmail.com)
Department of Chemical Engineering, Vellore University
March, 2013
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Shantanu Gaurav Srivastava after having received his basic education from famous Modern School , Nagpur ( Maharashtra) completed his B.Tech degree from Department of Chemical Engineering , Vellore Institute of Technology , Vellore University , Vellore , Tamil Nadu ,India. This is the part of his work accomplished during his dissertation completed at Oil and Natural Gas commission , Mumbai.
 

Abstract

Selection of Suitable Sulfur Recovery Process for Small to Medium Acid Gas Quantity

Shantanu Gaurav Srivastava
Department of Chemical Engineering
Vellore Institute of Technology, Vellore 632 014, Tamil Nadu, India
Email : shantanu57@gmail.com


Abstract

Increasingly stringent environmental emission standards have raised certain pertinent issues with regard to off-shore gas containing SO2 since elemental sulfur has traditionally been a problem in aqueous system due to its extremely insoluble in water, and thus nucleates rapidly forming small particles. Among the options available for the ultimate disposal of off-gas containing SO2, the production of elemental sulfur is highly attractive. Acid gas treating has traditionally required an amine plant to remove hydrogen sulphide and a Claus unit to convert the concentrated hydrogen sulphide stream to sulfur. The SulFerox process on the other hand, is an alternative to these steps, by removing hydrogen sulphide directly from gas streams and converting it to elemental sulfur. Over the years, acid gas popularly known as sour gas predominantly containing CO2 and H2S gas released from the Oil and Natural Gas Commission (ONGC) plant becomes increasingly sour, and it has increased the H2S gas concentration from 700-800 ppm in 1998-99 to 1200 ppm, and maximum of 1950 ppm occasionally is recorded. This is a potential source for future H2S hazard, a long term solution for the disposal of such acid gas is, therefore, required. Accordingly, a study for selecting a suitable process to remove the H2S from acid gases generated in gas sweetening unit (GSU) was undertaken.

Removal of sour gases from acid gas during processing of natural gas is one of the necessary steps towards harnessing fuel efficiency. Our studies on selection of suitable sulfur recovery process from acid gas revealed that liquid phase oxidation process is best suited for safe disposal of acid gas. The liquid redox processes such as LOCAT process (Hydrogen sulphide being absorbed in chelated iron solution) and SulFerox process (converting H2S in sour gas to elemental sulfur through reaction with ferric ion) were observed highly efficient. Iron chelate based liquid phase oxidation process has been observed most suitable for treating the acid gas generated at Oil and Natural Gas Commission (ONGC) Plant. Both LOCAT and SulFerox processes are, hence, recommended to ONGC in the turnkey package for potential decision support in favour of designing ONGC plant.

The conclusions drawn from the studies conducted comprised of : i. Maximum sulfur recovery of 97-98% was obtained with Claus process. Therefore, this process requires a subsequent tail gas clean up unit like Scot process; ii. SulFerox proved to be flexible system (with regard to changes in gas volume and H2S content) with comparatively lower operating cost (suitable at both low and high pressure) and non-toxic elemental sulfur product; and iii. use of chelated iron enables desired acceleration in reaction between H2S and O2 to form elemental sulfur.