Essay: Analysis of the Claus Process (Sulphur recovery)

Project Basis:
The process aims to recover 99.8% of sulphur from refineries in order to minimise the concentration of pollutants such as hydrogen sulphide and sulphur dioxide vented to the atmosphere to ensure environmental regulations are met.
Business Need:
The Claus process is a non-discretionary process and it is essential in ensuring refineries are able to meet their required regulations of gases to the atmosphere. The incinerator waste gas from refinery processes must meet the environmental discharge limit. The current limit for sulphur dioxide requires refineries to emit no more than 150 mg/m3.1
Hydrogen sulphide is normally formed during the production of natural gas and crude oil. Sulphur recovery units are situated at most oil and gas refineries across the world.
During the Claus process, hydrogen sulphide is partially oxidised to sulphur with air using an aluminium oxide catalyst reactor in order to produce elemental sulphur. The Claus process consists of a sequence of reheating, reaction and catalyst with the purpose of increasing the sulphur conversion.
Hydrogen sulphide is a toxic gas, it is, therefore, vital for it to be removed before being vented to the atmosphere. It is characterised by its distinct smell being similar to the smell of rotten eggs.
Historical and current status of the process
Carl Friedrich Claus created the Claus process in 1883. The end products of the Claus process were sulphur, water and thermal energy. The reaction operated at a temperature of between 400-600 degrees Fahrenheit. In order to prevent the reaction overheating, only a small amount of hydrogen sulphide could be removed at one time as the reaction heat was only removed by direct radiation. The Claus process was modified in 1938 by I.G. Farbenindustrie A.G, in order to increase the overall sulphur yield by revising the catalyst step and incorporating free-flame oxidation before the catalyst bed, which is now known as the thermal step2. The Shell Claus Off-Gas Treating unit (SCOT) was created in the seventies; it aims to treat the tail gas with the purpose of increasing the sulphur recovery to greater than 98%. The Claus process is the most widely used desulphurising process. Currently, 84,000 tons of sulphur are recovered worldwide by various methods including mining and the Claus process.3
Product use
Sulphur can be sold to other industries including the manufacture of cosmetics and pharmaceuticals. The majority of sulphur (65%) is used to produce sulphuric acid, sulphur is also used to make ammonium sulphates and as a direct soil additive in fertilisers.3 The addition of sulphur to fertilisers helps to increase the crop yield. The primary nutrient of plants is sulphate which is used for growth and in order to create proteins.
Future trends in production/use
Sulphur recovery is expected to increase in the future due to the growing demand for cleaner emission fuels. In the future, the use of sulphur concrete is likely to increase therefore increasing the need for sulphur production. The carbon footprint of sulphur concrete is reduced due to there being no requirement of water and cement reducing both costs and energy. 4The global population is expected to increase by approximately 2.3 billion people, which is an increase of 30% according to the FAO. The increase in population will result in an increased food consumption demand. The increase in demand leads to a greater need for fertilisers and consequently sulphur.
SWOT Analysis
Strengths: The Claus process is able to recover a minimum of 99% sulphur in the original feed streams. Relatively low temperatures can be used therefore reducing the amount of energy to heat the process.
Weaknesses: One of the weaknesses of the Claus process is although the concentration of sulphur dioxide is massively reduced, it comes with the cost of increasing the carbon dioxide emissions due to the running of the reactors. A major disadvantage of the addition of the SCOT process increases capital costs as well as requiring a larger area5.
Opportunities: From the Claus process, the sulphur produced can be sold to other industries allowing a profit to be made from the product. The need for further sulphur recovery is likely to increase due to the demand for cleaner emissions from refineries and fuels.
Threats: Potentially if the environmental regulations continue to increase, the Super Claus process could be a better investment developed by Stork Comprimo6, which has the addition of a selective oxidation reactor and sulphur coalescer. It has the advantage of a lower unit downtime and significantly lower costs than the SCOT process7.
2019-2-18-1550486391