The WSA technology is used in a number of very different industries:

Oil refining

The sulphur level in the crude oil being processed by the refineries today is steadily increasing. The refiner needs to develop a strategy to handle the extra sulphur.

Converting the sulphur to concentrated sulphuric acid without the intermediate elemental sulphur (Claus) plant is a strategy chosen by more and more refiners. One or two WSA plants in a refinery will achieve the goal.

WSA is used for the following purposes in refineries:

• treatment of H2S gas from amine regenerators
• treatment of sour water stripper gas containing H2S and NH3 
• regeneration of spent sulphuric acid from alkylation
• cleaning of tail gases from Claus plants
• cleaning of flue gases from FCC units
• cleaning of flue gases from combustion of high sulphur fuels, e.g. petroleum coke (SNOX™)

Coal gasification

Coal gasification is used to produce synthesis gas for production of e.g. ammonia, methanol, dimethyl ether (DME), liquid hydrocarbons and substitute natural gas (SNG). The acid gas containing H2S and CO2 formed during purification of the synthesis gas needs to be treated. A very efficient way of treating such streams is to produce sulphuric acid using the WSA process. One very significant advantage of this method is the large amount of byproduct steam produced that is highly valued by the gasification plant.

Coking

The WSA process is applied for conversion of H2S from the coke gas cleaning systems and catalytic hydrodesulphurisation of BTX. The WSA process treats H2S along with contaminants, such as NH3, HCN and COS. Regeneration of spent sulphuric acid from BTX rectification can also be performed in a WSA plant.

Metallurgy

Sulphur dioxide contained in off-gases from non-ferrous roasters and smelters can be converted into commercial quality sulphuric acid without generating waste products or waste water. The WSA technology is presently used after molybdenum sulphide roasters, lead and zinc sulphide roasters and sintering plants and copper sulphide smelters.

Viscose

Topsoe’s WSA process is ideal for treatment of off-gases in the viscose industry. The most efficient use is for staple fibres, sponges and other products where the process gas typically contains 10-20 g/Nm³ of H2S + CS2. Off-gases from spin bath degassing and from spinning machines and other sources can be combined in the WSA plant.

Furthermore, sulphur can be used as support fuel, thereby increasing the acid production to balance the demands of the viscose plant. Waste heat is used for production of steam and for pre-heating of the spin bath liquor before the sodium sulphate crystallizer.

Production of sulphuric acid from elemental sulphur

The WSA technology has in recent years found a niche for production of sulphuric acid on the basis of elemental sulphur. One reason is the very high energy efficiency of the WSA process compared to a conventional dry gas sulphuric acid plant.