gas is recovered and converted into high-pressure, superheated steam. This steam can be integrated into plant operations to offset steam from fossil-fuel- fired boilers, thereby reducing energy costs and GHG emissions. The sulphuric acid produced is a high- purity, commercially valuable product with a broad range
Superheated HP steam
Hot air blower
Stack
Cleaned gas
Combustion air
Steam drum
SO converter
BFW
Cooling air blower
Interbed cooler
H S gas
Air
Waste heat boiler
Combustor
Process gas cooler
WSA condenser
Sulphuric acid
Acid cooler
CW
Figure 1 The WSA process
grade sulphuric acid (H₂SO₄). Unlike traditional methods, it treats wet off-gases directly, eliminating the need for costly and energy- intensive gas drying steps. The process is simple: using air, cooling water and boiler feed water, it achieves effective sulphur removal (WSA technology can be designed to achieve SO2 emissions below 10 ppmv) without any chemical additives or waste streams. The process is composed of three primary stages. First, sulphur in the feed gas is combusted or preheated, depending on its composition, to form SO₂ at the optimal temperature. Second, SO₂ is oxidised to SO₃ in a multi-bed converter using Topsoe’s VK-W series catalyst. Third, the SO₃ gas is hydrated by existing water vapour in the process gas to form sulphuric acid and condensed in the WSA condenser, where heat is also recovered. The final product is commercial-grade acid ready for storage, and the resulting cleaned gas can be released to atmosphere or used further downstream. WSA technology operates efficiently even at SO₂ concentrations as low as 0.1% and can seamlessly handle feed fluctuations without operator intervention. It also efficiently processes lean acid gases containing below 30% vol H₂S, a range where conventional Claus units often face operational challenges. Key advantages for refineries One of the WSA process’s most notable features is its superior energy efficiency. More than 90% of the thermal energy in the feed
of industrial applications – from fertiliser manufacturing and metallurgical leaching to water treatment chemicals. For Indian refiners, this creates a new revenue stream while contributing to national industrial supply chains. Operational reliability is another major advantage. WSA units are compact, modular and designed for high uptime. All process steps occur near atmospheric pressure, which enhances safety and ease of maintenance. In contrast to scrubbers or dry-gas systems, WSA requires no absorbents, activated carbon or heat transfer salts. This makes it inherently simpler to operate and more resilient to variable operating conditions. The process has the inherent capability to process a higher percentage of sour gases without any issue, as it operates in full combustion mode. This means there is no challenge related to ammonia slip from the combustion chamber. There is also no issue related to the choking of catalyst beds due to soot formation, which is quite common in partial combustion mode operation in the Claus process. The process operates at a lower pressure compared to the Claus process, requiring a lower battery limit feed pressure. This enables acid gas from the amine regenerator and sour gas from the sour water stripper to be supplied at reduced pressures, allowing both units to operate more efficiently with lower reboiler duties. The bottom line is that reboiler duty in upstream units is saved, reducing energy consumption.
Refining India
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