Technical and environmental comparison – WSA vs Claus
Feature
Modified Claus process
WSA technology
Sulphur recovery Energy efficiency
99.9+% with tail gas treatment Lower (due to tail gas treatment
Up to 99.99%
High (uses exothermic heat,
units & incinerators) Yes (requires fuel)
generates steam)
Direct CO₂ emissions
None
Capital & operational cost
High for multi-stage setups Tail gas chemicals, NaOH, etc.
Lower due to simpler design
Chemical usage Acid production
None
Elemental sulphur only
Market-grade sulphuric acid
Table 1
Technical and environmental comparison In comparing the WSA process to the traditional Claus method, key differences become immediately apparent (see Table 1 ). While both technologies aim for high sulphur recovery rates, their methods and outcomes diverge significantly. The Claus process, even with three catalytic stages and tail gas treatment, often falls short in energy recovery and environmental performance. It typically requires external fuel combustion, which increases operational complexity and CO₂ emissions. Tail gas treatment units and incinerators add further capital and utility costs. WSA, by contrast, operates without tail gas incineration or chemical consumption. It recovers more thermal energy from the gas- to-acid conversion and produces high-quality steam for direct use in refinery processes. This enables the technology to offset boiler fuel consumption and eliminate associated GHG emissions. While the Claus process yields elemental sulphur, WSA creates a liquid acid product that is easily stored, transported, and monetised in industrial markets. The net environmental impact of the technology is markedly lower, making it a strategic asset in any decarbonisation roadmap. Replacing or revamping older Claus units with WSA technology represents a strategically sound option, particularly compared to constructing entirely new Claus units. A gradual shift from sulphur to sulphuric acid production also enables refineries to gain operational experience in acid handling and develop robust off-take partnerships. Over time, increasing the volume
of acid gas directed toward WSA improves both environmental and economic performance. Role in India’s decarbonisation journey India has committed to reaching net-zero emissions by 2070 and has identified refining as a key sector for transformation. Enhancing energy efficiency, reducing emissions, and embracing circular business models are top priorities. WSA fits directly into this agenda. By removing nearly all sulphur content from off-gases and eliminating direct CO₂ emissions, the process contributes to cleaner air and lower long-term operational costs. Its ability to generate steam also aligns with India’s goal of reducing reliance on fossil fuels for process energy. The process also supports broader industrial resilience by supplying sulphuric acid to downstream sectors, decreasing dependence on imports, and strengthening domestic chemical manufacturing. Its modular design, flexible installation, and low utility demand make it adaptable for a wide range of facilities. For Indian refiners, WSA offers a practical and proven route to meet regulatory standards while improving margins. Its success at IndianOil’s Haldia site provides a strong precedent, backed by a scalable design that can be adapted to a wide range of facilities across the country. Getting started with WSA in India Transitioning to WSA does not require an overnight overhaul of existing sulphur recovery infrastructure. In fact, a phased replacement of ageing Claus units offers an efficient and lower- risk entry point.
Refining India
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