Most refineries today rely on the Claus process for sulfur recovery. By switching to the wet gas sulfuric acid (WSA™) process, refineries can improve their energy efficiency and lower their carbon emissions without making significant changes to their infrastructure.
This article outlines the benefits of the WSA process by exploring the results of a technical case study that examines in detail the WSA process and compares it to the modified Claus process (i.e. a 3-stage Claus process with an amine-based tail gas treatment unit and an incinerator in the back end) for sulfur recovery.
The global refining industry is a major source of greenhouse gas (GHG) emissions, but it holds significant potential for decarbonization. Enhancing energy efficiency across both primary and auxiliary processes within existing refinery operations can substantially reduce these emissions. Notably, Sulfur Recovery Units (SRUs) have the potential to play a critical role in minimizing CO2 emissions.
The modern refining landscape relies heavily on the modified Claus process for sulfur recovery. This well-established technology employs a series of catalytic stages to convert hydrogen sulfide (H₂S) into elemental sulfur. However, while the Claus process offers a reliable solution, it has limitations in terms of maximizing energy recovery and reducing environmental impact.
The WSA sulfur recovery process was introduced in 1980. It was initially a cost- effective solution for cleaning low-sulfur waste gases, but quickly demonstrated broader applicability.
In a 2024 case study, we at Topsoe compared the environmental performance of the modified Claus process and the WSA process in a refinery setting. Both systems were designed to recover 99.9% of sulfur.
By comparing the WSA process with the modified Claus process, we were able to assess the overall GHG impact of the two processes and their potential contribution to the refining industry’s decarbonization goals.
The preliminary findings indicate that the WSA process offers significant advantages in terms of energy efficiency and reduced carbon emissions compared to the modified Claus process, offsetting more than 2 tons of CO₂ per ton of sulfur processed. However, a more comprehensive analysis, including energy and mass balances, is necessary to quantify the full extent of these benefits.
Our WSA process offers a path to reducing CO₂ emissions by maximizing energy recovery and generating high pressure superheated steam. Here’s how it succeeds in delivering this:
While a complete overnight shift from sulfur to sulfuric acid production can be challenging, a gradual transition offers a strategic and effective solution. Replacing older Claus units with WSA plants is a more cost-effective approach than building new Claus plants.
This incremental shift allows refineries and gas plants to gain valuable experience not only with the WSA technology but also with navigating the sulfuric acid market, finding traders, and establishing robust trade routes. The produced commercial-grade sulfuric acid can be sold domestically or internationally, and Topsoe can introduce gas processors and refiners to reputable acid traders who will guarantee 100% offtake of the acid at any time.
Simultaneously, customers will immediately benefit from the high amounts of high-pressure steam generated by the WSA process, which can be seamlessly integrated into refinery operations to offset fossil fuel consumption in boilers.
This expert article summarizes a study presented in the article ‘From Waste to Clean Energy: The Acid Path to Reducing CO₂ Emissions’, originally published in Digital Refining in 2024. For a full exploration of the facts and figures that form the foundation of this article's conclusions, we recommend reading the full study.