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Handling increasing amounts of H2S


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Sulfur management

In the race to achieve more and deeper desulfurization of fuel oil and other refinery products, the challenges faced by refineries are many. For some, the issue is capacity. Existing H2S gas treatment facilities such as Claus plants may not have sufficient capacity to treat additional H2S gas. In other cases, refiners need to increase sulfur removal efficiency to comply with environmental regulations.

We’ve got answers today
Topsoe’s Wet gas Sulfuric Acid (WSA) technology was developed for H2S gas treatment as well as Claus tail gas applications.

Our compact WSA process converts H2S into concentrated sulfuric acid, which can then be used by the refinery itself or be marketed for use by companies such as fertilizer producers.

A major advantage of WSA technology is that it exports about three times more energy than a Claus plant. The energy is available in the form of superheated high-pressure steam that’s suitable for use in steam turbines.

WSA technology easily accepts ammonia, e.g. in SWS gas, and hydrocarbons, and many oil refineries worldwide have already adopted WSA technology to treat H2S gas.

Three ways to boost H2S gas processing capacity

Supplement Claus plants with WSA to treat extra H2S gas
Additional H2S gas can be directed to a WSA plant to produce sulfuric acid and generate a significant amount of steam. A WSA plant typically takes up less space than a Claus plant, so limited space in refineries shouldn’t be a problem. You can see a flow diagram of a typical WSA plant below.


Fig. 1: Typical WSA plant

Treat Claus tail gas
In cases of insufficient sulfur removal rates in Claus plants, a WSA plant can be installed to treat tail gases. Almost all sulfur will still be available as elemental sulfur, while a smaller portion will be processed into concentrated sulfuric acid.

Treat H2S and tail gas simultaneously
Here’s an elegant solution for simultaneously treating H2S gas and tail gas to increase overall sulfur removal efficiency and capacity. Configure a WSA plant to achieve both. Assume that after installation of additional HDS capacity, an additional 50% of H2S gas is generated. The problem is that the existing Claus plant can’t handle the extra load. A simple solution is to direct the additional H2S gas to a WSA plant that also treats the tail gas from the existing Claus plants. As a result, you can realize a combined total sulfur removal efficiency of more than 99.9% and a capacity increase of 50%.

With this approach, the energy-consuming operation of your existing Claus tail gas treatment units becomes superfluous. Two-thirds of the total sulfur will be produced in the Claus plants in the form of elemental sulfur, while the remainder will be produced in the form of concentrated sulfuric acid in the WSA plant. The set-up is illustrated below.


Fig. 2: Sulfuric acid in the WSA plant

Burning high-sulfur residual oil and petcoke
What if a refinery determines that desulfurization of all fuel oil isn’t a viable option? What do you do with the high-sulfur residue from the refinery that cannot easily be sold?

One possibility is to burn the residue to generate steam, heat and power for the refinery or nearby consumers.

The sulfur dioxide (SO2) rich flue gas from the combustion can be treated in a Topsoe SNOX™ plant. It converts SO2 into concentrated sulfuric acid. In contrast to other flue gas cleaning methods, SNOX™ operates without consuming absorption materials and without producing liquid or solid waste that would require handling and disposal.

Unlike other flue gas cleaning methods, the economics of SNOX gets better the more sulfur content there is in the fuel. At the same time, a boiler supplied with SNOX™ flue gas cleaning is more energy efficient, with a 5-7 % higher production of energy than a boiler outfitted with conventional flue gas treatment technologies.

The resulting lower carbon footprint (less CO2 per kWh of energy produced) and the absence of waste benefit both the climate and environment: It may generate carbon credits too. The SNOX process is a variant of the WSA process. This is illustrated below, along with an upstream boiler.

Fig. 3: SNOX process

Studies and answers
We recommend initiating a project by conducting a study to gain insights into how different technologies will perform at a customer’s facility and to discover which solutions are best.

Relevant topics for investigation could include:

  • Cost benefit analysis
  • Plot issues
  • Integration with upstream and parallel units
  • Emissions control
  • Tolerances for waste stream feeds

Whatever your challenges, contact us for insights that will help you perform a value-adding project.

See our video on WSA technology:



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