Nuova Solmine is a leader in the production of sulfuric acid in Italy and the Mediterranean basin. It operates a double absorption sulfuric acid plant with a capacity of approximately 1,700 mt/d in Casone di Scarlino. The plant originally was built in the 1960s to treat SO2 gas from a pyrite roaster. This was upgraded with sulfur burning in 1994 and the pyrite roaster was shut down. At that time, all the facility’s towers were constructed with brick lining. By early 2017, the brick lining was beginning to deteriorate and require frequent maintenance. Because Nuova Solmine plants work in a continuous production cycle 365 days per year, any increase in maintenance time potentially impacts production. So, the company decided to replace the final absorption tower (FAT) with a new, highly efficient one that would guarantee constant reliable emissions control and require less maintenance.
In July 2017, Nuova Solmine awarded a turnkey contract for the design, execution, supply and erection of the new FAT to DuPont Clean Technologies. The decision was taken to use DuPont’s proprietary MECS ZeCor alloy because of its light weight and corrosion resistance. One important factor in the choice of technology was the speed of replacement as Nuova Solmine was keen to limit lost production time when switching from the old to the new FAT. DuPont was able to provide a definite delivery and installation schedule. Other key criteria for the selected equipment and design strategy were optimal performance efficiency, low lifecycle costs and minimal maintenance.
DuPont Clean Technologies is a recognized specialist in sulfuric acid plant and tower design, as well as sulfuric acid emissions-reduction technology and was able to give Nuova Solmine both a performance and mechanical guarantee for the new FAT tower. Nuova Solmine had specified that the new FAT should keep outlet acid mist below 30 mg/Nm3 — a more stringent limit than that imposed by the local authorities (35 mg/Nm³).
DuPont Clean Technologies therefore set about designing and engineering a FAT with tower internals that would enable Nuova Solmine to stay well below its target emissions threshold. The new FAT included advanced equipment such as:
• a MECS UniFlo acid distributor to deliver continuous and precise distribution of acid for optimum absorption efficiency, minimal mist production and maximum service life for downstream equipment;
• a MECS ZeCor alloy packing support that features a greater-than-80% flow area to allow for very good gas distribution and enable the lowest possible gas pressure drop combined with high efficiency; and,
• MECS Brink CSII Plus mist eliminators to collect the most-difficult-to-capture aerosol mists down to submicron size.
Key to achieving the fast turnaround Nuova Solmine wanted, while also providing the desired performance and longevity for the new FAT, was the use of MECS ZeCor, which not only is extremely resistant to corrosion from acid and other substances but also is very light in weight.
To limit time spent on site, the new FAT tower was prefabricated in a DuPont Clean Technologies workshop, shipped to the Italian port of Piombino in four separate sections and transported 40 km by road to Scarlino, where final assembly and installation took place.
From start to finish, the entire project took 11 months. The replacement of the brick-lined tower with the new MECS ZeCor FAT was carried out to schedule during a planned plant turnaround in August 2018. Installation only required about two weeks and the pre-assembled new tower was lifted into position in exactly the same location as the old one (Figure 1).
Figure 1. New FAT was lifted into place during a plant turnaround in August 2018.
DuPont Clean Technologies handed over operation of the FAT to Nuova Solmine just after startup in August. Final testing took place between September and December 2018 to assess mg/Nm3 levels of acid mist. The results came in well below the contractual performance guarantee (30 mg/Nm³).
To date, the new MECS ZeCor FAT is performing very well, achieving a pressure drop that is under the contractual target, as well as SO3 acid mist emissions well below the environmental limit.
The design of the MECS ZeCor alloy FAT tower at Nuova Solmine is the result of several years of research, during which DuPont Clean Technologies developed alloy towers with improved absorption efficiency and acid distribution. Added benefits have been a reduced pressure drop, a decrease in packing height and lower operating cost. These qualities have provided Nuova Solmine with a very effective and timely way to meet its emissions, maintenance and installation goals.
GABRIELE PAZZAGLI is plant director for Nuova Solmine, Scarlino, Italy. GIOVANNI MARCHESI is Milan-based area manager for Southern Europe for DuPont Clean Technologies. Email them at [email protected] and [email protected].