Phosphoric Acid, Phosphates & Fertilizers Experts

Advantages of a Catenary Converter in a Sulphuric Acid Plant

SNC-Lavalin’s Sulphur and Emissions Solutions (SES) Group has been designing and constructing sulphuric acid plants for over 50 years. Sulphuric acid is one of the world’s top chemical commodities, with a wide range of applications in different sectors, from a catalyst in the petroleum industry to a leaching chemical in the mining industry.

The acid plant converter is at the heart of the acid plant. In the converter, sulphur dioxide (SO2) reacts with oxygen (O2) in the presence of a catalyst to form sulphur trioxide (SO3).

Within our SES Group, we have made significant advancements with our catenary converter design. We have been able to provide significant efficiencies in weight, footprint, time to construct and cost of fabrication. An internal core structure is utilized as the main supporting structural element, similar to the design of modern day high rise buildings. The division plates and catalyst bed grates are designed to a catenary shape and are of the same dimensions throughout the converter. The use of a stiffened core structure and the catenary design of the division plates and catalyst beds eliminates the requirement for internal support columns and vertical stiffeners leading to quicker fabrication as well as improved maintenance access inside the converter.

The use of an internal core structure also allows for the placement of the plant’s gas to gas heat exchangers inside the converter. In sulphur burning acid plants, the hot interpass heat exchanger can be replaced with an internal heat exchanger while in a metallurgical gas acid plant both the hot interpass and hot gas heat exchangers can be replaced with internal heat exchangers. The results in an overall reduced footprint for the acid plant leading to savings in ducting, foundations, etc.

There are a number of advantages that come with catenary converter design, some of which are noted below.

  1. Absence of internal columns.
  2. Efficient load carrying. The load path in the catenary converter design is through the inner core structure and the inner wall of the external shell all but eliminating the possibility of misalignment of division plates and the associated flexure stresses.
  3. Fewer fabricated parts. This leads to a savings in material costs as well as fabrication, handling and shipping costs.
  4. Fewer welded joints. The number of potential failure points and opportunities for leakage between division plates is greatly reduced.
  5. Less material. Cost savings are realized in materials, handling, freight, installation labor and welding as well as time related project costs.
  6. Consistent dimensions for division plates and catalyst bed gratings. The use of repetitive sizing of individual pieces is economical to fabricate.
  7. Reduced construction hours. One of the key cost savings made in employing the catenary converter is a reduced number of site construction man hours. This is due to fewer fabricated parts, fewer welded joints, less materials to handle and repetitive sizing of materials.
  8. Additional savings by employing internal heat exchangers. The internal core structure acts as the body for the internal heat exchangers. The results in an overall reduced footprint for the acid plant leading to savings in ducting, foundations, etc.
  9. Access for catalyst screening is simplified. The absence of internal columns improves the process of screening catalyst.
  10. Less inspection and maintenance of the structure. The catenary converter design has fewer connections requiring inspection and maintenance

We have also realized other advantages related to process design and overall operation of the converters in the facilities we have designed and constructed.

The catenary converter offers a number of performance, construction and operational advantages and is a design that should be considered when developing a new acid plant or when replacing converters in an existing facility.

Our engineering team in the SES Group at SNC-Lavalin has tremendous experience in the design, construction and operation of converters. Out teams are currently active in projects involving new converters as well as projects involving upgrades and repairs to existing units.

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