PP Precipitation Plates - Sulphuric Acid Recovery

Engineering Plastics in Sulphuric Acid Recovery: An 8-Metre Polypropylene Precipitation Plate

When chemical resistance, stiffness and cost all matter

Sulphuric acid recovery is an important part of many metallurgical operations, allowing sulphur-containing off-gases generated during smelting to be converted into a valuable sulphuric acid product rather than released to the atmosphere.

The process presents a challenging environment for materials. Components can be exposed to sulphuric acid and other aggressive chemical conditions, making material selection critical to achieving long service life and reliable operation.

For one smelter application, Dotmar was involved in the manufacture of four 8-metre-diameter polypropylene precipitation plates used within the sulphuric acid recovery process.

At this scale, the application presented more than simply a question of chemical compatibility. The material also needed to provide sufficient stiffness, remain cost-effective and be capable of being manufactured accurately from large sheets.

The application

The precipitation plate has an overall diameter of approximately 8 metres and is manufactured from 25 mm thick polypropylene sheet.

Rather than attempting to manufacture the plate as a single component, the large circular structure is produced from multiple segments. These segments are CNC machined from sheet before being assembled to form the complete plate.

The result is a large engineered plastic component designed specifically for the requirements of the sulphuric acid recovery process

Why polypropylene?

The selection of polypropylene was driven by a combination of factors rather than a single material property.

Chemical resistance

The first consideration was the operating environment.

Polypropylene offers good resistance to a wide range of aggressive chemicals and is widely used in chemical processing applications. This made it a suitable candidate for an application involving sulphuric acid recovery.

Material selection for chemical service must always consider the specific chemical concentration, temperature, exposure conditions and mechanical loads. In this application, polypropylene provided the required combination of chemical resistance and physical properties.

Stiffness

Polypropylene was also selected because it provides greater stiffness than polyethylene grades such as HDPE.

For a component approximately 8 metres in diameter, stiffness becomes particularly important. The plate needs to maintain its geometry and resist deformation during operation.

While HDPE also provides good chemical resistance and is widely used in chemical-processing applications, polypropylene provides a better balance of stiffness for this particular design.

Industrial-Workshop-with-Tactile-Floor-Mat

Cost

Higher-performance polymers are available that can provide excellent chemical resistance. However, these materials, which include fluoropolymers such as PVDF, can come at a substantially higher cost.

For a component of this size, material cost becomes a significant consideration.

Polypropylene provided the required chemical resistance and stiffness while offering a more economical solution than moving to higher-cost specialty polymers.

The result was a practical engineering solution that balanced performance, durability and cost.

Manufacturing an 8-metre component

The scale of the component created another challenge.

An 8-metre-diameter plate cannot simply be placed on a conventional CNC machining table and manufactured as one piece. Instead, the plate is divided into a series of accurately designed segments.

The segments are machined from 25 mm polypropylene sheet using CNC routers in Dotmar's in-house machine shop.

CNC machining provides the dimensional accuracy and repeatability required to produce the individual segments so that they can subsequently be assembled into the complete circular structure.

This approach also demonstrates one of the advantages of engineering thermoplastics: large components can be manufactured from commercially available sheet using conventional CNC machining techniques, without the need for specialised metal fabrication processes.

From engineering material to engineered solution

The application demonstrates that selecting an engineering plastic is rarely about choosing the polymer with the highest specification.

Instead, successful material selection considers the complete set of application requirements.

For this sulphuric acid recovery application, polypropylene provided the right combination of:

Chemical resistance
Stiffness
Dimensional stability
Machinability
Material availability
Cost effectiveness

Combined with Dotmar's in-house CNC machining capability, this allowed a very large and complex component to be manufactured from segmented polypropylene sheet.

The result

8-metre-diameter, 25 mm thick polypropylene precipitation plates, CNC machined from individual segments and manufactured for service in a sulphuric acid recovery application.

It is a good example of how the right engineering plastic, combined with appropriate design and manufacturing capability, can provide a practical alternative to more expensive materials in demanding industrial environments.

The engineering challenge isn't always finding the most advanced material. It's finding the material that provides the right balance of performance, practicality and cost for the application.

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Dotmar Engineering Plastics stands poised to address your unique challenges. Harness our expertise for bespoke engineering plastic solutions tailored to your specifications.