Process Issues: an Update from Sintered Sheet to Fabric Filter

The Challenge

Several years ago, Delta initially designed a Nutsche filter dryer for an Italian API producer to operate as per its typical use: producing a dried solid as the final product.

Over time, the customer changed its production and wanted to use the Nutsche filter dryer to separate the liquid, resulting in a new product.

The challenge was that the product needed to be kept between 90°C and 98°C since, at low temperatures, it would become solid. At higher temperatures, its chemical features would change and become unusable.

Initially, we equipped the Nutsche filter dryer with a standard multi-layer metal filtering sheet, heated with a coil, where it blew a heated liquid.

Before putting the machine into service, the customer discovered some issues during trials with the new product:

The multi-layer filtering sheet tended to get clogged with the limestone used as support during the reaction and needed to be separated from the product. It remained between the layers and was difficult to remove.
After dripping through the filtering sheet, the liquid fell on the flat bottom, where it was no longer directly heated. As a result, part of the product turned to a solid, slowly clogging the space between the flat bottom and the filtering sheet.

Our Solution

The scheduled production campaign prevented the plant from stopping. As such, Delta technicians and the local maintenance service found two solutions:

Interim Solution:

The team covered the sintered layer with a fabric filter. Then, they fastened it to the machine using compression between the bottom and the body.
The local service team added an external auxiliary electric heating system to the flat bottom.

Permanent Solution:

The technicians and service team modified the filtering sheet by installing a fabric filter with the requisite features. This allowed the implementation of the following modifications:
- They machined the supporting flange to install a perforated disk that would support the fabric filter.
- They created fabric filter fastening using a peripherical ring that was bolted to the perforated disk and the supporting flange.
The team also equipped the flat bottom with a half-coil heating system and sanitary insulation.

The Results

The Delta team identified a short-term solution once they discovered the problem. Then they quickly shared, modified, and validated it with the customer maintenance service team.

Within two weeks of pulling the machine from service for its yearly shutdown, the Delta team ultimately implemented the permanent solution. This allowed the customer’s production to start according to schedule.

Typically, the use of a fabric filter implies some differences compared to that of a standard sintered sheet:

Operation is more complicated since there is a need for regular intervention to replace the filtering media
Regular inspection of the space under the filtering sheet requires a longer time for maintenance.

The Delta Technical Team proposed a filtering sheet supporting and fastening system involving a few bolts that could be removed using standard tools to minimize these issues. This allows filtering sheet replacement and the complete machine inspection to occur quickly and by a single operator.

Ultimately, the provided mechanical solution not only solved a process issue but also improved the machine’s overall operation.