McLanahan Rotary Scrubber Screen Delivers robust outcome for Sand Plant Production
Written by: Jodi Thornton
Introduction
McLanahan has just shipped a 2.5M-3.2M-3.5M Rotary Scrubber with Trommel Screen to a customer in South Australia. The customer initially came to McLanahan in 2017, looking to replace an existing rubber tyre-supported Rotary Scrubber with Trommel Screen which had started to experience fatigue cracking in the main scrubber barrel.
At the time, the customer was processing approximately 200 t/h of alluvial sand for the concreting industry, with a maximum lump size of 150 mm and a final product size of -6 mm.
Requirements
McLanahan was commissioned to design and supply a Rotary Scrubber with trommel screen to replace the existing Rotary Scrubber on site. The goal McLanahan was tasked with was to increase the raw feed tonnage from 200 t/h to 400 t/h.
The customer had several requirements for the design of the Rotary Scrubber:
- First and foremost, double production rate
- Maintain the existing scrubber’s footprint
- Require no power increase over the existing installation
Testwork
In order to double the plant capacity within the same installed power and space envelope McLanahan first had to assess the process requirements for this product.
It was determined that screen area was critical to the process, and therefore to double the capacity the screen area had to approximately double as well. To achieve this the machine layout was reconfigured at the expense of the scrubber volume which would then ultimately provide shorter residence times and input energies. The impact this has on outcomes needed to be determined.
McLanahan carried out sample testing in our lab to assess performance in terms of product cleanliness and product yield. Test work data provided a direct comparison of the existing installation with the McLanahan machine with reconfigured layout.
Product cleanliness data is shown in the following graph:
When testing was complete, it was evident that there was no clear reason to scrub the raw feed for longer than 25 seconds, and that any scrubbing longer than this did not provide any added value to the cleanliness of the product.
Solution
The testing performed by McLanahan showed that through reducing the scrubber barrel length, that we could increase the trommel screen area. This improvement was imperative in order for the customer to double their production as requested.
Additionally, McLanahan’s Rotary Scrubber design used shrink-fit hardened steel tyres supported on a stiffened steel ring, which stiffened the cylinder significantly over the existing design, eliminating the likelihood of fatigue cracks forming in the new machine.
This enhancement allowed for a more robust Rotary Scrubber, something that was also important for the customer in achieving their production goals.
Testing
McLanahan performed a standard Factory Acceptance Test on the Rotary Scrubber from our Cameron Park workshop where we monitored no load power draw, bearing temperatures and motor currents.
Maintenance
Once the Rotary Scrubber is commissioned on site, maintenance of the trommel screens will be relatively easy, as the outer screens are easy to change out. McLanahan recommended to the customer that they keep a full set of the polyurethane outer screens on site, plus a full set of quench tempered steel inner screens.
