Reducing scale build up to extend bag life and improve worker safety

THE OBJECTIVE

An Australian alumina refinery approached SOLAFT to see if there was a way to improve Kelly Filter operation and bag handling, through reducing scale build up where the cuffs of the filter cloth is attached to the filter frame. The refinery was looking increase equipment uptime and improve worker safety.

THE ISSUE

The alumina refinery increased green liquor alumina-to-caustic (A/C) ratio in an effort to improve production yield, this lead to an increase in scale formation during clarification. The scale is formed in clarification through mechanisms including premature hydrate and DSP crystallisation seeded on un-extracted gibbsite in the bauxite mud, and through spontaneous hydrate and DSP crystallisation with a drop in liquor temperature in locations where green liquor is retained when cooled. The scale gradually builds with each filtration cycle and eventually the filter media permeability is reduced to a point where the set point liquor flow cannot be sufficiently maintained, or the filtration cycle time becomes uneconomically short (depending on the filtration control mechanism employed).

WHAT WE DID AND THE SOLUTION

SOLAFT, developed for the top section of the Kelly Filter, a custom-engineered fabric, specifically to reduce the rate of scale formation under the lid of the filter vessel. This resulted in extending the safe operating life of the filter media, minimising filter leaf removal hazards and reducing filter vessel down time. With this unique solution, the use of pneumatic tools has been eliminated, considerably reducing the hazards posed to operators.

SOLAFT’S Technical Team then worked with the on-site engineer to trial the newly constructed Kelly Filter.

OUTCOME

After a successful trial, the new Kelly Filter was put into full production. The benefits to the Alumina refinery include:

  • Filter life was extended by 10-20%
  • Uptime by up to 10%
  • Invaluable improvement in worker safety