Do you mean slurry that doesn't empty from the grate chamber?

Pulp flow-back and slurry pooling are hidden phenomena that many operators may not notice it. They know that if some operational parameters such as solid percentage would be adjusted then there won’t be any problems due to process issues. In my country every capacity reduction will be related to feed hardness and of course it’s the easiest way to escape from accurate investigations.

My pulp lifters are nearing their end of life and flow-back/ back-wash wear is becoming really evident. I'm not sure whether this is due to the lifters being so worn or whether it is a feature of the lifter design.

I am reluctant to change to a curved system as I am actively trying to retain mill weight and worry the curved system will pull too much slurry out for my current operating parameters. Are there other options?

We developed lifter, grate, pulp lifter and flow cavity through exit trommel model for the 40 ft Cadia mill in Australia. The study identified all wear zones, granular flow back into the mill and re-circulating flow inside the pan cavity for straight and curved lifters. At the time, we also modelled the water flow regime through the grate. A Population Balance Model (PBM) was also developed to synthesize the dual strength ore action evident as solved in the PBM selection Function.

From a mechanical point of view, curved pulp lifters increase the number and layout of liner bolt holes in the end wall for the mill. In addition, as the curve is either LH or RH, it can "lock" the operator into having a uni-directional mill forever. We normally drill the shell for bi-directional rotation so that the operators have the opportunity to run the mill in both directions, allowing even gear and pinion wear, allowing more flexibility in liner layout etc.

From a process point of view, I am not too sure whether or not the curved pulp lifter improve slurry discharge and prevent pooling or flow-back. The curve does provide a slight increase in pulp lifter volume as the radial length is slightly longer, but if the grates are worn or do not have the right open area, their benefit may be nullified against straight pulp lifters. Most large SAG mills are variable speed, so this can be used to further fine-tune slurry discharge.