Should the Optical Sorter or Gravity Separator Go First?

- Jon Moreland

In my previous column, I hit a nerve about optical sorters versus gravity separators. The idea was not to pit one against the other, but to instead discuss the functionality of each and shed light on how that function is performed. What we learned is that both the optical sorter and gravity separator can have a productive spot in any seed conditioning facility.

Assuming you now see the value each piece of equipment delivers to the task at hand, from an engineering design standpoint, we ask: “Where should each piece fit in a flow line?” There are two primary schools of thought, the practical approach and the outside-the-box approach.

The practical approach involves placement of the optical sorter after the gravity separator. It’s practical because the optical sorter addresses issues that no other upstream piece of equipment can address, including size (width/thickness), shape (length, roundness) and density. This becomes practical as the optical sorter brings new technology to the facility that addresses issues not previously handled It does this at a relatively high-cost-per-capacity compared to other means.

Again, it’s practical because you’re addressing every issue possible by a more cost-effective mechanical means. Then, the remaining issues are to be addressed by the optical sorter. This should minimize the issues of capacity and costs. A 500-bushel-per-hour color sorter will run at least two times as much as any other 500-bushel-per-hour piece of upstream equipment. This is the most technologically advanced piece of equipment in your line, and it’s also the most expensive. Use it late in the process to address issues that only optics can. Use it as the last line of defense for quality, or simply use it like your insurance policy.

Now, let’s look at the other school of thought. A growing number of facilities employ an outside-the-box strategy by placing the color sorter prior to the gravity separator. The idea is that if gravity is the only component in line that actually sorts by density, then employ all available courses of action upstream to allow the gravity separator to do just that, and then focus on differences in density.

Now hold on, because this gets more complicated. We are assuming that what goes to the gravity in this case is material accepted by the color sorter … the best product. I have seen instances where the accepts bypass the gravity (assuming quality is met with no density grade necessary), and the rejects would go to the gravity for further clarification. This is a third school of thought (and there are certainly more). Now you’re making the gravity work harder, with worse product and essentially in salvage mode.

It can get very complex, and what you will find, if you visit enough seed conditioning facilities, is that everything is conditional (by seed type, lot, size or contaminant type, or harvest conditions or any other mitigating factor).

Here’s an idea with an engineering design solution: What if you engineered your conditioning facility to be capable of running any of the above mentioned flows? Then you would have the flexibility to address any issue, including the ones you didn’t foresee.