Oil separation is somewhat of a contradiction, according to Aqueous Recovery Resources (ARR; Bedford Hills, NY). For starters, it’s not about oil. It’s about saving water and extending the life of other process fluids such as machine coolants and cleaning solutions. Process performance drops off with increasing oil and dirt levels until the only alternative is to replace the entire bath.
Second, oil is not the real problem, although too much of it can be. The real problem is dust, dirt and fines in the oil, which impede separation by making the oil heavier and create an interface layer between the oil and water. This interface layer is doubly nasty: it carries dirt that can redeposit at various locations in your installation, and it breaks up and mixes with water easily because of the entrained water and chemicals. For this reason, ARR says it’s imperative not only to get the oil out of your process fluids, but to remove dirt and other contaminants that mix with the oil.
So, how to get rid of the oil and attendant problems? According to ARR, conventional oil skimmers and separators remove the nice, clean oil at the top of your process tank; what they leave behind is the nasty stuff. Coalescers, for example, are inexpensive and can be effective in removing fine droplets of clean oil.
Unfortunately, they don’t handle contaminants very well. Dirt accumulates and deposits on the coalescing media, building oily sludge coatings that obstruct flow. Fluid is forced around the coalescer pack; flow velocity increases and residence time drops until no separation is possible. At that point the coalescer must be removed and cleaned.
The company says its Suparator thin-film separation technology, on the other hand, starts separating oil at very low concentrations and maintains oil concentration lower than other oil separators or skimmers. And, it removes the gunk that creates the nasty interface layer before it has the opportunity to disperse throughout your system.
The process works in four steps. First, it separates the upper fraction from the rest of the process flow, taking with it any trace of oil. Next, it collects and accumulates all oil traces while allowing water to drain through the bottom section. In the third step, oil is concentrated in a small area; remaining water and surfactants are displaced from the concentrate. Finally, pure oil is separated from the rest of the collected waste.
In one retrofit installation at ITW’s Miller Electric Div., immersion washers originally came with plate-pack coalescers that were difficult to adjust and clean and removed an oil/detergent mixture that was roughly 70% detergent. Five retrofit Suparators sit on top of the wash tank and remove pure oil with no detergent. The installation paid for itself in about 6 months in less washer maintenance, less disposal, and more effective chemical use. The oil is dry enough to be sold to a local oil recycler.