June 23, 2015
Olive oil production is a major industry, especially in countries such as Italy, Spain, Greece and Syria. Tunisia, Turkey, and Morocco are also significant producers. For many decades screw presses were used in this process, to separate the oil from the olive pulp. Today the use of decanters and centrifuges has taken over. GEA Westfalia and Alfa Laval are the principal suppliers.
The process starts when harvested olives are dumped into a trash removal machine and a washer. The trash (mostly leaves) is separated by air. The washer counts on the olives floating and the rocks sinking.
An in-line weigh scale is used as the olives are transported to storage bins. Different quality olives are separated into these bins.
From the storage bins the olives go to a small grinder which looks like a pellet mill. Inside it has a 1/4″ perf screen through which the olives are crushed. This breaks the seeds into pieces.
This mass then goes to a ribbon blender which makes the olives into a pulp. To improve yield, steam is used to bring up the temperature a little bit.
This pulp is pumped to a horizontal decanter, 4000 rpm, which separates liquid from the pulp. Typically this is a two phase decanter, something introduced in the olive industry in the 1990’s.
The centrate is screened and then pumped to a bowl style centrifuge. This separates the flow into three fractions: water, oil, and sludge.
Typical installations of this equipment are rated at 100,000, 150,000, and 250,000 kilos of olives per 24 hour day.
The oil goes to gravity decanter tanks followed by a final membrane filter. Virgin olive oil is the result. The tank bottoms are pumped back to a centrifuge, for oil recovery.
The yield is about one kilo of oil from six kilos of olives. This varies with green and black (ripe), along with other factors.
The pomace from the decanters goes to a de-stoner machine which separates almost 90% of the pit pieces from the pomace. This pomace is shipped off-site to a hexane solvent recovery plant to get out the residual oil. This is the lowest quality olive oil. In Spain it is called lampante, lamp oil.
The pits are sold as boiler fuel. They have only about 22% moisture content. Frequently some are burned in a small boiler to make steam to heat the facility. A small amount of steam is used in the ribbon blenders.
A few years ago Vincent had a foray into this industry, working with GEA Westfalia. The goal was to separate additional liquid from the pomace from the decanters. This liquid is rich in polyphenols, a class of pharmaceutical organic chemicals valuable because of antioxidant properties. There was also a possibility that the pomace could be made into animal feed.
As is always the case, the screw press could not separate liquid from decanter pomace. However, by dosing with cellulose fiber press aid, the screw press was made to work. There was about a 50/50 split between press cake and press liquor.
If the pomace was a couple weeks old, natural enzymatic reaction had released liquid which could be separated as press liquor. In the case of pressing fresh pomace, it was necessary to first add hydrated lime to react the pomace ahead of the screw press. Either way, press cake with only 40% moisture content could be produced.
Unfortunately the process did not pencil out. It is one more case of a technical success but a commercial failure.
Issue #274