African Palm

April 24, 2007

An industry exists for extracting vegetable oil from the nuts of the African Palm. We have visited factories doing this in Costa Rica, and plants in Mexico, Nicaragua, and Colombia have been heard of. The oil is high value, and it seems to be used mostly for cosmetics or blending with other oils.

Bunches of berries, or seeds, grow on the African palm, which is a tall and very bushy palm tree, usually with ferns growing on the trunk. Thousands of acres of banana plantation have been put to palms. The bunches are about 12" to 16" in diameter; the berries are about the size of large grapes.

The 14" bunches are first cooked in long steam tunnel cookers. The main plant we visited has four, each holding half a dozen short gondola rail cars full of bunches. This blanching operation is to loosen the berries from the stems. (The plant we were at processed 1,000 tons per day.)

Once steamed, the bunches are tumbled in huge trommel screens, to separate the berries. Sometimes the berries are called fruit. They have an outer pulpy mass with a hard seed inside. Both the pulp and the seed contain oils, of different qualities.

The waste stems go to a big hammer mill and then into a smallish sugar cane roller drum press (three 32" diameter rolls, 36" wide). The material from the shredder looks and acts like hemp cushion or mattress stuffing. We could never get a drop of liquid out by hand squeezing. They add some water to this material at the inlet to the roller drum press. The oil and water outflow (press liquor) is a good 5 gpm; it is sent to a Sweco filter, along with the press liquor from the pulp presses. Thus, some oil is recovered from the stems and mixed with the oil from the pulp.

The press cake from the roller drum has a damp or oily feeling, with about 55% moisture they said. Typical of a drum press, some of the cake comes out very dry, and some is dampish. They want to press it to a lower moisture content in order to get out more oil and to be able to burn it. The bulk density is very low, so they cannot get any capacity out of their existing 12" twin screw presses. The material is too wet to burn, so it is used as mulch. A Vincent Series VP press might work in this application, although a couple more stands of roller drum presses, like at a sugar cane mill, would be a better bet.

Once de-stemmed, the berries are stirred, with steam addition, mushing them. This is done in a vertical shaft agitator-cooker (100 psi steam, 120° C), referred to as a digester.

The cooked berries fall into very heavy duty screw presses, such as a Stork, Vetter, or Columbian knock-offs. These are all twin screw presses. There is an exceptionally large flow into these 12" machines, 12 MTPH each. The cake produced is tremendously dry, only 40% moisture. Despite the extremely high pressure, the seeds in the press cake are hardly broken at all. The oil, red, comes from berry pulp; it is mostly made into oleo margarine, some is sold for industrial cooking oil. None goes to consumers. (Vincent does not offer a screw press for this application.)

The press liquor is an oil/water emulsion which is separated in hydraclones, followed by centrifuges.

The press cake from these presses is blown to cyclone classifiers or separators. The nuts drop out of the first cyclone and then go to a Ripplemill (soft grinder; they have three). In the Ripplemills they crack the nuts into kernels and into shells. The shells go to the boilers, for fuel.

The second cyclone separates out the pressed pulp, which also goes to B&W boilers for use as fuel.

They have flakers, one each, French and Davidson (?). These are three-high drum machines, 48" wide, 12" drums, each feeding the next lower drum. Each has a pair of 25-hp 1200-rpm motors, pulley driven at 260 rpm. These grind the seeds into powder. That powder goes to rather large steam pre-heaters, and then into three Anderson Expellers®. (These are ~1935 Anderson presses, used first on sunflower seeds, then cotton seeds in Nicaragua, now for palm oil in Costa Rica.)

The press liquor (oil) is filtered, in either a drum filter or a plate and frame filter press. The oil is premium quality, sold for cosmetics and pharmaceuticals.

The press cake from the kernels goes to a hammer mill (this press cake from the Anderson's is hard as a rock), and then it is bagged and sold as animal feed.

They have 60 m3/h going to the WWTP, about 260 gpm. The Vincent FF-12 Fiber Filter was used to separate suspended solids from this flow, in order to reduce pond odor. This was relatively successful, although a small screw press was needed to dewater the sludge from the Fiber Filter. There was the potential for oil recovery in this application.

A better application for the Fiber Filter was in filtering oil and water emulsions ahead of centrifuges. Keeping fiber solids out of the centrifuges would greatly increase the service life of the components subject to abrasive wear. Once again, a small screw press was needed to dewater the sludge from the Fiber Filter.

Issue 186