How to Produce Palm Kernel Oil
Extracting palm kernel oil is basically done in three steps. The first process is kennel pre-treatment, followed by screw-pressing and finally oil-clarification.
1. Kernel pre-treatment
This involves cleaning the palm kernels to remove any foreign materials which can damage screw-presses, thus increasing downtime and maintenance costs. Metal debris is removed by installing magnetic separators. On the other hand, sand, stones as well as other undesirable materials are sieved using vibrating screens.
The palm kernels are then broken into small fragments using breaker rolls or swinging hammer grinder or both. The aim of this process is to increase palm kernel surface area and thus facilitate flaking. The kernel fragments are then exposed to flaking in the roller mill. Typically, one large roller mill may consist of a maximum of 5 rollers that are vertically mounted above one another.
After that, kernel flakes are moved to stack cooker for the purpose of steam conditioning. This achieves the following:
- Rupturing of cell walls
- Reducing oil viscosity
- Adjusting the meal's moisture content to a level that is optimum, and
- Coagulation of the protein contained in the meal so as to facilitate oil separation from protein materials.
At this stage, you have a properly cooked meal. This is fed to screw-press. The press is made of interrupted helical thread that revolves goes round a static perforated cylinder known as a barrel or a cage. The barrel forces the meal through the revolving thread's action. The volume displaced axially by the helical thread, also called the worm, lessens from the feeding point to the discharge point. Thus, the meal is compressed as it goes through the barrel.
The expelled palm kernel oil is made to drain through the barrel's lining bars perforations. At the same time, de-oiled cake is released via an annular orifice.
It is important that the extreme temperatures are regulated so as not to damage the cake and palm kernel oil quality, and this is done by passing circulating water over the warm shaft. Also, the barrel is externally cooled by recycling some of the cooled palm kernel oil.
3. Oil clarification
Ultimately, the expelled palm kernel oil contains a given quantity of "foots and fines 'which needs removing. Thereafter, the oil coming from the presses gets drained into a reservoir. After that, the palm kernel oil can be pumped either to the revolving coarse screen or to a decanter. The aim is to solid impurities. What follows is pumping the oil to filter press so that the remaining fines and solids can be removed. This ensures that clear palm kernel oil is produced before storage. The cakes that have been released from the presses are transported for bulk storage or bagging.
However, all crushers do not always use the same techniques for mechanical production of kernel oil. Basically, three variations exist and they are:
i. Direct screw pressing
In some mills, the palm kernels are crushed directly in presses and there is no pre-treatment. In order to guarantee efficient oil extraction, double pressing must be done. Usually, screw-presses used are below 10 tons per unit daily.
ii. Partial pre-treatment
Before screw-pressing, palm kernels are broken down first into much smaller fragments after which they are grinded. In certain instances, cooking is also done.
iii. Complete pre-treatment
Full pre-treatment are mainly done before screw-pressing. However, for plants with bigger capacities, like 50-500 tons daily, the best option is to choose complete pre-treatment.