The Background

The planting of Oil Palm for its oil has long been an established industry in Malaysia and is one of the major contributors of national economic growth. The process of extracting the oil from the fresh fruit bunch (FFB) has been evolving and changing ever since the first time such industry set foot on Malaysia. Sterilization is one of the critical operation steps in this process. Traditionally, this is done by cooking the FFB in a pressurized vessel. The capital outlay of mills using such type of pressurized vessel is higher due to its larger foot print as well as more associated equipments required.

CB Industrial Product Sdn Bhd (CBIP) in collaboration with Malaysia Palm Oil Board (MPOB) has developed a new method of sterilization to cater for this need. It is known as the Non-Pressurized Continuous Sterilization. This method manages not only to overcome the problem of high capital outlay with its associated larger foot print but also revolutionized the palm oil milling process and hence the palm oil industry.

The Concept

In the development of this method, the concept of sterilization needs is redefined. It views sterilization principally as a process of cooking the FFB and deactivating the enzyme and bacteria. Cooking FFB with steam will promote hydrolysis to take place at the contact point of fruit-lets and their stems. This hydrolysis will enable all the fruit-lets to be released from their stems. Once this happened, the fruit-lets can be easily detached and separated from the stems in the bunch stalks by threshing the FFB bunches in a Thresher Drum. The heat from the steam for cooking also deactivates the enzyme and bacteria, and hence arrests the rise of FFA of the oil still in the mesocarp.

This new Concept also views the process of softening the oil-bearing cells and pre-treating the nuts as separate but complimentary steps of the Continuous Sterilisation system. It shall be done immediately after the sterilization and threshing steps.

The Process

i. FFB Preparation

FFB is first put through a Bunch Conditioner to shear and condition it. This FFB is then fed into the Continuous Sterilizer Chamber via a totally sealed scrapper bar type Feeding Conveyor. This Conveyor is designed to take the advantage of the excess steam from the Continuous Sterilizer Chamber to pre-heat as well as to evacuate the air from the conditioned FFB. In doing so, it contains and controls the excessive steam from leaking into the atmosphere and pre-heat the conditioned FFB at the same time.

ii. FFB Cooking

The Continuous Sterilizer Chamber is constructed from stainless steel plate. Basically, it is a long rectangular non-pressurized chamber fitted with steam injection nozzles strategically distributed along its whole length. The reason for using a non-pressurized chamber is because only steam at atmospheric pressure is required to cook the FFB. The arrangement of the nozzles in the Chamber is to ensure and facilitate even distribution of steam to all the FFB inside it. This will promote proper cooking of the FFB.

The whole length of the Continuous Sterilizer Chamber is properly insulated to prevent heat loss. At the same time, for ease of maintenance and routine checking, removable covers and manholes are provided over the whole length of the Chamber.

Due to their pressure, blowing off of steam and condensate at the end of a conventional sterilization process always poses a messy and hazardous problem. This has being an operational problem in all the mills using the above system.

However, with this new Continuous Sterilization process, the problem is completely resolved and eliminated. There is no more blowing off of steam and condensate under pressure. Instead, the bottom of the Continuous Sterilizer Chamber is fitted with a series of condensate drain for draining off all the condensate continuously.

During operation, the whole Chamber is under steam of atmospheric pressure. Conditioned FFB is fed into this Chamber via a mechanical flap door which acts as a steam lock. The FFB is moved through the whole length of the Chamber by a chain type Conveyor driven by a high torque geared motor. As the FFB moves along the Chamber, it is cooked by the steam. The time of cooking varies with the types of FFB and is between 60 minutes to 80 minutes. At the end of the cooking cycle, the FFB is sufficiently sterilized and is ready for feeding into the Threshing Drum via another mechanical flap door.

iii. Threshing of Sterilized FFB

After the sterilized FFB is fed into the Threshing Drum of a conventional Thresher, the fruit-lets are stripped off from the bunch stalks.

Due to the design of the Continuous Sterilization system, the sterilized FFB is evenly and continuously fed into the Thresher Drum. This will, in turn, ensure even and continuous threshing of the FFB, hence improving the performance of the Thresher.

Improved performance means all the fruit-lets are completely stripped from every bunch that has gone through the threshing process.

iv. Post Cooking and Digestion Of Fruit-lets

Vertical Heating Vessel and Horizontal Digester are the additional equipments required to further cook the fruit-lets after Threshing.

These equipments are designed with mechanical agitators and steam injection facility. The purpose of the agitator is to provide the required shearing effect to the fruit-lets as well as tossing and mixing them continuously to maximize steam-fruit-lets contact. Shearing and tossing-mixing the fruit-lets under low pressure steam not only will soften their mesocarp but also will rupture the oil-bearing cell walls thus releasing the oil.

These equipments are properly sized to give adequate and sufficient retention time to fruit-lets so that the breaking of the oil-bearing cell walls in the mesocarp can be effectively accomplished.

Further, the low pressure steam in these equipments also help to condition the nuts without discoloring the kernel, a pre-requisite for effective nut cracking and kernel recovery.