Steam sterilization is the
first and very critical step in the palm oil extraction process in a palm oil
mill or factory. The objective of using
steam to sterilize the oil palm fresh fruit bunches (FFB) is to perform two
major functions:
(1) to soften the very hard FFB so that all the fruits can be
readily detached from the bunches, and
(2) to condition the mesocarp (pulp) of
the fruits for efficient extraction of the oil contained in it during the
subsequent steps.
The following is a brief
description of the various types of FFB sterilizer currently in commercial use
and their operational characteristics.
Conventional Horizontal FFB Sterilizer
The conventional horizontal FFB sterilizer is known to be inherently
inefficient in air removal from the stacks of fruit bunches loaded in cages
inside the sterilizer. Because of this technical weakness, horizontal FFB sterilizer would require high steam consumption of 360
to 400 kg per ton FFB at 4 barg pressure in triple-peak cycles over 90 minutes
to achieve satisfactory FFB sterilization.
Besides high steam (therefore energy) consumption, the conventional way
in handling the FFB and steamed fruit bunches (SFB) using cages, capstans,
winches and overhead lifting cranes is also the source of a host of operational
inefficiencies such as high oil losses, more frequent down-times leading to
higher maintenance costs and exposure of workers to higher risks of operational
hazards.
Development of New FFB Sterilizers
There are a number of second-generation
FFB sterilizers developed over the past 1-2 decades which are now used
commercially in new and upgraded palm oil mills. These can be categorized into three types as
listed below:
- Continuous
FFB Sterilizer
- Vertical
FFB Sterilizer
- Spherical
FFB Sterilizer
The continuous FFB sterilizer is an unpressurised sterilizer
system in which the fruit bunches are continuously moved through by conveyor inside a
steaming cabin. The vertical and
spherical sterilizers are pressurized batch sterilizers but are relatively
different in designs and mechanisms in FFB feeding, steaming control,
condensate removal as well as SFB evacuation.
Continuous FFB Sterilizer
In a continuous FFB sterilizer system, the fruit bunches are
first mechanically split and transported through a horizontal sterilizer cabin
via a scraper conveyor in a continuous process.
While inside the sterilizer cabin, the split fruit bunches are exposed
to steam at atmospheric pressure. After
the stripping step, the stripped fruits will be exposed to another round of
steaming to bring the fruits to the right condition for the digesting/pressing
stages.
In practice, the continuous FFB sterilizer requires 300 to
350kg of steam per ton of FFB and additional power consumption of 200kW to run the
FFB bunch splitting machine and the scraper conveyer inside the sterilizing
cabin in a 60mt/hr palm oil mill.
Vertical FFB Sterilizer
Vertical FFB sterilizer basically resembles the FFB horizontal
sterilizer in shape being positioned vertically. It has a top inlet door for FFB feeding and a
bottom outlet door for SFB evacuation.
By virtue of its vertical position, vertical FFB sterilizer occupies
much smaller footprint and therefore requires smaller area for the sterilizer
station.
However, its stacking height of some 8-10m tall would invariably result
in some degree of FFB compaction at the lower part of the sterilizing vessel. This compaction would pose certain degree of
restriction in steam penetration, air/condensate removal, and SFB
evacuation. Moreover, this lower-section FFB compaction phenomenon is
also the main cause of frequent repairs and maintenance required in running vertical sterilizer.
In practice, vertical FFB sterilizer consumes
250 to 300kg of steam per ton FFB over a steaming time of 60 minutes in a
triple-peak cycle.
Spherical FFB Sterilizer
The configuration
of the spherical FFB sterilizer station is about the same as for the vertical
FFB sterilizer station except for the different geometric shapes and internal
designs of the two types of sterilizing vessel.
Spherical FFB
sterilizer is a ball-shaped sterilizing vessel that can rotate 360 degree to
facilitate both FFB feeding and SFB discharge through its single door. The round geometry of the sterilizing vessel
(4.5m in diameter) minimizes FFB compaction inside the vessel and hence optimum
steam penetration, air and condensate removal resulting in great economy of
steam.
The simplicity in
its design results in minimum repairs to both its internal and external parts
and hence the lowest maintenance cost among all types FFB sterilizers in
commercial use.
In
practice, spherical FFB sterilizer consumes 220 to 250kg of steam per ton of
FFB over a steaming time of 60 minutes in a two-peak cycle.
For further enquiries, please contact:
CIMG Resources Sdn Bhd, Malaysia
Email: cimgrs@yahoo.com
