Feature Article

Significance of Oil Extraction Rate (OER) Efficiency

in a Palm Oil Mill
N Ravi Menon*

T
THE OER ISSUES clarifications for the planters to carefully
consider the relevant reasoning behind the
he other day, a mill manager rational that oil losses are a function of the
contacted us to say that his boss oil extraction ratio. Surprisingly, even the
was always finding fault with him mill engineers are not aware of this simple
when the oil loss was on the high truth. In order to justify this statement,
side. His boss, the General Manager, was a some definitions would be of help.
planter by profession but was vested with
the mandate to monitor mill operations as MISSING LABORATORY ANALYSES
well. As the General Manager was always
finding fault with the mill manager and In some mills, certain oil loss analyses are
turned a deaf ear to his explanations, he not carried out and they assign a value
was contemplating on resigning and taking of ‘zero’ for that. This is a wrong way
up a job overseas. We told to him to hold on of computation that can mislead the top
and find out a way to make him understand management.
the factors involved. This could be a tough
job as another factor called ego also played OER DEFINITIONS
a vital role in this. If the General Manager
said that the total mill process loss should Mechanical Machinery Extracted Oil
have been below 1.5%, it should have been Extraction Ratio
applicable in all the mills. He had a point
there, but not a valid one as there were This is the ratio of the oil extracted from
other factors he had overlooked. a known weight of fresh fruit bunches (FFB)
to the corresponding weight of the FFB,
As this issue is widespread among using mechanical oil extraction plants and
the organisations, where the plantation machinery.
managers take charge of the mills, we
thought perhaps we should make some Solvent Extracted Oil Extraction Ratio

* Malaysian Palm Oil Board, This is the ratio of the oil extracted from
P. O. Box 10620, 50720 Kuala Lumpur, Malaysia. a known weight of FFB to a corresponding
E-mail: nravi@mpob.gov.my

PALM OIL ENGINEERING BULLETIN NO. 105 35

 Feature Article

weight of the FFB using chemical solvents OIL EXTRACTION EFFICIENCY

like hexane.
As oil extraction efficiency is seldom
Process Oil Losses highlighted by the millers as well as the
researchers, they do not know about
This refers to the oil losses incurred its importance in monitoring process
during the flow of FFB through the series performance.
of process steps. It is represented as a
percentage of the weight of the oil lost to Oil Extraction Efficiency
the weight of FFB that is subjected to the
process steps. It is the ratio of the declared mill: oil
extraction rate (OER) (E%) to the sum of
Table 1 gives the normally accepted losses the declared mill OER (E%) and the percent
at different process steps during mechanical total oil losses (L%) = E/(E+L)%.
processing. Process losses are always higher
during mechanical processing than during The following benchmarking assumes
the solvent extraction. Solvent extraction is that the optimum process parameters are
not environment-friendly as a considerable adhered to and the worn out machinery
quantity of hexane evaporates during the parts are replaced when due. At low process
solvent extraction process. In Table 1, all the temperatures, the oil loss will tend to rise.
likely losses during mechanical processing
are listed out. If in a mill, a particular loss Assuming that the six mills under a
like oil loss in EFB is not done, an arbitrary particular plantation group get the data
figure (usually accepted by the industry) shown in Table 2 during the first year
must be assigned instead of a zero value. of its operation when the mills want to
The mill may use the figures given in Table 1. benchmark its oil extraction efficiency soon
after commissioning the mills.
Total Oil Losses
Tables 3 to 8 demonstrates that the total
This is the sum of all the individual oil oil losses will rise up in tandem with the
losses at the different process steps. If we mill OER when mill efficiency remains
follow Table 1 the total oil loss is 1.77% unchanged as in most cases. Note that (E+L)
and for the purposes of our analysis of oil was derived from (OE/efficiency) and oil
extraction efficiency, we shall adopt this losses computed by subtracting E from it.
figure as the average value.

TABLE 1. APPROXIMATE OIL LOSS IN PALM OIL MILLS

Source % on loss/fresh fruit bunches

Fruit trapped in empty fruit bunches (EFB) 0.02
Un-stripped bunches (USB) 0.05
Oil absorbed on the surface of EFB 0.45
Condensate from sterilisation 0.10
Nut surface after pressing 0.05
Fibre after pressing 0.55
Sludge from separator 0.45
General oil spillages or washing from tanks 0.10
Total milling losses 1.77
Source: Ng, S B (1993).

36 PALM OIL ENGINEERING BULLETIN NO. 105

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TABLE 2. BENCHMARKING OIL EXTRACTION EFFICIENCIES

OF THE MILLS IN THE GROUP

Mill name OER: Total losses E+L Efficiency (%)

E (%) (L) % (%) E/(E+L)
A 18 1.5 19.5 92.3
B 19 1.5 20.5 92.7
C 20 1.5 21.5 93.0
D 21 1.5 22.5 93.3
E 22 1.5 23.5 93.6
F 23 1.5 24.5 93.9
Note: OER – oil extraction rate.

TABLE 3. MILL A: EXPECTED OIL LOSS AT VARYING OIL EXTRACTION RATE (OER) AND
FIXED EXTRACTION EFFICIENCY

Mill name OER: Total losses E+L Efficiency (%)

E (%) (L) % (%) E/(E+L)
A 18 1.50 19.50 92.3
A 19 1.58 20.58 92.3
A 20 1.67 21.67 92.3
A 21 1.75 22.75 92.3
A 22 1.83 23.83 92.3
A 23 1.92 24.92 92.3
Note: Refering to Table 3, despite the low OER at 18% the milling efficiency is the same as when the
OER is high at 23%. The same is demonstrated in Tables 4, 5, 6, 7 and 8.

TABLE 4. MILL B: EXPECTED OIL LOSS AT VARYING OIL EXTRACTION RATE (OER) AND
FIXED EXTRACTION EFFICIENCY

Mill name OER: E (%) Total losses (L) % E + L (%) Efficiency (%) E/(E+L)
B 18 1.42 19.42 92.7
B 19 1.50 20.50 92.7
B 20 1.57 21.57 92.7
B 21 1.65 22.65 92.7
B 22 1.73 23.73 92.7
B 23 1.81 24.81 92.7

TABLE 5. MILL C: EXPECTED OIL LOSS AT VARYING OIL EXTRACTION RATE (OER) AND
FIXED EXTRACTION EFFICIENCY

Mill name OER: E (%) Total losses (L) % E + L (%) Efficiency (%) E/(E+L)
C 18 1.35 19.35 93.0
C 19 1.43 20.43 93.0
C 20 1.51 21.51 93.0
C 21 1.58 22.58 93.0
C 22 1.66 23.66 93.0
C 23 1.73 24.73 93.0

PALM OIL ENGINEERING BULLETIN NO. 105 37

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TABLE 6. MILL D: EXPECTED OIL LOSS AT VARYING oil extraction rate (OER) AND
FIXED EXTRACTION EFFICIENCY

Mill name OER: E (%) Total losses (L) % E + L (%) Efficiency (%) E/(E+L)
D 18 1.29 19.29 93.3
D 19 1.36 20.36 93.3
D 20 1.44 21.44 93.3
D 21 1.51 22.51 93.3
D 22 1.58 23.58 93.3
D 23 1.65 24.65 93.3

TABLE 7. MILL E: EXPECTED OIL LOSS AT VARYING OIL EXTRACTION RATE (OER) AND
FIXED EXTRACTION EFFICIENCY

Mill name OER: E (%) Total losses (L) % E + L (%) Efficiency (%) E/(E+L)
E 18 1.23 19.23 93.6
E 19 1.30 20.30 93.6
E 20 1.37 21.37 93.6
E 21 1.44 22.44 93.6
E 22 1.50 23.50 93.6
E 23 1.57 24.57 93.6

TABLE 8. MILL F: EXPECTED OIL LOSS AT VARYING OIL EXTRACTION RATE (OER) AND
FIXED EXTRACTION EFFICIENCY

Mill name OER: E (%) Total losses (L) % E + L (%) Efficiency (%) E/(E+L)
F 18 1.17 19.17 93.9
F 19 1.23 20.23 93.9
F 20 1.30 21.30 93.9
F 21 1.36 22.36 93.9
F 22 1.43 23.43 93.9
F 23 1.49 24.49 93.9

A Note to the Millers REFERENCE

We would like to advise the millers to NG, S B (1993). Measurement of oil

benchmark the oil extraction efficiency of extraction rate (OER) and milling losses.
their mills. This should be done when all Proc. of the National Seminar on Palm Oil
the machinery are in a good condition and Extraction Rate: Problems and Issues. PORIM,
the process parameters are at optimum Bangi. p. 99-104.
level. By doing this, the millers can check
whether at any time the mill oil losses are a
cause for concern. Higher oil losses do not
reflect the poor performance of a mill.

38 PALM OIL ENGINEERING BULLETIN NO. 105