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92 ISSUE NO. 92 (July - Sept. 2009) LEMBAGA MINYAK SAWIT MALAYSIA MALAYSIAN PALM OIL BOARD KEMENTERIAN PERUSAHAAN PERLADANGAN DAN KOMODITI MALAYSIA MINISTRY OF PLANTATION INDUSTRIES AND COMMODITIES, MALAYSIA Website: www.mpob.gov.my

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Page 1: LEMBAGA MINYAK SAWIT MALAYSIA MALAYSIAN PALM OIL …palmoilis.mpob.gov.my/publications/POEB/poeb92.pdf · LEMBAGA MINYAK SAWIT MALAYSIA MALAYSIAN PALM OIL BOARD KEMENTERIAN PERUSAHAAN

PALM OIL ENGINEERING BULLETIN NO. 92 �

ISSUE NO. 92 (July - Sept. 2009)

LEMBAGA MINYAK SAWIT MALAYSIAMALAYSIAN PALM OIL BOARD

KEMENTERIAN PERUSAHAAN PERLADANGAN DAN KOMODITI MALAYSIAMINISTRY OF PLANTATION INDUSTRIES AND COMMODITIES, MALAYSIA

Website: www.mpob.gov.my

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PALM OIL ENGINEERING BULLETIN NO. 92 �

CONTENTS

Editorial

RECENT EVENTS

FORTHCOMING EVENTS 2009 MPOB Training Programme

2009 MPOB Conferences/Seminars

FEATURE ARTICLESEffluent Treatment Systems in Palm Oil MillsPart 1 - Anaerobic Digestion

Lubrication and Lubricant Selection

Hazards Associated with Processingin a Palm Oil Mill

Mongana Basics: Part 18 - Deperoxidation

MILLING DIALOGUE

TITBITS

DATASHEET Datasheet for Engineers

1

3

9

10

11

EDITORIAL BOARD

ChairmanDatuk Dr Mohd Basri Wahid

• Datuk Dr Choo Yuen May• Dr Lim Weng Soon• Dr Ma Ah Ngan

• Ab Aziz Md Yusof • Ir N P Thorairaj

SecretaryIr N Ravi Menon

Malaysian Palm Oil BoardMinistry of Plantation Industries and Commodities,

MalaysiaP. O. Box 10620, 50720 Kuala Lumpur, Malaysia

Tel: 603-8769 4400Fax: 603-8925 9446

Website: www.mpob.gov.my

© Malaysian Palm Oil Board, 2009All rights reserved.

No part of this publication may be reproduced, stored in a retrieval system, in any form or by any means, electronic,

mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher.

Products and services advertised in thisPalm Oil Engineering Bulletin do not

connote endorsement by MPOB.

AEditorial

see page 2

29

39

19

47

51

on monthly intervals. The minutes of such meetings should be religiously filed up. This culture had been going on for about two decades now because it is mandatory to do so. Some mills even have large display boards at the mill entry points where the number of ac-cidents, the date of last accident, etc. of the mill are displayed. This no doubt is a good practice as it is a useful information for visitors like the Occupational Safety and Health Authority (OSHA) staff.

Probably the time is ripe now for mills to go a step forward and start improving whatever they have. Safety equipment and safety awareness are not something that when once installed remains for ever. It undergoes constant metamor-phosis so that it can remain useful all the time. The following shortcomings still exist in most mills and millers are ad-vised to take note and consider enforc-ing some positive measures so that the safety features are part and parcel of our safety culture.

Most of the metal platforms in the press station become slippery when oil gushes out during pressing and the press operators just throw some fibre on them and it remains in that position the whole day. This can cause a fire if the press operator is a smoker himself. Does the safety committee meetings ever bring issues of this nature? No, because they are satisfied with the set-up. Once satisfaction sets in there is no more room for improvement.

ll palm oil mills are obliged to have safety committees and as-sociated regular meetings at least

53

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PALM OIL ENGINEERING BULLETIN NO. 92�

from page 1

CALL FOR ARTICLES

The millers are requested to send in articles of relevance to the palm oil industry in Malaysia for publication in Palm Oil Engineering Bulletin. By sharing your expertise you will be helping the industry and the nation as a whole. The topics of interest are:

1. Plant modifications done in your mill that resulted in improvements in milling operation or maintenance.

2. Innovations done in your mill that produced improvements in the operation of the mill and that you are willing to share them with others.

3. Any special work done in your mill that directly resulted in improvements in OER and product quality.

Please submit your article to us and we shall be pleased to publish them in Palm Oil Engineering Bulletin. Feel proud to have your articles published in this Bulletin that is circulated throughout the industry and MPOB offices worldwide.

It is possible sometimes for the man-ager to ask a worker to climb up a lad-der of say the flocculation tank or the overhead water tank little realizing that the steps are corroded at the joints and it might give way due to the weight of the person stepping on them. It might even be the boiler chimney which itself might collapse at any time and its ladder if any, is extremely dangerous to rely on in the course of testing the chimney body thick-ness. There are many such areas where tentacles of the safety committee cannot reach and will never reach unless there is clear perception of what can go wrong with each machinery or plant.

It is no use trying to do something after an accident has already taken place and lives have been lost. It is impossible for the OSHA officers to tell all millers what and how an incidence will take place. There is a tendency for all of us to look at

only known areas where an incidence has taken place before but the right approach is to look at all possibilities and take steps to prevent an incident from happening based on common sense. Millers may even go to the extent of thinking of the role of everyone in the mill should an aircraft crashes on the mill building like where the survivors should assemble, how to put off a fire, shutting down the boiler, etc.

One important aspect of safety of work-ers is to educate them. The best way to in-culcate safety awareness among workers is to give a brief talk on one selected topic every Monday morning. Do not make it long – not more than 15 min and if there are 26 topics, the topic will only be repeat-ed after half year. It will not be difficult to get 26 topics to talk about in a mill. If the management is serious about this, the results will be astounding. In this issue, some of the safety aspects of milling op-eration are highlighted.

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PALM OIL ENGINEERING BULLETIN NO. 92 �

Recent Events Contributed by: Noor Asmawati Abd Samad*

* Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur, Malaysia.

COSTAM/SFRR International

Workshop 2009A workshop on chemoprevention and trans-lational research was jointly organized by MPOB, the Confederation of Scientific and Technological Association (COSTAM) and Society for Free Radical Research (SFRR) at Meritus Pelangi Beach Resort & SPA, Lang-kawi on 9-12 July 2009.

The workshop attended by more than 200 participants was officiated by Raja Nazrin Shah Ibni Sultan Azlan Muhibbuddin Shah, the Regent of Perak. Prof Sten Orrenius from the Karolinska Institute, Sweden, presented the keynote address entitled Mitochondrial Regulation of Cell Death. During this work-shop, 120 posters were also presented.

Development of MPOB Research Station at

BelagaAnother MPOB research station was launched by Tan Sri Bernard G. Dompok, the Minister of Plantation Industries and Commodities, at Belaga, Sarawak on 21 July 2009. The Belaga Research Station will focus on the development of a model sus-tainable plantation, biodiversity research, cultivation of an oil palm plantation locat-ed on peat area and the establishment of a seedling park. The project costing RM 10.5 million commenced operation in August 2009 (under Ninth Malaysia Plan).

Dato’ Sri Dr James Jemut Masing, the Minister of Sarawak Land Development; Datuk Abit Joo, Member of Parliament for Ulu Rajang; Mr Liwang Lagang, State As-semblyman of Belaga; Dato’ Sabri Ahmad, Chairman of MPOB; Datuk Dr Mohd Basri Wahid, Director-General of MPOB and Mr Dahim Nadot, Resident of Kapit Sarawak, graced the occasion with their presence.

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PALM OIL ENGINEERING BULLETIN NO. 92�

Recent Events

MICCOS 2009Tan Sri Muhyiddin Yassin, the Deputy Prime Minister, officially launched MICCOS 2009, organized by the Ministry of Plantation In-dustries and Commodities on 13-16 August 2009 at the Malaysia Agro-Exposition Parks, Serdang (MAEPS), Selangor.

MICCOS is a biennial event that brings together major industry players and en-trepreneurs in the commodities sector. It is supported by agencies and councils under the ministry including MPOB and MPOC.

MICCOS 2009 showed a wide range of latest products as well as technological de-velopments and innovations in the Malay-sian commodities sector that included palm oil, timber, rubber, cocoa, pepper, tobacco, kenaf and sago under the theme Commodity is an Industry. It also featured the participa-tion of major producers, manufacturers and exporters, as well as agencies responsible for the development and promotion of these commodities.

2009 International Conference on Oil Palm

and the EnvironmentTan Sri Bernard G. Dompok, the Minister of Plantation Industries and Commodities launched the conference at MAEPS, Selan-gor on 14-15 August 2009. This international conference with the theme Harmonizing Oil Palm with the Environment attracted almost 350 participants.

The conference in which 23 papers were presented during the two-day session was intended to provide a platform for discus-sion of oil palm and its impact on the en-vironment, deliberate issues such as global warming and climate change, which has been a hot topic, leading to a great deal of debate and controversy.

MPOB Signed MoU with Three Companies

Datuk Dr Mohd Basri Wahid, the Director-General of MPOB signed an MoU with Mr Joseph Lim, Director of Global Green Syn-ergy Sdn Bhd for the collaborative R&D and commercial production of oil palm-based biomass briquette in a palm oil mill.

Datuk Dr Mohd Basri Wahid, also signed another MoU with Prof Zhang Zhen Jia,

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PALM OIL ENGINEERING BULLETIN NO. 92 �

Recent Events

Director of Environmental Science & Engineering Department, Shanghai Jiao Tong University and Ms Woo Min Fong, Chairman of Ronser Bio-Tech Sdn Bhd on palm oil mill effluent zero discharge treatment system.

The Director-General also signed another MoU with Berita Harian Sdn Bhd for the re-newal of contract on publishing Berita Sawit. Mr Mior Kamarul Shahid, the Group Chief Editor signed on behalf of Berita Harian Sdn Bhd while Tan Sri Bernard G. Dompok, the Minister of Plantation Industries and Com-modities witnessed the ceremony.

Scheme on Integration of Livestock to Smallholders

The integration of livestock scheme was launched on 18 August 2009 by Dato’ Hamzah Zainudin, the Deputy Minister of Plantation Industries and Commodities, at Selama, Perak with 219 smallholders par-

ticipating in the scheme. The Deputy Min-ister also presented cheques for the Replant-ing Scheme and the 2nd Economic Stimulus Package (PRE2) to 15 recipients from planta-tion companies and smallholders.

Dato’ Sabri Ahmad, Chairman of MPOB; Dr Salmiah Ahmad, Deputy Director-Gen-eral (Services) and Tuan Haji Idris Omar, Director of Integration Research and Exten-sion Division, MPOB were also present dur-ing the presentation.

Transfer of Technology Seminar, Sabah

Tan Sri Bernard G. Dompok, the Minister of Plantation Industries and Commodities, of-ficially launched the Transfer of Technology (TOT) Seminar, Sabah on 24 August 2009 at the Sabah Hotel, Sandakan, Sabah.

This seminar jointly organized by MPOB and the East Malaysia Planters Association (EMPA) was intended to disseminate the latest research results available for adoption and commercialization by the industry to increase productivity, add value, generate wealth and contribute to the well-being of the oil palm industry.

Dato’ Sabri Ahmad, Chairman MPOB; Datuk Dr Mohd Basri Wahid, Director-Gen-eral of MPOB and Datuk Dr Choo Yuen May, Deputy Director-General (R&D) MPOB were also present.

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PALM OIL ENGINEERING BULLETIN NO. 92 �

Forthcoming Events

2009 MPOB TRAINING PROGRAMME SCHEDULE

CODENO.

TITLE DATE VENUE

A COURSES

1 OIL PALM

A1.1 Kursus Kemahiran Menggred Buah Sawit

Bil. �: Wilayah Selatan (PPNJ) Peperiksaan Bil. �� (PPNJ)

��-�� April�� Okt.

Hotel Prime City, Kluang,

Johor

Peperiksaan Kemahiran Menggred Buah Sawit

Peperiksaan Bil. ��: Sabah � Disember PLASMA,Lahad Datu,

Sabah

A1.2 Kursus Operator Mekanisasi Ladang � Sept. �00�-�� Feb. �0�0

MPOB UKM

A1.3 Kursus Pengurusan dan Penyelenggaraan Tapak Semaian Sawit

Bil. �: Wilayah Timur ��-�� Ogos FELDA Residence, Sg. Tekam, Kuantan, Pahang

Bil. �: Wilayah Utara �-� Okt. Hotel SSH Traders,

Kemunting, Perak

2 PALM OIL

A2.1 Diploma in Palm Oil Milling Technology and Management (DIPOM)Semester IIIExam. Semester III

�� June - � July��-�� August

MPOB HQ

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PALM OIL ENGINEERING BULLETIN NO. 92�0

Forthcoming Events

Note: * To be confirmed. + By invitation. ** Course approved under PROLUS scheme of Pembangunan Sumber Manusia Berhad.

For enquiry or further information, please contact:

HRD & Conference Management UnitTel. No. : 0�-������00 ext. ����, ���0, ����Fax No. : 0�-��������E-mail : [email protected]’s website : http://www.mpob.gov.my

A2.2 The 23rd MPOB Oil Palm Products Surveying Course

The 22nd MPOB Oil Palm Products Surveying Examination

�-�0 December

February �0�0*

MPOB HQ

MPOB HQ

A2.3 Kursus Penyelia Kilang Minyak SawitPeperiksaan

�-� Ogos� Okt.

MPOB HQ

A2.4 Kursus Pengendali Makmal Kilang Minyak SawitPeperiksaan

�0-�0 Julai

�� Julai

MPOB HQ

A2.5 Colour Cosmetic Course �-� August

MPOB HQ/ AOTD

1. International Conference on Palm Oil and the Environment

��-�� August MAEP,Serdang,Selangor

2. International Workshop on Awareness, Detection and Control of Oil Palm Devastating Diseases

� Nov. KLCC, Kuala Lumpur

3. PIPOC �00� �-�� Nov. KLCC, Kuala Lumpur

4. SME TOT Seminar �00� � Dec. MPOB HQ

2009 MPOB CONFERENCES/SEMINARS

CODENO.

TITLE DATE VENUE

B CONFERENCES/SEMINARS

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Feature Article

Effluent Treatment Systems in Palm Oil Mills:Part 1 - Anaerobic Digestion

N Ravi Menon* and Lai Mei Ee*

T

* Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur,

Malaysia.

INTRODUCTION

fundamentals in the effluent treatment sys-tem practiced in most mills. Some of the readers who have already acquired deeper knowledge of the subject may skip this top-ic or use this as a reference material.

The basic need to treat the palm oil mill effluent before discharging it to the water course is to make it suitable for marine life to survive in it, in terms of the quantity of dissolved oxygen required to oxidize the organic and inorganic contents of the efflu-ent stream. There are two tests for establish-ing this (a) biochemical oxygen demand or BOD and (b) the chemical oxygen demand or COD.

BIOCHEMICAL OXYGEN DEMAND

It is always refreshing to trace back the his-tory to gain some insight on how this term, BOD originated. According to historical background, the British Royal Commission on River Pollution, established in 1865 and the Royal Commission on Sewage Disposal in 1898 led to the selection in 1908 of BOD5 as the definitive test for the organic pollu-

his article is intended to refresh the memory of millers who, over a pe-riod of time might have lost sight of

tion of rivers. The subscript five refers to the number of days the selected micro organ-isms used up the oxygen in a sample of wa-ter kept in a sealed bottle at 20oC in a dark room. The five days period was selected for this test as this was the longest time required for the water to flow from the source to the estuary of the longest river in United King-dom. In 1912, the Commission also set up a standard of 20 mg litre-1 BOD5 as the maxi-mum concentration permitted in sewage works discharging to rivers, provided that it is diluted eight times before discharging at dry weather flow. This was contained in the land mark 20:30 (BOD: suspended solids) plus full nitrification standard, which was used as a yardstick in the United Kingdom up to the 1970s for sewage works effluent quality.

The BOD5 test is carried out as follows: • dilute the effluent sample with de-ion-

ized water, saturated with oxygen;• inoculate with a small fixed aliquot of

seed to this as well as the control sam-ple;

• measure the dissolved oxygen (DO);• seal the test bottle to prevent further

entry of oxygen;• store the bottle in a dark room at 20oC

for five days; and • measure the dissolved oxygen again.

The difference in DO is the BOD. Correct the result by subtracting the apparent BOD from the control sample.

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PALM OIL ENGINEERING BULLETIN NO. 92��

Feature Article

The biochemical demand, as the term im-plies is a chemical procedure for establish-ing the speed at which the biological organ-isms use up the oxygen in a body of water or effluent. According to some sources, BOD is not an accurate quantitative test. This is quite obvious as it fails to take into consid-eration the inorganic compounds that also will invariably participate in the oxidation process. Nevertheless, it can be used to give a rough indication of the quality of the wa-ter source like rivers.

CHEMICAL OXYGEN DEMAND

This method is more accurate to measure the chemical oxygen demand (COD). The COD is the measure of the capacity of wa-ter to consume oxygen during the decom-position of organic matter and the oxida-tion of inorganic chemicals. The chemical oxygen test is commonly used to indirectly measure the amount of both organic and in-organic compounds that can be chemically oxidized, the exception being the oxidation of ammonia into nitrate (which is referred to as nitrification) and the oxidation of ac-etate.

In the case of BOD, it only measures the amount of oxygen consumed by microbial oxidation, whereas COD measures the oxy-gen consumed by both organic and inorgan-ic compounds with some exceptions. The COD does not measure the oxygen consum-ing potential of certain organic compounds like acetate but it can be metabolized by micro organisms and would therefore be detected in a BOD test. Similarly, the oxy-gen consuming potential of cellulose is not measured during a short-term COD test but can be detected in a BOD analysis (Rank, 2009).

In the standard test, a fixed quantity with a known excess amount of the oxidant, po-tassium dichromate (K2 Cr2 O7) is added to a sample of the solution being analysed. After a refluxing digestion step, the oxidant used up by the organic and inorganic substances

in the sample is determined from titrimetric or spectrophotometric measurement of the oxidant still remaining in the sample.

ANAEROBIC DIGESTION PROCESS

During this process, biogas is generated. It will be interesting to note that biogas was produced using anaerobic digestion in the 10th century BC in Assyria, where the gas was used for heating bath water and very much later in the 16th century, Persia also used biogas for water heating. In the 17th century, Jan Baptita van Helmont observed that decaying organic matter produced flammable gases. In 1776, Count Alessandro Volta found that the volume of gas produced was proportional to the decaying volume of organic matter.

In 1808, Sir Humphry Davy reported that methane was present in the gases produced by cattle manure. The first anaerobic digest-er was built by a leper colony in Bombay, India in 1859. In 1895, the technology was further developed in Exeter, England where a septic tank was used to generate biogas for street lighting. This was followed by the setting up of a dual purpose tank in Hamp-ton, England for both sedimentation and sludge treatment. In Germany, a patent was issued for the Imhoff tank shown in Figure 1, an early form of digester.

Through scientific research, anaerobic di-gestion gained academic recognition in the 1930s. This led to the discovery of anerobic bacteria, the micro organism that facilitate the anaerobic digestion process. This was subsequently extended to find out the con-ditions under which the methanogenic bac-teria were able to grow and reproduce. This work was carried out during World War II by both Germany and France, where there was an increased interest in anaerobic di-gestion for treatment of animal manure.

Any organic material can be subjected to anaerobic digestion. This includes waste materials like waste water, grass clippings,

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Feature Article

left-over food, sewage and animal waste. Anaerobic digestion can also be fed with specially grown energy crops to boost bio-degradable content and hence, increase bi-ogas production. Some pre-treatment will be necessary to remove unwanted things in the feed before it is ready for treatment.

There are four stages of anaerobic diges-tion: (1) hydrolysis, (2) acidogenesis, (3) ac-etogenesis and (4) methanogenesis.

• Hydrolysis. The digestion process begins with bacterial hydrolysis of the input materials in order to breakdown insolu-ble organic polymers such as carbohy-drates and complex organic compounds like protein and lipids and make them available for other bacteria. During this process, they are converted into simpler molecules like amino acids, sugar and fatty acids by the actions of extra-cellu-lar enzymes from hydrolytic micro or-ganisms.

• Acidogenesis. During this process, fur-ther breakdown occurs. The hydrolysed products are fermented, forming simpler organic compounds particularly vola-tile fatty acids (VFA) and also producing ammonia, carbon dioxide and hydrogen sulphide as by-products.

• Acetogenesis. The simple molecules from acidogenesis are further digested by ac-etogens to produce carbon dioxide, hy-drogen and mainly acetic acid.

• Methanogenesis. During this process, the VFA are converted to methane, carbon dioxide and water produced by metha-nogens.

The overall generic equation for the proc-ess can be written as:

C6 H12 O6 ➞ 3CO2 + 3CH4

The retention time in these ponds is about 40 days and as a result, these ponds are deep (3 to 4 m deep) in order to minimize

the surface area so that there is less exposure to atmosphere. The organic loading is also low at 0.65 to 1.3 kg volatile solid per cubic metre of pond capacity.

VARIATIONS OF ANAEROBIC DIGESTER SYSTEMS

• Open steel tank digesters. This uses the same principle as the open pond sys-tem except that the solid from these tanks can be easily monitored and dis-charged;

• Enclosed steel tank digesters. These are high rate digesters capable of handling an organic loading of up to 4.8 kg vola-tile solid loading per cubic metre of di-gester capacity. This type of digesters can be equipped with stirrers and gas compressors. The contents of the digest-ers are well mixed and homogeneous so that it has excellent contact with the mi-cro organisms. The temperature also is uniform. The solids retention time is the same as the hydraulic retention time so that the effective capacity of the plant can be maintained. In this system, the biogas can be efficiently tapped with-out leakage. The only disadvantage is the additional cost when compared to conventional earth ponds. This also oc-cupies 20% of the land needed for the conventional ponds.

• Anaerobic contact digester. This is almost the same as the enclosed steel digester except that in this, the digested slurry is recycled back to the digester making this more stable than the conventional system as the micro organism popula-tion and the organic volatile solids are more balanced.

System Stability

The anaerobic process is not very stable and is very sensitive to environment. There are a wide variety of anaerobic bacteria. It is difficult to maintain a balance between the organic feed and the bacterial population.

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PALM OIL ENGINEERING BULLETIN NO. 92��

Feature Article

The hydrolysis and fermentation phases are stable as the organisms are fairly well bal-anced and the environment being condu-cive, they can thrive easily.

They are also able to respond to variation in feed volume. These bacteria are able to rapidly increase the volatile acid production rate as and when the feed rate increases. A rapid rise in volatile acids is kept in check by the buffer carbon dioxide in the form of ammonium bicarbonate alkalinity. How-ever, during shock loading, the buffer al-kalinity may not be able to keep the acidity under check as the pH falls below the nar-row acceptable limits of acetogens and the methogens, and the system will fail. When this happens, the methane production stops and the acid level rises beyond the tolerance levels.

Temperature

The temperature in the digester must be maintained fairly steady as it is a critical fac-tor to maintain. Fluctuation in temperature is harmful for the digester.

Toxic Materials

It is important to find out the unaccept-able materials that are present in the feed. Several substances are toxic to the system such as heavy metals, chlorinated com-pounds and detergents. Pre-treatment may be necessary in some cases.

Process Sensitivity

Methanogens are very sensitive to pH and temperature. They operate between a pH range of 6.5 and 7.5. Slight deviation on either side of this scale will quickly affect their metabolic rates and slows or totally stops methane production. The optimum temperature is 35oC. Here again, methane production rate slows down if the tem-perature deviates from this to either side. Methanogens are the deciding factor for the whole system as they are the weakest link. Irrespective of the performance of the meth-

anogens, the VFA formers will generate the VFA. If this is not taken up by the sensitive methanogens, the system will stop produc-ing methane. Therefore, a smooth flow must be established for the continuous operation of the flow in the process. Causes of System Failure

• Shock loading. This can happen when the oil content in the effluent is substantial-ly more than normal values either due to a spillage or failure of oil recovery from de-oiling tank. It can also happen when mills operate longer hours than normal.

• Sudden starvation of organic loading. Mill stops operation for a few days depriv-ing the bacteria from having food.

• Sudden increase in operating temperature. This can happen if the cooling ponds are by-passed for some reason or dur-ing very hot season.

• Contamination with a toxic material. In a mill, this may not take place. However, there are instances when mills have disposed toxic wastes in their effluent ponds. This may kill the bacteria.

• Pumping out excess supernatant. This will reduce bacteria population.

Suggested Operational Procedures

It is important to ensure the follow-ing for the system to operate efficiently: (a) there is a consistent feeding of effluent into the digester, (b) the temperature does not fluctuate widely and (c) the effluent is well mixed. The following operational pro-cedures are useful for the healthy operation of the digesters:

• the raw sludge input should be stored in a buffer pond and a regulated vol-ume of effluent fed into the digestion ponds so that the digester loading is maintained constant all the time. The nutrients for the bacteria are carbon, nitrogen, phosphorous and trace ele-ments to allow them to multiply. The optimum carbon to nitrogen ratio is be-

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Feature Article

tween 20:1 to 30:1. If the nitrogen con-tent is too low, the micro organism will not be able to produce the enzymes but if it is too high particularly if in the form of ammonia, the growth of micro organisms will be inhibited. Optimum carbon content can be estimated from COD. The optimum COD/N and COD/P are reported to be 100:1.25 and 100:0.25 respectively;

• maintain the optimum retention time to enable the slowest growing organ-ism to feed on the sludge. This can be done by not overflowing the digested effluent out of the pond;

• high concentration of VFA, actions, heavy metal ions, aromatic compounds, free ammonia and sulphide are consid-ered as toxic to anaerobic bacteria;

• maintain a constant temperature under all circumstances by ensuring a con-stant flow through the sludge heaters. Mesophillic bacteria has a temperature range of 35°C to 40°C, whereas ther-mophillic bacteria has an optimum temperature range of 55°C to 60°C;

• optimum pH lies between 7.0 and 7.2. Acid forming bacteria produces VFA which will reduce the pH but this is neutralized by the methane producing bacteria that breakdown these VFA and also by the reformation of ammonia bi-carbonate buffer during methanogene-sis. If any imbalance develops, the acid forming bacteria outpace the methane producing bacteria causing the digester content to turn sour and the methane production will cease. The optimum methane production is reported to oc-cur at redox potential between -520 and -530 mV;

• maintain pH balance by addition of al-kalis preferably using automatic con-trol system with feedback loop; and

• ensure that the gas composition is in the proper and consistent range.

In case, the digester turns sour:

• the first thing to do is to control the rate of feeding or totally stop feeding;

TABLE 1. CHARACTERISTICS OF DIGESTED EFFLUENT AFTER TREATMENT IN A CONTACT DIGESTER AS WELL AS A CONVENTIONAL DIGESTER

Final discharge

Parameter Feed No. 1 No. 2 No. 3 Contact digester

Conventional ponds

Temperature oC - 43.2 43.0 42.8 42.4 43

BOD, mg litre-1 17 900 381 364 414 218 1 900

COD, mg litre-1 51 700 9 209 10 785 13 522 6 388 -

TS, mg litre-1 28 900 11 228 12 560 16 178 14 046 -

SS, mg litre-1 20 000 7 640 8 900 11 950 5 060 3 725

O&G, mg litre-1 4 400 110 194 138 150 172

TN, mg litre-1 360 258 264 302 193 176

pH 4.7 7.2 7.3 7.3 7.3 7.15

VA, mg litre-1 - 240 348 156 - 266

Alkalinity, mg litre-1 - 2 750 2 750 2 750 - 2 300

Note: Rank, J (2009). http://Science.jrank.org/pages/1388/chemical-oxygen-demand. html

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PALM OIL ENGINEERING BULLETIN NO. 92��

Feature Article

• recycle the seed sludge from active di-gester or from digester overflow;

• increase stirring operation to help re-cover bacteria balance;

• monitor VFA and the alkalinity; and • keep records of all data as stated. This

is basic but more data may be recorded as necessary.a) gas production rate as m3 of sludge.b) gas composition – hourly analysis.c) pH of sludge – hourly reading.d) percentage of VFA in the digester.e) temperature of the sludge-continu-

ous recording.f) percentage of dry solid in raw sludge

and digested sludge-hourly to make

Figure 1. Standard rate single stage steel anaerobic digester tank.

sure that the process is working properly. Dry the sample in an oven at 500oC and compare the residue.

Steel Digester Tanks

Probably all mills may have to resort to this type of tanks if the industry is serious about tapping the potential biogas for pow-er generation. In steel tanks, the biogas gen-erated as a result of anaerobic digestion can be easily harnessed and utilized. As mixing and heating can also be easily incorporated in the system, the temperature can also be maintained. This will ensure more efficient capture of biogas. Figure 2 shows a standard type anaerobic digester.

Gas out

SupernatantSupernatant out

Raw sludge in

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Figure 2. Two-stage high rate anaerobic digester.

The standard reactors have air tight cov-ers and are suitable for throughputs not ex-ceeding 4000 t per day. This is far more than what any palm oil mill is capable of produc-ing in a single day. Sludge is admitted to the reactor intermittently. The supernatant is withdrawn and returned to the secondary treatment unit. The digested sludge accu-mulates at the bottom from where it is dis-posed off at regular intervals. Some mixing occurs at the active digestion zone due to the recycling of heated sludge.

The high rate digesters are smaller in size than the single stage units. In the first stage, the sludge is mechanically mixed for efficient mixing of the organic matter with

the bacteria. Heating is done to promote the metabolic digestion process. In the second stage, the sludge is allowed to stratify or form into layers. No heating is provided in the second stage as not much gas is expect-ed to generate here. Nevertheless, some gas is generated and is accumulated at the top of the floating cap. The supernatant, scum and digested sludge are discharged form this unit.

Types of Conventional Anaerobic Reac-tors

Some of the conventional anaerobic di-gestion systems are shown in Figure 3. It is not possible to show all types in this article.

Feature Article

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PALM OIL ENGINEERING BULLETIN NO. 92��

Figure 3. Types of anaerobic digestion tanks.

Feature Article

(a) SEPTIC

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

ABSTRACT

rate them. The force which resists relative move-ment between two surfaces in contact is known as friction, a consequence of which heat is gener-ated, energy consumed and wear. Any substance which is used to reduce the friction is known as a lubricant. Boundary and elastohydrodynamic lubrication are the two main regimes of lubri-cation which can be determined from Stribeck Curve. Type of motion, speed, temperature, load and operating environment are parameters of the tribological system that needs to be consid-ered and analysed so that the best lubricant for a specific application can be selected. Usually the specifications of a lubricant are determined by the respective equipment manufacturers. Used oil analysis is crucial for preventive maintance, equipment failure diagnosis, abnormal operating condition assessment, oil condition monitoring and checking for contamination. The tribology analysis shows that low viscosity lubricants are suitable for high speeds, high temperature and low pressures whereas high viscosity lubricants are good for low speeds, low temperature and high pressures.

Feature Article

T

Lubrication and Lubricant SelectionAndrew Yap Kian Chung*

* Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur,

Malaysia.

he actual contact of two surfaces is only at the peak of their asperities and great force is needed to sepa-

INTRODUCTION

Lubricant and lubrication are common is-sues in all palm oil mills, thus, it is useful to understand the theory of lubrication and proper selection of lubricant. The main func-tion of lubricant is to provide hydrostatic, hydrodynamic or elasto-hydrodynamic lu-brication by forming a physical barrier to keep moving parts apart so that friction, surface fatigue, formation of wear particles, heat generation, operating noise and vibra-tions could be reduced. Besides lubrication, liquid lubricant may also provide hydro-static power transmission based on the Pas-cal’s law or serves as a coolant (Wikipedia, 2009a).

A liquid lubricant usually with high spe-cific heat capacity typically contain 90% base oil and 10% additives to impart desir-able characteristics. Petroleum mineral oils, lanolin, vegetable oils and synthetic liquids such as hydrogenated polyolefins, esters, silicone, fluorocarbons and many others are used as base oils. Table 1 shows several types of lubricant base oils designated by the American Petroleum Institute (API). Addi-tives such as friction modifiers that chemi-cally bind to metal surfaces reduce surface friction even when there is insufficient bulk lubricant present for hydrodynamic lubri-cation. Detergent and dispersant additives could assist in debris and contaminant transport to the filter and their removal.

Feature Article

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PALM OIL ENGINEERING BULLETIN NO. 92�0

Feature Article

Anti-wear additives improve the perform-ance against wear and fatigue. Table 2 shows the common additives and their functions. Sulphur impurities in fuels, biodiesel and 2-T oil added to fuels provide some lubrica-tion properties to the fuel.

A good lubricant should cater for spe-cific operational environment needs of a machine such as dry, wet, cold, hot, fire risk, high load, high or low speed, chemical compatibility, atmospheric compatibility, pressure or vacuum and various combina-tions. The usual thermal characteristics are indicated as SAE number at 100°C, like SAE 30 and SAE 40. On low temperature scale, it is given as SAE xxW. Both markings can be combined together to form for example SAE 0W-60. Viscosity index (VI) marks vis-cosity changes with temperatures, with the higher VI numbers being more temperature stable. Total base number does not measure the accumulation of oxidation products or antioxidants, rather, it measures the deple-tion of a detergents present in an engine oil for the purpose of neutralizing acidic blow by gases which occurs due to low levels of antioxidants within the oil. As the deter-gent is consumed during its role of neutral-izing sludge and varnish, the base number decreases from its original new oil value. Monitoring this consumption allows one to

TABLE 1. AMERICAN PETROLEUM INSTITUTE LUBRICANT BASE OIL

Group Specification

I Less than 90% saturates and/or more than 0.03% sulphur, and SAE viscosity index of 80 to 120 such as 150 SN, 500 SN, and 150 BS.

II More than 90% saturates and less than 0.03% sulphur, and SAE viscosity indexing of 80 to 120 which has superior antioxidation properties.

III More than 90% saturates and less than 0.03% sulphur, and SAE viscosity index more than 120.

IV Polyalphaolefins (PAO).

V All others not included above such as naphthenics, PAG and esters.

Note: SAE - Society of Automotive Engineers.

pro-actively replenish the oil through be-fore the protection afforded by that additive is lost. Thus, high number in fact indicates a high detergent content that will keep the engine clean but the base oil can oxidize or breakdown faster than one with higher lev-els of antioxidants which will prevents ac-ids by neutralizing the acids as opposed to cleaning up the by-products of the oxidized oil. Lubricants degrade primarily due to the presence of free radicals that will attack against the base oil chemical composition and change their physical properties such as viscosity (Wikipedia, 2009b).

Solid lubricants include grease, organic polymers such as teflon (PTFE), non-metal components such as graphite, hexagonal boron nitride, molybdenum disulphide and tungsten disulphide, and metal-alloy such as cadmium and gold used for electro-plat-ing surfaces, lead, tin, zinc alloys and vari-ous bronze alloys used in bearings. Some of these solid lubricants are used as additives in grease. The generation of a compacted ox-ide glaze layer from metallic surfaces sliding against each other at high temperature is a phenomenon in relation to wear prevention and lubrication. The elimination of metallic contact and adhesion by the generated glaze layer will reduce friction and wear thus be-come self-lubricating.

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Feature Article Feature Article

TABLE 2. COMMON ADDITIVES AND FUNCTIONS

Additive Typical compounds Functions

Antifoamant Silicone polymers, organic copolymers. Reduces surface tension to speed collapse of foam.

Antioxidant Zinc dithiophosphates, hindered phenols, aromatic amines, sulphurized phenols.

Decompose peroxides and terminate free-radical reactions.

Anti-wear and EP agent

Zinc dithiophosphates, organic phosphates, acid phosphates, organic sulphur and chlorine compounds, sulphurized fats, sulphides and dissulphides.

Chemical reaction with metal surface to form a film with lower shear strength than the metal, thereby preventing metal-to-metal contact.

Corrosion and rust inhibitor

Zinc dithiophosphates, metal phenolates, basic metal sulphonates, fatty acids and amines.

Preferential adsorption of polar constituent on metal surface to provide protective film, or neutralize corrosive acids.

Detergent Metallo-organic compounds of sodium, calcium and magnesium phenolates, phosphonates and sulphonates.

Chemical reaction with sludge and varnish precursors to neutralize them and keep them soluble.

Dispersant Alkylsuccinimides, alkylsuccinic esters and mannich reaction products.

Contaminants are bonded by polar attraction to dispersant molecules, prevented from agglomerating and kept in suspension due to solubility of dispersant.

Friction modifier

Organic fatty acids and amides, lard oil, high molecular weight organic phosphorus and phosphoric acid esters.

Preferential adsorption of surface-active materials.

Metal deactivator

Organic complexes containing nitrogen or sulphur, amines, sulphides and phosphites.

Form inactive film on metal surfaces by complexing with metallic ions.

Pour point depressant

Alkylated naphthalene and phenolic polymers, polymethacrylates, maleate /fumerate copolymer esters.

Modify wax crystal formation to reduce interlocking.

Seal swell agent

Organic phosphates and aromatic hydrocarbons.

Chemical reaction with elastomer to cause slight swell.

Viscosity modifier

Polymers and copolymers of olefins, methacrylates, dienes or alkylated styrenes.

Polymers expand with increasing temperature to counteract oil thinning.

Source: http://www.bobistheoilguy.com

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PALM OIL ENGINEERING BULLETIN NO. 92��

Lubrication is the process or technique employed to reduce wear of one or both sur-faces in close proximity, and moving relative to each other, by interposing a substance called lubricant between the surfaces to carry or to help carry the load between the opposing surfaces. It can also be described as the phenomenon that result in the reduc-tion of wear without human intervention. In the most common case, the applied load is carried by the pressure generated within the fluid due to the frictional viscous resistance to motion of the lubricating fluid between the surfaces. As the load increases on the contacting surfaces, three distinct situations can be observed with respect to the mode of lubrication, which are called regimes of lubrication.

• Fluid film lubrication is the lubrication regime in which the load is fully sup-ported by the lubricant through viscous forces within the space or gap between the parts in motion relative to one an-other (the lubricated conjunction) and solid-solid contact is avoided.

• Hydrostatic lubrication is when an ex-ternal pressure is applied to the lubri-cant in the bearing to maintain the fluid lubricant film where it would otherwise be squeezed out.

• Hydrodynamic lubrication is where the motion of the contacting surfaces, and the exact design of the bearing is used to pump lubricant around the bearing to maintain the lubricating film. This de-sign of bearing may wear when started or stopped, as the lubricant film breaks down.

• Elastohydrodynamic lubrication. The opposing surfaces are separated but there occurs some interaction between the raised solid features called asperi-ties, and there is an elastic deformation on the contacting surface enlarging the load bearing area whereby the viscous resistance of the lubricant becomes ca-pable of supporting the load.

• Boundary lubrication. The bodies come into closer contact at their asperities; the heat developed by the local pressures causes a condition which is called stick-slip and some asperities break off. At the elevated temperature and pressure conditions, chemically reactive constitu-ents of the lubricant react with the con-tact surface forming a highly resistant tenacious layer, or film on the moving solid surfaces (boundary film) which is capable of supporting the load and major wear or breakdown is avoided. Boundary lubrication is also defined as that regime in which the load is carried by the surface asperities rather than by the lubricant.

Lubrication theory can be seen as exploit-ing the disparity between two length scales. The first is the characteristic film thickness, H, and the second is a characteristic sub-strate length scale L. The key requirement for lubrication theory is to minimize the ra-tio ε =

. The Navier-Stokes equations are

expanded in this small parameter, and the leading-order equations are then:

∂p/∂z = 0 ∂p/∂x = ∂2u/∂z2 (1)

where x and z are coordinates in the direc-tion of the substrate and perpendicular to it respectively. Here, p is the fluid pressure, and u is the fluid velocity component paral-lel to the substrate (Wikipedia, 2009c).

TRIBOLOGY

Tribology is the science and technology of interacting surfaces in relative motion in-cludes the study and application of the principles of friction, lubrication and wear. When one material slides or rubs over an-other, it is affected by complex tribological interactions. Leonardo Da Vinci (1452-1519) was the first to enunciate two laws of fric-tion where:

• the frictional resistance is the same for two different objects of the same weight

HL

Feature Article

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

NOMENCLATURE

SI unit

E Modulus of elasticity N m-2

H Film thickness m

L Characteristic substrate length scale m

N Speed M s-1

P Load projected on to the geometrical surface N

R Cylindrical radius m

di Inner diameter m

do Outter diameter m

h Lubricant film thickness m

hu Uniform lubricant film thickness m

h0 The minimum lubricant film thickness m

k Specific viscosity -

m Total number of asperities -

p Fluid pressure N m-2

q Reduced pressure N m-2

r1 Roller radius m

r2 Inner ring raceway radius m

u Fluid velocity m s-1

v Mean velocity m s-1

x Direction coordinates -

z Direction coordinates -

α Pressure-viscosity coefficient m2 N-1

β The deformation of the cylindrical surface m

δ The normal relative displacement of distant points in the two surfaces m

Ø Poisson’s ratio -

ε Thickness to length scale ratio -

σ Composite roughness of the two contact surfaces m

λ Specific film thickness -

η Dynamic viscosity N m2 s-1

η0 The pre-exponential viscosity coefficient N m2 s-1

Feature Article Feature Article

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PALM OIL ENGINEERING BULLETIN NO. 92��

The first parameter of the tribological system involves the type of motion which may be sliding requires the hydrodynamic lubrication theory for its analysis, or roll-ing where elastohydrodynamic lubrication theory would be applied.

Speed is the second parameter on the tri-bological system which can be broken into the general ranges of fast, moderate and slow determined by the speed factor.

Speed factor = η[ ] (2)

where di is the inner diameter and do is the outer diameter of a bearing.

The third tribological parameter is tem-perature. All lubricants have specific tem-perature ranges for optimal performance. There are some greases with synthetic hy-drocarbon-based oil and barium-complex thickener that can operate at temperatures as low as -60°C and greases with perfluori-nated aliphatic ether base oil thickened with polytetrafluoroethylene (PTFE) that can lu-

(di + do)2

but making contacts over different widths and lengths; and

• the force needed to overcome friction is doubled when the weight is doubled.

Based on the results of Professor Richard Stribeck (1861 – 1950), the friction regimes for sliding lubricated surfaces are related to a dimensionless lubrication parameter ηknown as Stribeck number where η is the dynamic viscosity, N is the speed of move-ment and P is the load projected on to the geometrical surface could be categorized into (i) solid/boundary friction, (ii) mixed friction, and (iii) fluid friction as shown in the Stribeck curve (Figure 1) (Wikipedia, 2009d).

There are five parameters of the tribologi-cal system to be considered and analysed so that the best lubricant for the specific appli-cation could be selected. However, the infor-mation obtained by defining the tribological system parameters also provides data for further in-depth technical analysis.

Figure 1. Stribeck curve.

Feature Article

Fric

tion

coef

ficie

nt

NP

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

bricate an oven chain bearing at 220°C for more than 15 000 hr. Knowing the tempera-ture of the tribological system enables the engineer to select a lubricant that will pro-vide optimum operating life and perform-ance at the application temperature.

Load is the fourth parameter on the tribo-logical system which is an important factor affecting the lubricant requirement.

The last parameter of the tribological sys-tem is the application’s operating environ-ment (Wikipedia, 2009d). Food safety issues need to be considered for lubrication points in food industries which could be critical control point. Federal Food and Drug Ad-ministration (FDA) defines ingredient and its concentration of lubricants that can con-tact with food in Group 21 CFR 178.3570 and US Department of Agriculture (USDA) later replaced by National Sanitation Foun-dation (NSF) since September 1998 classify approved food grade lubricants into two classes which are H1 – incidental food con-tact lubricant and H2 – no food contact pos-sible (Shell, 2000).

BOUNDARY LUBRICATED CONTACT MODELS

Lubricating layers as small as a single mol-ecule are capable of producing significant improvements in reduced friction and wear which is the subject of boundary lubrica-tion. Boundary friction and wear consists of a shear or adhesion component and a plow-ing or deformation component. The shear component predominates except when as-perities sink too deeply into a boundary lubricant film or a soft opposing surface. When movement or sliding occurs, the shear friction force depends on the shear re-sistance per unit area of any boundary film in the real load-supporting area between as-perities (George and Fennell, 2007). The to-tal load support of a rough surfaces contact could be defined as:

P = + dA (3)

where m is the total number of asperities and A is the area subject to hydrodynamic fluid pressures.

Boundary lubrication is the formation and maintenance of a single or multi-mo-lecular layer of lubricating material so as to prevent as much as possible the direct dry contact of the solid surfaces in the tribo-logical couple. Many chemicals form films when certain organic compounds react with the metal surfaces. Intervening films such as oxide material in the film intimate contact with the metal surface underneath and sulphide layers are good examples of chemical film effective in reducing friction and wear. Combinations of pure parafin oil and small amounts of fatty acid such as lauric acid can reduce friction effective-ly. The resulting metallic soap molecules formed at the surface perform well un-til the temperature becomes so high that soap melts and film breakdown. As a gen-eral rule, polar molecules such as straight chain organic molecules with one polar end, exhibit strong affinity for bare metal surfaces by physical adsorption, chemi-cal adsorption or by chemical reaction, are ideal candidates as boundary lubricants. Longer chain molecules or the presence of more than one molecular layer of lubricat-ing material leads to improve tribological performance. Surface coatings of materials with layered crystallographic structures, specifically graphite and molibdenum di-sulphide can also reduce friction and wear.

ELASTOHYDRODYNAMIC LUBRICATION MODELS

Elastohydrodynamic lubrication theory is used to identify thickness of lubricant film in a rolling contact that both surfaces are as-sumed perfectly smooth. The analysis starts with the appropriate form of Reynolds equation to incorporate the pressure sensi-tivity of viscosity followed by the Hertzian contact concept which gives the stress and strain fields as well as the deformation of unlubricated surfaces in contact under load and combined with the viscous effect. A

∑pii=1

m∫area p

Feature Article

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PALM OIL ENGINEERING BULLETIN NO. 92��

contact area with an approximately uniform film thickness, hu, is created while outside the uniform thickness zone the film thick-ness, h, varies approximately parabolic with distance in a pressurized liquid film. Con-sider now the analysis of pressure profiles in lubricating films incorporating the effect of elastic deformation of contacting solids. A common feature of full film hydrody-namic lubrication system is the presence of converging or diverging gaps around a min-imun clearance point. Since Hertzian con-tacts contain converging or diverging wedg-es, lubrication behaviour can be expected to occur under dynamic conditions. Under the combined influence of solid elasticity and fluid viscosity pressures in the liquid, film may rapidly rise up to Hertzian solid contact levels. As a result, the film thickness becomes approximately constant and equal to hu within the contact area. However, in order to maintain continuity and to com-pensate for the loss of viscosity towards the contact exit, a constriction of the gap down to size h0 is formed near the downstream exit. As a consequence, a pressure spike is formed and this is followed by a subsequent decay to values below the Hertz solution. The pressure on the upstream side lies also below the Hertzian value while it extends a greater distance towards the upstream di-rection. For line contact to two cylinders, the gradient in reduced pressure is given by:

= 6vη0 ; q ≈ = dx (4)

where q is reduced pressure and η0 is the pre-exponential viscosity coefficient. Grubin solved the above equation numerically by assumed the surfaces have the deformed shape of an unlubricated contact but sepa-rated by a gap h given by:

h = + β - δ (5)

where R is cylindrical radius, β is the de-formation of the cylindrical surface and δ is the normal relative displacement of distant points in the two surfaces. The minimum film thickness, h0 in a rolling contact situa-

tion which forms the basis for elastohydro-dynamic lubrication theory could be deter-mined as (Lauer, 2009):

h0 = •

(6)

where α is pressure-viscosity coefficient, v is the mean velocity, r1 is roller radius, r2 is inner ring raceway radius, E is modulus of elasticity and Ø Poisson’s ratio. It can be de-termined that if the pressure-viscosity coef-ficient is doubled, the film thickness increase by 51%. If the dynamic viscosity which can be directly related to the kinematic viscosity is doubled, the film thickness will increase by 62%. If the velocity of the roller bearing is doubled, the film thickness of the lubri-cant will be increased by 62% as well. Since surfaces are not perfectly smooth in real-ity, the elastohydrodynamic film thickness is not used directly even it is an important criteria for the lubricant selection. The spe-cific film thickness, λ, is widely used which is defined as the ratio between the average or mean elastohydrodynamic film thickness and the composite surface roughness of the rolling contacts, σ, as shown in the equation below.

λ = ; σ = (7)

If the specific film thickness is close to zero, there will be a dramatic increase in the metal-to-metal contact at the friction point and produces unacceptable wear. The tran-sition from boundary lubrication into the mixed lubrication occurs at λ=1 where the bearing will have only partially separated the metal asperities with some metal-to-metal contact. As the specific film thickness increases, metal-to-metal contact will de-crease, thus, reduce in wear. When variable speeds and/or shock loading is present, specific film thickness greater than 4 are de-sirable, however, depending upon the rela-tive bearing speed and oil viscosity, energy consumption and heat generation due to the internal fluid friction is unavoidable.

Feature Article

dqdx

h - hu

h3

h - hu

h3∫6vη0

h1

h∞

x2

2R

0.007ηvα0.6

1 1 P + r1 r2 L() ()0.43 0.13 []E

1 - Ø2

0.03

h0

σ(σ2+σ2)1 2√

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Appropriate lubricant is selected based on the specific viscosity, k, defined as the ratio of the actual viscosity of the selected lubricant to the minimum viscosity required to obtain separation of the moving surfac-es which is determined based on the mean bearing diameter and the operating speed at the given operating temperature as shown in Figure 2. At k values below 1, it is generally accepted that EP additives will be required to mitigate the effects of boundary lubrica-tion conditions. As k approaches 1, the bear-ing life approaches to DIN ISO 281 rate. At k values above 1, bearings life may exceed the rated value. If k values above 4, undesir-able effects may occur such as increase fluid friction, viscous drag and ball skidding. For most bearing applications, k values range from 1 to 2.5 are optimal (Lauer, 2009).

DISCUSSION AND CONCLUSION

The selection of lubricant is usually specified by equipment manufacturer. Used oil analy-sis is crucial for preventative maintenance,

equipment failure diagnosis, abnormal op-erating condition assessment, oil condition monitoring and checking for contamination. Different tests are carried out for different applications. Warning limits for various oil parameters have been defined as shown in Table 3 (Shell, 2000).

Viscosity is the most important property which affects friction and load carrying ca-pacity. Viscosity change indicates the oil de-terioration and contamination. Flash point indicates oil structure breakdown, safety hazard and contamination by fuel.

Total base number (TBN) applicable to diesel engine oils only measures the ability of the oil to neutralize strong acids.

Total acid number (TAN) measures the potential for corrosive wear caused by con-tamination with acidic products and organic acids from oil deterioration which indicates the rapid oil deterioration possibility and formation of sludge and lacquer.

Figure 2. Minimum allowable viscosities for lubrication at operating temperature.

Ope

ratin

g sp

eed

(rpm

)

Min

imum

kin

emat

ic v

isco

sity

(mm

2 s-1)

Operating speed (rpm)

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2

5

10

20

50

100

200

500

10001 5002 000

Mean bearing diameter (mm)0 20 50 100 200 500 1 000

1 000

500

200

100

50

20

10

5

3105 5E4 2E4 104 5 000 3 000

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PALM OIL ENGINEERING BULLETIN NO. 92��

TABLE 3. WARNING LIMITS FOR VARIOUS SYSTEM OILS

Oil type Viscosity change (%)

Water content (%)

Flash point(˚C min)

TBN(mg KOH g-1)

TAN(mg KOH g-1)

Engine 30 0.30 160 2X fuel S% -

Steam turbine 10 0.20 160 - 0.4

Hydraulic 10 0.20 160 - 0.2

Transformer - 0.005 160 - 0.4

Gears 25 0.20 160 - -

Compressors 25 0.20 160 - 0.4

Heat transfer 50 - 160 - -

Water promotes oil oxidation and cor-rosion. Water contamination may originate from atmospheric condensation, leaking and by-product condensation of internal combustion engine operating at low tem-peratures.

Wear elements are elements that indicate a part or component is wearing out and may fail such as iron, copper, lead, tin, alumini-um, chromium, nickel, sodium, silicon, sil-ver, zinc, vanadium, etc. Faulty component could be identified from the type of wear metals thus catastrophic failure could be prevented.

One off sample in used oil analysis do not tell very much, thus, decision should be made based on trend analysis which are more important than absolute figures.

There is no single lubricant good for all purposes in the market. Lubricant selec-tion is highly dependant on the system and application. The tribology analysis above shows that low viscosity lubricants are used for high speeds, high temperature and low pressures whereas high viscosity lubricants are good for low speeds, low temperature and high pressure.

REFERENCES

GEORGE C FENNELL, L E (2007). Boundary Film Lubrication Through Advanced Halogena-tion Techniques: Oxirane Acid Scavenging and Organo-Metallic Substitution. Steel Shield Inc., USA.

LAUER, D (2009). Tribology: The Key to Prop-er Lubricant Selection. Kluber Lubrication North America LP, USA.

SHELL (2000). Shell Lubricants & Lubrication Workshop: Shell Malaysia, Kuala Lumpur.

WIKIPEDIA (2009a). Lubrication. Wikime-dia Foundation Inc. http://en.wikipedia.org/wiki/Lubrication

WIKIPEDIA (2009b). Lubrication theo-ry. Wikimedia Foundation Inc. http://en.wikipedia.org/wiki/Lubrication_theory

WIKIPEDIA (2009c). Lubricant. Wikimedia Foundation Inc. http://en.wikipedia.org/wiki/Lubricant

WIKIPEDIA (2009d). Tribology. Wikimedia Foundation Inc. http://en.wikipedia.org/wiki/Tribology

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

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M

Hazards Associated with Processing in a Palm Oil Mill

N Ravi Menon*

INTRODUCTION

* Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur,

Malaysia.

terms of modernizing the thinking behind the safety features in the processing plant so that there shall have no accidents in the mill at any time. The right ‘thinking’ is rel-evant as safety measures employed must emanate from a caring mind rather than for the sake of satisfying regulations enforced by regulatory bodies. Millers may not even need to read regulations to implement good safety features in their mill if such a system is based on their own common sense rath-er than just some procedures contained in regulations as the regulations may miss out some important points.

If a person wants to throw a hammer from one end of the workshop to the other end for the purpose of passing it on to another person and in the process, someone else on the path gets hurt. Instances like this are common in palm oil mills mainly because the workers do not have a good education, refinement or a caring attitude. You may not find this specifically mentioned in regula-tions except like, “no person employed in a factory shall willfully and without reason-able cause do anything likely to endanger himself or others”.

illers are invited to take a second look at what they have imple-mented so far in their mills in

This article intends to highlight some of the causes of hazards that could be prevent-ed if the management is a caring lot. Look at the following questionnaire and try to see whether your mill complies with them or not. They are not by any means complete by themselves but sufficient to give you a hint on what are expected of them.

• Do the workers follow all safety rules specifically tailored for all employees?

• Have they read in detail the safety rules and understood the content?

• Do they know exactly how to react when an accident occurs?

• Do they know that a new recruit has to be given formal training on the job he is expected to do and this has to be docu-mented?

• Do they know that each machinery op-erator has to keep his work area clean?

• Do they know that they have to report all accidents to their direct supervisor?

• Do they know the procedure to follow when there is a fire?

In all honesty, most mills will not be able to say YES to many of the above. In some cases, the management may have imple-mented some of the above for the sake of

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PALM OIL ENGINEERING BULLETIN NO. 92�0

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mere documentation to satisfy authorities without really having any genuine concern to make them vibrant.

Hazards are created by humans and are the direct consequence of a non-caring management. All accidents can be avoided. Sounds harsh? But that is the truth. Let us review some of the avoidable hazards and how they can be prevented. They are given in the order of their frequency.

HANDLING AND LIFTING OF GOODS AND MATERIALS

In palm oil mills, lifting of welding sets, press and digester parts, motors, pulleys, steel plates and sections of conveyors are some items that are regularly lifted up, the most common one being the welding set. They are lifted by pulley block or by the overhead hoist. There are a number of ar-eas, where injuries can take place in this section. Ample training should be given to the concerned people with written proce-dures so that all are well trained to do the job safely. A new recruit may assist in the job for a period of say a minimum of six occasions before he is allowed to handle the job independently or as decided by the foreman or lead technician. There must be full documentation on the observations and the performance of the recruit. Apart from training, the management should not only provide adequate protective gear for the job but also ensure that they are used by all. The troublesome ones are the conveyors, which when handled by the pulley blocks can swing violently causing unexpected accidents unless they are constantly well-guided.

The best remedy is to have a few half-tonne overhead hoists in key areas like the press and the digester, centrifuge and workshop instead of pulley blocks which are troublesome, inconvenient and accident prone. The overhead hoists are relatively inexpensive and can be installed during the time of mill installation. The consulting engineer should decide where they should

be installed for maximum flexibility of op-eration. In addition, a number of permanent scaffolding and cat-walks would go a long way towards reducing potential accidents. If the mentioned facilities are in place, there are much to gain in terms of time and mon-ey saved for regular maintenance work.

ACCIDENTS INVOLVING MILL MACHINERY

Accidents involving machinerery are often serious with amputated fingers and arms arising mainly due to lack of an established system of procedure or sheer carelessness. One area where the accident can and must be prevented is the conveyors and to a less-er extent the sterilizers. When the welder is still on the job of welding the conveyor rib-bon or the paddle arm, someone starts the conveyor unaware of the person working inside the conveyor. The consequences need not be mentioned here as they are quite ob-vious.

These types of situations can be easily prevented if there was a system in place for facilitating maintenance crew to carry out their work without having the fear of the op-erational staff switching on the machinery while they are still working on machines. A caring management would issue a permit to work (PTW) with the necessary cautions (detailed below) for the maintenance team to work on machinery before they com-mence their work.

The authorized person to issue the PTW can be the mill supervisor and it may be is-sued to the foreman. After issuing the PTW, he is personally required to do the follow-ing:

• isolate the electricity supply to the mo-tor driving the machine;

• pull off the fuses if any and keep them safely away;

• wrap a chain around the switch gear; and

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• hang a danger board on the switch gear.

After the maintenance work has been completed, the foreman is required to return the PTW to the mill supervisor after certi-fying that the job has been completed and the PTW may be cancelled. Upon this cer-tification, the mill supervisor will examine the machinery; normalize the plant and test run it to his satisfaction followed by cancel-lation of the PTW. The mill supervisor now will certify that the plant is safe to operate. Until this point, no one including the mill manager, is allowed to switch on the plant.

In the case of sterilizers, the person in-volved is invariably a process operator. He enters a sterilizer with great difficulty through the narrow hot space between cages and the sterilizer body in order to en-gage the inter-linking hook between cages. But the marshalling yard crew, being una-ware that a person is still within the vessel, closes the sterilizer door and admits steam at 20 bar pressure. Do I need to describe the agony the person destined to have his life ending like this? Accidents of this type have happened sometime ago but have not recurred in recent times. But that does not mean that it will not take place again. Please do all that are possible to prevent such ca-lamities. Very often the cause of accidents can be traced to a change in attitude spring-ing from complacency that triggers mind to relax from the routine safety procedures. This can only be effectively dealt with if the safety procedures are religiously followed every single day.

PERSONS FALLING FROM HEIGHTS

This is not a common occurrence in palm oil mills but cannot be ruled out as people in mills do work in dangerous areas. The common area is the rain gutter on the roof. Generally, this is contracted out but as hu-man life is at stake, the mill management must ensure that the place is safe for the contract personnel to carry out their work. Many mill managers are satisfied with the

buying of insurance for the worker but that does not replace a lost life. The roof gutter in a palm mill needs replacement say every 10 years as it gets corroded resulting in sec-tions being torn off. The collection of boiler ash and other particles deposit in the gutter causing the water to collect there resulting rapid corrosion of the gutter. Every miller probably is facing this problem but no one has found a solution for this. It is difficult to get a contractor to renew rain gutters and if you do get some one, the charges are bound to be exorbitant. A simple way to resolve the problem is to place the rain gutter, say 1 m before the roof edge as shown in Figure 1. During the mill construction itself, the 1 m long gutter sections with lips (Figure 2) can be slid into the gap between the roof edge section and the main section of the roof. This gutter must be located within the mill building so that permanent scaffolding can be erected under the gutter for carrying out its regular maintenance. This may not be a conventional system but there is great ad-vantage in the system if it is incorporated

Figure 2. Simple sliding type roof gutter ideal if made of 2 mm stainless steel.

Figure 1. New roof gutter design for easy installation and replacement.

PERMANENTSCAFFOLDING

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PALM OIL ENGINEERING BULLETIN NO. 92��

during mill construction. There may cer-tainly be other better alternatives worth pursuing.

What is given here is to encourage mill engineers to deviate their thinking away from the routine and enter into the exciting world of innovation, which could be very fascinating and satisfying. Always remem-ber that you only need to have a good idea. If the manufacturers find it has the poten-tial, they will commercialize the idea and market the product and you will end up as a millionaire! Mill engineers have many op-portunities for generating new ideas to im-prove processing or maintenance to make it on par with other food industries.

STEPPING ON SLIPPERY FLOOR OR STRIKING AGAINST OBJECTS

The mill floor should be safe to walk without slipping as falling into the drain carrying the hot sludge water could be disastrous. This is a common occurrence especially when the sludge gets into the shoes. So we have to device a method to prevent this. The author would like to share his experience in this nasty accident in a palm oil mill way back in 1975. The situation with regard to the slippery floors has not undergone any drastic change since then and accidents arising from it are likely to be common in mills.

Many millers probably believe that the floor of the clarification station must have oil splashed all over it. Otherwise the clari-fication station is not performing its du-ties. There is no necessity for the clarifica-tion tank or any other tank to overflow at all. If for any reason, the clarification tank overflows it can be contained in an annular chamber built around the edge of the tank. The overflow can be channeled to a collec-tion tank.

In the choice of floor tile selection, care-

ful consideration is required in the selection of the right type of tiles that will last and at

the same time are non-slippery. There are so many options available in the market and it is worth spending some time to get the most suitable tiles. Some millers prefer to use tim-ber floor which probably is the best in terms of accidents and it is also a convenient floor for placing dismantled separator parts dur-ing routine maintenance.

In some mills, objects can be seen lying everywhere on the floor. Some workshops are so messy that workers cannot move around without climbing over objects that could be sharp and dangerous. The work-shop foreman could be a disorganized per-son to allow this non-conducive and unsafe environment. This could even be a culture carefully preserved for good luck!

All mill workers are provided with safety shoes and this to a certain extent can protect the tip of the foot. It is questionable whether the safety shoes can fully protect one’s foot if an object like a press screw falls partly on the leg and partly on the foot when hoisted by a pulley block. We cannot expect a long object like the press screw to land exactly on the tip of the safety shoe, where it is rein-forced by the stainless steel shield.

STRUCK BY FALLING OBJECTS

The falling objects in palm oil mill that has reasonable significance in accidents may be narrowed down to perhaps; the fresh fruit bunches (FFB). This can inflict bodily damage if it falls on workers because it is covered with spikes. The potential site is the hopper and when bunches are tipped unguided from a lorry or a trailer tipper, bunches gather momentum and scatter on a wide circle hitting many workers who are exposed to them. The damage can be seri-ous and painful if bunches fall on a worker and the spikes pierce the body. The easiest remedy for this is to keep away from the area but this is not often possible as some workers on the hopper apron might be en-gaged in other activities like crop quality inspection while FFB consignment is un-

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

loaded into hoppers. Another remedy is the wearing of protective gears that can prevent major injury to those exposed to accidents.

IMPACT BY VEHICLES OR CAGES

The accidents arising from the impact of ve-hicles or cages also can be significant if taken lightly. Most mills now have installed alarm systems on their vehicles to warn people of their movement. This has reduced the inci-dence of this type of accident involving ve-hicles but the same cannot be said of cages as no such consideration is given to acci-dents related to cages. A person standing in front of a charge of cages with his back fac-ing the cages can not see when it begins to move. Simultaneously, the person operating the pusher like the tractor also cannot see that there is a person standing in front of the cages. Here, during the initial movement of the cages, the person in front cannot only be knocked down but also be dragged along with it. By the time the incident is detected, it could have been too late to save the per-son’s life.

USE OF HAND TOOLS

The common tools involved are hammers, hand drills and perhaps chisels. It is not un-common to use the hammer on the finger or thumb by mistake. Most of the accidents can be avoided if the use of hand gloves is made mandatory when using hand tools.

ELECTRIC SHOCK

This can be dangerous if the electric shock happened at line voltage (440 v). Generally, the supply switch board would indicate the

supply voltage. Prevention of accidents can be enforced if the workers are aware of the dangers involved in working with electrical circuits operating at line voltages (440 v). All electric cables should have good insula-tions and rubber mats must be provided in front of the electrical control panels so that operators can stand on it while switching on electric motors. Generally, if there is an earth leakage in the motor control circuit, the earth fault relay will be energized to close the circuit. In Malaysia, motors used in the industry generally have proper start-er gears and hence, the incidences of electric shock arising from improper installation are not significant.

Let us now consider whether mills are equipped with emergencies associated with electric shocks. There is some weakness here. When an accident occurs, no one really knows what action to take in the absence of training. For some reason, this is given the least priority. In palm oil mills, the training for electric shocks is almost nil and all effort should be taken to ensure that every worker knows how to handle a real situation during emergency. The mobile telephone numbers of the management staff and the emergen-cy phone number of the hospital should be available and prominently displayed at the mill premises within easy reach.

What happens if the hospital is far away and the hospital assistant is on leave? Some-one within the mill should be able to carry out some life saving procedures on the per-son who was subjected to electric shock. This training must be given to a few mill staff if the mill management values human life.

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

A

Feature Article

Mongana Basics: Part 18 – Deperoxidation**N Ravi Menon*

* Malaysian Palm Oil Board, P. O. Box 10620, 50720 Kuala Lumpur, Malaysia.

** Continued from p. 31 of Palm Oil Engineering Bulletin Issue No. 91.

GENERAL

s the increase in peroxide value is considered as a sign of deterioration in the quality of oil, possible ways

of lowering this value were investigated. The lowering of the peroxide value can be achieved through reduction, in the chemical sense of the word. The laboratory results were very conclusive and the industrial im-plementation led to a marked decrease in peroxide value but it was not possible to re-duce it to nil as in laboratory experiments. The reason lies probably in the lack of inti-mate contact between the oil and the reduc-ing agent.

In the laboratory, the deperoxidation technique consists in stirring 100 g of oil at a temperature of 100°C with 10 ml of reduc-ing solution in a turbo-mixer or in the Ultra-Turax for 1 min and then to centrifuge the hot emulsion (minimum 70°C) at 3000 rpm for 10 min.

Laboratory Experiments

The experimental results obtained with a number of reducing agents appear in Table 1.

The most interesting results are those obtained with sodium bisulphate and me-tabisulphite. No satisfactory explanation was found for the unfavourable results re-corded with the sulphite even when used in acid medium. Instead of stirring the oil vigorously with the reducing solution, di-rect percolation of the oil through the reduc-ing compound (metabisulphite) or straight incorporation of the latter into the oil were also undertaken. Very encouraging results were obtained with these two techniques.

Large Scale Trials

The trials were carried out on batches of 1 t approximately. The oil was heated up and a quantity of reducing agents slightly higher than the theoretical amount stirred in. After an adequate time of contact between reducer and oil, the oil was centrifuged in a bowl centrifugal separator fitted with a suitable gravity disc to obtain thoroughly the dehydrated oil and a small oil loss in the separated aqueous phase.

It has been possible to decrease the per-oxide value without however, reaching the zero level as has been pointed out at the be-ginning of this article. In the large scale tri-als, homogenization was achieved by means of a heliccidal-strirrer. These required 4 kW power. The stirrer churned the mass of liquid far less efficiently than a laboratory turbo-mixer. The latter operated on approxi-mately 100 g of oil and used 400 W of power. The power required in the large scale trials

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was only 10 times higher than that necessary for the laboratory scale model although the quantity dealt with was 10 000 times higher. It would, of course, be possible to compen-sate for the low power used by increasing the time of contact but even if stirring were continued for 1 hr in the factory against 1 min in the laboratory, it would still be a long way away from theoretically achieving the same contact between oil and reducer (work is hundred times less).

EFFECT OF DEPEROXIDATION ON STABILITY

A series of experiments using the Swift test were carried out in order to assess the stabil-ity of deperoxidized oil.

The technique consists in oxidizing the oil at a temperature of 60°C in air, then in per-oxidizing it before subjecting the oil to the Swift test using the initial oil as a control. The results of one of these tests are given in Table 2. The corresponding graph (Figure 1) shows that the peroxide value increases sharply in the course of time in the case of the untreated peroxide value oil whilst the deperoxidized sample undergoes a consid-erably slower oxidation process.

In another trial, samples are drawn peri-odically during the oxidation at 60°C. They are then deperoxidized and subjected to the Swift test.

Table 3 and the graph of Figure 2 show the pattern of oxidation of five samples of oil as under:

• control – peroxide value 2.6;• control (peroxide value 2.6) deperoxi-

dized to 0.6 peroxide value;• oil oxidized to peroxide value 4.9 then

deperoxidized to 0.3; and• oil oxidized peroxide value 8.4 then de-

peroxidized to 0.

It may be observed that after reduction, the ability to oxidize is considerably less pronounced. In the above experiments, the deperoxidation is achieved through addi-

tion either of the theoretical amount of re-ducing agent or of a small excess of it.

The effect of that excess was examined. Generally, oil treated with just the theoreti-cal amount of reducing agent reaches a per-oxide value of 1. The peroxide values ob-tained with a slight excess of reagent and the increase recorded in the Swift test, are given in Table 4.

It may be observed that for a 30% excess of reducing agent, the peroxide value falls to nil. In the case of oil with very low peroxide value, this excess is inadequate. It must be increased without however exceeding twice the theoretical amount.

The effect of a large excess of reducing agent has also been studied. Based on this present work, it was seen that beyond a cer-tain limit the excess of reagent is detrimen-tal and that it even induces oxidization. The effect could be ascribed to the destruction of the natural antioxidants of the oil immedi-ately after that of the peroxides. Table 5 and Figure 2 provide data regarding the increase in peroxide value of oil after deperoxidation through increasing additions of bisulphate from 0.5 to 10 times the theoretical amount. The initial peroxide value of the oil was 3.2.

Antioxidants

A few experiments were carried out with a view to assessing what benefit might be derived from the use of antioxidants. Some of these are authorized by the legislation of several countries, particularly the gallates and the butyl-hydroxyanisole (BHA).

It should be noted that if the oil is treated carefully, that is if precautions are taken to prevent the destruction of natural antioxidants, a product of generally satisfactory stability is obtained. If resistance to oxidation were to be a requirement of primary importance, the deperoxidation of oil constitute a very efficient step towards stabilization. In order to highlight the resistance of the oil, it is sufficient to compare

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TABLE 2. RESULTS OF OXIDATION, DEPEROXIDATION AND REOXIDATION OF PALM OIL

Time (hr)

0 1 2 3 4 5 6 7 8 9 10

Swift test on underperoxided oil

1.1 3.6 7.2 10.4 14.3 16.4 19.8 21.7

Deperoxidation

Swift test on deperoxided oil 0 - 2.0 3.0 3.0 3.7 3.3 3.9 3.6 3.5 3.7

TABLE 1. TYPE OF WASHING SOLUTION AND FINAL PEROXIDE VALUE

Test No.

Type of washing solution Final peroxide value

123456789101112131415161718192021

2.5% SnC12, 2H20, 10% acetic acid3% sodium hydrosulphite (Na2SO4)3% sodium hydrosulphite, 10% acetic acid 2% pyrogallol2% pyrogallol, 0.1N sodium hydroxide 6% sodium hyposulphite (Na2S2O3, SH2O)3% sodium sulphite (Na2SO3)3% sodium metabisulphite (Na2S2O5)3% sodium sulphite + 1% NH2-SO3H3% sodium bisulphite (NaHSO3)6% sodium hyposulphite, 10% acetic acid 3% sodium sulphite, 10% acetic acid 3% sodium hydrosulphite, 1% NH2SO3H3% sodium sulphite, 1% potassium iodide3% sodium sulphite, 10% acetic acid, 0.1% potassium iodide3% sodium sulphite, N hydrochloric acid3% sodium sulphite, acetic acid, sodium acetate buffer0.5% formaldehyde3% sodium sulphite, 6% nono-potassium citrate3% sodium bisulphite 3% sodium metabisulphite

0.0 3.1 0.419.114.216.015.5 0.015.7 0.0 0.715.3 0.317.417.517.217.715.815.90.00.0

Initial peroxide value: 17.5

its oxidation curve to that of methyl oleate for instance, or to that of the methyl esters of palm oil. Figure 3 shows the results of the Swift test applied to esters, to a sterilized processed and bleached (SPB) oil and to a deperoxidized oil.

It should be pointed out that tocopherols are the chief antioxidants of palm oil.

The deterioration or the destruction of the natural antioxidants make the oil highly sensitive to oxidation. The destruction oc-curs as a result of bleaching and refining of the oil. In Table 4, a comparison is made be-tween the increase in peroxide value of four samples of bleached oil and one control oil.

Stabilization experiments were carried out with BHA, propyl and ethyl gallate. The

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PALM OIL ENGINEERING BULLETIN NO. 92��

TABLE 3. PEROXIDE VALUE (PV) AFTER TREATMENT AFTER THE FOLLOWING HOURS

Sample No.

PV before treatment

PV after treatment after the following hours

0 1 2 3 4 5 6 7 8 9

1 2.6 0.6 6.7 9.3 12.3 - 14.6 16.1 17.9 20.5 21.9

2 2.6 0.6 2.7 3.9 4.9 6.1 9.0 9.0 9.5 - -

3 4.9 0.0 1.3 1.6 1.4 1.3 1.4 1.7 1.7 - -

4 6.4 6.4 1.9 2.7 3.9 4.1 5.8 6.4 6.7 - -

5 8.2 8.2 1.6 1.6 1.9 1.7 1.5 1.5 1.3 1.4 11.9

TABLE 4. OXIDATION OF OIL IN SWIFT TEST vs. QUANTITY OF REDUCER USED

Sample No.

Sodium bisulphite times the theoretical amount

Oxidation of oil in the Swift test vs. the amount of reducer used for deperoxidation

Time (hr)

0 1 2 3 4 5 6 7

1 Not deperoxidized 8.3 13.7 16.4 16.4 18.6 20.3 23.7 25.0

2 1.1 0.2 1.5 - - 3.7 - - 6.6

3 1.3 0.0 1.3 - - 3.5 - - 6.1

4 1.5 0.0 1.3 - - 2.1 - - 2.3

Figure 1. Comparison between the oxidation curve of a low peroxide value (PV) (1.1) control oil and the same oil oxidized to 21.8 PV than deperoxidized with bisulphite.

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Figure 2a. Comparison between the oxidation curve of a low peroxide value (PV) (2.6) oil and the same oil oxidized then deperoxidized with bisulphite to various degrees of oxidation.

NDGA (nordihydrogaiaretaic acid) was not tried in view of the objections made against the use of that chemical.

The experimental results are given in Ta-bles 5, 6 and 7. Oil was stored in darkness at 50°C.

Tables 5, 6 and 7 show that ethyl gallate does not slow down in any way the oil oxi-dation process. Note that the results con-firm the beneficial effect of deperoxidation (to compare the results after seven days of standard oil and after 12 days on deper-oxidation oil). From a rate of 100 ppm, a

Figure 2b. Oil initial peroxide value of 3.2 deperoxidized through addition of increasing amounts of bisulphite.

Feature Article

1. Control oil2. Oil deperoxidized to 0.62. Oil oxidized to 4.9 then deperoxidized

4. Oil oxidized to 6.4 then deperoxidized5. Oil oxidized to 8.2 then deperoxidized

The effect of the amount of reducing agent on stability

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PALM OIL ENGINEERING BULLETIN NO. 92��

Figure 3. Resistance to oxidation of oil and its deperoxidized counterpart in comparison with that of the methyl esters and of methyl oleate (Swift test).

TABLE 4. OXIDATION OF BLEACHED OIL

Crude oil

control

Refined oil

Oil bleached at 240°C

Oil bleached at 240°C and with bleaching earth

Oil bleached by Avros

procedure

% FFA

Optical density at 420 m

Initial PV

PV after 3 days

2.00

140

145

18.6

0.47

0.25

10.00

17.60

1.97

0.89

0.00

11.80

1.74

0.33

0.10

16.70

1.53

0.33

0.00

17.50

Note: FFA – free fatty acid. PV – peroxide value.

TABLE 5. OXIDATION OF OIL TREATED WITH ETHYL GALLATE

Time(days)

Concentration in ppm

Control 0 5 25 50 100

0137

3.35.010.822.0

3.35.5

10.722.1

3.34.510.322.5

3.36.410.022.5

3.35.312.119.1

Feature Article

PV meq

Deperoxidized oil

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

TABLE 6. OXIDATION OF DEPEROXIDIZED OIL TREATED WITH ETHYL GALLATE

Time(days)

Concentration in ppm

Control 0 5 10 20 100

0137

1233

0.00.23.77.49.4

25.3

0.00.23.06.99.1

29.8

0.00.33.96.5

11.327.3

0.00.62.57.48.0

24.6

0.00.02.78.29.0

26.1

TABLE 7. OXIDATION OF OIL TREATED WITH ETHYL GALLATE

Time(days)

Concentration in ppm

Control 0 5 25 50 100

0381857

4.46.213.223.038.8

4.76.59.014.734.7

4.65.37.79.315.1

4.55.46.36.812.1

4.45.16.35.67.8

Feature Article

significant slowing down of oxidation be-comes apparent.

Similar experiments carried out with BHA show no inhibition activity for that antioxidant even at the rate of 100 ppm. The recommendation is made in technical publications to use mixtures of gallate and BHA. This kind of experiment was not car-ried out. They will be undertaken if and when the question is the object of revived interest.

CONCLUSION

The peroxides of palm oil can be reduced without difficulty through the use of a

number of reducing agents. The bisulphite and metabisuphite appear to be the most potent.

Deperoxidized oil possesses a greater stability as regards oxidation in comparison with the untreated oil. In other words, the lowering of peroxide value to almost the zero level seems to slow down the subse-quent formation of peroxides. It looks as if substances ultra susceptible to oxidation and present in minute quantity in the oil were reduced irreversibly during the deper-oxidation process.

To achieve the best stabilization of the oil, it would appear necessary first to oxi-

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PALM OIL ENGINEERING BULLETIN NO. 92��

Feature Article

dize all these substances and then to reduce them by deperoxidation.

Too large an excess of reducing substance offers no advantage and may even detri-mental since the excess reducer seems to destroy the natural antioxidants of the oil. An excess of 20% to 30% of reducing agent is adequate for oil with high peroxide value.

As much as 100% excess can be used for oil with low peroxide value.

Antioxidants such as ethyl gallate or BHA have practically no inhibition effect on oil oxidation. Propyl gallate however pos-sesses a reasonably marked effect when in amounts larger than 30 ppm.

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Milling Dialogue

Question 60/92

I am from Sibu, Sarawak and was a participant in the DIPOM course at Lahad Datu in 2007. I would like to consult and seek your advice re-garding a problem we are encountering in our newly commissioned (March 2009) 45 t FFB hr-1 CPO mill located in Pulau Bruit....not far out from Sibu, Sarawak.

Our new CPO mill is built on peat swamp area and less than 1 km away from coast line (sea water). The only water available is dug out ponds for storage of raw water having pH of be-low 3.0 with high TDS of ~ 500 ppm. Currently, there is no other means of raw water supply. We use soda (sodium carbonate) to boost up the pH to 7.5 for our ultra filtration (UF) and reverse osmosis (RO) filtration system. We use RO wa-ter for our boiler and mill operations. For a nor-mal 12 - 13 hr operation, the total soda used is 200 kg.

Our RO system has a capacity of 50 t hr-1 with an effluent output of 15 t hr-1. In view of our cur-rent dry spell that may extend for the next few months, we are considering the use of the efflu-ent (very high TDS concentration of more than 2000 ppm) for our mill operation as our raw water resources in the ponds is getting depleted for our mill operation. RO water is used for only boiler operation.

Before we switched over utilizing the reject water for mill operation, the OER was about 16.0% (new estates of three years and less) but before that, we could get about 18% OER. When we used the reject water for the mill op-eration, the OER drastically dropped by 3% to only 13.0%. We then reverted to use RO water

for mill operation and OER has now recovered back to 16%! Is the concentration of soda that would reduce the OER? What is the cause of this reaction? I hope with your expertise and years of experience in palm oil milling, you could pos-sibly enlighten us on this unusual phenomenon. Thank you and warmest regards.

- KKYii

This is a good query and indeed unu-sual. It looks like you have over-corrected your pH and made the water alkaline, and allowing the water to react with the FFA of the CPO resulting in the formation of soap. Soap can entrap oil and prevent it from be-ing separated from the crude oil and its loss in the heavy phase either in the clarifier or the centrifuge. This was the explanation given to me by two researchers, Dr Harrison Lau and Dr Andrew Yap of MPOB when I discussed the problem with them. They can be contacted at [email protected] and [email protected].

This explanation seems to be satisfac-tory as when there is an oil spill in the mill drains, addition of bunch ash was a quick way of getting the oil to sink to the bottom and make the effluent drain appear to be free from any trace of oil spillage. This was done by millers when senior management staff visited the mill.

Now for finding a solution to your prob-lem, reduce the sodium carbonate dosage so that the process water pH is around 5.8. This would prevent the saponification of oil and the consequent oil loss in the sludge. If you still have problems do not hesitate to write to us again.

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Titbits

THE EFFECT OF LAUGHTER ON HEART HEALTH

A new study finds proof that laughter may be the ‘best medicine’ after all - and not just because it relieves stress. It actually boosts cardiovascular health.

Researchers from the University of Mary-land monitored people as they watched two movies - one sad, one funny. After the show, 95% of those who had watched the funny movie had an increase of blood flow, while 74% of those who watched the sad movie had diminished blood flow.

And that’s not all. Laughter strengthens your immune system and releases pow-erful, pain killing endorphins into your bloodstream. So in addition to regular exer-cise, put a smile on your face and give in to a hearty laugh at every opportunity.

ORIGIN OF EXPRESSIONS

The next time you’re washing your hands and complain because the water temperature isn’t just how you like it, think about how things used to be. Here are some facts about the 1500s.

Most people got married in June because they took their yearly bath in May and still smelled pretty good by June. However, they were starting to smell, so brides carried a bouquet of flowers to hide the body odour. Hence, the custom today of carrying a bou-quet when getting married.

Baths consisted of a big tub filled with hot water. The man of the house had the privilege of the nice clean water, then all the other sons and men, then the women, and finally the children - last of all the babies. By then the water was so dirty that you could actually lose someone in it. Hence, the say-ing, ‘don’t throw the baby out with the bath water’.

Houses had thatched roofs (thick straw piled high), with no wood underneath. It was the only place for animals to get warm, so all dogs, cats and other small animals (mice, bugs) lived in the roof. When it rained, it be-came slippery and sometimes the animals would slip and fall off the roof. Hence, the saying, ‘it’s raining cats and dogs’.

There was nothing to stop things from falling into the house, which posed a real problem in the bedroom where bugs and other droppings could really mess up your nice clean bed. Hence, a bed with big posts and a sheet hung over the top afforded some protection. That’s how canopy beds came into existence.

The floor was dirt. Only the wealthy had something other than dirt. Hence, the say-ing, ‘dirt poor’. The wealthy had slate floors that would get slippery in the winter when wet, so they spread thresh (straw) on the floor to help keep their footing. As the win-ter wore on, they kept adding more thresh until when you opened the door it would all start slipping outside. A piece of wood was placed in the entranceway. Hence, the saying, a ‘threshhold’.

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PALM OIL ENGINEERING BULLETIN NO. 92��

In those old days, they cooked in the kitchen with a big kettle that always hung over the fire. Every day, they lit the fire and added things to the pot. They ate mostly vegetables and did not get much meat. They would eat the stew for dinner, leaving left-overs in the pot to get cold overnight and then start over the next day. Sometimes the stew had food in it that had been there for quite a while. Hence, the rhyme, ‘peas por-ridge hot, peas porridge cold, peas porridge in the pot nine days old’.

Sometimes they could obtain pork, which made them feel quite special. When visitors came over, they would hang up their bacon to show off. It was a sign of wealth that a man could bring home the bacon. They would cut off a little to share with guests and would all sit around and chew the fat.

Those with money had plates made of pewter. Food with high acid content caused some of the lead to leach onto the food, causing lead poisoning and death. This hap-pened most often with tomatoes, so for the next 400 years or so, tomatoes were consid-ered poisonous.

Bread was divided according to status. Workers got the burnt bottom of the loaf, the family got the middle, and guests got the top, or upper crust.

Lead cups were used to drink ale or whisky. The combination would sometimes knock them out for a couple of days. Some-one walking along the road would take them for dead and prepare them for burial. They were laid out on the kitchen table for a couple of days and the family would gather around and eat and drink and wait and see if they would wake up. Hence, the custom of holding a ‘wake’.

England is old and small, and the lo-cal folks started running out of places to bury people. So they would dig up coffins and would take the bones to a bone-house and re-use the grave. When re-opening these coffins, one out of 25 coffins were found to have scratch marks on the inside and they realized they had been burying people alive. So they thought they would tie a string on the wrist of the corpse, lead it through the coffin and up through the ground and tie it to a bell. Someone would have to sit out in the graveyard all night (the graveyard shift) to listen for the bell; thus, someone could be saved by the bell or was considered a dead ringer.

And that’s the truth...... Now, whoever said that history was boring!!

Titbits

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

Datasheet

a. Calorific Value of Common Fuels

Fuel Higher heat value

(MJ kg-1)

Lower heat value

(MJ kg-1)

Higher valuesheat of combustion

(MJ kg-1)

Lower valuesheat of combustion

(MJ kg-1) (25oC)

Hydrogen 141.8 121.00 141.90Methane 55.50 50.00 - 50.009Ethane 51.90 47.80 - 47.794Propane 50.35 46.35 49.90 46.357Butane 49.50 45.75 49.20 45.752Pentane - 45.35 - 45.357Gasolene 47.3 44.40 47.00 -Paraffin 46.00 - - -Kerosene 46.20 43.00 - -Diesel 44.80 - 45.00 -Coal (lignite) 27.00 - - -Coal (anthracite) 15.00 - - -Wood 15.00 - 15.00 -Peat (damp) 6.00 - 15.00 -Peat (dry) 15.00 - 27.00 -Natural gas - - 54.00 -Hexane - 44.752

b. kWhr Equivalent of Heat Content in Fuel (values may differ for different sources of fuel)

Type of fuel Fuel KJ kg-1 kWhr kg-1

Solid fuel Charcoal 33 10.7Coal (average) 25.33 8.1Wood 17 4.9 - 5.5Dung cake 6 - 8 2 - 2.6

Liquid fuel Kerosene 46 - 48 15 - 15.5Petrol 47 - 50 -Diesel 45 15.5Ethanol 30 9.7

Gaseous Biogas 35 - 40 11.3 - 20.9Butane (LPG) 50 -Methane 55 17.8Hydrogen 142 - 150 46 - 48.5

Datasheet for Engineers

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

ADVERTISEMENTue to the increased cost of printing, the advertisement rate for 2008 is RM 700 per issue for an A4 size page of black and white, whereas the cost for colour is RM 900. One year of complimentary Vendor’s List advertisement for every one page A4-size colour or black & white advertisement. Advertisers are required to submit to us either their own black and white artwork or colour separation films. Cheque should be made payable to the ‘Malaysian Palm Oil Board’. If you have any queries, please contact the following at MPOB.

Tel: 0�-������00 Fax: 0�-��������

Dr. Lim Weng Soon ext: ��0� • N. Ravi Menon ext: ���� • Lim Soo Chin ext: ���� E-mail: [email protected]

Advertising Schedule for MPOB Palm Oil Engineering Bulletin

Issue Quarter Deadline forRegistration

Deadline forSubmissionof Artwork

�� Oct - Dec �00� �� Oct �00� �0 Nov �00��� Jan - Mar �0�0 �0 Jan �0�0 �� Feb �0�0�� Apr - June �0�0 �0 Apr �0�0 �0 May �0�0�� July - Sept �0�0 �0 July �0�0 �0 Aug �0�0

REPLY-SLIP

Dr. Lim Weng Soon/Ir. N. Ravi MenonEngineering and Processing Division Palm Oil Engineering BulletinMPOB�, Persiaran InstitusiBandar Baru Bangi��000 Kajang, Selangor

PALM OIL ENGINEERING BULLETIN ADVERTISEMENT – FULL PAGE ADVT.

�. We confirm our intention to advertise in the MPOB Palm Oil Engineering Bulletin.

Company:

Address:

E-mail: Tel. No.: Fax No.: Contact Person: Issue No.:

�. The artwork is attached/will be sent on for your further action.

�. Please find enclosed *crossed cheque No.: for RM ( ) being payment for the advertisement fee.

�. Thank you.

(Signature and Date) (Company chop)

D

MPO

B P

ALM

OIL

EN

GIN

EERI

NG

BU

LLET

IN -

FULL

PA

GE

# * Made payable to ‘MALAYSIAN PALM OIL BOARD’.

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PALM OIL ENGINEERING BULLETIN NO. 92�0

MPO

B PA

LM O

IL E

NG

INEE

RIN

G B

ULL

ETIN

- V

END

OR

’S L

IST

ollowing a decision by the Editorial Board to further increase the role of Palm Oil Engineering Bulletin to serve the industry better, a new addition called Palm Oil Mill Vendor’s List has been introduced similar to Telekom Yellow Pages to assist mill engineers to know where to source materials or services pertaining to the industry. In order to make this useful, we need the co-operation of the mill engineers/managers to persuade their vendors to advertise in the Vendor’s List for a nominal fee of RM �00/year (four issues). If you have any queries, please contact the following at MPOB.

Tel: 0�-������00 Fax: 0�-��������

Ir. Ravi Menon ext. ���� or e-mail: [email protected] Ms. Lim Soo Chin ext. ���� or e-mail: [email protected]

REPLY SLIP

Dr. Lim Weng Soon/Ir. N. Ravi MenonEngineering and Processing Division Palm Oil Engineering Bulletin AdvertisementMPOB, �, Persiaran Institusi, Bandar Baru Bangi, ��000 Kajang, Selangor, Malaysia.

We wish to advertise in the MPOB Palm Oil Engineering Bulletin Vendor’s List

Company: Issue No.:

Contact Person: H/P:

Address:

E-mail: Tel: Fax:

Please find enclosed a crossed cheque No.: Bank:

for RM: (Ringgit Malaysia)

drawn in favour of MALAYSIAN PALM OIL BOARD

Please select the headings from the list given below (not more than five headings) under which you wish to advertise.

Air filters/dryersAir separatorsBearings/belts/bushesBiomass/bio-compost/productsBoiler spares/control/othersBoiler suppliers Bunch crushersCastingsCleaning - generalCivil engineeringCondition monitoringControl/automation/sparesConveyors/chains/elevatorsConsultancy services/certificationDiesel eng./services/sparesDynamic balancing Electric motors/systemsExpansion jointsFabrication works Fans

Signature:

Name:

Date: Company chop

ADVERTISEMENT

F

#

Filter press/materialsFluid control system/couplingsGaskets/packing materials/sealsGear boxesHardware Hydraulic systems/services/spares Laboratory analysisLaboratory equipmentLubricantsMill machinery/sparesMiscellaneousNut crackersOil recovery systemsPalm kernel oil crushing plantPollution control/safety systemsPressure vesselsPumps/services PurifiersRenewable energyScrew press/parts

ScrubbersSludge separators/decantersSteam turbines/generator/sparesSterilizer/partsStorage silosVacuum pumpsValves/seatsWaste water treatment Water treatmentWelding equipmentsWeighing machines/sparesWheel loaders/spares

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PALM OIL ENGINEERING BULLETIN NO. 92 ��

From:

Address:

Question/Comment:

Signed: Date:

(We have enclosed this form to assist you in sending to us any questions or comments)

#

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PALM OIL ENGINEERING BULLETIN NO. 92��

ChairmanThe Editorial BoardPalm Oil Engineering Bulletin Malaysian Palm Oil Board P. O. Box �0��0�0��0 Kuala LumpurMalaysia

STAMP