|Infobox on Oilcake expeller|
|Example of Oilcake expeller|
|Stowage factor (in m3/t)||1,8 m3/t (bulk)|
|Humidity / moisture||-|
|Ventilation||Surface ventilation with due care; see text|
|Risk factors||See text|
Description / Shipment / Storage / Risk factors
Oil Cake expeller is the residue which is left after various types of seed have undergone processing to remove the oil. The seeds involved include, inter alia, linseed, cottonseed, rapeseed, sunflowerseed, nigerseed and copra. It is of value as an animal feeding stuff as it normally contains a high proportion of protein as well as carbohydrates.
Products based on oil seed expellers may be of the following types:
1. Chips or flakes
These are broken pieces of thin, frequently curved, material. The thickness varies from about 2 to 10 mm and the area from 2 to 10 cm2. This is the material in the condition delivered from the oil presses. It may be shipped as bagged or Bulk Cargo.
This is fine material, usually originating from the solvent extraction process. It is normally supplied as bagged cargo.
These are normally between 7 and 12 mm in diameter and may be produced from pressed or extracted expellers. Pellets are normally shipped as bulk cargo.
This may be compressed material from oil presses. The cakes vary in dimensions but can be up to 50 mm thickness and 1 m2 area. Oil seed expellers were frequently shipped in this form in bags. In recent years, however, expeller products have been handled mainly in the other forms described. However, extraction ‘expellers’ are still produced in cake form.
The most effective way of removing the oil from the seed is by the solvent extraction process, in which the seed, or mechanically expressed residues, are continuously contacted with hot solvent from which the oil is subsequently recovered. The residual solvent is removed from the residue leaving a product usually with less than 1% of oil. The second method is by mechanical pressing, whereby the seed is placed in a press, usually worm driven, and the oil which is removed under pressure is allowed to trickle out. This process is not nearly so efficient as the solvent extraction process for removing the oil, and the cake normally contains between 6% and 10% of residual oil.
The principal problem when carrying Oil Cake expellers is self-heating. Two mechanisms for self-heating are recognised. The first may be called straightforward oxidation. This involves a combination of certain substances in the expellers with oxygen present in the air. All oxidation reactions are exothermic, that is they are accompanied by the production of heat. Under normal circumstances there are natural mechanisms present by which heat is lost, e.g. by conduction, radiation, etc. If the rate of heat loss is as rapid as the rate of heat production, then there will be no heat again in the expellers and the temperature will not rise. If, however, heat is produced more rapidly than it can be removed, then there will be a heat gain in a cargo and hence the temperature will rise. Oxidation reactions increase in rate as the temperature rises on a roughly exponential scale, i.e. the rate of heat production will double for each 15-20°C rise in temperature.
From this the following points are clear:
a) Once the temperature in the cargo starts to rise, it is difficult to prevent the process becoming progressive. Unless special steps are taken the temperature will continue to rise at an ever-increasing rate until either the cargo is discharged, or it reaches the point of combustion.
b) Cargo loaded at an initially high temperature is more likely to heat-up than one loaded at a low temperature.
c) If the cargo temperature is raised by another mechanism, e.g. microbiological activity, or heat transfer from an external source, such as a hot bulkhead, then the rate of oxidation will increase and the rate of heat production by this particular mechanism may reach a level at which it exceeds the rate of cooling.
Factors influencing the rate of heating apart from temperature, are firstly the quantity of reactive material present. It is normally considered that oxidation of expellers is largely oxidation of the oil present in the expellers. On this basis both the quantity and reactivity of the oils are of importance. Fairly obviously there would per se be more chance of heating if the quantity of oil present were doubled. Likewise some oils react more readily with oxygen than others. A measure of this reactivity is called the iodine value of the oil.
The iodine value is a measure of the degree of unsaturation of a fat or fatty acid, defined as the number of grams of iodine capable of reacting with 100 g of the sample. It is usually determined indirectly by measuring the amount of an iodine-containing reagent, e.g. iodine monobromide, that remains after excess has been added and reaction is complete. The iodine number of saturated Fatty Acids is zero, that of oleic acid is 90, of linoleic acid 181, and of linolenic acid 274.
For the oils mentioned earlier, typical (iodine) values are:
|Coconut (from Copra)||7,9-9,5|
A second factor is the surface area of the expellers. Expellers which are hard and do not break easily normally have an unbroken surface. The surface area per pound of expellers will be less with this type of surface than with a softer product, which will tend to crumble and will also tend to have a porous surface.
In terms of the product itself there may be other less well-defined factors which will promote or retard the rate of oxidation. The most reactive material will tend to oxidize first so that the rate of oxidation and heating will fall as the product ages, hence the requirement of loading properly ‘aged’ cargo. Natural substances such as antioxidants may be present in the seed, which will retard oxidation. Traces of metals such as copper will promote oxidation and so on.
If the oils listed above are considered in terms of their iodine value, linseed expellers should be by far the most dangerous being comparable to fishmeal as a potential source of self-heating. This would be followed by sunflowerseed expellers, then nigerseed, etc. However, general experience indicates that nigerseed expeller cargoes are more likely to heat than linseed expellers cargoes. The latter are certainly not nearly as critical as fishmeal. The precise reason for these various anomalies have never been investigated. There is little doubt, however, that some of the other factors mentioned above play a part. It is also generally accepted that the rate of temperature rise due to oxidation is less as the moisture content increases. It is therefore considered desirable to have a moisture content in excess of 6%. A final factor which may control heating is the availability of oxygen. In normal cargoes there is probably always sufficient oxygen present to initiate heating but under certain conditions the rate of heating may be retarded by lack of air (oxygen). In extreme cases, by using the modern technique of inert gas blanketing, heating can be prevented by replacing oxygen by an inert gas as the former is absorbed by the cargo.
The second mechanism normally accepted as a cause of fires in oil seed expellers is microbiological heating. The mechanism by which this occurs has been discussed at length for many natural products in recent years. Basically heating will not occur unless the moisture content of the product or part of the product is in excess of a critical value, which is about 12-13% for oil seed expellers. The greater the moisture content above this critical value, the more rapid will be any heat production. Likewise the rate of heat production as a result of microbiological activity is higher at higher temperatures within the normal ambient range. As has been explained previously the rate of heat production must exceed the rate of heat loss before the cargo temperature will start to rise. This point will be reached more quickly where microbiological activity is rapid, i.e. with a wet, warm cargo as opposed to a cool cargo with a marginally high moisture content. Microbiological activity will only raise the cargo temperature normally to about 60-70°C although in some instances higher temperatures may be achieved, because above these temperatures growth of nearly all species of micro-organisms is inhibited. However, normally at such temperatures chemical oxidation is sufficiently rapid to cause heating-up to continue.
It must be stressed that heating may occur if the moisture content of any part of the cargo is in excess of 12-13%. As there is always a variation in moisture content in a cargo there is a very real risk of heating if the average moisture content is in excess of 10-11%.
From the foregoing it will be seen that the following factors are likely to promote self-heating of expellers:
1. High oil content
2. High temperature
3. Fresh product
4. More reactive oil
5. Excessive moisture content or moisture content which is too low
6. Plentiful supply of air (oxygen)
It follows that any factor such as ventilation which will increase the rate at which heat can be lost from the cargo will tend to restrict the heating-up process. On the other hand, once the heating-up has reached a critical temperature, then ventilating air can supply the necessary oxygen for accelerating heating to the point of combustion.
The final factor which can produce heating-up of oil cake expeller is infestation, since insects produce metabolic heat and this heat tends to be retained in a non-conducting cargo. Heat of metabolism from insects like microbiological activity is self-limiting. Nevertheless heavy infestation can in theory raise the temperature of products of this type to the point at which uncontrolled oxidation supervenes.
Requirements for Loading, Stowage and Carriage
In the IMO Code, seed cake, meal, oil cake and seed expellers are divided into three categories:
a) Mechanically expelled seeds containing more than 10% of oil or more than 20% of oil and moisture combined.
b) Solvent extractions and expelled seeds containing not more than 10% of oil and when the amount of moisture is higher than 10% not more than 20% of oil and moisture combined.
c) Solvent extractions containing not more than 1,5% of oil and 11% of moisture.
Certificates from a recognized authority should state the oil and moisture contents and the cargo should be properly aged. For a voyage in excess of 5 days the carrying ship should be equipped with a CO2 injection system. Bulk stowage is only allowed with special permission from a competent authority.
With regard to carriage, the Code recommends for all types of cargo and stow:
1) Surface ventilation should be practiced.
2) Regular temperature readings should be made at different depths in the cargo and these should be recorded. If the temperature of the cargo exceeds 56°C ventilation should be restricted and if heating continues, CO2 injected.
Obviously the recommendations in the Code should be followed as far as possible. Thus when a Master arrives at a loading port to load a cargo of oil seed expellers he should first obtain evidence from the shippers, in writing, regarding the type of product, i.e. whether type a), b) or c). If it is type a) or b), he should get analysis certificates and check that all cargo covered by each certificate has an analysis which satisfies the type.
However, it should be pointed out that it is possible under the specification given for type b) to have a cargo of solvent extracted material with an excessively high moisture content. It is suggested that the maximum permissible moisture content for cargo accepted as type b) should be 11%. Any cargo with higher moisture content should be either rejected or treated as type a) cargo. It is recommended that should such a situation arise, the Master should supply details to his owners. Loading should then be carried out in accordance with that advice. Where cargo is stowed in bags, or delivered alongside in bags for bleeding into a hold, then such bags should be checked. Wet, stained, or otherwise damaged bags should be rejected. In addition, warm bags, i.e. those at a temperature more than about 5°C above ambient, should also be rejected. Cargo supplied in bulk should be checked for temperature and excessively warm cargo should not be loaded. It must be borne in mind that cargo of type a) may be particularly hazardous as it is known that certain types of expellers can catch fire even when well ventilated and in very small stacks (i.e. just a few bags). This cargo should be stowed in such a way that it can be checked regularly. Any bags found to be heating should be put on deck or jettisoned.
In case of severe heating or fire it should be borne in mind that cargo in adequately sealed holds, especially when blanketed with CO2 is not likely to present any special hazard until an attempt is made to discharge such cargo. It is therefore advisable for a Master and his owners to take the ship to a port which can handle an expeller fire. Extinguishing such a fire (as opposed to containing it) may well necessitate the use of water and possibly of one or more holds.
The Code makes special reference to the hazards associated with residual solvents where solvent extracted material is loaded. As the solvent extraction system involves use of fairly advanced technology and equipment, and as the solvents used are expensive, the likelihood of excess residual solvent being present is small. Obviously, however, processing errors are possible and Masters should seek advice if cargo being loaded, or cargo loaded, has a strong odour similar to gasoline. In such circumstances the possibility of fire and also explosion will exist. Other recommendations in the Code are basic to good seamanship, namely prohibition of smoking and the use of naked lights in the holds. It is also suggested that spark arresting screens should be fitted to the ventilators and that hold fuses should be extracted. Finally it is advised that with solvent extraction products, CO2 is not injected until fire is apparent.
Course of self-heating processes in feedstuffs of vegetable and animal origin containing residual oil.
- 10° to 35°C
Product comes on board at port outside air temperature or at a higher temperature because it has not been cooled to the outside air temperature after oil and starch extraction.
- 30° to 40°C
The incipient biotic activity of the microorganisms is at its most vigorous (biological activity with release of moisture).
- from approx. 40°C
In addition to microbial biotic activity, the heat released in conjunction with microbial activity promotes oxidation of the unsaturated fatty acids in feedstuffs containing residual oil, which, like any oxidation process, is associated with evolution of heat (chemical oxidation).
- from approx. 45°C
Marked temperature increase resulting from a combination of the biotic processes of the microorganisms and incipient chemical oxidation processes of the unsaturated fatty acids.
Still no great decline in product quality. First of all, the nutritional value of the proteins is impaired. Incipient brownish discoloration of the product.
- from 55°C
Critical temperature. Continuous temperature monitoring required
- 55° to 85°C
Critical cargo heating range
- from approx. 75°C
After the preceding overlap between biological and chemical evolution of heat, these temperatures result in death of the microorganisms and the end of their biotic activity. Microbial spoilage of the cargo stops. No further temperature increases occur above 90°C (longish temporary plateau).
- from 90°C
Visible release of white steam from the cargo through any openings remaining in the hatch, ventilation and access areas.
- from 100° to approx. 150°C
An unpleasant pungent smell penetrates to the outside as a result of protein decomposition. The steam starts to become discoloured.
- from 150°C to approx. 200°C
Substantial release of gases, increased formation of smoke as consequence of continuing dry distillation. Rapid progression of chemical processes in cargo. Considerable losses in nutritional value.
- from approx. 230°C
Frequent localized glowing at cargo surface when exposed to oxygen from the air.
- from 250°C
Added to the existing foul smell of smoke, which gets into clothing, is a smell of charring.
- from approx. 280°C
Once temperatures exceed 250°C and especially 280°C, it must be anticipated that the autoignition temperature of the cargo dust will be reached.
- from approx. 330°C
It must now be anticipated that the autoignition temperature of the cargo will be reached. However, this is seldom the case when organic feedstuffs are transported by sea, since the heating plateau which occurs at approx. 90°C continues for a relatively long time.
Once a cargo has spontaneously ignited, it burns with flames. If the hold is opened, open fire may break out. In practice, this very seldom occurs at sea and is highly unlikely if the supply air openings into the holds are properly closed.
A truly burning cargo leaves behind ash, which is the sole unmistakable proof that a cargo or other items has burnt.
Upon opening previously well sealed holds which have reached temperatures higher than 150°C, a thick, white-coloured cloud of steam escapes.
Generally, temperatures of up to 160°C are measured in heated cargoes of feedstuffs. As a rule, however, temperatures of up to approx. 90°C are found in heated feedstuffs containing residual oil.
Self-heated feedstuffs with temperatures of around 90°C in an as far as possible airtight hold should not be considered critical. There are no hot spots in the cargo, which have to be sprayed. Intensive extinguishing methods using water should only be used for feedstuff cargoes which, exceptionally, have undergone true spontaneous combustion at temperatures of over 280°C.
Holds containing self-heated cargo must never be flooded from beneath, since large amounts of water in the hold impair the stability of the ship. Never use a high-pressure extinguishing jet on a heated feedstuffs cargo, since the heated cargo must not be made to swirl around.
See also Expellers and Extractions, Oil Cake and Seedcake.