Tuesday March 27, 2012
Waste not the palm oil biomass
By MENG YEW CHOONG
The palm oil industry generates a fair amount of biomass, which the Government feels should be put to better use rather than just be left in the field as fertiliser.
FOR a long time, planters would spread the biomass that is left over after palm oil has been extracted from the oil palm fruit bunches, as a form of cheap soil conditioner. However, the Government is of the opinion that such low-value material could be put to better use rather than just be left to decay in the field, even though it still serves a useful function.
There is now a concerted effort to push for a more thoughtful utilisation of biomass, and the most concrete manifestation of this was the unveiling of the National Biomass Strategy 2020 (NBS2020) last November.
Biomass is defined as organic matter available on a renewable basis, and these include forest and mill residues, wood wastes, agricultural waste, domestic garbage, as well as livestock wastes.
As far as plant-based biomass is concerned, attention is naturally focused on oil palm plantations as Malaysia is the world’s second largest producer of palm oil.
Correspondingly, the sector is the largest generator of biomass, and in 2010 alone, it was estimated to have produced 80 million dry tonnes of residue, and this is expected to increase to 100 million tonnes by 2020, chiefly due to improved plants that give higher yield.
This amount of palm biomass is believed to be 85% of the total amount of biomass generated in the country.
Even before the unveiling of NBS2020, much research has already been done on how to economically utilise the various parts of the oil palm tree and fruit. Some of the notable achievements include research on palm lumber, and the production of biofuel from the fermentation of oil palm fronds.
Source of biofuel
For a group of Colombian researchers, the oil palm shell holds promise as a form of biofuel. That said, burning mill residues to fuel boilers is a long-adopted practice here, where empty fruit bunches are burned and their energy value is recovered in the form of heat, which is sometimes used to generate electricity.
Burning of raw biomass, however, is not without its problems, and it has been acknowledged that easily more than half of the boilers in the plantations cannot meet the Department of Environment’s emission standards. Even if there are no air quality issues, any palm oil plantation easily generates more biomass that it could ever need for its boilers, and in the case of oil palm shells, more than half has to be discarded.
According to Dr Nelson Arzola, a researcher from the Department of Mechanical Engineering of the National University of Colombia, very little work has been done on the enhancement of oil palm shells in order to turn them into an efficient biofuel (in the form of manufactured pellets).
At his university, Arzola is working with his departmental colleagues Dr Alexander Gomez and Dr Sonia Rincon in experimenting with different levels of pellet moisture as well as pellet binder percentage. A binder is an agent added to the finely crushed oil palm shells in order to glue them together so that the material is strong enough to form a rod.
According to Gomez, while oil palm shells can be incinerated directly, it may give rise to ash with undesirable qualities. Untreated palm shells, like other forms of raw biomass, can complicate the combustion process as it is difficult, if not impossible, to control their characteristic such as moisture content, density, as well as physical and chemical compositions.
Having a fuel with either varying or undefined characteristics makes it hard for the plant operator to ensure that combustion in his boiler is taking place in its most efficient and least-polluting form.
Other than burning it off as fuel, other ways of adding value to the shells are processing through pyrolysis (heating the material in an environment without oxygen) and gasification systems. “Oil palm shells have an energy density of about 22 megajoules (MJ) per kg. After pyrolysis, the value increases to about 33Mj per kg. And so, 1kg of pellets have more calories than 1kg of shells,’’ said Arzola, who added that another alternative to add value to the oil palm shells is their compression into pellets.
“Through this process, a product that has a major energetic density, is more stable mechanically and has a better performance during the combustion process, can be obtained,’’ said Arzola, who experimented with various levels of binding agent to make the pellets.
The pelletisation of biomass also confers upon it the advantage of higher energy density and ease of handling, transportation and storage. After all, it has been noted that raw biomass generally has medium to low energy density, which is a disadvantage when it comes to delivery, and does increase overall production costs.
Pelletisation of other forms of biomass has been taking place for many years in North America, Europe, and China. However, the raw materials used there tend to be from sawmills, logging as well as temperate agricultural product wastes.
With a sizable oil palm industry of its own, Colombia’s focus is how to utilise the large amounts of palm oil mill waste effectively. A tonne of oil palm fruits will yield around 70kg of shells after processing, or 7% of the original mass.
The starting material for the pellets are oil palm shells that have been crushed until no particle is larger than 0.6mm, before the binder is added to form them into cylindrical objects that resemble sticks of dynamite.
Another important experiment parameter is the moisture content of the pellets. In general, biomass pellets are made using mechanical pressure, though the actual pelletisation process is a bit more complex as there is an interplay between the chemical characteristics, particle size, and amount of pressure, as well as the amount of heat applied (if any).
Other than its actual performance in a boiler or burner, the appearance of the final product is equally important if the product is intended to be marketed to households and individuals. As such, evaluations were carried out on its general appearance, the presence of cracks, the appearance of a shiny or oily surface, the smoothness or roughness of the surface, and the tactility when handled with bare hands.
Other more “industrial” considerations are the durability of the pellets to rough handling (whether they would disintegrate easily under normal handling).
It was found that the durability of the pellets were greatly affected by the level of binding agent, with more binding agent giving a higher level of durability. On the contrary, the average particle size had an inverse effect, with the pellets made with larger-sized particles showing less resistance to bad handling.
Much more work is still needed to get more information on the performance of the pellets, and the current findings are still quite a distance from being marketed. “I think we need at least two more years before this product can be commercialised,” said Arzola, who remains hopeful that the final product can find its way into markets in developed countries, such as Europe, where it can be used for both industrial as well as domestic heating.