Ash Content and Quality of Premium Grade Wood Pellets

Compared to industrial wood pellets, which have looser specifications, particularly regarding ash content, which can reach 6%, premium-grade wood pellets, for use in space heating, have stricter specifications, specifically a maximum ash content of 1%. Premium-grade wood pellets generally have a diameter of 6 mm, while industrial pellets are generally 8 mm. The color or appearance of premium-grade wood pellets also plays a role, with brighter colors generally preferred. This is why premium-grade wood pellets are naturally more expensive. Demand for premium-grade wood pellets increases during the winter due to the increased need for space heating.

Regarding ash content, several standards even stipulate ash content lower than 1%, such as DIN Plus with a maximum of 0.5%, ENPlus-A1 with a maximum of 0.7%, and Ö NORM M7135 which requires a maximum of 0.5%. This is why strict control of raw material selection and treatment is applied in the production of wood pellets to meet these specifications. Although the ash chemistry for premium grade wood pellets may not be as stringent as for industrial pellets because the application operation is at lower temperatures, the production of wood pellets with very low ash content requires high-quality raw materials.

In premium grade wood pellets, even a slight difference in ash content can significantly impact the selling price. For example, wood pellets with a maximum ash content of 0.55% can differ by around USD 30 per ton compared to wood pellets with a maximum ash content of 0.35%. Because they are used for space heating, premium grade wood pellets are generally packaged in small plastic bags, such as 15 kg, while ordinary industrial pellets are packaged in jumbo bags or even bulk due to the much larger volume requirements.
 

Problems of Wood Harvesting from Calliandra Energy Plantation and High Potassium Content in Wood Pellet Ash: Two Things That Need Attention

The factor of production efficiency and standard and stable product quality is the mindset of the industry, including for the wood pellet industry from the calliandra energy plantation. Manual wood harvesting operations make production efficiency low. The high daily need for wood pellet raw materials from energy plantations requires mechanization equipments for harvesting the calliandra plantation. Meanwhile, calliandra wood pellet products with high ash content containing potassium also require certain treatments so that the wood pellet products meet the standards for power plants in general. The stability of production quality and quantity is closely related to the quality of the production equipment used. These two things must be an important concern for wood pellet producers from calliandra energy plantations with large capacity and export orientation.

The wood pellet industry from the calliandra energy plantation is new, so there are not many references. The history or the origin of this industry comes from the project of the Ministry of Forestry of the Republic of Indonesia at that time which created an incubator-scale industry as a pilot for the production of wood pellets from the calliandra energy plantation located around Geger Hill, Bangkalan, Madura, East Java about 12 years ago. At that time, there were actually several wood pellet industries operating, but all of these wood pellet factories or industries used raw materials from wood industry waste, such as sawmill industry waste, barecore industry waste, plywood industry waste and so on.

Calliandra trees are also not new plants to the public. This tree has been widely planted but previously with different purposes, namely for reforestation, for animal feed or for honey bee farming. While for bioenergy purposes or wood pellet production, planting calliandra trees in the form of energy plantations is something new. That is why in the early stages, calliandra wood harvesting was still done manually and this was ineffective and inefficient on large-capacity plantations. In addition, the wood pellet product has not been analyzed or examined completely / comprehensively so that the high potassium content (ash chemistry) in the ash has not been detected. When the requirements for the maximum content of potassium / potassium must be met, special treatment needs to be done.

In addition, an important thing to note is the target types of products produced. If the calliandra plantation not only produces wood as raw material for wood pellet products, but also processes leaves for animal feed, then the harvesting mechanism is very influential. The leaves from the calliandra plantation must also be harvested effectively and efficiently or the same as the wood products. This could be, for example, the trees and leaves are harvested together and then taken to a place and separated to be processed individually. Or it could be that the wood and leaf products have been separated at the time of harvesting, then each goes to its respective processing unit. The equipment used must also be different according to the choice of the harvesting mechanism. Meanwhile, honey products from bee farms that utilize calliandra nectar are not affected by this mechanism, this is a separate honey production process and is related to the flowering season of the calliandra tree itself.

Along with the global decarbonization trend, the prospects for calliandra plantations are increasingly bright. It is predicted that many calliandra plantations will be created, which are intended primarily for bioenergy production such as wood pellet production, and this is in line with the carbon neutral scenario that supports the net zero emission program. The use of wood pellets is mainly for fuel in coal-fired power plants through the cofiring mechanism. In the next stage, it is possible to use 100% of the power plant fuel using wood pellets (fulfiring). The high potassium content is generally a problem in applications for this power plant, although there are types of power plants that technically do not have a problem with the potassium content, but the production of wood pellets from calliandra with low potassium content is certainly preferred.

Why Has Large Capacity Wood Pellet Production from the Calliandra Energy Plantation Not Been Realized?

 

As a tropical country that has the largest land area in Southeast Asia, the potential for fuel or renewable energy from biomass, especially wood pellets, is very potential and promising. To maintain the stability of large capacity production volumes and their continuity, wood pellet production must use raw materials from energy plantations or biomass plantations. Energy plantations from short rotation coppice & fast growing species from legume groups such as red calliandra (Calliandra calothyrsus) have been a concern for quite a long time, but why has this large capacity wood pellet production not yet been realized or has no industry realized it? Below could be two main factors causing this:

1. Quality of calliandra wood pellets

The characteristics of rotational crops and fast growth of the legume group are that they contain quite high levels of potassium and sodium (K+Na) in their wood. Potassium has the property of having a low melting point so it will be problematic for heat exchangers in power plant boilers in general. The high potassium content makes its use unsuitable for power plants in general, namely those that use pulverized combustion (PC). Red calliandra (Calliandra calothyrsus)  in particular is the same, so with a large production capacity, the quality of export-oriented wood pellet products needs to be improved by reducing the content, especially potassium and sodium (K+Na). 

The process of reducing K + Na, which is part of the ash content, is carried out using a leaching / washing process. This unit needs to be added to the wood pellet production process from red calliandra. Apart from making calliandra wood, the raw material for wood pellets, this process becomes wetter, it also produces waste water. This will increase the production costs of red calliandra wood pellets.

Although it is possible that the leaching/washing process was not carried out so that the resulting wood pellets still have a fairly high K + Na content, they still have the potential to be used for certain types of power plants, such as those with fluidized bed and stoker technology. However, this type of power generation technology is not as common as the use of pulverized combustion (PC) technology. So that market acceptance for the production of calliandra wood pellets is large or can be used in all types of power plants, the leaching/washing process should be carried out.

2. Utilization of only certain parts (partial) of the plant, and not comprehensive (whole tree utilization)

When it only use wood for wood pellet production, it means that only part of the plant is used (partial) or there are other parts of the plant that are not used, namely the leaves and flowers. In fact, these two parts of the plant will be able to maximize income or profits which will provide the impetus to accelerate the realization of large capacity wood pellet production from the energy plantation. The additional costs incurred for the leaching/washing process will be compensated by the income/profits from leaf processing and flower utilization.

Calliandra leaves which have a high protein content are processed into animal feed, especially into flour or also pelleted into feed pellets. Meanwhile, the nectar from flowers is used as food for honey bees in beekeeping to produce calliandra honey. By maximizing the potential of all parts of the plant (whole tree utilization) of calliandra, various products (multiple products) are produced so that the driving force to accelerate the realization of large capacity wood pellet production from energy plantations becomes stronger.

One form of gratitude for Allah SWT's blessing in the form of a country with a tropical climate with vast land is to use it in an environmentally sound and sustainable manner. Tropical areas like Indonesia are a "paradise" for biomass production, especially for biomass energy (bioenergy) in the form of wood pellets. Optimizing this potential, especially with large capacity production of wood pellets and additional products, could be a boon and a blessing for prosperity as well as a solution to global climate problems (carbon neutral fuel). And basically business judgment is also needed from the entrepreneur's side so that the entrepreneur has the courage to decide to execute this business opportunity.

Production of LOF and EFB Pellets at The Same Time

The leaching process for palm oil empty fruit bunches (EFB) so that it has potassium and chlorine content suitable for EFB pelletproduction on a commercial scale that can be used maximally on a pulverized combustion (PC) boiler at a power plant is not easy and inexpensive. That is because the leaching process requires a solvent to extract the potassium and chlorine content from the EFB material. Ideally the leaching process is carried out with acid solvents, agitation and heat and a long time so the extraction process can run optimally. In fact this is the bottle neck to carry out the leaching process, so that almost no one has done this process commercially today. It is different if the leaching process also has other objectives that also have commercial value, for example for the production of liquid organic fertilizer (LOF).

By simultaneously producing LOF, the costs for leaching can be compensated with the benefits of the LOF. In CPO business operations, especially in palm oil plantations the cost of fertilizer is one of the highest cost components, estimated at 35.75 billion rupiahs (around 2.5 million USD) per year for every 10,000 hectares. If the cost of the fertilizer can be saved from the use of self-produced LOF as well as pellet EFB production, then this is one of the optimization of biomass utilization in the palm oil industry. LOF will have the main content in the form of potassium because the potassium content is quite high at EFB about 30% of the ash produced is potassium. Potassium fertilizer is very beneficial for plants because it is an essential nutrient with benefits including transporting sugar, controlling stomata in leaves by maintaining electro-neutrality in plant cells, co-factor of more than 40 enzymes and reducing the occurrence of various diseases. Some plantations also need large amounts of potassium fertilizer, for example banana plantations. The process of making LOF by soaking EFB for several days is expected to significantly reduce the potassium and chlorine content in EFB and make it a material for pellets that are friendly to the PC boiler power plant.

The EFB pellets produced can then be sold for export as well as meeting domestic needs. With EFB pellet production as well as LOF, it is hoped that export bioenergy will not damage or reduce the fertility of the existing soil, something that is sometimes indeed dilemmatic. In addition, other materials in the plantation such as leaves and frond can still be composted if they are also intended as fertilizer. EFB pellet production also always requires energy in the form of electricity for its plant operations. And for that electricity can be produced from biogas by treating the palm oil mill effluent (POME), for more details, read here. The location of palm oil mills which are generally remote are required to be able to produce their own electricity, including if they are going to process EFB into LOF and EFB pellets, the electricity needs should also be fulfilled by themselves.

EFB pellets without leaching process actually can also be used for FBC (fluidized bed combustion) boiler technology and for a limited number percentage of PC boilers. With this leaching process EFB pellets can be used optimally on the PC boiler. Majority of power plants or coal power plants currently use PC boiler technology. So that if the EFB pellet produced can be friendly with a PC boiler the market is more open automatically. Production of EFB pellets which are agricultural waste pellets will usually be the second priority after the production of wood pellets is constrained mainly in terms of the availability and supply of raw materials.