Production of Bark Briquettes from Wood Pellet Factory Waste

To reduce the ash content of wood pellets and thereby improve their quality, a process known as "debarking" (removing the tree bark) is commonly employed. Debarking allows for the production of premium-quality wood pellets, which are typically used for space heating—read more details here. Tree bark has a high ash content, which can reach as much as 10%, and it accounts for approximately 5–20% of the total mass of the tree trunk, with the remaining 80–95% consisting of the inner wood. Factors that influence this proportion include the tree species, the thickness of the bark, and the age of the tree.

Naturally, tree bark has a significantly higher ash content—potentially up to 10 times greater—than the inner wood (the wood core or material used for wood pellets), which typically contains less than 1% ash. This occurs because bark serves as an outer protective layer that absorbs and accumulates inorganic minerals, sand, and dust from the surrounding environment.

Despite its relatively high ash content, tree bark remains suitable for use as fuel due to its high calorific value. The calorific value of dry bark ranges from 3,500 to 4,000 calories per gram (approximately 14.6 to 16.7 MJ/kg). In general, the calorific value of bark is lower than that of the inner wood core, which, when dry, can reach an average of 4,200 to 4,700 calories per gram (17.5–19.6 MJ/kg). The high ash content is the primary factor contributing to the lower calorific value of the bark. Beyond being processed into pellets—known as "bark pellets"—tree bark can also be manufactured into briquettes; the choice between these forms typically depends on market demand.

From a technical standpoint, producing briquettes is easier than producing pellets. The requirements for particle size and moisture content are less stringent for briquettes than for pellets. Furthermore, there are several types of briquettes, depending on the machinery used. Three types of machines are employed for briquette production: screw presses, mechanical presses, and hydraulic presses. For large-scale briquette production intended for industrial fuel, a mechanical press is the most suitable type of machine.

Furthermore, given the high ash content and large volume of bark, a mechanical press is the most suitable choice. Another technical reason is that the friction generated within a mechanical press is lower than that in a screw press. Hydraulic presses, on the other hand, are generally designed for smaller production capacities and are better suited for household or small-scale industrial use. The density of the output from a mechanical press is also higher than that from a hydraulic press. Because the density of the product from a hydraulic press is not excessively high, it can be easily ignited with a standard lighter—making it well-suited for the aforementioned applications—whereas the higher-density product from a mechanical press requires a high-temperature combustion chamber to ignite, rendering it more appropriate for industrial applications.

In the combustion technology sector, reciprocating grate and fluidized bed systems are the most suitable for biomass fuels with high ash content, such as tree bark. In a fluidized bed system, the particle size must be reduced to a very fine level to allow for fluidization—meaning that briquettes would need to be crushed down to that size—whereas a reciprocating grate system can effectively accommodate larger particle sizes. Furthermore, when biomass has a high ash content, conventional combustion technologies—such as static grate or chain grate systems—are prone to issues like slagging (the formation of glassy deposits caused by melting ash) and the obstruction of airflow.

In Europe, bark briquettes are used for domestic heating during the winter, specifically as "night briquettes" (or "over-night logs"). European consumers typically burn standard wood briquettes during the day to warm their homes quickly. However, before going to bed, they place one or two bark briquettes into their wood stove and reduce the airflow. Due to the inherent characteristics of bark, these briquettes smolder for a very long time—lasting anywhere from 8 to 10 hours—without producing large flames. By morning, embers remain in the stove, sparing the residents the trouble of starting a fire from scratch and ensuring the home stays warm throughout the night.

By producing bark briquettes, wood pellet manufacturers can not only achieve a zero-waste operation but also generate additional revenue from this line of business. In general, bark waste from any type of wood processing industry can be utilized to produce these briquettes—as well as bark pellets. 

Stages in the Utilization of Empty Fruit Bunches at Indonesian Palm Oil Mills

In addition to palm kernel shells (PKS) and mesocarp fiber, another solid biomass waste product available in large quantities at palm oil mills is the empty fruit bunch (EFB). EFB represents the largest volume of biomass waste generated by these mills. Mesocarp fiber, along with a portion of the palm kernel shells (PKS), is typically consumed as fuel for boilers. In fact, the volume of EFB produced exceeds that of the mill's primary product, crude palm oil (CPO). Despite this, EFB—which accounts for approximately 20% of the fresh fruit bunch (FFB) weight—remains largely unutilized. Given its substantial volume, it also poses a significant potential for environmental pollution. 

Many mills are striving to achieve a "zero waste" status, which necessitates the processing of empty fruit bunches (EFB). However, the challenges lie in determining the appropriate processing methods, the resulting products, and the overall economic viability. Ideally, this waste should not only cease to be an environmental pollutant but also generate additional profit—ideally, by produce products that maximize returns. A realistic approach, therefore, involves processing EFB in a way that prevents environmental pollution while minimizing the capital investment required for the necessary processing equipment. These factors are critical considerations, grounded in both current realities and future developments.

Empty Fruit Bunches (EFB) have significant potential for use in various bioenergy and biochar products. Through a process of biomass densification, EFB can be converted into pellets, which—much like palm kernel shells (PKS)—can be utilized within the energy sector. Given the massive volume of EFB available, the potential for EFB pellet production is substantial. EFB pellets are expected to emerge as a future trend, following in the footsteps of palm kernel shells (PKS), primarily due to their abundant availability and the fact that the vast majority remains unutilized. When compared to other potential raw materials for pellets—such as wood waste from forestry or the wood working industry—the volume of EFB is highly competitive, if not greater. Furthermore, unlike wood pellets derived from energy plantation (which require the cultivation of species such as calliandra or gliricidia), the production route for EFB pellets is significantly faster.

Another use for EFB (Empty Fruit Bunches) is the production of biochar. Biochar can serve as a soil amendment in the agricultural sector—specifically within oil palm plantations, whether company-owned or managed by smallholders. The application of biochar enhances nutrient use efficiency (NUE) by effectively turning fertilizers into slow-release products. Furthermore, biochar producers can generate revenue through carbon credits by adhering to methodologies established by recognized carbon standards, such as Puro, Verra, or Isometric. Industrial-scale slow pyrolysis equipment used for biochar production also generates excess energy—such as syngas—which can be utilized as fuel for palm oil mill boilers (via co-firing) or for other applications.

Currently, many palm oil mills utilize empty fruit bunches (EFB) by burning them in simple incinerators (as shown in the photo), which yields EFB ash—a substance rich in potassium that can be used as fertilizer. However, these simple incinerators not only generate smoke pollution but also fail to harness the heat produced during combustion. Upgrading to more efficient incineration systems—such as those employing reciprocating grate combustors—and incorporating pollution control equipment, like water scrubbers, would render the utilization of EFB environmentally friendly. Furthermore, the heat generated from combustion (waste heat recovery) can be harnessed for various purposes, including cogeneration with palm oil mill boilers, electricity generation, or other applications. 

Biochar, Soil Health, and the Sustainability of Palm Oil Productivity

Healthy soil is invariably fertile, but fertile soil is not necessarily healthy. Healthy soil teems with life—such as earthworms and other organisms—that naturally provides nutrients. Continuous use of chemical fertilizers without a corresponding addition of organic matter depletes soil microorganism populations. Over the long term, this causes the soil to harden, reduces its nutrient-supplying capacity, and increases crop dependence on chemical fertilizers. Consequently, production costs rise while land quality steadily declines.

The future of the palm oil industry is no longer solely about increasing production; it is also required to demonstrate that productivity can go hand-in-hand with environmental protection and social acceptance. Palm oil plantations must be grounded in the three pillars of sustainability: generating economic profit, gaining social acceptance, and preserving the environment. These principles also guide the implementation of the Indonesia Sustainable Palm Oil (ISPO) standard. Balanced fertilization—combining chemical (inorganic) and organic fertilizers—serves as one such solution.

These two types of fertilizers serve complementary functions. Chemical or inorganic fertilizers provide nutrients rapidly, whereas organic fertilizers improve soil structure and health, thereby sustaining productivity over the long term. A well-balanced combination of the two can maintain high productivity while ensuring land sustainability. Another equally important factor is the use of superior-quality seedlings that are certified or come from reliable sources with proven quality; if the seedlings are unsuitable, the results will not be optimal, regardless of how well they are fertilized.

Biochar is not a fertilizer, so its nutrient content is very low. While some types of biochar do possess relatively high nutrient levels, these are exceptions or added bonuses. As an organic material, biochar is environmentally friendly and derived from renewable sources. Its use also enhances fertilization efficiency—specifically Nutrient Use Efficiency (NUE)—for both chemical (inorganic) and organic fertilizers. This is because biochar transforms fertilizers into slow-release products, allowing nutrient availability to better align with plant needs; read more details here.

Biochar significantly supports soil health due to its favorable physical, chemical, and biological properties. Physically, it features high porosity and low bulk density; chemically, it offers high cation exchange capacity (CEC), alkalinity (high pH), and high carbon stability; and biologically, it serves as a habitat for microorganisms and stimulates soil enzyme activity. Furthermore, biochar is capable of binding toxic substances. This is due to its strong adsorption capacity, which allows it to capture heavy metals (such as lead or cadmium) and chemical pesticide residues present in the soil. These harmful substances are trapped within the biochar's pores, preventing their uptake by plant roots. For more details on biochar quality parameters, read here.

Biochar application is also a climate solution. Biochar can store carbon for hundreds of years in the soil. Each ton of biochar can store up to 3 tons of carbon / CO2 equivalent. This makes it very possible to get carbon credits. For this reason, biochar producers must use methodologies created by carbon standard institutions such as Verra, Puro, CSI (Carbon Standard International), Isometric and so on. By using biochar, fertilizer application becomes optimal, environmentally friendly and improves social acceptance in the community. Economically, the use of biochar can also be very profitable. So regarding biochar, soil health and sustainable palm oil productivity, biochar is very suitable and relevant so its use needs to be widely socialized and increased.

When the soil is healthy, fertilizer use becomes more efficient. High dosages are not always necessary, yet productivity can still increase because the soil functions naturally. Shifting the paradigm to recognize that sustainable productivity depends on soil health is no longer merely an option, but a necessity. Global markets are increasingly scrutinizing production methods, making environmentally friendly cultivation practices a key factor in the competitiveness of Indonesian palm oil. A model that successfully boosts productivity while lowering production costs—all while preserving the environment for long-term sustainability—naturally serves as an exemplary standard.

Reject (Non-Standard) Coconut Fruit for Bioavtur / SAF Production

The international civil aviation organization (ICAO) has included non-standard coconuts on the ICAO positive list – ICAO document – ​​CORSIA Default Life Cycle Emissions Values ​​for CORSIA Eligible Fuels, 6th Edition on October 28 2024. Non-standard coconuts include very small old coconuts, already sprouted, starting to rot or mold and those that are broken. Based on data from a number of research studies, the number of non-standard coconuts in Indonesia is estimated to reach 30% of Indonesia's coconut production. Non-standard coconut is also a potential raw material for the production of sustainable aviation fuel (SAF).

Basically the raw materials sought for SAF bioavtur are pure triglycerides and long chain carbon chains. This is due to the volatility of jet fuel, the preferred components are hydrocarbons in the C10 to C15 paraffin range. Furthermore, to meet the freezing point specifications (-47oC), this paraffin must have many branches to reach this low freezing point. This means that bio-avtur or SAF must have carbon atom bonds or C bonds in the C10-C15 range, and in this range palm kernel oil and coconut oil are most suitable because of the high composition of lauric acid which consists of 12 C atoms.

With the high laurate content in palm kernel oil and coconut oil, the yield will be high because the oil content is in the bio-avtur range, namely C10 - C15. This is different if you use vegetable oil with a longer carbon chain, for example CPO, nyamplung oil or canola / rapeseed oil. If you use long chain vegetable oil, the yield will be small and an extra cracking process is needed to increase the bioavtur or SAF yield.

And because the raw material used for bioavtur / SAF is oil from coconut flesh, the coconut water can be used to produce nata de coco or bottled coconut water, then coconut shells for the production of charcoal, charcoal briquettes or activated charcoal, husk for fuel to produce energy and potassium-rich ash for fertilizer or for planting media (cocopeat) and cocofiber. Meanwhile, coconut cake are used for animal feed.

Biomass Boiler Testing and Selection of Suitable Biomass Fuel

In line with the trends toward decarbonization and sustainability across various sectors of life, particularly in the processing industries (manufacturing/process industries), the use of biomass boilers has become a realistic option today among boilers that utilize other renewable energy sources. Fossil-fuel-fired boilers—such as solid-fuel boilers (coal), liquid-fuel boilers (industrial diesel), and gas-fired boilers (natural gas)—must be replaced with renewable fuel boilers, namely biomass boilers. Apart from technical factors in the form of operational adjustments from previous fossil-based fuels, the suitability and availability of biomass fuels are important factors. Suitability refers to the technical aspect and availability refers to the economic aspect.

Combustion technology for biomass boilers also continues to develop so that efficiency continues to increase. From the beginning in the form of static grates to dynamic moving grates such as chain grates and reciprocating grates, even fluidized beds. And to get optimal performance, biomass fuel specifications must also match the shape, size, calorific value and dryness. If the specifications do not meet the requirements of the combustion technology in the boiler then of course the performance will not be optimal. For example, chain grates are suitable for using fuel that has a uniform size and low water content such as palm kernel shells, wood chips and wood pellets. Apart from that, biomass fuel with ash content which has a high melting point is highly preferred so that the ash does not melt and clog the chain lattice cavity.

Meanwhile, using a reciprocating grate, this system is very reliable for burning biomass with high moisture content (up to 60%), non-uniform size, and high ash content, such as empty oil palm fruit bunches (EFB), bark, and municipal solid waste (MSW). The combustion system moves back and forth periodically (like a moving staircase that moves back and forth) which functions to mechanically turn and stir the fuel. And for fluidized beds, this system has the highest thermal efficiency (>89%) and is very suitable for biomass with very small size (powder/dust), low calorific value, or fluctuating chemical content such as rice husks, sawdust, and coffee grounds. The biomass particle size must be maintained within certain limits so that it can float and fluidize perfectly with the sand bed media. The ideal particle size for a fluidized bed boiler (FBC) generally ranges from 0.1 mm to 10 mm (maximum 30–50 mm for certain components), depending on the specific type of technology used.

As a country located on the equator with a tropical climate, Indonesia is a biomass paradise in the world; read more here. A wide variety of biomass fuels in large volumes can be sourced in Indonesia. The most readily available biomass fuels in Indonesia today are wood chips, palm kernel shells, and wood pellets. Wood briquettes are also available but in limited quantities. Choosing the right biomass fuel will ensure optimal boiler performance, but of course, the economic factors for each metric ton of high-pressure steam produced are equally important. 

Ideally, biomass fuel is available in large quantities, ensuring affordability and high quality. The price of biomass fuel is influenced by various factors, including availability, location, logistics infrastructure, and transportation costs. Furthermore, if the biomass fuel undergoes processing, such as wood pellets and briquettes, production costs also contribute. Palm kernel shells for industrial boiler use in Indonesia require almost no processing; they are simply collected from palm oil mills or CPO mills, which produce waste in the form of palm kernel shells (PKS).

There is a case study regarding the selection of this biomass fuel involving a multinational company. In a certain country, the company’s boilers operate using wood briquettes—specifically, industrial briquettes produced by a mechanical press. This approach was also planned for the company’s plant in Indonesia. However, because producers of wood briquettes are still very scarce in Indonesia—making it impossible to secure a supply—the company ultimately conducted various experiments and trials with different types of biomass fuels and now operates its boilers using wood pellets. Thus, in addition to technical factors, economic factors are also crucial for ensuring optimal and sustainable biomass boiler operations. The trial phase is a critical step in achieving these conditions. 

Strengthening Sustainability Efforts by Reducing or Eliminating the Use of Chemicals in Palm Oil Mill Boiler Feedwater Treatment

A lot of palm oil companies now have sustainability certificates, such as ISPO (Indonesian Sustainable Palm Oil) and RSPO (Roundtable on Sustainable Palm Oil). To market palm oil and its derivatives to Europe, the European Union has implemented the EUDR, or European Union Anti-Deforestation Regulation. This regulation requires every business actor to prove that their palm oil does not originate from deforested land after the deadline of December 31, 2020. The EUDR itself will be implemented on December 30, 2026, for large and medium-sized companies. Sustainability certifications such as ISPO and RSPO are not the same as EUDR compliance, but they complement each other. This is because ISPO or RSPO serve as important tools to strengthen traceability and due diligence to comply with the EU's anti-deforestation regulations. Once certified, ISPO or RSPO simply add detailed spatial geolocation data to fully comply with the EUDR standard.

As the decarbonization trend continues to penetrate various sectors of life, various efforts aligned and relevant to decarbonization and aspirations will become a concern, even an option, and even an obligation. Sooner or later, these climate-smart efforts will become increasingly accepted and become an integral part of human life. For example, the palm oil industry is currently moving towards the use of electric vehicles in the plantation sector. The use of electric vehicles has the potential to provide added value, especially for companies that have obtained sustainability certifications such as the RSPO and ISPO. The use of electric vehicles allows palm oil companies to claim reduced fossil fuel use and reap sustainability benefits.

Another example is the use of organic fertilizers or biofertilizers. The use of biofertilizers or organic fertilizers can have several positive effects on environmental sustainability, as they can reduce the use of chemical fertilizers by up to 25%. This effort not only reduces environmental pollution and health risks but also enriches biodiversity and supports climate-smart agriculture. In an era where sustainability is a focus and a "selling point" for products (especially in Europe), this effort is very effective. This is especially true given the intense competition from other vegetable oils, such as soybean oil and sunflower seed oil.

This is also closely aligned with water treatment, particularly boiler feedwater treatment, which uses less or no chemicals. This also reduces environmental pollution and health risks. Boilers can be considered the "heart" of palm oil mills, converting water into high-pressure steam to power the production process and generate electricity for the mill and its employee housing. Like all production equipment, boilers have a lifespan. When a boiler's lifespan is exceeded, it is not only uneconomical due to high maintenance and operational costs but also dangerous. Good and well-maintained water quality will ensure the boiler's lifespan meets or even exceeds standards.

The average lifespan, which is the technical and economic life of a palm oil mill boiler, is 20 years, and by maintaining water quality, it is expected to be 20% longer, to 24 years. In addition to the technical and environmental benefits, there are also economic benefits. A palm oil mill with a capacity of 45 tons of fresh fruit bunches (FFB) per hour using electrochemical technology will achieve an estimated annual savings of over 250 million rupiah. For more detailed information, please contact us. Currently, according to data from the Indonesian Ministry of Agriculture, the number of palm oil mills in Indonesia is recorded at around 1,200 to 1,500. This is understandable, considering the increasing area of ​​oil palm plantations, currently reaching nearly 17 million hectares, thus increasing the need for palm oil mills.

Why make calculations or simulations for a palm oil mill with a capacity of 45 tons of fresh fruit bunches (FFB)/hour? This is because this capacity is the average capacity of palm oil mills in Indonesia. For example, one of the largest palm oil companies, PT Astra Agro Lestari (AALI), has 32 palm oil mills with a total capacity of 1,570 tons of fresh fruit bunches (FFB) /hour, or an average of 49 tons of FFB /hour, which is close to a capacity of 45 tons of FFB /hour. And with the number of mills in Indonesia, say 1,500 units and each mill can save 250 million rupiah/year, there will be an estimated savings of 375 billion rupiah per year from this boiler feed water treatment, in addition to technical and environmental benefits, especially to strengthen sustainability efforts to meet EUDR requirements.

Environmentally Friendly Boiler Feedwater Treatment in Palm Oil Mills & More in Line with Sustainability Missions

As the decarbonization trend continues to penetrate various sectors of life, various efforts aligned and relevant to decarbonization and aspirations will become a concern, even a choice, and even an obligation. Sooner or later, these climate-smart efforts will become increasingly accepted and an integral part of human life. The upstream palm oil industry (particularly palm oil mills/CPO mills) is no exception. With the use of biomass fuel for boiler operations, which outputs high-pressure steam for palm oil mill operations and electricity production, from a climate perspective, the palm oil industry contributes approximately 1.4% of carbon emissions to the atmosphere.

Emissions from the palm oil industry primarily come from carbon loss during land clearing/deforestation, emissions from peat drainage, and emissions from palm oil mill effluent (POME). In addition, there are also emissions from the use of vehicles for transporting raw materials and palm oil products, as well as for plantation operations (soil cultivation, fertilization, harvesting, etc.), and during palm oil mill start-up. Compared to other sectors, such as energy, power generation is the largest global contributor of emissions at 29%, followed by industry (cement, steel, chemical, etc.) at 21%, and transportation (land, sea, and air) at 15%. Although the global palm oil industry is quantitatively small at 1.4%, in the NZE (Net Zero Emission) effort, it must still be reduced.

This also includes the water treatment sector. In palm oil mills/CPO mills, where steam generated from boilers is used not only for electricity generation but also for mill operations, water treatment, especially for boiler feedwater (BFW), is crucial. Water is likened to blood for the human body. Environmentally friendly water treatment, without secondary pollution and without chemicals, is predicted to become a new trend in this era of decarbonization and sustainability. The high water quality specifications required for boiler feedwater (BFW) require a series of water treatment unit operations. In addition to being clean and clear (TDS <700 ppm), it must also have low hardness, mineral content, and oxygen content.

A number of equipment such as ion exchangers, activated carbon filters, RO membranes, and deaerators are used to produce boiler feedwater (BFW). For an environmentally friendly water treatment process that is more in line with the sustainability mission, the electrochemical method is the solution. By using the principle of redox reactions (reduction and oxidation), electrochemical cells will produce ions capable of sterilization, deodorization, scale prevention, rust protection, decomposition of organic compounds that are not easily biodegradable, remove heavy metal ions, remove residual chlorine, remove residual insecticides, and so on. The use of this method will also save or extend the service life of ion exchangers, activated carbon filters, and especially the RO membrane.

This not only provides environmental and sustainability benefits but also economic benefits. Technical and economic comparisons can also be made between conventional and chemical methods and this electrochemical method. Please contact us if you'd like to make such a comparison, and we'll create a simulation. Besides the longer lifespan of boiler feedwater treatment equipment, which requires less frequent cleaning, another important piece of equipment that can be saved or extended is the boiler. Boilers, which have a lifespan of around 15-20 years, can also last 30% or even more, depending on a number of factors, including water conditions.

Related to decarbonization and sustainability, the palm oil industry is also currently moving towards electric vehicles in the plantation sector. The use of electric vehicles has the potential to provide added value, especially for companies that have obtained sustainability certifications such as the RSPO (Roundtable on Sustainable Palm Oil) and ISPO (Indonesia Sustainable Palm Oil). The use of electric vehicles allows palm oil companies to claim fossil fuel reduction and benefit from sustainability aspects. Technically, when charging the electric vehicle's battery, it comes from renewable energy sources, namely electricity produced by palm oil mills that use biomass fuel (fiber and palm kernel shells) as their energy source, and not from PLN (Indonesia state owned company electricity) , which uses fossil fuels like coal.