Introduction
2024 was the warmest year since human beings began keeping temperature records in 1880. As the years progress, this record will likely be broken time and time again. Unless we do something about it.
If averting the climate crisis wasn't enough of an incentive to reduce fossil fuel combustion, rapidly depleting reserves of the resource might be. Moreover, as fuel prices fluctuate with geopolitical tensions, greenhouse gas emissions drive further temperature increases, and air pollution harms human and environmental health, it is high time that we, as a global community, accelerate the shift towards renewable energy.
At 9% of global primary energy supply, bioenergy i.e. energy derived from biomass, holds the largest proportion of global renewable energy supply. Producing bioenergy is a means to not only ensure energy security but also stimulate rural economies. Producing bioenergy is also integral to the mission of achieving the Sustainable Development Goals (SDGs); it contributes to goal 7 of "affordable and clean energy", goal 11 of "sustainable cities and communities", goal 13 of "climate action" and indirectly, also to the goals of good health and economic growth.
In other words, producing bioenergy can transform the world in multiple respects.
In this article, we're looking specifically at the role that biomass pellets play in the spheres of bioenergy, circular economy, and sustainable development.
Of the diverse plant-based feedstocks that can be used to produce pellets, wood is the most common. Even as far back as 2015, the global production of wood pellets was 25.6 million tonnes - global demand and production are only going up. As the demand for wood pellets exceeds supply and sustainability issues crop up, using non-woody biomass for pelletization has presented a massive opportunity - for biomass processors, for rural economies, and for individual and industrial consumers of clean energy.
Biomass pellets result in no net addition of carbon dioxide to the atmosphere, making them a carbon-neutral fuel. Additionally, when agricultural residues, forestry remains, and organic wastes are subjected to biomass pelletization, problems like open burning and overflowing landfills are mitigated.
In a nutshell, biomass pelletization is a way to divert millions of tonnes of waste from landfills, using it instead to generate energy, produce animal feed and animal bedding, and make other useful products.
What are biomass pellets? What are the benefits of biomass pelletization?
Biomass pellets are small, generally cylindrical, pieces of solid biofuel. They usually have a diameter of 6 to 8 mm, and a length no greater than 38 to 40 mm. When larger in size (diameter of 25 to 90 mm and length between 75 and 300 mm), they are referred to as briquettes. While pellets are more commonly used in small devices like residential stoves, briquettes are more popular in industrial applications.
High-quality pellets are durable, dry, and hard. They leave behind minuscule amounts of ash after combustion. Premium pellets, according to the Pellet Fuels Institute, must have an ash content of no more than 1%. Meanwhile, standard pellets' ash content can go up to 2%. In addition, all biomass pellets should have chloride levels of less than 300 parts per million and dust less than 0.5%.
The Pellet Fuels Institute suggests that one million homes in the United States already use wood pellets to generate heat in their furnaces, boilers, fireplaces, and stoves. Not to mention applications in schools and prisons.
Why use biomass pellets?
Well, when used as an energy source, pellets are clean-burning, renewable, and relatively price-stable compared to conventional fuels used for heating. Given their low moisture levels, compact nature, and standardization, they also have unparalleled consistency and burn efficiency, producing a small fraction of the particulate emissions of raw biomass. Moreover, the standardized shapes and sizes of pellets enable convenient handling, compact storage, cheaper transport, and automatic feeding in large-scale operations.
Essentially, the biomass pelletization process overcomes two of the main challenges of using raw biomass - low energy density and high costs of handling, storage and transportation.
What are the applications of biomass pellets?
Where are biomass pellets used and why?
Thus far, we've focused on the applications of biomass pelletization in the production of heat and power. These applications are popular because beyond direct combustion, biomass pellets can also be converted to the gaseous biofuel called producer gas via the thermochemical process of gasification. This producer gas comprises combustible gases like carbon monoxide and hydrogen, has an optimum heating value, can be burned directly to generate heat and electricity, and can be purified to produce fuel for transportation.
These use cases, while important, paint only part of the picture. As the owner of a biomass pellet manufacturing plant, you might find your ideal customer in a number of places, beyond the market for commercial heating.
The biomass pelletization process is most commonly deployed for the following applications:
Cooking. Biomass pellets can be used as a clean fuel in residential cookstoves, offering an efficient and environmentally friendly alternative to traditional fuels.
Space heating. Both residential and commercial spaces use pellet stoves or boilers to combust biomass pellets and generate heat safely and efficiently. Pellets are favored for their consistent burn and lower emissions compared to raw biomass or fossil fuels.
Heat and power generation. In power plants, industrial boilers, and residential spaces, biomass pellets are used to generate heat and electricity. They offer a much more sustainable alternative to coal.
Combined heat and power. Combined heat and power (CHP) systems use biomass pellets to simultaneously generate electrical power and useful heat.
Industrial processes. Industries may use biomass pellets as a source of direct heat for drying processes. They may also use pellets as supplementary fuel to power manufacturing processes.
Animal feed. Beyond meeting energy demands, biomass pellets are also used as animal feed. In this case, diverse ingredients including proteins, minerals, fibres, and fats are mixed in predefined ratios to obtain nutritious pellets for cattle, poultry and aqua farming.
Animal bedding. Alternatively, the animal farming sector also uses biomass pellets as a comfortable and absorbent bedding material for livestock.
The use of biomass pellets is spread wide in terms of not only application but also geography. Europe and China are leading consumers of biomass pellets. The UK, the Netherlands, Germany, Belgium and Denmark report widespread use of biomass pellets for residential heating. China, Japan, Germany, the UK, and the Netherlands commonly use wood pellets. In India, while biomass pellet-based energy generation is still growing, there have been successful examples of the use of rice husk biomass to electrify rural regions.
Since biomass pellets can be used easily in simple devices like boilers, stoves and gasifiers in residential and industrial settings, there is great potential to increase adoption in other parts of the world. This is particularly true for rural areas in developing countries in Asia and Africa, where biomass pellets can replace the direct combustion of firewood for cooking and heating.
In the first section of this article, we explored the basics: the what and why of biomass pellets. Now, let's dive straight into the biomass pelletization process.
Biomass pelletization process
Biomass pelletization is the process used to convert biomass into high-density, solid carriers of energy. These pellets are of different types and grades, manufactured for use as renewable energy or as animal feed or bedding. They are produced according to regional or international standards, like the European standards or ISO, for biomass pellets and raw material classification.
A biomass pellet manufacturing plant does a lot more than simply the pelleting process. Before and after pelleting, there are multiple preparatory and conditioning steps which ensure that the final product meets the desired quality standards. From feedstock selection and grinding to pelleting, cooling and sifting, let's explore the operations of a typical biomass pellet manufacturing plant.
Feedstock selection.
Feedstock selection is important for several reasons. Your choice of feedstock will depend on your desired product quality, raw material availability, the standards you are aiming to achieve, and the processing technologies available to you.
Common feedstocks used for biomass pelletization methods include wood industry waste, forestry residues, agricultural waste, energy crops, and commercial grasses. Regardless of what biomass you choose, you should ensure that its moisture content can be effectively reduced to about 10%, giving it a high energy conversion efficiency.
Cleaning and batching.
The selected biomass is pre-cleaned to eliminate iron, stones, and any other unwanted foreign materials that may affect the functioning of your process machinery.
If the biomass is being pelletized for animal feed, at this stage, the different constituents of the feed are weighed and mixed as per the formulation to make up a batch. Special containers equipped with gravity or screw feeders are used to facilitate controlled material discharge into weigh bins. The bins may also be fitted with vibrators to prevent jams and enable continuous material flow.
Feedstock grinding.
To prepare the feedstock for the biomass pelletization process, manufacturers must grind the biomass to a fine size. For standard pellet mills, the particle size should typically not be more than 3 mm.
Depending on the feedstock and the biomass pelletization methods being employed, the equipment used for grinding may also vary. Large and dense materials like wood may require the use of a chipper. Subsequently, a hammer mill may be used to reduce particle size even further. Meanwhile, biomass softer and smaller than wood, say, agricultural waste like straw, can be fed directly into a hammer mill. Hammer mills are usually fitted with screens of size 3.2 to 6.4 mm.
Moisture control.
Raw biomass can have a moisture content as high as 50 to 60%. Drying raw biomass increases its efficiency and results in the production of almost no smoke on combustion. This is why moisture control is an essential part of preparing biomass for the pelletization process.
Regardless of the type of feedstock, its moisture content must be reduced to about 15%. The specific percentage will vary based on the nature of your particular raw material. You can achieve the desired moisture control by either oven-drying or blowing hot air over or through the ground particles. Make sure you don't over-dry your feedstock - a small amount of moisture is necessary to help the biomass particles bind to one another.
Biomass pelleting, also called extrusion.
Once the biomass has been appropriately prepared, it is time for the central step of the biomass pelletization process: extrusion or pelleting. In this step, a roller is used to compress the biomass against a heated metal plate, referred to as a die. The die comprises several small holes of a fixed diameter which permit the biomass to squeeze through under the right temperature and pressure conditions.
The high temperatures generated in the process cause the lignin and resins in the biomass to soften and act as binding agents. As a result, the biomass particles fuse to form a solid mass, each of which is a pellet. When the chosen biomass does not naturally have the required lignin or resins, you may have to add binders during this stage. As the pellet exits the die, a blade is used to slice it to the desired standard length.
Cooling.
Pellets leaving the pellet mill are at fairly high temperatures, anywhere between 70 and 150°C. This lends them a softness. To eliminate the heat and the softness, biomass pellets are cooled and dried by blowing air through them. The final acceptable moisture content of the pellets is a maximum of 8%.
Sifting.
The extruded pellets may be passed through a vibrating screen to eliminate fines as well as oversized particles. These separated particles are re-pelleted to avoid wastage and maximise yield.
Packaging.
An overhead hopper and conveyor belt combination is typically used to package biomass pellets into larger bags. Best practices include clearly labelling each bag with the type of pellet, its grade, and its heat content.
Biomass pelletization process challenges and optimizations
Regardless of the biomass pelletization methods that you employ, you are likely to encounter certain challenges in your manufacturing journey. Nevertheless, there are ways to overcome these challenges and optimise your processes for quality, efficiency and sustainability.
Environmental concerns.
Using biomass pellets has many environmental benefits. However, producing and using these pellets can also have unintended negative impacts on the environment.
- Land use change. High demand for biomass pellets can encourage large-scale biomass production. Generating a supply of raw materials for the industry can result in harmful land use changes. This challenge can be circumvented by making well-informed sourcing decisions. Biomass pellet manufacturing plants which prioritise true sustainability use mainly agricultural and forestry residues which would have otherwise been discarded. When possible, they also ensure that the farms and forests they source from use sustainable practices.
- Air pollution. Poor quality pellets or improper combustion of biomass pellet fuels can result in the emission of harmful particulate matter. This is why quality and education are both important priorities in the ambition to increase biomass pellet adoption.
- Transport emissions. When pelletization is carried out in a plant far away from the original source of the raw material, the large size of the raw biomass can increase not only transport and storage costs but also carbon emissions. To prevent this, biomass pellet manufacturing plants should process the feedstock into pellets as close to the feedstock supply as possible. Suppliers of raw materials should also try to minimise the size and density of the materials they send to the plant.
Feedstock diversification.
As the biomass pelletization industry looks beyond wood as a raw material, it is considering several alternative feedstocks. With these varied feedstocks comes the challenge of developing appropriate biomass pelletization methods to ensure high-quality pellets for whatever their end use.
Experts in the industry are working to optimize the pelletization process for non-woody feedstocks. Our very own OM Innovation Centre is also equipped to research and innovate effective solutions for our customers who run biomass pellet manufacturing plants and want to explore the use of alternative feedstocks, say, barley straw, rice straw, garden waste, etc.
Process configuration.
During the pelleting process, there are two main challenges you may face. One is washthrough, when pellets don't form. Instead, the granulated feedstock simply falls through the die holes without fusing to form pellets. This happens when the back pressure in the die isn't sufficient to bind the particles together. This challenge can be overcome by ensuring you are operating your pelleting equipment at the right speed, setting and temperature, with the feedstock having the optimum moisture content. You may also have to mix in another material, like distillers dry grain, to establish the necessary conditions for biomass pelletization.
On the other hand, your biomass pellet manufacturing plant may be faced with the issue of clogging. This happens when the back pressure is too high, preventing any of the feedstock from getting pressed through. This problem can be addressed by changing the moisture content of the feedstock, the dimensions of the die, or the tightness of the rollers. The addition of oil may also yield favourable results.
Optimising your biomass pelletization methods.
On average, the energy needed to pelletize biomass is between 16 kWh/t and 49kWh/t. A large part of this energy is devoted to transporting the biomass through the inlets of the press channels. Given these high energy requirements, it is important to optimise your process to reduce energy consumption and consequently, control costs. The rate of electricity consumption as well as the rate of production are correlated to the type of raw material you use, the feed size, moisture content, and other such conditions. Make sure that you research and iterate the process with your engineering partner till you reach the most energy- and cost-efficient methods for your biomass pellet manufacturing plant.
At the end of the day, biomass pelletization is as much an art as it is a science. To develop a reliable process - in terms of moisture content, feedstock particle size, processing time, temperature and methods - needs adequate testing, attention to detail, and strong process expertise.
While it is vital for a biomass pellet manufacturer to understand the technicalities of the manufacturing process, simply having a hold over the technical parts is not enough. You must also have an understanding of the supporting infrastructure and systems you will need to ensure the smooth operations of your biomass pellet manufacturing plant.
That's exactly what we'll help you with in this final section of the article.
Infrastructure for biomass pelletization
Sourcing appropriate feedstock, processing it, and bringing it to market requires a strong infrastructural foundation, including processing equipment, utilities, logistics, and a resilient supply chain.
- Biomass pelletization equipment
When we say biomass pelletization equipment, we are referring to the entire range of machinery necessary to convert raw biomass into usable biomass pellets. This includes equipment like dryers-rotary drum dryers, superheated steam dryers, flash dryers, spouted bed dryers, or belt dryers; considering that drying is extremely energy intensive, ensure that you choose the most appropriate mechanism for the feedstock you are using.
You will also need pellet mills. Pellet mills or pellet-making machines are available in various sizes, making the biomass pelletization process feasible at many scales, from domestic to industrial production. They generally comprise a screw conveyor, a hard steel die, rollers, a barrel, and a hopper, with the size of die used depending on the desired pellet size.
We vouch for CPM's pellet mill technology for its practicality, robustness, and durability. Not only does it offer high efficiency, high production capacity and low maintenance but it also consumes relatively less power per unit and is economical for the value it offers. CPM also offers hammer mill technology and a gyro sifter for other processes in biomass pelletization.
Additionally, we also have in-house technologies for biomass pelletization - our screw conveyor, bucket elevator, chain conveyor, and ribbon blender mixer are ideal for different parts of the pellet manufacturing process.
- Power supply
Operating a biomass pellet manufacturing plant is an energy-intensive process. From drying damp feedstock, grinding it and pressurizing it through the die to operating all the other necessary machinery, large amounts of power are consumed. Generally, a pelletizer alone needs 50 to 100 kW of electricity per tonne per hour of production capacity.
Some large plants burn a portion of their feedstock to generate heat for drying. Other plants rely on any other reliable source of energy. Sometimes, gasoline or diesel-based equipment is also used.
- Supply chain and logistics
In any agriculture-dependent industry, there are strong interconnections between different elements in the value chain. This also holds for the biomass pelletization industry. All operations in the biomass pellet supply chain-from biomass production and harvest to collection, pretreatment, storage, pelleting, and packaging-depend on the availability and efficiency of the rest. This presents many challenges for biomass pellet manufacturing plants; their operations are affected by the seasonality of the supply of raw materials, scattered biomass distribution across geographic locations, and other environmental and social factors like climate change, labour availability, etc.
Before you enter the biomass pelletization industry, we recommend you study the value chain and identify potential partners you can work with every step of the way.
- Market access
Further downstream, you also have to think about market infrastructure so that you can sell the biomass pellets you produce to consumers who need them. Your market will depend on the type of feedstock you use and the application it is suited for. For instance, grass- or crop residue-based biomass pellets are less suitable for heating compared to wood pellets; so you may want to sell pellets made of these materials in non-energy markets, like animal bedding.
There are solutions to streamline your journey of producing and selling biomass pellets and briquettes. For instance, certain organisations connect farmers, biofuel producers, industrial buyers, and logistics players. Platforms like these bring all players in the supply chain to one place, making sourcing feedstock, selling pellets and briquettes, and accessing other supply chain services much easier and more efficient. Consider working with such platforms to ensure you are making the most of the infrastructure that exists in your regions of operation.
Biomass pellet manufacturing plant cost
Finally, we come to the question that is likely foremost on many of your minds: what is the average biomass pellet plant manufacturing cost?
Industrial biomass pellet manufacturing plants are a significant investment. Depending on the quality, production capacity, and demand dynamics of the product, you may end up shelling out anywhere between USD 70,000 to USD 250,000. In our projects at Kumar, we provide world-class CPM technology, with our pellet mill range starting from the price of INR 2 crores.
On a per-tonne production basis, larger-capacity equipment often turns out costlier than lower-capacity equipment because these machines demand greater durability. They also generally produce pellets of higher quality.
In general, while selecting equipment for biomass pelleting and allied processes, there are a few principles you should keep in mind. First, opting for the cheapest machinery often turns out to be a case of false economy; in future, you may end up paying a lot more for maintenance and repairs. Second, ensure that spare parts, maintenance, and other after-sales support are available for the equipment you invest in. Third, make sure that you budget for all the equipment you will need; generally, your pellet machine alone will account for half of your total equipment CAPEX costs. Fourth, remember to budget operating expenses-the cost of feedstock, labour, energy and maintenance-when assessing the true cost of your biomass pellet manufacturing plant. This assessment should also include the cost of new dies which must typically be replaced after every 1,000 to 1,500 hours of operation.
Conclusion
Given the relatively clean pollutant profile and carbon-neutral combustion of pellet fuels, biomass pelletization is an indispensable part of the world's journey towards net-zero emissions. As technologies as well as adoption improve, biomass pellets are also likely to have increasingly competitive prices. These circumstances are setting the stage for a world in which biomass pellets are commonplace - for heating, electricity, animal feed, and other needs.
Biomass pellets are among the most promising sustainable solutions to the problems of growing energy demand, agricultural waste management, rural development, and climate change. As you embark on the journey of setting up a biomass pellet manufacturing plant, Kumar is committed to supporting you in your efforts through our sustainable, robustly engineered, and operationally profitable solutions. Together, let us make our food, feed, and fuel ecosystems greener.
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