How do Biomass Boilers Work? A Guide for the UK

Written-by

Janet Richardson

Reviewed-by

Richard Burdett-Gardiner

Updated on

Oct 02, 2024

How do Biomass Boilers Work? A Guide for the UK

Biomass boilers work by burning biological matter and outputting the resulting heat for use in heating systems. They can burn a variety of biomass fuels, including wood pellets, chips, logs, or other organic materials. These materials are fed - automatically, semi-automatically, or by hand - into a combustion chamber where they are ignited.

The hot gas and air produced by this process travel through a flue, and are then passed through a heat exchanger, which transfers the heat to the water used in the property's central heating system. Excess heat can also be stored in a thermal tank (also called a buffer vessel), which helps improve the efficiency by storing heat for later use when the demand fluctuates. Biomass boilers can usually easily be integrated with existing space, under floor and water heating systems. 

Biomass boilers can operate similarly to traditional fossil fuel boilers but have a higher environmental benefit due to the renewable nature of biomass fuel. However, compared to fossil fuel boilers, they generally require more space and may need a dedicated fuel storage area for pellets, chips, or logs.

Typical Biomass installation illustration.

Typical Biomass CHP installation Illustration

Biomass and Pellet Boilers: Harnessing Sustainable Heat

Biomass and pellet boilers have emerged as sustainable alternatives to traditional fossil fuel-powered heating systems. As the world becomes more conscious of the environmental impacts of burning fossil fuels, these eco-friendly heating technologies have gained popularity for their efficient use of renewable resources. In this article, we will explore how biomass and pellet boilers work and their role in contributing to a greener future.

Understanding Biomass and Pellets:

Biomass refers to any organic matter derived from living organisms, such as plants and animals. This can include wood, agricultural residues, animal waste, and energy crops. Pellets, on the other hand, are cylindrical, compacted forms of biomass made through processes such as drying and compressing. Wood pellets are the most common type and are created from wood waste like sawdust or wood shavings.

Biomass boilers use a range of fuel types, each with different costs, efficiency levels, and storage needs:

Wood Pellets: Pellets offer high energy efficiency (around 90-95%) and burn consistently. They are often used in automatic systems, though they require dry storage to prevent degradation.
Wood Chips: Chips are less expensive but bulkier and less efficient (70-80%) than pellets, making them better suited for larger systems with ample storage.
Logs: Logs are a traditional, cost-effective fuel option but require manual handling and have lower efficiency (60-70%). They are best for rural properties with access to locally sourced wood.

Fuel prices may fluctuate depending on order size and location, and bulk orders tend to offer lower prices per ton. Delivery costs should also be factored in based on the accessibility of fuel in your area. 

Maintenance and Efficiency

Biomass boilers typically require more maintenance compared to traditional fossil fuel boilers. Regular cleaning of ash and residues is essential to maintain efficiency and prolong the system’s lifespan. Biomass boilers need periodic servicing to ensure efficient performance. Wood pellet and chip systems, in particular, require automatic feeding systems to work efficiently.

Most biomass boilers have an efficiency rating between 70% and 90%, depending on the fuel used and the type of boiler. Wood pellets tend to offer higher efficiency due to their lower moisture content.

How Biomass Boilers Work:

Biomass boilers operate on a straightforward principle of burning biomass to generate heat. The primary components of a biomass boiler include the fuel storage system, the combustion chamber, the heat exchanger, and the flue gas outlet. Let's take a closer look at the process:

Fuel Storage: Biomass boilers require a storage area for the biomass fuel. Fuel storage options include hoppers or larger silos, depending on the system size. This can be in the form of a fuel hopper that feeds the biomass to the combustion chamber automatically.

Combustion Chamber: The biomass fuel is fed into the combustion chamber, where it comes into contact with oxygen and ignites. The combustion process releases heat energy in the form of hot gases.

Heat Exchanger: The heat generated during combustion is transferred to water or another heat transfer fluid within a closed system. The heat exchanger facilitates this transfer and ensures the heat is efficiently utilized.

Heat Distribution: The heated fluid is then circulated throughout the building, providing warmth to the space. This can be achieved through radiators, underfloor heating systems, or forced air circulation.

Flue Gas Outlet: After the combustion process, flue gases containing water vapor and other by-products are produced. These gases are directed outside the building through a flue gas outlet or chimney. In urban areas or Air Quality Management Zones, these emissions may require additional filtration systems to meet local regulations.

Advantages of Biomass Boilers

Biomass boilers offer several advantages that make them attractive options for sustainable heating:

Renewable Energy Source:

Biomass is considered a renewable energy source because it can be replenished over time through responsible forestry and agriculture practices.

Carbon Neutral:

The carbon dioxide released during biomass combustion is balanced by the amount absorbed by growing plants, making it a carbon-neutral energy source.

Reduced Greenhouse Gas Emissions:

Biomass boilers emit fewer greenhouse gases compared to fossil fuel-based systems, helping to mitigate climate change.

Local Economic Benefit:

Utilizing locally sourced biomass fuels can provide economic benefits to rural communities and reduce dependence on imported energy sources.

How Pellet Boilers Differ:

Pellet boilers are a specific type of biomass boiler that operates on wood pellets as the primary fuel source. These pellets have a standard size and moisture content, ensuring consistent and efficient combustion. In addition, pellet boilers tend to have lower emissions due to the uniformity of the fuel and the precise control of the feeding mechanism.

Automated Fuel Feeding:

Pellet boilers often come with automatic fuel feeding systems, which regulate the pellet supply to the combustion chamber. This automation makes them more convenient to use.

Higher Energy Density:

Wood pellets have a higher energy density than other biomass forms, resulting in longer burning times and reduced refilling frequency.

Lower Emissions:

The uniformity of pellets and precise feeding mechanisms lead to lower emissions and higher combustion efficiency.

Additional Financial Considerations and Incentives

In the UK, biomass boilers may be eligible for financial incentives, such as the Boiler Upgrade Scheme (BUS), which offers £7,500 towards installation costs. This helps reduce the upfront investment, making biomass systems more accessible. Additionally, businesses and larger properties may benefit from tax relief programs or regional subsidies.

Conclusion:

Biomass and pellet boilers are proving to be valuable alternatives to conventional heating systems, offering a sustainable and efficient way to generate heat. However, potential buyers should carefully consider installation space, fuel storage, and maintenance requirements before making a decision. Consulting a qualified installer is essential to ensure the system is suitable for your property and local regulations. By utilizing renewable biomass resources, these boilers contribute to reducing greenhouse gas emissions.

As technology continues to advance, biomass and pellet boilers are likely to become even more efficient and affordable, making them an integral part of the UK's transition to sustainable heating.