As industries push toward decarbonisation, biomass and waste-derived fuels are increasingly seen as practical alternatives to fossil fuels. However, the transition is rarely straightforward. Biomass firing introduces fuel variability, ash-related challenges, and combustion instability that demand advanced engineering solutions rather than simple boiler replacement.
Biomass Is Not a Uniform Fuel
Unlike coal or natural gas, biomass fuels vary widely in moisture content, ash composition, and calorific value. These variations directly influence combustion stability, slagging tendency, and overall boiler availability.
One of the most demanding examples discussed was Empty Fruit Bunches (EFB), a by-product of crude palm oil production. While EFB offers strong sustainability benefits, it is considered one of the most difficult biomass fuels to fire consistently.
Key challenges associated with EFB include:
- Low ash melting point: below 750°C
- Lower heating value: approximately 7,770 kJ/kg
In comparison, wood chips typically have an ash melting point around 1,200°C and a higher heating value of about 9,000 kJ/kg. The lower ash melting point of EFB significantly increases the risk of clinker formation and slagging, which can disrupt operations and reduce plant availability.
Designing Combustion Systems for Difficult Fuels
The presentation emphasised that reliable biomass firing begins with fuel-specific combustion design, particularly when handling residues such as EFB that behave very differently from conventional fuels.
1. Water-Cooled Combustion for Temperature Control
To manage fuels with low ash melting points, water-cooled stepgrate combustion plays a critical role. This design allows precise temperature control throughout the combustion stages, including drying, pyrolysis, gasification, fixed carbon oxidation, and final burn-out.
By keeping combustion temperatures below critical ash melting limits, water-cooled grates help:
- Minimise clinker formation
- Prevent slag build-up
- Reduce unplanned shutdowns
- Maintain consistent steam generation
This controlled temperature profile is essential for maintaining operational stability when firing problematic biomass fuels.
2. High-Conductivity Refractory for Slag Resistance
In addition to the grate designs, furnace protection materials play a vital role in handling aggressive ash behaviour. The presentation highlighted the use of high-conductivity refractory linings, particularly in the first pass of the furnace.
These refractories are characterised by:
- High thermal conductivity
- Silicon carbide (SiC) content
- Slag-repulsive properties
Strategically placed, they protect critical components such as collector welds while maintaining stable heat transfer and reducing slag adhesion in high-temperature zones.
3. Optimised Furnace and Boiler Design Using CFD
To further refine combustion performance, Computational Fluid Dynamics (CFD) is used extensively during the design phase. CFD simulations help engineers analyse:
- Flue gas flow patterns
- Velocity distribution inside the furnace
- Temperature profiles along furnace walls and boiler surfaces
This approach ensures complete fuel burnout, uniform heat absorption, and controlled emissions, even when fuel quality fluctuates. Optimised flow patterns also reduce local hot spots that can accelerate slagging or material wear.
From Environmental Benefit to Commercial Viability
Beyond combustion engineering, the presentation addressed a critical question for plant owners: Does biomass cogeneration make financial sense?A case study compared an existing system using coal-fired steam and grid electricity with a proposed biomass cogeneration plant firing rice husk.
1. Existing Configuration: Coal and Grid Power
Under the existing setup:
- Steam generation using coal costs 119.5 million THB per year
- Grid electricity costs 68.0 million THB per year
This results in a total annual utility cost of 187.5 million THB.
2. Biomass Cogeneration Scenario
In the biomass cogeneration configuration:
- Biomass steam generation costs 141.8 million THB per year
- Grid electricity demand is partially offset, reducing costs to 15.1 million THB per year
The total annual utility cost drops to 156.9 million THB.
3. Net Savings and Sensitivity Factors
The shift to biomass cogeneration delivers a net saving of 30.6 million THB per year when compared with coal-fired steam and full grid electricity dependence.
Savings can increase further if:
- Coal prices rise beyond current levels
- Electricity consumption grows in the future
- Natural gas becomes the baseline fuel instead of coal
- Biomass prices decrease
Impact of BOI Tax Incentives
The financial outlook improves significantly when BOI tax incentives are applied. With a 100% BOI tax exemption, the project economics demonstrate:
- Internal Rate of Return (IRR): 17.82%
- Project payback period: 3.34 years
These figures underline that biomass cogeneration is not only an environmental decision, but also a commercially robust investment under supportive policy frameworks.
Proven Across Geographies and Applications
The presentation also showcased operational biomass plants across multiple regions, including Southeast Asia, Europe, China, Africa, and Latin America. These reference installations demonstrate the adaptability of biomass systems across different fuels, climates, and industrial processes.
Key Success Factors for Biomass Conversion
The session concluded by identifying three critical factors that determine the success of any biomass conversion project:
- Fuel- Long-term availability, supply security, and flexibility to handle fuel variation
- Technology- High efficiency, high availability, and consistently low emissions
- Plant Layout- Well-designed boiler island and efficient fuel storage and handling systems
Conclusion
Biomass firing is not a simple fuel switch. It demands a deep understanding of fuel behaviour, advanced combustion design, and careful integration with plant economics. When executed correctly, biomass cogeneration can deliver lower emissions, a reliable energy supply, and measurable cost savings, making it a compelling pathway for industries moving toward net-zero goals.
Author:
Mr Sakdichote Kijjaroenwong (Chai)
Project Sales Manager
Vyncke, Thailand
