Combustion and Ash Behavior of High-Alkali Coals
Summary
High-alkali coals, distinguished by elevated concentrations of sodium, potassium and other alkali elements, present unique challenges and opportunities in thermal conversion processes. During combustion, these elements volatilise readily, interact with silicates and aluminates, and precipitate as sticky deposits on furnace walls and heat-transfer surfaces. Such slagging and fouling phenomena reduce thermal efficiency, accelerate corrosion and demand frequent maintenance. Ash behaviour is governed by mineral transformations, sintering and fusion events that depend on temperature, atmosphere and coal chemistry. Understanding the mechanisms of alkali release, transport and recondensation is critical to controlling deposit formation and to improving boiler reliability. Globally, high-alkali coals are abundant in regions such as Central Asia, Australia and China; their effective utilisation can support energy security and decarbonisation by enabling co-firing with biomass or by optimising fluidised-bed systems. Practical approaches include coal blending, use of sorbents or bed-material modification, advanced combustion staging and targeted boiler retrofits. Integrating these strategies with real-time monitoring offers a pathway to harness the large reserves of high-alkali coal while mitigating environmental and operational impacts.
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Combustion and Ash Behavior of High-Alkali Coals publication trend
The graph below shows the total number of articles in combustion and ash behavior of high-alkali coals across all publications each year (not limited to Nature Index journals).
Technical terms
Slagging: Formation of molten or partially fused deposits on furnace refractory surfaces due to low-melting ash components.
Fouling: Accumulation of ash and sintered particles on heat-transfer surfaces, reducing heat exchange and promoting corrosion.
Ash fusion temperature: The temperature at which ash transitions from solid to fluid phases, indicating its propensity to form deposits.
Alkali metals: Group 1 elements (notably Na and K) in coal that volatilise during combustion and contribute to deposit formation.
Computational fluid dynamics (CFD): A numerical method for simulating fluid flow, heat transfer and chemical reactions within combustion systems.
References
- Numerical Simulation and Analysis of Semi-Industrial Retrofit for Tangentially Fired Boilers with Slag-Tap Technology. Energies (2024).
- Experimental and Numerical Simulation Research on Combustion and NOx Emission of Low Calorific Value and High‐Alkaline Coal Based on Jet Characteristics of Flow Field. International Journal of Energy Research (2023).
- Understanding the Competition Mechanism between Na2O and CaO for the Formation of the Initial Layer of Zhundong Coal Ash. Energies (2024).
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