Thermal Drying Technologies in Power Generation Systems

Thermal drying technologies play a pivotal role in enhancing the efficiency and sustainability of power generation systems by reducing the moisture content of solid fuels. Moisture in fuels such as lignite, woodchips or agricultural residues diminishes heating value, increases combustion instability and elevates emissions of particulates and pollutants. A range of drying methods has been developed, classified broadly into direct and indirect heat transfer approaches. Steam dryers employ extracted steam from turbines to evaporate moisture, while flue gas dryers recycle exhaust gases to supply heat. Rotary and screw dryers offer robust mechanical designs for continuous biomass handling, leveraging co-flow or counter-flow configurations to optimise heat utilisation. Superheated steam drying has emerged in coal and lignite applications, enabling high thermal efficiency and mitigating acid corrosion risks. Recent advances focus on integration of drying units within combined-cycle and integrated gasification combined cycle (IGCC) plants, where waste heat recovery and hybrid drying schemes deliver significant energy savings. These developments are underpinned by rigorous process simulations, energy and exergy analyses, and techno-economic assessments that demonstrate improved boiler efficiency, reduced fuel consumption and favourable payback periods. Globally, thermal drying innovations support transitions to low-carbon power by enabling more reliable use of biomass and lower-grade coals, while also facilitating co-production of heat and power in decentralised and industrial cogeneration facilities.

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Thermal Drying Technologies in Power Generation Systems publication trend

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Technical terms

Moisture content: The proportion of water in a fuel sample, expressed as a percentage of its wet mass, which influences heating value and combustion behaviour.

Steam dryer: A device that uses low-pressure steam extracted from turbines or boilers to evaporate moisture from solid fuels before combustion.

Flue gas dryer: A system that utilises exhaust gases from the boiler as a heat source to reduce fuel moisture, often in combination with a heat exchanger or rotary drum.

Heat carrier: A solid medium, such as steel spheres, that absorbs waste heat from combustion residues and transfers it to moist biomass for indirect drying.

Exergy efficiency: A measure of how effectively a process converts available energy into useful work, taking into account irreversibilities and quality of energy streams.

References

1. Assessing economic feasibility of retrofitting steam dryer and steam-air preheater to existing biomass power plant. Energy Reports (2023).
2. An analysis of integration of a power plant with a lignite superheated steam drying unit. Journal of Cleaner Production (2020).
3. Reduction in Fuel Consumption in Biomass-Fired Power Plant Using Hybrid Drying System. Energies (2023).
4. Drying biomass using waste heat from biomass ash by means of heat carrier. BioResources (2022).