Gas-Solid Reactions in Combustion and Gasification Systems

Gas-solid reactions underpin the transformation of solid fuels—such as coal, biomass and synthetic carbon—into energy carriers via combustion or into synthesis gases through gasification. These processes involve heterogeneous chemical steps at the interface between a gaseous reactant (typically O₂, H₂O or CO₂) and the solid matrix, coupled with heat and mass transport within porous particles. Reaction rates may be governed by intrinsic surface kinetics or by diffusion of gases through boundary layers and intraparticle pores. The interplay of pore structure, temperature, gas composition and mineral inclusions dictates overall conversion behaviour, which in turn impacts reactor design, emission control and process efficiency. Advances in experimental characterisation and numerical modelling have deepened understanding of rate-limiting phenomena, informing optimised reactor configurations for power generation, waste valorisation and carbon-negative technologies.

Research from Nature Portfolio

Recent studies have revealed that classical diffusion-limited descriptions of char combustion may underestimate the complexity of the gas-solid interface. High-speed videography and thermogravimetric analysis in oxygen-enriched, temperature-controlled environments show that a CO-rich film can envelop reacting particles, imposing additional convective resistance that elevates the apparent diametric exponent above the usual value of two. This finding challenges prevailing single-film and two-film models by demonstrating that film growth and transport resistance must be coupled explicitly to conversion time. Analytical extensions incorporating the expanding CO layer yield improved agreement with observed conversion times, offering a refined framework for predicting char burnout under a range of industrially relevant conditions.

Gas-Solid Reactions in Combustion and Gasification Systems publication trend

The graph below shows the total number of articles in gas-solid reactions in combustion and gasification systems across all publications each year (not limited to Nature Index journals).

Technical terms

Char: Carbonaceous residue produced by pyrolysis of coal or biomass, possessing a porous structure and reactive surface sites.

Diffusion-controlled regime: Reaction regime where external or internal mass transfer of gas to the solid surface limits the overall rate.

Reaction kinetics: Study of intrinsic chemical rates and mechanisms at the gas–solid interface, often expressed via Arrhenius parameters.

Mass transfer coefficient: Parameter quantifying the rate at which a gaseous species moves through a boundary layer or pore network to reach reactive sites.

Fluidised bed: Reactor type in which solid particles are suspended and mixed by an upward flow of gas, promoting uniform temperature and enhanced gas–solid contact.

References

1. Numerical approaches for thermochemical conversion of char. Progress in Energy and Combustion Science (2022).
2. Experimental investigation and modeling of mass transport properties of O2 in biomass chars. Chemical Engineering Science (2024).
3. Analysis of deviation from classical d02-law for biochar conversion in an oxygen-enriched and temperature-controlled environment. Scientific Reports (2022).
4. The kinetics and mechanism of the combustion of the carbon in biochar from oak, as studied in an electrically heated, fluidised bed of sand. Fuel (2024).