Rheological Behavior of Coal-Water Slurries

Coal-water slurries (CWS) are dense suspensions of finely milled coal particles dispersed in water, offering a transportable and cleaner-burning alternative to solid coal. The rheological behaviour of these slurries governs their pumpability, pipeline stability and combustion performance. Key factors include particle size distribution, solid concentration and the nature of coal surface chemistry. Under shear, CWS typically exhibit non-Newtonian, shear-thinning behaviour: viscosity decreases with increasing shear rate, facilitating flow under high-stress conditions while maintaining stability at rest. Yield stress characterises the minimum stress required to initiate flow, reflecting the strength of the particle network. Thixotropy, or time-dependent viscosity recovery, influences static storage and dynamic delivery. Additives such as surfactants, dispersants and polymers modify interparticle forces—electrostatic repulsion, steric hindrance and wetting properties—to control flocculation, reduce yield stress and tailor shear-thinning profiles. Temperature and pH further modulate viscosity by altering water–coal interactions. A deep understanding of these parameters is essential for optimising slurry formulations for efficient pipeline transport, combustion uniformity and reduced environmental impact.

Research from Nature Portfolio

Recent studies have shown that the introduction of a minute secondary fluid phase in particulate suspensions can dramatically adjust rheological parameters. In particular, the formation of a thin hydrophobic layer around coal-like particles, augmented by hydrophobic nanoparticles, has been demonstrated to lower both yield stress and apparent viscosity. This hierarchical surface structuring, inspired by lotus-leaf micromorphology, enhances water repellency and diminishes interparticle attractions under low shear, while preserving shear-thinning flow under operational conditions. Such findings open pathways to novel surface-engineering strategies for coal particles, enabling more stable slurries at high solid loadings without compromising pumpability.

Rheological Behavior of Coal-Water Slurries publication trend

The graph below shows the total number of articles in rheological behavior of coal-water slurries across all publications each year (not limited to Nature Index journals).

Technical terms

Apparent viscosity: Resistance to flow measured under specified shear conditions, reflecting the slurry’s effective viscosity at a given shear rate.

Yield stress: Minimum stress required to initiate flow by breaking the particle network structure.

Shear thinning: Non-Newtonian behaviour where viscosity decreases with increasing shear rate.

Thixotropy: Time-dependent reduction and recovery of viscosity under constant shear and rest, respectively.

Dispersant: Additive that adsorbs onto particle surfaces to enhance electrostatic or steric repulsion, preventing aggregation and lowering viscosity.

References

1. How to Decrease the Viscosity of Suspension with the Second Fluid and Nanoparticles?. Scientific Reports (2013).
2. Progress of Dispersants for Coal Water Slurry. Molecules (2023).
3. Synthesis of a novel amphoteric copolymer and its application as a dispersant for coal water slurry preparation. Royal Society Open Science (2021).
4. Effect of Coal Blending on Ash Fusibility and Slurryability of Xinjiang Low-Rank Coal. Processes (2022).