## 4 CWS Development
### CWS Research
The static stability CWS was achieved 3 to 4 weeks after employing the additive [46]. [PERSON] et al. (2009) prepared a highly concentrated CWS using three Indian LGCs with different ash contents. The properties of the slurry were investigated using saponin as a dispersant. Saponins were found to stabilize the slurry. Authors claim that saponin can be replaced by a synthetic compound, such as sodium dodecyl sulphate [47]. [PERSON] et al. (2009) reported the effect of the granulometry, solvent type and ratio, temperature and shear time on Shengli lignite-solvent slurries. Three solvents were used: a hydrogenated recycled solvent obtained from a liquefaction pilot plant, quartic-hydrogenated products of heavy oil from the Anqing Oilfield and tetralin. The results showed changes from pseudoplastic to Newtonian behavior with the increment of the temperature [48]. [PERSON] et al. (2010) applied the Herschel-Bulkley model to analyze the rheological properties of a concentrated CWS. The slurry was dispersed with lignin-based dispersant. Two slurries were prepared with a coal concentration of 64% and a dispersant dosage of 0.7% and 1.5%. The authors found that when the dispersant dosage was 0.7%, the slurry showed shear-thinning characteristics, and at a 1.5% dosage, it showed shear-thickening characteristics. Factors affecting rheological properties, such as solid load and the dispersant content, were also studied. Results showed that the slurry tends toward pseudoplastic characteristics with the increment in solids concentration, but tends toward dilatant flow characteristics with an increase in dispersant dosage [49]. [PERSON] et al. (2010) analyzed the effects of size distribution on the flow in the pipeline. Authors observed three distinct patterns for different size distributions and velocities. Particle size distribution affects flow significantly. Lighter fine- and medium-size particles tend to be lifted up by the turbulent dispersive action of the fluid. In this way, a uniform and suspended flow is achieved, whereas coarser and heavierparticles can also be lifted. However, it is difficult for these particles to become fully suspended, even with high flow velocities [50]. [PERSON] et al. (2012) studied the influence of several variables (fly ash size distribution and ratio) at each one of the four levels on the yield stress and viscosity of the blend. From the experiments, the authors concluded that both particle density and surface area are critical parameters influencing the rheological properties of the slurry [51]. [PERSON] and [PERSON] (2012) studied the effects of size distribution on the rheology behavior of a CWS. A sub-bituminous coal of Indonesian origin was used to prepare the samples. The samples were classified into six particle size ranges. Naphthalene sulphonate formaldehyde and Na-carboxy methylcellulose were used as dispersant and stabilizer, respectively. Viscosities were measured using an MV-2000 series II Cannon Rotary Viscometer at different solid loadings ranging from 60% to 65% by weight. The different packing characteristics of the coal samples were defined by making monomodal, bimodal and multimodal distributions at different coarse-to-fine ratios. The authors observed that maximum coal loading was possible when the coal-water slurry was made from a bimodal particle size distribution [52]. [PERSON] et al. (2014) carried out research using a coal sample of Indian origin. The characterization studies were done prior to the rheological study to determine the ash content, particle size distribution, morphology and coal-water mixture pH values. pH decreased with the increment in solids concentration. After the characterization studies, rheological data were generated for the coal sample to determine the coal-water slurry flow behavior [53]. The same group of researchers continued to develop this area of knowledge, presenting several works in the same and following years [54; 55; 56].