## 4 CWS Development
### CWS Research
Results showed that the additives were effective and increased the stability of the slurry. S-194, with a concentration of 0.2%, was recommended for the preparation of a stable fly-ash-water slurry [39]. [PERSON] et al. (2002) investigated how coal properties affect CWS behavior using Turkish and Siberian bituminous coals with average particle sizes of 50, 36, and 19 \(\upmu\)m. Sodium polystyrene sulphonate and sodium salt of carboxy methyl cellulose were used as dispersant and stabilizer. pH value varied from 7.05 to 7.25 for all tests, with a constant temperature of \(25\pm 2\)\({}^{\circ}\)C. pH varied according to the addition of HCl or NaOH [40]. [PERSON] et al. (2002) analyzed the rheology of Indian CWS using Talcher field coals. It was observed that the viscosity increases with an increment in the solids concentration. The viscosity of a CWS is higher in an acidic medium, with the highest around pH 6 and the lowest around pH 8 [41]. [PERSON] et al. (2003) studied the effects of different dispersants and stabilizers on the rheology of CWS. In the experiments, anionic chemicals such as polyisoprene sulphonic acid soda and sodium salt of carboxy methyl cellulose were used as dispersants and stabilizers. A Turkish bituminous coal was used with an average volatile content. It was found that polymeric anionic dispersants, such as Dynaflow, have greater effects on the viscosity and the stability [42]. [PERSON] et al. (2004) studied the effect of particle size distribution, volume fraction and grade on the slurries' rheology. Experiments were conducted using two Turkish lignites, from Soma and Agacil, and a Siberian bituminous coal. The samples were prepared by mixing different size fractions until the desired d50 (19, 35, 50 um) was obtained. pH of the sample was stabilized by adding an acid or base. The measurements were taken using a shear rate of 100 rpm. The pH value and temperature were kept constant at 7.0 and 25 \(\pm\) 2 \({}^{\circ}\)C [43]. [PERSON] et al. (2005) analyzed the stabilization properties using carboxy methyl cellulose. The materials chosen were brown coals from Soma and Istanbul and bituminous coal from Zonguldak Coal particles were ground to less than 63 um, and the mixtures prepared included 61%, 55%, and 52% coal. Stability was measured using the rod penetration test method. The effect of changing the carboxy methyl cellulose concentration upon penetration after 7 days was studied. The authors found that there was a negligible effect from changing the concentration of carboxy methyl cellulose on the stability of the coal from Soma and Istanbul, as the penetration remained the same after 7 days, and the hydrophilic nature of the lignite coals was attributed to this phenomenon. However, the authors also found that varying the concentration of carboxy methyl cellulose had a profound effect as a stabilizer on the bituminous slurry, increasing the stability, with penetration from 60% to 100% due to the hydrophobic nature of bituminous coal, and the optimum concentration of carboxy methyl cellulose was found to be 0.01% [44]. [PERSON] et al. (2008) studied the effect of coal blending on a CWS using three different samples from Daliuta, Linhuan, and Yongcheng. The maximum size of the coal was 300 um, and 75% of the particles were smaller than 74 um. The dispersant used was a naphthalene sulphuric acid formaldehyde condensate. Linhuan and Yongcheng coal was mixed with Daliuta with a weight percentage of 10-40%. It was observed that the addition of coal with a high grade can improve the slurryability of LGC [45]. [PERSON] et al. (2008) analyzed the rheological behavior of a CWS using a natural additive. Two samples with different ash contents were obtained from the Talcher coal field in Orissa, India. CWS was prepared with a concentration ranging between 55% and 63.7%. Additives varied from 0.4-1.2% by weight. The static stability was measured using a rod penetration test. The authors found that the CWS in the presence of natural additives exhibited Bingham plastic behavior.