## 4 CWS Development
### CWS Research  
The development of CWSs and the aforementioned trials demonstrated the concept of using these types of fuels as a potential substitute for conventional oil-derived fuels. In several previous studies, coal-fueled operations have been characterized quantitatively and qualitatively by analyzing their combustion processes and by their products' properties. [PERSON] et al. (1995) investigated the effects of the type of coal used, solid amount, and particle size on the rheology of CWM. Seven bituminous coals were used in the study, with the particle size distribution obtained by sieving for particles greater than 38 um and using a Coulter counter for particles less than 38 um. Rheological tests were conducted using a Haake RV-12 viscometer.The authors found that allthe slurries exhibited pseudoplastic behavior. Blending with the coarse coal fraction was useful in reducing the slurries' viscosity, and static stability measurements performed with a rod penetration test revealed that stability was greatest when the same optimum coarse/fine ratio was utilized [34]. [PERSON] et al. (1996) analyzed particle size effects on the flow properties of a Southern Australian CWS. A low-grade Lochiel coal from Southern Australia was used for the preparation of the CWS. The particle size distribution was varied by introducing a coarser fraction of coal into the finer fraction in different proportions. The solid loadings were in the range of 23% to 50% by weight. The authors found that the slurries prepared from only a finer fraction, i.e., under 45 \(\upmu\)m, were more viscous than the coal-water slurries prepared from a mixture of coarse and fine particles, with coarse particles varying from 208-279 \(\upmu\)m. The ratio of coarse to fine was 40:60 and showed the lower apparent viscosities [35]. [PERSON] et al. (1997) analyzed the effect of granulocyte of coal particles on the rheology of the slurries. The coals studied included two raw lignites, Lochiel and Bowman's coal, obtained from Southern Australia. The rheological properties were measured using a Haake RV-100 viscometer. The prepared coal-water slurry consisted of 23% to 50% Lochiel coal and 40% Bowman's coal. The authors found that the solid concentration affected the nature of the slurry, with 23% Newtonian showing shear-thinning at higher concentrations. Above 40%, the slurry showed viscoplastic behavior, and adding a coarser fraction to the suspension substantially reduced viscosity. No additives were used [36]. [PERSON] et al. (1997) analyzed the sedimentation stability of a CWS using deashed coal with and without a stabilizer. Three CWMs were prepared with equal apparent viscosities, controlling coal concentration, using polymethacrylate as a dispersant and rhamsan gum as a stabilizer. The study found that very small quantities of rhamsan gum were enough to avoid sedimentation of the particles [37]. [PERSON] et al. (1998) conducted research about the granulometry effect on the rheology of a lignite-water slurry. The lignite sample was divided into six: 125-90, 90-75, 75-63, 63-53, 53-45, and \(<\)45 \(\upmu\)m. The authors used a concentration of 60% of solids. The results showed that the slurry with a particle distribution pending just for fines was not suitable, as its viscosity was very high. Thus, the authors mixed several different fractions to obtain an optimized distribution of particle sizes lower than 125 \(\upmu\)m. The authors also investigated the sedimentation behavior of the slurries and found that with size increment, sedimentation also increases. However, above a given particle size (\(>\)35 \(\upmu\)m), sedimentation became slower [38]. [PERSON] et al. (2002) analyzed the rheology and stability of a slurry using four different additives, such as rhamsan gums, carboxy methyl cellulose or xanthan gum. In the study, fly ashes from Matsuura Power Station in Kyushu Island (Japan) were used. Fly ashes were dispersed in deionized water at a concentration of 68 wt %. Dispersant concentration was 0.3 wt %.