| How to have an efficient utilization on the traditional energy is still a focus of attention in China. The Coal-water slurry(CWS) is widely applied as a coal-based clean fuel. The CWS which meets the requirements of industrial application should have the characteristics of high concentration, low viscosity, excellent rheological property and stability. In the process of producing slurry, a small quantity of special additive must be added.At present, the main kinds of dispersants for CWS are anionic and non-ionic dispersants. The pulping process of huminc series CWSs dispersants are composed of the humic acid salt and its modified product composition. The characteristics are readily available of the raw material, cheap prices. Besides, the dispersibility of slurrying is excellent, and it can be used separately, but there are also problems such as poor pulping CWS stability, and sensitive to metal ion etc..Studies have shown that: amphoteric dispersant can effectively reduce the apparent viscosity of CWS, but also improve the stability of slurry.In this paper, A new type of zwitterionic humic acid-based graft copolymer dispersant(HSC) for the coal-water slurry(CWS) are synthesized by aqueous solution polymerization with Humic acid(HA), Sodium allyl sulfonate(SAS), Diallyl dimethyl ammonium chloride(DMDAAC), and charactrised via FT-IR, TG and DSC. The effects of DMDAAC dosage, initiator amount and reaction temperature on the CWS performance are discussed. The optimized process conditions are as follows: m(DMDAAC):m(SAS):m(HA)=0.3 ∶ 1.0 ∶ 2. 0, amount of initiator 7 wt%,and reaction temperature 80 ℃. The CWSs performance investigation shows that HSC has better ability in reducing the slurry viscosity than anionic humic acid-based graft copolymer dispersant(HS), and could effectively enforce the CWS stability. The Turbiscan Lab type stability analyzer is used in stability research of the CWS that prepared from HSC,HS and a industrialized naphthalene sulfonate formaldehyde condensate dispersant(NSF).The results shows that the settlement phenomenon is mainly occurred in the CWS prepared from the HSC and HS. with the extension of time, the clarifying zone and destabilisation kinectics index increased, while the coal particle size reduced,which the stability of slurry become poor. However, the CWSs prepared from the NSF is mainly generated reunion and settlement phenomenon with the extension of time,the coal particles began to reunion and settled, while the clear liquid height and destabilisation kinectics index increased, which the stability of slurry become poor. The dispersants ability of enforcing the CWSs stabilities are in the following order: HSC>HS>NSF.The adsorption behavior, surface contact angle and Zeta potential of the dispersants HSC and HS on binchang coal surfaces are all investigated. The results shows that the adsorption behaviors of the zwitterionic humic acid graft copolymer dispersants HSC on binchang coal surfaces are found to be multilayer adsorption. However the adsorption behaviors of the anionic humic acid graft copolymer dispersants HS are found to be single molecular adsorption, that well fit the Langmuir isothermal adsorption, besides, the static saturated adsorption capacity is 12.2224 mg/g. HSC, HS dispersant could diminish effectively the contact angle at coal-water interface, and the HSC has more excellent wetting effect.The Zeta potential measurements show that: HSC, HS dispersants could increase the Zeta potential absolute values of the coal particle surface,therefor HSC and HS had better viscosity reduction effect of electrostatic repulsion.The Binchang CWSs are prepared from HSC, HS and NSF dispersants so as to investigate the influence of various dispersants, slurry concentration and temperature on slurry rheological behaviors. Meanwhile, the rheological curve of CWSs were fitted by Herschel-Bulkley model. The results shows that the rheological properties of Binchang-coal CWSs followed the Herschel-Bulkey model. The CWSs prepared from HSC and HS dispersants that with graft structures shown evident yield pseudoplastic fluid characteristic. However, the CWSs prepared from humate dispersant HA and NSF show slight yield pseudoplastic fluid characteristic. With the increasing of CWSs slurry concentration, the apparent viscosity, yield stress, flow coefficient showed a trend of increase, besides the fluidity characteristics of CWSs would be transformed to yield dilatant fluid. The CWSs prepared from HSC and HS shown higher apparent viscosity and yield stress at 5 ℃, at the same time the slurry shown slightly yield dilatant characteristic. However, the CWSs shown evident yield pseudoplastic fluid characteristic at 25 ℃. With the increasing of pulping temperature, the apparent viscosity, the yield stress and the consistency coefficient were decreased, meanwhile the flow coefficient was increased. Increasing the pulp temperature was benefit to slurry became to Bingham fluid.Effects of electrolytes(Ca Cl2, Mg Cl2, Fe Cl3 and Al Cl3) on the properties such as slurry ability, stability and rheological property of Binchang CWSs that prepared from the HSC and HS are studied. The results shows that the electrolytes has more effect on the slurry forming ability. With increasing the concentration of electrolytes, the apparent viscosity of the CWSs prepared from HSC is increased, however the apparent viscosity of the CWSs prepared from HS is decreased and then increased. The effects of electrolytes on the CWSs forming ability are in the following order: Al3+>Fe3+>Ca2+>Mg2+. The addition of metal ions could effectively enforce the CWS stability, but at the same time reduce the flow of CWSs. The coal particles size remain unchanged and the coal particle sedimentation suppressed. With the increase of the metal ions concentration, the yield pseudoplastic fluid characteristics of Binchang CWSs gradually reduced, The CWSs will be transformed to yield dilatant fluid when the metal ion concentration exceeds the Critical concentration, and then the higher concentration of the metal ions, the more significant of the yield dilatant fluid characteristics. The effect of the trivalent metal ions Al3+ on the yield press and flow coefficient of Binchang CWSs is more significant than divalent metal ions Ca2+. The effect of the dispersants on the rheological properties of the CWSs after the addtion of metal ions is mainly reflected in the improvement of the flow coefficient. For the CWSs prepared from HS, the critical concentration of transform the rheology to yield dilatant fluid is 1000 mg/L, but the Critical concentration of HSC is above 10000 mg/L. HSC shows more excellent characteristics than HS in resistance of metal ion interference. |
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