Experimental Studies On Dispersion, Softening And Application Of Coal Ash Fiber

Coal ash has become the world's largest solid waste which has seriously polluted the environment. There are a lot of research reports on coal ash utilization, but more belong to the low-end application, such as road building material and building stuff. And the comprehensive utilization ratio of coal ash in China is less than 50%. In recent years, coal ash was made into ultra-fine staple fiber which can be used in papermaking, giving a higher application value to coal ash. The coal ash fiber is a new kind of material lack of basic and applied research, moreover, dispersion and softening of it is the inhibiting bottleneck during the papermaking process. In view of the above, starting from a study on the characteristics of the coal ash fiber and facing to the experiment research on the dispersion and softening of it. In the meantime, considering that coal ash fiber may be used in fiber sand control technology in the petroleum exploitation, the exploratory experiment research on control of proppant flow-back by the coal ash fiber and proppant mixtures was carried out in this thesis. Studies of this dissertation have an important theoretical meaning and practical value on the application technology development of the coal ash fiber.Above all, the morphological features, physical and chemical properties, structure and surface electricity of the coal ash fiber were studied in detail which provides basic data and basis for subsequent treatment and application of it.To solve the problem of fiber breakage induced by the crisp hard features and high hydrophobicity when the coal ash fiber used in paper making, the systemic experiment research on the dispersion and softening of the coal ash fibers was carried out in this thesis.(1) Dispersion experiment research of the coal ash fiber was carried out by chemical dispersing method combined with mechanical agitation. Dispersion effect was evaluated by sedimentation method, suspension and SEM observation method. Finally, the optimal dispersion scheme of coal ash fiber was obtained by adding the combined dispersant, that is, the complex formulation of anionic surfactant, nonionic surfactant and electrolyte salt:1.2% sodium carboxymethyl cellulose, 0.8% sodium dodecyl sulfate, 0.4% sodium polyphosphate and 0.4% hydroxyethylcellulose, then further discussed the dispersion mechanism of coal ash fiber. Referring to methods of surface modification of nano-materials, calcium hydroxide was used for surface modification of the coal ash fiber. Their strength increased significantly and dispersion stability in anionic surfactant solution was improved to some extent.(2) This thesis used chemical method to soften the coal ash fiber, and investigated the impact of the species and amount of softener and softening time on the soften effect of the coal ash fiber. The best scheme was determined as follows: the dosage of softener of dodecyl dimethyl betaine (BS-12) was 2.0%, softening time was 60 minutes, then further discussed the softening mechanism of the coal ash fiber.The experiment indicated that, after dispersion and softening treatment, the coal ash fiber can not only disperse stable in the suspension but also their strength increased significantly.According to conditions of the fiber/proppant mixtures sand-control technology, the coal ash fiber and fiber-mixed proppant properties were evaluated and experiment study on influence of the coal ash fiber on proppant flow conductivity was carried out. The results showed that when the coal ash fiber content is 1.0%, it can be mixed with the proppant to form a good three-dimensional network structure which can play very well in the role of the stability of sand and increase the proppant conductivity significantly under high closure pressure.