| Coal quality-based utilization is an important development direction of clean coal technology and has broad prospects.However,it will produce a large amount of by-products,semicoke and wastewater.It is an issue to be resolved that effective treatment of these by-products is in urgent need.In this thesis,semicoke was made into semicoke water slurry by coal water slurry technology.It is difficult to prepare high concentration semicoke water slurry because of its low bulk density and narrow particle distribution.Semicoke slurry was blended with coal powder to prepare coal-semicoke-water slurry(CSWS)by gradation technology,which can significantly improve the performance of the slurry and make CSWS suitable for gasification.Naphthalene sulfonate formaldehyde copolymer sodium salt(NSF)was selected as the additive.The constant-viscosity concentration was improved with the increase of dosage until the adsorption of NSF on the surface of coal and semicoke became saturated at the dosage of 0.6wt%.The increase of mass ratio of coal and semicoke can improve the concentration at a cost of reducing the fluidity and static stability.Under the premise of ensuring good fluidity and stability,the concentration reached 64.11 wt%when the mass ratio of coal and semicoke was about 7:3.As the grinding time of semicoke slurry increased,the concentration of CSWS first increased and then decreased slightly.The concentration was highest when the ratio of average particle size of semicoke and coal was about0.07.In addition,the concentration of CSWS became higher as the particle size dirtibution was wider.The comparison between gradation and non-gradation indicated that gradation can improve the concentration by 10%relative to non-gradation.The absolute value of zeta-potential and yield stress of the former was higher and hence the static stability was better.The coarse coal particle can support the slurry and hinder the agglomeration and sedimentation of the fine-grained semi-coke.Therefore,it is important to add coarse coal particle into the CSWS.All the CSWS exhibited pseudo-plastic behavior.It is convenient for the slurry to store and transport by pipeline.Coal chemical wastewater,as another by-product of coal quality-based utilization,is of complex composition and harmful to the environment.The treatment process is sophisticated and the cost is high.If wastewater is directly made into coal water slurry,the slurryability will be reduced.The adsorption effect of semicoke can mitigate the adverse impact on the slurryability and reduce the pollution as well.Coal and semicoke was blended to prepare coal-semicoke-wastewater slurry.The performance of compound additive,which is composed of NSF and acrylic acid CWS additive,is best among several common additives on the market.The slurry prepared from coarse coal particle and fine semicoke particle is better than other samples because the difference of particle size between coal and semicoke is greater.The constant-viscosity concentration can reach to 62wt%and higher.Grinding experiments indicated that if the difference of grindability between coal and semicoke is greater,the performance of slurry prepared by "wet grinding" method is better.The addition of wastewater will reduce the concentration of the coal slurry,but has little effect on the concentration of the coal-semicoke water slurry.Semicoke can adsorb organic matter in wastewater by 0.6%of its own mass and reduce the absorbance of wastewater by 70%.This thesis contributes to the effective treatment and resource utilization of semicoke and coal chemical wastewater,providing insights for industrial production of high performance coal-semicoke-water slurry and coal-semicoke-wastewater slurry. |
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