The Regulation Method Of Suspensions Viscosity Based On Particle Interface Modification

This paper is set in coal water slurry(CWS)gasification technology.In order to prepare CWS with high concentration and low viscosity,we investigated the effects of particle surface properties and additives on the rheology of concentrated particle suspensionsn.In order to alleviate the increasingly serious water pollution by CWS gasification,the influence of common components of wastewater on CWS was researched.The main research contents and conclusions are as follows:In this study,the effects of the second fluid on the viscosity and yield stress of particle suspension were systemically investigated.As the dosage of the second fluid increased,the viscosity and yield stress initially decreased then increased and finally decreased again.The microstructure of the suspension was observed using a confocal laser scanning microscope(CLSM)by marked secondary fluid.It showed three different states with the increasing dosage of the second fluid:dispersive sate,cluster state and cell state in sequence.The presence of these states interpreted the non-monotonic trend of viscosity and yield stress in the suspensions.Low rank coal is rich in pores.In the process of CWS preparation,water will enter into plenty of pores of coal particle to form inner water,resulting in a decrease in free water among particles and an increase in viscosity.Therefore,low rank coal is difficult to prepare CWS with high concentration.However,we found pre-absorption of moisture from air resulted in a sharp decrease of suspension viscosity,since small amount of air were sealed in particle pores.Coal particles have many polar functional groups and pre-absorbed water sealed the entrance of pores through hydrogen bonds like a "bottle stopper",which effectively inhibited the diffusion of water from slurry into the pores of coal particles.Pre-absorption of water from air was also found to improve the efficiency of the second fluid and cause a further decrease in viscosity and yield stress.This idea is promising to be used in CWS preparation with low rank coal.The influences of common components in industrial wastewater,small oxygen-containing organic molecules,on the rheology of CWS were researched.The viscosity and yield stress of CWS were found to increase with the presence of small organic molecules.The microstructures of slurries were characterized using confocal laser scanning microscope(CLSM),FT-IR and contact angle measurement.In CWS,hydrophobic surface of coal particle was found to absorb small oxygen-containing organic molecules with nonipolar group and turn hydrophilic.It resulted in thicker hydration layers and less amount of free water.Thereby,industrial wastewater(containing small oxygen-containing organic molecules)has negative impacts on CWS preparation.Surfactants widely exist in domestic and industrial wastewater.For studying the effects of surfactant on CWS,hollow glass beads in water were choosed as model suspension.Small amouts of anionic surfactant was found to transform hollow glass bead suspension from viscous state to gel-like state,and the folwability become critically bad.Through microstructure characterization,the anionic surfactant was discovered to reduce surface tension and facilitate micro-bubbles produce.Particles gathered around micro-bubbles.Particles in inter-bubble film created a steric barrier and retarded drainage,which was favor to the stability of bubbles.Besides,small bubbles were introduced as the third phase,acting as the secondary,preferentially nonwetting fluid.Suspension therefore was transformed into"cluster state",with great increase of viscosity and yield stress.This paste suspension is a reversible and sub-stable system,which would be destroyed owing to drainage after standing several hours.