Study On Rheology And Stability Of Coal-Oil Slurry In Coal/Heavy Oil Hydrogenation Co-Processing

China's coal reserves are abundant but petroleum resources are scarce.The use of coal/heavy oil hydrogenation co-processing technology can effectively improve the utilization rate of coal and heavy oil,providing a path for the production of light fuel oil,which has great development prospects.However,the coal-oil slurry prepared from coal and heavy oil is a solid-liquid dispersion system with the thermodynamic instability.In the process of storage,transportation and preheating,there exists phenomenon of viscosity mutation and coal deposition,causing series of engineering problems such as pipeline blockage and equipment damage.In this paper,XJ,YN and MD were used as three raw coal,while MRAR,FCCS and M:F=1:x were used as three raw oils to prepare different kinds of coal-oil slurries.The effects of temperature,oil viscosity,coal type,coal content,coal particle size and surfactant on the viscosity-temperature and rheological properties of slurries were investigated by using rotational viscometer.Also the effects of above factors and shear conditions on static and dynamic stability of slurries were investigated by stratified sampling method.Finally,the slurry was treated by thermal swelling in autoclave.The effect of coal swelling behaviour on the rheology,stability and hydrogenation reactivity of the slurry was studied and the structural characteristics of lignite and reaction residues before and after swelling were analyzed.Results showed that coal-oil slurry is a typical non-Newtonian fluid.When temperature rises,the viscosity of system generally exponentially decreases,but the non-Newtonian fluid characteristics of system become more obvious,and the thixotropy and flow pattern may change.The higher the aromatics content of oil,and the stronger the swelling property of coal,the more obvious the viscosity peak of slurry.In addition,the feeding viscosity of slurry increases with all kinds of surfactants addition,especially to PEG-6000 with high molecular weight and strong hydrophilicity.The stability of slurry is determined by its viscosity and coal particle size.When temperature increases,the stability of slurry within the temperature range of 80 to 350^oC is reduced at first and then improved.When oil type is changed from low-viscosity FCCS to high-viscosity M:F=1:1,coal content is increased from 25 wt%to 42 wt%,coal particle size is diminished from 150 to 28?m,the relative deviation of slurry upper liquid is decreased,which means the stability of slurry is improved.Meanwhile,the addition of macromolecule weight surfactant,dispersion at higher shear rate or lower shear time during mixing,storage at higher stirring rate or transport at higher fluid velocity,are all effect measures to improve the stability of slurry.Futhermore,the effects of temperature,coal particle size and shearing state are significant.The feeding viscosities of slurries were all increased after thermal swelling treatment at different temperatures between 200 and 350^oC,but the rheologies at high temperature were improved,as well as the stabilities and hydrogenation reactivities.Especially,the dry base ash free coal conversion rate was increased most obviously after 300^oC treatment.As for lignite,after swelling treatment,the mean particle size,specific surface area and porosity,surface roughness were all increased,as well as the degree of condensation,but the content of CH₂/CH₃became lower.While as for reaction residues,the degree of condensation was decreased after swelling treatment.