| Bio-oil is the liquid product from biomass pyrolyzing,and exhibits high water and oxygen content,low heating value,strong acidity,corrosiveness and instability.These drawbacks make it difficult for direct utilization.A novel method as a new fuel for combustion and gasification has been proposed to make slurries by blending coal with bio-oil.Both compositions and structure of bio-oil and coal are extremely complex,therefore,bio-oil compositions,coal type and adsorption behavior between coal and bio-oil components would significantly affect CBS properties,which further influence CBS preparation and utilizationCoal samples with different rank were used to prepare CBS,and the effect of coal type on the rheology,thixotropy,apparent viscosity and stability of CBS was studied Results show that anthracite and high rank bituminous coal can be used to prepare CBS with stable performance and low viscosity,indicating they are suitable for CBS preparation.CBS prepared by lignite coal is unstable and high viscosity,indicating it is not suitable for CBS preparation.The stability of CBS prepared by low rank bituminous coal is closely related to bio-oil compositions.The O/C ratio,total acid functional group,phenolic hydroxyl functional group and carboxyl functional group content of coal are determined as main factors affecting the characteristic viscosity of CBS by the method of grey relational analysis.This research provides foundation for selecting coal samples suitable for CBS preparation.Bio-oil samples with different water content were prepared by vacuum distillation of raw bio-oil,and the influence of water content on CBS properties was investigated CBS samples can be divided into strong pseudoplastic and weak pseudoplastic CBS based on the rheological index of CBS whether it is larger than 0.800,most of weak pseudoplastic CBS is stable,while the stability of strong pseudoplastic CBS is related to coal type and water content in bio-oil.Water is the most important component in bio-oil affecting CBS properties,and rheological behavior of CBS would change from weak pseudoplastic to strong pseudoplastic with the increase of water content in bio-oil.There is a special water content in bio-oil,CWmin,at which CBS has the minimum characteristic viscosity.The value of CWmin is related to coal type and coal concentration in CBS.Therefore,the properties of CBS could be improved by regulating the water content in bio-oil.Bio-oil samples with different co-solvent and sugar content were prepared by adding model compounds into bio-oil,and the influence of co-solvent and sugar content on CBS properties were investigated.The results show that the stability of CBS is less influenced by the content of co-solvent and sugar in bio-oil.As the content of amphiphilic co-solvent increases,bio-oil viscosity and CBS characteristic viscosity would decrease.While the content of hydrophobic co-solvent in bio-oil increases,bio-oil viscosity would slightly decrease and CBS characteristic viscosity would increase.But as the content of sugar in bio-oil increases,both bio-oil viscosity and CBS characteristic viscosity would increase.Thus,bio-oil with high content of amphiphilic co-solvent or low content of hydrophobic co-solvent and sugar tends to prepare stable CBS with low viscosity.The adsorption characteristic of coal to bio-oil components were studied by measuring the compositions of bio-oil before and after adsorption and the quantity of free liquid in CBS,and the effect of bio-oil compositions and coal type on adsorption behavior of coal to bio-oil components were investigated.Different bio-oil samples prepared by model compounds were used to study the effect of pyrolytic lignin on CBS stability.Results show that coal has strong adsorption selectivity to co-solvent but weak adsorption to water and sugar,and the adsorption behavior of coal to pyrolytic lignin is related to bio-oil compositions,where coal shows weak adsorption selectivity to pyrolytic lignin in bio-oil with low water content but strong adsorption selectivity when in bio-oil with high water content.Pyrolytic lignin is the most important component that keep CBS stable,but CBS would be unstable as the quantity of pyrolytic lignin precipitates in CBS is large.CBS could keep stable during storage when the content of pyrolytic lignin in free liquid of CBS is larger than 4.50 wt.%.The O/C ratio,total acid function group content,phenolic hydroxyl group and carboxyl group content of coal are major factors affecting adsorption quantity of coal to bio-oil components by the method of Pearson correlation analysis.The stability of CBS is closely associated with the adsorption characteristic of coal to bio-oil components and decided by free liquid content in CBS.Strong adsorption ability of lignite and low rank bituminous coal to bio-oil components was observed,and the free liquid content in CBS prepared by these coals is low.Weak adsorption ability of high rank bituminous coal and anthracite to bio-oil components was found,and free liquid content in CBS prepared by these coals is high.Combining results of previous research,the dispersion and stabilization mechanism of CBS is proposed. |
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