Study On Lignite Drying Process In A New Moving-fluidized Bed Dryer With Internal Heat Source

Lignite reserves are abundant in China,and the efficient and clean utilization of lignite is an important direction of energy development.Lignite has high water content,low calorific value,easy weathering and spontaneous combustion.Among them,high water content is the main factor affecting its application in industry.Therefore,lignite drying is the key to the efficient utilization of lignite.In this paper,a new moving-fluidized bed dryer with internal heat source was developed on the basis of fluidized bed dryer for the lignite drying process with wide particle size distribution and high water content.The hollow horizontal spiral blade where saturated steam flows was equipped in the conventional fluidized bed.Under combined pneumatic and mechanical force,it formed a stable gas-solid two phase flow field with large particles moving and small particles fluidized,and the new moving-fluidized bed with internal heat drying model was established.The hydrodynamic performance,drying process and heat transfer characteristics were studied in the new moving-fluidized bed dryer with internal heat source.The results of fluid mechanics show that,the bed pressure drop decreases and the critical fluidization velocity increases with the increase of the particle size of the material.The height of the static bed increases,the bed pressure drop increases,but the critical fluidization velocity does not change.When the mechanical force field is added to the bed,the bed pressure drop becomes larger;as the strength of the mechanical force field increases,the bed pressure drop decreases,but the effect of the high spiral blade speed on the bed pressure drop is no longer obvious.The bed pressure drop in the moving-fluidized bed is between 630 and 700 Pa.The experimental results of drying process and heat transfer characteristics show that,the drying rate of lignite increases with the increase of operating gas velocity and the increase of inlet gas temperature.The mechanical force increased the drying rate and the heat transfer coefficient;and in the range 3.33 ~ 5.40 r/min of the blade speed,heat transfer coefficient increases by about 35%.The saturated steam within the spiral blade in the form of the internal heat source conducts heat through the spiral blade,greatly strengthened the effect of heat transferring and drying.In the case of other conditions unchanged,the capacity of heat transmission improved by about 45%.The relative formula of heat transfer coefficient in the new moving-fluidized bed dryer with internal heat source was established by dimensional analysis method.