Research Of Multi-scale Lignite Heat And Mass Transfer Process

Lignite is relatively poorer in quality compared to bituminous coal, with the increasingly serious crisis of resources, development and utilization of lignite gets more and more attention. Lignite in China is relatively abundant, drying is important before going through all the lignite processing. Lignite drying researching contains the mechanism and impact of many factors, but most models ignore the lignite muitiphysics feature.In this paper, theory of porous media and multi-scale theory are applied to the fluid flow and heat transfer in the lignite drying process, the overall analysis of the convection state with the most complex multiphase flow model of the Euler-Euler model, and obtained:in the importing wind speed of0.52m/s, solid fill rate for40%of the normal temperature and pressure conditions, the smaller the particle, the smaller the overall wind speed, wind speed value position of the bed height from top to bottom to reduce; the description of more than0.64m/s distribution of wind speed on the solid content is very small. The result can be relatively accurately simulated the actual situation under the lignite fluidized state, the different particle size and solid-phase stratified gas streaming in the wind speed results in a fluidized bed provide a basis for understanding of lignite as a whole, regions, particles and micro-scale inner state, and also, the analysis points out the boundary conditions for next work.Saturated and unsaturated zones are respectively controlled by Brinkman and Richards’ equations, and obtained:saturation region in the porosity of41.25%penetration rate of5e-15m2conditions, the existence of the temperature field throughout the fluid density distribution, the density inhomogeneity of the flow field generated resistance, the entrance of the coupling field on the pressure boundarythe region larger than the impact on the overall region, slowing down the border at a distance of10-20mm pressure changes; The solid-liquid two-phase flow simulation of the unsaturated region, the paper investigated porosity, temperature and permeability results, and obtained:regional pressure drop gradient becomes larger with increase of porosity from4%to14%; the scope of a certain pressure drop with increasing temperature by5-10mm at the border to penetrate to the15-20mm, viscosity and density have an impact on pressure drop, but the viscosity greater impact; higher temperature promote the flow of lignite water; the critical water head is about15mm, and the critical penetration is about0.5e-7m2.The paper did a detailed analysis from single particle to multi-particle flow and heat transfer on the state of the presence of water in the lignite particles and the coupling migration. At last the paper concerns particle tracking coupled particle dissipation, Obtained:With the increase in the number of particles, pressure and gas flow rate differential has increased; water in small size pore heat transfer effect is superior to the large size of gaps between the individual water, different pressure significantly impact on the relative deformation and the boundary velocity, suitable for analysis of the conditions of particle size of3mm, lmm particles streaming media speed of0.52m/s, feed speed below O.lm/s inlet velocity of the particles the greater the better the flow effect is relatively; to3mm-particulate material, speed of0.2m/s, turbulence intensity in a certain range of about30-40m2/s2is relatively better. The view of particle point flow analysis gives more intuitive understanding of heat and mass transfer.The paper simplified stress under the orders of magnitude in10-6m lignite moisture, considering the condition of the surface tension and viscous force, using moving mesh analysis for an ideal the lignite porous internal state of water flow, and obtained:moist angle of75°, the pore size of more than60um, the performance of weak gravity, water flows to both sides of contraction, the greater the scale, the speed of the peak position of symmetry, the better; the better the wetting liquid equilibrium surface tension gradient the smaller, the result gives an intuitive understanding of the role of the wetting angle and pore scale changes in water status.