Optimization And Improvement For DMF Distillation Process And Reseaech On Compound Taper Dual-Flow Tray

As an important organic chemical and excellent neutral solvent,N,N-Dimethylformamide(DMF)is widely used in petrochemical,pharmaceutical,rubber and plastics,chemical fiber,pesticide,dyeing,leather and other chemical industries.This dissertation will focus on the problems of DMF wastewater recovery and gas absorption in the leather industry from the aspects of process improvement and equipment optimization.For the process aspect,an annual output of 120,000 tons of DMF three-effect distillation process is simulated by using commercial simulation software Aspen Plus.Through the investigation of the feed position,operating pressure and reflux ratio of DMF three-effect distillation system,especially the DMF content and energy consumption,the corresponding optimization process parameters were obtained.Based on deficiencies of the current process,three kinds of DMF heat-pump distillation process were proposed,namely double heat-pump distillation process,single heat-pump distillation process and improved double heat-pump distillation process.By comparing the energy consumption of DMF heat-pump distillation process and DMF three-effect distillation process,an optimized process scheme was selected out.The results show that the improved double heat-pump distillation process has the most significant energy saving effect.Comparing with the DMF three-effect distillation process,the improved double heat-pump distillation process introduced reductions of 84.5% in steam consumption and 86.62% in cooling water usage,with additional electricity consumption 1040.8 kW for heat-pump,and the total operating costs reduction rate is 49.03%.For the equipment aspect,a type of compound taper dual-flow tray with merits of low cost,simple structure,low pressure drop and good anti-clogging was developed,based on our previous work of the structure optimization of dual-flow tray.The hydrodynamic characterizations of the compound taper dual-flow tray with down taper ratio of 5%,10%,20% and traditional dual-flow tray were performed in a plexigls column with an inner diameter of 600 mm.The influences of gas load and liquid spraying density on the gas-liquid contacting status,dry/wet tray pressure drop were investigated.The gas-liquid contacting status on compound taper dual-flow tray could be divided into wetting zone,bubbling zone and flooding zone.Due to the shrinking phenomenon of the gas stream,the upper taper owns the lowest dry pressure drop and the highest coefficient,while the down taper with the contrary situations.With the design of the compound tapers,the paths for gas and liquid are selective.For the low gas load situations,the gas phase passes mainly through the upper taper while the liquid phase passes mainly through the down taper,which improves the liquid-passing capacity,reduces the obstruction rate and decreases the wet pressure drop.However,for the high gas load,the turbulence phenomenon of the clear liquid layer on the plate causes the gradual failure of the selectivity of the compound taper dual-flow tray,and the wet pressure drop of the compound taper dual-flow tray was equivalent to that of the traditional dual-flow tray.The difference in wet pressure drop between the compoundtaper /traditional dual-flow trays gradually decreased with the increase of spray density for certain gas loads.