| ABSTRACT:Research on recovery and reutilization of printed circuit board (PCB) is a hotspot in recent domestic and international studies because of the high metallic values and environmental risk of PCB.The development of urban mines, cyclic economy, energy saving and emission reduction demands great effort in the research of environmental technology and equipment for PCBs’ recycling and disposal.Itis helpful to save time and momey during the researchfor developing a theoretical tool based on numerical simulation.The incinerator is of U-shape structure,composed of combustion tower,smelting pool and disinfection tower and integrates the technology advantages of swirl-flow combustion and high-temperature combustion.Based on the structure of the U-shape incinerator, employing RNG turbulence model, finite-rate/eddy-dissipation model, particle surface reaction model, discrete phase model and P-1radiation model, a numerical simulation of burning and smelting system was built.Compared with experimental date,the simulated relative errord of furnace temperature,O2concentration,SO2concentration were+3.23+8.44%,-5.6%, SO2+2.7%.And the accuracy of simulation was proved.The pollutant emissions such as NO、SO2、O2、CO、Br2、ash were used as the constraint condition to optimize the operating parameters.The conclusions are as follows.(1)The simulation result indicates that recirculation zone exists between the air column and inner wall of the combustion tower and smelting pool.The inner wall at the bottom of the combustion tower and the tail end of smelting poll are eroded and corroded by gas-particleflowwith high speed and temperature. It is necessary to extend the distance between the tail end of smelting polland disinfection tower. The dust rate comes out to be0.16%.(2)With the increase of secondary air preheat temperature,the efficiency of oxygen usage increases,low temperature regionShortens,the peak values of the flame temperature increases,the effective area for burning and smelting becomes larger,the temperature of slap surface in smelting poor increases,fuel burnout rate inceases,but SO2emissionsisexceeding.With the decreased of secondary oxygen concentration, the high temperature region in combustion tower and smelting poor becomes smaller,the flame boundary becomesunclear, the efficiency of oxygen usageand the emissions of NOX and SO2decrease,so is the fuel burnout rate.It can improve the economic and environmental performance of the incinerator to achieve dispersion combustion with low oxygen-content.(3)With the increase of excess air coefficient,the efficiency of oxygen usage decreasesseriously, andthe soot emissionsisexceeding. when excess air coefficientis more than1.4, SO2emissionsisexceeding,Thebest choice for excess air coefficient is1.4.With the decrease of particle size, the efficiency of oxygen usage increases, the peak values of the flame temperature increases, the ignition point and reaction stop point advance and fuel burnout rate inceases.However,the dust generation rate may increase, incinerator inner wall may suffer more corrosion.As a result,the best choice for particle sizeis109μm。 When the loading rateratio of combustion tower nozzle to smelting poor is0.47, the efficiency of oxygen usage and the fuel burnout rate are the highest, the dust generation rate is the lowest.The best choice for ratio is0.47.(4)Grey system research shows that:The main factor affecting NO and O2concentration is excess air coefficient;the main factor affecting SO2and Br2concentration is secondary oxygen concentration;the main factor affecting fuel burnout rate is particle size. |
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