Study On The Purification Mechanism To Reduce The Accumulation Of Harmful Gases In Circulated Ventilation Of Foundry

The existing circulated ventilation technology has solved the problem of particulate emissions in the foundry industry,and the recycling of dust-free flue gas has reduced the amount of ambient air used and dust emissions.However,it has also brought about the accumulation of harmful gases such as NO and CO in the dust-free flue gas,which poses a hazard to the environment and workers’health.This paper investigates the accumulation and purification of harmful gases in foundry circulated ventilation technology to improve circulated ventilation utilisation technology.First,the simulation and analysis of the diffusion and accumulation of harmful gases was studied in a closed control room in a foundry.Based on the optimisation of the airflow organisation in the confined room,the effects of different fresh air rates and air changes on the flow field characteristics,diffusion and accumulation of harmful gases in the confined room were analysed.The results show that when the number of air changes in the control room is 10 times/h and the fresh air rate is 20%,the airflow in the control room is best organised and the air velocity near the ground is 0.When the number of air changes is 40 times/h and the fresh air rate is 20%,the concentration of harmful gas accumulation in the purification and dust removal control room is best controlled,and the NO_x concentration is 2.14 mg/m~3 and CO concentration is 40.92 mg/m~3 after 10 cycles,which still exceeds the exposure limit and circulation limit of the staff.Further,at a removal rate of30%,the indoor NO concentration was maintained at 2.95 mg/m3after 14 cycles and the indoor CO concentration was maintained at 17.10 mg/m3after 12 cycles,both of which met the worker exposure limit and the cycle limit.In addition,a series of Cu-Mn-Ce-O_x multi-metal oxide catalysts were prepared by co-precipitation method in order to obtain catalysts with good SCR performance even under low temperature and high oxygen environment of circulated ventilation.The results showed that when the active component ratio Cu:Mn:Ce=1:3:2,the NO and CO removal rates could reach 23%and32%at 80°C and 16%oxygen content,and the catalysts prepared under low temperature and high oxygen conditions still exhibited certain catalytic performance.The effect of the molar ratio of metal components on the catalyst activity and physicochemical properties was also analysed.The results showed that the appropriate amount of Mn-Ce doping increased the specific surface area and pore size of the catalyst,increased the amount of Cu⁺,Mn⁴⁺and surface chemisorbed oxygen species on the metal oxide surface,and the mutual redox reactions between Cu²⁺/Cu⁺and Mn²⁺/Mn³⁺/Mn⁴⁺electron pairs improved the low temperature redox capacity of the catalyst.At the same time,the weakened CO oxidation capacity and enhanced NO oxidation capacity may be the reason why the catalyst still has high NO removal rate in the environment.Furthermore,this paper optimized the surface modification method,loads the CO-SCR catalyst on the surface of the filter media fibres to provide dust removal,NO and CO removal in a synergistic manner.In this study,the above Cu-Mn-Ce-O_x multi-metal oxide catalyst and the filter media were firmly bonded together by grafting a cladding layer on the fibre surface using the etching effect of hydrochloric acid on the filter media and the Si-O-Si interaction bond between the silane coupling agent and the filter media.The structure and properties were also investigated by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,infrared（FTIR）and CO-SCR activity evaluation.The SEM photographs showed that the catalyst was uniformly dispersed on the filter media;the FTIR results indicated that the coupling agent was successfully grafted onto the filter media;the XRD spectra of the catalytic filter media showed that the polymetallic composite oxides were loaded on the filter media in an amorphous state.within the range of 50°C to 260°C,the prepared Cu-Mn-Ce-O_x/KH550/HCl@HSF catalytic filter media had good NO,CO removal effect.Finally,CO-SCR and CO oxidation catalytic reaction kinetics were used to study the effect of variables such as flue gas concentration,air velocity and temperature on the catalytic reaction rate during the reaction process of the above catalytic filter media.The NO reaction rate of low temperature（80℃）and high oxygen（16%）in the foundry purification and dust removal control room was obtained,which wasR_{N O}=-200.65C_{C O}C_NO^0.17.And the CO reaction rate was R_CO=-1.03C_C~1._O~4 C _N~0._O~2 C _O2^0.5.By the way,the apparent activation energy was solved,and the activation energy of CO-SCR and CO oxidation reaction were about 19.70 k J and 16.40 k J,respectively,and the key indexes for evaluating the reaction efficiency and development potential of catalytic filter media were obtained.The development and application of Cu-Mn-Ce-Ox/KH550/HCl@HSF catalytic filter media was of great significance for the integrated removal of dust,NO and CO in the foundry cycle.It provided an important theoretical basis for the further optimization and promotion of circulating air technology.