Research On Treatment Of Salt-containing And Halogen-containing Solid Wastes By Molten Salts

During the process of industrial production,a huge amount of salt-containing and halogen-containg solid wasts are generated.The disposal of salt-containing and halogen-containing solid wastes using molten salts has unique advantages.At present,the systematic research on treatment of salt-containing,halogen-containing solid wastes using molten salts is still absent.A series of experimental studies on disposal of salt-containing and halogen-containing solid wastes using molten salts have been conducted aiming to obtain the characteristics of oxidation and pollutants emissions during the treatment of salt-containing and halogen-containing solid waste using molten salts in this study.The conclusions are placed as follows:1)Flow behavior of multiphase flow in molten salt oxidation reactor has been investigated.The results show that the characteristics of multi-phase flow in reactor are mainly affected by superficial gas velocity.With superficial gas velocity rising,the gas hold-up of multiphase flow first increases and later tends to be stable,and the flow pattern changes from uniform flow to transitional flow and finally to non-uniform flow.The standard deviation of wavelet decomposition coefficients d6 can be used to characterize the flow structure of the multiphase flow.2)Molten salt oxidation(MSO)is used for the disposal of salt-containing residue.With temperature changes from 600 to 750?,the organic components can be destructed effectively and the oxidation efficiency is ranged from 92.5%to 98.3%,molten carbonates have high absorption efficiency for SO2,the emission of SO2 is ranged from 0-60mg/Nm3,the transformation ratio of N to NO is ranged from 2.8%to 7.5%,the emission of PCDD/Fs is below 60 pg/g residue.The main incomplete oxidation product is CO,molten salt oxidation efficiency of residue rises with temperature raises,the oxidation efficiency reaches to 98.3%at 750?.The retention efficiency of sulphur by molten carbonates is higher than 98.5%.The main NOx during MSO of residue is NO.The transformation ratio of N to NO is as low as 2.87%at 650?.Part of the nitrogen in the residue has been oxidized to form nitrates and remains in the salt bath,due to the nitrates decompose and the transformation of NO to nitrates is suppressed after molten salts temperature exceeds 650?,NO emission increases.For residues with high nitrogen content,in order to control NO emission,temperature of moten carbonates shoud be suitably controlled around 650?.A system of industrial scale molten salt oxidation for the disposal of salt-containing wastes is designed on base of the above research.The disposal cost is estimated around 970 ?/ton salt-containing residue.3)In order to decrease the emission of PCDD/Fs,molten salt gasification(MSG)is selected for the treatmeant of two typical halogen-containing solid wastes(PVC and WPCBs).Results show that the emission of PCDD/Fs is ranged from 18.5 to 632.9 pg/g,which are much lower than the emissions from combustion,pyrolysis and gasification of PVC.The absorption efficiency of halogen by molten carbonates is higher than 99.8%,makes the distribution ratio of halogen in gas phase less than 0.2%during MSG process.Emission of PCDD/Fs in MSG process of PVC is inhibited by the high efficient absorption of chlorine by molten carbonates,excess air factor has little effect on the generation of PCDD/Fs.Temperature has big effect on emission of PCDD/Fs.With temperature raising from 600? to 750?,the emission of PCDD/Fs decreases from 632.9 pg/g to 18.4 pg/g under excess air factor at 0.4,significantly.Molten salt gasification efficiencies of WPCBs and PVC are between 60-86%and 26-42%between 600 to 750?,respectively.Temperature plays a dominent role in the gasification of WPCBs and PVC,the main combustible components in the syngas are CO and H2.For MSG of WPCBs and PVC,the temperauture should be suitably controlled around 750?,with excess air factor between 0.2-0.4.