Experimental Study On Steam Gasification Characteristics Of Char Pellets Of Typical Organic Technical Waste

Technical waste with high organic content,low radioactivity,and large volume,is generated during the operation of a nuclear power plant.It needs to be greatly reduced in volume before packaging and landfill for reducing the disposal cost of technical waste.Steam gasification is an effective treatment method for thermochemical conversion of pyrolysis chars,which can further reduce the volume of technical waste.In this work,the steam gasification characteristics of char pellets of typical organic technical waste are evaluated.The steam gasification characteristics of char pellets for typical technical waste?gloves,paper towel,coveralls,sawdust and mixture?were examined in a self-designed fixed-bed gasifier.The effects of reaction temperature?700-900°C?and steam concentration?20%-80%?on the kinetics of steam gasification were considered.The average gasification reaction rate of the four samples was in the order of paper towel char pellets>sawdust char pellets>coveralls char pellets>gloves char pellets.The differences in characteristics of gasification between samples could be attributed to the differences in sample composition especially for alkali index.The experimental value of the average gasification rate of the mixture sample was about 8%higher than the theoretical value,which indicated that there was a clear synergy between the components of the mixture sample.The average gasification reactivity index of the samples was enhanced with the increase of reaction temperature and steam concentration,and the reaction temperature had a more significant effect on the gasification reactivity index.The average gasification reactivity index for gloves char,paper towel char,coveralls char,sawdust char and mixture char increased by 69%,160%,88%,40%and 47%,with lifting the steam concentration from 20%to 80%,and it increased by 349%,545%,243%,232%and 694%,respectively,with lifting the gasification temperature from 700°C to 900°C.The kinetic parameters of steam gasification were well estimated based on random pore model,in which the activation energy of different samples were gloves char pellets?75.4k J/mol?>mixture char pellets?62.8 k J/mol?>paper char pellets?62.7 k J/mol?>coveralls char pellets?58.7 k J/mol?>sawdust char pellets?48.9 k J/mol?.The yields and the characteristics of gasification products were concerned combine with the characteristic detection experiments of gasification products and thermodynamic equilibrium calculations.The effects of reaction temperature and steam concentration on steam gasification products of solid waste were obtained.The average gasification residues of char pellets for gloves,paper towel,coveralls,sawdust and mixture showed a significant decrease with the increase of reaction temperature and steam concentration.For example,the mixture char pellets fell by about 71%,with the steam concentration increased from 20%to 80%,and it reduced by about 91%,with the reaction temperature increased from 700°C to 900°C.The maximum total mass reduction ratio of two-stage thermal degradation after pyrolysis and gasification exceeded 98.5%.The average content of the main components of syngas was H₂>CO₂>CO>CH₄.At the chemical equilibrium state,both lifting the reaction temperature or steam concentration could increase the content of H₂ and reduce the content of CH₄ and it also can reduce the yield of solid residue.This investigation can provide basic data for further research and industrial application on the thermal degradation characteristics of typical technical waste in nuclear power plants.