Solid Waste Pyrolysis Based On Fluidized Bed And Chracterization And Analysis Of Gas And Solid Products

Sludge is the solid by-product of polluted water treatment plants.Due to the increasingly strict wastewater treatment requirements and the construction of more waste water treatment plants,the global sludge volume is expected to increase significantly in the next few years.The sludge composition is complex,contains a large number of pathogenic bacteria and various organic matter and heavy metals.Traditional disposal technology has problems such as large area required and secondary pollution.Therefore,a cleaner sludge disposal technology is urgently needed.In this study,the fluidized bed was used to pyrolyse textile dyeing sludge(DS)and sewage sludge(SS),and the char(DC)after DS pyrolysis and the char(SC)after SS pyrolysis were carried out elemental analysis,X-ray fluorescence spectrometer(XRF),Fourier transform infrared spectroscopy(FTIR),X-ray diffractometry(XRD),scanning electron microscopy(SEM),inductively coupled plasma mass spectrometry(ICP-MS),etc.The gas products were analyzed by gas chromatography(GC),and the effects of pyrolysis on the two sludge were compared.The main results are as follows:(1)The pyrolysis experiment of textile dyeing sludge showed that with the increase of temperature,the yield of pyrolysis gas increased.The pyrolysis gas was mainly CO2,CO,CH4,H2,and CO2 has the highest yield(i.e.19.16 wt%).Kaolin and Ca-bentonite were favorable for gas generation.XRD analysis showed that heavy metals in DS and DC exist mainly in the form of oxides and silicates of various heavy metals.The results of ICP-MS showed that there were six heavy metals in DS and DC.The concentration decreased in the order of Zn>Pb>Cr>Cu>Ni>As.Ni,Zn and Pb were enriched in DC,and Ca-bentonite showed the best immobilization of heavy metals.The BCR four-step extraction experiment showed that most of the zinc existed in exchangeable and residual fractions.Copper mainly existed in the residual fraction and oxidizable fraction,and Cr transferred from oxidizable fraction to residual fraction during pyrolysis.All heavy metals contents were in line with national standards(CJ/T 362-2011,China)and showed the slight risk to the environment.(2)Sewage sludge pyrolysis experiments showed that higher temperature was favorable for gas generation and reduced SC yield.The highest SC yield was 74.60 wt%under the pyrolysis conditions of 650?+CaO.CaO addition inhibited gas production.The results of elemental analysis showed that CaO has the best sulfur retention ability.XRD results showed that Cu was mainly in the form of Cu2O and CuSiO3,Cr and Ni were mainly in the form of oxides,Zn was in the form of oxides and sulfides,and Pb was in the form of chlorides,and As can exist in combination with heavy metals and elements such as Si or O.The FTIR results indicated that pyrolysis promoted the conversion of organic macromolecules to small molecular organic compounds such as alcohols,carboxylic acids,amides,amines,aromatics and aliphatic hydrocarbons.The results of ICP-MS showed that pyrolysis had a good immobilization effect on heavy metals.Most of relative enrichment factor(RE)of the six heavy metals after pyrolysis were greater than 1.The potential ecological risk of the six heavy metals to the environment were mild.(3)Pyrolysis had a better effect on the immobilization of heavy metals in SS.Ca-bentonite and CaO exhibited the best and worst heavy metals retention effects during DS pyrolysis,while kaolin had the best ability to retain heavy metals at 650? and the worst ability at higher temperatures 850? during SS pyrolysis.It was calculated that the maximum energy consumption of the fluidized bed pyrolysis of dried DS and SS were 0.02 kWh/kg and 0.03 kWh/kg,respectively.