Thermal Analysis Of Sewage Sludge And Co-sintering Characteristics Of Incineration Sewage Sludge Ash (ISSA) And Coal Fly Ash(FA)

The treatment and disposal of massive sludge is one of the urgent problems in the current society.Incineration treatment is becoming the preferred treatment method for sludge management due to its advantages of volume reduction and harmlessness.However,incineration treatment will generate a certain amount of incinerated sewage sludge ash?ISSA?,and the incinerated sewage sludge ash is harmful to the environment.Meanwhile,the ISSA contains a small amount of silicon,aluminum and relatively higher quantity of iron,which is not conducive to improve the compressive strength of sintered samples,the subsequent application of ISSA was difficult.Considering the high production of fly ash?FA?with high content of silica and aluminum in China,although the amount of FA utilized is increasing year by year,the added value of comprehensive utilization is still low.Therefore,in this paper,the thermal analysis of sludge combustion and the co-sintering experiment of ISSA and FA were carried out,and the combustion characteristics and kinetics of sludge at different heating rates were analyzed.The basic properties of ISSA and FA as well as the related performance,heavy metal safety evaluation and energy consumption analysis of different ratios of ISSA and FA co-sintered samples at a series of sintering temperatures were investigated.The main contents and conclusions of this paper are as follows:?1?According to the TG/DTG curves of sludge and combustion characteristics parameters,there were dehydration stage,the decomposition of organic matter and the precipitation of partial volatiles stage,residual volatiles precipitation and fixed carbon burnout stage,and coke burnout stage or residual matter burnout stable stage in the sludge combustion process.The weight loss peaks of organic matter decomposition stage,partial volatilization stage,residual volatilization stage and fixed carbon burnout stage were more obvious,being about 24%and 26%respectively.With the increase of the heating rate,the maximum weight loss rate in sludge combustion increased from 8.21%/min to 43.45%/min,which indicated that the combustion was more intensive.The heating rate had no significant influence on the residual amount after sludge combustion,remaining about 40%.The increase of heating rate is beneficial to the improvement of comprehensive combustion index of sludge.Iso-conversional method and compensation effect were used to calculate and analyze the sludge combustion kinetics.The results showed that the activation energy of sludge combustion changed significantly.?2?The comprehensive properties of co-sintering of ISSA and FA at different sintering temperatures and ratios were studied.XRF and XRD were used to analyze the composition and phase of ISSA and FA.The results showed that the content of SiO₂ and Al₂O₃ in ISSA was54.85%,and the content in FA was 75.77%.The content of network improvement compounds Fe₂O₃,MgO,CaO,K₂O and Na₂O in ISSA was 31%,and that in FA was 18%.The ash melting point tester was used to test the ash melting point of different ratio samples,and the results showed that the ratio of ISSA and FA had singinicant effect on the ash melting point.With the reduction of ISSA proportion,four characteristic temperatures showed a decreasing trend followed by an increasing trend.When the ISSA:FA was 3:1,the lowest characteristic temperatures were achieved.The XRD and SEM results showed that the maximum compressive strength was achieved when ISSA:FA ratio was 3:1.After sintering,the main crystal phase of the sample was SiO₂ and Fe₂O₃,etc.When the proportion of ISSA was large,silicate compounds would appear to promote the densification of sintered samples.?3?ICP-MS was used for the determination of heavy metals in ISSA and FA.Compared with GB15618-2018"Soil Environmental Quality Control Standards for Agricultural Land Soil Pollution Risk Control?Trial?",the results showed that the content of heavy metals in ISSA was exceeded the screening value.The content of Cu was slightly higher than the screening value.The content of As in FA was slightly higher than the screening value,and the content of Cd in ISSA and FA both exceeded the screening value.The content of other heavy metals in ISSA and FA did not exceed the screening value of soil risk in agricultural land.HaKanson method was used to evaluate the ecological hazard index?RI?of ISSA and FA,the results showed that both of them showed higher pollution risks.Toxic leaching of heavy metals in sintered samples by TCLP method showed that the leaching concentration of heavy metals in sintered samples was below the limit,and sintering was beneficial to inhibit leaching of heavy metals.According to the ash melting temperature,the energy consumption analysis showed that when ISSA:FA was 3:1 the energy consumption was the lowest.