Study On The Co-pyrolysis Characteristic Of Sewage Sludge And Straw

Sludge disposal and utilization is an important environmental problem to be solved in our country.In this paper,considering the high moisture of dehydrated sludge?about 80%moisture content?,the small diameter straw biomass which owns the low water content,high volatile and fixed carbon was used as the medicament in the co-cracking gasification process.Firstly,the pyrolysis kinetics of sludge/straw was studied by using DAEM model,and the pyrolysis kinetics of single raw materials and different proportions of blends have been analyzed.Secondly,the effects of different mixing ratio,pyrolysis temperature,the additive of CaO and different water content on the properties of pyrolysis products were investigated.The pyrolysis mechanism of CaO on sludge/straw mixture was analyzed by XRD and SEM.Finally,a set of technical scheme of sludge/straw/CaO co-pyrolysis based on micron fuel outside-heating was presented on the basis of small test.The main conclusions are as follows:?1?The results of elemental analysis and industrial analysis of sludge and rice straw showed that the content of N and S in rice straw was much lower than that in sludge,which indicated that the SO_X and NO_X substances released during the thermochemical conversion process were relatively less.Compared to sludge,volatile and fixed carbon content of biomass were higher,ash and moisture content were relatively lower.Adding biomass to the sludge can effectively regulate the volatiles and moisture content of the mixed samples.The heavy metal elements were not found by XRF analysis,which indicated that the straw biomass was an ideal Apyrolysis raw material.In addition,the analysis of the functional groups of sludge/straw by FTIR showed that the sludge and straw were rich in organic functional groups,and the difference was not significant.TGA analysis showed that the main weight loss stage of sludge and straw was in the range of180?⁶00?.?2?As far as the aspect of the pyrolysis characteristics,the pyrolysis rate of SS was lower than that of RS,and there was no very large interaction between SS and RS during the co-pyrolysis process mixed in different proportions.The activation energy of RS pyrolysis was also lower than that of SS,and the activation energy of the mixed pyrolysis sample tends to be the activation energy of RS pyrolysis with the increase of RS mixing fraction.In the dynamic point of view,RS and SS co-pyrolysis process did not show a very significant interaction.The results of the distributed activation energy model were in good agreement with the experimental results.The linear relationship between the pre-exponential factor and the activation energy was very poor.So,the single-step reaction model can not describe the pyrolysis of the sample well.?3?With the increase of the blending ratio from 0 to 50%,the yield of gaseous product increased from 19.9%to 68.3%.When the mixing ratio increased further,the yield of gas product was about 70%and the change was small.The liquid product yielded the opposite trend,and the liquid tar yield decreased from 70.3%to 13.5%with the increase of blending ratio.When the temperature rose from 600?to 900?,the yield of solid products and liquid products were reduced from 22%and 31%to 19.4%and 21%,respectively,and the yield of gaseous products increased from 47%to 59.6%.When the water content grew constantly,the gaseous product and the liquid product were significantly increased and the solid product was reduced.As the[Ca]/[C]increased from0 to 1.5,the gas yield rose,both the solid yield and the liquid yield decreased,while the H₂ volume fraction and the yield increased and the CO₂ volume fraction decreased.The results of XRD and SEM analysis showed that the increase of temperature was favorable for the pyrolysis gasification reaction,however,it restricted the CaO carbonation reaction.In addition,a pilot scale technology of sludge/straw/CaO co-pyrolysis based on micron fuel outside-heating was proposed on the basis of lab test.