Study On The Transformation Of Alkali Metals And Chlorine During Co-gasification Of Biomass And Plastic

Co-gasification biomass and plastic in a suitable scale can not only solve the deficiencyof pure biomass gasification,and improve the gas heat value and quality,but also realize thepurpose of plastic waste reduction and recycling. However amounts of volatile alkali metalsand chlorie can cause deposition,corrosion and agglomeration during biomass and plasticco-gasification.Furthermore,the metalloid element chlorine can influence the migration andtransformation of alkal metals. So it is necessary to investigate the transformation of alkalimetals and chlorine and discuss the competition relationship between them.In this paper, HSC6.0chemical thermodynamic equilibrium software was applied toinvestigateing and forecasting the migration and transformation of alkali and chlorine duringbiomass and plastic co-gasification. The results showed that alkali choride transfromed fromsolid phase to gas phase at700℃during80%rice straw co-gasification with20%PVC. TheCl was mainly in the form of HCl(g), KCl(g) and NaCl(g) at900℃. Compared to pure ricestraw gasification, the molar fraction of alkali ulfates and alkali silicates in the solid phasewas very low and the molar fraction of gaseas alkali metal was two times than pure rice strawgasification. The effects of blending ration and temperature on the migraction behavior ofalkali metals and chlorine dure biomass and plastic co-gasification were carried out in a fixedbed combined with X-ray power diffraction and scanning electron microscope/energydispersive spectrometer,and the analysis of the modynamical equilibrium. The resultsindicated that the content of PVC in the blend played an important role in the release of Clespecially between800℃a nd900℃. The release of Cl during gasification of blend with20%PVC（11.5%Cl）was improved by16.5%compared to pure rice straw gasification at900℃.Increasing temperature increase the release rate of alkali metal, which was in gaseas.Meanwhile increasely the Cl content in the blends also prompted the release of K, Na. Whenthe fraction of PVC was more than20%(＞11.5%Cl),increasing the content of Cl couldrestrain the release of K, Na at850℃. K and Na was retained in the ash as KCl andNaCl,during co-gasification of rice straw and PVC at850℃,the content of which decreased with the increase of PVC contend in the blend.When the Cl/K was between0.6-2.0, and therelease of K increased strongely.The release of radio of alkali metals was analyzed by gray association degree theory indifferent C/H, Cl/K, Cl/Na amolar ratio and different gasification temperature. The resultsshowed that Cl/K molar ratio in the fuel is the most important element influencing the releaseof alkali metal and chlorine.