Study On The Co-combustion And Ash Fusion Characteristic Of Coal And Biomass

The excessive use of coal resources has caused serious environment issues,such as greenhouse effect.Therefore,the realization of clean and efficient utilization of coal is helpful to the development of China.It is known that the reactivity of coal can be obviously improved by adding catalyst,but the high cost led to the limit use of commercial catalyst,so researchers turn their attention to biomass which also can improve the reactivity of coal.The co-utilization of coal and biomass has been considered as a promising method to resolve the energy shortage and environmental issues.In this paper,wheat straw（WS）,a common agricultural waste in China,was selected as the research to study the reactivity and kinetic behavior of WS and bituminous coal（BC）blends.Then,the effect of biomass ash on the combustion reactivity of coal was studied.Finally,the fusion characteristics of coal and biomass blended ash was investigated.On the one hand,the ignition temperature of the volatile is low,and the combustion reaction can begin at 300^oC,which improves the combustion performance of the blends.The catalytic component in the biomass ash can transfer surface oxygen into the surface of coke.On the other hand,volatiles and alkali metals can improve the structural characteristics of blended coke,thus improving the combustion of coke in the later stage of reaction.The kinetic results show that the decrease of fixed carbon increased the activation energy during the combustion of volatile,while in that of semi-coke,the activation energy decreases due to the both effect of biomass volatiles and the ash.In order to further know the effect of biomass ash on coal combustion,the combustion reactivity of coal blended with biomass ash was studied.The combustion performance of BC-1%BA is inferior to BC,which may be due to that the ash covered the surface of coal particles limited the mass transfer.However,when the biomass ash content reached to 2%,the catalytic effect of biomass ash on the combustion reactivity of coal was greater than the inhibition effect.The addition of biomass ash can obviously improve the combustion reactivity of coal,and the best catalytic effect was obtained by K₂CO₃ and Na₂CO₃.The increase of K₂CO₃ can transfer more surface oxygen to the surface of coke,resulting in the decrease of the kinetic activation energy.The addition of biomass can improve the combustion reactivity of coal,and worsen the operating conditions of the reactor,so the ash fusibility of the blends was studied.The results show that the ash DT decreases by 150^oC after blended with 40%biomass.On the one hand,the decrease of coal ash melting temperature is due to the decrease of Si O₂,Al₂O₃,kaolin and hematite content in coal ash with the increase of biomass proportion,on the other hand,the increase of KCl content with the increase of biomass mixing ratio.The results show that the ash fusion temperature decreases with the addition of catalyst.Alkali metal K and Na have the best effect on the ash fusion temperature,followed by alkali earth metal Ca,and Fe and Mg oxides are the worst.With the increase of K₂CO₃ ratio,the diffraction peak intensities of Si O₂,Al₂O₃,kaolin and Ca CO₃ are gradually weakened,and K₂SO₄ peak appears when the K₂CO₃ ratio reaches2%,and increases with the increase of K₂CO₃ ratio.The addition of biomass can improve the coal combustion reactivity,and reduce the ash fusion temperature,which is not conducive to the operation of the reactor.Therefore,the use of biomass and coal blends is necessary to base on an appropriate biomass blend ratio.Combined with the interaction of coal and biomass mixed combustion,it can be found that when the biomass mixing ratio is 20%,the combustion reaction can be improved In addition,the operation problems caused by low ash fusion temperature can be avoided.