Study On The Ash Formation And Deposition Characteristics Of High Calcium Or High Alkali Coal Under Oxy-fuel Combustion

China is a typical country rich in coal,but lean in oil and gas.In a very long period,coal is still an important support for China's development.Oxy-fuel combustion technology is a new type of combustion technology that can realize large-scale CO₂ enrichment,and it is easy to be retrofitted to existing coal-fired power plant boilers.Changes of the atmosphere under oxy-fuel combustion will affect the ash formation of pulverized coal.Changes in the physical and chemical characteristics of the coal ash will inevitably affect the ash deposition characteristics in the furnace.In this thesis,the ash formation and deposition characteristics of Shenhua coal and Zhundong coal?two typical high calcium or alkali?are are studied under oxy-fuel combustion.Firstly,using the DTF we studied the the ash formation characteristics of included and excluded minerals in Shenhua coal and Zhundong coal.The results show:21%O₂/CO₂ and28%O₂/CO₂ atmosphere do not significantly change the chemical composition of coal ash,but have a great influence on the composition of the crystal.21%O₂/CO₂ atmosphere inhibits the decomposition of calcite and the eutectic melting of the included quartz,it will also promote the eutectic melting of the excluded quartz.Under 28%O₂/CO₂ atmosphere,the diffraction peaks of included Ca is disappeared,indicating the formation of amorphous minerals;Under air or oxy-fuel combustion,the included calcite produces amorphous minerals or CaSO₄ due to the sulfur fixation and the excluded calcite decomposes to CaO.Secondly,the deposition characteristics of Shenhua coal and Zhundong coal were studied using cooling deposition coupons in the DTF.The results show:At the flue gas temperature of 900°C,when the content of Na,K,and Ca in the coal is relatively low,the low-melting point aluminosilicates of alkali metals and alkaline-earth metals are the main deposits.While,when the content of Na,K,and Ca content is relatively high,there will be an initial deposition layer of the alkali and alkaline earth metal's sulphate.The initial sulphate deposits are more denser than the low-melting point eutectic deposit,which contributes to the formation and growth of the deposits,thereby exacerbating ash deposition trend.When the flue gas temperature rises to 1150°C,sulfate and low-melting aluminosilicates form a sintered and molten deposit.Finally,using the Factsage thermodynamic equilibrium calculation,the deposition characteristics of Shenhua coal and Zhundong coal in air and oxy-fuel combustion conditions were simulated.The results show:the presence form of alkali metal at high temperature is highly correlated with the deposition characteristics.When the alkali metal is mainly in the liquid phase,low-melting eutectic deposits are formed.When the alkali metal exists mainly in the gas phase,sulfate deposition occurs.The oxy-fuel combustion does not significantly affect the slag formation characteristics,the elemental composition in the slag,and the existing form of the alkali metal.