Effects Of Dry/Wet Flue Gas Recirculation Mode On Thermodynamic Characteristics And Safty In An Oxy-fuel Combustion Boiler

Oxy-fuel combustion technology is a new generation of clean coal powergeneration technology, which flue gas recirculation system including dry, wet twotypes. The main difference is whether the part flue gas of the boiler exhaust afterdrying process is then fed into the furnace through the recirculation system, two typesof flue gas circulation each have advantages and disadvantages. Based on oxy-fuelcombustion boiler, this paper attempts to research the effects of dry/wet flue gasrecirculation mode on thermodynamic characteristics and safty, which is important forits later practical engineering purposes.Take a600MW pulverized coal boiler as an example, the thermal analysis of coalunder dry/wet cycle of oxy-fuel modes were done, and the results were compared withthat under air combustion. Based on energy balance, the boiler was redesigned.Theemissivities for tri-atom gases have already been calculated by the improved model ofgas mixtures overlapping band and the benchmark models under dry/wet cycle ofoxy-fuel modes. Based on flue gas components, effect of recirculation mode on aciddew point of flue gas was discussed for the first time. Against existing problem of coalmill low-temperature corrosion in the conventional boiler, the paper tried to study thecorrosion characteristics of coal mill at oxy-fuel combustion mode.Flue gas components are sensitive to desulfurization and dehydration atrecirculation modes under oxy-fuel combustion.Compared with dry cycle mode, theresult of higher boiler efficiency and less coal consumption are caused under wet cyclemode. The optimized total heated area is reduced, this can save part initial investment.The improved model is in good agreement with LBL model, WSGG model, maximumdeviation is only10.0%,17.4%.The emissivities under wet cycle mode are higher thanunder dry cycle mode. The dew point of flue gas at oxy-fuel atmosphere is muchhigher than that at air atmosphere. When using wet cycle mode, the tail of the boilermay cause corrosion problems. At the same time, when burning using wet cycle modeor high sulphur coal, the mill will cause serious corrosion problem. In addition, thechanges of boiler load effect little on the characteristics of coal mill low-temperature corrosion.