Experimental Research On The Simultaneous Reduction Of Pollutants By Calcium-based Sorbents With Oxidant Staged Oxy-fuel Combustion

Oxy-fuel combustion technology is one of the most promising CO₂capture andstorage technology. Oxy-fuel combustion uses pure oxygen and part of the cycle gasinstead of air to tissue burning. The CO₂volume concentration in flue gas for oxy-fuel combustion can be more than95%（dry gas）, which reduces the difficulty andcost of the capture of CO₂. Oxy-fuel combustion has a unique advantage in reducingNOx and SO₂, along with the capture of CO₂.Combined removal of different pollutions from coal burning with oxy-fueltechnology is researched in this paper. Firstly, the technical ideas of oxy-fuelcombustion technology with the development status at home and abroad areintroduced. Secondly the boiler heat transfer characteristics, NO and SO₂emissioncharacteristics under oxy-fuel combustion has been elaborated. Finally, theexperiments of Entrained Flow combuster with Multiple Reaction Segment（EFCM）,which uses staged combustion technology and furnace sorbent injectiontechnology, is performed to research the oxy-fuel combustion conditions, thecombined removal of NO and SO₂in oxy-fuel combustion process.This experiment is done under the oxy-fuel atmosphere of30%O₂/70%CO₂and uses typical Chinese coal, Yuanbaoshan lignite and Datong bituminous as fuel.The influences of stoichiometry in reducing zone, the reduce time in reducing zone,calcium to sulfur ratio and the rank of coal on pollution removing are considered inthe experiment. The results show that NO emission in oxy-fuel combustion is lowerthan that in air combustion. Compared to conventional air combustion, oxy-fuelcombustion can reduce NO emission by34.2%（Yuanbaoshan lignite）,45.3%（Datongbituminous）, without utilizing any other measures. With oxygen staged, oxy-fuelcombustion can reduce NO emission more significantly. Oxygen staged has noeffect on reducing SO₂emission. When the residence time in burnout zone is greaterthan1.5s, the burnout rate of oxy-fuel combustion can be more than98%.Oxy-fuel combustion has a strong effect on the removal of recycling NO.Without staged combustion, rate of recycled NO reduction can reach by50%,andunder staged combustion it gets up to97%.There is no apparent removal efficiencyfor recycling SO₂. The addition of calcium based sorbents under oxy-fuel conditioncan receive good desulfurization. The desulfurization rate increases with theincreasing of calcium to sulfur ratio, but the utilization of calcium is lower. Whenthe calcium to sulfur ratio increased to2, the desulfurization rate is tend to be steady,and the removal rate of recycled SO₂is about35%. CaO can simultaneouslyenhance the catalytic effects on the reduction reaction and oxidation reaction of NO. When calcium sulfur ratio is less than1, catalytic reduction is foremost. Whilecalcium to sulfur ratio is greater than1, catalytic oxidation reaction will bedominant rapidly. Therefore, taking the boiler efficiency, operating costs andcombined removal effects of NO and SO₂into account, calcium to sulfur ratioshould not be too large.