The Study On Cooperative Control Mechanism Of Coal Fired Flue Gas’s SO₂and Hg Using Wheat Straw Pulping Black Liquor

The increasing Coal consumption, the grim situation of pollution reductiontargets, treatment and recovery of black liquor are tests on the road of thedevelopment of China. WFGD is the mainstream of flue gas desulfurization processfor SO2emission reduction of large coal-fired boiler. Because of the strong alkalineand its complex components, wheat straw pulping black liquor maybe can controlcoal-fired flue gas to combine with WFGD. So it can achieve the function that treatwastes with processes of wastes against one another. In this paper, the authors usedpapermaking black liquor as absorbent to cooperative control SO2and Hg incoal-fired flue gas by using the desulfurization tower with multi-stage water film,combining alkali and complex composition in simulation of papermaking blackliquor. Then we can provide technical support for desulfurization and mercuryremoval of flue gas using black liquor as absorbent, to achieve the purpose oftreating waste by waste.The desulfurization efficiency as index, the black liquor used for absorbent offlue gas desulfurization cold test. When the analog black liquor without dilution(pH=12.5~13), the optimization scheme by orthogonal test to study the properties ofblack liquor from flue gas desulfurization is：the concentration of SO2(A)=3500~4000mg/m3; L/G（B）=14L/m3; empty tower gas velocity=0.315m/s.Running in the optimal conditions, the desulfurization efficiency is99.58%. In thispaper, the economic and reasonable L/G is14L/m3, empty tower gas velocity is0.3m/s, the concentration of SO2is2000~3000mg/m3by the desulfurization effect ofsingle factor test. When the entrance concentration of SO2=2800~4000mg/m3,L/G<8L/m3, outlet concentration of SO2exceeds200mg/m3.The result of the test that the effect of flue gas mercury removal with theconcentration of black liquor composition changes shows that：the Hg removal rateof simulated flue gas that be treated with pure black liquor is48.14%. And theconditions for the black liquor are: pH=12, C(NaOH)=3%(w.w), C(lignin)=7%(w.w). With the increasing of the concentration of NaOH, NaBr, NaCl, Na2SO4,lignin in black liquor the flue gas mercury removal plays a promoting role. Toincrease the concentration of Na2S, sucrose, Dimethyl sulfone in black liquor canpromote the flue gas mercury removal after suppression. Finally the increasing of theconcentration of Na2CO3and sodium gluconate has little effect of mercury in flue gas.The desulfurization efficiency, mercury removal efficiency as the index, thebest choice of black liquor diluted5times. And now the conditions for the blackliquor are: pH=11.04, C(NaOH)=0.4%(w.w), C(lignin)=1.2%(w.w). Theoptimization scheme by orthogonal test to study the properties of black liquor fromflue gas desulfurization and mercury removal is：the concentration of SO2(A)=700~900mg/m3; the concentration of Hg (B)=11~14μg/m3; L/G(C)=16L/m3;empty tower gas velocity(D)=0.315m/s. Running in the optimal conditions, thedesulfurization efficiency is98.12%, the mercury removal efficiency is80.54%. Inthis paper, the economic and reasonable L/G is13L/m3, empty tower gas velocity is0.283m/s, the concentration of SO2is2000~3000mg/m3, the concentration of Hg inthe entrance choice about50μg/m3.by the desulfurization and mercury removaleffect of single factor test.When the test conditions are: black liquor was diluted5times, L/G=13L/m3,gas velocity=0.283m/s, the concentration of SO2=2200mg/m3, slurry volume=38L, the concentration of Hg=50μg/m3.The test result of desulfurization andmercury removal in Flue gas used a fixed amount of black liquor shows that thecycle time choice3h~3h20min. With prolonging circulation time of paper-makingblack liquor, liquor pH value, CODcr value decreased rapidly, and the trend ofaverage. At the same time, the treatment of coal fired flue gas, the black liquor ispreprocessed itself.