Study On Flue Gas Desulfurization Technology By Sodium Phosphate Method In High Gravity

The research status of wet flue gas desulfurization (FGD) methods and devices werereviewed in this work. By comparison of the research and application situation of severaltypical wet FGD processes and their desulfurization reagents, the sodium phosphate buffersolution is the most promising wet regenerable desulfurization reagent as it has someadvantages of stable physical and chemical qualities, no degradation and deterioration, lowloss, easy availability and cheap, and high desulfurization efficiency, etc. On the other hand,the improvement and development of wet FGD devices have obtained some good results,however, some problems such as large volume, low mass transfer efficiency, serious sidereaction of oxidation, scaling and blocking, high operating costs, etc. High development andapplication values of rotating packed bed (RPB) were pointed out, and a new type ofmulti-stage cross flow RPB was developed and used as a desulfrizaiton device. Thetheoretical and experimental study for FGD using sodium phosphate method in high gravitywas carried out to provide theoretical instructions and experimental data for industrialapplication of FGD using RPB.In terms of desulfurization theory, the saturated desulfurization capacity was calculated,and the experiment for validation of the theoretical values was carried out. Results indicatedthat the average relative deviation of calculated values and experimental values is less than5%. The saturated desulfurization capacity increases with the increase of pSO2, initial pH andCP. when initial pH value is7and Cpequals to1mol/L, the saturated desulfurization capacityof the buffer solution could reach above25g/L, which is around60times higher than water.With respect to the oxidation resistance of SO2-riched sodium phosphate solution, theself-made bubbling reactor was used to determain the oxidation rate of sodium sulfite insodium phosphate buffer solution by dynamical method. Orthogonal test was designed and the influence of some factors on oxidation rate of sodium sulfite was compared. Results indicatedthat the significant sequence of influence for each factor on the oxidation rate was:C(Na2SO3)>CP>pH>T>G. During the operational range, the oxidation rate of sodium sulfitewas between0.00116~0.01875mol/(L·h). Under the conditions of C(Na2SO3)=10g/L, G=150L/h, pH=7and T=35°C, the oxidation rate of sodium sulfite with CP=1mol/L isdecreased by54.3%than that with no sodium phosphate, and the apparent activation energyEa=48.48kJ/mol, which is larger by23.4times than the later. Therefore, the absorbent ofsodium phosphate could significantly inhibit the oxidation of sodium sulfite and theSO2-riched sodium phosphate solution has an excellent oxidation resistance, which couldefficiently decrease the accumulatation of Na2SO4and the loss of absorbent in regenerationprocess.In terms of the FGD process by multi-stage cross flow RPB, the influence of operatingparameters, such as high gravity factor β, initial pH value of absorbent, liquid to gas ratio L/G,SO2inlet concentration C1, on desulfurization efficiency η were investigated., and it iscompared with the mass transfer performance of SO2absorption by water. Results indicatedthat, under the conditions of CP=1mol/L、pH≈7、C1=2831mg/m3、u=1.5m/s、β=24、L/G=2L/m3, the η is82%when the absorbent only gets through the below packing layer, however,the η could reach above97%and the outlet SO2concentration could below85mg/m3,whichcould meet the new national emission standards. When L/G or β was further increased, theoutlet SO2concentration could below50mg/m3, and meet the emission standards in specialarea. In addition, the sodium phosphate buffer solution as an absorbent could adapt to a widerSO2concentration in flue gas.