Basic Study On Flue Gas Desulphurization Technology By Ammonia Method Under The Condition Of High Gravity

With the continue increase of efforts in national energy conservation, SO₂annualemission decreased year by year in China, but still more than20million tons, the largest inthe world, so it has a long way to go to take effective desulfurization ways to control SO₂emissions. Ammonia-based flue gas desulfurization, which don’t produce waste water, wasteresidue, the by-product ammonium sulfate can be used as agricultural fertilizer, is atechnology of the sulfur resource recovery. However, the existing ammonia-based flue gasdesulfurization process using tower as absorption device, since the tower equipment gasliquid contact area is lesser, surface renewal rate is slower, the mass transfer effect is not ideal,and the tower equipment of gas-liquid contact time is long at the same time, leading to theabsorbent oxidation in the absorption process and the problems that the absorbent and processwater consumption and the desulfurization efficiency is low, affecting the industrialapplication of ammonia-based flue gas desulfurization process.High gravity technology is a new and efficient technology in chemical process and thehigh gravity absorption process has advantages in high mass transfer efficiency, in shortcontact time, small devices and low power consumption etc. This article will use the highgravity rotating packed bed instead of the tower equipment, simulated flue gas was preparedthrough mixture of air and SO₂, absorbing liquid was used ammonium sulfite and ammoniumbisulfite mixed solution, by ammonia added to the absorbent to maintain absorption capacityin the absorption process, begin the oxidation experiments of the desulfurized-rich liquidthrough oxidation tank. The SO₂absorption, desulfurized-rich liquid oxidation andammonium sulfate crystallization process has been studied to form a more perfect technologyof high gravity ammonia-based flue gas desulfurization. In the absorption experimental part of the Sulfur dioxide, firstly, the significance test ofthe operating conditions was investigated by orthogonal experiment. Significant impacts ondesulfurization rate from big to small in turns was absorbing liquid pH value, inlet SO₂concentration, high-gravity, liquid to gas ratio. Secondly, the influence of the desulfurizationrate and gas phase total volumetric mass transfer constant was investigated through singlefactor experiments under different high-gravity, liquid to gas ratio, absorbing liquid pH value,inlet SO₂concentration and the gas flow, the desulphurization rate and gas phase totalvolumetric mass transfer constant along with the increase of the high gravity factor and liquidto gas ratio, first increase and then tends to stable and increase with the increasing pH value ofabsorption liquid, reduce with the increase of inlet SO₂concentration, desulfurization ratedecreases with increasing gas flow rate, gas phase total volumetric mass transfer constant withincreasing gas flow rate increases first and then reduces. The optimum operating conditionswas that: the high-gravity coefficient was55.64, liquid to gas ratio was2.5L/m³to3.15L/m³,absorbing liquid pH value was6.0to6.5, the gas flow rate was8m³/h, the concentration of（NH₄）₂SO₃and NH₄HSO₃was0.24mol/L to0.28mol/L in absorbing liquid. When the inletSO₂concentration was2860mg/m³, the efficiency of desulfurization to the simulated flue gascan be stabilized at more than98%. Compared with the tower equipment, the gas phase totalvolumetric mass transfer constant has been significantly improved, more then15s^-1. Finally,we examined the variation that salt concentration in the absorbing liquid changed with thedesulfurization time and the desulfurization rate changed with the salt concentration in theabsorbing liquid, compared with tower equipment we can get that: in the desulfurizationabsorption process, the oxidation rate of the SO₃2-was reduced to1/10of the original, theoxidation of asian ammonium sulfate salt in the absorbent has been effectively suppressed andthe salt blocking was reduced.The （NH₄）₂SO₃oxidation efficiency was investigated under it initial concentration, pHvalue of the desulfurized-rich liquid, oxidation air flow, reaction temperature in thedesulfurized-rich liquid oxidation experiments. The oxidation rate of （NH₄）₂SO₃indesulfurized-rich liquid along with the desulfurized-rich liquid initial （NH₄）₂SO₃ concentration and desulfurized-rich liquid pH value increase, decreases, increases with theincreasing forced oxidation air flow, increases first and then decrease with increasing reactiontemperature of the desulfurized-rich liquid. The influence of （NH₄）₂SO₃oxidation efficiencywas investigated under it initial concentration, pH value of the desulfurized-rich liquid,oxidation air flow, oxidation reaction temperature in the desulfurized-rich liquid oxidationexperiments. Combined with the high gravity absorption experiments, the optimum operatingparameters for the desulfurized-rich liquid as follows: the （NH₄）₂SO₃initial concentration was0.3mol/L to0.4mol/L, pH value of the desulfurized-rich liquid was5.5to6.0, the air flow was6m³/h, the oxidation reaction temperature was50℃. For the12L desulfurized-rich liquidoxidation in the above-metioned conditions, the oxidation rate can reach70%or more whenoxidation time was30minutes, and reach90%or more with60minutes. We integratedabsorption and oxidation experiments could found that, when the concentration of （NH₄）₂SO₃in absorption liquid achieved0.4mol/L, oxidation desulfurized-rich liquid at oxidation tank,then the desulfurized-rich liquid pH value was adjusted to about6after fully oxidized, and thereaction product of （NH₄）₂SO₄solution was evaporated by crystallization experiments toobtain （NH₄）₂SO₄crystal, the crystal purity was99.3%and the crystal particle size mainlydistributed in the range of50μm to130μm.It could be inferred from above research that applying high gravity technology toammonia flue gas desulfurization can enhance the SO₂absorption and inhibit the occurrenceof oxidation reactions in the absorption process, reduce the equipment salt blocking, greatlylower the absorbent and water use, decrease the energy loss of evaporating and crystalling thefollow-up by-product ammonium and reduce the cost of desulfurization when maintain a highdesulfurization rate.