Theoretical And Experimental Study On Desulphurization Through Electrostatic Atomization Of Lime Slurry

SO₂ generated from coal-burning has become the greatest source of ecological damage to the environment, so SO₂ pollution control has been the worldwide major issue which is the urgent task to be studied and resolved. Flue gas desulphurization is the only large-scale commercial application of desulphurization technology in the world now; especially the wet-calcium-desulphurization is the most mature and reliable desulphurization technology, accounting for the dominant position. Wet calcium flue gas desulphurization is mass transfer and chemical reaction process between gas and liquid. It becomes a mainstream technology for its high rate of desulphurization, reliable operation, and easy to get desulfurizer, etc, but how to further improve the effectiveness of lime slurry spray and SO₂ absorption conditions, reduce investment and operating costs is one of the keys to popularize at large. Introduced here the high-voltage electrostatic technology into wet calcium desulphurization is the effective new way for this purpose. This paper is funded by the University Natural Science Foundation of Jiangsu Province, targeting the wet calcium flue gas desulphurization slurry droplet charged arising from the mechanism of desulphurization gain an in-depth theoretical and experimental research.Based on the comprehensive analysis of the current typical FGD technology and high-voltage electrostatic atomization technology, and on the basis of lime slurry through electrostatic spray mechanism analysis and pilot studies, this paper explored the relation between the lime slurry flow, charging mode and structure, charging voltage, and the effect of charge, to grasp the lime slurry charge atomization characteristic. Analyzed the mass transfer of droplet SO₂ absorption and chemical reaction kinetics mechanisms, initially established droplet desulphurization model under the charge condition; Analyzed conversation of mass, momentum, energy for internal desulfurizer charge gas and liquid two-phase flow, and established lime slurry atomization desulphurization gas-liquid phase flow basic equation and turbulence model, considering the mass transfer factors and reaction kinetics factors; On the basis of the flow test, theoretically simulated desulphurization flow field, and studied the flow characteristics under different conditions; Designed, established the lime slurry charge atomization tester, experimented in different modes, and explored lime slurry charge atomization desulphurization mechanism.In this paper, the results of innovative are as follows: 1.First studied the mechanism of droplet charge impacting SO₂ absorption, deemed that the serous spray let the droplet get excess charge, while droplets across the outer electric fields may result the non-excess charge polarization charged. Droplet charged affect the droplets surface characteristics and mass transfer process in three main aspects: droplets formated dipole moment and static force effect of the polar molecule SO₂ in gas, increases gas film diffuse speed; droplet charge arouses the drop of surface tension and liquid SO₂ part pressure, increases mass transfer driving force of SO₂ absorption ; calcium ion accumulates on the droplet surface, promotes the solution of Ca (OH)₂, and shortens the liquid diffuse distance of sulfur, accelerates mass transfer process at the mean time.2.First established the desulphurization model of droplets charge desulphurization, lies the foundation for the establishment of the internal desulfurizer flow model.3.First considered the quality exchange of SO₂ absorption and inter-phase mass transfer driving force in the establishment of the mathematical model of charge gas-liquid two-phase flow, to make the model more appropriate to reflect desulphurization flow situation.4. First comparison tests on three different size droplet contacts with the gas in different charging voltage, Ca / S, flue gas SO₂ concentration parameters, respectively measured the SO₂ removal efficiency of these systems. Experimental study showed: short desulphurization segment is sensitizer to the inlet concentration change of SO₂ than long desulphurization segment; whether Ca / S or charge voltage is different, droplet charge can make desulphurization rate increased in different degrees, and combining theoretical study, analyzed the mechanism of droplet charged produced plus function to desulphurization effect; clearly indicated that the desulphurization rate of flow in the same direction is better than reverse, when the droplet is charged the desulphurization rate amplitude of flow in the same direction is superior to reverse.In this paper, the important conclusions are as follows:1.Clearly pointed out that for the induction charge, the charge-to-mass ratio increases with the increasing of slurry flow, the nominal spray angle, but the role of the charge-to-mass ratio is not obvious when flow has increased to some extent, or even lower, so it should adopt the larger spray angle and the optimum flow value as far as possible from the charged electronic effect; The charge-to-mass ratio increases with the increasing voltage, but in this paper ,under this charged electronic equipment conditions , there exists a best voltage value when flow is low; initial electrode discharge voltage decreases when the polar distance H value, the nominal spray angle and flow increases; Found the mathematiac model of the ring electrode high-voltage static electric field intensity distribution .2. Used PDA and PIV to test lime slurry charge atomization desulphurization flow field, qualitatively and quantitatively researched the law of charge affect lime slurry droplet size and movement velocity; qualitatively researched the changes of gas-liquid two phase flow in the jet when the droplet charged. The changes will be beneficial to the droplet and gas quality, momentum and energy exchange developing to the full-facestrengthened the contact of droplet and gas in time and space.3.Used turbulence k-ε-k_p model, first theoretically simulated the lime slurrycharge atomization desulphurization flow field, the results showed that: charged slurry droplet caused significant changes of the flow law, entrainment, and the emergence of vortex flow and reduce of velocity of flow difference in the mainstream is propitious to smoke mix and contact with droplet, improve the condition of droplet absorption SO₂, characteristics of flow in the same direction will help to improve the desulphurization effect better than reverse.4.Charge voltage, Ca / S and L / G play a key role on desulphurization rate. It increases with the accretion of Ca / S, charge voltage, and that in both cases; the same amplitude of increase is more notable than the reverse; usually increasing L/G can enhance the desulphurization rate, but exorbitant slurry flux will affect the effect of droplet charged and the contact time of droplet and flue gas. This is a engender negative factor.