The Mechanism Research On WFGD Characteristic Under High CO₂ Concentration

Limestone-gypsum wet process is the main flue gas desulfurization methodin the coal-fired power plant due to the advantage of its maturity andlow operating cost.Compared with the air-firing,the oxy-firing technology can make the concentration of CO₂ in the flue gas more than 80%,which will facilitate to the CO₂ reduction.Under high concentrations of CO₂,the characteristics of limestone dissolution and SO₂ absorption on the limestone-gypsum WFGD process is explored by this paper,to support the equipment selectionanddesignfor limestone-gypsum WFGDunder oxy-firing.Firstly,the WFGD mechanism under high CO₂ concentration is discussed according to the chemical reaction thermodynamic principles.The influence of high CO₂ concentration and reaction temperature on the WFGD is analyzed in detail.The results show that the Gibbs free energy of less than 0,therefore,the reaction can be carried forward spontaneously.The CO₂ concentration and reaction temperature have negative influence on SO₂ removal.Then,the limestone dissolution characteristics under high CO₂ concentration are studied by using hydrochloric acid titration method.The influence of CO₂ concentration,slurry pH,particle diameter on limestone dissolution characteristicsareinvestigated in detail.The results show that in case of high CO₂ concentration,the slurry pH can obviously affect the limestone dissolved;at the same pH value,the higher CO₂ concentration causes faster limestone dissolution rate;the smaller the particle size of limestone,lead to thefasterlimestone dissolve rate;while the high CO₂ concentration is positive to the limestone dissolved.Further,the influence of various conditions on desulfurization efficiency are investigated by a small test rig.The results show that at the same inlet SO₂ concentration,the desulfurization efficiency decreases as theCO₂ concentration increase,while at the same inlet CO₂ concentration,the desulfurization efficiency decreases as the inlet SO₂ concentration increases;with the increasing flow rate of the flue gas,desulfurization efficiency declines,but the decreasing tend is extremely small;at the same flue gas velocity,with increasing CO₂ concentration,desulfurization efficiency decreases slowly;at the same liquid-gas ratio,with increasing CO₂ concentration,the desulfurization efficiency is slightly changed,while at the same CO₂ concentration,the higher liquid-gas ratio causes higher desulfurization efficiency;invariousslurry pH,with increasing CO₂ concentration,desulfurization efficiency will totally decline.At the same CO₂ concentration,the desulfurization efficiency increases with the higher slurry pH.It can be observed that suppose the slurry pH be5.0,5.5,CO₂ concentration has less influence on the desulfurization efficiency,but keep the slurry pH be 4.5,the effect of CO₂ concentration on desulfurization efficiency is significant.