Studies On The Technology Of Simultaneous Desulfurization And Denitrification By Ferrous Cysteine Solution

In order to prevent the pollution of acid deposition, the SO₂governance work has beencarried out for many years, yielding the maturity of technology in various aspects. But thesurge of NOXemissions in recent years makes that the development of high-efficiencydesulphurization and denitrification new technology is urgently required. Ferrous cysteinesolution is circulated and regenerated for reuse while purificating the flue gas, which is animportant research direction of simultaneous desulfurization and denitrition.There are threemain methods for regenerating technology, the drawbacks of electric reduction process isenergy consumption and the refractory product, and biological method is both low inregeneration speed and reprocessing rate, while the chemical method is not only with highregeneration efficiency, but also available to produce sulphur in alkaline conditions, whichhas good application value and development prospects.Considering the presence of both SO₂and NOX, the mechanism and kinetics ofdesulfurization and denitrification process was analysed by adding sodium hydrosulfide intoferrous cysteine, and from the point of absorbent that avoided the gas analysis problems thathard to sampling and measuring. The characteristic of the method is that combined with thefractional step and integration method, which makes full use of the advantages tocomplement its shortcomings. The three major results are listed as follows:（1）Under the conditions of55℃,[CySH]/[Fe2+]=4and pH=7.0～10.0, the ferrouscysteine additives for simultaneous removal of S02/N0Xwas analyzed by resultants content ofFe, cysteine and cystine. It concluded that, when the pH value of absorbent was7, ferrous cysteine reacted with NO to produce dinitroso complexe, and cystine mainly existed in solidproduct; but when the pH value was8or greater, there was not dinitroso complexe in finalproducts, and cystine mainly existed in solution; during the resorption of CySSCy and SO₂,calculating NaHS and SO₂distribution coefficients showed that reducers reaction consumedwas HS-and SO32-, and element sulfur was produced.（2）The mass transfer and kinetics of the absorption had been studied. Determining thedynamic region by measuring the absorption rate of solution, with changing the liquid phasevolume, stirring speed and concentration of solution. The experimental result indicated themass transfer and kinetics region of the absorption of NO into aqueous fenous cysteinesolutions was a pseudo-first order reaction, N’=0.1779CL1/2, and desulfurization process areawas a pseudo-m order reaction; experimental values of the enhancement factor reactionbetween ferrous cysteine with NO had a good agreement with calculated values; thevolumetric mass-transfer coefficient of ferrous cystine reacting with sulfur dioxide hadnothing to do with thickness of layered film, so did enhancement factor and SO₂concentration.（3）On the basis of demonstrating that ferrous cysteine is reproducible, the influence oftemperature on the rate of cysteine regeneration and sulphur recycle was observed further.When reaction temperature changed in a span of50～80℃, the rate of cysteine regenerationis basically constant, ηregeneration≥90％; temperature variation was almost no effect on the rateof element sulphur recycle, ηrecycle≥93％.