Theoretical And Experimental Study Of Simultaneous Removal Of Sulfur, Nitrogen And Mercury Pollutant In WFGD System

The pollution of SO₂ has many great influences on environment,human health and economic development.The pollution of SO₂,NO and mercury is becoming worse and worse with the rapid development of power industry in recent days.More and more large-scale wet flue gas desulfurizaiton(WFGD) systems were constructed to control the pollution of SO₂.In order to control the pollution of NO,the in-furnance control technologies such as low NOx burner(LNB) and selective non-catalytic reduction(SNCR) and flue gas deNOx technologies such as selective catalytic reduction(SCR) were taken.If the NO emission standard improves in future,the in-furnance control technologies can not gurantee the NO emission below the emission standard.The application of SCR technology is confined because of its space need.Control of emission of more pollutant is required to protect the environment and satisfy the policy of energy conservation and emission reduction in China.Therefore,it is meaningful to realize the multi-pollutants control in existed pollutant control system.Limestone/gypsum WFGD technique is applied widely for control the SO₂ emission in China.The technique to control multi-pollutants in the WFGD system is economical and attractive,especially for those power plants with limited space to take great construction.Based on the review of advance of multi pollutant removal technology,kinetics of DeSO₂ and DeNOx in the compound solutions was studied.Effects of partial pressure and concentration of reagents to the absorption rate of SO₂ and NO were determined in the experiments of absorption characteristic in stirred reactor with plate mass transfer surface. The kinetics parameters such as reaction order,rate constant,activated energy were determined according to experimental data.After the study of kinetics,effects to efficiency of removal of SO₂,NOx and Hg in the compound solutions were studied.The effects such as pH value,flow of flue gas,reagents concentration,and molar rate reagents to pollutants and liquid to gas rate to the efficiency of removal of SO₂,NOx were determined in the experiments with different reators.The absorptions of Hg⁰ in the compound solutions with washing bottle were taken.Effects of parameters mentioned above to the efficiency of Hg removal were determined.Aimming at the application of the WFGD systems in power plants,the numerical simulation of performance optimization for multi-pollutant removal in spray scrubber of WFGD system was studied.Based on computational fluid dynamics(CFD) technology and structuralized-non-structuralized hybrid grid technology,the standardκ-εturbulent model which describe the flue gas turbulent motion in the tower,the Discrete Phase Models which trace the movement of droplets,Discrete Random Walk model which describe the turbulent motion influence to the movement of droplets,the Rosin-Rammler model which describe droplets distribution,the gas-liquid fluid flow field in spraying tower was simulated with the SIMPLE calculation method.The pollutants concentration fields in the scrubber were determined by desulfurization and deNOx mathematical model which build up non-steady state mass transfer theory.The numerical calculation of the scrubber of a 300 MW power unit was taken in different design and operation conditions. The calculation results of desulfurization are in good agreement with the results measured in the performance test.Based on the numerical simulation results,some advices were proposed for the optimization of multi-pollutants removal in the spray scrubber.Based on the results of numerical simulation,the programme of removal of SO₂,NOx and Hg in WFGD system was proposed and the economy of the programme was analyzed.Limestone/gypsum WFGD technique is the most popular technique used in the desulfurization because of its advantages.Nearly all the limestone/gypsum WFGD techniques are from foreign corperation and lots of WFGD systems are in malfunction or out of service because the operation modes of utility boilers in China are different to those of foreign utility boilers.It is necessary to develop WFGD technique with independent intellectual property rights.Material balance is the key and base for the WFGD design and optimization.Based on the basic theory of material balance and system design,the system of sod energy balance,water balance,solid balance,gas balance,chlorine balance and magnesium balance of WFGD system are analyzed detailedly to form a material balance calculation software package.The calculation results of several WFGD systems by the software package are in good agreement with design and operation results in the large scale WFGD systems in power plants.The software package can be applied to the material balance calculations of WFGD system.