Experimental Study Of Flue Gas Desulphurization From MSW Incinerator In Fixed-bed

The characteristic of flue gas from MSW incinerator is that concentration of SO₂ is low and changes frequently., and the temperature of flue gas is higher than 500℃. It is problems that should be settled quickly to control SO2 especially which with lower concentration. According to absorbent with or without water during desulphurization, desulphurization methods conclude wet method, semidry method and dry method. In all the methods, effect of wet one is the best, semidry one is better. Though effect of dry system is lower than wet and semidry ones, its techniques is simple, expenditure in investment and function is lower than the other two, demanding for operation level is relaxed, disposal of waste residue is convenience and there is no waster water. In recent years, equipments of dry system were improved continuously in developed countries and purificatory efficiency of contamination is advanced, so this techniques is also practicability, especially for areas which develop slowly and whose emission criterion are loose.Theoretical analysis and idiographic experiment are combined in the study. First, effect on desulfur capability of absorbent are analyzed in thermodynamics and kinetics, and optimum conditions during reaction are also forecasted;experiments are done at idiographic conditions, experimental and theoretic results are analyzed contrastively. Thermodynamic analysis is done by HSC system, experiments developed in fixed-bed, thermal gravimetric, SEM photos and XRD analysis are assistant to analyze experimental results.In experiment, absorbent is CaO powder, mixture of air and SO₂ in different proportions simulates flue gas from MSW incinerator, outlet concentration of SO₂ is measured by intelligent flue gas analyzer online, effects of temperature, Ca/S, inlet concentration of SO₂, particle diameter and resident time of flue gas on desulphurization efficiency of CaO are studied. The results showed that the above factors have different effect on desulphurization of CaO: desulphurization efficiency and utilization efficiency of Ca increase with increasing of temperature, Ca/S and decreasing of outlet concentration of SO₂ and resident time of flue gas. When Ca/S is bigger than 3.1,desulphurization efficiency goes to be constant. But at generalconditions, outlet concentration of SO2 cannot arrive at emission control regulations completely if only use CaO as absorbent. Because solubility of calcic compound is low, desulphurization efficiency and utilization efficiency of Ca are low.People have studied many methods to enhance desulphurization efficiency and utilization efficiency of Ca. Improving activity of absorbent through adding additive is one of the methods. Additives used in the literatures can be classified into four kinds: (1) deliquescent easily and other inorganic salt;(2) alkaline materials contained natrium;(3) organic compound;(4) oxidation catalyzer. Effects of Fe2O3 and plant ash on desulphurization capability of CaO are studied respectively in experiment. There is about 10% Fe2O3 in pulverized coal ash and Fe can be changed into Fe2+ and Fe3+> Fe2O3 can make CaO disperse and reunite after mix and act as catalyzer in reaction;plant ash has the characters of porous, no pollution and strong absorbency to SO2. In order to study effect of Fe2O3 and plant ash on CaO in desulphurization capability, Fe2O3 and plant ash are used as additive, they are mixed with CaO in different proportion to absorb SO2. The result showed that these mixture can increase absorbency of CaO in spite of the ratio, and optimum proportion is 10:100;Fe2O3 quicken reaction rate and plan ash make reaction durative better;but optimal temperature and reaction mechanisms are not same. Optimal temperature after addition Fe2O3 ranges from 650°C to 750°C;and plant ash from 800'C to 900°C,it increases sintered temperature of CaO after adding plant ash. Existing of FeaOs not only expands speice surface area but can catalyze reaction obviously at certain temperature. Disperse, agglomerate and catalysis to CaO taken by Fe2O3 makes CaO deposit outside of Fe2O3 during reaction. It creates conditions for desulphurization reaction and SO2 diffusing to deep level. Its promotion to CaO is not obvious after adding the mixture of CaO and pulverized coal ash, effect on desulphurization is not so much as CaO. Desulphurization effect is better when additive is plant ash than Fe2O3, so plant ash is appropriate additive in experiment.