Research On The New Type Of Synergistic Additives Based On The Limestone-gypsum Wet Flue Gas Desulfurization Technology

The SO₂ produced by coal-fired power generation is very harmful to forests,crops,buildings,soil,human and water.Wet flue gas desulfurization?WFGD?occupies a dominant position in flue gas desulfurization in coal-fired power plants for a long time.However,the limestone-gypsum wet flue gas desulfurization unit has a difficult problem of high energy consumption,high operating cost and poor adaptability to the sulfur content of coal.With the issue of the stricter SO₂ emission standard,a lot of WFGD units will inevitably paid expensive improvement cost for their urgent need of upgrading.It is the core of limestone-gypsum wet flue gas desulfurization process to promote limestone dissolution and calcium sulfite oxidation,which is the breakthrough point to solve the key problems of the WFGD units.The effect of desulphurization synergistic additive?organic acids,organic salts,inorganic salts and organic amines?on PH buffering,calcium carbonate dissolution,calcium sulfite oxidation,SO₂ absorption in bubbling bed and crystal structure of gypsum was studied at the conditions of pH?5.5?,temperature?50??and stirring rotation number?300r/min?.Developing a reasonable ratio of desulphurization compound synergistic additive,which can not only improve limestone dissolution,calcium sulfite oxidation,desulfurization efficiency and gypsum quality,but also make auxiliary machine energy saved and consumption reduced for improving economy.What's more,the utilization value of limestone could be maximized and the high quality utilization of desulfurization by-product could be realized.Firstly,the effect of single component synergist?organic acids,organic salts,inorganic salts and organic amines?on pH buffering property of slurry was studied by the pH buffering experiment,which was intended to select single additive with satisfactory effect to reduce the consumption of limestone.The results show that,MDEA had a satisfactory effect of pH buffering in the organic amine.The pH buffering capacity of organic acids:benzoic acid>acetic acid>adipic acid>tartaric acid.The pH buffering capacity of organic salt was better than that of inorganic salt.Sodium benzoate,sodium acetate and sodium two EDTA show a satisfactory effect.Except for MDEA,the higher the concentration,the better the effect is.The pH buffering effect:organic amines>organic acids>organic salts>inorganic salts.Then,the effect of single component synergist?organic acids,organic salts,inorganic salts and organic amines?on accelerating the limestone dissolution rate was investigated with an automatic potentiometric titrator.Based on the single-component results,A-J series of composite synergists were prepared.Meanwhile the effect of composite synergists on accelerating the limestone dissolution rate was explored to select composite synergists with satisfactory effect.The results show that,The effect of single component synergist?organic acid,organic salt and organic amine?on accelerating the limestone dissolution rate was better than that of inorganic salt.The effect of acetic acid,adipic acid and benzoic acid in organic acid was remarkable?effect:acetic acid>adipic acid>benzoic acid?.The effect of sodium benzoate and sodium acetate in organic salts was satisfactory.The effect of Magnesium Sulfate on accelerating the limestone dissolution rate was greater than that of sodium sulfate.The higher the concentration of synergists,the better the effect is.Considering the synergistic effects and cost,the D series composite synergist was the optimal one for industrial application.After that,the effect of synergist on promoting the oxidation rate of calcium sulfite was explored.The ability of D series synergistic additives on promoting the oxidation rate of calcium sulfite was verified in order to screen out composite synergists with more excellent properties.The results show that,the optimized pH value of the synergist utilization by the experiment was 5.5.The ability on promoting the oxidation rate of calcium sulfite:SDS>Magnesium Sulfate>adipic acid>citric acid>sodium sulfate.The higher the concentration of synergists,the better the effect is.The ability of D series synergistic additives on promoting the oxidation rate:D4>D0>D2>D12>D8?A>D7.Finally,the effect of synergist on SO₂ absorption was studied with a bubbling bed.Meanwhile the effect of composite synergists on promoting the quality of gypsum was studied.The results show that,the desulfurization efficiency of the compound synergist?D0,D2,D4 and D12?was better than that of A?the original compound synergist?,which was more than 96%.The structure of gypsum particle with D4 compound synergist was short prism,not flaky structures,which was favorable for the dehydration of gypsum.The reaction of compound synergist?F,I and L?on SO₂ absorption was sharp and efficient,which could be used as a emergency synergist.Economic analysis shows that,if a power generation equipment with 2*600MW uses the D4 compound synergist,the operational cost can be saved by approximately 4.4 million Chinese Yuan per year.