Deep Purification Of Flue Gas In Simulated Coal-fired Power Plant By Porous Calcium Carbonate

At present,the flue gas treatment technology commonly used in small and medium-sized industrial boilers in China can not deeply purify the flue gas such as Hg⁰ and SO₃,which has great limitations.Among the three types of mercury found in coal-fired flue gas,elemental mercury?Hg⁰?is the most difficult species to eliminate.Mercury is abundant in both human beings and the environment and is easily accumulated in the ecological cycle,with the passage of time,it is bound to have adverse effects on any environment.For SO₃,the negative effect of SO₃ on plant operation is mainly achieved by the formation of sulfuric acid?H₂SO₄?.SO₃ can cause corrosion on the surface of the heat recovery zone.At the same time,SO₃ forms an adsorption layer on the dedusting plate,which weakens the surface resistivity efficiency of the whole particle.Moreover,SO₃ can also lead to the deactivation of SCR catalyst.At present,the selectivity of catalysts is the starting point,but it can not solve the problem obviously.At the same time,there is the risk of secondary pollution of the system.Moreover,these catalysts can not be effectively recovered because of their high toxicity,which increases the operation cost.All kinds of hazards show that the development of cheap,efficient,stable and recyclable adsorbents has great application and promotion value.Porous calcium carbonate,a porous material with SDS as template,emerges at the historic moment.Porous calcium carbonate promotes the integration of Ca²⁺and CO₃^2-through the intermolecular force of soft template SDS.The preparation conditions of porous calcium carbonate were screened by response surface test,orthogonal test and single factor test.The effects of pH,molar ratio of CaCl₂ to SDS,temperature and stirring rate on the specific surface area were investigated.The optimum conditions for the preparation of adsorbents were obtained as follows:pH=9,the molar ratio of CaCl₂ to SDS is 0.5,the stirring temperature is 30 ^oC,and the stirring rate is 600 r/min.The reaction time was 2 h,the static time was 10 h and the calcination time was 3.5 h.For gaseous mercury elements,it is not easy to capture and measure directly in the gaseous way,so the gaseous zero-valent mercury is oxidized to divalent mercury by Ontario method.Then the concentration of porous calcium carbonate was measured by atomic fluorescence spectrophotometer.The effects of different adsorbents,different additions,different adsorption temperature,inlet concentration,humidity and other gases on the adsorption of porous calcium carbonate on Hg⁰ were studied under different working conditions.Combining the model of Langmuir adsorption isotherm and Freundlich adsorption isotherm,it can be seen that the whole adsorption process conforms to Langmuir adsorption isotherm.It can be concluded that the whole adsorption process is mainly physical adsorption,and is bilayer adsorption.For SO₃,it is not easy to capture and measure directly in the form of gaseous state,so isopropanol ice bath method is used to collect SO₃ in the gaseous state,and then ion chromatography and conductivity meter are used to ma ke standard curves for them to obtain the specific amount of substances.Then,the effects of porous calcium carbonate on SO₃ adsorption under different work ing conditions,such as different adsorbents,different additions,different adsorption temperatures,import concentration,humidity and other gases,were studied by measuring and analyzing the effects of porous calcium carbonate on SO₃ adsorption.According to the calculated results,it is found that the adsorption of SO₃ by porous calcium carbonate conforms to the quasi-second-order kinetic adsorption model.In comparison,chemical adsorption is dominant in this process.Generally speaking,the adsorption efficiency of porous calcium carbonate on Hg⁰ and SO₃ is relatively good and basically achieves the expectation.