Study On The Mechanism And Control Technology Of Denitrification And Desulphurization Fly Ash On Cement Performance

Fly ash is an industrial waste discharged from coal-fired boilers in thermal power plants,and it is a man-made volcanic ash material.The use of fly ash as an auxiliary gelling component to produce cement is one of the effective ways of its resource utilization.But in recent years,the thermal power plant in the original desulfurization process on the basis of the installation of denitrification equipment,resulting in the use of fly ash in the building materials industry in the abnormal smell,the mixture of high gas content,plastic volume expansion,decreased strength and other anomalies,the utilization of fly ash in cement concrete is limited.In order to solve the above problems,the paper adopts the form of simulate the denitrification and desulfurization fly ash.The effects of single addition of denitrification byproducts?NH₄HSO₄?,single addition of desulfurization byproducts?CaSO₄?2H₂O and CaSO₃?0.5H₂O?and combined of denitrification and desulfurization byproducts?NH₄HSO₄,CaSO₄?2H₂O and CaSO₃?0.5H₂O?of cement system on the standard water requirement,setting time,cement soundness,mechanical and other macro performance were studied.The use of XRD,SEM-EDS,TG-DSC,cement hydration heat meter,pore structure analysis,research on the denitrification desulfurization byproducts of cement phase composition,microstructure,hydration products and hydration degree and pore structure,the regularity and mechanism of the influence on cement properties are obtained.The modification method of fly ash for denitration desulfurization is put forward.The research results have great economic value and social significance to the comprehensive utilization of fly ash and cement industry.The main conclusions are as follows:?1?When the content of NH₄HSO₄ is more than 1.5 wt.%,with the increase of the dosage,the initial setting time and final setting time are obviously prolonged.The content of byproducts has little effect on the cement water demand and stability.When the content is more than 1.5 wt.%,the compressive strength and flexural strength increase gradually with the increase of the content.The crystal phase composition of ammonium hydrogen sulfate.Byproduct leads to a decrease in harmless hole and less harmful pore number of cement structure 28 d,and multi hole number increased,total porosity increased.The exothermic rate of the initial hydration period of the cement system increases,accelerated phase and decay phase of the heat release rate decreased,3d significantly increased the total cumulative heat.?2?The greater the ratio of CaSO₄?2H₂O to the by-product of desulfurization,the longer the initial setting time and final setting time of the cement;when the content of byproduct is less than 2.0 wt.%,the compressive strength of the two groups was higher than that of the blank group at 28 days,and when the content of CaSO₄?2H₂O and CaSO₃?0.5H₂O had little effect on the compressive strength of 3 days and 7 days,when the content is more than 2.0 wt.%,the compressive strength of each group is reduced by 3⁶ MPa;as the solubility of CaSO₄?2H₂O is higher than that of CaSO₃?0.5H₂O,it is easy to react with cement to generate AFt,which improves the early strength of cement;CaSO₄?2H₂O plays an important role in the activation of fly ash,with the increase of age,the diffraction peaks of the vitreous phase?mullite and quartz?and Ca?OH?₂ in the system decrease gradually.?3?Under the condition of 2.0 wt.% of desulphurization byproducts,with the increase of denitrification byproducts,the compressive strength of cement structure 3 days,7 days and 28 days is 1³ MPa,1⁵ MPa and 1¹0 MPa,with the single-doped desulfurization byproducts age higher than the blank sample 1⁷ MPa in stark contrast;the number of harmful pores increased and the total porosity increased,and the degradation rate of the denitrification products was much higher than that of the desulphurization byproducts;the CaSO₄?2H₂O higher proportion of byproducts desulfurization and denitrification,the higher the degree of hydration of fly ash,the lower the diffraction peaks of the vitreous phase,the higher the nonvolatile water content in the system,and the lower the Ca?OH?₂ content.?4?The compressive strength and flexural strength of the cement structure were improved by 1%,4% and 9% at 3 days,7 days and 28 days respectively by the pre-hydration method;after treatment,the nitrogen content of the cement slurry structure decreased by 68%,the nitrogen content decreased by 36% on the 7 days,and the nitrogen content of the system was about 5% after 28 days;the treated denitrification desulphurized fly ash can effectively improve the pore structure of the fly ash-cement system;the total porosity of the system is reduced by 2.18%;in the aspect of durability,its ability to resist chloride ion penetration and sulfate resistance is greatly improved.