Experimental Research On High Calcium CFB Desulfurization Ash As Raw Material And Admixture Of Sulphoaluminate Cement

In recent years,with the increase of the number and capacity of CFB boilers,the output of desulfurization ash has increased on a large scale,and its utilization of resources,high value and high performance has become the development trend of bulk solid waste.In the current context of energy conservation and emission reduction,cement industry has attracted the focus of social and policy attention due to its high energy consumption and high CO₂ emission.Sulphoaluminate cement has more advantages in reducing carbon emissions than Portland cement,and because of its high early strength,excellent corrosion resistance and other characteristics,it has become the largest non-silicate special cement in China.In this paper,the application of CFB high-calcium desulfurization ash and slag produced in Guizhou 660MW National Demonstration Project is investigated based on the national key research and development program.On the one hand,CFB high-calcium desulfurization ash and slag were used as raw materials to produce sulphoaluminate cement clinker.The effects of calcination system and ingredients parameters on the compressive strength,f-CaO content and mineral composition of the clinker were mainly studied,and the hydration characteristics of the clinker were characterized.On the other hand,CFB desulfurization ash and slag were used as admixtures to directly add sulphoaluminate cement in different proportions,so as to explore the influence of the type and amount of admixtures on the compressive strength,setting time and expansion rate of cement.The main research work and conclusions of this paper are as follows:（1）Effects of calcination temperature and alkalinity coefficient on clinker strength and f-CaO content:In the clinker firing range between 1250℃and 1350℃,the compressive strength of clinker increases with the increase of calcination temperature and the prolongation of curing age,the content of f-CaO in the clinker decreases with the increase of temperature and increases with the increase of alkalinity coefficient Cm value.The optimal basicity coefficient of the clinker prepared with desulfurization ash is Cm=1,and that prepared with desulfurization slag is Cm=0.98.Under the same conditions,the content of f-CaO in the slag system is higher than that in the ash system,and the compressive strength is lower than that in the ash system.（2）The mineral composition and influencing factors of clinker were studied,and the hydration process of clinker was characterized.The main minerals in the prepared clinker are close to the design values.In the range of clinker firing temperature,the increase of temperature can promote the formation of main minerals.Compared with anhydrous calcium sulfoaluminate,the hydration process of clinker is more complex and the hydration time is longer.（3）In the experiment,desulfurization ash slag was used as admixture and directly mixed into sulphoaluminate clinker at different proportions of 5%-25%,and the conclusions are drawn as follows:within the content range of 5%-25%desulfurization ash and slag,the relationship between the compressive strength of the complex doping system and the content of desulfurization ash is negatively correlated,and the expansion rate is positively correlated with the content of ash,the compressive strength of the mixing system is negatively correlated with the amount of admixture,and the expansion rate is positively correlated with the amount of admixture.When the content of the admixture is more than 10%,the desulfurization ash and slag have the retarding effect,and the setting time meets the requirements of the standard.When the amount of admixture is less than 10%,the desulfurization ash and slag have the function of limiting the expansion rate,and the expansion rate is less than the original cement.