Research On The Performance Of Dry And Semi-dry Calcium-based FGD Ash And Its Application On Manufacturing Steam-cured Brick

As China's SO₂ emissions control constantly increasing,flue gas desulfurization of power plant has entered a rapid development stage.However,the disposal problem of large number of desulfurization waste has become the main constraints of the promotion of dry and semi-dry flue gas desulphurization technology.Comparing to the wet FGD technology,dry and semi-dry FGD technology has some advantages, such as low investment and operation cost,small space-occupancy,less water consumption and simple process,which is recognized as the most cost-effective flue gas desulphurization means of small power plants and industrial boiler,so such issues as disposal and use of FGD ash arises,while up to now the nature and application of FGD ash is at a research stage,it's mainly abandoned.This paper studied the performance,recycling application,oxidation and decomposition characteristics of FGD ash and is of great realistic significance and far-reaching historical significance.In the experiment,three kinds of FGD ashes collected from different power plant and desulfurization process were studied by XRD,XRF,TG / DSC,SEM,and other modern testing means,phase of its composition,chemical composition,thermal stability,particle morphology and the physical nature were discussed,and thermal stability,catalytic properties under high and low temperature and the acid stability at room temperature of the unstable phase——calcium sulfite were to focus on the research.At last a pilot study of the FGD ash on manufacturing steamed-cured brick was conducted.1,FGD ash is a kind of high-sulfur and high-calcium ash and is composed of calcium carbonate,calcium hydroxide,calcium sulfite,calcium sulfate,silica, magnesia and mullite,etc.Its chemical composition and physical properties are very different with fly ash.Its thermal chemical processes includes:water decomposition of CaSO₃·0.5H₂O,decomposition of calcium hydroxide,oxidation(or decomposition) of CaSO₃ and decomposition of calcium carbonate.2,Water decomposition of CaSO₃·0.5H₂O occurs during 330～410℃,and then if in the air atmosphere CaSO₃ will be oxidized to CaSO₄ during 430～500℃,while in an atmosphere of nitrogen above 700℃CaSO₃ will decompose:CaSO₃→CaO+SO₂(1)and CaSO₃→CaSO₄+CaS(2), with temperature increasing reaction(1)reacts faster than reaction(2).During 600℃～100℃,the decomposition rate of calcium sulfite is below 5%in air and very high in N₂ atmosphere.3,Under high temperature and low temperature conditions,the transition metal salts X is a cheap and effective catalyst,the increasing of temperature and the addition of catalyst can all improve the oxidation rate of calcium sulfate significantly,and the influence of temperature is higher than the amount of catalyst.4, With the concentration and capacity of acid solution increasing,decomposition rate of calcium sulfite is gradually increasing,when the reaction solution PH＞5.2, decomposition rate of calcium sulfate is less than 1%,which will not cause pollution to the environment.Calcium hydroxide and calcium carbonate in FGD ash can effectively inhibit the decomposition of calcium sulfite in the acidic environment.5,FGD ash is characteristics of hydration and hardening.The optimum condition is 100℃in temperature and 8-10h for streamed hour,Added by the appropriate amount of additives,Si-Al materials and aggregate,moulded by semi-dry method,streamed for 10h,the FGD ash brick can reach the requirement of M15 brick,but dry-shrinkage property of FGD ash brick should be improved.