Experimental Study On Release Of Alkali Metals From Cement Raw Meal During Its Decomposition

China has become the world's largest cement producer for many years.The cement industry has already become the second largest source of CO₂ emission after industrial thermal power generation.The use of oxygen combustion to enrich CO₂ is of great significance for carbon reduction in the cement industry.The cyclic enrichment of volatile components?sulfur,chlorine,and alkali metals?in the cement production process during the cement production process is a unique phenomenon in the new dry process cement production process,in which the recycling of alkali metals will result in a series of Adverse effects:Alkali metal oxides are an important component of the cement kiln crust.Excessive alkali metal content will also increase the viscosity of the liquid phase at high temperatures,resulting in agglomeration during calcining of the clinker.In addition,the alkali metals will pass through In the raw material,Al₂O₃,SiO₂,SiC and other substances react to lose refractory materials,causing abnormal expansion of the silica-alumina refractory material,hot surface spalling and severe erosion,greatly reducing the life of the refractory material;alkali metal also affects the clinker The quality of firing will seriously affect the durability of the concrete structure.In this paper,the raw material of a cement plant is selected as the research object,and the isothermal and non-isothermal experiments are carried out to study the release of alkali metals during the decomposition of cement raw materials through a tubular furnace combined with a J200 LIBS integrated machine and a self-built laser bench.The effect of decomposition atmosphere and decomposition temperature on the release characteristics of alkali metals was analyzed.In combination with the experimental results,the mechanism of the effect of decomposition atmosphere and temperature on alkali metal release was analyzed.In the 20%O₂⁸0%N₂ decomposing atmosphere,the alkali metal release rate increases with the increase of decomposition temperature when the cement raw material decomposes.The volatilization rates of Na and K are 52%and 53%respectively at 850°C.At 1000°C,the volatilization rates of Na and K were 64%and 71%.The reason for this is that the potassium compound is more volatile than the sodium compound,and the next different alkali metal compounds have different volatilization temperatures,of which the chloride is most volatile,followed by the alkali metal hydroxide,and finally the alkali metal sulfide.Under20%O₂⁸0%CO₂ atmosphere,the volatilization rates of Na and K at 850°C were 16.4%and43.7%,respectively,and were 54%and 60%at 1000°C.The reason is that the increase of CO₂ partial pressure will have a greater impact on the heat transfer and mass transfer during the decomposition of limestone in the raw meal,thereby affecting the heat release of alkali metals therein,and secondly,the high CO₂ partial pressure may promote the production of alkali metal carbon.Acid salts,while alkali metal carbonates are not volatile.The release of alkali metals from cement raw materials under non-isothermal decomposition conditions is different from that under isothermal decomposition conditions.Under non-isothermal decomposition conditions,it was found through energy metering that under the same heating power,the temperature in the 20%O₂⁸0%N₂ atmosphere was higher than that in the 20%O₂⁸0%CO₂ atmosphere.The reason was CO₂.The specific heat capacity is larger.In addition,because it is impossible to accurately measure the temperature of the heating place,only the release characteristics of alkali metals under the same atmosphere and different heating power are compared.When the cement raw material decomposes,the content of alkali metal in the flue gas changes with the time of single peak,and reaches the peak near 20s,then rapidly decreases and maintains at a lower level and approaches zero.In the 20%O₂⁸0%N₂ atmosphere,the release time of the alkali metal decreases with the increase of the heating power,and the release time of the alkali metal increases with the heating power in the 20%O₂⁸0%CO₂ atmosphere.Invariable,the main volatilization time of its alkali metal is around 50s...