Technology And Mechanism Of Silicon-retention/Silicon-removal With Synergistic Autocausiticizion

In order to reduce "silicon disturbance", silicon could be retained in pulp when produced common chemical pulp using bamboo, but silicon should be remove as much as possible when produced some high value-added pulp. Moreover, introduced autocausticizing technology could relieve the pressure of chemical recovery and reduce emission load of lime mud in process of silicon-retention/silicon-removal. Aimed at the different demand of producing common chemical pulp and high value-added pulp, technology of simultaneous silicon-remain cooking cooperated by autocausticizing and silicon-removal through black liquor combustion simultaneous with autocausticizing was been studied, and the mechanism of silicon-remain/silicon-removal was been preliminary explorated.In this paper, the added location and dosage of autocausticizing agent in cooking process and the silicon-remain result of different loading cooperated by autocausticizing agent were been contrasted and analyzed. The residual content of aluminium ion and boron ion in black liquor were been detected; the effect of process of simultaneous silicon-remain cooking cooperated by autocausticizing on scale formation performance of black liquor was preliminary evaluated; the process of simultaneous silicon-remain cooking with NaAlO2 and Na2Si03 was simulated, and the product was detected by using modern analysis instrument and technology such as SEM-EDAX、XRD; the mechanism of simultaneous silicon-remain cooking was analyzed; furthermore, the mechanism and process of silicon-removal through black liquor combustion simultaneous with autocausticizing were been researched; and the effect of the process on chemical and physical property of black liquor was been studied; thermogravimetric analysis of black liquor was been analyze. The result of research were as follow:When silicon-remain agent and autocausticizing agent were added in cooking, synergistic action of silicon-remain was discovered, and the adding location in pre-impregnation stage was better than in impregnation stage.When the loading of silicon-remain agent was 2wt% and the loading of autocausticizion agent was 0.05wt%, the ash content and silicon content of pulp were all increased, silicon removal rate in black liquor of pre-impregnation could reach to 93.55%, and all silicon removal rate in black liquor could reach to 88.24%, the aluminium ion content in black liquor of impregnation was 152.62mg/L, the silicon content in black liquor of impregnation was 0.12g/L, which had no disadvantage effect on scale formation performance in fluid transportation,mass transfer and evaporation section. The VIE scale of black liquor in impregnation stage reached 5.89mg/L. Silicon of raw material dissolved in black liquor and reacted with silicon-remain agent/autocausticizing agent to form silicoaluminate which constituted of Na、Al、Si、O. The silicoaluminate exsited as spherical particles with a diameter of only 4 μm. The simulated process of simultaneous silicon-remain cooking could obtain spherical particles as well, but the appearance size of spherical particles was impacted by different cooking process and different Na2SiO3/NaAlO2 ratio, the substance of spherical particles was effected by Na2SiO3/NaAlO2 ratio. According to the optimized laboratorial simultaneous silicon-remain cooking process entirely, Na8Al6Si6O24(OH)2(H2O)2,1.08Na2O·Al2O3·1.68SiO2·1.8H2O and Na2Al2Si1.85O7.7·5.1H2O could be found in the product.When silicon-removal agent and autocausticizing agent were added in black liquor combustion, slight reduction of silicon-removal rate and autocausticizing rate in green liquor could be found, indicating that it’s no problem to finish autocausticizing reaction in stage of silicon-removal. When causticizing efficiency setpoint was 20%, that is the autocausticizing agent loading was 3.6wt% and silicon-removal agent loading was 3wt%, silicon-removal rate in green liquor could reach to 56.68% and actual causticizing efficiency reached 17.14%, a certain amount of magnesium sulfate could benefit on silicon-removal rate. The effect of a specified volume of silicon-removal agent and autocausticizing agent on the VIE of black liquor was advantageous, but the result was contrary when the loading was excess. The TG-DTG fingerprint showed that silicon-removal agent and autocausticizing agent led to the pyrolysis rate became slow down, along with the rise of black liquor remnant. SEM-EDAX showed that silicon-removal agent/autocausticizing agent could react with silicon in black liquor to form substance of spherical or ellipsoidal, then flocculated granular substance with different shape, and granular substance united with something undissolved to form undissolved substance in green liquor, thus silicon-remove was finished in the black liquor combustion stage.