Reserch On Waste Heat Drying Mechanism Of Municipal Sludge Based On A Rotational Spout-fluidized Bed

With the development of our economy, acceleration of urbanization and sharpincreasement of population incities, urban sewage treatment capacity and treatment rate isincreasing year by year. As the product of waste water treatment, the production of municipalsludge is also increasing. Traditional sludge treatment techniques include concentrating,stabilization, dewatering and drying. However, water content of sludge can be reduced to80%,while only the sludge which water content is blow30%can be further utilized. Thus, thermaldrying treatment is the extremely important pretreatment process for sludge utilization.At present, thermal drying techniques of sludge include direct drying technology, indirectdrying technology and mixed drying technology. In this article, the direct drying technologyand indirect drying technology were compared, the characteristic, advantages anddisadvantages, the representative drying equipments were analyzed, and the research statusand developmental trend of the thermal drying technology were also introduced.This article makes research from aspects of experiment and numerical simulation, theeulerian multi-phase model was applied in three-dimensional numerical simulation of therotational spouted-fluidized bed test bench, the effect of different velocity ratios betweenbottom wind and tangential wind on gas velocity distribution and particle velocity distributioncharacteristics in the rotational spouted-fluidized bed dryer was analyzed, and the change lawof gas-solid flow state with the time at the velocity ratio of30m·s-1/30m·s-1was studied. Theresults show that the increase of tangential wind velocity is propitious to increase the gas flowrate in the region near the wall and make the gas-solid phase mix completely, increase thecontact area of gas and particle phase, reduce the gas flow dead zones and reduce the adhesionof viscous materials to cylinder wall. However, the negative pressure formed by theentrainment effect of tangential wind goes against the development of gas flow in the centralregion, reduces the penetration effect of axial wind to the granular layer.Taking the corrosion depth as the evaluation index, the influence law of different factorssuch as pH and moisture content of sludge, corrosion temperate, corrosion time on two kindsof metal used in dryer corrosion behavior is studied by single factor experiment andorthogonal experiment. The primary and secondary order of the factors influence and thesignificance of different factors on metal corrosion depth are given out though the analysis ofpoor and variance. The corrosion product is characterized by SEM and EDX at last. Theresults show that the corrosion depth of A3carbon steel increases with the increase of temperature, moisture content and acidity of sludge. The primary and secondary order of theinfluence of factors on metal corrosion depth is steel type, temperature, pH of sludge, time,and sludge type. The maximum corrosion condition is A3B4C4D2E1, namely corrosiontemperature is100℃, corrosion time is288h, pH of sludge is4.9, sludge type is manicipalsludge, and metal material is A3carbon steel. The corrosion product of A3carbon steel ismainly brown loose substance, while the corrosion product of304stainless steel is mainlylight color porphyritic material. The corrosion extent of carbon steel is deeper that of stainlessand the elements soaked into carbon steel are more than that in stainless steel. Metal corrosionresults from different temperatures and different pH of sludge is non-uniform, while metalcorrosion results from different moisture content of sludge is uniform.Through the results of this research, it provides theoretical analysis methods for the design,optimization of the rotational spouted-fluidized bed dryer.