油渣经喷嘴在加压固定床熔渣气化炉喷射效果数值模拟

Numerical simulation of oil residue spray effect by nozzlein pressurized fixed bed slag gasifier

为了探索油渣在固定床熔渣气化炉气化的可行性,利用固定床熔渣气化炉将油渣与煤共气化,生产清洁合成气或燃气,拓宽油渣的高效利用途径,研究油渣在加压固定床熔渣气化炉内经喷嘴喷射后的分散效果,以神华煤直接液化残渣为研究对象,利用数值模拟软件Ansys Fluent,采用Realizableκ-ε湍流模型模拟湍流流动,采用欧拉-欧拉法中的VOF模型模拟气液两相流动,研究了加压下油渣温度、油渣喷射速度、空气喷射速度对油渣在工业级加压固定床熔渣气化炉内喷射效果的影响,喷嘴结构采用双通道结构,喷嘴中心通道输送油渣,环隙通道输送气化剂(用空气代替),通过分析比较确定了最优的喷射方案。结果表明,加压条件下油渣黏度随温度上升总体呈下降趋势;210~240℃,随温度升高,油渣黏度急剧下降;240~400℃,随温度升高,油渣黏度仍下降,但降幅逐渐减弱;温度超过400℃后,随温度升高,油渣黏度逐渐上升,这可能是油渣发生缩聚反应导致。喷射温度对油渣在气化炉内的喷射效果起决定性作用,油渣温度越低,油渣喷射后的扩散效果越好,但油渣喷射温度过低时,大量油渣因为黏度较大导致喷射较短距离即开始受重力影响向下流动,甚至出现沿壁面流入渣池中的现象,存在一个较优化的喷射温度区间,油渣雾化效果的选择应综合考虑扩散和贴壁的现象。油渣在加压下喷射,通过气化炉压力和动力黏度两方面影响油渣在气化炉内的喷射效果,提高喷射压力,如需达到同样的喷射效果,需要提高油渣的喷射温度,以降低油渣动力黏度;油渣喷射速度2.5~10.0 m/s时,对油渣在气化炉内的雾化效果影响不大,空气喷射速度5~20 m/s时,空气喷射速度越高,油渣在气化炉内的雾化效果越好。综合考虑,4.5 MPa下,油渣喷射温度230~260℃,油渣喷射速度5 m/s左右,空气喷射速度10 m/s左右是比较合适的喷射方案,油渣喷射综合效果更好。

In order to explore the feasibility of oil residue gasification in fixed bed slag gasifier,gasifying oil residue and coal together in the fixed bed slag gasifier can produce clean syngas or gas,so as to broaden the efficient utilization way of oil residue.In this paper,the dispersion effect of oil residue after being sprayed by the nozzle in a fixed pressure bed slag gasifier was studied.Taking Shenhua Coal Direct Liquefaction residue as the research object,the impact of oil residue temperature,oil residue spray velocity and air spray velocity on the spray effect of oil residue under pressure in the industrial-grade pressurized fixed bed slag gasifier was studied by using the numerical simulation software Ansys Fluent.Realizableκ-εturbulence model was adopted to simulate turbulence flow,and the gas-liquid two-phase flow was simulated by VOF model of Euler-Euler method.The nozzle structure was double-channel.The center channel of the nozzle was used for conveying oil residue,and the annular gap channel was used for conveying gasification agent(replace with air).The optimal spray scheme was determined by analysis and comparison.The following conclusions are drawn:The viscosity of oil residue decreases with the increase of temperature under pressure condition,the viscosity of oil residue drops sharply with the increase of temperature from 210℃ to 240℃;the viscosity of oil residue decreases with the increase of temperature from 240℃ to 400℃,but the decrease gradually weakens.When the temperature exceeds 400℃,the viscosity of oil residue gradually increases with the increase of temperature,which may be caused by polycondensation reaction of oil residue.The spray temperature plays a decisive role in the spray effect of oil residue in the gasifier.The lower the oil residue temperature is,the better the diffusion effect will be after the oil residue spray.However,when the oil residue spray temperature is too low,a large amount of oil residue will begin to flow downward under the influence of gravity,which leads to the relatively short distance of spray due to the great viscosity,and even flow into the slag pool along the wall.There is a relatively optimized spray temperature range.the phenomena of diffusion and adherence should be considered in the selection of the atomization effect of oil residue.The spray effect of oil residue in gasifier under pressure is influenced by pressure and dynamic viscosity.To increase the spray pressure and achieve the same spray effect,it is necessary to increase the spray temperature of the oil residue to reduce the dynamic viscosity of the oil residue.When the spray velocity of oil residue is in the range of 2.5-10.0 m/s,it has little effect on the atomization effect of oil residue in gasifier.In the range of 5-20 m/s,the higher the spray velocity of air is,the better the atomization effect of oil residue in the gasifier is.Considering comprehensively,under 4.5 MPa,the spray temperature of oil residue is 230-260℃,the spray velocity of oil residue is about 5 m/s,and the spray velocity of air is about 10 m/s,which is a more suitable spray scheme and the spray comprehensive effect of oil residue is better.