Abstract:

The liquid backmixing characteristics were investigated experimentally using pulse tracing technique in an ebullated bed reactor of 7.2 m in height and 0.3 m in diameter. Air and water were used as the gas and liquid phases, respectively. The superficial gas velocity ranged from 0.26 to 12.97 cm·s^-1, while the liquid velocity was fixed at 0.86 cm·s^-1. The particles of aluminum oxide with an average diameter of 0.4 mm were used as the solid phase. All experiments were carried out under the solids holdup from 0 to 42.9%(vol). The results showed that each response curve demonstrated obvious long tail phenomenon, which implied that there existed evident liquid backmixing in the ebullated bed reactor at different operating conditions. A tanks-in-series with backflow model was adopted to interpret the response data, which showed an excellent agreement between the prediction and experimental data. It also indicated that the number of stages N was 8, while the backmixing coefficient k varied between 1.320 and 4.218. Most of the variances of the predicted model were within +18% of their corresponding experimental values.

Key words: ebullated bed reactor, backmixing, solid holdup, residence time distribution, tanks-in-series with backflow model, numerical simulation, experimental validation

摘要：

在直径0.3 m、总高7.2 m的沸腾床反应器内采用脉冲示踪法研究液相的返混特性。实验中分别以空气和水作为气相和液相，气体操作速度从0.26 cm·s^-1变至12.97 cm·s^-1，液体表观速度固定为0.86 cm·s^-1。采用三氧化二铝颗粒作为固相，其中固体颗粒的平均粒径为0.4 mm，床层固体含量（体积分数）从0变至42.9%。实验结果表明，在所有考察条件下每组响应曲线均存在明显的长拖尾现象，沸腾床内存在剧烈的液体返混现象。尝试采用带回流的多釜串联模型拟合实验数据，结果表明模型预测值与实验数据吻合得非常好，其中拟合得到的全混釜个数N为8，回流比k从1.320至4.218不等，方差预测值与实验值之间的最大误差不超过+18%。

关键词: 沸腾床, 返混, 固含率, 停留时间分布, 带回流的多釜串联模型, 数值模拟, 实验验证