摘要
底部区域的研究对于深入理解循环流化床流动特性具有重要的意义。本文对内径400 mm,高度9100 mm提升管底部区域不同轴向截面12个水平方向位置的颗粒浓度进行了系统的测量,采集了不同轴向壁面位置的压力。根据实验结果,确定了底部区域颗粒浓度的轴向和水平方向分布规律,利用统计方法、功率谱和小波系统分析了压力波动和浓度波动。最后,对双上升管循环流化床煤气化制氢进行了技术经济分析。
平均颗粒浓度在轴向上呈现上稀下浓的单调指数分布,增大颗粒循环速率或减小表观气速颗粒浓度均增大,且底部区域增大值大于上部区域。水平方向不同位置颗粒浓度受轴向高度和操作参数的影响与平均浓度相同,且边壁区域受到的影响大于中心区域。颗粒浓度水平方向分布呈现环-核结构。边壁区域颗粒浓度高,变化明显,随r/R的增大,颗粒浓度增大,在边壁处达到最大;中心区域颗粒浓度低,而且变化不大。r/R=0.8可以作为环-核分界点。表观气速不变,增大颗粒循环速率可使颗粒浓度增大;颗粒循环速率不变,增大表观气速则使颗粒浓度减小。随操作参数变化,边壁区域受到的影响大于中心区域。水平方向不均匀指数RNI的变化趋势与颗粒浓度的变化趋势相一致。
压力波动信号分析表明,平均值和标准偏差的轴向分布与颗粒浓度分布一致。分析功率谱发现,存在一个明显的主频。颗粒循环速率增大或表观气速减小,主频减小,振幅则增大。随轴向位置的增高,压力波动的主频基本不变,振幅减小。对压力波动信号进行db2小波的五尺度分解表明,压力波动主要是由低频段引起的。颗粒循环速率减小,4与5尺度差别减小,幅度减小;增大表观气速,低频信号的差别变小;增大轴向高度,幅度减小。
颗粒浓度波动分析表明,正常流化条件下,标准偏差水平方向上随r/R的增大而增大,轴向上与浓度分布一致。分析浓度波动的功率谱发现,主频不明显,0~10Hz范围内振幅较大,且振幅随操作参数和位置的变化规律与平均颗粒浓度变化规律一致。采用db2小波对浓度波动进行六层分解表明,颗粒浓度波动与压力波动的规律一致。
最后,在计算双上升管循环流化床煤气化制氢项目总投资的基础上,计算出财务评价所需要素,编制财务评价主要报表,以动态和静态两种指标对项目进行评价。评价分析证明上述项目具有可行性。
An understanding of flow hydrodynamics in bottom zone is very important for circulation fluidized bed. Particle concentrations at 12 horizontal locations at different axial levels in a riser of 400 mm in diameter and 9100 mm in height were measured, and pressure fluctuations at riser wall of different axial levels were studied. Then the distribution of particle concentration at the horizontal and axial directions in the bottom zone were collected, and pressure fluctuations and concentration fluctuations were systematically analyzed using statistical method, power spectrum and wavelet. In addition, technology and economics analysis of coal gasification to product hydrogen utilizing dual risers circulation fluidized bed was carried out.
Average particle concentration at different axial heights is characterized by monotone exponential function, which is dense in the bottom zone and dilute in the upper zone. Average particle concentration increases with increasing solid circulation rate or decreasing superficial gas velocity. And it increases more sharply in the bottom zone than in the upper zone. Axial height and operating parameters have the same influence on particle concentration at different horizontal locations as well as average concentration, such influence varies more sharply in the wall region than in the centre region. Furthermore, horizontal distribution of concentration is nonuniform with a core-annulus structure, concentration in the centre region is low with slight change, whereas it increases significantly toward the wall, and reaches the highest at the wall. Furthermore, it is found that r/R=0.8 could be the dividing point for the core-annulus structure. At the same superficial gas velocity, particle concentration increases with increasing solid circulation rate, and it increases more sharply in the wall region than in the centre region. By contrast, at a given solid circulation rate, particle concentration decreases with increasing superficial gas velocity, and it decreases more sharply in the wall region than in the centre region. Horizontal Nonuniformity Index has the similar trend with concentration.
By analyzing pressure fluctuations signal, it is found the distributions of average value and standard deviations in the axial direction have the similar trend with concentration distribution. Using power spectrum, it is found there is an obvious principal frequency. Principal frequency decreases and amplitude increases with increasing solid circulation rate or decreasing superficial gas velocity. Pressure amplitude increases with increasing axial height, and principal frequency keeps general constant. Using db2 wavelet to analyze pressure fluctuation with 5 scales, it is found that low frequency band mainly causes fluctuation. Discrepancies among low frequency bands decreases and amplitude decreases with decreasing solid circulation rate. And with increasing superficial gas velocity, discrepancies among low frequency bands decreases. And amplitude decreases withincreasing axial height.
By analyzing concentration fluctuation signal, it is found standard deviations increase with increasing the value of r/R in the horizontal direction. And standard deviations has the similar trend with concentration in the axial direction. There is not an obvious principal frequency, and concentration amplitude has peak value in the frequency range from 0-10Hz, and its variation has the similar trend with concentration. Six scales db2 wavelet analysis of concentration fluctuation indicates that concentration fluctuation has the similar trend with pressure fluctuation.
Finally, gross investment of coal gasification to product hydrogen utilizing dual-riser circulation fluidized bed is evaluated. Then factors of financial evaluation and main statements are carried out. And the project is analyzed through static and dynamical indicators. It is found that this project is feasible.
引文
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