An Investigation On Gas-solid Hydrodynamics In The Bottom Zone Of A Plant Circulation Fluidized Bed

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.