Experimental investigations of flow dynamics in the riser of supercritical water circulating fluidized bed

There are few experimental reports about supercritical water circulating fluidized beds (SCWCFBs) as far as we know. Experiments were conducted to investigate flow dynamics in the riser of a SCWCFB. The average, standard deviation, and power spectral density of pressure signals were analysed. The main frequencies of pressure drops were mainly below 1 Hz. The axial void fractions were obtained, and they were low at the bottom and high at the top of the riser in the SCWCFB. Several types of axial void fraction distributions of conventional gas-solid circulating fluidized beds were also observed in this SCWCFB. The transition velocity between fast fluidization and pneumatic conveying (U_pt), was obtained according to the axial void fractions. U_pt increased with increasing return flow velocities, and decreased with increasing pressures. An empirical correlation of U_pt for SCWCFBs was proposed, Re_pt = 0.182 × Ar^0.6161 × (U_ret/U_mf)^−0.00916+78.8, and its error range was in ±20%.