Illinois No. 6 bituminous coal with small concentrations of coal-derived solvent was subjected to hydroliquefaction in batch reactors to which substantial amounts of water were sometimes added. The reactions were catalyzed by 0.1% molybdenum on mf coal, added as a water-soluble salt. It was shown previously that a substantial water partial pressure, at fixed hydrogen partial pressure, increases coal conversion in uncatalyzed systems. The present work investigated the effect of added water in catalyzed systems. Considerations of process economics led to the performance of series of reactions at constant total pressure while the partial pressures of water and hydrogen were varied. For catalyzed systems containing solvent, at fixed total pressure, highest conversions are obtained without added water. Conversion to THF solubles is independent of the solvent-to-coal (S/C) ratio to very low values, S/C ^0.25, due to the catalyst. At 427 °C and 1500 psig hydrogen partial pressure, THF and benzene conversions exceeding 90% and 85%, respectively, were achieved. It is concluded that reaction systems with catalyst deposited from solution on the coal particles are highly reactive. Added water is preferentially excluded from the reactor, but water retains a role as a solvent for the catalyst and potentially as a transport medium for coal feed in continuous processing.
A generalized methodology for estimating minimum fluidization velocity at elevated pressure and temperature was developed on the basis of a general correlation for pressure drop through fixed beds of spherical particles proposed by Barnea and Mizrahi (1973) and extended by Barnea and Mednick (1975
SCOPEThe minimum fluidization velocity is a fundamental characteristic of a fluidized bed. Its accurate prediction is important for successful design and operation of a fluidized bed. There are numerous studies and proposed correlations on the prediction of the minimum fluidization velocity at ambient conditions (Babu et al., 1978;Grewal and Saxena, 1980). Their extrapolation to elevated pressure and temperature is uncertain, however. The general approach is to estimate the effect of pressure and temperature by employing Ergun's (1952) equation or its variations, such as that suggested by Wen and Yu (1966). Since the correct shape factor of the particles and the voidage to be used in the Ergun equation are generally not available, the effect of shape factor and voidage are thus lumped into two separate constants. So far no less than five sets of constants have been proposed in the literature with various degrees of success. The accuracy is uncertain for particles with characteristics outside the range of the data correlated by different authors. Undoubtedly, more sets of constants will be proposed later in the literature to take care of this difficulty. A more fundamental approach, extending the general correlation for pressure drop through fixed beds of spherical particles developed by Barnea and Mizrahi (1973), is described here.
CONCLUSIONS AND SIGNIFICANCEA generalized methodology, extending the general correlation for pressure drop through fixed beds of spherical particles by Barnea and Mizrahi (1973), has been developed for prediction of minimum fluidization velocity at elevated pressure and temperature. The methodology successfully correlated the experimental minimum fluidization velocities obtained at the Pittsburgh Energy Technology Center (PETC) and in the literature using coal, char, ballotini, catalyst, and sand of sizes ranging from 88 to 3,376 p m as the bed material and at pressures up to 6,300 kPa and temperatures up to 1,123 K. The proposed methodology can also be ap- plied to bed materials of relatively wide size distribution as long as the harmonic mean particle size is used. To apply the methodology, the minimum fluidization velocity of the system under study needs to be determined experimentally at ambient conditions. This usually is not a severe limitation for most applications.The approach is believed to be fundamental and is generally applicable in all systems except those systems with particles substantially deviate from the spherical shape such as the graphite particles with a sphericity of 0.65. The methodology also cannot be applied to Geldart's class A powders (Geldart, 1973) where the voidage at minimum fluidization changes substantially with pressure. The methodology allows accurate predi...
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