Abstract
A semi-cylindrical bubble column of 50cm in diameter equipped with a simultaneous injection nozzle of gas and liquid was used as a cold model for s liquefier of the direct coal liquefaction.The gas holdup and the jet length in the column were affected significantly by the liquid flow. After the temperature of the feed fluids was suddenly changed, thermal image pictures were taken at regular time intervals, and the presence of the stagnant zone in the periphery was revealed.Unsteady-state thermal behavior in the bottom part of a liquefier was simulated on the basis of a heat balance model with lumped parameters such as heat exchange rate, heat capacity of the reactor wall, and heat evolution by the liquefaction reaction. The possibility of heat ac-cumulation in the stagnant zone was elucidated in cases where the heat capacity of the reactor wall was larger than that of the stagnant liquid and where the heat exchange rate between the jet and stagnant zone was small.
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