Controlling gas to slurry volume ratio to achieve a gas holdup of about 0.4 when heating a flowing coal oil slurry and a hydrogen containing gas stream allows operation with virtually any coal to solvent ratio and permits {TAIL ~ operation} with {HEAD ~ efficient heat transfer} and satisfactory pressure drops 
Controlling gas to slurry volume ratio to achieve a gas holdup of about 0.4 when heating a flowing coal oil slurry and a hydrogen containing gas stream allows operation with virtually any coal to solvent ratio and permits { TAIL ~ operation } with { HEAD ~ efficient heat transfer } and satisfactory pressure drops
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