The present invention relates to a method for gas-
solid contacting in a
bubbling fluidized bed reactor by: (a) introducing into a reactor with
bed length to
bed diameter ratio below about 5.0, a primary gas consisting essentially of reactant(s) of the reaction to be carried out in the
bed of
solid particles through a primary gas
distributor located at the reactor bottom at a superficial gas velocity Up, which is very close or equivalent to the minimum
fluidization velocity Umf, required for achieving the incipient
fluidization of the
solid particles in the bed to obtain an
emulsion phase consisting essentially of the solid particles and the primary gas with little or
no formation of gas bubbles to achieve incipient
fluidization or liquid-like behavior of fluidizable solid particles; (b)
forming gas bubbles in the incipiently
fluidized bed by introducing through a secondary gas
distributor located immediately above the primary gas
distributor a secondary gas, selected from one of the reactants which is used in excess of that required for the reaction
stoichiometry, steam, an
inert or a mixture of two or more thereof at a superficial gas velocity, Us, which is related to the superficial velocity of the primary gas such that a ratio of the superficial velocity of the secondary gas to the superficial velocity of the primary gas Us / Up, is in the range from about 0.5 to about 10.0, preferably from about 1 to about 5.