The present invention relates to a process and a system for generating energy from biomass/organic wastes. A process for generating a product gas from biomass comprises of pyrolyzing the biomass in a pyrolyzer by contacting the biomass with hot heat carriers to obtain pyrolysis gas and char; passing the pyrolysis gas to a reformer containing a reactant to obtain a product gas; and firing a part of the product gas coming out of the reformer back to the heater tubes of the reformer. Firing a part of the product gas through the fired heater tubes of the reformer provides the heat for sustaining the reaction between the pyrolysis gas and the reactant to form the product gas.