NOVELTY - The process comprises cooling synthesis gas in a series of heat exchangers (13), cooling fumes in another series of heat exchangers for generating steam from water, sending the steam mixed with hydrocarbon feedstock (1) in the steam reforming reactor, controlling a flow rate of steam to adjust a ratio of the steam on the hydrocarbon feed to a value of 1.5-2, compressing a purge gas to form a combustion gas that is fed to a combustion chamber, and introducing the synthesis gas into a unit of sieve separation for producing hydrogen having a purity of greater than 99.9 wt.%.    USE - The process is useful for producing hydrogen by steam reforming of a petroleum fraction using a combustion chamber producing hot fumes from an air stream and fuel gas.    ADVANTAGE - The process is capable of energy-efficiently, simply and economically producing the hydrogen with high purity and without any undesirable emission such as carbon dioxide.    DETAILED DESCRIPTION - The process comprises cooling synthesis gas in a series of heat exchangers (13), cooling fumes in another series of heat exchangers for generating steam from water, sending the steam mixed with hydrocarbon feedstock (1) in the steam reforming reactor, controlling a flow rate of steam to adjust a ratio of the steam on the hydrocarbon feed to a value of 1.5-2, compressing a purge gas to form a combustion gas that is fed to a combustion chamber, and introducing the synthesis gas into a unit of sieve separation for producing hydrogen having a purity of greater than 99.9 wt.%. The hot fumes are brought into pressure by a compressor (32), where a heat from the hot fumes is supplied to an exchange reactor within which steam reforming reactions of hydrocarbon feed is carried out by mixing with the steam and reaction effluent. The generated steam is supplied to a steam turbine associated with the compressor. An air flow feeding the compressor is controlled through a valve (36) placed on a circuit of a downstream of the exchangers so that an operating pressure of the compressor fits between 3-5 bars absolute to stay on a characteristic curve of the compressor. The steam-reforming reactor feed is a petroleum fraction having 1-5C.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a process for producing hydrogen.    Hydrocarbon feedstock (1)    Conduit (10)    Heat exchanger (13)    Compressor (32)    Valve. (36)