Process for producing synthesis gas by steam reforming in a reactor-exchanger

A process for producing a synthesis gas SG from a general feed F constituted by hydrocarbons and optionally recycled compounds, F comprising a first feed Fl, a second feed F2 and a third feed F3, in which:

• a stream comprising the first feed Fl supplemented with steam undergoes steam reforming to produce at least one fraction of synthesis gas SG in a multi-tube reactor-exchanger R comprising a plurality of reaction tubes (38) containing a steam reforming catalyst, and a shell containing said tubes, the first feed Fl supplemented with steam circulating inside a plurality of tubes in one direction;
• said reaction tubes (38) are heated principally by convection by circulating a heating fluid HF external to and in direct contact with said tubes in said shell, as a cross-current but overall as a counter-current to said one direction of the circulation of Fl, in which HF comprises at least a first stream of gas from partial or total combustion of the second feed F2, then said fluid HF is mixed in one to four staged complementary combustion zones, separated by baffles extending across the tubes, to form a mixture inside the shell with at least a portion of the third feed F3 and a gas containing oxygen to increase the temperature of said first stream, with the provision that at least a portion of F3 and said gas containing oxygen are injected at a point inside the shell of the reactor-exchanger R under turbulent conditions and/or recirculation conditions sufficient to obtain homogeneous flameless combustion in at least one zone of the shell of the reactor-exchanger R, and with the further provisions that F3 is hydrogen separated from a fraction of said synthesis gas SG, then said mixture is circulated in the reactor-exchanger R substantially throughout the shell guided by said baffles in alternating opposite directions across the tubes to provide complementary heat to the reaction tubes (38) before leaving the reactor-exchanger;
• and
• synthesis gas SG is produced from the steam reforming effluent F1 and optionally from part or all of the HF.