Gas injection system, furnace provided with such a system and use thereof

A gas injection system comprising:

• a tubular wall having a proximal extremity and a distal extremity,
• the distal extremity, at least one extremity opening through which at least one gas is projected, and
• a cooling system located in said tubular wall and comprising axial channels which, between a proximal terminal and a distal terminal, extend axially towards said distal extremity of the tubular wall and in which a cooling fluid is circulated, connecting channels circumferentially joining the axial channels to each other at the distal terminal, the connecting channels having a rounded shape in the direction of the distal extremity of the tubular wall, passage channels circumferentially joining the axial channels having a rounded shape in an opposite direction to the distal extremity of the tubular wall,
• wherein said tubular wall is monobloc, wherein said axial channels pass axially through the monobloc tubular wall which has, at the distal terminal of the axial channels, a circumferential groove,
• a closing crown closing the circumferential groove of the monobloc tubular wall, wherein said rounded connecting channels are arranged between said circumferential groove and said closing crown.