The invention relates to an injector (21) for adding a solid granular material into a mixing chamber, comprising a central tube (3) for adding the solid granular material; an adding device (5) that surrounds the central tube (3) for adding a propellant gas, said central tube (3) and adding device (5) that surrounds the central tube (3) forming an annular gap (9) at the end of the central tube (3); a mixing section (11) with a constant cross-section, said mixing section adjoining the annular gap (9); and a tube portion (31) which comprises a discharge opening and which adjoins the mixing section (11). The cross-section of the tube portion (31) with the discharge opening changes from a circular inlet cross-section into a noncircular discharge cross-section of the discharge opening, and the tube portion can be rotated about a central axis.