Combustion chamber of an industrial boiler which can be heated with a combustion device, having a static flow mixing device, comprising at least one static mixer element and at least one standing plate to which the at least one static mixer element can be connected, the static mixer element comprising a base body with a material thickness, which is formed from a heat-resistant material and which has a through-channel, wherein - the through channel runs in its longitudinal axis direction from a front side of the base body, the so-called inflow side, through the base body to a rear side of the base body opposite the inflow side, the so-called outflow side, wherein the through-channel is positioned with its inlet opening essentially centrally on the inflow side of the static mixer element and wherein the at least one standing plate has one or more recesses for positively receiving a respective base section of a static mixer element, wherein the flow mixing device is positioned in the combustion chamber in such a way that the at least one static mixer element is set up with its inflow side essentially transverse to an inflow direction of a gaseous flow medium, wherein the longitudinal axis direction of the at least one through-channel and/or the longitudinal axis direction of the at least one adjusting ring is or are arranged parallel to the longitudinal axis direction of the combustion chamber, preferably coaxially with the longitudinal axis direction of the combustion chamber, characterised in that - a plurality of spaced-apart flow guide elements are arranged on the inflow side of the static mixer element, which flow guide elements are each in the form of flat guide vanes projecting from the inflow side, and which each extend distally from an edge portion of the inlet opening of the through-channel to the outer edge of the inflow side, wherein - a swirl surface which is recessed in comparison with the flow guide elements is arranged in each case between two flow guide elements, which swirl surface is inclined (a) obliquely downwards towards the outer edge of the inflow side, the flow guide elements being raised by a guide vane height (36, 37, 39, 40) in comparison with an adjacent swirl surface. - the through channel runs in its longitudinal axis direction from a front side of the base body, the so-called inflow side, through the base body to a rear side of the base body opposite the inflow side, the so-called outflow side, wherein the through-channel is positioned with its inlet opening essentially centrally on the inflow side of the static mixer element and wherein the at least one standing plate has one or more recesses for positively receiving a respective base section of a static mixer element, wherein the flow mixing device is positioned in the combustion chamber in such a way that the at least one static mixer element is set up with its inflow side essentially transverse to an inflow direction of a gaseous flow medium, wherein the longitudinal axis direction of the at least one through-channel and/or the longitudinal axis direction of the at least one adjusting ring is or are arranged parallel to the longitudinal axis direction of the combustion chamber, preferably coaxially with the longitudinal axis direction of the combustion chamber, characterised in that the at least one standing plate has one or more recesses for positively receiving a respective base section of a static mixer element, wherein the flow mixing device is positioned in the combustion chamber in such a way that the at least one static mixer element is set up with its inflow side essentially transverse to an inflow direction of a gaseous flow medium, wherein the longitudinal axis direction of the at least one through-channel and/or the longitudinal axis direction of the at least one adjusting ring is or are arranged parallel to the longitudinal axis direction of the combustion chamber, preferably coaxially with the longitudinal axis direction of the combustion chamber, characterised in that - a plurality of spaced-apart flow guide elements are arranged on the inflow side of the static mixer element, which flow guide elements are each in the form of flat guide vanes projecting from the inflow side, and which each extend distally from an edge portion of the inlet opening of the through-channel to the outer edge of the inflow side, wherein - a swirl surface which is recessed in comparison with the flow guide elements is arranged in each case between two flow guide elements, which swirl surface is inclined (a) obliquely downwards towards the outer edge of the inflow side, the flow guide elements being raised by a guide vane height (36, 37, 39, 40) in comparison with an adjacent swirl surface.