A vertical ring shaft kiln comprising • a vertical burning region having an intermediate sintering zone (Z 3) defined by a first wall and an opposite second wall, • a gap between the first wall and the second wall having a length in a predetermined distance wherein the first wall and second wall are formed in a ring shape one inside the other, • a support wall connects the bottom part of the first wall and an opposite bottom part of the second wall with an outlet, • a number of burners having outer nozzles provided at the first wall and having inner nozzles provided the second wall to develop a flame in adjustable manner throughout the length by injecting fuel and oxygen/air inside the sintering zone, characterized by further comprising • outer and inner auxiliary nozzles (63, 65) provided at a distance from the corresponding inner and outer nozzles (62, 64) to inject oxygen/air inside the sintering zone, • a number of heat sensors disposed at the outer side of the first wall providing actual heat change information at the first wall, • a detection unit producing a thermal map of the sintering zone (Z 3) to find over burned or unburned spots comparing a detected heat value (t d) with the homogenous heat pattern previously set by a threshold heat value (t t), • a control unit in connection with the detection unit, which providing a homogenous heating pattern at the unburned or over burned spots by changing the vertical flow speed (v f) or by activating the neighboring corresponding burner or auxiliary nozzle, • a roller crusher provided at the outlet of the vertical burning region and fed by the sintered material thus determining the vertical flow speed (vf). • a vertical burning region having an intermediate sintering zone (Z 3) defined by a first wall and an opposite second wall, • a gap between the first wall and the second wall having a length in a predetermined distance wherein the first wall and second wall are formed in a ring shape one inside the other, • a support wall connects the bottom part of the first wall and an opposite bottom part of the second wall with an outlet, • a number of burners having outer nozzles provided at the first wall and having inner nozzles provided the second wall to develop a flame in adjustable manner throughout the length by injecting fuel and oxygen/air inside the sintering zone, • outer and inner auxiliary nozzles (63, 65) provided at a distance from the corresponding inner and outer nozzles (62, 64) to inject oxygen/air inside the sintering zone, • a number of heat sensors disposed at the outer side of the first wall providing actual heat change information at the first wall, • a detection unit producing a thermal map of the sintering zone (Z 3) to find over burned or unburned spots comparing a detected heat value (t d) with the homogenous heat pattern previously set by a threshold heat value (t t), • a control unit in connection with the detection unit, which providing a homogenous heating pattern at the unburned or over burned spots by changing the vertical flow speed (v f) or by activating the neighboring corresponding burner or auxiliary nozzle, • a roller crusher provided at the outlet of the vertical burning region and fed by the sintered material thus determining the vertical flow speed (vf).