Process for producing cement clinker, comprising the steps of a) preheating of the starting material to the calcination temperature, b) calcination of the preheated starting material, c) firing of the calcined starting material in a rotary furnace, d) cooling of the cement clinker, e) introduction of an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen into i) the calciner, wherein - no gases from the rotary furnace are fed to the calcination, - cyclone preheaters (7, 8, 9) of which the individual cyclones are connected to one another in a cascade-like manner are used for preheating, where at least one first preheater and one second preheater are used, - mass transfer and/or gas transfer is/are possible between the individual cyclone preheaters (7, 8, 9), with mass transfer and/or gas transfer being possible between the first preheater section and the second preheater section, and - no recirculation of the preheater exhaust gases occurs, characterized in that the ratio of solid fed in to exhaust gas in step a) is set to greater than 1.3 kg to 1.9 kg of solid per 1 kg of gas, where crossing over of meal streams but no crossing of the gas streams occurs after each stage between the preheaters of a multitrain cyclone preheater (7, 8, 9). a) preheating of the starting material to the calcination temperature, b) calcination of the preheated starting material, c) firing of the calcined starting material in a rotary furnace, d) cooling of the cement clinker, e) introduction of an oxygen-containing gas having a proportion of 15% by volume or less of nitrogen and a proportion of 50% by volume or more of oxygen into i) the calciner, wherein - no gases from the rotary furnace are fed to the calcination, - cyclone preheaters (7, 8, 9) of which the individual cyclones are connected to one another in a cascade-like manner are used for preheating, where at least one first preheater and one second preheater are used, - mass transfer and/or gas transfer is/are possible between the individual cyclone preheaters (7, 8, 9), with mass transfer and/or gas transfer being possible between the first preheater section and the second preheater section, and - no recirculation of the preheater exhaust gases occurs, i) the calciner, wherein - no gases from the rotary furnace are fed to the calcination, - cyclone preheaters (7, 8, 9) of which the individual cyclones are connected to one another in a cascade-like manner are used for preheating, where at least one first preheater and one second preheater are used, - mass transfer and/or gas transfer is/are possible between the individual cyclone preheaters (7, 8, 9), with mass transfer and/or gas transfer being possible between the first preheater section and the second preheater section, and - no recirculation of the preheater exhaust gases occurs, - no gases from the rotary furnace are fed to the calcination, - cyclone preheaters (7, 8, 9) of which the individual cyclones are connected to one another in a cascade-like manner are used for preheating, where at least one first preheater and one second preheater are used, - mass transfer and/or gas transfer is/are possible between the individual cyclone preheaters (7, 8, 9), with mass transfer and/or gas transfer being possible between the first preheater section and the second preheater section, and - no recirculation of the preheater exhaust gases occurs,