Reduction of harmful emissions in cement manufacture involves mixing preheated powder with highly heated powder to bind sulfur oxide and remove carbon monoxide before calcination

摘要

Reducing emission of volatile contaminants (A) in heat exchanger waste gas during heating of raw cement powder (B) comprises (a) discharging (A) at 300-400 deg C from upper preheater stage(s) and mixing with enough highly heated raw powder (C) to liberate (A), so that sulfur (di)oxide is bound by calcium oxide in (C) as calcium sulfate etc. and carbon monoxide is removed in carrier gas; and (b) preheating and (partial) calcination at higher temperature. The process concerns the reduction of emissions of volatile contaminants (A), especially sulfur oxides, sulfur compounds, combustible organic substances etc. in waste gases from a heat exchanger during heating of raw cement powder (B), when (B) is preheated and (partly) calcined in stages in a multistage fluidized gas preheated with hot waste gas from a calciner before transfer to the calciner, where it is calcined, and the preheated (B) is (partly) brought to a temperature at which (A) are liberated. In stage (a), (part of) (B) (partly) preheated to about 300-400 deg C is discharged from upper preheater stage(s) and mixed in a mixing zone with enough highly heated raw powder (C) to bring the mixture to the temperature at which (A) are liberated, so that volatile sulfur oxides, especially sulfur dioxide (SO2) are bound by the calcium oxide (CaO) in (C) as calcium sulfate (CaSO4) and/or similar gypsum compounds, whilst the carbon monoxide (CO) formed is removed with a carrier gas. In stage (b), the powder mixture is discharged from the mixing zone and subjected to further heating and (partial) calcination in a preheating stage at a temperature higher than that in the upper preheating stage.