In situ measurements of O₂ and CO eq.  in cement kilns

Abstract. The simultaneous in situ measurement of O₂ and CO eq.  in cement kilns is a great challenge due to the high process temperatures and high dust load. The standard method for measurement for flue gas in cement kilns is extractive. Extractive measurements have a higher response time due to the flue gas conditioning including the length of heated extraction lines for electrochemical or optical analysis. This delayed response is not optimal for fast process control.

A probe was developed for this purpose in which the in situ solid electrolyte oxygen sensor and an in situ CO eq.  mixed potential sensor are implemented. Due to the high temperatures, the probe is cooled by a water–coolant mixture. In order to prevent deposits of raw material forming and sintering on the probe, it rotates 90° in programmable intervals. In addition, an automated probe plunger pneumatically removes plugging at the probe flue gas entrance, also in programmable intervals. These self-cleaning functions allow the probe to continually stay in the process for combustion optimisation (low excess O₂ and CO) and enable the plant operator to measure additional process-related gas components (NO, SO₂, HCl etc.) and optimise the SNCR (selective non-catalytic reduction) for NO_x reduction. Combustion air supply can be adapted very quickly due to the in situ sensors, which has been demonstrated by a CEMTEC® probe over years (Märker Cement Harburg, 2017).