smoothing and or derivation normalization a selection of the spectral range which is to be observed and the discarding of obviously incorrect measurements operating parameters which leave behind their chemical fingerprint in the flame spectrum can be determined with this method they are for example the distinction as to whether an operation of the gasifier with gas for example pressure maintenance or the gasification operation with input material flame is present through the different fuel the spectra are able to be assigned to the two classes since gas only contains very few metals which emit light the totality of anorganic material which produces slag the slag content is a very important parameter for maintenance the influencing of the spectrum by light emitting absorbing metals represents a quantitative signal and the slag content can be quantitatively derived from the spectra temperature of the carbon flame the shape of the spectrum is influenced by the excitation varying with the temperature spectra can be quantitatively assigned to the temperature stochiometry of the combustion if the stochiometry of the combustion is adhered to precisely the gas yield is optimized thereby the stochiometry massively influences the chemical composition and is thus accessible with this method a spectroscopic method is involved in which the information content lies in the shape of the curve therefore in accordance with one embodiment the measured flame spectrum is normalized in the evaluation unit before being supplied.