Unburned carbon from lignite fly ash as an adsorbent for SO2 removal

The aim of this work is to investigate the possibility of application of unburned carbon from lignite fly ash for the purpose of SO2 adsorption from flue gases. The subject of research are three fraction of unburned carbon, which were formed during the nominal operation of Bełchatów Power Station (PGE GiEK) in Poland. In order to characterize the adsorption properties of the investigated materials, a comprehensive research procedure was carried out, including: proximate and ultimate analysis, determination of calorific value, textural characterization (C6H6 and CO2 physisorption, SEM (scanning electron microscope)), surface chemistry characterization (XRD (X-ray diffraction), ICP-OES (inductively coupled plasma-optical emission spectrometry), TPD (temperature-programmed desorption), PZC (point of zero charge)), determination of ignition temperature (DSC (differential scanning calorimetry)) and SO2 adsorption tests using fixed-bed of an adsorbent. Conducted analyses shows, that high carbonaceous wastes, being a result of rapid and intense oxidation of lignite in an industrial boiler, exhibit high potential for adsorption and are characterized by the competitive properties relative to carbon materials, obtained in the laboratory conditions and presented in the literature. It has also been shown, that the chemical nature of adsorbent surface has a significant impact on the effectiveness of SO2 adsorption and on the adsorbate selectivity. Own research demonstrates, that an increase of sulphur dioxide adsorption is observed with an increase of the oxygen surface groups content, i.e. carboxylic acids and lactones, which formation is favoured in conditions prevailing in the industrial boiler. Own research, dedicated to determination of ignition temperature of unburned carbons, confirmed the validity of application of DSC analysis for this purpose. The research results, presented in this work show, that unburned carbons from lignite fly ash, in particularly UN-B and UN-C, have competitive surface structure properties relative to commercially available activated carbons: AKP-5 and AKP-5/A, and can be successfully used as adsorbents for flue gases desulphurization.