Release of pollutant components in CLC of lignite

Abstract

The recently developed Chemical Looping Combustion technology (CLC) is nowadays considered an interesting option to capture CO2 at low cost in fossil fuelled power plants. In the past years, significant advances have been achieved in the combustion of both gaseous and solid fuels. Nevertheless, pollutant gas emissions from CLC systems have received little attention. This paper focuses on sulphur, nitrogen and mercury emissions during lignite combustion in a 500Wth CLC unit. Ilmenite was used as oxygen carrier, as it is one of the most common materials used for CLC of solid fuels. The main sulphur species detected in the fuel reactor were H2S and SO2. The amount and proportion depended on the temperature of the fuel reactor. The higher the temperature, the more H2S converted to SO2. In the air reactor, the sulphur in the unconverted char was released as SO2. Regarding the emission of nitrogen in coal, most of the nitrogen was found as N2 at the outlet of the fuel reactor. No NH3 or HCN were registered and only small amounts of NO were detected. The nitrogen contained in the char reaching the air reactor was released as NO. Mercury speciation was also analyzed and the ratio Hg2+/Hg0 determined. In the fuel reactor, the major mercury species was Hg0 and in the air reactor Hg2+. The incorporation of a carbon separation unit between fuel and air reactors would help to reduce the sulphur emissions in the air reactor and comply with the current legislation for power generation systems.