Flue Gas Cleaning

Flue gases from industrial sources like power, waste incineration, glass manufacturer and cement plants as well as ships meet increasingly stricter regulations regarding emission of several pollutants in particular nitrogen and sulfur oxides. These pollutants lead to formation of nitric and sulfuric acid in the atmosphere causing precipitation of acid rain resulting in death of forests and destruction of buildings and monuments in addition to human health problems. The most common state-of-the-art methods applied today industrially for cleaning of flue gases will be addressed, including wet and dry scrubbing for sulfur oxides (SO2) and catalytic removal of nitrogen oxides (NOx). There is however, a desire of increasing the energy produced in electrical power plants by firing CO2-neutral biomass/waste or biomass/waste in combination with fossil fuels. Thus, the EU reached agreement in March 2007 specifying that 20 % and recently in 2014 this was increased to 40 % of the energy should be produced from renewable fuels by 2020 and 2030, respectively to cut emissions of the greenhouse gas CO2. This, however, challenges not only the power plant itself due to enhanced slagging, fouling and corrosion, but also the downstream cleaning of the flue gas for nitrogen oxides (NOx) which is almost exclusively carried out using selective catalytic reduction (SCR) with ammonia (NH3) as reductant. It is now well known that the traditional industrial catalyst used for SCR of NOx by ammonia is severely deactivated by the aggressive flue gas, originating from the high content of potassium salts found in the biomass compared to fossil fuels. Also the formation of large amounts of more or less useful gypsum by the traditional lime scrubbing for sulfur oxides in the flue gas pose an increasingly new waste problem. In Centre for Catalysis and Sustainable Chemistry, DTU Chemistry we are carrying out research dedicated to solve this problem not only by traditional catalytic routes where we from a molecular understanding of the catalyst performance try to improve the composition and catalyst life-time. But the problems may also be attacked by new materials like supported ionic liquid phase (SILP) gas absorbers where the pollutants may be selectively absorbed, desorbed and finally converted to useful mineral acids of commercial grade – really a green waste-to-value approach that we persue instead of the traditional cleaning processes that use chemicals to form new wastes.