Promoting biofuels for power generation
Biofuel is a renewable source of energy derived from biomass used either as the only fuel in dedicated plants or as a secondary fuel in coal combustion. Unlike other fuels coming from natural sources, such as petroleum, its burning does not result in an increase of atmospheric carbon dioxide content. However, its use has the disadvantage of accelerating the deactivation of specialised catalysts in the flue gas cleaning system of power plants. The Selective Catalytic Reduction (SCR) of nitrogen oxides (NOx) is a widely accepted, highly effective and technologically proven method for high percentage removal of NOx from flue gases. Deactivation of SCR-DeNOx-catalysts not only leads to higher emissions of NOx and trace elements, but it also involves extremely high follow-up costs. Urged by this, the CATDEACT project investigated the key processes in SCR-DeNOx-catalysts during (co-)combustion of biomass and biowaste fuels. Part of the project work involved deactivation tests with gaseous alkali compounds in the flue gas for understanding the deactivation behaviour of different alkali compounds. Alkali metals have been already considered as one of the strongest poisons to SCR catalysts by increasing the deactivation rate. The tests run showed that potassium, normally found in straw-fired power plants in the form of chlorides and sulphates, is very harmful and can lead to even higher deactivation. The studies also showed that high concentrations of potassium, phosphorous, sodium and calcium can contribute to the faster deactivation of the catalyst during co-combustion. Additionally, alkaline earth metals reacting on the catalyst could result in catalyst surface masking, inhibiting diffusion of reactants into the interior surface of the catalyst. Understanding of the deactivation mechanisms of the different elements is expected to lead to the development of suitable countermeasures. These may be either of primary nature, such as fuel additives or modified catalyst compositions, or secondary measures, such as catalyst regeneration.
