PROJECT DESCRIPTION
BACKGROUND
Different techniques are developed and used to reduce air pollutants emissions. From an historical point of view, the dust cleaning systems were the first techniques to reduce air emissions; air filtering with electrostatic filters is a technique which is applied for more than thirty years. A widespread and serious environmental problem is the occurrence of sulphur containing gaseous waste streams such as seen in coal and oil fired power plants. For SO2, the most common technique is the lime(stone)-gypsum process, by which the flue gases are washed with a lime(stone) suspension. The technique used for the reduction of NOx emissions is based on the catalytic reduction with injection of ammonia (SCR). This method requires high investment costs and also presents risks related to the use of ammonia.
OBJECTIVES
The objective of the original project was to prove the feasibility and the environmental, technical and cost advantages of a biological flue gas desulphurisation system, called bio-FGD, on a technical scale. It was expected that this new technology would be an alternative to the traditional limestone FGD process which converts sulphur oxides present in the flue gases (SOx) into gypsum. For several reasons, this initial objective was abandoned. At the beginning of 1999, the beneficiary proposed to restructure the project towards biotechnological flue gas denitrification, called BioDeNOx. In the new proposal the system would be combined with standard lime/limestone desulphurisation. It was expected that the proposed combined technology of desulphurization and denitrification could lead to an enormous reduction of investment costs, which would make this technology also applicable for smaller coal based power stations. The main advantages presented by the combined system were: - the BioDeNOx technology is an innovative biological technology that could be implemented in existing desulfurization plants, making use of the existing available equipment and so saving costs; - the BioDeNOx method is based on biological processes and should prove to be less expensive than the traditional selective catalytic reduction (SCR) based methods; - desulphurisation and denitrification are performed in one single treatment unit while the traditional methods require two stages (FGD and SCR).
RESULTS
It has been demonstrated that the simultaneous removal of SO2 and NOx ispossible by utilising and modifying a pilot wet limestone gypsum FGD plant. The basic principle of SO2 removal remains unaffected by the integration of the BioDeNOx process. It has been shown in this project that the NOx solubility can be improved by using a transition metal chelate to bind the NO. Bacteria or biomass are then used to convert this NOx into nitrogen by the consumption of a reducing agent like ethanol. The maximum NOx removal achieved by the project was low (30%) when compared with the results obtained with the SCR method (up to 90%). However, the efficiency is expected to improve significantly in real scale applications due to improved mass transfer efficiency and the decrease of wall effect. Further improvement is also expected from tuning the operational parameters such as optimised droplet size, liquid/gas volume ratio and EDTA concentration. The main advantage of this technology is its low cost. However, until this new technology is validated in real scale, in particular with respect to the operational costs, the benefits remain hypothetical.It has been demonstrated that the simultaneous removal of SO2 and NOx ispossible by utilising and modifying a pilot wet limestone gypsum FGD plant. The basic principle of SO2 removal remains unaffected by the integration of the BioDeNOx process. It has been shown in this project that the NOx solubility can be improved by using a transition metal chelate to bind the NO. Bacteria or biomass are then used to convert this NOx into nitrogen by the consumption of a reducing agent like ethanol. The maximum NOx removal achieved by the project was low (30%) when compared with the results obtained with the SCR method (up to 90%). However, the efficiency is expected to improve significantly in real scale applications due to improved mass transfer efficiency and the decrease of wall effect. Further improvement is also expected from tuning the operational parameters such as optimised droplet size, liquid/gas volume ratio and EDTA concentration. The main advantage of this technology is its low cost. However, until this new technology is validated in real scale, in particular with respect to the operational costs, the benefits remain hypothetical.