PROJECT DESCRIPTION
BACKGROUND
Mercury is a well-known environmental problem. Mercury emissions from chemical, medical, metallurgy, electronic and recycling industries are significant across Europe. Around 340 tonnes of mercury are emitted annually from anthropogenic sources in Europe. The idea to tackle pollution at the production site is one of the cornerstones in the EU environmental policy. There is a substantial need for clean technologies that both prevent emissions as well as recycle the mercury. Throughout the European Union, soil contaminated with mercury exists in large quantities at site remedy projects in the chemical and building industry. Other sources of waste containing mercury are the military use of mercury (spent ammunition), and wastewater cleaning (adsorbents, sludge). Waste containing mercury is traditionally treated by incineration or by underground storage. Although traditional techniques reduce mercury emissions, they often cause problems when the concentration varies. Moreover, by traditional methods large quantities of hazardous waste are produced.
OBJECTIVES
The project addressed the problem of abating mercury in flue gases, by using a technique, named the MercOx process, to abate elemental mercury in flue gases in a more efficient way. The objective was to optimise the MercOx process to minimise further discharge of mercury to the environment. The process uses hydrogen peroxide to oxidise elemental mercury to water soluble, oxidised mercury. In a scrubber, sulphur dioxide and elemental mercury are oxidised by the hydrogen peroxide, forming sulphuric acid and oxidised mercury. The oxidised mercury can be precipitated and collected as mercuric sulphide (the form of mercury that occurs in nature) for safe deposit, or be recycled as elemental mercury.
RESULTS
With the increased knowledge about the process achieved through the project, MercOx could solve the problems with mercury abatement in a wide range of installations all over Europe in the future. The process has proven to be a very suitable or interesting solution mainly for the following types of applications: •Hazardous waste incineration – very suitable, due to large buffer capacity; •Soil and sediment remediation – very suitable, due to its high capacity to oxidise and absorb elemental mercury; •Sludge incineration – MercOx is most probably very suitable. Other methods have problems in cleaning this type of flue gas due to its high distribution of elemental mercury; •Crematories – the MercOx process is especially useful due to its high oxidation potential and large buffer capacity; •Coal fired power plants – MercOx has not been tested yet at coal combustion conditions, but based on other tests it is probable that the process would work. A full scale MercOx scrubber has successfully been implemented at Sydkraft SAKAB, the largest hazardous waste incineration plant in Sweden. The table below shows the efficiency in abatement of mercury in the experiments performed in the project in pilot plants and full scale plants. Plant Type of plant Mercury removal efficiency (%) AGATE-2 Experimental pilot plant 95-99.9 % Sydkraft SAKAB Hazardous waste incineration (full scale) 95-99.99 % Eka Soil Thermal soil remediation (full scale, pilot) 90-99 % TAMARA Municipal waste incineration (pilot plant) 97-98 % The main benefits of the MercOx process are high removal efficiencies, low investment costs and low quantities of residues. The latter has, however, at the moment no effect due to the fact that deposit costs are low and the requirements for depositing residues containing mercury are not harsh enough. Other processes with dry absorption of mercury are therefore more favourable at the moment. But the disposal cost for mercury-contaminated waste will probably increase in the future. Standard techniques have problems to abate elemental mercury in flue gases in such a way that emission limits are fulfilled. Other techniques such as fixed bed activated carbon filters or addition of activated carbon to the flue gases, generate huge volumes of waste that leads to new problems. Through the MercOx process the waste generation is reduced to approximately 25% compared to conventional techniques. If desired, mercury can be recovered as metallic mercury and reused. Several presentations of the MercOx process were made at fairs and conferences. Several articles have also been published in regional and national newspapers and technical magazines.