Reduction of mercury concentration from flue gases
We are engaged in studies and consultancy focusing on technologies for reducing and removing mercury concentrations from flue gases generated during the combustion of brown coal in power plants and heating plants. We process studies for small local sources up to large industrial units in the range of flue gas flows from 10,000 – 3,000,000 m3/h.
The study is prepared by our engineering division, see the contact.
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Dosing of activated carbon into flue gases
In practice, the most common method is to reduce the mercury content by dosing powdered activated carbon into the flue gas. Thanks to its large specific surface area, activated carbon is able to bind mercury to the surface on the basis of the absorption principle. Dosing coal into the system is a complex process, as it depends on the very thorough distribution of activated carbon in the flue gas stream. Most often, activated carbon is injected into the system at a point before the flue gas enters the air heater, namely the flue gas temperature range 140 – 180 ° C. The activated carbon is then carried by the flue gas stream to the subsequently installed hose filter, where the mercury bound to the surface of the activated carbon on the filter fabric is separated. The separated coal is then taken together with the separated ash from the hose filter hoppers to the storage system by an installed pneumatic transport or a part of the separated material is led back to the entrance to the fabric filter for reuse.
The system using activated carbon dosing in combination with the installation of a fabric filter can separate up to 99% of the mercury contained in the flue gas. In addition to the oxidic forms of mercury, the elemental form of mercury can be trapped to a certain extent on the surface of activated carbon. In order to increase the capture efficiency of the elemental form of mercury, halogen-based compounds (eg bromides) can be added to the activated carbon additive due to the oxidation to the divalent form of mercury described above. The amount of activated carbon fed into the process must be optimized based on the actual operating parameters of the boiler and the connected system. Because when burning brown coal with high ash content, a higher concentration of fly ash can be expected in the flue gas. The ash produced by burning coal has similar properties as injected activated carbon, ie a large specific surface area. With a sufficient amount in the flue gas, the fly ash is able to bind mercury to the surface. This process can save on the consumption of expensive activated carbon.
Modifications of desulphurisation absorbers
This method is based on a suitable modification and modification of droplet separators of existing absorbers of wet desulphurisation technologies installed at coal-fired power plants.