1. Field of the Invention
The present invention relates to a method for the removal of mercury from a stream of flue gas obtained from the combustion of at least one coal. The method includes the step of introducing a kaolin- or metakaolin-containing sorbent into the stream of flue gas for removing mercury from the stream of flue gas and contacting the mercury with the kaolin or metakaolin-containing sorbent in the presence of active free silica.
2. Description of the Related Art
Such a method is known from W002/058823 which teaches that mercury can be removed from a gas stream using a metakaolin-comprising sorbent.
It has been found that at some facilities where coal is combusted to generate electricity, the amount of mercury captured using a metakaolin-comprising sorbent is unexpectedly low, requiring larger amounts of sorbent. This use of more sorbent increases the cost of removal of mercury, and not just because of the cost of the sorbent. The cost is also increased because spent sorbent has to be removed from the flue gas, e.g. using an electrostatic filter or a bag filter, and if more spent sorbent is to be removed from the stream of flue gas, both the financial outlay for filters and the cost of operating them is increased. In addition or alternatively, the mercury can be removed from the flue gas at relatively lower temperatures, i.e. after it has cooled down more. This also increases the cost of a facility and the operation thereof, because in this low-temperature case carbon-containing sorbents have to be used. These carbon-containing sorbents generally reduce the sale-potential of the fly-ash and spent sorbent mixture collected from the filters. Moreover, these carbon-containing sorbents are more difficult to handle and may cause fires in downstream equipment.
What is needed in the art is an improved method for the removal of mercury from a stream of flue gas obtained from the combustion of coal.