sox and nox in cfbc boiler
Post on 08-Apr-2015
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Virendra Patil
patvirendra@gmail.com
SOx and Nox in CFBC Boiler :
The CFB boiler is able to remove sulfur dioxide directly in the furnace. This is
accomplished by contact between sulfur oxide and the calcium oxide contained in the coal
ashes or in the added limestone. The limestone calcines in the furnace to form calcium oxide
(CaO) and then reacts with the SO2 to form calcium sulfate, as follows :
CaCO3 � CaO + CO2
CaO + SO2 + ½ O2 � CaSO4
This reaction takes place preferably at 850-900°C, which is the controlled furnace
temperature over a wide range of operating loads.
Further, the staging of the combustion and the relatively low combustion temperature
reduce NOx formation to a large extent.
So, CFB process offers :
� an intense internal mixing of the particles (fuel, limestone, hot ashes constituting
the bed)
� a homogeneous temperature in the bed
� a long residence time of the fuel in the furnace
� the possibility to keep the temperature within the optimum range of SO2 capture by
the limestone
Bed Temperature vs Sulfur Capture
Virendra Patil
patvirendra@gmail.com
The combination of these characteristics offers the following advantages in terms of
performance :
� high carbon burnout
� high desulphurization efficiency
� low NOx emission
high flexibility of operation.
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