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.