Flue Gas De-Sulfurization

(FGD) is a technology used to remove sulfur dioxide (SO2) from the exhaust flue gases of fossil fuel power plants. Fossil fuel power plants burn coal or oil to produce steam for steam turbines, which in turn drive electricity generators.

Sulfur dioxide is one of the elements forming acid rain. Tall flue gas stacks disperse emissions by diluting the pollutants in ambient air and transporting them to other regions.

As stringent environmental regulations regarding SO2 emissions have been enacted in many countries, SO2 is now being removed from flue gases by a variety of methods. The below is among the common methods used:

* Wet scrubbing using a slurry of alkaline sorbent, usually limestone or lime, or seawater to scrub gases;
* Spray-dry scrubbing using similar sorbent slurries;
* Wet sulfuric acid process recovering sulfur in the form of commercial quality sulfuric acid;
* SNOX Flue gas desulfurization removes sulfur dioxide, nitrogen oxides and particulates from flue gases;
* Dry sorbent injection systems.

But on this title only describe on wet scrubbing method as limestone for absorb sulfur gas.


This picture beside could you find at boiler air fuel ratio in coal calculation that 1 pound coal need 11.671 pound air for perfect combustion.




At 760 mm Hg pressure (14.7 psia) and 32F, 1 mole of any gas occupies 359 cu ft. The volume per pound at standard condition will, therefore be obtained directly by dividing 359 by the molecular weight of any gas.

Total volume gas production is 327.301 cu ft at temperature 600F consist CO2 50.655 cu ft, NO2 221.489 cu Ft, H20 21.502 cu ft and SO2 0.247 cu ft.

















% Volume of SO2 gas is (0.247/327.301)*100 = 0.075% = 750 ppm
% Volume of CO2 gas is (50.655/327.301)*100 = 15.47 % = 150,000 ppm

When using the unit mg/Nm3, the standard volume (standard cubic meter, Nm3) is used as a reference and the mass concentration of the flue gas is given in milligrams (mg). Since this unit is pressure and temperature dependent, the volume is expressed at standard conditions. There are different sets of standard conditions used for different purposes. Flue gas analysis commonly uses the following standard conditions:

Temperature: 0°C
Pressure: 1013 mbar (hPa)

Conversion to mg/Nm3 from ppm
CO (mg/Nm3) = (21 - O2ref/21 - O2) x CO (ppm) x 1.25
NOx (mg/Nm3) = (21 - O2ref/21 - O2) x (NO + NO2 in ppm) x 2.05
SO2 (mg/Nm3) = (21 - O2ref/21 - O2) x SO2 (ppm) x 2.86

The conversion factors used in the formula come from the density of the gas components at standard conditions (O2ref take 6% and O2dry usually 4.5%).

So we can say total sulfur gas production 0.247 ft3 or 753 PPM or 1924 mg/Nm3.
But now we consider to how much limestone slurry could capture SO2 gas.













































































Summary:

If 1 lb of coal produce 0.247 ft3 SO2 in unity of time (hours), limestone needs (0.247 x 1.56) = 0.385 ft3

If 248 T = 2204 lb/T x 248 T = 546,592 lb of coal will produce(546,592 x 0.247) = 135,008 ft3 SO2

Limestone consumption 135,008 x 1.56 = 210,612 ft3

There are three pumps of Absorber Recirculation Pump, so that 210,612 / 3 = 70,204 ft3 x (7.48 gallon / ft3 ) = 525,127 gallon

Limestone consumption per ARP = 525,127 gallon per hour =8,725 GPM

If Limestone slurry TSS product per ARP is 23%, so (8,725 GPM : 23%) =37,934 GPM

Absorber Recirculation Pumps need 380 RPM and 2.1 Barg.

This calculation will be continued to how to created the gypsum, please visit http://idpowerstation.blogspot.com/2011/12/gypsum-product.html.