Flue Gas Desulfurization Calculating Gypsum Produced from Coal Bunkered

Stoichiometric Calculation of Gypsum from Coal Bunkered

This is a sample calculation that shows how to calculate the gypsum produced from a scrubber using the amount of coal consumed and stoichiometry.

Firstly, data is required.  The following shows sample data which should be known. See table 1.

• Coal Bunkered:  this should be tons of coal bunkered in the boiler or coal burned.
• Heat content of the coal:  this data is an analysis done in the lab.
• Sulfur content of the coal:  this data is an analysis done in the lab.  Five percent of the sulfur content is assumed to be lost in the slag or ash.  Therefore, a five percent loss of sulfur dioxide from 4.80 lb SO2 /mmbtu would be 4.56 lb SO2/mmbtu. 
• Removal efficiency: this data can be gathered from the continuous monitoring system.  The thirty day average removal efficiency is sufficient for the calculation.
• Gypsum purity:  the calcium sulfate content of the end product which can be determined in the lab by thermo gravimetric method.

Table 1

Data Needed	Sample Data
Coal Bunkered	200 000 tons coal bunkered or burned
Heat Content of the Coal	11 500 btu/lb
Sulfur Content of the Coal	4.80 lb SO2/mmbtu
Removal Efficiency	95%
Gypsum Purity	98%

Thus, the sample calculation would be:

Notice that the stoichiometry is based upon the overall reaction equation for the production of calcium sulfate di-hydrate.

Determining the Mass of the Gypsum End Product (Moisture)

How do we account for the moisture in the mass of the gypsum in the end product (i.e. gypsum coming off the filter drums or filter belts)?  For instance, let us say that the end product gypsum has 10 percent moisture. Firstly, we need to determine the percent solids of the end product gypsum.

                                                                                                                                   

Therefore, percent solids = 100% -% moisture.

Let us call the gypsum end product the Wet Gypsum and the gypsum calculated by stoichiometry Dry Gypsum.  Note that the gypsum calculated by stoichiometry has no free moisture in it.  The only moisture in the gypsum calculated by stoichiometry is molecular moisture.

Therefore,

Dry gypsum = Percent Solids * Wet Gypsum

Wet Gypsum = Dry Gypsum / Percent Solids

The following is a sample calculation using the data from above.

Therefore, I have found this calculation to be a good baseline calculation if your process lack weigh scales on the gypsum conveyors.  In addition, this calculation can be used to assign the mass of gypsum produced from coal burned from each boiler in a multiple unit plant that have belts or drums in common.