An electric power generating plant burns bituminous coal in

An electric power generating plant burns bituminous coal in a wet-bottom, pulverized coal-fired furnace (also called a steam boiler) equipped with a wet scrubber to remove 98% of the SO_2 from the exhaust gases. Assume the following: Power plant output = 100 MW Overall thermal cyclic efficiency (eta) = 20% Coal assay: sulfur (by mass) = 2.1% Higher heating value (HHV) = 12, 500 BTU per lbm coal burned Average molecular weight = 12 Ash (by mass) = 8% Wet scrubber converts SO_2 to gypsum (CaSO_4 2H_2O) by the following overall equation: SO_2 + CaO +2H_2O + 1/2 O_2 CaSO_4 2H_2O i) Estimate the following in tons/h a. Coal consumption rate b. SO_2 mass flow rate entering the scrubber c. Total ash accumulation rate d. CaO consumption rate c. Gypsum accumulation rate ii) Do you see any drawbacks of the wet scrubber process? iii) If the power plant switches to natural gas from coal, what potential benefits and drawbacks are associated with this switch?

Solution

HEAT IN COAL= 100 MW * 1000 * 860/ 20%= 430 * 10 ^6 KCAL/HR

1. COAL CONSUMPTION= 430 * 10^6/ (12500*0.555)= 61981.98 KG/HR ( 1BTU/LB= 0.555KCAL/KG)

2. ASH ACCUMALATION RATE= 61981.98*8%= 4958.55 KG/HR

3. SO2 MASS FLOW RATE = S*64/32= (61981.98*2.1 %)*64/32= 2603.24 Kg/HR

4. SULFURE RATE = 1301.62 KMOL/HR

CA TO S RATIO TAKE 3, SO2 to CaO = 2603.24*56/32=4555.67 kg/hf ( 56 is Cao molecular weight g/mol)

5. Gypsum accumlation (molecular weight 172)= 2603.24*172/32= 13991.125 kg/hr

ii wet Scrubber is good for this type of poower plant, also sulfure contain is high in fuel.

iii Coal to NG switch over coast more in modification of plant burner system but benfit in SO2 reduction comapre to coal & no need of wet scrubber in the NG fired power plant.