2. Given: In the control of acid rain, power plant sulfur emissions are controll
ID: 1822694 • Letter: 2
Question
2. Given: In the control of acid rain, power plant sulfur emissions are controlled by scrubbing and spraying the flue gas with lime slurry, Ca(OH)2. The calcium reacts with sulfur dioxide to form calcium sulfate dihydrate (CaSO4·2H2O), a white powder (gypsum) suspended in water. The volume of this waste slurry is large, therefore it must be thickened. Suppose a power plant produced 27 metric tons of CaSO4·2H2O per day (dry weight), and this is suspended in water. The total mass of waste slurry produced each day (water plus calcium sulfate dihydrate) is 135 metric tons. The suspension is to be thickened to a solids concentration (mass fraction) of 40% solids (mass solids/mass total). The thickener unit has a solids capture efficiency of 95%.Required: How much water (tons/day) will be produced as effluent from the thickening operation? Approach: Use the Material Balance Technique (all steps).
Explanation / Answer
A power plant produced 27 metric tons of CaSO4·2H2O per day (dry weight), and this is suspended in water. The total mass of waste slurry produced each day (water plus calcium sulfate dihydrate) is 135 metric tons.
means mass of water = 135 tons - 27 tons = 108 tons before the thekening of the suspension into a solid concentration.
The suspension is to be thickened to a solids concentration (mass fraction) of 40% solids (mass solids/mass total).
from here, we can calculate the mass of solids produces per day = total mass *40% = 135*0.4 = 54 tons
but The thickener unit has a solids capture efficiency of 95%.
means total solids mass used by thickner unit = 54/efficiency = 54/0.95 = 56.842 tons
therefore, required mass of water per day = total mass - mass of solids = 135 - 56.842 = 78.158 tons
hence, 78.158 tons/day will be produced as effluent from the thickening operation.
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