Page 234 - Air Pollution Control Engineering

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Wet and Dry Scrubbing 213

Tables 5
Pressure Drop Constants for Tower Packing
Nominal size Range of L''
2
Packing (in.) g r (lb/h-ft )
Raschig rings 0.5 139 0.00720 300–8,600
0.74 32.90 0.0045 1,800–10,800
1 32.10 0.00434 360–27,000
1.5 12.08 0.00398 720–18,000
2 11.13 0.00295 720–21,000
Berl saddles 0.5 60.40 0.00340 300–14,100
0.74 24.10 0.00295 360–14,400
1 16.10 0.00295 720–78,800
1.5 8.10 0.00225 720–21,600
Intalox saddles 1 12.44 0.00277 2,520–14,400
1.5 5.66 0.00225 2,520–14,400
Drip-point No. 6146 1.045 0.00214 3,000–17,000
grid tiles Continuous flue
Cross-flue 1.218 0.00227 300–17,500
No. 6295 1.088 0.00224 850–12,500
Continuous flue
Cross flue 1.435 0.00167 900–12,500
Source: ref. 13.

The value for Q can be obtained from Q
e,a e
Q = Q (T + 460) / 537 (24)
e,a e e
where Q is the emission stream flow rate (scfm) and T is the emission stream temper-
e e
ature (°F). Equation (25) is used to determine annual electricity cost (AEC) of a packed
tower wet scrubber. In January 1990, the UEC was $ 0.059/kWh.

AEC = UEC (F ) (25)
p
where UEC is the unit electricity cost ($/kWh).
The electric power needed to operate the fan feeding the gaseous stream to the scrubber
tower is directly related to the total pressure drop of the fan. The Electric Power Institute
of Palo Alto, California has provide a correlation between the acfm of gas being treated
and the horsepower, hp, needed to drive the fan at a given pressure drop:
hp = Q P /5,390 (25a)
e total
This correlation assumes an 80% efficient motor and 10% annual downtime. The
cost of operating 1 hp (again from the Electric Power Institute), for 1 yr, at various
electric power costs is
$/kWh 0.04 0.06 0.08 0.10 0.12 0.14 0.16
Cost /yr $326 $492 $650 $816 $975 $1, 134 $1, 309
Thus, per this example, if the cost of power is $0.10/kWh (during California’s power
crisis in the summer of 2001, this cost escalated to greater than $0.30), and a plant has a