Wet Scrubbers for Emission Control - Mathematics and Statistics for the Environment - page 545

N t = α( P T )β = 1.47 × (1.018) 1.05 = 1.50

Calculate the collection efficiency based on the design data given by the vendor:

N t = ln[1/(1 - η)]

1.50 = ln[l/(l - η)

Thus,

η = 0.777 = 77.7%

Now calculate collection efficiency required by state regulations. Because the inlet loading is known
and the outlet loading is set by the regulations, the collection efficiency can be readily calculated.

Inletloading − Outlet loading

×= −

50 . 005

50

.

×=

Collectionefficiency = 100 100 99 .%

Inletloading .

Does the spray tower meet the regulations? No. The collection efficiency based on the design data
given by the vendor should be higher than the collection efficiency required by the state regulations.
Assuming that the spray tower does not meet the regulations, propose a set of operating conditions
that will meet the regulations. Note that the calculation procedure is now reversed.
Calculate the total pressure loss ( P T ) in hp/1000 acfm using the collection efficiency required by
the regulations. Calculate the number of transfer units for the efficiency required by the regulations:

N t = ln[l/(l - η)] = ln[l(l - 0.99)] = 4.605

Calculate the total pressure loss, P T , in hp/1000 acfm:

N t = α( P T ) β

4605 = 1.47( P T ) 1.05

Thus,

P T = 2.96 hp/1000 acfm

Calculate the contacting power based on the gas stream energy input ( P G ) using a ∆ p of 15 in. H 2 O.
A pressure drop ∆ p of 15 in. H 2 O is the maximum value allowed by the design:

P G = 0.157∆ p = 0.157 × 15 = 2.355 hp/1000 acfm

Calculate the contacting power based on the liquid stream energy input P L :

P L = P T - P G = 2.96 - 2.355 = 0.605 hp/1000 acfm

Calculate Q L / Q G in gal/acf using a p L of 100 psi:

P L = 0.583 p L ( Q L / Q G )

Q L / Q G = P L /0.583 p L = 0.605/(0.583 × 100) = 0.0104