Particulate Emission Control - Mathematics and Statistics for the Environment - page 521

Express the value of the dust collected in terms of pressure drop ∆ p . Recall that

η = ∆ p /(∆ p + 5.0)

Thus,

Value of dust collected = 0.143[∆ p /(∆ p + 5.0)]($/min)

Express the cost of power in terms of pressure drop ∆ p :

Brake horsepower ( Bhp ) = Q ∆ p /η′

where
Q = Volumetric flow rate.
∆ p = Pressure drop (lb/ft 2 ).
η′ = Fan ef iciency.

= (

) × ( ) ×

( )

2 3

Cost of power p lbf/ft2 50,000 ft /min 1/44,200 kW-min/ft-lb

( ) ×

× ( 1/0.55) × 0.06 $/kW -h ( 1/60 hr/min )

= 0 002 p $/min

Set the cost of power equal to the value of dust collected and solve for ∆ p in lb/ft 2 . This represents
breakeven operation. Then, convert this pressure drop to in. H 2 O. To convert from lb/ft 2 to in. H 2 O,
divide by 5.2.

(0.143)∆ p /(∆ p + 5) = 0.002∆ p

Solving for ∆ p ,

∆ p = 66.5 lb/ft 2 = 12.8 in. H 2 O

Calculate the collection efficiency using the value of ∆ p calculated above:

η = 66.5/(66.5 + 5) = 0.93 = 93.0%

■ EX AMPLE 17.16
Problem : Determine capital, operating, and maintenance costs on an annualized basis for a textile
dye and finishing plant (with two coal-fired stoker boilers) where a baghouse is employed for par-
ticulate control. Operating, design, and economics factors age given (USEPA, 1984b, p. 123).

Given:
Exhaust volumetric flow from two boilers = 70,000 acfm
Overall fan efficiency = 60%
Operating time = 6240 hr/yr
Surface area of each bag = 12.0 ft 2
Bag type = Teflon® ® felt
Air-to-cloth ratio = 5.81 acfm/ft 2
Total pressure drop across the system = 17.16 lb f /ft 2
Cost of each bag = $75.00
Installed capital costs = $2.536/acfm
Cost of electrical energy = $0.03/kWh
Yearly maintenance cost = $5000 plus yearly cost to replace 25% of the bags