Unformatted text preview: + 0.030(0.124)]/1.524 = 0.468/1.524 = 0.307 lb H2O/lb silica gel.
Thus, 0.307/0.440 x 100% = 70% utilization of the bed. Exercise 15.26 (continued)
Analysis: (continued) Concentration profiles 1.0
0.9
0.8
0.7 c/c F 0.6
0.5
0.4
0.3
0.2
0.1
0.0
0 100 200 300 400 Time, minutes 500 600 700 Analysis: (continued) Exercise 15.26 (continued)
Loading Profiles 1.0
0.9
0.8
0.7 q bar/q F * 0.6
0.5
0.4
0.3
0.2
0.1
0.0
0 100 200 300
400
Time, minutes 500 600 700 Exercise 15.27
Reduction of nitroglycerine (NG) content of wastewater by fixedbed adsorption
Subject:
with activated carbon in a train of 55gallon cannisters Given: Train of four 55gallon cannisters of activated carbon (ρb = 32 lb/ft3), each with an
inside diameter of 2 ft and containing 200 lb of carbon. Flow rate of wastewater = 400 gph with
2,000 ppm (by weight) of NG. When effluent from the first cannister reaches 1 ppm of NG, that
cannister is removed and a fresh one added to the end of the train. The following test results are
available for one cannister: water flow rate = 10 gpm with 1,020 ppm of NG by weight.
Breakthrough time in hours = tB = 3.90 L  2.05 for 1ppm NG, with L = bed depth in ft.
Assumptions: Plug flow.
Find: Number of cannisters needed each month. Monthly cannister cost at $700/cannister.
Analysis: Bed volume of activated carbon = 200/32 = 6.25 ft3 = V = πD2L/4.
Solving for L, with D = 2 ft, gives L = 2 ft.
Rearrange the breakthrough correlation for the test, by solving for L,
L = tB/3.90 + 2.05/3.90 = 0.256 tB + 0.526
This is the same form as Eq. (15120), where the term 0.256 tB is LES and the term 0.526 is
LUB.
Assume that the width of the MTZ = constant, independent of flow rate.
Therefore, LUB is constant at 0.526 ft.
From Eq. (15122), LES is directly proportional to the feed rate, QF . If a linear adsorption
isotherm is assumed, then LUB is independent of the ratio qF/cF in Eq. (15122).
That is, for the proposed operation, the higher value of cF (2,000 ppm compared to 1,020 ppm for
the test) is of no consequence. The higher concentration of NG in the feed, cF, is couterbalanced
by the higher loading in equilbrium with the feed, qF. The breakthrough equation becomes: L = 0.256 QF of operation
400
t B + 0.526 = 0.256
t B + 0.526 = 0.171t B + 0.526
QF of test
600 Solving for tB, with L of operation also equal to 2 ft,
tB = L − 0.526
= 586 L − 3.08 = 586(2) − 3.08 = 8.64 hours = 8.64/24 = 0.36 day
.
.
0.171 Assume a month of 30 days. Then need 30/0.36 = 84 cannisters per month.
Cost = $700(84) = $58,800/month Exercise 15.28
Subject:
Sizing of fixedbed adsorption unit for removal of ethyl acetate (EA) from air with
activated carbon (C), using adsorption equilibrium isotherm and breakthrough data
Given: Gas feed is 12,000 scfm (60oF and 1 atm) containing 0.5 mol% EA and 99.5 mol% air.
Adsorbent is C (ρb = 30 lb/ft3 and dp = 0.011 ft. Adsorption equilibrium data at 100oF.
Breakthrough lab data at a gas superficial velocity of 60 ft/min in a 2ft high bed at 100oF and 1
atm.
Assumptions: Plug flow.
Find: Diameter and h...
View
Full Document
 Spring '11
 Levicky
 The Land

Click to edit the document details