Field Aerator Capacity Design parameter
Design Parameter
Designers must choose equipment based on: - O2 requirement - capital costs - operating costs - non-economic factors Therefore, she/he must know the field oxygen transfer capacity. Usually expressed as:
lb O2 / hp hr
or
Kg O2 / Kwh
Manufacturers usually supply transfer capacity for their equipment under standard conditions (1 atm, air, 20 C=0) i n tap water. C,
Designers must correct this stated capacity to that expected in the field conditions. M&E presents Eqn, 5-62, p. 447, for this correction.
C Walt C N = No 9 . 17
L
1 . 024
T 20
Where: N = lb O2/hp-hr in the field No = lb O2/hp-hr in water at 20C, C = 0 = salinity-surface tension factor Cwalt = O2 saturation conc. for tap water at temp., alt. CS20 = O2 saturation conc. for tap water at 20C CL = operating O2 conc. T = temp C = O2 transfer coeff. for waste (M&E, Table 5-32)
However, O2 saturation is outdated , so : CWalt C L 1.024T 20 N = No CS 20
CS20 = 9.08 (from M&E, App. D)
Equation 5-62 is derived as follows:
dC A = K L (CS Ct ) = K L a (CS Ct ) dt V
Where: Kla = overall mass transfer coeff. CS = saturation conc. in soln. Ct = conc. at time t
Eqn. 4 30
Correct K standard L a * for waste compositio n K L a = ( K L a*) = K L a ( waste) K L a (test ) * denotes standard test conditions
-Correct standard Kla* for temperature
K L a = ( K L a*)
T T20
-Correct CS* for temperature using Henrys Law -Correct CS* for altitude (pressure) using Fig. 5-68, p 447
Corrected CS * = Cwalt
water temperature altitude
-Correct for difference in saturation between tap water and wastewater
C S ( waste ) = C S (tap )
(same T, P)
CWalt C L 1.024T 20 N = No CS 20
Eqn. 5-62, p 447
A more sophisticated equation: Eqn. 5-55, p. 429
Cs ,T , H CL (1.024T 20 )( )( F ) AOTR = SOTR Cs , 20
Where: AOTR = actual oxygen transfer rate under field conditions, kg/O2/h SOTR = standard oxygen tra...