DELFT UNIVERSITY OF TECHNOLOGY Department of civil engineering Division of sanitary ...

188 Pages·2007·6.26 MB·English

DELFT UNIVERSITY OF TECHNOLOGY
2 5 1
Department of civil engineering
7 4 A E
Division of sanitary engineering
AERATION AND GAS TRANSFER
^Div^lng. H.J.
I'
LIBRARY
International Reference Centra
for Community Water Supply
herdruk
maart 1976
2 5-1
DELFT UNIVERSITY OF TECHNOLOGY
Department of civil engineering
Division of sanitary engineering
r*
£\l
AERATION AND GAS TRANSFER
__-,._•. I •-'.!";.;
wo-- oupf-iy
n . 'v
Prof. Dr.-lng.H.J.P6pel
Ltgave 2e herdruk
753070
197^ jan. 1979 / *•,--
L.S.
Bij de samenstelling van elk diktaat wordt er uiteraard
naar gestreefd om fouten te voorkomen en de inhoud zo over-
zichtelijk mogelijk aan te bieden.
Niettegenstaande dat kunnen toch onduidelijkheden voorkomen
en kunnen fouten zijn ingeslopen.
Indien U dan ook bij de bestudering van dit diktaat:
- onjuistheden ontdekt
- op onduidelijkheden stuit
- of gedeelten ontmoet, die naar Uw mening nadere uitwerking
behoeven, verzoeken de samenstellers U dringendhendaarvan
mededeling te doen.
Bij de volgende drukken kunnen dan op- en aanmerkingen worden
verwerkt ten gerieve van toekomstige gebruikers.
Zonodig kan ook nog in de lopende cursus voor verduidelijking
worden gezorgd.
^
I
Table_of_Contents Page
List of Abbreviations and Symbols TV
References XI
Text and Figures 1
Tables 162'
1. Introduction < 1
1.1 Definition and Terms 1
1.2 Elements of Aeration and Gas Transfer Operations . 3
1.3 Aeration and Gas Transfer within Processes of
Water Purification and Sewage Treatment . . . . .. 8
2. Theoretical Aspects of Aeration and Gas Transfer . 9
2.1 Solubility of Gases 9
2.11 Influence of the Gas Concentration
on Solubility 9
2.12 Influence of Temperature on Solubility 1^
2.13 Influence of Impurities on Solubility 16
2.2 Diffusion 17
2.3 Gas Transfer Coefficients 22
2.31 The Concept of Gas Transfer Coefficients 22
2.32 Theories on the Mechnism of Gas Transfer 2U
2.321 Film Theory 2k
2.322 Penetration Theory >. 25
2.323 Surface Renewal Theory 28
2.32U Film-Surface-Renewal Theory 28
2.325 Comparison of the Discussed Theories 29
2.33 Some Applications of the Penetration Theory .... 31
2.3U Factors Affecting the Gas Transfer Coefficient . . 32
2.1+ Practical Approach to Gas Transfer Rate
Formulations 36
2.1+1 The Overall Gas Transfer Coefficient 36
II
Page
2.U2 The Efficiency Coefficient 38
2.U3 The Oxygenation Capacity kl
2.5 Change of the Gas Phase by Gas Transfer
Operations kf
3. Practical Aspects of Aeration and
Gas Transfer 61
3.1 Gravity Aerators 61
3.11 Weir Aeration and Cascades 61
3.111 Single Free Fall in Weir Aeration . 62
3.112 Step Weirs or Conventional Cascades 6U
3.12 Stacks of Perforated Pans or Tower Cascades ... 68
3.121 Tower Cascades for Removal of Carton Dioxide ... 70
3.122 Packed Towers for Ammonia Stripping 75
3.2 Spray Aeration 80
3.21 The Dresden Nozzle 83
3.22 The Amsterdam Nozzle 86
3.3 Bubble Aeration or Air Diffusion 89
3.31 General Considerations 89
3-32 Fine Bubble Aeration 97
3.321 Types of Diffusers and Their Arrangement 97
3.322 Factors Influencing the Rate and Efficiency
of Oxygen Transfer 103
3.323 Practical Aspects 106
3.33 Medium Bubble Aeration (High Pressure) 109
3.331 Types of Diffusers and Their Arrangement 109
3.332 Factors Influencing the Rate and Efficiency
of Oxygen Transfer > 110
3.333 Practical Aspects 112
3.33^ Medium Bubbles Aeration (Low Pressure) 112
3.33U1 The Inka Aeration System 112
3.33^2 The Inka Intensive Aeration 115
3.3^ Coarse Bubble Aeration 117
3.3*+1 Types Diffusers and Their Arrangement 117
Ill
Page
3.31+2 Factors Influencing the Rate and Efficiency
of Oxygen Transfer 118
3.3*0 Practical Aspects 119
3.35 Air Diffusion by Means of Entrained Air 119
3.351 The Venturi Aerator 120
3.352 The Deep Well Aerator (U-Tube Aerator) 121
3.1* Mechanical or Surface Aeration 123
3.1+1 General Considerations 123
3.1+2 Rotor Aerators . 127
3.1+21 Types of Rotor Aerators and Their Arrangement . . 127
3.1*22 Factors Influencing the Rate and Efficiency
of Oxygen Transfer 132
3.1+23 Practical Aspects 137
3.1+3 Cone Aeration 138
3.1+31 Types of Cones and Their Arrangement 138
3.1+311 Plate Aerators 1l+0
3.1+312 Updraft Aerators 11+1
3.1*313 Downdraft Aerators 11+8
3.1+32 Factors Influencing the Rate and Efficiency
of Oxygen Transfer 11+9
3.H33 Practical Aspects 156
3.5 Combined Aerator Types 159
IV
Abbreviations and Symbols
The dimensions of the following abbreviations and symbols are chosen
in accordance with the International System and are hence based on
the following basic dimensions:
length (m), mass (kg), time (s), temperature (K, °C is also being
used here).
Deducted units are
force (Newton) : 1 N = 0,101972 kgf
1 kgf = 9,80665 N
work, energy (Joule) 1 J =1 N.m
power (Watt) 1 W = 1 J/s
pressure (Pascal) 1 Pa = 1 N/m2
(bar) 1 bar = 105 Pa
The various units used in the literature for pressure require some
further explanation, whereas the conversion of other applied units is
straight forward.
Basically, pressure has been defined in terms of "atmosphere" by the
following ways:
o
a) 1 technical atmosphere = 1 kgf/cm
b) 1 physical atmosphere = 760 mm Hg (Torr)
c) 1 absolute atmosphere = 1 bar
3
From the above definitions and the density of mercury of 13595,1 kg/m
the following conversion table is obtained.
Convenient units for the pressure of gases within the International
System would be
- mbar, the normal atmospheric pressure being 1013 mbar
- kPa , the normal atmospheric pressure being 101,3 kPa
In the following "kPa" is used as the standard unit for pressure.
Roughly is 1 kPa = 30/U mm Hg
1 mm Hg = U/30 kPa
Further it is seen from the conversion table that there is not too
great a difference between the "atmospheres", the smallest (technical
atmosphere) being but 3,2 % less than the greatest (physical atmosphe
re) .
00
1
o
M 0\ OJ OJ
w LLAA NoO \ooo ""
g LA o o LA
oo MD LA «*
t— t— t— c—
LA OJ
«s LA o OJ
NO CO o 00
OJ VO 00 o #*
CM o r— o 1— 00
CO o o 00
ON
r
a i 00
b 1
= o
.
co a LA •
-P •p VD LA OJ
•H ai VD OJ LA OJ
a O 00 1 oo
3 • • CO T— 1— o 00
CO CT\ o 1— 00
<u £> * #N «>
r cd o *- "-
u
s
s
0) LA
*H 1 oo
P. , o 1
o
U a • T—
o -p 1— 00 00 •
tH aJ _3- OJ OJ o\
co ON ON t—
cu • t— 1— MD NO LA
H co NO CO CO *—
£> >> ON ON ON 00
a) x: •* •» #» ft
-P ft o o O *-
C
O
i
s
r LA oo
CD • 1 1
!> a o o
C •p r— T-
O ctf • •
o 00 OJ OJ r-
• 0J c— t— LA
c 1— 00 ON ON ON
£1 00 t— *— LA
O o o O 00
CU A ** #* *
•p
^ "
= II = II II
r
a
b

1
m. =
at •aP m.
. nJ at
n bO
x; CO K
o co
0) .G £> ctj g
•p ft 0) Pn
VI
Qreek_Svmbols
factor to account for the influen
ce of surface active agents on the
rate of gas transfer
W/m gross power input per unit volume
-, % efficiency-
activity coefficient
Pa.s absolute viscosity
N/m surface tension
s theoretical detention time (V/Q)
temperature coefficient
Dimension(s) Description
2 3
m /m specific interfacial area
2
m area, surface
2
m /s interfacial area produced per
unit time
g/m gas concentration in water
g/m gas concentration in the effluent
of an aerator
g/m concentration of a gas in the
gaseous phase
3
g/m gas concentration in the gaseous
phase at the interface
,3 ... v
g/m initial concentration of a gas in
the gas phase
3
g/m gas concentration in a liquid
3
g/m gas concentration in the liquid
phase at the interface
g/m saturation concentration of a gas
in water
o
g/m like c , but under conditions de-
g
fined under t
VII
3
g/m initial saturation concentration
of a gas in water
3
kg/m concentration of activated sludge
suspended solids
3
g/m gas concentration in a liquid in
dependence of x and t as a conse
quence of molecular diffusion
2
m /s coefficient of molecular diffusion
in a liquid
2
m /s coefficient of eddy diffusion
2
m /s coefficient of molecular diffusion
in a gas
p
m /s ttoottsa l coefficient of diffusion:
D+D,
2 E
m /s coefficient of diffusion of a gas
in water at a temperature of T
2
m /s coefficient of molecular diffusion
of a gas in water at 10°C
m depth (of tank, of packing, etc.)
m diameter of gas bubbles in a liquid
m thickness of gas film
m depth of immersion (or submergence)
of an aeration device below the
water level
m thickness of liquid film
mm diameter of the opening of a spray
nozzle
•2
m /m .s
rate of air flow Qg (m°/s) per
unit volume of water V (m^)
m height, head
m total head
kmole/m ionic strength