UNIVERSITY OF CALIFORNIA Los Angeles Heat Loss in Aeration

100 Pages·2012·3.54 MB·English

UNIVERSITY OF CALIFORNIA
Los Angeles
Heat Loss in Aeration Tanks
A thesis submitted in partial satisfaction of · the
requirements for the degree Master of Science
in Civil Engineering
by
Shailendra Niranjan Talati
1988
b
The thesis of' Shailendra Niranjan Talati is approved.
~~LQ U, ~~~~J\-
Michael K. Stenstrom, CommiUee Chair
University of California, Los Angeles,
1988
ii
TABLE OF CONTENTS
Page
v
LIST OF FIGURES
vi
LIST OF TABLES
vii
ACKNOWLEDGEMENT
viii
ABSTRACT
1
1 INTRODUCTION
4
2 LITERATURE REVIEW
8
2.1 Solar Radiation
11
2.2 Atmospheric Radiation
18
2.3 Surface Convection
21
2.4 Evaporative Heat Losses
27
2.5 Aeration Heat Loss
29
2.6 Heat Loss from Power Input
30
2.7 Biological Reaction
33
2.8 Tank Wall Heat Loss
36
2.9 Summary
37
3 MODEL DEVELOPMENT & VERIFICATION
38
3.1 Model Development
43
3.1.1 Solar Radiation
44
3.1.2 Atmospheric Radiation
47
3.1.3 Swface Convection
iii
49
3.1.4 Evaporative Heat Losses
49
3.1.5 Aeration Heat Loss
52
3.1.6 Heat Loss from Power Input
53
3.1.7 Biological Reaction
54
3.1.8 Tank Wall Heat Loss
56
3.2 Model Verification
64
4 SENSITIVITY ANALYSIS & ENGINEERING
SIGNIFICANCE
80
5 CONCLUSIONS
82
6 NOMENCLATURE
85
7 REFERENCES
89
8 APPENDIX I
90
9 APPENDIX II
iv
LIST OF FIGURES
Page
Figure 1 Relationship between Atmospheric Radiation Factor 14
and Vapor Pressure for Various Cloud Covers
Figure 2 Components of Overall Heat Balance in Aeration Tank 39
Figure 3 Components of Heat Exchange with Environment 42
Figure 4 Comparison of Heat Loss from Radiation 48
Figure 5 Comparison of Aeration Tank Temperature 61
Figure 6 Comparison of Heat Loss from Aeration Tank 63
Figure 7 Comparison of Heat Loss from Aeration Tank 68
(Surface Aeration vs Diffused Aeration)
Figure 8 Comparison of Air, Influent and Tank Temperatures 69
Figure 9 Influence of wind speed on Aeration Tank Temperature 70
Figure 10 Effect of Wastewater Flow Rate on Tank Temperature 72
(Surface Aeration)
Figure 11 Effect of Wastewater Flow Rate on Tank Temperature 73
(Diffused Aeration)
Figure 12 Comparison of Aeration Tank Temperature for 74
Diffused Aeration (Open Tank vs Closed Tank)
Figure 13 Cities Selected to Study the Effects of Climatic 75
Conditions on Aeration Tank Temperature
Figure 14 Effect of Climatic Conditions on Aeration Tank 79
Temperature for different Cities
v
LIST OF TABLES
Page
17
Values of the constants a and b for Various
Table 1
Cloud Covers
35
Thermal Conductivity of Commonly Used Materials
Table 2A
35
Overall Heat Transfer Coefficient for Various
Table 2B
Portions of Aeration Tank
45
Comparison of Average Daily Absorbed Solar Radiation
Table 3
58
Input Process Data Selected for Verification
Table 4A
59
Input Meteorological Data Selected for Verification
Table 4B
60
Comparison of Tank Temperature for Various Models
Table 5
71
Influence of Exit Air Humidity ( leaving Aerator
Table 6
Spray ) on Tank Temperature
76
Site -Specific Data for Selected Cities
Table 7A
77
Process Data for Comparison of Tank Temperature
Table 7B
for Selected Cities
78
Comparison of Tank Temperature for Selected Cities
Table 8
ACKNOWLEDGEMENT
I wish to express deep sense of gratitude to my graduate advisor, Dr.
M. K. Stenstrom for lending me extraordinary cooperation, friendly
guidance and continued encouragement. Also, I wish to acknowledge
the assistance and advice of the other members of my thesis committee.
I am highly indebted to my present Company-CM&E INTERNATIONAL,
for making available all the resources needed for this study. I would
like to extend special thanks to W. James Smart and Thomas E. Miles
for their counsel and wholehearted support.
I am thankful to my parents, wife and family for their continued support
and encouragement which has made this study possible.
vii
ABSTRACT OF THE THESIS
Heat Loss in Aeration Tanks
by
Shailendra Niranjan Talati
Master of Science in Civil Engineering
University of California, Los Angeles, 1988
Professor Michael K. Stenstrom, Chair
Recent developments in wastewater treatment aeration systems have
focused on aeration efficiency and minimizing energy cost. Other
operating characteristics have often been ignored. The impact of aer
ation system alternatives on aeration tank temperature can be sub
stantial and design engineers should include these potential effects in
the evaluation of alternatives.
To predict aeration tank temperature and its influence on system design,
a survey of all previous literature was made and a new computer model
on Lotus 123 spreadsheet was developed. The model was based in part
upon previous works, but significant improvements were made in the
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areas of heat loss from aeration and atmospheric radiation. The new
model was verified with 17 sets of literature data, and predicts tem
perature with an RMS error of 1.24 for these 17 sets.
The model was used to determine the relative influence of design,
operation and climatic variables. Heat loss from aeration was found to
exert a great influence on surface aeration, accounting for 50% of the
total heat loss. Heat loss from sub-surface system was 50% of the total
heat losses from surface aeration. Wind speed and air humidity are
important parameters in determining aeration tank temperature.
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1 INTRODUCTION
Biological systems have gained major importance in wastewater treat
ment in view of stringent regulatory standards for discharging organic
wastes. Thus, there is a need to incorporate all possible operating
parameters in design stages and then to closely monitor these parameters
for design and operation.
The efficiency of a biological system is largely determined by the activity
of biomass. Factors affecting biomass activity, such as substrate con
centration, oxygen supply rate and oxygen saturation, are significantly
influenced by temperature. Moreover, substrate removal rate is related
to aeration basin detention time which is the design parameter for cal
culating basin volume. Biomass activity tends to increase with increasing
temperature from 20 ° C to 40 ° C which is the normal ambient
temperature at which the biological system operates. It leads to the
necessity of accurately predicting equilibrium temperature of waste
water in aerated biological system. Inaccurate estimation of tempera
ture can result in failure to comply with effluent discharge standards or
cause gross over design of the system.
Equilibrium water temperature of the biological system can be predicted
by making a heat balance around the system. The overall heat balance
1