THE EFFECT OF FOULING ON
PERFORMANCE AND DESIGN ASPECTS OF
MULTIPLE EFFECTS DESALINATION
SYSTEMS
Furqan Tahir
Maimoon Atif
Mohammed A. Antar
CONTENTS
 Introduction
 Problem Definition & Objectives
 Methodology
 Results & Discussion
 Conclusion
 References
WHAT IS IT ALL ABOUT
OVERVIEW OR CONCLUSION
Preheater
D1
mf
Rejected seawater
Feed seawater
mcw
D4
D2
Down Condenser
ms
Brine
Brine
To
boiler
Brine
B1
Seawater in
From
boiler
Brine
Product line
Flash boxes
Rejected brine
Features
• TBT < 70oC (Steam, waste heat, solar,…..)
• PR ~ N
• Exists in several layout
U and Effect of fouling
To ejector
Non-condensable gases
Rejected seawater
From
boiler
Brine
Brine
Brine
Brine
Down Condenser
Seawater in
Feed seawater
Product line
To
boiler
Flash boxes
Rejected brine
OTHER
LAYOUTS!!
To ejector
Non-condensable gases
Rejected seawater
From
boiler
Brine
Brine
To
boiler
Brine
Brine
Down Condenser
Product line
Flash
boxes
Rejected brine
Seawater in
Feed seawater
INTRODUCTION
 Water comprises of more than 70% of our
earth but it has unfortunately only 0.3% of
usable water.
INTRODUCTION
 The uneven distribution of this asset is very
critical especially in the Middle East .
 To overcome this dwindling resource of
fresh water in the Kingdom of Saudi Arabia;
Thermal Desalination is a logical & Practical
approach.
INTRODUCTION
 Among
thermal
desalination
technologies,
Multi Effect Desalination (MED) is getting more
attention.
 Reasons could be:
 Low energy consumption compared to MSF.
 Higher overall heat transfer coefficients
 Less specific Area as compared to MSF
 Low operating steam temperature, other low grade
heat sources can be used to power it.
PROBLEM DEFINITION
MED-FF
‘n’ effects, ‘n-1’ Flash boxes, ‘n-2’ Pre heaters.
OBJECTIVES
 After comparing the model with other
models available in literature. We want:
 To investigate the effects of Steam
temperature, Cooling water temperature,
fouling on the design aspects of plant.
 To analyze the effect of fouling on the
performance of the plant
METHODOLOGY
 The jth effect is illustrated for applying mass & Heat
balances.
METHODOLOGY
The parameters to evaluate performance
of Plant are:
i. Performance ratio (PR)
ii. Specific mass flow rate of cooling water
iii. Specific Heat Transfer Area (sA)
md
PR =
ms
sM cw
n
∑A
n −1
+ ∑ Ap j + Ac
ej
=j 1 =j 2
sA =
mcw
=
md
md
METHODOLOGY
The Plant is modeled for the following operating parameters:
 Operation is steady state.
 The plant is normalized for distillate flow of 1 kg/s.
 The number of effects vary from 4-8.
 Steam temperature is taken as Ts=70 oC, Cooling water
temperature Tcw=25 oC, Last effect temperature Tn=40 oC
and Feed Temperature Tf=35 oC.
 The intake and rejected salinity of seawater are taken
Xf=42,000 ppm and Xn= 70,000 ppm respectively.
.
RESULTS & DISCUSSION
 The PR of present model is comparable with the model of El
Dessouky et al.
 The specific areas are in good agreement with Karan et al. and
El dessouky’s model. Darwish’s model predicts less specific
area due to simplified assumptions.
450
400
8
7
6
Present study
5
El dessouky
4
Karan
3
4
5
6
7
No of effects (n)
8
350
300
250
200
El dessouky
150
Karan Mistry
Present study
100
Darwish
3
sA (m2/(kg/s))
Performance Ratio(PR)
9
Darwish
50
9
3
4
5
6
7
No of effects (n)
8
9
RESULTS & DISCUSSION
 Due to increase in steam temperature, the flashing in Flash
boxes and evaporators’ increases, hence improving the PR,
however the rise is very little. Also less heat transfer area is
required for the same performance.
RESULTS & DISCUSSION
 The seasonal variations cause the temperature of seawater to
vary.
 The cooling water flow rate & Condenser Area will vary in
order to keep same performance as the Temperature of
seawater/cooling water changes.
RESULTS & DISCUSSION
 The fouling factor has an asymptotic profile, so the resistance
will increase sharply in the beginning, and then the rate of
increase will be reduced as the time passes
RESULTS & DISCUSSION
 As the time passes the overall heat transfer coefficient
decreases due to the fouling and hence specific area required
to keep the same performance will increase.
RESULTS & DISCUSSION
 Once the plant is designed and commissioned, its performance
won’t be the same as time passes.
 It is important to predict
the performance of the
plant over time to decide
major overhauling time so
that the plant can retain its
original performance
CONCLUSION
 MED-FF plant modeling has been carried
out and validated.
 Performance Rating of the plant as well as
design considerations have been discussed
for different parameters such as steam
temperature, cooling water temperature and
fouling resistance.
CONCLUSION
System rating is performed as f(time) such
that suggestions for the right overhauling
time can be planned.
Design parameters such as surface areas are
selected based on predicting the overall heat
transfer coefficient as a function of time.
CONCLUSION
 Over
sizing can be avoided once fouling
resistance can be estimated and incorporated
into the model and hence time intervals
between shutdowns are determined for a
given plant size.
THANKS