design considerations & optimization of forward feed multi effect ... - SQU
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THE EFFECT OF FOULING ON. PERFORMANCE AND DESIGN ASPECTS OF. MULTIPLE EFFECTS DESALINATION. SYSTEMS. Furqan Tahir. Maimoon Atif.
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design considerations & optimization of forward feed multi effect ... - SQU
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THE EFFECT OF FOULING ON PERFORMANCE AND DESIGN ASPECTS OF MULTIPLE EFFECTS DESALINATION SYSTEMS
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.
