Water Desalination Through MED-TVC -...

Water Desalination Through MED-TVC

IMPROVEMENT OF MULTI-EFFECT DESALINATION

SYSTEMS: LOCATION OF VAPOR COMPRESSOR

Mohammed Antar

Professor

Mechanical Engineering Department

KFUPM

[email protected]

Introduction

Desalination Processes

Previous Work

Objectives

Forward Feed Model

Outlines1

4

3

2

5

Parallel Feed Model6

2

Remarks7

Conclusion8

11/2/2017 3

NEED FOR WATER FOR WATER

DESALINATION

• The volume of the water available in the

earth is 1.4 10^9 Km^3 covers 70% of the

earth surface area.

• 97.5 % of this water is salt water

• 80 % of the rest is frozen in the icecaps or

combined as a soil moisture

• The remaining quantity which is (20% of

2.5% = 0.5 %) of the total quantity

available in the earth used to support the

live in our planet


Introduction

Conclusions

Forward Feed Model Previous Work

Parallel Feed ModelObjectives

Remarks

11/2/2017 4

NEED FOR WATER FOR WATER

DESALINATION

• The water quantity is almost constant

• The population is increasing

significantly

http://www.kivu.com/


Introduction

Conclusions

Forward Feed Model Previous Work


Remarks

11/2/2017 5

Definition of desalination processes

• Desalination process is a process of separation of

fresh water from saline water

• Desalination process based on thermal or

membrane separation .

https://www.emaze.com/

Desalination Processes Conclusions

Forward Feed Model Introduction Previous Work


Thermal Separation Include

• Evaporation followed be condensation (MSF, MED, HDH)

• Freezing followed by melting

The membrane separation include

• Reverse osmosis (RO)

Remarks

11/2/2017 6


Electrical Energy Thermal Energy Mechanical Energy

MVC ROED Steam Solar

Solar Still

Heating Steam

MED

MSF

HDH




Remarks

11/2/2017 7

• It is a formed a sequence of single effect evaporators

• The vapor created in the first effect is used as a source of heat in the next effect

• Avoid rejection of heated brine , which was the main drawback of the single effect system

Multi effect evaporation system Developments

Darwish* and Abdulrahim Feed water arrangement in multi effect desalination systems




Remarks

11/2/2017 8

• It is a formed a sequence of single effect evaporators

• The vapor created in the first effect is used as a source of heat in the next effect

• Avoid rejection of heated brine , which was the main drawback of the single effect system

Multi effect evaporation system Developments




http://www.sidem-desalination.com/en/process/MED/Process/

Remarks

http://www.sidem-desalination.com/en/process/MED/Process/

11/2/2017 9

Darwish* and Abdulrahim Feed water arrangement in multi effect desalination systems

Schemes of supplying feed water to the

evaporators

• Forward feed MED distillation system

• Backward feed MED distillation system

• Parallel feed MED distillation system




Remarks

11/2/2017 10

Previous Work

Authors Year Remarks

El-Dessouky et al. 1998 Introduced mathematical model describing the MED system

They concluded that the PR of the plant is nearly independent of the TBT

El-Dessouky et al. 2000

Running of both systems parallel/cross flow and parallel flow systems is

preferential at higher temperatures as a result of the extreme reduction in the

specific heat transfer area

Ali and El-Figi 2003 Studied the performance of MED-FF system, they pointed that the PR is

notably dependent on the number of effects rather than the TBT

Ophir and Lokiec 2005

Reported that the MED is better thermodynamically and it is known as lower

energy consumption compared to MSF system

Very low specific energy costs for water desalination .

ConclusionsDesalination Processes

Introduction

Objectives Parallel Feed Model

Forward Feed Model Remarks

11/2/2017 11


Darwish et al. 2006

Normal MED system has the advantage of exploiting a low-temperature

heat source when it works at low TBT

The heat transfer areas increase considerably due to decreases of ΔT to less

than 2˚ C

The Multi Effect Boiling system consumes about half of the Multi Stage

Flash system pumping power.

Darwish and

Abdulrahim2008

Developed MED model and analyzed different arrangements

In all arrangements, increasing the number of effects increases the gain ratio,

and the used specific heat transfer area.

Mistry et al. 2013 Illustrated that the advantage of Cogeneration systems is being able to

produce both water and power at lower costs .

Previous Work


Introduction



11/2/2017 12


HAMED et al. 1996 MED-MVC and MED-TVC for 4 effects

They reported that the MED-TVC system is more efficient than

MED-MVC system.

El- Dessouky et

al.

2000 MED-MVC (P & PC).

The specific power consumption for MED-MVC parallel cross is

lower than MED-MVC parallel feed.

Bahar et al. 2004 MED-MVC.

Results showed that the brine concentration rate affects the distillate

flow rate.

Previous Work


Introduction



11/2/2017 13


Ophir et al. 2007 MED with turbo-compressor at low temperature

An auxiliary turbine and a compressor of higher efficiency than

thermo-compressor results in considerable energy savings.

Lara et al. 2008 MVC system operating at high temperature

At high temperature, heat transfer area is small, compression work is

low. They used a small compressor to reduce the capital cost.

Fuad et al. 2011 The effect of stage temperature drop on

MED-MVC

The specific power consumption decreases as MVC brine

temperature increase, and volume flow rate is decreased as MVC

brine temperature increase.

Previous Work


Introduction



11/2/2017 14

Objectives

• To develop mathematical model for design and operation of multi effect

desalination system based on energy and mass balances

• To assess several layouts of MED-TVC.

• Improving MED-MVC performance through the use of a secondary

compressor that extracts vapor from one of the effects.

• To study the effect of changing the position of thermal vapor

compression (TVC or MVC)

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

Remarks

11/2/2017 15

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

Forward Feed MED Model

Remarks

11/2/2017 16

Forward Feed MED TVC Model

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

Remarks

11/2/2017 17

Forward Feed MED TVC Model Results

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

At lower steam temperature, PR is high, as

the steam temperature increases, PR

decreases due to increasing of the motive

steam flow rate to get higher compression

ratio.

Increasing the number of effects increases

PR due to better use of energy and vapors

gained.

Remarks

11/2/2017 18

Forward Feed MED TVC Model Results

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

Increasing heating steam temperature

increases the cooling water flow rate

due to increase of the last effect

thermal load as a result of increasing

the compression ratio and the heat

load of the first effect.

In addition, increasing the number of

effects reduces the specific cooling

water flow rate due to reducing the

thermal heat load by increasing the

number of effects.

Remarks

11/2/2017 19

Forward Feed MED TVC different ejector positions Model

The heat load enters to the condenser

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

Remarks

11/2/2017 20

Forward Feed MED TVC different ejector positions Model Results

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

Remarks

11/2/2017 21

Forward Feed MED TVC Exergy Analysis Results

0

10

20

30

40

50

60

70

80

90

Exerg

ati

c E

ffic

ien

cy

Exergy Analysis Break Down

TVC After effect 4

Conclusions

Forward Feed Model


Introduction

Objectives

Previous Work

Parallel Feed Model

Remarks

11/2/2017 22

Parallel Feed MED TVC Model

Parallel Feed Model ConclusionsDesalination Processes

Introduction

Objectives

Previous Work Forward Feed Model Remarks

11/2/2017KFUPM ME Dept. 23

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8 9

Flo

w r

ate

ratio [

-]

PR

and C

R [

-]

Effect number

Forward Feed -TVC- 8 effects system

Compression ratioPerformance ratioMotive steam flow rate ratio

Ts=80 ºC

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10

Flo

w r

ate

ratio [

-]

PR

and C

R[-

]

Effect number

Forward Feed-TVC- 8 effects system

Compression ratio

Performance ratio

Ts=70 ºC

Effect of changing the location of TVC on the

performance ratio at steam temperature of 80

°Cfor a MED-FF system, N = 8

Effect of changing the location of TVC on the

performance ratio at steam temperature of 70

°C for a MED-FF system, N = 8


Introduction

Objectives

Previous Work Forward Feed Model

Parallel Feed Model

TVC


4

4.2

4.4

4.6

4.8

5

5.2

0 500 1000 1500 2000 2500 3000 3500 4000

Perf

orm

ance r

atio[-

]

Motive steam pressure [Kpa]

Steam temprature of 60 C

Steam temperature of 70 C

Steam temperaturre of 80

Effect of changing motive steam pressure on performance

ratio


Introduction

Objectives


Parallel Feed Model

TVC



Introduction

Objectives


Parallel Feed Model

MVC

http://www.sidem-desalination.com/zoom?media=zoomimg&doc=26716&id=c12238873151-img&src=kit_vwst_rwd

Features:

• Compact

• Independent of

external heating source

• Remote areas,

operated by Diesel

engine, wind turbine….

http://www.sidem-desalination.com/zoom?media=zoomimg&doc=26716&id=c12238873151-img&src=kit_vwst_rwd



Introduction

Objectives


Parallel Feed Model

MVC

(1)(1) (2)(2) (3)(3)(n)(n)

C1

C2

The First Mechanical Compressor

The second Mechanical Compressor

Compressed Vapor

Distillate md

Brine mb

Feed

mf , Tcw

Feed seawater

mf, Tcw

Flashing Box

Extraction

PROPOSED

Patent Disclosed



Introduction

Objectives


Parallel Feed Model

MVC

Patent Disclosed

This addition improves the system performance

through

• Effective heating of the sprayed seawater in the first

effect

• Generating more vapor that may eventually increase the

system productivity

• Reduced specific power consumption

Is there a best location for secondary compressor??



Introduction

Objectives


Parallel Feed Model

MVC

0 0.2 0.4 0.6 0.8 17

8

9

10

11

12

Extraction

Sp

ecif

ic p

ow

er

co

nsu

mp

tio

n (

kw

h/m

^3)

E.1E.1

E.2E.2

E.3E.3

E.4E.4

E.5E.5

n = 6

without Extractionwithout Extraction

0 0.2 0.4 0.6 0.8 16

7

8

9

Extraction

Sep

cif

ic p

ow

er

Co

nsu

mp

tio

n (

Kw

h/m

^3)

E. 2E. 2

E. 3E. 3

E. 4E. 4

E.5E.5

E.6E.6

E.7E.7

without Extractionwithout Extraction

E.1E.1

n = 8

Change in the consumed power for the parallel feed

(MED-MVC) with Extraction for n = 6,8 effects.

11/2/2017 29

• TVC increases PR of the system and reduces the specific

cooling water flow rate.

• Changing the position of the ejector affects the Performance ratio

and the specific cooling water flow rate

• However, the best performance occurs for wide range of heating

steam temperature when the ejector is situated in the middle

• Increasing the number of effects increases the second law

efficiency.


Introduction

Objectives

Previous Work Forward Feed Model MVC

11/2/2017 30

• Adding a secondary compressor improves Performance of MED-

MVC-PF desalination system by about 10%.

• Decrease in the vapor specific volume at higher operating

temperature reduction in specific power for vapor compression.

• Extracting formed vapor from the middle effect (n/2) results in a best

for the system performance.

• Insignificant effect of extraction rate on the specific heat transfer

area.


Introduction

Objectives

Previous Work Forward Feed Model Remarks

11/2/2017 31

Date post:	31-Mar-2018
Category:	Documents
Upload:	lydat
View:	220 times
Download:	2 times

Water Desalination Through MED-TVC -...

Documents