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Exergy Analysis and Optimization of Multi-effect Distillation with Thermal Vapor Compression System of Bandar Abbas Thermal Power Plant Using Genetic Algorithm

  • Jamshid KhorshidiEmail author
  • Nafiseh Sardari Pour
  • Taleb Zarei
Research Paper
  • 97 Downloads

Abstract

Multi-effect distillation desalination system with thermal vapor compression is one of the systems of producing fresh water based on distillation desalination. This type of desalination system is one of the most appropriate and economic types of desalination systems for low to high capacities of seawater and brackish water in which evaporation and distillation have occurred in a vacuum and in temperature below 70 °C. This research provides a mathematical model in the steady-state conditions for multi-effect distillation desalination system with thermal vapor compression in Bandar Abbas thermal power plant in south of Iran. The genetic algorithm is used for maximizing the produced fresh water and minimizing total exergy destruction rate. Exergy analysis shows that the thermo-compressor and effects are the main sources of exergy destruction in the system (more than 80%). The actual operating data in summer and winter were used for the exergy destruction study. The results show that the exergy destruction in winter is more than summer. Parametric analysis for studying the effects of key parameters shows that increasing the top brine temperature leads to increase in the total exergy destruction of the system. The optimization of the system with two-target genetic algorithm causes distillate production to increase by 16.62%, and the total exergy destruction rate decreases by 3.58%.

Keywords

Desalination Multi-effect distillation Exergy Irreversibility Genetic algorithm 

List of symbols

\( B \)

Brine flow rate (kg/s)

BPE

Boiling point elevation (°C)

\( C \)

Specific heat capacity of water (kJ/kgK)

\( {\text{CR}} \)

Compression ratio

Di

Distillate (kg/s)

di

Flash vapor flow rate (kg/s)

E

Exergy

\( E_{{{\text{D}},{\text{c}}}} \)

Exergy destruction rate of component (kW)

\( E_{{{\text{D}},{\text{t}}}} \)

Total exergy destruction rate (kW)

\( E_{\text{SD}} \)

Specific exergy destruction (kJ/kg)

\( {\text{ER}} \)

Expansion ratio

Fi

Feed water flow rate (kg/s)

\( {\text{GOR}} \)

Gain output ratio

\( h_{\text{d}} \)

Enthalpy of the discharge steam (kJ/kg)

\( h_{\text{fs}} \)

Saturated liquid enthalpy (kJ/kg)

\( h_{\text{ev}} \)

Enthalpy of the Entrained vapor (kJ/kg)

\( h_{\text{m}} \)

Motive steam enthalpy (kJ/kg)

\( h_{\text{s}} \)

Input steam enthalpy to first effect (kJ/kg)

\( h_{\text{w}} \)

Enthalpy of Spray water (kJ/kg)

h0

Environment state enthalpy (kJ/kg)

L

Latent heat (kJ/kg)

\( M_{\text{c}} \)

Condenser vapor flow rate (kg/s)

\( M_{\text{cw}} \)

Cooling water flow rate (kg/s)

\( M_{\text{d}} \)

Discharge steam flow rate (kg/s)

\( M_{\text{ev}} \)

Entrained vapor flow rate (kg/s)

\( M_{\text{m}} \)

Motive steam flow rate (kg/s)

Ms

Input steam flow rate to first effect (kg/s)

\( M_{\text{sw}} \)

Seawater flow rate (kg/s)

NEA

Non-equilibrium allowance

n

Number of effects

PCF

Pressure correction factor

\( P_{\text{d}} \)

Discharged vapor pressure (kPa)

\( P_{\text{ev}} \)

Entrained vapor pressure (kPa)

\( P_{\text{m}} \)

Motive steam pressure (kPa)

\( P_{\text{s}} \)

Input steam pressure to first effect (kPa)

\( Q_{\text{d}} \)

Specific heat consumption (kJ/kg)

Ra

Entertainment ratio

\( s_{\text{ev}} \)

Entrained vapor entropy (kJ/kgK)

\( s_{\text{fs}} \)

Condensate vapor entropy (kJ/kgK)

ss

Input steam entropy to first effect (kJ/kgK)

TBT

Top brine temperature

TCF

Temperature correction factor

\( T_{\text{d}} \)

Discharge steam temperature (°C)

\( T_{\text{ev}} \)

Entrained vapor temperature (°C)

\( T_{\text{f}} \)

Feed water temperature (°C)

Ti

Effect temperature (°C)

\( T_{\text{m}} \)

Motive steam temperature (°C)

\( T_{\text{s}} \)

Input steam temperature to first effect (°C)

\( T_{\text{sw}} \)

Seawater temperature (°C)

\( T_{{{\text{v}},i}} \)

Output vapor temperature from effect (°C)

T0

Dead state temperature (K)

\( \Delta T \)

Temperature difference per effect (°C)

\( X_{{{\text{b}},i}} \)

Brine salinity (g/kg)

\( X_{\text{f}} \)

Seawater salinity (g/kg)

Greek symbols

ψ

Exergy efficiency

δ

Exergy destruction rate

Subscripts

b

Brine

c

Condenser

D

Destruction

d

Discharge steam

de

Desuperheater

dis

Distillate

e

Effect

ej

Ejector

ev

Entrained vapor

f

Feed

in

Input

m

Motive steam

out

Output

rej

Rejection

s

Input vapor to first effect

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Copyright information

© Shiraz University 2018

Authors and Affiliations

  • Jamshid Khorshidi
    • 1
    Email author
  • Nafiseh Sardari Pour
    • 1
  • Taleb Zarei
    • 1
  1. 1.Department of Mechanical EngineeringUniversity of HormozganBandar AbbasIran

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