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Optimization of cold-end system of thermal power plants based on entropy generation minimization

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Abstract

Cold-end systems are heat sinks of thermal power cycles, which have an essential effect on the overall performance of thermal power plants. To enhance the efficiency of thermal power plants, multi-pressure condensers have been applied in some large-capacity thermal power plants. However, little attention has been paid to the optimization of the cold-end system with multi-pressure condensers which have multiple parameters to be identified. Therefore, the design optimization methods of cold-end systems with single- and multi-pressure condensers are developed based on the entropy generation rate, and the genetic algorithm (GA) is used to optimize multiple parameters. Multiple parameters, including heat transfer area of multi-pressure condensers, steam distribution in condensers, and cooling water mass flow rate, are optimized while considering detailed entropy generation rate of the cold-end systems. The results show that the entropy generation rate of the multi-pressure cold-end system is less than that of the single-pressure cold-end system when the total condenser area is constant. Moreover, the economic performance can be improved with the adoption of the multi-pressure cold-end system. When compared with the single-pressure cold-end system, the excess revenues gained by using dual- and quadruple-pressure cold-end systems are 575 and 580 k$/a, respectively.

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Abbreviations

A cond :

The condenser area/m2

A sp :

The area of single-pressure condenser/m2

c cw :

The specific heat capacity of the cooling water/(J·(kg·K)−1)

CC L :

The levelized carrying cost/$

d i :

The tube inner diameter/m

D h :

The hydraulic diameter on the waterside/m

e :

The specific entropy/(kJ·kg−1)

ĖF :

The exergy fuel/kW

ĖD :

The exergy destruction/kW

ĖP :

The exergy product/kW

ĖL,tot :

The exergy loss in the cold-end system/kW

ER:

The excess revenue/$

F :

The cross section of the cooling water mass/m2

h :

The steam enthalpy/(kJ·kg−1)

L sp :

The tube length of single-pressure condenser/m

:

The mass flow rate/(kg·s−1)

s :

The mass flow rate of the steam into condensers/(kg·s−1)

K cond :

The heat transfer coefficient/(W·(m2·°C)−1)

OMCL :

The operating and maintenance cost/$

PEC:

The purchased-equipment cost/$

T :

The temperature/K

T 0 :

The ambient temperature/K

TIC:

The total investment capital/$

:

The heat transfer in the condenser/kW

Ṡg tot :

Entropy generation rate on the cold-end system/(kW·K−1)

Ṡg :

Sentropy generation rate/(kW·K−1)

t s :

The steam saturation temperature/°C

t :

The temperature/°C

v cw :

The velocity of the cooling water/(m·s−1)

η st :

The isentropic efficiency of the turbine/%

Δt :

The cooling water temperature difference/°C

Δt m :

The log mean temperature difference in the condenser/°C

λ :

The flow resistance coefficient on the cooling waterside

ρ cw :

The density/(kg·m−3)

i eff :

Average interest rate/%

r n :

The nominal escalation ratio for OMC/%

r nf :

The nominal escalation ratio for FC/%

n :

Plant economic life/a

RT:

Annual operation hours/(h·a−1)

Load:

Annual capacity factor

φ :

Maintenance factor (OMC/TCI)

C e :

A feed-in tariff/(cent·(kW·h)−1)

ω :

Annual capacity factor

γ :

TCI/ΣPECk

st:

Steam turbine

cond:

Con

pump:

Pump

fdh:

Regenerative heater

cw:

Cooling water

in:

Inlet

out:

Outlet

t:

Theoretical value

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Acknowledgements

This work was supported the National Key R&D Program of China (No. 2018YFB0604405).

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Correspondence to Ming Liu.

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Fu, Y., Zhao, Y., Liu, M. et al. Optimization of cold-end system of thermal power plants based on entropy generation minimization. Front. Energy 16, 956–972 (2022). https://doi.org/10.1007/s11708-021-0785-5

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