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Proposing a novel combined cycle for optimal exergy recovery of liquefied natural gas

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Abstract

The effective utilization of the cryogenic exergy associated with liquefied natural gas (LNG) vaporization is important. In this paper, a novel combined power cycle is proposed which utilizes LNG in different ways to enhance the power generation of a power plant. In addition to the direct expansion in the appropriate expander, LNG is used as a low-temperature heat sink for a middle-pressure gas cycle which uses nitrogen as working fluid. Also, LNG is used to cool the inlet air of an open Brayton gas turbine cycle. These measures are accomplished to improve the exergy recovery of LNG. In order to analyze the performance of the system, the influence of several key parameters such as pressure ratio of LNG turbine, ratio of the mass flow rate of LNG to the mass flow rate of air, pressure ratio of different compressors, LNG pressure and inlet pressure of nitrogen compressor, on the thermal efficiency and exergy efficiency of the offered cycle is investigated. Finally, the proposed combined cycle is optimized on the basis of first and second laws of thermodynamics.

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Abbreviations

m :

Mass flow rate (kg/s)

h :

Enthalpy (kJ/kg)

LHV:

Lower heating value (kJ/kg)

T :

Temperature (K)

e :

Specific exergy (kJ/kg)

E :

Exergy (kW)

LA:

Ratio of LNG mass flow rate to air mass flow rate (−)

NA:

Ratio of nitrogen mass flow rate to air mass flow rate (−)

r p :

Pressure ratio (−)

P :

Pressure (MPa)

s :

Specific entropy (kJ/kg-K)

I :

Irreversibility (kW)

W :

Power (kW)

η:

Efficiency (%)

CMB:

Combustion

inlet:

Inlet of device

outlet:

Outlet of device

c :

Cold stream

h :

Hot stream

loss:

Loss

0:

Ambient

fuel:

Fuel

in:

Input

out:

Output

th:

Thermal

ex:

Exergy

s :

Stack

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Authors and Affiliations

  1. Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 84156-83111, Iran

    M. R. Salimpour & M. A. Zahedi

Authors
  1. M. R. Salimpour
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  2. M. A. Zahedi
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Correspondence to M. R. Salimpour.

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Salimpour, M.R., Zahedi, M.A. Proposing a novel combined cycle for optimal exergy recovery of liquefied natural gas. Heat Mass Transfer 48, 1309–1317 (2012). https://doi.org/10.1007/s00231-012-0977-y

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  • DOI: https://doi.org/10.1007/s00231-012-0977-y

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