Thermodynamic optimization of a triple-shaft open intercooled, recuperated gas turbine cycle. Part 2: power and efficiency optimization
International Journal of Low-Carbon Technologies
Wenhua Wang
Lingen Chen
Fengrui Sun
The power and the efficiency of a triple-shaft open intercooled, recuperated gas turbine cycle are analyzed and optimized based on the model established using thermodynamic optimization theory in Part 1 of this paper by adjusting the low-pressure compressor inlet relative pressure drop, the mass flow rate and the distribution of pressure losses along the flow path. First, the power output is optimized by adjusting the intercooling pressure ratio, the air mass flow rate or the distribution of pressure losses along the flow path. Second, the thermodynamic first-law efficiency is optimized subject to a fixed fuel flow rate and a fixed overall size by seeking the optimal intercooling pressure ratio, the compressor inlet pressure drop and optimal flow area allocation ratio between the low-pressure compressor inlet and the power turbine outlet. The numerical examples show that increase in effectiveness of intercooler increases power output and its corresponding efficiency and increase in effectiveness of recuperator decreases power output appreciably but increases its corresponding efficiency; there exist an optimal low-pressure compressor inlet relative pressure drop and an optimal intercooling pressure ratio, which lead to a maximum power. For a fixed fuel mass rate and a fixed overall area of low-pressure compressor inlet and power turbine outlet, maximum thermodynamic first-law efficiency is obtained by optimizing low-pressure compressor inlet relative pressure drop and intercooling pressure ratio. The double-maximum thermodynamic firstlaw efficiency is obtained by searching optimal flow area allocation between low-pressure compressor inlet and power turbine outlet.
gas turbine cycle; intercooled; recuperated cycle; power; efficiency; thermodynamic optimization
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*Corresponding author.
or
1 INTRODUCTION
A thermodynamic model for open-cycle intercooled, recuperated
(ICR) gas turbine is established using thermodynamic optimization
theory in Part 1 [1] of this paper based on Refs. [2 – 9]. The
analytical formulae about the relations between power output, thermal
conversion efficiency and the low-pressure compressor pressure
ratio are derived with 19 pressure drop losses in the intake,
low-pressure compression, intercooling, high-pressure
compression, recuperation, combustion, expansion, recuperation and
discharge processes, and flow process in the piping, the heat transfer
loss to ambient, the irreversible compression and expansion losses
in the compressors and the turbines, and the irreversible
combustion loss in the combustion chamber. The power output and
thermal conversion efficiency will be analyzed and optimized by
using the similar principle and method used in Refs. [2 – 9] in this
part. The principle of optimally tuning the air flow rate and
subsequent distribution of pressure drops [10–14] was used.
The power output is optimized by adjusting the intercooling
pressure ratio, the air mass flow rate or the distribution of
pressure losses along the flow path. The thermodynamic first-law
efficiency is optimized subject to a fixed fuel flow rate and a fixed
overall size by seeking the optimal intercooling pressure ratio, the
compressor inlet pressure drop and optimal flow area allocation
ratio between the low-pressure compressor inlet and the power
turbine outlet. The numerical examples show the effects of design
parameters on the power output and heat conversion efficiency.
2 POWER OPTIMIZATION
The effects of the intercooling pressure ratio, the air mass flow
rate and pressure drops on the net power output are examined
by numerical examples. According to analyses in Refs. [2, 4], the
range covered in the calculations is 0 f1 0.5, 5 p 42,
1.8 p1 p, T0 ¼ 288 K, t ¼ 5, hLC ¼ 0.84, hHC ¼ 0.85, hB ¼
0.97 and hHT ¼ hLT ¼ hPT ¼ 0.89, and the range covered in the
ratio of the extreme flow cross-sections (low-pressure
compressor inlet/power turbine outlet) is 0.25 a1 – 7 4, where a1 – 7 is
the dimensionless group,
K7 1=2
Ki 1=2
ði ¼ 2; 21; 3; 31; 4; 5; 6; 71Þ:
In the calculations, a1 – 2 ¼ a1 – 21 ¼ a1 – 3 ¼ a1 – 31 ¼ 1/3,
a1 – 4 ¼ 1/2, a1 – 7 ¼ 1/3 and a1 – 71 ¼ 1/2 are set which means that
A2, A21, A3, A31, A4, A7 and A71 vary in proportion with A1 (or x)
during the optimization process, when x varies between 0 and 1.
Detail numerical calculations indicate that there exists an
optimal intercooling pressure ratio ðp1ÞPopt ; which leads to an
optimal power output Popt: Figure 1 illustrates the characteristics
of Popt and its corresponding efficiency hPopt ; intercooling
pressure ðp1ÞPopt ; heat absorbed by the working fluid QPopt and excess
air ratio lPopt versus the low-pressure compressor relative
pressure drop f1. It shows there exists an optimal compressor inlet
pressure drop ðf1ÞPmax ; which leads to a maximum net power
output Pmax and its corresponding efficiency hPmax ; intercooling
pressure ðp1ÞPmax ; heat abso (...truncated)