Maximum overall efficiency for a solar-driven gas turbine power plant

Abstract

SUMMARY A general model for an irreversible solar‐driven Brayton multi‐step heat engine is presented. The model incorporates an arbitrary number of turbines (Nt) and compressors (Nc) and the corresponding reheating and intercooling processes; thus, the solar‐driven Ericsson cycle is a particular case where Nt, Nc → ∞. For the solar collector, we assume linear heat losses, and for the Brayton multi‐step cycle, we consider irreversibilities arising from the non‐ideal behavior of turbines and compressors, pressure drops in the heat input and heat release, heat leakage through the plant to the surroundings, and non‐ideal couplings of the working fluid with the external heat reservoirs. We obtain the collector temperatures at which maximum overall efficiency ηmax is reached as a function of the thermal plant pressure ratio, and a detailed comparison for several plant configurations is given. This maximum efficiency is obtained in two cases: when only internal irreversibilities are considered and when both internal and external irreversibilities (which corresponds to the fully irreversible realistic situation) are simultaneously taken into account. Differences between both situations are stressed in detail. In the fully irreversible realistic case, it is possible to perform an additional optimization with respect to the pressure ratio, ηmax∗. In particular, this double optimization leads to a valuable increase in efficiency (between 34% and 65%) for a plant with two turbines and two compressors compared to the simple solar‐driven one‐turbine one‐compressor Brayton engine. Copyright © 2012 John Wiley & Sons, Ltd.

Performance Optimization of a Solar-Driven Multi-Step Irreversible Brayton Cycle Based on a Multi-Objective Genetic Algorithm

“…As illustrated in Table 1, the deviation indices of the multi-objective optimization method throughout the current study are 0.4159, 0.4253 and 0.4562 for outcomes that were gained by utilizing the FUZZY, LINMAP and TOPSIS decision-makers, correspondingly. These values are analogous with the relevant value gained previously by performing the single objective-single variable optimization approach [56,59] where the deviation index is 0.4785. This indicates that the deviation indices of the single objective-single variable optimization are greater than the multi-objectivemulti-variable optimization for all decision-makers while the ideal deviation index is zero.…”

“…Table 1 demonstrates results gained from the aforementioned decision-makers for the solar-driven multi-step irreversible Brayton cycle and outcomes described by Sa´nchez-Orgaz et al [56,59]. For better grasp regarding the situation of different outcomes gained here in contrast with the outcome of the single objective-single variable approach [56,59], a deviation index which determines the deviation of each outcome from the ideal outcome is introduced here:…”

“…Thanks to this consideration, in our approach, the effective energy attributed to the heat engine, _ Q H , and the solar collector's efficiency, g s , can be formulated as following as [56,58,59]:…”

“…Furthermore, it can be formulated as nðs À 1Þ, in which n ¼ C i =C w stands for the internal conductance ratio of the plant in terms of the working fluid and C i represents the power plant internal conductance [6, 35,56,59]. Equations (3) and (4) express the Brayton heat engine efficiency for heat release and heat input, correspondingly…”

“…GA a can be formulated as the product of the effectiveness of the Brayton heat engine with multi-step and of the solar collector [30, 56,59]:…”