**7. Nomenclature**




### **Greek symbols**

116 Efficiency, Performance and Robustness of Gas Turbines

Figure 10 shows the magnitudes of the thermal efficiency, the useful thermal efficiency (equation 35) and the exergetic thermal efficiency (equation 40) for 0 0.5 ≤ ≤

extraction pressure of 3.5 bars. It is clear that utilization of the cooling energy for any

figure. In general, the thermal efficiency weights all thermal energy equally, whilst the exergetic efficiency acknowledges the usefulness of irreversibilities on its quality and quantity. Thus, exergetic efficiency is more suitable for determining the precise power gain ratio. The figure shows also that the useful efficiency whether energetic or exergetic is higher than the corresponding values when wasting the heat exchanger heat rejection *Qout*

In this study a new approach for boosting the power of gas turbine power plants by cooling the intake air is analyzed by the energy and exergy methods. The gas turbine inlet temperature is reduced by mixing chilled air from a Brayton refrigeration cycle and the main intake air stream. The air intake temperature depends on two parameters, the cold air stream temperature from the reverse Brayton cycle and the ambient hot humid air conditions. The energy analysis of the coupled Brayton-reverse Brayton cycles showed that the intake air temperature could be reduced to the ISO standard (15oC) and the gas turbine performance can be improved. This study demonstrated the usefulness of employing exergy analysis and the performance improvement was expressed in terms of generic dimensionless terms, *exergetic power gain ratio* (*PGRex*) and *exergetic thermal efficiency change*

The performance improvement of a GT irreversible cycle of 10 pressure ratio operating in hot weather of 45oC and 43.4% relative humidity was investigated for extraction pressures from 2 to 9 bars and cold to hot air mass rate ratio from 0.1 to 0.5. The results showed that the combustion chamber and the cooling heat exchanger are the main contributors to the exergy destruction terms; the combustion chamber irreversibility was the highest and presented 62 to 85% of the total irreversibility. The heat exchanger comes next with nearly 5 % to 46% of the combustion chamber. The irreversibility of mixing chamber was found to be small compared to other components and can be safely ignored. On basis of the energy analysis the GT power can be boosted up by 19.58 % of the site power, while the exergy analysis limits this value to only 14.66% due to exergy destruction in the components of the plant. The irreversibility can be reduced by optimal design of the combustion chamber, the heat exchanger and selecting optimum operational parameters of the coupled power and

η*th u th* , >η

 and η*ex u ex* , >η

process enhances the use of the input fuel for which

**6. Conclusions** 

(*TECex*) factor.

refrigeration units.

**7. Nomenclature** 

*I*

*E* = total exergy rate, *kW f* = fuel to air ratio

 = rate of exergy destruction, *kW h* = specific enthalpy, *kJ.kg-1*

*cpa* = specific heat of air at constant pressure, *kJ kg-1 K-1 cpg* = specific heat of gas at constant pressure, *kJ kg-1 K-1*  α

and

.

as seen in the


### **Subscripts**



### **Superscripts**

*~* = mean molar value of a property

Energy and Exergy Analysis

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**0**

**5**

*Poland*

**Gas Turbines in Unconventional Applications**

The Chapter presents unconventional gas turbine applications. Firstly some selected non-MAST (Mixed Air and Steam Turbine) solutions are discussed – these are intended for smaller gas turbine systems, where the regenerative heat exchanger supplies energy for an

The gas turbine cycle (Brayton) may be coupled with several other thermal engines (like another Brayton, Diesel, Kalina, and Stirling). Those hybrid systems have several previously

The next section describes hydrogen-fuelled gas turbine solution. Big international programme – WE-NET – is discussed. Several hydrogen-fuelled gas turbine concepts based on those programmes are proposed: Westinghouse, Toshiba, Graz, New Rankine. The section provides description of them all, including specification of possible efficiency values. The development programmes themselves are also reviewed. This part of the text describes also potential combination of a hydrogen-fuelled gas turbine and a nuclear power generation unit

Last section of the chapter discusses integration of a fuel cell into a gas turbine system. High temperature fuel cells can play a role similar to a combustion chamber but simultaneously generating additional power. Fuel cell hybrid systems for both high-temperature types of fuel cells – Solid Oxide Fuel Cell (SOFC) and Molten Carbonate Fuel Cell (MCFC) – are proposed. Additionally, some specific properties of the MCFC can be used to reduce carbon dioxide

Gas turbine systems, particularly combined cycle units, are among the most popular power systems in the modern world. This results from the very fast technical progress allowing to gradually increase the parameters at the turbine inlet as well as unit outputs. There is also a parallel development trend of searching for new unconventional solutions, which would allow to achieve efficiencies higher than enabled by a simple cycle. Scheme of the simple

Internal power *Ni* of a gas turbine can be obtained by an analytical approach by using the relation 1, which is obtained with assumption that the process is real (contained losses) and

cycle process is presented in Fig. 1. Simple cycle efficiency in many cases is too low.

unrecognised advantages. They may find applications in some market niches.

which might be used to cover peak load power demands in a power system.

**1. Introduction**

additional thermal cycle, where it is utilised.

emissions from the gas turbine itself.

working fluid is modelled as semi-ideal gas.

Jarosław Milewski, Krzysztof Badyda and Andrzej Miller *Institute of Heat Engineering at Warsaw University of Technology*

