Gas Turbine Thermal Efficiency Research Articles

Performance optimization of a printed circuit heat exchanger for the recuperated gas turbine

To further improve the thermal efficiency of gas turbines, the recuperator needs to be employed and the printed circuit heat exchanger with airfoil fins meets the recuperator's requirements of high heat transfer capacity, low flow resistance, and high reliability. However, the effect of airfoil fin pitches is not clear and the structure optimization method should be developed. In this study, the heat transfer quantity and pressure drop per length of the flue gas in the airfoil channels are numerically investigated under different Reynolds numbers and airfoil fin pitches. The results show that the effect of the airfoil transverse pitch has a great effect on the performance of the flue gas and the heat transfer quantity is increased by 82.39 %–96.08 % when the transverse pitch is decreased from 6.0 mm to 1.2 mm. At the same time, the pressure drop per length is increased to 189.39–842.47 Pa/m. The heat transfer performance is varied not obviously when the airfoil longitudinal pitch is varied from 4 mm to 15 mm. Based on the numerical data, the multiple-objective genetic algorithm combined with the backpropagation neural network is proposed for the performance predictions and optimizations. The corresponding Pareto front is obtained and the technique for order preference by similarity to the ideal solution method is employed to obtain the optimal point. Under the current conditions, the heat transfer quantity of the optimal point is 521.25 kW/m2, which is decreased by 34.5 % compared to the highest value, and the pressure drop per length of the optimal point is 108.45 Pa/m, which is decreased by 85.2 % compared to the highest value.

Heat transfer and flow features of a Bifacial-enhanced U channel

High-performance blade cooling improves turbine inlet temperature and thus promotes thermal efficiency of gas turbine. In the present study, a Bifacial-enhanced U channel used for rotor blade cooling is proposed and studied. The definition of the Bifacial-enhanced U channel is that a rotating U channel with orientation angle of 90° to rotating shaft and covered with ribs on both pressure and suction sides, and that the radial outward flow passage of the channel must locate near the pressure side of a blade, and that the radial inward coolant path must situate close to the suction side of the blade. The heat transfer and flow features of the Bifacial-enhanced U channel are experimentally and numerically studied by transient liquid crystal and Reynolds-averaging Navier–Stokes approaches under constant Re of 16,000 and Ro from 0 to 0.024. The novelties of the work are to research how the ribs play roles and to investigate the interactions of ribs, Coriolis force and bend on the flow field and heat transfer features of the Bifacial-enhanced U channel. Wall Nusselt number ratio distributions, pressure loss and total performance of the channel varied with Ro are obtained and discussed in the study. The results indicate that the Bifacial-enhanced U channel possesses superior heat transfer performance on both pressure and suction sides, which is the source of the “Bifacial-enhanced”. Meanwhile, the application of the Bifacial-enhanced U channel on a rotor blade is demonstrated for the first time, providing a guide for next-generation turbine design.

Numerical investigation on film cooling and aerodynamic performance for gas turbine endwalls with upstream vane-type and cascade-type slots

To further improve the thermal efficiency of gas turbine, the turbine inlet temperature (TIT) increases up to 2000 K, leading to an extremely high heat load on the first-stage vane. Taking into consideration that there are complex endwall secondary flow and the passage vortices which have significant effect on the flow field and thermal behavior near the endwall, it is essential to study the aero-thermal characteristics of endwall and develop efficient endwall cooling approach. In this work, two novel upstream slot structures, referred to as the vane-type slot and cascade-type slot, are proposed, and a comprehensive numerical analysis is conducted to reveal their mechanism and superiority in improving the film cooling and aerodynamic performance of first-stage vane compared with the conventional slot structure. The results indicate that compared with the conventional rectangular straight slot, the coolant jets from two novel slots have a more significant inhibition effect on the development of the endwall secondary flow due to their lower outflow angle and thus higher momentum in streamwise direction, which contributes to reducing the strength of the endwall secondary flow. This is beneficial to provide a lower cascade aerodynamic loss and a higher film cooling effectiveness of the endwall near the suction side leading edge and the higher film cooling effectiveness along the trajectory of the horseshoe vortex on the more downstream region. Moreover, the vane-type slot provides the largest coolant coverage and cooling effectiveness of endwall and the lowest total pressure loss within slot and cascade aerodynamic loss, followed by the cascade-type slot and conventional slot.

Use of high salinity water in a power plant by connecting a direct contact membrane distillation (DCMD) to a steam-injected gas turbine (STIG)

Unlike steam turbines, electricity production in gas turbines is inherently independent of freshwater consumption. However, the thermal efficiency of gas turbines decreases as the temperature of input air increases. As a result, many methods of cooling the inlet air require the use of fresh water. Moreover, when it comes to humid gas turbine technology, the practice of injecting steam or humid air into the turbine to improve its thermal efficiency and output power consumes a substantial amount of freshwater. Therefore, reducing the use of fresh water to enhance the output power and thermal efficiency of gas turbines can be a necessary option, especially in hot and dry regions. Alternatively, considering the significant amounts of waste heat in gas turbines, one solution to reduce fresh water consumption is to connect them to thermal desalination units. However, conventional thermal desalination is only practical for seawater desalination in coastal areas. Therefore, this study explores the possibility of linking a direct contact membrane distillation (DCMD) unit to a Steam-injected gas turbine (STIG), which can use high salinity water sources like reverse osmosis (RO) brine in inland regions. The freshwater generated by the DCMD is used to chill the input air to the compressor and produce steam injected within the turbine. Simulation results show that this connection can raise the net output power by [9 to 17.2] MW and thermal efficiency by [3.3 to 15.6] % for compressor pressure ratios between [5 to 30], when compared to a simple gas turbine.

Flow and Combustion Characteristics of Wave Rotor–Trapped Vortex Combustor System

Breaking through the limit of conventional compression and combustion, wave rotor and trapped vortex combustors are able to improve the thermal efficiency of gas turbines. Detailed two-dimensional numerical simulations based on Ansys Fluent were performed to study the flow and combustion characteristics of the wave rotor–trapped vortex combustor system. The calculated pressure characteristics agree with the experimental results giving a relative error for average pressure of 0.189% at Port 2 and of 0.672% at Port 4. The flow stratification characteristics and the periodic fluctuations were found to benefit the zonal organized combustion in the trapped vortex combustor. For the six cases of different rotor speeds, as the rotor speed increased, the oxygen mass fraction at the combustor inlet rose and then fell. The proportion of exhaust gas recirculation fell at first and then rose, and the combustion mode became unstable with the dominant frequencies of the fluctuations increasing.

Inlet air fogging strategy using natural gas fuel cooling potential for gas turbine power plants

Fogging is an effective cooling system used for gas turbine (GT) inlet air cooling. In this study, three fogging strategies were tested: direct fogging, fogging with a natural gas (NG) heat exchanger (FNGE), and FNGE using a storage tank (FNGET). The discrete phase model (DPM) with the standard k-ω turbulence model was used. A computational parametric study was conducted using the standard k-ω turbulence model on a GT compressor inlet duct to optimize the effect of the FNGET cooling strategy. The effects of duct length, number of nozzles, uniform droplet diameter, and nozzle angle on the compressor inlet air temperature and relative humidity (RH) were examined in this parametric study. A duct with 15 m length, 48 nozzles in each half, 100 μm droplet diameter, and 60° nozzle angle exhibited the maximum decrease in the temperature of the compressor inlet air. The minimum (maximum) reduction in temperature was 5.54 °C (15.77 °C), which was observed at 30 °C (40 °C) ambient dry-bulb temperature (DBT) and 60% (15%) RH. The minimum (maximum) increase in the GT output power was 8.99 MW (26.44 MW), or 3.87% (11.15%), which was under the ambient conditions of 34 °C (30 °C) and 60% (15%) RH. The maximum enhancement in GT thermal efficiency was 1.47%, which occurred under the ambient conditions of 30 °C DBT and 15% RH. The maximum decrease in GT specific fuel consumption (SFC) was 4.30%, which was seen under the ambient conditions of 30 °C and 15% RH. FNGET was the most effective cooling strategy in terms of GT output power, thermal efficiency, and SFC. This novel cooling strategy can be applied to various GT models.

Thermodynamic analysis of gas turbine performance using the enthalpy–entropy approach

The enthalpy–entropy approach, which is a rigorous and accurate method, was used to model the actual cycle of a gas turbine (GT). The constructed GT C# programming language code was used to study the effects of ambient temperature ( T am ), relative humidity (RH), and ambient pressure ( P am ) on GT output parameters. The results of the GT modeling program showed that the maximum (minimum) difference in GT output power ( P GT ) was 1.12% (0.01%) at a T am of 39.7 °C (23.3 °C) compared with the actual output power of El Atf power station. As T am increased from 14 °C to 40 °C, the P GT decreased by 19.01% (18.38%) of nominal GT power (250 MW) at 15% (95%) RH while GT thermal efficiency ( η th ) decreased by 2.3058% (2.4431%) and the specific fuel consumption (SFC) increased by 7.12% (7.59%). The P GT decreased by 0.1497% and 0.7674% with an RH increase from 15% to 95%, respectively. The P GT decreased by 0.03675 and 0.16835 MW while η th decreased by 0.0047% and 0.0243% at T am values of 15 and 40 °C, respectively, when P am was decreased from 1.013 to 0.990 bar. Using the compressor assumptions of each stage increases the humid air pressure by the same value and the efficiency of each stage is the same and equal to the compressor overall efficiency is more logical and leads to accurate results. The compressor isentropic efficiency was not affected by the bleeding air percent according to the assumptions used.

Multi-objective performance optimization and control for gas turbine Part-load operation Energy-saving and NOx emission reduction

This work aims to apply the multi-objective optimization method to gas turbine part-load energy-saving and NOx (Nitrogen Oxides) emission reduction problem. For power generation gas turbines, energy-saving is based on raising the thermal efficiency of the system. This is always based on regulating the variable geometries of the plant. However, in this process, the combustion condition would be changed, which would further change the NOx pollutant emission level. Therefore, in this paper, the conflict between gas turbine thermal efficiency enhancement and NOx emission reduction is discovered and analyzed with a nonlinear model. To solve this multi-objective optimization problem, GA (Genetic Algorithm), a global optimization algorithm, is applied. The two objectives are thermal efficiency for energy-saving and NOx Emission Index (EINOx) for pollution reduction. The fuel mass flow rate and compressor Inlet Guide Vane (IGV) position are the decision variables. Optimization is conducted for 50% to 90% nominal power levels and 5 °C to 25 °C ambient temperatures. With the non-inferior solutions on the Pareto Front and a trade-off decision, the selected gas turbine optimum working point can be obtained with a nonlinear converter module. For 15 °C, 70% nominal power working condition, increasing the fuel mass flow rate by 0.216% and IGV degree by 10.344% can bring a 46.273% reduction of EINOx, with the cost of a 0.212% decline in the thermal efficiency. The sensitivity analysis of the Pareto Frontiers to power level and ambient temperature is carried out. Then the level of energy-saving is analyzed by calculating the cost of fuel, and a trade-off suggestion is given. In the end, the values of the decision variables and objective functions under three trade-off scenarios are calculated and listed in a table, with which the final solution can be decided conveniently according to practical demands.

Impact of Cooling with Thermal Barrier Coatings on Flow Passage in a Gas Turbine

Inlet temperature is vital to the thermal efficiency of gas turbines, which is becoming increasingly important in the context of structural changes in power supplies with more intermittent renewable power sources. Blade cooling is a key method for gas turbines to maintain high inlet temperatures whilst also meeting material temperature limits. However, the implementation of blade cooling within a gas turbine—for instance, thermal barrier coatings (TBCs)—might also change its heat transfer characteristics and lead to challenges in calculating its internal temperature and thermal efficiency. Existing studies have mainly focused on the materials and mechanisms of TBCs and the impact of TBCs on turbine blades. However, these analyses are insufficient for measuring the overall impact of TBCs on turbines. In this study, the impact of TBC thickness on the performance of gas turbines is analyzed. An improved mathematical model for turbine flow passage is proposed, considering the impact of cooling with TBCs. This model has the function of analyzing the impact of TBCs on turbine geometry. By changing the TBCs’ thickness from 0.0005 m to 0.0013 m, its effects on turbine flow passage are quantitatively analyzed using the proposed model. The variation rules of the cooling air ratio, turbine inlet mass flow rate, and turbine flow passage structure within the range of 0.0005 m to 0.0013 m of TBC thicknesses are given.

Review: The flow and heat transfer investigation inside tapered and straight two pass channels with rib turbulators

This paper is a review of the number of experimental and CFD experiments performed with rib turbulators about the heat transfer and the at two pass channel. In respect to achieve higher thermal efficiency of gas turbines, efforts are made to raise the inlet temperature. The secondary fluxes resulting from the rib and U-shaped curvature play an important role enhancing heat transfer in the two pass ribbed channels. The ribs on the internal surface of cooling passage will increase the strength of heat transfer. This paper deals with the effect of tapered and straight two-pass channels with the influence of the variable rib cross-section on flow and heat transfer enhancement

Efficiency Analysis of the Turbine using Calorific Value Parameters for a 10 Megawatt Gas Turbine

This research is based on the thermodynamic performance of a gas turbine power plant. It considered the variation of operating conditions, i.e. the ambient temperature, the compressor outlet temperature, pressure ratio, etc. on the performance of the gas turbine thermal efficiency, turbine work, compressor work, etc. which were derived and analyzed. The Gross (higher) calorific values at constant pressure () heat of combustion in a flow process from state 1 to state 2 was considered and used to analyze our thermal efficiency. The results show that the ambient temperature and air to fuel ratio strongly influence the turbine work, compressor work and thermal efficiency. In addition, the thermal efficiency and power decreases linearly with increase of the ambient temperature. However, the efficiency analyzed when the calorific parameters were considered was higher than the efficiency when the basic thermodynamic theories (first and second law principles) were used. The first ranges between 31% to 33, while the second ranges between 28% to 32% under the same ambient temperature conditions

Experimental investigation of low-temperature organic Rankine cycle using waste heat from gas turbine bearings for different conditions

In power plants, a special type of oil is used for the lubrication and cooling of turbine bearings. The temperature of the cooling oil used for heat extraction from the bearings varies between 78 and 90 °C. Using waste heat from this oil will be a great advantage in terms of heat recovery. The overall thermal efficiency of gas turbine in power plants will also increase using this heat. In the literature, there are studies on organic Rankine cycle systems, but it has been seen that there are no studies on the use of waste heat from gas turbine bearings. In this paper, low-temperature organic Rankine cycle using waste heat from gas turbine bearings for different working conditions was investigated as experimentally. For this purpose, a prototype experiment setup was designed and thermodynamic analyses were carried out experimentally. Experimental organic Rankine cycle system was designed to operate in the temperature range of 78–90 °C using the waste heat in the lubricating oil. R134a was used as the working fluid in the prototype organic Rankine cycle system. The thermal efficiency, turbine expansion ratio and turbine power of the prototype organic Rankine cycle system were determined depending on different waste heat source temperatures and working fluid volumetric flow rates. According to experimental results for prototype organic Rankine cycle system, the highest thermal efficiency, turbine expansion ratio and turbine power are 6.84%, 1.94 and 1.22 kW, respectively, at a waste heat source temperature of 86.5 °C and volumetric flow rate of working fluid is 4.7 L/min.

Lean Operation of a Pulse Detonation Combustor by Fuel Stratification

Abstract Pressure gain combustion is a promising concept to substantially increase the thermal efficiency of gas turbines. One possible implementation that has been frequently investigated is pulse detonation combustors (PDCs), as they permit stable and reliable operation. At the same time, the need for part-load operation and low NOx emissions requires combustion concepts in the lean regime. However, realizing lean combustion is still very challenging in PDCs since the deflagration to detonation transition (DDT) is very sensitive to the reactant composition. This work investigates an approach to realize lean combustion in PDC by applying fuel stratification experimentally. The scope is to find the necessary increase of fuel concentration inside the predetonation chamber to provide reliable DDT with respect to the overall equivalence ratio. Emission measurements in the exhaust of the PDC allow for a quantification of the NOx emissions as a function of the injected fuel profile. A valveless PDC test rig is used, which contains a shock focusing geometry for detonation initiation and is ignited by a spark plug close to the upstream end wall. The subsequent expansion of the burned gas and interaction of the flame front with turbulence leads to the formation of a leading shock inside the predetonation chamber, which is then focused inside a converging-diverging geometry. The successful initiation of a detonation wave by shock focusing is very sensitive to the pressure ratio across the leading shock, which can be influenced by initial pressure, reactant composition and flow velocity. Results reveal that fuel stratification allows for reliable detonation initiation at a global equivalence ratio of φglob=0.65, whereas repeatable successful operation with nonstratified fuel injection is limited to φglob≥0.85.

Aspects of Gas Turbine Thermal Efficiency

Abstract In the family of heat engines, the gas turbine is unique in that it is used to produce two different kinds of useful power. By converting combusted fuel heat into work, a gas turbine engine can produce external shaft power (e.g., to drive a connected electric generator) or jet power (e.g., as a jet engine, to produce thrust forces to propel an aircraft). This means that the gas turbine’s thermodynamic figure of merit, thermal efficiency, is multifaceted, and calls for a nuanced examination.

Effects of Boot-Shaped Rib on Heat Transfer Characteristics of Internal Cooling Turbine Blades

Abstract Gas turbine engine has been widely applied to many heavy industries, such as marine propulsion and aerospace fields. Increasing turbine inlet temperature is one of the major ways to improve the thermal efficiency of gas turbines. Internal cooling for gas turbine cooling system is one of the most commonly used approaches to reduce the temperature of blades by casting various kinds of ribs in serpentine passages to enhance the heat transfer between the coolant and hot surface of gas turbine blades. This paper presents an investigation of the boot-shaped rib design to increase the heat transfer performances in the internal cooling turbine blades for gas turbine engines. By varying the design parameter configuration, the airflow is taken with higher momentum, and the minor vortex being at the front rib is relatively removed. The object of this investigation is increasing the reattachment airflow to the heated wall and reducing the vortex occurring near the rib for improving the performances of heat transfer using three-dimensional (3D) Reynolds-averaged Navier–Stokes (RANS) with the SST model. A parametric study of the boot-shaped rib design was performed using various geometric parameters related to the heel-angle, toe-angle, slope-height, and rib-width to find their effect on the Nusselt number, temperature on the ribbed wall, friction factor ratio of the channel, and thermal performance factor. The numerical results showed that the heat transfer performances are significantly increased with the heel-angle, toe-angle, slope-height, while that remained relatively constant with the rib width.

APPLICATION OF NEWTON – RAPHSON METHOD TO ANALYZE THERMAL EFFICIENCY OF GAS TURBINE BEFORE AND AFTER ENGINE REPLACEMENT

Gas turbine performance is one of the main concerns in the operating of industrial plants. Thermal efficiency is vital to analyze the performance of the gas turbine. This research purpose is to analyze the gas turbine's thermal efficiency after performed engine replacement in one of the gas industries in Kutai Kartanegara, East Kalimantan, Indonesia. The data was taken during the period from August 2017 to July 2018, while engine replacement was performed in February 2018. The data were processed to develop simulation models expressing the characteristics of the equipment. The simulation models were then solved simultaneously using the Newton – Raphson Method. A beneficial advantage of Newton Raphson is that it enables to handle a massive number of data and provides faster iteration compare to other methods. Based on the simulation results, the thermal efficiency before performed engine replacement was 23.43% with a net power of 18.109 MW and fuel consumption of 1.640 Kg/s. Meanwhile, the development of thermal efficiency after performed engine replacement was 28.24% with a net power of 18.597 MW and fuel consumption of 1.397 Kg/s. This indicates that after performing engine replacement, the thermal efficiency increased by 4.81% and saved fuel by 0.243 Kg/s.

Reduction of fuel consumption of a small-scale gas turbine engine with fine bubble fuel

Thermal efficiency of the small-scale gas turbines (SSGTs) is much less than that of large-scale gas turbine. Therefore, improvement of thermal efficiency of SSGTs is very important. In this paper, fine bubble fuel (FBF) which is fuel mixed with air fine bubbles (AFBs) was introduced to SSGT to improve its thermal efficiency. Control fuel (CF) and FBF were tested on a SSGT. Specific fuel consumption (SFC) of the engine can be reduced about 2.6%–5.7% at a maximum and about 1.7%–2.7% as an average by using FBF compared to CF. To validate the effect AFBs on the reduction of fuel consumption (FC), droplet size distribution of CF and FBF injected by a nozzle was measured. It was found that atomization of droplets can be promoted by introducing AFBs to fuel, and D32 can be reduced about 4.4%. However, from the results of a simulation of combustion in the combustion chamber, considerable effect of atomization was not observed. Therefore, the effect of atomization of fuel on the reduction of FC is relatively small, and there are other reasons, such as promotion of diffusive combustion due to air which exists in fuel as AFBs.

Performance prediction of the combined cycle power plant with inlet air heating under part load conditions

A combined cycle power plant with inlet air heating (CCPP-IAH) system is proposed to solve the problems of ice and humidity blockages in winter climate. The performance of the CCPP-IAH system under part load conditions is analyzed via both experimental and simulation methods. The application of the inlet air heating technology significantly improves the part load efficiency and enhances the operational safety of the combined cycle power plant under complex meteorological conditions. Results show that a higher inlet air temperature will contribute a lower gas turbine thermal efficiency for proposed system. However, the heated inlet air by the recovered energy in heat recovery steam generator raises efficiencies for both the heat recovery steam generator and the overall system. The fuel consumption drops by 0.02 kg/s and 0.03 kg/s under the power load of 65% and 80%, respectively. The inlet air humidity decrease to 30% under the heated inlet air temperature of 303 K. Moreover, the exergy destruction for both Brayton cycle part and Rankine cycle part decrease with the inlet air temperature increasing. The daily fossil fuel will raise up to 2.9 ton/day and to 5.1 ton/day under the power load of 65% and 80%, respectively. The annual economic benefit from energy saving is more than $ 5.88 × 105 and the payback period is less than 3 years.

THERMO-ECONOMIC IMPACT FROM USING EXHAUST GASES HEAT LOST FOR POWERING AN ABSORPTION REFRIGERATION SYSTEM USED FOR INLET AIR COOLING OF COMPRESSOR

The heat lost from gas turbine power plants with exhaust gases represents the most important source for lowering its thermal efficiency. Also, the thermal efficiency of gas turbine can be affected significantly by the ambient surrounding temperature. In Basrah, a lot of gas turbine units have been installed during the last period. In this study, the thermal-economic impact of the heat lost from gas turbine power plant (GTPP) to the atmosphere for different ambient temperature is studied. Heat recovery system is used, the heat recovery system is an absorption refrigeration system used for cooling the air inlet to the gas turbine cycle. For combined system gas turbine-refrigeration cycle, the performance and economic analysis are performed. The results shows that as, the output power and thermal efficiency are decreased by 0.97 MW and 0.0726% respectively for each unit temperature rise of the ambient temperature. The used of the absorption chiller would increase the output power by 23.3%. Also, the thermal efficiency increased by 23.35%.

Thermodynamic performance analysis of a solar-assisted distributed system driven by natural gas

Abstract Based on the principle of temperature counterpart and energy cascade utilization a solar-hybird distributed system driven by natural gas is designed. In this paper, the thermal performance and environmental performance of the system are calculated. The results show that the thermal efficiency of gas turbine is significantly increased with the increase of heat collector area, and when the collector area reaches 1949m2 the thermal efficiency of the gas turbine run up to 44.43% and the fuel consumption reduce by 43.5%. Meanwhile, the introduction of solar subsystem makes the system’s environmental performance greatly improved, and when the collector area reaches 1949m2, the CO2 emission reduction reaches 257.5kg/h. The simulation results show that the supplementary way of solar energy and natural gas is an effective method in distributed energy systems.