Energy and exergy analyses of an externally fired gas turbine (EFGT) cycle integrated with biomass gasifier for distributed power generation

Biomass based decentralized power generation using externally fired gas turbine (EFGT) can be a technically feasible option. In this work, thermal performance and sizing of such plants have been analyzed at different cycle pressure ratio (r_p = 2−8), turbine inlet temperature (TIT = 1050–1350 K) and the heat exchanger cold end temperature difference (CETD = 200–300 K). It is found that the thermal efficiency of the EFGT plant reaches a maximum at an optimum pressure ratio depending upon the TIT and heat exchanger CETD. For a particular pressure ratio, thermal efficiency increases either with the increase in TIT or with the decrease in heat exchanger CETD. The specific air flow, associated with the size of the plant equipment, decreases with the increase in pressure ratio. This decrease is rapid at the lower end of the pressure ratio (r_p < 4) but levels-off at higher r_p values. An increase in the TIT reduces the specific air flow, while a change in the heat exchanger CETD has no influence on it. Based on this comparison, the performance of a 100 kW EFGT plant has been analyzed for three sets of operating parameters and a trade-off in the operating condition is reached.     

Turbine startup methods for externally fired micro gas turbine (EFMGT) system using biomass fuels

The concept of external fired micro gas turbine (EFMGT) using biomass fuels is getting more attention in the last two decades. However, most of the studies were conducted using computer simulation to evaluate the EFMGT systems with a lack of experimental studies. A small scale EFMGT was developed using a vehicular turbocharger as a micro gas turbine. Different micro turbine startup methods were experimentally investigated with maximum turbine inlet temperature and pressure of about 694 °C and 2.1 bar, respectively. The difficulties experienced during the turbocharger engine startup process are reported in this paper. Driving the turbocharger shaft from the compressor side using the air flow hydraulic power was not a sufficient method for the EFMGT unlike the directly fired turbine. The only proven turbine startup method for the EFMGT is the mechanically driven turbine shaft.     

Comparative exergoeconomic analyses of the integration of biomass gasification and a gas turbine power plant with and without fogging inlet cooling

Inlet cooling is effective for mitigating the decrease in gas turbine performance during hot and humid summer periods when electrical power demands peak, and steam injection, using steam raised from the turbine exhaust gases in a heat recovery steam generator, is an effective technique for utilizing the hot turbine exhaust gases. Biomass gasification can be integrated with a gas turbine cycle to provide efficient, clean power generation. In the present paper, a gas turbine cycle with fog cooling and steam injection, and integrated with biomass gasification, is proposed and analyzed with energy, exergy and exergoeconomic analyses. The thermodynamic analyses show that increasing the compressor pressure ratio and the gas turbine inlet temperature raises the energy and exergy efficiencies. On the component level, the gas turbine is determined to have the highest exergy efficiency and the combustor the lowest. The exergoeconomic analysis reveals that the proposed cycle has a lower total unit product cost than a similar plant fired by natural gas. However, the relative cost difference and exergoeconomic factor is higher for the proposed cycle than the natural gas fired plant, indicating that the proposed cycle is more costly for producing electricity despite its lower product cost and environmental impact.     

Exergy analysis and optimization of a biomass gasification, solid oxide fuel cell and micro gas turbine hybrid system

A hybrid plant producing combined heat and power (CHP) from biomass by use of a two-stage gasification concept, solid oxide fuel cells (SOFC) and a micro gas turbine was considered for optimization. The hybrid plant represents a sustainable and efficient alternative to conventional decentralized CHP plants. A clean product gas was produced by the demonstrated two-stage gasifier, thus only simple gas conditioning was necessary prior to the SOFC stack. The plant was investigated by thermodynamic modeling combining zero-dimensional component models into complete system-level models. Energy and exergy analyses were applied. Focus in this optimization study was heat management, and the optimization efforts resulted in a substantial gain of approximately 6% in the electrical efficiency of the plant. The optimized hybrid plant produced approximately 290 kW_e at an electrical efficiency of 58.2% based on lower heating value (LHV).     

Thermodynamic characteristics of a low concentration methane catalytic combustion gas turbine

Low concentration methane, emitted from coal mines, landfill, animal waste, etc. into the atmosphere, is not only a greenhouse gas, but also a waste energy source if not utilised. Methane is 23 times more potent than CO₂ in terms of trapping heat in the atmosphere over a timeframe of 100 years. This paper studies a novel lean burn catalytic combustion gas turbine, which can be powered with about 1% methane (volume) in air. When this technology is successfully developed, it can be used not only to mitigate the methane for greenhouse gas reduction, but also to utilise such methane as a clean energy source. This paper presents our study results on the thermodynamic characteristics of this new lean burn catalytic combustion gas turbine system by conducting thermal performance analysis of the turbine cycle. The thermodynamic data including thermal efficiencies and exergy loss of main components of the turbine system are presented under different pressure ratios, turbine inlet temperatures and methane concentrations.     

From biomass and electrolytic hydrogen to substitute natural gas and power: The issue of intermediate gas storages

The possibility to upgrade biomass and intermittent power from renewable energy sources generating stable power and substitute natural gas (SNG) has been discussed in previous papers. Such papers focussed mainly on the choice and design of the most suitable power units to generate power and a high purity carbon dioxide stream to feed the methanation section; moreover, heat recovery strategies to improve the plant efficiency were investigated and implemented. In the proposed plant, power for electrolysis potentially comes from renewable energy sources (RES), thus arises the need to introduce gas storages in order to fully decouple the outputs (SNG flow and stable electric power) from the input intermittency. This paper analyses some different possible layouts for intermediate gas storages and compares them from an energy consumption point of view.     

Energy and exergy analysis of internal reforming solid oxide fuel cell–gas turbine hybrid system

The aim of this work is to analyze methane-fed internal reforming solid oxide fuel cell–gas turbine (IRSOFC—GT) power generation system based on the first and second law of thermodynamics. Exergy analysis is used to indicate the thermodynamic losses in each unit and to assess the work potentials of the streams of matter and of heat interactions. The system consists of a prereformer, a SOFC stack, a combustor, a turbine, a fuel compressor and air compressor, recuperators and a heat recovery steam generator (HRSG). A parametric study is also performed to evaluate the effect of various parameters such as fuel flow rate, air flow rate, temperature and pressure on system performance.     

Operation window and part-load performance study of a syngas fired gas turbine

Integrated coal gasification combined cycle (IGCC) provides a great opportunity for clean utilization of coal while maintaining the advantage of high energy efficiency brought by gas turbines. A challenging problem arising from the integration of an existing gas turbine to an IGCC system is the performance change of the gas turbine due to the shift of fuel from natural gas to synthesis gas, or syngas, mainly consisting of carbon monoxide and hydrogen. Besides the change of base-load performance, which has been extensively studied, the change of part-load performance is also of great significance for the operation of a gas turbine and an IGCC plant.In this paper, a detailed mathematical model of a syngas fired gas turbine is developed to study its part-load performance. A baseline is firstly established using the part-load performance of a natural gas fired gas turbine, then the part-load performance of the gas turbine running with different compositions of syngas is investigated and compared with the baseline. Particularly, the impacts of the variable inlet guide vane, the degree of fuel dilution, and the degree of air bleed are investigated. Results indicate that insufficient cooling of turbine blades and a reduced compressor surge margin are the major factors that constrain the part-load performance of a syngas fired gas turbine. Results also show that air bleed from the compressor can greatly improve the working condition of a syngas fired gas turbine, especially for those fired with low lower heating value syngas. The regulating strategy of a syngas fired gas turbine should also be adjusted in accordance to the changes of part-load performance, and a reduced scope of constant TAT (turbine exhaust temperature) control mode is required.     

Two new high-performance cycles for gas turbine with air bottoming

The objective of this research is to model steam injection in the gas turbine with Air Bottoming Cycle (ABC). Based on an exergy analysis, a computer program has been developed to investigate improving the performance of an ABC cycle by calculating the irreversibility in the corresponding devices of the system. In this study, we suggest two new cycles where an air bottoming cycle along with the steam injection are used. These cycles are: the Evaporating Gas turbine with Air Bottoming Cycle (EGT-ABC), and Steam Injection Gas turbine with Air Bottoming Cycle (STIG-ABC). The results of the model show that in these cycles, more energy recovery and higher air inlet mass flow rate translate into an increase of the efficiency and output turbine work. The EGT-ABC was found to have a lower irreversibility and higher output work when compared to the STIG-ABC. This is due to the fact that more heat recovery in the regenerator in the EGT-ABC cycle results in a lower exhaust temperature. The extensive modeling performed in this study reveals that, at the same up-cycle pressure ratio and turbine inlet temperature (TIT), a higher overall efficiency can be achieved for the EGT-ABC cycle.     

Thermodynamic optimization for an open cycle of an externally fired micro gas turbine (EFmGT). Part 1: Thermodynamic modelling

The principle of optimally tuning the air flow rate and subsequent distribution of pressure drops is applied to optimize the performance of a thermodynamic model for an open regenerative cycle of an externally fired micro gas turbine power plant with pressure drop irreversibilities by using finite-time thermodynamics and considering the size constraints of the real plant. There are eight flow resistances encountered by the working fluid stream for the cycle model. Two of these, the friction through the blades and vanes of the compressor and the turbine, are related to the isentropic efficiencies. The remaining flow resistances are always present because of the changes in flow cross-section at the compressor inlet and outlet, the turbine inlet and outlet and the regenerator hot/cold-side inlet and outlet. These resistances associated with the flow through various cross-sectional areas are derived as functions of the compressor inlet relative pressure drop, and control the air flow rate and the net power output and thermal efficiency. The analytical formulae for the power output, efficiency and other coefficients are derived, which indicate that the thermodynamic performance for an open regenerative cycle of an externally fired micro gas turbine power plant can be optimized by adjusting the mass flow rate (or the distribution of pressure losses along the flow path). It is shown that there are optimal air mass flow rates (or the distribution of pressure losses along the flow path) which maximize the net power output.     

Modelling of biomass gasifier and microturbine for the olive oil industry

The olive oil industry generates several solid wastes. Among these residues are olive tree leaves, prunings, and dried olive pomace (orujillo) from the extraction process. These renewable energy sources can be used for heat and power production. The aim of this paper consists of modelling and simulation of a small‐scale combined heat and power (CHP) plant (fuelled with olive industry wastes) incorporating a downdraft gasifier, gas cleaning and cooling subsystem, and a microturbine as the power generation unit. The gasifier was modelled with thermodynamic equilibrium calculations (fixed bed type, stratified and with an open top). This gasifier operates at atmospheric pressure with a reaction temperature about 800°C. Simulation results (biomass consumption, gasification efficiency, rated gas flow, calorific value, gas composition, etc.) are compared with a real gasification technology. The product gas obtained has a low heating value (4.8–5.0 MJ Nm^?3) and the CHP system provides 30 kW_e and 60 kW_th. High system overall CHP efficiencies around 50% are achievable with such a system. The proposed system has been modelled using Cycle‐Tempo software^®. Copyright © 2010 John Wiley & Sons, Ltd.     

Prediction of some performance characteristics of shale oil in the gas turbine combustor

Measurements of radiation, smoke and temperature in a developed experimental combustor at various air pressures, inlet temperatures and air-fuel ratios have shown the effects of such fuel properties as volatility, boiling range and H percentage mass content on ignition, lean blow-out, liner temperature and exhaust smoke. This study has been extended to cover some of these performance characteristics for shale oil.     

Second law analysis of a natural gas‐fired gas turbine cogeneration system

The influence of operating conditions such as reheat, intercooling, ambient temperature and pressure ratio are analyzed from a second law perspective on the performance of a natural gas‐fired gas turbine cogeneration system. The effect of these operating parameters on carbon dioxide emissions is also discussed. The second law efficiency of gas turbine cogeneration system increases markedly with reheat option. Higher pressure ratios lead to decreased second law cogeneration efficiency but this effect can be reduced with a higher level of reheat option. The effect of intercooling on second law efficiency is strongly related to pressure ratio with higher pressure ratios significantly decreasing efficiency. The second law efficiency is not so sensitive to the environment temperature for levels of reheat or intercooling greater than 50%. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermodynamic analysis of a tri-generation system based on micro-gas turbine with a steam ejector refrigeration system

In the present work, performance of new configuration of Micro-gas turbine cogeneration and tri-generation systems, with a steam ejector refrigeration system and Heat recovery Steam Generator (HRSG) are studied. A micro-gas turbine cycle produces 200 KW power and exhaust gases of this micro-gas turbine are recovered in an HRSG. The main part of saturated steam in HRSG is used through a steam ejector refrigeration system to produce cooling in summer. In winter, this part of saturated steam is used to produce heating. In the first part of this paper, performance evaluation of this system with respect to Energy Utilization Factor (EUF), Fuel Energy Saving Ratio (FESR), thermal efficiency, pinch point temperature difference, net power to evaporator cooling load and power to heat ratio is carried out. It has been shown that by using the present cogeneration system, one can save fuel consumption from about 23% in summer up to 33% in winter in comparison with separate generation of heating, cooling and electricity.     

Energy and exergy analyses of a combined molten carbonate fuel cell - Gas turbine system

This study deals with the thermodynamic analysis of molten carbonate fuel cell combined with a gas turbine, based on the first- and second-law of thermodynamics. The mass, energy, entropy and exergy balance equations are written and applied to the system and its components. Some parametric studies are performed to investigate the change of system performance through energy and exergy efficiencies with the change of operating conditions. The irreversibilities occuring in different devices of the integrated system are also investigated through the exergy destruction analysis in these devices. The maximum output work of the MCFC is estimated to be 314.3 kW for an operating temperature of 650 °C. The overall energy and exergy efficiencies achieved for this system are 42.89% and 37.75%, respectively.     

Performance comparison of two combined SOFC–gas turbine systems

A necessary step in the use of natural gas (methane) in solid oxide fuel cells (SOFCs) is its preliminary conversion to hydrogen and carbon monoxide. To perform methane conversion within fuel cells and avoid catalyst carbonization the molar ratio between methane and steam (or steam with carbon dioxide) should be 1:2 or higher at the SOFC inlet. In this article two possible technological approaches to provide this desirable ratio in a combined SOFC–gas turbine system are compared. The first approach involves generation of the required steam in the coupled gas turbine cycle. The second (which is more traditional) involves recycling some part of the exhaust gases around the anodes of the SOFC stack.     

Test and evaluation of a solar powered gas turbine system

This paper describes the test and the results of a first prototype solar powered gas turbine system, installed during 2002 in the CESA-1 tower facility at Plataforma Solar de Almería (PSA) in Spain. The main goals of the project were to develop a solar receiver cluster able to provide pressurized air of 1000 °C and solve the problems arising from the coupling of the receivers with a conventional gas turbine to demonstrate the operability of the system. The test set-up consists of the heliostat field of the CESA-1 facility providing the concentrated solar power, a pressurized solar receiver cluster of three modules of 400 kWth each which convert the solar power into heat, and a modified helicopter engine (OST3) with a generator coupled to the grid. The first test phase at PSA started in December 2002 with the goal to reach a temperature level of 800 °C at the combustor air inlet by the integration of solar energy. This objective was achieved by the end of this test phase in March 2003, and the system could be operated at 230 kWe power to grid without major problems. In the second test phase from June 2003 to August 2003 the temperature level was increased to almost 1000 °C. The paper describes the system configuration, the component efficiencies and the operation experiences of the first 100 h of solar operation of this very successful first test of a solar operated Brayton gas turbine system.     

A new approach for enhancing performance of a gas turbine (case study: Khangiran refinery)

There are various methods which are commercially available for turbine air inlet cooling aiming to improve gas turbine efficiency. In this study a new approach has been proposed to improve performance of a gas turbine. The approach has been applied to one of the Khangiran refinery gas turbines. The idea is to cool inlet air of the gas turbine by potential cooling capacity of the refinery natural-gas pressure drop station. The study is part of a comprehensive program aimed to enhance gas turbines performance of the Khangiran gas refinery. The results show that the gas turbine inlet air temperature could be reduced in range of 4–25 K and the performance could be improved in range of 1.5–5% for almost 10 months.     

Energy,exergy, and sustainability a novel comparison of conventional gas turbine with fuel cell integrated hybrid power cycle

In this paper, six novel modified exergy relations are explored to determine the precise estimation of exergy destruction and to identify which component has the most improvement potential. For this, three power generation cycles are considered, i.e., simple gas turbine (SGT), recuperated gas turbine (RGT), are compared with a novel hybrid system (SOFC-RGT: Solid Oxide Fuel Cell-RGT), which operates with fuel flexibility as well as enhanced work-output and thermal efficiency. For energy, exergy, and sustainability studies, numerical modeling is conducted using MATLAB. At r_p = 4, TIT = 1250 K, an exclusive comparison has been made between proposed configurations based on thermodynamic modeling and exergy-based sustainability index. It is found that with the inclusion of a recuperator and a fuel cell in the proposed cycles, the thermal and sustainability performance tend to increase significantly. Whereas, exergy destruction increases but has minimal impact on comparing thermal performance and sustainability index. In terms of sustainability, RGT is 30.76% more sustainable than SGT, while SOFC-GT is 63.39% more sustainable than RGT.     

Some trends and progress in gas turbine technology and research

Gas turbine technology is witnessing continuous advances in its major components. In this work, a brief coverage is provided for the relative merits of the engine and major trade-offs in research and development, with special emphasis on current areas of combustion research. Combustor durability, as related to liner temperature, is tackled more thoroughly by briefly presenting some results of experimental research and modelling efforts relevant to typical tubular, annular and cannular gas turbine combustors.