STIG Cycle Research Articles

Thermodynamic analysis of the thermal and exergetic performance of a mixed gas-steam aero derivative gas turbine engine for power generation

A thermodynamic analysis is performed for an aero derivative gas turbine engine which utilizes steam injection to increase its efficiency. The target was to explore the performance of a high efficiency gas turbine unit for electric power generation without downstream Rankine cycle. A Rankine cycle for exhaust heat recovery is unattractive because of its large response time and cost of investment. The main purpose of this research was to develop a better understanding of how the optimal cycle efficiency is reached, when the steam for injection is generated by use of the turbine exhaust heat. The STIG cycle becomes attractive for grid stabilization because of its low CAPEX and small footprint and response time.A thermodynamic model has been developed to simulate the simple cycle gas turbine, steam generation and effects of steam injection. Reference input parameters for the model are taken for the GE LM6000 turbine as publicly available. The performance of the engine without steam injection as predicted by the model is compared with literature for validation and compares well.The performance of the STIG cycle as a function of operation parameter steam mass flow and design parameters pressure ratio and turbine inlet temperature is investigated and the optimal parameter settings determined. It is found that this type of cycle shows a very specific parameter setting for optimal efficiency. By using steam injection for the chosen turbine and its parameters an efficiency gain of around 11% points and an output power augmentation of 45% can be achieved.

Exergy Analysis of a Single-Shaft Gas Turbine Power Plant with Steam Injection

Exergy analysis has been performed on a single-shaft gas turbine with steam injection upstream (STIG) of the combustion chamber. The analysis will be performed to study the effect of increasing of compressor inlet temperature O1T design compressor pressure ratio cd PR and turbine inlet temperature O3T on the exergy destruction of STIG cycle components. For a specific value of steam mass flow rate: the increasing in O1T has a worthless effect on the exergy destruction of compressor and turbine while leads to increase in the exergy destruction of the combustion chamber. The increasing in cd PR leads to increase in the exergy destruction for all gas turbine power plant components. The increasing in O3 T leads to decrease in the exergy destruction of the combustion chamber, increase in the exergy destruction of the turbine, while has a worthless effect on the compressor. The biggest exergy destruction occurs in the combustion chamber For a specific values of O1T , cd PR , and O3 T steam injection will lead to improve the exergy destruction of the the combustion chamber, while has a reverse effect on the turbine, and has no effect on the compressor.

Thermoenvironomic evaluation of simple, intercooled, STIG, and ISTIG cycles

Low-technology cycle modifications available for improving gas turbine performance are still largely unexploited. Among those proven modifications, steam injection is found to be the most effective in boosting both the output capacity and thermal efficiency while reducing NOx emissions. It further improves part load performance under varying ambient conditions. Intercooling is another low-technology modification which can improve performance of simple and steam injected gas turbine cycles. Because of the uncertainties relating to an efficiency comparison of steam injected and simple cycle designs, the decision as to whether it is worthwhile to give more emphasis to steam injected cycles should be made on grounds other than efficiency alone. Therefore, this study comparatively evaluates simple, intercooled, steam injected (STIG), and intercooled steam injected (ISTIG) gas turbine cycles from the points of efficiency, network output, economics, and pollutant emissions using an advanced validated thermoenvironomic model. Optimum cycle parameters are investigated. Economic feasibility of steam injection and intercooling on simple and intercooled cycles are evaluated using an updated plant cost data. Total and environmental costs as well as profit of the plant owner are estimated for varying fuel costs and varying cycle parameters such as pressure, steam injection, and equivalence ratio. Results of our analysis based on the characteristic cycle parameters show that network output increases up to 22.2% and 14% respectively, when steam injection is implemented on simple and intercooled gas turbine cycles which correspond to up to 6.7% and 4.4% decrease in specific fuel consumption. Steam injection decreases NOx emissions of simple and intercooled cycles up to 67.2% and 65.2% respectively, and provides up to approximately 126.3% increase in net profit of intercooled cycle at the expense of an increase in total cost by 3.3%.

Control Strategies of Steam-injected Gas Turbine in CCHP System

Abstract In order to relieve energy crisis, more and more distributed energy systems are established and a large number of them use gas turbine as power units. For the in-depth study on the performances of steam injected gas turbine (STIG), the results and discussion show that STIG operation can increase power output and efficiency of generating unit compared with conventional gas turbine. The combined cooling heating and power (CCHP) system with STIG which can adjust the ratio of heat to power elastically and independently, has the ability of accommodating a wider range of electrical loads. The overall off-design characteristics of STIG are obtained using analytical method. For STIG cycle, each operating point is determined by the ratio of steam to air and the turbine inlet temperature calculated by monitoring the turbine outlet temperature. The results present the equal power output curve and equal quantity of heat curve that are meaningful for optimizing operation of CCHP system which works under the off-design conditions.

Thermodynamic, environmental and economic performance optimization of simple, regenerative, STIG and RSTIG gas turbine cycles

Regeneration and steam injection are both well proven as well as promising modifications which can boost power, increase thermal efficiency, part load performance and limit NOx emissions. However, their benefits are still largely unexploited. To investigate these modifications, a comprehensive but practical model is established as an essential improvement on the air standard models. Our multipronged modeling approach enables simultaneous monitoring and optimization of thermodynamic, economic and environmental performance. Additionally, it provides a more accurate analysis by using specifically calculated thermodynamic properties, precisely calculated adiabatic flame temperature, a realistic definition of regenerator effectiveness coefficient and updated cost parameters. Simulating this improved model, a detailed parametrical analysis of steam injected and regenerative gas turbine cycles is performed for varying pressure, steam injection and equivalence ratios. Optimal operating parameters are investigated considering the state of the art cycle parameters and component efficiencies along with non-equilibrium NOx and CO emissions. Contradictory traits of steam injection and regeneration as well as their combinations are presented and comparatively discussed. Conditions of maximum economic profit are demonstrated regarding the up-to-date equipment cost data and escalations in fuel prices. We suggest, this study will contribute to optimization of novel and future gas turbine designs and applications.

Thermodynamic Analysis on Steam Injected Gas Turbine cycle

This paper presents thermodynamic methodology for the performance evaluation of steam injected gas turbine(STIG) cycle. The effects of pressure ratio, turbine inlet temperature and specific mass flow rate of steam per kg of air used in the thermodynamic analysis of steam injected gas turbine(STIG) cycle on thermal efficiency of the cycle, specific work output and specific fuel consumption have been investigated. From the results obtained in graphs it is observed that thermal efficiency of steam injected gas turbine(STIG) cycle increases and net work output increases and specific fuel consumption decreases as pressure ratio increases; thermal efficiency of steam injected gas turbine(STIG) cycle and specific work output increases with increase in turbine inlet temperature. Results also show that STIG cycle efficiency is always greater than simple gas turbine cycle for same pressure ratio and turbine inlet temperature and for wide range of parameters STIG cycle is superior to simple gas turbine cycle. In STIG cycle as specific mass flow rate per kg of air increases cycle efficiency and net work output also increases.

Performance analysis of a partial oxidation steam injected gas turbine cycle

Partial oxidation gas turbine (POGT) has great potential in improving efficiency because of staged releasing of the chemical energy of fuel. Several researchers have studied the applications of POGT in repowering of different existing power plants. In this study, the POGT is integrated with a steam injected gas turbine (STIG) cycle. This research evaluated the overall thermodynamic performance of a partial oxidation steam injected gas turbine (POSTIG) cycle and investigated the influences of key variables. In addition, comparisons with the STIG cycle were conducted based on exergy analysis. Results show that the combustor outlet temperature of the bottoming gas turbine cycle, the pressure ratio of the bottoming gas turbine cycle compressor, and the temperature of partial oxidation affected the efficiency and specific work output of the POSTIG cycle obviously. Compared with the simple gas turbine cycle, the oxygen concentration in the combustor outlet gas of the POSTIG cycle decreases significantly, and the cooling flow rate increases. Efficiency of the POSTIG cycle is at least two percentage points higher than that of the STIG cycle because of the production and utilization of higher quality steam, along with lower exergy destruction during the graded release of the fuel's chemical energy.

Performance of the solar hybrid STIG cycle with latent heat storage

Abstract The solar hybrid Steam Injection Gas turbine (STIG) cycle uses both recuperated heat and solar heat in order to generate steam at a low temperature and pressure, and inject it into the cycle in order to augment the power output. This work addresses the addition of thermal energy storage to allow operation from solar energy beyond the daylight hours. An annual performance analysis of the Solar STIG cycle with latent heat phase change material (PCM) storage is presented for the climatic conditions of Sede Boqer, Israel. We show that the heat transfer limitation present in a real PCM storage leads to a slight performance penalty only compared to an ideal storage. We also analyze the impact of shifting electricity generation from daytime to evening, which can lead to a surprisingly high contribution of the thermal storage. Results show annual solar fraction of up to 35.2%. The annual solar to electricity efficiency was 20.1% when using the recuperated Brayton cycle as reference, and 13.9% for an optimal conventional STIG cycle as reference. These values are similar to or higher than the annual efficiency of current solar thermal power technologies, even though the hybrid STIG cycle uses low-grade solar heat at 200–280 °C.

Exergy analysis and annual exergetic performance evaluation of solar hybrid STIG (steam injected gas turbine) cycle for Indian conditions

The STIG (steam injected gas turbine) cycle offers a way for increasing the power, efficiency and NOx reduction in gas turbines by injecting steam into the combustor. The present exergetic study is to investigate the influence of compressor PR (pressure ratio), TIT (turbine inlet temperature) and SAR (steam to air ratio) on the solar hybrid STIG cycle. Exergy analysis was performed for four cases based on the parameters of real gas turbines. Annual exergetic performance is also presented for the sites Indore and Jaipur in India under constant and variable power modes. The analysis suggests that the steam injection does not affect the performance of compressor. The total exergy destruction in the cycle increases with SAR and TIT. The exergetic efficiency also increases in the range of 40%–54.2% with SAR up to 0.9. The magnitude of exergy destruction in all components in the cycle (except compressor) increases by increasing SAR. Nevertheless, largest component of exergy destruction in the combustion chamber increases with SAR and TIT about 53% at SAR 0.9. The exergetic efficiency of combustor increases from 74.5% to 81.8% with increasing SAR from 0.3 to 0.9. The exergy destruction in the turbine increases considerably with compressor pressure ratio, sparingly with SAR and independent of TIT. The exergy destruction in the SH (super heater) is less compared to the economiser in the HRSG (heat recovery steam generator). The contribution of solar energy (exergetic solar fraction) is more sensitive to TIT and SAR than PR. It is noticed that increase in turbine outlet temperature, led by PR and TIT, decreases the exergetic solar fraction, and the cycle exergetic efficiency improves as the exergetic solar fraction increases, which leads to an improved performance device. The second largest percentage of exergy destruction is in the flue gas condenser to recover water for recycling, and the heat removed from the condenser is lost to the surroundings by cooling air. The annual values of exergetic solar fraction and exergetic efficiency at Indore are higher than Jaipur in both constant and variable power modes of operation.

Annual performance of the solar hybrid STIG cycle

The solar hybrid Steam Injection Gas turbine (STIG) cycle uses both recuperated heat and solar heat in order to generate steam at a low temperature and pressure, and inject it into the cycle in order to augment the power output. An annual performance analysis of the Solar STIG cycle is presented for sites in Israel and India, with moderate and high annual direct insolation. The cycle operation was simulated in two modes: constant power output and variable power output following the variation of solar input. The solar contribution to the electricity production of the hybrid cycle and the solar to electricity efficiency were calculated, where the conventional reference system was either a conventional STIG or a conventional recuperated Brayton cycle. Results show annual solar fraction of up to 31% in constant power mode and up to 33% in variable power mode. The annual solar to electricity efficiency was in the range of 22–26% when the reference efficiency was based on the recuperated Brayton cycle, and 12–16% when the reference efficiency was based on an optimal conventional STIG cycle. These values are similar to or higher than the annual efficiency of current solar thermal power technologies, even though the hybrid STIG cycle uses low-grade solar heat at only 200°C.

Performance and Water Consumption of the Solar Steam-Injection Gas Turbine Cycle

Solar heat at moderate temperatures around 200 °C can be utilized for augmentation of conventional steam-injection gas turbine power plants. Solar concentrating collectors for such an application can be simpler and less expensive than collectors used for current solar power plants. We perform a thermodynamic analysis of this hybrid cycle, focusing on improved modeling of the combustor and the water recovery condenser. The cycle's water consumption is derived and compared to other power plant technologies. The analysis shows that the performance of the hybrid cycle under the improved model is similar to the results of the previous simplified analysis. The water consumption of the cycle is negative due to water production by combustion, in contrast to other solar power plants that have positive water consumption. The size of the needed condenser is large, and a very low-cost condenser technology is required to make water recovery in the solar STIG cycle technically and economically feasible.

Plasma Fuel Nozzle as a Prospective Way to Plasma-Assisted Combustion

This paper presents the results of development and experimental investigations of a plasma fuel nozzle (PFN) concept as the most prospective tool to realize plasma-assisted combustion in different heat engines. The results of plasma source selection and optimization, fuel atomizer options consideration and comparison, and influence on the combustion process parameters are reported. Experiments show that PFN is the most advanced solution for lean burn and low-Btu fuel combustors, STIG cycle turbines, flexi-fuel systems, and liquid and gaseous feedstock gasification units.

Optimization of cogeneration thermal power units

We present a procedure for comparing the efficiencies of cogeneration thermal power units that takes variable conditions of their operation into account. A combined-cycle plant operating in accordance with the STIG cycle (i.e., with mixing of working fluids), a gas turbine unit equipped with a gas economizer, and a steam turbine unit equipped with a backpressure turbine are compared during their operation as part of a cogeneration station.

Blade cooling optimisation in humid-air and steam-injected gas turbines

Humidified gas turbine cycles such as the humidified air turbine (HAT) and the steam-injected gas turbine (STIG) present exciting new prospects for industrial gas turbine technology, potentially offering greatly increased work outputs and cycle efficiencies at moderate costs. The availability of humidified air or steam in such cycles also presents new opportunities in blade and disk cooling architecture. Here, the blade cooling optimisation of a HAT cycle and a STIG cycle is considered, first by optimising the choice of coolant bleeds for a reference cycle, then by a full parametric optimisation of the cycle to consider a range of optimised designs. It was found that the coolant demand reductions which can be achieved in the HAT cycle using humidified or post-aftercooled coolant are compromised by the increase in the required compression work. Furthermore, full parametric optimisation showed that higher water flow-rates were required to prevent boiling within the system. This corresponded to higher work outputs, but lower cycle efficiencies. When optimising the choice of coolant bleeds in the STIG cycle, it was found that bleeding steam for cooling purposes reduced the steam available for power augmentation and thus compromised work output, but that this could largely be overcome by reducing the steam superheat to give useful cycle efficiency gains.

A Systematic Comparison and Multi-Objective Optimization of Humid Power Cycles—Part I: Thermodynamics

The steam injected gas turbine (STIG), humid air turbine (HAT), and TOP Humid Air Turbine (TOPHAT) cycles lie at the center of the debate on which humid power cycle will deliver optimal performance when applied to an aeroderivative gas turbine and, indeed, when such cycles will be implemented. Of these humid cycles, it has been claimed that the TOPHAT cycle has the highest efficiency and specific work, followed closely by the HAT, and then the STIG cycle. In this study, the systems have been simulated using consistent thermodynamic and economic models for the components and working fluid properties, allowing a consistent and nonbiased appraisal of these systems. Part I of these two papers focuses purely on the thermodynamic performance and the impact of the system parameters on the performance; Part II will study the economic performance. The three humid power systems and up to ten system parameters are optimized using a multi-objective Tabu Search algorithm, developed in the Cambridge Engineering Design Centre.

A Systematic Comparison and Multi-Objective Optimization of Humid Power Cycles—Part II: Economics

The steam injected gas turbine (STIG), humid air turbine (HAT), and TOP Humid Air Turbine (TOPHAT) cycles lie at the center of the debate on which humid power cycle will deliver optimal performance when applied to an aeroderivative gas turbine and, indeed, when such cycles will be implemented. Of these humid cycles, it has been claimed that the TOPHAT cycle has the highest efficiency and specific work, followed closely by the HAT and then the STIG cycle. In this study, the systems have been simulated using consistent thermodynamic and economic models for the components and working fluid properties, allowing a consistent and nonbiased appraisal of these systems. Part I of these two papers focused on the thermodynamic performance and the impact of the system parameters on the performance, Part II studies the economic performance of these cycles. The three humid power systems and up to ten system parameters are optimized using a multi-objective Tabu Search algorithm, developed in the Cambridge Engineering Design Centre.

Performance analysis of combined humidified gas turbine power generation and multi-effect thermal vapor compression desalination systems — Part 1: The desalination unit and its combination with a steam-injected gas turbine power system

Humidified gas turbines (HGT) have been identified as a promising way of producing power. The use of the steam-injected gas turbine (STIG) HGT cycle in a combined power and water desalination system was analyzed using energy and exergy performance criteria. A brief description and rationale of the background of HGT cycles and dual-purpose power and water systems is given. A thermal desalination unit was modeled and analyzed, and the results led to the selection of a multi-effect thermal vapor compression (METVC) unit for producing fresh water from seawater for both general use and humidification; then the performance of a STIG-based combined system was investigated. The analysis performed improved the understanding of the combined STIG power and water desalination process and of ways to improve and optimize it. Some specific conclusions are that: (1) a METVC desalination system is preferred to a multieffect evaporation one when the pressure of the motive steam is high enough, >∼3 bar, to run a steam jet ejector; (2) the steam injection rate in the STIG cycle has a strong effect on water and power production, offering good flexibility for design and operation; (3) higher pressure ratios and higher steam injection rates in the STIG cycle increase power generation, but decrease water production rates, and higher turbine inlet temperatures increased both power and water production; (4) a distinct water production gain can be obtained by recovering the stack gas energy. The results indicate that such dual-purpose systems have good synergy, not only in fuel utilization, but also in operation and design flexibility.

Combinations of solid oxide fuel cell and several enhanced gas turbine cycles

Combined power generation systems with combinations of solid oxide fuel cell (SOFC) and various enhanced gas turbine (GT) cycles were evaluated. In the GT part, steam injected gas turbine (STIG) cycle, GT/steam turbine (ST) combined cycle, and humid air turbine (HAT) cycle were considered. Moreover, additional recuperation was considered by means of air preheating (APH) in the STIG cycle. Effects of operating turbine inlet temperature (TIT) and pressure ratio (PR) on overall system performance were assessed. Although the SOFC–HAT system shows the lowest specific work output compared to other systems, its highest thermal efficiency presents a significant advantage. Furthermore, at high TITs and PRs the SOFC–HAT system gives the best performance in terms of both thermal efficiency and specific work. Results indicate that energy recuperative features in the HAT promote the positive effect of increasing TIT by means of enhancing GT efficiency, leading to the improvement in thermal efficiency of the overall system.

Performance improvement for a simple cycle gas turbine GENSET––a retrofitting example

Due to the serious power shortage in Taiwan, many simple cycle gas turbine generation sets (GENSETs) that were originally designated to serve as peak load units are forced to operate continuously during the entire summer season. The retrofitting projects have been seriously considered to convert these GENSETs (which have the advantage of fast startup, but suffer from low power output and thermal efficiency at high ambient temperature) into more advanced cycle units with higher efficiency and higher output. Among many proven technologies, such as inlet air cooling, intercooling, regeneration, reheating and steam-injection gas turbine (STIG) etc., STIG is found to be one of the most effective in boosting both the output capacity and thermal efficiency. The results from computer simulation indicated that the retrofitting of existing GE Frame 6B simple cycle unit into STIG cycle can boost the output from about 38 to 50 MW, while the generation efficiency can be increased from about 30% to 40%. Besides, the power output of STIG cycle is less sensitive to ambient temperature than that of simple cycle. NO x reduction to less then 25 ppm (when LNG is used) and operating flexibility under variable heat demand could be achieved.

Thermoeconomic analysis of mixed gas–steam cycles

In this paper the direct thermoeconomic analysis approach developed by the authors [ASME Paper 95-CTP-38; ASME Cogen Turbo Power Conference, Wien, 23/25 August, 1995] is applied to the assessment of the thermoeconomic performance of mixed gas–steam cycles such as the steam injected cycle (steam injected gas turbine, STIG), regenerated water injected (RWI) cycle, and humid air turbine (HAT) or evaporative cycle. All the simulations were carried using the thermo-economic modular program (TEMP) code developed at the University of Genoa [ASME Trans., J. Engng. Gas Turbine Power 119 (1997) 885; Thermo-economic and environmental optimisation of energy systems, Tesi di Dottorato, Università di Genova (DIMSET), 1997] and carefully tested here, mainly for the HAT cycle and saturator, using the experimental data provided by the HAT pilot-plant operating at the Lund University, Sweden [Theoretical and experimental evaluation of the EvGT-process, Thesis for Degree of Licentiate in Engineering, Lund Institute of Technology, Sweden, 1999; Evaporative cycles – in theory and in practice, Doctoral Thesis, Lund Institute of Technology, Sweden, 2000]. Three different mixed cycles (STIG, RWI, and HAT) are analysed in detail together with an additional fourth layout proposed by the authors [Thermoeconomic analysis of STIG, RWI and HAT cycles with carbon dioxide (CO 2) emissions penalty, Tesi di laurea, Università di Genova (DIMSET), 2000], named HAWIT, humid air water injection turbine, that appears to be the most attractive solution. The thermoeconomic results of mixed cycles are presented here for the first time in open literature. These results are compared to the data of a conventional two-pressure level combined cycle considered as representative of the state of the art of high efficiency conversion systems. A new representation proposed by the authors [ASME Trans., J. Engng. Gas Turbine Power 122 (2000)], such as cost of electricity versus cycle efficiency or internal rate of return versus electric efficiency, is used to demonstrate the main features of these types of innovative energy plants.