Open Cycle Gas Turbine Research Articles

Exergy analysis and assessment of performance criteria for compressed air energy storage concepts

Compressed air energy storage (CAES) systems provide power reserve to compensate for intermittent renewable electric energy. The compressed air is stored to drive an open gas turbine. Enthalpy is close to zero at ambient air temperatures, which implies low storage efficiencies of the CAES open gas turbine cycle. Thus, in this project, the characterisation of CAES concepts based on exergy in contrast to enthalpy is discussed. The CAES energy efficiency defined as ηcaes = Wel,G / (Wel,M + Qfuel), resulting in approximately 42% for Huntorf and 54% for McIntosh, is unsuitable for characterizing CAES as an electrical energy storage. Instead, an alternative round trip energy efficiency ηrt4 is presented. An exergy-based counterpart is deemed ideal to evaluate storage properties of CAES. Calculations emphasize the efficient generation characteristics of fuel-driven CAES (e.g., McIntosh with 82% fuel efficiency of the turbine process as compared to a Carnot value of 75%).

Exergy analysis and assessment of performance criteria for compressed air energy storage concepts

Compressed air energy storage (CAES) systems provide power reserve to compensate for intermittent renewable electric energy. The compressed air is stored to drive an open gas turbine. Enthalpy is close to zero at ambient air temperatures, which implies low storage efficiencies of the CAES open gas turbine cycle. Thus, in this project, the characterisation of CAES concepts based on exergy in contrast to enthalpy is discussed. The CAES energy efficiency defined as ηcaes = Wel,G / (Wel,M + Qfuel), resulting in approximately 42% for Huntorf and 54% for McIntosh, is unsuitable for characterizing CAES as an electrical energy storage. Instead, an alternative round trip energy efficiency ηrt4 is presented. An exergy-based counterpart is deemed ideal to evaluate storage properties of CAES. Calculations emphasize the efficient generation characteristics of fuel-driven CAES (e.g., McIntosh with 82% fuel efficiency of the turbine process as compared to a Carnot value of 75%).

Comprehensive Thermodynamic Analysis of the Humphrey Cycle for Gas Turbines with Pressure Gain Combustion

Conventional gas turbines are approaching their efficiency limits and performance gains are becoming increasingly difficult to achieve. Pressure Gain Combustion (PGC) has emerged as a very promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine thermodynamic cycles. Up to date, only very simplified models of open cycle gas turbines with pressure gain combustion have been considered. However, the integration of a fundamentally different combustion technology will be inherently connected with additional losses. Entropy generation in the combustion process, combustor inlet pressure loss (a central issue for pressure gain combustors), and the impact of PGC on the secondary air system (especially blade cooling) are all very important parameters that have been neglected. The current work uses the Humphrey cycle in an attempt to address all these issues in order to provide gas turbine component designers with benchmark efficiency values for individual components of gas turbines with PGC. The analysis concludes with some recommendations for the best strategy to integrate turbine expanders with PGC combustors. This is done from a purely thermodynamic point of view, again with the goal to deliver design benchmark values for a more realistic interpretation of the cycle.

Definition of cycle based comprehensive efficiency of a cooled turbine

As known that the cooling technology is commonly used in the turbine to protect the turbine blade. The mixing and heat transfer between the high pressure cooling air from the compressor and the turbine main flow would cause energy loss, and it will influence the gas turbine cycle performance. However, the existing definitions of the cooled turbine efficiency always take no account of the work which is added to the cooling air to product high pressure in the compressor, thus, the cooling influence on the gas turbine cycle performance cannot be indicated by using the existing cooled turbine efficiency. In this paper, a definition of cycle based comprehensive efficiency for a cooled turbine is presented, in which the work added to the cooling air during its compression process is considered. The existing efficiency definitions are first reviewed, then, the definition of the cooled turbine comprehensive efficiency is presented and validated numerically to show its capacity. Finally, the redesign of a high-pressure turbine is provided. The result shows that the new efficiency can evaluate a cooled turbine performance comprehensively, and can be used as a reliable evaluation criterion for the optimal design of a turbine or a gas turbine cycle.

Effect of ideal gas model with temperature-independent heat capacities on thermodynamic and performance analysis of open-cycle gas turbines

The ideal gas model with temperature-independent heat capacities is the most widely used thermodynamic model in gas turbine cycle simulations. This model is sometimes known as the “perfect gas model”. Closed analytical expressions for specific works and temperatures of the cycle are obtained in this way. If the results are accurate enough then the perfect gas model becomes a powerful analysis tool because its simplicity. For this reason it is the usually chosen option when energy, exergy or thermoeconomic assessments and optimizations of gas turbine cycles are carried out. However, there is a shortage of research works about the analysis of the uncertainty in the calculation of the performance parameters of open-cycle gas turbines with respect to the ideal gas model-based approach (ideal gas with temperature-dependent heat capacities). This analysis is presented in this paper for the simple cycle taking the net specific work output or specific power of the cycle and its Specific Fuel Consumption (SFC) as the performance parameters to be analyzed. First, to gain in internal coherence, an accurate thermodynamic model of the simple cycle based on the ideal gas assumption with temperature-dependent heat capacities is presented. For the sake of accuracy the isobaric heat capacity functions used in this model for every gaseous component present in the cycle are the employed in developing its actual multiparameter equations of state as real fluids. Once this model is established the perfect gas simplification is applied which requires a procedure or rule to evaluate the constant heat capacity values needed. In many cases this rule is not always given or is not clearly specified in the specific literature. In this paper four different evaluation methods (named as A, B, C and D) are considered. These methods are designed to be directly run from known input fixed parameters of the cycle model. The analysis of the absolute and relative errors in computations with the perfect gas approach with the four heat capacity evaluation methods is then carried out. The main result from the analysis is that the own configuration of the open-cycle can lead to an increase (amplification) of the uncertainty in the values of the performance parameters. It is also observed that: (1) this amplification also depends on the method used to evaluate the heat capacities and (2) for a given evaluation method the amplification of the deviations may affect the performance parameters differently. As an example, maximum relative errors of 4.4% and −19.2% are observed in the net specific work output with methods C and D respectively for compressor pressure ratios from 5:1 to 40:1 and turbine inlet temperatures from 1200 K to 1800 K. For the SFC maximum values are −19.51% with method C and 3.95% with method D.

A comprehensive study of simple and recuperative gas turbine cycles with inlet fogging and overspray

Ambient temperature has an adverse effect on gas turbine performance. This problem could be overcome through air cooling technologies such as evaporative cooling, fogging, mechanical cooling, absorption chillers, and thermal energy storage. Therefore, this article aims to evaluate the performance of simple and regenerative gas turbine cycles at dry and wet compression cases. A numerical model was constructed for this purpose then the model was validated for dry cycle conditions with an existing turbine SULZER S3 performance data. An inlet fogging was used to full saturate the inlet air and overspray was used for decreasing the compressor inlet temperature at various ambient temperatures. The results showed that the inlet fogging and overspray reduce the compressor work up to 12%. The results also showed that the thermal efficiency was improved with using the inlet fogging and by increasing the overspray rate. The highest thermal efficiency of 44% was achieved when overspray 3% with recuperation was applied. It can be concluded from this work that the specific fuel consumption is reduced significantly and the output power increases, increasing the thermal efficiency when using the recuperator combined with the wet compression and the overspray.

Long‐term impact of variable generation and demand side flexibility on thermal power generation

This study presents the potential role of thermal power generation in a future power system with high shares of variable generation while considering different sources of demand side flexibility such as heat pumps and heat storages in district heating, demand response from industries and electric vehicles. The study was carried out using a generation planning model combined with a unit commitment and economic dispatch model. The results from the planning model show a strong shift away from combined cycle gas turbines to open cycle gas turbines and gas engines as the share of wind power and solar photovoltaic increases. Demand side flexibility measures pushed this trend further. The results from the unit commitment and economic dispatch model demonstrate that the flexibility measures decrease the ramping frequency of thermal units, while the ramp rates of thermal units remain largely unchanged or increased. This indicates that the flexibility measures can cover smaller ramps in the net load more cost-effectively but that thermal power plants are still valuable for larger ramps. Impacts on emissions and electricity prices are also explored.

Pressure Gain Characteristic of Continuously Rotating Detonation Combustion and its Influence on Gas Turbine Cycle Performance

Considering the pressure gain characteristic of continuously rotating detonation (CRD) combustion, a rotating detonation gas turbine cycle was established using methane as fuel. The variation of pressure gain characteristic and its influence on cycle performance at different compressor pressure ratios and air distribution proportions were investigated combined with a series of two-dimensional numerical simulations. The results were demonstrated that compared with the conventional approximate iso-pressure combustion, rotating detonation combustion could significantly improve the thermodynamic performance of gas turbine in various conditions. Due to the difference of entropy generation between rotating detonation and iso-pressure combustion, the pressure gain characteristic of the CRD combustor was provided a higher cycle efficiency. The efficiency gain was higher at lower compressor pressure ratio and air proportion entering CRD combustor. In the calculated cases, the pressurization ratio of the CRD combustor was higher than 1.37, cycle efficiencies of rotating detonation gas turbine were reached 0.395, cycle efficiency increasing rates were more than 22.5%, and power generation enhancements were greater than 1500 kW.

Influence of Different Steam Cooling Techniques for High Pressure Turbine Blades on the Performance of Gas Turbine

Gas turbines are always intended to give more specific work output for which continuous exposure to hot combustion gases is necessary. To increase the lifespan of the turbine blades active cooling should be applied to the High Pressure (HP) turbine blades. In the present work, a simple open cycle gas turbine is modeled to carry out thermodynamic analysis with different open loop steam cooling techniques: steam internal convection cooling (SICC), steam film cooling (SFC) and steam transpiration (STC) cooling. The effect of Turbine inlet temperature (TIT), Turbine blade temperature (T_b), and Compressor pressure ratio (CPR) on the coolant flow requirement and effect of T_b on the performance are estimated. The entire analysis is carried out with contemplation of variable specific heat (VSH) along with constant specific heats (CSH) for air and gas. Between VSH and CSH approaches, the former analysis leads to better performance from the first and second law efficiencies point of view. Irreversibility and Entropy generation rate are maximum in the combustor and they are less for VSH case in all cooling schemes and are decreased by 38.53%, 40.01%, and 40.40% for SICC, SFC and STC schemes respectively when compared with CSH(at TIT=1580 K, T_b=1123 K, CPR=19.1) analysis.

Thermodynamic analysis of steam-injected advanced gas turbine cycles

This paper deals with thermodynamic analysis of steam-injected gas turbine (STIGT) cycle. To analyse the thermodynamic performance of steam-injected gas turbine (STIGT) cycles, a methodology based on pinch analysis is proposed. This graphical methodology is a systematic approach proposed for a selection of gas turbine with steam injection. The developed graphs are useful for selection of steam-injected gas turbine (STIGT) for optimal operation of it and helps designer to take appropriate decision. The selection of steam-injected gas turbine (STIGT) cycle can be done either at minimum steam ratio (ratio of mass flow rate of steam to air) with maximum efficiency or at maximum steam ratio with maximum net work conditions based on the objective of plants designer. Operating the steam injection based advanced gas turbine plant at minimum steam ratio improves efficiency, resulting in reduction of pollution caused by the emission of flue gases. On the other hand, operating plant at maximum steam ratio can result in maximum work output and hence higher available power.

Energy and exergy analysis of air-film cooled gas turbine cycle: Effect of radiative heat transfer on blade coolant requirement

Gas turbine blade cooling is critical to continuous reliable operation of gas turbines. Literature suggests that air-film cooling is one of the most widely used blade cooling techniques. This paper compares previously developed blade cooling models which are relevant to film cooling technique and it also proposes a gas turbine blade cooling model for the estimation of blade coolant mass fraction, considering radiative heat transfer from hot combustion gases to gas turbine blade surface. The proposed model gives an enhanced coolant mass fraction (≈5–6% over a wide range of TIT) as compared to previously developed models while analyzing gas turbine cycle. Gas turbine cycle performance has been evaluated based on two blade cooling models to compare blade coolant flow mass fraction, gas turbine plant specific work which are function of both compressor-pressure ratio and turbine inlet temperature. Both the blade cooling models closely follow each other with radiative cooling model. For the proposed blade cooling model, gas turbine specific work is around 417.39 kJ/kg (rpc = 22 and TIT = 1650 K) and gas turbine thermal cycle efficiency has been found to be 41.25% at (rpc = 22 and TIT = 1550 K). Exergy analysis of gas turbine cycle has also been done which shows combustor to be main source of exergy destruction (≈29%).

Assessment of Solar Gas Turbine Hybridization Schemes

A simulation environment allowing steady state and transient modeling is used for assessing several gas turbine based cycles proposed for solar hybridization. First, representative open cycle gas turbine configurations, namely, (a) single shaft (SS), (b) recuperated single-shaft, (c) twin shaft (TS), and (d) two-spool three-shaft, intercooled, recuperated, are evaluated. The importance of design point selection in terms of solar share value is highlighted. Solar steam injection gas turbine cycle (STIG) alternatives, namely, solar steam only and solar/fuel gas steam, are then assessed. Finally, the concept of a dual fluid receiver (DFR) for exploiting the rejected solar power by producing steam during sunny hours with high irradiation is demonstrated. The effects of hybridization on performance and operability are established and evaluated. Solarization effect on performance is estimated in terms of annual produced power and fossil fuel savings. The results indicate that the spool arrangement affects the suitability of a gas turbine for hybridization. Recuperated configurations performed better for the design constrains imposed by current technology solar parts. Solar steam injection is a promising solution for retrofitted fuel-only and conventional STIG engines.

Modelling of a combustible ionised gas in thermal power plants using MHD conversion system in South Africa

The generation of electric power through the conventional conversion systems may no longer be sufficient to keep pace with the increasing electricity usage and demands. Therefore, an enhancement to these systems can be made by incorporating a topping unit to the existing power plants (thermal, hydroelectric), a direct energy conversion system. Among such is the Magnetohydrodynamics (MHD) system. In an MHD conversion system, electricity is generated when heat energy is converted into electrical energy without the use of mechanical rotating parts. Additionally, the heat energy (ionised gas) required inside the MHD system usually comes from the combustion of fossil fuels. However, this system is still under development in developing countries like South Africa. The current study aims to investigate through simulations and theoretical modelling two existing Open-Cycle Gas Turbines (OCGT) in South Africa (Ankerlig and Gourikwa), which can be converted into Combined-Cycle MHD Gas-Steam Turbines (CCMGST). The processes involved by incorporating the MHD system with these conventional turbines have been further discussed. With setting up a CCMGST in South Africa, the obtained modelling results project an additional generation of electric power which will further improve the existing power generation.

Analysis of Nigerian Electricity Generation Multi Year Tariff Order Pricing Model

The Multi Year Tariff Order (MYTO) is the Nigerian Electricity Regulatory Commission (NERC) pricing framework for determining the Nigerian Electricity Supply Industry (NESI) pricing model. One of the objectives of the NERC’s MYTO pricing model is to ensure regulated electricity end user tariff without compromising return on investment. Achieving this objective is imperative to attract investors in the growing Nigerian electricity market. However, NESI has hitherto been faced with challenges ranging from its inability to provide sufficient power to its customers to not being viable enough to provide return on capital invested. In this paper, sensitivity analysis of power plant operation and performance parameters on the cost of electricity (CoE) generation using MYTO (power generation) pricing model were evaluated. Thermodynamic modeling and simulation of an open cycle gas turbine (OCGT) was carried out to augment scarce data on power plant performance and operation in Nigeria. Sensitivity analysis was carried out using probabilistic method based on Monte Carlo simulation (MCS) implemented in commercial software (@ Risk®). The result highlighted sensitivity of the model input parameters to cost of electricity generation based on technical and financial assumptions of MYTO model. Seven most influential parameters affecting generation cost were identified. These parameters and their correlation coefficients are given as: 1) foreign exchange rate, 0.76; 2) cost of fuel, 0.51; 3) thermal efficiency, -0.23; 4) variable operation and maintenance cost, 0.22; 5) fixed operating and maintenance cost, -0.03; 6) capacity factor, -0.02; and 7) average capacity degradation, 0.01. Based on the gas turbine engine and input parameter distributions statistics for this study, the generation cost lies between 9.84 to 15.45 N/kWh and the probabilities of CoE within these values were established.

Comparison of novel concepts of cogeneration systems used to regasify liquefied natural gas (LNG)

Liquefied natural gas (LNG) will contribute in future significantly to the overall energy supply in the world. During the last two decades the effectiveness of the technologies associated with the chain “natural gas – LNG – natural gas” has increased. However, the regasification systems, which use approximately 1.5% of the LNG energy, have not been considerably improved. The objective of this paper is to demonstrate the potential for generating electricity while regasifying LNG, and to compare some novel concepts developed for this purpose. The concepts are based on combination of the open- and closed-cycle gas-turbine systems with combustion of natural gas as the heat source and regasification of LNG as the heat sink. The comparisons are conducted from the thermodynamic, economic and ecological points of view. The complications introduced to the Base Case in order to maximize the utilization of useful energy (transferred to the environment from the open-cycle gas-turbine system) have the following consequences: The overall energetic efficiency increases from 68% to 86%, the overall exergetic efficiency increases from 52.6% to 54.3% while the specific fixed capital investment is approximately 1.0 mil US$/MW for all schematics. The specific CO2 emissions (per unit of generated electricity) increase from 0.145 to 0.19 kg CO2/kWh while per kg of regasifyed LNG, the specific CO2 emissions decrease significantly from 0.09 to 0.067 kg CO2/kg LNG.

Most promising flexible generators for the wind dominated market

The intermittent nature of wind power and other forms of variable renewable energy requires complementary dispatchable flexible generators in order to guarantee the efficient, reliable and secure operation of electricity systems. The most popular solution to date has been peaking plant, usually in the form of open-cycle-gas- turbines (OCGT). Energy storage technologies have so far been considered too expensive, however technology development, as well as challenging renewable targets could potentially make storage economically viable. Although new advanced flexible combined-cycle gas turbines (CCGT) have been developed by some manufacturers, they have not yet been investigated in electricity market models. This paper describes a techno-economic assessment of the most suitable flexible technologies for the wind-dominated all Ireland electricity market (the Single Electricity Market (SEM)). The analysis is conducted by considering the impact of a series of policy scenarios which are compared in an electricity market model. The comparison is quantified using three primary metrics: technical benefits to the system, economic advantages to the consumer and investment viability. Modelling results suggest that advanced CCGT and energy storage solutions are the most advantageous, however they need strong governmental support to attract potential investors and guarantee deployment in the market.

Thermodynamic analysis of steam-injected gas turbine cycle power plant with inlet air cooling

Steam-injected gas turbine cycle is the modified arrangement of simple gas turbine (GT) cycle, wherein part of steam generated in a heat recovery steam generator is injected into the combustion chamber to increase power output and the efficiency. This paper studies the effect of integration of inlet air cooling, steam injection (SI) and film cooling (FC) on the performance of GT cycle. Two different methods for cooling the inlet air, namely inlet fogging and evaporative cooling, are considered for analysis here. Results show that the inlet fogging is better than evaporative cooling to achieve the lowest temperature at the compressor inlet. Thermodynamic performance of simple GT cycle is also compared with SI in GT cycle. The present study shows that GT cycle with integration of inlet fogging, SI and FC is a better configuration for achieving higher performance.

Demonstrating demand response from water distribution system through pump scheduling

Significant changes in the power generation mix are posing new challenges for the balancing systems of the grid. Many of these challenges are in the secondary electricity grid regulation services and could be met through demand response (DR) services. We explore the opportunities for a water distribution system (WDS) to provide balancing services with demand response through pump scheduling and evaluate the associated benefits. Using a benchmark network and demand response mechanisms available in the UK, these benefits are assessed in terms of reduced green house gas (GHG) emissions from the grid due to the displacement of more polluting power sources and additional revenues for water utilities. The optimal pump scheduling problem is formulated as a mixed-integer optimisation problem and solved using a branch and bound algorithm. This new formulation finds the optimal level of power capacity to commit to the provision of demand response for a range of reserve energy provision and frequency response schemes offered in the UK. For the first time we show that DR from WDS can offer financial benefits to WDS operators while providing response energy to the grid with less greenhouse gas emissions than competing reserve energy technologies. Using a Monte Carlo simulation based on data from 2014, we demonstrate that the cost of providing the storage energy is less than the financial compensation available for the equivalent energy supply. The GHG emissions from the demand response provision from a WDS are also shown to be smaller than those of contemporary competing technologies such as open cycle gas turbines. The demand response services considered vary in their response time and duration as well as commitment requirements. The financial viability of a demand response service committed continuously is shown to be strongly dependent on the utilisation of the pumps and the electricity tariffs used by water utilities. Through the analysis of range of water demand scenarios and financial incentives using real market data, we demonstrate how a WDS can participate in a demand response scheme and generate financial gains and environmental benefits.

Optimising the deployment of renewable resources for the Australian NEM (National Electricity Market) and the effect of atmospheric length scales

This study sheds new light on the variability of wind power across the Australian NEM (National Electricity Market) and in doing so gives an insight on the potential network configuration for a high RE (Renewable Electricity) future. We present idealised cost-minimised simulations for the NEM utilising onshore wind, large-scale solar, pumped hydro and OCGT (open cycle gas turbines) technologies. A model using gridded meteorological data from the regional ACCESS-R (Australian Community Climate and Earth-System Simulator) simulates wind and solar technology output along with generation from OCGT to meet demand in the NEM for the period 2010–2011. A cost for connecting each location to the nearest major load centre is introduced and a base scenario created from an initial connection cost of $1 M/km. A sensitivity study reveals that a cost of $8 M/km results in the contraction of all renewable resources to four major wind installations. Compared to the base scenario the four major wind locations share much of the variability in renewable energy output, demonstrating that the NEM region has four distinct wind regimes. Separated by 1,400 km these four wind installations provide an optimisation-based decorrelation length for the NEM. This information is particularly useful for long-term planners of large-scale energy infrastructure.

An analysis of the power market in Saudi Arabia: Retrospective cost and environmental optimization

This paper provides an overview of the power sector in the Kingdom of Saudi Arabia (KSA) with the latest data and applies a retrospective modeling approach for its power market under (i) a cost minimization and (ii) an environmental impact minimization objective for the period 2003–2013 with domestic and international fuel prices. For the analysis an enhanced version of Open Source energy MOdelling SYStem (OSeMOSYS) is utilized. Implemented model improvements include (a) temperature adjustments as the temperature difference between winter and summer of 20–30°C is common almost all over the world and has significant impact on power generation efficiency, (b) a multi-objective target function considering both costs and emissions to create a Pareto frontier, and (c) emissions are assessed with the ‘quality enhanced life days’ (QELD) indicator to consider global (e.g. carbon dioxide) and local emissions (e.g. NOx) simultaneously. Results show that the biggest reductions in emissions can be reached by considering international fuel prices. While the amount of new technology is quite similar within the minimize emission cases, the installed type of technology differs significantly within the minimize cost cases: cost minimization with international fuel prices is forcing Combined Cycle Gas Turbine (CCGT or CC) plants and Steam Turbine (ST) plants whereas when considering domestic fuel prices, the share of inefficient Open Cycle Gas Turbine (OCGT or GT) plants is 100%. Focusing on emission reduction within the international fuel price scenario a 19% cost increase results in 43% emission reductions while a 33% cost increase reduces emissions by 60%. Notably, an emission reduction of 50% can be reached independently of fuel pricing when the weight of emission criterion is 95% or higher within the enhanced OSeMOSYS model.