Hybrid energy plants (HEPs), which include both fossil fuel technologies and renewable energy systems, can provide an important step toward a sustainable energy supply. In fact, the hybridization of renewable energy systems with gas turbines (GTs), which are fed by fossil fuels allows an acceptable compromise, so that high fossil fuel efficiency and high share of renewables can be potentially achieved. Moreover, electrical and thermal energy storage systems increase the flexibility of the energy plant and effectively manage the variability of energy production and demand. This paper investigates the optimal sizing of a HEP, which combines an industrial GT, renewable energy systems, and energy storage technologies. The considered renewable energy system is a photovoltaic system (PV), while the energy storage technologies are electrical energy storage and thermal energy storage. Moreover, a compression chiller and a gas boiler (GB) are also considered. For this purpose, the load profiles of electricity, heating, and cooling during a whole year are taken into account for the case study of the Campus of the University of Parma (Italy). The sizing optimization problem of the different technologies composing the HEP is solved by using a genetic algorithm, with the goal of minimizing the primary energy consumption (PEC). Moreover, different operation strategies are analyzed and compared so that plant operation is also optimized. The results demonstrate that the optimal sizing of the HEP, coupled with the optimized operation strategy, allows high average cogeneration efficiency (up to 84%), thus minimizing PEC.

Wet compression is a strategy adopted to increase the power output of gas turbines, with respect to dry conditions, usually also incrementing the operating range of the compressor. However, stall and surge are two aerodynamic instabilities which depend on many factors, and they are expected to occur even in wet compression at low flow rates. Despite the many studies carried out in the last 80 years, literature does not offer many works concerning these instability phenomena in wet compression. In this paper, an experimental analysis of stall and surge in wet compression conditions is carried out on an axial-centrifugal compressor installed in an existing test rig at the Engineering Department of the University of Ferrara. The intake duct was implemented with a water injection system (WIS) which allows the uniform mixing of air and water before the compressor inlet. The control and data acquisition system of the test bench was updated with new hardware and software to obtain faster data sampling. Transient and steady-state tests were carried out to make a comparison with the experimental results in dry conditions. The analysis was carried out using traditional thermodynamic sensors, by means of both classic postprocessing techniques and cyclostationary analysis. The aim is to (i) evaluate the influence of wet compression on the stable performance of the compressor, (ii) qualitatively identify the characteristics of stall and surge in wet compression, and (iii) demonstrate the reliability of cyclostationary analysis in wet compression conditions for stall and surge analysis.

The compressor surge is a phenomenon which has to be avoided since it implies the deterioration of performance and leads to mechanical damage to the compressor and system components. As a consequence, compression system models have a crucial role in predicting the phenomena which can occur in the compressor and pipelines during operation. In this paper, a dynamic model, developed in the matlab / simulink environment, is further implemented to allow the study of surge events caused by rapid transients, such as emergency shutdown events (ESD). The aim is to validate the model using the experimental data obtained in a single-stage centrifugal compressor installed in the test facility at Southwest Research Institute. The test facility consists of a closed loop system and is characterized by a recycling circuit, and thus a recycling valve, which is opened in case of surge or driver shutdown. Simulations were carried out at 17,800 and 19,800 rpm; the comparison with experimental data showed the accuracy of the model in simulating different opening rates and different sizes of the recycle valve, at both low and high suction pressure (HSP). Moreover, different actions for recovering/preventing surge were simulated by controlling different valves along the piping system and by adding a check valve immediately downstream the compressor. The results demonstrated the fidelity of the model and its capability of simulating piping systems with different configurations and components, also showing, qualitatively, the different effects of some alternative actions which can be taken after surge onset.

Industrial compressors suffer from strong aerodynamic instability that arises when low ranges of flow rate are achieved; this instability is called surge. This phenomenon creates strong vibrations and forces acting on the compressor and system components due to the fact that it produces variable time-averaged mass flow and pressure. Therefore, surge is dangerous not only for aerodynamic structures but also for mechanical parts. Surge is usually prevented in industrial plants by means of anti-surge systems, which act as soon as surge occurs; however, some rapid transients or system upsets can lead the compressor to surge anyway. Despite the fact that surge can be classified as mild, classic, or deep, depending on the amplitudes and frequency of the fluctuations, operators are used to simply referring to surge, without making a distinction between the three main classes. This is one of the reasons why, when surge occurs in industrial plants, it is a common practice to stop the machine to perform inspections and check if any damage occurred. Obviously, this implies maintenance costs and time, during which the machine does not operate. On the other hand, not all surge events are dangerous in terms of damage, and they can be tolerated by the mechanical structures of the compressor; thus, in these cases, inspections would not be required. Unfortunately, a method for establishing the potential damage of a surge event is not available in literature. In order to fill this gap, this paper proposes a final formulation of a surge severity index, which was only preliminarily formulated by the authors in a previous work. The preliminary form of this coefficient demonstrated some limitations, which are overcome in this paper. The surge severity index derives from an energy-force based analysis. The coefficient demonstration is carried out in this paper by means of (i) the application of the Buckingham's Pi-theorem, and (ii) a careful analysis of the causative and restorative factors of surge. Finally, some simple practical evaluations are shown by means of a sensitivity analysis, using simulation results of an existing model, to effectively further highlight the consistency of this coefficient for industry.

Over recent decades, the variability and high costs of the traditional gas turbine fuels (e.g., natural gas) have pushed operators to consider low-grade fuels for running heavy-duty frames. Synfuels, obtained from coal, petroleum, or biomass gasification, could represent valid alternatives in this sense. Although these alternatives match the reduction of costs and, in the case of biomass sources, would potentially provide a CO 2 emission benefit (reduction of the CO 2 capture and sequestration costs), these low-grade fuels have a higher content of contaminants. Synfuels are filtered before the combustor stage, but the contaminants are not removed completely. This fact leads to a considerable amount of deposition on the nozzle vanes due to the high temperature value. In addition to this, the continuous demand for increasing gas turbine efficiency determines a higher combustor outlet temperature. Current advanced gas turbine engines operate at a turbine inlet temperature (TIT) of (1400–1500) °C, which is high enough to melt a high proportion of the contaminants introduced by low-grade fuels. Particle deposition can increase surface roughness, modify the airfoil shape, and clog the coolant passages. At the same time, land-based power units experience compressor fouling, due to the air contaminants able to pass through the filtration barriers. Hot sections and compressor fouling work together to determine performance degradation. This paper proposes an analysis of the contaminant deposition on hot gas turbine sections based on machine nameplate data. Hot section and compressor fouling are estimated using a fouling susceptibility criterion. The combination of gas turbine net power, efficiency, and TIT with different types of synfuel contaminants highlights how each gas turbine is subjected to particle deposition. The simulation of particle deposition on 100 gas turbines ranging from 1.2 MW to 420 MW was conducted following the fouling susceptibility criterion. Using a simplified particle deposition calculation based on TIT and contaminant viscosity estimation, the analysis shows how the correlation between type of contaminant and gas turbine performance plays a key role. The results allow the choice of the best heavy-duty frame as a function of the fuel. Low-efficiency frames (characterized by lower values of TIT) show the best compromise in order to reduce the effects of particle deposition in the presence of high-temperature melting contaminants. A high-efficiency frame is suitable when the contaminants are characterized by a low-melting point thanks to their lower fuel consumption.

Nowadays, the operative range limit of compressors is still a key aspect of the research into turbomachinery. In particular, the study of the mass flow rate lower limit represents a significant factor in order to predict and avoid the inception of critical working conditions and instabilities such as stall and surge. The identification of these instabilities and typical precursors of these two phenomena can imply many advantages, in both stationary and aeronautic applications, such as avoiding the loss of production (in industry) and efficiency of systems and reducing the maintenance and repairing cost. Many approaches can be adopted to achieve this target, but one of the most fascinating is the vibro-acoustic analysis of the compressor response during operation. At the Engineering Department of the University of Ferrara, a test bench, dedicated to the study of the performance of an aeronautic turboshaft engine multistage compressor, has been equipped with a high frequency data acquisition system. A set of triaxle accelerometers and microphones, suitable for capturing broad-band vibration and acoustic phenomena, were installed in strategic positions along the compressor and the test rig. A great amount of vibro-acoustic data were first processed through an innovative data analysis technique, and then correlated to the thermodynamic data recorded. Subsequently, the precursor signals of surge were detected and identified demonstrating the reliability of the methodology used for studying compressor instabilities. The experimental data and results offer a valid alternative way of analyzing and detecting unstable compressor behavior characteristics by means of nonintrusive measurements.

This paper documents the setup and validation of nonlinear autoregressive network with exogenous inputs (NARX) models of a heavy-duty single-shaft gas turbine (GT). The data used for model training are time series datasets of several different maneuvers taken experimentally on a GT General Electric PG 9351FA during the start-up procedure and refer to cold, warm, and hot start-up. The trained NARX models are used to predict other experimental datasets, and comparisons are made among the outputs of the models and the corresponding measured data. Therefore, this paper addresses the challenge of setting up robust and reliable NARX models, by means of a sound selection of training datasets and a sensitivity analysis on the number of neurons. Moreover, a new performance function for the training process is defined to weigh more the most rapid transients. The final aim of this paper is the setup of a powerful, easy-to-build and very accurate simulation tool, which can be used for both control logic tuning and GT diagnostics, characterized by good generalization capability.

Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. In particular, in industrial applications, the microparticles not captured by the air filtration system can cause deposits on blading and, consequently, result in a decrease in compressor performance. In the literature, there are some studies related to the fouling phenomena in transonic compressors, but in industrial applications (heavy-duty compressors, pump stations, etc.), the subsonic compressors are widespread. It is highly important for the manufacturer to gather information about the fouling phenomenon related to this type of compressor. This paper presents three-dimensional (3D) numerical simulations of the microparticle ingestion (0.15–1.50 μ m) in a multistage (i.e., eight stage) subsonic axial compressor, carried out by means of a commercial computational fluid dynamic (CFD) code. Particles of this size can follow the main air flow with relatively little slip, while being impacted by flow turbulence. It is of great interest to the industry to determine which zones of the compressor blades are impacted by these small particles. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The adopted computational strategy allows the evaluation of particle deposition in a multistage axial compressor thanks to the use of a mixing plane approach to model the rotor/stator interaction. The compressor numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in the literature. The number of particles and sizes is specified in order to perform a quantitative analysis of the particle impacts on the blade surface. The blade zones affected by particle impacts and the kinematic characteristics (velocity and angle) of the impact of micrometric and submicrometric particles with the blade surface are shown. Both blade zones affected by particle impact and deposition are analyzed. The particle deposition is established by using the quantity called sticking probability (SP), adopted from the literature. The SP links the kinematic characteristics of particle impact on the blade with the fouling phenomenon. The results show that microparticles tend to follow the flow by impacting on the compressor blades at full span. The suction side (SS) of the blade is only affected by the impacts of the smallest particles. Particular fluid dynamic phenomena, such as corner separations and clearance vortices, strongly influence the impact location of the particles. The impact and deposition trends decrease according to the stages. The front stages appear more affected by particle impact and deposition than the rear ones.

The force acting on centrifugal compressors is an important parameter to be considered throughout the operating life of these turbomachines. When the compressor is operating in surge conditions, these forces can become highly dangerous for the mechanical and aerodynamic structures. This instability is usually avoided in industrial applications, but the antisurge system may not react in time when emergency shutdowns or power failures take place. During these rapid transients, surge can develop, generating unsteady forces which can harm the close clearance components of the compressor. Therefore, the capability to predict the characteristics and the dynamics of these surge forces would allow the estimation of the off-design fatigue cycles produced on these components by surge. Currently, no validated method exists to predict the frequency and amplitude of the surge forces and determine the potential damage of these components. In this paper, a lumped parameter model, developed by using the bond graph approach to predict the dynamic surge fluid-dynamic oscillations, is presented. The model requires the geometry and the steady-state performance maps of the compressor as inputs, together with the piping system configuration characteristics. The simulator is provided with a supplementary tool to estimate the axial force frequency and amplitude, taking into consideration all the contributions to the axial fluid-dynamic thrust, the stiffness-damping of the thrust bearing, and the mass of the rotor. The model was tuned and validated using the test case axial force data from the Southwest Research Institute (SWRI) facility. The model has shown good agreement with the experimental results which implies that it can offer significant information about the severity of a surge event and the quantification of the machine performance losses together with possible damage to the close clearance components. This study is a first important step that can lead to schedule optimization for maintenance and repair activities.

Centrifugal compressor impellers and shafts are subject to severe fluctuating axial and radial forces when operating in surge. These forces can cause severe damage to the close clearance components of a centrifugal compressor such as the thrust and radial bearings, interstage and dry gas seals, and balance piston. Being able to accurately quantify the cyclic surge forces on the close clearance components of the compressor allows the user to determine whether an accidental surge event, or emergency shutdown (ESD) transient, has caused damage requiring inspection, repair, or part replacement. For the test, a 700 hp (∼520 kW) industrial air centrifugal compressor was operated in surge at speeds ranging from 7000 to 13,000 rpm and pressure ratios from 1.2 to 1.8. The axial surge forces were directly measured using axial load cells on the thrust bearings. Suction and discharge pressures, proximity probe axial shaft position, flows, and temperatures were also measured. Time domain and frequency plots of axial vibration and dynamic pulsations showed the impact of the operating conditions on surge force amplitudes and frequencies. A surge severity coefficient was also derived as a simple screening tool to evaluate the magnitude of potential damage to a compressor during surge.