1,721,024 research outputs found
Performance Evaluations of Steam Power Plants with Dry Cooling Towers
No full textA theoretical model is presented to design dry cooling tower systems and to evaluate their off-design performances. The influence of the more important design parameters on the tower dimensions is shown. A preliminary optimum size is predicted by means of a computer code using a simplified cost model. Moreover, the influence of the designed cooling system on the performance of thermoelectric and/or nuclear power plants is analyzed. The study of the performance of air heat exchangers with plastic tubes (e. g. high-density polyethylene) and of wet and dry-wet cooling systems, as well as a deeper economical cost analysis represent the natural development of this research
Control of Gas turbine power plants by means of the weighted one-step-ahead adaptive technique
No full textThe one-step-ahead controllers represent a branch of minimum prediction error adaptive controllers. They combine the parameter estimation of the controlled system model with the control scheme; therefore, they are especially suitable for non-linear and time-varying systems. Since the estimated parameters are updated at each time step (by using the sampled data), these methods can be adopted for non-linear applications. Consequently, the one-step-ahead controllers do not require knowledge of the dynamic characteristics of the controlled system (e.g. state-space systems or transfer functions). Sometimes, in the gas turbine field, the control system could produce an excessive control effort, due to sudden variations of the electric load. In order to reduce this control action, the weighted one-step-ahead adaptive (WOSAA) control algorithm considers a penalty associated with the control effort using an appropriate cost function. In this way, the control variable does not assume values that are too large, even when the gas turbine undergoes sudden changes in the external load. As a consequence, the robustness and stability features of the WOSAA control system are increased. The results show that the WOSAA control technique, applied to both the double-shaft aero-derivative gas turbine and the single-shaft heavy-duty gas turbine, effectively counteracts the load reduction with limited overshoot in the controlled variables with reduced control effort
Simplified theoretical model to predict the melting time of a shell-and-tube LHTES
No full textA theoretical model to predict the complete melting time of a Latent Heat Thermal Energy Storage (LHTES) considering a shell-and-tube configuration is presented and applied to several geometries. The shape of the device has been modified according to the internal radius (r i ), external radius (r e ) and total height (L) retaining constant the volume of the storage and the heat exchange area. The model has been validated by means of multiphase numerical simulations of the charging phase. The numerical simulations have been performed considering four configurations, with a radii ratio, r e /r i , equal to 1.5, 2, 4.375 and 6. The comparison between the model predictions and the numerical simulations confirms the reliability of the theoretical model in terms of melting time within the range investigated. The study reveals that, even considering the same storage volume, heat exchange area and wall temperature, for low values of radii ratio (r e /r i ), the shape of the device is able to reduce the charging time of the LHTES up to 50% for a radii ratio r e /r i =1.5 with respect to r e /r i =4.375. Increasing further the radii ratio from r e /r i =4.375 to 6, the melting time decreases. The unsteady numerical simulations support the prediction of the theoretical model. Thus, in the here studied geometrical configurations the proposed approach represents a simplified and accurate design tool to predict the charging time of a LHTES shell-and-tube device
VGT Turbocharger Controlled by an Adaptive Technique
No full textThis paper provides an adaptive technique for the control of the variable geometry turbine in a turbocharged compression ignition engine. The adaptive control is based on a one-step-ahead (OSA) technique and a least-square parameter estimator algorithm. In order to test the performance of the proposed control technique, a numerical model of the engine has been developed, which employs a thermodynamic (zero-dimensional) approach. The paper will show that the OSA technique is able to improve dramatically the control performance with respect to that provided by a commonly applied proportional integral derivative control technique
Predicting the performances of marine two-stroke compression ignition engines
No full textA theoretical model is presented to predict the thermodynamic phenomena in a two-stroke supercharged compression-ignition engine and to evaluate its off-design performances. A computer program is used to obtain the theoretical performances, which are then compared with the experimental ones
CFD Simulation of Humid Air Prefixed Flame Combustion Chamber for Evaporative Gas Turbine Cycles
No full textFuzzy logic controller applied to a variable geometry turbine turbocharger
No full textThis paper provides an adaptive technique for the control of a variable geometry turbine (VGT) in a turbocharged compression ignition engine. The adaptive control is based on a fuzzy logic control scheme and a least-squares parameter estimator algorithm. In order to test the performance of the proposed control technique, a numerical model of the engine has been used, which employs a thermodynamic (zero-dimensional) approach. The paper will show that the fuzzy logic control technique is able to take into account the non-linearity of the controlled system and to reject white noise affecting the measurement chain
Small scale biomass CHP: Techno-economic performance of steam vs gas turbines with bottoming ORC
Full text linkSmall scale Combined Heat and Power (CHP) plants present lower electric efficiency in comparison to large scale ones, and this is particularly valid when biomass fuels are used. In most cases, the use of both heat and electricity to serve on site energy demand is a key to achieve acceptable global energy efficiency and investment profitability. However, the heat demand follows a typical daily and seasonal pattern and it is influenced by climatic conditions. During low heat demand periods, a lot of heat produced by the CHP plant is discharged. In order to increase the electric conversion efficiency of small scale biomass CHP plants, a bottoming ORC system can be coupled to the cycle, however this decreases the temperature and quantity of cogenerated heat available to the load. In this perspective, the paper proposes a thermo-economic analysis of small scale CHP plants based on steam turbine (ST) or externally fired micro gas turbine (EFGT) coupled to different typologies of bottoming Organic Rankine Cycles (ORC). The research assesses the influence of the thermal energy demand and CHP plant operational strategies on the global energy efficiency and profitability of the proposed cogeneration options, taking into account the part load efficiency and the heat to electricity ratio flexibility that could be achieved through a switch on-off of the bottoming ORC. The thermodynamic cycles and their part load efficiency are modeled by Gate-Cycle (Brayton cycles) and Cycle-Tempo (Rankine cycles). The research explores the profitability of bottoming ORC in view of the higher efficiency and electricity generation revenues but higher costs and reduced heat available for cogeneration in the case of bottoming ORC. The results indicate the optimal CHP technology and configuration for each energy demand segment and the relative key technical and economic factors in the Italian legislative framework
Dynamic Modelling of Recuperative Gas Turbines
No full textThis paper describes the mathematical model and the computational procedure adopted for the development of a modularly structured computer code able to simulate the dynamic behaviour of recuperative gas turbine power plants. For accurate simulation of the turbine components, the model includes a stage-by-stage procedure for the air-cooled turbine based on the blade geometry and the characteristics of the cooling system. The counter-flow surface heat exchanger, assumed as recuperator, is described by a set of partial differential equations, giving a one-dimensional description of the temperature for air, hot gas and metal. A single-shaft recuperated cycle gas turbine, provided with compressor variable inlet guide vanes, is analyzed. The transient cases caused by a step variation in the fuel flow and compressor guide vanes geometry are simulated and a linearized model is obtained, in order to identify the dynamic behaviour of the gas turbine and to design a multivariable controller. Finally, the transient case of a controlled turbine after a sudden variation in the electric load is simulated
Technical-economic optimization of a wind power plant by means of a stochastic analytical model
No full textStochastic analytical approaches are particularly suitable to design and study engineering systems based on aleatory information, as wind systems are. The present paper provides a stochastic analytical model to evaluate the performance of a wind power plant. The model has been applied to a small isolated wind system. The results obtained indicate a strong influence of wind speed stochastic variability on the minimum production costs turbine size. The results also point out the economic advantage in the use of a stochastic analytical approach in wind system design compared with a design procedure based on system average performances evaluated according to a determinist approach
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