Tae Won Song

Exergy-based performance analysis of the heavy-duty gas turbine in part-load operating conditions

Abstract The present study describes details of exergy-based performance characteristics of a heavy-duty gas turbine, 150MW-class GE 7F model. Results have shown that a chemical reaction in the combustor of which the exergy destruction ratio is 28.3% at full-load is one of the major sources of exergy destructions in the gas turbine. It was found that, in spite of its usefulness to the performance enhancement of the combined cycle plant in part-load operations, the variable inlet guide vane located in front of the multi-stage compressor caused the increase of exergy destruction in the first stage (about 10 times lager than that of other stages below 80% load) and decreased the overall compressor efficiency. Also, it was discovered that the magnitude of exergy destruction by the cooling air in turbine stages is large enough to influence the overall turbine efficiency. The exergy destruction by the cooling air is more than half of the total exergy destruction of each cooled turbine stage.

Parametric Studies for a Performance Analysis of a SOFC/MGT Hybrid Power System Based on a Quasi-2D Model

Solid oxide fuel cell / micro gas turbine (SOFC/MGT) hybrid power system has been theoretically demonstrated that it can achieve higher thermal efficiency than any other power generation systems. To understand performance characteristics of the SOFC/MGT hybrid power system, it is necessary to analyze sensitivities of operating and design parameters on its performance. In this study, a quasi-2D model for the mathematical modeling of a tubular type indirect internal reforming solid oxide fuel cell (IIR-SOFC) is proposed and applied to a performance analysis of a SOFC/MGT hybrid power system. Using this model, temperature distributions along the longitudinal direction of the IIR-SOFC, which cannot be predicted by the lumped model, are calculated. In addition, sensitivities of parameters governing fuel cell performance such as current density, fuel utilization factor, steam-carbon ratio and parameters governing gas turbine performance such as pressure ratio, turbine inlet temperature, adiabatic efficiencies of compressor/turbine, and heat exchange effectiveness of the recuperator on the performance of the SOFC/MGT hybrid power system are investigated. Results in this study show how a quasi-2D model can improve accuracy of the performance analysis and its implementation to the performance analysis with discussion about sensitivities of design and operating parameters to the performance of the SOFC/MGT hybrid power system.Copyright

Detailed Performance Analysis of a Solid Oxide Fuel Cell: Micro Gas Turbine Hybrid Power System

Performance of a solid oxide fuel cell (SOFC) can be enhanced by converting thermal energy of its high temperature exhaust gas to mechanical power using a micro gas turbine (MGT). A MGT plays also an important role to pressurize and warm up inlet gas streams of the SOFC. Performance behavior of the SOFC is sensitively influenced by internal constructions of the SOFC and related to design and operating parameters. In case of the SOFC/MGT hybrid power system, internal constructions of the SOFC influence not only on the performance of the SOFC but also on the whole hybrid system. In this study, influence of performance characteristics of the tubular SOFC and its internal reformer on the hybrid power system is discussed. For this purpose, detailed heat and mass transfer with reforming and electrochemical reactions in the SOFC are mathematically modeled and their results are reflected to the performance analysis. Effects of different internal constructions of the SOFC system and design parameters such as current density, recirculation ratio, fuel utilization factor, and catalyst density in internal reformer on the system performance are investigated and, as a result, some guidelines for the choice of those parameters for optimum operations of the SOFC/MGT hybrid power system are discussed.Copyright

Model Development and Simulation of Transient Behavior of Heavy Duty Gas Turbines

This paper describes models for a transient analysis of heavy duty gas turbines, and presents dynamic simulation results of a modern electricity generation engine. Basic governing equations are derived from integral forms of unsteady conservation equations. Mathematical models of each component are described with the aid of unsteady one-dimensional governing equations and steady state component characteristics. Special efforts have been made to predict the compressor characteristics including the effect of movable vanes, which govern the running behavior of the whole engine. The derived equation sets are solved numerically by a fully implicit method. A controller model that maintains constant rotational speed and target temperature (turbine inlet or exhaust temperature) is used to simulate real engine operations. Component models, especially those of the compressor, are validated through a comparison with test data. Simulated is the dynamic behavior of a 150MW class engine. The simulated time-dependent variations of engine parameters such as power, rotational speed, fuel, temperatures and guide vane angles are compared with field data. Simulated results are fairly close to the operation data.Copyright

Analysis on the Performance Characteristics of SOFC/GT Hybrid Systems Based on a Commercially Available MW-Class Gas Turbine

To investigate the possible applications of the SOFC/MGT hybrid system to large electric power generations, a study for the kW-class hybrid power system conducted in our group is extended to the MW-class hybrid system in this study. Because of the matured technology of the gas turbine and commercial availability in the market, it is reasonable to construct a hybrid system with the selection of a gas turbine as an off-the-shelf item. For this purpose, the performance analysis is conducted to find out the optimal power size of the hybrid system based on a commercially available gas turbine. The optimal power size has to be selected by considering specifications of a selected gas turbine which limit the performance of the hybrid system. Also, the cell temperature of the SOFC is another limiting parameter to be considered in the selection of the optimal power size. Because of different system configuration of the hybrid system, the control strategies for the part-load operation of the MW-class hybrid system are quite different from the kW-class case. Also, it is necessary to consider that the control of supplied air to the MW-class gas turbine is typically done by the variable inlet guide vane located in front of the compressor inlet, instead of the control of variable rotational speed of the kW-class micro gas turbine. Performance characteristics at part-load operating conditions with different kinds of control strategies of supplied fuel and air to the hybrid system are investigated in this study.Copyright

Predictions of Fouling Phenomena in the Axial Compressor of Gas Turbine Using an Analytic Method

The performance of gas turbines is decreased as their operating hours increase. Fouling in the axial compressor is one of main reasons for the performance degradation of gas turbine. Airborne particles entering with air at the inlet into compressor adhere to the blade surface and result in the change of the blade shape, which is closely and sensitively related to the compressor performance. It is difficult to exactly analyze the mechanism of the compressor fouling because the growing process of the fouling is very slow and the dimension of the fouled depth on the blade surface is very small compared with blade dimensions. In this study, an improved analytic method to predict the motion of particles in compressor cascades and their deposition onto blade is proposed. Simulations using proposed method and their comparison with field data demonstrate the feasibility of the model. It if found that some important parameters such as chord length, solidity and number of stages, which represent the characteristics of compressor geometry, are closely related to the fouling phenomena. And, the particle sloe and patterns of their distributions are also Important factors to predict the fouling phenomena in the axial compressor of the gas turbine.

Effective Performance Prediction of Axial Flow Compressors Using a Modified Stage-Stacking Method

In this work, a modified stage-stacking method for the performance prediction of multi-stage axial flow compressors is proposed. The method is based on a simultaneous calculation of all interstage variables (temperature, pressure, flow velocity) instead of the conventional sequential stage-by-stage scheme. The method is also very useful in simulating the effect of changing angles of the inlet guide vane and stator vanes on the compressor operating characteristics. Generalized stage performance curves are used in presenting the performance characteristics of each stage. General assumptions enable determination of flow path data and stage design performance. Performance of various real compressors is predicted and comparison between prediction and field data validates the usefulness of the present method.