A. Peretto

Gas Turbine Fogging Technology: A State-Of-The-Art Review, Part I: Inlet Evaporative Fogging- Analytical And Experimental Aspects

Ambient temperature strongly influences gas turbine power output causing a reduction of around 0.50% to 0.90% for every 1°C of temperature rise. There is also a significant increase in the gas turbine heat rate as the ambient temperature rises, resulting in an increased operating cost. As the increase in power demand is usually coincident with high ambient temperature, power augmentation during the hot part of the day becomes important for independent power producers, cogenerators, and electric utilities. Evaporative and overspray fogging are simple, proven, and cost effective approaches for recovering lost gas turbine performance. A comprehensive review of the current understanding of the analytical, experimental, and practical aspects including climatic and psychrometric aspects of high-pressure inlet evaporative fogging technology is provided. A discussion of analytical and experimental results relating to droplets dynamics, factors affecting droplets size, and inlet duct configuration effects on inlet evaporative fogging is covered in this paper. Characteristics of commonly used fogging nozzles are also described and experimental findings presented.

Inverted Brayton cycle employment for low-temperature cogenerative applications

The employment of cogeneration plants for thermal and electric power production is constantly increasing especially for low power requirements. In most cases, to match these low power needs, the cogeneration plant is built up with diesel or gasoline engine or with gas turbine units. In this paper, the performance, in terms of the most utilized cogenerative indexes, of an inverted Brayton cycle working with the gas exhausted by the open power plant have been evaluated. Subsequently, the analysis of a cogenerative gas turbine equipped with IBC was carried out and the benefits numerically calculated. It resulted that the IBC employment may increase of about five percentage points the plant electric efficiency, making this solution particularly attractive for cogenerative applications.

Gas Turbine Fogging Technology: A State-Of-The-Art Review, Part II: Overspray Fogging - Analytical And Experimental Aspects

The strong influence of ambient temperature on the output and heat rate on a gas turbine has popularized the application of inlet fogging and overspray for power augmentation. One of the main advantages of overspray fogging is that it enhances power output as a result of decrease in compression work associated with the continuous evaporation of water within the compressor due to fog intercooling. A comprehensive review on the current understanding of the analytical and experimental aspects of overspray fogging technology as applied to gas turbines is presented in this paper.

Thermo-Economic Analysis of an Intercooled, Reheat and Recuperated Gas Turbine for Cogeneration Applications–Part I: Base Load Operation

The knowledge of off-design performance for a given gas turbine system is critical particularly in applications where considerable operation at low load setting is required. This information allows designers to ensure safe operation of the system and determine in advance thermoeconomic penalty due to performance loss while operating under part-load conditions. In this paper, thermoeconomic analysis results for the intercooled reheat (ICRH) and recuperated gas turbine, at the part-load conditions in cogeneration applications, have been presented. Thermodynamically, a recuperated ICRH gas turbine-based cogeneration system showed lower penalty in terms of electric efficiency and Energy Saving Index over the entire part-load range in comparison to the other cycles (nonrecuperated ICRH, recuperated Brayton and simple Brayton cycles) investigated. Based on the comprehensive economic analysis for the assumed values of economic parameters, this study shows that a midsize (electric power capacity 20 MW) cogeneration system utilizing nonrecuperated ICRH cycle provides higher return on investment both at full-load and part-load conditions, compared to the other same size cycles, over the entire range of fuel cost, electric sale, and steam sale values examined. The plausible reasons for the observed trends in thermodynamic and economic performance parameters for four cycles and three sizes of cogeneration systems under full-load and part-load conditions have been presented in this paper.

Parametric Analysis of Combined Cycles Equipped With Inlet Fogging

In recent years, deregulation in the power generation market worldwide combined with significant variation in fuel prices and a need for flexibility in terms of power augmentation specially during periods of high electricity demand (summer months or noon to 6:00 p.m.) has forced electric utilities, cogenerators and independent power producers to explore new power generation enhancement technologies. In the last five to ten years, inlet fogging approach has shown more promising results to recover lost power output due to increased ambient temperature compared to the other available power enhancement techniques. This paper presents the first systematic study on the effects of both inlet evaporative and overspray fogging on a wide range of combined cycle power plants utilizing gas turbines available from the major gas turbine manufacturers worldwide. A brief discussion on the thermodynamic considerations of inlet and overspray fogging including the effect of droplet dimension is also presented. Based on the analyzed systems, the results show that high pressure inlet fogging influences performance of a combined cycle power plant using an aero-derivative gas turbine differently than with an advanced technology or a traditional gas turbine. Possible reasons for the observed differences are discussed.

Gas Turbine Based Power Cycles - A State-of-the-Art Review

Gas turbines have been used in wide ranging applications since their world’s first use in aviation and power generation in the jet engine powered flight of Heinkel aircraft (model He-178) and Brown Boveri & Cie’s (BBC) 4 MW power generation plant in Neuchatel, Switzerland, respectively during 1939. This paper provides the historical evolution of the gas turbine (GT) based power cycles. A detailed parametric thermodynamic cycle analysis is presented for various GT cycles (mostly, which have been implemented). In addition, a comparative performance evaluation of various cycles is presented clearly showing ranges within which a particular arrangement can be beneficial. The simulation results are compared with the performance of existing machines with similar design conditions. A discussion is presented to show limitations and advantages of each GT cycle and the associated technological advancements made. To complete the review, modified Brayton cycles under development by the gas turbine manufacturers, researchers, etc. have also been identified.

A Feasibility Study of Existing Gas Turbines for Recuperated, Intercooled, and Reheat Cycle

In the present paper, a comprehensive and simple in application design methodology to obtain a gas turbine working on recuperated, intercooled, and reheat cycle utilizing existing gas turbines is presented. Applications of the proposed design steps have been implemented on the three existing gas turbines with wide ranging design complexities. The results of evaluated aerothermodynamic performance for these existing gas turbines with the proposed modifications are presented and compared in this paper. Sample calculations of the analysis procedures discussed, including stage-by-stage analysis of the compressor and turbine sections of the modified gas turbines, have been also included. All the three modified gas turbines were found to have higher performance, with cycle efficiency increase of 9% to 26%, in comparison to their original values.

A Parametric Study of Interstage Injection on GE Frame 7EA Gas Turbine

In recent years, among various available inlet air cooling techniques for gas turbine power enhancement, high pressure fogging has seen an increasing attention mainly because of its comparatively low initial investment cost and less downtime for its installation. The various fogging strategies such as inlet evaporative, overspray (or wet compression) and interstage injection have been implemented in simple and combined cycle applications. Unlike wet compression, air at the compressor inlet is not fully saturated with the interstage injection. However, both wet compression and interstage injection involve multi-phase flow and water evaporation during the compression process. The phenomenon of two phase flow compression in axial compressor is not yet fully understood. This paper investigates effects of interstage injection on the performance of a GE Frame 7EA gas turbine using aero-thermodynamic modeling. In addition to estimating the overall gas turbine performance changes achievable with the interstage injection approach, the study presented here discusses impact of interstage injection on the stage-by-stage compressor performance characteristics of the selected gas turbine. The plausible reasons for the observed performance changes are discussed.Copyright

Influence of Water Droplet Size and Temperature on Wet Compression

In the last years, among all different gas turbine inlet air cooling techniques, an increasing attention to fogging approach is dedicated. The various fogging strategies seem to be a good solution to improve gas turbine or combined cycle produced power with low initial investment cost and less installation downtime. In particular, overspray fogging and interstage injection involve two-phase flow consideration and water evaporation during compression process (also known as wet compression). According to the Author’s knowledge, the field of wet compression is not completely studied and understood. In the present paper, all the principal aspects of wet compression and in particular the influence of injected water droplet diameter and surface temperature, and their effect on gas turbine performance and on the behavior of the axial compressor (change in axial compressor performance map due to the water injection, redistribution of stage load, etc.) are analyzed by using a calculation code, named IN.FO.G.T.E. (IN terstage FO gging G as T urbine E valuation), developed and validated by the Authors.Copyright

Application of a Computational Code to Simulate Interstage Injection Effects on GE Frame 7EA Gas Turbine

This paper investigates effects of interstage water injection on the performance of a GE Frame 7EA gas turbine using aero-thermodynamic modeling. To accomplish this objective a computational code, written in Fortran 90 language and developed by DIEM – University of Bologna, has been used. The calculation procedure considers effects of evaporation of injected water within the compressor including droplets dynamics which are necessary in order to fully evaluate effects of wet compression on the gas turbine performance. The robustness of the computational code is demonstrated by evaluating stage-by-stage compressor performance and the overall gas turbine performance in presence of inlet evaporative fogging, overspray fogging and interstage water injection. The presented results show that water injection location influences compressor stage loading redistribution differently. The plausible explanations to the observed trends of various performance parameters are presented in the paper.Copyright