F. Melino

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.

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.

Development and Validation of a Computational Code for Wet Compression Simulation of Gas Turbines

In this paper, a calculation code, developed in house by the authors, able to evaluate the performance of a gas turbine with all possible fogging strategies (high pressure fogging, overspray, and interstage injection) is presented and discussed. The code has a flexible structure and can be applied to evaluate the performance of every commercial gas turbine model. The aim of the calculation code is to overcome the limits of the most widespread commercial software, especially with regard to the two phase flow compression process simulation. The calculation code was validated on results available in the literature showing a good agreement with experimental and theoretical results.

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.

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

Gas Turbine Power Augmentation Technologies: A Systematic Comparative Evaluation Approach

Increasing electric rates in peak demand period, especially during summer months, are forcing power producers to look for gas turbine power augmentation technologies (PATs). One of the major undesirable features of all the gas turbines is that their power output and fuel efficiency decreases with increase in the ambient temperature resulting in significant loss in revenues particularly during peak hours. This paper presents a systematic comparative evaluation approach for various gas turbine power augmentation technologies (PATs) available in the market. The application of the discussed approach has been demonstrated by considering two commonly used gas turbine designs, namely, heavy-duty industrial and aeroderivative. The following PATs have been evaluated: inlet evaporative, inlet chilling, high pressure fogging, overspray, humid air injection and steam injection. The main emphasis of this paper is to provide a detailed comparative thermodynamic analysis of the considered PATs including the main variables, such as ambient temperature and relative humidity, which influence their performance in terms of power boost, heat rate reduction and auxiliary power consumption.Copyright

Gas Turbine Fogging Technology: A State-of-the-Art Review—Part III: Practical Considerations and Operational Experience

The strong influence of ambient temperature on the output and heat rate of a gas turbine has popularized the application of inlet fogging and overspray for power augmentation. In this paper we focus on practical considerations for the implementation of the fogging technology such as water quality requirements, foreign object damage, gas turbine inlet icing, intake duct design, changes in compressor performance characteristics, and blade coating distress problems. It also provides a checklist for users and project developers to facilitate the design and implementation of fogging systems. In addition, in this paper we cover operational experience and review the work pursued by gas turbine OEMs in the field of fogging technology. A list of unresolved issues and ongoing research related to the fogging technology is also provided.

Thermo-Economic Evaluation of ORC System in Off-Shore Applications

This paper presents a study related with off-shore oil & gas production and processing facilities, where required energy, for electric power, mechanical power and process heat, is mostly produced using gas turbines, as the fuel source (natural gas) is available onsite. Since size and weight of all equipment on an offshore facility are critical, it becomes necessary for the facility engineering team to ensure that all equipment are sized and selected appropriately to obtain better return on the investment. Therefore, any approach which could help in utilizing energy resources effectively will influence the bottom-line of the project, namely reduced capital cost and/or increased return on investment. In this paper, one such approach of recovering power and thermal energy through the use of Organic Rankine Cycle system is discussed. A detailed thermo-economic analysis, conducted considering a system with four gas turbines operating, shows that power recovery equivalent to one topping gas turbine is achievable with a suitable working fluid. The presented thermo-economic analysis clearly shows that use of the Organic Rankine Cycle system for waste heat recovery is a technically viable and economically attractive solution for the offshore applications.Copyright