Chapter

Thermodynamic Analysis of Inlet Air Cooling System for a Centrifugal Compressor: Fundamentals

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

In large air compressor installations consisting of multiple compressors operating continuously, even a small reduction in the inlet air temperature can improve the plant efficiency. Exergy efficiency is more rational than energy efficiency, and exergy analysis is more helpful than energy analysis for locating and evaluating available energy-saving potentials, identifying opportunities for improvements in system design, and establishing cost-effective system maintenance programs. When exergy analysis is performed on a system, thermodynamic imperfections can be quantified as exergy destruction, which represent losses in energy quality. In the present study, a thermodynamic analysis is made on the inlet air cooling system employed in a centrifugal compressor. Exergy input rate, exergy output rate, exergy loss rate, exergy destruction rate, and exergy efficiency were calculated with five different dead state temperatures and five different dead state relative humidities. Sustainability assessment is done by estimating the sustainability based on exergy efficiency.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

Article
Full-text available
This study presents energy and exergy analyses and sustainability assessment of the novel evaporative air cooling system based on Maisotsenko cycle which allows the product fluid to be cooled in to a dew point temperature of the incoming air. In the energy analysis, Maisotsenko cycle’s wet-bulb and dew point effectiveness, COP and primary energy ratio rates are calculated. Exergy analysis of the system is then carried out for six reference temperatures ranging from 0°C to 23.88°C as the incoming air (surrounding) temperature. The specific flow exergy, exergy input, exergy output, exergy destruction, exergy loss, exergy efficiency, exergetic COP, primary exergy ratio and entropy generation rates are determined for various cases. Furthermore, sustainability assessment is obtained using sustainability index method. As a result, maximum exergy efficiency is found to be 19.14% for a reference temperature of 23.88°C where the optimum operation takes place.
Article
Full-text available
Inlet fogging of gas turbine engines has attained considerable popularity due to the ease of installation and the relatively low first cost compared to other inlet cooling methods. With increasing demand for power and with shortages envisioned especially during the peak load times during the summers, there is a need to boost gas turbine power. There is a sizable evaporative cooling potential throughout the world when the climatic data is evaluated based on an analysis of coincident wet bulb and dry bulb information. This data is not readily available to plant users. In this paper, a detailed climatic analysis is made of 106 major locations over the world to provide the hours of cooling that can be obtained by direct evaporative cooling. This data will allow gas turbine operators to easily make an assessment of the economics of evaporative fogging. The paper also covers an introduction to direct evaporative cooling and the methodology and data analysis used to derive the cooling potential. Simulation runs have been made for gas turbine simple cycles showing effects of fogging for a GE Frame 7EA and a GE Frame 9FA Gas turbine for 60 and 50 Hz applications.
Article
Chapter 1 describes the characteristics of a thermodynamic concept, exergy, in association with building heating and cooling systems. Exergy is the concept that explicitly indicates 'what is consumed'. All systems, not only engineering systems but also biological systems including the human body, work feeding on exergy, consuming its portion and thereby generating the corresponding entropy and disposing of the generated entropy into their environment. The whole process is called 'exergy-entropy process'. The features of 'warm' exergy and 'cool' exergy and also radiant exergy are outlined. General characteristics of exergy-entropy process of passive systems, which would be a prerequisite to realize low exergy systems, are discussed together with the exergy-entropy process of the global environmental system. Chapter 2 introduces the various forms of exergy and the mathematical formulations used to evaluate them. The exergy balance on an open steady state system, which is much more relevant to thermodynamic analysis of energy systems, is also described, as well as the different exergetic efficiency factors introduced in the thermodynamic analysis of energy systems. Next, an exergy analysis example is outlined through an air-conditioning application. Air-conditioning applications are widely used in heating and cooling of buildings. Chapter 3 introduces an example of exergy calculation for space heating systems. The issues to have a better understanding of low-exergy systems for heating and cooling are raised. It is suggested that a prerequisite for low exergy systems would be rational passive design of building envelope systems.
Conference Paper
Gas Turbine output is a strong function of the ambient air temperature with power output dropping by 0.3–0.5 % for every 1°F rise in ambient temperature. This loss in output presents a significant problem to utilities, cogenerators and IPPs when electric demands are high during the hot months. In the petrochemical and process industry, the reduction in output of mechanical drive gas turbines curtails plant output. One way to counter this drop in output is to cool the inlet air. The paper contrasts the traditional evaporative cooling technique with direct inlet fogging. The state of the art relating to fog generation and psychrometrics of inlet fogging are described.
Article
Of evaporative cooling or energy recovery potential in HVAC, the conventional thermodynamic analysis is based on the enthalpy of moist air. In fact, the available energy of moist air is its exergy and the available energy saving potential ought to be the exergy. Isoexergic lines on psychometric charts associated with different ambient states persuade us that exergy and enthalpy are completely independent of each other. Thus, the enthalpy analysis is at least imperfect. Selecting the saturated state of moist air at ambient temperature (T 0) and pressure (p 0) as the dead-state, this paper analyses the exergy of moist air. It is broken down into three components: thermal, mechanical and chemical, so that each of them may be represented with a special devised diagram applicable to various conditions and ambient states among HVAC applications. Two guidelines for such applications are extracted from the diagrams as these: lower dead-state temperature (T 0) with the same difference of the humidity ratio (ω -ω 0S) is related with higher chemical exergy, and hence, the recovery of latent heat availability will probably be more valuable in winter than in summer; the exergy loss due to air flow resistance in a heat exchanger is usually small when compared with the potential of thermal and chemical exergy gaining. Further, the exergies of outdoor and exhaust room air are calculated and tabled for some Chinese cities and different types of air conditioning based on some statistic average parameters. Some general conclusions are drawn. For most districts on average room air parameters, the exhaust room air exergy is greater in winter than in summer. In winter, when exhaust room air temperature is low, the exergy of sensible heat is the main component of available energy saving potential. On contrast, the latent heat usually makes the prevailing contribution in summer, while at some dry locations, the exergy of outdoor air is even greater than that of exhaust room air.
Article
Evaporative cooling is a widely used air cooling technique. In this method, evaporation of a liquid in the surrounding air cools the air in contact with it. In the current investigation, numerical simulations are carried out to visualize the evaporation and dynamics of tiny water droplets of different diameters in a long air duct. The effect of initial droplet size on the temperature and relative humidity distribution of the air stream in the duct is investigated. Three different initial conditions of air are considered to verify the influence of ambient conditions. Droplet spray patterns are also analyzed to identify the suitable locations for the spray nozzles within the duct. The results obtained are displayed in a series of plots to provide a clear understanding of the evaporative cooling process as well as the droplet dynamics within the ducts.
Article
This study presents the energy, exergy, environmental, exergoeconomic, enviroeconomic and sustainability analyses of the Maisotsenko cycle based novel air cooler considering the nine different dead state temperatures, while the environment temperature is kept constant. In the energy analysis, the wet bulb and dew point effectivenesses, cooling capacity, energetic coefficient of performance and primary energy ratio rates are calculated. Also, in the exergy analysis, exergy input, output, loss and destruction rates as well as exergetic coefficient of performance and primary exergy ratio and exergy efficiency values are determined. Furthermore, sustainability analysis of the system is conducted through a sustainability index method. The electrical energy consumption cost of this novel air cooler shows that, it consumes only 59.85 $/year, when it is operated 8 h a day and 125 days in a year. The maximum exergetic cost rate is found to be 0.0228 kWh/$-year at a dead state temperature of 37.77 °C. Also, according to the enviroeconomic (environmental cost) analysis, this novel air cooler has very CO2 emissions cost as 6.96 $/year. Consequently, these results show the originality of the Maisotsenko cycle based novel air cooler.
Article
The severe dependence of gas turbine output on ambient temperature has created the need for inlet cooling technologies. This paper focuses on the practical aspects of direct evaporative cooling by fogging of the inlet air to a gas turbine compressor. This paper covers several of the practical considerations relating to the location of nozzles, water quality and operations and maintenance issues that relate to implementation of such systems. A design and implementation checklist is provided to assist users in ensuring a reliable installation.
Article
The exergy efficiency of three standard thermodynamic cycles, i.e., Brayton, Rankine and Otto cycles, are developed and the corresponding analytical equations are derived accordingly. The resultant expressions are applied to typical operating conditions and numerical results are obtained, when the heat of each engine is supplied by burning natural gas as a fuel with 100 percent theoretical air. A common result is the significant effect of the maximum cycle temperature, which causes an increase of exergy efficiency. It is shown that the compression ratio of the Brayton and Otto cycles, as well as the turbine inlet pressure in a steam power plant, raise the exergy efficiency. Moreover, increasing the ambient temperature has a negative influence on the exergy efficiency in the Brayton and Otto cycles, which occurs due to ambient air fed to these systems, thereby decreasing the deviation of the system from ambient conditions and reducing the exergy efficiency. Further findings include an optimal performance point of the Brayton and Rankine cycle, with a high sustainability and exergy efficiency. For instance, at the optimal operating point of the Brayton cycle with a compression ratio of 8 (or 12 for a second case), the exergy efficiency is 73 (60) percent, CO2 emissions is 530 (590) g/kWh and the sustainability index is 3.8 (2.8). The optimal operating point for an example of a Rankine cycle is found to be 50 percent for the exergy efficiency, with 440g/kWh of emitted CO2 and a sustainability index of two.
Article
The relation between work and changes in entropy generation arises from the simultaneous treatment of the first and second laws referred to as exergy (or available energy) analysis. In this paper, we discuss thermodynamic analysis of various psychrometric processes using the concept of exergy. A parametric study of each of the processes is carried out to determine the variation of second-law efficiency as a function of mass flow rate, relative humidity and temperature. Other trends such as variation of temperature with relative humidity are also shown where applicable. Irreversible losses are calculated by applying an exergy balance on each system. In this regard, an engineering equation solver (EES) programme is used, which is unique because it has built-in functions for most thermodynamic and transport properties; removing the need for approximate equations. The concept of total exergy as the sum of thermomechanical and chemical parts is employed in calculating the flow exergies for air and water vapor mixtures. It is shown for some processes investigated that an increase in the relative humidity of the incoming air stream increases second-law efficiency. We notice that a decrease in mass flow rate of fresh air (second incoming stream) in the case of adiabatic mixing decreases the second-law efficiency of the process. Also, it is shown that the mass flow rate (of both water and steam) has almost a linear relationship with relative humidity in the range investigated. Copyright © 2003 John Wiley & Sons, Ltd.
Article
Large-capacity compressors in industrial plants and the compressors in gas turbine engines consume a considerable amount of power. The compression work is a strong function of the ambient air temperature. This increase in compression work presents a significant problem to utilities, generators and power producers when electric demands are high during the hot months. In many petrochemical process industries and gas turbine engines, the increase in compression work curtails plant output, demanding more electric power to drive the system. One way to counter this problem is to directly cool the inlet air. Inlet fogging is a popular means of cooling the inlet air to air compressors. In the present study, experiments have been performed to investigate the suitability of two-fluid nozzle for inlet fogging. Compressed air is used as the driving working gas for two-fluid nozzle and water at ambient conditions is dragged into the high-speed air jet, thus enabling the entrained water to be atomized in a very short distance from the exit of the two-fluid nozzle. The air supply pressure is varied between 2.0 and 5.0 bar and the water flow rate entrained is measured. The flow visualization and temperature and relative humidity measurements are carried out to specify the fogging characteristics of the two-fluid nozzle. KeywordsEvaporative Cooling-Inlet Fogging-Energy Savings-Two-fluid Nozzles
Article
Increasing power demands have necessitated the development of energy efficient systems in the industrial sector. At present, about 10% of the overall electric power used by large industrial plants is consumed by high-capacity compressors supplying compressed air. Likewise, in a gas turbine power plant, nearly half the generated power is used for driving the compressor. The work of compression is proportional to inlet air temperature, and cooling the inlet air can save considerable amount of power in large turbo machines during hot summer months. Inlet fogging is a popular means of inlet air cooling, and fog nozzles are the most critical components in an inlet fogging installation. Majority of these installations employ impaction pin nozzles. In the present work, experiments are conducted over a wide range of operating parameters in variable length wind tunnels of different cross sections in order to investigate the performance of impaction pin nozzle in inlet fogging. Flow visualization and measurements are carried out to analyze the fog behavior and identify suitable nozzle locations in typical air ducts. The results show that impaction pin nozzles are suitable for inlet fogging applications. KeywordsEnergy saving–Evaporative cooling–Impaction pin nozzle–Inlet fogging
Article
Energy resources and their utilization intimately relate to sustainable development. In attaining sustainable development, increasing the energy efficiencies of processes utilizing sustainable energy resources plays an important role. The utilization of renewable energy offers a wide range of exceptional benefits. There is also a link between exergy and sustainable development. A sustainable energy system may be regarded as a cost-efficient, reliable, and environmentally friendly energy system that effectively utilizes local resources and networks. Exergy analysis has been widely used in the design, simulation and performance evaluation of energy systems.
Article
The use of exergy is described as a measure for identifying and explaining the benefits of sustainable energy and technologies, so the benefits can be clearly understood and appreciated by experts and non-experts alike, and the utilization of sustainable energy and technologies can be increased. Exergy can be used to assess and improve energy systems, and can help better understand the benefits of utilizing green energy by providing more useful and meaningful information than energy provides. Exergy clearly identifies efficiency improvements and reductions in thermodynamic losses attributable to more sustainable technologies. A new sustainability index is developed as a measure of how exergy efficiency affects sustainable development. Exergy can also identify better than energy the environmental benefits and economics of energy technologies. The results suggest that exergy should be utilized by engineers and scientists, as well as decision and policy makers, involved in green energy and technologies in tandem with other objectives and constraints.
Article
The exergy of an energy form or a substance is a measure of its usefulness or quality or potential to cause change. A thorough understanding of exergy and the insights it can provide into the efficiency, environmental impact and sustainability of energy systems, are required for the engineer or scientist working in the area of energy systems and the environment. Further, as energy policies play an increasingly important role in addressing sustainability issues and a broad range of local, regional and global environmental concerns, policy makers also need to appreciate the exergy concept and its ties to these concerns. During the past decade, the need to understand the connections between exergy and energy, sustainable development and environmental impact has become increasingly significant. In this paper, a study of these connections is presented in order to provide to those involved in energy and environment studies, useful insights and direction for analyzing and solving environmental problems of varying complexity using the exergy concept. The results suggest that exergy provides the basis for an effective measure of the potential of a substance or energy form to impact the environment and appears to be a critical consideration in achieving sustainable development.
Inlet fogging of gas turbine engines-Part B: fog droplet sizing analysis, nozzle types, measurement and testing
  • M Chaker
  • C B Meher-Homji
  • T R Mee
Analytical study on evaporative cooling potential and power gains by inlet fogging
  • A Suryan
  • D S Kim
  • H D Lee
  • J K Kwon
  • H D Kim
Experimental measurement of fog droplet distributions from impaction pin nozzle using global sizing velocimetry
  • A Suryan
  • J K Lee
  • C K Kim
  • H Y Jeong
  • H D Kim
Inlet fogging of gas turbine engines-Part A: fog droplet thermodynamics, heat transfer and practical considerations
  • M Chaker
  • C B Meher-Homji
  • T R Mee
Gas turbine power augmentation by fogging of Inlet Air
  • C B Meher-Homji
  • T R Mee