Humidification Processes in Gas Turbine Cycles

The global climate change caused by emissions of greenhouse gases from combustion processes has been recognized as a continuously growing problem and much research focuses on improving the environmental performance of gas turbines. The potential of improving gas turbine component efficiencies has become smaller each decade and therefore, thermodynamic cycles have become more interesting for power producing units. One of these cycles is the evaporative gas turbine cycle, also known as the humid air turbine. This thesis presents a theoretical model developed for the humidification tower in an evaporative gas turbine. The developed theoretical model has been validated with measurements from experiments conducted in a 600 kWe pilot plant. This thesis presents the installation of a plate heat exchanger in the pilot plant. The experience from the pilot plant is used in a comparative study. This study evaluates the influence of the aftercooler on the performance of the evaporative gas turbine. A test facility for evaporation processes at elevated pressures and temperatures have been built. Evaporation of binary mixtures into a compressed air stream has been performed. Experimental studies with the pilot plant have revealed that it is possible to use a plate heat exchanger as aftercooler in the evaporative gas turbine. The pressure drop on the air side in the aftercooler has been experimentally determined to 1.6% and the pinch-point to 0.1°C. The reconstruction of the pilot plant from a simple cycle to an evaporative cycle has resulted in an increase in thermal efficiency from 21% to 35%. A theoretical model has been developed for the humidification process that predicts the height of the humidification column with an error of 10?15%. Thermodynamic analysis of the bio-EvGT has been performed which have showed that the bio-EvGT cycle has an optimum efficiency of 34%. Further thermodynamics analysis has indicated that the bio-EvGT is a viable alternative to the biomass fueled steam turbine cycle

Non-conventional working fluids for thermal power generation: A review

New technology requirements derived from the exploitation of novel energy resources, and the needs for improvement of the energy efficiency of current power generation systems are pushing the industry towards the search of alternative working fluids. The great challenge for these non-conventional fluids is to provide satisfactory performances and fill the existing lack of media for some innovative energy applications. In this review a number of emerging working fluids for thermal power generation are presented. Also, a special emphasis is devoted to the discussion about new promising fluids, such as nanofluids or ionic liquids, that could be an important breakdown for power generation in the near future

Energy and Exergy Analysis of a Cruise Ship

In recent years, the International Maritime Organization agreed on aiming to reduceshipping’s greenhouse gas emissions by 50% with respect to 2009 levels. Meanwhile, cruise shiptourism is growing at a fast pace, making the challenge of achieving this goal even harder.The complexity of the energy system of these ships makes them of particular interest from anenergy systems perspective. To illustrate this, we analyzed the energy and exergy flow rates of acruise ship sailing in the Baltic Sea based on measurements from one year of the ship’s operations.The energy analysis allows identifying propulsion as the main energy user (46% of the total) followedby heat (27%) and electric power (27%) generation; the exergy analysis allowed instead identifyingthe main inefficiencies of the system: while exergy is primarily destroyed in all processes involvingcombustion (76% of the total), the other main causes of exergy destruction are the turbochargers,the heat recovery steam generators, the steam heaters, the preheater in the accommodation heatingsystems, the sea water coolers, and the electric generators; the main exergy losses take place in theexhaust gas of the engines not equipped with heat recovery devices. The application of clustering ofthe ship’s operations based on the concept of typical operational days suggests that the use of fivetypical days provides a good approximation of the yearly ship’s operations and can hence be usedfor the design and optimization of the energy systems of the ship

Temporary CO2 capture shut down: Implications on low pressure steam turbine design and efficiency

The Natural gas Combined Cycle (NGCC) with post combustion capture using liquid solvents may in some cases be of interest to design with a flexible steam bottoming cycle, so that it can operate both with and without CO2 capture. It is then important that the choice of the low pressure (LP) steam turbine exhaust size is made accordingly. The paper describes why a flexible NGCC requires a LP steam turbine with smaller exhaust than the corresponding NGCC without CO2 capture, and how this will affect the LP turbine exhaust loss and NGCC process efficiency. Handling large variations in LP steam flow is in fact wellknown technology in combined heat and power (CHP) plants, and the use of 3D simulation tools can further help making the best LP steam turbine design choice.publishedVersio

Auto Machine Learning for predicting Ship Fuel Consumption

In recent years, machine learning has evolved in a fast pace as both algorithms and computing power are constantly improving. In this study, a machine learning model for predicting the fuel oil consumption from engine data has been developed for a cruise ship operating in the Baltic Sea. The cruise ship is equipped with legacy volume flow meters and newly installed mass flow meters, as well as an extensive set of logged time series data from the machinery logging system. The model is developed using state-of-the-art Auto Machine Learning tools, which optimises both the model hyper parameters and the model selection by using genetic algorithms. To further increase the model accuracy, a pipeline of different models and pre-processing algorithms is evaluated. An extensive model trained for a certain system can be used for optimisation simulation, as well as online energy efficiency prediction. As the models automatically adapt to noisy sensor data and thus function as a watermark of the machinery system, these algorithms show a potential in predicting ship energy efficiency without installation of additional mass flow meters. All tools used in this study are Open Source tools written in Python and can be applied on board. The study shows great potential for utilising large amounts of already available sensor data for improving the accuracy of the predicted ship energy consumption

A new IPSEpro library for the simulation of binary mixtures of real fluids in power cycle analysis

Increasing efforts to produce power from renewable resources and improve the efficiency of current industrial processes have turned the spotlight on organic Rankine cycles (ORC). The use of refrigerant mixtures in these cycles offers a wide range of possibilities for fluid selection and optimization. Moreover, zeotropic mixtures are reported to yield better cycle performances due to their better thermal match with the source and sink streams. In this work a new IPSEpro® library for the simulation of power cycles using binary mixtures was developed. With this library the working fluid can be defined as the mixture of any pair of suitable fluids contained in the Refprop database

Thermodynamic studies of a HAT cycle and its components

The electric power grid contains more and more renewable power production such as wind and solar power. The use of renewable power sources increases the fluctuations in the power grid which increase the demand for highly efficient, fast-starting power-producing units that can cope with sudden production losses. One of the more innovative power plant cycles, that have the potential of competing with conventional combined power plants in efficiency but has a higher availability and faster start up time, is the Evaporative Gas Turbine (EvGT) or Humid Air Turbine (HAT). A thermodynamic evaluation of different HAT cycle layouts has been done in this paper. Each layout is evaluated separately which makes it possible to study different components individual contribution to the efficiency and specific power. The thermodynamic evaluation also shows that it is important to look at different cool-flow extracting positions. The effect of water temperature entering the cycle, called make-up water, and where it is introduced into the cycle has been evaluated. The make-up water temperature also affects the optimal pressure level for intercooling and it is shown that an optimal position can be decided considering design parameters of the compressor and the water circuit. (C) 2011 Elsevier Ltd. All rights reserved

Power generation from low heat sources

In this chapter a thorough review of the latest research findings on power generation from non-conventional low heat sources is presented. Main discoveries and results of research works ranging from source exploitation technologies to final power production are reported and discussed to offer an overview of their potential. Firstly the concept of low-grade source is presented and the main energy sources in this group (i.e. geothermal energy, solar thermal systems, industrial waste heat and ocean thermal energy) are introduced. Each of them is briefly described and the latest developments and improvements on the technologies for their exploitation are enumerated. Afterwards the state-of-the-art available power cycles for the conversion of low heat into electricity are reported. Only thermal power conversion technologies are presented due to their higher presence in commercial applications and their potential for small scale power generation. Among these technologies, last findings and results on organic Rankine cycles (ORC) and power cycles based on working fluid mixtures (e.g. Kalina cycle) are described. A special emphasis is placed on organic Rankine cycles (ORC) since over the last few years this technology has experienced a significant global growth, boosted by their viable performance and the inherited knowledge from the refrigeration industry. In addition, the suitability of less known technologies such as Stirling cycles and their current development status and perspectives are also commented. After this review it follows an examination of the implementation of these technologies in present power production systems. Discussion will be provided on which are the current barriers that the mentioned technologies are facing for their introduction or during their operation. On the other hand, practical restrictions concerning the availability of suitable technology, environmental requirements or economic viability are stated. Limitations regarding thermodynamic and technological aspects, as well as operational concerns will be considered of special interest. In the final section we deal with the future scenario for the integration of small-scale power generation. Potential solutions for overcoming technology development barriers are presented and directions of current research works on this topic are pointed out

Theoretical and experimental evaluation of a plate heat exchanger aftercooler in an evaporative gas turbine cycle

The evaporative gas turbine pilot plant (EvGT) has been in operation at Lund Institute of Technology in Sweden since 1997. This article presents the experimental and theoretical results of the latest process modifications made, i.e. the effect of the installation of an aftercooler. The purpose of the aftercooler is to increase the performance of the cycle by utilizing more low-level heat in the humidification tower. The chosen aftercooler is of plate heat exchanger type, which, is very compact, has high thermal efficiency and low pressure drop. The installation of an aftercooler lowers the temperature of the air entering the humidification tower. This also lowers the temperature of the circulating humidification water, which facilitates the extraction of more low-level heat from the economizer. This low-level heat can be utilized to evaporate more water in the humidification tower and thus increase the gas flow in the expander. The pilot plant has been operated at different loads and the measured results has been evaluated and compared with theoretical models. The performance of a plate heat exchanger in power plant applications has also been evaluated. Experience from the measurements has then been used for the potential cycle calculations. It has been shown that the aftercooler lowers the flue gas temperature in the pilot plant to 9

Efficiency improvements in an industrial steam turbine stage - Part 1

The present work approaches the idea of increasing the efficiency of an industrial steam turbine stage. For this endeavor, an industrial steam turbine stage comprising of prismatic stator and rotor is considered. With the velocity triangles as input, airfoil design is carried out. Firstly, the rotor is redesigned to take care of any incidence issues in the baseline case. In rotor blades, the peak Mach number is reduced in blade to blade flow passage and hence, efficiency of stage is increased. Rotor is made front loaded. After finalizing the rotor, the stator is redesigned. Stator is made more aft-loaded when compared to the baseline case. By making the stator aft-loaded, the efficiency increased by reducing profile losses. This design modification also showed advantage in secondary losses. The total pressure loss in the stator was reduced by a delta of 0.15. When creating an airfoil for stator or rotor, MISES was used in order to evaluate profile losses. The design verification for the stage was numerically done using commercial CFD software ANSYS CFX. Steady state RANS simulations were carried out. The stator and the rotor still being prismatic, only by virtue of airfoil design, the total to total stage efficiency improvement of 0.33% was predicted