Sotirios Karellas

Inlet Air Cooling Methods for Gas Turbine Based Power Plants

Background: Power generation from gas turbines is penalized by a substantial power output loss with increased ambient temperature. By cooling down the gas turbine intake air the power output penalty can be mitigated. Method of Approach: The purpose of this paper is to review the state of the art in applications for reducing the gas turbine intake air temperature and examine the merits from integration of the different air-cooling methods in gas-turbine-based power plants. Three different intake air-cooling, methods (evaporative cooling, refrigeration cooling, and evaporative cooling of precompressed air) have been applied in two combined cycle power plants and two gas turbine plants. The calculations were performed on a yearly basis of operation. taking into account the time-varying climatic conditions. The economics from integration of the different cooling systems were calculated and compared. Results: The results have demonstrated that the highest incremental electricity generation is realized by absorption intake air-cooling. In terms of the economic performance of the investment, the evaporative cooler has the lowest total cost of incremental electricity generation and the lowest payback period (PB). Concerning the cooling method of pre-compressed air the results show a significant gain in capacity, but the total cost of incremental electricity generation in this case is the highest. Conclusions: Because of the much higher capacity gain by an absorption chiller system. the evaporative cooler and the absorption chiller system may both be selected for boosting the performance of gas-turbine-based power plants, depending on the prevailing requirements of the plant operator.

Conversion of Syngas From Biomass in Solid Oxide Fuel Cells

Conversion of biomass in syngas by means of indirect gasification offers the option to improve the economic situation of any fuel cell system due to lower costs for feedstock and higher power revenues in many European countries. The coupling of an indirect gasification of biomass and residues with highly efficient solid oxide fuel cell (SOFC) systems is therefore a promising technology for reaching economic feasibility of small decentralized combined heat and power production (CHP).The predicted efficiency of common high temperature fuel cell systems with integrated gasification of solid feedstock is usually significantly lower than the efficiency of fuel cells operated with hydrogen or methane. Additional system components like the gasifier as well as the gas cleaning reduce this efficiency. Hence common fuel cell systems with integrated gasification of biomass will hardly reach electrical efficiencies above 30

Hydrogen Production from Biomass Gasification

Upgrading of gas streams formed from biomass gasification for the production of pure hydrogen or hydrogen-rich gases is facing many technical and technological challenges. Both gasification and hydrogen separation technologies play a significant role in the total efficiency of the production process. The aim of this chapter is to analyze gasification processes and examine the possible options for hydrogen production from the product gas streams from a gasification process. Gas conditioning and hydrogen purity will be taken into consideration as well as economic aspects of the integrated process.

Renewable and Conventional Electricity Generation Systems: Technologies and Diversity of Energy Systems

In this chapter, the primary technical aspects of conventional and renewable energy systems are presented. The description focuses on commercial systems installed across the world, together with a brief introduction to some promising technologies currently under development, such as Carbon Capture and Storage (CCS). Conventional energy systems include power plants using fossil fuels (natural gas, coal, etc.), while renewable energy systems include solar, wind, geothermal, biomass, and small-hydropower applications. These technologies are briefly described accompanied by economic figures (installation cost, fuel cost, specific cost of electricity, etc.) and emissions data (where applicable). Some insight on the energy strategy in specific countries is provided and how this can be related to local conditions and electric power requirements.

Technoeconomic Analysis and Comparison of a Solar-Based Biomass ORC-VCC System and a PV Heat Pump for Domestic Trigeneration

AbstractA great deal of energy is consumed annually for domestic heating and cooling. Meanwhile, the policies adopted for the reduction of CO2 emissions and fossil fuel consumption have led to the development of technological solutions based on renewable energy such as biomass and solar, along with the implementation of efficient multigeneration systems. In this study, two trigeneration systems, a microscale system based on a combined organic Rankine cycle (ORC) and a vapor compression cycle (VCC), incorporating a biomass boiler and parabolic trough collectors (PTC), are economically analyzed and evaluated against a heat pump (HP) powered by photovoltaic (PV) panels (PV heat pump). The thermal loads of a building located in Crete, Greece, are considered for the analysis. The efficiency of the ORC ranges between 3.7 and 10.05% for different organic fluids and conditions, while the cogeneration efficiency is up to 73.5%. For the PV heat pump, an average efficiency equal to 15% was calculated. The payback pe...

Piston Expanders Technology as a Way to Recover Energy From the Expansion of Highly Wet Organic Refrigerants

The design of expanders for organic fluids is gaining an increasing attention due to the large opportunities opened by the ORC as a way to recover low grade heat. The possibility of recovering at least a fraction of the energy related to throttling in inverse cycles could have interesting relapses on the market of heating (heat pumps) and refrigeration machines. The main challenge to be faced is the management of a highly wet fluid (typical quality is in the 0–0.6 range), which puts off side dynamic expanders like turbines. For this reason, piston technology is proposed and analyzed. The potential recovery from the throttling of a 20 kW target domestic heat pump cycle is determined by modeling the real expansion cycle with two different codes, a commercial one (largely widespread and very easy to use) and a purposely developed one, which is much more customizable and may include different approaches to the physical behavior of the two–phase expansion.The results show interesting possibility of energy recovery from this generally wasted source, which opens the way to improvements of the heat pump COP from 4% to about 7%, depending on the working (i.e. seasonal) conditions. The analysis also points out the agreement in the results of two different adopted simulation tools (commercial AMESim® and self-made customizable EES®), which can be thus considered valuable in the design, analysis and optimization of the proposed expander.Due to the biphasic nature of the working fluid, the performance of the expander is strongly influenced by the inlet conditions of the fluid from the condenser of the heat pump to the cylinders, such as throttling of the inlet/outlet valves and friction through the ducts.On the whole, this expander technology has very interesting chances to effectively manage fluids under highly wet conditions, like those related to the throttling from upper to lower pressure of inverse cycles.Copyright

EU Emissions Trading Scheme Application in Bulgaria, Greece and Romania from 2008 to 2012

Emission trading in three European Union (EU) member states in the Balkans during the second phase (2008–2012) of the EU emissions trading scheme (EU ETS) is investigated in terms of allocation submission of emission credits (assigned amount units (AAU), certified emission reductions (CER), emission reduction units (ERU) and potential trading activities). Greece, Bulgaria and Romania are analyzed as three individual cases under the scope of the EU Directive 2003/87/EC with the aim to identify the adequacy of emission allowances in individual sectors and their resulting utilization. The aforementioned Balkan countries produced over 750 Mt of verified emissions in the first commitment period of 2008–2012, of which approximately 70 % correspond to combustion installations. A deficit emerged for individual installations; although at the sector level, deficits appeared only in the aviation sector for all countries. Greece also experienced a deficit in the emissions trading scheme (ETS) combustion sector prior to the use of CER or ERU under the clean development mechanism (CDM) and the joint implementation (JI) mechanism. This study mainly focuses on the combustion sector while attempting to identify differences in use of international emission credits among the three Balkan countries and sectors therein.

The driving factors of CO2 emissions from electricity generation in Greece: an index decomposition analysis

The present paper investigates the driving factors of CO2 emissions from electricity generation in Greece during the period 2005-2012 and compares the revealed trends with those recorded in EU-28. The analysis focuses on the following determinant factors: a) economic growth; b) electricity intensity of the economy; c) electricity trade; d) fuel mix; e) efficiency of electricity generation. By using a decomposition analysis based on the Logarithmic Mean Divisia Index-I (LMDI-I) method, the effect of each factor is calculated under the ceteris paribus assumption. The obtained results show that in times of economic growth, changes in the fuel mix and the more efficient use of electricity in the economy have retained the upward trend of emissions, while the economic downturn has driven emissions down but at the same time it contributed to a less efficient use of energy resources in power generation and in the final demand sectors.