Stefan POSTRZEDNIK
Net calorific value as a parameter of a biomass energy usefulness
The dominant source of primary energy is nowadays the chemical energy of fossil fuels but the perspectives of depletion of these fuel sources and a threat to human environment increased an interest in renewable energy sources. Biomass is also the primary energy source and is utilized mainly as fuel in combustion processes. The basic parameter determining the energy usefulness of this fuel is the net calorific value of its combustible parts but the characteristic feature of this parameter is a relatively wide range (dispersion) of its values. That is why the biomass net calorific value (“daf” state) is generally treated as a random sample assuming values from the range that is of our interest with the probability resulting from the worked out distribution.
Keywords: biomass, net calorific value, energy usefulness
Sylwester FILIPIAK
Application of a coevolutionary algorithm integrated with a classifier system to optimize the work of power distribution grids
The methodology of restoring power supply to consumers in case of a distribution grid failure is an important issue in the literature on operation and reliability of electrical energy distribution grids. Presented is here a concept of a new method which supports the work of distribution grids operators in case of a failure with the use of a classifier system working in tandem with a coevolutionary algorithm. The method presented here enables constructing scenarios for adjustments of medium voltage power distribution grids configuration (power system switchgear operation adjustments). The developed method is based on theoretical rudiments of genetic-based machine learning systems. This method uses informations on previous power distribution grid failures and enables using information from the simulated failures. Decision variables which, among other things, take into account the reliability parameters of distribution grid elements, have been described using the fuzzy set theory. Described are also sample calculations related to failures of a selected power distribution grid with the aid of the developed method.
Keywords: distribution grids, grid configuration, configuration optimization
Andrzej WARACHIM, Krzysztof DEKARZ
Selected problems of MV grid nodes modernization
Illustrated is the importance of investing in MV grid modernization and its impact on the entire power system operation. Described are practical concepts and solutions that are used in MV networks.
Keywords: MV distribution grids, modernization of indoor and open-air substations
Stanisław ANWEILER, Grzegorz NOWOSIELSKI, Zbigniew PLUTECKI
Application of numerical modeling for optimization of a lignite fluidized-bed dryer
Fluidized bed drying process is a gas/solid multiphase flow where the dispersed phase concentration is the object of this scientific research. The article provides a methodology for estimation of the lignite granules and the air two-phase flow inside fluidized bed dryers. The aim of the research is the identification of: a) geometrical parameters of the fluidized bed chamber and: b) necessary properties of the flow, providing a large intensity of the drying process while the minimum energy consumption is achieved. Research was based on the use of process visualization methods and a digital image analysis of obtained experimental data. Gathered data were then applied for construction of a numerical model describing the two-phase flow phenomena. The experimental research was carried out on a measurement setup made of a transparent plastic, which was adequately illuminated by headlamps and screens. Bright field illumination technique was applied for the image acquisition. As a result of the process visualization, image sequences illustrating the evolution of the two-phase gas/solid flow structure have been obtained. Images of the flow regime were then analyzed with the use of Digital Particle Image Velocimetry (DPIV) technique. The obtained results were accepted as the assessment criterion for the simulation studies using numerical models. The mathematical simulation of the two-phase flow was conducted with the use of the Euler–Euler approach, and the calculations were performed with ANSYS software. The results of the simulations were then verified showing satisfactory qualitative and quantitative convergence between the experiment and the simulation. Finally, on a basis of the conducted reasearch, it was ascertained that the proposed numerical model of a fluidized bed dryer can be an effective tool in the procedure of lignite drying energy optimization process.
Keywords: lignite drying, modeling of the two-phase flow, visualisation, image analysis, simulation, numerical modeling
Krzysztof WACŁAWIAK
Influence of a superheater tube shape on the ash particle striking efficiency
Presented are results of numerical simulations regarding influence of a single superheater tube shape on the ash particle striking efficiency. All the simulations were done with a Fluent code of Ansys software package. The following shapes of a tube were analyzed: square, circular, elliptical of various radii ratio and a square one but turned at a different angle to the gas flow. Studied were the trajectories of 20, 40, 60 and 100 μm ash particles. The velocity of gas laden with ash particles at the inlet to the studied duct was 7,5 m/s. Temperature of the gas and ash particles at the inlet was 727ºC and the temperature of the tube wall was equal 400ºC. The numerical simulations confirmed that the streamlined shape of elliptical tubes leads to reduction of the amount of ash particles striking its surface. Attention is also called to the fact that in some conditions it can come to secondary striking of a tube-wall by ash particles.
Keywords: heat exchanger, superheater shape, ash particles
Ireneusz ORZEŁ
Designing of substation ligthning protection using the rolling sphere method and IT-tools
Presented are, elaborated by Energoprojekt-Kraków, basic assumptions and the program itself which help designing of electric power substation lightning protection. The program is based on the „classic” rolling sphere method and also a method deriving from the PN-EN 61936-1 standard (modified rolling sphere method). Particularly important is the possbility to apply the method derived from the above mentioned standard as it is intended for electric power installations.
But practical application of that method which is defined in the standard for only two basic cases (for one downconductor and for two downconductors of the same height) is not possible without working out detailed interpretation extending the method application range to the occurring in reality, more complex downconductor configurations (installed in an irregular way and of various heights). The program reproduces the protected areas in a form of 3D blocks created directly in AutoCad drawings and is a powerful designing tool.
Keywords: electric power overhead substations, lightning protection, designing methods
Grażyna ROZKOSZ, Jacek KARMIŃSKI
Validity of a cogeneration subsidy system
Energetyka 2014, nr 10, p. 612
Presented are benefits from combined heat and power production, the comparative analysis made by ENERGOPROJEKT-KATOWICE SA and concerning various options of meeting the heat market industrial needs in the next 15 years and finally the amount of necessary subsidy for cogeneration without which this option is presently not cost-competitive. It is worth mentioning, though, that the subsidy costs do not exceed the benefits coming from energy production in cogeneration plants. Outlined is also the presently functioning cogeneration subsidy system in Poland.
Keywords: cogeneration, cogeneration subsidy system
Ryszard ŚNIEŻYK
Attempt to apply natural gas as a supplementary fuel for coal-fired district heating system
Described is an attempt to apply natural gas as a supplementary fuel for coal fired district heating systems. Presented are results of an investment consisiting in building of a natural gas-fired peaking heating station realized in Szczecin. Because of a fundamental change in the heat tariff approved by URE (Energy Regulatory Office), instead of a 5,3 mln zł/year decrease of ordered power costs only a 1,5 mln was achieved. That caused an approximate loss of 2,0 mln zł/year and the economic results will be borne by heat customers.
Keywords: coal-fired heating system, natural gas, supplementary fuel