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The measurement of the heterogeneous particles in the steam
Bartoš, Ondřej ; Hrubý, Jan ; Ždímal, Vladimír ; Kolovratník, Michal ; Jiříček, I. ; Moravec, Pavel ; Zíková, Naděžda
The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of droplets in low-pressure steam turbines has a significant impact on the efficiency of energy conversion due to the strongly nonequilibrium nature of this process . The condensed water also erodes the turbine blades. A very important question is to what extent heterogeneous nucleation contributes to the phase transition process . In the case of heterogeneous nucleation , the number of droplets depends only on the number of h eterogeneous particles in the system, whereas in the case of homogeneous nucleation, the number of created droplets is determined rather by the expansion rate - in a faster expansion, greater supersaturation and more droplets are formed until the released condensation enthalpy quenches the nucleation.\nThe specific number of droplets (number of droplets per unit mass of steam) formed in the turbine can be determined by optical probes, developed first by Walters and later in the Czech Republic improved by Petr and Kolovratník. Until recently, no information was available on the relative importance of heterogeneous nucleation in forming these droplets.
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Comparison of Instrumental Techniques for Analysis of Ashes from Biomass.
Farták, J. ; Jiříček, I. ; Pohořelý, Michael
Unburned carbon (UC) in six different combustion residues from solid biofuels has been examined using several methods of analysis, such as Loss On Ignition (LOI) and Thermogravimetric Analysis (TGA). Most of the samples came from the heating plants and local heat utilities in the Czech Republic. The amount of unburned carbon in the residues varied widely over an order of magnitude and in several samples accounted for about 7% of the ash mass. Experimental results have shown that LOI overestimated unburned carbon in nearly all samples. Some of these findings can be associated with previously identified thermal decomposition of minerals present in ash. Volatile organic compounds also appear to play a role in the final UC value. Out of TGA methods, first, we used strongly endothermic Boudouard reaction method as an advanced TGA method. However, this reaction was affected by the high potassium content in the samples which could cause incomplete conversion of carbon during Boudouard reaction, because of sintering and formation of the deposits of glass at high temperatures. The second method was a simple TGA method with a controlled atmosphere of nitrogen or air. For ashes, which tend to form a glassy coating and undergo a sintering process, it is not suitable to carry out the measurement at high temperatures, because the Boudouard reaction does not proceed entirely. For these types of samples, it is more appropriate to use TGA methods with a controlled atmosphere of nitrogen or air.
Fulltext: content.csg -  DOCX
Plný tet: cheo12_Farták - DOCX
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Nonequilibrium condensation processes in steam turbines in the light of new measurements of heterogeneous particles
Hrubý, Jan ; Kolovratník, M. ; Ždímal, Vladimír ; Bartoš, Ondřej ; Moravec, Pavel ; Jiříček, I.
In a steam turbine, droplets are formed either homogeneously or via heterogeneous nucleation on pre-existing heterogeneous particles. In a pioneering work, the present team developed a system to measure the number and size of heterogeneous particles down to diameter of 3 nm. This work reports on measurements at Power Plant Prunéřov II. For the first time, the data is at higher parameters (0.27 MPa, 250°C), and the diffusion battery was used to determine the size distribuition of the particles, showing count-mean diameter of about 13 nm.
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Heterogenní částice v parních turbínách: měření na elektrárně Prunéřov II a další vývoj měřicích metod
Hrubý, Jan ; Kolovratník, M. ; Ždímal, Vladimír ; Jiříček, I. ; Bartoš, O. ; Moravec, P.
The form in which various impurities and admixtures are transported in steam circuits of power plants is a missing piece of knowledge needed to fully understand the processes of liquid phase formation in the low-pressure stages of steam turbines and, consequently, to model these processes and suggest modifications of turbine operation and design. The existence of heterogeneous particles in the superheated steam has been proven by the present team using an original sampling device, enabling using standard aerosol instrumentation to characterize the heterogeneous particles in superheated steam. We report measurements at power plant Prunéřov II, where 5.6E9 particles per kilogram of dry steam was found. The Sauter diameter of the particles d32=30nm was determined. The mass balance indicates, that substantial part of the mass of impurities is contained in particles <3nm, the current detection limit. For this reason an expansion chamber is being developed with a goal of detecting particles down to 1nm.
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