Michal Kolovratník

Wet steam energy loss and related Baumann rule in low pressure steam turbines

This paper presents the results of a computational analysis of the wet steam energy loss occurring in a 210 MW fossil-fired and a 1000 MW nuclear LP steam turbine. The turbines operate under considerably different conditions as regards pressure level in the droplet nucleation zone, exit moisture level and droplet size spectra determined from optical extinction measurements. An evaluation of the basic wetness energy losses has been carried out including the thermodynamic loss, drag loss of the fine and coarse droplets, impact loss, collected water loss, centrifuging loss and exit loss. A statistical 2D evaluation method has been employed for the computational simulation of the loss. The objective of the analysis was to determine whether an equilibrium based Baumann factor of order 0.6 can be used for predicting the wet steam loss.

Experimental research on the flow at the last stage of a 1090 MW steam turbine

This paper presents the experimental research for the flow of the last stage of a turbine for saturated steam with the nominal output 1090 MW. In addition, the flows in 600, 800, and 1070 MW output turbines were also measured. Pneumatic probes were used to determine the distribution of static pressures and absolute angles at the outlets from the penultimate and the last stages of the turbine. Optical probes were used to measure wetness distribution and were placed in positions similar to the pneumatic probes. The courses of static pressures, angles, and wetness for all outputs respectively were compared and discussed. The difference between wetness courses on the left and right side of the turbine as well as before and behind last stage was minimal. Absolute angles of steam behind the last stage are strongly influenced by the vacuum level in the condenser. Big difference between the outlet angles from last stage on the left and right side of the turbine is confirmed. The influence of the tie-boss was evident in both pneumatic and wetness measurements. Differences of the flow field on the left and right sides of the turbine behind the penultimate stage are noted and discussed. These differences lead to a dynamic loading of the penultimate rotor blades and could reduce the service life.

Results of the International Wet Steam Modeling Project

The purpose of the “International Wet Steam Modeling Project” is to review the ability of computational methods to predict condensing steam flows. The results of numerous wet-steam methods are compared with each other and with experimental data for several nozzle test cases. The spread of computed results is quite noticeable and the present paper endeavours to explain some of the reasons for this. Generally, however, the results confirm that reasonable agreement with experiment is obtained by using classical homogeneous nucleation theory corrected for non-isothermal effects, combined with Young’s droplet growth model. Some calibration of the latter is however required. The equation of state is also shown to have a significant impact on the location of the Wilson point, thus adding to the uncertainty surrounding the condensation theory. With respect to the validation of wet-steam models it is shown that some of the commonly used nozzle test cases have design deficiencies which are particularly apparent in the context of two- and three-dimensional computations. In particular, it is difficult to separate out condensation phenomena from boundary layer effects unless the nozzle geometry is carefully designed to provide near-one-dimensional flow.

Nucleation rates of droplets in supersaturated steam and water vapour–carrier gas mixtures between 200 and 450 K

We compare experimental nucleation rates for water vapour in various carrier gases, estimated nucleation rates for steam, and nucleation rates obtained from molecular simulations. The data for steam are deduced from empirical adjustments of the classical nucleation theory developed by various authors to reproduce pressure and optical data for condensing steam flows in converging-diverging nozzles and turbine stages. By combining the data for nucleation in carrier gases and the data for steam nucleation, an unprecedented temperature range of 250 K is available to study the temperature dependence of nucleation rate. Original results of molecular dynamic simulations for TIP4P/2005 force field in the NVE (system constrained by number of particles, volume and energy) conditions are provided. Correction of classical nucleation theory for non-isothermal nucleation conditions is applied to experimental and simulated data. The nucleation rate data for steam follow a similar temperature trend as the nucleation rate data for water vapour in carrier gases at lower temperatures. The ratio of observed nucleation rates to classical nucleation theory predictions decreases more steeply with temperature than the empirical correlation by Wölk et al. (J Chem Phys 2002; 117: 4954–4960). On the contrary to experimental data, the ratios of nucleation rates computed from molecular simulations to classical nucleation theory predictions do not show a significant temperature trend.

Absorption Power Cycles with Various Working Fluids for Exergy-Efficient Low-Temperature Waste Heat Recovery

This chapter introduces absorption power cycles (APC) as a perspective option for power production from low-temperature heat. The multicomponent mixture working fluid can provide low exergy destruction in heat exchangers through variable temperature phase change, thus achieve higher efficiency than alternatives such as ORC. Except for commonly known Kalina cycle using NH3-H2O mixture, there is a wide choice of other absorbent-absorbate pairs. This work theoretically explores APC with various types of working fluids compared with ORC (also several configurations and working fluids). Potential of APC is mainly in small systems for low-temperature heat sources around 100 °C regarding both performance and design parameters. It is comparable with the zeotropic ORC, while traditional ORC is the best choice for higher heat source temperatures.

The assessment of the effect of binary homogeneous nucleation on wet steam energy loss in a low pressure steam turbine

The objective of the paper was to recognize the possible effect of a low concentration of chemical impurity (NaCl) present in the inlet steam (2.27 ppb) in the assessment of the wet steam energy loss occurring in a 1000 MW nuclear low pressure steam turbine. The presented analysis suggests that the used binary nucleation model, accounting for the electrolytic nature of the droplets, predicts a reduced wet steam energy loss of order –9 %, in comparison with the unary pure steam droplet nucleation model. This minor difference, considering the uncertainties of the existing measurements and the incomplete knowledge of the real droplet nucleation conditions in the steam of the turbine (primarily in relation to the necessary input data of chemical impurities), suggests that unary pure steam droplet nucleation (Becker–Döring) is an acceptable approximation at the current state of knowledge.

Measurement of O2 in the Combustion Chamber of Apulverized Coal Boiler

Operational measurements of the O2 concentration in the combustion chamber of a pulverized coal boiler are not yet common practice. Operators are generally satisfied with measuring the O2 concentration in the second pass of the boiler, usually behind the economizer, where a flue gas sample is extracted for analysis in a classical analyzer. A disadvantage of this approach is that there is a very weak relation between the measured value and the condition in specific locations in the fireplace, e.g. the function of the individual burners and the combustion process as a whole. A new extractionline was developed for measuring the O2 concentration in the combustion chamber. A planar lambda probe is used in this approach. The extraction line is designed to get outputs that can be used directly for diagnosis or management of the combustion in the boiler.

Chapter 7 – Binary homogeneous nucleation in selected aqueous vapor mixtures

Publisher Summary Phase transitions are a fascinating feature of the physics of fluids. The water–steam phase transition plays an essential role in the power industry. The common properties of phase transition kinetics are intensively studied in chemistry and physics, and it is applied in several fields, such as metallurgy, biology, medicine, and in chemical engineering. The four stages in phase transition are: the supersaturated state, the origination of the new phase (nucleation), the growth of nuclei to form larger particles, and the relaxation processes such as coagulation and agglomeration. This chapter deals with the second and third stage: nucleation and droplet growth. Nucleation may be understood to be an initial stage of the complex, first-order phase transition leading to the formation of droplets of a new liquid phase, within the meta-stable gaseous phase. Within the framework of the kinetic approach, the evolution of nucleation is described by the nucleation equation, connecting thermodynamic and kinetic features of the process. The underlying idea of atoms clustering during nucleation is based on the Szilard assumption that the dominant role in this process is the attachment (detachment) of single particles to (from) the cluster surface. The nucleation equation may be solved either numerically or analytically. The principles of the most frequently used experimental techniques can be summarized as: thermal diffusion, cloud chamber, expansion chamber, nucleation pulse technique, nozzle flow, and condensation wave technique.