MERENJE VLAŽNOSTI PARE

Abstract

Steam separation from the boiling two-phase mixture in the natural or forced circulation steam boilers takes place in the steam drums or vertical cylindrical separation vessels. Water and steam are never completely separated, and the wet steam outflows towards the steam superheaters. The moisture content in the steam must be limited, since its transport into the steam superheater is undesirable. Therefore, it is important to keep the steam moisture within the prescribed setpoints. In order to determine the real efficiency of the separating devices in the steam boiler, it is necessary to conduct specific measurements. In the paper the possible methods for the measurement of the steam moisture content are presented. The new method is proposed, which is based on the suitable combination of the thermodynamic processes that are conducted in the sampled wet steam. The proposed method is absolute in a sense that it does not require calibration, while its accuracy is determined by the accuracy of the pressure and temperature measurement of the wet and superheated steam within the measuring device. The measuring accuracy of the device is determined for the application of the standard pressure and temperature measuring instruments. Compared to other measuring methods, the proposed method is reliable, it provides the acceptable accuracy, and it is simple for the application at all pressure levels of sampled wet steam.