NUMERICAL METHOD FOR DETERMINING ALLOWABLE MEDIUM TEMPERATURE DURING OPERATION OF STEAM GATE VALVE

Construction elements of power blocks such as collectors, separators or steam valves work in hazardous environment. During start-up and shut-down operations they are exposed to sudden temperature and pressure changes, that cause high stresses at certain points. Additionally, the cyclic character of loading causes material fatigue, known as low-cyclic fatigue, which may lead to the formation of fracture. Manufacturers of steam boilers provide instructions for heating and cooling processes in order to operate safely. It is important to find the optimum parameters for heating and cooling operations, i.e. parameters that enable to conduct heating and cooling in the shortest time and keep the maximum stresses in the construction within allowable limits. Efforts are made to develop an appropriate method for determining optimum operating parameters during start-up and shut-down phase of the power units. In this paper two optimum parameters will be found. Based on these parameters heating and cooling processes will be carried out and compared with heating and cooling operations processed according to the German boiler regulations Technische Regeln für Dampfkessel 301 (TRD)