Improving reliability of turbine units of TPPs and NPPs with mixing heaters in regeneration system

Abstract

When developing designs of mixing heat exchangers used in low-pressure regeneration system for turbines with power from 200 to 1200 MW of TPPs and NPPs, special attention is paid to protecting the turbine flow parts from dripping moisture. Many years of work of JSC "NPO CKTI" on the research, development and implementation of low-pressure heaters (LPH) have shown that their installation in the vacuum zone of the condensate path, as well as in the zone of relatively low overpressure, ensures the maximum cost-efficiency and reliability of the turbine plant regeneration systems. However, an insignificant difference in operating pressures in the LPH and the heating steam from steam turbine extractions, typical for connection options for heaters, requires the development of additional organizational and technical measures to prevent water from entering the turbine. For stationary operating modes, there are two stages of protection against rising levels in the apparatus, providing reliable removal of water through the emergency overflow system or by stopping condensate pumps. In cases of emergency load dump of a turbine unit, the process of increasing the level in the LPH is much faster, up to boiling the entire volume of condensate. The article discusses the possible conditions for the formation and penetration of droplet moisture into the flow part of the turbine. Analysis of well-known field and laboratory studies of the operation of LPH in the most unfavorable operating conditions (in particular, load shedding of a turbine unit) is carried out. A description of the process of boiling water in mixing LPH during turbine load shedding is given. A variant of methodology for estimating the time of swelling of the water level in mixing LPH is proposed. The presented theoretical justifications make it possible to estimate the time of formation and growth of bubbles in deaerated water. The physical process under study is characteristic of the operating conditions of mixing heaters of the low-pressure regeneration system of turbine units and is of interest from the point of view of substantiating the action speed of the system for turbine protection from moisture entering the turbine with a return steam flow.