Enhancement of the leningrad metal works K-200(225)-12.8 turbine regeneration system

Abstract

204In domestic power engineering, modernization of one of the most widespread turbine installations, the Leningrad Metal Works (LMZ) K 200 12.8, is pro ceeding, with the goal of increasing capacity to 210-225 MW and increasing the efficiency of the flow path by 6-9%. LMZ employees are focusing primarily on modernizing the turbine itself, which will make it pos sible to obtain a significant (but not complete) effect, since the regeneration system and its equipment will not change. In the best case, the old equipment will be replaced by newly manufactured equipment whose designs were elaborated 50-60 years ago.It is known that the regeneration system increases the efficiency of the cycle by 12-14%; therefore, enhancing it could yield a significant effect. The convential regeneration system of the K 200 12.8 turbine installation has the following structure (see Fig. 1, design a):3 HPH-EFP-0.69 D-4 LPH-PGH100-OGK-PGH50-OE-ECP1 st.During maintenance and special studies, substan tial shortcomings in the regeneration system and its equipment were revealed. Increased, as opposed to calculated values, condensate subcoolings in LPH 1 and LPH 2 (7-10°С)) and HPH 6-HPH 8 (5-7°С) reduce the thermal efficiency of the turbine installa tion by 0.9-1.2% [1,2]. Increased subcoolings in LPH 1 and LPH 2 lead to thermal hydraulic overload of LPH 3, which results in an increase in heating steam pressure, pipe vibration, and their destruction. This addition only reduces the efficiency and reliabil ity of turbines.A deaerator operating at a constant pressure decreases efficiency, and when there is a change in loading, fittings and control devices are required for HPH heating steam and drainage switchover, which complicates the system and its maintenance and reduces its reliability.Unstable operation of discharge pumps draining LPH 2 leads to its dumping into the condenser (due to switching off of the pumps), which also decreases the regeneration system's efficiency.Underproduction of electric power and reduction in efficiency is aggravated by deposition of ferric oxide carried out of the LPH pipe system into the boiler and the flow path of the turbine, which decreases the effi ciency of units and requires blowing of the boiler and flushing of the turbine. It is known [1, 3] that the main source of iron is the first HPH along feedwater flow. This is caused by the fact that, in the water tempera ture range of 160-190°C in which this HPH operates, the oxide film formation rate is less than its decompo sition rate. Therefore, ferric oxides are carried out into the water-steam circuit and are deposited there, wors ening heat exchange in the HPH and boiler; as well, losses in the flow path of the turbine increase. Unsuc cessful condensation tank design and protection sen sor connection schematics for the first and second HPH boundaries limit the rate of change in steam pressure in the casing to 0.06 MPa/min, or they lead to triggering of a safeguard, which reduces maneuver ability and reliability of apparatus and steam genera tors due to the ...