Analysis of efficiency and power upgrades at the lignite-fired 2x620 MWe power plant by steam boiler waste heat utilization and different balance of plant modifications

Abstract

A substantial potential exists for the thermal power plants efficiency and power upgrades by the utilization of flue gas waste heat at the steam boiler. The paper presents solutions for the waste heat utilization and different balance of plant modifications for the regeneration of waste heat into the plant thermodynamic cycle. A comparative analysis of different solution modes is performed for the more than 30 years aged lignite-fired 2x620 MWe power plant “Nikola Tesla B”. Different modes of waste heat regeneration into the plant cycle are flue gas cooling by the “cold” feedwater taken from the main feedwater pump discharge line before high pressure heaters, by the “hot” feedwater after the high pressure heaters and by the condensate taken from the low pressure condensate line. The energy efficiency and power upgrades of proposed methods is evaluated and compared. The highest increase of power plant efficiency is achieved by the flue gas cooling by the feedwater taken from the feedwater pump discharge line. This solution was implemented within the first phase of power plant overhaul, with a reduction of the flue gas temperature for more than 20 oC and the boiler and power plant efficiency increases of approximately 2 and 0.53 percentage points respectively.