Specifics in the operating modes of thermosyphon air heater of steam generators №1 and №2 in TPP "Republika" at fuel switch from coal to natural gas

¹ Dept. of Thermotechnics, Hydraulic and Ecology, University of Ruse, Ruse, Bulgaria
² Dept. of Power Engineering and Power Machines, Technical University of Sofia, Sofia, Bulgaria
³ Agrarian and Industrial Department, Ruse University, Ruse, Bulgaria
⁴ College of Engineering and Physical Sciences, University of Birmingham, United Kingdom

^* Corresponding author: iki@uni-ruse.bg

Abstract

A fuel switch is motivated both by the necessity of increasing energy efficiency and the compliance with the ever-stricter regulations regarding the release of harmful emissions in the environment. In this paper a thorough financial and energy analysis on the fuel switch from coal to natural gas is carried out, in particular with respect to waste heat recovery systems (two phase thermosyphons). As a result of the calculation of the heat transfer coefficients for both fuels, it is established that the system running on natural gas has a lower value, due to the lower air velocity, caused in turn by the lower requirement for excess air. The heat transfer coefficients of the evaporation and condensation zones respectively are established h_fgas=104.9 И h_air=84.9 (W/m².K) for coal and hfgas И h_air =84.7 (W/m².K) respectively for gas. A numerical study is also carried out and a methodology for the analysis of the efficiency of two phase thermosyphons with complex geometry is presented.