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 hfgas=104.9 И hair=84.9 (W/m2.K) for coal and hfgas И hair =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.
Highlights
In the majority of cases a fuel switch is dictated by: the increase of energy efficiency, compliance with the stricter regulations regarding the release of harmful emissions in the environment; decreased operational costs, a low payback period
The fuel switch itself leads to a number of changes, which most often affect the systems for flue gases discharge
From the results presented in table 1 it is apparent that a more considerable reduction of CO2 emissions is exhibited by an air heater with thermosyphons operating using solid fuel
Summary
In the majority of cases a fuel switch is dictated by: the increase of energy efficiency, compliance with the stricter regulations regarding the release of harmful emissions in the environment; decreased operational costs, a low payback period. In case waste heat recovery mechanisms are in place along the path of discharging of flue gases, their operational parameters will change. This has an impact on both the systems’ efficiency as well as on the financial parameters for the proposed waste heat recovery system. А number of developments exist in literature related to the numerical study of the heat and mass transfer processes in two phase thermosyphons. The effects of the two-phase flow regime along with the degree of filling of the thermosyphon on the heat and mass transfer processes are examined. A detailed numerical analysis of the heat and mass transfer processes in a multiphase thermosyphon is presented in [7]. The software successfully predicted the overall temperature distribution for the investigated thermosyphon at three different heat inputs
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