Comparative analysis of the exergy efficiency of methods for protecting gas exhaust ducts of boiler plants

Abstract

This paper reports the results of studying the exergy effectiveness of thermal methods for anti-corrosion protection of the gas-draining tracts of boiler plants. These include the method of mixing heated air into flue gases, the method of passing part of the hot gases of the boiler through the bypass chimney, and a flue gas drying method. The research involved the devised comprehensive procedure based on an exergy approach. The dependences of exergy loss E_los and the heat- exergy criterion ε on the following parameters of thermal methods have been established: the amount of heated air N mixed into flue gases, the proportion of bypassed flue gases K, and the amount of dried flue gases R. A comparative analysis of the effectiveness of heat recovery systems when applying the methods considered has been performed. It has been established that for the method of mixing, E_los and ε at ambient temperature t_en=10 °C demonstrate the lowest values, that is, the efficiency of the system, in this case, is the highest. The most effective, when implementing the bypass method, is the heat recovery system at t_en=10 °C. Under the method of drying, at all values of the amount of dried flue gases, the loss of exergy is the lowest at t_en=0 °C. As regards the heat- exergy criterion, at values R≤20 %, the lowest values of ε are observed at t_en=10 °C. At R>20 %, the lowest values of ε are at t_en=0 °C. Thus, the efficiency of the system when implementing the method of drying is the highest at t_en=0 °C and at the amount of dried air of R>20 %. The study reported here would provide the necessary information for designing optimal heat recovery schemes. The development of this study is to establish the relationship between the exergy and environmental efficiency of thermal protection methods in order to further reduce toxic emissions.