STUDY OF EXERGY LOSSES IN PLATE AND SMOOTH-TUBE AIR-HEATING EXCHANGERS OF BOILER PLANTS

The study results of exergy losses in the heat transfer processes through a flat wall and cylindrical wall in heat-recovery exchangers of recovery systems for heat of boiler plants exhaust gases are presented. We considered plate and smooth-tube air-heating heat recovery systems, which are included in the heat recovery systems of a heating boiler with a nominal capacity of 2 MW. The values of exergy losses were chosen as a criterion for the exergetic efficiency of heat recovery exchangers.The purpose of the work is to determine the directions for increasing the exergy efficiency of plate and smooth-tube air-heating heat exchangers of boiler plants by establishing the regularities of the technological parameters influence of heat exchangers on exergy losses in heat transfer processes.A complex methodology for calculating exergy losses in the heat transfer processes through flat wall and cylindrical wall has been developed for air-heating heat-recovery exchangers of boiler plants and the corresponding dependencies have been obtained.The methodology includes integral equations for calculating exergy losses and differential equations of heat transfer theory when applied to heat recovery systems.The developed methodology was used to calculate of various types exergy losses in heat transfer processes for air-heating heat recovery exchangers and to conduct a comparative analysis of exergy losses in heat recovery exchangers with different technological parameters.It was established that for all types exergy losses, heating capacity values of heat recovery exchanger and ambient temperature, the exergy losses values for a smooth-tube heat recovery exchanger are higher than the corresponding values for a plate heat recovery exchanger. For all heating capacity values of heat recovery exchanger, the largest exergy losses are associated with heat transfer from the wall to the air. To increase the exergetic efficiency of heat utilization systems, it is necessary first of all to reduce exergetic losses during heat transfer from the wall to the air and to use plate heat exchangers as much as possible.