Prevention of condensation in chimneys of boiler plants with heat-recovery systems

Abstract

The results of studies of the effectiveness of using the air method of preventing condensation formation in the gas-exhaust ducts for anticorrosive protection of chimneys of gas-fired heating boiler plants are presented. This method is used in heat-recovery systems of boiler plants, characterized by deep cooling of gases (below the dew point temperature of water vapor contained in exhaust-gases). The essence of this method is to change the thermal and humidity characteristics of exhaust-gases after heat-recovery by mixing dry and heated air in front of the chimney. Schematic solutions of heat-recovery systems using two options for using the air method are presented. The first option corresponds to the use of the air method when mixing air from the heater of boiler plant. In the second option, for the implementation of the air method, air heated in the heat-recovery system itself is used. To assess the efficiency of the air method, computational studies were carried out to determine the thermal and moisture characteristics of flue gases at the mouth of different types of chimneys under different operating modes of the boiler during the heating period. The studies were carried out for two proposed options for using the air method when using air with a change in its temperature over a wide range. The values of the dew point of the flue gases at the mouth of the chimney and the temperature of its inner surface were calculated at various proportions of the mixed air. The parameters of flue gases and mixed air were determined, ensuring the absence of condensation in the chimneys. Based on the values of the obtained parameters, a comparative analysis of the effectiveness of the considered options for using the air method was carried out. It is shown that for heating boilers the use of this method is the most effective in complex heat-recovery systems when using recovered heat for heating return heat-network water and combustion air. Key words: gas-fired boilers, exhaust-gases, deep cooling, air method, thermal and humidity condition, chimney, anticorrosive protection