The Process of Heat Exchange in a Chimney Stack on Cooling Exhaust Gases Below the Dew Point

A mathematical model and a program for calculating heat exchange in a flow of combustion products cooled below the dew point in a condensation heat exchanger, in a gas exhaust pipe with a clamp lining have been created. Analytical dependences are presented making it possible to determine the temperature of the exhaust gases, as well as temperature fields and thermal stresses in the wall of the gas exhaust pipe depending on the proportion of bypassed uncooled gases, thermophysical characteristics of the materials of the pipe wall and combustion products, geometric parameters of the pipe, and the intensity of the impact of environment on it. Calculations of the processes of heat exchange of gases moving in a reinforced concrete chimney were carried out for the case of its protection from hydrate corrosion by the bypass method. It has been established that for a three-layer reinforced concrete chimney with a height of 180 m, the quantity of bypassed gases is 30–35% of the total amount of gases. If there is a condensing heat-utilization unit in the boiler plant, the temperature difference in the gas exhaust pipe, its free thermal deformation and thermal stresses in the structural elements of the pipe are reduced by 2.12–2.99 times, which increases the reliability of the pipe.