CFD simulation of fuel/flue gas section of the fire tube steam boiler system

Abstract

Fire tube steam boilers produce steam to be used in process heating applications. In these boilers, fuel and air are fed to the first zone called furnace zone, where combustion occurs and hot flue gases are produced. In the three pass boiler system these gases are passed in first and second convection zones having several tubes of smaller diameters. In the shell side of this boiler system, water flows at the desired flow rate. In the furnace and convection zones, heat is transferred to the water by radiation and convection. Water upon receiving heat gets converted to steam of desired pressure. In this process, temperature varies in the flue gas as well as in the water/steam side. It is important to know these variations for effectively designing the boiler system. Hence, a 3-D mathematical model was developed and CFD simulations were performed for the fuel/flue gas section of a fire tube boiler system using COMSOL Multiphysics 5.4TM. The simulation results showed that the average temperature at the outlets of the furnace, convection zone-I and II are 1300 K, 500 K and 470 K respectively and that agrees well with the industrial operational data. The average velocities obtained in all these zones are also in agreement with the corresponding industrial data. This comparison validates the model and can be used for the effective and efficient design of the boiler system. Water and steam side simulations are currently in progress to predict water level fluctuations.