Numerical study of a large-scale pulverized coal-fired boiler operation using CFD modeling based on the probability density function method

Abstract

The paper presents results of numerical modeling of pulverized coal combustion process in the front wall coal-fired boiler. The developed numerical model of the coal combustion process included particle heating, devolatilization, char combustion, as well as turbulent flow and radiative heat transfer. In gas phase combustion process modeling, the mixture fraction approach with PDF was used. Presented modeling results were carried out using the Open Source CFD code – Code_Saturne, and were used to study the pulverized coal combustion in a 225 MWe power plant unit. The input data and boundary conditions were defined based on the collected data about boiler operating conditions and Rosin-Rammler law was used to calculate coal particle distribution. The behavior of pulverized coal and air flow through the burners, as well as the three-dimensional flue gas path through the combustion chamber, was analyzed. Results in form of velocity, temperature, unburned coal and combustion products distribution were presented to show places inside the boiler with high erosion hazard and place where intensive particle deposition may occur, as well as to show the impact of coal particle diameters on Unburned Carbon (UBC) content. Calculation results confirm proper locations of Over-Fire Air (OFA) nozzles and allowing continuing of combustion process at the furnace outlet using only OFA II and OFA III nozzles set. Based on the obtained results is possible to increase the understanding and conduction detailed investigation of boiler operation. The results have been validated with data collected from the power station measurement system and were analyzed in order to find an answer for operational questions regarding optimization of combustion characteristics.