Analysis of the impact of coal quality on the heat transfer distribution in a high-ash pulverized coal boiler using co-simulation

Abstract

The burning of very high ash coal can adversely affect heat absorption in boiler furnaces and radiant superheater heat exchangers, while the lower calorific value can lead to lower bulk furnace temperatures and higher tube wall temperatures in the radiative superheaters. This paper presents the results of a numerical study that compares the heat transfer characteristics of a subcritical boiler firing coal with a very high ash content to that of the same boiler burning the original design coal. The analysis is based on a detailed furnace combustion and heat transfer CFD model using ANSYS Fluent®, applied in a co-simulation mode together with a system level thermofluid network model using Flownex® SE. Furthermore, the particulate radiation models include the effects of variable emissivity and scattering as the particles transition from parent fuel to ash. The aim is to demonstrate the extent to which the effects of differences in the coal quality can be identified in utility scale boilers using this approach. The results show that it is possible to identify the impact on furnace and radiant heat exchanger heat uptake, steam generation rate, as well as potential areas of high heat exchanger tube wall temperatures.