Modeling of Superheater Operation in a Steam Boiler

Abstract

A numerical method for modeling actual steam superheaters is presented. The finite volume method was used to determine flue gas, tube wall and steam temperature. The numerical technique presented in the paper can especially be used for modeling boiler superheaters with a complex tube arrangement when detail information on the tube wall temperature distribution is needed. The method of modeling the superheater can be used both in the design, performance as well as in upgrading the superheaters. If the steam temperature at the outlet of the superheater is too low or too high, the designed outlet temperature can be achieved by changing a flow arrangement of the superheater. For example, the impact of the change of the counter to parallel flow or to mixed flow can be easily assessed. The presented method of modeling is a useful tool in analyzing the impact of the internal scales or outer ash fouling on the superheater operating conditions. Both ash deposits at the external and scales at the internal surfaces of the tubes contribute to the reduction of the steam temperature at the outlet of the superheater. Furthermore, scale deposits on the inner surface of the tubes cause a significant temperature rise and may lead to the tube damage. The higher temperature of the flue gas over a part of parallel superheater tubes increases the steam temperature and decreases steam mass flow rate through the tubes with excessive heating. This results in an additional increase in the steam temperature at the outlet of the superheater.