Identification of local heat flux to membrane water-walls in steam boilers

Abstract

A heat flux entering steam generating tubes in power station boilers may be a critical factor in considering the safety of the tubes. The knowledge of the distribution and magnitude of this flux during the operation of the power boiler is very important. The design of a modern boiler furnace requires the computation of furnace wall metal temperatures for the proper selection of the tube thickness and material. These temperatures are functions of the heat fluxes and the internal heat transfer coefficients. In this study, a measuring device (flux-tube) and a numerical method for determining the heat flux in boiler furnaces, based on experimentally acquired interior tube temperatures, are presented. An inverse method was developed, which can estimate the following parameters: the absorbed heat flux, the heat transfer coefficient on the inner tube surface and the temperature of water-steam mixture from temperature measurements at several interior locations of the flux-tube. The least squares method was used to minimize the differences between the calculated and measured temperatures. The unknown parameters are found using the Levenberg–Marquardt method. The number of temperature sensors (thermocouples) is greater than three because the additional information can help in more accurate estimations of the unknown parameters. The temperature dependent thermal conductivity of the flux-tube material was assumed. The developed flux-tube can work for a long time in the destructive high temperature atmosphere of a coal-fired boiler.