Mathematical procedure for predicting tube metal temperature in the second stage reheater of the operating flexibly steam boiler

Abstract

Deployment of renewables introduces new regimes of large scale boiler operation. The units are required to operate at flexible rather than baseload mode. One of the requirements is to reduce the minimum load of the existing boilers which adds thermal stress to pressure parts. Significant operational issue is the local overheating of the heat exchangers material due to lower steam flow rates and poor heat dissipation conditions. The problem is particularly intensified in low-pressure reheaters. The current paper demonstrates a novel computational method of predicting tube metal temperature of specific reheater platens. The proposed numerical procedure incorporates coupling of CFD simulations of the boiler fire side with 1-D pipe flow model in the heat exchanger. Simulation results are compared to measurement data. The numerical method can be used to make decision on the modification strategy of the reheater design to achieve uniform temperatures of the tube metal in each platen by restriction orifices adjustment.