Influence of Heat Flux and Friction Coefficient on Thermal Stresses in Risers of Drum Boilers under Dynamic Conditions of Steam Demand

Abstract

Boiler swing rate, which is the rate at which the boiler load is changed, has significant influence on the parameters of the boiler operating conditions such as drum water pressure and level, steam quality in the riser tubes, wall temperatures of riser tubes, and the associated thermal stresses. In this paper, the thermal stresses developed in boiler tubes due to elevated rates of heat transfer and friction are presented versus thermal stresses developed in tubes operated under normal conditions. The differential equations comprising the nonlinear model and governing the flow inside the boiler tubes were formulated to study different operational scenarios in terms of resulting dynamic response of critical variables. The experimental results and field data were obtained to validate the present nonlinear dynamic model. The calculations of the heat flux and the allowable steam quality were used to determine the maximum boiler swing rates at different conditions of riser tube of friction factor and heat flux. Diagrams for the influence of friction factor of the boiler tubes and the heat flux, that the tube is subjected to, on the maximum swing rate were examined.

Boiler dynamic control with optimized nitric oxides and efficiency

“…The data contain 21,600 samples of SFR with sampling rate of 1 s. The behavior of all the other variables is simulated using Å stro¨m and Bell's model 7 of boiler. The results of that are validated against experimental data and extensively discussed in Elshafei et al 12 and Habib et al; 33 but using our PID gains, the entire system is simulated again as shown in Figure 4 to provide a modest overview of available results in the literatures.…”

“…The experimental AFR is used to present the main results of Elshafei et al, 12 Alzaharnah et al 17 and Habib et al 33 to have a composite summary of available literature. All these works including ours are based on a commonly acquired data from an industrial boiler installed in eastern province in Saudi Arabia.…”