A frequency domain mathematical model is proposed to address the instability of gas-liquid two-phase flow in water-cooled wall pipelines of supercritical circulating fluidized bed boilers during deep peak shaving,suitable for various operating conditions.The transfer function characterizing the stability of gas-liquid flow within the tubes is derived by linearizing the mass,energy,and momentum equations with small disturbances and applying Laplace transform.The stability of the working fluid flow in the tubes is assessed using Nyquist diagram interpretation.Using this model,the instability boundary of the water wall tube segment of a 350 MW supercritical circulating fluidized bed boiler is calculated,and the impact of different parameters on the flow instability characteristics is investigated.The results show that the heat loads at which flow instability occurs during 20％and 50％of the boiler's maximum continuous evaporation rate are 76.09 kW·m-2 and 113.52 kW·m-2,respectively,indicating the stability and safety of the water wall tube flow.The effect of inlet subcooling on critical heat flux density exhibits a non-monotonic relationship.Increasing the mass flow rate reduces the density difference between the inlet and outlet fluids,promoting flow stability.Moreover,raising the inlet throttling coefficient can dampen flow pulsations at the inlet,further enhancing flow stability.Altering the tilt angle of the tube section under different operational conditions leads to varying effects on flow stability.
deep peak shavingflow instabilityfrequency domain methodsupercritical circulating fluidized bed boiler
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