Safety analysis on the water wall in the 350 MW supercritical CFB boiler under sudden electricity failure

Highlights: • Three emergency strategies for sudden electricity failure were proposed. • A mathematical model was set up to simulate the physical process in the furnace. • The dynamic processes of the working fluid in the water wall were predicted. • The pipe-broken times under the above three strategies were estimated. • A conclusion on the necessity of setting up emergency water supply system was made. -- Abstract: The necessity of setting up the emergency water supply system in the supercritical circulating fluidized bed (CFB) boiler is still in controversy in the industry. Based on the research methods in the previous literature and the operating experience, this paper proposed three possible emergency strategies for sudden electricity failure. And by analyzing the physical process in the furnace under sudden electricity failure condition, a mathematical model consisted of the mass and energy conservation equation was built, and the accuracy of this model was validated by the experiment data from a supercritical CO₂ experimental system. With the help of the model, this paper can quantitatively predict the dynamic process of the working fluid concerning temperature, pressure, and mass in the water wall in the 350 MW supercritical CFB boiler under the above three emergency strategies. In addition, an estimation of the pipe-broken time for the water wall under such condition was given. Results showed that the longest pipe-broken time was about 52 mins considering the pressure effect. Thus this paper can draw a preliminary conclusion that setting up an emergency water supply system was not a necessity in the 350 MW supercritical CFB boiler.