Prediction of the minimum load of operation for utility pulverized coal-fired boilers

Any combustion process in utility boilers could not avoid to be influenced by fluctuations of fuel feed rate. The minimum load of operation (MLO), is just the load under which the combustion process can overcome a certain degree of normal fluctuation of fuel feed rate without firing oil, when CSI, a combustion stability index proposed by the authors, equals a critical value (as 0.05 recommended). In order to predict the value of MLO by using a three-dimensional simulation computer code for combustion processes, the simple, chemical reaction system model has been modified by means of the concept of lean flammability of gases. The three-dimensional combustion simulation computer code integrated with the modified model was used to analyze the combustion process in a 200 MW pulverized coal fired utility boiler under different load levels for three different contents of volatile matter of 10%, 20% and 30%. The results showed that as the content of volatile matter increase, the MLO decreases. In addition, the Minimum Coal Quality, which is the lowest heat value of coal varied with volatile content for stable combustion, is also predicted. The identity of the results with general operation experiences has verified our methods.