Modeling of fire-tube boilers

Abstract

In fire-tube boilers, the flue gas passes inside boiler tubes, and heat is transferred to water on the shell side. A dynamic model has been developed for the analysis of boiler performance, and Matlab has been applied for integrating it. The mathematical model developed is based on the first principles of mass, energy and momentum conservations. In the model, the two parts of the boiler (fire/gas and water/steam sides), the economizer, the superheater and the heat recovery are considered. The model developed can capture the dynamics of the boiler level and boiler pressure with confidence, and it is adequate to approach the boiler performance and, hence, to design and test a control strategy for such boilers. Furthermore, it gives insight of dynamics performance not only during nominal operating conditions, or transient behavior when a parameter is changed, but also for the start-up. The model proposed can be easily implemented and thus, it is useful to assist plant engineers and even for training future operators. A case study of an 800 HP fire-tube boiler burning fuel-oil has been simulated to test the boiler performance by varying operating conditions using a pulse and a step change in fuel and steam flow-rate as well as simulating a start-up form the beginning up to achieve the steady state. The results match qualitatively well when compared to results from the literature.