Projeto e simulação operacional do circuito evaporador de uma caldeira piloto de leito fluidizado circulante

Abstract

Circulating fluidized bed boilers (CFB) are systems that use modern technology to produce steam with high thermal efficiency and low environmental impact, especially when employing renewable fuels. The extensive knowledge related to these systems on a commercial scale contrast with the scarce information available on the design and operating simulation of the water´s evaporator loop coupled to small boilers, which can be used to reduce risks and costs in experimental research. In this sense, this work proposes a procedure for designing and obtaining operational estimates of na evaporator loop coupled to a laboratoryscale CFB boiler. This loop was designed to meet steam flow demands using only the effect of natural circulation produced from previously established conditions of gassolid flow inside the furnace. After defining the loop´s geometry, mathematical simulations were performed to estimate the operational behavior of the evaporator loop under different conditions. Results obtained from these simulations showed how the mass flow rates of the water entering the downcomer tube and the steam generated in the passage through the evaporator, the quality of the liquidvapor mixture, the circulation rate of the evaporator loop, and the velocity of the fluid are affected by the pressure, the length of the downcomer tube, and the rate of heat transfer received by the evaporator. The mathematical model algorithm was implemented in the Engineering Equation Solver (EES®) software to solve the equations and obtain the working fluid properties. The validation of the mathematical model, carried out under commercial scale conditions, indicated that the velocity and the quality of the liquidvapor mixture at the evaporator outlet follow the same behavior found in the literature. However, is also emphasized about the importance of carrying out experiments to verify the suitability of the model in smallscale CFB boilers.