Search

The present work introduces a way of predicting the local heat transfer coefficient in the combustion chamber of a circulating fluidized bed combustor (CFBC) by the fuzzy logic (FL) approach. Fuzzy logic techniques have been successfully applied to calculate the overall heat transfer coefficient for membrane-walls in the combustion chamber of the 670 t/h CFB boiler. The previously obtained heat transfer coefficients values have been used to build up a simple FL model. It has been shown, that the presented fuzzy logic approach give quick and accurate results as an answer to the input data set. The local heat transfer coefficients evaluated using the developed model have been in a good agreement with the desired data. [ABSTRACT FROM AUTHOR]

In this paper, heat transfer experiments were conducted in order to evaluate the contributions of particle convection, gas convection, cluster convection and also radiation from cluster and dispersed phases to the overall heat transfer coefficient in a furnace chamber of a large-scale supercritical CFB reactor. Heat transfer behavior in a circulating fluidized bed between the water membrane wall and bed inventory has been analyzed for Geldart B particles. Bed inventory used in the tests had particle density in the range of 2650–2750 kg/m 3 . The experimental CFB facility has the dimension of 27.6 × 5.3 m in bed rectangular cross-section and 48 m in height of the furnace. The performance tests have been carried out at three different sizes of the bed material with Sauter mean particle diameters of 0.246, 0.272 and 0.444 mm. Above heat transfer studies have been conducted for the operating parameters covering the range of 1082–1183 K for bed temperature, 2.92–5.25 m/s for superficial velocity, 6.86–8.25 kPa for pressure drop, 23–25.6 kg/(m s 2 ) for the circulation rate of solids and 0.4–0.44 for the bed voidage at minimum fluidization velocity. In order to predict the overall heat transfer coefficient, a cluster renewal approach was used. The bed-to-wall heat transfer coefficients obtained in these operating ranges were about 78–226 W/(m 2 K). The contributions of convective and radiative heat transfer to the overall heat transfer coefficient were estimated. The variation in contributions depended on solid suspension density and bed temperature. The average contribution of convective and radiative heat transfer components varied between 13.5–54% and 46–86.5%, respectively. [ABSTRACT FROM AUTHOR]

The role of bed particle size in the heat transfer to membrane walls of a supercritical circulating fluidized bed (CFB) combustion system was studied. In this work, values of the heat transfer coefficient between the membrane walls and the bed include contributions of particle convection, gas convection, cluster convection, gas conduction and also radiation. The heat transfer conditions in the CFB combustor were analyzed for five sizes of bed inventory, with Sauter mean particle diameters of 0.219, 0.232, 0.246, 0.365 and 0.411 mm (Geldart group B). The operating parameters of a circulating fluidized bed combustor covered a range of 3.13–5.11 m s −1 for superficial gas velocity, 22.3–26.2 kg m −2 s −1 for the circulation rate of solids, 0.11–0.33 for the secondary to primary air ratio and 7.16–8.44 kPa pressure drop. Furthermore, the bed temperature, suspension density and the main parameters of cluster renewal approach were treated as experimental variables along the furnace height. To estimate the local bed to wall heat transfer coefficient, some experimental data from CFB boiler and some simple correlations were used. A simple semi-empirical method was proposed to estimate the overall heat transfer coefficient inside the furnace as a function of particle size and suspension density with an accuracy of 21%. Computationally obtained results were compared with the experimental data for CFB unit in a large-scale. It was observed that both bed particle sizes as well as the suspension density significantly influence heat transfer conditions. [ABSTRACT FROM AUTHOR]

Abstract: The present work introduces a way of predicting the local heat transfer coefficient in the combustion chamber of the circulating fluidized bed boiler (CFB) by the artificial neural network (ANN) approach. Neural networks have been successfully applied to calculate the local overall heat transfer coefficient for membrane walls, Superheater I (SH I, Omega Superheater) and Superheater II (SH II, Wing-Walls) in the combustion chamber of the 260MWe CFB boiler. The previously verified numerical model has been used to obtain the overall heat transfer coefficients, necessary for training and testing the ANN. It has been shown, that the neural networks give quick and accurate results as an answer to the input pattern. The local heat transfer coefficients evaluated using the developed ANN model have been in a good agreement with numerical and experimental results. [Copyright &y& Elsevier]