Effect of flue gas recirculation on heat transfer in a supercritical circulating fluidized bed combustor

Abstract

This paper focuses on assessment of the effect of flue gas recirculation (FGR) on heat transfer behavior in 1296t/h supercritical coal-fired circulating fluidized bed (CFB) combustor. The performance test in supercritical CFB combustor with capacity 966 MWth was performed with the low level of flue gas recirculation rate 6.9% into furnace chamber, for 80% unit load at the bed pressure of 7.7 kPa and the ratio of secondary air to the primary air SA/PA = 0.33. Heat transfer behavior in a supercritical CFB furnace between the active heat transfer surfaces (membrane wall and superheater) and bed material has been analyzed for Geldart B particle with Sauter mean diameters of 0.219 and 0.246 mm. Bed material used in the heat transfer experiments had particle density of 2700 kg/m3. A mechanistic heat transfer model based on cluster renewal approach was used in this work. A heat transfer analysis of CFB combustion system with detailed consideration of bed-to-wall heat transfer coefficient distributions along furnace height is investigated. Heat transfer data for FGR test were compared with the data obtained for representative conditions without recycled flue gases back to the furnace through star-up burners.

A comparison of fuzzy logic and cluster renewal approaches for heat transfer modeling in a 1296 t/h CFB boiler with low level of flue gas recirculation

“…The solid suspension density profile confirmed that above the secondary air injection levels bed particles transport occurred without a splash zone. This trend was also confirmed by Blaszczuk et al [7] and Błaszczuk [57] in several previous studies of solids flow structure.…”

“…The analyzed CFB boiler is described in detail in the works by Blaszczuk et al [7,8,31,38,56], particularly presenting the construction data, cross-sectional area, geometry of membrane wall, arrangement of measuring points and also data acquisition system. Besides, more detailed information on the flue gas recirculation system, flue gas analysis system and properties of such flue gases fed to the combustion chamber are described by Blaszczuk [57]. Before test, the experimental conditions referred to this heat transfer study were stabilized for four hours.…”

Investigation of Heat Transfer in a Large-Scale External Heat Exchanger with Horizontal Smooth Tube Bundle

“…In the last decade, it has been observed that the diffusion, jointly with the dynamic development of CFB boilers around the world, has led to the increase in capacity of single-unit CFB boilers [1][2][3]. Recently, CFB boiler capacities increased up to 1000 MWe with supercritical and ultra-supercritical working medium parameters [4][5][6][7][8][9]. The fluidized bed technology is very efficient and economically preferable due to the high heat transfer rates that are attained from the fluidized bed to the active heat transfer surface.…”