Experimental Study Of Ceramic Balls Heated Directly With High Temperature Flue Gas Generated By Fluidized Bed

Biomass is one of environment friendly and renewable resources, which is considered as an ideally clean energy. In general, the development and utilization of biomass energy aim at converting the solid agricultural and forestry wastes into gaseous, solid or liquid fuels by physical or chemical processing methods. Biomass fast pyrolysis for bio-oil production is a thermochemical conversion technology. The technology via solid heat carrier(ceramic balls) directly heating biomass powders to pyrolysis temperature for bio-oil production has many advantages, such as low quenching load, easy energy recovery and so on.In this study, based on the solid heat carrier directly heating biomass process, experimental investigation of ceramic balls heated directly with high temperature flue gas generated by a fluidized bed was performed to solve the problems of heating efficiency and energy waste during the process of the solid heat carrier heating up.A transparent experimental apparatus was designed and built to investigate the movement of ceramic balls characteristics at cold conditions. Experiments of solid heat carriers flow characteristics at different conditions were conducted using Particle Image Velocimetry(PIV) and High-speed Photography Techno1 ogies. With Tecplot software, the ceramic balls vortex was displayed and the local vorticity field was extracted. The results indicated that the axial velocity distribution of ceramic balls is a parabola-like curve along the radius direction and the change of the velocity is larger in the region within 0%~25% of the pipe width(about 25 mm) from the pipe wall than that at other positions. At different baffle position, the vorticity and velocity fields of ceramic balls have adherent appearance and the intensity of the vorticity field increases when the ceramic balls dropping distance increased. With the increase of ceramic balls particle size, the spatially distribution of ceramic balls are more uniform. The baffles increase the of ceramic balls’ collision rates between the ceramic balls and the wall, the ceramic balls and the baffles and they also changes the velocity direction simultaneously which increase the residence time of the particles in the heater and dedicates to enhancing heat exchange between the ceramic balls and hot flue gas. Through the analysis and calculation of the experimental data, the residence time of ceramic balls in the heater was obtained which is approximately 0.79 s.On the basis of particle flow cold experimental research, a heat carrier heater heated by hot flue gas which is generated by fluidized bed was designed and built to investigate the heating performance of the heater and the combustion performance of the fluidized bed. The results showed that the heat utilization efficiency of the heat carrier heater reaches 66.3%. The high temperature flue gas produced by biomass combustion in fluidized bed could satisfy the need of the heating of ceramic balls for biomass pyrolysis. The convection was the main heat transfer in the heat carrier heater and the convection heat transfer coefficient between ceramic balls and the high temperature flue gas is 475 W/(m2·℃). By heat balance analysis and heating capacity theory analysis of the device,it indicated that heat transfer experiment can further guide the actual heat carrier heating device of the test parameters, which satisfy the heat carrier heating device design requirements in biomass pyrolysis process.