Mixing Patterns and Residence Time Determination in a Bubbling Fluidized Bed System

Abstract

Fluidized bed gasification can be used to convert the solar energy stored as carboneous compounds in bio-mass into a carbon neutral fuel with reduced emissions. Canada produces 20.57 million tonnes of wheat straw annually which could be used for green energy production. Wheat straw residue gasification has the capability of replacing 7.5 % (0.62 EJ) of Canada’s annual fossil fuel consumption. To achieve efficient gasification in a fluidized bed proper fuel mixing and residence time must be achieved. The aim of this study was to investigate the effects of sand particle size, distributor plate shape and angle, bed height and fluidizing velocity on particle mixing and residence time in the fluidized bed reactor. Greater values of the residence time were obtained with course sand whereas lower values were obtained with fine sand. An in-crease in the angle of convex or a decrease in the angle of a concave of the distributor plate resulted in an increase in the residence time. Both the concave and convex distributor plates achieved vertical upward and downward movements of the bed material resulting in continuous bed material turnover and, thus, good mixing. However, the concave plate achieved longer residence time which will result in better conversion efficiency. To improve the mixing properties of the binary mixture, which has great tendency for segregation due to density differences, an angled distributor plate (concave or convex) should be used. Considerable increases in the residence time were recorded with increases in the bed height. Increasing the fluidizing velocity decreased the residence time due to the increase in the bubble velocity. However, since the conversion efficiency is affected by the degree of mixing, it will also be improved by increasing the fluidization velocity. A velocity above 1.50 U_mf is recommended for better fluidization and improved mixing

Experimental and computational studies on biomass gasification in fluidized beds

“…according to the balanced equation, the stoichiometric air to biomass ratio (mass of biomass/mass of air) is 5.08. the equivalence ratio, f, is the actual air to biomass ratio divided by the stoichiometric air to biomass ratio: f = ( ) ( ) air biomass air biomass actual stoich (2) the equivalence ratios for the gasification experiments are given in table 3, and are low in all the experiments. figure 7 shows the composition of the product gas for the three different air-to-biomass ratios.…”

“…in a fluidized bed gasifier, a bed material (inert sand or particles with catalytic effect) is used to improve the fluidization quality. fluidized bed gasifiers are used to achieve uniform material and heat distribution, and thereby enhancing the reaction rates and conversion efficiency of the biomass [1], [2], [3]. gasification is a process where different types of biomass are converted into a combustible gas mixture, which has a variety of applications depending on the composition.…”

Experimental Comparisons of Anchovy Drying using Centrifugal and Gravitational Fluidized Bed Techniques

“…Fluidized bed dryers are one of the hot air dryers that show a high rate of heat and mass transfer (Chok et al, 2010). They consist of a vertical drying chamber and the products are dried in high velocity hot air which is supplied by a blower (Ghaly et al, 2012). Fluidization techniques had been applied in many industries (Rieck et al, 2015), i.e., micro-granulation of fine powders, coaters, nano-agglomerates, etc.…”