1. Fluidized Bed Name : Salman Alfihed Instructor : Dr. M. Alahmed King saud university Chemical Engineering Department

2. O utline O utline : Introduction –Fluidization and fluidized bed. –Uses of fluidization.. Heat transfer with fluidized bed : –Heat transfer coefficient. –Bubbling fluidized bed combustion boiler furnaces. –Heat transfer between gas and solid particles in bubbling fluidized beds. Advantages and disadvantages of fluidized bed. Design Recommendations. Conclusions. References.

3. I ntroduction Many types of fluidized bed based on flow rate. A bed of lose particles offers resistance to fluid flow through it. Fluidized beds are commonly used in chemical, biochemical and petrochemical industries in processes. Fluidized bed in horizontal, vertical tune. It used in reactor, heat exchange, Drying operations …

4. H eat t ransfer c oefficient Heat transfer coefficients for the vertical fluidized bed are higher than for the horizontal bed at the same cross- sectional velocity. Heat transfer coefficient can be calculated by: where P is the heater power, ΔT is the difference between the heater and bed temperatures, and Ah is the surface area of the heater.

5. Bubbling fluidized bed combustion boiler furnaces specific conditions for heat transfer exist. Average furnace temperature in Fluidized Bed boilers is not dramatically changed along the height Heat transfer from bed particles to fuel particles needs to be analyzed and studied in order to correctly model the combustion process.

6. Heat transfer between gas and solid particles in bubbling fluidized beds The temperature field in the fluidized bed is practically homogenous due to intensive mixing of particles in both horizontal and vertical directions. Heat transfer from gas to particles is never the limiting factor in organization of processes in the fluidized bed. Because of that heat transfer between emulsion and bubbles is not crucial for fluidized bed combustion processes.

7. Advantages and disadvantages of fluidized bed Advantages Disadvantages -- Applicable for large or small scale operations. - Uniform Particle Mixing. - Uniform Temperature Gradients. - Ability to Operate Reactor in Continuous Statt - Heat and mass transfer rates are high, requiring smaller surfaces. -Bubbling beds of fine particles are difficult to predict and are less efficient. -Particle (breakup) is common. -Increased Reactor Vessel Size. -Pumping Requirements and Pressure Drop. - Pipe and vessel walls erode due to collisions by particles

8. D esign Recommendations A disengagement section of approximately 15 cm must be left above the bed to prevent particle carryover. This means that the top 15 cm of tubes will not be covered with the fluidized bed. The horizontal design is more conducive to large flow rates. This is due to a larger cross- sectional area presented by horizontal vessels for the same length and number of tubes. To increasing the flow capacity of the vertical unit, supply a larger shell than is needed for the tube bundle andincrease the density of the bed material.

9. C onclusions : Smaller particles tend to become entrained at lower fluid velocities than larger ones and the way that bubble. the actual cross sectional velocity does not change linearly with increased flow rate. Fluidization is uses for reactor, heat exchanging, drying operations..etc. Heat transfer coefficients for the vertical fluidized bed are higher than for the horizontal bed. Fluidized bed has many advantage, also has many disadvantage. Approximately 15 cm of each tube at the top of the unit must be left uncovered by the bed. In design the vertical tube is best because its give good heat transfer rate.

10. R eferences : L. T. Cole, LIQUID-FLUIDIZED-BED HEAT EXCHANGER FLOW DISTRIBUTION MODELS, 1979. J. S. M. Botterill, FLUID-BED HEAT TRANSFER, academic press, 1975. Wen-Ching yang, FLUIDIZATION SOLIDS HANDLING AND PROCRSSING, noyes publications usa,1999. J. R. Howard, FLUDIZED BED COMBUSTION AND APPLICTIONS, applied science publishers London and new york, 1983. E.J.Anthony, Fluidized Bed Combustion, MARCEL DEKKER, INC.,1994.

11. T hank y ou