Heat-transfer studies in circulating fluidized beds
Circulating fluidized bed combustors (CFBC) employing fine limestone offer many potential advantages over the design approach using a shallow bed of coarse limestone, which has dominated efforts to date. Potential advantages include higher combustion efficiencies, reduced limestone needs, simpler fuel and limestone feed system, elimination of unacceptable heat transfer surface erosion, and better turn-down and response rate. These studies investigated the heat transfer in circulating fluidized beds with externally-heated (bed-to-wall) and internally-heated (bed-to-suspended vertical surface) flow. The fluidized particles used were sands (300, 500 {mu}m) and glass beads (600 {mu}m) respectively. The measurement covered a range of superficial gas velocities 4-17 m/sec, suspension densities from 3-140 kg/m{sup 3} and suspension temperature from 40-350 C. The heat transfer coefficients depend strongly on suspension density, but show almost no dependence on gas velocities and bed temperature. A model which predicts the observed relation of heat transfer coefficient to solid thermal properties is based on particle heat absorption. The residence time was assumed to be the same for all particles and calculated to be the time for a particle to fall the length of the jacket. Particles were assumed to move at the terminal velocity along the wall. The results were in good agreement with the prediction of this model.
- Research Organization:
- Mississippi Univ., University, MS (USA)
- OSTI ID:
- 7230168
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
014000* -- Coal
Lignite
& Peat-- Combustion
42 ENGINEERING
420400 -- Engineering-- Heat Transfer & Fluid Flow
CARBONATE ROCKS
CIRCULATING SYSTEMS
COMBUSTORS
DENSITY
ENERGY TRANSFER
FLOW MODELS
FLOW RATE
FLUID FLOW
FLUIDIZED-BED COMBUSTORS
FUEL FEEDING SYSTEMS
FUEL SYSTEMS
GAS FLOW
GLASS
HEAT TRANSFER
LIMESTONE
MATHEMATICAL MODELS
PARTICLE SIZE
PHYSICAL PROPERTIES
ROCKS
SAND
SEDIMENTARY ROCKS
SIZE
TECHNOLOGY ASSESSMENT
TEMPERATURE DEPENDENCE
TIME DEPENDENCE