Application of noncatalytic gas-solid reactions for a single pellet of changing size to the modeling of fluidized-bed combustion of coal char containing sulfur

Technical Report · Mon Sep 01 00:00:00 EDT 1980

DOI:https://doi.org/10.2172/6738073· OSTI ID:6738073

Rehmat, A.; Saxena, S. C.; Land, R. H.

A mechanistic model is developed for coal char combustion, with sulfur retention by limestone or dolomite sorbent, in a gas fluidized bed employing noncatalytic single pellet gas-solid reactions. The shrinking core model is employed to describe the kinetics of chemical reactions taking place on a single pellet; changes in pellet size as the reaction proceeds are considered. The solids are assumed to be in back-mix condition whereas the gas flow is regarded to be in plug flow. Most char combustion occurs near the gas distributor plate (at the bottom of the bed), where the bubbles are small and consequently the mass transfer rate is high. For such a case, the analysis is considerably simplified by ignoring the bubble phase since it plays an insignificant role in the overall rate of carbon conversion. Bubble-free operation is also encounterd in the turbulent regime, where the gas flow is quite high and classical bubbles do not exist. Formulation of the model includes setting up heat and mass balance equations pertaining to a single particle (1) exposed to a varying reactant concentration along the height of the bed and (2) whose size changes during reaction. These equations are then solved numerically to account for particles of all sizes in the bed in obtaining the overall carbon conversion efficiency and resultant sulfur retention. In particular, the influence on sorbent requirement of several fluid-bed variables such as oxygen concentration profile, particle size, reaction rate for sulfation reaction, and suflur adsorption efficiency are examined.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• DOE Contract Number: W-31-109-ENG-38
• OSTI ID: 6738073
• Report Number(s): ANL/CEN/FE-80-13
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
FLUIDIZED-BED COMBUSTION
MATHEMATICAL MODELS
CHEMICAL REACTIONS
COAL
DOLOMITE
ENERGY BALANCE
LIMESTONE
MASS BALANCE
PARTICLES
ALKALINE EARTH METAL COMPOUNDS
CARBON COMPOUNDS
CARBONACEOUS MATERIALS
CARBONATE ROCKS
CARBONATES
COMBUSTION
ENERGY SOURCES
FOSSIL FUELS
FUELS
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MATERIALS
MINERALS
OXIDATION
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
THERMOCHEMICAL PROCESSES
014000* - Coal
Lignite
& Peat- Combustion