Extinction studies in fluidized-bed combustors

Conference · Sat Jan 01 04:00:00 EST 1983

OSTI ID:6252991

Annamalai, K

The problem of thermal extinction in Fluidized Bed Combustors (FBC) and its relevance to turn down ratio (TDR) are addressed in this paper. Unlike the suspension mode burners, particles in FBC has a longer residence time compared to residence time of volatiles. Thus char combustion is expected to be better than combustion of volatiles. First analysis is carried out by treating the bed as a two phase reactor (TPR). Volatiles combustion is treated as a single step second order reaction in emulsion phase. For char combustion the size distribution is obtained from mass balance and weight of the char in bed and burnt char fraction are then obtained for both diffusion controlled and kinetics controlled burning. Thus heat generated in the bed is determined. The heat loss from the bed occurs via exhaust as sensible heat and via the heat exchangers as load transfer. Perfectly stirred reactor (PSR) results are obtained as a simple extension of TPR results. PSR results with assumption of complete char combustion reveal the multi-valuedness of the problem clearly exhibiting the ignition and extinction of volatiles. It appears to be possible to operate the FBC at low and high temperature modes if char is highly reactive and if FBC is operated in circulating mode. The low temperature operation is especially advantageous for low melting ash coals. With incomplete kinetics controlled char burning only high temperature mode of operation is possible. Parametric results are generated for the effects of volatile matter of solid, particle size etc. The TPR results are also presented. The TDR is improved for larger sized particles, low volatile solid fuels, circulating mode of operation and if the FBC behaves more like a PSR. Based on the analysis and results, possible remedies are given for various problems encountered in the operation of FBC. 10 figures, 4 tables.

• Research Organization: Texas A and M Univ., College Station (USA). Dept. of Mechanical Engineering
• OSTI ID: 6252991
• Report Number(s): CONF-830358-8; ON: DE83902030
• Country of Publication: United States
• Language: English

Related Subjects

01 COAL, LIGNITE, AND PEAT
014000* -- Coal
Lignite
& Peat-- Combustion
42 ENGINEERING
421000 -- Engineering-- Combustion Systems
CHARS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMBUSTION
COMBUSTION KINETICS
COMBUSTORS
DATA
EXPERIMENTAL DATA
FLUIDIZED BED
FLUIDIZED-BED COMBUSTION
FLUIDIZED-BED COMBUSTORS
HEAT EXCHANGERS
INFORMATION
KINETICS
MATTER
NUMERICAL DATA
OXIDATION
PARTICLE SIZE
PERFORMANCE
PYROLYSIS PRODUCTS
REACTION KINETICS
RECOMMENDATIONS
SIZE
STABILITY
THERMOCHEMICAL PROCESSES
VOLATILE MATTER