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Title: Characterizing fuels for atmospheric fluidized bed combustion

Abstract

A complete methodology for characterizing coal combustion in atmospheric fluidized bed reactors is presented. The methodology comprises studies of fragmentation and particle size variations during combustion, necessary to allow an accurate determination of kinetic parameters and attrition rates. Samples of three different carbonaceous materials (a medium-ash lignite, a medium-ash anthracite and a graphite) were pyrolyzed in N{sub 2} and partially burned in air in a bench-scale fluidized bed reactor at different operating conditions. The particle size distribution, apparent density and number of particles were evaluated by Image Analysis. Additionally, the sphericity factors were calculated. Combustion studies were carried out in batch experiments in the laboratory-scale, fluidized bed reactor at the same operating conditions. The reactor outlet concentrations of O{sub 2}, CO{sub 2}, and CO were monitored continuously. The results indicate that only anthracite particles experienced both primary (due to devolatilization) and secondary (during char combustion) fragmentation. Graphite particles underwent secondary fragmentation, whereas lignite particles did not significantly vary in number during combustion. Size and density variations during combustion suggest that graphite particles burn under regime II, interparticle diffusion being the rate controlling step. On the other hand, anthracite and lignite particles developed an ash layer, which may control combustion. Themore » attrition constants of the medium-ash materials (lignite and anthracite) were found to be very low whereas that of graphite was much higher due mainly to peripheral percolation during combustion.« less

Authors:
; ;  [1]
  1. CSIC, Oviedo (Spain). Instituto Nacional del Carbon
Publication Date:
OSTI Identifier:
116457
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 103; Journal Issue: 1-2; Other Information: PBD: Oct 1995
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; LIGNITE; COMBUSTION PROPERTIES; COMBUSTION KINETICS; ANTHRACITE; GRAPHITE; FLUIDIZED-BED COMBUSTION; ATMOSPHERIC PRESSURE; OXYGEN; CARBON DIOXIDE; CARBON MONOXIDE; ASH CONTENT

Citation Formats

Marban, G., Pis, J.J., and Fuertes, A.B.. Characterizing fuels for atmospheric fluidized bed combustion. United States: N. p., 1995. Web. doi:10.1016/0010-2180(95)00048-B.
Marban, G., Pis, J.J., & Fuertes, A.B.. Characterizing fuels for atmospheric fluidized bed combustion. United States. doi:10.1016/0010-2180(95)00048-B.
Marban, G., Pis, J.J., and Fuertes, A.B.. Sun . "Characterizing fuels for atmospheric fluidized bed combustion". United States. doi:10.1016/0010-2180(95)00048-B.
@article{osti_116457,
title = {Characterizing fuels for atmospheric fluidized bed combustion},
author = {Marban, G. and Pis, J.J. and Fuertes, A.B.},
abstractNote = {A complete methodology for characterizing coal combustion in atmospheric fluidized bed reactors is presented. The methodology comprises studies of fragmentation and particle size variations during combustion, necessary to allow an accurate determination of kinetic parameters and attrition rates. Samples of three different carbonaceous materials (a medium-ash lignite, a medium-ash anthracite and a graphite) were pyrolyzed in N{sub 2} and partially burned in air in a bench-scale fluidized bed reactor at different operating conditions. The particle size distribution, apparent density and number of particles were evaluated by Image Analysis. Additionally, the sphericity factors were calculated. Combustion studies were carried out in batch experiments in the laboratory-scale, fluidized bed reactor at the same operating conditions. The reactor outlet concentrations of O{sub 2}, CO{sub 2}, and CO were monitored continuously. The results indicate that only anthracite particles experienced both primary (due to devolatilization) and secondary (during char combustion) fragmentation. Graphite particles underwent secondary fragmentation, whereas lignite particles did not significantly vary in number during combustion. Size and density variations during combustion suggest that graphite particles burn under regime II, interparticle diffusion being the rate controlling step. On the other hand, anthracite and lignite particles developed an ash layer, which may control combustion. The attrition constants of the medium-ash materials (lignite and anthracite) were found to be very low whereas that of graphite was much higher due mainly to peripheral percolation during combustion.},
doi = {10.1016/0010-2180(95)00048-B},
journal = {Combustion and Flame},
number = 1-2,
volume = 103,
place = {United States},
year = {Sun Oct 01 00:00:00 EDT 1995},
month = {Sun Oct 01 00:00:00 EDT 1995}
}
  • Fluidized bed combustion is an energy conversion technology that is very suitable for biomass combustion because of its fuel flexibility and low process temperatures. However, agglomeration of bed material may cause severe operating problems. To prevent or at least reduce this, peat has been suggested as an additive to the main fuels. Nevertheless, the characteristics of peat fuels vary and there is limited information of the effect of different peat fuels and of the mechanisms behind the agglomeration prevention. The objectives of the present work were therefore to: (I) quantify the potential positive effect by co-combustion peat with forest fuelsmore » in terms of initial agglomeration temperatures; (ii) determine the amount of peat fuel that is needed to significantly reduce the agglomeration tendencies; and, if possible, (iii) elucidate the governing mechanisms. The results showed that all peat fuels prevented agglomeration in the studied interval of 760-1020{sup o}C and even as little as 5% peat fuel was found to have significant effects. The results also indicated that the mechanism of the agglomeration prevention varies between different peat fuels. Possible mechanisms are the minerals in the peat fuel retain alkali, which then is either elutriated up from the bed or captured in the bed; calcium and other refractory elements increase the melting temperature and thereby counteract the melting of alkali; and sulfur reacts with alkali metals and the alkali sulfates is either elutriated up from the bed or prevents agglomeration by increased melting temperature and lowered viscosity. Results from elemental analysis of the coating on bed particles showed that all mixtures with peat fuel resulted in a decreased or unchanged fraction of potassium and an increased fraction of aluminum in the coatings. The results also indicated a complex relationship between the fuel inorganic contents and the agglomeration process. 21 refs., 6 figs., 5 tabs.« less
  • The Electric Power Research Institute is sponsoring development of a new method of characterizing fuels for bubbling atmospheric fluidized-bed combustion (AFBC) boilers. Compared to today's alternative of testing at a large-scale AFBC unit, the fuels characterization method will allow low-cost characterization for utilities considering AFBC applications or a change of fuel in an existing unit. The method utilizes bench-scale test equipment for characterization and a mathematical model, or performance code, to predict combustion performance at large scale using the bench-scale test results. To validate the bench-scale tests and the performance code, the code predictions are compared with actual large-scale AFBCmore » units. This interim report documents the early stages of the fuels characterization method development at Babcock and Wilcox, during 1985 and 1986. During this period, pertinent fuel characteristics were identified, tests to obtain data on those characteristics were developed, and test facilities built and tested. The in-bed combustion portion of the performance was developed. When preliminary data from the test rigs were input into the code, the code predicted in-bed combustion efficiency that agreed well with actual results from a small- to pilot-scale AFBC units. A final report documenting the entire project will be prepared at the close of the project, scheduled for mid-1990.« less
  • The Electric Power Research Institute is sponsoring development of a new method of characterizing fuels for bubbling atmospheric fluidized-bed combustion (AFBC) boilers. Compared to today's alternative of testing at a large-scale AFBC unit, the fuels characterization method will allow low-cost characterization for utilities considering AFBC applications or a change of fuel in an existing unit. The method utilizes bench-scale test equipment for characterization and a mathematical model, or performance code, to predict combustion performance at large scale using the bench-scale test results. To validate the bench-scale tests and the performance code, the code predictions are compared with actual large-scale AFBCmore » units. This interim report documents the early stages of the fuel characterization method development at Babcock and Wilcox, during 1985 and 1986. During this period, pertinent fuel characteristics were identified, tests to obtain data on those characteristics were developed, and test facilities built and tested. The in-bed combustion portion of the performance code was developed. When preliminary data from the test rigs were input into the code, the code predicted in-bed combustion efficiency that agreed well with actual results from small- to pilot-scale AFBC units. A final report documenting the entire project will be prepared at the close of the project, scheduled for mid-1990. 75 refs.« less
  • This report summarizes the results of an Electric Power Research Institute (EPRI) project to develop fuel characterization procedures for atmospheric fluidized-bed combustion (AFBC). The project established a reliable basis for estimating the combustion performance of candidate AFBC fuels based on relatively inexpensive bench-scale characterization tests. The characterization tests developed in this project focus on the physical processes identified as dominating AFBC. These processes include feed system attrition, swelling fragmentation, devolatilization, residual char combustion, and in-bed attrition. Using the test results, candidate fuels can be compared with each other with a broad-ranging database of reference fuels. Example applications of the bench-scalemore » data to fuel ranking problems are described in the report. The database has been designed so that it can be continually updated as new fuels are tested. Computer simulation models have also been developed to estimate combustion performance using the characterization data in conjunction with operating conditions and boiler design parameters. 14 refs., 24 figs., 25 tabs.« less
  • The use of coal in atmospheric bubbling fluidized bed combustors for the generation of process steam is still a viable option for industrial applications world wide but interest in this as and electricity generation technology has also grown. The general advantages of AB-FBC are environmental acceptability and great fuel flexibility. As will be shown in this paper, it has a great potential for meeting possible future, even more stringent, regulations. Since 1979, Stork Boilers, TNO and Twente University have been carrying out a joint national research programme aimed at the design of industrial installations operating to stringent emission standards. Thismore » has led to the demonstration of a 90 MWth industrial boiler at the AKZO Chemical Works. The work has been under the control of NOVEM, the Netherlands Agency of Energy and the Environment. This body provides the financial resources on behalf of the Dutch Ministry of Economic Affairs by awarding annual contracts.« less