Natural gas combustion in fluidised bed reactors between 600 and 850 degrees C: experimental study and modelling of the freeboard

In this paper, an experimental study of the natural gas-air mixture combust ion in a fluidised bed containing sand particles with 350-mum mean diameter and operating at temperatures lower than the critical temperature (less th an 850 degreesC) has been presented. A particular attention has been given to the freeboard zone where the main part of the reaction rate takes place at such temperatures. The experimental results obtained at different operat ing conditions has shown the essential role played by the projection zone i n the global thermal efficiency of the reactor working between 600 and 800 degreesC. Parallel to this experimental study, a model of natural gas-air c ombustion taking in consideration the interaction between dense and dilute regions of the reactor has been proposed. The proposed model takes into acc ount thermal exchange by conduction and radiation in both between gaseous a nd particular phases, and gas-particle suspension and reactor walls. The pr edictions of this model agree well with the experimental data. (C) 2001 Els evier Science B.V. All rights reserved.