THE OBJECTIVES OF THE PROJECT ARE :
- DEVELOPMENT OF THIS FLASH-EXPANSION BURNER FOR USE WITH COAL/WATER MIXTURES;
- DEVELOPMENT OF A MIXTURE PREHEATING AND INJECTION SYSTEMS WITH RELIABLE THROUGHPUT CONTROL - I.E. WHICH TAKES ACCOUNT OF THE PARTICULAR PROBLEMS OF COAL/WATER MIXTURES, SUCH AS VISCOSITY, EROSION AND CLOGGING BY SOLID PARTICLES IN SUSPENSION.
A burner has been developed for use in the combustion of coal water slurry. Studies have shown a worldwide interest in such a system, although further work is required before an industrial scale burner is developed.
A rheological study was carried out in collaboration with CERCHAR. This consisted of the determination of the limiting additive used when decanting particles of coal suspended in water, which permitted the slurry to retain its fluidity with temperature. In this study only the use of DAXAD 16 (anionic additive) provided a mixture which was not degraded at atmospheric pressure at temperatures up to 80 C.
During the atomisation phase, the influence of different injection parameters (temperature, pressure, geometry of the duct, coal content) on the instantaneous release of water have been studied. The numerous experiments carried out have shown that the atomization of water is achieved at a temperature of around 105 C, wheras that of a coal-water mixture containing 52% coal is around 125 C. The relationship between particle size distribution and droplet diameter as a function of different injection parameters, has been measured with the aid of a Malvern granulometer. The analysis of results has led to the precise definition of injector dimensions for obtaining medium Sauter diameter slurry droplets of about 85 um with temperature and pressure in the order of 135 C and 7 bar.
INDUSTRY IS CURRENTLY DEVELOPING COAL/WATER BURNERS USING AIR INJECTION TO ATOMIZE THE MIXTURE, THUS PERMITTING EFFICIENT COMBUSTION. MEANWHILE, LABORATORY-SCALE STUDIES SUGGEST THAT "FLASH" VAPORIZATION COULD BE USED TO ACHIEVE FINE ATOMIZATION OF THE MIXTURE WITHOUT AIR INJECTION. BERTIN PROPOSES USING THIS SAME PRINCIPLE TO DEVELOP A NEW TYPE OF BURNER. IT INVOLVES SUPERHEATING THE MIXTURE UNDER PRESSURE - I.E. TO BETWEEN 100 AND 180 DEGREES C AT 1 TO 10 BAR - SO THAT THE TRANSITION TO ATMOSPHERIC PRESSURE IN THE FURNACE WILL CAUSE THE WATER TO EVAPORATE ALMOST INSTANTANEOUSLY.