| OCR Text |
Show -7- both the internal and external air staged burner types, where there was geometrical similarity between the semi-industrial and full scale versions of the burner. These predictions look promising. - A limitation to the final applicability of the information is concerned with char burnout, where the semi-industrial scale results (see for example figure 6) may only be used to predict trends. -In-principle, increasing the scale of the combustion system and thus in flame residence times, should always improve char burnout relative to the semi-industrial scale. Nevertheless, indications are that even at full scale, problems are being experienced with excess carbon in ash (>5% w/w) and further information on this aspect is important not only from the point of view of combustion efficiency, but also due to aspects such as fly ash separation and disposal. Information gaps which still exist include the possibility to improve further the performance of internal air staged burners, particularly in view of their advantage in connection with retrofitting of existing boilers. More information is required on the field of char reactivity for various coal types particularly in relation to the time/temperature/ chemical environmental histories experienced by the coal particles immediately after injection into the flame. There is a need for information in relation to the effect upon coal mineral matter, of transit through substoichiometric primary flame zones with changed temperature regiemes, in connection with potentially increased tendencies towards slagging of the combustion chamber heat transfer surfaces and fouling of the convection banks. Further it is considered that the information already generated in this investigation plus the extra information concerning the combustion characterisation of coals, which may be generated within *n |
