Method and apparatus of gas-coal combustion in steam boilers

Various embodiments of apparatus and methods are disclosed for the conversion of steam boilers from being oil fired to coal and natural gas fired without adversely affecting the normal power density of the boilers or the emission pollution therefrom. In some cases even the resultant coal ash can be modified by injecting a powdered catalyst or phosphate slimes into the flame to produce a fertilizer ash having desirable minerals to enhance the economic value thereof. Basically all embodiments include a swirling coal-air mixture directed along a path to form a sheath and a swirling gas-air mixture internally thereof with the swirling of the latter being in the same direction and fortifying the motion of the former. A gas-air mixture, swirling or non-swirling, may be supplied outwardly of such sheath to enhance the more complete burning of the coal-air mixture.