The refractory grain can be loaded into an enclosure body as shown in FIG. 2', from feed hoppers located above station 2C, with the grain fed through one or more feed chutes 135 in the enclosure body top section at 2C, and with one or more shutters 136 in a chute 135 moved by means such as ram 137 or similar means, to repetitively control the amount of grain fed to the enclosure body.