if the characteristics of the solids changes during operation due to changes in grind or segregation in surge bin 102 the mass flow rate of coal or solids to the gasifier or reactor 150 can be maintained by maintaining a substantially constant feed system pressure as shown in fig5 the coal from the pressure control device 117 moves down a short inclined downcomer section of the pipe 140 the coal then moves through a short vertical riser 141 before being discharged to the conveying line through feeder exit 123 a part of the conveying gas 125 enters the top of the riser through pipe 142 and exits into the riser 141 through an inverted cone 144 coupled to the end of pipe 142 the conveying gas as it leaves the inverted cone 144 picks up coal particles from the top of the moving expanded bed to convey the coal to the downstream unit both the control gas and conveying gas can flow upward through section 143 depending upon the characteristics of feed material and downstream process the superficial gas velocity in section 143 of the riser 141 can be maintained between about 3 and 10 ft s by adjusting the conveying gas flow rate additional conveying gas is added downstream of the feeder device exit 123 to maintain a superficial gas velocity in the line to convey coal to the gasifier or reactor 150 even though one configuration of feed rate control device 117 is shown in fig5 a person skilled in the art of handling solids should appreciate other configurations involving changes to the way conveying gas is introduced into the riser and the way the coal is conveyed out of the riser that are consistent with this disclosure the size of the inclined.