Device comprises hopper provided with a needle valve and micrometric depth gage for control and measurement of the supply flow rate. The hopper has air-operated vibrator. The bottom section of the hopper receives the distributing chamber that has primary and secondary lines for compressed air. The distributing chamber is provided with means for connecting it to the reactor of the furnace. The hopper is made of nonreacting material, e.g. stainless steel. The needle valve is composed of the members for control of the supply flow rate by means of moving the needle in the vertical direction. At least one member for control of supply flow rate has movable shaft. The micrometric depth gage is connected with the needle valve via the movable shaft. The air-operated vibrator is provided with means for control of compressed air.The distributing chamber is connected with the bottom section of the hopper and reactor of furnace by means of a flange joint.