Sand bed downdraft furnace and activated carbon scrubber

A downflow hearth furnace comprising:

• a refractory-lined furnace lid suspended in a stationary rest position;
• a burner thermally coupled through the lid;
• a combustible material entry port disposed in the lid;
• a combustible material conveyor system communicating with the entry port;
• a rotatable combustible material disperser positioned under the entry port and coupled to a rotation shaft;
• a disperser motor coupled to the rotation shaft;
• a variable speed motor drive circuit electrically coupled to the disperser motor.
• a refractory-lined furnace shell having a top edge configured to mate with a bottom edge of the furnace lid;
• a raising and lowering mechanism mechanically coupled to the furnace shell for moving the furnace shell between an open position where the furnace shell is clear of the furnace lid and a closed position where the furnace shell makes contact with the furnace lid;
• a hearth disposed within the furnace shell;
• a sacrificial or partially replaced bed of gas-permeable heat resistant material at a bottom end of the hearth suspended on a layer of filter material;
• a plenum disposed below the hearth;
• an outlet duct communicating with the plenum and having a horizontally disposed outlet flange;
• a fixedly mounted scrubber input duct having a horizontally disposed inlet flange vertically positioned to mate and form a vacuum seal with the outlet flange of the outlet duct at when the furnace shell is raised to a position above which the furnace shell lid makes contact with the furnace lid.