Fuel Gas Fired Drop Bottom Furnaces
If heat treat process specifications allow for products of combustion in the air stream, then a direct gas fired furnace is the most economic choice. If no products of combustion are allowed in the air stream, then an indirect fuel gas fired or electric heated furnace is the choice. Our furnaces meet pyrometric requirements of AMS 2750E, NADCAP AS7102, MILSPEC H6088, BAC 5621, Rolls Royce RPS 953 and DPS 1.700.
Fuel gas fired drop bottom furnaces can reduce energy cost by a factor of four. AQMD rule 219 exempts heat treat equipment with less than 2 Mio Btu heat input per hour from obtaining an air contamination permit; if the heat input is above 2 Mio Btu per hour, AQMD rule 1147 specifies a NOx limit of 60ppm for metal heat treat furnaces. Solution heat treating of castings requires more heat input then solution heat treating of aluminum sheets, but loads of less than 2000 lbs rarely require heat inputs of above 2 Mio Btu per hour.
Direct gas firing:
Gas burners are firing directly into the heating chamber from where a fan transports the heated air into the furnace chamber.
Indirect gas firing:
The load is heated by convection. Gas burners heat up a gas tight firing tube positioned in the airstream generated by a fan. The combustion gases are exhausted directly into a duct. The furnace chamber is designed as a downdraft system, meaning the hot air enters the top of the chamber and exits at the bottom of the chamber. This design has the advantage that potentially cold air (entering through worn out seals on the bottom door) is first pulled into the heating chamber where it is mixed with the air from the furnace chamber. This results in greater temperature uniformity in the furnace chamber.