Process and device for cleaning furnace gas includes flowing in a main flow direction (A) the furnace gas passes an array of bag filters. Filtered furnace gas having passed the filter bags, is partly returned via one or more nozzles which are moved along downstream ends of the bag filters. Each bag filter is passed at least once by at least one nozzle during a cycle. A nozzle passing a bag filter blows filtered furnace gas in a backflow direction (B) through said bag filter. The backflow direction is opposite to the main flow direction.

Process and device for cleaning furnace gas includes flowing in a main flow direction (A) the furnace gas passes an array of bag filters. Filtered furnace gas having passed the filter bags, is partly returned via one or more nozzles which are moved along downstream ends of the bag filters. Each bag filter is passed at least once by at least one nozzle during a cycle. A nozzle passing a bag filter blows filtered furnace gas in a backflow direction (B) through said bag filter. The backflow direction is opposite to the main flow direction.

A blast furnace system is used wherein the coke rate is decreased by recycling upgraded top gas from the furnace back into its shaft section (which upgraded top gas is heated in a tubular heater prior to being recycled). The top gas, comprising CO, CO.sub.2 and H.sub.2, is withdrawn from the upper part of the blast furnace; cooled and cleaned of dust, water, and CO.sub.2 for increasing its reduction potential and is heated to a temperature above 850 C. before being recycled thus defining a first gas flow path used during normal operation of the blast furnace. Uniquely, a second gas flow path for continued circulation of top gas selectively through the heater and a cooler during operation interruptions of the blast furnace allows time for gradual controlled cool down of the heater in a manner to avoid heat-shock damage to the tubular heater.

A blast furnace system is used wherein the coke rate is decreased by recycling upgraded top gas from the furnace back into its shaft section (which upgraded top gas is heated in a tubular heater prior to being recycled). The top gas, comprising CO, CO.sub.2 and H.sub.2, is withdrawn from the upper part of the blast furnace; cooled and cleaned of dust, water, and CO.sub.2 for increasing its reduction potential and is heated to a temperature above 850 C. before being recycled thus defining a first gas flow path used during normal operation of the blast furnace. Uniquely, a second gas flow path for continued circulation of top gas selectively through the heater and a cooler during operation interruptions of the blast furnace allows time for gradual controlled cool down of the heater in a manner to avoid heat-shock damage to the tubular heater.