Abstract

In the production of reduced iron pellets from a material mainly comprising dust exhausted from metallurgical furnaces for iron and steel production, such as blast furnaces, converters, hearth furnaces and electric furnaces, and/or a mixture thereof, by means of a grate-kiln a furnace including a pretreatment furnace comprising, a drying zone, a preheating zone a hardening zone and travelling grate passing sequentially through said zones, and a rotary kiln receiving the output pellets from the hardening zone, hot exhaust gases from the rotary kiln are first passed through said hardening zone and then through said preheating zone to harden and preheat green pellets moving therein. Said exhaust gases are then introduced into a first dust collector, where dust of a high zinc content is almost completely collected from said exhaust gases. Said exhaust gases so purified are then passed through said drying zone to dry green pellets moving therein. Said exhaust gases are then introduced into a second dust collector, where dust is further collected from said exhaust gases before said exhaust gases are discharged out of a stack to open air. When the temperature of said exhaust gases which have passed said first dust collector is not high enough for a heat source for drying green pellets moving in said drying zone, the temperature of gases for drying is raised by blowing hot gases, which are separately produced by a fuel burner, into said drying zone. The dust of a high zinc content collected by said first dust collector is used as a material for zinc refining.