Method for preheating steel scrap by exhaust gas from steelmaking electric furnace

A method of preheating steel scrap by an exhaust gas from a steelmaking electric furnace in a steelmaking system, and in which the steelmaking system comprises an electric furnace;

• an exhaust gas discharge duct coupled to said furnace;
• an exhaust gas combustion chamber coupled in said exhaust discharge duct;
• a branch duct branching off of said exhaust gas discharge duct downstream of said exhaust gas combustion chamber;
• and at least one steel scrap preheating chamber coupled in said branch duct to receive exhaust gas from said branch duct;
• the method comprising:
• directing, when manufacturing steel from steel scrap in said electric furnace, an exhaust gas produced in said electric furnace to said exhaust gas combustion chamber via said exhaust gas discharge duct to cause in said exhaust gas combustion chamber combustion of carbon monoxide contained in said exhaust gas to form a combustion exhaust gas;
• selectively directing only part of said combustion exhaust gas from said exhaust gas combustion chamber into said at least one scrap preheating chamber via said branch duct branching off from said exhaust gas discharge duct to preheat steel scrap in said at least one scrap preheating chamber to a prescribed temperature;
• and
• feeding back all of said combustion exhaust gas from said at least one scrap preheating chamber, after said preheating of steel scrap in said at least one scrap preheating chamber, to said exhaust gas combustion chamber to cause combustion in said exhaust gas combustion chamber of an incomplete-combustion gas produced by the incomplete combustion of combustible substances entrapped in steel scrap being preheated, and which incomplete-combustion gas is contained in said combustion exhaust gas fed back from said at least one scrap preheating chamber.