Method for operating a coke oven plant

A coke oven plant comprising

• a) a source of blast furnace gas configured for providing a blast furnace gas stream comprising carbon monoxide CO, carbon dioxide CO2 and hydrogen H2, and a source of coke oven gas configured for providing a coke oven gas stream comprising hydrogen H2, carbon monoxide CO and methane CH4;
• b) a CO converter unit connected to said source of blast furnace gas and configured for treating a part of the blast furnace gas stream by converting carbon monoxide to carbon dioxide to obtain a treated blast furnace gas stream;
• c) a CO2-depletion unit connected to said CO converter unit and configured for removing carbon dioxide from said treated blast furnace gas stream to obtain a primary CO2-depleted blast furnace gas stream;
• d) a first mixing unit connected to said CO2-depletion unit and controllably connected to said source of blast furnace gas, said first mixing unit being configured for mixing the primary CO2-depleted blast furnace gas stream from the CO2-depletion unit with a proportion of the blast furnace gas stream to obtain a secondary CO2-depleted blast furnace gas stream, said controllable connection to said source of blast furnace gas comprising a controllable blast furnace bypass stream regulator;
• e) a second mixing unit connected to said first mixing unit and controllably connected to said source of coke oven gas, said second mixing unit being configured for mixing the secondary CO2-depleted blast furnace gas stream from the first mixing unit with a proportion of the coke oven gas stream to obtain a tertiary CO2-depleted gas stream, said controllable connection to said source of coke oven gas comprising a controllable coke oven gas stream regulator;
• f) a coke oven from the coke oven plant comprising an underfiring system connected to said second mixing unit and configured for burning said tertiary CO2-depleted gas stream to convert coal to coke thereby producing a coke oven gas and an exhaust gas;
• wherein the coke oven plant further comprises a first analyzer downstream the first mixing unit configured for determining properties of the secondary CO2-depleted blast furnace gas stream and a second analyzer downstream the second mixing unit configured for determining properties of the tertiary CO2-depleted gas stream;
• a control unit configured for controlling operation of the underfiring system by determining the proportion of the blast furnace gas stream and the proportion of the coke oven gas stream based on said properties provided by said first and second analyzers and by controlling the controllable blast furnace bypass stream regulator and the controllable coke oven gas stream regulator so as to adjust at least one of CO2 content, CO content, H2 content, Wobbe Index, stoichiometric combustion air demand and Lower Heating Value in said tertiary CO2-depleted gas stream.