TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method includes calculating the ratio of converter exhaust gas and coke oven gas based on ratio requirement of hydrogen with carbon monoxide and carbon dioxide in the methanation reaction and hydrogen, carbon monoxide and carbon dioxide in the converter exhaust gas and coke oven gas, where after the reaction, the gases hydrogen, carbon monoxide and carbon dioxide content are in line with defined criteria. The methanation reaction of converter exhaust gas and coke oven gas is carried out after purification of converter exhaust gas and coke oven gas. The volume ratio of converter exhaust gas and coke oven gas is 1:9-12. The preparation of converter exhaust gas comprises connecting three level or four level methanation device in series to achieve and complete the methanation reaction, when the three-level methanation device is used: adding 40% coke oven gas in the first stage methanation device, then discharging 50% coke oven gas into the second methanation device, add 20% of converter exhaust gas and remaining coke oven gas, then passing into third stage methanation device, adding the remaining converter exhaust gas; when four-level methanation device is used: adding 20% coke oven gas into first stage methanation device, then discharging 30% of the total gas volume of the coke oven gas as a recycle gas into the second stage methanation device, then adding 30% converter exhaust gas and 20% coke oven gas, and discharging all gases into the third stage methanation device, adding 30% converter exhaust gas and 30% coke oven gas, then all gases discharging into fourth stage methanation device, and adding the remaining converter exhaust gas and remaining coke oven gas. Preferred Components: The content of hydrogen in coke oven gas after methanation is 0.25-0.8%.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The methanation device is set with a heat exchanger for cooling the gas after methanation reaction, where a nitrogen separation device is set behind the heat exchanger for separating the nitrogen contained in the gas, and the inlet temperature and outlet temperature of each methanation device is controlled at 250-300 degrees C and 400-500 degrees C. A circulating gas pipeline is connected to methanation device exhaust pipe. The methanation device is further provided with converter exhaust gas purification device and coke oven gas purification device, where the converter exhaust gas purifying device outlet is connected converter exhaust gas storage container via pipeline, and the coke oven gas purification device outlet is connected to coke oven gas container via coke oven gas supply pipe.