NOVELTY - Nanometer calcium carbonate, calcium carbide, and fuel gas are prepared by sintering limestone to obtain calcium oxide and carbon dioxide; dividing carbon dioxide into 2 parts; crushing calcium oxide and dividing into coarse and fine particle parts; introducing first part of carbon dioxide and calcium oxide in furnace filled with wet coke and reacting them to obtain calcium carbide and fuel gas; adding water to fine part of calcium oxide, filtering coarse particles, and adding water; adding second part of carbon dioxide in slurry, and adding crystal control agent; and solid-liquid separating.    USE - Method for preparing nanometer calcium carbonate, calcium carbide, and fuel gas (claimed).    ADVANTAGE - The method reduces crushing process. Carbon dioxide can be recycled in reactor for preparing calcium carbide and calcium carbonate, thus increasing purity of fuel gas product and utilization ratio of raw material.    DETAILED DESCRIPTION - Preparing nanometer calcium carbonate, calcium carbide, and fuel gas involves:    (A) sintering limestone at high temperature and obtaining calcium oxide (CaO) and carbon dioxide (CO2);    (B) dividing CO2 into 2 parts, CO2 (I) and CO2 (II);    (C) crushing CaO to obtain grain size of 5-400 mm, passing in sieve with diameter of 2-4 mm, dividing CaO into 2 parts, and taking the coarse particle part as CaO (I) and the fine particle part as CaO (II);    (D) introducing CO2 (I) and CaO (I) in reaction furnace filled with wet coke or coal and reacting them at 900-1300 degrees C to obtain calcium carbide and fuel gas containing CO2, hydrogen (H2), and methane (CH4);    (E) adding water to CaO (II), agitating to dissolve them, passing through sieve, filtering coarse particles, and adding water to dilute the filtered slurry until calcium hydroxide (Ca(OH)2) is 40 wt.%;    (F) agitating the obtained slurry, introducing CO2 (II) in the slurry and adding crystal control agent which comprises first control agent and second control agent, and reacting them for 2 hours; and    (G) performing solid-liquid separation on the obtained product, drying the solid product, and obtaining the nanometer calcium carbonate powder comprising cubical particles and spherical particles, in which an average particle diameter of the particle is 30-40 nm.    Inlet conditions of CO2 (II) are different in terms of addition of the first control agent and the second control agent. An inlet mode of CO2 is a bubbling mode when the first control agent is added and the flow rate is 200 l/hour. The second control agent is added after reacting for 1 hour then the inlet mode of CO2 is a bubbling intermitting agitating mode and the flow rate is 400 l/hour. Agitating speed is converted at 200 and 400 rpm. The first crystal control agent is aluminum chloride (0.5 mass%) and the second control agent is gamma -aminopropyl triethoxysilane (0.8 mass%). The reaction is controlled at 30-40 degrees C.