A method for producing methane by reacting carbon dioxide and hydrogen in the presence of a catalyst, a tower type reactor in which multiple stages of powder beds are arranged vertically, comprising:
- preparing a reactor in which each powder bed contains at least one inorganic powder selected from the group consisting of sand, silica, magnesia, alumina and calcia and the catalyst;
- introducing a reaction mixture gas containing carbon dioxide and hydrogen into the space below the lowermost powder bed in the reactor;
- passing, sequentially through the ascending flow of the reaction mixture, gas from the lowest powder bed to the uppermost powder bed to form a multi-stage fluidized bed;
- extracting a product gas containing methane produced by contacting the reaction mixture gas with the catalyst arranged in each powder bed from the space above the uppermost powder bed;
- supplying, continuously, the inorganic powder to the uppermost powder bed;
- causing the inorganic powder in each stage of the powder bed to continuously flow down to the adjacent lower powder bed, by:
- discharging, continuously, the inorganic powder from the lowermost powder bed, while maintaining the amount of the inorganic powder in each powder bed constant;
- and
- forming a downward flow of the inorganic powder that flows down in the reactor through the plurality of stages of powder beds in sequence, in the reactor, the ascending flow of the reaction mixture gas and the downward flow of the inorganic powder are in countercurrent contact;
- constructing a continuous multi-stage fluidized bed reactor having a temperature gradient in which the temperature of the plurality of powder beds decreases sequentially from the lowest powder bed to the uppermost powder bed;
- adjusting the cooling amount of the inorganic powder so that the temperature of the inorganic powder supplied to the uppermost powder bed is in the range of 100 to 300° C.;
- and
- adjusting the circulation amount of the inorganic powder so that the temperature of the inorganic powder extracted from the lowermost powder bed is in the range of 300 to 600° C., wherein:
- the inorganic powder fed to the uppermost powder bed contains magnesium hydroxide, magnesium carbonate or a mixture thereof;
- the inorganic powder extracted from the lowermost powder bed contains magnesium oxide produced by dehydration of the magnesium hydroxide or decarbonation of magnesium carbonate, or a mixture thereof and unreacted inorganic powder in the reactor;
- and
- the inorganic powder extracted from the lowermost powder bed is cooled in an atmosphere in which water vapor or carbon dioxide is contained, thereby converting magnesium oxide contained in the inorganic powder into magnesium hydroxide or magnesium carbonate.