NOVELTY - A methane gas-concentrating apparatus (1) comprises primary concentration apparatus (11), secondary concentration apparatus (12) and recovery equipment (13). The methane gas concentration apparatus isolates carbon dioxide from mixed gas containing methane gas and carbon dioxide, and concentrates methane gas. The primary concentration apparatus concentrates methane gas using separation membrane permeating carbon dioxide from mixed gas. The recovery equipment recovers methane by membrane permeating carbon dioxide from the permeation gas of primary concentration apparatus.    USE - Apparatus for concentrating methane gas used for manufacturing fuel gas (both claimed).    ADVANTAGE - The apparatus efficiently provides highly concentrated methane gas in high recovery rate. The highly stable fuel gas containing methane gas is manufactured efficiently and easily. The variation in blend ratio of methane gas and high heating value gas after performing permeation is prevented.    DETAILED DESCRIPTION - A methane gas-concentrating apparatus comprises primary concentration apparatus, secondary concentration apparatus and recovery equipment. The methane gas concentration apparatus isolates carbon dioxide from a mixed gas containing methane gas and carbon dioxide, and concentrates methane gas. The primary concentration apparatus concentrates methane gas using a separation membrane which preferentially permeates carbon dioxide from the mixed gas. The methane gas is further concentrated in the secondary concentration apparatus using separation membrane which preferentially permeates carbon dioxide from impervious gas of primary concentration apparatus. The recovery equipment recovers methane gas by separation membrane which further permeates carbon dioxide from the permeation gas of primary concentration apparatus. INDEPENDENT CLAIMS are included for the following:    (1) methane gas concentration method, which involves subjecting mixed gas containing carbon dioxide and methane gas to primary and secondary concentration processes, and recovering methane gas from permeation gas obtained from primary concentration process;    (2) manufacturing apparatus of fuel gas, which comprises a high-heating-value-gas addition unit, primary concentration apparatus and recovery equipment. The high-heating-value-gas addition unit adds high-heating-value gas with respect to biogas obtained by decomposing organic material, to provide mixed gas containing biogas and high heating value gas. The primary concentration apparatus concentrates methane gas and high-heating-value gas by separation membrane permeating carbon dioxide from the mixed gas. The recovery equipment recovers methane gas and high-heating-value gas by permeating carbon dioxide from permeation gas of primary concentration apparatus through separation membrane; and    (3) manufacture of fuel gas containing methane gas and high-heating-value gas for controlling heat amount, which involves adding high-heating-value gas with respect to biogas, concentrating methane gas and high heating value gas, and recovering methane gas and high heating value gas from permeation gas of primary concentration process.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of methane gas concentrating apparatus. (Drawing includes non-English language text)    Methane gas concentration apparatus (1)    Primary concentration apparatus (11)    Secondary concentration apparatus (12)    Recovery equipment (13)    Compressor (23)