NOVELTY - The assembly to decompose and clean a synthesis gas gives a partial condensation followed by a nitrogen scrubbing. A heat exchanger (A) reduces the temperature of the gas inflow, with a separation stage (B) to break the gas flow (2) down into a gas fraction (4) mostly of hydrogen and carbon monoxide, and a liquid fraction (5) mostly of carbon monoxide and methane.    USE - The gas, used for chemical synthesis, is broken down and cleaned for further use.    ADVANTAGE - The heat exchange is more efficient, without a special cooling system using an expander. The assembly is kept cool on a reduced demand for carbon monoxide or ammonia synthesis gases, by the continued cleaning of other gases, with a rapid return to full production.    DETAILED DESCRIPTION - An evaporator (C) separates the gas fraction into a further gas fraction (6) mainly of hydrogen and a carbon monoxide liquid fraction (7). The liquid fraction is separated in a further evaporator (D) into a hydrogen vapor and a carbon monoxide liquid (8) to be fed to a distillation column (F). An additional evaporator (E) takes the liquid fraction from the first separation stage, to vaporize and remove any hydrogen, leaving a liquid residue of carbon monoxide and methane for distillation. At the distillation column, carbon monoxide gas is separated, and liquid methane is taken from the column base. A washing column (G) scrubs impurities from the gas fraction from the first evaporator with liquid nitrogen (3), and the extracted impurities are used as a combustion gas (12).    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of the assembly to break down and clean a synthesis gas. (The drawing includes non-English language text).    Synthesis gas (2)    Liquid nitrogen (3)    Gas fraction (4)    Liquid fraction (5)    Gas fraction (6)    Liquid fraction (7)    Carbon monoxide liquid fraction (8)    Combustion gas (12)    Heat exchanger (A)    Separator (B)    Evaporators (C,D,E)    Distillation column (F)    Washing column (G)