Plant and method for fractionating and purifying synthesis gas

A plant for the fractionation and purification of a synthesis gas, the plant comprising the following interconnected devices:

• a primary heat exchanger for cooling off the synthesis gas fed to the plant;
• a separator connected to the primary heat exchanger for fractionating the synthesis gas into a gas fraction mainly consisting of hydrogen and carbon monoxide, and into a liquid fraction mainly consisting of carbon monoxide and methane;
• a first evaporator for further fractionating the gas fraction supplied from the separator in order to produce a gas fraction predominantly consisting of hydrogen and a liquid predominantly consisting of carbon monoxide;
• a second evaporator in which the hydrogen absorbed in the liquid from the first evaporator is evaporated and remaining liquid mainly containing carbon monoxide is fed to a distillation column;
• a third evaporator in which the remaining, absorbed hydrogen in the liquid fraction 5 of separator B is removed by evaporation and that produces a liquid mainly containing carbon monoxide and methane;
• a distillation column receiving the liquid from the third evaporator for the separation of gaseous carbon monoxide and for obtaining methane therefrom as a liquid depositing at the bottom of the distillation column;
• and
• a washing column for removing contaminants from the gas fraction from the first evaporator and mainly consisting of hydrogen, this purification using liquid nitrogen and the contaminants being used as a burnable gas.